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Vol 57 Issue 4

October 2013

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E-ISSN 1471-0676 • Platinum Metals Rev., 2013, 57, (4), 233•

Editorial Team: Sara Coles (Assistant Editor); Ming Chung (Editorial Assistant);Keith White (Principal Information Scientist)

Platinum Metals Review, Johnson Matthey Plc, Orchard Road, Royston, Hertfordshire SG8 5HE, UKEmail: [email protected]

Platinum Metals ReviewA quarterly journal of research on the platinum group metals

and developments in their application in industryhttp://www.platinummetalsreview.com/

OCTOBER 2013 VOL. 57 NO. 4

Contents The Directed ortho Metallation–Cross-Coupling Fusion: 234 Development and Application in Synthesis By Johnathan Board, Jennifer L. Cosman, Toni Rantanen, Suneel P. Singh and Victor Snieckus

The Role of Platinum in Proton Exchange Membrane Fuel Cells 259 By Oliver T. Holton and Joseph W. Stevenson

“Organometallics as Catalysts in the Fine Chemical Industry” 272 A book review by Michel Picquet

A Study of Platinum Group Metals in Three-Way Autocatalysts 281 By Jonathan Cooper and Joel Beecham

Recovery of Palladium from Spent Activated 289

Carbon-Supported Palladium Catalysts By Şerife Sarioğlan

“Catalysts for Alcohol-Fuelled Direct Oxidation Fuel Cells” 297

A book review by Alex Martinez Bonastre

Investigations into the Recovery of Platinum Group Minerals from the 302 Platreef Ore of the Bushveld Complex of South Africa By Cyril T. O’Connor and Natalie J. Shackleton

“The Fuel Cell Industry Review 2013” 310

PGMs in the Lab: New, Effi cient Tools for Palladium-Catalysed 311 Functionalisation of Heteroaromatics Featuring Jean-Cyrille Hierso

Publications in Brief 313

Abstracts 316

Patents 319

Final Analysis: Platinum Group Metal Catalysts for the 322 Development of New Processes to Biorenewables By Andrew D. Heavers, Michael J. Watson, Andrew Steele and Jeanette Simpson

•Platinum Metals Rev., 2013, 57, (4), 234–258•


The Directed ortho Metallation–Cross-Coupling Fusion: Development and Application in SynthesisPlatinum group metals catalytic synthetic strategy for pharmaceutical, agrochemical and other industrial products

http://dx.doi.org/10.1595/147106713X672311 http://www.platinummetalsreview.com/

By Johnathan Board

Snieckus Innovations, Innovation Park, 945 Princess Street, Kingston, Ontario, K7L 3N6, Canada

Jennifer L. Cosman

Department of Chemistry, Queen’s University, 90 Bader Lane, Kingston, Ontario, K7L 3N6, Canada

Toni Rantanen, Suneel P. Singh and Victor Snieckus*

Snieckus Innovations, Innovation Park, 945 Princess Street, Kingston, Ontario, K7L 3N6, Canada

*Email: [email protected]

This review constitutes a detailed but non-exhaustive

examination of the directed ortho metallation (DoM)–

cross-coupling fusion in its many fl avours. Special

attention is paid to the application of the concept of the

linked reactions and the synthetic utility that it endows,

particularly in the case of one-pot reactions that can

greatly increase the ease and effi ciency of the process.

Personal experience of particular issues that can arise

from these reactions and examples of their solutions

are given, as well as illustrations of the rapid access to

complex molecules that the technique encourages.

IntroductionSince its disclosure, the combination of DoM and

transition metal-catalysed cross-coupling has evolved

into a common strategy in synthesis (1, 2) and,

in particular, has found widespread use in the

preparation of biologically interesting aromatic and

heteroaromatic compounds. A variety of functional

groups such as I, Br, Cl, SiR3, SnR3, B(OR)2 have been

introduced using DoM, followed by different cross-

coupling reactions to form carbon–carbon, carbon–

oxygen, carbon–nitrogen and carbon–sulfur bonds

in order to prepare synthetically and biologically

interesting molecules. Herein we present selected

examples of the use of the DoM–cross-coupling strategy

from the period of 2000 to 2012 in order to demonstrate

its advantages and outline the potential issues that

may be faced in its application. The main focus will

be on cross-couplings involving the platinum group

metals (pgms); however several examples using other

metals such as copper are included for comparison.

In order to make this review more accessible, it is

divided into sections according to the type of bond

being formed and the type of metallation reaction. For

further clarifi cation, a scheme describing the reaction

discussed appears at the beginning of each section.

http://dx.doi.org/10.1595/147106713X672311 •Platinum Metals Rev., 2013, 57, (4)•


1. DoM–C–C Cross-Coupling Reactions

1.1 Sequential (Multi-Pot) DoM–Cross-Coupling MethodsThe formation of C–C bonds through the sequence

of DoM–halogenation to insert an ortho halide

or pseudohalide, followed by cross-coupling has

been carried out using Ullmann, Heck, Sonogashira,

Negishi, Stille and Suzuki-Miyaura reactions,

among others. As an example, Sanz et al. (3) have

synthesised valuable 4-fl uoro-2-substituted-1H-

indoles 4 through a sequence involving DoM

mediated iodination of 3-fl uorotrifl uoroacetanilide

1, followed by reaction with terminal aromatic

or aliphatic alkynes by a Sonogashira coupling–

cyclisation process (Scheme I). When the DoM

reaction was carried out at temperatures higher

than –60ºC, competitive lithium fl uoride elimination

took place forming a benzyne intermediate 5 which

underwent subsequent intramolecular cyclisation to

provide iodinated benzoxazole 7. This phenomenon

occurring during the directed metallation of

3-fl uoroaniline bearing N-pivaloyl, N-Boc directing

metallation groups (DMGs) or an N-benzoyl group

had been previously observed (4).

The Suzuki-Miyaura cross-coupling is one of the

most popular and widely used reactions in the C–C

DoM–cross couple fusion strategy (for examples, see

(5, 6)). When partnered with DoM, the major advantage

of the Suzuki-Miyaura reaction is that boronation

reagents such as B(OR)3 are often compatible with

lithium bases (usually lithium dialkylamides, but

some boronates are even compatible with s-BuLi )

(7). This allows the boronating agent to be present

in the same reaction vessel as the base in order to

quench the metallated species as it is formed. These

conditions are known in our laboratories as either

Barbier or Martin (8, 9) type conditions according

to the order of addition. (Descriptions of these in

situ quench conditions are as follows: under Barbier

type conditions the base is added to a mixture of

substrate and electrophile; under inverse Barbier

conditions a solution of substrate and electrophile

are added to a solution of the base; under Martin

conditions the substrate is added to a solution of base

and electrophile; under inverse Martin conditions

a solution of base and electrophile are added to a

solution of the substrate. Compatible electrophiles

include, but are not limited to, trimethylsilyl

chloride (TMSCl), Me2SiCl2, B(OMe)3 and B(OiPr)3.)

Halide sources are not usually compatible with

strong bases; for instance, premixing I2 and lithium

DMG DMG

X

DMG

R

DoM Cross-coupling

X = Halide or pseudohalideR = Carbon-based substituent

F

OF3C

NH

1. tBuLi/TMEDA (2.3 equiv.)THF, –78ºC

2. I2 (1.4 equiv.)–78ºC to RT63% yield OLiF3C

N

LiF

OLiF3C

N

>–60ºC–LiF

21

5

3

6

4

7

R1 (1.5 equiv.)PdCl2(PPh3)2 (3 mol%)

CuI (5 mol%)

Et2NH (1.5 equiv.)DMA, 80ºC

R1 = Ph, 87% yieldR1 = nHex, 78% yield

OF3C

NH

IF F

Li IO

NCF3 33% yield

O

NCF3

NH

R1

Scheme I. Sequential DoM and Sonogashira cross-coupling for the synthesis of indoles



2,2,6,6-tetramethylpiperidide (LiTMP) before addition

of the metallation substrate has resulted in low yields

of iodinated material in our laboratories. Vedsø et al.

have shown that ester, cyano and halogen substituents

are tolerated when LiTMP/B(OiPr)3 is used for in situ

boronation of unstable ortho metallated species (10).

In our group we have found that the DoM–cross-

coupling strategy fi nds particular utility in the

functionalisation of indoles. Stimulated by work

performed by Iwao et al. (11), we have developed

routes to 3,4-substituted indoles by utilising DoM–

Negishi cross-coupling sequences to afford gramines

8 which undergo useful retro-Mannich fragmentation

to give indoles 9 (12). Similarly, C-7-substituted

indoles 12 have also been synthesised by either

sequential or one-pot C-2 metallation, C-2 silylation,

C-7 metallation and C-7 electrophile treatment of

indoles 10 to provide the boronates or halides 11,

followed by Suzuki-Miyaura cross-coupling to give

12 (13). In addition, 2-aryl/heteroarylindoles 15

have also been synthesised from N-carbamoyl-2-

bromoindoles using either Suzuki-Miyaura (13a) or

one-pot ipso borodesilylation–Suzuki-Miyaura (13b)

reactions to provide indoles 14, followed by a lithium

diisopropylamide (LDA)-induced anionic N–C

carbamoyl migration (Scheme II) (14).

Due to the higher C–H acidity of heteroaromatic

systems, the DoM component of the DoM–cross-

coupling fusion of these systems is dominated by the

use of bases other than butyllithium, such as the lower

N N

N N N

N

N

N

HN

C and Het

DME (refl ux) or DMF (100ºC)6–18 h, 85–92% yields

BCl3 (1.1 equiv.), CH2Cl2, –45ºC, 60 min, then pinacol (4 equiv.) and evaporate, then Ar3Br (0.8 equiv.),

Pd(PPh3)4 (5 mol%), K3PO4 (4 equiv.)

DMF, 100ºC, 12–20 h, 67–89% yields

Ar3B(OH)2 (1.2 equiv.), Pd(PPh3)4 (5 mol%)Na2CO3 (1.5 equiv.) or K3PO4 (3 equiv.)

LDA (4 equiv.), THF0ºC to RT, 1–12 h

R1 = Me, 50–92% yieldsR1 = H, 36%–quant.

yields17 examples

Ar2X (1.1–1.2 equiv.) Pd(PPh3)4

(2–10 mol%)K3PO4 (3 equiv.)

DMF, 80ºC15–20 h

83–99% yields

1. tBuLi (1.1 equiv.) TMSCl (1.05 equiv.)

2. sBuLi/TMEDA (1.5 equiv.)

3. I2, BrCH2CH2Br or B(OiPr)3 (1.5 equiv.), THF, –78ºC to RT, 5 h total

N-bromosuccinimide (1 equiv.)MeOH, RT, 2 min

or1. TBAF (1 equiv.), THF, RT, 10 min

2. N-iodosuccinimide (1 equiv.), MeOH, 0ºC, 5 min3. (Boc)2O (1.5 equiv.), Et3N (1.5 equiv.)

DMAP (cat.), CH2Cl2, RT, 15 min24–81% yields

TIPS

DoM/cross-coupling

NMe2Ar1 Ar1

Ar2

Ar3

PG

X

TMSTMS

TMS

CONEt2 CONEt2 CONEt2

CONEt2 CONEt2

CONEt2CONEt2

CONEt2CONEt2CONEt2

CONEt2

CONEt2

HN

HN

HN

HN

HN

E

Br

Me

Me Me OMe Me

R1 R1

N

SS

8 9

10 11 12

13a

14

13b

15

Select examples:

15a 92% yield from 13 15b 55% yield from 13 15c 56% yield from 13 15d 73% yield from 13 15e 75% yield from 13 using PhB(OH)2 using 2-MeOC6H4B(OH)2 using 3-thienylboronic acid using 3-bromothiophene using 3-bromopyridine

PG = TIPS or Boc; Ar1 = Ph, o-Tol, pyridin-3-yl; X = Br or IE = I, Br, BPin (after pinacolation); Ar2 = 8 examples including Ph, 2-MeOC6H4, pyridin-3-ylR1 = H, MeAr3 = CHCH(4-MeC6H4), Ph, 2-MeOC6H4, 3-MeOC6H4, 4-MeOC6H4, 4-FC6H4, 4-ClC6H4, 4-BrC6H4, furan-3-yl, thiophen-3-yl, pyridin-3-yl, naphthalen-1-yl, isoquinolin-4-yl

Scheme II. Indole functionalisation utilising the DoM and cross-coupling protocol



pKa lithio dialkylamides or Grignard bases; the cross-

coupling component has been dominated by Suzuki-

Miyaura and Negishi reactions. The consideration

of which base to choose is heavily infl uenced by

the DMG and by the other functionalities within the

system. For instance, if the DMG is a halogen then

benzyne formation may need to be avoided through

the use of lower temperatures or milder bases

less prone to induce MX elimination. On the other

hand, if the DMG is weak and the system is electron

rich then stronger bases will be required which

may result in nucleophilic attack of the base upon

the heteroaromatic ring, especially in the case of

π-defi cient systems. Usually the accepted wisdom is to

use as mild a base as possible, at a temperature as close

to room temperature as is possible in order to achieve

the greatest degree of functional group compatibility

and experimental simplicity. Certain DMGs are less

tolerant of higher temperatures than others, such as

N,N-diethyl-O-carbamate which may undergo the

anionic ortho Fries rearrangement (1, 15, 16). We have

found also that the variation of solvents can have a

profound effect on the selectivity of the metallation; in

particular the switch between tetrahydrofuran (THF)

and diethyl ether can make the difference between

the success or failure of a reaction.

Although in many cases this type of DoM–cross-

coupling strategy can be performed with relative ease

simply by using conditions precedented for a similar

system, both the DoM and cross-coupling may have

non-trivial problems which should be solved through

methodical application of standard optimisation

techniques, such as variation of solvent, base and

catalyst system. An instructive example concerns work

which eventually led to the discovery of soraprazan

(16, Figure 1), a clinically studied H+/K+-ATPase

inhibitor (17).

Thus, as shown by deuterium quench experiments,

the ortho deprotonation of an N-pivaloyl

imidazo[1,2-a]pyridine 17 gave the highest ratio of

C-5:C-7 (18:19) deprotonation when t-butyllithium was

used in diethyl ether (Scheme III). When this reaction

was performed in THF, products 18 and 19 were

obtained in almost equal conversion. These results

were rationalised by the observed poor solubility of

the kinetically preferred C-7-anion in diethyl ether

which presumably prevented it from undergoing

equilibration with the more thermodynamically

preferred C-5-anion. On the other hand, in THF

the greater solubility of the C-7 anion allowed it to

equilibrate with the C-5 anion thereby eradicating

N

NH

OO

HOPh

Me

Me

MeN

16

Fig. 1. Soraprazan, a H+/K+-ATPase inhibitor (17)

tBuLi (2.8 equiv.)solvent, –78ºC, 15 min

then D2O quenchexamined using 1H NMR

Me

Me

tBu

O

HN

17tBuLi (3 equiv.), TMEDA (3 equiv.)

diethyl ether, –78ºCthen addn. of Bu3SnCl (3 equiv.)–78ºC, 1 h, then RT overnight1:9 ratio, 20:21 obtained in

41% yield

Me

Me

tBu

O

HN

18

Me

Me

tBu

O

HN

19

Me

Me

tBu

O

HN

20

Me

Me

tBu

O

HN

21

D

D

SnBu3

Bu3Sn

++

others, mainly bis-deuterated products

+

Solvent Conversion, %THF 23 25 53Ether 18 82 <3N

N

N

N

N

N

N

N

N

N

Scheme III. DoM studies of the N-pivaloyl-imidazo[1,2-a]pyridine 17 (17)



the selectivity. When the reaction was performed

using the weaker n-butyllithium, no selectivity

between C-5 and C-7 metallation was achieved, and

a large amount of starting material was recovered

even when the reaction was conducted over longer

periods of time or at higher temperatures. This is

presumably due to the moderate ortho-directing

ability of the N-pivaloyl group. Use of the optimised

deprotonation conditions followed by stannylation

afforded the desired C-7 product 21 in acceptable

yield in a 1:9 ratio together with the undesired C-5

regioisomer 20.

The derived compound 21 was used in acylative

Stille cross-couplings with cinnamoyl chlorides to

give compounds 23, which by straightforward acid-

mediated Michael cyclisation-depivaloylation afforded

compounds 24, which are intermediates for sorapazan

(16) and its analogues (Scheme IV). The execution

of the Stille cross-coupling was far from trivial and

therefore deserves comment. Experiments with a

variety of palladium sources were unsuccessful and

only the combination of PdCl2(MeCN)2 and a three-fold

excess of the cinnamoyl chloride led to cross-coupled

products 23, in poor yields, which precipitated from

the reaction mixture as the hydrochloride salts. The

known advantages of using halide salts in Stille cross-

couplings of aryl trifl ates (18–20) led to speculation

about the role of halide salts in the reaction. Thus,

on addition of one equivalent of lithium chloride to

the reaction mixture, conversion to products 23 was

achieved in moderate yield.

Despite the demonstration in our laboratories

of the advantages of performing a DoM–Suzuki

Miyaura cross-coupling in a one-pot fashion (such

as fewer chemicals used, eradication of at least one

workup step, higher effi ciency and convenience),

most reported reactions are performed with isolation

of the DoM products. Schemes V and VI (21, 22)

N

N

Me

Me Me

Me

Me

Me

tBu

O

HN tBu

O

HNBu3Sn

ArAr Ar

OO O

Cl

21 2223 24(1–1.28 equiv.)

Pd2(dba)3•CHCl3 (1 mol%)LiCl (1–1.28 equiv.)

THF, 60ºC, 2.5 hthen RT overnight

NH

N

NN

N

Conc. HClor 50% H2SO4

100ºC

3–4 h

Ar Yield, % Yield, %Ph 66 692-ClC6H4 4 732,6-Cl2C6H3 50 412-F3CC6H4 50 41

Scheme IV. Acylative Stille cross-coupling of 21 to provide products 23 and thence sorapazan precursors 24

N

25

NOMe

Ar1

NNOMe

Ar1

NNOMe

Ar1

1. nBuLi (2 equiv.)iPr2NH (2 equiv.)

Et2O, 30 min, 0ºC to –78ºC then 25 (1 equiv.)/Et2O, 1 h, then B(OiPr)3 (3 equiv.)

1.5 h, –78ºC to RT

2. Acidic workup 61–69% yields

B(OH)2

26

28

NNOMe

Ar1

27

BPinPinacol (1 equiv.)MgSO4, toluene

12–19 h, RT73–90% yields

Ar2

Ar2Br, Pd2(dba)3 (1 mol%)PCy3 (2.4 mol%)K3PO4 (aq. 1.3 M, 1.7 equiv.)1,4-dioxane, refl ux, 24 h18–76% yields

Ar1 = Ph, 4-MeOC6H4, 2-MeO-pyridin-5-yl, 2-F-pyridin-5-ylAr2 = pyridin-2-yl, 5-O2N-6-H2N-pyridin-2-yl, pyrimidin-5-yl

Scheme V. Sequential DoM–Suzuki Miyaura synthesis of arylpyridazines 28 (21)



depict cases in which the boronic acids 26 and 30, generated from DoM reactions, are isolated prior to

cross-coupling. Of particular note is the low yield of

boronic acid 30, which is likely attributable in part to

the instability of this heterocyclic boronic acid.

1.2 One-Pot DoM–Cross-Coupling MethodsA more effi cient process than shown so far is a DoM–

cross-coupling protocol carried out without isolation

of the intermediate species (boronic acid, zincate for

instance) which is most often accomplished using

Suzuki-Miyaura or Negishi cross-coupling reactions.

For instance, as part of a campaign towards the

synthesis of the antimicrobial agent GSK966587 (32,

Figure 2), a ‘one-pot’ DoM–cross-coupling method

was developed (23).

Thus, the DoM–iodination reaction of 33 was

investigated (Scheme VII) in preparation for Heck

coupling chemistry (Scheme VIII). The use of the

more traditional alkyllithium and lithium amide

bases was complicated by the formation of dianions

and by competitive fl uoride displacement. The use of

LDA at low temperatures under short reaction times

was promising but gave mixtures of both mono-

iodides 34 and 35 and bis-iodide 36. Although the

Uchiyama zincate mixed metal base TMPZn(tBu)2Li

gave predominantly the undesired mono-iodide 35,

the analogous (iPr)2NZn(tBu)2Li gave an encouraging

result. A further shift to (iPr)2NZnEt2Li (prepared by

mixing Et2Zn and LDA) gave excellent selectivity

for the desired iodide 34 which was eventually

isolated in 85% yield (74% from starting material 39, Scheme VIII).

After extensive screening, Heck coupling of iodide

34 with allyl alcohol was achieved to give the

-coupled product 37 in 77% yield (57% yield from

39, Scheme VIII). As a more effi cient alternative to this

sequential procedure, the Negishi cross-coupling of

the zincate intermediate 38 (the presumed metallated

species from the DoM reaction of 33) was realised and

gave a comparable yield of 37 (68% yield from 39)

but required no iodine and fewer purifi cation steps.

N29

ClR1O N30

ClR1O N31

ClR1O

(HO)2B Ar1. LDA (1.1 equiv.)2. B(OiPr)3 (1.2 equiv.)

THF, –78ºC to RTacidic workup, 13% yield

ArX (0.9 equiv.) Pd(PPh3)2Cl2 (5 mol%)

Na2CO3 (aq. 1 M)

1,4-dioxane, refl ux, 24 h, 29–98% yields

R1 = Me, EtAr2 = 2-MeO-pyridin-5-yl, 2-MeO-pyridin-6-yl, pyrimidin-5-yl, 2-MeO-pyrimidin-5-yl

Scheme VI. Sequential DoM–Suzuki Miyaura synthesis of aryl-2-chloropyridines 31 (22)

N

NHO

FO

NHO

ON

32

N

Fig. 2. Antimicrobial agent GSK966587

N

NMeO F

33N

NMeO F

34N

NMeO F

35N

NMeO F

36

++

I I

II

Base Equiv. Time, min Temp., ºC Area, %, by HPLC analysisLDA 1.5 15 –70 42 8 40LDA 1.1 5 –60 83 8 1.5TMPZn(tBu)2Li 1.1 30 23 26 34 23(iPr)2NZn(tBu)2Li 1.0 120 23 45 5 0(iPr)2NZnEt2Li 1.2 30 –10 96a 4 0a85% isolated yield

Scheme VII. DoM route to 7-fl uoro-8-iodo-2-methoxynaphthyridine 34 (23)



By its nature, the DoM–Negishi cross-coupling

protocol lends itself to a one-pot procedure whereby

the deprotonation, transmetallation (if necessary)

to a zincate and transition metal-catalysed cross-

coupling occur sequentially in the same reaction

vessel. Among the cases illustrated in Schemes IX–XI (24–26), of note is the use of the oxazole DMG which

by hydrolysis provides the desired carboxylic acid

in the target molecule 43 (Scheme IX). This is a

further demonstration of the use of tetrazole as a DMG

in the synthesis of the ‘sartan’ pharmaceutical 46

(Scheme X) and the use of catalytic zinc chloride and

of the pyridine N-oxide as a DMG in the preparation of

azabiaryl 49 (Scheme XI).

Recently, a one-pot DoM–Negishi cross-

coupling strategy that can utilise esters as DMGs

N

NMeO F

34

N

NMeO F

33N

HNO F

39N

NMeO F

N

NMeO F

37

I HO

Li+ –ZnEt2

38

1. SOCl2(nBu)2NCHO

toluene

2. MeOHno yield given

1. (iPr)2NZnEt2Li (1.1 equiv.)2. I2 (3.9 equiv.)

THF, –10ºC to RT, 85% yield74% yield from 39

HOBr (2.2 equiv.)

LDA (2.2 equiv., addn. at –30ºC)Tri(2-furyl)phosphine (8 mol%)Pd2(dba)3•CHCl3 (2 mol%)

THF, 45ºC, 60 min, 68% yield from 39

(iPr)2NZnEt2Li(1.1 equiv.)

THF, –10ºC to RT

Allyl alcohol (15 equiv.)Pd(OAc)2 (2.5 mol%)

dppf (5.5 mol%)NH4OAc (2 equiv.)

ethylene glycol130ºC, 7–8 h, 77% yield

57% yield from 39

Scheme VIII. Sequential and ‘one-pot’ DoM–Heck coupling synthesis of naphthyridine 37 (Note: The authors provide the yields for the optimisation, but also for a process whereby all of the batch is taken through the whole process with only minimal purifi cation. Hence overall yields comparing the two processes are given even though no yield is given for the conversion of 39 to 33)

N

O

Me

Me40

O

N

N

Me

Me

NnPr

N

OH

N

N

Me

Me

NnPr

N

Br

N

O

Me

Me

N

N

Me

Me

NnPr

N

42

41

43

nBuLi (1.2 equiv.)ZnCl2 (1.8 equiv.)0ºC, THF, 120 min

then Pd(PPh3)4 (1 mol%)41 (1 equiv.)

55ºC, 24 h, 55% yield

HCl, refl ux

30 min, 85% yield

Scheme IX. One-pot DoM–Negishi cross-coupling strategy for the synthesis of telmisartan 43 angiotensin II receptor antagonist (24)



has been developed by Knochel and coworkers

involving the amide bases tmpMgCl·LiCl (tmp =

2,2,6,6-tetramethylpiperidyl), tmp2Mg·2LiCl and

tmp2Zn·2MgCl2·2LiCl (27). These bases are used

in stoichiometric amounts (no extreme excess is

required), facilitated by LiCl which complexes and

solubilises the bases and leads to monomeric metallic

amides. Due to its stability (at least 6 months at 25ºC

under inert atmosphere) (28, 29) tmpMgCl·LiCl is

commercially available and is capable of metallating

moderately C–H acidic aromatic compounds. For

more demanding aromatic cases tmp2Mg·2LiCl (30)

may be used and for systems that contain sensitive

functional groups tmp2Zn·2MgCl2·2LiCl (31) has

proven to be effective. Unfortunately the latter two

bases are not as stable as tmpMgCl·LiCl; for instance

tmp2Mg·2LiCl is stable only for 24 h at 25ºC (27).

These reagents are usually prepared fresh for each

reaction, or set of reactions, from tmpMgCl·LiCl by

the addition of LiTMP or ZnCl2, respectively. The

use of these bases for combined metallation–cross-

coupling reactions greatly increases the potential

substrate scope of this strategy, as illustrated by

the synthesis of aromatic esters 51, 53 and 55

(Schemes XII–XIV). Noteworthy is the last case

since nitrile groups are not normally compatible

with the use of Grignard reagents. In addition, only

0.5 equivalents of tmp2Zn·2MgCl·2LiCl are required

(i.e. both potential TMP anions are available) and

transmetallation is unnecessary as this reagent

N NN NPh3C

44

N NN NPh3C

46

O

N

nBu

CO2Me

nBuLi (1.2 equiv.)ZnCl2 (1.8 equiv.)

–20ºC to RT, THF, 90 minthen

Pd(OAc)2 (5 mol%)QPhos (5 mol%)

45 (1 equiv.)75ºC, 2 h, 80% yield

O

N

nBu

CO2Me

45Br

Scheme X. One-pot DoM–Negishi cross-coupling strategy to synthesise valsartan 46 angiotensin II receptor agonist (25)

I+

–OTf

48

47 49

N+

O–

MeMe

N+

O–

MeMeiPrMgCl (1.2 equiv.)

–78ºC, 60 minthen

ZnCl2 (5 mol%)Pd(PPh3)4 (5 mol%)

48 (1.5 equiv.)70ºC, 10 min, 51% yield

Scheme XI. One-pot DoM–Negishi cross-coupling strategy using catalytic zinc chloride for the synthesis of azabiaryl N-oxide 49 (26)

1. TMPMgCl•LiCl (1.1 equiv.)0ºC, 6 h

2. Benzoyl chloride (1.0 equiv.)CuCN•2LiCl (10 mol%)

–40ºC to 25ºC, 3 h86% yield

50 51

Cl CO2Et Cl CO2Et

O PhScheme XII. One-pot DoM–Negishi cross-coupling protocol using commercially available tmpMgCl·LiCl



directly provides a zincate suitable for Negishi

cross-coupling under relatively standard conditions.

Although these reactions were developed and

optimised on 1–2 mmol scale, all of these examples

were performed on 80–100 mmol scale in order to

demonstrate good scale up potential.

The combined DoM–Suzuki-Miyaura cross-

coupling also lends itself to a one-pot procedure. An

illustration of this is our recent extension of previous

work on one-pot DoM–Suzuki-Miyaura reactions (32),

in which the synthesis of heterobiaryl sulfonamides

was developed with the aim of increasing the

available methodology for the construction of

bioactive molecules bearing the popular sulfonamide

pharmacophore (Scheme XV) (7).

This one-pot metallation-boronation–cross-coupling

procedure was generalised for tertiary and secondary

sulfonamides 56 in couplings with electron-rich and

-poor aryl and heteroaryl bromides and chlorides to

furnish biaryl sulfonamides 57. A change to a bulkier

catalyst was needed when meta or ortho substituted

sulfonamides were used as shown by example 57c.

1.3. Iridium-Catalysed Boronation–Suzuki-Miyaura Cross-Coupling: A Complementary MethodThe knowledge that iridium-catalysed boronation of

aromatics is qualitatively determined by steric effects

(33–37) led us to explore this reaction in DMG-bearing

substrates in order to establish complementarity with

52

CO2Et

53

CO2Et

Me

1. TMPMg•2LiCl (1.1 equiv.)25ºC, 45 h

2. ZnCl2 (1.1 equiv.)–40ºC, 15 min

3. 4-Bromotoluene (1.05 equiv.)Pd(OAc)2 (0.5 mol%)RuPHOS (1.0 mol%)–40ºC to 25ºC, 12 h

71% yield

Scheme XIII. One-pot DoM–Negishi cross-coupling protocol using tmp2Mg·2LiCl

54

CO2Et

55

CO2Et1. TMP2Zn•2MgCl•2LiCl (0.5 equiv.)25ºC, 48 h

2. Iodobenzene (1.0 equiv.)Pd(dba)2 (0.5 mol%)(o-Fur3)P (1.0 mol%)

25ºC, 6 h84% yield

PhNCNC

Scheme XIV. One-pot DoM–Negishi cross-coupling protocol using 0.5 equivalents tmp2Zn·2MgCl·2LiCl

1. nBuLi or LDA (1.3 equiv. or 2.3 equiv.)2. MeOBpin or iPrOBpin (3.5–4.0 equiv.)

THF, –78ºC to RT, 13 h

3. Pd(dppf)Cl2•CH2Cl2 (8 mol%)Na2CO3 (4 equiv.), DME:H2O (4:1), 80ºC, 12 h

15–74% yields

ArHetAr

H

SO2NRR1

56

ArHetAr

SO2NRR1

57

ArHetAr

57a (71%) 57b (65%) 57c (15%) [Pd(dppf)Cl2•CH2Cl2] (60%) [Pd(DtBPF)Cl2]

SO2NEt2

SO2PhN

SO2NEt2

SO2PhN

N

N

SO2NEt2

MOM

Scheme XV. One-pot DoM–Suzuki-Miyaura cross-coupling route to heterobiaryl sulfonamides 57 (7)



the DoM–Suzuki-Miyaura cross-coupling process

(Scheme XVI) (38). Thus, complementary methods

of considerable scope for the synthesis of biaryls and

heterobiaryls were demonstrated by C–H activation at C-2

(DoM) and at C-3 (Ir-catalysed boronation) of 58 which

offer new routes for the regioselective construction of

substituted biaryls 60 and 59 respectively.

1.4 The Use Of DoM–Cross-Coupling Strategies in Total SynthesisWe have also employed the DoM–cross-coupling

strategy as part of syntheses of targeted drugs and

natural product intermediates. In 2004, we reported

a synthesis of the tetracyclic A/B/C/D ring core 66 of

the antitumour agent camptothecin (Scheme XVII) (39).

This route is highlighted by an anionic ortho-Fries

rearrangement of O-carbamate 61 to give the

quinolone 62, a Negishi cross-coupling of trifl ate 63

to give biaryl 65, and a modifi ed Rosenmund–von

Braun reaction to provide the tetracyclic core 66 of

the antitumour alkaloid camptothecin in seven steps

with an overall 11% yield.

Most recently, we have completed a total synthesis

of schumanniophytine 72 (Scheme XVIII) (40), a

natural product which had been prepared only once

previously (41). Starting with DoM chemistry to obtain

the cross-coupling partners 68 from 67, our route

takes advantage of a combined DoM–cross-coupling

strategy using Stille or Suzuki-Miyaura reactions to

synthesise biaryl 69, and also incorporates a key ortho-

silicon-induced O-carbamate remote anionic Fries

rearrangement of carbamates 70 to provide amides 71.

ArHetAr

DMG

H

R

60

DMGR

DMGR

H HH

ArHetAr

5859

1. DoM

2. Suzuki-Miyaura

C2–H activation

1. Ir/B2Pin2

2. Suzuki-Miyaura

C3–H activation

DMG = CONEt2, OCONEt2, OMOM, SO2NEt2

Scheme XVI. Complementary ortho and meta boronation/Suzuki–Miyaura cross-coupling reactions of DMG bearing aromatics (38)

N OCONEt2

61 62 63

NH

CONEt2

O N

CONEt2

OTf

1. LDA (1.3 equiv.)THF, –78ºC, 1 h

2. MeOH61% yield

Tf2O (1 equiv.)NEt3 (1.8 equiv.)

CH2Cl2, 0ºC, 1 h70% yield

NBr OMe

N

CONEt2

N OMe

64 65

Steps

NN

O

66

1. tBuLi (2.0 equiv.)THF, –78ºC, 15 min

2. Anhyd. ZnBr2 (1.1 equiv.)–78ºC, 1 h

3. 63/Pd(PPh3)4 (3 mol%) THF/refl ux, 60 h

57% yield

Scheme XVII. Key reactions in the synthesis of the tetracyclic core 66 of camptothecin: anionic ortho-Fries rearrangement 61–62 and Negishi cross-coupling 64–65 (39)



2. DoM–C–Heteroatom (N, S, O) Cross-Coupling Reactions

With the advent of transition metal-catalysed C–N,

C–O and C–S cross-coupling technologies, these

reactions have also been fused with DoM and

the combined DoM–heteroatom cross-coupling

methodology has become viable for the construction

of biologically interesting molecules and natural

products. Thus the naphthyldihydroisoquinoline

alkaloid ancistrocladinium B 76 (Scheme XIX),

which shows high in vitro antileishmanial activities,

has been synthesised from 73 via methoxymethyl

(MOM) directed metallation-bromination to provide

bromide 74, followed by Buchwald-Hartwig amination

to furnish the key intermediate 75. The synthesis of

ancistrocladinium C (77) was also achieved using a

similar strategy (42).

Similarly, the construction of a C–O bond has been

accomplished using DoM–cross-coupling strategies.

Although copper catalysis is the preferred choice for

C–O bond formation (43–45), it is also possible to use

pgm catalysis as an alternative (46–48).

Among the DoM–C–heteroatom cross-coupling

strategies, the DoM–C–S regimen is far less evident in

the literature. In an instructive study which shows the

utility of inverting the coupling partners, substituted

2-iodo-anisoles 79 (Scheme XX) were synthesised

using DoM chemistry and subjected to Buchwald-

Hartwig coupling with 3-fl uorobenzenethiol 81,

to afford biaryl sulfi de derivatives 83 which were

further modifi ed to give the desired compounds 84.

Alternatively, 3-chloro-2-methoxyphenyl thiol 80

was coupled with 3-fl uoroiodobenzene 82 to furnish

similar analogues 83. These were demonstrated

to possess in vitro potency for blocking glycine

transporter-1 (GlyT-1), which has been recognised

as a potential strategy for the treatment of

schizophrenia (49).

OMeMeO

OCONEt2

OMeMeO

OCONEt2

OMeMeO

Et2NOCOR1

N

67 69

OMeMeO

Et2NOCO N

Yield, %R = Me 70a 94R = Et 70b 91

R3Si

OMeMeO

R2OR3Si

HO

72

N

OEt2N Me

O

OOSteps

TMEDA (1.3 equiv.)sBuLi (1.3 equiv.)

THF, <–72ºC, 10 min thenI2 (1.5 equiv.), <–72ºC to RT

or

1. B(OiPr)3 (2.6 equiv.), THFLDA (1.2 equiv.)

–78ºC, 1 h–78ºC to RT, 1 M HCl

2. Pinacol (1.05 equiv.), EtOAc

68a, PdCl2(PPh3)2 (10 mol%)4-tributylstannylpyridine (1.5 equiv.)

DMF, refl ux, 1 h, 73% yieldor

68b, Pd(PPh3)4 (4 mol%)4-bromopyridine hydrochloride (1.0 equiv.)/Na2CO3 (2 equiv.)

DME/Na2CO3 (2 M)90ºC, 20 h, 99% yield

LDA (3.5 equiv.), Me3SiCl(4.5 equiv.), THF

–78ºC to RT, 10 hor

nBuLi (1.2 equiv.), THF –100ºC, 5 min, then

Et3SiCl (2.5 equiv.)–100ºC, 1.5 h

LDA (4 equiv.)THF, 0ºC to RT, 1 h

then

Ac2O or BzCl (5 equiv.)0ºC to RT

Yield, %R2 = Ac 71a 75R2 = Bz 71b 65

Yield, %R1 = I 68a 86R1 = Bpin 68b 95

NO

Scheme XVIII. Key reactions in the total synthesis of schumanniophytine 72 (40)

DMG DMG

X

DMG

Y

DoM Cross-coupling

X = Halide or pseudohalideY = NR2, SR, OR



OMe

OMe

Me

O

73

OMe

OMe

Me

O

74

BrOMe

Me

OMe

O

MeO

OMe

NH2

Me

(1.2 equiv.)

1. nBuLi (1.9 equiv.)TMEDA (1.9 equiv.)

THF, –10ºC, 1 h

2. (CBrCl2)2 (1.5 equiv.)–10ºC to RT

74% yieldPd2(dba)3 (1 mol%)rac-BINAP (2 mol%)KOtBu (1.4 equiv.)toluene, refl ux, 2 d

49% yield

MeO

OMe

HN

Me

75

OMe

Me

OHN

Me

76

1. AcCl (3 equiv.)DMAP (3 equiv.)

toluene, refl ux, 1 h86% yield

2. POCl3 (5 equiv.) CH3CN, refl ux, 1 h

95% yield

+

MeOMe

MeOTFA–

OMeOHN

Me

77

+

MeOMe

MeOTFA–

Me

Scheme XIX. Synthesis of ancistrocladinium B 76 as atropo-diasteromers (P/M) 46/54 and ancistrocladinium C 77 as atropo-diasteromers (P/M) 3/2 using a DoM–C–N cross-coupling strategy (42)

OMe

R1

OMe

R1

OMe

R1O

R2

F

F

F

F

IHS

+

IOMeSHCl

+

S

S

N

O

HO

78 79 81

80 82

83

84

For R1 = 3-Cl:1. sBuLi, TMEDA THF, –95ºC, 1 h

2. I2, –95ºC to RT 16 h

Pd2(dba)3, KOtBu, toluene

Pd2(dba)3 DPEPhos, KOtBu

toluene, 100ºC, 90 min 55% yield

R1 = 3-Cl, 4-Cl, 5-Cl, 6-Cl, 4-Br, 5-BrR2 = 3-Cl, 4-Cl, 5-Cl, 6-Cl, 4-Ph, 4-thiophen-3-yl, 3-MeOC6H4-4-yl, 4-MeOC6H4-4-yl, 4-ClC6H4-4-yl, 5-Ph

Scheme XX. DoM–C–S cross-coupling route to diaryl sulfi des 84

3. DoM–Halogen Dance–Cross-Coupling Reactions

The DoM reaction on halogenated aromatic and

heteroaromatic compounds may be accompanied

by halogen dance reactions in which halogens, most

notably iodine, undergo migration to the incipient

DMG DMG

X

DMGDoMHalogen dance

X = Br, IR = Substituent inserted through cross-coupling

(Het) (Het) (Het)

R

X

R R

Cross-coupling DMG(Het)

R

R



anion and provide, generally but not invariably,

the most thermodynamically stable anion (50).

This not only provides an option to halogenate

positions which are otherwise diffi cult to access,

but also enables the introduction of an external

electrophile at the site bearing the newly formed

anion. In this context, we have developed routes

to polyfunctionalised pyridines (51) and others

have utilised halogen dance in the formation of

heterobiaryls (Scheme XXI) to provide substituted

2-arylquinolines as novel CRF1 receptor antagonists

(52). Thus, metallation-iodination of quinoline 85

afforded iodoquinoline 86 which, when subjected

to a second metallation-protonation, gave the

halogen dance product 87. Suzuki-Miyaura cross-

coupling and subsequent steps led to the substituted

arylquinolines 88. We have found that it is important

to be vigilant for potential undesired halogen dance

reactions which may arise in many metallation

reactions of halogenated heterocycles.

N

Cl

N

Cl

N

Cl

N

Cl

I

I

OMeMeO

OMe

Me

NEt2

LDA, THF, –78ºCI2

Metallation

LDA, THF, –78ºC

Halogen dance

85 86 (49% yield) 87 (56% yield)

88

Scheme XXI. Metallation–halogen dance–Suzuki-Miyaura route to 2-arylquinoline 88 CRF1 receptor antagonist

DMG DMG

X

DMGDoM Cross-coupling

R

O

( )nDreM

X = Halide or pseudohalideR = H, Men = 0, 1

4. DoM–Cross-Coupling–DreM Reactions

The synthesis of interesting polycyclic aromatic and

heteroaromatic molecules has a long history in the

Snieckus laboratories (a recent example uses the

Suzuki-Miyaura cross-coupling (53)). To construct

these systems, the directed remote metallation (DreM)

reaction (54, 55) on specifi cally designed 2-DMG

biaryls is the key reaction to forge the central aromatic

bridging ring. Generally this method complements

already established methods for their synthesis

and allows easy access to previously unreported

compounds. The standard conditions for a DreM

reaction are formation of the anion by treatment with

LDA at –20ºC or 0ºC, followed by warming to room

temperature to ensure completion of the anionic

cyclisation. Depending on the type of substituents

in the biaryl starting material, often a minimum of 2

equivalents of LDA is required, proposed to be due to

‘losing’ one or more equivalents to coordination with

these substituents.

4.1 Synthesis of Biaryls Using DoM–Cross-Coupling ReactionsFor the construction of requisite biaryls, the

DoM–Suzuki-Miyaura protocol is frequently

practiced, although other cross-coupling strategies

such as DoM–Negishi are also used. Thus, in

general (Scheme XXII), cross-coupling partners

2-halodiethylbenzamides 91 and boronic acids 92

are synthesised using standard DoM conditions

from diethylbenzamides 89 and by metal halogen

exchange on bromobenzenes 90 respectively,

although currently many of the boronic acids may be



purchased. Alternatively, the cross-coupling partners

may be inverted so that DoM derived boronic

acids 91 (X = B(OH)2) may be directly coupled with

aromatic trifl ates or with bromobenzenes 90 without

the need for metal halogen exchange. We have found

that the Suzuki-Miyaura reaction usually requires

only minimal development using standard palladium

sources and ligands, although the reactions are still

substrate dependent. On the other hand, certain

boronic acids, especially heteroaromatic cases,

can be diffi cult to handle and unstable due to their

propensity for protodeboronation. As a notable

example, we have learned from experience that

3-methoxy-N,N -diethylbenzamide-2-boronic acid

is diffi cult to isolate, and is reliably synthesised

only if the aqueous quench of the reaction mixture

is performed at –40ºC slowly by the addition of a

CH2Cl2/H2O mixture. Others have reported similar

problems regarding this boronic acid (56).

The absence of reports concerning aryl sulfonamide

ortho-boronic acids prompted a study in which the

problems associated with the synthesis of this class

of unstable boronic acids was solved, at least in this

particular case (7). Although it was determined

that metallation of aryl sulfonamides proceeds

uneventfully, as evidenced by deuterium quench

experiments, quenching the metallated species

with B(OR)3 reagents followed by aqueous workup

provided boronic acids in low yields, accompanied

by recovery of starting material, which suggested

instability of the ortho-boronic acids. This problem

was circumvented by utilising an in situ quench with

MeOBpin or iPrOBpin as electrophiles, leading directly

to the boropinacolate derivatives which are known to

be more stable than the corresponding boronic acids.

Similarly in the even more unstable pyridine boronic

acid series, in situ formation of boropinacolates was

advantageous in isolation of compounds useful for

Suzuki-Miyaura cross-coupling reactions (32).

Another solution for the synthesis of problematic

arylboronic acids stemming from our laboratories

is the ipso-borodesilylation reaction of trimethylsilyl

arenes (57). The silylated starting materials are

readily obtained in high yields using DoM chemistry,

and are quite stable with the exception of certain

heteroaromatic silanes. Treatment with BCl3 or BBr3

affords the Ar-BX2 species which, without isolation, may

be converted into the corresponding boropinacolates

by stirring with pinacol, or otherwise may be used

directly in a one-pot cross-coupling process.

4.2 Combined DoM–Suzuki-Miyaura–DreM Synthesis of FluorenonesTreatment of biaryl-2-amides 93a, derived from

DoM–cross-coupling reactions, under standard DreM

conditions results in alternate ring deprotonation

followed by cyclisation to provide fl uorenones 94

in good yields (Scheme XXIII). As ourselves and

others (58, 59) have demonstrated, various substituted

fl uorenones, azafl uorenones and two natural products

dengibsinin 95 and dengibsin 96 may be synthesised

using this strategy (60, 61).

Generally the highest yields are obtained for

biaryl cases bearing an additional 3-DMG which

promotes synergistic metallation, thereby leading

to regioselective cyclisation. In the synthesis of

azafl uorenones 99 using this strategy (Scheme XXIV),

the use of a one-pot DoM–Suzuki-Miyaura protocol was

CONEt2

R1DoM

Metal-halogen exchange

–

–R3

R2Br

CONEt2

R1

R2

R3

B(OH)2

X

Et2NOC

R1

R2

R3

Cross-coupling

1. sBuLi/TMEDA THF, –78ºC

2. Electrophile

1. nBuLi THF, –78ºC

2. Electrophile

X = halogen (or B(OH)2 when coupled with 90)R3 = H 93a Me 93b

89 91

90 92

93

Scheme XXII. DoM–Suzuki-Miyaura cross-coupling synthesis of biaryls 93



essential due to the instability of the pyridyl boronates

towards protodeboronation (32).

This method proved useful for the construction of

diverse azafl uorenones with electron-donating and

electron-withdrawing substituents. This sequential

DoM–cross-coupling–DreM strategy allows the

construction of azafl uorenones which are inaccessible

or afford isomeric mixtures by the traditional Friedel-

Crafts reactions.

4.3 Combined DoM–Suzuki-Miyaura–DreM Synthesis of Phenanthrols and PhenanthrenesTreatment of biaryls exhibiting 2-methyl substituents

93b under standard DreM conditions affords

9-phenanthrol derivatives 100 (Scheme XXV). The

deprotonation is often – but not always – indicated

by a deep red colour attributed to the generated tolyl

anion. Conversion of the resulting phenanthrols 100 to

phenanthrenes 101 is readily achieved using trifl ation

followed by palladium-catalysed hydrogenolysis. Often

no purifi cation is required for the intermediate steps,

and the fi nal phenanthrenes may be obtained in good

yield and high purity after a simple recrystallisation.

This route is scalable and reliably provides

substituted phenanthrenes in high purity which have

been used successfully in our collaborative projects

to conduct toxicity studies concerning the effects of

substituted polyaromatic hydrocarbons on fi sh (62).

R1

Et2NOCR2

R1 R2

OLDA (2.5 equiv.), THF –20ºC or 0ºC

93a 94O

OMeOH

OHO

OMeOH

OH

OMe

95 96

Scheme XXIII. Synthesis of fl uorenones using the combined DoM–cross-coupling–DreM strategy for dengibsinin 95 and dengibsin 96

DMGN DMG

N

RR

N

O

97 98 99

1. B(OiPr)3 (1.1 equiv.)THF, –78ºC to –10ºC

2. LDA (1.1 equiv.), 0ºC, 45 min3. Pinacol (1.2 equiv.), RT, 1 hor N-methyldiethanolamine

(1.1 equiv.), 0ºC, 2 h

3. ArBr (1.1 equiv.)Na2CO3 (aq., 2 M, 5 equiv.)

Pd(PPh3)4 (5 mol%)PhMe, refl ux, 12 h

30–76% yields

DMG = CONEt2

LDA (1.2–3.0 equiv.)THF, –78ºC to 10ºC

55–81% yields

DMG = 2-CONEt2, 3-CONEt2, 4-CONEt2, 4-Cl, 2-F, 3-OCONEt2ArBr = various, containing R = MeO, CN, NO2, CONEt2, Cl groups

Scheme XXIV. One-pot DoM–Suzuki-Miyaura–DreM synthesis of azafl uorenones 99 (32)

R1

Et2NOCR2

93bMe

R1

R2HO

100 101

R1

R2LDA, THF, –20ºC or 0ºC 1. Tf2O, pyridine, CH2Cl2 2. Pd(OAc)2, PPh3, Et3N

HCO2H, DMF

Scheme XXV. Synthesis of phenanthrenes 101 by the combined DoM–Suzuki-Miyaura–DreM strategy



4.4 Combined DoM–Suzuki-Miyaura–DreM Synthesis of Acridones and BenzazepinonesA DreM process analogous to that shown in

Scheme XXV may also be achieved on diarylamines

103, which are prepared using palladium-catalysed

Buchwald-Hartwig cross-coupling of anilines 102 with

DoM derived halo or pseudohalo diethylbenzamides

91, followed by N-alkylation. Thus treatment of

diarylamine 103a (R2 = H), under standard DreM

conditions provides acridones 104a (n = 0) in

good to excellent yields. In an analogous fashion to

the formation of phenanthrenes (Scheme XXV),

subjection of the diarylamine 103b (R2 = Me) to

standard DreM conditions affords dibenzazepinones

104b (n = 1), also in good to excellent yields

(Scheme XXVI) (63).

These protocols constitute anionic equivalents of

Friedel-Crafts type cyclisations affording acridones, and

complement existing syntheses of dibenzoazepinones,

compound classes which both exhibit signifi cant

bioactivities. For instance, acridone derivatives possess

antimalarial properties (64), and dibenzoazepinone

derivative trileptal is an antiepileptic drug (65).

In a collaborative study, we investigated the multi-

nitrogen-containing imidazo[1,5-a]pyrazine 105 for

use as a scaffold for the preparation of potentially

bioactive molecules. Without prediction based

on available precedent, the metallation of 105a and 105b followed by iodination afforded C-5

iodinated compounds 106a and 106b in high yields.

Subsequent Suzuki-Miyaura cross-coupling with

2-(diethylcarbamoyl)phenylboronic acid (synthesised

from N,N-diethylbenzamide using a DoM protocol)

provided biaryls 107a and 107b. Treatment of 107b

with LiTMP at cryogenic temperatures furnished

the previously unknown triazadibenzo[cd,f]azulen-

7(6H)-one 108b (Scheme XXVII) (66). To the

best of our knowledge, DreM processes of complex

heterocycles such as 107 had not been previously

reported.

91

R1

OEt2N

X

R3

R2

HN+

R2 = H 102a Me 102b

1. [Pd]

2. MeI

R2 = H 103a Me 103b

R1

OEt2N

R3

R2Me

NLDA (2–4 equiv.)

n = 0 104a 1 104b

R1 R3

( )n

O

NMe

Scheme XXVI. Synthesis of acridones and dibenzazepinones using DoM–C–N cross-coupling–DreM strategy

N

Me

X

X = Cl 105a OMe 105b

X = Cl (quant.) 106a OMe (79%) 106b

N

Me

X

I

B(OH)2CONEt2

(1.1–1.2 equiv.)Pd(PPh3)4 (5 mol%)

K2CO3 (3 equiv.)

DME:H2O (50:7) refl ux, 4 h

1. nBuLi (1.0–1.2 equiv.)15 min, THF, –78ºC

2. I2 (1.2–1.3 equiv.), 15 min THF, –78ºC

NN N

N

N

Me

X

NN

CONEt2

X = Cl (79%) 107a OMe (61%) 107b

N

OMe

NN

O

X = OMe (45%) 108

HTMP (3 equiv.), nBuLi (3 equiv.), THF, –78ºC, 90 min

107b

Scheme XXVII. DoM–Suzuki–DreM–cyclisation route to triazadibenzo[cd,f]azulen-7(6H)-one 108b (64)



5. Scale-Up and Industrial use of DoM–Cross-Coupling–DreM ReactionsIf proper safety protocols are followed and

temperature and stirring of the reaction mixture are

controlled and maintained, metallation chemistry

may be effectively used for large scale synthesis. In

fact, there is often no viable alternative to the use of

a DoM–cross-coupling sequence at multi-kilogram

scale in the pharmaceutical and fi ne chemical

industry (67–69). For instance, Merck has recently

demonstrated a practical, effi cient and multi-hundred

gram synthesis of 3-bromo-6-chloro-phenanthrene-

9,10-dione 113 using a DoM–cross-coupling–DreM

sequence (Scheme XXVIII) (70). Compound 113

is a useful building block for the preparation of

pharmaceutically important phenanthrenequinones

and phenanthreneimidazoles.

Similarly, as further evidence of utility, Merck

has achieved a kilogram-scale chromatography-

free synthesis of mPGE synthase I inhibitor

MK-7285 119 (Scheme XXIX) (71). Thus DoM–

boronation of 114 provided the lithioborate 115

Cl

CONEt2

Cl

CONEt2

Cl

Et2NOCB(OH)2

Me

HO

Cl Cl

O

O

Br

109 110 111(89% yield over 2 steps)

112 113

1. B(OiPr)3 (1.6 equiv.)DME

2. LDA (1.6 equiv.)–35ºC to 25ºC

3. H2O(regioselectivity 97>1)

2-Iodotoluene (0.93 equiv.) Pd(OAc)2 (0.5 mol%)

PPh3 (1 mol%)K2CO3 (2.5 equiv.)

DME/THF/H2O, 8 h, 70ºC

1. LiNEt2 (1.3 equiv.), DME, –45ºC, 2 h2. HCl (4 equiv.), 0ºC to 5ºC

85% yield

Scheme XXVIII. Large scale synthesis of phenanthrene-9,10-diones 113 using a combined DoM–cross-coupling–DreM strategy. 109 was used at a scale of 245.7 g, 111 was produced at a scale of 311.5 g and 112 at 200 g (68)

O O

CONEt2

MeBr

OH

MeMe

O

Li+ –B(OiPr)3CONEt2CONEt2

1. B(OiPr)3 (2 equiv.)THF, –25ºC

2. LDA (2 equiv.)<–20ºC, 2 h 3. H2O, 20ºC

quantitative conversion

(0.7 equiv.)

PdCl2•dppf (2.5 mol%)H2O, refl ux, 12 h

88–98% yield

114115

116

117

MeOH

MeMe

O

OH

OH

MeMe

118O

OH

MeMe

119

NC

NC

FN

NH

Et2NLi (3.5 equiv.)THF (<0.24 M)

0ºC to –5ºC, 14 h63% yield

Scheme XXIX. Large scale synthesis of mPGE synthase I inhibitor 119 using the combined DoM–cross-coupling–DreM strategy. 114 was used at a scale of 3.75 kg, 117 was produced at a scale of 7.69 kg (69)



which, without isolation, was subjected to Suzuki-

Miyaura cross-coupling with bromobenzene 116

to afford biaryl 117. In the key step, treatment of

biaryl 117 with lithium diethylamide resulted in

a DreM cyclisation to provide the phenanthrol

118 in acceptable yield. A significant observation

was that in the DreM reaction, at concentrations

greater than 0.24 M, competitive intermolecular

condensation provided 5–10% of an undesired

product.

6. Diversifi cation of the DoM–Cross-Coupling Strategy

The unique power and considerable synthetic

advantage of DoM chemistry is the regioselective ortho

introduction of only one functional group per DMG.

Furthermore, synthetic strategies may be devised

to use the same DMG to achieve 2,6-disubstitution

and thus to construct 1,2,3-trisubstituted aromatic

systems (72). Using the N-cumylsulfonamide DMG,

this strategy has been adapted for the synthesis of

7-substituted saccharins (Scheme XXX) (73). Thus,

as conceptually illustrated below, the straightforward

DMG DMG

R1

DMGFirst DoM

Cross-coupling R1

R1, R2 = Substituent introduced through cross-couplingR3 = Substituent introduced through DoM

Second DoM

Cross-coupling

Cross-coupling

DMG

R3

R2

DMG

R3

R1

First DoM

Second DoM

First DoM (E+ = halide source)

Second DoM (E+ = ClCONEt2)

SO2NHCumylFirst DoM

Cross-couplingSecond DoM

SO2NHCumyl

CONEt2

Ar

TFAAcOH

O

Ar

SO2

NH

SO2NHCumyl

120

SO2NHCumyl

SO2NHCumyl SO2NHCumyl

I

ArAr

CONEt2

121

122 123 124

O

Ar

S O2

NH

ArB(OH)2 (1.1–2.0 equiv.)Pd(PPh3)4 (5 mol%), A or B or C or D, 24 h

A. K3PO4 (3 equiv.), DMF, 100ºC B. Na2CO3 (8–10 equiv.), THF, 70ºCC. Cs2CO3 (2–8 equiv.), THF, 70ºCD. Na2CO3 (10 equiv.), DME, 90ºC

57–99% yields

1. sBuLi (2.2 equiv.)TMEDA (2.2 equiv.)

THF, –78ºC

2. I2 (1.2 equiv.)–78ºC to RT

3. NH4Cl (aq.)88% yield

1. nBuLi (2.2 equiv.)TMEDA (2.2 equiv.)

THF, 0ºC, 1 h

2. ClCONEt2 (1.2 equiv.)0ºC to RT

3. NH4Cl (aq.)78–99% yieldsa

1. TFA, RT, 10 min2. AcOH, refl ux, 12 h

3. HCl

42–89% yields (over two steps)

Ar = C6H5, 2,3-di-MeC6H3, 3,5-di-ClC6H3, 2-Et2NC(O)C6H4, naphthalen-2-yl, thiophen-3-yla Some of the products were taken to the next steps without purifi cation

–

–

Scheme XXX. Double use of the N-cumylsulfonamide DMG in the synthesis of substituted saccharins 124

122



DoM–halogenation–Suzuki-Miyaura coupling of

N-cumylbenzenesulfonamides 120 provided,

via iodide 121, the biaryls 122. Then the same

N-cumyl sulfonamide DMG served for a second

DoM–carbamoylation to furnish the biaryl amide

sulfonamide 123. Decumylation of 123 using TFA,

followed by acid-mediated cyclisation gave rapid

access to saccharins 124 in good overall yield.

Aside from interesting pharmaceutical properties

and use in the fi elds of fl avour, polymer and

coordination chemistry, the saccharin core has

played a role in the discovery of a human leukocyte

elastase inhibitor, KAN400473 (125, Figure 3), used

for the treatment of emphysema (74). It also features

in the Merck carbapenem antibacterial agents (126,

Figure 3) (75).

Double DoM–double cross-coupling reactions

involving multiple DMGs are also useful synthetic

tactics. Thus the fi rst total syntheses of natural,

unsymmetrical 2,3-diacyloxy-p-terphenyls, thelephantin

O 131a (Scheme XXXI) and terrestrins C and D

(131b and 131c, respectively), were achieved using

double DoM and bromination of 127 to give the

hexasubstituted benzene 128 which, after Suzuki-

Miyaura cross-coupling with 129, afforded the key

intermediate teraryl 130. Synthesis of the symmetrical

diesters vialinin A/terrestrin A 131d and terrestrin B

131e was also achieved using the same sequence (76).

O

O

O

NR3+

O

CO2–

HO Me

Me N

NSO2

126

NNN

N

NSS

O2

125

Fig. 3. Biologically active saccharins KAN400473 125 and Merck antibacterial agents 126

MeMe

OMOMMOMO

O O

MeMe

OMOMMOMO

O O

MeMe

OMOMMOMO

O O HO OH

O OO O

OHHO

R1 R2

Br Br

TBSO OTBS

127

130

128

131a–e

129

TBSOOB

(1.5 equiv.)3

1. nBuLi (3 equiv.)THF, 0ºC, 1 h

2. BrCF2CF2Br (3 equiv.)0ºC, 1 h3. H2O

94% yield

Pd(PPh3)4 (5 mol%)K2CO3 (6 equiv.)

1,4-dioxane:H2O (3:1) 2 h, refl ux78% yield

R1 R2

131a Ph CH2Ph131b Pr CH2Ph131c Me CH2Ph131d CH2Ph CH2Ph131e Pr Pr

Scheme XXXI. Synthesis of teraryl natural products using double DoM–Suzuki-Miyaura cross-coupling sequence



7. The DMG as a Pseudohalide in Cross-Coupling Reactions

As documented in this review, cross-coupling of DoM

derived species such as B, Zn, Sn and Mg has become

a highly useful synthetic strategy. The development of

DMGs that themselves act as cross-coupling partners

was fi rst achieved in our group with O-carbamates

(77) and subsequently with sulfonamides (78) under

Ni(acac)2 conditions. Furthermore, these DMGs may

be excised from the aromatic framework using the

-hydride donor properties of iPrMgCl and iPr2Mg

respectively, thus establishing the latency concept

of DMGs (77, 78). Recently additional DMGs such as

ethers, esters, O-carbamates under Suzuki-Miyaura

conditions (79, 80) and O-sulfamates (79) have

been established as cross-coupling partners (81).

The non-reactive nature of some of these groups in

palladium-catalysed coupling reactions allows the

establishment of orthogonal processes (82, 83). For

example, subsequent to work in our laboratories

(80), Garg et al. (84) recently explored regioselective

construction of biaryls based on differential reactivity

of bromide, O-carbamate and O-sulfamate groups

toward Pd and Ni catalysts (Scheme XXXII). Thus,

DoM–bromination of 132 furnishes aromatic bromide

133, which undergoes sequential and selective

palladium-catalysed Stille, nickel-catalysed Suzuki-

Miyaura and nickel-catalysed C–N cross-coupling

to rapidly provide biaryl 136 in good yield. Recent

efforts on transition metal-catalysed cross-coupling

reactions of new O-based electrophiles via C–O bond

activation have focused on nickel and iron based

catalysis (85–87).

Authors’ note added in proof: after the submission

of this review, Feringa and co-workers established the

palladium-catalysed cross-coupling of alkyl, alkenyl

and aromatic lithiates (some derived using DoM) with

aromatic bromides (88).

132

1. TMEDA (1.1 equiv.) sBuLi (1.1 equiv.)

THF, –93ºC, 45 min 2. BrCF2CF2Br (1.4 equiv.)

–93ºC to RT

3. NH4Cl (aq.)78% yield

LiCl (5 equiv.) PdCl2(PPh3)2Me4Sn, DMF100ºC, 16 h

74% yield

p-MeOArB(OH)2 (5 equiv.) NiCl2(PCy3)2 (20 mol%)

K3PO4 (7.2 equiv.)

toluene, 130ºC, 8 h52% yield

Morpholine (2.4 equiv.) Ni(cod)2 (10 mol%)SIPr4•HCl (20 mol%) NaOtBu (2.2 equiv.)

dioxane, 80ºC, 3 h64% yield

OCONEt2

OSO2NMe2

OCONEt2 OCONEt2

OCONEt2

133 134

135 136

Br Me

Me Me

OMeOMe

O

N

OSO2NMe2 OSO2NMe2

Scheme XXXII. Use of O-carbamate and O-sulfamate DMGs as cross-coupling partners

DMG DMG

R1

DoM

R1

Cross-coupling R2

R1 = Substituent introduced through DoMR2 = Substituent introduced through cross-coupling



Conclusions This brief review has demonstrated that the combined

DoM–cross-coupling strategy, fi rst developed in our

laboratories in the mid-1980s, has considerable value

in organic synthesis. In this aim, we have attempted

fi rstly to provide supportive evidence using selected

recent examples derived from industrial and

academic laboratories, including many from our own

work. Emphasis has been placed on heterocycles,

which constitute 80% of current marketed drugs,

with synthetic case studies on a variety of bioactive

molecules in early, clinical or process stages of

development, including soraprazan (Figure 1),

GSK966587 (Figure 2), ancistrocladinium B and

C (Scheme XIX) and CRF1 receptor antagonist

(Scheme XXI). As will be recognised, the

heterocycles range from recognisable to more

unusual and complex frameworks (for example

Scheme XXVII). The pgms, particularly palladium,

catalyse many of the processes, contributing to the

enormous versatility of this strategy.

The second aim of the review has been to offer,

in various described processes, practical from-the-

bench tips based on our experience, at least in

small-scale reactions. These include the advantage

of deuterium-quench experiments to establish the

extent of the DoM step before taking the road to

scale-up (for example Scheme III), and the caveat

regarding purity of starting materials and their

instability.

Prognosis for the DoM–Cross Coupling StrategyEmerging from the content of this review are the

following features:

1. DoM–C–C Cross-Coupling Reactions This section suggests that among the cross-

coupling reactions used in combination

with DoM: Ullmann, Heck, Sonogashira,

Negishi, Stille and Suzuki-Miyaura, the latter

dominates the synthetic landscape with

increasing presence of the Negishi protocol.

The advent of new nontraditional lithium

bases such as the commercial Knochel

type tmpMgCl·LiCl combined with zinc

transmetallation and Negishi coupling

(Scheme XII) are beginning to provide more

convenient conditions for the DoM–cross-

coupling strategy.

Iridium-catalysed boronation offers a

complementary method for meta boronation

compared to the DoM–Suzuki-Miyaura

coupling process (Scheme XVI).

Only an inkling has been given of the

potential for DoM–cross-coupling in natural

product synthesis (Schemes XVII and XVIII)

and this can only be expected to grow in

importance.

2. DoM–C–Heteroatom (N, S, O) Cross-Coupling Reactions Based on our literature review, this motif has

considerable use in combined DoM–Hartwig-

Buchwald C–N and C–O cross-coupling

processes and is as yet underdeveloped for

C–S fusion reactions.

3. DoM–Halogen Dance–Cross-Coupling Reactions Although the agreeably named halogen

dance is of some vintage, its application in

the construction of substituted aromatics

and heteroaromatics has considerable, as yet

unfulfi lled, promise.

Among the practical tips is the caveat that, to

eventual regret, it may be easy to overlook the

occurrence of the halogen dance in the dash

to publication.

4. DoM–Cross-Coupling–DreM Reactions The DoM–cross-coupling sequence fi nds

additional advantage in synthesis when

combined with the DreM process.

Thus, the regioselective synthesis of

substituted fl uorenones (Schemes XXIII and

XXIV), phenanthrenes (Scheme XXV) and

acridones and dibenzazepinones (Scheme XXVI) become feasible in practical, effi cient

and environmentally friendly ways compared

with, for example, traditional electrophilic

substitution methods. Specifi cally, the DreM

approach to fl uorenones and azafl uorenones

(Scheme XXIV) demonstrates the

complementarity between Friedel-Crafts and

DreM tactics.

5. Scale-Up and Industrial use of DoM–Cross-Coupling–DreM Reactions As in the case of DoM chemistry which

was dormant for about a decade after

developments in our laboratories in the late

1970s, the DreM concept has been nurtured

in industry and is now appearing in the

open literature. It is encouraging to see the

application of the combined DoM–cross-

coupling technology (Scheme XXVIII),



including DreM (Scheme XXIX) methods,

on a multi-kilogram scale.

6. Diversifi cation of the DoM–Cross-Coupling Strategy While DoM reactions constitute one

functional group per DMG for synthetic

considerations, signifi cant advantage is

gained in diversifi cation, with or without

protection requirements, to the creation of

2,6-disubstituted DMG-bearing aromatics.

Perhaps insuffi ciently appreciated and

adapted as yet, such a sequence is shown in

Scheme XXX.

Another conceptual element, a double DoM

process (Scheme XXXI), may also be the tip

of the iceberg in synthesis.

7. The DMG as a Pseudohalide in Cross-Coupling Reactions Adaption of methodology which uses the

DMG aromatic as a pseudohalide coupling

partner, already demonstrated in our Corriu-

Kumada reaction of aryl O-carbamates

in the early 1990s, has taken on new

possibilities in O-carbamate, O-sulfamate

and sulfonamide Corriu-Kumada and

Suzuki-Miyaura reactions (Scheme XXXII)

in our laboratories as well as others. The

potential of this chemistry, including the

excision of the DMG by transition metal-

catalysed -hydride elimination processes,

is only now surfacing in the literature.

We hope the aims of this review have been met and

will be valuable to synthetic chemists. The prognostic

views expressed throughout this fi nal section are, as

many times experienced by all, dangerous to place, as

we do, into the literature.

AcknowledgementsThis review is dedicated to Alfred Bader, benefactor

of Snieckus Innovations, for giving us the opportunity

to impel our basic knowledge of chemistry to reach

practical ends.

Victor Snieckus thanks the Natural Sciences and

Engineering Research Council of Canada (NSERC)

for support by the Discovery Grant program. Suneel

Singh is grateful to NSERC for an industrial post

doctoral fellowship award.

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DreM directed remote metallation

DMG directed metallation group

Het heterocycle



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67. M. Cameron, B. S. Foster, J. E. Lynch, Y.-J. Shi and U.-H. Dolling, Org. Process Res. Dev., 2006, 10, (3), 398

68. B. A. Mayes, N. C. Chaudhuri, C. P. Hencken, F. Jeannot, G. M. Latham, S. Mathieu, F. P. McGarry, A. J. Stewart, J. Wang and A. Moussa, Org. Process Res. Dev., 2010, 14, (5), 1248

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74. D. J. Hlasta, C. Subramanyam, M. R. Bell, P. M. Carabateas, J. J. Court, R. C. Desai, M. L. Drozd, W. M. Eickhoff, E. W. Ferguson, R. J. Gordon, R. P. Dunlap, C. A. Franke, A. J. Mura, A. Rowlands, J. A. Johnson, V. Kumar, A. L. Maycock, K. R. Mueller, E. D. Pagani, D. T. Robinson, M. T. Saindane, P. J. Silver and S. Subramanian, J. Med. Chem., 1995, 38, (5), 739

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The Authors

Victor Snieckus was born in Kaunas, Lithuania and spent his childhood in Germany during World War II. His training was at the University of Alberta, Canada, (BSc Honors), strongly infl uenced by the iconoclastic teacher, Rube Sandin; the University of California, Berkeley, USA, (MSc), where he gained an appreciation of physical organic principles under D. S. Noyce; the University of Oregon, USA, (PhD), discovering his passion for organic synthesis under the excellent mentor, Virgil Boekelheide; and at the National Research Council, Ottawa, Canada, where he completed a postdoctoral tenure with the ardent Ted Edwards. His appointments have been at the University of Waterloo, USA, (Assistant Professor, 1966); Monsanto (NRC Industrial Research Chair, 1992–1998); and Queen’s University, Canada, (Inaugural Bader Chair in Organic Chemistry, 1998–2009). Some of his awards include A. C. Cope Scholar (2001, one of 4 Canadians); Order of the Grand Duke Gediminas (2002, from the President of Lithuania); Arfedson-Schlenk (2003, Geselschaft Deutscher Chemiker); Bernard Belleau (2005, Canadian Society for Chemistry); Givaudan-Karrer Medal (2008, University of Zurich, Switzerland); Honoris causa (2009, Technical University Tallinn, Estonia); and Global Lithuanian Leader in the Sciences (2012). In research, the Snieckus group has contributed to the development and application of the directed ortho metallation reaction

(DoM) and used it as a conceptual platform for the discovery of new effi cient methods for the regioselective synthesis of polysubstituted aromatics and heteroaromatics. The directed remote metallation (DreM) reaction and DoM–linked transition metal catalysed cross-coupling reactions (especially Suzuki-Miyaura) were fi rst uncovered in his laboratories. These have found broad application in the agrochemical and pharmaceutical industries, e.g. the fungicide silthiofam (Monsanto), the anti-AIDS medication efavirenz and the anti-infl ammatory losartan (Bristol-Myers Squibb). He continues fundamental research as Bader Chair Emeritus as well as Director of Snieckus Innovations, an academic unit that undertakes synthesis of small molecules for the pharmaceutical and agrochemical industries.

Johnathan Board received his MChem from the University of Sussex, UK, and subsequently undertook his PhD with Professor Philip J. Parsons, also at the University of Sussex, working towards the synthesis of the backbone of lactonamycin. He joined the Snieckus group at Queen’s University Kingston, Ontario, Canada in 2007 as a postdoctoral fellow and worked on projects with industrial partners. In 2010 he helped set up Snieckus Innovations in which organisation he is currently a laboratory and research manager.

Jennifer Cosman received her BScH in Chemistry at Queen’s University Kingston in 2010. She joined Snieckus Innovations in early 2011, working on the custom synthesis of small molecules. In 2013 she began her MSc degree under the co-supervision of Professors P. Andrew Evans and Victor Snieckus, and is currently at Queen’s University completing this programme.

Suneel Pratap Singh was born in India, where he obtained his PhD degree (Organic Chemistry) in 2008 from the Indian Institute of Technology, New Delhi, under the supervision of Professor H. M. Chawla. After postdoctoral training on synthetic aspects of organosulfur chemistry with Professor Adrian Schwan at University of Guelph, Guelph, Ontario, Canada, he joined Snieckus Innovations in 2011. His research interests include directed ortho metallation and development of new synthetic methodologies for heterocycles.

Toni Rantanen received his PhD from RWTH Aachen University, Germany, where he studied under the supervision of Professor Carsten Bolm on the topics of organocatalysis, microwave chemistry and ball milling. In 2007 he joined the Snieckus group fi rst as an industrial postdoctoral fellow followed by academic research on the synthesis and functionalisation of heterocycles. In 2010, he helped to inaugurate Snieckus Innovations at which he is currently utilising his formidable experience as a laboratory and research manager.



The Role of Platinum in Proton Exchange Membrane Fuel CellsEvaluation of platinum’s unique properties for use in both the anode and cathode of a proton exchange membrane fuel cell


By Oliver T. Holton* and Joseph W. Stevenson**

Johnson Matthey, Orchard Road, Royston, Hertfordshire SG8 5HE, UK

Email: *[email protected]; **[email protected]

Proton exchange membrane fuel cells (PEMFCs)

dominate the transportation fuel cell market and

platinum (Pt) is the catalyst material used for both anode

and cathode. This review sets out the fundamentals of

activity, selectivity, stability and poisoning resistance

which make Pt or its alloys the best available materials

to use in this application. It is clear that Pt is the

only element which can meet the requirements for

performance while avoiding slow reaction kinetics,

proton exchange membrane (PEM) system degradation

due to hydrogen peroxide (H2O2) formation and catalyst

degradation due to metal leaching. Some of the means

by which the performance of Pt can be enhanced are

also discussed.

IntroductionA PEMFC is a device that electrochemically reacts

hydrogen (H2) with oxygen (O2) to produce electricity

with water as the only by-product. Fuel cells offer the

capability to provide clean energy transportation with

zero tailpipe carbon dioxide (CO2) emissions. Even

where their fuel must be sourced from fossil fuels,

the high effi ciency of fuel cells relative to internal

combustion engines still offers the potential for

reduced well to wheel CO2 emissions (1).

PEMFCs have dominated the transportation fuel

cell market and will do so for the foreseeable future

(2) for several reasons. They have a unique set of

advantages for use in vehicles: a suffi ciently low

working temperature (80ºC) that they can be started

up quickly; a good energy density versus other fuel

cell types; robust and relatively simple mechanics; the

ability to run on pure hydrogen, therefore emitting no

CO2; and the ability to use ambient air as the oxidant.

PEMFCs currently use Pt as the catalyst both at

the cathode and at the anode, for reasons which

will be described in this paper. The most recent

US Department of Energy analysis (3) indicates

that Pt would be around 17% of the total cost of

an 80 kW PEMFC system using 2012 technology at



mass production scale. Naturally there is interest in

developing substitute catalysts based on cheaper

metals, although any other catalyst developed would

need to exceed Pt in terms of performance against

total system cost.

This review focuses on the fundamentals that are

required for an idealised PEMFC electrode material

and evaluates the performance of pure Pt compared

to other pure metals. It fi nishes with a discussion of

alternatives to pure Pt.

The Role of the Catalyst in a Proton Exchange Membrane Fuel CellFigure 1 shows how a PEMFC works. Hydrogen gas

is fed to the anode where it adsorbs onto the catalyst

surface. The adsorbed hydrogen atoms each lose an

electron (e–) and are released from the metal surface

as protons (H+). The electrons fl ow to the cathode as

current through an external circuit and the protons

fl ow across the PEM towards the cathode. Air is fed to

the cathode and oxygen is adsorbed onto the catalyst

surface. This bound oxygen is subsequently protonated

by incoming H+ and reduced by incoming electrons to

produce water which is then released from the catalyst

surface. This water is forced to exit the fuel cell by the

hydrophobic nature of the surrounding media.

Pt is used as the catalyst for both the hydrogen

oxidation reaction (HOR) occurring at the anode and

the oxygen reduction reaction (ORR) at the cathode.

Usually, the Pt catalyst takes the form of small particles

on the surface of somewhat larger carbon particles

that act as a support.

Anode Processes Hydrogen fl ows into the fuel cell and reaches the Pt

anode where the HOR takes place. Here the hydrogen

adsorbs onto the surface of the Pt electrode, breaking

the hydrogen–hydrogen bond to give adsorbed atomic

hydrogen (H*) (4), Equation (i):

½ H2 + * H* (i)

(where * denotes a surface site).

Subsequent loss of an electron from each adsorbed

hydrogen leads to hydrogen leaving the surface as

protons (H+), Equation (ii):

H* H+ + * + e– (ii)

In a PEMFC, the kinetics of the HOR on a Pt

electrode are very fast. Voltage losses are vanishingly

small even for very low Pt loadings (less than 5 mV

loss at Pt anode loadings of 0.05 mg cm–2) (5). As the

HOR is fast, the main focus of catalyst improvement

has always been on the cathode process.

Cathode Processes The ORR that occurs at the cathode has a more

complicated mechanism and it is well known for

its sluggish kinetics (6, 7). The ORR is the major

challenge for PEMFCs because the catalyst material

must be stable under the extremely corrosive

Oxygen

Electron fl ow

Hydrogen

Hydrogen ions

Excess hydrogenAnode Electrolyte Cathode

Water

Fig. 1. A schematic of a proton exchange membrane fuel cell (Copyright Johnson Matthey)



conditions at a fuel cell cathode yet chemically

active enough to be able to activate O2. In addition

it must be noble enough for facile release of product

water from the catalyst surface in order to free up

catalytic sites once the reaction is complete. Due to

the diffi culties of the ORR, the cathode requires a

higher Pt loading, typically more than several times

that of the anode (8). The ORR at the cathode is the

source of more than half of the voltage loss for a

PEMFC system (9).

There are two pathways by which ORR can occur in

acidic media (4). The fi rst mechanism is the preferred

dissociative pathway and follows a concerted ‘four

electron’ transfer process leading to direct formation

of water. First O2 adsorbs to the metal surface and

the oxygen–oxygen bond breaks to give adsorbed

oxygen atoms (O*), Equation (iii):

½ O2 + * O* (iii)

These single oxygen atoms are then protonated by

the incoming fl ow of H+ across the PEM and reduced

by incoming fl ow of electrons to give surface bound

hydroxyl (OH*) (10) groups, Equation (iv):

O* + H+ + e– OH* (iv)

The surface bound OH* is then further reduced and

protonated to give water which then leaves the metal

surface, Equation (v):

OH* + H+ + e– H2O + * (v)

The alternative pathway is an associative mechanism

where the O=O bond does not break upon O2 adsorption

onto the metal surface (Equations (vi) to (vii)) (11):

O2 + * O2* (vi)

O2* + H+ + e– HO2* (vii)

This alternative ‘two electron’ route is observed

to produce H2O2. The details of the mechanism are

unclear, but the reaction may proceed as follows

(11) (Equation (viii)):

HO2* + H+ + e– H2O2* (viii)

The H2O2 may react further or desorb (Equation (ix)):

H2O2* H2O2 + * (ix)

Figure 2 shows a simplifi ed representation of

possible associative and dissociative mechanisms (4).

Generation of H2O2 in a PEMFC is highly undesirable

as it diffuses into the PEM and results in radical

oxidative degradation of the membrane (12). Poor

ORR catalysts produce signifi cant amounts of H2O2

through associative ORR (13) whereas a good catalyst

should produce little or no H2O2.

Although the kinetics of HOR and ORR are different,

the overall trend in reaction rates on different metal

electrodes is similar for both.

Required Characteristics of an Effective Proton Exchange Membrane Fuel Cell CatalystThere are four main characteristics that are essential

for an effective PEMFC catalyst:

(a) Activity – to be able to adsorb the reactant strongly

enough to facilitate a reaction but not so strongly

that the catalyst becomes blocked by the reactant

or products.

(b) Selectivity – to make the desired product

and minimise the production of undesirable

intermediates and side products.

(c) Stability – to withstand the operating environment

in a fuel cell, including strong oxidants, reactive

radicals, an acidic environment and high and

rapidly fl uctuating temperatures, all whilst under

an applied voltage.

(d) Poisoning resistance – to be resistant to poisoning

by impurities likely to be found in the fuel cell

itself and in the feed gases.

The following sections will discuss the performance

of pure Pt compared to other pure metals with respect

to these characteristics.

ActivityFor heterogeneous catalysis on a metal surface, the

catalyst must adsorb species with suffi cient strength

O2

dissociative

associative

O2* H2O2*

H2O2

H2O

Fig. 2. Generation of hydrogen peroxide through associative oxygen reduction reaction (4)



to allow chemical bonds to break but weakly enough

to release the product when the reaction has occurred.

If the binding interaction is too weak, the substrate will

fail to adsorb well on the catalyst and the reaction will

be slow or not take place; if the binding interaction is

too strong, the catalytic surface will quickly become

blocked by bound substrate, intermediate or product

and the reaction will stop. The Sabatier principle (14)

describes the ideal interaction between substrate and

catalyst as a balance between these two extremes.

This principle is best illustrated by Balandin’s volcano

diagrams (15, 16), which plot the catalyst activity

against adsorption energy for a given reaction. As

described, too weak or too strong a catalyst–substrate

interaction leads to a low catalytic activity. Therefore

the diagrams show a clear activity peak at which there

is optimal binding.

Balandin volcano plots (Figure 3 (17)) for metal

hydrogen bonding energy show that Pt has the highest

activity of all bulk metals. The HOR is extremely quick

and already requires much lower Pt loadings than

the ORR. That said, Pt is currently used for the anode

catalyst for the HOR and hence is a target for fuel

cell cost reduction. This effort is primarily focused on

reducing the Pt loadings still further and progress on

metal thrifting is still being made.

More interesting is the effort to improve the cathode

where the ORR takes place. With ORR as the slowest

step, the vast majority of research effort has focused

on improving the ORR activity. Figure 4 shows the

Balandin plot for binding between single O atoms and

various metals (11). It is observed that Pt again is the

pure metal that is closest to the theoretical activity

peak, although it binds oxygen too strongly by about

0.2 eV (18). The preferred ORR mechanism is actually

a two-step process requiring the catalyst fi rst to bind

O (Equation (iii)) and then OH (Equation (iv)) and

Figure 5 shows the activity against both O and OH

binding energies (11). Pt is closest to the optimal

binding energy for both reactions and has the highest

activity.

Metals such as copper (Cu) and nickel (Ni) bind

oxygen too strongly. For metals that bind oxygen

too strongly the activity is limited by the removal

of adsorbed O and OH species; that is, the surface

quickly becomes oxidised and thus unreactive.

For metals such as silver (Ag) and gold (Au), the

opposite is true and it is diffi cult to bind oxygen onto

Au

InTi

Cd

GaPbAgZn

Sn Bi

FeCu Co

Ni

PtReRh

Ir

W

MoTi

Nb Ta

30 50 70 90EM–H, kcal mol–1

3

5

7

9

–log

i 0, A

cm

–2

Fig. 3. The logarithm of exchange current densities (log i0) for cathodic hydrogen evolution vs. the bonding adsorption strength of intermediate metal-hydrogen bond formed during the reaction itself (17)



Ru

O binding too strong

Pt

Pd

–3 –2 –1 0 1 2 3 4

O binding too weak

0.0

–0.5

–1.0

–1.5

–2.0

–2.5

Act

ivity

∆EO, eV

FeW

Mo

Co

Ni

RhCu

Ir Ag

Au

Fig. 4. Trends in oxygen reduction activity plotted as a function of the oxygen binding energy (Reprinted with permission from (11). Copyright 2004 American Chemical Society)

–0.5

–1.0

–1.5

–2.0

–2.5

–3.0

–3.5

–4.0

–4.5

–5.0

Ag

Au

Pt

Pd

IrCu

RhNi

Ru

Co

Fe

Mo

W

Activity

–1.5 –1 –0.5 0 0.5 1 1.5 2

∆EOH, eV

3

2

1

0

–1

–2

∆E 0

, eV

Fig. 5. Trends in oxygen reduction activity plotted as a function of both the oxygen and the hydroxyl group binding energy (Reprinted with permission from (11). Copyright 2004 American Chemical Society)



the metal surface. For these metals the rate is limited

by the dissociation of O2 or the transfer of electrons

and protons to adsorbed oxygen species (12).

SelectivityThe second requirement is selectivity. The catalyst must

progress the reaction to make the desired product

whilst minimising the production of undesirable

intermediates and side products. The HOR has only

one mechanism and can produce only H+ and e–.

As such, selectivity is not an issue in the context of

the HOR.

At the cathode, the ORR reaction can follow one of

two pathways and the pathway is determined by the

selectivity of the catalyst in the fi rst step (adsorption

of O2). The discussion of activity above has focused on

the desired, dissociative four electron ORR mechanism

to produce water (Equations (iii) to (v)). However, it

is important to discuss the alternative two electron

reaction associative mechanism which produces

H2O2. Catalyst materials must be chosen to minimise

the undesired associative mechanism as the presence

of free H2O2 within the cell environment is highly

damaging (12).

The associative mechanism which leads to H2O2

starts when O2 is adsorbed on a metal surface without

the O=O bond being broken. On a Pt surface however,

the O=O bond is usually broken upon adsorption.

The reaction therefore proceeds almost exclusively

according to the desired dissociative mechanism.

Since there is no adsorbed O2 on the Pt surface, H2O2

cannot be formed (4).

The amount of H2O2 produced on various metal

catalyst surfaces has been investigated using scanning

electrochemical microscopy and calculation of the

total number of electrons transferred (n) (Figure 6

Fig. 6. Number of electrons transferred (n) during oxygen reduction reaction at: (a) mercury, gold, silver, copper and Au60Cu40; and (b) platinum, palladium and Pd80Co20 as a function of applied potential in an oxygen saturated 0.5 M sulfuric acid solution (Reprinted with permission from (19). Copyright 2009 American Chemical Society)

Cu4.0

3.8

3.6

3.4

3.2

3.0

2.8

2.6

2.4

2.2

2.00.3 0.2 0.1 0.0 –0.1 –0.2 –0.3 –0.4

Esubs (V) vs. RHE

Au60Cu40

Ag

AuHg

n

0.8 0.7 0.6 0.5 0.4 0.3

4.0

3.8

3.6

3.4

3.2

3.0

2.8

2.6

2.4

2.2

2.0

n

Esubs (V) vs. RHE

PtPd80Co20

Pd

(a)

(b)



(19)). A result of n = 2 signifi es only H2O2 production,

with n = 4 showing no H2O2 (only H2O) formation.

From the study, mercury (Hg) shows the lowest value

of n at close to 2, whereas Pt and Pd80Co20 show the

highest values n at almost 4. The other materials tested

show intermediate n values which vary as a function

of potential.

Thus it may be concluded that Pt is the most selective

metal towards the desired ORR at the cathode as it is

nearly 100% selective for the dissociative mechanism

over a broad potential range.

Stability For any metal to be suitable as a fuel cell electrocatalyst,

it must not only have suitable catalytic activity and

selectivity, but it must also be able to withstand the

harsh chemical environment within a fuel cell. The

presence of strong oxidants, reactive radicals, low pH,

high temperatures and rapid potential fl uctuations,

especially on the cathode, rules out the use of most

transition metals in their pure forms. The main

problem is that very few metals are suffi ciently noble

to avoid dissolution at the low pHs and high electrode

potentials experienced at the fuel cell cathode. Those

that are stable tend to be covered with oxide fi lms

that inhibit dissolution, but also the ORR. Lack of short

term stability is most immediately obvious as a loss in

kinetic activity, but long term stability of the catalyst is

key to overall system durability.

Pourbaix diagrams (20) show the thermodynamic

stability of different metals under different applied

voltages and pH conditions. These diagrams map out

the most thermodynamically stable species in each

domain on a plot of pH versus applied voltage for a

particular element. When conditions stray into areas

of the diagram that represent a change of the most

stable elemental metallic form to an oxide or different

oxidation state, then corrosion or passivation –

formation of a ‘protective’ layer on the surface of the

given metal – can then occur. As an example, the

Pourbaix diagram for cobalt (Co) is Figure 7 (21, 22).

It can be seen that the low pH conditions in a fuel

cell will corrode Co; the immunity domain for Co (in

plain white) only exists below around –0.5 V in acidic

conditions. This has been observed experimentally;

pure Co reacts in acidic media to form soluble

products and Co has been shown to rapidly leach out

of Co-based electrode materials (23, 24).

Figure 8 shows Pourbaix diagrams for different

metals listed in order of nobility (unreactivity) (21, 22).

It can be seen that noble metals such as Au, iridium

(Ir) and Pt are quite stable in the fuel cell environment

(high cell potential, low pH), whereas metals such as

Ni, Co and iron (Fe) are predicted to dissolve. This

is indeed what is experimentally observed; these

transition metals are electrochemically soluble at

a potential range between 0.3 V and 1 V in low pH

conditions (25).

The handful of other acid-stable metals have lower

activities and selectivities compared to Pt. Therefore

the acid/base stability of Pt under typical PEMFC

operating conditions, in combination with its activity

and selectivity, renders it the only suitable pure metal

to be used in the PEMFC application (26).

Poisoning ResistanceA good catalyst must be resistant to poisoning by

impurities likely to be found in the fuel cell itself and

in the feed gases. Impurities in both the hydrogen and

the air streams may have a negative impact upon the

workings of a PEMFC. All catalysts are susceptible to

poisoning but there are so many different poisons and

poisoning mechanisms that it is very diffi cult to make

any meaningful absolute ranking (27).

Most problematic for Pt in PEMFC applications are

sulfur species (28) and carbon monoxide (CO) (29).

Pt is neither the least nor the most sensitive metal to

these or other poisons. In fuel cell applications, as

Fig. 7. The Pourbaix diagram for cobalt (With kind permission from Springer Science+Business Media (21, 22))

Corrosion yielding soluble productsCorrosion yielding gaseous productsCorrosion yielding soluble and gaseous productsPassivation by a fi lm of oxide or hydroxidePassivation by a fi lm of hydrideImmunity

2

1

0

–1

–2

E H, V

0 7 14pH



1. G

old

2. Ir

idiu

m

3. P

latin

um

4. R

hodi

um

5. R

uthe

nium

6.

Pal

ladi

um

7. M

ercu

ry

8. S

ilver

9.

Osm

ium

10

. Sel

eniu

m

11. T

ellu

rium

12

. Pol

oniu

m

13. C

oppe

r 14

. Tec

hnet

ium

15. B

ism

uth

16. A

ntim

ony

17. A

rsen

ic

18. C

arbo

n 19

. Lea

d 20

. Rhe

nium

21

. Nic

kel

22. C

obal

t 23

. Tha

lium

24

. Cad

miu

m

25. I

ron

26. T

in

27. M

olyb

denu

m

28. T

ungs

ten

2 1 0 –1 –2 2 1 0 –1 –2 2 1 0 –1 –2 2 1 0 –1 –2

EH, V EH, V EH, V EH, V

Fig. 8. The Pourbaix diagrams for different elements listed in order of nobility (With kind permission from Springer Science+Business Media (21, 22)). For key to this fi gure see Figure 7



in other catalytic applications for Pt, there are two

methods of protection: keeping the poisons out of the

system and alloying the Pt with other metals to reduce

susceptibility to poisoning. The nature of impurities in

the hydrogen fuel stream depends on the source of

the hydrogen (29). Strict quality specifi cations have

been agreed for hydrogen intended for use in fuel cell

vehicles (30). However improved tolerance to poisons

will still be advantageous to avoid any sub-standard

batches of hydrogen causing irreversible damage to

PEMFCs.

For complicated systems such as alloys, there is

no simple way to predict in advance the precise

susceptibility to sulfur poisoning (31). Many

fundamental studies on the interaction of sulfur

species with elemental catalysts have been undertaken

(32–41). Unsupported or supported Pt-based alloy

catalysts have been demonstrated to exhibit high

tolerance to CO poisoning. These include binary,

ternary and quaternary Pt alloys, Pt-based metal oxide

catalysts (42–44), Pt-based composites and organic

metal complexes (45, 46). More information on the

development of high-performance and cost-effective

CO-tolerant anode electrocatalysts for PEMFCs can

be found in several comprehensive review articles

(47–52).

Alternatives to Pure PlatinumThere is a limited amount of interest in improving

the HOR (53); as this review has discussed the major

focus has always been on improving the ORR. While

Pt is the best pure metal in terms of activity, selectivity

and stability for both anode and cathode in a PEMFC,

it does not sit at the peak of the Balandin volcano

plot for the ORR. The perfect catalyst according to

the Sabatier principle would have slightly different

electronic properties. Therefore a lot of research

focuses on fi ne tuning the electronic properties of Pt

in order to optimise the resulting catalyst material.

Approaches currently used to improve Pt activity are:

(a) Alloying with one or more other metals;

(b) Layering Pt on or just below the surface of another

metal;

(c) A core–shell approach where a core of cheaper

metal is coated with Pt;

(d) Alloying Pt followed by dealloying such that the

fi nished Pt lattice structure retains some of the

original structural strain associated with alloying.

The objective of all of these approaches is to modify

the electronic properties of Pt to bring the adsorption

energy for the O and OH reduction reactions closer

to the Sabatier ideal. The improved activity of these

modifi ed Pt structures has been attributed to many

factors including changes in the number of nearest

Pt neighbours, average Pt–Pt distance and Pt 5d band

vacancy (54, 55).

In addition, various ‘novel technologies’ have been

used to support and fi ne tune the electronic structure

of potential catalysts such as supporting metals on

graphene or using metal ions held in chelating organic

frameworks.

AlloyingPt-based binary alloys (Pt-X) have shown enhanced

activity towards the ORR (56). In the last few years

results have shown that many alloys with the general

formula Pt3X (where X is a 3d transition metal) give

high activity (Figure 9) (18, 57). Pt3Ni(111) has been

presented as the most active surface yet observed with

a mass activity 10 times that of Pt(111) and up to 90

times higher than polycrystalline Pt (58). This result has

not yet been reproduced in polycrystalline PtNi alloys.

However it should be noted that care must be taken

when assessing any comparison of activity between

Pt systems and alternatives as the mass activity of Pt

systems themselves can differ by a large factor.

Whilst these Pt3X alloys have proven to be highly

active towards the ORR, stability as well as activity is

crucial for any viable PEMFC catalyst. Hence it must

be ascertained whether or not base metal leaches

from these systems. Both theoretical predictions (59)

and experimental observations (55) indicate that

strong leaching takes place.

In the acidic fuel cell environment, dissolution of

the base metal in the oxidised form will occur. Base

transition metals are electrochemically soluble in low

pH media (25). Observed leaching may have several

main causes:

(a) Excess of deposited base metal;

(b) Incomplete alloying of the base metal due to a low

alloying temperature applied during formation;

(c) Thermodynamic instability of the base metal in

the alloy.

Ni, Co and Fe have all been found to migrate easily

from the surface of Pt alloys (55) although the bulk

of the alloy remained unchanged, indicating it was

mainly leaching from the top few monolayers of the

alloy surface. Ni has also been found to leach out of

the Pt3Ni system at a high initial rate before a steady

state is reached (60).



Transition metal ions provide sites for radical

formation from any peroxide that is present as a

result of the associative ORR mechanism (12), or

that is formed on the anode by the reaction between

crossed-over oxygen and hydrogen. H2O2 will degrade

the PEM and other parts of the fuel cell, especially in

the presence of any transition metal ions that have

migrated there. For example, Fe is widely recognised

to catalyse radical formation from peroxide (61). Thus

any Fe-containing catalyst could leach Fe into the

membrane and cause damage through the associated

Fenton chemistry (62). Amongst other transition metal

ions, Cu ions are also known to poison the HOR activity

of the anode if they migrate through the PEM (63).

LayeringThe use of overlayer or underlayer structures is also

an area of substantial research interest (64) in order

to create a surface that binds O a little more weakly

than Pt. Again, in practice it is likely that overlayer/

underlayer structures will suffer from metal leaching,

reducing the catalyst stability and shortening PEMFC

lifespan.

Core–Shell ApproachesThe core–shell approach was fi rst used by Adzic and

co-workers in order to address both catalytic activity

and Pt thrifting in fuel cells. This approach uses a

core of a cheaper metal, such as palladium (Pd), Co

or Ni, coated with a monolayer of Pt. Results have

been extremely successful in terms of initial activity

but stability remains an issue (65). As the catalyst is

cycled, the core transition metal atoms tend to diffuse

to the surface of the nanoparticles and leach out into

the ionomer and membrane (12). If there are any gaps

in the Pt monolayer, the same will happen even more

quickly.

Dealloying Approaches The base metal content from the exterior layers of

nanoparticles can be leached from PtyXz catalysts

by voltammetric surface dealloying. Strasser and

co-workers have demonstrated that the residual

compressive Pt strain in the dealloyed surface layers

is key to the observed activity (66). Experimental

control of the Pt shell thickness and the composition

of the alloy core controls lattice strain and hence

ORR activity because the decrease in Pt–Pt lattice

parameter reduces the oxygen binding strength. From

this perspective, the initial alloy composition and

thickness of the dealloyed layer are important factors

that determine catalytic activity (67).

Similar effects were reported by Gottesfeld for

electrochemically leached Pt65Cr35 and Pt20Cr80

Fig. 9. Activity versus the experimentally measured d-band centre relative to platinum. The activity predicted from DFT simulations is shown in black, and the measured activity is shown in red (Reprinted with permission from (18). Copyright 2006 John Wiley and Sons)

0.06

0.05

0.04

0.03

0.02

0.01

0–0.8 –0.6 –0.4 –0.2 0

E(d-band centre), eV

A, e

V

Pt3Ni

Pt3Co

Pt3Fe

Pt3TiPt

Pt3Ti

Pt3Fe Pt3Co

Pt3Ni



catalysts (68). This work suggested that the selective

electrochemical dissolution (dealloying) of non-

noble components from noble metal bimetallics

could serve as a general strategy towards tuning

surface electrocatalytic properties. This approach can

be considered as a more sophisticated improvement

to core–shell catalysts. Expanding these ideas, some

groups are already working towards controlled shape

nanoparticles grown with faces composed of the most

preferential orientation for the ORR (53, 69). Dealloyed

Pt electrode materials would be less likely to leach

base metal into the electrolyte solution, depending

on the exact near-surface composition, offering the

possibility for cheaper catalyst materials without an

associated increase in fuel cell degradation.

Novel Technologies Numerous novel alternatives to Pt have been

investigated such as doped graphenes (70),

macrocyclic transition metal complexes (71–76),

transition metal carbides and nitrides, chalcogenides

(23, 77, 78) and carbonaceous electrodes (79–81),

although none are likely to represent viable options

in the near or mid term. Novel base metal containing

technologies still suffer from the same lack of stability

in the harsh conditions of a PEMFC and none has yet

been able to exhibit the activity of Pt.

ConclusionsThe great value of platinum as a catalyst in PEMFC

applications is that it outperforms all other catalysts

in each of three key areas: its activity, its selectivity

and its stability. Any potential alternative catalyst must

demonstrate not only improved performance in one of

these areas, but at least equivalence in the other two. Of

all transition metals, Pt is the closest to an ideal catalyst

for both the HOR and ORR in the PEMFC system. Bulk

Pt is commonly chosen as the benchmark for non-Pt

systems, particularly with reference to activity, but it can

still be improved by an order of magnitude or more if

its electronic properties are fi ne-tuned by alloying with

other metals. It is the performance of these modifi ed Pt

systems that represents the true benchmark.

The relative cost of a gram of Pt makes the promise

of systems using cheaper metals seductive. However,

alternative systems containing base metals have

fundamental limitations such as a lack of activity,

poor selectivity leading to H2O2 formation, or catalyst

degradation caused by a lack of stability under the fuel

cell operating conditions which all must be addressed.

As academia and industry continue to develop both

Pt and non-Pt systems, the question for the future is

whether the great lead that the Pt systems have in both

utility and economics will reduce or, as seems more

likely, increase.

AcknowledgementsThe authors would like to thank Misbah Sarwah and

Jonathan Sharman, Johnson Matthey Technology

Centre, Sonning Common, UK, for useful advice and

input throughout.

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The AuthorsOliver Holton works for Johnson Matthey Precious Metal Products division and is part of Johnson Matthey’s graduate training programme. He prepared the present review while working for Johnson Matthey Precious Metals Marketing. He is now based in Shanghai where he is involved in market analysis, sales and new business development. Mr Holton graduated from the University of Oxford, UK, studying Chemistry.

Joe Stevenson works for Johnson Matthey in the UK and at the time of writing was responsible for Clean Energy Technologies in the Precious Metals Marketing department. He graduated from the University of Oxford and has worked at Johnson Matthey in roles related to platinum group metals catalysis for process and environmental applications since 1995.



“Organometallics as Catalysts in the Fine Chemical Industry”Edited by Matthias Beller (Leibniz-Institut für Organische Katalyse, Universität Rostock, Germany) and Hans-Ulrich Blaser (Solvias AG, Basel, Switzerland), Topics in Organometallic Chemistry, Vol. 42, Springer, Berlin, Heidelberg, Germany, 2012, 154 pages, ISBN: 978-3-642-32832-9, £171.00, €203.25, US$259.00 (Print version)


Reviewed by Michel Picquet

Institut de Chimie Moléculaire de l’Université de Bourgogne (ICMUB), UMR 6302, CNRS, 9 Avenue Alain Savary, 21078 Dijon, France

Email: [email protected]

IntroductionThis new volume of Springer’s famous series Topics

in Organometallic Chemistry, Volume 42, entitled

“Organometallics as Catalysts in the Fine Chemical

Industry”, presents the state-of-the-art in the industrial

use of organometallic or coordination complexes

as catalysts for the production of fi ne chemicals. A

range of reactions is covered through an overview of

chapters and case studies, from catalytic C–C bond

formation, hydroformylation and hydrogenation

to olefi n metathesis (see below). All of these are

noteworthy for involving platinum group metal

(pgm) complexes as catalysts. Interestingly, technical

challenges encountered in scaling up the reactions

from small quantities to production amounts, as well

as how these issues were tackled, are often described

by the authors, who all belong to the industrial

world. Their contributions make this book a helpful

source of information for specialists in the fi eld of

organometallic catalysis, as well as beginners who

have just entered the fi eld or intend to do so.

Palladium-Catalysed Coupling ReactionsExtensively reviewed by Johannes G. de Vries (DSM

Innovative Synthesis BV, Geleen, The Netherlands)

in the fi rst chapter, palladium-catalysed coupling

reactions appear to be among the most popular

reactions for the production of fi ne chemicals at

the ton-scale. Provided inhibition and deactivation

of the catalyst is avoided, catalytic C–C coupling

may offer several advantages such as total cost

reduction, tolerance to many functional groups (no

waste-producing protection/deprotection steps) and

lower reaction temperatures. Thus, several industrial

processes were developed in fi ne chemistry using

the well known Heck-Mirozoki, Suzuki-Miyaura,

Sonogashira, Kumada-Corriu and Negishi couplings.

Some of them are given below.



Using the Heck reaction in one of its synthetic steps,

the herbicide prosulfuron is produced on a large scale

by Syngenta (Figure 1). Tris(dibenzylideneacetone)-

dipalladium(0) (Pd2(dba)3) is used as a catalyst

precursor without any phosphine ligand and the

precipitated palladium is trapped at the end of the

reaction simply by using charcoal. Naproxen (Figure 1)

is also produced by Albemarle with a scale around

500 tons year–1 using the same technology. In this case,

palladium(II) chloride (PdCl2) is used as a metal

source and the neomenthyldiphenylphosphine ligand

is used to reach a substrate-to-catalyst ratio of 2000–3000.

The ability of the Heck reaction to be performed

without the need of protection/deprotection steps

on the substrate is illustrated by the production of

montelukast, an anti-asthma agent, by Merck and of

the calcium-regulator cinacalcet hydrochloride by

Teva (Figure 1). In the fi rst case, palladium(II) acetate

(Pd(OAc)2) is used as a precatalyst while Teva’s

process makes use of the simple Pd/C catalyst. More

sophisticated metal precursors are sometimes used for

maximum effi ciency of the reaction. As an example,

for the production of resveratrol (Figure 1), DSM has

reported the use of a chloropalladacycle dimer based

on the acetophenone oxime ligand. Other examples of

the industrial production of fi ne chemicals involving

a Heck reaction are described, including rilpivirine

(AIDS treatment, Janssen Pharmaceuticals), eletriptan

(anti-migraine, Pfi zer), the generic of nebivolol (blood

pressure lowering agent, Zach System), pemetrexed

disodium (anticancer agent, Eli Lilly) and varenicline

(smoking cessation aid, Pfi zer).

Twelve industrial processes using another useful

C–C bond formation reaction, the Suzuki coupling, are

reported. The largest is operated by Merck to produce

more than 1000 tons year–1 of the fungicide boscalid

(Figure 2). In a pivotal step, o-chloronitrobenzene is

coupled to p-chlorophenylboronic acid using catalytic

amounts of Pd(OAc)2 and triphenylphosphine. A

similar catalytic system is used by Clariant to obtain

o-tolylbenzonitrile (OTBN, Figure 2) as a common

intermediate for the production of hundreds of

tons of an entire family of Sartan derivatives as

blood pressure lowering agents. This process is

advantageously run in an aqueous medium using

the water-soluble phosphine 3,3,3-phosphanetriyl-

tris(benzenesulfonic acid) trisodium salt (TPPTS),

thus allowing easy recovery of the catalyst. Crizotinib

(Figure 2), an anticancer drug marketed by Pfi zer,

is also obtained through a Suzuki coupling step.

In this case, the optimised catalytic precursor was

found to be (1,1-bis(diphenylphosphino)ferrocene)-

palladium(II) chloride. Interestingly, after work up,

traces of residual Pd could be removed by simple

treatment with silica-alumina loaded with 15% cysteine.

To replace the unscalable Stille coupling reaction in

the original synthesis of the other anticancer drug

lapatinib (Figure 2), GSK has developed a more

Prosulfuron

HN

HN N

N N

OMe

OSO2

CF3Naproxen Resveratrol

MontelukastCinacalcet

CO2H

MeO

OH

OH

HO

Cl N

SOH

CO2HHN

CF3

Fig. 1. Examples of fi ne chemicals industrially produced using the palladium-catalysed Heck reaction (creation of the bold red bond)



convenient Suzuki route using Pd/C. In this case, the

residual catalyst is eliminated by simple fi ltration.

Several synthetic schemes, all containing a Suzuki

reaction step, have also been developed to access

ruxolitinib phosphate, a molecule marketed by

Incyte for the treatment of myelofi brosis. However,

for an industrial process, this Pd-catalysed coupling

should preferably not be the last step in order to

avoid tedious removal of Pd traces down to the

<10 ppm criteria. As counter examples, Hoffmann-

La Roche and Janssen Pharmaceuticals have

scaled up convergent syntheses of vemurafenib and

abiraterone acetate (Figure 2), respectively. Both

use dichlorobis(triphenylphosphine)palladium(II)

(PdCl2(PPh3)2) as a catalyst to perform a Suzuki

coupling in the ultimate step for the synthesis of these

anticancer compounds. Some additional examples

of the use of the Suzuki reaction in industrial

processes include the synthesis of the antifungal

agent anidulafungin by Pfi zer, of febuxostat (Teijin

Pharma), a molecule used in the treatment of gout

and hyperuricemia, of the quinolone antibiotic

garenoxacin by Toyama Chemical and of nebivolol

by Zach System.

Despite the obvious drawback of using a Grignard

reagent intolerant of many functional groups,

several fi ne chemicals are produced using the

cheapest Kumada-Corriu reaction at the multiton

year–1 scale. Most of them are out of the scope of

this review, as they involve the non-pgms nickel,

copper and iron as catalysts. However, for some

peculiar reactions, palladium derivatives are the

preferred catalysts. Thus, Hokko Chemical Industry

is using a catalyst made in situ from PdCl2 and

1,1-bis(diphenylphosphino)ferrocene (dppf) to

couple 1,3-dichlorobenzene and n-propylmagnesium

chloride or p-fl uorobromobenzene and p-tert-

butoxyphenylmagnesium chloride (Figure 3).

The obtained compounds are precursors for

pharmaceuticals and liquid crystals. In a same

manner, Zambon uses the Kumada-Corriu coupling to

produce difl unisal, a non-steroidal anti-infl ammatory

drug (Figure 3). In this case, Pd(OAc)2 is used as

precatalyst and triphenylphosphine is added. It is

noteworthy that chemists at Zambon found that

the homo-coupling of the Grignard reagent could

be reduced to less than 1% when using ultrapure

magnesium. Indeed, any traces of Cu, Fe, Ni and

Boscalid

OTBNCrizotinib

RuxolitinibLapatinib

Vemurafenib Abiraterone acetate

ClN

NH

Cl Cl

Cl

Cl

Cl

O

O

O

O

O

NH

NH

N

N

N

NN

NN

HN

NHNN

H2N N

F

CN

N

AcO

F

F

O2 S

SO2

NH HN

F

NC

Fig. 2. Examples of fi ne chemicals industrially produced using the palladium-catalysed Suzuki reaction (creation of the bold red bond)



manganese that are typically found in commercial

magnesium could promote this side reaction.

Alternatively, biaryl compounds can be produced

by the RZnX-based Negishi reaction. However, the only

two known industrial processes using this reaction

involve nickel catalysts and thus will not be described

in this review. The Sonogashira reaction, which allows

a terminal alkyne to be coupled with an aryl or

alkenyl halide or pseudohalide, makes effi cient use of

palladium catalysts. The fi rst industrial large-scale use

of this reaction was the second-generation process

developed by Sandoz for the synthesis of the antifungal

terbinafi ne with less than 0.05 mol% of PdCl2(PPh3)2

(Figure 4). Two companies, Medichem and Dipharma

Francis, patented synthetic routes to cinacalcet

(Figure 4) using the Sonogashira coupling, the two

approaches almost only differing by the nature of the

palladium source (Pd/C vs. PdCl2). Initially published

by the academic group of Takeshi Fujita (Tohoku

University, Japan), a methodology to obtain fi ngolimod

hydrochloride (Figure 4) via a Sonogashira reaction

was further developed by Novartis. The worldwide

rights to the process were acquired by this company

and its use in production seems likely. Other examples

of the use of the palladium-catalysed Sonogashira

reaction at the industrial level include the synthesis

of pemetrexed by Eli Lilly, of tazarotene, used for

the treatment of acne, psoriasis and photoageing

and marketed by Allergan, and of vemurafenib by

Hoffmann-La Roche.

In addition to the above-mentioned lead reactions,

other palladium-catalysed coupling reactions can be

used in industrial fi ne chemical production, although

only two examples are reported. Bristol-Myers Squibb

developed the synthesis of ixabepilone, marketed

for breast cancer treatment, using a Pd2(dba)3/PMe3-

catalysed allylic substitution step, while an elegant

Pd(OAc)2/PtBu3-mediated C–H activation step is

used by Servier to produce ivabradine, an alternative

treatment for angina pectoris.

Applications of Rhodium-Catalysed Hydroformylation Chapter 2 is written by Gregory T. Whiteker (Dow

AgroSciences, Indianapolis, USA) and Christopher J.

Cobley (Chirotech Technology Ltd, Cambridge, UK),

and gathers information about the rare commercial

applications of rhodium-catalysed hydroformylation

in the pharmaceutical and fi ne chemical industries.

So far these have been limited by cost, complexity

or waste treatment issues. However, the authors have

thoroughly reviewed the patent literature to detect the

fi ne chemicals already obtained on a multikilogram

scale that may thus be on the way to industrial-scale

production.

In the pharmaceutical domain, both BASF and

Roche are operating industrial processes based on

a rhodium-catalysed hydroformylation to produce

vitamin A acetate (Figure 5), starting from different

substrates. The only other recent industrial-scale

application of hydroformylation was reported by

Chirotech for the synthesis of (S)-allysine ethylene

acetal (Figure 5), an important intermediate in the

manufacture of some enzyme inhibitors. In this case,

Fine chemical intermediates Difl unisalCl

O F F

F CO2H

OH

Fig. 3. Examples of fi ne chemicals industrially produced using the palladium-catalysed Kumada-Corriu reaction (creation of the bold red bond)

Cinacalcet

HN

CF3N

C7H15

OH

OH

NH2

Terbinafi ne Fingolimod

Fig. 4. Examples of fi ne chemicals industrially produced using the palladium-catalysed Sonogashira reaction (creation of the bold red bond)



the Rh-biphephos catalyst is used with a 4000:1 molar

substrate to catalyst ratio and the reaction was run

in a 300 l pressure reactor. The aldehyde is isolated

through water extraction, while the catalyst remains in

the organic layer. A multiton amount of (S)-allyl lysine

ethylene acetal was produced this way. A multikilogram

quantity of a pharmaceutical building block (Figure 5)

was produced by Pfi zer using a hydroformylation of

norbornene catalysed by 0.15% of Rh(CO)2(acac)

in the presence of dppf. Additionally, examination of

the patent literature also reveals that Pfi zer used a

Rh-biphephos-catalysed hydroformylation reaction to

obtain N-Boc-(4-oxobutyl)caprolactam on a 250 g scale

and that Dow performed a 200 g hydroformylation

step to produce a protected amino aldehyde.

Asymmetric hydroformylation is a powerful tool

to introduce chirality in pharmaceuticals. However,

it has remained so far a purely academic domain

with no industrial-scale application. As an example,

(S)-naproxen can be effi ciently obtained with

excellent enantioselectivity and regioselectivity

using the chiral hydroformylation approach, but the

currently more economically viable resolution route

dominates at the industrial level.

In the fragrance domain, Vertral®, a green melon-

scented component, and Florhydral® are produced

by hydroformylation of exo-cyclopentadiene using

Rh2(2-ethylhexanoate)4 or 1,3-dipropenylbenzene

using a Rh-PPh3 catalyst, respectively (Figure 6). The

citrus-scented limonenal is commercially obtained

by Celanese through the same pathway, while the

woody and spicy Spirambrene® is manufactured

by Givaudan and Vigon International according to

a hydroformylation–Tollens reaction–acetalisation

scheme (Figure 6). Many other examples from the

fragrance industry issued from the patent survey are

reported.

Finally, although examples of the use of

hydroformylation as an alternative access to

agrochemicals are reported, none of them seems to

be currently operated for industrial-scale production.

Ruthenium-Catalysed Selective HydrogenationIn this chapter, Philippe Dupau (Firmenich SA, La

Plaine, Switzerland) fi rst focuses on the ruthenium-

catalysed reduction of conjugated dienes used at

Firmenich. Indeed, although the Ru version of this

reaction has been known for more than a decade,

it suffered until recently from a narrow reaction

scope and a lack of activity which hampered its

implementation at the industrial production level.

In 2008, it was discovered at Firmenich that these

limitations could be overcome by the use of a cationic

[(Cp-type)Ru(diene)][Y] catalyst in the presence

of some weakly acidic additives. This technology

is illustrated by the case study of the industrial

production of (Z)-hex-3-en-1-ol, also called leaf

alcohol, a useful component in fl avour and fragrance

chemistry (Figure 7). With their process, this compound

CH

OAcCO2HH2N

C HO

O

OC

HONa

Vitamin A acetate (S)-Allylsine ethylene acetalPharmaceutical building block

Fig. 5. Examples of pharmaceutical derivatives or intermediates industrially produced using a rhodium-catalysed hydroformylation step

H

CHO

CHOCHO

O

OCH2

Spirambrene®LimonenalFlorhydral®Vertral®

Fig. 6. Examples of fragrances industrially produced using a rhodium-catalysed hydroformylation step



is effi ciently obtained starting from either sorbic acid

esters (followed by reduction of the ester function) or

sorbic alcohol. In the fi rst case, the reaction is run neat

at 70–80ºC under 1–5 bar H2 in the presence of 0.005%

of [(Cp*)Ru(COD)][BF4] and 0.1–0.2% of maleic acid.

When starting from sorbic alcohol, acetone is used as

solvent, all other reaction parameters being the same.

Interesting kinetic and mechanistic investigations

reveal that for sorbic acid ester, the reaction should be

stopped at 95% conversion to maintain high selectivity,

whereas the sorbic alcohol route requires all-trans

starting material to prevent catalyst deactivation.

The chemoselective hydrogenation of carbonyl-

containing compounds is another very interesting

reaction in fl avour and fragrance chemistry and is

widely operated by Firmenich. To avoid the use of the

patented (diphosphine)(diamine)RuCl2 complexes,

they have developed a series of proprietary amino- or

imino-phosphine Ru complexes, either with bidentate

(PN) or tetradentate (PNNP) ligands. For production-

scale use, 2-bis(diphenylphosphino)ethylamine (DPPAE)

was selected and its reaction with (PPh3)3RuCl2 in

tetrahydrofuran (THF) serendipitously led to the

easy-to-handle cationic [(DPPAE)2(PPh3)RuCl][Cl]

complex. With this complex in hand, Polysantol®

and nirvanol (Figure 7) are effi ciently produced

by hydrogenation of the corresponding ketones under

20 bar H2 using a catalyst loading of 0.00125 mol% at

the multi-ton scale. Several hundreds of tons of another

sandalwood fragrance, DartanolTM (Figure 7), are

also produced yearly using 0.005 mol% of the same

catalyst, although in this case the temperature has

to be lowered from 70–80ºC to 60ºC due to substrate

thermal instability. Finally, the very interesting

example of the grapefruit and woody smelling

Pamplewood® is reported (Figure 7). In this ton-

scale production, [(DPPAE)2(PPh3)RuCl][Cl]

(0.002 mol%) effi ciently catalyse the hydrogenation

of 7,7-dimethyl-10-methylenebicyclo[4.3.1]decan-3-one

to the corresponding alcohol. However, the latter is

obtained in a 82:18 exo:endo mixture that does not

meet the requirements for optimal olfactive properties.

Nevertheless, this alcohol is further epimerised to

the desired exo:endo ratio using the same catalyst,

simply by increasing the temperature of the batch

while maintaining the hydrogen pressure after the

hydrogenation reaction. A reaction model has been

developed and simulation has enabled the calculation

of the different rate constants in this epimerisation

process.

Asymmetric HydrogenationAfter some general remarks on metal complexes

and chiral ligands, Hans-Ulrich Blaser et al. (Solvias

AG, Basel, Switzerland) review the C=C, C=O and

C=N asymmetric hydrogenation reactions that are

currently (or have been) operated for production

of fi ne chemicals. Pilot-scale processes as well as

some industrially interesting bench-scale reactions

are also considered, all being catalysed by rhodium-,

ruthenium- or iridium-based complexes.

It is noteworthy that rhodium is the principal metal

used in industrial asymmetric hydrogenation processes,

with 11 identifi ed cases. As an early example from the

1970s, Knowles’ [Rh(dipamp)(COD)][BF4] catalyst has

been applied for years to the production of L-dopa

(Figure 8) by Monsanto. Good turnover frequency

(TOF) (1000 h–1), turnover number (TON) (20,000)

and enantioselectivity (95%) were attained at a

ton year–1 scale. A similar process was later used by

NSC Technologies for the production of unnatural

amino acids, whereas a slightly different one using

[Rh(eniphos)(nbd)][PF6] was developed by EniChem/

Anic for the large-scale production of phenylalanine

(15 tons year–1) as a step towards aspartame. Other

examples of the use of defi ned cationic rhodium

CH2

OH

OH

Leaf alcohol

HC

HOPolysantol®

DartanolTM

HC

HONirvanol

Pamplewood®

CH

MeO

Fig. 7. Examples of fragrances industrially produced using the ruthenium-catalysed Firmenich chemoselective hydrogenation processes (hydrogenated bonds in bold red)



complexes include the asymmetric hydrogenation of

a -enamide in the presence of [Rh(tcfp)(COD)][BF4]

to access 3.8 tons of imagabalin (Figure 8) at Pfi zer

or of a duloxetine intermediate, marketed by Eli Lilly,

with [Rh(duanphos)(NBD)][SbF6]. However, in many

cases, the preliminary synthesis of well-defi ned species

is not compulsary and in situ formed cationic or

neutral Rh-catalysts could be successfully employed.

Indeed, Solvias, then DSM, have reported on the use

of [Rh(NBD)2][BF4]/Walphos or [Rh(COD)2][BF4]/

phosphoramidite/(m-Tol)3P mixtures, respectively,

for the production of an intermediate of aliskiren

(Figure 8), a renin inhibitor. In a similar way, Merck

is currently operating the asymmetric hydrogenation

of an unprotected dehydro -amino amide in the

production of sitagliptin (Figure 8). In this last case,

mechanistic studies have shown that the tautomeric

imine is reduced rather than the initially targeted

C=C bond of the starting enamine. A number of

other interesting examples are given by the authors,

including transfer hydrogenations reactions using

mainly [Rh(Cp*)Cl2]2 as precursor and that were

scaled up to 200 kg.

Triggered by Noyori’s discovery of the Binap-

Ru system, ruthenium-catalysed asymmetric

hydrogenation is now widely used (or at least

under development) in industry. As a fl agship of

this chemistry, the production of 300 tons year–1 of

citronellol (Figure 9) by Takasago International, with

[Ru(Binap)(CF3CO2)2] as a C=C hydrogenation catalyst

and with excellent enantiomeric excess (ee) (97%),

TON (50,000) and TOF (500 h–1), probably remains the

most famous example. Roche has reported a similar

[Ru(MeO-biphep)(CF3CO2)2] catalyst for the

asymmetric C=O reduction of a -keto ester used

as an intermediate in the synthesis of orlistat

(Figure 9), a drug used to treat obesity. In this case,

a TON of 50,000 was reached by adding hydrochloric

acid as a co-catalyst, enabling the process to be scaled

up to 2.2 tons. A process involving a Ru-catalysed C=O

hydrogenation (Ru = [Ru(Tol-Binap)Cl2]2•xNEt3) is also

operated by Takasago to produce (R)-1,2-propanediol,

a precursor of the bactericide (S)-oxfl oxacin, on a

50 ton year–1 scale.

Arene-ruthenium precursors are another class

of effi cient pre-catalysts. At Takasago again, an

elegant hydrogenation/dynamic kinetic resolution is

operated to produce a penem antibiotic intermediate

(Figure 9) on a 50–120 tons year–1 scale. In this process,

[Ru(Tol-Binap)(p-cymene)I][I] is effi ciently used

CO2H CO2H

CO2H

HO

NH2

CF3

FHO NH2

MeO

MeO

NH2

FF

O

O

NN

N

Imagabalin

L-Dopa

Sitagliptin

Aliskiren intermediate

Fig. 8. Some products of industrial rhodium-catalysed asymmetric hydrogenation processes (hydrogenated bonds in bold red)

CO2Me

CO2Me

CO2Me

NHCOPhCH

OHOHCHOH C11H23

OCitronellol Orlistat intermediate Penem intermediate cis Methyl

dihydrojasmonate

Fig. 9. Examples products made by industrial ruthenium-catalysed asymmetric hydrogenation processes (hydrogenated bonds in bold red)



as a pre-catalyst and affords the desired compound

in ee >97% and diastereomeric excess (de) >94%.

Interestingly, in situ formed catalysts can sometimes be

employed as illustrated by the Firmenich production

of the fl oral-scented cis-methyl dihydrojasmonate

(several tons year–1, Figure 9) which makes use

of a [RuH(COD)(COT)][BF4]/chiral diphosphine

system. It is also worth noting that ketones without

- or -coordinating groups can be enantioselectively

reduced to the corresponding alcohols using

Ru(diphosphine)(diamine) systems. Several pilot

plant-scale operations are described but it is not clear

whether they have been implemented as production

processes. The same observation stands for the use of

ruthenium catalysis in transfer hydrogenations.

Finally, the last member of this metal-based tryptich,

iridium-catalysed asymmetric hydrogenation, has been

more rarely used in industry at the production scale.

However, a remarkable example is operated by Syngenta

with the synthesis of more than 10,000 tons year–1 of

(S)-metolachlor (Figure 10), a grass herbicide. The

asymmetric step of this process consists of an imine

hydrogenation under 80 bar H2 at 50ºC and is catalysed

by an in situ generated species obtained by mixing

[Ir(COD)Cl]2 with one of Solvias’ Josiphos ligands.

Impressive TON (2,000,000) and TOF (>400,000 h–1)

are obtained, while asymmetric induction remains

fairly good (ee 80%). Following this example, DSM and

Solvias have developed another example based on

the [Ir(COD)Cl]2/(4-MeO-3,5-(tBu)2C6H2)-MeO-Biphep

couple to produce several tons of biotin from a cyclic

anhydride.

With the three pgms Rh, Ru and Ir, an impressive

number of pilot processes or bench-scale reactions

up to several hundreds of kilograms are also

described, thus making one anticipate that many

more production processes using metal-catalysed

asymmetric hydrogenations will appear in the near

future.

Case StudiesThe four other chapters are devoted to case studies

of scaling up syntheses involving transition metal-

catalysed steps and the associated challenges that

had to be tackled. Thus, Ioannis N. Houpis (Janssen

Pharmaceuticals Companies of Johnson & Johnson,

Beerse, Belgium) describes the modifi cation of the

synthetic sequence and scale-up optimisation studies

of an ‘all-transition-metal-process’ to yield a potential

active pharmaceutical ingredient (API). The chosen

route involves some palladium-catalysed Sonogashira

and Suzuki coupling steps (Figure 11). Among the

problems that were solved, it is interesting to note that

the homogeneous Pd(PPh3)4 catalyst could be simply

replaced by Pd/C for the Suzuki coupling step, thus

allowing easy reduction of palladium traces in the

fi nal API (from 250 ppm to 10 ppm).

Another example is given by Adriano F. Indolese

(RohnerChem, Pratteln, Switzerland) for the pilot-

scale production of 3.7 kg of 5-(4-cyanophenyl)indole

(Figure 11) with a four month deadline. A palladium-

catalysed Suzuki coupling was chosen. From catalyst

screening, a mixture of PdCl2 and P(Tol)3 was selected

and other reaction parameters were optimised by

‘design of experiment’ (DOE) at the small-scale level.

With these optimised conditions, no scale-up effect

was observed and two pilot runs of ca. 2 kg each

could be run, affording the targeted compound with

the required purity specifi cations.

Per Ryberg (AstraZeneca, Södertälje, Sweden)

depicts scale-up studies of a cyanation reaction that

was performed at AstraZenaca in 2003 and 2004.

This reaction, used as the last step of a multikilogram

synthesis of a drug candidate for the treatment of

glycogen synthase kinase 3 disorder (Figure 11),

was found to be effi ciently catalysed by either a

Pd(dba)2/PtBu3 mixture or the preformed

[PdBr(PtBu3)]2 dimer, the latter being preferred for

large-scale application. Technical issues that infl uence

the large-scale synthesis were addressed: delayed

heating of the reaction mixture was found to be

detrimental, while the cyanide source (Zn(CN)2) had

to be added as the fi nal reagent, both parameters

being linked to poisoning of the Pd catalyst.

Finally, Cheng-yi Chen (Merck Research Laboratories,

Rahway, USA) fully describes a scalable and cost-

effective synthesis of vaniprevir (Figure 11), a

20-membered ring protease inhibitor that possesses

activity against the hepatitis C virus. The key step

of this synthesis was identifi ed as a 20-membered

macrolactamisation through ring-closing metathesis

(RCM) which had to be optimised in terms of volume

productivity. This could be achieved using the Grubbs-

Hoveyda second generation catalyst and simultaneous

MeOO

NCl

Metolachlor

Fig. 10. Metolachlor, a grass herbicide produced using an iridium-catalysed asymmetric hydrogenation



introduction of solutions of the starting diene and the

Ru catalyst. Additionally, by raising the temperature,

but adding 2,6-dichloroquinone, the catalyst amount

could be lowered to 0.2 mol%. Interestingly, other

routes involving Heck, Sonogashira or Suzuki

couplings were examined but were found less

effective.

ConclusionsDespite the massive use of metal-based catalysis in

the manufacture of bulk chemicals for many years,

the development of organometallic-based processes

for pharmaceuticals, fragrances or agrochemicals

production is surprisingly still in its adolescence.

However, the industrial processes described in this

book clearly illustrate the great potential of pgms as

valuable tools in this fi eld. Moreover, the numerous

examples of production processes, pilot plant or

bench-scale reactions depicted will surely inspire

chemists who are facing synthetic problems. Finally,

this book may also serve as a valuable source of

information not only for research purposes, but also

for students and colleagues teaching organometallic

catalysis.

The ReviewerDr Michel Picquet obtained his PhD in Chemistry from the Université de Rennes I, France, under the supervison of Professor P. H. Dixneuf and Dr C. Bruneau in 1998. After a year’s post-doctoral position in the group of Professor R. A. Sheldon (Delft Technical University, The Netherlands), he was hired by the Université de Bourgogne in 1999 as an Assistant Professor. His research interests include organometallic catalysis and the use of ionic liquids. Since 2009, he is also interested by organometallics for biological applications. He also teaches Organometallic Synthesis and Catalysis at Master’s level.

HN

HN

N H

O

O

O

OO

OO

O

OS

N

NRCM

Vaniprevir from Merck

N H

NC Suzuki

5-(4-cyanophenyl)indolefrom RohnerChem

O

CO2H

S

N

SonogashiraSuzuki

Suzuki

API from Janssen Pharmaceuticals

O

OH

HN

N

N

NC

Cyanation

Drug candidate from AstraZeneca

Fig. 11. Products illustrating case studies of some scaled up pgm-catalysed reactions

“Organometallics as Catalysts in the Fine Chemical Industry”



A Study of Platinum Group Metals in Three-Way AutocatalystsEffect of rhodium loading outweighs that of platinum or palladium


By Jonathan Cooper* and Joel Beecham

Johnson Matthey Emission Control Technologies, Orchard Road, Royston, Hertfordshire SG8 5HE, UK


The price differential between platinum and palladium

has driven the industry to adopt emissions control

catalyst formulations for gasoline engines that contain

higher levels of Pd than Pt, and in most cases no Pt.

In addition fl uctuations in the price of rhodium have

led to thrifting of this metal. This study compares the

performance of ten different catalyst compositions with

varying ratios of Pt, Pd and Rh for a Euro 5 vehicle and

under bench test conditions. The results show that a

system with low Rh loading can readily be improved by

increasing the Rh loading and there is a relatively large

effect of doing this by a small amount. Increasing the

Pd or Pt loading also improves emissions performance

but by a signifi cantly smaller amount than the effect of

changing the Rh loading. Conversely it may be possible

to decrease the Pt or Pd loading with only a small

effect on emissions. Furthermore it was found that Pd

outperforms Pt under most conditions, although not

signifi cantly. The difference appears greater under more

stressful conditions such as high-speed driving or wide

perturbation amplitude.

IntroductionSince their introduction in 1974 three-way catalysts

(TWCs) have used platinum group metals (pgms)

to control emissions of hydrocarbons (HCs), carbon

monoxide (CO) and oxides of nitrogen (NOx) in

gasoline powered cars (1). A mixture of some or all of

Pt, Pd and Rh have always been used, with Rh being

especially active for NOx conversion and both Pd and

Pt having excellent activity for oxidation reactions of

CO and HC species (2). However in the intervening

decades a wide range of factors have at various

times infl uenced the usage of these pgms in terms

of both type and quantity. These include: fuel quality,

especially sulfur content; emissions legislation; vehicle

technology including engine calibrations and fuelling

systems; exhaust layout, packaging and design; relative

prices of the pgms; and catalyst washcoat technology.

In recent years Pd/Rh catalysts have been the most

common, aided by lower sulfur fuel and improved



washcoat technology and also attractive due to the

>10 year trend of Pd being lower in price than Pt (3). A

further recent phenomenon has been the signifi cant

efforts focused on thrifting of Rh from TWCs in

response to a sharp price spike in 2007 and 2008.

Today the majority of TWCs are Pd/Rh with Pt

much less common. It seems reasonable to expect

however that there will in future be a similar variety of

competing factors which may affect pgm choice just

as there has been in the past. For this reason a periodic

appraisal of the current status of modern catalysts

using the three pgms at a range of typical loadings is

of interest. In particular the near 90% fall in the price of

Rh since mid-2008 and three-fold increase in the price

of Pd since 2009 are reasons why a study may be of

interest now.

Catalyst Test ProgrammeIn order to compare the relative activities of TWCs at a

range of Pd, Pt and Rh loadings, the following catalysts

were prepared. The loadings were chosen without

regard to pgm cost, allowing a relevant technical

comparison on the basis of pgm mass alone. Details

of the compositions are given in Table I. Throughout

this paper pgm loadings are reported in grams per

cubic foot (g ft–3) in the format: T/Pt:Pd:Rh where T

is the total pgm loading. All three are included for

clarity even though in all cases either the Pt or Pd

loading is zero.

All catalysts were made on the same substrate, a

4.16 × 4.5 600/4 ceramic. The catalysts were aged

in groups of four at Johnson Matthey in Royston, UK,

using a lean spike ageing cycle of 80 hours duration

with 950ºC inlet temperature, which is correlated to

160,000 km road ageing. The total pgm loadings were

chosen to be towards the lower end of the range of

those currently supplied to the market, with a view to

being able to compare the relative effects of Pd and

Pt at constant Rh, the effect of the absolute loading of

each of Pt and Pd and also the effect of Rh loading at

constant Pd and Pt. A reference catalyst was included

in each set to allow comparison of the ageing runs.

The Pd/Rh catalysts evaluated were a current

Johnson Matthey production Euro 5 technology. The

Pt/Rh washcoat was modifi ed slightly to better suit

Pt but was otherwise unchanged in terms of total

washcoat loading, oxygen storage material and total

rare earth content to better allow comparison of the

Table I

Platinum Group Metal Loadings on Model Three-Way Catalysts Selected for the Present Study

Set Catalyst description Total pgm,

g ft–3

Platinum,

g ft–3

Palladium,

g ft–3

Rhodium,

g ft–3

1 Medium Pd + Rha 30 0 25 5

High Pd + Rh 40 0 35 5

Low Pd + Rh 20 0 15 5

High Pt + Rh 40 35 0 5


High Rh + Pd 32.5 0 25 7.5

Low Rh + Pd 27 0 25 2

Low Pt + Rh 20 15 0 5


Medium Pt + Rh 30 25 0 5

High Rh + Pt 32.5 25 0 7.5

Low Rh + Pt 27 25 0 2

a Reference catalyst



effect of pgm alone. Furthermore if a hypothetical

switch from a Pd/Rh technology to a Pt/Rh one was

deemed desirable, taking this approach of changing

as little as possible other than the pgm would be the

easiest and most likely path and so affords the most

relevant comparison.

The catalysts were tested over the Motor Vehicle

Emissions Group (MVEG-B) European drive cycle as

set out in UN/ECE Regulation number 83 (4) on a

1.2 l vehicle with a (current) Euro 5 calibration and

were further tested over light-off and lambda sweep

protocols on a 2.0 l Euro 5 bench engine. In the light-

off test a stable fl ow of exhaust gas at 125 kg h–1 and

0.998 was generated down a bypass exhaust leg, this

fl ow was then diverted by means of a valve to a parallel

leg containing a cold catalyst in order to monitor

dynamic light-off. A catalyst inlet temperature of 450ºC

was eventually reached at the end of the test. For the

sweep test the fl ow was maintained at the same

temperature and fl ow rate but the engine’s air:fuel ratio

was adjusted in 15 equal steps from 0.99 to 1.01

and a perturbation of ±4% at 1 Hz was applied. After

a stabilisation period of 10 seconds at each condition,

gaseous emissions were measured and averaged

over a further 5 seconds before moving to the next

setpoint. These fl ow conditions are designed to be

stressful for the catalyst, representing a similar fl ow rate

to the highest speed part of the European drive cycle

but a lower temperature than would ordinarily be seen

on a typical close-coupled catalyst at this point of the

cycle, with a higher perturbation amplitude.

Vehicle Testing ResultsThe results of the vehicle tests on the reference

catalysts (30/0:25:5) are shown in Table II. Each

result is the average of at least three tests. These

results would be expected to be identical under ideal

conditions; however in practice slight differences in

ageing severity from run to run combined with test-

to-test error has led to some variation in the results

observed. In particular the ageing of Set 2 appears to

have been slightly milder than the other two and this

makes it diffi cult to compare results across the sets.

Nevertheless the data are considered suffi ciently close

to make useful comparisons between sets, with care.

Table II also shows the limits specifi ed by Euro 5/6

and it can be seen that in all cases the emissions fall

well within those limits.

The results of Set 1 of the test catalysts are shown

in Table III. This set allows comparison of the effect

Table II

Vehicle Emission Test Results for the Reference Catalysts Compared to Euro 5 and 6 Limitsa

Set HC, g km–1 Non-methane HC, g km–1 CO, g km–1 NOx, g km–1

1 0.068 0.052 0.281 0.044

2 0.061 0.047 0.243 0.037

3 0.066 0.051 0.245 0.038

Euro 5/6 limits 0.100 0.068 1.000 0.060a All Reference catalyst loadings were 30/0:25:5

Table III

Vehicle Emission Test Results for Catalyst Set 1

Catalyst composition,

T/Pt:Pd:Rh

HC, g km–1 Non-methane HC,

g km–1

CO, g km–1 NOx, g km–1

30/0:25:5 a 0.068 0.052 0.281 0.044

40/0:35:5 0.066 0.051 0.264 0.044

20/0:15:5 0.070 0.054 0.263 0.051

40/35:0:5 0.069 0.055 0.297 0.045a Reference catalyst



of Pd loading at constant Rh and also a comparison

of Pt with Pd. In the former case there is a clear but

undoubtedly small effect of improved emissions as

Pd loading increases. This was, on closer inspection,

evident in improved light-off as the Pd loading

increased. The emissions of the Pt/Rh catalyst were

again clearly, if only slightly, worse for HC and CO. The

emissions of all catalysts in this set were actually very

similar, suggesting that the most relevant factor is that

the Rh loading remains the same in all cases.

Larger differences were seen in Set 2 (Table IV). The

effect of Rh loading at constant Pd in the fi rst three

catalysts was clear, with the NOx emissions of the low

Rh catalyst being ~75% higher than those of the high Rh

catalyst. This is not unexpected given the well known

role of Rh as an excellent catalyst for the removal of

NOx. A 27% increase in HC emissions was also seen

however, demonstrating that Rh is also important here.

Detailed analysis of the second-by-second emissions

shows that the NOx benefi t could be seen in light-

off and also in the extra-urban (high-speed) section

of the drive cycle. A consideration of the emissions

from this portion of the drive cycle alone showed that

the catalyst with 2 g ft–3 Rh emitted ~175 mg of NOx,

both of the catalysts with 5 g ft–3 Rh emitted ~140 mg

and the catalyst with 7.5 g ft–3 Rh emitted only 90 mg

(Figure 1).

The HC benefi t was mainly seen at light-off, however

a small difference was also seen in the high-speed

section, again corresponding to the Rh loading for the

Pd catalysts. The Pt/Rh catalyst with 5 g ft–3 Rh slipped

a similar amount of HC in the high-speed section as

the Pd/Rh catalyst with 2 g ft–3 Rh and more than the

Pd/Rh catalyst with 5g ft–3 Rh, suggesting a very small

inherent defi cit in HC conversion for Pt.

Set 3 allows a comparison of Rh loading in a catalyst

with constant Pt loading (Table V). Once again a large

improvement in NOx was seen as Rh increases and

Table IV


Catalyst

composition,

T/Pt:Pd:Rh


g km–1


30/0:25:5 a 0.061 0.047 0.243 0.037

32.5/0:25:7.5 0.056 0.042 0.261 0.027

27/0:25:2 0.071 0.056 0.289 0.047


800 850 900 950 1000 1050 1100 1150 1200Time, s

0.18

0.16

0.14

0.12

0.10

0.08

0.06

0.04

0.02

0

Emis

sion

s, g

140

120

100

80

60

40

20

0

Speed, km h

–1

Catalyst Loadings

32.5/0:25:7.5

20/15:0:5

27/0:25:2

30/0:25:5

Scheduled speed

Fig. 1. Normalised EUDC NOx emissions for Set 2 catalysts, showing a clear effect of rhodium loading



HC also improved, although the benefi t on increasing

from 5 g ft–3 to 7.5 g ft–3 was less marked than that

seen on going from 2 g ft–3 to 5 g ft–3. The emissions

from the 27/25:0:2 Pt/Rh catalyst were relatively poor

and in fact the weakest of all in this study. The effect

of Rh on HC light-off and on NOx light-off and high-

speed performance was seen again, with NOx slip in

the high-speed section again varying clearly with Rh

loading and with similar performance from both the

Pt and Pd-containing 30 g ft–3 catalysts. The second-by-

second HC emissions are shown in Figure 2.

Engine Bench Testing ResultsAnalysis of the second-by-second data shows that the

majority of differences occur at the beginning of the

test on the pre-lightoff period where there are some

variations in engine-out emissions. For this reason

analysis was done on emissions post-lightoff or in the

Extra-Urban Driving Cycle (EUDC) (4) section of the

drive cycle where these cold start effects are not seen.

Here light-off results are reported by reference to

the temperature at which 50% conversion effi ciency

is reached, known as T50, and so a lower fi gure refl ects

a more active catalyst. The CO/NOx crossover is a

standard measure of catalyst effi ciency and is derived

from analysis of the separate CO and NOx effi ciency

curves as a function of . A higher reported effi ciency

naturally refl ects a more active catalyst. Typically the

crossover occurs just rich of 1.00, the stoichiometric

air:fuel ratio.

The clear and expected trend of better light-off with

more Pd can be seen in the engine bench test results

for Set 1 (Table VI) and this is also refl ected in higher

conversion effi ciencies. The Pt/Rh catalyst was slightly

inferior in light-off and noticeably worse in conversion

effi ciency under these stressful test conditions.

Table V


Catalyst

composition,

T/Pt:Pd:Rh


g km–1


30/0:25:5 a 0.066 0.051 0.245 0.038

30/25:0:5 0.065 0.050 0.228 0.035

32.5/25:0:7.5 0.063 0.051 0.242 0.030


0 200 400 600 800 1000 1200Time, s

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

Cum

ulat

ive

HC

emis

sion

s, g

140

120

100

80

60

40

20

0

Speed, km h

–1

Catalyst Loadings

32.5/0:25:7.5

27/25:0:2

30/25:0:5

30/0:25:5

Scheduled speed

Fig. 2. Second-by-second total hydrocarbon emissions for Set 3 catalysts



The results for Set 2 are shown in Table VII. In this

case the reference catalyst gave the best HC emissions

and the conversion effi ciencies were higher overall

than for the other two sets, indicative of the milder

ageing experienced by this set. Nevertheless the effect

of Rh on light-off was once again seen here and the

trend in hot effi ciencies was the same as that observed

for the vehicle tests. The CO/NOx crossover plot is

shown in Figure 3.

The engine bench results for Set 3 (Table VIII),

which were all Pt catalysts except for the reference

catalyst, show the same broad trends as the vehicle

tests. Again the 5 g ft–3 Rh and 7.5 g ft–3 Rh catalysts

were closer in performance than the 2 g ft–3 Rh and 5

g ft–3 Rh catalysts, suggesting that 2 g ft–3 is too low a

Rh loading for the Pt/Rh catalyst used in this study and

that increasing the loading above 2 g ft–3 Rh is highly

effective at improving the catalyst performance. There

Table VI

Engine Bench Test Results for Catalyst Set 1

Catalyst composition, T/Pt:Pd:Rh HC T50, ºC NOx T50, ºC Effi ciency at CO/NOx crossover, %

30/0:25:5 a 370 374 96.6

40/0:35:5 365 371 97.4

20/0:15:5 377 375 94.7

40/35:0:5 379 376 95.6a Reference catalyst

Table VII



30/0:25:5 a 370 375 98.4

32.5/0:25:7.5 354 356 99.0

27/0:25:2 376 379 97.4


0.99 0.995 1 1.005 1.01Lambda

100

95

90

85

80

75

CO/N

Ox

conv

ersi

on, % Catalyst Loadings

32.5/0:25:7.5

20/15:0:5

27/0:25:2

30/0:25:5

Fig. 3. CO/NOx crossover for Set 2 catalysts



is further evidence from the hot conversion effi ciency

that a Pt/Rh catalyst does not perform as well as a

Pd/Rh catalyst under these conditions.

The Effects of Different PGM LoadingsThe milder ageing experienced by Set 2 compared to

the other two sets makes it diffi cult to compare the

effect of Pt loading when the Rh loading was kept

constant at 5 g ft–3, because the tests were carried

out across different sets. This may explain why the

expected trend towards lower emissions with higher

Pt loading cannot clearly be seen. Further tests would

be required to confi rm this.

Direct comparisons of Pd and Pt are possible both

within and between sets. In the vehicle emissions tests

the difference was small or even non-existent. However

on the engine bench the clear trend was that, when

comparing equally loaded Pd/Rh vs. Pt/Rh catalysts,

the Pd/Rh catalysts performed better by a noticeable

margin. The sweep test in particular was intended to

be stressful for the catalyst, allowing small differences

to be exaggerated.

When Pd and Pt are compared, it should be

borne in mind that the Pd/Rh catalysts tested were a

commercially produced technology which has been

optimised for Pd/Rh during development. For the

reasons outlined earlier Pt/Rh washcoat development

has received less attention and as such the Pt/Rh

catalysts tested here should not be considered as

fully optimised but as possible readily implemented

alternatives to current technology.

Across all sets the effect of a change in the Rh

loading was undoubtedly, mass for mass, signifi cantly

greater than that of a change in either the Pt or Pd

loading. The reduction in emissions which could be

achieved by adding a given mass of Rh was greater

than that which could be achieved by adding the same

mass of either Pd or Pt. Conversely the removal of an

equivalent amount would have the largest detrimental

effect. Rh has a clear benefi cial effect on light-off for

all pollutants both on the specifi c vehicle chosen for

this study and on the engine bench. Rh also helped

NOx emissions in the high-speed section of the vehicle

test and conversion effi ciency on the engine bench.

Finally, it must be noted that each of the ten different

pgm compositions tested here for a Euro 5 vehicle

has been proven to result in emissions below the

Euro 5 (and Euro 6) limits (Table II). This implied

fl exibility immediately raises the question of which

of these is ‘best’, or indeed if another system could be

designed based on this information which might fi t

that description. Typically of course this decision will

be made on a balance of technical and commercial

factors and this study has only begun address the

technical aspects of a possible system design.

ConclusionsThis study has found, as expected, that increasing

either the Pt or Pd loading results in lower emissions

and better catalyst performance. The highest and

lowest Pd and Pt loadings considered were more

than a factor of two different and yet the effect on

performance was in the main rather small over the

majority of the legislative European drive cycle. The

lower amounts of Pd and Pt used were suffi cient, at

least in this application, and it may be possible to lower

them further. There is a small but noticeable defi cit in

performance when comparing Pt with Pd technology.

A slightly wider relative spread of Rh loadings was

investigated and here the effect on emissions and

performance was signifi cantly larger. In mass terms

the changes investigated were much smaller than

for Pt or Pd, yet the effect of increasing Rh loading

from the lowest levels considered was much greater.

This was primarily seen in NOx emissions but a clear

effect on HC emissions was also observed. Rh has

been shown therefore to be of signifi cant benefi t to

both light-off and catalyst performance. Rh thrifting in

Table VIII



30/0:25:5 a 360 357 98.9

30/25:0:5 380 381 97.4

32.5/25:0:7.5 362 360 99.4




recent years has been in some cases signifi cant and

on occasion has been done in conjunction with an

increase in overall pgm (most often Pd) loading; this

study raises the question of whether in some cases a

partial reversal of both of these changes is worthy of

serious consideration.

It is not possible in one study to fully evaluate all

the many possible combinations of pgms and in terms

of legislated vehicle emissions this study is of course

confi ned to one application only. The conclusions

therefore are necessarily limited, but the following

general statements can be made:

(a) A system with low Rh loading can readily be

improved by increasing this Rh loading and there

is a relatively large effect of doing this by a small

amount.

(b) Increasing Pd or Pt loading improves emissions

performance by a signifi cantly smaller amount

than the effect of Rh loading. Conversely

decreasing Pt or Pd may have only a small effect

on emissions.

(c) Pd outperforms Pt by a small margin under most

conditions, although the difference appears

greater under more stressful conditions such

as high-speed driving or wide perturbation

amplitude.

AcknowledgmentsThe authors would like to thank the catalyst test

laboratories at Johnson Matthey Emission Control

Technologies, Royston, for carrying out the work.

Johnson Matthey Precious Metals Marketing is thanked

for useful discussions.

References1 M. V. Twigg, Platinum Metals Rev., 1999, 43, (4), 168

2 R. M. Heck, R. J. Farrauto and S. T. Gulati, “Catalytic Air Pollution Control: Commercial Technology”, 3rd Edn., John Wiley & Sons, Inc, Hoboken, New Jersey, USA, 2009

3 Platinum Today, Price charts: http://www.platinum.matthey.com/prices/price-charts (Accessed on 19th August 2013)

4 ‘Regulation No 83 of the Economic Commission for Europe of the United Nations (UN/ECE) — Uniform provisions concerning the approval of vehicles with regard to the emission of pollutants according to engine fuel requirements’, Offi cial Journal of the European Union, L 42/1, 15th February, 2012

The Authors

Jonathan Cooper is Gasoline Development Manager at Johnson Matthey Emission Control Technologies in Royston, UK, and has over 13 years’ experience in global gasoline aftertreatment systems research at Johnson Matthey. He holds a degree and DPhil in Chemistry from the University of Oxford, UK.

Joel Beecham has been a Gasoline Product Development Chemist at Johnson Matthey since joining the company in 2011. He researches new washcoat technologies for three-way catalysts and lean NOx traps, and has an interest in the emission control properties of platinum group salts. He holds an MChem in Chemistry from Kingston University, London.



Recovery of Palladium from Spent Activated Carbon-Supported Palladium CatalystsPrecipitation by sodium borohydride allows high grade recovery of palladium


By Serife Sarioglan

TÜBITAK Marmara Research Center, Chemistry Institute, 41470 Gebze, Kocaeli, Turkey


Activated carbon-supported palladium catalysts are

liable to progressive deactivation even in the absence

of any gaseous contaminants during the oxidation of

hydrogen under ambient conditions. The high value of

palladium coupled with environmental considerations

means that new, effi cient and cost effective methods

for the quantitative recovery of palladium from such

materials are required. In the present study, a process

for extracting precious metals from spent catalyst or

inorganic waste was developed. Palladium was extracted

from the spent catalyst with an acid solution containing

dilute hydrochloric acid and hydrogen peroxide at

leaching temperatures of around 90ºC. Palladium in the

leached solution was then precipitated by use of sodium

borohydride solution. The effectiveness of the method

for recovery of precipitated palladium was investigated

by ultraviolet-visible (UV-vis) spectrophotometry, X-ray

diffraction (XRD) and scanning electron microscopy

(SEM). The recovered metallic palladium was of a

suffi cient grade to manufacture fresh activated carbon-

supported palladium catalysts.

1. IntroductionHydrogen is prone to leakage and can form an

explosive atmosphere due to its wide range of

fl ammability limits. Methods of hydrogen elimination

before accumulation of a detonable mixture in

confi ned spaces are thus very important. Catalytic

combustion of hydrogen is the most common

method used in commercial hydrogen detection and

elimination systems. Palladium is frequently used as

the active component of the catalysts for such systems

(1–4). These systems can respond to hydrogen when

maintained at temperatures of 80ºC, and in some cases

less (5). However, for reasons which remain unclear,

the catalyst is liable to progressive deactivation even

in the absence of any gaseous contaminants (2).

The high value of palladium makes its recovery

economically desirable: for example, in 2011 22% of

the palladium market was supplied by recovery from



autocatalysts and jewellery scrap (6). In addition

environmental considerations mean that effective

recovery of the residual precious metals from spent

catalysts is of paramount importance for a process to

be environmentally acceptable (7, 8).

Spent organic-based catalysts which contain

precious metals have traditionally been treated by

incineration to recover the precious metal content.

However, palladium is recovered in oxide form, which

is not ideal for the production of fresh catalyst (9).

Hydrometallurgical techniques are also widely

used for the recovery and separation of precious

metals from spent catalysts. The processes can be

categorised into two types: support dissolution and

precious metal dissolution (10). In the fi rst of these, the

support is dissolved with a nonoxidising acid or base,

after which the precious metals remain as a residue. A

major disadvantage is that this process requires large

quantities of reagents.

In the second type of process the precious metals

are extracted from the support by an acidic oxidant

solution, leaving the bulk of the support undissolved.

Different leaching mixtures such as sulfuric acid,

hydrochloric acid or chloride salts in the presence

of oxidising agents such as nitric acid, bromine or

chlorine have been used for palladium recovery

(11–15). Disadvantages of this technique are the

environmental impact of the reagents, the high cost of

nitric acid and the potential for evolution of hazardous

nitric oxides. In addition, after leaching, nitric acid

must be completely removed from the solution,

adding to the complexity and cost. Separation of Pd

from solution has also been carried out by reduction

in phosphoric acid solution by formalin at 150ºC

(16); in hydrochloric acid by formic acid (17); by

polyoxometallates (18); by bioreduction (19); and by

reduction using aluminium powder (20).

Lastly, the development of new innovative and

sustainable chemical processes with high energy

effi ciency and ideally 100% selectivity will require a

new generation of catalytic materials with tailored

functionality at the surface. Since the material

properties change at the nanoscale, nanosized

catalytic materials are expected to enable highly

complex catalytic processes to be created on the

basis of a controlled sequence of surface reactions

and active sites. Nanostructured catalysts show great

promise in the fi eld of environmentally friendly,

fl exible and effi cient materials processing (21). The

kinetics of adsorption/desorption of hydrogen on the

catalytic surface is closely related with its diffusion

rate, and it is possible to improve these diffusion rates

by use of nanoscale catalytic surfaces. The ability to

obtain recovered palladium in a form which can be

effectively re-used to generate fresh catalysts will be an

advantage in this regard.

In the present work, new process conditions have

been tested and optimised for the recovery of

palladium from spent carbon-supported catalyst.

Palladium was extracted from a spent catalyst matrix

with a mixture of dilute hydrochloric acid and

hydrogen peroxide and then precipitated from the

leached solution by sodium borohydride. NaBH4 was

selected as a much milder reducing agent which is

safer to handle than the conventional alternatives. It has

the further advantage that it can be used in aqueous

or alcohol solutions. UV-vis spectrophotometry, XRD

and SEM were used to monitor the effectiveness of

the chosen recovery method and the resultant solid

residue was shown to be suitable for manufacturing

fresh activated carbon-supported palladium catalysts.

2. Experimental2.1 MaterialsCommercial activated carbon-supported palladium

catalysts containing a polytetrafl uoroethylene (PTFE)

binder in pellets of 100 g were used. The catalyst, sold

for hydrogen elimination in confi ned spaces, was in

the shape of rectangle with dimensions of 160 mm ×

76 mm. The thickness of the catalyst plate was 1 mm.

The palladium loading of the catalyst was determined

to be 10% by weight. (Note that due to commercial

confi dentiality the supplier name and the detailed

compositional analysis of the catalyst material have

been withheld).

2.2 ChemicalsHydrochloric acid (37%) and hydrogen peroxide

(30%) were used for the preparation of the leaching

solution. Sodium borohydride (99%) was used as a

reducing agent for palladium. An aqueous solution

of 5% sodium hydroxide was used to prevent the self-

oxidation of sodium borohydride. All chemicals were

of high grade for laboratory usage. Distilled water was

used for dilutions.

2.3 Ageing of the Palladium CatalystThe thermal conductivity of both activated carbon and

PTFE is around 0.25 W m–1 K–1 (22) while palladium has

a thermal conductivity of about 75 W m–1 K–1 (23). The

thermal conductivity of gases is generally much lower

at around 0.02 ± 0.005 W m–1 K–1 (24). The thermal



conductivity of a porous solid such as found in a

catalyst support can approach that of gases provided

the porosity is high. For this reason, the catalyst body

may be classified as a non-thermally conductive

material (24, 25). As a result the transport of thermal

energy out of a fi xed bed catalytic reactor generally

proceeds slowly, which can cause an increase in

temperature in the catalyst bed at a level approaching

the adiabatic temperature rise.

When the surface temperature of the catalyst

exceeds 300ºC, the PTFE binder of the catalyst starts

to melt, agglomerates the active palladium species

and fi nally leads to the deactivation of the catalyst.

For this reason, the normal operating conditions of

a hydrogen removal catalyst require a maximum

hydrogen concentration in the order of hundreds

or thousands of ppmv in air at 25ºC and 1 atm. The

maximum allowable effl uent gas temperature has

been determined to be between 150ºC and 200ºC to

maintain the catalyst surface temperature below 300ºC

(26). Under normal operating conditions, the lifetime

of the catalyst is at least two years. To quickly age the

catalyst for the present study, a high fuel content of

3% hydrogen was intentionally chosen. Fresh catalyst

was chopped and exposed to 3% hydrogen in air as

described previously (26). The completion of ageing

was monitored by the loss of catalytic activity with

time-on-stream. An effl uent gas temperature of ~246ºC

was reached indicating that the ageing condition had

been met. The deactivated catalyst was subsequently

tested for the recovery of palladium.

2.4 Method for the Recovery of Palladium100 g of the spent catalyst was crushed, ground and

sieved below 500 μm. The fi nely powdered spent

catalyst was put into a jacketed 250 ml reactor. The

leaching solution of hydrochloric acid and hydrogen

peroxide was added slowly to the reactor under

magnetic stirring. The reaction was carried out for

180 min at 90ºC. At the end of the leaching process,

the mixture was fi ltered via a fi ltration funnel under

vacuum at 90ºC. The Pd concentration of the leached

solution was measured using inductively coupled

plasma emission spectrometry (ICPES). The leached

solution was used as a stock solution for the separation

of palladium.

In the separation phase, in order to reduce the

leached palladium species to the form of the

palladium salt, alkaline sodium borohydride solution

was added drop by drop onto 10 g of the stock solution

in a 100 ml conical fl ask. To optimise the precipitation

conditions, different concentrations of borohydride

solution and different process temperatures were

applied. The solution was then fi ltered off, and the

precipitated palladium powder was washed, dried

at 105ºC and weighed to calculate the reduction

effi ciency. Figure 1 shows the process diagram for

the recovery of palladium from the spent Pd/activated

carbon (AC) catalyst.

2.5 CharacterisationElemental analysis of the fi ltrate solution received

after leaching was carried out by ICPES using a

Thermo Jarrell Ash Atomscan 25. UV-vis absorption

spectra of the samples were taken in the range

200 nm to 400 nm using a Shimadzu UV-1650PC

UV-vis spectrophotometer. Wide-angle XRD patterns

of the spent catalysts before and after leaching were

recorded on a Shimadzu XRD-6000 diffractometer

with CuK radiation ( of 0.154178 nm at 40 kV

Spent catalystPd/AC

Grinding and sieving

Reaction(HCl, H2O2 at 90ºC)

Hot fi ltration

Main solution

Pd powder

Precipitation of Pd at 100ºC

Filtrate

Washing and fi ltration

Solid after fi ltration

NaBH4 solution

Waste

Fig. 1. Diagram showing the recovery of palladium from spent catalyst (AC = activated carbon)



and 30 mA). XRD scans were performed at ambient

temperature with a 2 range between 10º and 60º

at a scanning rate of 0.048º min–1. The morphology

of the spent catalysts before and after leaching was

investigated by SEM using a JEOL 6335F FEG-SEM fi eld

emission gun. Additionally, the average particle size of

recovered palladium was measured using a Malvern

Zetasizer Nano ZSP characterisation system.

3. Results and Discussion3.1 Effect of HCl and H2O2 ConcentrationsTreatment of activated carbon-supported palladium

catalysts with a mixture of hydrochloric acid

and hydrogen peroxide gives palladium chloride

according to the Reaction (i):

Pd/AC + 4HCl (aq) + H2O2 (aq)

H2PdCl4 (aq) + AC + 2H2O (i)

The effects of the hydrogen peroxide and

hydrochloric acid concentrations were studied by

changing the concentration of hydrogen peroxide

while keeping the concentration of hydrochloric

acid constant or vice versa. In the fi rst case, hydrogen

peroxide concentration was increased from 0 to 15%

in the presence of 5% hydrochloric acid. The results

are plotted in Figure 2(a). It can be seen that the

percentage recovery of palladium steadily increased

with H2O2 concentration up to 5%, reaching a maximum

palladium recovery of ~85%. For H2O2 concentrations

above 5%, there was no further increase in palladium

recovery. In the second case, HCl concentration was

increased from 0 to 20% in the presence of 5% H2O2.

The results are shown in Figure 2(b). The percentage

recovery of palladium gradually increased with

increasing HCl concentration, reaching a maximum

of 99% recovery at 10% HCl. Thus a mixture of 10%

HCl and 5% H2O2 was concluded to be effective for

extracting palladium from activated carbon-PTFE

organic matrix. Similar results have been reported for

spent Pd/Al2O3 catalyst by Barakat et al. (20).

3.2 Effects of Temperature and TimeThe effects of leaching time and reaction temperature

on palladium recovery were studied over the

temperature range 30ºC to 100ºC with leaching

times of 1 h, 2 h or 3 h. Spent catalyst was treated

with an acid/peroxide mixture having HCl and H2O2

concentrations of 10% and 5%, respectively. As seen

in Figure 3, the percentage recovery of palladium

increased with reaction temperature for each of

the treatment time periods. The treatment time was

seen to signifi cantly affect the maximum percentage

recovery of palladium, and a treatment time of

1 h was not suffi cient to extract the highest levels of

palladium. The results were closer for the treatment

times of 2 h and 3 h. The maximum palladium

recovery of >98% was obtained after treatment with

an acid/peroxide mixture of 10% of HCl and 5% of

H2O2 at 90ºC for 3 h.

3.3 Effect of Reducing AgentSodium borohydride was used as the reducing agent

to precipitate metallic palladium from the stock

solution after fi ltration. The precipitation of palladium

via reduction proceeds according to the following

reactions:

0 5 10 15 20H2O2 or HCl concentration, %

Reco

very

of

Pd, %

100

80

60

40

20

0

(b)

(a)

Fig. 2. The effects of: (a) H2O2 concentration (in the presence of 5% HCl); and (b) HCl concentration (in the presence of 5% H2O2) when reacted at 90ºC for 3 h

0 20 40 60 80 100Temperature, ºC

Reco

very

of

Pd, %

100

80

60

40

20

0

3 h 2 h 1 h

Fig. 3. The effects of leaching time and temperature in the presence of 10% HCl and 5% H2O2



NaBH4 + 2H2O NaBO2 + 8H+ + 8e – (ii)

4H2PdCl4 + 8e – 4Pd0 + 8H+ + 16Cl– (iii)

The overall reaction is:

NaBH4 + 2H2O + 4H2PdCl4 NaBO2 + 4Pd0

+ 16HCl (iv)

In the absence of any reducible species in the

solution, sodium borohydride decomposes into

sodium metaborate and hydrogen gas according to

Reaction (v):

NaBH4 + 2H2O NaBO2 + 4H2 (v)

It is apparent from Equations (ii) and (iii) that

stoichiometrically four moles of palladium chloride

would be reduced to metallic form per one mole of

sodium borohydride.

To optimise the precipitation conditions, different

concentrations of alkaline sodium borohydride

solution and different process temperatures

were applied for a fi xed duration of 20 minutes.

Figure 4 shows the change in percentage recovery

of palladium versus the concentration of NaBH4 at

different reduction temperatures. It can be seen that

the percentage recovery of palladium increased both

with temperature, as also verifi ed by Barakat et al.

(20), and with sodium borohydride concentration.

The percentage recovery increased steadily with

temperature, while the effect of NaBH4 concentration

disappeared above 7% for the reduction temperature

of 90°C. 100% palladium recovery was accomplished

with a NaBH4 concentration and a reduction

temperature of 7% and 100ºC, respectively.

3.4 UV ResultsBecause of ligand-to-metal charge transfer, the

transition of PdCl42– to H2PdCl4 exhibits two absorption

bands at 209 nm and 237 nm, as reported by Yang et al.

(27). These two strong UV absorption bands can be

used to measure the reduction of H2PdCl4 to metallic

palladium. To monitor the reduction upon treatment

with different concentrations of NaBH4 at 100ºC, UV-vis

spectra of treated solutions were taken. Leached and

alkaline sodium borohydride solutions were used in

equimolar proportions. Figure 5 shows the results. It

can be seen that the two absorption bands at 209 nm

and 237 nm decreased with increasing concentrations

of NaBH4. When the concentration of NaBH4

reached 10%, these absorption bands disappeared.

This indicates that the H2PdCl4 precursor has been

completely reduced to metallic palladium.

3.5 XRD and SEM ResultsTo prove the completeness of palladium recovery

from the spent activated carbon-supported palladium

catalyst, XRD measurements were taken on the solid

residue before and after leaching (Figures 6(a)

0 2 4 6 8 10Concentration of NaBH4, %

Reco

very

of

Pd, %

100

80

60

40

20

0

40ºC 60ºC 80ºC 90ºC

Fig. 4. The effect of addition of sodium borohydride in 5% NaOH to the palladium solution

200 250 300 350 400, nm

Abs

orpt

ion

2.0

1.5

1.0

0.5

0

(b)

(a)

(c)

(d)

Fig. 5. UV-VIS spectra of the palladium solution after adding the reducing reagent with different percentages of NaBH4 in the fi rst step of chemical reduction: (a) 0%; (b) 2%; (c) 7%; (d) 10%



and 6(b)). The XRD pattern of the fi nal reduced

palladium sample is also shown (Figure 6(c)). In

the spectra of the spent catalyst before leaching, the

sharp and narrow peaks at 2 = 40.1º and 46.6º were

attributed to the presence of crystalline palladium

in the form of large crystals, in line with fi ndings

reported by A. Drelinkiewicz et al. (28) and J. Y. Ying

et al. (29). These crystalline palladium peaks were

clearly separated from the relatively broad ‘halo’

centred shoulder of activated carbon at around 2

= 26º (Figure 6(a)). After the leaching process, the

characterisation peaks of Pd at 2 = 40.1º and 46.6º

were not detected indicating the completeness of the

leaching process (Figure 6(b)). Upon reduction of

the H2PdCl4 precursor to metallic Pd by NaBH4, the

solid reside exhibited only the peaks at 40º and 47º

(Figure 6(c)) indicating complete reduction. The

unstrained Pd phases should exhibit an XRD pattern

according to the powder diffraction fi les (PDF)

database as follows: Pd(1 1 1) (39.8º), Pd(2 0 0) (46.3º)

and Pd(3 1 1) (81.6º) (30). This confi rms the crystal

structure of bulk palladium. The peak at 81.6º is not

shown as the XRD scans were performed at ambient

temperature with a 2 range between 10º and 60º.

Scanning electron micrographs for the samples

before and after leaching are shown in Figures 7(a) and 7(b), respectively. The morphology of the

spent catalyst samples before and after leaching

was compared, confi rming the presence of small

discrete particulates before the leaching, as seen in

Figure 7(a). These micrometre scale zero-valent Pd

metal particles disappeared after the leaching process

as shown in Figure 7(b). Along with the results

obtained by XRD, this confi rms that 100% recovery

of palladium from the spent Pd/AC catalyst was

successfully achieved.

Figure 7(c) shows the SEM image of metallic

palladium after recovery. The morphology of the

submicron crystallites can be clearly seen. The

presence of very tiny particles in the range 250 nm to

550 nm was also verifi ed by Zetasizer measurements.

The recovered palladium is therefore demonstrated

to be suitable for preparing fresh nanostructured

activated carbon-supported catalyst.

10 20 30 40 50 602

Coun

ts p

er s

econ

d

2000

1000

2000

1000

2000

1000

0

(b)

(a)

(c)

Fig. 6. XRD pattern of Pd/AC spent catalyst: (a) before leaching; (b) after leaching; and (c) the recovered palladium powder



4. ConclusionsA process for the recovery of palladium from spent

activated carbon-supported palladium catalysts was

described. Palladium was extracted from the matrix

of the spent catalyst with an acid mixture of dilute

hydrochloric acid and hydrogen peroxide. Palladium

was precipitated from the leached solution by NaBH4.

For leaching, a mixture of 10% HCl and 5% H2O2

was seen to be suffi ciently effective to extract all

palladium from the activated carbon-PTFE organic

matrix. The maximum palladium recovery was

obtained after treatment at 90ºC for 3 h. Complete

precipitation of palladium was accomplished using

a NaBH4 concentration of 7% and a reduction

temperature of 100ºC.

Characterisation by UV-vis, XRD and SEM was used

to prove the effectiveness of the developed process.

It was shown by these studies that all palladium was

recovered from the spent catalyst. The XRD study

verifi ed the metallic form of recovered palladium.

The reduction of H2PdCl4 to metallic palladium

was monitored by UV-vis, showing that the optimum

concentration of NaBH4 in alkaline solution was 10%

to completely reduce the H2PdCl4 precursor. The

production of metallic nanoparticles by treatment

with sodium borohydride was verifi ed by SEM

imaging and Zetasizer measurements. The metallic

palladium recovered using the method described

here is believed to have the required specifi cation

to manufacture fresh activated carbon-supported

palladium catalysts.

AcknowledgementI greatly acknowledge The Turkish Scientifi c and

Technological Council (TÜBITAK) for supporting the

study. The author thanks technical support provided

by Osman Kurulu, senior technician.

References

1 D. H. France, Int. J. Hydrogen Energy, 1980, 5, (4), 369

2 M. G. Jones, T. G. Nevell, R. J. Ewen and C. L. Honeybourne, Appl. Catal., 1991, 70, (1), 277

3 J. G. Firth, ‘Measurement of Flammable Gases and Vapours’, in “Detection and Measurement of Hazardous Gases”, eds. C. F. Cullis and J. G. Firth, Heinemann Educational Books, London, UK, 1981, p. 29

4 J. G. Firth, A. Jones and T. A. Jones, Ann. Occup. Hyg., 1972, 15, (2–4), 321

5 M. G. Jones and T. G. Nevell, Sens. Actuators, 1989, 16, (3), 215

6 J. Butler, “Platinum 2012 Interim Review”, Johnson Matthey Plc, Royston, UK, 2012

7 J. P. Rosso, Chem. Eng. Prog., 1992, 88, (12), 66

8 J. A. Lassner, L. B. Lasher, R. L. Koppel and J. N. Hamilton, Chem. Eng. Prog., 1994, 90, (8), 95

1 m

1m

Pd

(a)

1m

10 m

(b)

1 m

(c) Fig. 7. SEM results of Pd/AC spent catalyst: (a) before leaching; (b) after leaching; and (c) the recovered palladium powder



9 P. Grumett, Platinum Metals Rev., 2003, 47, (4), 163

10 J. E. Hoffmann, JOM, 1988, 40, (6), 40

11 R. Lait and D. R. Lloyd-Owen, Laporte Chemicals Ltd, ‘Recovery of Palladium from Catalysts’, British Patent 922,021; 1963

12 R. V. Jasra, P. K. Ghosh, H. C. Bajaj and A. B. Boricha, ‘Process for Recovery of Palladium from Spent Catalyst’, US Appl. 2004/0,241,066

13 J.-M. Lalancette, Nichromet Extraction Inc, ‘Method for the Recovery of Base and Precious Metals by Extractive Chloridation’, World Appl. 2002/053,788

14 X. Xie, X. Meng and K. N. Han, Miner. Metall. Process., 1996, 13, (3), 119

15 C. D. McDoulett Jr. and G. W. Reschke, North American Palladium Ltd, ‘Metal Leaching and Recovery Process’, European Appl. 0,637,635; 1995

16 V. V. Patrushev, Hydrometallurgy, 1998, 50, (1), 89

17 H. Suehide and S. Tatsuya, Kawasaki Kasei Chemicals Ltd, ‘Method for Separating, Enriching and Recovering Palladium’, World Appl. 2002/061,156

18 A. Troupis, A. Hiskia and E. Papaconstantinou, Appl. Catal. B: Environ., 2004, 52, (1), 41

19 P. Yong, N. A. Rowson, J. P. G. Farr, I. R. Harris and L. E. Macaskie, Biotechnol. Bioeng., 2002, 80, (4), 369

20 M. A. Barakat, M. H. H. Mahmoud and Y. S. Mahrous, Appl. Catal. A: Gen., 2006, 301, (2), 182

21 B. Zhou, R. Balee and R. Groenendaal, Nanotechnol. Law Bus., 2005, 2, (3), 222

22 A. Uhl, A. Völpel and B. W. Sigusch, J. Dentistry, 2006, 34, (4), 298

23 The PGM Database: http://www.pgmdatabase.com/ (Accessed on 21st August 2013)

24 J. W. Geus and J. C. van Giezen, Catal. Today, 1999, 47, (1–4), 169

25 H. Kuwagaki, T. Meguro, J. Tatami, K. Komeya and K. Tamura, J. Mater. Sci., 2003, 38, (15), 3279

26 A. Sarioglan, Ö. Can Korkmaz, A. Kaytaz, E. Akar and F. Akgün, Int. J. Hydrogen Energy, 2010, 35, (21), 11855

27 J. Yang, C. Tian, L. Wang and H. Fu, J. Mater. Chem., 2011, 21, (10), 3384

28 A. Drelinkiewicz, M. Hasik and M. Kloc, Catal. Lett., 2000, 64, (1), 41

29 J. Y. Ying and N. Erathidiyil, Agency for Science, Technology and Research, Singapore, ‘Palladium Catalysts’, US Appl. 2010/0,113,832

30 T. Arunagiri, T. D. Golden and O. Chyan, Mater. Chem. Phys., 2005, 92, (1), 152

The AuthorŞerife Sarıoğlan is a Chief Senior Researcher at TÜBİTAK Marmara Research Center Chemistry Institute, Turkey. She completed her PhD in Polymer Chemistry at Istanbul Technical University, Turkey. Prior to taking part in industrial projects on recycling of oxidation catalysts and their preparation for end-use, she was primarily involved in inorganic after-treatment and shaping of minerals. Her research interests include heterogeneous catalysis for the petrochemical industry and various niche applications.



“Catalysts for Alcohol-Fuelled Direct Oxidation Fuel Cells”Edited by Zhen-Xing Liang (South China University of Technology, Guangzhou, China) and Tim S. Zhao (The Hong Kong University of Science and Technology, Hong Kong), RSC Energy and Environment Series, No. 6, The Royal Society of Chemistry, Cambridge, UK, 2012, 264 pages, ISBN: 978-1-84973-405-9, £153.99, US$246.00


Reviewed by Alex Martinez Bonastre

Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, UK


“Catalysts for Alcohol-Fuelled Direct Oxidation Fuel

Cells” is aimed at a general audience with an interest

in low power fuel cells, as well as experts in the area.

The book is edited by Zhen-Xing Liang, Lecturer at

the South China University of Technology, and Tim

S. Zhao, Professor of Mechanical Engineering at the

Hong Kong University of Science and Technology

(HKUST) and director of the HKUST Energy Institute.

The book contains seven chapters in 264 pages and

reviews the catalysis of alcohol electrooxidation

in low-temperature fuel cells. The reader will fi nd

a general overview of the catalysis involved in the

oxidation of alcohols such as methanol and ethanol.

More unusually the oxidation of ethylene glycol and

glycerol are also described in detail. Although the

title for this book is specifi c to alcohol fuel cells it

also contains individual chapters describing the

oxidation of other fuels of interest such as formic acid,

borohydride and sugars. The book concludes with a

chapter on the challenges that alcohol fuel cells need

to overcome.

Role of the Platinum Group Metals Many of the book’s chapters are easy to read even for

people with little experience in the area. Chapter 1,

‘Electrocatalysis of Alcohol Oxidation Reactions at

Platinum Group Metals’, by Claude Lamy (University

of Montpellier, France) and Christophe Coutanceau

(Université de Poitiers, France), starts with a good if

simplistic overview about what constitutes fuel cell

effi ciency. This is an important subject and the authors’

general description can easily be followed by students

in chemistry or related subjects. The authors highlight

that the theoretical effi ciencies for methanol/air

and ethanol/air fuel cells are actually higher than

hydrogen/oxygen fuel cells. This is a great foundation

for the book because it really justifi es the need for

research in this area. The chapter continues with a

very simplistic description of the methods used for



the synthesis and characterisation of fuel cell catalysts,

from well-known chemical and electrochemical

approaches to more exotic methods such as plasma-

enhanced techniques. The content fl ows in a logical

order with this introduction followed by dedicated

sections describing in detail the oxidation of different

fuels. The oxidation of methanol or ethanol is

described in acidic environments, mainly for the well-

known platinum-based binary catalysts PtM/C (M =

ruthenium or tin), at different atomic ratios.

The authors describe the differences in reactivity

when using different atomic ratios such as Pt0.5Ru0.5,

Pt0.8Ru0.2, Pt3Sn and Pt9Sn. These binaries are known

to be active because of the effi cient removal of

adsorbed carbon monoxide (via the bifunctional

mechanism), a common intermediate in the oxidation

of primary alcohols. In contrast, the oxidation of

ethylene glycol and glycerol is described mainly in

alkaline media with the authors focusing on the use

of carbon supported platinum, platinum-palladium

and platinum-palladium-bismuth for the oxidation

of ethylene glycol and platinum, palladium and gold

catalysts and their binaries and ternaries such as

PtPd, PtBi, PdBi and PtPdBi for the oxidation of glycerol.

The chapter offers a good introduction, although it

lacks references to the use of commercial catalysts for

methanol oxidation (1, 2).

Catalyst Preparation Chapter 2, ‘Nanoalloy Electrocatalysts for Alcohol

Oxidation Reactions’, by Jun Yin (Cornell University,

New York, USA) et al. describes the use of PtAu

catalysts for alcohol oxidation. The synthesis of PtAu

catalysts is a very interesting topic with challenging

nanoscale catalyst preparation. Nanoscale gold has

been shown to produce surface oxygenated species

such as gold(III) oxide, adsorbed gold hydroxide or

gold(III) hydroxide which are highly active for the

M1M2

Precursors

Capping agent

Reduction or decomposition

Wet chemical synthesis

Assembly on support

Thermal treatment

Supported catalyst

AssemblyActivation

(a)

(b)

30 nm

(c)

30 nm

M1mM2100–m

+

Fig. 1. (a) A general scheme showing the molecularly engineered synthesis of bimetallic nanoparticles capped with a monolayer shell of oleic acid/oleylamine and the preparation of bimetallic nanoparticles supported on carbon powders or carbon nanotubes by assembly and activation. Transmission electron microscopy images showing: (b) Au22Pt78 nanoparticles supported on carbon black; and (c) Au nanoparticles supported on carbon nanotubes (Reproduced by permission of The Royal Society of Chemistry)



removal of adsorbed CO, especially in alkaline media.

Traditional methods for PtAu catalyst preparation are

mentioned such as co-precipitation, impregnation

with subsequent reduction, and calcination. More

interestingly, the synthesis of Au and PtAu supported

nanoparticles via the molecular encapsulation

synthesis is described (Figure 1). This approach

involves three steps: (a) chemical synthesis of metal

nanocrystal cores with molecular encapsulation;

(b) assembly of the encapsulated nanoparticles

on support materials; and (c) thermal treatment

of the supported nanoparticles. A brief mention of

core–shell type PtAu nanoparticles is also included

although no characterisation data is shown. PtAu

nanoparticles with different atomic compositions are

presented for the oxidation of methanol in alkaline

and acidic media. An iron(II,III) oxide Fe3O4@Au@Pt

ternary is presented as a more active catalyst than Pt

in acidic media. The chapter fi nishes with a section

dedicated to the characterisation of PtAu particles and

includes experimental data from different techniques

such as X-ray diffraction (XRD), Fourier transform

infrared (FTIR) spectroscopy and X-ray photoelectron

spectroscopy (XPS) which adds detailed information

to help understand the catalysis.

Quantum Mechanical ModellingChapter 3, ‘Theoretical Studies of Formic Acid

Oxidation’, by Wang Gao and Timo Jacob (Universität

Ulm, Germany), is the only chapter dedicated to

the use of quantum mechanical modelling for the

understanding of chemical reactions at the molecular

level. Although formic acid is not an alcohol, it is of

interest in terms of fuel cell effi ciency for low power

electronics. The authors cover the oxidation of formic

acid in ultra-high vacuum conditions and also with

increasing water coverage. Importantly, they pay

attention to the effect of the electrochemical potential

on the formic acid dehydrogenation and include a

detailed discussion of the adsorbed products that

are formed. A detailed and informative discussion of

the different reaction pathways, direct and indirect, is

presented. Readers with some experience in the fi eld

will fi nd the content extremely interesting. It is slightly

disappointing that the editors did not include more

content towards the use of theoretical modelling for

the oxidation of alcohols.

Catalysis by GoldChapter 4, ‘Gold Leaf Based Electrocatalysts’, by

Rongyue Wang and Yi Ding (Shandong University,

China) is dedicated to the use of nanoporous gold leaf

(NPG-leaf) as an alternative catalyst for the oxidation

of formic acid and alcohols in alkaline media. The

chapter describes the formation of NPG by chemical

dissolution also known as dealloying. This is a well-

known process and has been applied for many years

in the manufacturing of high surface area catalysts.

The authors present as an example the formation of

NPG from a gold-silver alloy. Selective dissolution of Ag

leads to the formation of a porous structure (Figure 2)

(3). The authors describe the excellent research done

by John Newman (University of California, Berkeley,

USA) et al. (4) and Jonah Erlebacher (Johns Hopkins

University, USA) et al. (5) and the reader is advised

to follow up these references for further, detailed

information. Overall NPG-Pt catalysts give very low

benefi t compared to Pt/C.

In fact, the area of dealloying is currently an on-

going research topic aimed at the design of highly

active catalysts for the oxygen reduction reaction in

H2/O2 fuel cells. Experts in the area such as Professor

Doctor Peter Strasser, now at Technische Universität

Berlin, Germany, have documented very interesting

results with the study of dealloyed particles and their

use as catalysts for the oxygen reduction reaction

(6, 7). However, the use of dealloyed catalysts has not

been well documented for alcohol oxidation.

(a)

120 nm

(b)

500 nm

Fig. 2. Scanning electron microscopy images of a nanoporous gold leaf (Reproduced by permission of The Royal Society of Chemistry and (3))



Alkali Metal BorohydridesChapter 5, ‘Nanocatalysts for Direct Borohydride

Oxidation in Alkaline Media’ by Christophe

Coutanceau et al. considers the use of alkali metal

borohydrides as fuels. Sodium borohydride is

preferred because it offers a compromise between

specifi c energy density and relative abundance. The

authors clearly explain the anodic and cathodic

reactions that occur in a direct borohydride fuel

cell (DBFC) and the theoretical effi ciency of a

system capable of achieving the 8 electron reaction.

Due to the alkaline environment used the catalysts

considered are the usual binaries and ternaries,

such as PdAu, PdNi and PdPtBi. The authors

describe a very interesting study of the kinetics

of the electrode reaction but most importantly

they present a discussion of what makes a catalyst

selective towards complete oxidation and also to

the inhibition of hydrogen oxidation. The use of

Pt0.9Bi0.1/C is presented as the most selective catalyst

that leads to the 8e-- pathway without signifi cant

hydrogen evolution. Although this anode catalyst led

to lower performance compared to Pt/C, in terms of

current density, it is of interest for a DBFC because

of increased fuel effi ciency, a prime parameter for

the use of the fuel. It is important to highlight that a

system with high cell effi ciency is more attractive for

many practical applications than a system with low

effi ciency and high current density. The authors have

written a very interesting chapter and this reader

gained useful knowledge about the technology.

The Use of EnzymesChapter 6, ‘Bioelectrocatalysis in Direct Alcohol Fuel

Cells’, by Holly Reeve and Kylie Vincent (University

of Oxford, UK), is dedicated to the use of enzymes

for the oxidation of sugars such as fructose, lactose

and glucose. The use of sugars for fuel cells is a

very interesting area for research since it is based

on the generation of electricity by the oxidation of

natural products. Actually, the full oxidation of a

primary alcohol to carbon dioxide is also possible

when using a chain of enzymes via a sequence of

chemical reactions. This is a key characteristic that

differentiates enzymes from metal nanoparticles.

For instance, there are very few metal catalysts

capable of achieving the full oxidation of dilute

ethanol to CO2 without the formation of incomplete

products such as acetaldehyde and acetic acid

(8). The authors give a fair and realistic view of

the practical problems of enzymes as catalysts

due to their relatively large size, which leads to

low volumetric density and their limited stability

when varying conditions such as pH, temperature,

pressure and solvent type. The authors highlight

that biofuel cells could have their main application

as bioimplantable fuel cells for pacemakers and for

the purifi cation of waste water. Although research

in this area is in its infancy, the authors give an

excellent overview of the use of biofuel cells and the

reader with an interest in biocatalysis will fi nd this

chapter extremely interesting.

Problems in Alcohol OxidationThe book closes with Chapter 7, ‘Challenges and

Perspectives of Nanocatalysts in Alcohol-Fuelled

Direct Oxidation Fuel Cells’, by Eileen Hao Yu

(Newcastle University, UK) et al. This chapter covers

some of the main problems in alcohol oxidation

focusing on the factors affecting activity and stability,

including the need for more active catalysts capable of

oxidising adsorbed CO. The authors report on the use

of binary and ternary catalysts in alkaline and acid

media, such as PtRu, PtSn and PtRuM (M = tungsten,

molybdenum, nickel) and PtSnM (M = Ni or Ru), PtAu,

PdNi and PdIrNi. The use of metal oxides such as

cerium(IV) oxide, nickel(II) oxide, cobalt(II,III) oxide

and manganese(II,III) oxide as promoters capable of

introducing oxygenated species to remove adsorbed

CO is also described. A brief mention of the benefi ts

and disadvantages of the use of core–shell catalysts

is presented with a special emphasis on PtAu core–

shell catalysts. In terms of stability, some interesting

approaches are mentioned such as the use of

alternative carbon supports (graphene and N-doped

carbon nanotubes) and supports such as titanium

dioxide and tungsten carbide. The authors, however, do

not mention the main problems of anode stability, such

as base metal dissolution, membrane contamination

and the impact on cathode performance or relate

these issues to real fuel cell data.

ConclusionThe authors describe in a detailed manner the

electrocatalytic oxidation of primary alcohols and

other relevant fuels of interest for low power fuel

cells in both acid and alkaline media. The reader

gains a useful introduction to the catalysis involved

in the oxidation of different fuels, such as methanol,

ethanol, ethylene glycol, glycerol, borohydride and

sugars. While enzymes and gold catalysts have been

introduced, platinum group metal catalysts, especially



those based on Pt and Pd, are the state of the art for

these technologies. The book only disappoints in

some areas such as the lack of real fuel cell data and,

for this reviewer’s taste, an overemphasis on alcohol

oxidation in alkaline media. Overall, this book can

be a good starting point for students and researchers

with an interest in low power fuel cells.

References

1 N. Cabello-Moreno, E. Crabb, J. Fisher, A. E. Russell and D. Thompsett, ECS Trans., 2008, 16, (2), 483

2 J. M. Fisher, N. Cabello-Moreno, E. Christian and D. Thompsett, Electrochem. Solid-State Lett., 2009, 12, (5), B77

3 J. Erlebacher, M. J. Aziz, A. Karma, N. Dimitrov and K. Sieradzki, Nature, 2001, 410, (6827), 450

4 R. C. Newman and K. Sieradzki, Science, 1994, 263, (5 154), 1708

5 R. Zeis, A. Mathur, G. Fritz, J. Lee and J. Erlebacher, J. Power Sources, 2007, 165, (1), 65

6 P. Mani, R. Srivastava and P. Strasser, J. Phys. Chem. C, 2008, 112, (7), 2770

7 L. Gan, M. Heggen, R. O’Malley, B. Theobald and P. Strasser, Nano Lett., 2013, 13, (3), 1131

8 A. Kowal, M. Li, M. Shao, K. Sasaki, M. B. Vukmirovic, J. Zhang, N. S. Marinkovic, P. Lui, A. I. Frenkel and R. R. Adzic, Nature Mater., 2009, 8, (4), 325

The ReviewerAlex Martinez Bonastre received his PhD from Southampton University, UK, in 2007 and joined the Fuel Cells Research Group at Johnson Matthey Technology Centre, Sonning Common, UK, in 2006, where he is a Senior Scientist. His work centres on the electrochemical characterisation of catalysts and fuel cell components and he is a technical leader in the areas of alcohol and hydrogen fuel cells, working mostly with pgm catalysts.

“Catalysts for Alcohol-Fuelled Direct Oxidation Fuel Cells”



Investigations into the Recovery of Platinum Group Minerals from the Platreef Ore of the Bushveld Complex of South AfricaCopper sulfate addition shown to be of limited value for treatement of Platreef ore


By Cyril T. O’Connor*

Centre for Minerals Research, Department of Chemical Engineering, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa


Natalie J. Shackleton

Anglo American Technical Solutions Research, PO Box 106, Crown Mines 2025, South Africa

In the fl otation of platinum group minerals (PGMs)

it has generally been assumed that they will behave

similarly to base metal sulfi des and thus sulfi de reagent

regimes are generally used in such fl otation plants.

However the tellurides and arsenides of platinum and

palladium contribute about 50% of the PGMs present

in the Platreef ore, located in the northern limb of the

Bushveld Complex of South Africa, and there is evidence

of these minerals reporting to the fl otation tailings.

The present investigation was aimed at studying the

fl otation behaviour of tellurides, arsenides and sulfi des

of Pt and Pd and relating these observations to their

surface characteristics. Microfl otation, zeta potential

determinations, time-of-fl ight secondary ion mass

spectrometry (ToF-SIMS) and X-ray photoelectron

spectroscopy (XPS) analyses were used to study the

synthesised samples after various treatments. It was

shown that in almost all cases the addition of a typical

sulfi de collector, sodium isobutyl xanthate (SIBX),

increased the recovery of all the Pt and Pd minerals

investigated but that the presence of copper sulfate

widely used to activate sulfi de minerals caused the

recoveries to decrease. These results may question

the value of adding copper sulfate in the treatment of

Platreef PGM-bearing ore.

IntroductionMost of the world’s supply of Pt and Pd and associated

elements comes from mines within four major

layered igneous intrusions: the Bushveld Complex in

South Africa, the Stillwater Complex in the USA, the

Great Dyke in Zimbabwe and the Noril’sk-Talnakh

Complexes in Russia (1).

The Bushveld Complex in South Africa is a vast

repository of value minerals which spreads over

an area of 65,000 km2 and has a thickness of 7 km

to 9 km (2). It is a layered intrusion of variable



mineralisation of mafi c to ultramafi c rocks associated

with two felsic intrusive suites. The Bushveld Complex

consists of fi ve main limbs, known as the Far Western,

Western, Northern, Eastern and Southeastern Limbs

respectively (Figure 1). The Bushveld Complex’s

upper zone has the largest concentration of platinum

group elements (PGEs): platinum, palladium, rhodium,

iridium, osmium and ruthenium. These are contained

in the Upper Group Chromitite No. 2 (UG2), the

Merensky Reef and the Platreef. The mineral ores from

these reefs differ according to grain size, association

and concentration of the PGEs.

The Merensky Reef contains base metal sulfi de

grains and associated PGMs. The rock-forming

silicate minerals of the Merensky Reef consist of

orthopyroxene (~60%), plagioglase feldspar (~20%),

pyroxene (~15%), phlogopite (~5%) and occasional

olivine. Interspersed in the mineral rock are secondary

minerals of talc, serpentine, chlorite and magnetite. The

base metal sulfi des are pyrrhotite (~40%), pentlandite

(~30%), chalcopyrite (~15%) and trace amounts of

millerite, troilite, pyrite and cubanite (1, 4).

The UG2 reef consists of chromitite layers in the

Bushveld Complex which are localised in the Critical

Zone. They are further subdivided, according to their

height in the Critical Zone, into three groups: Lower

Group (LG), Middle Group (MG) and Upper Group

(UG). The UG2 chromitite layer presents the second

layer of the Upper Group and lies between 20 m to 400 m

below the Merensky Reef (1). UG2 is a platiniferous

chromitite layer whose mineralogy varies depending

on the geographic location within the complex. UG2

contains chromite (60% to 90%) with interstitial

orthopyrexene (5% to 25%). Minor amounts, less than

5%, of subordinate minerals such as clinopyroxene,

biotite, phlogopite, talc, chlorite, quartz and serpentine

are also present. Chalcopyrite, pyrrhotite, pyrite and

pentlandite are the major base metal sulfi de minerals,

usually present in trace amounts (<0.1%) (1, 4).

The Platreef is located in the Northern Limb

of the Bushveld Complex. This reef consists of a

complex assemblage of rock types, with pyroxenites,

serpentinites and calc-silicates being the most

abundant. The predominant PGMs in the mined

area of the Platreef are the PGE tellurides, arsenides,

sulfi des and alloys. The Pt and Pd tellurides, being the

most important, may contribute between 20% and 45%

of the PGMs present in the Platreef ore, followed by

the alloys (26%), arsenides (21%) and sulfi des (19%).

Their abundances vary from north to south and from

section to section. The major sulfi de minerals are

pyrrhotite, pentlandite and chalcopyrite (5). Non-

sulfi de gangue minerals consist mainly of pyroxene

and feldspar along with quantities of chlorite, tremolite,

Far Western Limb

Villa Nora

Thabazimbi

Younger sedimentary cover and intrusionsFelsic BushveldMafi c ComplexTransvaal supergroupArchaean basement and pre-Transvaal formationsFaults

}

Western Limb

Southeastern/Bethal Limb( )

Bethal

Johannesburg

PretoriaBritsRustenburg

Stoffberg

Burgersfort

Potgietersrus

Northern/Potgietersrus

Limb

Eastern Limb

Nietverdiend

Rhenoster-hoekspruit

Moloto

BelfastUitkomst

Roossenekal

0 25 50 75 100km

24º

26ºS

26º 28º 30º

f

f

ff

f f

ff

f

N

f

Fig. 1. Geological map of the Bushveld Complex, South Africa (3)



talc and mica. Table I summarises the approximate

occurrences of the major PGMs in the various reefs.

The telluride minerals present in the Platreef

ore are moncheite ((Pt,Pd)(Bi,Te)2 and PtTe2)

and merenskyite ((Pd,Pt)(Bi,Te)2 and PdTe2) and

the arsenides are mainly sperrylite (PtAs2) and

palladoarsenide (Pd2As). The high concentrations

of these minerals make it necessary to explore

opportunities to maximise the recovery of these

minerals by fl otation. Presently the current fl otation

practice is to treat these minerals using reagent suites

typical of sulfi de fl otation but this may not be the

optimal approach.

The present paper describes recent investigations

into the fl otation behaviour of tellurides, arsenides and

sulfi des. Given the fact that it is inordinately diffi cult

to obtain natural samples of these minerals the study

required the synthesis of the relevant minerals. The

prepared samples were then investigated in terms of

their surface charges using measurements of their zeta

potential and of their hydrophobicity when exposed

to different reagent suites in a microfl otation cell.

Experimental ProceduresThe specifi c Pt minerals synthesised for the purposes

of the present investigation were sperrylite (PtAs2),

moncheite (PtTe2) and cooperite (PtS), and the Pd

minerals were merenskyite (PdTe2), palladoarsenide

(Pd2As) and vysotskite (PdS). The synthesis of the

samples has been described elsewhere (6, 7). Table II summarises the results of the synthesis procedure used

for the various minerals.

The minerals were subsequently characterised

using X-ray diffraction (XRD) with Rietveld refi nement.

Back scattered electron (BSE) micrographs of all

samples were obtained. Microfl otation, zeta potential

determinations and ToF-SIMS and XPS analyses were

used to characterise the surface of the minerals

and their fl otation behaviour. These techniques

and experimental methods have been described

elsewhere (6, 7). The compositions of all samples were

obtained using energy dispersive spectroscopy (EDS)

obtained from the scanning electron microscope

investigation. BET surface areas were also determined.

In the microfl otation tests, purifi ed SIBX was used

as a collector and sodium carbonate (0.1 M) or

hydrochloric acid (0.1 M) were used for pH adjustment.

Copper sulfate was used as an activator on the basis

of the assumption that the tellurides and arsenides

would behave like sulfi des which are activated by

using this reagent. For these tests synthetic plant water

was used (ionic strength = 3.5 E–02) and the particles

were in the 38 μm to 106 μm range.

Results and DiscussionThe main question being addressed in this investigation

was the fl oatability of the different minerals and to

what extent they respond to the reagents currently in

use on the fl otation plants in the various concentrators.

Given the very small amounts of mineral available

it was necessary to use microfl otation tests to carry

out this investigation. Since microfl otation does not

incorporate any froth phase it is really a measure of

the mineral’s hydrophobicity after treatment with the

collector molecules. In other words, it merely gives an

indication, important as that is, of the extent to which

a mineral exposed to different chemical environments

will adhere effectively to a bubble and report to the

launder at the top of the cell.

The cell used in this study has been described

elsewhere (8). The results of the microfl otation

studies are summarised in Table III. The results with

no reagent refl ect the natural hydrophobicity of the

mineral. It can be seen that sulfi des and tellurides

were both reasonably fl oatable in the absence of

any collector whereas the arsenides were hardly

Table I

Platinum Bearing Minerals in the Different Reefs of the Bushveld Complex

Reef Mineral composition, %

Sulfi des Tellurides Arsenides Alloys Others

Merensky 36 30 7 7 20

UG2 70 <5 <5 20 <5

Platreef 3 30 21 26 20



Tab

le II

Syn

thes

is P

roce

du

res

for

the

Plat

inu

m M

iner

als

Use

d in

th

is S

tud

y

Min

eral

Sto

ich

iom

etri

c

com

po

siti

on

Ther

mal

tre

atm

ent

Yiel

d a

nd

ph

ase

pu

rity

by

XR

D

Coop

erite

PtS

Pt2.

00S 2

.00

(34.

35 g

Pt,

5.6

5 g

S)

Am

poul

e he

ated

to

1000

ºC a

t a

rate

of

20ºC

min

–1, h

eld

for

96 h

ours

, the

n al

low

ed t

o co

ol a

t a

rate

of

10ºC

min

–1. B

reak

tub

e, r

egrin

d, r

esea

l and

reh

eat

to 1

000º

C at

a r

ate

of 2

0ºC

min

–1, h

eld

for

96 h

ours

, the

n al

low

ed t

o co

ol a

t a

rate

of

10ºC

min

–1

40 g

>99

% p

urity

Vys

otsk

ite

PdS

Pd8.

00 S

8.00

(30.

74 g

Pd,

9.2

6 g

S)

Am

poul

e he

ated

to

800º

C at

a r

ate

of 2

0ºC

min

–1, h

eld

for

30 m

inut

es,

subj

ecte

d to

con

trol

led

linea

r sl

ow c

oolin

g do

wn

to 3

50ºC

ove

r 60

hou

rs40

g

97.4

% p

urity

Sper

rylit

e

PtA

s 2 (S

ampl

e 1)

Pt4.

00A

s 8.0

0

(33.

93 g

Pt,

26.

06 g

As)

Am

poul

e he

ated

to

800º

C at

a r

ate

of 1

0ºC

min

–1, h

eld

for

6 ho

urs

then

slo

wly

co

oled

to

ambi

ent

tem

pera

ture

at

a ra

te o

f 5º

C m

in–1

60 g

90.6

% p

urity

Sper

rylit

e

PtA

s 2 (S

ampl

e 2)

Pt4.

00A

s 8.0

0

(33.

93 g

Pt,

26.

06 g

As)

Am

poul

e he

ated

to

800º

C at

a r

ate

of 1

0ºC

min

–1, h

eld

for

12 h

ours

the

n sl

owly

coo

led

to a

mbi

ent

tem

pera

ture

at

a ra

te o

f 5º

C m

in–1

60 g

93.5

% p

urity

Palla

doar

seni

de

Pd2A

s

Pd2.

65A

s

(44.

38 g

Pd,

15.

62 g

As)

Am

poul

e he

ated

to

800º

C at

a r

ate

of 1

0ºC

min

–1, h

eld

for

12 h

ours

the

n sl

owly

coo

led

to a

mbi

ent

tem

pera

ture

at

a ra

te o

f 5º

C m

in–1

60 g

>95

% p

urity

Mon

chei

te

PtTe

2

Pt1.

00Te

2.00

(20

g Pt

, 40

g Te

)

Am

poul

e he

ated

to

1150

ºC a

t a

rate

of

20ºC

min

–1, h

eld

for

30 m

inut

es,

subj

ecte

d to

con

trol

led

linea

r sl

ow c

oolin

g do

wn

to 3

50ºC

ove

r 60

hou

rs, t

hen

slow

ly c

oole

d to

am

bien

t te

mpe

ratu

re a

t a

rate

of

10ºC

min

–1

60 g

75.7

% p

urity

Mer

ensk

yite

PdTe

2

Pd1.

00Te

2.00

(20

g Pd

, 40

g Te

)

Am

poul

e he

ated

to

800º

C at

a r

ate

of 2

0ºC

min

–1, h

eld

for

30 m

inut

es,

subj

ecte

d to

con

trol

led

linea

r sl

ow c

oolin

g do

wn

to 3

50ºC

ove

r 60

hou

rs, t

hen

slow

ly c

oole

d to

am

bien

t te

mpe

ratu

re a

t a

rate

of

10ºC

min

–1

60 g

68.7

% p

urity



Table III

Recoveries of Various Platinum and Palladium Tellurides, Arsenides and Sulfi des in a Microfl otation

Cell at pH = 9 in Synthetic Plant Water

Mineral No reagenta SIBXb CuSO4 + SIBXc

PtTe2 50 99 50

PdTe2 61 99 98

PtAs2 (Sample 1) 4 72 68

PtAs2 (Sample 2) 0 2 8

PdAs2 24 95 66

PtS 94 94 89

PdS 64 95 99a Natural hydrophobicityb Sodium isobutyl xanthatec Treatment with copper sulfate before addition of SIBX

fl oatable. Addition of SIBX improved the fl oatability

of all the minerals except for the sample labelled

PtAs2 (Sample 2). Figures 2 and 3 show plots of the

recovery vs. time for the case of Pd2As and PtTe2 with

no reagent, the addition of SIBX and the addition of

SIBX after conditioning in copper sulfate. These plots

show clearly the decrease in both the recoveries and

the rates of fl otation of the mineral when copper

sulfate is present.

The microfl otation results of the Pt arsenides

are of particular interest. Empirical observations

on plants have suggested that PtAs2 (sperrylite) is

a poorly fl oatable mineral. This is shown to be the

case for Sample 2 in this study, but not signifi cantly

for Sample 1. It is clear that samples prepared using

different synthesis times have quite different fl otation

behaviour. The BSE micrographs of PtAs2 (Sample 1)

prepared using a synthesis time of 6 h (Table II) show

the presence of Pt blebs with a size range of 2 μm to 5 μm

within the sperrylite phase (Figure 4(a)). Sample 2,

which was synthesised for 12 h, showed fewer such Pt

blebs on the surface (Figure 4(b)).

The EDS results show that the Pt blebs in Sample

2 were much richer in arsenic relative to those in

Sample 1. These treatments were repeated and the

results were found to be reproducible. It appears that

the longer synthesis time resulted in a sample in which

the Pt was more homogeneously distributed and that

Reco

very

, %

100

80

60

40

20

0 5 10 15 20Time, min

no reagent SIBX CuSO4 + SIBX

Fig. 2. Palladoarsenide (Pd2As) recovery-time curves at pH 9 comparing no reagents, SIBX and CuSO4 + SIBX in synthetic water, ionic strength = 3.5 E–02

Reco

very

, %

100

80

60

40

20

0 5 10 15 20Time, min

no reagent SIBX CuSO4 + SIBX

Fig. 3. Platinum telluride (PtTe2) recovery-time curves at pH 9 comparing no reagents, SIBX and CuSO4 + SIBX in synthetic water, ionic strength = 3.5 E–02



a type of annealing process may have occurred. The

higher recoveries of Sample 1 are ascribed to the ease

of interaction of the SIBX collector molecules with the

Pt blebs. Such an interaction was much less in the case

of Sample 2.

Zeta potential measurements over the range pH 6 to

pH 10 showed that the surface charges on each sample

were very similar. ToF-SIMS on samples treated with

SIBX showed a higher degree of adsorption of xanthate

on Sample 1, which correlates with the fl otation results.

It is also possible that the high concentration of arsenic

in the Pt blebs in Sample 2 may be due to the arsenic

inhibiting, through poisoning of Pt, the conversion

of xanthate to dixanthogen which is known to be

catalysed by the surfaces of metallic sulfi des (9). It is

interesting to note that when Sample 2 was ground to

38 μm its recovery increased to 40%. This increase in

recovery may have been due to the exposure of new

free Pt blebs.

Compared to the samples of PtAs2, PdAs2 was much

more fl oatable especially when treated with SIBX. This

sample had a zeta potential value of almost 0 over

the entire pH range which in itself is a remarkable

observation. ToF-SIMS showed a high coverage of

xanthate after exposure to SIBX and this is consistent

with the high fl otation recoveries.

The sulfi des, as expected, showed high recoveries

after treatment with SIBX although the relative

differences between the natural fl oatability of PtAs2

and Pd2As are interesting. The differences, although

small, are opposite to that observed for PtTe2 and PdTe2

and so it is not possible to ascribe these differences to

the relative roles of the Pt and the Pd. Differences in

crystal structures have also been invoked to explain

such differences (10) but this is purely speculative.

It is most likely that such relatively small differences

are due to the variabilities in the product of the

synthesis process. Both the sulfi des and the tellurides

fl oated readily when treated with SIBX with recoveries

between 94% and 99%.

The role of copper sulfate is of great interest

since copper sulfate is generally used on sulfi de

concentrators given its widely known function as

an activator (11). As can be seen from Table III the

addition of copper sulfate resulted in a signifi cant

decrease in the recovery of all the Pt compounds,

especially PtTe2. PtAs2 also showed a marked decrease

in recovery. In the fl otation of PGMs it is general

practice to add copper sulfate for reasons referred to

above. However, as noted here, copper sulfate caused

a decrease in the recovery of minerals typical of PGMs

occurring in the Platreef ore.

The addition of copper sulfate to the pure mineral

during this study always resulted in an increase in

the zeta potential of the mineral. At pH>7 the species

Cu(OH)+ is dominant and the adsorption of this

species to the surface may explain this increase. At

higher pHs the dominant species becomes Cu(OH)2

and precipitates of this species may essentially mask

the surface, which may explain the more positive

zeta potential. When copper sulfate was added after

the SIBX collector the zeta potential became more

negative relative to copper sulfate alone. This may

be due to formation of Cu(OH)X. ToF-SIMS showed

that in the case of the tellurides the addition of SIBX

after treatment with CuSO4 resulted in a much lower

concentration of xanthate on the surface compared to

addition of xanthate alone.

Polished section matrix

Pt blebs

Grey phase (PtAs2)

100 m200 kV ×200

(a)Polished

section matrix

Pt blebs

Grey phase (PtAs2)

100 m200 kV ×200

(b)

Fig. 4. Back scattered electron (BSE) micrograph of PtAs2: (a) Sample 1; (b) Sample 2. (See Table II for synthesis procedures)



What is clear from the fl otation experiments is that

the presence of copper sulfate, added as an activator

for the sulfi de minerals, signifi cantly decreased the

recovery of PtTe2 and of PtAs2. This may be due to

the deposition of Cu(OH)2 colloids which could

inhibit access of xanthate ions to the surface. The

effect on PdTe2 was less signifi cant. The zeta potential

measurements do not predict the fl otation behaviour

and there were no obvious correlations observed

between the zeta potential values and the percentage

recoveries. The xanthate concentrations on the

surface in the absence or presence of copper were not

signifi cantly different and hence the mere detection

of xanthate species on the surface is not an indicator

of fl oatability. It can therefore be concluded that it is

the chemical nature of the xanthate species which is

crucial to promoting fl otation. XPS analysis on PtTe2

suggests that part of the xanthate is converted via a

redox reaction with Cu(II) to Cu(I)X which appears

not to contribute to rendering the surface hydrophobic.

It is also clear that the theories proposed for the role

of copper sulfate as an activator are not necessarily

relevant to the case of the tellurides and arsenides.

The unexpected negative effect of copper sulfate

addition may thus be ascribed to either the preferential

occupation of specifi c sites by colloidal Cu(OH)2

species, inhibiting the adsorption of xanthate, or the

slow conversion of the hydrophilic Cu(OH)2 colloids

present on the mineral surfaces to the hydrophobic

Cu(I)X species. This has potential major ramifi cations

for the operation of fl otation plants since it is inevitable

that recycled process water will contain copper

species and these may interact with the mineral

surfaces before they are exposed to the xanthate

collector, thus reducing the recoveries.

ConclusionsThis study has examined the fl oatability of synthetic

tellurides, arsenides and sulfi des of Pt and Pd. It has

been shown that these minerals fl oat readily when

treated with SIBX. Unlike base metal sulfi des, the

addition of copper sulfate as an activator resulted in a

decrease in both the rate of fl otation and, especially in

the case of PtTe2 and PtAs2, in the fi nal recoveries. There

were no clear correlations between the observations

made of the surface charges of the minerals and their

fl otation behaviour. XPS and ToF-SIMS results showed

xanthate adsorption on the mineral surfaces, although

in lesser concentrations in the presence of copper

sulfate, using the addition sequence of CuSO4, followed

by xanthate. There were indications that Cu(I)X was

formed but this was associated with a lowering in

fl otation recovery.

It is inferred from the results that the active species

for fl otation was dixanthogen and the presence of

copper sulfate in some way inhibited this formation. In

the case of the PtAs2 it was suggested that the relatively

small number of Pt blebs on the surface, as well as

their high arsenic concentration, may have reduced

the extent of xanthate conversion to dixanthogen. It

is speculated that the negative effect of copper on the

recovery may be due to Cu(OH)2 precipitation on the

mineral surfaces occurring in patches and thus when

xanthate ions are subsequently added, most of the

active sites are already occupied by the hydrophilic

Cu(OH)2 which reduces the degree of xanthate

adsorbing directly onto the vacant Pt and Pd mineral

surface sites. Given that the minerals fl oat readily in

the presence of xanthate alone, processes which

minimise the exposure of these minerals to copper

sulfate would probably result in higher recoveries.

AcknowledgementsThe authors wish to thank Anglo American Platinum

(Pty) Ltd for permission to publish this paper.

References 1 R. P. Schouwstra, E. D. Kinloch and C. A. Lee, Platinum

Metals Rev., 2000, 44, (1), 33

2 R. G. Cawthorn, S. Afr. J. Sci., 1999, 95, 481

3 R. G. Cawthorn and S. J. Webb, Tectonophysics, 2001, 330, (3–4), 195

4 C. J. Penberthy, E. J. Oosthuyzen and R. K. W. Merkle, Miner. Petrol., 2000, 68, (1–3), 213

5 M. J. Viljoen and L. W. Schürmann, ‘Platinum Group Minerals’, in “The Mineral Resources of South Africa”, Handbook 16, Sixth Edition, eds. M. G. C. Wilson and C. R. Anhaeusser, Council for Geoscience, Pretoria, South Africa, 1998, pp. 532–568

6 N. J. Shackleton, V. Malysiak and C. T. O’Connor, Int. J. Miner. Proc., 2007, 85, (1–3), 25

7 N. J. Shackleton, V. Malysiak and C. T. O’Connor, Miner. Eng., 2007, 20, (13), 1232

8 D. J. Bradshaw and C. T. O’Connor, Miner. Eng., 1996, 9, (4), 443

9 S. R. Rao and J. Leja, “Surface Chemistry of Froth Flotation”, 2nd Edn., Kluwer Academic/Plenum Publishers, New York, USA, 2004, Volume 2, p. 405

10 Y. Hu, W. Sun and D. Wang, “Electrochemistry of Flotation of Sulphide Minerals”, Tsinghua University Press/Springer, Berlin, Heidelberg, Germany, 2009, pp. 20–22

11 N. P. Finkelstein, Int. J. Miner. Proc., 1997, 52, (2–3), 81



The AuthorsCyril O’Connor is the Director of the Centre for Minerals Research at the University of Cape Town, South Africa. He holds a PhD from the University of Cape Town and a DSc (Metallurgical Engineering) from Stellenbosch University, South Africa. His main research interest is in fl otation.

Natalie Shackleton is currently a Technical Specialist at Anglo American Technical Solutions Research, South Africa, where she has 29 years of experience in analytical chemistry, hydrometallurgical processes, and mineral processing. Her main area of specialisation is fl otation, particularly surface chemistry. She holds a PhD from the University of Cape Town.

http://dx.doi.org/10.1595/147106713X674292 •Platinum Metals Rev., 2013, 57, (4), 310•


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cell adoption over the next three years.

Availiability of the Industry ReviewThe Industry Review 2013 is available as a free

download from the website www.fuelcelltoday.com.

About Fuel Cell Today

Fuel Cell Today is the leading organisation for

market based intelligence on the fuel cell and

hydrogen industries. Covering key trends and

developments in industry and government,

Fuel Cell Today has for ten years provided

relevant, unbiased and objective information to

companies, policymakers, investors and other

stakeholders.

Contact InformationDr Dan Carter

Tel: +44 (0)1763 256326


Web: www.fuelcelltoday.com

“The Fuel Cell Industry Review 2013”

“The Fuel Cell Industry Review 2013”


http://dx.doi.org/10.1595/147106713X672221 •Platinum Metals Rev., 2013, 57, (4), 311–312•

PGMS IN THE LAB

Here another researcher whose work has benefi ted

from the support of Johnson Matthey and Alfa Aesar, A

Johnson Matthey Company, is profi led. Jean-Cyrille

Hierso is a Full Professor and Member of the Institut

Universitaire de France (IUF) at the University of

Burgundy in Dijon, France. He is interested in metal

and ligand chemistry, catalysis and nanomaterials.

About the Research A project has been initiated at the University of

Burgundy based on ligand chemistry for catalysis

under ultra-low metal loading. For this purpose, novel

polyphosphine ligands based on a ferrocene

backbone have been developed (see for example

Figure 1). A library of more than fi fty ferrocenyl di-,

tri- and tetraphosphines has been obtained, from

which some ligands displaying outstanding

performance have been identifi ed. Carbon–carbon

and carbon–nitrogen bond formation (Suzuki, Heck,

Sonogashira and Tsuji-Trost reactions) proceeded with

high turnover numbers and catalyst loadings as low as

10–4 mol% relative to the substrates.

The mechanistic features of cooperating polydentate

ligands are being explored with electrochemistry for

measuring kinetics and the identifi cation of

intermediary species. Additionally, internationally

recognised work has been done in the fi eld of

phosphines characterisation through the discovery

and investigation of nonbonded ‘through-space’ NMR

spin–spin couplings in organophosphorus and

organometallic compounds. Recently a patent was

deposited, jointly held by the CNRS and the University

of Burgundy, on the heterogenisation of a new family

of ligands for recycling and heterogeneous

catalysis. Low-loading palladium catalysis is now

being explored for direct functionalisation of C–H

bonds in heteroaromatics and for the formation of

C–N, C–O and C–S bonds. C–C coupling for C–H

funtionalisation has been achieved in cooperation

with Henri Doucet at the University of Rennes, France,

and the success of ferrocenyl polyphosphine ligands

in low-loading catalysis has led to their

commercialisation under the name “HiersoPHOS”.

In addition to the work on screening conditions for

palladium-catalysed C–C bond and C–X bond

formation (X = S, O, N), iridium and rhodium precursor

New, Effi cient Tools for Palladium-Catalysed Functionalisation of HeteroaromaticsJohnson Matthey and Alfa Aesar support new platinum group metals research

About the Researcher

* Name: Jean-Cyrille Hierso

* Position: Full Professor – Member of the Institut Universitaire de France (IUF)

* Department: Institute of Molecular Chemistry – Mixte CNRS Unit 6302

* University: University of Burgundy

* Street: 9 Avenue Alain Savary – Faculté Mirande

* City: Dijon

* Post or Zip Code: 21000

* Country: France

* Email Address: [email protected]

* Website: http://www.icmub.fr/185-membres?r=185&action=view&id=15

Professor Jean-Cyrille Hierso



salts are now also being investigated for direct specifi c

C–H functionalisation.

This fundamental research in synthesis methodology

may fi nd many applications in total synthesis or

synthesis of fi ne chemicals, including pharmaceuticals,

agrochemicals and molecular materials.

Selected PublicationsJ.-C. Hierso, M. Beauperin and P. Meunier, Centre National de

la Recherche Scientifi que, ‘Supported Ligands Having a High Local Density of Coordinating Atoms’, World Appl. 2012/001,601

D. Roy, S. Mom, S. Royer, D. Lucas, H. Cattey, J.-C. Hierso and H. Doucet, ACS Catal., 2012, 2, (6), 1033

M. Platon, L. Cui, S. Mom, P. Richard, M. Saeys and J.-C. Hierso, Adv. Synth. Catal., 2011, 353, (18), 3403

D. Roy, S. Mom, M. Beaupérin, H. Doucet and J.-C. Hierso,

Angew. Chem. Int. Ed., 2010, 49, (37), 6650

R. V. Smaliy, M. Beaupérin, H. Cattey, P. Meunier, J.-C. Hierso, J. Roger, H. Doucet and Y. Coppel, Organometallics, 2009, 28, (11), 3152

D. Evrard, D. Lucas, Y. Mugnier, P. Meunier and J.-C. Hierso, Organometallics, 2008, 27, (11), 2643

J.-C. Hierso, J. Boudon, M. Picquet and P. Meunier, Eur. J. Org. Chem., 2007, (4), 583

D. H. Nguyen, M. Urrutigoïty, A. Fihri, J.-C. Hierso, P. Meunier and P. Kalck, Appl. Organomet. Chem., 2006, 20, (12), 845

J.-C. Hierso, A. Fihri, R. Amardeil, P. Meunier, H. Doucet and M. Santelli, Tetrahedron, 2005, 61, (41), 9759

J.-C. Hierso, A. Fihri, R. Amardeil, P. Meunier, H. Doucet, M. Santelli and V. V. Ivanov, Org. Lett., 2004, 6, (20), 3473

J.-C. Hierso, A. Fihri, R. Amardeil, P. Meunier, H. Doucet, M. Santelli and B. Donnadieu, Organometallics, 2003, 22, (22), 4490

Fig. 1. Direct arylation at C3 or C4 of heretoaromatics in the presence of a palladium catalyst with the sterically relieved ferrocenyl diphosphane Sylphos, developed by the Hierso group (Reprinted with permission. Copyright 2012 American Chemical Society)

H+X

YZ R1

Cl

R2

Pd(OAc)2/Sylphos 0.5 mol%

DMAc, KOAc Bu4NBr, 150ºC

X

YZ R1

R2 Fe

Ph2P

Sylphos

PPh2



BOOKS“Chemical Information for Chemists: A Primer”

Edited by J. Currano (University of Pennsylvania, USA) and D. Roth (Caltech, USA), Royal Society of Chemistry, Cambridge, UK, 2013, 250 pages, ISBN: 978-1-84973-551-3 (Paperback), £24.99

This book is aimed at practicing

chemists. Written and edited by

chemical information experts, it

covers techniques in retrieving and

evaluating chemical information using the unique

entry points of the chemical literature, including

structure, formula, substructure and sequence.

Contents include:

(a) Introduction to the chemical literature;

(b) Using the primary literature: journals and impact;

patents; conference papers, reports and abstracts;

(c) Searching by text;

(d) Physical properties;

(e) Structure and substructure searching;

(f) Reaction searching;

(g) Basic Markush searching for patent information;

(h) Polymers and information retrieval;

(i) Commercial availability, safety and hazards

information.

“Computational Approaches to Energy Materials”

Edited by A. Walsh (Department of Chemistry, University of Bath, UK), A. A. Sokol and C. R. A. Catlow (Department of Chemistry, University College London, UK), John Wiley & Sons, Ltd, Chichester, West Sussex, UK, 2013, 318 pages, ISBN: 978-1-119-95093-6, £100.00, €125.20, US$185.00

This book is a detailed survey

of the current computational

techniques for the development and optimisation of

energy materials. The review of techniques includes

current methodologies based on electronic structure,

interatomic potential and hybrid methods. Topics

covered include:

(a) Introduction to computational methods and

approaches;

(b) Modelling materials for energy generation

applications: solar energy and nuclear energy;

(c) Modelling materials for storage applications:

batteries and hydrogen;

(d) Modelling materials for energy conversion

applications: fuel cells, heterogeneous catalysis

and solid state lighting;

(e) Nanostructures for energy applications.

“Organometallics in Synthesis: Third Manual”Edited by M. Schlosser (Swiss Federal Institute of Technology, Lausanne, Switzerland), John Wiley & Sons, Inc, Hoboken, New Jersey, USA, 2013, 1026 pages, ISBN: 978-0-470-12217-4 (Paperback), £83.50, €100.20, US$125.00

Each reaction is in the book’s

acclaimed ‘recipe-style format’

so that readers can replicate

the results in their own laboratories. Each chapter

offer hands-on guidance and practical examples.

Of special interest is Chapter 5, ‘Organopalladium

Chemistry’, by Stefan Bräse (Institute of Organic

Chemistry, Karlsruhe Institute of Technology, Karlsruhe,

Germany). This chapter contains the sections: ‘π-Allyl

or π-Propargyl Intermediates’; ‘Carbopalladation of

Alkenes and Alkynes’; ‘Cross-Couplings for C-C-Carbon

Single Bonds’; ‘Cross-Coupling Reactions toward

C-X Single Bonds’; ‘Heteropalladation of Alkenes

and Alkynes’; ‘Telomerization and Oligomerization

Reactions’; ‘Cycloaddition Reactions’; ‘Rearrangement

Reactions’; ‘Wacker and Other Oxidation Reactions’;

‘Hydrogenation, Reduction, and Isomerization

Reactions’; and ‘Domino and Multicomponent

Reactions’.

“Palladium-Catalyzed Coupling Reactions: Practical Aspects and Future Developments”

Edited by Á. Molnár (University of Szeged, Department of Organic Chemistry, Hungary), Wiley-VCH Verlag GmbH & Co KGaA, Weinheim, Germany, 2013, 692 pages, ISBN: 978-3-527-33254-0, £125.00, €150.00, US$190.00

While covering homogeneous

and heterogeneous Pd-catalysed

coupling reactions, the book focuses on key aspects

such as using different reaction media, microwave

techniques, catalyst recycling and large-scale

applications. It provides comprehensive coverage

of coupling reactions and emphasises those topics

Publications in Brief



that show potential for futher development, such

as continuous fl ow systems, water as the reaction

medium and catalyst immobilisation.

“Right First Time in Fine-Chemical Process Scale-Up”

B. Hulshof (Eindhoven University of Technology, The Netherlands), Scientifi c Update LLP, Mayfi eld, East Sussex, UK, 2013, 483 pages, ISBN 978-0-9533994-1-3, £99.50

Bringing a fi ne chemical product

to plant and market quickly

benefi ts from a “right fi rst time in

(fi ne-chemical) process scale-up”.

This book describes how to bridge the gap between

scales avoiding scale-up problems. The author makes

available 240 real-life examples and analyses them

answering these questions: (a) what was the primary

cause of the initial failure in scale-up; (b) what was the

solution; and (c) how could the incident have been

avoided in the early stages of process development?

Includes seven catalyst examples concerning

palladium/carbon and one with rhodium.

JOURNALSACS Photonics

Editor: H. A. Atwater (Caltech, USA); ACS Publications

The new journal ACS Photonics

will publish its fi rst issue in January

2014. The aim is to meet the growing

need for an interdisciplinary journal

dedicated to high-impact research

in the fi eld of photonics. Published

as soon as accepted and summarised in monthly

issues, ACS Photonics will publish research articles,

letters, perspectives and reviews, to encompass the full

scope of published research in this fi eld. Among the

areas the journal will cover are LEDs and solid state

lighting and photonics for energy materials.

MRS Energy & Sustainability—A Review JournalEditors-in-Chief: D. S. Ginley (National Renewable Energy Laboratory, USA), D. Cahen, (Weizmann Institute of Science, Israel) and S. M. Benson (Stanford University, USA); Materials Research Society/Cambridge University Press; ISSN: 2329-2229; e-ISSN: 2329-2237

Published jointly by the Materials Research Society

and Cambridge University Press, MRS Energy &

Sustainability—A Review Journal will have reviews

on key topics in materials science

and development as they relate to

energy and sustainability. Topics to

be covered include research and

development of both established

and new areas; interdisciplinary

systems integration; and objective

application of economic, sociological

and governmental models, enabling research and

technological developments.

Nanoparticles for CatalysisAcc. Chem. Res., 2013, 46, (8), 1671–1910

This special issue is a series of

accounts by leading experts

giving an overview of recent major

developments in nanoparticles

for catalysis. The most powerful

synthetic methods and state-of-

the-art characterisation techniques that have been

utilised to control and analyse these nanoparticle-

based catalysts are described. The guest editors hope

that the reader can see the relationship between

the structural details of the nanoparticles and their

catalyst performance, while at the same time develop

a fundamental understanding of the basic principles

that dictate these relationships. Examples involving

platinum and palladium nanoparticle-based catalysts

are included.

Virtual Issue: Catalysis at the Shanghai Institute of Organic Chemistry

ACS Catal., 2013, 3, (7), 1633

The Shanghai Institute of Organic Chemistry (SIOC),

China, was founded in May 1950 as one of the fi rst

fi fteen institutions established by the Chinese Academy

of Sciences (CAS). This virtual issue of ACS Catalysis

highlights the world-class catalysis research being

Reprinted with permission from ACS. Copyright 2013 American Chemical Society



carried out at SIOC. The topics of catalysis research

at SIOC are organometallic catalysis, organocatalysis,

asymmetric catalysis and biocatalysis. Items of interest

include: ‘Recent Advances in Asymmetric Catalysis in

Flow’, ‘Palladium-Catalyzed C-C Triple Bond Cleavage:

Effi cient Synthesis of 4H-Benzo[d][1,3]oxazin-4-ones’

and ‘Enantioselective Intramolecular Carbene C–H

Insertion Catalyzed by a Chiral Iridium(III) Complex

of D4-Symmetric Porphyrin Ligand’.

Web Themed Issue: Medicinal Inorganic ChemistryChem. Commun., 2013

This web themed issue of Chem.

Commun. celebrates current

achievements and future perspectives

in the fi eld of medicinal inorganic

chemistry, including, but not limited

to: metal-based diagnostics, metal-

based therapeutics, mechanistic

studies of metallotherapeutics, the role of metal ions

and metal ion homeostasis in disease, chelation therapy,

inhibitors of medically-relevant metalloproteins and

metal ion sensing. The guest editors are Amy Barrios

(University of Utah, Salt Lake City, USA), Seth Cohen

(University of California, San Diego, USA) and Mi

Hee Lim (University of Michigan, Ann Arbor, USA).

The feature article by Nicolas Barry and Peter Sadler

(University of Warwick, UK) entitled ‘Exploration of the

Medical Periodic Table: Towards New Targets’ provides

an excellent overview. Drugs and therapies based on

Pt, Pd, Rh, Ir and Ru are covered and the collection will

be added to as more articles are published.

ON THE WEBHow Can I Find Out What Research is Being Done on Uses of Iridium?

Questions & Answers | Platinum Metals Review

This item has a movie that shows the progress in patent

applications involving iridium over time from 1993 to

the present day (August 2013).

Find this at: http://www.platinummetalsreview.com/

resources/view-questions-answers/how-can-i-fi nd-out-what-

research-is-being-done-on-uses-of-iridium/

Johnson Matthey Noble Metals Wins Award at Sante Fe Symposium

Johnson Matthey Noble Metals, 01/07/2013

For its part in the manufacture of

parts for a specially commissioned

palladium claret jug crafted by

master goldsmith and silversmith

Martyn Pugh, Johnson Matthey

was awarded a Collaborative

Research Award at the 2012 Santa

Fe Symposium “in recognition of published research,

done in collaboration between a manufacturing

jeweller and a supplier, that uses good scientifi c

principles to result in useful information that can

be applied for the greater good of the industry”. The

work is summarised in ‘Final Analysis: Challenges and

Opportunities in Palladium: The Claret Jug Experience

at the Santa Fe Symposium’, C. Corti, Platinum Metals

Rev., 2012, 56, (4), 284.

Find this at: http://www.noble.matthey.com/news2.asp?id=79



CATALYSIS – APPLIED AND PHYSICAL ASPECTSCatalytic Properties of Ru Nanoparticles Embedded on Ordered Mesoporous Carbon with Different Pore Size in Fischer-Tropsch SynthesisK. Xiong, Y. Zhang, J. Li and K. Liew, J. Energy Chem., 2013, 22, (4), 560–566

3 wt% Ru NPs embedded on ordered mesoporous

carbon (OMC) catalysts with different pore sizes were

obtained by autoreduction between Ru precursors

and C sources at 1123 K. The catalyst activity for

Fischer-Tropsch synthesis (FTS) was measured in a

fi xed bed reactor. These 3 wt% Ru-OMC catalysts with

different pore sizes were more stable than 3 wt% Ru/

AC catalyst during the FTS reactions because Ru NPs

were embedded on the C walls, suppressing particle

aggregation, movement and oxidation. The catalytic

activity and C5+ selectivity increased with increasing

pore size; CH4 selectivity had the opposite trend.

CATALYSIS – REACTIONSPlatinum Catalysed Hydrosilylation of Propargylic AlcoholsC. A. McAdam, M. G. McLaughlin, A. J. S. Johnston, J. Chen, M. W. Walter and M. J. Cook, Org. Biomol. Chem., 2013, 11, (27), 4488–4502

The selective synthesis of E-vinyl silanes derived from

propargylic alcohols can be achieved using PtCl2/

XPhos. The reaction provides a single regioisomer

at the -position with E-alkene geometry. Good

reactivity was observed at extremely low catalyst

loadings. This methodology was extended to a one-pot

hydrosilylation Denmark–Hiyama coupling.

Hydroxyapatite Supported Palladium Catalysts for Suzuki–Miyaura Cross-Coupling Reaction in Aqueous MediumA. Indra, C. S. Gopinath, S. Bhaduri and G. K. Lahiri, Catal. Sci. Technol., 2013, 3, (6), 1625–1633

Catalyst 1 was prepared by the immobilisation of

[Pd(COD)Cl2] on hydroxyapatite. Catalyst 2 was

prepared by reduction of 1 with sodium borohydride

in ethanol. With 1 electronically neutral, electron rich,

electron poor or sterically hindered aryl boronic acids

and aryl halides underwent Suzuki-Miyaura cross-

coupling in water as the solvent. Catalyst 1 with Pd2+

exhibited much better catalytic activities than 2.

Conversion of Carbohydrate Biomass to -Valerolactone by Using Water-Soluble and Reusable Iridium Complexes in Acidic Aqueous MediaJ. Deng, Y. Wang, T. Pan, Q. Xu, Q.-X. Guo and Y. Fu, ChemSusChem, 2013, 6, (7), 1163–1167

Carbohydrate biomass can be converted to

-valerolactone in acidic aqueous media using a

catalytic method. Water-soluble Ir complexes were

extremely active for providing -valerolactone in high

yields with high TONs. The homogeneous Ir catalysts

could be recycled by using a simple phase separation.

EMISSIONS CONTROL

Preparation and Characterization of Pt-Rh-Pd/Al2O3 Three Way CatalystC. Kuang, K. Liu and F. Li, Precious Met. (Chin.), 2013, 34, (1), 17–20

Pt-Rh-Pd/Al2O3 catalysts were prepared by: (a)

successive impregnation method and (b) co-

impregnation method. TPD and XRD were used to

investigate the catalytic activity. The co-impregnation

method gave a catalyst of catalytic performance

superior to that of the successive impregnation

method. The catalytic process proceeds according to

the Langmuir-Hinshelwood mechanism.

Synthesis of Pd/Al2O3 Coating onto a Cordierite Monolith and Its Application to Nitrite Reduction in Water

AbstractsA. Indra et al., Catal. Sci. Technol., 2013, 3, (6), 1625–1633

Catalyst 1

Pd2+ Ca2+

O O O O

P P P P

HydroxyapatiteHyHydrdroxoxyayappaatitit tetet

[Pd][PPPd]d]d]d]

Catalyst 2

Ca2+

O O O O

P P P P

HydroxyapatiteHyHydrdroxoxyayappaatitit tetet



A. Devard, M. A. Ulla and F. A. Marchesini, Catal. Commun., 2013, 34, 26–29

A stable layer of Pd/Al2O3 on the walls of a cordierite

(COR) monolith was obtained by forming an alumina

layer via washcoat and then immersing into a PdCl2

solution. Pd/Al2O3-COR was shown to be active in

the reduction of nitrites and had the advantage of

generating low amounts of ammonium, indicating a

greater selectivity to nitrogen. The coating had good

adherence even after the reaction in a batch system

under stirring and under a pH ~5.

Pd-Doped Perovskite: An Effective Catalyst for Removal of NOx from Lean-Burn Exhausts with High Sulfur ResistanceX. Li, C. Chen, C. Liu, H. Xian, L. Guo, J. Lv, Z. Jiang and P. Vernoux, ACS Catal., 2013, 3, (6), 1071–1075

The Pd-doped La0.7Sr0.3CoO3 perovskite

(La0.7Sr0.3C0.97Pd0.03O3) has been shown to be an

effective LNT catalyst operating in periodically

alternate lean/rich atmospheres. This smart perovskite

displayed excellent NOx reduction activities for lean-

burn exhausts over 275–400ºC, as well as an extremely

high S tolerance. The results indicate that Pd is

dissolving into or segregating out of perovskite in lean-

burn and fuel-rich atmospheres.

FUEL CELLSIn Situ Measurement of Active Catalyst Surface Area in Fuel Cell StacksE. Brightman, G. Hinds and R. O’Malley, J. Power Sources, 2013, 242, 244–254

The application of a galvanostatic technique that

enables in situ monitoring of electrochemical surface

area (ECSA) in each cell throughout the lifetime

of a PEMFC stack was proven. The concept was

demonstrated at single cell (Pt/C anode/cathode,

perfl uorosulfonic acid membrane) level using both

H adsorption and CO stripping, and the H adsorption

method was extended to stack testing. The undesirable

effects of H2 crossover on the measurement may be

minimised by appropriate selection of current density

and by working with dilute H2 on the anode electrode.

Effi cient Pt/Carbon Electrocatalysts for Proton Exchange Membrane Fuel Cells: Avoid Chloride-Based Pt Salts!N. Job, M. Chatenet, S. Berthon-Fabry, S. Hermans and F. Maillard, J. Power Sources, 2013, 240, 294–305

A Pt/C xerogel catalyst with 2 nm Pt particles was

prepared by impregnation with H2PtCl6 using the

strong electrostatic adsorption method. Increasing

the reduction temperature and duration gave

better cleaning of the Pt surface and improved

the electrocatalytic performance. The effect of Cl

contamination was investigated on two model

reactions: the electrochemical COads oxidation and

the ORR.

Preparation of Electrocatalysts for Polymer Electrolyte Fuel Cell Cathodes from Au-Pt Core-Shell Nanoparticles Synthesized by Simultaneous Aqueous-Phase ReductionW. Yamaguchi and Y. Tai, J. Fuel Cell Sci. Technol., 2013, 10, (4), 041006 (5 pages)

PVP-protected Au-Pt core–shell NPs were prepared

by simultaneous aqueous phase reduction of Au

and Pt, and they were deposited on C black support.

The obtained powder was processed in air at 170°C

to remove the PVP. Stability of the core–shell catalyst

in water was improved after the removal of PVP. The

oxidation state of the Pt shell was found to be very

close to zero. The Au-Pt core–shell catalyst exhibited

mass activity 20% higher than that of a Pt catalyst.

APPARATUS AND TECHNIQUEFlexible Palladium-Based H2 Sensor with Fast Response and Low Leakage Detection by Nanoimprint LithographyS. H. Lim, B. Radha, J. Y. Chan, M. S. M. Saifullah, G. U. Kulkarni and G. W. Ho, ACS Appl. Mater. Interfaces, 2013, 5, (15), 7274–7281

High resolution and high throughput patterning of Pd

gratings over a 2 cm × 1 cm area on a rigid substrate

was achieved by heat treating nanoimprinted

Pd benzyl mercaptide at 250ºC for 1 h. A fl exible

and robust H2 sensing device was fabricated by

subsequent transfer nanoimprinting of these Pd

gratings into a polycarbonate fi lm at its glass transition

temperature. At ambient pressure and temperature,

the sensor showed a fast response time of 18 s at a H2

concentration of 3500 ppm.

ELECTROCHEMISTRYPlatinum Ordered Porous Electrodes: Developing a Platform for Fundamental Electrochemical CharacterizationB. Kinkead, J. van Drunen, M. T. Y. Paul, K. Dowling, G. Jerkiewicz and B. D. Gates, Electrocatalysis, 2013, 4, (3), 179–186

A set of high surface area Pt electrodes with an



ordered porous structure (Pt-OP electrodes) were

prepared by controlled electrodeposition of Pt

through a self-assembled array of spherical particles

and subsequent removal of the spherical templates

by solvent extraction. The Pt-OP electrodes had clean

Pt surfaces and a large ECSA resulting from both

the porous structure, and the nano- and micro-scale

surface roughness. The Pt-OP electrodes exhibited a

surface area enhancement comparable to commercial

electrocatalysts.

MEDICAL AND DENTALWater-Soluble Platinum(II) Complexes of Reduced Amino Acid Schiff bases: Synthesis, Characterization, and Antitumor ActivityL.-J. Li, C. Wang, C. Tian, X.-Y. Yang, X.-X. Hua and J.-L. Du, Res. Chem. Intermed., 2013, 39, (2), 733–746

Water-soluble Pt(II) complexes of reduced amino

acid Schiff bases were synthesised and characterised.

The complexes were tested for their DNA interaction

with salmon sperm DNA, and their in vitro anticancer

activities were validated against HL-60, KB, BGC-823 and

Bel-7402 cell lines by the MTT assay. The cytotoxicity of

one complex was better than that of cisplatin against

BGC-823 and HL-60 cell lines, and showed close

cytotoxic effect against Bel-7402 cell line.

Ruthenium (II) Polypyridyl Complexes Stabilize the bcl-2 Promoter Quadruplex and Induce Apoptosis of Hela Tumor CellsC. Wang, Q. Yu, L.Yang, Y. Liu, D. Sun, Y. Huang, Y. Zhou, Q. Zhang and J. Liu, BioMetals, 2013, 26, (3), 387–402

The interaction between GC-rich sequence of bcl-2

gene P1 promoter (Pu39) and [Ru(bpy)2(tip)]2+, 1,

and [Ru(phen)2(tip)]2+, 2, was investigated by UV-

vis, fl uorescence spectroscopy, circular dichroism,

fl uorescence resonance energy transfer melting assay

and polymerase chain reaction stop assay. The results

indicated that the two complexes can effectively

stabilise the G-quadruplex of Pu39. 2 exhibited greater

cytotoxic activity than 1 against human Hela cells

and can enter into Hela cells to effectively induce

apoptosis. Further experiments found that 1 and 2 had

as potent inhibitory effects on ECV-304 cell migration

as suramin.

NANOTECHNOLOGYA Simple Method for Producing Colloidal Palladium Nanocrystals: Alternating Voltage-Induced Electrochemical SynthesisJ. E. Cloud, K. McCann, K. A. P. Perera and Y. Yang, Small, 2013, 9, (15), 2532–2536

Alternating voltage-induced electrochemical synthesis

(AVIES) gave well-dispersed, size-controlled, single-

crystalline, colloidal Pd nanocrystals (Pd-NCs). An

alternating voltage was applied to 2 Pd wires inserted

in an electrolyte solution containing capping ligands.

Pd-NCs were directly ejected from the Pd electrodes

through cathodic reduction of the PdO intermediates.

The Pd-NCs were soluble in either polar or non-polar

solvents, depending on the nature of the capping

ligands.

PHOTOCONVERSIONLight Extraction Enhancement in Organic Light-Emitting Diodes Based on Localized Surface Plasmon and Light Scattering Double-EffectY. Gu, D.-D. Zhang, Q.-D. Ou, Y.-H. Deng, J.-J. Zhu, L. Cheng, Z. Liu, S.-T. Lee, Y.-Q. Li and J.-X. Tang, J. Mater. Chem. C, 2013, 1, (28), 4319–4326

The performance of OLEDs was improved by

incorporating Pt3Co alloy NPs into the devices as the

anodic buffer layer. The enhancement in the current

effi ciency and EL intensity was achieved without

affecting the spectral intensity distribution. A study on

the devices with and without unannealed Pt3Co alloy

NPs found that the enhanced effi ciency was mainly

due to the resonance of localised surface plasmon.

R2

N

OHR1

O

OKNaBH4

CH3OH R1 OH

NH

R2

OK

O

K2PtCl4

pH = 8~9 R1 O

NH

R2 O

O

Pt

Cl

K+

L.-J. Li et al., Res. Chem. Intermed., 2013, 39, (2), 733–746



CATALYSIS – APPLIED AND PHYSICAL ASPECTSFischer-Tropsch Catalyst with Ruthenium PromoterJohnson Matthey PLC, World Appl. 2013/054,091

A procedure for preparing a Fischer-Tropsch catalyst

precursor comprising 10–40 wt% Co3O4 crystallites

and 0.05–0.5 wt% of a precious metal promoter

selected from Pt, Pd, Ir, Ru, Re or Au, preferably Ru,

dispersed over the surface of a porous transition

Al2O3 is claimed. The process consists of: (a) forming a

modifi ed catalyst support by impregnating a transition

Al2O3 with Mg(NO3)2; (b) drying and calcining the

impregnated Al2O3 in a fi rst calcination at ≤600ºC

to convert Mg(NO3)2 into oxidic form; (c) forming

a catalyst precursor by impregnating the modifi ed

catalyst support with a mixture of Co(NO3)2 and Co

acetate and a precious metal promoter compound

selected from Pt, Pd, Ir, Ru, Re or Au, preferably Ru; and

(d) drying and calcining the impregnated catalyst

support in a second calcination to convert the Co

compound to Co3O4.

Preparation of cis-Rose Oxide using Ruthenium CatalystBASF SE, US Appl. 2013/0,109,867

A heterogeneous catalyst comprising (in wt%):

0.001–10 Ru, 0–5 alkaline earth metals, 0–5 alkali

metals, 0–10 rare earth metals and 0–10 metals

selected from Pt, Pd, Ir, Os, Ag, Au, Cu and Re on -Al2O3

support and in the presence of hydrogen is used in the

catalytic hydrogenation of 2-(2-methylprop-1-enyl)-

4-methylenetetrahydropyran, 1, to prepare cis-2-(2-

methylprop-1-enyl)-4-methyltetrahydropyran, 2, which

is also referred to as cis-rose oxide.

Platinum-Ruthenium CatalystCanan New Material (Hangzhou) Co Ltd, Chinese Appl. 102,861,573; 2013

The catalyst for selective hydrogenation consists of

0.1–20 wt% Pt and Ru with a Pt/Ru weight ratio

of 1:0.01--5 supported on SiO2, Al2O3, activated C,

molecular sieve, ZrO2, SiO2 gel, BaSO4 and/or diatomite.

The catalyst is dispersed together with a halogen-

containing nitro compound which has a ratio of 0.01–

10 wt% in a solvent for hydrogenation at a H2 pressure

of 0–10 MPa at 30–150ºC. Pt and Ru are loaded onto

the same support to increase the catalyst activity for

the selective hydrogenation of halogen-containing

nitro compounds. The advantages of this catalyst are

high conversion rate and high selectivity under a

lower temperature and pressure.

Gold-Sputtered Carbon Supported Iridium CatalystChangchun Institute of Applied Chemistry, Chinese Appl. 102,872,864; 2013

The preparation of Au-sputtered C supported Ir

catalyst involves: (a) dissolving C, selected from

activated C, graphene or CNT, and Ir salt in deionised

water, adjusting the pH to a weak base, mixing the

solution with NaNO3, stirring and heating at 80–120ºC;

(b) sintering the solution at 300–800ºC for 30–120 min

to obtain C supported Ir catalyst; and (c) sputtering

Au on the C supported Ir catalyst to obtain the fi nal

product. This catalyst is used for water electrolysis and

the advantage of this preparation is the improvement

of the condition and stability of Ir catalyst due to the

Au layer protection.

CATALYSIS – INDUSTRIAL PROCESS

Catalyst for Manufacturing AmmoniaSumitomo Chemical Co Ltd, Japanese Appl. 2013-111,563

The catalyst composition contains ≥1 metals or alloys

or compounds selected from Rh, Ir, Os, Ru, Sc, Ti, V, Cr,

Mn, Co, Cu, Y, Zr, Nb, Mo, Tc, Ag, Hf, Ta, W or Re; and porous

metal complexes of which the structure will not be

destroyed at 200ºC in 1 atm NH3. NH3 is prepared by

reacting N2 and H2 over this catalyst.

Patents

O O

1 2

US Appl. 2013/0,109,867



CATALYSIS – REACTIONSPalladium Catalyst for Purifi cation of Sulfate TurpentineZAO Torgovyi Dom “Orgkhim”, Russian Patent 2,485,154; 2013

The purifi cation of sulfate turpentine from sulfur

compounds involves preheating the turpentine to

70–80ºC and bringing it into contact with a catalyst,

which is an active substrate made from 7.7–8 wt%

sulfated ZrO2 and 0.18–0.2 wt% catalytically active Pd

on a highly porous cellular blocked material based on

-Al2O3, at 60–90ºC under an initial hydrogen pressure

of 0.7–0.9 MPa. The benefi ts of this method are the

reduction of residual content of sulfur compounds

and the simplifi cation of the purifi cation process.

EMISSIONS CONTROLMagnetic Platinum CatalystS. M. Chen et al., US Appl. 2013/0,152,375

A procedure for making a magnetic Pt catalyst consists

of: (a) using powder metallurgy to form a neutral Nd

magnetic alloy containing ~25–50% Nd into a catalyst

carrier; (b) making the catalyst carrier into a cylinder

with a diameter of ~13 mm and a length of ~9 mm;

(c) treating the surface of the catalyst carrier with an

antioxidant; (d) producing a catalyst acid soaking

solution with ~0.01–0.2% Pt and ~0.01–0.15% Rh;

(e) adjusting the pH of the solution to 4 with oxalic

acid; (f) soaking the catalyst carrier in the solution

for 12–24 h; (g) draining the catalyst carrier from the

solution; (h) drying the catalyst carrier; and (i) baking

the catalyst carrier in a muffl e furnace at ~300–600ºC

to attach the catalyst onto the surface of the catalyst

carrier. This catalyst is used in connection with engine

fuel to enhance its operation.

FUEL CELLSFuel Cell Catalyst with RutheniumSamsung Electronics Co Ltd, US Appl. 2013/0,137,009

A fuel cell catalyst comprises an alloy which has the

core--shell structure and various compositions: (a) the

core comprises a Group 8 metal, selected from Ru, Os

or Fe, preferably Ru and the shell comprises an alloy of

a Group 8 and Group 9 metal selected from Rh, Ir or

Co, preferably Ir; or (b) the core consists of an alloy of

Group 8 and Group 9 metal and the shell comprises

the Group 9 metal only. The at% of the Group 8 metal is

~8–92 and ~8–90 of the Group 9.

Collector Plate for Fuel CellsNippon Light Metal Co, Japanese Appl. 2013-105,629

The surface of a collector plate for fuel cells

includes Al or Al alloy, a Ni plating film and a noble

metal plating film selected from Pt, Pd, Ir, Os, Rh, Ag

or Au. The collector plate is located on both ends of

a fuel cell stack. The benefits of the collector plate

are low contact resistance, excellent corrosion

resistance and it can be reliably used for a long

period of time.

METALLURGY AND MATERIALSPrecipitation Hardenable Palladium Alloy for JewelleryS. A. Kostin and A. K. Nikolaev, World Appl. 2013/085,420

The alloy consists of (in wt%): 50–95 Pd, 3–5 Ni, 0.5–2

Si, 1–40 Cu, 1–30 Au, 1–10 In, 1–10 Ga and 0.01–1 B. The

Pd base is prepared by alloying with two components

which form a compound that does not contain base

metal atoms and hardening the alloy in the casts

for jewellery by thermal and thermomechanical

processing. The thermal processing enables a selection

of desired strength properties from soft to hard to be

produced.

Surface Hardening of PlatinumOtkrytoe Aktsionernoe Obshchestvo “Krasynoyarskii Zavod Tsvetnykh Metallov im. V. N. Gulidova”, Russian Patent 2,482,203; 2013

Pt and Pt-based alloys are exposed to a

thermochemical treatment with a C-containing

material at 1050–1400ºC. This treatment hardens the

surface of jewellery, coins and pins made from Pt and

Pt-based alloys and improves their wear resistance

without reduction in fi neness or deterioration of

appearance.

APPARATUS AND TECHNIQUEPalladium-Silver Alloy Gas Separation MembraneShell Oil Co, US Appl. 2013/0,152,785

A procedure for preparing a Pd-Ag alloy gas separation

membrane system involves: (a) providing a porous

support which contains a Pd layer; (b) activating the

surface of the Pd layer by abrading it with an abrasion

media to impose an abrasion pattern and a mean

surface roughness of >0.8 μm–2.5 μm; (c) depositing

an overlayer comprising Ag onto the surface of the

activated Pd layer; and (d) annealing both layers at

400–800ºC.



ELECTRICAL AND ELECTRONICSBonding Wire for SemiconductorsHeraeus Materials Technology GmbH & Co KG, European Appl. 2,595,184; 2013

A method for manufacturing a bonding wire consists

of: (a) pouring Ag alloy including at least one selected

from Zn, Sn and Ni at 5 ppm to 10 wt% and further

comprising Pt, Rh, Os, Pd, Au or Cu at 0.03–10 wt% into

a mould; (b) melting the Ag alloy; (c) continuously

casting the melted Ag alloy; and (d) drawing the

continuously cast Ag alloy. The bonding wire is used

to connect the LED chip to the lead frame in an LED

package.

MEDICAL AND DENTALPlatinum-Based TherapyAtlas Antibodies AB, European Appl. 2,602,622; 2013

A method for determining whether a mammalian

subject has cancer which is categorised in the fi rst or

second group comprises: (a) evaluating the amount

of Dachshund homologue 2 (DACH2) present in the

nuclei of tumour cells; (b) comparing the sample

value obtained in (a) with a reference value; and

(c) concluding whether the sample belongs to the fi rst

or second group, if the sample value is ≤ the reference

value the subject belongs to the fi rst group which is

more responsive to a Pt-based treatment. The intensity

of the Pt-based treatment depends on steps (a)–(c).

The Pt-based treatment is selected from carboplatin,

paraplatin, oxaliplatin, satraplatin, picoplatin and

cisplatin.

Radiopaque Intraluminal StentsP. A. Kramer-Brown et al., US Appl. 2013/0,204,353

A radiopaque stent comprises a cylindrical main body

which consists of a Co-based alloy including Cr, Mn and

one or more pgms or refractory metals selected from

Pt, Pd, Rh, Ir, Os, Ru, Zr, Nb, Mo, Hf, Ta, W, Re, Ag and Au,

preferably Pt or Pd. The Co-based alloy is entirely free of

Ni and comprises (in wt%): ~18–50 Co, ~10–25 Cr and

~10–65 of one or more pgms or refractory metals. The

Co-based alloy is formed by having each constituent

metal either in solid or powder or both and melting

these by arc melting, electro-slag remelting, electron

beam melting, induction melting, radiant heat melting,

microwave melting or a combination.



FINAL ANALYSIS

Platinum Group Metal Catalysts for the Development of New Processes to Biorenewables

There is a growing move away from so called fi rst

generation biorenewables (which use food crops as the

feedstock) towards second generation biorenewables

which use non-food sources of biomass. Biorenew able

products have the potential to support growing

resource needs while addressing concerns regarding

climate change and energy security.

Examples of second generation biorenewable

feedstocks include:

Wood from natural forests and woodlands;

Forestry plantations and residues;

Agricultural residues such as straw and corn

stover;

Algae;

Municipal solid wastes (MSWs);

Industry processing wastes.

Process developers have been looking to utilise

lower cost biofeedstocks, including those traditionally

classifi ed as waste streams. The use of cheaper

biomass feedstocks and waste streams, which are often

accompanied by higher impurity levels, do however

present additional purifi cation and processing

challenges such as the need for new feedstock

pretreatment steps and the solving of catalyst

deactivation issues. Catalysis is playing a leading

role in addressing and solving these conversion and

purifi cation challenges.

Key Reactions for Biorenewables ProcessesSome of the key reactions being targeted in

biorenewables processes include hydrogenation,

dehydration, decarbonylation, dehydrogenation and

oxidation. Each of these processes covers a number

of important potential reaction steps which are

necessary to achieve effi cient renewable processes.

For some processes, the removal of oxygen and water

and addition of hydrogen are key to success, and there

are a range of base and precious metal catalysts to

address this.

As can be seen from Figure 1, each of these

conversions can lead to important products for

industries and end consumers. Bioplastics, for

example, fi nd many applications in consumer

goods and household items. Biochemicals can

themselves be consumed in or converted into

products for industry, such as fi bres, coatings,

automotive components and many more. Therefore

by integrating biorenewable analogues of chemical

intermediates into manufacturing processes through

the use of chemical catalysis or otherwise, the

sustainability of all products in the supply chain can

be enhanced.

ln many cases, using low cost biorenewable raw

materials reduces the overall production costs of the

end chemical product. However, it is important to note

that many of the processing steps required in this

expanding fi eld are new and this presents exciting

challenges for the development of new, custom

designed catalysts.

The unique properties of the platinum group

metals (pgms) can be applied to these complex

challenges, such as catalyst deactivation and low-

temperature operation. One of the problematic

features of biorenewable feedstocks is the level and

type of impurities they contain. Consequently, work is

being focused on exploiting the resistance of pgms



to common poisons, such as sulfur, encountered in

biomass processing and seeking to take advantage

of their high activity to enable milder operating

conditions (1).

Bio-Based Routes to Valuable Chemicals There is interest in using biomass as a raw material

for the production of a range of valuable chemical

building blocks including diols, oxygenates such

as ethanol and biosyngas (a mixture of hydrogen

and carbon oxides). Three main processes can be

identifi ed:

1. Conversion of lignocellulose (dry plant matter) to high value chemicals. The

biochemical conversion of biomass, such as

sugars, via fermentation is well established

but thermochemical conversion of cellulosics

may offer alternative pathways to valuable

chemicals such as diols. ln particular the focus

on lignocellulosic feedstocks such as wood

and agricultural waste avoids the ‘food to fuel’

dilemma.

2. Conversion of bioderived syngas to oxygenates. Although oxygenates (such as

ethanol) are already commonly produced

from biomass via fermentation routes, the

thermochemical synthesis of C2 oxygenates from

syngas using rhodium-on-silica-based catalysts

with a range of promoters is being investigated as

an alternative route.

3. Hot conditioning of syngas derived from gasifi ed biomass. Gasifi cation of biomass

consists of reacting biomass with steam/

oxygen to produce a mixture of carbon

monoxide, carbon dioxide and hydrogen. This

route offers a more effi cient way of producing

power (as an alternative to combustion) or

syngas (which can be used as a building block

for many other chemical products). Biomass

gasifi cation at a relatively small scale produces

tar (aromatic condensable hydrocarbons) and

light hydrocarbons, in particular methane. These

hydrocarbons make up a signifi cant proportion

of the carbon content of the gas and need to be

converted or ‘reformed’ into syngas to improve

the economics of the process and prevent

downstream fouling (2). Biomass derived syngas

also contains sulfur as an impurity and promoted

rhodium catalysts have been found to work

better for reforming methane than conventional

nickel-based steam reforming catalysts in this

environment.

C5 + C6 Sugar

Hydrogen

Ethanol

Lipi

ds

Diols

Diesters

Esters

Alcohols

Amines

Diamines

EthyleneDehydrationAlumina

AminationNi, Co, Cu

HydrogenolysisCu, Ni

Aqueous phase reformingNi, pgm

HydrogenolysisNi, Cu, pgm

Hydroformylation/carbonylation

Rh, PdMetathesis

Ru, Mo

Transesterifi cationHeterogeneous

Fermentation

Biop

last

ics

Bioc

hem

ical

s

HydrogenationNi, Cu, pgm

Fig. 1. Reaction scheme showing the conversion of lipids and carbohydrates to biorenewable products by a variety of pgm- and base metal-catalysed processes



Conversion of Biomass to Liquid Fuels With continued focus on the availability of oil and

gas and interest in alternative energy sources it

is not surprising that the feasibility of producing

hydrocarbon fuels from biomass is a topic of much

research.

Triglycerides and fatty acids are naturally

occurring molecules that have attracted much

interest. They have the potential to be catalytically

converted into long chain hydrocarbons which can

be used as a drop-in replacement for traditional

fuels. These compounds occur in feedstocks such as

palm oil, soya oil and algae. The molecular structure

of the triglycerides and acids found in algae in

particular makes them an excellent starting point

for the production of long chain hydrocarbons,

such as those found in diesel fuel. This conversion

can be carried out catalytically in high yield, over

pgm-based catalysts, as illustrated in Figure 2 for a

palmitic acid feed.

Recent catalyst developments have demonstrated

the potential of more complex, bifunctional catalysts

for the single step conversion of fatty acid feeds to the

branched and aromatic molecules that are important

constituents of aviation fuel. Figure 3 compares the

performance of a 5% palladium-on-carbon catalyst

with a novel bifunctional catalyst, 0.3% platinum-

on-ferrierite (3), for the conversion of a palmitic

acid feed. The palladium on carbon catalyst gives

high yields of linear hydrocarbons suitable for diesel

fuels, while the bifunctional catalyst gives a product

that contains good levels of branched and aromatic

hydrocarbons in the C9 to C16 chain length range, in

addition to linear hydrocarbons.

This technology is being investigated within

projects that are developing the biology and

fermentation systems to produce a fatty acid feed

from CO2 and H2 which can then be converted to

an infrastructure-compatible fuel using catalysts.

An example of the composition of the product

from one project is shown in Figure 4 where

complete conversion of the fatty acid feed has been

achieved with high selectivity to a range of linear

hydrocarbons in the range C11 to C18, as would be

found in diesel fuel.

100

90

80

70

60

50

40

30

20

10

0

Yiel

d, %

5% Pd-on-carbon 0.3% Pt-on-ferrierite

Hydrocarbons: Linear Branched Aromatic

Palmitic acid

H2

Catalyst

Hexadecane

Pentadecane

O OH

Fig. 2. The pgm-catalysed conversion of palmitic acid to long chain (C15 and C16) linear hydrocarbons such as those found in diesel fuel

Fig. 3. Performance of palladium-on-carbon compared to a novel, bifunctional platinum-on-ferrierite catalyst for the conversion of palmitic acid to hydrocarbons



Conclusion The move to second-generation biorenewables will

require innovative solutions in terms of both catalyst

and process technology capabilities. Catalysts based

on pgms can provide both high selectivity and good

resistance to the poisons typically found in biomass.

They are set to play a leading role in providing cost

effective solutions to manufacturing biorenewable

products. By opening up access to milder operating

conditions and pathways to new, valuable products,

they will contribute to environmental stewardship and

sustainability.

This article is adapted from the 2013 edition of Assay,

Johnson Matthey’s in-house technology magazine.

ANDREW D. HEAVERS* AND MICHAEL J. WATSON

Johnson Matthey Plc, PO Box 1, Belasis Avenue, Billingham TS23 1LB, UK


ANDREW STEELE

Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, UK

JEANETTE SIMPSON

Johnson Matthey Plc, Orchard Road, Royston,Hertfordshire SG8 5HE, UK

References 1 ‘Alternative Catalytic Solutions Take Centre Stage’,

Biofuels Int., 2013, 7, (2), 54

2 A. Steele, S. Poulston, K. Magrini-Blair and W. Jablonski, Catal. Today., 2013, 214, 74

3 D. Davis, C. M. Lok, M. J. Watson and A. Zwijnenburg, Johnson Matthey Plc, World Appl. 2009/095,711

The AuthorsDr Andrew Heavers is a Business Development Director for New Technologies in Johnson Matthey’s Process Technologies Division. He has a central role across the Johnson Matthey group leading biomass related projects.

Dr Michael Watson is a Project Manager in Johnson Matthey’s Technology Centre at Billingham, UK. His current research activities are focused on the development of heterogeneous catalysts for a wide range of industrial processes, including the use of biorenewable feedstocks.

Dr Andrew Steele is a Principal Scientist at Johnson Matthey’s Technology Centre at Sonning Common, UK. His current interests are in research and development of new commercial opportunities for the platinum group metals with particular focus on rhodium.

Jeanette Simpson is Business Development Manager for the Chemical Catalyst business in Johnson Matthey’s Process Technologies Division. She identifi es and assesses new opportunities in the fi eld of chemical catalysis, with a particular interest in biorenewable chemical processes.

Fig. 4. Linear hydrocarbons produced via catalytic transformation of fatty acids

5 7.5 10 12.5 15Time, min

350

300

250

200

150

100

50

0

Volta

ge, m

V

5.02

9

6.06

4

8.91

4

6.14

9

10.5

55

7.03

5

8.07

87.

994

7.94

2

9.72

49.

666

9.85

2

12.0

80

12.5

94

13.3

27

14.5

40

13.7

92

14.9

54

15.6

27

6.41

5

10.0

9910

.038

11.1

9211

.378

11.3

3511

.549

12.6

47

This page is intentionally blank.

EDITORIAL TEAM

Sara ColesAssistant Editor

Ming ChungEditorial Assistant

Keith WhitePrincipal Information Scientist


Platinum Metals Review is Johnson Matthey’s quarterly journal of research on the science and technologyof the platinum group metals and developments in their application in industry

http://www.platinummetalsreview.com/

www.platinummetalsreview.com

Platinum Metals ReviewJohnson Matthey PlcOrchard Road RoystonSG8 5HE UK

%: +44 (0)1763 256 325@: [email protected]

Editorial Team

Sara Coles Assistant Editor

Ming Chung Editorial Assistant

Keith White Principal Information Scientist

johnson matthey technology review - vol 57 issue …...published by johnson matthey plc vol 57 issue...

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