transformation of formaldehyde aminals into diaminocarbenes and carbeniurn salts
TRANSCRIPT
Transformation of Formaldehyde Aminals into Diaminocarbenes
and Carbeniurn Salts
b y
José M. Rodezno
A thesis submitted in conformity with the requirements
for the Degree of Master of Science, MSc.,
Department of Chemistry,
University of Toronto
O Copyright by José M. Rodezno, 2001
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Fie: Transformation of Fomaldehyde Aminals into Diaminocarbenes and Carbenium Salts
Degree: Master of Science, MSc.
Year of convocation: 2001
Author: Jose M. Rodezno
Department of Chemistry, University of Toronto
Abstract
The reactivities of the two stable diaminocarbenes 1 ,3-di-tert-butyl-irnidazole-2-
ylidene 1 and 1 13-di-tert-butyl-imidazolidine-2-ylidene 2 toward hydrogen, oxygen, water
and carbon monoxide and SOg were investigated. Contrary to comrnon belief the
deterioration of 1 and 2 is not due to oxidation by triplet oxygen, but is the result of
hydrolysis. The hydrolysis rate ab room temperature is very low for the aromatically
stabilized 1 but very rapid for the non-arornatic 2. The reactions are not acid or base
catalyzed. Computational data show that the reaction with triplet oxygen is only kinetically
hindered and that the oxidation of 1 and 2 to the respective ureas is in fact strongly
exothermic. Both carbenes insert into dihydrogen only in the presence of hydrogenation
catalysts. Carbene 2 foms a 1 : 1 adduct with S02 that is best described as a Lewis adduct
The ammatic ring protons in 1 undergo rapid deuteiium - hydrogen exchange n
DMSO-d6, CD30D and D20. The oxidation of aminals by oxidizing agents like N BS,
NCS, CC14, CBr4. 12 or CuC12 leads to diaminocatbenium salts in high yields. These
oxidations c m be extended to 1,3,5-triazacyclohexane R3TAC systems, to give the
monocaüonic sak [R3TAC] [XI. The carbene, 1,3,5-tri-tert-butyl-l,3,5-triazacyclo hexane-
2-ylidene 9, derived through deprotonaiion of the [R3fAC][Br] has been observed n
benzene-d6 solutions. Reaction of R3TAC with CuCI2 leads to metal-1,3,5-
triazacyclohexane complexes.
For Lisa
"We are here for this - to make rnistakes and to corredourselves, to stand the blows and
hand thern out." Primo Levi.
III
Acknowledgements
First and foremost 1 would like to express my sincere gratitude to Prof. Michael Denk,
who introduced me to one of the most exciting fields of chemistry.
To ail those who ai someway or another have helped me 1 am dso grateful. h
W * c u I , I would like to thank Dr. Garnil Aihakirni for çtirnulating discussions, Sébastien
Fournier and former group mernbers Liça H. Studnicki (pobie) and John H. Brownie.
1 must also thank Dr. Alan Lough, who I bothered throughout the course of two years
with pseudo-crystals, along with Dr. Tim Burrow and Dr. Paul Isbester (York University) for
NMR spectroscopy and Dr. Alex Young for mass spectrai analysis.
Finally, I would like to thank my family for ail the support provideci.
List of Abbreviations
A
A d
Ar
b p
br
cm-'
d
dd
DMSO
S
A
AH
E ~ I
Et
Eth
El-MS
ES-MS
R - I R
9
GC-MS
h
ipr
J
LH2
L'
LDA
m
Angstrom (1 0-10 m)
Adamantyl
Aryl group
boiling point
broad
cetimetre inverse (1 R)
doublet (NMR)
double of doublets (NMR)
Dimethylsulfoxide
denotes chernical shift (NMR)
denotes high temperature
reaction enthaipy
Electronic Energy
Ethyl
Thermal Energy
Electron Impact Mass Spectrum
Electrospray Mass Spectrum
Fourier-Transfomi lnfrared Spectroscopy
Q-
Gas Column - Mass Spectroscopy
hair
iso-Propyl
Coupling constant
(CH3)3C-N(H)-CH2-CH2-N(H)-C(GH3)3
(CH3)3C-N=CH-CH=N-C(CH3)3
Lithium Diisopropylamine
multiplet (NMR); or medium (IR); or meta position v
Me
Mes
MHz
mL
mmol
m/z
mol
mP
MS
NBS
NCS
NMR
Hz
O
P
Ph
PPm
qr
qn
rel. int. %
r.t
s
Sb
t
TAC
tBu
tert
THF
Methyl
Mesityl
Megahertz
millilitre
millimole
mass to charge ratio (MS)
mole
melting point
Mass Spectroscopy
/Ubromosuccinirnide
Nd-ilorosuccinimide
Nuclear Magnetic Resonance
Hertz
ortho
Para
Phenyl
parts per million
quartet (NMR)
quintet (NMR)
percent relative intensity
room temperature
singlet (NMR); strong (IR)
subvalent compound
triplet (NMR)
1,3,5-Triazacyclohexane
tertiary-Butyl
terh'ary
Tetrah ydrofuran
TMS
U
v
W
X
ZPE
Tetramethylsilane
wavenumbers
ve'Y
weak (IR)
halogen
Zero Point Energies
Table of Contents
..........................................................................................
........... .................................................................................. Carbenes ..,
Origins of Diaminocarbene Chemistry ............ .... ........................... WanziicKs Contributions ................. ... ...............................................
Electronic Structure of Carbenes ........................................................... ...... Influence of Substituent on the Electronic Structure of Carbenes
Electronic Effects .................. .... ...........................................................
Steic Effects ............................................................................................ ............................. ............................ Synthesis of Stable Carbenes ....
............. ............................................. Structure of Stable Carbenes ..
Diaminocarbene Congeners ................................................................. Starting Materiais for the Synthesis of Diaminocarbene .....................
Carbenium Cations ....................... .. ..................................................
lonic Liquids ...........................................................................................
Thioureas .................................................. ...... ...................................... . .
Research Objectives ..............................................................................
Chapter 2: Resuits and Discussion ......................................................................
.............................................................. 2.1 Oxidation of Diaminocarbenes
2.2 "Air Sensitivity" of Diaminocarbenes ..................................................
.......................................................... 2.3 Oxop hiiicily of Diaminocarbenes
2.4 Deuterium Labeling of I,3-Di-fert-butylimidazole- 2-ylidene ..............
2.5 ...................................... Formation of a Diaminocarbene-S02 Adduct
.................................................................... 2.6 Reactions with CO and H2
................................ 2.7 Synthesis of Carbenium Salts .................... ....
2.8 Thauer's Hydrogenase .........................................................................
Synthesis of 1.3.Di.tert.butyl.3.4.5. 6.tetrahydropyrhkhe-Z
yiidene ........................................ .. 47 ........................................................ ..................................................................... 1 ,3, 5.Triazacyclo hexanes 48
Synthesis of lI3,5.Tri.ted4utyl-1,3, 54riazacyclohexyl Cahenium
.............................................................................. Cation [tBu3TAC]M 49
Deprotonation of 1,3,S.Tri4ert-butyl4,3, 5.triazacyclohexyl
Carbenium Bromide rBu3TAC][Br] .......................... .. ......................... 51
Attempted Synthesis of 1,3,5.Tri4ert.butyl.l,3, 5.triazacyclohexyl
............................... triscarbenium Cation PBu3TAC]k] ....... .. .. .. 52
1,3,5.Tri~tert.butyl.l, 3,5.triazacyclohexan e.CuCh Adduct ............... 53
Chapter 3: Expairnent al ....................................................................................... 56
Expimental Notes ............................................................................... 57
Preparation of Compounds ........................ .. ...................................... 58
.................. Preparation of 1,3.Di~tert.butylirnidazole. 2.ylidene (1 ) .... 58
Preparation of 1,3~Di.tert~butyl.imidazolidine. 2.ylidene (2) ............... 59
Preparation of 1.3.Di.tert-butyl.3.4.5.64etrahydropyrimidine. 2.
.......................................................... yiidene (3) .................................. ... 60
Preparation of 1.3.Di.tert~butyîimidazolidine. 24hÏone (2=S) ............. 61
................... Preparation of 1.3.D i. tert-butylimidazole-2-thione (1 =S) 62
...................... Preparation of 13-Di- tert-butylimidazole-2-one (1 =O) 63
Preparation of 1.3~Di~tert~butylimidazolidine~ 2.one (2=0) ................ 64
Preparation of 1.3~Di4ert~butylimida~olidine~2~thione~S. S-dioxide
.......................................................... ....................................... (2-SQ) .. 66
Preparation of 1.3.Di.tert. butylimidazolidine (2-Hz) ........................... 66
Preparation of 1. 3.Diphenylimidazolidine (2Ph-H2) ........................... 67
Preparation of 1. 3=Dimethylimidazolidine (2Me.Hz) ........................ 68
Preparation of 1.3-Di-tert-butyl-3,4,5,6-tetrahydropyrimidine
(3-H2) ............................................ - . . . . . . . . . . . ....- 69
Prepamtkn of 1 ,3-Di-terC-butylimidazolium Chloride ([l -H][CI])........ 70
Preparation of 1,3-Di-tert-butylimidazolidinium Chloride (12-H][CII) .. 7 1
Oxidation of 1,3-Di-tee-butylimidazolidinium Chloride with CuC12 ... 73
Preparation of 1,3-Di-tert-butylirnidazolidinium Bromide (12-H][Br]).. 74
Preparation of 1,3-Di-tert-butylimidazolidinium lodide ([2-HJ[l]) ......... 75
Preparation of 1,3-Diphenylimidazolidinium Brornide ([2Ph-HI[Br]). . 76
Preparation of 1.3-Dimethylimidazolidinium Brornide ([2Me-H][Br]) . 77
Preparation of 1,3-Di-tefi-butyl-3,4,5,6-tetrahydropyrimidinium
Bromide ([3-H]prJ). . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . .. . . . . . . . . . . - . . . . . . . . . . . . . 7 8
Preparation of 1.4-Di-tert-butyl-4-fomyl-l,4-diaza-but-1 -ene (4). ... 79
Preparation of NFormyl-N, N'di-tert-butyi-ethylenediamine (5) .... ... 79
Preparation of 1,3-di-tert-butyl-4,5-bis-deutero-imidazole-2-
yiidene (1 -D2) ................................................................................ 80
Preparation of 1,3,5-Tri-tert-butyI11,3,5-triazacyclohexane
(tBu3TAC). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - . . . 8 1
Dissociation of tBu3TAC into tertautylimine.. . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Synthesis of 1,3,5-Tri-phenyi-l,3,5-triazacyclohexane
(P h3TAC). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3
Synthesis of 1,3,5-Tri-methyl-l,3,5-triazacyclohexane
(Me3TAC) ................................................... ....................... 84
Synthesis of 1,3,5-Tri-terf-butyl-l,3,5-triazacyclohexyl Carbenium
Chioride (~Bu3TAC][CI]) ................................................................... 85
Synthesis of 1,3,5-Tri-tert-butyl-l,3,5-triazacyclohexyl Carbenium
Bromide (pBu3TAC][Br]). . . . . . . . . .. . .... . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . 86 S ynthesis of S ynthesis of 1,3,5-Trimethyl-l , 3,s-triazacyclohexyl
Carbenium Bromide ([Me3TAC][Br]). . . . . . . . . . . . .. . . .. . . . . . - . . . - - . . . . . . . . . . . . . . . 8 8
Attempted Synthesis of 1,3,5-Tri-tert-butyC1,3,5-triazacyclohexyl
Triscarbenium Bromide ([tBu3TAC][Br3]). . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 9 Attempted Synthesis of 1,3,5-Tri-fert-butyl-1,3,5-triazacyclohexyl
Tik-carbeniurn Chloride (PBu3TACI[Cl3]) ...... ..... ... .--. - --. - - - . . - ......... 90 Attempted Preparation of 1,3,5-Tri-te@-butyl-1,3,5-
triazacyclohexane-2-yiidene (9). . . . . . . . . . . . . . . . .. . . . . .. . -.. . -. . - . . . . . . . . . . . . . . . . 9 1
Attempted Preparation of 1,3,5-Tri-te@-butyl-1,3,5-
triazacyclohexane-2-thione (StBu3TAC). . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 Preparation of Copper Dichlonde / 1,3,5-Tri-tert-butyl-l,3,5-
triazacyclohexane Adduct (tBu3TAC*CuCI2) ................ . . . . . . ... . . 93
References ............................. .. ................................................................... 94
Appendix 1 - Supplementary Crystallographic Data for X-ray Swturai
Detemination of [2-H][CI] ....................................................................................... 1 03
Appendix II - Supplementary Crystallographic Data for X-ray Structural
Detemination of ([Cu4C18]4 Ciuster ...... ......--..-mm .-.-..-.---. .- ......... . - . . . 1 1 1
Appendix III - Supplementary Crystallographic Data for X-ray Structural
Detemination of (tBu3TAC)CuCI2 ..... ... . ..... ...... . . - . - - - - . - - . - - - - .-.-..-. . 1 1 9
Chapter 1 : Introduction
1.1 Carbenes
A carbene is a neutraJ rnolecule which features a divalent carbon with only six
electrons in its valence shell. The desire to prepare isolable carbenes can be traced back to
the early nineteenth century, when the quadrivalency of carbon had not yet been
established. Many chemists including Dumas (1 835) [l a] and Nef (1 895) [1 b], embarked n
a bold attempt to synthesize methylene, the simplest carbene (CH*), through the
dehydration of methanof. During this period, it appeared that the fascination with carbenes
evolved into an obsession for many chemists based on ernotional, rather than empirical
grounds.
Thereafter, the evolved into the more sophisticated level of highly reactive
divalent carbon intemediates, a concept that dates back to the early 1950s; more
precisely, to the eariy kinetic investigations of Hine who postulated the interrnediacy of
dichlorocarbene (CC[*) in the hydrolysis of chloroform (scheme 1 -1 ) [2].
CHCI3 + OH- - fast - C C I 3 + H20
O H , fast CC12 CO + HC02-
H20
Scheme 1.1. Base catalyzed hydrolysis of chloroform.
Since then, a substantial number of carbenes have been observed in frozen
matrices and investigated spectroscopically [3]. They have been subject to numerous
computational studies, most of them now obsolete as a result of better expenmental, as
well as computational data. However, the highly reactive nature of carbenes made the goal
of isolating them seem unattainable.
During the eady 1960s Wanzlick et al. recognized that the electron ri& imidazole
nucleus would be capable of stabilizing a carbene centre at the 2-position between the two
nitrogen atoms [4d]. His fundamental work provided a valuable foundation that led to the
3
isolation of the fi& stable d iamindene. This goal was finally reaiized in 1991 when
Arduengo et al. described the synthesis and çtnichire of the aromatic 1,3-di-
adamanty!imidazole-2-ylidene; a cdouiiess, crystailine and themaliy stable solid obtained
through the deprotonation of 1,3-di-adamantyl-imidazolium chloride with sodium hydride n
the presence of catafytic amounts of DMSO (scheme 1.2) [5]. In the last decade, wr
understanding of carbene chemistry has increased dramatically with the isolation of N-
heterocyclic diaminocarbenes [6] and advances in the synthesis of persistent triplet
NaH. ïDMSO +-* THF, -NaCl. -A2 I r
Arduengo (1 991 )
Ad= 1 -AdamanVI
[i Ad-HICI 1 Ad
Scheme 1.2. Synthesis of the first stabfe N-heterocyclic carbene.
1.2 Origins of Diaminocarbene Chemistry
We witnessed the introduction of carbenes into inorganic chemistry in 1964 with the
synthesis of 1.2-A (figure 1.1 ), the first authenticated metal-carbene complex by E. O.
Fischer and CO-workers [8]; a compound belonging to a daçç of reagents with a steadily
increasing number of applications in carbon-cabon bond formation [9].
1.2-A 1.2-B
Figure 1 .l. Notable carbene-metal complexes.
4
Shortly after, 0fele [l O] and Wandick, in 1968, [a] independently synthesized
compounds 1.2-B and 1 -2-C, respectively (figure 1.1). These carbene complexes
featured diaminocarbenes attached as ligands to metal centres and were obtained b y
deprotonating imidazolium saltç. (çcheme 1 -3).
Scheme 1.3. Formation of N-heterocyclk carbene complexes.
Although compounds 1.2-8 and 1 - 2 4 were highly unuçual at that time, it took
several years for these two reports to receive the recognition they desewed.
1 -2.1 Wanzlick's Contributions
Wanzlick paved the way toward the isolation of the first stable carbene, with hi
attempts to synthesize imidazole-2-ylidenes 1 and imidazolidin-2-ylidenes II (figure 1 -2).
Figure 1.2. Imidazole- and imidazolidin-2-ylidene.
Wanzlick studies focused primarily on carbenes of type II. He attempted the
synthesis of N,N%liphenyl-imidazolidin-2-ylidene 2Ph through the thermal elimination of
chlorofom [4c]. But isolated only the carbene dimer 2'Ph. No unarnbiguous proof for the
presence of a carbene was provided (scheme 1.4). However, the unusual reactivity of
2'Ph led Wanrlick to the conclusion that it exists in equilibrium with the carbene 2Ph.
Scheme 1.4. Synthesis of enetetramines.
The lack of explicit evidence for this equilibrium prompted a study by former group
member Ken Hatano, in which mixtures of enetetramines were investigated by muitinudear
NM R studies (1 H, 3C) at elevated temperatures in sealed tubes [I 1 a]. The rapid and
statistical formation of metathesis products of type AB has been interpreted by us and
others [II b] as evidence for this equilibrium (scheme 1.5).
A B
Scheme 1 .S. Olefin metathesis.
In 1970, Wanzlick succeççfully demonstrated that imidazdium salts can b e
deprotonated by potassium terf-butoxide to afford the corresponding imidazole-2-
ylidenes, which in a most unfortunate tum of events were only trapped as metal complexes
but not isolated (scheme 1.6) 1121. Using the same reacüon conditions almost two decades
6
later, Arduengo synthesized and isolated the first stable carbene, 1,3-di-
adamantylimidazoIe-2-yiidene [5], which led to a resuvection of the interest in the area of low
valent main group compounds.
Scheme 1.6. Deprotonation of Imidazoliurn SaIt.
1.3 Electronic Structure of Carbenes
Carbenes can be either linear or bent, each geometry corresponding to a varying
degree of s, p hybridization The linear geometry implies an sp-hybridized carbene center
with two nonbonding degenerate orbitals (pz and py)- Bending the molecule breaks this
degeneracy and the carbon atom adopts an sp2-type hybridization: the pz obita1 remains
almost unchangeci (ii is usually called p,), while the orbital that starts as pure py orbital is
stabilized since it acquires some s character (it is therefore d l e d o) (figure 1.3) [6c]
Iinear
1 Triplet carbene
SP
- O
bent
Figure 1.3. Electronic structure of carbenes.
Singlet carbene
sp2
The linear geometry is an extreme case and most carbenes are bent, hence ttieir
frontier orbitals are systematically calleci o and p,. Understanding the ground-state
7
multiplicity of carbenes s necesçary ri order to gain insight into their reacüvky. The singlet
cahene features a filled and a vacant orbital, hence, it should possess sorne arnbiphilic
charader. As sextet species, carbenes are highiy electron deficient, yet, singlet carbenes
possess a lone pair of electrons similar to that of cahions. Triplet carbenes possess two
singly filled orbitals and may be considered as diradicals, although the interaction of two
unpaired electrons on the same carbon atom gives rise to some peculiarities [6c, 131.
Table 1.1. Simple intermediates in the chemistry of carbon compounds.
Number of Number of Species covalent bonds valence electrons
Carbanions 3 8
Radicals
Carbenium ions
Carbenes 2 6
The carbene ground-state muitiplicity is related to the energy gap between the o
and p, orbitals. A large o-p, separation favours the singlet state; Hoffmann determined that
a value of at least 2 eV is necessary to impose a singlet ground state, whereas a value
below 1.5 eV leads to a triplet state [14].
1.3.1 Influence of Substituents on the Electronic Structure of Carbenes
The magnitude of the CF-p, separation is infiuenced by the nature of the substituents
on the carbene carbon and it can analyzed in ternis of electronic and steric effects.
1.3.2 Electronic Effects
Electronic effects can be divided into inductive and mesomeric effects. The
importance of Inductive effects for the stabilization of carbenes was recognized early [15]. L
is now well established that O-withdrawing substituents favour the singlet state. They
inductively stabilize the o orbital by increasing its s charader but leave the px orbital
relatively unperhirbed; this increases the magnitude of the o-p, separation. Consequently,
o-donating substituents reduce the a-px gap and favour the triplet state. Inductive effects
dictate the ground state multiplicity of carbenes such as CH2 or CLi2.
Mesomeric effects consist of interactions of the carbon p orbitals with the appropriate
orbitals (p or x ) of substituents and when present, they dominate over inductive effects.
Substituents that interact with the carbene carbon can be categorized as either n-acceptors
of n-donors. When both substituents are n-donors (-F, -CI, -Br, -OR, -NR2) the carbene is
predicted to have a singlet ground-state as is the case with the stable diaminocarbenes.
6 +
Figure 1 -4. Electronic effects of the substituents of diaminocarbenes.
The energy of the vacant pK orbital is increased by the symmetric combination with
the nitrogens' lone pairs, but the carbenic o otbital remains unchanged (figure 1.4). This
interaction increases the G-p, gap hence favours the singlet ground-state. The mesomeric
interaction should lead to a considerabte shortening of the carbon-nitrogen bonds. This has
been observed for the single crystal X-ray structures of stable amido and diaminocarbenes.
The same mesomeric effects apply to describe dialkoxy- and dihalocarbenes [6c].
1.3.3 Steric Effects
The effect of stericdly dernanding substituents on the stability of carbenes is two
fold. In the absence of any notable electronic effects, sterics can determine the ground-state
multipiicity of carbenes.
Figure 1 .S. Steric effects of the substituents of carbenes.
The triplet state is favoured when the a and p, orbitals are degenerate, which
implies a linear geometry. Moreover, increasing the steric bulk of the substituents will
broaden the angle about the carbene centre. Dimethylcarbene has a singlet ground-state
and an angle of 11 1 O about the catbene centre [16]. Di-terf-butylcarbene [1/1 and di-
adarnantylcarbene 1181 possess triplet groundstates with the angles about the carbene
centres being 143" and 152O, respectively. The magnitude of these angles has been
inferred from electron spin resonance (ESR) rneasurernents (figure 1.5).
The second effect of bulky substituents is kinetic only: They prevent the dimerkation
(diaminocarbenes) or polymen'zation (alkyl carbenes) of the carbene.
1.4 Synthesis of Stable Carbenes
Arduengo obtained 1,3-di-adamantyiirnidazole-2-ylidene 1 Ad as a wlourless,
crysdline solid by deprotonation of 1,3-di-adamantylimidazolium chloride with NaH. In
order to obtain reasonable rates for the deprotonation, catalytic amounts of DMSO were
1 O
added, since the sodium hydnde, and m some cases the imidazolium çalts, are insoluble n
THF (scheme 1.2) [a. Altematively, stoichiornetric arnounts of rrBuLi or LDA have been
employed by us as deprotonating bases, wioi satisfying results 1191. Hemnann et aL
showed that deprotonation oaxirç faster m liquid arnmonia as a solvant (homogeneous
phase). This method is applicable for a wide range of different carbenes, including nitrogen-,
oxygen-containing carbenes, and chiral carbenes [20]
Kuhn et al. [21] devised a method to obtain alkyl-substihited imidazole-2-ylidenes,
which relied primarily on the reduction of imidazole-2-thiones with potassium metal; a
methodology that was used to obtain the previously unknown imidazolidin-2-thiones in wr
group (scheme 7) [22].
Denk 1997
'Èu 2
Scheme 1.7. Reduction of imidazole- and imidazolidin-2-thione.
Compound 1.4-8 was the firçt commercially available carbene and was obtained
quantitatively from the corresponding 5-methoxy-l,3,4-triphenyl-4,5-dihydro-1 H-1,2,4-
triazole by themai elimination of rnethanol under reduced pressure (0.1 mbar) (scheme
1.8) [23]. The 1,l elimination of rnethanol is a less genera! route and takeç advantage of the
relative lack of volatility of the Nheterocyclic carbene, rendered so by the presence of three
phenyl substituents on the triazole ring and its lack of syrnmetry.
Scheme 1.8. Synthesis of 5-methoxy-l,3,4-triphenyl4,5-dihydro-1 H-l,2,4-triazole.
Following these synthetic approaches, a number of stable carbenes have been
isolated induding: imidazole-2-ylidenes (1), imidazolidin-2-ylidenes (Il), tetrahydropyrimid-
2-ylidenes (III), 1,2,4-triazole-5-ylidenes (IV), 1,3-thiazoie-2-ylidenes (V), as well as
acyclic diaminocarbenes (VI), aminoxycarbenes (VI 1) and aminothiocarbenes (VI II) (figure
1.6).
Figure 1.6. Stable carbenes.
1.5 Structure of Stable Carbenes
All stable carbenes isolated to date bear two n donating substituents with at least
one of these being a nitrogen atom. This is due to the efficient stabilizing effects offered b y
the nitrogen atorns which is by far superior to that offered by oxygen atoms. This has been
proven experimentally; indeed, bis(dimethylamino)carbene, Me2N-C-NMe2, has been
characterized by NMR spectroscopy [24a] whereas dimethoxycarbene, MeO-C-OMe,
has only been characteized in frozen matrices due to its relative instability [25].
The carbene carbon resonates at rather low fields in the 1% NMR (200 - 300 ppm)
compared to the cationic precursors, where the 1% NMR of the N-C-N carbon appears
between 130 - 180 pprn. More precisely, the N-C-N carbon in carbenes of type i
12
resonate in the range of 205 - 220 pprn in the 1% NMR, which is 15 -25 ppm upfield from
the resmance of the N-C-N carbon of type II carbenes.
The structures of many carbenes have been elucidated by X-ray diffraction studies.
The bond angles observed at the N-C-N fragment are between 100 - 11 0°, which is h
very good agreement with that expected for singlet carbenes bearing r donor substituents,
Le., F-C-F = 102" [26]. The larger N-C-N angle found m the acydi:
bis(diisopropylamino)carbene (121 .O0) has been attributed to the increased steric demand
around the carbene carbon [24b]. The nitrogen atoms in diaminocarbenes are aiways planar
or close to planar and the N-C bond lengths are rather short (1 -32 - 1 -37 A), whi i indicates
that they have strong double bond character.
As shown in section 1.3.2 and 1.3.3, carbene centres are highly sensitive to
electronic interactions with their substituents. The nature of the stabilization stems from the
structure of the molecules as well as their reactivity. While carbenes of type 1 do not require
steflcally demanding substituents for their stabilization. Denk et al. has shown [22] that stecic
interactions in carbenes of type II play a crucial role in their isolation (scheme 1.9).
II
R = Mes R = 'BU
Scheme 1.9. Dirnerization of imidazolidin-2-yiidenes.
The 6n aromatic character of diaminocarbenes of type I has been controversial and it
gained credibility in 1996 when Apeloig [27a] and Frenking [27b] independently
investigated carbenes of type I according to the following crtterk structural, themodynamic,
ionization potentials, magnetic properties and n: populations. The ammatic charader of type
I carbenes was also confitmeci by inner-shell electron energy Ioss spectroscopy, the work
13
of Denk et a/. [27c]. Although the aromaticrty is l e s pronounced than in the conesponding
irnidazolium çalt precursors, it brings an additional stabilizing effect that has peculiar effects n
the reactivity of carbenes of type 1.
1.6 Diaminocarbene Congeners
Shortly after the isolation of the fnçt stable diaminocarbene by Arduengo et a/. [5],
the stable germylenes with the çarne substitution pattern were obtained by Hemnann and
CO-workerç, through the reductive dehalogenation of a dihalo-diaminogermanium
compounds and through the reaction of the conesponding lithiated di-substituted-
diazadiene or ethylenediamine ligands with germanium dichloride-1,4ilioxane [28].
The preparation and characterization of the stable or margnially stable silylenes, IÇi
and IlSi, was accomplished by Denk et al. (figure 1.7) [29], through the reductive
dehalogenation of the dihalo-diarninosilicon compounds with alkali metals.
Other stable diaminogemylenes IXGe, -stannylenes IXSn, and -plumbylenes
lXPb have been known for a longer tirne and have since been shown to possess an
extensive chemistry (figure 1.7) [30]. A correspondingly substituted silylene has now also
been detected, although it is only stable in a matrix up to 77 K [31].
1 !Si IGe If IlSi IlGe lXGe lXSn lXPb
E = C, Si, Ge E = Ge, Sn, Pb
Figure 1.7. Silicon, germanium, tin and lead analogues of stable carbenes.
As in the case of diaminocarbenes, the heavier analogues feature a lone pair of
electrons on the nitrogen atoms, or on other donor atoms as well, which cari either allow
14
delocalkation, as in the five rnember rings ISi and IGe, or as m the saturated systems cai
stabilize the electron deficient center through rc-interactions. As a result, the tendency of
these species to dimenze is quite low. This is in contrast to the behaviour of dialkyl, diaryl or
disilyl derivatives of silicon, germanium, t h and lead. These species do not experience rc-
interactions and dimerize to afford the homonuclear double-bond systems of these
elements [32].
The chernistry of the heavier analogues of stable carbenes is an area of airrent
interest. This is obvious from the number of annual publications in this field as well as the
growing number of groups involved in this research.
In a further extension of this chemistry, the existence of isoelectronic cationic species
containing N+, P+, and As+ [33] centres have also been considered and investigated by US
and others. The anionic counterparts with low-valent group 13 dements are still unknown for
B and AI-, but they are known for Ga- 1341.
1.7 Starting Materials for the Synthesis of Diaminocarbene
In addition to other applications, thioureas and related catbenium cations are useful
-ng materials for the preparation of stable carbenes. The main synthetic routes leading
to carbenes include: (1) deprotonation of diarninocarbeniurn salis with strong bases; and (2)
the reduction of thioureas with alkali rnetals (scheme 1.1 0).
R2N 0 R 2'Y s-H - /
C-- F = S R2N R2N
Deprotonation Reduction
Scheme 1.1 0. Synthesis of stable diaminocarbenes.
1.7.1 Carbenium Cations
Most of the research on stable diaminocarbenes has been conducteci using the
unsaturated imidazole-2-ylidenes 1, mainly because of the ease with midi the çtarting
materials Nsubstituted irnidazolium salts are obtained. The latter are synthesized through a
one-step process patented by DuPont (scheme 1.1 1) 1351.
Scheme 1.1 1. Synthesis of substituted imidazolium cations-
Research on saturated imidazolidin-2-ylidenes II has not been as widely pursued.
This may be due to a ladc of good methods for the synthesis of their precurçors. For
example, there are only three published procedures for the synthesis of irnidazolidinium
salts and due to their low yields, they are subject to improvement [36, 371.
NH HX, A + HC(OEt)3 .--
T yields 36 % - 99 O h
(GYH (
R nv'
R [ZR-HID(1, n = 1 [3R-H][>CI, n = 2
Scheme 1.12. Synthesis of imidazolidinium salts: reaction of orthoesters with MN'-dialkyl-a,*
alkanediamine [371.
Saba and co-workers [37l found that the reaction of orthoesters with N, N'dialkyl-a,o
alkanediamine, in the presence of ammonium tetrafluoroborate or ammonium
hexafluorophosphate, affords the corresponding imidazolidinium, tetrahydropyrimidinium
16
and tetrahydro-l,3-diazepinium cations m good to excellent yields (76 - 99 %) for ail R
groups, except for the bulky tBu (n = 1). For the case of the tert-butyl group a 36 % yield is
obtained (scheme 1 -1 2).
1.7.2 lonic Liquids
Apart from being valuable starting materiais for the synthesis of stable carbenes,
some diarninocatbenium saits have gained notorîety as "ionic liquids". They act as both
cataiysts and solvents for a broad range of chemical processes. lonic liquids possess a
wide spectnim of physical and chemical properties, much larger than that of dassicai organic
or inorganic solvents çuch as water [38a]. They are liquid at ambient temperatures and
typically have a fluid range of ca. 300 OC. This compares favourably with the 100 OC range
for water or 44 OC range for arnmonia Moreover, ionic liquids are proving to be suitable
replacements for the toxic, flammable and volatile organic solvents that are wrrentiy used h
Iiquid-liquid separation processes.
lonic liquids posses a very attractive combination of properties [38c, dJ:
They do not emit vapours and can be easily recycled.
They are undemanding and inexpensive to manufacture.
They are good solvents for many inorganic and organic compounds.
They are highly polar yet non-coordinating.
They are imiscible with a number of organic solvents and provide a polar non-aqueous
alternative for two-phase systems.
1 -Ethyl-3-methylimidazolium aluminum chioride, [emimJCI-[AiCls] (1.7.2-A, figure
1.8), is the typical ionic liquid with a liquid range from -100 OC to 200 OC, depending on the
molar ratio of [emimJCI and AIC13. The 1 :1 mixture melts at 6 OC. The lowest melting point
(-96 OC) is observed for a mixture containing 35% [emimJCI and 65% [AICI31 [38b].
Figure 1.8. 1 -Ethyl-3-methyl-imidazolium alurninum chloride.
It is important to note that there is currently no reliable way to predict whether or not a
carbenium sait will be a Iiquid at room temperature and as a consequence the identification
of new ionic liquids becomes a rnatter of trial and error.
1.7.3 Thioureas
Thioureas are used in the pharma~e~cal sector, in various technical applications, and
in the synthesis of heterocycles [39]. In the context of Our research, they have proven to b e
good starting materials for diaminocarbenes [40].
A number of diierent methods are available for the synthesis of thioureas bearing
substituents on nitrogen [41]. Thiourea itself is not a good starting materiai for the synthesis
of its N-substituted derivatives because electrophiles react witti the suhr in most cases. A
closer examination of the synthetic repertoire reveals serious deficiencies.
Existing rnethods typically use the highly toxic, and extremely flarnmable carbon
disulfide or the toxic and expensive isothiocyanates R-N=C=S as smng materiais, not to
mention that the standard synthesis from isothiocyanates and amines is restricted to the
synthesis of thioureas with the general formula RI-NH-C(S)-NR*R3. In addition, the
methods described in the literature are generally incompatible with bulky substituents on the
nitrogen atoms. For example, reaction of N, N'-dialkyl-ethylenediamines with c a h n
disulfide and iodine in pyridine, as reaction medium, bears the desired cydic Nsubstituted
thioureas, but the product yields decrease drarnaticaliy as the steric bulk of the R substituent
on the nitrogen atom increases (scheme 1.1 3).
- - 2R=S, R = Me, Et, ' ~ r 'BU( 20 2=S, R = 'BU
ckH Pyridine, CS2 Me
la A r)= Et
Scheme 1.1 3. Synthesis of imidarolidin-2-thiones.
70
60
Shilpi Gupta, a former member of wr group, has investigated a new methodology
1" A ' ~ r 1 50
for obtaining thioureas from arninals. Cyclic thioureas can now be obtained by reacting
elemental suifur, SB, with the componding cyclic aminals, e.g. Nsubstituted irnidazolidines
at 1 50-1 70 OC in sealed stainless steel containers (scheme 1.14).
The nature of the yields is intimately tied to that of the R substituents. Furthemiore,
the yields of the thioureas decrease as the size of the R substituent increases. In addition,
when R is tBu, the major isolated reacüon product is the isothiocyanate 1,3-di-tert-
butylimidazolidinium salt (scheme 1 -14) [Ml.
[ZR-H][SCN] 2R-H2 2R=S
Scherne 1.1 4. Dehydrosulfurization of aminals.
R
Me
Et
'Pr Ph
'BU
1.8 Research Objectives
The chernistry of diaminocarbenes was for a long time limited to transition metai
complexes. The isolation of stable carbene in 1991 sparked a renaissance m the
coordination chemistry of these compounds. Moreover, some diaminocarbene complexes
are remarkably stable and have appeared as promising catalysts in many organic reacn'ons,
induding; Hec k-type reactions [42a, b], h ydrogenation [42c], h ydrofo rmy lation [6c],
hydrosilation [42d] and olefin metathesis [42e]. Carbenes have long been compared to
phosphines and phosphites in their coordination to metals and are anticipateci to replace
these ligands in some cataiyücally important reactions.
The goal of this study is to explore the reactivity of stable carbenes and to find new
methodologies for their synthesis. An approach that has been attractive to us, due to itç
inherent sirnplicity, is the dehydrogenation of amin&. This report investigates the reactions
of aminals with oxidizing agents including: Nchlorosuccinimide (N CS), Nbromosuccinimide
(NBS), carbon tetrachloride (CCl4), c a b n tetrabromide (CBr4), iodine and copper
dichloride (CuC12).
Scheme 1.1 S. Oxidation of arninals.
Oxidation of arninals was also investigated as a synthetic approach to the hitherto
u n b w n tris-carbenes 9R. In this context, the em plo yment of 1,3,5-triazacyclohexanes
R3TAC (R = Alkyl) as starting materials offers several advantages. In addition to being
obtained from inexpensive and readily available precursors, R3TAC possess the required
structurai features that makes them ideal templates for tris-carbenes 9R. R3TAC possess
an extensive chemistry w], however for more than 20 years most investigation focused
20
primady on the confornational effects caused by a combination of steric effects and
repulsions between non-bonding electrons on the heteroatoms. 1431
9R S3R3TAC
Scheme 1.1 6. Proposed synthesis for tris-carbenes from tris-thioureas.
As of yet, two synthetic routes using R3TAC have been envisaged. The first
approach focuses on the reducüon of tris-thioureas (scheme 1.16) while the second
involves deprotonation of tris-carbenium cations (scheme 1.17). The synthesis of tris-
thiourea precursors has previously been investigated by our group [40] as an extension of
the dehydrosulfurization of aminals [40] (section 1 J.2). This method is sîill being refined as
an altemative to the existing routes for the synthesis of tris-thioureas (S&TAC), which are
laborious. The existing routes normally require the use of specialized cataiysts as well as
pressures exceeding 1 000 MPa [44].
Attempts to prepare S3R3TAC have included the solvent-free treatment of
RITAC (R = Me. tBu) with elemental suMir in ~wagelok@ stainless steel bombs, ab
temperatures in the range of 140-160 OC and periods exceeding 10 hours. Although no
S3R3TAC or S2R3TAC have been detected thus far, GC/MS experiments indicate the
presence of SR3TAC along with open chain thioureas.
base - Scheme 1.17. Proposed synthetic approach to tris-carbenes from tris carbenium salts.
The synthetic method hereby discussed for the synthesis of ttis-carbenes 9R
focuses on the second approach, the formation of tris-carbenium cations [R3TAC]3+ from
RaTAC, to use as potential precursors. Conceptually, [R3TAC]3+ will be synthesized b y
reacting R3TAC with suitable oxidizing agents, eioier as a one step or multi-step process.
The transformation will employ NCS, NBS, CCh, CBr4 and CG12 as oxidants.
Chapter 2: Results and Discussion
2.1 Oxidation of Diaminocarbenes
Since their discovery in 1991, stable carbenes have been described as air sensitive
compounds. The exact reason for this sensitivity was unknown. It seemed likely that
diaminocarbenes would react readily with oxygen to yield the respective cydic ureas. Such
expectation found precedence in the behaviour of enetetramines ("masked carbenes") with
oxygen (Scheme 2.1), as well as in the behaviour of thplet carbenes [45].
Scheme 2.1. Oxidation of carbenes by triplet oxygen.
During the course of this study, we found that benzene soIutions of stable carbenes
1 and 2 are not only inert towards oxygen even after prolonged exposure (Scheme 2.1),
but also unreactive towards a number of oxidizing agents. Carbenes 1 and 2 do not react
with CuO, Cu20 or HgO, despite exposure to extended periods of heating. Evidence for
this ia& of reactivity comes from 'H and 1% NMR spectra of the reaction mixtures. The
NMR spectra demonstrate the presence of 1 and 2 and the absence of any respective
byproducts. On the other hand, dean oxidation to the respective ureas 1=0 and 2=0 is
immediately observed when nitric oxide (NO) is bubbled through cooled benzene
solutions (5 OC) of stable carbenes 1 and 2. The nature of the side products is under
investigation.
thf
2.2 eq. CI-COOMe rH n-hexane LY-COOMe n-hexane
'BU 'BU
Scheme 2.2. Synthesis of cyclic ureas.
The imidazole-2-one 1 =O has been previously obtained by carbonylation of 1,4-di-
te*butyI-1,4-dia~a-1~3-diene with Fe(C0)5 or Fe2(C0)9 [46]. However, the reaction
gives a rather complex product mixture, and 1 =O was only obtained afîer chromatographie
separation in an unspecified yield. Vrieze et al. [471 obtained 1 =O in an analogous fashion
by using only catdytic amounts of Fe2(C0)9 and high pressures of CO [471, but isolation
of 1=0 still required HPLC separation [471. In response to this, we developed a high yield
synthesis for 1=0 that enables us to avoid lengthy separation procedures. It was found that
reduction of the easily accessible 1,4-di-tert-butyl-l,4-diaza-1,3-diene L', with 2 equivalents
of lithium, and subsequent reaction with methyi chloroformate affords, in good yield, 1 =O as
the only product (Scheme 2.2).
The saturated imidazolidine-2-one 2=0 was obtained via the reactÏon of the dilithio
salt of N,Nidi-tert-butyl-ethylenediamine L and methyl chloroformate. Use of the dilithio çalt
is necessary because the reaction of the free amine wiai rnethyl chloroformate leads to the
biscarbamic acid ester L(COOMe)2.
2.2 "Air Sensitivity" of Diaminocarbenes
The deterioradion of the stable diarnino carbenes 1 and 2 in air is not due to
oxidation, but to hydrolysis. Although both carbenes are ultimately hydrolyzed to the ring
opened products 4 and 5 (Figure 2.1 ), there is a remarkable diierence in their reactwity
towards water. While 2 is instantly hydrolyzed by moist THF, or by bief exposure to air,
hydrolysis of the aromatidly stabilized carbene 1 m solution requires days to become
noticeable and months to be complete. 5 had been characterized previously through single
crystal X-ray crystallography by former group member Shilpi Gupta 1401.
'Bu I
'Bu I
AH c N ~ o 1 'Bu
5
Figure 2.1. Carbene hydrolysis products.
The hydrolysis of 1 and 2 can, in principle, proceed through a polar, stepwise
mechanism (attack of H+ or OH- as initiai step) or as an insertion redan. In the case of the
conveniently slow hydrolysis of 1, the rate of hydrolysis was not noticeably accelerated b y
the addition of dilute hydrochloric acid (HCI) or aqueous arnmonia (NH3). Addition of HCI
leads to the immediate precipitation of the imidazolium salt [l-H][CI] which is stable
towards hydrolysis under the conditions of its formation. The addition of NH3 does not
accelerate this hydrolysis process. it is therefore unlikeiy that protonation of the carbene, or
nudeophilic attadc by OH-, are rate determining steps of the hydrolysis. Most likely, the
reaction with water proceeds via insertion of the carbene c a h n into the OH bond (Scheme
2.3).
Scheme 2.3. Insertion of carbene into O-H water bond as a synchronous process.
2.3 Oxophilicity of Diaminocarbenes
The thermodynamic potential of cornpounds to serve as deoxygenating agents
(also referred to as "oxophilicrty"), has been reviewed comprehensively by Holm and
Donahue 1481. Their review has anal yzed experimental data scattered throug hout the
literature to estabiish a thermodynarnic d e of increasing oxophilicity for subvalent
compounds X. In the gas phase, the limits of the oxophilicity scale are defined by the pairs
o2 / 0 3 (Afl298.15 = +34 kcal / mol) [48] and Me6Si2 / MesSi-O-SiMe3 (AH298.15 = -99.0
I d / mol) 1481. The only divalent carbon compound listed m their review is carbon
monoxide (CO) vvhich is only a moderately strong deoxygenating agent (di298.15 =
-67.6 kcal / mol, for the pair CO / CO2) [48].
X 4- 1/202 - XO
Scheme 2.4. Oxidation of subvalent cornpounds X.
In principle, stable carbenes like 1 or 2 should have a high affinity towards oxygen.
However, as noted in section 2.1 , the reacüon towards oxygen is kinetically hindered. W e
were interested to study the thermodynamic driving force behind the reacüon (Çcheme 2.4)
of oxygen with stable carbenes 1 and 2, using their respective mode1 compounds 1 H and
2H, where R = H. The reactions 1 H + 1 /2 0 2 -> 1 H=O and 2H + 1 /2 0 2 -> 2H=0 were
investigated, and the data was compared to experimental oxophilicity values gathered b y
R. Holm and J. P. Donahue (Table 2.1) [48].
27
Table 2.1. Experimental [48] and computational (IH, 2H) enthalpies of oxygen transfer reactions in the
gas phase.
X XO AH298.15
O2 O3 t34.1
C5H5N C5H5NO -1 2.6
NO NO2 -1 3.6
Me2S Me2S=O -27.1
CO Co2 -67.6
[CNI- [OC NI- -70.9 a
Me3P Me3PO -79.7
1 H 1H=O -80.3 C
2 H 2 H = 0 -86.4 C
(Et0)3P (Et0)sPO -88.6
NbC13 C13NbO -93.8
Si2Me6 (MegSi)2O -99.0
Mg Mg0 -144.0 b Ca Ca0 -1 52.0 b
a In aq. solution; solid phase; this study.
The structures and energies of the model compounds were caiculated [49] at the
B3LYP/6-31 G*//B3LYP/6-31 G* level. The stnictures (not shown) are in excellent
agreement with those obtained experimentally. The final energies are comected by the
addion of zero point energies (ZPE) and, where indicated, thermal energies (298.15 K).
fhe vibratory energies were scaJed by 0.9804, the çcaling factor recommended for
B3LYP/6-31 G* calculations [50].
28
Table 2.2. Energies (in kcai mol-l) of the model compounds at the B3LYP/6-31 G'//B3LYP/6-31 G*
level. Converted into kcal morl with 1 Hartree = 627.51 kcal. Scaled zero point energies (ZPE*) were
obtained with the recommended [SOI scaling factor of 0.9804 (ZPE' = 0.9804 ZPE).
Eel ZPE Eth EO E298 .15 (298.1 5K) (Eei + ZPE*) ( € 0 + €th)
It is of obvious interest to establish the position of carbenes, and m particular stable
carbenes, on this scale. To avoid the errors resulting from the cornparison of open shell with
closed shell systems, the oxophiliciiy of model compounds 1 H (eq. a+c) and 2H (eq. b+c)
was established through isodesmic reactions wifh CO2. The cornputationally derived
reaction energies were then referenced to the experimental reaction enthalpy for the
oxidation of CO to CO2 [48].
Scheme 2.5. Determination of degree of oxophilicity for carbenes 1 H and 2H.
It is evident from the isodesmic reactions (Scheme 2.5) that the reactions of 1 H and
2H with 0 2 to yield the respective ureas are both strongly exothermic. The experimentally
observed stability of 1 and 2 towards 0 2 is therefore only kinetic. Thermodynamicaliy, the
carbenes 1H and 2H are stronger deoxygenating agents ttian carbon monoxide and
should accordingly be able to reduce Con. The oxophilicity of the aromatically stabilized
carbene (-80.3 kcall mol) 1H resembles that of ttirnethylphosphine (-79.7 kcal / mol), while
the non-aromatic 2H is about as oxophilic as (Et0)3P. Apart from triethylphosphite, only
30
two mdecular deoxygenating agents listed in Table 2.1 can rival the stable carbenes,
namely Me3Si-SiMe3 (Eo, = -99 kcal / mol) and NbC13 (Eox = -93.8 kcal / mol).
According to Table 2.1, metals like Mg or Ca should alço be capable of reducing the ureas
1 H=O and 2H=0 to the respective carbenes. However, attempts to obtain the respective
carbenes 1 or 2 from the ureas 1=0 and 2=0 m analogy to the successful redudion of
thioureas [22J have been unsuccesçful in Our hands [a].
2.4 Deuteriurn Labeling of 1 ,3-Di-ter&butylimidazole-2-ylidene
The cornputational data shown in section 2.3 indicates that the oxidation of 1 and 2 to
the respective ureas is in fact strongly exothemiic. The la& of reactiwty of 1 and 2 towards
oxygen donors seems to be kinetic only. For example, stable carbenes were first obtained
by deprotonating the respective imidazolium sait with NaH in tetrahydrofuran using cataiytic
amounts of dimethylsulfoxide at roorn temperature, without oxygen transfer [SI. In contrast,
non-stabilized carbenes react readily with DMSO to give the respective carbonyl
compounds and dimethylsulfide [51].
Scheme 2.6. Oxidation of non-stabilized carbene by DMSO.
To further investigate possible oxygen transfer between DMSO and stable
carbenes, we studied mixtures of DMSO-d~ and 1 through temperature dependent 'H
NMR. No oxygen tran,sfer was observed. Instead, the H NMR signais of the carbene
backbone (N-C(ti2)=C(H2)-N) decreased in intensity while the residuai DMSO peak
increased. The observed deutetium-hydrogen exchange (HID) proceeds readily at
ambient temperature.
31
The selective deuteration of the ring protons was readily verified by the presence of
the characteristic 1:1:1 deuterium triplet at 114.90 ppm [(150.9 MHz, C6D6); IJ(C,D} =
27.20 Hz] m the 13C NMR spectrum of carbene 1. In addition, the IR spectrum of the
deuterated carbene shows a strong broad band at 2309 cm-1 with a shoulder of almost the
sarne intensity at 231 8 cm-l, both assigned to the antisymmetnc and symmetric carbon-
deuterium stretches of the unsaturateci ring backbone, respectively. Final evidence for the
deuterium-hydrogen exchange was provided by electron impact m a s spectrometry data
which displayed the expected value of (rn/z) 182 for the deuterated carbene.
The deuterated carbene 1-02 can be isolated from the DMSO-ci6 solution b y
repeated extraction with hexanes. Dissolution of 1-D2 in DMSO showed that the
deute ration is readily reversibIe.
Scheme 2.7. Backbone deuteration of 1 by DMSO-d6.
The formation of 1-De from 1 suggests the reversible formation of an o-complex 8.
The formation of 8 is however counter intuitive. Protonation of the highly basic carbene
carbon atom to give 6 should be thermodynamically more favorable than protonation of the
backbone. We have therefore investigated the relative thermodynamic stability of the
different imidazole-2-ylidenes protonation products [52] through calculation of the mode1
cornpounds with R = H, 6H - 8H, to prove that in fact the protonation of the carbene carbon
is more favorable than other sites within the carbene structure.
At the B3PW91 / cc-pVDZ // E33PW91 / cc-pVDZ level [49], the structures 6H -
8H are stationary points on the hypersurface. The sequence of relative stabilities (Table
2.3) kcal / mol, added zero point vibrational energies ZPE) is 6H z 8H z 7H. This confirms
32
that the protonation of 1 at the olefinic carbon atoms (formation of 8H) is indeed
therrnodynamically unfavorable versus the formation the imidazolium cation 6H. The
observed H / D exchange reacüon must therefore be khetically favored with respect to
protonation of the carbene carbon atom or proceed through an entirely different mechanism.
6H 7H 8H 0.0 kcal +73.94 kcal +61.41 kcal
Figure 2.2. Relative electronic energies of 6H, 7H and 8H.
B3PW91 /cc-pVDZ//B3PW91 /cc-pVDZ level, T = O K.
Table 2.3. Electronic energies and (in brackets) zero point vibrational energies in kcal 1 mol for
protonated irnidazole-2-ylidenes 7H - 9H at different levels of theory. R = H.
E [kcai / mol] 6 H 7 H 8 H
Converted into kcal -rnol-l with 1 Hartree = 627.51 kcal.
In pnnciple, the imidazolium cation 6H could süll be an intemediate of the isotope
exchange reaction. However, the reacüon of the imidazolium saft [1 -H ][Cl] with DMSO-d6
did not lead to the exchange of the ring protons.
Scheme 2.8. HA3 Exchange of irnidazole-2-ylidenes via imidazolium cations.
The rapid H / D exchange of 1 may involve the participation of DMSO in the
transition state of the reacüon. However, replacement of DMSO-de as deuterium source
with D20 or CD30D did Iikewise lead to the rapid formation of 1-D2- This makes a specific
participation of the comterion (dimsyl, methoxy of hydroxy) unlikely.
2.5 Formation of a Diaminocarbene-S02 Adduct
Sulfenes R2C=S02 (thiocarbonyl-S.S-dioxides) have long been invoked as
reactive intermediates and can be regarded as sulfonyl analogues of ketenes [53a]. They
have only recently been diaracten'zed spectroscopically in the gas phase [53bI and n
cryogenic matrices [53c]. Their high reactivity usually precludes their isolation.
Sulfene Ketene
Figure 2.3. Sulfenes and ketenes.
Sulfenes are stabilized b y donor su bstituents on the carbon atorn. Thiourea-S,S-
dioxide, the only sulfene characterized by single crystai X-ray crystallography thus far, is
indeed of the type N2C=S02. The compound was described by E. de Berry Bamett n
1 91 0 [54] but recognized as thione-S,S-dioxide only after the compound was stnicturally
characterized in 1 962. [55]
34
The reaction of S02 with carbenes presents itself as a simple one-step approach to
sulfenes, but eariy studies dong this line were not parüwlarfy promising. The readion of
methylene (CH2) with S02 resulted in a broad spectrum of products [53c] and the reaction
of diphenylcarbene (CPh2) with SO2 was investigated m a frozen rnatrix by Sander et al.
The sulfene obtained could be detected by IR and Raman spectroscopy, however the
product decomposes readily above cryogenic temperatures [56].
Along simiiar lines, it has been reported [571 that the stable catbene, 1,3-di-
adamantylimidazole-2-ylidene 1 Ad reacts with SO2 to give a yellow, crystailine product,
reported as being a sulfene. The presumed sulfene was isolated and characterized by itç
melting range, elementai analysis, 1 H and 3C N M R spectra, IR and UV spectra and alço
by single crystal X-ray crystallography.
Scheme 2.9. Reported reaction of 1Ad with S02.
The authors indicate that a mixture of sulfene and carbene can be observed in the
1 H and '3C NMR spectrum in CDC13. Confrary to this report, it is unlikely that sud^
information could be obtained from an NMR spectnim carrieci out m such a solvent. It has
been observed in our laboratory, as well as others, that diaminocarbenes are reactive
towards chlorinated solvents. There are also unusual chemicai shifts reported sudi as -1 6.3
ppm in the 13C NMR assigned to the N-C-N carbon, as opposed to the Merature values
of 200 - 300 ppm (section 1.5). In addition, close analysis of the cryçtal data reveals that
the density reported of 1.21 gkm3 is significantly difFerent from the value of 1.46 gkm3
calculateci from the cell parameters and fonnula given [58]. Experiments conducted in our
laboratory by Dr. Ken Hatano did not show evidence for the formation of sulfene-like
products from the unsaturated 1,3-di-tert-butylimidazole-2-ylidene 1 and S02 gas.
Scheme 2.10. Reaction between 1 and S 0 2 .
We reasoned that carbenes 2 are not stabilized by aromaticity [22] and might
therefore be better candidates to give stable S02 adducts han arornatic carbenes sudi as
1. Hence, Dr. Hatano investigated the reaction of 2 with S 0 2 and found that ttiis carbene
reacts cleaniy to form a stable compound. The product 2-S02 was obtained as only
component of the reaction and was studied by single crystai X-ray crystallography and
muitinuclear NMR.
2 6 0 2 can be crystallized from n-hexane, is thermally stable up to 100 OC but
cannot be sublimed without decomposition. The compound is stable towards oxygen, but
easily hydrolyzed. Deoxygenation of the S02 adduct by the stable carbene 2 to give the
urea 2=0 waç ruied out by addition of authentic material to the crude reaction mixture.
Deoxygenation of the SO2 adduct to yield 2=S was aiso niled out by the addition of
triphenylphosphine to the pure compound.
Recent work on transient sulfenes, notably by the group of Sundermeyer [59], has
demonstrated substantiai variation in structure and reactivity. Depending on R, suifenes
have been described as sulfur(lV)ylides (a, a') or sulfuranes(Vl) (b) (Figure 2.4), thus we
wanted to distinguish between these bonding situations.
b c
Figure 2.4. Structural variation in transient sulfenes.
The long CS bond is a strong indication that 2-S02 could be described as a
carbene802 adduct c. This would be m agreement with the low solubility of 2-S02. The
stmctures a' and c seem to be identical but differ 87 as much as a' is one structure of a
mesornetic pair. The pseudetetrahedral SO2 fragment is tilted relative to the N2C- plane
by 6.3' (NCS = 129.94(11) and 117.33(11) pm). The geometrical parameters of 2-S02
closely resemble those of the stable carbene 2 and free SO2 (Table 2.4). The observed
CS bond distance of 203.0(2) pm exceeds the sum of covalent single bond radii of s u h r
and carbon (1 87 pm). The S02 group in 2-S02 is rotated away from the "C2~-position" to
interlock with the syn *Bu group.
Figure 2.5. Molecular structure of 2 4 0 2 .
TabIe 2.4. Selected bond lengths [Al and angles [O] for 2402 .
-- - - --
S-O - 146.85(13) - 1 46.4
146.93(13)
C-S - 203.0(2) 167.4(4) - C-N 134.83(13) 132.9(2) 135.4(5) -
133.9(2) 135.8(4)
C-S-O - 100.25(7) - - 1 04.04(7)
O-S-O - 1 13.09(8) - 119.1
N-C-N 1 06.44(9) 1 1 1.61 (3) 1 09.2(3) - N-C-C 7 01.34(9) 1 03.52(12) 1 02.2(3) -
1 OO.96(9) 1 O3.3O(l2) 1 O2.O(3)
Apart from the structural similarities of 2 -Sa with the free carbene, -ts fomulation as
a carbene complex is in line wlh the unusually deshielded '3C resonance of the N&-S02
fragment of 231 ppm, a value that closely resembles the one observed for the free
carbene (237 ppm). Concluding evidence that 2-S02 is best described as a Lewis base
adduct came from NMR studies. The fert-butyl groups on the nitrogens are equivalent. This
equivalence implies the rapid equilibration of conformers a and b (Figure 2.4) by either
rotation around of the CS bond or inversion of the S 0 2 fragment and it persist even at -1 00
OC as confirmed by the low temperature 1 H NMR experiments M e d out THF-d8 during
the course of this thesis.
2.6 Reactions with CO and H2
The reaction of carbenes 1 with carbon monoxide (CO) has been controversial. In
agreement with earfier studies by Arduengo [Goa], we could not observe the previously
38
reported formation [60b] of a ketene-aminal 1 =C=O from 1 and CO. Carbene 2 was
unreactive towards CO.
In the absence of a catdyst, both carbenes are inert towards hydrogen. Addition of
cataiytic arnounts of palladium or platinum leads to slow hydrogen uptake and to the dean
formation of the 1 , 1 -addition products 1 -Hz and 2-Hz. For 2-Hz, the reaction of N,/V'-di-tert-
butyl-ethylenediamine with formaldehyde (30-40% aqueous) or paraformaldehyde is a
more convenient route. The highly reactive irnidazolidine 1442 is best obtained from the
imidazolium chloride 11 -H][CI] and LiAIH4 [40].
Scheme 2.1 1. Reaction of carbenes 1 and 2 with H2 1 Pt.
The aminals 1-Hz and 2-Hz, differ remarkably in their chernical reactivity. The aminal
2-H2 is thetmaily stable and not aitacked by air or moisture, while aminal 1-Hz is very 5Y
sensitive [40]. Even traces of oxygen lead to the complete decomposition of 1-H2 and to
the formation of a resin-like material that iç insoluble in organic solvents. This leads to the
condusion that 1-H2 is catayticaîly polymerized by traces of oxygen [40]. Under strict
exclusion of air, 1 -Hz is themally stable and can be stored indefinitely. The high reactivity of
1-Hz can be linked to the presence of an unstabilized, electron rich 1,2-diamino-olefin
moiety. The closely related urea 1=O, which contains the same 1 ,Bdiamino-olefin unit, but
stabilized by the amide resonance and aromatic delocalization, rendering it air stable w].
Scheme 2.12. Amide resonance and arornatic delocalization in 1=0.
2.7 Synthesis of Carbenium Salts
Two different approaches for the synthesis of [2-H][CI] were examined. The first
approach compnsed the formation of 1 $3-di-tert-butylimidazolidinium chloiide [2=H][CI]
from N,NI-di-tert-butyl-ethylenediamine and a suitable synthon. The second approach is the
oxidation of 1,3-di-tert-butylimidazolidine 2-H2.
Scheme 2.1 3. Synthetic approaches for [2-H][CI].
In the first case, we obtained [2-H][CI] from the readion of N,Nldi-tert-butyl-
ethylenediamine and (chloromethylene)dimethylammonium chloiide (DMF chloride)
(Scheme 2.14). The carbenium sait was isolated as a crystalline compound from the
sublimation residue of the crude reaction mixture (41 Yo) and used without further purification
for the synthesis of the corresponding imidazolidine-2-ylidene. The high cost of DMF
chloride combined with the low yield of carbenium sait (43 %) makes the reaction
unappealing as a synthetic route to the carbene.
Scheme 2.14. Synthesis of 12-HICCI] from DMF chloride and N,Na-di-terf-
The single crystal X-ray structure of [2-H][Cl] is shown in Figure 2.6 depicts a typical
diaminocahenium moiety. The N-C-N fragment of [2-H][CI] is planar and the N-C bond
lengois are rather short (1 -31 A), which indicates that they have some multiple charader
(see appendix 1 for complete single crystal x-ray data).
@ ciio Figure 2.6. Molecular structure of [2-H][CI] in the solid state. Selected bond distances [Al and
bond angles [O]: Ci(1)-H(1) 2.628(1 S ) , N(1)-C(1) 1.31 15(17), N(2)-C(l) 1.3l29(l7), C(1)-H(l) 0.91 9(16),
N(l )-C(2) l.4774(17), N(2)-C(3) l.4779(17), C(2)-C(3) 1.5369(18), N(1)-C(1)-N(2) 1 l4.59(12), N(l )-C(2)-
C(3) 1 03.27(1 O), N(2)-C(3)-C(2) 1 02.98(10).
The second approach studies the formation of carbenium çalts from aminais and also
complements previous oxidative studies by Denk and Gupta, who investigated the
conversion of aminais to thioureas. The aminals used in this study are readily obtained b y
stining N, N'ai-substituted-ethylenediamines or N, N'-di-substituted-propylenediamineç,
with 30-40 % aqueous solutions of formaldehyde [61]. The use of paraformaldehyde
41
instead of an aqueous forrnaldehyde solution allows visual monitoring of the reacüon, and is
therefore the preferred method.
CH2=0
-H20 FH2 R = Me, Et, i ~ r , ph, fBu YH
Scheme 2.1 5. Synthesis of aminals from a condensation reaction.
As of yet, there are only two published procedures for the transformation of aminaJs
into cabniurn salts. Wanzlick and CO-workers [62] prepared 1,3-diphenylimidazolidinium
chloride [2Ph-H][CI] by the readon of 1,3-diphenylimidazolidine and a large excess of
carbon tetrachloride (1 : 1 00 equivalents). Bildstein et al. [63] oxidized 7 -ferrocenyl-3-
methyl-benzimidazolidine with tntyl tetrafluoroborate, used as a hydride abstracting reagent,
and obtained the benzimidazolidiniurn tetrafluoroborate sait in a 67 % yield. Ulbasonic
promoted anion exchange with sodium iodide in acetone afforded the corresponding 1 - ferrocenyl-3-methyl-benzimidinium iodide, albeit in a relatively poor yield of 24%.
Aithough these two benzimidazolidinium & serve as key progenitors for vanous
benzirnidazolidine-2-ylidene derivatives, the authors were not able to obtain the free
carbene. Both published procedures, however, fail to investigate the generality of aminal
oxidations.
[Oxidant]
2-H2 [2-HI[xJ
Scheme 2.16. Oxidation of 2-H2 into [2-H][X].
We studied the transfomation of 2-H2 into the carbenium salt 12-HJ[X] by reacting
the former with various oxidizing agents induding: CuC12, 12, NCS, NBS, CC14 and CBr4.
42
In ail cases, the formation of carbenium A t was monitored by H and 3C NMR, which
shows the characteristic carbenium C(+)g signal at 6 8.80 ppm andÇ(+)-H at 6 154 ppm,
respectively, for [2-Hl[)<].
The reactions with CuCI2 and iodine, aithough they form carbenium çaltç, are not of
much use as they resuft in a complex mixture of products. Reaction of 2-H2 and two
equivalents of CuC12 was camed out in isopropanol. 1 H and 13C NMR data indicates the
presence of [2-H][X]. CuClp has been postulated as the negative counterion frorn the
isotopic distribution displayed in the compound's negative electrospray ionization m a s
spectrum (ES- (rn/z) = 168, 170, 172, 174). Attempts to grow crystals, of the product
observed by NMR spectroscopy, for further X-ray anaiysis were unsuccessful. In one
attempt, the isupropanol soluti'on was layered with chlorofom and stored at 5 OC, which
leads to the formation of green crystals together with brown amorphous material. The
crystals were characterized by single crystai X-ray spectroscopy and the resutts shown n
Figure 2.7.
Figure 2.7.
angIes Pl: 2.6399(6),
2.4821 (1 O),
u
Molecular structure of [CU&I& in the solid state. Selected bond distances [A] and bond
Cu(1)-CI(3)#1 2.1 924(1 O), Cu(1)-CI(2) 2-31 2O(9), Cu(1 )-CI(1) 2.3328(1 O), Cu(1 )-Cu(2)
Cu(1 )-Cu(1 )#l 2.9230(9), Cu(2)-Cl(3) 2.2762(9), Cu(2)-CI(1) 2.4249(9), Cu(2)-Cf(2)
C1(3)#1-Cu(1)-CI(2) 126.1 2(4), Cl(3)#l -Cu(l )-CI(1) 124.1 5(4), CI(2)-Cu(1)-CI(1) 105.71 (3),
The X-ray structure shown in Figure 2.7 shows an anionic duster composed of four
copper atoms bridged altematively by one and two chlorine atoms. The closest distance
between copper atoms is 2.64 A w h i i is longer than the sum of the ionic radii (1 -92 A,
Cu+). The duster is surrounded by two dicationic fragments of N, N'di-tert-
butylethylenediamine.
Similariy, [2-H][l] was obtained from 12 and 2-H2 in THF. One extra equivalent of
aminal is required in order to scavenge the hydrogen iodide evolved dunng the readon,
\ivhich leads to a secondary undesired product 2-HpHI. Despite ail attempts, the latter
could not be separated from mixtures of either [2-H][13] or [2-H][l]. This second equivalent
44
of 2-H2 is consumed by Hl despite the addition of other auxiliary bases, indudng pyridine,
tert-butylarnine, di-is~propylarnine or triethylamine to the reaction mixture (Scheme 2.1 7).
2-H2 [2-H][13] (Brown) 2-H2-HI
Brown 2-H2 [2-Hl [l] (White) 2-H241
overall equation
td u [2-H][l] (White)
Scheme 2.17. Oxidation of 2-H2 into [S-HI[[] by lodine.
In contraçt to the above rnentioned oxidizing agents 12 and CuC12, NCS, CC14,
NBS, and CBr4 dl yield the desired carbenium sait 12-H][X] in excellent yield by reacüon
with 2-H2 while refiuxing in THF or chlorofom for extended penods of time. In order to
identify which of these oxidizing agents is most effective, these reactions were monitored
for one hour, without refluxing in THF. Table 2.5 shows that the formation of cabnium sait
is complete within the fi& hwr when NBS is used as oxidizing agent Separation of the
former cahenium salt from succinimide, the inevitable byproduct of the reaction, is achieved
by repeated washing with hot THF. This removes the succinimide but leaves the
carbenium sait undissolved.
Due to the fact that other oxidizing agents did not produce this outstanding yield n
the absence of heat, NBS was chosen in order to investigate the generality of the oxidative
pathway from arninals (tert-butyl R group) to carbenium salts.
Table 2.5. Percent yield of [2-H][X] from the reaction between 2-H2 and NCS, CCl4, NBS and CBr4.
Product R X= CI X= Br Time Method NCS Cela NBS CBrn
P H 1 1x1 t~ u 51 % 0% 94 O h 67 % 1 h A [2-H i[X] 'BU 96 % 82 % 97 % 97 % 8h 6
'Method A = vigorous stirring only.; Method B = heat solvent to reflux.
It is obvious that NBS and NCS produce excellent yields of the carbenium salts but
only after boiling of the reaction mixtures. The generaiity of the method was investigated b y
subjecting a number of different arninais to protocol A. The results shown m Table 2.6
indicate that the nature of the R substituent and ring size have no significant effect under
these experimental conditions (NBS in THF, r.t.).
NBS 0
t ch$H2 .Y - THF ( ~ ' $ H Br n Y
Scheme 2.18. Oxidation of AminaIs by NBS.
Table 2.6. Percent yield of various carbenium-bromide salts from the reaction between various arninais
with NBS.
Product R n % Yield Method* Time
[2Me-H][Br] Me 1 97 A 1 h
[2P h-Hl [B r] Ph 1 89 A 1 h
P-HIIBr] 'B u 1 94 A 1 h
13-H][Br] t~ u 2 84 A 1 h
'Method A = vigorous stimng only.
2.8 Thauer's Hydrogenase
Hydrogenases are enzymes that catalyze readions involving molecular hydrogen,
either as a substrate or as produd Al1 hydrogenases are metalloenzymes, with the
exception of that found in the methanogenic archaeon Methano bacterium
thennoautotmphicum which catalyzes the reaction of its substrate m, Ni 0-m eth en y 1
tetrahydromethanopterïn (met hen y l-H4M PT, Scheme 2.1 9) with mdecular h ydrogen
without the aid of nickel or iron-suifur dusters [64].
methenyl-H4MPT methenyl-H4MPT- H
Scheme 2.19. Metal-free Organic Hydrogenation Catalyst.
Methenyl-H4MPT uülizes a formarnidinium cation moiety as the enzymes' active
site, similar in sbudure to imidazolidinium and imidazolium s a k . In view of the enzymes'
reactivity towards hydrogen and the high stabil-w of the cahnium saits [l-Hl+ and 12-Hl+
we decided to investigate the possible hydrogenase type reactivity of the saits [l-H][Ci]
and [2-HICI.
- + H P * + base
pH2 + base*Hf
Scheme 2.20. Possible hydrogenase-type reactivity of 11-HIJCI] and [2-HJ[CI].
The carbenium saits 11-H][CI] and 12-H][CI] were exposed to 1 atm of H p m the
absence and in the presence of auxiliary bases like pyridine and 4-dimethylarnino-pyridine
in chlorofom. The formation of 1 -Hz or 2-H2 was not observed m any of these reactions.
This demonstrates that the ability of met hen y l-H4M PT to reversibly dissociate hydrogen
is not general to imidazolium or imidazolidinium salts but is rather specifically tied to the
structure methenyl-H4MPT.
2.9 Synthesis of 1,3-Di-fert-butyl-3,4,5,6-tetrahydropyrimdine-2-ylidene
Carbene 3 can be prepared in 40% yield by deprotonation of 13-H][Br] with lithium
diisopropyl amine (LDA) m THF at room temperature, exchange of solvent to benzene,
followed by filtration. Evaporation of the solvent leads to a white solid which, when heated
under vacuum m a sublimation apparatus, leads to the collection of a colouriess liquid,
characterizad as 3. The nature of the white solid is still being investigated, but it is possibly a
lithium bromide-carbene adduct, the kind that has been isolated and studied by Alder [65].
Precurçor [3-H][Br] is conveniently made by süning an equimolar mixture of 3-H2 and
NBS in THF (84%).
Figure 2.7. Stable carbene 3 and related compounds-
Diaminocarbene 3 is not the first example where the N-C-N group is part of a six-
rnembered ring. 1,3-Di-isopropyl-3,4,5,6-tetrahydorp~midine-2-ylîdene 3iPr was
prepared by Alder et al. 1651 m 40 % yield by deprotonation of [3iPr-H][BF4] with
NaN(SiMe3)a in THF at -78 OC. The latter carbene appears to be thermodynamically
stable to dimerization, unlike the five-rnembered ring analogue PiPr. A solution of 3 n
benzene-d6 shows a carbene carbon resonance in the NMR at 6 237 ppm (versus 6
236 ppm in toluene-ds for Alder's 3iPr). These 13C shifts are well within the 6 200 to 300
ppm range reported for stable carbenes.
The first member of the series is triazacyclohexane TAC, also known as hexahydro-
symtriazine, which has yet to be isolated hwn solution. There is, however, enough
chemid [66a] and spectroscopic evidence [66b] to conclude that th& compound is ai
intermediate in the formation of hexamethylenetetraarnine (urotropin) which is synthesized
from the reaction of arnrnonia and formaldehyde solutions. This result is in agreement with
the early reports of Duden and Scharff [671 who were the first to correctly deduce the
structure of TAC m 1895 (Figure 2.1 0). Prior to 1900, early researchers regarded the
condensation products of fomaldehyde and primary amines as monomeric alw Schiff's
bases. Cryoscopic woik later showed that these substances are trimeric in nature.
49
However, by careiùl technique, these monomers can be obtained in high purity and their
Raman spectra may be measured prior to undergoing trimerization [68].
TAC Urotropin
Figure 2.8. Triazacyclohexane (TAC) and urotropin.
The most common and simpiest means of preparation of this group of R3TAC is
by the r d o n of equimolar quantities of fonaldehyde, usuaiiy 30-40% aqueous, or
parafonnaldehyde, with the corresponding primary amine. As in the case of aminais, we
prefer the use of parafomaldehyde over formaldehyde, since dissolution of the former
provides a visuai means of monitoring the end of the reaction (Scheme 2.22).
Scheme 2.22. Synthesis of 1,3,5-triazacyclohexanes (R3TAC).
2.1 1 Synthesis of 1,3,5-Tri-tert-butyl-1,3,5-triazacyclohexyl Carbenium Cation [1Bu3TAC][X]
The carbenium salt FBu3TAC][Br] can be obtained as a cdourless crystalline solid
in excellent yields, from room temperature THF solutions of tBu3TAC and NBS.
Purification of the sait consists of the removal of succinimide from the crude mixture with
wam THF.
Scheme 2.23. Synthesis of ['B u~TAc][B~] .
A solution of PBu3TAC][Br] in CDCI3 shows a h e n i u m carbon resonance in the
13C NMR at 6 152 ppm. These 1% NMR shÏfts are well within the range of the cationic
precursors for stable diaminocarbenes (6 135-1 80 ppm)-
The carbenium salts, pBu3TAC][Br] and [tBu3TAC][CI], can be obtained through
the room temperature reaction of tBu3TAC with CBr4 in THF and tBu3TAC with NCS in
THF, respectively. Albeit, complete transformation into the carbeniurn salt is significantly
slower than that observed with NBS under simik conditions. Reaction with CC14 does not
proceed at room temperature and heating tBu3TAC with CC4 in order to prornote the
reaction yields mixtures of starting materials, PB u3TAC][CI], and 1,3-di-tert-
butylformamidinium chloride. The presence of the latter has been confimed by 1 H and 3C
NMR as well as m a s spectral analysis [69].
Gompounds of the type [R3TAC][X] are not entirely unknown. The saits
[Me3TAC] [f 3], [Me3TAC][I5] and [Me3TAC][I7] have been described in the literature
by Tebbe and CO-workers. These products result from the reaction of Me3TAC with
varying amounts of iodine [70]. [Bz3TAC][CIO4] has been isolated by Kohn et al. as a
decomposition product of [(Bz3TAC)Zn(Et)][CIO4] from dichloromethane / hexane
solutions. The yields were not discussed [71].
Bz Slow decomposition I CH2CI2/ hexane rN\ @ O BZ-N F-H c104
'-Y Bz
Scheme 2.24. Decomposition of [(Bz3TAC)Zn(Et)][C104].
2.1 2 Deprotonation of 1,3,5-Tri-tertlbutyl-l,3,5-triazacyclohexyl Carbenium Bromide pBu3TAC][BrJ
Diaminocarbene 9 is the firçt example where the N-C-N group is part of a 1,3,5-
triazacyclohexane ring. 9 cran be prepared by the deprotonation of pBu3TAC][Br] with
LDA in THF at room temperature.
Scheme 2.25. Synthesis of 9.
1% NMR data in benzene-d6 solutions show resonances at 6 238 ppm for the N-
C-N carbon of 9 versus 6 237 ppm for N-C-N carbon of the pyrimidine-2-ylidene 3,
section 2.9. The similarity in shifts demonstrates that the presence of the third nitrogen in 9
does not have any significant influence in the mesomeric or inductive interactions of the N-C-
N fragment. As of yet, attempts to isolate 9 have not been successful in our hands, and the
compound has only been observed in benzene.de solutions.
t ~ f l
Base - ". s8
F=s HN
1 'BU
Scheme 2.26. Formation of N,NWi-tert-butylthiourea.
52
Attempts to derivatize 9 into a thiourea by deprotonating PBu3TAC][Br] m the
presence of suMir, did not yield the expected compound S~BU~TAC, instead the major
isolated reacüon cornponent was N,Nr-di-tert-butylthiourea (Scheme 2.26). These resultç
are consistent despite the use of other deprotonating bases, induding sodium hydride and
~~butyllithiurn.
2.1 3 Attempted Synthesis of 1,3,5-Tri-tert-butyl-l,3,5-triazacyclohexyl tris- Carbenium Cation PB u3TAC][X3]
The compound [R3TAC][X3] is of interest as a potential çtarting material for the
respective poly-carbenes 9R. In w r efforts to prepare [tBu3TAC][X3], we reacted
tBu3TAC with three equivalents of NCS.
H @ r ; . I @ H deprotonation
Scheme 2.27. Proposed synthesis of 9R.
The reactions were camkd out in chlorofom, using one equivalent of tBu3TAC and
three equivalents of the oxidizing agent. The use of a polar solvent such as chloroform
would ensure that the carbenium salt formed would remain in solution in order to react further
with the oxidizing agent. In al cases, the suspected formation of the tris-cation
FBu3TAC]+3 or the bis-cation PBu3TAC]+* was dismissed upon inspection of H N M R
data, which showed the unexpected formation of the 1,3-di-tert-butylfomiamidinium
whose presence was confinned by mass spectral and 1 H and 1% NMR data (Scheme
2.28).
Scheme 2.28. Attempted synthesis of ~ B U ~ T A C ] [ X ~ ] .
The formation of this compound haç been observed in solutions involving the
reaction between tBu3TAC and an oxidizing agent m the presence of heat. The nature of
the byproducts for çuch transformation have not been isolated or identified as of yet, and
their elusiveness is attributed to their possible volatility.
2.1 4 1,3,5-Tri-tert-butyl-1,3,5-triazacyclohexane-CuCI2 Adduct
Unlike the reaction of the irnidazolidine 2-H2 with CuC12, Mich leads to an
imidazolidinium sait, treatment of a suspension of CuC12 in a CHCI3 solution with an
equimdar amount 'Bu3TAC did not yield the carbeniurn sak, instead the reaction
immediately yielded green cryçtals swimrning on the surface of the solution. These were
characterized crystallographically as [(tB u3TAC)Cu Cl2]. The molecular structure of
(tBu3TAC)CuCI2 is shown in Figure 2.1 1 . The asymmetric unit contaihs 3 molecules of
the complex and 3 molecules of chloroform. Two molecules of chloroform are disordered
and have been omitted for clarity. Only one of the three molecules of [(tBu3TAC)Cu Cl2]
is shown below, the other two molecules are shown in appendix II.
Figure 2.9. Molecular structure of ( t ~ u g ~ ~ ~ ) ~ u ~ 1 2 in the solid state. Selected bond
distances [AI and bond angles [q: Cu(1A)-N(3A) 2.1 15(3), Cu(1 A)-N(2A) 2.1 36(4), Cu(1 A)-CI(1 A)
2.21 95(13), Cu(1 A)-Cl(2A) 2.2288(12), CU(^ A)-N(f A) 2.342(4), N(3A)-Cu(1 A)-N(2A) 65.72(13), N(3A)-
Cu(1A)-CI(1 A) 99.38(1 O), N(2A)-Cu(1 A)-CI(1 A) l64.59(1 O), N(3A)-Cu(1A)-Cl(2A) l64.23(11), N(2A)-
Cu(1A)-Cl(2.A) 98.53(1 O), CI(1A)-Cu(1 A)-CI(2A) 96.39(5), N(3A)-Cu(1 A)-N(l A) 63.26(12), N(2A)-Cu(1 A)-
N(l A) 62.93(14), CI(1A)-Cu(1A)-N(1A) 11 5.14(1 O), Cl(2A)-Cu(1A)-N(l A) 109.82(9).
This complex has three facialiy mrdinating nitrogen atoms and, with the indusion of
the two chlorine atoms, it foms a distorted square pyramid. The basal plane is occupied b y
two chlorine and---Mo nitrogen atoms with an angle between nitrogen atoms of only
(65.72(13)"). The third nitrogen atom of the tBu3TAC fragment approaches the axial
position with respect to the basal plane. We were unable to obtain useful H or 3C N M R
spectra due to the paramagnetism of (tBu3TAC)CuCI2.
A number of complexes having tnazacyclononane and larger rnacrocydic amines are
known F2aJ. These compounds play an important role as catalysts for olefin polymerization
172bI. In addition, metal complexes having three facially coodinating atoms have been
described as models for biological systerns. Copper (I)/(II) complexes which possess
these structural requirements have been studied for their role in the binding and activation of
oxygen. However, only a few have been characterizci as peroxo and superoxo
55
complexes [72c]. Kôhn et al. have recentiy investigated MesTAC and ~ P ~ ~ T A C
complexes of copper (1) and (11) [73]. The study relied on the use of 1,3,5-
triazacycIohexanes m order to increase the reactivity of the triaza-copper systems. The
authors erroneously believed that the use of the smaller ring size R3TAC systems would
strain the coordination around the copper, thus making the complexes highly reactive.
In accord to K6hn1s study of (iPr3TAC)CuCln and the dimeric
[{(Me3TAC)CuCI2)2], we have found that (tB u3TAC)CuCI2 is a highly stable
compound, even when exposed to air and moisture, despite the high steric strain.
Chapter 3: Experimental Section
3.1 Experimentat Notes
Unless noted othewise, ail starhg materials were obtained from commercial
suppliers and were used without further purification. Chloroform and dichloromethane were
distilled over phosphorous pentoxide. Methanol was distilled over sodium metal.
Tetrahydrofuran, hexanes, and benzene were distilled from blue or purple potassium /
benzophenone solutions under nitrogen prior to use. Deuterated solvents (CDC13, C6D6,
THF-d8) were dned by 30 minutes sonication with CaH2, followed by deoxygenation with
three freeze-pump-thaw cycles. All aminals used in this study were distilled and stored in é i r
free tubes over CaH2.
All reactions involving organometallic reagents or amines were -ed out under
Argon (99.996 %) with the usuai Schlenk equipment or m a nitrogen filled glove box
(Braun, 0 2 < 2 ppm, H20 c 2 ppm).
NMR ('H, 1%) spectra were recorded on a Gemini 200 MHz, Varian Unity 500
MHz or 400 MHz or a Bruker 600 MHz instrument in solution. Chernicd shifts are
expressed in parts per million (pprn, 6) downfield from tetramethylsilane (TMS) unfess
otherwise indicated. NMR signals are reported as s, singlet; d, doublet; t, triplet; qr, quartet;
qn, quintet; m, multiplet and br, broad. Coupiing constants are given in Hertz. The '3C
NMR shifts were sirnulated on a l3C NMR ACD software.
IR spectra were recorded in nujol or neat with sodium chloride or potassium bromide
plates using a Peria'n Elmer AVATAR 360 FT-IR spectrometer and are reported n
wavenurnbers (cm-'). IR signals are reported as v s, very strong; s, strong; m, medium; w,
weak; v w, very weak; br, broad; v br, very broad-
Poly(ethy1ene glycol) (Aldrich cat # 37,299-4) was used as heating fluid up to 220
OC. The glycol baths emit toxic fumes and decompose readily, hence they were operated
in fume hoods at al1 times.
El mass spectra were obtained from a Micrornass 70s El m a s spectrometer. ES
mass spectra were obtained from a Micromass Platforni Electrospray rnass spectrometer.
3.2 Preparation of Compounds
3.2.1 Preparation of 1,3-Di-tert-butylimidazole-2-ylidene (1 )
[4@ nButi +
1 pH -C4Hio (g) Y -LiCl (s) b u 'Bu
40.8 mL of n-BuLi (2.5 My 102 mmol) was added dropwise to a 60 mL THF
suspension of 1,s-di-tert-butylimidazolium chloride [this thesis pg. 701 (22.1 2 g, 0.1 02 mol)
in a 250 m l two-neck round bottorn f lask The teaction was allowed to çtir for 8 h and the
suspension was fiitered using a fine porosity glas frit under the exclusion of air and
moisture. The solvent was then removed under reduced pressure (0.1 Torr). The solid
residue was then transferred to a sublimation flask in the glove box. 14.78 g (80% yield) of
1,3-di-tert-butylimidazole-2-ylidene was isolated by sublimation (0.1 Torr, 40 OC) as a
FT-I R (Neat, NaCI): u = 2967 cm-' v br, 1661 s, 1474 s, 1403 br, 1 361 s,
1263 s, 1228 s, I l 7 0 m, 1077 m, 1027 m, 926 w, 878 rn, 812 m. l H NMR (200 MHz, C6D6, 25 OC): 6 = 1.51 ppm [s, C(CHg)3]1 6.79
[s,CH=Cf=J 13C(lH) NMR (100.4 MHz, C6Ds, 25 OC): 6 = 31.46 ppm [C(C-H3)3], 55.76
[C(CH3)3], 1 15.00 [CH=GH], 212.87 [S. N&:]. 13C NMR (100.4 MHz, C&, 25 OC): 6 = 31.46 ppm [qr, C(CH3)3, 'J (C,H) =
126-6 HZ, 3J (CyH) = 4-4 HZ], 55.76 [s, c(CH3)39 2J (C,H) = 12.1 HZ, 3J(C,H) =3.6 Hz], 115.00 [d,CH=cH, lJ(CIH) = 185.3 HZ, * J C , H ) = 13.2 Hz], 212.87 [s, NpC:].
lsN NMR (500 MHz, C6D6, 25 OC): 6 = -167.62 PpiTi.
El-MS (70 eV): m/z (rei. int %): 181 (48) [Ml +O, 125 (13), 11 1 (IO), 95 (IO), 82 (3), 69 (1 OO), 57 (32), 41 (20).
3.2.2 Preparation of 1.3-Di-terf-butyl-imidazolidine-2-ylidene (2) [22]
Method A
2=S 2
1,3-Di-tert-butyl-imidazdidine-2-thione [this thesis pg. 611 (9.59 g, 44.7 mmol) and
potassium metal (5.25 g, 134.2 mmol) were mixed in a 500 mL round bottom fiask
attached to a condenser, and 90 m l of THF was added at room temperature. The solution
was refluxed for 6 h at 70 OC under a positive pressure of argon, the cdwr slowly changed
to green and the viscosity of the mixture increased. After ailowing the solution to cool to r.t.,
1 was fiitered through a fine porosity g las frit into a 1 00 mL Schlenk fiask and the resulting
filtrate was concentrated under reduced pressure, giving 5.90 g (72 % yield) of a yellowish
viscous liquid. The product was purified by sublimation at 0.1 Torr and 60 OC. 3.64 g (45 %
yield) of 1,3-di-tert-butyl-imidazole-2-ylidene was isolated as a colourless oil.
Method B
[2-HIICll 2
ln a 500 mL round bottom flask attached to a condenser, 84.6 mL of n-BuLi (1.6
mdar in hexanes, 135 rnmol) was added to a suspension of 1,3-di-tert-butyl-
imidazolidinium chloride b i s thesis pg. 71 ] (29.6 g, 135 mmol) in 70 mL of hexane. The
addition of n-BuLi was camed out over a period of 1 h and the solution was kept at ca O OC
for 1.5 h with vigorous stimng. The mixture was then allowed to reach room temperature and
60
the çtirting was stopped once the evdution of butane gas, as monitored through an oil
bubbler, ceased. The cmde solution was filtered through a fine porosity g las frit and the
filtrate was concentrated, giving 14.9 g of crude mixture. The mixture was then distilled
under reduced pressure (0.1 TOIT) and two fractions were collected. 8.2 g (35 % yield) of
1,3-Di-tert-butyl-imidazole-2-ylidene was collected at 60 OC as a colourless oil.
m.p. 23 OC. FT-l R (Neat, NaCI): u = 2967 cm-' v br, 1661 s, 1474 s, 1403 br, 1361 s,
1263 s, 1228 s, 1170 m, 1077 m, 1027 m, 926 w, 878 m, 812 m.
1H NMR (200 MHz, CsD6, 25 OC): 6 =1.36 ppm [s, 18H, C(C&)3], 3.03 [s, 4H, C M .
13C{1H) NMR (100.4 MHz, CfjD6, 25 OC): 6 = 29.83 ppm [C(CH3)3], 55.68
[C(CH3)3], 44.36 [CH&H2], 238.25 [s, N&:].
lsN NMR (500 MHz, C6D6, 25 OC): 8 = -227.6 ppm.
3.2.3 Preparation of 1,3-Di-tert-bu~l-3,4,5,6-tetrahydropyrimidine-2-ylidene
(3)
A 2.0 M solution of LDA in heptame / THFI ethylbenzene (8.9 mL , 17.8 rnmol) was
added dropwise to a 20 mL THF suspension of 13-H][Br] [this thesis pg. 781 (4.94 g, 17.8
mmol) in a 100 mL Schlenk flask The reaction was allowed to stir for 2 h and the mixture
was filtered using a fine porosity g l a s frit The solvent was removed under reduced
pressure leaving behind an off-white solid. The solid was transferred to a diça'llation
apparatus in a glove box. The solid was heated for approximately 1 h under vacuum (0.1
Torr, 90 OC) and the carbene 3 condensed in the receiver flask as a colourless oil. Yield 1.5
FT-IR
1H NMR
(Neat, NaCI): u = 2970 cm-' br ,s, 2874 br, s, 1623 rn, 1482 s, 1433 s,
1386 m, 1358 s, 1306 s, 1238 m, 1222 m, 1184 w, 1086 w, 987 m, 847 m, (300 MHz, C&6,25 OC): 6 = 1.38 ppm Cs, 9H, NC(C&)3], 1.42 [qn,
2H, CH2C&CH2, 3~ = 6.1 HZ], 2.67 [t, 4H, C&CH2Ci&, 3~ = 6.0
Hz].
13C{lH) NM R (75.44 MHz, C6D6, 25 OC): 6 = 26.37 ppm [CH2CH2CH2], 29.60
[NC(CH3)3], 36.1 7 EH2C HAHA, 58.54 [NC(CH3)3], 237.41 [NpC:].
El-MS (70 eV): m/z (rel. int. %): 1 96 (36) [Ml +, 1 40 (43), 125 (1 OO), 98 (30), 83 (38), 70 (7), 57 (28), 41 (29), 29 (1 5).
3.2.4 Preparation of 1,3-Di-tert-butylimidazolidine-2-thione (2=S)
pyridine
In a 250 mL boiler flask, N,Nldi-teH-butylethylenediarnine (25 ml, 120 mmol) was
dissolved in 60 mL of pyridine. Gas evolution was observed as 7.08 mL of CS2 (120
mmol) was added dropwise to this solution. The mixture was heated to reflux for 10 h, it
was then cooled using an ice bath, prior to the addition of 12 (14.9 g, 60 mmol). The resulting
mixture was refluxed for 30 minutes, cooled to rmm temperature and concentrated down to
a black tar-like solid under reduced pressure (0.1 Torr). The product was then extracteci from
an aqueous KOH solution with dichloromethane and the solvent concentrated to dryness
under vacuum (0.1 Torr). The yield of 2=S after sublimation (0.1 Torr, 1 30 OC) was 3 g (1 2
?O).
m.p. 128 OC. 1H NMR (200 MHz, CDCI3, 25 OC): 6 = 1.60 ppm [s, (C&)3C], 3.44 [CHz-
CHZ]. (200 MHz, C&, 25 OC): 1-55 [s, (C&)3C], 2.73 [CH2-CH2].
13C{1H) NMR (100.4 MHz, C6D6, 25 OC): 6 = 28.09 ppm [C(cH3)3], 56.41 [ç(CH3)3], 44.22 sH2-GH2], 184.43 [s, N2çl
' S N NMR (500 MHz, CsD6,25 OC): 6 = 18.73 pprn.
3.2.5 Preparation of 1,3-Di-tert-butylimidazole-2-thione (1 =S)
25 mL of hexane was added to a solid mixture of 1 [this thesis pg. 581 (2.47 g, 14
rnrnol) and S8 (0.44 g, 14 mmol) in a 100 mL Schlenk fkk The resuiüng suspension was
stirred for 3 days. The solvent was removed under vacuum (0.1 Torr) and the remaining
peach coloured solid was transferred to a sublimation flask l=S was isolated by
sublimation (0.1 Torr, 40 OC) as a colourless crystalline solid. Yield 2.43 g (84 %).
m.p. 160 OC.
1H NMR (200 MHz, CsD6, 25 OC): 6 = 1.66 ppm [s, (C&)3C], 6.30 [CH=CH]. 13C{1H) NM R (100.4 MHz, C6D6, 25 OC): 6 = 28.09 ppm [C(W3)3], 58.96
[ç(CH3)3], 1 12.91 EH=CH], 162.60 [s, NS] .
3.2.6 Preparation of 1,3-Di-tert-butylimidazole-2-one (1 =O)
Method A
NO
benzene
'BU
Nibic oxide was bubbled for 5 min into a benzene solution of 1,s-di-tert-butyl-
imidazole-2-ylidene [this thesis pg. 581 (40 mg) which had been previously cooled using
an ice bath. 1 H NMR (C6D6) revealed that the carbene had been cornpletely transformed
into the corresponding u rea 1 S.
Method B
'BU 't3u 'Bu I
thf 'BU
1 =O
N,N'di-tert-butyl-diazabutadiene (5.05 g, 30 mmol) dissolved in 30 mL of
anhydrous THF was stirred with 2.2 equiv. of finely aR lithium wire (1 % Na, 66 rnmol, 46
mg) for 8h. If the deep red color of the diazadiene di-anion is not observed within minutes
after the addition of the lithium, the reaction can be usually started by brief sonicaton. The
resulting dark red solution was cooled to -30 OC (formation of cdoriess precipitate) and 1
equiv. of methyl chloroformate (3.26 g, 2.87 mL, 30 mmol) dissolved in 10 mL of THF was
added over a period of 5 min (heat evolution). The resulting yellow-orange solution was
diluted with 50 m l of toluene and filtered under exclusion of air and moisture. After removal
of the solvents the residue was sublimed at 130 OC oil bath / 0.1 Torr to give 65 5% (3.8 g)
m.p. 117 OC.
FT-IR (Nujol, Cd): u = 1685 cm-1 s, 1366 s, 1306 w, 1261 ml 1231 m, 1 163
w, 1097 ml 1022 m, 801 ml 722 w, 662 w, 631 W.
1H NMR (200 MHz, C6D6, 25 OC): 6 = 1.42 ppm [s, 18H, c(c&)], 5.96 [s,
4H, NCH=CHN]. (200 MHz, CDsCN, 25 OC): 1.46 E, 18H, C(C&)],
6.34 [s, 4H, NC_H=CHN]. 1% NMR (100.4 MHz, C6D6, 25 OC): 6 = 28.2 ppm [qr, C(Q-l3)3, 1J (C-H) =
125.7 HZ], 54.3 [s, C(CH3)3], 106.4 [dd, NSH=ÇHN, J (C-H) =
192.1 HZ, 3 J (C-H) = 9.0 HZ], 152.7 [s, c=O]. (100.4 MHz, CD3CN,
25 OC): 6 = 28.3 ppm [qr, C(CH3)3, 1 J (C-H) = 125.7 Hz], 55.1 [s,
C(CH3)3]1 107.6 [dd, NÇH=CHN, 1J (C-H) = 192.1 HZ, 3J (C-H) = - 9.0 Hz], 153.3 [s, Ç=O].
' 70 NMR (500 MHz, CD3CN, 25 OC): 6 = 209 ppm. (500 MHz, C6D6, 25 OC):
F = 215 ppm.
El-MS (70 eV): m/z (rel. Rit %) : 1 96 (25) [Ml", 1 40 (24), 1 25 (4), 84 (1 00) ,
57 (20).
3.2.7 Preparation of I,3-Di-tert-butylimidazolidine-2-one (2=0)
Method A
2 2=0
Nitric oxide was bubbled for 5 min into a benzene solution of 1,3-di-terf-butyl-
imidazolidine-2-ylidene [this thesis pg. 591 (ca. 35 mg) which had been previously cooled
using an ice bath. 1H NMR (CsD6) revealed that ail the starting carbene 2 had been
transfomed into the corresponding wea 2=0.
Method B
'BU 'BU
2.2 eq. n-Buti
2.2 eq. CI-COOMe n-hexane 'BU
To a stirred solution of N,NLdi-ter?-butyl ethylenediamine (5.0 ml, 24 mmol) in 1 00
mL of n-hexane were added 2 equiv. of 2.5 M n-6uLi in n-hexane. The reactbn mixture
was boiled to reflux until the evolution of mbutane ceased. The solution tumed yellow and a
white solid precipitated. The reaction mixture was cwled to -20 OC and 1 equiv. of methyl
chloroformate (2.61 g, 2.30 mL, 24 mmol) dissolved in 10 mL of mhexane was added
dropwise under stimng. After refluxing the reaction mixture for 2 houn and letüng t come to
rwm temperature, the mixture was filtered thmugh a medium porosity glas f r i t The filtrate
was evaporated in vacuo and the residue was purified by sublimation (0.1 Torr, 100 OC) to
afford 3.6 g (75 %) of pure 2=0 as coloriess crystals.
m.p. 64 OC. FT-IR (Neat, KBr): u = 2751 cm-' s, 2729 s, 2667 s, 171 0 s, 1699 s, 1402 m,
1271 s, 1244 s, 1 104 w, 1096 w, 1030 w, 946 w, 802 m, 739 m. 1H NMR (200 MHz, C&, 25 OC): 6 = 1.32 ppm [s, 18H, C(CH3)3], 2.67 [s,
4H, NCH2-CH2NI. (200 MHz, CD3CN, 25 OC): 6 = 1.27 ppm [s, 18H, C(CH,?)3], 3.14 [s, 4H, NCH2-ChN].
13C NMR (100.4 MHz, C6D6, 25 OC): 6 = 27.4 ppm [qr, C(QH3)3, J (C-H) = 125.7 HZ], 40.4 [t, C&-Ckl2, J (C-H) = 141.8 HZ], 52.8 [s, C(CH3)3], 161.6 [s, C=O]. (100.4 MHz, CDsCN, 25 OC): 6 = 27.6 -
pprn [qr, C(C-H&, J (C-H) = 125.7 HZ], 41 -1 [t, Ct&-CH2, J (C-H)
= 141 -8 HZ], 53.4 [s,C(CH~)~], 162-8 [s, s=O].
l7O NMR (CDsCN, 25 OC): 6 = 247 ppm. (CeDe, 25 OC): 6 = 250 ppm.
El-MS (70 eV): m/z (rel. int %): 198 (9) 183 (55), 142 (3), 127 (IOO), 86 (1 O), 70 (8), 57 (1 9).
3.2.8 Preparation of 1,3-Di-tert-butylimidazolidine-2-thione-S,Ç-dioxide
(2-SO2)
As performed by Dr. Ken Hatano: SO2 gas was introduced into an anhydrous THF
solmon of 2 [this thesis pg. 591 (0.72 g, 4 mmol) ai O OC. A dear yellow solution was
obtained after 1/2 h. The solvent was removed under reduced pressure (0.1 Torr) to leave
a yellow solid. Yield 1 .O2 g (quantitative).
1H NMR (399.3 MHz, Ce&, 25 OC): 6 =1.25 ppm [s, 18H, C(C&)3], 2.78 [s,
4H, C b ] .
13C{1H) N M R (1 00.4 MHz, C&, 25 OC): 6 = 29.7 ppm [C(CH3)3], 44.6 KHz], 55.2 [C(CH3)3], 231 [br, Ns ] .
MS (CI+, CHq) m/z (rel. Int. %) = 245 (14) [Ml*, 229 (IO), 183 (62) [LC-Hl+, 167 (IO), 126 (61), 111 (56), 99 (31), 84 (IO), 71 (100) [C3H7N2]+, 57 (51).
3.2.9 Preparation of l,3-Di-tert-buvlimidazolidine (2-H2)
N,N'di-fertbutylethylenediamine (33 mL, 25.8 g, 0.15 mol) was slowly added tu
4.50 g of paraformaldehyde (0.1 5 mol) in a 100 mL Schlenk Rask The resulting cloudy
solution was stirred for 2 h or until it becomes dear. A slight increase of temperature was
noted throughout the entire reaction but did not require the aid of a cooling bath. The product
was then extracted into dichloromethane from a 1 :1 mixture of dichloromethane and water.
67
After the removal of the solvent under reduced pressure, 2-H2 was distilleci in vacuo. Yield
FT-I R
1H NMR
13C{lH) NMR
El-MS
80 OC (0.1 Torr). (Neat, NaCI): u = 2967 cm-' s br, 2872 s br, 2822 s br, 1654 w, 1 472
ml 1462 m, 1393 s, 1360 s, 1275 s, 1225 s br, I l 5 7 m, 1103 w, 1085
w, 1037 m, 922 w, 861 w, 829 rn, 779 w, 743 W.
(200 MHz, CDC13, 25 OC): 6 = 1 .O7 ppm [s, WH, C(CH3)3], 2.83 [s, 4H, C&-CHi], 3.50 [s, 2H, N2CH2]. (200 MHz, CsD6, 25 OC): 6 =
1.09 ppm [s, 9H, C(C&)3 1, 2.75 [s, 4H, C h - C u , 3.67 [s, 2H,
N2CbI . (100.4 MHz, C6D6, 25 OC): 6 = 26.10 ppm [C(GH3)3], 46.00 KH2-
CH2], 52.00 E(CH3)3], 53.32 [N&Hd - (70 eV): m/z (rel. int %): 184 (20) [Ml+, 183 (1 OO), 169 (1 5), 127
(34), 1 1 3 (89), 84 (Z), 71 (86), 57 (35).
3.2.1 0 Preparation of t ,3-Diphenylimidazolidine (2Ph-H2)
30 mL of dichloromethane was added to a solid mixture of I12-dianilinoethane (8.59
g, 40.5 mmol) and paraformaldehyde (1.21 g, 40.5 mmol) in a 1 00 mL round bottom fiask
attached to a condenser and equipped with an oil bubbler. Upon refluxing over a 3 d
period the cdour of the suspension graduaily changed from dear to black and the solvent
was removed under reduced pressure. Sublimation of the light brown residue (0.1 Ton;
110 OC) results in the isolation of the white crystalline solid 2Ph-Hz. Yield 7 g (77 %).
m.p, FT-I R
1H NMR
119 OC. (Mull, KBr): u = 3092 cm1 w, 3064 w, 3037 w br, 2941 w, 2845 w,
1596 s, 1577 s, 1497 s, 1455 w, 1442 w, 1384 m, 1333 m, 1384 m, 1333m, 1228s, 1202s, 1162s, 1127m, 1034m, 984m, 971 rn, 971
m, 933 s, 881 m, 837 m, 751 s, 689 s, 507 m, 478 W.
(200 MHz, CDC13, 25 OC): 6 = 3.66 ppm [s, 4H, Ci&-CM, 4.67 [S.
2H, N2C&], 6.68 [d, 4H, o-CH~, 1J(H, H) = 8.1 HZ], 6.80 [t 2H, p- C k , 'J(H, H)=7.3Hz], 7.30 [t,4H, mC&, 'J(H, H)=7.7Hz].
1 3 C { l ~ ) NM R (100.4 MHz, CDC13, 25 OC): F = 46.47 ppm [CH&H2], 65.85
[N&H2], 1 12-44 [O-SM, 1 17.64 [p-CHA, 129-36 [m-GHd, 1 46.41
CNC(CH2)21. El-MS (70 eV): m/z (rel. int. %): 224 (60) [Ml+, 223 (81 ), 1 1 9 (70), 1 06 (63),
91 (IOO), 77 (54), 65 (9), 51 (21).
3.2.1 1 Preparation of 1,3-Dimethylimidazolidine (2Me-Hz)
N,NLdimethylethylenediamine (8.46 g, 96 mmol) was added dropwise into a 100
mL Schlenk flask contahing parafonaldehyde (2.89 g, 96 mmol). The mixture was stined
for 2 h, which resulted in a dear yellow colour. The product was then dissolved in a mixture
of 15 mL of water and 20 mL of dichloromethane. 2Me-H2 was then extracted by removal
of the organic dichloromethane layer. The solvent was removed in vacuo and the crude
product distilled (0.1 Torr, 42 OC) to give a colourless liquid. Yield 8.5 g (89 %).
b.p. 42 OC (0.1 Torr).
FT-I R (Neat, NaCI): u = 2942 cm-' s br, 2793 s br, 2703 m br, 1 665 m br, 1453 s br, 1369 s, 1227 s br, 1339 m, 1115 m, 1032 s br, 871 m br, 809 m.
1H NMR (200 MHz, CDCI3, 25 OC): 6 = 2.40 ppm [s, 6H, C h 1, 2.80 [s, 4H, C&-Ck], 3.33 [s, 2H, N2CHpJ.
13C{lH} NMR (50.28 MHz, CDC13, 25 OC): 6 = 41.60 ppm [CH3], 54.67 [CH2- CHz], 79.85 [N&H2]. -
El-MS (70 eV): mlz (rel. int. %): 1 98 (22) [Ml+., 1 97 (1 OO), 1 83 (8), 1 41 (25), 98 (22), 84 (31 ), 70 (37), 57 (36).
3.2.1 2 Preparation of 1,3-Di-tert-butyl-3,4,5,6-tetrahydropyrimidine (%Hz)
In a 1 00 mL Schlenk flask, paraformaldehyde (1 .O6 g, 35.4 mmol) was added to
Nldi-tert-butylpropanediamine (6.60 g, 35.4 mmol) dissolved in 20 mL of diethyl ether.
The reaction was stirred until dl of the parafomaldehyde was consumeci. The upper organic
layer is physically removed from the lower aqueous layer, and the product is fu-r
extracted from the aqueous layer with diethyl ether. CaH2 is added to the combined ether
layers and, after stimng for one day, the solution is fiitered. Removal of the ether under
reduced pressure leaves behind a white crystailine solid charaderized as 3-Hz. Yield 6.03
m.p. 129 OC. FT-I R (Neat, NaCI): u = 3037 cm-' w, 2969 br, 2872 w br, 2790 m br, 2690
w br, 2666 m, 261 6 w, 2526 w, 1478 m, 1465 rn, 1429 w, 1409 w, 1387m, 1358s, 1271 s, 1216sbr, 1169m, 1149 m, 1072 s, 1023 s, 985 rn, 963 m, 929 w, 904 w, 805 m, 756 m.
'H NMR (200 MHz, C&, 25 OC): 6 = 1.04 ppm [ç, 9H, NC(C&)3], 1.61 [qn,
2H, CH2C&CH2, 3~ = 5.4 Hz], .2.52 [t, 4H, CH&H2Ci&, 3~ = 5.4
Hz], 3.44 ppm [s, 2H, NC&N].
13C{1H) NMR (100.4 MHz, C6D6, 25 OC): 6 = 26.83 ppm [CH&H2GH2], 29.31
[NC(CH3)3], 45.99 [CH&H&H$J, 53.24 [NC(CH3)3], 65.31
INSH21. El-MS (70 eV): rn/z (rel. int %): 1 98 (22) [Ml*, 1 97 (1 OO), 1 83 (8). 1 41 (25),
98 (22), 84 (31 ), 70 (37), 57 (36).
3.2.1 3 Preparation of 1,3-Di-tert-butylimidazolium Chloride (11 -H][CII)
I
12M HCI O 2 'BUNH~ + (CHWn cN$ CI
bJ
Using a 2000 mL 3neck round bottom fia& equipped with a condenser,
themorneter and an addition funnel, tert-butylamine (630 rnL, 6 mol) was slowly added to
90 g of paraformaldehyde (3 mol). During the addition, water was passed through the
condenser and the temperature of the solution was not allowed to exceed 45 OC. The fiask
was allowed to cool to room ternperature and HCI (2.50 mL, 12 M, 3 mol) was slowly
added to the mixture. A 40% aqueous solution of glyoxal (344 mL, 3 mol) was then added
to the white suspension, resulting in a red solution which was refluxed at 11 5 OC (oil bath
ternperature) for 24 h. Water was removed under reduced pressure using a rotary
evaporator. The brown residue [l-H][CI] was spectroscopically pure (AH NMR, 85 %
yield) and was used without further purification. A colourless solid can be obtained when the
crude product is washed with acetone (67 % recovery).
1H NMR (200 MHz. CDC13, 25 OC): 6 = 1.80 ppm [s, 18H, C(C&)3], 7.63 [s, 2H, CH, 10.36 [s, 1 H, CH].
13C{1H) NMR (500 MHz, CDCI3, 25 OC): 6 = 30.29 ppm [C(Ql-f3)3], 60.76
E(CH3)3], 1 19.71 EH=CH], 134.51 TC-Hl.
13C NMR (500 MHz, CDC13, 25 OC): 6 = 30.29 ppm [qr, C(cH3)3. J (C,H) = 128.2 HZ, 3J (C,H) = 128.9 HZ], 60.76 (s, C(CH3)3], 119.71 [d,
ÇH=CH, 'J(C,H) = 199.9 HZ], 134.51 [d,C-H, 1J(C,H) = 219.7 HZ].
3-2.1 4 Preparation of 1,3-Di-tert-butylimidazolidinium Chloride ([2-H][Cl])
Method A
I NCS O
CHCl I
In a 100 mL round bottom flask attached to a condenser, 6.67 mL of 1,3-di-tert-
butylimidazolidine [this thesis pg. 661 (5.89 g, 32 mmol) was added dropwise to a cooled
(ice bath) suspension of Nchlorosuccinimide (4.27 g, 32 mmol) in 30 mL of chloroform.
Stimng the mixture for 15 min resulted in the complete dissolution of NCS and the formation
of a ciear yellow solution, w h i i was refluxed for 8 h. The solution was transferred to a
sublimation flask and the solvent removed under vacuum (0.1 Torr). Succinimide was
removed by sublimation (0.1 Ton; 170 OC) and [2-H][CI] was isolated as the brown
sublimation residue. Yield 6.72 g (96 Oh).
Method 8
'7 u 'BU NCS O
I THF
'BU -Succinimide ' B ~
Nchlorosuccinimide (0.58 g, 4.3 mmol) was slowly added to a 20 mL THF solution
of 1,3-di-tee-butylimidazolidine [mis thesis pg. 661 (0.80 g, 4.3 rnrnol). The addition of
NCS caused the solution to become yellow and turbid. The suspension was stirred for 1 h
12-HIICI1 was collected by fiitration and washed hot anhydrous THF (2 x 10 mL), this
process removes traces of succinimide. Yield 0.48 g (51 %). Note: This reaction will go to
completion (monitored by 'H NMR), if mixing time is increased.
Method C
N,N'-tert-butylethylenediarnine (1.07 g, 6.2 mmol) was slowly added to a
suspension of DMF chloride (0.74 g, 6.2 mmol) and potassium carbonate (m. 0.3 g) n
dichloromethane. The exothermic reaction was accompanied by the evolution of gas. The
solution was stirred for about 1 hl filtered through a fine porosity g las frit and transferred to a
sublimation flask, where it was concentrateci under reduced pressure to yield a yellow solid.
The I H NMR spectnim of this yellow solid shows 'Bu peaks of a second volatile,
unidentifieci reaction product. Separation cm be achieved by sublimation (0.1 Torr, 140
OC). The brown crystalline sublimation residue has been characterized as [2-H][CI]. Y ield
0.55 g (41 %).
Method D
1,3-Di-tert-butylirnidazolidine [this thesis pg. 661 (1 2.70 g, 69 mmol) and carbon
tetrachloride (53.1 g, 345 mmol) were mixed together in a 100 mL round bottom fiask
attached to a condenser equipped with and inert gas inlet and an oil bubbler. The solution
was refluxed for 8 h under argon. The solvent was removed under reduced pressure and
the residue rectystallized from 20 mL of 1,2-dichloroethane and 8 mL of petroleurn spirits to
produce light brown crystals of [2-H][CI]. Yield 1 2.30 g (82 5%). Stimng a 1 : 1 mixture of 2-
73
Hz and CC4 in THF also led to the fomiation of 12-H][CI]. This is extremely slow and no
traces of product can be seen within the first 3 hours.
m.p. 163-166 OC.
FT-IR (Nujol, NaCI): u = 2922 cm-1 s br, 1545 m, 1455 s br, 1375 s, 1204 rn,
1222 m, 809 w, 748 w, 604 m.
rH NMR (399.3 MHz, CDC13, 25 OC): 6 = 1.55 pprn [s, 18H, C(CH3)3], 4.05
Cs, 4H, C&], 8.83 [s, 1 H, CH].
13C NMR (1 00.4 MHzy CDC13, 25 OC): 6 = 28.1 0 ppm [qr, C(CH3)3, J(C,H)
=127.7 HZ], 45.19 [t, cH2-GH2, 1 J(C,H) = 147.9 HZ], 57.1 1 [S C(CH3)~], 153.86 [d, - H , 1 J(C,H) = 201.4 HZ]. -
ES-MS ES(+) m/z = 181 [Ml+. ES(-) m/z = 35, 37 [CI]-.
3.2.1 5 Oxidation of 1,3-Di-tert-butylimidazolidinium Chloride with CuC12
tEp 'BU 2 CuCI2
I iso-propanoi y 'BU 'BU 2-H2 I2-HIlXI
1,3-Di-terf-butylimidazolidine [this thesis pg. 661 (0.87 g, 4.70 mmol) and copper
dichloride (1.27 g, 9.00 rnmol) were mixed together m 20 mL of isepropanol in a 1 00 m L
round bottom flask attacheci to a condenser and equipped with an oil bubbler. The solution
was refluxed for 17 h. As the solution is being cooled to room temperature the growth of
fine needles of product is noticed. These crystais characterized as 12-H][X] were collecteci
by filtration, dried and weighed. Yield 0.576 g.
1H NMR (200 MHz, CDCI3, 25 OC): 8 = 1.54 ppm [s, 4H, Ci&], 7.28 [ç, 1 H, CH]-
13C{1H} NM R (100.3 MHz, CDC13, 25 OC): 6 = 28.34 ppm
CH21, 57.1 1 [C(CH3)3], 152.08 [CH]. - ES-MS ES(+) m/z = 183 [Ml+. ES(-) m/z = 132, 134,
3.2.1 6 Preparation of 1,3-Di-tertlbutyiimidazolidinium Bromide
Method A
1,3-Di-tert-butylimidazoIidine [this thesis pg. 661 (0.93 g, 5.0 mmol) and carbom
tetrabromide (1.67 g, 5.0 mmol) were dissolved m 20 mL of THF in a 100 mL Schlenk
fia& The d o u r of the solution immediately changes frorn cdouriess to yellow and a white
precipitate is fonned. The mixture was allowed to stir for 1 h and then filtered through a fine
porosity g las frit to isolate [2-H][Br]. The white powder was washed with THF (2 X 1 Q
m l ) and dried in vacuo. YieId 0.89 g (67 %). For spectroswpic data see under "Method
Method B
2-H2 [Z-Hwr]
1,3-Di-tert-butylirnidazolidine [this thesis pg. 661 (0.9 g, 5.0 mmol) and carbon
tetrabromide (1.6 g, 5.0 mmol) were dissolved m 20 mL of CHCI3 in a 100 mL round
bottom Rask attached to a condenser. The resulting yellow solution was heated to reflux foq
8 h, The solution was allowed to cool to r.t and the solvent was then rernoved under
reduced pressure (0.1 Torr). The brown residue was characterized as [2-H][Br]. Yield 1.28
g (97 %).
Method C
NBromosuccinimide (0.69 g, 3.9 mmol) was slowly added to a 20 mL THF solution
of 1,3-di-tert-butylimidazolidine [this thesis pg. 661 (0.72 g, 3.9 mmol). A light brown
precipitate drops out of solution as NBS k added to the mixture. The suspension was
çtirred for 1 h and the product [2-H][Br] was fiitered through a fine porosity glas frit. The
solid was washed with hot THF (2 x 10 mL) to remove succinimide. The brown solid is then
dried under reduced pressure (0.1 Torr) and weighed. Yield 0.97 g (94 %).
m.p. 115-116 OC. FT-1 R (Nujol, NaCI): u = 2922 cm-' s br, 2854 s br, 1627 m. 1461 s, 1376 S.
1202 w, 1056 W.
1H NMR (200 MHz, CDCI3, 25 OC): 6 = 1.55 ppm [s, 18H, C(C&)3], 4.1 2 [s,
4H, C&], 8.1 8 [s, 1 H, CH].
13C{tH) NMR (50.29 MHz, CDC13, 25 OC): 6 = 28.60 ppm [s, C(CJH3)3], 46.07 [s, CH?-CHd, 57.42 [s, C(CH3)3], 1 52.81 [s, C-HL -
ES-MS ES(+) m/z = 183 [Ml+. ES(-) m/z = 79, 81 [Br]-.
3.2.1 7 Preparation of 1,3-Di-tert-butylimidazolidinium lodide (12-HI[[])
2-H2 [2-HI[1I 2-H2. h
le (0.57 g, 2.27 mmol) and 1,3-di-ter+butylimidazolidine [this thesis pg. 661 (0.84 g,
4.5 mmol) were stirred together using 20 mL of THF m a 100 mL Schlenk flask until the
brown suspension tumed colouriess. The solvent was removed under reduced pressure
76
leaving 1.39 g of a white crystalline residue in the flask. H and '3C NMR indicate that this is
a mixture of two compounds. Attempts to separate the undesired product from the mixture
by sublimation, s i l i column chromatography (DMSO eluent) or recrystailization form
dichloromethane and hexane solutions were not successful.
12-Hl [Il : 1H NMR (200 MHz, CDC13, 25 OC): 6 = 1.55 ppm [s, l8H, C(C&)3], 3.99 [s,
4Hy C M , 8.17 [s, lHy CH].
13CC H) N M R (50.29 MHz, CDCI3, 25 OC): 6 = 28.60 ppm [s, C(ÇH3)3], 46.1 1 [s,
CH2-CH2], 152-74 [s, C-Hl. -
2-HpI2:
1 f l NMR (200 MHz, CDC13, 25 OC): 6 =1.32 ppm [SI, 1.84 [s], 3.21 [SI, 4.13 [SI. 13C{lH) N M R (50.29 MHz, CDC13, 25 OC): 6 = 28.84 ppm, 45.71, 63.03.
3.2.1 8 Preparation of 1,3-Diphenylimidazolidinium Bromide ([2Ph-H][Br])
NBromosuccinimide (0.16 g, 0.9 mmol) was slowly added to 1,3-
diphenylirnidazolidine [this thesis pg. 671 (0.2 g, 0.9 mmol) dissolved in M F . A white
precipitate drops out of solution within the first minute of stimng the mixture. The suspension
was filtered through a medium porostty glas frit after 1 h of vigorous stimng. The white solid
[2Ph-H][Br] collected in the frit was washed with hot THF (10 ml ) to remove any traces of
succinimide. Yield 0.24 g (89 %).
m.p. 168-170 OC. FT-IR (Nujol. NaCI): u = 3382 cm-l w br, 2923 s br, 2853 v br, 1714 w br,
1618 s, 1587 s, 1494 w, 1462 s, 1376 ml 1296 s, 761 m, 688 m.
1H NMR (200 MHz, CDCI3, 25 OC): 6 = 4.61 ppm [s, 4H, Cb-CH2], 7.38 -7.71 [m, 4H, +CH2, p-Ci&, rn-C&J, 10-03 [s, 1 H, CH].
13C{1H) NM R (50.98 MHz, CDC13, 25 OC): 6 = 48.55 ppm KH&H2], 118.50 [e CHz], 127.20 [p-GHA, 129.40 [m-ÇHA, 146.41 [NÇ(CH2)2], l5l.9O - TC-Hl.
ES-MS ES(+) rn/z = 223 [Ml+. ES(-) m/z = 79, 81 [Br]-.
3.2.1 9 Preparation of 1,3-bimethylimidazolidinium Bromide (DMe-H][Br])
N-Bromosuccinimide (5.64 g, 32 mmol) was slowly added to a 30 mL THF solution
of 1,3-dirnethylimidazolidine [this thesis pg. 681 (3.1 7 g, 32 mmol). The solution became
cloudy as the NBS was being added to the solution. The mixture was allowed to for 2 h
of. The solvent was removed under reduced pressure and the yellow solid was tramferreci
to a sublimation flask. Succinimide sublimeci out of the cmde mixture (0.1 Torr, 120 OC) and
the [2Me=H][Bq was isolated as the black gum-iike residue. Yield 5.4 g (94 %).
I H NMR
13C{1~} NMR
ES-MS
oiI. (Neat, NaCI): u = 3444 cm-' v br, 3038 br, 2966 br, 2814 w, 2361 w,
2069 w, 1660 s, 1537 m, 1443 ml 1 41 6 m, 1301 s, 1205 w, 1 150 s,
1098 w, 1080 w, 978 w, 897 w, 666 S.
(399.3 MHz, üMSO-d6, 25 OC): 6 = 3.08 ppm [s, 6H, C b ] , 3.85 [s, 4H, CH2], 8.42 [s, 1 H, CFI].
(1 00.4 MHz, DMSO-d6, 25 OC): 6 = 34.07 ppm [qr, ÇHs,], 50.20 [s, C HP-C H2], 1 58.29 [d, - H l . -
ES(+) m/z = 99 [Ml+. ES(-) rn/z = 79, 81 [Br]-.
3.2.20 Preparation of 1,3-Di-tert-butyl-3,4,5,6-tetrahydropyrimidium Bromide
(P-Hl[Brl)
NBromosuccinimide (1.44 g, 8.10 mrnol) was slowly added to a 30 mL THF
solution of 1,3-di-tert-butyltetrahydropyrimidine [this thesis pg. 691 (1.60 g, 8.1 0 mmol) in a
100 mL Schlenk flask. A white solid precipitates irnmediately after the addition of NBS. 13-
H][Br] was collected by filtration through a fine porosity glass frit after 1 h of vigorous stimng,
washed with hot THF (1 0 mL x 2) to remove succinimide. and dried in vacuo. Yield 1.87 g
1H NMR
ES-MS
205-207 OC. (Nujol, NaCI): u = 2923 cm-' br s, 2854 br s, 1652 m br, 1462 m br,
1387 m br, 1337 w br, Il86 w, 997 W.
(200 MHz, CDCI3, 25 OC): 6 = 1.56 ppm [S. 18H, C(C&)3]. 2.20 [qr, 2H, CH2Ci&CH2], 3.60 [t, 4H, NCt&CH2], 7.94 [s, 1 H, CH]. (1 00.4 MHz. CDC13, 25 OC): 6 = 19.84 ppm [CH&H2CH2Iy 27.87 [C(C33)3], 40.1 2 [NÇH2CH2], 69.30 [C(CH3)3], 146.46 E-Hl.
ES(+) rn/z = 197 [Ml+- ES(-) m/z = 79, 81 [Br]-.
3.2.21 Preparation of 1,4-Di-tert-butyl-4-formyl-1 ,Cdiaza-but4 sne (4)
H20 &. .-- p b'
- THF
Water (23 PL, 23 mg) was added to a solution of 1,3-di-ted-butylimidazole-2-
ylidene (ci 25 mg) dissolved m 5 mL of THF. This mixture was stirred for 1 week
hydrolyzing the carbene in quantitative yield. The product can be distilled (0.1 Torr, 50 OC).
m.p. FT-I R
1H NMR
oil. (Neat, NaCI): u = 2969 cm-' v br, 1736 m, 1651 br, 1473 br, 1425 br,
1378 br, 1274 s, 1207 br, 1064 m, 1031 m, 996 rn, 937 m, 872 m,
829 w, 810 w, 752 w, 702 W.
(200 MHz, CDCI3, 25 OC): 6 = 1.16 ppm [s, C(C&)3], 1.36 [s,
C(CH3)3]y 4.1 5 [d, Cki2], 7.44 [t, HC=N], 8.53 [s, HC=O]. (200 MHz,
C6D6. 25 OC): 6 = 0.88 ppm [s, C(C&)3], 1.08 [s, C(CH3)3], 4.16 [d, CHJ, 7.53 [t, HC=N], 8.44 [s, &=O].
(100.4 MHz, C&, 25 OC): 6 = 29.4 ppm [s, C(C-H3)3], 29.5 [s,
c(CH3)3l, 45.9 [s, CH2], 54-9 [S. C(CH3)3], 56.7 [s, C.(CH3)3], 155.8 [s, HÇ=N], 161 .O [s, HS=O].
(70 eV): nVz (rel. int %): 198 (10) [Ml+., 141 (8), 127 (21), 115 (41),
99 (23), 97 (24), 85(14), 69 (24), 59 (72), 57 (1 00).
3.2.22 Preparation of WFormyl-N,N'-di-tert-butyi-ethylenediamine (5)
Distilled water (43 PL, 0.043 g, 2.4 mmol) was added to a solution of 1,3-di-tert-
butylimidazolidine-2-ylidine [ais thesis pg. 591 (0.43 g, 2.4 mmol) dissolved in 6 mL of
80 THF, the mixing was accompanied by heat evolution. The solution was stirred for 30 min
and the solvent removed under reduced pressure gives 5 m a quantitative yieel as a
crystailine white product, which sublimes at 0.1 Torr and 60 OC.
FT-I R
1H NMR
(Nujol, NaCI): 3303 s, 2957 s, 2924 s, 2851 br s, 2725 br w, 2659 br
w, 2400 br w, 1716 w, 1663 s, 1643 s, 1563 w, 1516 br w, 1463 s, 1 3 7 7 ~ ~ 1364 s, 1311 ml 1297 w, 1284 w, 1264 w, 1231m, 1211 m, 1198s, 1138 rn, 1098 m, 1052rn, 1032 m, IO18 m. (200 MHz, CsD6, 25 OC): 6 = 0.86 ppm [s, NH-C(Cb)3], 1 .O1 [s, O=CH-N-C(C&&], 2.72 [t, NH-Cf&J, 3.33 [t CbN(CHO)], 8.40 [s,
H-CO]. (400 MHz, CeDe, 25 OC): 6 = 0.85 ppm [s, NH-C(CH3)3JY - 1.02 [s, O=CH-N-C(C&J)~], 2.74 [t NH-Cm, 3.33 [t, C&N(CHO)],
8.41 [s, H-CO].
(100.4 MHz, C&, 25 OC): 6 = 29.2 ppm [s, NH-C(CH3)3], 29.4 [OSH-N-C(CH3)3], 42.3 [NHÇHA, 43.1 EH2N(CHO)], 50.0 [NH- C(CH3)3], 54.2 [O=CH-N-Ç(CH3)3], 161.1 [H-O]. - (70 eV): m/z (rel. int. 5%): 201 (5) [Ml", 186 (27), 173 (2), 158 (4), 144
(1 l ) , 129 (17), 116 (4), 99 (92), 86 (IOO), 72 (44), 57 (47).
3.2.23 Preparation of 1,3-Di-tert-butyl-4,5-bis-deutero-imidazole-2-ylidene
(1 '02)
1 1 -D2
D-= DMSO-d6 or MeOD-d4 or D20
1,3-Di-tert-butylimidazole-2-ylidine [this thesis pg. 581 (1.3 g, 7.2 mmol) was
dissolved in 5 mL of dimethylsulfoxide-d6 and stirred for 10 minutes. The solution was
extracted with hexane (3 x 5 ml). The cornbined hexane extracts are evaporated giving a
colourles crystalline product which can be purified by sublimation (0.1 Ton; 40 OC). Yield
0.7 g (53 %)
m.p. FT-IR
1H NMR
13C{1H) NMR
59-61 OC. (Neat, NaCI): u = 31 61 cm-' w, 31 00 S. 3071 s, 3000 - 2901 br, 2708
w, 2591 w, 2387 w, 2371 w, 2309 s, 1671 m, 1457 s br, 1392 s br,
1362s br, 1317 s, 1277~~ 1231 s br, 1134 m, 1120 s, 1101 s, 1030
ml 995 s, 982 s, 970 ml 920 w, 877 s, 860 s, 826 s, 786 s, 766 s, 669,
s, w, 659 S.
(399-3 MHz, DMSO, 25 OC): 6 = 1.48 ppm [s, C(CHJ)~]; (600.1
MHz, C6D6, 25 OC): 6 = 1.51 ppm [s, C(CH3)3].
(150.9 MHz, DMSO, 25 OC): 6 = 30.95 ppm [s, C(CH3)3], 55.16 [s,
C(CH3)3], 115.44 [t, ÇD=ÇD, lJ(C,D) = 27.53 Hz], 208.7 [s br, - N&]; (150.9 MHz, C6D6, 25 OC): 6 = 31.46 ppm [s, C(ÇH3)3], 55.76 [s, C(CH3)3], 1 14.90 [t, ÇD=CD J(C,D) = 27.20 HZ].
(70 eV): m/z (rel. int O/): 182 (21) [Ml+., 126 (36), 11 1 (17), 83 (12),
71 (1 00) , 70 (76), 57 (64).
3.2.24 Preparation of 1,3,5-Tri-tert-butyl-1,3,5-triazacyclohexane (tBu3TAC)
B U~TAC
Paraformaldehyde (1 7.9 g, 0.58 mol) was slowly added to a 250 mL round bottom
flask containing tert-butylamine (40.4 g, 0.58 mol). The fiask was cooled using an ice bath
prior to the addition of parafomaldehyde. The mixture was allowed to çt-r unül ail the
paraformaldehyde had dissolved. 20 mL of water were then added to the reacüon mixture
and 1,3,5-tri-tert-butyl-1,3,5-triazacyclohexane was extraded with dichlorornethane (3 x 50
mL). The combined organic layerç were dried with MgS04 (30 min) which was
subsequently removed by filtration. The fihte was evaporated lR vacuo and the residue
separated by fractional distillation. 5-Tert-butyl-l,3,5-dioxinane was collecteci at 80 OC (1 7
Torr) and characten'zed by NM R spectroscopy. 1,3,5-Tri-terf-butyl-l,3,5-triazacycIohexane
distilled at 140 OC (1 7 Torr) as a colourless liquid (0.42 mol , 72%).
1,3,5-Tri-tert-butyl-1,3,54riazacyclohexane: b.p. 140 OC (17 Torr).
FT-I R (Neat, NaCI): u = 3028 cm-' m, 2970 s, 2873 w, 2797 m, 2672 m,
1478 m, 1409 w, 1387 m, 1358 s, 1269 s, 1202 s, 1 175 m, 1 150 m,
1074 m, 1025 m, 1008 m, 985 m, 909 m, 898 m, 836 m. 1H NMR (200 MHz, C&, 25 OC): 6 = 1.12 ppm [s, W. C(CH3)3], 3.72 [s, 6H,
NzCb]. (200 MHz, CDC13, 25 OC): 6 = 1.05 pprn [s, 9H, C(Cii3)3],
3.45 Cç, 6H, N2C&J. 13C{lH} NMR (500 MHz, C & 3 , 25 OC): 6 = 27.25 pprn [C(CH3)3], 52.85
[ç(CH3)3], 63.77 [N&H2]- (500 MHz, CDCI3, 25 OC): 6 = 26.8 pprn
[C(W3)31, 53.1 K(CH3)31. 63.94 [N&H21- El-MS (70 eV): m/z (rel. int 5%): 254 (c 3) [Ml+., 223 (c 3 ), 198 (< 3). 170
(Z8) , 1 55 (1 4), 86 (79), 70 (1 OO), 57 (84).
btert-Butyl-l,3,5-dioxinane: b.p. 80 OC (1 7 Torr).
1H NMR (399.3 MHz, CDC13. 25 OC): 6 = 1.29 ppm [s, 9H, C(CH3)3], 4.86 [s, 4H, NC&O], 5.20 [s, 2ti, OCi&O].
13C{lH} NMR (100.4 MHz, CDC13, 25 OC: 6 = 30.24 pprn [s, C(eH3)3]. 79.52 [s,
NCH201, 95.32 [s, XH201.
El-MS (70 eV): rn/z (rel. int. %): 145 (8) [Ml*, 144 (15 ), 130 (45), 88 (28), 70
(1 00), 60 (1 2), 57 (56), 55 (1 1 ).
3.2.25 Dissociation of 'Bu3TAC into tert-Butylimine
A commonly observed phenomenon for some 1,3,5-triazacyclohexaneç is their
equilibrium with the respective imines. In oie case of 1,3,5-tri-tert-butyl-l,3,5-
tnazacyclohexane, the corresponding imine is observed when BU 3TAC is dissolved n
83
polar or polarizable solvents (CHCI3, CC14). The signais of the imine are visible m the 1 H
NMR spectrum immediately upon dissolving.
1H NMR (200 MHz, CDCI3, 25 OC): 6 = 1.12 ppm [s, C(C&)a], 7.28 [m, N=C&].
13C{lH) NM R (500 MHz, CDC13, 25 OC): 6 = 28.9 ppm [G(GH3)3], 58.1 [C(CH3)3], 147.1 [N=CH2].
3.2.26 Synthesis of 1,3,5-Tri-phenyl-l,3,5-triazacyclohexane (PhsTAC)
Aniline (3.70 g, 40 rnrnol) and paraformaldehyde (1 .O0 g, 33.3 mmol) were &in&
neat for 2 days in a 100 mL Schlenk flask at room temperature. The crude material was
recrystallized from chlorofon to give 2.80 g (80 %) of orange crystals.
m.p. 134 OC. FT-IR (Neat, KBr): u = 3092 cm-' w, 3064 w, 2940 w, 2845 w, 1921 w, 1596
s, 1577s, 1496s, 1455m, 1384m, 1333m, 1228 s, 1202 S. 1161 s, 1121 m, 1034 m, 920 s, 837 rn, 751 s, 689 s, 507 m, 478 W.
1H NMR (399.3 MHz, CDC13, 25 OC): - = 4.87 ppm [s, 6H, N2CH21, 6.85 [t, 3H, p-CH2, 1 J(H, H) = 7.3 HZ], 7.00 [d, 6H, O-CH2, 1 J(H, H) = 7.7 Hz], 7.20 [t, 6H, m-CH2, 1 J(H, H) = 8.0 Hz].
13C(1~) NMR (100.4 MHz, CDC13, 25 OC): 6 = 68.57 pprn [N&.H2], 11 7.69 [e CHz], 120.94 [pCH2],129.20 [m-.Hz], 148.67 [&(CH&]. -
El-MS (70 eV): rn/z (rel. int %): 315 (1 1) [Ml+., 210(97), 105 (100), 91 (7),
77 (35), 51 (1 5).
3.2.27 Synthesis of l,3,5-Tri-methyl-l,3,5-triazacyclohexane (Me3TAC)
M e3TAC
A 40% aqueous soiution of methylarnine (30.5 mL, 12.2 g, 0.4 mol) was added
slowly to a 250 mL round bottom Rask containing paraformaldehyde (1 1.8 g, 0.4 mol). The
flask is set in an ice bath and the mixture was stirred for 3 h. The mixture was then
transferred to a separatory funnel and 1,3,5-trimethyl-l,3,5-triazacyclohexane extracted with
dichloromethane (5 x 50 mL). The combined extracts (lower phase) were dried over
M gSO4 and filtered prior to evaporating the dichloromethane in a rotary evaporator. The
rernaining clear liquid was distilled (32 OC 1 1 5 TOIT) to give 21 g (0.34 mol, 86 5%) of pure
1H NMR
13C(1H) NMR El-MS
32 OC (1 5 Torr). (Neat, NaCI): u = 2940 cm-' s, 2890 m, 2843 m, 2786 s br, 2725 m, 2629 m, 2596 m, 2571 m, 1684 m, 1469 s, 1442 s, 1427 s, 1385 s, l372s, l262s, 1237s, 1157s, 1116s, 1049m, 1025s, 1003 s, 859
s, 836 w, 623 m. (200 MHz, CDC13, 25 OC): 6 = 2.29 ppm [s, 9H, Ci&], 3.20 [s, 6H,
N2CbI. (50.29 MHz, CDC13, 25 OC): 6 = 40.25 ppm EHJ], 77.37 [NzÇHA.
(70 eV): mlz (rel. int %): 129 (9) [Ml+', 128 (22), 86 (34), 57 (18), 44
(IOO), 28 (17), 18 (41), 15 (10).
3.2.28 Synthesis of 1,3,5-Tri-tert-butyl-1,3,5-triazacyclohexyl Carbeniurn Chloride (pBu3TAC][CI])
Method A
A
'BU
'BU~TAC If B U,TAC][C l]
A solution containing 1,3,5-tris-terf-buw-l,3,5-triazacyclohexane [this thesis pg. 811 (1 0.69
g, 41 .O0 mm01 ) and of CC14 (1 0 mL, 88.00 mrnol) was heated to reflux in a 100 rnL round
bottom fiask attached to a condenser for 3 d. An hair into the reaction buoyant colourless
crystals appear. After 3 d the solution is allowed to corne to r-t. and CC14 is removed under
reduced pressure (0.1 Torr). The solid residue (8.9 g) was washed with benzene and
characterized as PBu3TAC][CI] by NMR. Yield 4.36 g (31 %). The benzene soluble part
consists of 'Bu3TAC and traces of N, NI-di-te~~utyifomiarnidinium chloride (1 -37 g, 17 %),
which was isolated by sublimation as a crystalline colourless solid (0.1 Torr, 1 30 OC).
Method B
'q u
CC1 /--"!,O O - 'Brr~ ÇH CI
Y benzene
'Bu L~
'BU 'BU~TAC ~ ~ U ~ T A C ] [ C I ]
1,3,5-Tri-te&-butyl-1,3,5-triazacyclohexane [this thesis pg. 811 (5 mL, 4.45 g, 17.4
mmol) was added to a solution of carbon tetradiloride (6.70 g, 43.5 mmol) in 20 mL
benzene. The mixture was refluxed for 2 d in a 100 mL round bottom flask attached to a
condenser and equipped with an oil bubbler. PBu3TAC][CI] was allowed to crystallize out
of the solution for 5 d and collected by filtration through a fine porosity glass frit. Yield 1.89 g
(38 %). Unlike method A, where N,Nt4i-teH-butylformamidinium chloride is obtained n
86
substantial amounts (17 %), method B leads only to trace arnounts of byproduct ('H
NMR).
Method C
'BU
NCS ~ B F N ~ ~ ) -
L?' THF
'Bu I
'BU 'BU~TAC ~BU~TAC][CI]
NChlorosuccinimide (1.1 g, 8.0 mmol) was slowly added to a cooled (ice bath)
solution of tBu3TAC [this thesis pg. 811 (2.0 g, 8.0 mmol) in 20 mL of THF. The
precipitation of a light yellow solid is noted as the NCS is added to the solution. The
mixture was allowed to çtir at room temperature for 9 h. rBu3TAC][CI] was collected b y
filtration through a fine porosity frit filter, washed with 3 x 5 rnL of hot THF in order to remove
succinimide, and dried under vacuum (0.1 Torr). Yield 1.7 g (74 5%).
1,3,5-Tri-tert-butyl-1,3,5-triazacyclohexyl Carbenium Chloride: m.p. FT-I R
1H NMR
13C{1H) N MR
ES-MS
123-1 26 OC. (Nujol, NaCI): u = 2924 cm-' br s, 1663 s, 1462 s, 1376 s, 1320 w,
I l 9 6 m, 1102 w, 905 W.
(200 MHz, C6D6, 25 OC): 6 = 1 .O4 pprn [s, 9H, C(Cl&)3], 1.45 [s, 1 8Hy C(C&)3]l 4.61 [s, 4H1 N 2 C u y 8-43 [s, 1 Hy CH].
(399.3 MHz, CDCI3, 25 OC): 6 = 27.89 ppm [C+(H)NC(CH3)3],
28.33 [CH2NC(CH3)3], 55.40 [CH2NC(CH3)3Iy 56.95 [NZHzl, 60.63 [C+(H)NC(CH3)3], 150.92 [C-Hl.
ES(+) m/z = 254 [Ml+. ES(-) m/z = 35, 37 [CI]-.
N,N'Di-tert-butylformamidinium Chloride: m.p. 277-280 OC. FT-IR (Nujol, NaCI): u = 3158 cm-' w br, 2923 s br, 1689 rn br, 1551 w br,
1463 m br, 1376 m br, 1334 w br, 1205 w br, 1076 W.
1H NMR
'3C<1H) NM R
ES-MS
87
(200 MHz, CsD6, 25 OC): 6 = 1.40 ppm [s, 9H, C(C&)3], 7.55 [s, 1 H, CH, 1, 10.37 [s, 2H, NH]. (50.29 MHz, CDC13, 25 OC): 6 = 29.87 ppm [C(CH3)3], 59.30
[C(CH3)j], 150.62 E-Hl.
ES(+) m/z = 157 [Ml+. ES(-) m/z = 35, 37 [CI]-.
3.2.29 Synthesis of 1,3,5-Tri-tert-butyl-1,3,5-triazacyclohexyl Carbenium Bromide (PBu3TAC][Br])
Method A
:3 NBS rN,@ vu O 'BU-N - %-y PH Br
LN THF EL Y
b u 'BU~TAC [tf3u3~~c J P ~ I
NBromosuccinimide (7.1 2 g, 40 rnmol) in 40 mL of THF was slowly added to a
cooled solution of tBu3TAC [this thesis pg. 811 (1 0.81 g, 40 mmol). The readion was
highly exotherrnic and the formation of a yellow precipitate is observed as soon as the
NBS is added. After 30 min stirring, the yellow solid PBu3TAC][Br] is collected by Ritration
through a fine porosity glas frit. The solid in the frit was washed (2 x 20 mL) wlh hot THF ii
order to remove succinimide. The product is then dried under reduced pressure (0.1 Torr).
Yield 10.4 g (78 %).
Method 6
'yu 'BU I
C8r4 r N , 0 O - benzene
I 6 u 'BU
'BU~TAC [ t ~ u 3 ~ ~ ~ ] [ ~ r ]
1 ,3,5-Tri-tefibutyl-1 ,3,5-triazacyclohexane [this thesis pg. 811 (5 mL, 3.90 g, 15.3
mmol) was added to a solution of carbon tetrabromide (5.07 g, 15.3 mmol) in 30 mL of
benzene in a 100 mL Schlenk flaçk The solution immediately tumed yellow and small
crystals started foming within 1 /2 h. After 2 d of vigorous stimng, the white precipitate was
isolated by decanting the solution into a second 100 mL Schlenk flask The precipitate was
washed twice with 10 rnL of benzene and the washings added dong with the former
decanted solution, ailowing for the isolation of [tBu3TAC][Br]. Yield 3.30 g (65 %). A
second crop of crystals was isolated from the decanted solution after 18 d (1.27 g, 25 %).
The solution was decanted and the white solid washed three tirnes with 15 mL of hexanes.
Combined yield = 90 %.
1H NMR
13C{1H) NMR
ES-MS
121-122 OC. (Nujol, NaCI): II = 2923 cm-' br s, 2854 br s, 1652 m br, 1456 m br,
1376 m br, 1324 w br, I l 8 6 w br, I l 8 6 w br, 1104 w br, 886 w- (600.1 MHz, CDCI3, 25 OC): 6 = 1.25 ppm [s, 9H, C(CH3)3], 1.58 [s,
18H, C(C&)3], 4.26 [s, 4H, N2CH71, 8.07 [s, 1 H, CH]. (150.9 MHz, CDCI3, 25 OC): 6 = 27.93 pprn [CC(H)NC(CH3)3], 28.38 [CH2NC(a3)3], 55.39 [CH2NÇ(CH3)3], 57.75 [NSHâ], 60.56 [C+(H)NC(CH3)3], 153.00 E-Hl.
ES(+) m/z = 254 [Ml+, 169, 86. ES(-) mlz = 79, 81 [Br]-.
3.2.30 Synthesis of Synthesis of 1,3,5-Trimethyltriazacyclohewyl Carbenium Bromide ([Me3TAC] [B r])
CBr4 r\@ @ Me-N - MF\ p H Br
hexanes N
Me I Me
Me3TAC [M e3TAC][B r]
Carbon tetrabromide (2.28 g, 7.0 mmol) and Me3TAC [this thesis pg. 841 (0.9 g,
7.0 mmol) were dissolved in 20 mL of anhydrous hexanes. The solution was sonicated for
1 /2 h at which point a significant amount of white precipitate was visible, and then sti~ed at
r.t for 3 d. The hexanes was decanted into a separate fi& and the precipitate
[Me3TAC][Br] washed twice wioi 10 mL of dry hexanes and dried under vacuum (0.1
Torr). Yield 1.35 g (93 %).
m.p. I l 5 OC. FT-IR (Nujol, NaCI): u = 3418 cm-' br w, 2923 br s, 2854 br s, 1693 m br,
1455 mbr, I W 4 m br, 1322 w br, I l 6 8 br, 9Wm, 835 W.
1H NMR (399.3 MHz, DMsO-d6, 25 OC): 6 = 2.48 ppm [s, 3H, CH2NC&],
3.08 [s, 6H, C+(H)NC&], 4.26 [s, 4H, N2CH2], 8.43 [s, 1 H, CH]. 13C(lH) N M R (1 00.4 MHz, DMSO-d6, 25 OC): 6 = 38.91 pprn [CH2NcH3], 39.16
[C+(H)NCH3], 65.91 [N&H2], 153.00 TC-Hl.
ES-MS ES(+) rnlz = 128 [Ml*, 85, 44. ES(-) mlz = 79, 81 [Br]-.
3.2.31 Attempted Synthesis of 1,3,5-Tri-tert-butyltriaracyclohexyl Tris- carbenium Bromide (PBu3TAC][Br3])
k I , O 2.2 NBS H,@ ,N @ ,H 'WN PH -
L?J CHCI3 F F N Q N t 'CA 'bu
PBu3TAC][Br] [mis thesis pg. 861 (1.66 g, 4.90 mmol) and Nbromosuccinimide
(1.94 g, 10.90 mmol) were dissolved in 30 mL of chloroform in a 100 mL round bottom
90
flask attad'ied to a condenser. The mixture was heated at reflux for 4 d. The dou r of the
solution at the end of the heating penod was light yellow and no precipitate was visible. 1 H
and 1% NMR showed that al1 pBu3TAC][Br] had been consumed m the reaction. The
only identifable component of the reaction was succinimide. The possibility of the presence
of bis- or triçcation was eliminated from inspection of the H and '3C NMR data. The only
product observed in the 1% NMR was succinimide.
1H NMR (200 MHz, CDC13, 25 OC): 6 = 1.61 ppm br, 1.87, 2.76, 3.86, 7.31,
9-1 7 (200 MHz, DMSO-d6, 25 OC): 1934, 1-38, 1 -45, 1-84, 2.53, 4.02,
8.34, 11 -05.
13C{1H) NM R (1 00.4 MHz, DMSO-d6, 25 OC): 6 = 29-40 ppm, 179.27.
3.2.32 Attempted Synthesis of 1,3,5-Tri-tert-butyltriaracyclohexyl Tris carbenium Chloride
'Bu 'BU~TAC
1,3,5-tri-tert-butyl-l,3,5-triazacyclohexane [this thesis pg. 811 (1 -78 g, 6.96 mmol)
were slowly added to a cooled 20 mL solution of Nchloroçuccinimide (2.79 g, 20.8 mmol)
in chloroform. The solution tumed cloudy during the addition the former compound. The
mixture was refluxed for 5 h. and an NMR of the crude components were taken h
chlorofom. The main product was later identified as N,N%li-tert-butylformamidinium chloride.
This product is found in a mixture of NCS, succinimide and traces of PBu3TAC][Br].
1H NMR (200 MHz, CDCI3, 25 OC): 6 = 1.15 ppm, 1.26, 1.35, 1.59, 2.67, 2.76,
4.67, 4.70.
3.2.33 Attempted Preparation of 1,3,5-Tri-tert-butyl-1,3,5-triazacyclohexane- 2-ylidene (9)
Method A
r i ( ( @ @ LDA t b ~ P H Br ---- {&-N
THF
~BU~TAC][B~] 9
A suspension of pBu3TAC][Br] [this thesis pg. 861 (1.53 g, 4.57 mmol) m 30 rnL
of M F was treated with 2.3 mL of LDA (2.0 M, 4.57 mmol). The suspension dissolved
within 1 min to yield a dear light yellow solution. At this point a 1 H and 1% NMR of the
cmde mixture was taken and it showed the presence of the desired cornpound. The THF
solutjon was wncentrated to dryness under reduced pressure (0.1 TOIT). The contents of
the 100 mL Schlenk Raçk were redisolved in benzene and filtered through a fine porosity
glass frit to yield 0.47 g of an off-white solid. The 1H NMR spectnim of the solid was similar
to the one obtained prior to filtration. i-iowever, the expected carbene should be an oil. This
can be said with confidence as the parent 1,3,5-triazacyclohexane is ako a liquid. An
attempt to separate the carbene from radion byproducts by sublimation was not
NMR (300 MHz, CsD6, 25 OC): 6 = 1.06 ppm [s, 9H, C(C&)3], 1.39 [s, 18H, C(Ct&)3], 3.91 [s, 4H, N2Ct&J.
13C{lH) NMR (75.44 MHz, C6D6, 25 OC): 6 = 27.71 ppm [CH2NC(ÇH3)3], 29.92
[C:NC(GH3)3], 52.40 [CH2NC(CH3)3Iy 58.23 [C:NC(CH3)3], 68.1 1 [N&H2], 238 [NG:].
Method B
'BU
J"4l * NaH dl
tBwN95H gr
* 'Bu-NT >: THF
'BU -H2 '--Y
'BU -NaBr 1% U~TAC] [ ~ r ] 9
A 1 5 m l THF suspension of PBu3TAC][Br] [this thesis pg. 863 (2 g, 5.98 mmol)
and NaH (0.1 437 g, 5.98 mmol) was stirred ovemight vigorously in a 100 mL Schlenk flask
The colour of the solution changed from yellow to gray. At this point no more hydrogen
evoiution was noticed. H and 1 3C NM R of the cnide solution did not show the expected
1H NMR (200 MHz, CsD6, 25 OC): 6 = 0.86 ppm, 0.95, 0.98, 1.1 2, 1.24, 1.26
3.2. 33 Attempted Preparation of 1 ,3,5-Tri-tert-butyl-1 ,3,5-triazacyclohexane- 2-thione (StBu3TAC)
6.73 mL (1.6 M, 9.79 mmol) of n-BuLi were slowly added to a 25 mL THF suspension of
3.27 g (9.79 rnmol) of PBuaTAC][Br] [this thesis pg. 861. An NM R of the cnide solution
(which did not show free carbene) was taken prior to the addition of suMir (0.31 g, 9.79
mmol). The desired product StBuTAC was not observed, instead the product was
identified as N,/V'di-terf-butylthiourea.
I I 4 NMR (399.2 MHz, CDC13, 25 OC): 6 = 1.47 ppm [s, 18H, C(CH3)3], 5.78
[s, 2H, NH]. 13C{lH) N MR (100.4 MHz, CDC13, 25 OC): 6 = 29.41 ppm [C(CH3)3], 53.23
[C(CHg)3J, 180.03 @=SI.
3.2.34 Preparation of Copper Dichloride 1 1,3,5-Tri-tert-butyl-1,3,5- triazacyclohexane Adduct (tB u3TACmCuCl2)
'BU~TAC ' B U ~ ~ A C c UCI*
1,3,5-tri-tert-butyl-1 ,3,5-triazacyclohexane [mis thesis pg. 811 (0.80 g, 3.1 mmol),
copper dichloride (0.42 g, 3.1 mmol) and 6 mL of chlorofom were mixed in a 50 mL ai-
free tube. The mixture was sonicated until the cdour of the solution became dark green.
Toluene (2 ml) was added to the mixture and it was left undisturbed unül the appearance
of dark green crystals, whicn floated on top of the solution. Yield after filtration 0.70 g (57 5%).
The paramagnetic nature of the crystals impeded the characterimtion by NMR
spectroscopy, thus it was characterized by X-ray crystallograp hy.
m.p. 1 70 OC (dec.).
El-MS (70 eV): mlz (rel. int. %): 396 [Ml+*, 342, 296, 261, 197 (8), 156 (35), 141 (50), 85 (1 OO), 70 (1 7), 58 (71).
References
(a) A histon'd review: Arduengo, A. J., III; Krafcqk, R. Chem. Unserer Zeit 1998,
32, 6. (b) Nef, J. U. Justus Liebigs Ann. Chem. 1 895, 287 359.
(a) Hine, J. J. Am- Chem. Soc. 1950, 72, 2438. (b) Hine, J.; Dowell, A- M. J. Am.
Chem. Soc. 1954, 76,2688.
(a) Marchand, A. P.; Broddiart, N. M. Chem. Rev. 1973, 73, 431. (b) Stang, P.S.
Chem. Rev. 1978, 78, 383. (c) Sander, W.; Bucher, G.; Wierlacher, S. Chem. Rev.
1993,93, 1583.
(a) Wanziick, H. W.; Schikora, E. Angew. Chem. 1960, 72, 494. (b) Wandick, H.
W-; Schikora, E. Chem. Ber. 1961, 94, 2389. (c) Wanzlick, H. W.; Kleiner, H. J.
Angew. Chem. 1961, 73, 493. (d) Wanzlick, H.W. Angew. Chem. 1962, 74, 128.
(e) Wanzlick, H. W. Angew. Chem., ht Ed- Engi. 1 962, 1, 75. (f) Wanziick, H .-W.;
Ahrens, H. Chem. Ber. 1964, 97, 2447. (g) Wanzlick, H. W.; Lachrnann, B.;
Schikora, E. Chem. Ber. 1965, 98, 31 70. (h) Wanzlick, H. W.; SchGnhetr, H. J.
Angew. Chem. 1968,80, 153.; Angew. Chem., /nt. Ed. Engl. 1968, 7, 141.
Arduengo, A. J., III; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1991, 173, 361.
(a) Hemnann, W. A.; Kocher, C. Angew. Chem., lnt Ed. Engl. 1997, 36, 2162. (b)
Boursissou, D.; Bertrand, G. Adv. Organomet. Chem. 1999, 44, 175. (c) Bourissou,
D.; Guerret, O.; Gabbaï, F. P.; Bertrand, G. Chem. Rev. 2000, 100, 39.
Tomioka, H. Acc. Chem. Res. 1997, 30, 31 5.
Fischer, E. O. ; Maasbd, A. Angew. Chem. 1964, 76, 645; Angew. Chem., /nt Ed.
Engl. 1964, 3, 580.
The OrganometaMic Chemistry Of The Transition Metais, Crabtree, R. H., 2nd Ed.; A
Wiley-Interscience publication: Toronto, 1 994; Chapter 1 1.
Ofele, K. J. Organomet. Chern. 1968, 12,42.
(a) Denk, M. K.; Hatano K.; Ma M. Tetrahedron Letf. 1999, 40, 2057. (b) Hahn, F.
E.; Wittenbecher, L.; Fr6hlich, R; Le Van, D. Angew. Chem., Int. Ed. Engl. 2000,39,
541.
(a)Wanzlick, H. W.; Sdiijnhen; H. J- Liebigs Ann. Chem. 1970, 731 176.
(b)Wanzlick, H. W.; Schonherr, H. J. Chem. Ber. 1970, 103, 1037.
O w c Chemistry: A Series of Monographs. Kitmse, W., 2nd Ed.; Academic
Press: New York, 1971 ; Vol. 1, p 159-1 92.
Gleiter, R.; Hoffmann, R- J. Am. Chem. Soc. 1968, 90, 1475.
Inkura, K 1.; Goddard, W. A., III; Beauchamp, J. L. J- Am. Chem. Soc. 1 992, 1 14,
48.
Richards, C. A., Jr.; Kim, S. J.; Yamaguchi, Y.; Shaefer, H. F., III J. Am. Chem. Soc.
1995, 117, 10104.
Myers, D. R.; Senthilnathan, V. P.; Platz, M. S.; Jones, J., Jr. J. Am. Chem. Soc.
1986, 108,4232.
Gano, 3. E.; Wettach, R. H-; Platz, M. S.; Senthilnathan, V. P. J. Am. Chem. Soc.
1982, 104,2326.
Denk, M. K.; Rodezno, J. M. unpublished results.
(a) Hemnann, W. A.; Elison, M.; Fischer, J.; Kkher, Cs; Artus G. R. J. Chem. Eur. J.
1996, 2, 772. (b) Hermann, W. A.; Kodier, C.; Goossen, L. J.; Artus, G. R. J.
Chem. Eur. J. 1996,2, 1627.
Kuhn, N.; Kratz, T. Synthesis 1993, 561.
Denk, M. K.; Thadani, A.; Hatano, K.; Lough, A. J. Angew. Chem., /nt Ed. Engl.
1997, 36,2607.
Enders, D.; Breuer, K.; Raabe, G.; Runsink, J.; Teles, J. H.; Melder, J. P.; Ebel, K.;
Brode, S. Angew. Chem., lnt. Ed. Engl. 1995, 34, 1021.
(a) Alder, R. W.; Blake, M. E.; Bortolotti, C.; Bufali, S.; Butts, C. P.; Linehan, E.;
Oliva, J. M.; Orpen, A. G.; Quayle, M. J. J. Chem. Soc., Chem. Commun. 1999,
241. (b) Alder, R. W.; Allen, P. R.; Murray M.; Orpen, A. G. Angew. Chem., Int. Ed.
Engi. 1 996, 35,1121 .
[25] Du, X. M.; Fan, H.; Goodman, J. 1.; Kesselmayer, M. A.; Krogh-Jespersen, K.; La
Villa, J. A.; Moss, R. A.; Shen, S.; Sheridan, R. S. J. Am. Chem. Soc. 1 990, 1 12,
1 920.
[26] Bauschlicher, C. W. Jr.; Schaefer, H. F., III; Bagus, P. S. J. Am. Chem. Soc. 1977,
99, 7106.
[27l (a) Heinemann, C.; Müller, T.; Apeloig, Y.; Schwarz, H. J. Am. Chem. Soc. 1996,
7 18,2023. (b) Boehme, C.; Frenking, G. J. Am. Chem. Soc. 1 996, 1 18, 2039. (c)
Lehmann, J. F.; Urquharî, S. G.; Ennis, L. E.; Hitchcock, A. P.; Hatano, K.; Gupta, S.;
Denk, M. K. Organomefallics 1999, 18, 1862.
(281 (a) H e m n , W. A; Denk M.; Behm, J.; Scherer, W.; Klingan, F.-R.; Bock, H.;
Solouki, B.; Wagner, M. Angew. Chem. 1992, 104, 1489; Angew. Chem., ht Ed.
Engl. 1992, 31, 1485. (b) Denk, M. K.; Khan, M.; Lough, A. J.; Shuchi, K. Acta
Crystallogr. Sect C 1998, 54, 1830.
[29] (a) Denk M.; Lennon, R.; Hayashi, R.; West, R.; Belyakov, A. V.; Verne, H. P.;
Haaland, A.; Wagner, M.; Metzler, N. J. Am. Chem. Soc. 1994, 116, 2691. (b)
Denk, M. K.; Greene, J. C.; Metzler, N.; Wagner, M. J. Chem. Soc., Dalton Tms.
1994, 2405. (c) Gerhus, B.; Lappert, M. F.; Heinicke, J.; Boese, R.; Blaser, D. J.
Chem. Soc., Chem. Commun. 1995, 1931. ( d ) West, R.; Denk, M. Pure Appl.
Chern. 1996, 68,785.
[30] Veith, M. Angew. Chem. 1987, 99,1214; Angew. Chem. ht Ed. Engl. 1987,
26,1214.
1311 Veith, M.; Werle, E.; Lisowsky, R.; Loppe, R.; Schnkkel, H. Chem. Ber. 1992,
125, $375.
[32] Weidenbruch, M. Eur. J. Inorg. Chem. 1999, 37, 373.
[33] (a) Denk, M. K.; Gupta, S., Rarnachandran, R. Tetrahedron Lett. 1996, 37, 9025. (b)
Denk, M. K.; Gupta, S.; Lough, A. J. Eur. J. Inorg. Chem. 1999, 41, and ref. therein.
[34] Schmidbaur, H.; Schmidt, E. S.; Jockisch, A. J. Am. Chem. Soc. 1999, 121, 9758.
98
(a) Arduengo, A. J., III; Barsotti, R. J.; Corcoran, P. H. Curable compositions
containhg 1,3-dialwimiazole-2-thione cataiyst. U.S. Patent No. 5291 498, 1 992. (b)
Arduengo, A. J., III Curing Agents for EpoqdAnhydride Resins. US. Patent No.
51 62482, 1992.
(a) Wanzlick, H. W.; Rabe, E. Liebigs Ann. Chem. 1973, 40. (b) Bildstein, B. J.
Organomet. Chem. 1999, 572, 177.
Saba, S.; Brescia, A-M.; Kaloustian, K. K. Tetrahedron Le@. 1991, 32, 5031.
(a) Bayer E.; Schurig, V. CHEMTECH 1976, 212. (b) Freemantle, M. C&EN,
1 998, March 30, p 32-37. (c) Welton T. Chem. Rev. 1 999, 99, 2071. (d) Aqueos-
Phase Organometallc Catalyss: Concepts and Applications. Hemnann W. A.;
Comils, B., Eds., Vedag Chemie: Weiheim, 1998; p 555. (e) Guterman, L.
Chemistry 1999, 12.
Mertschenk, B.; Beck, F. Ullmann'ç Encyclopedia of Industriid Chernistry 1995, A26,
803.
Denk, M. K.; Gupta, S. unpublished results.
(a) Bogatskii, A. V.; LuKyanenko, N. G.; Kirichenko, T. 1. Chem. Heterocycl- Compd.
(Engl. TTran) 1 983, 19, 577. (b) Wier, D. R., Philips Petroleum, U.S. Patent No.
41 24073, 1978 .
(a) Hemnann, W. A.; Eliçon, M.; Fischer, J.; K&her, C.; Artus, G. R. J. Angew.
Chem., [nt. Ed. Eng1. 1995, 34, 2371. (b) Hemnann W. A.; Resinger, C. P.;
Spiegler, M. J. Organomet. Chern. 1998, 557, 93. (c) Lappert, M. F. In Transition
Metal Chemistry, (Müller, A., Diemann, E., Eds.) Verlag Chemie: Weinheim, 1981 ;
p 287. (d) HiN, T. E.; Nile, T. A. J. Organomet. Chem. 1977, 137, 293. (e) Scholl,
M.; Trnka, T. M.; Morgan, J. P; Gmbbs, R. H. Tetrahedron Le@. 1999, 40, 336.
(a) Gutowsky, H. S.; Ternussi, P. A. J. Am. Chem. Soc. 1967, 89, 4358. (b)
Anderson, J. E.; Casanni, D.; Ljeh, A. 1.; Lunazi L.; Tod-ier, D. A. J. Am. Chem.
Soc. 1 995.1 7 7, 3054. (c) Rivero, B. E.; Apreda, M. C.; Castellano, E. E.; Orazi O.
O.; Corral, R. A. Tetrahedron 1978, 34, 341 3.
[44] (a)Taguchi, Y.; Yasumoto, M.; Tsuchiya, T.; Oishi, A-; Shibuya, 1. Chem. Lett 1993,
1097. (b) Taguchi, Y.; Yasumoto, M.; Tsuchiya, T.; Shibuya, 1.; Yonernoto, K.
Nippon, Kagaku Kaishil992,4,383. (c) Taguchi, Y.; Shibuya, 1. JP 03258768 A2
(in Japanese) [CA 1 1 6: 1 51 7981.
[45] (a) Çetinkaya, B.; Hitchcock, P. B.; Lappert, M. F.; Shaw, D. B.; Spyropoulos, K.;
Warhurst, N. J. W . J. Organomet. Chem. 1993, 459, 31 1. (b) Lappert, M. F. J.
Organomet. Chem. 1988, 358, 185. (c) Çetinkaya, E.; Hitchcock, P. B.; Küçükbay,
H.; Lappert, M. F.; Al-Juaid, S. J. Organomet. Chem. 1994, 481, 89. (d) Goldwhite,
H.; Kaminski, J.; MiIlhauser, G.; Ortiz, J.; Vargas, M.; Vertal, L.; Lappert, M. F.;
Smith, S. J. J. Organomet. Chem. 1986, 310, 21. (e) Çetinkaya, B.; King, G. H.;
Krishnarnurthy, S. S.; Lappert, M. F.; Pedley, J. B. J. Chem. Soc., Chem.
Commun. 1971, 1370. (f) Lappert, M. F.; Maskell, R. K. ' Chem. Soc., Chem.
Commun. 1982,580- ( g ) Hoffmann, R. W. Angew. Chem., ht Ed. Engl. 1968, 1 1,
754. (h) Hocker, J.; Merten, R. Angew. Chem., lnt. Ed. Engl. 1972, 11, 964. (i)
Roeterdink, F.; Scheeren, J. W.; taarhoven, W. H. Tetrahedm LeK 1983, 24,
2307. (j) Cardin, D. J.; Doyle, M. J.; Lappert, M. F. J. Chem. Soc., Chem.
Commun. 1972,927.
[46] Fnihauf, H.-W.; Landers, A.; Goddard, R.; Krliger, C. Angew. Chem., Int. Ed. Engl.
1978, 17, 64.
[471 Staal, L. H.; Polm, L. H.; Vrieze, K. Inorg. Chim. Acta 1980, 40, 165.
[48] Holrn, R. H.; Donahue, J. P.; Polyhedron 1993, 12, 571 -589 (Polyhedron Special
Report 45).
[49] The calculationç were -ed out with the Spartan 5.02 and Gaussian 94 suite of
programs: Gaussian 94, Revision D.4, M. J. Frisch, G. W. Trucks, H. B. Schlegel, P.
M. W. Gill, B. G. Johnson, M. A. Robb, JI R. Cheeseman, T. Keith, G- A.
Petersson, J. A. Montgomery, K. Raghavachan, M. A. Al-Laham, V. G. Zakrzewski,
J. V. O&, J. B. Foresman, J. Cioslowski, B. B. Stefanov, A. Nanayald<ar;i, M.
Challacombe, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S.
Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. BinWey, D. J. Defrees, J.
Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez, and J. A. Pople, Gaussian,
Inc., Pittsburgh PA, 1995. Molecular geometries were fully optimized and vibrational
frequencies were caiculated at ail levels- The absence of virtual frequencies ensures
that the caiculated structures are minima rather than saddle points.
[SOI (a) Foresman, J. B.; Frisch, A. Ekploring Chemistty with Elecfronic St~cture
Methods, 2nd ed., Gaussian Inc., Pittsburgh, PA, 1996. (b) Bytheway, 1.; Wong, M.
W. Chem. Phys- Leff. 1998, 282, 21 9. (c) Scott, A. P.; Radom, L. J. Phys. Chem.
1996, 100, 1 6502.
[51] (a) Depuy, C. H.; Froemsdorf, D. H. J. Am. Chem. Soc. 1960, 29, 1744. (b) Oda,
R.; Mieno, M.; Hayashi, Y. Tetrahedron Letf. 1967, 25, 2363.
1521 The protonation of stable carbenes at the carbene carbon atom has been previously
investigated through calcu~ations: (a) D. A, Dixon, A. J. Arduengo, J. Phys. Chem.
1991, 95,4180. (b) R. W. Alder, M. E. Blake, J. M. Oliva J. Phys. Chem. A, 1999,
103, 11200-1 121 1.
1531 (a) Opitz, G. Ange W. Chem., /nt Ed. Engl. 1 967, 6, 1 07. (b) Reich, M. F.; Lee, V .
J.; Ashcrofy, J.; Morton, G. O. J. Org. Chem. 1993, 58, 5288. (c) Hiraoka, H. J.
Chem. Soc., Chem. Commun. 1974,1014.
[54] de Berry Bamett, E. J. Chem. Soc. 1910, 97,63.
[55] Sullivan, R. A. L.; Hargreaves, A. Acta Cryst. 1962, 15, 675.
[56] Sander, W.; Kirschfeld, A.; Halupka, M. J. Am. Chem.Soc. 1997, 119, 981.
[571 Skrypnik, Y. G.; Lyashchuk, S. N. Sulfur LeK 1994, 17, 287.
Calculation of Ce11 Volume: for rnonoclinic system volume formula is: V = abcsinp.
Mews, R.; Watson P. G.; Lork, E. Coordin. Chem. Rev. 1997, 158, 233.
(a) Arduengo, A. J.; Dixon, D. A.; Dobbs, K D. Tetrahedron Lett 1995, 36, 645.
(b) Lyashchuk, S. N.; Skiypnik, Y. G. Tetrahedron Lett. 1994, 35, 5271. (c) for
reactions of transient carfienes wifh CO in frozen mafnfnces see: Visser, P.; Zuhse, R;
Wong, M. W.; Wentrup, C. J. Am. Chem. Soc. 1996, 178,12598.
Wanzlick, H. W.; Lachmann, B.; Schikora, E. Chem. Ber. 1965, 98, 3170.
Eckhard, R.; Wanzlick, H. W. Liebigs Ann. Chem. 1 973, 40.
Bildstein, B.; Maiaun, M.: Kopacka, H.; Ongania, K-H.; Wurst, K J. Organometal.
Chem. 1999, 572, 177.
Teles, J. H.; Brode, S.; Berùessel, A. J. Am. Chem. Soc. 1998, 720, 1345.
Alder, R. W.; Blake, Midiael E.; Bortolotti, C.; Bufali, S.; Butts, C. P.; Linehan, E;
Oliva, J. M.; Orpen, A. O.; Quayle, M. J. Chem. Commun. 1999, 241.
(a) Richmond, H. H.; Myers, G. S.; Wright, G. F. J. Am. Chem. Soc. 1948, 70,
3659. (b) Nielsen, A. T.; Moore, D. W.; Ogan, M. D.; Atkns, R. L. J. Org. Chem.
1979,44,1678.
Duden, P.; Scharff, M. Justus Liebigs Ann. Chem. 1895, 288, 218. (b) Duden, P.;
Scharff, M. Chem. Ber., 1895,28,938.
Kahovec, L. 2. Physik. Chem. 1939, 843,364.
This compound has been synthesized by Sébastien Fournier-Bidoz in Our group
through independent methods.
Stegemann, H.; Oprea, A; Tebbe, K. F. Anorg. Allg. Chem. 1995, 621, 871.
Haufe, M.; Kohn, R. D.; Weimann, R.; Seifert, G.; Zeigan, D. J. Organomet Chem.
1996,520, 121.
(a) Ainscough, E. W.;. Brodie, A. M.; Ingharn, S. L.; Waters, J. M. J. Chem. Soc.
Dalton 1994, 215. (b ) Kohn, R. D.; Haufe, M.; Kociok-Kohn, G.; Filippou, A. C.
Inorg. Chem. 1997, 36, 6064. (c) Tyeklar Z.; Jacobson, R. R; Wei, N.; Murthy, N.
N.; Zubieta, J.; Karlin, K. D. J. Am. Chem. Soc. 1993, 1 15, 2677.
Kohn, R. D.; Seifert, G.; Kociok-Kdm, G. Chem. Ber. 1996, 129, 1327.
Appendix I
Supplementary Crystallographic Data for X-ray Structural
Determination of [2-H][CI]
Table 1. Crystai data and structure refinement for [2-H][CI].
Identification code kg8230
Empiricai formula Cf 1 H H22 CI IV2
Formula weight 21 8.76
Temperature 100.0(1) K
Wavelength 0.71073 A Crystal system Monoclinic
Space group P2(l )/n
Unit cell dimensions a = 9.1 142(3) A b = 11.8722(2) A c = 11 -4.471 (3) A
Volume 1229.91 (6) A3
z 4
Density (calculated) 1.181 ~ ~ / m ~
Absorption coefficient 0.279 mmd1
F(000) 480
Crystal size 0.30 x 0.25 x 0.20 mm3
Theta range for data collection 4.1 1 to 27.8a0.
Index ranges Oc=hc=l1, 0<=k<=15, -1 5<=1<=14
Reflections collected 9245
Independent reflections 2907 [R(int) = 0.0411
Cornpleteness to theta = 27.88" 99.3 %
Absorption correction Denzo-SMN
Max. and min. transmission 0.9463 and 0.9210
Refinement method Full-matrix least-squares on ~2
Data / restraints / parameters 2907 10 1138
Goodness-of-fit on F~ 1 .O74
Final R indices [I>2sigrna(l)] R I = 0.0333, wR2 = 0.0802
R indices (ail data) RI = 0.0458, wR2 = 0.0857
Extinction coefficient 0.004(2)
Largest diff. peak and hole 0.270 and -0.241 e.A-3
Table 2. Atomic coordinates ( x 1 04) and equivalent isotropie displacement parameters (A2x 1 03)
for [2-H][CI]. U(eq) is defined as one third of the trace of the orthogonalized uij tensor.
Table 3. Bond lengths [A] and angles [0] for [2-H][CI].
Symmetry transformations used to generate equivalent atoms:
Table 4. Anisotropic dis placement parameters (A2x 1 03) for [2-H][CI].The anisotropic
displacement factor exponent takes the f o n : -2p2[ h2 a**ul + ... + 2 h k a* b* LJ12 ]
Table 5. Hydrogen coordinates ( x 1 04) and isotropic displacement parameters (A2x 10 3)
for [2-H][CI].
Table 6. Torsion angles [O] for [2-ii][CI].
Symmetry transformations used to generate equivaIent atoms:
Appendix II
Supplementary Crystallographic Data for X-ray Structural Determination of [C~&18]'~ Cluster
Table 1. Crystal data and structure refinement for [cu~cI~] '~ Cluster.
Identification code
Empiricai formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Unit ce11 dimensions
Volume
z Density (calculated)
Absorption coefficient
F(00 0)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta = 27.50"
Absorption correction
Max. and min. transmission
Refinement method
Data / restraints 1 parameters
Goodness-of-fit on ~2
Final R indices [1>2sigrna(l)]
R indices (al1 data)
Extinction coefficient
Largest diff. peak and hole
k9984
C20 H52 Cl8 Cu4 N4
886-42
1 OO(2) K
0.71 073 A Triclinic
P-1
a = 8.581 O(6) A b = 10.1 O61 (6) A c = 1 1.3845(7) A 863.98(1 O) A3
1
1 -704
3.065 mm'l
452
0.25 x 0.20 x 0.20 mm3
4.17 to 27-50".
O<=h<=ll, -1 1 <=kc=13, -1 4<=1<=14
12583
3936 [R(int) = 0.0701
99.3 %
mulri-scan (Denzo-SMN)
0.5792 and 0.5145
Full-matrix least-squares on ~2
3936 / O I l 8 6
0.941
RI = 0.0385, wR2 = 0.0835
RI = 0.0733, wR2 = 0.091 2
0.001 3(11)
1 .O23 and -0.598 e.A-3
Table 2. Atomic coordinates ( x 1 04) and equivaient isotropic displacement parameters (A2x 1 03)
for [ C U ~ C I ~ ] - ~ Cluster. U(eq) is defined as one third of the trace of the orthogonalized uij tensor.
able 3. Bond lengths [Al and angles [O] for [ C U ~ C I ~ ] ~ Cluster.
Symmetry transformatio~s used to generate equivaient atoms: #1 -x+l ,-y,-z+l
Table 4. Anisotropic displacernent parameters (A2x 1 03) for [ C U ~ C I ~ ] ~ Cluster. The anisotropic
displacement factor exponent takes the fom: -2p2[ h2 ae2u1 + ... + 2 h k a' b' u1 ]
Table 5. Hydrogen coordinates ( x 1 04) and isotropic displacement parameters (A2x 10 3, for [ C U ~ C I ~ ] - ~ Cluster.
Table 6. Hydrogen bonds for [Cu4~lg14 Cluster. [A and '1.
N( l )-H(l NA) ... C1(2)#1 0.98(3) 2.1 9(4) 3.1 49(3) 1 67(3)
N(2)-H(2NA) ... Cl(4)#2 0.96(3) 2.24(4) 3.1 62(3) 162(3)
N(l )-H(l NB)-..Cl(1 ) 0.78(4) 2.51 (4) 3.1 97(3) 147(3)
N(l )-H(l NB) ... CI(1)#3 0.78(4) 2.96(3) 3.490(3) 1 27(3)
N(2)-H(2NB) ... C1(4)#3 0.92(4) 2.31 (4) 3.1 87(3) 160(3)
--
Symmetry transformations used to generate equivalent atoms:
Appendix III
Supplementary Crystallographic Data for X-ray Structural
Determination of (tBugTAC)CuCl2
Table 1. Crystal data and structure refinement for ( t ~ u 3 ~ ~ ~ ) ~ u ~ 1 2 .
Identification code k00107
Empirical formula C l 6 H34 Cl5 Cu N3
Formula weight 509.25
Temperature 150(1) K
Wavelength 0.71073 A Crystal system Orthorhornbic
Space group W 1 )2(1)2(1)
Unit cell dimensions a = 12.8040(3) A b = 22.0396(5) A c = 25.9312(3) A
Volume 731 7.7(3) A3
z 12
Density (calculated) 1.387 ~ g / m ~
Absorption coefficient 1.449 mm-1
F(000) 31 80
Crystai size 0.12 x 0.1 0 x 0.05 mm3
Theta range for data collection 2.56 to 26-03'.
Index ranges -1 5<=h<=l5, -27<=k<=27, -31 <=1<=31
Reflections collected 43350
Independent reflections 14275 [R(int) = 0.0501
Completeness to theta = 26.03" 99.4 %
Absorption correction multi-scan
Max. and min. transmission 0.931 1 and 0.8454
Refinement method Full-matrix least-squares on F~
Data 1 restraints / parameters 14275 130 / 781
Goodness-of-fit on F~ 1 .O21
Final R indices [1>2sigrna(l)] RI = 0.0494, wR2 = 0.0893
R indices (dl data) RI = 0.0821, wR2 = 0.0996
Absolute structure parameter 0.456(11)
Extinction coefficient 0.00042(6)
Largest diff. peak and hole 0.450 and -0.378 e .k3
Table 2. Atomic coordinates ( x 1 04) and equivalent isotropie displacement parameters (A2x 1 03)
for ( t ~ ~ 3 ~ ~ ~ ) ~ ~ ~ ~ 2 . U(eq) is defined as one third of the trace of the orthogonalized uij tensor.
Table 3. Bond lengths [A] and angles fl for ( t ~ ~ 3 ~ ~ ~ ) ~ ~ ~ 1 2 .
Cu(1 A)-N(3A)
Cu(1 A)-N(2.A)
Cu(1 A)-CI(1 A)
Cu(1 A)-Cl(2A)
Cu(1 A)-N(l A)
N (1 A)-C(l A)
N (1 A)-C(3A)
N (1 A)-C(4A)
N (24-C(l A)
N(2A)-C(W
N (2A)-C (8A)
N(3A)-C(2A)
N(3A)-C(3A)
N (3A)-C (1 2 4
C (4A)-C(7A)
C(4A)-C(6A)
C(4A)-C(5A)
C(8A)-C(9A)
C(8A)-C(ll A)
C(8A)-C(l OA)
C(l2A)-C(I3A)
C(12A)-C(14A)
C(l2A)-C(15A)
Cu(1 B)-N(3B)
Cu(1 B)-N(2B)
Cu(1 B)-CI(1 B)
Cu(1 B)-Cl(2B)
Cu(1 B)-N(l 8)
N (1 B)-C(3B)
N(l B)-C(l B)
N(l B)-C(4B)
N(2B)-C(2B)
N(2B)-C(l B)
N(2B)-C(8B)
N (3B)-C(2B)
N (3B)-C (3B)
N(3B)-C(12B)
C(4B)-C(6B)
C(4B)-C(78)
C(4B)-C(5B)
C(8B)-C(ll B)
C(8B)-C(9B)
C(8B)-C(l OB)
C(l2B)-C(13B)
C(12B)-C(14B)
C(12B)-C(15B)
Cu(1 C)-N(2C)
Cu(1 C)-N(3C)
Cu(1 C)-CI(1 C)
Cu(1 C)-Cl(2C)
Cu(1 C)-N(l C)
N (1 C)-C(1 C)
N(l C)-C(3C)
N (1 Cl-C(4C)
N(2C)-C(1 C)
N (2C) -C(2C)
N(2C)-C(8C)
N(3C)-C(2C)
N(3C)-CW)
N(3C)-C(12C)
C(4C)-C(5C)
c(4c)-C(W
C(4C)-C(7C)
C(8c)-C(=)
C(8C)-C(l1 C)
C(8C)-C(l OC)
C(12C)-C(15C)
C(12C)-C(14C)
C(12C)-C(13C)
CI(1 S)-C(l S)
C(2A)-N (3A)-Cu(1 A)
C(7A)-C(4A)-C(5A)
C(6A)-C(4A)-C(5A)
C(9A)-C(8A)-N(2A)
C(9A)-C(8A)-C(ll A)
N(2A) -C(8A) -C (1 1 A)
C(9A)-C(8A)-C(l OA)
N(2A)-C(8A)-C(1 OA)
C ( l l A)-C(8A)-C(l OA)
C(13A)-C(12A)-C(14A)
C(2B)-N(3B)-Cu(1 B)
C(3B)-N(3B)-Cu(1 B)
C(12B)-N(3B)-Cu(1B)
N(l B)-C(l B)-N(2B)
N(2B)-C(2B)-N (3B)
C(4B)-N(l B)-Cu(1 B)
C(2B)-N(2B)-C(l B)
C(2B)-N(28)-C(8B)
C(l B)-N(2B)-C(8B)
C(2B)-N(2B)-Cu(1 B)
C(l B)-N(2B)-Cu(1 B)
C(8B)-N(2B)- CU(^ B)
C(2B)-N(3B)-C(3B)
C(2B)-N(3B)-C(12B)
C(3B)-N(3B)-C(12B)
N(l B)-C(3B)-N(3B)
N(l B)-C(4B)-C(6B)
N(l B)-C(4B)-C(7B)
C(6B)-C(4B)-C(7B)
N(l B)-C(4B)-C(5B)
C(6B)-C(4B)-C(5B)
C(7B)-C(4B)-C(5B)
C ( l l B)-C(8B)-C(9B)
C(l C)-N(2C)-C(8C)
C(2C)-N(2C)-C(8C)
C(6B)-C(4B)-C(7B)
N(l B)-C(48)-C(5B)
C(6B)-C(4B)-C(5B)
C(7B)-C(4B)-C(5B)
C( l l B)-C(8B)-C(9B)
C(I1 B)-C(8B)-N(2B)
C(9B)-C(8B)-N(2B)
C( l l B)-C(8B)-C(l OB)
C(9B)-C(8B)-C(l OB)
N(2B)-C(8B)-C(l OB)
C(13B)-C(12B)-C(14B)
C(I 3B)-C(12B)-C(15B)
C(14B)-C(12B)-C(l SB)
C(I3B)-C(12B)-N(3B)
C(14B)-C(12B)-N(3B)
C(1 SB)-C(12B)-N(3B)
N (2c)-C~(1 C)-N(3C)
N(2C)-Cu(1 C)-CI(1 C)
N(3C)-Cu(1 C)-CI(1 C)
N(2C)-Cu(1 C)-CI(2C)
N(3G)-Cu(1 C)-Cl(2C)
CI(1 C)-Cu(1 C)-CI(2C)
N(2C)- CU(^ C)-N(l C)
N(3C)-Cu(1 C)-N(l C)
CI(1 C)- CU(^ C)-N(l C)
CI(~C)-CU(I C)-N(l C)
C(l C)-N(l C)-C(3C)
C(1 C)-N(l C)-C(4C)
C(3C)-N (1 C)-C(4C)
C(l C)-N(1 C)-Cu(1 C)
C(3C)-N(l C)-Cu(1 C)
C(4C)-N(1 C)-Cu(1 C)
C(l C)-N(2C)-C(2C)
C(l C)-N(ZC)-CU(I C)
C(2C)-N(2C)-Cu(1 C)
C(8C)-N(2C)-Cu(1 C)
C(2C)-N(3C)-C(3C)
C(2C)-N(3C)-C(12C)
C(3C)-N(3C)-C(12C)
C(2C)-N(3C)-Cu(1 C)
C(3C)-N(3C)-Cu(1 C)
C(12C)-N<3C)-Cu(1 C)
N(l C)-C(1 C)-N(2C)
N (3C)-C(2C) -N (2C)
N(l C)-C(3C)-N(3C)
N (1 C)-C(4C)-C(5C)
N(l C)-C(4C)-C(6C)
C(SC)-C(4C)-C(6C)
N(l C)-C(4C)-C(7C)
C (5C)-C(4C)-C (7C)
C(6C)-C(4C)-C(7C)
N (2C)-C(8C)-C(9C)
N (2C)-C(8C)-C(ll C)
C(9C)-C(8C)-C(l1 C)
N(2C)-C(8C)-C(l OC)
C(9C)-C(8C)-C(1 OC)
C ( l l C)-C(8C)-C(l OC)
C(l SC)-CC1 2C)-C(14C)
C(l SC)-CC1 2C)-N(3C)
C(l4C)-C(l2C)-N(3C)
C(l SC)-CC1 2C)-C(13C)
C(14C)-C(12C)-C(13C)
Symmetry transformations used to generate equivalent atoms:
131
Table 4. Anisotropic displacernent parameters (A2x 1 03) for ( t ~ u 3 ~ ~ ~ ) ~ u ~ f 2 . The anisotropic
displacement factor exponent takes the form: -2p2[ h2 a*2~1 + ... + 2 h k a' b' uI2 ]
134
Table 5. Hydrogen coordinates ( x 1 04) and isotropic displacement parameters (A2x 10 3,
for kOOlO7.
-
H(1
H(l AB)
W U )
H(2AB)
H ( 3 W
H(3AB)
H ( 5 W
H(5AB)
H(5AC)
H ( 6 W
H(6AB)
H(6AC)
H ( 7 W
H (7AB)
H(7AC)
H(9444
H (9AB)
H(9AC)
H(1OD)
H(l OE)
H(l OF)
H(11D)
H(11E)
H(11 F)
H(13D)
H(13E)
H(13F)
H(14D)
H(14E)
w 4 m
H(I5D)
H(15E)
H(15F)
H( l BA)
H(1 BB)
H(2BA)
H(2BB)
H (3BA)
H(3BB)
H (5BA)
H(5BB)
H(5BC)
H (6BA)
H(6BB)
H(6BC)
H (7BA)
H(7BB)
H(7BC)
H(9BA)
H(9BB)
H(9BC)
H(l OG)
H(1 OH)
H(101)
H ( l l G)
H ( l l H)
H(l I I )
H(13G)
H(13H)
H(131)
H(14G)
H(14H)
H(141)
H(15G)
H(15H)
H(151)
H(l CA)
H(l CB)
H(2CA)
ii(2CB)
H(3CA)
H (3CB)
H(5CA)
H(5C B)
H(5CC)
H (6CA)
H(6CB)
H(6CC)
H(7CA)
H(7CB)
H(7CC)
H (9CA)
H(9CB)
H(=C)
H(l OA)
H(1 OB)
H(l OC)
H(11 A)
H(11 B)
H( l l C)
H (1 3A)
H(138)
H(13C)
H (1 4A)
H(14B)
H(14C)
H(l SA)
H(l SB)
H (1 5C)
H(l SA)
H(2SA)
H(2SB)
H(3SA)
H(3SB)