macromolecular science and engineering tuesday june 1 pm ma3 regatta advances in olefin...
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Macromolecular Science and Engineering
Tuesday June 1 PM MA3 Regatta Advances In Olefin Polymerization Organizer - H. ZahalkaChair - H. Zahalka
13:30-14:00 0080 Olefin Polymerization Catalysts Beyond Group-IV Metallocenes Ziegler T., Deng L., Schmid R., Margl P.
Polyethylene• … is one of the commercially most
important plastics
• … is conveniently produced by the Ziegler-Natta catalytic process
• … can be tailor-made to suit specificpurposes of the customer
n
n
Successful Catalysts• Commercial homogeneous catalysts are usually
of the group 4 “metallocene” type.
• Metallocene catalysts have severalundesirable drawbacks and are heavilyshielded by patents.
TiSiN
R1R2
R3
++CR1
R2Zr
N
NFe
iPr
iPrPri
Pri
MeMe
N
McConville
Getting the idea
Cr
R
X
ZrSi
R'
R
NR"
do
Bercaw/Marks
ZrSi
R'
R'
Rdo
Kaminsky/Brinzinger
do
d3
Brookhart/Gibson
M=Fe,Cod6-d7 N
NM
R'R
'R
R"
R"
Brookhart
M=Ni,Pd
d8
NTi
NR'
R'
R"R
"R
NM
N RR'
R'
"R
"RTheopold
d1 - d3 M=Ti,V,Cr
M= ?
L= ?d?
Focus: d0 and d0fn Catalysts
• Most viable catalysts are systems with(formally) no d electrons
• We shall first develop a picture of how d0
systems work ...
• … and later generalize to systems withhigher d occupation
+ Lanthanides, Actinides
The Sample
NH
MNH
Et
NM
N
Et
BH2
BH2
OM
O
Et OMO
Et
O
PrM
NH
NH
PrM
O
O
EtM
EtM
NHSiH2
EtM
CH3
CH3
90oEt
MOH
OH90o
EtM
NH2
NH2
90o
M = Sc(III),Y(III), La(III), Lu(III), Nb(III), Ti(III), Ti(IV), Zr(IV), Hf(IV), Ce(IV), Th(IV), V(V)
LM
Η2CαCβ
P
H
HL
MH
H2Cα
HCβ
P
L
(c) Termination
LL
MH
L
-CH2=CHP
(d) Ejection
≠
LM
CαΗ2
CβP
H
HL
M
Ca
Cb P
H H
HHL
L
Front-Side
(a) UPTAKE
Principles for d0 Polymerization Catalysts
LM
CαΗ2H2Cb
P
LM
L
LH
P
≠
(b) Propagation
Margl et al. Organometallics 1998, 1998,17, 933
Margel et al. J ACS 1999,121,154
Margl et al JACS, 1998,120,5517
Margel et al, Top.in Catl. 1999,7,187
A Test for Activity:Ethylene π- Complexation Energetics• Ethyleneπ-complexation precedes insertion
as well as the dominant chain termination step• If ethylene does not stick , to the catalyst there
will be no insertion• If ethylene sticks too well, the insertion
barrier will be high
L2
M
H
P
+
L2
M
H
P
Insertion
Termination
-200
-150
-100
-50
0
50
Ethylene Complexation Energy (kJ/mol)
0 2 0 4 0 6 0 8 0 1 0 0Acces s ib le Surface (bohr2 )
Sc-4
Sc-1,2,7,8,9Y-1,7,8,9
La-1,7,8,9Ti-4
V-6
Zr-4
Hf-4
Ti-5
Ti-1,2,7,8,9
Sc-3
Zr-1,7,8,9Hf-1,7,8,9
Th-1Ce-1
Ti-3 Zr-3
Ethylene Uptake Energies
Sampling the C2H4 Uptake
Uncharged
Cations (+1)
Cations (+2)
0 20 40 60 80 100
-160
-140
-120
-100
-80
-60
-40
-20
0
Olefin
Complexation
Energy (kJ/
mol
)
Accessible Surface of Metal Ion (bohr2)
• Residual spread of complexation energies– due to varying d orbital energies of the metal and
deformability of the metal-ligand framework
Dominant Factors forEthylene Complexation
• Accessible surface area– must be large enough to allow interaction
• Total charge on the complex– positive charge lowers d orbitals and enhances
electrostatic interactions
The Essential Step:The Olefin Insertion Barrier
• The olefin insertion barrier is the key factorfor catalyst performance
• A high insertion barrier will retardpolymerization
• If the insertion barrier is higher than thetermination barrier, no polymer will beproduced at all
L2
M
H
P
ML2
H
P
ML2
H
P
Sampling the Insertion Barriers
-20
0
20
40
60
80
100
120
140
160
180
200
220
240
Insertion Barrier (kJ/
mol
)
Metal-Ligand Combination
Sc(III)
Y(III)
La(III)
Lu(III)
Ti(III)
Nb(III)
Ti(IV) Zr(IV) Hf(IV)
Ce(IV)Th(IV)
V(V)
Important Trends forInsertion Barriers
• d0 systems in general have small barriers
• insertion barriers increase down a triad
• Especially for group 4
• Group 3 potentially better than group
Barrier Height isRegulated by Deformability!
• Insertion process deforms the catalyst framework
strong deformation
MLL
C
H
P
π Complex pyramidal
MLL
C
H
P
- / -Front Side Back Side Insertion Transition State
planar
Means to Controlthe Insertion Barrier
• The insertion barrier is determined by thedeformability of the metal-ligandframework
• Insertion step gets faster ...– ... from group 4 to group 3 and...
– ... up a triad and...– ... from bad π donor ligands to good ones
Make or Break:The Chain Termination Barrier
• Even if the insertion barrier is low, an evenlower chain termination barrier will renderthe catalyst ineffective
L2
M
H
P
L2
M H
P
L2
M
P
H
Activation Barriers
Reaction (ADF) (CP/PAW)
1 Front-Side Insertion 20 n/a
2 Back-Side Insertion 22 n/a3 β- Hydrogen Transfer 40 43 +/- 84 β - Hydrogen Elimination 54 57 +/- 35 - Polymer C H Activation 72 70 +/- 36 - Ethylene C H Activation 92 87 +/- 5
• Future investigations can focus on 1-3 reactions !
ΔF‡ (300 )K
0
20
40
60
80
100
Termination Barrier (kJ/mol)
Metal-Ligand Combination
Sampling the Termination Barrier
Sc(III)
Y(III)
La(III)
Lu(III)
Ti(III)
Ti(IV)Zr(IV)
Hf(IV)
Th(IV)
V(V)
Dominant Factors forTermination Barriers
• Termination barriers rise down the triad
• Termination barriers are higher for group 3metals than for group 4 metals
• Termination barriers are very high forsterically encumbered systems– since there is no space to form the termination
transition state
10203040506070
La[III]Y[III]Sc[III]
Barrier (kJ/mol)
Species
BHT FSP
020406080
100
Ti[III][7]-Ti[III]
283236404448
Th[IV]Lu[III]
020406080
100
V[V]Hf[IV]Zr[IV]Ti[IV]
Barrier (kJ/mol)
Barriers of Insertion and Termination
Z-N
The Final Step:Combining Insertion and Termination
Sc(III)Y(III)
La(III)
Lu(III)Ti(III)
Ti(IV)Zr(IV)
Hf(IV)
Ce(IV)Th(IV)
V(V)
Nb(III)
-20
0
20
40
60
80
100
120
140
160
180
200
220
240
Insertion Barrier
Termination Barrier
Barrier Heigh
t (kJ/
mol
)
Metal-Ligand Combination
A Set of Rules (I)• To achieve better sticking probabilities:
– use a group 4 cation instead of a group 3 neutral– or increase the surface area of the metal– do not increase the d electron count
• To achieve a faster insertion process:– use a 3d or 4d metal instead of a 5d one or an f
element– use a bulky ligand or a ligand with good π-
(donor abilitiesamido)– 3, 4 5 never use a group or transition metal with
- a non zero d electron count
A Set of Rules (II)
• To better balance insertion vs. termination– use a 3d or 4d metal
– using Hf is dangerous
– termination can be selectively curtailed byincreasing the steric bulk of the auxiliaryligands
• These rules are currently in use in our andour industrial collaborator’s laboratory
MeTi
NR
NR
R'
Me+ B(C6F5)3
23oC R'
x
Ti
NR
NRMe
x
Me - B(C6F5)3-
+
McConville Systems: Living Polymerization of α-Olefins
(a) R = 2,6-iPr2C6H3
(b) R = 2,6-Me2C6H3
R' = n-Bu, n-Pr, n-Hex
the chelating diamide complexes of titanium proved to be efficient catalystsfor living polymerization of α-olefinsthe zirconium analogue displayed little on no activity for the polymerizationof olefins
McConville et al., J ACS, 1996, 118, 10008; Organometallics, 1997, 16, 1810;Macromolecules, 1996, 29, 5241
Observations:
precursors
cocatalyst
catalysts
C
NC
C
C
M
C
C
C
CN
NC
C
C
C
M
C
C
C
C
N
Insertion
Ti: 5.6Zr: 6.0Hf:9.6 (8.6)
Barriers kcal/mol
Termination
Generic Transition States
Ti: 7.8Zr: 6.8Hf: 8.1 (7.6)
Barriers kcal/mol
McConville Ti(IV) Insertion and Termination Transition States
Term. Barrier kcal/mol
9.2 (QM)17.8 (QM/MM)
Ins. Barrier kcal/mol
5.6 (QM)9.4 (QM/MM)
MwuptakeΔE≠insertionΔE Δ
≠Δ ( E )
MwuptakeΔE insertion≠ΔE Δ(Δ ≠E )
MH
H
H
H
R
iPr iPr
iPr iPr
13 R' = Me, R" = Me14 R' = Me, R" = iPr
ZrR"
R'
R"
R'
R
iPr iPr
iPr iPr
1A M=Ti1B M=Zr
5.6 x 108 (living)
dimmer (2 - 7)
9.411.8
9.22.9
17.022.4
22.313.8
3.3 x 10 3
1.8 x 104
9.9-0.1
2.83.8
LIGAND MODIFICATIONS
MwuptakeΔE≠insertionΔE Δ
≠Δ ( E )
5.6 x 108 (living)
dimmer (2 - 7)
9.411.8
9.9-0.1
MwuptakeE insertion≠ΔE Δ(Δ ≠E )
9.22.9
22.313.8
3.3 x 10 3
1.8 x 1042.83.8
LIGAND MODIFICATIONS
17.022.4
Zr
H
R
R' R'
R' R'
H
HH
Zr
H
R
R'
H
HH
iPr iPr
15 R' = fluoro- iPr
16 R' = 1-Me- cyclo-Pr
17 2 2 4 2R' = -CH (CH ) CH -
18 R' = -CMeH(CH 2)4CMeH-
Brookhart Polymerization Catalyst
C&EN Feb. 5, 1996:“Polymer Catalyst System:Dupont Eyes New Polyolefin Business”
Brookhartcatalyst
highly linear to moderately branched
Johnson, L. K.; Killian, C. M.; Brookhart, M. J. Am. Chem. Soc. 1995, 117, 2343.
• high MWs
• good activities
N
Ni+N
RRiPr
iPriPr
iPr
R
• temperature: Temp branching
• monomer pressure: [Et] branching
• bulk of substituents: bulk branching MW
Pure QM Transition States for Brookharts Ni(II)-catalyst
Insertion TS
Termination TS
10.8 kcal/mol
17.5 kcal/mol
Experimental Observations
1 R = R’ = i-Pr2 R = R’ = Me3 R = t-Bu, R’=H4 R = i-Pr, R’ = H5 R = Et, R’ = H6 R = Me, R’ = H
Fe/Co catalysthighly linear high density
Gibson, V. C. et al. Chem. Commun., 1998, 849.Small, B.L.; Brookhart, M.; Bennett, A.M.A. J. Am. Chem. Soc. 1998, 120, 4049.Small, B.L.; Brookhart, M.; J. Am. Chem. Soc. 1998, 120, 7143.
N
NFe
MeMe
NR
R'R'
R
• monomer pressure: [Et] activities: Fe Co no change
• bulk of substituents: bulk MW no branching
• Metals : activities of Fe complexes = activities of analogous Co ones
no mechanistic details!
C
NC C
C
C
C
N
C
Fe
C C
C
C
NC
CN
C C
C
C
C
N Fe
C
C
C
C
C
NC
Barrier ofinterconversion
ΔEincv = 23 kcal/mol
Generic Iron(II)-Bisimino Pyridine Catalyst
Deng,L.;Margl, P.; Ziegler, T., J.Am. Chem. Soc.,1999, in pressa
b
a. Olefin complex resting state:
axial Cα-conformation preferred electronically
ΔEcomplex = -29.7 kcal/mol
ΔEins = 23 kcal/mol ΔEBHT = 4 kcal/mol
b. Olefin complex: the insertion precursor
equatorial Cα-conformation disfavored electronically
ΔEcomplex = -23.8 kcal/mol
ΔEins = 7.4 kcal/mol
CC
C
C
C
CCN
C
C
C
C
C
N N
C
Fe
C
C
C
C
C
C
C
CC
C
C
C
C
C
C
C
C
CC
C
C
C
C2H4
E = -4.5 kcal/mol
ΔEterm = 9.0 kcal/mol
Formation of olefin-complex as precursorfor termination surpressed
Real Iron(II)-Bisimino Pyridine Catalyst
Olefin-complex
CC
C
C
C
CCN
C
C
C
C
C
N N
C
Fe
C
C
C
C
C
C
C
CC
C
C
C
C
C
C
C
C
CC
C
C
C
Real Iron(II)-Bisimino Pyridine Catalyst
Formation of olefin complexas precursor for insertionnow competative
E = -3.6 kcal/mol
ΔEinsert ~ 0-3 /kcal mol
Neutral Ni(II)-Based Catalyst for Ethylene Polymerization
CH
HC C
H
H
H
H
H
C
C
C
H C C
H
C
C
C
C C
H
C
H
H
C
H
H
C
H
C
C
C
N
H
H
C
O
C
C
C
C
H
C
H
C
C
C
H
H
H
C
Ni
C
C
C
H
H
H
H
H
H
C
H
H
C
H
H
C
H
CH
H
H
Wang and Grubbs et al. Organometallics, 1998, 17, 3149-3151
Experiment:Highly active for Polymerization ofethylene
Calculation:Without bulky substituents, the insertion and termination barrierAbout the same both as high as 26 kcal/mol
M
L
'L
R
M = Ti, V, Cr, Mn
L = NH3, NH2
-
R = Me, Et
Possible Polymerization CatalystsPossible Polymerization Catalysts
First row transition metals Cationic high-spin complexes Two nitrogen ligands Me or Et as model for the growing
polymer chain
Olefin Binding EnergyOlefin Binding Energy
0
10
20
30
40
TiVCrMn
d1 d2 d3 d4
Olefin binding energy for R = Me
Olefin binding energy correlates with the number of d-electrons.
d3 and d4 systems have lowest binding energy because of destabilized the acceptor orbital for the -d-interaction.
M
M R
M
M
R
R
R
M R
M R
M RM R
d-levels
a.b.
b.
b.
sp3
OC IN
π
π
π
Orbital Orbital Interactions Interactions during the during the Olefin Olefin Insertion Insertion
for example:a d1 system
SOMO becomes significantly destabilizedduring the insertion.
b. = bonding; a.b. = antibonding
Termination ReactionsTermination Reactions
BHE reaction is in most cases less facile than the BHT reaction.
BHT reaction coordinate involves a shift of the olefin in the BHT plane similar to the insertion reaction.
The major contribution for BHT barrier stems from the breaking of the C-H bond.
M
CH2
CH 2'L
L
OC BHT
H M
H 2CCH 2
'L
LH
CH 2
H2C
Ligand Design: Ligand Design: Real size non-chelating ligandsReal size non-chelating ligands
Cr
N
N
R
H3Si
H3Si
H3SiH3Si
N(SiH3)2
Cr
Ligand Design: Ligand Design: Promising ResultsPromising Results
UPT INS BHT
NH2 -18.3 6.2 11.4 3
HN-(CH2)3-NH -16.8 13.2 14.8 7
NMe2-14.711.9 18.6 3
N(SiH3)2 -10.49.6 20.2 3(Energies in kcal/mol)
19
42
C7
N2
C 4
5
6
M
C 111
C 2
9
12
C3
8
10
N1
C9
[(Ph)2nacnac]MR+ (M = Ti,V, Cr) Catalysts
Kim and Theopold et al. Organometallics, 1998, 17, 4541-4543
N
N
R
R
R'
R'
Nacnac ligand:
- monoanionic- symmetric- bidentate nitrogen coordination- 0/180 arrangement
R = Ph, R’ = Me
d-electron count:Ti: d1; V: d2; Cr: d3
Polymerization ability (Wn):V >> Ti > Cr
Performance of the model system: electronic behaviers of the nacnac ligand
N
N
R
R
R'
R'
R = Me R’ = H
21
19
22
C8
C7
23
C6
18
N2
C
4
24
N1
5
M
6
25
C1
C5
27
26
11
9
12
C3
8
10
2
C
M
TiVCr
ΔEcomplex
-24.7 < -25.2 -15.8
ΔEins
11.3 > 13.110.4
ΔEBHT
11.6 ~ 9.78.3
ΔEBHE
11.3 13.913.1
ΔEEHT - ΔEins
0.3< -3.4-2.1
- Insertion βαrrier usuαlly higher thαn d0 metαl system- Terminαtion βαrrier is not greαter thαn the insertion βαrrier due to the BΗT trαnsition Stαte lies on the lower sπin stαte surfαce
NSERC
A.BeckeE.J.BaerendsFree UniversityAmsterdam
Queens UniversityKingston,Canada
PRF NovacorDr. Rochus Schmid
Dr. Tom K. Woo
Dr. Peter Margl
Dr. L.Deng