Macromolecular Science and Engineering

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Macromolecular Science and Engineering
Tuesday June 1 PM MA3 Regatta Advances In
Olefin Polymerization Organizer - H.
Zahalka Chair - H. Zahalka
1330-1400 0080 Olefin Polymerization
Catalysts Beyond Group-IV Metallocenes Ziegler
T., Deng L., Schmid R., Margl P.
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Fe
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Brookhart Polymerization Catalyst
CEN Feb. 5, 1996
Polymer Catalyst System Dupont Eyes New
Polyolefin Business
Brookhart catalyst
highly linear to moderately branched

• temperature Temp ? branching ?
• monomer pressure Et ? branching ?
• bulk of substituents bulk ? branching ? MW ?

• high MWs
• good activities

Johnson, L. K. Killian, C. M. Brookhart, M. J.
Am. Chem. Soc. 1995, 117, 2343.
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Gibson
Brookhart
- Robust - Low-cost - Simple to make
- High activities - High selectivity
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Experimental Observations
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.
1 R R i-Pr 2 R R Me 3 R t-Bu, RH 4
R i-Pr, R H 5 R Et, R H 6 R Me, R H
Fe/Co catalyst
highly linear high density

• 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!
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a
Deng,L.Margl, P. Ziegler, T., J.Am. Chem.
Soc.,1999, in press
a. Olefin complex resting state axial
Ca-conformation preferred electronically
DEcomplex -29.7 kcal/mol DEins 23
kcal/mol DEBHT 4 kcal/mol
b
b. Olefin complex the insertion precursor
equatorial Ca-conformation disfavored
electronically
DEcomplex -23.8 kcal/mol DEins 7.4
kcal/mol
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Neutral Ni(II)-Based Catalyst for Ethylene
Polymerization
Wang and Grubbs et al. Organometallics, 1998, 17,
3149-3151
Experiment Highly active for Polymerization
of ethylene
Calculation Without bulky substituents, the
insertion and termination barrier About the same
both as high as 26 kcal/mol
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Possible Polymerization Catalysts
M Ti, V, Cr, Mn
L
L NH3, NH2-

M
R
'L
R Me, Et

• First row transition metals
• Cationic high-spin complexes
• Two nitrogen ligands
• Me or Et as model for the growing polymer chain

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Olefin Binding Energy

• 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.

Olefin binding energy for R Me
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Orbital Interactions during the Olefin Insertion
??
a.b.
M
R
M
R
d-levels
M
R
??
b.
for example a d1 system
M
R
R
M
3
sp
M
R
SOMO becomes significantly destabilized during
the insertion.
?
b.
M
M
R
R
IN
OC
b. bonding a.b. antibonding
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Termination 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.

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Nobel-Price 1998 in Chemistry for The Theory
W. Kohn (DFT) and J. Pople (ab initio)
Theory as a valuable tool in chemical research