The Challenge of the Copolymerization of Olefins with Nitrogen-Containing Polar Monomers

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The Challenge of the Copolymerization of Olefins
with Nitrogen-Containing Polar Monomers
ACS Meeting, Chicago August 28, 2001

• Dirk V. Deubel and Tom Ziegler
• Dept. of Chemistry, University of Calgary, Canada
• deubel_at_ucalgary.ca, ziegler_at_ucalgary.ca

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New Catalysts for Olefin Copolymerization with
O-Containing Monomers

• Incorporation of polar monomers in the polymer
  chain of polyolefins is of industrial interest
• Common random copolymers such as
  polystyrene-acrylonitrile are still produced in
  radical processes
• Promising Nickel(II) and Palladium(II) catalysts
  with diimine ligands (Brookhart) and
  salicylaldiminato ligands (Grubbs) were
  recently reported

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New Catalysts for Olefin Copolymerization with
N-Containing Monomers?

• The Brookhart and Grubbs late transition metal
  (late TM) catalysts are less oxophilic than their
  Ziegler-Natta and metallocene counterparts and
  have been used for copolymerization with
  oxygen-containing monomers
• Despite the industrial importance, little is
  known about whether copolymerization of olefins
  with nitrogen-containing polar monomers can also
  be achieved
• Objective Initial screening of late TM catalysts
  and polar monomers toward an incorporation of
  amines or nitriles in the polymer chain of
  polyolefins
• Quantum-chemical methods Gradient-corrected
  density functional theory (DFT) at the BP86
  level Basis sets VTZP at the metals and VDZP at
  the other atoms
• Quantum-chemical software ADF 2000

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DFT Model Study on Polar Monomer Binding to Late
TM Catalysts

• N-containing polar monomers can bind either with
  the ? moiety or with the N-containing polar site
  to the catalyst
• The ? coordination leads to polymer growth while
  the N coordination is a dead end
• Catalyst-monomer combinations that prefer ?
  coordination over the N coordination are promising

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Model Catalysts

• Model catalysts have been used, because steric
  effects on monomer coordination energies are
  comparably small

Brookhart Grubbs 1 Ni
3 Pd 2 Ni 4 Pd
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Model Monomers

• Monomers of the type CH2CH(CH2)n(PolarGroup)
  have been considered
• Conjugated systems (n 0) have explicitly been
  investigated
• Non-conjugated systems (n 1) have been studied
  efficiently using CH2CHCH3 and CH3(PolarGroup)
  as models
• A large number of catalyst-monomer combinations
  was considered at a high computational level

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Model ComplexesExample Nitriles and Brookhart
Nickel

• CH2CHCN
• ? N
• CH2CH(CH2)nCN, n 1
• ? N

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? versus N Coordination Calculated Stabilization
Energies for the Ni Catalysts
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? versus N Coordination

• Large effect of ? conjugation in the polar
  monomer on ? binding with the Brookhart catalyst
  electron-rich CC bonds increase ? complex
  stability
• The polar monomers form very strong N complexes
  with the cationic Brookhart catalysts
• Vinylamine (CH2CHNH2) prefers ? coordination
  over N coordination
• Small effect of ? conjugation in Grubbs
  catalysts both electron-rich and electron-poor
  CC bonds slightly increase the ? complex
  stability
• The polar monomers form N complexes with the
  Grubbs catalysts of the same stability as ?
  complexes
• Destabilization of amine-N complexes by N-alkyl
  substituents (Grubbs ligands have a larger bite
  angle than Brookhart ligands)

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Large Differences in ? Complex Stability
Rationalization by Orbital Interactions

• Donation from the monomer to the catalyst is
  predominant in Brookhart complexes
• Considerable amount of backdonation from the
  catalyst to the monomer in the Grubbs complexes

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Calculated ? and N Coordination Energies for the
Pd Catalysts
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Ni versus Pd Catalysts Systematic Trends in ?
and N Coordination

• The ? complexes with the Brookhart Pd catalysts
  are more stable than the corresponding Ni
  complexes ? by 3 kcal/mol
• The N complexes with the Brookhart Pd catalysts
  are as stable as the corresponding Ni complexes ?
• The ? complexes with the Grubbs Pd catalysts are
  more stable than the corresponding Ni complexes ?
  by 6 kcal/mol
• The N complexes with the Grubbs Pd catalysts are
  more stable than the corresponding Ni complexes ?
  by 3 kcal/mol
• Replacing Ni by Pd favors ? coordination relative
  to N coordination by 3 kcal/mol
• Explanation by larger overlap between Pd d
  orbitals and CC ligand orbitals

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Summary

• The stabilization energies for the ? and N
  binding modes of unsaturated amines and nitriles
  to Brookhart and Grubbs polymerization catalysts
  have been calculated using DFT
• A reasonable choice of computational models has
  enabled us to study a large number of
  catalyst-monomer combinations at a high level of
  theory
• ?-Conjugated amines prefer ? binding mode in its
  complexes with all investigated model catalysts,
  including the cationic Brookhart catalysts
• The ? complexes formed by the polar monomers and
  the Grubbs catalysts are as stable as the
  corresponding N complexes, indicating a very
  promising research direction
• The Pd ? complexes are more stable than their Ni
  counterparts
• N-alkyl substituents destabilize the N complexes
  and therefore indirectly favor ? coordination

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Acknowledgments

• Dr. Artur Michalak and the other members of the
  Ziegler research group
• Multimedia Advanced Computational Infrastructure
  (MACI), University of Calgary, Canada
• German Academic Exchange Service (NATO
  Fellowship)
• Alexander-von-Humboldt Foundation