1. ACS Meeting, Chicago
August 28, 2001
The Challenge of the Copolymerization of Olefins with Nitrogen-Containing Polar Monomers
Dirk V. Deubel and Tom Ziegler
Dept. of Chemistry, University of Calgary, Canada

2. 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:

3. 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

4. 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

5. Model Catalysts
Model catalysts have been used, because steric effects on monomer coordination energies are comparably small
Brookhart Grubbs
1: Ni 3: Pd : Ni 4: Pd

6. Model Monomers
Monomers of the type CH2=CH(CH2)n(PolarGroup) have been considered
Conjugated systems (n = 0) have explicitly been investigated
Non-conjugated systems (n ≥ 1) have been studied efficiently using CH2=CHCH3 and CH3(PolarGroup) as models
A large number of catalyst-monomer combinations was considered at a high computational level

7. Model Complexes Example: Nitriles and Brookhart Nickel
CH2=CHCN
: N:
CH2=CH(CH2)nCN, n ≥ 1

8.  versus N Coordination: Calculated Stabilization Energies for the Ni Catalysts

9.  versus N Coordination
Large effect of  conjugation in the polar monomer on  binding with the Brookhart catalyst: electron-rich C=C bonds increase  complex stability
The polar monomers form very strong N complexes with the cationic Brookhart catalysts
Vinylamine (CH2=CHNH2) prefers  coordination over N coordination
Small effect of  conjugation in Grubbs catalysts: both electron-rich and electron-poor C=C 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)

10. 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

11. Calculated  and N Coordination Energies for the Pd Catalysts

12. 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 C=C ligand orbitals

13. 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

14. 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