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

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 deubel@ucalgary.ca, ziegler@ucalgary.ca

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

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