Phosphine–Imidate-Supported Nickel Catalysts for Ethylene/Acrylate Copolymerization
John R. Rivet, Briana S. Henderson, Steve Marshall, Keosha Cade, David R. Wilson, Heather A. Spinney, Jianbo Hou, Alex J. Nett
Abstract
Phosphine–imidate-supported nickel catalysts were synthesized and tested for ethylene/acrylate copolymerization activity. Phosphine–amide metalation studies with (pyridine) 2 Ni(CH 2 Si(CH 3 ) 3 ) 2 (py 2 Ni(CH 2 TMS) 2 ) suggest that the metalation proceeds via an intermediate phosphine–amide complex ([P,O–amide]Ni(CH 2 TMS) 2 ). Subsequent deprotonation of the amide N–H gives access to the phosphine–imidate-supported nickel complex ([P,O–imidate]pyNi(CH 2 TMS)). The imidate form of the ligand proved to be critical for polymerization activity. The phosphine–imidate nickel catalysts described herein were capable of producing ethylene/acrylate copolymers with molecular weights ( M w ) from 700 to 120,000 g/mol and with acrylate incorporation >2.6 mol % in some cases. It was determined that hemilabile alkoxy groups on the phosphine aryl groups were necessary to achieve high M w and acrylate incorporation. These results demonstrate that phosphine–amides, a well-studied ligand class, can be utilized in the imidate form to access highly active neutral nickel polymerization catalysts.