Phosphine–Imidate-Supported Nickel Catalysts for Ethylene/Acrylate Copolymerization

Abstract

Phosphine–imidate-supported nickel catalysts were synthesized and tested for ethylene/acrylate copolymerization activity. Phosphine–amide metalation studies with (pyridine)₂Ni(CH₂Si(CH₃)₃)₂ (py₂Ni(CH₂TMS)₂) suggest that the metalation proceeds via an intermediate phosphine–amide complex ([P,O–amide]Ni(CH₂TMS)₂). Subsequent deprotonation of the amide N–H gives access to the phosphine–imidate-supported nickel complex ([P,O–imidate]pyNi(CH₂TMS)). 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.