Highly Active Single-Component Neutral Nickel Ethylene Polymerization Catalysts: The Influence of Electronic Effects and Spectator Ligands

Abstract

A series of neutral nickel complexes [6-CHN(2,6-iPr2C6H3)-2-(2-NO2C6H4)-C6H3O-κ2- N,O]Ni(Ph)(PPh3) (6a), [6-CHN(2,6-iPr2C6H3)-2-(C6F5)-C6H3O-κ2-N,O]Ni(R)(L) (R = Ph, L = PPh3 (6b-PPh3); R = Me, L = pyridine (6b-Py); R = CH2Ph, L = PMe3 (6b-1Bz); R = η3-CH2Ph (6b-3Bz)), and [6-CHN(2,6-iPr2C6H3)-2-(2-OCH3C6H4)-C6H3O-κ2-N,O]Ni(Ph)(PPh3) (6c) based on 2-nitrophenyl-, pentafluorophenyl-, and 2-methoxyphenyl-substituted salicylaldimine ligands, respectively, have been synthesized and characterized by 1H NMR, 13C NMR, and elemental analysis. The solid structures of 6a, 6b-PPh3, 6b-Py, and 6b-1Bz have been further confirmed by X-ray crystallography. By combining the benefits of both electronic and steric factors, all the complexes with electron-withdrawing groups proved to be highly active single-component catalysts for ethylene polymerization, producing polymer with moderate molecular weights. Among these catalysts, 6b-PPh3 exhibited very high productivity of up to 5.87 × 106 g PE/molNi·h under optimal condition...