Accessible, Highly Active Single-Component β-Ketiminato Neutral Nickel(II) Catalysts for Ethylene Polymerization

A series of novel neutral nickel complexes based on cyclic β-ketiminato ligands, [(2,6-iPr2C6H3)N═CHC6H8O]Ni(Ph)(PPh3) (3b), [(2,6-iPr2C6H3)N═CHCn+3H2n+2O(C6H4)]Ni(Ph)(PPh3) (6a−c), and [(2,6-iPr2C6H3)N═CHCn+3H2n+2O(C6H4)]Ni(CH3)(Py) (7a−c: a, n = 0; b, n = 1; c, n = 2) have been synthesized and characterized. These conveniently accessible complexes proved to be highly active catalysts for ethylene polymerization without an activator. Under the optimized conditions, an activity of 71.4 kg of PE/((mol of Ni) h atm) was observed using 6c as a catalyst. Particularly, it is of great interest that a bulky substituent proximate to the oxygen atom of the β-ketiminato complex is no longer a prerequisite to attain high catalytic efficiency, which is much different from the case for salicylaldiminato neutral nickel catalysts. This is effectively supported by the lower activation enthalpy changes of complexes 3b and 6a−c relative to values for the classic salicylaldiminato complexes. Moreover, for complexes 6a−c and...