Synthesis, Molecular Structures, and Norbornene Addition Polymerization Activity of the Neutral Nickel Catalysts Supported by β-Diketiminato [N, N], Ketiminato [N, O], and Schiff-Base [N, O] Ligands

Abstract

A series of neutral nickel complexes [Ni(Ph)(PPh3)(N, O)] with Schiff-base ligands (N, O) [N, O = 5-Me-3-tert-Bu-(Ar−NCH)C6H2O (1, Ar = 2,6-Me2C6H3; 2, Ar = 2,6-i-Pr2C6H3)], [Ni(Ph)(PPh3)(N,O)], with β-ketiminato ligands (N, O) [N, O = CH3COCHC(CH3)N−Ar (3, Ar = 2,6-Me2C6H3; 4, Ar = 2,6-i-Pr2C6H3)] and [Ni(N, N)(PPh3)], and with β-diketiminato ligands (N, N) [5, N, N = [2,6-i-Pr2(C6H3)NC(CH3)]2CH] have been synthesized and characterized. The molecular structures of complexes 1, 4, and 5 have been confirmed by X-ray single-crystal analyses. Although their ligands have similar structures, complex 4 possesses a structure similar to that of four-coordination nickel with complex 1, while complex 5 reveals a rare three-coordination nickel geometry. These compounds show high catalytic activities of up to 3.16 × 107 g PNB mol-1 Ni h-1 for the addition polymerization of norbornene in the presence of modified methylaluminoxane (MMAO) as cocatalyst. Catalytic activities, polymer yield, molecular weights, and molecular weight distributions of polyborbornene have been investigated under various reaction conditions.