Nickel(II) Complexes with Mono(imino)pyrrole Ligands: Preparation, Structure, and MMA Polymerization Behavior

Abstract

A simplified synthetic method was initiated to prepare the corresponding nickel complexes NiL2 (I–III) with direct condensation of mono(imino)pyrroles (L1–L3) and nickel dichloride, the structures and methyl methacrylate (MMA) catalytic polymerization behavior of this series of mono(imino)pyrrole nickel complexes were presented. The mono(imine)pyrrole ligands and the corresponding nickel complexes were determined by 1H NMR, 13C NMR, IR and MS, etc. Complexes I and III were further characterized by X-ray crystal diffraction (CIF files CCDC nos. 1890965 (I), 1890964 (III)). Both of the structures showed that the ligand chelated to nickel with 2 : 1 molar ratio. The systematic studies were focused on the relationship between the catalytic behavior of these complexes for MMA polymerization and catalyst structure, reaction time, reaction temperature, and ratio of monomer with catalyst. The optimum reaction conditions of the molar ratio of monomer to catalyst is of 1200 : 1, the polymerization temperature of 100°C, time of 10 h, the nickel complex with two bulky substituents on the o-position of phenyl ring linked with imine showed excellent catalytic activities for MMA polymerization (4.791 × 104 g mol–1 h–1), high molecular weight (Mn = 65.873 × 103 g mol–1), and narrow molecular mass distribution (polymer dispersity index = 3.9877), and azodiisobutyronitrile acted as co-catalyst during MMA polymerization.