Tri- and tetra-dentate imine vanadyl complexes: synthesis, structure and ethylene polymerization/ring opening polymerization capability.

Abstract

Reaction of the ligand 2,4-tert-butyl-6-[(2-methylquinolin-8-ylimino)methyl]phenol (L(1)H) with [VOCl3] in the presence of triethylamine afforded the complex [VOCl2L(1)] (1), whereas use of [VO(OnPr)3] led to the isolation of [VO2L(1)] (2) or [VO2L(1)]·2/3MeCN (2·2/3MeCN). Reaction of 2-((2-(1H-benzo[d]imidazol-2-yl)quinolin-8-ylimino)methyl)-4,6-R(1),R(2)-phenols (R(1) = R(2) = (t)Bu; L(2)H), (R(1) = R(2) = Me; L(3)H) or (R(1) = Me, R(2) = Ad; L(4)H) with [VO(OnPr)3] afforded complexes of the type [L(2-4)VO] (where L(2) = 3, L(3) = 4, L(4) = 5). The molecular structures of 1 to 3 are reported; the metal centre adopts a distorted octahedral, trigonal bipyramidal or square-based pyramidal geometry respectively. In Schlenk line tests, all complexes have been screened as pre-catalysts for the polymerization of ethylene using diethylaluminium chloride (DEAC) as co-catalyst in the presence of ethyltrichloroacetate (ETA), and for the ring opening polymerization (ROP) of ε-caprolactone in the presence of benzyl alcohol. All pre-catalyst/DEAC/ETA systems are highly active ethylene polymerization catalysts affording linear polyethylene with activities in the range 3000-10,700 g (mol h bar)(-1); the use of methylaluminoxane (MAO) or modified MAO as co-catalyst led to poor or no activity. In a parallel pressure reactor, 3-5 have been screened as pre-catalysts for ethylene polymerization in the presence of either DEAC or DMAC (dimethylaluminium chloride) and ETA at various temperatures and for the co-polymerization of ethylene with propylene. The use of DMAC proved more promising with 3 achieving an activity of 63,000 g (mol h bar)(-1) at 50 °C and affording UHMWPE (M(w) ~ 2,000,000). In the case of the co-polymerization, the incorporation of propylene was 6.9-8.8 mol%, with 3 exhibiting the highest incorporation when using either DEAC or DMAC. In the case of the ring opening polymerization (ROP) of ε-caprolactone, systems employing complexes 1-5 were virtually inactive at temperatures <110 °C; on increasing the CL : V ratio at 110 °C, conversions of the order of 80% were achievable.