Vanadium(V) imido chlorides and n-propoxides — Towards a rational design of vanadium imido precatalysts for ethylene polymerization

Abstract

Vanadium(V) imido complexes are widely used in olefin polymerization and oligomerization. In this report we present the synthesis and the results of ethylene polymerization studies for a series of vanadium(V) imido complexes with various substituents at the imido fragment. All complexes have been prepared in nearly quantitative yields by the interaction of N-sulfinylamines with VOCl3 or VO(OnPr)3 and characterized using 1H, 13C, 51V NMR and elemental analysis. The solid-state structure of complex V(=NArOMe)(OnPr)3 was established using X-ray. Vanadium(V) imido chlorides and n-propoxides exhibited similar moderate catalytic activities (320–547 kgPE·mol(V)−1·h−1·atm−1). The maximum catalytic activity (547 kgPE·mol(V)−1·h−1·atm−1) was achieved for (adamantylimido)vanadium(V) n-propoxide. The molecular weights of the resulting polyethylenes were higher (Mv = 3.7–6.5·105 Da) for imido n-propoxide complexes as compared to the corresponding imido chlorides (Mv = 2.1–5.5·105 Da). The localization of DFT calculated HOMO on imide nitrogen was proposed to favor the reaction between imide ligand and Et2AlCl used as activator.