Synthesis and characterization of new di- and tetra-meric vanadium intermediates of olefin polymerization catalysts. Crystal structures of [V2(µ-Cl)2Cl4(MeCo2Et)4] and [{VOCl2[CH2(CO2Et)2]}4]·2CH2Cl2

Abstract

The direct reaction of VCl₃ and ethyl acetate yields [V₂(µ-Cl)₂Cl₄(MeCO₂Et)₄]1. The compound [V₂(µ-Cl)₂Cl₄{CH₂(CO₂Et)₂}₂]2 was obtained in dichloromethane via the substitution of MeCO₂Et in 1 by ethyl malonate. During crystallization of 2, under the influence of dioxygen and moisture, the tetrameric compound [{VOCl₂[CH₂(CO₂Et)₂]}₄]·2CH₂Cl₂3 was formed. The crystal structures of 1 and 3 have been determined by single-crystal X-ray diffraction studies. The dimeric compound 1 exhibits six-co-ordinate V^III centres [separated by a V ⋯ V distance of 3.590(1)Å] surrounded by two terminal Cl atoms, two carbonyl oxygen atoms of co-ordinated ethyl acetate molecules and linked by two bridging Cl atoms. In the tetrameric species 3, the four vanadium(IV) atoms have equivalent octahedral geometries, being bonded by two mutually cis chlorine atoms, two mutually cis oxygen atoms. High catalytic activity was found for 1, 2 and [V₂(µ-Cl)₂Cl₄(thf)₄](thf = tetrahydrofuran).