Chloride-bridged oxovanadium(v) complexes with alkoxyalkoxide ligands. Synthesis, structure, electrochemistry and reactivities

Abstract

A series of mixed alkoxyalkoxo chloro complexes of vanadium(V), [VOCl₂(OCH₂CH₂OR)]₂ (R = Me, Et, ⁱPr, Bz), [VOCl₂(OCMe₂CH₂OMe)]₂ and [VOCl₂(OCH₂(cyclo-C₄H₇O)]₂, were synthesised and characterised. The title compounds can be obtained either from VOCl₃ and the alkoxyalcohols by HCl elimination or from the corresponding lithium alkoxides and VOCl₃ by salt metathesis reaction. X-Ray diffraction studies revealed the title compounds to be dimers with chloride bridging ligands and intramolecular ether coordination. Electrochemical results obtained by cyclic voltammetry indicate irreversible, reductive behaviour. The interactions of the title compounds with oxygen, nitrogen and phosphorus donor ligands were examined. Phosphorus and nitrogen donors lead to reduction products whereas tetrahydrofuran coordinates to the vanadium(V) centre by breaking the chloride bridge. All tetrahydrofuran complexes, [VOCl₂(OCH₂CH₂OR)(thf)] (R = Me, Et, ⁱPr) and [VOCl₂(OCMe₂CH₂OMe)(thf)], have been characterised by single-crystal X-ray diffraction. The solid-state structures of these complexes show that they consist of six-coordinate monomers. Reaction of [VOCl₂(OCH₂CH₂OMe)]₂ with Me₃SiCH₂MgCl gave [VO(CH₂SiMe₃)₃], which has been structurally characterised. The compounds were tested as catalysts for epoxidation and polymerisation reactions. They convert unfunctionalised olefins into the corresponding epoxides with moderate activity. They are good pre-catalysts for the polymerisation of ethene and oligomerise 1-hexene.