A fresh look into VO(salen) chemistry:: synthesis, spectroscopy, electrochemistry and crystal structure of [VO(salen)(H2O)]Br•0.5 CH3CN

The reaction of (VO)-O-IV(salen) with [Et4N][SnBr3] in air proceeds via an initial reduction to give a [V-III (salen)](+) intermediate, which is then oxidised to dark green [(VO)-O-V(salen)(H2O)]Br, 1. As determined by X-ray crystallography, 1 in the solid state contains hexacoordinate vanadium. V-51 NMR spectra indicate that dissociation of the aqua ligand occurs to give a pentacoordinated [(VO)-O-V(salen)] cation in methanol-d(4) solution, while in DMSO-d(6) solutions, coordination of the solvent occurs to give [(VO)-O-V(salen)(DMSO-d(6))](+). The colour of 1 can be accounted for by O-oxo --> V-V and phenolate --> V-V LMCTs. Results from this study have led to the re-assignment of LMCTs and V-N and V-O-phenolate stretching frequencies in the IR spectrum. Cyclic voltammetry of 1 indicates three redox processes. The first is typical of [VO(salen)]/[VO(salen)](+) couple and the other two are bromide oxidations. (C) 2004 Elsevier B.V. All rights reserved.