Reaction of transition metals with bromine in acetonitrile

Abstract

The reactions of titanium, vanadium, and chromium with bromine in acetonitrile have been re-examined. The major products of the reaction were TiBr₄(MeCN)₂, VBr₂(Br₃)(MeCN)₃, and [CrBr₂(Br₃)(MeCN)₂]_n. The latter polymeric complex breaks down in two steps in the parent solvent to form CrBr₂(Br₃)(MeCN)₃ followed by CrBr₃(MeCN)₃. The simple halide complex was found to be identical with the complex formed from CrBr₃ and MeCN. Spectral and conductivity studies indicate that the tribromide ion is bonded directly to the metal in these cases. In solution the vanadium complex appears to undergo co-ordination disproportionation. The mechanism of the reaction and the bonding in the complexes are discussed.