Epoxide ring opening catalysed by imidochromium complexes‡

Abstract

tert-Butylimidochromium complexes catalysed ring opening of epoxides by SiMe₃(N₃) to give azidohydrins in good yields. The proposed mechanism for the chromium-mediated epoxide azidolysis involves the intermediacy of a chromium–azide species which delivers nucleophilic azide to the epoxide substrate. The azido complexes [{Cr(NBu^t)₂Cl}₂µ-N₃)₂] 1 and [Cr(Bu^tNNNNSiMe₃)(N₃)Cl₂] 2 have been isolated in the reactions of SiMe₃(N₃) with [Cr(NBu^t)₂Cl₂] and [Cr(NBu^t)Cl₃(dme)] (dme = 1,2-dimethoxyethane), respectively. The structure of complex 1 has been established by X-ray crystallography. The mean Cr–N (imide) and Cr–N (azide) distances are 1.605 and 2.061 Å, respectively. Reaction of [Cr(NBu^t)Cl₃(thf)₂] (thf = tetrahydrofuran) with (S,S)-diop {4,5-[bis(diphenylphosphino)methyl]-2,2-dimethyl-1,3-dioxolane} gave the dimeric complex [{Cr(NBu^t)Cl₃}₂{µ-(S,S)-diop}], which has been characterised by X-ray crystallography. The Cr–N and Cr–P distances are 1.593(9) and 2.449(4) Å, respectively.