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(NBut)2Cl}2(μ-N3) 2] 1 and [Cr(ButN=NN=NSiMe3)(N3)Cl2] 2 have been isolated in the reactions of SiMe3(N3) with [Cr(NBut)2Cl2] and [Cr(NBut)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(NBut)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(NBut)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.