Synthesis and Reactivity of Electronically Unsaturated Dirhenium Carbonyl Compounds Containing Bridging Gold-Carbene Groups

The electronically unsaturated compounds Re2(CO)8[μ-Au­(NHC)]­(μ-Ph), 1, and Re2(CO)8[μ-Au­(NHC)]2, 2, were obtained from the reaction of Re2(CO)8[μ–η2-C­(H)C­(H)­Bun]­(μ-H) with MeAu­(NHC), NHC = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene. Compound 1 was converted to the new compound Re2(CO)8[μ-Au­(NHC)]­(μ-H), 3, by reaction with H2. Addition of CO to 3 yielded the new compound Re2(CO)9­[Au­(NHC)]­(μ-H), 4, which contains a terminally coordinated Au­(NHC) group on one of the rhenium atoms, and the hydrido ligand was shifted to bridge the Re–Au bond. The mechanism of the formation of 4 was established by DFT computational analyses. Compound 3 also reacted with C2H2 by an addition with insertion into the Re–H bonds to yield the compound Re2(CO)8[μ-Au­(NHC)]­(μ-C2H3), 5, which contains a σ–π coordinated, bridging C2H3 ligand. The stereochemistry of the insertion was found to proceed preferentially with a cis- (syn-) stereochemistry. Compound 1 reacted with HCl to yield Re2(CO)8[μ-Ph]­(μ-H), 6, and ClAu­(NHC) by selective removal of the bridging Au­(NHC) group. All new compounds were characterized by single-crystal X-ray diffraction analyses.