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.

•Multicenter C–H bond transformations of a methyl group at a triosmium center.•Synthesis of osmium-gold cluster complexes with bridging acetyl and bridging methylidyne ligands.•Computational analyses of agostically coordinated bridging methyl and bridging methylene ligands.•CO induced cluster opening reactions.Os3(CO)11(NCCH3) and Os3(CO)10(NCCH3)2 react with (CH3)AuPPh3 to yield the new Os3Au cluster complexes, Os3(CO)10(μ-OCCH3) (AuPPh3), 1 and Os3(CO)9(μ-η3-CH) (μ-H)2(μ-AuPPh3), 2 containing bridging acetyl and bridging methylidyne ligands, respectively, by two competing reaction pathways: 1) a methyl migration/CO insertion pathway that produces a complex with a bridging acetyl ligand. and 2) C–H bond cleavage transformations via a series of decarbonylated intermediates containing an agostically coordinated bridging methyl group, a bridging methylene group, a triply bridging methylidyne ligand and bridging hydride ligands. It has also been found that carbon monoxide can induce shifts of the bridging hydride ligands back to methylidyne ligand in 2 with subsequent cleavage of Os–Au and Os–Os bonds to yield two open cluster complexes (CH3)Os3(CO)12AuPPh3, 4 and (CH3)Os2(CO)8AuPPh3, 5 having terminally coordinated methyl ligands. The open cluster complex 4 can be converted back to 1 and 2 via decarbonylation process by using either thermal or irradiation treatments. The CO dissociation mechanisms related to the CH bond transformation processes were studied by DFT computational analyses. It has been demonstrated that the Os3Au(CH3) cluster provides a robust platform to studying multicenter C–H bond transformations and for C–C bond formation via methyl migration/CO insertion processes.