Multicenter transformations of the methyl ligand in CH3Os3Au carbonyl cluster complexes: Synthesis, characterization and DFT analyses

Abstract

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.