Synthesis of Heterometallic Trinuclear Polyhydrido Clusters Containing Ruthenium and Osmium and Their Electronic and Structural Deviation from Homometallic Systems

A trinuclear heterometallic pentahydrido complex, (Cp*Ru)2(Cp*Os)(μ-H)5 (3), was synthesized by dehydrogenative coupling between a diruthenium tetrahydride complex, Cp*Ru(μ-H)4RuCp*, and an osmium pentahydride, Cp*OsH5; an analogous complex, (Cp*Ru)(Cp*Os)2(μ-H)5 (4), was obtained by the reaction of a dimeric ruthenium methoxo complex, Cp*Ru(μ-OMe)2RuCp*, with a diosmium tetrahydride complex, Cp*Os(μ-H)4OsCp*, under an atmospheric pressure of dihydrogen. Complexes 3 and 4 were sufficiently basic to be protonated with HBF4, leading to the formation of corresponding hexahydrido cations, [(Cp*Ru)2(Cp*Os)(μ-H)6]+ (7) and [(Cp*Ru)(Cp*Os)2(μ-H)6]+ (8), respectively. An experiment on proton transfer between the two heterometallic systems 7 and 4 showed that the RuOs2 pentahydride was more basic than the Ru2Os pentahydride. Optimized structures of the heterometallic polyhydrido complexes 3, 4, 7, and 8 were derived using their C5H5 analogues as model compounds. Unlike the Ru3 system, the complex (CpRu)n(CpOs)3−n(μ-H)5 (3a: n = 2, 4a: n = 1), which has five doubly bridging hydrido ligands, was the most stable. Although X-ray structural studies of these complexes were conducted using a labeled cyclopentadienyl group, C5EtMe4, in all cases, their structures were disordered with respect to metal atoms. The most plausible structures of these complexes were obtained by solving simultaneous equations for metal−metal bond lengths. The estimated lengths were fully consistent with structures optimized by density functional theory calculations.