Synthesis and Reactivity of a Diruthenium Diazoalkane Complex

Reaction of [Ru2(μ-CO)(CO)4(μ-dppm)2], 1, dppm = Ph2PCH2PPh2, with N2CHCO2Et gives the complex [Ru2(μ-NNCHCO2Et)(CO)4(μ-dppm)2], 2, in which the diazoalkane acts as a novel 2-electron ligand bridging a metal−metal bond. Complex 2 reacts with phenylacetylene, with displacement of a carbonyl ligand, to give [Ru2(μ-CO)(CO)2{μ-NN(CHCO2Et)(CPhCH)}(μ-dppm)2], 3a, which contains a new type of metallacycle formed by coupling of the diazoalkane and alkyne ligands at the diruthenium center. Protons attack complex 2 first at the NCH center to give the alkyldiazonium complex [Ru2(CO)4(μ-NNCH2CO2Et)(μ-dppm)2]+, 4, and then, with the strong acid H[BF4], at the Ru−Ru bond to give the dicationic complex [Ru2(μ-H)(CO)4(μ-NNCH2CO2Et)(μ-dppm)2]2+, 5. Complex 2 is a precatalyst for the decomposition of formic acid to give CO2 and H2, and the chemistry leading to the active catalyst is described.