Synthesis and Reactivity of a Diruthenium Diazoalkane Complex

Reaction of [Ru 2 (μ-CO)(CO) 4 (μ-dppm) 2 ], 1, dppm = Ph 2 PCH 2 PPh 2, with N 2 CHCO 2 Et gives the complex [Ru 2 (μ-NNCHCO 2 Et)(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 [Ru 2 (μ-CO)(CO) 2 {μ-NN(CHCO 2 Et)(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 [Ru 2 (CO) 4 (μ-NNCH 2 CO 2 Et)(μ-dppm) 2 ] +, 4, and then, with the strong acid H[BF 4 ], at the Ru−Ru bond to give the dicationic complex [Ru 2 (μ-H)(CO) 4 (μ-NNCH 2 CO 2 Et)(μ-dppm) 2 ] 2+, 5 . Complex 2 is a precatalyst for the decomposition of formic acid to give CO 2 and H 2, and the chemistry leading to the active catalyst is described.