Reactivity of Methyl Diruthenium Complexes with the Bis(diphenylphosphino)methane (dppm) Ligand and Formation of Dinitrogen and Dihydrogen Complexes via Methane Loss

A diruthenium complex with a μ-CH3 ligand, [cis-{(η5-C5H2(t-Bu))2(CMe2)2}Ru2(dppm)2(μ-CH3)][B(ArF)4] (dppm = 1,1-bis(diphenylphosphino)methane) has been synthesized, structured, and its reactivity explored. Reaction of the μ-CH3 complex with H2 led to a fluxional dihydrogen/hydrido complex with the hydrogens exchanging between the two ruthenium centers, results consistent with the NMR spectroscopy, the crystal structure, and density functional theory. The activation barrier for this exchange was calculated to be ∼12 kcal/mol. The μ-1,2-N2 complex formed when the μ-CH3 diruthenium or dimethyl diruthenium complexes were treated with acid, and the crystal structure showed a Ru–N–N–Ru geometry with a smaller Ru–N–N angle than other related complexes. The stability of a methane diruthenium complex with either a dppm or dmpm (1,1-bis(dimethylphosphino)methane) ligand has also been computationally investigated, with the less sterically demanding dmpm forming a more stable methane complex than that with the dppm ligand.