A diruthenium μ-methylene complex

The reaction of [Ru-2(mu -CO)(CO)(4)(mu -dppm)(2)] (1; dppm = Ph2PCH2PPh2) with CH2N2 gives the mu -methylene complex [Ru-2(mu -CH2)(CO)(4)(mu -dppm)(2)] (2), and complex 2 resets with CO to regenerate complex 1 with loss of ketene. Complex 2 reacts with HBF4 or CF3SO3H at low temperature to form the fluxional mu -methyl complex [RU2(mu -CH3)(CO)(4)(mu -dppm)(2)](+) (3). Variable-temperature H-1, C-13, and P-31 NMR studies establish that the mu -CH3 group has an unsymmetrical coordination mode with an agostic hydrogen and is fluxional. At room temperature, the reaction of 2 with formic acid gives an equimolar mixture of complex 1 and [Ru-2(mu -H)(H)(mu -CO)(CO)(2)(mu -dppm)(2)] (4), which is an active catalyst for the decomposition of formic acid to hydrogen and carbon dioxide, and the reaction is shown to occur via the intermediate complexes 3 and [Ru-2(mu -H){mu -C(O)Me}(HCOO)(CO)(3)(mu -dppm)(2)](+) (5). The reaction of 2 with acetic acid at room temperature gives in sequence the complexes [Ru-2{mu -C(O)-Me}(OAc)(CO)(3)(mu -dppm)(2)] (6) and [Ru-2(mu -H){mu -C(O)Me}(OAc)(CO)(3)(mu -dppm)(2)](+) (7) before loss of methane occurs with formation of [Ru-2(mu -OAc)(CO)(4)(mu -dppm)(2)](+) (8). Complex 2 reacts with methyl triflate to give ethylene and [Ru-2(mu -H)(mu -CO)(CO)(3)(mu -dppm)(2)](+) (9), as the triflate salt, probably via an intermediate with an ethylruthenium group. In the presence of HBF4, complex 2 is an efficient precatalyst for the ring-opening polymerization of norbornene.