A Diruthenium μ-Methylene Complex

Abstract

The reaction of [Ru2(μ-CO)(CO)4(μ-dppm)2] (1; dppm = Ph2PCH2PPh2) with CH2N2 gives the μ-methylene complex [Ru2(μ-CH2)(CO)4(μ-dppm)2] (2), and complex 2 reacts with CO to regenerate complex 1 with loss of ketene. Complex 2 reacts with HBF4 or CF3SO3H at low temperature to form the fluxional μ-methyl complex [Ru2(μ-CH3)(CO)4(μ-dppm)2]+ (3). Variable-temperature 1H, 13C, and 31P NMR studies establish that the μ-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 [Ru2(μ-H)(H)(μ-CO)(CO)2(μ-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 [Ru2(μ-H){μ-C(O)Me}(HCOO)(CO)3(μ-dppm)2]+ (5). The reaction of 2 with acetic acid at room temperature gives in sequence the complexes [Ru2{μ-C(O)Me}(OAc)(CO)3(μ-dppm)2] (6) and [Ru2(μ-H){μ-C(O)Me}(OAc)(CO)3(μ-dppm)2]+ (7) before loss of methane occurs with formation of [Ru2(μ-OAc)(CO)4(μ-dppm)2]+ (8). Complex 2 reacts with methyl triflate to give ethylene and [Ru2(μ-H)(μ-CO)(CO)3(μ-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.