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.

Reactivity of a coordinatively unsaturated diruthenium hydride: reversible insertion of alkynes

“…, 5, reacts with CO to give hydrogen and complex 3. 5 It is likely that CO reacts with 5 to give the adduct 6, which is an isomer of 4, and which then eliminates hydrogen as shown in eqn. (3).…”

“…6 The µ-vinyl group acts as a three-electron ligand and the complex is coordinatively saturated, with structural features similar to those of other µ-alkenyl complexes. 2,4 Scheme 1 (5) The low symmetry of complex 9, as determined by the solid state structure, is maintained in solution. Thus, the 31 P NMR spectrum at room temperature exhibits an ABCD pattern of peaks indicating that all four phosphorus atoms are inequivalent.…”

“…The reaction of 1, as the triflate salt, with HCCH in toluene solution occurred with immediate precipitation of a yellow solid, that was characterized as [Ru 2 (µ-HC᎐ ᎐ CH 2 )-(CO) 4 (µ-dppm) 2 ][CF 3 SO 3 ], 9[CF 3 SO 3 ], according to eqn. (5).…”

“…Although easy insertion of an alkyne into a Ru-H bond is well-known, the direct observation of an equilibrium between the hydride ϩ alkyne and the alkenyl complex is rare. [2][3][4][5][6][7][8] No further rearrangement of 12 to form a bridging alkenyl complex analogous to 11 was observed, presumably because steric effects prevent it.…”

Advances in Ruthenium Catalysed Hydrogen Release from C1 Storage Materials

“…There were few significant advances in the field until the publication of work, conducted by Puddephatt and co-workers, investigating the use of binuclear ruthenium complexes [28][29][30]. These metal centres were shown to Brought to you by | University of Queensland -UQ Library Authenticated Download Date | 7/12/15 3:39 PM act cooperatively resulting in a much greater efficiency reported for the catalytic dehydrogenation of formic acid than the previously reported mononuclear catalysts.…”