Synthesis and reactivity of dimetallacyclopentenone complexes [Ru-2(CO)(mu-CO){mu-C(O)(CRCR2)-C-1}(eta-C5H5)(2)] (R-1 = Me or Ph; R-2 = CO2Me)

Reactions of the dimetallacyclopentenone complex [Ru-2(CO)(mu-CO){mu-C(O)C2 Ph2}(eta-C5H5)(2)] (1) with alkynes RC=CCO2Me (R=Me or Ph) lead to alkyne e xchange, forming inseparable isomeric mixtures of [Ru-2(CO)(mu-CO){mu-C(O)C (R)C(CO2Me)}(eta-C5H5)(2)] and [Ru-2(CO)(mu-CO){mu-C(O)C(CO2Me)C(R)}(eta-C5 H5)(2)] (2i,j, R=Ph; 2k,l, R=Me), whereas with HC=CCO2Me the mu-vinylidene complex [Ru-2(CO)(2)(mu-CO){mu-C=C(H)CO2Me}(eta-C5H5)(2)] (4c) is produced. The new dimetallacyclopentenone complexes undergo fluxional processes whic h interconvert the isomers with free energies of activation similar to thos e seen previously for other diruthenacyclopentenone species. Both 2i,j and 2k,l are thermally stable but UV irradiation of 2i,j yields [Ru-2(mu-CO){mu -eta(2):eta(2)-C(Ph)C(CO2Me)}(eta-C5H5)(2)] (5), [Ru-2(CO)(2){mu-eta(2):eta (2)-C(O)C6H4C=C(H)CO2Me)}(eta-C5H5)(2)] (6) and [Ru-3(CO)(mu-CO)(2){mu(3)-e ta(2)-C(Ph)C(CO2Me)}(mu-eta(1):eta(5)-C5H4)(eta-C5H5)(2)] (7), while photol ysis of 2k,l generates the mu-allylidene complex [Ru-2(CO)(mu-CO){mu-C(CO2M e)CH=CH2}(eta-C5H5)(2)] (8). The structures of the unusual complexes 6 and 7 have been determined by X-ray diffraction studies. Complexes 5, 6 and 7 a re shown to be formed from 2i,j via independent pathways.