Linking and fragmentation of alkynes at a triruthenium centre

Abstract

The triruthenium µ3-alkyne complex [Ru3(CO)3(µ-CO)(µ3-CO){µ3-C2(CF3)2}(η-C5H5)2]1 reacted with Me3NO in MeCN to give [Ru3(MeCN)(CO)2(µ-CO)(µ3-CO){µ-C2(CF3)2}(η-C5H5)2]2. This with hexafluorobut-2-yne at or below room temperature gave [Ru3(CO)2(µ-CO){µ3-η3-C3(CF3)3}(µ3-CCF3)(η-C5H5)2]3, shown by X-ray diffraction to contain a ruthenium triangle with µ3-perfluoroethylidyne and µ3-η3-C3(CF3)3 ligands arising from cleavage of one of the hexafluorobut-2-yne molecules. In contrast, 2 reacted at room temperature with the alkynes diphenylethyne, methyl but-2-ynoate and but-2-yne to yield the species [Ru3(CO)2(µ-CO)2{µ3-C4(CF3)2R(R′)}(η-C5H5)2](R = R′= Ph; R = Me, R′= CO2Me; or R = R′= Me) respectively. X-Ray diffraction studies on the first two of these showed that the alkynes have linked to form a µ3-C4(CF3)2R(R′) ligand bound to a closed Ru3 triangle via a doubly bridging interaction with one pair of metal atoms and an η3-allyl mode with the other. Dimethyl acetylenedicarboxylate (dmad) reacted with 2 at room temperature differently again to give a structurally unidentified species [Ru3(CO)5{C2(CF3)2}{C2(CO2Me)2}(η-C5H5)2], which on heating afforded [Ru3(CO)3{µ3-C4(CF3)2(CO2Me)2}(η-C5H5)2]12, revealed by X-ray diffraction to contain a closo-pentagonal-bipyramidal Ru3C4 cluster in which a µ3-C4(CF3)2(CO2Me)2 ligand bridges an open ruthenium triangle. This complex was formed directly when 1 was heated with dmad in refluxing toluene. Analogous complexes [Ru3(CO)3{µ3-C4(CF3)2R(R′)}(η-C5H5)2](R = Me, R′= CO2Me; R = R′= Ph; or R = R′= Me) were produced on heating 1 with methyl but-2-ynoate, diphenylethyne and but-2-yne respectively. The last two reactions also gave isomers [Ru3(CO)3{µ3-C4(CF3)R2(CF3)}(η-C5H5)2](R = Ph or Me) in which formal insertion of the incoming alkyne into the co-ordinated CF3CCCF3 bond has occurred. In addition, the reaction of 1 with but-2-yne produced [Ru3(CO)2(µ-CO){µ3-η3-C3(CF3)Me2}(µ-CCF3)(η-C5H5)2] analogous to 3. Diruthenium species [Ru2(CO){µ-C4(CF3)2R(R′)}(η-C5H5)2] are formed in both toluene reflux reactions of 1 and room-temperature reactions of 2 as a result of triruthenium cluster degradation. Heating the room-temperature products [Ru3(CO)2(µ-CO)2{µ3-C4(CF3)2R2}(η-C5H5)2] confirms that these are intermediates in the formation of the complexes [Ru3(CO)2(µ-CO){µ3-η3-C3(CF3)R2}(µ3-CCF3)(η-C5H5)2] and the isomeric closo clusters [Ru3(CO)3{µ3-C4(CF3)2R2}(η-C5H5)2] and [Ru3(CO)3{µ3-C4(CF3)R2(CF3)}(η-C5H5)2]. Pathways for the processes leading to the various products are discussed.