Synthesis of an Electron-Deficient Triruthenium Hydrido Complex Having a Bridging Carbonyl Ligand: Influence of a CO Ligand on the Properties and Reactivities of a Hydrido Cluster

A novel triruthenium hydrido cluster, (Cp*Ru)3(μ3-H)­(μ-H)2(μ-CO) (4; Cp* = η5-C5Me5), having a bridging CO ligand was synthesized by the reaction of {Cp*Ru­(μ-H)}3(μ3-O) (3) with methanol. Upon introduction of a CO ligand, the cyclic voltammogram of 4 demonstrated a significant shift of the redox potential in the positive direction in comparison to a pentahydrido complex, {Cp*Ru­(μ-H)}3(μ3-H)2 (1), which adopts the same 44-electron configuration. Owing to its coordinatively unsaturated nature, 4 readily reacted with butadiene, terminal alkynes, and alkenes similarly to the parent pentahydrido complex 1. However, the reactivity was slightly different from that of 1, and the influence of the CO ligand at the triruthenium site was evaluated by the reaction of various unsaturated hydrocarbons. The reaction of 4 with 1,3-dienes yielded a diene adduct, {Cp*Ru­(μ-H)}3(μ-η2:η2-s-cis-H2C═CRCH═CH2)­(CO) (5a, R = H; 5b, R = Me) without elimination of dihydrogen. In the same manner as for 1, 4 reacted with phenylacetylene to yield a μ3-η2:η2(⊥)-alkyne complex, (Cp*Ru)3(μ-H)­{μ3-η2:η2(⊥)-PhCCH}­(μ3-CO) (7a); in contrast, an isomeric μ3-pentenylidene complex, (Cp*Ru)3(μ-H)­{μ3-η2-C═C­(nPr)­H}­(μ-CO) (9b), was obtained by reaction with 1-pentyne. A series of products was obtained by the reaction of 4 with ethylene molecules. A μ3-ethylidyne complex, (Cp*Ru)3(μ-H)2(μ3-CMe)­(μ-CO) (11), was initially formed, accompanied by the formation of ethane at ambient temperature. The treatment of 11 with ethylene resulted in the removal of hydrido ligands, affording a μ3-vinylidene complex, (Cp*Ru)3(μ-H)­(μ3-η2-C═CH2)­(μ-CO) (9a). At higher temperatures, a second ethylene molecule was incorporated in the triruthenium plane and an equilibrated mixture of a μ3-ethylidyne−μ-ethylidyne complex, (Cp*Ru)3(μ-H)­(μ-CMe)­(μ3-CMe)­(μ-CO) (13), and μ3-ethylidyne−μ-vinyl complex, (Cp*Ru)3(μ-H)­(μ3-CMe)­(μ-η2-CH═CH2)­(μ-CO) (12), was obtained. The formation of a μ3-η3-C3 ring on the Ru3 plane was observed upon the thermolysis of the equilibrated mixture at 180 °C, which clearly demonstrates the coupling of the two C2 moieties placed on each face of the triruthenium plane.