Photochemistry and photocatalytic activity of H₄Ru₄(CO)₁₂ and H₂Ru₄(CO)₁₃ for isomerization and hydrogenation of alkenes

The tetranuclear complex H₄Ru₄(CO)₁₂ undergoes dissociative loss of CO upon near-uv, 355 nm, irradiation to give substitution products H₄Ru₄(CO)₁₁L (L = P(OMe)₃, PPh₃) in the presence of L with a quantum yield of ∼5 X 10^-3. In the presence of an olefin H₂Ru₄(CO)₁₃ is the principal Ru containing photoproduct and stoichiometric reduction of the olefin is observed, e.g. cyclopentene gives cyclopentane. Presumably the intermediate H₄Ru₄(CO)₁₁ (olefin) gives alkane and the unsaturated H₂Ru₄(CO)₁₁ that rapidly reacts with CO to form H₄Ru₄(CO)₁₃. The H₂Ru₄(CO)₁₃ reacts slowly with H₂ to give H₄Ru₄(CO)₁₂ at 25 °C. Irradiation of H₂Ru₄(CO)₁₃ in the presence of an olefin such as 1-pentene accelerates the catalyzed isomerization and effects stoichiometric reduction of the olefin, e.g. n-pentane forms from 1-pentene at 25 °C under irradiation whereas no reduction occurs thermally at 25 °C.