Isomerisation of pentenes with H₄Ru₄(CO)₁₂

Catalytic isomerisation of 1-pentene to 2-cis and 2-trans-pentene with H₄Ru₄(CO)₁₂ in toluene at 70.4 °C is described. Carbon monoxide, hydrogen, weak acids and polar substances, such as ethyl acetate, decrease the isomerisation rate. Reactions of H₄Ru₄(CO)₁₂ with trans-C₂H₂D₂ and [1,2-D₂] 1-pentene and of D₄Ru₄(CO)₁₂ with 1-pentene suggest the operation of a metal-hydride addition-elimination mechanism involving σ-alkyl intermediates. The active species is supposed to be mainly originated by loss of CO to give H₄Ru₄(CO)₁₁. Catalytic hydrogenation of the pentene isomers occurs at the approaching of the equilibrium and is largerly enhanced by addition of hydrogen to the reaction system.