Efficient synthesis of ruthenium(II) η5-dienyl compounds starting from di-μ-chlorodichloro-bis[(1-3η:6-8η)-2,7-dimethyloctadienediyl]diruthenium(IV).: Versatile precursors for enantioselective hydrogenation catalysts

The dimeric complex di-mu -chlorodichloro-bis[(1-3 eta :6-8 eta)-2,7-dimethyloctadienediyl] diruthenium(IV) in the presence of base reacts with cyclic and acyclic dienes to the corresponding bis(eta (5)-dienyl)ruthenium(II) compounds. Crystalline yellow compounds have been isolated in high yields for dienyl = cyclopentadienyl, pentamethylpentadienyl, cycloheptadienyl, indenyl, dimethylpentadienyl, and trimethylpentadienyl. The analogous reaction of cyclohexa-1,3-diene gives the ruthenium(0) compound (eta (6)-benzene)(eta (4)-cyclohexa-1,3-diene)ruthenium. The "open" bis(dienyl)ruthenium complexes can be converted into half-sandwich complexes through protonation and subsequent ligand exchange. These compounds can be used as precursors for efficient enantioselective hydrogenation catalysts.