Efficient synthesis of ruthenium(II) eta(5)-dienyl compounds starting fromdi-mu-chlorodichloro-bis[(1-3 eta : 6-8 eta)-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-dimeth yloctadienediyl] diruthenium(IV) in the presence of base reacts with cyclic and acyclic dienes to the corresponding bis(eta (5)-dienyl)ruthenium(II) c ompounds. Crystalline yellow compounds have been isolated in high yields fo r dienyl = cyclopentadienyl, pentamethylpentadienyl, cycloheptadienyl, inde nyl, dimethylpentadienyl, and trimethylpentadienyl. The analogous reaction of cyclohexa-1,3-diene gives the ruthenium(0) compound (eta (6)-benzene)(et a (4)-cyclohexa-1,3-diene)ruthenium. The "open" bis(dienyl)ruthenium comple xes can be converted into half-sandwich complexes through protonation and s ubsequent ligand exchange. These compounds can be used as precursors for ef ficient enantioselective hydrogenation catalysts.