Experimental Investigations of a Partial Ru-O Bond during the Metal—Ligand Bifunctional Addition in Noyori-Type Enantioselective Ketone Hydrogenation

摘要

The transition state for the metal—ligand bifunctional addition step in Noyori's enantioselective ketone hydrogenation was investigated using intramolecular trapping experiments. The bifunctional addition between the Ru dihydride trans-[Ru((R)-BINAP)(H)_2((R,R)-dpen)] and the hydroxy ketone 4-HOCH_2C_6H_4(CO)CH_3 at —80 °C exclusively formed the corresponding secondary ruthenium alkoxide trans-[Ru((R)-BINAP)(H)(4-HOCH_2C_6-H_4CH(CH_3)O)((R,R)-dpen)]. Combined with the results of control experiments, this observation provides strong evidence for the formation of a partial Ru—O bond in the transition state.