Development of optically active transition metal complexes with molecular chirality

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Asymmetric organometallic complexes are usually prepared from optically active compounds as ligands.However, some asymmetric complexes are reported to be exist without containing optically active ligands.Hitherto known stable these complexes with molecular chirality are prepared by optical resolution of racemic complexes and show no catalyst activity.In this study, we investigated asymmetric catalysts with molecular chirality.So far, we have reported several multifunctional catalysts which contain (R) -or (S) -1,1'-bi-2-naphthol (BINOL) as a ligand.That is, the heterobimetallic lanthanoid catalysts promote asymmetric nitroaldol reactions, asymmetric Michael additions, asymmetric hydrophosphonylation of imines and/or aldehydes, etc.However when these type of lanthanoid complexes were prepared from achiral biphenol as a ligand, no asymmetric induction was observed due to the rapid ligand exchange.therefore we made examination of developing another type of complex with catalyst activity.After a number of attempts, we succeeded in obtaining asymmetric complexes which contain aluminum, and/or gallium by use of BINOL as a ligand.We also developed alkali metal free rare earth-BINOL complexes. These complexes were found to be effective in either asymmetric tandem Michael-aldol reactions, asymmetric ring opening of symmetric epoxides, or asymmetric epoxidation of enones.Preparation of a rare earth complex from biphenol instead of BINOL in the presence of small amount of optically active diamines afforded a new complex with molecular chirality.Although the catalyst efficiency is unsatisfactory at present, we believe this type of complex would open up a new field in asymmetric synthesis.