Development of optically active transition metal complexes with molecular chirality

不对称有机金属配合物通常是以光学活性化合物为配体合成的。然而，有报道称存在一些不含光学活性配体的不对称有机金属配合物。迄今已知的稳定的具有分子手性的配合物是通过外消旋化合物的光学拆分而合成的，没有显示出催化活性。在本研究中，我们研究了具有分子手性的不对称催化剂。到目前为止，我们已经报道了几种以(R)-或(S)-1，1‘-双-2-萘酚(BINOL)为配体的多功能催化剂。这类催化剂促进了不对称的硝醛反应、不对称的Michael加成、不对称的亚胺和/或醛的不对称膦酰化反应、不对称的加成反应、不对称的亚胺和/或醛的不对称膦酰化反应然而，当以非手性联苯酚为配体制备这类稀土配合物时，由于配体的快速交换，没有观察到不对称诱导，因此我们进行了开发另一类具有催化活性的配合物的研究，经过多次尝试，我们成功地以BINOL为配体合成了含铝和/或镓的不对称配合物，并制备了无碱金属的稀土-BINOL配合物。这些配合物在不对称串联Michael-Aldol反应、对称环氧化物的不对称开环和烯酮的不对称环氧化反应中都表现出较好的催化活性。在含有少量光学活性二胺的情况下，以联苯酚代替联苯二酚合成稀土配合物，得到了具有分子手性的稀土配合物。虽然目前催化效率不高，但我们相信这类配合物将为不对称合成开辟一个新的领域。

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.