Development of optically active transition metal complexes with molecular chirality

不对称金属有机配合物通常是由光学活性化合物作为配体来制备的。然而，据报道，也存在一些不含光学活性配体的不对称配合物。这些已知稳定的具有分子手性的配合物是通过外消旋配合物的光学拆分来制备的，并且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'-联-2-萘酚（BINOL）为配体的多功能催化剂，即杂镧系元素催化剂促进不对称硝基醛醇缩合反应，不对称Michael加成反应，亚胺和/或醛的不对称氢膦酰化反应，然而，当这些类型的镧系元素配合物由非手性联苯酚作为配体制备时，由于快速的配体交换，没有观察到不对称诱导。因此，我们进行了开发另一种类型的具有催化剂活性的配合物的研究。经过多次尝试，我们成功地获得了含有铝的不对称配合物，和/或镓的配合物，并开发了不含碱金属的稀土-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反应和烯酮的不对称环氧化反应中均有效.在少量光学活性二胺存在下，用双酚代替BINOL制备了一种具有分子手性的稀土配合物.虽然目前催化剂的催化效率还不理想，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.