Development of optically active transition metal complexes with molecular chirality

不对称有机金属配合物通常由光学活性化合物作为配体制备。然而，也有一些不对称配合物不含光学活性配体。这些具有分子手性的稳定配合物是通过光学拆分外消旋配合物制备的，不具有催化活性。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。也就是说，杂双金属镧系催化剂促进了不对称硝基醛反应、不对称Michael加成反应、亚胺和/或醛的不对称氢膦化反应等。然而，当以非手性双酚为配体制备这些类型的镧系配合物时，由于配体交换迅速，没有观察到不对称诱导。因此，我们对开发另一种具有催化剂活性的配合物进行了研究。经过多次尝试，我们成功地用BINOL作为配体获得了含铝和/或镓的不对称配合物。我们还开发了不含碱金属的稀土-双酚配合物。这些配合物在不对称串联Michael-aldol反应、对称环氧化合物的不对称开环或烯酮的不对称环氧化反应中都有效。在少量光学活性二胺的存在下，用双酚代替双酚制备稀土配合物，得到了具有分子手性的新配合物。虽然目前催化剂的效率还不能令人满意，但我们相信这种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.