Asymmetric Syntheses by Use of Intercalation of Multi-nuclear Chiral Metal Complexes into a Clay

本项目的目的是开发一种利用粘土矿物进行不对称合成的新催化体系。我们的方法是合成一种具有光学活性金属配合物的粘土插层化合物。手性金属配合物有望在粘土层内形成手性反应空间。如果金属配合物能够催化某些反应（如氧化、还原、加氢等），则可以高效地实现不对称合成。因此，我们建立了以下涉及粘土的反应体系。两种金属配合物被胶体分散的粘土共吸附；(Fe (terpy)) ^ < 3 + > terpy = 2, 2’,”——terpyridyl)和(Ni(苯酚的)_3)^ < 2 + >(苯酚的= 1,10-phenanthroline)。铁络合物能够氧化有机物质，如抗坏血酸或半胱氨酸，但它没有光学活性。镍配合物没有氧化还原性质，但由于三个菲罗啉配体的螺旋性质，它是手性的。当铁配合物和镍配合物同时存在于粘土表面时，其氧化反应可能是在Ni配合物的手性条件下进行的。这是通过比较D-或l -半胱氨酸在吸收[Fe (terpy)] ^<3+>和DELTA- [Ni (phen) _3] ^<2+>的胶体分散粘土存在下的氧化速率实现的。l -半胱氨酸被氧化的速率高于d -半胱氨酸，在反应中表现出立体选择性。用不同的光谱学方法研究了粘土催化剂的结构：诱导CD、电二色光谱和原子力显微镜观察。

The purpose of the present project is to develop of a new catalytic system for asymmetric syntheses by use of clay minerals. Our approach is to synthesize an intercalation compound of a clay with optically active metal complexes. The chiral metal complexes are expected to form a chiral reaction space within the clay layrs. If the metal complexes are capable to catalyze some reactions (e.g.oxidation, reduction, hydrogenation etc), they will achieve asymmetric syntheses with high efficiency.As a result, we have established the following reaction systems involving a clay. Two kinds of metal complexes were coadsorbed by a colloidally dispersed clay ; [Fe (terpy) ] ^<3+> terpy=2,2', 2''- terpyridyl) and [Ni (phen) _3]^<2+> (phen=1,10-phenanthroline). The Fe complex is capable of oxidizing an organic substance such as ascorbic acid or cystein, but it has no optical activity. The Ni complex has no redox properties but it is chiral due to the helical nature of three phenanthroline ligands. It was expected that the oxidation by the Fe complex proceeded under the chiral circumstances of the Ni complex when these two kinds of complexes were on the same clay surface. This was realized by comparing the oxidation rates of D- or L-cystein in the presence of a colloidally dispersed clay absorbing [Fe (terpy) ] ^<3+> and DELTA- [Ni (phen) _3] ^<2+>. L-Cystein was found to be oxidized at the higher rate than D-cystein, showing the stereoselectivity in the reaction.The structures of the present clay catalysis have been investigated with various spectroscopic methods : the measurements of induced CD,the electric dichroism spectra and the observations with atomic force microscopy.