Mechanistic Study on Asymmetric Oxidations with Metallosalen Complexes as Catalysts and Exploitation of New Metallosalen Complexes

金属salen配合物是不对称氧烯和卡宾转移反应的优良催化剂，但对不对称诱导反应机理的认识还不成熟。虽然salen配体被认为具有平面结构，但手性（salen）钴配合物催化硫醚叶立德反应的立体化学分析表明，salen配体不是平面结构，而是阶梯结构。在手性轴向配体存在下，用非手性（salen）锰配合物作为催化剂实现不对称环氧化反应，有力地支持了配体构象上的这一发现。此外，手性（salen）锰配合物的X-射线衍射分析证明，salen配体采用阶梯构象。在此基础上，我们成功地进行了联烯类化合物的动力学拆分和苄基C-H键的不对称羟基化反应，并利用亚硝基（salen）钌配合物进行了独特的不对称环丙烷化反应。虽然钌络合物是无催化活性的，但光照射使它们具有活性。此外，基于对配合物的X射线分析，预期配合物具有高度柔韧的结构。利用钌配合物的高柔韧性，我们可以通过选择溶剂来控制配体的构象，首次实现了高顺式和对映选择性的环丙烷化反应。

Metallosalen Complexes are excellent catalysts for asymmetric oxene and carbene transfer reactions but our understanding of the mechanism of asymmetric induction is still immature. However, knowledge on the mechanism is indispensable for understanding the stereochemistries of the asymmetric reactions and developing new type of highly efficient asymmetric reactions.Although salen ligand had been recognized to have a planar structure, the analysis of stereochemistry in the ylide formation of sulfide using chiral (salen)cobalt complex suggested that the salen ligand had not a planar but stepped structure. This finding on the ligand-conformation was strongly supported by realizing as asymmetric epoxidation with achiral (salen)manganese complexes as catalysts in the presence of chiral axial ligands. Furthermore, X-ray analysis of chiral (salen)manganese complexes proved that the salen ligands adopt stepped conformation. Basing on these findings, we succeeded in an efficient kinetic resolution of allene compounds and asymmetric hydroxylation of benzylic C-H bonds.In addition to these results, unique asymmetric cyclopropanation was also developed by employing nitroso (salen) ruthenium complexes. Though the ruthenium complexes are catalytically inactive, photo-irradiation makes them active. Furthermore, the complexes are expected to have highly pliable structure basing on the X-ray analysis of the complex. Taking advantage of high pliability of the ruthenium complex, we could controlled the ligand conformation by choosing solvent and achieve for the first time highly cis- and enantio-selective cyclopropanation.