Synthesis And Catalytic Study Of New Type Chiral(Salen)Mn(Ⅲ) Complex

Chiral epoxides are versatile intermediates that can be readily converted into a wide variety of enantiomerically pure compounds by means of regio- and stereo-selective ring opening reactions. In the last two decades, various methods have been developed for the preparation of chiral epoxides.Until now, Mn(III)-salen complexes [salen=(bis(salicylidene) ethylene diaminato] have emerged as efficient and practical catalysts for the asymmetric epoxidation of various unfunctionalized cis-disubstituted, tri- and tetra-substituted alkenes. The literatures review from this thesis outlines the development of Mn-salen-based asymmetric epoxidation methodology. The essentials of Mn(III)-salen catalysis, such as design of catalyst, the steric and electronic effects of catalyst structure on stereoselectivity, and the effects of additives (axial ligand) and in-built quaternary ammonium on the catalytic activity, the recycle of the catalyst and the mechanism of asymmetric epoxidation are surveyed.The present studies paid attention on the modification of the salen ligand to design new chiral (salen)Mn(III) catalyst with high activity and stereoselectivity. Six new Mn-salen or Mn-salalen type catalysts were synthesized and characterized. All these complexes available were effectively used in the asymmetric epoxidation of substituted chromenes and trans-alkenes with NaClO/PPNO (4-phenylpyridine N-oxide) as oxidant system. One of them can efficient catalysed the alkene in the absence of dear additives by introducing an imidazole in the salen ligand. Complexes with in-built phase transfer ability displayed significantly higher activity than analogous complexes featuring amide unit(s) with comparable yields and ee values.Also attention was paid on the synthesis of (salalen)Mn(III) and dimeric (salalen) Mn(III) complex according to the recent report concerning the (salalen)Ti complex or (salan) Ti.complex. Improved enantioselectivity was attained in epoxidation of unfunctionalized alkenes The role of intra hydrogen bonding was explored and possible reasons for the change of catalytic and stereoslectivity was briefly discussed.