Design And Asymmetric Catalytic Properties Of Built-in Phase Transfer Chiral Salen Complexes In Aqueous-organic Biphase System

Chiral epoxides and cyanohydrins are very important and useful synthetic intermediates. In recent years, scientists have developed many ways to prepare chiral epoxides and cyanohydrins, which the asymmetric reactions catalyzed by chiral salen metal complex are considered to be one of the most efficient strategies found to date.The asymmetric epoxidation of non-functionalized olfins catalyzed by chiral salen MnIII complex usually utilizes the m-CPBA, PhIO, NaIO4, H2O2, O2or air as an oxidant. Sodium hypochlorite (NaOCl) used as an oxygen source has been drawn much attention due that it is reasonably stable, readily available, environment friendly, and inexpensive. However, the epoxidation reactions with the neat chiral salen MnIII complex generally requires a long reaction time. One of the main objectives in this paper is to design and sythesize the chiral salen MnIII complexes with built-in phase transfer capability in the NaOCl aqueous/organic biphasic system.First, a series of novel chiral salen MnIII complexes with inherent phase-transfer capability were prepared by covalent linkage of the limidazolium IL moieties containing various PEG chains with chiral salen ligand at two sides of5,5’-position. Technologies of characterization well suggested the presence of polyether chain, the IL linker, and the intact active sites in the complexes. Compared with the neat complex and simple ionic-liquid functionalized chiral salen MnⅢ complex, the amphipathic nature of the PEG chain allowed the PEG-based catalysts to undergo built-in phase transfer, which in turn increased the reaction rates in water/organic biphasic systems. Especially,>99%of conversions with93%of enantioselectivity were obtained for the epoxidation of nitro-chromene and cyano-chromene within60min.Furthermore, a novel polymeric PEG400-based salen MnⅢ complex was successfully synthesized by covalently-polymerization. Similarly, it also acts as the phase transfer catalyst in the above-mentioned biphase system and could be separated from the reaction mixture by control of the solvent. The integration of reaction and separation made the catalysts perform as "one-phase catalysis and two-phase separation" and it can be reused more than six times.Finally, a novel chiral bifunctional salen Vv complex was firstly synthesized by covalent linkage of ionic liquids containing the urea moieties. Then the effects of the catalyst in the asymmetric trimethylsilylcyanation of benzaldehyde was investigated and further studies are in progress.