Preparation Of Chiral Metal Complexes Held In Mesoporous Silica-supported Ionic Liquid Brushes And Their Application For Asymmetric Reactions

Reported in 1895, the Henry reaction and Aza-Henry reaction for the construction of carbon-carbon bond and carbon-nitrogen bond, repectively, in the presence of a base are classic organic reactions for the synthesis of asymmetric compounds. The products are ?-nitro alcohols and ?-amine bifunctional compounds which are important materials in organic synthesis. It is highly desirable to achieve high efficiency and enantiomeric(or diastereomeric) selectivity in the asymmetric Henry and Aza-Henry reactions, and many types of catalysts were developed. Nonetheless, there are shortcomings such as restriction of substrates, harsh reaction conditions, use of expensive catalysts in large amount, and poor reusability of catalysts. These problems limit the application of the catalyst in chiral industry. So far, chiral catalysts used in industrial production is not many. Therefore, it is of significance to develop cheap, efficient and environment-benign catalysts for the asymmetric reactions. 1. Preparation and use of chiral bidentate amine metal complexes held in mesoporous silica-supported ionic liquid for asymmetric Henry reactionA class of chiral bidentate amine metal complexes held in mesoporous silica-supported imidazole ionic liquid brushes were designed and synthesized, and used as catalysts in the Henry reaction. We explored the effects of metal, catalyst preparation method, ligand, reaction temperature and time, and solvent on catalytic performance. The results suggest that the ligand coordinates with the metal and then immobilizes on the surface of mesoporous silica, resulting in the Silica/ILs-Cu L6(5) catalyst. The best yield(96%) and ee(76%) are obtained in ethanol medium at 0? for 48 h. Under the optimizing conditions, different aromatic aldehydes were studied, and better yield and enantioselectivity of aromatic aldehydes are achieved with the substrates that have electron withdrawing groups on the phenyl ring. Finally, we studied catalyst recovery and reusability. It was found that the catalyst can be reused for five times without showing significant loss of catalytic efficiency. 2. Preparation and use of chiral tetradentate ligand metal complexes held in mesoporous silica-supported ionic liquid for asymmetric Henry and Aza-Henry reactionIn the synthesis and use of silica-supported catalysts for asymmetry Henry reaction, we found that the recyclability of catalyst is not satisfactory. We hence explored the use of tetradentate ligands of a different kind that were held in mesoporous silica-supported imidazole ionic liquid brushes, and monitored them in Henry reaction. We studied the influence of metal, ligands, auxiliary ligands and reaction time and temperature on catalytic performance. The results show that the metal complexes of ligand L8 and Cu(OAc)2·H 2O are catalytically active, and medium yield(89%) and ee(52%) are obtained in ethanol medium, at 0? for 48 h in the presence of an equivalent amount of anhydrous toluene.We found that the catalytic effect of tetradentate ligand metal complexes for asymmetric Aza-Henry reaction is excellent, and supported catalysts used for Aza-Henry reactions are rarely reported. We selected the Aza-Henry reaction of N-(4-nitrobenzylidene)-p-toluenesulfonamide and nitromethane as model for further research. The effect of ligand structures, metal salts, reaction temperature and time and other factors on catalytic performance were investigated. The results show that the metal complexes of ligand L3 and Cu(OAc)2·H 2O are catalytically effective, and good yield(86%) and ee(95%) are obtained in ethanol medium at 0? for 48 h. Furthermore, a different approach to immobilize metal complex CuL3 on mesoporous silica-supported ionic liquid was explored. The obtained Silica/ILs-CuL2(?) and Silica/ILs-CuL2(?) catalysts were characterized by BET method. And we compared the two catalysts in terms of performance and examined the effect of reaction medium on the reaction. The results show that the best yield(82%) and ee(96%) are obtained in ethanol medium at 0?. Under the optimizing conditions, different N-Ts-imines were studied, and better yield(85%) and enantioselectivity(97%) of N-(2-nitrobenzylidene)-p-toluenesulfonamide are obtained. Finally, we studied catalyst recovery and reusability. It was found that the catalyst can be reused for four times without showing significant loss of catalytic efficiency.