新型多相不对称加氢催化剂的设计合成和性能研究

Platinum catalyst modified with cinchonidine (CD) and nickel catalyst modified with tartaric acid (TA) are the promising and well-investigated catalysts for the heterogeneous enantioselective hydrogenation of a- and b-ketoesters. The possible interactions and the resulted coordination species between modifier and metal are unknown exactly and require further attention. The direct investigation of the interaction between the modifier and nickel in the process of heterogeneous enantioselective hydrogenation is not yet possible, any indirect evidence for the adsorption mode and the erosion process is therefore of importance for a better understanding of the reaction. Here we have isolated and well-characterized several new kinds of nickel chiral a-hydroxyl carboxylates cis-[Ni(S-C3H5O3)2(H2O)2], cis-[Ni(S-C4H5O5)2 (H2O)2]·2H2O, cis-[Ni(R,S-C4H5O5)2(H2O)2]·2H2O, [Ni(S-C4H4O5)(H2O)2]n·nH2O, [Ni2(R,R-C4H4O6)2(H2O)4]·3H2O, cis-[Ni2(R,R-C4H4O6)2(H2O)2]n·3nH2O and cis-[Ni2(S,S-C4H4O6)2(H2O)2]n·3nH2O. Of these complexes, the bond distances (?) Ni-Ohydroxyl in S-lactate, S-malate, polymeric S-malate and R,R-tartrate are 2.032(4)、2.077(3) and 2.082(4) ? respectively, and the bond distance of Ni-Ocarboxyl are 2.050(5)、2.009(3)、2.021(4) ? respectively. The chiral ligands of S-lactate and S-malate resulted in the isolation of D-S and L-S isomers, while the racemic malate only resulted in the mixture of D- and L-S isomers. The bond strengths of a-hydroxyl and a-carboxyl groups with nickel are comparable. It is proposed that the a-hydroxyl group in the modifier of asymmetric catalysts may participate in the coordination when considering the adsorption model of tartaric acid on nickel surface. This is different from the Ni/TA adsorption model proposed (Ravel, Nature, 2000).From the conversions between the water soluble malato and tartrate nickel and insoluble polymer, it is considered that the kinetic mononuclear malato nickel and Sachtler binuclear tartrato nickel formed on the nickel surface may be related to the active species in the Ni/TA heterogeneous catalysis, which are formed at low temperature and easily converted into the thermodynamic stable polymeric species. Upon increasing the temperature, the enantioselectivity of the catalysis system decreased as the mononuclear and binuclear active complex are converted into the polymeric species through the further coordination of the carboxyl groups..Moreover, (3R,4S,8S,9R)-cinchonidinium R,R-tratrate, bis(3R,4S,8S,9R)- cinchonidinium R,R-tratrate and 2-phenyl-9-deoxy-10,11-dihydrocinchonidine are synthesized from cinchonidine, which show better enantioselectivity in the hydrogenation of tiglic acid over 5 wt% Pd/Alumina modified with CD derivatives (CD-tart, ee 41%; CD, ee 38%). The structure of bis(3R,4S,8S, 9R)-cinchonidinium R,R-tratrate dihydrate is a hydrate salt of cinchonidine, in which two protonated quinuclidinic nitrogen groups interact with the ionized carboxylate group of the tartrate. The water molecule interacts with the hydroxyl group of the cation and the O atoms of the carboxylate residues to afford a three-dimensional network structure.

设计同时含有金鸡纳碱和酒石酸等手性羟羧酸的季胺盐为手性修饰剂，负载吸附在镍、钯或铂的担载催化剂表面，制备具有双功能的不对称多相氢化催化剂。考察这类催化剂对ａ和Ｂ不饱和羧酸的不对称氢化活性和光学选择性，总结手性配体的电子和立体效应、金属中心的种类和载体的类型与不对称催化反应性能关系的一些规律，为设计手性催化剂提供科学构思。