二氧化硅微球负载钌催化剂的制备及其在苯乙酮不对称氢转移反应中的应用

Preparation of mesoporous silica microsphere supported ruthenium catalysts for asymmetric transfer hydrogenation of acetophenone

采用一步原位聚合诱导沉淀法制得了形貌多样、结构复杂的二氧化硅介孔微球,将其与Noyori配体Ru Cl(p-cymene)[(R,R)-Ts-DPEN]络合制得负载型钌催化剂并应用于苯乙酮不对称氢转移反应。利用场发射扫描电镜和氮气等温吸脱附手段证明了二氧化硅微球和负载型钌催化剂的微球型介孔结构,结合透射电镜表明了钌元素均匀分布在二氧化硅微球上;通过红外光谱显示该催化剂与反应底物之间存在氢键作用;在此基础上考察了载体孔结构,反应条件等因素对催化性能的影响。研究结果表明,钌配体负载到具有小孔径、高比表面积的二氧化硅微球上有利于苯乙酮的不对称氢转移反应,由此引出介孔氧化硅微球的孔道限域效应对不对称催化反应的活性和光学选择性存在明显的促进作用。在40℃、0.2 ml苯乙酮的条件下反应16 h,负载型钌催化剂用于苯乙酮不对称转移加氢反应其转化率和对映选择性最高可分别达到64.1%和93.4%。

Supported ruthenium catalyst, complexes of Ts DPEN supported with mesoporous silica microspheres of various morphologies and structures, which were synthesized by a simple one-step in situ polymerizationinduced precipitation procedure, were prepared for the asymmetric transfer hydrogenation of acetophenone. The mesoporous structure of silica microspheres were observed by the nitrogen adsorption/desorption isotherms and field emission scanning electron microscopy（FESEM）, ruthenium complex well distributed on silica microspheres by transmission electrum microscopy（TEM）, and the existence of hydrogen bonds between catalyst and regents by infrared spectrometry（IR）. Effect of support structure and reaction conditions such as reaction temperature and time, and reactant concentration on catalytic performances for the asymmetric transfer hydrogenation of acetophenone were investigated. It showed that the interaction between ruthenium complexes with supports of small pore size and high specific surface area promoted the asymmetric transfer hydrogenation and channel stereo-confinement of mesoporous silica microspheres, resulting in significant enhancement of the activity and optical selectivity of the reaction. Under the optimum of 40℃, 16 h and 0.2 ml acetophenone of reaction conditions, the catalyst achieved its highest 64.1% and 93.4% of acetophenone conversion and enantio selectivity of R-α-phenethyl alcohol for asymmetric transfer hydrogenation of acetophenone, respectively.