The Study Of Ethyl Bridged Silicon-based Catalysts In A One-pot Series Reaction

Multiple-step organic transformations in one-pot catalytic process,as an important aspect of green chemistry,have attracted a great deal of interest due to atomic economy and minimum workup.However,intrinsic disadvantages,such as reuse of expensive organometallic complexes and product contamination from leaching,do still hinder practical applications in industrial process.Thus,it is very necessary to develop an immobilized strategy to overcome these shortcomings.Organosilica-based mesoporous materials as supports to immobilize organometallic complexes have exhibited some attracting features in catalysis.Furthermore,an important challenge in asymmetric cascade reactions is solving the intrinsic incompatibility of the two distinct types of organometallic complexes that participate in a one-pot catalytic processs.How to adjust the extrinsic conflict imposed on the reaction conditions is another synthetic problem.Although a catalytic cascade reaction should theoretically display a higher efficiency than the corresponding two single-step reaction because it involves several transformations in situ,most cascade reactions are still based on the compatible pairs of organometallic complexes.Therefore,investigations to overcome the incompatible nature of distinct organometallic complexes is warranted towards the development of a general and practical,one-pot enantio-relay catalytic process.(1)Construction of multifunctional heterogeneous catalysts and exploration their applications in multi–step sequential organic transformation are a significant challenge in heterogeneous asymmetric catalysis.In this work,by taking advantage of the combined covalent bonding and hydrogen bonding methods,we anchor palladium/carbene and chiral ruthenium/diamine dual active centers within a hollow–shell–mesostructured organosilica,fabricating a bifunctional heterogeneous catalyst.As presented in this study,the designed catalyst performs more challenging Suzuki coupling–asymmetric transfer hydro genation enantioselecitve tandem reactions of low active chloroacetophenones and arylboronic acids,where Pd–catalyzed Suzuki cross–coupling reaction and Ru–catalyzed asymmetric transfer hydrogenation proceed simultaneously to afford various chiral biaryl alcohols with up to 99% enantioselectivity.Highly catalytic performances are attributed to the cooperative contributions of multifunctionalities,including hydrophobic hollow–shell nanosphere,well–defined single–site dual catalytic species and highly dispersed active centers.Furthermore,the heterogeneous catalyst is recovered easily and reused repeatedly for six times without obvious loss of enantioselectivity,showing an atracting feature in a practical of sequential organic transformation.(2)Assembly of multiple catalytically functionalities within a hollow dendritic mesoporous organosilica nanoparticles as a catalyst for multi-step enantioselective organic transformation in an environmentally friendly medium is a significant challenge in heterogeneo us asymmetric catalysis.Herein,we anchor conviently a chiral rhodium/diamine complex within base–functionalized mesostructured organosilica nanoparticles,constructing a bifunctional heterogeneous catalyst.Solid-state carbon spectrum discloses its well-defined chiral rhodium/diamine active species,and its X-ray diffraction,nitrogen adsorption–desorption measurement and electron microscopy reveal its ordered mesostructure.As presented in this study,the combination of bifunctionality in organosilica nanoparticles enables efficiently enantioselective organinc transformations with high yields and enantioselectivities,where asymmetric transfer hydrogenation of ?–haloketones followed by an amination process provides various chiral ?-amino alcohols.Furthermore,catalyst can be recovered and recycled for seven times without loss of its catalytic activity,showing an attracting feature for multi-step organic transformations in a sustainable benign process.