Its Catalytic Asymmetric Mesoporous Core-shell Type Metal Catalyst Preparation

The development of silica-supported mesoporous heterogeneous catalysts forasymmetric catalysis has attracted a great deal of interests due to their relativelylarge surface area and pore volume, and tunable pore dimension and well-definedpore arrangement. These salient features are not only beneficial to control thedispersibility of active species but also to adjust the chiral microenvironment ofactive centers, showing potential superiority in stereocontrol performance.Core-shell structured mesoporous silica spheres (CSSMSS) as a type of novelsilica-based meterials show potential advantage in asymmetric catalysis, in which thecore of silica spheres is convenient to assemble various chiral functionalities whilethe shell of silica spheres is beneficial to prevent the leaching of chiralorganometallics, showing a potential superiority in recyclability of heterogeneouscatalyst.In this paper, the functionlized Core-shell structured mesoporous silica spheresand Yolk-Shell mesoporous silica spheres catalysts has been made. Then, we used itin the the asymmetric transfer hydrogenation of aromatic ketones to explore theircatalytic activities.(1) We used the hexadecyl trimethyl ammonium chloride (CTAC) as the templateto prepared the core-shell structured mesoporous silica spheres with Cp*RhTsDPENfunctionality in the internal core of silica spheres, abbreviated asCp*RhTsDPEN-CSSMSS (4), through the co-condensation way. And then, we usedsame method to prepared Cp*IrTsDPEN-CSSMSS (5) and Cp*RhTsDACH-CSSMSS (6).We also used this way to make a core-shell structured organic-inorganic mesoporoussilica catalyst with Cp*RhTsDPEN functionality in the internal core of silica spheres,abbreviated as Cp*RhTsDACH-PMO (7). After that, we used these four catalysts in thethe asymmetric transfer hydrogenation of aromatic ketones to explore theircatalyistic activities. The results showed high catalytic activities and outstandingenantioselectivity. Moreover, the catalysts can be recycled by centrifugation and be reused by12times without the loss of catalytic activities and enantioselectivity.(2) We firstly used the hexadecyl trimethyl ammonium bromide (CTAB) as thetemplate to prepare the core-shell structured mesoporous silica spheres with(1S,2S)-(+)-N-p-Tosyl-1,2-diphenylethylenediamine and PS100-b-PAA16as theinternal spheres under the way of co-condenstaion. Then, we added the TEOS to getthe core. After eliminating the hexadecyl trimethyl ammonium bromide andPS100-b-PAA16, we got the Yolk-Shell mesoporous silica spheres. After that, weadded some [HMB*RuCl2]2to get the catalyst HMB*RuTsDPEN-yolk-shellNPs (8).Afterwards, we used the catalyst in the the asymmetric transfer hydrogenation ofaromatic ketones to explore their catalyistic activities. The results showed highcatalytic activities and outstanding enantioselectivity. Moreover, the catalysts can bereused by12times without the loss of catalytic activities and enantioselectivity.