Ordered Mesoporous Silica as Supports in the Heterogeneous Asymmetric Catalysis

Abstract

Enantioselective synthesis of organic compounds has been studied by homogeneous catalysts for several years. However, these catalysts have yet to make a significant impact on industrial scales for fine chemical synthesis. A primary reason is the designing of a homogeneous asymmetric catalyst, which requires relatively bulky ligands and catalyst recovery and recycling often causes problems. One of the convincing ways to overcome this problem is to immobilise the asymmetric catalyst onto a solid support and the resulting heterogeneous asymmetric catalyst system can, in principle, be readily re-used. A large number of supports such as inorganic oxides including zeolites, alumina, zirconia, silica and organic polymers have been employed as supports in heterogeneous asymmetric catalysis. Therefore, in this review article we have summarized the work done by us in our laboratory on the immobilization of chiral transition metal complexes such as Ru, Ir, Mn and Ti onto ordered mesoporous silica and its asymmetric catalysis. All these immobilized catalysts were well characterized by different physicochemical techniques to confirm the structural retention of the support as well as the active metal complex after immobilization. This report includes our asymmetric catalytic investigations in enantioselective reactions such as hydrogenation of ketones, olefins, oxidation of sulfides and oxidative kinetic resolution of alcohols and sulfoxides through immobilized heterogeneous catalyst systems.

Synthesis of new zirconium complex supported on MCM‐41 and its application as an efficient catalyst for synthesis of sulfides and the oxidation of sulfur containing compounds

“…Various approaches have been suggested for the immobilization of homogeneous transition metal complexes on silica, zeolites, alumina and other metal oxides. Despite their easy synthesis, anchoring of homogeneous transition metal catalysts on solid supports often decreases the catalytic activity or efficiency . Therefore in the last few years, nano‐catalysts have been used as ideal heterogeneous supports because they can act as efficient bridge between homogeneous and heterogeneous catalysts .…”

An Overview of One-Dimensional Metal Nanostructures for Electrocatalysis

“…Mesoporous silica is characterized by interconnected porous framework, which has unique chemical and physical properties such as high specific surface area, uniform pore diameters, and ordered channel structures [14,74]. The conventional impregnation method, which includes an impregnation step followed by a reduction step, has been typically used to synthesize 1D metal nanostructures over the mesoporous silica templates, as listed in Table 3.…”

Insightful understanding of the correlations of the microstructure and catalytic performances of Pd@chitosan membrane catalysts studied by positron annihilation spectroscopy

“…Therefore, the preparation of transition metal heterogeneous catalysts by immobilization of transition metal on inert materials or functional solid materials with high activity, good selectivity, and excellent stability/ recyclability, has been one of the hotspots in green and sustainable chemistry. 6 Inorganic materials, like zeolites, [7][8][9][10][11] alumina, [12][13][14][15] silica, [16][17][18] and clay, [19][20][21] are commonly used supports for the preparation of supported transition metal catalysts. However, the inorganic carries oen need modication to further improve their chelating ability with transition metal catalysts.…”