Recently, organocatalysts, such as amino acids, phosphoric acids, amines, and imidazolidium salts, have been received much attentions for selective organic synthesis [1]. Utilization of organic compounds for design of tremendous catalysts has an inherent advantage due to their easily tunable structures. No use of expensive and hazardous metals is another advantage in practical chemical processes from economical and environmental viewpoints. In addition, the optimization of conformation and electronic states around active centers can be efficiently achieved by organic functional groups [2]. Several single site catalysts with organofunctional groups have been demonstrated to enhance catalytic activity and selectivity [2].
Immobilization of catalytically active species on inorganic solid materials enables not only generation of recyclable catalysts but also higher catalytic activities compared with their homogeneous precursors and analogues owing to unique environments of the surfaces [3]. Creation of new geometries/arrangements by surfaces, increasing stability of active structures by site isolation at surfaces, bifunctionality with surface chemical functions, modification of electronic states by surfaces, and enhancement of substrate density around active sites may be reasons for the increase in catalytic performances.
From these backgrounds, our simple but efficient strategy for novel catalyst design is to immobilize organofunctional groups on inorganic oxide surfaces to develop heterogeneous organicinorganic hybrid materials. In this paper, we review our previous reports and also present new data on organofunctionalized heterogeneous catalysts, (i) silica-alumina-supported organic amines (SA-NR 2 ) [4] and (ii) organofunctionalized SiO 2 -supported chiral Cu-bis(oxazoline) (BOX) complexes [5], for various carboncarbon bond-forming reactions, including cyano-ethoxycarbonylation, Michael reaction, nitro-aldol reaction, and asymmetric Diels-Alder reaction. Interestingly, performances of these catalysts were significantly higher than those of homogeneous precursors and counterparts.
Multifunctional catalytic materials play a pivotal role for highly efficient organic synthesis. Especially, much attention has been paid for double catalytic activation of electrophiles and nucleophiles by