Acid–Base Cooperative Catalysis for Organic Reactions by Designed Solid Surfaces with Organofunctional Groups

This chapter deals with acid–base bifunctional heterogeneous catalyst surfaces with organofunctional groups. One of the most important issues for bifunctional heterogeneous catalysis is the coexistence of incompatible catalytic species, such as acid and base, nearby on a same solid particle surface. In nucleophilic reactions, acid–base bifunctional catalysts enable the activation of both nucleophilic and electrophilic substrates to enhance their reactions. Generally, there are two types of catalytic nucleophilic addition reactions: the first one is activation of the nucleophile precursors by basic catalysts to abstract their acidic parts, such as α-hydrogen atoms, and the other is the lowering of lowest unoccupiedmolecular orbital (LUMO) levels of electrophiles by interactionwith Brønsted or Lewis acidic catalysts. From this fact, an ideal pathway for the nucleophilic reaction is dual activation of both electrophiles andnucleophiles by acidic and basic functions of catalysts, respectively (Scheme 1.1) [1]. Strongly acidic and basic species in a solution reactor induces neutralization immediately, thus affording inactive salts. However, immobilization of both the acidic and basic species on solid surfaces can avoid mutual neutralization. Some catalytic reaction systems containing both acidic and basic solid catalysts as separate catalyst particles have been reported for one-pot reaction sequences [2]. In these reaction systems, the acid and base sites are immobilized on different catalyst particles. Therefore, it is difficult to accelerate a single reaction step by cooperative activation of two substrates by both acid and base sites. Immobilization of acidic and basic species nearby on a same solid surface can create a bifunctional catalytic surface possessing acid and base species that are able to participate in a single reaction step, resulting in significant acceleration of the catalytic reaction. Several reviews have been published on such heterogeneous acid–base catalysts having organic functional groups [3]. These heterogeneous acid–base bifunctional catalysts can be categorized into the following two types: (i) catalysts possessing both immobilized acidic and basic organic groups on their surfaces and (ii) catalysts possessing immobilized basic organic groups and acid sites derived from their support surfaces. In this chapter, these two types of