Chapter 3 - Enantioselective Hydrogenations

Abstract

Enantioselective catalytic surfaces can be synthesized by three basic ways—attach a catalyst to, or embed a catalyst in, a chiral matrix, create a chiral arrangement of active sites on a catalytic surface, and adsorb or attach chiral molecules onto a catalytic surface. An excellent enantioselective heterogeneous metal catalyst should be one in which the active metal sites are set in a chiral arrangement fulfilling the Ogston principles. Three factors seem to be important for enantioselectivity to occur on surfaces—the steric factor, the polar factor, and the mobility factor. Each of these factors affects the chiral environment in ways that determine its magnitude and stability. The steric factor results from physical interactions between atoms. From this factor comes the basic chirality. For the cases of solid metal catalysts, chirality may come from the support, the arrangement of active sites on the metal surface, or from an adsorbed or attached chiral entity. The polar factors address how the modifier interacts with the prochiral substrate, and the mobility factor acknowledges the fact that organic molecules seem to move about on surfaces.