New approaches to and mechanistic studies of homogeneous asymmetric catalysis

Although much is known about the activity and selectivity of chiral homogeneous catalysts, the optimal catalyst system and reaction conditions for a given substrate must still be empirically determined. Rational design of chiral catalysts remains a formidable task. The research described in this thesis has been directed towards gaining a more complete understanding of how selectivity is induced during catalytic reactions.; Direct investigation of catalytic systems can be difficult because the species which control reaction selectivity are often unstable. This thesis describes an attempt to model the turnover limiting and enantiodetermining step in the catalytic asymmetric hydrogenation of prochiral enamides by studying the oxidative addition of dihydrogen to a series of iridium bisolefin complexes. While the selectivities of the oxidative addition reactions do not directly correlate to those observed for the rhodium catalyzed asymmetric hydrogenation of prochiral enamides, these studies offer insight into the nature of H{dollar}sb2{dollar} activation and diastereomer exchange. A detailed study of one of the oxidative addition reactions is presented. The complex and somewhat surprising chemical behavior of the iridium dihydrides is discussed and a mechanism for diastereomer exchange is proposed.; This thesis also reports on the ongoing efforts towards rational catalyst design. The design, synthesis, and characterization of a class of novel boron-containing ferrocenyl ligands is described. These ligands are designed to induce selectivity in catalytic reactions via covalent or Lewis acid-base "secondary interactions," which occur outside the primary coordination sphere of the metal. A variety of ligand architectures have been prepared, and their structural characteristics are discussed in some detail. The crystal structures of metal complexes of these ligands are presented. The chemical reactivity of the ferrocene complexes is analyzed. Preliminary catalytic studies for one of the ligands yields promising selectivity for the rhodium catalyzed hydrogenation of a tris(allyl)borate (approx. 78% ee).