| Ligand supported metal complexes have been extensively employed as highly efficient and selective catalysts for a wide range of useful organic transformations. Use of chiral molecules as ligands can enantioselectively affect these transformations to give optically enriched products, which have become more and more important for human life. Development of efficient phosphorus containing ligands, chiral and non-chiral, for transition metal catalyzed reactions, i.e. hydrogenation and carbon-carbon bond formation, is the focus of this dissertation. A P-chiral trialkyl bisphospholane ligand, DuanPhos, has been prepared in both enantiomeric forms through a concise and potentially practical synthesis. A Rh-complex of this electron-rich P-chiral (third generation) ligand has exhibited very high enantioselectivity (>99% ee) and reactivity (up to 10,000 TON) for the hydrogenation of various functionalized alkenes (five different substrate classes) and unprotected alpha-and beta-amino ketones, providing an efficient catalytic system for the enantioselective preparation of various synthetically useful compounds. A new class of conformationally rigid phosphino-oxazoline ligands was synthesized from inexpensive phenyl glycinol via a novel ortho-substitution of phenyl glycinol as the key step. The catalytic potential of these P, N ligands has been demonstrated in various highly enantioselective reactions, including the Ir-catalyzed hydrogenation of unfunctionalized alkenes and alpha, beta-unsaturated esters, Pd-catalyzed allylic substitution and intermolecular Heck reactions. An air-stable ferrocene-based poly-substituted bisphospholane has been developed as efficient ligand for Rh-catalyzed asymmetric hydrogenation of alpha-dehydroamino acid derivatives and itaconic acid derivatives. The significantly higher ee's observed with this ligand than those with its disubstituted bisphospholane analogue indicate the importance of steric bulk and conformational rigidity of the phospholane ring for enantioselectivity. Several DIOP derivatives have been synthesized and applied as effective ligands for the asymmetric hydrogenation of a series of electron-rich enamides with high ee's. The differences in the enantioselectivities with ligands bearing a cyclic or acyclic backbone indicate that the conformational analysis of ligand backbone can be an effective principle for ligand design. A set of non-chiral triazole-based monophophines, ClickPhos, has been prepared via an efficient 1,3-dipolar cycloaddition of readily available phenylazide and phenylacetylene. These ligands have been investigated in the Pd-catalyzed Suzuki-Miyaura coupling of electronically unactivated aryl chlorides. Besides the steric bulk and electron-richness, the potentially hemilabile feature of these ligands could account for their high catalytic performance in crossing coupling reactions. |
