New phosphorus ligands: Development and applications in transition metal catalysis

Transition metal catalyzed reactions are among the most powerful and direct approaches for the synthesis of organic molecules. During the past several decades, phosphorous-containing ligands have been extensively used in transition metal catalyzed C-C and C-H bond forming reactions. Development of new phosphine ligands for palladium catalyzed coupling reactions and rhodium-catalyzed asymmetric hydrogenations are the focus of this dissertation. A variety of triazole-containing monophosphine ligands have been prepared via efficient 1,3-dipolar cycloaddition of readily available azides and acetylenes. Their palladium complexes have been investigated in amination reactions (up to 98% yield) and Suzuki-Miyaura coupling reactions (up to 99% yield) of electronically unactivated aryl chlorides. A CAChe model for one of the Pd-complexes shows that a Pd-arene interaction might be a rationale for its high catalytic reactivity. A new class of C1-symmetric bisphosphine ligands with three hindered quadrant motif has been obtained through facile synthesis from chiral binol derivatives. Their rhodium complexes have exhibited high enantioselectivities (up to 98% ee) in the asymmetric hydrogenation of various unsaturated prochiral olefins, providing an efficient catalytic system for the enantioselective synthesis of chiral amino acids and amines. Utilizing a rhodium complex of an electron-donating bisphosphine ligand (TangPhos), a highly efficient method for the enantioselective synthesis of a new class of N-aryl substituted beta-amino acid derivatives has been developed with high conversions and enantioselectivities (up to 96.3% ee). This methodology exhibited the potential application in the synthesis of several biological active molecules. Chiral C2-symmetric bisphospholane ligand (S,S,S,S-Me-ketalphos) and ( R,S,S,R-Me-ketalphos) were prepared from readily available D-mannitol. Their rhodium complexes were isolated and further investigated as catalysts in the asymmetric hydrogenation of various functionalized olefins such as alpha-dehydroamino acids, enamides and itaconic acid derivatives with high enantioselectivities. An improved synthetic route is reported for the synthesis of a series of phosphine-oxazoline ligands from commercially available phenyl glycinol. The catalytic potential of these P, N ligands has been demonstrated in several highly enantioselective metal catalyzed reactions, including Pd-catalyzed allylic substitution and intermolecular Heck reactions in addition to the previously reported Ir-catalyzed asymmetric hydrogenation of unfunctionalized alkenes and alpha,beta-unsaturated esters.