NEW PHOSPHORUS LIGANDS: DEVELOPMENT AND APPLICATIONS IN TRANSITION METAL CATALYSIS
Open Access
- Author:
- Dai, Qian
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 06, 2007
- Committee Members:
- Xumu Zhang, Committee Chair/Co-Chair
Steven M Weinreb, Committee Member
Blake R Peterson, Committee Member
Qing Wang, Committee Member - Keywords:
- asymmetric hydrogenation
rhodium
amination
suzuki coupling
palladium
chiral
phosphine - Abstract:
- 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 ƒÒƒ{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 ƒÑ-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 ƒÑ,ƒÒ-unsaturated esters.