Asymmetric hydrophosphination of cyano-functionalised 1, 3-diphenylphosphine and catalytic asymmetric hydrophosphination of enones with diphenylphosphines

• Main Author: Lee, Zhi Yi
• Other Authors: Leung Pak Hing
• Format: Theses and Dissertations
• Language: English
• Published: 2012
• Subjects: DRNTU::Science
• Online Access: http://hdl.handle.net/10356/48904
• Institution: Nanyang Technological University

Over the past decades, the design, synthesis of chiral diphosphines in the field of asymmetric catalysis has grown tremendously due to its widespread applications[1, 2]. The optical pure diphosphines containing the 1,3-bis(diphenylphosphino)propane backbone have widespread applications as bidentate ligands in transition metal catalyzed asymmetric reactions[3-15]. Hence, the development of new methods or strategies for the synthesis of enantiomerically pure diphosphines ligand continues to be an important topic in chemical research. On the other hand, organometallic complexes can act as efficient reaction promoters, by means of coordination; they could protect the phosphine substrate from oxidation during addition reaction. When the chiral auxiliaries were incorporated with these organometallic reagent, they also provide the protocol to synthesize chiral version of the bidentate diphosphine ligand.[16-19] Using these concepts, a strategy is reported herein to synthesize a monophosphine palladium complexes with cyano-functionality from 3-chloro-1,1-diethoxypropane, and also its subsequent hydrophosphination reaction and functional group transformation reaction under mild conditions that generate the corresponding novel chiral 1,3-diphosphine products. Additionally, we have synthesized a novel chiral, C-stereogenic cyclopalladated complex derived from phosphine ligand and aromatic enone in a one pot catalytic reaction in optically active, high stereoselectively and relatively high yield after purification. This five mem1bered ortho-palladated complexes was derived from E-3-(1-Naphthyl)-1-phenyl-2-propen-1-one with diphenylphosphine with the presence of triethylamine as base in dichloromethane at -80 oC. The resulting diastereomers formed were separated by fractional crystallization. The obtained optically pure complexes were then subjected to chemoselective removal of the (R)-N, N-dimethylamino-1-(1-naphthyl)ethylaminate auxiliary by treatment with concentrated hydrochloric acid in acetone. This process generated the binuclear dimer complexes containing the resolved phosphorus ligand. Ortho-palladation of these coordinated ligands was achieved by heating the binuclear dimer complexes with sodium acetate in ethanol. The ortho-palladated complex was further treated with Silver (I) perchlorate to produce the optically active diperchlorato-bridged dimeric complex. The phosphapalladacycles were shown to exist in solution as a mixture of cis and trans geometric isomers and the VT 31P NMR spectroscopy studies further verified the equilibrium situation of these two isomers. The five membered palladacycle structure of these five ligands was confirmed by NMR spectroscopic studies and X-ray crystallography. The absolute stereochemistry of the palladacycle complex in solid state was established by the X-ray diffraction studies. In this thesis, the efficient strategies of both stoichiometric and catalytic method of synthesizing useful phosphine ligands using (R, R)- di-μ-chlorobis{1-[1-(N, N-dimethylamino)ethyl]naphthyl – C2, N}dipalladium(II) as the catalyst with high selectivity and yield will be presented.