Synthesis and structure of enantiomerically pure platinum complexes of phosphino-oxazolines and their use in asymmetric catalysis

Novel organoplatinum complexes of the enantiomerically pure P, N ligand, (4S)-2-(2-(diphenylphosphino)phenyl)-4-isopropyl-1,3-oxazoline, have been synthesized and shown to act as Lewis acids. These complexes consist of the bidentate P, N ligand, an achiral organic ligand, and a solvent ligand that can be readily displaced by organic substrates. The solvent ligand is situated cis to the nitrogen donor and, as such, is in a "chiral pocket" created by the oxazoline ring. The complexes are readily prepared from the well-known, and versatile, precursors (COD)PtR₂ and are obtained as single isomers. Two of the complexes have had their structures elucidated by X-ray crystallography. The cationic complexes were shown to be enantioselective catalysts in the Michael reaction of α-cyano carboxylates with methyl vinyl ketone.