Asymmetric Synthesis of New Diphosphines and Pyridylphosphines via a Kinetic Resolution Process Promoted and Controlled by a Chiral Palladacycle

A chiral palladacycle has been used successfully to promote the asymmetric hydrophosphination reactions between the racemic secondary phosphine ethylphenylphosphine and (E)/(Z)-diphenyl-1-propenylphosphine or 2-vinylpyridine in high regio- and stereoselectivities under mild conditions. Hydrophosphination of (E)-diphenyl-1-propenylphosphine with ethylphenylphosphine gave the asymmetric diphosphine chelate containing one stereogenic phosphorus donor with the R absolute configuration and one neighboring chiral S-carbon center as the major product in 60% yield. Using the same chiral metal template, the corresponding hydrophosphination reaction with (Z)-diphenyl-1-propenylphosphine gave the diastereomeric diphosphine in 40% yield with a chiral R-carbon center, but the controlled formation of the R-phosphorus configuration was not affected by the different stereochemistry in the carbon chain. A pair of separable diastereomeric palladium templates containing the naphthylamine auxiliary and the enantiomeric forms of (Rp/Sp)-[1-ethylphenylphosphino-2-(2-pyridine)]ethane were also generated in the ratio 1.5:1 via hydrophosphination of 2-vinylpyridine with ethylphenylphosphine. The optically pure diphosphine ligands and P, N ligands could be stereospecifically liberated from the template complexes. The coordination chemistry and the absolute stereochemistry of the template complexes and dichloro complexes were determined by X-ray crystallography.