Palladium-catalyzed asymmetric phosphination: enantioselective synthesis of a p-chirogenic phosphine

The racemic secondary phosphine PH(Me)(Is) (1, Is = 2,4,6-(i-Pr)3C6H2) was coupled with PhI in the presence of NaOSiMe3 and the catalyst Pd((R,R)-Me-Duphos)(Ph)(I) (3) to give P(Ph)(Me)(Is) (2) in up to 78% ee. The intermediate phosphido complex Pd((R,R)-Me-Duphos)(Ph)(P(Me)(Is)) (5a,b) was observed as a mixture of diastereomers by low-temperature 31P NMR. The rate of interconversion of 5a,b by phosphorus inversion is greater than or equal to that of reductive elimination, which suggests that the enantiodetermining step occurs after Pd-P bond formation.