46. "Metal-Catalyzed Asymmetric Synthesis of P-Stereogenic Phosphines." Glueck, D. S. Synlett 2007, 2627-2634 (invited review).

Abstract

Abstract: This account summarizes our attempts to develop metal-catalyzed asymmetric syntheses of P-stereogenic phosphines. While such phosphines undergo pyramidal inversion slowly at room temperature, inversion is rapid in metal-phosphido complexes (M-PR2).  These observations were the basis for catalytic dynamic kinetic resolution processes in which racemic secondary phosphines PR(R’)(H) were converted into enantioenriched tertiary phosphines PR(R’)(R’’) by Pt-catalyzed asymmetric hydrophosphination of acrylonitrile or related Michael acceptors, Pd-catalyzed asymmetric phosphination of aryl iodides using secondary phosphines or phosphine-boranes, and Pt-catalyzed asymmetric alkylation of secondary phosphines.  The key intermediates were diastereomeric phosphido complexes with chiral ancillary ligands (*Ln-M-PRR’). Their relative rates of P inversion and P-C bond formation controlled the enantioselectivity of product formation, whether P-C bonds were formed by reductive elimination (for Pd), or by reaction of a Pt-phosphido complex with an electrophile (an alkene in hydrophosphination, or a benzyl bromide in alkylation).  The results of mechanistic studies and their use in design of improved catalytic reactions are described.