Access to C-Stereogenic PN(sp²)P Pincer Ligands via Phosphapalladacycle Catalyzed Asymmetric Hydrophosphination

Abstract

A series of PN(sp2)P ligands containing two stereogenic carbon centers were generated via the palladium(II) catalyzed asymmetric hydrophosphination of 2,6-pyridyl dienones using diphenylphosphine. Although the targeted tridentate products are powerful metal ion sequesters, poisoning of the metal catalyst due to irreversible chelation by the adducts during the course of the addition reaction was circumvented via this protocol. The reported procedure thus enabled the efficient access toward chiral PN(sp2)P pincer-type ligands in a one-pot, single-step process with good conversions and high enantioselectivities. The formed ligands can be further coordinated to various metal centers to form chiral PNP complexes with potential synthetic applications.