Chiral palladacycles with N‑heterocyclic carbene ligands as catalysts for asymmetric hydrophosphination

Abstract

Design of chiral palladacycles with N-heterocyclic carbene (NHC) ligands has been carried out in good yields starting form commercially available enantiopure benzylamines. The methodology developed consists of the formation of palladium dimers with orthometalated benzylamines. The dimers undergo facile chloride-bridge-splitting with azolium salts under basic conditions to afford the chiral palladacycles with NHC ligands and tertiary or even the more challenging primary amines. The steric and electronic properties of the resulting complexes have been modulated both by using different chelating amines and varying the topology of the NHC ligand. The new complexes have been fully characterized by means of NMR, ESI/MS, and X-ray crystallography. All new complexes complexes have been used as catalysts in the 1,4-addition of diarylphosphines to α,β-unsaturated ketones.