First enantiopure imine CN-palladacycle of non-metallocenic planar chirality with the [2.2]paracyclophane backbone

Abstract

Herein the preparation of a planar chiral imine CN-palladacycle free of redox activity is reported. The direct cyclopalladation of a [2.2]paracyclophane-derived imine (HL) afforded the racemic dimer {Pd(η 2-L)(-Cl)} 2 1; its ortho-palladated structure was confirmed by spectroscopic ( 1H and 31P NMR) data for mononuclear derivatives and the X-ray study of the phosphane adduct (η 2-L)PdCl(PPh 3) 4. Both the ( S pl , S pl )- and ( R pl , R pl )-enantiomers of dimer 1 were isolated by the diastereoselective decoordination of the ( R C )-valinate auxiliary ligand (Val) from the adduct (η 2-L)Pd(κ 2-Val) 5 using column chromatography on silica gel. The absolute configuration of these new CN-palladacycles was established by the independent synthesis of the ( R pl , R pl )-enantiomer of dimer 1 from the pre-resolved ( S pl )-4-formyl[2.2]paracyclophane.