Chiral palladium complexes from N-diphenylphosphinoamino methyl esters

Abstract

(S)-N,S-Bis(diphenylphosphino)cystein methyl ester (bdppcys 3) is obtained from the reaction of chlorodiphenylphosphine with (S)-cystein methyl ester hydrochloride in the presence of Et₃N as (S)-N-diphenylphosphinoalanine methyl ester (dppal 1) and (S)-N-diphenylphosphinomethionine methyl ester (dppmet 2). Compounds 1–3 show different coordination behaviour to [PdCl₂(cod)]. Ligand 1 and [PdCl₂(cod)] give an unexpected chloro-bridged binuclear complex trans-[PdCl(μ-Cl)(dppal-P)]₂4. Compound 2 interacts with [PdCl₂(cod)] to give a chelate complex cis-[PdCl₂(dppmet-S,P)] 5. Reaction of 3 with [PdCl₂(cod)] leads to an unstable chelate complex cis-[PdCl₂(dppcys-P,P′)] 6, which gradually decomposes into a novel sulfur-bridged binuclear complex trans-[PdCl(μ-S)-dppcys-P)]₂7 and a chloro-bridged binuclear complex trans-[Pd(μ-Cl)(P(O)Ph₂-P)(P(OH)Ph₂-P)]₂8.