Synthesis and characterization of a new chiral phosphinothiol ligand and its palladium(II) complexes

Abstract

The chiral ligand (1-diphenylphosphino-3-benzyloxy)propane-2-thiol 3 has been prepared both in racemic and enantiomerically enriched (92% e.e.) form. Addition of 2 equiv. of ligand 3 to a solution of [Pd(PPh 3) 4] gave the diastereoisomeric bischelate complexes [Pd(phosphinothiolato) 2] 4 which exhibit a cis– trans equilibrium in solution. Formation of the diastereoisomeric complexes 4 allows the determination of the enantiomeric purity of ligand 3 by 31P NMR spectroscopy. Addition of 1 equiv. of ligand 3 to a solution of [PdCl 2(PPh 3) 2] gave the enantiomeric complexes [PdCl(phosphinothiolate)(PPh 3)] 5, which can be converted to the bischelate complexes 4 by addition of a second equivalent of ligand 3. This process allows the selective preparation of the two diastereoisomeric forms of complex 4.