Streamlined Preparation and Coordination Chemistry of Hybrid Phosphine–Phosphaalkene Ligands

Abstract

A rationally designed and selective synthesis of hybrid phosphine–phosphaalkene ligands E -1a (Cy 2 PCH 2 CH═PMes*, Mes* = 2,4,6-tri- tert -butylphenyl) and E -1b (Ph 2 PCH 2 CH═PMes*) was developed using phospha-Wittig methodology. The new hybrid ligands E -1a and E -1b were used to prepare the Pd and Pt dichloride complexes Pd(Cy 2 PCH 2 CH═PMes*)Cl 2 ( 2a ), Pd(Ph 2 PCH 2 CH═PMes*)Cl 2 ( 2b ), Pt(Cy 2 PCH 2 CH═PMes*)Cl 2 ( 3a ), and Pt(Ph 2 PCH 2 CH═PMes*)Cl 2 ( 3b ). The crystal structures of E -1a, E -1b, 2a ·1.33CHCl 3, 3a ·CH 3 CN, and 3b were determined. DFT calculations (M06/LACV3P**) on 2a revealed that the π* orbital located on the P═C unit is low-lying and accessible. An NBO analysis concluded that the phosphaalkene ligand is a significantly poorer σ donor and a slightly better π acceptor than its tertiary phosphine counterpart, due to the presence of the P═C double bond.