Streamlined Preparation and Coordination Chemistry of Hybrid Phosphine–Phosphaalkene Ligands

Abstract

A rationally designed and selective synthesis of hybrid phosphine–phosphaalkene ligands E-1a (Cy2PCH2CH═PMes*, Mes* = 2,4,6-tri-tert-butylphenyl) and E-1b (Ph2PCH2CH═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(Cy2PCH2CH═PMes*)Cl2 (2a), Pd(Ph2PCH2CH═PMes*)Cl2 (2b), Pt(Cy2PCH2CH═PMes*)Cl2 (3a), and Pt(Ph2PCH2CH═PMes*)Cl2 (3b). The crystal structures of E-1a, E-1b, 2a·1.33CHCl3, 3a·CH3CN, 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.