Streamlined Preparation and Coordination Chemistry of Hybrid Phosphine–Phosphaalkene Ligands

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.