Streamlined Preparation and Coordination Chemistry of Hybrid Phosphine–Phosphaalkene Ligands

Abstract

A rationally designed and selective synthesis of hybrid phosphine–phosphaalkene ligands <i><b>E</b></i><b>-1a</b> (Cy₂PCH₂CHPMes*, Mes* = 2,4,6-tri-<i>tert</i>-butylphenyl) and <i><b>E</b></i><b>-1b</b> (Ph₂PCH₂CHPMes*) was developed using phospha-Wittig methodology. The new hybrid ligands <i><b>E</b></i><b>-1a</b> and <i><b>E</b></i><b>-1b</b> were used to prepare the Pd and Pt dichloride complexes Pd­(Cy₂PCH₂CHPMes*)­Cl₂ (<b>2a</b>), Pd­(Ph₂PCH₂CHPMes*)­Cl₂ (<b>2b</b>), Pt­(Cy₂PCH₂CHPMes*)­Cl₂ (<b>3a</b>), and Pt­(Ph₂PCH₂CHPMes*)­Cl₂ (<b>3b</b>). The crystal structures of <i><b>E</b></i><b>-1a</b>, <i><b>E</b></i><b>-1b</b>, <b>2a</b>·1.33CHCl₃, <b>3a</b>·CH₃CN, and <b>3b</b> were determined. DFT calculations (M06/LACV3P**) on <b>2a</b> 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