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.

采用磷-维蒂格方法，成功设计并合成了一种选择性较高的磷-磷烷烯杂环配体E-1a（Cy2PCH2CH=PMes*，其中Mes*代表2,4,6-三叔丁基苯基）和E-1b（Ph2PCH2CH=PMes*）。新合成的杂环配体E-1a和E-1b被应用于制备Pd和Pt的双氯化物配合物，包括Pd­(Cy2PCH2CH=PMes*)­Cl2（2a）、Pd­(Ph2PCH2CH=PMes*)­Cl2（2b）、Pt­(Cy2PCH2CH=PMes*)­Cl2（3a）和Pt­(Ph2PCH2CH=PMes*)­Cl2（3b）。通过单晶X射线衍射技术确定了E-1a、E-1b、2a·1.33CHCl3、3a·CH3CN以及3b的晶体结构。基于密度泛函理论（DFT）的计算（采用M06/LACV3P**泛函）对2a的研究表明，位于P≡C单元的π*轨道处于较低能级且易于接近。非键轨道自然底态分析（NBO）结果显示，由于P≡C双键的存在，磷烷烯配体相对于其叔磷烷配体而言，是较差的σ供体，但作为π受体则略有优势。