Steric influence on the constitution of beryllium phosphine complexes

The phosphine complexes of beryllium chloride, bromide and iodide, [(PMe2Ph)2BeX2], [(PMePh2)2BeX2] and [(PPh3)BeX2]2 (X = Cl, Br, I) were prepared and characterised with multinuclear NMR spectroscopy. Additionally the molecular structure of dinuclear [(PPh3)BeCl2]2 was determined with single crystal X-ray diffraction techniques. The threshold cone angle of the phosphines, below which two ligands can coordinate to the beryllium dihalide fragments, is between 136° and 145°. Halide-chloride exchange in dichloromethane is observed for [(PPh3)BeBr2]2 and [(PPh3)BeI2]2, which leads to the formation of [(PPh3)BeCl2]2. Due to the relatively low Lewis basicity of PPh3, it almost exclusively acts as a spectator ligand with only little formation of phosphonium cations.