Synthesis and Coordination Chemistry of a Tridentate o-Phenylene-Bridged Diphosphine-NHC System

The preparation of a di-o-phenylene-bridged tridentate PCP donor set is described starting with t-BOC-aniline followed by a series of steps that include lithiation, quenching with (Pr2PCl)-P-i, conversion to the phosphine sulfide, and assembling the unsaturated N-heterocyclic carbene unit. After desulfurization, the imidazolinium unit flanked by two phosphine units, represented as [(PCP)H]PF6 is obtained. Subsequent reaction with group 10 M(0) reagents (Ni(COD)(2), Pd(PPh3)(4), and Pt(PPh3)(4)) generates good yields of the Corresponding metal hydride complexes, [(PCP)MH]PF6 salts (where M = Ni(II), Pd(II), and Pt(II)). Each of these species has been characterized by elemental analyses, NMR spectroscopy, and X-ray crystallography. All of the structures show that the PCP unit is twisted with respect to the square plane of the d(8) metal complex.