Tridentate NNN Ligand Associating Amidoquinoline and Iminophosphorane: Synthesis and Coordination to Pd and Ni Centers

The synthesis of a tridentate NNN ligand incorporating an amidoquinoline and an iminophosphorane (L^RH; R = Ph, Cy) was carried out. Coordination to Pd^II and Ni^II precursors gave, as expected, square-planar complexes of the general formula [L^RMCl]. The most surprising result came from the reaction of L^PhH with [Ni­(COD)₂], which gave a Ni^II phenyl complex bearing a tridentate amidoquinoline-aminophosphine ligand. This rearrangement would result from a proton transfer assisted by the Ni⁰ on stabilization by a phenyl substituent at the phosphorus, as suggested by DFT calculations and complementary experiments. This nickel phenyl complex formed the corresponding benzoyl complex under a CO atmosphere.