Unsymmetrical Chiral PCN Pincer Palladium(II) and Nickel(II) Complexes of (Imidazolinyl)aryl Phosphinite Ligands: Synthesis via Ligand C-H Activation, Crystal Structures, and Catalytic Studies

Six unsymmetrical chiral PCN pincer Pd(II) complexes 3a-f based on (imidazolinyl)aryl phosphinite ligands were easily synthesized from imidazolinyl-containing m-phenol derivatives 2a-e by one-pot phosphorylation/palladation reaction via C-H bond activation of the related ligands. An unsymmetrical chiral PCN pincer Ni(II) complex, 4a, was first obtained in a similar way. The palladium-chloride complex 3e could be readily converted to the corresponding iodide derivative 5e by the halide exchange reaction with KI. All eight complexes were characterized by X-ray crystal structure determination. Each complex adopts a typical distorted-square-planar geometry. The Pd complexes were shown to be active catalysts with rather moderate enantioselectivities (up to 32% ee) for asymmetric Suzuki-Miyaura reaction.