Synthesis, Characterization, and Catalytic Studies of Unsymmetrical Chiral NCC Pincer Pd(II) and Ni(II) Complexes Bearing (Imidazolinyl)aryl NHC Ligands

摘要

A series of palladium(II) and nickel(II) complexes based on unsymmetrical chiral (imidazolinyl)aryl NHC ligands are reported. The new ligand presursors 3a-g were prepared from commercially available 3-bromobenzoic acid, in which the carboxyl and bromo functionalities were converted to chiral imidazoline and NHC moieties, respectively, in three steps. Treatment of 3a-g with Pd(OAc)(2) in dimethylacetamide in the presence of NaOAc, followed by addition of LiCl, gave the seven palladium(II) pincer complexes 4a-g via direct aryl C-H activation. Likewise, the six nickel(II) pincer complexes 5a-f were obtained by reacting 3a-f with anhydrous NiCl2. All of the ligand precursors and pincer complexes are bench-stable and were fully characterized. The absolute configurations of palladium complexes 4a,c and Se were further determined by X-ray diffraction. Finally, Pd pincer complex catalyzed asymmetric Friedel Crafts alkylation and aza-Morita-Baylis-Hillman reactions were briefly assessed.