Oxazoline chemistry. Part VIII. Synthesis and characterization of a new class of pincer ligands derived from the 2-(o-anilinyl)-2-oxazoline skeleton — Applications to the synthesis of group X transition metal catalysts

The synthesis and characterization of a new and readily synthesized class of potentially anionic pincer ligands with C1 point group symmetries is described. These materials can be made via amide coupling of a 2-(2′-anilinyl)-2-oxazoline unit with picolinic acid; the incorporation of enantiopure oxazoline fragments facilitates the construction of chiral C1 pincers. Treatment of the free ligands with Pd metal sources leads to the formation of amido–Pd pincer complexes in good yield. One of these Pd complexes has been characterized by single crystal X-ray diffraction methods, which confirms the proposed tridentate binding mode of the ligand and the formation of an amido N—Pd bond. The metal complexes have been shown to be suitable precusors for catalytically active Pd species that are useful for C—C bond forming reactions, notably the Heck reaction under standard conditions. Key words: oxazoline, 4,5-dihydro-2-oxazole, palladium, pincer ligand, amido, Heck reaction.