Synthesis and palladium(II) metal chemistry of thiazoline/imidazoline derived ligands: An efficient catalyst for cross-coupling reactions of arylboronic acids with acid chlorides and aryl halides

Abstract

The synthesis, reactivity, spectroscopic characterization and catalytic activities of a series of Pd(II) complexes bearing the chelating ligands 2-(4,5-dihydrothiazol-2-yl)aniline (2) and 2-(4,5-dihydro-1H-imidazol-2-yl)aniline (3) are reported. The reactions of 2 with [Pd(COD)Cl2] in 1:1 and 1:2 (ligand into metal and metal into ligand) molar ratios afforded the mononuclear complexes, PdCl2{κ2−N,S − 2−(4,5-dihydrothiazol-2-yl)aniline} (4), Pd{κ2−N,N’−2−(4,5-dihydrothiazol-2-yl)aniline}2 (5) and Pd{κ12−N,N’−κ22−N,S − 2−(4,5-dihydrothiazol-2-yl)aniline}2 (6), respectively, in good yields. The neutral mononuclear palladium complexes PdCl2{κ2−N,N’−(4,5-dihydro-1H-imidazol-2-yl)aniline} (7) and Pd{κ2−N,N’−2−(4,5-dihydro-1H-imidazol-2-yl)aniline}2 (8) were synthesized using [Pd(COD)Cl2] with appropriate molar ratios. The palladium complexes 4–8 were evaluated for their catalytic activities in base assisted cross coupling reactions between acid chlorides and aryl halide with boronic acids. The complex 4 was found to be an efficient catalyst for producing unsymmetrical ketones (TOF = 19.8 min−1) while complex 7 was effective for making biaryls (TOF = 19.8 min−1).