Palladium(II) and Nickel(II) Complexes Bearing N,N,O‐Chelate Ligands: Syntheses, Characterization and Catalysis in Heck and Kumada Coupling Reactions

Abstract

AbstractTwo new anionic ligands, namely [2‐{OC(Ph)2CH2}‐6‐(3,5‐Me2C3HN2)C5H3N]– (L1–) and [2‐{OC(Ph)=CH}‐6‐(3,5‐Me2C3HN2)C5H3N]– (L2–), and their palladium and nickel complexes, were synthesized and characterized. 6‐(3,5‐Dimethyl‐1H‐pyrazol‐1‐yl)‐2‐methylpyridine was lithiated with nBuLi and the lithiated product treated with benzophenone to give Li(L1) (2), whereas treatment of 2‐[6‐(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)pyridin‐2‐yl]‐1‐phenylethanone with NaH afforded Na(L2) (6). The palladium and nickel complexes [(L1)PdCl] (3), [(L1)NiAr] [Ar = o‐MeC6H4 (4a), 1‐C10H7 (4b)], [(L2)PdCl] (7) and [(L2)NiAr] [Ar = o‐MeC6H4 (8a), 1‐C10H7 (8b)] were obtained by ligand‐transfer reactions between Li(L1) or Na(L2) and [PdCl2(PhCN)2] or [(Ph3P)2Ni(Ar)Cl] (Ar = o‐MeC6H4 and 1‐C10H7, respectively). These complexes are diamagnetic and were characterized by NMR spectroscopy and elemental analyses. The structures of complexes 4b and 8a were determined by single‐crystal X‐ray diffraction techniques. The catalytic activity of the nickel and palladium complexes in the Heck and Kumada cross‐coupling reactions were investigated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)