Palladium(II) complexes bearing the new pincer ligand 3,5-bis(indazol-2-ylmethyl)toluene; synthesis and catalytic properties

The reaction of 3,5-bis(bromomethyl)toluene with 1H-indazole in toluene, in the presence of triethylamine, yields the ligand 3,5-bis(indazol-2-ylmethyl)toluene (1). Compound 1 reacts with Pd(OAc)2 in refluxing acetic acid, followed by a metathetic reaction with lithium chloride and with [PdCl2(cod)] (cod = 1,5-cyclooctadiene) in refluxing acetonitrile to give the complexes [PdCl{3,5-bis(indazol-2-ylmethyl)tolyl-N,C,N}] (2) and [PdCl2{3,5-bis(indazol-2-ylmethyl)toluene-N,N}] (3), respectively. Compounds 1–3 were characterized by elemental analyses, mass spectra and IR and NMR (1H, 13C) spectroscopies. The molecular structure of 1 was also determined by single-crystal X-ray diffraction. The palladium(II) complexes (2,3) were tested as catalysts in ethylene polymerization and in C–C coupling reactions involving aryl halides substrates.

Graphical abstractThe reaction of 3,5-bis(bromomethyl)toluene with 1H-indazole in toluene, in the presence of triethylamine, yields the ligand 3,5-bis(indazol-2-ylmethyl)toluene. This ligand reacts with Pd(OAc)2 in refluxing acetic acid, followed by a metathetic reaction with lithium chloride and with [PdCl2(cod)] (cod = 1,5-cyclooctadiene) in refluxing acetonitrile to give the complexes [PdCl{3,5-bis(indazol-2-ylmethyl)tolyl-N,C,N}] and [PdCl2{3,5-bis(indazol-2-ylmethyl)toluene-N,N}], respectively. The molecular structure of the new ligand was determined by single-crystal X-ray diffraction. The palladium(II) complexes were tested as a catalyst in ethylene polymerization and in C–C coupling reactions involving aryl halides substrates.Figure optionsDownload full-size imageDownload as PowerPoint slide