Nickel(II) Schiff base complexes: Synthesis, characterization and catalytic activity in Kumada–Corriu cross-coupling reactions

The syntheses of ten new Ni(II) complexes 5a–5j with H2L tridentate (ONO) Schiff-base ligand (2-((2-oxybenzylidene)amino)phenolate) have been described and fully characterized by means of elemental analysis, FT–IR, electronic, 1H NMR and 13C NMR spectroscopy and single-crystal X-ray diffraction. In all [Ni(L)B] complexes (where B are imidazole, 4-benzylpyridine, 2-methyl-5-ethylpyridine, 3-hydroxymethylpyridine, 2-methylbenzimidazole, 2,6-dimethylpyridine, 4-methylpyridine, 2-isopropylbenzimidazole, 4-methylpiperidine or triphenylphosphine) the Schiff base completely deprotonates and coordinates to the metal ion as a dianionic tridentate ligand via the donor oxygens and nitrogen atoms. The coordination number of Ni(II) atoms is four with distorted square-planar stereochemistry. This is in a good agreement with the ligand field band position in their electronic spectra, as well as with the X-ray structure analysis for all complexes under study. Six selected complexes are used as catalysts for Kumada–Corriu cross-coupling reactions and exhibit a moderate to good catalytic activity in the synthesis of biaryl derivatives.

Graphical abstractThe article presents a synthesis of novel square-planar nickel(II) Schiff base complexes, which could be good catalysts. Desired products are prepared in moderate to good yields, depending on coordinated ligands on nickel atom.In this article, we describe preparation of this nickel(II) catalysts, characterization and their significant catalytic activity in Kumada–Corriu cross-coupling reactions.Figure optionsDownload full-size imageDownload as PowerPoint slide