2-(N-Alkylcarboxamide)-6-iminopyridyl palladium and nickel complexes: coordination chemistry and catalysis

The 2-(N-alkylcarboxamide)-6-iminopyridine ligands (L1–L7) can bind as either mono-anionic tridentate NNN ligands on reaction with PdCl2(CH3CN)2, to form complexes LPdCl (C1–C7), or as neutral tridentate NNO ligands with NiCl2·6H2O, to produce complexes LNiCl2 (C8–C14). All metal complexes were characterized by IR spectroscopy and elemental analysis, and in the case of the palladium complexes, by 1H and 13C NMR spectroscopy. The crystal structures of C3, C4, C6, C10, and C12 were determined by X-ray crystallography, and revealed a distorted square geometry around the palladium centre, whereas for nickel, a distorted square-pyramidal geometry was adopted. The representative palladium complex (C3) was further reacted with AgBF4 in acetonitrile affording the salt [L3Pd(CH3CN)][BF4] (C15) and the structure of this was confirmed by single-crystal X-ray diffraction. By contrast, carrying out the reaction in dichloromethane rather than acetonitrile, in the presence of malononitrile (CNCH2CN), resulted in the formation of the bimetallic palladium complex [L3Pd(CNCH2CN)PdL3]·2[BF4] (C16). Upon activation with diethylaluminium chloride, all the nickel complexes showed high activity for ethylene dimerization. Furthermore, the palladium complexes exhibited good activities in the vinyl-polymerization of norbornene upon activation with MAO.