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 N^N^N ligands on reaction with PdCl(2)(CH(3)CN)(2), to form complexes LPdCl (C1-C7), or as neutral tridentate N^N^O ligands with NiCl(2)·6H(2)O, to produce complexes LNiCl(2) (C8-C14). All metal complexes were characterized by IR spectroscopy and elemental analysis, and in the case of the palladium complexes, by (1)H and (13)C 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 AgBF(4) in acetonitrile affording the salt L3Pd(CH(3)CN)]BF(4)] (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 (CNCH(2)CN), resulted in the formation of the bimetallic palladium complex L3Pd(CNCH(2)CN)PdL3]·2BF(4)] (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.