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

Abstract

The 2-(N-alkylcarboxamide)-6-iminopyridine ligands (L1–L7) can bind as either mono-anionic tridentate N⁁N⁁N ligands on reaction with PdCl₂(CH₃CN)₂, to form complexes LPdCl (C1–C7), or as neutral tridentate N⁁N⁁O 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.