Oxidative Addition of Ammonium and Iminium Tetraphenylborates to Low-Valent Metal Complexes. Evidence of Selective N-C and N-H Activation. A New, Easy Route to Cationic Allyl-and Hydrido Nickel Complexes

The reaction of ammonium and iminium tetraphenylborate salts ((CH2CHCH2NH3)BPh4, [(CH2CHCH2)HNCMe2]BPh4, and [(PhCH2)HNCMe2]BPh4) with transition-metal systems in a low oxidation state has been investigated. We report the oxidative addition to (Cy3P)2Ni(η2-CO2) or (Cy3P)2NiNNNi(PCy3)2 under mild conditions (253−293 K) and describe a very selective NC or NH bond activation. (CH2CHCH2NH3)BPh4 or [(CH2CHCH2)HNCMe2]BPh4 react with (Cy3P)2Ni(η2-CO2) and (Cy3P)2NiNNNi(PCy3)2 to afford the cationic π-allyl−Ni complexes [(η3-C3H5)Ni(PCy3)(NH3)]BPh4 (1) and [(η3-C3H5)Ni(PCy3)(η1(N)-HNCMe2)]BPh4 (2), respectively. The reaction of [(PhCH2)HNCMe2]BPh4 with (Cy3P)2NiNNNi(PCy3)2 leads to the hydrido−imino complex [trans-(H)Ni(PCy3)2(η1(N)-PhCH2NCMe2)]BPh4 (3) through NH bond activation. Complexes 1−3 have been fully characterized in solution by NMR (1H, 13C, 31P) spectroscopy. The hydrido−imino complex 3, characterized in the solid state by a X-ray diffraction study, shows a distorted-square-planar coordination around the nickel atom with a very narrow P−Ni−P angle, 148.6(2)°, involving the two P atoms from the trans PCy3 ligands.