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 Hydridonickel Complexes

The reaction of ammonium and iminium tetraphenylborate salts ((CH 2 CHCH 2 NH 3 )BPh 4, [(CH 2 CHCH 2 )HN CMe 2 ]BPh 4, and [(PhCH 2 )HN CMe 2 ]BPh 4 ) with transition-metal systems in a low oxidation state has been investigated. We report the oxidative addition to (Cy 3 P) 2 Ni(η 2 -CO 2 ) or (Cy 3 P) 2 NiN⋮NNi(PCy 3 ) 2 under mild conditions (253−293 K) and describe a very selective N C or N H bond activation. (CH 2 CHCH 2 NH 3 )BPh 4 or [(CH 2 CHCH 2 )HN CMe 2 ]BPh 4 react with (Cy 3 P) 2 Ni(η 2 -CO 2 ) and (Cy 3 P) 2 NiN⋮NNi(PCy 3 ) 2 to afford the cationic π-allyl−Ni complexes [(η 3 -C 3 H 5 )Ni(PCy 3 )(NH 3 )]BPh 4 ( 1 ) and [(η 3 -C 3 H 5 )Ni(PCy 3 )(η 1 ( N )-HN CMe 2 )]BPh 4 ( 2 ), respectively. The reaction of [(PhCH 2 )HN CMe 2 ]BPh 4 with (Cy 3 P) 2 NiN⋮NNi(PCy 3 ) 2 leads to the hydrido−imino complex [ trans -(H)Ni(PCy 3 ) 2 (η 1 ( N )-PhCH 2 N CMe 2 )]BPh 4 ( 3 ) through N H bond activation. Complexes 1 − 3 have been fully characterized in solution by NMR ( 1 H, 13 C, 31 P) 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 PCy 3 ligands.