Diamidophosphine complexes of niobium(III) and (IV): imide formation via ancillary ligand decomposition

The diamidophosphine complexes of niobium (CyPh)[NPN]NbCl(DME) (2), (CyPh)[NPN]NbCl2 (6), and (PhPh)[NPN]NbCl2 (9), where (RR')[NPN]=RP(CH2SiMe2NR')(2) have been prepared, isolated and characterized. Generation of (RR')[NPN]NbCl(DME) species competes with the production of ((RR')[NPN]NbCl)(2)(mu-N-2) and can be controlled with N-2 pressure. (CyPh)[NPN]NbCl2 spontaneously decomposes into (CyPh)[NPN]NbCl(=NPh) (7), CyP(CH2SiMe2)(2)NPh (8), and a paramagnetic impurity. Compound 7 was characterized by an X-ray diffraction study and its structural features are discussed. The Nb-N-imido bond length is 1.789(2) Angstrom with a Nb-N-imido-C bond angle of 167.9(2)degrees in a distorted square pyramidal structure. Reduction of (PhPh)[NPN]NbCl2 (9), with KC8 produced (PhPh)[NPN]NbCl(=NPh), PhP(CH2SiMe2)(2)NPh, and a paramagnetic impurity. (C) 2002 Elsevier Science B.V. All rights reserved.