Dinitrogen Fixation by Vanadium Complexes with a Triamidoamine Ligand

Dinitrogen-divanadium complexes with triami-doamine ligands, 1-3, were synthesized and characterized by resonance Raman, UV-vis, and NMR spectroscopy and elemental and X-ray structure analyses. X-ray structure analyses reveal that all three of the complexes have a dimeric structure with a mu-N-2 ligand (N-N bond length 1.200-1.221 angstrom). Resonance Raman and NMR spectra of 1-3 in solution show that these complexes maintain a dimeric structure in benzene and toluene solutions. N-15 NMR spectra of 1 and 3 have peaks assignable to mu-N-2 ligands at 33.4 and 27.6 ppm, respectively, but 2 does not have a similar peak under the same conditions. In V-51 NMR spectra, the peaks of vanadium ions were observed at -173.3, -143.8, and -240.2 ppm, respectively, which are in a higher magnetic field region in comparison to those of dinitrogen-divanadium complexes reported previously. The structure and electronic properties of 1 are supported by DFT calculations. Additionally, all complexes react with excess amounts of M[C10H8] (M = Na, K) and the proton sources HOTf, HCl, and [LutH]OTf (Lut = 2,6-dimethylpyridine) to produce ammonia without hydrazine. The ammonia produced was evaluated as an ammonium salt by H-1 and N-15 NMR spectroscopy. The yield of NH3 produced in the reaction of 1 with Na[C10H8] and HOTf under N-2 was 181% (per V atom).