Nitrogen fixation. Part II¹ 1 For Part I (involving titanium compounds) see ref. 1.. Nitrogen reduction by electrochemically generated vanadium(II) promoted by various organic ligands in basic methanol

The reduction of dinitrogen by vanadium(II) with various organic ligands in a basic methanol solution within an electrochemical cell was investigated under ambient conditions. We have confirmed Shilov's work that a slight excess of base relative to catechol is best for this reduction, but at a different catechol: vanadium ratio; 7:1 rather than 10:1, respectively. Under these conditions, 64% of NH₃ per mol vanadium was generated. We tested more than twenty organic bidentate ligands, which included heterocycles, thiols, hydroxyls, amines, and carboxyl groups, under the same conditions. Two catechol-like ligands were found to be better promoters of ammonia formation than catechol itself: 1,2-dihydroxy-naphthalene (15.2%) and 2,3-dihydroxypyridine (7.5%). For the first time we discovered that non-catechol ligands also could promote this reaction, although less so than catechol, among these ligands are 1,2-dihydroxycyclohexane (2.8%), 2-pyridine methanol (4.6%) and ethylene glycol (0.1%). The decreased efficiency of the latter in promoting nitrogen reduction suggests that the steric bulk of the ligand may play an important role. While ammonia is formed selectively in the presence of most of the ligands used, in one experiment, with tetrahydropyrol-2-methanol, hydrazine (0.6%) is the exclusive product (it had not been observed as an end product before in a soluble, vanadium-based system). In three other cases, both ammonia and hydrazine were formed. None of the reactions examined gave a catalytic yield of ammonia, despite the application of relatively high negative potentials.