Catalytic reduction of acetylene and dinitrogen was carried out by sodium, zinc, and europium amalgams in the presence of polymolybdenum clusters and the iron-molybdenum cot'actor of nitrogenase isolated from the enzyme. The activity of both catalysts toward acetylene changes in the sequence Zn(Hg) < Eu(Hg) < Na(Hg), increasing as the redox potential of the reducing agent is shifted to the negative region. The catalytic reduction of N;~ occurs only by the action of sodium and europium amalgams and only in the presence of synthetic polymolybdenum complexes; in the case of Na(Hg), the ma/.n product is hydrazine; in the case of Eu(Hg), it is ammonia.In 1964, M. E. Volpin and V. B. Shur published pioneering work I demonstrating the possibility of reducing molecular nitrogen in solutions of metal complexes. This work laid the foundation for a new area in chemistry: the low-temperature chemistry of molecular nitrogen. The first systems reducing N 2 under mild conditions contained transition metal (titanium, iron, molybdenum, and others) compounds in combillation with strong reducing agents, such as organomagnesium and organolithium compounds, metal hydrides, and free metals. The further study of these systems showed that the reaction of the reducing agent and a transition metal compound results in the reduction of the latter, and the derivative of the transition metal in the low oxidation state that formed reacts with dinitrogen to give complex nitrides. The subsequent hydrolysis of the reaction mixture gives ammonia, z Of course, the reaction with dinitrogen can occur only in an aprotic medium, because the strong reducing agents used are unstable in protic solvents (water, alcohols) and react with the solvent. The amount of ammonia (after hydrolysis of the products) does not exceed the stoichiometric amount calculated with respect to the transition metal taken; however, catalytic systems were also observed, z For example, in the reaction of N 2 with the TiCIa--AI--AIBr 3 mixture (with an excess of the reducing agent AI--A1Br3), the amount of ammonia formed after the hydrolysis of the products is hundreds of times greater than that of titanium taken.However, no catalytic reduction of N 2 involving protons was observed in the first works.Nevertheless, in the well-known process of biological nitrogen fixation, which also involves the transition metals iron and molybdenum, the N 2 reduction involves protons of water. The stoiehiometric equation of this complicated reaction catalyzed by the nitrogenase enzyme includes the biological reducing agent ferredoxin or flavodoxin (in vivo) or dithionite in experiments in vitro and takes into account the conjugated hydrolysis of adenosine triphosphate (ATP).
N 2 + 8 H "~ + 8 e-($2042-) + 16 MgATP
NH 3 + H + 16 MgAC'P + 16 1~O42-The enzymatic process occurs under the action of considerably weaker reducing agents than those in the first nitrogen-reducing Volpin--Shur systems. Protons of the medium most likely participate in the early stages of the reaction without preliminary formati...