Reduction of N3− by [Mo2Fe6S8(SPh)9]3− Modified Glassy Carbon Electrode—Model Study of Nitrogenase

Abstract

The reduction of N3− by a (Bu4N)3[Mo2Fe6S8(SPh)9] modified glassy carbon electrode has been conducted in a pH region 5 to 12 in water. In neutral and acidic conditions, N3− undergoes two-and six-electron reductions to afford not only N2 and NH3 but also N2H4, and the total amounts of N2 and N2H4 produced were essentially consistent with that of NH3. On the other hand, no N2H4 formation was observed in the pH region higher than 10, where an equal amount of N2 and NH3 was formed. The rate of N2H4 formation was linearly proportional to a concentration of N3H, which exists as an equilibrium mixture with N3− in the aqueous phase, while that of N2 evolution was controlled by the concentration of free N3− in H2O. These observations indicate that N2H4 and N2 result from the coordination of N3H and N3− to the molybdenum–iron sulfur cluster, respectively.

Catalytic functions of cubane-type M4S4 clusters

“…64 Depression of H 2 evolution and improvement of the ammonia yield was achieved by using the working electrodes, which were prepared by modifying glassy-carbon plates with 2a. 65 Superiority of this electrode in multielectron reduction of HOCH 2 CH 2 N 3 was demonstrated in aqueous solution to give large amounts of ammonia with high catalytic rates (Eq 4). 61,63 Electrodes modified with 1a and the double-cubane cluster [{(Cl 4 -cat)MoFe 3 S 4 (SPh) 2 } 2 (m 2 -SPh) 2 ] 4À (5: Chart 6), which was regarded as the dimer form of 3, were also tested for the reduction of HOCH 2 CH 2 N 3 in water (Eq 5).…”