ELECTROCATALYTIC REDUCTION OF ACETYLENE BY MOLYBDENUM-CYSTEINE AND MOLYBDENUM-EDTA COMPLEXES

Binuclear oxo- and sulfide-bridged Mo(V)-cysteine and Mo(V)-EDTA
complexes are chosen as model compounds for nitrogenase enzyme.
Both groups of complexes undergo electrochemical reduction in a single
four- electron step to Mo(III) dimers. The reduced binuclear Mo (III)
units dissociate into catalytically active species capable of reducing
the nitrogenase substrate, acetylene. Ease of dissociation increases
as oxygen is replaced by sulfur in the bridging unit. Electrocatalytic
reduction products of acetylene consist primarily of C2H4 and C2H6 at
low partial pressures, but C4H6, C4H8, and higher hydrocarbons predominate
at higher pressures. The reduction of substrate is believed
to occur by a Mo(III) catalyst adsorbed on the electrode surface. A
mechanism is proposed for the e lectrocatalysis, and its relationship
to the enzymic catalysis is discussed.