Electrochemical cleavage of N=N bonds at a Mo-2(mu-SMe)(3) site relevant to the biological reduction of dinitrogen at a bimetallic sulfur centre

The reduction of diazene complexes [Mo2Cp2(mu-SMe)(3)(mu-eta(2)-H-N=N-R)](+) (R=Ph (3a); Me (3b)) and of the hydrazido(2-) derivative [Mo2Cp2(mu-SMe)(3){mu-eta(1)-N=N(Me)H}](+) (1b) has been studied by cyclic voltammetry, controlled-potential electrolysis, and coulometry in THE The electrochemical reduction of 3 a in the presence of acid leads to cleavage of the N=N bond and produces aniline and either the amido complex [Mo2Cp2(mu-SMe)(3)- (mu-NH2)] 4 or the ammine complex [Mo2Cp2(mu-SMe)(3)(NH3)(X)] 5, depending on the initial concentration of acid (HX = HTsO or CF3CO2H). The N=N bond of the methyldiazene analogue 3b is not cleaved under the same conditions. The ability of 3a but not 3b to undergo reductive cleavage of the N=N bond is attributed to electronic control of the strength of the Mo-N(R) bond by the R group. ne electrochemical reduction of the methylhydrazido(2-) compound 1b in the presence of HX also results in cleavage of the N=N bond, with formation of methylamine, 4 (or 5) and the methyldiazenido complex [Mo2Cp2(mu-SMe)(3)(mu-eta(1)-N=N-Me)]. Formation of the last of these complexes indicates that two mechanisms (N=N bond cleavage and possibly H-2 production) are operative. A pathway for the reduction of N-2 at a dinuclear site of FeMoco is proposed on the basis of these results.