Electrochemical cleavage of N=N bonds at a Mo2(mu-SMe)3 site relevant to the biological reduction of dinitrogen at a bimetallic sulfur centre.
The reduction of diazene complexes [Mo(2)Cp(2)(mu-SMe)(3)(mu-eta(2)-H-N=N-R)](+) (R=Ph (3 a); Me (3 b)) and of the hydrazido(2-) derivative [Mo(2)Cp(2)(mu-SMe)(3)[mu-eta(1)-N=N(Me)H]](+) (1 b) has been studied by cyclic voltammetry, controlled-potential electrolysis, and coulometry in THF. 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 [Mo(2)Cp(2)(mu-SMe)(3)(mu-NH(2))] 4 or the ammine complex [Mo(2)Cp(2)(mu-SMe)(3)(NH(3))(X)] 5, depending on the initial concentration of acid (HX=HTsO or CF(3)CO(2)H). The N=N bond of the methyldiazene analogue 3 b is not cleaved under the same conditions. The ability of 3 a but not 3 b 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. The electrochemical reduction of the methylhydrazido(2-) compound 1 b 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 [Mo(2)Cp(2)(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.
UMR 6521 Chimie, Electrochimie Moléculaires et Chimie Analytique, Université de Bretagne Occidentale, 6 Av. V Le Gorgeu B.P. 809, 29285 Brest Cedex, France.
Nathalie
N
Le Grand
Kenneth W
KW
Muir
François Y
FY
Pétillon
Christopher J
CJ
Pickett
Philippe
P
Schollhammer
Jean
J
Talarmin
D000641:Ammonia; D020134:Catalytic Domain; D004563:Electrochemistry; D006865:Hydrogenation; D007094:Imides / Q000737:chemistry*; D007506:Iron-Sulfur Proteins / Q000737:chemistry; D008024:Ligands; D008667:Metalloproteins / Q000737:chemistry*; D008958:Models, Molecular; D008982:Molybdenum / Q000737:chemistry*; D009586:Nitrogen Fixation
D007094:Imides; D007506:Iron-Sulfur Proteins; D008024:Ligands; D008667:Metalloproteins; D000641:Ammonia; D008982:Molybdenum; C038867:diazene