Catalytic Reduction of Hydrazine to Ammonia with MoFe₃S₄−Polycarboxylate Clusters. Possible Relevance Regarding the Function of the Molybdenum-Coordinated Homocitrate in Nitrogenase

Abstract

The catalytic function of the previously synthesized and characterized [(L)MoFe(3)S(4)Cl(3)](2)(-)(,3)(-) clusters (L = tetrachlorocatecholate, citrate, citramalate, methyliminodiacetate, nitrilotriacetate, thiodiglycolate) and of the [MoFe(3)S(4)Cl(3)(thiolactate)](2)(4)(-) and [(MoFe(3)S(4)Cl(4))(2)(&mgr;-oxalate)](4)(-) clusters in the reduction of N(2)H(4) to NH(3) is reported. In the catalytic reduction, which is carried out at ambient temperature and pressure, cobaltocene and 2,6-lutidinium chloride are supplied externally as electron and proton sources, respectively. In experiments where the N(2)H(4) to the [(L)MoFe(3)S(4)Cl(3)](n)()(-) catalyst ratio is 100:1, and over a period of 30 min, the reduction proceeds to 92% completion for L = citrate, 66% completion for L = citramalate, and 34% completion for L = tetrachlorocatecholate. The [Fe(4)S(4)Cl(4)](2)(-) cluster is totally inactive and gives only background ammonia measurements. Inhibition studies with PEt(3) and CO as inhibitors show a dramatic decrease in the catalytic efficiency. These results are consistent with results obtained previously in our laboratory and strongly suggest that N(2)H(4) activation and reduction occur at the Mo site of the [(L)MoFe(3)S(4)Cl(3)](2)(-)(, 3)(-) clusters. A possible pathway for the N(2)H(4) reduction on a single metal site (Mo) and a possible role for the carboxylate ligand are proposed. The possibility that the Mo-bound polycarboxylate ligand acts as a proton delivery "shuttle" during hydrazine reduction is considered.

Nitrogen Fixation under Mild Ambient Conditions: Part I—The Initial Dissociation/Association Step at Molybdenum Triamidoamine Complexes

“…The role of Mo is evident in Schrocks complex and has often been considered essential for dinitrogen binding by various authors (see also the recent work in references [38][39][40][41][42][43][44]). Very recently, studies on molybdenum complexes have been reported, [45,46] which discuss results for intermediate steps of N 2 reduction in the light of Yandulov and Schrocks Figure 1.…”

The anaerobic oxidation of hydrazine: a novel reaction in microbial nitrogen metabolism

“…It is used as a rocket fuel, as an antioxidant or as an intermediate for the production of explosives and pesticides [1]. Hydrazine is a strong reducing agent, which reacts easily with metal ions [2]. In the presence of catalysts like Cu(II) and phosphate ions hydrazine radicals are formed via a one-electron oxidation, which ultimately are converted into ammonia and dinitrogen gas (2N P H R C2N P H Q CN R H T CN P +2NH Q .…”

Theoretical study on the mechanism of catalytic reduction of hydrazine to ammonia mediated by vanadium (III) thiolate complexes

“…Hence, to understand the mode of action of the enzyme, the chemistry of vanadium centre which contains three sulfur (MS 3 sites) donor atoms is of great importance. So far, limited synthetic models are known that catalyze the conversion of N 2 H 4 to NH 3 , the late stage of ammonia synthesis [9][10][11][12][13][14][15]. Davies and coworkers reported vanadium complexes of the NðCH 2 CH 2 SÞ 3À 3 and OðCH 2 CH 2 SÞ 2À 2 ligands [16].…”