Dinuclear Fe^IIFe^II Biomimetics for the Oxidized State Active Site of [FeFe]-Hydrogenases: Synthesis, Characterization, and Electrocatalytic H₂ Production

Abstract

As the oxidized state models for the active site of [FeFe]-H2ases, a series of new diphosphine-chelated dinuclear FeII(μ-X)FeII (X = Cl, Br, I) complexes have been prepared using a simple and convenient one-pot synthetic method. Thus, treatment of the diphosphine dppv-chelated Fe dithiolate (dppv)Fe(CO)2(pdt) with equimolar amounts of the dppv-chelated Fe dihalides (dppv)Fe(CO)2X2 in the presence of a 2-fold excess of NaBF4 at room temperature gave the corresponding homodiphosphine dppv/dppv-chelated dinuclear Fe complexes [(dppv)2(CO)2Fe2(μ-pdt)(μ-X)](BF4) ([1(μ-X)](BF4)), whereas their dppe analogues [(dppe)2(CO)2Fe2(μ-pdt)(μ-X)](BF4) ([2(μ-X)](BF4)) could be prepared by treatment of the dppe-chelated Fe complex (dppe)Fe(CO)2(pdt) with dppe-chelated Fe dihalides (dppe)Fe(CO)2X2 and NaBF4 under similar conditions. Furthermore, the heterodiphosphine dppv/dppe-chelated dinuclear Fe complexes [(dppv)(dppe)(CO)2Fe2(μ-pdt)(μ-X)](BF4) ([3(μ-X)](BF4)) could be similarly prepared by the one-pot reactions of the dppv-chelated Fe dithiolate (dppv)Fe(CO)2(pdt) with equimolar dppe-chelated Fe dihalides (dppe)Fe(CO)2X2 and a 2-fold excess of NaBF4. All the prepared new complexes [1(μ-X)](BF4)–[3(μ-X)](BF4) were fully characterized by elemental analysis and various spectroscopic techniques and particularly for some of their representatives by X-ray crystallography. In addition, on the basis of an electrochemical study, complexes [1(μ-X)](BF4) were found to be catalysts for H2 production from Cl3CCO2H under CV conditions.