Synthesis, crystal structure and electrocatalysis of 1,2-ene dithiolate bridged diiron carbonyl complexes in relevance to the active site of [FeFe]-hydrogenases

A series of binuclear FeIFeI complexes have been prepared by the treatment of N–heterocyclic 1,2-dithiols, such as, quinoxaline-6,7-dithiol (H26,7-qdt), 2,3-diphenyl-6,7-quinoxaline dithiol (H2diph-6,7-qdt) and 2,1,3-benzothiadiazole-5,6-dithiol (H2btdt) with Fe2(CO)9 resulting in the formation of [Fe2{μ-6,7-qdt}(CO)6] (1), [Fe2{μ-diph-6,7-qdt}(CO)6] (2) and [Fe2{μ-btdt}(CO)6] (3) respectively, that serve as model systems for the active site of [FeFe]-hydrogenase. These new complexes 1–3 have been characterized by IR, 1H, 13C, and 31P{1H} NMR, mass spectroscopy, elemental analysis and single-crystal X-ray structure analysis. The electrochemistry of 1–3 was performed by cyclic voltammetry and the electrocatalytic activities of model complexes 2 and 3 toward proton reduction of a strong acid p–HOTs have been described.

Graphical abstractIn an attempt to model the active sites of [FeFe]–hydrogenase, a series of heterocyclic 1,2-ene-dithiolate bridged diiron complexes [Fe2{μ-6,7-qdt}(CO)6] (1), [Fe2{μ-diph-6,7-qdt}(CO)6] (2) and [Fe2{μ-btdt}(CO)6] (3) have been synthesized and structurally characterized. The electrochemistry and the electrocatalytic proton reduction of a strong acid p–toluenesulfonic acid (p–HOTs), mediated by complexes 2 and 3, have been described.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Reaction of N–heterocyclic 1,2-dithiols with Fe2(CO)9 yields the title compounds. ► These complexes serve as model systems for the active site of [FeFe]-hydrogenase. ► The electrochemistry of these model compounds have been described. ► Electro-catalytic proton reduction has been demonstrated.