Steric effect of the dithiolato linker on the reduction mechanism of [Fe2(CO)6{μ-(XCH2)2CRR'}] hydrogenase models (X = S, Se).

Studying the redox features of the [FeFe]-hydrogenase models is essential for understanding the function of the H cluster. The reduction of the [FeFe]-hydrogenase models of the type [Fe2(CO)6{μ-(XCH2)2E}] (X = S, Se) is described to occur either via sequential transfer of two electrons at and for the first and the second reduction steps, respectively, where , or via transfer of two electrons at the same applied potential due to potential inversion of the two reduction steps, i.e.. Typically, the phenomenon of potential inversion is observed when a structural change intervenes in the cathodic process stabilizing the reduced species. In this report, we investigate the mechanism of the cathodic process of series of models [Fe2(CO)6{μ-(XCH2)2E}] (X = S or Se and E = CH2, CHMe or CMe2) applying cyclic voltammetry. The studies herein show the remarkable influence of the steric bulk of E toward the cathodic process, such that only complexes with E = CMe2 are reduced with inverted potentials due to occurrence of an ECE mechanism (E = electrochemical process, C = chemical process) of reduction. Moreover, we describe the catalytic behaviour of these models toward reduction of protons using acetic acid, AcOH, as a proton source.