Triiron clusters derived from dinuclear complexes related to the active site of [Fe-Fe] hydrogenases: Steric effect of the dithiolate bridge on redox properties, a DFT analysis

A series of triiron clusters [Fe3(CO)5(κ2-dppe)(μ-pdtR2)(μ-pdt)] featuring different combinations of dithiolate bridges have been prepared by using dinuclear and mononuclear precursors, [Fe2(CO)6(μ-xdt)] (xdt = pdt, pdtEt2, pdtBn2, adtBn) and [Fe(CO)2(κ2-dppe)(κ2-pdt)]. Novel triiron compounds, featuring sterically crowded dithiolate bridges (pdtEt2, pdtBn2), were spectroscopically and structurally characterized. Their protonation and redox behaviours are discussed. The effect of the dithiolate bridges on the electrochemical properties (oxidation and reduction) of the complexes [Fe3(CO)5(κ2-dppe)(μ-xdt)(μ-pdt)] has been examined by cyclic voltammetry and rationalized by DFT calculations. Studies on the protonation of these species and their proton reduction behaviour were considered.