Normal vs. Inverted Ordering of Reduction Potentials in [FeFe]‐Hydrogenases Biomimetics: Effect of the Dithiolate Bulk
Federica Arrigoni, Luca De Gioia, Catherine Elléouet, François Y. Pétillon, Philippe Schollhammer, Jean Talarmin, Giuseppe Zampella
Abstract
Abstract Three hexacarbonyl diiron dithiolate complexes [Fe 2 (CO) 6 (μ‐(SCH 2 ) 2 X)] with different substituted bridgeheads (X=CH 2 , CEt 2 , CBn 2 (Bn=CH 2 C 6 H 5 )), have been studied under the same experimental conditions by cyclic voltammetry in dichloromethane [NBu 4 ][PF 6 ] 0.2 M. DFT calculations were performed to rationalize the mechanism of reduction of these compounds. The three complexes undergo a two‐electron transfer whose the mechanism depends on the bulkiness of the dithiolate bridge, which involves a different timing of the structural changes (Fe−S bond cleavage, inversion of conformation and CO bridging) vs redox steps. The introduction of a bulky group in the dithiolate linker has obviously an effect on normally ordered (as for propanedithiolate (pdt)) or inverted (pdt Et2 , pdt Bn2 ) reduction potentials. Et→Bn replacement is not theoretically predicted to alter the geometry and energy of the most stable mono‐reduced and bi‐reduced forms but such a replacement alters the kinetics of the electron transfer vs the structural changes.