Proton Shuttle Mediated by (SCH<sub>2</sub>)<sub>2</sub>P═O Moiety in [FeFe]-Hydrogenase Mimics: Electrochemical and DFT Studies
Laith R. Almazahreh, Federica Arrigoni, Hassan Abul‐Futouh, Mohammad El‐khateeb, Helmar Görls, Catherine Elléouet, Philippe Schollhammer, Luca Bertini, Luca De Gioia, Manfred Rudolph, Giuseppe Zampella, Wolfgang Weigand
Abstract
The synthesis, characterization, and protonation of [Fe2(CO)6{(μ-SCH2)2(Et)P═O}] (1) using the moderately strong acid CF3CO2H (pKaMeCN = 12.7) are reported. Digital simulations of the cyclic voltammetry of 1 in the presence of CF3CO2H and DFT calculations have allowed us to obtain a detailed mechanistic picture of the processes underlying the catalytic hydrogen evolution reaction (HER) that 1 can mediate. Moreover, DFT has shed light on the role of the P═O functionality in the whole catalytic cycle of proton reduction. The reductive behavior of 1 features a double electron transfer with potential inversion, which is associated with deep structural rearrangement of the catalyst. The double reduction appears also functional to the intramolecular proton transfer from the P═O group to the diiron core, a crucial process for the H+/H– heterocoupling yielding H2. The key intermediate for the H2 formation and release is predicted to be a 3H+/3e– species, in which P═O is perfectly poised to shuttle protons from solution to the Fe–H–Fe moiety. Therefore, the R-P═O bridgehead installed in a dithiolato linker of a diiron core proves a valid and versatile alternative to the natural nitrogen-based Fe2 strap.