Proton Shuttle Mediated by (SCH2)2PO Moiety in [FeFe]-Hydrogenase Mimics: Electrochemical and DFT Studies

• Published in: ACS catalysis 2021-06, Vol.11 (12), p.7080-7098
• Main Authors: Almazahreh, Laith R, Arrigoni, Federica, Abul-Futouh, Hassan, El-khateeb, Mohammad, Görls, Helmar, Elleouet, Catherine, Schollhammer, Philippe, Bertini, Luca, De Gioia, Luca, Rudolph, Manfred, Zampella, Giuseppe, Weigand, Wolfgang
• Format: Article
• Language: English
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.0c05563

The synthesis, characterization, and protonation of [Fe2(CO)6{(μ-SCH2)2(Et)­PO}] (1) using the moderately strong acid CF3CO2H (pK a MeCN = 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.