Electrocatalytic dihydrogen evolution mechanism of [Fe2(CO)4(kappa(2)-Ph2PCH2CH2PPh2)(mu-S(CH2)3S)] and related models of the [FeFe]-hydrogenases active site: a DFT investigation.
A DFT study of protonation thermodynamics in H(2)-evolving biomimetic catalysts related to [FeFe]-hydrogenases active site is presented here. Taking as a reference system the electrocatalytic dihydrogen evolution mechanism recently proposed for the synthetic assembly [Fe(2)(CO)(4)(kappa(2)-Ph(2)PCH(2)CH(2)PPh(2))(mu-S(CH(2))(3)S)] (a, which is able to release H(2) after having undergone monoelectron reduction steps and three sequential protonation reactions), we show how the reduction of model complexes to oxidation states lower than those observed in [FeFe]-hydrogenases cofactor leads to a protonation regiochemistry that has no counterpart in the enzymatic mechanism of H(2) production. In particular, double protonation of the metal centers turned out to be disfavored in a by up to 12.5 kcal mol(-1) with respect to alternative protonation paths; as for the regiochemistry of triple protonation, the formation of eta(2)-H(2) adducts is disfavored by at least approximately 25 kcal mol(-1). Structural analysis of the theoretical models also revealed that over-reduction of synthetic complexes, though necessary for observing H(2) evolution from the currently available biomimetic electrocatalysts, can generally impair their structural integrity. Possible approaches for the modulation of protonation regiochemistry are then proposed; in particular, it turned out that a targeted use of sigma-donating ligands showing low basicity can favor double protonation of iron centers.
Greco
Claudio
C
Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2 20126-Milan. Italy. claudio.greco@unimib.it
Fantucci
Piercarlo
P
De Gioia
Luca
L
Suarez-Bertoa
Ricardo
R
Bruschi
Maurizio
M
Talarmin
Jean
J
Schollhammer
Philippe
P
D002384:Catalysis; D020134:Catalytic Domain; D056831:Coordination Complexes / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D006864:Hydrogenase / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D008958:Models, Molecular; D013816:Thermodynamics
D056831:Coordination Complexes; D005296:Ferrous Compounds; D007506:Iron-Sulfur Proteins; D006859:Hydrogen; C118830:iron hydrogenase; D006864:Hydrogenase