Density functional theory was used to compare reaction pathways for H <sub>2</sub> formation and H<sup>+</sup> reduction catalyzed by models of the binuclear cluster found in the active site of [Fe] hydrogenases. Terminal H <sup>+</sup> binding to an Fe<sup>I</sup>-Fe<sup>I</sup> form, followed by monoelectron reduction and protonation of the di(thiomethyl)amine ligand, can conveniently lead to H<sub>2</sub> formation and release, suggesting that this mechanism could be operative within the enzyme active site. However, a pathway that implies the initial formation of Fe<sup>II</sup>-Fe<sup>II</sup> μ-H species and release of H<sub>2</sub> from an Fe<sup>II</sup>-Fe<sup>I</sup> form is characterized by only slightly less favored energy profiles. In both cases, H<sub>2</sub> formation becomes less favored when taking into account the competition between CN and amine groups for H<sup>+</sup> binding, an observation that can be relevant for the design of novel synthetic catalysts. H<sub>2</sub> cleavage can take place on Fe<sup>II</sup>-Fe<sup>II</sup> redox species, in agreement with previous proposals [Fan, H.-J.; Hall, M. B. J. Am. Chem. Soc. 2001, 123, 3828] and, in complexes characterized by terminal CO groups, does not need the involvement of an external base. The step in H <sub>2</sub> oxidation characterized by larger energy barriers corresponds to the second H<sup>+</sup> extraction from the cluster, both considering Fe <sup>II</sup>-Fe<sup>II</sup> and Fe<sup>II</sup>-Fe<sup>III</sup> species. A comparison of the different reaction pathways reveals that H<sup>2</sup> formation could involve only Fe<sup>I</sup>-Fe<sup>I</sup>, Fe <sup>II</sup>-Fe<sup>I</sup>, and Fe<sup>II</sup>-Fe<sup>II</sup> species, whereas Fe<sup>III</sup>-Fe<sup>II</sup> species might be relevant in H <sub>2</sub> cleavage. © 2006 American Chemical Society.
Zampella, G., Greco, C., Fantucci, P., DE GIOIA, L. (2006). Proton Reduction and Dihydrogen Oxidation on Models of the [2Fe]H Cluster of [Fe]-Hydrogenases. A DFT Investigation. INORGANIC CHEMISTRY, 45(10), 4109-4118 [10.1021/ic051986m].
Proton Reduction and Dihydrogen Oxidation on Models of the [2Fe]H Cluster of [Fe]-Hydrogenases. A DFT Investigation.
ZAMPELLA, GIUSEPPE;GRECO, CLAUDIO;FANTUCCI, PIERCARLO;DE GIOIA, LUCA
2006
Abstract
Density functional theory was used to compare reaction pathways for H 2 formation and H+ reduction catalyzed by models of the binuclear cluster found in the active site of [Fe] hydrogenases. Terminal H + binding to an FeI-FeI form, followed by monoelectron reduction and protonation of the di(thiomethyl)amine ligand, can conveniently lead to H2 formation and release, suggesting that this mechanism could be operative within the enzyme active site. However, a pathway that implies the initial formation of FeII-FeII μ-H species and release of H2 from an FeII-FeI form is characterized by only slightly less favored energy profiles. In both cases, H2 formation becomes less favored when taking into account the competition between CN and amine groups for H+ binding, an observation that can be relevant for the design of novel synthetic catalysts. H2 cleavage can take place on FeII-FeII redox species, in agreement with previous proposals [Fan, H.-J.; Hall, M. B. J. Am. Chem. Soc. 2001, 123, 3828] and, in complexes characterized by terminal CO groups, does not need the involvement of an external base. The step in H 2 oxidation characterized by larger energy barriers corresponds to the second H+ extraction from the cluster, both considering Fe II-FeII and FeII-FeIII species. A comparison of the different reaction pathways reveals that H2 formation could involve only FeI-FeI, Fe II-FeI, and FeII-FeII species, whereas FeIII-FeII species might be relevant in H 2 cleavage. © 2006 American Chemical Society.
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