Using Naphthalene-2-Thiolate Ligands in the Design of Hydrogenase Models With Mild Proton Reduction Overpotentials

Diiron-carbonyl complexes coupled to naphthalene-2-thiolate ligands, [(μ-naphthalene-2-thiolato)2Fe2(CO)6 (1) and [(μ-naphthalene-2-thiolato)2Fe2(CO) 5PPh3 (2), have been usefully prepared and structurally characterized. As models for the active site of hydrogenase enzymes, these compounds have been examined as electrocatalysts for the reduction of proton to produce molecular hydrogen. In the presence of acetic acid, 1 and 2 catalyze the electrochemical production of molecular hydrogen with mild overpotentials of -0.54 and -0.51 V versus Fc/Fc+, respectively. The overpotential for compound 1 is 260 mV smaller than that of the analogous compound, [(μ-SPh)2Fe2(CO)6. © 2012 Elsevier Ltd. All rights reserved

Phenylthiolate-Diironhexacarbonyl Complexes: A Comparative Conceptual DFT and Electrochemical Study

The electrocatalytic reduction of acetic acid by the previously studied [(μ-biphenyl-2,2€²-dithiolato)2Fe2(CO)6 (1), has been explored. Complex 1 generates hydrogen at -2.53 V versus Fc/Fc+. Comparatively, the overpotential for the reduction of protons to hydrogen by 1 (1.07 V vs Fc/Fc+) is higher by 270 mV than that of the non-bridging analog [(μ-SPh)2Fe2(CO)6 (2). Global reactivity descriptors, chemical hardness and electrophilicity index for 1 and 2 have been computed from frontier molecular orbital energies determined using HF and DFT/B3LYP methods. The results indicate that complex 1 is softer with a higher electrophilicity index than 2, in agreement with the minimum electrophilicity principle

[Fe-Fe] Hydrogenase Models: Iron(I)-Carbonyl Clusters Coupled To Alpha- and Para-Toluenethiolate Ligands

Two linkage isomers composing of diironhexacarbonyl clusters coupled to α and p-toluenethiolate ligands have been usefully prepared in moderate yields. The composition of both compounds, [(μ2-(p-toluenethiolato))2Fe2(CO)6] (1) and [(μ2-(α-toluenethiolato))2Fe2(CO)6] (2), have been determined by elemental analysis and NMR spectroscopy. A tetrairondodecacarbonyl complex, [μ4-S(μ2-(α-toluenethiolato)Fe2(CO)6)2] (3), was isolated from the reaction mixture of 2. The molecular structures of 2 and 3 determined by X-ray diffraction are discussed. An exploration of the influence of the α- and p-toluenethiolate ligands on the electronic and electrochemical properties of the iron-carbonyl units have been accomplished using infrared spectroscopy, UV–Vis spectroscopy and cyclic voltammetry. In the presence of acetic acid, compounds 1, 2 and 3 catalyze the electrochemical generation of molecular hydrogen. The proton reduction overpotentials for compounds 1 and 2 were determined to be 0.76 V and 0.85 V versus Fc/Fc+ respectively in acetonitrile as solvent. Comparatively, compound 1 produces hydrogen at an overpotential 90 mV lower than compound 2

Iron(I)-Carbonyl Clusters Tethered To (Trifluoromethyl)Thiophenolates

Two diironhexacarbonyl clusters containing (trifluoromethyl)thiophenolates, as models for the active site of [Fe-Fe hydrogenase enzyme, have been prepared and characterized. The crystal and electronic structures of the complexes have been probed by X-ray crystallography and spectroscopic methods. Cyclic voltammetric studies in the presence of acetic acid show that both compounds catalyze the electrochemical reduction of acetic acid to produce hydrogen with favorable overpotentials. © Springer Science+Business Media B.V. 2012

Synthesis of Diiron Hydrogenase Mimics Bearing Hydroquinone and Related Ligands. Electrochemical and Computational Studies of the Mechanism of Hydrogen Production and the Role of O-H S Hydrogen Bonding

A new synthetic method for annulating hydroquinones to Fe2S 2(CO)6 moieties is reported. Piperidine catalyzed a multistep reaction between Fe2(μ-SH)2(CO)6 and quinones to afford bridged adducts in 26-76% yields. The hydroquinone adducts undergo reversible two-electron reductions. In the presence of acetic acid, hydrogen is produced catalytically with these adducts at potentials more negative than that of the initial reversible reduction. Spectroscopic studies suggest the presence of intramolecular hydrogen bonding between the phenolic OH groups and the adjacent sulfur atoms. Computations, which are in good agreement with the electrochemical studies and spectroscopic data, indicate that the hydrogen bonding is most important in the reduced forms of the catalysts. This hydrogen bonding lowers the reduction potential for catalysis but also lowers the basicity and thereby the reactivity of the catalysts. © 2010 American Chemical Society

[Fe-Fe] hydrogenase models: Iron(I)-carbonyl clusters coupled to alpha- and para-toluenethiolate ligands

Two linkage isomers composing of diironhexacarbonyl clusters coupled to α and p-toluenethiolate ligands have been usefully prepared in moderate yields. The composition of both compounds, [(μ2-(p-toluenethiolato))2Fe2(CO)6] (1) and [(μ2-(α-toluenethiolato))2Fe2(CO)6] (2), have been determined by elemental analysis and NMR spectroscopy. A tetrairondodecacarbonyl complex, [μ4-S(μ2-(α-toluenethiolato)Fe2(CO)6)2] (3), was isolated from the reaction mixture of 2. The molecular structures of 2 and 3 determined by X-ray diffraction are discussed. An exploration of the influence of the α- and p-toluenethiolate ligands on the electronic and electrochemical properties of the iron-carbonyl units have been accomplished using infrared spectroscopy, UV-Vis spectroscopy and cyclic voltammetry. In the presence of acetic acid, compounds 1, 2 and 3 catalyze the electrochemical generation of molecular hydrogen. The proton reduction overpotentials for compounds 1 and 2 were determined to be 0.76 V and 0.85 V versus Fc/Fc+ respectively in acetonitrile as solvent. Comparatively, compound 1 produces hydrogen at an overpotential 90 mV lower than compound 2