Charles A. Mebi

Diironhexacarbonyl clusters with imide and amine ligands: hydrogen evolution catalysts

The reaction of Fe3(CO)12 and N-(4-thiolphenyl)-1,8-naphthalimide afforded a new diironhexacarbonyl complex (3). The integrity and electronic structure of 3 has been determined by elemental analysis and spectroscopy (NMR and infrared). Infrared spectrum of 3 shows peaks at 2000, 2040, and 2075 cm−1 ascribed to stretching frequencies of the terminal metal carbonyls. Compound 4 was obtained from the reaction of Fe3(CO)12 and 4-aminothiolphenol. A comparison of the electronic, electrochemical, and electrocatalytic properties of 3 and 4 are discussed. Cyclic voltammetric studies show that 3 and 4 catalyze the reduction of acetic acid to produce hydrogen at −2.19 V and −1.88 V versus Fc/Fc+, respectively.

Biomimetic hydrogen generation catalyzed by triironnonacarbonyl disulfide cluster

Triironnonacarbonyl disulfide cluster, a stable and synthetic precursor for active site models of [Fe-Fe] hydrogenase enzyme, has been evaluated as catalyst for the electrochemical generation of hydrogen by cyclic voltammetry. In the presence of acetic acid, Fe3S2(CO)9 catalyzes the reduction of proton to hydrogen at -2.24 V (vs. Fc/Fc+) with an overpotential of -0.78 V (acetonitrile as solvent). The overpotential is comparable to those reported for diironcarbonyl models of [Fe-Fe] hydrogenase.

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.

Diironcarbonyl-coumarin complex: preparation, intramolecular electron transfer, and electro-generation of hydrogen

AbstractA new organometallic complex coupling photoactive coumarin to a diironhexacarbonyl unit has been successfully prepared and its composition and electronic structure confirmed by elemental and spectroscopic analyses. Emission spectral analysis of the complex reveals photoinduced intramolecular electron transfer from coumarin to the iron-carbonyl moiety. The compound is electrochemically reduced at −1.24 V vs. Fc/Fc+. This reduction is irreversible, attesting to the instability of the complex. Electrochemical evolution of hydrogen in the presence of the complex has been studied and results are discussed.

Catalysis of Electrochemical Reduction of Weak Acids to Produce H2: Role of O‒H…S Hydrogen Bonding

Abstract The role of intramolecular OH…S hydrogen bonding in the electrochemical reduction of protons from acetic acid using biomimetically inspired catalysts has been studied. The catalysts, hydroquinone moieties annulated to an Fe2S2(CO)6 core, were synthesized by piperidine-mediated conjugate addition of the dithiol Fe2(SH)2(CO)6 to quinones in 26–76% yields. These complexes catalyze electrochemical H2 production from acetic acid. Evidence for weak intramolecular OH…S hydrogen bonding in the neutral complexes is presented. Such hydrogen bonding becomes stronger as the charge increases on the sulfur in the electrochemically produced dianions due to “charge assistance,” and this has chemical consequences.

Crystal and electronic structure of a hexa­carbonyl­diiron cluster tethered to naphthalene-2-thiol­ate ligands

The structure of the previously reported complex bis(μ-naphthalene-2-thiolato-κ2S:S)bis(tricarbonyliron)(Fe-Fe), [Fe2(C10H7S)2(CO)6], has been characterized by X-ray diffraction. In the solid state, the dinuclear complex adopts a butterfly-like shape, with an equatorial-axial spatial orientation of the naphthalene groups covalently coupled to the [S2Fe2(CO)6] unit. The asymmetric unit contains three independent [(μ-naphthalene-2-thiolato)2Fe2(CO)6] molecules. These molecules show intermolecular π-π stacking interactions between the naphthalene rings, which was confirmed by Hirshfield surface analysis. The electronic spectrum of the complex recorded in acetonitrile shows a band centered at 350 nm (ℇ = 4.6 × 103 M-1 cm-1) and tailing into the visible region. This absorption can be attributed to a π→π* electronic transition within the naphthalene moiety and a metal-based d→d transition.