Spectroscopic, Electrochemical, and Computational Studies on an [FeFe]-Hydrogenase Active Site Mimic with a Terthiophene Bridging the 2Fe2S Core

Persistent Link:
http://hdl.handle.net/10150/321551
Title:
Spectroscopic, Electrochemical, and Computational Studies on an [FeFe]-Hydrogenase Active Site Mimic with a Terthiophene Bridging the 2Fe2S Core
Author:
Sill, Steven M.
Issue Date:
2014
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
As a means of reducing the dependence on fossil fuels, generation of hydrogen (H₂) has been proposed as a route for storing energy in a chemical bond. To access this energy, H₂ can be combusted with oxygen or used in a fuel to release the energy stored in the chemical bond, while generating water as the byproduct. To generate the hydrogen necessary to fuel a hydrogen economy, an energy efficient and stable catalyst needs to be designed. The work presented in this thesis describes the investigation of a catalytic mimic inspired by the [FeFe]-hydrogenase enzyme. The design of this and similar mimics have been pursued as the active site of the enzyme is composed of readily available and abundant elements, and has a turnover rate of 6000-9000 molecules of H₂ s⁻¹. The catalyst in this work was studied via cyclic voltammetry and density functional theory calculations to determine the catalytic activity as well as a mechanism for H₂ production of the complex. The complex 2,5-bis-(2',2"-thiophen-2-yl)-thiophene-µ-3,4-dithiolato)diiron hexacarbonyl, 1, was prepared and found to catalyze the production of molecular hydrogen in CH₂Cl₂, however the overpotential for catalysis was not determined as the standard potential of acetic acid in CH₂Cl₂ is not known. Comparison of the catalytic potentials of terthiophene-cat to µ-(1,2-benzenedithiolato)diiron hexacarbonyl, 2, and µ-(3,4-thiophenedithiolato)diiron hexacarbonyl, 3, in CH₂Cl₂ showed that 1 had a less negative potential (0.14 V and 0.16 V, respectively) for the catalytic reduction of protons to H₂. Electrochemical investigations combined with density functional theory (DFT) indicated that 1 has an ECEC mechanism for the reduction of protons, where E is an electrochemical step and C is a chemical process. The proposed mechanism for 1 is similar to that of 2 and 3, with 1 catalyzing the production of H₂ using acetic acid at a less negative potential than 2 and 3.
Type:
text; Electronic Dissertation
Keywords:
Chemistry
Degree Name:
M.S.
Degree Level:
masters
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona
Advisor:
Lichtenberger, Dennis L.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen
dc.titleSpectroscopic, Electrochemical, and Computational Studies on an [FeFe]-Hydrogenase Active Site Mimic with a Terthiophene Bridging the 2Fe2S Coreen_US
dc.creatorSill, Steven M.en_US
dc.contributor.authorSill, Steven M.en_US
dc.date.issued2014-
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractAs a means of reducing the dependence on fossil fuels, generation of hydrogen (H₂) has been proposed as a route for storing energy in a chemical bond. To access this energy, H₂ can be combusted with oxygen or used in a fuel to release the energy stored in the chemical bond, while generating water as the byproduct. To generate the hydrogen necessary to fuel a hydrogen economy, an energy efficient and stable catalyst needs to be designed. The work presented in this thesis describes the investigation of a catalytic mimic inspired by the [FeFe]-hydrogenase enzyme. The design of this and similar mimics have been pursued as the active site of the enzyme is composed of readily available and abundant elements, and has a turnover rate of 6000-9000 molecules of H₂ s⁻¹. The catalyst in this work was studied via cyclic voltammetry and density functional theory calculations to determine the catalytic activity as well as a mechanism for H₂ production of the complex. The complex 2,5-bis-(2',2"-thiophen-2-yl)-thiophene-µ-3,4-dithiolato)diiron hexacarbonyl, 1, was prepared and found to catalyze the production of molecular hydrogen in CH₂Cl₂, however the overpotential for catalysis was not determined as the standard potential of acetic acid in CH₂Cl₂ is not known. Comparison of the catalytic potentials of terthiophene-cat to µ-(1,2-benzenedithiolato)diiron hexacarbonyl, 2, and µ-(3,4-thiophenedithiolato)diiron hexacarbonyl, 3, in CH₂Cl₂ showed that 1 had a less negative potential (0.14 V and 0.16 V, respectively) for the catalytic reduction of protons to H₂. Electrochemical investigations combined with density functional theory (DFT) indicated that 1 has an ECEC mechanism for the reduction of protons, where E is an electrochemical step and C is a chemical process. The proposed mechanism for 1 is similar to that of 2 and 3, with 1 catalyzing the production of H₂ using acetic acid at a less negative potential than 2 and 3.en_US
dc.typetexten
dc.typeElectronic Dissertationen
dc.subjectChemistryen_US
thesis.degree.nameM.S.en_US
thesis.degree.levelmastersen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineChemistryen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorLichtenberger, Dennis L.en_US
dc.contributor.committeememberLichtenberger, Dennis L.en_US
dc.contributor.committeememberGlass, Richard S.en_US
dc.contributor.committeememberZheng, Zhipingen_US
dc.contributor.committeememberTomat, Elisaen_US
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