Preparation and Characterization of [FeFe]-Hydrogenase Active Site Mimics Studied by Gas-Phase Photoelectron Spectroscopy, Electrochemistry, and Computational Models

Persistent Link:
http://hdl.handle.net/10150/311862
Title:
Preparation and Characterization of [FeFe]-Hydrogenase Active Site Mimics Studied by Gas-Phase Photoelectron Spectroscopy, Electrochemistry, and Computational Models
Author:
Stratton, Laura M.
Issue Date:
2012
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.
Embargo:
Release 03-Dec-2013
Abstract:
Hydrogen is an attractive fuel because it is clean, carbon neutral, energy dense, and sustainable, but in order for a hydrogen economy to become a reality it is necessary to develop inexpensive and efficient methods of hydrogen production. The [FeFe]-hydrogenase enzymes are efficient at catalyzing the reduction of protons to dihydrogen. Nature-inspired functional active site mimics which feature sulfur and iron have been the focus of much research, yet there are still challenges to overcome. The challenges of the [FeFe]-H₂ase active site mimic catalysts which are addressed in this dissertation are (1) the reversibility of the catalyst to reduction and (2) the overpotential required to achieve catalytic activity. One of the active site-inspired catalysts is (μ-1,3-propanedithiolato)diironhexacarbonyl. When studied by cyclic voltammetry, CV, this catalyst produces hydrogen but also transforms into catalytically inactive products. (μ-2,4-pentanedithiolato)diironhexacarbonyl, 3, was prepared and found be fully reversible to reduction at all scan rates, indicating that it does not decompose on the CV timescale. Compound 3 is prepared as a mixture of cis and trans isomers. The trans isomer is able to undergo inversion of the bridgehead and the cis isomer is fixed with no evidence of bridgehead fluxionality. NMR studies verify proton assignments and the barrier of inversion for the fluxional trans compound. DFT studies indicate that multiple pathways to catalysis are possible for 1 depending upon the pKₐ of acid present and the potential applied. [FeFe]-H₂ase-inspired catalysts which produce hydrogen in the presence of a weak acid require a higher than desired overpotential. To overcome this, an ideal catalyst would use captured solar energy to produce hydrogen. The catalyst (μ-1,2-benzenedithiolato)diironhexacarbonyl 5, is well studied and understood. Thiophene has a π-system that is isoelectronic with benzene. Thiophenes are air-stable and may be polymerized into electrically conductive polymers which may be light active. The catalyst (μ-3,4-thiophenedithiolato)diironhexacarbonyl, 6, was prepared as a proof of concept model for catalysts with polythiophene features. As predicted, compound 6 was found to reduce protons at the same potential as 5. DFT computations indicate these catalysts go through the same catalytic mechanisms. X-ray crystal structures indicate similar bond lengths and angles.
Type:
text; Electronic Dissertation
Keywords:
Chemistry; Inorganic chemistry
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Chemistry
Degree Grantor:
University of Arizona
Advisor:
Lichtenberger, Dennis L.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titlePreparation and Characterization of [FeFe]-Hydrogenase Active Site Mimics Studied by Gas-Phase Photoelectron Spectroscopy, Electrochemistry, and Computational Modelsen_US
dc.creatorStratton, Laura M.en_US
dc.contributor.authorStratton, Laura M.en_US
dc.date.issued2012-
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.releaseRelease 03-Dec-2013en_US
dc.description.abstractHydrogen is an attractive fuel because it is clean, carbon neutral, energy dense, and sustainable, but in order for a hydrogen economy to become a reality it is necessary to develop inexpensive and efficient methods of hydrogen production. The [FeFe]-hydrogenase enzymes are efficient at catalyzing the reduction of protons to dihydrogen. Nature-inspired functional active site mimics which feature sulfur and iron have been the focus of much research, yet there are still challenges to overcome. The challenges of the [FeFe]-H₂ase active site mimic catalysts which are addressed in this dissertation are (1) the reversibility of the catalyst to reduction and (2) the overpotential required to achieve catalytic activity. One of the active site-inspired catalysts is (μ-1,3-propanedithiolato)diironhexacarbonyl. When studied by cyclic voltammetry, CV, this catalyst produces hydrogen but also transforms into catalytically inactive products. (μ-2,4-pentanedithiolato)diironhexacarbonyl, 3, was prepared and found be fully reversible to reduction at all scan rates, indicating that it does not decompose on the CV timescale. Compound 3 is prepared as a mixture of cis and trans isomers. The trans isomer is able to undergo inversion of the bridgehead and the cis isomer is fixed with no evidence of bridgehead fluxionality. NMR studies verify proton assignments and the barrier of inversion for the fluxional trans compound. DFT studies indicate that multiple pathways to catalysis are possible for 1 depending upon the pKₐ of acid present and the potential applied. [FeFe]-H₂ase-inspired catalysts which produce hydrogen in the presence of a weak acid require a higher than desired overpotential. To overcome this, an ideal catalyst would use captured solar energy to produce hydrogen. The catalyst (μ-1,2-benzenedithiolato)diironhexacarbonyl 5, is well studied and understood. Thiophene has a π-system that is isoelectronic with benzene. Thiophenes are air-stable and may be polymerized into electrically conductive polymers which may be light active. The catalyst (μ-3,4-thiophenedithiolato)diironhexacarbonyl, 6, was prepared as a proof of concept model for catalysts with polythiophene features. As predicted, compound 6 was found to reduce protons at the same potential as 5. DFT computations indicate these catalysts go through the same catalytic mechanisms. X-ray crystal structures indicate similar bond lengths and angles.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectChemistryen_US
dc.subjectInorganic chemistryen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_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.committeememberWalker, F. Annen_US
dc.contributor.committeememberEnemark, John H.en_US
dc.contributor.committeememberGlass, Richard S.en_US
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