This dissertation describes computational and experimental studies of synthetic
complexes that model the active site of the iron-iron hydrogenase [FeFe]H2ase enzyme.
Simple dinuclear iron dithiolate complexes act as functional models of the ironiron
hydrogenase enzyme by catalyzing isotopic exchange in D2/H2O mixtures. Density
Functional Theory (DFT) calculations and new experiments have been performed that
suggest reasonable mechanistic explanations for this reactivity. Evidence for the
existence of an acetone derivative of the di-iron complex, as suggested by theory, is
presented.
Bis-phosphine substituted dinuclear iron dithiolate complexes react with the
electrophilic species, H+ and Et+ (Et+ = CH3CH2
+) with differing regioselectivity; H+
reacts to form a 3c-2eâ Fe-H-Fe bond, while Et+ reacts to form a new C-S bond. The
instability of a bridging ethyl complex is attributed to the inability of the ethyl group, in
contrast to a hydride, to form a stable 3c-2eâ bond with the two iron centers.
Gas-phase density functional theory calculations are used to predict the solutionphase
infrared spectra for a series of CO and CN-containing dinuclear iron complexes
dithiolate. It is shown that simple linear scaling of the computed C-O and C-N stretching frequencies yields accurate predictions of the experimentally determined ν(CO) and
ν(CN) values.
An N-heterocyclic carbene containing [FeFe]H2ase model complex, whose X-ray
structure displays an apical carbene, is shown to undergo an unexpected simultaneous
two-electron reduction. DFT shows, in addition to a one-electron Fe-Fe reduction, that
the aryl-substituted N-heterocyclic carbene can accept a second electron more readily
than the Fe-Fe manifold. The juxtaposition of these two one-electron reductions
resembles the [FeFe]H2ase active site with an FeFe di-iron unit joined to the
electroactive 4Fe4S cluster.
Simple synthetic di-iron dithiolate complexes synthesized to date fail to
reproduce the precise orientation of the diatomic ligands about the iron centers that is
observed in the molecular structure of the reduced form of the enzyme active site.
Herein, DFT computations are used for the rational design of synthetic complexes as
accurate structural models of the reduced form of the enzyme active site.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1014 |
| Date | 15 May 2009 |
| Creators | Tye, Jesse Wayne |
| Contributors | Darensbourg, Marcetta Y., Hall, Michael B. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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