My research primarily focuses on biomimetics of the active sites of the [FeFe]- and
[Fe]-hydrogenases (H2ase) and is classified into three parts.
Part A: The one-electron oxidation of asymmetrically disubstituted FeIFeI models of
the active site of the [FeFe]-H2ase, (mu-pdt)[Fe(CO)2PMe3][Fe(CO)2NHC] (pdt = 1,3-
propanedithiolate, NHC = N-heterocyclic carbene) generates mixed valent FeIIFeI
models of the Hox state of [FeFe]-hydrogenase. The spectroscopic properties, structures,
reactivities and relative stabilities of the one-electron oxidized mixed valent complexes,
(mu-pdt)(mu-CO)[FeII(CO)2PMe3][FeI(CO)NHC]+ are discussed in the context of
experimental and theoretical data and biological relevance.
Part B: DFT computations find the Fe-Fe bond in the FeIFeI diiron models ((mu-
pdt)[Fe(CO)2L][Fe(CO)2L'] ( L, L' = CO, PPh3, or PMe3) is thermodynamically favored
to produce the mu-oxo or oxidative addition product, FeII-O-FeII, nevertheless the sulfurbased
HOMO-1 accounts for the experimentally observed mono- and bis-O-atom
adducts at sulfur. The FeII(mu-H)FeII diiron model, (mu-pdt)(mu-H)[Fe(CO)2PMe3]2 (IV-5), for which the HOMO is largely of sulfur character, exclusively yields S-oxygenation.
Deoxygenation with reclamation of the mu-pdt parent complexes occurs in a
proton/electron coupled process. The possible biological relevance of oxygenation and
deoxygenation studies is discussed.
Comprehensive investigations of intramolecular CO site change and intermolecular
CO/L (L = PMe3 or CN-) exchange of (mu-pst)[Fe(CO)3]2 (IV-1-O), (mu-pdt)[Fe(CO)3]2
(V-1), and their mono-CN-/PMe3 substituted derivatives indicated that the factors
influencing the rate of the CO/L exchange reaction of such diiron carbonyls are
intramolecular structural rearrangement (or fluxionality) and nucleophilic attack by the
incoming ligand.
Part C: X-ray diffraction and spectroscopic studies of a series of mono- and disubstituted
complexes, FeI2(CO)xL4-x, x = 2 or 3, showed them to be rudimentary
structural models of the [Fe]-H2ase active site in native (FeII(CO)2) or CO-inhibited
(FeII(CO)3) states. Full characterization of the advanced model complexes
((NS)FeI(CO)2P, NS = 2-amidophenothiolate; P = phosphine) including x-ray
diffraction, DFT computations, and Mossbauer studies revealed the interesting "noninnocent"
character of these complexes due to the NS ligand. Ligand-based protonation
with a strong acid, HBF4Et2O, interrupted the pi-delocalization over Fe and ligand of
complex VII-1 and switched on CO uptake (1 bar) and 12CO/ 13CO exchange of VII-1.
The intermediate, VII-1-H+, capable of CO uptake, was defined by DFT calculations.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-12-7344 |
| Date | 2009 December 1900 |
| Creators | Liu, Tianbiao |
| Contributors | Darensbourg, Marcetta Y. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | application/pdf |
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