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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Organometallic Complexes that Model the Active Sites of the [FeFe]- and [Fe]-Hydrogenases

Liu, Tianbiao 2009 December 1900 (has links)
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.

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