Organometallic models for the active site of Fe-only hydrogenase /
A series of dinuclear complexes, ([]-SRS)Fe₂(CO)₆, have been examined for specific characteristics that might relate to structural similarity with the active site of Fe-only hydrogenases. Two approaches have been taken in this endeavor: the first is to address how changes in the dithiolate bridge a...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2000.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=726066931&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | A series of dinuclear complexes, ([]-SRS)Fe₂(CO)₆, have been examined for specific characteristics that might relate to structural similarity with the active site of Fe-only hydrogenases. Two approaches have been taken in this endeavor: the first is to address how changes in the dithiolate bridge affect the physical features and reactivity of the complex towards CN⁻ producing ([]-SRS)Fe₂(CO)₄(CN)₂²⁻; and, the second is to synthesize dithiolate bridges that contain a functional group which is able to coordinate to the metal, i.e., a tridentate ligand, or is able to interact in such a way as to produce an asymmetric model complex. Three complexes with 2, 3, and 4 carbon links between the sulfurs have been used throughout this work, ([]-SRS)Fe₂(CO)₆ where R = -CH₂CH₂₋, -CH₂CH₂CH₂₋, -CH₂C₆H₄CH₂₋ (edt, pdt, o-xyldt, respectively). Kinetic studies of the intermolecular CN⁻/CO exchange established sequential associative steps to the formation of the dianion, ([]-SRS)Fe₂(CO)₄(CN)₂²⁻. The reaction rates for the ethanedithiolate (edt) and propanedithiolate (pdt)-bridged diiron hexacarbonyl complexes were nearly identical. The xylenedithiolate-bridged complex, on the other hand, displayed a dramatic increase in the rate of the first CN⁻/CO exchange to produce ([]-xyldt)Fe₂(CO)₅(CN)⁻ but displayed very similar rates for the second exchange reaction. Variable temperature NMR studies show the fluxionality of the irondithiocyclohexane unit in ([]-pdt)Fe₂(CO)₆ while in the ([]-xyldt)Fe₂(CO)₆ complex the bridge is fixed to one side in our temperature range. C-13 NMR studies revealed an intramolecular CO site exchange process that was influenced by the identity of the []-SRS unit. Theoretical calculations (DFT) of transition state structures for the intramolecular CO site exchange suggest cooperativity between intermolecular ligand exchange and intramolecular coordination sphere flexibility. Several new compounds having functional groups within the organic linker were synthesized with the intention of placing an internal base (or []-donating ligand) in close proximity to the Fe(CO)₃ unit. These novel complexes have displayed several features which provide information regarding stability and reactivity. First, ([]-SRS)Fe₂(CO)₆ complexes show greater preference for short linked dithiolates, with a propensity to form 2-atom linkers when given the opportunity. The second is that ironcarbonyls are reductive toward the dithiolate bridge; reduction of both [S₂C₂(CN)₂][=] and [SCH₂CH₂SCH₂CH₂S][=] was observed. |
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| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | xvii, 171 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 132-138). |