Chemical studies of diiron complexes related to Fe-only hdrogenase /
The focus of my research is the study of the fundamental properties of diiron organometallic complexes of the type ([]-SRS)[Fe(CO)₃]₂ as models of the [Fe]H₂ase active site. An interesting feature of these complexes is their reaction with CN⁻ to readily substitute CO and give dicyanide derivatives w...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
2002.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=765073151&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | The focus of my research is the study of the fundamental properties of diiron organometallic complexes of the type ([]-SRS)[Fe(CO)₃]₂ as models of the [Fe]H₂ase active site. An interesting feature of these complexes is their reaction with CN⁻ to readily substitute CO and give dicyanide derivatives with one CN- on each Fe atom. A series of (m-SRS)[Fe(CO)3]2 complexes with different bridges were employed in kinetic studies of CN⁻/CO exchange that showed a complicated R-dependent reactivity pattern for the first CN⁻ addition. The explanation of the kinetic results came in combination with the fluxional mobility of the Fe(CO)₃ units in these complexes that results in basal/apical CO site exchange. The relationship of this fluxionality and the reactivity of the molecule towards CN⁻ was substantiated by DFT calculations that modeled these intramolecular processes and found that the semi-bridging []-CO that results from the Fe(CO)₃ unit rotation is also formed upon CN⁻ attack. Thus, the assumption that the Fe(CO)₃ rotational barrier is an important contributor to the overall activation energy of CN⁻ attack, explains the experimental observation that generally the second CN⁻ addition finds a lower Fe(CO)₃ rotational barrier due to the presence of the already coordinated CN⁻ ligand. From the above Fe¹Fe¹ complexes, homovalent Fe[II]Fe[II] complexes can be obtained through binuclear oxidative addition of electrophiles such as H⁺ or SMe⁺ to yield Fe[II]([]-H)Fe[II] or Fe[II]([]-SMe)Fe[II] respectively. These complexes serve as functional models of [Fe]H₂ase based on hydrogenase activity test reactions that typically involve H/D exchange reactivity in H₂/D₂O or H₂/D₂/H₂O mixtures. Activity studies using the Fe[II]Fe[II] complexes {([]-H)([]-pdt)[Fe(CO)₂(PMe₃)]₂}⁺ and {([]-SMe)([]-pdt)[Fe(CO)₂(PMe₃)]₂}⁺ indicated that both demonstrate H₂ (or D₂) uptake and heterolytic cleavage by D₂O (or H₂O) under photolytic conditions. The singular requirement for these processes is an open site on an Fe[II] center. Studies using the nitrogen-containing bridged complex ([]-SCH₂N(Me)CH₂S)[Fe(CO)₃]₂ suggest that the lone pair on the nitrogen induces instability to the complex and it is responsible for decomposition of the bridge or even split of the dinuclear to a mononuclear complex. This is a phenomenon that has not been observed in any of the hydrocarbon bridged compounds. |
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| Item Description: | Vita. "Major Subject: Chemistry". |
| Physical Description: | xvi, 178 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 144-150). |