UVM Theses and Dissertations
Format:
Print
Author:
Stewart, Michael P.
Dept./Program:
Chemistry
Year:
2010
Degree:
PhD
Abstract:
Several avenues oforganic and organometallic chemistry have been advanced through the use of non-aqueous anodic electrochemistry.
An electrochemical process is described for the rapid and efficient conversion of unsubstituted cyclic olefins into cycloaddition products. When a potential of 1.3 V vs Fc ⁰/ was applied to a solution of cis-cyclooctene in [NBu₄][TFAB] / CH₂Cl₂ containing a catalytic amount (5 mol %) of CpRe(CO)₃ the olefin was converted to a diastereomeric mixture of the cyclodimerization product, C₁₆H₂₄, with the major isomer having a cisanti-cisgeometry. Smaller cyclicolefins (C₅ to C-- membered ring compounds) also formed cycloaddition products.
The cyclization reactions require the electrogeneration of [CpRe(CO)₃] as an electron-transfer mediator which triggers the one-electron oxidation of the olefin in spite of the fact that the potentials of the latter lie at considerably higher values. The electrochemical conversion of cis-cyclooctene to cyclized products is complete in a few minutes, in contrast to the week-long photochemical processes previously needed for preparation of the same cycloaddition products. Comparisons are made between the efficacy of CpRe(CO)₃ and the organic N(C₆H₃Br₂)₃ in its role as an electron transfer mediator under the described conditions.
A method for the redox initiated haptotropic rearragenment of chromium naphthohydroquinoids is presented. Anodic oxidation has provided a means of initiating an [Greek Eta]⁶ to [Greek Eta]⁶ haptotropic migration for a chromium tricarbonyl moiety along a naphthohydroquinoid skeleton. Undermining the strength of the chromium arene bond by anodic oxidation decreases the activation energy necessary to facilitate this migration at temperatures as low as -20° C. Yields of ca. 60% pure isomerized material have been obtained by the described electrochemical method. Confinnation of this isomerization has been attained by means of voltammetric and infrared analysis. An alternative chemical isomerization procedure has also been presented which features [thianthrene][TFAB] as a one-electron oxidant. This chemical oxidation induced method also produced pure isomerized material but at a lower yield of ca. 30 %.
Anodic voltammetry and electrolysis of the metallocenes ferrocene, ruthenocene, and nickelocene have been studied in dichloromethane containing two different fluorine-containing anions in the supporting electrolyte, [Al(OC(CF₃)₃)₄]⁻ and [AsF₆]⁻. In terms of applications of these two anions to the anodic oxidation of organometallic sandwich complexes, the behavior of [Al(OC(CFCF₃)₃)₄]⁻ is similar to that of other weakly-coordinating anions such as [TFAB]⁻, whereas that of [AsF₆]⁻ is similar to the more traditional electrolyte anions such as PF₆]⁻ and [BF₄]⁻.
Fundamental voltammetry for a series of half-sandwich manganese group complexes involving the [Greek Eta]⁶-PhC₃B--H₉ ligand have been presented. Redox potentials and electrochemical behavior for each of the observed processes have been collected. Deviations in behavior from their more familiar cyclopentadienyl counterparts are particularly noted. An electrochemical ligand factor, EL, of 0.63 was calculated for the tricarbadecaboranyl ligand based on the data collected in this study.
An electrochemical process is described for the rapid and efficient conversion of unsubstituted cyclic olefins into cycloaddition products. When a potential of 1.3 V vs Fc ⁰/ was applied to a solution of cis-cyclooctene in [NBu₄][TFAB] / CH₂Cl₂ containing a catalytic amount (5 mol %) of CpRe(CO)₃ the olefin was converted to a diastereomeric mixture of the cyclodimerization product, C₁₆H₂₄, with the major isomer having a cisanti-cisgeometry. Smaller cyclicolefins (C₅ to C-- membered ring compounds) also formed cycloaddition products.
The cyclization reactions require the electrogeneration of [CpRe(CO)₃] as an electron-transfer mediator which triggers the one-electron oxidation of the olefin in spite of the fact that the potentials of the latter lie at considerably higher values. The electrochemical conversion of cis-cyclooctene to cyclized products is complete in a few minutes, in contrast to the week-long photochemical processes previously needed for preparation of the same cycloaddition products. Comparisons are made between the efficacy of CpRe(CO)₃ and the organic N(C₆H₃Br₂)₃ in its role as an electron transfer mediator under the described conditions.
A method for the redox initiated haptotropic rearragenment of chromium naphthohydroquinoids is presented. Anodic oxidation has provided a means of initiating an [Greek Eta]⁶ to [Greek Eta]⁶ haptotropic migration for a chromium tricarbonyl moiety along a naphthohydroquinoid skeleton. Undermining the strength of the chromium arene bond by anodic oxidation decreases the activation energy necessary to facilitate this migration at temperatures as low as -20° C. Yields of ca. 60% pure isomerized material have been obtained by the described electrochemical method. Confinnation of this isomerization has been attained by means of voltammetric and infrared analysis. An alternative chemical isomerization procedure has also been presented which features [thianthrene][TFAB] as a one-electron oxidant. This chemical oxidation induced method also produced pure isomerized material but at a lower yield of ca. 30 %.
Anodic voltammetry and electrolysis of the metallocenes ferrocene, ruthenocene, and nickelocene have been studied in dichloromethane containing two different fluorine-containing anions in the supporting electrolyte, [Al(OC(CF₃)₃)₄]⁻ and [AsF₆]⁻. In terms of applications of these two anions to the anodic oxidation of organometallic sandwich complexes, the behavior of [Al(OC(CFCF₃)₃)₄]⁻ is similar to that of other weakly-coordinating anions such as [TFAB]⁻, whereas that of [AsF₆]⁻ is similar to the more traditional electrolyte anions such as PF₆]⁻ and [BF₄]⁻.
Fundamental voltammetry for a series of half-sandwich manganese group complexes involving the [Greek Eta]⁶-PhC₃B--H₉ ligand have been presented. Redox potentials and electrochemical behavior for each of the observed processes have been collected. Deviations in behavior from their more familiar cyclopentadienyl counterparts are particularly noted. An electrochemical ligand factor, EL, of 0.63 was calculated for the tricarbadecaboranyl ligand based on the data collected in this study.