Synthesis and Electrochemistry of Electronegative Spiroannelated Methanofullerenes: Theoretical Underpinning of the Electronic Effect of Addends and a Reductive Cyclopropane Ring-Opening Reaction
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- 作者：Brian Knight ; Nazario Martí ; n ; Toshinobu Ohno ; Enrique Ortí ; Concepció ; Rovira ; Jaume Veciana ; José ; Vidal-Gancedo ; Pedro Viruela ; Rafael Viruela ; and Fred Wudl
- 刊名：Journal of the American Chemical Society
- 出版年：1997
- 出版时间：October 15, 1997
- 年：1997
- 卷：119
- 期：41
- 页码：9871 - 9882
- 全文大小：289K
- 年卷期：v.119,no.41(October 15, 1997)
- ISSN：1520-5126
文摘
Spiroannelated methanofullerenes bearing quinone-type addendsincluding TCNQ and DCNQI analogues(3a-c, 6a,b,8, 10, and 11) have been prepared, andtheir structural and electronic properties have beencharacterizedby both experimental techniques and quantum-chemical calculations.The spiro[2,5-cyclohexadienone-4,61'-methanofullerene] derivatives(3a-c), thespiro[10-anthrone-9,61'-methanofullerene] (8),and the TCNQ- and DCNQI-type derivatives (10 and 11) were isolated as[6,6] adducts. Thespiro[cyclohexanone-4,61'-methanofullerene](6)was however obtained as a mixture of [5,6] and [6,6] isomers.The novel methanofullerenes, with the only exceptionof 6, show irreversible cyclic voltammograms with additionalreduction peaks. The conjugated cyclohexadienonederivatives 3 exhibit better acceptor abilities than theparent C60. Semiempirical PM3 calculations show thattheaddend lies perpendicular to the transanular bond in 3,while it folds down and adopts a butterfly shapedstructurefor compounds 8, 10, and 11. Forcompounds 3, periconjugative interactions transmit theinductive effect of theaddend and produce a small stabilization of the orbitals ofC60, resulting in a less negative first-reductionpotentialscompared to C60. For compounds 8,10, and 11, the folding of the addend preventspericonjugative effects. Theoreticalcalculations performed on3a
-and 3a2- at the semiempirical(PM3), density functional (B3P86/3-21G), and abinitio (HF/6-31G*) levels indicate that the attachment of the firstelectron causes the homolytic cleavage of one ofthe bonds connecting the addend to C60. The resultingopen-cyclopropane structure is stabilized by thearomaticityof the phenoxyl radical structure presented by the addend. Thesecond electron enters in the addend forming thephenoxyl anion. This ring opening is supported by ESR measurementsand explains the irreversible electrochemicalbehavior of compounds 3. The nonconjugated nature ofthe cyclohexanone ring in 6 determines that reductiontakesplace via a closed-cyclopropane structure with an electrochemicalbehavior similar to that observed for C60.Compounds 8, 10, and 11 areproposed to undergo reduction via an open-cyclopropane structure nowobtained afterthe attachment of the second electron which produces the heterolyticopening of the cyclopropane ring. The lack ofplanarity shifts the reduction of the addend to more negativepotentials.
-and 3a2- at the semiempirical(PM3), density functional (B3P86/3-21G), and abinitio (HF/6-31G*) levels indicate that the attachment of the firstelectron causes the homolytic cleavage of one ofthe bonds connecting the addend to C60. The resultingopen-cyclopropane structure is stabilized by thearomaticityof the phenoxyl radical structure presented by the addend. Thesecond electron enters in the addend forming thephenoxyl anion. This ring opening is supported by ESR measurementsand explains the irreversible electrochemicalbehavior of compounds 3. The nonconjugated nature ofthe cyclohexanone ring in 6 determines that reductiontakesplace via a closed-cyclopropane structure with an electrochemicalbehavior similar to that observed for C60.Compounds 8, 10, and 11 areproposed to undergo reduction via an open-cyclopropane structure nowobtained afterthe attachment of the second electron which produces the heterolyticopening of the cyclopropane ring. The lack ofplanarity shifts the reduction of the addend to more negativepotentials.