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Diels-Alder and Retro-Diels-Alder cycloadditions of (1,2,3,4,5-pentamethyl)cyclopentadiene to La@C2v-C82: Regioselectivity and product stability

One of the most important reactions in fullerene chemistry is the Diels–Alder (DA) reaction. In two previous experimental studies, the DA cycloaddition reactions of cyclopentadiene (Cp) and 1,2,3,4,5-pentamethylcyclopentadiene (Cp*) with La@C2v-C82 were investigated. The attack of Cp was proposed to occur on bond 19, whereas that of Cp* was confirmed by X-ray analysis to be over bond o Moreover, the stabilities of the Cp and Cp* adducts were found to be significantly different, that is, the decomposition of La@C2v-C82Cp was one order of magnitude faster than that of La@C2v- C82Cp*. Herein, we computationally analyze these DA cycloadditions with two main goals: First, to compute the thermodynamics and kinetics of the cycloadditions of Cp and Cp* to different bonds of La@C2v-C82 to assess and compare the regioselectivity of these two reactions. Second, to understand the origin of the different thermal stabilities of the La@C82Cp and La@C82Cp* adducts. Our results show that the regioselectivity of the two DA cycloadditions is the same, with preferred attack on bond o. This result corrects the previous assumption of the regioselectivity of the Cp attack that was made based only on the shape of the La@C82 singly occupied molecular orbital. In addition, we show that the higher stability of the La@C82Cp* adduct is not due to the electronic effects of the methyl groups on the Cp ring, as previously suggested, but to higher long-range dispersion interactions in the Cp* case, which enhance the stabilization of the reactant complex, transition state, and products with respect to the separated reactants. This stabilization for the La@C82Cp* case decreases the Gibbs reaction energy, thus allowing competition between the direct and retro reactions and making dissociation more difficult

The following organizations are thanked for financial support: the Ministerio de Ciencia e Innovaci n (MICINN, project numbers CTQ2011-23156/BQU and CTQ2011-25086/BQU), the Generalitat de Catalunya (project numbers 2009SGR637 and 2009SGR528 and Xarxa de Refer ncia en Qu mica Te rica i Computacional), and the FEDER fund (European Fund for Regional Development, grant number UNGI08-4E-003). M.G.-B. thanks the Spanish MEC for a doctoral fellowship (number AP2010-2517)

© Chemistry - A European Journal, 2013, vol. 19, núm. 14, p. 4468 – 4479

http://hdl.handle.net/10256/11399

Wiley-VCH Verlag

Author: Garcia Borràs, Marc
Luis Luis, Josep Maria
Swart, Marcel
Solà i Puig, Miquel
Date: 2013
Abstract: One of the most important reactions in fullerene chemistry is the Diels–Alder (DA) reaction. In two previous experimental studies, the DA cycloaddition reactions of cyclopentadiene (Cp) and 1,2,3,4,5-pentamethylcyclopentadiene (Cp*) with La@C2v-C82 were investigated. The attack of Cp was proposed to occur on bond 19, whereas that of Cp* was confirmed by X-ray analysis to be over bond o Moreover, the stabilities of the Cp and Cp* adducts were found to be significantly different, that is, the decomposition of La@C2v-C82Cp was one order of magnitude faster than that of La@C2v- C82Cp*. Herein, we computationally analyze these DA cycloadditions with two main goals: First, to compute the thermodynamics and kinetics of the cycloadditions of Cp and Cp* to different bonds of La@C2v-C82 to assess and compare the regioselectivity of these two reactions. Second, to understand the origin of the different thermal stabilities of the La@C82Cp and La@C82Cp* adducts. Our results show that the regioselectivity of the two DA cycloadditions is the same, with preferred attack on bond o. This result corrects the previous assumption of the regioselectivity of the Cp attack that was made based only on the shape of the La@C82 singly occupied molecular orbital. In addition, we show that the higher stability of the La@C82Cp* adduct is not due to the electronic effects of the methyl groups on the Cp ring, as previously suggested, but to higher long-range dispersion interactions in the Cp* case, which enhance the stabilization of the reactant complex, transition state, and products with respect to the separated reactants. This stabilization for the La@C82Cp* case decreases the Gibbs reaction energy, thus allowing competition between the direct and retro reactions and making dissociation more difficult
The following organizations are thanked for financial support: the Ministerio de Ciencia e Innovaci n (MICINN, project numbers CTQ2011-23156/BQU and CTQ2011-25086/BQU), the Generalitat de Catalunya (project numbers 2009SGR637 and 2009SGR528 and Xarxa de Refer ncia en Qu mica Te rica i Computacional), and the FEDER fund (European Fund for Regional Development, grant number UNGI08-4E-003). M.G.-B. thanks the Spanish MEC for a doctoral fellowship (number AP2010-2517)
Format: application/pdf
ISSN: 0947-6539 (versió paper)
1521-3765 (versió electrònica)
Document access: http://hdl.handle.net/10256/11398
Language: eng
Publisher: Wiley-VCH Verlag
Collection: MICINN/PN 2012-2014/CTQ2011-23156
MICINN/PN 2012-2014/CTQ2011-25086
AGAUR/2009-2014/2009 SGR-637
AGAUR/2009-2014/2009 SGR-528
Reproducció digital del document publicat a: http://dx.doi.org/0.1002/chem.201203517
Articles publicats (D-Q)
Is part of: © Chemistry - A European Journal, 2013, vol. 19, núm. 14, p. 4468 – 4479
See also: http://hdl.handle.net/10256/11399
Rights: Tots els drets reservats
Subject: Reaccions d’addició
Addition reactions
Diels-Alder, Reacció de
Diels-Alder reaction
Ful·lerens
Fullerenes
Ciclització (Química)
Ring formation (Chemistry)
Title: Diels-Alder and Retro-Diels-Alder cycloadditions of (1,2,3,4,5-pentamethyl)cyclopentadiene to La@C2v-C82: Regioselectivity and product stability
Type: info:eu-repo/semantics/article
Repository: DUGiDocs

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