DUGi

The role of aromaticity in determining the molecular structure and reactivity of (endohedral metallo)fullerenes

http://dugi.udg.edu/item/http:@@@@hdl.handle.net@@2072@@295610

The encapsulation of metal clusters in endohedral metallofullerenes (EMFs) takes place in cages that in most cases are far from being the most stable isomer in the corresponding hollow fullerenes. There exist several possible explanations for the choice of the hosting cages in EMFs, although the final reasons are actually not totally well understood. Moreover, the reactivity and regioselectivity of (endohedral metallo)fullerenes have in the past decade been shown to be generally dependent on a number of factors, such as the size of the fullerene cage, the type of cluster that is being encapsulated, and the number of electrons that are transferred formally from the cluster to the fullerene cage. Different rationalizations of the observed trends had been proposed, based on bond lengths, pyramidalization angles, shape and energies of (un)occupied orbitals, deformation energies of the cages, or separation distances between the pentagon rings. Recently, in our group we proposed that the quest for the maximum aromaticity (maximum aromaticity criterion) determines the most suitable hosting carbon cage for a given metallic cluster (i.e. EMF stabilization), including those cases where the IPR rule is not fulfilled. Moreover, we suggested that local aromaticity plays a determining role in the reactivity of EMFs, which can be used as a criterion for understanding and predicting the regioselectivity of different reactions such as Diels-Alder cycloadditions or Bingel-Hirsch reactions. This review highlights different aspects of the aromaticity of fullerenes and EMFs, starting from how this can be measured and ending by how it can be used to rationalize and predict their molecular structure and reactivity

The following organizations are thanked for financial support: the Ministerio de Ciencia e Innovacion (MICINN, project numbers CTQ2011-23156/BQU and CTQ2011-25086/BQU), the Generalitat de Catalunya (projects number 2009SGR637 and 2009SGR528 and Xarxa de Referencia en Quimica Teorica i Computacional), and the FEDER fund (European Fund for Regional Development) for the grant UNGI08-4E-003. M. G.-B. thanks the Spanish MEC for a doctoral fellowship no. AP2010-2517. S.O. thanks the MICINN for the Juan de la Cierva fellowship and the European Community for the CIG project (FP7-PEOPLE-2013-CIG-630978). The authors are also grateful to the computer resources, technical expertise, and assistance provided by the Barcelona Supercomputing Center Centro Nacional de Supercomputacion. Support for the research of M. Sola was received through the ICREA Academia 2009 prize for excellence in research funded by the DIUE of the Generalitat de Catalunya. Excellent service by the Centre de Serveis Cientifics i Academics de Catalunya (CESCA) is gratefully acknowledged

Elsevier