The Key Role of Aromaticity in Determining the Molecular Structure and

Reactivity of (Endohedral Metallo)Fullerenes

M. Garcia-Borràs,1 S. Osuna,1 M.Swart,1,2 J.M. Luis,1 Miquel Solà1 1 Institut de Química Computacional and Departament de Química, Universitat de Girona, Campus

Montilivi, 17071 Girona, Catalonia, Spain 2 Institució Catalana de Recerca i Estudis Avançats (ICREA), Pg. Lluís Companys 23, 08010

Barcelona, Catalonia, Spain marc.garcia@udg.edu

Encapsulation of metal clusters in endohedral metallofullerenes takes place in cages

that in most cases are far from being the most stable isomer in the corresponding hollow fullerenes.1 In large metal clusters and small fullerene cages, the election is mainly driven by the need to reduce strain. For the not so large metal clusters, it is usually said that the cage is chosen to minimize the electrostatic repulsion between charged five-membered rings.2 We have proved that maximizing the aromaticity is the main driving force that determines the most suitable hosting carbon cage for a given metallic cluster.3 This simple rule, the so-called Maximum ARomaticity Criterion, allow us to directly compare IPR (isolated pentagon rule) and non-IPR anionic isomers regardless the number of adjacent pentagon pairs (APP) they have. We have tested our aromaticity criterion for the majority of endohedral metallofullerenes from C66 to C104 reported to date and the results show that this criterion successfully predicts the most suitable C2n cage for hosting a given metal cluster among the manifold existing C2n isomers. In addition, using the Maximum ARomaticity Criterion, one can justify for the first time why the IPR rule is not always fulfilled when EMFs are considered. Finally, we have introduced the aromaticity as a tool for analyzing and predicting the reactivity of different organic reactions on EMF structures with successful results.4,5

References: 1. M. N. Chaur, F. Melin, A. L. Ortiz and L. Echegoyen, Angew. Chem. Int. Ed., 48, 7514 (2009). 2. M. Garcia-Borràs, S. Osuna, M. Swart, J.M. Luis, and M. Solà, Angew. Chem. Int. Ed., 52, 9275 (2013). 3. M. Garcia-Borràs, S. Osuna, M. Swart, J.M. Luis, and M. Solà, Chem. Soc. Rev., Accepted for publication,

DOI: 10.1039/C4CS00040D (2014). 4. M. Garcia-Borràs, S. Osuna, M. Swart, J.M. Luis, L. Echegoyen, and M. Solà, Chem. Commun., 49, 8767

(2013). 5. M. Garcia-Borràs, S. Osuna, M. Swart, J.M. Luis, and M. Solà, Chem. Commun., 49, 1220 (2013).