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Essential factors for control of the equilibrium in the reversible rearrangement of M3N@Ih-C80 fulleropyrrolidines: Exohedral functional groups versus endohedral metal clusters

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The effects of exohedral moieties and endohedral metal clusters on the isomerization of M3N@Ih-C80 products from the Prato reaction through [1,5]-sigmatropic rearrangement were systematically investigated by using three types of fulleropyrrolidine derivatives and four different endohedral metal clusters. As a result, all types of derivatives provided the same ratios of the isomers for a given trimetallic nitride template (TNT) as the thermodynamic products, thus indicating that the size of the endohedral metal clusters inside C80 was the single essential factor in determining the equilibrium between the [6,6]-isomer (kinetic product) and the [5,6]-isomer. In all the derivatives, the [6,6]- and [5,6]-Prato adducts with larger metal clusters, such as Y3N and Gd3N, were equally stable, which is in good agreement with DFT calculations. The reaction rate of the rearrangement was dependent on both the substituent of exohedral functional groups and the endohedral metal-cluster size. Further DFT calculations and 13C NMR spectroscopic studies were employed to rationalize the equilibrium in the rearrangement between the [6,6]- and [5,6]-fulleropyrrolidines

The authors are grateful to the computer resources, technical expertise, and assistance provided by the Barcelona Supercomputing Center (Centro Nacional de Supercomputacion) and technical assistance provided by the NMR service in the Laboratorium fur Organische Chemie in ETH. This study was supported in part by the Swiss National Foundation (200021 140451 (Y.Y.)); ETH Individual Investigator’s Research Award (ETH-2511- 1 (Y.Y.)); PRESTO program from JST (Y.Y.); American Heart Association Researcher’s Developing Grant (0930140N (Y.Y.)); Spanish MECD for a PhD fellowship (AP2010-2517 (M.G.B.)); Spanish MINECO for projects CTQ2011-23156/BQU, CTQ2011-25086/BQU, and Juan de la Cierva postdoctoral grant (JCI-2012-14438 (S.O.)); and the European Community for CIG project (PCIG14-GA-2013-630978 (S.O.)

Elsevier