Full Exploration of the Diels–Alder Cycloaddition on Metallofullerenes M3N@C80 (M=Sc, Lu, Gd): The D5h versus Ih Isomer and the Influence of the Metal Cluster

Abstract

In this work a detailed investigation of the exohedral reactivity of the most important and abundant endohedral metallofullerene (EMF) is provided, that is, Sc3N@Ih-C80 and its D5h counterpart Sc3N@D5h-C80, and the (bio)chemically relevant lutetium- and gadolinium-based M3N@Ih/D5h-C80 EMFs (M=Sc, Lu, Gd). In particular, we analyze the thermodynamics and kinetics of the Diels–Alder cycloaddition of s-cis-1,3-butadiene on all the different bonds of the Ih-C80 and D5h-C80 cages and their endohedral derivatives. First, we discuss the thermodynamic and kinetic aspects of the cycloaddition reaction on the hollow fullerenes and the two isomers of Sc3N@C80. Afterwards, the effect of the nature of the metal nitride is analyzed in detail. In general, our BP86/TZP//BP86/DZP calculations indicate that [5,6] bonds are more reactive than [6,6] bonds for the two isomers. The [5,6] bond D5h-b, which is the most similar to the unique [5,6] bond type in the icosahedral cage, Ih-a, is the most reactive bond in M3N@D5h-C80 regardless of M. Sc3N@C80 and Lu3N@C80 give similar results; the regioselectivity is, however, significantly reduced for the larger and more electropositive M=Gd, as previously found in similar metallofullerenes. Calculations also show that the D5h isomer is more reactive from the kinetic point of view than the Ih one in all cases which is in good agreement with experiments

The following organizations are thanked for financial support: the Ministerio de Ciencia e Innovacion (MICINN; project numbers CTQ2008-06532/BQU, CTQ2008-06549-C02-01/BQU, CTQ2011-23156/BQU, and CTQ2011-25086/BQU), the DIUE of the Generalitat de Catalunya (project numbers 2009SGR637, 2009SGR528, 2009SGR462, and XRQTC), and the European Community (postdoctoral fellowship PIOF-GA-2009-252856). Excellent service by the Centre de Serveis Cientifics i Academics de Catalunya (CESCA) is gratefully acknowledged. 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