Supramolecular Mask-Mediated Regioselective bis-Bingel-Functionalization of M3N@Ih-C80 (M = Lu, Sc)

Exohedral functionalization of endohedral metallofullerenes (EMFs) is essential for exploiting these intriguing molecules as novel materials in applications such as biomedicine and organic solar cell device design. In the case of trimetallic nitride template EMFs (TNT-EMFs), many functionalization methods effective for empty fullerenes are inaccessible or less efficient due to the presence of the encapsulated cluster. This inner cluster increases the electron density on the carbon cage surface, reducing its reactivity. Moreover, it has been demonstrated that the inner cluster controls both the reactivity and regioselectivity of bare TNT-EMFs. The supramolecular mask strategy (SMS) has yielded promising results in the functionalization of C60 and C70 and, for the first time, is applied here to endohedral fullerenes to achieve mono- and bis-functionalization of Lu3N@Ih-C80 and Sc3N@Ih-C80. Encapsulation of both TNT-EMFs within a tetragonal prismatic cage host is crucial for enhancing their reactivity, enabling bis-functionalization under milder conditions and with shorter reaction times. Comprehensive spectroscopic and spectrometric characterization, combined with molecular dynamics (MD) simulations and density functional theory (DFT) calculations, identified the most favorable and stable bis-adducts by considering the positive alignment between the geometry imposed by the inner cluster and that allowed by the tetragonal prismatic nanocapsule mask. This resulted in preferential formation of five bis-adducts (out of 27 possible), two of them bearing a 120° angle between the addends and aligning with the inner TNT cluster trigonal geometry.