Exceptional Chemical Properties of Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ Probed with Adamantylidene Carbene

Abstract

It has been an interesting finding that reactions of M@<i>C</i>_2<i>v</i>(9)–C₈₂ (M = Y, La, Ce, Gd) with diazirine adamantylidene (AdN₂, <b>1</b>) gave rise to only two monoadduct isomers, indicating that the cage reactivity of monometallofullerenes is not dependent on the type of the internal metal. However, we found here that Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ shows an exceptional chemical reactivity toward the electrophile <b>1</b>, affording four monoadduct isomers (<b>2a</b>–<b>d</b>). Single-crystal X-ray diffraction crystallographic results of the most abundant isomer (<b>2a</b>) confirm that the addition takes place at a [6,6]-bond junction which is very close to the internal metal ion. Theoretical calculations reveal that 2 out of the 24 nonequivalent cage carbons of Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ are highly reactive toward <b>1</b>, but only one cage carbon of the other M@<i>C</i>_2<i>v</i>–C₈₂ (M = Y, La, Ce, Gd) is sufficiently reactive. The exceptional chemical property of Sc@<i>C</i>_2<i>v</i>(9)–C₈₂ is associated with the small ionic radius of Sc³⁺, which allows stronger metal–cage interactions and makes back-donation of charge from the cage to the metal more pronounced. Our results have provided new insights into the art of altering the chemical properties of fullerene molecules at the atomic level, which would be useful in the future in utilizing EMFs in quantum computing systems