Unexpected Formation of Metallofulleroids from Multicomponent Reactions, with Crystallographic and Computational Studies of the Cluster Motion

Abstract

New multicomponent reactions involving an isocyanide, terminal or internal alkynes, and endohedral metallofullerene (EMF) Lu 3 N@C 80 yield metallofulleroids which are characterized by mass-spectrometry, HPLC, and multiple 1D and 2D NMR techniques. Single crystal studies revealed one ketenimine metallofulleroid has ordered Lu 3 N cluster which is unusual for EMF monoadducts. Computational analysis, based on crystallographic data, confirm that the endohedral cluster motion is controlled by the position of the exohedral organic appendants. Our findings provide a new functionalization reaction for EMFs, and a potential facile approach to freeze the endohedral cluster motion at relatively high temperatures.

Multicomponent Reactions Among Alkyl Isocyanides, sp Reactants, and sp2 Carbon Cages

“…Not reported in our papers, 27 28 similar reactions were performed on Lu 3 N@C 80 . The reaction involving 7a , t -BuNC and Lu 3 N@C 80 gives only one product spot on TLC (although the combined conversion rate is rather low), which was isolated via flash chromatography and then studied with HPLC on 5PYE column (Figure 2b ).…”

“…30 Replacing the triple bond with cumulated double bonds, ethyl buta-2, 3-dienoate 7a and dimethyl 2, 3-pentadienedioate 7b, the allenoate counterpart of 1a and DMAD, were attempted in the multicomponent reactions, which yielded 8a and 8b from four-component reactions among t-BuNC, allenoate, C 60 , and one molecule of water. 28 Not reported in our papers, 27,28 similar reactions were performed on Lu 3 N@C 80 . The reaction involving 7a, t-BuNC and Lu 3 N@C 80 gives only one product spot on TLC (although the combined conversion rate is rather low), which was isolated via flash chromatography and then studied with HPLC on 5PYE column (Figure 2b).…”

“…We started with the multicomponent reactions among Lu 3 N@C 80 , t -BuNC and an EWG-bearing terminal alkyne, with the EWG being a carbonyl or an ester group ( 1a – c in Scheme 3 ). 27 All three generated a dominate product in decent yields. Then, keeping an ester EWG, we changed the terminal alkynes to internal alkynes, none of the 1d – f worked, and the only exception was the symmetric internal alkyne DMAD.…”

“…As cycloadditions dominate the successful reactions on NCFs, one strategy to develop new reactions is to find reactive species that can react with alkenes, similar to the diene in a Diels–Alder reaction or the 1,3-dipole in a Prato reaction. In our recent work, 27 28 we had our eye on sp -hybridized carbon reactants linked to an electron-withdrawing group (EWG), which react with alkyl isocyanide to generate reactive dipolar species, to be captured by a third, alkenyl reactant. These multicomponent reactions have been widely used to construct cyclic structures in organic synthesis using alkynes 29 and allenes.…”

“…We carefully examined the report and found that the structural elucidation of the products lacked crystallographic proof, while the spectroscopic characterization of the [2+2] product was rather ambiguous. Therefore, we explored the utility of the isocyanide-induced reactions with various sp -hybridzed substrates, on fullerene C 60 28 and EMF Lu 3 N@ I h -C 80 27 concurrently. In the notably stable family of M 3 N@ I h -C 80 , Lu and Sc are the more inert members, 32 which means if the reactions on Lu 3 N@C 80 were successful, they are likely to work on other EMFs as well.…”