Angew. Chem. Int. Ed. http://doi.org/f3ms3z (2016)

The controlled synthesis of fullerenes with two functional groups, known as bis-adducts, is a topic of keen interest for exploiting these molecules in materials. However, this is not trivial given the number of near-identical double bonds on C60. Previous controlled syntheses have only been possible by tethering with a covalently linked spacer. Now, Dirk Guldi of the Friedrich-Alexander University in Nurenburg and Tomás Torres from the Autonomous University of Madrid, along with colleagues in Spain, Germany, Japan and the US, have devised a supramolecular-directed functionalization approach to form C60 bis-adducts with regio-, stereo- and atropselectivity.

Zinc (II) phthalocyanine (Pc) aldehydes were mixed with N-methylglycine and C60 to give the right- (P) and left-handed (M) helical forms of a single bis-adduct. Without this control, up to 130 adducts with different regio- and stereochemistry could form. Non-covalent (π-stacking) interactions between the two ZnIIPc arms give solely the cis C60 addition product. Remarkably, the bis-adduct was isolated in 14% yield, a 2,800-fold increase from the theoretical yield, and significantly higher than those from untethered reactions (∼1.4%). This also represents the first atropselective reaction with fullerenes; the atropisomerism results from the restricted rotation of the two macrocycles to give a fullerene derivative with point, axial and helical chirality.