Playing with Protic Additives to Improve the Outcome of Rhodium-Catalyzed Hydroarylation of Fullerene C60 with Arylboronic Acids

A new one-phase process for hydroarylation of C₆₀ fullerene using arylboronic acids and a rhodium catalyst in an aromatic solvent containing soluble protic additives is described. Yields of monohydroarylated product with tert-butanol and water as the protic additive range from 14 to 50 % depending on which arylboronic acid is used after reaction times of 4 hours or less which is a significant improvement from the outcome of reactions carried out using conditions from the literature. Accurate monitoring of reaction outcomes was achieved by a combination of UV-Vis spectroscopy and ¹H-NMR spectroscopy: C₆₀ conversion was determined using an analytical HPLC-UV-vis method employing commonly available columns for the separation, while product formation was quantified by ¹H-NMR spectroscopy with an internal standard. Moreover, two new arylboronic acids carrying 4-alkynyl aryl substituents, synthesized using Sonogashira couplings, are reported, as well as the use of these in the hydroarylation of C₆₀.