Pushing the Ir-Catalyzed C-H Polyborylation of Aromatic Compounds to Maximum Capacity by Exploiting Reversibility

The Scott lab is pursuing the functionalization of corannulene to prepare molecular building blocks for the assembly of large polycyclic aromatic hydrocarbons and carbon nanotube end-cap precursors. Toward that end, a new approach to the direct five-fold borylation of corannulene via C-H activation with bis(pinacolato)diborane and iridium (I) catalyst has been explored. It has been discovered that the addition of catalytic amounts of base to the reaction mixture favors formation of the symmetrical penta-borylated corannulene by promoting reversibility of the borylation. Continuous deborylation and reborylation of undesired compounds leads to the product with the maximum number of Bpin groups, 1,3,5,7,9-pentakis(Bpin)corannulene, which has been isolated in high yield by methanol precipitation. Several other aromatic compounds have been successfully polyborylated by this new Ir-catalyzed borylation method.