Stable Borocyclic Radicals via Frustrated Lewis Pair Hydrogenations

The synthesis and isolation of stable main group radicals remains an ongoing challenge. Here we report the application of frustrated Lewis pair chemistry to the synthesis of boron-containing radicals. H₂ activation with polyaromatic diones and B­(C₆F₅)₃ leads to radical formation in good yields. These radicals are robust; they do not decompose on silica gel or react with O₂ and are stable at 35 °C under N₂ indefinitely. The mechanism of formation is explored experimentally, with support from DFT calculations. EPR and UV/vis spectroscopy as well as cyclic voltammetry data are provided, and the radicals are shown to react with cobaltocenes in one-electron chemical reductions to their corresponding borate anions.