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.