Oxidative Generation of Boron-Centered Radicals in Carboranes

We
report the first indirect observation and use of boron vertex-centered
carboranyl radicals generated by the oxidation of modified carboranyl
precursors. These radical intermediates are formed by the direct oxidation
of a B–B bond between a boron cluster cage and an exopolyhedral
boron-based substituent (e.g., −BF3K, −B­(OH)2). The in situ generated
radical species are shown to be competent substrates in reactions
with oxygen-based radicals, dichalcogenides, and N-heterocycles, yielding
the corresponding substituted carboranes containing B–O, B–S,
B–Se, B–Te, and B–C bonds. Remarkably, this chemistry
tolerates various electronic environments, providing access to facile
substitution chemistry at both electron-rich and electron-poor B–H
vertices in carboranes.