Reductive Cleavage of Dioxygen Mediated by a Lewis Superacidic Bis(borane).

The bis-(borane) -{(CF)B}CF () reacts with dioxygen in the presence of decamethylferrocene (FeCp*, Cp* = pentamethylcyclopentadienyl) to deliver the salt [(μ-OH)-{B-(CF)}CF]-[FeCp*] () featuring a hydroxide sequestered by the two adjacent boron atoms. Mechanistic investigations of this formal 4-electron reduction of O suggest that it goes through the formation of a superoxide adduct [-O], which evolves through disproportionation into O and a peroxo-adduct [-O]. Upon coordination of another equivalent of , the thus-generated 4-fold boron-sequestered peroxide {[]-O} undergoes homolytic O-O bond cleavage to yield a pair of oxyl radicals [-O]. These highly reactive intermediates subsequently perform hydrogen atom abstraction to lead to the hydroxide salt . Our observations point to FeCp* being the H atom purveyor in this final step.