Catalytic sulfoxidation and epoxidation with a Mn(III) triazacorrole: evidence for a 'third oxidant' in high-valent porphyrinoid oxidations

The reaction between (TBP)8(Cz)Mn(III) (1) and the oxygen atom donors iodosylbenzene (PhIO) or p-cyanodimethylaniline-N-oxide (CDMANO) leads to the manganese(V)−oxo complex (TBP)8(Cz)Mn(V)⋮O (2), which has been isolated and characterized previously. Under catalytic conditions with 1 as added catalyst and PhIO as oxidant, both sulfoxidation of PhSMe and epoxidation of cis-stilbene is observed, whereas with CDMANO no sulfoxidation takes place, suggesting that 2 is not the active oxidant. Examination of the independent reactivity of isolated 2 toward PhSMe and cis-stilbene supports this conclusion. A mechanism which relies on a novel type of oxidant involving Lewis acid activation of PhIO by the Mn(V)−oxo complex 2 accounts for these observations and is confirmed by 18O-labeling experiments.