Hydrogen atom transfer (HAT) reactions from dihydroanthracene to ArINTs (Ar = 2-tert-butylsulfonyl)benzene and Ts = p-toluenesulfonyl) is catalyzed by Mn(tpfc) (tpfc = 5,10,15-tris(pentafluorophenyl)corrole). Kinetics of HAT was monitored by gas chromatography. Conversion to the major products anthracene, TsNH2, and Arl is too fast to be explained by direct HAT from the terminal imido complex TsN=Mn(tpfc), which forms from the reaction of Mn(tpfc) with ArINTs. Steady-state kinetics, isotope effects, and variation of the initial catalyst form (Mn-III(tpfc) vs TsN=Mn-V(tpfc)) support a mechanism in which the active catalytic species is an adduct of manganese(III) with the oxidant, (ArlNTs)Mn-III(tpfc). This species was detected by rapid-scan stopped-flow absorption spectroscopy. Kinetic simulations demonstrated the viability of this mechanism in contrast to other proposals.