To confirm that the Mn(IV)-oxo species 9 decays predominantly through the HAA mechanism, we measured its decay kinetics by tracking the total effective magnetic moment of the solution in anhydrous DCM and correlated it with the corresponding changes observed in the electronic absorption (Figure ). The effective magnetic moment was found to increase during the decay from 3.88 BM (immediately after the addition of sPhIO to complex 8) to 4.91 BM over the course of 4 hours -fully consistent with the transformation of a d 3 into a d 4 system. This one-electron reduction clearly followed 1 st order kinetics, with a half-life of t1/2 = 47±2 min.. A very similar kinetic profile and half-life (t1/2 = 50±1 min.) was also obtained by tracing the decrease of the absorption band centered at λmax = 507 nm -strongly suggesting that both measurements reflected the same process, i.e. the HAA from DCM by complex 9. Finally, we attempted to obtain complex 10 directly, by reacting complex 8 with an excess of t BuOOH -a hydroxyl radical source (Fig. ). Surprisingly, upon its addition the solution of 8 immediately turned emerald-green, displaying a distinct absorption pattern different from the one we obtained for the decay product(s) of complex 9 (Figure , plots B vs A).