In fact, formation of complex 11 provides an additional indication of the HAA taking place between the Mn(IV)-oxo intermediate and DCM, as it explains what happens to the dichloromethyl radical formed in this reaction. Previous studies on mono-and dichloromethyl radicals generated in situ from DCM in the gas phase have shown that these highly reactive species tend to couple, especially at high pressures, with the elimination of HCl (Fig. , inset). If a similar process occurs in solution as well, one would expect the decay of 9 by HAA to result in the accumulation of HCl in the reaction medium. This in turn would result in the protonation of the terminal hydroxy ligand of 10, followed by the chloride ion displacing the resulting water molecule, gradually converting 10 into 11 (Fig. ). Presumably, the same process occurs even more rapidly in the presence of excess t BuOOH. It is generally accepted that the HAA reaction represents the first and rate-determining step, in the C-H activation by Mn(IV)-oxos, which is also true for Fe(IV)-oxo species (operating via the rebound mechanism). However, whereas in the case of Fe-oxos this step has been shown to progress via either σ or π pathways (with the latter being more favored kinetically), no experimental evidence for the feasibility of a σ-approach in the case of Mn(IV)-oxo has been presented to date. In fact, it has been postulated that in a Mn(IV)-oxo system such a pathway is inaccessible, due to the high energy of its dz2 orbital, compared to an Fe-based congener (Fig. ). In light of the above, the XRD structure of complex 9 appears even more intriguing, as it shows the DCM molecule at the suitable distance (1.981 Å) and angle (177.83°) for the HAA to proceed via the σ-pathway. This raises the possibility that, despite being energetically unfavorable for typical Mn(IV)oxo species, this reaction pathway may still occur in the cavitand system -being driven by the interaction of the metaloxo center with the secondary coordination sphere (provided by the macrocyclic ligand).