Monitoring the evolution of 7 within the MOF pore over a period of 50 ps showed that more than 72% of the carboncentered radicals were converted into the hydrosilylation product via HAT with Rh(III)-H. Interestingly, as our model contained only one Rh(III)-H bond, the observed product is exclusively formed from 7 that did not escape its solvent cage and reacted with "its own" Rh center. Only 8% of 7 left the solvent cage and thus could potentially undergo HAT with other Rh(III)-H bonds or be trapped by Rh(II) (Fig. ). The H and Si atoms present in the hydrosilylation product therefore predominantly originate from the same silane precursor molecule. As anticipated, ethylene expulsion from 7 to yield 8 was not observed, so that we attribute the silyl radical 8 observed experimentally as originating from bimolecular HAT. Half of the remaining 20% of 7 underwent addition to the porphyrin linker (Figure ). Circumstantial experimental evidence that a small fraction of the radicals generated may undergo addition to the porphyrin ligand could be obtained from radical trapping experiments with PBN (Figure ). Specifically, trapping of a carbon centered radical was also observed for experiments in which only silane but no ethylene was present, so that the carbon-centered radical that was trapped could not be 7. Instead, a porphyrin-based radical formed upon addition of 8 to the porphyrin linker may account for the carbon centered radical trapped by PBN. Alternatively, PBN could have undergone reaction with methyl radicals generated from residual Rh(Me)-3 that was still present in the Rh(II)-3 sample. Digestion of Rh(II)-3 followed by solution 1 H-NMR analysis did not reveal the presence of any remaining Rh(III)-Me. However, considering the higher sensitivity of EPR compared to NMR, we cannot rule out that the carbon-based radical trapped by PBN corresponds to methyl radicals derived from Rh(Me)-3 impurities in Rh(II)-3. EPR analysis of recovered catalyst samples also repeatedly showed peaks of varying intensity with g = 2, which could indicate the presence of a porphyrin centered radical or a Rh superoxo species. While prior EPR studies of porphyrin-containing MOFs have attributed similar features to porphyrin centered radicals, we also observed the presence of the signal in question for 3 which had never been subjected to hydrosilylation catalysis (Figure ). Considering all available data, we conclude that radical addition to the porphyrin linker may take place, but we cannot comment to the extent or reversibility of this process. Should the porphyrin linker in 3 undergo derivatization, however, it does not appear to affect its catalytic performance, at least within the first 8 uses of the catalyst.