In an attempt to quantify the beneficial effect that the MOF host imparts on olefin hydrosilylation catalysis, we considered the minimum energy pathways that would enable hy-drosilylation to take place in the absence of MOF-specific effects. In solution, 18 rapidly generates 19, 20 and 21 (Figure ), and the Rh-Si BDFE for 21 was computationally estimated to be 67.4 kcal•mol -1 . A thermal cleavage to generate silyl radicals which could engage in hydrosilylation is consequently not feasible. Next, we considered a system containing site-isolated Rh(II) centers which could stabilize a 3c-3e silane σ-adducts. H-Si cleavage to release silyl radical would be thermodynamically accessible (ΔGcalc = 28.7 kcal•mol -1 ), but kinetically inaccessible due to the entropic contribution to the activation barrier which results in ΔG ǂ calc = 39.1 kcal•mol -1 . Furthermore, cleavage of the weak Rh-H bond (ΔGcalc = 3.1 kcal•mol -1 ) in σ-adduct 6 to re-form Rh(II) and silane would be expected to take place in preference to silyl radical formation. Lastly, a direct transfer pathway, analogous to the one observed within the MOF host, is associated with ΔG ǂ calc = 39.9 kcal•mol -1 if no proximally located electron acceptor is available. The MOF platform thus permitted not only the stabilization of a highly unusual 3c-3e σadduct, but also enabled a formal silyl radical transfer at room temperature that leverages the spatial organization of Rh(II) centers in the framework. An experimental activation barrier of ΔG ǂ exp = 19.4 ± 0.6 kcal•mol -1 was determined for Rh(II)-3-catalyzed ethylene hydrosilylation in benzene, which is substantially lower than the barriers associated with both observed and hypothetical reaction pathways outside the MOF.