We have shown that olefin hydrosilylation catalyzed by site isolated Rh(II) metalloradicals 3 or 4 can proceed via two pathways, both of which involve 3c-3e silane σ-adduct 6. In the presence of light, free silyl radicals are generated from 6, which subsequently add to olefins. H-atom transfer between the resulting carbon-centered radical and Rh(III)-H regenerates the active Rh(II) catalyst. In the absence of light, however, σ-adduct 6 is stable at room temperature both in the dry state and when suspended in benzene. Intermediate 6 pre-organizes Rh(II) and silane for participation in a tri-component transition structure with olefins that permits facile thermal hydrosilylation. By synchronizing Rh-H bond formation, H-Si bond cleavage and Si-C bond formation, the direct silyl transfer pathway limits the number of high-energy intermediates that need to be formed over the course of the reaction. The MOF-based catalyst, which has access to a direct silyl transfer pathway from intermediate 6 can thus promote hydrosilylation at room temperature, while a molecular analogue which was unable to stabilize a 3c-3e silane σ-adduct furnished negligible amounts of product even at 140 °C.