Photons are a necessary component of a rapidly increasing number of synthetic transformations. In the majority of cases, illumination is used to generate high-energy open shell intermediates, which can engage in subsequent reaction steps with small kinetic barriers. The development of photocatalysts that permit the use of visible rather than UV light to cleave strong bonds vastly increased the scope and practical utility of photochemical reactions. Even visible light photons are highly energetic, however, with 450 nm photons carrying an energy of 63.6 kcal•mol -1 . Since many synthetic reactions have low quantum yields, the high reactivity of radical intermediates comes at a substantial energy cost. Ideally, we could harness the versatile reactivity of high-energy radicals without ever having to generate them as free species. An energy-efficient direct transfer of an incipient radical to a radical acceptor could unlock more energy efficient and sustainable radical reactions. For a reaction involving a catalyst, a radical generator and a radical acceptor species, a direct transfer reaction would be possible if all three species could be assembled together. But except under extreme conditions, such as those present during the formation of a star, triatomic collisions rarely take place. An additional challenge is that the catalyst and both reagents are not atoms, but molecules of reasonable complexity. For multi-atomic molecules, not only the minute collision frequency but also the need for correct alignment of all species renders it unlikely for termolecular steps to contribute noticeably to reaction rates (Figure ). Terrestrial chemical transformations thus generally proceed via successive uni-and bi-molecular reaction steps. In the case of catalytic radical hydrosilylation reaction, an initial encounter between catalyst and silane leads to the formation of a free silyl radical, which then reacts with an olefin in a separate reaction step (Figure ). For Rh(II) porphyrin catalysis, the difference in Gibbs free energy between the reagents (silane and Rh(II)) and the products (Rh(III)-H and silyl radical) is calculated to be 25.5 kcal•mol -1 (Figure ). However, for hydrogen atom transfer (HAT) to take place, two molecules need to associate into a transition structure which results in energy penalty due to the loss of translational and rotational degrees of freedom that corresponds to approximately 10 kcal•mol -1 . 6-8 A catalyst that is able to assemble a silane and an olefin into a transition state for direct radical transfer with an energy input of less than 25.5 + 10 = 35.5 kcal•mol -1 would thus permit a more energy-efficient transformation. Such a transition state would need to be assembled in a step-wise fashion to limit the entropic penalty. We define here the term "tri-component" as a transition state that brings together three individual species but is not assembled via a termolecular collision, and thus entropically accessible (Figure ). To render the formation of a tri-component transition state feasible, the Rh(II) catalyst and the silane need to be able to form an adduct with sufficient stability that it survives under the reaction conditions for an appreciable amount of time.