As the C4 intermediate forms, the ethylene-assisted β-hydride transfer is the most favorable pathway due to a generally lower free energy landscape (species 4 to 7c, Fig. ). In this pathway, the physisorption of a third ethylene moiety is exothermic (step 4 to 5c, -0.3 eV), and the activation barrier of β-hydride transfer is 0.8 eV (step 5c to ‡ c ). Overall, the free energy of forming a Ga-ethyl intermediate from a clean 3CN Ga (species 1 in Fig. ) site is -1.7 eV, which is an exothermic process, and the Ga-ethyl species is thus quite likely to form. In contrast to this βhydride transfer, high barriers are observed for both the proton transfer and the β-hydride elimination steps. Indeed, the proton transfer step entails recovery of the cleaved Ga-O bond, which is quite high in energy due to the strained nature of the 3CN site. We note, in passing, that similarly high activation barriers for β-hydride elimination have also been observed for Zn-propyl species during propane dehydrogenation.