| Sumario: | The C-C vs C-C site selectivity in the C-C bond activation in Rh-catalyzed ring opening of benzocyclobutenol was systematically investigated using density functional theory (DFT). The catalytic cycle includes three elementary steps: the proton transfer from the substrate to a rhodium hydroxide, the C-C cleavage, and the proton transfer from water onto a carbon forming the final product with regeneration of the rhodium hydroxide. The site selectivity is determined by the C-C cleavage step; the C-C cleavage is favored over the C-C cleavage because the former transition state is stabilized by an interaction between the benzene ring of the substrate and Rh. DMSO, a more polar solvent, reduces the site selectivity as the more polar C-C transition state (TS) is stabilized more than the C-C TS and decreases the advantage of the latter TS. DPPF ligand is bulky, and the steric repulsion on the tighter C-C TS causes the loss of the site selectivity. For the even more crowded Rh(P(t-Bu)) catalyst, one phosphine has to dissociate before the C-C cleavage reaction takes place, and the advantage of the C-C TS is regained for the less crowded RhP(t-Bu) active catalyst.
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