Fig. 2. (A) Key mechanistic steps for cROP of 2 and 3 catalyzed by Lewis acid. Transition-state structures for the ring-opening of 1,6-anhydro linkages (TS1) and nucleophilic additions of monomers 2 and 3 (TS2) catalyzed by various Lewis acids. Computed energetics indicate that nucleophilic addition of monomers 2 or 3 to I2 to form intermediate I4 (pseudo-equatorial approach) is energetically disfavored compared to formation of intermediate I3 (pseudo-axial approach; Fig. S46†). (B) Table depicting computed energetics in kcal mol⁻¹ for key mechanistic steps. (C) Alternative pathway for cROP of 2 catalyzed by Sc(OTf)₃ and the cROP of 3 catalyzed by Bi(OTf)₃. The corresponding free energies of activation (kcal mol⁻¹) with respect to I1 at the SMD_(DCM)/ωB97X-D/def2-TZVP, def2-TZVP|SDD(Bi)//SMD_(DCM)/M06-L/6-31+G(d,p), LanL2DZ(Bi) level.