Why do the [PhSiO1.5]8,10,12 cages self-brominate primarily in the ortho position? Modeling reveals a strong cage influence on the mechanism

Abstract

(PhSiO_1.5)_8,10,12 cages are bulky, electron withdrawing like CF₃; yet self-brominate (60 °C), favoring ortho substitution: PhT₈ (≈85%), PhT₁₀ (≈75%) and PhT₁₂ (60%). First-principles calculations suggest bromination initiates when Br₂ is “trapped” via H-bonding to ortho-H's, followed by polarization via strong interactions with cage faces, possibly cage LUMOs.