Why do the [PhSiO 1.5] 8, 10, 12 cages self-brominate primarily in the ortho position? Modeling reveals a strong cage influence on the mechanism

Richard Laine

M Bahrami, H Hashemi, X Ma, J Kieffer, and Richard M Laine (2014)

Physical Chemistry Chemical Physics, 16(47):25760-25764.

(PhSiO1. 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.

silsesquioxanes