The dissociative stereoisomerization of persulfuranes via 10-S-5 persulfonium salts. Geometrical isomers of octahedral 12-S-6 species
作者:Ronald S. Michalak、J. C. Martin
DOI:10.1021/ja00370a039
日期:1982.3
kcal/mol. The rapid, acid-catalyzed isomerization of trans isomer to give cis isomer occurs by a dissociative mechanism through a pentacoordinate cationic sulfur intermediate, a 10-S-5 persulfonium ion, which was isolated at its hexafluorophosphate salt. A lower limit for the activation barrier of the unobserved nondissociative isomerization of trans to cis is 50 kcal/mol in quinoline solution. Polarization
三氟化溴与硫烷的反应首次报道了 12-S-6 硫的几何异构体、反式和顺式二氟二烷氧基二芳基过硫醚的分离。在 25/sup 0/C 的二氯甲烷溶液中,顺式异构体比全反式异构体的自由能高 1.6 +/- 0.1 kcal/mol。量热法显示反式到顺式异构化放热2.0 +/- 0.5 kcal/mol。反式异构体在酸催化下快速异构化为顺式异构体,通过五配位阳离子硫中间体(10-S-5 过锍离子)的解离机制发生,该中间体在六氟磷酸盐中分离。在喹啉溶液中,未观察到的反式异构化为顺式异构化的激活屏障的下限为 50 kcal/mol。讨论了极化和其他对异构体的相对键长和能量的影响。反式和顺式的完整 X 射线结构测定结果与 PMO 论证一起描述,使观察到的键长顺序合理化。