Protonation studies on isomeric tetrafluoro‐2,11‐dithia[3·3]cyclophanes, tetrafluoro[2·2]metaparacyclophane and their corresponding non‐fluorinated analogs. Comparison with fluorinated and non‐fluorinated[2·2]cyclophanes: A stable ion and semi‐empirical (AM1, PM3) investigation

Abstract

AbstractProtonation of tetrafluoro‐2,11‐dithia [3·3]paracyclophane and tetrafluoro‐2,11‐dithia [3·3]metaparacyclophane in high‐acidity super acid media, namely FSO3H.SbF5 (1:1) ‘magic acid’–SO2CIF, gave their corresponding acidic disulfonium ions. Additional ring protonation to give a disulfonium–monoarenium trication was not observed. With the non‐fluorinated 2,11‐dithia [3·3] cyclophanes, the disulfonium ions can be ring protonated in equilibrium to give a dynamic disulfonium–monoarenium trication. Tetrafluoro [2·2]‐metaparacyclophane is monoprotonated at the meta ring and gives a complex mixture of conformational isomers. Multinuclear magnetic resonance data on the cyclophane precursors and their derived cations are compared and analysed. The energies, conformations and charge distributions of the isometric fluorinated and non‐fluorinated [2·2] ‐ and dithia [3·3] cyclophanes were calculated by the AM1 and PM3 methods, respectively. In all but one case the cyclophane arenium ions predicted by theory to be energetically most favoured are those observed in solution under stable ion conditions. In agreement with experiment, the instabilities of S,S,C‐cyclophane trications are also theoretically predicted.