Synthesis, Conformation, and Complexation of Novel 25,26,27,28- Tetrahydroxy-5,11:17,23-bis[[2,2‘-thioxydi(o-phenylene)dithioxy]- diphenylthio]calix[4]arene

Calix[4]arenes 1a,b having an electron-donating group, i.e., OH and OMe, at the lower rim reacted with thianthrene cation radical perchlorate in CH₃CN at room temperature to give the corresponding thianthrenium perchlorates 3a,b in excellent yields. Treatment of 3a,b comprising a mixture of conformational isomers with NaSH·xH₂O in DMF at reflux afforded the sulfur-containing cyclized compounds 4a,b, respectively. Compound 4a having a cone conformation consisted of two conformational isomers in a ratio of 0.077:1. Temperature-dependent ¹H NMR study in DMF showed that conformational isomerization between the two isomers occurred with energy barriers of 14.97 and 14.10 kcal/mol at 100 and 110 °C, respectively. The Jobs plot of 4a against Ag⁺ picrate indicated that compound 4a strongly produced a 1:2 complex with Ag⁺ ions. Molecular mechanics calculations indicated that the conformation of the energy-minimized 4a−2Ag⁺ picrate complex had two crushed pyramidal geometries made up of Ag⁺ ion and four sulfur atoms, i.e., S1, S2, S4, S5 and S6, S7, S9, S10, respectively.