Bromine Adducts of 9,10-Diheteratriptycene Derivatives

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Abstract
2,3,6,7,14,15-Hexamethyl-9,10-diphosphatriptycene (1), 2,3,6,7,14,15-hexamethyl-9-phospha-10-stibatriptycene (2), and 2,3,6,7,14,15-hexamethyl-9,10-distibatriptycene (3) were synthesized and their molecular structures were determined by X-ray crystallography. Reactions of 2 and 3 with bromine gave the corresponding adducts 8 and 9 with the compositions 2·2Br2 and 3·2Br2, respectively. Both of the adducts 8 and 9 have a zwitterionic structure composed of a hexacoordinate stiborate anion, (R3SbBr3−) and a tetracoordinate phosphonium/stibonium cation (R3MBr+: M = P or Sb) in the crystalline state. 1H and 31P NMR spectra of the adduct 8 indicated that the structure is static in solution at room temperature. On the other hand, 1H NMR spectra of the adduct 9 suggested fast topomerization at 27 °C, which becomes slow on the NMR time scale at −90 °C. Recrystallization of the adduct 9 from THF–mesitylene gave crystals with the composition of 3·2Br2·2THF, in which each antimony atom bonds to two bromine atoms and one THF oxygen to give an octahedral geometry.