Cation Radicals, Borenium Cations, and Dication from Oxidation of B-Tolyl BIII Subporphyrins

Abstract

Oxidation of B-tolyl B^III 5,10,15-tritolylsubporphyrin with tris(4-bromophenyl)ammoniumyl hexachloroantimonate gave its cation radical instantaneously, which slowly dissociated to give B^III subporphyrin borenium hexachloroantimonate in 89% after stirring overnight. This is a much more convenient synthesis of B^III borenium cation. Oxidants such as tris(4-bromophenyl)ammonium tetrakis(perfluorophenyl)borate and AgSbF₆ can be used for the synthesis of the borenium cation. Oxidation of B-tolyl B^III 5,10,15-trianisylsubporphyrin with AgSbF₆ gave a cation radical that was stable at room temperature but dissociated to give the corresponding borenium cation upon refluxing in CH₂Cl₂, while B-tolyl B^III 5,10,15-tris(4-dibutylaminophenyl)subporphyrin was oxidized to give a cation radical that was easily oxidized to afford a quinonoidal dication. Oxidation of B-tolyl B^IIIβ-hexaethyl-5,10,15-tri(4-diethylaminophenyl)subporphyrin with AgSbF₆ gave a borenium cation instantaneously. As such, the reactivities of the cation radicals depend on the peripheral substituents.