Planar Subporphyrin Borenium Cations

Subporphyrin borenium cations with a carborane counterion have been prepared by treatment of B-methoxy subporphyrins with the silylium reagent Et₃Si(CH₆B₁₁Br₆). In contrast to the distinctly domed subphthalocyanine borenium cation, a nearly planar structure with sp² hybridized boron is found in the X-ray structure of the triphenylsubporphyrin borenium cation. The cations exhibit absorption and fluorescence spectra that are quite similar to those of B-methoxy subporphyrins. B-phenyl subporphyrins were prepared in good yield by reaction of subporphyrin borenium cations with phenyllithium.