Silicon complexation of a octaphyrin (1) was accomplished by reaction with an excess amount of MeSiCl3 in the presence of N,N-diisopropylethylamine, thus giving an aromatic octaphyrin bis(silicon) complex 2. This complex was interconvertible with an antiaromatic octaphyrin congener (3) by oxidation with MnO2 and reduction with NaBH4. Curiously, mild oxidation of 2 with ferrocenium hexafluorophosphate afforded a octaphyrin bis(silicon) complex 4 as an stable radical cation that can be stored under ambient conditions in the solid state. Owing to the two NNNCC-five-coordinated Si atoms bearing trigonal bipyramidal geometry, these octaphyrin bis(silicon) complexes take on similar and rigid figure-of-eight structures with different consecutive numbers of conjugated π-electrons (38, 37, and 36), and are all stable.
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