Synthesis of (bis)Silicon Complexes of [38], [37], and [36]Octaphyrins: Aromaticity Switch and Stable Radical Cation

Silicon complexation of a 38]octaphyrin ( 1 ) was accomplished by reaction with an excess amount of MeSiCl₃ in the presence of N,N‐diisopropylethylamine, thus giving an aromatic 38]octaphyrin bis(silicon) complex 2 . This complex was interconvertible with an antiaromatic 36]octaphyrin congener ( 3 ) by oxidation with MnO₂ and reduction with NaBH₄. Curiously, mild oxidation of 2 with ferrocenium hexafluorophosphate afforded a 37]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.