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.
Bibliographical noteFunding Information:
The work at Kyoto was supported by JSPS KAKENHI Grant Numbers (Nos.: 25220802 (Scientific Research (S)), 16K13952 (Exploratory Research). The work at Yonsei was supported by the Global Research Laboratory (GRL) Program funded by the Ministry of Science, ICT & Future, Korea (2013K1A1A2A02050183). The authors thank Prof. Dr. N. Aratani at the Nara Institute of Science and Technology (NAIST) for X-ray diffraction analysis and Prof. Dr. T. Ikeue and Mr. Y. Ide at Shimane University for ESR measurement. S.I. and D.S. acknowledge JSPS Fellowship for Young Scientists.
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