Si^IV incorporation into a [28]hexaphyrin that triggered formation of möbius aromatic molecules

Incorporation of Si^IV into an expanded porphyrin has been achieved for the first time. Treatment of [28]hexaphyrin 1 with CH ₃SiCl₃ and N,N-diisopropylethylamine gave Si^IV complex 2 and its N-fused product 4 that both have Möbius aromatic nature. In both complexes, the coordinated Si atom is satisfied in a typical trigonal bipyramidal coordination. Si^IV incorporation induces conformational rigidification and redshifted absorption profiles due to σ-π conjugation between the Si atom and hexaphyrin macrocycle. Tamao-Fleming oxidation of 2 with H₂O₂ gave β-hydroxy [28]hexaphyrin 5, which exists as a ruffled rectangular shape in the solid state, yet it has been revealed to exist predominantly as a twisted Möbius aromatic conformer in CH₂Cl₂.