SiIV Incorporation into a [28]Hexaphyrin That Triggered Formation of Mobius Aromatic Molecules

Incorporation of Si-IV into an expanded porphyrin has been achieved for the first time. Treatment of [28]hexaphyrin 1 with CH3SiCl3 and N,N-diisopropylethylamine gave Si-IV complex 2 and its N-fused product 4 that both have Mobius 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 sigma-pi conjugation between the Si atom and hexaphyrin macrocycle. Tamao-Fleming oxidation of 2 with H2O2 gave beta-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 Mobius aromatic conformer in CH2Cl2.