SiIV 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(3)SiCl(3) 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 H(2)O(2) 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 CH(2)Cl(2).