Synthesis of Stable [28π] m-Benzihexaphyrins (1.0.0.1.1.1)

Four new expanded [28π] m-benziporphyrins (1.0.0.1.1.1) were synthesized by [3+3] condensation of 10,10'-bis[(p-toly)hydroxymethyl]-1,3-bis(2-thienyl)benzenediol with various 16-tripyrranes such as 16-thiatripyrrane, 16-oxatripyrrane, 16-azatripyrrane, and 16-selenatripyrrane under mild trifluoroacetic acid-catalyzed reaction conditions. The macrocycles are freely soluble in common organic solvents, and their identities were confirmed by HRMS and detailed 1D and 2D NMR spectroscopy. The macrocycles showed one sharp Soret-type band at ∼500 nm and broad ill-defined Q-type band(s) in the region 600-950 nm, which supports their nonaromatic nature. Upon protonation, the macrocycles exhibited bathochromically shifted absorption bands with a distinct change in the color of the solutions. The preliminary studies carried out with one of the macrocycles indicated that the macrocycles have a weak tendency to form coordination complexes.