N-Methylation of 14π aromatic triphyrin(2.1.1)s by treating appropriate triphyrin(2.1.1)s with CH3I in THF at 60 °C resulted in the formation of nonaromatic stable N-methylated triphyrin(2.1.1)s by converting one of the meso-sp2 carbons to an sp3 carbon. 1H, 1H-1H COSY, NOESY, and 1H-13C HSQC NMR were used to deduce the molecular structures of the N-methylated triphyrin(2.1.1)s. The DFT studies revealed that the presence of a meso-sp3 carbon induced significant distortion in the nonaromatic N-methylated triphyrin(2.1.1)s, unlike planar aromatic triphyrin(2.1.1)s. The nonaromatic N-methylated triphyrin(2.1.1) 2 showed absorption features very different from those of its aromatic congeners. An intense band at 378 nm, two ill-defined shoulders at 442 and 470 nm, and a broad band in the 500-750 nm region were observed. Electrochemical studies revealed that nonaromatic triphyrin(2.1.1)s are more electron-rich than aromatic triphyrin(2.1.1)s, and computational studies are in agreement with the experimental observations.
Sharma et al. (Thu,) studied this question.