Distortion and aromatization factors on the complexing ability of tetrapyrrole macrocycles in acetonitrile

The kinetics of complexation between porphyrins and zinc acetate in acetoni trile was studied for the porphyrins belonging to various structural groups , including aza-, benzo-, and distorted N- and multiply substituted macrocy cles. The effects of the distortion, on the one hand, and the enhanced rigi dity of a macrocycle, on the other, on the complexation process were consid ered, The coordination of the distorted porphyrins to metal salts is facili tated because of the disturbance of the steric component of the macrocyclic effect (MCE), whereas the complexation of the rigid macrocycles is facilit ated because of the activation of the electronic component of MCE.