Acid–base equilibria and coordination chemistry of the 5,10,15,20-tetraalkyl-porphyrins: implications for metalloporphyrin synthesis

Abstract

A spectrophotometric study of the acid–base equilibria and complexation with metal ions has been carried out for 5,10,15,20-tetrakis(trifluoromethyl)porphine and 5,10,15,20-tetrakis(iso-buthyl)porphine in acetonitrile solutions. Protonation and deprotonation of these porphyrins was found to be stepwise with sequential formation of mono- and doubly protonated/deprotonated species. The overall basicity and acidity constants have been determined. The porphyrin complexation with Zn²⁺ and Cu²⁺ ions was studied and the rates constants of the macrocycle metallation have been determined. The structure–property relationship derived from the metal chelation studies and the prospects for the use of the above systems for the design of highly sensitive sensors for metal ions were discussed in detail.