Synthesis, characterization and the thermodynamic study of intermediate sitting-atop (i-SAT) complexes of free base meso-tetraarylporphyrins with InCl 3

Abstract

The reaction of free base para-substituted meso-tetraarylporphyrins (H 2T( p-X)PP, X = H, OMe, Me, and Cl) with indium(III) chloride in CHCl 3 and mild conditions produced intermediate sitting-atop (i-SAT) complexes, [InCl 2(H 2T( p-X)PP)]InCl 4, as sole products. In the proposed structures of these complexes, four pyrrole rings are tilted alternatively up and down the porphyrin plane. This distortion makes suitable orientation of lone pairs of two pyrrolenine nitrogens for electron donation to an indium center of InCl 2 + cation. The 1:2 (porphyrin:indium) formation constant of resulting i-SAT complexes were calculated by the computer fitting of the complexes absorbance versus mole ratio data based on appropriate equations. Thermodynamic parameters, Δ G 0, Δ H 0, and Δ S 0, have been determined and the influence of electron donation of the para-substituted aryl groups in the free base porphyrins on the stability of the complexes is discussed.