Synthesis, characterization and the thermodynamic study of intermediate sitting-atop (i-SAT) complexes of free base meso-tetraarylporphyrins with InCl3

The reaction of free base para-substituted meso-tetraarylporphyrins (H2T(p-X)PP, X = H, OMe, Me, and Cl) with indium(III) chloride in CHCl3 and mild conditions produced intermediate sitting-atop (i-SAT) complexes, [InCl2(H2T(p-X)PP)]InCl4, 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 InCl2+ 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, ΔG0, ΔH0, and ΔS0, 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.

Graphical abstractPara-substituted meso-tetraarylporphyrins (H2T(p-X)PP) and InCl3 react for the formation of [InCl2(H2T(p-X)PP)]InCl4 i-SAT complexes, in which two nitrogen atoms of pyrrolenine in the porphyrin act as electron donors to an indium center, and two protons on the pyrrole nitrogens remained. Kf and ΔG0 for i-SAT complexes are directly related to the electron donation for the aryl rings of the porphyrins.Figure optionsDownload full-size imageDownload as PowerPoint slide