Push‐Pull Effect at Formation of Sitting‐Atop Metal‐Porphyrin Complex in Solvating Media: H‐Bonding and Electrostatic Repulsion

Abstract

AbstractThis work presents the results of experimental and theoretical studies of the solvation effects on the kinetics of the porphyrins reaction with zinc and cadmium acetate, the structure and characteristics of the intermediate ‐ sitting‐atop (SAT) complex. Kinetic rate constants of metal complexes of tetra‐p‐substituted tetraphenylporphins formation in binary solutions with a regulated solvating ability were obtained. Extreme dependences of the rate constants on the solvent composition were found. The acceleration of the reaction was shown to be observed with an enhancement of the electron‐donating properties of the substituent. These data indicate the formation of the SAT complex as limiting stage. The structure and energy parameters of porphin‐zinc SAT complexes and its solvates were studied by DFT method using B3LYP and long range corrected CAM‐B3LYP hybrid functionals. A significant distortion of the porphin structure during the formation of an intermediate and its solvation was ascertained. The influence of these processes on structural and energy changes was founded to be the consequence of push‐pull effect due to the repulsion of NH hydrogen atoms by a metal ion (push) and stretching of these bonds (pull) during the formation of H‐bonds.