Metal exchange reactions in cadmium complexes with porphyrins of various structures

The reaction kinetics of the metal exchange Cd(II)-Cu(II) and Cd(II)-Zn(II) in the cadmium complexes (CdP) with porphyrin ligands (H₂P) differing by degree of stiffness (tetraphenylporphin, N-methyltetraphenylporphin, and tetraphenyltetrabenzoporphin) in the DMSO medium, was studied using spectrophotometric method. The rate of metal exchange reaction depends on the nature of the non-planatrity of H₂P in the structure of CdP complexes, as well as on the additional screening of the reaction center MN₄ by the extra-ligands and substituents. The reduction of the coordinating ability of the anion X⁻ in the structure of the solvate-salt of incoming metal M’X₂(Solv) _n−2 in a series: acetylacetonate > acetate > chloride > nitrate favors the metal exchange. In the most studied cases the reaction of CdP proceeds along a combined associative-dissociative mechanism. The order of the metal exchange reaction is found to be depending on temperature indicating a change in the contributions of associative and combined routes. The “pure” associative reaction mechanism in a medium of DMSO was for the first time found for the labile complex CdTPTBP with the saddle-type nonplanar ligand.