The Silver Complexes of Porphyrins, Corroles, and Carbaporphyrins: Silver in the Oxidation States II and III

Complexes of silver in the oxidation states II and III are frequently considered to be unstable and rare. However, the silver complexes of porphyrins, corroles, and carbaporphyrins are stable and well characterized examples of silver in these high oxidation states. Moreover, these complexes should not be regarded as exceptions or curiosities as their formation follow classic coordination chemistry rules. Their existence supports one of the tenets of coordination chemistry, namely, that a given ligand environment largely determines the oxidation state of a coordinated metal ion. The discussion will explain why stable Ag II and Ag III complexes should not surprise, and why tetrapyrrolic ligands are ideally suited to provide these high oxidation state complexes. While the focus of the discussion is on the silver complexes, a discussion of the tetrapyrrolic metal complexes of the metals surrounding silver in the periodic table in group 10 (nickel group), 11 (coinage metal group), and 12 (zinc group) will help to put the silver chemistry into perspective and will highlight the generality of the findings.