Size- and charge-matching effect between porphyrin core and central metal on the stability of cuprous ion

Cuprous(I) catalysts have been widely used in the coupling reaction of forming C-X bond. The core-modified porphyrins are known to stabilize the unusual oxidation state of many metals. Thus, in this work, a 21-oxaporphyrin was obtained under the improved Adler-Longo condensation condition and successfully used for complexing the cuprous ion. It is found that the synergy of the two factors, the diameter expansion and the univalent form of the N3O core in the ligand, plays a decisive role in stabilizing the metastable ion; the former effectively stabilizes the electron pair of the equatorial d orbital by aiding the d-pi interaction, and the latter exactly balances the single charge of the ion. A size axis of copper species in porphyrinate systems is established by comparing with two previously reported distorted copper(II) porphyrin series.