Alkyl- and Aryl-Substituted Corroles. 5. Synthesis, Physicochemical Properties, and X-ray Structural Characterization of Copper Biscorroles and Porphyrin−Corrole Dyads

The synthesis and characterization of cofacial copper biscorroles and porphyrin−corroles linked by a biphenylenyl or anthracenyl spacer are described. The investigated compounds are represented as (BCA)Cu₂ and (BCB)Cu₂ in the case of the biscorrole (BC) derivatives and (PCA)Cu₂ and (PCB)Cu₂ in the case of porphyrin (P)−corrole (C) dyads, where A and B represent the anthracenyl and biphenylenyl bridges, respectively. A related monomeric corrole (Me₄Ph₅Cor)Cu and monomeric porphyrin (Me₂Et₆PhP)Cu that comprise the two halves of the porphyrin−corrole dyads were also studied. Electron spin resonance (ESR), ¹H NMR, and magnetic measurements data demonstrate that the copper corrole macrocycle, when linked to another copper corrole or copper(II) porphyrin, can be considered to be a Cu(III) complex in equilibrium with a Cu(II) radical species, copper(III) corrole being the main oxidation state of the corrole species at all temperatures. The cofacial orientation of (BCB)Cu₂, (BCA)Cu₂, and (PCB)Cu₂ was confirmed by X-ray crystallography. Structural data:  (BCB)Cu₂(C₁₁₀H₈₂N₈Cu₂·3CDCl₃), triclinic, space group P1̄, a = 10.2550(2) Å, b = 16.3890(3) Å, c = 29.7910(8) Å, α = 74.792(1)°, β = 81.681(1)°, γ = 72.504(2)°, Z = 2; (BCA)Cu₂(C₁₁₂H₈₄N₈Cu₂·C₇H₈·1.5H₂O), monoclinic, space group P 2₁/c, a = 16.0870(4) Å, b = 35.109(2) Å, c = 19.1390(8) Å, β = 95.183(3)°, Z = 4; (PCB)Cu₂(C₈₉H₇₁N₈Cu₂·CHCl₃), monoclinic, space group P2₁/n, a = 16.7071(3) Å, b = 10.6719(2) Å, c = 40.8555(8) Å, β = 100.870(1)°, Z = 4. The two cofacial biscorroles, (BCA)Cu₂ and (BCB)Cu₂, both show three electrooxidations under the same solution conditions. The reduction of (BCA)Cu₂ involves a reversible electron addition to each macrocycle at the same potential of E_1/2 = −0.20 V although (BCB)Cu₂ is reversibly reduced in two steps to give first [(BCB)Cu₂]^- and then [(BCB)Cu₂]^2-, each of which was characterized by ESR spectroscopy as containing a Cu(II) center. These latter electrode reactions occur at E_1/2 = −0.36 and −0.51 V versus a saturated calomel reference electrode. The half-reduced and fully reduced (BCB)Cu₂ show similar Cu(II) ESR spectra, and no evidence of a triplet signal is observed. The two well-separated reductions of (BCB)Cu₂ to give [(BCB)Cu₂]^2- can be attributed to a stronger π−π interaction between the two macrocycles of this dimer as compared to those of (BCA)Cu₂. The copper porphyrin−corrole dyads, (PCA)Cu₂ and (PCB)Cu₂, show five reversible oxidations and two reversible reductions, and these potentials are compared with corresponding values for electrochemical reactions of the porphyrin and corrole monomers under the same solution conditions.