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)Cu<sub>2</sub> and (BCB)Cu<sub>2</sub> in the case of the biscorrole (BC) derivatives and (PCA)Cu<sub>2</sub> and (PCB)Cu<sub>2</sub> in the case of porphyrin (P)−corrole (C) dyads, where A and B represent the anthracenyl and biphenylenyl bridges, respectively. A related monomeric corrole (Me<sub>4</sub>Ph<sub>5</sub>Cor)Cu and monomeric porphyrin (Me<sub>2</sub>Et<sub>6</sub>PhP)Cu that comprise the two halves of the porphyrin−corrole dyads were also studied. Electron spin resonance (ESR), <sup>1</sup>H 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)Cu<sub>2</sub>, (BCA)Cu<sub>2</sub>, and (PCB)Cu<sub>2</sub> was confirmed by X-ray crystallography. Structural data:  (BCB)Cu<sub>2</sub>(C<sub>110</sub>H<sub>82</sub>N<sub>8</sub>Cu<sub>2</sub>·3CDCl<sub>3</sub>), triclinic, space group <i>P</i>1̄, <i>a</i> = 10.2550(2) Å, <i>b</i> = 16.3890(3) Å, <i>c</i> = 29.7910(8) Å, <i>α</i> = 74.792(1)°, <i>β</i> = 81.681(1)°, <i>γ</i> = 72.504(2)°, <i>Z</i> = 2; (BCA)Cu<sub>2</sub>(C<sub>112</sub>H<sub>84</sub>N<sub>8</sub>Cu<sub>2</sub>·C<sub>7</sub>H<sub>8</sub>·1.5H<sub>2</sub>O), monoclinic, space group <i>P</i> 2<sub>1</sub>/<i>c</i>, <i>a</i> = 16.0870(4) Å, <i>b</i> = 35.109(2) Å, <i>c</i> = 19.1390(8) Å, <i>β</i> = 95.183(3)°, <i>Z</i> = 4; (PCB)Cu<sub>2</sub>(C<sub>89</sub>H<sub>71</sub>N<sub>8</sub>Cu<sub>2</sub>·CHCl<sub>3</sub>), monoclinic, space group <i>P</i>2<sub>1</sub>/<i>n</i>, <i>a</i> = 16.7071(3) Å, <i>b</i> = 10.6719(2) Å, <i>c</i> = 40.8555(8) Å, <i>β</i> = 100.870(1)°, <i>Z</i> = 4. The two cofacial biscorroles, (BCA)Cu<sub>2</sub> and (BCB)Cu<sub>2</sub>, both show three electrooxidations under the same solution conditions. The reduction of (BCA)Cu<sub>2</sub> involves a reversible electron addition to each macrocycle at the same potential of <i>E</i><sub>1/2</sub> = −0.20 V although (BCB)Cu<sub>2</sub> is reversibly reduced in two steps to give first [(BCB)Cu<sub>2</sub>]<sup>-</sup> and then [(BCB)Cu<sub>2</sub>]<sup>2-</sup>, each of which was characterized by ESR spectroscopy as containing a Cu(II) center. These latter electrode reactions occur at <i>E</i><sub>1/2</sub> = −0.36 and −0.51 V versus a saturated calomel reference electrode. The half-reduced and fully reduced (BCB)Cu<sub>2</sub> show similar Cu(II) ESR spectra, and no evidence of a triplet signal is observed. The two well-separated reductions of (BCB)Cu<sub>2</sub> to give [(BCB)Cu<sub>2</sub>]<sup>2-</sup> can be attributed to a stronger π−π interaction between the two macrocycles of this dimer as compared to those of (BCA)Cu<sub>2</sub>. The copper porphyrin−corrole dyads, (PCA)Cu<sub>2</sub> and (PCB)Cu<sub>2</sub>, 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.