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

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posted on 15.11.2004, 00:00 by Roger Guilard, Claude P. Gros, Jean-Michel Barbe, Enrique Espinosa, François Jérôme, Alain Tabard, Jean-Marc Latour, Jianguo Shao, Zhongping Ou, Karl M. Kadish
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 E1/2 = −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 E1/2 = −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.