Three-metal coordination by novel bisporphyrin architectures.

The synthesis and characterization of a new type of bisporphyrin system is reported where the two macrocycles are linked in a cofacial arrangement by a substituted carbazole bridge. The three nitrogen atoms of the carbazole bridge in the compounds may complex a metal ion and thus provide a new parameter for varying the physical properties and flexibility of the dyad after formation of a three-metal system. In the present study, four bis-metalloporphyrin complexes were synthesized and examined by electrochemistry and thin-layer spectroelectrochemistry in CH(2)Cl(2) and PhCN. Two of the examined compounds contain Cu(II) or Zn(II) porphyrins and a carbazole linker with a bound Cu(II) ion, giving a three metal system, while the other two examined compounds contained the same porphyrins but with a carbazole bridge which lacks the Cu(II) component. Since carbazoles and Cu(II) ions are both electroactive, redox properties of several unlinked carbazoles with and without bound Cu(II) ions were also examined as to their electrochemical behavior under the same solution conditions as the dyads to better understand the redox reactions which may occur at the carbazole group linking the two porphyrin macrocycles. Several mononuclear porphyrins with structures related to macrocycles in the dyads were also investigated.