Tetrapyrrole derivatives substituted with ferrocenylethynyl moieties. Synthesis and electrochemical studies

Up to eight redox-active ferrocenyl units have been incorporated, through t he unsaturated ethynyl linkers; on the periphery of a series of cyclic tetr apyrrole derivatives including zinc(II) phthalocyanine and 2,3-naphthalocya nine, and nickel(II) meso-diphenylporphyrin. The synthesis of the former tw o macrocycles 4 and 7 involves the Sonogashira coupling reaction of ferroce nylethyne with 4,5-dichlorophthalonitrile (1) or 6,7-dibromonaphthalonitril e (5), respectively, followed by a base-promoted cyclization. The meso-bis( ferrocenylethynyl)porphyrin 11 has been prepared from the dibromo analogue 10 also by a palladium-catalyzed coupling reaction. These novel macrocyclic compounds have been spectroscopically and electrochemically characterized. As revealed by cyclic voltammetry, the ferrocenyl moieties appear to be el ectrochemically independent in these complexes and there is no significant electronic coupling among the iron(II) centers.