Coordination behaviour of metalloporphyrins with intramolecularly linked thiolate ligand

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meso-Tetraphenylporphyrin was derivatized at different positions of one of the meso aryl groups to obtain interesting bisporphyrin systems bearing a disulfide group. Various metal (VO(IV), Ni(II), Co(II), Cu(II), Zn(II) and Ag(II)) derivatives of these porphyrins have been prepared. In situ reduction of these derivatives results in well-defined five coordinate complexes with thiolate as the axial ligand exhibiting hyperporphyrin spectra. The relative extent of thiolate coordination to the metal ion depends on the nature of the substitution as o > m > p. The electrochemical redox behaviour of these systems reveals the existence of the disulfide group and spectroelectrochemical studies unambiguously show the formation of negatively charged pentacoordinate porphyrin complexes. Possible structures have been proposed for the o, m and p substituted porphyrin derivatives based on the 1H NMR data.