Synthesis and Characterization of Some New Oxorhenium(V) Complexes with Annulene Derivatives and Their Biological Activities

Abstract

Mononuclear and binuclear oxorhenium(V) complexes were prepared from the reaction of 8,17‐dimethyl‐5,7,14,16‐tetrahydrodibenzo[a,h]annulene‐6,15‐dione (H₂N₄L) with the oxorhenium(V) complex H₂[ReOCl₅] in 6 M HCl solution. The composition of the prepared complexes depends on the concentration of hydrochloric acid in which the starting rhenium(V) complex is dissolved. The mononuclear oxorhenium(V) complex, [ReO(H₂N₄L)(H₂O)]Cl₃, was obtained in 6 M HCl solution, while the binuclear complex, [Re₂O₃(H₂N₄L)₂]Cl₄·2H₂O, was obtained in 2 M HCl solution. The reaction of H₂N₄L mixed with PPh₃, NaSCN or 2‐aminopyridine, with the starting oxorhenium(V) complex in 6 M HCl solution, yielded the mononuclear complexes, [ReO(H₂N₄L)(PPh₃)]Cl₃·H₂O, [ReO(H₂N₄L)(SCN)]Cl₂·½ H₂O and [ReO(H₂N₄L)(C₅H₆N₂)]Cl₃, respectively. The reaction of NH₃ gas with the isolated solid complex, [ReO(H₂N₄L)(H₂O)]Cl₃, yielded a binuclear oxorhenium(V) complex, [Re₂O₃(H₂N₄L)₂]Cl₄. These complexes decompose through several isolable, as well as non‐isolable, intermediates during heating. [Re₂O₃(N₄L)]Cl₄, [ReO(N₄L)Cl], [ReO(N₄L)(PPh₃)]Cl, [ReO(N₄L)(SCN)] and [ReO(N₄L)(C₅H₆N₂)]Cl, were synthesized pyrolytically in the solid state from the corresponding rhenium complexes. The electronic absorption spectra and magnetic moments indicate an octahedral configuration for the complexes. The macrocyclic ligand in these complexes behaves either as neutral tetradentate or dianionic tetradentate towards the oxorhenium ions. The structures of all complexes and the corresponding thermal products were elucidated by elemental analyses, conductance, IR and electronic absorption spectra, magnetic moments, ¹H NMR and TG‐DSC measurements as well as by mass spectroscopy.

Keywords:

• Oxorhenium(V) complexes
• Biological activity
• Synthesis
• Characterization

Acknowledgment

The author expresses his great thanks to Dr. Usama Fahmy Ali, Department of Biological and Geological Sciences, Faculty of Education, Ain Shams University, Cairo, Egypt, for evaluating the biological assays.