Reduction of rhenium (V) oxo Schiff Base Complexes with triphenyl phosphine ligands

Abstract

One approach to the treatment of cancer is to direct beta-emitting radionuclide to the cancer site where the radiation destroys the cancer cells. This can be achieved by coordinating the radioisotope in a very stable environment and linking it to a specific biological targeting molecule, which interacts specifically with particular cancer cells. It is necessary to have extremely stable in vivo radionuclide complexes so that limited amounts of radiation are released to other parts of the body before the radionuclide can reach the cancer cells. Isotopes of radioactive Rhenium are characteristic of such a nuclide. Our emphasis was to obtain a Rhenium (III) metal ligand complex since the lower oxidation state is more kinetically inert relative to Rhenium (V).

The method employed was to first produce the ReV-ligand complex, [ReVOCl(Sal2phen)], by reacting a 1:2 molar ratio of TBA[ReVIIOCl4] to Sal2phen. Next, [ReVOCl(Sal2phen)] was reacted with three equivalents of triphenylphosphine to determine whether a mono-substituted ReV complex or a di-substituted ReIII complex was formed. After purifying the product by solvent extraction, the coordinated complex was reacted with ammonium hexaflurophoshate, NH4PF6, to induce crystallization of the target compound, [ReIII(PPh3)2(Sal2phen)][PF6]. Preliminary 1H NMR, and FT-IT spectra suggest formation of trans-[ReIII(PPh3)2(sal2phen)]PF6. The Re=O stretch at 951.36 cm-1 observed for [ReOCl(sal2phen)] in the IR spectrum is missing from our product, implying the Re (III) product has been formed.