Re(VII) and Tc(VII) trioxo complexes stabilized by tridentate ligands and their potential use as radiopharmaceuticals

• Overview of [ReO3]+ and [TcO3]+ complexes stabilized by tridentate ligands.
• Various synthetic strategies for preparation of these complexes are outlined.
• Effects of the ligands on complex structure and electronic properties are discussed.
• Their reactivity toward olefins focused on the [3 + 2] cycloaddition is reported.
• The potential application in radiopharmacy is discussed.

Tc(VII) and Re(VII) trioxo complexes are currently arousing interest because of their potential use as radiopharmaceuticals due to their hydrophilic character and stability in a biological environment. The radioactive isotopes 99mTc and 188Re are readily obtained from commercially available 99Mo/99mTc or 188W/188Re generators, respectively. Stabilization of the [MO3]+ species is achieved by coordination of tridentate ligands (N, O, S and Pt donors). Herein, the various synthetic strategies to synthesize these complexes starting from M2O7, [MO4]−, M(+V), M(+III) or M(+I) species are revised. The main structural features of the obtained distorted octahedral metal compounds are presented on the basis of their characterization by NMR and IR spectroscopy, and X-ray crystallography. Interestingly, the [MO3]+ complexes undergo cycloaddition reactions, either to form the corresponding M(+V) diolate complexes via [3 + 2] cycloaddition, or carbene complexes via [2 + 2] cycloaddition. In this review we also comment on the few reported examples using [3 + 2] cycloaddition to label the trioxo compounds with bioactive molecules for their potential application as radiopharmaceuticals.

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