Structure and reactivities of rhenium and technetium bis-arene sandwich complexes [M(η6-arene)2]+

Sandwich complexes are important building blocks in medicinal inorganic chemistry for group 6 and 8 elements but are almost unknown for the manganese triad. We present the syntheses and full characterization of the mixed-arene 99Tc sandwich complexes [99Tc(η6-hmbz)(η6-C6H5–NH3)](PF6)2 and [99Tc(η6-hmbz)(η6-C6H5–Br)](PF6). Both comprise functionalities for conjugation to targeting molecules or for being included as substructures in pharmaceutically active lead compounds. Since η6-benzene ligands are too stably bound to be replaced with incoming ligands, we prepared naphthalene complexes [Re(η6-C6H6)(η6-napht)]+ and [Re(η6-napht)2]+. Their reactivities towards substitution are increased and one or both naphthalene ligands can be replaced with mono- or multi-dentate ligands. Combining the features of 99Tc and Re may lead to a molecule-based theranostic approach.