Bis-arene complexes of technetium represent a fundamental class of organometallic compounds. Detailed insights into their properties are obtained due to novel and convenient synthetic routes.

Reported herein is a new concept for the labelling of biomolecules with small [(99m)TcO(3)](+) complexes through a [3+2] cycloaddition with alkenes for radiopharmaceutical applications. We developed convenient reactions for the synthesis of small, water stable fac-[TcO(3)(tacn-R)](+) complexes ((99)Tc and (99m)Tc, tacn = 1,4,7-triazacyclononane, R = H, -CH(2)-C(6)H(5), -CH(2)-C(6)H(4)COOH). With alkenes, these high valent [(99m)TcO(3)](+) complexes undergo [3+2] cycloaddition with formation of the corresponding Tc(V)-glycolato complexes. The (99m)Tc(V) and (99m)Tc(VII) complexes are stable at 37 degrees C in water and in the presence of serum proteins. Therefore, new opportunities in technetium chemistry are enabled with a high potential for medicinal and biological applications. In contrast to classical labelling, the presented strategy is ligand and not metal-centred.

Too hot to handle: Unprecedented affinity and specificity for (99)TcO(4)(-) in aqueous solution was shown with the p-xylyl azacryptand in the hexaprotonated form. A crystal structure of the complex reveals how the anion fits within the cavity of the cage, and the formation of multiple H-bond interactions with protonated amino groups stabilize the adduct.

Cationic dioxorhenium and dioxotechnetium complexes of the composition [MO(2)(L(1))(4)](+) (L(1) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) have been prepared from various starting materials and studied spectroscopically and by X-ray crystallography. The metal-carbon distances range from 2.216(4) to 2.232(4) A indicating mainly sigma-bonding.

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 Tc sandwich complexes [Tc(η-hmbz)(η-CH-NH)](PF) and [Tc(η-hmbz)(η-CH-Br)](PF). Both comprise functionalities for conjugation to targeting molecules or for being included as substructures in pharmaceutically active lead compounds. Since η-benzene ligands are too stably bound to be replaced with incoming ligands, we prepared naphthalene complexes [Re(η-CH)(η-napht)] and [Re(η-napht)]. 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 Tc and Re may lead to a molecule-based theranostic approach.