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

Abstract

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.

Fully Solvated, Monomeric Re(II) Complexes: Insights into the Chemistry of [Re(NCCH3)6]2+

“…In the past few years, we developed synthetic strategies towards new [Re( 6 -C6R6)2] + and [ 99(m) Tc( 6 -C6R6)2] + sandwich complexes. [14][15][16][17][18] Similar to other [M( 6 -C10H8)2] bis-naphthalene complexes (M = Cr, Mo), [19][20][21] coordination of the naphthalene ligands to the Re I center is comparably weak in [Re( 6…”

[Re(η6-arene)2]+ as a highly stable ferrocene-like scaffold for ligands and complexes

“…The symmetry of all NMR spectra and therefore the free rotation around the rhenium axis is found for all [Re(arene) 2 ] + synthesized by our group so far. [5][6][7]16,17,27 Pyridines are prototypical ligands in many catalytic processes, e.g. for proton reduction in photocatalysis.…”

“…In contrast to its neighbouring elements, we found that [Re(η 6 -C 6 H 6 ) 2 ] + type complexes are remarkably stable. 4,5,16 For instance, [Re(η 6 -C 6 H 6 ) 2 ] + does not decompose or lose benzene rings even when heated to 160°C or when irradiated with UV light. [Re(η 6 -C 6 R 6 ) 2 ] + offers structural flexibilities in three dimensions as depicted in Scheme 1.…”

“…The symmetry of all signals observed in the NMR spectra (see ESI †) supports the notion of free rotation at room temperature. [5][6][7]16,17 Electrochemistry showed that Re(I) is reversibly oxidized at E°1 /2 > +1.3 V (Re I /Re II ). Irreversible reductions take place at low potentials <−2.0 V, both vs. Ag/AgCl.…”

Towards 99mTc- and Re-Based Multifunctional Silica Platforms for Theranostic Applications

“…In combination with isotopes 186 and 188 of its heavier homolog rhenium ( 186/188 Re), it represents one of the first "theranostic pairs" for nuclear medical diagnosis and therapy [6]. Recently, a conceptual extension of the "theranostic pair" Tc/Re was described by the combination of a 99m Tc-based bio-mimetic with its organometallic but non-radioactive rhenium homologue [7]. The rhenium complex should be therapeutically active through its structure, while the 99m Tc homologue allows for visualizing the pharmacology.…”