Arene

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Background

Bis-arene complexes are very fundamental complexes in organometallic chemistry, comparable to metallocenes but much less explored in bioorganometallic chemistry. With the neighboring elements, this class of complexes has been studied in detail. Although the respective 99Tc and Re complex are known since a long time, its chemistry remained essentially undeveloped, especially the one of 99Tc. With the aim of elucidating the physico-chemical properties of the group 7 analogues, we found a new route to rhenium and especially to 99mTc bis-arenes along an unexpected route. It turned out that [M(arene)2]+ are extraordinarily stable, against air and water even at high temperature. This makes them very convenient for application in life sciences. Due to the beauty and the properties, we investigate this class now with great enthusiasm. The perspective is complementing metallocene chemistry with these bis-arenes congeners.  
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Figure 2. ORTEP presentation of [99Tc(tetraline)2]+

Current research

To generalize the accessible type of bis-arenes, we are exploring different synthetic approaches in particular the replacement of AlCl3 in the procedure. Mixed arene compounds and complexes with one arene only are of great interest to achieve a structural diversity. However, the arene ligands are tightly bound and its replacement is not straight forward. For the introduction of targeting functions, organic chemistry at the coordinated arene rings is ongoing.

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Scheme 1. Synthetic procedure to bis-arene complexes of
99(m)Tc and Re.
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Figure 2. Cyclovoltamograms of different bis-arene complexes of 99Tc (left) and 99Tc NMR of a reaction mixture showing trans-alkylation in the synthetic process

Challenges

Synthesis of bis-arene complexes directly from water – replacement of one ring by other incoming ligands – metal-centered reactivities – ligand-centered reactivities – photochemistry of these complexes

Coworkers

Giuseppe Meola, Carla Gotzmann, Daniel Valdes Hernandez (PhD students), Dr. Paul Schmutz, Dr. Henrik Braband

Selected publication

From TcVII to TcI; facile syntheses of bis-arene complexes [99(m)Tc- (arene)2]+ from pertechnetate. Benz, M., Braband, H., Schmutz, P., Halter, J. and Alberto, R. (2015): Chem. Sci. 6, 165-169.