Tromancenium chemistry

In this research project the chemistry of cationic (cycloheptatrienyl)(cyclopentadienyl)manganese sandwich complexes will be explored in detail for the first time. New high-power LED photochemical synthesis and advanced organometallic synthetic strategies will be applied to get access to a range of new functionalized complexes that will serve as redox-responsive ligands in coordination chemistry, aiming at the generation of multimetallic conjugated complexes that are of interest as potential re- dox catalysts in homogeneous catalysis or as abiotic anticancer metallodrugs. Methodically, state of the art synthetic methods and spectroscopic techniques will be utilized, including multinuclear NMR, IR, UV-Vis, high-resolution mass spectrometry, cyclic voltammetry, single crystal structure analysis and density functional theory calculations.

Metallocenes are basic compounds in organometallic chemistry with many applications in catalysis, electrochemistry, sensorics, materials and nano science, and medicinal chemistry. The parent compound, ferrocene, was discovered over 70 years ago and in the following years further examples across the periodic table of elements were made and analyzed with regard to their chemical and physical properties and applications. However, cationic metallocenes are much less studied, mainly because of their deactivating positive charge which makes common synthesis and derivatization difficult. In this research project, new innovative synthetic methods for the preparation of so-called tromancenium salts were performed and their reactivity and applications was studied for the first time. Tromancenium salts contain the central metal manganese in oxidation state +1 and -bonded cycloheptatrienyl C7H7 and cyclopentadienyl C5H5 ring ligands. The synthesis of these metal complexes is accomplished starting from (cyclopentadienyl)(tricarbonyl)-manganese(0) precursors by a sequence of photochemical CO substitutions and oxidation or hydride-abstraction with triarylcarbenium salts. It could be shown that chemical functionalization is much more facile on the 5-ring ligand and that the 7-ring ligand is distinctly weaker bonded to the metal center. Electrochemical oxidation to Mn2+ and electrochemical reduction to Mn0 is possible, but reversibility depends on the substitution pattern, as expected. First applications in redox catalysis and medicinal chemistry could be realized with Mn/Fe/Co cage compounds containing apical tromanceniumyl substituents. Overall, the results of this research project are the base of any further development of these heteroleptic manganese metallocene complexes. In a broader context, the application of innovative LED photochemistry has general potential in preparative inorganic chemistry.