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Probing Avenues for Isolation of Simple Organic Radical Anions – Of Metal Coordination and Encapsulation Between Cations

Subject Area Inorganic Molecular Chemistry - Synthesis and Characterisation
Term from 2016 to 2024
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 325302919
 
Final Report Year 2024

Final Report Abstract

The overarching aim of this project was to provide a comprehensive understanding of linear complexes of late 3d-metals in the oxidation state +I in terms of synthetic access and variability, elucidation of their electronic structure as well as their use in bond activation and transformation processes. The primary subject was developing a broader synthetic access to homoleptic quasilinear metal(I) complexes of mid to late 3d-metals (Cr - Ni). This could be well established using a variety of silylamide ligands, remains a challenge for other anionic ligand types, and could be extended to heteroleptic complexes with N-heterocyclic ligands. The obtained library of compounds allowed for insights into the single molecule magnetic features of respective iron compounds. Here it showed most notably that for a two-coordinate iron(I) ion it has to be sterically locked in a linear fashion to be able to observe magnetic blocking. Examination of linear metal(I) complexes in their behaviour towards organic substrates bearing different bond types (e.g. C-C/N double and triple bonds, C=O bonds, C-halide) show a multitude of unusual bond activation scenarios. Most of them are result of a partial or complete oneelectron transfer onto antibonding orbitals. This created a multitude of metal stabilized radical anions, which could exploited amongst other for isomerisation catalysis. Given the pivotal role of radical anions in organic transformations, we further developed a synthetic approach for the isolation of named radical anions via encapsulation in between two bulky cations. Quasilinear complexes also turned out to be a very useful platform for the generation of highly reactive, low-coordinate imido metal complexes in higher spin states. As such one of the first examples of a cobalt imidyl was obtained. In addition a trigonal alkyl imido cobalt compound was identified as highly competent in C–H bond activation via H atom transfer. Chalcogene activation by quasilinear metal(I) complexes is a further, fruitful field from a structural perspective. Most notable examples a monosulfide bridged iron complex ([L2FeII-Ch- FeIIL2]n) in three different oxidation state was obtained. In addition an [Fe2S2] cluster with very low-coordinate iron ions could be obtained. These biological relevant motifs were shown to be cleaved by the CS2. This yields insights into its biologically inhibitory mode of action for iron sulfur clusters. Furthermore, an alternative approach of reacting metal(II) complexes with partially reduced alkali metal chalcogenides was also pursued, leading to a new set of metal chalcogenides. This methodology was further expanded to tetrahedral ZINTL anions, that are isoelectronic to P4 (e.g. [Sb2Sn2]-), leading to unique structural 3d-metal/main group motifs. Attempts to expand these findings into a dinuclear setting, to probe interactions between two linked, linear metal(I) units, proved however unsuccessful so far.

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