Synthesis and properties of cyclic sandwich compounds

Luca Münzfeld; Sebastian Gillhuber; Adrian Hauser; Sergei Lebedkin; Pauline Hädinger; Nicolai D Knöfel; Christina Zovko; Michael T Gamer; Florian Weigend; Manfred M Kappes; Peter W Roesky

doi:10.1038/s41586-023-06192-4

Synthesis and properties of cyclic sandwich compounds

Nature. 2023 Aug;620(7972):92-96. doi: 10.1038/s41586-023-06192-4. Epub 2023 Aug 2.

Affiliations

¹ Institute of Inorganic Chemistry, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.
² Institute of Nanotechnology, Karlsruhe Institute of Technology (KIT), Eggenstein-Leopoldshafen, Germany.
³ Department of Chemistry, Philipps University of Marburg, Marburg, Germany.
⁴ Institute of Physical Chemistry, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.
⁵ Institute of Inorganic Chemistry, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany. roesky@kit.edu.

PMID: 37532814
DOI: 10.1038/s41586-023-06192-4

Abstract

Cyclic nanometre-scale sandwich complexes assembled from individual building blocks were synthesized. Sandwich complexes, in which a metal ion is π-coordinated by two planar aromatic organic rings belong to the foundations of organometallic chemistry. They have been successfully used in a wide variety of applications ranging from catalysis, synthesis and electrochemistry to nanotechnology, materials science and medicine^1,2. Extending the sandwich structural motif leads to linear multidecker compounds, in which aromatic organic rings and metal atoms are arranged in an alternating fashion. However, the extension to a cyclic multidecker scaffold is unprecedented. Here we show the design, synthesis and characterization of an isomorphous series of circular sandwich compounds, for which the term 'cyclocenes' is suggested. These cyclocenes consist of 18 repeating units, forming almost ideally circular, closed rings in the solid state, that can be described by the general formula [cyclo-M^II(μ-η⁸:η⁸-Cot^TIPS)]₁₈ (M = Sr, Sm, Eu; Cot^TIPS = 1,4-(ⁱPr₃Si)₂C₈H₆^2-). Quantum chemical calculations lead to the conclusion that a unique interplay between the ionic metal-to-ligand bonds, the bulkiness of the ligand system and the energy gain on ring closure, which is crucially influenced by dispersion interactions, facilitate the formation of these cyclic systems. Up to now, only linear one-dimensional multidecker sandwich compounds have been investigated for possible applications such as nanowires^3-10. This textbook example of cyclic sandwich compounds is expected to open the door for further innovations towards new functional organometallic materials.