Confined Lewis Pairs: Investigation of the X−→Si20 Interaction in Halogen‐Encapsulating Silafulleranes

• Published in: Angewandte Chemie 2024-02, Vol.136 (6), p.n/a
• Main Authors: Gasevic, Thomas, Bamberg, Marcel, Wicke, Julius, Bolte, Michael, Virovets, Alexander, Lerner, Hans‐Wolfram, Grimme, Stefan, Hansen, Andreas, Wagner, Matthias, Bursch, Markus
• Format: Article
• Language: English
• Subjects: 35Cl NMR; Confined Lewis Pairs; Coupled-Cluster; DFT; Lewis acid; Magnetic resonance spectroscopy; NMR spectroscopy; Silafulleranes; Supramolecular compounds
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202314238

A joint theoretical and experimental study on 32 endohedral silafullerane derivatives [X@Si20Y20]− (X=F‐I; Y=F‐I, H, Me, Et) and Th ${T_h }$ ‐[Cl@Si20H12Y8]− (Y=F‐I) is presented. First, we evaluated the structure‐determining template effect of Cl− in a systematic series of concave silapolyquinane model systems. Second, we investigated the X−→Si20 interaction energy ( Eint ${E_{{\rm{int}}} }$ ) as a function of X− and Y and found the largest Eint ${E_{{\rm{int}}} }$ values for electron‐withdrawing exohedral substituents Y. Given that X− ions can be considered as Lewis bases and empty Si20Y20 clusters as Lewis acids, we classify our inseparable host–guest complexes [X@Si20Y20]− as “confined Lewis pairs”. Third, 35Cl NMR spectroscopy proved to be highly diagnostic for an experimental assessment of the Cl−→Si20 interaction as the paramagnetic shielding and, in turn, δ ${\delta }$ (35Cl) of the endohedral Cl− ion correlate inversely with Eint ${E_{{\rm{int}}} }$ . Finally, we disclose the synthesis of [PPN][Cl@Si20Y20] (Y=Me, Et, Br) and provide a thorough characterization of these new silafulleranes. A joint theoretical and experimental study on 32 endohedral silafulleranes is presented. Template effects of Cl− are investigated for the [X@Si20Y20]− complexes that are classified as “confined Lewis pairs”. The origins of the diagnostic 35Cl NMR chemical shifts are elucidated computationally. Finally, we disclose the synthesis of [PPN][Cl@Si20Y20] (Y=Me, Et, Br) including their thorough characterization.