Nukleophile Übertragungsreaktionen der [Si(C2F5)3]−-Einheit

Evidence of the Lewis-Amphoteric Character of Tris(pentafluoroethyl)silanide, [Si(C2 F5 )3 ]. Angew Chem Int Ed Engl 2021;60:12124-12131. [PMID: 33617080 PMCID: PMC8252080 DOI: 10.1002/anie.202016455]

According to a first view on the geometrical and electronic structure of the tris(pentafluoroethyl)silanide, this anion appears as a Lewis base. Quantum chemical calculations on perfluoroalkylated silanides show significantly lower HOMO and LUMO energy levels in comparison to their non-fluorinated counterparts, which implies reduced Lewis basicity and increased Lewis acidity of the [Si(C2 F5 )3 ]- ion. With these findings and a HOMO-LUMO gap of 4.80 eV similar to N-heterocyclic silylenes (NHSis), perfluoroalkyl silanides are predestined to exhibit Lewis-amphoteric character similar to silylenes. Deprotonation of Si(C2 F5 )3 H with sterically demanding phosphazene bases afforded thermally stable phosphazenium salts of the [Si(C2 F5 )3 ]- anion, which add to benzaldehyde, benzophenone, CS2 , and CO2 in various manners. This behavior also mirrors the reactivity of silylenes towards ketones as well as heterocumulenes and is rationalized by Lewis amphotericity being inherent in these silanides.