2026/06/23 by J.P. Borel, Morten Lehmann, Martin Kaupp +1 · 1 voice
Chemistry · Pharmacology, Toxicology and Pharmaceutics · #Inorganic Fluorides and Related Compounds #Fluorine in Organic Chemistry #Synthesis and characterization of novel inorganic/organometallic compounds
paper · doi:10.1002/chem.71282
ABSTRACT Lewis acidic compounds such as germylium ions can be applied to C─F bond activations to access fluorinated building blocks or degrade fluorinated alkyl compounds in order to address environmental concerns and to promote a circular economy. Germylium ions [R 3 Ge][B(C 6 F 5 ) 4 ] (R = Et, n Bu, and Ph) were isolated after treatment of [Ph 3 C][B(C 6 F 5 ) 4 ] with tertiary germanes. Derivatization reactions include the formation of binuclear fluoronium ions [R 3 Ge–F–GeR 3 ][B(C 6 F 5 ) 4 ] (R = Et, n Bu, Ph) or fluorogermanes R 3 GeF (R = Et, n Bu, Ph) after reaction with CsF. Various Lewis pairs such as [ n Bu 3 Ge–PPh 3 ][B(C 6 F 5 ) 4 ] were also generated. The strong Lewis acidity of the germylium ions enables the C─F bond dehydrofluorination of mono‐ and polyfluorinated substrates. Thus, fluorocyclohexane was selectively converted into cyclohexene along with the production of H 2 and fluorogermane. DFT calculations and experimental investigations revealed a concerted E2‐type mechanism where the tertiary germane reacts as a base to generate the olefinic products. The reaction pathway is in kinetic competition with an also concerted S N 2‐type hydrodefluorination step. In contrast, the analogous silylium‐based reactions occur via a step‐wise S N 1 mechanism, with the silane acting as a hydride donor to a fluorosilane‐stabilized carbenium ion leading exclusively to the thermodynamically favoured hydrodefluorination product.