Bipyridinium and Phenanthrolinium Dications for Metal-Free Hydrodefluorination: Distinctive Carbon-Based Reactivity

The development of novel Lewis acids derived from bipyridinium and phenanthrolinium dications is reported. Calculations of Hydride Ion Affinity (HIA) values indicate high carbon-based Lewis acidity at the ortho and para positions. This arises in part from extensive LUMO delocalization across the aromatic backbones. Species C₁₀H₆R₂N₂CH₂CH₂]²⁺ (R=H 1 a]²⁺ , Me 1 f]²⁺ , tBu 1 g]²⁺ ), and C₁₂H₄R₄N₂CH₂CH₂]²⁺ (R=H 2 a]²⁺ , Me 2 b]²⁺ ) were prepared and evaluated for use in the initiation of hydrodefluorination (HDF) catalysis. Compound 2 a]²⁺ proved highly effective towards generating catalytically active silylium cations via Lewis acid-mediated hydride abstraction from silane. This enabled the HDF of a range of aryl- and alkyl- substituted sp³(C?F) bonds under mild conditions. The protocol was also adapted to effect the deuterodefluorination of cis-2,4,6-(CF₃)₃C₆H₉. The dications are shown to act as hydride acceptors with the isolation of neutral species C₁₆H₁₄N₂ ( 3 a ) and C₁₆H₁₀Me₄N₂ ( 3 b ) and monocationic species C₁₄H₁₃N₂]⁺ ( 4 a]⁺ ) and C₁₈H₂₁N₂]+ ( 4 b]⁺ ). Experimental and computational data provide further support that the dications are initiators in the generation of silylium cations.