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 ion 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. The use of novel organic dications as carbon‐based Lewis acids is reported. The Hydride Ion Affinity (HIA) of these bipyridinium and phenanthrolinium salts is exploited to initiate hydrodefluorination catalysis. Further, the participation of these species enables deuterodefluorination. Experimental and DFT analysis support the role of the dications in the initiation of silylium‐mediated catalysis.