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 sp(3)(C-F) bonds under mild conditions. The protocol was also adapted to effect the deuterodefluorination of cis-2,4,6-(CF3)(3)C6H9. 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.

Automated summary

The development of novel Lewis acids derived from bipyridinium and phenanthrolinium dications has shown high carbon-based Lewis acidity, making them effective catalysts for hydrodefluorination reactions. These Lewis acids are capable of generating catalytically active silylium cations and have been successfully used for the initiation of deuterodefluorination reactions. Experimental and computational data support the role of these dications as initiators in the generation of silylium cations.