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 [C H R N CH CH ] (R=H [1 a] , Me [1 f] , tBu [1 g] ), and [C H R N CH CH ] (R=H [2 a] , Me [2 b] ) were prepared and evaluated for use in the initiation of hydrodefluorination (HDF) catalysis. Compound [2 a] 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 (C-F) bonds under mild conditions. The protocol was also adapted to effect the deuterodefluorination of cis-2,4,6-(CF ) C H . The dications are shown to act as hydride acceptors with the isolation of neutral species C H N (3 a) and C H Me N (3 b) and monocationic species [C H N ] ([4 a] ) and [C H N ]+ ([4 b] ). Experimental and computational data provide further support that the dications are initiators in the generation of silylium cations.