Development of electronically tuneable N-heterocyclic borates

In this contribution, we describe the synthesis and characterization of novel borates constructed with N-heterocyclic arene substituents. Beyond providing comparable electronic and redox properties to their fluoroarene analogues, the use of N-heterocycles allows for facile protonation of aromatic nitrogen atoms, thus providing a framework for tuneable reagents with varying Lewis basicity. The synthesized protonated borates were further examined as Brønstead-Lowry acids through pK_a bracketing and evaluation of the kinetic accessibility of their protons by variable temperature NMR. Finally, we report the synthesis of onium and alkali metal salts of these borates through deprotonation by a variety of bases providing useful starting points for future applications.