Reactivity of Two-Electron-Reduced Boron Formazanate Compounds with Electrophiles: Facile N–H/N–C Bond Homolysis Due to the Formation of Stable Ligand Radicals

The reactivity of a boron complex with a redox-active formazanate ligand, LBPh2 [L = PhNNC­(p-tol)­NNPh], was studied. Two-electron reduction of this main-group complex generates the stable, nucleophilic dianion [LBPh2]2–, which reacts with the electrophiles BnBr and H2O to form products that derive from ligand benzylation and protonation, respectively. The resulting complexes are anionic boron analogues of leucoverdazyls. N–C and N–H bond homolysis of these compounds was studied by exchange NMR spectroscopy and kinetic experiments. The weak N–C and N–H bonds in these systems derive from the stability of the resulting borataverdazyl radical, in which the unpaired electron is delocalized over the four N atoms in the ligand backbone. We thus demonstrate the ability of this system to take up two electrons and an electrophile (E+ = Bn+, H+) in a process that takes place on the organic ligand. In addition, we show that the [2e–/E+] stored on the ligand can be converted to E• radicals, reactivity that has implications in energy storage applications such as hydrogen evolution.