Controlling the Redox Speciation of N,C,N-Bi Complexes Using the Anion Coordination Index

Recently, N,C,N-bismuth pincer complexes have been shown to engage in a rich repertoire of redox chemistry, which has been harnessed in a myriad of catalytic organic reactions. Despite their ability to maneuver between various oxidation states, the thermodynamic landscape of the redox speciation has never been systematically studied, hampering a deeper understanding of low-valent bismuth redox manifolds. In this work, we probed the stability of a dimeric N,C,N-Bi-(II) pincer (2OTf) toward disproportionation in the presence of strongly and weakly coordinating anions, categorized by their coordinating ability index (α). While the complex persists in the presence of noncoordinating anions (α ≤ -0.4), it undergoes disproportionation to the corresponding Bi-(I) (1) and Bi-(III) (3X) complexes in the presence of coordinating anions (α ≥ 1). When the α falls between -0.4 and 1, excess electrolyte is required for disproportionation. These findings were guided by cyclic voltammetry experiments and further corroborated by spectroscopic and crystallographic characterization of the reaction products.