Electrochemical Properties of a Pyridine-Tunable Trisferrocenylborane

Non-aqueous redox flow batteries (NARFBs) offer promising solutions for sustainable and long-term energy storage. Herein, trisferrocenylborane (BFc₃; Fc = ferrocene, Cp₂Fe, and Cp = C₅H₅^–) is examined for its potential role as a tunable anolyte for use in NARFBs. BFc₃ contains three readily oxidized ferrocene units along with a mediating borane that hosts an empty p orbital, allowing tuned access to specific redox properties as a function of nucleophile choice. The electrochemical behavior (cyclic voltammetry, charging/discharging cycles, etc.) of BFc₃ are accordingly examined in the presence of a series of 4-R-substituted pyridines (R = NMe₂, NH₂, ^tBu, Et, or I), with a range of nitrogen donor strengths. These adducts produce a linear correlation that relates E_1/2 to the para-substituent constant (σ_p), showing a tunability of 200–300 mV based on donor choice alone; solvent effects using tetrahydrofuran, acetonitrile, and dichloromethane are additionally discussed.