Carbon‐ and SO₂‐Locked Diarylnitroxides: Quantum Chemical Consideration, Synthesis, and Electrochemistry

Abstract

Selection of linkers connecting two phenyl rings as a part of molecular design of diarylnitroxides with increased kinetic stability of redox forms was performed using quantum chemical estimation of the geometry and oxidation potential values. It revealed that introduction of the carbon bridge cannot be considered as efficient “instrument” for structural tuning of the nitroxide properties since altering neither the length of the bridge nor its position results in significant changes in the oxidation potential, in contrast to a heteroatomic bridge, which makes more perturbation in the electronic structure of diarylnitroxide. To support the prediction, new SO2‐bridged diarylnitroxide was synthesized and characterized using spectral and electrochemical methods. It is extremely stable in benzene solution, exhibits the maximal anodic potential value achieved for reversibly oxidized nitroxides to date (1.33 V, Ag/AgCl/KCl) and seems promising as cathodic redox active material providing maximal potential gap as compared to the previously reported compounds.

Chameleonic Behavior of the α‐Methylcyclopropyl Group and Its Through‐Space Interactions: A Route to Stabilized Three Redox States in Diarylnitroxides

“…As practical applications of nitroxide radicals are mainly based on their redox properties, electrochemical investigation of compounds 1 MCP – 5 MCP was of primary importance. Voltammetric curves for nitroxides 1 MCP – 5 MCP are given in Figure .…”

A PROXYL‐Type Norbornene Polymer for High‐Voltage Cathodes in Lithium Batteries

“…Diaryl nitroxide radicals currently give the highest redox potentials of over 4 V versus Li/Li + , although the long-term stability is not ideal. [20,21] Nitronyl nitroxide (3.5 V), [15] verdazyl (around 2.9 V), [22] and triphenylmethyl radicals (around 2.9 V) [23] would offer improved stability, but lower voltages. On the other hand, a nitroxide radical with a five-membered ring, tetramethylpyrrolidine 1-oxyl (PROXYL), and their derivatives are reported as chemically robust and to give higher potentials than TEMPO (≈3.7 V).…”

Redox: Organic Robust Radicals and Their Polymers for Energy Conversion/Storage Devices

“…143 Methyl groups in TEMPO can be partially or totally replaced with aromatic groups (NO41−NO43). 128,144 The redox potential could be increased to 1.33 V vs Ag/AgCl by withdrawing electrons with sulfone via the aromatic structure, although the stability of the radical was sacrificed. 144 2.1.1.2.…”