Dynamic Covalent Bonds in the Ebselen Class of Antioxidants Probed by X‐ray Quantum Crystallography

Abstract

AbstractDynamic bonds are essential structural ingredients of dynamic covalent chemistry that involve reversible cleavage and formation of bonds. Herein, we explore the electronic characteristics of Se−N bonds in the organo‐selenium antioxidant ebselen and its derivatives for their propensity to function as dynamic covalent bonds by employing high‐resolution X‐ray quantum crystallography and complementary computational studies. An analysis of the experimentally reconstructed X‐ray wavefunctions reveals the salient electronic features of the Se−N bonds with very low electron density localized at the bonding region and a positive Laplacian value at the bond critical point. Bond orders and percentage covalency and ionicity estimated from the X‐ray wavefunctions, along with localized orbital locator (LOL) and electron localization function (ELF) analyses show that the Se−N bond is unique in its closed shell‐like features, despite being a covalent bond. Time‐dependent DFT calculations simulate the cleavage of Se−N bonds in ebselen in the excited state, further substantiating their nature as dynamic bonds.