A series of 4- and 2,4,6-substituted diaryl sulfur diimides induce a large dependence on redox properties, such as the one-electron reduction CV waves shown here, that correlate linearly with the redox MO energies. One-electron transfers are confirmed using in situ EPR spectroscopy, identifying radical anions that have longer lifetimes the more electron withdrawing the substituents.

Abstract

The synthesis and extensive characterization of nine aryl sulfur diimides (SDIs, Ar−NSN−Ar) are presented with a robust computational and experimental investigation of the fundamental properties of these important members of the thiazyl family of compounds, with particular attention paid to their highly tunable electrochemical behaviour. This is the first work to undertake a systematic comparison of the electrochemical profiles of a coherent series of SDIs to demonstrate and quantify the response of their reduction potentials to substituent electron-donating and -withdrawing properties. This effect is found to be not only exceptionally strong, but also correlates very closely with computed orbital energies. Electron paramagnetic resonance spectroscopy is used to determine the nature, localization, and qualitative lifetimes of the radical anions of SDIs. This work also addresses significant misconceptions about physical properties of SDIs. Experimental data and modern computational methods are employed to provide a resolute answer to the long-standing contention of the solution-state conformations of SDIs, and to correct historical mistakes in the assignment of infrared spectroscopic data. High-quality crystal structures of all SDIs in this work showcase the utility of the recently introduced structural refinement software NoSpherA2, enabling full anisotropic refinement of H-atoms with accurate C−H bond lengths.