N-Heterocyclic Carbene-Carbodiimide (NHC-CDI) Adducts as a Tunable Scaffold for Distonic Radical Cation and Dication Stabilization

Reactive organic intermediates – particularly radical cations and dications – possess unique structural and electronic properties significant for the advancement of fundamental chemistry and materials. However, stabilizing motifs for these highly reactive species have limited synthetic accessibility and tunability. N-Heterocyclic carbene-carbodiimide (NHC-CDI) adducts are a promising platform to stabilize these intermediates due to their tunability and synthetic accessibility. Herein, we report a simple NHC-CDI framework – containing substituted diphenyl CDIs with one “super radical stabilizer” (4-dimethylamino) and one tunable handle – that can stabilize distonic radical cation and dication species. We synthesized six systematically-varied adducts that undergo two sequential, reversible oxidations with half-wave potentials (E1/2,1 = −0.528 to −0.205 V; E1/2,2 = −0.005 to 0.115 V) correlating strongly to the electronics of the CDI (i.e., Hammett σp parameters). Cyclic voltammetry was used to characterize the electrochemical behavior of the NHC-CDIs. Scan rate studies revealed a reversible, diffusion-controlled system. Additionally, cycling experiments resulted in minimal changes in current density after ten cycles. The facile synthetic tunability and accessibilty make this platform promising for the study and development of reactive intermediates for catalysis and energy materials.