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

Abstract 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 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 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). Electrochemical studies confirmed each redox event as a reversible, one-electron, and diffusion-controlled process. Additionally, spectroscopic experiments of a chemically oxidized NHC-CDI support the formation and stability of the radical cation and dication species. The facile synthetic tunability and accessibility make this platform promising for the study and development of reactive intermediates for catalysis and energy materials.