Influence of sp² Nitrogen Atom Replacement on the Structure and Redox Properties of Allylic Intermediates

Heteroatom doping offers an opportunity for engineering the electronic structure of a conjugated system. Herein, we report the isolation and characterization of multiredox allyl and 2-azaallyl intermediates, including anions, radicals, and cations. The replacement of ═CH moiety with ═N at the C-2 position significantly stabilizes the 2-azaallyl cation [Ph₂CNCPh₂]⁺, resulting in reduced hydride affinity and decreased hydride abstraction reactivity, which have been proven by thermodynamic and kinetic studies. The contribution of a nitrogen lone pair to bonding and π-interactions between phenyl groups is attributed to a bent geometry of [Ph₂CNCPh₂]⁺. The substitution of electronegative nitrogen reduces the energy level of π₁ (bonding) and π₃ (antibonding) orbitals of allyl systems, causing a red shift in ultraviolet-visible (UV-vis) absorption for the allyl radical but a blue shift for the cation. This study reveals the distinct regulatory effects of sp²- and sp³-hybridized nitrogen on the electronic and molecular structures of multiredox intermediates, providing guidance for selecting heteroatom doping strategies based on the specific needs of conjugated materials.