Synthesis of a Carbene-Stabilized (Diphospha)aminyl Radical and Its One Electron Oxidation and Reduction to...

Herein, we report the synthesis of an acyclic carbene-stabilized diphospha(aminyl) PNP radical CAAC^MePNPCAAC^Me 4 (CAAC^Me = 1-[2,6-bis(isopropyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylidene) by a facile one-pot, seven-electron reduction of hexachlorophosphazene chloride [Cl₃PNPCl₃][Cl]. The PNP radical 4 features a conjugated framework with spin density primarily localized on the central nitrogen atom as well as the flanking carbenes. Unlike other tripnictogen radicals, 4 undergoes facile one-electron oxidation and reduction to yield nonclassical nitrenium and amide species [5]⁺ and [6]^-, respectively. The cation [5]⁺ exhibits conformational flexibility in the solution state between the expected W-shaped geometry [5]⁺ and a previously unobserved linear heteroallene-type structure [5]⁺, which was characterized in the solid state. The equilibrium was explored both computationally and experimentally, showing that [5]⁺ is favored over [5]⁺ both enthalpically (ΔH = -2.9 × 10³ ± 80 J mol^-1) and entropically (ΔS = 4.2 ± 0.25 J mol^-1 K^-1). The formal amide [6]^- displays remarkable flexibility in its coordination chemistry due to the presence of multiple Lewis basic centers, as evidenced by the structure of its potassium complex K6, which exhibits μ, κ-P, κ-P, and η³-PNP coordination modes. Protonation of [6]^- leads to the formation of an amine 7, which features a trigonal planar geometry around nitrogen.