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

Herein, we report the synthesis of an acyclic carbene-stabilized diphospha(aminyl) PNP radical CAACPNPCAAC (CAAC = 1-[2,6-bis(isopropyl)phenyl]-3,3,5,5-tetramethyl-2-pyrrolidinylidene) by a facile one-pot, seven-electron reduction of hexachlorophosphazene chloride [ClPNPCl][Cl]. The PNP radical features a conjugated framework with spin density primarily localized on the central nitrogen atom as well as the flanking carbenes. Unlike other tripnictogen radicals, undergoes facile one-electron oxidation and reduction to yield nonclassical nitrenium and amide species [] and [], respectively. The cation [] exhibits conformational flexibility in the solution state between the expected W-shaped geometry [] and a previously unobserved linear heteroallene-type structure [], which was characterized in the solid state. The equilibrium was explored both computationally and experimentally, showing that [] is favored over [] both enthalpically (Δ = -2.9 × 10 ± 80 J mol) and entropically (Δ = 4.2 ± 0.25 J mol K). The formal amide [] 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 , which exhibits μ, κ-P, κ-P, and η-PNP coordination modes. Protonation of [] leads to the formation of an amine , which features a trigonal planar geometry around nitrogen.