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 CAAC Me PNPCAAC 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 [Cl 3 PNPCl 3 ][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 b ] + and a previously unobserved linear heteroallene-type structure [ 5 a ] + , which was characterized in the solid state. The equilibrium was explored both computationally and experimentally, showing that [ 5 a ] + is favored over [ 5 b ] + both enthalpically (Δ H = -2.9 × 10 3 ± 80 J mol -1 ) and entropically (Δ S = 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 K 2 6 2 , which exhibits μ, κ-P, κ-P, and η 3 -PNP coordination modes. Protonation of [ 6 ] - leads to the formation of an amine 7 , which features a trigonal planar geometry around nitrogen.