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Herein, we report the synthesis of an acyclic carbene-stabilized diphospha(aminyl) PNP radical CAACMePNPCAACMe4 (CAACMe = 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 [5b]+ and a previously unobserved linear heteroallene-type structure [5a]+, which was characterized in the solid state. The equilibrium was explored both computationally and experimentally, showing that [5a]+ is favored over [5b]+ 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 K262, 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.
Gate-tunable Josephson junctions embedded in a microwave environment provide a promising platform to in situ engineer and optimize novel superconducting quantum circuits. The key quantity for the circuit design is the phase-dependent complex admittance of the junction, which can be probed by sensing a radio frequency SQUID with a tank circuit. Here, we investigate a graphene-based Josephson junction as a prototype gate-tunable element enclosed in a SQUID loop that is inductively coupled to a superconducting resonator operating at 3 GHz. With a concise circuit model that describes the dispersive and dissipative response of the coupled system, we extract the phase-dependent junction admittance corrected for self-screening of the SQUID loop. We decompose the admittance into the current-phase relation and the phase-dependent loss, and as these quantities are dictated by the spectrum and population dynamics of the supercurrent-carrying Andreev bound states, we gain insight to the underlying microscopic transport mechanisms in the junction. We theoretically reproduce the experimental results by considering a short, diffusive junction model that takes into account the interaction between the Andreev spectrum and the electromagnetic environment, from which we estimate lifetimes on the order of ∼10 ps for nonequilibrium populations.