Direct Detection of a Triplet Vinylnitrene, 1,4-Naphthoquinone-2-ylnitrene, in Solution and Cryogenic Matrices

The photolysis of 2-azido-1,4-naphthoquinone (1) in argon matrices at 8 K results in the corresponding triplet vinylnitrene 3 2, which was detected directly by IR spectroscopy. Vinylnitrene 3 2 is stable in argon matrices but forms 2-cyanoindane-1,3-dione (3) upon further irradiation. Similarly, the irradiation of azide 1 in 2-methyltetrahydrofuran (MTHF) matrices at 5 K resulted in the ESR spectrum of vinylnitrene 3 2, which is stable up to at least 100 K. The zero-field splitting parameters for nitrene 3 2, D/hc = 0.7292 cm–1 and E/hc = 0.0048 cm–1, verify that it has significant 1,3-biradical character. Vinylnitrene 3 2 (λmax ∼ 460 nm, τ = 22 μs) is also observed directly in solution at ambient temperature with laser flash photolysis of 1. Density functional theory (DFT) calculations support the characterization of vinylnitrene 3 2 and the proposed mechanism for its formation. Because vinylnitrene 3 2 is relatively stable, it has potential use as a building-block for high-spin assemblies.