Magnetically Bistable Nitrenes: Matrix Isolation of Furoyl­nitrenes in Both Singlet and Triplet States and Triplet 3‑Furyl­nitrene

Two simple acyl­nitrenes, 2-furoyl­nitrene (<b>2</b>) and 3-furoyl­nitrene (<b>6</b>), were generated through 266 nm laser photolysis of the corresponding azides. Both are magnetically bistable in cryogenic matrices, as evidenced by the direct observation of the closed-shell singlet state with IR spectroscopy in solid Ne, Ar, Kr, Xe, and N<sub>2</sub> matrices (3–40 K) and the triplet state in toluene (10 K) with EPR spectroscopy (<sup>3</sup><b>2</b>: |<i>D</i>/<i>hc</i>| = 1.48 cm<sup>–1</sup> and |<i>E</i>/<i>hc</i>| = 0.029 cm<sup>–1</sup>; <sup>3</sup><b>6</b>: |<i>D</i>/<i>hc</i>| = 1.39 cm<sup>–1</sup> and |<i>E</i>/<i>hc</i>|<i>c</i> = 0.039 cm<sup>–1</sup>). Subsequent visible-light and UV laser irradiations led to the formation of furyl isocyanates (<b>3</b> and <b>7</b>) and ring-opening product 3-cyanoacrolein (<b>9</b>-<i>E</i> and <b>9</b>-<i>Z</i>), respectively, in which the elusive 3-furyl­nitrene (<sup>3</sup><b>8</b>) was also identified by IR and EPR spectroscopy (|<i>D</i>/<i>hc</i>| = 1.12 cm<sup>–1</sup> and |<i>E</i>/<i>hc</i>| = 0.005 cm<sup>–1</sup>).