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

Two simple acyl­nitrenes, 2-furoyl­nitrene (2) and 3-furoyl­nitrene (6), 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 N₂ matrices (3–40 K) and the triplet state in toluene (10 K) with EPR spectroscopy (³2: |D/hc| = 1.48 cm^–1 and |E/hc| = 0.029 cm^–1; ³6: |D/hc| = 1.39 cm^–1 and |E/hc|c = 0.039 cm^–1). Subsequent visible-light and UV laser irradiations led to the formation of furyl isocyanates (3 and 7) and ring-opening product 3-cyanoacrolein (9-E and 9-Z), respectively, in which the elusive 3-furyl­nitrene (³8) was also identified by IR and EPR spectroscopy (|D/hc| = 1.12 cm^–1 and |E/hc| = 0.005 cm^–1).