The missing link: triplet fluorocarbonyl nitrene FC(O)N.

The elusive triplet fluorocarbonyl nitrene, FC(O)N (X(3 A''), has been generated in high yield from matrix-isolated FC(O)N(3) by ArF excimer laser photolysis (λ=193 nm). As a side product FNCO was formed. The novel nitrene was characterized by IR, UV/Vis, EPR spectroscopy, and quantum-chemical calculations. All six fundamental vibrations of FC(O)N at 1681.3, 1193.8, 879.8, 646.5, 588.7, and 434.8 cm(-1) (argon matrix, 16 K), their (12/13)C, (16/18)O, and (14/15)N isotopic shifts, and four electronic transitions at T(0) =13 890, 25 428, 29 166, and 30 900 cm(-1) that exhibit vibrational fine structures have been detected. Under visible-light irradiation at λ≥495 nm, FC(O)N reacted with molecular N(2) in the matrix cage at 6 K to give back FC(O)N(3), whereas near-UV irradiation at λ≥335 nm yielded FNCO. The singlet-triplet energy gaps of different carbonyl nitrenes are discussed.