N-Methylcarbamoyl azide: spectroscopy, X-ray structure and decomposition via methylcarbamoyl nitrene

Abstract

N-Methylcarbamoyl azide Me(H)NC(O)N₃ has been synthesized and structurally characterized. Both N₃ and CH₃ groups in the molecule adopt a syn conformation with the CO bond. Upon flash vacuum pyrolysis at 800 K, the azide mainly decomposes into Me(H)NNCO/N₂ and MeNCO/HN₃ through Curtius-rearrangement and a retro-ene reaction, respectively. In contrast, 193 and 266 nm laser photolysis of Me(H)NC(O)N₃ in cryogenic matrices (Ar, Ne, and N₂) leads to stepwise Curtius-rearrangement via the intermediacy of carbamoylnitrene Me(H)NC(O)N, for which two conformers with the CH₃ group being in syn and anti conformations to the CO bond have been unambiguously identified by matrix-isolation IR spectroscopy. Triplet multiplicity of Me(H)NC(O)N (|D/hc| = 1.57 cm⁻¹ and |E/hc| = 0.012 cm⁻¹) and another two carbamoylnitrenes H₂NC(O)N (|D/hc| = 1.59 cm⁻¹ and |E/hc| = 0.018 cm⁻¹) and Me₂NC(O)N (|D/hc| = 1.55 cm⁻¹ and |E/hc| = 0.016 cm⁻¹) has been further established by matrix-isolation EPR spectroscopy. Subsequent visible light irradiation (420–460 nm) of Me(H)NC(O)N results in the exclusive formation of Me(H)NNCO. The molecular structures of Me(H)NC(O)N₃ and Me(H)NC(O)N, multiplicities of the nitrene, and the underlying mechanism for the decomposition of the azide are reasonably explained with quantum chemical calculations by utilizing the B3LYP, CBS-QB3, CCSD(T), and CASPT2 methods.