The Simplest, Isolable, Alkynyl Isocyanate HC≡CNCO: Synthesis and Characterization

Alkynyl isocyanates have been postulated as highly reactive intermediates in synthetic chemistry. Herein, the parent molecule HC≡CNCO is isolated for the first time. In sharp contrast to the previously reported short lifetime (ca. 15 s) at room temperature, we found that HC≡CNCO has a lifetime of 55 h in the gas phase (2 mbar, 300 K) with a melting point of -79.5 °C and vaporization enthalpy (ΔH_vap ) of 23.1(1) kJ mol^-1 . Apart from the IR (gas, solid, and matrix), ¹ H and ¹³ C NMR, and UV/Vis spectroscopic characterization, its photoisomerization with a acylnitrene HC≡CC(O)N and cyanoketene NCC(H)CO has been observed.