Preparation and Properties of Methoxycarbonylsulfenyl Isocyanate, CH₃OC(O)SNCO

Pure methoxycarbonylsulfenyl isocyanate, CH₃OC(O)SNCO, is quantitatively prepared by the metathesis reaction between CH₃OC(O)SCl and AgNCO. This novel species has been obtained in its pure form and characterized by ¹H and ¹³C NMR, UV−vis, FTIR, and FT-Raman spectroscopy. The conformational properties of the gaseous molecule have been studied by vibrational spectroscopy and quantum chemical calculations (B3LYP and MP2 methods). The compound exhibits a conformational equilibrium at room temperature having the most stable form <i>C</i><i>_S</i> symmetry with the CO double bond synperiplanar with respect to the S−N single bond. A second form was observed in the IR spectrum and corresponds to a conformer possessing the C−S bond antiperiplanar with respect to the NC double bond of the isocyanate group. The structure of a single crystal of CH₃OC(O)SNCO was determined by X-ray diffraction analysis at low temperature using a miniature zone melting procedure. The crystalline solid (triclinic, <i>P</i>1̄, <i>a</i> = 8.292(6) Å, <i>b</i> = 9.839(7) Å, <i>c</i> = 11.865(8) Å, α = 67.290(2)°, β = 71.5570(10)°, γ = 83.4850(10)° and <i>Z</i> = 6) shows the presence of molecules having exclusively a synperiplanar conformation with respect to the three φ(CO−CO), φ(OC−SN), and φ(CS−NC) dihedral angles.