Chlorodifluoroacetyl isocyanate, ClF2CC(O)NCO: Preparation and structural and spectroscopic studies

Abstract

Chlorodifluoroacetyl isocyanate, ClF2CC(O)NCO, was prepared by the reaction of ClF2CC(O)Cl with excess of AgNCO. The colorless compound melts at -83 °C and the vapor pressure follows the equation ln p = -3868.3 (1/T) + 10.89 (p [Atm], T [K]) in the range -38 to +22 °C, extrapolated bp ca. 82 °C. It has been characterized by IR (gas phase, Ar matrix), liquid Raman, 19F and 13C NMR, gas UV-vis spectrum, photoelectron spectroscopy (PES), photoionization mass spectrometry (PIMS), and gas electron diffraction (GED). The matrix photochemistry has been studied and the conformational properties of ClF2CC(O)NCO have been analyzed by joint application of vibrational spectroscopy, GED, and quantum chemical calculations. Two conformers were detected in gaseous and liquid phases, in which the C-Cl bond adopts a gauche orientation with respect to the C=O group, whereas this group can be in syn or anti orientation with respect to the N=C bond of the NCO group. An enthalpy difference δHexp° = 1.3 ± 0.2 kcal mol-1 between the most stable syn-gauche and the less stable anti-gauche form was derived using the van't Hoff equation, which is in reasonable agreement with the computed difference of δH° = 0.8 kcal mol-1 (B3LYP/6-311+G(3df) approximation). The most significant gas phase structural parameters for gauche-syn ClF2CC(O)NCO are re(NC=O) = 1.157(1) Å, re(N=CO) = 1.218(1) Å, re(N-C) = 1.378(9) Å, re(C=O) = 1.195(1) Å,e(CNC) = 128.6(19)°. Photolysis of ClF 2CC(O)NCO using an ArF excimer laser (193 nm) mainly yield ClF 2CNCO along with some ClF2CC(O)N nitrene. The valence electronic properties of the title compound were studied using the PES and PIMS. The experimental first vertical ionization energy of 11.54 eV corresponds to the ejection of a carbonylic oxygen lone pair electron.