Photolytic insertion of carbon monoxide into nitrosyl chloride: formation of nitrosoformyl chloride

Abstract

Nitrosocarbonyls are exotic intermediates that remain scarcely characterized. By UV photolysis (365 nm) of nitrosyl chloride (ClNO) embedded in solid CO ice at 20 K, the elusive nitrosoformyl chloride (ClC(O)NO) has been synthesized via CO-insertion into the Cl–N bond in ClNO. The characterization of ClC(O)NO with matrix-isolation IR spectroscopy is supported by ¹³C and ¹⁵N isotope labeling and quantum chemical calculations at the B3LYP/6-311+G(3df) level of theory. Upon subsequent laser irradiation at 266 nm, CO-elimination in ClC(O)NO occurs by reformation of ClNO. In line with the calculated potential energy surface for ClC(O)NO at the CCSD(T)-F12a/aug-cc-pVTZ//B3LYP/6-311+G(3df) level, the observed IR frequencies and the corresponding isotopic shifts coincide with the calculated values for the lowest-energy planar conformer, in which the CO and NO moities adopt trans configuration with respect to the C–N bond. Furthermore, the CO-insertion in ClNO involves a stepwise pathway by first homolytic cleavage of the Cl–N bond in ClNO (→ Cl˙ + ˙NO), followed by successive CO-trapping (CO + Cl˙ → ClCO˙) and radical combination (ClCO˙ + ˙NO → ClC(O)NO) inside the solid CO-matrix cages.