Photolytic Decarbonylation of Oxalyl Diisothiocyanate in Solid Argon Matrices tosyn‐antiCarbonyl Diisothiocyanate and Its Isomerization

Abstract

AbstractOxalyl diisothiocyanate, ((CO)NCS)2, has been studied in solid argon matrices at 4.2 K with the aid of infrared (IR) spectroscopy. The spectra show mainly signals attributed to the most stableanti‐anticonformer, which is corroborated by comparison to computed anharmonic fundamental IR transitions. Upon irradiation with 254 nm UV light, oxalyl diisothiocyanate eliminates carbon monoxide under formation of carbonyl diisothiocyanate, CO(NCS)2. This reaction is only slightly exothermic by 0.4 kcal mol−1at the DLPNO‐CCSD(T)/def2‐QZVPP//B3LYP‐D3/def2‐TZVPP level of theory. Remarkably, photolysis produces mostly the less stablesyn‐anticonformer of carbonyl diisothiocyanate. Subsequent annealing at 30 K for two minutes results in a structural relaxation to the 0.7 kcal mol−1more stablesyn‐synconformer confirming a low torsional barrier height between the isomers.