Double Addition vs. Ring Closure: Systematic Reactivity Study of CO(NCO)2 and CO(NCS)2 towards Hydrogen Halides

Abstract

AbstractThe reactivity of carbonyl diisocyanate, CO(NCO)2, and carbonyl diisothiocyanate, CO(NCS)2 with nucleophiles shows different patterns: Whereas carbonyl diisocyanate adds two equivalents of nucleophile forming carbonyl bis(carbamoylhalides), carbonyl diisothiocyanate only adds one equivalent and undergoes intramolecular ring closure, resulting in the formation of substituted thiadiazines. In this study we have reacted both carbonyl diisocyanate and carbonyl diisothiocyanate with the full series of hydrogen halides HF to HI, isolating carbonyl bis(carbamoylfluoride) (1), ‐chloride (2), ‐bromide (3), and ‐iodide (4) as well as (6‐chloro‐2,3‐dihydro‐2‐thioxo‐4H‐1,3,5‐thiadiazin‐4‐one (5), and 6‐bromo‐2,3‐dihydro‐2‐thioxo‐4H‐1,3,5‐thiadiazin‐4‐one (6). The compounds were analysed by single‐crystal X‐ray diffraction, NMR spectroscopy, IR and Raman spectroscopy, and elemental analysis. Quantum mechanical calculations show thermodynamic reasons for the differences in reactivity.