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

Area of Science:

• Inorganic Chemistry
• Organic Chemistry
• Computational Chemistry

Background:

• Carbonyl diisocyanate and carbonyl diisothiocyanate show differing reactivity patterns with nucleophiles.
• Carbonyl diisocyanate typically forms bis(carbamoylhalides), while carbonyl diisothiocyanate undergoes cyclization to thiadiazines.

Purpose of the Study:

• To investigate the reactions of carbonyl diisocyanate and carbonyl diisothiocyanate with the complete series of hydrogen halides (HF to HI).
• To synthesize and characterize novel carbonyl bis(carbamoylhalides) and substituted thiadiazines.
• To elucidate the underlying thermodynamic reasons for the observed differences in reactivity.

Main Methods:

• Synthesis of carbonyl bis(carbamoylhalides) and thiadiazine derivatives.
• Characterization using single-crystal X-ray diffraction, NMR, IR, and Raman spectroscopy, and elemental analysis.
• Quantum mechanical calculations to determine thermodynamic stability and reaction pathways.

Main Results:

• Isolation of carbonyl bis(carbamoylfluoride), -chloride, -bromide, and -iodide.
• Synthesis of 6-chloro- and 6-bromo-2,3-dihydro-2-thioxo-4H-1,3,5-thiadiazin-4-one derivatives.
• Quantum mechanical calculations provided thermodynamic explanations for the divergent reaction pathways.

Conclusions:

• The study successfully synthesized and characterized new halogenated compounds derived from carbonyl diisocyanate and diisothiocyanate.
• Thermodynamic factors were identified as key drivers for the distinct reactivity observed between carbonyl diisocyanate and diisothiocyanate.
• This research contributes to understanding the reaction mechanisms of isocyanates and isothiocyanates with hydrogen halides.