DOI: 10.1007/s11224-019-01381-2

Prototropic tautomerism of the addition products of N-heterocyclic carbenes to CO₂, CS₂, and COS 

The energies of 62 minima and 6 transition states have been calculated with the M06-2x functional and the aug-cc-pVDZ basis set. They correspond to carbenes and neutral molecules related to the products obtained by addition of N-heterocyclic carbenes (NHCs) to CO₂, CS₂, and COS. The NHCs belong to two “classical” NHCs (imidazoles and benzimidazoles) and one “remote” NHC (pyrazole). Several of these structures in the same series are related by prototropic tautomerism. To compare these calculated energies with experimental X-ray structures, solvation effects by water, calculated with a continuous model (PCM), as well as some dihydrates and dimers, have also been calculated.