Supramolecular structure and tautomerism of trifluoromethanesulfonamidines.

DFT calculations were performed for a series of N-triflyl substituted amidines, their dimers, and hydrogen-bonded complexes with hexafluoroisopropanol (HFIP) and DMSO, as well as transition states of tautomeric interconversion RNH−C(Me)=NTf ⇆ RN=C(Me)–NHTf (R = Me). The free energy barrier ΔG‡ for the equilibrium gradually decreases in going from monomers to H-complexes with DMSO, cyclic dimers, and H-complexes with HFIP. The X-ray analysis of crystals and FT-IR analysis of neat compounds and their solutions in the temperature range of 298–190 K was performed in comparison with the computed vibrational frequencies. The predominance of the E-syn and E-anti conformational isomers of the studied compounds and their cyclic and linear dimers is shown. For R = 2-norbornyl, the above tautomeric equilibrium in HFIP solution is shifted towards the NHTf form with lowering the temperature. [ABSTRACT FROM AUTHOR]