Synthesis and Structural Characterization of 1-Mesityl-1,3-dihydro-imidazole-2-selone and Bis(1-mesitylimidazol-2-yl)diselenide: Experimental Evidence That the Selone Is More Stable Than the Selenol Tautomer

1-Mesityl-1,3-dihydro-imidazole-2-selone, (seimMes)H, may be obtained from 1-mesitylimidazole
via (i) deprotonation with BunLi, (ii) treatment with elemental selenium, and (iii) addition of HCl(aq). Structural
characterization of (seimMes)H by X-ray diffraction demonstrates that the compound exists as the selone
rather than selenol tautomer, a result that is in accord with DFT calculations. Solutions of (seimMes)H are
oxidized by air to give bis(1-mesitylimidazol-2-yl)diselenide, (seimMes)2. A corresponding investigation of
(seimMe)H demonstrates that, in contrast to a previous report, the selenium analogue of methimazole exists
in the selone form with a structure analogous to that of methimazole. 1H and 77Se NMR studies demonstrate
that the (seimR) groups of the selone (seimR)H and diselenide (seimR)2 undergo facile exchange on the
NMR time scale.