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, (seim(Mes))H, may be obtained from 1-mesitylimidazole via (i) deprotonation with Bu(n)Li, (ii) treatment with elemental selenium, and (iii) addition of HCl(aq). Structural characterization of (seim(Mes))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 (seim(Mes))H are oxidized by air to give bis(1-mesitylimidazol-2-yl)diselenide, (seim(Mes))(2). A corresponding investigation of (seim(Me))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. (1)H and (77)Se NMR studies demonstrate that the (seim(R)) groups of the selone (seim(R))H and diselenide (seim(R))(2) undergo facile exchange on the NMR time scale.