Diamino- and Mixed Amino–Amido-N-Heterocyclic Carbenes Based on Triazine Backbones

The synthesis of novel hexahydrotriazine-based NHCs from easily available starting materials is described. Tribenzyltriazacyclohexane <b>1</b> is converted stepwise to the six-membered diamino carbene <b>3</b> with a saturated ring structure. Analogously, the cyclic mixed amino–amido carbene <b>12</b> is obtained starting from a cyclic urea derivative. Both carbenes were characterized by trapping reactions with sulfur and selenium as well by the preparation of metal complexes of the type (COD)­MX-NHC (M = Rh, Ir; COD = 1,5-cyclooctadiene), which were converted to the respective dicarbonyl complexes (CO)₂MX-NHC. IR spectra of the carbonyl derivatives allowed the Tolman electronic parameter to be determined for carbenes <b>3</b> (2052 cm^–1) and <b>12</b> (2058 cm^–1) and revealed a shift of 6 cm^–1 due to the presence of one amide function. X-ray structure determinations are reported for an amidinium species, a carbene sulfide, and the (COD)­RhBr complex of the amino–amido carbene <b>12