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

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The synthesis of novel hexahydrotriazine-based NHCs from easily available starting materials is described. Tribenzyltriazacyclohexane 1 is converted stepwise to the six-membered diamino carbene 3 with a saturated ring structure. Analogously, the cyclic mixed amino–amido carbene 12 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) 2 MX-NHC. IR spectra of the carbonyl derivatives allowed the Tolman electronic parameter to be determined for carbenes 3 (2052 cm –1 ) and 12 (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 12 .