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 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)2MX-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.