The synthesis of a new mixed amino−amido N-heterocyclic carbene (type A) starting from anthranilic acid is presented. A new straightforward synthetic approach to related diaminocarbenes of type B is also described. Both NHCs react with group 6 elements to form heteroureas and coordinate to L 2 ClM fragments (M = Rh, Ir; L 2 = COD, (CO) 2 ). IR spectroscopic analysis of the carbonyl complexes reveals that the diamino-NHC is a better donor ligand (TEP: 2054 cm −1 ) compared to the amino− amido NHC (TEP: 2060 cm −1 ). In line with this behavior, a carbene dimerization to give the corresponding olefin is observed only for derivatives of type A. X-ray structure determinations are reported for two Rh complexes of ligand A and its cationic precursor.

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.

The synthesis of the new mixed amino–amido N-heterocyclic carbene 2, featuring a hypoxanthine structural unit, starting from caffeine via the hypoxanthinium precursor 4 is described. NHC 2 forms adducts with group 6 elements, coordinates to L2ClRh fragments (L2 = COD, (CO)2), or dimerizes to yield olefin 8. The donor properties of NHC 2 were evaluated by IR spectroscopic assessment of its TEP value (2058 cm–1), which is typical for an amino–amido NHC. Dicarbenes are also easily obtained by converting the imidazole moieties of the hypoxanthinium cation 4 or the olefin 8 into NHC functions. X-ray structure determinations of a Rh complex of carbene 2 and the olefinic dicarbene precursor 13 are presented.

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