Exploring different coordination modes of the first tetradentate NHC/1,2,3-triazole hybrid ligand for group 10 complexes

Synthesis and characterisation of the first tetradentate N-heterocyclic carbene (NHC)/1,2,3-triazole hybrid ligand obtained by means of copper(i) catalyzed "click" chemistry and its application for the synthesis of group 10 complexes is reported. For palladium(ii), two complexes with different ligand coordination modes were obtained. One compound depicts a NCCN coordination sphere with all 1,2,3-triazole and NHC moieties coordinating to the metal, whereas the other one depicts a CCCC coordination sphere resulting from NHC coordination of two ligands. The non-coordinating 1,2,3-triazoles form strong intramolecular hydrogen bonds as proven by SC-XRD. The resulting rigid conformation is retained in solution even at 70 °C as demonstrated by variable temperature NMR spectroscopy. In contrast to palladium(ii), both nickel(ii) and platinum(ii) exclusively form complexes with a CCCC coordination sphere regardless of reaction conditions. Both compounds share characteristics with their palladium(ii) counterpart, including strong intramolecular hydrogen bonds.