Palladium(II) coordination of N-heterocyclic carbene ligands with a triazole moiety in the nitrogen substituent

• Synthesis and characterization of Pd(II) complexes with N-heterocyclic carbene ligands having a triazole pendant group. • Characterization of geometrical and rotational isomers for complexes of general formula [PdI 2 (NHC) 2 ]. • Evaluation of the energetics of the different isomers via DFT calculations. • Possibility to functionalize the triazole moiety affording a precursor of triazol-based N -heterocyclic carbenes. • Dinuclear complex formed by bridging coordination through the N-triazole and the C-imidazole atoms to two trans -PdI 2 units. A series of N -heterocyclic carbene (NHC) palladium complexes derived from N -methyl or N -mesityl-imidazolium salts bearing a triazole ring as pendant group to the second nitrogen atom, have been synthesized and characterized by NMR spectroscopy, mass spectrometry and single-crystal X-ray diffraction. Deprotonation of the imidazolium salt with palladium(II) acetate in acetonitrile affords square-planar Pd(II) complexes of general formula [PdI 2 (NHC) 2 ] with trans geometry. The steric hindrance of the NHC ligand substituents allows to characterize in solution both rotation syn and anti isomers. In contrast, in the crystallization process, the cis -[PdI 2 (NHC) 2 ] form was isolated, and its structure was determined by XRD. The stability of the possible geometrical and rotational isomers has been assessed also via DFT calculations (level of theory: COSMO-ZORA-BLYP(D3(BJ))/TZP). A second product forms along with the mononuclear complex and was identified as a dinuclear complex with the NHC and the nitrogen atom of the triazole ring bridging two trans -PdI 2 units. Finally, the nitrogen atom on the triazole ring was methylated affording a pendant triazolium salt, which can also give a carbene ligand upon deprotonation.