Copper(II) NHC pincer complexes containing 1,2,3-triazole units: Synthesis, structure and catalysis for CN bond forming reactions

Two new tridentate copper(II) N-heterocyclic carbene (NHC) pincer complexes with triazolyl donor groups, L2, [TrzmPymBI][PF₆] and L3, [bTrzmBI][PF₆], were synthesized and characterized by X-ray single crystal analysis and elemental analysis. The 5-coordinate τ value shows distorted square pyramidal geometry for both complexes. These copper(II)-NHC complexes exhibited excellent catalytic activity (95–100 % conversion) for NH insertion reactions toward the formation of new NC bonds between aniline and methyl phenyldiazoacetate. Under optimized conditions, the catalyst was screened against 22 different aniline derivatives and achieved high conversion (65–100 %) toward both electron-donating and electron-withdrawing functional groups on the amine substrates, while limiting self-coupling of activated diazo compounds. The substrate scope study revealed that steric hindrance and basicity are key factors influencing reactivity. Secondary and aliphatic amines showed weak reactivity. Moreover, the utility of this catalyst was demonstrated through a gram-scale synthesis of a diarylhydantoin, a class of compound known to act as a COX-2 inhibitor. These results highlight the versatility and efficiency of copper(II)-NHC complexes in facilitating selective carbene insertions and provide a promising approach for the synthesis of valuable nitrogen-containing compounds.