Fig. 2: Schematic illustration and characterization of Cu₃NC^(NHC).

a Structure of the N-heterocyclic carbene (NHC) ligand. Color legend: blue, N; gray, C; and white, H. b Total structure of the Cu₃NC^(NHC). Color legend: brown, Cu; blue, N; gray, C; and white, H. c ESI‒MS spectra of Cu₃NC^(NHC) dissolved in dimethylformamide (DMF) /DCM solution and measured in the positive mode. Inset: experimental (black) and simulated (red) isotopic distributions of Cu₃NC^(NHC). d ¹H NMR spectra of Cu₃NC^(NHC) in MeCN-d₃ (0–7 days). Hd, Hb and Hc represent the characteristic H atoms of Cu₃NC^(NHC). e ¹H NMR spectra of Cu₃NC^(NHC)-HNBn₂ (1:3) in MeCN-d₃ (0–72 h). Hd, Hb and Hc represent the characteristic H atoms of the Cu₃NC^(NHC). The characteristic peaks in the pale blue box represent the methylene peak of the HNBn₂.