The mechanisms of the ruthenium(II)-catalyzed reaction of organic azide with terminal alkyne have been investigated using density functional theory. All the stationary points on the potential energy surfaces were fully optimized at the B3LYP/LANL2DZ level of theory. The reactants, intermediates, transition states and products in the reaction pathways were examined by frequency analysis at the same level of theory. Intrinsic reaction coordinate (IRC) calculations were performed to confirm that the optimized transition states correctly connect the relevant reactants and products. The investigation of the concerted and stepwise reaction channels shows that the concerted channel Ic and the stepwise channel IIc are favored over other channels to produce 1,5-disubstituted 1,2,3-triazole, which is in good agreement with experimental re-sults.

Key words: density functional theory, ruthenium(II)-catalyzed, azide, alkyne, reaction mechanism