Prediction of the regioselectivity of the ruthenium-catalyzed [3+2] cycloadditions of benzyl azide with internal alkynes using conceptual DFT indices of reactivity

[GRAPHICS] [3+2] Cycloadditions of benzyl azide with unsymmetrical internal alkynes, in the presence of pentamethylcyclopentadienyl ruthenium chloride [Cp*RuCl] complex as catalyst, leading to trisubstituted 1,2,3-triazole regioisomers are rationalized by means of DFT-based reactivity indices. The four activated azide/[Ru]/alkyne complexes have been modeled for all their possible conformers and were classified using the Maxwell-Boltzmann distribution. The local electrophilicity and nucleophilicity indices, based on Parr functions, have been calculated for the terminal sites of the benzyl azide and the carbon atoms of the internal alkynes. The calculations were performed at the B3LYP level of theory together with the LANL2DZ basis set for Ru and Cl and the standard 6-31G(d) basis set for the other atoms. The obtained results agree well with the experimental findings which stipulate that the formed cycloadducts depend strongly on the nature of substituents carried