Computational insights into the dual reactivity of 1,2,3,4-tetrazole: a metalloporphyrin-catalyzed click reaction and denitrogenative annulation

Abstract

The mechanism and origins of chemoselectivities of Mn- and Fe-porphyrin catalyzed click reactions and denitrogenative annulation between 1,2,3,4-tetrazole and phenylacetylene have been studied by performing density functional theory (DFT) calculations. In the Mn-porphyrin-based catalytic system, 1,2,3,4-tetrazole prefers to follow the click reaction pathway to afford a 1,5-disubstituted click product, and the denitrogenation pathway is disfavored by 0.9 kcal mol⁻¹. In contrast, in the Fe-porphyrin-based catalytic system, 1,2,3,4-tetrazole prefers to follow the denitrogenative annulation pathway to afford an annulation product, and the click reaction is disfavored by 15.9 kcal mol⁻¹. The denitrogenative annulation involves the formation of a metal-nitrene radical intermediate by the loss of dinitrogen gas from the metal-azide complex, which is calculated to be the chemoselectivity-determining step. The sluggish dinitrogen elimination in the Mn-catalyzed system may be arising from the destruction of the stable electronic structure of the d-orbital half-filled shell of the Mn-azide complex.