Mechanisms and origin of regioselectivity for manganese-catalyzed denitrogenative annulation and click reactions

Abstract

This paper presents a density functional theory study concerning the mechanisms and origin of regioselectivity associated with a Mn-catalyzed denitrogenative annulation involving benzonitrile as the substrate and a click reaction with phenylacetylene as the substrate, respectively. These calculations fully addressed multi-spin-state reactivity. The catalytic cycle for the Mn-catalyzed denitrogenative annulation was found to involve tetrazole ring opening followed by N₂ elimination and the formation of C–N and N–N bonds. The proposed catalytic cycle for the Mn-catalyzed click reaction involves three stages: tetrazole ring opening, isomerization and 1,3-cycloaddition. A manganese-copper/zinc cooperative mechanism is proposed to account for experimental results. CuI promotes C–N bond formation between the benzonitrile and Mn-nitrene, promoting the predominant formation of the 1,2,4-triazolo-pyridine. An analysis of the click reaction using the distortion/interaction model indicated that distortion energy plays the primary role in determining regioselectivity.