Noncovalent Interaction- and Steric Effect-Controlled Regiodivergent Selectivity in Dimeric Manganese-Catalyzed Hydroarylation of Internal Alkynes: A Computational Study

Abstract

Selective hydroarylation of internal alkynes catalyzed by a dimeric manganese complex provides a powerful strategy for the construction of multisubstituted alkenes. In this work, density functional theory (DFT) calculations and experimental studies were carried out to explore the mechanism and origin of regiodivergent hydroarylation of internal alkynes reported by our group. The results demonstrate that this reaction first proceeds via a bimetallic mechanism to generate the active catalyst that subsequently undergoes a monometallic mechanism to run the three-stage catalytic cycle: alkyne migratory insertion, protonation, and active catalyst regeneration. Alkyne migratory insertion is considered as the regioselectivity-determining step. Energy decomposition analyses on insertion transition states suggest that the interaction between the substrate and catalyst is mainly responsible for the observed exclusive γ-selectivity of 1a, while the deformation of these two sections induced by the sterically hindered phenyl group and aryl group accounts for the complete β-position arylation of 1e. The decrease of γ-selectivity with the regulation of a tertiary alcohol motif in 1a originates from the reduced noncovalent interaction. The computational results provide important insights into the origin of regiodivergent selectivities and useful information for further designing and adjusting the strategy in Mn-catalyzed alkyne hydroarylation.

Homogeneous Manganese-Catalyzed Hydrofunctionalizations of Alkenes and Alkynes: Catalytic and Mechanistic Tendencies

“…Regarding the mechanism, it has been recently studied by Yuan, Bi, Xie, and co-workers. 86 In this work they found that the activation step proceeds via a bimetallic mechanism, yielding a monomeric catalytically active species, which subsequently undergoes an alkyne migratory insertion, a protodemetalation, and catalyst regeneration, completing the catalytic turnover. From these, precatalyst activation was identified as the rate-determining step, whereas alkyne migratory insertion was proposed to be mainly responsible for the regioselectivity, which is highly dependent on the steric properties of the species involved.…”

“…Regarding the mechanism, it has been recently studied by Yuan, Bi, Xie, and co-workers . In this work they found that the activation step proceeds via a bimetallic mechanism, yielding a monomeric catalytically active species, which subsequently undergoes an alkyne migratory insertion, a protodemetalation, and catalyst regeneration, completing the catalytic turnover.…”