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

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.