Computational Study on the Mechanisms and Origins of Selectivity in Hydroarylation of 1,3-Diyne Alcohol Catalyzed by Di- and Mononuclear Manganese Complexes

A computational study is conducted to understand the mechanisms and exclusive chemo- and regioselectivity in di- and mononuclear manganese-catalyzed hydroarylation of unsymmetrical 1,3-diyne alcohols reported by the Xie group [Yan, Z., Angew. Chem., Int. Ed. 2018 57 12906−12910]. The results find that the main difference in di- and mononuclear manganese-catalyzed hydroarylation reactions lies in the initial generation of active Mn­(I) species and the rate-determining step. In the dinuclear Mn₂(CO)₈Br₂-catalyzed hydroarylation process, the active Mn­(I) species is generated by the reaction of the precatalyst Mn₂(CO)₈Br₂ with NaOAc and 2a via ligand substitution. The diyne migratory insertion step is identified as the rate- and selectivity-determining step. However, in the mononuclear Mn­(CO)₅Br-catalyzed hydroarylation reaction, the generation of the active Mn­(I) species undergoes the ligand substitution of Mn­(CO)₅Br with NaOAc and the decarbonylation process, which is the rate-determining step in this catalytic process. The bromine anion is found to play a significantly important stabilization role in this decarbonylation process. After the generation of the active Mn­(I) catalyst, the catalytic hydroarylation reaction follows a four-stage mechanism: transmetalation, alkyne insertion, protonation, and active catalyst regeneration. The 2,1-migratory insertion of the C¹C² unit in diyne into the Mn–C­(aryl) species is the energetically most favorable pathway compared with other insertions (1,2-, 3,4-, and 4,3-insertions). The calculated selectivity is in good agreement with the experimental selective functionalization of diynes. Energy decomposition analysis (EDA) on the diyne insertion transition state suggests that the deformation of the diyne section is mainly responsible for the observed exclusive selectivity, combined with the OH···π interaction between the hydroxyl group of diyne and the aryl phenyl ring. However, for monoalkyne, EDA demonstrates the interaction between monoalkyne and Mn section accounts for the experimentally obtained reactive selectivity. This study provides deeper insights into the mechanisms and the origins of the exclusive selectivity of the title reaction and guides the design of efficient Mn-based catalysts for the hydroarylation reaction.