Computational Study on the Mechanisms and Origins
of Selectivity in Hydroarylation of 1,3-Diyne Alcohol Catalyzed by
Di- and Mononuclear Manganese Complexes
posted on 2021-09-10, 17:42authored byXiang-Ai Yuan, Congcong Huang, Xiaoyu Wang, Peng Liu, Siwei Bi, Dan Li
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
C1C2 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.