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Mechanism and Substituent Effects of Benzene Arylation via a Phenyl Cation Strategy: A Density Functional Theory Study
Author(s) -
Li Xiaoyan,
Sun Ling,
Zhang Qiaochu,
Li Shijun,
Wang Yang,
Wei Donghui,
Zhang Wenjing,
Lan Yu
Publication year - 2019
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201901120
Subject(s) - substituent , chemistry , steric effects , density functional theory , kinetic isotope effect , dissociation (chemistry) , aryl , transition state , catalysis , carbocation , medicinal chemistry , reaction mechanism , photochemistry , computational chemistry , stereochemistry , organic chemistry , deuterium , physics , quantum mechanics , alkyl
In this study, density functional theory (DFT) calculations were performed to gain insight into the possible reaction mechanism and substituent effects of benzene arylation at the molecular level. The results showed that both [Me 3 Si] + [WCA] − and [Et 3 Si] + [WCA] − promoted the reaction. The whole catalytic cycle generally involved three processes, namely, carbocation formation, Wheland intermediate formation, and catalyst regeneration. For the second process, the stepwise mechanism (C−C coupling followed by proton transfer) was shown to be preferred over the concerted mechanism, with successive [1,2]/[1,4]‐proton transfer as the preferred pathway. C−C coupling, rather than C−H insertion, was shown to be the rate‐determining step of the reaction, which was consistent with the kinetic isotope effect experimental results. Bond dissociation energy calculations showed that the ortho ‐TMS substituent played a major role in activating the C−F bond to facilitate phenyl cation formation, leading to the most weakly C−Cl bonded intermediate, which facilitated the C−C coupling. Ortho ‐phenyl substituents resulted in more severe steric hindrance of fluoride abstraction and a weaker C−H⋅⋅⋅π interaction in the C−C coupling transition state compared with meta ‐phenyl substituents. Better stabilization of the cation center by an electron‐rich meta ‐substituent was concluded to be the main reason for the better yield obtained compared with substrates containing an electron‐deficient meta ‐substituent.