Meta-to-Fluorine Regioselectivity in Iridium-Catalyzed Fluoroarene Borylation: A DFT Investigation toward the
Deqing Kong1, Yuting Liu1, Junfei Wang1
1College of Chemistry and Materials Engineering, Key Laboratory of Carbon Materials of Zhejiang Province, Wenzhou University, Wenzhou, Zhejiang 325035, P. R. China.
Abstract:
A DFT mechanistic study of C-H borylation of 3-fluorobenzotrifluoride catalyzed by Ir complexes ligated by 4,4'-bis(trifluoromethyl)-2,2'-bipyridine (btfbpy), 4,4'-ditert-butyl-2,2'-bipyridine (dtbpy), and 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen), respectively, demonstrates that the C-H bonds distal to the steric -CF3 group exhibit comparable, albeit slightly lower, rate and regioselectivity-determining barriers compared to those proximal to -CF3, which corroborates with the experimental observations of statistical regioselectivity among aryl C-H bonds in the absence of significant steric hindrance. Conversely, utilizing a bulky spirobipyridine ligand that imposes substantial steric hindrance at the activation sphere is predicted to effectively promote meta-to-fluorine regioselectivity, which was found to arise from the stronger catalyst-substrate interactions due to the steric-screening effect, leading to the lower C-H activation barrier.
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