Angewandte
Chemie
À
C F Activation
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Rhodium-Catalyzed ortho-Selective C F Bond Borylation of
Polyfluoroarenes with Bpin Bpin**
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Wen-Hao Guo, Qiao-Qiao Min, Ji-Wei Gu, and Xingang Zhang*
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Abstract: An ortho-selective C F bond borylation between
N-heterocycle-substituted polyfluoroarenes and Bpin-Bpin
with simple and commercially available [Rh(cod)2]BF4 as
a catalyst is now reported. The reaction proceeds under mild
reaction conditions with high efficiency and broad substrate
scope, even toward monofluoroarene, thus providing a facile
access to a wide range of borylated fluoroarenes that are useful
for photoelectronic materials. Preliminary mechanistic studies
reveal that a RhIII/V catalytic cycle via a key intermediate
rhodium(III) hydride complex [(H)RhIIILn(Bpin)] may be
involved in the reaction.
feasibility of the rhodium-catalyzed selective C F bond
borylation of polyfluoroarenes. Partially fluorinated aromat-
ics constitute a distinct class of compounds in life and
materials science.[9] However, synthetic access to such a struc-
tural motif is difficult,[10] and there is only limited commercial
availability of fluoroaromatic sources. In this study, we
focused our research on addressing three crucial issues:
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1) regiochemical selectivity of C F bond borylation; 2) a
simple and efficient catalytic system that enables the use of
a commercially available catalyst with broad substrate scope;
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3) mechanistic insight into the Rh-catalyzed C F bond
borylation. As a result, we disclose the first example of
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F
luorinated compounds play an important role in life and
ortho-selective C F bond borylation of polyfluoroarenes with
material sciences due to the unique properties of fluorine
simple and commercially available [Rh(cod)2]BF4 as a cata-
lyst. Preliminary mechanistic studies revealed that a RhIII/V
catalytic cycle may be involved in the reaction, thus providing
atom and/or C F bond.[1] Over the past few years, there have
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been substantial efforts on developing new methods to access
such valuable compounds.[2] Among the developed methods,
us with a new view to understand C F bond activation.
À
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selective C F bond activation catalyzed by transition metals
We began our study based on the fact that the formation
has emerged as a striking approach,[3] because it paves a new
way to prepare a number of fluorinated molecules that are
difficult to synthesize by conventional methods. On the other
hand, the degradation of environmentally persistent fluori-
nated molecules has also stimulated fundamental research in
of the B F bond is thermodynamically favorable. There-
[11]
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fore, if
a
rhodium boryl complex [RhIIILn(Bpin)2]
A
(Scheme 1), which was generated in situ between rhodium
catalyst [RhILn] and Bpin-Bpin, chelates with a directing
group, such as N-containing heteroaromatics, the ortho-
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understanding C F bond activation. Recently, significant
advances have been made in this area, but most of the
selective C F bond borylation would be possible after
reductive elimination of key intermediate B.
reactions mainly focus on hydrodefluorination.[4,5] Although
examples of the construction of the C C bond by transition-
Accordingly, our initial study focused on the reaction of 2-
(perfluorophenyl)pyridine 1a[12] with bis(pinacolato)diboron
(Bpin-Bpin, 2) in the presence of different simple and
commercially available [RhI] catalysts (Table 1, entries 1–5).
To our delight, 66% yield (determined by 19F NMR spectros-
copy) of 3a was obtained when the reaction was carried out
with 1a (1.0 equiv), 2 (2.0 equiv), [Rh(cod)2]BF4 (5 mol%),
KOAc (2.0 equiv) in toluene at 1208C for 12 h (Table 1,
entry 4). Other [RhI] catalysts also showed activity, but led to
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[6]
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metal-catalyzed C F bond activation have been reported,
the selective replacement of fluorine with a versatile func-
tional group to access highly valuable fluorinated molecules is
very limited. In particular, the transition-metal-catalyzed
selective C F bond borylation has been scarcely studied,
and remains challenging because of the robustness of the C F
bond and difficulty in controlling the selective activation of
[7]
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the C F bond in perfluorinated and polyfluorinated mole-
cules.
As part of an ongoing study on transition-metal-catalyzed
polyfluoroarene chemistry,[8] herein we demonstrate the
[*] W.-H. Guo, Q.-Q. Min, J.-W. Gu, Prof. Dr. X. Zhang
Key Laboratory of Organofluorine Chemistry
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences
345 Lingling Lu, Shanghai 200032 (China)
E-mail: xgzhang@mail.sioc.ac.cn
[**] This work was financially supported by the National Basic Research
Program of China (973 Program) (Nos. 2012CB821600 and
2015CB931900), the NSFC (21425208, 21421002, 21172242, and
21332010), and SIOC.
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Supporting information for this article is available on the WWW
Scheme 1. Hypothesis for Rh-catalyzed ortho-selective C F bond bor-
ylation.
Angew. Chem. Int. Ed. 2015, 54, 9075 –9078
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
9075