Journal of the American Chemical Society
Article
Figure 5. We propose that the two fluorine atoms give rise to a
ate complex. This fluoroarylboronate undergoes trans-
metalation to form an arylcopper(III) fluoride, which under-
goes reductive elimination to form the aryl fluoride product.
single broad 19F resonance due to a combination of
ASSOCIATED CONTENT
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S
* Supporting Information
Text, figures, and tables giving experimental procedures,
characterization data for new compounds, and details of the
calculations. This material is available free of charge via the
Figure 5. Proposed structure of the arylboronate Cu(III) fluoride
intermediate. L is 2,4,6-trimethylpyridine.
AUTHOR INFORMATION
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stereoisomerism and transfer of the boron center from one
fluorine to the other. This species was formed in 90% yield
(based on the conversion of ArBPin).
Corresponding Author
We propose that the arylboronate Cu(III) fluoride complex
undergoes rate-limiting transmetalation of the aryl group to
copper. The aryl Cu(III) fluoride complex formed from
transmetalation would then undergo fast reductive elimination
of the Ar−F product. Fast reductive elimination of an aryl
fluoride is consistent with a recent report by Ribas and co-
workers in which an aryl Cu(III) fluoride complex was
proposed to be formed as an unobserved, reactive intermediate
during the reaction of a macrocylic aryl Cu(III) complex with
fluoride to form a macrocyclic fluoroarene.26
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We thank the NIH-NIGMS (R29-55382) for support of this
work, Yichen Tan for checking the procedure, Prof. J. Scott
McIndoe and Eric Janusson at the University of Victoria for
help in obtaining ESI-MS data, and Dr. Qian Li for help with
DFT calculations.
Scheme 5 shows a mechanism for the fluorination of
arylboronate esters with (tBuCN)2CuOTf, [Me3pyF]PF6, and
REFERENCES
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Scheme 5. Proposed Mechanism for the Fluorination of
ArBPin with (tBuCN)2CuOTf and Me3pyF-PF6
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AgF that is consistent with our data. Our data indicate that the
fluorination of arylboronate esters does not occur by the
formation of arylcopper(I) species. Instead, the fluorination
reactions appear to occur by generation of a cationic
copper(III) fluoride intermediate that reacts with the
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SUMMARY AND CONCLUSIONS
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In summary, we have developed an operationally simple, direct
method for the fluorination of arylboronate esters and revealed
the formation of two copper(III) fluoride intermediates. This
reaction occurs with readily available reagents under mild
conditions. Electron-rich, electron-deficient, ortho-substituted,
and diversely functionalized arylboronate esters undergo
fluorination in good yield. In addition, sequential, one-pot
processes allow the fluorination of arenes and aryl bromides to
occur through arylboronate ester intermediates generated in
situ. We provide evidence that the fluorination of arylboronate
esters with (tBuCN)2CuOTf and [Me3pyF]PF6 occurs by facile
formation of a cationic copper(III) fluoride complex, which
reacts with AgF and ArBpin to form a neutral fluoroarylboron-
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(17) In acetonitrile, the 19F NMR specrum of [Me3pyF]PF6 contains
a singlet at +17.5 ppm (N-F) and a doublet at −71.4 ppm (PF6, J =
706 Hz).
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dx.doi.org/10.1021/ja310909q | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX