Distinct mechanism of oxidative trifluoromethylation with a well-defined Cu(II) fluoride promoter: Hidden catalysis

Article abstract of DOI:10.1021/ja5103508

The fluoride [(bpy)CuF₂(H₂O)]·2H₂O (1) reacts with CF₃SiMe₃ and PhB(OH)₂ in DMF at rt to give PhCF₃ in >95% yield within 15 min. Although 1 is a Cu(II) complex, this reaction occ

Full text of DOI:10.1021/ja5103508

Communication
pubs.acs.org/JACS
Distinct Mechanism of Oxidative Trifluoromethylation with
a Well-Defined Cu(II) Fluoride Promoter: Hidden Catalysis
Noel Nebra and Vladimir V. Grushin*
Institute of Chemical Research of Catalonia (ICIQ), 43007 Tarragona, Spain
S
* Supporting Information
toward arylboron and terminal alkyne nucleophiles to a higher
oxidation state, reactive electrophilic Cu complexes.
ABSTRACT: The fluoride [(bpy)CuF2(H2O)]·2H2O (1)
reacts with CF3SiMe3 and PhB(OH)2 in DMF at rt to give
PhCF3 in >95% yield within 15 min. Although 1 is a Cu(II)
complex, this reaction occurs only in air; no Ph-CF3 coupling
takes place under anaerobic conditions. A distinct mechanism
is operational in this transformation. First, 1 is trifluoro-
methylated with TMSCF3 to give “[(bpy)Cu(CF3)2]” that
spontaneously disproportionates to two Cu(III) ([Cu-
(CF3)4]− and [(bpy)Cu(CF3)3]) and two Cu(I) ([(bpy)-
Cu(CF3)] and [Cu(CF3)2]−) complexes. In contrast with
the Chan−Evans−Lam reaction, where the Cu(III) products
of the Cu(II) disproprotionation effect the coupling,
those formed in the 1-TMSCF3 system, [Cu(CF3)4]− and
[(bpy)Cu(CF3)3], are stable and unreactive, remaining
dead-end spectators throughout the coupling process.
Consequently, the trifluoromethylation of PhB(OH)2 with
1-CF3SiMe3 does not and cannot occur in the absence of
O2. Only by air oxidation of the Cu(I) disproportionation
product, [(bpy)Cu(CF3)] in equilibrium with [Cu(CF3)2]−,
is the reactive species generated, serving as a catalyst for the
Ph-CF3 bond formation even if 1 is used in stoichiometric
quantities.
In theory, if the oxidative trifluoromethylation was mechanis-
tically10,11 similar to the CEL reaction, the C-CF3 coupling with
stoichiometric Cu(II) could occur to 50% conversion in the
absence of an oxidant. In an elegant mechanistic study, Stahl
et al.10 have demonstrated that p-TolB(OH)2 reacts with MeOH
in the presence of 1 equiv of Cu(II) to give p-TolOMe in 50%
yield in an inert atmosphere. The disproportionation of the
added Cu(II) promoter leads to 50% of inactive Cu(I) and 50%
of active Cu(III) that effects the methoxylation. On introduction
of O2, the Cu(I) is oxidized to the Cu(III), thereby raising the
yield of p-TolOMe to quantitative.10
Is the same mechanism operational in the oxidative
trifluoromethylation reactions with nucleophilic CF3 reagents
(Scheme 1)? In other words, can the C-CF3 bond formation
occur with stoichiometric Cu(II) in the absence of an oxidant?
Cu(II) promoters have been successfully used for the Ar-CF3
coupling of arylboronic acids and boronate esters with
nucleophilic CF3 reagents CF3SiMe3 (TMSCF3)4a and K[(CF3)-
B(OMe)3].4e All of these reactions, however, were performed
under O2 as an external oxidant. Whether or not ArCF3 would
be still produced, at least in some quantities, under identical
conditions with a Cu(II) promoter but in the absence of O2,
remains unknown.
n 2010, Chu and Qing reported their pioneering findings
Iof Cu-promoted/catalyzed oxidative trifluoromethylation
of terminal acetylenes1 and arylboronic acids2 (Scheme 1).
Publications of alternative/improved protocols for both trans-
formations from Qing’s group3 and others4,5 as well as a compu-
tational study of the alkyne trifluoromethylation6 quickly followed.
These C-CF3 bond forming reactions contribute significantly to
trifluoromethylation methods7 for medicinal chemistry, agro-
chemical, and materials science research. Considering the high
synthetic value of these transformations, it is important to
understand their mechanism that is “still unclear and remains to
be elucidated”.3c
Herein we report that in contrast to the CEL reaction, oxi-
dative trifluoromethylation of arylboronic acids in the presence
of electrophilic Cu(II) may not occur without an oxidant (O2).
We demonstrate that a Cu(II)-promoted oxidative trifluorome-
thylation reaction is governed by a peculiar mechanism that is
distinct from that of the classical CEL coupling. This unexpected
mechanism involves “hidden catalysis” even if the Cu(II)
promoter is used in equimolar quantities.
Given the high affinity of silicon and boron for fluorine, we
originally selected anhydrous CuF2 as a model Cu(II) promoter
for the coupling of PhB(OH)2 with TMSCF3. Agitating a 1:1:1
mixture of CuF2, PhB(OH)2, and TMSCF3 in a variety of dry
solvents at ambient temperature under argon or in air for 12 h did
not produce PhCF3 in 19F NMR-detectable quantities.12 Consider-
ing the exceptionally poor solubility of CuF2, we then turned our
attention to soluble Cu(II) fluorides. Well-defined, structurally
characterized fluoro complexes of Cu(II) are rare. For our studies, we
selected [(bpy)CuF2(H2O)]·2H2O (1; bpy = 2,2′-bipyridyl) and
[(phen)CuF2(H2O)]·2H2O (2; phen = 1,10-phenanthroline).13,14
On addition of TMSCF3 (10 equiv) to 1 or 2 in dry DMF, the pale-
4b−d,g,i,5
+
Unless an electrophilic (“CF3 ”) source is employed,
these seemingly Chan−Evans−Lam (CEL)-type8,9 coupling reac-
tions require an oxidant to occur. The role of the oxidant such
as Ag(I),1,3 pure O2,4a or air4h is to convert the conventionally used
for the reaction nucleophilic Cu(I) species that are unreactive
Scheme 1. Oxidative Trifluoromethylation of Arylboronic
Acids and 1-Alkynes
Received: October 15, 2014
© XXXX American Chemical Society
A
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Communication
Figure 1. CuCF3 region of the 19F NMR spectrum of the reaction mixture obtained upon treatment of 1 with TMSCF3 (20 equiv) in DMF under argon
with integral intensity of the peak from 4,4′-difluorobiphenyl as an internal standard (−118.0 ppm) set at 2.00. See Figure S1 for the full spectrum.
blue fluorides dissolved within 1 min. Adding PhB(OH)2 (1 equiv)
to the resultant dark orange-red solution in air prompted the
formation of PhCF3 in a fast reaction that was complete within 15−
30 min at 23 °C. In the initial runs, the yield of PhCF3 in the reaction
with 1 was higher (75%) than with 2 (25%). Therefore, 1 was
chosen for further studies. After optimization (see the Supporting
Information), the reaction of 1 (1 equiv) with TMSCF3 (10 equiv)
and PhB(OH)2 (1 equiv) in DMF in air furnished PhCF3
quantitatively (>95%). The need to use a large excess of TMSCF3
for the reaction was dictated by the presence in 1 and 2 of one
coordinated and two H-bonded H2O molecules that hydrolyze
TMSCF3 (see below).
The reaction of 1 with TMSCF3 and PhB(OH)2 was then
repeated under identical conditions but under argon, i.e., in the
absence of O2. Although visual signs of the reaction (quick
dissolution of 1 and color change) were the same, no PhCF3 was
produced. The lack of Ph-CF3 bond formation under anaerobic
conditions using a Cu(II) complex suggested that the
trifluoromethylation mechanism in the 1-TMSCF3-O2 system
might be different from that of the CEL coupling (see above). We
therefore undertook a more detailed study of the reaction of 1
with TMSCF3 in the absence and in the presence of O2.
The dark orange-red solution produced on addition of
TMSCF3 (20 equiv) to 1 in dry DMF under rigorously O2-free
conditions (argon glovebox) was analyzed by 19F NMR in the
presence of an internal standard (4,4′-difluorobiphenyl). The
spectrum (Figure S1) indicated full transfer of both F atoms from
Cu to the SiMe3 unit to give TMSF quantitatively (2 equiv).
Fluoroform (CHF3) was also produced (6 equiv) as a result of
hydrolysis of 6 equiv of TMSCF3 with the three H2O molecules
present in 1 (eq 1). In excellent agreement of the mass balance
with the stoichiometry, 12 of the originally used 20 equiv of
TMSCF3 remained intact.
and a septet at −25.6 ppm with the same coupling constant, in
a 2:1 integral ratio. These assignments were confirmed by spiking
experiments with authentic samples. The other two resonances, a
broadened singlet at −23.6 ppm and a singlet at −31.9 ppm were
assigned to Cu(I) complexes [(bpy)Cu(CF3)] and [Cu(CF3)2]−,
respectively, on the basis of the reported data for the analogous phen
complex18 and a structurally characterized salt of [Cu(CF3)2]−.19
These two Cu(I) complexes most likely equilibrate, similar to the
phen18 and NHC19 systems. The yields of [Cu(CF3)4]− (5%),
[(bpy)Cu(CF3)3] (15%), [(bpy)Cu(CF3)] (5%), and [Cu(CF3)2]−
(15%) were quantified using the internal standard. Therefore, ∼40%
of the CF3Cu(II) species produced in the reaction of 1 with TMSCF3
disproportionated to Cu(I) and Cu(III) (eq 2).20 The Cu(II), Cu(I),
and Cu(III) equilibrated within minutes, after which no evolution of
the 19F NMR spectral pattern (Figure 1) was observed for at least 4 h.
Two of the four species formed in the disproportionation,
[Cu(CF3)4]− and [Cu(CF3)2]−, are anionic and hence must
have countercations, such as [(bpy)2Cu]2+, [(bpy)3Cu]2+, or
[(bpy)2Cu(CF3)]+. With the latter two, the disproportionation
equations (eqs 3 and 4) can be balanced, the stoichiometry being
in full accord with the experimental data, i.e., [Cu(CF3)2]−:
[(bpy)Cu(CF3)]: [Cu(CF3)4]−:[(bpy)Cu(CF3)3] = 3:1:1:3. In
contrast, the equation with [(bpy)2Cu]2+ as the counterion is not
balanceable. Well-known and stable [(bpy)3Cu]2+ (eq 3) is more
likely the countercation than [(bpy)2Cu(CF3)]+ (eq 4).15
The experimentally demonstrated stoichiometry (eq 1)
suggested full conversion of 1 to “[(bpy)Cu(CF3)2]”,15
a
paramagnetic Cu(II) species that should be unobservable by
NMR. Unexpectedly, however, a number of resonances could be
clearly seen in the characteristic “CuCF3” region of the 19F NMR
spectrum (−20 to −40 ppm), pointing to the presence of dia-
magnetic Cu complexes bearing a CF3 ligand (Figure 1).
Examination of these signals indicated that two CF3Cu(I) and
two CF3Cu(III) species were produced. The Cu(III) complexes
were [Cu(CF3)4]− resonating as a singlet at −35.1 ppm16 and
[(bpy)Cu(CF3)3]17 displaying a quartet at −38.2 ppm (JF‑F =8.9Hz)
Adding PhB(OH)2 (1 equiv) to the equilibrated system
(eqs 2 and 3) under argon produced no reaction, indicating that
the Cu(III) species from the disproportionation are cou-
pling incompetent. Opening the resultant solution to air, how-
ever, triggered the formation of PhCF3 in ∼40% yield within
10 min. The coupling was obviously effected by the products of
oxidation of the Cu(I) complexes emerged from the dispro-
portionation.
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Communication
Scheme 2. Air Oxidation of [(bpy)Cu(CF3)] in the Presence
of TMSCF3 Leading to [(bpy)Cu(CF3)2(OTMS)]
Scheme 3. Mechanism of Oxidative Trifluoromethylation of
PhB(OH)2 with 1-TMSCF3
The reaction of 1 with TMSCF3 (20 equiv) in DMF was then
repeated in air. Just as under anaerobic conditions, blue 1 quickly
dissolved to give a dark-orange solution. Again, TMSF (2 equiv)
and CHF3 (6 equiv) were quantitatively produced, with 12 equiv
of TMSCF3 remaining intact (eq 1 and Figure S3). Both
previously observed Cu(III) complexes, [(bpy)Cu(CF3)3] and
[Cu(CF3)4]−, were also formed. The signals from the Cu(I)
species [(bpy)Cu(CF3)] and [Cu(CF3)2]−, however, were
absent. Instead, the spectrum exhibited two new resonances,
broadened quartets of equal intensity at −27.1 and −32.2 ppm
with the same coupling constant JF‑F = 11.6 Hz (Figure S4). A
new singlet resonance at −0.55 ppm was concomitantly observed
in the 1H NMR spectrum of the reaction solution, suggesting a
TMSO-Cu complex.21 It was reasoned that the 19F NMR
quartets and the −0.55 ppm 1H NMR singlet were probably from
the same species, [(bpy)Cu(CF3)2(OTMS)], with one CF3 and
OTMS in the apical positions. Integration of the singlet at
−0.55 ppm against the aromatic protons of the internal stan-
dard provided strong support to this proposal, as the yield of
[(bpy)Cu(CF3)2(OTMS)] determined independently from the
19F NMR and 1H NMR data was the same, ∼10−15%. Scheme 2
accounts for the formation of the [(bpy)Cu(CF3)2(OTMS)],
lending additional support from the mechanism6 of oxidation of
[(phen)Cu(CF3)] with O2.
Once formed, the Cu-OTMS complex was slowly (hours)
transforming to [Cu(CF3)4]− and [(bpy)Cu(CF3)3]. The latter
was predominantly produced, suggesting that [(bpy)Cu-
(CF3)2(OTMS)] reacted with TMSCF3 to give [(bpy)Cu(CF3)3]
and (TMS)2O. After 30 h, the overall yield of [Cu(CF3)4]− and
[(bpy)Cu(CF3)3] was ∼90%. Adding PhB(OH)2 to the sample
at that point resulted in no reaction, confirming, again, the
incapability of [Cu(CF3)4]− and [(bpy)Cu(CF3)3] to effect the
coupling.
In another experiment, PhB(OH)2 (1 equiv) was added to the
freshly generated [(bpy)Cu(CF3)2(OTMS)], and the tube was
sealed in air. Shaking the contents for ∼15 min resulted in full
disappearance of the OTMS complex and the formation of PhCF3,
albeit in only 80% yield (19F NMR). Both [(bpy)Cu(CF3)] and
[Cu(CF3)2]− were also observed. The formation of the Cu(I)
species was evidently due to full consumption of the O2 present in
the sealed tube as a limiting reagent. Replenishing the supply of O2
to the reaction byre-opening the tubeto air resultedinquantitative
formation of PhCF3 and disappearance of the Cu(I) complexes.
The current study uncovers the mechanism of the oxidative
trifluoromethylation reaction (Scheme 3). First, 1 reacts with
TMSCF3 to give rise to “[(bpy)Cu(CF3)2]”,15 a Cu(II) complex
that undergoes spontaneous facile disproportionation22 to Cu(I)
([Cu(CF3)2]− and [(bpy)Cu(CF3)]) and Cu(III) ([Cu(CF3)4]−
and [(bpy)Cu(CF3)3]) at ∼40% conversion. None of the Cu(I),
Cu(II), and Cu(III) species in the resultant system is reac-
tive toward PhB(OH)2 under anaerobic conditions. Both of the
Cu(III) complexes produced are stable and unreactive, remaining
spectators throughout the process. It is the Cu(I) products of the
disproportionation, [Cu(CF3)2]− in equilibrium18 with [(bpy)-
Cu(CF3)], that effect the coupling. The more reactive bpy-ligated
species enters the catalytic loop to undergo facile oxidation with
O2,6 which initiates the formation of the key intermediate
[(bpy)Cu(CF3)2(OTMS)] (Scheme 2). Two reaction pathways
are available for [(bpy)Cu(CF3)2(OTMS)] (Scheme 3). One is
the trifluoromethylation of the Cu-OTMS bond with TMSCF3,
leading to inactive [(bpy)Cu(CF3)3]. This unproductive pathway
irreversibly pulls out the active species from the catalytic cycle. The
other, luckily faster productive pathway involves transmetalation
with PhB(OH)2, followed by Ph-CF3 reductive elimination from
the resultant CF3(Ph)Cu(III) species.23 The thus regenerated
[(bpy)Cu(CF3)] then commences another catalytic turnover.
As catalytically competent [(bpy)Cu(CF3)] is consumed, pro-
ductively or nonproductively, the disproportionation equilibrium
is shifted toward the formation of more of the Cu(I) precursors to
the active species and inactive Cu(III) complexes. In this way, the
CF3Cu(II) species produced in the reaction of 1 with TMSCF3
serves as a reservoir of the productive Cu(I) and the “dead-end”
Cu(III) ina 1:1 ratio. Therefore, the oxidativetrifluoromethylation
with 1-TMSCF3 is, mechanistically, catalytic in Cu even if 1 is used
in stoichiometric quantities for the reaction.
In conclusion, 1, a well-defined Cu(II) fluoride complex, is a
highly efficient promoter for the high-yielding oxidative
trifluoromethylation of PhB(OH)2 with TMSCF3 at rt in air. A
distinct mechanism is operational in this transformation. Like in
the classical CEL reaction, disproportionation of Cu(II) occurs
first to give Cu(I) and Cu(III). In contrast, however, both of the
Cu(III) species produced, [Cu(CF3)4]− and [(bpy)Cu(CF3)3],
are unreactive toward PhB(OH)2, remaining spectators through-
out the process. Only through air oxidation of the Cu(I) products
of the disproportionation ([(bpy)Cu(CF3)] in equilibrium with
[Cu(CF3)2]−) does the reactive species emerge, serving as a
catalyst for the coupling. Consequently, unlike the CEL reaction
that can produce the desired product in 50% yield in the presence
of stoichiometric Cu(II) under anaerobic conditions,10 the
trifluoromethylation with TMSCF3 in the presence of 1,
also a Cu(II) complex, cannot occur in the absence of O2. This
key difference prompts us to arrive at the striking conclusion that,
at least in some instances, Cu(I) rather than Cu(II) added
catalysts/promoters can exhibit higher efficiency in oxidative
trifluoromethylation reactions. The novel mechanistic insights
C
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Journal of the American Chemical Society
Communication
S.; Adams, J.; Winters, M. P.; Chan, D. M. T.; Combs, A. Tetrahedron
Lett. 1998, 39, 2941.
from the current work may find use in the development of new,
more efficient catalysts and promoters for trifluoromethylation
methods.24
(9) For selected reviews, see: (a) Ley, S.; Thomas, A. W. Angew. Chem.,
Int. Ed. 2003, 42, 5400. (b) Beletskaya, I. P.; Cheprakov, A. V. Coord.
Chem. Rev. 2004, 248, 2337. (c) Evano, G.; Blanchard, N.; Toumi, M.
Chem. Rev. 2008, 108, 3054. (d) Monnier, F.; Taillefer, M. Angew. Chem.,
Int. Ed. 2009, 48, 6954. (e) Qiao, J. X.; Lam, P. Y. S. Synthesis 2011, 829.
(f) Allen, S. E.; Walvoord, R. R.; Padilla-Salinas, R.; Kozlowski, M. C.
Chem. Rev. 2013, 113, 6234. (g) Casitas, A.; Ribas, X. Chem. Sci. 2013, 4,
2301.
ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental details and NMR spectra. This material is available
free of charge via the Internet at http://pubs.acs.org.
(10) King, A. E.; Brunold, T. C.; Stahl, S. S. J. Am. Chem. Soc. 2009, 131,
5044.
(11) Wendlandt, A. E.; Suess, A. M.; Stahl, S. S. Angew. Chem., Int. Ed.
2011, 50, 11062.
AUTHOR INFORMATION
Corresponding Author
vgrushin@iciq.es
■
(12) (a) Solvents explored: DMF, THF, DME, DCE, DME, NMP,
MeCN, toluene, DMSO, and DMAC. After prolonged heating at 85 °C
in DMSO or DMF, small quantities of PhCF3 (∼5%) were formed. (b)
A mixture of 1-naphthylboronic acid pinacol ester (1 equiv) and
K+[(CF3)B(OMe)3]− (2 equiv) has been reported4e to react with CuF2
in DMSO under O2 at 80 °C to give 1-C10H7CF3 (15%), 1-C10H7OMe
(37%), and 1,1′-binaphthyl (42%).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank F. M. Miloserdov and A. Lishchynskyi for discussions
and for valuable comments. This work was supported by the ICIQ
Foundation and the Spanish Government (grant CTQ2011-
25418). N.N. is thankful to ICIQ and Marie Curie Actions for the
cofunded “ICIQ-IPMP” postdoctoral grant award 291787.
(13) (a) These complexes were originally prepared by Levason et al.13b
by the reaction of CuF2·xH2O with bpy or phen in MeOH and
subsequently structurally characterized by Hursthouse.13c,d (b) Gibbs,
P. R.; Graves, P. R.; Gulliver, D. J.; Levason, W. Inorg. Chim. Acta 1980,
45, L207. (c) Emsley, J.; Arif, M.; Bates, P. A.; Hursthouse, M. B. J.
Crystallogr. Spectrosc. Res. 1987, 17, 605. (d) Emsley, J.; Arif, M.; Bates, P.
A.; Hursthouse, M. B. J. Chem. Soc., Dalton Trans. 1987, 2397.
(14) N-ligated Cu(II) fluorides conventionally contain H2O or HF
molecules H-bonded to the strongly basic F ligands.
REFERENCES
(1) Chu, L.; Qing, F.-L. J. Am. Chem. Soc. 2010, 132, 7262.
(2) Chu, L.; Qing, F.-L. Org. Lett. 2010, 12, 5060.
■
(3) (a) Jiang, X.; Chu, L.; Qing, F.-L. J. Org. Chem. 2012, 77, 1251.
(b) Zhang, K.; Qiu, X.-L.; Huang, Y.; Qing, F.-L. Eur. J. Org. Chem. 2012,
58. (c) Chu, L.; Qing, F.-L. Acc. Chem. Res. 2014, 47, 1513.
(15) While the established stoichiometry-based (eq 1) composition
[(bpy)Cu(CF3)2] is correct, the exact structure of this complex is
unknown. CF3Cu(II) complexes are extremely rare; see: Jacquet, J.;
Salanouve, E.; Orio, M.; Vezin, H.; Blanchard, S.; Derat, E.; Desage-El
Murr, M.; Fensterbank, L. Chem. Commun. 2014, 50, 10394.
(16) (a) The [Cu(CF3)4]− anion has been originally observed by
Burton et al.16b and structurally characterized by Naumann’s group.16c
(b) Willert-Porada, M. A.; Burton, D. J.; Baenziger, N. C. J. Chem. Soc.,
Chem. Commun. 1989, 1633. (c) Naumann, D.; Roy, T.; Tebbe, K.-F.;
Crump, W. Angew. Chem., Int. Ed. Engl. 1993, 32, 1482.
(4) Boronic acids and boronate esters: (a) Senecal, T. D.; Parsons, A.;
Buchwald, S. L. J. Org. Chem. 2011, 76, 1174. (b) Xu, J.; Luo, D.-F.; Xiao,
B.; Liu, Z.-J.; Gong, T.-J.; Fu, Y.; Liu, L. Chem. Commun. 2011, 47, 4300.
(c) Zhang, C.-P.; Cai, J.; Zhou, C.-B.; Wang, X.-P.; Zheng, X.; Guc, Y.-
C.; Xiao, J.-C. Chem. Commun. 2011, 47, 9516. (d) Liu, T.; Shen, Q. Org.
Lett. 2011, 13, 2342. (e) Khan, B. A.; Buba, A. E.; Gooßen, L. J. Chem.
Eur. J. 2012, 18, 1577. (f) Litvinas, N. D.; Fier, P. S.; Hartwig, J. F. Angew.
Chem., Int. Ed. 2012, 51, 536. (g) Liu, T.; Shao, X.; Wu, Y.; Shen, Q.
Angew. Chem., Int. Ed. 2012, 51, 540. (h) Novak
Grushin, V. V. Angew. Chem., Int. Ed. 2012, 51, 7767. (i) Ye, Y.; Sanford,
M. S. J. Am. Chem. Soc. 2012, 134, 9034. (j) Ye, Y.; Kunzi, S. A.; Sanford,
́
, P.; Lishchynskyi, A.;
(17) [(bpy)Cu(CF3)3] has been recently synthesized by an
independent route and structurally characterized in our laboratories.
Results of these studies will be reported separately.
̈
M. S. Org. Lett. 2012, 14, 4979. (k) Li, Y.; Wu, L.; Neumann, H.; Beller,
M. Chem. Commun. 2013, 49, 2628. (l) Presset, M.; Oehlrich, D.;
Rombouts, F.; Molander, G. A. J. Org. Chem. 2013, 78, 12837.
(5) Terminal acetylenes: (a) Luo, D.-F.; Xu, J.; Fu, Y.; Guo, Q.-X.
Tetrahedron Lett. 2012, 53, 2769. (b) Weng, Z.; Li, H.; He, W.; Yao, L.-
F.; Tan, J.; Chen, J.; Yuan, Y.; Huang, K.-W. Tetrahedron 2012, 68, 2527.
(c) Wang, X.; Lin, J.; Zhang, C.; Xiao, J.; Zheng, X. Chin. J. Chem. 2013,
31, 915. (d) Serizawa, H.; Aikawa, K.; Mikami, K. Chem.Eur. J. 2013,
19, 17692. (e) Tresse, C.; Guissart, C.; Schweizer, S.; Bouhoute, Y.;
Chany, A.-C.; Goddard, M.-L.; Blanchard, N.; Evano, G. Adv. Synth.
Catal. 2014, 356, 2051. (f) Dubbaka, S. R.; Nizalapur, S.; Atthunuri, A.
R.; Salla, M.; Mathew, T. Tetrahedron 2014, 70, 2118. (g) Deng, X.; Lin,
J.; Zheng, J.; Xiao, J. Chin. J. Chem. 2014, 32, 689.
(18) Morimoto, H.; Tsubogo, T.; Litvinas, N. D.; Hartwig, J. F. Angew.
Chem., Int. Ed. 2011, 50, 3793.
(19) Dubinina, G. G.; Ogikubo, J.; Vicic, D. A. Organometallics 2008,
27, 6233.
(20) These diamagnetic CF3Cu(I) and CF3Cu(III) complexes are
NMR-observable evidently due to a lack of fast exchange between them
and paramagnetic Cu(II) species in the system.
(21) Wyss, C. M.; Tate, B. K.; Bacsa, J.; Gray, T. G.; Sadighi, J. P.
Angew. Chem., Int. Ed. 2013, 52, 12920.
(22) (a) The disproportionation in our system is not driven by an
irreversible process such as the intramolecular aromatic cupration in the
formation of Cu(I) and Cu(III) from Cu(II) and a macrocyclic arene
ligand.9g,22b−e (b) Ribas, X.; Jackson, D. A.; Donnadieu, B.; Mahía, J.;
Parella, T.; Xifra, R.; Hedman, B.; Hodgson, K. O.; Llobet, A.; Stack, T.
D. P. Angew. Chem., Int. Ed. 2002, 41, 2991. (c) Xifra, R.; Ribas, X.;
(6) Jover, J.; Maseras, F. Chem. Commun. 2013, 49, 10486.
(7) For selected reviews, see: (a) Burton, D. J.; Yang, Z. Y. Tetrahedron
1992, 48, 189. (b) McClinton, M. A.; McClinton, D. A. Tetrahedron
1992, 48, 6555. (c) Schlosser, M. Angew. Chem., Int. Ed. 2006, 45, 5432.
(d) Roy, S.; Gregg, B. T.; Gribble, G. W.; Le, V.-D.; Roy, S. Tetrahedron
2011, 67, 2161. (e) Qing, F.-L.; Zheng, F. Synlett 2011, 1052.
(f) Tomashenko, O. A.; Grushin, V. V. Chem. Rev. 2011, 111, 4475.
(g) Jin, Z.; Hammond, G. B.; Xu, B. Aldrichimica Acta 2012, 45, 67.
(h) Chen, P.; Liu, G. Synthesis 2013, 45, 2919. (i) Landelle, G.;
Panossian, A.; Pazenok, S.; Vors, J.-P.; Leroux, F. R. Beilstein J. Org.
Chem. 2013, 9, 2476.
̀
Llobet, A.; Poater, A.; Duran, M.; Sola, M.; Stack, T. D. P.; Benet-
Buchholz, J.; Donnadieu, B.; Mahía, J.; Parella, T. Chem.Eur. J. 2005,
11, 5146. (d) King, A. E.; Huffman, L. M.; Casitas, A.; Costas, M.; Ribas,
X.; Stahl, S. S. J. Am. Chem. Soc. 2010, 132, 12068. (e) Casitas, A.; King,
A. E.; Parella, T.; Costas, M.; Stahl, S. S.; Ribas, X. Chem. Sci. 2010, 1,
326.
(23) Konovalov, A. I.; Lishchynskyi, A.; Grushin, V. V. J. Am. Chem. Soc.
2014, 136, 13410.
(24) We have developed an efficient protocol for oxidative
trifluoromethylation of a broad variety of arylboronic acids and
1-alkynes with 1-TMSCF3. These results will be reported separately.
(8) (a) Chan, D. M. T.; Monaco, K. L.; Wang, R. P.; Winters, M. P.
Tetrahedron Lett. 1998, 39, 2933. (b) Evans, D. A.; Katz, J. L.; West, T. R.
Tetrahedron Lett. 1998, 39, 2937. (c) Lam, P. Y. S.; Clark, C. G.; Saubern,
D
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