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10.1002/anie.201905782
Angewandte Chemie International Edition
Argentination of Fluoroform: Preparation of Stable AgCF3
Solution with Diverse Reactivities
Jia-Xiang Xiang, Yao Ouyang, Xiu-Hua Xu, and Feng-Ling Qing*
Abstract: The transformation of large-volume industrial by-product
and stable greenhouse gas fluoroform (HCF3) to useful products has
recently received significant attention. Herein, we disclose a simple
and scalable preparation of AgCF3 by treatment of HCF3 with t-
BuOK and AgOAc. The reactivity of the HCF3-derived AgCF3 has
been demonstrated by hydrotrifluoromethylation of alkenes and C─H
trifluoromethylation of (hetero)arenes. This work not only provides a
new avenue for the utilization of HCF3, but also presents a reliable
and easy-to-execute synthesis of the relatively stable AgCF3 solution.
salts.[8] Following Grushin’s pioneering work, several groups
further extended the application of HCF3-derived CuCF3 for Cu-
promoted trifluoromethylation of a wider range of substrates.[9]
Beside cupration of HCF3, the direct metallation of HCF3 with
other metals (Zn,[10] Ir,[11] and Pd[12]) has also been reported.
However, the synthetic applications of these metal-CF3
complexes are limited. [10-12]
(E)
(E)
[P4-t-Bu/H]
CF3
E
[CF3]
CF3
K
E
[CF3]
Fluoroform (HCF3) is
a large-volume by-product from
(b)
(c)
inorganicand
fluoropolymer manufacturing and has high greenhouse effect.[1]
The utilization of fluoroform as a feedstock for the preparation of
valuable fluorinated compounds is a clearly preferred alternative
to the destruction of fluoroform. Obviously, the application of
fluoroform for trifluoromethylation reaction is a highly attractive
and much-sought-after goal,[2] as it is the cheapest and most
atom-economical but low reactivity CF3 source.
base = KHMDS
aldehyde
or ketone
base =
P4-t-Bu
organic
(E)
CF3
B
N
O
(a)
[CF3]
base
B3N3Me6
DMF
N
B
F3C
NMe2
(d)
B
N
nucleophilic trifluoromethylation
HCF3
fluoroform
t-BuOK
The common strategy to use HCF3 in trifluoromethylation
reactions is based on deprotonation with strong bases. Several
groups have reported the nucleophilic trifluoromethylation of
carbonyl compounds with HCF3 in the presence of
electrogenerated bases or alkali metal bases in DMF (Scheme
1a).[3] The solvent DMF traps the in situ generated CF3 anion,
CF3
CF3
R
E
t-BuOK
AgOAc
DMF
(E)
R
CuCl
DMF
(e)
(f)
CF
[Ag
CF3
CF
[Cu
]
Ar
Ar CF3
]
3
3
Ar
H
Ar FG
This work
Cu-promotedtrifluoromethylation
Ag-promoted trifluoromethylation
which
easily
decomposes
to
fluoride
anion
and
difluorocarbene,[4] producing a reservoir of trifluoromethylating
hemiaminolate species. Prakash (Scheme 1b)[5] and Shibata
(Scheme 1c)[6] described the nucleophilic trifluoromethylation
with HCF3 in common organic solvents such as THF, ether, and
toluene using KHMDS or P4-t-Bu respectively as the base. Very
recently, Szymczak disclosed that hexamethylborazine
(B3N3Me6) could act as a suitable Lewis acid to stabilize CF3
Scheme 1. Use of HCF3 in Trifluoromethylation Reactions.
Recently, our group[13] and others[14,15] developed a series of
Ag-promoted trifluoromethylation reactions, in which AgCF3 was
formed as the reactant[14] or reaction intermediate.[13,15] Due to
the thermal and light sensitivity, normally AgCF3 needs to be
freshly prepared[14] or in situ generated[13,15] from TMSCF3 and
AgF. On the other hand, although the stable ligand-supported
AgCF3 complexes[14d,15b,16] are available, they are only used as
transmetalating agents. Therefore, the synthesis of stable AgCF3
with diverse reactivities is highly desirable. As part of our
research interest in the development of trifluoromethylation
reaction using cheap CF3 sources,[17] herein we disclose a
practical preparation of the stable AgCF3 solution from simple
and inexpensive materials HCF3, t-BuOK, and AgOAc (Scheme
1f). The synthetic utility of the HCF3-derived AgCF3 is
exemplified by hydrotrifluoromethylation of alkenes and C─H
trifluoromethylation of (hetero)arenes. Notably, it is difficult to
achieve these transformations directly from the HCF3-derived
CuCF3.
Our investigation started with the preparation of AgCF3 by
treatment of excess of HCF3 with t-BuOK in the presence of AgI
salts using DMF as the solvent (Table 1). The use of AgCl
afforded the [AgCF3] (resonates at δ = −20.7 ppm, d, J(107/109Ag-
F) = 109.0/124.1 Hz)[14a,18] in 41% yield along with [Ag(CF3)2]-
(resonates at δ = −25.4 ppm, d, J(107/109Ag-F) = 86.5/101.5
Hz)[14a,18] in 8% yield (entry 1). Then, other AgI salts were
screened to improve the yield of AgCF3. Among all the AgI salts
-
anion.[7] This HCF3-derived borazine CF3 adduct is highly
nucleophilic and reacts with a broad variety of inorganic and
organic electrophiles (Scheme 1d).
In 2011, Grushin discovered a methodologically different
approach to activation of HCF3 through direct cupration of HCF3
with t-BuOK and CuCl in DMF (Scheme 1e).[8a] This HCF3-
derived CuCF3 not only reacts with electrophiles, but also
trifluoromethylates aryl halides, boronic acids, and diazonium
[a]
[b]
J.-X. Xiang, Y. Ouyang, Dr. X.-H. Xu, Prof. Dr. F.-L. Qing
Key Laboratory of Organofluorine Chemistry, Center for Excellence
in Molecular Synthesis, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 345 Lingling Lu, Shanghai 200032,
China
Prof. Dr. F.-L. Qing
Key Laboratory of Science and Technology of Eco-Textiles, Ministry
of Education, College of Chemistry, Chemical Engineering and
Biotechnology, Donghua University, 2999 North Renmin Lu,
Shanghai 201620, China
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.
Xiang, Jia-Xiang
