Cu-deposits on Mg metal surfaces promote electron transfer reactions

Article abstract of DOI:10.1016/j.tet.2011.11.082

The enhancement of the electron transfer processes in the Grignard reagent formation-type ring silylation and the defluorination-silylation of perfluoroalkyl benzenes by Cu(0)-deposited Mg metal were confirmed. Microscopic analysis and substituent effects implied a different reduction process in the presence of Cu-deposited Mg metal than in the presence of bare Mg metal.

Full text of DOI:10.1016/j.tet.2011.11.082

Tetrahedron 68 (2012) 1085e1091
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Cu-deposits on Mg metal surfaces promote electron transfer reactions
*
Shinya Utsumi, Toshimasa Katagiri , Kenji Uneyama
Department of Applied Chemistry, Faculty of Engineering, Okayama University, 3-1-1, Tsushimanaka, Kita-ku, Okayama 700-8530, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 27 October 2011
Received in revised form 25 November 2011
Accepted 26 November 2011
Available online 7 December 2011
The enhancement of the electron transfer processes in the Grignard reagent formation-type ring sily-
lation and the defluorinationesilylation of perfluoroalkyl benzenes by Cu(0)-deposited Mg metal were
confirmed. Microscopic analysis and substituent effects implied a different reduction process in the
presence of Cu-deposited Mg metal than in the presence of bare Mg metal.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Copper-deposited magnesium
Electron transfer
Reductive defluorination
Selective dehalogenation
Grignard reagent formation-type silylation
1. Introduction
prior to the reaction. The reaction using commercially available Mg
powder without Cu-deposited magnesium resulted in the complete
Mg metal is a cheap, nontoxic, easy-to-handle, environmentally
friendly reducing agent. In addition, the Mg metal has greater re-
ducing ability than Al or Zn metal.1 Mg metal sometimes requires
prior activation to efficiently participate in reactions, such as
Grignard reagent formation. Popular activation methods for Mg
metal are the addition of iodine, the addition of 1,2-dibromoethane,1
and sonication.2 The activation of Mg metal by copper metal or
copper salts has been less popular, in the previous half century. In
the 1920s and the 1930s, Grignard reagent formations using MgeCu
alloys instead of pure Mg were reported.3 For example, the MgeCu
method enabled Grignard reagent formation from fluorobenzene,
which was proven by the production of biphenyl.3f In another ex-
ample, diaryl vinyl Grignard reagents were promptly formed from
the corresponding bromide using a MgeCu alloy.3a However,
Grignard reagent formation using MgeCu alloys sometimes resulted
in lower yields of the reagents because of the formation of homo-
coupling products via Kharasch reactions.3d,g,h This disadvantage
of reduced yields of Grignard reagents has resulted in little use of
MgeCu alloys.
recovery of the ethyl trifluoroacetate in DMI. Thus, in this paper, the
effect of the Cu-deposits (micrometer-sized particles) on the Mg
surface is discussed, focusing on the two following points; (1) how
Cu deposition enhanced the reducing ability of Mg and (2) to what
extent the reducing ability of the Mg metal was enhanced by Cu
deposition. To make these determinations, ring silylation of chlor-
o(pentafluoroethyl)benzenes and the defluorinationesilylation of
substituted benzotrifluorides were studied.
Scheme 1.
Recently, we reported a reductive defluorination of ethyl tri-
fluoroacetate by Cu-deposited Mg metal and trimethylsilyl chloride
(TMS-Cl) in N,N-dimethylimidazolidinone (DMI) to give ethyl 2,2-
difluoro-2-(trimethylsilyl)acetate in a 62% isolated yield (Scheme
1).4 In our previous study, the Cu-deposited Mg was prepared by
mixing 4 M equiv of Mg powder and 0.5 M equiv of CuCl in DMI just
2. Results and discussion
2.1. Regiocontrol of the reductions initiated by electron
transfer(s): Grignard reagent formation-type ring silylation
versus defluorinationesilylation of chloro(pentafluoroethyl)
benzenes
Preparations of (trifluoromethyl)phenylmagnesium halides
(m- and p-CF3eC6H4eMgX) are hazardous due to their risk of
* Corresponding author. Tel.: þ81 86 251 8605; e-mail address: tkata@cc.
okayama-u.ac.jp (T. Katagiri).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.11.082

1086
S. Utsumi et al. / Tetrahedron 68 (2012) 1085e1091
explosions,5 which has been attributed to the highly exothermic
process of defluorinations as the result of magnesium reduction.5b
This hazard has necessitated a method to suppress the defluori-
nation process. However, the simultaneous promotion of Grignard
reagent formation and the suppression of defluorination is difficult
to attain, because both Grignard reagent preparation and
defluorination are initiated by electron transfer from magnesium to
the halide (Scheme 2).
(entry 5).6a Although THF is a common solvent for the prepa-
ration of Grignard reagents, the reactions in THF resulted in the
recovery of the starting compound 1a or 1b (entries 2 and 6,
respectively). This lack of reaction could be caused by a lack of
self-catalytic action of the Grignard reagent species.1,3d
The recovery of the compound 1 after reaction in THF, a less polar
solvent (entries 2 and 6), indicated that no initial electron transfer
from Mg to compound 1 occurred. Therefore, Cu-deposited Mg was
used under the same conditions. The use of Cu-deposited Mg pro-
moted the reaction (entries 3 and 7). The reaction of 1a in THF (entry
3) gave compound 2a as the major product, while that of 1b in THF
(entry 7) gave compound 4b as the major product. The reaction in
THF/Et2O (1:9), and in even less polar solvent, at 30 ꢀC gave com-
pound 2a as the sole product (entry 4). Likewise, the reaction of 1b in
THF/Et2O (1:9) gave 2b in 79% yield and defluorinated product 4b
only in 4% yield (entry 8). A larger-scale reaction of 1b (5 mmol) gave
2b in 80% isolated yield under the same conditions. Defluorination
was avoided with the use of the less polar solvent.
The solvent effect on the product distribution in Table 1 is
consistent with the conventional ‘diffusion mechanism of the
Grignard reagent formation’ (Fig. 1).1,7 The diffusion mechanism
suggests that anion radicals on the surface of the Mg metal are
converted into the Grignard reagent, whereas those far from the
surface are converted into side products, such as homo-coupling
products. In the present case, a less polar solvent prevented long-
distance electron transfer and/or the diffusion of anion radical
species from the Mg surface by destabilizing the negative charges.
The occurrence of the concerted electron transfer and CeCl bond
cleavage processes only at the surface would promote the pre-
dominant formation of the Grignard reagent, which would be fol-
lowed by the transmetalation to yield the ring silylated product 2.
In contrast, a highly polar solvent would promote diffusion of the
anion radical species away from the Mg surface. The ‘solvent-caged’
anion radical species would lead to defluorinated product 4 due to
Scheme 2.
We encountered a similar problem during our study of the re-
ductive defluorination of 1-chloro-4-(pentafluoroethyl)benzene
(1a) with Mg metal powder and TMS-Cl. In this study, the
defluorination of the benzylic fluorine of the pentafluoroethyl
group was found to be easier than that of the trifluoromethyl
group.6a Moreover, Grignard reagent formation from aryl chloride
is more difficult than that from the bromide.5c Thus, the reaction of
compound 1 with Mg/TMS-Cl could be a model reaction to de-
termine conditions for the suppression of defluorination.
1-Chloro-4-(pentafluoroethyl)benzene (1a) and 1-chloro-3-
(pentafluoroethyl)benzene (1b) were reduced using Mg metal
powder (Table 1). The reduction of 1-chloro-4-(penta-
fluoroethyl)benzene (1a)6c in 1,3-dimethyl-3,4,5,6-tetrahydro-
2(1H)-pyrimidinone (DMPU) gave the 1-trimethylsilyl-4-
pentafluoroethylbenzene (2a: via the Grignard reagent forma-
tion) in 30% yield and 1-(1,2,2,2-tetrafluoro-1-trimethylsilyl)-4-
chlorobenzene (4a: via defluorination)6 in 32% yield (entry 1).
In the course of the reaction in entry 1, precipitations of white
solids were observed, which made the solution viscous and
prevented stirrings. This change of the state of the solution
would result in a large deviation of the result of entry 1. The
reduction of 1-chloro-3-(pentafluoroethyl)benzene (1b) by
Mg/TMS-Cl in DMPU gave the defluorinated product 4b as the
sole product in a quantitative yield, as previously reported
p*e
s
* negative hyperconjugation.8
The reaction of 1a and 1b with Mg in DMPU gave different
distribution of the products. The reaction of 1a gave both ring
silylated product (2a) and defluorinationesilylation product with-
out ring silylation (4a) (Table 1, entry 1). While, the reaction of 1b
gave defluoro-silylated product 4b solely (Table 1, entry 5). This
difference of the product distribution would be explainable by the
stability of benzylic anion species from 1b and 1a. Benzylic anion
species of 1b would be more stabilized by the chlorine atom sub-
stituent because the chlorine atom at 3-position withdraws elec-
tron much stronger than that at 4-position (sm¼0.37, sp¼0.23).
Table 1
Solvent effect on silylation of chloro(pentafluoroethyl)benzenes by Mg/TMS-Cl
Entry
X
Solventb
Activation of Mg
Temp [ꢀC]
Time [h]
Product distributionsa [%]
1
2
3
4
5
1
2
3
4
5c
6
7
8
4-Cl (a)
4-Cl (a)
4-Cl (a)
4-Cl (a)
3-Cl (b)
3-Cl (b)
3-Cl (b)
3-Cl (b)
DMPU
THF
THF
THF/Et2O (1:9)
DMPU
THF
THF
THF/Et2O (1:9)
d
0
1
5
1.5
24
5
5
5
10
29 (ꢁ11)
100 (ꢁ0)
9 (ꢁ7)
6 (ꢁ6)
0
100 (ꢁ0)
0 (ꢁ0)
0 (ꢁ0)
30 (ꢁ5)
0 (ꢁ0)
46 (ꢁ5)
69 (ꢁ2)
0
0 (ꢁ0)
5 (ꢁ1)
79 (ꢁ5)
3 (ꢁ1)
0 (ꢁ0)
9 (ꢁ1)
12 (ꢁ1)
0
0 (ꢁ0)
2 (ꢁ0)
13 (ꢁ4)
32 (ꢁ6)
0 (ꢁ0)
19 (ꢁ2)
0 (ꢁ0)
99
0 (ꢁ0)
73 (ꢁ15)
4 (ꢁ1)
3 (ꢁ3)
0 (ꢁ0)
6 (ꢁ6)
2 (ꢁ0)
0
0 (ꢁ0)
15 (ꢁ10)
0 (ꢁ0)
I2
30
32
30
0
30
32
Reflux
CuCl
CuCl
d
I2
CuCl
CuCl
Results were mean values with standard deviations of five experiments, which were determined by 19F NMR integration with benzotrifluoride as an internal standard.
a
Experiments in every entry were performed in 0.5 mmol scale.
b
Concentration of the substrate was 0.25 M.
The result was cited from Ref. 6a.
c

S. Utsumi et al. / Tetrahedron 68 (2012) 1085e1091
1087
would promote interactions with the negatively charged halogen
atoms of the substrates. This interaction between the Mg metal
surface and the halogen atoms would promote C-halogen bond
cleavage with an initial outer-sphere electron transfer from the
Cu-deposits.
2.3. Reductive defluorinations of benzotrifluoride derivatives
by Mg or Cu-deposited Mg metal
Fig. 1. A plausible mechanisms for defluorination-silylatio (route A), and Grignard
reagent formation (route B).
The results shown in chapter 2.1 and chapter 2.2 prompted us to
semiquantitatively evaluate the effect of Cu-deposits on the Mg
metal surface. The scope and limitation of the reductive defluori-
nations of benzotrifluoride derivatives were studied.9
Thus, the reduction of the compound 1a via route A would be less
favorable than that of the compound 1b, thus the route B would
take part in of the reaction of compound 1a. While, the compound
1b could be reduced predominantly via route A in DMPU.
The results of the reductive defluorinations of compound 6 by
both Mg metal and Cu-deposited Mg in DMI are summarized in
Table 2. The LUMO energy levels of the substrates were calculated
by HF/6-31G** on MacSpartan plus package program. Here, we used
DMI solvent for defluorinations in Table 2, because the reaction in
DMI gave higher conversion of substrates 6 than that in DMPU. The
reduction by Mg of the substrates 6a (X¼3-Cl), 6b (X¼3-F), 6c
(X¼4-Cl), and 6h (X¼4-TMS) gave compound 6g (X¼3-TMS), 7b
(X¼3-F), 7h (X¼4-TMS), and 7h (X¼4-TMS) as main products, re-
spectively (entries 1e3 and 8, Scheme 3). The reductions by Mg of
compounds 6d (X¼3-OMe), 6h (X¼H), and 6g (X¼3-TMS) resulted
in a little conversions of the substrates (entries 4, 6, and 7). And, the
reduction by Mg of compounds 6e (X¼4-F), 6i (X¼3,5-Me2), 6j
(X¼3-NMe2), 6k (X¼4-Me), 6l (X¼4-OMe), and 6m (X¼4-NMe2)
resulted in recovery of the substrates (entries 9e13). Meanwhile,
the reductions by Cu-deposited Mg of 6a (X¼3-Cl), 6b (X¼3-F), 6c
(X¼4-Cl), 6d (X¼3-OMe), 6e (X¼4-F), 6f (X¼H), 6g (X¼3-TMS), 6h
(X¼4-TMS), 6i (X¼3,5-Me2), 6j (X¼3-NMe2), and 6k (X¼4-Me)
gave compounds 6g (X¼3-TMS), 8b (X¼3-F), 7d (X¼3-OMe), 7e
(X¼4-F), 7f (X¼H), 7g (X¼3-TMS), 7h (X¼4-TMS), 7i (X¼3,5-Me2),
7j (X¼3-NMe2), and 7k (X¼4-Me), respectively (entries 1e11). And,
the reductions by Cu-deposited Mg of 6l (X¼4-OMe), 6m (X¼4-
NMe2) resulted in recovery of the substrates (entries 12 and 13).
Results of larger scale (5 mmol) reductions for product isolations
were shown in Experimental section.
2.2. Microscope observations of the Cu-deposited Mg metal
surfaces
The surface of Cu-deposited Mg was observed with a micro-
scope to shed light on the role of Cu-deposits on Mg (Fig. 2). The Mg
surface washed with TMS-Cl shown in Fig. 2A, exhibits a metallic
luster. The activated Mg metal surface with Cu-deposits, which was
prepared by the addition of CuCl to the magnesium metal in the
presence of TMS-Cl in THF, is shown in Fig. 2B. Several micrometer-
sized Cu metal-deposits were observed on the Mg surface. The
metal surface after the reaction of 1-chloro-3-(pentafluoroethyl)
benzene (1b) is shown in Fig. 2C. Cu-colored (dark brown) metal
was found at the bottom of the roughly sculpted area of Mg surface.
Meanwhile, the Mg metal surface distal to the Cu-deposits retained
its metallic luster. These observations suggest that the consumption
of the Mg metal proceeded only near the Cu-deposits.
These observations of the Mg metal surfaces and the results of
Table 1 are consistent with the hypothetical scheme in Fig. 1. The
Cu metal on the surface attracts some free electrons from the Mg
metal because Cu is a nobler metal than Mg. As a consequence,
the surface of the Mg metal gains some positive charge, which
Fig. 2. (A) TMS-Cl-washed Mg metal surface. (B) MgeCu prepared in THF and TMS-Cl. (C) MgeCu after the reaction of 1b under the conditions shown in Table 1, entry 8.
(consumption of Mg¼approx. 8 wt %.). (D) A 3D image of Fig. 2C.

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S. Utsumi et al. / Tetrahedron 68 (2012) 1085e1091
Table 2
The effects of substituent on benzotrifluoride derivatives in reductive defluorination with use of Mg/TMS-Cl system
Entry
X (compound)
sm or sp
LUMO levelb
[eV]
Time [h]
Results in cases Mg was useda [%]
Results in cases MgeCu was useda [%]
Conv.
7
8
Conv.
7
8
1
2
3
4
5
6
7
8
3-Cl (a)
3-F (b)
4-Cl (c)
3-OMe (d)
4-F (e)
0.37
0.34
0.23
0.12
0.06
2.776
2.602
2.769
2.945
2.908
3.049
2.881
2.657
3.070
3.063
3.300
3.053
3.422
5
5
5
100ꢁ0
98ꢁ2
100ꢁ0
2ꢁ1
See Scheme 3
93ꢁ2
See Scheme 3
2ꢁ1
100ꢁ0
100ꢁ0
100ꢁ0
46ꢁ24
57ꢁ12
70ꢁ14
95ꢁ2
99ꢁ2
16ꢁ4
5ꢁ2
See Scheme 3
2ꢁ3
5ꢁ2
97ꢁ3
See Scheme 3
45ꢁ22
57ꢁ12
67ꢁ13
53ꢁ5
15
15
15
5
15
15
15
15
15
15
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
1ꢁ2
0ꢁ0
0ꢁ1
0ꢁ1
H (f)
0
2ꢁ1
2ꢁ1
3ꢁ2
3-TMS (g)
4-TMS (h)
3,5-Me2 (i)
3-NMe2 (j)
4-Me (k)
4-OMe (l)
4-NMe2 (m)
ꢂ0.04
ꢂ0.07
ꢂ0.14
ꢂ0.16
ꢂ0.17
ꢂ0.27
ꢂ0.83
1ꢁ0
1ꢁ0
42ꢁ6
63ꢁ16
0ꢁ0
17ꢁ16
0ꢁ0
17ꢁ16
0ꢁ0
35ꢁ15
16ꢁ4
9
10
11
12
13
0ꢁ0
0ꢁ0
5ꢁ2
0ꢁ0
0ꢁ0
0ꢁ0
8ꢁ2
8ꢁ2
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
0ꢁ0
a
Product distributions were determined by 19F NMR. Other products were not detected by 19F NMR and GC.
LUMO energy levels of substrates 6 were calculated by MacSpartan plus with HF/6-31G**.
b
Scheme 3.
Here, we should note that the s values showed the limitations of
the reaction on the Cu-deposited Mg metal, although the LUMO
level showed the limitations of the reaction on Mg metal. Table 2
Scheme 4.
is arranged according to the
s values of the substrates and
clearly shows the limitations of the reaction on Cu-deposited Mg
Cu-deposits on an Mg metal surface may enable the constitution of
a micro-redox circuit to reduce the internal resistance of the re-
action by avoiding the formation of unstable ionic species.
between ꢂ0.27< limit<ꢂ0.17. Meanwhile, the order of the sub-
s
strates does not show the limitations of the reaction on Mg without
Cu-deposits. The limitation of the reaction on Mg without Cu-
deposits is shown by the arrangement according to the LUMOs
instead of that according to the
s values. This alteration of the scale
4. Experimental section
4.1. General
of the limitations is consistent with the hypothetical scheme shown
in Scheme 4.10 That is, the extent of the concerted electron transfer
reactions involving outer-sphere and inner-sphere electron trans-
fers on the surface of Cu-deposited Mg metal would be determined
by the stability of the possible metal anionoid species of Scheme
4A. Meanwhile, the stepwise outer-sphere electron transfer on
the Mg metal without Cu-deposits would be determined by the
LUMO levels of the substrates (Scheme 4B).
All NMR spectra were recorded as CDCl3 solutions. 1H NMR
(600 MHz) was recorded with Varian Unity INOVA AS600. 1H NMR
(400 MHz), 13C NMR (100 MHz), 19F NMR (376 MHz) spectra were
recorded with Varian VNMRS-400 instrument. 1H NMR (300 MHz),
13C NMR (75 MHz), spectra were recorded with Varian-Mercury-
300 instrument. 13C NMR (50 MHz) spectra were recorded with
Varian GEMINI-200 instrument. The chemical shifts are reported in
3. Conclusions
d
(ppm) related to the CHCl3 (7.26 ppm for 1H NMR), CDCl3 (77 ppm
The Cu-deposited Mg metal was found to be a stronger reducing
agent than the Mg metal itself. Moreover, different routes for re-
duction were suggested: concerted inner-sphere and outer-sphere
electron transfer for Cu-deposited Mg metal and stepwise outer-
sphere electron transfers for Mg metal. The combination of
for 13C NMR), and C6F6 (0 ppm for 19F NMR: The relative chemical
shift of C6F6 to CFCl3 is ꢂ162.2 ppm). Coupling constants (J) are
reported in hertz (Hz). Infrared spectra were recorded on a Hitachi
270e30 spectrometer. Only selected absorbances are reported
(
n a Shimadzu
in cmꢂ1). MS analyses were performed on

S. Utsumi et al. / Tetrahedron 68 (2012) 1085e1091
1089
GCMS-QP5050A. Elemental analyses were performed on a Per-
kineElmer series II CHNS/O Analyzer 2400. Microscope observa-
tions were performed on KEYENCE VHX-1000. Mg powder was
purchased from Merck (particle size 0.1 mm, 97% pure, synthetic
grade. catalog# 8.18506.0100). Magnesium ribbon for microscope
observations was purchased from SigmaeAldrich (ꢃ99.5% Mg ba-
sis, catalog# 13103-25G). Copper(I) chloride was purchased from
Wako pure chemicals (99.9% purity, catalog# 033-12482).
1F), 90.1 (d, J¼12 Hz, 3F). EI MS m/z (% relative intensity) 230
(MþꢂMe3SiF, 19), 215 (100), 77 (26), 73 (82). Elemental Anal. Calcd
for C14H22F4Si2: C, 52.14; H, 6.88. Found: C, 51.88; H, 6.85.
4.2.5. 1-[10,20,20,20-Tetrafluoro-10-(trimethylsilyl)ethyl]-3-(trime-
thylsilyl)benzene (5b). Colorless oil. 15% Yield (determined by 19F
NMR). Bp 50 ꢀC/0.1 mmHg. IR nmax (neat) 2970 cmꢂ1 1H NMR
(600 MHz, CDCl3)
d
0.15 (s, 9H), 0.27 (s, 9H), 7.33 (d, J¼8 Hz, 1H),
7.37 (tt, J¼8, 1 Hz, 1H), 7.46 (partially overlapping d, J¼1 Hz, 1H),
4.2. Representative procedure for selective reductive
dechloro-silylation from chloro(pentafluoroethyl)-benzenes
(1) with use of MgeCu/TMS-Cl
7.48 (partially overlapping dt, J¼8, 1 Hz, 1H). 13C NMR (50 MHz,
CDCl3)
d
ꢂ3.5 (s), ꢂ1.2 (s), 95.7 (dq, J¼184, 33 Hz), 125.4 (dq, J¼281,
25 Hz), 124.2 (d, J¼12 Hz), 127.6 (s), 128.5 (d, J¼10 Hz), 132.7 (s),
134.0 (d, J¼19 Hz), 140.5 (s). 19F NMR (283 MHz, CDCl3)
d
ꢂ37.4 (q,
Mg powder (0.486 g, 20 mmol) and copper(I) chloride (0.248 g,
2.5 mmol) were stirred in THF (2.0 ml) for 5 min under an argon
atmosphere. The solution became dark suspension. Then, Et2O
(18.0 ml) and TMS-Cl (40 mmol, 5.0 ml) was added to the solution
and stirred for 10 min at 40 ꢀC (bath temperature). 1-Chloro-3-
(perfluoroethyl)benzene (1b) (1.1578 g, 5 mmol) was added drop-
wise over 10 min into the stirred suspension. The suspension was
stirred for additional 10 h at 40 ꢀC (bath temperature, reflux). After
evaporation of the solvent, residual Mg and Cu were filtrated
through Celite with hexane. The mixture of the products was pu-
rified by column chromatography on silica gel (hexane eluent), and
provided compound 2b as colorless oil (1.07 g, 80%). Additional
distillation gave the product of higher purity.
J¼9 Hz, 1F), 90.1 (d, J¼9 Hz, 3F). EI MS m/z (% relative intensity) 230
(MþꢂMe3SiF, 31), 215 (94), 77 (28), 73 (100). Elemental Anal. Calcd
for C14H22F4Si2: C, 52.14; H, 6.88. Found: C, 52.03; H, 6.71.
4.3. Representative procedure for reductive defluorination
from benzotrifluoride derivatives with use of MgeCu/TMS-Cl
(a) For Table 2, copper(I) chloride (0.025 g, 0.25 mmol) and Mg
powder (0.049 g, 2 mmol) were stirred in DMI (2 ml) and TMS-
Cl (0.5 ml, 4 mmol) for 15 min under an argon atmosphere.
Then, a benzotrifluoride derivative 6 (0.5 mmol) was added
dropwise into the dark suspension. The solution was stirred for
additional time (see Table 2), keeping the temperature at 25 ꢀC
(bath temperature). After decantation, supernatant liquid was
analyzed by GC and 19F NMR with (4-trifluoromethyl)anisole as
an internal standard.
(b) For isolations of the major products, copper(I) chloride
(0.248 g, 2.5 mmol) and Mg powder (0.486 g, 20 mmol) were
stirred in DMI (20 ml, 10 ml for 7i, 7j, 7k) and TMS-Cl (5 ml,
40 mmol) for 15 min under an argon atmosphere. Then,
a benzotrifluoride derivative 6 (5 mmol) was added dropwise
over 5 min into the dark suspension. The solution was stirred
for additional time (see Table 2), keeping the temperature 25 ꢀC
(bath temperature, 50 ꢀC for 7i, 7j, 7k). After addition of 5 ml of
hexane, MgeCu was removed by decantation and the suspen-
sion was simultaneously extracted with hexane (5 mlꢄ5). Then,
the combined hexane layer was washed with 10 wt % HCl aq
and brine. After drying over sodium sulfate, purification by
column chromatography on silica gel (hexane eluent) and
distillation afforded the product.
4.2.1. 1-(Pentafluoroethyl)-4-(trimethylsilyl)benzene (2a). Colorless
oil. 69% Yield (determined on 19F NMR). Bp 95 ꢀC/40 mmHg. IR nmax
(neat) 2960 cmꢂ1 1H NMR (300 MHz, CDCl3)
d
0.35 (s, 9H), 7.62 (d,
J¼8 Hz, 2H), 7.71 (d, J¼8 Hz, 2H). 13C NMR (50 MHz, CDCl3)
d
ꢂ1.4
(s), 113.6 (tq, J¼251, 37 Hz), 119.3 (qt, J¼284, 39 Hz), 125.5 (t,
J¼7 Hz), 129.1 (t, J¼24 Hz), 133.6 (s), 145.7 (s). 19F NMR (283 MHz,
CDCl3) d 46.6 (s, 2F), 77.0 (s, 3F). EI MS m/z (% relative intensity) 268
(Mþ, 3), 253 (100), 92 (21), 77 (11). Elemental Anal. Calcd for
C11H13F5Si: C, 49.24; H, 4.88. Found: C, 49.07; H, 5.01.
4.2.2. 1-(Pentafluoroethyl)-3-(trimethylsilyl)benzene (2b). Colorless
oil. 80% Yield. Bp 95 ꢀC/40 mmHg. IR nmax (neat) 2970 cmꢂ1 1H NMR
(600 MHz, CDCl3)
1H), 7.71 (partially overlapping d, J¼8 Hz, 1H), 7.69 (partially
overlapping s, 1H). 13C NMR (150 MHz, CDCl3)
d
0.30 (s, 9H), 7.48 (t, J¼8 Hz, 1H), 7.57 (d, J¼8 Hz,
d
ꢂ1.42 (s), 113.7 (tq,
J¼254, 39 Hz), 119.2 (qt, J¼286, 40 Hz), 126.7 (t, J¼6.3 Hz), 127.9 (s),
128.1 (t, J¼24 Hz), 130.8 (t, J¼6 Hz), 136.8 (s), 141.8 (s). 19F NMR
(283 MHz, CDCl3)
d 46.8 (s, 2F), 76.9 (s, 3F). EI MS m/z (% relative
intensity) 268 (Mþ, 2), 253 (100), 203 (25), 92 (28), 77 (16). Ele-
mental Anal. Calcd for C11H13F5Si: C, 49.24; H, 4.88. Found: C, 49.18;
H, 5.11.
4.3.1. Difluoro(trimethylsilyl)methylbenzene (7f). Colorless oil. 90%
Yield (5 mmol scale). Bp 100 ꢀC/15 mmHg. IR nmax (neat) 2970 cmꢂ1
1H NMR (300 MHz, CDCl3)
d
0.14 (s, 9H), 7.3e7.4 (m, 5H). [
9H), 7.26e7.45 (m, 5H) (Ref. 9b)] 13C NMR (50 MHz, CDCl3)
(s), 124.6 (t, J¼7 Hz), 128.2 (s), 128.2 (t, J¼263 Hz), 128.7 (s), 138.2 (t,
d
0.21 (s,
d
ꢂ4.8
4.2.3. 1-[10,20,20,20-Tetrafluoro-10-(trimethylsilyl)ethyl]-4-
chlorobenzene (4a). Colorless oil. 32% Yield (determined by 19F
NMR). Bp 40 ꢀC/0.1 mmHg. IR nmax (neat) 2970 cmꢂ1 1H NMR
J¼20 Hz). [ ꢂ4.9 (s), 128.3 (s), 124.7 (t, J¼8 Hz), 128.8 (t, J¼2.6 Hz),
d
134.5 (t, J¼265 Hz), 138.3 (t, J¼20.4 Hz). (Ref. 9b)] 19F NMR
(300 MHz, CDCl3)
d
0.16 (s, 9H), 7.28 (d, J¼8.4 Hz, 2H), 7.38 (d,
(376 MHz, CDCl3) d 49.4 (s). [d 49.7 (s) (Ref. 9b)] EI MS m/z (% rel-
J¼8.4 Hz, 2H). 13C NMR (125 MHz, CDCl3)
d
ꢂ3.7 (s), 95.4 (dq, J¼185,
ative intensity) 127 (MþꢂMe3Si, 3). 108 (MþꢂMe3SiF, 100), 81 (19),
77 (15), 73 (44). Elemental Anal. Calcd for C10H14F2Si: C, 59.96; H,
7.04. Found: C, 59.99; H, 7.23.
34 Hz), 124.9 (qd, J¼282, 25 Hz), 125.4 (d, J¼11 Hz), 128.7 (d,
J¼3 Hz), 133.6 (d, J¼18 Hz), 134.0 (s). 19F NMR (283 MHz, CDCl3)
d
ꢂ36.3 (q, J¼12 Hz, 1F), 89.9 (d, J¼12 Hz, 3F). EI MS m/z (% relative
intensity) 194 (MþꢂMe3SiF, 26), 192 (78), 157 (8), 73 (100). Ele-
mental Anal. Calcd for C11H13ClF4Si: C, 46.40; H, 4.60. Found: C,
46.62; H, 4.53.
4.3.2. [Fluoro-bis(trimethylsilyl)]methylbenzene (8f). Colorless oil.
6% Yield (5 mmol scale). 1H NMR (600 MHz, CDCl3)
d
0.08 (s, 18H),
7.04 (br, 2H), 7.09 (dt, J¼7, 1 Hz, 1H), 7.29 (t, J¼8 Hz, 2H). [ 0.23 (s,
18H), 7.08e7.40 (m, 5H) (Ref. 9b)] 19F NMR (376 MHz, CDCl3)
d
4.2.4. 1-[10,20,20,20-Tetrafluoro-10-(trimethylsilyl)ethyl]-4-(trime-
thylsilyl)benzene (5a). Colorless oil. 6% yield (determined by 19F
NMR). Bp 50 ꢀC/0.1 mmHg. IR nmax (neat) 2960 cmꢂ1 1H NMR
d
ꢂ56.2 (s). [ ꢂ56.7 (s) (Ref. 9b)] EI MS m/z (% relative intensity)
d
162 (MþꢂMe3SiF, 41), 147 (100), 135 (43), 77 (22), 73 (53).
(300 MHz, CDCl3)
d
0.16 (s, 9H), 0.27 (s, 9H), 7.31 (d, J¼8 Hz, 2H),
4.3.3. 1-Fluoro-3-[difluoro(trimethylsilyl)methyl]benzene
(7b). Colorless oil. 86% Yield (5 mmol scale). Bp 110 ꢀC/20 mmHg. IR
7.52 (d, J¼8 Hz, 2H). 19F NMR (283 MHz, CDCl3)
ꢂ37.5 (q, J¼12 Hz,
d

1090
S. Utsumi et al. / Tetrahedron 68 (2012) 1085e1091
nmax (neat) 2970 cmꢂ1 1H NMR (600 MHz, CDCl3)
d
0.14 (s, 9H), 7.04
(11), 73 (53). Elemental Anal. Calcd for C12H18F2Si: C, 63.12; H, 7.95.
(partially overlapping dq, J¼11,1 Hz,1H), 7.07 (partially overlapping
Found: C, 63.15; H, 7.56.
tq, J¼8, 1 Hz, 1H), 7.11 (tq, J¼8, 1 Hz, 1H), 7.38 (q, J¼8 Hz, 1H). 13C
NMR (100 MHz, CDCl3)
d
ꢂ4.9 (s), 111.9 (dt, J¼24, 8 Hz), 115.8 (dt,
4.3.9. 1-[Difluoro(trimethylsilyl)methyl]-3-(trimethylsilyl)benzene
(7g). Colorless oil. 82% Yield (5 mmol scale). Bp 70 ꢀC/0.6 mmHg. IR
J¼19, 2 Hz), 120.4 (td, J¼7, 3 Hz), 127.5 (t, J¼265 Hz), 130.0 (d,
J¼7 Hz), 140.7 (td, J¼21, 7 Hz), 162.6 (d, J¼245 Hz). 19F NMR
nmax (neat) 2970 cmꢂ1 1H NMR (400 MHz, CDCl3)
d 0.14 (s, 9H), 0.28
(376 MHz, CDCl3)
d
49.4 (td, J¼9, 6 Hz, 1F), 49.5 (s, 2F). EI MS m/z (%
(s, 9H), 7.32 (d, J¼8 Hz, 1H), 7.39 (t, J¼8 Hz, 1H), 7.46 (s, 1H), 7.53 (d,
relative intensity) 145 (MþꢂMe3Si, 5), 126 (MþꢂMe3SiF, 100), 77
(16), 73 (61). Elemental Anal. Calcd for C10H13F3Si: C, 55.02; H, 6.00.
Found: C, 54.87; H, 6.30.
J¼7 Hz, 1H). 13C NMR (100 MHz, CDCl3)
ꢂ4.89 (s), ꢂ1.23 (s), 125.0
d
(t, J¼8 Hz), 127.5 (s), 128.5 (t, J¼264 Hz), 129.4 (t, J¼8 Hz), 133.7 (t,
J¼3 Hz), 137.2 (t, J¼39 Hz), 140.6 (s). 19F NMR (376 MHz, CDCl3)
d
49.2 (s). EI MS m/z (% relative intensity) 257 (MþꢂCH3, 5), 180
4.3.4. 1-Fluoro-3-[bis(trimethylsilyl)fluoromethyl]benzene
(8b). Colorless oil. 96% Yield (5 mmol scale). Bp 110 ꢀC/20 mmHg. IR
(MþꢂMe3SiF, 67), 165 (28), 73 (100). Elemental Anal. Calcd for
C13H22F2Si2: C, 57.30; H, 8.14. Found: C, 57.42; H, 8.41.
nmax (neat) 2970 cmꢂ1 1H NMR (400 MHz, CDCl3)
d
0.07 (d, J¼1 Hz,
18H), 6.76 (br, 2H), 6.77 (tdd, J¼8, 2, 1 Hz 1H), 7.23 (q, J¼7 Hz, 1H).
13C NMR (75 MHz, CDCl3)
4.3.10. 1-[Fluoro-bis(trimethylsilyl)methyl]-3-(trimethylsilyl)benzene
(8g). Colorless oil (a mixture with isomer 8h). 16% Yield (5 mmol
scale). Bp 110 ꢀC/0.6 mmHg. IR nmax (neat) 2960 cmꢂ1 1H NMR
d
ꢂ2.46 (d, J¼44 Hz), 99.6 (d, J¼158 Hz),
108.4 (t, J¼29 Hz), 110.8 (d, J¼21 Hz), 116.6 (d, J¼12 Hz), 129.3 (d,
J¼7 Hz), 147.6 (dd, J¼14, 7 Hz), 163.2 (d, J¼245 Hz). 19F NMR
(400 MHz, CDCl3) d 0.08 (s, 18H), 0.26 (s, 9H), 7.09 (br, 1H), 7.13 (br,
(376 MHz, CDCl3)
d
ꢂ54.0 (s, 1F), 48.6 (br, 1F). EI MS m/z (% relative
1H), 7.23 (dt, J¼7, 1 Hz, 1H), 7.28 (t, J¼7 Hz, 1H). 13C NMR (100 MHz,
intensity) 180 (MþꢂMe3SiF, 53), 165 (100), 153 (43), 139 (38), 77
(72), 73 (87). Elemental Anal. Calcd for C13H22F2Si2: C, 57.30; H, 8.14.
Found: C, 57.67; H, 8.23.
CDCl3)
d
ꢂ2.38 (d, J¼4 Hz), ꢂ1.14 (s), 100.0 (d, J¼155 Hz), 121.8 (d,
J¼15 Hz), 126.0 (d, J¼11 Hz), 127.3 (s), 128.9 (s), 139.2 (s), 143.3 (d,
J¼7 Hz). 19F NMR (376 MHz, CDCl3)
ꢂ57.0 (s). EI MS m/z (% relative
d
intensity) 311 (MþꢂCH3, 1), 234 (MþꢂMe3SiF, 3). 146 (53), 73 (100).
4.3.5. 1-[Difluoro(trimethylsilyl)methyl]-3-methoxybenzene
(7d). Colorless oil. 91% Yield (5 mmol scale). Bp 110 ꢀC/3 mmHg. IR
4.3.11. 1-[Difluoro(trimethylsilyl)methyl]-4-flourobenzene
(7e). Colorless oil. 85% Yield (5 mmol scale). Bp 100 ꢀC/15 mmHg. IR
nmax (neat) 2970 cmꢂ1 1H NMR (400 MHz, CDCl3)
d 0.15 (s, 9H),
3.82 (s, 3H), 6.87 (q, J¼1 Hz, 1H), 6.90 (dq, 8, 1 Hz, 1H), 6.92 (dq, 8,
nmax (neat) 2980 cmꢂ1 1H NMR (600 MHz, CDCl3)
d 0.13 (s, 9H), 7.09
1 Hz, 1H), 7.32 (t, J¼8 Hz, 1H). 13C NMR (100 MHz, CDCl3)
d
ꢂ4.9
(t, J¼8 Hz, 2H), 7.31 (dd, J¼8, 6 Hz, 2H). 13C NMR (100 MHz, CDCl3)
(s), 55.1 (s), 110.2 (t, J¼8.2 Hz), 114.3 (t, J¼2 Hz), 117.0 (t, J¼7 Hz),
d
ꢂ5.04 (s), 115.3 (d, J¼22 Hz), 126.7 (q, J¼24 Hz), 128.0 (t,
128.0 (t, J¼263 Hz), 129.4 (s), 139.7 (t, J¼20 Hz). 19F NMR
J¼264 Hz), 134.3 (dt, J¼21, 3 Hz), 163.0 (dt, J¼246, 3 Hz). 19F NMR
(376 MHz, CDCl3)
d
49.6 (s). EI MS m/z (% relative intensity) 230
(376 MHz, CDCl3)
d
48.8 (tt, J¼8, 6 Hz, 1F), 50.4 (d, J¼3 Hz, 2F), EI MS
(Mþ, 12) 138 (MþꢂMe3SiF, 70), 109 (58), 77 (26), 73 (100). Ele-
mental Anal. Calcd for C11H16F2OSi: C, 57.36; H, 7.00. Found: C,
57.42; H, 7.26.
m/z (% relative intensity) 145 (MþꢂMe3SiF, 7), 126 (MþꢂMe3SiF,
100), 73 (44). Elemental Anal. Calcd for C10H13F3Si: C, 55.02; H, 6.00.
Found: C, 55.07; H, 6.06.
4.3.6. 1-[Fluoro-bis(trimethylsilyl)methyl]-3-methoxybenzene
4.3.12. 1-[Fluoro-bis(trimethylsilyl)methyl]-4-fluorobenzene
(8e). Colorless oil. 2% Yield (5 mmol scale). Bp 70 ꢀC/0.6 mmHg 1H
(8d). Colorless oil. 2% Yield (5 mmol scale). Bp 150 ꢀC/3 mmHg. IR
nmax (neat) 2960 cmꢂ1 1H NMR (400 MHz, CDCl3)
d
0.07 (d,
NMR (400 MHz, CDCl3) d
0.06 (s, 18H), 6.9e7.0 (m, 4H). 19F NMR
J¼1 Hz, 18H), 3.79 (s, 3H), 6.58 (br m, 2H), 6.61 (ddd, J¼8, 3, 1 Hz,
(376 MHz, CDCl3)
d
ꢂ55.1 (s, 1F), 41.5 (quint, J¼7 Hz, 1F). EI MS m/z
1H), 7.19 (t, J¼8 Hz). 13C NMR (100 MHz, CDCl3)
d
ꢂ2.39 (d,
(% relative intensity) 180 (MþꢂMe3SiF, 47), 165 (100), 153 (50), 77
J¼4 Hz), 55.0 (s), 99.9 (d, J¼156 Hz), 107.1 (d, J¼16 Hz), 109.2 (s),
113.6 (d, J¼12 Hz), 128.7 (s), 146.2 (d, J¼13 Hz), 159.5 (br).
(67), 73 (90).
19F NMR (376 MHz, CDCl3)
d
ꢂ55.0 (s). EI MS m/z (% relative
4.3.13. 1-[Difluoro(trimethylsilyl)methyl]-4-toluene (7k). Colorless
oil. 68% Yield (5 mmol scale). Bp 110 ꢀC/15 mmHg. IR nmax (neat)
intensity) 285 (Mþ, 11), 192 (MþꢂMe3SiF, 25), 177 (65), 165 (36),
89 (37), 77 (46), 73 (100).
2970 cmꢂ1 1H NMR (600 MHz, CDCl3)
d 0.13 (s, 9H), 2.37 (s, 3H), 7.20
(d, J¼8 Hz, 2H), 7.22 (d, J¼8 Hz, 2H). 13C NMR (100 MHz, CDCl3)
4.3.7. 1-[Difluoro(trimethylsilyl)methyl]-3-(dimethylamino)benzene
(7j). Colorless oil. 32% Yield (5 mmol scale). Bp 110 ꢀC/0.8 mmHg.
d
ꢂ4.90 (s), 21.1 (s), 124.6 (t, J¼8 Hz), 128.5 (t, J¼263 Hz), 128.9 (s),
135.4 (t, J¼20 Hz),138.6 (t, J¼3 Hz). 19F NMR (376 MHz, CDCl3)
d 50.1
IR nmax (neat) 2970 cmꢂ1 1H NMR (600 MHz, CDCl3)
d
0.15 (s, 9H),
(s). EI MS m/z (% relative intensity) 122 (MþꢂMe3SiF, 100), 73 (35).
Elemental Anal. Calcd for C11H16F2Si: C, 61.64; H, 7.52. Found: C,
61.42; H, 7.64.
2.96 (s, 6H), 6.66 (s, 1H), 6.68 (d, J¼8 Hz, 1H), 6.73 (d, J¼8 Hz, 1H),
7.25 (t, J¼8 Hz, 1H). 13C NMR (100 MHz, CDCl3)
d
ꢂ4.78 (s), 40.4
(s), 108.5 (t, J¼8 Hz), 112.8 (partially overlapping t, J¼2 Hz), 112.8
(partially overlapping t, J¼8 Hz), 128.5 (t, J¼263 Hz), 128.9 (s),
4.3.14. 1-[Difluoro(trimethylsilyl)methyl]-4-(trimethylsilyl)benzene
(7h). White solid. 78% Yield (5 mmol scale). Mp 42e43 ꢀC. Bp
70 ꢀC/0.6 mmHg. IR nmax (KBr) 2970 cmꢂ1 1H NMR (400 MHz,
138.8 (t, J¼20 Hz), 150.3 (s). 19F NMR (376 MHz, CDCl3)
d 49.5 (s).
EI MS m/z (% relative intensity) 243 (Mþ, 60), 150 (MþꢂMe3SiF,
100), 136 (42), 77 (13), 73 (60). Elemental Anal. Calcd for
C12H19F2NSi: C, 59.22; H, 7.87; N, 5.76. Found: C, 59.35; H, 8.02.
N, 5.87.
CDCl3)
d
0.14 (s, 9H), 0.28 (s, 9H), 7.30 (d, J¼8 Hz, 2H), 7.55 (d,
J¼8 Hz, 2H). 13C NMR (100 MHz, CDCl3)
ꢂ4.83 (s), ꢂ1.20 (s), 123.9
d
(t, J¼8 Hz), 128.3 (t, J¼263 Hz), 133.2 (s), 138.5 (t, J¼20 Hz), 141.3 (t,
J¼2 Hz). 19F NMR (376 MHz, CDCl3)
d 49.4 (s). EI MS m/z (% relative
4.3.8. 1-[Difluoro(trimethylsilyl)methyl]-3,5-dimethylbenzene
(7i). Colorless oil. 57% Yield (5 mmol scale). Bp 60 ꢀC/0.8 mmHg. IR
intensity) 257 (MþꢂCH3, 8). 180 (MþꢂMe3SiF, 68), 165 (29), 73
(100). Elemental Anal. Calcd for C13H22F2Si2: C, 57.30; H, 8.14.
Found: C, 57.46; H, 8.29.
nmax (neat) 2980 cmꢂ1 1H NMR (600 MHz, CDCl3)
d
0.13 (s, 9H), 2.34
(s, 6H), 6.93 (s, 2H), 7.00 (s, 1H). 13C NMR (100 MHz, CDCl3)
d
ꢂ4.82
(s), 21.3 (s), 122.4 (t, J¼8 Hz), 128.4 (t, J¼263 Hz), 130.4 (t, J¼2 Hz),
4.3.15. 1-[Fluoro-bis(trimethylsilyl)methyl]-4-(trimethylsilyl)benzene
(8h). White solid. 94% Yield (5 mmol scale). Mp 55e56 ꢀC.
Bp 110 ꢀC/0.6 mmHg. IR nmax (KBr) 2960 cmꢂ1 1H NMR
137.8 (s), 138.1 (t, J¼39 Hz). 19F NMR (376 MHz, CDCl3)
d 50.0 (s). EI
MS m/z (% relative intensity) 228 (Mþ, 1), 136 (MþꢂMe3SiF, 100), 77

S. Utsumi et al. / Tetrahedron 68 (2012) 1085e1091
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Uneyama, K. Chem. Rev. 2009, 109, 2119e2183; (c) Chloro-substituted (penta-
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Ref. 6a.
7. Garst, J. F.; Soriaga, M. P. Coord. Chem. Rev. 2004, 248, 623e652.
8. (a) Uneyama, K. Organofluorine Chemistry; Blackwell: Oxford, 2006, pp 52e60
and references therein; (b) Roberts, J. D.; Webb, R. L.; McElhill, E. A. J. Am. Chem.
Soc. 1950, 72, 408e411.
(400 MHz, CDCl3)
d
0.07 (s,18H), 0.24 (s, 9H), 6.99 (br d, J¼7 Hz, 2H),
7.40 (d, J¼7 Hz, 2H). 13C NMR (100 MHz, CDCl3)
ꢂ2.32 (d, J¼4 Hz),
d
ꢂ0.94 (s), 100.0 (d, J¼155 Hz), 120.5 (d, J¼13 Hz), 132.8 (s), 135.0 (s),
144.9 (d, J¼13 Hz). 19F NMR (376 MHz, CDCl3)
ꢂ56.6 (s, 1F). EI MS
d
m/z (% relative intensity) 311 (MþꢂCH3, 2), 234 (MþꢂMe3SiF, 10),
146 (44), 73 (100). Elemental Anal. Calcd for C16H31FSi3: C, 58.83; H,
9.56. Found: C, 58.71; H, 9.58.
Acknowledgements
We are grateful to Dr. Yutaka Nakamura and Mr. Yuji Tsuchikura
for their preliminary studies on the preparations of substrates. We
thank the SC-NMR Laboratory of the Graduate School of Natural
Science and Technology, Okayama University, for NMR analyses.
This work was supported in part by the Okayama Foundation for
Science and Technology. We would like to thank Mr. Katsuya Seki,
Keyence Co., for the use of the microscope.
References and notes
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