Catalytic hydrodefluorination of fluoromethanes at room temperature by silylium-ion-like surface species

Article abstract of DOI:10.1002/anie.201300608

'Al'l about F: Aluminum chlorofluoride (ACF) catalyzes the hydrodefluorination, as well as Friedel-Crafts reactions of fluorinated methanes in the presence of Et₃SiH. A surface-bound silylium-ion-like species is considered to be a crucial intermediate in achieving the C-F bond cleavage. Copyright

Full text of DOI:10.1002/anie.201300608

.
Angewandte
Communications
DOI: 10.1002/anie.201300608
À
C F Activation
Catalytic Hydrodefluorination of Fluoromethanes at Room
Temperature by Silylium-ion-like Surface Species**
Mike Ahrens, Gudrun Scholz, Thomas Braun,* and Erhard Kemnitz*
À
Breaking C F bonds catalytically under moderate reaction
conditions can be considered a fundamental challenge in
synthetic chemistry.[1] The conversions can provide new
reaction pathways to otherwise unaccessible fluorinated
compounds and building blocks.[2] From an environmental
point of view, the defluorination of (poly)fluorinated com-
pounds is also of considerable interest because of the “super-
greenhouse gas” behavior of chlorofluorocarbons (CFCs),
hydrofluorocarbons (HFCs), and perfluorocarbons (PFCs).[3]
Although significant progress was made for the intermolec-
ular activation of highly fluorinated aromatics and olefins,[1]
Jones et al., by using [Cp*2ZrH2] under an H2 atmosphere for
the hydrodefluorination of CH2F2,[9] and by Mikami et al. for
the a-difluoromethylation of lithium enolates when using
CHF3 as the difluoromethylation agent.[10] Some heteroge-
À
neous catalysts were developed and are capable of C F
activation of fluoromethanes at elevated temperature in the
gas phase. Thus, aluminum, transition-metals, and alkaline-
earth-metal oxides,[3a,11] sulfated metal oxides,[3a,11b] or metal
phosphates[3a] are able to catalyze the decomposition of
fluoromethanes to yield metal fluorides and carbon oxides, or
result in the hydrolysis of fluoromethanes at 250–8508C.
Recently, it was shown that CHF3 can be mineralized by solid
alkali hydroxides to give the corresponding fluorides, CO, and
À
C F bond cleavage reactions of fluorinated alkanes are less
developed. Major achievements include the employment of
silylium or alumylium ions as homogeneous Lewis-acidic
catalysts, which are stabilized by weakly coordinating
anions.[4] In the presence of hydrogen sources such as tertiary
silanes, the hydrodefluorination of highly fluorinated, but not
perfluorinated alkanes, was achieved under exceptionally
mild reaction conditions.[4b,c] Carbocationic species are dis-
cussed as intermediates, and in the presence of aromatic
À
H2O at moderate temperatures. An initial C H interaction is
considered as the crucial reaction step.[12] Mass spectrometric
experiments revealed that lanthanide cations can react with
CH3F in the gas phase, whereas no reaction was found for
[13]
CHF3 and CF4.
À
Herein we report on the heterogeneous C F activation of
fluoromethanes in solution with nanoscopic aluminum
chlorofluoride (ACF) in the presence of Et3SiH. ACF is an
amorphous chlorine-containing aluminum fluoride AlClxF3Àx
(x ꢀ 0.05–0.3) and is considered to be a Lewis acid with an
À
compounds Friedel–Crafts products were generated. A C F
bond cleavage step or even a hydrodefluorination of fluoro-
methanes has so far not been reported with these catalytic
[14]
À
systems. Note, that for a homolytic cleavage, the C F bond
acidity comparable to SbF5. Catalytic experiments under
strengths in poly- and perfluorinated alkanes are less
very mild reaction conditions led either to hydrodefluorina-
tion or, in the presence of benzene, Friedel–Crafts-type
reactions. The conversions are presumably mediated by
compared to those in polyfluorinated methanes.[5] This bond
À
strength has to be considered as one reason for the C F bond
cleavage of polyfluorinated methanes being considerably
more difficult. However, for breaking a C F bond heterolyti-
cally, C2F6 would have a higher bond dissociation energy than
À
a silylium-ion-like surface species which initiates the C F
activation step.
À
In an initial experiment ACF was treated with Et3SiH in
benzene. A 19F NMR spectrum of the reaction solution
revealed the formation of small amounts of Et3SiF. 19F Hahn
spin-echo MAS NMR studies showed that weakly bound
surface fluorine species, which were present at the ACF
before treatment with Et3SiH, vanished after the contact with
the silane (see Figure S1 in the Supporting Information).
Because of the small amounts of the formed Et3SiF, it was not
possible to identify any hydride species on the solid surface by
MAS NMR spectroscopy. Nevertheless, the 1H MAS NMR
spectrum revealed broad signals for surface-bound Et3SiH
(Figure 1a). The immobilized Et3SiH species were also
detected by 29Si{1H} CP MAS NMR spectroscopy. We pre-
sume that Et3SiH reacts with the Lewis-acidic sites of ACF to
[6]
CF4. In addition, increasing fluorine content leads to
À
a substantial strengthening of each C F bond in fluorinated
methanes.[1a,7] Remarkably, Goldman et al. reported stoichio-
À
metric C F activation reactions of CH3F and CHF3 with an
iridium pincer compound.[8] In these cases, an initial C H
À
À
activation step is required to achieve a net C F activation.
Stoichiometric C Factivation reactions were also reported by
À
[*] Dr. M. Ahrens, Priv.-Doz. Dr. G. Scholz, Prof. Dr. T. Braun,
Prof. Dr. E. Kemnitz
Department of Chemistry, Humboldt-Universitꢀt zu Berlin
Brook-Taylor-Str. 2, 12489 Berlin (Germany)
E-mail: thomas.braun@chemie.hu-berlin.de
erhard.kemnitz@chemie.hu-berlin.de
À
give a surface bound entity ACF···H SiEt3 (Figure 1b), which
[**] We thank the DFG (German Research Foundation) for financial
support and funding of the Research Training Group 1582 “Fluorine
as a Key Element”. M.A. thanks the Fonds der Chemischen Industrie
for additional financial support. Dr. Thoralf Krahl is kindly
acknowledged for the synthesis of a batch sample of ACF.
has considerable silylium ion character. Note that the result-
ing particles are not active anymore in the isomerization of
1,2-dibromohexafluoropropane into 2,2-dibromohexafluoro-
propane, whereas ACF catalyzes this isomerization at room
temperature.[15]
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201300608.
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Chemie
Figure 1. a) 1H MAS NMR spectrum which shows the signals for sur-
face-bound Et3SiH (nrot =10 kHz) with the SiH resonance at
d=3.45 ppm. For Et3SiH in C6D6 solution the resonance is observed at
À
d=3.85 ppm. b) Schematic representation of ACF···H SiEt3.
Figure 2. 1H NMR spectrum of the ACF-catalyzed reaction of CH3F
The presence of silylium-like species at the surface
prompted us to study the reactivity towards fluorinated
methanes. On treatment of CH3F with ACF in C6D6 in the
presence of Et3SiH at room temperature at one atmosphere
(Table 1, entry 1), a vigorous reaction and the evolution of
with Et3SiH in C6D6 as the solvent (Table 1, entry 1; * denotes 29Si
satellites from the signal for Et3SiH).
1
gaseous products was observed. The H (Figure 2), 13C, 19F,
and 29Si{1H} NMR spectra (see Figure S3 in the Supporting
Information) of the solution revealed the formation of
C6D5CH3 as well as Et3SiF and traces of Et2SiF2. Small
amounts of xylenes and methane were also detected. In
addition, H2 and HD were generated as a result of Friedel–
Crafts reactions with C6D6 (Scheme 1a). H2 formation can be
explained by H/D exchange reactions. Note that catalytic H/D
exchange between deuterated alkanes and benzene at ACF
was described recently.[16]
CH3F in C6D6 was consumed completely after 24 hours at
room temperature in the presence of an excess of silane
(2 equivalents), thus resulting in a turnover number (TON) of
100 (based on the amount of Lewis-acidic sites at the ACF;
À
Scheme 1. ACF-catalyzed C F activation reactions of fluoromethanes
and trifluorotoluene.
À
Table 1: ACF-catalyzed C F activation reactions;
Entry
Substrate
Solvent[a]
nsubstrate
nact. sites
[mmol]
nEt3SiH
[mmol]
T
[8C]
t
[d]
Conv.
[%][c]
Main
TON[e]
[mmol]
product[d]
1
2
3
4
5
6
7
8
CH3F
CH2F2
CHF3
C6H5CF3
C6H5CH2F
C6H5CF3
C6H5CF3
CH3F
CH3F
CH3F
CH2F2
CH2F2
CH2F2
CHF3
C6D6
C6D6
C6D6
C6D6
C6D6
o-C6H4Cl2
neat
C6D6
o-C6H4Cl2
neat
C6D6
o-C6H4Cl2
neat
C6D6
o-C6H4Cl2
neat
n.d.[b]
n.d.[b]
n.d.[b]
0.3
0.15
0.3
1.5
0.3
0.3
0.6
0.9
25
25
70
70
70
70
70
25
25
25
25
25
25
70
70
70
1
4
4
7
1
7
7
2
2
2
4
4
4
4
4
4
50
88
20
70
35
25
42
75
73
89
17
65
90
81
17
13
C6D5CH3
(C6D5)2CH2
(C6D5)2CH2
(C6D5)PhCH2
(C6D5)PhCH2
PhCH3
PhCH3
C6D5CH3
CH4
CH4
(C6D5)2CH2
CH4
CH4
(C6D5)2CH2
CH4
100
21.1
4.8
25.2
n.d.[f]
9
12.5
25.0
25.0
12.5
25.0
25.0
6.00
6.00
6.00
12.5
12.5
12.5
25.0
25.0
25.0
0.15
0.9
0.9
1.56
1.56
2.68
1.56
1.56
1.56
0.6
0.3
15
2.55
2.64
2.62
2.73
2.58
2.63
2.57
2.77
2.72
195
190
400
21
82
112
20
9
10
11
12
13
14
15
16
CHF3
CHF3
0.6
1.2
4
6.3
CH4
Experiments corresponding to entries 8–16 were performed in flame-sealed glass ampoules. Please see the Supporting Information for experimental
details. [a] V[C6D6]=0.6 mL (entries 1–5), 0.9 mL (entries 8,11,14); V[o-C6H4Cl2]=0.3 mL (entry 6), 0.7 mL (entries 9, 12, 15). [b] Substrates bubbled
into the solvent for 3 min. [c] Based on the conversion of Et3SiH into Et3SiF (determined by 1H NMR spectroscopy). [d] In addition to Et3SiF.
[e] Calculated based on the amount of Et3SiF formed per number of active acidic sites at the ACF (assuming that 1 g ACF contains 1 mmol of active
sites).[16,17] [f] Not determined; see the Supporting Information for further details.
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estimated to be 0.978 mmolgÀ1 ACF by NH3-TPD).[16,17]
Condensation of excess CH3F (1.6 equiv) with a mixture of
Et3SiH and ACF in C6D6 as the solvent in a glass ampoule led
to an increase of the TON to 195 after leaving the reaction
mixture for two days in the sealed ampoule at room temper-
ature (Table 1, entry 8).
With CH2F2 or CHF3 as fluorinated substrates (Sche-
me 1b), the formation of the Friedel–Crafts product
[D10]diphenylmethane was observed in the C6D6 solution.
In addition, minor amounts of CH4 were generated. For CHF3
the [D10]diphenylmethane formation involves two Friedel–
Crafts reaction steps and a subsequent hydrodefluorination
reaction. In general, the TONs [21 for CH2F2 at room
temperature (Table 1, entry 2) and 4.8 for CHF3 at 708C
(Table 1, entry 3)] decrease with increasing fluorine content
on the fluorinated methane, but the reactions remain
clearly catalytic. When the conversion of CHF3 into
[D10]diphenylmethane was performed in a glass ampoule at
708C the TON increased to 20 (Table 1, entry 14). However,
using this strategy for CH2F2 (Table 1, entry 11) did not lead
to an increase of the TON, possibly because of the formation
of larger (insoluble) Friedel–Crafts products by reaction of
CH2F2 with [D10]diphenylmethane, and thus deactivation of
the catalyst. Note that for all substrates a complete defluori-
nation was observed. A comparable observation was found by
Ozerov et al. for fluorinated alkyl groups and it was con-
cluded that in polyfluorinated substrates the first fluoride
abstraction is the rate-limiting step.[6] However, for the C F
À
activation reactions with ACF, the reason for the absence of
partly defluorinated products could also be that the substrates
stay at the active site until the defluorination is complete. It is
also worth mentioning that 19F MAS NMR measurements of
À
the ACF···H SiEt3 catalyst before and after the catalytic
reactions reveal no changes in the spectra, thus suggesting
that the identity of the catalytic material remains unchanged
(see Figure S2 in the Supporting Information).
Mechanistically, we presume that Et3SiH initially binds at
the Lewis-acidic sites of ACF, thus resulting in the surface-
À
bound Et3SiH entities ACF···H SiEt3. A polarization of the
À
Si H bond might lead to species which have a silylium ion
À
character. The latter are able to cleave a C F bond to yield
Et3SiF and carbenium-like species, which in turn attack the
solvent (C6D6) to form the corresponding Wheland inter-
mediates. These intermediates subsequently react with the
remaining hydrogen atom on the ACF, which has hydride
character, to release the Friedel–Crafts product as well as HD.
The Lewis-acidic ACF site is thereby regenerated (Sche-
me 2a). However, in an alternative process ACF···H-SiEt3
À
Scheme 2. Proposed mechanisms for a) the ACF catalyzed C F activa-
tion reaction including a Friedel–Crafts reaction with the solvent C6D6
via a carbenium-like intermediate and b) the ACF-catalyzed hydrode-
fluorination by a concerted mechanism. Both mechanisms are shown
for the substrate CH3F.
À
À
converts the C F bonds into C H bonds to yield the
hydrodefluorination product methane and Et3SiF. This
might occur by a concerted reaction pathway (Scheme 2b)
or again by a two-step mechanism which also involves the
carbenium-like species and the ACF-bound hydrogen (Sche-
me 2a). Hence, the latter entity could be regarded as a weakly
coordinating anion (WCA) which stabilizes the carbenium-
like species. Note, that the stabilization of fluorinated
carbocations by weakly coordinating anions and the resulting
Friedel–Crafts reactivity has also been described for
Et3Si(carborane) in homogeneous phase.[4i]
To evaluate the scope of the reactions we also tested the
reactivity of benzyl fluoride, which should be an intermediate
in the Friedel–Crafts reactions of CH2F2 or CHF3, to yield
diphenylmethane. Full conversion was obtained at 708C in
C6D6 to give C6D5PhCH2 (Table 1, entry 5). Compatible
results were found on using trifluorotoluene in C6D6 (Sche-
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me 1c), and C6D5PhCH2 and toluene were furnished with
a TON of 25 (Table 1, entry 4). The values are comparable to
those found for CH2F2 or CHF3 in C6D6. No activation of
CHF2CHF2 or C2F6 was observed at 708C, possibly because
activation at the active site at the surface is hampered by their
dissimilar steric demand in comparison to that of the other
fluorinated substrates.
To achieve a selective hydrodefluorination of the fluori-
nated methanes, ACF was treated with Et3SiH and fluori-
nated substrates in glass ampoules with 1,2-dichlorobenzene
as the solvent (Scheme 3). Indeed, a reaction of CH3F with
formations with transition-metal complexes, which formally
bear an anionic silyl ligand.[2b,c,e,18]
Received: January 23, 2013
Revised: February 22, 2013
Published online: April 15, 2013
À
Keywords: C F activation · fluorine · heterogeneous catalysis ·
Lewis acids · silanes
.
[1] a) J. Burdeniuc, B. Jedlicka, R. H. Crabtree, Chem. Ber. 1997,
130, 145 – 154; b) G. Meier, T. Braun, Angew. Chem. 2009, 121,
1575 – 1577; Angew. Chem. Int. Ed. 2009, 48, 1546 – 1548; c) H.
Amii, K. Uneyama, Chem. Rev. 2009, 109, 2119 – 2183; d) T.
Braun, F. Wehmeier, Eur. J. Inorg. Chem. 2011, 613 – 625; e) E.
Clot, O. Eisenstein, N. Jasim, S. A. Macgregor, J. E. McGrady,
R. N. Perutz, Acc. Chem. Res. 2011, 44, 333 – 348; f) L. Keyes,
A. D. Sun, J. A. Love, Eur. J. Org. Chem. 2011, 3985 – 3994;
g) J. L. Kiplinger, T. G. Richmond, C. E. Osterberg, Chem. Rev.
1994, 94, 373 – 431; h) A. D. Sun, J. A. Love, Dalton Trans. 2010,
39, 10362 – 10374; i) J.-F. Paquin, Synlett 2011, 289 – 293; j) H.
Torrens, Coord. Chem. Rev. 2005, 249, 1957 – 1985; k) W. D.
Jones, Dalton Trans. 2003, 3991 – 3995; l) M. F. Kꢀhnel, D. Lentz,
T. Braun, Angew. Chem. 2013, 125, 3412 – 3433; Angew. Chem.
Int. Ed. 2013, 52, 3328 – 3348.
[2] See for example: a) M. Teltewskoi, J. A. Panetier, S. A. Mac-
gregor, T. Braun, Angew. Chem. 2010, 122, 4039 – 4043; Angew.
Chem. Int. Ed. 2010, 49, 3947 – 3951; b) T. Braun, F. Wehmeier,
K. Altenhçner, Angew. Chem. 2007, 119, 5415 – 5418; Angew.
Chem. Int. Ed. 2007, 46, 5321 – 5324; c) T. Braun, M. A.
Salomon, K. Altenhçner, M. Teltewskoi, S. Hinze, Angew.
Chem. 2009, 121, 1850 – 1854; Angew. Chem. Int. Ed. 2009, 48,
1818 – 1822; d) M. F. Kꢀhnel, D. Lentz, Angew. Chem. 2010, 122,
2995 – 2998; Angew. Chem. Int. Ed. 2010, 49, 2933 – 2936; e) G.
Haufe, S. Suzuki, H. Yasui, C. Terada, T. Kitayama, M. Shiro, N.
Shibata, Angew. Chem. 2012, 124, 12441 – 12445; Angew. Chem.
Int. Ed. 2012, 51, 12275 – 12279; f) M. F. Kꢀhnel, T. Schlçder, S.
Riedel, B. Nieto-Ortega, F. J. Ramꢁrez, J. T. L. Navarette, J.
Casado, D. Lentz, Angew. Chem. 2012, 124, 2261 – 2263; Angew.
Chem. Int. Ed. 2012, 51, 2218 – 2220; g) T. Schaub, M. Backes, U.
Radius, J. Am. Chem. Soc. 2006, 128, 15964 – 15965; h) T. Braun,
R. N. Perutz, M. I. Sladek, Chem. Commun. 2001, 2254 – 2255;
i) M. I. Sladek, T. Braun, B. Neumann, H.-G. Stammler, J. Chem.
Soc. Dalton Trans. 2002, 297 – 299; j) A. Steffen, M. I. Sladek, T.
Braun, B. Neumann, H.-G. Stammler, Organometallics 2005, 24,
4057 – 4064; k) T. Braun, V. Schorlemer, B. Neumann, H.-G.
Stammler, J. Fluorine Chem. 2006, 127, 367 – 372.
À
Scheme 3. ACF-catalyzed C F activation reaction of fluoromethanes in
absence of C6D6.
ACF/Et3SiH at room temperature (Table 1, entry 9) led, with
a high selectivity, to the formation of the hydrodefluorination
product CH4 (TON = 190), and C C coupling products were
À
only found in traces. Moreover, CH4 was furnished with
a TON of 82 on using CH2F2 as the fluorinated substrate
(Table 1, entry 12). Note the substantial improvement in
activity compared to the reaction in C6D6 (TON = 21) leading
to the Friedel–Crafts product. Reactions of CHF3 or trifluoro-
toluene (Table 1, entries 15 and 6) also gave the hydro-
defluorination products CH4 or toluene, but no increase of the
TONs was observed compared to the reactions in C6D6
(Table 1, entries 14 and 4).
Remarkably, the reaction of CH3F with Et3SiH in a glass
ampule, without any additional solvent (Table 1, entry 10),
yielded Et3SiF and CH4 with a TON of 400. Using the same
set-up for CH2F2, the TON can be increased up to 112
(Table 1, entry 13). A hydrodefluorination of CHF3 was also
achieved. However, for CHF3 as well as for trifluorotoluene
(Table 1, entries 16 and 7), no improvement was found
compared to the reactions in C6D6.
This work shows that the Lewis acid aluminum chloro-
fluoride can be used in an unprecedented heterogeneous
catalytic process for the C F activation of fluoromethanes in
À
À
the presence of Et3SiH. The C F bonds are either converted
[3] a) W. Han, Y. Li, H. Tang, H. Liu, J. Fluorine Chem. 2012, 140,
7 – 16; b) K. P. Shine, W. T. Sturges, Science 2007, 315, 1804 –
1805.
À
À
into C H bonds by hydrodefluorination or into C C bonds by
a Friedel–Crafts-type reaction. A surface-bound silylium-ion-
like species is considered to be a crucial intermediate to
[4] a) O. Allemann, S. Duttwyler, P. Romanato, K. K. Baldridge,
J. S. Siegel, Science 2011, 332, 574 – 577; b) C. Douvris, C. M.
Nagaraja, C.-H. Chen, B. M. Foxman, O. V. Ozerov, J. Am.
Chem. Soc. 2010, 132, 4946 – 4953; c) C. Douvris, O. V. Ozerov,
Science 2008, 321, 1188 – 1190; d) S. Duttwyler, C. Douvris,
N. L. P. Fackler, F. S. Tham, C. A. Reed, K. K. Baldridge, J. S.
Siegel, Angew. Chem. 2010, 122, 7681 – 7684; Angew. Chem. Int.
Ed. 2010, 49, 7519 – 7522; e) W. Gu, M. R. Haneline, C. Douvris,
O. V. Ozerov, J. Am. Chem. Soc. 2009, 131, 11203 – 11212; f) M.
Klahn, C. Fischer, A. Spannenberg, U. Rosenthal, I. Krossing,
Tetrahedron Lett. 2007, 48, 8900 – 8903; g) R. Panisch, M. Bolte,
T. Mꢀller, J. Am. Chem. Soc. 2006, 128, 9676 – 9682; h) H. F. T.
Klare, M. Oestreich, Dalton Trans. 2010, 39, 9176 – 9184; i) C.
Douvris, E. S. Stoyanov, F. S. Tham, C. A. Reed, Chem.
À
achieve the C F bond cleavage step. The established strategy
for the hydrodefluorination of fluorinated alkyl groups by
WCA-stabilized silylium ions was realized for a heterogene-
ous system, thus bridging a gap between homogeneous and
heterogeneous catalysis. Moreover, the protocol paves a way
for the activation of fluorinated methanes. Notably, ACF
costs approximately 25 $gÀ1 and is considerably less expen-
sive than the catalysts that are characterized by common
weakly coordinating anions. Note that the activation of C F
bonds with silylium-ion-like surface species is complementary
to other silyl-group-induced C F activations, including trans-
À
À
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.
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Communications
Commun. 2007, 1145 – 1147; j) C. B. Caputo, D. W. Stephan,
Organometallics 2012, 31, 27 – 30.
[13] H. H. Cornehl, G. Hornung, H. Schwarz, J. Am. Chem. Soc. 1996,
118, 9960 – 9965.
[5] J. Shi, J. He, H.-J. Wang, J. Phys. Org. Chem. 2011, 24, 65 – 73.
[6] D. G. Gusev, O. V. Ozerov, Chem. Eur. J. 2011, 17, 634 – 640.
[7] K. B. Wiberg, P. R. Rablen, J. Am. Chem. Soc. 1993, 115, 614 –
625.
[8] J. Choi, D. Y. Wang, S. Kundu, Y. Choliy, T. J. Emge, K. Krogh-
Jespersen, A. S. Goldman, Science 2011, 332, 1545 – 1548.
[9] B. M. Kraft, R. J. Lachicotte, W. D. Jones, J. Am. Chem. Soc.
2001, 123, 10973 – 10979.
[10] T. Iida, R. Hashimoto, K. Aikawa, S. Ito, K. Mikami, Angew.
Chem. 2012, 124, 9673 – 9676; Angew. Chem. Int. Ed. 2012, 51,
9535 – 9538.
[11] a) S. P. Decker, J. S. Klabunde, A. Khaleel, K. J. Klabunde,
Environ. Sci. Technol. 2002, 36, 762 – 768; b) X. Fu, W. A.
Zeltner, Q. Yang, M. A. Anderson, J. Catal. 1997, 168, 482 – 490.
[12] A. Vakulka, G. Tavcar, T. Skapin, J. Fluorine Chem. 2012, 142,
52 – 59.
[14] a) T. Krahl, E. Kemnitz, J. Fluorine Chem. 2006, 127, 663 – 678;
b) V. A. Petrov, C. G. Krespan, B. E. Smart, J. Fluorine Chem.
1996, 77, 139 – 142; c) T. Krahl, R. Stçsser, E. Kemnitz, G.
Scholz, M. Feist, G. Silly, J.-Y. Buzarꢂ, Inorg. Chem. 2003, 42,
6474 – 6483.
[15] V. A. Petrov, C. G. Krespan, B. E. Smart, J. Fluorine Chem. 1998,
89, 125 – 130.
[16] M. H. G. Prechtl, M. Teltewskoi, A. Dimitrov, E. Kemnitz, T.
Braun, Chem. Eur. J. 2011, 17, 14385 – 14388.
[17] J. K. Murthy, U. Gross, S. Rꢀdiger, V. V. Rao, V. V. Kumar, A.
Wander, C. L. Bailey, N. M. Harrison, E. Kemnitz, J. Phys.
Chem. B 2006, 110, 8314 – 8319.
[18] a) M. Aizenberg, D. Milstein, Science 1994, 265, 359 – 361; b) Y.
Ishii, N. Chatani, S. Yorimitsu, S. Murai, Chem. Lett. 1998, 27,
157 – 158; c) R. J. Lindup, T. B. Marder, R. N. Perutz, A. C.
Whitwood, Chem. Commun. 2007, 3664 – 3666.
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