Activation of Chlorinated Methanes at the Surface of Nanoscopic Lewis Acidic Aluminum Fluorides

Article abstract of DOI:10.1002/cctc.201601238

We report on the activation of chlorinated methanes by the heterogeneous catalysts aluminum chlorofluoride (ACF) and high-surface aluminum fluoride (HS-AlF₃) under moderate conditions. For comparison, chlorinated toluenes and 1,2-dichloroethane

Full text of DOI:10.1002/cctc.201601238

Accepted Article
Title: Activation of Chlorinated Methanes at the Surface of Nanoscopic
Lewis Acidic Aluminium Fluorides
Authors: Thomas Braun, Erhard Kemnitz, Agnieszka Siwek, Mike
Ahrens, and Michael Feist
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ChemCatChem
10.1002/cctc.201601238
FULL PAPER
Activation of Chlorinated Methanes at the Surface of
Nanoscopic Lewis Acidic Aluminium Fluorides
[a]
[a]
[a]
[a]
[a]
Agnieszka K. Siwek , Mike Ahrens , Michael Feist , Thomas Braun* and Erhard Kemnitz*
We report on the activation of chlorinated methanes at the
heterogeneous catalysts aluminum chlorofluoride (ACF) and high
using the above mentioned catalysts are fairly harsh; for all
cases the temperatures exceed 100°C and are often higher than
250°C. Current research also focuses on the investigation of
homogeneous catalysts immobilized on solid materials, such as
3
surface aluminum fluoride (HS-AlF ) under moderate conditions. For
comparison, chlorinated toluenes and 1,2-dichloroethane were also
tested. The strong Lewis acids are able to promote the cleavage of
8
rhodium(I) complexes supported on MCM-41.
C-Cl bonds in the presence of Et
3
SiH. The C-Cl bonds were
We recently reported on C-F bond activation reactions at
9
converted into C-H bonds via hydrodechlorination reactions or in the
presence of benzene into C-C bonds via Friedel-Crafts type
reactions. The catalytic reactions show high conversions.
nanoscopic solid Lewis acids like ACF. ACF (AlCl
F
x 3−x
,
x ≈ 0.05–0.25) is an amorphous strong Lewis acid, the acidity of
which is comparable with that of SbF . In the presence of
Et SiH, the fluorinated methanes CH F, CH and CHF as well
as C CF and C CH F are converted into Friedel-Crafts or
5
3
3
2
F
2
3
6
H
5
3
6
H
5
2
hydrodefluorination products.
Introduction
The present paper focuses on the activation of C-Cl bonds
in the presence of Et
HS-AlF were studied as catalysts in the activation of chlorinated
methanes, and for comparison toluenes and
,2-dichloroethane.
3
SiH. Microporous ACF and mesoporous
Chlorinated organic compounds are often used as starting
materials for various Friedel-Crafts or hydrodechlorination
reactions. Friedel-Crafts reactions of halogenated compounds
are of current interest because they open up reaction routes to
3
1
1
access pharmaceuticals, dyes, agro- and fine chemicals.
Various heterogeneous catalysts, such as zeolites, protonated
titanate nanotubes, clays, nafion, resin–silica nanocomposites
and heteropolyacids (HPAs) have been applied for Friedel-
Results and Discussion
The reactions of the chlorinated methanes CCl
Cl , and CH Cl with Et SiH in the presence of the Lewis acid
ACF in C as solvent at 24°C or 70°C led to the formation of
both Friedel-Crafts and hydrodechlorination products. (Scheme
, Table 1).
4 3
, CHCl ,
2
Crafts reactions.
CH
2
2
3
3
Hydrodechlorination reactions of chlorinated organic
compounds are of interest because of environmental issues
related to their "super greenhouse gas" behavior and ozone
6
D
6
1
3
depletion potential. A wide range of heterogeneous catalytic
reactions to achieve hydrodechlorination reactions is reported in
the literature. For instance, Z. M. de Pedro et al., M. A. Álvarez-
Montero et al., N. Chen et al., C. D. Thompson et al., Makkee et
al. and Coq et al. described the application of palladium or
4
platinum catalysts supported on carbon. Furthermore, palladium,
platinum or ruthenium catalysts supported on alumina are known
5
for their reactivity in the activation of C-Cl bonds. To improve
the selectivity and activity, alumina-supported bimetallic systems
like Pd/Pt, Pd/Cu, Pd/Ni, Ni/Au were investigated thoroughly as
6
hydrodechlorination catalysts as well. In addition, Ni/C, Ni-Pd/C,
Pt/Al
2 3 2 2 3
O , Ag-Pd/ZrO and Pd-Ag/Al O , have proven to be highly
Scheme 1. ACF-catalyzed hydrodechlorinations and Friedel-Crafts reactions
active, especially for the catalytic hydrodechlorination of
3
of chlorinated methanes in the presence of Et SiH.
7
1,2 dichloroethane. However, the conditions for the depletion of
chlorine-containing molecules in hydrodechlorination reactions
Polychlorinated methanes in
6 6
C D yielded deuterated
diphenylmethane as the main product, which is formed via two
Friedel-Crafts reaction steps and up to two hydrodehalogenation
reactions. Apparently, Friedel-Crafts-like reactions are favoured
over hydrodechlorination steps. Deuterated toluene was also
formed in small amounts in the reactions of polychlorinated
[
a]
A. K. Siwek, Prof. Dr. T. Braun, Prof. Dr. E. Kemnitz, Dr. M. Ahrens,
Dr. M. Feist
Humboldt-Universität zu Berlin
Department of Chemistry
D
D
3 3 6 5
methanes. For CH Cl, the main product is Ph CH (Ph = C D )
Brook-Taylor-Straße 2
and considerable amounts of methane are also generated.
12489 Berlin, Germany
E-mail: thomas.braun@cms.hu-berlin.de
erhard.kemnitz@chemie.hu-berlin.de
Supporting information for this article is given via a link at the end of
the document.
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ChemCatChem
10.1002/cctc.201601238
FULL PAPER
Table 1. Conversions and product distributions for the catalytic activation of
Table 2. Conversions and product distributions for the catalytic activations
chlorinated methanes in the presence of silane
of chlorinated methanes in the absence of silane
T
t
conv.
TON
[c]
T
t
conv.
TON
[b]
main
product
minor
products
subs.
main
product
minor
products
subs.
[
a]
[b]
[a]
[
°C]
[d]
[%]
[°C]
[d]
[%]
D
D
Ph
(
2
CH
2
2
Ph CH
(6%)
3
CCl
4
70
24
3
3
-
-
-
CCl
CCl
4
4
24
70
70
24
70
3
3
2
3
3
12
90
88
13
1
7
94%)
D
3
D
Ph
CH
Ph
2
CH
2
2
D
2
D
CHCl
CHCl
3
3
17
74
2
Ph
CH
Ph CH
3
(88%)
(12%)
D
3
(
99%)
Ph
CH
D
D
3
Ph
2
CH
Ph
CH
D
2
D
Ph
CH
2
2
2
Ph CH
3
70
3
(7%),
Ph’CH
3
7
CHCl
CHCl
CHCl
3
3
3
D
3
9
(91%)
(
98%)
Ph
CH
D
2
D
D
D
Ph
CH
Ph CH
(6%)
3
Ph
2
CH
2
2
Ph CH
(1%)
3
1
CH
CH
2
Cl
Cl
2
2
24
70
3
3
65
95
9
(
94%)
(99%),
D
2
D
D
D
Ph
CH
Ph CH
3
Ph
2
CH
Ph CH
3
>99
D
3
10
2
13
(
99%)
Ph
CH
(99%)
(1%)
D
D
D
Ph
(
2
CH
2
2
Ph CH
(5%)
3
CH
CH
3
Cl
Cl
24
70
3
3
27
79
Ph CH
3
-
-
16
46
CH
CH
CH
CH
2
Cl
Cl
Cl
Cl
2
2
70
70
70
70
2
3
2
3
35
46
35
46
5
6
95%)
D
3
Ph CH
3
D
2
D
Ph
CH
Ph CH
3
2
Experiments for the activation of CH
tubes whereas the other reactions were carried out in standard NMR tubes.
All reactions were carried out in 0.9 ml of C as solvent and using 25 mg of
3
Cl were performed in JYoung NMR
(
95%)
(5%)
6 6
D
D
Ph CH
3
CH
(49%)
4
the catalyst ACF. [a] Based on the products to substrate ratio determined by
H NMR spectroscopy. [b] Calculated based on the amount of the products
per number of active acidic sites at the ACF (1 g ACF contains 1 mmol of
3
3
21
27
1
(
51%)
10
D
3
active sites determined by NH -TPD).
Ph CH
3
CH
(46%)
4
(
54%)
For comparison, the C-Cl-bond activation was also
investigated in the absence of silane (Scheme 2 and Table 2).
Experiments for the activation of CH
whereas all the other reactions were carried out in standard NMR tubes. All
reactions were carried out in 0.9 ml of C as solvent and using 25 mg of the
catalyst ACF. Et SiH was added stoichiometrically to the number of chlorine
atoms in the substrate [a] Based on the conversion of Et SiH into Et SiCl or
the ratio products to substrate, if the signals overlapped in H NMR spectrum.
3
Cl were performed in JYoung NMR tubes
6 6
D
CH
di- and triphenylmethane as the main products, respectively.
Note that CCl was not activated in the reaction in the absence
of silane. In contrast to the reactions with silane, CHCl was
3
converted mainly into Ph CH. Note that the generation of minor
3 2 2 3
Cl, CH Cl and CHCl reacted to give the deuterated mono-,
3
3
3
1
4
D
[
b] Ph = C
6
D5. [c] Calculated based on the amount of products per number of
3
active acidic sites at the ACF (1 g ACF contains 1 mmol of active sites
10
D
determined by NH
3
-TPD).
products which are formed via C-C coupling and
hydrodechlorination steps was also observed. We tentatively
suppose an occurrence of Cl/H exchange reactions at the Lewis
1
1
acid ACF.
It can be assumed that in the Friedel-Crafts reactions of
chlorinated methanes partially chlorinated toluenes are formed
as intermediates. Therefore, chlorinated toluenes were treated
with Et
the transformations Ph PhCH
main product. Small amounts of Ph
the reaction of polychlorinated toluenes.
3
SiH in the presence of ACF (Scheme 3, Table 3). In all
D
2
(Ph= C
6
H
5
) was formed as the
D
2
PhCH were generated in
The activation of chlorinated toluenes was also
investigated in the absence of silane (Scheme 4). Table 4
summarizes the results of these reactions. The activation of
α-monochlorotoluene
PhCHCl led to the formation of diphenylmethane Ph PhCH
and triphenylmethane Ph
respectively. No activation of α,α,α-trichlorotoluene PhCCl was
3
observed.
PhCH
2
Cl
and
α,α-dichlorotoluene
D
2
2
D
2
PhCH as the main products,
Scheme 2. ACF-catalyzed Friedel-Crafts reactions of chlorinated methanes in
the absence of Et SiH
3
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ChemCatChem
10.1002/cctc.201601238
FULL PAPER
3
respectively. No activation of α,α,α-trichlorotoluene PhCCl was
observed.
Scheme 3. ACF-catalyzed hydrodechlorinations and Friedel-Crafts reactions
3
of chlorinated toluenes in the presence of Et SiH.
Scheme 4. ACF-catalyzed hydrodechlorination and Friedel-Crafts reactions of
chlorinated toluenes in the absence of Et SiH.
Table 3. Conversions and product distributions for the catalytic activations
of chlorinated toluenes in the presence of silane
3
T
t
conv.
TON
[b]
main
product
minor
product
substrate
[
a]
Table 4. Conversions and product distributions for the catalytic activations
of chlorinated toluenes in the absence of silane
[
°C]
[d]
[%]
D
D
Ph PhCH
2
2
2
Ph
2
PhCH
T
t
conv.
TON
[b]
PhCCl
PhCCl
PhCCl
3
3
3
24
24
70
24
24
70
24
24
70
1
2
3
1
3
2
1
2
3
82
96
95
64
66
84
78
88
92
9
9
9
5
5
6
5
5
5
main
product
minor
products
(91%)
(9%)
substrate
[
a]
[
°C]
[d]
[%]
D
D
2
Ph PhCH
91%)
Ph
PhCH
(
(9%)
PhCCl
PhCCl
3
3
24
70
3
3
0
0
-
-
-
-
-
D
D
Ph PhCH
83%)
Ph
2
PhCH
-
(
(17%)
D
2
D
Ph
PhCH
Ph PhCH
2
2
D
D
PhCHCl2
PhCHCl2
24
70
3
3
22
36
2
3
Ph PhCH
82%)
2
2
2
Ph
2
PhCH
(87%)
(13%)
PhCHCl
PhCHCl
PhCHCl
2
2
2
(
(18%)
D
D
Ph
2
PhCH
88%)
Ph PhCH
D
D
2
Ph PhCH
83%)
Ph
PhCH
(
(12%)
(
(17%)
D
Ph PhCH
(98%)
2
PhCH
3
D
D
D
2
Ph PhCH
82%)
Ph
PhCH
PhCH
2
Cl
24
70
3
3
93
6
6
Ph
2
PhCH
(
(18%)
D
Ph PhCH
2
PhCH
Ph PhCH
2
3
D
PhCH Cl
>99
Ph PhCH
2
2
2
2
D
(98%)
PhCH
PhCH
PhCH
2
2
2
Cl
Cl
Cl
-
-
-
(
>99%)
6 6
All reactions were carried out in 0.9 ml C D as solvent and using 25 mg
1
D
ACF. [a] Based on the products to substrate ratio determined by H NMR
spectroscopy. [b] Calculated based on the amount of the products per
number of active acidic sites at the ACF (1 g ACF contains 1 mmol of
Ph PhCH
(
>99%)
10
3
active sites determined by NH -TPD).
D
Ph PhCH
(
>99%)
Possible steric effects were further studied by using
,2-dichloroethane ClCH CH Cl. The latter was activated both in
the presence and absence of Et SiH in C as solvent at ACF
Scheme 5, Table 5). 1,2-Dichloroethane ClCH CH Cl reacted to
All reactions were carried out in 0.9 ml C
Et SiH was added stoichiometrically to the number of chlorine atoms in the
substrate. [a] Based on the conversion of Et SiH into Et SiCl or the ratio
6 6
D as solvent and 25 mg ACF.
1
2
2
3
3
3
3
6 6
D
1
products to substrate, if the signals overlapped in H NMR spectrum [b].
Calculated based on the amount of the products per number of active acidic
sites at the ACF (1 g ACF contains 1 mmol of active sites determined by
(
2
2
D
D
D
the Friedel-Crafts products Ph CH
2
CH
in both the presence and
absence of silane. In the absence of the solvent C and
Et SiH, ClCH CH Cl undergoes rearrangement to form
exclusively 1,1-dichloroethane.
2 2 3
Ph and Ph CH CH and
10
D
NH
3
-TPD).
2 3
1,1-diphenylethane Ph CHCH
6
D
6
The activation of chlorinated toluenes was also
investigated in the absence of silane (Scheme 4). Table 4
summarizes the results of these reactions. The activation of
3
2
2
a
α-monochlorotoluene
PhCHCl led to the formation of diphenylmethane Ph PhCH
and triphenylmethane Ph
PhCH
2
Cl
and
α,α-dichlorotoluene
D
2
2
D
2
PhCH as the main products,
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ChemCatChem
10.1002/cctc.201601238
FULL PAPER
methanes with Et
3
SiH at HS-AlF
3
. Both, chlorinated methanes
D
and chlorinated toluenes reacted to yield Ph
2
CH
2
and
D
Ph PhCH
2
as the main products. The conversions were higher
in the presence of silane in
for chlorinated toluenes at HS-AlF
3
comparison with the results achieved with ACF (Table 3).
Literature data indicate that ACF is in liquid phase/solid state
3
reactions slightly more reactive than HS-AlF , which might be an
explanation for the higher reactivity of ACF towards chlorinated
1
3
methanes.
However, the lower activity of ACF towards
chlorinated toluenes might, in contrast, be due to diffusion-
limited accessibility which is related to the different porosity of
the two catalysts.
Scheme 5. ACF-catalyzed hydrodechlorination and Friedel-Crafts reactions of
3
1,2-dichloroethane in the presence and absence of Et SiH.
Table 6. Conversions and product distributions for the catalytic activations
3
with HS-AlF of chlorinated methanes and toluenes in the presence of silane
Table 5. Conversions and product distributions for the catalytic activations
T
T
conv
TON
[b]
of 1,2-dicholoroethane in the absence and presence of silane
main
product
minor
products
substrate
[
a]
[
°C] [d]
[%]
Et
3
SiH
T
conv.
TON
[b]
main
products
minor
product
[
a]
D
[mmol]
[°C] [%]
Ph CH
(4%)
3
D
2
Ph
CH
2
CCl
4
70
3
28
2
(
87%)
CHCl
9%)
3
D
Ph CH
2
CH
3
(
D
D
Ph CH
2
CH
2
Ph
(18%)
D
2
0.60
24
70
3
0.4
8
(74%)
Ph
CHCH
8%)
3
D
2
D
Ph
CH
2
2
2
Ph CH
(3%)
3
3
3
3
3
(
CHCl
3
70
70
70
70
70
2
2
3
2
3
43
6
4
1
1
4
5
(97%)
D
Ph CH
2
CH
3
D
2
D
Ph
CH
Ph CH
D
D
Ph CH
2
CH
2
Ph
(13%)
CH
CH
2
Cl
Cl
2
2
D
2
0.60
63
35
(95%)
(5%)
(78%)
Ph
CHCH
9%)
3
(
D
2
D
Ph
CH
Ph CH
2
7
(92%)
(8%)
D
Ph CH
2
CH
3
(
4%)
D
Ph CH
D
D
D
D
D
2
CH Cl
7
4
CH (82%)
Ph CH
2
CH
2
2
2
Ph
Ph
Ph
Ph
CHCH
3
3
(18%)
-
24
70
4
7
(93%)
(2%)
CHCH
(
D
2
D
D
D
Ph
2
Ph
D
Ph CH
CH
3
Cl
10
4
CH (82%)
1%)
(18%)
D
Ph CH
2
CH
3
D
Ph PhCH
79%)
2
2
2
(
D
2
9%)
PhCCl
3
24
70
24
2
2
1
>99
>99
>99
-
10
8
(
D
Ph CH
2
CH
Ph
CHCH
3
-
60
(78%)
(12%)
CHCH
(
D
D
Ph PhCH
98%)
2
Ph PhCH
D
2
Ph
2
Ph
PhCHCl
2
(
(2%)
1%)
D
Ph PhCH
>99%)
D
Ph CH
2
CH
3
PhCH
2
Cl
-
6
(
(
D
10%)
D
Ph CH
2
CH
Ph
2
CHCH
3
All reactions were carried out in 0.9 ml of C
HS-AlF . Et SiH was added stoichiometrically to the number of chlorine
atoms in the substrate [a] Based on the conversion of Et SiH into Et SiCl in
the presence of silane or the ratio of products to substrate if the signals
overlapped in H NMR spectrum; determined by H NMR spectroscopy. [b]
Calculated on the basis of the amount of the products per number of active
6 6
D as a solvent and using 25 mg
70
91
1
11
5
3
3
(68%)
(14%)
CHCH
(
D
2
3
3
Ph
2
Ph
8%)
1
1
Cl
2
CHCH
3
-
70
3 3
acidic sites at the HS-AlF (1 g HS-AlF contains 1 mmol of active sites
determined by NH -TPD).
3
10
All reactions were carried out in 0.9 ml of C
5 mg of ACF. The reaction was carried on for 72 h. If adopted, Et
added stoichiometrically to the number of chlorine atoms in the substrates
a] Based on the conversion of Et SiH into Et SiCl in the presence of silane
or the ratio of products to the substrate if the signals overlapped, whereas
in the absence of silane it was always calculated based on the ratio of
6
D
6
as a solvent and using
2
3
SiH was
To gain a better understanding about the interaction of the
[
3
3
®
substrates with ACF, PulseTA (PTA) experiments were
performed.
studying both reactivity and adsorption/desorption phenomena
of solid fluorides.
as an usual TA-MS device equipped with a gas dosing unit
allowing for the injection of gases into the purge gas thus
enabling an interaction with the solid. Evaporable liquids can be
1
4
PTA was successfully employed before for
1
products to the substrate; determined by
H NMR spectroscopy. [b]
Calculated based on the amount of the products per number of active
acidic sites at the ACF (1 g ACF contains 1 mmol of active sites
15,16
The experimental setup can be understood
1
0
3
determined by NH -TPD).
Unlike ACF, which is microporous, HS-AlF
mesoporous. Table 6 shows the conversions of chlorinated
3
is
1
2
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ChemCatChem
10.1002/cctc.201601238
FULL PAPER
pulsed as well by using a septum-tightened heated (120 °C) GC
injector and ordinary µL syringes. One obtains usual
thermoanalytical curves (under heating or, as in the present
case, isothermally) and additional information about adsorption
processes being due the reactant injections. Isothermal PTA
revealed to be of extraordinary sensitivity vs. enthalpic effects
and mass changes. The injection pulses as well as changes of
the product composition of the gas phase are monitored by the
ionic current (IC) curves of pre-chosen characteristic mass
numbers for the injected starting compound and for presumed
reaction products.
which is then continued by further benzene pulses. Note that the weak m/z=
50 intensity for the benzene pulses belong to the mass spectrum of benzene,
whereas for pulses 9-11 it represents CH Cl.
3
Fig. 1 shows the loading of ACF with six pulses of 2 mL
CH
exothermal DTA peaks and a (decreasing) persistent mass gain
for each CH Cl pulse. The following two injections of 2 µL and
one injection of 4 µL Et SiH did neither lead to significant DTA
peaks nor to any persistent mass gain. On the contrary, the
interaction of prior formed ACF◦Et SiH did not show any
remarkable interaction with CH Cl (Figure S11 in the ESI). Thus,
both Et SiH and CH Cl adsorb at ACF in a first loading.
Regardless of the sequence of pulsing the silane or CH Cl, no
3
Cl(g). Chemisorption is indicated by comparably large
3
3
3
3
3
3
3
reaction at least at the solid/gas interphase was observed.
Scheme 6. Proposed mechanism for ACF-catalyzed hydrodechlorination and
Friedel-Crafts reactions of CH Cl in the presence of Et SiH.
3
3
®
Figure 1. TA-MS curves of an isothermal (31°C) PulseTA experiment with
thermally pretreated (200 °C) ACF (34.4 mg) under Ar with the IC curves for
+
+
the mass numbers m/z= 50 (CH
3
Cl ), and 59 (EtSiH ). ACF was preloaded
with six pulses of 2 mL CH Cl. Next, Et
3
3
SiH was added in 3 pulses.
Scheme 7. Proposed mechanism for ACF-catalyzed Friedel-Crafts reactions
of CH
3
Cl.
®
The mechanism for the hydrodechlorination might proceed
Figure 2. TA-MS curves of an isothermal PulseTA experiment with thermally
via a similar reaction pathway as previously reported for
hydrodefluorination reactions in the presence of silane. Initially,
pretreated (180°C) ACF (35.1 mg) with the IC curves for the mass numbers
9
+
+
6
m/z= 50 (CH
3
Cl ), and 78 (C
6
H
). The eight benzene pulses led to a constant
3
Et SiH can be adsorbed at the Lewis acidic sites of ACF which
loading of ACF. Pulsing then of 2 mL gaseous CH
3
Cl led to further loading
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results in a more electrophilic silicon atom in Et
3
SiH (see
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Scheme 6 for CH
bound species of silylium-like character are generated, which
can initiate C-Cl bond cleavage reaction to give the
chlorosilane and formally surface bound hydride. The
generated carbenium-like species might react with the latter or
initiates Friedel-Crafts reaction. However, reverse
3
Cl). As a result of this polarization, surface-
a
a
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a
a
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subsequent reaction with a silane or benzene. For the reactions
without silane we suggest a similar C-Cl activation, and Friedel-
Crafts reaction pathway to give the C-C-coupling product and
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fluorides, such as aluminium chlorofluoride (ACF) and high
surface-aluminium fluoride (HS-AlF
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[a]
Agnieszka K. Siwek , Mike
[a]
[a]
Ahrens ,
Michael
Feist
,
[a]
Thomas Braun*
and Erhard
[a]
Kemnitz*
Page No. – Page No.
ACF and HS-AlF
hydrodechlorination reactions.
3
as a powerful Lewis acid for Friedel-Crafts type and
Activation of Chlorinated Methanes at
the Surface of Nanoscopic Lewis
Acidic Aliminium Fluorides
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