Application of Silicon-Initiated Water Splitting for the Reduction of Organic Substrates

Article abstract of DOI:10.1002/cplu.201800131

The use of water as a donor for hydrogen suitable for the reduction of several important classes of organic compounds is described. It is found that the reductive water splitting can be promoted by several metalloids among which silicon shows the best efficiency. The developed methodologies were applied for the reduction of nitro compounds, N-oxides, sulfoxides, alkenes, alkynes, hydrodehalogenation as well as for the gram-scale synthesis of several substrates of industrial importance.

Full text of DOI:10.1002/cplu.201800131

Accepted Article
Title: Application of Silicon-Initiated Water Splitting for the Reduction of
Organic Substrates.
Authors: Ashot Gevorgyan, Satenik Mkrtchyan, Tatevik Grigoryan, and
Viktor Iaroshenko
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Application of Silicon-Initiated Water Splitting for the Reduction
of Organic Substrates.
Ashot Gevorgyan,[a,b] Satenik Mkrtchyan,[a] Tatevik Grigoryan,[a] Viktor O. Iaroshenko*[a]
Abstract: The present work describes the utilization of water as a
donor for hydrogen suitable for the reduction of several important
classes of organic compounds. We have found that the reductive
water splitting can be promoted by a number of metalloids among
which silicon shows the best efficiency. The developed methodologies
were applied for the reduction of nitro compounds, N-oxides,
sulfoxides, alkenes, alkynes, hydrodehalogenation as well as for the
gram-scale synthesis of several substrates of industrial importance.
compounds,7 phosphines,8 DMF/Cu system,9 iron powder,10
SmI211 and TiIII-complexes.12
Introduction
Catalytic hydrogenation is one of the basic transformations of
organic synthesis that is being used in most of the multistep
transformations of industrial importance.1 These reactions usually
are performed by the use of either hydrogen gas or hydrogen
donors2 which is widely known as transfer hydrogenation.3 The
transfer hydrogenation is becoming more popular since it
excludes the direct use of highly flammable gaseous H2. There
are a number of classes of compounds which can be used as
hydrogen donors2 in catalytic transfer hydrogenation reactions;3
nevertheless, perhaps the most promising source of hydrogen
was and remains water, the most abundant molecule on Earth.
Despite enormous efforts made over the last century the direct
use of water as a hydrogen donor in organic synthesis remains a
challenging and unsolved task. According to the known data the
splitting of water can follow the following three pathways: (1)
oxidative splitting generating O2;4 (2) reductive splitting
generating H2;5,7-12 (3) direct splitting into elements (O2 + H2).6
Most of the presently known strategies of water splitting are
photocatalytic or photoelectrochemical processes.4-6 In spite of
enormous potential, the catalytic water splitting is accompanied
with numerous inconveniences and complications (overall
efficiency, stability of the catalysts etc.) limiting its practical
applications.4-6 Subsequently, the development of novel reductive
water splittings used in catalytic hydrogenations remains one of
the ''holy grails'' of modern organic synthesis. In this connection,
the research made within the last few years indicates that the
reductive water splitting can be initiated by various diboron
Figure 1. Our strategy on the instance of nitro compounds.
Results and discussion
Continuing our ongoing research devoted to the selective
reductive transformations13 we found that the reductive water
splitting can be initiated by elemental silicon generating simple
sand as the sole byproduct.14 Noteworthy, the silicon mediated
reductive water splitting can be easily combined with catalytic
reductive transformations of a wide range of functional groups
(Figure 1).
The advantages of our strategy over others are obvious: (1)
silicon is the second most abundant element in the earth's crust;
(2) except nanosized silicon, all other types of silicon are rather
stable under ambient conditions, thus, can be easily transported
and used; (3) the reductive water splitting can be conducted
without transition metal-based catalysts, light, electricity or
substantial heating; (4) the reductive water splitting proceeds by
the full conversion of silicon producing simple sand as the only
byproduct; (5) the reductive transformations can be performed in
''green'' solvents using heterogeneous catalysts which can be
regenerated and reused. The developed process can be
successfully applied for the gram-scale production of several
commercial drugs and other substrates of industrial importance.
Besides, it should be particularly emphasized that via using D2O
the deuterium can be completely incorporated into the molecules
being reduced.
Initially, the reaction conditions were optimized on the instance of
nitrobenzene I (Table 1, see also SI, Table S1). After the
screening of a wide range of parameters, it was found that
depending on the conditions the reduction of nitrobenzene leads
to the formation of aniline 1a, azobenzene 2a or their mixtures.
For instance, heterogeneous Pd-based catalysts (Pd/C,
Pd/BaCO3, Pd/Al2O3) have shown the best efficiency for the
synthesis of aniline (Table 1, entries 1-3). While Cu-based
catalysts leaded to a mixture of aniline and azobenzene (entry 5),
the Fe(OAc)2 provided the formation of azobenzene as the only
[a]
Dr. A. Gevorgyan, Dr. S. Mkrtchyan, M Sc. T. Grigoryan, Dr. V. O.
Iaroshenko, Homogeneous Catalysis and Molecular Design
Research Group at the Center of Molecular and Macromolecular
Studies, Polish Academy of Sciences, Sienkiewicza 112, PL-90-
363 Łodꢀ, Poland.
E-Mail: iva108@googlemail.com , viktori@cbmm.lodz.pl .
[b]
Dr. A. Gevorgyan, Department of Chemistry and Centre for
Theoretical and Computational Chemistry (CTCC), University of
Tromsø, 9037 Tromsø, Norway
Supporting information for this article is given via a link at the end
of the document.
1
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10.1002/cplu.201800131
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product (entry 6). In addition, it should be mentioned that other
Pd- or Fe-based salts/complexes and especially other transition
metal-based catalysts were fare less effective.
the products dramatically. For more details, see Table S1 in
supplementary information.
Table 2. Screening of reducing agents.a,b
Table 1. Reaction optimization.a
Catalyst
(mol%)
Base
Yield (%)
1a/2ab
98/0
Entry
Additive
oC
h
(mol%)
1
2
Pd/C(2)
NaOH(20)
NaOH(20)
NaOH(20)
NaOH(20)
NaOH(20)
NaOH(20)
NaOH(20)
KOH(20)
KOtBu(20)
CsF(400)
KF(400)
TBAB
TBAB
100
100
100
100
100
100
100
100
100
100
100
100
70
12
12
12
12
24
24
6
Pd/BaCO3(2)
Pd/Al2O3(2)
Pd(OAc)2(2)
Cu(OAc)2(20)
Fe(OAc)2(20)
Pd/C(2)
95/0
3
TBAB
96/0
4
TBAB
88/0
5
TBAB
18/46
0/89(82)c
98(95)c/0
96/0
6
TBAB
TBAB
TBAB
a
7
Reaction conditions: I (0.3 mmol), reducing agent (5 equiv.), base (20-400
mol%), TBAB (4 equiv.), Pd/C (2 mol%), 100ºC, 6h. b GC-yield.
8
Pd/C(2)
6
9
Pd/C(2)
TBAB
6
98/0
Further, we examined the range and efficiency of metalloids and
related chemicals as reducing agents (Table 2). By screening of
silicons of various sizes, we concluded that the size matters only
when the used bases are fluorides. In addition, we noticed that
the silicon powder of -325 mesh slowly reacts with the hot water
to some extent even in the absence of bases; however, in this
case the conversion of silicon was not completed even at
prolonged periods. The amount of used bases has direct influence
on the speed of the conversion of silicon to silicon dioxide. For
instance, the full conversion of silicon powder of -325 mesh at
80oC using 20 mol% of NaOH takes about 6h. For the
temperatures lower than this the full conversion requires either
more base or longer reaction time. Among other Si-based
reductants we got a quite positive results when using Si(II) oxide
which can be one of possible intermediates of reduction with
silicon. While screening of other metalloids of groups 13 and 14
we have found that the reaction fails only with B and In, whereas
others are quite effective (Tl and Pb were not examined).
Meanwhile Al16 and Ga are tend to induce the reductive water
splitting even without a base (Table 2).
It should be clarified that depending on the substrate being used
the reaction should be conducted in different glassware/reactors.
Particularly, the reduction of substrates, which do not possess
functional groups sensitive under basic conditions, can be
conducted either in Ace Pressure Tube or Schlenk flask equipped
with an empty balloon. In order to avoid any decomposition all
other substrates must be reduced in either COware gas reactor
or two interconnected Schlenk flasks equipped with an empty
balloon. The reactions performed in Schlenk flasks equipped with
an empty balloon took longer (72h) since in these cases the
pressure of hydrogen was close to the atmospheric pressure.
Besides, in this case the amount of silicon need to be multiplied
(see SI).
10
11
12
13
14
Pd/C(2)
TBAB
6
98/0
Pd/C(2)
TBAB
6
70/0
Pd/C(2)
CsF(20)
TBAB
6
13/0
Pd/C(2)
NaOH(20)
NaOH(20)
BMIMCl
BMIMPF6
6
98/0
Pd/C(2)
20
72
86(82)c/0
a Reaction conditions: I (0.3 mmol), Si powder (5 equiv.), base (20-400 mol%),
additive (4 equiv.), catalyst (2-20 mol%), 20-100ºC, 6-72h. b GC-yield. c Isolated
yield.
The following crucial component of the reaction was the base,
which is required for the activation of silicon. Particularly,
screening of various bases showed that the silicon mediated
water splitting occurred effectively only in the presence of alkali
hydroxides, alkoxides and fluorides. While hydroxides and
alkoxides are able to catalyze this transformation (entries 1-9), the
fluorides need to be used in stoichiometric quantities (entries 10-
12). Next, we examined the influence of various ammonium salts
on the outcome of the reaction. Noteworthy, most of the
ammonium salts are considered as ''green'' reagents and/or
solvents.15 In particular, the overall duration of the reaction and
the temperature were directly dependent on the ammonium salt
being used. For instance, when using TBAB we needed to
increase the reaction temperature up to 100oC (melting point of
TBAB), whereas in the cases of BMIMCl and BMIMPF6 the
reaction went at 70oC and room temperature respectively (entries
13, 14). Even though in case of BMIMPF6 for the full conversion
of starting material the reaction time needed to be extended up to
72h (entry 14). In addition, it should be mentioned that the Fe-
catalyzed synthesis of azobenzene despite the prolonged
reaction time was not effective at room temperature. In summary,
the best conditions for the synthesis of aniline were found to be
nitrobenzene (1 equiv.), Si (5 equiv.), NaOH (20 mol%), TBAB/
BMIMPF6 (4 equiv.), Pd/C (2 mol%), 100oC/20oC, 6/72h (entries
7, 14). Optimal conditions for the preparation of azobenzene are
nitrobenzene (1 equiv.), Si (5 equiv.), NaOH (20 mol%), TBAB (4
equiv.), Fe(OAc)2 (20 mol%), 100oC, 24h (entry 6). The absence
of any of the components of the reactions decreased the yields of
2
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10.1002/cplu.201800131
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(Scheme 1, A, Scheme 2).18 Further, we have concentrated on
the exploration of the scope of Fe-catalyzed synthesis of
azobenzenes 2a-h (Scheme 1, B, Scheme 2).19 In this case as
well the developed conditions were applicable for a wide range of
substituted nitroarenes showing the best efficiency on electron
deficient systems 2b,e-h. Another crucial finding was that using
the present strategy it was possible to couple two different
nitroarenes into asymmetrically substituted azobenzenes 2e-h
(Scheme 2). This intention was possible to achieve by the usage
of 1:3 stoichiometry of two different nitroarenes. In this case the
only side product was the homocoupling of nitroarene being used
in excess. We could also extend the substrate scope towards the
reduction of nitroalkanes III (Scheme 1, C, Scheme 2).17 It should
be particularly emphasized that nitroalkanes did not survived the
basic aqueous conditions and in order to succeed we had to use
COware gas reactor or two interconnected Schlenk flasks. Doing
so it was possible to prepare corresponding aliphatic amines 3a-
d in quite reasonable yields (Scheme 2). In addition, the reduction
of β-nitrostyrene leaded to the formation of phenethylamine 3e.
Application of Ge powder was quite efficient also in this case 3b.
Besides, the reduction of nitroarenes possessing an adjacent
carbonyl functionality IV was accompanied by further cyclization
into fused quinolines 4a,b (Scheme 1, D, Scheme 2).13
Among other related systems, our conditions turned to be quite
successful for the reduction of N-oxides V20 and sulfoxides VI21
(Scheme 1, E, F, Scheme 2). As a result of Pd-catalyzed
reduction N-oxides were transformed to corresponding
heterocycles 5a-d or N,N-disubstituted anilines 5e,f, while
sulfoxides turned into appropriate sulfides 6a-d (Scheme 2). In
most of the cases the reduction of N-oxides proceeded almost
quantitatively, whereas the yields of sulfides were moderate.
Besides, in order to increase the conversion of sulfoxide the
reaction time needed to be extended up to 24h. In these cases
also the Si can be successfully replaced by Ge 5a,b.
The developed strategy was efficient not only for the reductions
accompanied by deoxygenation but also for the hydrogenation of
unsaturated double and/or triple bonds VII (Scheme 1, G, Scheme
2).22 First we have noticed this during the reduction of β-
nitrostyrene that was followed by simultaneous reduction of both
nitro group and the double bond 3e. The main alteration in the
typical conditions was the duration of the reaction; thus, the con-
version of starting olefins and acetylenes was not complete when
the reactions were conducted less than 24h. Overall, under these
conditions the hydrogenation of both olefins 7a-e and acetylenes
7c,e,f underwent smoothly resulting in appropriate saturated
systems in excellent yields (Scheme 2). The replacement of Si by
Ge can also be accomplished for this reductive transformation
7a,c. In addition, using poisoned Pd-based catalysts we were able
to find suitable conditions for the selective semi-hydrogenation of
diphenylacetylene into corresponding cis-olefin 7g that was
isolated in 72% yield (see also SI, Table S2).23 The work devoted
to the further optimization is currently in progress.
Scheme 1. Scope of reductive transformations.
Following the optimization of reaction conditions, we have
concentrated on the examination of the scope and limitations of
our strategy. In particular, a wide range of anilines 1a-r can be
prepared from corresponding nitro compounds I in good to
excellent yields (Scheme 1, A, Scheme 2).17 It should be
emphasized that a number of reactive functional groups remain
intact when conducting the reaction in COware gas reactor or two
interconnected Schlenk flasks (such as Cl, Br, F etc., 1k-n). The
optimal conditions are also quite effective for heterocyclic
scaffolds 1o,p (Scheme 2). In addition, our conditions can be
successfully applied for the reduction of dinitro compounds to
corresponding diamines 1q,r; however, in this case the amount
silicon and the based need to be doubled. Besides, the silicon
powder of -325 mesh can be effectively replaced by Ge powder
of -100 mesh (Scheme 2, 1a,c,j,o) or other forms of silicon without
any noticeable differences in the yields. Screening of other
nitrogen-containing scaffolds indicated that the developed
conditions can be used for the reduction of arylhydrazines II to
appropriate anilines 1a,d,g from moderate to good yields
3
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a The reductive water splitting was conducted by the use of Ge (5 equiv.). b Yields of the reduction of corresponding hydrazines. c The amount of silicon and base
was doubled. d 3e was prepared by the reduction of β-nitrostyrene. e Yields of the reduction of corresponding acetylenes. f Yield of the reduction of corresponding
diacetylene. g The reduction of corresponding acetylene was performed using Lindlar catalyst, see also SI, Table S2. h GC-yield. i Starting material (10 mmol), Si
powder (10 equiv.), NaOH (20 mol%), EtOH (8 mL), Pd/C (2 mol%), 20ºC, 72h. ii 9a (1 mmol), CDI (1.2 equiv.), DMF (4 mL), 80ºC, 5h. iii Starting material (10
mmol), Si powder (10 equiv.), NaOH (20 mol%), TBAB (4 equiv.), Pd/C (2 mol%), 100ºC, 72h. iv Squalene (10 mmol), Si powder (15 equiv.), NaOH (60 mol%),
TBAB (8 equiv.), Pd/C (6 mol%), 100ºC, 144h.
Scheme 2. Scope of the products and gram-scale production of substrates of industrial importance.
4
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The final transformation examined in the frames of present study
is hydrodehalogenation of aryl halides VIII (Scheme 1, H,
Scheme 2). This is another crucial reductive transformation
widely used for the neutralization of commercial halogenated
pollutants.24 It should be noted that the Pd-based conditions
were not effective for this task, since they resulted in a mixture
cis,cis-muconic acid XV.31 For the simplification of the isolation
process the hydrogenation of cis,cis-muconic acid XV was
conducted in ethanol.
The major advantage of heterogeneous catalysts over
homogeneous catalysts is the possibility of separation and
reusability.32 The reusability of our system was evaluated on the
instance of the reduction of nitrobenzene I (Table 3, for the
general setup of the reaction see SI, Figure 1). After each run,
the catalyst (Pd/C), slightly contaminated by silicon and SiO2,
can be easily separated by simple filtration of the dissolved
reaction mixture (in DCM) through a glass-edged frit (4-8 µm
porosity). Accordingly, the activity of the catalyst remains
unchanged within the first two runs, while within third and fourth
runs in order to get better conversion of the starting material the
duration of the reaction need to be doubled (Table 3). At the fifth
run, the activity of the catalyst dropped significantly. The
mentioned contaminants did not affect visibly the efficiency of the
reused catalyst. Besides, the conversion of nitrobenzene was
not complete during fourth and fifth runs; thus, in these cases the
separation of the product was possible only by the use of column
chromatography. In this connection, TBAB can be separated
from the reaction mixture via extraction using distilled water. The
separated TBAB can be used repeatedly without any noticeable
drop of activity.
consisting
of
starting
material,
corresponding
hydrodehalogenation product and biaryl (see SI, Table S3).
Fortunately, via screening of a wide range of catalysts and other
parameters we have found that this transformation can be
effectively catalyzed by Co(OAc)2/PPh3 system. In addition, it
should be mentioned that the amount of the base needed to be
increased up to 130 mol% in order to neutralize the acid formed
during the reaction (see SI, Table S3). Overall, the Co-catalyzed
hydrodehalogenation proceeds smoothly with electron-deficient
heteroarenes 8a-e and arenes possessing electron-withdrawing
groups 8f-h whereas electron-rich systems 8i,k are far less
reactive (Scheme 2). In addition, the best results were observed
on hydrodehalogenation of aryl iodides and bromides. Aryl
chlorides turned to be quite stable under these conditions. It
should be noted that the base has a decisive role in this
transformation, which explains why the halogens survive during
the reduction of halogenated nitro compounds to corresponding
anilines 1k-n that is conducted in the absence of a base.
According to our observations the reduction of the nitro group
occurs rather fast resulting in electron-rich systems, which are
quite stable towards hydrodehalogenation. We are currently
working on the further optimization of this transformation towards
hydrodehalogenation of aryl chlorides.
Table 3. Reuse of catalyst
Following the examination of the scope and limitations of
developed transformations, we have concentrated on the
practical applications of developed methodologies (Scheme 2).
It should be noted that the reductive transformations described
below were performed on
a multigram-scale using two
interconnected Schlenk flasks equipped with an empty balloon
(for the general setup of these reactions see SI, Figure 1). Thus,
the reduction of nitrophenol IX leads to corresponding aniline 9a
(86%) which can be further transformed to chlorzoxazone
(muscle relaxant) in 88% isolated yield.25 In case of the reduction
of nitrophenol IX the best yields were observed using ethanol as
a solvent. The reduction of nitroarene X resulted in appropriate
aniline 10a (92%) which is the key intermediate in the synthesis
of Linezolid (antibiotic).26 Similarly, the reduction of nitroarene XI
gives rise to benzocaine 11a (96%), one of the most frequently
used local anesthetics.27
Following the same strategy, a number of other valuable
substrates of industrial importance can be prepared from suitably
substituted olefins. For instance, nabumetone 12a (90%,
nonsteroidal anti-inflammatory drug) can be easily synthesized
by the reduction of corresponding naphthyl-based olefin XII.28
Menthol 13a (94%, food industry, perfumery) can be prepared by
the hydrogenation of Isopulegol XIII, which is the key step in the
chemical production of menthol from citronellal.29 Another
important constituent of cosmetic industry is Squalane 14a
(89%) which can be synthesized by the hydrogenation of
Squalene XIV derived from the shark liver oil.30 Last but not least,
one of the key ingredients of nylon industry, adipic acid 15a
(96%), can be prepared by the reduction of biomass-derived
Further studies dealt with the incorporation of deuterium into
products of the reduction (Scheme 3). This task can be easily
achieved via replacement of simple water by deuterated water.
Besides, in order to exclude other sources of protium the NaOH
must be replaced by either KOtBu or CsF. Accordingly, the
strategy based on the application of D2O can be applied for the
deuteration of nitro compounds (A), unsaturated hydrocarbons
(B) and arenes (C) via deuteriodehalogenation (Scheme 3). It
should be mentioned that the deuterated aniline was not
separated since this could be accompanied by the loss of
deuteriums. In this case the extent of deuteration was evaluated
by NMR of the reaction mixture (aniline/TBAB), while the yield of
aniline was determined by GC. On the other hand, the
deuteration of unsymmetrically substituted olefin revealed
uneven distribution of deuterium atoms (Scheme 3, B. The NMR
5
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10.1002/cplu.201800131
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data to the mentioned experiment is presented in the SI). This
phenomenon can be explained by the overall reversibility of Pd-
catalyzed hydrogenation of unsaturated systems7b,33 along with
the fact that TBAB under elevated temperatures can act as a
source of protium. As compared with deuterated aniline the
products of the deuteration of olefin and 3-bromoquinoline are
quite stable and can be separated by column chromatography.
Besides, CsF was not effective for deuteriodehalogenation of 3-
bromoquinoline whereas in the case of commercial KOtBu the
extent of deuteration was 85% (Scheme 3, C. For details see the
NMR data in the SI).
Scheme 4. Mechanism of Si-initiated water splitting.
Conclusions
In conclusion, we have developed new methodology of reductive
water splitting that can be accompanied by subsequent
hydrogenation of a wide spectrum of organic compounds. It was
found that the main metalloids of groups 13 and 14 are able to
initiate the reductive water splitting. Nevertheless, the best
efficiency shows silicon that produces simple sand as the main
byproduct of the transformation. The developed strategy can be
applied for the hydrogenation of nitro compounds, N-oxides,
sulfoxides, unsaturated hydrocarbons as well as for the
hydrodehalogenation. It should be noted that the catalyst and the
solvent could be easily separated and reused. Besides, our
methodology is suitable for the gram-scale production of several
commercial drugs and other products of industrial importance.
Finally, yet importantly, the replacement of water by D2O can be
successfully applied for the introduction of deuterium labels into
the substrates being reduced.
a GC-yield.
Scheme 3. Incorporation of Deuterium into Products.
Basing on obtained results and known data14,34 the possible
mechanism of Si-initiated water splitting on the smallest unit of
silicon is depicted on Scheme 4. The reaction is initiated by the
base which in the first stage of the process attacks empty d
orbitals of silicon; thus, cleaving the Si-Si bond (Scheme 4, A).
On the next stage of the reaction the silylium anion deprotonates
water regenerating the catalyst (Scheme 4, B). On the final stage
of the process the base catalyze the dehydrocoupling of Si-OH
and H-Si units which results in the liberation of hydrogen and
formation of a siloxane linkage (Scheme 4, C). These processes
are running as long as all Si-Si bonds are being transformed into
Si-O-Si linkages, which is accompanied by the liberation of
hydrogen. Noteworthy, the base catalyzed dehydrocoupling of
hydrosilanes and alcohols was reported recently.34 Besides,
during the screening of reducing agents it was found that the
combination of methylphenylsilane and water in the presence of
catalytic quantities of a base liberates hydrogen; thus, reducing
nitrobenzene (Table 2). The IR spectra of the solid product
formed by the reaction of silicon and water showed only the
asymmetric stretches typical for Si-O-Si linkages of SiO2 (see SI).
Acknowledgements
Financial support by the Polish National Center of Sciences
(NCN) (SONATA 10, Nr. 2015/19/D/ST5/02774) is gratefully
acknowledged.
Keywords: Silicon, reductive splitting of water, transfer
hydrogenation, catalysis, scope.
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8
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FULL PAPER
Ashot Gevorgyan,[a,b] Satenik
Mkrtchyan,[a] Tatevik Grigoryan,[a] Viktor
O. Iaroshenko*[a]
Page No. – Page No.
Application of Silicon-Initiated Water
Splitting for the Reduction of Organic
Substrates.
Text for Table of Contents
Abstract: The present work describes the
utilization of water as a donor for hydrogen
suitable for the reduction of several
important classes of organic compounds.
We have found that the reductive water
splitting can be promoted by a number of
metalloids among which silicon shows the
best
efficiency.
The
developed
methodologies were applied for the
reduction of nitro compounds, N-oxides,
sulfoxides,
alkenes,
alkynes,
hydrodehalogenation as well as for the
gram-scale synthesis of several substrates
of industrial importance.
9
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10
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