Ruthenium clay catalyzed chemoselective hydrogenation of unsaturated esters, epoxides, sulfones and phosphonates

Article abstract of DOI:10.1016/S0022-328X(97)00493-2

Ru-clays were prepared using montmorillonite-PPh₂ or montmorillonite-bpy and RuCl₃·H₂O. The clays obtained were found to be effective catalysts for the reduction of unsaturated esters, epoxides, sulfones and phosphonates.

Full text of DOI:10.1016/S0022-328X(97)00493-2

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Journal of Organometallic Chemistry 551 1998 349–354
Ruthenium clay catalyzed chemoselective hydrogenation of unsaturated
1
esters, epoxides, sulfones and phosphonates
)
Raluca Aldea, Howard Alper
Department of Chemistry, UniÕersity of Ottawa, 10 Marie Curie, Ottawa, ON, Canada KIN 6N5
Received 21 July 1997
Abstract
Ru-clays were prepared using montmorillonite–PPh2 or montmorillonite–bpy and RuCl3PH2O. The clays obtained were found to be
effective catalysts for the reduction of unsaturated esters, epoxides, sulfones and phosphonates. q 1998 Elsevier Science S.A.
Keywords: Hydrogenation; Ruthenium; Clay
1. Introduction
supported on clay and the use of this new system, as a
catalyst, for the selective reduction of functionalized
olefins.
There is substantial interest in immobilized transition
metal catalysts, because they are capable of combining
the advantages of homogeneous and heterogeneous
catalysis. The catalyst is easily removed after reaction, a
high yield of the products can often be obtained, and the
lifetime of the catalyst is good in some cases. From the
variety of possible supports for hydrogenation reactions,
the option for clays comes from their capacity to mimic
to some extent, but at a much lower cost, the properties
of a rare noble metal and to make possible synthesis
2. Results and discussion
Ruthenium complexes, fixed between the interlayers
of clays by cation exchange, were reported previously
w
x
and their catalytic activity already investigated 10–12 .
X
2
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.
w x
L-Ru 2,2 -bipyridyl -montmorillonite 10 is efficient
3
w x
with improved selectivity 1 . The immobilization of a
for the oxidation of alkyl phenyl sulfides to optically
2
3
metal complex in a clay structure modifies the chemical
and physical forces acting in the interlayer space of the
clay and this can result in improved catalytic specificity
w x
2 .
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.
active sulfoxides and Ru 1,10-phenanthroline -pillared
montmorillonite is the catalyst precursor for the selec-
tive reduction of the carbon:carbon double bond of
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x
Ž . Ž
.
unsaturated ketones 11 . RuCl2 H AsPh3 interca-
2
2
We have been examining the catalytic activity of
metals immobilized on clays for different processes
Ž .
lated in montmorillonite is reported to be active for the
w
x
hydrogenation of jojoba oil and castor oil 12 . Our
approach was to use either phosphine or bipyridine as
the ligands to attach to the clay, and these ligands serve
as the link for binding ruthenium to the clay. Two
methods were used for the preparation of ruthenium
w
x
3–9 . Montmorillonite–bipyridinyl palladium II was
used for the reductive carbonylation of nitroarenes to
w x
urethanes 3 the oxidative carbonylation of aliphatic
mono, di- and triamines 4 and for the sterospecific
w x
w x
synthesis of b, g-unsaturated acids 5 . Rhodium–
montmorillonite was an effective catalyst for the hydro-
formylation of vinylsilanes 6 and allyl acetates 7 .
We now wish to report the preparation of ruthenium
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. Ž
.
clay, one involving the reaction of Si OMe CH2 3Cl
3
with OH groups present in the clay, followed by the
w x
w x
w
x
addition of KPPh2 13 , and subsequent treatment with
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RuCl3 PH2O Scheme 1, catalyst 1 . In the second
method the clay, in its acidic form, is reacted with
SOCl2 , followed by treatment with n-BuLi and bipyri-
)
Corresponding author.
w
x
dine 14 , and finally by addition of RuCl3 PH2O
Scheme 1, catalyst 2 .
1 Dedicated to Professor Peter Maitlis, a splendid person who has
made outstanding contributions to science. We have learned so much
from him.
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.
The Ru-clays obtained were analyzed for ruthenium
0022-328Xr98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.

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R. Aldea, H. AlperrJournal of Organometallic Chemistry 551 1998 349–354
phosphorus atom and the enhanced absorption at 697
cmy1, compared to pure K-10 montmorillonite, is typi-
cal of the substitution pattern of an aromatic phosphine.
In the CPrMAS 31 P NMR spectrum of the ligand
bound to the clay, a signal at y17.6 ppm was assigned
to the phosphorus in siloxypropyldiphenylphosphine,
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.
which is close to the value y16 ppm reported for the
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x
same ligand grafted on silica 15 . The NMR study also
indicates the presence of a P V species 32.7 ppm
15 . After the coordination of ruthenium the spectrum
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.
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.
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x
shows a broad peak at 32 ppm and the signal at y17.6
ppm disappeared. It is known that the coordination of
Ru to phosphorus produces the shift of the 31 P signal in
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. w x
the upper field region 40 ppm 16 and a similar shift
takes place in the case of Pd coordinated to phosphine
w
x
on clay 17 .
X-Ray powder diffraction showed a basal region
˚
˚
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expansion d001 of 13.36 A for 1 from 9.6 A in the
dehydrated sodium montmorillonite.
Scheme 1.
content by flame emission with 0.17 mmol Rugy1 and
0.018 mmol Rugy1 found for 1 and 2, respectively.
The IR spectra of both Ru-clays show strong absorp-
tions due to the montmorillonite. For catalyst 1 the
2880–2900 cmy1 band can be assigned to the carbon–
hydrogen stretch from the propyl group attached to the
For catalyst 2, the IR spectrum of the clay containing
the dipyridyl ligand, before complexation of the metal,
indicated the characteristic absorption of bipyridine in
the region of 1562–1438 cmy1. After treatment with
RuCl3 PH2O a sharp absorption at 1642 cmy1 was
observed. It is known that dipyridyl ligands coordinated
Table 1
Reduction of unsaturated esters using 1 and 2 as catalystsa
a
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.
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.
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Reaction conditions: substrate 2.0 mmol ; 30 mg 1 or 2 0.005 mmol Ru ; temperature: 758C; benzene 8.0 ml .
b Determined by 1H NMR using an internal standard.
c1 mmol substrate.
d Isolated yield.

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R. Aldea, H. AlperrJournal of Organometallic Chemistry 551 1998 349–354
351
to ruthenium are characterized by the sharp 1600 cmy1
600 psi H2 , while 2 catalyses the hydrogenation in 45 h
Table 1, entry 3 . Neither 1 or 2 was effective for the
w
x
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.
peak 18 and, once the ligand is fixed on a solid
support, a shift of the band can take place. In this
particular case the peak corresponding to bipyridine is
overlaped with the band near 1642–1633 cmy1 dis-
played by montmorillonite. The basal region expansion
w
x
hydrogenation of ethyl 2,3-dimethyl-2-butenoate 22
Table 1, entry 4 . In contrast with the increased activity
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.
of 2 for the reduction of carbon5carbon double bond in
ethyl 3-methyl-2-butenoate, 1 is the catalyst of choice
for ethyl trans cinnamate: 100% conversion resulting in
the formation of ethyl 3-phenylpropanoate in 85% iso-
˚
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.
d001 for 2 was 14.11 A.
It is important to note that, when Ru-clays were used
in the catalysis process, no leaching of Ru was ob-
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.
lated yield Table 1, entry 5 . Catalyst 2 gave only 21%
conversion of ethyl trans cinnamate to the saturated
ester, the rest being unreacted starting material. Ru-clay
1 is also effective in the case of ethyl trans-b-methyl-
cinnamate with 100% conversion to the saturated ester
Ž
served. The recycling capacity of the catalyst both 1
.
and 2 was tested by reusing the Ru-clays three times
consecutively without loss of activity.
An investigation was made on the effectiveness of 1
and 2, for the selective reduction of the double bond of
unsaturated esters, a reaction of substantial interest in
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.
Table 1, entry 6 . The activity displayed by 2 for this
substrate is similar to that of catalyst 1 Table 1, entry
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x
.
7 .
organic chemistry 19–21 .
The hydrogenation of methyl methacrylate catalyzed
by Ru-clays 1 and 2 with a substrate to catalyst ratio of
370:1 showed complete conversion to the corresponding
propionate ester in 22 h at 300 psi H2 and 758C. Clays
1 and 2 had comparable catalytic activity for the selec-
tive reduction of double bond of methyl methacrylate
The hydrogenation reactions were performed in ben-
zene and, in the crude mixture, cyclohexane, obtained
from the reduction of aromatic ring, was observed.
Several other solvents were used for the hydrogenation
reaction with 1 as the catalyst. Reaction of methyl
methacrylate catalyzed by 1 in methylene chloride gave
complete conversion to methyl 2-methylpropionate,
while in the reaction using methanol as the solvent, the
starting material was recovered and only traces of hy-
drogenated product were found. To make sure that the
Ru-clay system is the active catalyst, the reaction of
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.
and methyl crotonate Table 1, entries 1 and 2 .
The two catalysts behaved differently when both
terminal hydrogens of the double bond are replaced by
methyl groups, as in the case of ethyl 3-methyl-2-
butenoate: 1 is inactive towards the substrate even at
Table 2
Reduction of unsaturated epoxides using 1 as the catalysta
a
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.
Reaction conditions: 1 mmol substrate; 30 mg 1 0.005 mmol Ru ; temperature: 758C; 8 ml benzene as solvent.
bConversion determined from 1H NMR.
c By-products obtained: entry 1: benzyl ethyl ketone 10% ; entry 2: 2-methyl-2-phenyl-butanal 30% and 2-phenyl-3-pentanone; entry 3:
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.
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.
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.
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.
cyclohexanone 84% ; entry 4: cycloheptanone 50% .
d Yield determined by 1H NMR using an internal standard.
e Yield determined by GC with an internal standard.

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R. Aldea, H. AlperrJournal of Organometallic Chemistry 551 1998 349–354
methyl methacrylate at 300 psi H2 and 758C using
Fluka K-10 montmorillonite, without any metal, was
tested in which case no reaction was observed. The use
of RuCl3 PH2O, as the catalyst, for the same substrate,
in benzene, gave only 27% conversion to methyl 2-
methylpropionate. It was also demonstrated that the
solid obtained by stirring a dry THF solution of K-10
montmorillonite and RuCl3 PH2O, under nitrogen, and
then washing with water and THF, followed by drying
in vacuo, does not give any reduction of methyl
methacrylate.
product being cycloheptanone. Cycloheptene oxide is
obtained in lower yield 33% when 1,3-cyclo-
heptadiene monoxide is reduced at 300 psi H2.
The catalytic activity of 1 was investigated for two
other classes of functionalized compounds a, b-un-
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.
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.
saturated sulfones and phosphonates Table 3 .
Ž
Ethyl vinyl sulfone and phenyl vinyl sulfone Table
3, entries 1 and 2 afforded diethyl sulfone and ethyl
.
phenyl sulfone in 64% and 94% yield, respectively. The
use of ruthenium clay for the reduction of the
carbon5carbon double bond in sulfones compares fa-
vorably with commonly used hydride reagents such as
Catalyst 1 was also tested for the selective hydro-
Ž
w
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.
x w
x
genation of the double bond of vinyl epoxides Table
NaBH4 or PPh3 CuH 27–29 or with the catalyst
1
t
.
w
Ž
.
x2
2 , a reaction which occurs using palladium or rhodium
on carbon for butadiene monoxide 23 and with homo-
generated from the reaction of Bu2 PH PdPBu2 with
3
w
x
w x
O2 in THF 30 . The hydrogenation also proceeded
readily for diethyl vinyl phosphonate 100% conversion
and 90% yield Table 3, entry 3 , but the reaction is of
limited scope as the presence of another substituent at
the carbon5carbon double bond inhibits reduction e.g.,
w
x
Ž
geneous palladium and iridium catalysts 24 .
. Ž
.
Good selectivity was obtained for 2-phenyl-3-vinyl-
w
x
oxirane 25 , which afforded, at 500 psi H2 , 2-ethyl-3-
phenyl-oxirane in 60% isolated yield Table 2, entry 1 .
Ž
.
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w
x
In the case of 2-methyl-2-phenyl-3-vinyloxirane 25 , an
appreciable amount of saturated aldehyde 2-methyl-2-
phenyl butanal together with 2-phenyl-3-pentanone was
a-phenyl-substituted vinyl diethylphosphonate or di-
Ž
.
ethyl 1-propenylphosphonate did not react .
.
obtained in addition to the saturated epoxide, which
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.
represented only 30% of the products Table 2, entry 2 .
The hydrogenation reaction of 1,3-cyclohexadiene
3. Conclusion
w
x
monoxide 22 at 500 psi H2 gave cyclohexene oxide in
16% yield, the principal product being cyclohexanone
RuCl3, immobilized on clay by means of phosphine
or bipyridine containing units, showed good catalytic
activity for the reduction of a,b-unsaturated esters and
unsaturated sulfones but was less selective for unsatu-
rated epoxides and not generally efficient for
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.
Table 2, entry 3 . In the case of 1,3-cycloheptadiene
w
x
monoxide 26 the yield of cycloheptene oxide was
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. Ž
.
good 50% Table 2, entry 4 with the accompanying
Table 3
Reduction of unsaturated sulfones and phosphonates using 1 as the catalysta
a
Ž
.
Ž
.
Reaction conditions: substrate 0.5 mmol ; 1 30 mg, 0.005 mmol Ru ; temperature: 1258C for sulfones and 1008C for phosphonate; pressure:
500 psi H2; 8 ml benzene as solvent.
bConversion determined by 1H NMR.
c1 mmol substrate used.
d Yield determined by GC with an internal standard.

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R. Aldea, H. AlperrJournal of Organometallic Chemistry 551 1998 349–354
353
phoshonates. It is an attractive method because of facile
separation and reuse of the catalyst.
The montmorillonite was washed with THF, ethyl ac-
etate and benzene followed by Soxhlet extraction with
THF for 24 h. The solid obtained was dried under
Ž
.
vacuum and then 41.5 mg of RuCl3 PH2O 0.2 mmol
4. Experimental
was added to 2 g of bipyridine–montmorillonite sus-
pended in THF and the mixture was stirred for 8 h
under nitrogen. The resulting Ru-clay was thoroughly
washed with water and THF to remove excess RuCl3
and dried in vacuo. The Ru content was determined to
All solvents were dried and distilled by standard
1
methods prior to use. H NMR and 13C NMR spectra
were recorded on a Varian Gemini 200 and XL 300
spectrometers; a Bomen MB 100-C15 spectrometer was
used for FT-IR spectra and a Varian 3400 Chromato-
graph for GC analyses. The substrates were purchased
from Aldrich Chemical and were used as received. The
substrates which were not commercially available were
be 0.18 mmol gy1 flame emission .
Ž
.
4.2. General procedure for the hydrogenation reactions
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.
A mixture of unsaturated substrate 2 mmol and
Ž
synthesized by literature methods i.e., ethyl 2,3-di-
Ž
.
Ru-clay, 1 or 2, 30 mg–0.005 mmol Ru in 8 ml
methyl crotonate, 2-phenyl-3 vinyl-oxirane, 2-methyl-
2-phenyl-3-vinyl-oxirane, 1,3-cyclohexadiene monoxide
Ž
.
benzene 8 ml were placed in a 45-ml autoclave. The
autoclave was purged three times with H2 and then
pressurized to the desired level. The reactor was then
placed in an oil bath and maintained at constant temper-
ature. After the appropriate reaction time, the autoclave
was cooled to room temperature, excess H2 gas was
released and the reaction mixture was filtered through
Celite and the solvent was removed by rotary evapora-
tion. The products were purified by vacuum distillation
or column chromatogaphy.
.
w
x
and 1,3-cycloheptadiene monoxide 22,25,26 . Physical
data for all starting materials and products are in accord
with literature data.
4.1. Synthesis of Ru-clays
Synthesis of 1: H–montmorillonite was prepared from
Ž
.
montmorillonite K-10 Fluka by treatment with satu-
rated NaCl solution followed by 0.1 N HCl solution. It
was dried in air and then in vacuum. H–montmoril-
Ž
.
Ž
.
lonite 4 g was suspended in benzene 40 ml ,
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.
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.
MeO SiCH2CH2CH2Cl 5 ml, 0.027 mol was added
Acknowledgements
3
and the mixture was refluxed for 12 h. The clay was
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.
w x
extracted Soxhlet with toluene for 24 h, and dried 13 .
We are grateful to the Natural Sciences and Engi-
neering Research Council of Canada for support of this
research.
Ž
.
Ž
The clay 2.5 g was then suspended in dry THF 30
ml , KPPh2 4 mmol, 8 ml 0.5 M solution in THF was
added dropwise and the mixture was refluxed overnight
.
Ž
.
w
x
under nitrogen 13 . The excess KPPh2 was quenched
with methanol and the clay was subjected to extraction
with methanol for 24 h and then toluene for additional
24 h, and subsequently dried in vacuum. The dried
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Ž
.
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.
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w x
Ž .
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