Hoveyda-Grubbs type metathesis catalyst immobilized on mesoporous molecular sieves MCM-41 and SBA-15

Article abstract of DOI:10.3762/bjoc.7.4

A commercially available Hoveyda-Grubbs type catalyst (RC303 Zhannan Pharma) was immobilized on mesoporous molecular sieves MCM-41 and on SBA-15 by direct interaction with the sieve wall surface. The immobilized catalysts exhibited high activity and nearly 100% selectivity in several types of alkene metathesis reactions. Ru leaching was found to depend on the substrate and solvent used (the lowest leaching was found for ring-closing metathesis of 1,7-octadiene in cyclohexane - 0.04% of catalyst Ru content). Results of XPS, UV-vis and NMR spectroscopy showed that at least 76% of the Ru content was bound to the support surface non-covalently and could be removed from the catalyst by washing with THF.

Full text of DOI:10.3762/bjoc.7.4

Hoveyda–Grubbs type metathesis catalyst
immobilized on mesoporous molecular
sieves MCM-41 and SBA-15
Hynek Balcar*, Tushar Shinde, Naděžda Žilková and Zdeněk Bastl
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2011, 7, 22–28.
J. Heyrovský Institute of Physical Chemistry of AS CR, v.v.i,
Dolejškova 3, 182 23 Prague 8, Czech Republic
doi:10.3762/bjoc.7.4
Received: 31 August 2010
Accepted: 16 November 2010
Published: 06 January 2011
Email:
Hynek Balcar* - balcar@jh-inst.cas.cz
* Corresponding author
Guest Editor: K. Grela
Keywords:
© 2011 Balcar et al; licensee Beilstein-Institut.
License and terms: see end of document.
alkene metathesis; catalyst immobilization; hybrid catalysts;
mesoporous molecular sieves; Ru–alkylidene complexes
Abstract
A commercially available Hoveyda–Grubbs type catalyst (RC303 Zhannan Pharma) was immobilized on mesoporous molecular
sieves MCM-41 and on SBA-15 by direct interaction with the sieve wall surface. The immobilized catalysts exhibited high activity
and nearly 100% selectivity in several types of alkene metathesis reactions. Ru leaching was found to depend on the substrate and
solvent used (the lowest leaching was found for ring-closing metathesis of 1,7-octadiene in cyclohexane – 0.04% of catalyst Ru
content). Results of XPS, UV–vis and NMR spectroscopy showed that at least 76% of the Ru content was bound to the support
surface non-covalently and could be removed from the catalyst by washing with THF.
Introduction
Ru–alkylidene complexes (Grubbs and Hoveyda–Grubbs cata- catalyst residues is especially important in the synthesis of
lysts, 1 and 2, respectively, Figure 1) belong to the most active drugs and some other fine chemicals. Several strategies have
and frequently used metathesis catalysts. These catalysts are been developed for the immobilization of Grubbs and
important tools in organic synthesis due to their high tolerance Hoveyda–Grubbs catalysts on solid supports [1-6]. Generally,
of heteroatoms in substrate molecules. Immobilization of these the complex can be attached to the supports: (a) by exchanging
complexes on solid supports has attracted attention, because it halide ligands X [7-11], (b) by exchanging phosphine and NHC
opens the possibility for easy catalyst–product separation ligands L [12,13], and (c) through the alkylidene ligand [14-19].
and catalyst reuse. The production of products free from For these purposes, special ligand molecules with tags suitable
22

Beilstein J. Org. Chem. 2011, 7, 22–28.
for the reaction with the support surface (linkers) are used. This high surface area, high pore volume and narrow distribution of
usually requires a sophisticated synthetic procedure. Moreover, pore size. Because of these unique qualities, they often find
the changes in the Ru coordination sphere may lead to the applications as supports of modern catalysts, including those
decrease in catalyst activity (e.g., the exchange of chloro used for metathesis reactions [22].
ligands for carboxylates [10,11]).
Results and Discussion
Catalyst activity
Mixing a toluene solution of 3 with dried MCM-41 and SBA-
15, respectively, for 30 min at room temperature led to green
solids, which after isolation and drying afforded heterogeneous
catalysts 3/MCM-41 and 3/SBA-15. The immobilization
proceeded almost quantitatively: 97% and 94% of the Ru com-
plex was transferred from the solution onto the MCM-41 and
SBA-15 surface, respectively. The established catalyst loading
was 0.98 wt % and 0.93 wt %, for 3/MCM-41 and 3/SBA-15,
respectively.
Figure 1: Grubbs 1 and Hoveyda–Grubbs 2 catalysts.
The catalytic activity was tested in the RCM of 1,7-octadiene
(Scheme 1, entry 1) and diethyl diallylmalonate (DEDAM)
(Scheme 1, entry 2), in the metathesis of methyl oleate
(Scheme 1, entry 3) and methyl 10-undecenoate (Scheme 1,
entry 4), and in the ROMP of cyclooctene (Scheme 1, entry 5).
Recently, a convenient method for the immobilization of
Hoveyda–Grubbs catalysts was reported [20]. A second genera-
tion Hoveyda–Grubbs catalyst was immobilized on silica
without any linkers by simply placing the Ru complex in
contact with silica in a suspension. Heterogeneous catalysts
(loading from 0.05 to 0.6 wt % Ru) were prepared, which were
active in ring-opening metathesis polymerization (ROMP) of
cyclooctene, ring-closing metathesis (RCM) of diallylsilanes
and several types of cross-metathesis reactions. High stability of
catalysts, reusability and low Ru leaching were also reported.
However, the mode of attachment of the Ru species on the silica
surface was unclear.
Figure 3 shows conversion curves for the RCM of DEDAM in
dichloromethane, benzene, and cyclohexane, and the RCM of
1,7-octadiene in cyclohexane. For the RCM of DEDAM, 3 (as a
homogeneous catalyst) and 3/SBA-15 were used. The reaction
proceeded very rapidly in all solvents used (TOF at 10 min was
approximately 2500 h−1). No decrease in the reaction rate was
observed as a result of the immobilization of complex 3. For the
RCM of 1,7-octadiene, 3/SBA-15 and 3/MCM-41 in cyclo-
The aims of this paper are the following: to report the hexane were used. The reaction profile was the same for both
immobilization of the Hoveyda–Grubbs type catalyst 3 catalysts and the reaction rate was significantly lower compared
(Figure 2, Zhan catalyst-1B) on mesoporous molecular sieves to the RCM of DEDAM. The selectivity was near 100% in all
SBA-15 and MCM-41 as supports with this simple immobiliz- cases (no side products were observed by GC).
ation method; to describe the activity and stability of hetero-
geneous catalysts prepared; and to clarify the nature of the bond The Ru leaching (in % of starting content of Ru in catalyst) for
between the Ru complex and the support surface. Mesoporous the reactions shown in Figure 3 is given in Table 1. It was
molecular sieves are advanced siliceous materials [21], with observed that leaching was dependent on both the solvent and
substrate used in the reaction – the highest leaching was found
for the RCM of DEDAM in CH2Cl2 whilst negligible leaching
was observed for the RCM of 1,7-octadiene in cyclohexane.
Filtration experiments carried out with 3/SBA-15 (Figure 4)
showed that the catalytic activity was completely bound to the
solid phase for the RCM of 1,7-octadiene in cyclohexane. At
5 min after starting the reaction, about ½ of the volume of the
liquid phase was separated by filtration and transferred into a
new reactor, kept under identical reaction conditions. No
increase in conversion was observed in this reactor. For the
Figure 2: Zhan catalyst-1B.
RCM of DEDAM in benzene, however, a considerable increase
23

Beilstein J. Org. Chem. 2011, 7, 22–28.
Scheme 1: Metathesis reactions studied.
Table 1: Ru leaching for 3/SBA-15.
Reaction Solvent
Ru
Maximal Ru
leaching content in producta
(1)
(2)
(2)
(2)
cyclohexane
0.04%
4%
0.6 ppm
28 ppm
66 ppm
100 ppm
benzene
cyclohexane
9%
dichloromethane 14%
molar ratio substrate/Ru = 600, c0substrate = 0.2 mmol/mL, T = 30 °C
acalculated as the amount of Ru per weight unit of substrate
35 h−1 for methyl 10-undecenoate, both with 3/MCM-41). The
metathesis of methyl oleate reached the equilibrium after 2 h. In
the case of methyl 10-undecenoate, the reaction rate was lower
than for methyl oleate (because of probable non-productive
metathesis [23]) and the final conversion was about 65% (due to
the evolution of ethylene into the gas phase). There was no
significant difference observed in the conversion curves for
reactions with 3/MCM-41 and 3/SBA-15. Selectivity near 100%
Figure 3: Conversion curves for the RCM of DEDAM with 3 in CH2Cl2
(open squares), 3/SBA-15 in CH2Cl2 (inverted filled triangle), 3/SBA-15
in benzene (filled diamond), 3/SBA-15 in cyclohexane (filled triangle),
and for the RCM of 1,7-octadiene with 3/SBA-15 (filled squares) and 3/
MCM-41 (filled circles) in cyclohexane (T = 30 °C, molar ratio sub-
strate/Ru = 600, c0substrate = 0.2 mol/L).
of substrate conversion in liquid phase after its separation from was achieved in all cases.
solid catalyst indicated that the Ru species released from the
solid catalyst were capable of initiating catalytic reactions.
The ROMP reactions were carried out for cyclooctene with both
3/MCM-41 and 3/SBA-15 (cyclooctene/Ru molar ratio = 500,
Figure 5 shows the activity of 3/MCM-41 and 3/SBA-15 in the c0cyclooctene = 0.6 mol/L, T = 30 °C). High molecular weight
metathesis of methyl oleate and methyl 10-undecenoate. The polymers (Mw = 250 000, Mn = 110 000) were obtained in high
reaction proceeded more slowly than in the case of the RCM of yields (70% and 64% for 3/MCM-41 and 3/SBA-15, respective-
DEDAM (TOF at 30 min = 260 h−1 for methyl oleate and ly) after 3 h.
24

Beilstein J. Org. Chem. 2011, 7, 22–28.
achieved in [20] are of the same order as the TOF values
obtained in our work. However, in the case of the ROMP of
cyclooctene, catalysts 3/MCM-41 and 3/SBA-15 led to high
molecular weight polymers, whereas in [20] the formation of
polymer was not referred.
Interaction between the Ru complex and the
support
For Hoveyda–Grubbs catalyst immobilized on silica, the
authors in [20] proposed a direct chemical interaction between
the Ru species and the silanol groups of the surface, instead of a
weak physisorption. In order to shed light on the mode of com-
plex attachment to the sieve surface, UV–vis and XPS spectra
were measured. In Figure 6, the UV–vis spectra of 3/SBA-15
and 3 in CH2Cl2 are compared. The bands at λ = 375 nm and at
λ = 600 nm (2 orders of magnitude lower ε, not visible in
Figure 6) in the spectrum of 3 reflect the d–d transition of the
Ru(II) atoms [24]. Supported catalyst 3/SBA-15 exhibits the
same spectrum suggesting no changes in the coordination
sphere of Ru atoms occurred during immobilization of 3 on the
sieve.
Figure 4: Filtration experiments with 3/SBA-15. RCM of DEDAM in
benzene (circles), 1,7-octadiene in cyclohexane (squares), liquid
phase in contact with solid catalyst (filled symbols), liquid phase after
filtration (open symbols), arrows indicate time of filtration. Substrate/Ru
molar ratio 600, T = 30 °C, c0DEDAM = 0.22 mol/L, c01,7-octadiene = 0.16
mol/L.
Figure 5: Metathesis of methyl oleate (open symbols) and methyl
10-undecenoate (filled symbols) with 3/MCM-41 (circles) and 3/SBA-
15 (squares). Molar ratio substrate /Ru = 500, T = 30 °C, c0substrate =
0.15 mol/L.
Figure 6: UV–vis spectra of 3/SBA-15 (curve 2) and of 3 (curve 1) in
dichloromethane (c = 0.001 mol/L, l = 0.2 cm).
The catalysts 3/MCM-41 and 3/SBA-15 exhibited some Assuming non-covalent interactions between the Ru species and
features similar to those of Hoveyda–Grubbs catalyst the support surface, we attempted to wash out the Ru species
immobilized on silica [20]: (a) Filtration experiments proved from 3/SBA-15 with THF-d8 and characterise the eluate by
complete catalyst heterogeneity only for nonpolar solvents NMR spectroscopy. About 100 mg of 3/SBA-15 was mixed
(cyclohexane and hexane, respectively); (b) catalyst leaching in with 1.5 mL of THF-d8 and stirred for 2 h at room temperature.
these solvents was extremely low, ensuring more than one order The dark green supernatant was then transferred into a NMR
of magnitude lower Ru concentration in products compared to tube and the solid phase was washed with THF and dried in
the upper limit permissible in pharmaceutical production vacuo. According to the elemental analysis, 76% of the Ru was
(10 ppm [3]); and (c) similar catalyst activity was observed. removed. In the supernatant, the presence of compound 3 was
Although the slightly different reaction conditions applied in demonstrated by comparing 1H and 13C NMR spectra of the
[20] do not allow an exact comparison, the initial TOF values supernatant and corresponding spectra of a fresh solution of 3 in
25

Beilstein J. Org. Chem. 2011, 7, 22–28.
THF-d8. The catalytic activity of the solid phase was then tested which was not possible to remove from 3/SBA-15 with THF at
in the RCM of DEDAM in cyclohexane (molar ratio DEDAM/ room temperature, might be due to 3 more firmly attached to the
Ru = 600, T = 30 °C, c0DEDAM = 0.2 mol/L). After 1 h, 55% surface (e.g., adsorbed at special sites on the surface, or
conversion of DEDAM was achieved and 62% after 6 h. Only embedded into micropores, etc.). Because of the low concentra-
the RCM products were observed. This indicates that the tion of these species, we have not been able to investigate their
remaining Ru species after washing was catalytically active; bonding to the surface in greater detail.
however, these species were rapidly deactivated.
Conclusion
Figure 7 shows high-resolution spectra of the Ru 3d–C 1s The Hoveyda–Grubbs type catalyst 3 was immobilized on
photoelectrons of neat compound 3, catalyst 3/SBA-15 and the mesoporous molecular sieves MCM-41 and SBA-15 by mixing
same catalyst after leaching in THF. The measured binding a suspension of 3 and sieves in toluene at room temperature.
energy of the Ru 3d5/2 electrons (281.2 ± 0.2 eV) was identical The immobilization proceeded quickly and almost quantita-
for all these samples and was in accord with the value tively. Heterogeneous catalysts prepared in this way exhibited
280.95 eV reported in literature [25] for a similar compound. high activity and 100% selectivity in the RCM of 1,7-octadiene
This result indicates that the structure of the Ru complex is not and diethyl diallylmalonate, in the metathesis of methyl oleate
substantially changed by the immobilization on the support and methyl 10-undecenoate, and in the ROMP of cyclooctene.
surface. This conclusion is corroborated by the results of quanti- Ru leaching was found to depend on the polarity of substrate
tative analysis. For this catalyst, the atomic concentration ratios and solvent used. The lowest leaching was found for the RCM
Ru/Si = 3.5 × 10−3 and Cl/Ru = 2.0 were obtained from inte- of 1,7-octadiene in cyclohexane – 0.04% of catalyst Ru content.
grated intensities of Ru 3d, Si 2p and Cl 2p photoemission lines. On the other hand, for the RCM of diethyl diallylmalonate in di-
For the sample leached by THF, the ratio Ru/Si = 9 × 10−4, chloromethane, leaching reached 14% of initial Ru content in
which is in accord with the amount of Ru removed from the the catalysts.
support by leaching as determined from elemental analysis.
Results from UV–vis and XPS studies suggested that 3 was at-
tached to the sieve surface by non-covalent interactions.
Approximately 76% of the Ru content could be recovered from
the sieve as 3 (as shown by NMR) by washing with THF at
room temperature (indicating physical adsorption of 3 on the
sieve). The residual Ru species on the sieve exhibited catalytic
activity in RCM but were rapidly deactivated.
The advantage of these catalysts is their simple preparation,
avoiding support modification with special linker molecules. In
nonpolar systems, they can function as true efficient hetero-
geneous catalysts. In the case of polar systems, the possibility of
Ru leaching to a significant extent should be taken into account.
Experimental
Materials
Toluene was dried overnight over anhydrous Na2SO4, then
distilled with Na and stored over molecular sieves 4 Å. Benzene
(Lach-Ner, Czech Republic) was dried over anhydrous Na2SO4,
distilled with P2O5 and then with NaH in vacuo. Dichloro-
methane (Lach-Ner) was dried overnight over anhydrous CaCl2,
then distilled with P2O5 and stored over molecular sieves 4 Å.
Cyclohexane was distilled with P2O5, then dried with CaH2 and
stored over molecular sieves 4 Å. Diethyl diallylmalonate
(Sigma-Aldrich, purity 98%), cyclooctene (Janssen Chimica,
Figure 7: Spectra of the Ru 3d–C 1s photoelectrons for neat com-
pound 3 (1), catalyst sample 3/SBA-15 (2) and catalyst sample 3/SBA-
15 after leaching in THF (3).
The results obtained suggest that the Ru species in 3/SBA-15 purity 95%), 1,7-octadiene (Fluka, purity ≥ 97.0%), methyl
were attached to the sieves by a non-covalent interaction (prob- oleate (Research Institute of Inorganic Chemistry, a.s., Czech
ably via physical adsorption). The small residual Ru content, Republic, purity 94%: methyl palmitate, methyl stearate and
26

Beilstein J. Org. Chem. 2011, 7, 22–28.
methyl linolate as the main impurities) were used as received. Catalyst preparation
Methyl 10-undecenoate was prepared from 10-undecenoic acid About 1 g of support was transferred into a Schlenk tube and
[26]. The Ru complex 3 was purchased from Zannan Pharma. dried for 3 h at 300 °C in vacuo. After drying, the Schlenk tube
Ltd., China.
was filled with argon. Then 10–20 mL of toluene and a calcu-
lated amount of 3 was added with stirring at room temperature.
The synthesis of siliceous MCM-41 and SBA-15 was performed After stirring for 30 min, the solid phase turned green and the
according to the procedure described in [27]. Their textural supernatant became colorless. Then, the supernatant was
characteristics were determined for MCM-41 and SBA-15, res- removed by filtration and the solid catalyst was washed two
pectively, from nitrogen adsorption isotherms: surface area times with 10 mL toluene. Finally, the catalyst was dried in
SBET = 972 and 934 m²/g, average pore diameter d = 3.8 and 6.9 vacuo at room temperature.
nm and volume of pores V = 1.14 and 0.96 cm³/g. The particle
size (by SEM) ranged from 1 to 3 μm for all supports used.
Catalytic experiments
Catalytic experiments were performed in Schlenk tubes under
an Ar atmosphere in CH2Cl2 or cyclohexane. In a typical
Techniques
UV–vis spectra of catalysts were recorded with a Perkin-Elmer experiment, 1,7-octadiene (225 mg, 2.05 mmol) was added to 3/
Lambda 950 spectrometer. A Spectralon integration sphere was SBA-15 (34 mg, 3.4 μmol of Ru) in cyclohexane (10 mL) at
applied to collect diffuse reflectance spectra of powder samples. 30 °C with stirring. Samples of the reaction mixture (100 μL)
Spectralon served also as a reference. Catalyst samples were were taken at given intervals, quenched with ethyl vinyl ether
placed in a quartz cuvette under an Ar atmosphere. 1H and analyzed by GC. In the ROMP experiments, the reaction
(300 MHz) and 13C (75 MHz) NMR spectra were recorded on a conditions were similar to those for the RCM of 1,7-octadiene,
Varian Mercury 300 spectrometer in THF-d8 at 25 °C.
with an initial concentration of cyclooctene of 0.6 mol/L. After
3 h, the reaction mixture was terminated with ethyl vinyl ether,
The photoelectron spectra of the samples were measured with the solid catalyst was separated by centrifugation and the
an ESCA 310 (Scienta, Sweden) spectrometer equipped with a polymer isolated by precipitation in methanol (containing 2,6-
hemispherical electron analyzer operated in a fixed transmis- di-tert-butyl-p-cresol as an antioxidant). The polymer yield was
sion mode. Monochromatic Al Kα radiation was used for the determined gravimetrically. The molecular weight was deter-
electron excitation. The samples were spread on aluminium mined by SEC and the values related to the polystyrene stan-
plates and the spectra were recorded at room temperature. The dards.
Si 2p, O 1s, Cl 2p, C 1s and Ru 3d photoelectrons were
measured. Sample charging was corrected using the C 1s peak Acknowledgements
at 284.8 eV as internal standard. For the overlapping C 1s and The authors thank M. Lamač (J. Heyrovský Institute) for
Ru 3d lines, the contributions of individual components were recording NMR spectra and J. Sedláček (Department of Phys-
determined by curve fitting. The spectra were curve-fitted after ical and Macromolecular Chemistry, Charles University in
subtraction of the Shirley background [28] using a Prague) for determination of polymer molecular weights by
Gaussian–Lorentzian line shape. The decomposition of the Ru SEC. Financial support from the Grant Agency of the Academy
3d and C 1s profiles was made subject to the constraints of the of Science of the Czech Republic (project IAA400400805), and
constant Ru 3d doublet separation (4.17 eV) and the constant the Academy of Sciences of the Czech Republic (project
Ru 3d5/2/Ru 3d3/2 intensity ratio equal to the ratio of the corres- KAN100400701) is gratefully acknowledged.
ponding partial photoionization cross sections (1.45) [29].
References
1. Buchmeiser, M. R. Catal. Today 2005, 105, 612–617.
Quantification of the elemental concentrations was accom-
plished by correcting photoelectron peak intensities for their
doi:10.1016/j.cattod.2005.06.005
cross sections, analyzer transmission function and assuming a
2. Dragutan, I.; Dragutan, V. Platinum Met. Rev. 2008, 52, 71–82.
homogeneous sample.
doi:10.1595/147106708X297477
3. Clavier, H.; Grela, K.; Kirschning, A.; Mauduit, M.; Nolan, S. P.
A high-resolution gas chromatograph Agilent 6890 with DB-5
Angew. Chem., Int. Ed. 2007, 46, 6786–6801.
column (length: 50 m, inner diameter: 320 μm, stationary phase
thickness: 1 μm) was used for reaction product analysis.
Nonane was used as an internal standard when required. The Ru
content was determined by ICP-MS (by Institute of Analytical
Chemistry, ICT, Prague).
doi:10.1002/anie.200605099
4. Copéret, C.; Basset, J.-M. Adv. Synth. Catal. 2007, 349, 78–92.
doi:10.1002/adsc.200600443
5. Buchmeiser, M. R. Chem. Rev. 2009, 109, 303–321.
doi:10.1021/cr800207n
27

Beilstein J. Org. Chem. 2011, 7, 22–28.
6. Burtscher, D.; Grela, K. Angew. Chem., Int. Ed. 2009, 48, 442–454.
doi:10.1002/anie.200801451
29.Scofield, J. H. J. Electron Spectrosc. Relat. Phenom. 1976, 8,
129–137. doi:10.1016/0368-2048(76)80015-1
7. Nieczypor, P.; Buchowicz, W.; Meester, W. J. N.; Rutjes, F. P. J. T.;
Mol, J. C. Tetrahedron Lett. 2001, 42, 7103–7105.
doi:10.1016/S0040-4039(01)01460-5
License and Terms
8. Halbach, T. S.; Mix, S.; Fischer, D.; Maechling, S.; Krause, J. O.;
Sievers, C.; Blechert, S.; Nuyken, O.; Buchmeiser, M. R. J. Org. Chem.
2005, 70, 4687–4694. doi:10.1021/jo0477594
This is an Open Access article under the terms of the
Creative Commons Attribution License
9. Krause, J. O.; Nuyken, O.; Wurst, K.; Buchmeiser, M. R. Chem.–Eur. J.
2004, 10, 777–784. doi:10.1002/chem.200305031
10.Vehlow, K.; Maechling, S.; Köhler, K.; Blechert, S.
J. Organomet. Chem. 2006, 691, 5267–5277.
(http://creativecommons.org/licenses/by/2.0), which
permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.
doi:10.1016/j.jorganchem.2006.08.019
11.Bek, D.; Žilková, N.; Dědeček, J.; Sedláček, J.; Balcar, H. Top. Catal.
2010, 53, 200–209. doi:10.1007/s11244-009-9418-7
12.Melis, K.; De Vos, D.; Jacobs, P.; Verpoort, F. J. Mol. Catal. A: Chem.
2001, 169, 47–56. doi:10.1016/S1381-1169(00)00563-X
13.Mayr, M.; Buchmeiser, M. R.; Wurst, K. Adv. Synth. Catal. 2002, 344,
712–719.
The license is subject to the Beilstein Journal of Organic
Chemistry terms and conditions:
(http://www.beilstein-journals.org/bjoc)
The definitive version of this article is the electronic one
which can be found at:
doi:10.1002/1615-4169(200208)344:6/7<712::AID-ADSC712>3.0.CO;2
-W
doi:10.3762/bjoc.7.4
14.Kingsbury, J. S.; Garber, S. B.; Giftos, J. M.; Gray, B. L.;
Okamoto, M. M.; Farrer, R. A.; Fourkas, J. T.; Hoveyda, A. H.
Angew. Chem., Int. Ed. 2001, 40, 4251–4256.
doi:10.1002/1521-3773(20011119)40:22<4251::AID-ANIE4251>3.0.CO
;2-L
15.Fischer, D.; Blechert, S. Adv. Synth. Catal. 2005, 347, 1329–1332.
doi:10.1002/adsc.200505106
16.Zarka, M. T.; Nuyken, O.; Weberskirch, R. Macromol. Rapid Commun.
2004, 25, 858–862. doi:10.1002/marc.200300297
17.Yao, Q.; Motta, A. R. Tetrahedron Lett. 2004, 45, 2447–2451.
doi:10.1016/j.tetlet.2004.01.036
18.Elias, X.; Pleixats, R.; Man, M. W. C. Tetrahedron 2008, 64,
6770–6781. doi:10.1016/j.tet.2008.04.113
19.Lim, J.; Lee, S. S.; Ying, J. Y. Chem. Commun. 2010, 46, 806–808.
doi:10.1039/b917986k
20.Van Berlo, B.; Houthoofd, K.; Sels, B. F.; Jacobs, P. A.
Adv. Synth. Catal. 2008, 350, 1949–1953.
doi:10.1002/adsc.200800211
21.Beck, J. S.; Vartuli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.;
Schmitt, K. D.; Chu, C. T.-W.; Olson, D. H.; Sheppard, E. W.;
McCullen, S. B.; Higgins, J. B.; Schlenker, J. L. J. Am. Chem. Soc.
1992, 114, 10834–10843. doi:10.1021/ja00053a020
22.Martín-Aranda, R. M.; Čejka, J. Top. Catal. 2010, 53, 141–153.
doi:10.1007/s11244-009-9419-6
23.Stewart, I. C.; Keitz, B. K.; Kuhn, K. M.; Thomas, R. M.; Grubbs, R. H.
J. Am. Chem. Soc. 2010, 132, 8534–8535. doi:10.1021/ja1029045
24.Lever, A. B. P. Inorganic electronic spectroscopy; Elsevier:
Amsterdam, 1984; p 468.
25.Jarzembska, K.; Seal, S.; Wozniak, K.; Szadkowska, A.; Bieniek, M.;
Grela, K. ChemCatChem 2009, 1, 144–151.
doi:10.1002/cctc.200900052
26.Balcar, H.; Dosedlová, A.; Hanuš, V.; Petrusová, L.; Matyska, B.
Collect. Czech. Chem. Commun. 1984, 49, 1736–1745.
27.Topka, P.; Balcar, H.; Rathouský, J.; Žilková, N.; Verpoort, F.; Čejka, J.
Microporous Mesoporous Mater. 2006, 96, 44–54.
doi:10.1016/j.micromeso.2006.06.016
28.Shirley, D. A. Phys. Rev. B 1972, 5, 4709–4714.
doi:10.1103/PhysRevB.5.4709
28