A PS-DES immobilized ruthenium carbene: A robust and easily recyclable catalyst for olefin metathesis

Article abstract of DOI:10.1016/S0040-4039(02)02283-9

The butyldiethylsilyl polystyrene (PS-DES) supported ruthenium carbene 7 is a robust, practical and easily recyclable catalyst for olefin metathesis of substituted olefins.

Full text of DOI:10.1016/S0040-4039(02)02283-9

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 43 (2002) 9055–9059
A PS-DES immobilized ruthenium carbene: a robust and easily
recyclable catalyst for olefin metathesis
a,
b
b
Karol Grela, * Mariusz Tryznowski and Michał Bieniek
a
Institute of Organic Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, PO Box 58, 01-224 Warsaw, Poland
b
Faculty of Chemistry, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland
Received 21 August 2002; revised 27 September 2002; accepted 14 October 2002
Abstract—The butyldiethylsilyl polystyrene (PS-DES) supported ruthenium carbene 7 is a robust, practical and easily recyclable
catalyst for olefin metathesis of substituted olefins. © 2002 Published by Elsevier Science Ltd.
During recent years, olefin metathesis has gained a
position of increasing significance. The development of
well-accessible metathesis catalysts combining high
activity with an excellent tolerance to a variety of
functional groups has been key to the widespread appli-
cation of olefin metathesis in organic synthesis and
polymer chemistry (Fig. 1). The most notable examples
of such catalysts are ruthenium carbenes with bulky
electron-rich phosphine (1a) or heterocyclic carbene
Several attempts have been made to immobilize
Grubbs-type carbenes 1a–c on solid supports. Endeav-
ors to prepare catalysts permanently immobilized on
solid supports has met with only limited success and the
resulting polymer-supported carbenes were found to be
less reactive than their homogeneous analogues. More-
over, their recovery and reuse led to significant losses in
activity.
4
1
ligands (1b–c). Despite the major advantages offered
5a
Barrett reported a ‘boomerang’ catalyst, in which the
by this group of catalysts, they share some
disadvantages.
carbene precatalyst becomes soluble during the course
of the reaction and can be recaptured by the polymer
5
once the substrate in solution has been consumed.
Since metathesis reactions are expected to be used in
pharmaceutical processes, the most undesirable feature
of these complexes is that they decompose to form
highly colored ruthenium byproducts, which are
Recently Hoveyda established 2a–b as remarkably
robust complexes promoting olefin metathesis by a
6
similar ‘release/return’ mechanism. Carbenes 2a–b
6
b
7a
2
were subsequently attached to a dendrimer, glass,
a
difficult to remove from the reaction products. From
7b
soluble polyethylene glycol resin and to cross-linked
the point of view of the chemical-economy recyclability
is another important attribute. In this respect, immobi-
lized or heterogeneous catalysts offer inherent opera-
tional and economic advantages over their
7c,d
insoluble polystyrene polymers
as well as hydrophilic
7e
PEGA–NH resin.
2
3
homogeneous counterparts.
Although these systems give very promising results, this
area is far from being fully explored. The need for
further developments led us to try another approach to
efficiently immobilize a metathesis catalyst. From
numerous resins known, we selected butyldiethylsilyl
8
polystyrene (PS-DES, 3), due to its advantages, such
as availability, stability, high loading capacity and good
swelling characteristics in solvents commonly used for
metathesis. We envisaged that the butylsilyl fragment
could be used for attachment of the phenol–ether part
of 2b to a solid support. The CꢀSi bond is perfectly
stable under metathesis conditions, but is cleaved quan-
titatively under the action of fluoride.
Figure 1. Ruthenium olefin metathesis catalysts.
*
Corresponding author. Tel.: +48226323221; fax: +48226326681;
e-mail: grela@icho.edu.pl
0
040-4039/02/$ - see front matter © 2002 Published by Elsevier Science Ltd.
PII: S0040-4039(02)02283-9

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K. Grela et al. / Tetrahedron Letters 43 (2002) 9055–9059
Scheme 1. Reagents and conditions: (i) NaH, iPrI, DMF, rt, 24 h; (ii) Ph PꢁCH , THF, −78°C to rt, 1 h, 69% over two steps; (iii)
3
2
1
,3-dichloro-5,5-dimethylhydantoin, CH Cl , rt, 5 h; (iv) 5, tBuLi, Et O, −78°C then 4, THF, −78°C to rt, 24 h; (v) 1b, CH Cl ,
2
2
2
2
2
rt, 24 h, four times; (vi) 1b 5, CuCl, CH Cl , 45°C, 1 h, 93%.
2
2
Quick and reliable determination of ruthenium loadings9
on insoluble supports is sometimes a difficult task.
Various techniques have been used for this purpose,
and in many cases ruthenium loadings were calculated
only from indirect measurements, such as ele-
mental analysis of other elements, mass increase which
accompanies functionalization of the polymer surface,
etc.
Our approach allows a more direct and easy method of
ruthenium loading determination based on the cleavage
of the carbene complex from the PS-DES resin with
TBAF and further spectroscopic Ru measurement in
solution.
The use of the longer butylsilyl linker increases the
distance between the metal centre and the polymer and,
Table 1. Olefin metathesis using 7

K. Grela et al. / Tetrahedron Letters 43 (2002) 9055–9059
9057
1
2
therefore should result in an improvement in catalyst
reactivity and recyclability. The easy three steps
method of preparation renders additional advantages
to the PS-DES system.
(Table 1). It is notable, that the rates of reaction
were somewhat slower than those obtained using the
soluble analogue 8, e.g. when the diene 9a was
treated with 2.5 mol% of catalyst 7 for 3 h at reflux,
the reaction was only 41% complete, compared to the
90% conversion when 2.5 mol% of 8 was used. How-
ever, after an additional 5 h the diene 9a was con-
verted cleanly by supported catalyst 7 to the cyclic
olefin 10a in greater than 99% conversion (Table 1,
entry a).
Preparation. The PS-DES resin 3 was first activated
to form the silyl chloride 4 by treatment with 1,3-
8
b
dichloro-5,5-dimethylhydantoin.
The reactive silyl
chloride derivative was then used immediately for
coupling with an organolithium, prepared from 2-iso-
propoxy-5-bromostyrene 5 and 2 equiv. of tert-butyl-
lithium. The support-bound ruthenium complex 7 was
then prepared from 6 by washing of the resin with
four successive portions of 25 mol% of 1b (Scheme
Ring-closing metathesis of other challenging sub-
strates goes cleanly, with typically high conversion, as
determined by GC–MS and H NMR analysis, lead-
ing to a,b-unsaturated lactone (entry b) and products
containing a trisubstituted double bond (entries a, b);
however, the tetrasubstituted olefin was not formed
entry d). We have also demonstrated the ability of 7
to perform cross-metathesis (CM) of n-butyl acrylate
entry c) and a substrate having an unprotected
1
1
). The catalyst was obtained after filtration as deep-
green beads showing ruthenium loading of 0.22–0.35
mmol/g (as determined from the inductively coupled
plasma mass spectrometry (ICP-MS) analysis of Ru).
Samples of resin 7 did not lose activity after three
(
11
months of storage in air at room temperature.
(
hydroxy function (entry f ). The catalyst 7 can be
readily recovered by simple filtration and washing
with dichloromethane. The resulting unpurified prod-
ucts were pure according to GC–MS and H NMR
analyses.
Activity study. PS-DES supported complex 7 (2.5–5.0
mol%) was then tested for activity using representa-
tive substrates for ring-closing metathesis leading to
the formation of different carbo- and heterocycles
1
Recyclability study. As we demonstrated with model
substrate 9e, the same batch of PS-DES catalyst can
be used for up to 5–6 cycles of metathesis and gave
similarly high conversions with only a slight loss of
activity. It was also possible to perform metathesis
using the PS-DES supported carbene 7 in reagent-
grade non-degassed dichloromethane under air, but in
this case the resin cannot be recycled more than three
times without almost complete loss of activity.
Table 2. Recyclability study using 7
More importantly, the same batch of a recycled cata-
lyst can be used sequentially in different reactions
(
Table 2), as the catalyst from the metathesis of 9e
was subsequently used for the metathesis of the sili-
13
con-tethered diene 9g. The same batch of recovered
catalyst was then used for the formation of macro-
cyclic musk-odored ester 10h (cycle 3) and carbonate
1
3
1
0i (cycle 4). Finally, in cycle 5 the substrate 9j was
converted to the a,b-unsaturated lactone 10j in 95%
conversion with recycled resin 7. In this experiment
we did not observe contamination from a previous
reaction substrate/product, as the crude reaction mix-
tures consist of only the substrate and cyclized
product 10g–j (GC–MS analyses). We have addition-
ally checked the ruthenium content in selected crude
products and found only low levels of ruthenium con-
1
2
tamination (50.1 wt%, ICP–MS analysis of Ru).
In summary, we have reported a robust, stable and
easy to (re)use supported catalyst for olefin metathe-
sis, which can be easily prepared in three steps from
commercial butyldiethylsilyl polystyrene. The possibil-
ity of instant ruthenium determination renders addi-
tional advantages of this PS-DES system. Detailed
studies regarding preparation and recycling of other
PS-DES bound ruthenium carbenes are in progress.

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K. Grela et al. / Tetrahedron Letters 43 (2002) 9055–9059
Acknowledgements
Gooding, O. W.; Trost, B. M. J. Org. Chem. 1998, 63,
518–4521.
. For example: cf. footnote 16 in Ref. 7a.
4
9
This work was supported by the State Committee of
Scientific Research (Grant No. 4T09A13622). The
authors wish to thank the Alexander von Humboldt
foundation for donating books and equipment.
10. F u¨ rstner, A.; Ackermann, L.; Gabor, B.; Goddard, R.;
Lehmann, C. W.; Mynott, R.; Stelzer, F.; Thiel, O. R.
Chem. Eur. J. 2001, 7, 3236–3253.
11. Butyldiethylchlorosilane polystyrene PS-DES-Cl (4). To
a 5 mL solid-phase synthesis flask (equipped with a
glass-frit) were added PS-DES silane resin (131 mg,
0.21 mmol) and 1,3-dichloro-5,5-dimethylhydantoin (124
References
mg, 0.63 mmol) in CH Cl2 (2.5 mL). After 5 h, the
2
mixture was filtered and washed with CH Cl (4×2 mL)
2
2
1
2
. F u¨ rstner, A. Angew. Chem., Int. Ed. 2000, 39, 3012–
043.
. For approaches where ruthenium impurities are
removed by addition of various scavengers, see: (a)
Maynard, H. D.; Grubbs, R. H. Tetrahedron Lett.
and dry THF (4×2 mL). The resin was used immedi-
ately after washing. The chlorination reaction can be
monitored by examination of the SiꢀH stretch (IR:
3
−
1
2100 cm ).
Butyldiethyl(4-isopropoxy-3-vinylphenyl)silane polystyrene
(6). To a stirred solution of t-BuLi (1.0 mL, 1.70
mmol, 1.7 M in pentane) at −78°C was added a solu-
2
000, 40, 4137–4140; (b) Paquette, L. A.; Schloss, J. D.;
Efremov, I.; Fabris, F.; Gallou, F.; Mendez-Andino, J.
Yang, J. Org. Lett. 2000, 2, 1259–1261; (c) Ahn, Y.
M.; Yang, K.; Georg, G. I. Org. Lett. 2001, 3, 1411–
tion of 5 (202 mg, 0.84 mmol) in dry Et O (5 mL).
2
After stirring for 15 min the clear yellow solution was
transferred via syringe to a cooled (−78°C) suspension
of 4 (0.21 mmol) in THF (1 mL). The reaction mixture
was stirred at −78°C for 3 h, and was then gently
agitated at rt for 24 h. The mixture was filtered and
washed with THF (4×2 mL), a THF–MeOH 2:1 v/v
1
413.
3
. Yet another ‘green-chemistry’ approach is the use of
supercritical CO2 as the reaction medium. The ruthe-
nium carbenes 1a and 1c act as heterogenous catalysts
in this environmentally benign medium: (a) F u¨ rstner,
A.; Koch, D.; Langemann, K.; Leitner, W.; Six, C.
Angew. Chem., Int. Ed. 1997, 36, 2466–2469; (b) F u¨ rst-
ner, A.; Ackermann, L.; Beck, K.; Hori, H.; Koch, D.;
Langemann, K.; Liebl, M.; Six, C.; Leitner W. J. Am.
Chem. Soc. 2001, 123, 9000–9006.
mixture (2×2 mL) and CH Cl2 (2×2 mL) and dried in
2
vacuo to give 6 as a white solid (169 mg).
PS-DES polymer-bound ruthenium complex (7). A 5 mL
solid-phase synthesis flask was charged with the resin 6
(169 mg) and a solution of Grubbs’ carbene 1b (0.05
4. (a) Nguyen, S. T.; Grubbs, R. H. J. Organomet. Chem.
mmol, 0.25 equiv.) in CH Cl2 (2 mL) was added. The
2
1
995, 195–200; (b) Sch u¨ rer, S. C.; Gessler, S.;
Buschman, N.; Blechert, S. Angew. Chem., Int. Ed.
000, 39, 3898–3901; (c) Melis, K.; De Vois, D.;
Jacobs, P.; Verpoort, F. J. Mol. Catal. A: Chem. 2001,
69, 47–56; (d) Mayr, M.; Mayr, B.; Buchmeiser, M.
flask was gently agitated at rt for 24 h. The resin was
then washed with CH Cl (1 mL) and the cycle of reac-
2
2
2
tion and washing was continued a further three times.
From this point, all manipulations were carried out in
air with reagent-grade CH Cl . The polymer was
1
2
2
R. Angew. Chem., Int. Ed. 2001, 40, 3839–3842.
washed with CH Cl2 until the filtrate was clear (4×1
2
5
. (a) Ahmed, M.; Barrett, A. G. M.; Braddock, D. C.;
Cramp, S. M.; Procopiou, P. A. Tetrahedron Lett.
mL) affording 7 as dark green beads, showing loading
of 0.22 mmol Ru/g (ICP–MS analysis). Samples of
resin 7 (loadings of 0.22–0.35 mmol/g) did not lose
activity after 3 months of storage in air at rt.
General procedure for ICP–MS determination of Ru. A
solution of TBAF (0.5 mL, 1 M in THF) was added to
the resin 7 (20 mg). The mixture was stirred at rt for 2
h. The resin was filtered and washed with THF (4×2
mL) and MeOH (2×2 mL). The combined filtrate was
analyzed by ICP–MS using standard procedure.
1
999, 40, 8657–8662; (b) Ahmed, M.; Arnauld, T.; Bar-
rett, A. G. M.; Braddock, D. C.; Procopiou, P. A.
Synlett 2000, 1007–1009; (c) Jafarpour, L.; Nolan, S. P.
Org. Lett. 2000, 2, 4075–4078.
. (a) Kingsbury, J. S.; Harrity, J. P. A.; Bonitatebus, P.
J.; Hoveyda, A. H. J. Am. Chem. Soc. 1999, 121, 791–
6
7
99; (b) Garber, S. B.; Kingsbury, J. S.; Gray, B. L.;
Hoveyda, A. H. J. Am. Chem. Soc. 2000, 122, 8168–
179.
8
12. General procedure for metathesis utilizing 7. The sub-
strate 9a–i (0.1 mmol) was dissolved in CH Cl (5 mL)
7
. (a) 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,
2
2
and added to a solid-phase synthesis flask charged with
resin 7 (2.5–5 mol%). The suspension was gently agi-
tated at rt or 45°C. The product 10a–j was obtained as
a colorless oil or solid after filtration and concentra-
tion. The products were identified by GC–MS compari-
4
3
251–4256; (b) Yao, Q. Angew. Chem., Int. Ed. 2000,
9, 3896–3898; (c) Dowden, J.; Savovic, J. Chem. Com-
mun. 2001, 37–38; (d) Randl, L.; Buschmann, N.; Con-
non, S. J.; Blechert, S. Synlett 2001, 1547–1550; (e)
Connon, S. J.; Blechert, S. Bioorg. Med. Chem. Lett.
1
son with authentic samples and H NMR analysis.
Selected data for 10g: colorless oil, purity ]98% (GC–
2
002, 12, 1873–1876.
MS analysis, HP5972A MSD, column HP-5); Ru-con-
8
. (a) PS-DES is available from Argonaut Technologies
and from Aldrich Chemical Co; (b) For a general refer-
ence, see: Hu, Y.; Porco, J. A., Jr.; Labadie, J. W.;
tent 0.07 wt% (ICP–MS analysis, Perkin–Elmer Elan
1
6100DRC); R 0.20 (c-Hexane); H NMR (500 MHz,
f
CD Cl , ppm): 0.066, 0.069 (2s, 6H), 0.88, 0.89 (2d,
2
2

K. Grela et al. / Tetrahedron Letters 43 (2002) 9055–9059
H, J=6.8 Hz), 1.13 (s, 3H), 1.15–1.28 (m, 2H), 1.41–
9059
6
1
1
5
.61 (m, 5H), 2.25 (dd, 1H, J=8.0, 14.0 Hz), 2.37 (dd,
H, J=8.0, 14.0 Hz), 5.57 (dtt, 1H, J=8.0, 7.0, 1.0 Hz),
13
.91 (dt, 1H, J=7.0, 10.0 Hz); C NMR (125 MHz,
CD Cl , ppm): 0.97, 18.7, 22.8, 22.9, 27.8, 29.0, 33.7,
2
2
−
1
4
2
7
1
0.1, 41.4, 53.4, 96.5, 125.9, 129.9; IR (film, cm ) 3023,
957, 2935, 2871, 1635, 1465, 1372, 1250, 1066, 1025, 840,
51; MS (EI): 226 (4, M ), 211 (5), 183 (40), 171 (21),
55 (47), 142 (18), 129 (57), 116 (9), 113 (14), 97 (31), 75
+
’
(
100), 59 (6); HRMS (EI) C H OSi 226.1753. Found:
13 26
2
26.1754.
13. Homoallylic alcohols 11g and 11j can be conveniently
obtained, using poly(ethylene)-supported activated zinc
(
12), which has been developed in our laboratory:
M a˛ kosza, M.; Nieczypor, P.; Grela, K. Tetrahedron 1998,
4, 10827–10836.
5