Immobilisation of the Grubbs III olefin metathesis catalyst with polyvinyl pyridine (PVP)

Article abstract of DOI:10.1055/s-2005-918958

A new concept for immobilising Grubbs III catalyst by direct coordination of ruthenium to poly vinyl pyridine (PVP) is presented. PVP was prepared by precipitation polymerisation, which led to small bead sizes (0.2-2 μm) and large surface areas. Compared

Full text of DOI:10.1055/s-2005-918958

2
948
LETTER
Immobilisation of the Grubbs III Olefin Metathesis Catalyst with Polyvinyl
Pyridine (PVP)
a
b
c
a
I
K
mmobilisationof
l
the Gr
u
a
bbs III
O
le
a
fin Metathe
s
sis
C
atalyst Mennecke, Karol Grela, Ulrich Kunz, Andreas Kirschning*
a
Institut für Organische Chemie, Universität Hannover, Schneiderberg 1b, 30167 Hannover, Germany
E-mail: andreas.kirschning@oci.uni-hannover.de
b
c
Institute of Organic Chemistry, Polish Academy of Science, Kasprzaka 44/52, 01-224 Warsaw, Poland
Institut für Chemische Verfahrenstechnik, Technische Universität Clausthal, Leibnizstr. 17, 38678 Clausthal-Zellerfeld, Germany
Received 4 September 2005
6
return mechanism. Recently, various Hoveyda–Grubbs
carbenes were attached to different resins or soluble sup-
ports preferentially via the 2-alkoxy-benzylidene frag-
Abstract: A new concept for immobilising Grubbs III catalyst by
direct coordination of ruthenium to polyvinyl pyridine (PVP) is pre-
sented. PVP was prepared by precipitation polymerisation, which
led to small bead sizes (0.2–2 mm) and large surface areas. Com- ment.7
pared to commercial resins, this phase showed superior properties
However, for practicability reasons reversible attachment
when employed in model ring-closing metathesis (RCM) and in
representative RCM, enyne and CM reactions with various sub-
strates. The concept of immobilisation was also applied to Raschig
rings made from a glass polymer composite material, which can be
incorporated into devices for continuous flow processes.
8
of catalysts to a solid phase is highly desirable. The pos-
sibility of reloading the solid phase opens the door for util-
ising solid supports which have been specially designed
for the individual catalytic process without considering
their costs as much as would be relevant for covalently
bound catalysts. Indeed, this concept should be of
Key words: catalysis, immobilisation, olefin metathesis, micro-
wave assistance, Ru-catalyst, polymer support
9
particular relevance in continuous flow processes using
reactors filled with heterogeneous or immobilised homo-
geneous catalysts.10 The attachment ought to be strong
enough in order to suppress leaching of the catalyst. How-
ever, after inactivation of the catalyst it is beneficial if it
can be removed and the solid phase can be reactivated
with fresh catalyst. In fact, this strategy would particularly
gain interest in industrial applications.11
During recent years, olefin metathesis using modern
ruthenium catalysts such as Grubbs I–III (1, 2, 5) and
Hoveyda–Grubbs carbenes (3, 4, Figure 1) has become a
1
key reaction in organic synthesis.
Br
L
L
Cl
Cl
Cl
In this report we describe a straightforward procedure for
immobilisation Grubbs III by means of coordinative bind-
ing. In contrast to the concept of grafting, we pursued a
polymerisation strategy using the active species as part of
N
Cl
Ru
Ru
L
Ph
Cl
Cl
Ru
O
N
Ph
PCy3
Br
12
1, 2
3, 4
5
the monomer in order to guarantee high loading. Thus,
as polymeric material, we chose polyvinyl pyridine (PVP)
as part of a monolithic highly porous polymer/glass com-
posite material which was obtained by precipitation poly-
merisation of vinyl pyridine and divinyl benzene (DVB)
1
, 3: L- = :PCy3 2, 4, 5: L- = MesN
NMes
Figure 1 Ruthenium-based catalysts 1–5 for olefin metathesis
Cy = cyclohexyl, Mes = 2,4,6-trimethylphenyl).
(
13
as cross linker. The polymeric phase was prepared from
a heated solution (70 °C) of the monomers and AIBN as
In order to remove various ruthenium by-products from radical initiator in a nonpolar solvent (n-alkane C –C
1
4
17
the reaction mixture several protocols such as scaven- mixture). After 12 hours the precipitation of small inter-
2
a–c
2d
gers, biphasic extraction, and silica gel chromatogra- connected polymer particles (5.3 mass% degree of
phy have been proposed. Another strategy to make Ru- crosslinking) occurred. The BET surface area is low (<5
2
14,15
based olefin metathesis more economical is immobilisa- m /g).
The polymeric material consists of very small
tion of these homogeneous catalyst on a solid phase.3 particles (0.2–2 mm) compared to commercial resins (10–
Several attempts have been made to immobilise Grubbs- 50 mm). Despite the small size of the individual bead-like
type carbenes 1 and 2 on solid or soluble supports either particles the material can easily be filtered. Indeed, the op-
timised polymerisation process creates polymeric bridges
Hoveyda established catalysts 3 and 4 as remarkably ro- between these particles, which resulted in an extended,
4
via ligand L (Figure 1) or via the alkylidene moiety.
5
bust complexes promoting olefin metathesis by a release– monolithic polymeric phase (Figure 2, a and b).
Recently, Grubbs and coworkers showed that 3-bromo
pyridine can form a 2:1 complex with the Grubbs II cata-
lyst 2 to yield the active olefin metathesis catalyst 5. Ru-
SYNLETT 2005, No. 19, pp 2948–2952
Advanced online publication: 27.10.2005
0
1
.1
2
.2
0
0
5
16
DOI: 10.1055/s-2005-918958; Art ID: G28605ST
thenium complex 5 is active in many types of metathesis
reactions including challenging CM with acrylonitrile.
17
16
©
Georg Thieme Verlag Stuttgart · New York

LETTER
Immobilisation of the Grubbs III Olefin Metathesis Catalyst
2949
samples were employed in ring-closing metathesis of
malonate 7 (5 mol%, toluene, 110 °C, 4 h) and were
repeatedly used. The results of these experiments are
summarised in Scheme 2 and Figure 3.
6
a (5 mol%),
EtO2C
CO2Et
EtO2C CO2Et
toluene, 110 °C, 4 h
Figure 2 a) Bridging to neighbouring polymer particles visualised
by scattering electron microscopy (visualised by SEM). b) Morpholo-
gy of polyvinyl pyridine (PVP; by SEM).
7
8
Scheme 2
We found that the Grubbs III catalyst 5 can easily be
immobilised through ligand exchange using polyvinyl
pyridine (obtained by precipitation polymerisation,
1
8,19
Scheme 1).
The immobilisation was achieved by em-
ploying PVP in ten-fold excess (with reference to pyridine
moieties on the polymer) which resulted in complete
(
96%) immobilisation of catalyst 5 as was judged gravi-
metrically as well as by ICP-MS. The resulting immobil-
ised catalyst 6a is relatively stable towards air.
2
0
Degradation was encountered after two weeks. For com-
parison reasons, we also employed commercial polyvinyl
pyridine (from Acros) and treated it with Ru-complex 5 to
yield immobilised Ru-complex 6b.
Figure 3 Reusability of Ru-doped PVP polymer (prepared by pre-
cipitation polymerisation) treated with a) Grubbs III 5 (black), b)
Grubbs II 2 (grey) and c) Grubbs II 2 + CuCl (white) in RCM [prepa-
N
N
21
Mes
Mes
Ph
ration of cases b) and c) see text].
Cl
N
Ru
N
Cl
Obviously, the Grubbs III catalyst is the best choice for
conducting ligand exchange reaction with polymer-bound
pyridine. In terms of reusability polymer 6a behaves sim-
ilar to many covalently attached examples described in the
Br
N
Br
toluene, 25 °C, 72 h
5
4
literature although in selected cases longer living systems
4
b
have been described. After the fifth run, activity is lost
N
N
22
Mes
Mes
which can either be ascribed to lack of thermal stability
Cl
6
a (PVP by precipitation
polymerisation)
or to the inherent problem of leaching during the catalytic
cycle. Importantly, the solid phase can be reactivated by a
N
Ru
N
Ph
6b (commercial PVP)
Cl
washing protocol (1 N HCl, 1 N NaOH, H O, MeOH,
2
toluene, then addition of 5), which is an advantage over
the solid phase concepts described so far.
Br
Scheme 1 Preparation of polymer-bound Ru-complexes 6a (pow-
der) and 6b (the exact stereochemistry in the coordination sphere of
the Ru centre is unknown).
Having evaluated the coordinative immobilisation of ole-
fin metathesis catalysts to PVP we studied the applicabil-
ity of catalyst 6a in a more general sense (Table 1).21
1
9
In the case of allylethers 12 and 13 only double bond
migration to the E/Z-mixture of enol ethers occurred, a
phenomenon that has frequently encountered in olefin
metathesis chemistry.2 Snapper and coworkers showed
that the Grubbs II catalyst 2 in the presence of small
Malonate 7 served as model diene. Transformation of 7 to
cyclopentane 8 in the presence of catalyst 6a (5 mol%, tol-
uene, 110 °C, 4 h; 0.297 mmol Ru/g polymer) was quan-
titative, while polymer 6b yielded the cyclisation product
3,24
8
in only 11% under identical conditions. In addition, we
amounts of H is able to isomerise a cyclic allyl ether into
2
tested whether coordination can only be achieved with the
Grubbs III catalyst 5. Thus, PVP (10 equiv) generated by
precipitation polymerisation was treated for 72 hours with
the Grubbs II catalyst 2 (1 equiv) in toluene in the absence
the corresponding enol ether via postulated Ru–hydride
complexes.2 However, in the present case, the isomeri-
sation proceeds without the presence of any external hy-
drogen source.2 It is known that in the presence of an
additional base isomerisation of olefinic double bonds
5a
4a
5
as well as in the presence of CuCl. In both cases it was
hoped that ligand exchange with PCy occurs, in the latter
3
25b
may also proceed. Here, the additional base may come
case the addition of the copper salt should facilitate disso-
ciation of the remaining phosphane ligand. The resulting
from the vacant sites on the PVP phase.
Synlett 2005, No. 19, 2948–2952 © Thieme Stuttgart · New York

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K. Mennecke et al.
LETTER
Table 1 RCM and CM with Solid-Phase-Bound Catalyst 6a (Powder)a
Substrate
Product
Temp, time
100 °C, 5 h
Yield (%)
Ts
N
9
14
96
Ts
N
Ph
Ph
10
7
Ph
Ph
15
8
100 °C, 5 h
100 °C, 5 h
100 °C, 4 h
99
99
80
Si
Si
EtO2C CO2Et
EtO2C
CO2Et
1
1
1
2
16
6
6
2
CO2Me
CO2Me
17
18
100 °C, 7 h
98b
O
O
O
O
AcO
TfaHN
AcO
TfaHN
E/Z = 1:2
1
3
100 °C, 5 h
77c
O
O
NHTfa
NHTfa
O
O
O
O
E/Z = 1:3
a
b
c
Conditions: reactions were carried out under argon in toluene with 5 mol% of catalyst 6a.
A 50% yield in toluene at 40 °C and no conversion in CH Cl at 40 °C.
2
2
A 25% yield (E/Z = 1:3) with catalyst 2.
Exploiting Barrett’s concept of boomerang catalysts using Acknowledgment
-octene or triphenyl phosphane was tested here to im-
prove reusability of 6a but it rather gave reduced yields
1
The work was funded by the Deutsche Forschungsgemeinschaft–
Polish Academy of Sciences joint project ‘Synthetische Nutzung
von immobilisierten Ruthenium-Carben-Katalysatoren in Durch-
flussmikroreaktoren’ (436 POL 113/109/0-1) and the Fonds der
Chemischen Industrie. We thank Prof. C. Vogt and S. Gruhl (insti-
tute of inorganic chemistry, Univ. Hannover) for conducting the
ICP-MS analyses and T. Jöge and B. Oelze for expert preparative
assistance.
(
35% for 14 compared to 96%; conditions: 5 mol% 6a,
2
6
toluene, 100 °C).
In summary, we have described a new metod for the coor-
dinative immobilisation of Grubbs III olefin metathesis
catalyst to polyvinyl pyridine (PVP) with coordinative
properties. The solid-phase-bound catalyst shows very
good chemical reactivity and good recyclability and im-
portantly can easily be reactivated with fresh catalyst,
which opens the possibility of using catalysts of type 6a
under continuous flow conditions in flowthrough reactors.
References
(1) General reviews: (a) Schrock, R. R.; Hoveyda, A. H. Angew.
Chem. Int. Ed. 2003, 42, 4592. (b) Trnka, T. M.; Grubbs, R.
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Kreye, P. Org. Process Res. Dev. 2005, 9, 513. For
Current work focuses on altered, non-covalently attached
catalysts which show a longer life time when repeatedly
used and which can be employed in multistep applications
under continuous flow conditions.
approaches where ruthenium impurities are removed by
Synlett 2005, No. 19, 2948–2952 © Thieme Stuttgart · New York

LETTER
Immobilisation of the Grubbs III Olefin Metathesis Catalyst
2951
addition of various scavengers, see: (b) Maynard, H. D.;
Grubbs, R. H. Tetrahedron Lett. 2000, 40, 4137.
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(
1259. (d) Ahn, Y. M.; Yang, K.; Georg, G. I. Org. Lett.
2
001, 3, 1411. (e) For a recent example of use of biphasic
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(
3) Reviews on polymer-bound reagents and catalysts:
(
a) Solodenko, W.; Frenzel, T.; Kirschning, A. In Polymeric
Materials in Organic Synthesis and Catalysis; Buchmeiser,
M. R., Ed.; Wiley-VCH: Weinheim, 2003, 201–240.
(15) Preparation of Polyvinyl Pyridine Phase by Precipitation
Polymerisation.
(
b) Kirschning, A.; Monenschein, H.; Wittenberg, R. Angew.
Chem. Int. Ed. 2001, 40, 650. (c) Ley, S. V.; Baxendale, I.
R.; Bream, R. N.; Jackson, P. S.; Leach, A. G.; Longbottom,
D. A.; Nesi, M.; Scott, J. S.; Storer, R. I.; Taylor, S. J. J.
Chem. Soc., Perkin Trans. 1 2000, 3815.
First, a mixture of 4-vinylpyridine (43.20 g, 410.8 mmol)
and divinylbenzene (3.86 g; purity 65% besides ethyl
benzene) was prepared. This mixture was filled up with an
n-alkane (C14–C17 fraction) to a total volume of 300 mL,
AIBN (327 mg, 2 mmol) was added and the temperature was
raised to 70 °C. The reaction mixture is kept at this
temperature for 24 h. Then the solid material formed was
(
(
(
(
4) Reviews: (a) Kingsbury, J. S.; Hoveyda, A. H. In Polymeric
Materials in Organic Synthesis and Catalysis; Buchmeiser,
M. R., Ed.; Wiley-VCH: Weinheim, 2003, 467.
(
b) Buchmeiser, M. R. New J. Chem. 2004, 28, 549.
filtered, rinsed with CHCl and further purified by extraction
3
5) (a) Kingsbury, J. S.; Harrity, J. P. A.; Bonitatebus, P. A.;
in a Soxhlet extractor with CHCl and finally dried under
3
Hoveyda, A. H. J. Am. Chem. Soc. 1999, 121, 791.
reduced pressure to yield PVP (4.85 mmol/g capacity).
(16) Love, J. A.; Morgan, J. P.; Truka, T. M.; Grubbs, R. H.
Angew. Chem. Int. Ed. 2002, 41, 4035.
(b) Garber, S. B.; Kingsbury, J. S.; Gray, B. L.; Hoveyda, A.
H. J. Am. Chem. Soc. 2000, 122, 8168.
6) (a) Hoveyda, A. H.; Gillingham, D. G.; Van Veldhuizen, J.
J.; Kataoka, O.; Garber, S. B.; Kingsbury, J. S.; Harrity, J. P.
A. Org. Biomol. Chem. 2004, 2, 1. (b) Kingsbury, J. S.;
Hoveyda, A. H. J. Am. Chem. Soc. 2005, 127, 4510.
7) For syntheses of supported variants of 3, 4, see inter alia:
(17) For selected applications of 5, see inter alia: (a) Kanemitsu,
T.; Seeberger, P. H. Org. Lett. 2003, 5, 4541. (b) Rai, A. N.;
Basu, A. Org. Lett. 2004, 6, 2861. (c) Aggarwal, V. K.;
Astle, C. J.; Rogers-Evans, M. Org. Lett. 2004, 6, 1469.
(d) Kulkarni, A. A.; Diver, S. T. Org. Lett. 2003, 5, 3463.
(e) Giessert, A. J.; Brazis, N. J.; Diver, S. T. Org. Lett. 2003,
5, 3819. (f) Chen, B.; Sleima, H. F. Macromolecules 2004,
37, 5866. (g) Rezvani, A.; Bazzi, H. S.; Chen, B.;
Rakotondradany, F.; Sleiman, H. F. Inorg. Chem. 2004, 43,
5112. (h) Schuehler, D. E.; Williams, J. E.; Sponsler, M. B.
Macromolecules 2004, 37, 6255. (i) Parrish, B.; Emrick, T.
Macromolecules 2004, 37, 5863. (j) Hansen, E. C.; Lee, D.
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(18) Indeed, this idea has been shown to be powerful for the
immobilisation of enzymes using nickel NTA-linkers on
sepharose for coordinatively trapping enzymes tagged with
a His-tag.
(19) Preparation of Functionalised Polyvinyl Pyridines 6a
and 6b.
(
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, 4251. (b) Grela, K.;
Tryznowski, M.; Bieniek, M. Tetrahedron Lett. 2002, 43,
9
055. (c) Connon, S. J.; Dunne, A. M.; Blechert, S. Angew.
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2
004, 10, 5761. (k) Krause, J. O.; Nuyken, O.; Wurst, K.;
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A suspension of ruthenium catalyst 5 (140 mg, 0.16 mmol;
prepared according to ref. 16) and PVP (6a: 400 mg, 1.84
mmol; 6b: 373 mg, purchased from Acros) in toluene (3 mL)
was shaken under argon at r.t. for 72 h. The polymer was
filtered and washed with five portions of toluene (2 mL) to
yield functionalised polymer 6 (polymer obtained by
precipitation polymerisation: 510 mg, 0.15 mmol ruthenium;
96% and polymer from Acros: 477 mg, 0.09 mmol
ruthenium; 80%).
(
2
(
2
(
8) For an excellent review on strategies of non-covalent
immobilisation of catalysts refer to: Horn, J.; Michalek, F.;
Tzschucke, C. C.; Bannwarth, W. Top. Curr. Chem. 2004,
(20) In comparison, treatment of catalyst 5 with pyridine yielded
a new material which from mass spectrometric analysis does
not contain bromine but which turned out to be highly
unstable and quickly degraded under nitrogen even at –20 °C.
(21) General Procedure for Metathesis Reactions with
Polymer 6a.
2
42, 43.
(9) (a) Kirschning, A.; Jas, G. Top. Curr. Chem. 2004, 242, 209.
(b) Jas, G.; Kirschning, A. Chem.–Eur. J. 2003, 9, 5708.
(
c) Fletcher, P. D. I.; Haswell, S. J.; Pombo-Villar, E.;
Warrington, B. H.; Watts, P.; Wong, S. Y.; Zhang, X.
Tetrahedron 2002, 58, 4735. (d) Pombo-Villar, E.;
Warrington, B. H.; Watts, P.; Wong, S. Y.; Zhang, X.
Tetrahedron 2002, 58, 4735.
To a suspension of polymer 6a (5 mol%) in dry toluene (0.02
M, 10 mL) under nitrogen was added the substrate (0.25
mmol). The resulting mixture was shaken for 4–7 h at
100 °C. At the end of the reaction (GC monitoring) the
polymer was filtered off and washed with several portions of
CH Cl . The solution was concentrated under reduced
(
10) Kunz, U.; Leue, S.; Stuhlmann, F.; Sourkouni-Argirusi, G.;
Wen, H.; Jas, G.; Kirschning, A. Eur. J. Org. Chem. 2004,
3
601.
2
2
pressure and in most cases the crude material was
Synlett 2005, No. 19, 2948–2952 © Thieme Stuttgart · New York

2
952
K. Mennecke et al.
LETTER
sufficiently pure. In order to obtain analytically pure samples
the crude material was purified by flash column
(23) Review: Uma, R.; Crevisy, C.; Gree, R. Chem. Rev. 2003,
103, 27.
chromatography (mixture of PE–EtOAc as eluent).
(24) (a) Chen, G.-w.; Kirschning, A. Chem.–Eur. J. 2002, 8,
2717. (b) Arisawa, M.; Terada, Y.; Nakagawa, M.; Nishida,
A. Angew. Chem. 2002, 114, 4926. (c) Gurjar, M. K.;
Yakambram, P. Tetrahedron Lett. 2001, 42, 3633.
(d) Braddock, D. C.; Wildsmith, A. J. Tetrahedron Lett.
2001, 42, 3239. (e) Hoye, T. R.; Zhao, H. Org. Lett. 1999, 1,
1123.
(25) (a) Sutton, E.; Seigal, B. A.; Finnegan, D. F.; Snapper, M. L.
J. Am. Chem. Soc. 2002, 124, 13390. (b) Schmidt, B. Chem.
Commun. 2004, 742.
(26) (a) Ahmed, M.; Arnauld, T.; Barrett, A. G. M.; Braddock, D.
C.; Procopiou, P. A. Synlett 2000, 1007. (b) Reaction was
carried according to the general procedure given for the
metathesis reactions with polymer 6a. Additionally, 1-
octene (5 mol%) was added to the reaction mixture to yield
2,5-dihydro-1-tosyl-1H-pyrole(15) in 35% instead of 96%
without 1-octene.
Studies on the Stability of Polymer-Bound Catalysts 6a.
Repeated reactions were carried out according to the general
procedure given above by dissolving diallyl malonate 7 (55
mL, 0.228 mmol) in toluene (3 mL). After each reaction the
polymer was filtered, washed with five portions of toluene (2
mL), dried under vacuum and reused for the next run. The
crude products were isolated quantitatively; the yield of the
RCM product 8 was determined after purification by flash
st
column chromatography: 1 run (2 h; 43.5 mg, 0.2 mmol;
nd
rd
8
3
2
9%); 2 run (2 h; 31.7 mg, 0.14 mmol; 65%); 3 run (2 h;
th
0.5 mg, 0.14 mmol; 64%); 4 run (2 h; 13.8 mg, 60 mmol;
th
9%); 5 run (6 h; 4.8 mg, 22 mmol; 10%).
(
22) Recently, Grubbs and coworkers were able to isolate a
ruthenium–hydrido complex, formed as a thermal
degradation product of catalyst 2 which could be made
responsible for double-bond migration: Hong, S. H.; Day,
M. W.; Grubbs, R. H. J. Am. Chem. Soc. 2004, 126, 7414.
Synlett 2005, No. 19, 2948–2952 © Thieme Stuttgart · New York