Supported Ru olefin metathesis catalysts: Via a thiolate tether

Article abstract of DOI:10.1039/c8dt04592e

Thiolate-coordinated ruthenium alkylidene complexes can give high Z-selectivity and stereoretentivity in olefin metathesis. To investigate their applicability as heterogeneous catalysts, we have successfully developed a methodology to easily immobilize prototype ruthenium alkylidenes onto hybrid mesostructured silica via a thiolate tether. In contrast, the preparation of the corresponding molecular complexes appeared very challenging in solution. These prototype supported complexes contain small thiolates but still, they are slightly more Z-selective than their molecular analogues. These results open the door to more active and selective heterogeneous catalysts by supporting more advanced thiolate Ru-complexes.

Full text of DOI:10.1039/c8dt04592e

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DOI: 10.1039/C8DT04592E
Journal Name
COMMUNICATION
Supported Ru Olefin Metathesis Catalysts via a Thiolate Tether
a
a
a
a
b
Marc Renom-Carrasco, Philipp Mania, Reine Sayah, Laurent Veyre, Giovanni Occhipinti, David
Received 00th January 20xx,
Accepted 00th January 20xx
c
c
b
a
Gajan, Anne Lesage, Vidar R. Jensen, Chloé Thieuleux*
DOI: 10.1039/x0xx00000x
www.rsc.org/
Thiolate-coordinated ruthenium alkylidene complexes can give
high Z-selectivity and stereoretentivity in olefin metathesis. To
investigate their applicability as heterogeneous catalysts, we
have successfully developped a methodology to easily immobilize
prototype ruthenium alkylidenes onto hybrid mesostructured
silica via a thiolate tether. In contrast, the preparation of the
corresponding molecular complexes appeared very challenging in
solution. These prototype supported complexes contain small
thiolates but still, they are slightly more Z-selective than their
molecular analogues. These results open the door to more active
and selective heterogeneous catalysts by supporting more
advanced thiolate Ru-complexes.
MesN
NMes
Cl
MesN
NMes
Cl
Ru
Ru
Ph
S
Ar
S
S
O
Py
Ph
Ar
iPr
Ph
1
Ar
2
Jensen-Occhipinti (2013)
Jensen-Occhipinti (2017)
Ar = 3,5-dimethylphenyl
MesN
O
NMes
Ph
MesN
NMes
S
Ru
S
Ru
S
O
S
B
Cl
[
BCl4]
Cl
Olefin metathesis is a very powerful reaction for the
construction of carbon-carbon bonds in organic chemistry.
3
4
1
Stephan (2013)
Hoveyda (2013)
However, the implementation of olefin metathesis in
Figure 1. Reported homogeneous thiolate Ru olefin metathesis catalysts.
pharmaceutical and specialty-chemicals manufacturing is still
2
far from reaching its full potential. Some of the drawbacks compounds display reasonable activities, and some of them
that have hampered industrial uptake may be overcome by are Z-selective (1 and 2) or highly stereoretentive (4).
8
Our
3
immobilizing
molecular
complexes.
For
example, group has already reported the anchoring of olefin metathesis
heterogenization can: i) prevent some deactivation pathways, Ru complexes onto silica materials through the NHC ligand.
9
ii) increase the stability of the intermediates, iii) ease the Besides obtaining highly active Ru olefin metathesis catalysts,
separation of the catalysts from the products, and iv) facilitate we demonstrated the beneficial interaction and stabilization of
recycling of the catalyst. The anchoring of Ru olefin metathesis the Ru complex with the silica surface.10 Herein, we report the
catalysts on solid supports has been accomplished through immobilization of Ru-olefin metathesis catalysts on
3
three different parts of the catalyst: a) the alkylidene moiety, mesostructured silica via an anionic exchange with a thiolate-
b) a neutral ligand or c) an anionic ligand. The few reports on supported ligand.
the latter strategy exclusively employ carboxylate anions as
replacement for chloride. However, in recent years, several approach commonly employed in our group.
The supported catalysts were prepared via a two-step
4
9,11
First, we
homogeneous Ru-olefin metathesis catalyst containing prepare a hybrid mesostructured silica matrix containing
5
,6,7
thiolate ligands have been reported (Figure 1).
These homogeneously distributed thiolate tethers on its pore-
surface. Then, a selective surface organometallic reaction
between a molecular organometallic complex and the surface
a
University of Lyon, Institute of Chemistry of Lyon, Laboratory C2P2 UMR 5265-
CNRS-University Lyon 1-CPE Lyon, 43 Bd du 11 Novembre 1918, 69616 Villeurbanne
1
2
ligands gives the immobilized complexes.
(
France)*E-mail: thieuleux@cpe.fr
For this study, we developed two materials differing by the
b
c
Department of Chemistry, University of Bergen, N-5007 Bergen (Norway).
Institut des Sciences Analytiques UMR 5280 (CNRS/Université Lyon 1/ENS Lyon),
nature of the silica-supported thiols (Scheme 1): material Mat-
13
Université de Lyon, Centre de RMN à Très Hauts Champs, 69100 Villeurbanne
France)
Electronic Supplementary Information (ESI) available: experimental methods,
NMR,
PrSH contains a flexible mercaptopropyl linker and Mat-PhSH
(
a more rigid and bulkier mercaptophenyl group. These hybrid
N
2
adsorption-desorption isotherms, elemental analysis. See silica materials were prepared by sol-gel process using a
DOI: 10.1039/x0xx00000x
14
templating route. This route involved co-hydrolysis and co-
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condensation of tetraethoxysilane and the corresponding of a toluene solution of HG-II to the thiolatVeie-wcAorntictlae iOnnilninge
thiol-containing organo-triethoxysilane precursor in the material under stirring. The S/Ru ratios DoOfI:th10e.10fi3n9a/lC8sDoTli0d4s59(b2Ey
presence of Pluronic® P-123 as the structure-directing agent. elemental analysis) showed a 50% grafting for Mat-A
This method offers control of the loading and distribution (containing the propanethiolate linker) and a 74% grafting for
homogeneity of the organic groups along the silica pore Mat-B (containing the phenylthiolate linker). These grafting
channels. Furthermore, to be able to perform the catalyst degrees are much higher than the 20% reported in literature
immobilization, the surface had to be passivated, first by precedents when grafting Ru olefin metathesis catalysts
9
13
hydrolyzing all remaining surface ethoxy- groups into silanols through the NHC moiety. C SS NMR showed the appearance
and then converting those silanol groups into of signals in the aliphatic region (δ = 10-20 ppm),
trimethylsiloxanes. However, in this latter step, the thiol corresponding to methyl groups present in HG-II, and in the
groups were also silylated, requiring an extra step to aromatic region (δ = 120-140 ppm), attributed to aromatic
selectively deprotect them. The intermediates were carbon atoms of the mesityl and the alkylidene moieties (see
characterized by 1H MAS SS NMR, C CP-MAS SS NMR,
13
1
H and C spectra in Supplementary Information). As expected
13
1
3
elemental analysis, and nitrogen adsorption-desorption from the fact that C labels were not used, the carbenic signal
analyses (see Supplementary Information). Materials Mat- was not observed, even using cutting edge NMR techniques
9
,11d
PrSH and Mat-PhSH displayed the expected physical features like dynamic nuclear polarization.
This can be explained by
1
5
of a SBA-15 type mesostructured silica: a BET specific surface the inherent large CSA for this type of complexes and
area of 593 and 574 m g and a mean pore diameter (DpBJH) of absence of close protons around the carbenic carbon.
and 8 nm, respectively. The 13C SS NMR spectra exhibited a
Molecular analogues of supported stereogenic-at-metal
2
-1
7
dominating signal at δ ≈ 0 ppm, corresponding to the complexes Mat-A and Mat-B in which only a single chloride
trimethylsilyl groups on the surface and the expected peaks has been exchanged with the corresponding thiolate, were
from the propyl chain in Mat-PrSH (δ = 28 [broad signal] and very challenging to obtain (Figure 2). Reaction of HG-II with a
1
1
1 ppm) and the aromatic moiety in Mat-PhSH (δ = 133 and small excess of propanethiolate (for A) or phenylthiolate (for
26 ppm).
B) renders the monosubstitued complex within a mixture of
complexes (starting material, bis-thiolate and others). Isolation
and purification of these complexes turned out to be
particularly challenging because they decompose on silica gel
and co-precipitate along with other complexes. However, a
few milligrams of the pure complexes could be obtained after
several time-consuming recrystallizations (see ESI). In this case,
the advantage of supporting a catalyst becomes clear, since it
is not possible to form the bis-substituted complexes and the
remaining unreacted material can be easily washed away, thus
giving much higher yields.
O
O
O
SH
O
O
O
Si
Si
Si
O
OZ
O
OTMS
O
OTMS
or
a
c
d
SH
Si(OEt)3
O
O
O
Si
T
SH
Si
T
STMS
Si
T
SH
O
O
O
O
O
O
Si(OEt)3
Z = H or Et
Z = H
Mat-PrSH: T = (CH2)3
Mat-PhSH: T = p-Ph
b
O
O
O
O
OTMS
MesN
Si
Si
O
OTMS
O
e
f
NMes
Cl
MesN
S
NMes
Cl
MesN
S
NMes
Cl
O
O
Ru
Si
T
S
Si
T
S
O
O
Ru
Ru
K
O
O
O
iPr
O
O
Mat-A: T = (CH2)3
Mat-B: T = p-Ph
iPr
iPr
A
B
5
% yield
32% yield
Reaction conditions: a) 40 equiv. Si(OEt)4, pH = 1.5, Pluronic 123, NaF, 45 °C, 3
days; b) HCl (2 M), 45 °C, 2 h; c) TMSBr, Et3N, toluene, 25 °C, 24 h; d) K2CO3,
MeOH, 25 °C, 16 h; e) KHMDS, toluene, 25 °C, 2 h; f) HG-II, toluene, 25 °C, 20 h.
Figure 2. Isolated and characterized molecular analogues A and B.
Scheme 1. Synthesis of materials Mat-PrSH and Mat-PhSH and catalyst immobilization.
To investigate the nature of the surface Ru-NHC active
sites, we studied the stereoselectivity of Mat-A and Mat-B in
the self-metathesis of methyl oleate. This reaction gives four
products: E/Z-9-octadecene (P1’) and dimethyl E/Z-9-
octadecene-1,18-dioate (P1). The cross metathesis between
the two products leads back to the formation of methyl oleate
In order to incorporate the Ru complex, the surface thiol
group was first deprotonated with a strong base and then
reacted with the Ru precursor for ligand anionic exchange
(
Scheme 1). Potassium hexamethyldisilazide (KHMDS) was
9
chosen for its compatibility with silica materials. However,
treatment of Hoveyda-Grubbs 2 generation (HG-II) with one
(MO, Z-S1) and methyl elaidate (ME, E-S1). The initial
nd
selectivity (i.e. the initial E/Z ratio) of a Ru-olefin metathesis
complex can be considered as a finger-print of the catalyst,
and depends on the metal, its coordination sphere, and the
equivalent of KHMDS in C
6
D
6
showed a slow decomposition of
1
the complex by H NMR. Thus, to avoid base-induced
decomposition of the Ru precursor, the thiolate-containing
material was thoroughly washed with toluene to remove any
KHMDS excess before adding the Ru precursor. The Ru
anchoring was carried out under inert atmosphere by addition
9
,16
stability of the metallacyclobutane intermediate.
For that
reason, by plotting the E/Z ratios of the diester product versus
the E/Z ratios of the reactants (ME/MO), we can extrapolate
2
| J. Name., 2012, 00, 1-3
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the initial E/Z values (at 0% conversion) of a given catalyst flexible propyl linker.10 Similarly, the short and flexViiebwleArltiicnlekOenrlionef
(
Table 1 and Supplementary Information). The results for Mat-A might explain its lower E/Z ratiDoO(I:a1t0.010%39/cCo8nDvTe0r4s5io92nE)
different molecular complexes and supported catalysts show compared to Mat-B, HG-II, A and B. These results suggest that
that all initial E/Z ratios are around 2.0 - 2.5 (Table 1), which the flexibility of the organic tether influences the catalytic
indicates that all complexes, including those of Mat-A and properties of the resulting supported complex, generating a
Mat-B, are truly Ru-NHC complexes, and that no degradation surface active site different from that of the molecular
happened during immobilization.
complex in solution or from a supported analogue complex
isolated from the silica surface by a more rigid tether.
Table
1.
Stereoselectivities
of
different
catalysts
in
the
self-metathesis of methyl oleate.
Table 2. Homometathesis of 1-hexene (S2) and 4-phenyl-1-butene (S3).
7
7
7
[
Ru]
P1'
Cat. (0.01 mol%)
Neat
+
CO2Me
7
7
CO2Me
MeO2C
7
S2
20 °C, 2h
P2
S1
P1
Cat.
HG-II
A
Mat-A
B
Isom. (%)a,b Yield P2 (%)b
TON to P2
3640
30
460
1460
250
E/Z of P2b
5.3
E/Z of P1
at 0% conv
2.7
2.9
0.8
1.0
1.2
36.4
0.3
4.6
14.6
2.5
#
Catalysta
n.d.
2.7
2.2
1.4
1
2
3
4
5
6
7
8
9
5
Mat-5
6
Mat-6
7
Mat-7
HG-II
A
Mat-A
B
2.1b
1.8b
2.0b
2.0b
2.0c
2.0c
2.5b
2.6
2.1
2.8
2.5
Mat-B
Cat. (0.01 mol%)
Ph
Ph
Ph
Neat
50 °C, 2h
S3
P3
Cat.
HG-II
A
Mat-A
B
Isom. (%)a,b Yield P3 (%)b
TON to P3
4310
20
100
1280
80
E/Z of P3b
3.8
15.1
60.0
3.3
8.9
1.7
43.1
0.2
1.0
12.8
0.8
1
1
0
1
n.d.
1.8
1.3
0.9
Mat-B
a
See below the corresponding structure of the Ru catalysts. b Values
c
Mat-B
from Ref. 9. Values from Ref. 10.
(iPrO)3Si
aIsomerization of S + metathesis of the isomers. bCalculated by GC using
i
Si(O Pr)3
dodecane as internal standard. n.d. = not determined due to the low yield.
MesN
Cl
NMes
Cl
N
NMes
Cl
N
NMes
Cl
Ru
Ru
Ru
Catalysts Mat-A and Mat-B were further tested in the
homometathesis of two terminal olefins (Table 2): 1-hexene
Cl
Cl
O
Ph
Ph
PCy3
PCy3
iPr
5
6
HG-II
(
S2) and 4-phenyl-1-butene (S3). When comparing the two
Ph
N
N
Cl
supported catalysts, Mat-A displayed a better activity than
Mat-B with both substrates, while Mat-B gave a lower E/Z
ratio. The higher Z-selectivity can be explained by the higher
Ru
Ph
N
Cl
i
Ph
Si(O Pr)3
PCy3
Ph
PCy3
Cl
7
Ru
5
N
bulkiness around the Ru in Mat-B compared to Mat-A. For
Cl
NMes
Cl
molecular analogues, the same trend was observed when
comparing HG-II and B, where the latter was found less active
but more Z-selective than HG-II. Homogeneous complex A
proved to be very unstable under the reaction conditions,
leading to big amounts of isomerization and limited metathesis
production. However, it is remarkable the stabilization induced
by anchoring the Ru complex onto silica in Mat-A. When
comparing homogeneous catalysts to immobilized catalysts
N
NMes
Ph
N
Ru
Cl
Ru
Cl
PCy3
Ph
OTMS
Cl
OTMS
OTMS
O
O
O
Si
O
O
O
Si
O
O
O
Si
O
O
O
Si
Si
O
Si
Si
O
Si
Si
O
O
O
O
O
Si
O
Si
Si
O
Mat-5
Mat-6
Mat-7
For sake of comparison, the E/Z ratios observed for
relevant literature precedents describing silica-supported Ru-
NHC complexes via different organic tethers (a flexible propyl
chain for Mat-5, a semi-rigid benzyl group for Mat-6 and a
rigid phenyl-mesityl unit for Mat-7) are shown in table 2. While
Mat-5 has a lower E/Z ratio than its homogeneous equivalent
(HG-II and B vs Mat-A and Mat-B), the same trend was
observed: the increased steric bulk around the Ru center
generated by the silica surface for the supported sites leads to
higher Z-selectivities, but a decrease in productivity (TOF = 10
3
-1
2
-1
h
vs 10 h , after 2 h), which may be partly related to
1
7
initiation problems. Unfortunately, these materials were not
reusable and deactivated with time, probably via
intramolecular pathways, as suggested in the literature.18
(
5), this tendency is not observed for Mat-6 and Mat-7 when
compared to their molecular analogues (6 and 7). This
difference was proven to arise from interactions of the active
site with the silica surface in Mat-5, made possible by the
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Finally, we studied the possibility of HG-II physisorption on
silica during the immobilization of the Ru complex. To do so,
the immobilization of HG-II on Mat-PhSH was carried out
without addition of KHMDS. The resulting material was tested
in the homometathesis of 1-hexene in the conditions from
Table 2. After 7 hours, a poor yield (0.1% for P2) demonstrated
that the active complexes are in fact properly anchored.
In summary, we have developed an effective methodology
for the immobilization of Ru-olefin metathesis catalysts via a
single anionic exchange with a silica-supported thiolate ligand.
This experimental procedure gave new supported stereogenic-
at-metal Ru-NHC complexes for which the molecular
analogues are very challenging to prepare and isolate.
Furthermore, a great enhance of stability was observed when
immobilizing catalyst A. In the metathesis of terminal alkenes,
increased Z-selectivity was observed when increasing the size
of the thiolate ligand and due to possible interactions of the Ru
active site with the silica surface. This new immobilization
protocol opens the door to support other ruthenium
alkylidene catalysts bearing thiolate ligands, as for example
highly Z-selective or stereoretentive olefin metathesis
catalysts, like 1, 2 or 4. We are currently exploring this
possibility.
View Article Online
DOI: 10.1039/C8DT04592E
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The authors gratefully acknowledge financial support from
the Research Council of Norway via the GASSMAKS program
(grant number 208335), and via the Norwegian NMR Platform,
NNP (226244). Dr. Bjarte Holmelid is thanked for assistance
+
with the HRMS (ESI ). The authors would also like to 10 M. K. Samantaray, J. Alauzun, D. Gajan, S. Kavitake, A.
acknowledge Prof. Christophe Copéret for fruitful discussions
and Dr. David Gajan for his work in the synthesis of
mercaptopropyl materials and for the DNP SS NMR.
Mehdi, L. Veyre, M. Lelli, A. Lesage, L.Emsley, C. Copéret
and C. Thieuleux, J. Am. Chem. Soc., 2013, 135, 3193–3199.
11 a) M. P. Conley, C. Copéret and C. Thieuleux, ACS Catal.,
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014, 4, 1458–1469; b) T. K. Maishal, J. Alauzun, J.-M.
Basset, C. Copéret, R. J. P. Corriu, E. Jeanneau, A. Mehdi, C.
Reyé, L. Veyre and C. Thieuleux, Angew. Chem. Int. Ed.,
2008, 47, 8654–8656; c) M. P. Conley, R. M. Drost, M.
Baffert, D. Gajan, C. Elsevier, W. T. Franks, H. Oschkinat, L.
Veyre, A. Zagdoun, A. Rossini, M. Lelli, A. Lesage, G.
Casano, O. Ouari, P. Tordo, L. Emsley, C. Copéret and C.
Thieuleux, Chem. Eur. J., 2013, 19, 12234–12238; d) I.
Romanenko, D. Gajan, R. Sayah, D. Crozet, E. Jeanneau, C.
Lucas, L. Leroux, L. Veyre, A. Lesage, L. Emsley, E. Lacôte
and C. Thieuleux, Angew. Chem. Int. Ed., 2015, 54, 12937–
12941.
Conflicts of interest
There are no conflicts to declare.
Notes and references
1
2
3
Handbook of Metathesis, Vol. 1, ed. R.H. Grubbs, Wiley-
VCH, Weinheim, 2003.
C. S. Higman, J. A. M. Lummiss and D. E. Fogg, Angew.
Chem. Int. Ed., 2016, 55, 3552−3565.
a) M. Hasib-ur-Rahman, S. Hamoudi and K. Belkacemi, Can. 12 a) C. Copéret, M. Chabanas, R. Petroff Saint-Arroman and
J. Chem. Eng., 2017, 95, 1850-1863; b) J. Suriboot, H. S.
Bazzi and D. E. Bergbreiter, Polymers, 2016, 8, 140-162; c)
M. R. Buchmeiser, Immobilization of olefin metathesis
catalysts, in Olefin Metathesis: Theory and Practice, ed.
Grela, K., Wiley-VCH, Weinheim, 2014.
J.-M. Basset, Angew. Chem. Int. Ed., 2003, 42, 156–181; b)
C. Copéret, A. Comas-Vives, M. P. Conley, D. P. Estes, A.
Fedorov, V. Mougel, H. Nagae, F. Núñez-Zarur and P. A.
Zhizhko, Chem. Rev., 2016, 116, 323–421.
13 For other reports of mercaptopropyl-functionalized
mesoporous silica materials see, for example: a) Y. Guari, C.
Thieuleux, A. Mehdi, C. Reyé, R. J. P. Corriu, S. Gomez-
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Pleas De ad l to o nn oT tr aa nd sj au cs t ti omn as rgins
Journal Name
COMMUNICATION
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DOI: 10.1039/C8DT04592E
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1
H liquid state NMR by monitoring the release of 1-
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