Imidazolium-salt-functionalized ionic-CNT-supported Ru-carbene/palladium nanoparticles for recyclable tandem metathesis/hydrogenation reactions in ionic liquids

Article abstract of DOI:10.1002/asia.201300360

NP and tuck: Two different catalysts, a Ru-carbene complex and palladium nanoparticles, were immobilized onto the same imidazolium-salt-functionalized ionic CNTs. These supported dual-function catalysts showed excellent catalytic activity in tandem metathesis/hydrogenation reactions in an ionic liquid and could be recovered and reused four times. RCM=ring-closing metathesis. Copyright

Full text of DOI:10.1002/asia.201300360

COMMUNICATION
DOI: 10.1002/asia.201300360
À
Imidazolium-Salt-Functionalized Ionic-CNT-Supported Ru Carbene/
Palladium Nanoparticles for Recyclable Tandem Metathesis/Hydrogenation
Reactions in Ionic Liquids
Sujin Lee, Ju Yeon Shin, and Sang-gi Lee*[a]
Interest in the development and application of tandem
catalytic reactions continues to grow for obvious reasons.[1]
Tandem catalytic processes allow several transformations to
be performed in a one-pot operation, thereby negating the
need for handling and isolating intermediates. Furthermore,
the substantial decrease in waste generation that accompa-
nies tandem process has significant benefits on the environ-
ment. One class of reaction that has come to prominence in
tandem reactions is the olefin-metathesis reaction. Grubbs
and co-workers elegantly developed tandem metathesis/hy-
drogenation processes by using Grubbs’s 1st- (A) or 2nd-
generation Ru complexes (B).[2] It has been proposed that,
under the hydrogenation conditions, Ru complexes A or B
servations, we envisioned that the immobilization of both
À
Ru carbene complexes and Pd NPs onto the same IM-f-
MWCNTs could allow us to devise a new supported, dual-
function catalyst for tandem metathesis/hydrogenation reac-
tions in an ionic liquid. Herein, we report the immobiliza-
À
tion of a Hoveyda-type Ru carbene catalyst and Pd NPs
onto imidazolium-salt-functionalized ionic multi-walled
À
carbon nanotubes (Ru carbene/PdNP@IM-f-MWCNT) as
a recyclable catalyst for tandem metathesis/hydrogenation
reactions in an ionic liquid.
First, we investigated the stability of Ru complexes A–D
and imidazolium-salt-tagged complex E under hydrogena-
tion conditions (Figure 1). As reported by Grubbs and co-
À
are transformed into their corresponding Ru hydride com-
plexes, which are effective hydrogenation catalysts. Numer-
ous other tandem processes have also been developed by
combining Ru-catalyzed metathesis reactions with hydroge-
nation reactions,[3] aza-Michael reactions,[4] Claisen rear-
rangements,[5] Diels–Alder reactions,[6] Kharasch additions,[7]
dihydroxylations,[8] Wittig olefinations,[9] etc.[10] However,
most of these reported metathesis-based tandem transforma-
tions employ homogeneous catalysis. The use of supported
catalysts that enable their recovery and reuse could make
tandem catalysis more sustainable.[11]
In recent years, the hybridization of imidazolium-based
ionic liquids (ILs) with carbon nanotubes (CNTs) and/or
metal nanoparticles (MNPs) has found increasing use in
many areas of technology and science.[12,13] In this context,
we previously reported that palladium nanoparticles
(Pd NPs) that were supported on imidazolium-salt-function-
alized ionic multi-walled carbon nanotubes (IM-f-
MWCNTs) showed high reactivity and recyclability in an
ionic liquid.[14] More recently, we found that Ru carbene
À
complexes that were supported on IM-f-MWCNTs also
showed excellent catalytic activity and recyclability in ring-
closing metathesis (RCM) reactions.[15,16] Based on these ob-
[a] S. Lee,+ Dr. J. Y. Shin,+ Prof. Dr. S.-g. Lee
Department of Chemistry and Nano Science
Ewha Womans University
Seoul 120-750 (Korea)
Fax : (+82)2-3277-3419
E-mail: sanggi@ewha.ac.kr
[+] These authors contributed equally to this work.
À
Figure 1. Plot that shows the stability of Ru carbene complexes A–E
under hydrogenation conditions (1 atm H2, RT, 3 h, in the presence of
À
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201300360.
1.0 equiv Pd/C); the percentage residual Ru complex was determined by
1H NMR analysis with 1,2-dimethoxyethane as an internal standard.
1
&
&
Chem. Asian J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
These are not the final page numbers! ÞÞ

www.chemasianj.org
Sang-gi Lee et al.
workers, Ru complexes A and B were labile under the hy-
drogenation conditions[2] and, thus, only 30% of the Ru
complex remained after 3 h under 1 atm H2 in the presence
of one equivalent of Pd/C at room temperature. In contrast,
the chelated Ru complexes (C–E) were stable under the hy-
drogenation conditions. These results suggested that the
À
Hoveyda-type Ru carbene complexes were promising can-
didates for our study.
À
The preparation of the supported Ru carbene/
PdNP@IM-f-MWCNT catalyst is shown in Scheme 1. First,
the immobilization of Pd NPs onto imidazole-functionalized
MWCNTs (PdNP@imidazole-f-MWCNT) was achieved by
the hydrogenation (1 atm) of Na2PdCl4 with imidazolium-
chloride-functionalized MWCNTs in water at room temper-
ature. Then, the reaction of PdNP@imidazole-f-MWCNT
with bromide 1, followed by metathesis with Grubbs’ 2nd-
À
generation Ru carbene complex B, afforded the supported
À
Ru carbene/PdNP@IM-f-MWCNT (for details, see the Sup-
porting Information). Notably, this result represents the first
example of an immobilized dual-functional Ru/Pd catalyst
on CNTs for tandem metathesis/hydrogenation catalysis.
High-resolution transmission electron microscopy (HR-
TEM, Figure 2a) and X-ray diffraction (XRD, Figure 2b)
À
Scheme 1. Synthesis of the supported dual-functional Ru carbene/
PdNP@IM-f-MWCNT.
À
analyses of the Ru carbene/PdNP@IM-f-MWCNT catalyst
clearly indicated that highly crystalline Pd NPs were densely
decorated over the MWCNTs. X-ray photoelectron spectros-
copy (XPS) analysis showed that the oxidation states of
both RuIV (Ru 3p(3/2) at 462.4 eV, Ru 3p(1/2) at 485.8 eV) and
Pd0 remained unchanged during the anchoring process of
[17]
À
the Ru carbene complex (Figure 2c,d). ICP-MS analysis
indicated that 0.13 mmolgÀ1 Ru and 0.42 mmolgÀ1 Pd were
À
incorporated onto the Ru carbene/PdNP@IM-f-MWCNT
catalyst. Moreover, this supported catalyst was highly disper-
À
Figure 2. a) HR-TEM image, b) XRD pattern, and XPS data of the c) Ru and d) Pd regions of Ru carbene/PdNP@IM-f-MWCNT.
&
&
2
Chem. Asian J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

www.chemasianj.org
Sang-gi Lee et al.
sible in ionic liquid 1-butyl-3-methylimidazolium hexafluor-
ophosphate ([bmim][PF6]).
methyl acrylate, thereby affording compounds 3e and 3 f, re-
spectively (Table 1, entries 5 and 6).
N
À
Next, we investigated the catalytic activity of the support-
ed catalyst for tandem metathesis/hydrogenation reactions
Finally, the recyclability of the Ru carbene/PdNP@IM-f-
MWCNT catalyst was investigated in the tandem RCM/hy-
drogenation reactions of N-tosylated bisallylamine (2a).
After the tandem RCM/hydrogenation process, the ionic
liquid phase, which contained the catalyst, was easily sepa-
rated with 2-propanol, which was immiscible with [bmim]-
À
(Table 1). As shown in Table 1, the supported Ru carbene/
PdNP@IM-f-MWCNT catalyst could efficiently catalyze the
RCM of dienes 2a–2d in CH2Cl2/ACHTNUGTRENNUG[bmim]ACHTUGNTERN[NUGN PF6] (1:1 v/v). For
the tandem hydrogenation reaction, the CH2Cl2 solvent was
evaporated and then 2-propanol was added to the remained
ionic-liquid phase that contained the catalyst and the meta-
thesis product. Then, the solution was subjected to 1 atm H2
pressure at room temperature to afford compounds 3a–3d
in up to 97% overall yield (over two steps; Table 1, en-
tries 1–3). This tandem procedure can be successfully ap-
plied to the RCM/hydrogenation of dienyne 2e and the
cross-metathesis/hydrogenation of compound 2 f with
AHCTUNTGREG[NUNN PF6], by extraction of the ionic-liquid phase with 2-propa-
À
nol three times. As shown in Table 2, the Ru carbene/
PdNP@IM-f-MWCNT catalyst was retained in the ionic-
liquid layer, which could be reused up to four times. Howev-
er, the catalytic activity of the Ru catalyst started to decline
during the 4th run. Inductively coupled plasma mass spec-
trometry (ICP-MS) analysis of the 2-propanol layer indicat-
ed that no leaching of Pd was observed, but about 100 ppm
Ru leached out during each
run, which was ascribed to an
À
Table 1. Tandem metathesis/hydrogenation reactions catalyzed by the supported Ru carbene/PdNP@IM-f-
ineffective return of the active
Ru species to its initial resting
state and/or to a rapid decom-
position of the Ru species.
In summary, we have immo-
À
MWCNT.[a]
bilized both
a Ru carbene
complex and Pd nanoparticles
onto the same imidazolium-
functionalized ionic CNTs for
recyclable tandem metathesis/
hydrogenation reactions. The
supported dual-function cata-
Entry
1
2
t1 [h] (conversion
t2 [h] (conversion
3
Yield
[%][c]
[%])[b]
[%])[b]
1.5 (96)
1.0 (97)
0.5 (>99)
0.5 (>99)
95
96
À
lyst, Ru carbene/PdNP@IM-f-
MWCNT, showed excellent
catalytic activity in tandem
metathesis/hydrogenation reac-
tions in an ionic liquid. This
catalyst could be easily recov-
ered and reused up to four
times. The decreased catalytic
activity in the fourth run was
ascribed to leaching of Ru the
species. To address this prob-
lem, variation in the anchoring
positions of the Ru catalyst is
currently under investigation.
2
3
1.0 (98)
1.5 (99)
0.5 (>99)
97
83
4
24 (85)
Experimental Section
5
6
2.5 (80)
12 (95)
71
95
À
To
a
flask that contained Ru car-
bene/PdNP@IM-f-MWCNT (30 mg,
2.5ꢁ10À3 mmol,
2.5 mol%) was added a solution of
substrate (0.05 mmol) in
CH2Cl2/A[bmim][PF6] (v:v=1:1, 2 mL)
Ru
content:
2
C
ACHTUNGTRENNUNG
3.0 (>99)
1.0 (>99)
through a syringe and the mixture
was stirred at 408C for 1 h. After
completion of metathesis step (by
GC), the CH2Cl2 was evaporated, 2-
propanol (1 mL) was added, and the
[a] The metathesis step was performed with the diene (0.05 mmol) in CH2Cl /CHUTTGNRENNGU[bmim]ACHUTNGTREN[NUNG PF6] (1 mL/1 mL) at
2 A
408C and the hydrogenation step was performed in 2-PrOH/
G
N
1
by GC or H NMR analysis. [c] Yield of isolated product.
3
&
&
Chem. Asian J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
These are not the final page numbers! ÞÞ

www.chemasianj.org
Sang-gi Lee et al.
Table 2. Catalyst-recycling experiments.[a]
[5] a) D. A. Clark, A. A. Kulkarni, K. Kalbarczyk, B. Schertzer, S. T.
Diver, J. Am. Chem. Soc. 2006, 128, 15632–15636; b) M. D. Swift,
A. Sutherland, Org. Lett. 2007, 9, 5239–5242.
[6] a) H. Park, Y. L. Hong, Y. B. Kim, T. L. Choi, Org. Lett. 2010, 12,
3442–3445; b) R. J. Spandl, H. Rudyk, D. R. Spring, Chem.
Commun. 2008, 3001–3003; c) H. Y. Lee, H. Y. Kim, H. Tae, B. G.
Kim, J. Lee, Org. Lett. 2003, 5, 3439–3442.
[7] B. A. Seigal, C. Fajardo, M. L. Snapper, J. Am. Chem. Soc. 2005,
127, 16329–16332.
[8] a) N. M. Neisius, B. Plietker, J. Org. Chem. 2008, 73, 3218–3227;
b) A. A. Scholte, M. H. An, M. L. Snapper, Org. Lett. 2006, 8, 4759–
4762.
[9] R. P. Murelli, M. L. Snapper, Org. Lett. 2007, 9, 1749–1752.
[10] a) J. Gavenonis, R. V. Arroyo, M. L. Snapper, Chem. Commun.
2010, 46, 5692–5694; b) C. S. Consorti, G. L. P. Aydos, J. Dupont,
Chem. Commun. 2010, 46, 9058–9060; c) B. G. Kim, M. L. Snapper,
J. Am. Chem. Soc. 2006, 128, 52–53; d) D. F. Finnegan, M. L. Snap-
per, J. Org. Chem. 2011, 76, 3644–3653; e) Z. B. Zhu, M. Shi, Org.
Lett. 2010, 12, 4462–4465.
Run
RCM [%][b]
Hydrogenation [%][b]
Yield [%][c]
1
2
3
4
96
94
94
76
>99
99
98
96
93
93
71
98
[a] The metathesis step were performed with compound 2a (0.05 mmol)
in CH2Cl2/A[bmim][PF6] (1 mL/1 mL) at 408C for 1.5 h. After the evapora-
G
ACHTUNGTRENNUNG
tion of CH2Cl2, 2-PrOH (1 mL) was added and the hydrogenation step
was performed for 30 min at RT. For the catalyst recovery and reuse, the
2-PrOH layer was separated and the ionic-liquid layer, which contained
the catalyst, was extracted with 2-propanol (1 mLꢁ3) and reused in the
next run by the addition of compound 2a and CH2Cl2 (1 mL). [b] Deter-
mined by GC. [c] Yield of isolated product.
[11] For reviews of heterogeneous multifunction catalysts for tandem re-
actions, see: a) F. X. Felpin, E. Fouquet, ChemSusChem 2008, 1,
718–724; b) M. J. Climent, A. Corma, S. Iborra, Chem. Rev. 2011,
111, 1072–1133.
reaction mixture was stirred vigorously under 1 atm H2 (balloon) at RT.
After completion of the hydrogenation step (by GC), the top (2-propa-
nol) layer was separated and ionic-liquid layer was extracted three times
with Et2O (3ꢁ3 mL). The combined extract was concentrated under
vacuum and the residue was purified by column chromatography on
silica gel to give the corresponding product (3). For the recycling experi-
ments, CH2Cl2 (1 mL) and substrate 2a were added into the remained
ionic-liquid layer, which contained the catalyst, and the metathesis and
hydrogenation reactions were repeated.
[12] a) J. Snyder, T. Fujita, M. W. Chen, J. Erlebacher, Nat. Mater. 2010,
9, 904–907; b) S. S. Moganty, N. Jayaprakash, J. L. Nugent, J. Shen,
L. A. Archer, Angew. Chem. 2010, 122, 9344–9347; Angew. Chem.
Int. Ed. 2010, 49, 9158–9161; c) K. Richter, A. Birkner, A. V. Mudr-
ing, Angew. Chem. 2010, 122, 2481–2485; Angew. Chem. Int. Ed.
2010, 49, 2431–2435; d) H. Chu, Y. Shen, L. Lin, X. Qin, G. Feng,
Z. Lin, J. Wang, H. Liu, Y. Li, Adv. Funct. Mater. 2010, 20, 3747–
3752; e) J. M. Campelo, D. Luna, R. Luque, J. M. Marinas, A. A.
Romero, ChemSusChem 2009, 2, 18–45; f) D. Wei, H. E. Unalan, D.
Han, Q. Zhang, L. Niu, G. Amaratunga, T. Ryhanen, Nanotechnolo-
gy 2008, 19, 424006; g) F. Jia, C. Shan, F. Li, L. Niu, Biosens. Bio-
electron. 2008, 24, 945–950; h) P. Migowski, J. Dupont, Chem. Eur.
J. 2007, 13, 32–39; i) T. Fukushima, T. Aida, Chem. Eur. J. 2007, 13,
5048–5058; j) S.-g. Lee, Chem. Commun. 2006, 1049–1063; k) L.
Rodrꢆguez-Pꢃrez, E. Teuma, A. Falqui, M. Gꢅmez, P. Serp, Chem.
Commun. 2008, 4201–4203.
[13] For our previous work on the hybridization of ionic liquids with
CNTs, see: a) Y. S. Kim, J. Y. Shin, H. J. Jeon, A. Cha, C. Lee, S.-g.
Lee, Chem. Asian J. 2013, 8, 232–237; b) Y. S. Kim, A. Cha, J. Y.
Shin, H. J. Jeon, J. H. Shim, C. Lee, S.-g. Lee, Chem. Commun. 2012,
48, 8940–8942; c) J. Y. Shin, Y. S. Kim, Y. Lee, J. H. Shim, C. Lee,
S.-g. Lee, Chem. Asian J. 2011, 6, 2016–2021; d) M. J. Park, J. K.
Lee, B. S. Lee, Y. W. Lee, I. S. Choi, S.-g. Lee, Chem. Mater. 2006,
18, 1546–1551.
Acknowledgements
This work was supported by the National Research Foundation (NRF-
20120005673). We thank Prof. J. Bouffard for providing helpful com-
ments.
Keywords: heterogeneous catalysis
·
hydrogenation
·
nanotubes · ring-closing metathesis · tandem reactions
[14] Y. S. Chun, J. Y. Shin, C. E. Song, S.-g. Lee, Chem. Commun. 2008,
942–944.
[1] a) M. C. Haibach, S. Kundu, M. Brookhart, A. S. Goldman, Acc.
Chem. Res. 2012, 45, 947–958; b) J. C. Wasilke, S. J. Obrey, R. T.
Baker, G. C. Bazan, Chem. Rev. 2005, 105, 1001–1020; c) V. Dragu-
tan, I. Dragutan, J. Organomet. Chem. 2006, 691, 5129–5147;
d) D. E. Fogg, E. N. Santos, Coord. Chem. Rev. 2004, 248, 2365–
2379.
[15] a) S. Lee, J. Y. Shin, S.-g. Lee, Tetrahedron Lett. 2013, 54, 684–687.
For our previous work on supported Ru complexes, see: b) S. W.
Chen, J. H. Kim, K. Y. Ryu, W. W. Lee, J. Hong, S.-g. Lee, Tetrahe-
dron 2009, 65, 3397–3403; c) S. W. Chen, J. H. Kim, H. Shin, S.-g.
Lee, Org. Biomol. Chem. 2008, 6, 2676–2678; d) S. W. Chen, J. H.
Kim, C. E. Song, S.-g. Lee, Org. Lett. 2007, 9, 3845–3848.
[16] a) F. J. Gꢅmez, R. J. Chen, D. Wang, R. M. Waymouth, H. Dai,
Chem. Commun. 2003, 190–191; b) Y. Liu, A. Adronov, Marcromol.
2004, 37, 4755–4760; c) G. Liu, B. Wu, J. Zhang, X. Wang, M. Shao,
J. Wang, Inorg. Chem. 2009, 48, 2383–2390.
[2] J. Louie, C. W. Bielawski, R. H. Grubbs, J. Am. Chem. Soc. 2001,
123, 11312–11313.
[3] For selected examples, see: a) A. Fꢂrstner, A. Leitner, Angew.
Chem. 2003, 115, 320–323; Angew. Chem. Int. Ed. 2003, 42, 308–
311; b) J. Cossy, F. Bargiggia, S. BouzBouz, Org. Lett. 2003, 5, 459–
462; c) X. Miao, C. Fischmeister, C. Bruneau, P. H. Dixneuf, J. L.
Dubois, J. L. Couturier, ChemSusChem 2012, 5, 1410–1414; d) X.
Miao, C. Fischmeister, C. Bruneau, P. H. Dixneuf, ChemSusChem
2009, 2, 542–545; e) B. Schmidt, S. Krehl, V. Sotelo-Meza, Synthesis
2012, 44, 1603–1613.
[17] K. C. Park, I. Y. Jang, W. Wongwiriyapan, S. Morimoto, Y. J. Kim,
Y. C. Jung, T. Toya, M. Endo, J. Mater. Chem. 2010, 20, 5345–5354.
Received: March 18, 2013
Published online: && &&, 0000
[4] S. Fustero, D. Jimꢃnez, M. Sꢄnchez-Rosellꢅ, C. d. Pozo, J. Am.
Chem. Soc. 2007, 129, 6700–6701.
&
&
4
Chem. Asian J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

COMMUNICATION
NP and tuck: Two different catalysts,
a Ru carbene complex and palladium
Heterogeneous Catalysis
À
nanoparticles, were immobilized onto
the same imidazolium-salt-functional-
ized ionic CNTs. These supported
dual-function catalysts showed excel-
lent catalytic activity in tandem meta-
thesis/hydrogenation reactions in an
ionic liquid and could be recovered
and reused four times. RCM=ring-
closing metathesis.
Sujin Lee, Ju Yeon Shin,
Sang-gi Lee*
&&&& — &&&&
Imidazolium-Salt-Functionalized Ionic-
À
CNT-Supported Ru Carbene/Palla-
dium Nanoparticles for Recyclable
Tandem Metathesis/Hydrogenation
Reactions in Ionic Liquids
5
&
&
Chem. Asian J. 2013, 00, 0 – 0
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
These are not the final page numbers! ÞÞ