Hydrogenation and dehalogenation under aqueous conditions with an amphiphilic-polymer-supported nanopalladium catalyst

Article abstract of DOI:10.1021/ol047670k

(Chemical Equation Presented) An amphiphilic polystyrene-poly(ethylene glycol) resin supported nanopalladium particle catalyzed hydrogenation of olefins and hydrodechlorination of chloroarenes under aqueous conditions is presented.

Full text of DOI:10.1021/ol047670k

ORGANIC
LETTERS
2
005
Vol. 7, No. 1
63-165
Hydrogenation and Dehalogenation
under Aqueous Conditions with an
Amphiphilic-Polymer-Supported
Nanopalladium Catalyst
1
†
Ryu Nakao, Hakjune Rhee, and Yasuhiro Uozumi*
Institute for Molecular Science (IMS), Myodaiji, Okazaki 444-8787, Japan
uo@ims.ac.jp
Received November 12, 2004
ABSTRACT
An amphiphilic polystyrene−poly(ethylene glycol) resin supported nanopalladium particle catalyzed hydrogenation of olefins and hydrodechlo-
rination of chloroarenes under aqueous conditions is presented.
1
In recent years, much attention has been focused on aqueous
supported nanoparticles that can be used in an appropriate
reaction medium and readily removed by filtration. We
previously reported that alcohol oxidation to produce car-
bonyl compounds was catalyzed by an amphiphilic PS-PEG
resin dispersion of nanoparticles of palladium (ARP-Pd,
Figure 1) in water under aerobic conditions to realize clean,
2
and heterogeneous switching of organic transformations. We
have developed a variety of amphiphilic polystyrene-
poly(ethylene glycol) (PS-PEG) resin supported transition
metal complexes, which catalyze various synthetic organic
3
reactions smoothly in water under heterogeneous conditions.
However, with the advent of accessible methods for the
preparation and/or handling of nanometal particles, catalytic
organic transformations with nanometal particles have been
5,6
safe oxidation. The ARP-Pd catalyst was designed to
combine the amphiphilic polymer-based heterogeneous aqua-
catalytic properties and high catalytic activity because of the
large surface area of the nanoparticles. Our continuing
interest in the utility of ARP-Pd under aqueous conditions
led us to examine its catalytic potential in reductive reactions.
We wish to report the catalytic hydrogenation of olefins and
hydrodechlorination of aryl chlorides catalyzed by ARP-Pd
under mild, aqueous conditions.
4
gaining popularity. One approach employs functional polymer-
†
Visiting professor from Hanyang University, Korea.
(
1) For reviews on aqueous switching, see: (a) Li, C.-J.; Chan, T.-H.
Organic Reactions in Aqueous Media; Wiley-VCH: New York, 1997. (b)
Grieco, P. A., Organic Synthesis in Water; Kluwer Academic Publishers:
Dordrecht, 1997. (c) Herrmann, W. A.; Kohlpaintner, C. W. Angew. Chem.,
Int. Ed. Engl. 1993, 32, 1524. (d) Lindstr o¨ m, U. M. Chem. ReV. 2002, 102,
751.
2) (a) For reviews on heterogeneous switching, see: Bailey, D. C.;
2
(
Langer, S. H. Chem. ReV. 1981, 81, 109. (b) Shuttleworth, S. J.; Allin, S.
M.; Sharma, P. K. Synthesis 1997, 1217. (c) Shuttleworth, S. J.; Allin, S.
M.; Wilson, R. D.; Nasturica, D. Synthesis 2000, 1035. (d) D o¨ rwald, F. Z.
Organic Synthesis on Solid Phase; Wiley-VCH: Weinheim, 2000. (e)
Leadbeater, N. E.; Marco, M. Chem. ReV. 2002, 102, 3217. (g) McNamara,
C. A.; Dixon, M. J.; Bradley, M. Chem. ReV. 2002, 102, 3275. (h) De Vos,
D. E., Vankelecom, I. F. J., Jacobs, P. A., Eds. Chiral Catalyst Immobiliza-
tion and Recycling; Wiley-VCH: Weinheim, 2000. (i) 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. (j) Fan, Q.-H.; Li, Y.-M.; Chan, A. S. C. Chem.
ReV. 2002, 102, 3385.
(3) For examples of aquacatalytic organic transformations with am-
phiphilic polymer-supported palladium catalysts reported by the author’s
group, see: (a) Uozumi, Y.; Shibatomi, K. J. Am. Chem. Soc. 2001, 123,
2919. (b) Uozumi, Y.; Nakai, Y. Org. Lett. 2002, 4, 2997. (c) Uozumi, Y.;
Kimura, T. Synlett 2002, 2045. (d) Hocke, H.; Uozumi, Y. Synlett 2002,
2049. (e) Uozumi, Y. J. Synth. Org. Chem. Jpn. 2003, 60, 1063. (f) Uozumi,
Y.; Tanaka, H.; Shibatomi, Org. Lett. 2004, 6, 281.
(4) For reviews, see: (a) Kr a´ lik, M.; Biffis, A. J. Mol. Catal. A 2001,
177, 113. (b) Corain, B.; Kr a´ lik, M. J. Mol. Catal. A 2001, 173, 99.
(5) Uozumi, Y.; Nakao, R. Angew. Chem., Int. Ed. 2003, 42, 194.
(6) ARP is the abbreviation for Amphiphilic Resin-dispersion of nano-
Particles.
1
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© 2005 American Chemical Society
Published on Web 12/10/2004

Table 1. Hydrogenation of Styrenes with ARP-Pd Catalysta
Figure 1. Microscopic images of ARP-Pd: (left) SEM image of
ARP-Pd beads; (right) TEM image of palladium nanoparticles of
ARP-Pd.
A preliminary study on the catalytic utility of ARP-Pd7
in reductive reactions examined the hydrogenation of styrenes
8
(
Table 1). A mixture of styrene and 4 mol % palladium of
ARP-Pd in water was shaken under an atmospheric pressure
of hydrogen gas at 25 °C for 24 h to give a quantitative
yield of ethylbenzene (run 1). Styrene derivatives bearing
electron-donating and -withdrawing substituents on their
aromatic rings, indene, and â-methylstyrene underwent
hydrogenation under similar conditions to give the corre-
sponding olefin-reduced products in >99% yield (runs 2-6).
Hydrogenation of styrenes having hydroxymethyl, formyl,
acetyl, methyl ester, and carboxylic acid groups at their
â-positions took place at their olefinic units with their
â-functional groups intact to give hydrocinnamic products
in yields of 87-100% (runs 7-11). Trisubstituted olefins,
R-methylcinnamic acid and R-phenylcinnamic acid, were also
subjected to ARP-Pd-catalyzed hydrogenation in water to
give the hydrocinnamic acids in quantitative yields (runs 12
and 13).
Hydrodehalogenation of aryl halides, especially of chloro-
arenes, has been recognized as an important chemical
transformation in organic synthesis as well as in industrial
a
All reactions were carried out in the presence of 5 mol % Pd of ARP-
Pd in water under H2 (1 atm) at 25 °C for 24 h. b GC yields for runs 1-6.
Isolated yields for runs 7-13. All products showed >95% similarity with
9
applications. Furthermore, because of the harmful nature
authentic data on GC-MS analysis. c One equivalent of KOH was added.
of aryl chlorides, dechlorination has attracted increasing
attention. Consequently, a wide variety of hydrodehaloge-
nation reaction systems have recently appeared in the
literature, among them catalytic systems, which are usually
performed with transition metal catalysts (e.g., Ni, Rh, Pd)
hydrazine).10 If the hydrodechlorination of aryl chlorides
proceeded in aqueous media with a recyclable catalyst and
a mild hydrogen source, the reaction system would be an
enormous plus since it would meet most environmental
requirements.
It was found that hydrodechlorination of aryl chlorides
took place smoothly in aqueous reaction media with am-
monium formate in the presence of the amphiphilic resin
2
and hydrogen sources (e.g., H , metal hydrides, formic acid,
(
7) 1% DVB cross-linked, average diameter of polymer beads ) 170
µm, average diameter of palladium particle ) 9.0 nm, palladium loading
0.4 mmol/g.
8) For several examples of polymer-stabilized palladium nanoparticles,
)
(
see: (a) Ley, S. V. Mitchell, C.; Pears, D.; Ramarao, C.; Yu, J.-Q.; Zhou,
W. Org. Lett. 2003, 5, 4665. (b) Bremeyer, N.; Ley, S. V.; Ramarao, C.;
Shirley, I. M.; Smith, S. C. Synlett 2002, 1843. (c) Ley, S. V.; Ramarao,
C.; Gordon, R. S.; Holmes, A. B.; Morrison, A. J.; McConvey, I. F.; Shirley,
I. M.; Smith, S. C.; Smith, M. D. Chem. Commun. 2002, 1134. (d) Yu,
J.-Q.; Wu, H.-C.; Ramarao, C.; Spenver, J. B.; Ley, S. V. Chem. Commun.
(10) For recent examples of palladium-mediated hydrodechlorination of
chloroarenes, see: (a) Kang, R.; Ouyang, X.; Han, J.; Zhen, X. J. Mol.
Catal. A 2001, 175, 153. (b) Desmarets, C.; Kuhl, S.; Schneider, R.; Fort,
Y. Organometallics 2002, 21, 1554. (c) Maleczka, R. E., Jr.; Rahaim, R.
J., Jr.; Teixeira, R. R. Tetrahedron Lett. 2002, 43, 7087. (d) Sajiki, H.;
Kume, A.; Hattori, K.; Hirota, K. Tetrahedron Lett. 2002, 43, 7247. (e)
Sajiki, H.; Kume, A.; Hattori, K.; Nagase, H.; Hirota, K. Tetrahedron Lett.
2002, 43, 7251. (f) Cellier, P. P.: Spindler, J.-F.; Taillefer, M.; Cristau,
H.-J. Tetrahedron Lett. 2003, 44, 7191. (g) Navarro, O.; Kaur, H.; Mahjoor,
P.; Nolan, S. P. J. Org. Chem. 2004, 69, 3173. (h) Selvam, P.; Sonavane,
S. U.; Mohapatra, S. K.; Jayaram, R. V. Tetrahedron Lett. 2004, 45, 3071.
2
002, 678. (e) Toshima, N.; Shiraishi, Y.; Teranishi, T.; Miyake, M.;
Tominaga, T.; Watanabe, H.; Brijoux, W.; B o¨ nemann, H.; Schmid, G. Appl.
Organomet. Chem. 2001, 15, 178. (f) Teranishi, T.; Miyake, M. Chem.
Mater. 1998, 10, 594. (g) Bergbreiter, D. E.; Chen, B.; Lynch, T. J. J. Org.
Chem. 1983, 48, 4179.
(9) For a review, see: Alonso, F.; Beletskaya, I. P.: Yus, M. Chem.
ReV. 2002, 102, 4009.
164
Org. Lett., Vol. 7, No. 1, 2005

because of the high toxicity of the perchloroarenes. Hydro-
dechlorination of dichloroarenes (runs 13-16) and tri-
chloroarenes (runs 17-20) took place smoothly with the
ARP-Pd catalyst and ammonium formate to give benzene,
phenol, aniline, and benzoic acid in excellent yields. Neither
partially dechlorinated monochloroarenes or dichloroarenes
were detected by GC-MS analysis. Dechlorination of
pentachloroaniline was carried out using 3 equiv of am-
monium formate, with respect to the chloroarene, under
otherwise similar conditions to give aniline in 85% isolated
yield, using 1 mol % of palladium to the chloroarene (run
Table 2. Hydrodechlorination of ArCl using ARP-Pd and
Ammonium Formatea
21). Recycling experiments were examined for dechlorination
of methyl 4-chlorobenzoate (Scheme 1). After the first use
Scheme 1
of the polymeric nanopalladium catalyst (Table 2, run 10)
to give 94% of methyl benzoate, the recovered catalyst ARP-
Pd was taken on to 10 subsequent reuses and exhibited stable
catalytic activity. Thus, all 10 recycling runs gave >99%
GC yields of methyl benzoate, the first, third, and tenth runs
of which were chosen to confirm the isolated chemical yields
of the dechlorinated product to give 95%, 93%, and 94%
yield of methyl benzoate, respectively.
In summary, a novel amphiphilic PS-PEG resin dispersion
of nanoparticles of palladium exhibited high catalytic
performance in the hydrogenation of olefins and the hydro-
dechlorination of chloroarenes under aqueous conditions.
Dechlorination was found to take place smoothly using
aqueous ammonium formate with high recyclability, which
would provide a safe and clean detoxification protocol for
aqueous chloroarene pollutants. Development of a flow
system for the dechlorination catalysis is currently underway.
a
All reactions were carried out in 10% aqueous 2-propanol in the
presence of 5 mol % palladium (with respect to substrate) of ARP-Pd and
equiv of ammonium formate with respect to the chloroarene at 25 °C for
20 min. Isolated yield unless otherwise noted. GC yield.
3
1
b
c
dispersion of palladium nanoparticles, ARP-Pd. Representa-
tive results are shown in Table 2. When chlorobenzene was
treated with ammonium formate in 10% aqueous 2-propanol
in the presence of 5 mol % palladium of the ARP-Pd catalyst
at 25 °C for 120 min, hydrodechlorination proceeded
smoothly to give benzene in quantitative yield (>99% GC
yield) (Table 1, run 1). Electron-rich (runs 2-6) as well as
electron-deficient (runs 7-10) aromatics were readily dechlo-
rinated under similar conditions to give the corresponding
reduced products in high yields ranging from 89% to >99%,
where wide functional group tolerance for benzylic hydroxyl,
phenolic hydroxyl, amine, ketone, amide, carboxylic acid,
and carboxylic ester was noted. Naphthyl chloride and
pyridyl chloride underwent hydrodechlorination to afford
naphthalene and pyridine in 95% and 99% yield, respectively
Acknowledgment. This work was supported by the
CREST program, sponsored by the JST. We also thank the
JSPS (Creative Scientific Research, no. 13GS0024; Grant-
in-Aid for Scientific Research, no.15205015) and the MEXT
(Scientific Research on Priority Areas, nos. 412 and 420)
for partial financial support of this work.
Supporting Information Available: Experimental pro-
cedure for hydrogenation (Table 1) and hydrodechlorination
(Table 2). This material is available free of charge via the
Internet at http://pubs.acs.org.
(
runs 11 and 12). Complete dechlorination of perchlorinated
aromatics to nonchlorinated aromatics is of great value
OL047670K
Org. Lett., Vol. 7, No. 1, 2005
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