Soluble iron nanoparticles as cheap and environmentally benign alkene and alkyne hydrogenation catalysts

Article abstract of DOI:10.1039/b820048c

Iron nanoparticles prepared by reducing FeCl₃ with three equivalents of EtMgCl in THF are effective catalysts for the hydrogenation of alkenes and alkynes under moderate conditions.

Full text of DOI:10.1039/b820048c

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Soluble iron nanoparticles as cheap and environmentally benign alkene
and alkyne hydrogenation catalystsw
a
a
a
b
Pim-Huat Phua, Laurent Lefort, Jeroen A. F. Boogers, Mar Tristany
a
and Johannes G. de Vries*
Received (in Cambridge, UK) 11th November 2008, Accepted 5th May 2009
First published as an Advance Article on the web 28th May 2009
DOI: 10.1039/b820048c
Iron nanoparticles prepared by reducing FeCl
3
with three
of olefins, dienes, and alkynes at high temperatures and
2
pressures.
2
equivalents of EtMgCl in THF are effective catalysts for
the hydrogenation of alkenes and alkynes under moderate
conditions.
In addition, a finely divided iron catalyst, prepared according
s
to the Raney method by leaching away aluminum, has been
2
3
used for the hydrogenation of alkynes. However, hydro-
genation with soluble Fe-NPs has not been reported to date.
Herein, we report the use of Fe-NPs as catalysts for the
selective hydrogenation of alkenes and alkynes using molecular
hydrogen. The Fe-NPs were prepared, as reported by Bedford
For the hydrogenation of olefins and alkynes, palladium or
nickel-based heterogeneous catalysts are state-of-the-art.
Homogeneous catalysts are almost exclusively used for
asymmetric hydrogenation reactions. We were interested in
the development of new non-chiral homogeneous hydrogenation
catalysts to enable continuous hydrogenation processes in
microreactors. In principle, it would be possible to use Pd,
Pt, Rh, Ru or Ni nanoparticles (NPs) as catalysts, since these
et al., by reducing a solution of FeCl with 3 equiv. of EtMgCl
3
1
5b
in Et O or THF. z TEM showed the presence of NPs with an
2
average size of 2.67 ꢀ 0.60 nm (Fig. 1). EDX showed the
presence of iron, magnesium and chlorine. Presumably, the
24
1
have been used extensively for hydrogenation reactions.
NPs are stabilised by MgCl and possibly by THF. Finke
ꢁ
2
However, the first four metals are rather expensive, and most
transition metals are highly toxic, necessitating the removal of
the catalyst to very low ppm levels for pharmaceutical
applications. In view of the above, we wanted to explore the
recently revealed that even BF4 is a better stabiliser of NPs
than ethereal solvents. It thus seems highly likely that the
2
chloride ions of MgCl will bind to the outer rim of the
Fe-NPs. The Fe-NPs prepared in this manner were tested in
the hydrogenation of olefins. The conversions under various
reaction conditions are listed in Table 1.
use of a homogeneous iron catalyst. In the past, Fe(CO) has
5
2
been used as a poorly active hydrogenation catalyst. More
3
4
5
recently, the groups of Budzelaar, Chirik and Casey have
developed homogeneous iron complexes that show interesting
properties as hydrogenation catalysts. Beller et al. have
The results indicate that Fe-NPs in THF are active catalysts
for the hydrogenation of norbornene (Table 1, entries 1, 2 and 4),
6
developed the use of iron complexes as transfer hydrogenation
7
and asymmetric hydrosilylation catalysts. Morris and
co-workers recently reported an iron-based asymmetric transfer
8
hydrogenation catalyst. Fe-NPs have been used for different
9
applications, including magnetic fluids, catalysts for carbon
1
nanotube formation, magnetic resonance imaging (MRI)
0
1
1,12
contrast agents,
nickel–iron batteries, catalysts and sorbents
1
3,14
for environmental remediation,
and as catalysts for C–C
A number of synthetic methods for
their preparation have been reported, such as the thermal
1
5,16
bond formation.
1
7
decomposition of iron carbonyl complexes, the hydrogenation
1
8
19,20
of iron amides and the chemical reduction of iron salts.
Commonly used NaBH leads to a colloidal material containing
4
2
1
some boron. Heterogeneous iron catalysts are well-known
and used industrially in the Haber–Bosch and in Fischer–
Tropsch reactions. There are also several publications on
the use of heterogeneous iron catalysts for the hydrogenation
a
DSM Pharmaceutical Products-Innovative Synthesis & Catalysis,
P.O. Box 18, 6160 MD Geleen, The Netherlands.
E-mail: hans-jg.vries-de@dsm.com; Fax: +31 46 4767604;
Tel: +31 46 4761572
Laboratoire de Chimie de Coordination du CNRS, 205 route de
Narbonne, 31077-Toulouse Cedex 04, France
b
Fig. 1 A TEM micrograph of Fe-NPs and a histogram showing their
w Electronic supplementary information (ESI) available: Further
experimental details and data. See DOI: 10.1039/b820048c
particle size distribution.
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Chem. Commun., 2009, 3747–3749 | 3747

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a
Table 1 The hydrogenation of olefins catalysed by Fe-NPs
experiments. Thus, when using any of the following as
catalysts: MgCl
2
,
EtMgCl, FeCl
3
,
EtMgCl/MgCl and
Olefin/Fe
(mol/mol)
d
Conv. (%)
FeCl /MgCl , no reaction was obtained. In fact, the addition
2
3
Entry
1
Olefin
t/h
0.5
0.5
0.5
of an extra equivalent of MgCl to the pre-formed Fe-NPs
2
Norbornene
Norbornene
Norbornene
Norbornene
1-Hexene
cis-2-Hexene
trans-2-Hexene
1-Octene
20
20
20
200
20
20
20
20
20
20
20
20
20
20
20
100
100
3
100
100
100
22
100
only served to retard the hydrogenation of norbornene.
The catalyst is very sensitive to water (Table 1, entry 3). The
presence of even 1% of water in the reaction mixture strongly
retarded the reaction. We assume that water oxidises the NPs
to Fe(II) or Fe(III) species. Similarly, the presence of air
completely inhibited the reaction, presumably for similar
reasons. The catalyst loading could be reduced to 0.5 mol%,
but a longer reaction time was required to achieve full
conversion (Table 1, entry 4).
b
2
3
c
4
5
6
7
8
9
15
15
15
15
15
15
15
15
15
15
15
15
2-Methyl-1-pentene
2,3-Dimethyl-2-butene
Cyclohexene
100
1
1
1
1
1
1
0
1
2
3
4
5
0 (0)
22 (100)
11 (100)
0 (0)
0 (0)
6 (100)
Cyclooctene
1-Methyl-1-cyclohexene
1-Phenyl-1-cyclohexene
trans-Stilbene
Experiments were also carried out to investigate the fate of
the catalyst after the hydrogenation had finished. Thus,
norbornene was added successively to the reaction mixture
after the previous hydrogenation had finished. It was found
that up to five consecutive additions of substrate resulted in
full conversion without compromising the activity of the
catalyst. This bodes well for continuous applications.
Interestingly, traces of positional isomers were observed,
along with the hydrogenated product, in the hydrogenation of
trans-2-hexene. Since we also found that the Fe-NPs serve as
an isomerisation catalyst for 1-octene in the absence of
molecular hydrogen, it appears that the isomerisation
proceeds via an allylic mechanism rather than via the
b-hydride elimination of an iron alkyl complex.
a
Reaction conditions: 5 mol% Fe-NPs, 1 mmol olefin, THF (3 mL),
r.t. All hydrogenation products are known, were identified by GC, and
characterised by comparison with authentic samples and spectral
b
data. Pressure of H
d
c
was 1 bar. Presence of 1% (v/v) of H
2
2
O.
Values in parentheses were obtained at 100 1C.
terminal olefins (Table 1, entries 5 and 8), cis-disubstituted
0
olefins (Table 1, entry 6) and 1,1 -disubstituted olefins
(
Table 1, entry 9), even at room temperature and hydrogen
pressures as low as 1 bar. trans-Olefins (Table 1, entry 7 and
5) and cis-cyclic olefins (Table 1, entries 11 and 12), other
1
than norbornene, could be hydrogenated, but at a lower rate;
full conversion was nevertheless obtained at 100 1C. At room
temperature, tri- (Table 1, entries 13 and 14) and tetra-
Next, we examined the hydrogenation of alkynes (Table 2).
The catalyst was found to be active for the hydrogenation of a
variety of alkynes, with good to excellent conversion under
mild reaction conditions. Terminal alkynes were easily
converted to the corresponding alkanes within 15 h at 20 bar
pressure (Table 2, entries 1 and 2). The selectivity to the alkene
increases by decreasing the reaction time and H2 pressure
(Table 2, entries 3 and 4).
(
Table 1, entry 10) substituted olefins did not react. Increasing
the temperature to 100 1C did not change this to a large extent;
only non-cyclic tri-substituted olefins could be hydrogenated
under these conditions. This clearly offers possibilities for the
selective hydrogenation of substrates containing more than
one differentially-substituted double bond.
The hydrogenation of internal alkynes only furnished
alkanes (Table 2, entries 5 and 6). Introducing a hydroxyl
group onto the alkynes seemed to retard the hydrogenation
reaction (Table 2, entry 7), although 3-hexyn-1-ol was
completely converted to the corresponding alkane at high
pressure after a long reaction time (Table 2, entry 8). Under
these conditions, 4-pentyn-1-ol and 2-methyl-3-butyn-2-ol
were also converted by 43 and 56%, respectively. In
these cases, more alkene than alkane was formed (Table 2,
entries 9 and 10).
To substantiate the involvement of Fe-NPs as active
hydrogenation catalysts, we performed a number of control
a
Table 2 The hydrogenation of alkynes catalysed by Fe-NPs
As we wanted to gain more insight into the selectivity
change to the cis-alkene over time, we monitored the progress
of the hydrogenation of 1-octyne over a 5 h period (Fig. 2).
Interestingly, we observed an induction period of about
10 min. Thus far, we have no explanation for this.
Disappointingly, almost immediately after the hydrogenation
commenced, 1-octene and octane were produced in a fixed
ratio of 1 : 0.6. Only after 2 h did this ratio diminish. In a
similar experiment performed at substrate/catalyst = 200, the
alkene/alkane ratio did not improve (Fig. 3).
Entry Olefin
p(H
2
)/bar t/h
Conv. (%) Select. (1 : 2)
1
2
3
4
5
6
7
8
9
1
1-Hexyne
20
20
10
10
10
10
15
15
0.5 100
0.5 100
0.5 100
0.5 100
0.5
15
15
15
100
100
0 : 1
0 : 1
1 : 0.6
1 : 0.6
0 : 1
0 : 1
—
0 : 1
1.3 : 1
2 : 1
1-Octyne
1-Hexyne
1-Octyne
3-Hexyne
3-Octyne
3-Hexyn-1-ol 10
3-Hexyn-1-ol 20
4-Pentyn-1-ol 20
0
100
43
0
2-Methyl-3-
butyn-2-ol
20
56
In this experiment, we also explored the effects of pressure
and temperature on the rate of the hydrogenation. Increasing
the pressure from 5 to 30 bar raised the turnover frequency
a
Reaction conditions: 5 mol% Fe-NPs, 1 mmol alkyne, THF (3 mL),
r.t. All hydrogenation products are known, were identified by GC and
characterised by comparison with authentic samples and spectral data.
ꢁ1
(
TOF) from 5 to 14 h . Raising the temperature from r.t. to
3
748 | Chem. Commun., 2009, 3747–3749
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(
b) A. Roucoux, A. Nowicki and K. Philippot, in Nanoparticles
in Catalysis, ed. D. Astruc, Wiley-VCH, Weinheim, 2008,
pp. 349–388.
2
3
B. R. James, Homogeneous Hydrogenation, John Wiley & Sons,
New York, 1973, pp. 64–72.
Q. Knijnenburg, A. D. Horton, H. Van der Heijden, A. W. Gal,
P. H. M. Budzelaar, to Stichting voor de Technische Wetenschappen,
Int. Pat. Appl., WO03/042131, 2003.
4
5
6
7
8
9
S. C. Bart, E. Lobkovsky and P. J. Chirik, J. Am. Chem. Soc.,
2
004, 126, 13794–13807.
C. P. Casey and H. Guan, J. Am. Chem. Soc., 2007, 129,
816–5817.
5
S. Enthaler, B. Hagemann, G. Erre, K. Junge and M. Beller,
Chem.–Asian J., 2006, 1, 598–604.
N. S. Shaikh, S. Enthaler, K. Junge and M. Beller, Angew. Chem.,
Int. Ed., 2008, 47, 2497–2501.
C. Sui-Seng, F. Freutel, A. J. Lough and R. H. Morris, Angew.
Chem., Int. Ed., 2008, 47, 940–943.
K. T. Wu, Y. D. Yao, C. R. C. Wang, P. F. Chen and E. T. Yeh,
J. Appl. Phys., 1999, 85, 5959–5961.
Fig. 2 The conversion of 1-octyne into 1-octene and octane.
1
0 E. W. Wong, M. J. Bronikowski, M. E. Hoenk, R. S. Kowalczyk
and B. D. Hunt, Chem. Mater., 2005, 17, 237–241.
1
1 Y. W. Jun, Y. M. Huh, J. S. Choi, J. H. Lee, H. T. Song, S. Kim,
S. Yoon, K. S. Kim, J. S. Shin, J. S. Suh and J. Cheon, J. Am.
Chem. Soc., 2005, 127, 5732–5733.
1
2 S. Mornet, S. Vasseur, F. Grasset and E. Duguet, J. Mater. Chem.,
2
004, 14, 2161–2175.
3 F. Li, C. Vipulanandan and K. K. Mohanty, Colloids Surf., A,
003, 223, 103–112.
4 W. X. Zhang, J. Nanopart. Res., 2003, 5, 323–332.
5 (a) A. Furstner, A. Leitner, M. Mendez and H. Krause, J. Am.
Chem. Soc., 2002, 124, 13856–13863; (b) R. B. Bedford,
M. Betham, D. W. Bruce, S. A. Davis, R. M. Frost and
M. Hird, Chem. Commun., 2006, 1398–1400; (c) G. Cahiez,
V. Habiak, C. Duplais and A. Moyeux, Angew. Chem., Int. Ed.,
2007, 46, 4364–4366.
1
2
1
1
¨
´
Fig. 3 The effect of pressure and temperature on the rate and
selectivity of 1-octyne hydrogenation.
8
0 1C at 30 bar had a stronger effect on the rate and led to an
ꢁ
1
1
6 For recent reviews on iron-catalysed reactions, see: (a) C. Bolm,
J. Legros, J. Le Paih and L. Zani, Chem. Rev., 2004, 104, 6217;
increase in the TOF to 118 h . Although the rate was
somewhat lower than that achievable with currently used
palladium- and nickel-based catalysts, the catalyst cost is
significantly reduced.
(
¨
b) A. Furstner and R. Martin, Chem. Lett., 2005, 34, 624;
(c) A. Correa, O. G. Mancheno and C. Bolm, Chem. Soc. Rev.,
2008, 37, 1108–1117; (d) D. Farrell, S. A. Majetich and
J. P. Wilcoxon, J. Phys. Chem. B, 2003, 107, 11022–11030.
3
In conclusion, Fe-NPs prepared from FeCl and EtMgCl
1
7 D. Farrell, S. A. Majetich and J. P. Wilcoxon, J. Phys. Chem. B,
in THF are an economic and non-toxic catalyst for the
hydrogenation of olefins and alkynes. Work is in progress to
expand the application of this catalyst to the hydrogenation of
other substrates.
2
003, 107, 11022–11030.
18 O. Margeat, F. Dumestre, C. Amiens, B. Chaudret, P. Lecante and
M. Respaud, Prog. Solid State Chem., 2005, 33, 71–79.
¨
9 H. Bonnemann, W. Brijoux, R. Brinkmann, R. Fretzen,
T. Joussen, R. Koppler, B. Korall, P. Neiteler and J. Richter,
J. Mol. Catal., 1994, 86, 129–177.
20 A. Furstner, R. Martin, H. Krause, G. Seidel, R. Goddard and
¨
C. W. Lehmann, J. Am. Chem. Soc., 2008, 130, 8773–8787.
1 G. N. Glavee, K. J. Klabunde, C. M. Sorensen and
G. C. Hadjipanayis, Inorg. Chem., 1995, 34, 28–35.
2 (a) Z. Lu, C. Wang, D. Liang and L. Lin, Shiyou Huagong, 1991,
2
1
We thank the European Union for their financial support
of this research, which was carried out as part of the
Research Training Network (R)evolutionary Catalysis
2
2
(
MRTN-CT-2006-035866).
Notes and references
0, 454–457; (b) Y. Nitta, S. Matsugi and T. Imanaka, Chem.
Express, 1989, 4, 547–550; (c) Y. M. Bondarev, Y. S. Mardashev,
A. D. Mokrushin, V. F. Blokhin and I. V. Razumovskaya, Zh. Fiz.
Khim., 1985, 59, 2343–2345.
z Bedford used 5 equiv. of EtMgCl. We find no difference in catalytic
activity between the material prepared with 3 or 5 equiv. of EtMgCl.
For a discussion on the possible presence of iron in the ꢁ2 oxidation
state upon addition of 5 equiv. of EtMgCl, see ref. 20.
2
3 A. F. Thompson, Jr. and S. B. Wyatt, J. Am. Chem. Soc., 1940, 62,
2
555–2556.
1
(a) A. Roucoux and K. Philippot, in Handbook of
Homogeneous Hydrogenation, ed. J. G. de Vries and
C. J. Elsevier, Wiley-VCH, Weinheim, 2007, vol. 1, pp. 217–256;
24 (a) L. S. Ott and R. G. Finke, Inorg. Chem., 2006, 45, 8382–8393;
(b) L. S. Ott and R. G. Finke, Coord. Chem. Rev., 2007, 251,
1075–1100.
This journal is ꢂc The Royal Society of Chemistry 2009
Chem. Commun., 2009, 3747–3749 | 3749