Table 1 Hydrogenation of benzene derivatives under biphasic conditionsa
1st Run
2nd Run
Stabilizing
agent
Substrate/
Rh0
Entry
Substrate
Product yield (%)b
t/h
TOFc/h21
t/h
TOFc/h21
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Benzene
Benzene
Toluene
Ethylbenzene
Cumene
Anisole
Anisole
Anisole
Anisole
Phenol
Phenol
Ethyl benzoate
Bromobenzened
Aniline
1c
1d
1c
1c
1c
100
100
100
100
100
100
500
100
100
100
100
100
100
100
100
100
Cyclohexane (100)
Cyclohexane (100)
5.3
9.1
5.7
6.9
7.8
5
57
33
53
43
38
60
65
36
59
58
54
32
—
30
55
40
6.2
13.3
6.9
7.4
8.6
5.3
24
11.5
24
5.7
8.4
11.9
—
48
23
43
40
35
57
63
26
13
53
36
25
—
—
48
34
Methylcyclohexane (100)
Ethylcyclohexane (100)
Isopropylcyclohexane (100)
Methoxycyclohexane (100)
Methoxycyclohexane (100)
Methoxycyclohexane (100)
Methoxycyclohexane (100)
Cyclohexanol (100)
Cyclohexanol (100)
Ethyl cyclohexanoate (100)
—
Cyclohexylamine (100)
Ethylcyclohexane (100)
1,2-Dimethylcyclohexane
cis (95), trans (5)
1c
1c
23
1d
CTAB
1c
1d
1c
1c
1c
1c
1c
8.4
5.1
5.2
5.6
9.5
—
10
7.3
7.5
—
8.4
8.9
Styrene
o-Xylene
17
18
a
m-Xylene
p-Xylene
1c
1c
100
100
1,3-Dimethylcyclohexane
cis (87), trans (13)
1,4-Dimethylcytclohexane
cis (70), trans (30)
7.3
7.1
41
42
8.5
8.2
35
37
Conditions: catalyst (3.8 3 1025 mol), surfactant (7.6 3 1025 mol), water (10 ml), substrate (3.8 3 1023 mol), hydrogen pressure (1 atm),
temperature (20 °C), stirred at 1500 min21
PhI, PhCl and PhF are not reduced.
.
b Determined by GC analysis. c Turnover frequency defined as mol of H2 per mol of rhodium per h. d Similarly
mesh covered with carbon. The colloidal dispersion was removed after
1 min using cellulose, then the samples were quickly frozen in liquid ethane
before transfer to the frozen microscope.
the aromatic ring, exo-C–C double bonds are hydrogenated
(Table 1, entry 15). A complete hydrogenation is also observed
with disubstituted benzene derivatives (Table 1, entries 16–18).
The cis-compounds are largely the major products as usually
observed in heterogeneous catalytic systems.14 Finally, we have
observed the formation of cyclohexylamine by reduction of
aniline (Table 1, entry 14) but in this case, the colloidal
suspension is insufficiently stable and aggregates. Accordingly
the catalytic activity during the second run dramatically
decreases to become negligible. We suggest a reaction between
the product and the surfactant.
The durability of the catalytic system was tested by using it
for four successive hydrogenations of anisole. In the first cycle,
the turnover frequency (TOF) was 60 h21. Then, the aqueous
phase containing the catalyst was separated from the hydro-
genated product by simple decantation and re-used in a second
hydrogenation cycle. In the same manner the catalyst was
recycled for a third and fourth run. The aqueous suspension
shows a comparable turnover activity during the four runs of
catalysis. As the activity during recycling depends on the
amount of colloidal particles which remain in water after
decantation, an efficient biphasic catalytic system with good
remaining activity at the fourth run is a demonstration of the
stability of the catalytically active suspensions with compound
1c.
1 A. Stanislaus and B. H. Cooper, Catal. Rev., 1994, 36, 75.
2 K. Weissermel and H. J. Arpe, in Industrial Organic Chemistry, VCH,
New York, 2nd edn, 1993, p. 343.
3 S. Siegel, in Comprehensive Organic Synthesis, ed. B. M. Trost and I.
Fleming, Pergamon Press, New York, 1991, vol. 9; H. Pines, The
Chemistry of Catalytic Hydrocarbon Conversions, Academic Press,
New York, 1981; M. S. Eisen and T. J. Marks, J. Am. Chem. Soc., 1992,
114, 10 358; R. D. Profilet, A. P. Rothwell and I. P. Rothwell, J. Chem.
Soc., Chem. Commun., 1993, 42; M. A. Keane, J. Catal., 1997, 166, 347;
H. Gao and R. J. Angelici, J. Am. Chem. Soc., 1997, 119, 6937.
4 J. S. Yu, B. C. Ankianiec, M. T. Nguyen and I. P. Rothwell, J. Am.
Chem. Soc., 1992, 114, 1927; I. P. Rothwell, Chem. Commun., 1997,
1331; L. Plasseraud and G. Su¨ss-Fink, J. Organomet. Chem., 1997, 539,
163.
5 K. Nasar, F. Fache, M. Lemaire, J. C. Be´ziat, M. Besson and P. Gallezot,
J. Mol. Catal., 1994, 87, 107; F. Fache, S. Lehuede and M. Lemaire,
Tetrahedron Lett., 1995, 36, 885; K. S. Weddle, J. D. Aiken III and
R. G. Finke, J. Am. Chem. Soc., 1998, 120, 5653 and references
therein.
6 For example, see: B. Cornils and W. A. Herrmann, in Aqueous-Phase
Organometallic Catalysis, Wiley–VCH, Weinhem, 1998; W. A.
Herrmann and C. W. Kohlpaintner, Angew. Chem., Int. Ed. Engl., 1993,
32, 1524; B. Cornils, Angew. Chem., Int. Ed. Engl., 1995, 34, 1575.
7 G. Schmid, in Clusters and Colloids, VCH, Weinheim, 1994, p. 459;
L. N. Lewis, Chem. Rev., 1993, 93, 2693.
In conclusion, these results show that rhodium nanoparticles,
protected by hydroxyalkylammonium salts containing at least
16 carbons leading to electrosteric stabilization, can be readily
used for quantitative reduction of arenes. The interfacial tension
parameter can be modulated to favour the contact between the
catalyst and the substrate localised in two phases. Finally, we
describe an efficient recycling process for hydrogenation of
benzene derivatives without loss of activity and usable under
standard conditions (20 °C, 1 atm H2).
8 C. W. Chen and M. Akashi, Langmuir, 1997, 13, 6465; A. B. R. Mayer
and J. E. Mark, J. Polym. Sci., Part A: Polym. Chem., 1997, 35, 3151;
L. M. Bronstein, S. N. Sidorov, A. Y. Gourkova, P. M. Valetsky, J.
Hartmann, M. Breulmann, H. Co¨lfen and M. Antonietti, Inorg. Chim.
Acta, 1998, 280, 348.
9 T. Yonezawa, T. Tominaga and N. Toshima, Langmuir, 1995, 11, 4601;
Y. Berkovich and N. Garti, Colloids Surf., Part A: Physicochem. Eng.
Asp., 1997, 128, 91.
10 C. Larpent and H. Patin, J. Mol. Catal., 1988, 44, 191.
11 C. Larpent, E. Bernard, F. Brisse-Le Menn and H. Patin, J. Mol. Catal.,
1997, 116, 277.
12 O. N. Efimov, O. N. Ermenko, A. G. Ovcharenko, M. L. Khidekel and
P. S. Chekrii, Bull. Acad. Sci., USSR, Chem. Sect., 1969, 778; K. R.
Januszkiewicz and H. Alper, Organometallics, 1983, 2, 1055; J. Blum,
I. Amer, K. P. C. Vollhardt, H. Schwarz and G. Ho¨hne, J. Org. Chem.,
1987, 52, 2804.
We thank CNRS and the Region Bretagne for financial
support. We would also like to thank Dr Rolland (University of
Rennes 1) for helpful comments and TEM micrographs.
Notes and references
13 G. Cerichelli, L. Luchetti, G. Mancini and G. Savelli, Tetrahedron,
1995, 51, 10281.
14 H. Nagahara, M. Ono, M. Konishi and Y. Fukuoka, Appl. Surf. Sci.,
1997, 121/122, 448.
† Surface tension measurements were performed at 20 °C using the ring
method with a Du Nouy tensiometer (Kru¨ss K10T).
‡ TE Cryo-Microscopic studies were conducted using a PHILIPS CM 12
transmission electron microscope at 100 keV. Samples were prepared by a
dropwise addition of the stabilized colloid in water onto a copper sample
Communication 9/00551J
536
Chem. Commun., 1999, 535–536