Development of a co-mediated rearrangement reaction

Article abstract of DOI:10.1002/1521-3773(20020715)41:14<2584::AID-ANIE2584>3.0.CO;2-I

Simultaneous generation of an enolate and Nicholas carbocation unit (2) occurs on treatment of enol ether-cobalt complexes 1 with Lewis acids (X). Subsequent cyclization provides α-functionalized β-alkynyl cycloalkanones 3 in a regiospecific fashion. The

Full text of DOI:10.1002/1521-3773(20020715)41:14<2584::AID-ANIE2584>3.0.CO;2-I

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bond-forming reaction.[1] This process is extremely versatile
for alkyl, alkenyl, and aryl group incorporation, however, the
inclusion of an alkynyl unit in this fashion is much more
limited.[2] Nonetheless, the conjugate addition of alkynyl
alanes does take place in the presence of a Ni catalyst.[3]
Additionally, the use of Lewis acids such as aluminum tris(2,6-
diphenylphenoxide) (ATPH),[4] silyl triflates,[5] and iodotri-
methylsilane[6] can promote the conjugate addition of alkynyl
metal compounds to cyclic enones, although the employment
of b-substituted substrates generally prevents addition com-
pletely or leads to very poor product yields.
Millam, A. D. Daniels, K. N. Kudin, M. C. Strain, O. Farkas, J. Tomasi,
V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo,
S. Clifford, J. Ochterski, G. A. Petersson, P. Y. Ayala, Q. Cui, K.
Morokuma, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B.
Foresman, J. Cioslowski, J. V. Ortiz, B. B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R. L. Martin, D. J.
Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, C.
Gonzalez, M. Challacombe, P. M. W. Gill, B. G. Johnson, W. Chen,
M. W. Wong, J. L. Andres, M. Head-Gordon, E. S. Replogle, J. A.
Pople, Gaussian, Inc., Pittsburgh, PA, 1998 (compiled to run under
Windows OS).
[15] G. A. Jeffrey, An Introduction to Hydrogen Bonding, Oxford Uni-
versity Press, New York, 1997, p. 22.
[16] M. Weber, D. Kuppert, K. Hegetschweiler, V. Gramlich, Inorg. Chem.
1999, 38, 859.
[17] F. M. Menger, J. Am. Chem. Soc. 1966, 88, 3081; F. M. Menger, J. H.
Smith, J. Am. Chem. Soc. 1972, 94, 3824. For more recent references,
see A. B. Maude, A. Williams, J. Chem. Soc. Perkin Trans. 2 1995, 69l;
H. J. Koh, S. I. Kim, B. C. Lee, I. Lee, J. Chem. Soc. Perkin Trans. 2
1996, 1353.
[18] The reactions of n-butylamine and aliphatic diamines with phenyl
acetate in water are both first order in the amine. T. C. Bruice, R. G.
Willis, J. Am. Chem. Soc. 1965, 87, 53l.
We envisaged a strategically different approach to these
À
compounds (Scheme 1), whereby disconnection of the C2 C3
bond in the cyclic ketone would generate an enolate bearing a
R4
R3
O
O
–
R3
R4
O
1
R3
2
3
R4
[19] M. L. Bender, Mechanism of Homogeneous Catalysis from Protons to
Proteins, Wiley-Interscience, New York, 1971.
[20] X. Duan, S. Scheiner, J. Am. Chem. Soc. 1992, 114, 5849.
[21] A. J. Kirby, Adv. Phys. Org. Chem. 1980, 17, 183.
[22] B. Capon, Quart: Rev. Chem. Soc. 1964, 18, 45.
R1
R1
+
R2
R1
R2
R2
Scheme 1. Retrosynthetic analysis of the formation of cyclic ketones
through an enol ether rearrangement.
[23] F. M. Menger, Acc. Chem. Res. 1985, 18, 128; F. M. Menger, Adv. Mol.
Model. 1988, 1, 189; F. M. Menger, Proc. Natl. Acad. Sci. USA,
submitted.
distal propargylic carbocation. We further surmised that this
intermediate might be generated from a cyclic enol ether. To
À
aid scission of the propargylic C O bond of the enol ether, we
examined the effect of the hexacarbonyldicobalt unit on the
alkyne because of its ability to stabilize positive charge at the
a-position strongly.[7] Notably, related intramolecular addi-
tions of enolates to cobalt-stabilized carbocations have been
reported, however, these studies required the propargyl ether
and enolate moieties to be prepared independently and in a
linear fashion. Furthermore, problems associated with regio-
chemical enolate formation can result in poor cyclization
regioselectivity.[8] We anticipated that the proposed rear-
rangement technique would overcome some of these prob-
lems whilst providing a direct method for the preparation of
a-substituted products from appropriately armed enol ether
substrates. We report herein our initial findings on the scope
of the rearrangement process for the synthesis of b-alkynyl
substituted cyclic ketones.
Development of a Co-Mediated
Rearrangement Reaction**
David R. Carbery, Serge Reignier, James W. Myatt,
Neil D. Miller, and Joseph P. A. Harrity*
Dedicated to Professor Peter L. Pauson
The conjugate addition of organocuprates to enones
represents an important fundamental approach to the elab-
oration of carbonyl-containing compounds through a C C
À
We embarked on this study by examining the rearrange-
ment of readily available and easily handled gem dichloro
substituted enol ethers. These compounds were prepared
from the corresponding lactones following the method of
Lakhrissi and Chapleur (Scheme 2).[9] Addition of an alkynyl
zinc reagent to commercially available 1 provided keto esters
3a and 3b; the homologous compound 3c was prepared in a
similar manner from 2. Substituted d-lactones 4a,b were
generated by a Luche reduction and saponification before
ring closure. The quaternary substituted analogue 5 was
prepared by an analogous procedure but with alkylation of
[*] Dr. J. P. A. Harrity, D. R. Carbery, Dr. S. Reignier, J. W. Myatt
Department of Chemistry
University of Sheffield
Brook Hill, Sheffield S37HF (UK)
Fax : (‡44)114-273-8673
E-mail: j.harrity@sheffield.ac.uk
Dr. N. D. Miller
Department of Medicinal Chemistry, Neurology CEDD
GlaxoSmithKline Research and Development
Gunnels Wood Road, Stevenage, Hertfordshire SG12NY (UK)
[**] The authors are grateful to the EPSRC and GlaxoSmithKline for a
studentship (D.R.C.), Pfizer central research for an unrestricted grant
(J.W.M.), and the Leverhulme Trust for a research fellowship (S.R.).
We also thank Simon Thorpe and Sue Bradshaw for assistance in
acquiring spectroscopic data.
[10]
3b using MeLi/TiCl4 in the initial step. e-Lactone 6 was
prepared from keto ester 3c by a similar route. With the key
intermediates lactones 4 6 in hand, we prepared the corre-
sponding enol ethers in one step using PPh3/CCl4.[9] Finally,
exposure of the enol ethers to octacarbonyldicobalt at room
Supporting information for this article is available on the WWW under
http://www.angewandte.org or from the author.
2584
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Table 1. Rearrangement of ester and gem dichloro-substituted enol ethers.[a]
O
O
O
O
a
R1
ZnCl
( )n
Entry Lewis
acid
Enol ether
Product
Time Yield
[%]
+
OR
( )n
Cl
OR
R1
R=Et, R1=Ph, n=3; 3a; 82%
R=Et, R1=nBu, n=3; 3b; 98%
R=Me, R1=nBu, n=4; 3c; 97%
n=3, R=Et; 1
n=4, R=Me; 2
O
Cl
1
2
BF3 ¥ OEt2
TiCl4
18 h
9 h
86
83
(CO)6Co2
Ph
Cl
Cl
b, d, e
O
Cl
Ph
7a
11a
c, d, e
b, d, f
Co2(CO)6
O
O
Cl
O
O
O
3
4
BF3 ¥ OEt2
TiCl4
4 h
10 min 97
90
Cl
(CO)6Co2
O
Cl
Cl
O
O
O
nBu
nBu
nBu
R1
nBu
6; 65%
5; 48%
g, h
nBu
Cl
Cl
11b
7b
R1=Ph; 4a; 77%
R1=nBu; 4b; 79%
Co2(CO)6
g, h
Cl
(CO)6Co2
g, h
Cl
O
Me
5
TiCl4
4 h
3 h
84
98
nBu
nBu
Me
12
Cl
8
Cl
nBu
O
O
Co2(CO)6
Cl
O
Cl
Cl
Co2(CO)6
Co2(CO)6
8; 33%
R1
Cl
O
Cl
Co2(CO)6
Cl
(OC)6Co2
9; 49%
R1=Ph; 7a; 73%
R1=nBu; 7b; 85%
Cl
O
6
BF3 ¥ OEt2
nBu
Co2(CO)6
nBu
Cl
9
13
Scheme 2. a) À 788C 08C, THF, 1 h. b) NaBH4, CeCl3 ¥ 7 H2O, MeOH,
258C, 1 h. c) MeLi, TiCl4, Et2O, À78 ! À 108C. d) KOH, tBuOH/H2O
(1:1), 0.5 h. e) 2-Chloro-1-methylpyridinium iodide, Et3N, CH2Cl2, 408C,
2 h. f) DCC, DMAP, CH2Cl2, 258C, 2 h. g) PPh3, CCl4, 7 78C. h) [Co2-
(CO)8], CH2Cl2, 258C. DCC ˆ N,N'-dicyclohexylcarbodiimide, DMAP ˆ
4-dimethylaminopyridine.
O
(CO)6Co2
CO2Me
CO2Me
O
7TiCl
30 min 92[b]
4
nBu
(E)-10
nBu
Co2(CO)6
14
[a] All reactions were initiated at 08C in CH2Cl2 with 1.5 equivalents of Lewis
acid, allowed to warm to ambient temperature, and stirred until the starting
material was completely consumed. [b] Complexation and rearrangement were
carried out in one pot.
temperature afforded complexes 7 9 as deep red solids/
oils.[11]
We initially screened a wide variety of Lewis acid pro-
moters[12] such as silyl triflates, Et2AlCl, and SnCl4, but were
disappointed to find that these produced complex reaction
mixtures.[13] In contrast, BF3 ¥ OEt2 and TiCl4 were excellent
promoters of the rearrangement process and furnished the
a,a-dichloroketone products in high yield (Table 1, entries 1
and 2). The rearrangement of 1-hexynyl substituted enol
ether 7b under our optimized
lactone 4b was reduced to the corresponding lactol and
subsequently treated with PPh3 ¥ HBF4, which provided the
requisite phosphonium salt for elaboration to alkyl substitut-
ed enol ethers by the method of Ley et al.[17] Generation of the
phosphonium ylide by treatment with n-butyllithium at
À858C, followed by addition of isobutyraldehyde, gave enol
ether 15a as a 7:1 mixture of E/Z isomers on complexation
with octacarbonyldicobalt. Additionally, the phenyl substitut-
ed enol ether complexes 15b were readily generated as an
equal mixture of E/Z isomers by an identical procedure
(Scheme 3).
(CO)3
Co+
H
conditions proceeded much more
rapidly than that observed for 7a
(compare entries 1/2 with 3/4).
This may reflect reduced steric
MLnO
R1
Cl
Co
(CO)3
I
Cl
À
congestion in I during C C bond
formation with R1 ˆ nBu in com-
a-d
parison to R1 ˆ Ph.[14] Notably, this technique is applicable to
the formation of quaternary substituted b-alkynyl cyclohex-
anones, for example, the dichloroenol ether 8 smoothly
underwent rearrangement at 08C in the presence of TiCl4 to
provide the corresponding ketone 12 in 84% yield (entry 5).
We also found that the conversion of seven-membered cyclic
enol ethers to the corresponding ketones is possible and
indeed highly efficient in the one example studied (entry 6).[15]
Finally, ester-containing enol ether 10 was prepared from
lactone 4b by following the method of Shibasaki and co-
workers[16] and underwent rapid and clean rearrangement to
the corresponding keto ester 14 in excellent yield.
(OC)6Co2
R
O
O
O
nBu
nBu
4b
15a,b
R=iPr; 15a; 7:1 E:Z
R=Ph; 15b; 1:1 E:Z
Scheme 3. a) 1) DIBAL-H, TMSCl, À788C, THF, 1 h. 2) K2CO3, MeOH,
84%. b) PPh3 ¥ HBF4, CH3CN, 4 ä molecular sieves, 828C, 2 h. c) nBuLi;
RCHO, À858C, THF, 1 h. d) [Co2(CO)8], hexanes, 2 h, 258C. R ˆ iPr: 15a,
61%; R ˆ Ph: 15b, 78% (over three steps from b). DIBAL-H ˆ diiso-
butylaluminum hydride, TMS ˆ trimethylsilyl.
Unfortunately, the E/Z isomers of 15a were inseparable
and accordingly were subjected to the rearrangement reaction
as a mixture. Treatment of complexes (E/Z)-15a with TiCl4
led to rapid and clean rearrangement to provide the
corresponding a-substituted ketones 16 as a 5:1 mixture of
Having demonstrated the feasibility of the rearrangement
process, we next turned our attention to examining alkyl
substituted enol ethers which would provide a direct means of
a-alkyl incorporation into the ketone products. Therefore,
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[1] a) B. H. Lipshutz, S. Sengupta, Org. React. 1992, 41, 135; b) P.
Perlmutter, Conjugate Addition Reactions in Organic Synthesis,
Pergamon, Oxford, 1992.
[2] This moiety is often included in mixed cuprates as a nontransferable
ligand: a) E. J. Corey, D. J. Beames, J. Am. Chem. Soc. 1972, 94, 7210;
b) G. H. Posner, M. J. Chapdelaine, C. M. Lentz, J. Org. Chem. 1979,
44, 3661.
[3] a) R. T. Hansen, D. B. Carr, J. Schwartz, J. Am. Chem. Soc. 1978, 100,
2244; b) J. Schwartz, D. B. Carr, R. T. Hansen, F. M. Dayrit, J. Org.
Chem. 1980, 45, 3053.
[4] K. Maruoka, I. Shimada, H. Imoto, H. Yamamoto, Synlett 1994, 519.
[5] a) S. Kim, J. H. Park, S. Y. Jon, Bull. Korean Chem. Soc. 1995, 16, 783;
b) S. Kim, J. H. Park, Synlett 1995, 163.
isomers (Scheme 4; major isomer tentatively assigned as
trans) in high yield.[18] In contrast to 15a, the individual
E/Z isomers of 15b were readily separable by column
chromatography, which allowed the rearrangement of each
isomer to be studied individually. To our surprise, we found
that the rearrangement of complexes 15b proceeded stereo-
specifically such that (E)-15b provided the cis-substituted
ketone 17, whereas the trans-substituted ketone 18 was
formed exclusively from (Z)-15b.[19, 20]
[6] M. Eriksson, T. Iliefski, M. Nilsson, M. Olsson, J. Org. Chem. 1997, 62,
182.
[7] a) K. M. Nicholas, Acc. Chem. Res. 1987, 20, 207; b) A. J. M. Caffyn,
K. M. Nicholas in Comprehensive Organometallic Chemistry II,
Vol. 12 (Eds.: E. W. Abel, F. G. A. Stone, G. Wilkinson, L. S.
Hegedus), Pergamon, Oxford, 1995, p. 685.
1.5 equiv TiCl4, CH2Cl2
(OC)6Co2
(OC)6Co2
iPr
−78 °C→ 25 °C
30 min, 70%
O
O
nBu
nBu
iPr
16; 1:5 cis/trans
15a; 7:1 E/Z.
[8] a) E. Tyrrel, P. Heshmam, L. Sarrazin, Synlett 1993, 769; b) P. Magnus,
P. Carter, J. Elliot, R. Lewis, J. Harling, T. Pitterna, W. E. Bauta, S.
Fortt, J. Am. Chem. Soc. 1992, 114, 2544; c) for an alternative
approach which uses oxonium ion stabilization see: A. B. Smith III,
P. R. Verhoest, K. P. Minibiole, J. J. Lim, Org. Lett. 1999, 1, 909;
d) A. B. Smith III, K. P. Minibiole, P. R. Verhoest, T. J. Beauchamp,
Org. Lett. 1999, 1, 913.
[9] M. Lakhrissi, Y. Chapleur, J. Org. Chem. 1994, 59, 5752.
[10] M. T. Reetz, K. Kesseler, S. Schmidtberger, B. Wenderoth, R.
Steinbach, Angew. Chem. 1983, 95, 1003; Angew. Chem. Int. Ed.
Engl. 1983, 22, 989.
1.5 equiv TiCl4, CH2Cl2
−78 °C→ 25 °C
(OC)6Co2
(OC)6Co2
Ph
O
O
O
30 min, 81%
nBu
15b
nBu
Ph
(E)-
17
18
1.5 equiv TiCl4, CH2Cl2
−78 °C→ 25 °C
(OC)6Co2
(OC)6Co2
O
30 min, 78%
nBu
Ph
nBu
Ph
(Z)-15b
Scheme 4. Transformation of enol complexes 15 to alkynyl ketones.
[11] For a review on the preparation of cobalt alkyne complexes see: R. S.
Dickson, P. J. Fraser, Adv. Organomet. Chem. 1974, 12, 323.
[12] The addition of Lewis acids to noncomplexed enol ether substrates did
not result in rearrangement to the corresponding ketones, but
returned starting materials together with the products of alkene
isomerization.
[13] Mild Lewis acids such as AgOTf and Yb(OTf)3 were unsuccessful in
mediating the reaction and returned starting material even after
prolonged reaction times. For an excellent overview on Lewis acid
strength and selectivity see: S. Kobayashi, T. Busujima, S. Nagayama,
Chem. Eur. J. 2000, 6, 3491.
The origin of these different stereochemical outcomes is
intriguing. At present, we are pursuing three possible ration-
ales: 1) Rearrangement of complexes 15a is mechanistically
distinct from that of 15b. 2) Enol ether isomerization (E $ Z)
proceeds rapidly for 15a (or the intermediate metal enolate)
such that the relative ratios of cis/trans-16 are determined by
relative rates of rearrangement of each enol(ate) isomer.
3) Product 16 isomerizes under the reaction conditions.[21]
In conclusion, we report a novel approach to b-alkynyl
[14] The reduced reaction rates of Ph versus nBu substituted alkynes may
also be caused by the delocalization of positive charge in the cationic
intermediate. We thank a referee for this suggestion.
substituted cyclic ketones through
a
cobalt-mediated
rearrangement reaction of cyclic enol ethers. This tech-
nique allows the direct and regiospecific a-incorporation of
dichloro-, ester, aryl, and alkyl substituents which can be
readily controlled by judicious choice of the enol ether
substituent.
[15] Although the full scope of this methodology must await further study,
it does not appear to be applicable to the rearrangement reaction of
five-membered cyclic substrates. Indeed, all efforts to promote the
rearrangement reaction of dichloro, ester, and unsubstituted enol
ethers failed and complex mixtures were returned in all cases
examined. The failure of these substrates to perform well under the
rearrangement conditions is perhaps not surprising as the cyclization
of the intermediate enolate/Nicholas carbocation can be classified as a
5-(enolendo)-exo-trig process, which is disfavored on stereoelectronic
grounds: J. E. Baldwin, M. J. Lusch, Tetrahedron 1982, 38, 2939.
[16] A. Takahashi, Y. Kirio, M. Sodeoka, H. Sasai, M. Shibasaki, J. Am.
Chem. Soc. 1989, 111, 643.
Experimental Section
Typical experimental procedure as exemplified by the rearrangement of
complex 7b: To a solution of 7b (2.0 g, 3.75 mmol) in CH2Cl2 (20 mL) at
08C was added TiCl4 (616 mL, 10.0 mmol, 1.5 equiv) by syringe under
nitrogen. The reaction mixture was stirred at 08C for 10 min and quenched
by addition of saturated aqueous NaHCO3 solution. The reaction mixture
was poured into water, extracted with CH2Cl2, dried with MgSO4, and the
solvent removed in vacuo. Recrystallization of the crude complex afforded
11b as a deep red solid (1.95 g, 97%), m.p. 77.1 78.38C; 1H NMR
(400 MHz, CDCl3): d ˆ 0.99 (3H, t, J ˆ 7.2 Hz), 1.46 1.56 (2H, m), 1.58
1.72 (2H, m), 1.75 1.86 (1H, m), 2.06 2.24 (3H, m), 2.64 (1H, dd, J ˆ 9.0,
1.2 Hz), 2.91 3.04 (2H, m), 3.18 (1H, td, J ˆ 14.4, 5.8 Hz), 3.63 ppm (1H,
dd, J ˆ 11.4, 3.7Hz); 13C NMR (100.6 MHz, CDCl3): d ˆ 13.9, 22.7, 24.1,
32.7, 33.9, 34.5, 35.5, 57.0, 92.9 (2 C), 101.2, 194.3, 199.8 ppm (br); nÄ ˆ 2962
(s), 2936 (s), 2875 (s), 2092 (s), 2036 (s), 2022 (s), 1739 cmÀ1 (s); HR-MS
calcd for C18H16O7Cl2Co2: 531.8937, found: 531.8941.
[17] S. V. Ley, B. Lygo, H. M. Organ, A. Wonnacott, Tetrahedron 1985, 41,
3825.
[18] Assignment of the cis/trans-16 NMR spectrum was made based on
1
400 MHz COSY H NMR spectroscopy of the demetalated cis isom-
er 20; see Supporting Information for spectra and details.
[19] E/Z Enol ether assignments of 15a and 15b were made by comparison
to 1H NMR spectroscopic data reported in reference [16]. The
configuration of isomers (E)/(Z)-15a could also be assigned on the
basis of the chemical shifts of the 13C NMR signal arising from the
carbon atom b to the ether oxygen: D. Barillier, M. P. Strobel, L.
Morin, D. Paquer, Tetrahedron 1983, 39, 767.
[20] The configurations of 17 and 18 were assigned by measurement of the
coupling constants of the protons at the benzylic position. These data
were found to be in good agreement with those of similar disubstituted
¬
cyclohexanones: a) M. Rettig, A. Sigrist, J. Retey, Helv. Chim. Acta
Received: February 11, 2002
2000, 83, 2246; b) E. Hatzigrigoriou, L. Wartski, J. Seyden-Penne, E.
Revised: April 22, 2002 [Z18688]
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COMMUNICATIONS
corrosive chemisportion to yield a mononuclear {RhI(CO)2}
species. In addition, the oxidation of Rh/Al2O3 under an
atmosphere of air and oxygen has also been demonstrated by
XAFS.[5] Recently, using in situ, microreactor-based, energy-
dispersive EXAFS (EDE)[6] and mass spectrometry[7] we have
used the improved time resolution of these techniques to
demonstrate that Rh on alumina is rapidly oxidized by NO.[8]
Herein we utilize these procedures to probe the correlation
between metal structure and catalytic performance for the
reduction of NO by H2.
Toromanoff, Tetrahedron 1985, 41, 5045. Spectral and analytical data
for all new compounds can be found in the Supporting Information.
CCDC-177450 (7a) and CCDC-177451 (11a) contain the supplemen-
tary crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12, Union Road,
Cambridge CB21EZ, UK; fax: (‡44)1223-336-033; or deposit@
ccdc.cam.ac.uk).
[21] Subjection of individual isomers cis- and trans-16 to 1.5 equiv TiCl4 at
À788C !258C for 90 min resulted in only slight (ca.
5 10%)
isomerization at the a center. Therefore, the lack of stereospecificity
in 15a !16 cannot be fully explained by rapid equilibration at the a-
alkyl moiety of the product.
Figure 1 shows the total NO conversion and N2O (mass 44)
production as a function of reaction temperature and feed-
stock composition. The net conversions and selectivity of the
Rapid Phase Fluxionality as the
Determining Factor in Activity and
Selectivity of Highly Dispersed,
Rh/Al2O3 in deNOx Catalysis**
Mark A. Newton, Andrew J. Dent,
Sofia Diaz-Moreno, Steven G. Fiddy, and
John Evans*
Rhodium has for many years been a
primary component in the make up of auto-
exhaust catalysts because of its ability to
catalyze the selective reduction of NOx to
N2.[1, 2] A historical view of this type of system
is of an active, but essentially static, phase
comprising particulate metal; it is from this
axiom that studies of metal single crystals[2]
have been accepted as models of macroscopic
catalyst behavior. However, it has been
established by IR[3] and XAFS[4] (X-ray
absorption fine structure) spectroscopy that
small rhodium particles (on alumina) undergo
[*] Prof. J. Evans, M. A. Newton, S. G. Fiddy
Department of Chemistry
University of Southampton
Southampton, SO171BJ (UK)
Fax : (‡44)2380-593-781
E-mail: je@soton.ac.uk
A. J. Dent
CLRC Daresbury Laboratory
Warrington, WA4 4AD (UK)
S. Diaz-Moreno
The European Synchrotron Radiation Facility
(ESRF)
38043 Grenoble (France)
[**] This work was funded under the ™Catalysis and
Chemical Processes initiative of the EPSRC∫ and
through a ™long-term project∫ allocation of beam-
time by the ESRF. We thank the ESPRC (MAN)
and ICI (SGF) for postdoctoral funding. The
technical skills of John James, Melanie Hill,
Sebastian Pasternak, and Ralph Wiegel, are grate-
fully acknowledged as is the beamline (ID 24)
stewardship of Dr. Sakura Pascarelli.
Figure 1. a) NO conversion as a function of reaction temperature and active feedstock
composition in the reduction of NO/He by H2/He over 5 wt% Rh/g-Al2O3 catalysts derived
from RhCl3 ¥ 3H2O: catalyst charge: 20 mg; NO H2/He ˆ 4/96; total gas flow ˆ
10 mLminÀ1, GHSV ca. ꢀ104 hÀ1. b) N2O production (mass 44) as a function of reaction
temperature and active feedstock composition in the reduction of NO by H2 over 5 wt% Rh/
g-Al2O3 catalysts derived from RhCl3 ¥ 3H2O: conditions as for Figure 1a.
Angew. Chem. Int. Ed. 2002, 41, No. 14
¹ WILEY-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002
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