A remarkably effective catalyst for the asymmetric transfer hydrogenation of aromatic ketones in water and air

Article abstract of DOI:10.1039/b507276j

A Rh(III) complex generated in situ from [Cp*RhCl₂] ₂ and (1-R,2R)-N-(p-toluenesulfonyl)-1,2-cyclohexanediamine (TsCYDN) serves as a remarkably effective, robust catalyst for the asymmetric transfer hydrogenation of aromatic ketones by HCOONa in water in air, affording alcohols in up to 99% ee. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b507276j

View Article Online / Journal Homepage / Table of Contents for this issue
COMMUNICATION
www.rsc.org/chemcomm | ChemComm
A remarkably effective catalyst for the asymmetric transfer
hydrogenation of aromatic ketones in water and air
a
Xiaofeng Wu, Daniele Vinci, Takao Ikariya and Jiangliang Xiao*
a
b
a
Received (in Cambridge, UK) 24th May 2005, Accepted 6th July 2005
First published as an Advance Article on the web 29th July 2005
DOI: 10.1039/b507276j
A Rh(III) complex generated in situ from [Cp*RhCl
and (1R,2R)-N-(p-toluenesulfonyl)-1,2-cyclohexanediamine
TsCYDN) serves as a remarkably effective, robust catalyst
2
]
2
reductant. The M-TsCYDN and related catalysts were first
11
6
c
12
described by the groups of Tani, Knochel and Ikariya for
the same reactions under anaerobic conditions in organic media;
(
6c,11–13
but the reactions tend to be slow (vide infra).
for the asymmetric transfer hydrogenation of aromatic ketones
by HCOONa in water in air, affording alcohols in up to 99% ee.
We started
with the ATH of acetophenone by HCOONa using M-TsCYDN
as catalyst in water. The precatalyst was generated by simply
reacting the (R,R)-TsCYDN ligand with [RuCl (p-cymene)] ,
Enantioselective reduction of prochiral ketones leading to optically
pure secondary alcohols is a subject of considerable interest from
both an academic and industrial perspective because of the
significance of these intermediates for the manufacture of
pharmaceuticals and advanced materials. During the last decade,
remarkable efforts have been devoted to the development of this
2
2
[Cp*RhCl2]2 and [Cp*IrCl2]2 respectively in undegassed water
(2 mL) at 40 uC for 1 h in the open air with no use of a base. The
resulting suspensions were used for the ATH without purification,
and the ATH was initiated by introducing HCOONa (5.0 mmol)
and acetophenone (1.0 mmol) and carried out without any inert
gas protection. Much to our delight, with Rh-TsCYDN, the
acetophenone was almost fully converted into (R)-1-phenylethanol
in 95% ee in 15 min. The Ir-TsCYDN was less active, furnishing a
1
method by using organometallic complexes as catalysts. Noyori
and co-workers first reported on the use of monotosylated
diamines and 1,2-aminoalcohols as ligands for ruthenium-
catalyzed asymmetric transfer hydrogenation (ATH) of aromatic
ketones in 2-propanol or the azeotropic formic acid–triethylamine
99% conversion and 93% ee in 1 h, while the Ru-TsCYDN
required 2 h for the same reduction to give an 85% ee (Table 1). In
contrast, as shown in Table 1, the ATH of acetophenone in
2–4
mixture. This significant discovery led to the development of a
5–8
series of new chiral ligands by a number of research groups. In
terms of rates and turnover numbers, there is still room for
improvement, however. Additionally, as with most organometallic
complexes, these catalysts necessitate conditions devoid of air and
water, thus rendering practical applications cumbersome. We now
report that the Rh-TsCYDN catalyst alongside M-TsCYDN
2
-propanol with Rh-TsCYDN and Ir-TsCYDN and in HCOOH–
3
Et N with Ru-TsCYDN necessitated much longer reaction
11a,12
times.
In the same azeotrope for the same reaction, an
analogous chiral ‘roofed’ cis-diamine in combination with
ruthenium was recently reported to give a 53% conversion
11b
(86% ee) in 67 h at 25 uC.
(M 5 Ru, Ir) displays superb activities and excellent enantioselec-
tivities in the reduction of ketones in water, with no need for
organic solvents or inert gas protection throughout the entire
operation.
We recently reported that the ATH of aromatic ketones with the
Noyori–Ikariya Ru-(R,R)-TsDPEN [TsDPEN 5 (1R,2R)-N-
(
p-toluenesulfonyl)-1,2-diphenylethylenediamine] catalyst can be
9,10
considerably accelerated by using water as solvent.
We have
now found that significantly faster reduction is delivered when the
Rh-TsCYDN catalyst is adopted in neat water with formate as
Encouraged by the results obtained with Rh-(R,R)-TsCYDN,
we then extended this system to a wide range of substituted
acetophenones 1, the related ketones 2–4, and the heteroaryl
ketones 5–8. As before the reaction was carried out in neat water
without using any co-solvent in the open air and without any
degassing throughout. The Rh-(R,R)-TsCYDN catalyzed ATH
a
Liverpool Centre for Materials and Catalysis, Department of
Chemistry, University of Liverpool, Liverpool, UK L69 7ZD.
E-mail: j.xiao@liv.ac.uk; Fax: +44 151 794 3589; Tel: +44 151 794 2937
Graduate School of Science and Engineering and Frontier Collaborative
b
Research Centre, Tokyo Institute of Technology, 2-12-1 O-okayama,
Meguro-ku, Tokyo 152-8552, Japan
This journal is ß The Royal Society of Chemistry 2005
Chem. Commun., 2005, 4447–4449 | 4447

View Article Online
Table 1 Comparison of the ATH of acetophenone with M-TsCYDN
under different conditions
cis-diamine catalyst gave a 91% conversion (92% ee) in 24 h at
11b
3
25 uC in HCOOH/Et N at a S/C ratio of 200/1. The ATH of
49-chloroacetophenone and 49-fluoroacetophenone catalyzed by
Rh-(R,R)-TsCYDN in water gave . 99% conversions in 94% ee in
a short reaction time of 10–20 min (entries 1 and 2, Table 2).
1
-Tetralone and 1-indanone were reduced with Rh-
R,R)-TsCYDN in water to give up to 98% conversion and
7% ee in half a hour (entries 16 and 17, Table 2); switching to
-propanol the reduction resulted in a 43–53% conversion with
(
9
Catalyst
Solvent
formate
iPrOH
t/h
% Con
% ee
2
a
Ru-TsCYDN
2
—
24
99
—
99
. 99
85
—
99
36
85
—
94
95
97
—
93
96
—
12
9
5–97% ee in 24 h (30 uC, 200/1 S/C ratios), however. The
heterocyclic ketones were also reduced in general at fast rates with
good to excellent enantioselectivities by HCOONa with
Rh-(R,R)-TsCYDN in water (entries 18–21, Table 2). The most
notable is the reduction of 2-acetylfuran, which afforded a . 99%
conversion and 99% ee in 5 min (entry 18, Table 2).
b
c
c
c
azeotrope
a
Rh-TsCYDN
Ir-TsCYDN
a
formate
iPrOH
0.25
b
12
—
1
12
—
azeotrope
a
formate
iPrOH
b
9
azeotrope
—
As with reactions catalysed by related Ru-TsDPEN catalysts,
Reaction was carried out at 40 uC, using 1 mmol of ketone,
equiv. HCOONa, and a S/C ratio of 100 in 2 mL of water, with
acetophenones bearing electron donating substituents tend to give
slower reactions, e.g. entries 1 and 4 vs. 5 and 8, and o-substitution
eroded significantly the enantioselectivities (entries 9–11, Table 2).
Considering that the reduction of the carbonyl CLO bond by the
Ru(II)-H hydride intermediate resembles somewhat a nucleophilic
5
b
conversion and ee determined by GC. 30 uC reaction temperature,
0
.1 M ketone in 2-propanol with 200/1 S/C ratio, reference 12.
mixture, 30 uC and 100/1
c
azeotrope 5 azeotropic HCOOH–NEt
S/C ratio, reference 11a..
3
1
5
addition reaction, this is not surprising. However, the very
electron-withdrawing –CN and –NO substituents did not lead to
faster reduction.
This aerobic catalysis by Rh-TsCYDN in water also applies to
2
with sodium formate in water delivered almost completed
conversions for most ketones within 1 h, as is shown in
14
Table 2. In most cases the enantioselectivities were good to
excellent. For instance, the reduction of 4-methoxyacetophenone
led to a 99% conversion in 93% ee at 40 uC in 30 min in water
1a,3b,c,5
higher S/C ratios.
Table 3 gives a few examples. As can be
seen, the reduction of 2-acetylfuran furnished a 98% conversion in
1
.5 h with 99% ee at S/C 5 1000 in the open air, with the initial
21
h . This
(entry 8, Table 2). In comparison, the reaction performed in
21
turnover frequency (TOF) reaching 3500 mol mol
2
-propanol using the same catalyst at 30 uC gave a 22% conversion
represents one of the best results in terms of rates and ee’s reported
for ketones of this type. Even the totally water-insoluble
12
(. 99% ee) in 24 h with a S/C ratio of 200/1, and a similar
49-isobutylacetophenone could be readily reduced with a 94% ee
Table 2 ATH of ketones with Rh-TsCYDN by HCOONa in H
air
2
O in
at S/C 5 1000 (entry 3, Table 3). The reduction could be
performed at a higher temperature of 65 uC with a faster rate but a
decreased ee (1c, entry 2, Table 3).
a
In conclusion, our results show that the Rh-TsCYDN complex
is an excellent ATH catalyst for use in water. It delivers fast rates,
high enantioselectivities and high turnover numbers, and requires
b
b
3b,c
Entry
Ketone
t/min
% Con
% ee
neither organic solvents nor inert gas protection,
or substrate
solubility in water. The aqueous phase catalysis thus provides an
attractive alternative for conducting asymmetric transfer hydro-
genation in a less costly, simpler and ‘‘greener’’ manner.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
a
1b
1c
1d
1e
1f
1g
1h
1i
1j
1k
1l
1m
1n
1o
2
10
20
15
10
30
25
45
30
20
60
60
30
15
60
45
30
20
5
. 99
. 99
99
. 99
. 99
98
98
99
. 99
98
98
94
94
91
91
92
90
87
93
77
80
79
93
89
92
95
97
95
99
96
94
99
We thank the DTI MMI project and its industrial and academic
partners (Prof. R. Catlow, Royal Institution; Dr A. Danopoulos,
University of Southampton; Drs F. Hancock, A. Zanotti-Gerosa,
and F. King, Johnson Matthey; Drs P. Levett and A. Pettman,
Pfizer; Drs P. Hogan and M. Purdie, AstraZeneca; Drs M. Anson
0
1
2
3
4
5
6
7
8
9
0
1
97
Table 3 Aerobic ATH of ketones with Rh-TsCYDN in H
ratio of 1000
2
O at a S/C
. 99
97
99
94
98
99
99
98
99
a
b
b
c
Entry
Ketone
t/h
% Con
% ee
TOF
3
4
5
6
7
8
1
2
3
4
a
1c
1c
1p
5
2.5
0.75
3.5
1.5
. 99
98
. 99
98
93
89
94
99
2200
4100
1100
3500
d
10
15
45
Reactions were carried out at 40 uC, using 10 mmol of ketone,
Reactions were carried out at 40 uC, using 1 mmol of ketone,
mmol HCOONa and a S/C ratio of 100 in 2 mL of water.
Determined by GC. The alcohol configuration was R.
50 mmol HCOONa and a S/C ratio of 1000 in 10 mL of water.
Determined by GC.
b
c
5
Based on 5-min conversions; in
b
21 21 d
h .
mol mol
The reaction was carried out at 65 uC.
4
448 | Chem. Commun., 2005, 4447–4449
This journal is ß The Royal Society of Chemistry 2005

View Article Online
D. Guijarro, P. Pinho, O. Temme and P. G. Andersson, J. Org. Chem.,
1998, 63, 2749; (d) K. Everaere, J.-F. Carpentier, A. Mortreux and
M. Bolliard, Tetrahedron: Asymmetry, 1998, 9, 2971; (e) L. Schwink,
T. Ireland, K. Puntener and P. Knochel, Tetrahedron: Asymmetry, 1998,
and P. Ravenscroft, GlaxoSmithKline) for financial support and
valuable suggestions. We are particularly grateful to Dr Zanotti-
Gerosa for suggestions.
9, 1143; (f) K. Everaere, J.-F. Carpentier, A. Mortreux and M. Bulliard,
Tetrahedron: Asymmetry, 1998, 9, 2971; (g)D. G. I. Petra, P. C. J. Kamer,
P. W. N. M. van Leeuwen, K. Goubitz, A. M. van Loon, J. G. de Vries
and H. E. Schoemaker, Eur. J. Inorg. Chem., 1999, 2335; (h) C. G. Frost
and P. Mendoca, Tetrahedron: Asymmetry, 2000, 11, 1845; (i)
M. Henning, K. Puntener and M. Scalone, Tetrahedron: Asymmetry,
Notes and references
1
Recent reviews: (a) S. E. Clapham, A. Hadzovic and R. H. Morris,
Coord. Chem. Rev., 2004, 248, 2201; (b) H.-U. Blaser, C. Malan,
B. Pugin, F. Spindler, H. Steiner and M. Studer, Adv. Synth. Catal.,
2000, 11, 1849.
2003, 345, 103; (c) K. Everaere, A. Mortreux and J.-F. Carpentier, Adv.
8
Other related ligands: (a) T. Langer and G. Helmchen, Tetrahedron
Lett., 1996, 37, 1381; (b) Y. T. Jiang, Q. Z. Jiang, G. X. Zhu and
X. M. Zhang, Tetrahedron Lett., 1997, 38, 215; (c) Y. Nishibayashi,
I. Takei, S. Uemura and M. Hidai, Organometallics, 1999, 18, 2291; (d)
J. X. Gao, H. Zhang, X. D. Yi, P. P. Xu, C. L. Tang, H. L. Wan,
K. R. Tsai and T. Ikariya, Chirality, 2000, 12, 383; (e) T. Ohta,
S. Nakahara, Y. Shigemura, K. Hattori and I. Furukawa, Appl.
Organomet. Chem., 2001, 15, 699; (f) H. Y. Rhyoo, Y. A. Yoon,
H. J. Park and Y. K. Chung, Tetrahedron Lett., 2001, 45, 5045; (g)
J. W. Faller and A. R. Lavoie, Organometallics, 2001, 20, 5245; (h)
H. Brunner, F. Henning and M. Weber, Tetrahedron: Asymmetry, 2002,
Synth. Catal., 2003, 345, 67; (d) Q. H. Fan, Y. M. Li and A. S. C. Chan,
Chem. Rev., 2002, 102, 3385; (e) T. Dwars and G. Oehme, Adv. Synth.
Catal., 2002, 344, 239; (f) M. J. Palmer and M. Wills, Tetrahedron:
Asymmetry, 1999, 10, 2045; (g) R. Noyori and S. Hashiguchi, Acc.
Chem. Res., 1997, 30, 97.
2
3
(a) S. Hashiguchi, A. Fujii, J. Takehara, T. Ikariya and R. Noyori,
J. Am. Chem. Soc., 1995, 117, 7562; (b) J. Takehara, S. Hashiguchi,
A. Fujii, A. Inoue, T. Ikariya and R. Noyori, Chem. Commun., 1996,
233; (c) A. Fujii, S. Inoue, S. Hishiguchi, N. Uemastu, T. Ikariya and
R. Noyori, J. Am. Chem. Soc., 1996, 118, 2521; (d) N. Uematsu, A. Fujii,
S. Hashiguchi, T. Ikariya and R. Noyori, J. Am. Chem. Soc., 1996, 118,
13, 37.
4916.
9
(a) X. F. Wu, X. G. Li, W. Hems, F. King and J. L. Xiao, Org. Biomol.
Chem., 2004, 2, 1818; (b) X. G. Li, X. F. Wu, W. P. Chen,
F. E. Hancock, F. King and J. L. Xiao, Org. Lett., 2004, 6, 3321; (c)
X. F. Wu, X. G. Li, F. King and J. L. Xiao, Angew. Chem., Int. Ed.,
(a) T. Hamada, T. Torri, T. Onishi, K. Izawa and T. Ikariya, J. Org.
Chem., 2004, 69, 7391; (b) T. Hamada, T. Torii, T. Onishi, K. Izawa and
T. Ikariya, Tetrahedron, 2004, 60, 7411; (c) T. Hamada, T. Torii,
K. Izawa, R. Noyori and T. Ikariya, Org. Lett., 2002, 4, 4373; (d)
M. Watanabe, K. Murata and T. Ikariya, J. Org. Chem., 2002, 67, 1712;
2005, 44, 3407.
1
0 Aqueous ATH: (a) C. Letondor, N. Humbert and T. R. Ward, Proc.
(e) T. Koike, K. Murata and T. Ikariya, Org. Lett., 2000, 2, 3833; (f)
Natl. Acad. Sci. U. S. A., 2005, 102, 4683; (b) P. N. Liu, J. G. Deng,
Y. Q. Tu and S. H. Wang, Chem. Commun., 2004, 2070; (c) Y. P. Ma,
H. Liu, L. Chen, X. Cui, J. Zhu and J. G. Deng, Org. Lett., 2003, 5,
K. Murata, K. Okano, M. Miyagi, H. Iwane, R. Noyori and T. Ikariya,
Org. Lett., 1999, 1, 1119; (g) K. Matsumura, S. Hashiguchi, T. Ikariya
and R. Noyori, J. Am. Chem. Soc., 1997, 119, 8738; (h) S. Hashiguchi,
A. Fujii, K. J. Haack, K. Matsumura, T. Ikariya and R. Noyori,
Angew. Chem., Int. Ed. Engl., 1997, 36, 288; (i) K. J. Haack,
S. Hashiguchi, A. Fujii, T. Ikariya and R. Noyori, Angew. Chem., Int.
Ed. Engl., 1997, 36, 285.
Recent examples: (a) A. M. Hayes, D. J. Morris, G. J. Clarkson and
M. Wills, J. Am. Chem. Soc., 2005, 127, 7318; (b) R. W. Guo, C. Elpelt,
X. H. Chen, D. T. Song and R. H. Morris, Chem. Commun., 2005, 3050;
2
103; (d) Y. Himeda, N. Onozawa-Komatsuzaki, H. Sugihara,
H. Arakawa and K. Kasuga, J. Mol. Catal. A: Chem., 2003, 195, 95;
e) H. Y. Rhyoo, H. J. Park, W. H. Suh and Y. K. Chung, Tetrahedron
(
Lett., 2002, 43, 269; (f) T. Thorpe, J. Blacker, S. M. Brown, C. Bubert,
J. Crosby, S. Fitzjohn, J. P. Muxworthy and J. M. J. Williams,
Tetrahedron Lett., 2001, 42, 4037–4041.
1 Ru-TsCYDN catalyzed ATH: (a) K. Puntener, L. Schwink and
P. Knochel, Tetrahedron Lett., 1996, 37, 8165; (b) H. Matsunaga,
T. Ishizuka and T. Kunieda, Tetrahedron Lett., 2005, 46, 3645; (c)
G. J. Kim, S. H. Kim, P. H. Chong and M. A. Kwon, Tetrahedron
Lett., 2002, 43, 8059; (d) C. M. Marson and I. Schwarz, Tetrahedron
Lett., 2000, 41, 8999.
4
1
(c) W. Baratta, E. Herdtweck, K. Siega, M. Toniutti and P. Rigo,
Organometallics, 2005, 24, 1660; (d) I. C. Lennon and J. A. Ramsden,
Org. Process Res. Dev., 2005, 9, 110; (e) J. B. Sortais, V. Ritleng,
A. Voelklin, A. Houluigue, H. Smail, L. Barloy, C. Sirlin,
G. K. M. Verzijl, J. A. F. Boogers, A. H. M. De Vries, J. G. De Vries
and M. Pfeffer, Org. Lett., 2005, 7, 1247; (f) D. M. Tan and K. S. Chan,
Tetrahedron Lett., 2005, 46, 503; (g) Y. Chen, T. Wu, L. Jiang, J. Deng,
H. Liu, J. Zhu and Y. Jiang, J. Org. Chem., 2005, 70, 1006; (h) X. Y. Sun,
G. Manos, J. Blacker, J. Martin and A. Gavriilidis, Org. Process Res.
Dev., 2004, 8, 909; (i) J. Hannedouche, G. J. Clarkson and M. Wills,
J. Am. Chem. Soc., 2004, 126, 986; (j) P. Brandt, P. Roth and
P. G. Andersson, J. Org. Chem., 2004, 69, 4885; (k) A. Schlatter,
M. Kundu and W. D. Woggon, Angew. Chem., Int. Ed., 2004, 43, 6731.
Examples of commercial applications: (a) J. Blacker and J. Martin, in
Asymmetric Catalysis on Industrial Scale: Challenges, Approaches and
Solutions; H. U. Blaser and E. Schmidt, Eds, Wiley-VCH, Weinheim,
Germany, 2004; (b) M. Miyagi, J. Takehara, S. Collet and K. Okano,
Org. Process Res. Dev., 2000, 4, 346; (c) K. Tanaka, M. Katsurada,
F. Ohno, Y. Shiga and M. Oda, J. Org. Chem., 2000, 65, 432.
Earlier examples of diamino ligands: (a) P. Gamez, F. Fache,
P. Mangeney and M. Lemaire, Tetrahedron Lett., 1993, 34, 6897; (b)
P. Gamez, B. Dunjic and M. Lemaire, J. Org. Chem., 1996, 61, 5196; (c)
K. Mashima, T. Abe and K. Tani, Chem. Lett., 1998, 1199, 1201; (d)
J. M. Mao and D. C. Baker, Org. Lett., 1999, 1, 841; (e) Y. C. Chen,
T. F. Wu, J. G. Deng, H. Liu, Y. Z. Jiang, M. C. K. Choi and
A. S. C. Chan, Chem. Commun., 2001, 1488.
Earlier examples of aminoalcohol ligands: (a) M. J. Palmer,
T. Walsgrove and M. Wills, J. Org. Chem., 1997, 62, 5226; (b)
J. Blacker and B. Mellor, WO9842643 26/03/97; (c) D. A. Alonso,
12 Rh/Ir-TsCYDN catalyzed ATH: K. Murata, T. Ikariya and R. Noyori,
J. Org. Chem., 1999, 64, 2186.
13 Recent reviews on 1,2-cyclohexanediamines: (a) F. Fache, E. Schulz,
M. L. Tommasino and M. Lemaire, Chem. Rev., 2000, 100, 2159; (b)
T. Naota, H. Takaya and S. I. Murahashi, Chem. Rev., 1998, 98, 2599;
(c) Y. L. Bennani and S. Hanessian, Chem. Rev., 1997, 97, 3161.
14 All products were extracted with ether before GC analysis. Analytical
data for the products of 1p and 8. 1p, GC (Chirasil Dex CB, 80 psi
5
6
helium as carrier gas, 250 uC injection temperature, 150 uC column
1
temperature): 6.15 min (R), 6.51 min (S); H NMR (CDCl
3
/TMS): d
0.90 (d, J 5 6.7 Hz, 6 H), 1.49 (d, J 5 6.4 Hz, 3 H), 1.77 (bs, 1 H), 1.85
(m, 1 H), 2.46 (d, J 5 7.2 Hz, 2 H), 4.87 (q, J 5 6.4 Hz, 1 H), 7.12 (m, 2
1
3
H), 7.28 (m, 2 H); C NMR (CDCl
70.7, 125.6, 129.6, 141.4, 143.5; Anal. Calcd for C12H
10.18. Found: C, 80.84; H, 10.16%. 8, GC (Chirasil Dex CB, 80 psi
3
/TMS): d 22.8, 25.4, 30.6, 45.5,
18O: C, 80.85; H,
helium as carrier gas; 250 uC injection temperature, 135 uC column
1
temperature): 3.97 min (R), 4.77 min (S); H NMR (CDCl
1.53 (d, J 5 6.4 Hz, 3 H), 1.83 (bs, 1 H), 4.98 (q, J 5 6.4 Hz, 1 H), 7.11
3
/TMS): d
1
3
(d, J 5 4.8 Hz, 1 H), 7.20 (d, J 5 0.8 Hz, 1 H), 7.30 (dd, 1 H); C NMR
(CDCl /TMS): d 24.9, 67.0, 120.6, 126.0, 126.6, 147.7; Anal. Calcd for
OS: C, 56.22; H, 6.29; S, 25.01. Found: C, 56.15; H, 6.34; S,
3
6 8
C H
9b
7
24.78%. Data for all other products have previously been reported .
15 M. Yamakawa, H. Ito and R. Noyori, J. Am. Chem. Soc., 2000, 122,
1466.
This journal is ß The Royal Society of Chemistry 2005
Chem. Commun., 2005, 4447–4449 | 4449