Remarkably effective phosphanes simply with a PPh2 moiety: Application to Pd-Catalysed cross-coupling reactions for tetra-ortho-substituted biaryl syntheses

Article abstract of DOI:10.1002/chem.201000723

Chemical equation presented Expanding the horizons of ArPPh₂: New applications of triarylphosphane ligands are presented. The Pd-L1 and Pd-L2 complexes offer exceptionally high activity in Suzuki-Miyaura cross-couplings of aryl chlorides. The extremely congested synthesis of tetraortho-substituted biaryl compounds is achieved for the first time by simply using triarylphosphane ligands.

Full text of DOI:10.1002/chem.201000723

DOI: 10.1002/chem.201000723
Remarkably Effective Phosphanes Simply with a PPh2 Moiety:
Application to Pd-Catalysed Cross-Coupling Reactions for
Tetra-ortho-substituted Biaryl Syntheses
Chau Ming So, Wing Kin Chow, Pui Ying Choy, Chak Po Lau, and Fuk Yee Kwong*[a]
Dedicated to Professor Albert S. C. Chan on the occasion of his 60th birthday
ortho-Substituted biaryl compounds are important struc-
tural motifs present in a number of natural products from
various origins and have a wide range of biological proper-
ties.[1,2] The biaryl substructures in vancomycin, a glycopep-
tide antibiotic from Streptomyces orientalis,[3] steganacin, a
cytotoxic tubulin-binding dibenzocyclootadiene lignan from
Steganotaenia araliacea,[4] and michellamine B, an anti-HIV
naphthylisoquinoline alkaloid from Ancistrocladus abbrevia-
tus,[5] have aroused the interest of many synthetic chemists
within the field of sterically congested biaryl synthesis.
However, the ability to prepare extremely hindered asym-
metric biaryl compounds by using Suzuki–Miyaura coupling
reactions has proven to be an extremely difficult task.
Recent superb findings by the Buchwald group have demon-
strated that PCy2-substituted phenanthrene-based phos-
phanes[6] and 2-dicyclohexylphosphino-2’,6’-dimethoxybi-
phenyl (S-Phos)[7] are effective ligands for the synthesis of
tetra-ortho-substituted biaryl compounds, mainly from aryl
bromides (Figure 1). To date, in the exploration of phos-
phane ligands, only the ruthenocenylphosphane R-Phos de-
veloped by Hoshi/Hagiwara[8] and, very recently, the diaza-
phospholidine chloride disclosed by Ackermann[9] allowed
the successful synthesis of tetra-ortho-substituted biaryls
from unactivated aryl chlorides (Figure 1). Besides phos-
phanes, carbene IBiox12·OTf with a tuneable ring size,
“flexible-steric-bulk” PEPPSI-IPent and phenanthryl-based
H2-ICP·HCl, reported by Glorius,[10] Organ[11] and Ma/
Andrus,[12] respectively, are also appropriate for sterically
congested couplings (Figure 1).
The lore in the field of demanding cross-coupling reac-
tions reveals that successful phosphane ligands often contain
dialkylphosphane groups, such as PCy2 or PtBu2 (Figure 1).
In contrast to ArPCy2 and ArPtBu2 ligands, the correspond-
ing ArPPh2 compounds have received less attention due to
the accepted rationale indicating that they are less electron-
rich and less bulky than the corresponding ArPCy2 and
ArPtBu2 compounds (Figure 2)[13] and, thus, provide a less
favourable outcomes for the oxidative addition and reduc-
tive elimination steps in unactivated aryl chloride cou-
plings.[14–16]
[a] C. M. So, W. K. Chow, P. Y. Choy, Prof. Dr. C. P. Lau,
Prof. Dr. F. Y. Kwong
However, triarylphosphanes are attractive compounds as
they are reasonably air stable and can be readily prepared
from the relatively inexpensive Ph2PCl.[17] Herein, we report
an unexpected finding that advances coupling technology by
showing that the previously omitted triarylphosphane family
can effectively deal with difficult coupling reactions. We dis-
close their ability to perform the most difficult biaryl cou-
State Key Laboratory of Chiroscience and
Department of Applied Biology and Chemical Technology
The Hong Kong Polytechnic University
Hung Hom, Kowloon, Hong Kong (Hong Kong)
Fax : (+852)2364-9932
E-mail: bcfyk@inet.polyu.edu.hk
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201000723.
7996
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 7996 – 8001

COMMUNICATION
Figure 3. Exploration of a series of modular indolylphosphanes.
group is incorporated within the indole ring (L1–L4;
Figure 3).
With our newly developed ligands in hand, we attempted
one of the most difficult coupling reactions, the synthesis of
tetra-ortho-biaryl compounds (Scheme 1). 2-Chloro-meta-
xylene and 2-mesitylboronic acid were initially used as
Scheme 1. Unusual reactivity difference between triarylphosphane L4
and aryldialkylphosphane L5 ligands; dba=1,5-diphenylpenta-1,4-dien-3-
one.
Figure 1. Phosphanes and carbenes used in Pd-catalysed Suzuki-type syn-
theses of asymmetric tetra-ortho-substituted biaryls.
model substrates. L4 gave a slightly better conversion than
L3. To our surprise, the allegedly more reactive aryldialkyl-
phosphane L5 showed an inferior outcome, yet the ligand
L4, in which the scaffold consists of the PPh2 group, gave a
superior coupling-product yield (Scheme 1).
To further probe and ensure the effectiveness of the Pd–
L4 catalytic system, an array of sterically congested aryl
chlorides and arylboronic acids were examined in this reac-
tion (Table 1). The slightly activated 2,6-dimethoxyphenyl-
and 2-methoxy-6-substituted-phenylboronic acids were not
used in our investigations.[21] The L4 ligand showed slightly
higher activity than L3 in promoting the extremely hindered
biaryl synthesis (Table 1, entries 1 vs. 2). Cs2CO3 provided a
better substrate conversion than K3PO4·H2O (Table 1, en-
tries 2 vs. 3). Tetra-ortho-substituted biaryl coupling in the
presence of cyano and methoxy groups was also accom-
plished in excellent yield (Table 1, entry 4). Anthracenyl
chlorides furnished the coupling products smoothly (Table 1,
entries 6 and 7).[22] In particular, 2,6-dimethyl-4-chloroani-
sole could be coupled smoothly to afford the desired prod-
uct in moderate to good yield (Table 1, entry 8). The im-
pediments to this particular transformation are not only due
Figure 2. The normal reactivity of aryldialkylphosphane and triarylphos-
phane ligands in cross-coupling processes.
plings, forming tetra-ortho-substituted compounds from un-
activated aryl chlorides, for the first time.
À
We recently disclosed a series of indolyl N P-bonded ami-
nophosphane[18] and C P-bonded phosphane ligands,[19]
À
which were prepared by straightforward Fischer indolisation
and phosphonation (Figure 3). The CM-phos ligand succeed-
ed in catalysing the challenging aryl mesylate coupling reac-
tions.[20] In order to show the attractive features of this mod-
ular ligand synthesis, we communicate, herein, the assembly
À
of a new series of C P-type ligands, in which the phosphane
Chem. Eur. J. 2010, 16, 7996 – 8001
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7997

F. Y. Kwong et al.
Table 1. Tetra-ortho-substituted biaryl synthesis catalysed by the Pd–L4 catalytic system.[a]
Entry
ArCl
Ar’B(OH)2
Product
Pd
Yield
[%][b]
AHCTUNGTRENNUNG
1[c]
2
2.0
1.0
4.0
82
82
3[d]
34[e]
4
5
1.0
1.0
94
82
6
7
1.0
2.0
96
48
8
9
2.5
1.0
68
88
10
11
R=3-C(O)Me
R=4-COOMe
1.0
1.0
82
80
[a] Reaction conditions: ArCl (1.0 mmol), Ar’B(OH)2 (2.0 mmol), [Pd2ACHTNUGTRENUNG(dba)3] (mol% as indicated), ligand (Pd/L, 1:4), Cs2CO3 (3.0 mmol) and dioxane
(3.0 mL), under N2 at 1108C for 24 h (reaction times for each substrate were not optimised). [b] Isolated yields are reported. [c] L3 was used instead of
L4. [d] K3PO4·H2O was used as the base. [e] GC yield is reported.
to the steric encumbrance of both the aryl chloride and the
arylboronic acid, but also to the very electron-rich nature of
the aryl chloride. Functional groups such as a methyl ester
or ketone groups were also compatible with these reaction
conditions (Table 1, entries 10 and 11).
Another set of unactivated aryl chlorides was also exam-
ined (Table 2). In contrast to the specifically tetra-ortho-sub-
stituted biaryl couplings, Pd–L3 showed a slightly better re-
activity than Pd–L4 for these reactions. During the course
of our investigation, the complete conversion of the ArCls
was generally observed if 0.5 mol% Pd was used. The cou-
pling of sterically hindered substrates (both electrophilic
and nucleophilic partners) that generate tri-ortho-substitut-
ed biaryl compounds was also accomplished (Table 2, en-
tries 3 and 4). This result represents the lowest catalyst load-
ing achieved so far for tri-ortho-substituted biaryl coupling
in which a phosphane ligand with a PPh2 moiety is used. A
deactivated aryl chloride also smoothly coupled with 2-bi-
phenylboronic acid (Table 2, entry 5).
In addition to unactivated aryl chlorides, the Pd–L3 cata-
lyst system was applied to functionalised aryl chloride cou-
plings (Table 3). Catalyst loading for these reactions could
7998
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 7996 – 8001

Tetra-ortho-substituted Biaryl Synthesis
COMMUNICATION
Table 2. Palladium–ArPPh2-catalysed Suzuki–Miyaura couplings of unactivated aryl chlorides.[a]
dered arylboronic acids as the
nucleophilic partners. Excellent
product yields were obtained
when 3-nitrophenylboronic acid
was used (Table 3, entries 1 and
2). A 2,6-disubstituted-arylbor-
Yield onic acid also furnished the
Entry
ArCl
Ar’B(OH)2
Product
Pd
G
[%][b]
coupling products in an almost
1
2
0.5
0.25
97
quantitative yield (Table 3, en-
tries 3 and 4). Common func-
tional groups, such as enolisable
ketones, aldehydes, methyl
esters and cyano groups, were
all compatible with these reac-
tion conditions (Table 3, en-
tries 1 and 4–8). Nitrogen het-
erocycles, such as pyridine, iso-
82[c]
3
4
0.67
0.67
87
92
quinoline
and
unprotected
indole, proved to be proficient
at affording their corresponding
products in excellent yields
(Table 3, entries 9–13).
5
0.5
80
In addition to the aryl cou-
pling partners, the reactions of
vinyl chlorides and alkylboronic
6
7
8
0.5
0.4
0.4
84
95
92
acids
were
also
Cyclopentenyl
tested
(Scheme 2).[24]
chloride coupled with para-ani-
sylboronic acid in good yield.
Catalyst loading can be reduced
to 0.1 mol% Pd for the cou-
pling of n-butylboronic acid
with
an
aryl
chloride
(Scheme 2).
[a] Reaction conditions: ArCl (1.0 mmol), Ar’B(OH)2 (1.5 mmol), [Pd2ACHTNUTRGNEUNG(dba)3] (mol% as indicated), ligand
(Pd/L, 1:4), K3PO4·H2O (3.0 mmol) and dioxane (3.0 mL), under N2 at 1108C for 24 h (reaction times for each
substrate were not optimised). [b] Isolated yields are reported. [c] GC yield is reported.
In conclusion, we have pre-
pared a new set of easily acces-
sible and tuneable triarylphos-
phane ligands.[25] These ligands
be reduced to 0.02 mol% Pd at 908C. In order to show the
efficiency of the newly developed system, we avoided using
the “privileged” phenylboronic acid as the substrate, but in-
stead used challenging electron-deficient[23] or sterically hin-
significantly expand the scope of Pd-catalysed cross-cou-
plings by enabling the use of non-electron-rich boranes for
the coupling of aryl chlorides. Notably, we have succeeded
in achieving the most difficult Pd-catalysed cross-coupling,
the synthesis of tetra-ortho-substituted asymmetric biaryl
compounds, by using an arylphosphane ligand possessing a
PPh2 group. These unusual findings highlight the versatility
of triarylphosphanes and indicate that the PCy2 or PtBu2
moieties are not necessary to deal with difficult coupling
processes. We anticipate that further enhancements of the
reactivity of the previously unexplored triarylphosphane
family towards a variety of coupling reactions are attainable.
Experimental Section
General experimental procedures are given in the Support-
ing Information.
Scheme 2. The feasibility of the Pd–triarylphosphane-catalysed Suzuki
coupling of vinyl chloride and alkylboronic acid. [a] Isolated yields.
[b] 3 equivalents of RB(OH)2 was used (with respect to the ArCl).
Chem. Eur. J. 2010, 16, 7996 – 8001
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
7999

F. Y. Kwong et al.
Table 3. Palladium-catalysed cross-couplings of functionalised ArCl.[a]
[2] For book chapters and reviews
concerning cross-coupling reac-
tions in biaryl syntheses, see:
a) Metal-Catalyzed
Cross-Cou-
pling Reactions, Vol. 1–2, 2nd ed.
(Eds.: A. de Meijere, F. Dieder-
ich), Wiley-VCH, Weinheim,
2004; b) M. Beller, C. Bolm,
Transition Metals for Organic
Synthesis Building Blocks and
Fine Chemicals, Vol. 1–2, 2nd ed.,
Wiley-VCH, Weinheim, 2004;
c) L. Yin, J. Liebscher, Chem.
Rev. 2007, 107, 133; d) J.-P.
Corbet, G. Mignani, Chem. Rev.
2006, 106, 2651; e) A. Roglans, A.
Pla-Quintana, M. Moreno-Manas,
Chem. Rev. 2006, 106, 4622;
f) G. A. Molander, N. Ellis, Acc.
Chem. Res. 2007, 40, 275; g) L.
Ackermann, Modern Arylation
Methods, Wiley-VCH, Weinheim,
2009; h) N. Miyaura, Top. Curr.
Chem. 2002, 219, 11; i) A. Suzuki
in Modern Arene Chemistry (Ed.:
D. Astruc), Wiley-VCH, Wein-
heim, 2002, pp. 53–106.
Entry
ArCl
Ar’B(OH)2
Product
Pd
Yield
[%][b]
AHCTUNGTRENNUNG
1
2
R=3-C(O)Me
R=4-C(O)Ph
0.1
0.067
98
95
3
4
R=C(O)Ph
R=COOMe
0.05
0.05
99
91
5
6
R=COOMe
R=CN
0.05
0.025
92
97
7
0.02
84
[3] a) A. V. R. Rao, M. K. Gurjar,
K. L. Reddy, A. S. Rao, Chem.
Rev. 1995, 95, 2135; b) K. C. Nic-
olaou, C. N. C. Boddy, S. Brꢂse,
N. Winssinger, Angew. Chem.
1999, 111, 2230; Angew. Chem.
Int. Ed. 1999, 38, 2096.
8[c]
0.1
0.1
96
82
9[c]
[4] O. Baudoin, F. Guꢃritte in Studies
in Natural Product Chemistry,
Vol. 29 (Ed.: A.-U. Rahman)
10[c]
11[c]
R=H
R=Me
0.01
0.01
97
95
Elsevier,
Amsterdam,
2003,
pp. 355–418.
[5] G. Bringmann, F. Pokorny in The
Alkaloids, Vol. 46 (Ed.: G. A.
Cordell), Academic Press, New
York, 1995, pp. 127–271.
[6] For an example that uses the
slightly activated 9-chloroanthra-
12[c]
13[c]
0.01
1.5
96
70
cene
with
electron-rich
ArB(OH)2 and a phen-based tri-
arylphosphane, see J. Yin, M. P.
Rainka, X. X. Zhang, S. L. Buch-
wald, J. Am. Chem. Soc. 2002,
124, 6343.
[a] Reaction conditions: ArCl (1.0 mmol), Ar’B(OH)2 (1.5 mmol), [Pd2ACHTNUTRGNEUNG(dba)3] (mol% as indicated), ligand
(Pd/L, 1:4), K3PO4·H2O (3.0 mmol) and dioxane (3.0 mL), under N2 at 908C for 24 h (reaction times for each
substrate were not optimised). [b] Isolated yields are reported. [c] Reaction temperature=1108C.
[7] a) S. D. Walker, T. E. Barder,
J. R. Martinelli, S. L. Buchwald,
Angew. Chem. 2004, 116, 1907;
Acknowledgements
We thank the Research Grants Council of Hong Kong (CERG:
PolyU5005/07P) and the UGC Areas of Excellence Scheme (AoE/P-10/
01) for financial support.
Angew. Chem. Int. Ed. 2004, 43, 1871; b) T. E. Barder, S. D. Walker,
J. R. Martinelli, S. L. Buchwald, J. Am. Chem. Soc. 2005, 127, 4685.
[8] T. Hoshi, T. Nakazawa, I. Saitoh, A. Mori, T. Suzuki, J. I. Sakai, H.
Hagiwara, Org. Lett. 2008, 10, 2063.
[9] L. Ackermann, H. K. Potukuchi, A. Althammer, R. Born, P. Mayer,
Org. Lett. 2010, 12, 1004.
[10] G. Altenhoff, R. Goddard, C. W. Lehmann, F. Glorius, J. Am. Chem.
Soc. 2004, 126, 15195.
Keywords: biaryls · cross-coupling · palladium · phosphane
ligands · Suzuki–Miyaura coupling
[11] M. G. Organ, S. C¸ alimsiz, M. Sayah, K. H. Hoi, A. J. Lough, Angew.
Chem. 2009, 121, 2419; Angew. Chem. Int. Ed. 2009, 48, 2383.
[12] C. Song, Y. Ma, Q. Chai, C. Ma, W. Jiang, M. B. Andrus, Tetrahe-
dron 2005, 61, 7438.
[13] For reviews describing the Tolman electronic parameter and cone
angle of phosphane ligands, see: a) C. A. Tolman, Chem. Rev. 1977,
[1] G. Bringmann, G. Gꢁnther, M. Ochse, O. Schupp, S. Tasler in Prog-
ress in the Chemistry of Organic Natural Products, Vol. 82 (Eds.: W.
Herz, H. Falk, G. W. Kirby, R. E. Moore, C. Tamm), Springer, New
York, 2001, pp. 1–249.
8000
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 7996 – 8001

Tetra-ortho-substituted Biaryl Synthesis
COMMUNICATION
77, 313. For a recent review, see: b) K. A. Bunten, L. Chen, A. L.
Fernandez, A. J. Poe, Coord. Chem. Rev. 2002, 223–234, 41.
our group, see: d) C. M. So, C. C. Yeung, C. P. Lau, F. Y. Kwong, J.
Org. Chem. 2008, 73, 7803.
[19] C. M. So, Z. Zhou, C. P. Lau, F. Y. Kwong, Angew. Chem. 2008, 120,
6502; Angew. Chem. Int. Ed. 2008, 47, 6402.
´
[14] For an activated ArCl, see: a) P. Koꢄovsky, S. Vyskoꢄil, I. Cꢅsaøovꢆ,
ˇ
J. Sejbal, I. Tislerovꢆ, M. Smrꢄina, G. C. Lloyd-Jones, S. C. Stephen,
[20] a) C. M. So, H. W. Lee, C. P. Lau, F. Y. Kwong, Org. Lett. 2009, 11,
317; b) C. M. So, C. P. Lau, F. Y. Kwong, Angew. Chem. 2008, 120,
8179; Angew. Chem. Int. Ed. 2008, 47, 8059; c) C. M. So, C. P. Lau,
A. S. C. Chan, F. Y. Kwong, J. Org. Chem. 2008, 73, 7734.
[21] Electron-rich ArB(OH)2 compounds are generally more nucleophil-
ic and readily undergo transmetallation, see: a) reference [2a]. In
contrast, electron-deficient ArB(OH)2 compounds are less nucleo-
philic and undergo transmetallation at a slower rate than electron-
neutral and -rich arylboronic acids. Hence, electron-deficient
ArB(OH)2 compounds are usually regarded as more challenging
substrates. Moreover, electron-poor boronic acids are prone to
homo-coupling side reactions, see: b) M. S. Wong, X. L. Zhang, Tet-
rahedron Lett. 2001, 42, 4087. Furthermore, electron-poor
ArB(OH)2 compounds are more susceptible to metal-catalysed pro-
todeboronation, see: c) H. G. Kuivila, J. F. Reuwer, J. A. Mangravite,
J. Am. Chem. Soc. 1964, 86, 2666.
[22] The GC yield of Table 1, entry 7 was significantly higher than the
isolated yield. The moderate isolated yield obtained is due to the
difficultly in chromatographically separating the desired product
from some dechlorinated anthracene. Note: commercially available
9-chloroanthracene consists of 1–4% anthracene impurity.
[23] Electron-deficient ArB(OH)2 compounds are less nucleophilic and
undergo transmetallation at a slower rate than electron-neutral and
-rich arylboronic acids. Hence, they are usually regarded as more
challenging substrates.
C. P. Butts, M. Murray, V. Langer, J. Am. Chem. Soc. 1999, 121,
7714. For Suzuki coupling of activated ArCls by
a [PdPPhACHTNUTGNRUEGN(2-
ClC6H4)2] catalyst, see: b) M. R. Pramick, S. M. Rosemeier, M. T.
Beranek, S. B. Nickse, J. J. Stone, R. A. Stockland, Jr., S. M. Bald-
win, M. E. Kastner, Organometallics 2003, 22, 523; for our investiga-
tions, see: c) F. Y. Kwong, K. S. Chan, C. H. Yeung, A. S. C. Chan,
Chem. Commun. 2004, 2336; for the triferrocenylphosphane system,
see: d) T. E. Pickett, F. X. Roca, C. J. Richards, J. Org. Chem. 2003,
68, 2592.
[15] Suzuki-type syntheses of difficult tri-ortho-substituted biaryls have
been sporadically studied, for the first example, see: a) S.-Y. Liu, M.
Choi, G. C. Fu, Chem. Commun. 2001, 2408; for Buchwaldꢇs devel-
opments, see: b) reference [7b]; for an example of trimethyl-substi-
tuted biaryls reported by Tsuji, see: c) T. Fujihara, S. Yoshida, H.
Ohta, Y. Tsuji, Angew. Chem. 2008, 120, 8434; Angew. Chem. Int.
Ed. 2008, 47, 8310; d) H. Ohta, M. Tokunaga, Y. Obora, T. Iwai, T.
Iwasawa, T. Fujihara, Y. Tsuji, Org. Lett. 2007, 9, 89; e) T. Iwasawa,
T. Komano, A. Tajima, M. Tokunaga, Y. Obora, T. Fujihara, Y.
Tsuji, Organometallics 2006, 25, 4665.
[16] To the best of our knowledge, no example of the use of the
[Ar3PPd] catalyst system for tri-ortho-substituted biaryl coupling
with o-substituents larger than tri-ortho-methyl has been reported.
[17] For [Ph2PCl], 500 g, USD=298.0; for [Cy2PCl], 5 g, USD=162.8,
from the Aldrich catalogue 2006.
[18] a) C. M. So, C. P. Lau, F. Y. Kwong, Org. Lett. 2007, 9, 2795; for in-
dolylphosphane independently developed by Beller and co-workers,
see: b) F. Rataboul, A. Zapf, R. Jackstell, S. Harkal, T. Riermeier,
A. Monsees, U. Dingerdissen, M. Beller, Chem. Eur. J. 2004, 10,
2983; for a related imidazolylphosphane, see: c) S. Harkal, F. Rata-
boul, A. Zapf, R. Jackstell, T. Riermeier, M. Beller, Adv. Synth.
Catal. 2004, 346, 1742; for other indolylphosphanes developed by
[24] For a recent review on alkylboronic acid couplings, see: H. Doucet,
Eur. J. Org. Chem. 2008, 2013.
[25] For all steps in new the ligand synthesis, products were simply puri-
fied by washing or crystallisation. No tedious column chromatogra-
phy is required.
Received: March 23, 2010
Published online: June 16, 2010
Chem. Eur. J. 2010, 16, 7996 – 8001
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8001