Polyhydrido(silylene)osmium and silyl(dinitrogen)ruthenium products through redistribution of phenylsilane with osmium and ruthenium pincer complexes

Article abstract of DOI:10.1002/anie.200390082

Migration/Redistribution Galore! The reaction of phenylsilane with a series of Os and Ru pincer complexes has led to the isolation of complexes 1-3, thus allowing the direct observation of 1,2-addition and redistribution reactions that are so fundamental in the transformations of organosilanes in catalysis. Complex 1 represents a rare example of a complex containing a donor-stabilized SiH₂ ligand.

Full text of DOI:10.1002/anie.200390082

Communications
complexes reported to date[5] the silylene moiety requires
stabilization from coordinating Lewis bases and/or hetero-
atom-based substituents (e.g., OR, SR, NR2),[6] whereas
nonstabilized silylene complexes are difficult to isolate.[7]
The tendency of Os and Ru pincer complexes to give
coordinatively unsaturated alkylidene and vinylidene prod-
ucts in reactions with alkynes[8a] prompted us to investigate
their reactivity towards hydrosilanes with the expectation that
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.
[15] C. Gonzalez, T. C. Allison, E. C. Lim, J. Phys. Chem. A 2001,
105, 10583; C. Gonzalez, E. C. Lim, J. Phys. Chem. A 1999, 103,
1437; C. Gonzalez, E. C. Lim, Chem. Phys. Lett. 2002, 357, 161.
[16] F. Piuzzi, I. Dimicoli, M. Mons, P. Milliÿ, V. Brenner, Q. Zhao, B.
Soep, A. Tramer, Chem. Phys. 2002, 275, 123.
[17] S. Y. Han, J. K. Song, J. H. Kim, H. B. Oh, S. K. Kim, J. Chem.
Phys. 1999, 111, 4041.
[18] J. K. Song, N. K. Lee, S. K. Kim, J. Chem. Phys. 2002, 117, 1589.
[19] J. Schiedt, R. Weinkauf, D. M. Neumark, E. W. Schlag, Chem.
Phys. 1998, 239, 511.
ꢀ
addition or 1,2 migration of the Si H bonds might afford
silylene products. Here we describe silylene and silyl com-
plexes obtained from the reaction of PhSiH3 with
[OsH2Cl{CH(C2H4PtBu2)2}]
tBu2)2C6H3}]
C6H4}] (3).[8d]
(1),[8b]
and [RuHCl{1,3-(CH2PtBu2)2-
[OsH2Cl{2,6-(CH2P-
(2),[8c]
Addition of 2 equiv of PhSiH3 to 1 in toluene afforded the
pentahydrido complex 4 in 83% yield [Eq. (1), P ¼ PtBu2]. A
Migration/Redistribution
Polyhydrido(silylene)osmium and
Silyl(dinitrogen)ruthenium Products Through
Redistribution of Phenylsilane with Osmium and
Ruthenium Pincer Complexes**
single-crystal X-ray analysis of 4 showed that the Os center
adopts an 8-coordinate, dodecahedral geometry consisting of
two orthogonal, trapezoidal planes defined by the atoms
Si1,H1Os,H5Os,P2 and Si2,H3Os,H4Os,H2Os (Figure 1, left). The
Dmitry G. Gusev,* Frÿdÿric-Georges Fontaine,
Alan J. Lough, and Davit Zargarian*
ꢀ
Os Si distances for the silyl (2.374 ä) and the base-stabilized
ꢀ
Transition-metal silylene complexes, silicon analogues of
metal carbenes, are reactive species believed to be important
intermediates in the industrial synthesis of chloromethylsi-
lanes,[1] the catalytic oligomerization of hydrosilanes,[2] and
the redistribution chemistry of organosilanes.[3] The high
reactivity of metal silylenes is related to the electron
deficiency of the silicon center, which is presumably due to
the very weak p bonding between the silicon atom and the
transition metal.[4] Consistent with this notion, in most of the
silylene (2.386 ä) ligand are in the normal range for Os Si
single bonds in hydrido(silyl)osmium complexes (3.34 to
2.49 ä).[9] The anticipated uncertainty associated with locat-
ing the hydride ligands in the solid-state structure of 4
prompted a study of its structure using ONIOM (DFT/HF)
geometry optimization (Figure 1, right);[10] the closeness of
the computational and experimental data indicates that the
structure of this complex has been established reliably.
Solution NMR data are also consistent with the proposed
structure for 4 and showthat the hydride ligands are highly
fluxional. For example, the averaged OsH5 resonance did not
decoalesce down to ꢀ1008C (1H NMR, [D8]toluene) and its
[*] Prof. D. G. Gusev
Department of Chemistry
Wilfrid Laurier University
Waterloo, ON, N2L3C5 (Canada)
Fax:( þ1)519-746-0677
E-mail:dgoussev@wlu.ca
Dr. A. J. Lough
Department of Chemistry (X-Ray Laboratory)
University of Toronto
Toronto, ON, M5S3H6 (Canada)
Prof. D. Zargarian, F.-G. Fontaine
Dÿpartement de chimie
Universitÿ de Montrÿal
Figure 1. Partial experimental (left) and calculated (right) structures of
4 with the methyl groups and the co-crystallized toluene molecule
omitted for clarity. Key experimental parameters [ä, deg]:Os-Si1
2.3739(8), Os-Si2 2.3857(8), Os-P2 2.4044(8), P1-Si2 2.361(1); P1-Si2-
Os 120.29(3), P2-Os-Si1 140.63(3), P2-Os-Si2 100.96(3), Si1-Os-Si2
104.84(3), H1Si-Si2-H2Si 102.9(19), HSi-Si2-Os (av.) 120.2(14). Calculat-
ed parameters [ä, deg]:Os-Si1 2.417, Os-Si2 2.409, Os-P2 2.454, P1-
Si2 2.363, Si1¥¥¥H1 2.071, Si2¥¥¥H3 2.246, Os-H1 Os-H5 1.638, 1.635,
1.670, 1.642, 1.653; P1-Si2-Os 124.3, P2-Os-Si1 142.2, P2-Os-Si2 99.8,
Si1-Os-Si2 101.3, H1Si-Si2-H2Si 101.0, HSi-Si2-Os (av.) 120.9, H2¥¥¥H5
1.883 (the shortest H¥¥¥H separation).
Montrÿal, PQ, H3C 3J7 (Canada)
Fax:( þ1)514-343-7586
E-mail:zargarian.davit@umontreal.ca
[**] We gratefully acknowledge research funding from NSERC (D.G. and
D.Z.), Research Corporation (D.G.), and FCAR (D.Z.). F.-G.F. is
grateful to NSERC for PGS(A&B) scholarships.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
216
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Angewandte
Chemie
average relaxation time T1min was long (215 ms at ꢀ208C and
300 MHz), which is typical of polyhydrides with no short
H¥¥¥H contacts.
Evidently, complex 1 and two molecules of PhSiH3 have
undergone a series of redistribution reactions culminating in
ꢀ
the net hydrogenation of the Os C bond and the generation
of one silyl, one base-stabilized silylene, and five hydride
ligands. Complex 4 is the first compound bearing a base-
stabilized SiH2 ligand. We have briefly probed the relative
stability of the P!Si interaction in the presence of other
Lewis bases. Thus, addition of 1 equiv of NEt3 to a C6D6
solution of 4 reduced the intensities of the 31P resonances
attributed to the P nuclei coordinated to the SiH2 moiety (d ¼
14.5 ppm) and the Os center (d ¼ 56.6 ppm), and gave rise to
two new resonances at d ¼ 27.4 and 50.3 ppm (conversion ca.
50%). The chemical shift of one of the newresonances is very
close to that of the uncoordinated bis(di-tert-butylphospha-
nyl)pentane ligand (d ¼ 27.7 ppm in C6D6), indicating that this
ligand is monodentate in the resulting complex. Similar
observations were made when 1 equiv of PCy3 was reacted
with 4: new 31P resonances emerged at d ¼ 27.5, 48.9, and
ꢀ4.9 ppm (conversion ca. 80%); decoupling experiments
have allowed us to assign the latter resonance to the Cy3P!
SiH2 moiety. These preliminary observations demonstrate
that good Lewis bases can displace the PtBu2 group, thereby
generating newdonor-stabilized SiH 2 complexes.
Figure 2. Partial calculated structure of 5a with the methyl groups
omitted for clarity. Key parameters [ä, deg]:Os-Si 2.281, Os-C1 2.171,
Os-P1 2.387, Os-P2 2.394, Os-H1 1.670, Os-H2 1.641, Os-H3 1.651,
H2¥¥¥H3 1.652; P1-Os-P2 157.3, Si-Os-C1 161.9, Si-Os-H1 82.4, Si-Os-
H2 63.9, C1-Os-H1 79.9, C1-Os-H3 74.3, H2-Os-H3 60.2.
vations to indicate that 5 is a silylene complex with a plane of
symmetry that renders the two phosphorus nuclei equivalent;
ꢀ
the rotation of the silylene moiety about the Os Si bond gives
rise to two rotamers, which were assigned the structures 5a
and 5b on the basis of the difference NOE spectra. For
example, isomer 5a showed a strong NOE between the SiPh
and the H2/H3 signals, whereas no NOE was detected
between the signals for the ortho hydrogen atoms of SiPh
and H1 (numbering according to Figure 2). In contrast, a
strong NOE was detected in isomer 5b between the ortho
hydrogen atoms of SiPh and H1. The NOE experiments also
indicated a slowexchange at ꢀ708C between 5a and 5b:
irradiation of the H1 resonance of one isomer resulted in a
partial saturation transfer to the corresponding hydride
resonance of the other. Integration of the hydride signals
allowed us to determine that the 5b/5a equilibrium has a
small DG (ꢀ0.7 kcalmolꢀ1); consistent with this, the compu-
To better understand the influence of the ligand on the
reactivity of 1, we investigated the reaction of PhSiH3 with
complex 2, a direct analogue of 1 that has a pincer ligand with
a more rigid backbone. In this case, the trihydrido(silylene)
product 5 was obtained in 60% yield [Eq. (2), P ¼ PtBu2].
tational study showed
a very small energy difference
(ꢀ0.01 kcalmolꢀ1) between the two isomers.
The different reactivities of 1 and 2 underline the
importance of the auxiliary ligand in determining the course
and outcome of the reaction with PhSiH3. We have also
probed the importance of the metal atom by reacting PhSiH3
with 3, the Ru analogue of 2 that displays an agostic
ꢀ
Complex 5 undergoes a slowdecomposition at room temper-
ature, both in the solid and in solution, as evident from a
gradual color change from yellowto dark brown. The thermal
instability of 5 prevented crystallographic characterization,
but NMR spectra collected at lowtemperature using samples
prepared at ꢀ708C established the identity of the product as a
trihydrido(silylene) complex that exists as two rotamers in
solution, as described below. In addition, a computational
study using the ONIOM (DFT/HF) methodology supported
the structural assignments for both isomers (the optimized
structure of 5a is shown in Figure 2).
interaction between the central C H moiety and the Ru
center. This reaction gave the dinitrogen(silyl) complex 6 in
75% yield [Eq. (3), P ¼ PtBu2]. The identity of 6 was
The 31P{1H} NMR spectrum of the isolated solid showed a
single resonance (d ¼ 85.7 ppm), whereas the 29Si{1H} NMR
spectrum showed two triplets (6:1 signal intensity ratio) in a
chemical shift region characteristic of silylenes (d ¼ 239.3 (5a)
established by spectroscopic studies and X-ray crystallogra-
phy (Figure 3), as described below.
2
ꢁ
and 246.5 ppm (5b), JPSi ¼ 9.4 Hz). Two sets of resonances
The IR spectrum of complex 6 features strong N N and
1
Si H stretches at 2142 and 2105 cmꢀ1, respectively. The
ꢀ
were also observed in the hydride region of the H NMR
ꢀ
spectrum (1:2 intensity ratio within each set), implying two
different trihydrido substructures. We interpret these obser-
presence of the Si H group was also evident from the NMR
1
3
spectra, which showed a H signal (d ¼ 5.37 ppm, d, JPH
¼
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217

Communications
transformations with the Os complex 1 are even more
interesting, since they involve complex redistribution reac-
tions that convert two molecules of PhSiH3 to the silyl ligand
Ph2SiCl and the unprecedented parent silylene moiety SiH2.
Experimental Section
Spectroscopic data for compounds 4 6 are given below; all other
information pertaining to the synthetic and computational work is
provided in the Supporting Information. Complete crystallographic
data for the structural analyses have been deposited with the
Cambridge Crystallographic Data Centre. CCDC-190307 (4) and
CCDC-190308 (6) contain the supplementary 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: (þ 44)1223-336-033; or deposit@ccdc.cam.ac.uk).
Complex 4: elemental analysis calcd for C33H63ClOsP2Si2¥toluene
Figure 3. Partial experimental structures of 6 with the methyl groups
omitted for clarity. Key parameters [ä, deg]:Ru-C3 2.068(3), Ru-Si
2.2821(7), Ru-N1 2.014(2), Ru-P1 2.3512(7), Ru-P2 2.3632(7), N1-N2
1.099(3); P1-Ru-P2 157.35(3), C3-Ru-Si 78.23(7), C3-Ru-N1 178.5(1),
Si-Ru-N1 100.33(7).
(895.811): C 53.63, H 7.99; found: C 53.61, H 8.40. IR (Nujol): n˜ (nSiH
,
nOsH) ¼ 2079, 2066, 2001, 1913 cmꢀ1. NMR (208C, C6D6, J in Hz):
1H NMR: d ¼ ꢀ9.70 (ddt, 2JHP ¼ 5.9, 3JHP ¼ 8.1, 3JHH ¼ 1.6, 5H, OsH5),
1.00 (d, 3JHP ¼ 12.9, 18H, CH3), 1.16 (d, 3JHP ¼ 12.3, 18H, CH3), 1.1 1.8
2
3
1
(m, 10H, CH2), 4.74 (dd, JHP ¼ 19.0, JHP ¼ 3.0, JHSi ¼ 179.3, SiH2),
17.7 Hz) featuring the anticipated Si satellites (1JSiH ¼ 206 Hz)
and a 29Si{1H} signal with the appropriate multiplicity (d ¼
31.5 ppm, t, 2JPSi ¼ 24 Hz). The asymmetric nature of this silyl
ligand renders the CH2 and PtBu2 groups inequivalent in the
NMR spectra of 6. According to the X-ray data, the geometry
around Ru in 6 is square-pyramidal with the silyl ligand
occupying the apical position; the absence of a ligand trans to
the silyl moiety is presumably responsible for the very short
7.12, 7.30, 8.34 ppm (m, 10H, Ph). 13C{1H} NMR: d ¼ 14.0 (d, JCP
¼
21.7, CH2), 20.3 (s, CH2), 21.0 (d, JCP ¼ 17.7, CH2), 22.9 (d, JCP ¼ 1.6,
CH2), 29.6 (dd, JCP ¼ 8.5, 10.2, CH2), 29.4 (s, CH3), 30.0 (s, CH3), 34.6
(d, JCP ¼ 17.1, PC), 35.3 (d, JCP ¼ 20.7, PC), 127.0 (s, CH), 127.5 (s,
CH), 135.4 (s, CH), 151.5 ppm (d, JCP ¼ 2.7, C). 31P{1H} NMR: d ¼ 56.6
(2JPSi ¼ 27.8), 14.5 ppm (1JPSi ¼ 44.6). 29Si{1H} NMR: d ¼ 30.4 (dd,
3JSiP ¼ 2.8, 2JSiP ¼ 27.8), ꢀ67.4 ppm (dd, 2JSiP ¼ 5.5, 1JSiP ¼ 44.7).
Complex 5: IR (Nujol): n˜ (nOsH) ¼ 2177, 2089, 1870 cmꢀ1. NMR
(ꢀ708C, [D8]toluene, J in Hz): 1H NMR: d ¼ ꢀ7.50 (5a), ꢀ7.34 (5b)
2
(br, 2H, OsH2), ꢀ6.98 (5b) (t, JHP ¼ 11.4, OsH), ꢀ6.33 ppm (5a) (t,
ꢀ
ꢀ
ꢁ
Ru Si bond (2.282 ä). The Ru N (2.014 ä) and N N
(1.099 ä) distances are similar to the corresponding distances
in related neutral dinitrogen complexes: [RuH(N2)-
{CH(C2H4PtBu2)2}] (1.965/1.117 ä),[11a] [RuH2(N2){k3(P,P,P)-
PhP(C3H6PCy2)2}] (2.005/1.093 ä),[11b] and [(PPh3)2RuH-
(m-H3)Ru(N2)(PPh3)2] (2.003/1.086 ä).[11c]
2JHP ¼ 13.8, OsH). 1H{31P} NMR: d ¼ 1.01 (s, 18H, CH3), 1.18 (s, 18H,
2
2
CH3), 3.24 (d, JHH ¼ 15.9, 2H, CH2), 3.41 (d, JHH ¼ 15.9, 2H, CH2),
7.0 7.3 (m, 6H, Ar), 8.66 ppm (d, 2JHP ¼ 7.5, 2H, Ph). 31P{1H} NMR:
d ¼ 85.7 ppm (s). 13C{1H} NMR: d ¼ 29.2 (br, CH3), 34.0 (vt, vJ ¼ 10.5,
v
v
v
PC), 35.9 (vt, J ¼ 12.0, PC), 42.8 (vt, J ¼ 14.8, CH2), 120.0 (vt, J ¼
7.8, CH, Ar), 123.3 (s, CH, Ar), 132.4 (s, CH, Ph), 128.8 (s, CH, Ph),
135.2 (s, CH, Ph), 149.3 (vt, vJ ¼ 8.5, C, Ar), 149.9 (s, C, Ph), 155.2 ppm
(t, 2JCP ¼ 3.7, RuC). 29Si{1H} NMR: d ¼ 239.3 (5a), 246.5 ppm (5b) (t,
2JSiP ¼ 9.4).
A comparison of the reactivities observed for complexes 2
and 3 provides some insight into the mechanism of their
reactions with PhSiH3. The following sequence of steps can be
envisaged: 1) addition of PhSiH3 to 2/3 generates the initial
silyl ligand PhSiH2 and releases H2; 2) a redistributive SiH/
MCl exchange gives the 16-electron intermediate [(PCP-
ligand)MH2(PhSi(H)Cl)]; 3) the OsIV intermediate undergoes
a 1,2 migration of SiH to give the trihydrido(silylene) complex
5, whereas its Ru counterpart loses H2 to give the dinitro-
gen(silyl) complex 6. The difference in the reactivities of 2
Complex 6: elemental analysis calcd for C30H49ClN2P2RuSi
(664.29): C 54.24, H 7.43, N 4.22; found: C 53.90, H 7.64, N 4.02. IR
(Nujol): n˜ ¼ 2142(nN N), 2105 cmꢀ1 (nSiH). NMR ([D8]toluene, J in
¼
1
3
1
1
Hz): H NMR: d ¼ 5.37 ppm (d, JHP ¼ 17.7, JHSi ¼ 206, SiH). H{31P}
NMR: d ¼ 0.90, 0.94, 1.20, 1.42 (s, 36H, CH3), 2.56 (d, 2JHH ¼ 16.4, 1H,
2
2
CH2), 2.78 (d, JHH ¼ 16.4, 1H, CH2), 3.09 (d, JHH ¼ 16.7, 1H, CH2),
3.73 (d, JHH ¼ 16.7, 1H, CH2), 6.9 7.1 ppm (m, 8H, Ar). 31P{1H}
2
NMR: d ¼ 74.8, 80.7 ppm (d, 2JPP ¼ 217). 13C{1H} NMR: d ¼ 30.5, 30.6,
1
1
32.1, 32.9 (d, CH3), 35.3 (d, JCP ¼ 21.9, CH2), 36.3 (d, JCP ¼ 19.3,
CH2), 35.0, 36.6, 37.5, 38.1 (d, PC), 121.9 (d, 3JCP ¼ 17.0, CH, Ar), 122.5
(d, 3JCP ¼ 16.7, CH, Ar), 124.2 (s, CH, Ar), 126.5, 127.8, 135.6 (s, CH,
ꢀ
and 3 is presumably due to the weaker Ru H bonds
ꢀ
(compared to Os H bonds) and the prevalence of the þ 2
3
oxidation state in the chemistry of Ru complexes stabilized by
phosphanes.
Ph), 144.6 (d, JCP ¼ 2.3, SiC, Ph), 156.0 (m, C, Ar), 178.1 ppm (t,
2JCP ¼ 2.9, RuC). 29Si{1H} NMR: d ¼ 31.5 ppm (t, JSiP ¼ 24).
2
In summary, the described reactions of PhSiH3 with
complexes 1 3 have provided an opportunity to study the
direct and unassisted conversion of a hydrosilane to transi-
tion-metal silylene derivatives, a transformation believed to
be important in many catalytic processes involving organo-
silicon compounds.[12] The spontaneous silyl-to-silylene con-
versions observed here are rather rare, though they can be
induced by photolysis[13] or assisted by Lewis acids.[14] On the
Received: July 25, 2002 [Z19819]
[1] For details on the preparation of chloromethylsilanes from
elemental silicon and chloromethane, the so-called Direct
Process, see: a) M. P. Clarke, J. Organomet. Chem. 1989, 376,
165; b) M. P. Clarke, J. Organomet. Chem. 1991, 408, 149; c) for
information on the reactivities of silylenes with chloroalkanes in
solution see: P. W. Wanandi, P. B. Glaser, T. D. Tilley, J. Am.
Chem. Soc. 2000, 122, 972.
ꢀ
other hand, silylene formation by Si SiR3 migrations has
been observed with RhI,[15] IrI,[16] and NiII[17] systems. The
218
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Angewandte
Chemie
[2] a) K. A. Brown-Wensley, Organometallics 1987, 6, 1590; b) E. A.
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[3] H. Yamashita, M. Tanaka, M. Goto, Organometallics 1992, 11,
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Dolgushin, M. Y. Antipin, Organometallics 2001, 20, 1001;
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Asbestos Decontamination
Soil Fungal Hyphae Bind and Attack Asbestos
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Elena Martino, Laura Prandi, Ivana Fenoglio,
Paola Bonfante, Silvia Perotto,* and Bice Fubini*
Once a major issue in occupational health and safety, asbestos
has nowbecome a general environmental problem. [1] Several
mountain areas–from the western Alps in Italy to the Sierra
Nevada in the USA–are rich in asbestos and asbestiform
minerals, and many defunct asbestos industries and mines
have left substantial amounts of asbestos fibers on the
abandoned sites. Exposure to airborne asbestos fibrils causes
a severe pneumoconiosis (asbestosis) and malignancies such
[10] a) The computational studies were performed on a 2.2 GHz
Pentium IV PC using Gaussian98 (RevisionA.11), M. J. Frisch,
G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R.
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4]
as bronchogenic carcinoma and pleural mesothelioma.[2
The decontamination of asbestos fibers dispersed over wide
areas of soil and in waters obviously requires a different
approach from what was proposed for asbestos localized in
buildings.[5] The fibers cannot be removed but have to be
inactivated in situ without damaging the environment. New,
environmentally friendly techniques are thus required for
[*] Prof. Dr. S. Perotto, Dr. E. Martino,+ Prof. Dr. P. Bonfante
Interdepartmental Center ™G. Scansetti∫ for Studies on Asbestos
and Other Toxic Particulates
University of Torino, Dipartimento Biologia Vegetale
via le Mattioli 25, 10125 Torino (Italy)
Fax:( þ39)11-670-7459
E-mail:silvia.perotto@unito.it
Prof. Dr. B. Fubini, Dr. L. Prandi,+ Dr. I. Fenoglio
Interdepartmental Center ™G. Scansetti∫ for Studies on Asbestos
and Other Toxic Particulates
University of Torino, Dipartimento di Chimica IFM
via P. Giuria 7, 10125 Torino (Italy)
Fax:( þ39)11-670-7566
E-mail:bice.fubini@unito.it
[+] E.M. and L.P. contributed equally to the work.
[**] The research was funded in part by CNR, Finalized Project on
Biotechnology (Subproject 2) and by Regione Piemonte, Italy.
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2003, 42, No. 2
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1433-7851/03/4202-0219 $ 20.00+.50/0
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