Syntheses and characterization of dimolybdenum and dirhodium complexes containing 2-pyridylphosphine ligands

Article abstract of DOI:10.1016/S0277-5387(02)01023-9

Reaction of dimolybdenum tetrakis(trifluoroacetate) with 2-pyridylphosphines leads to a replacement of one or two of the trifluoroacetato ligands as equatorial ligands, depending on the excess ligand used. In the product molecules, the replaced acetato ligands are found as monodentate ligands in the axial positions and the Mo-Mo quadruple bond is significantly weakened. The examined complexes are fully characterized, including two single crystal X-ray structures. Dimolybdenum tetraacetate does not react with 2-pyridylphoshpines. Dirhodium tetraacetate, in contrast, reacts readily with 2-pyridylphosphines. The 2-pyridylphosphines are attached to the product molecule in axial position by a P → Rh donor interaction, which weakens the Rh-Rh single bond. Reaction of 2-pyridylphosphines with dirhodium tetrakis(trifluoroacetate) leads to a product mixture.

Full text of DOI:10.1016/S0277-5387(02)01023-9

Polyhedron 21 (2002) 1737ꢀ1746
/
www.elsevier.com/locate/poly
Syntheses and characterization of dimolybdenum and dirhodium
complexes containing 2-pyridylphosphine ligands
Guofang Zhang, Jin Zhao, Gabriele Raudaschl-Sieber, Eberhardt Herdtweck,
Fritz E. Kuhn *
¨
Anorganisch-Chemisches Institut der Technischen Universitat Munchen, Lichtenbergstraße 4, D-85747 Garching bei Munchen, Germany
¨ ¨ ¨
Received 28 January 2002; accepted 23 April 2002
Abstract
Reaction of dimolybdenum tetrakis(trifluoroacetate) with 2-pyridylphosphines leads to a replacement of one or two of the
trifluoroacetato ligands as equatorial ligands, depending on the excess ligand used. In the product molecules, the replaced acetato
ligands are found as monodentate ligands in the axial positions and the Moꢀ/Mo quadruple bond is significantly weakened. The
examined complexes are fully characterized, including two single crystal X-ray structures. Dimolybdenum tetraacetate does not
react with 2-pyridylphoshpines. Dirhodium tetraacetate, in contrast, reacts readily with 2-pyridylphosphines. The 2-pyridylpho-
sphines are attached to the product molecule in axial position by a P0
/
Rh donor interaction, which weakens the Rhꢀ
/Rh single
bond. Reaction of 2-pyridylphosphines with dirhodium tetrakis(trifluoroacetate) leads to a product mixture. # 2002 Elsevier
Science Ltd. All rights reserved.
Keywords: Metalꢀmetal interactions; Molybdenum; Pyridylphosphines; Rhodium
/
1. Introduction
some dimeric complexes of that type are active catalysts
for the reduction of alkenes [7b].
The coordination chemistry of 2-pyridylphosphine
ligands (Scheme 1) has been studied in some detail
during the recent years, mainly because of their ability
to coordinate both with their phosphorus and their
nitrogen atoms, which possess different coordination
properties [1]. In addition to numerous mononuclear
complexes [2] several binuclear species [3] as well as
clusters [4] and oligomers [5] containing 2-pyridylpho-
sphine ligands have been described.
We have recently published some work on the
polymerization of cyclopentadiene with solvent ligated
metalꢀmetal complexes [8]. One of the drawbacks of
/
cyclopentadiene polymerized by a cationic mechanism is
its pronounced sensitivity to oxygen, for it is easily
possible to attack the remaining double bond in the
polymer chain [9]. Therefore, it would be of interest to
combine both polymerization and subsequent hydro-
genation with one catalytic system. Already in the late
1960s Wilkinson and coworkers showed that the reac-
tion of Mo2(m-O2CCH3)4 with HBF4 in methanol and
the subsequent treatment with a twofold excess of PPh3
leads to a compound that is able to hydrogenate alkenes
and alkynes [10].
For the coordination of complexes containing metalꢀ
metal multiple bonds, mainly diphenyl-2-pyridylpho-
phine, PPh2py, has been used [3f,3g,3h,3i,3j,6]. Metalꢀ
/
/
metal bonded complexes containing the ligands PPhpy2
and Ppy3 are comparatively rare [7], especially few X-ray
crystal structures with these ligands bridging two metal
centers have been reported to date [7c,7d]. However,
We, therefore, attempted to synthesize molecules with
both acetato ligands and phenyl pyridylphospine li-
gands. It is of particular interest whether the nitrogen
donor atoms of the ligands are strongly fixed to the
metal centers or whether opening and closing of the Nꢀ
/
M bond can be observed especially in donor solvents.
This could enable the (reversible) binding of substrate
molecules to the metal center to initiate a polymeriza-
* Corresponding author. Tel.: ꢁ
289-13473
E-mail address: fritz.kuehn@ch.tum.de (F.E. Kuhn).
/
49-89-289-13108/081; fax: ꢁ49-89-
/
¨
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 0 2 3 - 9

1738
G. Zhang et al. / Polyhedron 21 (2002) 1737ꢀ
/
1746
Scheme 1.
tion process while the pyridine ligand would otherwise
protect the potential coordination site, thus enhancing
the initiator stability. In this work, we report the
syntheses and characterization of dimolybdenum and
dirhodium compounds bridged and/or axially coordi-
nated by PPh2py, PPhpy2 and Ppy3 ligands. The X-ray
crystal structures of selected complexes are described as
well.
well. The reason for this behavior might be that a
coordination of Ppy3 disfavors the coordination of a
second ligand of this type in trans position, due to the
more pronounced trans effect of Ppy3 in comparison to
PPhpy2. The cis position is probably not available for a
second Ppy3 ligand because of steric reasons. The
compounds 1ꢀ6 are insoluble in CH2Cl2, CH3CN,
/
diethyl ether, and decompose in methanol, DMF and
DMSO. This decomposition could be due to an opening
of the pyridineꢀ
presence of donor solvents with subsequent cleavage of
the metalꢀmetal bond.
/
N bond to the metal center in the
2. Results and discussion
/
2.1. Synthesis
The reaction of Mo2(m-O2CCF3)4 with 2 equiv. of the
corresponding ligand at room temperature yields the
ð1Þ
complexes 1ꢀ
3, respectively, with only one CF3CO2ꢂ
group in the axial position according to Eq. (1). When
excess of ligand (fourfold in these cases) is used at room
/
temperature, complexes 4ꢀ6 (complex 6 is always
/
ð2Þ
contaminated with derivative 3), with two axial
CF3CO2ꢂ groups are formed according to Eq. (2).
Even under reflux conditions a mixture of 3 and 6 is
isolated after 4 h, containing only approximately 73% of
complex 6. Reaction of a much higher excess of Ppy3
with Mo2(m-O2CCF3)4 leads to a mixture of products as
The orangeꢀ
/
red complexes 7ꢀ
/
9 can be prepared by
reacting excess of ligand with Rh2(m-O2CCH3)4 at room
temperature (Eq. (3)). The same products 7ꢀ9, however,
are also formed when Rh2(m-O2CCH3)4 and the ligands
are reacted in a 1:1 stoichiometric relationship. Half of
/

G. Zhang et al. / Polyhedron 21 (2002) 1737ꢀ
/
1746
1739
the Rh2 starting complex remains unchanged, but no
product with only one axial ligand is formed. Heating or
even refluxing the reaction mixture also does not
influence the outcome to our experience (i.e. no
equatorial substitution products are formed). The rho-
We found no indication for the formation of ortho-
metallated triaryl phosphines bridging the MꢀM bonds
/
in any of our reactions. Despite the fact that there are
several related compounds forming orthometallated
products, this was not observed in our case since our
reaction conditions obviously do not favor the abstrac-
tion of aryl ring protons. With appropriately
changed reaction conditions, however, it might be
possible to generate orthometallated derivatives [4j]
[11]. The geometry of the examined compounds (see
dium complexes 7ꢀ9 are soluble in CH2Cl2, but
/
insoluble in THF, acetone and CH3CN. It is noteworthy
in this context that Mo2(m-O2CCH3)4 does not react
with PPh2py, PPhpy2 and PPy3 (see Eq. (1)). The
interaction of Rh2(m-O2CCF3)4 with PPh2Py, PPhPy2
and PPy3 leads to a mixture of different products and
decomposition products (Eq. (4)). It was, unfortunately,
not possible to separate the compounds and characterize
them properly.
X-ray part) would*
/
at least in principle*allow such
/
reactions.
2.2. Thermogravimmetry
The complexes 1, 4 and 7 as well as the pyridylpho-
sphine PPh2py and the starting materials
Mo2(O(O)CCF3)4 and Rh2(O(O)CCH3)4 have been
examined by thermogravimmetry (TGA). PPh2py starts
subliming at approximately 179 8C and sublimes com-
pletely, not leaving any residue. Rh2(O(O)CCH3)4 has a
decomposition onset at 278 8C and Mo2(O(O)CCF3)4
starts subliming at 226 8C. The compound 7 displays a
decomposition onset at 296 8C, being about 20 8C
higher than that of the Rh2 starting material, while
compound 4 starts decomposing at approximately
220 8C, slightly below the sublimation point of the
Mo2 starting material. The same is true for compound 1,
which starts decomposing at 211 8C. In the case of
compound 1 only one pronounced decomposition step is
observed. It starts decomposing slowly with an onset at
approximately 211 8C, continues (beginning at 290 8C)
with a sharper decline and then keeps loosing mass until
the end of the measurement at 650 8C. The total mass
loss until the end of the more pronounced step is about
40% of the original mass, which would be the sum of one
trifluoro acetate ligand and the PPh2py ligand. The total
mass loss until the end of the measurement at 650 8C is
about 68% of the original mass. In the case of
compound 7, one clear decomposition step is observed.
It accounts for 30% of the original mass and leads to an
unspecific further decomposition, which reaches a total
mass loss of 45% at 650 8C.
ð3Þ
ð4Þ
The explanation for the different reaction behavior of
the Mo2 and Rh2 complexes seems to be that the
stronger Moꢀ
RhꢀO interactions) in the tetra acetato derivatives
cannot be easily cleaved by the pyridylphosphines under
the reaction conditions applied. The weaker Moꢀ
/
O interactions (in contrast to the weaker
/
/O
bonds to the electron withdrawing tetrakis(trifluoroace-
tato) ligands are easier to break. In both cases, however,
an attack on the axial positions is not observed,
probably due to the generally weak interactions of
Mo(II)2 units with ligands in this position. In the case
of the Rh2 complex, the tetra acetato complex reacts
with the pyridylphosphines, since the interactions with
The observed curve shapes and mass losses indicate
that in all three cases (complexes 1, 4 and 7) the
decomposition starts-as expected-with a loss of an axial
ligand. Then the complexes start losing equatorial
ligands. A sublimation of the complexes without decom-
position is not observed.
ligands in the axial positions of the Rhꢀ
/
Rh unit are
stronger and lead to more stable products. Equatorial
bonds, however, are also not cleaved in the Rh2
complexes. In the case of the more reactive
Rh2(O(O)Cꢀ
/
CF3)4 derivative, the axial and equatorial
positions are available to an attack and the reaction
leads to a product mixture. Some of the products are
probably not stable and undergo further reactions, thus
leading to an inseparable mixture of product com-
pounds.
2.3. X-ray crystallography
The molecular structures of compounds 5 and 6 have
been determined by single crystal X-ray crystallography.
PLATON representations of compounds 5 and 6 are

1740
G. Zhang et al. / Polyhedron 21 (2002) 1737ꢀ1746
/
Fig. 1. ORTEP [15] drawing of the molecular structure of the major form of 5 in the solid state; thermal ellipsoids are at the 50% probability level and
hydrogens omitted for clarity.
shown in Figs. 1 and 2, respectively. Selected bond
distances and angles are listed in Table 1 for the
compounds 5 and 6.
The dimolybdenum centers are coordinated by two
bridging CF3COOꢂ ligands, which are trans positioned
to each other. The complex resides on a crystallographic
Fig. 2. ORTEP [15a] drawing of the molecular structure of 6 in the solid state; thermal ellipsoids are at the 50% probability level and hydrogens
omitted for clarity.

G. Zhang et al. / Polyhedron 21 (2002) 1737ꢀ
/
1746
1741
Table 1
away from the axial region cause a displacement of the
axial CF3COOꢂ group away from the ‘linear’ axial site
by 156.69(5)8 (compound 5) or 156.11(4)8 (complex 6),
respectively.
Comparison of selected structural data for complexes 5 and 6. Mo and
Mo? are connected via the symmetry operation (ꢂx, ꢂy, 1ꢂz) for 5
and (ꢂx, ꢂy, ꢂz) for 6, respectively
Similar observations are reported for other dimolyb-
denum(II) compounds in the literature [3h]. Due to the
5
6
˚
Bond distances (A)
strong interaction of axial CF3COOꢂ group with the
˚
Mo distances, 2.1901(3) A for 5
MoꢀP
2.5085(8)
2.105(2)
2.399(2)
2.1901(3)
2.118(2)
2.212(2)
1.261(4)
1.254(4)
1.253(4)
1.206(5)
2.5254(5)
2.1265(13)
2.3492(13)
2.1884(2)
2.1123(13)
2.2056(16)
1.265(2)
Mo24ꢁ moiety, the Moꢀ
/
MoꢀO2
MoꢀO3
MoꢀMo?
Mo?ꢀO1
Mo?ꢀN1
O1ꢀC2
O2ꢀC2
O3ꢀC4
O4ꢀC4
˚
and 2.1884(2) A for 6, respectively, are approximately
˚
0.1 A longer than in the precursor complex Mo2(m-
˚
O2CCF3)4 (Moꢀ
/
Mo: 2.090(4) A) [12]. The Moꢀ
/Mo
bond lengths observed in the compounds 5 and 6 are
among the longest Moꢀ
/
Mo quadruple bond distances
reported to date. [13,14] This lengthening in comparison
1.254(2)
1.259(2)
1.219(3)
to the starting material is due to the weakening of the
Moꢀ
/
Mo bond by the axial ligand coordination.
Bond angles (8)
PꢀMoꢀO2
94.36(6)
74.75(5)
83.48(2)
88.39(6)
166.93(6)
98.52(7)
91.23(5)
177.11(8)
90.70(8)
156.69(5)
81.32(7)
92.60(7)
89.98(5)
108.49(6)
86.42(8)
125.6(3)
117.0(3)
117.4(3)
129.1(3)
115.3(3)
115.6(3)
91.57(4)
73.18(4)
83.96(1)
PꢀMoꢀO3
2.4. Vibrational spectroscopy
Mo?ꢀMoꢀP
PꢀMoꢀO1?
PꢀMoꢀN1?
O2ꢀMoꢀO3
Mo?ꢀMoꢀO2
O1?ꢀMoꢀO2
O2ꢀMoꢀN1?
Mo?ꢀMoꢀO3
O1?ꢀMoꢀO3
O3ꢀMoꢀN1?
Mo?ꢀMoꢀO1?
Mo?ꢀMoꢀN1?
O1?ꢀMoꢀN1?
O1ꢀC2ꢀO2
O1ꢀC2ꢀC1
O2ꢀC2ꢀC1
O3ꢀC4ꢀO4
O3ꢀC4ꢀC3
O4ꢀC4ꢀC3
90.96(4)
The solid-state IR spectra of complexes 1ꢀ
strong absorption bands in the range of 1650ꢀ
/6 show
167.46(4)
84.17(5)
89.74(4)
/
1700
cmꢂ1, indicating the presence of monocoordinated
carboxylate group(s) [3f]. The vibrations observed at
1687 (4), 1690 (5) and 1684 cmꢂ1 (6) are assigned to
terminal carboxylate groups. The vibrations at 1650 (1),
1654 (2) and 1647 cmꢂ1(3) are also assigned to the
terminal carboxylate group. The vibrations located at
approximately 1600 cmꢂ1 represent the asymmetric
stretching vibration of the bridging trifluoroacetates.
177.15(5)
89.79(5)
156.11(4)
95.33(5)
94.57(5)
91.81(4)
108.51(4)
87.46(5)
126.33(17)
116.48(16)
117.09(17)
130.10(19)
114.76(17)
115.09(18)
The Raman active n(Moꢀ
case of 4, 5 and 6 the Moꢀ
significantly weakened by the change of the coordina-
tion mode (4 (305 cmꢂ1), 5 (307 cmꢂ1), 6 (308 cmꢂ1))
in comparison to the axially uncoordinated precursor
Mo2(m-O2CCF3)4 (397 cmꢂ1) [8]. The Moꢀ
/Mo) band shows that in the
/Mo bond strength is
/
Mo stretch-
ing modes of the complexes 1, 2 and 3, observed at 375
cmꢂ1 for 1, 376 cmꢂ1 for 2 and at 378 cmꢂ1 for 3
indicate a much less pronounced influence on the
center of inversion. The other two CF3COOꢂ groups
coordinate to one of the metal centers in the axial
position. The two 2-pyridylphosphine ligands are in a
head-to-tail (HT) relationship and are trans to each
other. A similar structure has been reported for Mo2(m-
PPh2Py)2(m-CH3COO)2Cl2 by Cotton and Matusz
[3h,3i]. In our case and in that of Cotton’s compound
the thermodynamically more favored HT relationship
and not the generally more common head-to-head (HH)
arrangement is observed. The reason for the formation
of the HT product might in our case be the stepwise
strength of the Moꢀ
/
Mo quadruple bond, since only
one axial ligand is present. The influence of exchanging
a Ph group in the ligand by a py ligand, however, has
seemingly very little influence on the Moꢀ
/
Mo bond
strength and is of the same order of magnitude as the
error range of the measurement.
The vibrations of the bidentate acetato groups are
located at 1600, 1423, 623, 507 cmꢂ1 for 7, 1596, 1434,
650, 542 cmꢂ1 for 8 and at 1594, 1422, 695, 561, 525
cmꢂ1 for 9, respectively. These vibrations indicate that
only one type of carboxylate exists; the strong Raman
band at 335 cmꢂ1 (7), 337 cmꢂ1 (8) and 338 cmꢂ1 (9)
formation of 4ꢀ
/
6 from the in-situ precursors 1ꢀ3, which
/
display only one bridging ligand. The first P(Ar)3 ligand
probably directs the second P(Ar)2 ligand to the
thermodynamically more favored HT arrangement,
assisted by the long reaction time at high temperature
and the steric bulk of the ligands. As can be seen in Fig.
refers to the complete symmetric Rhꢀ/O vibrations of
RhO4 square-planar fragments. Its asymmetric vibra-
tions can appear as IR active mode. In addition, the very
intensive Raman band at 285 cmꢂ1 (7), 287 cmꢂ1 (8)
1, the short Moꢀ
coordination, together with the long Moꢀ
the other two uncoordinated pyridyl groups directed
/
N distance, close to the region of axial
and 289 cmꢂ1 (9) can be assigned to the Rhꢀ
/
Rh
Rh vibration of Rh2(Ac)4 is
/P distance and
stretching mode. The Rhꢀ
/

1742
G. Zhang et al. / Polyhedron 21 (2002) 1737ꢀ1746
/
located at 351 cmꢂ1. Unlike equatorial coordination
patterns of these pyridylphosphine ligands to the Mo2(m-
O2CCF3)4 moiety, these pyridylphoshpines prefer axial
interaction with Rh2(m-O2CCH3)4 under the conditions
served for the free ligands in solution. The shift
difference between coordinated and free ligands is ꢀ
/
30 ppm. Shift differences of this order of magnitude are
not uncommon for equatorially coordinated phoshine
ligands. The shift differences between the complexes
with one or two axial ligands observed here, however,
are in quite small, only in the order of 1 ppm. In the case
of the axially coordinated phoshine ligands in the
applied. The compounds Rh2(m-O2CR)4Ln (nꢃ
/1 or 2)
are the largest class of dirhodium(II) compounds known
to date [14].
2.5. NMR spectroscopy
compounds 7ꢀ
above) also holds for the solid state. The shift difference
between solid state and solution is in all three cases B
ppm. The splitting of the solid-state 31P NMR signals
Rh coupling cannot be observed. The solid
/
9 the trend observed in solution (see
The 1H NMR signals of the pyridyl groups in
complexes 7, 8 and 9 display only a slight downfield
shift in comparison to the free ligand. Complexes 7 and
8 display seven signals in the aromatic region and one
/2
due to a Pꢀ
/
state signal are in general very broad.
singlet for the acetate ꢀ
/
CH3-group, while complex 9
shows four signals in the aromatic region and one singlet
for the acetate CH3-group. All observed 1H NMR
signals are very sharp and the signals in the aromatic
region display the expected J-couplings. This is in
accord with the postulated structures of the complexes
2.6. Electronic absorption spectroscopy
The electronic absorption spectra of the soluble
complexes 7, 8 and 9 were measured in methylene
chloride at room temperature. The lowest energy
7ꢀ
/
9. Temperature-dependent 1H NMR spectroscopy
absorptions centered at 486 nm (oꢃ
for compound 7, at 496 nm (oꢃ
600 Mꢂ1 cmꢂ1) for
compound 8 and at 568 nm (oꢃ
250 Mꢂ1 cmꢂ1) for
/
350 Mꢂ1 cmꢂ1
)
was performed to examine fluxionality of the acetates,
i.e. exchange of axial and equatorial ligands in solution.
However, no broadening or splitting in the temperature
/
/
compound 9 are tentatively assigned to p*(Rh2)0
s*(Rh2) transitions [14].
/
range of ꢂ
/
90 to 30 8C was observed.
The 13C{1H} NMR spectra of the complexes 7 and 8
show nine signals in the aromatic region, the spectrum
of compound 9 displays five signals in the aromatic
3. Conclusions
region. These signals as well as the signals of the ꢀ
/
CH3
groups and the C(O)O moieties are in accord with the
expectations for the suggested structures of the com-
Compounds of the formula M2(m-O2CCR3)n(O2-
CCR3)4ꢀ
/
(PPhmPy3ꢂm x
)
(Mꢃ
/
Mo or Rh; RꢃH or F;
/
plexes 7ꢀ
The 31P{1H} NMR signals, located at ꢂ
pound 7) ꢂ8.99 (complex 8) and ꢂ2.64 ppm (complex
9), are broad triplets (half widths ca. 150ꢀ160 Hz) in all
three cases at room temperature. At ꢂ75 8C the signals
get significantly sharper. The signals appear to be a
/
9.
nꢃ2 or 3; mꢃ
/
/
1 or 0; xꢃ/1, or 2) can be synthesized
/15.26 (com-
depending on the starting material and the reaction
/
/
conditions. The trans-Mo2(m-O2CCF3)2(O2CCF3)2ꢂ
/
(PPhPy2)2
(5)
and
trans-Mo2(m-O2CCF3)2(O2-
/
CCF3)2(PPy3)2 (6) are among the first complexes of
this general type characterized by X-ray crystallography.
While the Mo2-complexes displaying two phosphine
ligands in equatorial positions and one or two trifluor-
oacetato ligands in axial positions are insoluble or
instable in all common organic solvents, the Rh2-
complexes with two 2-pyridylphosphine ligands in axial
positions as bridging ligands are soluble. These latter
complexes could, in principle, act as model initiators/
catalysts for the polymerization/hydrogenation of cyclo-
pentadiene, and are currently under investigation with
regard to this aspect in our laboratory.
1
2
doublet of doublets with JPꢀRh
:
/
45 Hz, JPꢀRh
:35
/
Hz. The ligand signals are shifted almost 11 ppm upfield
for complex 7 and about 6 ppm upfield in the case of
complex 8 in comparison to free ligand. The shift change
in comparison to the free ligand in the case of complex 9
is smaller, only approximately 1.5 ppm. These observa-
tions indicate that the Ppy3 ligands do not exchange so
readily electron density with the metal centers as the
PPh2py and the PPhpy2 ligands. The ability to act as
electron acceptor is less pronounced in the electron rich
Ppy3 ligand.
Since the complexes 1ꢀ6 are insoluble in all common
/
organic solvents, 31P solid-state NMR spectra were
measured of all complexes described in this work.
Only complex 4 shows sufficient solubility in CH2Cl2
to receive a 31P{1H} solution NMR spectrum. In the
case of the Mo2 derivatives the solid-state 31P NMR
signals are slightly more low field shifted in the row
4. Experimental
All preparation and manipulation were carried out
under an oxygen- and water-free argon atmosphere
using standard Schlenk techniques. Methylene chloride
was distilled over calcium hydride and diethyl ether over
˚
benzophenone, and kept over 4 A molecular
PPh2pyꢀ
/
PPhpy2ꢀ
/
Ppy3. The opposite trend is ob-
sodiumꢀ
/

G. Zhang et al. / Polyhedron 21 (2002) 1737ꢀ
/
1746
1743
˚
sieves. Acetone was dried over 4 A molecular sieves, too.
1192vs, 1161vs, 984m, 854m, 723s, 597w, 543w, 518m.
31P MAS NMR (d, ppm): 30.48.
Anhydrous THF, Mo2(m-O2CCF3)4, Rh2(m-O2CCH3)4,
bisphenyl-(2-pyridyl)phosphine (PPh2py), phenyl-bis-(2-
pyridyl)phosphine (PPhpy2) and tri-(2-pyridyl)pho-
sphine (Ppy3) were prepared according to literature
procedures [14,2g].
4.3. Preparation of Mo2(m-O2CCF3)3(O2CCF3)(PPy3)
(3)
Elemental analyses were performed in the Mikroana-
lytisches Labor of the TU Munchen in Garching (M.
¨
The synthetic procedure applied was similar to that
used for compound 1a. PPy3 was employed instead of
PPhPy2. Yield: 87%. Anal. Calc. for C23H12F12Mo2-
N3O8P (909.20): C 30.38, H 1.33, N 4.62; Found: C
29.95, H 1.45, N 4.60%. Selected IR data (n, cmꢂ1):
1647s, 1608s, 1452m, 1426s, 1193vs, 1164sh, 990w,
856m, 803m, 777w, 730s, 520m. 31P MAS NMR (d,
ppm): 29.19.
Barth). Solution 1H, 13C and 31P{1H} NMR were
measured with a Bruker Avance DPX-400 spectrometer.
The solid-state 31P NMR spectra were recorded at room
temperature (298 K) on a Bruker MSL 300 NMR
spectrometer using a 4 mm double bearing MAS
probehead and ZrO2 rotators. A spinning speed of
8000 Hz was applied. Chemical shifts are reported on
the scale with respect to d (H3PO4(concentration))ꢃ
ppm and were referenced to the second, external
standard [NH4(H2PO4)]; d (NH4H2PO4)ꢃ1.1 ppm. IR
spectra were obtained on a PerkinꢀElmer FT IR
spectrometer using KBr pellets as IR matrix. Electronic
absorption spectra were run using a PerkinꢀElmer
Lambda 2UVꢀVis spectrometer. TGA data were ob-
tained by a PerkinꢀElmer TGA 7 thermobalance. Each
3ꢀ10 mg sample was heated in a dynamic He atmo-
/
0
4.4. Preparation of trans-Mo2(m-
O2CCF3)2(O2CCF3)2(PPh2Py)2 (4)
/
/
The same procedure was applied as described for
compound 1, only the molar ratio of the Mo2(m-
O2CCF3)4: PPh2Py being 1:2. The resulting compound
was of purple color and partial soluble in CH2Cl2. The
product was, therefore, extracted with portions of cold
CH2Cl2. Yield: 60%. Anal. Calc. for C42H28F12Mo2-
N2O8P2 (1170.50): C 43.10, H 2.41, N 2.39. Found: C
43.26, H 2.64, N 2.12%. Selected IR data (n, cmꢂ1):
1687s, 1650vs, 1606vs, 1436m, 1192vs, 1166s, 1094m,
856m, 838m, 793m, 730s, 696m, 528m, 425w; Selected
Raman data (n, cmꢂ1): 1690s, 1199vs, 860w, 836m,
/
/
/
/
sphere (purity 5.0, flow 45 sccm) using a 50ꢀ650
/
temperature program at a rate of 10 K minꢂ1
.
4.1. Preparation of Mo2(m-
O2CCF3)3(O2CCF3)(PPh2Py) (1)
429w, 305s; UVꢀ
(sh), lmax 339 nm, (oꢃ
(oꢃ
500 Mꢂ1 cmꢂ1), 31P MAS NMR (d, ppm): 31.04.
/
Vis (CH2Cl2 solution): lmax
ꢃ 276 nm
/
To a stirred solution of Mo2(m-O2CCF3)4 (0.322 g, 0.5
mmol) in 15 ml of CH2Cl2 was added an equimolar
amount of PPhPy2 (0.132 g, 0.5 mmol) in 10 ml of
CH2Cl2. An immediate reaction took place with the
formation of a bright red precipitate, which was
collected after 2 h stirring, washed with portions of
CH2Cl2 and dried under oil pump vacuum. Yield: 90%.
Anal. Calc. for C25H14F12Mo2NO8P (907.23): C 33.10,
H 1.56, N 1.54. Found: C 32.82, H 1.52, N 1.48%.
Selected IR data (n, cmꢂ1): 1650s, 1606vs, 1436m,
1192vs, 1166vs, 1094m, 987m, 856m, 730s, 600w,
547w, 518m. 31P MAS NMR (d, ppm): 32.28.
ꢃ
/
/
50 900 Mꢂ1cmꢂ1), 548 nm
/
4.5. Preparation of trans-Mo2(m-
O2CCF3)2(O2CCF3)2(PPhPy2)2 (5)
The same procedure was applied as described for
compound 1a, only the molar ratio of the Mo2(m-
O2CCF3)4: PPhPy2 being 1:4. The resulting compound
was of purple color. Yield: 85%. Crystals suitable for X-
ray crystallography were obtained by layering a solution
of Mo2(m-O2CCF3)4 in CH2Cl2 with PPhPy2, dissolved
in diethyl ether. Anal. Calc. for C40H26F12Mo2N4O8P2
(1172.47): C 40.98, H 2.24, N 4.78. Found: C 40.46, H
2.10, N 4.62%. Selected IR data (n, cmꢂ1): 1690vs,
1650sh, 1607m, 1192vs, 1166s, 856m, 831m, 791m,
597w, 425w, 379w, 331w, 223w, 137vw. Selected Raman
data (n, cmꢂ1): 1693vw, 1670vw, 1589vs, 1203w, 1144m,
865w, 831w, 772w, 619w, 430w, 376w, 344s, 307vs. 31P
MAS NMR (d, ppm): 30.99.
4.2. Preparation of Mo2(m-
O2CCF3)3(O2CCF3)(PPhPy2) (2)
To a stirred solution of Mo2(m-O2CCF3)4 (0.322 g, 0.5
mmol) in 15 ml of CH2Cl2 was added an equimolar
amount of PPhPy2 (0.132 g, 0.5 mmol) in 10 ml of
CH2Cl2. An immediate reaction took place with the
formation of a bright red precipitate, which was
collected after 2 h stirring, washed with portions of
CH2Cl2 and dried under oil pump vacuum. Yield: 90%.
Anal. Calc. for C24H13F12Mo2N2O8P (908.21): C 31.74,
H 1.44, N 3.08. Found: C 31.82, H 1.42, N 2.98%.
Selected IR data (n, cmꢂ1): 1654s, 1608vs, 1431m,
4.6. Preparation of trans-Mo2(m-
O2CCF3)2(O2CCF3)2(PPy3)2 (6)
The procedure was similar to that described for
compound 1 with the following exceptions: the molar

1744
G. Zhang et al. / Polyhedron 21 (2002) 1737ꢀ1746
/
ratio of starting materials used was Mo2(m-
O2CCF3)4:PPy3ꢃ1:4. And the reaction mixture was
Found C 49.42, H 4.03, N 5.58%. Selected IR data (n,
cmꢂ1): 1596vs, 1434vs, 1422vs, 1374s, 1320m, 1128w,
1015w, 650w, 542s, 380w, 289w. Selected Raman data
(n, cmꢂ1): 1587m, 1438w, 1386vw, 1327w, 1128s,
580vw, 337s, 287vvs, 240sh. 1H NMR(CD2Cl2, d,
ppm): 1.63(s, 12H, CH3C), 7.26(dd, 4H), 7.47(m, 6H),
7.62(dt, 4H), 7.88(d, 4H), 8.02(d, 4H), 8.70(d, 4H). 13C
NMR(CD2Cl2, d ppm): 24.2(CH3C), 123.6, 128.4,
130.4, 131.8, 133.3, 135.3, 136.5, 150.2, 159.5 (aromatic
/
refluxed for 4 h. The resulting product was purple. The
product yield is 63%, however, the obtained material is
mixed with complex 1 (27% based on elementary
analysis). Attempts to isolate clean complex 6 were not
successful due to its insoluble in all common organic
solvents. Anal. Calc. for C38H24F12Mo2N6O8P2
(1174.45): C 38.86, H 2.06, N 7.16. Found: C 38.38, H
1.94, N 7.50%. Selected IR data (n, cmꢂ1): 1684sh,
1647s, 1608vs, 1194vs, 1164s, 857m, 836w, 795w, 509m,
382w. selected Raman data (n, cmꢂ1): 1685vw, 1648vs,
1608vs, 1592m, 1209vw, 867w, 839w, m, 798s, 523vvs,
510s, 388vs, 354s, 308vs. 31P MAS NMR (d, ppm):
29.45.
C ꢀ
/
H signals), 193.0(CO2). 31P{1H} NMR (CD2Cl2, d,
ppm): ꢂ
/
8.99(t). 31P MAS NMR (d, ppm): ꢂ
/
9.45. UVꢀ
/
Vis (CH2Cl2 solution): lmax
cmꢂ1), lmax
nm (sh).
ꢃ
/
496 nm (oꢃ
/
600 Mꢂ1
ꢃ
/
318 nm, (oꢃ
/
36 500 Mꢂ1 cmꢂ1), lꢃ
/
356
4.9. Preparation of trans-Rh2(m-O2CCH3)4(PPy3)2 (9)
4.7. Preparation of trans-Rh2(m-O2CCH3)4(PPh2Py)2
(7)
The procedure applied was analogous as described for
complex 3. PPy3 was used instead of PPhPy2 as a ligand.
The yield based on Rh2(m-O2CCH3)4 is 92%. Anal. Calc.
for C38H36N6O8P2Rh2 (972.50): C 46.93, H 3.73, N 8.64.
Found: C 46.96, H 3.70, N 8.53%. Selected IR data (n,
Rh2(m-O2CCH3)4 (0.111 g, 0.25 mmol) and twofold
stoichiometric amount of PPh2Py (0.133 g, 0.50 mmol)
was put into a Schlenk tube and 10 ml CH2Cl2 was
added. A red-brownish solution was immediately
formed and the solution was stirred for 2 h. Then the
volume of the solution was reduced to 5 ml and layered
by n-hexane. After 4 days red-brownish tiny crystals
were collected. The yield is 65% based on Rh2(m-
O2CCH3)4. Anal. Calc. for C42H40N2O8P2Rh2
(968.55): C 52.06, H 4.16 N 2.89. Found: C 52.23, H
4.12, N 2.61%. Selected IR data (n, cmꢂ1): 1600vs,
1585s, 1423s, 1346m, 1192vs, 1154s, 1020w, 854m, 777w,
731s, 623w, 507m; Selected Raman data (n, cmꢂ1):
Table 2
Summary of crystallographic data and details of data collection and
structure refinement for 5 and 6
5
6
Empirical formula
Molecular weight
Crystal system
Space group
C
40H26F12Mo2N4O8P2 C38H24F12Mo2N6O8P2
1174.45
Triclinic
1172.47
triclinic
¯
1 (Number 2)
¯
P1 (Number 2)
P/
/
1
˚
a (A)
9.6660(3)
10.4678(3)
12.0317(3)
110.453(1)
91.656(2)
105.882(1)
1086.58(5)
1
9.1327(2)
9.8729(2)
12.8791(4)
111.895(1)
91.209(1)
100.520(1)
1054.31(5)
1
1590m, 1425m, 1352w, 1120s, 285s; H NMR(CD2Cl2,
˚
b (A)
d, ppm): 1.63(s, 12H, CH3C), 7.21(d, 2H), 7.33(m, 12H),
7.55(dt, 8H), 7.69(d, 2H), 7.84(d, 2H), 8.66(d, 2H); 13C
NMR(CD2Cl2, d ppm): 30.05 (CH3C), 123.8, 128.8,
129.0, 129.1, 133.0, 135.3, 136.0, 150.3, 159.5 (aromatic
˚
c (A)
a (8)
b (8)
g (8)
3
V (A )
C ꢀ
ppm): ꢂ
UVꢀVis (CH2Cl2 solution): lmax
363 nm, (oꢃ
14 400 Mꢂ1 cmꢂ1), 486 nm (oꢃ
cmꢂ1).
/
H signals), 193.3(CO2). 31P{1H} NMR (CD2Cl2, d,
15. 67(t). 31P MAS NMR (d, ppm): ꢂ
17.44.
332 nm (sh), lmax
350 Mꢂ1
˚
Z
/
/
Dcalcd (g cmꢂ3
m (mmꢂ1
Reflections collected 7202
)
1.792
0.760
1.850
0.784
/
ꢃ
/
ꢃ
/
)
/
/
7909
4467/4821
Independent
reflections
3541/3797
[I ꢀ2s(I)/all data]
Rint
4.8. Preparation of trans-Rh2(m-O2CCH3)4(PPhPy2)2
(8)
0.0172
3797/0/348
0.0196
4821/0/355
Data/restraints/
parameter
a
R1 [I ꢀ2s(I)/all
data]
0.0300/0.0331
0.0240/0.0273
0.0548/0.0561
Rh2(m-O2CCH3)4 (0.111 g, 0.25 mmol) was dissolved
in 10 ml of THF to produce a bright green solution. The
fourfold stoichiometric amount of PPhPy2 (0.264 g, 1.00
mmol) in 10 ml of acetone was then added. The red-
brownish precipitate was gradually formed and the
suspension was stirred for 2 h. The crude product was
b
wR2 [I ꢀ2s(I)/all 0.0720/0.0737
data]
c
Goodness-of-fit
d
Weights a/b
1.029
0.0241/1.8741
0.91/ꢂ0.55
1.049
0.0087/0.9617
0.66/ꢂ0.45
ꢂ3
˚
Drmax/min (e A
)
washed several times with THF (3ꢄ
/
5 ml), acetone (3ꢄ
/
a
R1ꢃS (jjFoꢂjFcjj)/SjFoj.
5 ml), and then dried in oil pump vacuum. The yield is
83% based on Rh2(m-O2CCH3)4. Anal. Calc. for
C40H38N4O8P2Rh2 (970.53): C 49.50, H 3.95, N 5.77.
b
c
wR2ꢃ[S w(Fo2ꢂFc2)2/S w(Fo2)2]1/2
.
Goodness-of-fitꢃ[S w(Fo2ꢂFc2)2/(NOꢂNV)]1/2
.
d
wꢃ1/[s2(Fo2)ꢁ(aP)2ꢁbP], with Pꢃ[max (0 or Fo2)ꢁ2Fc2]/3.

G. Zhang et al. / Polyhedron 21 (2002) 1737ꢀ
/
1746
1745
cmꢂ1): 1594vs, 1422vs, 1284m, 1129vw, 1086m,
1066vvw, 695s, 561w, 525w, 382m, 303vw, 278w.
Selected Raman data (n, cmꢂ1): 1421s, 1278m, 581vw,
527m, 338s, 289vvs. 1H NMR (CD2Cl2, d, ppm): 1.63 (s,
12H, CH3C), 7.28 (dt, 6H), 7.67 (dt, 6H), 7.98 (d, 6H),
8.68 (d, 6H). 13C NMR (CD2Cl2, d ppm): 24.0 (CH3C),
Acknowledgements
G.Z. thanks the Katholischer Akademischer Auslan-
¨
der-Dienst (KAAD) for a Ph.D. stipend. J.Z. is grateful
to the Deutscher Akademischer Austauschdienst
(DAAD) for a Ph.D. grant. Professor Dr. W.A.
Herrmann is acknowledged for continuous support of
our work, the Fonds der Chemischen Industrie (FCI)
for financial support and Dr. E. Bencze for helpful
discussions and experimental assistance in vibrational
spectroscopy.
123.6, 132.0, 135.2, 150.2, 158.3 (aromatic C ꢀ
nals), 192.7 (CO2). 31P{1H} NMR (CD2Cl2, d, ppm): ꢂ
2.64 (t). 31P MAS NMR (d, ppm): ꢂ
3.27. UVꢀVis
(CH2Cl2 solution): lmax 568 nm (oꢃ
250 Mꢂ1 cmꢂ1),
lmax 318 nm (oꢃ 370 nm (sh).
28100 Mꢂ1 cmꢂ1), lꢃ
/H sig-
/
´
/
/
ꢃ
/
/
ꢃ
/
/
/
References
4.10. X-ray crystal structure determination
[1] (a) Z.Z. Zhang, H. Cheng, Coord. Chem. Rev. 147 (1996) 1;
(b) G.R. Newcomer, Chem. Rev. 93 (1993) 2067.
[2] (a) C.Y. Kuo, Y.S. Fuh, J.Y. Shiue, S.J. Yu, G.H. Lee, S.M.
Peng, J. Organomet. Chem. 588 (1999) 260;
Crystallographic data for 5 and 6 are summarized in
Table 2. Data were collected at low temperature (123 K)
on a Nonius KappaCCD device at the window of a
(b) N.D. Jones, K.S. MacFarlane, M.B. Smith, R.P. Schutte, S.J.
Rettig, B.R. James, Inorg. Chem. 38 (1999) 3956;
(c) T. Nicholson, M. Hirsch-Kuchma, A. Shellenbarger-Jones, A.
Davison, A. Jones, Inorg. Chim. Acta 267 (1998) 319;
(d) R.P. Schutte, S.J. Rettig, A.M. Joshi, B.R. James, Inorg.
Chem. 36 (1997) 5809;
rotating anode (5: theta range: 1.82ꢀ
ranges: ꢂ115h 511, ꢂ125k 512, ꢂ
crystal dimensions: 0.13ꢄ0.15ꢄ0.20 mm; 6: theta
range: 2.26 to 27.508, index ranges: ꢂ115h 511, ꢂ
125k 512, ꢂ165l 516, crystal dimensions: 0.24ꢄ
0.28ꢄ0.33 mm) [15b]. Absorption correction and decay
/
26.078, index
/
/
/
/
/
/
/
145l 514,
/
/
/
/
/
/
/
/
/
/
/
/
/
/
(e) I.R. Baird, M.B. Smith, B.R. James, Inorg. Chim. Acta 235
(1995) 291;
/
correction were applied during the scaling procedure
[15c]. Both structures were solved by direct methods
[15d] and refined anisotropically by full-matrix least-
squares on F2 [15e]. Neutral atom scattering factors for
all atoms and anomalous dispersion corrections for the
non-hydrogen atoms were taken from the International
Tables for Crystallography [15f]. All non-hydrogen
atoms of the two complexes where refined anisotropi-
cally. All hydrogen atoms were placed in calculated
positions riding on the parent carbon atom (5). All
hydrogen atoms were found in the difference Fourier
map and refined with individual isotropic thermal
displacement parameters (6). Both molecules reside on
a crystallographic center of inversion. In 5 both
trifluormethyl groups are disordered over two positions
in the bridging (O2C)CF3 ligand (91:9) and in the
monodentate (O2C)CF3 ligand (71:29).
(f) P. Braunstein, D.G. Kelly, A. Tiripicchio, F. Ugozzoli, Bull.
Soc. Chim. Fr. 123 (1995) 1083;
(g) H. Schmidbaur, Y. Inoguchi, Z. Naturforsch. 35b (1980) 1329.
[3] (a) G. Francio`, R. Scopelliti, C.G. Arena, G. Bruno, D. Drommi,
F. Faraone, Organometallics 17 (1998) 338;
(b) W.H. Chan, Z.Z. Zhang, T.C. Mak, C.M. Che, J. Chem. Soc.,
Dalton Trans. (1998) 803;
(c) S.M. Kuang, F. Xue, Z.Z. Zhang, W.M. Xue, C.M. Che,
T.C.W. Mak, J. Chem. Soc., Dalton Trans. (1997) 3409;
(d) S.M. Kuang, H. Cheng, L.J. Sun, Z.Z. Zhang, Z.Y. Zhou,
B.M. Wu, T.C.W. Mak, Polyhedron 15 (1996) 3417;
(e) L.Y. Xie, B.R. James, Inorg. Chim. Acta 217 (1994) 209;
(f) E. Rotondo, G. Bruno, F. Nicolo`, S. Lo Schiavo, P. Piraino,
Inorg. Chem. 30 (1991) 1195;
(g) P.W. Schrier, D.R. Derringer, P.E. Fanwick, R.A. Walton,
Inorg. Chem. 29 (1990) 1290;
(h) F.A. Cotton, M. Matusz, Inorg. Chim. Acta 143 (1988) 45;
(i) F.A. Cotton, M. Matusz, Polyhedron 7 (1988) 2201;
(j) T.J. Barder, F.A. Cotton, G.L. Powell, S.M. Tetrick, R.A.
Walton, J. Am. Chem. Soc. 106 (1984) 1323;
(k) R.H. Cayton, M.H. Cisholm, E.F. Putilina, K. Folting, J.C.
Huffman, K.G. Moodley, Inorg. Chem. 31 (1992) 2928;
(l) P. Lahuerta, M.A. Ubeda, J. Paya, S. Garciagranda, F.
Gomezbeltran, A. Anillo, Inorg. Chim. Acta 205 (1993) 91;
(m) F. Estevan, P. Lahuerta, E. Peris, M.A. Ubeda, S. Gracia-
granda, F. Gomezbeltran, E. Perezcarreno, G. Gonzalez, Inorg.
Chim. Acta 218 (1994) 189.
5. Supplementary material
Crystallographic data (excluding structure factors) for
the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Center as
supplementary publication numbers CCDC-175526 (5)
and -175527 (6). Copies of the data can be obtained free
of charge on application to CCDC, 12 Union Road,
[4] (a) R. Gobetto, C.G. Arena, D. Drommi, F. Faraone, Inorg.
Chim. Acta 248 (1996) 257;
(b) A.J. Deeming, M.B. Smith, J. Chem. Soc., Chem. Commun.
(1993) 844 and references therein.
[5] P. Braustein, M. Knorr, M. Strampfer, A. De Cian, J. Fischer, J.
Chem. Soc., Dalton Trans. (1994) 117.
[6] N.W. Alcock, P. Moore, P.A. Lampe, K.F. Mok, J. Chem. Soc.,
Dalton Trans. (1982) 207.
Cambridge CB2 1EZ, UK (fax: ꢁ44-1223-336-033; e-
/
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk].
[7] (a) W.J. Zao, T.Q. Fang, S.Q. Zhang, Z.Z. Zhang, L.M. Yang, J.
Chem. Eng. Natural Gas 17 (1992) 3;

1746
G. Zhang et al. / Polyhedron 21 (2002) 1737ꢀ1746
/
(b) CA: 119, P 202967;
(c) Y. Xie, C.L. Lee, Y. Yang, S.J. Rettig, B.R. James, Can. J.
Chem. 70 (1992) 751;
[11] (a) T.J. Barder, S.M. Tetrick, R.A. Walton, F.A. Cotton, G.L.
Powell, J. Am. Chem. Soc. 105 (1983) 4090;
(b) F.A. Cotton, K.R. Dunbar, J. Am. Chem. Soc. 109 (1987)
2199;
(d) Z. Galdeki, A. Kowalski, F.P. Pruchnik, K. Wajda-Herma-
nowicz, R. Starosta, Pol. J. Chem. 73 (1999) 859.
[8] (a) F.E. Kuhn, J.R. Ismeier, D. Schon, W.M. Xue, G. Zhang, O.
(c) E.C. Morrison, D.A. Tocher, Inorg. Chim. Acta 157 (1989)
139;
¨
¨
Nuyken, Macromol. Rapid Commun. 20 (1999) 555;
(b) F.E. Kuhn, D. Schon, G. Zhang, G.O. Nuyken, J. Macromol.
(d) E.C. Morrison, D.A. Tocher, J. Organomet. Chem. 408 (1991)
105;
¨
¨
Sci. Chem. A37 (2000) 971;
(c) M. Pillinger, I.S. Goncalves, A.A. Valente, P. Ferreira, D.
Schon, O. Nuyken, F.E. Kuhn, Design. Monomers Polym. 4
(e) P. Lahuerta, R. Martinez-Manez, J. Paya, E. Peris, W. Diaz,
Inorg. Chim. Acta 173 (1990) 99.
¸
[12] K. Teramoto, Y. Sasaki, K. Migita, M. Iwaizumi, K. Saito, Bull.
Chem. Soc. Jpn. 61 (1988) 83.
¨
¨
(2001) 269;
(d) P. Ferreira, F.E. Kuhn, Trends Inorg. Chem. 7 (2001) 89;
[13] (a) E.B. Boyar, S.D. Robinson, Coord. Chem. Rev. 50 (1983) 109;
(b) T. Kawamura, H. Katayama, H. Nishikawa, T. Yamabe, J.
Am. Chem. Soc. 111 (1989) 8156;
¨
(e) M. Pillinger, I.S. Goncalves, P. Ferreira, J. Rocha, M. Schafer,
¸
D. Schon, O. Nuyken, F.E. Kuhn, Macromol. Rapid Commun.
¨
¨
22 (2001) 1306.
¨
(c) H. Kitamura, T. Ozawa, K. Titsukawa, H. Masuda, H.
Einago, Chem. Lett. (1999) 1225.
[9] (a) W. Risse, C. Mehler, E. Connor, Ger. Patent 19729817, 1999,
BASF AG;
[14] (a) F.A. Cotton, J.G. Norman, J. Coord. Chem. 1 (1971) 161;
(b) G. Winkhaus, P. Ziegler, Z. Anorg. All. Chem. 350 (1967) 51;
(c) K. Kurtev, D. Ribola, R.A. Jones, D.J. Cole-Hamulton, G.
Wilkinson, J. Chem. Soc., Dalton Trans. (1980) 55;
(d) F.A. Cotton, R.A. Walton, Multiple Bonds between Metal
Atoms, second ed. (Chapter 10), Wiley, New York, 1993, p. 705.
[15] (a) A.L. Spek, PLATON, A Multipurpose Crystallographic Tool,
Utrecht University, Utrecht, The Netherlands, 2001;
(b) Data Collection Software for Nonius KappaCCD Devices,
Delft, The Netherlands (1997);
(b) G. Heublein, W. Freitag, East Ger. Patent 126837, 1976,
Chem. Abstract 88 (1978) 74896;
(c) C. Aso, K. Ito, T. Kunitake, Makromol. Chem. 97 (1966) 40;
(d) G. Heublein, W. Freitag, W. Mock, Makromol. Chem. 181
(1980) 267;
(e) G. Heublein, G. Knoppel, D. Stadermann, Polym. Bull. 20
¨
(1988) 109;
(f) G. Heublein, W. Freitag, J. Prakt. Chem. 321 (1979) 544;
(g) G. Heublein, W. Barth, J. Prakt. Chem. 316 (1974) 649;
(h) G. Heublein, G. Albrecht, Acta Polym. 33 (1982) 505.
[10] (a) P. Legzdins, G.L. Rempel, G. Wilkinson, J. Chem. Soc.,
Chem. Comm. (1969) 825;
(c) Z. Otwinowski, W. Minor, in: W.C. Carter, Jr., R.M. Sweet
(Eds.), Methods in Enzymology, vol. 276, Academic Press, New
York, USA, 1997, p. 307;
(b) J. Telser, R.S. Drago, Inorg. Chem. (23) (1984) 1798;
(c) F.A. Cotton, A.H. Reid, W. Schwotzer, Inorg. Chem. 24
(1985) 3965;
(d) A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi,
M.C. Burla, G. Polidori, M. Camalli, J. Appl. Cryst. 27 (1994)
435;
(d) W. Clegg, G. Pimblett, C.D. Garner, Polyhedron 5 (1986) 31;
(e) G. Pimblett, C.G. Garner, W. Clegg, J. Chem. Soc., Dalton
Trans. (1986) 1257;
(e) G.M. Sheldrick, SHELXL-97, University of Gottingen, Gottin-
¨ ¨
gen, Germany, 1997;
(f) In: A.J.C. Wilson (ed.), International Tables for Crystal-
lography, vol. C, Kluwer Academic Publishers, Dordrecht, The
(f) F.A. Cotton, F.E. Kuhn, Inorg. Chim. Acta 252 (1996) 257;
¨
(g) F.A. Cotton, F.E. Kuhn, A. Yokochi, Inorg. Chim. Acta 252
¨
Netherlands, 1992, Tables 6.1.1.4 (pp. 500ꢀ
/
502), 4.2.6.8 (pp. 219ꢀ
/
(1996) 251.
222), and 4.2.4.2 (pp. 193ꢀ199).
/