A molecular loop with interstitial channels in a chiral environment: Exploration of the chemistry of Mo24+ species with chiral and non-chiral dicarboxylate anions

Article abstract of DOI:10.1039/b310151g

An enantiomerically pure chiral loop containing two cis-Mo₂(DAniF)₂²⁺ (DAniF = di-p-anisylformamidinate) units was obtained by reaction of cis-[Mo₂(DAniF)₂(NCMe)₄] (BF₄)₂ with a chiral dicarboxylate which is easily prepared from hydroquinone and ethyl (S)-lactate. The compound crystallizes in the non-centrosymmetric I222 space group with molecules stacking so as to form channels capable of hosting guest molecules such as CH₂Cl₂. These properties of the compound, which has been synthesized in high yield, makes it promising for applications in stereoselective catalysis. Similar reactions with isomeric dicarboxylate linkers, as well as with some non-chiral ligands, were studied. The nature of the products depends on the bite angle of the ligand.

Full text of DOI:10.1039/b310151g

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A molecular loop with interstitial channels in a chiral environment:
4؉
exploration of the chemistry of Mo2 species with chiral and
non-chiral dicarboxylate anions
John F. Berry, F. Albert Cotton,* Sergey A. Ibragimov, Carlos A. Murillo* and
Xiaoping Wang
Department of Chemistry and Laboratory for Molecular Structure and Bonding,
Texas A&M University, PO Box 30012, College Station, TX 77842-3012, USA
Received 22nd August 2003, Accepted 5th September 2003
First published as an Advance Article on the web 18th September 2003
An enantiomericaly pure chiral loop containing two cis-Mo2(DAniF)22ϩ (DAniF = di-p-anisylformamidinate) units
was obtained by reaction of cis-[Mo2(DAniF)2(NCMe)4](BF4)2 with a chiral dicarboxylate which is easily prepared
from hydroquinone and ethyl (S)-lactate. The compound crystallizes in the non-centrosymmetric I222 space group
with molecules stacking so as to form channels capable of hosting guest molecules such as CH2Cl2. These properties
of the compound, which has been synthesized in high yield, makes it promising for applications in stereoselective
catalysis. Similar reactions with isomeric dicarboxylate linkers, as well as with some non-chiral ligands, were studied.
The nature of the products depends on the bite angle of the ligand.
Interestingly, most of these compounds crystallize in such
Introduction
way that the molecules stack to form channels,3 which can be
Metal–metal-bonded compounds have proven useful in
filled with other molecules, and the size of the channels can be
controlled by the length of the linkers. For example, the
many areas, such as catalysis,1 medicine2 and for building
supramolecular arrays.3 Some of the most notable catalytic
Ru2(CO)4L2 corner piece produces a molecular square and
processes employ chiral ligands that induce optical activity in
a molecular loop in conjunction with oxalate and malonate
the products.4 Chirality is also of great importance in medicine,
linkers, respectively.14 Bonar-Law15 and others16 before him have
as many processes, e.g. enzymatic processes,5 are controlled by
optically active centers. In the field of supramolecular chem-
shown that bidentate ligands with well-separated carboxylate
groups can be used to bind two cis equatorial positions of a
dimetal unit. For example, with dirhodium units, the use of
m-HO2CC(CH3)2O–C6H4–OC(CH3)2CO2H dicarboxylic acid
istry, efforts have been made to study the use of chiral ligands
attached to metal centers,6 but structural characterization is
often hampered by difficulties in crystallizing large chiral mole-
yields a chelated compound (Chart 2). This chelated species
cules.7 Only two systems having chiral species bound to metal–
reacts further with rigid dicarboxylic acids to form squares,15,17
metal-bonded centers have been structurally characterized. One
or with pyridine to form π-stacked columns with hexagonal
of them is a triangle made with Ru2(CO)4L2 (L = axial MeCN
or PPh3) corner pieces with optically active tartrate dianions
as linkers.8 The other is a set of molecular pairs containing
holes.18 A similar tetracarboxylate has been used to link two
dirhodium units into a dimer.19 With a long rigid dicarboxylate
ligand, these dimetal units can be linked together in a vertical
manner along the Rh–Rh axis.20
ϩ
two Mo2(DAniF)3 units (DAniF = N,NЈ-di-p-anisylform-
amidinate) bridged by either -tartrate or -aspartate.9
A useful type of dimetal unit in the construction of poly-
gonal supramolecules is M2(DAniF)2 (M = Mo, Ru and Rh),
which can form loops, triangles, squares or more complex
entities,10 depending on the nature of the linker and the pres-
ence or absence of axial ligation. For example, we have shown
that M2(DAniF)2 corner pieces give squares with rigid di-
carboxylate linkers, such as the dianion of terephthalic
acid,11 triangles with the less constrained 1,4-dicyclohexane-
dicarboxylate12 and loops with more flexible or bent bridges,
such as homophthalate, phenylenedicarboxylate and malonate
anions,13 as summarized schematically in Chart 1.
Chart 2
In this report, we describe exploratory work combining
quadruply bonded [Mo2(DAniF)2]2ϩ units with enantio-
merically pure ligands21,22 of the type shown in Chart 3, which
Chart 1
Chart 3
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 4 2 9 7 – 4 3 0 2
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Table 1 Selected interatomic distancesa for 1ؒ4CH2Cl2 and 4ؒC6H6.
have been labeled as p-H2L1, m-H2L2 and o-H2L3 for the para-,
meta- and ortho-substituted species, respectively. The meta
ligand, L22Ϫ, is akin to the one shown in Chart 2. The latter
has Me2C units, whereas L22Ϫ has chiral MeHC units. We
report the first structural characterization of a chiral molecular
loop and show that it crystallizes to form chiral cavities. We also
report the structure of a related dinuclear species in which a
dicarboxylate anion wraps around to chelate it.
1ؒ4CH2Cl2
4ؒC6H6
Mo–Mo
Mo–N
2.081(2)
2.08 [3]
2.13 [2]
2.0812(7)
2.112 [2]
2.141 [2]
—
Mo–O
Overall torsion angleb
Ϫ75.8
a Distances given in Å. Numbers in square brackets correspond to aver-
age values. b The torsion angle (in Њ) is defined as the angle between the
two Mo–Mo bonds. Since 4 has only one Mo2 unit, no torsion angle is
given.
Results and discussion
The quadruply bonded corner-piece precursor [cis-Mo2-
(DAniF)2(CH3CN)4](BF4)2 (compound 0) reacts with the tetra-
ethylammonium salt of the chiral dicarboxylate (NEt4)2L1 to
give [cis-Mo2(DAniF)2]2(L1)2 (1) in high yield according to
eqn. (1).
those found in other paddlewheel compounds having carb-
oxylate or formamididate bridging ligands.23 The ligands are
attached to each dimolybdenum unit by one carboxyl group, as
in other molecular loops, though the conformation here is quite
different from those previously described. Loops with the di-
anions 1,4-phenylenediacetate [p-C6H4(CH2CO2)2], homo-
phthlate [o-C6H4(CH2CO2)(CO2)] and malonate [CH2(CO2)2]
have the two Mo2 units essentially parallel to each other.13
Because of the chiral nature of the ligands in 1, there is a
significant twist between the vectors of the two Mo2 species,
which are at an angle of Ϫ75.8Њ. This twist has consequences
in the packing of the molecules (Fig. 3). In the previously
described molecular loops,13 the molecules stack with the Mo–
Mo bonds aligned, thus creating channels that can vary in size
depending on the length of the linkers. This is not possible in 1
due to the S shape of the molecule. Here again, the molecules
stack, but now, parallel stacks of loops form channels along the
a axis. These channels, which provide a chiral environment
because of the chirality of the dicarboxylate linkers, are large
enough to allow interstitial solvent molecules to reside in them,
as shown in Fig. 3.24 This could be of importance in enantiomer
resolution or in catalysis and efforts are being made to prepare
ruthenium and rhodium analogs for which catalytic activity
should be highly relevant.1 In this context, it is important to
note that the chiral linker can be made in high purity and very
cheaply from readily available commercial sources.21,22
2[cis-Mo2(DAniF)2(CH3CN)4](BF4)2 ϩ 2(NEt4)2L1
[cis-Mo2(DAniF)2]2(L1)2 ϩ 4NEt4BF4 (1)
In this compound, two cis-Mo2(DAniF)2 units are held
together by two of the carboxylate anions, producing a molecu-
lar loop, as shown in Fig. 1. It is clear that the dicarboxylate
anions displace the labile equatorial acetonitrile groups and
each of the two L1 dianions has a carboxylate group attached
to each of the two Mo24ϩ units, resembling the claws of a crab,
as can be seen in Fig. 2. The entire molecule resembles a second-
order Möbius strip, which is a Möbius-type ring in which there
are two twists (rather than one), both in the same direction. The
idealized molecular symmetry would be 222 (D2 in Schönflies
notation). As noted below, the 1H NMR spectrum is consistent
with this symmetry.
Fig. 1 Thermal ellipsoid plot of 1 with ellipsoids drawn at the 30%
probability level. Hydrogen atoms, solvent molecules and anisyl groups
have been omitted for clarity.
Fig. 3 A stereoscopic view of the packing of 1ؒ4CH2Cl2 showing
channels filled with dichloromethane guest molecules.
The first stage of the ligand synthesis has been described as
taking place via a nucleophilic attack, which inverts the S
conformation of the ethyl lactate triflate derivative to the R
conformation for the precursor of the linker. Effenberg and co-
workers showed by chiral gas chromatography that the reaction
occurs with 92% enantiomeric inversion.22 We also determined
the enantiomeric purity of the (NEt4)2L1 salt by NMR spectro-
scopy and found it to be similar, that is, ca. 95%. For 1, the
cyclic voltammogram (CV) and differential pulse voltam-
mogram (DPV) show a single reversible oxidation wave at
0.388 V versus Ag/AgCl, which is similar to that for [cis-
Mo2(DAniF)2]2(O2CCH2C6H4CH2CO2)2.13 The NMR spectrum
(vide infra), electrochemical measurements and elemental
analysis indicate that the purity of the product is good.
Fig. 2 Thermal ellipsoid plot of 1 showing the twisted nature of the
loop. The torsion angle between the two Mo2 units is 76Њ. Ellipsoids are
drawn at the 30% probability level; hydrogen atoms, solvent molecules
and anisyl groups have been omitted for clarity.
Since the two Mo2 units in each molecule are related by a
crystallographic two-fold axis, they are equivalent and the
Mo–Mo bond distance of 2.081(2) Å (see Table 1) is similar to
D a l t o n T r a n s . , 2 0 0 3 , 4 2 9 7 – 4 3 0 2
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1
The H NMR spectrum in acetone-d6 shows the singlet at
8.55 ppm for the methine proton of the formamidinate ligands
and two singlets in a 1 : 1 ratio for the OCH3 groups of the
anisyl groups at 3.68 and 3.70 ppm, which is in agreement with
D2 being the highest possible symmetry of the molecule. A
complicated multiplet in the range 6.62 to 6.98 ppm corre-
sponds to the aromatic protons of the anisyl groups and those
of the linkers. The remaining signals for the chiral linkers are a
quartet at 5.23 ppm for the CH unit and a doublet for CH3 at
1.74 ppm. The ratio of carboxylate to formamidinate signals of
1 : 2 is consistent with a structure of D2 symmetry.
Chart 4
symmetry (vide infra). The CV and DPV show a single revers-
ible oxidation wave at 0.344 V versus Ag/AgCl. The 1H
NMR spectrum, electrochemical measurements and elemental
analysis indicate that the purity of the product is good.
Exploration of reactions with analogous ligands
Reactions similar to that in eqn. (1) have been carried out for
the isomeric ortho and meta ligands using the corresponding
tetraethylammonium salts (NEt4)2L2 and (NEt4)2L3. Because
of the smaller bite angles of these ligands it was considered less
likely that they could form compounds similar to 1. Neverthe-
less, we decided to investigate their reactivity towards the
corner-piece precursor 0 to determine how the geometry of the
ligands might impact the structure of the dimolybdenum com-
pounds. This is important as small changes in the structures of
the ligand can have a significant effect on the structure of
the metal complexes and the manner in which they pack in the
crystal.3
The structure of 4 (Fig. 4) shows that the dicarboxylate anion
wraps around the dimetal unit to form a chelate in the same way
4ϩ
as described by others for similar Rh2 compounds.15,16 The
Mo–Mo bond distance of 2.0812(7) Å (see Table 1) is similar to
that in other paddlewheel compounds having mixed carb-
oxylate and formamididate bridging ligands. Because of the
similarity of L22Ϫ and L42Ϫ, it is likely that the structure of 2 is
similar to that of 4 and thus 2 has a chelated dicarboxylate
anion and only one Mo24ϩ unit.
Reactions of 0 and L22Ϫ or L32Ϫ proceeded similarly to that
for the preparation of 1 with the formation of yellow solids, 2
and 3, in high yields that show δ δ* transitions at 410 and 412
nm, respectively. These are similar to that for 1, which occurs at
428 nm in CH2Cl2 solution. Like that for 1, the results of the
elemental analyses were consistent with the empirical formula
Mo2C42H42N4O10 (i.e. 1 : 1 adducts of L2 or L3 with an
1
Mo2(DAniF)2 unit). The H NMR spectrum of 2 in C6D6 is
similar to that of 1, indicating the formation of a single product
with a formamidinate to carboxylate ratio of 2 : 1. But whether
this is a chelated dinuclear compound with C2 symmetry or a
tetranuclear loop like 1 cannot be determined solely by analysis
of the 1H NMR spectrum.
Sharp signals in the 1H NMR spectrum of 3 in C6D6 indicate
that the product is diamagnetic, as required by the presence of
the quadruply bonded Mo2 unit. The spectrum is more com-
plex, however, having two singlets at 8.42 and 8.49 ppm in a
ratio of ca. 1 : 2 that correspond to methine groups. There are
also two doublets in a similar ratio at 1.91 and 1.98 ppm for the
CH3 groups at the chiral centers and two quartets assigned to
CH groups at the chiral centers at 5.22 and 5.51 ppm. A com-
plicated multiplet in the range 6.50 to 6.64 ppm corresponds to
the aromatic protons of the anisyl groups and those of the
linkers. This doubling of the signals suggests the formation of
two products which are isolated in a relative ratio of 1 : 2. The
CV is also consistent with the presence of two species in
solution.
Because attempts at crystallizing 2 and 3 produced only
amorphous materials unsuitable for single crystal X-ray diffrac-
tion, we tried to gain insight by looking at the type of products
formed by analogous non-chiral ligands in which the OCMe-
HCO2 groups are replaced by OC(Me)2CO2 groups to give the
meta analog H2L4,15 or by OCH2CO2 groups to give the ortho
analog H2L525 (Chart 4).
Fig. 4 Thermal ellipsoid plot of 4 with thermal ellipsoids drawn at the
50% probability level. Hydrogen atoms, interstitial solvent molecules
and anisyl groups have been omitted for clarity.
A similar reaction of 0 with L52Ϫ was performed in CH3CN
and a crystalline product (5) was obtained by extracting the
product with hot CH2Cl2, then adding hexanes and storing at
Ϫ10 ЊC. Unfortunately these crystals diffracted poorly and were
twinned, which prevented a structural characterization, but the
product was analyzed by 1H NMR spectroscopy. The spectrum
in CDCl3 of either the crystals or the yellow powder shows the
presence of the carboxylate and formamidinate ligands in a 1:2
ratio but as in the reaction with L32Ϫ, the signals show signs of
doubling suggesting again the presence of two compounds but
in a 1:3 ratio. There are two singlets at 8.42 and 8.40 ppm from
methine groups (ratio of 1:3), two singlets at 3.64 and 3.67 ppm
for two types of OCH3 groups, and two singlets at 5.18 and 5.22
ppm assigned to the CH2 groups. A complicated multiplet in the
range of 6.47 to 7.10 ppm corresponds to the aromatic protons
of the anisyl groups and those of the linkers. This suggests
again the formation of two types of products, possibly a loop
Using L42Ϫ, a reaction with 0 was performed in CH3CN fol-
lowing eqn. (1). The yellow solid which formed was dissolved
in C6H6 and this solution was mixed with hexanes to produce
crystals of cis-Mo2(DAniF)2(L4)ؒC6H6 (4ؒC6H6). The 1H NMR
spectrum in C6D6 shows the presence of one compound (4) with
a carboxylate to formamidinate ratio of 1 : 2, as in 2. A singlet
at 8.46 ppm corresponds to the methine protons. We observed
only one singlet for the OCH3 groups at 3.19 ppm and a doublet
for the methyl groups of the non-chiral dicarboxylate at 1.96
ppm, which is in agreement with a molecule in an idealized C2v
and a chelated product, analogous to those obtained with L32Ϫ
.
The UV-vis spectra for 4 and 5 show δ δ* transitions at 430
and 431 nm, respectively, consistent with the presence of an
Mo24ϩ core.
Conclusions
We have shown that the type of compound formed between
4ϩ
quadruply bonded Mo2 units in a cis-Mo2(DAniF)2 species
D a l t o n T r a n s . , 2 0 0 3 , 4 2 9 7 – 4 3 0 2
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and chiral and non-chiral dicarboxylate anions derived from
ortho, meta and para substitution of aromatic entities such as
those in L12Ϫ–L52Ϫ is very dependent on the ligand configur-
ation, with those having para substitution favoring the form-
ation of molecular loops and those with meta substitution
favoring dinuclear complexes in which the dicarboxylate gives
a chelate. Enantiomerically pure compounds 1 and 2 were
obtained. Insight into the structure of 2 was obtained by
making a non-chiral analog, namely 4. The structure of the
loop 1 shows channels capable of holding guest molecules. This
opens the possibility for using dirhodium instead of dimolyb-
denum units, which might be useful as catalysts.
Hydrolysis of the diester was performed, as previously
described21,22 for Et2L1, Et2L2 and Et2L3, by stirring it for 2 h
with NaOH in H2O–MeOH solution. The insoluble H2L5 was
collected by filtration and used without further purification.
Neutralization with Et4NOH was performed as described above
for the other chiral ligands. 1H NMR (CDCl3, δ): 1.20 (t,
NCH2CH3, 24H), 3.30 (q, NCH2CH3, 16H), 4.36 (s, CH2, 4H),
6.68–6.85 (m, aromatic, 4H).
Preparation of [Mo2(DAniF)2(L1)]2 (1). A mixture of 0 (0.300
g, 0.267 mmol) and (NEt4)2L1 (0.137 g, 0.267 mmol) was placed
in one flask. In another flask, 10 ml of CH3CN was degassed by
freezing in liquid nitrogen and pumping under vacuum. The
solvent was then added to the solid mixture via cannula. A
yellow solid formed upon mixing. The mixture was stirred for
30 min, the solvent decanted via cannula and the yellow residue
was washed with EtOH and hexanes. The yield was essentially
quantitative. IR (KBr, cmϪ1): 3448 (w, br), 2935 (w), 2832 (w),
1609 (w), 1542 (s), 1503 (vs), 1461 (m), 1441 (m), 1415 (w), 1292
(m), 1245 (s), 1217 (s), 1177 (m), 1103 (m), 1035 (s), 941 (w), 874
(w), 827 (m), 764 (w), 703 (w), 644 (w), 619 (w), 591 (w), 522
(w), 453 (w). Elemental analysis, calc. for Mo4C84N8O25H94: C,
50.46; H, 4.74; N, 5.60; found: C, 50.37; H, 4.47; N, 5.55%. 1H
NMR (CD3COCD3, δ): 1.74 (d, CHCH3, 12H), 3.68 (s, OCH3,
12H), 3.70 (s, OCH3, 12H), 5.23 (q, CHCH3, 4H), 6.62–6.98 (m,
aromatic, 40H), 8.55 (s, CH, 4H). Crystals of 1 were obtained
by dissolving the yellow solid in 10 ml of CH2Cl2 and layering
the solution with 40 ml of hexanes. Needle-like yellow crystals,
suitable for X-ray single crystal diffraction, formed within 24 h.
Experimental
General
Unless otherwise stated, all operations were carried out in Sch-
lenkware under an inert atmosphere using carefully dried and
oxygen-free solvents. Acetonitrile was dried by distillation over
CaH2 in a nitrogen atmosphere. Ethanol was prepared by boil-
ing with Mg(OEt)2 in a nitrogen atmosphere, followed by distil-
lation. All other solvents were purified using a Glass Contour
solvent purification system. cis-Mo2(DAniF)2(CH3CN)4ؒ2BF4ؒ
2CH3CN26 (0), the chiral diacids21,22 o-H2L3, m-H2L2 and
p-H2L3, and the non-chiral diacid m-HO2C(CH3)2O–C6H4–
OC(CH3)2CO2H, H2L4, were prepared following published
methods.15 The non-chiral ortho ligand H2L5 was prepared
as described below, following a modified experimental pro-
cedure.25 Commercially available chemicals were used as
received. IR spectra were recorded on a Perkin-Elmer 16PC
Preparation of Mo2(DAniF)2(L2) (2). This was prepared simi-
larly to 1. The yield was quantitative. IR (KBr, cmϪ1): 3448 (w,
br), 2935 (w), 2832 (w), 1609 (w), 1542 (s), 1503 (vs), 1461 (m),
1441 (m), 1415 (w), 1292 (m), 1245 (s), 1217 (s), 1177 (m), 1103
(m), 1035 (s), 941 (w), 874 (w), 827 (m), 764 (w), 703 (w), 644
(w), 619 (w), 591 (w), 522 (w), 453 (w). Elemental analysis, calc.
for Mo2C42N4O13H48: C, 50.01; H, 4.80; N, 5.55; found: C,
49.87; H, 4.58; N, 5.29%. 1H NMR (C6D6, δ): 1.83 (d, CHCH3,
6H), 3.17 (s, OCH3, 6H), 3.19 (s, OCH3, 6H), 5.02 (q, CHCH3,
2H), 6.39–7.26 (m, aromatic, 20H), 8.48 (s, CH, 2H).
1
FTIR spectrometer from KBr pellets. H NMR spectra were
obtained on a Varian XL-300 spectrometer, with chemical shifts
(δ/ppm) referenced to the signal of the deuterated solvent. Ele-
mental analyses were performed by Canadian Microanalytical
Services in British Columbia, Canada. The electrochemical
measurements were recorded on a BAS 100 electrochemical
analyzer, with Bu4NPF6 (0.1 M) electrolyte, Pt working and
auxiliary electrodes, and a Ag/AgCl reference electrode, at a
scan rate of 100 mV sϪ1 (for CV). UV-vis measurements were
made with a UV2501 PC spectrophotometer.
Preparation of Mo2(DAniF)2(L4) (4). This was prepared simi-
larly to 1. Yield: (90%). IR (KBr, cmϪ1): 2986 (w), 2944 (w),
2905 (w), 2831 (w), 1696 (w), 1594 (m), 1534 (s), 1499 (s), 1467
(m) 1439 (w), 1413 (w), 1362 (w), 1312 (m), 1284 (m), 1244 (s),
1210 (m), 1176 (m), 1036 (m), 826 (m), 779 (w), 780 (w), 700
(w), 621 (w), 588 (w), 537 (w), 450 (w). Elemental analysis, calc.
for Mo2C47N4O10H49: C, 55.25; H, 4.83; N, 5.48; found: C,
55.46; H, 4.85; N, 5.09%. 1H NMR (C6D6, δ): 1.96 [s, C(CH3)2,
12H], 3.19 (s, OCH3, 12H), 3.19 (s, OCH3, 6H), 5.02 (q,
CHCH3, 2H), 6.39–7.26 (m, aromatic, 20H), 8.48 (s, CH, 2H).
Preparation of (Et4N)2L1, (Et4N)2L2, (Et4N)2L3 and (Et4N)2-
L4. The salts were obtained by adding a 0.1 M solution of
Et4NOH in MeOH (1.15 g, 7.87 mmol) to a 1 M solution of the
corresponding H2L acid in MeOH (1.00 g, 3.94 mmol). After
stirring for a few minutes, the solvent was removed under vac-
uum and the residue was dried under vacuum overnight at 50
1
ЊC. For (Et4N)2L1, H NMR (CDCl3, δ): 1.16 (t, NCH2CH3,
24H), 1.54 (d, CHCH3, 6H), 3.19 (q, NCH2CH3, 16H), 4.53 (q,
1
CHCH3, 2H), 6.61–6.94 (m, aromatic, 4H); for (Et4N)2L2, H
NMR (CDCl3, δ): 1.22 (t, NCH2CH3, 24H), 1.48 (d, CHCH3,
6H), 3.26 (q, NCH2CH3, 16H), 4.52 (q, CHCH3, 2H), 6.33–6.99
Reaction of 0 with (NEt4)2L3. This was carried out similarly
to the preparation of 1. IR (KBr, cmϪ1): 3034 (w), 2933 (w),
3831 (w), 1560 (m), 1542 (s), 1500 (vs), 1459 (m), 1440 (m), 1291
(m), 1411 (m), 1291 (m), 1246 (s), 1214 (s), 1104 (m), 1031 (s),
940 (w), 878 (w), 825 (s), 762 (w), 590 (w), 532 (w), 449 (w).
Elemental analysis, calc. for Mo4C84N8O25H94: C, 50.46; H,
1
(m, aromatic, 4H); for (Et4N)2L3, H NMR (CD3COCD3, δ):
1.55 (t, NCH2CH3, 24H), 1.64 (d, CHCH3, 6H), 3.68 (q,
NCH2CH3, 16H), 4.47 (q, CHCH3, 2H), 6.99 (s, aromatic, 4H);
1
for (Et4N)2L4, H NMR (CDCl3, δ): 1.20 (t, NCH2CH3, 24H),
1.50 [s, C(CH3)2, 12H], 3.25 (q, NCH2CH3, 16H), 6.47–6.77 (m,
aromatic, 4H).
1
4.74; N, 5.60; found: C, 50.70; H, 4.84; N, 5.91%. H NMR
(C6D6, δ): 1.91, 1.98 (2d, CHCH3, 18H), 3.11, 3.19 (2d, OCH3,
36H), 5.22, 5.51 (2q, CHCH3, 6H), 6.36–7.42 (m, aromatic,
60H), 8.42, 8.49 (2s, CH, 6H).
Preparation of (Et4N)2L5. A solution of ICH2CO2C2H5
(0.936 g, 4.37 mmol) in 10 ml of CH3CN, which was prepared in
a flask protected from light by aluminium foil, was added via
cannula to a suspension of catechol (0.2372 g, 2.156 mmol) and
K2CO3 (0.716 g, 5.19 mmol) in 10 ml of CH3CN. The mixture
was stirred overnight in a flask wrapped with aluminium foil.
The solvent was then removed under vacuum and the residue
was dissolved in 30 ml of CH2Cl2; an insoluble portion was
removed by filtration. The CH2Cl2 was removed from the
filtrate and yielded the corresponding diester Et2L5.
Reaction of 0 with (NEt4)2L5. A yellow solid was obtained
following the procedure for the preparation of 1. IR (KBr,
cmϪ1): 2947 (w), 2832 (w), 1623 (m), 1543 (s), 1534 (s), 1500
(vs), 1452 (m), 1426 (m), 1384 (w), 1341 (w), 1286 (s), 1246 (s),
1215 (s), 1176 (w), 1131 (w), 1106 (w), 1030 (m), 941 (w), 830
(m), 789 (w), 763 (w), 742 (w), 712 (w), 618 (w), 592 (w), 542
(w), 470 (w), 449 (w). Elemental analysis, calc. for Mo2C40-
D a l t o n T r a n s . , 2 0 0 3 , 4 2 9 7 – 4 3 0 2
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Table 2 Crystal data for 1ؒ4CH2Cl2 and 4ؒC6H6
1ؒ4CH2Cl2
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4ؒC6H6
Formula
Formula weight
Mo4N8O20C88Cl8H92
2249.06
Mo2N4O10C50H52
1060.84
Space group
a/Å
b/Å
c/Å
I222 (no. 23)
13.970(3)
20.450(5)
37.216(5)
90
10632(4)
4
1.405
0.726
Ϫ60
P21/c (no. 14)
16.837(5)
16.094(5)
19.036(6)
115.727(5)
4647(3)
β/Њ
V/Å3
Z
4
Dc/g cmϪ3
1.516
0.604
Ϫ173
0.0334, 0.0746
0.0457, 0.0796
µ(Mo-Kα)/mmϪ1
T/ЊC
R1a, wR2b [I > 2σ(I )]
R1a, wR2b (all data)
Flack parameterc
0.1102, 0.2226
0.1488, 0.2404
0.03(14)
a R1 = Σ||Fo| Ϫ |Fc||/Σ|Fo|. b wR2 = [Σ[w(Fo Ϫ Fc2)2]/Σ[w(Fo )2]]1/2, w = 1/
2
2
σ2(Fo ) ϩ (aP)2 ϩ bP, where P = [max(0 or Fo ) ϩ 2(Fc2)]/3. c See: H. D.
Flack, Acta Crystallogr. Sect. A, 1983, 39, 876.
2
2
3 (a) F. A. Cotton, C. Lin and C. A. Murillo, Acc. Chem. Res., 2001,
34, 759; (b) F. A. Cotton, C. Lin and C. A. Murillo, Proc. Natl. Acad.
Sci. USA, 2002, 99, 4810.
N4O11H40: C, 50.86; H, 4.27; N, 5.78; found C, 50.77; H, 4.10;
4 (a) J. Pérez-Prieto, S.-E. Stiriba, E. Moreno and P. Lahuerta,
Tetrahedron: Asymmetry, 2003, 14, 787; (b) M. Barberis, J. Pérez-
Prieto, K. Herbst and P. Lahuerta, Organometallics, 2002, 21,
1667; (c) M. Barberis, J. Pérez-Prieto, P. Lahuerta and M. Sanaú,
Chem. Commun., 2001, 439; (d ) F. Estevan, P. Krueger, P. Lahuerta,
E. Moreno, J. Pérez-Prieto, M. Sanaú and H. Werner, Eur. J. Inorg.
Chem., 2001, 105; (e) M. P. Doyle and D. C. Forbes, Chem. Rev.,
1998, 98, 911; ( f ) M. P. Doyle, in Catalytic Asymmetric Synthesis,
ed. I. Ojima, Wiley-VCH, New York, 2nd edn., 2000, ch. 5.
5 See, for example: (a) G. Scapin, S. G. Reddy and J. S. Blanchard,
Biochemistry, 1996, 35, 13540 and references therein; (b) T. Koyama,
K. Ogura and S. Seto, J. Am. Chem. Soc., 1997, 99, 1999.
6 T. Habereder, M. Warchhold, H. Nöth and K. Severin,
Angew. Chem., Int. Ed., 1999, 38, 3225.
7 (a) H. Jiang and W. Lin, J. Am. Chem. Soc., 2003, 125, 8084; (b) S. J.
Lee, A. Hu and W. Lin, J. Am. Chem. Soc., 2002, 124, 12948;
(c) M. M. Ali and F. M. MacDonnell, J. Am. Chem. Soc., 2000, 122,
11527; (d ) S. J. Lee and W. Lin, J. Am. Chem. Soc., 2002, 124,
4554; (e) S. J. Lee, C. R. Lumman, F. N. Castellano and W. Lin,
Chem. Commun., 2003, 2124.
8 G. Süss-Fink, J.-L. Wolfender, F. Neumann and H. Stoeckli-Evans,
Angew. Chem., Int. Ed. Engl., 1990, 29, 429.
9 F. A. Cotton, J. P. Donahue and C. A. Murillo, Inorg. Chem.
Commun., 2002, 5, 59.
10 F. A. Cotton, C. Lin and C. A. Murillo, Inorg. Chem., 2001, 40,
5886.
11 (a) F. A. Cotton, C. Lin and C. A. Murillo, Inorg. Chem., 2001, 40,
478; (b) F. A. Cotton, L. M. Daniels, C. Lin and C. A. Murillo,
J. Chem. Soc., Dalton Trans., 2001, 502; (c) P. Angaridis, J. F. Berry,
F. A. Cotton, C. A. Murillo and X. Wang, J. Am. Chem. Soc., 2003,
125, 10327.
12 (a) F. A. Cotton, C. Lin and C. A. Murillo, Inorg. Chem., 2001, 40,
575; (b) F. A. Cotton, C. Lin and C. A. Murillo, J. Am. Chem. Soc.,
1999, 121, 4538.
13 F. A. Cotton, C. Lin and C. A. Murillo, Inorg. Chem., 2001, 40,
472.
14 K.-B. Shiu and H.-C. Lee, Organometallics, 2002, 21, 4013.
15 R. P. Bonar-Law, T. D. McGrath, N. Singh, J. F. Bickeley and
A. Steiner, Chem. Commun., 1999, 2457.
16 (a) J. F. Gallagher, G. Ferguson and A. J. McAlees, Acta Crystallogr.,
Sect. C, 1997, 53, 567; (b) D. F. Taber, R. P. Meagley, J. P.
Louey and A. L. Rheingold, Inorg. Chim. Acta, 1995, 239,
25.
17 J. F. Bickley, R. P. Bonar-Law, C. Femoni, E. J. MacLean,
A. Steiner and S. J. Teat, J. Chem. Soc., Dalton Trans., 2000,
4025.
18 R. P. Bonar-Law, T. D. McGrath, N. Singh, J. F. Bickley, C. Femoni
and A. Steiner, J. Chem. Soc., Dalton Trans., 2000, 4343.
19 R. P. Bonar-Law, T. D. McGrath, J. F. Bickley, C. Femoni and
A. Steiner, Inorg. Chem. Commun., 2001, 4, 16.
1
N, 5.57%. H NMR (CDCl3, δ): 3.64, 3.68 (2s, OCH3, 36H),
5.18, 5.22 (2s, CH2, 12H), 6.44–7.10 (m, aromatic, 60H), 8.39,
8.42 (2s, CH, 6H)
X-Ray crystallography
For 1, a single crystal was mounted on the tip of a quartz fiber
and transferred to the goniometer of an Enraf-Nonius FAST
diffractometer. 250 strong reflections were indexed to a body-
centered orthorhombic unit cell. The cell dimensions, lattice
type and Laue symmetry were confirmed from axial images.
Data collection and integration were performed using the
MADNES software27 and the integrated data were processed
and corrected for Lorentz and polarization effects with the pro-
gram PROCOR.28 An absorption correction was applied using
the program SORTAV.29 The crystal showed broad reflections in
ω indicative of a high degree of mosaicity. A single crystal of
4 was mounted on a nylon loop and transferred to the
goniometer of a SMART APEX CCD diffractometer. Data
collection and integration were performed with the SMART
software30 and the integrated data were processed and
corrected for Lorentz and polarization effects using the SAINT
program.31 An absorption correction was applied with the pro-
gram SADABS.32 Both structures were solved by the Patterson
method and refined by alternate cycles of full-matrix least
squares and difference Fourier maps with the SHELXTL
package.33 Except for the disordered aryl groups found in 1 and
O6A in 4, non-hydrogen atoms were refined anisotropically and
hydrogen atoms were added at calculated positions and
included in the structure factor calculations. Selected bond dis-
tances for 1 and 4 are listed in Table 1. Crystal data are listed in
Table 2.
CCDC reference numbers 217277 and 217278.
See http://www.rsc.org/suppdata/dt/b3/b310151g/ for crystal-
lographic data in CIF or other electronic format.
Acknowledgements
We thank the National Science Foundation for financial sup-
port. J. F. B. is grateful to the National Science Foundation for a
Predoctoral Fellowship. We thank R. P. Bonar-Law for provid-
ing details on the synthetic method for making H2L4. Also, we
would like to thank Dr E. E. Simanek and Dr V. I. Bakhmoutov
for helpful discussions.
20 R. P. Bonar-Law, J. F. Bickley, C. Femoni and A. Steiner, J. Chem.
Soc., Dalton Trans., 2000, 4224.
21 F. Effenberg, U. Burkard and J. Willfahrt, Liebegs Ann. Chem.,
1986, 314.
22 U. Burkard and F. Effenberg, Chem. Ber., 1986, 119, 1594.
23 F. A. Cotton and R. A. Walton, Multiple Bonds Between Metal
Atoms, Clarendon Press, Oxford, 2nd edn., 1993.
References
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(b) Catalysis by Di- and Polynuclear Metal Cluster Complexes,
D a l t o n T r a n s . , 2 0 0 3 , 4 2 9 7 – 4 3 0 2
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24 For a recent 3D network with channels in a chiral environment, see:
Y. Zhang, M. K. Saha and I. Bernal, CrystEngComm, 2003, 5, 34.
25 Y. Wenfa and D. Zixiu, Huaxue Shiji, 2002, 24, 363.
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J. Huffman, S. Iyer, C. Lin, A. M. MacIntosh and C. A. Murillo,
J. Chem. Soc., Dalton Trans., 1999, 1387.
30 SMART, version 5.625, Software for the CCD Detector System,
Bruker Analytical X-ray Systems, Inc., Madison, WI, USA,
2001.
31 SAINT, version 6.33B, Data Reduction Software, Bruker Analytical
X-ray Systems, Inc., Madison, WI, USA, 2001.
32 SADABS, version 2.03, Program for Bruker/Siemens Area Detector
Absorption and Other Corrections, Bruker Analytical X-ray
Systems, Inc., Madison, WI, USA, 2001.
27 A. Messerschmidt and J. W. Pflugrath, J. Appl. Crystallogr., 1987, 20,
306.
28 (a) W. Kabsch, J. Appl. Crystallogr., 1988, 21, 67; (b) W. Kabsch,
J. Appl. Crystallogr., 1988, 21, 916.
29 R. H. Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33.
33 G. M. Sheldrick, SHELXTL, version 6.10, Programs for Crystal
Structure Solution and Refinement, Bruker Analytical X-ray
Systems, Inc., Madison, WI, USA, 2000.
D a l t o n T r a n s . , 2 0 0 3 , 4 2 9 7 – 4 3 0 2
4302