Supramolecular assemblies of dimolybdenum transoids built by Mo 2-enhanced perfluorophenyl-perfluorophenyl synthons

Article abstract of DOI:10.1039/c1dt11490e

Two supramolecular assemblies were developed by the dimmolybdenum paddlewheel complex trans-Mo₂(DAniF)₂(O₂CC ₆F₅)₂ (1) (ancillary ligand DAniF = N,N′-di-(p-anisyl)formamidinate) through int

Full text of DOI:10.1039/c1dt11490e

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PAPER
Supramolecular assemblies of dimolybdenum transoids built by Mo2-enhanced
perfluorophenyl-perfluorophenyl synthons†
Li Juan Han,a Li Yan Fan,a Miao Meng,b Xuefeng Wanga and Chun Y. Liu*a,b
Received 6th August 2011, Accepted 15th September 2011
DOI: 10.1039/c1dt11490e
Two supramolecular assemblies were developed by the dimmolybdenum paddlewheel complex
trans-Mo2(DAniF)2(O2CC6F5)2 (1) (ancillary ligand DAniF = N,N¢-di-(p-anisyl)formamidinate)
through intermolecular offset face to face C6F5 ◊ ◊ ◊ C6F5 interactions. The two networks are different
because of the presence and absence of tetrahydrofuran (THF) axial coordination to the Mo2 units, but
feature commonly short interplanar distances between the two paired perfluorophenyl groups, that is,
˚
˚
3.30 A and 3.23 A, respectively, which are similar to the shortest intermolecular C ◊ ◊ ◊ F contacts
between two atoms in meta and ortho positions. Consistently, as indicated by the Mulliken population
analysis, the dipole moments for the meta and ortho C–F bonds are considerably enlarged because the
pentafluorobenzoate groups are bonded to the dimetal unit. In comparison, X-ray structural and
theoretical analyses were also made for the parent molecule pentafluorobenzoic acid. The resultant data
show that charge distribution on the perfluorophenyl group has a major influence on the C6F5 ◊ ◊ ◊ C6F5
binding mode. Therefore, it is evidenced that the dimetal unit plays a role in further polarizing the
highly polarized C–F bonds and the intermolecular perfluorophenyl-perfluorophenyl interactions are
dominated by the C ◊ ◊ ◊ F dipole–dipole interaction, rather than aromatic-aromatic p–p stacking.
the differences between perfluorophenyl–perfluorophenyl and the
Introduction
well defined aromatic–aromatic interactions were insufficiently
acknowledged.7,9,10 It is also noteworthy that C6F5 ◊ ◊ ◊ C6F5 in-
teraction occurs frequently in perfluorinated coordination and
organometallic crystalline solids,8–11 which prompts further ex-
planation.
In order to gain additional insights into perfluorophenyl-
perfluorophenyl interactions, specifically in the metal-containing
solids, a novel quadruply bonded dimolybdenum compound
with two transoid C6F5 pendants was prepared. Com-
pound 1 (Fig. 1) is a mixed-ligand complex, namely trans-
Mo2(DAniF)2(O2CC6F5)2, on which the auxiliary ligands DAniF
(N,N¢-di-p-anisylformamidinate) are used to block the unneces-
sary coordination sites. Given the transoid geometry of the Mo2
complex, the intermolecular C6F5 ◊ ◊ ◊ C6F5 binding interaction was
expected to generate infinite extension of the supramolecular
motifs along a single direction.
As is well known, the metal-metal bond distance is a probe of
electron density on the dimetal center which is tunable by electron
donation from the axial ligand. In this work, we found that the
electronic property of the metal center has a critical impact on the
binding mode of the perfluorophenyl synthons. Self-assembling of
the trans Mo2 building blocks produced two distinct networks,
which is attributed to the difference in axial coordination.
Scheme 1 depicts the observed two different C6F5 ◊ ◊ ◊ C6F5 binding
patterns for the two supramolecular structures, along with that
for pentafluorobenzoic acid. Pattern A is for the network derived
from the THF solvated complex, while pattern B is for the one
Face to face phenyl-perfluorophenyl stacking is a fairly strong
(3.7–4.7 kcal mol-1) non-covalent interaction which encompasses
three attractive forces, quadrupole–quadrupole, p–p and C–
F ◊ ◊ ◊ H–C.1,2 This concomitant binding interaction has been widely
exploited in numerous studies.3–5 Perfluorophenyl-perfluorophenyl
interaction, on the other hand, has been much less observed until
recently. An increasing number of examples have shown the offset
face to face stacking between two C6F5 rings with short interplanar
distances.6 It was unexpected that in the cases where hydrophenyl
and perfluorophenyl groups coexist, the C6F5 ◊ ◊ ◊ C6F5 stacking,
rather than C6H5 ◊ ◊ ◊ C6H5, was crystallographically defined.7,8
However, the nature of this type of interaction is not yet well
understood. Owing to the presence of the most electronegative
atoms (F) on a C6 ring periphery, the quadrupole and dipole
properties for the C6F5 group are significantly altered. In addition,
electronic delocalization creates a deficiency of the p electron
cloud on the fluorinated phenyl ring, which impedes efficient
p–p stacking. However, in the literature including recent works,
aDepartment of Chemistry, Tongji University, 1239 Siping Road, Shanghai,
200092, P.R. China
bDepartment of Chemistry, Jinan University, 601 Huangpu Avenue West,
Guangzhou, 510632, P. R. China. E-mail: cyliu06@tongji.edu.cn; Fax: +
01186 021-65980513; Tel: + 01186 021-65980510
† Electronic supplementary information (ESI) available. CCDC reference
numbers 825961, 825962. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1dt11490e
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(Scheme 1, A and B). In the crystal structure, the molecules
of pentafluorobenzoic acid are also packed via C6F5 ◊ ◊ ◊ C6F5
12
˚
interaction with interplanar distance 3.20 A. In this case, the
C6F5 groups are paired by interactions of the ortho F atom with the
˚
center of the benzene ring (3.19 A), and C ◊ ◊ ◊ F contacts between
˚
the meta F atom and C atom of the carboxylate group (3.20 A)
(Scheme 1, C). Therefore, these perfluorophenyl–perfluorophenyl
interactions occur commonly in offset face to face mode but
with different binding sites. Furthermore, from the geometries
of the three structural motifs, these C6F5 ◊ ◊ ◊ C6F5 interactions
are unlikely classified as conventional aromatic–aromatic p–p
stacking. Mulliken population analyses at the density functional
theory (DFT) level reveal that in the complex system, the Mo2
unit plays a role in further polarizing the highly polarized C–
F bonds and the C6F5 ◊ ◊ ◊ C6F5 interactions are dominated by
intermolecular C ◊ ◊ ◊ F dipole–dipole interactions.
Results and discussion
Dimolybdenum complex trans-Mo2(DAniF)2(O2CC6F5)2 (1) was
prepared by starting with trans mixed-ligand complex precursor,
or trans-Mo2(DAniF)2(O2CCH3)2. Ligand replacement between
carboxylates is a kinetically unfavorable reaction, which may
yield a ligand scribbling mixture. However, this transformation
can be readily achieved by addition of sodium methoxide to the
reaction system. Reaction of sodium methoxide (in methanol)
with the precursor removes the acetates and generates the
methoxide-methanol coordinated intermediate. This material is
very active toward pentafluorobenzoic acid, thus producing the
target molecule in good yield without geometry alternation. A
similar procedure has been utilized for substitution of the acetate
in Mo2(DAniF)3(OAc),13 from which the methoxide-methanol in-
termediate Mo2(DAniF)3(OCH3)(OHCH3) has been structurally
characterized.14 This preparative method can be described by the
equations as follows.
Fig. 1 Molecular structures of trans-Mo2(DAniF)2(O2CC6F5)2 (THF)2ax
(A) and trans-Mo2(DAniF)2(O2CC6F5)2 (B). For the THF solvated
molecule, Mo(1)–Mo(1A): 2.1176(6) A, Mo(1)–O(1): 2.119(3) A,
˚
˚
˚
˚
Mo(1)–O(2): 2.117(3) A, Mo(1)–O(THF): 2.615 A and C(1)–C(7):
trans-Mo2(DAniF)2(OAc)2 + 2NaOCH3(CH3OH) ⎯T⎯HF⎯→
˚
1.494(5) A. For the non-solvated molecule, Mo(1)–Mo(1A): 2.0895(4),
rt
˚
˚
Mo(1)–O(1): 2.126(2) A, Mo(1)–O(2A): 2.113(2) A and C(1)–C(7):
trans-Mo2(DAniF)2(OCH3)2(CH3OH)2 + 2NaOAc
˚
1.492(3) A.
trans-Mo2(DAniF)2(OCH3)2(CH3OH)2 + 2HO2CC6F ⎯T⎯HF⎯→
5
rt
trans-Mo2(DAniF)2(O2CC6F )2 + 4CH3OH
without axial THF molecules. Importantly, for both A and B, the
5
˚
˚
interplanar distances, 3.30 A and 3.23 A, respectively, are similar
to the shortest intermolecular C ◊ ◊ ◊ F distances. This implies that
the C ◊ ◊ ◊ F contacts occuring at the meta and ortho atoms may be
responsible for the perfluorophenyl–perfluorophenyl interaction
When compound 1 crystallized in tetrahydrofuran, two THF
molecules occupied the axial sites of the Mo2 unit, while crys-
tallization in CH2Cl2/hexane produced a non-solvated molecule.
Scheme 1
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Fig. 2 Single crystal structures of the dimolybdenum supramolecular aggregate I showing: the perfluorophenyl–perfluorophenyl interaction (inset); the
view along the Mo–Mo bond vector (top) and the projection on the perfluorophenyl planes (bottom). The anisyl groups in the top diagram have been
removed for clarity.
Table 1 Crystallographic data for 1·CH2Cl2 and 1·2THF
The crystallographic data are presented in Table 1 and the crystal
structures are shown in Fig. 1 with selected structural parameters.
It is worthy to note that complexation of THF lengthens the Mo–
Complex
1·CH2Cl2
1·2THF
˚
Mo bond from 2.0895 (4) to 2.1175(7) A due to the extra electron
Empirical formula
fw
C45H32F10Mo2N4O8Cl2
1209.53
Monoclinic
C2/c (No. 15)
293(2)
22.421(3)
12.265(2)
17.654(2)
90
106.386(1)
90
4657.3(1)
4
C52H46F10Mo2N4O10
1268.81
Triclinic
P¯ı (No. 2)
293(2)
9.226(2)
11.920(2)
12.857(2)
76.551(2)
82.545(2)
72.299(2)
1307.3(3)
1
density added to the antibonding orbitals of the Mo2 unit. The
increased metal–metal bond distance implies that the solvated Mo2
unit is less electron-withdrawing from the ligands. Furthermore,
for both molecules, the C–C bond that connects the C6F5 group
and dimolybdenum chelating ring, ca. 1.49 A in length, is slightly
but significantly shorter than a normal C–C single bond, e.g., 1.54
Crystal system
Space group
T/K
˚
a/A
˚
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
˚
A. This result suggests that electronic charge transfer may take
place between the perfluorophenyl group and the dimetal unit.
In the THF-containing crystal lattice, denoted as I, the Mo2
molecules are packed in layers perpendicular to the Mo–Mo bond
vector (Fig. 2); between the layers are the solvated THF molecules.
In I, the methine H atoms on the DAniF ligands are bonded to
the neighboring molecules through C–F ◊ ◊ ◊ H–C interactions with
3
˚
V/A
Z
Dc/g cm-3
1.725
0.751
0.0289
0.0810
1.612
0.577
0.0394
0.0921
m/mm-1
Final R1(I > 2s(I))
WR2 (all data)
GOF on F2
1.055
1.018
short F ◊ ◊ ◊ H contacts (ca. 2.66 A).15 As shown in Fig. 2 (inset), the
˚
perfluorophenyl–perfluorophenyl interaction occurs in an offset
face to face stacking mode with the interplanar distance Dperp
=
perfluorophenyl pair, one C6F5 ring is placed on the other via two
C ◊ ◊ ◊ F contacts. The C ◊ ◊ ◊ F contacts occur at the ortho C and
meta F atoms with a distance equal to the interplanar separation
˚
˚
3.30 A, center to center distance Dcent = 3.53 A and relatively small q
(21.2◦), an angle defined by the Dperp and Dcent vectors. Projection
onto the C6F5 ring planes (Fig. 2, bottom) shows that for each
˚
(3.30 A).
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Fig. 3 Single crystal structures of the dimolybdenum supramolecular aggregate II showing: the perfluorophenyl-perfluorophenyl interaction (inset and
top); the projection on 100 direction (bottom). The anisyl groups have been removed for clarity.
The p–p stacking in displaced or offset mode between two
parallel hydrophenyl groups has been predicted at various levels of
theory to give an interplanar distance of 3.4–3.6 A,16 which agrees
˚
metal ◊ ◊ ◊ F (ArF) weak coordination has been documented,17 this
is the first example that shows the Mo ◊ ◊ ◊ F (ArF) interaction.
In II, the interplanar separation for the C6F5 pair is observed
˚
well with the experimental observation in many crystal structures.
to be as short as 3.23 A, but the two aromatic rings slide away
˚
The short planar separation (3.30 A) and near center to center
from each other as indicated by the◦large center to center distance
stacking (q = 21.2◦) would impose a considerable quadrupole–
quadrupole repulsion between the two stacked C6F5 groups. Thus,
it is believed that the network (I) is retained by a strong attractive
C6F5 ◊ ◊ ◊ C6F5 interaction, which may not share the same physical
origin with aromatic p–p stacking.
(Dcent = 4.78 A) and q angle (47.8 ) (Fig. 3, inset). The C ◊ ◊ ◊ F
˚
interactions occur once again between the ortho and meta atoms
˚
˚
with a distance (3.30–3.32 A) similar to the Dperp in I (3.30 A),
although the perfluorophenyl–perfluorophenyl motifs for the two
structures differ in stacking pattern. This observation reflects that
the C ◊ ◊ ◊ F contact, rather than p–p stacking, is likely the physical
origin for the C6F5 ◊ ◊ ◊ C6F5 binding interactions occurring in the
supramolecular assemblies I and II. As shown by the projection
onto the 100 direction (Fig. 3, bottom), in II, intermolecular
In the absence of a donor solvent, intermolecular interactions
associated with the perfluorophenyl groups generated a distinct
supramolecular array (II). One commonality among the two
supramolecular aggregates is that the perfluorophenyl rings are
paired and arranged in parallel to one another. The architecture
of II also has a layered structure but the complex building blocks
lie in two orientations within each layer and thus, the molecular
chains are developed in two directions (Fig. 3, top). The formation
of the different lattice structure can be likely attributable to the
˚
interactions include F ◊ ◊ ◊ F contact of 2.85 A (< van der waals radii
2.94 A), which should be considered as an attractive interaction.
18
˚
On this basis, we conclude that the supramolecular architecture II
is sustained by cooperative intermolecular interactions including
Mo ◊ ◊ ◊ F, C ◊ ◊ ◊ F and F ◊ ◊ ◊ F with exclusion of aromatic p–p
stacking interaction.
˚
observed intermolecular Mo ◊ ◊ ◊ F interaction of 3.49 A. Although
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◦
˚
Table 2 Calculated charge distributions over a C6F5 group in pentafluo-
robenzoic acid and the dimolybdenum models of 1
is 4.16 A and q = 40.6 , indicating that the aromatic rings
have largely slid away from the normal position. From these
structural parameters, aromatic–aromatic p–p interaction cannot
account for the C6F5 ◊ ◊ ◊ C6F5 interaction in pentafluorobenzoic
acid. However, it can be understood by “point to point” binding
interaction within the pair of pentafluorobenzoate. The binding
sites are determined by selection of two attractive points with a
C6F5-CO2H
C(1)a
0.080
C(2), C(6)
0.137
C(3), C(5)
0.113
C(4)
0.152
F(1), F(5)
-0.144
F(2), F(4)
-0.151
F(3)
-0.142
˚
distance close to the Dperp (3.20 A). It is found there are two types
C6F5-Mo2-THFb
C(1)
-0.086
C(2), C(6)
0.176
C(3), C(5)
0.122
C(4)
0.156
of binding sites which are completely different from those for the
complex architectures I and II. As shown by Scheme 1C, each
C6F5 group has an ortho F atom located on the other C6F5 ring
with a distance of 3.20 A from the center; the C ◊ ◊ ◊ F contacts of
3.19 A are established between the meta F atom and the C atom
F(1), F(5)
-0.166
F(2), F(4)
-0.175
F(3)
-0.166
˚
˚
c
on the carboxylate group. The Mulliken population analysis for
the pentafluorobenzoate group gives an acceptable explanation
for this C6F5 ◊ ◊ ◊ C6F5 stacking pattern. As mentioned above, the
C–F bonds in pentafluorobenzoic acid are less polarized relative
to those in the complexes and on the other hand, the ring center
has a large positive potential. Thus, one of the F atoms connects
the other C6F5 group by dipole interaction with the ring center.
According to the calculation, the C atom of the carboxylate group
has a Mulliken charge of +0.205, larger than those for the C atoms
on the aromatic ring. Consistently, the shortest C ◊ ◊ ◊ F distance is
found between this carbon atom and the most negative meta F
atom (-0.151).
C6F5-Mo2
C(1)
-0.082
C(2), C(6)
0.185
C(3), C(5)
0.125
C(4)
0.160
F(1), F(5)
-0.161
F(2), F(4)
-0.171
F(3)
-0.163
a For the two calculation models, the atoms on
a
C6F5 group
trans-
trans-Mo2-
are labeled as shown in Fig. 1. b C6F5-Mo2-THF
=
Mo2(NHCHNH)2(O2CC6F5)2(THF)2ax
(NHCHNH)2(O2CC6F5)2.
.
c C6F5-Mo2
=
In order to understand the nature of the perfluorophenyl–
perfluorophenyl interaction that occurs between the dimetal
complex motifs, we have performed theoretical work at DFT
level to calculate the charge distribution over a perfluo-
rophenyl ring. The computation models employed are trans-
Mo2(NHCHNH)2(O2CC6F5)2(THF)2ax and trans-Mo2(NHCH-
NH)2(O2CC6F5)2 as the representatives of compound 1 with and
without axial THF, respectively. Pentafluorobenzoic acid was also
computed for comparison. The calculated Mulliken charges on the
atoms of the C6F5 moieties, presented in Table 2, are compatible
with the published data for perfluorobenzene (C6F6).19 It is noted
that there are some significant differences in charge distribution
between the molecule C6F6 and the substituted C6F5 groups.
The three models have anisotropic charge distributions over the
aromatic ring and only the para atoms with charges similar to
those of hexafluorobenzene, e.g., +0.15 for the C and -0.15 for
the F atoms23 (See Table 2). Clearly, the C–F bonds in the Mo2
complexes are further polarized by the [Mo2] unit in comparsion
with those in C6F6 and HO2CC6F5.
The enlarged dipole moments for the C–F bonds imply that the
metal centers in metal coordination and organometallic aggrega-
tions would facilitate the C6F5 ◊ ◊ ◊ C6F5 dipole–dipole interaction.
It is also interesting to note that in the parent acid, the para C
atom, or C(4), is the most positive atom (Table 2); in contrast,
for both of the two complex models, the ortho carbon atoms, or
C(2) and C(6), are more positively charged. The most negatively
charged fluorine atoms are those of the meta positions, or F(2)
and F(4). This result is in good agreement with the experimental
observation that in both I and II, the C6F5 ◊ ◊ ◊ C6F5 interactions are
established via C ◊ ◊ ◊ F contacts between the ortho and meta atoms.
By examination of the published X-ray structural data for
pentafluorobenzoic acid,12 it is found that the C6F5CO2H
molecules are also packed in pairs and the two perfluorophenyl
rings are parallel with an interplanar distance (Dperp) of 3.20
It is significant that calculations based on the two dimolyb-
denum models reveal that the electron density and the charge
distribution over a C6F5 group are quite sensitive to the electronic
property of the substituent. As mentioned above, there is a subtle
difference in structure parameters between the Mo2 units for the
molecules with and without axial THF, which is a reflection that
the electron-withdrawing capability for the dimolybdenum unit is
altered by the coordination environment. Consistently, theoretical
work indicates that the perfluorophenyl group bonded to the Mo2
unit with coordinated THF molecules bears more electron density
than that attached to the axial free dimetal unit. As shown in
Table 2, the carbon atoms on the C6F5 are less positive but the
fluorine atoms are slightly more negative in comparison with the
corresponding atoms in the second model compound. In light
of this point, the better centroid to centroid stacking in I can
be attributed to the reduced quadrupole–quadrupole repulsion
between the C6F5 groups. The calculation shows that the Mo2
unit has a major influence on ortho atoms that are closer to the
dimetal center (Table 2), implying the electrostatic nature for the
Mo2 ◊ ◊ ◊ C6F5 interaction. On the other hand, the shortened C–C
˚
single bond (1.492–1.494 A) signals the electronic delocalization
via d–p p orbital interaction. Therefore, further polarization of the
highly polarized C–F bonds is likely due to the two concomitant
effects.
Interestingly, the C ◊ ◊ ◊ F contacts found in I and II are nearly
perpendicular to the associated C–F bond vector. As is known, the
fluorine atom on a perfluorous moiety has an anisotropic electron
density distribution, that is, negative electrostatic potential for
the side region but positive for the bond axial position.20 The
covalent C–F bond has significant electrostatic character,21 which
is significantly enhanced in the perfluorinated metal complex
as discussed. Further polarization of the C–F bonds should
lead to a relatively strong intermolecular Cd+ ◊ ◊ ◊ Fd- dipole–
dipole interaction. The normality of C ◊ ◊ ◊ F contact to the C6F5
˚
˚
A, which is considerably smaller than 3.4–3.6 A for displaced
face to face p–p stacking. The center to center distance (Dcent
)
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rings is indicative of the electrostatic donor–acceptor nature
for the perfluorophenyl–perfluorophenyl interaction. Based on
these experimental and theoretical results, it is believed that
in our case, the perfluorophenyl–perfluorophenyl interaction is
essentially electrostatic and the aromatic p–p stacking makes
negligible contribution in holding the supramolecular motifs in
the networks.
during optimization, and the optimized geometry was confirmed
by vibrational analysis.
Synthesis of trans-Mo2(DAniF)2(OOCC6F5)2(1)
To an orange-red solution of trans-Mo2(DAniF)2(O2CCH3)2
(0.410 g, 0.500 mmol) in 15 mL of THF, was added 2.0 mL of a
NaOCH3 solution (0.5 M in methanol). After stirring for about 2 h,
a colorless microcrystalline material, presumably sodium acetate,
was removed by filtration. To the filtrate was added an excess of
pentafluorobenzoic acid (0.276 g, 1.300 mmol). After stirring at
room temperature for an additional one hour, the solvent was
removed under vacuum, and the residue was washed with ethanol
(2 ¥ 15 mL), and then dried under vacuum, yielding compound 1
of 0.478 g (85%). Diffusion of ethanol into the CH2Cl2 solution of
the product produced block-shaped yellow crystals of 1·CH2Cl2
Conclusion
In summary, we have studied the first perfluorinated dimolyb-
denum complex in terms of its functionality as supramolecular
synthons through X-ray structural analyses and DFT calculations.
The present work demonstrates that the perfluorophenyl group
as the pendant to a metal unit offers versatile non-covalent
interactions at varying bindng sites, of which the C ◊ ◊ ◊ F dipole to
dipole interactions and F ◊ ◊ ◊ F contacts dominate over aromatic p–
p stacking. Through Mulliken population analysis, it is realized for
the first time that the metal center in perfluorous coordination or
organometallic compounds has the capability of further polarizing
the highly polarized C–F bonds and consequently strengthening
the intermolecular C ◊ ◊ ◊ F dipole interaction. Therefore, metal
complexes functionalized with perfluorophenyl groups can be
valuable supramolecular synthons of crystal engineering.
1
or II. Yield: 0.014 g (65%). H NMR(CDCl3, ppm): 8.51 (s, 2H,
–NCHN–), 6.83 (d, 8H, aromatic), 6.80 (d, 8H, aromatic), 3.74
(s, 12H, –OCH3). UV-vis, lmax (e, L mol-1 cm-1): 441 nm (5.0 ¥
103). Anal. Calcd. for C44H30N4O8F10Mo2 (1): C, 46.99; H, 2.69;
N, 4.98. Found: C, 46.68; H, 2.46; N, 5.07.
Synthesis of 1·2THF
Compound 1 of 0.281 g was dissolved in 8 mL THF and the
solution was layered with hexanes. Slow diffusion yielded red
needle-shaped crystals of I quantitatively. 1H NMR (CDCl3, ppm):
8.50 (s, 2H, –NCHN–), 6.83 (d, 8H, aromatic), 6.80 (d, 8H,
aromatic), 3.75 (m, 8H, THF), 3.74 (s, 12H, –OCH3), 1.85 (m,
8H, THF). UV-vis, lmax (e, L mol-1 cm-1): 442 nm (1.1 ¥ 104).
Experimental
Materials and methods
All reactions and manipulations were performed under a N2 atmo-
sphere, using either drybox or standard Schlenk-line techniques.
Solvents were purified under N2 using a Vacuum Atmospheres
Company (VAC) solvent purification system or distilled over
appropriate drying agents under N2. The starting material trans-
Mo2(cis-DAniF)2(O2CCH3)2 was prepared as reported.22
Acknowledgements
This work is supported by NSFC (20741004 and 20871093)
through CYL and STCSM (10PJ1409600) through XW.
References
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