Dirhodium paddlewheel with functionalized carboxylate bridges: New building block for self-assembly and immobilization on solid support

Article abstract of DOI:10.1021/ic300382j

A new dirhodium(II,II) paddlewheel complex, [Rh₂(O ₂CC₆H₄COOC₂H₅) ₄] (1), has been synthesized using a predesigned functionalized carboxylate, namely, 4-(ethoxycarbonyl)benzoate. The target product has been crystallized from the acetone solution and structurally characterized as a bis-acetone adduct, [Rh₂(O₂CC₆H ₄COOC₂H₅)₄(OCMe₂) ₂]C₆H₁₄ (2). By utilizing the ability of dangling ester groups to coordinate to open axial ends of neighboring dirhodium units, 1 can self-assemble to form 2D networks upon crystallization from solutions of noncoordinating solvents such as chlorobenzene and chloroform. The resulting [Rh₂(O₂CC₆H₄COOC ₂H₅)₄]2C₆H₅Cl (3) and [Rh₂(O₂CC₆H₄COOC ₂H₅)₄]2CHCl₃ (4) products have microporous solid state structures with the pores filled with the corresponding disordered solvent molecules. Notably, 3 and 4 represent unique examples of 2D extended frameworks based on dirhodium tetracarboxylate paddlewheel units devoid of any exogenous ligands. In solution, the dangling ends of carboxylate bridges of 1 have been successfully utilized for condensation reaction with the selected solid support, benzylamine-functionalized polystyrene, allowing successful heterogenization of dirhodium units through the equatorial covalent attachment to the substrate. The resulting solid product was tested as a catalyst in the cyclopropanation reaction of styrene with methyl phenyldiazoacetate to show good yields and diastereoselectivity.

Full text of DOI:10.1021/ic300382j

Article
pubs.acs.org/IC
Dirhodium Paddlewheel with Functionalized Carboxylate Bridges:
New Building Block for Self-Assembly and Immobilization on Solid
Support
D. Krishna Kumar, Alexander S. Filatov, Margaret Napier, Jinyu Sun, Evgeny V. Dikarev,
and Marina A. Petrukhina*
Department of Chemistry, University at Albany, 1400 Washington Avenue, Albany, New York 12222, United States
S
* Supporting Information
ABSTRACT: A new dirhodium(II,II) paddlewheel complex, [Rh2(O2CC6H4COOC2H5)4] (1), has been synthesized using a
predesigned functionalized carboxylate, namely, 4-(ethoxycarbonyl)benzoate. The target product has been crystallized from the
acetone solution and structurally characterized as a bis-acetone adduct, [Rh2(O2CC6H4COOC2H5)4(OCMe2)2]·C6H14 (2). By
utilizing the ability of dangling ester groups to coordinate to open axial ends of neighboring dirhodium units, 1 can self-assemble
to form 2D networks upon crystallization from solutions of noncoordinating solvents such as chlorobenzene and chloroform.
The resulting [Rh2(O2CC6H4COOC2H5)4]·2C6H5Cl (3) and [Rh2(O2CC6H4COOC2H5)4]·2CHCl3 (4) products have
microporous solid state structures with the pores filled with the corresponding disordered solvent molecules. Notably, 3 and
4 represent unique examples of 2D extended frameworks based on dirhodium tetracarboxylate paddlewheel units devoid of any
exogenous ligands. In solution, the dangling ends of carboxylate bridges of 1 have been successfully utilized for condensation
reaction with the selected solid support, benzylamine-functionalized polystyrene, allowing successful heterogenization of
dirhodium units through the equatorial covalent attachment to the substrate. The resulting solid product was tested as a catalyst
in the cyclopropanation reaction of styrene with methyl phenyldiazoacetate to show good yields and diastereoselectivity.
work, in order to support the dirhodium core we propose to
utilize 4-(ethoxycarbonyl)benzoate (Scheme 1) having two
different functions, such as carboxylic and ester groups.9 The
target dirhodium(II,II) paddlewheel should be able to self-
assemble without any additional linkers to form extended
architectures, where porosity can be further tuned through
specific guest inclusion or additional modification of benzoate
bridges.
We also envision that the dangling ester ends of this complex
can be used for a peptide-type covalent bond formation with
functionalized solid supports to provide efficient heterogeniza-
tion of predesigned dimetal units. Recently, the use of solid
support materials for grafting the rhodium-based catalysts10 has
become an important new direction for increasing the
INTRODUCTION
■
Porous coordination polymers or metal−organic frameworks
(MOFs) constructed from the assembly of organic linking units
with metal ions or metal clusters constitute an exciting class of
inorganic materials with unique properties and applications1
such as gas storage, selective adsorption and separation of small
molecules, ion exchange, and catalysis. A common strategy for
assembling such frameworks is the use of multidentate organic
linkers and metal-based secondary building units (SBUs) with
linear, triangular, tetrahedral, square-planar, octahedral, and
trigonal-prismatic geometries.2 Paddlewheel metal complexes
with multiply bonded dinuclear cores and rich redox proper-
ties3 have been broadly utilized as rigid linear building blocks
for self-assembly reactions.4−6 Among those, dirhodium
tetracarboxylates received considerable attention as very
attractive linear units for formation of coordination networks
with a variety of axially bound exogenous linkers.7,8 In this
Received: February 20, 2012
Published: April 4, 2012
© 2012 American Chemical Society
4855
dx.doi.org/10.1021/ic300382j | Inorg. Chem. 2012, 51, 4855−4861

Inorganic Chemistry
Article
Scheme 1. Construction of Target Dirhodium Tetracarboxylate
durability of catalytic systems. The resulting heterogeneous
catalysts are more stable and degrade much slower than their
homogeneous counterparts; they are also reusable and allow
the final products to be readily separated from the catalyst.
Multiple efforts have been made to incorporate dirhodium(II)
core complexes onto polymeric networks by various groups.11
In our recent study, we explored a synthetic strategy based on
grafting dirhodium(II,II) tetracarboxylates inside the function-
alized channels of mesoporous silica having predesigned N-
donor anchor sites and utilizing sufficiently strong noncovalent
Rh···N interactions.12 Herein, we extend these efforts to test
the covalent bonding of dirhodium(II,II) paddlewheel complex
onto a polymeric host, which should be a more efficient way to
prepare recyclable and durable dirhodium-based catalysts for
broad applications in organic synthesis.13
Structural Description of [Rh2(O2CC6H4COOC2H5)4-
(OCMe2)2]·C6H14 (2). In the bis-adduct 2, the acetone
molecules are coordinated to both axial positions of the
dirhodium(II,II) core (Figure 1), which is characteristic of
RESULTS AND DISCUSSION
■
The target tetrakis(4-ethoxycarbonylbenzoato)dirhodium(II,II)
complex, [Rh2(O2CC6H4COOC2H5)4] (1), has been synthe-
sized using a ligand-exchange procedure of tetrakis-
(trifluoroacetato)dirhodium(II,II)14 with 4-(ethoxycarbonyl)-
benzoic acid by reflux in chlorobenzene for 4 days in the
presence of potassium carbonate and molecular sieves. 19F
NMR spectra were used to monitor the reaction progress: the
absence of a fluorine signal in a product indicated that all
trifluoroacetate groups were substituted with benzoate ligands.
Elemental analysis of the crude powder isolated from this
reaction was also consistent with formation of a fully
substituted product, [Rh2(O2CC6H4COOC2H5)4] (1). Slow
evaporation of the solution of 1 in acetone/hexanes (10:3, v/v)
afforded needle-shaped blue crystals of 2 in almost quantitative
yield. Single-crystal X-ray diffraction analysis revealed that a bis-
acetone adduct of 1, [Rh2O2CC6H4COOC2H5)4-
(OCMe2)2]·C6H14 (2), had been formed under these
crystallization conditions. At the same time, the plate-shaped
green crystals of [Rh2(O2CC6H4COOC2H5)4]·2C6H5Cl (3)
have been grown from the chlorobenzene solution of 1 at
elevated temperatures, while green blocks of
[Rh2(O2CC6H4COOC2H5)4]·2CHCl3 (4) were obtained by
slow diffusion of hexanes into a chloroform solution of 1 at
ambient conditions. Single-crystal X-ray diffraction analyses
established the 2D layered porous structures for both products
3 and 4 with the chlorobenzene and chloroform molecules
occupying the pores, respectively.
Figure 1. Molecular structure of [Rh2(O2CC6H4COOC2H5)4-
(OCMe2)2]·C6H14 (2) drawn with thermal ellipsoids at the 50%
probability level. Hydrogen atoms and hexane molecules have been
omitted for clarity. Acetone coordination to axial positions of a
dirhodium unit is shown by dashed lines.
dimetal paddlewheel complexes crystallized from coordinating
solvents. The Rh···Oaxial distance of 2.276(1) Å is comparable
to those usually found in dirhodium(II,II)-based adducts with
axially bound acetone ligands (2.20−2.33 Å).7,8a The Rh−Rh
distance of 2.388(1) Å is within the range of 2.35−2.45 Å
commonly observed in tetrakis(carboxylato)dirhodium(II,II)
complexes.7 The Rh−Oeq distances span the range from
2.020(1) to 2.043(1) Å (Table 1).
In the solid state structure of 2, there are solvent molecules
of hexane occupying the interstitial space in the crystal lattice.
Notably, the inability to form single crystals of 2, when 1 is
dissolved in neat acetone, demonstrates the necessity of a
second solvent for crystallization. X-ray powder diffraction
performed on bulk sample of 2 showed an excellent match with
the simulated pattern, indicating the presence of a single phase.
Thermal gravimetric analysis (TGA) of 2 reveals that the
product loses both hexane and coordinated acetone molecules
before 100 °C, while the complex starts to decompose at ca.
300 °C. X-ray powder diffraction (XRPD) analysis indicates
4856
dx.doi.org/10.1021/ic300382j | Inorg. Chem. 2012, 51, 4855−4861

Inorganic Chemistry
Article
Table 1. Comparison of Selected Distances (Å) and Angles (deg) in [Rh2(O2CC6H4COOC2H5)4(OCMe2)2]·C6H14 (2),
[Rh2(O2CC6H4COOC2H5)4]·2C6H5Cl (3), and [Rh2(O2CC6H4COOC2H5)4]·2CHCl3 (4)
2
3
4
Rh−Oeq
Rh···Oax
Rh−Rh
2.020(1)−2.043(1)
2.276(1)
2.024(4)−2.043(4)
2.306(4), 2.324(4)
2.387(1)
2.021(3)−2.039(3)
2.272(3)
2.388(1)
2.373(1)
Rh−Rh−Oax
175.25(4)
174.09(10), 177.02(10)
176.83(5)
that the crystallinity of 2 is lost after drying the sample at 100
°C under vacuum for 12 h.
Scheme 2. Schematic Representation of the 2D Layer
Formation in 3 and 4
a
Structural Description of [Rh2(O2CC6H4COOC2-
H5)4]·2C6H5Cl (3). Single-crystal X-ray diffraction analysis
revealed formation of a 2D layered network based on
Rh···Oax interactions between the rhodium centers and the
carbonyl groups of dangling ester ends of carboxylate bridges.
The Rh···Oax contacts are 2.306(4) and 2.324(4) Å (Table 1).
The Rh−Oeq distances are 2.024(4)−2.043(4) Å with the Rh−
Rh bond length of 2.387(1) Å being the same as in 2. Each
dirhodium unit is connected to four other such units (Figure
2a).
a
Arrows and shadowed ellipsoids represent ester groups and
dirhodium units, respectively. Arrow pointing toward the ellipsoid
corresponds to the O coordination at the axial Rh site.
of continuous channels in the solid structure. One runs along
the c axis and is filled with the CHCl3 molecules (Figure 3b),
while the other one remains free from solvent and extends
along the [101] direction (Figure 3c), thus intersecting with the
former at ca. 46.4°.
Figure 2. (a) Capped-stick representation of a single 2D layer in the
crystal structure of [Rh2(O2CC6H4COOC2H5)4]·2C6H5Cl (3). (b)
Space filling model of 3 showing the channels along the crystallo-
graphic a axis formed by an overlay of 2D layers.
Formation of different pores in 3 and 4 can be attributed to
the difference in size and shape of the guest chloroform and
chlorobenzene molecules occupying the pores. The intercon-
nected complex network in 4 has a noticeably larger solvent-
accessible area (43.2%) compared to that in 3 (30.1%).
Similarly to 2 and 3, the solid sample of 4 is losing crystallinity
upon removing solvent molecules. The phase purity of the bulk
materials 3 and 4 was confirmed by comparing the
experimental X-ray powder diffraction spectra with the
simulated patterns based on single-crystal structural data (see
Supporting Information, Figures S6 and S7).
Analysis of the Cambridge Structural Database (CSD)
revealed that there are two cases16 where the axial positions
of paddlewheel complexes are coordinated to the functional
group of equatorial carboxylate ligands displaying a 1D
polymeric structure. To the best of our knowledge, the new
products 3 and 4 are the first examples of 2D networks built
from dimetal paddlewheel units without employing exogenous
linkers.
Grafting of 1 onto Solid Support. Successful preparation
of 1 along with the confirmation of its molecular structure
allowed us to test the grafting of the predesigned dirhodium-
(II,II) units onto a functionalized solid support. This was
attempted via a peptide-type covalent linkage using the
dangling ester ends of bridging carboxylate ligands of 1
(Scheme 3). This approach provides stronger binding to solid
supports compared to axial coordination of dirhodium
tetracarboxylate units that we explored recently.12 For this
While both Rh centers of a dimetal unit are engaged in
intermolecular Rh···O axial interactions, not all four carboxylate
groups are involved in network formation. Only two ligands
that are positioned in a trans configuration to each other
coordinate to metal centers. Considering dirhodium units as
linear nodes, the overall topology can be described as a 4,4′
sheet-like architecture (Scheme 2). The overlay of 2D
coordination networks provides formation of channels running
along the crystallographic a axis. These pores are parallel to the
2D layered networks (Figure 2b) and filled with the
crystallization solvent molecules.
Crystals of 3 were subjected to thermal gravimetric analysis,
showing that heating at 80 °C is sufficient to drive off the
chlorobenzene molecules from the solid. Analysis shows no
additional weight loss until the temperature reaches 340 °C, at
which the weight loss of 70% is observed. XRPD analysis of 3
before and after heating revealed the loss of crystallinity upon
evacuation of solvent, which is commonly observed in porous
coordination polymers.15
Structural Description of [Rh2(O2CC6H4COOC2-
H5)4]·2CHCl3 (4). A 2D polymeric network based on
Rh···Oax interactions between the rhodium centers and the
carbonyl groups of carboxylate bridges is constructed in a
similar way as that in 3 (Figure 3a, Scheme 2). Rh−Rh and
Rh···Oax distances are 2.373(1) and 2.272(3) Å, respectively
(Table 1). In contrast to 3, the overlay of 2D layers in 4
provides a more complex porous network. There are two types
4857
dx.doi.org/10.1021/ic300382j | Inorg. Chem. 2012, 51, 4855−4861

Inorganic Chemistry
Article
Figure 3. (a) Capped-stick representation of a single 2D layer in the crystal structure of [Rh2(O2CC6H4COOC2H5)4]·2CHCl3 (4). Space filling
model showing the channels formed by an overlay of 2D layers running along the (b) crystallographic c axis and (c) [101] direction.
Scheme 3. Grafting of 1 through the Condensation Reaction with Benzylamine-Functionalized Polystyrene (baPS) and
Formation of an Amide Bond (R = −C6H4COOC2H5)
work, commercially available benzylamine-functionalized poly-
styrene (baPS) was selected as a recyclable support.17
Grafting was accomplished by heating the suspension of 1
with baPS in a freshly distilled 1,2-dichloroethane to produce a
dark olive-green solid (5). Several solvents, including dichloro-
methane and chlorobenzene, were tested for grafting reaction,
but 1,2-dichloroethane was found to be the preferred solvent
media for heterogenization of 1. The infrared (IR) spectrum of
the grafted product exhibits a new peak at 1719 cm−1 in
addition to the vibrational bands at 1724 (carboxylate) and
1689 cm−1 (ester) of the starting complex, thus illustrating
formation of an amide bond. In the solid state UV−vis
spectrum, a noticeable red shift of the absorption maximum of
1 after grafting also indicates successful heterogenization of
dirhodium units.
Table 2. Catalytic Data for 5 in the Cyclopropanation
Reaction of Styrene with MPDA
reaction cycle
ratio of isomers, % de
yield, %
1
2
3
4
5
6
88
88
88
88
88
88
86
81
81
74
76
64
and the solid host material (baPS) without grafted dirhodium
complex show no catalytic activity in the above reaction.
For comparison, we tested the catalytic activity of 1 under
homogeneous conditions and found it to produce cyclopropane
in the same yield (85%) but with a slightly higher selectivity
(96% de). Thus, immobilization of 1 onto baPS has not
affected the catalytic activity of the dirhodium(II,II) complex.
In conclusion, the presence of two different functional groups
makes the selected carboxylate ligand to be versatile for
bridging a dinuclear metal core (through a primary carboxylate
group) and allowing subsequent self-assembly or heterogeniza-
tion of the resulting paddlewheel units through the secondary
dangling group. In this work, the synthesis and full character-
ization of new tetrakis(4-ethoxycarbonylbenzoato)dirhodium-
(II,II) complex 1 have been successfully accomplished. X-ray
crystallographic analysis of the bis-acetone adduct 2 confirmed
the paddlewheel structure with the dirhodium core bridged by
four carboxylic groups and having the ester ends free for
secondary binding. These dangling ends of 4-(ethoxycarbonyl)-
benzoate ligands can be further utilized for self-assembly
processes, as shown by formation of 2D networks 3 and 4
crystallized from chlorobenzene and chloroform, respectively.
Interestingly, no examples of such self-assembly of dirhodium
tetracarboxylate complexes have been found in the literature.
Generally, strong σ-donating exogenous ligands are utilized for
this purpose, allowing self-assembly of various extended
Catalyst Evaluation. The catalytic properties of 5 were
evaluated in the standard cyclopropanation reaction of methyl
phenyldiazoacetate with styrene (Scheme 4) performed in
Scheme 4. Cyclopropanation of Styrene with Methyl
Phenyldiazoacetate (MPDA)
hexanes under anhydrous conditions. For catalytic tests, a
portion of 5 was suspended in hexanes and styrene and injected
with a solution of methyl phenyldiazoacetate in hexanes at a
rate of 0.7 mL/h. After 24 h of stirring at room temperature,
the yield of cyclopropane was calculated by purification through
a silica column using the solution of ethyl acetate in hexanes as
an eluent. The isomer ratio was verified by 1H NMR
spectroscopy. It was found that cyclopropane is formed in
86% yield and 88% diastereomeric excess (de) after the first
run. The catalyst efficiency was maintained over five repeated
cycles (Table 2). Importantly, both the supernatant solution
4858
dx.doi.org/10.1021/ic300382j | Inorg. Chem. 2012, 51, 4855−4861

Inorganic Chemistry
Article
Table 3. Crystallographic Data and Structural Refinement Parameters for [Rh2(O2CC6H4COOC2H5)4(OCMe2)2]·C6H14 (2),
[Rh2(O2CC6H4COOC2H5)4]·2C6H5Cl (3), and [Rh2(O2CC6H4COOC2H5)4]·2CHCl3 (4)
2
3
4
empirical formula
fw
C52H62O18Rh2
1180.84
C52H46Cl2O16Rh2
1203.61
C42H38Cl6O16Rh2
1217.24
cryst syst
space group
a (Å)
monoclinic
P21/n
monoclinic
P21/n
monoclinic
C2/c
9.8635(13)
13.1392(17)
20.333(3)
90.00
12.6460(10)
16.2693(12)
25.792(2)
90.00
22.3558(15)
16.8627(11)
16.4080(11)
90.00
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Z
94.940(2)
90.00
103.8910(10)
90.00
92.8000(10)
90.00
2625.4(6)
2
5151.3(7)
4
6178.1(7)
4
D
calcd (g/cm3)
1.494
1.552
1.309
F(000)
μ (mm−1
1216
2440
2440
)
0.701
0.814
0.847
temp. (K)
100(2)
173(2)
100(2)
reflns collected/unique/obsd [I > 2σ(I)]
data/restraints/parameters
19 722/5151/4719
5151/0/330
0.0279, 0.0731
0.0307, 0.0754
1.069
40 083/10176/5864
10176/24/665
0.0600, 0.1109
0.1211, 0.1332
1.022
23 277/6078/5125
6078/0/309
0.0341, 0.0978
0.0414, 0.1005
1.195
a
b
R1, wR2 [I > 2σ(I)]
a
b
R1, wR2 (all data)
c
quality of fit
largest diff. peak/hole (e/Å3)
0.989/−0.291
1.297/−1.006
1.301/−0.747
a
b
c
R1 = Σ∥Fo| − |Fc∥/Σ|Fo|. wR2 = [Σ[w(Fo − Fc2)2]/Σ[w(Fo )2]]1/2. Quality of fit = [Σ[w(Fo − Fc2)2]/(Nobs − Nparams)]1/2, based on all data.
2
2
2
Single crystals were selected and mounted on a goniometer head with
silicone grease. Frames were integrated with the Bruker SAINT
software package,19 and structures were solved and refined using
Bruker SHELXTL (version 6.12) software.20 Crystallographic data and
refinement parameters for 2−4 are listed in Table 3. X-ray powder
diffraction data were collected on a Bruker D8 Advance diffractometer
networks through intermolecular axial coordination to open
metal sites of paddlewheel units. Complex 1 was also
successfully immobilized onto an amine-functionalized solid
substrate using the peptide-type bond condensation reaction.
The resulting dirhodium-based solid product was tested as a
heterogeneous catalyst in the model diazo decomposition
reaction in the presence of styrene. The catalyst was recycled
and reused through several consequent runs to show good
catalytic activity by providing a mixture of cyclopropanes with
high yields and diastereoselectivity.
(Cu Kα radiation, focusing Gobel Mirror, LynxEye one-dimensional
̈
detector, step of 0.02° 2θ, 20 °C). Crystalline samples under
investigation were ground and placed in an airtight holder with a
plastic dome cover under an atmosphere of N2(g)
.
Synthesis of 4-(Ethoxycarbonyl)benzoic Acid. Diethyl tereph-
thalate (2.2 g, 10 mmol) was dissolved in 30 mL of ethanol by stirring
for 15 min with gentle heating. Potassium hydroxide (580 mg, 10
mmol) was added, and the previously clear solution slowly became
cloudy. The mixture was refluxed for 4 h, cooled, and evaporated to
dryness. The resulting product was then suspended in water and
extracted with dichloromethane. The aqueous layer was collected and
acidified with a 10% solution of hydrochloric acid to yield a colorless
precipitate. The product was extracted with ethyl ether 3 times, dried
over sodium sulfate, and decanted. Ether was removed by evaporation
under vacuum to afford a white solid. To recrystallize the product, it
was dissolved in dichloromethane and filtered through a Buchner
funnel. The solution was collected, reduced to ∼30 mL, and left for
slow evaporation. Colorless crystals deposited in 2 days. They were
collected, washed in cold dichloromethane, and dried. Yield: 1.01 g,
EXPERIMENTAL SECTION
■
Materials and Methods. All manipulations were carried out
under an oxygen-free, dinitrogen atmosphere by employing standard
glovebox and Schlenk techniques. All chemicals were reagent grade
and used as received without further purification. Anhydrous solvents
were obtained from a Solvent Purification System purchased from M.
Braun, Inc., USA, or freshly distilled according to published methods.18
Additionally, toluene and hexanes were dried over Na/benzophenone
and distilled prior to use. 1,2-Dichloroethane was refluxed over CaCl2
and fractionally distilled. Tetrakis(trifluoroacetato)dirhodium(II,II)
was synthesized according to the reported procedure.14 Benzyl-
amine-functionalized polystyrene (baPS) was purchased from Alfa
Aesar. Molecular sieves and potassium carbonate were activated at 125
°C for 3 days prior to use.
1
53%. H NMR (CDCl3, 22 °C, ppm): δ = 12.42 (s, 1H), 8.20−8.14
(m, 4H), 4.46−4.40 (q, 2H), 1.45−1.41 (t, 3H).
The attenuated total reflection (ATR) IR spectra were recorded on
a Perkin-Elmer Spectrum 100 FT-IR spectrometer. NMR spectra were
obtained using a Bruker Avance 400 spectrometer at 400 MHz for 1H
and at 376.47 MHz for 19F. Chemical shifts (δ) are reported in ppm
relative to residual solvent peaks for 1H and to CFCl3 for 19F.
Elemental analyses were performed by Guelph Chemical Laboratories,
Ltd., Canada. Thermogravimetric measurements were carried out
under N2(g) at a heating rate of 5 °C/min using a TGA 2050
Thermogravimetric Analyzer, TA Instruments. X-ray data were
collected at −100 or −173 °C (Bruker KYRO-FLEX) on a Bruker
APEX CCD X-ray diffractometer equipped with graphite-monochro-
mated Mo Kα radiation (λ = 0.71073 Å) operated at 1800 W power.
Synthesis of Tetrakis(4-ethoxycarbonylbenzoato)-
dirhodium(II,II), [Rh2(O2CC6H4COOC2H5)4] (1). Activated 4 Å
molecular sieves (6.0 g) and dried potassium carbonate (0.537 g)
were wrapped separately and placed in the thimble of a Soxhlet
extractor. Chlorobenzene (150 mL) was added to tetrakis-
(trifluoroacetato)dirhodium(II,II) (0.200 g, 0.30 mmol) and 4-
(ethoxycarbonyl)benzoic acid (0.300 g, 1.5 mmol) in a 250 mL
Schlenk flask. The flask was connected to the Soxhlet extractor under a
dinitrogen atmosphere and refluxed for 5 days at 150−160 °C. The
resulting solution was evaporated to dryness to afford a light-green
solid. Crude product was washed with 10 mL of a solution of hexanes/
dichloromethane (10:1, v/v) and dried under reduced pressure to
4859
dx.doi.org/10.1021/ic300382j | Inorg. Chem. 2012, 51, 4855−4861

Inorganic Chemistry
Article
yield a fine green powder of 1. Yield: 0.261 g, 89%. Anal. Calcd for
NMR spectra revealed the absence of any traces of carboxylate ligands,
showing the sufficient stability of the heterogeneous catalyst.
C40H36O16Rh2: C, 49.10; H, 3.71; O, 26.16. Found: C, 49.13; H, 3.71;
1
O, 29.10. 19F NMR (400 MHz, (CD3)2CO, 22 °C): no signal. H
NMR ((CD3)2CO, 22 °C, ppm): δ = 8.00−7.93 (m, 4H) 4.34−4.29
(q, 2H), 1.35−1.31 (t, 3H). FT-IR (cm−1): 1724m, 1689m, 1602m,
1560m, 1507w, 1396s, 1370m, 1259s, 1172m, 1141m, 1100s, 1016s,
880m, 838m, 797s, 736s, 713s. UV−vis (chloroform, 22 °C, λmax, nm
(ε, M−1 cm−1)): 456 (81), 604 (94). UV−vis (chlorobenzene, 22 °C,
λmax, nm (ε, M−1 cm−1)): 660 (613). UV−vis (solid, 22 °C, λmax, nm):
523.
ASSOCIATED CONTENT
* Supporting Information
CIF files providing crystallographic data for compounds 2−4;
X-ray powder patterns and TGA plots for 2−4. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
Synthesis of [Rh2(O2CC6H4COOC2H5)4(OCMe2)2]·C6H14 (2). A
portion of 1 (0.020 g, 0.02 mmol) was dissolved in 7 mL of acetone
and 3 mL of hexanes and left for slow evaporation in air. In 2 days,
dark-blue crystals of 2 appeared. Yield: 0.021 g, 83%. Anal. Calcd for
C52H62O181Rh2: C, 52.89; H, 5.29; O, 24.39. Found: C, 52.69; H, 5.42;
O, 24.10. H NMR (CDCl3, 22 °C, ppm): δ = 8.00−7.91 (m, 16H),
4.36−4.30 (q, 8H), 2.50 (s, 12H), 1.37−1.27 (m, 12H), 0.90−0.87 (m,
14H). FT-IR (cm−1): 2957w, 2925w, 2856w, 2161w, 1978w, 1719m,
1707m, 1683m, 1604m, 1560m, 1506w, 1472w, 1422w, 1393s, 1366s,
1261s, 1174w, 1140m, 1105s, 1018s, 881w, 837m, 800w, 737s, 715m.
UV−vis (acetone, 22 °C, λmax, nm (ε, M−1 cm−1)): 458 (115), 595
(177).
Crystal Growth of [Rh2(O2CC6H4COOC2H5)4]·2C6H5Cl (3). A
portion of 1 (0.010 g, 0.01 mmol) was placed in a 12.7 mm glass
ampule, to which 6 mL of anhydrous chlorobenzene was added. The
system was sealed and heated to ca. 100 °C. Green plate-like crystals of
3 were deposited on the sides of the ampule in 3 days.
Crystal Growth of [Rh2(O2CC6H4COOC2H5)4]·2CHCl3 (4). A
portion of 1 (0.020 g, 0.02 mmol) was dissolved in 4 mL of anhydrous
chloroform. This solution was carefully layered with 2 mL of
anhydrous hexanes and kept for crystallization. Green blocks of 4
were deposited in 3 days.
Grafting of 1 onto Benzylamine-Functionalized Polystyrene.
Grafting was done by dissolving a portion of 1 (0.040 g, 0.04 mmol) in
15 mL of the freshly distilled 1,2-dichloroethane to produce a
transparent green solution which was then mixed with white beads of
benzylamine on polystyrene (baPS) (0.100 g, 0.20−0.30 mmol active
sites). After 20 min of heating, the polymer beads started to darken in
color. The suspension was refluxed for 12 h. The resulting olive-green
solid (5) was separated from solution by cannula filtration and washed
at least 3 times in 10 mL of freshly distilled acetone or
dichloromethane, which remained colorless.
AUTHOR INFORMATION
Corresponding Author
*E-mail: mpetrukhina@albany.edu.
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the National Science Foundation, CHE-1152441
(ED) and CHE-0546945 (MP), for support of this work. We
are also grateful to the University at Albany for supporting the
X-ray Center at the Department of Chemistry.
REFERENCES
■
(1) (a) James, S. L. Chem. Soc. Rev. 2003, 32, 276−288. (b) Rowsell,
L. C.; Yaghi, O. M. Microporous Mesoporous Mater. 2004, 73, 3−14.
(c) Fujita, M.; Tominaga, M.; Hori, A.; Therrien, B. Acc. Chem. Res.
2005, 38, 369−378. (d) Lin, W. J. Solid State Chem. 2005, 178, 2486−
2490. (e) Kitagawa, S.; Noro, S.; Nakamura, T. Chem. Commun. 2006,
701−707. (f) Mueller, U.; Schubert, M.; Teich, F.; Puetter, H.;
Schierle-Arndt, K.; Pastre, J. J. Mater. Chem. 2006, 16, 626−636.
(g) Lin, X.; Jia, J.; Hubberstey, P.; Schroder, M.; Champness, N. R.
́
CrystEngComm 2007, 9, 438−448. (h) Dinca, M.; Long, J. R. J. Am.
Chem. Soc. 2007, 129, 11172−11176. (i) Morris, R. E.; Wheatley, P. S.
Angew. Chem., Int. Ed. 2008, 47, 4966−4981. (j) Tanaka, D.; Kitagawa,
S. Chem. Mater. 2008, 20, 922−931. (k) Banerjee, R.; Furukawa, H.;
Britt, D.; Knobler, C.; O’Keeffe, M.; Yaghi, O. M. J. Am. Chem. Soc.
2009, 131, 3875−3877. (l) Northrop, B. H.; Zheng, Y.-R.; Chi, K.-W.;
Stang, P. J. Acc. Chem. Res. 2009, 42, 1554−1563. (m) Klosterman, J.
K.; Yamauchi, Y.; Fujita, M. Chem. Soc. Rev. 2009, 38, 1714−1725.
(n) Chakrabarty, R.; Mukherjee, P. S.; Stang, P. J. Chem. Rev. 2011,
111, 6810−6918.
The olive-green solid was dried overnight in a ca. 70 °C sand bath in
vacuo. Yield: 0.140 g, 100% (based on initial amount of Rh). FT-IR
(cm−1): 2960w, 2928w, 2860w, 2161w, 1978w, 1721m, 1595w, 1558w,
1507w, 1493w, 1453w, 1393w, 1260m, 1119w, 1102w, 1071w, 1017w,
876w, 836w, 798w, 737m, 714w, 699w. UV−vis (solid, before catalysis,
22 °C, λmax, nm): 592. UV−vis (solid, after 6 catalytic cycles, 22 °C,
λmax, nm): 533.
(2) (a) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.;
Eddaoudi, M.; Kim, J. Nature 2003, 423, 705−714. (b) Ockwig, N. W.;
Delgado-Friedrichs, O.; O‘Keeffe, M.; Yaghi, O. M. Acc. Chem. Res.
́
2005, 38, 176−182. (c) Ferey, G. Chem. Soc. Rev. 2008, 37, 191−214.
(3) In Multiple Bonds Between Metal Atoms, 3rd ed.; Cotton, F. A.,
Murillo, C. A., Walton, R. A., Eds.; Springer Science and Business
Media Inc.: New York, 2005.
Catalyst Evaluation Details. Solutions of methyl phenyl-
diazoacetate (MPDA) (0.02 g/mL) and styrene (0.1 g/mL) were
prepared in hexanes and degassed three times. A solution of styrene (6
mL) was added to 0.015 g of the catalyst and stirred at room
temperature for 30 min. A solution of MPDA (3 mL) was added using
a syringe pump at a rate of 0.70 mL/h. The temperature of the MPDA
solution was kept at 6 °C throughout addition. The mixture was stirred
for 24 h at room temperature. After completion of the reaction, the
suspension was transferred to a centrifuge tube (under inert
atmosphere) and centrifuged. The supernatant liquid was removed
via a cannula, and 20 mL of anhydrous hexanes was added to the
remaining solid. The obtained suspension was sonicated and
centrifuged again. Extraction of the products was repeated twice.
The hexanes portions were combined, dried, and subjected to column
chromatography (EtOAc/hexanes). The product (mixture of isomers)
(4) (a) Mori, W.; Takamizawa, S.; Kato, C. N.; Ohmura, T.; Sato, T.
Microporous Mesoporous Mater. 2004, 73, 31−46. (b) Takamizawa, S.;
Nakata, E.; Saito, T.; Akatsuka, T. Inorg. Chem. 2005, 44, 1362−1366.
(c) Ueda, T.; Takahiro, K.; Eguchi, T.; Kachi- Terajima, C.;
Takamizawa, S. J. Phys. Chem. C 2007, 111, 1524−1534.
(d) Takamizawa, S.; Nataka, E.-I.; Akatsuka, T.; Miyake, R.;
Kakizaki, Y.; Takeuchi, H.; Maruta, G.; Takeda, S. J. Am. Chem. Soc.
2010, 132, 3783−3792. (e) Chen, M.-S.; Chen, M.; Takamizawa, S.;
Okamura, T.-A.; Fan, J.; Sun, W.-Y. Chem. Commun. 2011, 47, 3787−
3789.
(5) (a) Wesemann, J. L.; Chisholm, M. H. Inorg. Chem. 1997, 36,
3258−3267. (b) Rusjan, M.; Donnio, B.; Guillon, D.; Cukiernik, F. D.
Chem. Mater. 2002, 14, 1564−1575. (c) Chisholm, M. H.; Patmore, N.
J. Acc. Chem. Res. 2007, 40, 19−27. (d) Chisholm, M. H.; Dann, A. S.;
Dielmann, F.; Gallucci, J. C.; Patmore, N. J.; Ramnauth, R.; Scheer, M.
Inorg. Chem. 2008, 47, 9248−9255.
1
was collected, and H NMR spectra were recorded to calculate the
yield using dimethyl aminopyridine (DMAP) as an internal standard.
Leaching of the catalyst 5 has been monitored by 1H NMR
spectroscopy. After completion of the selected catalytic cycle, the
reaction mixture was separated from the catalyst by filtration,
evaporated to dryness, and then redissolved. Analysis of the 1H
(6) (a) Cotton, F. A.; Lin, C.; Murillo, C. A. Acc. Chem. Res. 2001, 34,
759−771. (b) Cotton, F. A.; Dikarev, E. V.; Petrukhina, M. A. Angew.
Chem., Int. Ed. 2000, 39, 2362−2364. (c) Bera, J. K.; Angaridis, P. A.;
4860
dx.doi.org/10.1021/ic300382j | Inorg. Chem. 2012, 51, 4855−4861

Inorganic Chemistry
Article
Petrukhina, M. A.; Cotton, F. A.; Fanwick, P. E.; Walton, R. A. J. Am.
Chem. Soc. 2001, 123, 1515−1516. (d) Cotton, F. A.; Dikarev, E. V.;
Petrukhina, M. A. Angew. Chem., Int. Ed. 2001, 40, 1521−1523.
(e) Cotton, F. A.; Hillard, E. A.; Murillo, C. A. J. Am. Chem. Soc. 2002,
124, 5658−5660. (f) Cotton, F. A.; Lin, C.; Murillo, C. A. Proc. Natl.
Acad. Sci. 2002, 99, 4810−4813.
(7) Chifotides, H. T.; Dunbar, K. R. Rhodium Compounds. In
Multiple Bonds between Metal Atoms, 3rd ed.; Cotton, F. A., Murillo, C.
A., Walton, R. A., Eds.; Springer Science and Business Media Inc.: New
York, 2005; pp 465−589.
(18) Perrin, D. D.; Armarego, L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, 2nd ed.; Pergamon Press, Oxford: New York,
1980.
(19) SAINT, version 6.02; Bruker AXS, Inc.: Madison, WI, 2001.
SADABS; Bruker AXS, Inc.: Madison, WI, 2001.
(20) (a) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112−122. (b)
SHELXTL, version 6.14; Bruker AXS, Inc.: Madison, WI, 2001.
(8) (a) Dikarev, E. V.; Andreini, K.; Petrukhina, M. A. Inorg. Chem.
2004, 43, 3219−3224. (b) Petrukhina, M. A.; Scott, L. T. Dalton
Trans. 2005, 2969−2975. (c) Petrukhina, M. A.; Andreini, K.;
Tsefrikas, V. M.; Scott, L. T. Organometallics 2005, 24, 1394−1397.
(d) Filatov, A. S.; Rogachev, A. Yu.; Petrukhina, M. A. Cryst. Growth
Des. 2006, 6, 1479−1484. (e) Petrukhina, M. A. Coord. Chem. Rev.
2007, 251, 1690−1698. (f) Filatov, A. S.; Petrukhina, M. A. Coord.
Chem. Rev. 2010, 254, 2234−2246.
(9) Chenot, E.-D.; Bernardi, D.; Comel, A.; Kirsch, G. Synth.
Commun. 2007, 37, 483−490.
(10) (a) Bluemel, J. Coord. Chem. Rev. 2008, 252, 2410−2423.
(b) Guenther, J.; Reibenspies, J.; Bluemel, J. Adv. Synth. Catal. 2011,
353, 443−460.
(11) (a) Doyle, M. P.; Timmons, D. J.; Tumonis, J. S.; Gau, H.-M.;
Blossey, E. C. Organometallics 2002, 21, 1747−1749. (b) Davies, H. M.
L.; Walji, A. M. Org. Lett. 2003, 5, 479−482. (c) Davies, H. M. L.;
Walji, A. M.; Nagashima, T. J. Am. Chem. Soc. 2004, 126, 4271−4280.
(d) Hulman, H. M.; de Lang, M.; Arends, I. W. C. E.; Hanefeld, U.;
Sheldon, R. A.; Maschmeyer, T. J. Catal. 2003, 217, 264−274.
(e) Takeda, K.; Oohara, T.; Anada, M.; Nambu, H.; Hashimoto, S.
Angew. Chem., Int. Ed. 2010, 49, 6979−6983.
(12) Dikarev, E. V.; K. Kumar, D.; Filatov, A. S.; Anan, A.; Xie, Y.;
Asefa, T.; Petrukhina, M. A. ChemCatChem 2010, 2, 1461−1466.
(13) (a) Doyle, M. P.; McKervey, M. A.; Ye, T. In Modern Catalytic
Methods for Organic Synthesis with Diazo Compounds; Wiley-
Interscience: New York,1998. (b) Davies, H. M. L.; Hedley, S. J.
Chem. Soc. Rev. 2007, 36, 1109−1119. (c) Hansen, J.; Davies, H. M. L.
Coord. Chem. Rev. 2008, 152, 545−555. (d) Davies, H. M. L.; Denton,
J. R. Chem. Soc. Rev. 2009, 38, 3061−3071. (e) Doyle, M. P.; Duffy, R.;
Ratnikov, M.; Zhou, L. Chem. Rev. 2010, 110, 704−724.
(14) Cotton, F. A.; Dikarev, E. V.; Feng, X. Inorg. Chim. Acta 1995,
237, 19−26.
(15) Dikarev, E. V.; Li, B.; Chernyshev, V. V.; Shpanchenko, R. V.;
Petrukhina, M. A. Chem Commun. 2005, 3274−3276.
(16) A CSD analysis performed for a transition-metal-based
paddlewheel core bridged by four benzoate ligands (leaving five C
atoms of the benzene ring open) resulted in 695 hits. Analysis of the
results revealed that there are two cases where the axial positions of
paddlewheel complexes are coordinated to the functional group of the
equatorial carboxylate ligand. First, the 1D polymeric chain was
formed when the axial positions of dicopper(II) paddlewheel units are
coordinated to the N atoms of bridging 3-cyano benzoate ligands.
Cueto, S.; Rys, P.; Straumann, H.-P.; Gramlich, V.; Rys, F. S. Acta
Crystallogr. 1992, C48, 2122−2124. Second, a dimolybdenum(II)
paddlewheel is coordinated to the O atoms of 4-diphenylphosphi-
nylbenzoate bridging ligands, also displaying a 1D propagation mode.
Kuang, S.-M.; Fanwick, P. E.; Walton, R. A. Inorg. Chem. Commun.
2002, 5, 134−138. Although the authors reported the structure as a
2D network, the propagation mode is one dimensional. There are also
structures of polymeric networks with ligands having different
functionality, but the frameworks are comprised of two different
metal units, for example, (a) a paddlewheel and square pyramidal
copper unit or (b) a paddlewheel and triangular planar copper unit.
(a) McManus, G. J.; Wang, Z.; Beauchamp, D. A.; Zaworotko, M. J.
Chem. Commun. 2007, 5212−5213. (b) Wen, Y.-H.; Cheng, J.-K.;
Zhang, J.; Li, Z.-J.; Kang, Y.; Yao, Y.-G. Inorg. Chem. Commun. 2004, 7,
1120−1123.
(17) McNamara, C. A.; Dixon, M. J.; Bradley, M. Chem. Rev. 2002,
102, 3275−3300.
4861
dx.doi.org/10.1021/ic300382j | Inorg. Chem. 2012, 51, 4855−4861