Palladium Nanoparticles Encapsulated in [M(C19H11N2O2)2·H2O] (M = Co and Mn) as a Potential Catalyst for the Homocoupling of Aryl Halides

Article abstract of DOI:10.1021/acs.cgd.6b01211

A new ligand, 4-(1,10-phenanthrolin-6-yl)benzoic acid, has been synthesized and employed to prepare new inorganic coordination polymer compounds, [M(C₁₉H₁₁N₂O₂)₂·H₂O] (M = Co, Mn). Both the compounds have identical structures formed by the connectivity between octahedral metal centers and the ligand, giving rise to a two-dimensional structure. The 2D structure is interpenetrated by identical units and forms a 2-fold interpenetrated structure. The lattice water molecules can be reversibly removed without altering the gross framework structure. The water removal has been investigated using in situ IR, PXRD, and in situ single-crystal XRD studies. Pd nanoparticles, prepared employing known procedures, were incorporated within the compound. We have successfully encapsulated up to 6.8% of Pd with a particle size of 4.8 ± 0.3 nm in the compound. The Pd@MOF compound was examined for homocoupling of aryl halides, resulting in good yields and recyclability. Magnetic studies indicate antiferromagnetic behavior in both the compounds with good orbital contribution for the cobalt compound.

Full text of DOI:10.1021/acs.cgd.6b01211

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Article
Palladium Nanoparticles Encapsulated in [M(C19H11N2O2)2.H2O] (M =
Co and Mn) as a Potential Catalyst for the Homo Coupling of Aryl Halides
Ajay Kumar Jana, Raghunandan Hota, and Srinivasan Natarajan
Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.6b01211 • Publication Date (Web): 14 Oct 2016
Downloaded from http://pubs.acs.org on October 18, 2016
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Palladium Nanoparticles Encapsulated in [M(C H N O ) .H O] (M = Co and
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Mn) as a Potential Catalyst for the Homo Coupling of Aryl Halides
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*
Ajay Kumar Jana, Raghunandan Hota and Srinivasan Natarajan
Framework solids Laboratory, Solid State and Structural Chemistry Unit, Indian Institute of Science,
Bangaloreꢀ560012, India.
*
Corresponding Author, Eꢀmail: snatarajan@sscu.iisc.ernet.in
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ABSTRACT:
A new ligand, 4ꢀ(1,10ꢀphenanthrolinꢀ6ꢀyl)benzoic acid, has been synthesized and employed to
prepare new inorganic coordination polymer compounds, [M(C H N O ) .H O] (M = Co, Mn). Both the
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compounds have identical structure formed by the connectivity between octahedral metal centers and the
ligand giving rise to a twoꢀdimensional structure. The 2D structure is interꢀpenetrated by identical unit
and forms a 2ꢀfold interpenetrated structure. The lattice water molecules can be reversibly removed
without altering the gross framework structure. The water removal has been investigated using inꢀsitu IR,
PXRD and inꢀsitu single crystal XRD studies. Pd nanoparticles, prepared employing known procedures,
were incorporated within the compound. We have successfully encapsulated up to 6.8 % of Pd with
particle size of 4.8 ± 0.3nm in the compound. The Pd@MOF compound was examined for homocoupling
of aryl halides, resulting in good yields and recyclability. Magnetic studies indicate antiꢀferromagnetic
behavior in both the compounds with good orbital contribution for the cobalt compound.
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INTRODUCTION
Heterogeneous catalysis based on noble metals such as Au, Pt, Pd as well as bimetallics such as
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,2
PtꢀRe, PtꢀIr and PtꢀRh have been generating continuing interest for over a century. The use of noble
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th
metal nanoparticles as a catalyst was demonstrated in early 18 century by Dobereiner for the catalyzed
production of water over Pt catalyst. The usefulness of the size and shape of the nanoparticles has been a
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topic of much discussion in recent years. The nanoparticles grown in zeolites, mesoporous silica and
other related porous supports underlines the importance as well as the catalytic activity, presumably due
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to their size confinement effects. The research on strong metal supported catalyst employing metal
oxides and noble metals continue to be intriguing due to their excellent performance in oil refining, autoꢀ
exhaust and other related areas. Studies on noble metal loaded graphene, graphene oxides and other
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similar compounds provide much hope due to their performance as efficient catalysts. Another area that
is attracting much attention is in exploiting the porous nature of the metalꢀorganic frameworks (MOFs).
These compounds posses considerable surface area as well as many chemical functionalities originating
both from the organic linker as well as the metal centers, which could be beneficially harvested for useful
purposes. In addition, the functional groups (associated with the organic linkers) could be exploited for
the encapsulation of metal nanoparticles within the pores of the MOFs. A strategy similar to this has been
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exploited recently. Noble metal nanoparticles within MOFs have been investigated before, both for
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enhancing the gas sorption (especially hydrogen) as well as for catalysis. The πꢁꢁꢁπ interactions, present
in some MOFs, have also been successfully employed for stabilizing the metal nanoparticles.
Pdꢀnanoparticles stabilized on MOFs have been examined as a possible route to enhance the
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hydrogen storage capacity. Recent studies include the usefulness of Pdꢀnanoparticles as a catalyst in the
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C–C bond formation. We have been interested in the study of nanoparticles assisted catalysis using
MOFs. As part of this study, we have now prepared a new ligand based on 1,10ꢀphenanthrolene, 4ꢀ(1,10ꢀ
phenanthrolinꢀ6ꢀyl)benzoic acid (Scheme 1.). This ligand on reaction with cobalt and manganese yielded
two new isoꢀstructural compounds, [M(C H N O ) .H O], (M = Co, Mn). We have incorporated Pdꢀ
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nanoparticles on this compound following a previously reported procedure. In this paper, we describe
the synthesis, structure, dehydrationꢀrehydration studies and Pdꢀnanoparticle assisted C–C bond
formation through Suzuki coupling.
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EXPERIMENTAL SECTION
Materials
The chemicals, 1,10ꢀphenathroline, oleum(15%), bromine, NH OH, THF, CHCl , CH Cl , N,Nꢀ
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dimethylformamide, 1,4ꢀdioxane, potassium carbonate, sodium hydroxide, sulphuric acid, hydrochloric
acid, Co(NO ) .6H O, MnCl .4H O were purchased from SDfine (India). 4ꢀcyanophenylboronic acid,
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Tetrakis(triphenylphosphine) palladium(0) were acquired from Sigma−Aldrich. All the chemicals were
used without further purification.
Synthesis
To prepare the ligand used for the synthesis of the present compounds, we needed to prepare 5ꢀBromoꢀ
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,10ꢀphenanthroline followed by 4ꢀ(1,10ꢀphenanthrolinꢀ6ꢀyl)benzonitrile. The initial compound 5ꢀBromoꢀ
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1,10ꢀphenanthroline was prepared employing a reported procedure (ESI).
Synthesis of 4-(1,10-phenanthrolin-6-yl)benzoic acid: The acid, 4ꢀ(1,10ꢀphenanthrolinꢀ6ꢀyl)benzoic
acid, was prepared from the nitrile compound, 4ꢀ(1,10ꢀphenanthrolinꢀ6ꢀyl)benzonitrile. Thus, 0.1 g (0.35
mmol) 4ꢀ(1,10ꢀphenanthrolinꢀ6ꢀyl)benzonitrile was taken in a 100mL round bottom flask, then 20 mL 6M
H SO solution was added and refluxed at 120 ºC for 12h. The reaction mixture was cooled to room
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temperature and 50 mL of ice cold water was added to the reaction mixture. The resulting solid was
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filtered and washed with water and dried under vacuum. Yield: 0.105 g (98%). H NMR (DMSOꢀd6): δ
9.23(t, 2H, J = 4.0 Hz, J = 4.0 Hz), 8.80(d, 1H, J = 8.0 Hz), 8.44(d, 1H, J = 8.0 Hz), 8.18(d, 2H, J = 4.0
Hz), 8.16(s, 1H), 8.02(q,1H, J = 4.0 Hz, J = 4.0 Hz, J = 4.0 Hz), 7.93(q, 1H, J = 4.0 Hz, J = 4.0 Hz, J =
4.0 Hz), 7.75(d, 2H, J = 8.0 Hz).
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Synthesis of [M(C H N O ) .H O] (M = Co, Mn): For the preparation of the cobalt compound; a
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mixture of Co(NO ) .6H O (97.2 mg, 0.334 mmol), 4ꢀ(1,10ꢀphenanthrolinꢀ6ꢀyl)benzoic acid (50 mg,
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0.167 mmol), N,Nꢀdimethylformamide (4 mL), ethanol (4 mL), and water (4 mL) was taken in a 23mL
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Teflonꢀlined autoclave and heated at 150ºC for 3 days. The resulting product contained red colored rod
like crystals, which were filtered, washed with water and ethanol and dried in vacuum. Yield: 42.9 mg
(
(
38%). Elemental analysis (%) for [Co(C H N O ) .H O] Found (Calculated): C 67.01 (67.56), H 3.39
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3.58), N 8.28 (8.29). A similar procedure was followed for the preparation of the Mn analogue by using
MnCl .4H O and heating the reaction mixture at 120ºC for 3 days. Yield: 26.9 mg (24%). Elemental
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analysis (%) for [Mn(C H N O ) .H O] Found (Calculated): C 67.61 (67.96), H 3.38 (3.60), N 8.18
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(8.34).
Initial Characterization and Physical Measurements: The ligand was characterized employing NMR
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spectroscopy. H NMR data were collected using Bruker 400 MHz spectrometer. Chemical shifts are
reported in ppm using tetramethylsilane as the internal reference (Supporting Information, Figure S1ꢀS3).
IR spectra were recorded as KBr pellets using a FTIR spectrometer (Perkin Elmer, model no: L125000P).
UV−Vis spectra were recorded at room temperature (Perkin Elmer Lambda 35 spectrophotometer)
(Supporting Information, Figure S4). Room temperature solid state photoluminescence studies were
carried out on the compounds (Perkin Elmer LS 55 luminescence spectrophotometer) (Supporting
Information, Figure S5). Elemental analyses (carbon, hydrogen, and nitrogen) were performed in a
Thermo Finnigan EA Flash 1112 Series. Thermogravimetric analysis (TGA) (Metler−Toledo) was carried
out in oxygen atmosphere (flow rate = 40 mL/min) in the temperature range 30−800°C (heating rate =
10°C / min) (Supporting Information, Figure S6). Powder X−ray diffraction (XRD) patterns were
recorded in the 2θ range 5−50° using Cu Kα radiation (Philips X’pert). Magnetic studies were carried out
in the temperature range of 2–300 K using a SQUID magnetometer (Quantum Design, USA). ICPꢀOES
study was performed using Perkin Elmer Optima 2000DV spectrometer. Transmission electron
microscopy (TEM), high resolution TEM (HRTEM) images and energyꢀdispersive Xꢀray spectroscopy
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(
EDS) were obtained with a JEM 2100F, JEOL transmission electron microscope at an accelerating
voltage of 200 kV.
Single−Crystal Structure Determination: Suitable single crystals were carefully selected under a
polarizing microscope and glued to a glass fiber. Single crystal data were collected at room temperature
and at 475 K on an Oxford Xcalibur (Mova) diffractometer equipped with an EOS CCD detector. The
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X−ray generator was operated at 50 kV and 0.8 mA using Mo K (λ= 0.71073 Å) radiation. The cell
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refinement and data reduction were accomplished using CrysAlis RED. The structure was solved by
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direct methods and refined using SHELX97 present in the WinGX suit of programs (version 1.63.04a).
The hydrogen positions were located initially from the difference Fourier maps and for the final
refinement, the hydrogen positions were fixed in a geometrically ideal position and refined employing a
riding model. The final refinements included the atomic positions for all the atoms, anisotropic thermal
parameters for all the non−hydrogen atoms, and isotropic thermal parameters for all the hydrogen atoms.
The details of the structure solution and final refinement parameters are given in Table 1. The CCDC
numbers for the compounds 1, 2, 1a and 2a are 1496623, 1497203, 1497207 and 1497209 respectively.
These data can be obtained free of charge from The Cambridge Crystallographic Data Center (CCDC) via
www.ccdc.cam.ac.uk/data_request/cif.
Synthesis of Pd@MOF: Pd nanoparticles loaded on the compounds were carried out by following a
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reported procedure (ESI).
Pd@MOF characterization: The Pd loaded compounds were characterized by IR, ICPꢀOES analysis
and electronꢀmicroscopic technique. Structurally, one of the carboxylate oxygen is found to be free and
available for chemical manipulation. From the infrared spectroscopic analysis, we find that the Pd loaded
ꢀ1
compound exhibits a shift in the carbonyl stretching frequency. We observed a shift of ~ 6 cm between
ꢀ1
ꢀ1
the as synthesized compound and the Pdꢀcontaining one (1607 cm for the compound and 1601 cm for
the Pd@MOF) (Figure 1). Similar shifting of the IR frequency has also been noted earlier for the Pdꢀ
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loaded compounds. This suggests that the Pd nanoparticles would be distributed evenly across the
compound. The shift in the carbonyl frequency could be due to the partial electron donation from the
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carbonyl group to the PdꢀNanoparticles, which would lead to a weakening of the carbonyl bond. The
inductively coupled plasma optical emission spectrometry (ICPꢀOES) analysis on the Pdꢀloaded
compound gave a Pdꢀloading of 6.8 wt%, which is also reasonably high. The transmission electron
microscopic (TEM) investigation on the Pdꢀloaded compound also suggests that the particles are evenly
distributed with particle sizes in the range of 4.8 ± 0.3 nm (Figure 2). The HRTEM studies on the
nanoparticles clearly indicated a lattice spacing of 0.23 nm, which would correspond to the [111] plane of
the fcc structure of the Pd. XPS analysis was carried out on the Pdꢀloaded samples, which clearly
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indicated the presence of Pd state (Figure 3).
Thermogravimetric Analysis: The thermogravimetric studies on cobalt compound indicated a small
weight loss in the temperature range 30ꢀ210°C followed by a sharp drop at ~380°C (Supporting
Information, Figure S6). The initial weight of ~ 2.5% corresponds to the loss of one lattice water
molecule (cal. 2.6%). The second weight loss at ~380°C of ~ 81% corresponds to the loss of the ligand
(
cal. 88.5%). The final calcined product was found to be crystalline by PXRD and can be identified as
Co O (JCPDS: 43ꢀ1003). A similar behavior was also observed for the manganese compound
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(Supporting Information, Figure S6). The decomposition product was found to be a mixture of Mn O4
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(
JCPDS: 89ꢀ4837) and Mn O (JCPDS: 89ꢀ4836). The loss of lattice water molecule from the structure
2 3
was also established employing inꢀsitu IR spectroscopic studies. From the inꢀsitu IR spectroscopic
ꢀ1
ꢀ1
studies, we observed that the OꢀH stretching bands (3466 cm for Co and 3420 cm for Mn) of the lattice
water molecule disappear as the temperature is raised from RT to 220°C (Figure 4). This indicates that the
water molecules can be removed in a facile manner from the structure. The PXRD studies on the
dehydrated sample also indicated that the samples are crystalline and comparable to the as synthesized
compound (Supporting Information, Figure S8). This suggested the possibility of obtaining single crystal
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structure on the dehydrated compound. To this end, we attempted an inꢀsitu study on the single crystal
and we did obtain the dehydrated structure (described below).
RESULTS AND DISCUSSION
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Structure of [M(C H N O ) .H O], (M = Co and Mn): The asymmetric unit consists of 25 non
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hydrogen atoms. The metal ions, occuping a special position with a site multiplicity of 0.5, are
octahedrally coordinated with two oxygen {O2(#1), O2(#2)} and four nitrogen {N1, N2, N1(#3), N2(#3)}
atoms (Figure 5). The average M–O and M–N bond lengths are 2.014Å, 2.166Å for Co and 2.026Å,
2.186Å for Mn (Supporting Information, Table S1). The ligand, 4ꢀ(1,10ꢀphenanthrolinꢀ6ꢀyl)benzoic acid,
connects with both the phenanthroline nitrogen as well as through the carboxylate oxygen with the metal
ions. Thus, the ligands links two metal centers, which gives rise to a twoꢀdimensional layer arrangement
(
Figure 6). The large size of the ligand separates the metal ions apart and results in the formation of
rhombus grid with an interior angle of 93.76° and 86.24°. The large opening within the layers allows
another two dimensional layer to be interpenetrated at an angle of 65.86° (Figure 7) and results in the
formation of a twoꢀfold interpenetrated structure (Figure 8). The two dimensional layers are further
hydrogen bonded with its adjacent layers (Supporting Information, Figure S11) through the lattice water
(
O3) molecule present in the crystal structure, with O3···O1 distances of 2.823(3)Å–2.836(3)Å and O3–
H3A···O1 angles of 168(3)°–172(3)° (Supporting Information, Table S2). This lattice water molecule
also occupies a special position with site multiplicity of 0.5. Apart from the hydrogen bonding involving
lattice water molecule, C–H···O interactions with C1–H1···O1, C4–H4···O3 are also observed in the
structure (Supporting Information, Figure S12, Table S2). In addition, we have also observed C–H···π
interactions as well.
The dehydrated structures of the compounds have exactly the same connectivity with respect to
the metal ion and the carboxylates. The absence of lattice water (O3) molecule in the structure resulted in
minor modifications in the lattice parameters as well as the cell volume (Table 1). In addition, the inter
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layer hydrogen bonding (O3–H3A···O1) as well as the C4–H4···O3 hydrogen bonding was absent. The
other interactions observed in the parent compound were also observed in the dehydrated compounds
(
Supporting Information, Table S2).
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Optical studies: The UVꢀVis spectra of the ligand (Supporting Information, Figure S4) indicated
absorptions corresponding to πꢀπ* and nꢀπ* transitions (see table S3, ESI). The compounds, expectedly,
exhibited a red shift in the absorption bands. In addition, we have been able to observe the allowed dꢀd
transitions of the central transition metal ions (Co / Mn). All the observed absorptions are listed in Table
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S3. Similar absorptions have been observed earlier for the Co and Mn compounds.
The room
temperature photo luminescence investigations also indicated a behavior that is expected of the
compounds and the ligand (ESI, Figure S5 and Table S3). As a case study, we have also carried out the
UVꢀVis spectroscopic analysis of the palladium loaded cobalt compound (ESI, Figure S4d), which did
not exhibit any changes in the 200 – 350nm region. After 350nm, the absorbance of the palladium loaded
compound was found to increase gradually, which may be due to the surface plasmon absorption of the
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0
Pd nanoparticles. Similar observations have been made earlier.
Infrared (IR) spectroscopic studies: Infrared (IR) spectroscopic studies were carried out in the midꢀIR
region on KBr pellets. The IR spectra of 4ꢀ(1,10ꢀphenanthrolinꢀ6ꢀyl)benzonitrile exhibited typical bands.
ꢀ1
The band at 2227 cm corresponds to the nitrile group. After acid hydrolysis of 4ꢀ(1,10ꢀphenanthrolinꢀ6ꢀ
ꢀ1
ꢀ
yl)benzonitrile the band at 2227cm disappeared along with the appearance of two new bands at 1715 cm
1
ꢀ1
,
3392 cm , which clearly indicated that the nitrile group transformed to a carboxylic acid group
Supporting Information, Figure S13). Other typical bands have also been observed. Important IR bands
have been tabulated (Supporting Information, Table S4). For the cobalt and manganese compounds, a
(
−
1
broad band in the region of ~3300–3500 cm , suggested the presence of water molecule (Supporting
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Information, Figure S14). Other bands typical of aromatic backbone of the ligand were also observed
(
Supporting Information, Table S4).
Magnetic Studies: The magnetic behavior as a function of temperature of the cobalt and manganese
compounds were carried out in the temperature range 300ꢀ2K (Figure 9). For the cobalt compound, the
magnetic susceptibility decreases very slowly up to 25K and then increases sharply (Supporting
Information, Figure S15a). A similar behavior was also noted for the Mnꢀcompound (Supporting
0
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Information, Figure S15b). The room temperature, the χ T (1000 Oe) values were found to be 4.767 and
m
−1
5
.841 emu mol K, respectively, for the Co and Mn compounds. For the Coꢀcompound, the obtained χ T
m
−
1
value at room temperature (4.767 emu mol K) was found to be higher than the expected spinꢀonly value
−
1
of 3.873 emu mol K. This suggests a large orbital contribution to the effective magnetic moment in the
2
1
case of Co. Cobalt compounds exhibiting large orbital contribution is well known. The Mn compound,
−
1
on the other hand, exhibits a spinꢀonly value of 5.916 emu mol K. The χ T value shows a continuous
m
ꢀ1
decrease with decreasing temperature up to 29K to reach a value of 2.66 emu mol K for the Coꢀ
ꢀ1
compound and 3.72 emu mol K for the Mnꢀcompound. On cooling further the χ T exhibits a sharp
m
ꢀ1
ꢀ1
increase to reach a maximum value of 4.4 emu mol K (Co) and 4.06 emu mol K (Mn) at 25K. The
χmT values starts to decrease on cooling below 25K. The sharp increase clearly suggests the onset of longꢀ
range magnetic ordering. The high temperature magnetic data was fitted to a CurieꢀWeiss behavior in the
temperature range 100ꢀ300 K, which gave a value of −90.2 K for Coꢀcompound and −61.1 K for Mnꢀ
compound (inset Figure 9a and 9b). The large negative values for the θ suggest that the magnetic centers
p
2+
2+
are antiꢀferromagnetically coupled. It may be noted that the metal ions (Co / Mn ) are separated from
each other by 13.397Å, but are connected by a conjugated ligand. We believe that the large negative
values indicates strong antiꢀferromagnetic coupling between the metal centers mediated through the
organic linker. The MꢀH studies at 2K indicate a typical behavior observed for samples exhibiting antiꢀ
ꢀ1
ferromagnetic interactions. The maximum saturation magnetization values of 2.58 emu mol (Co) and
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.33 emu mol (Mn) were observed at 9T (Supporting Information, Figure S16). These values are
2
+
2+
comparable to the expected saturation values of 3 (Co) and 5 (Mn) for one uncoupled Co and Mn ion.
Suzuki coupling reaction: The usefulness of Pdꢀnanoparticles encapsulated in the compound was
examined by carrying out a homocoupling (C–C coupling) reaction (Suzuki coupling). Thus, Suzuki
coupling reaction between iodobenzene (0.5 mmol) and phenylboronic acid (0.75 mmol) was carried out
with 2 mol% of Pd@cobalt and K CO (1.0 mmol) at 75°C in a mixture of THF:MeOH solvent. The
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3
various experimental conditions were arrived by carrying out reactions from room temperature to 90°C
Table 2). As can be noted, the C–C coupling reaction preceded only about 15% at room temperature. The
(
highest yield of 95.1% was achieved after 15h at 75°C. No increase in the yield was obtained at higher
temperature (90°C) under the same conditions. The same reaction when carried out on pristine cobalt
compound at 75°C for larger duration (24h) did not yield any additional significant progress of the
reaction. Our efforts at other derivatives such as with electron donating group (ꢀMe, ꢀOMe) gave smaller
22
yields of the product (Table 3). This observation appears to be consistent with those reported before.
Similar experiment carried out with Pd@manganese also behaved in a similar way with the iodo
derivative (Supporting Information, Figure S17). The same reaction, when carried out with bromoꢀ and
chloroꢀ derivatives gave much reduced products with the chloroꢀderivatives gave yields in the range of ~
12ꢀ19% (Table 3). The recyclability of the Pdꢀloaded catalyst was examined under the standardized
conditions which gave yields of ~ 85% and ~ 76%, respectively (Figure 10). The stability of the catalyst
after the coupling reactions was examined by PXRD (Supporting Information, Figure S18), which clearly
indicated that the compounds retain their structures even after the 3rd cycle.
We have also carried out XPS studies of the catalyst, after the reaction, to learn about the changes
in the oxidation state of the Pd metal. The studies indicated again two peaks at 340.85 eV and 335.67 eV
which are comparable to the as prepared sample and can be assigned to Pd(0) 3d3/2 and Pd(0) 3d5/2
respectively (Figure 3b). In order to probe the heterogeneous nature of the reaction, we have performed a
hot filtration experiment. Thus, a mixture of iodobenzene (0.5 mmol), phenylboronic acid (0.75 mmol),
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K CO (1.0 mmol), THF (2.5 mL), MeOH (0.25mL) and Pd@MOF (16 mg, 2 mol %) was reacted at
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3
75°C. After 1h of the reaction, the catalyst was separated from the reaction mixture by centrifugation and
the filtrate was allowed to continue the reaction at 75°C. The yield of the product was analyzed. The
yield of the reaction with the Pd@MOF and without Pd@MOF is shown in Figure 11. It may be noted
that in the absence of Pd@MOF, the change in the yield was found to be ~10%. The yield actually
increases from 25% at 1h to 35% at 12h. This observation suggests that there is no significant progress in
the reaction when the filtrate, containing the reaction mixture without the catalyst, was allowed to
continue at the same reaction conditions for longer duration. It is likely that the filtrate might have some
trace residue of the catalytically active Pd metal, which gives rise to this small increase in the yield. The
amount of Pd content in the filtrate was analyzed by ICPꢀOES analysis, which indicated a Pd
concentration (leached) of ~1.2 ppm, which would correspond to ~5.6 % of the original Pd amount in the
catalyst. We have also carried out a similar experiment by doubling the concentration of all the reactants,
including the catalyst. The results were found to be similar and consistent to the first experiment. The
efficiency of the Pd@MOF was compared with other Pd nanoparticles supported catalysts (Supporting
Information, Table S5). It can be noted that the catalytic activity of Pd@MOF is comparable with many
of the reported activities. It is clear that the activity of the catalyst depends on the size of the metal
nanoparticles with smaller metal nanoparticles giving better catalytic activity, possibly due to the
availability of higher active surface area for the reactants. We believe that the higher catalytic activity
observed in the presence of Pd@MOF could be due to the wide dispersion of smaller Pd nanoparticles
over the surface of the compound investigated in the present study.
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CONCLUSIONS
A solvothermal reaction involving 4ꢀ(1,10ꢀphenanthrolinꢀ6ꢀyl)benzoic acid and metal salts
(cobalt / manganese) resulted in two compounds, [M(C H N O ) .H O], (M = Co, Mn). Both the
1
9
11
2
2 2
2
compounds have identical structure and posses 2ꢀfold interpenetrated framework. The extraꢀframework
water molecules have been shows to be reversibly remove by inꢀsitu IR and single crystal investigations.
Palladium nanoparticles with 4.8 ± 0.3 nm size were successfully encapsulated in the compound. The
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Pd@MOF compounds exhibits excellent catalytic properties with good recyclability for the homoꢀ
coupling of aryl halides, especially for the iodo derivatives. Magnetic studies indicate strong antiꢀ
ferromagnetic exchanges between the metal centers mediated through the aromatic linker.
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ACKNOWLEDGEMENTS
SN thanks the Science and Engineering Research Board (SERB), Government of India for the award of a
research grant as well as a J. C. Bose National Fellowship. Council of Scientific and Industrial Research
(
CSIR), Government of India, is thanked for a research grant (S.N.) and a research fellowship (A.K.J.).
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS Publications website at DOI:.
Supporting materials contain selected bond lengths and bond angles for 1−2a, intermolecular
interactions present in the crystal structures, UVꢀVis and photoluminescence investigations, IR bands,
related reported Suzuki coupling reactions, synthesis of 5ꢀBrphen and 4ꢀ(1,10ꢀphenanthrolinꢀ6ꢀ
1
yl)benzonitrile. Figures of H NMR spectra, UV−Vis absorption spectra, photoluminescence spectra,
TGA, PXRD patterns, synthesis and color of Pd@MOF, EDX pattern of Pd@cobalt, size distribution of
Pd nanoparticles, sample preparation procedure for ICPꢀOES analysis, hydrogen bonding present in the
crystal structure, magnetic measurements plots, results of catalytic reactions and characterization data of
the catalytic products and figures of asymmetric unit of 1−2a.
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REFERENCES:
(
(
1)
2)
Thomas, J. M.; Angew. Chem. Int. Ed. 1994, 33, 913.
Thomas, J. M.; Angew. Chem. Int. Ed. 1999, 38, 3588.
0
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0
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9
0
(3)
(4)
Cao, S.; Tao, Fr.; Tang, Y.; Li, Y.; Yu, J. Chem. Soc. Rev. 2016, DOI: 10.1039/c6cs00094k.
Tanga, Y.; Cheng,W. Nanoscale 2015, 7, 16151.
(
(
(
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7)
Djakovitch, L.; Koehler, K. J. Am. Chem. Soc. 2001, 123, 5990.
Cai, M.; Sha, J.; Xu, Q. J. Mol. Catal. A: Chem. 2007, 268, 82.
Siamaki, A. R.; Khder, A. E. R. S.; Abdelsayed, V.; ElꢀShall, M. S. and Gupton, B. F. Journal of
Catalysis 2011, 279, 1.
(8)
(9)
Mondal, B.; Acharyya, K.; Howlader, P.; Mukherjee, P. S. J. Am. Chem. Soc. 2016, 138, 1709.
Suh, M. P.; Park, H. J.; Prasad, T. K.; Lim, D. Chem. Rev. 2012, 112, 782.
Cheon, Y. E.; Suh, M. P. Angew. Chem. Int. Ed. 2009, 48, 2899.
Seechurn, C. C. C. J.; Kitching, M. O.; Colacot, T. J.; Snieckus, V. Angew. Chem. Int. Ed.2012,
(
(
10)
11)
5
1, 5062.
(
12)
Li, L.; Zhao, H.; Wang, J.; Wang, R. ACS Nano 2014, 8, 5352.
Hissler, M.; Connick, W. B.; Geiger, D. K.; McGarrah, J. E.; Lipa, D.; Lachicotte, R. J.;
Eisenberg,R. Inorg. Chem. 2000, 39, 447.
(13)
(
14) CrysAlis CCD, CrysAlis PRO RED, version 1.171.33.34d; Oxford Diffraction Ltd.: Abingdon,
Boxfordshire, England, 2009.
(
15)
Sheldrick, G. M. SHELXSꢀ97, Program for Crystal Structure Solution and Refinement,
University of Göttingen, Göttingen, Germany, 1997.
(16)
(17)
Chen, L.; Chen, H.; Luque, R.; Li, Y. Chem. Sci. 2014, 5, 3708.
Nemamcha, A.; Rehspringer, J.; Khatmi, D. J. Phys. Chem. B 2006, 110, 383.
Ramaswamy, P.; Mandal, S.; Hegde, N. N.; Prabhu, R.; Banerjee, D.; Bhat, S. V.; Natarajan, S.
Eur. J. Inorg. Chem. 2010, 1829.
(
18)
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(
(
19)
20)
Bhattacharya, S.; Ramanujachary, K. V.; Lofland, S. E.; Magdalenoc, T.; Natarajan, S.
CrystEngComm. 2012, 14, 4323.
Leong, K. H.; Chu, H. Y.; Ibrahim, S.; Saravanan, P. Beilstein J. Nanotechnol. 2015, 6, 428.
Vallejo, J.; ForteaꢀPerez, F. R.; Pardo, E.; Benmansour, S.; Castro, I.; Krzystek, J.; Armentanoc,
D.; Cano, J. Chem. Sci. 2016, 7, 2286.
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(21)
(
22)
In´es, B.; SanMartin, R.; Moure, M. J.; Dom´ınguez, E. Adv. Synth. Catal. 2009, 351, 2124.
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Figure Captions.
Figure 1. The IR spectra of the cobalt compound and the palladium loaded one. Please note the shift in
the IR band (see text).
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Figure 2. Figure shows the palladium loaded cobalt compound: (a) TEM image of Pd(0)@cobalt
compound (b) HRTEM image of the palladium nanoparticles. Note the inter planar spacing of 0.224 nm
corresponding to Pd (111) lattice plane.
Figure 3. (a) The XPS spectra of Pd loaded compound, showing the peaks corresponding to Pd (0). (b)
The XPS spectra of the catalyst after the catalytic reaction, showing the peaks corresponding to Pd (0).
Figure 4: Variable temperature IR spectra for the compounds: (a) Cobalt (b) Manganese.
Figure 5. Figure shows the coordination environment around the metal ion forming the octahedral
geometry (shown in the inset).
Figure 6. (a) Two dimensional rhombus layer observed in the cobalt and the manganese compound. (b)
Schematic representation of the 2D grid (green ball represent the metal ions and the black stick represents
the ligand).
Figure 7. Figure shows the schematic representation of the interpenetration of the 2D layer. Note that the
other layer interpenetrates in an orthogonal manner.
Figure 8. Figure shows the interpenetration of layers.
Figure 9. Figure shows the thermal variation of χ T for both the compounds. Inset shows the 1/χ vs. T
m
m
(
a) Co (b) Mn.
Figure 10. Recyclability studies for the homocoupling reaction employing Pd@cobalt compound.
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Figure 11. Results of the hot filtration experiment for the Suzuki coupling reaction: (■ normal reaction in
the presence of the catalyst ● the measured yield when the catalyst was removed by centrifugation after
1h).
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Table 1. Crystal Data and Structure Refinement Parameters for 1−2a.
Structural
parameter
1
2
1a
2a
Empirical
formula
[Co(C H N O ) . [Mn(C H N O ) . [Co(C H N O ) ] [Mn(C H N O ) ]
19 11 2 2 2 19 11 2 2 2 19 11 2 2 2 19 11 2 2 2
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0
H O]
H O]
2
2
Formula
weight
675.54
671.55
657.53
653.54
Crystal
system
Orthorhombic
Orthorhombic
Orthorhombic
Orthorhombic
Space group
a (Å)
I b a 2
I b a 2
10.5810(5)
16.5660(9)
18.6370(10)
90
I b a 2
I b a 2
10.6323(5)
16.4151(9)
18.3130(10)
90
10.7196(10)
16.9591(13)
17.6231(15)
90
10.6843(10)
17.2404(13)
17.7573(15)
90
b (Å)
c (Å)
α (deg)
β (deg)
90
90
90
90
9
0
90
90
90
γ (deg)
3
V (Å )
3196.2(3)
3266.8(3)
4
3203.8(5)
4
3270.9(5)
4
Z
4
T/K
298
298
475
475
ꢀ
3
ρ (calc/gcm ) 1.404
1.365
1.363
1.327
ꢀ1
ꢂ (mm )
0.589
0.455
0.583
0.450
λ(Mo Kα/Å)
θ range ( °)
0.71073
3.19 – 24.99
0.71073
3.16 – 25.00
0.71073
3.22 – 25.00
0.71073
3.21 – 25.000
R indexes [ I R1 = 0.0271
> 2σ (I)]
wR2 = 0.0590
R1 = 0.0291
wR2 = 0.0677
R1 = 0.0436
wR2 = 0.0809
R1 = 0.0485
wR2 = 0.1056
R indexes (all R1= 0.0358
data) wR2 = 0.0611
R1 = 0.0384
wR2 = 0.0700
R1 = 0.0630
wR2 = 0.0917
R1 = 0.0691
wR2 = 0.1215
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a
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R = Σ||F | − |F ||/Σ|F |; wR = {Σ|w(F − F )]/Σ [w(F ) ]} . w = 1/[ρ (F ) + (aP) + bP]. P = [max
1
o
c
o
2
o
c
o
o
,
2
(
F O) + 2(F ) ]/3, where a = 0.0331 and b = 0.4577 for 1, a = 0.0385 and b = 0.4166 for 2, a = 0.0325 and
o
c
b = 0.0000 for 1a, a = 0.0542 and b = 0.0000 for 2a.
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5
5
5
5
5
6
Table 2. Suzuki coupling reaction of iodobenzene and phenylboronic acid with and without Pd@cobalt
catalysts at different temperature.
Entry
Catalyst
Temperature (°C)
Time
24h
% Yield
-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
Cobalt compound
75
25
50
75
90
Pd@cobalt compound
Pd@cobalt compound
Pd@cobalt compound
Pd@cobalt compound
24h
15
24h
62
15h
95.1
95.1
15h
Reaction conditions: Aryl iodide (0.5 mmol), phenylboronic acid (0.75 mmol), K CO (1.0 mmol), THF
2
3
(
2.5 mL), MeOH (0.25mL) and 6.8 wt% Pd@MOF (16 mg, 2 mol% of Pd, 0.01 mmol). Yield based on
column chromatography.
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Table 3. Suzuki coupling reaction of aryl halide derivative catalyzed by Pd@cobalt compound.
S. No.
Substrate
Reaction
time
Product
Yield %
Cl Br
I
1
2
15h (X=I, Br)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
X
X
2
4h ( X=Cl)
12.8 90.5 95.1
12.4 82.2 92.6
15h (X=I, Br)
24h ( X=Cl)
H C
3
H C
3
3
4
5
6
15h (X=I, Br)
O N
X
X
O N
2
2
2
4h ( X=Cl)
18.2 91.4 96.2
15.6 85.4 93.7
13.5 89.5 95.1
11.3 83.2 91.6
15h (X=I, Br)
4h ( X=Cl)
H CO
H CO
3
3
2
O
15h (X=I, Br)
24h ( X=Cl)
O
X
X
H C
3
H C
3
15h (X=I, Br)
24h ( X=Cl)
H N
2
H N
2
Reaction conditions: Aryl halide (0.5 mmol), phenylboronic acid (0.75 mmol), K CO (1.0 mmol), THF
2
3
(2.5 mL), MeOH (0.25mL) and 6.8 wt% Pd@MOF (16 mg, 2 mol % Pd, 0.01 mmol). Yield based on
column chromatography.
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1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
N
N
N
N
N
N
N
(i)
(ii)
(iii)
Br
N
OH
CN
O
Conditions for the reaction:
(
i) Br ,30% Oleum, 140°C, 24h (yield 81%); (ii) 4ꢀCyanophenyl boronic acid, Pd(PPh ) , K CO , 1,4ꢀ
2 3 4 2 3
dioxane, DMF, N atmosphere, 120°C, 3d (yield 62%); (iii) 6M H SO , 120°C, 12h (yield 98%).
2
2
4
Scheme 1. Schematic representation showing the steps in the synthesis of the ligand, 4ꢀ(1,10ꢀ
phenanthrolinꢀ6ꢀyl)benzoic acid.
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35
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
MOF
Pd@MOF
-
1
1
607 cm
-
1
1601 cm
1
700
1600 1500
1400
1300
1200
-1)
Wavenumber
(cm
Jana et al. Figure 1.
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5
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8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Pd (111)
.224 nm
0
(a)
(b)
Jana et al. Figure 2.
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50
Pd 3d5/2
35.52 eV
3
800
Pd 3d3/2
340.78 eV
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
7
7
6
50
00
50
344
342
340
338
336
334
Binding Energy (eV)
(
a)
3
35.67 eV
500
400
340.85 eV
300
200
100
0
344
342
340
338
336
334
332
Binding Energy (eV)
(
b)
Jana et al. Figure 3.
2
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8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
0
°
°
°
°
°
°
°
C
C
C
C
C
C
C
40
50
60
70
80
1
9
1
1
1
1
1
1
1
1
1
1
2
2
2
0
00
10
20
30
40
50
60
70
80
90
00
10
20
°C
°C
°C
°C
°C
°C
°C
°C
°C
°C
°C
°C
°C
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
600
3500
3400
3300
3200
3100
-
1)
Wavenumber cm
(
(a)
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
0
°
°
°
°
°
°
°
C
0
0
0
0
0
0
C
C
C
C
C
C
2
00
10
20
30
40
50
60
70
80
90
00
10
20
°C
°C
°C
°C
°C
°C
°C
°C
°C
°C
°C
°C
°C
3600
3500
3400
3300
3200
3100
-
1)
Wavenumber cm
(
(
b)
Jana et al. Figure 4.
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36
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Jana et al. Figure 5.
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5
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7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
a)
(
b)
Jana et al. Figure 6.
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60
8
6.28°
9
3.76°
114.14°
Jana et al. Figure 7.
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