A simple, phosphine free, reusable Pd(ii)-2,2′-dihydroxybenzophenone-SBA-15 catalyst for arylation and hydrogenation reactions of alkenes

Article abstract of DOI:10.1039/c5nj02686e

An efficient, simple, phosphine and co-catalyst free C-C coupling reaction heterogeneous catalyst via a post grafting method is developed and reported. A covalently anchored phosphine free Pd(ii) based 2,2′-dihydroxybenzophenone (DHBP) complex over organofunctionalized SBA-15 has been synthesized by the reaction between aminofunctionalized SBA-15 (NH₂SBA-15) and a 2,2′-dihydroxybenzophenone (DHBP) ligand, and further complexation with Pd(ii)Cl₂ to get Pd(ii)-DHBP@SBA-15. The synthesized catalysts were characterized by elemental analysis, XRD, N₂ sorption analyses, TG, DTA, FT-IR, solid state ¹³C and ²⁹Si NMR spectra, XPS, UV-Visible, SEM, EDAX and TEM. The synthesized catalysts were screened in arylation (Heck reactions) and hydrogenation reactions of alkenes, and the results show that Pd(ii)-DHBP@SBA-15 exhibits high conversion and selectivity towards arylation and hydrogenation reactions of alkenes with high stability. The anchored solid catalysts can be recycled effectively and reused several times without major loss in activity.

Full text of DOI:10.1039/c5nj02686e

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ARTICLE
A simple, phosphine free, reusable Pd(II)-2,2’-Dihydroxybenzo
phenone-SBA-15 catalyst for arylation and hydrogenation
reactions of alkenes
Received 00th January 20xx,
Accepted 00th January 20xx
Anish Lazar,ab Chathakudath P Vinod ab and Anand Pal Singha*
DOI: 10.1039/x0xx00000x
An efficient, simple, phosphine and co-catalyst free C-C coupling reaction heterogeneous catalyst via. post grafting method
is developed and reported. Covalently anchored phosphine free Pd(II) based 2,2’-dihydroxybenzophenone (DHBP) complex
over organofunctionalized SBA-15 has been synthesized by the reaction between aminofunctionalized SBA-15 (NH2SBA-
15) and 2,2’-dihydroxybenzophenone (DHBP) ligand, and further complexation with Pd(II)Cl2 to get Pd(II)-DHBP@SBA-15.
The synthesized catalysts were characterized by elemental analysis, XRD, N2 sorption analyses, TG, DTA, FT-IR, solid state
13C and 29Si NMR spectra, XPS, UV-Visible, SEM, EDAX and TEM. The synthesized catalysts were screened in arylation (Heck
reactions) and hydrogenation reactions of alkenes, and the results show that Pd(II)-DHBP@SBA-15 exhibits high
conversion and selectivity towards arylation and hydrogenation reactions of alkenes with high stability. The anchored solid
catalysts can be recycled effectively and reused several times without major loss in activity.
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alkenes with aryl halides. However, as with all homogeneous
catalysts, its separation and reusability are difficult, thereby
increasing the production cost with liberation of large volumes
Introduction
The discovery of C-C coupling reactions in 19th century has
opened up several alternative challenges for the production of
fine chemicals. A lot of materials such as ionic liquids,1 silica
supported2 and polymer supported3 catalysts, pure Pd/C4 etc
were used for the carbon-carbon coupling reactions. The
phosphine supported catalysts5 for C-C coupling reactions are
well established method in the past decades. However, several
drawbacks of phosphine ligands such as cost, toxicity and
recovery from the reaction mixture are challenging and has
resulted in the process being less preferred. In addition,
phosphine undergoes oxidation in catalytic cycle to get
phosphine oxide, and thereby causing the cleavage of P-C
bond and degradation of the catalytic cycle. Due to these
reason, there is a growing interest in the development of
phosphine free heterogeneous catalyst.6 Such a catalyst
should be stable under ambient conditions and should afford
coupling products in high yields at short reaction times. Out of
carbon-carbon cross-coupling reactions, the arylation of
alkenes7 in the presence of a base (Heck reaction) is an
excellent method for the synthesis of fine chemicals.
of hazardous wastes. To mitigate the above mentioned serious
problems, palladium based organofunctionalized mesoporous
catalysts,9-11 which shows high periodicity in the pore
arrangement as well as high surface area and pore sizes, have
been synthesized via. post grafting method and used for
coupling reactions.12 Further, liquid phase hydrogenation of
alkenes13,14 using heterogeneous catalysts are relevant
industrial process to obtain alkanes. An appropriate, cheap
and simple ligand is necessary for synthesis of highly active
palladium based organofunctionalized complexes. For this
purpose, a number of ligands such as C-N based and N,N’
based ligands15 have been reported for coupling reactions.
Due to the instability and tedious synthesis procedure of
previously said ligands, a robust and stable 2,2’-Dihydroxy
benzophenone ligand derivative is used in the present study.
To heterogenize the palladium based organofunctionalized
complexes with better stability and to avoid the diffusional
strain of reactants in the channels of other mesoporous or
microporous materials, solid support like SBA-15 is synthesized
by using neutral triblock polyether as templates and TEOS as
silica precursor. In addition, SBA-1516 has the advantage due to
its special characteristics such as high surface area, uniform
pore sizes, high wall thickness and high hydrothermal stability
compared to other mesoporous materials like MCM-41, MCM-
48. To explore the utility of SBA-15 materials, especially in
catalysis, the surface of SBA-15 was modified by organic
functional groups for anchoring of metals and metal
complexes.17
In the past decades, complexes of palladium such as
palladium acetate, palladium chloride or triarylphosphine
palladium complexes are used8 in the arylation reactions of
a. Catalysis Division, CSIR-National Chemical Laboratory, Pune-411008, India.
b. Academy of Scientific and Innovative Research (AcSIR), Anusandhan Bhawan, 2,
Rafi Marg, New Delhi-110001, India.
* Corresponding Author (Dr. A. P. Singh), E-mail Address: ap.singh@ncl.res.in
† Electronic Supplementary Information(ESI): [XPS spectra of Spent catalyst]
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In this work, we tried to synthesize and characterize highly
NJC
efficient, phosphine and co-catalyst free, reusable
heterogeneous catalyst, Pd(II)-DHBP@SBA-15 for arylation and
hydrogenation reactions of alkenes. Synthesis of Pd(II)-
DHBP@SBA-15 catalyst mainly divided into four steps and it is
described as (i) synthesis of parent solid support like SBA-15
(ii) aminofunctionalization of SBA-15 (iii) anchoring of 2,2’-
dihydroxybenzopheneone (DHBP) ligand over amino-
functionalized SBA-15 (NH2SBA-15) and (iv) metallation of
heterogenized ligand (DHBP@SBA-15) with Pd(II)Cl2.
Experimental
Synthesis of Pd(II)-DHBP@SBA-15
Pluronic 123 (P123, Average MolWt
=
5800),
tetraethylorthosilicate (TEOS), 3-aminopropyltrimethoxysilane
(3-APTMS), 2,2’-dihydroxybenzophenone (DHBP) and Pd(II)Cl2
were purchased from Aldrich. In addition, aryl halides and
alkenes as organic reagents used for the coupling and
hydrogenation reactions were purchased from Aldrich.
Further, hydrochloric acid (HCl) and solvents like
dichloromethane (DCM), acetonitrile (CH3CN) and toluene
were purchased from Merck. All chemicals were used as
received without further purification.
The synthesis of SBA-15 was carried out by using modified
literature procedure with the following initial molar gel
compositions : 18
0.043 TEOS: 4.4g P123 Mavg = 5800 [EO20-PO70-EO20]:
8.33 H2O: 0.24 HCl
Typically, Pluorinc123 called as P123 (4.4 g), a triblock co-
polymer consider as surfactant, was dispersed in 30 g distilled
water and stirred for 1.5 h. 120 g of 2 M HCl was added into
the above solutions with constant stirring and stirring was
continued for next 2 h. Eventually, 9 g of TEOS as silica
presursor was added drop wise and the resulting solution was
maintained at 35 °C for 24 h with stirring. The resulted
heterogeneous mixture was submitted to hydrothermal
treatment at 100°C for 48 h under static condition. The solid
product was filtered, washed with distilled water and dried in
oven at 70°C for 12 h, and then calcined at 540 °C for 8 h in air
to get calcined SBA-15. 18
The aminofunctionalized SBA-15 (NH2SBA-15) was
synthesized by using 3-aminopropyltrimethoxysilane (3-
APTMS) as organic linker via. Post-grafting method (scheme 1-
a). The reaction procedure briefly explained as: 3 g of calcined
SBA-15 was dispersed in 60 ml dry toluene followed by 1.5 g
of 3-APTMS was added into this solution under N2 atmosphere
and the reaction mixture was refluxed at 100 °C for 8 h. The
solid material was filtered, washed with toluene and
dichloromethane, and dried in oven at 70 °C for 12 h. The
dried material was extracted by Soxhlet apparatus with
dichloromethane as solvent to remove the unreacted silylating
agent like 3-APTMS and was vacuum dried at 473K to get
NH2SBA-15.
Scheme 1: Organofunctionalization and heterogenization of
2,2’-
Dihydroxybenzophenone (DHBP) complex over SBA-15 [Pd(II)-DHBP@SBA-15], 1-
a: Aminofunctionalization of SBA-15 [NH2SBA-15], 1-b: Immobilization of 2,2’-
Dihydroxybenzophenone Ligand (DHBP) over NH2SBA-15 [DHBP@SBA-15], 1-c:
Complexation of heterogenized ligand [Pd(II)-DHBP@SBA-15].
dihydroxybenzophenone ligand (DHBP) over amino-
functionalized SBA-15 (NH2SBA-15) (scheme 1-b) to get
DHBP@SBA-15 and (ii) complexation of heterogenized ligand
(DHBP@SBA-15) with Pd(II)Cl2 to achieve Pd(II)-DHBP@SBA-15
(scheme 1-c). In briefly, the first step involves the addition of
2,2’-dihydroxybenzophenone (0.52 g, 2.41 mmol) which is
dissolved in 35 ml of dry acetonitrile into the dispersed
solutions of NH2SBA-15 (1 g) in 15 ml of dry acetonitrile. The
reaction mixture was refluxed at 70 °C for 24 h with constant
stirring, and then filtered, washed thoroughly with acetonitrile
and dried in oven at 50 °C for 16 h to get DHBP@SBA-15
(scheme 1-b) . In second step, called as metallation process,
0.2 g of Pd(II)Cl2 (1.13 mmol) in 20 ml of dichloromethane was
added into the solution of heterogenized ligand, DHBP@SBA-
15 (1 g) in 10 ml of dichloromethane. The dispersed solutions
was stirred at room temperature for 24 h, and then filtered,
washed with dichloromethane and dried in oven at 50 °C for
12 h. The dried material was Soxhlet extracted with
dichloromethane to remove unreacted Pd(II)Cl2 to attain
Pd(II)-DHBP@SBA-15 (scheme 1-c).
The arylation of alkenes under palladium catalysts is one of
the important organic reactions, referred as Heck reaction,
which is helpful for the synthesis of various types of coupling
compounds. Arylations of alkenes were carried out in a 50 ml
double necked RB flask fitted with a water-cooled condenser
and magnetic stirrer by using Et3N as base. In typical Heck
reaction procedure, a mixture of 0.015 g of Pd(II)-
DHBP@SBA-15, aryl halide (1 mmol), alkenes (1.2 mmol), Et3N
(3.5 mmol) and 3.5 ml of DMF was refluxed at 120 °C for 12 h.
The samples were withdrawn periodically and cooled sample
was analyzed using a Gas chromatography (HP, Agilent 68909
N) equipped with a capillary column (HP-5) and FID detector.
Hydrogenation reactions of alkenes, especially aromatic
olefins, cycloolefins, aliphatic olefins and bicyclo olefins are
used to synthesize various hydrocarbons, which can be applied
in industrial chemistry. In a typical procedure, a mixture of
0.015 g of Pd(II)-DHBP@SBA-15 and olefins (5 mmol) in 50 ml
The synthesis of Pd(II)-DHBP@SBA-15 is mainly divided into
two steps as shortly described as (i) anchoring of 2,2’-
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methanol were taken in 100 ml Parr autoclave reactor and mesoporous structure, phase purity, degree of orderdness and
stirred with H2 Pressure (5 bar) at room temperature for 15 unit cell parameters of all synthesized catalysts were
minutes. The samples were withdrawn periodically and cooled determined by powder X-ray diffraction. The typical hexagonal
sample was analyzed using a Gas chromatography (HP, Agilent phase (p6mm) of SBA-15 showing three reflections, mainly
68909 N) equipped with a capillary column (HP-5) and FID (100) peak with weak (110) and (200) peaks are clearly visible
detector.
in all samples at 2θ = 0.90°, 1.50° and 1.74°, respectively. This
Elemental analysis (C, H and N) was performed on a Carlo indicates high degree of orderedness of the two dimensional
Erba (Model EA 1108) elemental analyzer. The palladium metal hexagonal mesophase.19 In all the synthesized catalysts [Fig.
content in the material was determined by EDAX analysis using 1(a-d)], (110) reflection is more intense than (200) reflection,
a dual beam scanning electron microscope (FEI company, which occurs due to the complete condensation of the wall
model Quanta 200 3D) operating at 30 kV. Powder X-ray structure owing to the higher hydrothermal synthesis
diffraction (XRD) patterns were measured on a PAN analytical temperature at calcination. Further, the XRD pattern of
X’pert Pro dual goniometer diffractometer using Ni-filtered calcined SBA-15 [Fig. 1(b)] shows intense peak compared with
CuKα radiation (λ = 1.5404 Å) over the range 0.5 – 5 ° (SAXRD). the as-synthesized SBA-15 which reveals that surfactant
N2 adsorption–desorption isotherms, pore size distributions as present in as-synthesized sample was completely removed
well as the textural properties of the hybrid materials were from calcined SBA-15. The peak intensities of (100) reflections
determined by using a Autosorb 1C Quantachrome USA. The in NH2SBA-15 and Pd(II)-DHBP@SBA-15 [Fig. 1(c,d)] were
program consisting of both an adsorption and desorption gradually decreasing from calcined SBA-15 due to the proper
branch and typically ran at -196 °C after samples were loading of organic modifier and homogeneous complexes,
degassed at 150 °C for 4 h. The BET method was applied to respectively, on calcined SBA-15.
calculate the total surface area at relative pressures of P/Po =
The physical properties of calcined SBA-15 and Pd(II)-
0.65–0.45 and the BJH model applied to the adsorption branch DHBP@SBA-15 are summarized in Table 1. The BET surface
of the isotherm to determine the total pore volume and area, pore volume, pore diameter, unit cell parameter and
average pore diameter at a relative pressure of P/Po = 0.99. pore wall thickness of calcined SBA-15 and Pd(II)-DHBP@SBA-
Pore size distribution curves were obtained via the NLDFT 15 are found to be 550 m2/g, 1.02 cc/g, 65.00 Å, 102.54 Å ,
model assuming cylindrical pore geometry. FTIR spectra of the 36.54 Å and 220 m2/g, 0.51 cc/g, 47.00 Å, 103.00 Å, 55.00 Å,
solid samples were recorded in the range of 4000–400 cm-1 on respectively. As shown in Table 1, compared to SBA-15, a
a Bruker alpha T FTIR spectrophotometer under room further reduction of surface area, pore volume and pore
temperatures. Magic angle spinning (MAS) NMR spectra for diameter were observed in Pd(II)-DHBP@SBA-15 catalyst,
29Si and 13C nuclei were recorded on BRUKER DSX300 indicating the successful anchoring of homogeneous complex
spectrometer at 7.05 T (resonance frequencies 59.595 MHz, on the channels of SBA-15. The N2 adsorption-desorption
rotor speed 10000 Hz and 75.43 MHz, rotor speed 10000 Hz). isotherm and pore size distribution curves (inset) of (a)
XPS measurements were performed on a VG Microtech ESCA calcined SBA-15 and (b) Pd(II)-DHBP@SBA-15 are plotted in
3000 instrument, using monochromatized MgKα radiation at Fig. 2. In both materials, calcined SBA-15 and Pd(II)-
pass energy of 50 eV and an electron take off angle of 60 °. DR DHBP@SBA-15, exhibit type IV type isotherm with H1
UV-Vis spectra of thecomplexes were analyzed by using a hysteresis loop related to capillary condensation step, a
Perkin-Elmer model Lambda 650 spectrophotometer.The characteristic feature of the highly ordered mesoporous
scanning electron micrographs of the samples were obtained materials (2-50 nm).20
in dual beam scanning electron microscope (FEI company,
The weight percentage of organomoities on SBA-15 and the
model Quanta 200 3D) operating at 30 kV. The samples were thermal stability of (a) as-synthesized SBA-15 (b) calcined SBA-
loaded on stubs and sputtered with thin gold film to prevent 15 (c) NH2SBA-15 and (d) Pd(II)-DHBP@SBA-15 were
surface charging and also to protect from thermal damage due determined by TGA (Fig. 3A) and DTA (Fig. 3B) in an
to electron beam. A JEOL JEM-3010 and Tecnai (Model F30) atmosphere of air from 30 to 1000 °C with a temperature
both operating at 300 kV were used for HRTEM samples ramp of 10 °C min-1. As-syntheiszed SBA-15 [Fig. 3A(a)] exhibits
observation. Samples were crushed and dispersed in a 50 % weight loss in TG analysis with observation of an
isopropanol with low power sonication before putting a drop exothermic peak in DTA analysis [Fig. 3B(a)], in the range of
over carbon coated Cu grid for observation.
175 °C to 230 °C. This it can be inferred that the decomposition
of surfactants present in as-synthesized SBA-15. In calcined
SBA-15[Fig. 3A(b)], a 11 % weight loss was observed in TGA
due to the physisorbed water molecules, and no peak was
observed in DTA analysis [Fig. 3B(b)]. This indicates a complete
removal of surfactants from parent SBA-15 with the
generation of pure siliceous material. The TG and DTA analyses
of NH2SBA-15 [Fig. 3A &B(c)] shows two distinct weight loss
regions; first one, corresponds to adsorbed moisture molecule
in the region of 75 °C to 150 °C and second one, indicates to
Results and discussion
Characterization of Pd(II)-DHBP@SBA-15
The synthesized catalysts were characterized by different
physico-chemical characterization techniques and the results
are discussed below. The XRD pattern of (a) as-synthesized
SBA-15 (b) calcined SBA-15 (c) NH2SBA-15 and (d) Pd(II)-
DHBP@SBA-15 are represented in Fig. 1. The uniqueness of
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Fig. 1: XRD pattern of (a) as-synthesized SBA-15 (b) calcined SBA-15 (c) NH2SBA-15 and
(d) Pd(II)-DHBP@SBA-15.
Table 1: Textural propertiesa of SBA-15 and Pd(II)-DHBP@SBA-15.
Sample
a0b [Å]
SA
[m2/g]
550
Dp
[Å]
65
Vp
[cc/g]
1.02
ωtc
(Å)
SBA-15
102.54
103.00
36.54
Pd(II)-DHBP
@SBA-15
220
47
0.51
55.00
a
a0, Unit Cell parameter; SA, BET Surface Area; Dp, Pore Diameter; Vp, Pore
Volume; ωt, Wall Thickness; Pd content=6.88 Wt% (EDAX); b a0=2d100/1.73; c ωt=
a0-Dp.
Fig. 3: TGA (A) and DTA (B) pattern of (a) as-synthesized SBA-15 (b) calcined SBA-15 (c)
NH2SBA-15 and (d) Pd(II)-DHBP@SBA-15.
Fig. 2: N2 adsorption-desorption isotherms and pore size distribution curves (inset) of
(a) calcined SBA-15 and (b) Pd(II)-DHBP@SBA-15.
the decomposition of aminopropyl moiety from NH2SBA-15 in
the range of 250 °C to 320 °C. In the case of Pd(II)-DHBP@SBA-
15 [Fig. 3A &B(d)], an extra peak was observed between 350 °C
and 420 °C along with the peaks for aminopropyl group in
NH2SBA-15. The combustion of Pd(II)-2,2’-dihydroxy
benzophenone (DHBP) complex can be confirmed along with
the high thermal stability of organomoities on SBA-15. The
Fig. 4: FT-IR spectroscopy of (a) as-synthesized SBA-15 (b) calcined SBA-15 (c) NH2SBA-
15 and (d) Pd(II)-DHBP@SBA-15.
TGA results of NH2SBA-15 [Fig. 3A(c)] exhibits 18 % weight loss
which is greater than calcined SBA-15 (11 %) [Fig. 3A(b)]
indicating the successful anchoring of 3-APTMS on the calcined
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SBA-15. Further, Pd(II)-DHBP@SBA-15 [Fig. 3A(d)] shows 31 %
of weight loss, being greater than the loss observed for the
NH2SBA-15, strongly supporting a 13 % loading of neat Pd(II)-
2,2’-dihydroxy benzophenone (DHBP) complex on calcined
SBA-15. All decomposition results of synthesized materials
from TG and DTA analyses confirms that the successful
anchoring of organo-modifier and neat homogeneous complex
over SBA-15.
DRIFTS was employed to find out the nature of surface
silanol groups and organomoities attached on SBA-15. The FT-
IR spectra of (a) as-synthesized SBA-15 (b) calcined SBA-15 (c)
NH2SBA-15 and (d) Pd(II)-DHBP@SBA-15 are depicted in Fig. 4.
The peaks at 2940 and 2867 cm-1 in the as-synthesized SBA-15
[Fig. 4(a)] are attributed to the -CH2 asymmetrical and
symmetrical stretching vibrations of surfactant molecules
present in host materials. After calcination, [Fig. 4(b)] the
above mentioned peaks disappeared due to the complete
removal of surfactants, and a broad band at 3800-3000 cm-1
and a medium sharp band at 1630 cm-1 were observed, which
corresponds to -OH stretching and bending vibrations of
isolated surface silanol groups in calcined SBA-15.21,22 After
aminofunctionalization, NH2SBA-15 [Fig. 4(c)], the peaks at
2940 and 2867 cm-1 due to the stretching vibrations of –CH2
Fig. 5: Solid state 13C NMR spectroscopy of (a) NH2SBA-15 and (b) Pd(II)-
DHBP@SBA-15.
17
groups in propyl chain of 3-APTMS indicating the successful
anchoring of organic linker on parent SBA-15. Further, the
peaks at ~3300 cm-1 and ~1500 cm-1 correspond to stretching
and bending vibrations of N-H bond 15 in NH2SBA-15 [Fig. 4(c)].
In the case of Pd(II)-DHBP@SBA-15 [Fig. 4(d)], an additional
peaks at 753 cm-1 and 1540 cm-1 are assigned to C–H bending
and C=C stretching vibrations,18 respectively, of the arene
groups. Moreover, a strong band at 1610 cm-1 is assigned to
the –C=N stretching vibration of the azomethylene group.18 In
addition, well pronounced band at 1450 to 1340 cm-1
17
correspond to the –CH2 bending vibrations
of propyl chain
in Pd(II)-DHBP@SBA-15. The spectrum of as-synthesized SBA- Fig. 6: Solid state 29Si NMR spectroscopy of (A) calcined SBA-15 (B) NH2SBA-15
and (C) Pd(II)-DHBP@SBA-15.
15, calcined SBA-15, NH2SBA-15 and Pd(II)-DHBP@SBA-15 [Fig.
4(a-d)] exhibit the bands at 1086 cm-1 and 805 cm-1 assigned
organomoities confirm the anchoring of Pd(II)-2,2’-
to the asymmetric and symmetric stretching vibrations of Si-O
dihydroxybenzophenone (DHBP) sites on SBA-15. The 29Si CP-
bond in Si-O-Si and a strong band at 935 cm-1 is attributed to
MAS NMR spectroscopy has been employed to find out the
degree of functionalization of surface silanol groups with
ν(Si–OH) vibrations in silica framework.23,24 The results from
FT-IR spectra indicates successfully anchoring of neat Pd(II)-
organic moieties on the mesostructured materials. 29Si solid
2,2’-dihydroxy benzophenone (DHBP) complex into parent
state NMR spectra of (a) calcined SBA-15 (b) NH2SBA-15 and
SBA-15.
(c) Pd(II)-DHBP@SBA-15 are represented in Fig. 6. A broad
The 13C solid state NMR spectra of (a) NH2SBA-15 and (b)
resonance peaks from -90 to -110 ppm are assigned to Si–O–Si
Pd(II)-DHBP@SBA-15
are
plotted
in
Fig.
5.
In
and Si–OH bonds in all synthesized catalysts [Fig. 6(a-c)]. The
peaks at -92 ppm, -100 ppm and -110 ppm are corresponds to
the Q2 [geminal silanol, (SiO)2Si(OH)2], Q3 [single silanol,
(SiO)3Si(OH)] and Q4 [siloxane, (SiO)4Si] sites of the silica
framework, respectively.21,22 The spectra of NH2SBA-15 [Fig.
6(b)] and Pd(II)-DHBP@SBA-15 [Fig. 6(c)] exhibit two additional
peaks at -64 ppm and -56 ppm assigned to T3 [SiR(OSi)3] and T2
[Si(OH)R(OSi)2] units, respectively which is conspicuously
absent in parent SBA-15. The presence of T3 and T2 signals
confirm that SBA-15 has been modified by organomoeities. In
addition, aminofunctionalized SBA-15 shows a decrease in Q2
aminofunctionalized SBA-15 [Fig. 5(a)], peaks at 10, 23 and 43
ppm corresponds to the carbon atoms of propyl chain in
organic
modifier,
indicating
the
successful
aminofunctionalization of SBA-15. In the case of Pd(II)-
DHBP@SBA-15 catalyst [Fig. 5(b)], peaks in the range of 110-
145 ppm, assigned to aromatic carbon atoms of 2,2’-
dihydroxybenzophenone (DHBP) ligand, which is anchored
over aminofunctionalized SBA-15. In addition, peaks at 156
ppm and 176 ppm are ascribed to –CH(OH) group in aromatic
ring and azomethine (-C=N) group in Pd(II)-DHBP@SBA-15
catalyst, respectively. All resonance peaks related with
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Fig. 9: SEM images of (A) calcined SBA-15 and (B) Pd(II)-DHBP@SBA-15.
Fig. 7: XPS spectroscopy oof 3d5/2 and 3d3/2 core levels of Pd(II)-DHBP@SBA-15.
Fig. 10: TEM images of (A) calcined SBA-15 and (B) Pd(II)-DHBP@SBA-15.
–OH groups and imine N donor sites10,11 present in 2,2’-DHBP
ligand. The DR UV-Visible spectra of (a) calcined SBA-15 (b)
NH2SBA-15 and (c) Pd(II)-DHBP@SBA-15 are presented in Fig.
8. A peak at 230 nm,25 typical for siliceous material is observed
in all synthesized catalysts [Fig. 8(a-c)]. The spectra of Pd(II)-
DHBP@SBA-15 [Fig. 8c] exhibits two peaks at 256 nm and 295
nm are attributed to Π →Π* transitions of the aromatic ring
and the azomethine group, respectively.26 Further, a broad
peak at 367 nm is assigned to n →Π* transitions of the
azomethine group. Two broad bands at 560 nm and 686 nm
are assigned to N → Pd(II) & O →Pd(II) ligand to metal charge-
transfer transitions (LMCT) and d-d transitions of Pd(II) species,
respectively.27 The above results also confirm the successful
anchoring of Pd(II)-2,2’-dihydroxybenzophenone (DHBP)
complex over SBA-15 with intact +2 oxidation state.
Transmission Electron Microscopy (TEM) and Scanning
Electron Microscopy (SEM) analysis were used to attain
nanometric and morphological details of the mesoporous
materials. The SEM images of (A) calcined SBA-15 and (B)
Pd(II)-DHBP@SBA-15 are shown in Fig. 9. The particle size of
calcined SBA-15 and Pd(II)-DHBP@SBA-15 was found to be in
the range of 1.10 to 1.31 µm with a hexagonal plate type
structure. The morphology of Pd(II)-DHBP@SBA-15 [Fig. 9B]
was retained with the parent SBA-15 [Fig. 9A] after the
anchoring of Pd(II)-DHBP sites on aminofunctionalized SBA-15.
The TEM images of (A) calcined SBA-15 and (B) Pd(II)-
DHBP@SBA-15 are shown in Fig. 10 and its images show
regular hexagonal array of uniform channels having a long-
range order and well defined 1-D channels. The nanometric
sized pore channels is in confirmation with SA and XRD
analysis.
Fig.
8
8
: DR UV-Vis spectroscopy of (a) calcined SBA-15 (b) NH2SBA-15 and (c) Pd(II)-
DHBPP@SBA-15.
and Q3 sites with the increase of Q4 site, compared to calcined
SB -15, indicating the effective consumption of the geminal as
well as isolated ilanol sites by using 3-APTMS as organic
mo
ifier. The results from 29Si NMR spectra confirm a highly
condensed siloxane network with organic group covalently
bo nd to the me oporous silica and the stability of Si-C bond
in Pd(II)-DHBP@SBA-15 catalyst.
-ray Photoelectron Spectroscopy and DR UV-Visible
AA
ss
dd
uu
ss
XX
spectroscopy can be used to find out the oxidation state and
chemical environment of synthesized catalysts. The XPS
spectra of Pd 3d
in Fig. 7. All the spectra were calibrated and charge corrected
to 1s peak of ca bon at 284.6 eV as standard reference. The
peaks at 337.5 eV and 343 eV in Pd(II)-DHBP@SBA-15 catalyst
corresponds to Pd3d5/2 and Pd3d3/2 spin orbit component,
indicating that ppalladium exists in +2 oxidation state. In
ccore levels of Pd(II)-DHBP@SBA-15 is plotted
CC
rr
addition, the XPS spectra of spent catalyst was shown in Fig. S1
[ESI †]. The 3d5/2 and 3d3/2 core levels of spent catalyst were
obs
e
e
rved at 335.7 eV and 340.8 eV, respectively, indicating the
palladium exists a
s
s
Pd(0) state, which is stabilized by phenolic
6 |
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Catalytic Activity
show higher and sudden conversion [95 to 100 wt.%] than
electron donating groups [75 to 80 wt.%] (Table 2, entries 1-3),
whereas the conversion of halides constantly decreases with
increasing the number of electron donating groups. This result
reveals that the presence of strong electron withdrawing
group in aryl halides makes the substrate more susceptible for
further oxidative-addition reactions during catalytic cycle.
Likewise, EDG present in alkenes like α-methyl styrene (Table
2, entries 6-10) exhibits higher conversion towards the
coupling products [ 87 to 100 wt.%] than a model substrate
like styrene [75 to 100 wt.%] (Table 2, entries 1-5). In the case
of acrylates as alkenes in Heck reactions (Table 2, entries 11-
20), ethyl acrylate (Table 2, entries 16-20) shows higher
conversion [ 90 to 100 wt.%] than methyl acrylate [90 to 95
wt.%] (Table 2, entries 11-15), due to the EDG effects. The
decreasing order of reactivity of aryl halides and alkenes in
Heck reactions are : 1-iodo-4-nitrobenzene > 1-iodo-4-chloro
benzene > iodo benzene >1-iodotoluene > 3,5-dimethyliodo
benzene and ethyl acrylate > methyl acrylate > α-methyl
styrene > styrene, respectively.
The catalytic activity of Pd(II)-DHBP@SBA-15 complex was
evaluated in arylation and hydrogenation reaction of alkenes.
Arylation of alkenes (Heck reaction) in which various aryl
halides couple with alkenes to give trans-stillbene derivatives,
using Et3N as a base and dimethylforamide (DMF) as a solvent.
The reaction progress (conversion in percentage) of Pd(II)-
DHBP@SBA-15 catalyst for heck reaction are shown in Table 2
(entries 1-20). To evaluate the influence of substrates, aryl
halides like iodobenzene, 1-iodotoluene, 3,5-dimethyl
iodobenzene, 1-iodo-4-chlorobenzene, 1-iodo-4-nitrobenzene
and alkenes like styrene, α-methyl styrene, methyl acrylate,
ethyl acrylate were screened, to produce coupling products (a-
t). The trans or
E
Isomer was formed as the dominant coupling
isomer. As shown in Table 2,
product in all cases than Cis or
Z
aromatic halides with electron withdrawing group (EWG) were
more imprudent than that of electron donating groups (EDG).
In both cases, electronic effects at para position is more
predominant than meta position. Thus, the electron
withdrawing group containing aryl halides (Table 2, entries 4,5)
Table 2: Arylationa of alkenes (Heck reactions)
No.
1
Aryl halides
Alkenes
Coupling products
Time (h)
8
Conv. (%)
80
TOFb (h-1)
0.155
a
b
2
3
10
12
78
76
0.121
0.098
c
d
e
f
4
5
6
7
8
6
2
95
100
85
0.245
0.774
0.164
0.126
0.101
8
10
12
82
g
78
h
i
9
4
92
0.356
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NJC, 2015, 00, 1-3 | 7

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NJC
10
2
2
100
94
0.774
0.726
j
k
l
11
12
13
4
8
90
90
0.348
0.174
m
n
14
15
16
17
18
2
1
2
4
6
95
95
95
92
90
0.735
1.470
0.735
0.359
0.232
o
p
q
r
s
t
19
20
2
1
95
0.735
1.548
100
a Reaction conditions: Pd(II)-DHBP@SBA-15: 0.015 g; aryl halide: 1 mmol; alkenes : 1.2 mmol; Et3N: 3.5 mmol; DMF: 3.5 ml; reaction temperature: 120 °C. b TOF [h−1] =
[the number of moles of reactant converted/the number of moles of metal active sites]/time in hours.
To test the efficiency of Pd(II)-DHBP@SBA-15 complex as
In order to check the stability and reusability of Pd(II)-
catalyst for hydrogenation reactions, aromatic olefins (styrene, DHBP@SBA-15 complex, the arylation and hydrogenation
α- methyl styrene), cyclic olefins (Cyclohexene. Cyclooctene, reactions of alkenes with styrene as model substrate were
and 1,4-Cyclohexadiene), aliphatic olefins (I-undecene, 1- performed under appropriate reaction conditions, which are
Nonene) and bicycloolefin (Bicylco[2.2.1]hepta2,5 diene) were presented in Table 4. For recyclability test, after each cycle, the
used as substrates (Table 3, entries 1-8). All olefins showed catalyst was separated by filtration, washed with suitable
100 % conversion under 15 minutes to give alkanes ( i-viii)
,
solvent and activated for 6 h at 150 °C in an air before use in
under ambient reaction conditions (room temperature, H2- the next experiment. The synthesized catalyst showed good
Pressure (5 bar) and MeOH as solvent).
(fresh+ four cycle) recyclability in arylation and
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Table 3: Hydrogenationa reactions of alkenes
Table 4: Recycling study of Pd(II)DHBP@SBA-15 catalyst
No.
alkenes
alkanes
Conv. (%)
100
TOFb
Arylationa
(Styrene)
Hydrogenationb
(Styrene)
(min-1)
No. of
Cycles
Conv.
Sele.
100
Conv.
Sele.
1
0.103
Fresh
80
100
100
i
I cycle
II cycle
III cycle
IV cycle
80
78
73
65
100
99
100
97
100
99
2
3
4
5
100
92
0.103
0.095
99
91
99
ii
98
84
99
a
Reaction conditions: Pd(II)-DHBP@SBA-15: 0.015 g; aryl halide: 1 mmol;
alkenes : 1.2 mmol; Et3N: 3.5 mmol; DMF: 3.5 ml; reaction temperature: 120 °C;
reaction time: 8 h. b Reaction conditions: Pd(II)-DHBP@SBA-15: 0.015 g; olefins: 5
mmol; MeOH: 50 ml; H2 Pressure: 5 bar; temperature: 30 °C; time: 15 min
iii
iv
retained its structural integrity, textural properties, organic
moieties, oxidation state, morphology and topographic
characteristics after heterogenization. The catalytic activity of
100
100
0.103
0.103
Pd(II)-DHBP@SBA-15 was screened in arylation
and
hydrogenation reactions of alkenes, and the results show that
Pd(II)-DHBP@SBA-15 exhibits high conversion and selectivity
towards arylation and hydrogenation reactions of alkenes in
combination with high stability. The electronic (EWG & EDG
effects) and steric effects (bulkier group) of groups on the
substrates are also probed and the trend follow those
reported in literature. In addition, aliphatic olefins or less
hindered olefins like acrylates gave better conversion and
selectivity than aromatic olefins like substituted styrene. Due
to these reasons, in Heck reaction, 4-nitro-1-iodobenzene
showed higher reactivity with ethyl acrylate to give the
coupling products with 100 % conversion and selectivity within
1 h. Moreover, in hydrogenation reactions, all olefins, except
conjugated olefins, showed 100 % conversion under 15
mintues to give alkanes, under mild conditions. The
recyclability test was carried out to confirm the stability and
heterogeneousous nature of catalyst and the results concluded
that that Pd(II)-DHBP@SBA-15 is reusable without much loss of
activity for several cycles.
v
6
7
CH3(CH2)8CH=CH2
CH3(CH2)6CH=CH2
CH3(CH2)8CH2CH3
100
100
0.103
0.103
vi
CH3(CH2)6CH2CH3
vii
100
0.103
8
viii
a
Reaction conditions: Pd(II)-DHBP@SBA-15: 0.015 g; olefins: 5 mmol; MeOH: 50
ml; H2 Pressure: 5 bar; reaction temperature: 30 °C; reaction time: 15 min. b TOF
[min−1] = [the number of moles of reactant converted/the number of moles of
metal active sites]/time in minutes.
hydrogenation reactions of alkenes with retension of
conversion and selectivity upto three cycles. A ~14 wt.% loss of
conversion was observerd from fresh cycle in hydrogenation
and Heck reactions after fourth cycle due to the 1.5 wt %
leaching of palladium metal from fresh catalyst. However, all
recycling studies reveals that Pd based catalyst exhibits higher
stability and heterogeneous nature in each and every steps.
Acknowledgements
AL thanks CSIR, New Delhi for SRF fellowship. APS thanks CSIR-
Emeritus Scientist Scheme (P-81103) for financial assistance.
Conclusions
In conclusion, an efficient, simple and phosphine free Pd(II)-
DHBP@SBA-15 catalyst has been synthesized by tethering of
References
2,2’-dihydroxybenzophenone
(DHBP)
ligand
over
1
2
3
Y. Liu, S.-S. Wang, W. Liu, Q.-X, Wan, H.-H. Wu and G.-H.
Gao, Curr. Org. Chem., 2009, 13, 1322.
V. Polshettiwar, C. Len and A. Fihri, Coord. Chem. Rev., 2009,
253, 2599.
aminofunctionalized SBA-15 via. post- grafting method. and
Further metallation with Pd(II)Cl2 resulted in well-ordered
mesostructure with long range order. The synthesized
catalysts were characterized by various characterization
techniques like elemental analysis, XRD, N2 sorption analyses,
TG, DTA, FT-IR, solid state 13C and 29Si NMR spectra, XPS, UV-
Visible, SEM, EDAX and TEM. All characterization techniques
proved that mesoporous SBA-15 and synthesized catalysts
P. Lu, J. Lu, H. You, P. Shi and Dong, J. Prog. Chem., 2009, 21
,
1434.
4
5
M. Seki, Synthesis, 2006, 2975.
C. Amatore, A. Jutand, M. Amine and M. Barki,
Organometallics, 1992, 11, 3009; H. A. Dieck and R. F. Heck,
J. Org. Chem., 1975, 40, 1083; C. A. Fleckenstein and H.
Plenio, Chem. Soc. Rev., 2010, 39, 694.
This journal is © The Royal Society of Chemistry 20xx
NJC, 2015, 00, 1-3 | 9

New Journal of Chemistry
Page 10 of 11
View Article Online
DOI: 10.1039/C5NJ02686E
ARTICLE
NJC
6
7
8
A. Zapf and M. Beller, Top. Catal., 2002, 19, 101; L. X. Yin and
J. Liebscher, Chem. Rev., 2007, 107, 133.
I. P. Beletskaya and A. V. Cheprakov, Chem. Rev., 2000, 100
3009.
,
R. F. Heck, Org. React., 1982, 27, 345; R. F. Heck, Palladium
Reagents in Organic Synthesis, Academic Press, Orlando, FL,
1985.
9
C. M. Crudden, M. Sateesh and R. Lewis, J. Am. Chem. Soc.,
2005, 127, 10045; J. Horniakova, T. Raja, Y. Kubota and Y.
Sugi, J. mole. Cata. A: Chem., 2004, 217, 73; P. Sharma and A.
P. Singh, Catal. Sci. & Tech., 2014, 4, 2978.
10 A. Modak, J. Mondal, V. K. Aswal and A. Bhaumik, J. Mater.
Chem., 2010, 20, 8099.
11 A. Modak, J. Mondal and A. Bhaumik, Green Chemistry, 2012,
14, 2840.
12 K.-I. Shimizu, S. Koizumi, T. Hatamachi, H. Yoshida, S. Komai,
T. Kodama and Y. Kitayama, J. Catalysis., 2004, 228, 141; K.
Yu, W. Sommer, J. M. Richardson, M. Weck and C. W. Jones,
Adv. Synth. Catal., 2005, 347, 161.
13 O. Schmidt, Chem. Rev., 1933, 12, 363; R. A. W. Johnstone, A.
H. Wilby and I. D. Entwistle, Chem. Rev., 1985, 85, 129; C. M.
Crudden, D. Allen, M. D. Mikoluk and J. Sun, Chem.
Commun., 2001, 1154.
14 L. Wang, M. Jia, S. Shylesh, T. Philippi, A. Seifert, S. Ernst, A.
P. Singh and W. R. Thiel, ChemCatChem, 2010, 11, 1477; L.
Wang, A. Reis, A. Seifert, T. Philippi, S. Ernst, M. Jia and W. R.
Thiel, Dalton Transactions, 2009, 3315.
15 V. P. W. Bohm, C. W. K. Gstottmayr, T. Weskamp and W.
Herrmann, J. Organomet. Chem., 2000, 595, 186; B. Tao and
D. W. Boykin, Tetrahedron Letters, 2002, 43, 4955; D. A.
Alonso, C. Najera and M. C. Pacheco, Org. Lett., 2000, 2,
1823; B. Bedford and C. S. Cazin, Chem. Commun., 2001,
1540; G. A. Grasa, A. C. Hillier and S. P. Nolan, Org. Lett.,
2001,
3, 1077; S. R. Borhade and S. B. Waghmode,
Tetrahedron Letters, 2008, 49, 3423.
16 D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F.
Chmelka and G. D. Stucky, Science, 1998, 279, 548.
17 A. Lazar, P. Sharma and A. P. Singh, Micropore. Mesopore.
Mater., 2013, 170, 331.
18 P. Sharma, A. Lazar and A. P. Singh, Appl. Catal. A: Gen.,
2012, 439–440, 101.
19 D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J.
Am. Chem. Soc., 1998, 120, 6024.
20 R. Ryoo, I. -S. Park, S. Jun, C. W. Lee, M. Kruk and M.
Jaroniec, J. Am. Chem. Soc., 2001, 123, 1650.
21 P. Sharma and A. P. Singh, RSC Advances, 2014, 4, 58467.
22 A. Lazar, W. R. Thiel and A. P. Singh, RSC Advances, 2014, 4,
14063.
23 A. G. S. Prado and C. Airoldi, J. Colloid Interface Sci., 2001,
236, 161.
24 M. D. Alba, Z. Luan and J. Klinowski, J. Phys. Chem., 1996,
100, 2178.
25 S. Shylesh and A. P. Singh, J. Catal., 2004, 228, 333.
26 B. I. Ceylan, Y. D. Kurt and B. Ulkuseven, J. Coord. Chem.,
2009, 62, 757.
27 J. H. Enemark and C. G. Young, Adv. Inorg. Chem., 1993, 40
,
1.
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An efficient, phosphine and co-catalyst free Pd(II)-DHBP@SBA-15 catalyst for arylation and
hydrogenation reactions of alkenes was synthesized and characterized.