Recyclable Pd ionic catalyst coated on cordierite monolith for high TOF Heck coupling reaction

Article abstract of DOI:10.1007/s12039-019-1594-9

Abstract : Pd ^{2 +} ionic catalyst, Ti _0.97Pd _0.03O _1.97 was coated over cordierite monolith by solution combustion method. The catalyst coated on the cordierite is nano-crystalline as seen from XRD studies. Coated catalyst was used for Heck coupling reactions with different substrates of aryl halides and olefins. Thus handling nano-crystalline catalyst powder is avoided by fixing it on a solid catalyst cartridge. Heck coupled products were characterized using ¹H NMR, ¹³C NMR, Mass and FTIR spectroscopy. This catalyst showed high selectivity towards Heck coupling reaction. Turnover frequencies (TOF) for each of the reactions were found to be very high. The catalyst was recycled up to 7 times with total TOF 3017 h ^{- 1}, which is found to be a new green technique in the Heck coupling reaction. Graphical abstract: Ti _0.97Pd _0.03O _1.97 catalyst is coated on cordierite monolith honeycomb (HC) by solution combustion method and it is used in the Heck coupling reaction. Reactions are done in a specially designed flask. Catalyst is recycled for 7 times. The total turnover frequency (TOF) after 7 cycles was 3017 h ^{- 1}. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-019-1594-9

J. Chem. Sci.
(2019) 131:20
© Indian Academy of Sciences
https://doi.org/10.1007/s12039-019-1594-9
REGULAR ARTICLE
Recyclable Pd ionic catalyst coated on cordierite monolith for high
TOF Heck coupling reaction
SHRIKANTH K BHATa,b, JAGADEESH D PRASADb,∗ and M S HEGDEa,∗
aTalent Development Centre, Indian Institute of Science, Challakere Campus, Chitradurga, Karnataka 577 536,
India
bDepartment of Chemistry, Mangalagangotri, Mangalore University, Konaje, Mangalore 574 199, India
E-mail: jprasad2003@gmail.com; mshegde@iisc.ac.in
MS received 16 November 2018; revised 19 December 2018; accepted 2 January 2019
Abstract. Pd2+ ionic catalyst, Ti0.97Pd0.03O1.97 was coated over cordierite monolith by solution combustion
method. The catalyst coated on the cordierite is nano-crystalline as seen from XRD studies. Coated catalyst
was used for Heck coupling reactions with different substrates of aryl halides and olefins. Thus handling nano-
crystalline catalyst powder is avoided by fixing it on a solid catalyst cartridge. Heck coupled products were
characterized using 1H NMR, 13C NMR, Mass and FTIR spectroscopy. This catalyst showed high selectivity
towards Heck coupling reaction. Turnover frequencies (TOF) for each of the reactions were found to be very
high. The catalyst was recycled up to 7 times with total TOF 3017 h−1, which is found to be a new green
technique in the Heck coupling reaction.
Keywords. Noble metal ionic catalyst; cordierite monolith; solution combustion method; Heck coupling.
1. Introduction
Palladium metal, ligands and the need to remove a metal
particle from the products.18 Due to the high cost of
Palladium and environmental issues, the development
of heterogeneous catalysis is important for the industrial
application to perform such coupling reactions. There-
fore researchers are looking towards a heterogeneous
catalyst which is highly stable and reusable.19–23 Recent
studies show that PdO supported carbon nanomateri-
als24 and palladium(0) on copper ferrite nanowires were
designed for traditional Heck reaction as well as Heck
reaction between iodoarenes and allylic alcohols.25
Instead of Pd metal nanoparticles or PdO, Pd2+
ion substituted in reducible oxides showed high rates
of redox catalytic reactions. A new class of cata-
lysts called “Noble Metal Ionic Catalysts” (NMIC)
were developed here.29 Noble metal ions substituted
in reducible oxide such as TiO2 is a new class of
catalyst which was synthesized by solution combus-
tion method.26–29 Among different metals, Pd showed
very good catalytic activity for CO oxidation reaction,
The Heck coupling reaction has been considered as one
ofthe most widely used a method forthe formation ofC–
C bonds.1–4 Literature indicated the application of this
coupling reaction in the synthesis of complex organic
molecules such as drugs, natural products and advanced
materials.5–11 For these reactions, Pd based catalysts
were used extensively where they ensure enhanced reac-
tion rates, high turnover frequencies and very good
selectivity.12–14 Homogeneous palladium-based cata-
lysts are extensively used in Heck coupling reaction
as it provides high reaction rates and turnover num-
ber (TON) and often ends up with high selectivity and
yields.15–17 In these cases, Palladium catalyst can be
activated with the help of ligands such as phosphines,
carbines, amines and dibenzylidene acetone(dba). On
the other hand, homogeneous catalysis has a number
of drawbacks such as reusing of the catalyst and impu-
rities in the products which leads to loss of expensive
*
For correspondence
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s12039-019-1594-9) contains
supplementary material, which is available to authorized users.
0123456789().: V,-vol

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J. Chem. Sci.
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hydrocarbon oxidation reaction and hydrogen–oxygen starting materials. A solution of TiO(NO3)2 (9.89 mmol),
recombination reaction.27–30 When catalyst coated over
which was prepared from titanium tetraisopropoxide, PdCl2
(0.31 mmol), and glycine (10.99 mmol) were taken in a
cordierite monolith, it showed very good catalytic activ-
300 mL crystallizing dish. The solution was kept in a 350 ◦C
ity towards hydrogen-oxygen recombination reaction at
room temperature.31 On Pd2+ ion substitution in TiO2
preheated muffled furnace and combustion of starting
materials took place followed by dehydration. The dish was
lattice, a stable stoichiometric compound Ti1−x Pdx O2−x
kept inside the furnace for more than 20 min to burn all
(x=0.03) is formed with one oxide ion vacancy per Pd2+
the carbon contents. Then the dish was removed from the
ion for charge compensation. When Pd2+ is substituted,
furnace, allowed to cool and collected the catalyst pow-
an oxide ion vacancy is automatically created in the lat-
der. The catalyst was ground in a pestle and mortar and
tice. Pd2+ ion and oxide ion vacancy were next to each
characterized by PXRD. The combustion reaction is given
other as seen from the structure.31 Pd ion acted as an
by:
electrophile and oxide ion vacancy as a nucleophile.
TiO2 is cheaper reducible oxide support and non-toxic.
100% Pd ion dispersion is achieved so that all the Pd
metal used becomes the active site.
Here we have attempted Heck coupling reaction with
ionic palladium substituted TiO2 having composition
9(1 − x)TiO(NO3)2 + 10(1 − x)C2H5NO2
+ 9xPdCl2 → 9Ti1−x Pdx O2−
δ
+ 20(1 − x)CO2 + 14(1 − x)N2
+ (25 − 34x)H2O + 18xHCl: x = 0.01, 0.02, 0.03.
Ti0.97Pd0.03O1.97. To avoid handling nano-material in the
form of powder, and also to see if a catalyst cartridge
can be developed, we coated the catalyst on cordierite
monolith by solution combustion method.31,32 We have
avoided the use of powder catalyst. The reaction was
carried out with the solid monolith and removed it from
the reaction flask, reused it and calculated overall TOF
which was very high. The Heck coupling reaction was
done in a specially designed reaction flask, which pre-
vents breaking of cordierite monolith from fast rotating
magnetic beads.
X-ray diffraction patterns were recorded on a Philips
X’Pert Diffractometer at a scan rate of 0.1◦/min with a step
size in the 2 range between 10◦ and 90◦. The diffraction
θ
profiles were refined by Rietveld refinement method.
γ
2.3 Coating of −Al2 O3 over cordierite monolith
γ
Before coating the catalyst over monolith, −Al2O3 was
coated over monolith to increase the surface area and adhe-
sion to TiO2. This process was done by solution combustion
method by taking 15 mmol of Al(NO3)3 and 9 mmol of
glycine. A solution of starting materials was made and pre-
weighed monolith was dipped in the solution and kept inside
the furnace for combustion. After 15 min, monolith was
removed from the furnace and allowed to cool. The weight
of the monolith was taken. This procedure was repeated until
2. Experimental
γ
the weight of the coated −Al2O3 was 2 to 2.5% of cordierite
2.1 General
monolith weight.
X-ray diffraction patterns of catalysts were recorded on a
Philips X’Pert Diffractometer. Reactions were monitored
by using pre-coated silica TLC plates. Mass spectra were
recorded on EI and ESI (TOF) modes. NMR spectra were
recorded in at 400 MHz spectrometers in CDCl3, tetramethyl-
silane (TMS; δ = 0.00 ppm) served as an internal standard
for 1H NMR. The corresponding residual non-deuterated
solvent signal (CDCl3; δ = 77.00 ppm) was used as inter-
nal standard for 13C NMR. Column chromatography was
carried out on silica gel 230–400 mesh or 100–200 mesh
(SDFCL) and thin-layer chromatography was carried out
using SILICA GEL GF-254. Chemicals obtained from Sigma
Aldrich and SD Fine chemicals were used without further
purification.
2.4 Coating Ti0.97Pd0.03 O1.97 catalyst over cordierite
monolith
The solution was prepared in a beaker using starting mate-
rials such as TiO(NO3)2, palladium chloride and glycine. A
piece of the pre-weighed monolith was dipped in the solution
and kept inside the preheated muffled furnace for combustion.
After 20–30 min the hot monolith was taken out and allowed
to cool to room temperature. Then the cooled monolith was
kept for sonication process to remove loosely held particles.
The monolith was dried again to remove the moisture and
allowed to cool down. This procedure was repeated to get the
desired weight of catalyst to be coated. About 50 mg of cat-
alyst was coated on the monolith of 2.5 cm diameter, 2 cm
height with 400 cells/inch. Alumina coated monolith and cat-
alyst coated monolith are shown in Figure 1. We observed that
2.2 Synthesis of Ti0.97Pd0.03O1.97 powder catalyst
The catalyst Ti0.97Pd0.03O1.97 was synthesized by solution catalyst becomes black during the reaction due to adsorption
combustion method. Titanium tetraisopropoxide of olefins on palladium. After the reaction, catalyst is regen-
(Ti(OC3H7)4), palladium chloride and glycine were used as erated by heating at 200 ◦C in the air for about 2 h. Then it

J. Chem. Sci.
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Figure 1. Photographs of (a) Alumina coated honeycomb monolith, (b) and (c) top view and
side view of catalyst coated monolith respectively, (d) catalyst coated honeycomb after several
cycles of reactions.
can be reused for many cycles consecutively. This Pd catalyst
The product was isolated using column chromatography.
showed excellent catalytic activity towards Heck coupling The eluents used were pet ether and ethyl acetate. The ratio
reaction.
wasstandardisedbyusingTLCaccordingtothepolarityofthe
products. Coupled products were characterized by 1H NMR,
13C NMR, IR spectra and mass spectra.
2.5 Procedure for the Heck coupling reaction
Screening reactions were carried out in 25 mL round bottom
flask. Iodobenzene (200 mg, 1 equivalent), methyl acrylate
(1.1 equivalents), catalyst (10 mg) and K2CO3 (1.5 equiva-
lent) were taken into a 25 mL round bottom flask. 3 mL of
DMF was added. The reaction was kept under an argon atmo-
sphere at 110 ◦C. Reaction was monitored by TLC. Extracted
the product with diethyl ether and 3 times water work up.
Percentage of yield was determined by using gas chromatog-
raphy.
3. Results and Discussion
Catalyst Ti0.97Pd0.03O1.97 was prepared by solution com-
bustion method from the starting materials TiO(NO3)2,
palladium chloride and glycine at 350 ◦C. Pd substituted
TiO2 crystalizes in anatase structure. Rietveld refined
XRD pattern for 3 atoms % Pd in TiO2 is given in
Figure 2. There are no peaks either of PdO or Pd metal in
Heck coupling reactions were done in the specially the difference profile. Lattice parameters are: a=3.796
designed reaction flask. Aryl halides (2 g, 1 equivalent),
olefins (1.1 equivalents) and base (1.5 equivalents) were taken
intothereactionflask. Catalystcoatedcordieritemonolithwas
put inside the flask. The reaction was kept under an argon
atmosphere at 110 ◦C. The reaction was monitored by TLC.
After completion of the reaction, the coupled product was
extracted by diethyl ether and washed 3 times with water to
remove the solvents and base. Catalyst coated monolith was
removed from the flask, washed with water to remove sol-
vent and base. Then washed with n-hexane to remove organic
impurities and dried in a hot air oven for 2 h at 200 ◦C. Dried
catalyst cartridge was reused for two more substrates of Heck
coupling reactions.
Å and c=9.534 Å which are close to pure TiO2 val-
ues, a=3.796 Å and c=9.533 Å. This is to be expected
because the ionic radius of Pd2+ is 0.64 Å which is close
to that of Ti4+ (0.605 Å). A detailed study of the struc-
ture of Ti0.97Pd0.03O1.97 has been reported earlier.31 The
XRD patterns of cordierite monolith and catalyst coated
cordierite monolith is shown in Figure 3. Cordierite
monoliths are in cylindrical shape with 2.5 cm diam-
eter and 2 cm height and are made up of Mg2Al4Si5O18.
One can see the (101) diffraction line of the catalyst
in the XRD pattern at angle 25.3◦ in the difference
plot between coated and uncoated cordierite monolith

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J. Chem. Sci.
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Figure 2. Rietveld refined XRD pattern of Ti0.97Pd0.03O1.97 catalyst. There is no peak of Pd
metal or TiO−2 rutile phase, which confirms the formation of single phase Pd substituted catalyst.
Figure 3. Powder XRD patterns of (a) cordierite monolith, (b) catalyst coated over cordierite
monolith and inset figure showing a broad peak of (101) line of the catalyst. * (101) line of
Ti0.97Pd0.03O1.97
.
showninsetofFigure 3. Eachmonolithishavingparallel brown. Average crystallite size is 8 2 nm which was
channels of a square shape. Thus high surface area is calculated from half-width of (101) line of coated cata-
exposed to the reactants. The color of the catalyst is lyst (inset of Figure 3) using Scherrer formula (d = 0.9

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20
λ/β cosθ) in the powder and on the surface also a similar 3.1 Heck coupling reaction flask
size is expected because half width of the (101) peak is
of the same order.
Figure 4 shows the two-necked cylindrical flask with
diameter 3.5 cm and height 12 cm. Above 1.5 cm from
the bottom, the diameter of the flask is reduced to
make two separate compartments with a small passage
between them. The bottom space contained magnetic
bead and reaction mixture. Above the passage, the cat-
alyst coated honeycomb (HC) catalyst was placed. The
sufficient solvent was taken such that the HC catalyst
was submerged in the solvent. Condenser and argon-
filled balloon were fitted above the flask. The flask was
kept on preheated oil bath at temperature 110 ◦C. The
rotation speed of stirrer was high enough to circulate
reaction mixture with solvent through the HC catalyst.
3.2 Screening studies
Screening of the Heck coupling reaction was started
with the reaction of iodobenzene and methyl acrylate as
starting materials. Powder catalyst was used in each of
the screening reaction. 0.98 mmol (200 mg) of Iodoben-
zene and 1.1 equivalent of methyl acrylate were taken.
Figure 4. Specially designed reaction flask for Heck cou-
pling reaction with the reaction mixture and coated honey-
comb catalyst.
Table 1. Screening of the reaction.
Entry
Base
Solvent
Time (h)
Temp. (◦C)
Yield (%)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
–
Acetonitrile
DMSO
DMF
1,4-Dioxane
THF
NMP
Toluene
DMF
4
4
1.5
4
4
4
4
2
2
2
2
2
2
2
2
8
1
1
110
110
110
110
110
110
110
110
110
110
110
110
110
80
60
RT
110
110
110
110
Nil
20
> 99(95b)
Nil
Trace
35
Nil
Trace
34
97
30
Nil
93
16
Cs2CO3
NEt3
CH3COONa
t-BuONa
KOH
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Trace
Trace
> 99c(92b)
> 99d(94b)
93e
2
2
92f
Reaction conditions: 1 equivalent (200 mg) of Iodobenzene, 1.1 equivalent of Methyl acrylate, 1.5 equivalent of base, 3 mL
b
of solvent, 5 weight % of powder catalyst, temperature at 110 ◦C, under Ar atmosphere. All are GC yield. Isolated yield,
d
e
f
c50mg of catalyst coated over monolith, 100 mg of catalyst coated over catalyst, 0.5 equivalent of base, 1 equivalent of
base. The converted reactions that are complete are given in bold.

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Table 2. Substrate scope of the reaction.
Time Yield
TOF
(h-1)
Entry
Aryl halide
Olefins
Product
(h)
(%)
1.
4
98
159
129
2.
5
99
3.
4.
6
5
80
91
81
110
5.
6.
6
2
80
92
81
299
7.
8.
9.
3
1
2
70
95
85
141
660
296
10.
11.
12.
1.5
6
98
70
73
454
105
150
6
13.
7
69
89

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20
Table 2. (contd.)
Time Yield
(h) (%)
TOF
(h-1)
Entry
Aryl halide
Olefins
Product
14.
7
8
3
90
91
45
15.
50
16.
17.
18.
91
211
463
348
1.5
2
100
100
19.
20.
21.
2
3
3
56
83
88
195
165
175
22.
4
75
112
Reaction condition: 1 equivalent (2g) of aryl halide, 1.1 equivalent of olefins,
1.5 equivalent of K2CO3 as base, 20 mL of DMF as solvent, 50 mg catalyst coated
over honeycomb monolith, temperature at 110 ◦C, under Ar atmosphere. All are
isolated yield.
TOF = [(No. of moles of product/ No. of moles of active site of catalyst)]/time
in hours.
10 mg of catalyst was used which contains 3.7 μmol done at 80 ◦C, 60 ◦C and at room temperature, the yields
of Pd2+ ion. Initially, solvent study was carried where were very low. So we have decided to keep DMF as a
different solvents were used for the reaction. Except for solvent, 1.5 equivalent of K2CO3 as base and tempera-
the reaction in N, N-dimethyl formamide (DMF) as a tureat110 ◦CasstandardreactionconditionfortheHeck
solvent, all other reactions with different solvents have coupling reaction. We have also tried the reaction with 1
given almost negligible yield. Time of the reaction with and0.5equivalentofK2CO3 andobservedslightlylesser
solvent DMF was 90 min at temperature 110 ◦C using yield compared to 1.5 equivalent of base. We have done
K2CO3 (1.5 equivalent) as a base. We tried the reaction two more reactions using honeycomb monolith catalyst
without base and resulted with a trace amount of yield. where, one monolith was coated with 100 mg catalyst,
Then we investigated the reaction with 1.5 equivalent of another with 50 mg of catalyst. 2 g of iodobenene was
different bases such as Cs2CO3, NEt3, CH3COONa, t- used as starting material. Both the reactions were ended
BuONa and KOH, the reaction with NEt3 and KOH have up with yield more than 99%. Interestingly, the time
ended up with very good yield same as that of K2CO3. taken for these two reactions was just one hour. Com-
Next step of screening was temperature; reactions were pared to the reactions with powder catalyst, honeycomb

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Figure 5. Flowchart of recycling of HC monolith catalyst in the Heck coupling reaction.
monolith catalyst shown faster rate. Finally, we decided is highest among all other substrates. Substrate scope
to coat 50 mg of catalyst over cordierite monolith for of aryl bromides were also done, yields were above
the remaining reactions. The screening of Heck cou- 50% in case of aryl bromides, but the time taken for
pling reactions is summarised in Table 1.
the reactions were about 6 to 8 h. Because of less reac-
tivity of bromides, the TOF were low compared to iodo
substrates (Table 2, entry 11–15). Finally 1 – chloro –
4 – iodobenzene reacted with different olefins (Table 2,
entry 20–22), reaction were ended up with more than
75% yield by substitution at iodo position and chlorides
remained as it is in the product which is confirmed by
mass spectra. All products were isolated and found to be
trans from 1H NMR. The catalyst was well-tolerated to
different varieties of aryl halides and olefins. Reaction
with aryl iodide ended up with very good yield com-
pared to aryl bromide.
3.3 Substrate scopes
22 substrates of aryl halides and olefins were used for
substrate scope of the Heck coupling reaction listed in
Table 2. We have used optimized condition that is 1
equivalent of aryl halide (2 g), 1.1 equivalent of olefins,
1.5 equivalent of K2CO3 as a base and 20 mL of DMF
as a solvent. About 50 mg of catalyst was coated on
cordierite monolith and every reaction was done with
the coated catalyst. Substituted aryl iodide compounds
showed very good reactivity towards olefins despite hav-
ing electron-withdrawing and electron-donating groups
(Table 2, entry 1–7); the time taken for the reaction
3.4 Recycling of the catalyst
was about 5 h. The reaction between un-substituted We have carried out the recycling of the catalyst for sev-
iodobenzene showed very high reactivity (Table 2, entry eral cycles. Iodobenzene (2 g) and methyl acrylate (1.1
8–10, 16–18) towards different olefins with very high equiv.) were taken as starting materials by employing
TOF. The TOF of the reaction between iodobenzene standard conditions. The whole process of recycling the
and methyl acrylate was found to be 660 h−1 which HC monolith catalyst is depicted in Figure 5. After each

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20
and the oxide ion vacancy is electro rich. The active site
in the catalyst is Pd2+ ion. There was no Heck reaction
on pure TiO2 which means that neither Ti4+ nor O2− is
the active sites in the catalyst. Olefins bind with Pd2+
ions because olefins can donate π electrons and thus
becomes a normal site for the adsorption of olefin. –I
or –Br of aryl halides that are accommodated on oxide
ion vacancy of the catalyst. Here oxide ion vacancy acts
as a nucleophile. HI is eliminated with the help of base,
which leads to C–C coupling.
4. Conclusions
Figure 6. Recycling of the catalyst by employing standard
reaction condition.
In summary, we have developed a new class of catalyst
for the C–C coupling reaction. This method is environ-
mentally friendly without using any toxic catalyst or
reagents. This reaction tolerates a variety of functional
groups. Reactions were done using catalyst coated over
cordierite monolith by a unique method, which is also
helpful for recovering the catalyst.
Supplementary Information (SI)
Supplementary information is available at www.ias.ac.in/
chemsci.
References
1. Beletskaya I P and Cheprakov A V 2000 The Heck Reac-
tion as a Sharpening Stone of Palladium Catalysis Chem.
Rev. 100 3009
2. Reetz M T, Lohmer G and Schiwikardi R 1998 A new
catalyst for the Heck reaction of unreactive aryl halides
Angew. Chem. Int. Ed. 1 37 481
Figure 7. The mechanism for Heck coupling reaction with
Ti0.97Pd0.03O1.97 catalyst.
3. Heck R F 1968 Arylation, Methylation, and Carboxy
alkylation of Olefins by Group VIII Metal Derivatives J.
Am. Chem. Soc. 90 5518
4. Yin L and Liebscher J 2007 Carbon-Carbon coupling
reactions catalysed by heterogeneous palladium cata-
lysts Chem. Rev. 107 133
5. Lin B, Huang S, Wu W, Mou C and Tsai F 2010
Sonogashira reaction of aryl and heteroaryl halides with
terminal alkynes catalyzed by a highly efficient and recy-
clable nanosized MCM-41 anchored palladium bipyridyl
complex Molecules 15 9157
6. Biajoli A F P, Schwalm C S, Limberger J, Claudino T S
and Monteiro A L 2014 Recent progress in the use of Pd-
catalyzed C–C cross-coupling reactions in the synthesis
of pharmaceutical compounds J. Braz. Chem. Soc. 25
2186
cycle, the used monolith was taken out from the reac-
tion flask and washed with distilled water to remove base
and solvent, then washed with hexane to remove organic
impurities. Washed monolith was dried in a hot air oven
at a temperature 200 ◦C for 2 h. Dried monolith was
reused for another reaction. We obtained 100% yield up
to 6th cycle and in the 7th cycle, we observed a drop in
the yield to 85%. The recycling chart of the catalyst is
given in Figure 6. The reaction time up to 6th cycle was
1 to 3 h and in 7th cycle, reaction time was 14 h. Total
TOF after 7 cycles of the reaction was 3017 h−1.
3.5 Mechanism for the Heck coupling reaction
7. Magano J and Dunetz J R 2011 Large-Scale Applica-
tions of Transition Metal-Catalysed Couplings for the
Synthesis of Pharmaceuticals Chem. Rev. 1112177
8. Roughley S D and Jordan A M 2011 The medicinal
chemist’s toolbox: An analysis of Reactions used in the
pursuit of drug candidates J. Med. Chem. 54 3451
A mechanism is proposed for the Heck coupling reac-
tion with Ti0.97Pd0.03O1.97 catalyst is given in Figure 7.
The catalyst is Ti0.97Pd0.03O1.97 where for every Pd2+ ion
there is an oxide ion vacancy. Pd ion is electron deficient

20 Page 10 of 10
J. Chem. Sci.
(2019) 131:20
9. Nicolaou K C, Bulger P G and Sarlah D 2005 Palladium- 21. Liu W, Wang D, Duan Y, Zhang Y and Bian F 2015
Catalysed Cross-Coupling Reactions in Total Synthesis
Angew. Chem. Int. Ed. 44 4442
10. Denmark S E and Hurd A R 2000 Synthesis of (+)-
Casuarine J. Org. Chem. 65 2875
Palladium supported on poly (ionic liquid) entrapped
magnetic nanoparticles as a highly efficient and reusable
catalyst for the solvent-free Heck reaction Tetrahedron
Lett. 56 1784
11. Häberli A and Leumann C J 2001 Synthesis of Pyrroli- 22. Sanjaykumar S R, Mukri B D, Patil S, Madras G and
dine C-Nucleosides via Heck Reaction Org. Lett. 3 489
12. de Vries A H M, Mulders J M C A, Mommers J H
M, Henderickx H J W and de Vries J G 2003 Home-
Hegde M S Ce0·98Pd0·02O2−δ: Recyclable, ligand free
palladium(II) catalyst for Heck reaction 2011 J. Chem.
Sci. 123 47
opathic Ligand-Free Palladium as a Catalyst in the Heck 23. Mpungose P P, Vundla Z P, Maguire G E M and
Reaction. A Comparison with a Palladacycle Org. Lett. 5
3285
13. Crisp G T 1998 Variations on a theme—recent develop-
Friedrich H B 2018 The Current Status of Heterogeneous
Palladium Catalysed Heck and Suzuki Cross-Coupling
Reactions Molecules 23 1676
ments on the mechanism of the Heck reaction and their 24. Lakshminarayana B, Mahendar L, Ghosal P, Sreedhar B,
implications for synthesis Chem. Soc. Rev. 27 427
14. Dieck H A and Heck R F 1974 Organophosphinepal-
ladium Complexes as Catalysts for Vinylic Hydro-
Satyanarayana G and Subrahmanyam C 2018 Fabrica-
tion of Pd/CuFe2O4 hybrid nanowires: a heterogeneous
catalyst for Heck couplings New J. Chem. 42 1646
gen Substitution Reactions J. Am. Chem. Soc. 96 25. Lakshminarayana B, Mahendar L, Ghosal P, Satya-
1133
narayana G and Subrahmanyam C 2017 Nano-sized
Recyclable PdO Supported Carbon Nanostructures for
Heck Reaction: Influence of Carbon Materials Chem-
istrySelect 2 2700
15. (a) Littke A F and Fu G C 1999 Heck Reactions in the
Presence of P(t − Bu)3: Expanded Scope and Milder
Reaction Conditions for the Coupling of Aryl Chlorides
J. Org. Chem. 64 10; (b) Littke A F and Fu G C 2001 A 26. Nagaveni K, Hegde M S and Madras G 2004 Structure
Versatile Catalyst for Heck Reactions of Aryl Chlorides
and Aryl Bromides under Mild Conditions J. Am. Chem.
Soc. 123 6989
and Photocatalytic Activity of Ti1−xMxO2−δ (M = W, V,
Ce, Zr, Fe, and Cu) Synthesized by Solution Combustion
Method J. Phys. Chem. B 108 20204
16. Yang C, Lee H M and Nolan S P 2001 Highly Efficient 27. HegdeMS, NagaveniKandRoyS2005Synthesis, struc-
Heck Reactions of Aryl Bromides with n-Butyl Acrylate
Mediated by a Palladium/Phosphine-Imidazolium Salt
System Org. Lett. 3 1511
ture and photocatalytic activity of nano TiO2 and nano
Ti1−xMxO2− (M = Cu, Fe, Pt, Pd, V, W, Ce, Zr) Pra-
δ
mana – J. Phys. 65 641
17. Xu L, Chen W and Xiao J 2000 Heck Reaction in Ionic 28. Mukri B D, Dutta G, Waghmare U V and Hegde M S
Liquids and the in Situ Identification of N-Heterocyclic
Carbene Complexes of Palladium Organometallics 19
1123
2012 Activation of Lattice Oxygen of TiO2 by Pd2+ Ion:
Correlation of Low-Temperature CO and Hydrocarbon
Oxidation with Structure of Ti1−xPdxO2−x (x = 0.01-
0.03) Chem. Mater. 24 4491
18. Garrett C E and Prasad K 2004 The Art of Meet-
ing Palladium Specifications in Active Pharmaceutical 29. Hegde M S, Madras G and Patil K C 2009 Noble Metal
Ingredients Produced by Pd-Catalyzed Reactions Adv.
Synth. Catal. 346 889
19. Sobhani S and Pakdin-Parizi Z 2014 Palladium-DABCO
complex supported on -Fe2O3 magnetic nanoparticles:
A new catalyst for C – C bond formation via Mizoroki–
Ionic Catalysts Acc. Chem. Res. 42 704
30. Sharma S and Hegde M S 2009 Ti0.99Pd0.01O2−δ: A New
Pt-free Catalyst for High Rates of H2 + O2 Recombina-
tionwithHighCOTolerantCapacityChemPhysChem 10
637
Heck cross-coupling reaction Appl. Catal. A: Gen. 479 31. Mukri B D and Hegde M S 2017 High rates of catalytic
112
hydrogen combustion with air over Ti0.97Pd0.03O2−
δ
20. Rostamnia S and Kholdi S 2017 Synthesis of hybrid
coated cordierite monolith J. Chem. Sci. 129 1363
interfacial silica-based nanospheres composite as a sup- 32. Sharma S and Hegde M S 2006 Single step direct
port for ultra-small palladium nanoparticle and applica-
tion of PdNPs/HSN in Mizoroki-Heck reaction J. Phys.
Chem. Solids 111 47
coating of 3-way catalysts on cordierite monolith by
solution combustion method: High catalytic activity of
Ce0.98Pd0.02O2− Catal. Lett. 112 69
δ