Pd(II)-immobilized on a nanoporous triazine-based covalent imine framework for facile cyanation of haloarenes with K4Fe(CN)6

Article abstract of DOI:10.1016/j.mcat.2019.110395

A porous covalent organic framework incorporated with both imine and triazine functionalities (TPA-TCIF) was synthesized by Schiff-base condensation of 2,4,6-tris(4-aminophenyl)triazine and tris(4-formylphenyl)amine under the solvothermal condition of a 1-butanol:1,2-dichlorobenzene mixture. The resulting TPA-TCIF was a highly ordered crystalline network with surface area of 2938 m² g^?1, which was among the highest reported imine-based porous covalent organic frameworks. TPA-TCIF was also stable in water and other organic solvents. Pd(II) was immobilized into TPA-TCIF network and the resultant Pd/TPA-TCIF was tested as a catalyst for the additive-free cyanation of haloarenes with non-toxic K₄[Fe(CN)₆]. The catalyst showed excellent catalytic activity, and both electron-donating / -withdrawing groups attached to the para- and meta-positions of bromoarenes produced the respective nitriles with good to excellent yields. The catalyst could be reused up to five times without noticeable loss of activity or catalyst poisoning by cyanide ions during the reaction.

Full text of DOI:10.1016/j.mcat.2019.110395

MolecularCatalysis473(2019)110395
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Pd(II)-immobilized on a nanoporous triazine-based covalent imine
framework for facile cyanation of haloarenes with K4Fe(CN)6
Pillaiyar Puthiaraj, Kwangsun Yu, Sang Eun Shim, Wha-Seung Ahn⁎
Department of Chemistry and Chemical Engineering, Inha University, Incheon 402-751, South Korea
A R T I C L E I N F O
A B S T R A C T
Keywords:
A porous covalent organic framework incorporated with both imine and triazine functionalities (TPA-TCIF) was
synthesized by Schiff-base condensation of 2,4,6-tris(4-aminophenyl)triazine and tris(4-formylphenyl)amine
under the solvothermal condition of a 1-butanol:1,2-dichlorobenzene mixture. The resulting TPA-TCIF was a
highly ordered crystalline network with surface area of 2938 m2 g−1, which was among the highest reported
imine-based porous covalent organic frameworks. TPA-TCIF was also stable in water and other organic solvents.
Pd(II) was immobilized into TPA-TCIF network and the resultant Pd/TPA-TCIF was tested as a catalyst for the
additive-free cyanation of haloarenes with non-toxic K4[Fe(CN)6]. The catalyst showed excellent catalytic ac-
tivity, and both electron-donating / -withdrawing groups attached to the para- and meta-positions of bro-
moarenes produced the respective nitriles with good to excellent yields. The catalyst could be reused up to five
times without noticeable loss of activity or catalyst poisoning by cyanide ions during the reaction.
Covalent organic frameworks
Schiff-base networks
Palladium
Cyanation
Potassium ferrocyanide
1. Introduction
based COF-SDU-1 with surface area of 1052 m2 g−1 for a coupling re-
action of silanes and iodoarenes [23]. Esteves et al. reported Pd
Covalent organic frameworks (COFs) are composed of organic
building blocks having light-weight elements (C, B, O, N, and Si) in-
terconnected through strong covalent bonding. The COFs have unique
features of low skeleton density, permanent porosity with large surface
area, structural diversity originating from the selection of synthesis
precursors, surface hydrophobicity, and high chemical stability [1–3].
These interesting features make them useful in various applications:
catalysis [4,5], gas storage [6], sensors [7,8], optoelectronics [9], and
drug delivery [2]. COFs can be prepared by various organic reactions
such as Schiff-base formation [3,10,11], trimerization of nitriles [12],
boronate-ester formation [13], nucleophilic reaction [14,15], coupling
reaction [16], Friedel-Crafts reactions [17,18], and others [19–21].
Among these, Schiff-base chemistry creating the imine (C]N) linkage is
attracting increased attention owing to the simple condensation of al-
dehydes and amines without the addition of any metal catalyst and the
formation of a structure containing π-conjugated free lone-pair elec-
trons.
(OAc)2@COF-300 with surface area of 270 m2 g−1 for Suzuki-, Heck-,
and Sonogashira coupling reactions [24]. Bimetallic Rh(I)/Pd(II)-in-
corporated imine-based COF with surface area of 847 m2 g-1 was also
reported for the one-pot addition-oxidation tandem reaction [25]. Gao
et al. reported a bimetallic Mn/Pd-incorporated imine-based COF for
the Heck-epoxidation tandem reaction [26]. Similarly, Cu, Ag, and Ir
ions could also be immobilized on imine-based COFs as catalysts for
other organic reactions [3,10,27–30]. Most of the above-mentioned
COF supported materials, however, were amorphous and suffered from
low stability under the reaction conditions [10,22,24,27–29]. In com-
parison, porous crystalline frameworks with a higher density of lone-
pair electrons would be more appropriate for immobilization of tran-
sition metal ions and promoting the diffusion of reactants, in order to
augment the catalytic activity and improve the reusability [30].
Nitriles are a valuable class of building blocks in pharmaceuticals,
dyes, agrochemicals, and other organic products [31,32]. Traditional
routes for the synthesis of nitriles have been Rosenmund-von Braun
reaction [33] and Sandmeyer reaction [34] at a temperature > 150 °C
with stoichiometric amount of CuCN. Recently, Cu- and Ni-catalyzed
cyanations have also been employed with a variety of cyanide sources
(NaCN [31], KCN [35], HCN [36], Zn(CN)2 [37], CuSCN [38], and
(CH3)3SiCN [39]). Nevertheless, toxic and expensive cyanide source
Taking advantages of the free lone-pair electrons, some imine-based
COFs have been used as catalyst supports to anchor Pd(II) ions for
various organic transformations [22–26]. Thus, Ding et al. prepared
Pd/COF-LZU1 with surface area of 146 m2 g−1 and used it for Suzuki
coupling reaction [22]. Zhang et al. prepared a Pd(II)-grafted triazine-
⁎ Corresponding author.
E-mail address: whasahn@inha.ac.kr (W.-S. Ahn).
https://doi.org/10.1016/j.mcat.2019.110395
Received 12 March 2019; Received in revised form 2 May 2019; Accepted 6 May 2019
2468-8231/©2019ElsevierB.V.Allrightsreserved.

P. Puthiaraj, et al.
MolecularCatalysis473(2019)110395
and high temperature were required. To overcome these problems,
Beller et al. proposed a Pd-catalyzed cyanation with low-cost cyanide
source of K4[Fe(CN)6] [40,41]. A number of homogeneous Pd-complex
catalysts were tested for this reaction, but they required expensive li-
gands and suffered from the problems of non-reusability, tedious
workup, and metal contamination in the product [42–45]. To avoid
these difficulties, heterogeneous Pd-catalysts such as NHC-Pd polymer
[46], Pd@CuFe2O4 [47], IL@SBA-15-Pd [48], Pd-LHMS-3 [49], Pd/si-
lica [50,51] and Pd/C [52] were also reported recently for the cyana-
tion of haloarenes. However, often the active Pd metal species were
leached out of the catalyst, or severe agglomeration of Pd nanoparticles
in successive runs was observed, which limited the scope of the ap-
plicable substrates [46–48,50–52]. Therefore, the synthesis of a func-
tional crystalline carrier with high stability for supporting Pd(II) ions is
strongly desired for this reaction.
spectra (XPS) were obtained from a hemispherical analyzer (Thermo
Scientific, USA). Elemental analysis was done on a Thermo EA1112
(USA). Powder X-ray diffraction (XRD) were conducted using a Rigaku
(DMAX-2500) diffractometer using Cu Kα radiation (λ = 1.5418Å).
The nitrogen sorption experiment was conducted at 77 K using a
BELsorp-max analyzer (BEL, Japan). Before the analysis, the materials
were treated at 200 °C under high vacuum for 12 h. Field emission
scanning electron microscope (FESEM) and field emission transmission
electron microscope (FETEM) with energy-dispersive X-ray spectro-
metry (EDS) images were taken on a Hitachi S-4300 and a JEM-2100 F
(JEOL), respectively. The palladium content on the support was de-
termined by inductively coupled plasma-optical emission spectrometry
(ICP-OES; PerkinElmer Optima 7300DV, USA).
2.5. Catalytic cyanation of haloarenes
In this work, a robust crystalline COF containing imine and triazine
functionalities with desirable textural properties was synthesized via a
solvothermal reaction between 2,4,6-tris(4-aminophenyl)triazine
(TAPT) and tris(4-formylphenyl)amine (TFPA). After establishing its
high stability in various solvents, it was utilized as a carrier for an-
choring Pd(OAc)2. The catalytic performance of the Pd(II)-immobilized
COF was examined systematically in the cyanation of haloarenes, de-
monstrating excellent activity and recyclability.
Haloarene (1 mmol), Na2CO3 (1 mmol), K4[Fe(CN)6] (0.2 mmol),
Pd/TPA-TCIF (40 mg), and DMF (4 mL) were charged into a 15-mL ACE
pressure tube and capped, and then heated at 110 °C with constant
stirring. After 20 h, the catalyst was isolated by centrifugation and
washed with ethyl acetate and water. The filtered organic phase was
collected and the conversion of haloarene was measured using an
Agilent HP6890 model gas chromatography (GC) furnished with a
flame ionization detector and an HP-5 capillary column. Subsequently,
the organic phase was concentrated, and then the nitrile product was
purified using a silica gel column chromatography.
2. Experimental section
2.1. Materials
3. Results and discussion
4-aminobenzonitrile, triflic acid, TFPA, 1,2-dichlorobenzene, 1-bu-
tanol, acetic acid, anhydrous N,N’-dimethylformamide (DMF), K4[Fe
(CN)6]·3H2O, Pd(OAc)2, ethanol, methanol, and 1,2-dichloromethane
were obtained from Sigma-Aldrich (USA). All other chemicals and
solvents used in this study were collected from TCI (Japan) and Merck
(Korea), and all were used without further purification. TAPT was
prepared according to the published procedure [53], and the product
was confirmed by nuclear magnetic resonance (NMR) spectroscopy
(Fig. S1-S2).
3.1. Catalyst characterization
The covalent imine framework containing both triphenylamine and
triazine units (TPA-TCIF) was synthesized by the Schiff-base reaction
between TFPA and TAPT as described in Scheme 1. The reaction was
conducted in the presence of 3 M acetic acid using a mixture of 1-bu-
tanol/1,2-dichlorobenzene solvent mixture (3:1 by volume) at 120 °C
for 72 h. The synthesized material was insoluble and highly stable in
both water and organic solvents such as toluene, acetone, tetra-
hydrofuran, chloroform, DMF, DMSO, and acetonitrile (Fig. S3). The
successful growth of the TPA-TCIF network was confirmed using in-
frared spectroscopy, elemental analysis, solid-state NMR, powder XRD,
N2 sorption isotherm, XPS, and electron microscope techniques.
The infrared spectra of TPA-TCIF in Fig. 1(a), the C]O (1689
cm−1) and –NH2 (3208, 3325, and 3464 cm−1) stretching bands com-
pletely disappeared and a new characteristic strong stretching peak at
1578 cm−1 was present, indicating the formation of imine bond via
Schiff-base reaction of TFPA and TAPT. These two precursors were fully
consumed. According to the elemental analysis results, the experi-
mental values of C (79.77%), H (4.19%), and N (15.13%) in the TPA-
TCIF sample matched well to the theoretical contents of C (80.11%), H
(4.32%), and N (15.57%) with a maximum deviation of ⁓1% for
carbon.
2.2. Synthesis of TPA-TCIF
TFPA (1 mmol; 329 mg), TAPT (1 mmol; 354 mg), 3 M acetic acid
(1 mL), 1-butanol (6 mL), and 1,2-dichlorobenzene (2 mL) were charged
into a 15-mL ACE pressure tube and sealed off, and then heated at
120 °C. After 72 h, the solid product was collected by filtration and
washed several times with DMF and ethanol. Finally, the obtained
product was dried at 200 °C for 10 h under high vacuum condition. The
product of porous covalent imine framework incorporated with both
triphenylamine and triazine functionalities was designated as TPA-
TCIF.
2.3. Synthesis of Pd/TPA-TCIF
The Pd/TPA-TCIF catalyst was synthesized via impregnation of Pd
(OAc)2 into TPA-TCIF. In a typical procedure, Pd(OAc)2 (30 mg) was
dispersed in dichloromethane (30 mL). After adding TPA-TCIF (500 mg)
to the solution, the mixture was refluxed with stirring for 3 h. The Pd(II)
bound TPA-TCIF was collected by filtration and washed with di-
chloromethane and acetone to remove the excess Pd(OAc)2. Finally, the
product was dried at 60 °C in a vacuum for 1 h.
In solid-state NMR (Fig. 1(b)), it displayed a characteristic peak at
159.2 ppm, which was assignable to imine carbons. The other peaks at
173.0, 147.5, and ⁓128 ppm were assignable to the carbons in triazine,
nitrogen attached phenyl groups, and carbons from phenyl, respectively
[3]. The deconvoluted C 1s XPS (Fig. 2(a)) revealed five peaks at 284.2,
285.8, 287.8, 288.9, and 291.2 eV, ascribed to the aromatic C]C, C]
N, C–N, triazine carbon, and π-π* transition, respectively [54,55]. The
N 1s spectrum (Fig. 2(b)) displayed three deconvoluted peaks at 397.8,
399.0, and 400.7 eV, which can be ascribed to the nitrogen in triazine,
imine, and triphenylamine groups, respectively [55,56]. These NMR
and XPS results also clearly indicated the formation of the imine bond
and the presence of triphenylamine and triazine moieties in the TPA-
TCIF network.
2.4. Characterization of the COF host and the catalyst prepared
Fourier transform-infrared spectra were obtained from a Bruker
VERTEX 80 V spectrometer. Solid-state 13C cross polarization-magic
angle spinning NMR and liquid-state 1H and 13C NMR were measured
on a Bruker Avance III 400 MHz spectrometer. X-ray photoelectron
The porosity of the synthesized TPA-TCIF material was inspected by
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P. Puthiaraj, et al.
MolecularCatalysis473(2019)110395
Scheme 1. Synthesis of TPA-TCIF and subsequent Pd(II) immobilization.
Fig. 1. (a) Infrared spectra of TFPA, TAPT, and TPA-TCIF and (b) Solid-state 13C NMR of TPA-TCIF.
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MolecularCatalysis473(2019)110395
Fig. 2. XPS of (a) C 1s and (b) N 1s core level in TPA-TCIF.
Table 1
Textural properties of the synthesized Schiff-base COF materials.
Frameworks
SABET (m2 g−1
)
V0.1 (cm3 g−1
)
Vtot (cm3 g−1
)
V0.1/Vtot (%)
Pore width (nm)
TPA-TCIF
Fresh Pd/TPA-TCIF
Reused Pd/TPA-TCIF
2938
2647
2629
1.09
0.95
0.93
1.32
1.21
1.18
82.6
78.5
78.8
1.5, 1.7
1.5, 1.7
1.5, 1.7
SABET = BET surface area; V0.1 = pore volume at 0.10 bar; Vtot = pore volume at 0.99 bar.
Fig. 3. (a) N2 sorption isotherms and (b) pore size distributions of TPA-TCIF and fresh/reused Pd/TPA-TCIF catalyst.
N2 sorption isotherms at 77 K (Table 1). As illustrated in Fig. 3(a), TPA-
TCIF showed a type I isotherm with a steep N2 uptake at < 0.03 bar
pressure, implying the existence of micropores in the networks. There
was also a secondary sharp increase at ∼0.08 bar corresponding to
another type of uniform pores close to ca. 2 nm in size [57]. Practically
no hysteresis was observed here, and the increase in the adsorbed vo-
lume at pressure > 0.9 bar is due to N2 condensation in the inter-par-
ticulate voids [19]. The levels of microporosity in the TPA-TCIF was
79.6%, as estimated by the ratio of micropore volume to total pore
volume [58]. The Brunauer-Emmett-Teller (BET) surface area of TPA-
TCIF was 2938 m2 g−1 and pore volume of 1.32 cm3 g−1, which was
among the highest reported recently for imine-based porous COFs
[2,3,59–68], and it is close to the TpBD-Me2 (3109 m2 g−1) and TpAzo
(3038 m2 g−1) networks [69]. Fig. 3(b) shows the pore size of the fra-
meworks estimated by non-local density functional theory with slit pore
geometry. TPA-TCIF was mainly microporous with uniform pores of 1.5
and 1.7 nm in size.
c = 3.94Å. The broad peak of (001) plane is due to the π-π stacking
between the framework layers [62]. The d-spacings between the planes
were calculated from the powder XRD pattern (Fig. 4) using the Bragg
equation (1).
(1)
nλ = 2d sinθ
where, λ = 1.5418Å, n = integer (here n = 1). The d100, d210, d200
,
d310, and d001 values for TPA-TCIF were estimated to be 19.90, 11.54,
9.96, 7.54, and 3.94Å, respectively.
The morphology of the synthesized TPA-TCIF was examined using
electron microscope techniques. FESEM image of TPA-TCIF (Fig. 5(a))
displayed a cauliflower-like morphology. FETEM image of TPA-TCIF
(Fig. 5(b)) showed a parallel aligned planar plate-like structure with a
uniform pore diameter.
The highly crystalline TPA-TCIF with a large surface area and high
nitrogen content was tested as support to stabilize a Pd salt for the
catalytic application. Pd/TPA-TCIF was prepared by treatment of Pd
(OAc)2 with TPA-TCIF in dichloromethane under reflux condition with
constant stirring for 3 h (Scheme 1). The powder XRD of Pd/TPA-TCIF
(Fig. 4) displayed the same peaks as TPA-TCIF, indicating that the TPA-
TCIF framework remained intact after the impregnation. The Pd 3d XPS
results of Pd/TPA-TCIF catalyst showed two de-convoluted peaks
The powder X-ray diffraction (Fig. 4) of TPA-TCIF displayed a
strong intense peak at 4.44° and additional weak peaks at 7.66, 8.88,
11.74, and 22.54°, which corresponded to (100), (210), (200), (310),
and (001) reflections of hexagonal 2D honeycomb-type framework,
respectively [68], with unit cell parameters a = b = 19.90Å and
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MolecularCatalysis473(2019)110395
FETEM image of Pd/TPA-TCIF (Fig. 5(c)) did not show any Pd(0) na-
noparticles formation, but the FETEM elemental mapping (Fig. 5(d))
showed the presence of C, N, and Pd species with uniform dispersion,
which indicate that the Pd2+ ions were successfully grafted on the TPA-
TCIF support. The surface area (2647 m2 g−1) of the Pd/TPA-TCIF
catalyst decreased a little compared to those of the pristine support
material, caused by the partial filling of Pd(OAc)2. The palladium
loading on TPA-TCIF was estimated to be 1.16 wt% by ICP-OES.
3.2. Cyanation of haloarenes over Pd/TPA-TCIF
The prepared Pd/TPA-TCIF was then explored as a heterogeneous
catalyst for the cyanation of haloarenes. Iodoarene has been widely
reported as a substrate for the homogeneous palladium-catalyzed cya-
nation reactions. However, it is not practical for industrialization due to
the need for expensive ligands, difficult product separation from the
reaction mixture, non-reusability, and the higher price of iodoarene
than bromo-/chloro-arenes [42,45]. Therefore, a reusable Pd-catalyst
for the cyanation reaction of low-cost bromoarene substrates will be
preferable. With these in mind, 4-bromoanisole and K4[Fe(CN)6] were
used as the model substrate and the cyanating agent, respectively, for
the cyanation reaction (Table 2). A series of the experiments were
conducted to locate the optimum reaction conditions that maximize the
yield of nitrile products. No product was detected in the presence of
TPA-TCIF support alone (40 mg) and K2CO3 (1 mmol) as a base in DMF
at 110 °C (Table 2, entry 1). The homogeneous Pd(OAc)2 gave only a
22% yield of 4-methoxybenzonitrile product (Table 2, entry 2). In
contrast, Pd/TPA-TCIF catalyst gave 79% yield of nitrile product
Fig. 4. Powder X-ray diffraction patterns of TPA-TCIF and Pd/TPA-TCIF cata-
lyst (fresh and reused).
centered at 336.8 and 341.9 eV, which were assigned to the Pd 3d5/2
and Pd 3d3/2 levels, respectively (Fig. 6(a)) [70]. In addition, the peak
of imine bond N 1s peak was shifted from 399.0 to 399.7 eV after in-
corporation of Pd(OAc)2 (Fig. 6(b)), which is probably due to the in-
teraction between the support nitrogen atom and the palladium salt.
Fig. 5. (a) FESEM and (b) FETEM images of TPA-TCIF, (c) FETEM image of Pd/TPA-TCIF and (d) EDS mapping images for C, N, and Pd elements of Pd/TPA-TCIF.
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P. Puthiaraj, et al.
MolecularCatalysis473(2019)110395
Fig. 6. (a) Pd 3d and (b) N 1s XPS of Pd/TPA-TCIF.
Table 2
(K2CO3, K3PO4, and NaOAc) or organic (TEA, and DBU) bases (Table 2,
entries 3, 13–17). The product yield decreased to 60% as the Na2CO3
amount was reduced to 0.5 mmol (Table 2, entry 18). The reaction
temperature and catalyst loading also strongly influenced the cyanation
reaction. When the temperature dropped from 110 to 100 °C, the pro-
duct yield was also decreased from 98% to 74% (Table 2, entry 19) and
further decreasing the temperature to 80 °C led to no cyanation product
(Table 2, entry 20), implying that the release of cyanide ion from K4[Fe
(CN)6] is difficult at low temperatures. K4[Fe(CN)6] shows low solubi-
lity in organic solvents and therefore high energy is required to dis-
sociate the ferrocyanide anion [32,72]. Similarly, when the catalyst
loading was decreased from 40 to 30 and 20 mg, the product yield
decreased from 98% to 77% and 53% (Table 2, entries 21–22). The
kinetics profile (Fig. 7(a)) revealed that the product yield gradually
increased and reached a maximum after 20 h. From these screening
experiments, the optimal condition for the cyanation of 4-bromoanisole
(1 mmol) was established to be Pd/TPA-TCIF catalyst (40 mg), Na2CO3
(1 mmol), K4[Fe(CN)6] (0.2 mmol), DMF (4 mL) at 110 °C for 20 h.
The cyanation reaction of a variety of substituted haloarenes under
the optimal condition (Table 3) was also examined. Both electron-do-
nating / -withdrawing groups attached to the para- and meta-positions
of bromoarenes produced the respective nitriles with good to excellent
yields (Table 3, entries 1–9). Notably, 1,4-dibromobenzene was suc-
cessfully converted to dicyanobenzene with 93% yield (Table 3, entry
10). The sterically hindered ortho-substituted and bulky substrates were
also converted with ⁓82% yield of the corresponding nitriles (Table 3,
entries 11–13). Further, catalytic runs of the less-active chloroarenes at
110 °C with longer reaction time produced nitriles with moderate yields
(Table 3, entries 14–16). The prepared aryl nitriles were confirmed by
NMR (Fig. S4-S27).
In order to check the heterogeneity of the Pd/TPA-TCIF catalyst,
both hot filtration test and recycling experiment were conducted using
4-bromoanisole under the optimal conditions. In the hot filtration test
(Fig. 7(a)), the catalyst was isolated by filtration after 8 h of reaction
(with 48% of 4-methoxybenzonitrile formation) under hot condition,
and the filtrate was kept at 110 °C for the remaining reaction time
(12 h). Upon termination of the reaction, no further increase in the
yield of 4-methoxybenzonitrile product was detected by GC. In addi-
tion, only a practically negligible amount of Pd (1.2 ppm) was detected
in the filtrate by ICP-OES. In the recycling studies (Fig. 7(b)), the cat-
alyst was recovered after the 1st run, washed with ethyl acetate and
water, and dried under vacuum condition at 100 °C for 2 h before
adding the recovered catalyst to a new reaction cycle. There was only a
negligible drop in the activity for up to five successive cycles. After
recycling, the catalyst was confirmed to retain its high crystallinity
(Fig. 4), large BET surface area (2629 m2 g−1, Fig. 3(a)), and the de-
convoluted Pd(II) binding energy peaks at 336.9 and 342.0 eV in Pd 3d
XPS data (Fig. 6(a)). These results confirmed that the crystalline Pd/
Studies of reaction conditions in the cyanation of 4-bromoanisole.a
Entry
Catalyst
Base
Solvent
GC yield (%)
1
TPA-TCIF
Pd(OAc)2
Pd/TPA-TCIF
Pd(OAc)2/TPA-
TCIF
K2CO3
K2CO3
K2CO3
K2CO3
DMF
DMF
DMF
DMF
Nil
22
79
61
2b
3
4c
5
6
7
8
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
Pd/TPA-TCIF
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
–
Na2CO3
K3PO4
NaOAc
TEA
1,4-Dioxane
tBuOH
MeCN
DMSO
Water
DMF:water
Toluene
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
Trace
6
Trace
62
Nil
28
Nil
7
98
30
67
12
14
60
74
Nil
77
9
10
11
12
13
14
15
16
17
18d
19e
20f
21g
22h
DBU
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
53
a
Reaction conditions: 4-bromoanisole (1 mmol), Pd/TPA-TCIF (40 mg), base
(1 mmol), K4[Fe(CN)6] (0.2 mmol), solvent (4 mL) 110 °C, 20 h.
b
Pd(OAc)2 (1 mg; 0.0045 mmol Pd).
TPA-TCIF (40 mg), Pd(OAc)2 (1 mg).
Na2CO3 (0.5 mmol).
100 °C.
80 °C.
Pd/TPA-TCIF (30 mg).
Pd/TPA-TCIF (20 mg).
c
d
e
f
g
h
(Table 2, entry 3), suggesting that the Pd anchored on TPA-TCIF is the
catalytic active species in the present cyanation reaction. When the
reaction was conducted with a mixture of Pd(OAc)2 and TPA-TCIF in-
stead of Pd/TPA-TCIF, a 61% yield of nitrile product was detected
(Table 2, entry 4).
Among the various polar (1,4-dioxane, tBuOH, MeCN, DMSO, DMF,
water, and DMF-water) and non-polar (toluene) solvents tested
(Table 2, entries 3, 5–11), cyanation proceeded well only in DMF. In the
absence of any base, a very low 4-bromoanisole conversion (7%) was
detected (Table 2, entry 12) because the base is crucial in the dehalo-
genation step [36,71]. Na2CO3 was better than another inorganic
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P. Puthiaraj, et al.
MolecularCatalysis473(2019)110395
Fig. 7. (a) GC yield of 4-methoxybenzonitrile as a function of reaction time and hot filtration test and (b) catalyst recycling studies for the cyanation of 4-bro-
moanisole over Pd/TPA-TCIF.
Acknowledgments
Table 3
Aromatic cyanation of haloarenes over Pd/TPA-TCIF.a
This research was supported by the Basic Science Research Program
through the National Research Foundation of Korea (NRF) funded by
the Ministry of Education (2015R1A4A1042434). PP acknowledges the
support by the Korea Research Fellowship program funded by the
Ministry of Science and ICT through the National Research Foundation
of Korea (2017H1D3A1A02013620).
Entry Haloarenes
Product
GC yield TON
(%)
1
2
3
4
5
6
7
Bromobenzene
4-Bromoanisole
4-Bromotoluene
4'-Bromoacetophenone
1-Bromo-4-nitrobenzene
4-Bromobenzonitrile
4-Bromobenzotrifluoride
Benzonitrile
99
98
95
97
99
100
96
230
228
221
226
230
233
223
4-Methoxybenzonitrile
4-Methylbenzonitrile
4'-Cyanoacetophenone
4-Nitrobenzonitrile
1,4-Dicyanobenzene
4-(Trifluoromethyl)
benzonitrile
4-Formylbenzonitrile
3-Methylbenzonitrile
1,4-Dicyanobenzene
2-Methylbenzonitrile
Appendix A. Supplementary data
Supplementary material related to this article can be found, in the
online version, at doi:https://doi.org/10.1016/j.mcat.2019.110395.
8
9
4-Bromobenzaldehyde
3-Bromotoluene
94
91
93
84
82
86
59
64
63
219
212
216
195
191
200
137
149
147
10b
11
12
13
14c
15c
16c
1,4-Dibromobezene
2-Bromotoluene
2,4-dimethylbromobenzene 2,4-Dimethylbenzonitrile
2-Bromonaphthalene
Chlorobenzene
4-Chloroanisole
4-Chlorotoluene
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4-Methoxybenzonitrile
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8