Pd(II)–acylthiourea complex and its immobilized counterpart catalyzed condensation of phenylacetylene with aryl halides

Article abstract of DOI:10.1016/j.inoche.2019.107695

New Pd(II) complex, trans-[PdCl₂L₂] (1) (L = N-carbamothioylthiophene-2-carboxamide), was prepared and characterized. Its heterogeneous counterpart, trans-[PdCl₂(L-SNPs)₂] (2) (L-SNPs = ligand immobilized on silica nanoparticles), was also prepared through covalent modification of the ligand using silica nanoparticles and characterized. Both 1 and 2 were exploited for their catalytic activity towards condensation of phenylacetylene with aryl halides. The complexes exhibited good activity when aryl halide bears I^? or Br^? group. Further, catalyst 2 can be reused for four cycles.

Full text of DOI:10.1016/j.inoche.2019.107695

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Pd(II)-acylthiourea complex and its immobilized counterpart catalyzed con-
densation of phenylacetylene with aryl halides
D. Sindhuja, P. Vasanthakumar, R. Karvembu
PII:
S1387-7003(19)31073-1
DOI:
https://doi.org/10.1016/j.inoche.2019.107695
INOCHE 107695
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21 November 2019
Please cite this article as: D. Sindhuja, P. Vasanthakumar, R. Karvembu, Pd(II)-acylthiourea complex and its
immobilized counterpart catalyzed condensation of phenylacetylene with aryl halides, Inorganic Chemistry
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Pd(II)‒acylthiourea complex and its immobilized counterpart catalyzed
condensation of phenylacetylene with aryl halides
D. Sindhuja, P. Vasanthakumar, R. Karvembu*
Department of Chemistry, National Institute of Technology, Tiruchirappalli 620015, India
Abstract
New Pd(II) complex, trans-[PdCl2L2] (1) (L = N-carbamothioylthiophene-2-carboxamide),
was prepared and characterized. Its heterogeneous counterpart, trans-[PdCl2(L-SNPs)2] (2)
(L-SNPs = ligand immobilized on silica nanoparticles), was also prepared through covalent
modification of the ligand using silica nanoparticles and characterized. Both 1 and 2 were
exploited for their catalytic activity towards condensation of phenylacetylene with aryl
halides. The complexes exhibited good activity when aryl halide bears I‒ or Br‒ group.
Further, catalyst 2 can be reused for four cycles.
Keywords: Palladium complexes; Acylthiourea ligand; Silica nanoparticles; Heterogeneous
catalysis; Phenylacetylene; Aryl halides
__________
* Corresponding author. Tel.: +91 431 2503636; fax: +91 431 2500133.
E-mail address: kar@nitt.edu (R. Karvembu).

Pd-catalyzed coupling reactions are versatile in the aspect of single-step formation of C-C
bond. The essential role of Pd assisted coupling in contemporary organic chemistry has been
recognized with the Nobel Prize [1,2]. Sonogashira coupling is one such reaction in which a
bond is formed between sp2 and sp hybridized carbons of aryl halide and terminal alkyne
respectively[3]. The synthesized alkyne derivatives constitute the backbone of many natural
products, pharmaceutically relevant compounds, sensors etc [4-6]. Although the literature
reports suggested that the coupling proceeded in the presence of catalytic amount of Cu along
with Pd, self-coupling of copper acetylinide species under O2 atmosphere was also seen [7,8].
In recent years, there have been considerable efforts to avoid the use of Cu and extend the
scope of Pd to various aryl halides [9,10]. Since the discovery of Sonogashira reaction, much
attention has been paid to the Pd catalysts containing NHC, phosphine, salen, etc. ligands,
and ligand/Cu-free systems [11-13]. Many heterogeneous catalytic systems like Pd/SiO2
[14,15], magnetic nanoparticles [16,17], MOFs [18], melamine network [19], Cu/Pd alloy
system on reduced graphene oxide [20] etc. were also reported. The coupling reaction was
also carried out in the presence of non-Pd equivalents like Au/SiO2 along with copper ferrite
nanoparticles [21].
Due to high activity and selectivity in catalytic processes, many organometallic
compounds of Pd [22], Ru [23], Rh [24] and Ir [25] were used as homogeneous catalysts for a
variety of organic transformations. But commercialization has happened only to a little extent
due to lack of reusable property. Heterogeneous catalysts are playing a major role in many
industrially relevant processes because of their easy separation and reusability.
Heterogeneous catalyst can be metal nanoparticles [26,27], nanoparticles doped on inert
support [28], MOFs [29-31], immobilized homogeneous catalyst [32–34] etc. Immobilization
of an active complex is an interesting strategy, which enable recovery of the catalyst from the
reaction medium [35-38]. Pd complexes were known for their superior catalytic and
biological activities [39-41]. To the best of our knowledge, there is no immobilized Pd
complex of acylthiourea ligand reported for the condensation of phenylacetylene with aryl
halide. Hence, we have prepared Pd(II)-acylthiourea complex which was then immobilized
on SiO2 nanoparticles (SNPs). Catalytic efficacy of both the complexes (homogeneous and
heterogeneous) has been studied in the condensation of phenylacetylene with aryl halide.
SNPs were used as a support since they are inert, have high surface area and can be easily
functionalized.

Synthesis and characterization of the ligand (L) were reported by us earlier [42].
Treatment of 2 equiv. of L with 1 equiv. of PdCl2 in CH3CN resulted the Pd complex (1) as
orange coloured precipitate (Scheme 1) [43]. Complex is stable in air, non-hygroscopic,
soluble in DMF, DMAc and DMSO, and insoluble in CHCl3, CH2Cl2 and H2O.
SNPs were activated and functionalized with L to give L-SNPs by following the
reported procedure [42]. PdCl2 (1 mmol) was added to L-SNPs (0.2 g) in dry acetone, and the
reaction mixture was stirred for 8 h under N2 atmosphere. The resulting solid was
centrifuged, washed with distilled water, dry acetone and dry ethanol, and dried at 100 ꢀC
under vacuum for overnight to get 2 (Scheme 2).
Sche
me 1
Synt
hesis
of 1
Sche
me 2
Synthesis of 2
UV-visible spectrum of 1 showed two bands at 264 and 296 nm, which may be
attributed to the ligand centred transitions. The FT-IR spectrum showed the presence of N-H,
NH2, C=O and C=S groups. The stretching frequencies at 3332, 3182 and 3203 cm-1
corresponded to NH2 and N-H moieties respectively. The C=O and C=S stretching occurred

at 1673 and 1251 cm-1 respectively. The reduction in C=S stretching frequency and un-
alteration of other frequencies compared to the ligand supported the coordination of ligand to
1
Pd via S atom only. In the H NMR spectrum (Figure S1), signals due to N-H (11.84 ppm)
and NH2 (10.46 and 10.21 ppm) protons appeared in the deshielded region as singlets. Also,
protons of the thiophene ring showed signals at 7.07-8.30 ppm. 13C NMR spectrum of 1
(Figure S2) showed signals due to C=O and C=S carbons at 161.69 and 177.85 ppm
respectively. Similarly, aromatic carbons in the thiophene ring resonated in the region
129.28-136.57 ppm. Molecular ion peak at 476.8804 [M-2Cl-H]+ in the mass spectrum
confirmed the complex formation. From the above observations, Pd is believed to have
square planar geometry with two acylthiourea ligands (L) trans to each other. Our attempts to
crystallize the complex have failed, and hence characterization was limited to spectroscopic
techniques.
The protocol used for the immobilization of Pd(II) complex on SNPs is shown in
scheme 2. EDAX results obtained for 2 is shown in Figure S4; it showed the presence of
various elements along with Pd. The TEM images are shown in Figure S5. SNPs in 2 were
found to be in spherical shape. The Pd(II) complex was homogeneously dispersed on the
silica surface, which was seen as dark spots in the images. There was no change in the
morphology of the support even after its modification. Surface area of SNPs and 2 was found
to be 200 and 95 m2/g respectively. Reduction in the surface area of 2 confirmed the
immobilization of 1 on the surface of SNPs. N2 adsorption-desorption isotherm (Figure S5)
showed type IV hysteresis loop for SNPs, which is characteristic of mesoporous material.
XPS analyses of 2 showed binding energies at 338.4 and 343.7 eV corresponding to Pd 3d5/2
and Pd 3d3/2 respectively (Figure 1) [44]. These values were due to divalent Pd ions, and the
possibility of formation of Pd(0) on SNPs was ruled out as no binding energy was seen at 335
and 340 eV [45]. Also, 2 did not show binding energy at 336.4 eV corresponding to PdO,
confirming the presence of Pd(II) complex on SNPs [46,47]. In addition, binding energies at
534, 401, 283 and 102 eV were assigned to O 1s, N 1s, C 1s and Si 2p respectively. Pd
loading in 2 was 0.920 mmol/g as determined by ICP-OES analysis.

(a)
(b)
(e)
(c)
(d)
Fig. 1 XPS spectra of 2 (a) wide spectrum of 2, (b) Si 2p peak, (c) N 1s peak, (d) O 2s
peak and (e) Pd 3d peak
The results obtained for the condensation of phenylacetylene with different aryl
halides are summarized in Table 1. Scope of 1 (homogeneous) and 2 (heterogeneous) was
extended to various aryl halides bearing I or Br, and electron releasing or electron
withdrawing group, and heterocyclic halide under optimized reaction conditions (Table S1).
Iodobenzene was reacted with phenylacetylene in the presence of 1 or 2 to give 1,2-
diphenylethyne (100%) in 3 h (3a, Table 1). Similarly, Pd-catalyzed (1 or 2) coupling of 4-
iodoanisole with phenylacetylene formed the desired coupled product in 100% selectivity
(3b, Table 1). As expected, reactivity of aryl iodides was more than that of bromides. 5-
bromoindole was coupled with phenylacetylene to produce 5-(phenylethynyl)-1H-indole in
100% selectively, but the conversion (81%) was better with 2 compared to that (71%) with 1
(3c, Table 1). While using 1-bromo-4-iodobenzene along with phenylacetylene in the
presence of 1, 1-bromo-4-(phenylethynyl)benzene was obtained in good selectivity (100%)
(3e, Table 1). The reaction of 4-bromoacetopheneone with phenylacetylene in the presence of
1 yielded 1-(4-(phenylethynyl)phenyl)ethanone in 55% selectivity (3e, Table 1). In this case,
phenylacetylene underwent self-coupling and gave 1,4-diphenylbuta-1,3-diyne as a side
product. Similarly, catalytic activity of 2 was studied with 4-iodonitrobenzene and
phenylacetylene; the reaction proceeded smoothly to offer 1-nitro-4-(phenylethynyl)benzene
(3f, Table 1) with good conversion (99%) and selectivity (100%). Also, 1-iodonaphthalene or

1-bromonaphthalene was coupled with phenylacetylene to provide only 1-
(phenylethynyl)naphthalene (3g and 3h, Table 1) in 76 or 65% conversion respectively.
While extending the scope to Br substituted aldehydes (2-bromobenzaldehyde, 3-
bromobenzaldehyde and 4-bromobenzaldehyde), desired product was not formed, but
cinromide was observed (Figures S15 and S16). Aldol reaction might have happened before
coupling in the presence of the catalyst [48]. In the presence of strong base (KOtBu), a-
hydrogen of N,N-dimethyl acetamide was removed to generate carbanion which might attack
the carbonyl carbon of Br substituted benzaldehyde, followed by dehydration leads to a,b-
unsaturated compound (cinromide). The reported magnetic nanoparticles supported Pd
catalyst performed the coupling using 1 mol% catalyst at 100 ꢀC [49]. However, present
conditions are comparatively milder and catalyst loading is also less.
Table
Condensati
on of
1
phenylacet
ylene with
aryl halides
in presence
of 1 and 2
3a, 3 h, 99/100%,a
99/100%b
3b, 12 h, 99/100%,a
99/100%b
3c, 24 h 71/100%,a
81/100%b
(X = I)
(X = I)
(X = Br)
3d, 24 h, 18/100%a (X = I) 3e, 24 h, 55/100%a (X = Br) 3f, 12 h, 99/100%b (X = I)

3g, 12 h, 76/100%b (X = I)
3h, 15 h, 65/100%b (X = Br)
Reaction conditions: Aryl halide (0.5 mmol), phenylacetylene (0.55 mmol), 1 (0.4 mol% when X = I;
b
a
0.6 mol% when X = Br), KOtBu (0.55 mmol), DMAc (3 mL), 80 ꢀC. 1 is used as a catalyst, 2 is
used as a catalyst, Conversion/selectivity were determined by GC-MS.
Condensation was performed between iodobenzene and phenylacetylene in the
presence of base without the catalyst. No coupled product (1,2-diphenylethyne) was seen, and
it demonstrated the catalytic involvement of Pd(II). Catalyst 2 was used for the condensation
of phenylacetylene with iodobenzene under optimum conditions. The catalyst was recovered
from the reaction mixture by simple centrifugation, washed with diethyl ether and dried under
vacuum. Recovered catalyst was used for the next run. Further cycles of catalysis were
proceeded under identical conditions, and the results were noted.
Fig. 2 Reusability of 2
Reaction conditions: Iodobenzene (0.5 mmol), phenylacetylene (0.55 mmol), 2 (5 µmol) and KOtBu
(0.55 mmol), DMAc (3 mL), 80 ꢀC, 3 h. Conversion and selectivity were determined by GC.
Homogenous and heterogeneous Pd(II) complexes of acylthiourea ligand (L) were
prepared and characterized. In the heterogenous catalyst, Pd(II) complex was uniformly
distributed over nano silica. Both the catalysts showed good activity in the condensation of
phenylacetylene with aryl halides. Bromobenzaldehyde derivatives could not be used as
substrate due to the formation of cinromide. Importantly, the heterogeneous Pd(II) catalyst
can be isolated easily and used satisfactorily at least for four cycles.

Acknowledgement
We thank BRNS (34/14/52/2014-BRNS/2069) for financial support.
References
[1] X. F. Wu, P. Anbarasan, H. Neumann, M. Beller, From noble metal to Nobel Prize:
Palladium-catalyzed coupling reactions as key methods in organic synthesis, Angew.
Chem. Int. Ed. 49 (2010) 9047–9050. doi:10.1002/anie.201006374.
[2] R. F. Heck, J. P. Nolley, Jr, Palladium-catalyzed vinylic hydrogen substitution
reactions with aryl, benzyl and styryl halides, J. Org. Chem. 37(14) (1972) 2320-2322.
doi:10.1021/jo00979a024.
[3] K. Sonogashira, Y. Tohda, N. Hagihara, A convenient synthesis of acetylenes:
Catalytic substitutions of acetylenic hydrogen with bromoalkenes, iodoarenes and
bromopyridines, Tetrahedron Lett. 16 (1975) 4467–4470. doi:10.1016/S0040-
4039(00)91094-3.
[4] S. M. I. Sanchita, M. Anupam, S. Roy, Synthesis and characterization of a polymer-
anchored palladium(II) Schiff base complex and its catalytic efficiency in phosphine-
free Sonogashira coupling reactions, Transition Met. Chem. 35 (2010) 305–313.
doi:10.1007/s11243-010-9328-3.
[5] S. H. Ryu, D. H. Lee, S. M. Lee, H. J. Kim, Y. -J. Ko, K. C. Ko, S. U. Son,
Morphology engineering of a Suzuki coupling-based microporous organic polymer
(MOP) using a Sonogashira coupling-based MOP for enhanced nitrophenol sensing in
water, Chem. Commun. 55 (2019) 9515–9518. doi:10.1039/c9cc05011f.
[6] Z. Tber, N. G. Biteau, L. Agrofoglio, J. Cros, S. Goffinont, B. Castaing, C. Nicolas, V.
Roy, Microwave-assisted Suzuki-Miyaura and Sonogashira coupling of 4-chloro-2-
(trifluoromethyl)pyrido[1,2- e]purine derivatives, Eur. J. Org. Chem. 2019 (2019)
5756–5767. doi:10.1002/ejoc.201900921.
[7] A. S. Hay, Oxidative coupling of acetylenes II, J. Org. Chem. 27 (1962) 3320–3321.
doi:10.1021/jo01056a511.
[8] P. Siemsen, R. C. Livingston, F. Diederich, Acetylenic coupling: A powerful tool in
molecular construction, Angew. Chem. Int. Ed. 39 (2000) 2632–2657.
doi:10.1002/1521-3773(20000804)39:15<2632::AID-ANIE2632>3.0.CO;2-F.
[9] K. W. Anderson, S. L. Buchwald, General catalysts for the Suzuki-Miyaura and
Sonogashira coupling reactions of aryl chlorides and for the coupling of challenging
substrate combinations in water, Angew. Chem. Int. Ed. 44 (2005) 6173–6177.
doi:10.1002/anie.200502017.
[10] L. Cassar, Synthesis of aryl- and vinyl-substituted acetylene derivatives by the use of
nickel and palladium complexes, J. Organomet. Chem. 93 (1975) 253–257.
doi:10.1016/S0022-328X(00)94048-8.
[11] S. Gu, W. Chen, Pincer complexes of palladium- and nickel-containing 3-butyl-1-
(1,10- phenanthrolin-2-yl)imidazolylidene as efficient aqueous Sonogashira and
Kumada
coupling
reactions,
Organometallics
28
(2009)
909–914.
doi:10.1021/om801056v.

[12] G. Borja, A. Monge-marcet, R. Pleixats, T. Parella, X. Cattoën, M. Wong, C. Man,
Recyclable hybrid silica-based catalysts derived from Pd–NHC complexes for Suzuki,
Heck and Sonogashira Reactions, Eur. J. Org. Chem. (2012) 3625–3635.
doi:10.1002/ejoc.201200205.
[13] M. Sarmah, M. Mondal, S. B. Gohain, U. Bora, Gallic acid-derived palladium(0)
nanoparticles as in situ-formed catalyst for Sonogashira cross-coupling reaction in
ethanol
under
open
air,
Catal.
Commun.
90
(2017)
31–34.
doi:10.1016/j.catcom.2016.10.034.
[14] D. A. Kotadia, U. H. Patel, S. Gandhi, S. S. Soni, Pd doped SiO2 nanoparticles: An
efficient recyclable catalyst for Suzuki, Heck and Sonogashira reactions, RSC Adv. 4
(2014) 32826-32833. doi:10.1039/C4RA01813C.
[15] P. Veerakumar, M. Velayudham, K. L. Lu, S. Rajagopal, Silica-supported PEI capped
nanopalladium as potential catalyst in Suzuki, Heck and Sonogashira coupling
reactions,
Appl.
Catal.
A:
Gen.
455
(2013)
247–260.
doi:10.1016/j.apcata.2013.01.021.
[16] A. De Cattelle, A. Billen, W. Brullot, T. Verbiest, G. Koeckelberghs, Magnetically
induced Suzuki and Sonogashira reaction performed using recyclable, palladium-
functionalized magnetite nanoparticles, J. Organomet. Chem. 899 (2019) 120905 1-8.
doi:10.1016/j.jorganchem.2019.120905.
[17] M. Daraie, M. M. Heravi, S. S. Kazemi, Pd@GO/Fe3O4/PAA/DCA: A novel magnetic
heterogeneous catalyst for promoting the Sonogashira cross-coupling reaction, J.
Coord. Chem. 72 (2019) 2279–2293. doi:10.1080/00958972.2019.1640360.
[18] M. Annapurna, T. Parsharamulu, P. Vishnuvardhan Reddy, M. Suresh, P. R. Likhar,
M. Lakshmi Kantam, Nano palladium supported on high-surface-area metal-organic
framework MIL-101: An efficient catalyst for Sonogashira coupling of aryl and
heteroaryl bromides with alkynes, Appl. Organomet. Chem. 29 (2015) 234–239.
doi:10.1002/aoc.3277.
[19] M. Shunmughanathan, P. Puthiaraj, K. Pitchumani, Melamine-based microporous
network polymer supported palladium nanoparticles: A stable and efficient catalyst for
the Sonogashira coupling reaction in water, ChemCatChem. 7 (2015) 666–673.
doi:10.1002/cctc.201402844.
[20] S. Diyarbakir, H. Can, Ö. Metin, Reduced graphene oxide-supported CuPd alloy
nanoparticles as efficient catalysts for the sonogashira cross-coupling reactions, ACS
Appl. Mater. Interfaces. 7 (2015) 3199–3206. doi:10.1021/am507764u.
[21] M. Gholinejad, J. Ahmadi, C. Nájera, Silica microparticles supported gold and copper
ferrite nanoparticles: A magnetically recyclable bimetallic catalyst for Sonogashira
reaction, ChemistrySelect. 1 (2016) 384–390. doi:10.1002/slct.201600049.
[22] S. Dharani, G. Kalaiarasi, D. Sindhuja, V. M. Lynch, R. Shankar, R. Karvembu, R.
Prabhakaran, Tetranuclear palladacycles of 3-acetyl-7-methoxy-2H-chromen-2-one
derived Schiff bases: Efficient catalysts for Suzuki-Miyaura coupling in an aqueous
medium, Inorg. Chem. 58 (2019) 8045–8055. doi:10.1021/acs.inorgchem.9b00794.
[23] Y. Zheng, Y. Tan, K. Harms, M. Marsch, R. Riedel, L. Zhang, E. Meggers, Octahedral
ruthenium complex with exclusive metal-centered chirality for highly effective
asymmetric catalysis, J. Am. Chem. Soc. 139 (2017) 4322–4325.

doi:10.1021/jacs.7b01098.
[24] T. J. Coxon, M. Fernández, J. Barwick-Silk, A. I. McKay, L. E. Britton, A. S. Weller,
M. C. Willis, Exploiting carbonyl groups to control intermolecular rhodium-catalyzed
alkene and alkyne hydroacylation, J. Am. Chem. Soc. 139 (2017) 10142–10149.
doi:10.1021/jacs.7b05713.
[25] L. S. Sharninghausen, J. Campos, M. G. Manas, R. H. Crabtree, Efficient selective and
atom economic catalytic conversion of glycerol to lactic acid, Nat. Commun. 5 (2014)
1–9. doi:10.1038/ncomms6084.
[26] R. V. Jagadeesh, D. Banerjee, P. B. Arockiam, H. Junge, K. Junge, M. -M. Pohl, J.
Radnik, A. Brückner, M. Beller, Highly selective transfer hydrogenation of
functionalised nitroarenes using cobalt-based nanocatalysts, Green Chem. 17 (2015)
898–902. doi:10.1039/C4GC00731J.
[27] C. Jiang, Z. Shang, X. Liang, Chemoselective transfer hydrogenation of nitroarenes
catalyzed by highly dispersed, supported nickel nanoparticles, ACS Catal. 5 (2015)
4814–4818. doi:10.1021/acscatal.5b00969.
[28] M. Bhardwaj, S. Sahi, H. Mahajan, S. Paul, J. H. Clark, Novel heterogeneous catalyst
systems based on Pd(0) nanoparticles onto amine functionalized silica-cellulose
substrates [Pd(0)-EDA/SCs]: Synthesis, characterization and catalytic activity toward
C–C and C–S coupling reactions in water under limiting basic conditions, J. Mol.
Catal. A: Chem. 408 (2015) 48–59. doi:10.1016/j.molcata.2015.07.005.
[29] G. H. Dang, Y. T. H. Vu, Q. A. Dong, D. T. Le, T. Truong, N. T. S. Phan, Quinoxaline
synthesis via oxidative cyclization reaction using metal-organic framework Cu(BDC)
as an efficient heterogeneous catalyst, Appl. Catal. A: Gen. 491 (2015) 189–195.
doi:10.1016/j.apcata.2014.11.009.
[30] J. S. Qin, S. Yuan, C. Lollar, J. Pang, A. Alsalme, H.C. Zhou, Stable metal-organic
frameworks as a host platform for catalysis and biomimetics, Chem. Commun. 54
(2018) 4231–4249. doi:10.1039/c7cc09173g.
[31] P. Puthiaraj, P. Suresh, K. Pitchumani, Aerobic homocoupling of arylboronic acids
catalysed by copper terephthalate metal-organic frameworks, Green Chem. 16 (2014)
2865–2875. doi:10.1039/C4GC00056K.
[32] C. Pereira, J. F. Silva, A. M. Pereira, J. P. Araújo, G. Blanco, J. M. Pintado, C. Freire,
[VO(acac)2] hybrid catalyst: From complex immobilization onto silica nanoparticles to
catalytic application in the epoxidation of geraniol, Catal. Sci. Technol. 1 (2011)
784-793. doi:10.1039/c1cy00090j.
[33] S. Sabater, J. A. Mata, E. Peris, Catalyst enhancement and recyclability by
immobilization of metal complexes onto graphene surface by noncovalent interactions,
ACS Catal. 4 (2014) 2038–2047. doi:10.1021/cs5003959.
[34] C. Wu, F. Irshad, M. Luo, Y. Zhao, X. Ma, S. Wang, Ruthenium complexes
immobilized on an azolium based metal organic framework for highly efficient
conversion of CO2 into formic acid, ChemCatChem. 11 (2019) 1256–1263.
doi:10.1002/cctc.201801701.
[35] R. Sayah, M. Le Floch, E. Framery, V. Dufaud, Immobilization of chiral cationic
diphosphine rhodium complexes in nanopores of mesoporous silica and application in

asymmetric hydrogenation, J. Mol. Catal. A: Chem. 315 (2010) 51–59.
doi:10.1016/j.molcata.2009.08.025.
[36] R. K. Sharma, S. Dutta, S. Sharma, Quinoline-2-carboimine copper complex
immobilized on amine functionalized silica coated magnetite nanoparticles: A novel
and magnetically retrievable catalyst for the synthesis of carbamates via C–H
activation
of
formamides,
Dalton
Trans.
44
(2015)
1303–1316.
doi:10.1039/C4DT03236E.
[37] K. Matsui, Y. Maegawa, M. Waki, S. Inagaki, Y. Yamamoto, Transfer hydrogenation
of nitrogen heterocycles using a recyclable rhodium catalyst immobilized on
bipyridine-periodic mesoporous organosilica, Catal. Sci. Technol. 8 (2018) 534–539.
doi:10.1039/C7CY02167D.
[38] D. Wang, L. Salmon, J. Ruiz, D. Astruc, Recyclable ruthenium(II) complex supported
on magnetic nanoparticles: A regioselective catalyst for alkyne azide cycloaddition,
Chem. Commun. 49 (2013) 6956–6958.
[39] A. Krogul, J. Cedrowski, K. Wiktorska, W. P. Ozimiński, J. Skupińska, G.
Litwinienko, Crystal structure, electronic properties and cytotoxic activity of
palladium chloride complexes with monosubstituted pyridines, Dalton Trans. 41
(2012) 658–666. doi:10.1039/c1dt11412c.
[40] R. Gerber, O. Blacque, C. M. Frech, Negishi cross-coupling reaction catalyzed by an
aliphatic, phosphine based pincer complex of palladium. biaryl formation via cationic
pincer-type PdIV intermediates, Dalton Trans. 40 (2011) 8996–9003.
doi:10.1039/c1dt10398a.
[41] J. B. Shaik, V. Ramkumar, S. Sankararaman, Synthesis of a new class of cationic
Pd(II) complexes with 1,2,3-triazol-5-ylidene ligand and their catalytic application in
the conversion of internal alkynes to 1,2-diketones, J. Organomet. Chem. 860 (2018)
1–8. doi:10.1016/j.jorganchem.2018.02.011.
[42] D. Sindhuja, P. Vasanthakumar, N. S. P. Bhuvanesh, R. Karvembu, An acylthiourea
ligated Fe(II) complex on silica nanoparticles for transfer hydrogenation of carbonyl
compounds,
Ind.
Eng.
Chem.
Res.
57
(2018)
14386–14393.
doi:10.1021/acs.iecr.8b02817.
[43] Yield: 85%; m.p.: 258 °C; UV-Vis: λmax (DMF, nm) 264, 296; FT-IR: (KBr, cm-1)
1
3332, 3182 (s, n(N-H)), 3203 (s, n(N–H)), 1673 (s, n(C=O)), 1251 (s, n(C=S)); H
NMR (500 MHz, DMSO): δ 11.84 (s, 2H), 10.46 (s, 2H), 10.21 (s, 2H), 8.30 (d, J =
3.5 Hz, 2H), 8.09 (d, J = 4.8 Hz, 2H), 7.50–7.07 (m, 2H); 13C NMR (126 MHz,
DMSO): δ 177.85, 161.69, 136.57, 136.50, 133.68, 129.28. ESI-MS: Cald. 476.8799,
observed 476.8804 [M-2Cl-H]+.
[44] B. Movassagh, A. Takallou, A. Mobaraki, Magnetic nanoparticle-supported Pd(II)-
cryptand 22 complex: An efficient and reusable heterogeneous precatalyst in the
Suzuki-Miyaura coupling and the formation of aryl-sulfur bonds in honor and memory
of late Prof. Mathias Mertes, J. Mol. Catal. A: Chem. 401 (2015) 55–65.
doi:10.1016/j.molcata.2015.03.002.
[45] C. I. Ezugwu, B. Mousavi, M. A. Asrafa, A. Mehta, H. Vardhan, F. Verpoort, An N-
heterocyclic carbene based MOF catalyst for Sonogashira cross-coupling reaction,
Catal. Sci. Technol. 6 (2016) 2050–2054. doi:10.1039/c5cy01944c.

[46] K. S. Kim, A. F. Gossmann, N. Winograd, X-ray photoelectron spectroscopic studies
of palladium oxides and the palladium-oxygen electrode, Anal. Chem. 46 (1974) 197–
200. doi:10.1021/ac60338a037.
[47] A. Miller, L. Yu, J. Blickensderfer, R. Akolkar, Electrochemical copper metallization
of glass substrates mediated by solution-phase deposition of adhesion-promoting
layers, J. Eectrochem. Soc. 162 (2015) D630–D634. doi:10.1149/2.1071514jes.
[48] S.W. Foo, S. Oishi, S. Saito, Aldol condensation of amides using phosphazene-based
catalysis, Tetrahedron Lett. 53 (2012) 5445–5448. doi:10.1016/j.tetlet.2012.07.129.
[49] P. Li, L. Wang, L. Zhang, G. Wang, Magnetic nanoparticles-supported palladium: A
highly efficient and reusable catalyst for the Suzuki, Sonogashira, and Heck reactions,
Adv. Synth. Catal. (2012) 1307–1318. doi:10.1002/adsc.201100725.

t
KO Bu, DMAc, 80 ꢀC, 3-24 h

Pd(II)‒acylthiourea complex and its immobilized counterpart catalyzed
condensation of phenylacetylene with aryl halides
D. Sindhuja, P. Vasanthakumar, R. Karvembu*
Department of Chemistry, National Institute of Technology, Tiruchirappalli 620015, India
Z Homogeneous Pd(II)-acylthiourea complex was prepared
Z It was immobilized on nano silica
Z Catalytic activity of homogeneous and heterogeneous catalysts was evaluated for
condensation of phenylacetylene with aryl halides
Z Heterogeneous catalyst can be reused up to four cycles

There are no conflicts to declare.

The manuscript is original. Authors certify that this has not been submitted/published anywhere.