Preparation anchored Pd nanoparticles on glyoxal modified metal- organic framework for Sonogashira coupling reactions

Article abstract of DOI:10.1016/j.jorganchem.2019.121069

UIO-66-NH₂-Gl?Pd nanocatalyst was successfully synthesized during post-synthetic modification (PSM) method and its application was investigated in the Sonogashira coupling reactions. Initially, UIO-66-NH₂ was synthesized and identifi

Full text of DOI:10.1016/j.jorganchem.2019.121069

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Preparation anchored Pd nanoparticles on glyoxal modified metal- organic framework
for Sonogashira coupling reactions
Heshmatollah Alinezhad, Mansoureh Cheraghian, Shahram Ghasemi
PII:
S0022-328X(19)30512-1
DOI:
https://doi.org/10.1016/j.jorganchem.2019.121069
JOM 121069
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 24 August 2019
Revised Date: 2 December 2019
Accepted Date: 4 December 2019
Please cite this article as: H. Alinezhad, M. Cheraghian, S. Ghasemi, Preparation anchored Pd
nanoparticles on glyoxal modified metal- organic framework for Sonogashira coupling reactions, Journal
of Organometallic Chemistry (2020), doi: https://doi.org/10.1016/j.jorganchem.2019.121069.
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Preparation anchored Pd nanoparticles on glyoxal modified metal- organic
framework for Sonogashira coupling reactions
Heshmatollah Alinezhada*, Mansoureh Cheraghiana, shahram Ghasemia
aFaculty of Chemistry, University of Mazandaran, Babolsar, Iran
*Corresponding author. Telephone: +98-1135302355; Fax: +98 1135302350; E mail: heshmat@umz.ac.ir;
postal address: Iran, Mazandaran, Babolsar, University of Mazandaran, Faculty of Chemistry, 47416-13534.
Abstract
UIO-66-NH2-Gl@Pd nanocatalyst was successfully synthesized during post-synthetic
modification (PSM) method and its application was investigated in the Sonogashira coupling
reactions. Initially, UIO-66-NH2 was synthesized and identified. This metal organic framework
(MOF) was modified with glyoxal, then, palladium nanoparticles (NPs) were supported on the
modified framework through PSM. This nanocatalyst was identified via Fourier-transform
infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (1HNMR) spectroscopy, N2
gas adsorption-desorption, thermo gravimetric analyses (TGA), energy dispersive X-ray
mapping spectroscopy (EDX-MAP), field emission scanning electron microscopy (FE-SEM),
and X-ray diffraction (XRD). 1HNMR analysis showed that around 30 % of the amine functional
groups of nanoporous UIO-66-NH2 were modified with glyoxal. The formation of Pd NPs
supported on MOF was confirmed by transmission electron microscopy (TEM) and EDX-MAP.
As well, according to the inductive couple plasma atomic emission spectroscopy (ICP), around
2.98 w% of Pd NPs was present in the modified MOF. Eventually, the nanocatalyst provided the
excellent catalytic activity in the Sonogashira coupling reaction. Also, the nanocatalyst has the
capability to be easily recycled up to 4 times, while its catalytic activity was maintained during
the activity.
Keywords: Metal-organic frameworks; Nanocatalyst; UIO-66-NH2; Post-synthetic modification;
Sonogashira coupling

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1.
Introduction
Metal-organic frameworks (MOFs) are a new class of porous materials, which are formed from
metal ions or metal clusters as nodes and organic ligands as linkers [1]. MOFs have received
much attention because of their special properties such as ultrahigh porosity, tunable cavity sizes,
various topologies and high surface area as well as the possibility of functionalization with
different modifier [2-4]. MOFs have been studied for the various applications, including gas
storage [5-7], separation [8, 9], catalysis [10, 11], and drug delivery [12-14]. In recent years,
numerous studies have also been focused on investigation of MOFs as active heterogeneous
catalysts in a variety of reactions such as alkene oxidation [15-17], aldol condensations [18],
hydrogenation [19], epoxide ring opening [20], the Knoevenagel condensation reaction [21],
acetalization [22] and isomerization [23]. An attractive feature of MOFs is the possibility of
post-synthetic modification (PSM) [24]. PSM can be performed via modification of metallic
nodes and/or organic ligands by active functional groups, without displeasing influences on the
MOFs stableness [25]. PSM is particularly attractive for production of catalyst materials. There
are many reports for the catalytic properties of MOFs prepared using PSM strategy. For instance,
Alinezhad et.al reported anchoring of Ni onto surface of MOFs through post-synthesis
modification for cross coupling reaction [26]. In the other research, Zhang et.al prepared
Ru/UiO-66 catalyst for the reduction of nitroarenes, alcohol oxidation and Knoevenagel
condensation [27]. Luan et.al also prepared UIO-66-Sal-CuCl2 catalyst and considered its
application in the selective aerobic oxidation of alcohols [28]. The palladium catalyzed cross
coupling reactions is one of the most powerful tools in organic synthesis. The Sonogashira
coupling reaction between sp2-hybridized carbon atoms of aryl and vinyl halides with sp-
hybridized carbon atoms of terminal acetylenes has been developed for synthesizing conjugated
alkynes. These alkynes are important class of compounds that can be found in wide range of
natural products and other bioactive materials [29, 30].
Although homogenous palladium catalysts have remarkable properties such as high activity and
selectivity, they inherently suffer from difficulty of reusing and separation from the products

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[31]. For instance, Pd-phosphan complex that has been frequently used under homogeneous
condition is unstable during reactions losing its high activity as catalyst. Because palladium
nanoparticles (NPs) as heterogeneous catalyst commonly lose their catalytic activity under
aggregation, they are not economical [32-35]. It is obvious from the given cases that the
development of a new catalytic system based on the benefits of both systems of homogeneous
and heterogeneous is a significant issue in the novel catalyst researches.
MOFs are suitable support for catalytic reagents. Anchoring Pd NPs to modified MOF can be
adjusted to prevent their aggregation. In addition to their high activity, they will have the
capability of easy separation. One of the significant features of MOFs is their thermal and
chemical stability. Due to the high chemical and thermal stability of UIO-66-NH2, it remains
unchanged during PSM. Some researchers synthesized and identified UiO-66-NH2 and offered
special property through a PSM procedure [36]. UiO-66-NH2 is made of [Zr6O4 (OH)4 (CO2)12]
clusters linked with 2-aminoterephthalic acid [37]. Moreover, UiO-66-NH2 has high porosity
[23] and the amine groups on MOF can react with other functional groups to obtain appropriate
chelating ligands.
Due to exceptional thermal, chemical, and mechanical stability as well as large specific surface
of UIO-66-NH2 area, in this project, nonporous MOF was prepared using organic ligand of 2-
amino-1, 4-benzenedicarboxilic acid (NH2-BDC) and zirconium (IV) chloride. Then, during the
process of PSM, MOF was modified by glyoxal due to the formation of N, N-chelating ligand
which is suitable for is coordination of the metal ions. Then Pd (II) ions were anchored onto the
surface of modified nanoporous UIO-66-NH2 and then reduced Pd0 NPs. Finally, we studied the
application of the catalyst in coupling reactions for synthesis of organic materials.
2.
Experimental
2.1.
Materials
Zirconium (IV) chloride, 2-aminoterephthalicacid, palladium (II) chloride (PdCl2), glyoxal, aryl
halides derivatives and terminal acetylenes and solvents as N, N-dimethyl formamide (DMF),
dichloromethane (DCM), hexane and methanol were purchased from Sigma-Aldrich and used
without further purification.
2.2.
Analysis methods