Core-shell structured magnetic mesoporous silica supported Schiff-base/Pd: An efficacious and reusable nanocatalyst

Article abstract of DOI:10.1039/c9nj06250e

In this research, a novel Schiff-base/palladium complex containing magnetic ordered mesoporous silica (Fe₃O₄@MCM-41-SB/Pd) material with a core-shell structure is prepared and characterized, and its catalytic application is developed. The Fe₃O₄@MCM-41-SB/Pd nanocatalyst was characterized using FT-IR, TGA, SEM, VSM, PXRD and energy-dispersive X-ray (EDX) spectroscopy. This nanocatalyst showed high performance in the Suzuki cross-coupling reaction under ultrasonic conditions and delivered the corresponding products in high to excellent yield. The recovery study of the nanocatalyst proved that its activity is maintained during several stages of reuse. Moreover, the high stability of palladium species on the core-shell surface was confirmed by leaching and poisoning tests.

Full text of DOI:10.1039/c9nj06250e

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Elhamifar, New J. Chem., 2020, DOI: 10.1039/C9NJ06250E.
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Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
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DOI: 10.1039/C9NJ06250E
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Core-shell structured magnetic mesoporous silica supported Schiff-
base/Pd: An efficacious and reusable nanocatalyst
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Masoumeh Shaker and Dawood Elhamifar*
Department of Chemistry, Yasouj University, Yasouj, 75918-74831, Iran
E-mail: d.elhamifar@yu.ac.ir
Abstract: In this research, a novel Schiff-base/palladium complex containing magnetic
ordered mesoporous silica (Fe3O4@MCM-41-SB/Pd) material with core-shell structure is
perapred, characterized and its catalytic application is developed. The Fe3O4@MCM-41-
SB/Pd nanocatalyst was characterized using FT-IR, TGA, SEM, VSM, PXRD and energy-
dispersive X-ray (EDX) spectroscopy. This nanocatalyst showed high performance in
Suzuki cross-coupling reaction under ultrasonic conditions and delivered corresponding
products in high to excellent yield. The recovery study of the nanocatalyst proved that its
activity is maintained during several stages of reuse. Moreover, the high stability of
palladium species on the core-shell surface was confirmed by leaching and poisoning tests.
Keywords: Magnetic ordered mesoporous silica, Schiff-base/palladium complex, Core-
shell, Biaryls, Suzuki cross-coupling.
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DOI: 10.1039/C9NJ06250E
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1. Introduction
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In recent years, the synthesis of metal oxide nanoparticles (NPs) has attracted much
attention due to their important role in various sciences such as chemistry, physics,
material, medicine, etc.1-14 Among these, iron oxide NPs occupy a special position due to
their easy preparation, easy separation, non-toxicity and inexpensive.15, 16 Also, the
possibility of their surface modification with active biological compounds has increased
the popularity of these particles.17-21 Accordingly, the iron oxide NPs are widely used in
various fields such as magnetic resonance imaging (MRI),19, 20, 22-25 sensors,26-29 labeling
and sorting of cells,30 ferrofluid,31, 32 drug delivery,21, 24 and catalyst immobilization.3, 33, 34
In spite of the aforementioned advantages, uncoated Fe3O4 NPs have low chemical stability
and lose much of their magnetic and chemical capacities in the presence of air and alkaline
and acidic media. Also, these NPs have strong tendency for self-assembly, due to the
existence of Van der Waals forces and the inherent magnetic interaction.35, 36 Hence, in
recent years, different methods such as doping, functionalization and compositing have
been used to coat a layer around MNPs and improve their stability.37-39 The coated layer
can be species such as metal or metal oxides, groups and compounds of mineral, organic,
sugar and peptide that surround the inner core and called as the shell. Between different
shells, silica has become widely considered due to high biocompatibility, non-toxicity,
poor chemical permeability and easy surface modification. In recent years, mesoporous
silica shells have created a major revolution in the synthesis of core-shell nanostructures,
due to their high adsorption capacity, relatively uniform and controllable pore size, easy
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surface modification and high surface area.40-50 Some of recently developed magnetic
nanostructures with mesoporous silica shells are GdIO@mSiO2@BNSCQD,51
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CuO/Silicalite-1@mSiO2,52
Fe3O4-mSiO2,
Fe3O4@nSiO2@mSiO2,
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Fe3O4@ZnO@mSiO2, Fe3O4@mSiO2 nanocapsules,56 Fe3O4@nSiO2@mSiO2-APTES-
VP16,57 Fe3O4@mSiO2@ICG58 and DOX-Fe3O4@mSiO2@Au.59
On the other hand, the Suzuki carbon-carbon coupling is a significant process that occurs
between aryl halides/triflates and the arylboronic acids to give biaryl compounds. This
reaction has been widely used in the synthesis of drugs, natural products, ligands for
catalysts, nucleoside analogues and liquid crystalline materials. Traditionally, this has been
accomplished in the presence of Pd-catalysts under homogeneous conditions. However,
due to the restrictions of these systems such as catalyst and product separation, various
heterogeneous catalysts have been reported for this reaction.60-64 Some of recently reported
catalytic systems are Mag-IL-Pd,62 SMNP@NHC-Pd,65 Fe3O4@SiO2/isoniazide/Pd,66
Fe3O4/DAG/Pd67 and MNP@SPGMA@AP@Pd.68 Following the above-mentioned
systems, in the present work a magnetic core-shell nanostructure modified with Schiff-
base/Pd complex is prepared for the Suzuki cross-coupling reaction under green conditions.
2. Experimental Section
1.2. Preparation of Fe3O4@MCM-41
For this, Fe3O4@SiO2 NPs were first prepared according to a previous procedure.69 The
Fe3O4@SiO2 (0.6 g) was then dispersed in a mixture of distilled water (80 mL) and ethanol (60
3