Y. Fatahi, A. Ghaempanah, L. Maˈmani et al.
Journal of Organometallic Chemistry 936 (2021) 121711
Pd@ABA@SPIONs@SiO2 catalyst was obtained after drying under
vacuum for 12 h.
the oxidation state of palladium was zero in the fresh and
reused Pd@ABA@SPIONs@SiO2 nanocatalyst samples. The VSM re-
sults demonstrated that functionalization of SPIONs@SiO2 nanopar-
ticles have slightly reduced its magnetization, but it was still su-
perparamagnetic and practical experiments showed that the cata-
lyst was easily separable from the reaction mixture using an exter-
nal magnet.
3.1.4. General procedure for Mizoroki-Heck reaction
The reaction mixture, containing halobenzene (1.0 mmol),
alkene (1.1 mmol), sodium acetate (1.5 mmol) in H2O (3.0 mL) and
Pd@ABA@SPIONs@SiO2 catalyst (0.08 mol%) was stirred at room
temperature until the reaction completion. TLC was used to moni-
tor the reaction performance. After the reaction was completed, an
external magnet was used to separate the nanocatalyst. The cat-
alyst was washed with water and EtOH, and dried in a vacuum
oven and retained for re-using in the next reaction. The product of
the reaction was separated by extracting the filtrate with ethyl ac-
etate. The organic phase was collected and dried over Na2SO4 and
then was obtained by evaporating the solvent under reduced pres-
sure. The product was purified by column chromatography, using
n-hexane: ethyl acetate (6:1, v/v) as eluent.
Pd@ABA@SPIONs@SiO2
nanocatalyst was evaluated for
Mizoroki-Heck reaction. The optimization studies showed that
the optimal reaction condition was observed to be water as
solvent, 1.5 equivalent of sodium acetate as base, 0.08 mol% of
Pd@ABA@SPIONs@SiO2 nanocatalyst at room temperature. Several
aryl halides reacted with styrene or n-butyl acrylate and gave the
products in high isolated yields. The nanocatalyst was magnetically
recoverable and did not lose its activity after 10 sequential runs.
After the 5th cycle of the recovery, the catalyst was separated and
characterized by XPS and SEM methods.
A comparison between the nanocatalyst before reaction and af-
ter the 5th cycle showed that its structure and properties has not
changed under the reaction conditions. The DFT method was used
to study the mechanism of the reaction. The calculations show that
palladium is coordinated to the “N” atom of amine and “C” atom of
amide groups of 2-aminobenzamide ligand. Additionally, the calcu-
lated mechanism shows the role of the nanocatalyst is critical for
the reaction performance and after each cycle of the reaction, the
catalyst goes back to its initial state and is available for the next
reaction cycle.
3.1.5. Reusability of the catalyst
To study the reusability of Pd@ABA@SPIONs@SiO2 nanocatalyst,
the reaction of styrene and bromobenzene was selected as a sam-
ple reaction. The reaction was performed under the optimized con-
ditions and the separation of the catalyst from the reaction mixture
was done by an external magnet. The separated nanocatalyst was
washed with water and EtOH, and dried under vacuum at room
temperature. The recovered nanocatalyst was used directly in the
next reaction. The reusability study was evaluated for 10 sequential
runs.
Declaration of Competing Interest
3.1.6. DFT calculations
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
All calculations were performed with Gaussian program 09.
B3LY hybrid was used in conjunction with the 6-31G and DKH-DZP
(for Pd atom) basis for optimizing all stationary points and transi-
tion states in the gas phase. The all electron contracted Gaussian
basis set of double zeta valence quality plus polarization functions
(DZP) for the atoms from Rb to Xe is presented. The original DZP
basis set has been re-contracted, the values of the contraction coef-
ficients were re-optimized using the relativistic DKH Hamiltonian.
First of all, the structure of each reactant and its product were op-
timized. These optimized structures defined the appropriate tran-
sition state structure for each mechanism, and optimal transition
state structures were obtained with the Qst2 and Qst3 approaches.
These calculations were done to find the minimum-energy paths.
Moreover, normal vibration frequencies (Hessian force constant
matrices) computation confirms that every point on each station-
ary point is a transition structure or not. One of the methods for
identifying the transition state structure is the existence of a neg-
ative frequency.
Acknowledgement
We are kindly grateful to Mr. Danial Pishyar for his kind help
and support in the preparation of the graphics of this paper.
References
4. Conclusion
In this paper, a novel supported palladium nanocatalyst was
designed and fabricated. To this, the superparamagnetic iron ox-
ide nanoparticles were synthesized and encapsulated by silica
shells (SPIONs@SiO2 NPs) and followed by surface functionaliza-
tion using 2-aminobenzamide, which was then utilized for im-
mobilization of palladium as a bidentate ligand. The immobi-
lized Pd@ABA@SPIONs@SiO2 nanocatalyst was characterized by
various characterization methods. TEM and SEM images showed
that the NPs are spherical in shape with an average particle size
of about 20–25 nm. As seen in the FT-IR spectrum, the adsorp-
tion bond related to the carbonyl functional group in the amide
proved the successful surface functionalization of SPIONs@SiO2
NPs with 2-aminobenzamide functionalities. The presence of pal-
ladium in the structure of the nanocatalyst was also proved by
XRD and EDS analysis. In addition, XPS spectroscopy showed
8