Synthesis and Characterization of Magnetic Zeolite Y-Palladium-Nickel Ferrite by Ultrasonic Irradiation and Investigating Its Catalytic Activity in Suzuki-Miyaura Cross-Coupling Reactions.

Zeolite faujasite is widely used as a catalyst in many industrial catalytic applications. In this study, synthesis and characterization of magnetic zeolite Y-palladium-nickel ferrite were studied. First, palladium nanoparticles were combined with nickel ferrite and then placed on zeolite Y by ultrasonic treatment. The structure and morphology of the synthesized magnetic zeolite Y-palladium-nickel ferrite were characterized using Fourier transform infrared, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray, vibrating sample magnetometer, and inductively coupled plasma optical emission spectroscopy analysis. Also, we investigated the catalytic activity of this prepared zeolite in Suzuki-Miyaura coupling reaction between phenylboronic acid and aryl halides. Our study shows that magnetic zeolite Y-palladium-nickel ferrite is a suitable catalyst for Suzuki-Miyaura coupling reaction. Short reaction time, high yield, and easy reusability are the advantages of using this catalyst in carbon-carbon cross-coupling reactions.

Introduction

Zeolites are microporous aluminosilicate materials with a large number of open channels, pores, and cages that are distributed on a molecular scale with a high mechanical, thermal, and chemical stability.[1] There are reports about various applications of zeolites such as ion-exchange, catalysis, adsorptive separation, renewable energy, and in biomedical devices.[2−7] One of the most studied zeolites, Na-Y (Z-Y), has been widely used as an industrial catalyst for several important processes, such as membranes[8] and catalytic conversions.[9] The crystalline structure of zeolite Y is the result of the spatial connection between silicate and aluminate units that can build 12-member ring pores (7.4 Å). These pores join together to form super cavities.[10]

Recently, there is a lot of interest in the use of microwave and ultrasonic energies. Microwaves are a form of electromagnetic radiation with frequencies ranging from 0.3 to 300 GHz. The microwave method is extensively applied in different fields such as dehydration of solid compounds, medicine, and formation of inorganic materials.[11] Also, ultrasonic wave is a kind of mechanical energy, which is characterized by vibrating particles in a medium with a frequency greater than 20 000 Hz. When ultrasonic waves pass through a solution, local high temperatures and high pressures are created. These results lead to the generation of microscopic cavities that grow. After that, these bubbles collapse in order to release a great local energy, for the formation or breaking of chemical bonds.[12] There are many reports about the use of ultrasound as a green source of energy in the preparation of micrometer-sized molecular sieves.[13−19] Compared with the common hydrothermal synthesis, the preparation of materials using microwaves and ultrasonic waves has benefits such as rapid reaction, narrow particle size distribution, and wide synthesis of compounds having a high degree of purity.[20]

The nickel ferrite (NF) compound, NiFe2O4, is a well-known inverse spinel including Ni2+ and Fe3+ ions distributed between the octahedral and tetrahedral sites, respectively.[21] There are many reports about the use of nickel ferrite such as biomedical, electric, and electronic devices, ferro-fluids, magnetic refrigeration, color imaging, and microwave devices.[22−25] Also, there are many techniques like citric acid combustion, organic gel-thermal decomposition, sol–gel autocombustion, hydrothermal process, thermolysis, co-precipitation, gel-assistant hydrothermal process, self-propagation, and use of microemulsion for the preparation of nanocrystallite NF.[26−28] Amongst the reported techniques for the preparation of NF nanostructures, the microwave technique has gathered the most attention because of some benefits such as feasibility, inexpensiveness, environmental friendliness, and short reaction time.[29]

The palladium-catalyzed Suzuki–Miyaura (S–M) carbon–carbon cross-coupling reaction between an aryl halide and phenylboronic acid (benzeneboronic acid) is among the most powerful tools for constructing C–S, C–N, and C–C bonds in the synthesis of organic compounds.[30] As biaryl derivatives are applied as the building block of a vast range of natural products, herbicides, polymers, and pharmaceuticals, much efforts have been spent on the development of simple and practical conditions for doing the S–M coupling reaction.[31,32] There are many catalytic systems limited to the couplings of aryl iodides and aryl bromides.[33] Recently, the use of available aryl chlorides and aryl fluorides in these transformations have received a lot of interesting, and a number of effective catalysts have been developed for this aim.[34] Generally, most of the phosphine ligands used in palladium-catalyzed processes are harmful, expensive, and air- or water-sensitive.[35] Also, the Pd-based bimetallic nanostructures with some low-cost elements such as Co, Fe, and Ni as the novel catalysts present excellent stability, selectivity, and performance in different organic reactions.[36,37] In some cases, the catalytic performance of non-noble metals can be increased by the use of ultrafine polyacrylonitrile fibers[38] and zeolite[39] or some phosphine ligands[40] as stabilizers.

Recently, we reported S–M cross-coupling reactions between aryl halides and benzeneboronic acid in the presence of zeolite Y/palladium nanoparticles as a catalyst.[41]

In this study, for the first time, the preparation and characterization of magnetic zeolite Y–palladium–nickel ferrite (Z-Y–Pd–NF) by ultrasonic treatment are reported. In this route, the crystallization temperature and synthesis time are shorter than in other methods. This catalyst displays three main advantages in the S–M reaction. (1) The contact between the reactants and the catalyst increase considerably because of having a high active surface area. (2) It is easily separated from the mixture of reaction by applying an external magnet because of insolubility and paramagnetic properties of the Z-Y–Pd–NF composite. (3) The Z-Y–Pd–NF shows high performance in carbon–carbon coupling reactions. Other advantages of the use of the prepared catalyst in S–M coupling reactions are rapid reaction, suitable yield, and reusability.

Results and Discussion

In this study, the preparation of a magnetic catalyst, Z-Y–Pd–NF, via ultrasonic treatment has been demonstrated, which can be suitable for S–M cross-coupling reactions (Figure ). First, Z-Y was synthesized by the sonochemical method. Second, NF NPs were synthesized using facile and fast microwave radiation. Then, ultrasonic treatment was used to deposit Pd and NF NPs on the Z-Y surface. Figure displays the X-ray diffraction (XRD) pattern with sharp reflections at 2θ of 6.08°, 10.04°, 11.7°, 13.48°, 15.5°, 20.2°, 23.4°, 26.8°, and 31.1° belong to 111, 220, 311, 331, 511, 440, 533, 642, and 555 planes of the Z-Y structure. According to Figure , there are no impurities in this compound, which proves the Z-Y phase.[41]

Figure 1

Common method for the preparation of Z-Y–Pd–NF.

Figure 2

XRD pattern of Z-Y.

The Fourier transform infrared (FT-IR) spectrum and scanning electron microscopy (SEM) image of the prepared Z-Y are presented in Figure . This synthesized zeolite shows the characteristic bands of the faujasite (FAU) framework. The appeared bands at 567 and 719 cm–1 are assigned to the bending and symmetric stretching vibrations of Si–O or Al–O bonds, respectively. Also, the band at 1002 cm–1 is ascribed to the Al–O tetrahedral vibration (Figure a). The small cavities on the external surface of Z-Y with uniform structure are observed in the SEM image as given in Figure b. Figure c shows a histogram of particle size distribution with the average particle size of 76 nm for the prepared Z-Y. According to these results, the structure and morphology of the prepared Z-Y were completely performed after 3 h by ultrasonic irradiation.

Figure 3

(a) FT-IR spectrum, (b) SEM image, and (c) histogram of particle size distribution of the prepared Z-Y.

Figure a–c reveals FT-IR spectra, SEM image, and the histogram of particle size distribution of the synthesized NF NPs under microwave radiation. Three different times for the synthesis of NF NPs were investigated (10, 20, and 30 min). The best time for the synthesis of NF NPs was 30 min [monitored by thin layer chromatography (TLC)]. According to Figure a(i), the C–O bending vibrations of NF NPs were observed in the range of 1380–1420 cm–1. Additionally, the appeared peaks at 470 and 560 cm–1 correspond to Ni–O and Fe–O, respectively.[42] The morphology of the product was examined by an SEM image (Figure b). It seems the agglomeration of particles had occurred because of the high magnetism of NF NPs. Furthermore, the average particle size is 58 nm for NF NPs (Figure c).

Figure 4

(a) FT-IR spectra of the prepared NF NPs in different times (i = 10 min, ii = 20 min and iii = 30 min), (b) SEM image of the synthesized NF NPs via microwave (360 W, 30 min) and (c) histogram of particle size distribution of NF NPs.

Transmission electron microscopy (TEM) images of the NF NPs are given in Figure . According to the TEM images, NF NPs have a core–shell structure with the average diameter size from ∼40 to ∼60 nm.

Figure 5

TEM images of NF NPs (a,b) with a core–shell structure.

The XRD pattern of NF NPs shows that the final product has a good match with the crystalline system of the cubic phase related to JCPDS card no. 01-088-0380 (Figure ). The diffraction peaks at 2θ value of 18.44°, 30.33°, 35.72°, 37.36°, 43.39°, 53.85°, 57.40°, and 63.03° belong to 111, 220, 311, 222, 400, 422, 511, and 440 planes of the NF phase. According to the XRD pattern, the pure phase of NF has been synthesized and there are no impurities in this compound.

Figure 6

XRD pattern of the prepared NF NPs.

The magnetic property of NF NPs was investigated by a vibrating sample magnetometer at 300 K. As shown in Figure , the magnetic hysteresis curve of NF NPs reveals a super-paramagnetic behavior.[43] Its saturation magnetization value is 41.5 emu g–1. Therefore, this magnetic material is separable using an external permanent magnet from the reaction solution.

Figure 7

Magnetization curve of the prepared magnetic NF NPs.

The characterization of the magnetic catalyst, Z-Y–Pd–NF, was investigated as a suitable candidate in S–M carbon–carbon coupling reaction. The FT-IR spectrum and SEM image of the prepared Z-Y–Pd–NF via ultrasonic treatment have been given in Figure . Three sharp peaks have been observed at 451, 730, and 1074 cm–1, which belong to T–O (T = Si, Al, Ni), T–O (T = Si, Fe), and Al–O tetrahedral vibrations, respectively (Figure a).[44] Because the vibration peaks of Fe and Ni are near the range of 400–800 cm–1, these peaks overlap with the peaks of Z-Y. The morphology of Z-Y–Pd–NF is resembling a rose flower as shown in Figure b,c.

Figure 8

(a) FT-IR spectrum, (b,c) SEM images of the synthesized Z-Y–Pd–NF by the ultrasonic method.

The XRD pattern of Z-Y–Pd–NF is given in Figure . There are a number of prominent Bragg reflections with indices [(111), (200), and (311)], which clearly reveal that the resultant product is Pd(0).[45] In addition, there are sharp reflections at 2θ of 10.1°, 12.4°, 13.51°, 20.07°, 21.59°, 26.86°, 27.71°, 28.6°, 30.07°, and 33.2° that confirm the Z-Y presence.[41] The diffraction peaks at 2θ of 18.40°, 30.29°, 35.8°, 37.32°, 43.31°, 53.6°, 57.38°, and 62.99° prove the existence of NF NPs.[43] The elemental analysis of Z-Y–Pd–NF were carried out by energy-dispersive X-ray (EDX) study and clearly displayed Pd, Ni, and Fe existence (Figure ). In addition, the elemental analysis of Pd, Ni, and Fe were determined as 0.05, 0.12, and 0.15 mol % by inductively coupled plasma optical emission spectroscopy (ICP–OES), respectively.

Figure 9

XRD pattern of the synthesized Z-Y–Pd–NF.

Figure 10

EDX of the prepared Z-Y–Pd–NF.

Figure displays TEM images of the prepared Z-Y–Pd–NF. This sample has a shell–core structure as well as the prepared NF NPs.

Figure 11

TEM images of the prepared Z-Y–Pd–NF (a,b) with core–shell structure.

Figure reveals the magnetization curve of Z-Y–Pd–NF. Accordingly, the saturation magnetization for Z-Y–Pd–NF is equal to 5.01 emu g–1. This study proves the paramagnetic behavior of the catalyst because of the presence of magnetic nanoparticles on the zeolite surface. The saturation magnetization of Z-Y–Pd–NF is considerably lower than that of the bulk magnetite because of the low amount of NF NPs dispersed on the zeolite surface.

Figure 12

Magnetization curve of magnetic Z-Y–Pd–NF.

Catalytic Evaluation

Carbon–carbon bond formation is one of the most fundamental reactions for the construction of molecular frameworks in organic chemistry. Therefore, first, the effect of temperature in the S–M catalytic system was studied (Table ). According to Table , when the temperature is 80 °C, better catalytic performance of Z-Y–Pd–NF is obtained in the product.

Table 1

S–M Coupling Reaction in Different Conditions to Get Optimum Temperature

entry	conditions	yieldsa (%)
1	room temperature	31
2	50 °C	82
3	80 °C	96

Isolated yields.

In addition, a solvent plays an important role in improving the rate of this coupling reaction. Therefore, several experiments were carried out to find the best solvent for the S–M coupling reaction (Table ). A high yield was achieved with the H2O/EtOH (1:1) solvent. The other solvents, namely, EtOH, H2O, DMF, DMSO, toluene, and tetrahydrofuran (THF), had lower yields in comparison to H2O/EtOH. It was found that the least yield was obtained when THF was utilized as the solvent. Potassium carbonate, K2CO3, was selected as the base for optimizing the conditions of the reaction.

Table 2

Effect of Different Solvents on the S–M Coupling Reaction of Bromobenzene with Benzeneboronic Acid

entry	solvent	yieldsa (%)
1	EtOH	90
2	H2O	90
3	EtOH/H2O (1:1)	96
4	toluene	81
5	DMSO	85
6	THF	61
7	DMF	67

Isolated yields.

ICP–OES elemental analysis shows that the amounts of Pd, Ni, and Fe are 0.05, 0.12, and 0.15 mol %, respectively. To optimize the amount of catalyst, Z-Y–Pd–NF, the reaction of bromobenzene with benzeneboronic acid in the H2O/EtOH solvent system at 80 °C was considered. Therefore, the optimal amount of the catalyst is 0.01 mol % (Table ).

Table 3

Effect of Catalyst Amount in the Reaction between Bromobenzene and Phenylboronic Acid at 80 °C in H2O/EtOH (1:1)

entry	amount of Z-Y–Pd–NF (mol %)	yieldsa (%)
1	0.003	87
2	0.008	91
3	0.010	96
4	0.015	96

Isolated yields.

The S–M carbon–carbon cross-coupling reactions of different aryl halides with benzeneboronic acid were examined using the magnetic catalyst, Z-Y–Pd–NF (Table ).

Table 4

S–M Coupling Reaction of Various Aryl Halides, with Benzeneboronic Acida

entry	substrate	product	time (h):yieldb (%)
1	C6H5I	a	0.5:99
2	C6H5Br	a	1.0:96
3	C6H5Cl	a	2.0:83
4	4-MeC6H4I	b	0.5:94
5	4-NO2C6H4Br	c	2.0:97
6	4-NO2C6H4Cl	c	2.5:88
7	4-CNC6H4Cl	d	2.5:87
8	4-CNC6H4F	d	4.0:62
9	C5H4NCl	e	3.5:91

Reaction conditions: aryl halide (0.5 mmol), Z-Y–Pd–NF (15 mg, 0.010 mol % Pd), benzeneboronic acid (0.75 mmol), K2CO3 (1.0 mmol), and water/ethanol (1:1).

Isolated yields.

There are three fundamental steps for the S–M carbon–carbon coupling reaction: oxidative addition, transmetalation, and reductive elimination as demonstrated in Figure . Oxidative addition is the rate-determining step in the catalytic cycle and the relative reactivity decreases in the order of I > OTf > Br > Cl. A pathway for the activation of the catalyst is proposed as in Figure . First, Pd(0) nanoparticles were placed on the surface of zeolite Y by the reaction between PdCl2 and zeolite Y in the presence of ultrasonic waves. The pathway for reducing palladium ions is organic radicals as per the following reactions 1–3

Figure 13

General catalytic cycle for the S–M cross-coupling via Z-Y–Pd–NF.

Rehspringer reported that ultrasonic waves can reduce some metals like Pd(II) and Pt(II).[46] Thus, initially Pd(0) converts into a Pd(II) complex in an oxidative addition step (intermediate 1 in Figure ). Under the participation of a base, phenyl boronic acid reacts with intermediate 1 in transmetalation to afford intermediate 2. This is followed by reductive elimination to give the desired product and regenerate the original Pd(0) species.

This study shows that aryl iodides (entries 1, 4) and aryl bromides (entries 2, 5) can easily react with phenylbronic acid. However, aryl chlorides (entries 3, 6, 7, and 9) and aryl fluoride (entry 8) react slowly with phenylbronic acid. Furthermore, the aryl halides having electron-withdrawing groups can efficiently couple with phenylboronic acid in comparison to aryl halides containing electron-donating groups with phenylboronic acid. Interestingly, Z-Y–Pd–NF causes the reaction between a deactivated 4-CNC6H4F and phenylboronic acid (entry 8) to occur with 62% of yield. To the best our knowledge a few catalysts can react with aryl fluorides. In the oxidative addition step, adding palladium into a C–X bond occurs in the order I > Br > Cl > F, based mainly on the strength of the C–X bond.[47] Considering the abovementioned reaction protocol, this magnetic catalyst can be applicable to a wide range of aryl halides in all cases.

The reaction of chlorobenzene with phenylboronic acid in this study has been compared with a number of noble metal-based compounds presented in recent investigations on S–M reactions (Table ). The catalytic performance of the synthesized Z-Y–Pd–NF by the ultrasonic method is very good because of short times and more yields in comparison with other catalysts. For example, when Fe3O4/P (GMA-AA-MMA)–Pd (entry 7) has been used as a catalyst, the yield of the final product is 9% after 3.0 h, but our catalyst shows 83% yield after 2.0 h. In another comparison, when PdPtZn (entry 4) has been used, CTAB has been applied as a stabilizer for catalyst stability, but in this work no stabilizer has been applied.

Table 5

Catalytic Activity of Various Catalysts in the Coupling of Chlorobenzene and Benzeneboronic Acid

entry	catalyst	solvent	base	temp (°C)	time (h)	yield (%)	refs
1	PdPtZn	H2O–CTAB	K2CO3	reflux	2.0	80	(35)
2	PtPdCu	H2O	K2CO3	reflux	1.5	80	(47)
3	CelFemImiNHC@Pd complex	EtOH	Cs2CO3	RT	2.0	54	(48)
4	IPrPdCl2	H2O/i-PrOH	K3PO4	RT	5.5	99	(49)
5	Pd/r-GO	H2O	K2CO3	reflux	3.0	80	(50)
6	Pd/Fe3O4/r-GO	H2O	K2CO3	reflux	2.5	85	(51)
7	Fe3O4/P (GMA-AA-MMA)–Pd	H2O/EtOH	K2CO3	80	3.0	9	(52)
8	PdCl2	PEG	K2CO3	RT	6.0	98	(53)
9	Pd-1/FSG	H2O	K2CO3	100	12.0	26	(54)
10	Z-Y–Pd NPs	H2O/EtOH	K2CO3	reflux	1.5	88	(41)
11	magnetic Z-Y–Pd–NF	H2O/EtOH	K2CO3	80	2.0	83	this work

Nowadays, catalyst recycling in the synthesis of organic compounds has received chemists’ attention. Therefore, the recycling of the prepared catalyst, Z-Y–Pd–NF, in the modified S–M reaction of phenylboronic acid with bromobenzene is considered and the findings are given in Figure . Upon completion of each reaction, the solid catalyst is separated by applying an external magnet, washed with ethyl acetate, and reused without further purification. According to Figure , no significant loss of catalytic activity is observed after eight consecutive reactions for magnetic Z-Y–Pd–NF.

Figure 14

Reusability of the prepared catalyst, Z-Y–Pd–NF, in the S–M reaction.

Conclusions

In this study, a suitable, green energy procedure, sonochemistry, was used to synthesize magnetic Z-Y–Pd–NF. The advantages of this method are application of green energy, short time synthesis of Z-Y–Pd–NF, and creation of regular zeolite with a uniform structure and cavities. The structure and properties of Z-Y–Pd–NF were characterized by various techniques. To investigate the performance of Z-Y–Pd–NF, it was used in the S–M coupling reaction as a catalyst. The Z-Y–Pd–NF showed excellent efficiency in carbon–carbon cross-coupling reactions and interestingly, fluorobenzene could react with phenylboronic acid in the presence of this catalyst. Other advantages of using Z-Y–Pd–NF in S–M carbon–carbon coupling reactions are short reaction time, high yield, and easy recoverability. More importantly, catalyst recycling is easily achieved using a permanent magnet.

Experimental Section

All of the chemicals were purchased from Merck Company and used without further purification. Microwave radiation was obtained by a domestic microwave oven (LG, Model: MC-3223CS/00, power: 360 W) at atmosphere pressure. Ultrasonic generation was carried out by an ultrasonic instrument (FAPA, Model: UP400) with a standard probe. The powder X-ray diffraction was performed by a STOE-STADV instrument (Cu Kα = 1.5418 Å). SEM images were obtained using TESCAN and ZEISS (Sigma VP-WDS detector) instruments. TEM images were obtained using a Zeiss-EM10C-100 kV instrument. FT-IR spectra were recorded with a Shimadzu spectrometer (KBr pellets) from 400 to 4000 cm–1. ICP–OES was obtained by a VISTA-PRO instrument. 1H NMR spectra of products were taken with a Bruker 400 MHz ultrashield spectrometer using CDCl3 and TMS as the solvent and internal standard, respectively.

Synthesis of NF NPs by a Domestic Microwave

Fe(NO3)3·9H2O (0.8 g) and Ni(NO3)2·5H2O (0.3 g) as metal sources, NH2CH2COOH (0.23 g) as a fuel and organic driving agent, and NH4NO3 (0.48 g) as an oxidizer were used for this part of the synthesis. These materials were mixed and transferred into a domestic microwave oven with a power of 360 W for 30 min. The resulting compound was collected, washed several times with ethanol and distilled water for removal of the residual initial materials, and dried at 70 °C for 24 h. Finally, the dark brown color NF powder was obtained.[55]

Synthesis of Magnetic Z-Y–Pd–NF

First, Z-Y was produced using a starting aluminosilicate gel with a molar ratio of 1 Al2O3/4 Na2O/9 SiO2/170 H2O. Then, H–Y zeolite was obtained by ion exchange of Z-Y with a solution of ammonium chloride (1 M, 4 h, and 80 °C), which we have reported in our previous paper.[41] The product was filtered and washed with distilled water. After that, it was dried at 120 °C for 12 h and then calcined at 500 °C in a furnace. This prepared sample was added to a 100 mL round-bottom flask containing 50 mL of EtOH, 0.05 g of PdCl2, and 0.05 g of NF. This mixture was transferred to an ultrasonic device (1 h, 150 W). After that, the final product was filtered, washed, and dried overnight at 100 °C. The yield of Z-Y–Pd–NF was obtained at 85 wt % (0.85 g).

Suzuki–Miyaura (S–M) Coupling Reaction

A 50 mL round-bottom flask was charged with aryl halides (Ar–X, X = F, Cl, Br, I) (0.5 mmol), benzeneboronic acid (0.75 mmol), K2CO3 (1.0 mmol), Z-Y–Pd–NF as catalyst (15 mg, 0.01 mol %), and stirred in a H2O–EtOH (1:1, v/v) solvent system at 80 °C. The reaction was monitored by TLC. After completion of the reaction, the product was extracted with dichloromethane. The extracted product was dried over MgSO4 and the pure product was obtained by the removing the solvent. NMR spectra of the purified products are given in the Supporting Information.[41]