A recyclable magnetic nanoparticles supported palladium catalyst for the Hiyama reaction of aryltrialkoxysilanes with aryl halides

Abstract

A highly efficient and easily recoverable magnetic nanoparticles supported palladium catalyst has been developed and used in the Hiyama reaction of aryltrialkoxysilanes with a variety of organic halides. The reactions generated the corresponding products in good yields. In addition, the supported catalyst exhibited high stability and could be recovered and reused at least 10 times without significant loss of its catalytic activity.

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Introduction

Recently, the palladium-catalyzed cross-coupling transformation of aryltrialkoxysilanes with aryl halides, known as Hiyama reaction, has attracted much attention in organic synthesis.¹ It is one of the important methodologies for the construction of biaryl subunits² and extensively used in the synthesis of pharmaceutical intermediates, bioactive molecules and functional materials.³ In the last two decades, many efforts have been made in homogeneous catalytic Hiyama reactions because the transition metal catalysts often show high catalytic activity and efficiency under homogeneous conditions.⁴ For example, DeShong et al. reported an efficient method for the cross-coupling reactions of aryl halides, aryl triflates and allylic benzoates with a hypervalent silane reagent.⁵ Then, Fu's group applied the PdBr₂/P(t-Bu)₂Me catalytic system in the Hiyama reaction of aryl silanes with alkyl halides and iodides.⁶ Recently, Denmark and co-workers achieved stereospecific products by using Pd-catalyzed cross-coupling reactions of (E)- and (Z)-alkenylsilanolates with aryl chlorides.⁷ Although most of the homogeneous catalysts exhibited excellent activity, the high expense, metal pollution and the difficulty of product purification could not be ignored.⁸ Due to the increasing environmental concerns,⁹ it is extremely necessary to develop environmentally benign catalysts for the organic transformations.

Over the past few decades, significant progress in this area has been made with a variety of supported catalysts by using different kinds of supports in various fields,¹⁰ including the use of mesoporous silica,¹¹ ionic liquids,¹² and polymers,¹³ which could be easily recovered and reused. However, these developed strategies often need a special solvent for the separation of the catalyst from the system, such as the ionic liquid system¹² and the polymer system.¹³ In order to simplify the catalyst separation, nanoparticles as an ideal support would be a good choice. More recently, application of functionalized magnetic nanoparticles (MNPs) has been extensively explored in organic synthesis.¹⁴ The MNPs of Fe₃O₄ are robust, readily available, chemically stable and can be prepared by simple methods, which can be used as an efficient alternative to heterogeneous catalyst supports. Most importantly, the MNPs-supported catalyst could be separated from the reaction system by using an external magnet conveniently without filtration. Recently, Che et al. have developed an efficient magnetic nanoparticles-supported Hoveyda–Grubbs catalyst for ring-closing metathesis reactions.¹⁵ Xia and co-workers reported Pd-catalyzed carbonylative Sonogashira reactions.¹⁶ To the best of our knowledge, application of MNPs-supported catalysts in Hiyama reactions is rare in the literature. Here we wish to report a nano-ferrite-supported, magnetically recyclable Pd catalyst for the Hiyama reactions (Scheme 1). A variety of aryltrialkoxysilanes reacted with organic halides in the presence of 0.5 mol% supported palladium catalyst and generated the corresponding products in good yields. It is important to note that the supported catalyst could be recovered and reused at least 10 times without significant loss of its catalytic activity.

Scheme 1 Preparation of magnetic nanoparticles-supported palladium catalyst and its application in Hiyama reaction.

Results and discussion

The magnetic nanoparticles-immobilized palladium catalyst was prepared according to the synthetic route in Scheme 1. The silica-coated Fe₃O₄ (SiO₂@Fe₃O₄) was prepared according to the literature.¹⁴ Commercially available Fe₃O₄ nanoparticles, with an average diameter of 10 nm after sonication, were coated with a thin layer of silica using a sol–gel process to give silica-coated Fe₃O₄. TEM images of the SiO₂@Fe₃O₄ showing the structure of the particles are shown in Fig. S1 (ESI†), and the silica coating has a thickness of about 10 nm. The phosphine was anchored onto the surface of SiO₂@Fe₃O₄ by using 2-(diphenylphosphino)ethyltriethoxysilane at refluxing temperature in toluene, with a loading of 0.18 mmol of phosphine per gram. The supported Pd catalyst was obtained by simply dissolving Pd(OAc)₂ in THF and treating it with the above phosphine-functionalized SiO₂@Fe₃O₄, with a loading of 0.049 mmol of palladium per gram determined via inductively coupled plasma atomic emission spectrometry (ICP-AES). XRD measurements of the supported catalyst shown in Fig. S2 (ESI†) exhibit diffraction peaks corresponding to the typical spinel maghemite structure and the diffraction peak of the layered amorphous silica was not obvious, and no peaks characteristic for palladium(0) nanoparticles were observed which proves the excellent dispersion of the palladium sites on the magnetic nanoparticles. The structure of supported palladium catalyst was also verified by X-ray photoelectron spectroscopy (XPS). The electron binding energy analysis shown in Fig. 1 indicated that the state of palladium in a freshly prepared catalyst was Pd(II), which coordinated to two phosphorus atoms.^14b However, the state of palladium in the used one (after 5th run) was mainly Pd(0), which could be coordinated to four P-ligands. It implies that the use of a silica-coated iron oxide support to carry phosphine–Pd for Hiyama reaction is a semi-heterogeneous way, and actually the reaction proceeds in the homogeneous phase (THF solution in this paper), especially for the freshly prepared MNPs-immobilized palladium catalyst, SiO₂@Fe₃O₄–Pd.^14a,f

Fig. 1 XPS of the supported Pd catalyst.

The initial studies of Hiyama reaction were performed by using phenyltrimethoxysilane (1a) and 4-iodoanisole (2a) as model substrates, in the presence of the MNPs-immobilized palladium catalyst (SiO₂@Fe₃O₄–Pd). The results are summarized in Table 1. At first, the effect of solvent on the reaction was examined, and a significant solvent effect was observed. Only 12% and 10% yields of product 3a were obtained when the reactions were performed in CH₃OH and C₂H₅OH, respectively (Table 1, entries 1 and 2). It is worth noting that no desired product 3a was observed when the reaction was performed in H₂O or DMSO (Table 1, entries 3 and 4). However, this reaction proceeded in DMF and CH₃CN to afford the corresponding product 3a in 26% and 40% yields, respectively (Table 1, entries 5 and 6). Further investigation indicated that the aprotic polar solvent, such as THF could efficiently promote the Hiyama reaction, and the desired cross-coupling product 3a was generated in 91% yield (Table 1, entry 7). However, inferior results were obtained when 1,4-dioxide and toluene were employed as reaction media in the reaction under the same conditions (Table 1, entries 8 and 9).

Table 1 Effect of solvent on the Hiyama reaction of phenyltrimethoxysilane with 4-iodoanisole^a

Entry	Solvent	Yield^b (%)
a Reaction conditions: phenyltrimethoxysilane (1a, 0.75 mmol), 4-iodoanisole (2a, 0.50 mmol), SiO2@Fe3O4–Pd catalyst (50 mg, containing Pd 0.0025 mmol, 0.5 mol%), TBAF (1.0 mmol) in solvent (2.0 mL) at 60 °C under a nitrogen atmosphere and stirred for 10 h. b Isolated yields.
1	CH3OH	12
2	C2H5OH	10
3	H2O	NR
4	DMSO	NR
5	DMF	26
6	CH3CN	40
7	THF	91
8	1,4-Dioxane	37
9	Toluene	31

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On the basis of the above preliminary optimized results, the next studies were focused on the effect of bases on the model reaction. Among the bases examined, it was found that tetra-n-butylammonium fluoride (TBAF) acts as an excellent base in the MNPs-supported Pd-catalyzed Hiyama reaction, but KF and CsF were less effective and gave the product 3a in 83 and 80% yields, respectively (Table 2, entries 1–3). However, tetra-n-butylammonium acetate (TBAA) did not work and no desired product 3a was detected in the reaction (Table 2, entry 4). Subsequently, other inorganic and organic bases, such as K₃PO₄, K₂CO₃, DBU and triethylamine, were also screened under the same conditions. The results indicated that the above bases failed to promote the cross-coupling reaction efficiently (Table 2, entries 5–8). Finally, we also found that the yields of 3a were not improved significantly upon increasing the amount of catalyst loading or the reaction temperature (Table 2, entries 9–12).

Table 2 Effect of base on the Hiyama reaction of phenyltrimethoxysilane with 4-iodoanisole^a

Entry	Base	Yield^b (%)
a Reaction conditions: phenyltrimethoxysilane (1a, 0.75 mmol), 4-iodoanisole (2a, 0.50 mmol), SiO2@Fe3O4–Pd catalyst (50 mg, containing Pd 0.0025 mmol, 0.5 mol%), base (1.0 mmol) in THF (2.0 mL) at 60 °C under a nitrogen atmosphere and stirred for 10 h. b Isolated yields. c 40 °C for 10 h. d 80 °C for 10 h. e 0.2 mol% of SiO2@Fe3O4–Pd catalyst was used. f 1.0 mol% of SiO2@Fe3O4–Pd catalyst was used.
1	TBAF	91
2	KF	83
3	CsF	80
4	TBAA	NR
5	K2CO3	20
6	K3PO4	NR
7	DBU	NR
8	Et3N	34
9	TBAF	67^c
10	TBAF	90^d
11	TBAF	54^e
12	TBAF	92^f

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In general, Pd-catalyzed Hiyama cross-coupling reactions of organosilanes with aryl halides were performed in the presence of TBAF, and the organosilanes, including aryl and alkenyl trialkoxysilanes, were effective.¹⁷ In order to figure out the role of TBAF in the reaction, a control experiment was carried out under the present reaction conditions in the absence of substrate 1a or 2a. After the reaction and isolation of the catalyst, the Pd content in THF solution was determined by ICP-AES and the result showed that there was less than 0.5 ppm Pd in THF solution. This result also indicated that TBAF has not attacked the “robust” silica shell, a C(sp³)–Si bond of supported catalyst SiO₂@Fe₃O₄–Pd in the reaction.

To examine the versatility of this protocol, the SiO₂@Fe₃O₄–Pd catalyzed Hiyama reactions of aryltrimethoxysilanes with a variety of aryl halides were investigated under the optimized reaction conditions, which involve supported Pd catalyst (0.5 mol%), TBAF (2.0 equiv.) in THF at 60 °C under a nitrogen atmosphere. It was found that, in most cases, the Hiyama reactions afforded the corresponding cross-coupling products in good to excellent yields. The results are listed in Table 3. For 4-iodoanisole, 91% yield of 3a was obtained under the present reaction conditions (Table 3, entry 1). The yield of product 3b was slightly improved while using iodobenzene instead of 4-iodoanisole as one of the substrates (Table 3, entry 2). It is important to note that p-iodoanisole reacted with phenyltriethoxysilane efficiently and generated the corresponding cross-coupling product 3a in 97% yield (Table 3, entry 3). In comparison with p-iodoanisole, m-iodoanisole also reacted with phenyltrimethoxysilane smoothly to give 94% yield of the desired 3c (Table 3, entry 4). It is also indicated that the electronic and steric effect of the substituent was observed when using the substituted iodobenzenes with electron-rich or electron-poor groups, such as CH₃, F and NO₂ groups on the benzene rings (Table 3, entries 5–12). para-Substitution of Cl or CH₃CO in the benzene iodide also led to excellent yields (Table 3, entries 13 and 14). The scope of this catalytic system with other aryl bromides was also examined and good results were also obtained (Table 3, entries 15 and 16). Finally, 2-bromopyridine was reacted with phenyltrimethoxysilane in the Hiyama reaction, and 81% yield of 3n was obtained under the present reaction conditions (Table 3, entry 17). However, no cross-coupling product was detected when phenyltrimethylsilane was used instead of phenyltrimethoxysilane in the Hiyama reaction under the same conditions (Table 3, entry 18).

Table 3 Hiyama cross-coupling reaction of aryl halides with aryltrimethoxysilanes^a

Entry	1	2	3	Yield^b (%)
a Reaction conditions: aryltrialkoxysilane (1, 0.75 mmol), aryl halide (2, 0.5 mmol), SiO2@Fe3O4–Pd catalyst (50 mg, containing Pd 0.0025 mmol, 0.5 mol%), TBAF (1.0 mmol) in THF (2.0 mL) at 60 °C under a nitrogen atmosphere and stirred for 10 h. b Isolated yields.
1			3a	91
2			3b	94
3			3a	97
4			3c	94
5			3d	93
6			3e	96
7			3f	90
8			3g	96
9			3h	93
10			3i	89
11			3j	99
12			3k	98
13			3l	95
14			3m	99
15			3m	85
16			3j	87
17			3n	81
18			3a	NR

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To evaluate the recyclability of the SiO₂@Fe₃O₄–Pd catalyst in the Hiyama reaction, 4-iodoanisole and phenyltrimethoxysilane were chosen as model substrates. After the model Hiyama reaction was carried out under the optimized reaction conditions, the catalyst was recovered by an external magnetic separation (Fig. 2), washed with ethyl ether completely, dried in air and reused for the next run. More than 99% of the catalyst could simply be recovered by fixing a magnet near the reaction vessel. For the model Hiyama reaction, the supported palladium catalyst SiO₂@Fe₃O₄–Pd could be recycled and reused 10 times without loss of its catalytic activity (Table 4). In addition, palladium leaching in the SiO₂@Fe₃O₄–Pd catalyst was determined and ICP analysis of the THF solution (3.0 mL) of the model Hiyama reaction indicated that the Pd content was less than 0.20 ppm. It is also indicated that more than 99.64 wt% of Pd was recovered through an external magnetic separation after the reaction. Meanwhile, iron leaching in the SiO₂@Fe₃O₄–Pd catalyst was also determined and analysis of the reaction solution (3.0 mL) indicated that the Fe content was less than 0.10 ppm in the solution, which also demonstrated that there was almost no corrosion on the silica layer of the supported catalyst in anhydrous weak basic reaction medium.

Fig. 2 (a) The reaction mixture, SiO₂@Fe₃O₄–Pd catalyst was dispersed in the reaction solution; (b) after the reaction, SiO₂@Fe₃O₄–Pd catalyst was separated from the reaction solution by using an external magnet.

Table 4 Recycling SiO₂@Fe₃O₄–Pd catalyst for the Hiyama reaction of phenyltrimethoxysilane with 4-iodoanisole^a

Run	Yield^b (%)	Run	Yield^b (%)
a Reaction conditions: phenyltrimethoxysilane (1a, 0.75 mmol), 4-iodoanisole (2a, 0.5 mmol), reused SiO2@Fe3O4–Pd catalyst (50 mg, containing Pd 0.0025 mmol, 0.5 mol%), TBAF (1.0 mmol) in THF (2.0 mL) at 60 °C under a nitrogen atmosphere for 10 h. b Isolated yields.
1	91	6	89
2	91	7	88
3	90	8	87
4	89	9	86
5	90	10	85

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Experimental

General methods

Unless otherwise stated, all the reactions were carried out under a nitrogen atmosphere. The chemicals were purchased from commercial suppliers (Shanghai Chemical Company, China, and Aldrich, USA) and were used without purification prior to use. Products were purified by flash chromatography on 200–300 mesh silica gel, SiO₂. All ¹H and ¹³C NMR spectra were recorded by a Bruker 400 MHz FT-NMR spectrometer. Chemical shifts are given as δ values with reference to tetramethylsilane (TMS) as internal standard.

Synthesis of the silica-coated magnetic nanoparticles (SiO₂@Fe₃O₄)

Fe₃O₄ (0.50 g, with an average diameter of 20 nm, from Aldrich) was diluted with 5.0 mL of pure water and 45.0 mL of iso-propanol, and the mixture was sonicated for 0.5 h. To this well dispersed magnetic nanoparticles solution, 2.0 mL of NH₃·H₂O followed by 1.6 g of tetraethoxysilane were added and stirred for further 4 h at room temperature. The material was washed with water until the solution was neutral, then the solid material was magnetically separated, washed with ethanol and diethyl ether, respectively, and dried under vacuum. The silica-coated magnetic nanoparticles, SiO₂@Fe₃O₄ (1.36 g), were obtained. IR (KBr, cm⁻¹): ν_O–H = 3397, ν_Si–O = 1082.

Synthesis of phosphine-functionalized SiO₂@Fe₃O₄

2-(Diphenylphosphino)ethyltriethoxysilane (0.38 g) dissolved in 5.0 mL of anhydrous toluene was added to a suspension of 1.0 g of SiO₂@Fe₃O₄ in 30.0 mL of anhydrous toluene. The mixture was then shaken at 100 °C under a nitrogen atmosphere for 24 h. Then the solid material (SiO₂@Fe₃O₄–P) was magnetically separated, washed with toluene and CH₂Cl₂ to remove unanchored species and dried under vacuum. The phosphine-functionalized SiO₂@Fe₃O₄ (brown nanoparticles, 1.05 g) was obtained. The loading of phosphine was quantified via microanalysis and was found to be 0.18 mmol g⁻¹ based on the carbon content determination. IR (KBr, cm⁻¹): ν_O–H = 3396, ν_C–H = 2925, 2863, ν_Ar,C–C = 1518, 1469, ν_Si–O = 1081.

Synthesis of SiO₂@Fe₃O₄–Pd

To a sealable reaction tube, palladium acetate (22.4 mg, 0.10 mmol) and THF (15.0 mL) were added. The solution was shaken at room temperature under a nitrogen atmosphere for 10 min, and then 2.0 g of the above phosphine-functionalized magnetic nanoparticles (SiO₂@Fe₃O₄–P) was added. The mixture was shaken at room temperature for 4 h, then the solid catalyst was magnetically separated, and the solid was washed with THF, and dried under vacuum at 50 °C for 3 h. The supported Pd catalyst, SiO₂@Fe₃O₄–Pd (brown nanoparticles, 2.01 g), was obtained with a loading of 0.049 mmol of palladium per gram determined via inductively coupled plasma atomic emission spectrometry (ICP-AES). IR (KBr, cm⁻¹): ν_O–H = 3397, ν_C–H = 2978, 2896, ν_Ar,C–C = 1650, 1521, ν_Si–O = 1080.

General procedure for SiO₂@Fe₃O₄–Pd catalyzed Hiyama reaction

Aryl halide (0.50 mmol), phenyltrialkoxysilane (0.75 mmol), TBAF (1.0 mmol), and SiO₂@Fe₃O₄–Pd catalyst (50 mg, containing Pd 0.0025 mmol) were mixed in THF (2.0 mL). The mixture was shaken at 60 °C under a nitrogen atmosphere for 10 h. After the catalyst was separated magnetically, the catalyst was washed with diethyl ether three times. The organic phase was evaporated under reduced pressure and the product was purified by column chromatography on silica gel.

Typical procedure for recovery of SiO₂@Fe₃O₄–Pd catalyst and palladium leaching in SiO₂@Fe₃O₄–Pd catalyst

In a reaction vessel, 4-iodoanisole (117 mg, 0.50 mmol), phenyltrimethoxysilane (148 mg, 0.75 mmol), TBAF (315 mg, 1.0 mmol), and the reused SiO₂@Fe₃O₄–Pd catalyst (50 mg, containing Pd 0.0025 mmol) were mixed in THF (2.0 mL). The mixture was shaken at 60 °C under a nitrogen atmosphere for 10 h. After reaction, the supported catalyst was magnetically separated, and washed several times with diethyl ether, dried and used directly for the next run. In addition, palladium leaching in the SiO₂@Fe₃O₄–Pd catalyst was determined. ICP analysis of the THF solution (3.0 mL) of the reaction indicated that the Pd content was less than 0.20 ppm.

Analytical data of the products of Hiyama reaction

4-Methoxybiphenyl (3a). White solid, mp: 85–87 °C (85–86 °C).¹⁸¹H NMR (400 MHz, CDCl₃): δ 7.54 (4H, t, J = 8.8 Hz), 7.41 (2H, t, J = 7.6 Hz), 7.30 (1H, t, J = 7.6 Hz), 6.98 (2H, d, J = 8.8 Hz), 3.84 (3H, s); ¹³C NMR (100 MHz, CDCl₃): δ 159.1, 140.8, 133.7, 128.7, 128.1, 126.7, 126.6, 114.2, 55.3.

1,1′-Biphenyl (3b). White solid, mp: 70–71 °C (70–70.5 °C).¹⁹¹H NMR (400 MHz, CDCl₃): δ 7.65–7.62 (4H, m), 7.50–7.46 (4H, m), 7.40–7.36 (2H, m); ¹³C NMR (100 MHz, CDCl₃): δ 141.2, 128.7, 127.2, 127.1.

3-Methoxybiphenyl (3c). Colorless oil (colorless oil).²⁰¹H NMR (400 MHz, CDCl₃): δ 7.57 (2H, d, J = 7.6 Hz), 7.41 (2H, t, J = 7.2 Hz), 7.34–7.31 (2H, m), 7.18–7.12 (2H, m), 6.87 (1H, d, J = 8.4 Hz), 3.82 (3H, s); ¹³C NMR (100 MHz, CDCl₃): δ 159.9, 142.7, 141.0, 129.7, 128.7, 127.4, 127.1, 119.6, 112.8, 112.6, 55.2.

4-Methylbiphenyl (3d). White solid, mp: 46–47 °C (46 °C).¹⁸¹H NMR (400 MHz, CDCl₃): δ 7.56 (2H, d, J = 7.6 Hz), 7.48 (2H, d, J = 8.0 Hz), 7.41 (2H, t, J = 7.6 Hz), 7.32–7.30 (1H, m), 7.24–7.22 (2H, m), 2.38 (2H, m); ¹³C NMR (100 MHz, CDCl₃): δ 141.1, 138.3, 137.0, 129.5, 128.7, 127.0, 126.9, 21.1.

3-Methylbiphenyl (3e). Colorless oil (colorless oil).²⁰¹H NMR (400 MHz, CDCl₃): δ 7.68 (2H, d, J = 7.6 Hz), 7.54–7.48 (4H, m), 7.44–7.40 (2H, m), 7.26 (1H, d, J = 7.6 Hz), 2.51 (3H, s); ¹³C NMR (100 MHz, CDCl₃): δ 141.4, 141.2, 138.3, 128.7, 128.6, 128.0, 127.9, 127.2, 127.1, 124.3, 21.5.

2-Methylbiphenyl (3f). Colorless oil (colorless oil).²¹¹H NMR (400 MHz, CDCl₃); δ 7.46–7.42 (2H, m), 7.38–7.34 (3H, m), 7.29–7.26 (4H, m), 2.30 (3H, s); ¹³C NMR (100 MHz, CDCl₃): δ 142.0, 141.9, 135.3, 130.3, 129.8, 129.2, 128.0, 127.2, 126.7, 125.7, 20.4.

4-Fluorobiphenyl (3g). White solid,²² mp: 76–78 °C. ¹H NMR (400 MHz, CDCl₃): δ 7.58–7.54 (4H, m), 7.47–7.43 (2H, m), 7.38–7.35 (1H, m), 7.17–7.12 (2H, m); ¹³C NMR (100 MHz, CDCl₃): δ 162.5 (d, J = 244.7 Hz), 140.3, 137.3, 128.8, 128.7 (d, J = 8.0 Hz), 127.2, 127.0, 115.6 (d, J = 21.3 Hz).

3-Fluorobiphenyl (3h). Colorless oil (colorless oil).²³¹H NMR (400 MHz, CDCl₃): δ 7.67–7.64 (2H, m), 7.54–7.50 (2H, m), 7.47–7.43 (3H, m), 7.39–7.36 (1H, m), 7.14–7.09 (1H, m); ¹³C NMR (100 MHz, CDCl₃): δ 163.2 (d, J = 243.9 Hz), 143.5 (d, J = 7.6 Hz), 139.9 (d, J = 2.2 Hz), 130.2 (d, J = 8.4 Hz), 128.8, 128.7, 127.8, 127.1, 122.7 (d, J = 2.8 Hz), 114.0 (d, J = 21.4 Hz).

2-Fluorobiphenyl (3i). White solid, mp: 70–71 °C (70–72 °C).²⁴¹H NMR (400 MHz, CDCl₃): δ 7.71–7.65 (2H, m), 7.55–7.51 (3H, m), 7.44–7.43 (1H, m), 7.40–7.36 (1H, m), 7.30–7.21 (2H, m); ¹³C NMR (100 MHz, CDCl₃): δ 159.8 (d, J = 246.0 Hz), 135.8 (d, J = 1.1 Hz), 130.8 (d, J = 3.5 Hz), 129.0 (d, J = 2.9 Hz), 128.9 (d, J = 8.2 Hz), 128.7, 128.4, 127.6, 124.3 (d, J = 3.7 Hz), 116.1 (d, J = 22.7 Hz).

4-Nitrobiphenyl (3j). Pale yellow solid, mp: 111–113 °C (112–114 °C).¹⁸¹H NMR (400 MHz, CDCl₃): δ 8.28 (2H, d, J = 8.4 Hz), 7.72 (2H, d, J = 8.8 Hz), 7.61 (2H, d, J = 8.2 Hz), 7.51–7.42 (3H, m); ¹³C NMR (100 MHz, CDCl₃): δ 147.6, 147.1, 138.8, 129.1, 128.9, 127.8, 127.3, 124.1.

3-Nitrobiphenyl (3k). Pale yellow solid, mp: 60–61 °C (60–61 °C).¹⁸¹H NMR (400 MHz, CDCl₃): δ 8.46–8.45 (1H, m), 8.21 (1H, dd, J = 8.4, 2.4 Hz), 7.93 (1H, d, J = 8.4 Hz), 7.65–7.60 (3H, m), 7.53–7.49 (2H, m), 7.47–7.44 (1H, m); ¹³C NMR (100 MHz, CDCl₃): δ 148.7, 142.8, 138.6, 132.9, 129.6, 129.1, 128.5, 127.1, 122.0, 121.9.

4-Chlorobiphenyl (3l). White solid, mp: 78–79 °C (78–78.5 °C).¹⁹¹H NMR (400 MHz, CDCl₃): 7.62–7.56 (4H, m), 7.52–7.40 (5H, m); ¹³C NMR (100 MHz, CDCl₃): δ 139.9, 139.6, 133.3, 128.9, 128.8, 128.3, 127.5, 126.9.

1-(4-Biphenylyl)ethanone (3m). White solid, mp: 119–121 °C (120–121 °C).¹⁸¹H NMR (400 MHz, CDCl₃): δ 8.05 (2H, d, J = 8.0 Hz), 7.71 (2H, d, J = 8.4 Hz), 7.64 (2H, d, J = 7.6 Hz), 7.51– 7.47 (2H, m), 7.43–7.39 (1H, m), 2.65 (3H, s); ¹³C NMR (100 MHz, CDCl₃): δ 197.7, 145.8, 139.9, 135.9, 128.9, 128.8, 128.2, 127.3, 127.2, 26.6.

2-Phenylpyridine (3n). Colorless oil (colorless oil).²¹¹H NMR (400 MHz, CDCl₃): δ = 8.71–8.69 (1H, m), 8.03–8.00 (2H, m), 7.71–7.70 (2H, m), 7.50–7.40 (3H, m), 7.21–7.18 (1H, m); ¹³C NMR (100 MHz, CDCl₃): δ 157.3, 149.5, 139.2, 136.6, 128.8, 128.6, 126.8, 121.9, 120.4.

Conclusions

In summary, we have successfully applied a recyclable MNPs-Pd catalyst in the Hiyama reactions. Aryltrialkoxysilanes reacted with a variety of organic halides in the presence of 0.5 mol% supported palladium catalyst and generated the corresponding products in THF with good yields. It is important to note that the supported catalyst could be recovered and reused at least 10 times without significant loss of its reactivity. The operationally simple procedure for the catalyst recovery and good recycling efficiency of the catalyst make it an ideal catalytic system for the Hiyama reaction. The further application of the MNPs-Pd catalyst in other organic reactions is currently underway in our laboratory.

Acknowledgements

Financial support from the National Natural Science Foundation of China (Nos 21172092, 20972057, and 21002039), the Natural Science Foundation of Anhui (No. 090416223), the Key Project of Science and Technology of the Department of Education, Anhui Province (No. ZD2010-9) is gratefully acknowledged.

Notes and references

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c2cy20162c

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