Role of TBATB in nano indium oxide catalyzed C-S bond formation.

Nano sized indium oxide is found to be an efficient catalyst for the conversion of thiols to sulfides using Na2CO3 as base and TBATB as reagent in DMSO at 110 °C. Here in situ generation of bromo intermediate by TBATB takes place through indium surface. A variety of aryl sulfides can be synthesized in excellent yields from less reactive chlorides, boronic acids and thiols.

The applications of metal-nanoparticle catalysis in organic synthesis has received considerable interest in recent years1. One of the important applications is toward the C-S bond formation has increased tremendously because of its high efficiency and compatibility with eco-friendly reaction media2. Transition metal-catalyzed cross-coupling is one of the most commonly used reactions in the construction of C-S bonds, in which the formation of diaryl sulfide motifs is particularly valuable due to its significance in biologically active molecules and chemical materials3. During the past decades, various Cu 45, Ni 6, Pd 78, Co 9, and Fe 1011 catalytic systems have been developed that allow aryl halides and aryl boronic acids that couple with arylthiols under mild reaction conditions. In the recent decades, however, indium-based12 catalytic systems have attracted considerable attention due to their high reactivity, low cost and lower toxicity. The indium-catalyzed C-S cross coupling of organyl halides with dichalcogenides was described in 20091314. Moreover, Reddy and co-worker15 reported nano-In2O3 catalyzed C-S cross-coupling of aryl halides with aromatic/alkyl thiols but this protocol reported a longer reaction time. Nevertheless, to the best of our knowledge, their application as catalysts for the C-S cross-coupling reaction of thiol with arylboronic acid has yet not been discovered. We report herein a facile synthesis of aryl thioethers employing nano indium oxide as catalyst in several transformations (Fig. 1). The catalyst efficiency can be increased by using TBATB (tetrabutylammonium tribromide).

Figure 1

Synthesis of aryl sulfide.

Results

Indium oxide nanoparticles (NPs) could be synthesized following a reported method16 with minor modifications. In a typical procedure, 0.10 mol ratio of In(NO3)29H2O were added to 20 ml distilled water in a three necked round-bottom flask and stirred at 100 °C for 30 min. 0.12 M NaOH solution were added dropwise untill white precipitate was obtained (pH = 9). The obtained precipitate was centrifuged and washed three times with double distilled water. The final white product was calcined at 400 °C. After calcination, the colour of the powder turned from white to light yellow indicating that the resultant product is In2O3. To investigate the composition and topography of the final calcination product, powder XRD, scanning electron microscopy (SEM) image and EDS were carried out. Figures (2) and (3) shows the typical transmission electron microscopy (TEM) image and scanning electron microscopy (SEM) image of indium oxide nanoparticles, where the sizes are estimated to be 10–20 nm.

Figure 2

TEM-images of In2O3 nanoparticles at (a,b) lower and (c) higher magnification (d) SAED pattern (e) powder XRD.

Figure 3

SEM-images of In2O3 nanoparticles at (a,b) lower and (c) higher magnification (d) Energy dispersive X-ray spectroscopy (EDS).

The N2 adsorption and desorption isotherm for nano indium oxide is type IV (Fig. 4). The surface area and average pore diameter of the prepared nano-In2O3 were 66.9 m2 g−1 and 7.7 nm, respectively.

Figure 4

N2 adsorption-desorption isotherm of indium oxide nanoparticles.

To optimize the reaction conditions a series of experiments were performed under varying reaction parameters, such as solvent, time, temperature and base for a representative C-S cross coupling reaction. In the preliminary phase of optimization, thiophenol and allyl chloride was chosen as a standard substrate and the trials were performed with different catalysts, ligands, and solvents at different temperature (Table 1). Nano-In2O3 was found to be the best choice among the various catalysts (Table 1, entry 1). The results shown that 2 equiv Na2CO3 and 1.5 equiv TBATB with 2 mol% nano-In2O3 were the best concentrations for the transformation to occur within a reasonable time period. When 5 moI% of catalyst was used, no appreciable change with respect to yield was observed (Table 1, entry 3). Nevertheless, other catalyst (Co2CO3) gave low yield. The coupling reaction was investigated in various solvents such as CH2Cl2, DMSO, CH3CN and CH3COOH. DMSO was found to be the best solvent.

Table 1

Optimization of reaction condition for thiophenol to sulfide (Bold examples).

Entry	Catalyst (mol %)	Reagent (2eq)(Temp °C)	Solvent (Base 2eq)	Time (h)	Yield (%)d
1	Nano-In2O3 (2)	TBATB (110)	DMSO(Na2CO3)	2	99a
		TBATB (110)	DMSO(Na2CO3)	2	99b
		TBATB (110)	DMSO(Na2CO3)	4	45c
		------- (110)	DMSO(Na2CO3)	18	75
		TBATB (rt)	DMSO(Na2CO3)	10	46
2	Nano In2O3 (2)	Br2 (110)	DMSO(NaOH)	2	40
3	Nano-In2O3 (5)	TBATB (110)	DMSO(Na2CO3)	2	95
4	Nano-In2O3 (2)	TBATB (130)	CH2Cl2 (KOH)	4	65
5	Nano-Co3O4(5)	TBATB (110)	CH3COOH(Na2CO3)	4	40
6	Nano-Co3O4 (10)	TBATB (110)	CH3CN(Na2CO3)	2	64

aReaction was carried out at mmol scale using 0.2 mmol (22 mg) of thiophenol, (2 moI%) catalyst, bromine source (1.5 equiv) and base (2.0 equiv).

bReaction was also carried out at gram scale using 1.10 g of thiophenol, (2 moI%) catalyst and TBATB (1.5 equiv), Na2CO3 (2.0 equiv).

cWithout catalyst.

dIsolated yield.

Having optimized conditions (Table 1 entry 1) for C-S reaction, we continued our pursuit with a variety of aromatic and aliphatic substrates (Fig. 5). As shown in Fig. 5, aryl thiols bearing electron-donating groups such as methoxy, methyl groups (3f-g) efficiently couple with allyl chlorides to yield the corresponding arylsulfide in excellent yields (88–89%). However, arylthiols with electron withdrawing groups gave the corresponding arylsulfides in lower yields (3i-j) and benzylthiols gave moderate to good yields (3b).

Figure 5

Synthesis of Aryl-allyl sulfide:

Reactions were carried out with allyl chloride (0.2 mmol) Arylthiol (0.2 mmol), nano-In2O3 (2 mol%), TBATB (1.5 equiv), Na2CO3 (2.0 equiv) in DMSO (2 mL) for 2 h.

Having same standard reaction conditions, we explored the scope of thiols with arylboronic acids (Fig. 6). A broad range of functional groups, such as ether, halides, ester, etc. were tolerated under the standard reaction condition to provide the expected products, 5a-x in good to excellent yields. Aryl thiols containing electron withdrawing and electron donating group were coupled to furnish the corresponding diarylsulfides in good to excellent yields. It is noteworthy that our protocol could also be extended to alkyl thiols giving good yields. Quite significantly, a wide range of boronic acids that incorporate electron donating groups (5b-e) and electron-withdrawing groups at the ortho, meta, and para positions are readily tolerated. However, low yields of respective diarylsulfides were obtained with 3-nitro-phenylboronic acid, 3,5-dichlorophenyl boronic acid and 4-chlorophenylboronic acid (5f-g, 5s).

Figure 6

Coupling of thiols with arylboronic acids:

Reactions were carried out with arylboronic acid (0.2 mmol), thiol (0.2 mmol), nano-In2O3 (2 mol%), TBATB (1.5 equiv), Na2CO3 (2.0 equiv) in DMSO (2 mL) for 2 h.

On the basis of previous literature reports17, the proposed reaction pathway for these reactions is based on oxidative addition followed by reductive elimination (Fig. 7). The consequent oxidative addition (pathway1) of In(nano) with allyl chloride may provide intermediate RIn(nano)Br (A) or RIn(nano)Cl A1. The product yield increased suddenly on addition of TBATB and might be it follows the formation of intermediate (A) largely rather than A1. Then in presence of base thiol react with A can give intermediate B, which undergoes a reductive elimination to provide the target product and to regenerate the catalyst In(nano).

Figure 7

Plausible mechanism for C-S bond formation

In pathway 2, ArSH on oxidative addition to form intermediate A/ and in presence of base arylboronic acid react with A/ to form intermediate B/ which undergo reductive elimination to form the product. The main significance of this work that In(nano) provides large surface area for which the Br- can easily form intermediate A or A/.

After completion of reaction the catalyst was recovered by centrifugation and reused for the fresh reaction of aryl thiol with allyl chloride/boronic acid and no loss of activity was observed (Fig. 8).

Figure 8

Recovery of In2O3 nps:

(a) Reactions were carried out with allyl chloride (0.2 mmol) phenylthiol (0.2 mmol), nano-In2O3 (2 mol%), TBATB (1.5 equiv), Na2CO3 (2.0 equiv) in DMSO (2 mL) for 2 h. (b) Reactions were carried out with phenyIboronic acid (0.2 mmol), phenyIthiol (0.2 mmol), nano-In2O3 (2 mol%), TBATB (1.5 equiv), Na2CO3 (2.0 equiv) in DMSO (2 mL) for 2 h.

We have reported a general synthetic protocol for the C-S bond, using nano-indium-catalyst. In this protocol, we recommend the use of 2 moI% indium-catalyst, TBATB (1.5 equiv) Na2CO3 (2 equiv), and DMSO as the solvent. We found the main advantages of this protocol were low toxicity of the catalyst, good turnover and high yield of products.

Methods

General Information

All solvents and chemicals were purchased commercially and used without further purification. Melting points were recorded on an electrothermal digital melting point apparatus and were uncorrected. Column chromatography was generally performed on silica gel (230–400 mesh) and reactions were monitored by thin layer chromatography (TLC) using UV light (254 nm) to visualize the course of reactions. 1H and 13C Nuclear Magnetic Resonance spectra of pure compounds were acquired at 400 and 100 MHz respectively. All NMR samples were recorded in deuterated chloroform. Chemical shifts (ppm) were recorded with tetramethylsilane (TMS) as the internal reference standard. Elemental analyses were performed on a Flash 2000 Thermo Scientific instrument at NIT Silchar. The TEM and SEM characterization were carried out at model no. CM-12 Philips TEM (IIT Kharagpur) and FEI Nova nano-SEM-450 (NIT Rourkela) respectively.

Allyl(phenyl)sulfane (3a)18

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and allyl chloride (15.2 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at the corresponding temperature for 2 h. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 25/1) to give the title compound 3a (149 mg, 99%) as a light yellow liquid; [Found: C, 71.98; H, 6.49; C9H10S. requires C, 71.95; H, 6.71%]; Rf = 0.4 (hexane/ethyl acetate = 20/1). 1H NMR (400 MHz, CDCl3): δ 7.39–7.28 (m, 5H), 5.94 (m, 1H), 5.28 (dd, J = 1.3 Hz, J = 16.4 Hz, 1H), 5.13 (dd, J = 1.2 Hz, J = 10.1 Hz, 1H),3.68 (d, J = 6.8 Hz, 2H) 13C NMR (100 MHz, CDCl3): δ 134.9, 133.9, 130.7, 129.8, 126.9, 118.9, 37.4.

(2-methylallyl)(phenyl)sulfane (3c)19

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 2-chloro-2-methyl-propene (18.2 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at the corresponding temperature for 2 h. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 10/1) to give the title compound 3c (114.8 mg, 70%) as a colourless liquid; [Found: C, 72.98; H, 7.39; C10H12S requires C, 73.12; H, 7.36%]; Rf = 0.4 (hexane/ethyl acetate = 10/1). 1H NMR (400 MHz, CDCl3): δ 7.44–7.33 (m, 5H), 5.16 (d, J = 1.2 Hz, 1H), 4.89 (d, J = 1.1 Hz, 1H), 3.65 (s, 2H), 1.87 (s, 3H). 13C NMR (100 MHz, CDCl3): δ 142.4, 135.3, 131.2, 129.1, 128.2, 112.5, 42.9, 21.7.

(2-bromoallyl)(phenyl)sulfane (3d)20

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 2-bromo-allyl bromide (39.6 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at the corresponding temperature for 2 h. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 15/1) to give the title compound 3d (201 mg, 88%) as a colourless liquid; [Found: C, 47.16; H, 3.93; S, 14.04; C9H9BrS requires C, 47.18; H, 3.96; S, 13.99%]; Rf = 0.4 (hexane/ethyl acetate = 15/1). 1H NMR (400 MHz, CDCl3): δ 7.53–7.30 (m, 5H), 5.89 (d, J = 1.8 Hz, 1H), 5.50 (d, J = 1.7 Hz, 1H), 4.01 (m, 2H). 13C NMR (100 MHz, CDCl3): δ 135.2,131.1, 129.4, 129.2, 127.5, 119.6, 45.2.

(2-chloroallyl)(phenyl)sulfane (3e)

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 2-chloro-allyl chloride (22 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at the corresponding temperature for 2 h. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 20/1) to give the title compound 3e (153 mg, 83%) as a colourless liquid; [Found: C, 58.58; H, 4.80; C9H9ClS requires C, 58.53; H, 4.91%]; Rf = 0.4 (hexane/ethyl acetate = 20/1). 1H NMR (400 MHz, CDCl3): δ 7.94–7.86 (m, 5H), 5.77–5.64 (m, 2H), 3.88 (d, J = 6.3 Hz, 2H). 13C NMR (100 MHz, CDCl3): δ 140.8, 137.7, 133.9, 128.4, 126.2, 119.7, 44.1.

Allyl(p-tolyl)sulfane (3g)21

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), 4-methylthiophenol (24.8 mg, 0.2 mmol) and allyl chloride (15.2 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at the corresponding temperature for 2 h. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 15/1) to give the title compound 3g (144 mg, 88%) as a colourless liquid; [Found: C, 73.13; H, 7.31. C10H12S. requires C, 73.12; H, 7.36%]; Rf = 0.5 (hexane/ethyl acetate = 10/1). 1H NMR (400 MHz, CDCl3): δ 7.38 (d, J = 8.1 Hz, 2H), 7.03 (d, J = 7.9 Hz, 2H), 5. 74–5.55 (m, 1H), 5.16–5.06 (m, 2H), 3.58 (d, J = 7.6 Hz, 2H), 2.35 (s, 3H).13C NMR (100 MHz, CDCl3): δ 138.7, 134.2, 132.8,131.6, 129.5, 117.9, 37.2, 20.1

allyl(3-chlorophenyl)sulfane (3 h)

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), 3-chlorothiophenol (28.8 mg, 0.2 mmol) and allyl chloride (15.2 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at the corresponding temperature for 2 h. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 15/1) to give the title compound 3h (105 mg, 65%) as a yellow liquid; [Found: C, 58.58; H, 4.94; C9H9ClS requires C, 58.53; H, 4.91%]; Rf = 0.5 (hexane/ethyl acetate = 15/1). 1H NMR (400 MHz, CDCl3): δ 7.38–7.29 (m, 4H), 5.86–5.75 (m, 1H), 5.27 (dd, J = 1.1 Hz, J = 16.1 Hz, 1H), 5.17 (dd, J = 1.3 Hz, J = 10.2 Hz, 1H), 3.59 (d, J = 6.1 Hz, 2H). 13C NMR (100 MHz, CDCl3): δ 137.7, 134.2, 132.5, 128.9, 127.9, 125.6, 124.3, 117.7, 35.9.

Allyl(4-nitrophenyl)sulfane (3i)22

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), 4-nitrothiophenol (31 mg, 0.2 mmol) and allyl chloride (15.2 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at the corresponding temperature for 2 h. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 15/1) to give the title compound 3i (105 mg, 54%) as a yellow solid, mp 39–41 °C; [Found: C, 55.31; H, 4.66; N, 6.99; C9H9NO2S requires C, 55.37; H, 4.65; N, 7.17%]; Rf = 0.6 (hexane/ethyl acetate = 15/1). 1H NMR (400 MHz, CDCl3): δ 8.45 (d, J = 8.1 Hz, 2H), 7.38 (d, J = 8.6 Hz, 2H), 5.89–5.83 (m, 1H), 5.36 (dd, J = 1.1 Hz, J = 16.3 Hz, 1H), 5.27 (dd, J = 1.4 Hz, J = 10.1 Hz, 1H), 3.76 (d, J = 6.3 Hz, 2H). 13C NMR (100 MHz, CDCl3): δ 147.8, 146.7, 133.9, 127.8, 124.8, 119.4, 35.2.

(2-bromoallyl)(4-nitrophenyl)sulfane (3j)

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), 4-nitrothiophenol (31 mg, 0.2 mmol) and 2-bromo-allyl bromide (39.6 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at the corresponding temperature for 2 h. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 10/1) to give the title compound 3j (167 mg, 61%) as a colourless liquid; [Found: C, 39.49; H, 2.99; N, 5.01; C9H8BrNO2S requires C, 39.43; H, 2.94; N, 5.11%]; Rf = 0.4 (hexane/ethyl acetate = 10/1). 1H NMR (400 MHz, CDCl3): δ 8.20 (d, J = 9.1 Hz, 2H), 7.36 (d, J = 8.2 Hz, 2H), 5.77 (d, J = 2.9 Hz, 1H), 5.47 (d, J = 2.6 Hz, 1H), 4.01 (s, 2H). 13C NMR (100 MHz, CDCl3): δ 143.1, 139.2, 125.7, 124.9, 121.1, 44.8.

Diphenyl sulfide (5a)23

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and phenylboronic acid (24.4 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at 110 °C. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 15/1) to give the title compound 5a (177 mg, 95%) as a colourless liquid; [Found: 77.55; H, 5.47; C12H10S requires C, 77.37; H, 5.41%]; Rf = 0.4 (hexane/ethyl acetate = 15/1). 1H NMR (400 MHz, CDCl3): δ 7.40 – 7.27 (m, 10H). 13C NMR (100 MHz, CDCl3): δ 135.5, 131.2, 129.2, 127.7.

2, 6-Dimethylphenyl phenyl sulfide (5b)24

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 2,6-dimethyl-phenylboronic acid (30 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at 110 °C. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 20/1) to give the title compound 5b (180 mg, 84%) as a colourless liquid; [Found: C, 78.65; H, 6.54; C14H14S requires C, 78.45; H, 6.58%]; Rf = 0.4 (hexane/ethyl acetate = 20/1). 1H NMR (400 MHz, CDCl3): δ 7.28–7.22 (m, 5H), 7.10– 6.96 (m, 3H), 2.46 (s, 6H). 13C NMR (100 MHz, CDCl3): δ 144.1, 138.2, 130.7, 129.4, 128.4, 128.0, 125.3, 124.0, 21.4.

4-tert-Butylphenyl phenyl sulfide (5c)

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 4-tert-butylphenylboronic acid (35.6 mg, 0.2 mmol were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at 110 °C. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 15/1) to give the title compound 5c (201 mg, 83%) as a colourless liquid; Rf = 0.6 (hexane/ethyl acetate = 15/1). 1H NMR (400 MHz, CDCl3): δ 7.35–7.19 (m, 9H), 1.31(s, 9H). 13C NMR (100 MHz, CDCl3): δ 150.4, 136.1, 131.0, 130.4, 130.1, 129.2, 126.4, 126.1, 34.6, 31.4.

4-isopropylphenyl)(phenyl)sulfide (5d)15

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 4-isopropylphenylboronic acid (35.6 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at 110 °C. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 25/1) to give the title compound 5d (198 mg, 87%) as a colourless liquid; Rf = 0.6 (hexane/ethyl acetate = 25/1). 1H NMR (400 MHz, CDCl3): δ 7.44–7.22 (m, 9H), 3.03–2.92 (m, 1H), 1.27 (d, J = 7.2 Hz, 6H). 13C NMR (100 MHz, CDCl3): δ 148.7, 136.7, 131.4, 131.0, 130.6, 129.4, 128.4, 127.3, 127.2, 126.3, 33.6, 23.4.

(2,4,6-trimethyl-phenyl)-phenyl sulfide (5e)25

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 2,4,6-trimethyl-phenylboronic acid (32.8 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at 110 °C. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 20/1) to give the title compound 5e (185 mg, 81%) as a colourless liquid; [Found: C, 78.86; H, 7.17; C15H16S requires C, 78.90; H, 7.06%]; Rf = 0.4 (hexane/ethyl acetate = 20/1). 1H NMR (400 MHz, CDCl3): δ 7.38–7.31 (m, 2H), 7.28–7.18 (m, 3H), 6.96–6.88 (m, 2H) 2.47 (s, 6H), 2.39 (s, 3H). 13C NMR (100 MHz, CDCl3): δ 143.4, 139.3, 138.4, 129.4, 128.0, 127.7, 125.8, 124.4, 21.6, 21.1.

3,5-Dichlorophenyl phenyl sulfide (5f)

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 3,5-dichlorophenylboronic acid (38 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at 110 °C. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 15/1) to give the title compound 5f (140 mg, 55%) as a colourless liquid; Rf = 0.6 (hexane/ethyl acetate = 15/1). 1H NMR (400 MHz, CDCl3): δ 7.64–7.54 (m, 5H), 7.37–7.26 (m, 3H). 13C NMR (100 MHz, CDCl3): δ 140.9, 133.2, 132.7, 131.5, 129.6, 129.3, 128.5, 122.2.

3-Nitrophenyl phenyl sulfide (5g)

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 3-nitrophenylboronic acid (33.4 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at 110 °C. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 15/1) to give the title compound 5g (120 mg, 52%) as a pale yellow liquid; Rf = 0.6 (hexane/ethyl acetate = 15/1). 1H NMR (400 MHz, CDCl3): δ 7.97–7.78 (m, 4H), 7.44–7.36 (m, 5H). 13C NMR (100 MHz, CDCl3): δ 134.7, 133.9, 132.3, 129.2, 129.0, 128.9, 128.6, 128.2, 123.4, 120.2.

2-Naphthalyl phenyl sulfide (5 h)

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 2-napthylboronic acid (34.4 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at 110 °C. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 15/1) to give the title compound 5 h (184 mg, 78%) as a white solid; mp 50–51 °C; Rf = 0.5 (hexane/ethyl acetate = 15/1). 1H NMR (400 MHz, CDCl3): δ 7.86–7.76 (m, 4H), 7.50–7.42 (m, 8H). 13C NMR (100 MHz, CDCl3): δ 135.7, 133.6, 133.2, 132.7, 130.8, 129.6, 129.4, 128.8, 128.4, 127.4, 127.1, 127.0, 126.9, 126.2.

2-(Phenylthio)thiophene (5i)24

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 2-thiopheneboronic acid (25.6 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at 110 °C. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 15/1) to give the title compound 5i (163 mg, 85%) as a colourless liquid; [Found: C, 62.59; H, 4.11; C10H8S2 requires C, 62.46; H, 4.19%]; Rf = 0.6 (hexane/ethyl acetate = 15/1). 1H NMR (400 MHz, CDCl3): δ 7.51(dd, J = 4.4 Hz, 1 H), 7.34–7.22 (m, 6H), 7.16–7.11 (m, 1H). 13C NMR (100 MHz, CDCl3): δ 138.7, 136.0, 131.5, 131.2, 128.9, 128.1, 127.4, 126.1.

3-(Phenylthio)thiophene (5j)24

To a 10 mL glass tube, In2O3 nanoparticles (1.1 mg, 0.004 mmol), TBATB (144 mg, 0.3 mmol), Na2CO3 (42 mg, 0.4 mmol), thiophenol (22 mg, 0.2 mmol) and 3-thiopheneboronic acid (25.6 mg, 0.2 mmol) were dissolved in DMSO (2 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at 110 °C. The reaction mixture was filtered and the solvent evaporated in vacuo to give the crude product, which was purified by column chromatography (hexane/ethyl acetate = 15/1) to give the title compound 5j (161 mg, 80%) as a colourless liquid; [Found: C, 62.56; H, 4.09; C10H8S2 requires C, 62.46; H, 4.19%]; Rf = 0.6 (hexane/ethyl acetate = 15/1). 1H NMR (400 MHz, CDCl3): δ 7.37–7.34 (m, 2H), 7.26–7.13 (m, 8H), 7.07 (dd, J = 8.2 Hz, 1H) 13C NMR (100 MHz, CDCl3): δ 137.8, 131.6, 129.2, 128.9, 128.6, 128.1, 126.7, 126.0.

Additional Information

How to cite this article: Gogoi, P. et al. Role of TBATB in nano indium oxide catalyzed C-S bond formation. Sci. Rep. 5, 13873; doi: 10.1038/srep13873 (2015).