Immobilized ruthenium metal-containing ionic liquid-catalyzed dehydrogenation of dimethylamine borane complex for the reduction of olefins and nitroarenes

Abstract

An efficient immobilized ruthenium metal containing ionic liquid (ImmRu-IL) catalyst has been developed for the transfer hydrogenation of olefins and nitroarenes. Various olefins and nitroarenes were reduced in excellent yields within 2–6 h at room temperature. This methodology uses eco-friendly dimethylamine borane as a reducing agent which is nontoxic, water soluble, highly stable and easy to handle. The reactions take place through tandem dehydrogenation and hydrogenation of dimethylamine borane complex in the presence of ImmRu-IL catalyst. The catalyst was reused in up to four consecutive cycles without any significance loss in its activity. The fresh and reused catalysts have been studied by XPS analysis.

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Introduction

Nowadays, dehydrogenation of ammonia-borane (NH₃BH₃, AB) and its derivatives like methylamine-borane (CH₃NH₂BH₃, MeAB) and dimethylamine-borane (Me₂NHBH₃, DMAB) has been gaining great attention¹ because of their high hydrogen (H₂) storage capacity which could solve the problem of hydrogen economy.² Several organic and inorganic materials such as metal–organic frameworks (MOF),³ organic materials⁴ and metal-hydrides⁵ have been employed for the storage of hydrogen. However, the uses of these materials are limited by (i) the need of high pressure systems, (ii) the need for high temperatures, (iii) low storage H₂ capacity and (iv) their difficulty to handle. On the other hand, the ammonia-borane family has great advantages compared to the above mentioned materials because of their high H₂ storage capacity, high stability and nontoxicity. In addition, they are easy to handle and are highly soluble in water at room temperature.⁶ Ammonia-borane and its analogs play vital roles in the polymer industry,⁷ materials chemistry,⁸ tandem dehydrogenation–hydrogenation reactions⁹ and transfer hydrogenation.¹⁰ In recent decades, cobalt-catalyzed transfer hydrogenations of unsaturated organic moieties have been achieved by the borane family.¹¹ In particularly, dehydrogenations of dimethylamine-borane (Me₂NHBH₃, DMAB) are known using various transition-metal catalysts such as ruthenium, iridium and palladium.¹² Berke and co-workers have reported homogenous Re-catalyzed alkenes hydrogenation using DMAB as a hydrogen source.¹³ Chirik's explored homogeneous system of titanium precursor complex [(η⁵-C₅H₃-1,3-(SiMe₃)₂)₂Ti]₂(μ₂,η¹,η¹-N₂) for dehydrogenation of DMAB.¹⁴ Of note, Williams and co-workers have described homogenous copper and ruthenium complexes for dehydrogenation of DMAB and in situ reduction of various organic moieties.¹⁵ In spite of their potential utility of these protocols, the use of homogeneous non recyclable catalytic systems and expensive phosphine ligands, harsh reaction conditions, longer reaction time and difficulty in catalyst-product separation have limited the applicability of these protocols. In additions to these limitations, it needs tedious preparation of homogeneous catalytic systems. Therefore, there is a need to develop a better cost-effective, heterogeneous, and reusable catalytic system for the dehydrogenation of DMAB.

The transition-metal catalyzed hydrogenation or transfer hydrogenation of olefinic bonds and the reduction of nitroarenes are one of the most significant reactions in organic chemistry.¹⁶ Hydrogenations of olefin bonds have been carried out in the presence of transition metals such as palladium,¹⁷ ruthenium,¹⁸ rhodium¹⁹ and iridium.²⁰ Beller and co-workers have documented heterogeneous iron and cobalt based catalytic systems for the reduction of nitroarenes using molecular hydrogen.²¹ Among the available reduction process, the transfer hydrogenation is the most attractive process because it does not require high pressure reaction vessel (autoclave) or use of flammable hydrogen gas. Nowadays, AB and DMAB have been become popular reducing agent due its high hydrogen realizing capacity, highly soluble in water and non-toxicity.²² Yurderi et al. studied Ru(0) NPs catalyzed olefins reduction using DMAB as hydrogen source.²³ The bimetallic catalytic systems such as NiPd graphene-supported and CoPd alloy and Au NPs for the reduction of nitroarenes using AB as hydrogen source are also known.²⁴

Immobilization of metals on various supports is important in heterogeneous catalysis as it could solve the problem of catalyst recycling and product separation thereby making process greener and cost-effective.²⁵ From this aspect, eco-friendly ionic liquids immobilized on solid materials have been use for many organic transformations.²⁶ In continuation of our interest in to develop efficient heterogeneous and environmentally benign protocols for the hydrogenation reactions,²⁷ herein we explore a immobilized ruthenium metal-containing ionic liquid [ImmRu-IL] for the transfer hydrogenation of olefins and nitroarenes using DMAB as hydrogen source at room temperature (Scheme 1).

Scheme 1 Transfer hydrogenation of olefins and nitroarenes using ImmRu-IL.

Experimental

Materials

3-Trimethoxysilylpropyl chloride (97+%), N-methylimidazole (99+%), dried redistilled 1-methylimidazole (99+%) and RuCl₃·3H₂O were purchased form Aldrich and all the dry solvents were obtained from WAKO commercially. Aerosil 300 (300 m² g⁻¹) was acquired from Japan Aerosil Co. and calcined at 573 K for 1.5 h in air for 30 min in vacuum. The catalyst loading was calculated by XRF measurements using Philips PW2402 XRF spectrometer (X-ray source 40 kV, 100 mA). The XPS of ImmRu-IL was measured using a PHI5000 Versa Probe with monochromatic focused (100 μm × 100 μm) Al Kα X-ray radiation (15 kV, 30 mA) and dual beam neutralization using a combination of argon ion gun and electron irradiation.

Catalyst synthesis (ImmRu-IL)

In a dry flask 3-trimethoxysilylpropyl chloride (0.690 mol) and N-methylimidazole (0.690 mol) were added under a nitrogen condition and the resulting reaction mass refluxed for 48 h. After completion of reaction, the reaction mass was allowed to cool at room temperature and then washed with dry ethyl acetate. The obtained residue (1-methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride) was dried at room temperature under reduced pressure for 48 h and then stored at 253 K under dry nitrogen. 1-Methyl-3-(3-trimethoxysilylpropyl) imidazolium chloride (weight ratio 1 : 1) and silica (Aerosil 300, surface area 300 m² g⁻¹, calcined at 573 K for 1.5 h in air) were dispersed in dry toluene and then the reaction mixture was refluxed for 48 h under nitrogen atmosphere. After the completion of reaction, material was filtered on glass filter and finally washed with hot dichloromethane to remove excess of ionic liquid. The obtained solid material is denoted as Imm-IL.

The 3.00 g of Imm-IL and 0.6721 g of RuCl₃·3H₂O were refluxed in 50 mL of acetonitrile for 24 h. Then solvent was removed using glass filter, followed by washing with acetone several times. The obtained catalyst denoted as ImmRu-IL, was dried by evacuation at room temperature for 24 h. The metal loading of catalyst was 5.82 wt% as determined by XRF measurements (Scheme 2).

Scheme 2 Preparation of ruthenium metal-ion-containing immobilized ionic liquid.

Results and discussion

Optimization study for transfer hydrogenation of styrene

The reaction conditions were optimized for the in situ reduction of styrenes using ImmRu-IL catalyst via tandem dehydrogenation of DMAB. For this purpose, styrene (0.5 mmol) was chosen as a model substrate in the presence of ImmRu-IL as a catalyst (Table 1).

Table 1 Effect of reaction parameter on transfer hydrogenation of styrene^a

Entry	Catalyst	Catalyst loading (mol%)	Solvent	Yield^b (%)
a Reaction conditions: styrene (0.5 mmol), ImmRu-IL (2.5 mol%), (CH3)2NHBH3 (1 equiv.), solvent (2 mL), RT, time (2 h).b Yield based on GC and GC-MS analysis.
Catalyst screening and catalyst loading
1	No catalyst	—	Toluene	00
2	Ru/C (5%)	2.5	Toluene	42
3	ImmRu-IL	2.5	Toluene	99
4	ImmRu-IL	1	Toluene	59
5	Ru-IL	2.5	Toluene	98
Effect of solvent
6	ImmRu-IL	2.5	Toluene	99
7	ImmRu-IL	2.5	Water	30
8	ImmRu-IL	2.5	THF	45
9	ImmRu-IL	2.5	Methanol	64
10	ImmRu-IL	2.5	Ethanol	69
11	ImmRu-IL	2.5	—	96

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At the beginning, the reaction was carry out in the absence of catalyst, the reaction did not proceed (Table 1, entry 1). Next, we compared the activity of synthesized ImmRu-IL with commercially available Ru/C (5%) and it was found that ImmRu-IL catalyzed furnished excellent of yield of desired product than Ru/C (Table 1, entries 2 and 3). It was found that the 2.5 mol% of ImmRu-IL catalyst provided the corresponding ethyl benzene in highest yield (Table 1, entries 3 and 4). Without silica supported Ru-IL also provided good yield of the desired product (Table 1, entry 5). In the next set of experiments, we screened various non-polar and polar solvents such as toluene, water, THF, methanol and ethanol and it was observed that non polar toluene gave excellent yield of desire product (Table 1, entries 6–10). We have performed the model reaction in absences of solvent and 96% yield of ethyl benzene was observed (Table 1, entry 11). Thus, the optimized reaction conditions for transfer hydrogenation of styrene are: styrene (0.5 mmol), DMAB (1 equiv.), and ImmRu-IL (3 mol%) and toluene as a solvent at room temperature.

With optimized conditions in hand, we extend the developed protocol for the transfer hydrogenation of various olefins using DMAB. The several unsaturated compounds were reduced to the saturated compounds in excellent yields within 2–6 h at room temperature (Table 2).

Table 2 ImmRu-IL catalyzed transfer hydrogenation of various substitute olefins^a

Entry	Substrate	Product	Time (h)	Yield^b (%)
a Reaction conditions: olefins (0.5 mmol), ImmRu-IL (2.5 mol%), (CH3)2NHBH3 (1 equiv.), toluene (2 mL), RT, time (2–6 h).b Yield based on GC and GC-MS analysis.
1			2	99
2			2	99
3	1-Decene	N-Decane	2	96
4	1-Hexene	N-Hexane	2	99
5			4	82
6			6	86
7			6	85
8			6	84
9			6	80
10			6	90
11			6	88

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Styrene was reduced to ethyl benzene with a yield of >99% in 2 h (Table 2, entry 1). Furthermore, cyclohexene, aliphatic 1-decene and 1-hexene were providing good yields of the desired saturated products (Table 2, entries 2–4). Next we also check present protocol for hydrogenation of p-CH₃ and p-amino styrene and it was found both substrates provided good yield of the desired products (Table 2, entries 5 and 6). Allylbenzene and substituted allylbenzene were easily reduced under optimized conditions (Table 2, entries 7 and 8). The biomass derived eugenol was successfully reduced in corresponding product with excellent yield (Table 2, entry 9). Furthermore, we have extended our protocol for the reduction of bulky and heterocyclic olefins and it was found that both substrate provided excellent yield of the desired products (Table 2, entries 10 and 11).

Further, the present methodology was used for the transfer hydrogenation of nitroarenes under the optimized conditions. A series of nitro compounds could be reduced into corresponding amines in excellent yields within 2–6 h. Interestingly, the reactions works well even at room temperature without forming any side products (Table 3).

Table 3 ImmRu-IL catalyzed transfer hydrogenation of various substitute nitroarenes^a

Entry	Substrate	Product	Time (h)	Yield^b (%)
a Reaction conditions: nitroarenes (0.5 mmol), ImmRu-IL (2.5 mol%), (CH3)2NHBH3 (3 equiv.), toluene (2 mL), RT, time (2–6 h).b Yield based on GC and GC-MS analysis.
1			2	99
2			6	86
3			6	82
4			6	70
5			4	86
6			4	90
7			4	92
8			5	86
9			2	96
10			2	97
11			6	85
12			6	80
13			6	84

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Nitrobenzene cleanly reduction into aniline with excellent yield in 2 h (Table 3, entry 1). Next, the halogen-substituted chloro, fluoro and iodo nitroarenes were studied and it was found that in all the halogenated nitrobenzenes reduced very easily into respective primary amines with good yield (Table 3, entries 2–4). The –NO₂ groups with o-, m- and p-methyl and p-methoxy nitrobenzene could also be reduced into related amine successfully (Table 3, entries 5–8). The present catalytic system also works well for nitro phenol reduction within 2 h (Table 3, entries 9 and 10). The reduction of nitro benzyl alcohol and 2-nitroaniline was employed providing products 2-aminobenzyl alcohol and o-phenylenediamine in good yields (Table 3, entries 11 and 12). Furthermore, chemoselectively only nitro groups was reduced when the 4-nitrobenzonitrile was employed under the optimized reaction conditions (Table 3, entry 13).

Recycle study

In an effort to make the present catalytic system more economical and greener, we focused on reusability of ImmRu-IL catalyst for reduction reaction. As shown in Fig. 1 catalyst was recycled for standard reaction of styrene in the presence of DMAB as a hydrogen donor. After completion of reaction, ImmRu-IL catalyst was isolated by filtration method. The filtrate catalyst was washed with toluene several times to remove the rest of organic residue. The recovered catalyst dried in oven and reused for next reaction. The catalyst was recycled up to four consecutive cycles without losing its activity (Table 4).

Fig. 1 Recyclability study of ImmRu-IL catalyst.

Table 4 Recent literature on catalytic transfer hydrogenation of various substitute olefins and nitroarenes^a

Sr. no.	Catalyst	H2 source	Recycle study	T (°C)	t (h)	Ref.
a ND: not demonstrated.
1	[Ru(p-cymene)Cl2]2	Me2NHBH3	ND	70	24	15
2	Cu(OTf)2	Me2NHBH3	ND	85	24	15
3	Re complex	Me2NHBH3	ND	85	1–4	13
4	Pd/KCC-1-NH2	HCOOH	Recycle	100	6–24	16a
5	RuNPs/ZIF-8	Me2NHBH3	Recycle	40	16	23
6	ImmRu-IL	Me2NHBH3	Recycle	RT	2–6	This work

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XPS study

XPS spectra were measured for the fresh ImmRu-IL, the 1^st recycle, and the 4^th recycle catalysts to identified elemental composition and valence states of the catalyst. Pollini reported binding energy values for RuCl₃ at 285.40 eV (3d_3/2) and 281.0 eV (3d_5/2), respectively.²⁸ Therefore, the fresh catalyst can be assigned as Ru³⁺ state. Ru⁰ exhibits 284.20 eV for 3d_3/2, and 279.01–280.20 eV for 3d_5/2.²⁹ Main component of the 1^st recycle and the 4^th recycle samples remain at Ru³⁺ state with a slight component of reduced Ru⁰ state, corresponding to the decrease in the intensity of Cl 2p signal for the 1^st recycle and the 4^th recycle samples (Fig. 2).

Fig. 2 (a) ImmRu-IL wide scan survey (b) XPS of Cl 2p region (c) XPS of Ru 3d region.

Conclusions

In summary, we have developed a simple, environmentally benign and recyclable catalytic system for transfer hydrogenation of C=C bonds and nitro compounds by ImmRu-IL as a versatile heterogeneous catalyst. Various olefins and nitroarenes were reduced via dehydrogenation of DMAB at room temperature. The use of DMAB as hydrogen source makes the developed methodology environmentally benign and nontoxic. The ImmRu-IL catalyst was easily recovered by filtration method and could be reused up to four consecutive cycles without loss of its catalytic activity.

General procedure of ImmRu-IL catalyzed transfer hydrogenation of olefins

The olefins (0.5 mmol) and ImmRu-IL catalyst (2.5 mol%) were mixed in 2 mL of toluene in a oven dried Schlenk tube and then DMAB (1 equiv.) was added. Then the reaction mixture was stirred at room temperature for 2–6 h. The progress of reaction was monitored by gas chromatography (GC) and GGMS. All products are well-known in the literature and were confirmed by GC (Perkin Elmer, Clarus 400) (BP-10 GC column, 30 m × 0.32 mm ID, film thickness 0.25 mm) and GCMS (Shimadzu GC-MS QP 2010) analysis.

Characterisation data of products

Ethyl benzene. Colorless liquid. ¹H NMR (400 MHz, CDCl₃) δ 7.40–7.33 (m, 2H), 7.31–7.25 (m, 3H), 2.74 (q, J = 7.6 Hz, 2H), 1.33 (t, J = 7.6 Hz, 3H); ¹³C NMR (101 MHz, CDCl₃) δ 144.28, 128.36, 127.91, 125.64, 28.96, 15.70.

Cyclohexane. Colorless liquid. ¹H NMR (400 MHz, CDCl₃) δ 1.41 (s, 12H); ¹³C NMR (101 MHz, CDCl₃) 26.88.

N-Decane. Colorless liquid. ¹H NMR (400 MHz, CDCl₃) δ 1.27 (d, J = 15.0 Hz, 16H), 0.87 (t, J = 6.7 Hz, 6H); ¹³C NMR (101 MHz, CDCl₃) δ 31.91, 29.65, 29.35, 22.67, 14.04.

4-Ethyltoluene. Colorless liquid. ¹H NMR (500 MHz, CDCl₃) δ 7.11 (s, 4H), 2.63 (q, J = 7.6 Hz, 2H), 2.33 (s, 3H), 1.24 (t, J = 7.6 Hz, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 141.20, 134.98, 128.98, 127.72, 28.43, 20.98, 15.79.

4-Ethylaniline. Yellow liquid. ¹H NMR (500 MHz, CDCl₃) δ 7.06 (d, J = 7.5 Hz, 2H), 6.68 (d, J = 7.9 Hz, 2H), 3.58 (s, 2H), 2.61 (q, J = 7.6 Hz, 2H), 1.26 (t, J = 7.6 Hz, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 144.13, 134.45, 128.64, 115.33, 28.05, 16.05.

Propylbenzene. Colorless liquid. ¹H NMR (500 MHz, CDCl₃) δ 7.30–7.25 (m, 3H), 7.18 (d, J = 7.1 Hz, 2H), 2.58 (t, J = 7.6 Hz, 2H), 1.69–1.60 (m, 2H), 0.94 (t, J = 7.3 Hz, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 142.68, 128.44, 128.18, 125.56, 38.06, 24.58, 13.85.

4-Propylanisole. Colorless liquid. ¹H NMR (500 MHz, CDCl₃) δ 7.12 (d, J = 7.3 Hz, 2H), 6.85 (d, J = 7.0 Hz, 2H), 3.81 (s, 3H), 2.55 (t, J = 7.6 Hz, 2H), 1.68–1.59 (m, 2H), 0.95 (t, J = 7.3 Hz, 3H). ¹³C NMR (126 MHz CDCl₃) δ 157.60, 134.80, 29.31, 113.61, 55.23, 37.15, 24.83, 13.80.

2-Methoxy-4-propylphenol. Colorless liquid. ¹H NMR (500 MHz, CDCl₃) δ 6.86 (d, J = 7.8 Hz, 1H), 6.70 (d, J = 8.8 Hz, 2H), 5.60 (s, 1H), 3.88 (s, 3H), 2.54 (t, J = 7.6 Hz, 2H), 1.69–1.59 (m, 2H), 0.96 (t, J = 7.3 Hz, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 146.29, 143.49, 134.71, 120.96, 114.12, 111.05, 55.83, 37.77, 24.89, 13.82.

1-(tert-Butyl)-4-ethylbenzene. Colorless liquid. ¹H NMR (500 MHz, CDCl₃) δ 7.33 (d, J = 8.0 Hz, 2H), 7.16 (d, J = 7.8 Hz, 2H), 2.64 (q, J = 7.6 Hz, 2H), 1.32 (s, 9H), 1.25 (t, J = 7.6 Hz, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 148.33, 141.14, 127.48, 125.16, 34.32, 31.42, 28.25, 15.50.

2-Ethylpyridine. Pale yellow liquid. ¹H NMR (500 MHz, CDCl₃) δ 8.46 (d, J = 4.6 Hz, 1H), 7.53 (t, J = 7.6 Hz, 1H), 7.10 (d, J = 7.8 Hz, 1H), 7.05–7.00 (m, 1H), 2.77 (q, J = 7.6 Hz, 2H), 1.25 (t, J = 7.6 Hz, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 163.40, 149.04, 136.31, 121.97, 120.82, 31.31, 13.85.

Aniline. Pale yellow liquid. ¹H NMR (500 MHz, CDCl₃) δ 7.22 (t, J = 6.8 Hz, 2H), 6.86–6.79 (m, 1H), 6.73 (d, J = 7.8 Hz, 2H), 3.66 (s, 2H). ¹³C NMR (126 MHz, CDCl₃) δ 146.48, 129.35, 118.58, 115.19.

2-Chloroaniline. Brown liquid. ¹H NMR (500 MHz, CDCl₃) δ 7.29 (d, J = 8.0 Hz, 1H), 7.10 (t, J = 7.7 Hz, 1H), 6.77 (d, J = 8.0 Hz, 1H), 6.73 (t, J = 7.6 Hz, 1H), 4.07 (s, 2H). ¹³C NMR (126 MHz, CDCl₃) δ 142.99, 129.45, 127.71, 119.29, 119.06, 115.97.

2-Fluroaniline. Yellow liquid. ¹H NMR (500 MHz, CDCl₃) δ 7.06–7.00 (m, 1H), 6.98 (t, J = 7.7 Hz, 1H), 6.80 (t, J = 8.5 Hz, 1H), 6.74 (dd, J = 12.9, 7.5 Hz, 1H), 3.76 (s, 2H). ¹³C NMR (126 MHz, CDCl₃) δ 152.72, 150.83, 134.63, 134.53, 124.53, 124.50, 118.68, 118.63, 117.05, 117.02, 115.33, 115.18.

4-Iodoaniline. Brown solid. ¹H NMR (500 MHz, CDCl₃) δ 7.41 (d, J = 7.9 Hz, 2H), 6.47 (d, J = 8.0 Hz, 2H), 3.24 (s, 2H). ¹³C NMR (126 MHz, CDCl₃) δ 146.01, 137.89, 117.30, 79.40.

o-Toluidine. Brown liquid. ¹H NMR (500 MHz, CDCl₃) δ 7.10 (d, J = 7.4 Hz, 2H), 6.76 (t, J = 7.1 Hz, 1H), 6.71 (d, J = 7.7 Hz, 1H), 3.61 (s, 2H), 2.21 (s, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 144.58, 130.47, 126.99, 122.35, 118.65, 114.96, 17.39.

m-Toluidine. Brown liquid. ¹H NMR (500 MHz, CDCl₃) δ 7.12 (t, J = 7.6 Hz, 1H), 6.66 (d, J = 7.4 Hz, 1H), 6.55 (d, J = 9.6 Hz, 2H), 3.64 (s, 2H), 2.34 (s, 3H). ¹³C NMR (126 MHz, CDCl₃) δ 146.46, 139.15, 129.22, 119.46, 115.98, 112.31, 21.51.

p-Toluidine. White solid. ¹H NMR (500 MHz, CDCl₃) δ 6.97 (d, J = 7.9 Hz, 2H), 6.62 (d, J = 7.9 Hz, 2H), 3.50 (s, 2H), 2.25 (s, 3H).

¹³C NMR (126 MHz, CDCl₃) δ 143.77, 129.74, 127.78, 115.24, 20.45.

p-Anisidine. Brown solid. ¹H NMR (500 MHz, CDCl₃) δ 6.75 (d, J = 8.6 Hz, 2H), 6.65 (d, J = 8.7 Hz, 2H), 3.74 (s, 3H), 3.23 (s, 2H). ¹³C NMR (126 MHz, CDCl₃) δ 152.78, 139.89, 116.41, 114.78, 55.73.

m-Aminophenol. White solid. ¹H NMR (500 MHz, DMSO-D₆) δ 8.79 (s, 1H), 6.73 (t, J = 7.9 Hz, 1H), 5.96 (s, 2H), 5.89 (d, J = 7.8 Hz, 1H), 4.84 (s, 2H). ¹³C NMR (126 MHz, DMSO-D₆) δ 158.46, 150.25, 129.83, 105.80, 103.66, 101.34.

p-Aminophenol. Reddish solid. ¹H NMR (500 MHz, DMSO-D₆) δ 8.29 (s, 1H), 6.39 (dd, J = 29.8, 7.6 Hz, 4H), 4.37 (s, 2H). ¹³C NMR (126 MHz, DMSO-D₆) δ 148.59, 141.08, 115.93, 115.61.

2-Aminobenzylacohol. Brown solid. ¹H NMR (500 MHz, CDCl₃3) δ 7.14 (t, J = 7.6 Hz, 1H), 7.07 (d, J = 7.4 Hz, 1H), 6.72 (dd, J = 13.5, 7.5 Hz, 2H), 4.66 (s, 2H). ¹³C NMR (126 MHz, CDCl₃) δ 146.04, 129.39, 129.19, 124.76, 118.14, 116.00, 64.41.

o-Phenylenediamine. Gray solid. ¹H NMR (500 MHz, CDCl₃) δ 6.75–6.69 (m, 4H), 3.24 (s, 4H). ¹³C NMR (126 MHz, CDCl₃) δ 134.71, 120.27, 116.74.

4-Aminobenzonitrile. White solid. ¹H NMR (500 MHz, CDCl₃) δ 7.41 (d, J = 8.2 Hz, 2H), 6.64 (dd, J = 8.2, 0.4 Hz, 2H), 4.17 (s, 2H).

¹³C NMR (126 MHz, CDCl₃) δ 150.35, 133.80, 120.13, 114.42, 100.17.

Acknowledgements

The author Nilesh. M. Patil is thankful to the University Grant Commission (UGC-SAP), India for providing the Senior Research Fellowship (SRF). XPS analysis was performed at the Research Hub for Advanced Nano Characterization, the University of Tokyo, supports by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. This work has been supported by JSPS and DST under the India-Japan Science Cooperative Program (Project No. DST/INT/JSPS/P-152/2013).

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Footnote

† Electronic supplementary information (ESI) available: GC-MS, ¹H NMR and ¹³C NMR data of all products. See DOI: 10.1039/c6ra09785e

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