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Article

Iron-Borophosphate Glass-Catalyzed Regioselective Hydrothiolation of Alkynes under Green Conditions

by
Nicoli Catholico
1,
Eduarda A. Tessari
2,
Isis J. A. Granja
3,
Martinho J. A. de Sousa
4,
Jorlandio F. Felix
5,
Flávia Manarin
2,
Marcelo Godoi
6,
Jamal Rafique
3,4,
Ricardo Schneider
7,*,
Sumbal Saba
3,* and
Giancarlo V. Botteselle
1,*
1
Department of Chemistry, Midwestern Parana State University-UNICENTRO, Guarapuava 85040-167, PR, Brazil
2
Center for Engineering and Exact Sciences, Western Parana State University-UNIOESTE, Toledo 85903-000, PR, Brazil
3
Instituto de Química IQ, Universidade Federal de Goiás-UFG, Goiania 74690-900, GO, Brazil
4
Institute of Chemistry-INQUI, Federal University of Mato Grosso do Sul-UFMS, Campo Grande 79074-460, MS, Brazil
5
Institute of Physics, University of Brasilia-UNB, Brasilia 70910-900, DF, Brazil
6
School of Chemistry and Food, Federal University of Rio Grande-FURG, Santo Antanio da Patrulha 95500-000, RS, Brazil
7
Group of Polymers and Nanostructures, Federal University of Technology Parana-UTFPR, Toledo 85902-490, PR, Brazil
*
Authors to whom correspondence should be addressed.
Catalysts 2023, 13(7), 1127; https://doi.org/10.3390/catal13071127
Submission received: 23 June 2023 / Revised: 18 July 2023 / Accepted: 18 July 2023 / Published: 20 July 2023
(This article belongs to the Special Issue Feature Papers in Catalysis in Organic and Polymer Chemistry)
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Abstract

:
Vinyl sulfides are an important class of organic compounds that have relevant synthetic and biological applications. The best-known approach to realize these compounds is the hydrothiolation of alkynes under different conditions using metals, toxic and carcinogenic solvents. The development of new catalysts using materials that are environmentally friendly, low in cost, and easy to handle is highly desirable for this reaction. In this regard, glasses have become an important class of materials, since they can be used as a catalyst for chemical reactions. We prepared and characterized an inexpensive and robust iron-doped borophosphate glass (Fe@NaH2PO4-H3BO3 glass). This eco-friendly material was successfully applied as a catalyst for the hydrothiolation of alkynes under solvent-free conditions, affording the desired vinyl sulfides in good-to-excellent yields, with high stereoselectivity. This method of synthesis is attractive because it enables the reuse of the iron-glass catalyst and the scaling up of reactions.

Graphical Abstract

1. Introduction

Glasses or glass-based materials are known for their stability and the high temperature commonly required for their synthesis. While glasses can be made using different approaches, the melting and fast-cooling method is widely used. Phosphates, and to some extent phosphate-based glasses, are a distinct group of materials that can be obtained from simple and eco-friendly raw chemicals. However, they usually have low chemical stability (e.g., high moisture sensitivity). Nevertheless, their ability to dissolve oxides at relatively low temperature overcomes the lability of the phosphate network [1,2]. Not only is the modification of the glass network achieved by addition of modifiers (dissolved ions) but also the reactivity of the glass surface [3]. Using appropriate oxides and/or metallic oxides will produce a glass that can be handled under ordinary conditions with superior catalyst performance. In this context, iron oxide is an abundant and affordable raw chemical that can be used in the synthesis of important classes of molecules, such as organosulfur [4,5] and organoselenium compounds [6,7].
Vinyl sulfides have emerged as a well-recognized class of organosulfur compounds, and can be used in various syntheses (e.g., as a key intermediate in the total synthesis of biologically active compounds) [8,9,10]. Due to the applicability of organosulfur compounds, a wide range of approaches for the preparation of vinyl sulfides has been reported [11,12,13,14].
The hydrothiolation of terminal alkynes (alkyne in which the carbon–carbon triple bond is at the end of the carbon chain) has become the most eco-friendly method because it produces vinyl sulfides with high atom efficiency, as well as high levels of chemo- and stereoselectivity [15,16]. Anti-Markovnikov addition products have been successfully synthesized in high yields in the presence of different catalysts and/or reaction promoters [17,18], including sulfamic acid [19], cesium carbonate [20], and potassium phosphate [21]. The water extract of straw ash has also been used as a suitable reaction medium for the hydrothiolation reaction [22,23].
However, the most applicable and widely explored methods [24,25,26] employ metals such as copper [27,28], iron [29], indium [30], rhodium [31], and ruthenium [32] as catalysts. Despite the high efficiency of these approaches, the development of environmentally friendly catalysts for the hydrothiolation reaction remains a great challenge. To our knowledge, the application of iron-glass catalysts in organosulfur chemistry has not yet been explored.
In addition, solvent-free reactions are attractive alternatives in organic synthesis and are considered an important contribution to the evolution of green chemistry [33,34]. Based on our interest in developing new sustainable materials and eco-friendly processes for organic reactions and material sciences [35,36,37,38,39,40], we describe herein the synthesis of a cheap and readily available iron-borophosphate glass and its application as a recyclable catalyst for the synthesis of vinyl sulfides. This novel approach worked smoothly under solvent-free conditions in a significantly short reaction time.

2. Results and Discussion

2.1. Iron-Borophosphate Glass Characterization

Figure 1 shows the powder X-ray diffraction (PXRD) analysis of the undoped borophosphate glass ((a) in Figure 1), borophosphate glass doped with trivalent aluminum ions (Al3+) ((b) in Figure 1), and borophosphate glass doped with aluminum and iron ions ((c) in Figure 1).
The diffractograms for all glasses show the characteristic halo of amorphous materials. Pure phosphate-based glasses suffer from moisture attack under normal conditions. Their chemical resistance can be improved by adding transition elements and/or trivalent ions, e.g., aluminum ions. A modification with aluminum and iron ions resulted in the formation of an amorphous material within the compositional range evaluated.
Figure 2 shows the Raman spectra of the borophosphate glasses. All the spectra show broad bands in the 1340–850 cm−1 and 810–430 cm−1 regions. These broad bands correspond to an overlapping phosphate network, and the deconvoluted spectra over a range of Voigt line shapes are shown in Figure S1 (Supplementary Material). Figure S1A shows the deconvoluted Raman spectrum of the undoped borophosphate glass (without aluminum or iron ions). The peak at 1256 cm−1 is attributed to the antisymmetric stretching mode νas (PO2−) of the Q2 units [41,42]. The peaks at 1127 cm−1 and 1069 cm−1 show the greatest overlap. The peak at 1127 cm−1 corresponds to the vibrations of the PØ2O2− (Ø = bridging oxygen atom) tetrahedra in the Q2 units, whereas the peak at 1069 cm−1 is associated with the P–O− vibrations of pyrophosphate (Q1 in a dimeric pyrophosphate unit, P2O74−) and/or (PO2)sym in the Q1 structure [43,44,45]. The shoulder at 926 cm−1 (Figure S1A) is a characteristic of orthophosphate (Q0) units, i.e., the symmetric stretching mode (νs) of P−O− non-bridging oxygen bonds in the PO43− tetrahedra [43,45]. In the phosphate glasses, the band at 700 cm−1 is associated with P−O−P stretching. The band splits into two distinct bands upon the addition of boron to the glass matrix [45]. The two shoulders at 768 cm−1 and 726 cm−1 are attributed to the P–O–P vibrations and the presence of boron atoms in the glass network, respectively. Anastasopoulou et al. [43] assigned the shoulder at 768 cm−1 (the dashed line in Figure 2) to the symmetric stretching (νs (P−O−P)) of the phosphate or borophosphate chains. The shoulder at 726 cm−1 (solid line in Figure 2) is tentatively attributed to the presence of borophosphate rings. The band at 343 cm−1 is assigned to the bending mode of the phosphate network [46].
The glass structure was considerably changed after the addition of aluminum ions (Figure S1B). Both aluminum ions and iron ions caused the phosphate network to depolymerize. Moguš-Milanković et al. [44] suggested that iron ions can depolymerize the P–O–P and P–O–Al bonds. The addition of aluminum shifted the main bands to lower wavenumbers. The deconvolution of the Q1 and Q2 overlap in the 1340–850 cm−1 region of the Al-doped borophosphate glass showed peaks at 928 cm−1, 1043 cm−1, 1108 cm−1, 1180 cm−1, and 1244 cm−1.
The shoulder at 928 cm−1 remains associated with the Q0 units, as discussed previously. After the addition of aluminum, the peak at 1069 cm−1, which is associated with the P–O− vibrations of pyrophosphate, increased in intensity and was displaced to 1043 cm−1 (Figure S1B) [43,44,45]. This increase in intensity is associated with the replacement of P−O−P bonds by P−O−Al bonds. The peak at 1108 cm−1, related to the vibrations of the PØ2O2− tetrahedra in the Q2 units and originally the most intense at 1127 cm−1 in the undoped sample, decreased in intensity due to depolymerization of the glass network. The peaks at 1180 cm−1 and 1244 cm−1 are assigned to νs (PO2) and νas (PO2) of the non-bridging oxygen bonds in the Q2 units, respectively [44]. In turn, the addition of iron ions to the glass matrix reduced the intensity of the main bands and shifted them to slightly lower wavenumbers (Figure S1C). The deconvoluted spectrum of the iron-doped borophosphate glass showed peaks at 919 cm−1, 1035 cm−1, 1104 cm−1, 1176 cm−1, and 1239 cm−1. The peak at 1035 cm−1, associated with the Q1 units, dominated the 1340–850 cm−1 region. Moreover, the intensities of the peaks related to the Q2 units at 1104 cm−1, 1176 cm−1, and 1239 cm−1 were reduced. For example, the shoulder on the right side of the main band, which consists of peaks at 1176 cm−1 and 1239 cm−1, became less intense with the addition of iron. From this, we can infer that at this concentration, the addition of iron depolymerizes the glass instead of replacing the P−O−Al bonds.

2.2. Regioselective Hydrothiolation of Alkynes

To determine the applicability of iron-borophosphate glass (Fe@NaH2PO4-H3BO3 glass), it was tested as a catalyst in the regioselective hydrothiolation of alkynes. We first conducted studies to determine the optimal synthesis conditions. For this purpose, methylbenzenethiol (1a) and phenylacetylene (2a) were used as the model substrates under solvent-free conditions. The catalytic potential of Fe@NaH2PO4-H3BO3 glass was then screened under various reaction conditions (Table 1).
Firstly, the optimal temperature for the hydrothiolation reaction was evaluated using catalytic amounts of Fe@NaH2PO4-H3BO3 glass (10 mg). At 0 °C, the desired product 3a was synthesized in a good yield, with high stereoselectivity (entries 1−4). Next, we evaluated the catalyst loading for the reaction. When the amount of the catalyst was decreased to 5 mg, the stereoselectivity was high (E/Z ratio = 90:10), but the yield of 3a was only 65% (entry 5). In the same way, when the loading of catalyst was increased to 15 mg, 3a was synthesized in 60% yield, with very poor stereoselectivity (entry 6). As such, 10 mg (approximately 4.3 mol % of Fe2O3) was the most appropriate catalyst load for this reaction, where the desired product was synthesized in 80% yield and with high stereoselectivity (entry 2).
After determining the best temperature and catalyst load, we evaluated the influence of the reaction time (entries 7–9). We found that 40 min was the best reaction time, where 3a was synthesized in 97% yield, with an E/Z ratio of 82:18 (entry 9). In addition, no improvement in yield or stereoselectivity was observed when the reaction was carried out in different temperatures for 40 min (entries 10–11).
Finally, to determine the efficiency of Fe@NaH2PO4-H3BO3 glass in the hydrothiolation reaction, we independently investigated the influence of the metal and pure borophosphate glass (NaH2PO4-H3BO3) on the reaction. When the reaction was carried out using pure NaH2PO4-H3BO3, 3a was obtained in a lower yield, with lower stereoselectivity (entry 12). Similarly, a low yield of product 3a was observed when commercial Fe2O3 was used (entry 13). No product was observed when the reaction was performed without the catalyst (entry 14). These results highlight that the presence of iron in the glass matrix affects the reaction and allows for the product to be synthesized in high yields with high stereoselectivity.
After determining the best reaction conditions (Table 1, entry 9), the synthesis method was extended to other thiols (1) and acetylenes (2) to evaluate its generality and scope (Figure 3). In general, the aromatic thiols reacted very smoothly with phenylacetylene, affording the desired products in 65–97% yields (Figure 3, 3a–e). In terms of selectivity, the aryl groups attached to the sulfur moiety played a significant role in the resulting stereochemistry of the products. Large amounts of E stereoisomer were obtained for compounds 3a–d. For example, the reaction of thiophenol 2b with phenylacetylene 1a delivered the compound 3b in 82% yield and stereoselectivity of E/Z ratio = 67:33. It is important to note that sulfide 3c, which is synthesized from 4-chlorothiophenol, was obtained in 76% yield exclusively in the E configuration. When the bromo atom was attached in a para position of the aromatic ring of thiol, the desired product 3d was obtained in 65% yield with an E/Z ratio of 70:30.
For sulfur moieties containing naphthyl and alkyl groups, however, the Z stereoisomer of the vinyl sulfides was preferred. For example, when 2-naphthalene thiol was employed, 3e was obtained in 81% yield, with an E/Z ratio of 32:68. The cyclohexyl vinyl sulfide derivative 3e was obtained in 73% yield, with high stereoselectivity (E/Z ratio = 10:90). Although a relatively low yield was obtained when thiol derivatives containing propyl and butyl groups were used, the stereoselectivity of 3g and 3h remained high.
The method was also found to be applicable to the hydrothiolation of 3-ethynylthiophene, where the products 3i and 3j were synthesized in excellent yields (93% and 82%, respectively), with high Z stereoselectivity. In particular, 3i was obtained in 100% of its Z stereoisomer. The method, however, was not applicable for the hydrothiolation of 1-heptyne and propargyl alcohol, as seen from the trace amounts of products 3k and 3l produced under similar reaction conditions.
In order to demonstrate the synthetic utility of this protocol, scaling up of the reaction was performed at 5.0 mmol (Figure 4). In this experiment, 4-methylbenzenethiol 1a and phenylacetylene 2a were used as the starting materials, affording the vinyl sulfide 3a with excellent yield: 97% (1.10 g). Thus, this methodology could be used for gram-scale synthesis of vinyl sulfides.
To further evaluate the efficacy of the catalyst (Fe@NaH2PO4-H3BO3 glass) for the subsequent catalytic cycle, a standard reaction was performed (Table 1, entry 9). After the reaction, the catalysts were recovered from the reaction medium by adding EtOAc (3 × 5.0 mL) and the organic phase was removed by using a Pasteur pipette. The recovered catalysts were dried in ambient atmosphere and used directly in other reactions without any purification. The recycled iron-glass catalyst was reused for more four reaction cycles, coupling 1a and 2a. To our delight, the catalyst maintained its effectiveness, yielding 3a without significant decrease in the yields (Figure 5). Furthermore, we performed PXRD ((d) in Figure 1) and Raman (Figure S1D) measurements of the glass-based catalyst after catalysis. The glass-based catalyst after the catalytic run retained its amorphous character. The Raman spectra show a profile similar to the glass structure.

3. Materials and Methods

3.1. General Information

The reagents and solvents were purchased commercially from Sigma-Aldrich-Merck and LabSynth. The organic reactions were monitored by thin-layer chromatography (TLC). The TLC plates were observed under UV light and iodine vapor. The nuclear resonance spectroscopy (NMR) spectra were obtained on a Bruker DPX-300 Avance spectrometer, using deuterated chloroform (CDCl3) as solvent. The structural information of the glass matrix was accessed by Raman spectroscopy. The spectra were obtained in powdered samples (325 mesh) using a 514.5 nm excitation source in a LabRAM HR Evolution System from Horiba. The spectra were collected in the 100–1400 cm−1 range using a CCD camera at room temperature. The powder X-ray diffraction (PXDR) analyses of the glasses were performed using a glass plate holder. The borophosphate glass powder was gently mounted on the glass holder. The diffractograms of the powder were obtained using Bragg–Brentano (BB) geometry in a SmartLab SE 3 kW diffractometer from Rigaku equipped with Cu-Kα radiation source (λ = 1.5418 Å) in the 15–80 θ–2θ (°) range.

3.2. Glass Synthesis

The borophosphate glass matrix was composed of NaH2PO4 and H3BO3 with NaH2PO4/H3BO3 (mol) ratio of 2, modified with 10 mol% of Al2O3, and doped with iron ions from Fe2O3 addition at 3 mol%.
Usually, a 30 mL Pt/Au (95%/5%) crucible with a lid is used to run 10 g batches of the raw chemicals previously homogenized for ten minutes in an agate mortar. The glass raw chemicals were fused in a preheated resistive furnace at 1050 °C for 60 min.
After that, the glass melts were quenched to room in a cylindrical graphite mold. The glass-based catalyst powder was obtained by crushing the pieces and sieving them through a 325-mesh sieve.

3.3. General Procedure for the Preparation of Vinyl Sulfides

To a test tube contain a stirring bar was added 10 mg of iron-borophosphate glass (catalyst) and placed in an ice bath at 0 °C. After that, the respective acetylene (0.25 mmol) was added and subsequently the thiol (0.25 mmol), followed by stirring for 40 min at 0 °C. The hydrothiolation reaction was monitored by thin-layer chromatography (TLC) using hexane as eluent to determine reaction time. The organic compounds were solubilized in ethyl acetate (3 × 5.0 mL), separated by filtration, and concentrated under vacuum. The purification of the products was carried out by column chromatography, using silica gel (silica gel 60, 0.005–0.10 mm) as stationary phase and hexane as mobile phase. The identity, purity and stereoselectivity of the products were confirmed by 1H NMR and 13C NMR analysis (see Supplementary Material).
In cases of mixture of stereoisomers, considering they have the same rf values, they were isolated as a mixture.

3.4. NMR Spectroscopic Data

Spectral data were in agreement with those reported in the literature, as follows.
  • Styryl(p-tolyl)sulfane [25] (3a): Yield: 97%. (E/Z): 82/18. 1H NMR (200 MHz, CDCl3): δ = 7.54–7.06 (m, 9H); 6.85 (d, J = 15.5 Hz, 0.82 × 1H); 6.63 (d, J = 15.5 Hz, 0.82 × 1H); 6.54 (d, J = 10.8 Hz, 0.18 × 1H); 6.44 (d, J = 10.8 Hz, 0.18 × 1H); 2.34 (s, 0.82 × 3H); 2.30 (s, 0.18 × 3H) ppm. 13C NMR (75 MHz, CDCl3): δ = 137.5, 136.7, 132.8, 130.7, 130.6, 130.1, 130.0, 128.9, 128.8, 128.4, 127.5, 127.2, 127.1, 126.6, 126.1, 124.6, 21.2.
  • Phenyl(styryl)sulfane [25] (3b): Yield: 82%. (E/Z): 67/33. 1H NMR (300 MHz, CDCl3): δ = 7.46 −7.14 (m, 10H); 6.80 (d, J = 15.5 Hz, 0.67 × 1H); 6.64 (d, J = 15.5 Hz, 0.67 × 1H); 6.50 (d, J = 10.8 Hz, 0.33 × 1H); 6.41 (d, J = 10.8 Hz, 0.33 × 1H) ppm. 13C NMR (75 MHz, CDCl3): δ = 136.6, 136.3, 135.3, 131.8, 130.1, 129.9, 129.2, 128.8, 128.7, 128.4, 127.6, 127.3, 127.2, 127.0, 126.1, 123.4 ppm.
  • (E)-(4-chlorophenyl)(styryl)sulfane [47] (3c): Yield: 76%. (E/Z): 100/0. 1H NMR (300 MHz, CDCl3): δ = 7.33–7.24 (m, 9H); 6.82 (d, J = 15.4 Hz, 1H), 6.73 (d, J = 15.4 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ = 136.3, 133.9, 133.0, 132.8, 131.0, 129.3, 128.7, 127.8, 126.1, 122.5 ppm.
  • (4-bromophenyl)(styryl)sulfane [17] (3d): Yield: 65%. (E/Z): 70/30. 1H NMR (300 MHz, CDCl3): δ = 7.56–7.24 (m, 9H); 6.75 (d, J = 15.4 Hz, 0.70 × 1H); 6.82 (d, J = 15.4 × 2H); 6.63 (d, J = 10.6 Hz, 0.30 × 1H); 6.41 (d, J = 10.6 Hz, 0.30 × 1H) ppm. 13C NMR (75MHz, CDCl3): δ =136.3, 134.6, 133.0, 132.8, 132.2, 131.4, 131.1, 129.0, 128.7, 128.4, 128.2, 127.9, 127.4, 126.3, 126.1, 124.9, 122.2, 120.9 ppm.
  • Naphthalen-2-yl(styryl)sulfane [48] (3e): Yield: 81%. (E/Z): 32/68. 1H NMR (300 MHz, CDCl3): δ = 7.87–7.11 (m, 12H); 6.87 (d, J = 15.3 Hz, 0.32 × 1H); 6.69 (d, J = 15.3 Hz, 0.32 × 1H); 6.55 (d, J = 10.5 Hz, 0.68 × 1H); 6.49 (d, J = 10.5 Hz, 0.68 × 1H) ppm. 13C NMR (75 MHz, CDCl3): δ = 136.5, 133.7, 133.6, 132.3, 132.2, 129.0, 128.9, 128.8, 128.5, 128.4, 128.2, 127.8, 127.7, 127.6, 127.5, 127.4, 127.3, 126.8, 126.6, 126.3, 126.1, 125.8, 125.7, 123.2 ppm.
  • Cyclohexyl(styryl)sulfane [25] (3f): Yield: 73%. (E/Z): 10/90. 1H NMR (300 MHz, CDCl3) δ = 7.41 (d, J = 7.20 Hz, 2H); 7.30–7.10 (m, 3H); 6.69 (d, J = 15.6 Hz, 0.10 × 1H); 6.50 (d, J = 15.6 Hz, 0.10 × 1H); 6.36 (d, J = 10.8 Hz, 0.90 × 1H); 6.26 (d, J = 10.8 Hz, 0.90 × 1H); 2.87–2.77 (m, 1H); 2.02–1.31 (m, 10H) ppm. 13C NMR (75 MHz, CDCl3) δ = 137.1, 128.6, 128.2, 126.5, 125.9, 125.0, 47.8, 33.7, 29.7, 26.0, 25.6 ppm.
  • Propyl(styryl)sulfane [30] (3g): Yield: 45%. (E/Z): 17/83. 1H NMR (300 MHz, CDCl3) δ = 7.48 (d, J = 6.20 Hz, 2H); 7.36–7.16 (m, 3H); 6.71 (d, J = 15.6 Hz, 0.17 × 1H); 6.50 (d, J = 15.6 Hz, 0.17 × 1H); 6.41 (d, J = 10.9 Hz, 0.83 × 1H); 6.23 (d, J = 10.9 Hz, 0.83 × 1H); 2.75 (t, J = 7.2 Hz, 2H); 1.77–1.65 (m, 2H); 1.02 (t, J = 7.2 Hz, 3H) ppm. 13C NMR (75 MHz, CDCl3) δ = 137.1, 128.6, 128.2, 127.7, 126.8, 126.6, 125.5, 125.4, 125.3, 37.9, 34.7, 23.6, 22.9, 13.4, 13.2 ppm.
  • Butyl(styryl)sulfane [47] (3h): Yield: 40%. (E/Z): 12/88. 1H NMR (300 MHz, CDCl3) δ = 7.47 (d, J = 6.99 Hz, 2H); 7.36–7.16 (m, 3H); 6.71 (d, J = 15.6 Hz, 0.12 × 1H); 6.45 (d, J = 15.6 Hz, 0.12 × 1H); 6.41 (d, J = 10.9 Hz, 0.88 × 1H); 6.23 (d, J = 10.9 Hz, 0.88 × 1H); 2.77 (t, J = 7.5 Hz, 2H), 1.66 (quint, J = 7.5 Hz, 2H), 1.49–1,37 (m, 2H), 0.92 (t, J = 7.5 Hz, 3H) ppm. 13C NMR (75 MHz, CDCl3) δ = 137.1, 128.6, 128.2, 127.7, 126.5, 125.3, 35.6, 32.3, 21.7, 13.6 ppm.
  • (Z)-3-(2-(p-tolylthio)vinyl)thiophene [49] (3i): Yield: 93%. (E/Z): 0/100. 1H NMR (300 MHz, CDCl3): δ = 7.49–7.47 (m, 1H); 7.37 (d, J = 8.2 Hz, 2H); 7.30–7.29 (m, 2H); 7.15 (d, J = 8.2 Hz, 2H); 6.56 (d, J = 10.5 Hz, 1H); 6.37 (d, J = 10.5 Hz, 1H); 2.34 (s, 3H) ppm. 13C NMR (75 MHz, CDCl3): δ = 137.9, 137.4, 132.3, 130.5, 130.0, 128.6, 125.7, 125.1, 123.7, 120.9, 21.1 ppm.
  • (Z)-3-(2-((4-bromophenyl)thio)vinyl)thiophene (3j): Yield: 82%. (E/Z): 30/70. 1H NMR (300 MHz, CDCl3): δ = 7.48–7.43 (m, 3H); 7.32–7.7.26 (m, 4H); 6.80 (d, J = 15.3 Hz, 0.30 × 1H); 6.66 (d, J = 10.5 Hz, 0.70 × 1H); 6.64 (d, J = 15.3 Hz, 0.30 × 1H); 6.34 (d, J = 10.5 Hz, 0.70 × 1H) ppm. 13C NMR (75 MHz, CDCl3): δ = 138.8, 137.7, 135.2, 134.9, 132.4, 132.3, 131.5, 131.1, 128.6, 128.2, 126.6, 125.4, 124.8, 124.3, 123.5, 122.8, 127.4, 121.7, 121.3, 120.9 ppm.

4. Conclusions

We developed an alternate, eco-friendly, robust, safe, and scalable method for the synthesis of vinyl sulfides via the hydrothiolation of alkynes with thiols using iron-borophosphate glass as a catalyst. In most cases, this new regioselective procedure affords the desired products in good yields. The features of this iron-glass-catalyzed reaction include: (1) ease of preparation; (2) simplicity, non-toxicity, and safety; (3) low catalyst loading; (4) atom economy; (5) solvent-free approach; (6) inexpensiveness; (7) gram scalability; (8) catalyst recyclability; and (9) applicability to structurally diverse substrates. These features render it an environmentally friendly alternative for synthesizing vinyl sulfides. Further applications of iron-borophosphate glass as catalyst in the thiolation of organic structures are in progress in our group.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/catal13071127/s1. Figure S1: Deconvolution spectra of glasses in the region between 800 and 1350 cm−1 with (A) 0% Al2O3 and 0% Fe2O3, (B) 10% Al2O3 and 0% Fe2O3, and (C) 10% Al2O3, 6% Fe2O3, and (D) full Raman spectra of the glass-based catalyst (i) after and (ii) before reaction. NMR spectroscopic data for all compounds 3a–3j. 1H and 13C NMR spectra for all compounds 3a–3j.

Author Contributions

Conceptualization, R.S., S.S. and G.V.B.; synthesis, spectral analysis, characterizations, and reagents/materials, N.C., E.A.T., I.J.A.G., M.J.A.d.S., F.M., M.G. and J.R., catalyst synthesis and characterizations, J.F.F. and R.S.; organic synthesis, N.C., E.A.T., I.J.A.G. and M.J.A.d.S.; writing—original draft, J.R., R.S., S.S. and G.V.B.; writing—review and editing, J.R., R.S., S.S. and G.V.B.; writing of the paper, J.R., R.S., S.S. and G.V.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The data used to support the findings of this study are included in the article. In addition, the Supplementary Materials include the spectral data of the compounds.

Acknowledgments

We gratefully acknowledge CAPES (001) and CNPq for financial support. G.V.B. acknowledges CNPq for funding (429831/2018-8). R.S. would like to acknowledge CNPq for funding (422774/2018-9). JR and SS are grateful to CNPq for funding (315399/2020-1, 422645/2021-4, 309975/2022-0, and 403210/2021-6). J.F.F. acknowledges CNPq (430470/2018-5) and FAPDF (193.001.757/2017), for financial support.

Conflicts of Interest

The authors declare no conflict of interest.

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Catalysts 13 01127 g001 550
Figure 1. Powder PXRD analysis for borophosphate glass with (mol) (a) 0% Al2O3 and 0% Fe3+ ions, (b) 10% Al2O3 and 0% Fe3+ ions, and (c) 10% Al2O3 and 6% Fe3+ ions and (d) sample (c) after catalysis.
Figure 1. Powder PXRD analysis for borophosphate glass with (mol) (a) 0% Al2O3 and 0% Fe3+ ions, (b) 10% Al2O3 and 0% Fe3+ ions, and (c) 10% Al2O3 and 6% Fe3+ ions and (d) sample (c) after catalysis.
Catalysts 13 01127 g001
Catalysts 13 01127 g002 550
Figure 2. Raman spectrum for borophosphate glass (in mol%) (a) 0% Al2O3 and 0% Fe3+ ions, (b) 10% Al2O3 and 0% Fe3+ ions, and (c) 10% Al2O3 and 6% Fe3+ ions.
Figure 2. Raman spectrum for borophosphate glass (in mol%) (a) 0% Al2O3 and 0% Fe3+ ions, (b) 10% Al2O3 and 0% Fe3+ ions, and (c) 10% Al2O3 and 6% Fe3+ ions.
Catalysts 13 01127 g002
Catalysts 13 01127 g003 550
Figure 3. Synthesis of vinyl sulfides catalyzed by iron-borophosphate glass. Reaction conditions: thiol (0.25 mmol), acetylene (0.25 mmol) and Fe@NaH2PO4-H3BO3 (10 mg). Isolation of products using column chromatography and stereoisomers determined by 1H NMR spectroscopy.
Figure 3. Synthesis of vinyl sulfides catalyzed by iron-borophosphate glass. Reaction conditions: thiol (0.25 mmol), acetylene (0.25 mmol) and Fe@NaH2PO4-H3BO3 (10 mg). Isolation of products using column chromatography and stereoisomers determined by 1H NMR spectroscopy.
Catalysts 13 01127 g003
Catalysts 13 01127 g004 550
Figure 4. Scaling up reaction for the synthesis of 1.1 g of compound 3a.
Figure 4. Scaling up reaction for the synthesis of 1.1 g of compound 3a.
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Catalysts 13 01127 g005 550
Figure 5. Recyclability of the catalyst.
Figure 5. Recyclability of the catalyst.
Catalysts 13 01127 g005
Table
Table 1. Determination of reaction conditions a.
Table 1. Determination of reaction conditions a.
EntryCatalyst Amount (mg)Time (min)Temp (°C)Yield (%) bE:Z c
1Fe@NaH2PO4-H3BO3 (10)10r.t.8060:40
2Fe@NaH2PO4-H3BO3 (10)1008075:25
3Fe@NaH2PO4-H3BO3 (10)10−53982:18
4Fe@NaH2PO4-H3BO3 (10)10506181:19
5Fe@NaH2PO4-H3BO3 (5)1006590:10
6Fe@NaH2PO4-H3BO3 (15)1006060:40
7Fe@NaH2PO4-H3BO3 (10)2005575:25
8Fe@NaH2PO4-H3BO3 (10)3006076:24
9Fe@NaH2PO4-H3BO3 (10)4009782:18
10Fe@NaH2PO4-H3BO3 (10)40r.t.6675:25
11Fe@NaH2PO4-H3BO3 (10)40−54488:12
12NaH2PO4-H3BO3 (10)4007777:23
13 dFe2O3 4005989:11
14-100--
a Reaction conditions: 4-methylbenzenethiol 1a (0.25 mmol), phenylacetylene 2a (0.25 mmol) and glass catalyst; b isolated yield; c stereoisomers were determined by 1H NMR spectroscopy; d 5.0 mol% was used as catalyst, which is approximately the amount of iron oxide in the glass matrix.
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Catholico, N.; Tessari, E.A.; Granja, I.J.A.; de Sousa, M.J.A.; Felix, J.F.; Manarin, F.; Godoi, M.; Rafique, J.; Schneider, R.; Saba, S.; et al. Iron-Borophosphate Glass-Catalyzed Regioselective Hydrothiolation of Alkynes under Green Conditions. Catalysts 2023, 13, 1127. https://doi.org/10.3390/catal13071127

AMA Style

Catholico N, Tessari EA, Granja IJA, de Sousa MJA, Felix JF, Manarin F, Godoi M, Rafique J, Schneider R, Saba S, et al. Iron-Borophosphate Glass-Catalyzed Regioselective Hydrothiolation of Alkynes under Green Conditions. Catalysts. 2023; 13(7):1127. https://doi.org/10.3390/catal13071127

Chicago/Turabian Style

Catholico, Nicoli, Eduarda A. Tessari, Isis J. A. Granja, Martinho J. A. de Sousa, Jorlandio F. Felix, Flávia Manarin, Marcelo Godoi, Jamal Rafique, Ricardo Schneider, Sumbal Saba, and et al. 2023. "Iron-Borophosphate Glass-Catalyzed Regioselective Hydrothiolation of Alkynes under Green Conditions" Catalysts 13, no. 7: 1127. https://doi.org/10.3390/catal13071127

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