catalysts Article Rhodium Nanoparticles Stabilized by PEG-Tagged Imidazolium Salts as Recyclable Catalysts for the Hydrosilylation of Internal Alkynes and the Reduction of Nitroarenes Guillem Fernández and Roser Pleixats * Department of Chemistry and Centro de Innovación en Química Avanzada (CINQA), Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Spain; guillem.fernandez@uab.cat * Correspondence: roser.pleixats@uab.cat; Tel.: +34-93-581-2067  Received: 28 September 2020; Accepted: 12 October 2020; Published: 15 October 2020  Abstract: PEGylated imidazolium (bromide and tetrafluoroborate) and tris-imidazolium (bromide) salts containing triazole linkers have been used as stabilizers for the preparation of water-soluble rhodium(0) nanoparticles by reduction of rhodium trichloride with sodium borohydride in water at room temperature. The nanomaterials have been characterized (Transmission Electron Microscopy, Electron Diffraction, X-ray Photoelectron Spectroscopy, Inductively Coupled Plasma-Optical Emission Spectroscopy). They proved to be efficient and recyclable catalysts for the stereoselective hydrosilylation of internal alkynes, in the presence or absence of solvent, and in the reduction of nitroarenes to anilines with ammonia-borane as hydrogen donor in aqueous medium (1:4 tetrahydrofuran/water). Keywords: alkynes; catalysis; hydrosilylation; nitroarenes; recycling; reduction; rhodium nanoparticles 1. Introduction Transition metal nanoparticles (M NPs) as catalysts have received an increasing attention from the chemical community during the last two decades [1–10]. This interest is mainly due to the physical and chemical properties derived from their small size, quantum size effects and high-surface-to volume ratio. Thus, metal nanocatalysts combine the benefits of both homogeneous and heterogeneous catalysis providing high efficiency and selectivity, as well as recyclability. Nanoparticles are thermodynamically unstable and the use of an appropriate stabilizer prevents their agglomeration to bulk metal [11]. Different types of protecting agents have been described (polymers, ionic and non-ionic surfactants, dendrimers, β-cyclodextrins, other ionic compounds, in addition to nitrogen-, sulfur-, and phosphorus-based ligands). The nature and concentration of the protecting shield not only play a role on the activity and selectivity of the nanocatalysts, but also determines their solubility properties. Thus, a suitable choice of the stabilizer allows us the obtention of nanoparticles soluble in organic, fluorous or aqueous media and facilitates the recycling. Particularly, both soluble and surface-immobilized rhodium nanoparticles (Rh NPs) have emerged as excellent catalysts with unique properties for hydrogenation reactions and, to a lesser extent, hydroformylation and carbonylation processes [12,13] by a careful design and control of the size/shape of the metallic core and the capping agent [14]. Regarding the hydrogenation reactions, Rh NPs have been mainly used in the reduction of olefins, the aromatic ring of arenes and heteroarenes, and carbonyl compounds. In this work, we have focused our attention on less studied catalytic reactions with Rh NPs, namely selective reduction of nitroarenes to arylamines and hydrosilylation of internal alkynes. Catalysts 2020, 10, 1195; doi:10.3390/catal10101195 www.mdpi.com/journal/catalysts Catalysts 2020, 10, 1195 2 of 18 Anilines are useful intermediates for the production of dyes, agrochemicals, fine chemicals, drugs and polymers. Thus, the reduction of nitroarenes [15–17] to anilines is a relevant process in academia and industry. Some encountered issues have to be solved, such as the low chemoselectivity in the presence of other reducible functional groups or the appearance of by-products (hydroxylamines, hydrazines, azoarenes and azoxyarenes) derived from partial reduction of the nitro group and from condensation steps occurring in the reduction process [18]. Catalytic hydrogenation of nitroarenes with dihydrogen has been undertaken with metal nanoparticles (Rh [19], Rh-Fe [20], Au [21,22], Pt [23,24], Pd [25,26], Ni [27,28]). In addition, Rh NPs have also been reported as catalysts for this reduction using hydrazine as hydrogen source [29–32]. Our group has described the catalytic reduction of nitroarenes with Au NPs stabilized by a nitrogen-rich PEG-tagged substrate [33] and with Ni NPs capped by mesitylene-containing tris-imidazolium salts bearing hexadecyl chains [34], using sodium borohydride and hydrazine as reducing agents, respectively. On the other hand, vinylsilanes are versatile building blocks involved in a range of transformations, such as protodesilylation to give the corresponding alkenes [35], vinyl iodide formation [36], Tamao-Fleming oxidation to provide carbonyl derivatives [37] or Hiyama cross-coupling reactions with vinyl or aryl halides [38]. A convenient and atom-efficient route for the preparation of vinylsilanes is the transition-metal catalyzed hydrosilylation of alkynes [39–44]. Although platinum species (Speier’s and Karstedt’s catalysts) have been the traditional choice for the addition of silanes to multiple carbon-carbon bonds, other metal complexes have also been investigated. In this context, some reports have appeared on the reaction of both the terminal and internal alkynes with silanes under catalysis by Rh(I) complexes [45–48]; in addition, Rh-NHC species have been used with terminal alkynes [49,50] and molecular Rh(0) complexes confined within carbon nanoreactors have been studied in the hydrosilylation of phenylacetylene [51]. Besides, in the last decade, metal nanoparticles (Pt [52–60], Pd [61,62], Rh-Pt [63], Au [64,65] and Rh [63,66]) have emerged as catalysts for these reactions. In particular, our group has described the catalytic hydrosilylation of internal alkynes with Pd [61] and Pt [60] NPs stabilized by a tris-imidazolium tetrafluoroborate, and with Rh nanoflowers stabilized by a nitrogen-rich polyethylenglicol (PEG)-tagged substrate [66]. As a particular feature, the Pd NPs [61] required anhydrous conditions, because a competitive transfer hydrogenation occurred in the presence of moisture to give the corresponding alkenes and/or alkanes. Moreover, we have recently reported the obtention of water-soluble gold nanoparticles stabilized by newly designed imidazolium salts bearing PEG-tagged chains (S1A, S1B and S2 in Figure 1), which have been found effective recyclable catalysts for the cycloisomerization of γ-alkynoic acids and the A3 coupling between carbonyl compounds, secondary amines and terminal alkynes [67]. Figure 1. PEG-tagged imidazolium salts as stabilizers (previous work: Au NPs; this work: Rh NPs). Following our interest on the development of soluble metal nanoparticles as recyclable catalysts, we describe herein the preparation and characterization of Rh NPs using these newly synthesized PEG-tagged imidazolium salts as capping agents. Taking into account the scarce precedents on the use of metal NPs for this process (particularly with Rh NPs) and our previous promising results, the hydrosilylation of internal alkynes was one of the catalytic goals that we considered. The second Catalysts 2020, 10, 1195 3 of 18 one was to develop a simple, clean and mild procedure for the chemoselective reduction of nitroarenes to anilines. Thus, we also present here the catalytic activity and recyclability of the Rh NPs for the hydrosilylation of alkynes and the reduction of aromatic nitro compounds. 2. Results and Discussion 2.1. Preparation and Characterization of Rhodium Nanoparticles We have prepared rhodium nanoparticles by a chemical reduction of rhodium trichloride hydrate (RhCl3 .xH2 O) with sodium borohydride (NaBH4 ) in degassed water (H2 O) at room temperature in the presence of the corresponding stabilizer S1A, S1B or S2 under nitrogen atmosphere (entries 1–3, Table 1). A molar ratio S:Rh around 0.02:1 was used, which was found convenient for other type of PEG-tagged ligands [66]. Upon addition of an excess of reducing agent (from 14 to 18 mol per mol of Rh), the reaction mixture changed from orange to blackish. The solution was stirred overnight at room temperature, then it was filtered through a Millipore filter, and the filtrate was extracted with dichloromethane. Upon removal of the solvent, the corresponding nanomaterial was obtained as a black solid, which was stored under inert atmosphere to prevent the oxidation. The obtained Rh NPs were soluble in water, tetrahydrofuran, dichloromethane and chloroform, and insoluble in diethyl ether and hexane. Table 1. Preparation of Rh NPs stabilized by S1A, S1B and S2. % Rh Entry S S/Rh/NaBH4 [Rh] (mM) Diameter (nm) 1,2 Yield (%) 3 Nanomaterial Theor Expt 1 S1A 0.02/1/14 1 2.9 ± 3 30.3 31.7 40 M1A 2 S1B 0.02/1/14 1 3.3 ± 2 30.3 29.9 27 M1B 3 S2 0.025/1/18 0.8 5.6 ± 3 24.2 27.4 41 M2 1Determined by TEM (500–1000 particles measured). 2 Larger aggregates of small particles were also formed in entries 2 and 3. See text. 3 Based on RhCl3 ·xH2 O (40 wt% Rh) used. Analysis by Transmission Electron Microscopy (TEM) confirmed the formation of small nanoparticles from 2.9 to 5.6 nm, together with flower-like larger aggregates, especially for M1B and M2 (around 33 and 21 nm). These aggregates were smaller (around 14 nm) and less abundant in M1A (Table 1 and Figure 2). The tendency to form Rh nanoflowers has been previously observed in the group by decreasing the stabilizer-to-metal ratio [66]. Moreover, the nanoflowers displayed in that case much better catalytic activity than nanomaterials formed by small dispersed nanoparticles. Figure 2. TEM images of M1A (a), M1B (b) and M2 (c). HRTEM image of M2 (d). The presence of rhodium was confirmed by Energy-Dispersive X-ray Spectroscopy (EDS). The spectrum of M2 is depicted as a representative example in Figure 3. Catalysts 2020, 10, 1195 4 of 18 Figure 3. EDS spectrum of M2. Moderate yields (from 27 to 41%) with respect to the initial amount of rhodium were calculated on the basis of elemental analysis of rhodium in the materials (Inductively Coupled Plasma-Optical Emission Spectroscopy, ICP-OES) (Table 1). The same stabilizers (S1A, S1B and S2) had been found more effective for the formation of gold nanoparticles [67]. High-Resolution Transmission Electron Microscopy (HRTEM) images of M2 (Figure 2d) showed the crystalline planes of the Rh NPs. This was consistent with the Electron Diffraction (ED) analysis, which gave interplanar distances close to those expected for the face-centered cubic (fcc) rhodium lattice (Table 2). Table 2. Electron diffraction pattern of M2. dhlk (nm) hlk [a] Exper. Theor. (111) 0.2186 0.2196 (200) 0.1907 0.1902 (220) 0.1340 0.1345 (311) 0.1157 0.1147 [a] Data according to American Mineralogist Crystal Structure Database. The nanoparticulated materials M1A, M1B and M2 were analysed by X-ray Photoelectron Spectroscopy (XPS). The doublet at 307.6 and 312.3 eV for Rh 3d5/2 and Rh 3d3/2 , respectively (M1B, Figure 4) was attributed to Rh(0) species [68,69]. We did not observe clear peaks at 308.9 and 313.6 eV corresponding to rhodium oxide binding energy [70]. The other nanomaterials (M1A and M2) displayed similar spectra. Catalysts 2020, 10, 1195 5 of 18 Figure 4. XPS spectrum of M1B. 2.2. Hydrosilylation of Alkynes under Catalysis by Rhodium Nanoparticles With Rh NPs in hand, we undertook the hydrosilylation of a variety of acetylenic compounds. We tested two experimental procedures. In method A the mixture of the alkyne, the catalyst (0.5 mol% Rh loading) and neat silane (4 equiv.) was heated in a sealed vessel at 90 ◦ C [61]. The excess of the volatile silane can be removed easily from the crude mixture. In order to reduce to excess of silane for non-volatile or more expensive silanes, we decided to perform the reaction in a suitable solvent. The use of ethanol did not give successful results, but tetrahydrofuran was found appropriate [60]. Thus, under method B the substrate (c = 0.5 M) was treated with the silane (1.2 equiv.) in tetrahydrofuran (THF) at 90 ◦ C in a closed vessel in the presence of the catalyst (0.5 mol% Rh loading). We summarize in Table 3 the results obtained with three symmetric internal alkynes. >=99:1 0.25 92 10 2 M2 >99:1 20 91 5 3 M1A >99:1 18 85 4 M1B 11 >99:1 18 77 6 5 M2 >99:1 0.83 81 12 6 M2 >99:1 0.83 89 7 M1A >99:1 0.83 92 8 M1B >99:1 0.83 48 13 9 M2 >99:1 0.83 58 14 10 M2 >99:1 1 64 11 M1A >99:1 1 72 12 M1B 157 >99:1 1 55 13 M2 >99:1 1 76 16 14 M2 >99:1 18 85 17 15 M2 >99:1 1 66 18 16 M2 >99:1 1 83 19 17 M2 >99:1 18 53 20 18 M2 >99:1 2 78 21 8 19 M2 >99:1 1 64 9 20 M1A 69:31 1 56 9 21 M1B 22 82:18 1 71 9 1Nitroarene (0.5 mmol), AB (2 mmol) and catalyst (1 mol%) in THF-H2 O 1:4 (10 mL); rt; in a closed vessel with a balloon. 2 Molar ratio by TLC or 1 H NMR. 3 Isolated yield. 4 Water as solvent. 5 1 H NMR yield. 4-Phenethylaniline 110 was also obtained. Molar ratio 11:110 = 91:9. 6 1 H NMR yield. 4-Phenethylaniline 110 was also obtained. Molar ratio 11:110 = 85:15. 7 From p-nitrobenzaldehyde. 8 From m-dinitrobenzene. 9 1 H NMR yield of the aniline 22. A minor amount of 1-(4-aminophenyl)ethan-1-ol 220 was observed. Taking advantage of the solubility of the rhodium nanocatalysts in water, the recyclability of M1A was investigated for the reduction of 3,4-dimethoxynitrobenzene with AB as hydrogen source (Table 8). Five consecutive runs were successfully performed, but longer reactions times were needed for full conversion after the first cycle. Catalysts 2020, 10, 1195 11 of 18 Table 8. Recycling of Rh NPs (M1A) in the reduction of 3,4-dimethoxynitrobenzene with AB. Cycle 1 Time (h) Yield (%) 2 1 0.83 92 2 1.25 88 3 18 90 4 18 85 5 24 87 1Nitroarene (0.5 mmol), AB (2 mmol) and catalyst (1 mol%) in THF-H2 O 1:4 (10 mL), rt, in a closed vessel with a balloon. 2 Full conversion in all cases; isolated yield. With the purpose to overcome the chemoselectivity problems encountered with some substrates, we also assessed the reduction of some nitroarenes using sodium borohydride (NaBH4 ) and hydrazine (NH2 -NH2 ) as reducing agents. We maintained the other reaction conditions (1 mol% Rh, THF-H2 O 1:4, rt). We summarize the results in Tables 9 and 10, respectively. Table 9. Reduction of nitroarenes with sodium borohydride under catalysis by Rh NPs. Entry 1 Cat. Product ArNH2 /ArNO2 2 Time (h) Yield (%) 1 M2 >99:1 0.83 66 3 13 2 M2 >99:1 24 77 4 3 M1A >99:1 18 92 5 11 4 M1B >99:1 18 70 6 5 M2 >99:1 18 83 3 17 6 M2 >99:1 0.5 -7 7 M1A 69:31 1 58 8 8 M1B >99:1 1 10 9 22 1 Nitroarene (0.5 mmol), NaBH4 (2 mmol) and catalyst (1 mol%) in THF-H2 O 1:4 (10 mL); rt; in a closed vessel with a balloon. 2 Molar ratio by TLC or 1 H NMR. 3 Isolated yield. 4 1 H NMR yield. 4-Phenethylaniline 110 was also obtained. Molar ratio 11:110 = 92:8. 5 1 H NMR yield. 4-Phenethylaniline 110 was also obtained. Molar ratio 11:110 = 97:3. 6 1 H NMR yield. 4-Phenethylaniline 110 was also obtained. Molar ratio 11:110 = 84:16. 7 Not determined, mixture of 22 with 1-(4-aminophenyl)ethan-1-ol 220 and products derived from the partial reduction of the nitro group. 8 1 H NMR yield of 22. Mixture of 22 with 1-(4-aminophenyl)ethan-1-ol 220 . Molar ratio: 74:26. 9 1 H NMR yield of the aniline 22. Mixture of 22 with 1-(4-aminophenyl)ethan-1-ol 220 . Molar ratio: 36:64. Catalysts 2020, 10, 1195 12 of 18 Table 10. Reduction of nitroarenes with hydrazine under catalysis by Rh NPs. Entry 1 Cat. Product ArNH2 /ArNO2 2 Time (h) Yield (%) 1 M2 >99:1 16 70 3 13 2 M1A 62:38 48 48 4 3 M1B 11 29:71 48 23 4 4 M2 >99:1 2 -5 5 M1A >99:1 24 -5 6 M1B 22 87:13 24 -5 1 Nitroarene (0.5 mmol), N H ·H O (2 mmol) and catalyst (1 mol%) in THF-H O 1:4 (10 mL); rt; in a closed vessel 2 4 2 2 with a balloon. 2 Molar ratio by TLC or 1 H NMR. 3 Isolated yield. 4 1 H NMR yield. 5 Not determined, mixture of the aniline 22 with other products derived from partial reduction of the nitro group. The reduction of 3,4-dimethoxynitrobenzene and p-nitrobenzonitrile with NaBH4 to the corresponding anilines 13 and 17 proceeded well with M2, obtaining similar results as for ammonia borane (entries 1 and 5 of Table 9). However, in the reduction of 4-nitrostilbene under catalysis by M1A, M1B and M2, certain amounts of 4-phenethylaniline 110 were also formed, arising from the reduction of both nitro and olefin groups (entries 2–4, Table 9). As expected, also the carbonyl group of p-nitroacetophenone was partially reduced with this reducing agent, affording mixtures of anilines 22 and 220 in variable proportions depending on the catalyst (entries 6–8, Table 9). For M2, complete conversion of the substrate was observed after 30 min, but the analysis of the mixture also revealed the presence of products derived from the partial reduction of the nitro group. In summary, sodium borohydride was not found a better alternative to ammonia borane for the selective reduction of nitroarenes. Longer reaction times were required for the full reduction of nitroarenes with hydrazine hydrate (NH2 -NH2 .H2 O) under these conditions, in comparison with the previously mentioned reducing agents. However, a 70% isolated yield of the aniline 13 was obtained after 18 h at room temperature (entry 1, Table 10). An increase of the temperature would be needed to accelerate the process. The reaction with p-nitrostilbene was sluggish and from low to moderate conversions were obtained after 48 h with M1B and M1A (entries 2 and 3, Table 10). Nanocatalyst M2 provided full conversion of p-nitroacetophenone after 2 h, but a complex mixture of the aniline 22 and several products derived from the partial reduction of the nitro group was obtained (entry 4, Table 10). The reductions of the same substrate under catalysis by M1A and M1B provided similar results after 24 h of reaction (entries 5 and 6, Table 10). In summary, hydrazine was not found to be a better alternative to ammonia borane for the mild and selective reduction of nitroarenes. 3. Materials and Methods 3.1. General Remarks Commercial reagents were used directly as received. Milli-Q water and HPLC grade solvents were used in the preparation and purification of products and nanomaterials. All NMR spectra were recorded with Bruker Avance DRX-250 (250 MHz for 1 H), Bruker Avance DPX-360 MHz (360 MHz for 1 H) and Bruker Avance III 400SB (400 MHz for 1 H) spectrometers (Bruker Biospin, Rheinstetten, Germany). Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES), measurements of metal content were carried out at the Servei d’Anàlisi Química of the Universitat Autònoma de Barcelona with a Perkin-Elmer instrument, model Optima 4300DV (Perkin-Elmer, Shelton, CT, USA). TEM, ED and Catalysts 2020, 10, 1195 13 of 18 EDS analyses were performed at the Servei de Microscòpia of the Universitat Autònoma de Barcelona, with a JEOL JEM-2011 model instrument operating at 200 kV (JEOL Ltd, Akishima, Tokyo, Japan). The nanoparticle sizes were determined by measuring 500–1000 particles using ImageJ (Fiji) program and were subsequently averaged to produce the mean NP diameter. XPS measurements were performed with a Phoibos 150 analyzer (SPECS GmbH, Berlin, Germany) in ultra-high vacuum conditions (base pressure 5E-10 mbar) with a monochromatic aluminium Kalpha X-ray source (1486.74 eV); the energy resolution as measured by the FWHM of the Ag 3d5/2 peak for a sputtered silver foil was 0.58 eV. 3.2. General Procedure for the Preparation of Rh NPs (M1A, Table 1, Entry 1) Stabilizer S1A (43 mg; 0.01 mmol) and rhodium(III) chloride hydrate (135 mg; 0.52 mmol) were dissolved in distilled water (450 mL) under inert atmosphere to afford an orange solution. Then, 50 mL of 0.15 M NaBH4 solution (7.5 mmol) were added dropwise for 10 min and the mixture turned black. The solution was stirred at room temperature overnight. The mixture was filtered through a Milli-Pore filter (0.45 µm, nylon) and then extracted with dichloromethane (CH2 Cl2 ) (6 × 30 mL). The organic phase was dried over anhydrous sodium sulfate (Na2 SO4 ), filtered and then the solvent was evaporated to obtain the Rh NPs M1A as a black powder (68.2 mg; 31.7% Rh (ICP-OES); 40% yield according to the starting Rh. 3.3. General Procedure for the Hydrosilylation of Alkynes by Rh NPs under Neat Conditions (Method A) To a mixture of alkyne (0.5 mmol) and Rh nanocatalyst (M1A, M1B or M2) (0.5 mol% Rh) into a screw-top sealable tube, triethylsilane (2 mmol) was added. The resulting solution was then heated under stirring at 90 ◦ C until total conversion of the alkyne (GC monitoring). Hexane was added to the mixture to precipitate the Rh NPs and the catalyst was separated by centrifugation/decantation. The supernatant was filtered through a plug of silica-gel eluting with hexane and the solvent was removed under an air flow to afford the corresponding vinylsilane. 3.4. General Procedure for the Hydrosilylation of Alkynes by Rh NPs in THF (Method B) A mixture of alkyne (0.5 mmol) and Rh nanocatalyst (M1A, M1B or M2) (0.5 mol% Rh) into a screw-top sealable tube was subjected to three evacuate-refill cycles with argon. Then the corresponding silane (0.6 mmol) and anhydrous and degassed THF (1 mL) were added under argon atmosphere. The reaction mixture was heated under stirring at 90 ◦ C until total conversion of the alkyne (Gas chromatography (GC) monitoring). Hexane was added to the mixture to precipitate the Rh NPs and the catalyst was separated by centrifugation/decantation. The supernatant was filtered through a plug of silica-gel eluting with hexane and the solvent was removed under an air flow to afford the corresponding vinylsilane. When the non-volatile triphenylsilane was used, the crude mixture was purified by column chromatography. In the recycling experiments, the Rh nanocatalyst recovered after the centrifugation/decantation process was dried and reused in the next cycle by adding new reagents and solvent in the tube. Spectral data of the vinylsilanes are provided in the Supplementary Materials. 3.5. General Procedure for the Reduction of Nitroarenes by Rh NPs with Ammonia Borane A solution of ammonia borane (2 mmol) in 8 mL of H2 O was added dropwise to a stirred solution of catalyst M2 (1 mol% Rh) and nitroarene (0.5 mmol) in THF (2 mL) into a sealed tube with an empty balloon to maintain the pressure. Upon completion of the reaction (Thin Layer Chromatography (TLC) monitoring), diethyl ether was added (5 mL), M2 was maintained in the aqueous phase and the product in the ethereal phase. The two phases were separated by decantation, the aqueous phase was extracted with more diethyl ether (2 × 5 mL). For the recycling of the catalyst the aqueous layer was then extracted with CH2 Cl2 (3 × 5 mL), dried over Na2 SO4 and the solvent was evaporated under reduced pressure to obtain the Rh NPs ready for another cycle. The combined fractions of diethyl ether were washed with water (2 × 5 mL). The organic phase was dried with anhydrous Na2 SO4 and then Catalysts 2020, 10, 1195 14 of 18 the solvent was evaporated under reduced pressure to afford the corresponding pure aniline. Spectral data of the anilines are provided in the Supplementary Materials. 4. Conclusions In summary, rhodium nanoparticles M1A, M1B and M2 have been prepared by reduction of RhCl3 with NaBH4 in water at room temperature in the presence of the recently reported PEG-tagged imidazolium salts S1A, S1B and S2, respectively. These rhodium nanomaterials are soluble in water and dichloromethane and insoluble in diethyl ether. They have been characterized by TEM, HRTEM, EDS, ED, XPS and ICP-OES. These Rh NPs M1A, M1B and M2 have been successfully used for the stereoselective syn-hydrosilylation of symmetric and unsymmetric internal alkynes. The corresponding (E)-vinylsilanes were obtained with good yields under two different procedures: (i) solvent-free conditions at 90 ◦ C with an excess of silane; (ii) with THF as solvent with one equivalent of silane at 90 ◦ C in a closed vessel. From low to moderate regioselectivities were achieved, the major regioisomer being the one presenting the silyl group closest to the more electron-withdrawing group. The addition of diethyl ether upon completion of the reaction resulted in the precipitation of the nanocatalyst, which was easily separated from the crude mixture by centrifugation/decantation process. Following this procedure, the nanocatalysts have been recycled up to five runs. On the other hand, the water-soluble Rh nanocatalysts M1A, M1B and M2 have been proved to be effective for the generation of hydrogen from the hydrolysis of ammonia borane (AB). This in situ released hydrogen acted as reductant for the transfer hydrogenation of nitroarenes to the corresponding anilines in THF-H2 O 1:4 at room temperature. The reaction was successfully carried out with a wide number of nitroaryl compounds bearing different functional groups. The chemoselectivity was not complete when olefin or carbonyl groups were present in the molecule. The Rh NPs were successfully reused up to five cycles. Supplementary Materials: The following are available online at http://www.mdpi.com/2073-4344/10/10/1195/s1, Spectral data of the hydrosilylation products. Spectral data of the anilines. Spectra collection. Author Contributions: Conceptualization, R.P.; methodology, G.F.; formal analysis, G.F., and R.P.; writing—original draft preparation, R.P.; writing—review and editing, G.F., and R.P.; supervision, R.P. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by Ministerio de Economía, Industria y Competitividad (MINECO) of Spain, (Projects CTQ2014-53662-P and CTQ2016-81797-REDC), Ministerio de Ciencia, Innovación y Universidades (MCINN) of Spain (Project RTI2018-097853-B-I00), DURSI-Generalitat de Catalunya (SGR2017-0465). Acknowledgments: We are thankful to Universitat Autònoma de Barcelona for predoctoral scholarship to G. F. Conflicts of Interest: The authors declare no conflict of interest. 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