Selective Hydrosilylation of 1,3-Diynes Catalyzed by Titania

Article pubs.acs.org/Organometallics

Selective Hydrosilylation of 1,3-Diynes Catalyzed by TitaniaSupported Platinum Francisco Alonso,*,† Robison Buitrago,‡ Yanina Moglie,† Antonio Sepúlveda-Escribano,*,‡ and Miguel Yus† †

Departamento de Quı ́mica Orgánica, Facultad de Ciencias, and Instituto de Sı ́ntesis Orgánica (ISO), Universidad de Alicante, Apdo. 99, E-03080 Alicante, Spain ‡ Departamento de Quı ́mica Inorgánica, Facultad de Ciencias, and Instituto Universitario de Materiales (IUMA), Universidad de Alicante, Apdo. 99, E-03080 Alicante, Spain S Supporting Information *

ABSTRACT: Titania-supported platinum (mainly as Pt(II)) has been found to effectively catalyze the hydrosilylation of 1,3diynes at 70 °C with low catalyst loading (0.25 mol %) under solvent-free conditions. Monohydrosilylation was achieved for diaryl-substituted diynes, whereas dialkyl-substituted diynes were transformed into the corresponding dihydrosilylated products in good yields. In every case, the process was proven to be highly stereoselective, with syn addition of the silicon−hydrogen bond, and regioselective, with the silicon moiety exclusively bonded to the most internal carbon atom of the 1,3-diyne (β-E product), as confirmed by X-ray crystallography.

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limitations.7b In this study, the standard protocol adopted for most reactions involved Karstedt’s catalyst in xylene at temperatures between 125 and 140 °C for 1−3 days. The combination of three diynes with six hydrosilanes allowed one to conclude that bis-hydrosilylation adducts could be obtained in high yields if the steric constraints were not too high. Owing to our dedication to studying and understanding the reactivity of active metals and nanoparticles,9 we reported the hydrogen-transfer reduction of ketones catalyzed by highly reusable platinum nanoparticles on carbon.10 More recently, we demonstrated that platinum on titania catalyzed the hydrosilylation of terminal and internal alkynes, bearing aryl and alkyl as well as different functional groups, with three different hydrosilanes to give the corresponding alkenylsilanes in high yields and short reaction times (Scheme 1).11 Reactions were performed in the absence of solvent, with exclusive syn addition of the Si−H bond and a β/α regioselectivity of up to 94/6. In contrast to previously reported heterogeneous platinum catalysts, reactions proceeded in air, even at room temperature, and the catalyst could be easily recovered and reused in several cycles. As part of our research on organic reactions promoted by platinum nanoparticles, we wish to present herein the results attained on the selective mono- and dihydrosilylation of 1,3diynes catalyzed by Pt/TiO2 under solvent-free conditions.

INTRODUCTION Vinylsilanes1 are very versatile organosilicon compounds of great interest in synthetic organic chemistry, with the transition-metal-catalyzed cross-coupling reaction with vinyl and aryl halides being one of the major applications of this type of compound.2 Due to their particular nontoxicity, high chemical stability, and relatively low molecular weight, these organometalloids act as attractive alternatives to other organometallic reagents (e.g., organotin, organoboron, or organozinc counterparts). Vinylsilanes are most conveniently and straightforwardly prepared by the hydrosilylation of alkynes, a reaction which proceeds with 100% atom efficiency.3 The control of the regio- and stereochemistry of the process is, however, a frequent difficulty encountered in the transition-metal-catalyzed addition of heteroatom−hydrogen bonds across the carbon− carbon triple bond,4 and in hydrosilylation in particular.5 In general, the final outcome of the reaction will depend on the catalyst, the alkyne, and the silane employed. Although the hydrosilylation of monoynes has been extensively studied,3,5,6 research on the hydrosilylation of diynes with monohydrosilanes is scanty.7 Some studies have been devoted to the hydrosilylation of 1,3-diynes with bishydrosilanes directed to the formation of polymers, in which silane functionalities cross-link the chains7a or are alternating with two α-vinylidene moieties.7b The rhodium- and nickelcatalyzed hydrosilylation of 1,3-diynes aimed at the asymmetric synthesis of allenes has been described by Tillack et al.8 To the best of our knowledge, there is only one article which deals in detail with the mono- and dihydrosilylation of 1,3-diynes, run as model reactions to determine any steric or electronic © 2012 American Chemical Society

Received: December 23, 2011 Published: March 6, 2012 2336

dx.doi.org/10.1021/om201274v | Organometallics 2012, 31, 2336−2342

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to apply a reaction temperature of 70 °C with the catalyst consisting of calcined platinum on titania in all cases. Characterization of the Calcined Pt/TiO2 Catalyst. Figure 1 shows two TEM micrographs obtained for the fresh calcined Pt/TiO2 catalyst. Very small (1−2 nm) platinum clusters (darker spots) with a narrow size distribution can be seen homogenously dispersed on the surface of the TiO2 crystals. The XPS spectrum in the Pt 4f region for this catalyst is shown in Figure 2. It can be deconvoluted into four peaks, two of them (those placed at lower binding energies) corresponding to the Pt 4f7/2 level and the others to the Pt 4f5/2 level. The peaks arising from the Pt 4f7/2 level are centered at 71.6−71.8 and 73.5−73.7 eV, which can be assigned to oxidized platinum species. An accurate assignment of the peaks is not easy, as the binding energies of the core electrons are affected not only by the metal oxidation state but also by the ligand atoms to which they are coordinated. The binding energy of the Pt 4f7/2 level for Pt(IV) coordinated to six chlorine atoms (as in the H2PtCl6 precursor compound) is reported to be 75.3 eV (for K2PtCl6), but it decreases to 74.8 eV for PtO2 and to 74.2 eV for Pt(OH)4. Additionally, the Pt 4f7/2 level for PtCl2 is about 73.4 eV, whereas that for Pt(OH)2 is about 72.4 eV.13 Thus, the XPS analysis of the catalyst reveals that it contains two different kinds of Pt(II) species, although the presence of some remaining Pt(IV) cannot be discarded.14 This indicates, on one side, that reductive decomposition of the metal precursor has taken place upon impregnation, by which the parent Pt(IV) is reduced to Pt(II). On the other hand, this surface decomposition is accompanied by both total (XPS band at around 71.7 eV) and partial (band centered at around 73.6 eV) dechlorination. This is confirmed by the data in Table 2, where it can be seen that the surface atomic Cl/Pt ratio in the fresh catalyst is 1.24, much lower than the value corresponding to the starting metal precursor. Hydrosilylation of 1,3-Diynes Catalyzed by Pt/TiO2. An array of differently substituted diynes was subjected to the hydrosilylation reaction under the optimized reaction conditions (0.25 mol % Pt/TiO2, 70 °C, neat). We first studied the hydrosilylation of symmetrically substituted diaryl diynes. Triethylsilane (2a), triphenylsilane (2b), and trimethoxysilane (2c) successfully added to 1,4-diphenylbuta-1,3-diyne (1a),

Scheme 1. Hydrosilylation of Terminal Alkynes Catalyzed by Pt/TiO2

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RESULTS AND DISCUSSION

Screening of the Catalysts. The platinum catalysts were prepared by the impregnation method (see the Experimental Section). The hydrosilylation of 1,4-diphenylbuta-1,3-diyne (1a) with triethylsilane (2a) was used as the model reaction at two different temperatures, with noncalcined and calcined catalysts (Table 1). Since solvent-free organic synthesis is one of the most promising steps toward waste prevention and environmental protection, all reactions were carried out in the absence of solvent.12 In a control experiment, the titania support was shown to be inactive in this reaction (Table 1, entry 1). Both noncalcined and calcined Pt/TiO2 provided the expected product in quantitative conversion, though the reaction with the latter was somewhat faster (Table 1, entries 2 and 3). The bimetallic Pt−Pd catalyst exhibited low catalytic activity (Table 1, entry 4), whereas that of Pt−Sn behaved similarly to noncalcined Pt/TiO2 (Table 1, compare entries 2 and 5). A decrease in the conversion and longer reaction times were noted at room temperature, irrespective of the catalyst, for a 1/1 or 2/1 diyne/silane stoichiometry (Table 1, entries 6− 10). A 1.5/1 diyne/silane ratio, however, shortened the reaction times and gave excellent conversion with calcined Pt/TiO2 (Table 1, entries 11 and 12). Unfortunately, the latter conditions were not as effective when extended to other substrates. Therefore, we decided that it was more convenient Table 1. Optimization of the Catalyst and Reaction Conditions

a

entry

cat.a

1a/2a

T (°C)

t (h)

3aa (%)b

1 2 3 4 5 6 7 8 9 10 11 12

TiO2 Pt/TiO2 nc Pt/TiO2 c Pt−Pd/TiO2 c Pt−Sn/TiO2 c Pt/TiO2 nc Pt/TiO2 c Pt−Sn/TiO2 c Pt/TiO2 nc Pt/TiO2 c Pt/TiO2 nc Pt/TiO2 c

1/1 1/1 1/1 1/1 1/1 1/1 1/1 1/1 2/1 2/1 1.5/1 1.5/1

70 70 70 70 70 rt rt rt rt rt rt rt

24 3 1 24 3 24 24 24 24 24 1 1

0 >99 >99 10 >99 82 82 63 87 85 83 >99

M/TiO2 (25 mg); c = calcined catalyst, nc = noncalcined catalyst. bConversion into 3aa determined by GC. 2337


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leading to the monohydrosilylation products 3aa, 3ab, and 3ac, respectively, in good to excellent yields (Table 3, entries 1−3). The least sterically hindered Et3SiH, however, reacted much more quickly than Ph3SiH and (MeO)3SiH. Then, different substituents were introduced at the para position of the diyne moiety in order to study any possible electronic effects. The electron-rich substrate 1c furnished vinylsilane 3ca in higher yield and shorter reaction time than for the electronically neutral 1b (Table 3, entries 4 and 5). In contrast, the electronpoor diyne 1d reacted sluggishly, producing 3da in moderate yield (Table 3, entry 6). We must underline that the dihydrosilylation of diaryl diynes failed even when using 5 equiv of the silane after prolonged heating (ca. 5% disilylated product from 1a and 2a was detected). Taking into account the regio- and stereochemistry of the reaction (see below), it seems rather unlikely to accommodate two vicinal silane moieties in a highly conjugated (and quite flat) 1,4-diarylbuta-1,3-diene skeleton. The monohydrosilylation of symmetrically substituted dialkyl diynes was proven to be elusive, leading to mixtures of mono- and diaddition products. Nevertheless, the reaction could be directed toward the dihydrosilylation by using an excess of the silane under the standard conditions. Dialkyl (1e)-, bis(chloroalkyl) (1f)-, and dicyclohexyl-substituted (1g) diynes were nicely transformed into the corresponding di(vinylsilanes) 3ea, 3fa, and 3ga, respectively, in good to high yields (Table 3, entries 7−9). Finally, the reaction of Et3SiH with the unsymmetrically substituted 5-phenylpenta2,4-diyn-1-ol (1h) readily afforded the silylated enyne 3ha in good yield (Table 3, entry 10). All products in Table 3, with the exception of the triphenylsilyl derivative 3ab,7b are new compounds. It is noteworthy that the monohydrosilylation of diynes was highly regio- and stereoselective. The only products detected arose from the syn addition of the Si−H bond across the carbon−carbon triple bond, with the silicon atom bonded to the most internal carbon atom of the diyne (Table 3, entries 1− 6). The presence of the (E)-2-trialkylsilylbut-1-en-3-yne moiety was initially proposed on the basis of NOE experiments effected for 3aa and unequivocally confirmed by X-ray crystallographic analysis of the triphenylsilyl derivative 3ab (Figure 3).15 The same regio- and stereochemical outcome was observed in the dihydrosilylation of dialkyl-substituted 1,3diynes. In these cases, only one of the nine possible addition products was selectively obtained containing the (E,E)-2,3bis(trialkylsilyl)buta-1,3-diene unit (Table 3, entries 7−9). The unsymmetrically substituted diyne 5-phenylpenta-2,4-diyn-1-ol (1h) followed a trend similar to that above, but the reaction was further regioselective as the addition occurred uniquely on the carbon−carbon triple bond of the propargyl alcohol fragment (Table 3, entry 10). The favored formation of this regioisomer could be due to an additional coordination of the platinum species to the hydroxyl group. The same regiochemistry, but opposite stereochemistry, was noted by Trost et al. in the ruthenium-catalyzed addition of ethoxydimethylsilane to a furyl diynol, furnishing a cyclic vinylsiloxane.16 No selectivity was observed when deca-1,3-diyn-1-ylbenzene was subjected to the hydrosilylation reaction, forming two monoaddition and one diaddition product. This fact reaffirms our proposal that the unsymmetrically substituted diynol (1h) undergoes extra coordination through the hydroxyl group. Stability and Recycling of the Catalyst. The catalyst was handled in air, and all the experiments were carried out without air exclusion, with these being advantages that make the

Figure 1. TEM micrographs of the fresh calcined Pt/TiO2 catalyst.

Figure 2. XPS Pt 4f spectra of the fresh calcined Pt/TiO2 catalyst.

Table 2. Surface Atomic Ratios in the Fresh and Used Calcined Pt/TiO2 Catalyst from XPS Analysis atoms

fresh

used

Pt/Ti O/Ti Cl/Pt

0.030 2.970 1.239

0.013 2.531 1.190 2338


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Table 3. Solvent-Free Mono- and Dihydrosilylation of 1,3-Diynes Catalyzed by Pt/TiO2a

a b

Reaction conditions: 1 (0.5 mmol), 2 (0.75 mmol, entries 1−6 and 10; 1.25 mmol, entries 7−9), Pt/TiO2 (25 mg, 0.25 mol %), neat, 70 °C. Isolated yield.

unchanged after the reaction, a strong decrease in the Pt/Ti ratio was observed. In principle, this decrease could be ascribed to sintering of the platinum particles upon reaction, giving rise to less exposed surface. However, the mild temperature at which the reaction was carried out rules out this possibility. It is more likely to assume that platinum species are partially leached from the surface during the reaction, yielding a lower amount of surface platinum in the used catalyst. Furthermore, the amount of surface chlorine also decreased after the reaction, whereas the Cl/Pt ratio remained nearly constant. The leaching of platinum was also confirmed by ICP-MS; the recovered catalyst after a third cycle was shown to contain 22% of the original platinum. Therefore, the decrease in the amount of platinum in the catalyst seems to be the origin of the loss of catalytic activity after successive reaction cycles.

procedure operationally simple. It is worthwhile mentioning that, despite the fact of the small amount of catalyst utilized (25 mg), it could be easily recovered by filtration and reused. We were, however, somewhat disappointed with the recycling capability, since the conversion drastically dropped in the third run (100, 70, and 15%). These results largely differ from those recorded by us in the hydrosilylation of terminal alkynes with a similar catalyst,11 where reutilization was successfully extended over four cycles without any apparent loss of activity (98, 98, 97, and 98%). In order to determine the origin of this loss of activity, XPS analysis was also conducted on the used catalyst after a third cycle. From a qualitative point of view, the XPS spectrum is very similar to that of the fresh catalyst, though the intensity of the platinum signal is lower (Figure 4). To try to rationalize this difference, the surface atomic Pt/Ti and O/Ti ratios, determined by XPS, are also reported in Table 2. It can be seen that, whereas the O/Ti ratio remained practically 2339


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EXPERIMENTAL SECTION

General Considerations. Degussa P25 TiO2 (60% anatase, 40% rutile) with a surface area of 50 m2 g−1 (N2, −195 °C, BET method) was used as support, after being calcined in air at 500 °C for 5 h. X-ray photoelectron spectra (XPS) were acquired with a VG-Microtech Multilab 3000 spectrometer equipped with a hemispherical electron analyzer and a Mg Kα (h = 1253.6 eV, 1 eV = 1.602 × 10−19 J) 300 W X-ray source. Conventional TEM analysis was carried out with a JEOL Model JEM-210 electron microscope working at 200 kV and equipped with a INCA Energy TEM 100 analytical system and a SIS Mega View II camera. Samples for analysis were suspended in methanol and placed on copper grids with a holey carbon film support. Dyines 1a−g were prepared by homocoupling of the corresponding terminal alkynes catalyzed by copper nanoparticles on titania.17 Diyne 1h was synthesized following a literature procedure.18 All other materials and reagents were the best grade commercially available and were used without further purification. All reactions were carried out on a multireactor apparatus using the corresponding reactor tubes. Melting points were meassured with a Reichert Thermovar apparatus and are uncorrected. NMR spectra were recorded on Bruker Avance 300 and 400 spectrometers (300 and 400 MHz for 1H NMR; 75 and 100 MHz for 13C NMR) using CDCl3 as solvent and TMS as internal standard; chemical shifts are given in (δ) parts per million and coupling constants (J) in hertz. Infrared analysis was performed with a Jasco 4100LE (Pike MIRacle ATR) spectrophotometer; wavenumbers are given in cm−1. Mass spectra (EI) were obtained at 70 eV on an Agilent 5973 spectrometer; fragment ions are given in m/z with relative intensities (%) in parentheses. HRMS analyses were were also carried out in the electron impact mode (EI) at 70 eV on a Finnigan MAT95S spectrometer. The purity of volatile compounds and the chromatographic analyses (GLC) were determined with a HewlettPackard HP-6890 gas chromatograph and Agilent 5973 GC-MS apparatus. Retention times (tr) were obtained with the latter under the following conditions: 30 m HP5MS capillary column (0.25 mm diameter, 0.25 μm film thickness), using helium (54.1 mL/min) as carrier gas, Tinjector = 250 °C, Tcolumn = 60 °C (3 min), and 60−270 °C (15 °C/min). Column chromatography was performed using 40−60 μm silica gel 60 (hexane or hexane/EtOAc as eluent). Thin-layer chromatography was carried out on TLC aluminum sheets with silica gel 60 F254 (Merck). Typical Procedure for the Preparation of Pt/TiO2.14,19 The Pt/TiO2 catalyst was prepared by the impregnation method with an aqueous solution of H2PtCl6·6H2O (Aldrich) of the appropriate concentration to achieve a Pt content of 1 wt %. The slurry (10 mL g−1 of TiO2) was stirred for 12 h, and then excess solvent was removed by heating at 90 °C under vacuum in a rotary evaporator. Finally, the catalyst was dried at 110 °C for 24 h (the “noncalcined catalyst”) and calcined at 400 °C for 5 h, with a heating rate of 3 °C min−1 (the “calcined catalyst”). General Procedure for the Hydrosilylation of 1,3-Diynes Catalyzed by Pt/TiO2. The diyne (1, 0.5 mmol) and the hydrosilane (2, 0.75 mmol, entries 1−6 and 10; 1.25 mmol, entries 7−9; Table 3) were added to a reactor tube containing PtNPs/TiO2 (25 mg, 0.25 mol %) without solvent. The reaction mixture was warmed to 70 °C without exclusion of air and monitored by TLC and/or GLC until total conversion of the starting material. EtOAc (3 mL) was added to the resulting mixture followed by filtration through Celite and washing with additional EtOAc (4 mL). The crude reaction mixture was purified by column chromatography (silica gel, hexane (hexane/EtOAc 90/10 for compound 3ha)), except compound 3ac, which was unstable on silica gel, to give the corresponding silylated enynes 3. (E)-(1,4-Diphenylbut-1-en-3-yn-2-yl)triethylsilane (3aa): yellow oil; Rf 0.55 (hexane); tr 17.69; 1H NMR (400 MHz, CDCl3) δ 8.00 (d, J = 10.0 Hz, 2H), 7.48−7.42 (m, 2H), 7.40−7.24 (m, 6H), 6.83 (s, 1H), 1.04 (t, J = 10.4 Hz, 9H), 0.82 (q, J = 10.4 Hz, 6H); 13C NMR (75 MHz, CDCl3) δ 145.2, 137.8, 131.2, 128.8, 128.4, 128.3, 128.2, 127.8, 124.4, 120.8, 100.4, 90.8, 7.4, 3.1; IR (neat) ν̃ 3058, 2952, 2909, 2873, 1595, 1488, 1237, 1017, 1004, 752, 733, 719 cm−1; MS (70 eV) m/z (%) 319 [M+ + 1, 100%], 318 [M+, 28], 289 (19), 261 (29), 259

Figure 3. Plot showing the X-ray structure and atomic numbering for compound 3ab.

Figure 4. XPS Pt 4f spectra of the reused Pt/TiO2 catalyst.

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CONCLUSION

A series of monometallic and bimetallic catalysts based on noncalcined and calcined platinum supported on titania have been prepared by the impregnation method and tested in the hydrosilylation of 1,3-diynes. The calcined Pt/TiO2 catalyst has shown the best performance in this reaction at 70 °C with low catalyst loading (0.25 mol %) under solvent-free conditions. This catalyst has been characterized by TEM and XPS, revealing the presence of platinum nanoparticles composed of Pt(II) species uniformly dispersed on the support. A variety of electronically different diaryl-substituted symmetric 1,3-diynes have been monohydrosilylated with three different silanes in moderate to excellent yields (55−98%), whereas several structurally different dialkyl-substituted symmetric 1,3-diynes successfully underwent dihydrosilylation (71−90%). The successful monohydrosilylation of an unsymmetric diyne is also reported. All reactions were highly stereo- and regioselective, affording the corresponding monosilyl enynes and disilyl dienes with exclusive E stereochemistry and with the silicon atom bonded to the internal carbon atom of the conjugated system. The reutilization of the catalyst is rather limited due to some platinum leaching. 2340


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(400 MHz, CDCl3) δ 5.59 (t, J = 6.6 Hz, 2H), 3.52 (t, J = 6.6 Hz, 4H), 2.02−1.91 (m, 4H), 1.82−1.71 (m, 4H), 1.54−1.44 (m, 4H), 0.94 (t, J = 8.0 Hz, 18H), 0.58 (q, J = 8.0 Hz, 12H); 13C NMR (75 MHz, CDCl3) δ 141.4, 138.4, 44.9, 32.6, 30.0, 26.7, 7.6, 3.9; IR (neat) ν̃ 2952, 2873, 1456, 1416, 1119, 1016, 717, 654 cm−1; MS (70 eV) m/z (%) 462 [M+, 5%], 161 (27), 123 (34), 122 (10), 121 (97), 119 (25), 115 (78), 95 (14), 93 (35), 91 (13), 88 (10), 87 (100), 79 (10), 59 (41); HRMS calcd for C24H48Cl2Si2 462.2672, found 462.2664. [ (1 E , 3E ) - 1, 4 - D ic y c l o h e x y l b ut a - 1, 3 - d i e n e - 2 , 3 - d iy l ]b i s (triethylsilane) (3ga): colorless oil; Rf 0.88 (hexane); tr 19.25; 1H NMR (400 MHz, CDCl3) δ 5.40 (d, J = 9.6 Hz, 2H), 2.16−2.05 (m, 2H), 1.72−1.44 (m, 12H), 1.21−1.12 (m, 4H), 1.09−1.05 (m, 4H), 0.94 (t, J = 8.0 Hz, 18H), 0.57 (q, J = 8.0 Hz, 12H); 13C NMR (75 MHz, CDCl3) δ 145.2, 137.3, 39.3, 33.2, 32.9, 26.3, 26.0, 25.9, 7.82, 4.17; IR (neat) ν̃ 2949, 2922, 2873, 1457, 1447, 1015, 720, 687 cm−1; MS (70 eV) m/z (%) 446 [M+, 11%], 417 (11), 302 (14), 301 (29), 273 (15), 214 (13), 116 (12), 115 (100), 87 (79), 59 (30); HRMS calcd for C28H54Si2 446.3764, found 446.3769. (E)-5-Phenyl-3-(triethylsilyl)pent-2-en-4-yn-1-ol (3ha): yellow oil; Rf 0.41 (hexane/EtOAc, 9/1); tr 15.72; 1H NMR (300 MHz, CDCl3) δ 7.42−7.36 (m, 2H), 7.34−7.28 (m, 3H), 6.31 (t, J = 5.7 Hz, 1H), 4.55 (d, J = 5.7 Hz, 2H), 2.04 (s, 1H), 1.01 (t, J = 7.8 Hz, 9H), 0.74 (q, J = 7.8 Hz, 6H); 13C NMR (75 MHz, CDCl3) δ 150.3, 137.6, 131.2, 128.3, 127.9, 123.9, 98.6, 88.0, 62.8, 7.2, 2.8; IR (neat) ν̃ 3311, 2952, 2909, 2874, 1597, 1456, 1415, 1377, 1237, 754, 734, 719, 689 cm−1; MS (70 eV) m/z (%) 271 [M+, 29%], 244 (12), 243 (38), 215 (34), 197 (11), 187 (18), 175 (32), 169 (17), 159 (26), 147 (40), 140 (38), 139 (78), 137 (50), 131 (37), 129 (15), 128 (15), 127 (14), 116 (12), 115 (87), 105 (13), 103 (48), 101 (15), 88 (11), 87 (100), 77 (12), 75 (58), 59 (43), 57 (12), 47 (13), 45 (12); HRMS calcd for C17H24OSi, 272.1596, found 272.1599.

(22), 233 (31), 232 (11), 231 (47), 202 (14), 187 (12), 183 (10), 131 (69), 129 (12), 115 (12), 105 (13), 87 (25), 59 (23); HRMS calcd for C22H26Si 318.1804, found 318.1813. (E)-(1,4-Diphenylbut-1-en-3-yn-2-yl)triphenylsilane (3ab):.7b yellow solid; mp 98.5−101.5 °C; Rf 0.58 (hexane/EtOAc, 9:1); 1H NMR (400 MHz, CDCl3) δ 7.97 (d, J = 8.0 Hz, 2H), 7.71 (dd, J = 8.0, 1.4 Hz, 6H), 7.44−7.23 (m, 12H), 7.21−7.16 (m, 5H), 6.97 (s, 1H); 13C NMR (75 MHz, CDCl3) δ 149.6, 137.5, 136.4, 133.2, 131.2, 129.8, 129.1, 128.9, 128.2, 127.9, 127.8, 123.9, 118.1, 102.0, 91.3; IR (neat) ν̃ 3049, 1580, 1485, 1426, 1108, 754, 740, 698, 688 cm−1; MS (70 eV) m/z (%) 463 [M+ + 1, 13%], 462 [M+, 32], 384 (18), 383 (14), 307 (13), 260 (24), 259 (100), 202 (13), 181 (23), 105 (10); HRMS calcd for C34H26Si 462.1804, found 462.1811. (E)-(1,4-Diphenylbut-1-en-3-yn-2-yl)trimethoxysilane (3ac): orange oil; Rf 0.23 (hexane/EtOAc, 9/1); tr 16.87; 1H NMR (400 MHz, CDCl3) δ 8.04 (d, J = 8.0 Hz, 2H), 7.50−7.46 (m, 2H), 7.37− 7.31 (m, 6H), 7.19 (s, 1H), 3.72 (s, 9H); 13C NMR (75 MHz, CDCl3) δ 149.1, 137.2, 132.6, 131.5, 129.5, 129.4, 128.5, 128.4, 124.1, 112.3, 99.7, 89.3, 51.5; IR (neat) ν̃ 3055, 2941, 2841, 1595, 1488, 1443, 1188, 1076, 810, 754, 688 cm−1; MS (70 eV) m/z (%) 325 [M+ + 1, 28%], 324 [M+, 100], 293 (14), 277 (16), 262 (15), 261 (16), 218 (24), 217 (34), 204 (41), 203 (33), 202 (44), 201 (12), 200 (12), 121 (58), 107 (14), 91 (59), 61 (11); HRMS calcd for C19H20O3Si 324.1182, found 324.1190. (E)-(1,4-Di-p-tolylbut-1-en-3-yn-2-yl)triethylsilane (3ba): yellow oil; Rf 0.40 (hexane); tr 19.35; 1H NMR (300 MHz, CDCl3) δ 7.92 (d, J = 8.0 Hz, 2H), 7.35 (d, J = 8.0 Hz, 2H), 7.21−7.11 (m, 4H), 6.78 (s, 1H), 2.36 (s, 6H), 1.04 (t, J = 8.0 Hz, 9H), 0.82 (q, J = 8.0 Hz, 6H); 13C NMR (75 MHz, CDCl3) δ 144.7, 138.3, 137.9, 135.3, 131.1, 129.1, 128.9, 128.8, 121.6, 119.5, 100.3, 90.4, 21.5, 21.4, 7.4, 3.1; IR (neat) ν̃ 3052, 2952, 2910, 2873, 1582, 1456, 1412, 1016, 1004, 812, 730, 718, 696 cm−1; MS (70 eV) m/z (%) 347 [M+ + 1, 31%], 346 [M+, 100], 289 (18), 287 (14), 261 (17), 259 (31), 215 (11), 197 (10), 173 (22), 145 (52), 87 (14), 59 (16); HRMS calcd for C24H30Si 346.2117, found 346.2125. (E)-[1,4-Bis(4-methoxyphenyl)but-1-en-3-yn-2-yl]triethylsilane (3ca): yellow oil; Rf 0.59 (hexane/EtOAc, 9:1); tr 23.76; 1H NMR (300 MHz, CDCl3) δ 8.02 (d, J = 8.4 Hz, 2H), 7.42 (d, J = 8.7 Hz, 2H), 6.96−6.87 (m, 4H), 6.75 (s, 1H), 3.85 (s, 3H), 3.84 (s, 3H), 1.06 (t, J = 7.8 Hz, 9H), 0.82 (q, J = 7.6 Hz, 6H); 13C NMR (75 MHz, CDCl3) δ 159.6, 159.3, 143.8, 132.6, 131.2, 130.3, 117.7, 116.9, 114.0, 113.5, 99.7, 39.9, 55.3, 7.4, 3.1; IR (neat) ν̃ 3050, 2952, 2873, 1603, 1505, 1287, 1171, 1031, 1022, 827, 729, 718, 696 cm−1; MS (70 eV) m/z (%) 379 [M+ + 1, 33%], 378 [M+, 100], 247 (14), 189 (18), 161 (35), 59 (12); HRMS calcd for C24H30SiO2 378.2015, found 378.2022. (E)-{1,4-Bis[4-(trifluoromethyl)phenyl]but-1-en-3-yn-2-yl}triethylsilane (3da): yellow oil; Rf 0.51 (hexane); tr 16.79; 1H NMR (400 MHz, CDCl3) δ 8.06 (d, J = 8.0 Hz, 2H), 7.65 (d, J = 8.4 Hz, 2H), 7.62 (d, J = 8.4 Hz, 2H), 7.54 (d, J = 8.0 Hz, 2H), 6.92 (s, 1H), 1.06 (t, J = 7.2 Hz, 9H), 0.86 (q, J = 7.2 Hz, 6H); 13C NMR (75 MHz, CDCl3) δ 144.6, 140.8, 131.6, 130.3 (q, 1JC−F = 42 Hz, CF3), 129.8 (q, 1 JC−F = 42 Hz, CF3), 129.0 127.8, 125.9 (q, 2JC−F = 23 Hz, CCF3), 125.5 (q, 3JC−F = 15 Hz, CH), 125.4 (q, 3JC−F = 15 Hz, CH), 124.1, 122.3 (q, 2JC−F = 23 Hz, CCF3), 99.8, 99.4, 7.4, 2.8; IR (neat) ν̃ 2955, 2876, 1613, 1320, 1164, 1124, 1105, 1066, 1015, 839, 733, 720, 700 cm−1; MS (70 eV) m/z (%) 455 [M+ + 1, 24%], 454 [M+, 77], 435 (14), 425 (22), 398 (10), 397 (37), 369 (23), 321 (21), 320 (89), 319 (14), 227 (36), 200 (16), 199 (100), 151 (38), 115 (42), 87 (51); HRMS calcd for C24H24F6Si 454.1551, found 454.1541. (7E,9E)-Hexadeca-7,9-diene-8,9-diylbis(triethylsilane) (3ea): colorless oil; Rf 0.91 (hexane); tr 18.09; 1H NMR (400 MHz, CDCl3) δ 5.60 (t, J = 6.4 Hz, 2H), 2.01−1.85 (m, 4H), 1.35−1.21 (m, 16H), 0.94 (t, J = 8.0 Hz, 18H), 0.93 (t, J = 8.0 Hz, 6H), 0.58 (q, J = 8.0 Hz, 12H); 13C NMR (75 MHz, CDCl3) δ 140.4, 139.8, 32.0, 31.0, 29.6, 29.6, 22.8, 14.2, 7.7, 4.1; IR (neat) ν̃ 2953, 2854, 1580, 1457, 1416, 1011, 716 cm−1; MS (70 eV) m/z (%) 450 [M+, 7%], 306 (19), 305 (51), 277 (15), 116 (12), 115 (100), 87 (79), 59 (26); HRMS calcd for C28H58Si2 450.4077, found 450.4079. [ ( 5 E , 7 E ) - 1 , 1 2 - Di c h l o r o d o d e c a - 5 , 7 - d i e n e - 6 , 7 - d i y l ] b i s (triethylsilane) (3fa): colorless oil; Rf 0.55 (hexane); tr 20.08; 1H NMR

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ASSOCIATED CONTENT

S Supporting Information *

Figures giving TEM micrographs of the calcined Pt/TiO2 catalyst, 1H and 13C NMR spectra of the silylated enynes 3, and the NOESY spectrum of compound 3aa and a CIF file giving crystallographic data for 3ab. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (F.A.); [email protected] (A.S.-E.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was generously supported by the Spanish Ministerio de Ciencia e Innovación (MICINN; CTQ2007-65218, CTQ2011-24151, and Consolider Ingenio 2010-CSD200700006), the Generalitat Valenciana (GV; PROMETEO/2009/ 002 and PROMETEO/2009/039), and FEDER. Y.M. thanks the ISO of the Universidad de Alicante for a grant. R.B. acknowledges the Universidad de Alicante, CAM, and Union Fenosa for his grant (UF2007-X9159987F).

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REFERENCES

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Selective Hydrosilylation of 1,3-Diynes Catalyzed by Titania

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