Article pubs.acs.org/Organometallics
Markovnikov-Selective Hydrosilylation of Electron-Deficient Alkenes with Arylsilanes Catalyzed by Mono(phosphine)palladium(0) Nobuyuki Komine,* Makoto Abe, Ryoko Suda, and Masafumi Hirano Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan S Supporting Information *
ABSTRACT: Markovnikov-selective hydrosilylation of electrondeficient alkenes with HSiPh3 is catalyzed by a mono(phosphine)palladium(0) complex, Pd(η2:η2-C6H10O)(PMe3) (1a). The hydrosilylation of acrylonitrile with HSiPh3 at 30 °C proceeds to completion within 40 min in the presence of 5 mol % of 1a. The complex 1a also shows the catalytic activity for the hydrosilylation with mono- and diarylsilanes and monochlorosilane such as HSiPhMe2, HSiPh2Me, and HSiClMe2. The hydrosilylation using para-substituted styrenes clearly shows the electron-withdrawing substituent promoting the reaction. Mechanistic studies indicate that the reaction is proceeding by a Chalk−Harrod mechanism with the reductive elimination of an (alkyl)(silyl)palladium(II) intermediate being the ratedetermining step.
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to give 2-(triphenylsilyl)propanenitrile exclusively within 40 min (eq 1).
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Among hydrosilanes, HSiPh3 is generally considered to be an inert silane for hydrosilylation,1c,7 and this is the first hydrosilylation of acrylonitrile with HSiPh3. The product was recrystallized from Et2O with hexane and was characterized by full spectroscopic data and elemental analysis. Figure 1 shows the time-course curves for the hydrosilylation of acrylonitrile with HSiPh3 catalyzed by Pd(η2:η2-C6H10O)L (L = PMe3 (1a), PCy3 (1b), PPh3 (1c)). The product linearly increased until the completion of the reactions. The PMe3 analogue showed the best activity among the mono(phosphine)palladium complexes Pd(η2:η2-C6H10O)L (L = PMe3 (1a), PCy3 (1b), PPh3 (1c)) screened (Figure 1). The reaction rate diminished by the addition of 1 equiv of PMe3 and was completely hampered in the presence of 2 equiv of PMe3 (Figure 2). These results suggest the active catalyst is a (monophosphine)palladium complex. Note that Karstedt-type catalysts such as Pt2(dvd)3 and Pt(dvd)(PCy3)8 (dvd = 1,3divinyl-1,1,3,3-tetramethyldisiloxane) show virtually no catalytic activity for this hydrosilylation under these optimized conditions. Scope of Silanes. The scope of silanes in the hydrosilylation of acrylonitrile catalyzed by 1a is given in Table 1.
INTRODUCTION Hydrosilylation is an important reaction in organic synthesis and polymer chemistry and for the production of organosilicon compounds. The addition of hydrosilane to alkenes normally requires a transition-metal catalyst.1 Among many transitionmetal catalysts for hydrosilylation reported, platinum compounds such as Speier’s and Karstedt’s catalysts are widely believed to be very powerful catalysts and are often used commercially.2 However, these catalysts generally show poor activity toward electron-deficient alkenes such as acrylonitrile as substrates in the hydrosilylations. Several catalytic α-selective hydrosilylations of acylonitrile were already reported by use of Rh, Pd, and Re catalysts.3 For example, in 1974 Tsuji and coworkers reported α-selective hydrosilylation of acylonitrile catalyzed by a Pd−phosphine system.3a Recently we found a palladium(0) complex to catalyze hydrometalation of electrondeficient alkenes and alkynes with transition-metal hydrides.4 Among the palladium(0) catalysts screened, mono(phosphine)palladium(0) complexes having a diallyl ether ligand, Pd(η2:η2C6H10O)L (1)5 was found to be the best catalyst.4c As one of the new and important aspects of this chemistry, we now evaluated this promising palladium(0) catalyst 1 for hydrosilylations because hydrosilylations catalyzed by an isolated mono(phosphine)palladium(0) complex are unprecedented to the best of our knowledge.6 In this paper, we disclose Markovnikov-selective hydrosilylations of electron-deficient alkenes promoted by 1 under ambient conditions. RESULTS AND DISCUSSION Reaction of Acrylonitrile with Triphenylsilane Catalyzed by Mono(phosphine)palladium(0). The reaction of acrylonitrile with HSiPh3 was catalyzed at 30 °C by the mono(phosphine)palladium(0) complex Pd(η2:η2-C6H10O)(PMe3) (1a; 5 mol %) © XXXX American Chemical Society
Received: September 21, 2014
A
DOI: 10.1021/om500964g Organometallics XXXX, XXX, XXX−XXX
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Organometallics
Table 2. Hydrosilylation of Alkenes with Triphenylsilane Catalyzed by Pd(η2:η2-C6H10O)(PMe3) (1a)a
Figure 1. Hydrosilylation of acrylonitrile with triphenylsilane catalyzed by mono(phosphine)palladium(0) complex, Pd(η2:η2-C6H10O)L (L = PMe3 (1a, red ■), PCy3 (1b, blue ◆), PPh3 (1c, green ▲)). Conditions: [HSiPh3]0 = 0.10 M, [acrylonitrile]0 = 0.10 M, [1] = 0.005 M, solvent C6D6, temperature 30 °C.
Figure 2. Effect of PMe3 added in hydrosilylation of acrylonitrile with triphenylsilane catalyzed by the mono(trimethylphosphine)palladium(0) complex Pd(η2:η2-C6H10O)(PMe3) (1a): [PMe3] = 0 (red ■), 0.005 (green ■), 0.010 M (blue ■). Conditions: [HSiPh3]0 = 0.10 M, [acrylonitrile]0 = 0.10 M, [1a] = 0.005 M, solvent C6D6, temperature 30 °C.
Table 1. Hydrosilylation of Acrylonitrile with Hydrosilanes Catalyzed by Pd(η2:η2-C6H10O)(PMe3) (1a)a entry
hydrosilane
time/h
conversn/%
yield/%
104(rate)/M s−1
1 2 3 4 5 6
HSiPh3 HSiPh2Me HSiPhMe2 HSiEt3 HSiMe2Cl HSi(OEt)3
0.6 1.3 7 8 1.2 13
98 100 87 22 97 100
97 96 85 0 74 0
50 24 3.7 25 a Conditions: [hydrosilane]0 = 0.10 M, [acrylonitrile]0 = 0.10 M, [1a] = 0.005 M, solvent C6D6, temperature 30 °C. b[HSiPh3]0 = 0.30 M, [1a] = 0.010 M. cThe yield was estimated by 1H NMR using hexamethyldisiloxane as an initial standard. dIsolated yield.
a
Conditions: [hydrosilane]0 = 0.10 M, [acrylonitrile]0 = 0.10 M, [1a] = 0.005 M, solvent C6D6, temperature 30 °C.
Mono- and diarylsilanes such as HSiPhMe2 and HSiPh2Me also gave the corresponding product3a,9 in excellent yield with complete Markovnikov selectivity. The monochlorosilane HSiMe 2 Cl also reacted with acrylonitrile to give the corresponding diorganochlosilane,3a whereas HSiEt3 and HSi(OEt)3 did not give the hydrosilylation products. The present hydrosilylation suggests that the acidic hydrosilane promotes the reaction.10 This interesting nature compensates traditional hydrosilylations.
Scope of Alkenes. Table 2 shows the substrate scope of alkenes using HSiPh3. Electron-deficient monosubstituted alkenes such as methyl vinyl ketone (entry 2) and methyl acrylate (entry 3) produced the corresponding products in high yields. In sharp contrast, electron-rich alkenes remained unreacted (entries 5−7). Consistent with this hypothesis, styrenes with an electron-withdrawing group such as p-CF3 (σp = 0.54), p-CN (σp = 0.66), and p-NO2 (σp = 0.78) encouraged the B
DOI: 10.1021/om500964g Organometallics XXXX, XXX, XXX−XXX
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Figure 4a shows the effect of concentration of palladium(0) catalyst on the reaction rate. The loading of 1a can be reduced to 1 mol %, but the complete conversion takes longer to achieve. When the concentration of 1a was increased to 5 and 10 mol %, the initial rate roughly increased 5 and 10 times, suggesting a reaction first order in the catalyst concentration. All of these reaction profiles appear to be similar to zero-order reactions to the substrates, but actually the initial rate depends on the HSiPh3 concentration, as shown in Figure 4b. Therefore, a more precise understanding is that the dependence of the initial rate on the HSiPh3 concentration is saturated when up to 0.10 M of HSiPh3 is employed under these conditions. On the other hand, the reaction was diminished by the addition of excess acrylonitrile (Figure 4c). This feature is discussed in the following section. When DSiPh3 (>95% D) was used in this reaction, the deuterium atom was exclusively incorporated in the methyl group of the product (eq 2).12 No isotope effect on the rate was observed in this reaction.
reaction (entry 8−10), while styrene (σp = 0.0) did not react with HSiPh3 at all (entry 7). Disubstituted electron-deficient alkenes also produced the products (entries 11−14). However, dimethyl fumarate unexpectedly remained unreacted (entry 15). Probably, this reaction requires a polarized CC bond or the putative Pd(dimethyl fumarate)2(PMe3) species cannot react with HSiPh3 (vide infra). In the reaction of ethyl isocrotonate (entry 13), ethyl crotonate was observed (Figure 3). This E/Z isomerization
Figure 3. Time course for the reaction of ethyl isocrotonate with HSiPh3 in the presence of Pd(η2:η2-C6H10O)(PMe3) (1a): ethyl isocrotonate (blue ◆), ethyl crotonate (purple ×), HSiPh3 (red ■), ethyl 2-(triphenylsilyl)butanate (green ◆). Conditions: [HSiPh3]0 = 0.10 M, [ethyl isocrotonate]0 = 0.10 M, [1a] = 0.005 M, solvent C6D6, temperature 30 °C.
In order to understand the reaction mechanism, the stoichiometric reactions of 1a with acrylonitrile was monitored by the 1H NMR spectrum at 30 °C in benzene-d6. The treatment of 1a with 2 equiv of acrylonitrile rapidly produced a 1:1 mixture of 1a and Pd(η2-CH2CHCN)2(PMe3) (2a) with the liberation of dialyl ether in 52% yield (Scheme 1).
suggests the reversible insertion of an alkene into the Pd−H bond and β-hydride elimination processes. This is consistent with a Chalk−Harrod mechanism11 for the present hydrosilylation reaction. Trisubstituted and 1,1-disubstituted alkenes also remained unreacted, probably due to difficulty in coordination (entries 16 and 17). Mechanistic Study. In order to obtain mechanistic information for the present hydrosilylation, a kinetic investigation of the stoichiometric reactions was carried out.
Scheme 1
Figure 4. Effect of concentration of palladium(0) catalyst and substrates on the reaction rate. (a) Effect of concentration of Pd(η2:η2C6H10O)(PMe3) (1a). Conditions: [HSiPh3]0 = 0.10 M, [acrylonitrile]0 = 0.10 M, [1a] = 0.001 (red ■), 0.005 (green ●), 0.010 M (blue ■) . (b) Effect of concentration of HSiPh3. Conditions: [HSiPh3]0 = 0.050 (blue ■), 0.10 (green ●), 0.20 M (red ■), [acrylonitrile]0 = 0.10 M, [1a] = 0.005 M. (c) Effect of concentration of acrylonitrile. Conditions: [HSiPh3]0 = 0.10 M, [acrylonitrile]0 = 0.050 (blue ■), 0.10 (green ●), 0.20 M (red ▲), [1a] = 0.005 M. Legend: (a) yields calculated on the basis of HSiPh3; (b) yields calculated on the basis of acrylonitrile. C
DOI: 10.1021/om500964g Organometallics XXXX, XXX, XXX−XXX
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would insert into the Pd−H rather than Pd−Si bond. The polarization of the coordinating alkene gives a rise to the regiospecific insertion reaction. The isotope experiment suggests reductive elimination being the rate-determining step. The major resting state of the active catalyst is probably the bis(alkene)palladium(0) species.
With 4 equiv of acrylonitrile, 2a was formed in 94% yield with the liberation of diallyl ether in 95% yield. In these reactions, the acrylonitrile resonances were broadened, suggesting the presence of dynamic behavior, and 2a was formed as a 6:4 mixture of isomers. Complex 2a was isolated as an analytically pure white powder of an isomeric mixture in 1:0.73 ratio by the reaction of 1 with 5 equiv of acrylonitrile in hexane in quantitative yield. The complex 2a was characterized by 1H, 13 C{1H}, and 31P{1H} NMR spectra, COSY and HETCOR, and elemental analysis. These isomers are assignable to the diastereomers that arise from the prostereogenic faces of two acrylonitrile ligands at the Pd(0) center.13 On the other hand, 1a did not react with HSiPh3 at all under these conditions. The treatment of 2a with HSiPh3 (1 equiv/Pd) at 30 °C in benzene-d6 produced the hydrosilylation product in 106% yield within 10 min. Complex 2a can be used as a catalyst precursor for the hydrosilylation. The reaction of acrylonitrile (0.1 M) with HSiPh3 (0.1 M) is catalyzed by 2a (5 mol %) to give the Markovnikov product in 100% yield within 50 min at 30 °C. The catalytic activity of 2a was exactly as same as that of 1a (cf. Figure 2). However, with 0.5 M of acrylonitrile, the reaction is significantly suppressed and yields the hydrosilylation product only in 84% yield after 190 min. This nature is also the same feature as 1a, suggesting the prior dissociation of an acrylonitrile fragment. With this fundamental information about the Pd species in hand, we have monitored the behavior of 1a in catalysis by 31 1 P{ H} NMR. In the catalytic reaction of acrylonitrile (0.1 M) with HSiPh3 (0.1 M) in the presence of 1a (10 mol %) as the catalyst precursor, 1a rapidly converted into a new singlet species at δ −16.1 in the 31P{1H} NMR along with 2a. No hydride species were observed in the 1H NMR. After completion of the reaction, all species converted to 1a.14 Unfortunately, although the new transient species was difficult to characterize, it was confirmed to be a resting state. All of these results are consistent with the Chalk−Harrod mechanism11 shown in Scheme 2. First of all, complex 1a is
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CONCLUSION In summary, the catalytic hydrosilylation of electron-deficient alkenes can be achieved by mono(phosphine)palladium(0) complexes in complete Markovnikov selectivity.
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EXPERIMENTAL SECTION
General Considerations. All procedures described in this paper were carried out under a nitrogen or argon atmosphere by use of Schlenk and vacuum line techniques. Benzene and hexane were dried and purified using a Glass Contour Ultimate Solvent System. Benzened6 was dried over sodium wire and stored under vacuum, and it was purified by vacuum distillation prior to use. HSiPh3, HSiPh2Me, HSiPhMe2, HSiMe2Cl, HSiEt3, HSi(OEt)3, diallyl ether, and alkenes were purchased from TCI or Aldrich. The mono(phosphine)palladium(0) complexes Pd{η2:η2-(CH2CHCH2)2O}(PR3) (R = Me (1a), Cy (1b), Ph (1c))5 and DSiPh315 were prepared by literature procedures with modification. 1H, 2H, 13C{1H}, and 31P{1H} NMR spectra were measured on a 400 MHz (for 1H) NMR spectrometer. The IR spectra were measured on a Fourier transform spectrometer. The elemental analyses were performed on a CHN analyzer. Hydrosilylation of Electron-Deficient Alkenes Catalyzed by Mono(phosphine)palladium(0) Complexes. As a typical procedure, the hydrosilylation of acrylonitrile with triphenylsilane is given. NMR Tube Reaction. In an NMR tube containing 410 μL of C6D6 were placed 90.7 μL of a 0.066 M C6D6 solution of 1/1 mixture of acrylonitrile (0.060 mmol) and HSiPh3 (0.060 mmol). To this was added a solution of hexamethyldisiloxane (0.067 M, 50 μL, 0.034 mmol) as an internal standard. After the addition of a C6D6 solution of Pd{η2:η2-(CH2CHCH2)2O}(PMe3) (1a; 0.060 M, 50 μL, 0.0030 mmol) to form a 6.0 mM solution of acrylonitrile and HSiPh3, the reaction was monitored by 1H NMR at 30 °C, and the yields were periodically estimated by 1H NMR. The final yield of 2-(triphenylsilyl)propanenitrile was 97%. Schlenk Tube Reaction. A reaction mixture of acrylonitrile (26.0 μL, 0.397 mmol), HSiPh3 (100.3 mg, 0.3852 mmol), and 1a (2.6 mg, 0.0093 mmol) in C6D6 (2 mL) was vigorously stirred at room temperature for 12 h. After filtration by Celite pad, the mixture was concentrated by an evaporator to dryness to give a crude product. The crude product was purified by recrystallization from diethyl ether with a small amount of hexane to give colorless crystals of 2-(triphenylsilyl)propanenitrile in 35% yield (42.3 mg, 0.135 mmol). 1 H NMR (400 MHz, C6D6, 30 °C): δ 1.04 (d, 3H, J = 7.4 Hz, CH3), 2.07 (q, 1H, J = 7.4 Hz, CH), 7.13 (m, 9H, m,p-C6H5), 7.57 (m, 6H, o-C6H5). 13C{1H} NMR (101 MHz,C6D6, 30 °C): δ 10.1 (CH3), 13.1 (CH), 122.6 (CN), 128.0 (C6H5), 130.7 (C6H5), 131.6 (C6H5), 136.3 (C6H5). Anal. Calcd for C21H19NSi: C, 80.46; H, 6.11; N, 4.47. Found: C, 80.03; H, 6.40; N, 4.63. Methyl 2-(Triphenylsilyl)propanate. The yield was estimated as 100% by 1H NMR. This compound was isolated as a white solid in 74% yield by column chromatography. 1H NMR (400 MHz, C6D6, 30 °C): δ 1.41 (d, JHH = 7.4 Hz, 1H, Me), 2.97 (q, JHH =7.4 Hz, 1H, CHMeCO2Me), 3.11 (s, 3H, CO2Me), 7.0−7.3 (m, 9H, m,p-C6H5), 7.6−7.8 (m, 6H, o-C6H5). 13C{1H} NMR (101 MHz, C6D6, 30 °C): δ. 13.4 (CH3), 28.8 (CH3), 50.7 (CH), 128.1 (C6H5), 130.0 (C6H5), 133.4 (C6H5), 136.6 (C6H5), 175.6 (CO). Anal. Calcd: C, 76.26; H, 6.40. Found: C, 76.07; H, 6.35. 3-(Trimethylsilyl)-2-butanone. The yield was estimated as 93% by NMR. 1H NMR (400 MHz, C6D6, 30 °C): δ 1.65 (dm, JHH =6.7 Hz, 3H, CHMeCOMe), 1.65 (s, 3H, CHMeCOMe), 4.44 (q, JHH =6.7 Hz, 1H, CHMeCOMe), 7.1−7.2 (m, 9H, m,p-C6H5), 7.7−7.8 (m, 6H, o-C6H5). 13C{1H} NMR (101 MHz, C6D6, 30 °C): δ 11.2 (CH3),
Scheme 2. Proposed Catalytic Cycle
converted into Pd(η2-CH2CHCN)(PMe3) (A), which is in equilibrium with bis(acrylonitrile)palladium(0) species 2a. Complex 2a was isolated by the stoichiometric reaction in hexane. In the presence of PMe3, the active species A would give bis(phosphine)palladium(0) (B). These 16e species 2a and B must be much more stable than A, but they can reversibly give A. Now A gives C by the oxidative addition of HSiPh3. Since we have observed a Z to E isomerization of alkene during the hydrosilylation, the coordinating alkene D
DOI: 10.1021/om500964g Organometallics XXXX, XXX, XXX−XXX
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JHP = 11 Hz, PMe3), 2.66 (br d, 2H, JHH = 11 Hz, CHHCHCN: trans to CN), 2.99 (distorted br t, 2H, JHH = 11 Hz, CH2CHCN), 3.03 (distorted br d, 2H, JHH = 13 Hz, CHHCHCN: cis to CN). 13 C{1H} NMR (101 MHz, C6D6, 20 °C): δ 15.8 (d, JCP = 23 Hz, PMe3), 42.5 (s, CH2CHCN), 59.9 (br s, CH2CHCN), 120.9 (s, CH2CHCN). 31P{1H} NMR (162 MHz, C6D6, 21 °C): δ −23.9 (s). These coupling constants in 1H NMR were evaluated by iteration of gNMR for Windows (5.0.6.0). Stoichiometric Reaction of 2a with Triphenylsilane. In an NMR tube containing HSiPh3 (9.04 mg, 0.0347 mmol) were placed 500 μL of C6D6 and a solution of hexamethyldisiloxane (0.37 M, 10 μL, 0.0037 mmol) as an internal standard. After the addition of a C6D6 solution of bis(acrylonitrile)palladium(0) complex 2a (0.346 M, 100 μL, 0.0346 mmol), the reaction was monitored by 1H and 31P{1H} NMR at 30 °C, and the yields were periodically estimated by 1H NMR. The final yield of 2-(triphenylsilyl)propanenitrile was 106%.
23.2 (CH), 103.6 (CH3), 128.2 (C6H5), 130.3 (C6H5), 135.2 (C6H5), 135.7 (C6H5), 147.8 (CO). Methyl 2-(Triphenylsilyl)butanate. The yield was estimated as 96% by NMR. 1H NMR (400 MHz, C6D6, 30 °C): δ 0.94 (t, JHH = 7.2 Hz, 3H, CH2CH3), 1.71 (dqd, JHH = 14.3, 7.2, 2.7 Hz, 1H, CH(SiPh3)CHH), 2.21 (ddq, JHH = 14.3, 12.0, 7.2, 2.7 Hz, 1H, CH(SiPh3)CHH), 2.91 (dd, JHH = 12.0, 2.8 Hz, 1H, CH), 3.13 (s, 3H, CO2Me), 7.0−7.3 (m, 9H, m,p-C6H5), 7.6−7.8 (m, 6H, o-C6H5). 13 C{1H} NMR (101 MHz, C6D6, 30 °C): δ 15.3 (CH3), 22.9 (CH2), 38.5 (CH), 50.6 (CH3), 128.1 (C6H5), 130.0 (C6H5), 133.5 (C6H5), 136.6 (C6H5), 174.9 (CO). Ethyl 2-(Triphenylsilyl)butanate. The yield was estimated as 84% by NMR. 1H NMR (400 MHz, C6D6, 30 °C): δ 0.72 (t, JHH = 7.2 Hz, 3H, CH2CH3), 0.97 (t, JHH = 7.2 Hz, 3H, CO2CH2CH3), 1.72 (dqd, JHH = 14.3, 7.2, 2.7 Hz, 1H, CH(SiPh3)CHH), 2.22 (ddq, JHH = 14.3, 12.0, 7.2, 2.7 Hz, 1H, CH(SiPh3)CHH), 2.90 (dd, JHH = 12.0, 2.3 Hz, 1H, CH), 3.66 (dq, JHH = 10.8, 7.2 Hz 1H, CO2CHHMe), 3.82 (dq, JHH = 10.8, 7.2 Hz 1H, CO2CHHMe), 7.0−7.3 (m, 9H, m,pC6H5), 7.6−7.8 (m, 6H, o-C6H5). 13C{1H} NMR (101 MHz, C6D6, 30 °C): δ 13.7 (CH3), 15.0 (CH2), 22.5 (CH2), 38.1 (CH), 59.6 (CH3), 127.8 (C6H5), 129.7 (C6H5), 133.3 (C6H5), 136.4 (C6H5), 174.2 (CO). Methyl 3-Phenyl-2-(trimethylsilyl)propanoate. The yield was estimated as 68% by NMR. 1H NMR (400 MHz, C6D6, 30 °C): δ 2.99 (s, 3H, CO2Me), 3.04 (dd, JHH = 14.9, 2.3 Hz, CH), 3.42 (dd, JHH = 12.0, 2.3 Hz, CH(SiPh3)CHH), 3.56 (dd, JHH = 14.3, 2.3 Hz, CH(SiPh3)CHH), 7.1−7.2 (m, 14H, C6H5), 7.6−7.8 (m, 6H, o-C6H5). 13 C{1H} NMR (101 MHz, C6D6, 30 °C): δ 35.1 (CH3), 38.8 (CH2), 50.7 (CH3), 126.5 (C6H5), 127.9 (C6H5), 128.5 (C6H5), 128.7 (C6H5), 130.2 (C6H5), 133.1(C6H5), 136.6(C6H5), 142.4 (C6H5),174.5 (CO). 1-Nitro-4-[1-methyl-1-(trimethylsilyl)ethyl]benzene. The yield was estimated as 81% by NMR. 1H NMR (400 MHz, C6D6, 30 °C): δ 1.29 (d, 3H, JHH = 7.4 Hz, CH3), 2.83 (q, 1H, JHH = 7.4 Hz, CH), 6.51 (d, 2H, JHH = 8.9 Hz, C6H4NO2), 7.1−7.2 (m, 9H, m,pC6H5Si), 7.63 (m, 6H, o-C6H5Si), 7.67 (d, 2H, JHH = 8.9 Hz, C6H4NO2). 13C{1H} NMR (101 MHz, C6D6, 30 °C): δ 17.1 (CH3), 29.2 (CH), 123.2 (C6H5), 129.1 (C6H5), 130.1 (C6H5), 133.1 (C6H5), 135.4 (C6H5), 136.6 (C6H5), 146.1 (C6H5),146.1 (CO). 1-Cyano-4-[1-methyl-1-(trimethylsilyl)ethyl]benzene. The yield was estimated as 80% by NMR. 1H NMR (400 MHz, C6D6, 30 °C): δ 1.32 (d, 3H, JHH = 7.4 Hz, CH3), 2.82 (q, 1H, JHH = 7.4 Hz, CH), 6.50 (d, 2H, JHH = 8.0 Hz, C6H4CN), 6.85 (d, 2H, JHH = 8.0 Hz, C6H4CN), 7.1−7.2 (m, 9H, m,p-C6H5Si), 7.36 (m, 6H, o-C6H5Si). 1-Trifluoro-4-[1-methyl-1-(trimethylsilyl)ethyl]benzene. The yield was estimated as 40% by NMR. 1H NMR (400 MHz, C6D6, 30 °C): δ 1.43 (d, 3H, JHH = 7.4 Hz, CH3), 2.93 (q, 1H, JHH = 7.4 Hz, CH), 6.74 (d, 2H, JHH = 8.0 Hz, C6H4CF3), 7.1−7.2 (m, 9H, m,pC6H5Si), 7.42 (d, 2H, JHH = 8.0 Hz, C6H4 CF3), 7.58 (m, 6H, oC6H5Si). 2-(Triphenylsilyl)propanenitrile-d. The yield was estimated as 97% by NMR. 1H NMR (400 MHz, C6D6, 30 °C): δ 1.04 (dm, 2H, JHH = 6.8 Hz, CH2D), 2.11 (t, 1H, JHH = 6.8 Hz, CH), 7.13 (m, 9H, m,p-C6H5), 7.57 (m, 6H, o-C6H5). 2H NMR (62 MHz, C6H6, 20 °C): δ 0.99 (br, 1D, CH2D). Synthesis of Bis(acrylonitrile)palladium(0) Complex 2a. The mono(phosphine)palladium(0) complex 1a (73.6 mg, 0.262 mmol) was placed in a Schlenk tube under nitrogen, and hexane (10 mL) was added. Then acrylonitrile (86 μL, 1.31 mmol) was added to the solution, giving a white participate immediately. After the mixture was stirred for 30 min, the white precipitate was filtered, washed with hexane, and dried under vacuum. Yield: 55.9 g (0.194 mmol, 74%), Anal. Calcd for C9H15N2PPd: C, 37.45; H, 5.24; N, 9.71. Found: C, 37.20; H, 4.98; N, 9.68. Data for the major isomer of 2a are as follows. 1 H NMR (400 MHz, C6D6, 21 °C): δ 0.84 (d, 9H, JHP = 8.0 Hz, PMe3), 2.71 (br d, 2H, JHH = 11 Hz, CHHCHCN: trans to CN), 2.90 (br t, 2H, JHH = 11 Hz, CH2CHCN), 3.13 (br d, 2H, JHH = 11 Hz, CHHCHCN: cis to CN). 13C{1H} NMR (101 MHz, C6D6, 20 °C): δ 15.6 (d, PMe3, JCP = 23 Hz), 41.6 (br s, CH2CHCN), 60.4 (br s, CH2CHCN), 120.9 (s, CH2CHCN). 31P{1H} NMR (162 MHz, C6D6, 21 °C): δ −23.3 (s). Data for the minor isomer of 2a are as follows. 1H NMR (400 MHz, C6D6, 21 °C): δ 0.80 (d, 9H,
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ASSOCIATED CONTENT
S Supporting Information *
A figure giving the 1H NMR spectrum and gNMR simulation for 2a. This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*N. K.: e-mail,
[email protected]; tel and fax, +81 423 887 044. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We thank Prof. S. Komiya for useful discussion and Ms. S. Kiyota for elemental analysis. We also thank Mr. R. Ito for the preliminary experiments. A part of this work was supported by a JSPS Grant-in-Aid for Scientific Research on Innovative Areas “3D Active-Site Science”: Grant No. 26105003.
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DOI: 10.1021/om500964g Organometallics XXXX, XXX, XXX−XXX
