PAPER
Organocatalytic Hydrosilylation of Isoprene
577
Triethyl[2-methyl-4-(triethylsilyl)but-2-en-1-yl]silane (5)
In summary, we report the hydrosilylation of isoprene
with triethylsilane without the need for expensive transi-
tion-metal catalysts. However, only a handful of solvents
were effective catalysts for this reaction, of which propy-
lene carbonate proved to be the most efficient. Because of
the biphasic nature of the reaction system, recycling of the
propylene carbonate phase was possible and the system
remained active over several catalytic cycles. We have
therefore developed a new, easy, and inexpensive method
for the continuous production of allylic silanes.
The reaction solution was distilled (7.8 mbar, 110 °C) to give a res-
idue containing the raw product 5, Et3SiOH (6), and (Et3Si)2O (7).
This residue was mixed with toluene (30 mL) and 20 wt% Pd/acti-
vated carbon then hydrogenated under 50 bar H2 pressure for 6 h at
100 °C to give a mixture containing triethyl[2-methyl-4-(triethylsi-
lyl)butyl]silane. (The spectra below relate to the hydrogenated
product).
1H NMR (CDCl3, 400 MHz): d = 0.35–0.44 (m, 2 H, CH2), 0.49–
0.56 (q, J = 6.0 Hz, 12 H, Si–CH2–CH3), 0.58–0.62 (m, 2 H, CH2),
0.94 (t, J = 6.0 Hz, 21 H, CH3), 1.10–1.28 (m, 2 H, CH2), 1.43–1.51
(m, 1 H, CH–CH3).
13C NMR (CDCl3, 100 MHz): d = 3.3, 4.1, 8.5, 19.3, 22.5, 32.5,
Isoprene (purity 98%), Et3SiH, and the solvents were obtained from
Acros Organics. The catalyst RhCl3⋅H2O was obtained from Umi-
core. The gas chromatographic analyses were carried out on an HP
6890 instrument (Hewlett-Packard GmbH, Waldbronn, Germany)
equipped with an FI detector and an HP-5 capillary column (30 m,
diameter 250 mm, film thickness 0.25 mm) connected to an autosam-
pler. Di-n-butyl ether was used as internal standard. The products
were characterized by mass spectrometry using an HP Series 5973
GC-MS (Hewlett-Packard GmbH, Waldbronn, Germany) with 70
eV and NMR spectroscopy with a Bruker Avance DRX-400 (400
MHz) instrument. For the NMR analyses, CDCl3 was used as sol-
vent.
34.8.
MS (EI, 70 eV): m/z (%) = 271 (>1) (–C2H5), 157 (2), 127 (6), 115
(100), 99 (4), 87 (43), 71 (2), 59 (25).
Triethylsilanol (6)
MS (EI, 70 eV): m/z (%) = 132 [M+] (2), 103 (86), 75 (8), 61 (5), 47
(37), 45 (46).
Hexaethyldisiloxane (7)
MS (EI, 70 eV): m/z (%) = 246 [M+] (0), 217 (100), 189 (79), 161
(52), 133 (22), 131 (9), 105 (27), 103 (17), 101 (3), 94 (8), 87 (8),
80 (13), 77 (10), 73 (6), 66 (16), 59 (17), 52 (5), 45 (3).
Hydrosilylation of Isoprene: Typical Procedure
Isoprene (1.36 g, 2.00 mL, 20 mmol), Et3SiH (2.33 g, 3.19 mL,
20 mmol), and propylene carbonate (30 mL) were transferred into a
70-mL Parr autoclave and heated at 80 °C for 3 h under argon (5
bar). The mixture was cooled and the two phases were separated.
Both phases were analyzed by gas chromatography (Bu2O internal
standard).
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Triethyl(3-methylbut-2-en-1-yl)silane (3)
The reaction solution was purified by column chromatography (sil-
ica gel, cyclohexane) to give the product as a light-yellow liquid.
1H NMR (CDCl3, 400 MHz): d = 0.54–0.59 (q, J = 6.0 Hz, 6 H, Si–
CH2–CH3), 0.95–0.98 (t, J = 6.0 Hz, 9 H, Si–CH2–CH3), 1.27 (d,
J = 2.0 Hz, 2 H, CH2–CH = Cq), 1.52 (s, 3 H, CH3), 1.69 (s, 3 H,
CH3), 5.05–5.09 (q, J = 2.0 Hz, 1 H, HC–CH3).
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MS (EI, 70 eV): m/z (%) = 184 [M+] (9), 155 (4) (– C2H5), 127 (3),
115 (58) (– C5H9), 99 (5), 97 (4), 87 (100), 73 (5), 69 (6), 59 (37),
45 (7).
Anal. Calcd for C11H24Si: C, 71.7; H, 13.1. Found: C, 72.1; H, 13.2.
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Triethyl(2-methylbut-2-enyl)silane (4)
The reaction solution was distilled (7.8 mbar, 110 °C) and the re-
sulting crude product was purified by column chromatography (sil-
ica gel, cyclohexane) to give the product as a light-yellow liquid.
1H NMR (CDCl3, 400 MHz): d = 0.52–0.57 (q, J = 6.0 Hz, 6 H, Si–
CH2–CH3), 0.90–0.96 (t, J = 6.0 Hz, 9 H, Si–CH2–CH3), 1.50 (s, 3
H, Cq–CH3), 1.52 (s, 2 H, Si–CH2–Cq), 1.67 (d, J = 2.0 Hz, 3 H,
CH–CH3), 5.02–5.07 (q, J = 2.0 Hz, 1 H, CH–CH3).
13C NMR (CDCl3, 100 MHz): d = 4.1, 7.4, 13.9, 17.5, 26.3, 115.8,
134.1.
MS (EI, 70 eV): m/z (%) = 184 [M+] (10), 155 (4) (– C2H5), 126 (2)
(– C2H5), 15 (60) (– C5H9), 99 (4), 97 (4), 87 (100), 73 (4), 69 (4),
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Anal. Calcd for C11H24Si: C, 71.7; H, 13.1. Found: C, 72.2; H, 13.2.
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Synthesis 2012, 44, 575–578