Effect of ether on regioselectivity in hydrosilylation of 1,5-hexadiene with chlorohydrosilanes catalyzed by homogeneous platinum catalysts

Article abstract of DOI:10.1080/10426500701693388

Hydrosilylation of 1,5-hexadiene with chlorohydrosilanes catalyzed by homogeneous platinum catalyst to produce 5-hexenylchlorosilanes was studied. The presence of ether additives was highly effective in improving the regioselectivity and the yield. The formation of a double-bond rearrangement isomer, cis-, or trans-4-hexenylchlorosilanes, during the hydrosilylation was reduced drastically, as well. Copyright Taylor & Francis Group, LLC.

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Phosphorus, Sulfur, and Silicon
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Effect of Ether on
Regioselectivity in
Hydrosilylation of
1,5-Hexadiene with
Chlorohydrosilanes Catalyzed
by Homogeneous Platinum
Catalysts
Takeaki Saiki a
a Silanes Development Group, Science &
Technology , Core Products Business, Dow Corning,
Toray Co., Ltd. , Chiba, Japan
Published online: 24 Jun 2008.
To cite this article: Takeaki Saiki (2008) Effect of Ether on Regioselectivity in
Hydrosilylation of 1,5-Hexadiene with Chlorohydrosilanes Catalyzed by Homogeneous
Platinum Catalysts, Phosphorus, Sulfur, and Silicon and the Related Elements, 183:7,
1556-1563, DOI: 10.1080/10426500701693388
To link to this article: http://dx.doi.org/10.1080/10426500701693388
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Phosphorus, Sulfur, and Silicon, 183:1556–1563, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701693388
Effect of Ether on Regioselectivity in Hydrosilylation
of 1,5-Hexadiene with Chlorohydrosilanes Catalyzed
by Homogeneous Platinum Catalysts
Takeaki Saiki
Silanes Development Group, Science & Technology, Core Products
Business, Dow Corning, Toray Co., Ltd., Chiba, Japan
Hydrosilylation of 1,5-hexadiene with chlorohydrosilanes catalyzed by homoge-
neous platinum catalyst to produce 5-hexenylchlorosilanes was studied. The pres-
ence of ether additives was highly effective in improving the regioselectivity and
the yield. The formation of a double-bond rearrangement isomer, cis-, or trans-4-
hexenylchlorosilanes, during the hydrosilylation was reduced drastically, as well.
Keywords 1,5-hexadiene; ether; hydrosilylation; platinum; silicon
INTRODUCTION
Hydrosilylation of dienes is a versatile and efficient method for the
synthesis of alkenylsilanes,1–4 which are important intermediates for
organosilicon and silicone industries.5–7 However, hydrosilylation of
1,5-hexadiene with chlorohydrosilanes catalyzed by platinum com-
pounds suffer from problems including poor regioselectivity and slow
reaction rate. Although hydrosilylation of 1-hexene, 1,4-pentadiene,
and 1,6-heptadiene gave a single isomer of n-hexylchlorosilanes, 4-
pentenylchlorosilanes, and 6-heptenylchlorosilanes, respectively, in
high yield, using 1,5-hexadiene gave a mixture of 5-hexenyl-, trans-
4-hexenyl-, and cis-4-hexenyl-chlorosilanes in low yields as illustrated
in Scheme 1. The use of heterogeneous platinum catalysts to achieve
regioselective hydrosilylation of 1,5-hexadiene with chlorohydrosilanes
has been reported with limited catalytic activity.8 In this paper, we
report that specific ethers work well to afford 5-hexenylchlorosilanes
regioselectively in the platinum catalyzed hydrosilylation of 1,5-
hexadiene with chlorohydrosilanes.
Received 30 October 2006; accepted 20 August 2007.
Address correspondence to Takeaki Saiki, Silanes Development Group, Science &
Technology, Core Products Business, Dow Corning, Toray Co., Ltd., 2-2 Chigusa-Kaigan,
Ichihara-Shi, Chiba 299-0108, Japan. E-mail: takeaki.saiki@dowcorning.com
1556

Hydrosilylation of 1,5-Hexadiene with Hydrosilanes
1557
SCHEME 1 Hydrosilylation of 1,5-hexadiene with chlorohydrosilanes.
RESULTS AND DISCUSSION
The hydrosilylation of 1,5-hexadiene (25.0 mmol) with trichlorosilane
(12.5 mmol) catalyzed by chloroplatinic acid (1.8 × 10−3 mmol) in
iPrOH (0.15 mmol)9 for 24 h at room temperature gave a mixture of
5-hexenyltrichlorosilane (4), trans-4-hexenyltrichlorosilane (5), cis-4-
hexenyltrichlorosilane (6), and 1,6-bis(trichlorosilyl)hexane (7) in a to-
tal yield of 19%. The ratio of these products is shown in Table I, entry 1.
By adding an ether, polyethylene glycol, tetrahydrofuran, diethylene
glycol dimethylether, or diethylene glycol dibutylether, the yield, as well
as the selectivity, was drastically improved as listed in entries 2, 3, 4,
TABLE I Hydrosilylation of 1,5-hexadiene 1 with trichlorosilane 2a.a
Entry
Additive
Silane
4a.5a:6a:7ab Yield [%]c
1
2
3
4
5
6
7
8
9
None
HSiCl3
HSiCl3
HSiCl3
HSiCl3
HSiCl3
HSiCl3
HSiCl3
HSiCl3
HSiCl3
48:39:13:0
89:9:0:2
89:10:0:1
86:9:0:5
19
99
99
99
99
68
48
40
34
Polyethylene glycold
Tetrahydrofuran
Diethylene glycol dimethylether
Diethylene glycol dibutylether
1,4-Dioxane
85:9:0:6
84:11:5:0
84:10:6:0
81:11:8:0
69:25:6:0
Ethylether
Butylether
i-Propylether
aA mixture of 1,5-hexadiene 1 (25 mmol), trichlorosilane 2a (12.5 mmol),
chloroplatinic acid (1.8 × 10−3 mmol) in 2-propylalcohol (0.15 mmol) and additives (0.2
mmol of ether oxygen atom) was stirred and allowed to stand at room temperature for
24 h. bThe isomer ratios were determined by GC and 1H NMR. cGC yields based on
trichlorosilane 2a. dThe average molecular weight is 400.

1558
T. Saiki
and 5 in Table I. It should be noted that cis-4-hexenyltrichlorosilane (6)
was completely absent (0%), when these additives were employed.
The addition of 1,4-dioxane exhibited slightly worse selectivity than
the reaction using the above ethers with moderate yield (Table I, entry
6). The use of ethylether and butylether resulted in moderate selectivity
with inferior yield (Table I, entries 7 and 8). Interestingly, the use of
isopropylether was less effective in both regioselectivity and reactivity
(Table I, entry 9). Diadduct 1,6-bis(trichlorosilyl)hexane (7) was not
generated in the presence of 1,4-dioxane, ethylether, butylether, and
isopropylether.
To extend the scope of the polyethylene glycol additive fur-
ther, hydrosilylation of 1,5-hexadiene with chlorodimethylsi-
lane or dichloromethylsilane was investigated (Table II). When
dichloromethylsilane was used without any additives, lower selectivity
with high yield was attained (Table II, entry 1). The addition of
polyethylene glycol to the reaction mixture resulted in higher selec-
tivity while keeping the high yield (Table II, entry 2). Hydrosilylation
with chlorodimethylsilane showed higher selectivity with moderate
yield without ether additives (Table II, entry 3). However, the addition
TABLE II Hydrosilylation of 1,5-Hexadiene 1 with Various
Chlorohydrosilanes.a
Entry
Additive
Silane 4b:5b:6b:7bbor 4c:5c:6c:7cb
Yield [%]c
1
2
3
4
None
Polyethylene glycold MeHSiCl2
None Me2HSiCl
Polyethyleneglycold Me2HSiCl
MeHSiCl2
66:27:1:6
88:0:0:12
98:1:1:0
99
99
58
57
100:0:0:0
aA mixture of 1,5-hexadiene 1 (25 mmol), chlorohydrosilane 2b or 2c (12.5 mmol),
chloroplatinic acid (1.8 × 10−3 mmol) in 2-propylalcohol (0.15 mmol) and additives
(0.2 mmol of ether oxygen atom) was stirred and allowed to stand at room
temperature for 24 h. bThe isomer ratios were determined by GC and 1H NMR. cGC
yields based on chlorohydrosilane 2b or 2c. dThe average molecular weight is 400.

Hydrosilylation of 1,5-Hexadiene with Hydrosilanes
1559
of polyethylene glycol to the hydrosilylation with chlorodimethylsilane
had little effect on the selectivity and the yield (Table II, entry 4).
The effect of polyethylene glycol with various platinum cata-
lysts was then examined with the results summarized in Table III.
The hydrosilylation catalyzed by 1,3-divinyltetramethyldisiloxane-
platinum complex10,11 exhibited low regioselectivity and moderate yield
(Table III, entry 3). With the addition of polyethylene glycol, excellent
regioselectivity and high yield were obtained (Table III, entry 4). The
use of platinum on carbon as a heterogeneous catalyst gave excellent
regioselectivity with very low yield (Table III, entry 5). The addition of
polyethylene glycol to this reaction was slightly effective in increasing
the yield (Table III, entry 6).
The effects of ethers were widely depended on the ether structures,
chlorohydrosilanes, and the type of the platinum catalyst. The effec-
tiveness of monoethers appeared to have increased with increasing co-
ordinating ability. The excellent catalyst performance of multidentate
ethers such as polyethylene glycol, diethylene glycol diethylether, and
diethylene glycol dibutylether was probably a result of their strong mul-
tidentate coordination.
TABLE III Hydrosilylation of 1,5-Hexadiene 1 with Trichlorosilane
2a Using Various Platinum Catalysts.a
Entry
Additive
Catalyst
4a:5a:6a:7ab
Yield [%]c
1
2
3
None
H2PtCl6-6H2O in i-PrOH 48:39:13:0
19
99
63
Polyethylene glycol d H2PtCl6-6H2O in i-PrOH
None
89:9:0:2
75:22:3:0
4
Polyethylene glycol d
97:1:0:2
99
5
6
None
Pt/C (0 .5%Ptw/w)
Pt/C (0.5%Ptw/w)
99:1:0:0
100:0:0:0
36
50
Polyethylene glycol d
aA mixture of 1.5-hexadiene 1 (25 mmol), trichlorosilane 2a (12.5 mmol), platinum
catalyst (1.8 × 10−3 mmol) and additives (0.2 mmol of ether oxygen atom) was stirred
and allowed to stand at room temperature for 24 h. bThe isomer ratios were determined
by GC and 1H NMR. cGC yields based on trichlorosilane 2a. dThe average molecular
weight is 400.

1560
T. Saiki
The widely accepted Chalk-Harrod mechanism for platinum-
catalyzed hydrosilylation involves initial insertion of the olefin into
the Pt-H bond followed by reductive elimination, forming a new Si C
bond.12 Although we have not investigated the reaction mechanism
yet, the double bond rearrangement may have proceeded through (a)
generation of a (silyl)platinum 1,5-hexadiene complex (9) by oxidative
addition of the Si-H bond to the platinum 1,5-hexadiene complex 8,
(b) anti-Markovnikov insertion of a double bond of 1,5-hexadiene to
the Pt-H bond to form a 1-methyl-4-hexenylplatinum complex (10),
(c) β-hydride elimination of the inner hydride to form a platinum
1,4-hexadiene complex (11) bearing a stable inner olefin, (d) insertion
of the terminal double bond of 1,4-hexadiene to the Pt-H bond to form a
4-hexenylplatinum complex (12) and (e) coordination of 1,5-hexadiene
(1) to 12 and reductive elimination of 4-hexenylsilanes (5 or 6) to regen-
erate a platinum 1,5-hexadiene complex 8 (see Scheme 2). We reasoned
that ethers block coordination sites to prevent bidentate coordination
of 1,5-hexadiene, and are suitable ligands of platinum compounds for
the hydrosilylation of 1,5-hexadiene with chlorohydrosilanes exhibiting
good catalytic performance.
SCHEME 2 Proposed double bond rearrengement mechanism.

Hydrosilylation of 1,5-Hexadiene with Hydrosilanes
1561
In conclusion, we observed that platinum catalyzed hydrosilylation of
1,5-hexadiene with chlorohydrosilanes using ether additives gave high
yield of 5-hexenylchlorosilanes as the major product. To our knowledge,
this is the first observation that the presence of ether additives can
change the product distribution in hydrosilylation and can improve the
catalytic activity.
EXPERIMENTAL
All reagents were commercially available and were used as received.
1H, 13C, and 29Si NMR spectra were recorded in CDCl3 solutions us-
ing a JEOL JNM-EX400 spectrometer (400 or 100MHz) with Me4Si or
residual protiated solvent as an internal standard. GC mass spectra
were obtained on a Shimadzu GCMS-QP5050A operating at an ioniza-
tion potential of 70 eV.
Catalytic Hydrosilylation of 1,5-Hexadiene—General
Procedure
A glass tube containing 1,5-hexadiene (25 mmol) and an additive (0.2
mmol as ether oxygen atom) was stirred under nitrogen, followed by
charging with a platinum catalyst (1.8 × 10−3 mmol) and a chlorohy-
drosilane (12.5 mmol). After sealing the tube with a screw cap, the
mixture was stirred for 1 minute and allowed to stand at room tem-
perature for 24 h. The product was isolated by distillation to give an
analytically pure sample.
Hexenyltrichlorosilane (4a, 5a, 6a)13
The purity determined by NMR and GC analyses was >95%; b.p. 69◦C/7
mmHg; 1H NMR (δ5-hexenyl isomer) 1.38–1.43 (m, 2H), 1.49–1.55 (m,
2H), 1.57–1.63 (m, 2H), 2.06–2.12 (m, 2H), 4.95–5.05 (m, 2H), 5.74–5.84
(m, 1H), (trans-4-hexenyl isomer) not assigned, (cis-4-hexenyl isomer)
not assigned; 13C NMR δ (5-hexenyl isomer) 21.72, 24.20, 30.98, 33.13,
115.03, 137.89, (trans-4-hexenyl isomer) 17.94, 22.18, 23.71, 34.48,
126.55, 129.60, (cis-4-hexenyl isomer) 12.87, 22.18, 23.80, 28.70, 125.45,
128.76; 29Si NMR δ (5-hexenyl isomer) 12.91, (trans-4-hexenyl isomer)
13.14, (cis-4-hexenyl isomer) 13.04; GCMS (EI) m/z (%) (5-hexenyl iso-
mer) 216 (M+, 1.6), 187 (2.5), 174 (17.6), 133 (22.4), 55 (100), (trans-4-
hexenyl isomer) 216 (M+, 3.1), 187 (3.0), 174 (10.6), 133 (11.7), 55 (100),
(cis-4-hexenyl isomer) 216 (M+, 4.0), 187 (5.5), 174 (13.0), 133 (15.1), 55
(100).

1562
T. Saiki
1,6-Bis(trichlorosilyl)hexane (7a)14
The purity determined by NMR and GC analyses was >95%; b.p.
149◦C/10 mmHg; 1H NMR δ 1.38–1.42 (m, 2H), 1.43–1.47 (m, 2H), 1.56–
1.64 (m, 2H); 13C NMR δ 22.00, 24.17, 31.12; 29Si NMR δ 12.84; GCMS
(EI) m/z (%) 216 (12.4), 187 (24.0), 174 (49.6), 133 (81.6), 55 (100).
Hexenyldichloromethylsilane (4b, 5b, 6b)15
The purity determined by NMR and GC analyses was >95%; b.p. 65
1
◦C/5 mmHg; H NMR (δ5-hexenyl isomer) 0.75 (s, 3H), 1.08–1.14 (m,
2H), 1.46-1.57 (m, 4H), 2.05–2.10 (m, 2H), 4.94–5.03 (m, 2H), 5.73–5.83
(m, 1H), (trans-4-hexenyl isomer) not assigned, (cis-4-hexenyl isomer)
not assigned; 13C NMR δ (5-hexenyl isomer) 5.18, 21.48, 21.89, 31.54,
33.25, 114.75, 138.30, (trans-4-hexenyl isomer) 5.18, 17.93, 21.05, 22.41,
35.07, 126.02, 130.19, (cis-4-hexenyl isomer) 5.18, 12.85, 21.15, 22.37,
29.27, 124.94, 129.37; 29Si NMR δ (5-hexenyl isomer) 32.71, (trans-4-
hexenyl isomer) 32.90, (cis-4-hexenyl isomer) 32.78; GCMS (EI) m/z
(%) (5-hexenyl isomer) 196 (M+, 0.6), 181 (0.2), 167 (3.4), 154 (32.1),
113 (100), (trans-4-hexenyl isomer) 196 (M+, 10.0), 181(0.7), 167 (9.3),
154 (13.7), 141 (10.7), 113 (100), (cis-4-hexenyl isomer) 196 (M+, 8.0),
181 (1.4), 167 (8.7), 154 (12.8), 141 (9.2), 113 (100).
1,6-Bis(dichloromethylsilyl)hexane (7a)16
The purity determined by NMR and GC analyses was >95%; b.p.
1
128◦C/5 mmHg; H NMR δ 0.76 (s, 3H), 1.09–1.13 (m, 2H), 1.38–1.44
(m, 2H), 1.48–1.55 (m, 2H); 13C NMR δ 5.18, 21.49, 22.18, 31.74; 29Si
NMR δ 32.82; GCMS (EI) m/z (%) 295 (6.61), 197 (1.9), 154 (9.6), 141
(34.2), 113 (100).
Hexenylchlorodimethysilane (4c17, 5c, 6c)
The purity determined by NMR and GC analyses was >95%; b.p. 73◦C/7
1
mmHg; H NMR δ (5-hexenyl isomer) 0.39 (s, 6H), 0.80–0.84 (m, 2H),
1.42–1.46 (m, 4H), 2.04–2.09 (m, 2H), 4.92–5.01 (m, 2H), 5.74–5.84 (m,
1H), (trans-4-hexenyl isomer) not assigned, (cis-4-hexenyl isomer) not
assigned; 13C NMR δ (5-hexenyl isomer) 1.64, 18.85, 22.48, 32.17, 33.41,
114.47, 138.63, (trans-4-hexenyl isomer) not assigned, (cis-4-hexenyl
isomer) not assigned; 29Si NMR δ (5-hexenyl isomer) 31.61, (trans-
4-hexenyl isomer) not assigned, (cis-4-hexenyl isomer) not assigned;
GCMS (EI) m/z (%) (5-hexenyl isomer) 176 (M+, 0.1), 161 (0.4), 134
(18.2), 119 (4.2), 93 (100), (trans-4-hexenyl isomer) 176 (M+, 4.7) 148

Hydrosilylation of 1,5-Hexadiene with Hydrosilanes
1563
(2.8), 134 (4.4), 121 (9.2), 93 (100), (cis-4-hexenyl isomer) 176 (M+, 5.5),
148 (2.5), 121 (10.9), 93 (100).
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