Regioselective platinum catalyzed β-hydrosilylation of allylic benzene derivatives with cyclic siloxane d4H

Article abstract of DOI:10.2174/157017811795684992

Conditions have been found for an efficient regioselective β-hydrosilylation of allylbenzene, 2-allyl-1-trimethylsiloxybenzene, 4-allyl-1,2-(methylenedioxy)benzene, allylpentafluorobenzene, and 4-allyl-2-methoxy-1-trimethylsiloxybenzene with D₄^H in the presence of Karstedt's-catalyst or platinum black under mild conditions leading quantitatively to functionalized tetramethylcyclosiloxanes 3.

Full text of DOI:10.2174/157017811795684992

Letters in Organic Chemistry, 2011, 8, 361-363
361
Regioselective Platinum Catalyzed ꢀ-Hydrosilylation of Allylic Benzene
H
Derivatives with Cyclic Siloxane D4
Abdelghani El Malkia, Abdellah Hanniouia, El Mostapha Rakib*,a, Nourredine Knouzib and
Michel Vaultierb
aLaboratoire de Chimie Organique et Analytique, Université Sultan My Slimane, Faculté des Sciences et Techniques,
B.P.523 Béni-Mellal, Morocco
bUniversité Hassan II, Faculté Des Sciences Sidi Othmane, BP6023, Casablanca, Morocco
cLaboratoire de Synthèse et Electrosynthèse Organiques UMR 6510, Université Rennes I, France
Received November 18, 2010: Revised March 31, 2011: Accepted March 31, 2011
Abstract: Conditions have been found for an efficient regioselective ꢀ-hydrosilylation of allylbenzene, 2-allyl-1-
trimethylsiloxybenzene, 4-allyl-1,2-(methylenedioxy)benzene, allylpentafluorobenzene, and 4-allyl-2-methoxy-1-
H
trimethylsiloxybenzene with D4 in the presence of Karstedt’s-catalyst or platinum black under mild conditions leading
quantitatively to functionalized tetramethylcyclosiloxanes 3.
H
Keywords: Allylbenzene derivatives, Karstedt’s-catalyst, Hydrosilylation, Siloxane D4 , Platinum catalyst.
INTRODUCTION
When the substituted allylbenzenes 1 (1.1 equiv.) were
reacted with D4H(1.0 equiv.), using 1.10-5 mole of Karstedt’s-
catalyst/mole olefin or 1.10-3 mole of platinum black/mole of
olefin in dry toluene at temperatures between 40 and 90°C for
3hours, a reaction leading to the ꢀ-hydrosilylated product 3
and 4 took place. Neither the 2160 cm-1 Si-H infrared band nor
Functionalized siloxanes are important silicon
derivatives essentially used as coupling agents in polymer
chemistry [1]. Most of the standard methods for forming
Si-C bonds may be used for the preparation of such
intermediates including the addition of silicon hydrides to
substituted olefins and acetylenes in the presence of
catalysts such as peroxides, bases or platinum salts [2].
Ring opening in cyclic siloxanes occurs in the presence of
anionic or cationic initiators to give polysiloxanes i.e.
silicones [1]. It is therefore of much interest to have at
hands efficient ways to make such compounds bearing a
variety of functional groups directly by hydrosilylation of
the corresponding olefins [2]. Few examples of this kind of
approach to functionalized siloxanes are reported in the
literature [3-5]. One interesting example is the quantitative
ꢀ-hydrosilylation of the tertiary aliphatic isocyanate m-iso-
1
its H NMR peak at 4.61 ppm were detectable in the final
crude product. Cyclosiloxanes 3 and 4 could be isolated in
excellent yields and good purity just by bulb to bulb
elimination under high vacuum at 100°C of the isomerized
olefins 5 (usually 3 to 11%) and traces (ꢂ1%) of the reduced
compound 6. Results are reported in Table 1.
A 10% excess of the starting olefins were necessary in
order to get a complete consumption of the cyclotetrasiloxane
D4H except in the case of 1d where one equivalent of the olefin
was used. Isomerization was in all the other cases a
competitive reaction consuming up to 11% of the starting
olefins 1 depending on substituents, catalyst and reaction
temperature (see Table 1). This last parameter was shown to be
a determining factor for regioselectivity. It has been found that
at 40°C, in the presence of either Karstedt’s-catalyst or
platinum black, a complete regioselective hydrosilylation
occurred leading to ꢀ regioisomer 3. Several reactions
conditions were checked showing that at higher temperatures
i.e. 70 to 90°C , mixtures of ꢁ and ꢀ hydrosilylation products,
in variable ratios (see Table 1), were obtained. This is in
agreement with Lestel et al. [10] who reported that reaction of
H
propenyl ꢁ,ꢁ’-dimethylbenzylisocyanate with D4
described by Zhou et al. [6]. Recent results revealed the
effect of aminoaromatic acids as promoter for the
platinum-catalyzed hydrosilylation of alkenes. Indeed,
100% conversion of many alkenes and 98.4% selectivity in
favor of the ꢀ-adduct were obtained [7]. The Pt-catalyzed
hydrosilylation of allyl chloride has recently been studied
in ionic liquids in a continuous loop reactor [8]. In this
paper, we wish to report our results on the hydrosilylation
of the substituted allylbenzene with D4 in the presence of
Karstedt’s-catalyst and platinum black leading to
regioselectivity under proper conditions to D4
(Scheme 1).
H
H
R
D4 with allyl methylpolyethylene glycol at 60°C in the
3
presence of either hexachloroplatinic acid or platinum divinyl
tetramethyldisiloxane as catalyst led to a 4:1 ratio of ꢀ and ꢁ
addition product. No reaction was observed at room
temperature in the presence of platinum black under our
conditions.
*Address correspondence to this author at the Laboratoire de Chimie
Organique et Analytique, Université Sultan My Slimane, Faculté des
Sciences et Techniques, B.P.523 Béni-Mellal, Morocco;
Tel: (212)05 23485182; Fax: (212) 05 23485201;
E-mail: elmostapha1@ymail.com
1570-1786/11 $58.00+.00
© 2011 Bentham Science Publishers Ltd.

362 Letters in Organic Chemistry, 2011, Vol. 8, No. 5
El Malki et al.
Pt
ꢁ
R
H
R
R
D4
(
)
O
Si
+
(
O
Si
)
+
+
+
ꢀ
4
4
4
5
6
1
2
3
R
R
O
H
O
F
OTMS
OMe
3a ; R =
3c ; R =
)
(
H
3e ; R =
O
Si
D4
=
4
F
F
F
3d ; R =
3b ; R =
F
OTMS
H
.
Scheme 1. Hydrosilylation with D4
Table 1. Reactions Conditions and Yields of Isolated Compounds 3(a-e) [9]
Ratio
% 5
%
Entry
Olefin
Catalyst
mol cat/mol olefin
T°Ca
ꢀ/ ꢁ(3/4)
isomerisation
Yieldb
1
1.10-5
1.10-5
1.10-3
1.10-3
1.10-3
1.10-5
3.10-5
1.10-5
1.10-3
1.10-3
1.10-5
1.10-4
1.10-5
5.10-3
1.10-3
1.10-3
1.10-5
1.10-5
1.10-3
1.10-3
1.10-3
1.10-4
1.10-5
1.10-5
1.10-3
1.10-4
1.10-3
80
40
70
40
20
90
85
40
80
40
90
80
40
80
90
40
90
40
85
40
20
90
85
40
80
90
40
97/3
100/0
97/3
100/0
-
5
5
6
4
-
97
2
Karstedt
96
3
1a
Platinum Black
96
4
94
No reactionc
5
6
96/4
93/7
100/0
97/3
100/0
95/5
92/8
100/0
93/7
95/5
100/0
95/5
100/0
96/4
100/0
-
6
8
6
4
5
6
9
7
5
10
8
-
96
7
95
Karstedt
8
1b
94
Platinum Black
9
97
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
93
92
96
Karstedt
94
1c
Platinum Black
88
84
95
94
Karstedt
-
98
1dd
Platinum Black
-
94
-
96
No reactionc
-
92/8
95/5
100/0
80/20
87/13
100/0
11
8
4
5
6
5
89
91
92
91
92
90
Karstedt
1e
Platinum Black
aReaction time: 3 hours.
bYields are for pure mixtures of 3 and 4 or pure 3, after elimination of 5 and 6 under high vacuum at100°C.
cReaction time: 14 hours.
dReaction is quantitative without an excess of the olefin. No isomerisation of 1d has been observed.
CONCLUSION
hydrosilylation of olefins with D4H proceeds regioselectivity to
the desired products provided that the temperature of the
reaction is fixed at 40°C. Karstedt’s-catalyst appeared to be the
In conclusion, we have developed a simple method for
the synthesis of functionalized cyclotetrasiloxanes. The

Regioselective Platinum Catalyzed ꢀ-Hydrosilylation
Letters in Organic Chemistry, 2011, Vol. 8, No. 5
363
argon. D4H (1 ml, 4.13 mmol) was added slowly and subsequently
heated at To this stirred solution wich was subsequently heated at
40°C for 3 h. the hydrosilylation was followed by H NMR and the
most efficient. The same kind of reactivity and selectivity
were observed with black platinum, although 100 times
more catalyst was used. The interest of this last catalyst is
that it can be easily removed by filtration once the reaction
has been completed.
1
reaction stopped once the Si-H signal has disappeared. The solvent
was then evaporated under reduced pressure. Volatile by-products
and excess of olefin were removed by bulb to bulb distillation
(100°C, 0.01 torr). (3a) was obtained as viscous oil in a 96% yields.
H
b) Preparation of (3a) from (1a) with D4 in the presence of
platinum black is representative. A solution of allylbenzene (1a) (2.4
ml, 18,2 mmol) and platinum black (0.244g, 1.10-3 mole of Pt/mole of
olefin) in toluene (5 ml) was warmed to 40°C. To this stirred solution,
D4H (1 ml, 4.13 mmol) was added slowly and subsequently heated at
40°C for 3 h. After filtration over glass wool, the solvent was
evaporated under reduced pressure; volatile by-products and excess
of olefin were removed by bulb to bulb distillation (100°C, 0.01 torr).
(3a) 1H NMR (300 MHz, CDCl3): ꢀ 0.09-0.14 (m, 12H, Si-CH3), 0.60
(t, J=6.88 Hz, 8H, Si-CH2), 1.65-1.76 (m, 8H, CH2-CH2-Ph), 2.60-
2.70 (m, 8H, CH2-Ph), 7.19-7.36 (m, 20H, CH-Ar) ; 13C NMR (75
MHz, CDCl3): ꢀ –0.52 (Si-CH3), 17.03 (Si-CH2), 25.15 (CH2-CH2-
Ph), 39.40 (CH2-Ph), 125.73, 128.33, 128.56 (CH-Ar), 142.66 (C-Ar);
29Si NMR: ꢀ -20.53, -20.46, -20.43; HRMS Calcd for C31H45O4Si4 [M
- (CH2)3C6H5]+ : 593.2395, Found : 593.2417.
(3b) 1H NMR (300 MHz, CDCl3): ꢀ -0.02-0.04 (m, 12H, Si-CH3),
0.17- 0.21 (m, 36H, Si(CH3)3), 0.49-0.54 (m, 8H, Si-CH2), 1.53-1.58
(m, 8H, CH2-CH2-Ph), 2.49-2.54 (m, 8H, CH2-Ph), 7.00-7.06 (m,
16H, CH-Ar); 13C NMR (75 MHz, CDCl3): ꢀ –0.63, -0.55 (Si-CH3),
0.58 (Si-(CH3)3), 17.49 (Si-CH2), 23.49 (CH2-CH2-Ph), 34.06 (CH2-
Ph), 118.74, 121.19, 126.62 (CH-Ar), 130.20, 133.30, 153.40 (C-Ar);
29Si NMR: ꢀ -20.50, -20.46, -20.38, -20.32 (Si-CH3), 17.79, 17.81
(Si-(CH3)3); HRMS Calcd for C52H88O8Si8 [M]+ : 1064.4632, Found :
1064.4636.
(3c) 1H NMR (300 MHz, CDCl3): ꢀ -0.07-0.03 (m, 12H, Si-CH3),
0.49 (t, J=7.94Hz, 8H, Si-CH2), 1.48-1.64 (m, 8H, CH2-CH2-Ph),
2.43-2.52 (m, 8H, CH2-Ph), 5.87 (s, 8H, CH2O2), 6.52-6.70 (m, 12H,
CH-Ar); 13C NMR (75 MHz, CDCl3): ꢀ 0.00 (Si-CH3), 17.39 (Si-
CH2), 25.89 (CH2-CH2-Ph), 35.57 (CH2-Ph), 101.28 (CH2O2), 108.62,
109.49, 121.73 (CH-Ar), 137.03, 146.07, 148.07 (C-Ar);29Si NMR: ꢀ
-20.48, -20.52, -20.53, -20.61, -20.63 (Si-CH3); HRMS Calcd for
C44H56O12Si4 [M]+ : 888.2849, Found : 888.2830.
(3d) 1H NMR (300 MHz, CDCl3): ꢀ -0.08-0.06 (m, 12H, Si-CH3),
0.40 (t, J=8.25 Hz, 8H, Si-CH2), 1.49-1.60 (m, 8H, CH2-CH2-Ph),
2.63 (t, J=7.21 Hz, 8H, CH2-Ph) ;13C NMR (75 MHz, CDCl3): ꢀ -
1.00, -0.92, -0.87, -0.79 (Si-CH3), 16.73 (Si-CH2), 22.96 (CH2-CH2-
Ph), 25.39 (CH2-Ph), 115.08, 136.76, 138.89, 145.04 (C-Ar); 29Si
NMR: ꢀ -20.93, -20.89, -20.82, -20.80 (Si-CH3); HRMS Calcd for
C39H33O4Si4F20 [M-CH3]+ : 1057.1136, Found: 1057.1183.
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Ying, B.; Jiajian, P.; Yingqian, H.; Jiayun, L.; Huayu, Q.;
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(3e) 1H NMR (300 MHz, CDCl3): ꢀ -0.03-0.02 (m, 12H, Si-CH3),
0.19 (s, 36H, Si(CH3)3), 0.52 (t, J=7.9 Hz, 8H, Si-CH2), 1.52-1.68 (m,
8H, CH2-CH2-Ph), 2.5 (t, J=7.25 Hz, 8H, CH2-Ph), 3.73 (s, 12H,
OCH3), 6.45-6.75 (m, 12H, CH-Ar);13C NMR (75 MHz, CDCl3): ꢀ -
0.91 (Si-CH3), 0.00 (Si-(CH3)3), 16.61 (Si-CH2), 24.80 (CH2-CH2-
Ph), 38.68 (CH2-Ph), 55.14 (OCH3), 112.12, 120.10, 120.18 (CH-Ar),
135.90, 142.12, 150.20 (C-Ar); 29Si NMR: ꢀ -20.43, -20.45, -20.52, -
20.57 (Si-CH3), 19.62, 19.59 (Si-(CH3)3); HRMS Calcd for
C56H96O12Si8 [M]+ :1184.5055, Found:1184.504.
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a
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[9]
H
(1a) with D4 in the presence of Karstedt's catalyst is
representative. The Solution of allylbenzene (1a) (2.4 ml, 18.2
mmol) and Karstedt's catalyst (0,3 ꢃl of a 0.336 mol/l solution of
Pt/mole of olefin) in toluene (5 ml) was warmed to 40°C under
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