Tris(dimethylsilyl)methyllithium: A reagent for the synthesis of vinylbis(silanes) containing Si-H functional groups

Article abstract of DOI:10.1080/00397910802563412

Reactions between a series of nonenolisable aldehydes and tris(dimethylsilyl)methyllithium, (HMe2Si)3CLi, are described. The Peterson reaction takes place readily to give vinylbis(silanes). Moreover, styrene and butyl acrylate 1:1 copolymer (P), prepared

Full text of DOI:10.1080/00397910802563412

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Tris(dimethylsilyl)methyllithium:
A Reagent for the Synthesis
of Vinylbis(silanes) Containing
Si–H Functional Groups
Kazem D. Safa a , Akbar Hassanpour a & Shahin
Tofangdarzadeh a
a Organosilicon Research Laboratory, Faculty of
Chemistry , University of Tabriz , Tabriz, Iran
Published online: 02 Apr 2009.
To cite this article: Kazem D. Safa , Akbar Hassanpour & Shahin Tofangdarzadeh
(2009) Tris(dimethylsilyl)methyllithium: A Reagent for the Synthesis of
Vinylbis(silanes) Containing Si–H Functional Groups, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 39:9,
1601-1610, DOI: 10.1080/00397910802563412
To link to this article: http://dx.doi.org/10.1080/00397910802563412
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Synthetic Communications1, 39: 1601–1610, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802563412
Tris(dimethylsilyl)methyllithium: A Reagent
for the Synthesis of Vinylbis(silanes)
Containing Si–H Functional Groups
Kazem D. Safa, Akbar Hassanpour, and Shahin Tofangdarzadeh
Organosilicon Research Laboratory, Faculty of Chemistry,
University of Tabriz, Tabriz, Iran
Abstract: Reactions between a series of nonenolisable aldehydes and tris(di-
methylsilyl)methyllithium, (HMe2Si)3CLi, are described. The Peterson reaction
takes place readily to give vinylbis(silanes). Moreover, styrene and butyl acrylate
1:1 copolymer (P), prepared by use of a,a0-azobis(isobutyronitrile) (AIBN) as an
initiator in toluene at 70 ꢀ 1ꢁC, was formylated via direct electophilic substitution
by methyl dichloromethyl ether (Cl2CHOMe) in the presence of tin(IV) chloride
(SnCl4) in nitrobenzene (PhNO2) as solvent. The reaction of (HMe2Si)3CLi with
formyl groups on the side chains of the copolymer led to new macromolecules
bearing vinylbis(silane) functional groups.
Keywords: Functionalized copolymer, Peterson reaction, Si–H functional group,
tris(dimethylsilyl)methyllithium, vinylbis(silanes)
INTRODUCTION
Vinylsilanes are useful reagents in organic synthesis because the C(sp2)-Si
bonds undergo numerous transformations.[1] Vinylbis(silanes), which
show a number of similar properties, have received significant attention
as potential synthons in organic and organosilicon synthesis.[2] The
Received August 20, 2008.
Address correspondence to Kazem D. Safa, Organosilicon Research
Laboratory, Faculty of Chemistry, University of Tabriz, 51664 Tabriz, Iran.
E-mail: dsafa@tabrizu.ac.ir
1601

1602
K. D. Safa, A. Hassanpour, and S. Tofangdarzadeh
potential of the vinylbis(silanes) as precursors for the preparation of
ketones and isoxazoline derivatives as well as a variety of important
organosilicon reagents, such as acylsilanes, epoxysilanes, and silanols,
has stimulated their development. In contrast to vinylsilanes, however,
vinylbis(silanes) are relatively unexplored.[3]
Organosilyl groups of various sizes have been incorporated into
polymer structures to modify the polymer properties, and this has
generated much new research.[4]
Peterson-type olefination is a useful method for the preparation of
alkenes from carbonyl compounds.[5] However, no Si–H functionalized
vinylbis(silanes) bearing heterocycle rings have hitherto been prepared
by this method. In the present work, we describe the synthesis of
some vinylbis(silane) derivatives bearing Si–H functional groups, the
preparation of acrylic copolymers of styrene bearing –CHO groups,
and conversion of these to new copolymers containing vinylbis(silanes).
RESULTS AND DISCUSSION
The precursor tris(dimethylsilyl)methane, (HMe2Si)3CH, has been conve-
niently prepared by the reaction of CHBr3 and Mg with HMe2SiCl in
tetrahydrofuran (THF). The generation of (HMe2Si)3CLi was easily
accomplished by deprotonation of (HMe2Si)3CH by lithium diisopropyl-
amide (LDA) in THF.[6] The direct reaction of (HMe2Si)3CLi with
benzaldehyde, 3-pyridinaldehyde, 2-thiophenealdehyde, 5-methylfurfural,
2-naphthaldehyde, cinnamaldehyde, and terephthaldehyde led to the
corresponding vinylbis(silanes) (Table 1). The reaction can also be used
for the synthesis of a bisaldehyde (entry 7) and a dienylsilane (entry 6).
The Si–H infrared (IR) stretching frequency for 2a was at 2115 cmꢂ1
.
The 1H NMR spectrum of 2a showed two doublets at 0.19 and 0.31 ppm
assigned to the two methyl groups on each silicon atom, one singlet at
7.83 ppm assigned to a proton on the b-carbon, and one septet in the
range 4.30–4.34 ppm for the Si–H proton, resulting from vicinal coupling.
All these results clearly show the formation of bisvinyl(silane) 2a.
To study the analogous reaction with copolymer containing
formyl groups in the side chain, a random copolymer (P) of styrene
and butyl acrylate was synthesized by free radical polymerization using
a,a-azobis(isobutyronitrile) (AIBN) as an initiator. To introduce formyl
groups in the side chain, P was treated with methyl dichloromethyl ether
(Cl2CHOMe) in the presence of tin(IV) chloride (SnCl4) (Scheme 1)[7] in
CH2Cl2 or PhNO2 at room temperature. PhNO2 appears to be more sui-
table than CH2Cl2 because of the completion of the hydrolysis step of the
formylation reaction.

Tris(dimethylsilyl)methyllithium
1603
Table 1. Vinylbis(silanes) from aromatic aldehyds
Yielda
(%)
Entry
1
Substrate
Product
74
2
59
3
4
62
70
5
63
(Continued )

1604
K. D. Safa, A. Hassanpour, and S. Tofangdarzadeh
Table 1. Continued
Yielda
(%)
Entry
6
Substrate
Product
68
7
58
aYields calculated by GC–mass spectroscopy.
The percentage of formyl groups on copolymer PCHO was
1
determined from the H NMR spectrum (Fig. 1a).[8] The molar fraction
of the formylated styrene was calculated from the ratio of the peaks at
9.89 ppm assigned to aldehyde groups to the total area between 6.59
and 7.51 ppm, attributed to the nine aromatic protons of the formylstyr-
ene and styrene. The molar composition of copolymer P was determined
by the same method. The results are listed in Table 2.
A solution of copolymer PCHO was treated with an excess of
(HMe2Si)3CLi in THF. As for simple aromatic aldehydes, Peterson
olefination gave a new macromolecule bearing Si–H functional and reac-
tive groups (Scheme 1). The spectroscopic results indicate that the
Scheme 1.

Tris(dimethylsilyl)methyllithium
1605
Figure 1. 1H NMR spectra: (a) formylated copolymer PCHO and (b) Si–H bearing
copolymer PSiH
.
conversion of carbonyl groups into vinylbis(silane) on the side chain of
the PCHO was complete (see Fig. 1b). It is also noteworthy that because
of high reactivity of the formyl group, the carbonyl group of the ester
remained unchanged during the reaction.
Table 2. Molar composition of all copolymers
Sample
BuAc (%)a
St (%)
St-CHO (%)
St-SiH (%)
P
PCHO
PSi-H
26
26
26
74
61.5
61.5
—
12.5
—
—
—
12.5
aAll the molar compositions were calculated from the corresponding 1H NMR
spectra.

1606
K. D. Safa, A. Hassanpour, and S. Tofangdarzadeh
EXPERIMENTAL
Solvents and Reagents
Reactions involving organolithium reagents were carried out under dry
argon. Solvents were dried by standard methods. Substrates for prepara-
tion of tris(dimethylsilyl)methyllithium, namely HSiMe2Cl (Merck), Mg
(Merck), CHBr3 (Merck), all aldehydes (Merck), Cl2CHOMe (Merck),
and SnCl4 (Merck), were used as received. For the synthesis of LDA,
n-BuLi (Fluka 1.6 M) was titrated by diphenylacetic acid.
Spectra
1
The H NMR and 13C NMR were recorded on a Bruker Fourier trans-
form (FT) 400-MHz spectrometer at room temperature with CDCl3 as
a solvent. The mass spectra were obtained with a GC-Mass Agilent quad-
rupole mode 5973 N instrument, operating at 70 eV. The FT-IR spectra
were recorded on a Bruker-Tensor 270 spectrometer. Elemental analyses
were carried out with an Elementar Vario EL III instrument.
Preparation of the Formylated Polymers (PCHO
)
The dissolved polymer in nitrobenzene was treated with Cl2CHOMe in
ꢁ
the presence of SnCl4 (molar ratio 1:1:2, 20–25 C, 3 h). After hydrolysis
and washing with water–1,4-dioxane–HCl, the organic layer was poured
into cooled methanol to precipitate the formylated polymer PCHO
.
FT-IR (KBr, cmꢂ1), 3033 (HC ¼), 2837, 2730 (CHO), 1690 (HCO),
1730 (O–CO); 1H NMR (400 MHz, CDCl3, ppm): d 0.84–2.12 (aliphatic),
3.5–3.7 (OCH2) 6.60–7.51 (aromatic), 9.89 (CHO).
Preparation of Polymer Bearing Vinylbis(silanes) (PSi–H
)
(HMe2Si)3CLi (15.8 mmol) was added dropwise with stirring to a
solution of copolymer PCHO (14 mmol) in THF at room temperature.
The reaction was quenched by adding a small amount of acidic methanol
after 2 h, and the reaction mixture was poured into cooled acidic metha-
nol to precipitate the polymer PSi–H. FT-IR (KBr, cmꢂ1), 3035 (HC ¼),
1
2108 (Si–H), 1251, 895 (Si–CH3); H NMR (400 MHz, CDCl3, ppm):
d 0.15–0.26 (SiMe2), 0.85–2.27 (aliphatic), 3.62 (OCH2), 4.03–4.11
(Si–H), 6.65–7.26 (aromatic).

Tris(dimethylsilyl)methyllithium
1607
General Procedure for Synthesis of Vinylbis(silanes)
A mixture of tris(dimethylsilyl)methyllithium (15.8 mmol) and aldehyde
(15 mmol) in ether (10 ml) was heated under reflux for 2 h, then poured
into water and extracted into ether. The organic layer was washed with
water and dried (Na2SO4). The solvent was evaporated to give a liquid,
which was separated by preparative thin-layer chromatography (TLC)
in n-hexane to give the 1,1-bis(silyl)-1-alkene.
Reaction of (HMe2Si)3CLi with Benzaldehyde (2a)
Colorless oil: Rf ¼ 0.95 (n-hexane); yield ¼ 74%; FT-IR (KBr, cmꢂ1),
1
2114 (Si–H), 1251, 898 (Si–CH3); H NMR (400 MHz, CDCl3, ppm): d
0.19 (d, 6H, 3JHH ¼ 3.82 Hz, SiMe2), 0.31 (d, 6H, 3JHH ¼ 3.68 Hz, SiMe2),
3
4.30–4.34 (septet, 2H, JHH ¼ 3.71, Si–H) 7.30–7.34 (m, 5H, Ph), 7.83 (s,
1H, HC ¼); 13C NMR (100 MHz, CDCl3, ppm): d ꢂ4.2, ꢂ3.3 (SiMe2),
125.3, 126.5, 127.1, 139.6, 140.0, 154.9 (Ph, C ¼ C); m=z (EI): 220
(15%, [M]þ), 205 (32%, [M-Me]þ), 161 (70%, [M–SiMe2H]þ), 143
(100%, [M–Ph]þ), 59 (18%, [SiMe2H]þ). Anal. calc. for C12H20Si2: C,
65.4; H, 9.1. Found: C, 65.7; H, 9.3.
Reaction of (HMe2Si)3CLi with 3-Pyridinaldehyde (2b)
Yellow oil: Rf ¼ 0.65 (n-hexane); yield ¼ 59%; FT-IR (KBr, cmꢂ1), 2112
1
(Si–H), 1255, 835 (Si–CH3); H NMR (400 MHz, CDCl3, ppm): d 0.09
3
3
(d, 6H, JHH ¼ 3.72 Hz, SiMe2), 0.21 (d, 6H, JHH ¼ 3.69 Hz, SiMe2),
3
4.17–4.24 (m, 2H, Si–H), 7.15–7.18 (dd, 1H, JHH ¼ 4.84 Hz, aromatic),
3
7.50 (d, 1H, JHH ¼ 7.81 Hz, aromatic), 7.63 (s, 1H, HC¼), 8.43 (d, 1H,
3JHH ¼ 4.75 Hz, aromatic), 8.47 (s, 1H, aromatic); 13C NMR (100 MHz,
CDCl3): d ꢂ4.3, ꢂ3.7 (SiMe2), 121.4, 133.9, 134.8, 14.1, 147.3, 148.1,
150.5 (aromatic, C ¼ C); m=z (EI): 222 (13%, [M]þ), 221 (100%, [M ꢂ
1]þ), 207 (5%, [M–Me]þ), 163 (15%, [M-SiMe2H]þ), 59 (20%, [SiMe2H]þ).
). Anal. calc. for C11H19Si2N: C, 59.5; H, 8.6; N, 6.3. Found: C, 59.7; H,
8.8; N, 6.2.
Reaction of (HMe2Si)3CLi with 2-Thiophenealdehyde (2c)
Dark brown oil: Rf ¼ 0.65 (n-hexane); yield ¼ 62%; FT-IR (KBr, cmꢂ1),
1
2113 (Si–H), 1250, 833 (Si–CH3); H NMR (400 MHz, CDCl3, ppm): d
0.33 (d, 6H, 3JHH ¼ 3.67 Hz, SiMe2), 0.37 (d, 6H, 3JHH ¼ 3.85 Hz, SiMe2),

1608
K. D. Safa, A. Hassanpour, and S. Tofangdarzadeh
3
4.32–4.38 (septet, 1H, JHH ¼ 3.67 Hz, Si–H), 4.64–4.70 (septet, 1H,
3JHH ¼ 3.85 Hz, Si–H), 7.07–7.09 (dd, 1H,3JHH ¼ 3.64 Hz, aromatic),
7.18 (d, 1H,3JHH ¼ 3.56 Hz, aromatic), 7.38 (d, 1H,3JHH ¼ 4.10 Hz, aro-
matic), 7.79 (s, 1H, HC ¼); 13C NMR (100 MHz, CDCl3): d ꢂ3.9, ꢂ3.8
(SiMe2), 125.1, 125.9, 128.0, 137.4, 143.2, 145.3 (aromatic, C ¼ C); m=z
(EI): 226 (30%, [M]þ), 211 (45%, [M-Me]þ), 167 (72%, [M-SiMe2H]þ),
143 (100%, [M-C4H3O]þ), 59 (16%, [SiMe2H]þ). Anal. calc. for
C10H18Si2S: C, 53.1; H, 8.0. Found: C, 53.4; H, 7.7.
Reaction of (HMe2Si)3CLi with 5-Methylfurfural (2d)
Brown oil: Rf ¼ 0.77 (n-hexane); yield¼ 70%; FT-IR (KBr, cmꢂ1), 2106
1
(Si–H), 1253, 896 (Si–CH3); H NMR (400 MHz, CDCl3, ppm): d 0.27
3
3
(d, 6H, JHH ¼ 3.52 Hz, SiMe2), 0.35 (d, 6H, JHH ¼ 3.76Hz, SiMe2), 2.34
(s, 3H, CH3), 4.26–4.31 (septet, 1H, 3JHH ¼ 3.36 Hz, Si–H), 4.37–4.43 (sep-
tet, 1H, 3JHH ¼ 3.73 Hz, Si–H), 6.05 (d, 1H,3JHH ¼ 3.04Hz, aromatic), 6.29
(d, 1H,3JHH ¼ 3.17 Hz, aromatic), 7.29 (s, 1H, HC¼); 13C NMR (100MHz,
CDCl3): d ꢂ4.2, ꢂ3.8 (SiMe2), 106.9, 111.7, 120.9, 131.8, 152.6 (aromatic,
C ¼ C); m=z (EI): 224 (55%, [M]þ), 209 (100%, [M-Me]þ), 165 (85%, [M-
SiMe2H]þ), 143 (40%, [M–C5H5O]þ), 59 (50%, [SiMe2H]þ). Anal. calc.
for C11H20Si2O: C, 58.9; H, 8.9. Found: C, 59.2; H, 9.1.
Reaction of (HMe2Si)3CLi with 2-Naphthaldehyde (2e)
Pale yellow oil: Rf ¼ 0.78 (n-hexane); yield ¼ 63%; FT-IR (KBr, cmꢂ1 2108
1
(Si–H), 1252, 825 (Si-CH3); H NMR (400MHz, CDCl3, ppm): d 0.4 (d,
3
3
6H, JHH ¼ 3.83Hz, SiMe2), 0.51 (d, 6H, JHH ¼ 3.68Hz, SiMe2), 4.54–
3
4.61 (septet, 2H, JHH ¼ 3.75, Si–H), 7.59–7.63 (m, 3H, aromatic), 7.93–
7.98 (m, 4H, aromatic), 8.14 (s, 1H, HC¼); 13C NMR (100MHz, CDCl3,
ppm): d ꢂ3.8, ꢂ3.1 (SiMe2), 125.0, 125.1, 125.3, 126.3, 126.4, 126.6, 127.1,
131.7, 131.9, 137.2, 140.6, 155.0 (aromatic, C ¼ C); m=z (EI): 270 (42%,
[M]þ), 255 (20%, [M-Me]þ), 211 (71%, [M–SiMe2H]þ), 195 (100%,
[M-Me-SiMe2H]þ), 127 (35%, [M-C10H7]þ), 59 (25%, [SiMe2H]þ). Anal.
calc. for C16H22Si2: C, 71.1; H, 8.1. Found: C, 71.5; H, 8.3.
Reaction of (HMe2Si)3CLi with Cinnamaldehyde (2f)
Yellow oil: Rf ¼ 0.65 (n-hexane); yield ¼ 68%; FT-IR (KBr, cmꢂ1), 2115
1
(Si–H), 1258, 896 (Si–CH3); H NMR (400MHz, CDCl3, ppm): d 0.31
3
3
(d, 6H, JHH ¼ 3.75Hz, SiMe2), 0.38 (d, 6H, JHH ¼ 3.80 Hz, SiMe2),

Tris(dimethylsilyl)methyllithium
1609
3
4.29–4.35 (septet, 1H, JHH ¼ 3.68Hz, Si–H), 4.58–4.64 (septet, 1H,
3JHH ¼ 3.86Hz, Si–H), 6.72-7.52 (m, 8H, aromatic, C¼ C); 13C NMR
(100 MHz, CDCl3): d ꢂ4.1, ꢂ3.4 (SiMe2), 125.7, 127.1, 127.6, 127.9,
132.4, 135.5, 135.9, 140.0, 144.7, 153.2 (aromatic, C ¼ C); m=z (EI): 246
(50%, [M]þ), 231 (100%, [M-Me]þ), 187 (15%, [M-SiMe2H]þ), 59 (52%,
[SiMe2H]þ). Anal. calc. for C14H21Si2: C, 68.3; H, 8.9. Found: C, 68.5;
H, 8.6.
Reaction of (HMe2Si)3CLi with Terephthaldehyde (2g)
Pale yellow oil: Rf ¼ 0.71 (n-hexane); yield ¼ 58%; FT-IR (KBr, cmꢂ1),
1
2110 (Si–H), 1251, 832 (Si-CH3); H NMR (400 MHz, CDCl3, ppm): d
3
3
0.23 (d, 12H, JHH ¼ 3.83 Hz, SiMe2), 0.33 (d, 12H, JHH ¼ 3.68 Hz,
SiMe2), 4.32–4.38 (m, 4H, Si–H), 7.32 (s, 4H, aromatic), 7.82 (s, 1H,
HC¼); 13C NMR (100 MHz, CDCl3): d ꢂ3.9, ꢂ3.3 (SiMe2), 126.8,
139.0, 140.4, 154.5 (aromatic, C ¼ C); m=z (EI): 362 (25%, [M]þ), 347
(15%, [M-Me]þ), 303 (30%, [M-SiMe2H]þ), 219 (40%, [M-C6H15Si2]þ),
143 (30%, [C6H15Si2]þ), 59 (50%, [SiMe2H]þ). Anal. calc. for
C18H34Si4: C, 59.7; H, 9.4. Found: C, 59.6; H, 9.5.
ACKNOWLEDGMENT
We thank Dr. J. D. Smith for helpful comments.
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