A novel route to chlorodimethylsilane

Article abstract of DOI:10.1139/v00-025

A new efficient laboratory method of preparation of chlorodimethylsilane (Cl(CH₃)₂SiH) has been elaborated, which is a modification of the Eaborn et al. method (34) and is based on a transsilylation reaction of substituted (amino)dimethylhydrosilanes, R₂NSiMe₂H (R₂ = Me₂, Et₂, (CH₂)_n, etc.) with dimethyldichlorosilane (Me₂SiCl₂). The reaction proceeds at reflux, at 70°C, preferably with an excess of Me₂SiCl₂. The most important feature of this novel method is a recovery of intermediate (amino)chlorodimethylsilanes (R₂NSiMe₂Cl), which can be again reduced to R₂NSiMe₂H. The transsilylation mechanism has been proven by reaction of (diethylamino)methylphenylsilane with Me₂SiCl₂. The products of this latter reaction are HMePhSiCl and R₂NSiMe₂Cl, thus a disproportionation mechanism has been excluded. New substituted bis(amino)dimethylsilanes ((R₂N)₂SiMe₂), (amino)dimethylchlorosilanes (R₂NSiMe₂Cl), and (amino)dimethylhydrosilanes (R₂NSiMe₂H) have been synthesized and characterized by NMR and IR.

Full text of DOI:10.1139/v00-025

1405
A novel route to chlorodimethylsilane
Jerzy J. ChruÑciel
Abstract: A new efficient laboratory method of preparation of chlorodimethylsilane (Cl(CH3)2SiH) has been elaborated,
which is a modification of the Eaborn et al. method (34) and is based on a transsilylation reaction of substituted
(amino)dimethylhydrosilanes, R2NSiMe2H (R2 = Me2, Et2, (CH2)n, etc.) with dimethyldichlorosilane (Me2SiCl2). The
reaction proceeds at reflux, at 70°C, preferably with an excess of Me2SiCl2. The most important feature of this novel
method is a recovery of intermediate (amino)chlorodimethylsilanes (R2NSiMe2Cl), which can be again reduced to
R2NSiMe2H. The transsilylation mechanism has been proven by reaction of (diethylamino)methylphenylsilane with
Me2SiCl2. The products of this latter reaction are HMePhSiCl and R2NSiMe2Cl, thus a disproportionation mechanism
has been excluded. New substituted bis(amino)dimethylsilanes ((R2N)2SiMe2), (amino)dimethylchlorosilanes (R2NSiMe2Cl),
and (amino)dimethylhydrosilanes (R2NSiMe2H) have been synthesized and characterized by NMR and IR.
Key words: chlorodimethylsilane, (CH3)2SiHCl, synthesis, new laboratory method, transsilylation mechanism.
Résumé : On a développé une nouvelle méthode de préparation du chlorodiméthylsilane, Cl(CH3)2SiH, efficace au
niveau du laboratoire. Il s’agit d’une modification de la méthode de Eaborn et al. (34) et elle est basée sur une réaction
de transsilylation de (amino)diméthylhydrosilanes substitués, R2NSiMe2H (R2 = Me2, Et2, (CH2)n, etc.). Avec le
diméthyldichlorosilane, Me2SiCl2. La réaction se produit à reflux, à 70°C, de préférence dans un excès de Me2SiCl2.
La caractéristique la plus importante de cette nouvelle méthode est la récupération des intermédiaires
(amino)chlorodiméthylsilanes, R2NSiMe2Cl2, qui peuvent être soumis à une nouvelle réduction pour donner du
R2NSiMe2H. On a démontré le mécanisme de transsilylation par la réaction du (diéthylamino)méthylphénylsilane avec
le Me2SiCl2. Les produits de cette dernière réaction sont le HMePhSiCl et le R2NSiMe2Cl qui permettent d’exclure la
possibilité d’une réaction de dismutation. On a synthétisé de nouveaux bis(amino)diméthylsilanes, (R2N)2SiMe2,
(amino)diméthylchlorosilanes, R2NSiMe2Cl, et (amino)diméthylhydrosilanes, R2NSiMe2H, que l’on a caractérisés par
RMN et IR.
Mots clés : chlorodiméthylsilane, (CH3)2SiHCl, synthèse, nouvelle méthode de synthèse, mécanisme de transsilylation.
[Traduit par la Rédaction] ChruÑciel 1411
Introduction
or hydropolysilanes (e.g., Si(SiMe2SiH)4 (24–27) and o-
(bisdimethylsilyl)benzene (28)).
Chlorodimethylsilane ((H)Me2SiCl) (CDMS) is a very
useful and valuable organosilicon monomer and reagent, bear-
ing two different functional groups: ϵSi-Cl and ϵSi-H. The
ϵSi-Cl bond can react with Grignard and organolithium re-
agents, or undergo alcoholysis and hydrolysis reactions. The
ϵSi-H group enables preparation of complex derivatives,
mainly through hydrosilylation reaction. HMe2SiCl finds
many synthetic applications in organosilicon synthesis and
silicone technology (2–6), as well as in general polymer
chemistry (7–12). Most often HMe2SiCl is used in a prepa-
ration of 1,1,3,3-tetramethyldisiloxane (HMe2SiOSiMe2H),
other Si-H terminated polysiloxanes (13–20), and multi-
functional hydrosiloxanes (e.g., Si(OSiMe2H)4 (11), octa(hy-
ridodimethylsiloxy)octasilsesquioxane (HMe2SiOSiO3/2)8 (21–23)),
Yields of HMe2SiCl in an industrial “direct process”
(from elemental silicon and methyl chloride) are poor, usu-
ally 0.1–1% (29–31), although, when H2 was added to the
methyl chloride gas phase, yields can be significantly im-
proved up to 8% (32), or 2.2–33% (33), depending on reac-
tion conditions.
Many synthetic methods lead to chlorodimethylsilane, but
some are unattractive due to expense and unavailability of
intermediates. In the present paper a new laboratory proce-
dure for preparation of HMe2SiCl is described, which is a
modification of the Eaborn et al. (34) method. The key of our
method is a transsilylation of substituted (amino)dimethyl-
hydrosilanes
Me2SiCl2.
R2NSiMe2H
with
dimethyldichlorosilane
Received September 21, 1999. Published on the NRC Research Press website on October 20, 2000.
This paper is dedicated to Professor Adrian G. Brook, very distinguished organosilicon and organic chemist, and my briliant
teacher, on the occasion of his 75th birthday. In 1982–83 Professor A.G. Brook gave me a chance to join his research group, at
the Department of Chemistry of the University of Toronto. In the Lash Miller Chemical Laboratories I had the pleasure to continue
studies on a very well known Brook rearrangement, work out some details of its mechanism, and discover a new silyl anion
rearrangement (1). I have learned a lot from Professor Adrian G. Brook, who opened for me a world of international science, and
I will be always grateful to him.
J.J. ChruÑciel. Institute of Polymers, Faculty of Chemistry, Technical University, 90-924 ºódï 40, Poland (e-mail: jchrusci@ck-
sg.p.lodz.pl).
Can. J. Chem. 78: 1405–1411 (2000)
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1406
Can. J. Chem. Vol. 78, 2000
with 170 mL of dry ether, after 4 h of reflux and an identical
work-up 37.9 g (63% yield) of Et2NSiMe2H was obtained.
Experimental
General procedures
All reactions were carried out under an atmosphere of dry
nitrogen. Most of the substrates and reaction products were
distilled through a Vigreux column (120 cm).
NMR spectra were determined with Tesla BS-487C
(80 MHz) and Bruker MSL-300 (300 MHz); ~10% solutions
of studied silanes in CCl4, CDCl3, or CD2Cl2 were used. In-
frared spectra were recorded for neat samples on a Carl
Zeiss Jena 75R spectrometer.
Reaction of (diethylamino)dimethylsilane with
dimethyldichlorosilane
(a) Into a 250 mL two-neck flask was placed 74.4 g
(0.567 mol) of (diethylamino)dimethylsilane and 74.0 g
(0.573 mol) of dimethyldichlorosilane. The reaction flask
was connected to a Vigreux column and heated to reflux. A
fraction of HMe2SiCl (containing traces of Me2SiCl2) was
continously distilled and collected to give 40.8 g (76%
yield) of HMe2SiCl (bp 36°C). Distillation of the reaction
flask residue gave 74.8 g (80% yield) of Et2NSiMe2Cl
(bp 152°C).
Reagents
Dimethyldichlorosilane (70.5–71.0°C) and methyltri-
chlorosilane (66°C) were purified by fractional distillation.
Diethylamine (POCh, Gliwice, Poland), triethylamine
(POCh), pyrrolidine (Aldrich), piperidine (Loba Chem.)
were dried with KOH (POCh) and purified by distillation
over small amounts of P2O5 (POCh). Dimethylamine (Fluka),
magnesium (POCh), and lithium aluminium hydride
(Aldrich) were used as received. Bromobenzene (POCh) was
distilled over CaH2 (Aldrich). Diethyl ether and tetra-
hydrofuran were dried with KOH and distilled over fresh so-
dium wire. Methylphenyldichlorosilane was prepared by a
Grignard method (35), from MeSiCl3 and PhMgBr, in ether,
and fractionally distilled (bp 103–104°C/20 mmHg).
(b) A similar reaction of 33.0 g (0.252 mol) of (diethyl-
amino)dimethylsilane was carried out with double excess of
dimethyldichlorosilane (61 mL, 0.573 mol). 20 mL of
Me2SiCl2 was added to a flask containing Et2NSiMe2H, the
reagents were heated to reflux under Vigreux column, and
the remaining amount of Me2SiCl2 was added dropwise at
reflux. Products were recovered by distillation: (i) 20.7 g
(87% yield) of HMe2SiCl (bp 36°C); and (ii) 37.7 g (90%
yield) of Et2NSiMe2Cl (bp 152°C) were obtained.
Preparation of bis(pyrrolidino)dimethylsilane
Into a four-neck 2.5 L sulphonation reactor, fitted with a
condenser and a mechanical stirrer, was added 126 mL (1.04
mol) of Me2SiCl2, 309 mL (2.22 mol) of Et3N, and 1800 mL
of dry ether. 175 mL (2.10 mol) of dry pyrrolidine was
added dropwise, within 2 h. A precipitate of triethylamine
hydrochloride was filtered off and washed with dry ether (3
× 100 mL). The ether was distilled off and the residue was
distilled to give [(CH2)4N]2SiMe2 (73% yield, bp 107–
110°C/15 mmHg).
Bis(diethylamino)dimethylsilane
Bis(diethylamino)dimethylsilane (142.2 g, yield 85%) was
prepared from 2.9 mol of diethylamine and 0.7 mol of
Me2SiCl2, in dry ether (36, 37). Solution of Me2SiCl2 was
added dropwise to a stirred solution of Et2NH in 1300 mL of
Et2O, followed by reflux for 7 h. The reaction mixture was
left overnight. A precipitate of diethylamine hydrochloride
was filtered off and washed with dry ether. The product was
fractionally distilled (bp 86°C/20 mmHg).
Preparation of (pyrrolidino)dimethylchlorosilane
(a) Into a 500 mL four-neck flask, fitted with a condenser
and a mechanical stirrer, was placed 90.9 g (0.458 mol) of
bis(pyrrolidino)dimethylsilane. The substrate was cooled to
–10°C and 56 mL (2.10 mol) of Me2SiCl2 was added
dropwise, within 2 h. Stirring was continued at –5°C for 4 h
and reaction mixture was left overnight. Products were frac-
Preparation of (diethylamino)dimethylchlorosilane
Into a 500 mL four-neck flask, fitted with a condenser and
a mechanical stirrer, was placed 116.3 g (0.575 mol) of
bis(diethylamino)dimethylsilane. Stirring was turned on and
the substrate was cooled down to –5°C. 70 mL (0.578 mol)
of Me2SiCl2 was added dropwise from an addition funnel, at
–5°C, within 2 h. The cooling bath was removed and stirring
was continued at room temperature for 6 h. The products
were fractionally distilled to give 152.4 g (80% yield) of
Et2NSiMe2Cl (bp 152°C) (36, 37).
tionally distilled to give 123.1
g (82% yield) of
(CH2)4NSiMe2Cl (bp 80–81°C/40 mmHg).
(b) Into a four-neck 1.5 L sulphonation reactor, fitted with
a condenser and mechanical stirrer, was added 124 mL (1.02
mol) of Me2SiCl2, 139 mL (1.00 mol) of Et3N, and 900 mL
of dry ether. 83.5 mL (1.00 mol) of dry pyrrolidine was
added dropwise, within 2 h. Reaction mixture was stirred
and refluxed for 2 h, and cooled to room temperature.
Triethylamine hydrochloride was filtered off and washed
with dry ether (2 × 150 mL). Ether was distilled off and a
residue was distilled to give 72.8 g (44% yield) of
(CH2)4NSiMe2Cl (bp 60–62°C/15 mmHg).
Preparation of (diethylamino)dimethylsilane
(a) Into a 500 mL four-neck flask, fitted with a condenser
and a mechanical stirrer, was placed 10.63 g (0.28 mol) of
LiAlH4 and 250 mL of dry ether. 148.5 g (0.90 mol) of
(diethylamino)dimethylchlorosilane in 80 mL of dry ether
was added dropwise from an addition funnel, within 1.5 h.
The reaction mixture was refluxed for 2.5 h, and cooled to
room temperature. Solids were filtered off and washed with
dry ether. Fractional distillation of the filtrate gave 94.0 g
(80% yield) of Et2NSiMe2H (bp 110–111°C).
Preparation of (pyrrolidino)dimethylsilane
Into a 500 mL four-neck flask, fitted with a condenser and
a mechanical stirrer, was placed 7.50 g (0.197 mol) of
LiAlH4 and 200 mL of dry ether. 64.3 g (0.393 mol) of
(CH2)4NSiMe2Cl in 70 mL of dry ether was added dropwise,
within 40 min. The reaction mixture was refluxed for 4 h,
(b) Similarly, from 5.43 g (0.14 mol) of LiAlH4 and
75.7 g (0.46 mol) of (diethylamino)dimethylchlorosilane,
© 2000 NRC Canada

ChruÑciel
1407
cooled to room temperature, and left overnight. Solids were
filtered off, washed with dry ether. The filtrate was fraction-
ally distilled to give an ether fraction and 21.8 g (43% yield)
of (CH2)4NSiMe2H (bp 47–48°C/40 mmHg).
4.88 (sept., 1H, Si-H); in CCl4: 0.45 (d, J = 3.0 Hz, 6H,
(CH3)2Si), 4.80 (sept., J = 3.0 Hz, 1H, Si-H).
Et2NSiMe2Cl
Boiling point 152–154°C. 1H NMR: 0.38 (s, 6H, (CH3)2Si),
0.98 (t, J = 7 Hz, 6H, CH3-C), 2.85 (q, J = 7 Hz, 4H, CH2-N).
Reaction of (pyrrolidino)dimethylsilane with
dimethyldichlorosilane
Into a 250 mL two-neck flask was placed 18.1 g (0.14
mol) of (pyrrolidino)dimethylsilane and 34 mL (0.28 mol) of
dimethyldichlorosilane. The reaction flask was heated to re-
flux, and HMe2SiCl (with traces of Me2SiCl2) was
continously distilled off through a Vigreux columnto give
9.0 g (68% yield) of HMe2SiCl (bp 36°C). Distillation of the
residue gave (CH2)4NSiMe2Cl (17.1 g, 74% yield; bp 80–
81°C/40 mmHg).
Et2NSiMe2(H)
Boiling point 111–112°C. IR (neat (cm–1)): 2120 (Si-H).
1H NMR (300 MHz, CDCl3, δ (ppm)): 0.185 (d, 6H, J =
2.79 Hz, (CH3)2Si), 1.11 (t, 6H, J = 7.14 Hz, CH3-C), 2.65
(q, 4H, J = 7.15 Hz, CH2-N), 4.68 (sept., 1H, J = 2.78 Hz,
Si-H). 13C NMR: –1.49 (s, CH3-Si), 15.63 (s, CH3), 41.00 (s,
CH2-N). 29Si NMR: –7.77 (s).
Et2NSiMePhCl
Boiling point 136–140°C/25 mmHg, 108–110°C/5 mmHg.
n2D0 1.5073. IR (neat (cm–1)): 3068, 1800–2000, 1588 (Ph),
1426 (Si-Ph), 1253 (Si- CH3), 2966, 2927, 2866 (C-H aliphat.),
1202, 1166, 1055 (C-N), 1028, 931 (Si-N), 640, 460, 413
Preparation of (diethylamino)methylphenylchlorosilane
Into a 1.5 L four-neck reactor, fitted with a condenser and
a mechanical stirrer, was placed 116.3 mL (0.72 mol) of
methylphenyldichlorosilane and 900 mL of dry ether.
151 mL (1.46 mol) of Et2NH was added dropwise, within
5 h, followed by reflux for 2 h. On the next day a precipitate
of Et2NH·HCl was filtered off (under nitrogen) and washed
three times with ether. After removal of ether, the liquid resi-
1
(Si-Cl). H NMR (80 MHz, CCl4, δ (ppm)): 0.79 (s, 3H,
CH3-Si), 1.21 (t, J = 6.4 Hz, 6H, CH3-C), 3.08 (q, J =
6.4 Hz, 4H, CH2-N), 7.47–7.65 (m, 3H (Ph, m-, p-)), 7.8–8.0
(m, C-H (Ph, o-)). 13C NMR (300 MHz, CDCl3, δ (ppm)):
1.63 CH3-Si, 15.12 CH3-C, 39.37 CH2-N, 128.06, 130.06,
134.32, 135.14 (Ph). Anal. calcd. (%): C 57.99, H 7.96, N
6.14, Cl 15.56; found (%): C 57.59, 57.59, H 8.02, 8.14, N
5.83, 5.63, Cl 15.16, 15.38.
due was distilled to give 130.2
g (79% yield) of
Et2NSiMePhCl (bp 108–110°C/5 mmHg).
Preparation of (diethylamino)methylphenylsilane
Into a 0.5 L three-neck flask, fitted with a condenser and a
mechanical stirrer, was placed 5.50 g (0.145 mol) of LiAlH4
and 90 mL of dry THF. 65.8 g (0.289 mol) of (diethyl-
amino)methylphenylchlorosilane in 70 mL of dry THF was
added dropwise, within 30 min. The reaction mixture was
refluxed for 4 h, and cooled to room temperature. Solids
were filtered off and washed with dry pentane (3 × 30 mL).
Solvents were removed and the residue fractionally distilled
Et2NSiMePh(H)
Boiling point 115–117°C/21 mmHg, 86–89°C/5 Tr. nD20
1.4969. IR (neat (cm–1)): 3067, 1800–2000, 1591 (Ph), 1428
(Si-Ph), 1252 (Si- CH3), 2965, 2927, 2864 (C-H aliphat.),
2126, 2085 (Si-H), 1211, 1180, 1065 (C-N), 1028, 931 (Si-
1
N), 1030, 930 (Si-N). H NMR (80 MHz, CCl4, δ (ppm)):
0.33 (d, J = 3.2 Hz, 3H, CH3-Si), 0.94 (t, J = 7 Hz, 6H,
CH3-C), 2.82 (q, J = 7 Hz, 4H, CH2-N), 4.80 (q, J = 3.2 Hz,
1H, Si-H), 7.25 (m, 3H (Ph, m-, p-)), 7.50 (m, C-H (Ph, o-)).
Anal. calcd. (%): C 68.33, H 9.90, N 7.24; found (%): C
67.63, 67.56, H 9.86, 9.89, N 6.67, 6.83.
to give 7.5 g of MePhSiH2 (bp 25–26°C/5 mmHg; nD20
=
1.5051 (Lit. (38) value: 1.5058) and 52.2 g (58% yield) of
Et2NSiMePhH (bp 87–90°C/5 mmHg).
Reaction of (diethylamino)methylphenylsilane with
dimethyldichlorosilane
HMePhSiCl
Into a 250 mL two-neck flask was added 13.75 g (0.071
mol) of (diethylamino)methylphenylsilane. 17 mL (0.140
mol) of Me2SiCl2 was added dropwise at ~30°C. Reaction
mixture was heated to reflux and then fractionally distilled
through a Vigreux column. Four fractions were collected and
Boiling point 174–176°C, bp 92–95°C/65 mmHg. n2D0 1.5073.
IR (neat (cm–1)): 2170 (Si-H). H NMR (80 MHz, CDCl3, δ
(ppm)): 0.65 (d, J = 3.4 Hz, 3H, CH3-Si), 5.25 (q, J =
3.4 Hz, 1H, Si-H), 7.35 (m (t), 3H, Ph (m-, p-), 7.55 (m (d),
2H, Ph (o-)).
1
1
analyzed by means of H NMR (and IR): (1) bp 69–72°C
(11.5 g, Me2SiCl2); (2) bp 82–86°C/63 mmHg (4.9 g, ~95%
of Et2NSiMe2Cl and ~5% of HMePhSiCl); (3) bp 97–
115°C/65 mmHg (7.2 g, 35% of Et2NSiMe2Cl and 65% of
HMePhSiCl); (4) bp 130–140°C/64 mmHg (7.0 g, 70% of
Et2NSiMePhH (conversion 64.4%)); and 30% of
HMePhSiCl). Contents of the above fractions are based on
[(CH2)4N]2SiMe2
1
Boiling point 107–110°C/15 mmHg. n2D0 1.4682. H NMR
(80 MHz, CCl4, δ (ppm)): 0.24 (s, 6H, (CH3)2Si), 1.46 (m,
4H, (CH2)2), 2.73 (m, 4H, (CH2)2N). 13C NMR (300 MHz,
CDCl3, δ (ppm)): –3.33 CH3-Si, 26.61 (CH2)2, 46.73
(CH2)2N. Anal. calcd. (%): C 60.54, H 11.18, N 14.12, Si
14.16; found (%): C 60.63, 60.71, H11.31, 11.31, N 13.54,
13.54, Si 14.10.
1
integrations of their H NMR spectra (80 MHz, in CCl4).
Analytical data for the products
(CH2)4NSiMe2Cl
Boiling point 80–81°C/40 mmHg, 60–62°C/15 mmHg.
HMe2SiCl
1
Boiling point 36.0°C. IR (neat (cm–1)): 2170 (Si-H). H
n20D 1.4533. 1H NMR (80 MHz, δ (ppm)) in CCl4: 0.44 (s,
NMR (80 MHz, δ (ppm)), in CDCl3): 0.50 (d, 6H, (CH3)2Si),
© 2000 NRC Canada

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Can. J. Chem. Vol. 78, 2000
6H, (CH3)2Si), 1.75 (quintette, J = 3.6 Hz, 4H, (CH2)2), 3.01(m, J = 6.4 Hz, 4H, (CH2)2N); in CDCl2: 0.44 (s, 6H, (CH3)2Si),
1.36 (quintette, J = 4.3 Hz, 4H, (CH2)2), 2.28 (m, J = 6.4 Hz, 4H, (CH2)2N).
(CH2)4NSiMe2(H)
Boiling point 47–48°C/40 mmHg, 59–63°C/15 mmHg. IR (neat (cm–1)): 2960, 2869, 2820, 1591 (C-H), 2120, 2074 (Si-H),
1457, 1420, 1352 (C-H, CH3), 1252 (Si- CH3), 1125, 1200, 1080 (C-N), 896, 835 (Si-N), 764, 628 (Si-C). 1H-NMR (80 MHz,
CDCl2, δ (ppm)): 0.07 (d, J = 4.6 Hz, 6H, (CH3)2Si), 1.22 (quintette, J = 4.6 Hz, 4H, (CH2)2), 2.11 (m, 4H, (CH2)2N), 3.14
(sept., J = 4.3 Hz, 1H, Si-H). Anal. calcd. (%): C 55.74, H 11.70, N 10.83; found (%): C 54.35, 54.21, H 11.33, 11.21, N
10.07, 9.95.
Results and discussion
Since yields of chlorodimethylsilane obtained in a direct Rochow and Müller process are very low, many attempts have
been made to find new efficient synthetic methods, especially useful on a laboratory scale. HMe2SiCl has been prepared by
the following methods: (i) the direct synthesis from elemental silicon and methyl chloride (29–33, 39–44); (ii) Grignard reac-
tion between MeHSiCl2 and MeMgBr (45); (iii) selective reduction of dimethyldichlorosilane Me2SiCl2 (DDS) with Na3AlH6,
NaH, NaBH4, LiAlH4 (46–49), Et3Al (50), or Me2SiCl(OMe) with i-Bu2AlH (51), and Me2NSiMe2Cl with LiAlH4 (followed
by cleavage of the intermediate silane with HCl) (34); (iv) disproportionation of hydrochlorosilanes (52) or
organohydrosilanes and -siloxanes with chlorosilanes (53–59); (v) cleavage of HMe2SiOSiMe2H with HCl (60, 61), HCl and
AlCl3 (62), BCl3 (63), and polymethylhydrolsiloxanes with Me2SiCl2, catalyzed by BF3, nBu4NCl, BCl3 and HMPT (64); and
with MeSiCl3, Me2SiCl2, PhSiCl3, catalyzed by HMPT and HCl (65); (vi) photolytic cleavage of polydimethylsilanes (66) and
Me3SiMe2SiCl (67) with HCl; cleavage of disilanes with HCl towards phosphine–nickel complexes (68) and hydrogenation of
chlorodisilanes obtained from the direct process, with copper catalysts (69) and phosphine–nickelocene (and nickel) com-
plexes (70, 71); (vi) selective (and quantitative) chlorination of Me2SiH2 with SnCl4 (72).
All of these procedures have limitations. Mainly due to safety precautions, the application of metal hydrides is limited to a
relatively small scale. According to Eaborn (2) partial reduction of organohalogenosilanes with LiAlH4 is not possible. Reduc-
tions of Me2SiCl2 with NaH afforded low yields of HMe2SiCl: 11–17% (46) or 38% (at 150°C) (47). Reduction of Me2SiCl2
with Et3Al, in c-C6H12, at 500°C, requires very short reaction time (1 s) and gives 17.7% of CDMS (50). Although reduction
of DDS with i-Bu2AlH, carried out at high temperature (at 330°C), gave 76% of CDMS (73). Also reaction of Me2Si(OMe)Cl
with i-Bu2AlH, at –23°C, gave good, 83% yield of CDMS. Similar reduction of DDS with NaBH4 in HMPT, at 50°C, within
2 h, gave 71% yield of HMe2SiCl (50). The symmetrical 1,1,3,3-tetramethyldisiloxane cannot be recommended as a substrate
for the preparation of chlorodimethylsilane, and HMe2SiOSiMe2H is synthesized from HMe2SiCl. Synthesis of
polydimethylsilanes is difficult, and the photolysis is limited to a small scale, requiring a special apparatus. The gaseous
dimethylsilane and SnCl4 are expensive substrates as well. The above reasons encouraged us to search for a new laboratory
method of synthesis of HMe2SiCl.
Our new method of preparation of Me2SiHCl (74, 75) is a modification of the Eaborn et al. method (34), which involves the
reduction of the Si—Cl bond to the Si—H bond, in the presence of the Si—N bond:
[1]
and a subsequent cleavage of of the Si-N bond with gasous hydrogen chloride
[2]
Our method is based on reaction of (dialkylamino)dimethylhydrosilanes (R2NSiMe2H) with dimethyldichlorosilane
[3]
© 2000 NRC Canada

ChruÑciel
1409
[4]
As a single step, the yield of chlorodimethylsilane was in the range 76–87%, with respect to Et2NSiMe2H. The overall yield
of four-step (or three-step) reaction, including synthesis of Et2NSiMe2Cl (see rxns. [4]–[6]), its reduction to
(diethylamino)dimethylsilane, followed by reaction (3) with Me2SiCl2, ranged from 45 to 58%. However, intermediate
Et2NSiMe2Cl and other (dialkylamino)dimethylchlorosilanes R2NSiMe2Cl were recovered, in a high yield (80–90%), and may
be used again for synthesis of HSiMe2Cl, after reduction with LiAlH4. When we are considering the recovery of R2NSiMe2Cl,
the overall yields of HMe2SiCl are much higher (within the range of 150–240% (!!!)), than yields calculated for the single
step reaction (3).
The starting (amino)chlorosilanes can be prepared either in two steps (36, 37)
[5]
or in one step (36, 37)
[6]
Alternatively a secondary amine can be used as an HCl acceptor.
(Dialkylamino)chlorodimethylsilanes were reduced with excess LiAlH4 in dry ether (or THF) at reflux. Yields of
R2NSiMe2H depend on reaction time, and amount of reducing agent. Longer reaction times lead to lower yields, presumably
due to reduction of Si—N bond; for Et2NSiMe2H: 80% after 2.5 h and 63% after 4 h (crude yields). Yields of reduction of
(CH2)4NSiMe2Cl with LiAlH4 were lower than in reduction of Et2NSiMe2Cl. Presumably a steric hinderance in this case di-
minishes the cleavage of the Si—N bond as a side reaction. In the case of reduction of Et2NSiMePh(Cl), small amounts of
MePhSiH2 were isolated. It has been reported (76), that (dimethylamino)trichlorosilane and bis(dimethylamino)dichlorosilane
are reduced to monosilane SiH4, as a result of the cleavage of Si—N bonds.
The final step of the synthesis of HMe2SiCl, reaction of substituted (amino)dimethylchlorosilanes with Me2SiCl2, was car-
ried out at reflux (~70°C), using a fractionation Vigreux column. During dropwise addition of Me2SiCl2 to Et2NSiMe2H,
crude HMe2SiCl was distilled off. When stoichiometric amounts of both substrates were used the reaction began at reflux and
it was quite vigorous (a bleeding of the column appeared); thus 76% of CDMS was obtained. With excess Me2SiCl2, the yield
of HMe2SiCl reached 87%. Other substituted (amino)dimethylsilanes (R2 = Me2, n-Bu2, (CH2)5), can be used for the synthesis
of HMe2SiCl, in the same manner.
Reaction mechanism
The Si—N bond (bond energy: 335 kJ/mol (77)) is slightly weaker than that of the Si—H bond (377 kJ/mole (78)). Thus it
seems that reaction of (amino)dimethylsilanes (R2NSiMe2(H)) with Me2SiCl2 proceeds through a transsilylation mechanism,
with a cleavage of the Si—N bond, rather than through a disproportionation mechanism, which would require breaking of the
Si—H bond, in the aminosilane substrate. To prove this mechanism, Et2NSiMePhH was reacted with Me2SiCl2 to yield
methylphenylchlorosilane (HMePhSiCl) and Et2NSiMe2Cl
[7]
The formation of HMePhSiCl confirms that the reaction of Et2NSiMePh(H) with Me2SiCl2 proceeds through the
transsilylation mechanism, with the cleavage of the Si—N bond. The alternative disproportionation process, which would re-
quire breaking of the Si—H bond, would give Et2NSiMePhCl and HSiMe2Cl, as reaction products. HSiMe2Cl was not de-
tected in products of the above reaction. Moreover in disproportionation reactions of chlorosilanes with hydrosilanes the
presence of various catalysts (e.g., AlCl3 or H2PtCl6) is necessary. So far we have not conducted comprehensive mechanistic
studies of reaction of (amino)hydrosilanes with chlorosilanes. It seems quite obvious, that this interesting and useful reaction
is a next example of the nucleophilic displacement at silicon and may be catalyzed by traces of amine hydrochlorides or
(amino)silanes hydrochlorides, which could be formed in the presence of traces of moisture, during the course of synthesis.
© 2000 NRC Canada

1410
Can. J. Chem. Vol. 78, 2000
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Conclusions
(1.) The new efficient laboratory method of the synthesis
of HMe2SiCl has been described, based on reaction of
(dialkylamino)chlorodimethylsilanes (R2NSiMe2H) with
dimethyldichlorosilane.
(2.) The main features of this novel method are as fol-
lows: (a) the intermediate products (dialkylamino)dimethyl-
chlorosilanes (R2NSiMe2Cl) are recovered in high yields and
are reused, in the synthesis cycle by reduction with LiAlH4
to give R2NSiMe2H; (b) a very simple procedure and good
yields of HMe2SiCl are obtained (usually above 80%).
(3.) The reaction of substituted (amino)dimethylchloro-
silanes with Me2SiCl2 proceeds through a nucleophilic sub-
stitution (transsilylation mechanism), and was confirmed by
reaction of Et2NSiMePhH with Me2SiCl2. Products of this
reaction are: HMePhSiCl and Et2NSiMe2Cl.
(4.) New compounds, not described in a literature, have
been prepared: (i) bis(pyrrolidino)dimethylsilane [(CH2)4N]2SiMe2,
from pyrrolidine and Me2SiCl2, in ether, in the presence of
Et3N; (ii) (pyrrolidino)dimethylchlorosilane (CH2)4NSiMe2Cl,
from reactions of bis(pyrrolidino)dimethylsilane or
pyrrolidine with Me2SiCl2, in ether (in the presence of Et3N,
in the latter case); (iii) (diethylamino)methylphenylchloro-
silane, from diethylamine and MePhSiCl2, in ether;
(iv) (diethylamino)methylphenylsilane, by reduction of
Et2NSiMePh(Cl) with LiAlH4, in THF.
15. J. ChruÑciel. Polimery (Warsaw), 44, 462 (1999), and
refs. therein.
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(5.) (Pyrrolidino)dimethylsilane was synthesized by re-
duction of (pyrrolidino)dimethylchlorosilane (CH2)4NSiMe2Cl
with LiAlH4, in ether.
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Acknowledgement
This work was supported by the Polish State Committee
for Scientific Research under the Research Project
1359/T09/95/08.
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