Stable trichlorosilane-pyridine adducts

Article abstract of DOI:10.1002/ejic.200800844

The prepapration, and first comprehensive spectroscopic and structural characterization of octahedral trichlorosilane adducts HSiCl₃(Rpy) ₂ with R = H, 4-CH₃, 4-C₆H₅, 3-Br, 4-CHCH₂, 4-C

Full text of DOI:10.1002/ejic.200800844

SHORT COMMUNICATION
DOI: 10.1002/ejic.200800844
Stable Trichlorosilane–Pyridine Adducts
Gerrit W. Fester,[a] Jörg Wagler,[a] Erica Brendler,[b] and Edwin Kroke*[a]
Keywords: Trichlorosilane / Hypercoordination / Solid-state NMR / Dismutation
The prepapration, and first comprehensive spectroscopic and
(218–223 pm) while the Si–N bonds (ca. 198 pm) are only
structural characterization of octahedral trichlorosilane ad- slightly longer than in the corresponding H2SiCl2(Rpy)2
ducts HSiCl3(Rpy)2 with R = H, 4-CH3, 4-C6H5, 3-Br, 4-
CHCH2, 4-C2H5, 4-C(CH3)3 and 4-N(CH3)2 is reported. The
products are surprisingly stable in the solid state and easily
obtained in high yield. Single-crystal X-ray diffraction analy-
sis of HSiCl3(3-Brpy)2 revealed relatively short Si–Cl bonds
adducts. Dismutation reactions were observed only in polar
solvents at elevated temperatures.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
ago.[2d] However, the reported characterisation included a
Si–H valence vibration at 2070 cm–1 and a powder dif-
fractogram, which was not further analysed. Interestingly,
the authors suggested that the pyridine molecules are in cis-
position to each other.
In some cases extraordinarily facile disproportionation
of hydridosilanes have been reported.[2f] Attempts to isolate
chelate complexes of trichlorosilane with chelate ligands
like 2,2Ј-dipyridine or 1,10-phenanthroline have been re-
ported, again by Wannagat et al. in the 1960s.[3] Only one
report describing the formation and structural characteriza-
tion of a chelate complex between HSiCl3 and tetramethyl-
ethylenediamine (tmeda) was published.[4]
Here we report the synthesis of octahedral trichloro-
silane–pyridine 1:2 adducts via careful direct reactions of
substituted pyridines with HSiCl3. The experiments have to
be performed at low temperatures in suitable solvents such
as toluene or hexane. The colorless solid 1:2 adducts are
obtained in good to excellent yields. They exhibit poor solu-
bility in most organic solvents.
Introduction
Trichlorosilane HSiCl3 belongs to the most important in-
dustrial silicon compounds. It is the key intermediate in the
so-called Siemens process used for the production of semi-
conductor-grade as well as solar-grade silicon. The pro-
duction capacities are currently strongly increased by many
companies due to the very fast growing demand for silicon
solar cells. Furthermore, trichlorosilane may be trans-
formed into numerous derivatives via hydrosilylation and/
or chlorine substitution.
It is known that many halosilanes of the type HnSiX4–n
–
in particular the highly reactive trichlorosilane – tend to
dismutate upon treatment with bases. These dismutation re-
actions are accompanied by the formation of Lewis acid-
base adducts (as intermediates) and driven by the formation
of silanes such as SiCl4 and SiH4 (Scheme 1).
Scheme 1. Dismutation of trichlorosilane to monosilane under base
influence.
Results and Discussion
Whereas octahedral adducts of tetrachlorosilane with
As a consequence of our work on octahedral adducts of
pyridines or related bases are easily formed, and many of dichlorosilane with substituted pyridines (Rpy)[5] we also
them have been comprehensively characterized,[1] most investigated the formation of the hexacoordinate com-
attempts to synthesize and isolate a trichlorosilane–pyridine pounds HSiCl3(Rpy)2, which exhibit various substitution
adduct or complexes with other Lewis bases failed.[2] Wan- patterns (R) at the pyridine donor molecule (py). These so-
nagat et al. synthesized HSiCl3(py)2 more than 40 years lid adducts were found to be stable at room temperature
(under inert atmosphere) and are directly accessible from
trichlorosilane and the respective pyridine in various sol-
vents.
In a representative reaction trichlorosilane (in aprotic
solvents such as n-hexane, toluene or THF) is mixed with
substituted pyridines to form compounds 1a–h (Scheme 2).
[a] Institut für Anorganische Chemie, TU Bergakademie Freiberg,
Leipziger Strasse 29, 09596 Freiberg, Germany
Fax: +49-3731-39-4058
E-mail: edwin.kroke@chemie.tu-freiberg.de
[b] Institut für Analytische Chemie, TU Bergakademie Freiberg,
Leipziger Strasse 29, 09596 Freiberg, Germany
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Stable Trichlorosilane–Pyridine Adducts
Figure 1. Molecular structure of 1b (ORTEP plot with thermal el-
lipsoids at the 50 percent probability level, C-bound hydrogen
atoms are omitted).
Scheme 2. Reaction of trichlorosilane with substituted pyridines.
Unlike the dichlorosilane adducts H2SiCl2(Rpy)2, which
Because of the poor solubilities of the complexes charac- all exhibited the Si atom on a crystallographically imposed
terization by solution NMR spectroscopy failed. Therefore, centre of symmetry,[5] compound 1b bears one Si complex
the hexacoordinate silicon complexes were characterized by molecule per asymmetric unit. Furthermore, compound 1b
13C and 29Si CP/MAS NMR as well as Raman spec- crystallized with 1/2 molecule of 3-bromopyridine in the
troscopy. As expected, compounds 1a–h show a characteris- asymmetric unit, which is located near a centre of inversion
tic Si–H valence vibration band at 2061–2128 cm–1 in the and, therefore, part of a symmetry-imposed disorder.
Raman spectrum (see Table 1), which in comparison to
The Si–N distances are slightly longer than in the pre-
HSiCl3 is shifted to lower wavenumbers accompanied by viously reported dichlorosilane adducts, i.e. 198.2(3) and
broadening of the signal. The latter can be attributed to 198.9(3) pm in 1b and 196.9(1) pm in the analogous dichlo-
increasing ionic contributions to the Si–H bond. The 29Si rosilane adduct.[5] This Si–N bond lengthening can be seen
NMR shifts range between δiso = –165 and –172 ppm and as a result of the increased steric impact around the Si
confirm hexacoordination of the silicon atom.[6] In com- atom. Whereas in the dichlorosilane adducts the pyridine
parison with the previously reported dichlorosilane adducts planes are tilted out of the Cl–Si–Cl axis by ca. 70–80° and
H2SiCl2(Rpy)2 the resonances of all compounds the Si–H bonds were nearly in plane with the pyridine li-
HSiCl3(Rpy)2 are significantly shifted to higher field (by gands, the third Si-bound chlorine atom of the HSiCl3 ad-
about 20 ppm). This effect can be attributed to the substitu- duct forces the other two Cl atoms closer to the pyridine
tion of one Si-bound hydrogen atom for a Cl substituent.
2,6-hydrogen atoms. Vice versa, well in accord with the Si–
N bond lengthening, the Si–Cl bonds of the above tri-
chlorosilane adduct [218.3(1) for Cl2, 221.9(1) for Cl1 and
222.7(1) pm for Cl3] are significantly shorter than in the
analogous dichlorosilane complex [228.1(1) pm].
Table 1. 29Si CP/MAS NMR spectroscopic data, selected bond
lengths and ν(Si–H) Raman bands for compounds 1a–h and
HSiCl3 (compounds in order of 29Si NMR shift).
The shorter Si–Cl bonds support the following observa-
tion: contrary to the experiments described for dichloro-
silane (formation of complexes [H2Si(Rpy)4]2+ possible)[5,9]
the cationic species of the type [HClSi(Rpy)4]2+ were not
observed so far.[10] Both, the increased steric demand
around the Si atom as well as the stronger (shorter) Si–Cl
bonds vs. longer Si–N bonds render the addition of two
further pyridine molecules less likely. Furthermore, the
dissociation of the Si–X bonds depends on a variety of pa-
rameters, in particular temperature, solvent, the nature of
the anion and further substituents at the Si atom.[11,12]
R
δiso 29Si [ppm]
ν(Si–H) [cm–1]
HSiCl3
1a
–9.6[7]
–164.8
–165.0
–165.6
–165.7
–168.2
–168.5
–170.0
–172.0
2244[8]
2095
2077
2092
2093
2111
2092
2128
2061
H
4-CH3
1c
1h
4-C6H5
3-Br
4-CHCH2
4-CH2CH3
4-C(CH3)3
4-N(CH3)2
1b
1e
1d
1f
1g
With increasing electron-releasing effects of the substitu- Whereas electron releasing groups promote the formation
ents at the pyridine moiety the Si atoms gain electron den- of higher coordinate siliconium cations, electron with-
sity which leads to a high field shift of the 29Si NMR signal. drawing substituents (e.g. further chlorine atoms) inhibit
This is most obvious for 1g due to the strong mesomeric ionic Si–Cl dissociation.
effect of the dimethylamino substituent.[5]
As mentioned in the introduction, dismutation of ad-
Under the synthesis conditions applied (–78 °C) the tri- ducts of trichlorosilane and related silanes by the action of
chlorosilane–pyridine adducts precipitated immediately. In polar solvents has been documented.[2,4] Thus, the predomi-
order to obtain single crystals of suitable for X-ray diffrac- nant decomposition reaction observed for the octahedral
tion analyses diffusion experiments of trichlorosilane into complexes was H vs. Cl redistribution. Pyridine adducts of
solutions of the respective pyridine were performed. Fortu- SiCl4 and H2SiCl2 formed upon treatment with polar sol-
nately, compound 1b formed single crystals suitable for X- vents at elevated temperatures (Scheme 3).
ray diffraction analysis. The molecular structure is depicted
in Figure 1.
This dismutation was monitored by 29Si CP/MAS NMR
spectroscopy. Whereas the complexes synthesized at lower
Eur. J. Inorg. Chem. 2008, 5020–5023
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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G. W. Fester, J. Wagler, E. Brendler, E. Kroke
SHORT COMMUNICATION
Conclusions
In summary, it is possible to deliberately prepare pyridine
adducts of HSiCl3 at low temperatures. These products can
be obtained in yields Ͼ95% and are stable under inert at-
mosphere at room temperature. The octahedral complexes
of HSiCl3 are susceptible to dismutation reactions in polar
solvents.
It is known that many reactions of (hydrido)-chloro-
silanes are catalysed by pyridine bases. Therefore, the pre-
sented results provide a basis for a better control of these
reactions, especially chlorine substitution and hydro-
silylation. First results in the latter direction will be pub-
lished soon.
Scheme 3. Dismutation of HSiCl3(Rpy)2 in polar solvents at ele-
vated temperatures.
temperatures delivered spectra with only one signal indica-
tive of the HSiCl3(Rpy)2 complex, prolonged heating in po-
lar solvents yielded solids which exhibit signals of the
dichlorosilane complex H2SiCl2(Rpy)2 and an additional
signal at higher field, which can be attributed to the com-
plex SiCl4(Rpy)2. Only small quantities of trichlorosilane– Experimental Section
pyridine adducts remained (see Figures 2 and 3).
General Procedure for the Synthesis of 1a–h: Trichlorosilane
(5 mmol) was dissolved in toluene (20 mL), stirred at –78 °C and
the desired pyridine base (10 mmol) was added dropwise. The prod-
ucts precipitated as colorless solids. The suspension was stirred for
one hour at –78 °C and than allowed to slowly adjust to ambient
temperature. The white precipitate was filtered off, washed with
toluene and dried under vacuum. Modifications to this procedure
are outlined if applicable. All adducts 1a–h slowly decompose upon
heating above ca. 100 °C forming the corresponding chlorosilane,
the pyridine and HCl. Therefore, melting or decomposition points
cannot be determined.
Trichloro(hydrido)bis(pyridine)silicon (1a): Yield 1.45 g (4.94 mmol,
98.8%). 29Si CP/MAS NMR: δiso = –164.8 ppm. IR (Raman): ν =
˜
651 (m), 1021 (s), 1066 (w), 1151 (w), 1207 (m), 1261 (w), 1483 (w),
1573 (w), 1614 (m), 1947 (w), [ν(Si–H)] 2095 (m), 2514 (w), 2922
(w), 2960 (w), 3007 (w), 3063 (m), 3082 (s), 3090 (s), 3147 (m), 3226
cm–1 (w). C10H11Cl3N2Si (293.65): calcd. Cl 36.2; found Cl 34.7.
Bis(3-bromopyridine)trichloro(hydrido)silicon (1b): Yield 1.26 g
(2.79 mmol, 55.8%). 29Si CP/MAS NMR: δiso = –165.7 ppm. IR
(Raman): ν = 247 (w), 265 (m), 308 (m), 335 (m), 348 (m), 457 (w),
˜
652 (w), 721 (m), 825 (w), 1035 (s), 1058 (m), 1094 (w), 1118 (w),
1199 (m), 1248 (w), 1320 (w) 1420 (w), 1468 (w), 1560 (m), 1605
(m), [ν(Si–H)] 2093 (m), 2491 (w), 2918 (w), 2968 (w), 3015 (w),
3056 (s), 3080 (s), 3096 (s), 3116 (w), 3205 cm–1 (w). Single crystals
of 1b·0.5(3-Brpy) were obtained by slow diffusion of trichlorosilane
into 3-bromopyridine.
Figure 2. 29Si CP/MAS NMR spectra of 1a, 1c, 1f and 1g (from
bottom to top), asterisks mark spinning side bands.
Trichloro(hydrido)bis(4-methylpyridine)silicon (1c): Yield 1.55 g
(4.82 mmol, 96.3%). 29Si CP/MAS NMR: δiso = –165.0 ppm. 13C
CP/MAS NMR: δiso = 23.4, 126.5, 142.4, 146.1 ppm. IR (Raman):
ν = 235 (m), 289 (m), 299 (m), 359 (w), 471 (m), 505 (w), 559 (w),
˜
669 (m), 796 (w), 824 (s), 972 (w), 1005 (w), 1040 (m), 1069 (m),
1214 (m), 1233 (m), 1261 (w), 1331 (w) 1388 (w), 1429 (w), 1564
(w), 1632 (m), 1930 (w), [ν(Si–H)] 2077 (w), 2512 (w), 2738 (w),
2926 (s), 2955 (m), 3005 (m), 3080 (s), 3106 cm–1 (s). C12H15Cl3N2Si
(321.71): calcd. Cl 33.1; found Cl 31.4.
Trichlorobis(4-ethylpyridine)(hydrido)silicon (1d): Yield 1.66 g
(4.75 mmol, 95%). 29Si CP/MAS NMR: δiso = –168.5 ppm. 13C CP/
MAS NMR: δiso = 11.5, 14.7, 27.6, 30.4, 121.2, 125.6, 141.8, 145.2,
146.5, 159.8, 162.2 ppm. IR (Raman): ν = 427 (w), 459 (w), 559
˜
(w), 668 (m), 793 (m), 842 (w), 972 (m), 983 (m), 1004 (s), 1038
(m), 1066 (m), 1131 (w), 1200 (m), 1209 (m), 1267 (w), 1314 (w),
1383 (w), 1423 (m), 1459 (m), 1506 (w), 1556 (w), 1626 (s), 1932
(w), [ν(Si–H)] 2092 (m), 2511 (w), 2733 (w), 2829 (m), 2883 (s),
Figure 3. 29Si CP/MAS spectrum of the product obtained by dis-
mutation of 1c in boiling acetonitrile after 6 hours (asterisks mark
spinning side bands).
5022
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Eur. J. Inorg. Chem. 2008, 5020–5023

Stable Trichlorosilane–Pyridine Adducts
2901 (s), 2923 (s), 2937 (s), 2972 (s), 2990 (m), 3066 (s), 3086 (s), CCDC-689839 (for 1b) contains the supplementary crystallo-
3104 (m), 3247 cm–1 (w).
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Trichloro(hydrido)bis(4-vinylpyridine)silicon (1e): Yield 1.72 g
(4.98 mmol, 99.5%). 29Si CP/MAS NMR: δiso = –168.2 ppm. 13C
CP/MAS NMR: δiso = 119.5, 126.5, 129.1, 131.5, 145.5, 149.7 ppm.
IR (Raman): ν = 222 (w), 248 (m), 290 (w), 318 (m), 398 (w), 444
˜
[1] a) O. Bechstein, B. Ziemer, D. Hass, S. I. Troyanov, V. B.
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(w), 473 (w), 640 (w), 666 (m), 757 (w), 811 (m), 848 (w), 947 (w),
984 (w), 1003 (w), 1025 (m), 1040 (m), 1069 (m), 1127 (w), 1211
(s), 1232 (w), 1259 (w), 1299 (w), 1338 (w), 1419 (m), 1437 (w),
1507 (w), 1548 (w), 1626 (s), [ν(Si–H)] 2111 (w), 2510 (w), 2919
(w), 2994 (w), 3015 (m), 3055 (m), 3084 (m), 3101 cm–1 (m).
Bis(4-tert-butylpyridine)trichloro(hydrido)silicon (1f): Yield 1.95 g
(4.8 mmol, 96.1%). 29Si CP/MAS NMR: δiso = –170.0 ppm. 13C
CP/MAS NMR: δiso = 29.9, 31.5, 37.0, 120.4, 123.0, 124.7, 145.2,
147.8, 167.1 ppm. IR (Raman): ν = 443 (m), 478 (w), 550 (w), 574
˜
(w), 666 (m), 735 (m), 845 (w), 930 (w), 987 (w), 1035 (m), 1070
(m), 1129 (m), 1204 (m), 1234 (m), 1254 (w), 1276 (w), 1334 (w),
1370 (w), 1398 (w), 1447 (m), 1467 (m), 1505 (w), 1548 (w), 1625
(s), 1944 (w), [ν(Si–H)] 2128 (m), 2468 (w), 2718 (w), 2786 (w),
2866 (m), 2906 (s), 2935 (s), 2969 (m), 2978 (s), 3050 (m), 3079 (s),
3110 cm–1 (m).
Trichlorobis[4-(dimethylamino)pyridine](hydrido)silicon (1g): THF
was used instead of toluene. To a solution of 4-(dimethylamino)
pyridine in 20 mL of THF trichlorosilane was added dropwise.
Yield 1.85 g (4.87 mmol, 97.4%). 29Si CP/MAS NMR: δiso
=
–172.0 ppm. 13C CP/MAS NMR: δiso = 39.2, 105.2, 143.8, 146.2,
155.2 ppm. IR (Raman): ν = 236 (m), 316 (m), 425 (m), 496 (w),
˜
524 (w), 558 (w), 644 (w), 663 (m), 745 (w), 768 (s), 812 (w), 951
(m), 1018 (m), 1072 (s), 1134 (w), 1195 (w), 1237 (m), 1309 (m),
1348 (w), 1425 (m), 1445 (m), 1480 (m), 1554 (m), 1632 (m), 1927
(w), [ν(Si–H)] 2061 (m), 2094 (w), 2309 (m), 2543 (w), 2612 (w),
2824 (m), 2869 (m), 2929 (s), 3012 (m), 3094 cm–1 (s).
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Received: August 22, 2008
Trichloro(hydrido)bis(4-phenylpyridine)silicon (1h): Yield 2.21 g
(4.95 mmol, 99%). 29Si CP/MAS NMR: δiso = –165.6 ppm. 13C CP/
MAS NMR: δiso = 123.1, 129.4, 135.5, 143.6, 148.4, 154.9 ppm. IR
(Raman): ν = 240 (m), 285 (w), 303 (w), 322 (w), 359 (w), 396 (w),
˜
448 (w), 558 (w), 619 (w), 666 (w), 765 (m), 850 (w), 1000 (m), 1016
(m), 1035 (m), 1076 (m), 1160 (w), 1181 (w), 1231 (m), 1599 (s),
1625 (s), [ν(Si–H)] 2092 (w), 2496 (w), 2572 (w), 2918 (w), 3063
cm–1 (s).
Published Online: September 30, 2008
Eur. J. Inorg. Chem. 2008, 5020–5023
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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