Tri(mesityloxy)silanethiol - the first structurally characterized organoxysilanethiol (contributions to the chemistry of silicon-sulfur compounds. 77 [1])

Article abstract of DOI:10.1002/zaac.200900524

Tri(mesityloxy)silanethiol (TMST) was isolated as the only product of the reaction between SiS₂ and 2,4,6-trimethylphenol. TMST crystallizes in the triclinic system. Good quality of the crystal allowed the unrestricted refinement of the mercapto group; the resulting S-H distance is 1.29(4) and the Si-S-H bond angle is 95.4(17)^°. Molecules of TMST show no hydrogen bonds in the crystal - the FT-IR spectrum of the solid sample exhibits a very sharp, well-resolved band of isolated -SH group at 2562 cm^-1.

Full text of DOI:10.1002/zaac.200900524

SHORT COMMUNICATION
DOI: 10.1002/zaac.200900524
Tri(mesityloxy)silanethiol – The First Structurally Characterized
Organoxysilanethiol (Contributions to the Chemistry of Silicon–Sulfur
Compounds. 77 [1])
Wojciech Marynowski,[a] Tomasz Klucznik,[a] Katarzyna Baranowska,[a] Anna Dołęga,*[a]
and Wiesław Wojnowski[a]
Keywords: Silicon; Sulfides; Silanethiols; Tri(mesityloxy)silanethiol; X-ray diffraction
Abstract. Tri(mesityloxy)silanethiol (TMST) was isolated as the only distance is 1.29(4) Å and the Si–S–H bond angle is 95.4(17)°. Molecu-
product of the reaction between SiS2 and 2,4,6-trimethylphenol. TMST les of TMST show no hydrogen bonds in the crystal – the FT-IR spec-
crystallizes in the triclinic system. Good quality of the crystal allowed trum of the solid sample exhibits a very sharp, well-resolved band of
the unrestricted refinement of the mercapto group; the resulting S–H isolated –SH group at 2562 cm–1.
trials were re-initiated by the reaction of 2,4,6-trimethylphenol,
Introduction
with SiS2, and the first results are described in this communi-
For over 40 years we have been developing a chemistry of
compounds containing silicon–sulfur bonds. In 1962, Wojnow-
ski and Piękoś identified trialkoxysilanethiols as major pro-
ducts of alcoholysis of silicon disulfide [2, 3] and suggested
the mechanism of the reaction [2]. In 1973, the first example
of the triaryloxysilanethiol was obtained by the direct reaction
of silicon disulphide with 2,6-dimethylphenol [4]. In this way,
over ten different silanethiols were obtained and their proper-
ties were thoroughly characterized [e.g. 5–8]. One of the fam-
ily of trialkoxysilanethiols – tri-tert-butoxysilanethiol – was
singled out as exceptionally resistant towards hydrolysis [7].
The coordination chemistry of tri-tert-butoxysilanethiol was
thoroughly studied and described in over 40 papers with the
emphasis on structural and lately bioinorganic aspect of the
studies [e.g. 5, 9–17]. However, the crystal structure of tri-
tert-butoxysilanethiol itself remained unknown, because of the
experimental difficulties: tri-tert-butoxysilanethiol is liquid in
a wide range of temperatures (the boiling point is 113–115 °C /
35 Torr [3] and the melting point is –19 °C [18]). Therefore
we decided to synthesize new silanethiols, with different physi-
cal properties, which would permit the structural analysis.
Having in mind possible future applications, we applied steri-
cally hindered, symmetrical substituents to make our new com-
pounds hydrolytically stable and prone to crystallization. The
cation.
Results and Discussion
Synthesis
The advantageous feature of the reaction between SiS2 and
2,4,6-trimethylphenol is that, similar to [4], tri(mesityloxy)si-
lanethiol (TMST) was isolated as the only product. It is most
probably the result of a relatively high temperature, which was
applied during the reaction carried out without any solvent.
The reaction of SiS2 with aliphatic alcohols usually leads to
several products. Typically the after-reaction mixture may con-
tain silanethiol, silanedithiol, cyclodisilthiane, and/or tetraalk-
oxysilane depending on the steric hindrance of the alcohol
used in the reaction and the reaction conditions [2–4, 18, 19].
The mechanism of the reaction between SiS2 and alcohols was
suggested in 1962 [2] and has never been questioned so far.
Structure
The molecular structure of TMST is presented in Figure 1.
The arrangement of silicon is close to tetrahedral with the an-
gles in the range 105–114 °. The H1 atom, located in the Fou-
rier density map and refined without constraints, converged to
a reasonable S1–H1 distance of 1.29(4) Å (1.33 Å in hydrogen
sulfide). Moreover, in a very good agreement with the theoreti-
cal predictions for tri-tert-butoxysilanethiol published by Choj-
nacki [20], the Si1–S1–H1 bond angle is close to 95 °, which
indicates that valence orbitals of sulfur essentially do not hy-
bridize. As usual, the non-bonding lone pair electrons occupy
a well-defined volume, exerting a steric effect, which leaves a
* Dr. A. Dołęga
Fax: +48-58-347-26 94
E-Mail: ania@chem.pg.gda.pl
[a] Gdańsk University of Technology,
Department of Inorganic Chemistry
Narutowicza St. 11/12
80–233, Gdańsk, Poland
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.200900524 or from the
author.
Z. Anorg. Allg. Chem. 2010, 636, 685–687
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
685

A. Dołęga et al.
SHORT COMMUNICATION
The FT-IR spectrum was measured with a Mattson Genesis II Gold
FTIR spectrometer equipped with a Momentum microscope and 1H
NMR spectroscopic measurements were performed with a Varian
Unity 500+ (500 MHz) spectrometer (TMS int.).
sulfur atom half-uncovered (see Figure 1S, Electronic Support-
ing Information). The structural parameters of TMST are com-
pared with those calculated for tri-tert-butoxysilanethiol [20]
and measured for bis(tri-tert-butoxysilyl) disulfide [21] in Ta-
ble 1S (Electronic Supporting Information).
Synthesis
Tri(mesityloxy)silanethiol (TMST) was obtained by phenolysis of SiS2
as described for tri(2,6-dimethylphenoxy)silanethiol [4]. SiS2 (11 g of
45 %) and 2,4,6-trimethylphenol (28 g) were stirred and heated for 20
hours at 150–180 °C. Afterwards, toluene (100 mL) was added to the
reaction mixture and the unreacted SiS2 was removed by centrifuga-
tion. Toluene was removed by vacuum distillation and the excess phe-
nol was removed by several cycles of vacuum sublimation. The solid
brownish remaining (5 g, 20 % yield with regard to SiS2) was recrys-
tallized from n-hexane in –18 °C yielding colorless prisms suitable for
X-ray measurements. Melting point: 103–105 °C, elemental analysis
found (calcd.): C 69.4 (69.5); H 7.30 (7.34); S 6.78 (6.87) %. FT-IR
(solids): ν = 3020 (s, sh), 3007 (s), 2970 (s), 2945 (s), 2916 (vs), 2858
˜
(s), 2736 (m), 2562 (m), 1771 (w), 1732 (w), 1601 (w), 1542 (w, sh),
1487 (vs, br), 1459 (vs, sh), 1437 (s), 1375 (m), 1316 (s), 1252 (s),
1244 (s), 1160 (s), 1038 (m), 1015 (m), 983 (s), 964 (m), 949 (m), 904
(m), 880 (w, sh), 853 (s), 752 (w), 730 (s) cm–1. NMR (500 MHz,
C6D6): 1H NMR (500 MHz): δ = 0.28 (s, 1 H, SH), 2.07 (s, 3 H, CH3,
p-methyl), 2.28 (s, 6 H, CH3, o-methyl), 6.66 (s, 2H CH, aromatic),
13C{1H} NMR (50.29 MHz): δ = 17.7 (s, o-CH3), 20.5 (s, p-CH3),
128.4 (s, p-C), 129.8 (s, m-C), 132.1 (s, o-C), 148.7 (s, Si-O-C).
Figure 1. Molecular structure of TMST with the labelling scheme (hy-
drogen atoms of Me groups are omitted). Displacement ellipsoids are
drawn at the 30% probability level. Important bond lengths /Å: S1–
H1 1.29(4), S1–Si1 2.1092(7), Si1–O1 1.6247(12), Si1–O2
1.6138(13), Si1–O3 1.6216(13). Important angles /deg: H1–S1–Si1
95.4(17); S1–Si1–O1 107.60(5), S1–Si1–O2 114.39(5), S1–Si1–O3
108.45(5), O1–Si1–O2 109.68(7), O1–Si1–O3 111.59(7), O2–Si1–O3
105.19(6).
Crystal Structural Analysis
The current version of CSD [22] lists only three structurally
characterized compounds with Si–S–H bonds: triphenylsilane-
thiol [23], (2,4,6-trimethylphenyl)(2,4,6-tris(bis(trimethyl-
silyl)methyl)phenyl)silanedithiol, and sulfanyl(2,4,6-trimethyl-
phenyl)(2,4,6-tris(bis(trimethylsilyl)methyl)phenyl)silanol [24]
and these are not aryloxy- but aryl-derivatives. Though it does
not contribute much to the overall quality of the refinement,
we strongly suggest that the fixed position of the mercapto
hydrogen atom with tetrahedral angle Si–S–H as in literature
[24] is incorrect.
Molecules of TMST pack as discrete units (Figure 2S, Elec-
tronic Supporting Information), and show no hydrogen bonds
in the crystal. This is a common feature of silanethiols and
silanols with the bulky substituents at silicon [24, 25]. Crystal-
lographic data are confirmed by FT-IR spectroscopy, the spec-
trum of the solid sample exhibits a very sharp, well-resolved
band of the isolated –SH group at 2562 cm–1 (Figure 3S, Elec-
tronic Supporting Information).
Crystal Structure Data: Empirical formula: C27H34O3SSi; formula
weight: 466.69 g·mol–1; unit cell dimensions: a = 844.31(9) pm, b =
914.50(9) pm, c = 1725.06(18) pm; α = 91.793(8) °, β = 98.228(9) °,
γ = 98.544(8) °; number of formula units in unit cell Z = 2; dcalcd. =
–3
¯
1.191 g·m ; crystal system: triclinic; space group: P1.
Data Collection: KUMA KM4 diffractometer, with Sapphire 2 CCD
camera (Oxford Diffraction); graphite-monochromated Mo-Kα radia-
tion (0.71073 Å); crystal dimensions: 0.32 × 0.22 × 0.08 mm; temper-
ature of measurement: 120(2) K; scan mode: Ω; theta range:
2.26<θ<25.5 deg; reciprocal lattice segments: –10 < h < 9, –10 < k <
11, –20 < l < 20; completeness to θmax: 100 %; reflections collected:
8362; symmetry independent reflections: 4838; reflections [I > 2σ(I)]:
3631; absorption coefficient: 0.195 mm–1; absorption correction: ana-
lytical.
Structure Analysis and Refinement: The structure was solved by
direct methods and refined with the SHELX97 program package [26]
with the full-matrix least-squares refinement based on F2. All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
usually refined in geometrically idealized positions with isotropic tem-
perature factors 1.2 (aromatic) or 1.5 (methyl) times the equivalent
The spacefill model of the molecule shows that the silicon
atom should be significantly protected against the hydrolysis
by the mesityloxy substituents but this must be established by isotropic temperature factors Ueq of their attached atoms. The hydrogen
atom H1 was localized in a density map and refined without con-
straints. R indices [I > 2σ(I)] R1 = 0.0404, wR2 = 0.1005; R indices
(all data) R1 = 0.0556, wR2 = 0.1075; residual electron density =
0.321/–0.233 e·Å–3.
further investigations (Figure 1S). Studies on the coordination
chemistry of tri(mesityloxy)silanethiol are in progress.
Experimental Section
Crystallographic data (excluding structure factors) for the structure re-
SiS2 (≈ 45 %) was obtained by the direct reaction of sulfur and silicon. ported in this paper have been deposited with the Cambridge Crystallo-
Commercially available (Alfa-Aesar, 98 %) 2,4,6-trimethylphenol was graphic Data Centre as supplementary publication No. CCDC-753794.
used as the other reagent.
Copies of the data can be obtained free of charge on application to
686 www.zaac.wiley-vch.de
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 685–687

Tri(mesityloxy)silanethiol – The First Organoxysilanethiol
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Z. Anorg. Allg. Chem. 2010, 685–687
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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