Synthesis and characterization of new aromatic-group substituted silanes bearing tris (trimethylsilyl)methyl bulky groups

Article abstract of DOI:10.1080/10426500903074866

Reaction of the Grignard reagent, p-ClC₆H₄MgCl, with SiCl₄ in toluene gave (p-ClC₆H₄) ₂SiCl₂, which was treated with KHF₂ to give (p-ClC₆H₄)₂SiF₂ (1). Reaction of the latter with [(Me₃Si)₃C]Li in THF leads to the preparation of [(Me₃Si)₃C](p-ClC₆H₄) ₂SiF (2). Treatment of (2) with LiAlH₄ gave [(Me ₃Si)₃C](p-ClC₆H₄)₂SiH (3) and [(Me₃Si)₃C](p-ClC₆H₄)(C ₆H₅)SiH (4). [(Me₃Si)₃C](p-ClC ₆H₄)SiCl₂ (5) was also prepared from the reaction of (p-ClC₆H₄)SiCl₃ with [(Me ₃Si)₃C]Li in a similar manner. The new highly sterically hindered organosilicon reagents (2) to (5) have been fully characterized by IR, 1H and 13C NMR, and mass spectrometry as well as elemental analysis. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500903074866

Phosphorus, Sulfur, and Silicon, 185:1463–1468, 2010
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500903074866
SYNTHESIS AND CHARACTERIZATION OF NEW
AROMATIC-GROUP SUBSTITUTED SILANES BEARING
TRIS (TRIMETHYLSILYL)METHYL BULKY GROUPS
Abbas Tarassoli and Ashrafolmolouk Asadi
Department of Chemistry, College of Sciences, Shahid Chamran University,
Ahvaz, Iran
Reaction of the Grignard reagent, p-ClC6H4MgCl, with SiCl4 in toluene gave (p-
ClC6H4)2SiCl2, which was treated with KHF2 to give (p-ClC6H4)2SiF2 (1). Reaction of the
latter with [(Me3Si)3C]Li in THF leads to the preparation of [(Me3Si)3C](p-ClC6H4)2SiF
(2). Treatment of (2) with LiAlH4 gave [(Me3Si)3C](p-ClC6H4)2SiH (3) and [(Me3Si)3C](p-
ClC6H4)(C6H5)SiH (4). [(Me3Si)3C](p-ClC6H4)SiCl2 (5) was also prepared from the
reaction of (p-ClC6H4)SiCl3 with [(Me3Si)3C]Li in a similar manner. The new highly
sterically hindered organosilicon reagents (2) to (5) have been fully characterized by IR, 1H
and 13C NMR, and mass spectrometry as well as elemental analysis.
Keywords Bulky group; Grignard reagent; organosilicon; steric hindrance; trisyl
INTRODUCTION
Considerable novel chemistry has emerged from the studies of compounds in which
a highly sterically hindered group, (Me3Si)3C (R), is attached to a metal or metalloid.1–7
This bulky group has successfully been used in the synthesis and characterization of the
first derivative of Mg and Mn, i.e., MR2, shown to be two-coordinate in the solid state,8 and
the first cobalt halide derivatives containing silanolato groups.9 The first stable silanetriol
RSi(OH)310 and the first cyanates of silicon, such as RSiMe2OCN, are also prepared by the
attachment of (Me3Si)3C to the silicon center.11 It has been shown that this bulky group has
a great role in the synthesis of thiocyanate of silicon (Me3Si)2C(MeOMe2Si)(Me2SiSCN)12
and the first mono-organolead(II) compound (PbClR)3.13 There are several reports concern-
ing the importance of this methodology in the preparation of the stable organotellurium and
organoselenium hydrides,14,15 the organomanganese and organocobalt halide RMCl as their
complexes [Li(THF)4][R3M3Cl4(THF)],16 and the solvent-free diorganolanthanides.17
Use of the (Me3Si)3C group as a bulky ligand in organosilicon chemistry began
with the demonstration that (Me3Si)3CH could be metallated with MeLi in Et2O-THF
to give the reagent [(Me3Si)3C]Li,18 which was found to react with Rnꢁ SiF4-n to give
Received 31 March 2009; accepted 28 May 2009.
Support of this work by Shahid Chamran University (Grant No. 1388), Ahvaz, Iran, is gratefully acknowl-
edged.
Address correspondence to Abbas Tarassoli, Department of Chemistry, College of Sciences, Shahid Chamran
University, Ahvaz, Iran. E-mail: tarassoli@scu.ac.ir
1463

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A. TARASSOLI AND A. ASADI
[(Me3Si)3C]RꢁnSiF4-n-1 (n = 1–3).1 The remarkable ability of the (Me3Si)3C bulky ligand to
induce considerable steric hindrance at a silicon center leads to the observation of a novel
competitive mechanism of reactions that are not normally competitive in the absence of the
(Me3Si)3C bulky group.19–21
A number of organosilicon compounds bearingtris(trimethylsilyl)methyl, (Me3Si)3C,
frequently denoted by Tsi, of the type TsiSiR2X (R Ph, alkyl, X H or halogen), have been
prepared,22,23 but examples of the type TsiSi(Y C6H4)2X (Y = substituent with electronic
effect) are rare.24
Thus it seemed of interest to synthesize and fully characterize organosilicon com-
pounds with general formula TsiSi(p-ClC6H4)2X (X F or H) (2 and 3) along with TsiSi(p-
ClC6H4)2(C6H5)SiH (4) and TsiSi(p-ClC6H4)SiCl2 (5) in order to examine the influence of
the electronic effect of chlorine and to introduce these compounds as potential precursors
and reagents for the new synthesis. The results of these studies are reported below.
RESULTS AND DISCUSSION
Although highly sterically hindered organosilicon compounds bearing tris
(trimethylsilyl)methyl groups are well known and common,22,23 a few references of the
type [(Me3Si)3C](Y C6H4)2SiX (X is mainly H or F and Y = substituent with inductive
effect) are seen in the chemistry literature.24 It has been shown that the nature of the
substituent has an important influence on direct nucleophilic attack at functional silicon
centers containing the (Me3Si)3C group.25–27 In our research work, Y is chlorine and the
syntheses of new compounds 2 to 5 were performed by employing Grignard reagents in a
similar manner.
The dichlorosilane, (p-ClC6H4)2SiCl2, usually does not react with TsiLi at all, but
sometimes coupling occurs with very low yields. So (p-ClC6H4)2SiCl2 was prepared from
the reaction of the Grignard reagent (p-ClC6H4)MgCl with SiCl4, and was treated with
KHF2 to give the less sterically hindered (p-ClC6H4)2SiF2 (1). The reaction of 1 with TsiLi
gave Tsi(p-ClC6H4)2SiF (2) in good yield. Treatment of 2 with LiAlH4 in THF gave a
mixture of Tsi(p-ClC6H4)2SiH (3) and Tsi(p-ClC6H4) (C6H5)SiF (4) (Scheme 1).
[(Me3Si)3C](p-ClC6H4)SiCl2 (5)
[(Me3Si)3C]Li
THF
SiCl4
p-ClC6H4MgCl
(p-ClC6H4)SiCl3 +(p-ClC6H4)2SiCl2
toluene
n-heptane
KHF2
[(Me3Si)3C]Li
THF
[(Me3Si)3C](p-ClC6H4)2SiF (2)
(p-ClC6H4)2SiF2 (1)
LiAlH4
THF
[(Me3Si)3C](p-ClC6H4)2SiH (3)+ [(Me3Si)3C](p-ClC6H4)( C6H5)SiH (4)
Scheme 1

NEW AROMATIC-GROUP SUBSTITUTED SILANES
1465
These were subsequently separated by fractional crystallization from ethanol. Tsi(p-
ClC6H4)SiCl2 (5) was obtained in low yield when (p-ClC6H4)SiCl3 was reacted with TsiLi
(Scheme 1). The products 2 to 5 were extensively characterized by MS and IR spectrometry
as well as 1H and 13C NMR techniques.
The MS data of 2 to 5 are easily related to the proposed structures, with the normal
loss of Me, PhCl, SiMe3, and other silicon moieties (see the Experimental section).
The IR spectra of 2 to 5 exhibit characteristic absorption bands at 850 and 1250 cm−1
due to C Si.18 The C C stretching of benzene rings is seen at the range of 1566–1470 cm−1
,
the Ph Cl absorption is observed at ∼1250 cm−1, and Si H stretching vibrations due to
3 and 4 appeared at 2095 and 2090 cm−1, respectively.
1
The H NMR spectra of compounds 2 to 5 clearly show a sharp singlet at δ 0.26,
0.24, 0.25, and 0.35 ppm, respectively, which is assigned to trisyl protons (Me3Si)3C. In the
spectra of 2 and 3, the quintet signal, which is expected for para-substituted rings, is seen at
δ 7.26–7.75 ppm, but in that of 4, a multiplet peak due to the overlap of signals of the two
different rings is clearly observed from δ 7.28 to 7.84 ppm with intensity corresponding to
9 protons. The four aromatic protons of 5 are observed at δ 7.35–7.90 ppm. There is also a
signal at δ ∼5 ppm in 3 and 4, which is assigned to the Si H proton.
The 13C NMR spectra of compounds 2 to 5 contain signals at δ ∼5.9, 5.3, 4.6, and
4.8 ppm, which belong to SiMe3-carbons, and the aromatic carbons are seen in the range
of δ 126.8–137.6 ppm.
It is concluded from MS, IR, 1H, and 13C NMR studies that the four new organosilicon
compounds 2 to 5 containing the bulky (Me3Si)3C ligand can be prepared with satisfactory
yields and fully characterized. In addition, these highly sterically hindered compounds with
trisyl group are excellent candidates as starting materials for the reactions with the various
suitable reagents in the synthesis of the new compounds based on the novel competitive
mechanism at the corresponding silicon centers. Therefore, we strongly recommend them
for further research in this field.
EXPERIMENTAL
Materials and Methods
Reactions involving LiAlH4, lithium metal, organolithium, or Grignard reagents
were carried out under dry argon. Solvents were dried and other chemicals were purified
by standard methods. TsiH,28 MeLi,18 TsiLi,18 and (p-ClC6H4)MgCl,29,30 were prepared
using the methods in the literature. The 1H NMR and 13C NMR spectra were recorded on
a Bruker FT (300 MHz) instrument. The IR spectra were recorded on a Shimadzu IR-470
infrared spectrometer using pressed KBr disks. Mass spectra were obtained at 70 eV Fisnos
VG Autospec. Elemental analysis (C and H) was performed by the microanalytical service
of N.I.O.C. Research Institute of Petroleum Industry.
Synthesis of (p-ClC6H4)SiCl3 and (p-ClC6H4)2SiCl2
A solution of p-ClC6H4MgCl in toluene prepared from the reaction of p-ClC6H4Cl
(73.5 g, 0.5 mol) and Mg turnings (12.15 g, 0.5 mol) was added dropwise to a solution
of SiCl4 (34 g, 0.2 mol) in toluene (50 mL). The mixture was stirred under reflux for 3 h
and then filtered. Volatile components were removed from the filtrate. The residue was

1466
A. TARASSOLI AND A. ASADI
distilled at 119◦C/35 mmHg to give (p-ClC6H4)SiCl3 and then at 182◦C/2 mmHg to give
(p-ClC6H4)2SiCl2.
Synthesis of (p-ClC6H4)2SiF2 (1)
KHF2 (7.8 g, 0.1 mol) was gradually added with stirring to (p-ClC6H4)2SiCl2 (16.1
g, 0.05 mol) at 75◦C in a water bath. n-Heptane (50 mL) was added, and the mixture was
stirred at 70–80◦C for 2 h, then filtered hot. The solvent was removed from the filtrate under
vacuum, and the residue was distilled at 127–128◦C/3 mmHg. Yield: 11.5 g (79%).
Synthesis of Tsi(p-ClC6H4)2SiF (2)
A solution of (p-ClC6H4)2SiF2 (5.78 g, 0.02 mol) in THF was added dropwise with
stirring to a solution of TsiLi in THF (50 mL) that had been made by the reaction of TsiH
(4.6 g, 0.02 mol) with MeLi generated from the reaction of MeI (3.4 g, 0.024 mol) with Li
(0.336 g, 0.048 mol). The mixture was refluxed for 5 h, then aqueous NH4Cl was added and
the organic compounds were extracted with Et2O. The extract was dried (MgSO4), filtered,
and evaporated, and the residue was recrystallized from EtOH to give Tsi(p-ClC6H4)2SiF,
mp 178◦C. Yield: 6.1g (59.8%). Anal. Calcd. For C22H35Cl2FSi4: C, 52.66. H, 7.03. Found:
C, 52.51. H, 6.99. 1HNMR (CDCl3): δ 0.26 (27H, s, SiMe3), 7.29–7.70 (8H, Aromatic-H).
13C NMR: δ 5.9 (SiMe3), 128.3, 129.5, 132.4, 135.7 (Aromatic-C). MS: m/z 485 (100,
M Me), 373 (16), 281 (7), 169 (11), 73 (57). IR (KBr, cm−1): ν 850, 1250 (C Si).
Synthesis of Tsi(p-ClC6H4)2SiH (3) and Tsi(p-ClC6H4)(Ph)SiH (4)
LiAlH4 (2.5 g, 0.065 mol) was gradually added with stirring to a solution of Tsi(p-
ClC6H4)2SiF (3 g, 0.006 mol) in dry THF (50 mL). The mixture was refluxed for 10 days.
After cooling of the mixture in ice water, aqueous saturated NH4Cl was slowly added, the
solution was extracted with Et2O, and then the extract was dried (MgSO4), filtered, and
evaporated, and the residue was recrystallized from EtOH to give Tsi(p-ClC6H4)2SiH, mp
169◦C. Yield : 0.8 g (28%). Anal. Calcd. For C22H36Cl2Si4: C, 54.62. H, 7.50. Found: C,
54.66. H, 7.61. 1H NMR (CD2Cl2): δ 0.24 (27H, s, SiMe3), 5.14 (1H, s, Si H), 7.26–7.75
(8H, Aromatic-H). 13C NMR (CDCl3): δ 5.3 (SiMe3), 127.6, 128.2, 131.2, 137.6 (Aromatic-
C). MS: m/z 467 (47), 433 (27), 355 (100), 281 (28), 169 (45), 73 (97). IR (KBr, cm−1):
ν 850–1250 (C Si), 2095 (Si H). A second crop of crystals was shown to be Tsi(p-
ClC6H4)(C6H5)SiH, mp 158◦C. Yield: 0.3 g (11%). Anal. Calcd. For C22H27ClSi4: C,
58.81; H, 8.30. Found: C, 59.03; H, 8.38. 1H NMR (CD2Cl2): δ 0.25 (27H, s, SiMe3), 5.17
(1H, s, Si H), 7.28–7.84 (9H, m, Aromatic-H). 13C NMR (CDCl3): δ 4.6 (SiMe3), 126.8,
127.9, 134.1, 137.0 (Aromatic-C). MS: m/z 433 (42 M Me), 399 (33), 355 (66), 321 (100),
247 (42), 175 (42), 135 (70), 73 (97). IR (KBr, cm−1): ν 850, 1250 (C Si), 1470 and 1413
(C C), 2090 (Si H).
Synthesis of Tsi(p-ClC6H4)SiCl2 (5)
A solution of (p-ClC6H4)SiCl3 (4.92 g, 0.02 mol) in THF (10 mL) was added dropwise
with stirring to a solution of TsiLi (prepared as above) in THF (50 mL). The mixture was
refluxed for 4 h, then aqueous NH4Cl was added and the organic compounds were extracted
with Et2O. The extract was dried (MgSO4), filtered, and evaporated, and the residue was

NEW AROMATIC-GROUP SUBSTITUTED SILANES
1467
recrystallized from EtOH to give Tsi(p-Cl C6H4)SiCl2, mp 187◦C. Yield: 3.1 g (35%).
1
Anal. Calcd. For C16H31Cl3Si4: C, 43.47; H, 7.07. Found: C, 43.59; H, 6.94. H NMR
(CDCl3): δ 0.35 (27H, s, SiMe3), 7.35–7.90 (4H, Aromatic-H). 13C NMR (CDCl3): δ 4.8
(Me3Si), δ 127.2, 128.3, 131.2, 137.6 ppm (Aromatic-C). MS: m/z 427 (97, M Me), 389
(93), 332 (24), 317 (30), 221 (52), 73 (100). IR (KBr, cm−1): ν 850, 1250 (C Si), 1563
and 1471 (C C).
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