1,3-Migration of trimethylsilyl group from carbon to oxygen in highly sterically hindered silanol of the type (Me3Si)3CSi(C6H4Me-p)MeOH and reaction of the related iodide with iodine monochloride and iodine mono

Article abstract of DOI:10.1080/10426500307890

The silanol (Me₃Si)₃CSi(C₆H₄Me-p)MeOH has been shown to isomerize to (Me₃Si)₂CHSi(C₆H₄Me-p)(Me)(OSiMe ₃) when it was kept at room temperature for 10 h in 0.

Full text of DOI:10.1080/10426500307890

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Phosphorus, Sulfur, and Silicon and the Related
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1,3-Migration of Trimethylsilyl Group from Carbon to
Oxygen in Highly Sterically Hindered Silanol of the
Type (Me 3 Si) 3 CSi(C 6 H 4 Me- p )MeOH and Reaction
of the Related Iodide with Iodine Monochloride and
Iodine Monobromide
Kazem D. Safa a b , Fatemeh Mosleh b & Parvaneh Kalantarzadeh b
a Faculty of Chemistry , University of Tabriz , Tabriz, Iran
b Research Institute for Fundamental Sciences , Tabriz, Iran
Published online: 27 Oct 2010.
To cite this article: Kazem D. Safa , Fatemeh Mosleh & Parvaneh Kalantarzadeh (2003) 1,3-Migration of Trimethylsilyl Group
from Carbon to Oxygen in Highly Sterically Hindered Silanol of the Type (Me 3 Si) 3 CSi(C 6 H 4 Me- p )MeOH and Reaction
of the Related Iodide with Iodine Monochloride and Iodine Monobromide, Phosphorus, Sulfur, and Silicon and the Related
Elements, 178:6, 1261-1268, DOI: 10.1080/10426500307890
To link to this article: http://dx.doi.org/10.1080/10426500307890
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Phosphorus, Sulfur, and Silicon, 178:1261–1268, 2003
C
Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print
DOI: 10.1080/10426500390200549
1,3-MIGRATION OF TRIMETHYLSILYL GROUP
FROM CARBON TO OXYGEN IN HIGHLY
STERICALLY HINDERED SILANOL OF THE TYPE
(Me3Si)3CSi(C6H4Me-p)MeOH AND REACTION OF
THE RELATED IODIDE WITH IODINE
MONOCHLORIDE AND IODINE MONOBROMIDE
Kazem D. Safa,a,b Fatemeh Mosleh,b
and Parvaneh Kalantarzadehb
Faculty of Chemistry, University of Tabriz, Tabriz, Iran;a
and Research Institute for Fundamental Sciences, Tabriz, Iranb
(Received October 3, 2002; accepted November 19, 2002)
The silanol (Me3Si)3CSi(C6H4Me-p)MeOH has been shown to isomer-
ize to (Me3Si)2CHSi(C6H4Me-p)(Me)(OSiMe3) when it was kept at room
temperature for 10 h in 0.2 M NaOMe/MeOH. Corresponding iso-
merizations of the above silanol (to give (Me3Si)2CHSi(C6H4Me-p)
(Me)(OSiMe3)) are complete after 26 h under reflux in pyridine.
The reaction involve 1,3-migration from carbon to oxygen within a
silanolate ion to give a carbanion, which rapidly acquires a proton from
the solvent. Treatment of (Me3Si)3CSi(C6H4Me-p)MeOH with MeLi
in Et2O/THF give, by the same rearrangement, the organolithium
reagent (Me3Si)2CLiSi(C6H4Me-p)(Me)(OSiMe3) which on treatment
with Me2SiHCl gives (Me3Si)2C(SiMe2H)Si(C6H4Me-p)(Me)(OSiMe3)
and (Me3Si)2CHSi(C6H4Me-p)(Me)(OSiMe3). When the experiment
was repeated, but with Me3SiCl in place of Me2SiHCl, it gives ex-
clusively (Me3Si)2CHSi(C6H4Me-p)(Me)(OSiMe3). Treatment of the
organolithium reagent (Me3Si)2CLiSi(C6H4Me-p)(Me)(OSiMe3) with
Mel gives exclusively (Me3Si)2CMeSi(C6H4Me-p)(Me)(OSiMe3). The re-
lated iodide (Me3Si)3CSi(C6H4Me-p)Mel reacts with ICI and IBr to give
rearranged (Me3Si)2C(SiMe2X)Si(C6H4Me-p)Me2 and unrearranged
products (Me3Si)3CSi(C6H4Me-p)MeX, (X = Cl, Br) respectively. The re-
arranged bromide (Me3Si)2C(SiMe2Br)Si(C6H4Me-p)Me2 reacts with
a range of silver [I] salts AgY (Y = OOCCH3, SO2 ) and Mercury [II]
salt HgY2 (Y = OOCCH3, SO2 ) in glacial CH3C4OOH to give the cor-
4
responding species (Me3Si)2C(SiMe2OOCCH3)Si(C6H4Me-p)Me2. The
reaction of the bromide with AgBF4 in MeOH or i-PrOH give the
We thank Professor C. Eaborn for helpful comments. This work has been supported
by the Research Institute for Fundamental Sciences, Tabriz, Iran.
Address correspondence to Kazem D. Safa, Faculty of Chemistry, University of Tabriz,
Tabriz, Iran. E-mail: kazemdsafa@yahoo.com
1261

1262
K. D. Safa et al.
corresponding rearranged products (Me3Si)2C(SiMe2Y)Si(C6H4Me-
p)Me2 (Y = OMe, OPri).
Keywords: Silicon; steric hindrance; trisyl
Several novel aspects of organosilicon chemistry have been revealed by
studies of highly sterically hindered compounds of the type TsiSiR2X
(Tsi = (Me3Si)3C).1–6 The novel chemistry in most cases arises
from the inhibition of the normally great ease of nucleophilic attack
at the functional silicon center, which allows observation of other
mechanisms that are not normally competitive. One example of this
is provided by the elimination reaction that occurs when a com-
pound of the type TsiSiRRX, X = halogen, is treated with NaOMe in
MeOH.7
A preliminary report appeared some years ago on the base-catalyzed
1,3-migration of organasilyl groups from carbon to oxygen in the silanol
TsiSiMe2OH.8
We present below details of the observation and the results of some
related experiments that were carried out on highly crowded organosi-
lanols of the type Tsi(C6H4Me-p)MeOH. We also present the results
obtained from the reactions of (Me3Si)2C(SiMe2Br)Si(C6H4Me-p)Me2
prepared by the reaction of Tsi(C6H4Me-p)MeI with IBr with a range
of electrophilic reagents.
RESULTS AND DISCUSSION
This type of rearrangement was first observed when (MeSi)3CSiMe2OH
was treated with potassium in boiling benzene to form the siloxane
(Me3Si)2CHSiMe2OSiMe3.9
Rearrangement of (MeSi)3CSiMe2OH later was found to take place in
MeOH containing 0.50 M NaOMe.10 The silanol (Me3Si)3CSi(C6H4Me-
p)MeOH was found to have reacted completely within 10 h at room
temperature in 0.2 M NaOMe/MeOH to give the expected siloxane
(Me3Si)2CHSi(C6H4Me-p)MeOSiMe3. Reaction in pyridine indicated
that rearrangement was complete within 26 h to give the above iso-
meric species under reflux. The course of the rearrangement can be
represented as in Scheme 1.
The formation of an Si O bond is energetically very favorable, but
this is offset by going from a negative oxygen center to a negative car-
bon centre. The migration is facilitated by relief of steric strain and
stabilization of the forming carbanionic centre by the three attached

1,3-Migration of Trimethylsilyl Group
1263
SCHEME 1
silyl group. The relative reactivities of the various silanols may be de-
termined by the inherent ease of the nucleophilic attack at the relevant
silicon center and at least at low base concentration, by the acidity of
the silanol. In cases in which the rearranged disiloxanes are obtained
fairly free from other products, the possibility of metallating the acidic
CH center gives them potential for further syntheses. The oranolithium
reagent (Me3Si)2CLiSi(C6H4Me-p)(Me)(OSiMe3) formed by treatment
of TsiSi(C6H4Me-p)MeOH with MeLi in Et2O/THF was found to re-
act with Me3SiCl, but it did react with the less hindered Me2SiHCl to
give the expected (Me3Si)2C(SiMe2H)Si(C6H4Me-p)(Me)(OSiMe3) and
the above isomeric species (Me3Si)2CHSi (C6H4Me-p)(Me)(OSiMe3).
When the experiment was repeated with MeI in place of Me2SiHCl
or Me3SiCl, it gives exclusively (Me3Si)2CMe(C6H4Me-p)(Me)(OSiMe3).
The reaction of the iodide TsiSi(C6H4Me-p)MeI with 2.5 M NaOMe
in refluxing MeOH for 8 h followed by aqueous work-up was found
to give the expected (Me3Si)2CHSi(C6H4Me-p)(Me)(OMe). We also
examined the corresponding reaction with 2.5 M NaOEt in EtOH,
which gives (Me3Si)2CHSi(C6H4Me-p)(Me)(OEt) after 21 h under
reflux.
The iodide TsiSi(C6H4Me-p)MeI11 was found to react with ICl in
CCl4 to give the rearranged chloride (Me3Si)2C(SiMe2Cl)Si(C6H4Me-
p)Me2, together with the unrearranged chloride TsiSi(C6H4Me-p)MeCl.
Treatment of the hydride TsiSi(C6H4Me-p)MeH with IBr in CCl4 gives
mainly the rearranged bromide (Me3Si)2C(SiMe2Br)Si(C6H4Me-p)Me2.
The bromide (Me3Si)2C(SiMe2Br)Si(C6H4Me-p)Me2 was found to re-
act with AgBF4 in MeOH to give (Me3Si)2C(SiMe2OMe)Si(C6H4Me-
p)Me2. This reaction is completed after 4.5 h under reflux (may be
complete at less than 4.5 h). The same bromide was refluxed with

1264
K. D. Safa et al.
AgBF4 in i-PrOH for 6 h (6-h period used may not be necessary) to
give the rearranged isopropoxide (Me3Si)2C(SiMe2Oi-Pr)Si(C6H4Me-
p)Me2. Reaction of the bromide with Ag2SO4 or AgOCOCH3 in
glacial CH3COOH gave the acetate displacement product species
(Me3Si)2C(SiMe2O2CCH3)Si(C6H4Me-p)Me2. The reaction of bromide
with HgSO4 or Hg(O2CCH3)2 in glacial CH3COOH also gave the ac-
etate displacement product.11 When the bromide was stirred with
AgOCOCF3 in CF3COOH at room temperature for 6 h, it gave the
displacement product species (Me3Si)2C(SiMe2O2CCF3)Si(C6H4Me-
p)Me2.
EXPERIMENTAL
Solvents
Cyclohexane, diethylether, dichloromethane, tetrachloromethane,
methanol, and pyridine were dried by standard methods.
Spectra
The 1H NMR spectra were recorded on a Perkin Elmer (80 MHZ) with
CDCl3 as solvent and CH2Cl2 or SiMe4 as internal standard. The IR
spectra were recorded in CCl4 on a Perkin Elmer 156G spectrome-
ter. Mass spectra (electron impact) were obtained with Finningan-Mat
model 8400, 70 eV. Melting points were determined on a 9100 elec-
trothermal apparatus.
Reaction of the (Me3Si)3CSi(C6H4Me- p)MeOH
with NaOMe/MeOH
A solution of the silanol (0.3 g, 0.78 mmol) in 0.2 M NaOMe/MeOH
(50 ml) was kept at room temperature for 10 h. Hexane was added
followed by a large excess of water. The organic layer was separated,
washed several times with water (MgSO4) and evaporated under re-
duced pressure at room temperature to leave an oil. The viscous residue
was purified by TLC (silicagel cyclohexane as eluent) to give the main
product i.e., the isomeric form of the starting silanol which was assigned
the structure (Me3Si)2CHSi(C6H4Me-p)(Me)(OSiMe3) (80%) from its
1HNMR (CDCl3) spectrum:- 0.2 (S, 1H, CH), 0.1 (S, 18H, SiMe3), 0.2
(S, 9H, OSiMe3), 0.45 (S, 3H, SiMe), 2.3 (S, 3H, Me-Aryl) and 7.1–
7.5 ppm (m, 4H, aryl); m/z 368 [M-Me]+, 290 [M-(C6H4-Me-p)]+, 278
[(M-MeOSiMe3)]+ and 73 [SiMe3]+. (Found: C, 56.6; H, 9.9. C18H38OSi4
calculated: C, 56.5; H, 9.9%).

1,3-Migration of Trimethylsilyl Group
1265
Reaction of TsiSi(C6H4Me-p)MeOH with Pyridine
A solution of the silanol (0.1 g, 0.26 mmol) in pyridine (20 ml)
boiled under reflux for 26 h and worked-up as above gave an oil.
The viscous residue was purified by preparative TLC (silicagel 1:1
dichloromethane-hexane as eluent) to give the isomeric (Me3Si)2CHSi
(C6H4Me-p)(Me)(OSiMe3) (40%) together with the starting silanol. The
properties were identical to those described above.
Trapping of (Me3Si)2CLiSi(C6H4Me-p)(Me)(OSiMe3)
(a) A solution of 0.1 M MeLi in Et2O (10 ml) was added to
TsiSi(C6H4Me-p)MeOH (0.2 g, 0.5 mmol) in THF (10 ml) and the
mixture was refluxed for 3 h. An excess of Me2SiHCl (2.0 cm3) was
added and the mixture refluxed for a further 3 h (possibly unneces-
sary). The volatile materials were removed under vacuum and light
petroleum (b.p. 60–80) was added, followed by water. The organic layer
was separated, dried (MgSO4), filtered and evaporated, to leave a vis-
cous liquid. The liquid product mixture was subjected to preparative
TLC (silicagel dichloromethane as eluent) to give the liquid product
(Me3Si)2CHSi(C6H4Me-p)(Me)(OSiMe3), with properties identical to
those listed in the section entitled Reaction of the (Me3Si)3CSi(C6H4Me-
p) MeOH with NaOMe/MeOH.
(b) When the experiment was repeated, but with Me3SiCl in place of
Me2SiHCl, the 1HNMR spectrum of the product indicated that it was ex-
clusively (Me3Si)2CHSi(C6H4Me-p)(Me)(OSiMe3). The properties were
identical to those described above.
(c) Treatment of the organolithium reagent (Me3Si)2CLiSi(C6H4Me-
p)(Me)(OSiMe3) with MeI gives exclusively (Me3Si)2CMeSi(C6H4
Me-p)(Me)(OSiMe3), 1HNMR (CDCl3): 0.01 (S, 3H, CMe), 0.01 (S, 18H,
(SiMe3)2), 0.1 (S, 9H, OSiMe3), 0.45 (S, 3H, SiMe), 2.35 (S, 3H, Me-aryl)
and 7.1–7.5 ppm (m, 4H, Aryl); m/z 381.2 [M-Me]+, 367.1 [M-2Me]+,
223 [M-(Me3Si)2MeC]+ and 73 [Me3Si]+. (Found: C, 57.57; H, 10.10.
C19H40OSi4 calculated: C, 57.31; H, 10.2%).
Reaction of TsiSi(C6H4Me-p)MeI with ICl
A solution of ICl (0.2 g, 0.75 mmol) in CCl4 (25 ml) was added
to TsiSi(C6H4Me-p)MeI (0.25 g, 0.5 mmol) in CCl4 (15 ml) and the
mixture was stirred at room temperature for 3 h. The solvent was
removed under reduced pressure to leave a solid, which was re-
crystaleized from EtOH to give (MeSi)2C(SiMe2Cl)SiMe2(C6H4Me-
p) (71%); m.p. 186 C; with properties identical with that reported
before.

1266
K. D. Safa et al.
Reaction of TsiSi(C6H4Me-p)MeH with IBr
A solution of IBr (0.21 g, 1 mmol) in CCl4 (20 ml) was added to
TsiSi(C6H4Me-p)MeH (0.18 g, 0.5 mmol) in CCl4 (10 ml) and the
mixture was stirred at room temperature for 6 h. The solvent was
removed under reduced pressure to leave a solid, which was re-
crystaleized from EtOH to give (Me3Si)2C(SiMe2Br)SiMe2(C6H4Me-p)
1
(42%); HNMR (CDCl3) 0.2 (S, 18H, SiMe3), 0.55 (S, 6H, SiMeBr), 1.1
(S, 6H, SiMe2Aryl), 2.3 (S, 3H, Me-aryl) and 6.7–7.8 ppm (m, 4H, Aryl);
m/z 430 [M-Me]+, 351, 291, 275 and 73. (Found: C, 49.18; H, 9.05.
C18H37BrSi4 calculated: C, 48.51; H, 8.37%).
This rearranged bromide has already been made by a different way.12
Reaction of (Me3Si)2C(SiMe2Br)SiMe2(C6H4Me-p)
with Ag2SO4
A mixture of the bromide (0.22 g, 0.5 mmol) with Ag2SO4 (0.78 g,
2.5 mmol) in glacial CH3COOH (15 mmol) was refluxed for 5 h. The
solution was decanted from AgBr, then water and diethylether was
added. The Et2O layer was dried (MgSO4) and then evaporated. The
viscous residue was then purified by preparative TLC (silicagel 3:1
dichloromethane-cyclohexane as eluent) to give the product species
(MeSi)2C(SiMe2OOCCH3)SiMe2(C6H4Me-p) (65%); 1HNMR (CDCl3)
0.1 S, 18H, SiMe3), 0.2 (S, 6H, SiMe2aryl), 0.45 (S, 6H, SiMe2OAc),
2.1 (S, 3H, Me-aryl), 2.2 (S, 3H, OAc) and 7–8 ppm (m, 4H, aryl); m/z
424 [M]+, 409 [M-Me]+, 365 [M-OAc]+ and 333 [M-(C6H4-Me-p)]+ with
properties identical to those described before.
Reaction of (Me3Si)2C(SiMe2Br)SiMe2(C6H4Me-p)
with HgSO4
A mixture of the bromide (0.22 g, 0.5 mmol) and HgSO4 (0.74 g,
2.5 mmol) in glacial CH3COOH (20 ml) was refluxed for 18 h
and the mixture worked-up as described in the section on the Re-
action of (Me3Si)2C(SiMe2Br)SiMe2(C6H4Me-p) with Ag2SO4. The
viscous residue was then purified by preparative TLC (Silicagel
3:1 dichloromethane-cyclohexane as eluent) to give the product
(Me3Si)2C(SiMe2OOCH3) SiMe2(C6H4Me-p) (60%) with properties
identical to those described before.
Reaction of (Me3Si)2C(SiMe2Br)SiMe2(C6H4Me-p)
with AgOOCCH3
A mixture of the bromide (0.22 g, 0.5 mmol) with AgOOCCH3 (0.25 g,
1.5 mmol) in glacial CH3COOH (20 ml) was refluxed for 3 h. The mixture

1,3-Migration of Trimethylsilyl Group
1267
was worked-up as described in the section on the Reaction of (Me3Si)2C-
(SiMe2Br)SiMe2(C6H4Me-p) with Ag2SO4. The viscous residue was
then purified by preparative TLC (silicagel 3:1 dichloromethane-
cyclohexane as eluent) to give (Me3Si)2C(SiMe2OOCH3)SiMe2(C6H4-
Me-p) with properties identical to those described before.
Reaction of (Me3Si)2C(SiMe2Br)SiMe2(C6H4Me-p)
with Hg(OOCCH3)2
A mixture of the bromide (0.22 g, 0.5 mmol) and Hg(OOCCH3)
(0.8 g, 2.5 mmol) in glacial CH3COOH (20 ml) was refluxed for
10 h. The mixture was worked up as described in the section on
the Reaction of (Me3Si)2C(SiMe2Br)SiMe2(C6H4Me-p) with Ag2SO4.
The viscous residue was then purified by preparative TLC (sil-
icagel 3:1 dichloromethane-cyclohexane as eluent) to give the prod-
uct (Me3Si)2C(SiMe2OOCH3) SiMe2(C6H4Me-p) (71%) with properties
identical to those described before.
Reaction of (Me3Si)2C(SiMe2Br)SiMe2(C6H4Me-p)
with AgBF4 in MeOH
A mixture of the bromide (0.22 g, 0.5 mmol) and AgBF4 (0.5 g,
2.5 mmol) in dried MeOH (20 ml) was stirred under reflux for 4.5 h.
The solution was decanted from AgBr, then water and Et2O was
added. The Et2O layer was shaken several times with water. The
residue was recrystalized from MeOH and then purified further with
sublimation at 100 C/5 mmHg to give pure rearranged methoxide
(Me3Si)2C(SiMe2OMe)SiMe2(C6H4Me-p) (64%); 1HNMR (CDCl3) 0.1
(S, 6H, SiMe2 aryl), 0.2 (S, 18H, SiMe3), 0.51 (S, 6H, SiMe2OMe), 2.4
(S, 3H, Me aryl), 3.4 (S, 3H, OMe) and 7–8 ppm (m, 4H, Aryl); m/z 397
[M+], 382 [M-Me]+, 306 [M-(C6H4Me-p)]+ and 73 (Me3Si)+. (Found: C,
57.4; H, 10.0. C19H40OSi4 calculated: C, 57.5; H, 10.1%).
Reaction of (Me3Si)2C(SiMe2Br)SiMe2(C6H4Me-p)
with AgBF4 in Pri OH
A mixture of the bromide (0.22 g, 0.5 mmol) with AgBF4 (0.5 g,
2.5 mmol) in dried PriOH (50 ml) was stirred under reflux for 6 h.
The solution was decanted from AgBr, then water and Et2O was
added. The Et2O layer was shaken several times with water and evap-
orated. The viscous residue was purified by preparative TLC (Sil-
icagel 1:1 dichloromethane-cyclohexane as eluent) to give the product
(Me3Si)2C(SiMe2OPri)SiMe2(C6H4Me-p) (40%); 1HNMR (CDCl3) 0.3
(S, 18H, SiMe3), 0.5 (S, 6H, SiMe2OPri), 0.65 (S, 6H, SiMe2-aryl), 1.1–1.4
(d, 6H, Me2CH-), 2.4 (s, 3H, Me- aryl), 3.9–4.1 (m, 1H, Me2CH),

1268
K. D. Safa et al.
6.7–7.8 ppm (m, 4H, Aryl); m/z 424 [M]+, 409 [M-Me]+, 318 [M-
Me(C6H4Me-p)]+, 146 [SiMe2(C6H4Me-p)]+, 73 [Me3Si]+.
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