1,3-Migration of a phenyl group in the conversion of (Me3Si)2(PhMe2Si)CSiMePhX into (Me3Si)2(Ph2MeSi)CSiMe2Y species

Article abstract of DOI:10.1016/S0022-328X(97)00697-9

The finding that compounds of the type (Me₃Si)₂(PhMe₂Si)CSiMePhX react with electrophiles to give very predominantly rearranged products (Me₃Si)₂(Ph₂MeSi)CSiMe₂Y, which would be

Full text of DOI:10.1016/S0022-328X(97)00697-9

Journal of Organometallic Chemistry 560 (1998) 41–46
1,3-Migration of a phenyl group in the conversion of
(Me3Si)2(PhMe2Si)CSiMePhX into (Me3Si)2(Ph2MeSi)CSiMe2Y species
Colin Eaborn a, Anna Kowalewska b, Wlodzimierz Stanczyk b,*
a School of Chemistry, Physics and En6ironmental Science, Uni6ersity of Sussex, Brighton BN1 9QJ, UK
b Polish Academy of Sciences, Centre of Molecular and Macromolecular Studies, ul. Sienkiewicza 112, 90-363, Lodz, Poland
Received 1 August 1997
Abstract
The finding that compounds of the type (Me3Si)2(PhMe2Si)CSiMePhX react with electrophiles to give very predominantly
rearranged products (Me3Si)2(Ph2MeSi)CSiMe2Y, which would be expected to be thermodynamically disfavoured, can be
rationalized in terms of a mechanism in which the anchimerically-assisted departure of X− gives the Ph-bridged cation
¸¹¹¹¹¹¹º
[(Me3Si)2CSiMe2(m-Ph)SiMePh]+ which is attacked by the nucleophile at the less hindered centre bearing two Me groups rather
than that bearing one Me and one Ph group, with the outcome determined by kinetic rather than thermodynamic factors. Both
(Me3Si)2(Ph2MeSi)CSiMe2Br and its isomer (Me3Si)2(PhMe2Si)CSiMePhBr react with AgBF4 in CH2Cl2 or Et2O to give \95%
of the fluoride (Me3Si)2(Ph2MeSi)CSiMe2F. Reaction of the bromide (Me3Si)2(PhMe2Si)CSiMePhBr with AgO2CCF3 in Et2O, and
that of the hydride (Me3Si)2(PhMe2Si)CSiMePhH with ICl in CCl4, likewise give \95% of the rearranged
(Me3Si)2(Ph2MeSi)CSiMe2O2CCF3 and (Me3Si)2(Ph2MeSi)CSiMe2Cl, respectively. © 1998 Elsevier Science S.A. All rights re-
served.
Keywords: 1,3-phenyl migration; Organosilanes; Anchimeric assistance; Reaction mechanism
1. Introduction
example, in reactions of the iodide (Me3Si)3CSiPh2I
with silver sa1ts AgY the exclusive or greatly predomi-
nant product in each case is the rearranged species
(Me3Si)2(Ph2MeSi)CSiMe2Y (actually the fluoride from
AgBF4), attack at the h-Si atom in an intermediate I
with R1R2=Ph2 being much more hindered than that
at the k-Si bearing two Me groups.
It is known that appropriate groups Z in compounds
of the type (Me3Si)2(ZMe2Si)CSiR1R2X can provide
anchimeric assistance to the leaving of X−, usually I−,
in reactions with some electrophiles, including AgI salts,
ICl, CF3CO2H and CF3CH2OH [1–7]. For example, Z
can be Me [2], Ph [3], CHꢀCH2 [4], OMe [5,6], N3 [7],
NCS [7], or OCOMe [8]. The anchimeric assistance is
associated with formation of a 1,3-bridged cation of
type I, which can be attacked by a nucleophile, with
ring opening, at either the h- or k-Si atom; that is,
1,3-migration of Z can occur [1–7]. In general, but by
no means always [9], the proportion of attack at the
two centres seems to be determined mainly by the
relative degrees of steric hindrance at those centres; for
It was recently shown that in reactions of
(Me3Si)2(Ph2MeSi)CSiMe2I, 1d, with electrophiles a Ph
group provides nucleophilic assistance to the leaving of
I− to give the intermediate cation II but that since this
is attacked by the nucleophile more readily at the SiMe2
* Corresponding author.
0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved.
PII S0022-328X(97)00697-9

42
C. Eaborn et al. / Journal of Organometallic Chemistry 560 (1998) 41–46
centre little, if any, migration of a Ph group is
observed, the products being exclusively or very
predominantly
of
the
unrearranged
type
(Me3Si)2(Ph2MeSi)CSiMe2Y 1 [10]. If the proposed
mechanistic picture is correct, the same intermediate
should be formed in corresponding reactions of com-
pounds (Me3Si)2(PhMe2Si)CSiMePhX, 2, which should
thus also give predominantly the species 1 with X=Y
(in this case the rearranged products). However, this
would involve going from a compound with the two Ph
groups on different Si centres to one with both of them
on a single Si centre, which in such a highly crowded
system would be expected to be thermodynamically
very unfavourable. We show below that compounds of
type 2 do, indeed, give wholly or very predominantly
products of type 1, the outcome evidently being deter-
mined by kinetic rather than thermodynamic factors.
The results serve to confirm the validity of the proposed
mechanism.
We concentrated primarily on the reactions of the
bromides 1c and 2c with AgBF4, since the identities and
relative proportions of formed fluorides can be estab-
lished by 19F-NMR spectroscopy; not only can the
chemical shifts be compared with those of authentic or
related fluorides but furthermore the multiplicity of the
signal distinguishes unambiguously between SiMe2F
and SiMePhF groups. To look for possible effects of
changing the leaving group X and the electrophilic
reagent we also examined the reactions of the bromide
2c with AgO2CCF3 and the hydride 2a with ICl.
Scheme 1. Reagents and conditions: (i) BuLi, THF–pentane–Et2O–
hexanes, −110°C. (ii) PhMeSiHCl. (iii) Br2 in CCl4. (iv) ICl (two
equivalents) in CCl4.
mining step. The product was very predominantly the
rearranged fluoride 1e along with ca. 5% of the unrear-
ranged 2e. When the reaction was carried out in
CH2Cl2 the product appeared to be exclusively the
rearranged fluoride 1e, but up to ca. 3% of the unrear-
ranged 2e could possibly have escaped detection. Under
comparable conditions the bromide 1c gave 1e and 2e
in a ca. 98/2 ratio in CH2Cl2 and apparently exclusively
1e in Et2O. Thus there is no significant difference
between the outcomes of the reactions of the two
bromides, in keeping with Scheme 2. (The apparent
formation of a little more 1e than 2e from 1c in Et2O
than in CH2Cl2, and correspondingly of a little more 2e
than 1e from 2c in CH2Cl2 than in Et2O, may not be
real, but it would be consistent with observations that
the extent of rearrangement in reactions of this general
type tends to be lower in Et2O than in CH2Cl2 [11]).
Reaction of the bromide 2c with AgO2CCF3 oc-
curred in Et2O at room temperature. The product
(Me3Si)2(Ph2MeSi)-
CSiMe2X
(Me3Si)2(PhMe2Si)-
CSiMePhX
la
b
c
XꢀH
2a
b
c
XꢀH
1
appeared from the H-NMR spectrum to be exclusively
Cl
Cl
the rearranged trifluoroacetate 1f, and GLC-MS re-
vealed only one product, with the expected mass spec-
trum. However, the19F-NMR spectrum showed two
peaks, one very small and possibly arising from the
presence of up to ca. 4% of the unrearranged 2f.
In the case of compounds of the type
Br
Br
d
e
I
F
d
e
I
F
f
O2CCF3
f
O2CCF3
(Me3Si)3CSiR2X,
reaction
of
the
hydride
2. Results and discussion
The hydride 2a, bromide 2c, and chloride 1b were
prepared by the methods outlined in Scheme 1.
The bromide 2c was found to react with an excess of
AgBF4 in Et2O at room temperature ca. ten times as
fast as (Me3Si)3CSiMe2Br under the same conditions.
(For details see Section 3) The rate of reaction of 1c in
Et2O was roughly similar to that of 2c, in agreement
with observations on the relative reactivities of the
iodides 1d and (Me3Si)2(PhMe2Si)CSiMe2I towards sil-
ver salts [10].) This confirmed that there is anchimeric
assistance by the k-Ph group, consistent with the view
that the intermediate cation is formed in the rate-deter-
Scheme 2. Course of the reaction of (Me3Si)2(PhMe2Si)CSiMePhBr,
2c, and (Me3Si)2(Ph2MeSi)CSiMe2Br, 1c, with AgBF4. (i) AgBF4,
–AgBr. (ii) BF4−, –BF3.

C. Eaborn et al. / Journal of Organometallic Chemistry 560 (1998) 41–46
43
(Me3Si)3CSiR2H with one molar equivalent of ICl usu-
ally gives the corresponding iodide (Me3Si)3CSiR2I,
which with a further molar equivalent of ICl gives the
rearranged chloride (Me3Si)2(R2MeSi)CSiMe2Cl, either
exclusively (e.g. R=Ph), or (e.g. R=Et) along with
unrearranged chloride (Me3Si)3SiR2Cl [2,12]. Thus in
order to determine the outcome of the reaction of the
iodide 2d with ICl we treated the hydride 2a with two
molar equivalents of ICl in CCl4. The product was
20°C. Solvents were dried by standard methods and
stored over molecular sieves or a sodium mirror as
appropriate.
1
The H and 19F-NMR spectra were recorded at 200
or 300 MHz on a Bruker AC or MSL spectrometer,
respectively. The 13C spectra were recorded at 300 Hz
on the MSL instrument; the signals from the quater-
nary carbons were not observed. The mass spectra were
obtained by electron impact at 70 eV unless otherwise
indicated. (Except in the case of the M+ ion, only ions
of relative intensity \10 are included. Suggested iden-
tities of ions are not meant to indicate fragmentation
patterns.) Gas chromatography was carried out with
linear programming from 50–250°C at 15 °C min−1 on
a 25 m capillary column coated with 10% OV-101
unless otherwise indicated.
1
judged from the H-NMR spectrum to be exclusively
the expected rearranged chloride 1b, though perhaps up
to 4% of the unrearranged 2b could have escaped
detection. (In contrast, when the hydride 2a was treated
with 2.4 equivalents of ICl3 a ca. 1:1 mixture of rear-
ranged 1b and unrearranged 2b was obtained, the latter
presumably being formed by direct chlorination of the
hydride, perhaps by some Cl2 liberated from the ICl3.)
Having obtained the chloride 1b as described above,
we examined its reactions with AgBF4. As expected, it
reacted more slowly than the bromide 1c, and faster in
CH2Cl2 than in Et2O, and the reaction was not taken to
completion in the latter. The fluorides 1e and 2e were
formed in ca. 92/8 ratio in CH2Cl2 and ca. 88/12 ratio
in Et2O, these ratios not being significantly different.
(There could have been a little 2b in the initial 1b, but
this would not have an appreciable effect since it would
also mainly give 1e.) There thus may be a small differ-
ence between the proportion of rearranged product
from the chloride and bromide but it is too little to
justify speculative discussion at this stage, and a more
detailed study might be appropriate.
The fact that the outcome of the attack of the
nucleophile on the cation II is determined by the com-
parative ease of attack at the relevant Si centres rather
than by the relative thermodynamic stabilities of the
products implies that the transition state for the reac-
tion of the nucleophile with the cation II is close to the
latter, so that the relative stabilities of the possible
products have little influence. It is noteworthy that in
the reaction of the iodide (Me3Si)3CSiMePhI with
AgO2CMe in MeCO2H, the attack on the closely re-
lated intermediate cation I with Z=Me, R1=Me, and
R2=Ph (i.e. differing from II only in having bridging
Me in place of Ph) is less selective, taking place at the
SiMe2 centre only ca. three times as readily as at the
SiMePh centre [2]a. This is consistent with expected
lower stability, and thus lower selectivity, of an Me-
than of a Ph-bridged cation.
3.2. Preparations of compounds 1a–c, 2a and 2c
3.2.1. Hydride 2a
A solution of (Me3Si)2(PhMe2Si)CCl [13] (10.05 g,
0.031 mol) in a mixture of THF (90 cm3), pentane (10
cm3) and Et2O (20 cm3) was treated with stirring at
−110°C with a 2.5 mol dm−3 solution of BuLi in
hexanes (13 cm3, 0.0325 mol of BuLi) precooled to
−78°C. The stirred mixture was kept at −110°C for 2
h and PhMeSiHCl (5.5 cm3, 0.035 mol) was added. The
mixture was stirred for 1 h at −110°C then allowed to
warm to room temperature. The solvents were removed
under reduced pressure and the residue was extracted
with pentane (50 cm3). The extract was filtered, the
solvent evaporated, and the residue recrystallized from
MeOH to give the hydride 2a (5.0 g, 40%); m.p. 73°C.
Ana1. Found: C, 64.2; H, 8.9. C22H38Si4 Calc.: C, 63.7;
1
H, 9.2%. H-NMR (C6D6): l 0.14 (9H, s, SiMe3), 0.30
(9H, s, SiMe3), 0.44 (3H, d, J=3.9 Hz, SiMePhH), 0.57
(3H, s, SiMe2Ph), 0.58 (3H, s, SiMe2Ph), 5.1 (1H, q
J=3.9 Hz, SiH) and 7.2–7.8 (m 10H, Ph). 13C-NMR
(C6D6):
l 2.5 (SiMePhH), 4.41 (SiMe2Ph), 4.61
(SiMe2Ph), 5.9 (SiMe3). 6.5 (SiMe3), 128.2, 128.4, 129.9,
130.2, 137.1, 137.5 (all Ph). 29Si-NMR (C6D6): l −0.69
(SiMe3), −0.84 (SiMe3), −7.08 (SiMe2Ph), −12.51
(SiMePhH). MS: m/z 414 (2%, M+), 399 (20, MꢁMe),
355 (40, MꢁSiMe2H), 321 (100, MꢁMeꢁPhH), 135 (5,
SiMe2Ph).
3.2.2. Bromide 2c
A 2.1 mol dm−3 solution of Br2 in CCl4 (0.42 cm3)
was added with stirring to a solution of the hydride 2a
(0.37 g, 0.90 mmol) in CCl4 (2.5 cm3). The mixture was
stirred for 0.5 h at room temperature and the solvent
was then removed under vacuum to leave the bromide
2c (0.44 g, 99%), which was recrystallized from light
petroleum to give a solid of m.p. 142°C. Anal. Found:
C, 53.0; H, 7.4. C22H37BrSi4 Calc.: C, 53.5; H, 7.6%.
1H-NMR (C6D6); l 0.33 (9H, s, SiMe3), 0.35 (9H, s,
3. Experimental
3.1. General
All reactions were carried out under argon with
exclusion of moisture. The room temperature was 18–

44
C. Eaborn et al. / Journal of Organometallic Chemistry 560 (1998) 41–46
SiMe3), 0.64 (3H, s, SiMe2Ph), 0.68 (3H, s, SiMe2Ph),
1.04 (3H, s, SiMePhBr), 7.0–7.6 (10H, m, Ph); 13C-
NMR (C6D6): l 5.8 (SiMe2Ph), 7.21 (SiMe3), 7.29
(SiMe3), 10.5 (SiMePhBr), 128.2, 129.9, 130.5, 137.1,
137.6 (all Ph). 29Si-NMR (C6D6): l −6.71 (SiMe2Ph),
−0.17 (SiMe3), 0.13 (SiMe3), 13.5 (SiMePhBr). MS:
m/z 492 (2%, M+), 477 (47%, MꢁMe), 278 (100,
MꢁMeꢁSiMePhBr), 135 (22), 73 (10).
(6H, s, SiMe2), 0.93 (3H, s, SiMePh2), 7.2–8.1 (10H, m,
Ph). 13C-NMR (C6D6): l 5.0 (SiMePh2), 7.5 (SiMe3),
12.1 (SiMe2Br), 128.2, 129.0, 130.1 and 137.9 (all Ph).
MS: m/z 492 (1%, M), 477 (35, MꢁMe), 413 (10,
MꢁBr), 280 (40, MꢁMeꢁSiMePh2), 216 (100,
MꢁMeꢁSiPh2Br), 73 (10).
3.3. Reactions with sil6er salts
(i) A mixture of the bromide 2c (0.142 g, 0.30 mmol)
and AgBF4 (0.086 g, 0.44 mmol) in CH2Cl2 (5 cm3) was
stirred for 16 h at room temperature. The solution was
then filtered and the solvent removed under vacuum, to
leave the fluoride 1e (0.127 g, 98%), m.p. 130°C. Anal.
Found: C, 61.3; H, 8.9. C22H37FSi4 Calc.: C, 61.0; H,
8.6%. 1H-NMR (C6D6); l 0.22 (6H, d, J=7.8,
SiMe2F), 0.23 (18H, s, SiMe3) 0.96 (3H, s, SiMePh2)
and 7.1–8.1 (10H, m, Ph): 19F-NMR (C6D6): l −134.5
ppm (heptet JFH=7.5 Hz). MS: m/z 432 (2%, M+),
417 (18, MꢁMe), 339 (68), 220 (34), 216 (100,
MꢁSiMePh2F), 197 (30, SiMePh2).
3.2.3. Chloride 1b
A 0.82 mol dm−3 solution of ICl (5.4 mmol) in CCl4
(6.7 cm3) was added to a solution of hydride 2a (1.06 g,
2.6 mmol) in CCl. (3 cm3). After 1 h at room tempera-
ture the solvent and traces of ICl were removed under
vacuum and the residue was recrystallized from pentane
to give the chloride 1b (86%), m.p. 151°C (lit. 156°C
[2]b). Anal. Found C, 58.2; H, 8.5. C22H37ClSi4 Calc. C,
58.8; H, 8.3%. 1H-NMR (C6D6); l 0.35 (18H, s, SiMe3),
0.58 (6H, s, SiMe2Cl), 0.99 (3H, s, SiMePh2), 7.2–8.1
(10H, m, Ph); 13C-NMR (C6D6): l 4.9 (SiMePh2), 7.3
(SiMe3), 10.7 (SiMe2Cl), 129.0, 129.2, 130.0, 137.8 (all
Ph). 29Si-NMR (C6D6): l −12.21 (SiMePh2), −0.77
(SiMe3), 26.3 (SiMe2Cl).(The presence of up to ca. 4%
of 2b could have escaped detection.) Examination by
GLC-MS revealed only peak, giving m/z 433 (13%,
MꢁMe], 398 (10, MꢁMeꢁCl),), 356 (38, MꢁMeꢁPh), 236
(20, MꢁMeꢁSiMePh2), 216 (100, MꢁMeꢁSiPh2Cl), 197
(33, SiMePh2
(ii) A mixture of the bromide 2c (0.085 g, 0.173
mmol) and AgBF4 (0.203 g, 1.04 mmol) in Et2O (40
cm3) was stirred for 80 min at room temperature, after
which analysis by GLC (on OV-17) indicated that only
ca. 62% of the substrate had been consumed (indicating
a half life of roughly 60 min). After 180 min no
detectable 2c remained; the solvent was removed and
the residue taken up in C6D6 and shown by 19F-NMR
spectroscopy to contain 1e and 2e in 95:5 ratio, as
indicated by the integrals of the heptet at −134.5 and
quartet at −147 ppm. The presence of the minor
3.2.4. Hydride la
A mixture of the chloride 1b (0.18 g, 0.40 mmol) and
LiAlH4 (0.25 g, 6.6 mmol) in THF (50 cm3) was
refluxed for 8 h and then allowed to cool to room
temperature before being added to wet hexane (40 cm3).
The mixture was then added to saturated aqueous
NH4Cl and the organic layer was separated, dried
(MgSO4), and evaporated. The residue was recrystal-
lized from MeOH to give 1a (0.083 g, 50%), m.p. 96°C
(lit. 121°C [10]). Anal. Found: 63.1; H, 9.0. C22H38Si4.
1
component was not evident from the H or mass spec-
tra, which were as in (i).
Reaction of (Me3Si)3CSiMe2Br under the same con-
ditions was ca. 18% complete after 3 h and 74% after 22
h (as indicated by GLC), pointing to a half-life of
roughly 10.5 h. The half life for 1c was less accurately
indicated because only a very small amount of the
substrate was available, but it was comparable with
that of 2c.
1
Calc. 63.7: H, 9.2%. H-NMR (C6D6); l 0.18 (6H, d,
JHH=3.7 Hz, SiMe2), 0.21 (18H, s, SiMe3), 0.91 (3H, s,
(iii) A mixture of the bromide 1c (0.0056 g, 0.010
mmol) and AgBF4 (0.023 g, 0.11 mmol) in CH2Cl2 (2
cm3) was stirred for 24 h at room temperature. The
solution was then filtered and the solvent removed
under vacuum, and the residue was extracted with C6D6
to give a solution whose19F spectrum showed the heptet
at −134.5 and quartet at −147 ppm in ca. 98:2 ratio.
SiMePh2), 7.5–8.0 (10H, m, Ph), 5.1 (1H, inept., SiH)
(the data are in agreement with those for a sample
obtained earlier by a different method [10]). MS: m/z
414 (1%, M+), 399 (14, MꢁMe), 321 (100,
MꢁMeꢁPhH), 247 (31), 197 (45, SiMePh2), 135 (42,
SiMe2Ph), 73 (30, SiMe3).
1
The H-NMR and mass spectra were as in (i).
3.2.5. Bromide 1c
(iv) A mixture of the bromide 1c (0.0043 g, 0.0090
mmol) and AgBF4 (0.0102 g, 0.050 mmol) in Et2O (2
cm3) was stirred for 24 h at room temperature. The
solution was then filtered, the solvent removed under
vacuum, and the residue extracted with C6D6 to give a
solution whose19F spectrum showed only the heptet at
A 1.83 mol dm−3 solution (0.070 cm3) of Br2 (0.131
mmol) in CCl4 was added to a stirred solution of the
hydride 1a (0.048 g, 0.121 mmol) in CCl4. After 30 min
solvent and traces of Br2 were removed under vacuum
to leave bromide 1c (0.056 g, 98%), m.p. 164°C. Anal.
Found: C, 54.1; H, 7.2. C22H37BrSi4 Calc.: C, 53.5; H,
1
−134.5 ppm. The H-NMR and mass spectra were as
1
7.6%. l H-NMR (C6D6); l 0.27 (18H, s, SiMe3), 0.67
in (i).

C. Eaborn et al. / Journal of Organometallic Chemistry 560 (1998) 41–46
45
SiMe2Cl), 0.98 (3H, s, SiMePh2), 7.0–7.8 (10H, m,
Ph). Examination by GLC-MS revealed only one
product, with m/z (15 eV) 433 (13%, MꢁMe], 397
(9), 355 (33, MꢁSiMe2Cl), 236 (20, MꢁMeꢁSiMePh2),
216 (100, MꢁMeꢁSiPh2Cl), 201 (10), 197 (33,
SiMePh2).
(v) A mixture of AgBF4 (0.0055 g, 0.028 mmol)
and chloride 1b (0.0078 g, 0.017 mmol) in CH2Cl2 (3
cm3) was stirred at room temperature for 48 h. Filtra-
tion of the solution, removal of the solvent, and ex-
traction of the residue with C6D6 gave a solution
showing in its 19F spectrum the heptet at −134.5 and
quartet at −147 ppm in 92/8 ratio. The presence of
the minor component was not detected in the 1H
spectrum, which was as in (i).
(vi) A mixture of AgBF4 (0.041 g, 0.21 mmol) and
chloride 1b (0.0197 g, 0.044 mmol) in Et2O (4 cm3)
was stirred at room temperature (ca. 18°C) for 168 h.
Work up as in (iv) gave a C6D6 solution showing in
its 19F-NMR spectrum the heptet at −134.5 and
quartet at −147 ppm in 88/12 integration ratio. The
1H-NMR spectrum revealed that ca. 24% of un-
changed 1b was present.
(ii) A solution of 2a (0.23 g, 0.55 mmol) in CCl4 (5
cm3) was treated with a solution of ICl3 (1.30 mmol)
in CCl4 (5 cm3) and the mixture was stirred at room
temperature for 30 min. The solvent was then re-
moved under vacuum and the residual solid (0.24 g,
98%), m.p. ca. 124°C, was shown by GLC-MS analy-
sis to be an ca. 1:1 mixture of the chlorides 1b and
l
2b. For 1b: H-NMR (C6D6): l 0.33 (18H, s, SiMe3),
0.55 (6H, s, SiMe2Cl), 0.98 (3H, s, SiMePh2) and
7.0–8.1 (10H, m, Ph); m/z 448 (1%, M+), 433 (50%,
MꢁMe), 397 (25), 355 (62, MꢁSiMe2Cl)), 236 (37),
1
197 (54, SiMePh2), 135 (2), 73 (4). For 2b: H-NMR
(vii) A mixture of the bromide 2c (0.036 g, 0.073
mmol) and AgO2CCF3 (0.0205 g, 0.093 mmol) in
Et2O (7 cm3) was stirred at room temperature. After 3
days analysis by GLC showed that only 77% of the
substrate had disappeared and so further AgO2CCF3
(0.045 g, 0.20 mmol) was added and stirring was con-
tinued for 24 h, after which reaction was complete.
The solution was filtered and the solvent removed
under vacuum to leave a solid (0.037 g, 96%) which
(C6D6): l 0.31 (9H, s, SiMe3), 0.34 (9H, s, SiMe3),
0.63 (3H, s, SiMe2Ph), 0.66 (3H, s, SiMe2Ph), 0.85
(3H, s, SiMePhCl) and 7.1–7.5 (10H, m, Ph). 13C-
NMR
l
5.71 (SiMe2Ph), 7.06 (SiMe3), 9.66
(SiMePhCl), 129–140 (Ph). MS m/z 448 (2%), 433
(50), 397 (25), 355 (100), 135 (15).
Acknowledgements
1
appeared from its H-NMR spectrum in C6D6 to be
virtually pure 1f, m.p. 91°C (lit. 94°C [10,14]); 1H-
We thank the State Committee for Scientific Re-
search (Poland) and the British Council for joint sup-
port, the EPSRC for a research grant (to CE) and Mr
R.W. Bott for helpful comments on the manuscript.
NMR:
l
0.24 (18H, s, SiMe3), 0.45 (6H, s,
SiMe2O2CCF3) and 0.87 (3H, s, SiMePh2), but along
with the expected 19F peak (in C6D6) at −75.6 ppm
there was a small peak at −75.4 ppm that could
have come from ca. 5% of 2f. Examination by GLC-
MS revealed only one product, with m/z 526 (7%,
M+), 511 (19, MꢁMe), 461 (15), 314 (16,
MꢁMeꢁSiMePh2), 216 (100, MꢁMeꢁSiPh2O2CCF3),
197 (35, SiMePh2) and 185 (17).
(viii) A mixture of the bromide 2c (0.11 g, 0.22
mmol) and AgO2CCF3 (0.048 g, 0.22 mmol) in
CH2Cl2 (4 cm3) was stirred for 60 h at 25 °C. The
solution was filtered and the solvent removed to leave
1f with a 1H-NMR spectrum in C6D6 identical with
that reported in (vii) above, and showing only one
peak in the 19F-NMR spectrum, at −75.6 ppm.
Anal. Found: C, 55.3; H, 7.8. C24H37F3O2Si4 Calc.: C,
54.7; H, 7.1%.
References
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46
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