Anchimeric assistance by γ-substituents Z, Z=MeO, PhO, MeS or PhS, in reactions of the bromides (Me3Si)2(ZMe2Si)CSiMe2Br with AgBF4

Article abstract of DOI:10.1016/S0022-328X(01)01169-X

The new organosilicon bromides (Me₃Si)₂(ZMe₂Si)CSiMe₂Br with Z=PhO or MeS have been prepared and new spectroscopic data obtained for the previously reported compounds with Z=H, F, Br, Me, Ph, MeO or PhS. Competitions between pairs of bromides for a deficiency of AgBF₄ in Et₂O, with the determination of the ratio of the fluoride products by ¹⁹F-NMR spectroscopy, have led to the following approximate relative reactivities of the bromides and so to the relative abilities of the γ-Z groups to provide anchimeric assistance to the leaving of Br^- in this reaction: Me, 1; Ph, 40; PhO, 3400; PhS, 5000; MeS, 7000; MeO, 54 000. In methanolysis in CH₂Cl₂, (Me₃Si)₂(MeOMe₂Si)CSiMe₂Cl has been found to be roughly 120 times as reactive as (Me₃Si)₂(PhOMe₂Si)CSiMe₂Cl. Combination of the results with previously available information suggests the following approximate order of ability of γ-groups Z to provide anchimeric assistance in reactions at the Si-X bonds in compounds (Me₃Si)₂(ZMe₂Si)CSiMe₂X: OCOMe>OMe>OCOCF₃>MeS>PhS, PhO>N₃, Cl>NCS>Ph>CH=CH₂>Me.

Full text of DOI:10.1016/S0022-328X(01)01169-X

Journal of Organometallic Chemistry 640 (2001) 29–36
www.elsevier.com/locate/jorganchem
Anchimeric assistance by g-substituents Z, Z=MeO, PhO, MeS or
PhS, in reactions of the bromides (Me3Si)2(ZMe2Si)CSiMe2Br with
AgBF4
Colin Eaborn a, Anna Kowalewska b, J. David Smith a, Włodziemierz A. Stan´czyk b,*
a School of Chemistry, Physics and En6ironmental Science, Uni6ersity of Sussex, Brighton, BN1 9QJ, UK
b Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90-363 Ło´dz´, Poland
Received 2 May 2001; accepted 28 July 2001
Abstract
The new organosilicon bromides (Me3Si)2(ZMe2Si)CSiMe2Br with Z=PhO or MeS have been prepared and new spectroscopic
data obtained for the previously reported compounds with Z=H, F, Br, Me, Ph, MeO or PhS. Competitions between pairs of
bromides for a deficiency of AgBF4 in Et2O, with the determination of the ratio of the fluoride products by 19F-NMR
spectroscopy, have led to the following approximate relative reactivities of the bromides and so to the relative abilities of the g-Z
groups to provide anchimeric assistance to the leaving of Br− in this reaction: Me, 1; Ph, 40; PhO, 3400; PhS, 5000; MeS, 7000;
MeO, 54 000. In methanolysis in CH2Cl2, (Me3Si)2(MeOMe2Si)CSiMe2Cl has been found to be roughly 120 times as reactive as
(Me3Si)2(PhOMe2Si)CSiMe2Cl. Combination of the results with previously available information suggests the following approxi-
mate order of ability of g-groups Z to provide anchimeric assistance in reactions at the SiꢀX bonds in compounds
(Me3Si)2(ZMe2Si)CSiMe2X: OCOMe\OMe\OCOCF3\MeS\PhS, PhO\N3, Cl\NCS\Ph\CHꢁCH2\Me. © 2001
Published by Elsevier Science B.V.
Keywords: Silicon; Trisyl; Mechanism; Anchimeric assistance
(Me3Si)2{MeC(O)OMe2Si)}CSiMe2Cl is even more re-
active [11b]. The anchimeric assistance is associated
1. Introduction
with the formation of a 1,3-bridged cation of the type I,
It is known that appropriate groups Z in compounds
which can then be attacked by a nucleophile at either
of the type (Me3Si)2(ZMe2Si)CSiR2X can provide an-
the a- (the original point of attachment of X) or the
g-Si atom. When R=Me, as in the compounds consid-
ered below, the same product is formed in both cases.
chimeric assistance to the leaving of X− in reactions
with electrophiles, including Ag(I) and Hg(II) salts [1],
ICl [2], CF3CO2H [1] and CF3CH2OH [3–5]. For exam-
ple, Z can be Me [1], Ph [4,6], CH2ꢁCH [5], MeO [7–9],
N3 [9], SCN [9b] or MeC(O)O [10,11]. Usually X is I,
but with Z groups that supply especially powerful
assistance, such as MeO or MeC(O)O, it can be Br, Cl
or even H [3], and where there is such activation even
MeOH can serve as the electrophile. Thus (Me3Si)2-
(MeOMe2Si)CSiMe2Cl reacts readily with MeOH, at
least 106 times as rapidly as (Me3Si)3CSiMe2Cl [7], and
The aim of the present work was to obtain informa-
tion on the relative abilities of the groups MeO, PhO,
MeS and PhS to provide anchimeric assistance, a com-
parison given added interest by the fact that in an-
chimeric assistance to ionisation of organic compounds
involving 1,2-bridging in ions of the type II, to which
the assistance to reactions of the silicon compounds
shows some analogy, RS groups are known to be
substantially more effective than RO groups [12].
* Corresponding author. Tel.: +48-42-681-8952x208; fax: +48-
42-684-7126.
E-mail address: wstancyk@bilbo.cbmm.lodz.pl (W.A. Stan´czyk).
0022-328X/01/$ - see front matter © 2001 Published by Elsevier Science B.V.
PII: S0022-328X(01)01169-X

30
C. Eaborn et al. / Journal of Organometallic Chemistry 640 (2001) 29–36
Throughout the account below R denotes Me3Si.
one molar proportion of ICl in the reaction with the
hydride R2(PhOMe2Si)CSiMe2H led to the forma-
tion of a chloride R2(PhOMe2Si)CSiMe2Cl rather
than an iodide which is the most usual outcome
of this type of reaction [2]. Similar behaviour
was observed previously for the reaction of
R2(MeOMe2Si)CSiMe2H [3].
2. Results and discussion
2.1. Syntheses
3. In Scheme 3 the use of N-bromosuccinimide, NBS,
to convert an SiꢀH into an SiꢀBr bond is notewor-
thy. When the usual reagent, bromine, was used in a
one molar proportion the organosilicon product
from R2(PhSMe2Si)CSiMe2H was almost exclusively
the dibromide R2C(SiMe2Br)2 with a substantial
amount of PhSSPh as a by product. It seems likely
that the initial reaction is to give the monobromide
R2(PhSMe2Si)CSiMe2Br and HBr, with the latter
then cleaving the SiꢀSPh bond. The hydride
R2(MeSMe2Si)CSiMe2H likewise gave very predom-
inantly the dibromide when treated with one equiva-
lent of Br2 but the required R2(MeSMe2Si)-
CSiMe2Br when NBS was used (Scheme 3). Use of
NBS in the place of Br2 also gave a slightly better
yield of the monobromide R2(HMe2Si)CSiMe2Br
from the dihydride R2C(SiMe2H)2.
For comparison the bromides R2(ZMe2Si)CSiMe2Br
with R=Me3Si and Z=Me, Ph, MeO, PhO, MeS, or
PhS were mainly used. Those with Z=Me [13] or MeO
[14] were prepared as described previously and the
others were obtained by the routes shown in Schemes
1–3. Comments on some aspects of the preparations
are given below:
1. The compound R2(PhMe2Si)CSiMe2Br (Scheme 1)
was prepared previously by a different route [15].
2. In the sequence shown in Scheme 2 the organo-
lithium reagent R2(PhOMe2Si)CLi was generated
and this could no doubt be used to attach the ligand
R2(PhOMe2Si)C to a range of metals, including
those to which the PhO group could be expected to
coordinate. It is also noteworthy that the use of a
2.2. Reacti6ity comparisons
For the reactivity comparisons the two substrates in
an 1:1 molar ratio were dissolved in anhydrous Et2O
and one molar proportion or less of AgBF4 was added,
After an appropriate time the solvent was evaporated
off under vacuum and the residue extracted with pen-
tane. The solution was filtered and evaporated to dry-
ness. The mixture was analysed by NMR spectroscopy,
with the identities of the products confirmed by GLC–
mass spectrometry. The 19F-NMR spectrum was used
to determine the ratio of the fluorides formed but this
does not correspond with the actual reactivity ratio.
This is because in a competition between initially
equimolar amounts of substrates A and B for a defi-
ciency of C to give AC and BC, as the reaction pro-
ceeds the ratio of the concentration of the more reactive
substrate A relative to that of the less reactive B falls
off and so does the instant rate ratio. Thus the final
ratio of AC/BC will not be equal to the ratio of the two
rate constants. The correction needed for the latter is
especially important when the reactivity ratio is high
and is also larger when the molar proportion of the
silver salt is higher. To calculate the course of the
reaction requires the use of two coupled non-linear
differential equations that cannot be obtained in a
closed analytic form. The equations were thus inte-
grated numerically (by implementation of Gear’s
method in the Nag Library [16]) for selected values of
the initial molar proportion of C. From these calcula-
tion graphs, we obtained the values of the correction
Scheme 1. Preparation of R2(PhMe2Si)CSiMe2Br
Scheme 2. Preparation of R2(PhOMe2Si)CSiMe2Cl
Scheme 3. Preparation of R2(R%SMe2Si)CSiMe2Br

C. Eaborn et al. / Journal of Organometallic Chemistry 640 (2001) 29–36
31
Table 1
Ratio
conditions in which the methoxy compound underwent
70% of methanolysis, only ca. 4% of the phenoxy
compound reacted. (Essentially identical results were
obtained when an equimolar amount of Et3N was
present to inhibit possible catalysis by formed acid.) If
pseudo-first order kinetics is assumed the results indi-
cate that the methoxy compound is roughly 120 times
more reactive. This figure should be regarded as only a
rough estimate, but it is clear that the PhO group does
provide markedly less anchimeric assistance than the
MeO group. The fact that the difference in reactivity
should be much larger in the methanolysis than in the
reactions with silver salts is not surprising, since
whereas the driving force in the latter reaction is pro-
vided mainly by the attack of the silver ion on the Cl
atom of the substrate, with secondary assistance from
the R%O group, in the methanolysis it is provided
mainly by the intramolecular nucleophilic attack of the
R%O group on silicon, with concerted solvation of the
leaving chloride ion.
R
of products (Me3Si)2(ZMe2Si)CSiMe2F and (Me3Si)2-
(Z’Me2Si)CSiMe2F from (Me3Si)2(ZMe2Si)CSiMe2Br and (Me3Si)2-
(Z%Me2Si)CSiMe2Br in 1:1 molar ratio with AgBF4
R (corr) b
a
Z
Z%
AgBF4
R
Ph
Me
Ph
PhS
MeS
PhO
1.0
1.0
0.33
0.65
0.34
18
68
10
5.7
2.0
38
130
12
8
2.0
PhS
MeO
MeO
MeS
a Molar proportion.
b Reactivity ratio after correction as described in text.
factor against the final AC/BC ratio for initial molar
proportions of C of 0.1, 0.5, and 1.0. These were used
to derive approximate correction factors for the final
ratios of the fluorides from the various R2(ZMe2Si)-
CSiMe2Br and R2(Z%Me2Si)CSiMe2Br pairs to give the
results shown in Table 1.
The procedure used provides only an approximate
measure of the relative reactivities and thus of the
ability of the groups Z to provide anchimeric assistance
in this type of reaction. It is clear, however, that the
R%O and R%S (R%=Me or Ph) groups provide much
greater assistance than the Ph group, but that there is
relatively little difference between the effects of the R%O
and R%S groups. For the range of Z groups the follow-
ing rough ratios of activating effects can be derived:
Me, 1; Ph, 40; PhO, 3400; PhS, 5000; MeS, 7000; MeO,
54 000. (The possible cumulative errors are such that
this last number can be regarded as correct only within
an order of magnitude.) As expected, for the PhO
group the delocalisation of the lone pair of electrons on
the oxygen atom into the phenyl ring substantially
lowers the ability to provide the anchimeric assistance
in comparison with that of the MeO group, and to an
extent that renders the group somewhat less effective
than the PhS and MeS groups. The difference between
PhS and MeS is smaller, in keeping with the less
effective delocalisation of the lone pair of electron on
sulphur, but even so it seems surprisingly small. (Direct
comparison of these groups was not possible because
the 19F-NMR shifts were the same for the two
fluorides.) However, we can conclude that while for the
ligands R2(ZMe2Si)C attached to metals such as Al or
Yb the PhO group would probably be significantly less
strongly coordinated than the MeO group, there should
be little difference between the PhS and MeS groups.
To provide a more direct indication of the effects of
MeO and PhO groups we made an approximate com-
parison of the reactivities of the chlorides (Me3Si)2-
Combination of the new data with those previously
available gives rise to the following approximate order
of increasing ability of g-groups Z to provide an-
chimeric assistance in reactions of compounds
R2(ZMe2Si)CSiMe2X: OCOMe [10,11]\OMe [3,7–
9]\OCOCF3 [3]\MeS\PhS, PhO\N3, Cl [9]\
NCS [9b]\Ph [3,4,6]\CHꢁCH2 [6]\Me.
3. Experimental
3.1. General
All reactions were carried out under Ar with exclu-
sion of moisture. Solvents were dried by standard meth-
ods and stored over a Na mirror or molecular sieves.
1
The H-, 13C-, 19F-, 31P- and 29Si-NMR spectra were
recorded in C6D6 solutions with a Bru¨ker MSL 300 or
Bru¨ker DRX spectrometer. The mass spectra were ob-
tained by electron impact at 70 eV with a Finnigan
MAT95 spectrometer; m/z values for bromine-contain-
ing ions refer to 79Br; assignments of some frequently
observed ions are: 201 (Me2SiꢁC(SiMe3)2SiMe2); 187
(Me2SiꢁC(SiMe2H)2SiMe2) or an isomer; 135
(SiMe2Ph); 73 (SiMe3). Suggested identities of ions are
not intended to indicate fragmentation routes. A Carlo
Erba CHNS-O EA 1108 elemental analyser was used
for microanalyses (C, H), and for GLC analysis a
Hewlett–Packard GC 5890A apparatus with capillary
columns HP17 or HP50 and linear programming at
50–260 °C min−1 was used.
3.2. Syntheses
(MeOMe2Si)CSiMe2Cl
and
(Me3Si)2(PhOMe2Si)-
CSiMe2Cl towards MeOH in CH2Cl2, a type of reac-
tion known to involve powerful anchimeric assistance
by the MeO group [8]. In a refluxing solution under
In the case of previously reported compounds infor-
mation is presented only when a different synthesis was
used or new spectroscopic data were obtained.

32
C. Eaborn et al. / Journal of Organometallic Chemistry 640 (2001) 29–36
3.2.1. (Me3Si )3CSiMe2Br
SiH). 13C-NMR: l 2.33 (SiMe2H), 5.2 (SiMe3). 29Si-
NMR: l −1.2 (SiMe3), −16.8 (SiMe2H). MS; m/z:
275 (100%, [M−Me]), 201 (20), 187 (5), 73 (5).
This compound was prepared as described previously
[12] and obtained in 92% yield after sublimation at
60 °C/1 mmHg, m.p. 255 °C. Anal. Found: C, 39.2; H,
1
9.2. Calc. for C12H33BrSi4: C, 39.0; H, 9.0%. H-NMR:
3.2.5. (Me3Si )2(PhMe2Si )CSiMe2H (cf. Ref. [18])
The procedure described for (Me3Si)2C(SiMe2H)2
was used but starting from a solution of (Me3Si)2-
(HMe2Si)CCl (5.0 g, 20 mmol) in a mixture of THF (40
cm3), Et2O (40 cm3) and pentane (10 cm3) and a 2.5
mol dm−3 solution of n-BuLi in hexane (12 cm3, 30
mmol) with subsequent addition of PhMe2SiCl (9 cm3,
42 mmol). Work up gave (Me3Si)2(PhMe2Si)CSiMe2H
(4.5 g, 64%). 1H-NMR: l 0.17 (d, 6H, J=3.7 Hz,
SiMe2H), 0.20 (s, 12H, SiMe3), 0.53 (s, 6H, SiMe2Ph),
2.24 (sept, 1H, SiH), 7.2–7.8 (m, 5H, Ph). 13C-NMR: l
2.24 (SiMe2H), 3.85 (SiMe2Ph), 5.67 (SiMe3), 128.2–
136.9 (Ph). 29Si-NMR: l −17.1 (SiMe2H), −7.6
(SiMe2Ph), −0.98 (SiMe3). MS; m/z: 352 (6%, [M+]),
337 (70, [M−Me]), 335 (100%, [M−MeH−H]), 274
([M−PhH]), 201 (20), 135 (20) 73 (20).
l 0.30 (s, 27H, SiMe3), 0.73 (s, 6H, SiMe2); 13C-NMR:
l 5.97 (SiMe3), 10.9 (SiMe2); 29Si-NMR: l −21.6
(SiMe3), 22.75 (SiMe2Br). MS; m/z: 353 (100%, [M−
Me]), 265 (5, [M−Me−SiMe4]), 201 (40), 73 (5).
3.2.2. (Me3Si )2C(SiMe2H)2 (cf. Ref. [17])
A stirred solution of (Me3Si)2(HMe2Si)CCl (12.8 g,
51 mmol) in a mixture of THF (90 cm3), Et2O (40 cm3)
and pentane (20 cm3) was maintained at −110 °C as a
2.5 mol dm−3 solution of n-BuLi in hexane (22 cm3, 55
mmol) cooled to −78 °C was added dropwise. The
mixture was stirred at −110 °C for a further 2 h and
then Me2HSiCl (10 cm3, 90 mmol) was added dropwise.
This mixture was stirred at −110 °C for 2 h and then
allowed to warm to room temperature (r.t.). The sol-
vents were removed under reduced pressure and the
residue was extracted with pentane. The extract was
filtered, the solvent removed, and the residue recrys-
tallised from MeOH to give (Me3Si)2C(SiMe2H)2 (9.71
g, 69%). 1H-NMR: l 0.23 (s, 18H, SiMe3), 0.29 (d,
12H, J=3.7 Hz, SiMe2H), 4.34 (sept, 2H, J=3.7 Hz,
SiH). 13C-NMR: l 1.35 (SiMe3), 4.31 (SiMe2H). 29Si-
NMR: l −0.67 (SiMe3), −16.5 (SiMe2H). MS; m/z:
261 (100%, [M−Me]), 187 (20, [M]).
3.2.6. (Me3Si )2(PhMe2Si )CSiMe2Br
A solution of (Me3Si)2(PhMe2Si)C(SiMe2H) [9] (2.33
g, 6.6 mmol) in CCl4 (20 cm3) was stirred at 20 °C as
Br2 (6.6 mmol) in CCl4 (6.6 cm3) was added dropwise.
After 20 min the solvent was removed in vacuum and
the residue was recrystallised from pentane at −78 °C
to give (Me3Si)2(PhMe2Si)C(SiMe2Br) (2.65 g, 93%),
m.p. 176 °C. Anal. Found: C, 47.2; H, 8.1. Calc. for
C17H35BrSi4: C, 473; H, 8.2%. 1H-NMR: l 0.31 (s, 18H,
SiMe3), 0.62 (s, 6H, SiMe2Ph), 0.68 (s, 6H, SiMe2Br),
7.2–7.8 (m, 5H, Ph). 13C-NMR: l 5.16 (SiMe2Ph), 6.76
(SiMe3), 11.33 (SiMe2Br), 128.3–140.5 (Ph). 29Si-NMR:
l −6.73 (SiMe2Ph), −0.91 (SiMe3), 22.9 (SiMe2Br).
MS; m/z: 415 (75%, [M−Me]), 335 (100, [M−MeH−
Br]), 216 (54, [M−SiMe2Ph−Br]), 201 (45), 135 (30),
73(30).
3.2.3. (Me3Si )2(BrMe2Si )CSiMe2H (cf. Ref. [17])
NBS (1.74 g, 9.8 mmol) was added to a solution of
(Me3Si)2C(SiMe2H)2 (2.69 g, 9.8 mmol) in hexane (10
cm3) and the mixture was stirred for 24 h at r.t. with
monitoring by GLC–MS. Filtration of the solution
followed by removal of the solvent gave a mixture that
was shown by GLC–MS analysis to consist of the
starting material (10%), (Me3Si)2(HMe2Si)CSiMe2Br
(80%) and (Me3Si)2C(SiMe2Br)2 (10%). Sublimation at
10 °C/0.05 mmHg gave (Me3Si)2(BrMe2Si)CSiMe2Br
3.2.7. (Me3Si )2(MeOMe2Si )CSiMe2H
This compound was prepared as described previously
1
1
(3.0 g). H-NMR: l 0.28 (s, 18H, SiMe3), 0.34 (d, 6H,
[14]. H-NMR: l 0.29 (s, 6H, SiMe2O), 0.31 (s, 8H,
J=3.7 Hz, SiMe2H), 0.69 (s, 6H, SiMe2Br), 4.28 (sept,
1H, J=3.7 Hz, SiH). 13C-NMR: l 2.02 (SiMe2H), 4.94
(SiMe3), 9.88 (SiMe2Br). 29Si-NMR: l −6.8 (SiMe2H),
−0.77 (SiMe3), 22.5 (SiMe2Br). MS; m/z: 339 (100%,
[M−Me]), 187 (20).
SiMe3), 0.35 (d, 6H, J=3.7 Hz, SiMe2H), 3.14 (sept,
1H, J=3.7 Hz, SiH). 13C-NMR: l 2.18 (SiMe2H), 3.15
(SiMe2O), 4.99 (SiMe3), 50.0 (OMe). 29Si-NMR: l −
17.2 (SiMe2H), −1.7 (SiMe3), 14.2 (SiMe2OMe). MS;
m/z: 305 (30%, [M−H]), (100, [M−Me]), 217 (20,
[M−SiMe2OMe]).
3.2.4. (Me3Si )3CSiMe2H (cf. Ref. [18])
The procedure described for (Me3Si)2C(SiMe2H)2
was used but starting from (Me3Si)2(HMe2Si)CCl (4.15
g, 16.4 mmol) in a mixture of THF (50 cm3), Et2O (20
cm3) and pentane (10 cm3) and a 2.5 mol dm−3 solu-
tion of n-BuLi in hexane (2 cm3, 19 mmol) and subse-
quent treatment with Me3SiCl (2.6 cm3, 20 mmol).
Yield 3.0 g, 63%. 1H-NMR: l 0.25 (s, 27H, SiMe3), 0.30
(d, 6H, J=3.7 Hz, SiMe2H), 4.33 (sept, 1H, J=3.7 Hz,
3.2.8. (Me3Si )2(MeOMe2Si )CSiMe2Br
This compound was prepared as described previously
1
[14]. H-NMR: l 0.29 (s, 6H, SiMe2O), 0.37 (s, 12H,
SiMe3), 0.80 (s, 6H, SiMe2Br), 3.04 (3H, OMe). MS:
m/z; 369 (2%, [M−Me]), 325 (100, [M−SiMe2H]),
305 (5, [M−Br]), 217 (10, [M−Me−SiMe2Br]), 201
(10, [M−SiMe3OMe−Br]), 305 [M−Br]), 217 (10,
[M−Me−SiMe3Br]), 201 (10), 73 (5).

C. Eaborn et al. / Journal of Organometallic Chemistry 640 (2001) 29–36
33
3.2.9. (Me3Si )2(PhOMe2Si )CCl
SiMe2Cl), 6.9–7.1 (m, 5H, OPh). MS; m/z: 402 (3%,
[M+]), 387 (100, [M−Me]), 309 (10, [M−SiMe2Cl]).
A solution of (Me3Si)2(BrMe2Si)CCl [9] (3.14 g, 9.5
mmol) in toluene (20 cm3) was added dropwise at 0 °C
to a stirred dispersion of lithium phenolate made by
adding n-BuLi (3.8 cm3 of 2.5 mol dm−3 solution in
hexanes) to a solution of phenol (1.69 g, 21 mmol) in
toluene (50 cm3). The mixture was stirred at 115 °C for
56 h, the solvent was then removed in vacuum, and the
solid residue extracted with n-pentane. The extract was
filtered and the solvent evaporated to give a white solid,
which was recrystallised from MeOH to yield 1.12 g
(32%) of (Me3Si)2(PhOMe2Si)CCl, Anal. Found: C,
52.0; H, 8.60. Calc. for C15H29OClSi3: C, 52.2; H,
3.2.12. (Me3Si )2(PhOMe2Si )CSiMe2Br
A 1.0 mol dm−3 solution of Br2 in CCl4 (0.35 cm3,
0.35 mmol of Br2) was added dropwise to a stirred
solution of (Me3Si)2(PhOSMe2Si)CSiMe2H (0.13 g, 0.35
mmol) in CCl4 (10 cm3). After 30 min the solvent was
removed under reduced pressure and the residue sub-
limed at 110 °C/1 mmHg to give (Me3Si)2(PhOMe2Si)-
CSiMe2Br (0.11 g, 70%), m.p. 132 °C. Anal. Found: C,
45.6; H, 7.7. Calc. for C17H35OBrSi4: C, 45.6; H, 7.9%.
1H-NMR: l 0.40 (s, 18H, SiMe3), 0.45 (s, 6H, SiMe2O),
0.84 (s, 6H, SiMe2Br), 6.9–7.1 (m, 5H, Ph). 13C-NMR:
l 5.24 (SiMe2OPh), 5.71 (SiMe3), 10.57 (SiMe2Br),
121.3–130.6 (Ph). MS; m/z: 446 (4%, [M+]), 431 (100,
[M−Me]), 353 (25, [M−OPh]), 280 (10, [M−
Me3SiOPh]), 265 (5, [M−Me−Me3SiOPh]), 201 (10),
73 (15).
1
8.47%. H-NMR: l 0.28 (s, 18H, SiMe3), 0.36 (s, 6H,
SiMe2OPh), 6.9–7.1 (m, 5H, Ph). MS; m/z; 344 (2%,
[M+]), 329 (25, [M−Me]), 221 (10, [M−Me−
SiMe3Cl]), 85 (100, SiPhMe2H), 73 (78).
3.2.10. (Me3Si )2(PhOMe2Si )CSiMe2H
To a stirred solution of (Me3Si)2(PhOMe2Si)CCl
(1.04 g, 3 mmol) in a mixture of THF (25 cm3), Et2O (5
cm3) and pentane (2 cm3) maintained at −120 °C a 2.5
mol dm−3 solution of n-BuLi in hexane (2.5 cm3, 6.2
mmol) cooled to −78 °C was added dropwise. The
mixture was stirred at −110 °C for a further 2 h and
Me2SiHCl (1.0 cm3, 9 mmol) was added dropwise. This
mixture was stirred at −110 °C for 2 h and then
allowed to warm to r.t. The solvents were removed
under reduced pressure and the residue extracted with
n-pentane (5 cm3). The extract was filtered and the
solvent removed. The residue was taken up in hot
MeOH, the solution allowed to cool, and the MeOH
decanted off. The viscous material obtained could not
be crystallised but was kept under vacuum to give a
viscous material that appeared to be essentially pure
(Me3Si)2(PhOMe2Si)CSiMe2H (0.52 g, 47%). Anal.
Found: C, 55.5; H, 9.75. Calc. for C17H36OSi4: C, 55.4;
3.2.13. (Me3Si )2(PhOMe2Si )CSiMe2F
A mixture of (Me3Si)2(PhOMe2Si)CSiMe2Cl (0.020 g,
0.050 mmol) and AgBF4 (0.12 g, 0.051 mmol) in
CH2Cl2 (2 cm3) was stirred for 15 h at r.t. The solvent
was removed and the residue extracted with pentane.
The extract was filtered and the pentane evaporated to
leave exclusively (Me3Si)2(PhOMe2Si)CSiMe2F. 1H-
NMR: l 0.36 (s, 18H, SiMe3), 0.40 (s, 6H, SiMe2O),
0.46 (d, 6H, J=7.5 Hz, SiMe2F), 6.8–7.2 (m, 5H,
OPh). 19F-NMR: l −144.2 (sept, J=7.5 Hz). MS;
m/z: 386 (3%, [M+]), 371 (100, [M−Me]), 279 (5,
[M−Me−Me3SiF]).
3.2.14. (Me3Si )2(PhSMe2Si )CSiMe2H
To a solution of (Me3Si)2(PhSMe2Si)CCl [19] (3.0 g,
8 mmol) in THF (75 cm3), Et2O (12 cm3) and pentane
(6 cm3) maintained at −110 °C a 2.5 mol dm−3 solu-
tion of n-BuLi in hexanes (36 cm3, 90 mmol) cooled to
−78 °C was added dropwise. The mixture was stirred
for 2 h at −110 °C then Me2HSiCl (13 g, 120 mmol)
was added dropwise. This mixture was stirred at
−110 °C for 1.5 h then allowed to warm to r.t. The
solvents were removed under reduced pressure and the
residue was extracted with n-pentane. The extract was
filtered, the solvent evaporated, and the residue recrys-
tallised from MeOH to give (Me3Si)2(PhSMe2Si)-
CSiMe2H (1.4 g, 43%), m.p. 61 °C. Anal. Found: C,
52.9; H, 9.3. Calc. for C17H36SSi4: C, 53.0; H, 9.4%.
1H-NMR: l 0.380 (s, 6H, SiMe2S), 0.384 (s, 18H,
SiMe3), 0.43 (d, 6H, J=3.7 Hz, SiMe2H), 4.44 (septet,
1H, J=3.7 Hz, SiMe2H), 7.0–7.45 (m, 5H, Ph). 13C-
NMR: l 2.60 (SiMe2H), 5.47 (SiMe2S), 5.48 (SiMe3),
127.9–137.1 (Ph). 29Si-NMR: l −16.3 (SiMe2H),
−0.37 (SiMe3), 15.5 (SiMe2SPh). MS; m/z: 369 (10%,
[M−Me]), 275 (100, [M−SPh]).
1
H, 9.8%. H-NMR: l 0.33 (s, 18H, SiMe3), 0.37 (s, 6H,
SiMe2O), 0.38 (d, 6H, J=3.7 Hz, SiMe2H), 4.42 (sep-
tet, 1H, J=3.7 Hz, SiH), 6.9–7.1 (m, 5H, OPh).
13C-NMR: l 3.91 (SiMe2H), 4.67 (SiMe2O), 4.98
(SiMe3), 121.4–130.5 (Ph). 29Si-NMR:
l
−4.5
(SiMe2O), −1.36 (SiMe3), −17.0 (SiMe2H. MS; m/z;
368 (35%, [M+]), 353 (100, [M−Me]).
3.2.11. (Me3Si )2(PhOMe2Si )CSiMe2Cl
A solution (2.0 cm3) of a 0.51 mol dm−3 solution of
ICl in CCl4 added dropwise to a stirred solution of
(Me3Si)2(PhOMe2Si)C(SiMe2H) (0.28 g, 0.76 mmol) in
CCl4 (10 cm3). The mixture was stirred for a further 30
min and the solvent was then removed under vacuum.
The residue was recrystallised from pentane at −78 °C
to give (Me3Si)2(PhOMe2Si)CSiMe2Cl (0.14 g, 46%),
m.p. 157 °C. Anal. Found: C, 50.4; H, 8.6. Calc. for
1
C17H35OClSi4: C, 50.6; H, 8.7%. H-NMR: l 0.39 (s,
18H, SiMe3), 0.44 (s, 6H, SiMe2O), 0.68 (s, 6H,

34
C. Eaborn et al. / Journal of Organometallic Chemistry 640 (2001) 29–36
3.2.15. (Me3Si )2(PhSMe2Si )CSiMe2Br
(SiMe3), 10.2 (SMe). 29Si-NMR: l 5.8 (SiMe3), 16.6
(SiMe2SMe). MS; m/z: 298 (30%, [M+]), 283 (100,
[M−Me]), 263 (10, [M−Cl]]), 210 (15, [M−SiMe4]),
190 (100, [M−Me3SiCl]), 175 (99, [M−Cl−SiMe4]),
73 (83).
A solution of (Me3Si)2(PhSMe2Si)CSiMe2H (0.23 g,
0.60 mmol) and NBS (0.11 g, 0.62 mmol) in heptane (5
cm3) was stirred at r.t. for 18 h. Analysis by GLC–MS
revealed the presence of unchanged hydride (2%), the
monobromide (Me3Si)2(PhSMe2Si)CSiMe2Br (92%),
and the dibromide (Me3Si)2C(SiMe2Br)2 (6%). The so-
lution was filtered and was removed and the residue
was sublimed (50–90 °C/0.1 mmHg) to give
(Me3Si)2(PhSMe2Si)CSiMe2Br (0.26 g). Anal. Found:
C, 43.9; H, 7.55. Calc. for C17H35SBrSi4: C, 44.0; H,
3.2.18. (Me3Si )2(MeSMe2Si )CSiMe2H
The procedure described for the preparation of
(Me3Si)2(PhSMe2Si)CSiMe2H was used but starting
from a solution of (Me3Si)2(MeSMe2Si)CCl [19] (5.0 g,
17 mmol) in THF (70 cm3), Et2O (25 cm3) and pentane
(15 cm3) and a solution of n-BuLi (2.5 mmol) in hexane
(10 cm3, 25 mmol), with subsequent addition of
Me2HSiCl (36 mmol). The recrystallisation from
MeOH gave (Me3Si)2(MeSMe2Si)CSiMe2H (1.7 g,
31%), m.p. 210 °C. Anal. Found: C, 44.5; H, 10.8.
1
7.6%. H-NMR: l 0.46 (s, 24H, SiMe3+SiMe2S), 0.92
(s, 6H, SiMe2Br), 6.9–7.4 (m, 5H, Ph). 13C-NMR: l
6.13 (SiMe2S), 6.40 (SiMe3), 11.38 (SiMe2Br), 128.2–
137.2 (Ph). MS; m/z: 447 (8%, [M−Me]), 353 (100,
[M−SPh]), 310 (8, [M−Me3SiBr]), 201 (19), 73 (5).
When the bromination was carried out with Br2 in
CCl4, as described for the preparation of (Me3Si)2-
(PhOMe2Si)CSiMe2Br, analysis of the product mixture
by GLC–MS showed it to consist of only 3% of the
monobromide along with (Me3Si)2C(SiMe2Br)2 (65%)
and PhSSPh (32%).
1
Calc. for C12H34SSi4: C, 44.65; H, 10.6%. H-NMR: l
0.35 (s, 18H, SiMe3), 0.40 (d, 6H, J=3.7 Hz, SiMe2H),
0.44 (s, 6H, SiMe2S), 1.72 (s, 3H, SMe), 4.37 (septet,
1H, J=3.7 Hz, SiMe2H). 13C-NMR: l 2.58 (SiMe2H),
4.54 (SiMe2S), 5.47 (SiMe3), 10.05 (SMe). 29Si-NMR: l
−16.4 (SiMe2H), −0.53 (SiMe3), 15.0 (SiMe2SMe).
MS; m/z: 307 (60%, [M−Me]), 291 (10, [M−Me−
MeH]), 275 (75, [M−SMe]), 233 (10, [M−Me−
Me3SiH]), 201 (60, [M−SMe−Me3SiH]), 187 (20,
[M−Me−Me3SiSMe]), 129 (20, [M−SiMe3−
Me3SiSMe]), 73 (100), 59 (20, SiMe2H).
3.2.16. (Me3Si )2(PhSMe2Si )CSiMe2F
This compound was not isolated in a pure state but
its NMR spectra were unambiguously obtained. A solu-
tion of AgBF4 (0.040 g, 0.21 mmol) and (Me3Si)2-
(PhSMe2Si)CSiMe2Br [0.096 g, 0.21 mmol, but contain-
ing ca. 6% of (Me3Si)2C(SiMe2Br)2] was stirred at r.t.
for 24 h. Work-up as described for (Me3Si)2-
3.2.19. (Me3Si )2(MeSMe2Si )CSiMe2Br
The procedure described for the preparation of
(Me3Si)2(PhSMe2Si)CSiMe2Br was used but starting
1
(PhOMe2Si)CSiMe2F gave a product that from its H-
NMR spectrum and GLC–MS analysis appeared to be
exclusively (Me3Si)2(PhSMe2Si)CSiMe2F but the 19F-
NMR spectrum showed it to contain ca. 6% of
from (Me3Si)2(MeSMe2Si)C(SiMe2H) (0.17
g (0.44
mmol) and NBS (0.08 g, 0.44 mmol) in heptane (5 cm3)
and with a reaction time of only 1 h. Sublimation at
1
(Me3Si)2C(SiMe2F)2. For the monofluoride: H-NMR:
50–90 °C/1
mmHg
gave
(Me3Si)2(MeSMe2Si)-
l 0.39 (s, 6H, SiMe2S), 0.41 (s, 18H, SiMe3), 0.53 (d,
6H, J=7.5 Hz, SiMe2F), 6.9–7.8 (m, 5H, SPh). 19F-
NMR: l −143.3 (sept, J=7.5 Hz). MS; m/z: 387
(10%, [M−Me]), 293 (100, [M−SPh]), 201 (30).
CSiMe2Br (0.14 g, 76%). Anal. Found: C, 35.5; H, 8.2.
1
Calc. for C12H33SBrSi4: C, 35.9; H 8.3%. H-NMR: l
0.42 (s, 18H, SiMe3), 0.52 (s, 6H, SiMe2S), 0.88 (s, 6H,
SiMe2Br), 1.66 (s, 3H, SMe). 13C-NMR: l 5.2 (SiMe2S),
6.3 (SiMe3), 10.2 (SMe), 11.3 (SiMe2Br). MS; m/z: 385
(30%, [M−Me]), 353 (85, M−SMe), 265 (5, M−
SMe−SiMe4), 233 (10, M−Me−Me3SiBr), 201(25,
M−SMe−Me3SiBr), 73 (10, SiMe3).
When Br2–CCl4 was used for the bromination a
mixture of (Me3Si)2(MeSMe2Si)CSiMe2Br (27%) and
(Me3Si)2C(SiMe2Br)2 (73%) was obtained.
3.2.17. (Me3Si )2(MeSMe2Si )CCl
A solution of BuLi (25 mmol) in a mixture of hex-
anes (10 cm3) and Et2O (10 cm3) cooled to 0 °C was
added dropwise to a solution of MeSH (1.4 g, 29 mmol)
in Et2O (50 cm3) maintained at 0 °C. The mixture was
stirred for 30 min to give a white suspension of MeSLi.
To this a solution of (Me3Si)2(BrMe2Si)CCl [9] (6.51 g,
19.6 mmol) in Et2O (10 cm3) cooled to 0 °C was added
slowly with stirring. The mixture was then stirred for 30
min at 0 °C and 38 h at r.t. The solution was filtered.
The solvents were removed, and the residue was recrys-
tallised from MeOH to give (Me3Si)2(MeSMe2Si)CCl
(5.5 g, 88%), m.p. 124 °C. Anal. Found: C, 39.8; H,
9.2. Calc. for C10H27ClSSi3: C, 40.2; H, 9.05%. 1H-
NMR: l 0.30 (s, 18H, SiMe3), 0.43 (s, 6H, SiMe2S),
1.77 (s, 3H, SMe). 13C-NMR: l 1.98 (SiMe2SMe), 2.14
3.3. Preparation of fluorides for recording of their
19F-NMR spectra
Samples of the various fluorides (Me3Si)2(ZMe2Si)-
CSiMe2F (except for Z=PhO) were prepared in small
amounts by reaction of the corresponding bromides
with AgBF4 in Et2O for the times shown below. The
solvent was then removed and the residue extracted

C. Eaborn et al. / Journal of Organometallic Chemistry 640 (2001) 29–36
35
with pentane. The extract was filtered and the solvent
removed. In each case the identity of the product was
confirmed by GLC–MS analysis. (These reactions were
also used to indicate what times should be used in the
competition experiments. Most of the fluorides had
been made previously in the same way but from the
iodides, much shorter reaction times then being re-
quired.) The fluoride (Me3Si)2(PhOMe2Si)CSiMe2F was
made from the corresponding chloride in CH2Cl2.
Relevant data were as follows:
0.26 (s, SiMe2OMe), 0.31 (s, 18H, SiMe3), 0.41 (d, 6H,
J=7.4 Hz, SiMe2F), 3.12 (s, 3H, OMe). 19F-NMR: l
−144.5 (sept, J=7.4 Hz). MS; m/z: 309 (20%, [M−
Me]), 305 (5, [M−F]), 291 (100, [M−Me−HF]), 217
(10 [M−Me SiMe3F]), 201(15), 187 (10) 129 (5), 73
(30), 59 (10, SiMe2H).
3.3.7. Z=PhS
Bromide 0.21 mmol; AgBF4 0.21 mmol; Et2O 15 cm3;
1
24 h. H-NMR: l 0.39 (s, 6H, SiMe2S), 0.41 (s, 18H,
SiMe3), 0.53 (d, 6H, J=7.5 Hz, SiMe2F), 6.9–7.8 (m,
5H, Ph). 19F-NMR: l −143.3 (heptet, J=7.5 Hz).
MS; m/z: 387 (10, [M−Me]), 293 (100, [M−SPh]),
201 (30).
3.3.1. Z=H (cf. Ref. [16])
Bromide 0.069 mmol; AgBF4 0.058 mmol, Et2O, 3
1
cm3; 22 h. H-NMR: l 0.25 (s, 18H, SiMe3), 0.30 (d
6H, J=3.7 Hz, SiMe2H), 0.34 (d, 6H, J=7.5 Hz,
SiMe2F). 19F-NMR: l −144.6 (hept, J=7.5 Hz). MS;
m/z: 279 (100%, [M−Me]), 205 (15, [M−Me−
Me3SiH]), 187 (25), 3 (10, SiMe3).
3.3.8. Z=MeS
Bromide 0.029 mmol; AgBF4 0.12 mmol; Et2O 2 cm3;
1
0.5 h. H-NMR: l 0.38 (s, 18H, SiMe3), 0.46 (d, 6H,
J=7.5 Hz, SiMe2F), 1.69 (SMe). 19F-NMR: l −
143.31 (sept, J=7.5 Hz). MS; m/z: 325 (30%, [M−
3.3.2. Z=Br
Bromide [(Me3Si)2C(SiMe2Br)2] 1.85 mmol; AgBF4
Me]),
293
(100,
[M−SMe]),
233
(10,
1
0.077 mmol; Et2O 3 cm3; 24 h. H-NMR: l 0.27 (s,
[M−Me−SiMe3F]), 201 (19).
18H, SiMe3), 0.37 (d, 12H, J=7.5 Hz, SiMe2F). 19F-
NMR: l −143.9 (heptet, J=7.5 Hz).
3.3.9. Z=PhO
Chloride 0.050 mmol; AgBF4 0.51 mmol; CH2Cl2 2
1
3.3.3. Z=F
cm3; 15 h. H-NMR: l 0.36 (s, 18H, SiMe3), 0.40 (s,
Bromide [(Me3Si)2C(SiMe2Br)2] 1.20 mmol; AgBF4
6H, SiMe2O), 0.46 (d, 6H, J=7.5 Hz, SiMe2F), 6.8–7.2
1
3.1 mmol; Et2O 20 cm3, 24 h. H-NMR: l 0.27 (s, 18H,
(m, 5H, Ph). 19F-NMR: l −144.2 (sept, J=7.5 Hz).
SiMe3), 0.37 (d, 12H, J=7.5 Hz, SiMe2F). 19F-NMR: l
−44.7 (sept, J=7.5 Hz). MS; m/z: 297 (100%, [M−
Me]), 205 (25, [M−Me−Me3SiF]), 73 (20).
3.4. Competition studies
In a typical procedure, a solution of (Me3Si)2(MeS-
Me2Si)CSiMe2Br (3.25 mmol), (Me3Si)2(MeOMe2Si)-
CSiMe2Br (3.25 mmol) and AgBF4 (2.2 mmol) in Et2O
(3.0 cm3) was stirred at r.t. under Ar for 2 h. The
solvent was then rapidly removed under vacuum and
the residue extracted with pentane (3 cm3). The extract
was filtered and the pentane removed. The 19F spec-
trum of the product mixture in C6D6 showed peaks at
−144.5 ppm [from (Me3Si)2(MeOMe2Si)CSiMe2F] and
−143.3 ppm [from (Me3Si)2(MeSMe2Si)CSiMe2F] in a
85:15 ratio. Analysis by GLC–MS confirmed the iden-
tities of the products.
3.3.4. Z=Me
Bromide 0.103 mmol; AgBF4 0.061 mmol; Et2O 24
1
cm3; 48 h. H-NMR: l 0.27 (s, 18H, SiMe3), 0.36 (d,
6H, J=7.5 Hz, SiMe2F). 13C-NMR: l 5.54 (SiMe3),
5.96 (SiMe2F). 29Si-NMR: l −2.2 (SiMe3), 26.9 (d,
J(SiF)=1431 Hz, SiMe2F). 19F-NMR: l −144.2 (sept,
J=7.5 Hz). MS; m/z: 293 (100%, [M−Me]), 201 (50),
73 (15).
3.3.5. Z=Ph
Bromide 0.67 mmol; AgBF4 0.67 mmol; Et2O 5 cm3;
1
24 h. H-NMR: l 0.23 (d, 6H, J=SiMe2F), 0.23 (s,
In some of the experiments small amounts of
(Me3Si)2C(SiMe2F)2 were detected in the product
mixture.
18H, SiMe3), 0.57 (s, SiMe2Ph), 7.1–7.8 (5H, Ph).
13C-NMR: l 4.51 (SiMe2Ph), 5.72 (SiMe2F), 5.9
(SiMe3), 128–137.1 (Ph). 29Si-NMR:l −6.67 (d,
3J(SiF)=16.5 Hz), SiMe2Ph), −25 (d, J(SiF)=18.5
3.5. Methanolysis of (Me3Si )2(R%OMe2Si )CSiMe2Cl
R=Me or Ph
3
SiMe3), 27.4 (d, J(SiF)=1431 Hz, SiMe2F). 19F-NMR:
l −143.9 (sept, J=7.5 Hz). MS; m/z: 355 (100%,
[M−Me]), 263 (10, [M−Me−MePh]), 216 (25, [M−
SiMe2F−Ph]), 201(30), 135 (10), 73 (10).
A solution of (Me3Si)2(MeOMe2Si)CSiMe2Cl (1.25×
10−2 mol dm−3) and MeOH (10.3 mol dm−3) in
CH2Cl2 (0.70 cm3) was kept at the reflux temperature
for 16 h. Analysis by GLC showed that 70% of the
chloride had been converted into (Me3Si)2-
(CSiMe2OMe)2. When the same procedure was used
3.3.6. Z=OMe (cf. Ref. [14])
Bromide 0.25 mmol; AgBF4 0. 25; mmol; Et2O 4 cm3;
1
24 h. (Reaction was only 80% complete.) H-NMR: l

36
C. Eaborn et al. / Journal of Organometallic Chemistry 640 (2001) 29–36
(c) C. Eaborn, A.I. Mansour, J. Chem. Soc. Perkin Trans. 2
(1985) 729.
[7] C. Eaborn, D.E. Reed, J. Chem. Soc. Chem. Commun. (1983)
495.
[8] C. Eaborn, N.M. Romanelli, J. Chem. Soc. Perkin Trans. 2
(1987) 657.
with (Me3Si)2(PhOMe2Si)CSiMe2Cl, only ca. 4% under-
went conversion into (Me3Si)2(PhOMe2Si)CSiMe2OMe.
Repetition of the reactions with the Et3N (1.25×10−2
mol dm−3) present gave essentially identical results.
[9] (a) C. Eaborn, P.D. Lickiss, S.T. Najim, M.N. Romanelli, J.
Organomet. Chem. 315 (1986) C5;
Acknowledgements
(b) C. Eaborn, N.M. Romanelli, J. Organomet. Chem. 451
(1993) 45;
We thank Dr J.G. Stamper for producing the graphs
used to derive the correction factors mentioned in the
text, the Polish State Committee for Scientific Research
(KBN) within the Centre of Excellence Scheme for
support of the work in Lodz, and the EPSRC for
support of that in Sussex (Grant GR/L83585).
(c) C. Eaborn, N.M. Romanelli, J. Chem. Soc. Perkin Trans. 2
(1985) 729;
(d) C. Eaborn, P.D. Lickiss, S.T. Najim, J. Chem. Soc. Perkin
Trans. 2 (1993) 391;
(e) N.H. Butruss, C. Eaborn, P.B. Hitchcock, P.D. Lickiss, S.T.
Najim, J. Chem. Soc. Perkin Trans. 2 (1987) 891;
(f) N.H. Butruss, C. Eaborn, P.B. Hitchcock, P.D. Lickiss, S.T.
Najim, J. Chem. Soc. Perkin Trans. 2 (1987) 1753.
[10] C. Eaborn, S.P. Hopper, J. Organomet. Chem. 170 (1979) C51.
[11] (a) C. Eaborn, P.D. Lickiss, A.D. Taylor, J. Organomet. Chem.
338 (1988) C27;
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