Kinetic Control in the Cleavage of Unsymmetrical Disilanes

Article abstract of DOI:10.1021/jo961131e

A series of 12 phenyl-substituted arylpentamethyldisilanes 1a-1 have been synthesized in order to examine the regioselectivity of their nucleophilic Si,Si bond cleavage reactions under Still's conditions (MeLi/HMPA/0°C). It has been found that the sensitivity of these reactions to the electronic effects of the substituents in the phenyl ring could be described by the Hammett-type equation log(k_A/k_B) = 0.4334 + 2.421(Σσ); (correlation coefficient R = 0.983). The k_A/k_B ratio represents the relative rate of attack at silicon atom A (linked to the aryl ring) or at silicon atom B (away from the aryl ring) of the unsymmetrical disilanes. Thus, the present investigation shows that the earlier belief according to which the nucleophilic cleavage of unsymmetrical disilanes always produces the more stable silyl anionic species (thermodynamic control) should be abandoned, or at least seriously amended: kinetic factors appear to exert a primary influence on the regioselectivity of such reactions. Since the two major kinetic factors (i.e., electrophilic character of and steric hindrance at a given silicon atom) have opposite effects on the orientation of the reaction, it may happen that kinetic and thermodynamic control lead to the same result. For some of the unsymmetrical disilanes studied, the major reaction path was not the Si,Si bond cleavage; instead, Si-aryl bond breaking occurred, producing the corresponding aryl anions.

Full text of DOI:10.1021/jo961131e

J . Org. Chem. 1997, 62, 2011-2017
2011
Kin etic Con tr ol in th e Clea va ge of Un sym m etr ica l Disila n es
La`szlo` Hevesi,* Michael Dehon, Raphael Crutzen, and Adriana Lazarescu-Grigore
Department of Chemistry, Faculte´s Universitaires Notre-Dame de la Paix, 61, rue de Bruxelles,
B-5000 Namur, Belgium
Received September 30, 1996 (Revised Manuscript Received J anuary 15, 1997X)
A series of 12 phenyl-substituted arylpentamethyldisilanes 1a -l have been synthesized in order
to examine the regioselectivity of their nucleophilic Si,Si bond cleavage reactions under Still’s
conditions (MeLi/HMPA/0 °C). It has been found that the sensitivity of these reactions to the
electronic effects of the substituents in the phenyl ring could be described by the Hammett-type
equation log(kA/kB) ) 0.4334 + 2.421(Σσ); (correlation coefficient R ) 0.983). The kA/kB ratio
represents the relative rate of attack at silicon atom A (linked to the aryl ring) or at silicon atom
B (away from the aryl ring) of the unsymmetrical disilanes. Thus, the present investigation shows
that the earlier belief according to which the nucleophilic cleavage of unsymmetrical disilanes always
produces the more stable silyl anionic species (thermodynamic control) should be abandoned, or at
least seriously amended: kinetic factors appear to exert a primary influence on the regioselectivity
of such reactions. Since the two major kinetic factors (i.e., electrophilic character of and steric
hindrance at a given silicon atom) have opposite effects on the orientation of the reaction, it may
happen that kinetic and thermodynamic control lead to the same result. For some of the
unsymmetrical disilanes studied, the major reaction path was not the Si,Si bond cleavage; instead,
Si-aryl bond breaking occurred, producing the corresponding aryl anions.
In tr od u ction
kinetic factors, such as the steric bulk of the goups
attached to silicon and to tin, can play a dramatic role
as to the preferential formation of silyl or stannyl anionic
species. Thus, tributylstannyl anion was efficiently
produced by the “naked” cyanide ion-mediated cleavage
of tributylstannylsilanes when the silyl moiety was Me3-
Si, PhMe2Si, or n-BuMe2Si, whereas stannylsilanes hav-
ing Et3Si or t-BuMe2Si groups were completely unreac-
tive.8 Even more remarkably, trialkylstannyl or tri-
alkylsilyl mixed cuprates could be formed selectively from
appropriately substituted stannylsilanes upon cleavage
with a higher order cuprate.9
These and other observations10 led us to undertake a
systematic investigation of the nucleophilic cleavage
reaction of unsymmetrical disilanes such as the series
1a -l (Scheme 1) where both electronic and steric effects
will alter the reactivity of one of the silicon atoms, the
other one being held constant. From the results reported
here we conclude that in the compounds studied under
the chosen conditions, the Si,Si bond cleavage is over-
whelmingly controlled by kinetic factors.
Silyl anionic species have become of increasing impor-
tance in various fields of organic chemistry,1 as well as
in materials sciences.2
Although the reaction of disilanes with alkali metals
is a well-known method for the production of silylmetal
species,3 the less economic but considerably faster cleav-
age of the same disilanes by strongly nucleophilic re-
agents, such as alkoxides,4,5 methyllithium,6a or fluoride
ion,7 has often been preferred as an alternative method.
Almost invariably, symmetrical disilanes have been
considered for this latter type of reaction, and the scarce
data reported for unsymmetrical disilanes5,7 indicate that
the Si,Si bond is cleaved in such a way as to generate
the more stable silyl metal species (thermodynamic
control of the reaction). However, in the conceptually
related Sn,Si bond cleavages it has been observed that
X Abstract published in Advance ACS Abstracts, March 15, 1997.
(1) (a) Fleming, I. In Comprehensive Organic Chemistry; Barton, D.
H. R., Ollis, W. D., Eds.; Pergamon Press: Oxford, 1979; Vol. 3. (b)
Colvin, E. W. Silicon in Organic Synthesis; Butterworths: London,
1981. (c) Weber, W. P. Silicon Reagents for Organic Synthesis; Springer
Verlag: Berlin, 1983. (d) Colvin, E. W. Silicon Reagents in Organic
Synthesis; Academic Press: London, 1988. (e) Comprehensive Organic
Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford,
1991. (f) Lipshutz, B. H. In Organometallics in Synthesis; Schlosser,
M., Eds.; J ohn Wiley & Sons: Chichester, U.K., 1994. (g) Hevesi, L.
In Comprehensive Organic Functional Group Transformations; Katritz-
ky, A. R., Meth-Cohn, O., Rees, C. W., Eds.; Pergamon: Oxford, 1995;
Vol. 2, Ley, S. V., Ed., Chapter, 2.18.
(2) (a) West, R. In The Chemistry of Organic Silicon Compounds;
Patai, S., and Rappoport, Z.,Eds.; J ohn Wiley & Sons: Chichester, U.K.,
1989; Vol. 2, p 1207. (b) J ones, R. G.; Benfield, R. E.; Cragg, R. H.;
Swain, A. C.; Webb, S. J . Macromolecules 1993, 26, 4878. (c) Organo-
silicon Chemistry II, From Molecules to Materials; Auner, N., Weis,
J ., Eds.; VCH: Weinheim, Germany, 1996.
Resu lts a n d Discu ssion
Disilanes 1a -l have been prepared in a straightfor-
ward manner by reacting pentamethylchlorodisilane with
the corresponding aryllithiums, themselves obtained by
bromine/lithium exchange (ArBr/2 equiv of t-BuLi/Et2O/
-78 °C/1 h). These disilanes were then subjected to the
cleavage reaction described by Still6a (1 equiv of MeLi/
HMPA/0 °C/15 min) followed by quenching of the reaction
mixtures with aqueous ammonium chloride. The so-
obtained product mixtures have been analyzed by gas
chromatography.
(3) See, for example: Davis, D. D.; Gray, C. E. Organomet. Chem.
Rev. A 1970, 6, 283 and references cited therein.
(4) (a) Sakurai, H.; Okada, A.; Kira, M.; Yonezawa, K. Tetrahedron
Lett. 1971, 1511. (b) Sakurai, H.; Okada, A. J . Organomet. Chem. 1972,
35, C13. (c) Sakurai, H.; Kondo, F. Ibid. 1975, 92, C46.
(5) Buncel, E.; Venkatachalam, T. K.; Edlund, U. J . Organomet.
Chem. 1992, 437, 85.
(8) Chenard, B. L.; Laganis, E. D.; Davidson, F.; RajanBabu, T. V.
J . Org. Chem. 1985, 50, 3666.
(6) (a) Still, W. C. J . Org. Chem. 1976, 41, 3063. (b) Still, W. C.;
Mitra, A. Tetrahedron Lett. 1978, 2659.
(7) Hiyama, T.; Obayashi, M.; Mori, I.; Nozaki, H. J . Org. Chem.
1983, 48, 912.
(9) Lipshutz, B. H.; Reuter, D. C.; Ellsworth, E. L. J . Org. Chem.
1989, 54, 4975.
(10) Dispa, J .-F.; Hevesi, L. Unpublished work on the cleavage by
methyllithium of (N-methyl-2-pyrrolyl)pentamethyldisilane.
S0022-3263(96)01131-0 CCC: $14.00 © 1997 American Chemical Society

2012 J . Org. Chem., Vol. 62, No. 7, 1997
Hevesi et al.
Sch em e 1
Ta ble 1. Com p etition betw een p a th s A a n d B (Sch em e
1) in th e clea va ge of u n sym m etr ica l d isila n es 1
aryldimethylsilyl anions corresponding to 5a -c would be
anticipated to be more stable. On the other hand, site A
of disilanes 1a -c is certainly the more electrophilic one,
suggesting thereby that these reactions are governed by
kinetic control.
On the other extreme of our disilanes series, cleavage
of compound 1l led to the quantitative formation of a 26/
74 mixture of silanes 2l and 5l. This result would also
appear surprising in terms of the relative stability of
trimethylsilyl and [4-(dimethylamino)phenyl]dimethyl-
silyl anions, since now the former one would be predicted
to be more stable, and yet, the latter one has been formed
predominantly. If, however, we admit that the strongly
electron-releasing 4-(dimethylamino) group is able to
reduce the electrophilicity of site A below that of site B,
then the observed 2l/5l ) 26/74 ratio can again be
explained by kinetic control of the reaction.
entry disilane 1
X
kA/kB
log(kA/kB)
Σσ
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
1g
1h
1i
H
4-Cl
95/5 ) 19
1.28
1.12
2.3
0.0
93/7 ) 13.3
0.24
0.70
0.74
1.13b
3-CF3; 4-Cl 99.5/0.5 ) 199a
3,5-Cl2
F5
2-Me
99/1 ) 99
1.99
2.4
99.6/0.4 ) 250a
52/48 ) 1.08
59/41 ) 1.44
47/53 ) 0.9
0.033 -0.14b
4-Me
0.16
-0.14
2,5-Me2
2,6-Me2
2-OMe
4-OMe
4-NMe2
-0.046 -0.20b
68/12 ) 5.7
0.76
0.44
0.21
-0.28b
-0.12b
-0.12
-0.32
10
11
12
1j
1k
1l
73.5/26.5 ) 2.8
62/38 ) 1.63
26/74 ) 0.35
-0.46
a
b
Estimated approximate value. Hammett σ for ortho substit-
uents taken equal to σpara
.
According to the two possible sites of attack A and B
of the nucleophile methyllithium, the expected cleavage
products are the silanes 2 and 5 (Scheme 1, paths A′ and
B). Therefore, in order to facilitate the analysis of the
chromatograms, authentic silanes 2 and 5 have also been
prepared. Nevertheless, with the exception of compounds
1a -c and 1l, the results obtained for all of the other
disilanes were complicated by the presence in the reac-
tion mixtures of unexpected products arising either from
cleavage of the aryl-silicon bonds (Scheme 1, path A′′)
or from other side reactions. However, since most of the
byproducts did arise from attack of methyllithium at one
or the other of the two silicon atoms of the starting
disilanes 1, the total of the products originating from each
site has to be considered rather than just the amounts
of silanes 2 and 5. For this reason, Table 1 lists the total
amounts of products generated by attack of the nucleo-
phile at sites A and B.
In the cases of disilanes 1a -c and 1l very clean
cleavage reactions were observed, leading only to the
corresponding silanes 2 and/or 5. However, it was
surprising to find that electron-attracting substituents
such as those present in 1b and 1c did not induce the
formation of substantial amounts of 5b or 5c. Similarly,
up to 95% of the attack of the unsubstituted 1a occurred
at site A forming 2a and the less stable trimethylsilyl
anion after Si,Si bond breaking. In all three cases, the
As judged from the nature of the products, the cleav-
ages of disilanes 1d and 1e may appear quite different;
in fact, these reactions took place in a very similar
manner. In both cases methyllithium attacked at silicon
atom A leading eventually to a negatively charged
pentacoordinate silicon species11 of type I that could in
principle expel trimethylsilyl anion or an aryl anion.
Due to the better leaving-group abilities of 3,5-dichlo-
rophenyl and pentafluorophenyl anions as compared to
that of trimethylsilyl anion, the silicon-aryl bond of 1d
and 1e was cleaved predominantly. The relative amounts
of primary products formed from 1d were as follows: 1,3-
dichlorophenyl anion 91% (detected as m-dichlorobenzene
(4d )), (3,5-dichlorophenyl)trimethylsilane (2d ) 8%, and
(11) For the mechanisms of nucleophilic substitution on silicon, see,
for example: (a) Corriu, R. J . P.; Guerin, C.; Moreau, J . J . E. In The
Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z.,
Eds.; J ohn Wiley & Sons: Chichester, U.K., 1989; Vol. 1, p 305. (b)
Bassindale, A. R.; Taylor, P. G. Ibid. p 839.

Cleavage of Unsymmetrical Disilanes
J . Org. Chem., Vol. 62, No. 7, 1997 2013
Sch em e 2
(3,5-dichlorophenyl)dimethylsilyl anion 1% (detected as
(3,5-dichlorophenyl)dimethylsilane (5d )). Thus, the ratio
of total attack at site A to that at site B is kA/kB ) 99/1
(Table 1, entry 4).
Under the same conditions the cleavage reaction of
disilane 1e occurred in a peculiar manner: a deep purple-
black precipitate formed upon dropwise addition of
methyllithium (eventually accompanied by the appear-
ance of a few gas bubbles), and by the end of the addition
the whole reaction mixture solidified. Quenching with
aqueous ammonium chloride and warming to room
temperature led to a more aboundant gas evolution and
bleaching of the mixture. Conventional workup gave a
light beige solid (insoluble in all common solvents) and
a small amount of liquid. Gas chromatographic analysis
of the latter showed the presence of traces of (pentafluo-
rophenyl)trimethylsilane (2e) and (pentafluorophenyl)-
dimethylsilane (5e). On the other hand, because of its
insolubility the light beige solid could not be analyzed
by conventional spectroscopic methods. However, XPS
spectroscopy has revealed carbon (57 atomic %) and
fluorine (40 atomic %) as major constituents; nitrogen,
oxygen, and silicon are present in the amounts of 1
atomic % each. Furthermore, the carbon peak could be
resolved into two components, one corresponding to
carbons bound to fluorine (65%) and one of the type
C-C-F (35%). Since these figures are very close to those
of perfluoropoly-p-phenylene, we assign this structure to
the beige solid. In a preliminary account12 of this work
we erroneously proposed poly(dimethyl)silane as the
structure of this solid material. On the basis of reported
precedents13 it was assumed that methyllithium might
have abstracted a methyl group from 1e. The silyl anion
produced would have decomposed with generation of
tetramethyldisilene, which would then have polymerized.
In light of the present data this pathway can be ruled
out.
Therefore, the apparent differences between the reac-
tions of 1d and 1e arise from the different fates of the
aryl anions formed in the cleavage steps: 1,3-dichlo-
rophenyl anion is stable under the reaction conditions
and gives m-dichlorobenzene on protonation, whereas
pentafluorophenyl anions polymerize by an SNAr-type
mechanism14 (Scheme 2). This process liberates fluoride
ions, which are known to react instantly with hexa-
methyldisilane7 to give trimethylsilyl fluoride and tri-
methylsilyl anion (converted into trimethylsilane upon
protonation). These low-boiling compounds may have
been the origin of the observed gas bubbles. On the other
hand, formation of perfluoropolyphenylene has been
confirmed by generating pentafluorophenyl anions from
pentafluorobromobenzene (1 equiv of n-BuLi/THF/-78
°C, 1 h, then 2 equiv of HMPA/0 °C, 1 h). The XPS
spectrum of the so-obtained off-white solid was identical
to that described above.
Analyses of the cleavage reaction mixtures have been
slightly complicated by the presence in these mixtures
of various but substantial amounts of silanols arising
from silanes 5f-h . Indeed, hydrosilanes are known to
undergo nucleophilic substitution reactions by strong
nucleophiles leading to displacement of hydride ions.15
In our case, we have noted that uncontrolled quenching
of the cleavage reactions of 1f-h with aqueous am-
monium chloride led to basic media where hydroxide ions
could partially transform 5f-h into the corresponding
silanols.16
Surprisingly, the cleavage behavior of disilane 1i
differed from that of 1f-h in that attack of site A was
seen to be predominating: kA/kB ) 5.7 (Table 1, entry 9).
The apparently complex product mixture consisted of
m-xylene (62%), (2,6-dimethylphenyl)trimethylsilane (2i)
(6%), (2,6-dimethylphenyl)dimethylsilane (5i) (5.5%),
(2,6-dimethylphenyl)dimethylsilanol (6.5%), as well as
another silane identified as [(3-methylphenyl)methyl]-
trimethylsilane (6) (20%). Silanes 2i and 5i are the
normal Si-Si bond cleavage products arising from attack
at sites A and B, respectively. Since the major 3,5-
dimethylphenyl anion can only have been formed by
attack at site A followed by Si-aryl bond cleavage, it
remains intriguing why this process is the most favored
one. Indeed, the cases of 1f-h show that, due to the
The members of the next group of disilanes, 1f-h , have
in common that their sites A and B display quite similar
reactivities toward methyllithium under the presently
used conditions; as a result, the corresponding kA/kB
ratios all have values close to unity (Table 1, entries 6-8).
(15) Reaction of hydrosilanes with nucleophiles: (a) Grignard and
organolithium reagents: Gilman, H.; Zuech, E. A. J . Am. Chem. Soc.
1959, 81, 5925 and references cited therein. (b) Hydroxides: Sommer,
L. H.; Korte, W. D.; Frye, C. L. J . Am. Chem. Soc. 1972, 94, 3463 and
references cited therein.
(16) In a control experiment the reaction of dimethyl-o-tolylsilane
5f with 1 equiv of lithium hydroxide in aqueous HMPA at room
temperature for 10 min gave essentially complete conversion into
dimethyl-o-tolylsilanol.
(12) Hevesi, L.; Dehon, M. Tetrahedron Lett. 1994, 35, 8031.
(13) Nadler, E. B.; Rappoport, Z. Tetrahedron Lett. 1990, 31, 555.
(14) We thank one of the reviewers for pointing out that in the
polymerization reactions attack of a neutral species such as 1e or 2e
by the pentafluorophenyl anion should be a more favorable process
than the latter’s self-condensation. The same remark pertains for the
synthesis of perfluoropolyphenylene from pentafluorobromobenzene.
A more detailed study of these reactions will be reported in due course.

2014 J . Org. Chem., Vol. 62, No. 7, 1997
Hevesi et al.
Sch em e 3
4-(trimethylsilyl)phenol (8) (72%) and (4-methoxyphenyl)-
dimethylsilane (5k ) (2%).
The presence of large amounts of phenolic compounds
in both reaction mixtures strongly suggested that de-
methylation reactions of the methoxy groups must have
occurred. The primary products, silyl anions, appeared
to be good candidates for effecting these nucleophilic
demethylation reactions. Control experiments estab-
lished indeed that trimethylsilyl and dimethylphenylsilyl
anions are able to transform anisole as well as 4-(tri-
methylsilyl)anisole (2k ) into the corresponding phenolate
anions. Furthermore, it was noted that the reactions of
the two above-mentioned silyl anions with anisole pro-
ceeded with quite comparable rates (approximately 50%
conversion after 0.5 h of reaction). Therefore, we as-
sumed that all phenolic products arose from demethyla-
tion of the corresponding methoxy compounds in equal
amounts by trimethylsilyl, (2-methoxyphenyl)dimethyl-
silyl, or (4-methoxyphenyl)dimethylsilyl anions. This
means that the 48% of 2-(trimethylsilyl)phenol (7) ob-
tained in the cleavage of 1j derived from demethylation
of 2j by Me3Si and Me2(2-MeOPh)Si anions to the extent
of 24% each (Scheme 4). However, since demethylation
of 2j by (2-methoxyphenyl)dimethylsilyl anion (5j′) re-
stores 2j, only those 24% have to be added to the observed
42% of 2j that have been demethylated by trimethylsilyl
anion (Scheme 4, path A′). This increases the amount
of initially formed 2j to 66%, which has to be comple-
mented by the amount of Si-aryl bond cleavage to get
the grand total of attack at site A. Indeed, anisole may
have originated from this route and phenol from the
demethylation of the so-formed anisyl anion by the two
silyl anions present (to the extent of 1.5% each; Scheme
4 path A′′). Thus, the total of attack at site A of 1j equals
42 + 24 + 9 - 1.5 ) 73.5% and at site B to 1 + 24 + 1.5
) 26.5% (Table 1, entry 10). An alternative to the
scenario of Si-aryl bond cleavage leading to the presence
of anisole and phenol might consist in the desilylation of
2j by its own demethylation product 2-(trimethylsilyl)-
phenolate anion. Regardless of which one (or both) of
these pathways were operative, the final figures would
not be changed appreciably.
Similarly, but in a more straightforward manner,
formation of 4-(trimethylsilyl)phenol (8) was attributed
to demethylation of 4-(trimethylsilyl)anisole (2k ) by Me3-
Si and dimethyl(4-methoxyphenyl)silyl anions in equal
parts (36% each). Therefore, the total attack at site A of
1k amounted in fact to 26 + 36 ) 62% and that at site B
to 2 + 36 ) 38% (Table 1, entry 11). Interestingly, we
have noted that purified 4-(trimethylsilyl)phenol (8)
decomposed on standing into phenol and trimethyl[4-
[(trimethylsilyl)oxy]phenyl]silane, which means that de-
silylation of this type of aromatic silanes can take place
even under the action of the weakly nucleophilic phenolic
hydroxy group.18
The results shown in Table 1 were correlated by a
Hammett equation. For this purpose, Table 1 also
includes the normal σ values, or when needed, their sums
Σσ. Figure 1 shows this correlation.
One can note that, while a fair number of points seem
to fit into a linear relationship, others deviate substan-
tially. It is worth specifying that among the latter we
find 1a with its unexpectedly high kA/kB value already
electron-donating effect of methyl substituents on the
phenyl ring, the electrophilic character of the two silicon
atoms became roughly equal. From a kinetic point of
view, steric hindrance by the two o-methyl groups present
in 1i should have further diminished the chances of
attack at site A. On the other hand, in spite of their
unfavorable electronic effects, steric hindrance by the
same o-methyl groups in the pentacoordinate intermedi-
ate of type I should favor the expulsion of 2,6-dimeth-
ylphenyl anion. This decomposition might well be faster
than that of the pentacoordinate intermediate resulting
from attack at site B. Thus, as long as formation from
1i of the two possible pentacoordinate intermediates are
equilibrium processes the overall equilibrium can be
driven in the observed direction.
While (2,6-dimethylphenyl)dimethylsilanol most prob-
ably was produced as above by further transformation
of silane 5i by fortuitous hydroxide ions, rationalization
of the benzylic silane 6 requires a new reaction pathway
(Scheme 3). Besides being an excellent nucleophile,
methyllithium in HMPA solution should also be a very
strong base capable of extracting a proton from one of
the o-methyl groups of 1i generating a benzylic anion.
Intramolecular nucleophilic attack of this anion on silicon
atom A would lead to a silabenzocyclobutene intermedi-
ate17 that upon ring opening by another methyl anion
followed by protonation would give silane 6 whose
structure has been confirmed by independent synthesis
(see the Experimental Section).
Quantitative evaluation of the two competing cleavage
pathways A and B of the methoxy-substituted disilanes
1j and 1k has met with some difficulty due to the
diversity of observed products. The more complex mix-
ture has been obtained from 1j in which five different
compounds could be identified: 2-(trimethylsilyl)anisole
(2j) (42%), 2-(trimethylsilyl)phenol 7 (48%), anisole (6%),
phenol (3%) and (2-methoxyphenyl)dimethylsilane (5j)
(1%). The mixture produced by cleavage of disilane 1k
was more simple: 4-(trimethylsilyl)anisole (2k ) (26%),
(17) Precedents for the formation of silabenzocyclobutene and stan-
nabenzocyclobutene systems by closely resembling pathways have been
reported: (a) Baines, K. M.; Groh, R. J .; J oseph B.; Parshotam, U. R.
Organometallics 1992, 11, 2176. (b) Weidenbruch, M.; Scha¨fers, K.;
Schlaefke, J .; Peters, K.; von Schnering, H. G. J . Organomet. Chem.
1991, 415, 343.
(18) For desilylation of 2-silylpyridines see: (a) Anderson, D. G.;
Bradney, M. A. M.; Webster, D. E. J . Chem. Soc, B 1968, 450. (b)
Anderson, D. G.; Webster, D. E. J . Chem. Soc. B 1968, 1008.

Cleavage of Unsymmetrical Disilanes
J . Org. Chem., Vol. 62, No. 7, 1997 2015
Sch em e 4
correlation line might be accommodated at least in part
by considering that the electrophilicity of silicon atom A
is in fact more strongly increased by the unsubstituted
phenyl ring than the ordinary hydrogen Hammett σ of
0.0 allows. Some sort of inductive σ (σI or σ*, or a
combination thereof) would probably be better suited.
In conclusion, the present investigation shows that the
earlier belief that nucleophilic cleavage of unsymmetrical
disilanes always produces the more stable silyl anionic
species (thermodynamic control) should be abandoned,
or at least strongly amended. Kinetic factors appear
indeed to exert a primary influence on the outcome of
such reactions: as long as nucleophilic attack at a given
silicon atom is not completely suppressed by unfavorable
steric effects, for example, the electrophilic character of
that silicon atom (as determined by electronic effects)
always seems to play a predominant role. Of course, the
nature of the nucleophile, its size, nucleophilicity, and
solvation properties should also be taken into account.
Therefore, we consider the results reported here as the
first stage of a more complete work that should include
the investigation of the nucleophile and the reaction
conditions used.
F igu r e 1. Hammett correlation of the regioselectivity of
cleavage of disilanes 1 (line drawn with “X” points).
mentioned, 1i and 1j bearing ortho substituents, as well
as the peculiar 1e, which also has ortho substituents.
Obviously, taking σortho ) σpara for the latter three
compounds is a very crude approximation since by doing
so no account is taken of the steric effects of the ortho
substituents. Neglecting the points corresponding to
these three compounds, we obtain the correlation equa-
tion (eq 1) represented by the line drawn on Figure 1.
Exp er im en ta l Section
All reactions were carried out in septum-fitted glassware
under an argon atmosphere. Solvents diethyl ether and THF
were freshly distilled from sodium benzophenone ketyl, and
log(kA/kB) ) 0.4334 + 2.421(Σσ)
(R ) 0.983) (1)
(19) A reviewer has proposed single-electron transfer (SET) as a
possible alternative mechanism for the cleavage of disilanes 1. The
compulsory first formed intermediate would be the radical anion of 1,
the extra electron residing either on one of the silicon atoms or on the
aryl moiety. This radical anion could decompose into a silyl radical
and a silyl anion that, on coupling with methyl radicals or by hydrogen
abstraction, could lead to the observed products. Therefore, such a
mechanism cannot be ruled out entirely. It seems to us, however, that
in our case SET can not be more than a minor side reaction since
otherwise considerable amounts of symmetrical 1,2-diaryltetramethyl
disilanes should also be formed. We have not observed these products.
It is also interesting to note that SET has often been observed in
reactions of silyl anions with various electrophiles4,6,7 and only under
particular circumstances in reactions of nucleophiles with silicon
substrates.11a,17a,20
This correlation line with its slope of 2.42 indicates a
relatively strong dependence of the rate ratio on elec-
tronic effects and nicely corroborates the prevalence of
kinetic control in the disilane cleavage reactions reported
here. It suggests that the slow step of these reactions is
the nucleophilic attack on silicon,19 which is favored by
the latter’s electrophilic character. Quite reasonably, the
electrophilicity of silicon atom A increases more with
electron-withdrawing substituents on the phenyl ring
than that of silicon atom B, hence the positive slope in
Figure 1. In this context, the deviation of 1a from the
(20) Corriu, R. J . P.; Ould-Kada, S.; Lanneau, G. F. J . Organomet.
Chem. 1983, 248, 39).

2016 J . Org. Chem., Vol. 62, No. 7, 1997
Hevesi et al.
HMPA was distilled from barium oxide and stored on molec-
ular sieves; other reagents were purchased from Aldrich, Fluka
(Bornem, Belgium), and Acros Chimica (Geel, Belgium). Un-
less otherwise noted, IR spectra were recorded on liquid films
between sodium chloride plates; 1H NMR spectra were ob-
tained at 90 MHz or at 400 MHz in CDCl3 solution with TMS
reference. 13C and 29Si NMR spectra were recorded under the
same conditions at 100.4 and 79.3 MHz, respectively. Gas
chromatographic analyses were effected on an SE-30HL
column using dodecane as internal standard.
Ch lor op en t a m et h yld isila n e was prepared from hexa-
methyldisilane and acetyl chloride in the presence of alumi-
num trichloride by a modified literature procedure.21 The
modification consisted in using a dichloromethane solution22
of CH3COCl/AlCl3 instead of letting the mixture react without
solvent;21b a typical experiment follows.
Acetyl chloride (7.9 g, 100 mM) was added dropwise from a
pressure-equalizing funnel to a stirred suspension of alumi-
num trichloride (13.3 g, 100 mM) in 20 mL of dichloromethane
cooled to 0 °C under argon. The so-obtained orange-yellow
homogeneous solution was transferred into another pressure-
equalizing funnel from which it was slowly added (over 20 min)
to a solution of hexamethyldisilane (14.6 g, 100 mM) in 20 mL
of dry dichloromethane stirred at 0 °C under argon. After the
addition was complete, the mixture was stirred for 1 h and
then extracted three times with 20 mL of dry pentane.
Fractionation of the pentane solution led to 12.5 g (65%) of
chloropentamethyldisilane, bp 128-132 °C (lit.21c bp 133-135
°C) >95% pure. Since the only detectable (NMR) impurity was
hexamethyldisilane, the sample was used without further
purification: 1H NMR (ref CH2Cl2) δ 0.16 (s, 9H), 0.47 (s, 6H).
1,2-Dichlorotetramethyldisilane21c can be prepared by the
same procedure but using twice the amount of acetyl chloride-
aluminum chloride complex.
(3,5-Dich lor oph en yl)pen tam eth yldisilan e (1d) (58% yield
after column chromatography): 1H NMR δ 0.07 (s, 9H), 0.33
(s, 6H), 7.25 (d, J ) 1.7 Hz, 2H), 7.28 (t, J ) 1.7 Hz, 1H); 13C
NMR δ -3.9, -2.1, 128.6, 131.8, 135.1, 145.0; 29Si NMR δ
-19.1, -19.5; IR 3065, 2951, 2893, 1567, 1542, 1390, 1247,
1099, 836, 807, 761 cm-1. Anal. Calcd for C11H18Cl2Si2: C,
47.64; H, 6.54. Found: C, 47.66; H, 6.59.
(P en taflu or oph en yl)pen tam eth yldisilan e (1e) (67% yield
after column chromatography): 1H NMR(ref CH2Cl2) δ 0.11
(s, 9H), 0.44 (s, 6H); 13C NMR δ -2.7, -2.2, 136.3, 138.9, 140.8,
143.0, 148.0, 150.4; 29Si NMR δ -17.6, -19.6; IR 2955, 2897,
1511, 1458, 1400, 1250, 1050, 798 cm-1; MS (m/e) 298 (M),
283 (M - CH3), 73 (SiMe3+). Anal. Calcd for C11H15F5Si2: C,
44.28; H, 5.07. Found: C, 44.35; H, 5.13.
(2-Meth ylp h en yl)p en ta m eth yld isila n e (1f) (62% yield
after distillation; bp0.2Torr 60-65 °C): 1H NMR (ref CH2Cl2) δ
0.08 (s, 9H), 0.39 (s, 6H), 2.41 (s, 3H), 7.15 (t, J ) 7.2 Hz, 2H),
7.24 (d, J ) 7.2 Hz, 1H), 7.41 (d, J ) 7.2 Hz, 1H); IR 3055,
3001, 2950, 2892, 1586, 1443, 1400, 1245, 1125, 836, 805, 762
cm-1; MS (m/e) 222 (M), 207 (M - CH3), 149 (M - SiMe3), 91
(M - Si2Me5), 73 (SiMe3+). Anal. Calcd for C12H22Si2: C,
64.78; H, 9.97. Found: C, 64.88; H, 10.07.
(4-Meth ylp h en yl)p en ta m eth yld isila n e (1g) (67% yield
after distillation; bp0.1Torr 60-63 °C): 1H NMR (ref CH2Cl2) δ
0.06 (s, 9H), 0.31 (s, 6H), 2.35 (s, 3H), 7.16 (m, 2H), 7.36 (m,
2H); IR 3063, 3009, 2949, 2892, 1600, 1437, 1391, 1244, 1100,
836, 808, 759; cm-1; MS (m/e) 222 (M), 207 (M - CH3), 149 (M
- SiMe3), 91 (M - Si2Me5), 73 (SiMe3+). Anal. Calcd for
C12H22Si2: C, 64.78; H, 9.97. Found: C, 64.80; H, 9.97.
(2,5-Dim eth ylp h en yl)p en ta m eth yld isila n e (1h ) (72%
yield after distillation; bp0.25Torr 68-72 °C): 1H NMR (ref CH2-
Cl2) δ 0.08 (s, 9H), 0.38 (s, 6H), 2.31 (s, 3H), 2.37 (s, 3H), 7.05
(s, 2H), 7.20 (s, 1H); IR 3083, 3026, 3002, 294, 2892, 1481,
1448, 1399, 1381, 1245, 1144, 1076, 836, 797, 765 cm-1; MS
(m/e) 236 (M), 221 (M - CH3), 163 (M - SiMe3), 105 (M -
Si2Me5), 73 (SiMe3+). Anal. Calcd for C13H24Si2: C, 66.02; H,
10.23. Found: C, 66.05; H, 10.31.
Syn th esis of Disila n es 1. All the unsymmetrical disilanes
have been prepared from the corresponding aryl bromides and
chloropentamethyldisilane.
Gen er a l P r oced u r e. tert-Butyllithium (20 mM, 1.7 M
solution in pentane) was added by a syringe to an ethereal
(15 mL) solution of the aryl bromide (10 mM) cooled to -78
°C under argon. After the solution was stirred at this
temperature for 1-2 h, chloropentamethyldisilane (1.7 g, 10
mM) dissolved in 5 mL of dry ether was added, and the
mixture was stirred for a further 2 h; during this time, the
temperature was allowed to reach 20 °C (in the case of 1i the
mixture was stirred for 24 h at room temperature and for 24
(2,6-Dim eth ylph en yl)pen tam eth yldisilan e (1i) (37% yield
after column chromatography and distillation; bp0.1Torr 63-65
°C): 1H NMR (ref CH2Cl2) δ 0.09 (s, 9H), 0.48 (s, 6H), 2.40 (s,
6H), 6.96 (d, J ) 8 Hz, 2H), 7.11 (t, J ) 8 Hz, 1H); IR 3049,
2949, 2892, 1585, 1559, 1448, 1399, 1375, 1245, 1144, 1076,
834, 801, 768; MS (m/e) 236 (M), 221 (M - CH3), 163 (M -
SiMe3), 105 (M - Si2Me5), 73 (SiMe3+). Anal. Calcd for C13H24
Si2: C, 66.02; H, 10.23. Found: C, 66.03; H, 10.29.
-
h
at reflux). Conventional aqueous ammonium chloride
(2-Meth oxyp h en yl)p en ta m eth yld isila n e (1j) (68% yield
after distillation; bp0.1Torr 54-57 °C): 1H NMR (ref CH2Cl2) δ
0.03 (s, 9H), 0.30 (s, 6H), 3.78 (s, 3H), 6.80 (d, J ) 7.8 Hz,
1H), 6.96 (t, J ) 7.3 Hz, 1H), 7.33 (m, 2H); IR 306, 2950, 2892,
1586, 1570, 1440, 1400, 1234, 1127, 1045, 833, 802 cm-1; MS
(m/e) 238 (M), 223 (M - CH3), 165 (M - SiMe3), 135 (M -
2Me - SiMe3), 107 (M - Si2Me5), 73 (SiMe3+). Anal. Calcd
for C12H22OSi2: C, 60.44; H, 9.30. Found: C, 60.51; H, 9.27.
workup followed by purification (vacuum distillation or column
chromatography (SiO2, eluent pentane/cyclohexane, 9/1 v/v))
led to pure 1 in 65-75% yields.
P h en ylp en ta m eth yld isila n e (1a ) (65% yield after column
chromatography of crude 1a ): 1H NMR(ref CH2Cl2) δ 0.10 (s,
9H), 0.38 (s, 6H), 7.35 (m, 3H), 7.50 (m, 2H); 13C NMR δ -3.7,
-2.0, 128.0, 128.6, 134.0, 139.9; 29Si NMR δ -19.4, -21.7; IR
3050, 3020, 2950, 1486, 1400, 1245, 1105, 833, 760, 698 cm-1
.
(4-Meth oxyp h en yl)p en ta m eth yld isila n e (1k ) (52% yield
after distillation; bp0.1Torr 68-72 °C):1H NMR (ref CH2Cl2) δ
0.06 (s, 9H), 0.31 (s, 6H), 3.81 (s, 3H), 6.91 (m, 2H), 7.38 (m,
2H); 13C NMR δ -3.8, -2.3, 54.7, 113.6, 130.0, 135.0, 160.0;
IR 3078, 2949, 2892, 1593, 1563, 1500, 1440, 1395, 1276, 1246,
1106, 1034, 833, 800, 760; MS (m/e) 238 (M), 223 (M - CH3),
165 (M - SiMe3), 135 (M - 2Me - SiMe3), 107 (M - Si2Me5),
73 (SiMe3+). Anal. Calcd for C12H22OSi2: C, 60.44; H, 9.30.
Found: C, 60.00; H, 9.12.
[4-(N,N-Dim eth yla m in o)p h en yl]p en ta m eth yld isila n e
(1l) (50% yield after recrystallization from ethanol/water 3.5/1
v/v, mp 45 °C): 1H NMR (ref CH2Cl2) δ 0.05 (s, 9H), 0.28 (s,
6H), 2.95 (s, 6H), 6.73 (m, 2H), 7.32 (m, 2H); IR (KBr pellet)
3078, 3020, 2948, 2889, 1601, 1515, 1442, 1400, 1364, 1243,
1108, 828, 794 cm-1; MS (m/e) 251 (M), 236 (M - CH3), 178
(M - SiMe3), 134 (M - NMe2 - SiMe3), 120 (M - Si2Me5), 73
(SiMe3+). Anal. Calcd for C13H25NSi2: C, 62.08; H, 10.02; N,
5.57. Found C, 62.60; H, 9.93; N, 5.31.
(4-Ch lor op h en yl)p en ta m eth yld isila n e (1b) (67% yield
after column chromatography): 1H NMR(ref CH2Cl2) δ 0.06
(s, 9H), 0.33 (s, 6H), 7.32 (m, 2H), 7.37 (m, 2H); 13C NMR δ
-3.7, -2.0, 128.0, 128.3, 134.4, 135.0, 138.4; 29Si NMR δ -19.4,
-21.1; IR 3070, 2892, 1574, 1482, 1400, 1246, 1086, 833, 796,
761 cm-1; MS m/ e 242 (M), 227 (M - CH3), 207 (M - Cl), 169
(M - SiMe3), 134 (M - SiMe3 - Cl), 73 (SiMe3+). Anal. Calcd
for C11H19ClSi2: C, 54.40; H, 7.88. Found: C, 54.47; H, 8.02.
[4-C h lo r o -3-(t r iflu o r o m e t h y l)p h e n y l]p e n t a m e t h -
yld isila n e (1c) (68% yield after column chromatography): 1H
NMR (ref CH2Cl2) δ 0.07 (s, 9H), 0.36 (s, 6H), 7.47 (d, J ) 8
Hz, 1H), 7.52 (d, J ) 8 Hz, 1H), 7.72 (s, 1H); 13C NMR δ -4.9,
-2.5, 130.0, 132.1, 132.2, 132.3, 138.1, 139.5; 29Si NMR δ
-19.3, -20.1; IR 3048, 2951, 1567, 1474, 1248, 1098, 838, 794,
761 cm-1
.
(21) (a) Frainnet, E.; Calas, R.; Gerval, P.; Dentone, Y.; Bonastre,
J . Bull. Soc. Chim. Fr. 1965, 1259. (b) Sakurai, H.; Tominaga, K.;
Watanabe, T.; Kumada, M. Tetrahedron Lett. 1966, 5493. (c) Ishikawa,
M.; Kumada, M.; Sakurai, H. J . Organomet. Chem. 1970, 23, 63.
(22) Calas, R.; Gerval, J . C. R. Acad. Sci., Ser. II: Mec., Phys., Chim.,
Astron. 1985, 301, 1289.
Syn th esis of Sila n es 2 a n d 5. These reference compounds
have been prepared by the same general procedure using
trimethylchlorosilane and dimethylchlorosilane, respectively,

Cleavage of Unsymmetrical Disilanes
J . Org. Chem., Vol. 62, No. 7, 1997 2017
instead of chloropentamethyldisilane. The yields in 2 and 5
were generally good (70-90%); silanes 2a and 5a are com-
mercially available.
SiMe2OH), 75 (SiMe2OH). Anal. Calcd for C9H14SiO: C,
65.00; H, 8.50. Found: C, 64.99; H, 8.48.
(4-Meth ylp h en yl)d im eth ylsila n ol (from alkaline hydrol-
ysis of 5g): 1H NMR δ 0.38 (s, 6H), 2.03 (bs, 1H), 2.36 (s, 3H),
7.20 (m, 2H), 7.48 (m, 2H); IR 3340, 3065, 3031, 3010, 2953,
1
(4-Ch lor op h en yl)tr im eth ylsila n e (2b): H NMR δ 0.26
(s, 9H), 7.33 (m, 2H), 7.43 (m, 2H); 13C NMR δ -0.7, 128.4,
135.1, 135.6, 139.1; IR 3050, 2954, 1576, 1483, 1406, 1250,
2895, 1604, 1448, 1404, 1258, 1130, 1083, 838, 786, 745 cm-1
.
1080, 840, 755 cm-1
.
1
(2,5-Dim eth ylp h en yl)d im eth ylsila n ol (from alkaline hy-
drolysis of 5h ): 1H NMR δ 0.42 (s, 6H), 2.10 (bs, 1H), 2.31 (s,
3H), 2.45 (s, 3H), 7.04-7.14 (m, 2H), 7.35 (bs, 1H); IR 3347,
3027, 3005, 2957, 2868, 1481, 1448, 1405, 1382, 1252, 1145,
1083, 1053, 838, 786, 745; MS (m/e) 180 (M), 165 (M - Me),
147 (M - Me - H2O), 105 (M - SiMe2OH), 75 (SiMe2OH).
(2-Meth ylp h en yl)tr im eth ylsila n e (2f): H NMR 0.37 (s,
9H), 2.51 (s, 3H), 7.21 (overlapping t + d, J ) 8 Hz, 2H), 7.32
(td, J ) 8 Hz, J ′ ) 1.6 Hz, 1H), 7.52 (d, J ) 8 Hz, 1H); IR
3055, 3001, 2955, 2897, 1588, 1564, 1447, 1407, 1263, 1248,
1128, 837, 741 cm-1
.
(4-Meth ylp h en yl)tr im eth ylsila n e (2g): 1H NMR (ref CH2-
Cl2) δ 0.26 (s, 9H), 2.36 (s, 3H), 7.19 (m, 2H), 7.44 (m, 2H); IR
3065, 3031, 3010, 2953, 2895, 1604, 1448, 1404, 1258, 1247,
(2,6-Dim eth ylp h en yl)d im eth ylsila n ol (from alkaline hy-
drolysis of 5i): 1H NMR δ 0.48 (s, 6H), 2.04 (bs, 1H), 2.48 (s,
6H), 6.97 (d, J ) 7.8 Hz, 2H), 7.15 (t, J ) 7.8 Hz, 1H); IR 3347,
1107, 838, 754 cm-1
.
(2,5-Dim eth ylp h en yl)tr im eth ylsila n e (2h ): 1H NMR δ
0.31 (s, 9H), 2.31 (s, 3H), 2.41 (s, 3H), 7.07 (m, 2H), 7.26 (bs,
1H); IR 3085, 3002, 2952, 2868, 1516, 1450, 1399, 1262, 1248,
3050, 2956, 1586, 1559, 1443, 1400, 1254, 1131, 836 cm-1
.
[(3-Meth ylp h en yl)m eth yl]tr im eth ylsila n e (6) (isolated
as an inseparable mixture of 2i, 5i, and 6 from the cleavage
reaction of 1i) has been synthesized independently as follows.
1119, 837, 760 cm-1
.
(2,6-Dim eth ylp h en yl)tr im eth ylsila n e (2i). 1H NMR δ
0.43 (s, 9H), 2.50 (s, 6H), 7.01 (d, J ) 7.3 Hz, 2H), 7.17 (t, J )
7.3 Hz, 1H).
A potassium ([K+/K-]) solution was prepared from 227 mg
(5.8 mM) of potassium and 768 mg (2.9 mM) of 18-crown-6 in
10 mL of THF under argon at -20 °C, according to our recently
described procedure.23 (3-Methylphenyl)methyl bromide, 430
mg (2.33 mM) dissolved in 2 mL of THF, was slowly added by
a syringe. During this addition the deep blue color of the
potassium solution progressively turned into deep yellow-
brown, characteristic of the formation of benzylic potassium
derivatives. After 0.5 h of stirring, 315 mg (2.9 mM) of
trimethylsilyl chloride, dissolved in 2 mL of THF, was added,
and the so-formed white mixture was allowed to reach room
temperature. Stirring was continued for another 0.5 h during
which time the mixture turned brown again. Quenching with
aqueous NaHCO3 followed by conventional workup led to 185
mg of colorless crude product that was shown by gas chroma-
tography to be a 57/43 mixture of m-xylene and 6. Bulb-to-
bulb distillation (50 °C/0.02 Torr) gave 80 mg (19%) of almost
pure silane 6. This synthesis has not been optimized, but the
large amount of m-xylene formed suggests that much better
yields of 6 should be feasible: 1H NMR (ref CH2Cl2) δ -0.01
(s, 9H), 2.04 (s, 2H), 2.30 (s, 3H), 6.80 (d, J ) 7.3 Hz, 1H),
6.83 (s, 1H), 6.88 (d, J ) 7.3 Hz, 1H), 7.10 (t, J ) 7.3 Hz, 1H);
MS (m/e) 178 (M), 163 (M - Me), 105 (M - SiMe3), 73 (SiMe3).
(2-Meth oxyp h en yl)tr im eth ylsila n e (2j): 1H NMR δ 0.26
(s, 9H), 3.80 (s, 3H), 6.83 (d, J ) 8.2 Hz, 1H), 6.95 (t, J ) 7.3
Hz, 1H), 7.3-7.4 (m, 2H); IR 3062, 2953, 2833, 1587, 1570,
1497, 1429, 1235, 1128, 1044, 839 cm-1
.
(4-Meth oxyp h en yl)tr im eth ylsila n e (2k ): 1H NMR δ 0.24
(s, 9H), 3.81 (s, 3H), 6.92 (m, 2H), 7.45 (m, 2H); IR 3081, 2953,
2835, 1595, 1564, 1502, 1441, 1396, 1276, 1246, 1111, 1033,
839.
[4-(N,N-d im eth yla m in o)p h en yl]tr im eth ylsila n e (2l): 1H
NMR δ 0.23 (s, 9H), 2.95 (s, 6H), 6.73 (m, 2H), 7.40 (m, 2H);
IR 3080, 2951, 2893, 2803, 1598, 1508, 1443, 1404, 1353, 1245,
1112, 845.
(4-Ch lor op h en yl)d im eth ylsila n e (5b): 1H NMR (ref CH2-
Cl2) δ 0.35 (d, J ) 4 Hz, 6H), 4.43 (heptet, J ) 4 Hz, 1H), 7.32
(m, 2H), 7.48 (m, 2H); IR 3065, 2959, 2903, 2155, 1569, 1498,
1413, 1250, 1138, 886, 780 cm-1
.
(2-Meth ylp h en yl)d im eth ylsila n e (5f): 1H NMR δ 0.35 (d,
J ) 4 Hz, 9H), 2.45 (s, 3H), 4.53 (heptet, J ) 4 Hz, 1H), 7.17
(overlapping t + d, J ) 7.2 Hz, 2H); 7.28 (td, J ) 7.2 Hz, J ′ )
1.8 Hz, 1H), 7.47 (bd, J ) 7.2 Hz, 1H); IR 3055, 3001, 2957,
2869, 2119, 1589, 1448, 1249, 1130, 836 cm-1
.
(4-Meth ylp h en yl)d im eth ylsila n e (5g): 1H NMR δ 0.32
(d, J ) 4 Hz, 6H), 2.35 (s, 3H), 4.41 (heptet, J ) 4 Hz, 1H),
7.18 (m, 2H), 7.44 (m, 2H); IR 3065, 3031, 3010, 2957, 2867,
2-(Tr im eth ylsilyl)p h en ol (7): 1H NMR δ 0.31 (s, 9H), 4.80
(bs, 1H), 6.68 (d, J ) 7.7 Hz, 1H), 6.93 (t, J ) 7.7Hz, 1H), 7.22
(dd, J ) 7.7 Hz, 2.6 Hz, 1H), 7.37 (dd, J ) 7.7, 2.6 Hz, 1H); IR
3353, 3065, 3015, 2953, 2896, 1593, 1571, 1484, 1437, 1275,
2117, 1601, 1458, 1248, 1109, 836 cm-1
.
(2,5-Dim eth ylp h en yl)d im eth ylsila n e (5h ): 1H NMR δ
0.35 (d, J ) 4 Hz, 6H), 2.31 (s, 3H), 2.41 (s, 3H), 4.51 (heptet,
J ) 4 Hz, 1H), 7.08-7.12 (m, 2H), 7.27 (bs, 1H); IR 3084, 3000,
1244, 1123, 839, 755 cm-1
.
2956, 2865, 2119, 1481, 1448, 1248, 1145, 1079, 810 cm-1
.
4-(Tr im eth ylsilyl)p h en ol (8): 1H NMR (ref CH2Cl2) δ 0.28
(s, 9H), 5.95 (bs, 1H), 6.90 (m, 2H), 7.45 (m, 2H); IR 3365, 3020,
2954, 2924, 2853, 1598, 1580, 1465, 1419, 1262, 1247, 1179,
(2,6-Dim eth ylp h en yl)d im eth ylsila n e (5i): 1H NMR (ref
CH2Cl2) 0.41 (d, J ) 4 Hz, 6H), 2.48 (s, 6H), 4.76 (heptet, J )
4 Hz, 1H), 7.00 (d, J ) 7.5 Hz, 2H), 7.17 (t, J ) 7.5 Hz, 1H).
(2-Meth oxyp h en yl)d im eth ylsila n e (5j): 1H NMR (ref
CH2Cl2) δ 0.34 (d, J ) 4 Hz, 6H), 3.83 (s, 3H), 4.41 (heptet, J
) 4 Hz, 1H), 6.85 (d, J ) 8.3 Hz, 1H), 6.97 (t, J ) 6.8 Hz, 1H),
7.38 (t, J ) 7.1 Hz, 1H), 7.44 (d, J ) 7.1 Hz, 1H); IR 3062,
3001, 2955, 2833, 2119, 1587, 1571, 1497, 1429, 1238, 1129,
1110, 860, 838, 756 cm-1
.
Ack n ow led gm en t. The authors thank Dow Corning
Ltd., Barry (South Glamorgan, U.K.) for the gift of a
significant batch of hexamethyldisilane, an important
starting material in this work.
1044, 838 cm-1
.
(4-Meth oxyp h en yl)d im eth ylsila n e (5k ): 1H NMR δ 0.34
(d, J ) 4 Hz, 6H), 3.82 (s, 3H), 4.41 (heptet, J ) 4 Hz, 1H),
6.91 (m, 2H), 7.46 (m, 2H); IR 3081, 3015, 2955, 2834, 2115,
1593, 1564, 1502, 1441, 1396, 1276, 1246, 1113, 1033, 822
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
spectra of compounds 1a ,d ,l, 2b-l, 5b-l, 6-8, and three
aryldimethylsilanols mentioned in the text as well as 13C NMR
spectra of 1a and 1d and 29Si NMR spectrum of 1a (28 pages).
This material is contained in libraries on microfiche, im-
mediately follows this article in microfilm version of the
journal, and can be ordered from the ACS; see any current
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cm-1
.
[4-(N,N-Dim eth yla m in o)p h en yl]d im eth ylsila n e (5l): 1H
NMR δ 0.30 (d, J ) 4 Hz, 6H), 2.97 (s, 6H), 4.40 (heptet, J )
4 Hz, 1H), 6.74 (m, 2H), 7.42 (m, 2H); IR 3081, 2955, 2803,
2107, 1596, 1507, 1443, 1405, 1355, 1246, 1112, 834 cm-1
.
(2-Meth ylp h en yl)d im eth ylsila n ol (from alkaline hydrol-
ysis of 5f): colorless oily liquid: 1H NMR (ref CH2Cl2) 0.45 (s,
6H), 2.13 (bs, 1H), 2.52 (s, 3H), 7.20 (t, J ) 8 Hz, 2H), 7.30 (t,
J ) 7.3 Hz, 1H), 7.55 (d, J ) 8 Hz, 1H); IR 3305, 3055, 3002,
2958, 1589, 1559, 1447, 1406, 1253, 1131, 862, 832 cm-1; MS
(m/e) 166 M), 151 (M - Me), 133 (M - Me - H2O), 91 (M -
J O961131E
(23) Hevesi, L.; Lacave-Goffin, B. Synlett 1995, 1047.