Reactions of dilithiobutadienes with monochlorosilanes: Observation of facile loss of organic groups from silicon

Article abstract of DOI:10.1016/j.jorganchem.2005.11.068

Reactions of 1,4-dilithiobutadienes (from 1,4-diiodo-1,2,3,4- tetraethylbutadiene (1) and 2,2′-dibromobiphenyl (7) with t-BuLi) with Me₃SiCl gave siloles (3 and 9a) as the major products. No evidence for a disilylated butadiene was obtained. Use of higher molecular weight chlorosilanes ((allyl)Me₂SiCl, BnMe₂SiCl, and PhMe ₂SiCl) with dibromide 7 gave dimethylsilole 9a and a silane (10a, 10b, or 10c) resulting from trapping of the organic group by the chlorosilane.

Full text of DOI:10.1016/j.jorganchem.2005.11.068

Journal of Organometallic Chemistry 691 (2006) 1257–1264
www.elsevier.com/locate/jorganchem
Reactions of dilithiobutadienes with monochlorosilanes: Observation
of facile loss of organic groups from silicon
*
Paul F. Hudrlik , Donghua Dai, Anne M. Hudrlik
Department of Chemistry, Howard University, 525 College Street, N.W., Washington, DC 20059, United States
Received 3 October 2005; received in revised form 29 November 2005; accepted 29 November 2005
Available online 19 January 2006
Abstract
Reactions of 1,4-dilithiobutadienes (from 1,4-diiodo-1,2,3,4-tetraethylbutadiene (1) and 2,20-dibromobiphenyl (7) with t-BuLi) with
Me3SiCl gave siloles (3 and 9a) as the major products. No evidence for a disilylated butadiene was obtained. Use of higher molecular
weight chlorosilanes ((allyl)Me2SiCl, BnMe2SiCl, and PhMe2SiCl) with dibromide 7 gave dimethylsilole 9a and a silane (10a, 10b, or 10c)
resulting from trapping of the organic group by the chlorosilane.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Silole; Chlorosilane; Dilithiobutadiene; Organosilicon; Pentacoordinate silicon
1. Introduction
responding reactions of 2,20-dibromobiphenyl (7), which
led to the dibenzosilole 9a.
Siloles [1–4] (silacyclopentadienes) are of interest
because of the aromaticity of some of their anions
[2b,2c,2d,2e,2f,2g,2h,2i,2j,2k], as ligands in transition metal
chemistry [3], and because their electronic properties sug-
gest that silole-containing polymers (especially polysiloles)
could be useful in materials chemistry [4]. One of the com-
mon ways of preparing siloles (and other metalloles) is by
reaction of a 1,4-dimetallobutadiene [5] with a dihalo- (or
tetrahalo-) silane. 1,4-Dilithiobutadienes are often gener-
ated from 1,4-di-iodobutadienes, easily prepared from zirc-
onacyclopentadienes [6–8]. In the course of preparing some
siloles to explore their potential use in organic synthesis, we
used the reactions of 1,4-diiodotetraethylbutadiene (1) with
alkyllithium reagents followed by chlorosilanes. In order to
characterize the presumed 1,4-dilithiobutadiene intermedi-
ate (5), we attempted to trap it with Me3SiCl, expecting to
obtain the 1,4-bis(trimethylsilyl) derivative 6. We saw no
evidence for the formation of 6; instead, the major product
was silole 3. We therefore decided to also explore the cor-
2. Results
2.1. 2,3,4,5-Tetraethylsilole series
The starting diiodo compound 1 was prepared by iodin-
ation of a zirconacyclopentadiene intermediate [2f,6,7] gen-
erated from 3-hexyne. Treatment of 1 with t-BuLi in THF
generated the dilithio intermediate 5, as shown by reaction
with water or MeOH to give tetraethylbutadiene 2 [7].
However, when 5 was treated with Me3SiCl/Et3N [9], silole
3 was the major product (Scheme 1). Diene 2 and trimeth-
ylsilyltetraethylbutadiene 4 were identified as the major
byproducts by GC/MS. No significant amount of higher
retention time material was observed.
Silole 3 was most likely formed in the Me3SiCl reaction
by cyclization of a monolithio monotrimethylsilylbutadi-
ene intermediate with loss of MeLi. The MeLi would be
expected to react with the excess Me3SiCl to form Me4Si.
Therefore, in one experiment the reaction mixture was
warmed to 42 ꢁC, and the volatiles were passed into a vial
containing CDCl3 at ꢀ15 ꢁC. 1H NMR analysis of the
CDCl3 showed a peak at d ꢀ0.005 (in addition to peaks
*
Corresponding author. Tel.: +1 202 806 4245; fax: +1 202 806 5442.
E-mail address: phudrlik@howard.edu (P.F. Hudrlik).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.11.068

1258
P.F. Hudrlik et al. / Journal of Organometallic Chemistry 691 (2006) 1257–1264
Et Et
Et
Et
Et
Et
Et
Et
t-BuLi
Me3SiCl
Et
Et
Et
Et
Et
Et
Et
Et
Si
Et3N
I
I
THF
SiMe3
4
1
2
3
Li
Me3Si
Et
Et
Et
Et
Et
Et
Et
Et
SiMe3
Li
5
6
not observed
Scheme 1.
from THF and pentanes), which disappeared when the
solution was concentrated to half its volume, consistent
with the formation of Me4Si. Silole 3 did not appear to
be very stable to aqueous workup, and in the presence of
aqueous acid, it began to decompose, forming a compound
having a somewhat higher retention time on GC, probably
a ring-opened silanol.
Similar reactions were carried out using several addi-
tional monochlorosilanes. In these reactions, the dibenzo-
silole (9a) was again formed as a major product, and the
silanes (10) from cleavage-trapping were observed by
NMR (and in some cases MS), and silanes 10b and 10c
were isolated.
Thus, treatment of 2,20-dibromobiphenyl (7) with t-
BuLi in THF followed by excess allyldimethylchlorosilane
in Et3N gave a mixture of silole 9a and diallyldimethylsi-
2.2. Dibenzosilole series
1
lane (10a) by GC analysis and by H and 13C NMR. In
These reactions were further studied using the dibenzo-
silole (silafluorene) system, since in our hands, these siloles
were more robust than those from the tetraethyl system.
Treatment of 2,20-dibromobiphenyl (7) with t-BuLi in
THF followed by excess Me3SiCl in Et3N gave silole 9a
as the major product, isolated by chromatography in
84% yield (Scheme 2). Again, there was no evidence for
the formation of a bis(trimethylsilyl) compound. We did
not attempt to trap the Me4Si which must have been
formed.
one experiment, the crude product was chromatographed,
and silole 9a was isolated in 68% yield. NMR yields were
obtained (using nitromethane as a standard) of 95–103%
for 9a and 94–97% for 10a.
Treatment of 7 with t-BuLi in THF followed by excess
benzyldimethylchlorosilane in Et3N gave a mixture of silole
9a and dibenzyldimethylsilane (10b) by GC analysis, and
1
by H and 13C NMR. GC/MS analysis showed mass spec-
tral evidence for silole 9a and silane 10b as well as a small
amount of biphenyl (presumably from protonation of 8).
Pure samples of 9a and 10b were obtained by column chro-
matography. In some experiments, NMR yields were
obtained (using nitromethane as a standard) of 81–100%
for 9a and 34–40% for 10b.
Br
Li
t-BuLi
THF
Treatment of 7 with t-BuLi in THF followed by excess
phenyldimethylchlorosilane in Et3N gave a mixture of sil-
ole 9a and diphenyldimethylsilane (10c), together with
smaller amounts of 1-methyl-1-phenyldibenzosilole (9b),
resulting from loss of methyl rather than phenyl. Com-
pounds 9a, 9b, and 10c were all observed in the crude prod-
uct by GC, GC/MS and NMR. In addition, small amounts
of PhMe2Si-t-Bu, biphenyl, and bis(phenyldimethyl)disil-
oxane (11c) were identified by GC/MS. Pure samples of sil-
ole 9a and silane 10c were obtained by column
chromatography followed by preparative GC, and a some-
what impure sample of silole 9b was isolated by column
chromatography. In some experiments, NMR yields were
obtained (using nitromethane as a standard) of 66–72%
for 9a, 20–32% for 9b, and 53–60% for 10c.
Br
Li
8
7
RSiMe2Cl
Et3N
R2SiMe2
+
Si
10
R'
Me
9
10a R = allyl
10b R = benzyl
10c R = Ph
9a R' = Me
9b R' = Ph
Authentic samples of siloles 3 and 9a, the silane cleav-
age-trapping products (10a, b, c), and the disiloxane hydro-
lysis products (11a, b, potential impurities) were
Scheme 2.

P.F. Hudrlik et al. / Journal of Organometallic Chemistry 691 (2006) 1257–1264
1259
independently synthesized for GC and spectral compari-
sons, and a commercial sample of 11c was available. The
assignment of silole 9b was based on the mass spectrum,
and on the 1H NMR spectrum (CDCl3) which was compa-
rable to that reported [10] (in CCl4); in particular the Si–
Me of 9b was found at d 0.72 (this work) and d 0.71
(reported).
reagents to form products of exchange of alkyl groups on
the silicon, and they proposed a pentacoordinate organos-
ilicate intermediate [10,15]. Klumpp and co-workers were
the first to observe an intermediate of this type by NMR
[12a,12b]. They showed that 15 (R = Me) could be gener-
ated from the organolithium derived from 2-bromo-20-
trimethylsilylbiphenyl and that it lost MeLi reversibly when
warmed.
3. Discussion
Recently Xi and co-workers reported the reactions of a
number of 1-bromo-4-silyl butadienes with t-BuLi, which
give siloles in good yields, accompanied by the cleavage
of C–Si bonds [16]. The RLi which was generated was
trapped by reaction with carbonyl compounds. The follow-
ing selectivity for cleavage was demonstrated: Me >> i-Pr,
Ph > Me, and vinyl > Me.
The reactions of 8 with PhMe2SiCl gave a mixture of 9a
and 9b (as well as 10c), indicating formation of both PhLi
(major) and MeLi (minor). This is in accord with the recent
work of Xi and co-workers [16], and is also reminiscent of
the alkoxide-induced rearrangements we studied some
years ago, where the predominant phenyl migration was
accompanied by a small amount of methyl migration [17].
The formation of siloles 3 and 9a from the presumed
dilithio intermediates 5 and 8 and the monochlorosilanes
most likely occurs via cyclization of a monolithio-monosi-
lyl intermediate e.g., 12, 14) to a pentacoordinated orga-
nosilicate such as 13 or 15 (Scheme 3). Pentacoordinated
silicon compounds are well known, but most examples
involve one or more electronegative groups attached to
the silicon [11], and pentaorganosilicates are rare. Recently
some have been observed by NMR [12,13], and a few have
been isolated and characterized by X-ray crystallography
[13]. Many of these are based on the silole nucleus.
Gilman has reported some reactions of dibenzosiloles
which probably involve pentaorganosilicon intermediates
[14]. In 1953, Gilman and Gorsich reported the reaction
of 8 with 1-chloro-1-methyldibenzosilole to give a mixture
of silole 9a (36%) and 1,10-spirobi[dibenzosilole] (38%)
[14b]. They proposed that this reaction involved the gener-
ation of methyllithium, which reacted with the starting
chlorosilane. They also observed some reactions of 8 with
RSiCl3 to give small amounts of the same spiro compound.
However, the reactions of 8 with Et3SiCl did not give the
corresponding diethyldibenzosilole.
Me
Ph
Ph
Si
RLi
Si
O
Si
O
HO
Ph
+
Me
Cl
Me
major
minor
In the present work, the loss of the organic group
(methyl, allyl, benzyl, or phenyl) from 13 or 15 most likely
takes place by loss of RLi, but direct reaction of the chlo-
rosilane with 13 or 15 is also a possibility. The novel aspect
of the present work is that the uncyclized organolithium
reagent (12 or 14) is not trapped by the excess chlorosilane.
The fact that cyclization (to 13 or 15) occurs instead of di-
silylation may be further evidence for the stability of pen-
taorganosilicate anions based on the silole nucleus [18].
In 1983, Ishikawa and co-workers reported that several
dibenzosiloles, including 9a, react with organolithium
5
4. Experimental
Me3SiCl
General. All reactions were run under argon, and trans-
fers of liquids were carried out with argon-flushed syringes
for all reactions except the preparation of siloxanes 11a and
11b. Low temperature reactions were cooled with either a
petroleum ether or hexanes/liquid nitrogen slush bath,
and the temperatures were measured using a thermometer
placed beside the flask. Glassware was dried overnight in
an oven at 120 ꢁC, and cooled in a desiccator. The verb
‘‘concentrated’’ refers to removal of solvent using a rotary
evaporator. Column chromatography was done as flash
chromatography [19] using 200–425 mesh silica gel.
NMR spectra were obtained in CDCl3 and are refer-
enced to chloroform (d 7.26, 1H; d 77.00, 13C) unless other-
wise indicated. Spectra recorded in benzene-d6 were
referenced to benzene (d 7.15, 1H; d 128.00, 13C). Analytical
gas chromatography (GC) analyses were performed using a
flame ionization detector with the following columns and
Et
Et
-
Et
Et
Li+
Et
Et
Et
Me
3
Et
SiMe3
Si
Li
Me
Me
12
13
8
RMe2SiCl
-
Li+
9a
Si
Me
Li
SiMe2R
R
Me
14
15
Scheme 3.

1260
P.F. Hudrlik et al. / Journal of Organometallic Chemistry 691 (2006) 1257–1264
conditions: (A) 10% OV-101 silicone on 80/100 mesh Gas-
Chrom Q; 2.6 m · 2.5 mm glass column: A1: 100 ꢁC,
10 ꢁC/min to 270 ꢁC; A2: 100 ꢁC, 10 ꢁC/min to 250 ꢁC;
A4: 200 ꢁC, 10 ꢁC/min to 250 ꢁC; and (B) Supelco SPB-1
(bonded polydimethylsiloxane), 30 m · 0.25 mm · 0.25 lm
capillary column: B1: 200 ꢁC, 10 ꢁC/min to 270 ꢁC; B2:
200 ꢁC, 10 ꢁC/min to 270 ꢁC. Preparative GC was per-
formed using a thermal conductivity detector.
Materials. Tetrahydrofuran (THF) and anhydrous ether
were distilled from sodium/benzophenone under nitrogen.
Et3N, Me3SiCl, and Me2SiCl2 were distilled from calcium
hydride. n-Butyllithium was obtained from Acros, and
tert-butyllithium was obtained from Acros and from Alfa
Aesar.
The chlorosilane/Et3N mixtures were prepared by cen-
trifuging (3 min) a mixture of equal volumes of the chloros-
ilane and Et3N in an argon-flushed centrifuge tube (capped
with a septum) and taking the supernatant solution by gas-
tight syringe. The supernatant solutions were clear and
almost colorless or light yellow. In two of the early exper-
iments (isolation of silole 3 from both the Me2SiCl2 and
Me3SiCl procedures), the chlorosilane/Et3N mixture was
not centrifuged, but was stored in the dark for several days
to allow the precipitate to settle.
Diiodide 1 [2f,6] was prepared by iodine treatment
[8a,8c] of the intermediate from Cp2ZrCl2, n-BuLi, 3-hex-
yne [6,7], and CuCl [6b]. Dibromide 7 was prepared from
o-dibromobenzene by treatment with n-BuLi in THF
[20].
1,1-Dimethyl-2,3,4,5-tetraethyl-1-silole (3) [16,27] was
prepared from 0.3380 g (0.81 mmol) of diiodide 1 in 4 mL
of anhydrous ether cooled to ꢀ64 ꢁC, and 0.65 mL
(1.63 mmol) of n-BuLi (2.5 M in hexanes) (then warmed
to 10 ꢁC over 45 min, and then cooled to ꢀ64 ꢁC) followed
by 0.20 mL (ꢁ0.82 mmol of chlorosilane) of a mixture of
equal volumes of Me2SiCl2 and Et3N in 4 mL of THF
(dropwise). The mixture was warmed to r.t. over 45 min,
stirred at r.t. for 1 h; then 12 mL of pentanes was added,
and stirring was continued for 1 h. The liquid was cannu-
lated into another flask through a sintered glass funnel,
the filtrate was concentrated, pentanes was added, and
the pentane soluble material was analyzed by GC (A1,
C20H42 at 19.2 min) showing the major peak at 9.7 min
(75%, 3) and two minor peaks at 6.4 min (5%, 2) and
10.7 min (6%). The crude product (0.2300 g) was purified
by preparative GC giving a sample of silole 3 as a light yel-
low oil. The 1H and 13C NMR spectra (300 MHz, benzene-
d6) were equivalent to those reported below (400 MHz,
benzene-d6), and the 1H NMR spectrum was consistent
with a reported spectrum of 3 taken in CCl4 [27]. Silole 3
appeared to be unstable in CDCl3.
1
In a separate experiment, a H NMR yield of 58% was
calculated for 3 by adding a nitromethane standard, and
integrating peaks for Si–CH3 of 3 at d 0.22 and for
CH3NO2 at d 3.12 (chemical shifts relative to residual ben-
zene at d 7.15).
1,1-Dimethyldibenzosilole (9a) [2i,2j,14,21] was pre-
pared from 0.2779 g (0.89 mmol) of dibromide 7 in 4 mL
of anhydrous ether cooled to ꢀ66 ꢁC, and 0.73 mL
(1.8 mmol) of n-BuLi (2.5 M in hexanes) (dropwise; then
warmed to r.t. over 30 min; then cooled to ꢀ67 ꢁC) fol-
lowed by 0.23 mL (ꢁ0.95 mmol of Me2SiCl2) of a mixture
of equal volumes of Me2SiCl2 and Et3N in 4 mL of THF
(dropwise). The mixture was warmed to r.t. over 25 min,
and stirred at r.t. for 2 h, the volatiles were removed by
oil pump vacuum, and the residue was mixed with water
and extracted with ether. The combined extracts were ana-
lyzed by GC (B2, C22H46 at 7.5 min) and showed the major
peak at 4.2 min (100%, 9a). The product was concentrated,
and placed under oil pump vacuum to give 0.1879 g (100%
crude yield) of the dibenzosilole 9a as a light yellow solid
having 1H and 13C NMR spectra consistent with the
reported spectra [2i,2j].
4.1. Authentic comparison samples
Silanes 10a [22], 10b [23], and 10c [24], and siloxanes 11a
[25] and 11b [26] were prepared as follows, and purified by
Kugelrohr distillation: 10a [(allyl)Me2SiCl (2.0 mmol),
THF, (allyl)MgBr (2.1 mmol) in Et2O, r.t. 30 min, 70 ꢁC
30 min]; 10b [BnMe2SiCl (2.2 mmol), THF, BnMgCl (from
0.50 mL of BnCl and 0.262 g of Mg in ether), r.t. 30 min,
98% yield]; 10c [PhMe2SiCl (2.3 mmol), THF, PhLi
(2.3 mmol, 1.8 M in 70:30 cyclohexane:ether), r.t., 1.5 h,
93% yield]; 11a [(allyl)Me2SiCl (2.7 mmol), excess aqueous
NaHCO3, r.t. 10 min, 88% yield]; 11b [BnMe2SiCl
(2.2 mmol), excess aqueous NaHCO3, r.t. 10 min, 99%
yield]. Compounds 10a, 10c, and 11a were obtained as col-
1
orless oils having H NMR and 13C NMR spectra consis-
tent with those reported. Compound 10b was obtained as
a white solid: m.p. 52.0–54.3 ꢁC (lit. [23b] m.p. 56–58 ꢁC);
1H NMR (400 MHz) d 7.24 (crude t, 4H), 7.10 (crude t,
2H); 7.01 (crude d, 4H), 2.12 (s, 4H), ꢀ0.04 (s, 6H); 13C
NMR (100 MHz) d 139.85, 128.19, 128.17, 124.03, 25.17,
ꢀ3.88. The 1H NMR spectrum is in line with those
reported [23]. Compound 11b was obtained as a colorless
4.2. NMR yields
NMR yields for silanes 10a, b, and c and for silole 9a
were obtained as follows. The crude product was dissolved
in CDCl3, and a measured amount (10–20 lL) of distilled
nitromethane was added. H NMR and 13C NMR spectra
1
were taken to confirm the presence of the silane (10a, b, or
c) and silole 9a. The H NMR (400 MHz) yields were cal-
culated based on the integration of nitromethane (set at d
4.24) relative to Si–CH3 peaks at d 0.40 (9a), 0.73 (9b),
ꢀ0.015 (10a), and 0.55 (10c), and the CH2 peak at 2.08
(10b). Other diagnostic peaks: 10b (ꢀ0.12), 11a, (0.054),
1
1
oil: H NMR (400 MHz) d 7.22 (crude t, 4H), 7.09 (crude
t, 2H), 7.01 (crude d, 4H), 2.08 (s, 4H), 0.01 (s, 12H); 13C
NMR (100 MHz), 139.38, 128.31, 128.11, 124.02, 28.51,
ꢀ0.10. The 1H NMR spectrum was consistent with a
reported spectrum of 11b taken in CCl4 [26].

P.F. Hudrlik et al. / Journal of Organometallic Chemistry 691 (2006) 1257–1264
1261
11b (ꢀ0.08, 2.04), 11c (0.33). To confirm peak assignments,
the NMR samples were then spiked with the authentic
sample of silane (10a, b, or c) and then with that of the cor-
responding siloxane (11a, b, or c). For silole 9b, the NMR
sample was spiked with the purified sample of 9b (see
below).
placed under oil pump vacuum to give 0.1107 g of a yellow
oil. Then 10.0 lL (0.183 mmol) of nitromethane and
10.0 lL (0.102 mmol) of ethyl acetate, together with
0.75 mL of benzene-d6 were added. 1H NMR and 13C
NMR showed peaks corresponding to silole 3. From the
1H NMR, an NMR yield based on integration with nitro-
methane was calculated for 3 to be 54%. The NMR yield
was based on the Si–CH3 peak of 3 at d 0.21 and CH3NO2
at d 3.05 relative to residual benzene at d 7.15.
4.3. Treatment of 1,4-diiodo-1,2,3,4-tetraethylbutadiene (1)
with t-BuLi followed by Me3SiCl: methyl as a leaving group
A solution of 0.2773 g (0.66 mmol) of diiodide 1 in 5 mL
of THF was cooled to ꢀ56 ꢁC, and 1.80 mL (2.9 mmol) of
t-BuLi (1.6 M in pentane) was added. The solution was
stirred at about ꢀ60 ꢁC for 1 h. Then 0.50 mL of a mixture
of equal volumes of Me3SiCl and Et3N (ꢁ2.0 mmol of
chlorosilane) was added dropwise. The resulting mixture
was warmed to r.t. over 40 min, and stirred at r.t. for
1.5 h. Then 5 mL of CCl4 (distilled from P2O5) was added
to the reaction mixture to give a yellow solution with a
white precipitate, and stirring was continued for 15 min.
Stirring was stopped, and after the solid settled down, the
supernatant was cannulated to another flask. The volatile
material was removed by oil pump vacuum, and pentanes
was added to the flask. The pentane-soluble material was
transferred to another flask via a cannula. GC analysis
(A1) showed the major peak at 9.7 min (66%, 3), and minor
peaks at 6.4 min (7%, 2) and 10.4 min (16%, 4).
The major component was purified by preparative GC
to give silole 3 as a colorless liquid. (GC analysis (A1)
showed a major peak at 9.9 min (99%)): 1H NMR
(400 MHz, benzene-d6): d 2.32 (q, J = 7.6 Hz, 4H), 2.23
(q, J = 7.6 Hz, 4H), 1.08 (t, J = 7.6 Hz, 6H), 0.98 (t,
J = 7.5 Hz, 6H); 0.23 (s, 6H); 13C NMR (100 MHz, ben-
zene-d6): d 153.65, 138.27, 22.48, 21.04, 15.65, 15.00,
ꢀ3.26. The 1H NMR and 13C NMR spectra are equivalent
to those of the sample prepared from 1 and Me2SiCl2
(which were recorded at 300 MHz), and the GC retention
times of the two samples were identical.
4.4. Treatment of 2,20-dibromobiphenyl (7) with t-BuLi
followed by Me3SiCl: methyl as a leaving group
A solution of 0.2719 g (0.87 mmol) of 2,20-dibromobi-
phenyl (7) in 6 mL of THF was cooled to ꢀ70 ꢁC, and
2.5 mL (3.8 mmol) of t-BuLi (1.5 M in pentane) was added.
The resulting mixture was stirred between ꢀ69 and ꢀ56 ꢁC
for 1 h and 20 min. Then 1.0 mL of a mixture of equal vol-
umes of Me3SiCl and Et3N (ꢁ4.0 mmol of chlorosilane)
was added. The mixture was warmed to r.t. over 40 min,
and stirred at r.t. for 1 h 15 min.
Methanol (ꢁ2 mL) was added, and the mixture was stir-
red for 15 min. Then 2 mL of saturated NaHCO3 was
added, and the resulting mixture was added to additional
saturated NaHCO3, and extracted with ether (2 · 20 mL,
10 mL). GC analysis (B1) of the combined extracts showed
peaks at 4.1 min (6%) and 4.2 min (92%). The solution was
dried (Na2SO4), concentrated, and chromatographed (hex-
anes) to give 0.1544 g (84% yield) of silole 9a as a white
solid: m.p. 55.5–58.1 ꢁC (lit. [14a] m.p. 60–61 ꢁC); GC anal-
1
ysis (B1) 4.2 min (99.8%). The H and 13C NMR spectra
and GC retention time were identical with those of 9a
obtained from Me2SiCl2 (above).
4.5. Treatment of 2,20-dibromobiphenyl (7) with t-BuLi
followed by allyldimethylchlorosilane: allyl as a leaving
group
A GC/MS was obtained on the product from a separate
experiment run using a larger excess of Me3SiCl/Et3N, and
with a slightly different workup. GC analysis (A2) showed
major peaks at 6.4 min (54%, 2), 9.6 min (22%, 3), and
10.4 min (17%, 4). No other significant peaks were seen
up to 25 min; under these conditions, C20H42 came at
20.9 min. GC/MS showed major peaks at 6.5 min (MS cor-
responded to tetraethylbutadiene 2 [7a]), 8.2, and 8.5 min.
The peak at 8.2 min showed m/z 222 (100, M+), 207 (24,
M+ ꢀ Me), 193 (44, M+ ꢀ Et), 163 (64), and was assigned
as silole 3. The peak at 8.5 min showed m/z 238 (18, M+),
223 (6, M+ ꢀ Me), 209 (2, M+ ꢀ Et), 135 (53), 73 (100,
Me3Si+), and was assigned as 1-trimethylsilyltetraethylbut-
adiene 4.
A solution of 0.2866 g (0.92 mmol) of 2,20-dibromobi-
phenyl (7) in 6 mL of THF was cooled to ꢀ70 ꢁC, and
2.7 mL (4.1 mmol) of t-BuLi (1.5 M in pentane) was added.
The resulting mixture was stirred at ꢀ75 to ꢀ60 ꢁC for 1 h.
Then 0.85 mL of a mixture of equal volumes of allyldim-
ethylchlorosilane and Et3N (ꢁ2.8 mmol of chlorosilane)
was added. The mixture was warmed to r.t. over 1 h and
stirred at r.t. for 2 h.
Water (ꢁ2 mL) was added, and the resulting mixture
was added to 50 mL of 0.1 M HCl overlaid with 50 mL
of pentanes. The organic layer was washed with 0.1 M
HCl (2 · 40 mL) followed by 40 mL of water, and then
dried (Na2SO4). GC analysis (A2) showed major peaks at
2.9 min (26%, 10a) and 13.8 min (47%, 9a) and minor
peaks including 5.3 min (4%). Under these conditions, the
comparison samples of silane 10a and siloxane 11a had
retention times of 2.9 and 5.4 min, respectively.
In a separate experiment (0.2081 g (0.50 mmol) of 1,
2.25 mmol of t-BuLi, 0.50 mL of Me3SiCl/Et3N, GC anal-
ysis (A2) of the crude product before concentration showed
the major peak at 9.7 min (72%, 3) and a minor peak at
10.4 min (10%, 4). The solution was concentrated, and then
About 1 mL of CDCl3 was added to the ether solution.
Most of the solvent was removed by fractional distillation

1262
P.F. Hudrlik et al. / Journal of Organometallic Chemistry 691 (2006) 1257–1264
(to b.p. 42 ꢁC). NMR yields were obtained of 94% for 10a,
and 103% for 9a.
of chlorosilane) was added. The mixture was warmed to r.t.
over 40 min and stirred at r.t. for 1 h 15 min.
A similar experiment was carried out using 0.2725 g
(0.87 mmol) of 7 and ꢁ2.6 mmol of (allyl)Me2SiCl. GC
analysis (B3) of the crude product showed peaks at
3.9 min (35%, 10a) and 11.1 min (43%, 9a). NMR yields
were obtained of 97% for 10a and 95% for 9a. The sample
was then concentrated and chromatographed (hexanes) to
give 0.1257 g (68% yield) of silole 9a as a white solid having
1H NMR, 13C NMR, and GC retention time identical to
those of 9a obtained above using Me2SiCl2.
Water (about 2 mL) was added, and the mixture was
stirred for 2 min. The mixture was added to 40 mL of
water, the resulting mixture was extracted with ether
(2 · 15 mL), and the combined extracts were dried
(Na2SO4). GC analysis (A4) showed peaks at 3.9 min
(31%, 10c), 4.8 min (35%, 9a), and 14.1 min (19%, 9b),
and several minor peaks including one at 5.2 min (3%).
In addition, a large peak prior to 2.5 min (believed to be
PhMe2Si-t-Bu) was observed. Under these conditions,
silane 10c and siloxane 11c had retention times of 3.9
and 5.2 min, respectively.
4.6. Treatment of 2,20-dibromobiphenyl (7) with t-BuLi
followed by benzyldimethylchlorosilane: benzyl as a leaving
group
The solution was concentrated, and placed under oil
pump vacuum (0.1 mm, 0.5 h) to give 0.6098 g of yellow
oil. NMR yields were obtained of 53% for 10c, 66% for
9a, and 32% for 9b. The region between d 0.27 and 0.9 in
A solution of 0.2622 g (0.84 mmol) of 2,20-dibromobi-
phenyl (7) in 5.6 mL of THF was cooled to ꢀ70 ꢁC, and
2.40 mL (3.6 mmol) of t-BuLi (1.5 M in pentane) was
added dropwise, and the resulting mixture was stirred at
ꢀ75 to ꢀ60 ꢁC for 1 h. Then 0.90 mL of a mixture of equal
volumes of benzyldimethylchlorosilane and Et3N
(ꢁ2.5 mmol of chlorosilane) was added. The mixture was
warmed to r.t. over 45 min and stirred at r.t. for 1.5 h.
Then water (ꢁ2 mL) was added to the reaction mixture,
and the resulting mixture was added to water and extracted
with ether (2 · 20 mL). The combined extracts were dried
(Na2SO4), and analyzed by GC (A4) and showed peaks
at 2.7 min (11%), 4.8 min (60%, 9a), and 6.1 min (22%,
10b) with a few minor peaks including 8.1 min (3%). Under
these conditions, authentic samples of silane 10b and silox-
ane 11b came at 6.0 and 8.1 min, respectively. The solution
was concentrated, and placed under oil pump vacuum
(0.15 mm, 1 h) to give 0.5152 g of a yellow oil. NMR yields
were obtained of 40% for 10b, and 100% for 9a. GC/MS of
the product showed the major peak at 10.4 min (MS corre-
sponded to the dibenzosilole 9a [28]), with a smaller peak at
11.1 min (MS corresponded to dibenzyldimethylsilane
(10b) [23a]), and several minor peaks including 8.7 min
(MS corresponded to biphenyl [28]).
1
the H NMR contained major peaks at d 0.27 (PhMe2Si-
t-Bu, 0.42 (9a), 0.55 (10c), and 0.88 (PhMe2Si-t-Bu) and a
smaller peak at 0.73 (9b). The peak at 0.73 was assigned
as 9b based on the fact the presence of 9b was indicated
by the GC/MS (below), isolation of 9b from an analogous
reaction mixture in 71% GC purity (below), and the
reported [10] NMR shift for MeSi in 9b (d 0.71 in CCl4).
GC/MS of the product showed major peaks at 9.8 min
(MS corresponded to diphenyldimethylsilane (10c) [28])
and 10.4 min (MS corresponded to dibenzosilole 9a [28]).
In addition, there were two smaller peaks at 7.7 and
13.4 min. The peak at 7.7 min showed m/z 192 (3, M+),
135 (100, PhMe2Si+), 105 (5, PhSi+), and was assigned as
phenyldimethyl-tert-butylsilane (presumably from excess
t-BuLi and PhMe2SiCl). The peak at 13.4 min showed m/z
272 (48, M+) and 257 (100, M+ ꢀ Me), and was assigned
as 1-methyl-1-phenyldibenzosilole (9b) [10]. A number of
very small peaks were present including one at 8.7 min
which corresponded to biphenyl [28], and one at 10.6 min
which corresponded to siloxane 11c [28].
An analogous experiment was carried out using 0.3384 g
(1.08 mmol) of 7 and ꢁ2.6 mmol of PhMe2SiCl. GC anal-
ysis (B1) of the crude product showed two major peaks at
3.8 min (40%, 10c) and 4.1 min (41%, 9a), and a smaller
peak at 8.5 min (8.1%, probably 9b). Under these condi-
tions, siloxane 11c came at 4.3 min; none was visible. Chro-
matography followed by preparative GC gave pure
samples of silole 9a and silane 10c. Silole 9a was obtained
as a white solid, and had 1H and 13C NMR and GC reten-
tion time identical to those of 9a obtained above using
Me2SiCl2. Diphenyldimethylsilane (10c) was obtained as
In a similar experiment, NMR yields of 34% for 10b and
81% for 9a and were obtained. Pure samples of silole 9a
and silane 10b were obtained after two chromatographies
of the product from an analogous experiment. Each had
1H NMR and 13C NMR spectra identical to those of the
authentic samples prepared above.
4.7. Treatment of 2,20-dibromobiphenyl (7) with t-BuLi
followed by phenyldimethylchlorosilane: phenyl as a leaving
group
1
a colorless oil having H and 13C NMR spectra identical
to those of the authentic sample of 10c. The IR spectrum
was consistent with the structure, and with the reported
spectrum [24]. GC analysis (B1) showed a peak at
3.8 min (100%). In a similar experiment, NMR yields of
60% for 10c, 72% for 9a, and 20% for 9b were obtained.
Chromatography of the remaining product followed by
Kugelrohr distillation (0.05 mm, 110–125 ꢁC) gave a sam-
ple of silole 9b [10] as a colorless oil. GC analysis (A4)
A solution of 0.2867 g (0.92 mmol) of 2,20-dibromobi-
phenyl (7) in 6 mL of THF was cooled to ꢀ75 ꢁC, and
2.65 mL (4.0 mmol) of t-BuLi (1.5 M in pentane) was
added. The resulting mixture was stirred at ꢀ75 ꢁC to
ꢀ60 ꢁC for 1 h. Then 0.90 mL of a mixture of equal vol-
umes of phenyldimethylchlorosilane and Et3N (ꢁ2.7 mmol

P.F. Hudrlik et al. / Journal of Organometallic Chemistry 691 (2006) 1257–1264
1263
(h) A.J. Boydston, Y. Yin, B.L. Pagenkopf, J. Am. Chem. Soc. 126
(2004) 10350–10354.
[5] (a) H.J. Reich, I.L. Reich, J. Org. Chem. 40 (1975) 2248–2250;
(b) A.J. Kos, P.v.R. Schleyer, J. Am. Chem. Soc. 102 (1980) 7928–
7929;
showed the major peak at 14.1 min (71%, 9b) and a minor
peak at 20.0 min (16%). GC/MS analysis showed peaks at
11.0 min (major, MS corresponded to 9b, above) and
1
11.8 min (minor). The H NMR spectrum (CDCl3, refer-
enced to CH3NO2 at d 4.24) showed a large singlet at
d 0.72 (MeSi) and multiplets at d 7.1–7.9 (ring protons),
as well as several small singlets between 0.08 and 0.56
(impurities); this includes the peaks reported (in CCl4) for
9b (SiMe at d 0.71) [10].
(c) A.J. Ashe III, S. Mahmoud, Organometallics 7 (1988) 1878–1880;
(d) Reactions of dilithiobutadienes are of current interest. For example,
see: G. Li, H. Fang, Z. Xi, Tetrahedron Lett. 44 (2003) 8705–8708,
and refs cited therein.
[6] (a) S.L. Buchwald, R.B. Nielsen, J. Am. Chem. Soc. 111 (1989) 2870–
2874;
(b) C. Xi, S. Huo, T.H. Afifi, R. Hara, T. Takahashi, Tetrahedron
Lett. 38 (1997) 4099–4102;
(c) Y. Ura, Y. Li, F.-Y. Tsai, K. Nakajima, M. Kotora, T.
Takahashi, Heterocycles 52 (2000) 1171–1189.
Acknowledgements
[7] (a) K.I. Gell, J. Schwartz, J. Am. Chem. Soc. 103 (1981) 2687–2695;
(b) S. Thanedar, M.F. Farona, J. Organomet. Chem. 235 (1982) 65–
68.
[8] (a) E. Negishi, S.J. Holmes, J.M. Tour, J.A. Miller, F.E. Cederbaum,
D.R. Swanson, T. Takahashi, J. Am. Chem. Soc. 111 (1989) 3336–
3346;
We are grateful to the National Science Foundation/
Chemical Instrumentation (CHE-0342500) for funding for
the Agilent 5973 inert GC/MS instrument used in this work.
References
(b) P.J. Fagan, W.A. Nugent, J.C. Calabrese, J. Am. Chem. Soc. 116
(1994) 1880–1889;
[1] Reviews: (a) J. Dubac, A. Laporterie, G. Manuel, Chem. Rev. 90
(c) A.J. Ashe III, J.W. Kampf, S. Pilotek, R. Rousseau, Organomet-
allics 13 (1994) 4067–4071.
(1990) 215–263;
(b) E. Colomer, R.J.P. Corriu, M. Lheureux, Chem. Rev. 90 (1990)
265–282;
(c) J. Dubac, C. Guerin, P. Meunier, in: Z. Rappoport, Y. Apeloig
(Eds.), The Chemistry of Organic Silicon Compounds. Part 3, vol. 2,
Wiley, Chichester, 1998, pp. 1961–2036;
[9] For silylation reactions, we frequently use mixtures of chlorosilanes
with Et3N. The amine neutralizes acids such as HCl which might
otherwise react with the organometallic reagent and lower the yield of
the silylated product, and also neutralizes HCl formed on aqueous
workup of the chlorosilane. For the reactions of 5 with Me3SiCl,
when Et3N was not used, byproducts (such as 2) increased.
[10] M. Ishikawa, T. Tabohashi, H. Sugisawa, K. Nishimura, M.
Kumada, J. Organomet. Chem. 250 (1983) 109–119.
[11] (a) C. Chuit, R.J.P. Corriu, C. Reye´, J.C. Young, Chem. Rev. 93
(1993) 1371–1448;
´
(d) Y. Pan, in: B. Arkles, G. Larson (Eds.), Silicon Compounds:
Silanes and Silicones, Gelest, Inc., Morrisville, PA, 2004, pp. 73–81.
[2] (a) W.-C. Joo, J.-H. Hong, S.-B. Choi, H.-E. Son, C.H. Kim, J.
Organomet. Chem. 391 (1990) 27–36;
(b) J.-H. Hong, P. Boudjouk, J. Am. Chem. Soc. 115 (1993) 5883–
5884;
(b) R.R. Holmes, Chem. Rev. 96 (1996) 927–950;
(c) D. Kost, I. Kalikhman, in: Z. Rappoport, Y. Apeloig (Eds.), The
Chemistry of Organic Silicon Compounds. Part 2, vol. 2, Wiley,
Chichester, 1998, pp. 1339–1445.
(c) J.-H. Hong, P. Boudjouk, S. Castellino, Organometallics 13
(1994) 3387–3389;
(d) U. Bankwitz, H. Sohn, D.R. Powell, R. West, J. Organomet.
Chem. 499 (1995) C7–C9;
[12] (a) A.H.J.F de Keijzer, F.J.J. de Kanter, M. Schakel, R.F. Schmitz,
G.W. Klumpp, Angew. Chem., Int. Ed. Engl. 35 (1996) 1127–1128;
(b) A.H.J.F de Keijzer, F.J.J. de Kanter, M. Schakel, V.P. Osinga,
G.W. Klumpp, J. Organomet. Chem. 548 (1997) 29–32;
(c) N. Rot, T. Nijbacker, R. Kroon, F.J.J. de Kanter, F. Bickelhaupt,
M. Lutz, A.L. Spek, Organometallics 19 (2000) 1319–1324.
[13] (a) A. Kolomeitsev, G. Bissky, E. Lork, V. Movchun, E. Rusanov,
P. Kirsch, G.-V. Ro¨schenthaler, Chem. Commun. (1999) 1017–1018;
(b) S. Deerenberg, M. Schakel, A.H.J.F. de Keijzer, M. Kranenburg,
M. Lutz, A.L. Spek, K. Lammertsma, Chem. Commun. (2002) 348–
349;
(e) R. West, H. Sohn, U. Bankwitz, J. Calabrese, Y. Apeloig, T.
Mueller, J. Am. Chem. Soc. 117 (1995) 11608–11609;
(f) W.P. Freeman, T.D. Tilley, L.M. Liable-Sands, A.L. Rheingold,
J. Am. Chem. Soc. 118 (1996) 10457–10468;
(g) B. Goldfuss, P.v.R. Schleyer, Organometallics 16 (1997) 1543–
1552;
(h) S.-B. Choi, P. Boudjouk, P. Wei, J. Am. Chem. Soc. 120 (1998)
5814–5815;
(i) S.-B. Choi, P. Boudjouk, Tetrahedron Lett. 41 (2000) 6685–6688;
(j) Y. Liu, T.C. Stringfellow, D. Ballweg, I.A. Guzei, R. West, J.
Am. Chem. Soc. 124 (2002) 49–57;
(c) D. Ballweg, Y. Liu, I.A. Guzei, R. West, Silicon Chem. 1 (2002)
57–60;
(d) E.P.A. Couzijn, M. Schakel, F.J.J. de Kanter, A.W. Ehlers, M.
Lutz, A.L. Spek, K. Lammertsma, Angew. Chem. Int. Ed. 43 (2004)
3440–3442.
(k) See also: R. West, H. Sohn, D.R. Powell, T. Muller, Y. Apeloig,
¨
Angew. Chem., Int. Ed. Engl. 35 (1996) 1002–1004.
[3] W.P. Freeman, T.D. Tilley, A.L. Rheingold, J. Am. Chem. Soc. 116
(1994) 8428–8429.
[4] (a) S. Yamaguchi, R.-Z. Jin, K. Tamao, M. Shiro, Organometallics
16 (1997) 2486–2488;
[14] (a) H. Gilman, R.D. Gorsich, J. Am. Chem. Soc. 80 (1958) 1883–
1886;
(b) T. Sanji, T. Sakai, C. Kabuto, H. Sakurai, J. Am. Chem. Soc. 120
(1998) 4552–4553;
(c) S. Yamaguchi, R.-Z. Jin, K. Tamao, J. Organomet. Chem. 559
(1998) 73–80;
(d) S. Yamaguchi, K. Tamao, J. Chem. Soc., Dalton Trans. (1998)
3693–3782;
(e) H. Sohn, R.R. Huddleston, D.R. Powell, R. West, K. Oka, X.
Yonghua, J. Am. Chem. Soc. 121 (1999) 2935–2936;
(f) S. Yamaguchi, R.-Z. Jin, K. Tamao, J. Am. Chem. Soc. 121
(1999) 2937–2938;
(b) H. Gilman, R.D. Gorsich, J. Am. Chem. Soc. 80 (1958) 3243–
3246;
(c) D. Wittenberg, H. Gilman, J. Am. Chem. Soc. 80 (1958) 2677–
2680.
[15] For additional reactions which may involve pentaorganosilicates, see:
(a) A. Maercker, R. Sto¨tzel, Chem. Ber. 120 (1987) 1695–1706;
(b) E. Vedejs, O. Daugulis, S.T. Diver, D.R. Powell, J. Org. Chem.
63 (1998) 2338–2341;
(c) G.P.M. van Klink, H.J.R. de Boer, G. Schat, O.S. Akkerman, F.
Bickelhaupt, A.L. Spek, Organometallics 21 (2002) 2119–2135.
[16] Z. Wang, H. Fang, Z. Xi, Tetrahedron Lett. 46 (2005) 499–501.
(g) S. Yamaguchi, K. Tamao, J. Organomet. Chem. 653 (2002) 223–
228;

1264
P.F. Hudrlik et al. / Journal of Organometallic Chemistry 691 (2006) 1257–1264
[17] P.F. Hudrlik, Y.M. Abdallah, A.M. Hudrlik, Tetrahedron Lett. 33
(1992) 6743–6746.
[23] (a) H.J.R. De Boer, O.S. Akkerman, F. Bickelhaupt, J. Organomet.
Chem. 321 (1987) 291–306;
[18] Boudjouk has summarized other observations which suggest that
pentacoordinate silicon may be stabilized by the silole ring: Y. Pan,
J.-H. Hong, S.-B. Choi, P. Boudjouk, Organometallics 16 (1997)
1445–1451.
[19] W.C. Still, M. Kahn, A. Mitra, J. Org. Chem. 43 (1978) 2923–2925.
[20] H.Gilman,B.J.Gaj,J.Org.Chem.22(1957)447–449,SeealsoRef.[21a].
[21] (a) J.Y. Corey, L.S. Chang, J. Organomet. Chem. 307 (1986) 7–14;
(b) J.Y. Corey, C.S. John, M.C. Ohmsted, L.S. Chang, J. Organomet.
Chem. 304 (1986) 93–105.
[22] C.J. Pouchert, J. Behnke, The Aldrich Library of 13C and 1H FT
NMR spectra, vol. 3, Aldrich Chemical Co., Inc., USA, 1993, p. 634.
(b) Y. Inoue, A. Sugimoto, K. Mizuno, J. Chem. Res. (S) (2000) 528–
529.
[24] C.A. van Walree, X.Y. Lauteslager, A.M.A. van Wageningen,
J.W. Zwikker, L.W. Jenneskens, J. Organomet. Chem. 496
(1995) 117–125.
[25] D.W. Smith Jr., K.B. Wagener, Macromolecules 26 (1993) 1633–1642.
´
[26] C. Eaborn, W.A. Stanczyk, J. Chem. Soc., Perkin Trans. II (1984)
2099–2103.
[27] H. Okinoshima, K. Yamamoto, M. Kumada, J. Am. Chem. Soc. 94
(1972) 9263–9264.
[28] NIST Chemistry Webbook: http://webbook.nist.gov/chemistry/.