B(C6F5)3-catalyzed synthesis of benzofused-siloles

Article abstract of DOI:10.1021/om501033p

The dehydrosilylation of 2-(SiR₂H)-biphenyls catalyzed by B(C₆F₅)₃ and a weak base forms silafluorenes with H₂ as the only byproduct. Attempts to extend this approach to synthesize siloles derived from 2,2′-bithiophenes and N-Me-2-Ph-indole resulted in competing reactivity, including protodesilylation. B(C₆F₅)₃ also catalyzed the one-pot, two-step formation of silaindenes from aryl-alkynes by alkyne trans-hydrosilylation, followed by an intramolecular Sila-Friedel-Crafts reaction facilitated by a weak base.

Full text of DOI:10.1021/om501033p

Article
pubs.acs.org/Organometallics
B(C6F5)3‑Catalyzed Synthesis of Benzofused-Siloles
Liam D. Curless and Michael J. Ingleson*
School of Chemistry, University of Manchester, Manchester, M13 9PL, U.K.
S
* Supporting Information
ABSTRACT: The dehydrosilylation of 2-(SiR2H)-biphenyls
catalyzed by B(C6F5)3 and a weak base forms silafluorenes
with H2 as the only byproduct. Attempts to extend this
approach to synthesize siloles derived from 2,2′-bithiophenes
and N-Me-2-Ph-indole resulted in competing reactivity,
including protodesilylation. B(C6F5)3 also catalyzed the one-pot, two-step formation of silaindenes from aryl-alkynes by alkyne
trans-hydrosilylation, followed by an intramolecular Sila-Friedel−Crafts reaction facilitated by a weak base.
iloles, 1, are five-membered, 4π electron heterocycles, and
benzofused derivatives, 2 (silafluorenes) and 3 (silain-
Significantly, this could be operated catalytically in trityl salt,
with additional silane acting as a hydride donor to form the
saturated cyclized product and regenerating [R2BnSi·(arene)]+
(eq 2). We were interested in developing catalytic routes to 2
and 3 by developing a SEAr methodology using catalytic
B(C6F5)3 (BCF) to activate silanes (via (C6F5)3B-(μ-H)-
SiR3)11 and 2,6-dichloropyridine (Cl2-py) to facilitate deproto-
nation of the silylated arenium cation.12 We hypothesized that
the competitive reduction that occurs alongside the inter-
molecular SEAr of thiophenes using catalytic BCF/Cl2-py (eq
3) would be disfavored with biphenyl-silyl derivatives due to
the increased energetic drive from rearomatization of the
arenium cation relative to the thiophenium cation. Herein is
reported a catalytic (in BCF) intramolecular SEAr route to
silafluorenes and to silaindenes, the latter preceded by a
catalytic (in BCF) alkyne trans-hydrosilylation.
S
denes), are privileged moieties in organic electronics.
Compounds containing 2 and 3 have been utilized in light
emitting materials, field effect transistors, and photovoltaics due
to their desirable optical and electronic properties.1−5 The most
established route to benzofused-siloles relies upon the
combination of organo-lithium or magnesium reagents with
R2SiCl2.6 However, recent years have witnessed the develop-
ment of multiple transition-metal-catalyzed approaches to 27
and 3.8
A conceptually different pathway to siloles, pioneered by
Kawashima and co-workers,9 utilizes an intramolecular Sila-
Friedel−Crafts reaction. Hydride abstraction using stoichio-
metric trityl salt (Ph3C+) generates a silicenium cation (or a
functional equivalent) that is attacked by a proximal aryl group
to form the silole in the presence of 2,6-lutidine to sequester
the protic byproduct from SEAr (eq 1). Recently, the same
Silafluorene Synthesis. The addition of stoichiometric
BCF and Cl2-py to 2-(SiPh2H)-biphenyl, 4a (Figure 1), in
CH2Cl2 at 20 °C resulted in the slow growth of new aromatic
1
resonances (by H NMR spectroscopy). Heating to 60 °C for
18 h in a sealed tube led to the full conversion of 4a to a single
new compound. Multinuclear NMR spectroscopy and X-ray
crystallography (see the Supporting Information) confirmed
Figure 1. Catalytic (in BCF and Cl2-py) formation of silafluorenes.
group extended this approach by reacting silicenium cations
with alkynes to form β-silyl vinyl cations that undergo
intramolecular SEAr to afford six-membered silacycles.10
Received: October 10, 2014
Published: November 26, 2014
© 2014 American Chemical Society
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Table 1. Dehydrosilylation of Silylated Biphenyls with BCF
a
entry
silane
BCF (mol %)
Cl2-py (mol %)
t (h)
T (°C)
5 (%)
b
1
4a
4a
4a
4a
4b
4c
4d
100
10
5
100
10
5
18
24
96
168
5
60
100
100
100
100
60
99
2
3
4
5
99
99 (90)
50
10
5
0
5
99 (87)
b
c
6
100
5
100
5
120
96
50
7
100
96 (79)
a
b
c
Yields based on conversion of 4 determined by 1H NMR spectroscopy, isolated yields in parentheses. Run in CH2Cl2 in a sealed tube. Complete
consumption of 4c occurs, forming 5c and other products derived from silicon substituent scrambling (by NMR spectroscopy and GC MS).
that this was the desired silole, 5a. When the reaction was
repeated using 10 mol % BCF and Cl2-py, full conversion to 5a
required 24 h at 100 °C in ortho-dichlorobenzene (o-DCB,
Table 1, entry 2). At 5 mol % BCF/Cl2-py loadings, full
conversion to the silole required 96 h at 100 °C (entry 3).
Previously, we have shown that BCF catalyzes the electrophilic
silylation of heteroarenes in the absence of a base.12 However,
when 4a and BCF (10 mol %) were heated to 100 °C in o-
DCB, only 50% conversion of 4a to 5a was observed even after
7 days (entry 4), with unreacted 4a still present. No
diphenylsilane or biphenyl was observed in this reaction (by
NMR spectroscopy), consistent with the arenium intermediate
reacting directly with [HBCF]− and not with another
equivalent of 4a (which would generate 5a and an equivalent
of protonated 4a[HBCF], ultimately leading to the proto-
desilylation products biphenyl, Ph2SiH2, and BCF). Thus, Cl2-
py is facilitating a key step in the catalytic cycle, presumably
deprotonation of the arenium cation. Catalytic dehydrosilyla-
tion was also effective for 4,4′-tBu2-2-(SiPh2H)-biphenyl (entry
5). Attempts to apply these catalytic SEAr conditions to
dimethyl substituted biphenylsilane, 4c, led to two new methyl
resonances in the 1H NMR spectrum. Multinuclear NMR
spectroscopy and GC-MS confirmed that the desired silole had
formed along with products arising from substituent scrambling
on silicon (entry 6). Related silane substituent scrambling has
been reported mediated by silicon cations.13 Isobutyl
substituents on silicon provide sufficient steric bulk to prevent
the substituent scrambling;13b therefore, clean formation of the
dialkyl substituted silole, 5d, was achieved on addition of 5 mol
% of both BCF and Cl2-py (entry 7).
isolation (only 5,5′-Me2-bithiophene, 7, was isolable from these
reactions). Multiple aliphatic resonances were also observed
(by 1H NMR spectroscopy), again indicating competitive
hydrogenation/hydrosilylation;12 however, these were only
present as extremely minor components in the reaction
mixture. Attempts to cyclize 6 using catalytic BCF led to a
more complex reaction mixture with four species now observed
in the 29Si{1H} NMR spectrum with 7 and new aliphatic
species also present (by 1H NMR spectroscopy). The repeated
formation of 7 is attributed to highly Brønsted acidic species
(e.g., [H(Cl2-py)]+) presumably formed as byproducts from
SEAr protodesilylating 6. A series of stronger bases (relative to
Cl2-py) were investigated as these form weaker conjugate acids
and thus may preclude protodesilylation. However, these did
not result in any improved outcome (see the Supporting
Information). Two H+ scavenging methods were also
investigated to improve the cyclization of 6: (i) the addition
of a sacrificial substrate that is rapidly reduced by the
combination of [H(Cl2-py)]+ and [BCF-H]− and (ii) in place
of Cl2-py, the use of a bulky strong base in stoichiometric
quantities that, on protonation, has sufficient hydride ion
affinity to abstract hydride from [BCF-H]−, regenerating
BCF.15 However, neither of these approaches enabled
formation of the dithienosilole due to undesired side reactions
(see the Supporting Information).
The sequential intermolecular/intramolecular dehydrosilyla-
tion of 2-aryl-indoles would represent a simple route to
heteroaromatic ring fused siloles such as 10 (Figure 2).
Attempted Synthesis of Heteroaromatic Ring Fused
Siloles. The extension of catalytic SEAr to form dithienosiloles
would be particularly desirable due to the prevalence of this
structure in compounds used for organic electronic applica-
tions.14 The combination of 5,5′-Me2-3-(SiPh2H)-2,2′-bithio-
phene, 6 (eq 4), with stoichiometric BCF and Cl2-py in o-DCB
Figure 2. Attempted double dehydrosilylation of 2-phenyl-N-
methylindole with Ph2SiH2.
Intermolecular electrophilic dehydrosilylation of N-Me-indole
with tertiary silanes has been previously reported catalyzed by a
cationic ruthenium(II) complex,16 and subsequently by BCF/
Cl2-py. However, the latter catalytic system proceeded with
competing reduction to the indoline.12 A phenyl group at the
C2 position of N-Me-indole should inhibit reduction by
increasing the steric bulk around C2, preventing H− transfer
at 100 °C formed one major new product by 29Si{1H} NMR
spectroscopy (at −21.4 ppm), which frustrated all attempts at
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from [BCF-H]− to the iminium cation (formed on electrophilic
attack at C3 of N-Me-indole). Initial dehydrosilylation of 2-Ph-
N-methyl-indole, 8, was investigated with Ph3SiH and
stoichiometric BCF and Cl2-py. After 48 h at 60 °C in
CH2Cl2, 64% of 8 had been dehydrosilylated. Importantly,
there was no evidence for formation of any indoline products
(by 1H NMR spectroscopy). With no reduced products
observed using Ph3SiH, the double-dehydrosilylation of 8 was
attempted with Ph2SiH2 to form silole 10 (Figure 2). At 5 mol
% BCF loading and stoichiometric Cl2-py (required for shorter
reaction times) after 24 h at 60 °C, there was a 70% conversion
to compound 9, with no further reactivity observed at longer
reaction times. Under these conditions, there was no evidence
vinylsilane, cis-12a, derived from trans-hydrosilylation (con-
firmed by NOESY; see the Supporting Information). The only
other product (accounting for the remaining 16% of material)
corresponded to the undesired trans isomer from cis-hydro-
silylation. Addition of Cl2-py (1 equiv) to this reaction mixture
and heating to 60 °C for 72 h resulted in the slow growth of
new resonances in the 1H and 29Si{1H} NMR spectra,
consistent with the silaindene 13a. X-ray crystallography
confirmed the formation of 13a (Figure 3, inset), which
forms in an overall 84% conversion based on 1-phenyl-1-
propyne (Table 2, entry 1).
The formation of 13a was repeated under catalytic
conditions with a 5% BCF loading. The hydrosilylation of
11a again gave approximately 85:15 trans:cis hydrosilylation
after 5 h heating at 60 °C in CH2Cl2 in a sealed tube. The ring-
closing step was extremely slow with catalytic loadings of BCF
and Cl2-py, with 3 days heating at 60 °C in CH2Cl2 yielding
only a 23% conversion to silaindene 13a (entry 2). Repeating in
o-DCB and heating to 100 °C led to no improvement in
conversion (entry 3); instead, decomposition of BCF occurs at
this temperature with the 11B/19F NMR spectra showing
multiple 3- and 4-coordinate BCF derived species. The reaction
was also repeated in CH2Cl2 at 60 °C with 5 mol % BCF and
stoichiometric Cl2-py, which led to an increase in the rate of the
electrophilic dehydrosilylation step (entry 4). Adding Cl2-py
prior to the initial hydrosilylation step was also possible, leading
to 13a in moderate overall conversion (entry 5). Attempts to
expand the scope of this reaction were extremely limited. While
1-phenyl-1-butyne reacted successfully and more rapidly to
form 13b (entry 6), attempts with a range of other alkynes,
including terminal alkynes, diaryl and bromo-substituted
internal alkynes, all failed with none of these substrates
undergoing any significant hydrosilylation with BCF and
Ph2SiH2 (see the Supporting Information). The hydrosilylation
of 1-(4-bromophenyl)-1-propyne with Ph2SiH2 and catalytic
BCF did proceed (entry 7), but no subsequent cyclization was
observed, attributed to the lower nucleophilicity of the bromo-
substituted arene. Silaindene formation was also attempted
using di-tert-butylsilane; however, no hydrosilylation of 11a was
observed presumably due to steric bulk at the silicon center
preventing attack from the alkyne nucleophile on the BCF-(μ-
H)-SiR3 species. The less bulky silane di-iso-propylsilane was
also used, and while hydrosilylation did occur slowly, the 19F
NMR spectrum showed that BCF degraded under these
conditions to produce multiple compounds. Because of the
catalyst decomposing, the hydrosilylation only proceeded to
35% in 24 h (entry 8). With BCF-catalyzed alkyne trans-
hydrosilylation using 2° silanes limited in alkyne scope,
alternative trans-hydrosilylation routes were investigated to no
avail. For example, the trans-hydrosilylation of alkynes with
catalytic AlCl3 has been previously reported using tertiary
silanes;18 however, attempts to extend this procedure to
secondary silanes predominantly resulted in the recovery of
starting materials at varied loadings of AlCl3 up to
stoichiometric (relative to the alkyne) and for prolonged
reaction times at a range of temperatures. An analogous route
to germole formation was also explored, with trans-hydro-
germylation of alkynes using catalytic BCF reported with
tertiary germanes.19 However, attempts to hydrogermylate 1-
phenyl-1-propyne using Ph2GeH2 in CH2Cl2, benzene, and o-
DCB led to no alkyne hydrogermylation, with BCF
decomposition observed.
1
for a second dehydrosilylation to form 10 (by H and 29Si
NMR spectroscopy). Analysis of the 11B and 19F NMR spectra
showed that BCF had been completely converted to [BCF-
H]−. The formation of [BCF-H]− is attributed to a small
amount of indole reduction to the indoline, which will
subsequently activate H2 in a FLP with BCF to form
[protonated indoline][BCF-H]. Minor resonances in the
aliphatic region of the 1H NMR spectrum are observed,
consistent with indoline formation. The reaction of 8 with
Ph2SiH2 catalyzed by BCF/Cl2-py was repeated, but with 1
equiv of 1,1-diphenylethene (DPE) to sequester H2; however,
DPE undergoes preferential hydrosilylation.
Catalytic Silaindene Synthesis. Following the catalytic
formation of the dibenzofused siloles, the formation of
silaindenes was explored. This requires an initial alkyne
hydrosilylation by a secondary silane, followed by an intra-
molecular dehydrosilylation (Figure 3, left). The geometry of
Figure 3. BCF-catalyzed synthesis of silaindenes. Right: the crystal
structure of silaindene, 13a (thermal ellipsoids at 50% probability).
the vinyl silane intermediate is key for subsequent cyclization,
with trans-hydrosilylation of the alkyne essential to provide a cis
arrangement of arene and silane. Trans-hydrosilylation of
alkynes has limited precedence, but is known using FLP
methodologies.17 1-Phenyl-1-propyne, 11a, was added to 1
equiv of diphenylsilane and BCF in CH2Cl2. Encouragingly,
after 5 h at 20 °C, all 11a was consumed and there was an 84%
1
conversion (by H NMR spectroscopy) to the desired cis-
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a
Table 2. One-Pot Hydrosilylation/Dehydrosilylation of Alkynes To Form Silaindenes (see Figure 3 for Labeling)
b
b
b
entry
11
R′
R″
silane
solvent
BCF (mol %) t (h) T (°C) cis-12 (%)
trans-12 (%)
Cl2-py (mol %) t (h) T (°C) 13 (%)
1
2
3
4
11a
11a
11a
11a
11a
11b
11c
11a
Me
Me
Me
Me
Me
Et
H
H
H
H
H
H
Br
H
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
Ph2SiH2
iPr2SiH2
CH2Cl2
CH2Cl2
o-DCB
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
b
100
5
5
5
5
4
20
60
60
60
84
85
84
84
16
15
16
16
100
5
72
48
30
72
72
24
48
60
60
84
23
17
70
50
75
0
5
5
100
60
5
100
100
100
100
c
5
5
60
6
7
8
5
2
48
24
60
60
60
75
89
35
25
0
60
Me
Me
5
60
5
a
c
1
All reactions performed in sealed tubes. Conversion based on 11 determined by H NMR spectroscopy. In one pot with both BCF and Cl2-py
added at the start of the reaction
stirred for 1 h. The reaction mixture was left to warm to ambient
temperature and stirred for 24 h. The product was extracted with ether
and washed with sodium hydrogen carbonate (aq.) and water. The
organic layer was dried over magnesium sulfate. The solvent was
removed under vacuum and purified by flash column chromatography.
4a 2-(Diphenylsilyl)biphenyl. Synthesized according to general
procedure 1, starting with 2.3 mL of diphenylchlorosilane. The solvent
was removed under vacuum and purified by flash column
chromatography, where the eluent was hexane:ethyl acetate (4:1).
This gave the title compound, 4a (2.2 g), as a white solid in 57% yield.
In conclusion, a catalytic (in B(C6F5)3) intramolecular Sila-
Friedel−Crafts route to silafluorene compounds has been
developed, which only produces H2 as byproduct. A metal-free
approach to silaindenes from alkynes has also been achieved by
a BCF-catalyzed one-pot hydrosilylation/dehydrosilylation
pathway. Both reactions are limited in scope due to (i)
competing protodesilylation/reduction of heteroaromatic spe-
cies, (ii) trans-hydrosilylation only proceeding for select
alkynes, and (iii) BCF being insufficiently robust in the
presence of highly electrophilic Lewis acids and/or strong
Brønsted acids.
3
1H NMR (CDCl3 400 MHz) δ 7.54 (d, JHH 7.3 Hz, 1H), 7.48 (dt,
3
3JHH 1.3 Hz, JHH 7.9 Hz, 1H), 7.45−7.43 (m, 4H), 7.40−7.29 (m,
8H), 7.25−7.18 (m, 5H), 5.16 (s, 1H). 13C {1H} NMR (CDCl3 100
MHz) δ 150.2, 143.1, 137.1, 135.7, 134.3, 132.3, 129.7, 129.5, 129.4,
129.3, 127.8, 127.7, 127.0, 126.4 ppm. 29Si {1H} NMR (CDCl3 80
MHz) δ −21.2 ppm. HRMS Found: 336.1329 m/z (expected for M+
336.1329). Elemental analysis expected C 85.70%, H 5.95%, Found: C
85.62%, H 6.39%.
EXPERIMENTAL SECTION
■
General Comments. Unless otherwise stated, all manipulations
were carried out using standard Schlenk techniques under argon, or in
a glovebox under an atmosphere of argon (<0.1 ppm of O2/H2O).
Unless otherwise indicated, solvents were distilled from appropriate
drying agents: Ether (NaK), n-hexane (NaK), dichloromethane
(CaH2), and o-dichlorobenzene (CaH2). Ether, o-dichlorobenzene,
and dichloromethane were stored over activated 3 Å molecular sieves,
while n-hexane was stored over a potassium mirror. All other
compounds (excluding B(C6F5)3) were purchased from commercial
sources and used as received. Solvents for column chromatography
were of technical grade and used without further purification. Column
chromatography was performed on silica gel (230−400 mesh). NMR
spectra were recorded on Bruker AvanceIII-400, Bruker AvanceII-500,
or Bruker Ascend-400 spectrometers. Chemical shifts are reported as
dimensionless δ values and are frequency referenced relative to
4b Bis(4,4′-di-tert-butylbiphenyl-2-yl)silane.9 Synthesized ac-
cording to general procedure 1, starting with 2.3 mL of diphenyl-
chlorosilane. The solvent was removed under vacuum and purified by
flash column chromatography, where the eluent was pentane:CH2Cl2
(10:1). This gave the title compound, 4b (2.6 g), as a white crystalline
1
solid in 75% yield. H and 13C {1H} data in accordance with the
literature.9 29Si {1H} NMR (CDCl3 80 MHz) δ −20.76 ppm.
4c 2-(Dimethylsilyl)biphenyl. Synthesized according to general
procedure 1, starting with 1.55 mL of dimethylchlorosilane. The
solvent was removed under vacuum and purified by flash column
chromatography, where the eluent was hexane. This gave the title
compound, 4c (1.8 g), as a colorless oil in 75% yield. 1H and 13C {1H}
NMR data were found to be in accordance with previously reported
literature data.20 29Si {1H} NMR (CDCl3 80 MHz) δ −17.9 ppm.
4d 2-(Di-iso-butylsilyl)biphenyl. Synthesized according to
general procedure 1, starting with 2 mL of di-iso-butylchlorosilane.
The solvent was removed under vacuum and purified by flash column
chromatography, where the eluent was pentane:CH2Cl2 (10:1). This
gave the title compound, 4d (2.3 g), as a colorless oil in 69% yield. 1H
NMR (CDCl3 400 MHz) δ 7.71 (d, 3JHH 7.3 Hz, 1H), 7.47−7.32 (M,
1
residual protio impurities in the NMR solvents for H and 13C{1H},
respectively, while 11B, 19F, and 29Si shifts are referenced relative to
external BF3-etherate, hexafluorobenzene, and tetramethylsilane,
respectively. Coupling constants J are given in hertz (Hz) as positive
values regardless of their real individual signs. High-resolution mass
spectra (HRMS) were recorded on a Waters QTOF mass
spectrometer. GCMS analysis was performed on an Agilent
Technologies 7890A GC system equipped with an Agilent
Technologies 5975C inert XL EI/CI MSD with a triple axis detector.
The column employed was an Agilent J&W HP-5 ms ((5%-phenyl)-
methylpolysiloxane) of dimensions: length, 30 m; internal diameter,
0.250 mm; film, 0.25 μm. Microanalysis was performed at the
University of Manchester microanalytical service. An INEPT
(Insensitive Nuclei Enhanced by Polarization Transfer) experiment
was utilized to improve the sensitivity of 29Si NMR experiments.
Procedure for Drying B(C6F5)3. B(C6F5)3 was stirred with excess
Et3SiH (5 equiv) in pentane for 72 h at ambient temperature. Solvent
was removed and B(C6F5)3 was dried in vacuo to give a dry white
powder, which was pure by 11B and 19F{1H} NMR spectroscopy.
General Procedure 1: The Synthesis of 2-(Dialkyl/Arylsilyl)-
biphenyls. To a solution of 2-bromobiphenyl (2 mL, 11.6 mmol) and
TMEDA (1.9 mL, 12.76 mmol), in diethyl ether (20 mL) was added
n-butyl-lithium (8 mL, 1.6 M in hexane) dropwise at −78 °C, and the
mixture was stirred for 5 h. To this solution was added diaryl/
alkylchlorosilane (1.1 equiv) dropwise at −78 °C, and the mixture was
3
3
8H), 4.31 (quintet, JHH 3.8 Hz, 1H, Si-H), 1.66 (septet, JHH 6.8 Hz,
3
2H), 0.89 (2 overlapped doublets, JHH 6.3 Hz, 12H), 0.65−0.52 (m,
4H). 13C {1H} NMR (CD2Cl2 100 MHz) δ 149.4, 143.8, 136.2, 134.9,
129.3, 129.2, 128.9, 127.7, 127.1, 126.3, 26.0, 25.4, 25.3, 23.8 ppm. 29Si
{1H} NMR (CDCl3 80 MHz) δ −13.07 ppm. HRMS Found:
296.1945 m/z (expected for M+ 296.1955). Elemental analysis
expected C 81.01%, H 9.52%, Found: C 81.42%, H 9.63%.
5a 9,9-Diphenyl-9-silafluorene.21 In an oven-dried J. Youngs tap
fitted Schlenk tube, 131 mg of 2-(diphenylsilyl)biphenyl was added to
a solution of BCF (10 mg, 5 mol %) in anhydrous o-DCB. This
solution was agitated for 5 min before the addition of Cl2-py (3 mg, 5
mol %) and then sealed and heated to 100 °C for 96 h. The solution
was passed through a plug of silica and then dried under vacuum.
Further purification by flash column chromatography (eluent:
CH2Cl2) and drying gave 117 mg of 5a as a white solid (90% isolated
yield). 1H NMR (CDCl3 400 MHz) δ 7.94 (d, 3JHH 7.9 Hz, 2H), 7.84
3
3
(d, JHH 6.6 Hz, 2H), 7.72−7.70 (m, 4H), 7.52 (td, JHH 7.6 Hz, 1.3
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3
Hz, 2H), 7.45 (tt, JHH 6.3 Hz, 1.3 Hz, 2H), 7.40−7.34 (m, 6H). 13C
ASSOCIATED CONTENT
* Supporting Information
Full experimental details for all reactions and crystallographic
data. This material is available free of charge via the Internet at
http://pubs.acs.org.
■
{1H} NMR (CDCl3 100 MHz) δ 148.8, 135.9, 135.5, 134.0, 132.7,
130.7, 130.1, 128.1, 127.8, 121.2 ppm. 29Si {1H} NMR (CDCl3 80
MHz) δ −12.7 ppm. HRMS Found: 335.1245 m/z (expected for M+
335.1251). Elemental analysis expected C 85.85%, H 5.78%, Found: C
85.19%, H 5.42%.
S
5b 2,7-Di-tert-butyl-9,9-diphenyl-9-silafluorene. In an oven-
dried J. Youngs tap fitted Schlenk tube, 86 mg of bis(4,4′-di-tert-
butylbiphenyl-2-yl)silane was added to a solution of BCF (10 mg, 5
mol %) in anhydrous o-DCB. This solution was agitated for 5 min
before the addition of Cl2-py (3 mg 5 mol %) and then sealed and
heated to 100 °C for 96 h. The solution was passed through a plug of
silica and then dried under vacuum. Further purification by flash
column chromatography (eluent: pentane) and drying gave 74 mg of
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
■
We thank the Royal Society (M.J.I.) and the University of
Manchester (L.D.C.) for support. This work was also funded by
the EPSRC (grant number EP/K039547/1).
1
5b as a white powder (87% isolated yield). H and 13C {1H} data in
accordance with the literature.9 29Si{1H} NMR (CDCl3 80 MHz) δ
−11.5 ppm.
REFERENCES
■
5d 9,9-Di-iso-butyl-9-silafluorene. In an oven-dried J. Youngs
tap fitted Schlenk tube, 1 mL of 2-(di-iso-butylsilyl)biphenyl was added
to a solution of BCF (86 mg, 5 mol %) in anhydrous o-DCB. This
solution was agitated for 5 min before the addition of Cl2-py (25 mg 5
mol %) and then sealed and heated to 100 °C for 96 h. The solution
was passed through a plug of silica and then dried under vacuum.
Further purification by flash column chromatography (eluent:
pentane) and drying gave 78 mg of 5d as a colorless oil (79%
(1) Murata, H.; Malliaras, G. G.; Uchida, M.; Shen, Y.; Kafafi, Z. H.
Chem. Phys. Lett. 2001, 339, 161−166.
(2) (a) Corey, J. Y. Adv. Organomet. Chem. 2011, 59, 1. (b) Beaupre,
́
S.; Boudreault, P.-L. T.; Leclerc, M. Adv. Mater. 2010, 22, E6−E27.
(3) (a) Hong, J.-H.; Boudjouk, P.; Castellino, S. Organometallics
1994, 13, 3387−3389. (b) West, R.; Sohn, H.; Bankwitz, J.; Calabrese,
J.; Apeloig, Y.; Mueller, T. J. Am. Chem. Soc. 1995, 117, 11608−11609.
(c) Freeman, W. P.; Tilley, T. D.; Yap, G. P. A.; Rheingold, A. L.
Angew. Chem., Int. Ed. 1996, 35, 882−884.
(4) Yamaguchi, S.; Tamao, K. J. Chem. Soc., Dalton Trans. 1998,
3693−3702.
(5) Zhan, X.; Barlow, S.; Marder, S. R. Chem. Commun. 2009, 1948−
1955.
1
3
isolated yield). H NMR (CD2Cl2 400 MHz) δ 7.84 (d, JHH 7.8 Hz,
2H), 7.66 (d, 3JHH 7.0 Hz, 2H), 7.42 (t, 3JHH 7.8 Hz, 2H), 7.26 (t, 3JHH
7.3 Hz, 2H), 1.71 (septet, 3JHH 6.5 Hz, 2H), 0.98 (d, 3JHH 7.0 Hz, 4H),
0.81 (d, JHH 6.5 Hz, 12H). 13C {1H} NMR (CD2Cl2 100 MHz) δ
3
148.7, 139.1, 134.0, 130.5, 127.8, 121.4, 26.5, 25.8, 24.3 ppm. 29Si {1H}
NMR (CD2Cl2 80 MHz) δ 1.36 ppm. HRMS Found: 294.1800 m/z,
(expected for M+ 294.1798).
(6) Gilman, H.; Gorsich, R. D. J. Am. Chem. Soc. 1955, 77, 6380−
6381.
(7) For select metal-catalyzed silafluorene syntheses: (a) Yabusaki,
Y.; Ohshima, N.; Kondo, H.; Kusamoto, T.; Yamanoi, Y.; Nishihara, H.
Chem.Eur. J. 2010, 16, 5581−5585. (b) Ureshino, T.; Yoshida, T.;
Kuninobu, Y.; Takai, K. J. Am. Chem. Soc. 2010, 132, 14324−14326.
(c) Shimizu, M.; Mochida, K.; Hiyama, T. Angew. Chem., Int. Ed. 2008,
47, 9760−9764. (d) Matsuda, T.; Kadowaki, S.; Goya, T.; Murakami,
M. Org. Lett. 2007, 9, 133−136.
(8) For select metal-catalyzed silaindene syntheses: (a) Matsuda, T.;
Yamaguchi, Y.; Murakami, M. Synlett 2008, 561−564. (b) Matsuda, T.;
Kadowaki, S.; Yamaguchi, Y.; Murakami, M. Chem. Commun. 2008,
2744−2746. (c) Zhang, Q.-W.; An, K.; He, W. Angew. Chem., Int. Ed.
2014, 53, 5667−5671.
(9) (a) Furukawa, S.; Kobayashi, J.; Kawashima, T. J. Am. Chem. Soc.
2009, 131, 14192−14193. (b) Furukawa, S.; Kobayashi, J.; Kawashima,
T. Dalton Trans. 2010, 39, 9329−9336.
(10) Arii, H.; Kurihara, T.; Mochida, K.; Kawashima, T. Chem.
Commun. 2014, 50, 6649−6652.
(11) (a) Rendler, S.; Oestreich, M. Angew. Chem., Int. Ed. 2008, 47,
13a 2-Methyl-1,1-diphenyl-1-silaindene. In an oven-dried J.
Youngs tap fitted Schlenk tube, 73 μL of diphenyl silane was added to
a solution of BCF (10 mg, 5 mol %) and 49 μL of 1-phenyl-1-propyne
in anhydrous CH2Cl2. This solution was then sealed and heated to 60
°C for 4 h. One equivalent of Cl2-py (58 mg) was added to the
reaction mixture before being sealed and heated for a further 72 h at
60 °C. Preparative TLC with an eluent of hexane:CH2Cl2 (9:1) lead to
several bands. Taking the top two-thirds of the top band gave ca. 82%
of the 1,1-diphenyl-2-methyl-1-silaindene (13a) and 18% of the cis-
1
and trans-vinylsilane mixture (12a). H NMR (CD2Cl2 400 MHz) δ
7.62−7.60 (m, 5H), 7.46−7.33 (m, 7H), 7.27−7.23 (m, 1H), 7.19 (t,
3JHH 7.3 Hz, 1H), 7.13 (s, br, 1H), 2.16 (d, 4JHH 1.3 Hz, 3H). 13C {1H}
NMR (CDCl3 100 MHz) δ 145.6, 135.7, 135.4, 134.3, 133.1, 132.3,
130.0, 128.2, 127.8, 126.3, 18.0 ppm. 29Si {1H} NMR (CD2Cl2 80
MHz) δ −9.16 ppm. HRMS Found: 298.1165 m/z, (expected for M+
298.1172).
13b 2-Ethyl-1,1-diphenyl-1-silaindene. In an oven-dried J.
Youngs tap fitted Schlenk tube, 73 μL of diphenyl silane was added to
a solution of BCF (10 mg, 5 mol %) and 56 μL of 1-phenyl-1-butyne
in anhydrous CH2Cl2. This solution was then sealed and heated to 60
°C for 2 h. One equivalent of Cl2-py (58 mg) was added to the
reaction mixture before being sealed and heated for a further 24 h at
60 °C. Preparative TLC with an eluent of hexane:CH2Cl2 (9:1) lead to
several bands. Taking the top two-thirds of the top band gave 89% of
the 1,1-diphenyl-2-ethyl-1-silaindene (13b) and 11% of the cis- and
5997−6000. (b) Houghton, A. Y.; Hurmalainen, J.; Mansikkamaki, A.;
̈
Piers, W. E.; Tuononen, H. M. Nat. Chem. 2014, 6, 983−988.
(12) Curless, L. D.; Clark, E. R.; Dunsford, J. J.; Ingleson, M. J. Chem.
Commun. 2014, 50, 5270−5272.
(13) For silicon substituent scrambling mediated by cationic silicon
species, see: (a) Schafer, A.; Reißmann, M.; Schafer, A.; Saak, W.;
̈
̈
Haase, D.; Muller, T. Angew. Chem., Int. Ed. 2011, 50, 12636−12638.
̈
́ ́ ́
(b) Muther, K.; Hrobarik, P.; Hrobarikova, V.; Kaupp, M.; Oestreich,
̈
M. Chem.Eur. J. 2013, 19, 16579−16594.
(14) For a recent organo-electronic device utilizing a dithienosilole
containing compound, see: Sun, Y.; Welch, G. C.; Leong, W. L.;
Takacs, C. J.; Bazan, G. C.; Heeger, A. J. Nat. Mater. 2012, 11, 44−48.
(15) Clark, E. R.; Ingleson, M. J. Angew. Chem., Int. Ed. 2014, 53,
11306−11309.
1
trans-vinylsilane. H NMR (CDCl3 400 MHz) δ 7.64−7.62 (m, 4H),
3
3
7.59 (d, JHH 7.6 Hz, 1H), 7.45−7.33 (m, 7H), 7.26 (d, JHH 7.6 Hz,
4
3
4
1H), 7.18 (dt, JHH 1.0 Hz, JHH 7.6 Hz, 1H), 7.13 (t, JHH 1.0 Hz,
4
3
3
1H), 2.56 (dq, JHH 1.8 Hz, JHH 7.3 Hz, 2H), 1.11 (t, JHH 7.6 Hz,
3H). 13C {1H} NMR (CDCl3 100 MHz) δ 150.3, 148.2, 143.2, 135.4,
135.2, 133.0, 132.5, 130.3, 130.0, 128.1, 126.3, 124.6, 25.5, 13.8 ppm.
29Si {1H} NMR (CDCl3 0 MHz) δ −9.11 ppm. HRMS Found:
312.1329 m/z, (expected for M+ 312.1338).
(16) Klare, H. F. T.; Oestreich, M.; Ito, J.; Nishiyama, H.; Ohki, Y.;
Tatsumi, K. J. Am. Chem. Soc. 2011, 133, 3312−3315.
(17) Holthausen, M. H.; Mehta, M.; Stephan, D. W. Angew. Chem.,
Int. Ed. 2014, 53, 6538−6541.
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Organometallics
Article
(18) Asao, N.; Sudo, T.; Yamamoto, Y. J. Org. Chem. 1996, 61,
7654−7655.
(19) Schwier, T.; Gevorgyan, V. Org. Lett. 2005, 7, 5191−5194.
(20) Ureshino, T.; Yoshida, T.; Kuninobu, Y.; Takai, K. J. Am. Chem.
Soc. 2010, 132, 14324−14326.
(21) Ishikawa, M.; Tabohashi, T.; Sugisawa, H.; Nishimura, K.;
Kumada, M. J. Organomet. Chem. 1983, 250, 109−119.
7246
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