Tris(biphenyl-4-yl)silyl-endcapped polyynes

Article abstract of DOI:10.1002/ejoc.200600878

The use of tris(biphenyl-4-yl)silyl (TBPS) as a large protecting group for polyynes has been investigated. The basic building block, TBPS-C≡C-TMS (1), is synthesized in a new "one-pot" reaction through the sequential addition of lithiated nucleophiles to

Full text of DOI:10.1002/ejoc.200600878

FULL PAPER
DOI: 10.1002/ejoc.200600878
Tris(biphenyl-4-yl)silyl-Endcapped Polyynes
Wesley A. Chalifoux,[a] Michael J. Ferguson,[b] and Rik R. Tykwinski*[a]
Keywords: Polyynes / Alkynes / Hay coupling / Cadiot-Chodkiewicz coupling / Ethynylsilanes / Alkyne protecting groups
The use of tris(biphenyl-4-yl)silyl (TBPS) as a large protect-
ing group for polyynes has been investigated. The basic
building block, TBPS–CϵC–TMS (1), is synthesized in a new
“one-pot” reaction through the sequential addition of lithi-
ated nucleophiles to tetrachlorosilane. The TMS group of
differentially protected 1 and the diyne 5 can be selectively
removed in the presence of the TBPS group under mild con-
ditions, allowing for the formation of TBPS-endcapped di-
and tetraynes (3 and 9) by oxidative homocoupling. For the
triyne, TBPS–(CϵC)3–TMS (11), chemoselectivity for de-
silylation decreases dramatically, preventing formation of the
corresponding hexayne. X-ray crystallographic analysis of 3
confirms a diameter of 20 Å for the TBPS group.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
within the 4 Å distance required for intermolecular cross-
linking to occur (decomposition from polymerization).[8]
Because this endgroup was also reasonably easy to access,
we explored its potential as a polyyne protecting group.
Introduction
Polyynes have shown potential for new optical materials
due to their unique electronic properties.[1,2] Furthermore,
there are many naturally occurring polyynes that have been
isolated, and these compounds often show interesting bio-
logical activity.[3] Polyynes are, therefore, desirable synthetic
targets, and a number of methods have been reported for
their formation.[4] The synthesis of polyynes can be
plagued, however, by decrease of stability as a function of
polyyne length, and this often leads to decomposition of
the polyyne resulting from indiscriminate intermolecular re-
actions (polymerization). It has been shown that the sta-
bility of the polyyne can be increased by placing bulky end-
groups at the termini of the polyyne, which act to shield the
reactive polyyne core from intermolecular reactions that
lead to decomposition.[2,5,6] Excellent examples of this ap-
proach have recently been reported by Hirsch and co-
workers,[5] and Gladysz and co-workers.[6]
Figure 1. Approximate size relationship of silyl endgroups.
Results and Discussion
The synthesis of the first TBPS-protected target, 1, was
achieved in a one-pot reaction with yields up to 76% by the
sequential addition of 3 equiv. of biphenyl-4-yllithium and
1 equiv. of (trimethylsilyl)ethynyllithium to tetrachloro-
silane (Scheme 1). While the one-pot synthesis of a tetra-
The bulky nature of the triisopropylsilyl (TIPS) end-
group has been utilized to increase the stability of polyynes,
allowing the successful synthesis of a series of polyynes up
to 20 carbon atoms in length.[2] Increasing the size of the
silyl endgroup could serve to increase the stability of the
polyyne even more. From simple modeling it was deter-
mined that the tris(biphenyl-4-yl)silyl (TBPS) group has
over twice the diameter of the TIPS group (Figure 1).[7] It
was predicted that the large size of this endgroup should
prevent the approach of extended polyyne molecules to
[a] Department of Chemistry, University of Alberta,
Edmonton, Alberta, T6G 2G2, Canada
Fax: +780-492-8231
E-mail: rik.tykwinski@ualberta.ca
[b] X-ray Crystallography Laboratory, Department of Chemistry,
University of Alberta,
Edmonton, Alberta, T6G 2G2, Canada
Scheme 1. “One-pot” synthesis of unsymmetrical acetylene 1.
Eur. J. Org. Chem. 2007, 1001–1006
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W. A. Chalifoux, M. J. Ferguson, R. R. Tykwinski
FULL PAPER
arylsilane containing at least two different functional
groups has been demonstrated,[9] to the best of our
knowledge this is the first example of a multi-component
reaction to obtain a triaryl(ethynyl)silane. The synthesis of
1 was also successful using the corresponding biphenyl-4-yl
Grignard reagent; however, the yields were lower (ca. 30%).
Under protiodesilylation conditions at 0 °C, the trimeth-
ylsilyl (TMS) group of 1 could be selectively removed to
yield 2 in excellent yield (Scheme 2). At higher tempera-
tures, or prolonged exposure to these conditions, the TBPS
group is also cleaved, leading to a decreased yield of 2. The
attempted synthesis of 3 using Hay[10] conditions was un-
successful, leading to poor yields. The synthesis of 3 has,
however, been carried out in good yield under Pd-catalyzed
homocoupling conditions reported by Zhang and co-
workers.[11,12]
Figure 2. a) A view of molecule 3 with an arrow showing the radius
of the TBPS endgroup (Si ↔ H). b) Crystal packing of 3, with the
arrow showing a distance of Ͼ 8 Å between neighboring molecules
(non-hydrogen atoms are represented by Gaussian ellipsoids at the
20% probability level, hydrogen atoms removed for clarity).
Scheme 2. Selective protiodesilylation of the TMS group followed
by Pd-catalyzed homocoupling to give diyne 3.
X-ray crystallographic characterization of 3 showed a ra-
dius of approximately 10 Å for the TBPS group and clearly
demonstrates its larger size in comparison to the TIPS
group (Figure 2, a).[2] This sterically demanding endgroup
places each polyyne a distance of Ͼ 8 Å from its nearest
Treatment of 1 with N-bromosuccinimide in the presence
neighbor in the crystal lattice, double of that required for of catalytic silver(I) nitrate gave the bromide 4 directly in
an intermolecular reaction to occur (Figure 2, b).[8,13] Diyne excellent yield without the need for prior desilylation
3 shows a melting point (296–298 °C) that is comparable to [Equation (1)].[16] The synthesis of 4 could also be carried
1,4-bis(triphenylsilyl)-1,3-butadiyne (304 °C)[14] and higher out using 2 under the same conditions.[17] The subsequent
than that of 1,4-bis(methyldiphenylsilyl)-1,3-butadiyne synthesis of differentially protected 5 was accomplished un-
(143 °C).[13] These values are higher than those of trialkyl- der Pd-catalyzed cross-coupling conditions between 2 (or 4)
silyl-endcapped diynes such as 1,4-bis(TIPS)-1,3-butadiyne and 6 (or 7)[18] in moderate yield (Table 1).[4e] The main side
(98–100 °C)[2] and 1,4-bis(TMS)-1,3-butadiyne (107 °C).[15] products from this reaction were the homocoupled product
This suggests a possible trend in melting point related to 3 and 1,4-bis(TMS)-1,3-butadiyne, which could be sepa-
structure of the terminal silyl group (i.e., aryl vs. alkyl sub- rated chromatographically. Many variations of this reaction
stituents), rather than overall size.
were attempted with surprisingly little difference in the
Table 1. Synthesis of 5 by Pd-catalyzed cross-coupling.
Entry
Substrate 1
Substrate 2
Catalyst system
Base
Oxidant
Yield of 5
1
2
3
4
5
6
4
4
4
2
2
2
6
6
6
7
7
6
[PdCl2(PPh3)2]/CuI
[Pd(PPh3)4]/CuI
[PdCl2(PPh3)2]/CuCl
[PdCl2(PPh3)2]/CuI
[PdCl2(PPh3)2]/CuI
[PdCl2(PPh3)2]/CuI
iPr2NH
iPr2NH
iPr2NH
Et3N
iPr2NH
iPr2NH
N/A
N/A
N/A
N/A
N/A
45%
39%
54%
44%
48%
57%
ethyl bromoacetate
1002
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Tris(biphenyl-4-yl)silyl-Endcapped Polyynes
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yield.[19] The best yield was ultimately obtained by coupling
The synthesis of hexayne 12 from triyne 11 proved to be
both terminal acetylenes (2 and 6) in the presence of ethyl frustratingly difficult due to the complete lack of chemo-
bromoacetate as the oxidant (Entry 6).
selectivity in the desilylation step (Scheme 5). Using the
mildest conditions, only a trace amount of 13 was detected
by thin-layer chromatography. The crude reaction mixture
was nonetheless subjected to Hay coupling conditions with-
out prior purification in the hope of obtaining quantities
of hexayne 12 sufficient for characterization. Only a trace
amount of material was obtained, which proved to be diffi-
cult to purify and characterize. Due to the apparent chemi-
cal instability of the TBPS group, no further attempts were
made to isolate or synthesize the hexayne 12.
(1)
The selective deprotection of 5 proved to be more prob-
lematic than anticipated. When the conditions that were
used for 1 were applied, the chemoselectivity for the TMS
group over the TBPS group was considerably diminished.
Using the milder base NaHCO3 in a 1:1 mixture of THF/
MeOH at low temperature gave 8 in excellent yield
(Scheme 3). Standard Hay coupling conditions then gave
tetrayne 9 in good yield. Tetrayne 9 shows exceptional sta-
bility in the solid state, decomposing only at temperatures
above 250 °C. By way of comparison, the analogous 1,8-
bis(TIPS)tetrayne melts prior to decomposition (M.p. 72–
75 °C),[2] while 1,8-bis(TMS)- and 1,8-bis(triethylsilyl)tet-
raynes show melting points of 94 °C[15] and 40 °C,[20]
respectively.
Scheme 5. Attempted selective desilylation of 11 using mild basic
conditions followed by Hay coupling to give hexayne 12.
Conclusions
A new and efficient one-pot procedure has been devel-
oped for the formation of an ethynylsilane (1) substituted
with a tris(biphenyl-4-yl)silyl (TBPS) endgroup. From the
precursor 1, the synthesis of unsymmetrical mono-, di- and
triynes differentially protected with the TBPS and TMS
endgroups has been achieved in good yields. Symmetrical
di- and tetraynes substituted at both ends with the TBPS
group have been synthesized by oxidative homocoupling.
The large size of the TBPS endgroup has been demon-
strated by X-ray crystallography of the diyne 3. Unfortu-
nately, the inability to selectively remove a TMS group in
the presence of the TBPS endgroup of longer precursors
such as triyne 11 has, to date, prevented the synthesis of
longer derivatives.
Scheme 3. Desilylation of 5 using mild basic conditions followed
by Hay coupling to give tetrayne 9.
The in situ desilylation/bromination of 5 giving 10 was
achieved in excellent yield by cooling the reaction mixture
to 0 °C (Scheme 4). An unfortunate problem with this reac-
tion was that it was very slow, requiring 3–6 d to reach com-
pletion. Higher temperatures, however, led to a decrease in
selectivity. The rate of the reaction could be enhanced by
adding five times the amount of silver(I) nitrate, allowing
for the complete reaction in 24 h. An interesting spectral
feature for 10 is found in the 13C NMR spectrum, where
the C(1) carbon atom resonates at δ = 42.4 ppm due to the
presence of bromine and the “heavy atom effect”.[21] Cross-
coupling with (trimethylsilyl)acetylene gave the unsymmet-
rical triyne 11 in moderate yield.
Experimental Section
General Procedures and Methods: Reagents (reagent grade) were
purchased from commercial suppliers and used without further pu-
rification. THF and Et2O were distilled from sodium/benzophe-
none. Evaporation and concentration in vacuo was done at H2O-
aspirator pressure. All reactions were performed in standard, dry
glassware under N2. Column chromatography: Silica gel 60 (230–
400 mesh) from Rose Scientific Ltd. Thin-layer chromatography
(TLC): aluminum sheets covered with silica gel 60 F254 from Mach-
erey–Nagel; visualization by UV light. M.p. (uncorrected): Gallen-
kamp apparatus. IR spectra [cm–1]: Nicolet Magna 750 FTIR (cast
film) or Nic-Plan FTIR Microscope (solids). 1H and 13C NMR:
Varian Inova 400, and 500, Varian Mercury 400 or Varian Unity
1
500 at room temp. in CDCl3; solvent peaks (δ = 7.24 ppm for H
and 77.0 ppm for 13C, respectively) as reference. EI MS (m/z):
Kratos MS50 instrument or Voyager Elite MALDI; the matrix em-
ployed was trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylid-
Scheme 4. The in situ desilylation/bromination of 5 followed by Pd-
catalyzed cross-coupling toward 11.
Eur. J. Org. Chem. 2007, 1001–1006
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W. A. Chalifoux, M. J. Ferguson, R. R. Tykwinski
FULL PAPER
ene]malononitrile (DCTB). Elemental analyses were performed by
the Microanalytical Laboratory at the University of Alberta.
6 H), 7.44 (app t, 3J = 7.4 Hz, 6 H), 7.35 (t, 3J = 7.4 Hz, 3 H), 2.85
(s, 1 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 142.9, 140.8,
136.0, 131.4, 128.8, 127.6, 127.2, 126.9, 98.1, 85.3 ppm. EI HRMS:
calcd. for C38H28Si 512.1960 [M+], found 512.1958. C38H28Si
(512.71): calcd. C 89.02, H 5.50; found C 88.76, H 5.74.
X-ray Crystallography: Unit cell parameters and intensity data were
obtained with a Bruker PLATFORM/SMART 1000 CCD dif-
fractometer using graphite-monochromated Mo-Kα radiation
(0.71073 Å). Programs for diffractometer operation, data collec-
tion, data reduction and absorption correction were those supplied
by Bruker. The structures were solved by direct methods using
SHELXS-86[22] and refined by full-matrix least squares on F2 using
SHELXL-93.[23] The crystallization of 3 was done by slow concen-
tration of a solution of 3 in CH2Cl2/toluene (1:9) at room temp.
C54H36Si2, M = 1023.4; crystal dimensions: 0.54ϫ0.34ϫ0.28 mm;
crystal system: monoclinic; space group P21/c (no. 14), a =
10.647(2), b = 22.251(4), c = 14.926(3) Å; β = 107.929(3)°; V =
3364.2(11) Å3, Z = 2; ρcalcd. = 1.192 gcm–3; µ = 0.101 mm–1; ab-
sorption correction by multi-scan (SADABS); range of trans-
mission factors 0.9723–0.9475; number of observed reflections
3650; number of independent reflections 5924; R1 [Fo2 Ն2σ(Fo2)] =
0.0645; wR2 [Fo2 Ն–3σ(Fo2)] = 0.1701; T = –80 °C; scan mode: ω
scans (0.3°) (20 s exposures); largest difference peak and hole 0.588
and –0.265 eÅ–3. CCDC-623034 contains the supplementary crys-
tallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
1,4-Bis(TBPS)-1,3-butadiyne (3): To a mixture of [PdCl2(PPh3)2]
(10 mg, 0.016 mmol), CuI (3 mg, 0.02 mmol) and Et3N (95 mg,
0.13 mL, 0.94 mmol) was added 2 (200 mg, 0.390 mmol) in THF
(5 mL). Ethyl bromoacetate (65 mg, 43 µL, 0.39 mmol) was added
and the mixture stirred at room temp. under N2 for 24 h. H2O
(5 mL) was added and the resulting mixture extracted with CH2Cl2
(2ϫ20 mL). The organic layers were combined, washed with brine
and dried with MgSO4. The resulting solution was concentrated
under vacuum. Et2O was added to the crude product, which
formed a precipitate. The mixture was filtered and the solid washed
with Et2O to give 3 (0.156 g, 77%) as a white solid. M.p. 296–
298 °C. Rf = 0.43 (CH Cl /hexanes, 1:2). IR (microscope): ν =
˜
2
2
3024, 2068, 1595, 1385, 1115 cm–1. 1H NMR (400 MHz, CDCl3):
3
3
δ = 7.78 (d, J = 7.9 Hz, 12 H), 7.65 (d, J = 7.9 Hz, 12 H), 7.60
3
3
3
(d, J = 7.5 Hz, 12 H), 7.43 (app t, J = 7.5 Hz, 12 H), 7.34 (t, J
= 7.5 Hz, 6 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 143.1,
140.8, 136.1, 130.9, 128.8, 127.7, 127.2, 127.0, 92.3, 82.4 ppm.
MALDI MS (DCTB): m/z (%) = 1272.5 (100) [M+ + matrix],
1022.4 (30) [M+].
1-Bromo-2-(TBPS)ethyne (4): To
a solution of 1 (163 mg,
1-(TBPS)-2-(TMS)ethyne (1): To a solution of 4-iodobiphenyl
(4.279 g, 15.27 mmol) in dry Et2O (50 mL) at –78 °C under N2 was
added dropwise BuLi (7.3 mL, 2.5  in hexanes, 18 mmol) over a
period of 5 min, and the solution was warmed to 0 °C over a period
of 30 min. This solution was added to a solution of SiCl4 (0.742 g,
0.500 mL, 4.37 mmol) in dry Et2O (10 mL) through a cannula and
the mixture was warmed to room temp. over a period of 10 min
and stirred for 1.5 h (solution A). Concurrently, to a solution of
(TMS)acetylene (1.28 g, 1.84 mL, 13.1 mmol) in dry Et2O (10 mL)
at –78 °C was added dropwise BuLi (5.2 mL, 2.5  in hexanes,
13 mmol) over a period of 5 min, and the reaction mixture was
warmed to 0 °C over a period of 30 min (solution B). Solution B
was added to solution A through a cannula and the mixture stirred
under N2 at room temp. for 7 h. The reaction was quenched with
saturated aqueous NH4Cl (5 mL) and H2O was then added to dis-
solve the inorganic salts. The organic layer was washed with brine
and then dried with MgSO4. The crude product was purified by
column chromatography (silica gel, CH2Cl2/hexanes, 1:4) to yield 1
(1.95 g, 76%) as a white solid. M.p. 142–144 °C. Rf = 0.49 (CH2Cl2/
0.279 mmol) and N-bromosuccinimide (58 mg, 0.33 mmol) in ace-
tone (10 mL) was added AgNO3 (5 mg, 0.03 mmol). The mixture
was stirred at room temp. under N2 for 30 min. H2O (5 mL) was
added and the resulting mixture extracted with hexanes
(2ϫ20 mL). The organic layers were combined, washed with brine
and dried with MgSO4. The crude product was purified by column
chromatography (silica gel, CH2Cl2/hexanes, 1:2) to yield
(143 mg, 87%) as a white solid. M.p. 166–168 °C. Rf = 0.61
(CH Cl /hexanes, 1:2). IR (CH Cl , cast film): ν = 3060, 3025,
4
˜
2
2
2
2
2122, 1596, 1386, 1117 cm–1. 1H NMR (500 MHz, CDCl3): δ =
7.78 (d, 3J = 8.0 Hz, 6 H), 7.65 (d, J = 8.0 Hz, 6 H), 7.62 (d, J =
3
3
3
3
7.5 Hz, 6 H), 7.45 (app t, J = 7.5 Hz, 6 H), 7.36 (t, J = 7.5 Hz, 3
H) ppm. 13C NMR (125 MHz, CDCl3): δ = 143.0, 140.8, 136.0,
131.4, 128.8, 127.6, 127.2, 126.9, 82.5, 67.2 ppm. EI HRMS: calcd.
for C38H27Si81Br 592.1045 [M+], found 592.1048. C38H27BrSi
(591.61): calcd. C 77.15, H 4.60; found C 77.40, H 4.67.
1-(TBPS)-4-(TMS)-1,3-butadiyne (5): To a mixture of 4 (208 mg,
0.352 mmol) and (TMS)acetylene (6) (70 mg, 0.10 mL, 0.71 mmol)
in THF (5 mL) was added [PdCl2(PPh3)2] (12 mg, 0.018 mmol),
CuI (3 mg, 0.02 mmol) and iPr2NH (0.18 g, 0.25 mL, 1.8 mmol) in
that order. The mixture was stirred at room temp. under N2 for
2 h. H2O (5 mL) was added and the resulting mixture was extracted
with Et2O (2ϫ20 mL). The organic layers were combined, washed
with brine and dried with MgSO4. The crude product was purified
by column chromatography (silica gel, EtOAc/hexanes, 1:10) to give
5 (96 mg, 45%) as a white solid. M.p. 222–223 °C. Rf = 0.55
hexanes, 1:4). IR (microscope): ν = 3024, 2955, 1597, 1386, 1248,
˜
1
3
1116 cm–1. H NMR (500 MHz, CDCl3): δ = 7.81 (d, J = 7.8 Hz,
3
3
6 H), 7.66 (d, J = 7.8 Hz, 6 H), 7.64 (d, J = 7.5 Hz, 6 H), 7.46
3
3
(app t, J = 7.5 Hz, 6 H), 7.37 (t, J = 7.5 Hz, 3 H), 0.31 (s, 9 H)
ppm. 13C NMR (125 MHz, CDCl3): δ = 142.7, 140.9, 136.1, 132.1,
128.8, 127.5, 127.2, 126.8, 120.0, 107.8, –0.1 ppm. EI HRMS:
calcd. for C41H36Si2 584.2355 [M+], found 584.2346. C41H36Si2
(584.90): calcd. C 84.19, H 6.20; found C 84.22, H 6.32.
(CH Cl /hexanes, 1:2). IR (microscope): ν = 3073, 3025, 2961,
˜
2
2
(TBPS)acetylene (2): A solution of 1 (2.143 g, 3.664 mmol) in a 1:1
mixture of THF (15 mL) and MeOH (15 mL) was cooled to 0 °C
and K2CO3 (0.506 g, 3.66 mmol) was added. After stirring at 0 °C
for 1 h, H2O (10 mL) was added and the mixture extracted with
Et2O (100 mL). The organic layer was washed with brine and dried
with MgSO4. The crude product was purified by column
2070, 1597, 1386, 1253, 1118 cm–1. 1H NMR (400 MHz, CDCl3):
3
3
δ = 7.76 (d, J = 8.1 Hz, 6 H), 7.63 (d, J = 8.1 Hz, 6 H), 7.60 (d,
3J = 7.4 Hz, 6 H), 7.44 (app t, 3J = 7.4 Hz, 6 H), 7.35 (t, 3J =
7.4 Hz, 3 H), 0.22 (s, 9 H) ppm. 13C NMR (125 MHz, CDCl3): δ
= 143.0, 140.8, 136.1, 131.1, 128.8, 127.6, 127.2, 126.9, 92.4, 88.1,
87.8, 80.5, –0.5 ppm. EI HRMS: calcd. for C43H36Si2 608.2355
[M+], found 608.2360.
chromatography (silica gel, CH2Cl2/hexanes, 1:2) to yield
2
(1.601 g, 85%) as a white solid. M.p. 172–175 °C. Rf = 0.46
(CH Cl /hexanes, 1:2). IR (CH Cl , cast film): ν = 3267, 3024, 1-(TBPS)-1,3-butadiyne (8): A solution of 5 (31 mg, 0.051 mmol)
˜
2
2
2
2
2035, 1596, 1117 cm–1. H NMR (400 MHz, CDCl3): δ = 7.79 (d, in a 1:1 mixture of THF (5 mL) and MeOH (5 mL) was cooled to
1
3J = 8.0 Hz, 6 H), 7.64 (d, J = 8.0 Hz, 6 H), 7.60 (d, J = 7.4 Hz,
1004
0 °C and NaHCO3 (21 mg, 0.25 mmol) was added. After stirring
3
3
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Tris(biphenyl-4-yl)silyl-Endcapped Polyynes
FULL PAPER
at 0 °C for 28 h, H2O (10 mL) was added and the mixture extracted
with hexanes (2ϫ30 mL). The organic layer was washed with brine
and dried with MgSO4. The crude product was purified by column
chromatography (silica gel, CH2Cl2/hexanes, 1:3) to yield 8 (25 mg,
93%) as a colorless oil: Rf = 0.50 (CH2Cl2/hexanes, 1:2). IR
Acknowledgments
This work was supported by the Natural Sciences and Engineering
Research Council of Canada (NSERC), the Alberta Ingenuity
Fund (studentship to W. A. C.), and the University of Alberta.
(CH Cl , cast film): ν = 3272, 3024, 2188, 2035, 1596, 1116 cm–1.
˜
2
2
1H NMR (500 MHz, CDCl3): δ = 7.78 (d, J = 8.0 Hz, 6 H), 7.66
3
3
3
3
(d, J = 8.0 Hz, 6 H), 7.62 (d, J = 7.5 Hz, 6 H), 7.45 (app t, J =
7.5 Hz, 6 H), 7.37 (t, 3J = 7.5 Hz, 3 H), 2.25 (s, 1 H) ppm. 13C
NMR (125 MHz, CDCl3): δ = 143.1, 140.8, 136.1, 130.8, 128.8,
127.7, 127.2, 126.9, 91.7, 79.6, 68.4, 68.2 ppm. EI HRMS: calcd.
for C40H28Si 536.1960 [M+], found 536.1989.
[1] a) Acetylene Chemistry – Chemistry, Biology, and Materials Sci-
ence (Eds.: F. Diederich, P. J. Stang, R. R. Tykwinski), Wiley-
VCH, Weinheim, 2005, chapters 7 and 9; b) W. A. Chalifoux,
R. R. Tykwinski, Chem. Rec. 2006, 6, 169–182; c) T. Luu, E.
Elliott, A. D. Slepkov, S. Eisler, R. McDonald, F. A. Hegmann,
R. R. Tykwinski, Org. Lett. 2005, 7, 51–54; d) A. D. Slepkov,
F. A. Hegmann, S. Eisler, E. Elliott, R. R. Tykwinski, J. Chem.
Phys. 2004, 120, 6807–6810.
1,8-Bis(TBPS)-1,3,5,7-octatetrayne (9): To a mixture of CuCl
(4 mg, 0.05 mmol) in CH2Cl2 (5 mL) was added TMEDA (10 mg,
14 µL, 0.090 mmol). O2 was bubbled through the solution for 5 min
and a solution of 8 (24 mg, 0.045 mmol) in CH2Cl2 (1 mL) was
added and stirred for 5 min. The reaction mixture was passed
through a plug of silica gel with CH2Cl2 and then concentrated
under vacuum to give 9 (20 mg, 83%) as a yellow solid. M.p. 273–
275 °C (decomposition observed at Ͼ 250 °C). Rf = 0.43 (CH2Cl2/
[2] S. Eisler, A. D. Slepkov, E. Elliott, T. Luu, R. McDonald, F. A.
Hegmann, R. R. Tykwinski, J. Am. Chem. Soc. 2005, 127,
2666–2676.
[3] A. L. K. Shi Shun, R. R. Tykwinski, Angew. Chem. 2006, 118,
1050–1073; Angew. Chem. Int. Ed. 2006, 45, 1034–1057.
[4] a) F. Cataldo, Carbon 2005, 43, 2792–2800; b) F. Cataldo, Tet-
rahedron 2004, 60, 4265–4274; c) Y. Morisaki, T. Luu, R. R.
Tykwinski, Org. Lett. 2006, 8, 689–692; d) S. Kim, S. Kim, T.
Lee, H. Ko, D. Kim, Org. Lett. 2004, 6, 3601–3604; e) P. Si-
emsen, R. C. Livingston, F. Diederich, Angew. Chem. 2000,
112, 2740–2767; Angew. Chem. Int. Ed. 2000, 39, 2633–2657.
[5] a) T. Gibtner, F. Hampel, J.-P. Gisselbrecht, A. Hirsch, Chem.
Eur. J. 2002, 8, 408–432; b) C. Klinger, O. Vostrowsky, A.
Hirsch, Eur. J. Org. Chem. 2006, 1508–1524.
[6] a) Q. Zheng, J. A. Gladysz, J. Am. Chem. Soc. 2005, 127,
10508–10509; b) J. Stahl, J. C. Bohling, E. B. Bauer, T. B. Pe-
ters, W. Mohr, J. M. Martin-Alvarez, F. Hampel, J. A. Gladysz,
Angew. Chem. 2002, 114, 1952–1957; Angew. Chem. Int. Ed.
2002, 41, 1872–1876; c) Q. Zheng, J. C. Bohling, T. B. Peters,
A. C. Frisch, F. Hampel, J. A. Gladysz, Chem. Eur. J. 2006, 12,
6486–6505.
[7] The approximate diameter was calculated from the radius,
measured from silicon to the proton in the 4Ј-position of bi-
phenyl. The distance was measured using SpartanЈ02 v.1.0.6
after performing a molecular mechanics minimization using an
MMFF94 force field.
[8] a) R. H. Baughman, K. C. Yee, J. Polym. Sci., Macromol. Rev.
1978, 13, 219–239; b) V. Enkelmann, Chem. Mater. 1994, 6,
1337–1340; c) S. Szafert, J. A. Gladysz, Chem. Rev. 2003, 103,
4175–4205.
hexanes, 1:2). IR (microscope): ν = 3071, 3024, 2041, 1595, 1386,
˜
1115 cm–1. H NMR (400 MHz, CDCl3): δ = 7.76 (d, J = 8.0 Hz,
12 H), 7.66 (d, 3J = 8.0 Hz, 12 H), 7.61 (d, 3J = 7.5 Hz, 12 H), 7.45
(app t, 3J = 7.5 Hz, 12 H), 7.36 (t, 3J = 7.5 Hz, 6 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 143.3, 140.7, 136.1, 130.4, 128.8,
127.7, 127.2, 127.0, 91.8, 83.3, 63.5, 62.9 ppm. MALDI MS
(DCTB): m/z (%) = 1321.6 (100) [M+ + matrix + H].
1
3
1-Bromo-4-(TBPS)-1,3-butadiyne (10): A solution of 5 (28 mg,
0.046 mmol) and N-bromosuccinimide (18 mg, 0.10 mmol) in ace-
tone (5 mL) was cooled to 0 °C and AgNO3 (5 mg, 0.03 mmol) was
added. The mixture was stirred at 0 °C under N2 for 24 h. H2O
(10 mL) was added and the resulting mixture extracted with hex-
anes (2ϫ20 mL). The organic layers were combined, washed with
brine and dried with MgSO4. The crude product was purified by
column chromatography (silica gel, EtOAc/hexanes, 1:10) to yield
10 (27 mg, 96%) as a pale yellow oil: Rf = 0.49 (CH2Cl2/hexanes,
1:2). IR (CH Cl , cast film): ν = 3057, 3024, 2247, 2179, 2093,
˜
2
2
1596, 1117 cm–1. 1H NMR (400 MHz, CDCl3): δ = 7.77 (d, 3J =
8.0 Hz, 6 H), 7.65 (d, 3J = 8.0 Hz, 6 H), 7.62 (d, 3J = 7.4 Hz, 6 H),
7.45 (app t, J = 7.4 Hz, 6 H), 7.36 (t, J = 7.4 Hz, 3 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 143.1, 140.8, 136.1, 130.9, 128.8,
127.7, 127.2, 126.9, 92.4, 78.3, 66.1, 42.4 ppm. EI HRMS: calcd.
for C36H27Si 487.1882 [M+ – C4Br], found 487.1890.
3
3
[9] H. Gilman, M. A. Plunkett, G. E. Dunn, J. Am. Chem. Soc.
1951, 73, 1686–1688.
[10] A. S. Hay, J. Org. Chem. 1962, 27, 3320–3321.
[11] A. Lei, M. Srivastava, X. Zhang, J. Org. Chem. 2002, 67, 1969–
1971.
[12] A similar Pd-catalyzed synthesis of symmetrical 1,3-diynes was
reported using chloroacetone as an oxidant, see: R. Rossi, A.
Carpita, C. Bigelli, Tetrahedron Lett. 1985, 26, 523–526.
[13] The structural and thermal characteristics of 1,4-bis(triorgano-
silyl)butadiynes have been studied, see: F. Carré, N. Devylder,
S. G. Dutremez, C. Guérin, B. J. L. Henner, A. Jolivet, W. Tom-
berli, F. Dahan, Organometallics 2003, 22, 2014–2033.
[14] J. L. Bréfort, R. J. P. Corriu, P. Gerbier, C. Guérin, B. J. L.
Henner, A. Jean, T. Kuhlmann, F. Garnier, A. Yassar, Organo-
metallics 1992, 11, 2500–2506.
1-(TBPS)-6-(TMS)-1,3,5-hexatriyne (11): To a mixture of 10
(141 mg, 0.229 mmol) and (TMS)acetylene (112 mg, 161 µL,
1.14 mmol) in THF (25 mL) was added [PdCl2(PPh3)2] (8 mg,
0.01 mmol), CuI (2 mg, 0.01 mmol) and iPr2NH (116 mg, 161 µL,
1.15 mmol) in that order. The mixture was stirred at room temp.
under N2 for 18 h. The reaction mixture was concentrated to ca.
5 mL, then co-evaporated with 2ϫ30 mL of CH2Cl2. The crude
product was purified by column chromatography (silica gel,
CH2Cl2/hexanes, 1:4) to give 11 (58 mg, 40%) as a yellow solid.
M.p. 142–144 °C (decomposition observed at Ͼ 100 °C). Rf = 0.34
[15] D. R. M. Walton, F. Waugh, J. Organomet. Chem. 1972, 37,
45–56.
(CH Cl /hexanes, 1:4). IR (microscope): ν = 3060, 3025, 2960,
˜
2
2
[16] T. Nishikawa, S. Shibuya, S. Hosokawa, M. Isobe, Synlett
1994, 485–486.
[17] H. Hofmeister, K. Annen, H. Laurent, R. Wiechert, Angew.
Chem. 1984, 96, 720–722; Angew. Chem. Int. Ed. Engl. 1984,
23, 727–729.
[18] The synthesis of 7 was carried out according to the analogous
procedure for alkynyl bromide formation and was used in situ
without purification or characterization, see: Y. Zhang, R. P.
2160, 2068, 1597, 1386, 1245, 1114 cm–1. 1H NMR (500 MHz,
3
3
CDCl3): δ = 7.78 (d, J = 8.1 Hz, 6 H), 7.65 (d, J = 8.1 Hz, 6 H),
3
3
7.61 (d, J = 7.4 Hz, 6 H), 7.45 (app t, J = 7.4 Hz, 6 H), 7.36 (t,
3J = 7.4 Hz, 3 H), 0.21 (s, 9 H) ppm. 13C NMR (125 MHz, CDCl3):
δ = 143.2, 140.7, 136.1, 130.7, 128.8, 127.7, 127.2, 127.0, 92.2, 88.7,
87.7, 82.1, 63.5, 61.9, –0.6 ppm. EI HRMS: calcd. for C45H36Si2
632.2355 [M+], found 632.2348.
Eur. J. Org. Chem. 2007, 1001–1006
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
1005

W. A. Chalifoux, M. J. Ferguson, R. R. Tykwinski
FULL PAPER
Hsung, M. R. Tracey, K. C. M. Kurtz, E. L. Vera, Org. Lett.
2004, 6, 1151–1154.
[19] Given the sensitivity of both the trimethylsilyl and TBPS
groups to base, standard Cadiot-Chodkiewicz cross-coupling
conditions were judged too harsh, see: W. Chodkiewicz, Ann.
Chim. (Paris) 1957, 2, 819–869.
Attempts to refine peaks of residual electron density as solvent
toluene carbon atoms were unsuccessful. The data were cor-
rected for disordered electron density through use of the
SQUEEZE procedure (P. van der Sluis, A. L. Spek, Acta Crys-
tallogr., Sect. A 1990, 46, 194–201) as implemented in PLA-
TON (A. L. Spek, Acta Crystallogr., Sect. A 1990, 46, C34;
PLATON – a multipurpose crystallographic tool, Utrecht Uni-
versity, Utrecht, The Netherlands). A total solvent-accessible
void volume of 738 Å3 with a total electron count of 197 (con-
sistent with four molecules of solvent toluene) was found in the
unit cell.
[20] R. Eastmond, T. R. Johnson, D. R. M. Walton, Tetrahedron
1972, 28, 4601–4616.
[21] S.-T. Lin, C.-C. Lee, D. W. Liang, Tetrahedron 2000, 56, 9619–
9623.
[22] G. M. Sheldrick, Acta Crystallogr., Sect. A 1990, 46, 467–473.
[23] a) G. M. Sheldrick, SHELXL-93, Program for crystal structure
determination, University of Göttingen, Germany, 1993. b)
Received: October 6, 2006
Published Online: December 21, 2006
1006
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 1001–1006