Efficient synthesis of a complete donor/acceptor bis(aryl)diyne family

Article abstract of DOI:10.1081/SCC-120021834

A facile route to a family of bis(aryl)diynes containing both an electron donating pyridine ring and an electron accepting iodobenzene has been developed. The convergent synthesis involves the coupling of 2-, 3-, or 4-bromopyridine with TMS-acetylene, followed by deprotection to form the first half of the molecule. Similarly, 2-, 3-, or 4-iodoaniline was coupled to TMS-acetylene after protection of the amine group as a diethyltriazine. After conversion of the triazine to an iodine, deprotection of the acetylene and formation of the corresponding bromophenyl-acetylene, the two halves of the molecule were coupled under Cadiot-Chodkiewicz conditions. Nine new compounds were prepared, each of which was found to thermally polymerize from the melt. None of the compounds underwent photochemical polymerization in the solid-state.

Full text of DOI:10.1081/SCC-120021834

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Efficient Synthesis of a Complete Donor/Acceptor
bis(Aryl)diyne Family
Brian T. Holmes a , William T. Pennington a & Timothy W. Hanks b
a Department of Chemistry, Hunter Chemistry Laboratories, Clemson University, Clemson,
South Carolina, USA
b Department of Chemistry, Furman University, Greenville, South Carolina, USA
Version of record first published: 20 Aug 2006.
To cite this article: Brian T. Holmes , William T. Pennington & Timothy W. Hanks (2003): Efficient Synthesis of a Complete
Donor/Acceptor bis(Aryl)diyne Family, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 33:14, 2447-2461
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 14, pp. 2447–2461, 2003
Efficient Synthesis of a Complete
Donor/Acceptor bis(Aryl)diyne Family
Brian T. Holmes,1 William T. Pennington,1, and
*
Timothy W. Hanks2,
*
1Department of Chemistry, Hunter Chemistry
Laboratories, Clemson University,
Clemson, South Carolina, USA
2Department of Chemistry, Furman University,
Greenville, South Carolina, USA
ABSTRACT
A facile route to a family of bis(aryl)diynes containing both an
electron donating pyridine ring and an electron accepting iodoben-
zene has been developed. The convergent synthesis involves the
coupling of 2-, 3-, or 4-bromopyridine with TMS-acetylene, fol-
lowed by deprotection to form the first half of the molecule.
Similarly, 2-, 3-, or 4-iodoaniline was coupled to TMS-acetylene
*Correspondence: William T. Pennington, Department of Chemistry, Hunter
Chemistry Laboratories, Clemson University, 223 South Palmetto Drive,
Clemson, South Carolina, 29634-0973, USA; Fax: 864-656-6613; E-mail:
BillP@Clemson.edu, and T. W. Hanks, Department of Chemistry, Furman
University, 3300 Poinsett Hwy., Greenville, South Carolina, 29613-1120, USA;
Fax: 864-294-3559; E-mail: Tim.Hanks@Furman.edu.
2447
DOI: 10.1081/SCC-120021834
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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2448
Holmes, Pennington, and Hanks
after protection of the amine group as a diethyltriazine. After
conversion of the triazine to an iodine, deprotection of the
acetylene and formation of the corresponding bromophenyl-
acetylene, the two halves of the molecule were coupled under
Cadiot-Chodkiewicz conditions. Nine new compounds were
prepared, each of which was found to thermally polymerize from
the melt. None of the compounds underwent photochemical polym-
erization in the solid-state.
Key Words: Diacetylene; Charge-transfer; Cross-coupling.
INTRODUCTION
The 1,3-butadiyne or diacetylene (DA) moiety is responsible for
some unique and important chemistry. In addition to its role in various
natural products,[1] the DA group can undergo polymerization to form
highly conjugated materials with interesting optical, nonlinear optical
and electrical properties.[2] If the DA-containing monomer crystallizes
with the proper packing geometry (described in the literature[3]) this
polymerization can be topotactic, leading to highly crystalline polymers.
Connection of the DA termini directly to aromatic rings leads to
extended conjugation, but the rigidity of the system decreases the likeli-
hood of solid-state polymerization. This is particularly true for hetero-
cyclic DAs, where polymerizable compounds are extremely rare.[4] Still,
bis(aryl)DAs have been widely investigated for use in supramolecular
synthesis, particularly in the realm of molecular electronics,[5] conju-
gated macrocycles[6] and as ligands for organometallic structures.[7]
Perhaps the reason for this interest is the relatively few degrees of free-
dom in the compounds, which makes the design of very large systems
conceptually simple.
RESULTS AND DISCUSSION
As part of an ongoing crystal engineering effort, we found it neces-
sary to prepare the nine possible isomers of DA 1 (Sch. 1). In addition to
the structural features found in all bis(aryl)DAs, this family of com-
pounds can form N ꢀ ꢀ ꢀ I halogen bonds[8] (or X-bonds) with themselves
or with other donors or acceptors. Of course, the pyridine lone pair is

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Donor/Acceptor bis(Aryl)diyne Family
2449
I
N
1a-i
Scheme 1. Targetcompounds: a) 4-I, 4-py; b) 4-I, 3-py; c) 4-I, 2-py; d) 3-I, 4-py;
e) 3-I, 3-py; f) 3-I, 2-py; g) 2-I, 4-py; h) 2-I, 3-py; i) 2-I, 2-py.
also available for coordination to metal centers, while the iodine provides
a convenient site for further structural elaboration.
While none of the members of this family have been previously
reported, DAs are generally prepared by the coupling or cross-coupling
of terminal acetylenes. Therefore, we designed a convergent synthesis
making use of the previously reported iodophenylacetylenes and the
ethynylpyridines. In order to prevent homocoupling by this route,
however, one of the acetylenes must be brominated.
Several synthetic routes to 2-, 3-, and 4-ethynylpyridine have been
previously reported, as these compounds have been used to construct a
number of polymeric and supramolecular species. Dehydrohalogenation
of vinylpyridines has been successful, butinvolves several espt s
from available starting materials, suffers from low yields and involves
[9]
difficultpurificaiotns.
Directpalladium/copper caatlyzed coupling
of 2-methyl-3-butyn-2-ol and the commercially available bromo-
pyridines, 2a–c, proceeds in excellentyields, buhtte subsequent
deprotection step does not.[10] The Stang group used TMS-protected
acetylene in a similar coupling reaction to prepare 3c, buthte depro-
tection step was again problematic, limiting the overall yield to
only 50%.[11] We prepared compounds 3a–c using the same starting
materials (Sch. 2), but effected the deprotection by stirring it in a
methanolic KOH solution rather than TBAF/THF. This improved
the yields to 85–90% overall and permitted easy purification of the
products. Bromination of the ethynylpyridines to give 4a–c was also
efficient, but the products lacked thermal and photochemical stability
and the route was not pursued.
The synthesis of the iodophenylacetylene precursors has also
been reported. Takahashi et al coupled TMS-acetylene to 4-iodoaniline,
followed by conversion of the amino group to an iodine using Sandmeyer
conditions and then deprotection of the acetylene.[12] Similar strategies
have been used by others, however, the yields, particularly of products
7b and 7c, are modest.[13] In developing routes to large phenylacetylene
macrocycles, the Moore group choose to first convert anilines to
phenyltriazines (Sch. 3) before reaction at the iodine.[14] Using a slight

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2450
Holmes, Pennington, and Hanks
N
N
N
a)
b)
Br
TMS
H
3a-c
2a-c
N
c)
Legend: a= 4-py,
b= 3-py, c= 2-py
Br
4a-c
Scheme 2. Reagents and conditions: a) (Ph3P)2PdCl2, CuI, i-Pr2NH, TMS-
acetylene; b) KOH, MeOH/CH2Cl2; c) NBS, AgNO3, acetone.
H N
Et N
2
N
N
2
a)
d)
I
I
b), c)
5a-c
Et N
2
N N
I
e)
TMS
TMS
6a-c
I
I
g)
f)
H
Br
8a-c
7a-c
Legend: a= 4-I, b= 3-I, c= 2-I
Scheme 3. Reagents and conditions: a) HCl/CH3CN; b) NaNO2/H2O;
c) K2CO3/DEA; d) (Ph3P)2PdCl2, CuI, Et3N, TMS-acetylene; e) CH3I, 120ꢁC;
f ) KOH, MeOH/CH2Cl2; g) NBS, AgNO3, acetone.
modification of these conditions, we were able to prepare 7a–c in
overall yields of 60–65%, significantly higher than the more
direct route, despite the additional step. Once again, in our hands the
methanolic KOH deprotection method gave superior results to
TBAF/THF or K2CO3. Conversion to the bromoacetylenes 8a–c by
treatment with NBS and AgNO3 proceeded in approximately 90%
yield in each case.
DAs 1a–i were prepared by Cadiot-Chodkiewicz coupling[15] of
the appropriate combinations of 3a–c and 8a–c. The ethynylpyridines
were added to a solution of CuCl (cat.), 70% aqueous ethylamine
and hydroxylamine hydrochloride in methanol. The bromoethynyl-
iodobenzene was then added slowly to this solution while maintaining

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Donor/Acceptor bis(Aryl)diyne Family
2451
a constant temperature between 30 and 35ꢁC. In each case, column
chromatography afforded a small amount of starting material as well
as the desired DA product. While the formation of symmetrical DA
dimer side products have commonly been reported during Cadiot-
Chodkiewicz cross-couplings, in only one case, the reaction of 3a
with 8b, was the presence of a homo-coupled DA detected (the dimer
of 3a). This compound could be cleanly separated from the desired
unsymmetrical DA by column chromatography.
Yields for the DAs were good, ranging from 70–88% for the single
coupling step. Each DA was stable under ambient conditions, with the
exception of 1f and 1i. These compounds initially crystallized as yellow
solids, butgradually darkened in the presence of room light. Exposure of
the solid DAs to UV radiation resulted in the slight darkening of some
material, but there was no evidence of topopolymerization (characterized
by the formation of intensely absorbing blue or red phases). This was
expected, not only because the polymerization is rare in bis(aryl)DA’s,
but also because the compounds are expected to exhibit N ꢀ ꢀ ꢀ I X-bond-
ing in the solid state, inhibiting the molecular motions required during
the reaction.[8d]
The thermal behavior of compounds 1a–i were also explored by
differential scanning calorimetry and thermal gravimetric analysis. All
compounds displayed generally similar behavior. The firshttermal
event was the melting of the solid, usually accompanied by a small
mass loss (on the order of 1–5%). The melting points varied from
65ꢁC to 160ꢁC, with the more linear compounds, such as 1a–c,
melting towards the high end of the range, while the less linear
compounds, such as 1h, and 1i, melted towards the low end. The
melting points were more sensitive to iodine position than to nitrogen
position. At higher temperature, an exothermic event occurred, again
accompanied by a small mass loss (1–15%). This usually occurred
with an onset temperature of around 220ꢁC, butcould be as high
as 240ꢁC or as low as 130ꢁC. Based on these data and hot stage
optical microscopy, we attribute the exothermic event to a thermally-
induced polymerization in the melt. Often, some of the monomer
would evaporate during this process, before it could be locked
into the matrix. Finally, between 310 and 325ꢁC the samples evapo-
rated, presumably concomitant with the decomposition of the
polymer.
In summary, nine new bis(aryl)DA supramolecular building blocks
have been synthesized in good yields and characterized by spectro-
scopic and thermal methods. The DAs do not undergo photochemical
topopolymerization, but do polymerize in the melt.

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2452
Holmes, Pennington, and Hanks
EXPERIMENTAL
All reagents were obtained from commercial sources and used with-
out further purification unless mentioned elsewhere. Diisopropylamine,
diethylamine, triethylamine, acetonitrile, and dichloromethane were
distilled from calcium hydride under
a
nitrogen atmosphere.
Methanol and acetone were dried over activated 3A molecular sieves.
All 1H and 13C NMR spectra were obtained on a Bruker AC-300
Fourier Transform Spectrometer using deuterated chloroform (CDCl3)
as the solvent. Chemical shifts are reported in parts per million (ꢀ)
downfield relative to tetramethylsilane (TMS). GC-MS analyses were
performed on a Hewlett-Packard 5970 Series Mass Selective Detector
with
a Hewlett-Packard 5890A Gas Chromatograph. Elemental
analyses of selected compounds were obtained from Atlantic
Microlab, INC, P.O. Box 2288, Norcross, Georgia, 30091. UV–vis
absorption spectra were recorded on a Shimadzu UV-2101PC UV–vis
Scanning Spectrophotometer. Thermal gravimetric analyses were per-
formed on a Mettler-Toledo TGA (SDTA851e) instrument with the
Stare software package (ver 6.0). Differential scanning calorimetry was
performed on a Mettler-Toledo TGA DSC820 instrument with the Stare
software package (ver 6.0). The TGA samples had a mass of approxi-
mately 5 mg each and all calculations were performed on data
represented as percent loss of starting mass. For onset calculations,
the samples were heated at a constant rate of 5ꢁC minꢂ1 from 25ꢁC
until all of the material had evaporated. Mass loss and onset calcula-
tions were performed by standard methods. Experiments were per-
formed under nitrogen gas (50 mL/min). The DSC samples had a
mass of approximately 5 mg each and were heated at a constant rate
of 5ꢁC minꢂ1 from 25ꢁC until all of the material had evaporated.
Experiments were performed under nitrogen gas with a flow of
50 mL/min.
4-[2-(Trimethylsilyl)ethynyl]pyridine. 4-Bromopyridine hydrochloride
(1.00 g, 5.1 mmol), bis(triphenylphosphine)palladium(II) chloride (0.09 g,
2.5 mol%) and copper iodide (0.024 g, 2.5 mol%) were placed in a three-
neck round bottom flask. The flask was flushed with nitrogen and diiso-
propylamine (10 mL) was added into the flask while stirring at 40ꢁC,
followed by the addition of trimethylsilylacetylene (0.8 mL, 5.7 mmol).
After 12 h, the reaction mixture was quenched with water; extracted
with dichloromethane, dried with magnesium sulfate and filtered. The
solventwas removed under reduced pressure and a clear solid (87%
yield) was obtained by Kugelrohr distillation (95ꢁC/3 mmHg). Spectral
data were consistent with literature reports.[5]

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Donor/Acceptor bis(Aryl)diyne Family
2453
General Procedure for 3-[2-(Trimethylsilyl)ethynyl]pyridine
and 2-[2-(Trimethylsilyl)ethynyl]pyridine
In a three neck round bottom flask, the appropriate bromopyridine
(1.00 mL, 10.5 mmol), bis(triphenylphosphine)palladium(II) chloride
(0.18 g, 2.5 mol%) and copper iodide (0.050 g, 2.5 mol%) were added.
The flask was flushed with nitrogen and diisopropylamine (17 mL) was
added into the flask while stirring at 30ꢁC, followed by trimethylsilylace-
tylene (1.7 mL, 11.6 mmol). After 3 h, the reaction mixture was quenched
with water; extracted with dichloromethane, dried with magnesium sulfate
and filtered. The solvent was removed under reduced pressure and the
product was obtained by Kugelrohr distillation (95ꢁC/3 mm Hg).
3-[2-(Trimethylsilyl)ethynyl]pyridine. Colorless oil, 93% yield. ꢀH
(300 MHz, CDCl3): 8.59 (s, 1H), 8.42 (d, J ¼ 6.0 Hz, 1H), 7.63 (d,
J ¼ 7.9 Hz, 1H), 7.11(dd, J ¼ 6.4 Hz, 1H), 0.18(s, 9H). ꢀC (75 MHz, CDCl3):
152.49 (CH), 148.56 (CH), 138.58 (CH), 122.69 (CH), 120.14, 101.36,
98.03, 0.00 (CH). GC-MS, m/z (relative intensity): 175 (21), 160 (100).
2-[2-(Trimethylsilyl)ethynyl]pyridine. Colorless oil, 91% yield. ꢀH
(300 MHz, CDCl3): 8.20 (d, J ¼ 4.1 Hz, 1H), 7.27 (m, 1H), 7.09 (m,
1H), 6.85 (m, 1H), 0.20 (s, 9H). ꢀC (75 MHz, CDCl3): 148.89 (CH),
142.04, 135.08 (CH), 126.24 (CH), 122.07 (CH), 102.93, 93.45, 0.00
(CH). GC-MS, m/z (relative intensity): 175 (21), 160 (100).
4-, 3-, and 2-Ethynylpyridines (3a–c): General Procedure
In a nitrogen flushed three neck round bottom flask, potassium
hydroxide (0.64 g, 11.4 mmol) was added to methanol (10 mL), dichloro-
methane (5 mL) and 2-, 3-, or 4-[2-(trimethylsilyl)-ethynyl]pyridine
(1.00 g, 5.7 mmol). After 2 h, the reaction mixture was quenched with
water; extracted with dichloromethane, dried with magnesium sulfate
and filtered. The remaining solution was then passed through a
silica gel plug, eluting with dichloromethane. The solvent was removed
under reduced pressure yielding the pure product (90, 86, and 85% yield,
respectively). Spectral data were consistent with literature reports.[9b]
1-(2,3, and 4-Iodophenyl)-3,3-diethyltriazene:
General Procedure
In a 25 mL three-neck round bottom flask fitted to a reflux condenser,
2-, 3-, or 4-iodoaniline (1.00 g, 4.6 mmol), acetonitrile (5 mL) and 6 M HCl

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2454
Holmes, Pennington, and Hanks
(1.8 mL) were heated and stirred under nitrogen at 70ꢁC for 15 min. The
mixture was then allowed to cool to room temperature, and then cooled
further in an ice bath until the temperature of the mixture was about 15ꢁC.
To this cooled solution was added a solution of sodium nitrite (0.41 g,
5.9 mmol) in water (1 mL). The resultant solution was allowed to stir for
15 min. In a separate 50 mL three-neck round bottom flask, potassium
carbonate (3.17 g, 22.9 mmol), diethylamine (0.72 mL, 6.9 mmol), water
(6.6 mL) and acetonitrile (2.2 mL) were stirred under nitrogen in an ice
bath for 20 min. The first solution was then poured slowly into the second
solution and allowed to stir for 10 min. The ice bath was removed and the
resulting solution was allowed to stir an additional hour. The organic
phase was extracted with dichloromethane, dried with magnesium sulfate
and filtered. The solvent was removed under reduced pressure and the
pure oil was isolated by column chromatography.
1-(4-Iodophenyl)-3,3-diethyltriazene. Red oil (silica gel, 3:2 hexane/
chloroform, Rf ¼ 0.44, 94% yield). ꢀH (300 MHz, CDCl3): 7.61 (d,
J ¼ 6.9 Hz, 2H), 7.18 (d, J ¼ 6.9 Hz, 2H), 3.73 (q, J ¼ 7.1, 4H), 1.25 (t,
J ¼ 6.9 Hz, 6H). ꢀC (75 MHz, CDCl3): 150.81, 137.58 (CH), 123.38 (CH),
88.89, 45.52 (CH), 13.12 (CH). GC-MS, m/z (relative intensity): 303 (12),
231 (35), 203 (100), 50 (21).
1-(3-Iodophenyl)-3,3-diethyltriazene. Brown oil (silica gel, 3:2 hexane/
chloroform, Rf ¼ 0.44, 96% yield). ꢀH (300 MHz, CDCl3): 7.81 (s, 1H),
7.44 (d, J ¼ 7.6 Hz, 1H), 7.38 (d, J ¼ 8.4 Hz, 1H), 7.04 (dd, J ¼ 8.0 Hz,
1H), 3.74 (q, J ¼ 7.1 Hz, 4H), 1.25 (t, J ¼ 6.5 Hz, 6H). ꢀC (75 MHz,
CDCl3): 152.40, 133.50 (CH), 130.18 (CH), 128.81 (CH), 120.27 (CH),
94.48, 48.92 (CH), 41.56 (CH), 12.90 (CH). GC-MS, m/z (relative inten-
sity): 303 (12), 231 (35), 203 (100), 50 (21).
1-(2-Iodophenyl)-3,3-diethyltriazene. Red oil (silica gel, 3:2 hexane/
chloroform, Rf ¼ 0.44, 92% yield). ꢀH (300 MHz, CDCl3): 7.86 (d,
J ¼ 6.7 Hz, 1H), 7.36 (d, J ¼ 6.5 Hz, 1H), 7.29 (dd, J ¼ 6.9 Hz, 1H), 6.85
(dd, J ¼ 6.2 Hz, 1H), 3.79 (q, J ¼ 7.2 Hz, 4H), 1.33 (t, J ¼ 7.1Hz, 6H). ꢀC
(75 MHz, CDCl3): 150.27, 138.88 (CH), 128.50 (CH), 126.40 (CH),
117.41 (CH), 96.52, 49.01 (CH), 42.05 (CH), 14.44 (CH), 10.98 (CH).
GC-MS, m/z (relative intensity): 303 (12), 231 (35), 203 (100), 50 (21).
1-[2-, 3-, and 4-[2-(Trimethylsilyl)ethynyl]phenyl]-3,3-
diethyltriazene (6a–c): General Procedure
In a three neck round bottom flask, 1-(2-, 3-, or 4-iodophenyl)-3,
3-diethyltriazene (1.00 g, 3.3 mmol), bis(triphenylphosphine)palladium(II)

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Donor/Acceptor bis(Aryl)diyne Family
2455
chloride (0.058 g, 2.5 mol%) and copper iodide (0.016 g, 2.5 mol%) were
added. The flask was flushed with nitrogen and triethylamine (12 mL) was
added via syringe into the flask, followed by trimethylsilylacetylene
(0.47 mL, 3.6 mmol). After 3 h at 30ꢁC, the reaction mixture was
quenched with water; extracted with dichloromethane, dried with
magnesium sulfate and filtered. The solvent was removed under
reduced pressure and the pure oil was isolated by performing column
chromatography.
1-[4-[2-(Trimethylsilyl)ethynyl]phenyl]-3,3-diethyltriazene (6a). Brown
oil (silica gel, 4:1 hexane/chloroform, Rf ¼ 0.91, 95% yield). ꢀH
(300 MHz, CDCl3): 7.42 (d, J ¼ 5.8 Hz, 2H), 7.33 (d, J ¼ 5.8 Hz, 2H),
3.74 (q, J ¼ 7.1 Hz, 4H), 1.25 (t, J ¼ 6.8 Hz, 6h), 0.24 (s, 9H). ꢀC
(75 MHz, CDCl3): 151.12, 132.63 (CH), 120.19 (CH), 119.21, 105.78,
93.41, 42.18 (CH), 13.01 (CH), 0.00 (CH). GC-MS, m/z (relative
intensity): 273 (28), 201 (25), 173 (100), 158 (35), 145 (36), 79 (14).
1-[3-[2-(Trimethylsilyl)ethynyl]phenyl]-3,3-diethyltriazene (6b). Yellow
oil (silica gel, 4:1 hexane/chloroform, Rf ¼ 0.91, 93% yield). ꢀH
(300 MHz, CDCl3): 7.56 (s, 1H), 7.38 (m, 2H), 7.25 (m, 1H), 3.73 (q,
J ¼ 7.1 Hz, 4H), 1.24 (t, J ¼ 7.0 Hz, 6H), 0.27 (s, 9H). ꢀC (75 MHz,
CDCl3): 150.97, 128.54 (CH), 128.34 (CH), 123.66 (CH), 123.34, 121.03
(CH), 105.50, 93.23, 45.54 (CH), 12.68 (CH), 0.00 (CH). GC-MS, m/z
(relative intensity): 273 (28), 201 (25), 173 (100), 158 (35), 145 (36), 79 (14).
1-[2-[2-(Trimethylsilyl)ethynyl]phenyl]-3,3-diethyltriazene (6c). Orange
oil (silica gel, 4:1 hexane/chloroform, Rf ¼ 0.91, 91% yield). ꢀH
(300 MHz, CDCl3): 7.46 (m, 1H), 7.38 (m, 1H), 7.23 (m, 1H), 7.02 (m,
1H), 3.77 (q, J ¼ 7.1 Hz, 4H), 1.29 (t, J ¼ 7.1 Hz, 6H), 0.24 (s, 9H). ꢀC
(75 MHz, CDCl3): 152.73, 133.16 (CH), 129.01 (CH), 124.48 (CH),
117.92, 116.70 (CH), 103.52, 97.72, 48.97 (CH), 41.69 (CH), 14.77
(CH), 11.64 (CH), 0.00 (CH). GC-MS, m/z (relative intensity): 273
(28), 201 (25), 173 (100), 158 (35), 145 (36), 79 (14).
1-[2-(Trimethylsilyl)ethynyl]-2-,3-, or 4-iodobenzene:
General Procedure
1-[2-, 3-, or 4-[2-(Trimethylsilyl)ethynyl]phenyl]-3,3-diethyltriazene
(1.00 g, 3.7 mmol) and methyl iodide (20 mL) were sealed in a heavy
walled flask under nitrogen and heated at 110ꢁC for 4 days. The reaction
mixture was quenched with water; extracted with dichloromethane, dried
with magnesium sulfate and filtered. The solvent was removed under
reduced pressure and the pure product was isolated by column chroma-
tography (silica gel, 3:2 hexane/dichloromethane). Yields were 86, 85,

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2456
Holmes, Pennington, and Hanks
and 90%, respectively. Spectroscopic data were consistent with literature
reports.[13]
1-Ethynyl-2-, 3-, and 4-iodobenzene (7a–c): General Procedure
In a nitrogen flushed three neck round bottom flask, potassium
hydroxide (0.37 g, 6.6 mmol) was added to methanol (10 mL), dichloro-
methane (5 mL) and 1-[2-(trimethylsilyl)ethynyl]-2-, 3-, or 4-iodobenzene
(1.00 g, 3.3 mmol). After stirring for 2 h, the reaction mixture was
quenched with water; extracted with dichloromethane, dried with mag-
nesium sulfate and filtered. The solvent was removed under reduced
pressure and the pure product was isolated by column chromatography
(silica gel, 4:1 hexane/dichloromethane ) and recrystallized from hexane.
Yields were 83, 80, and 87%, respectively. Spectroscopic data were con-
sistent with literature reports.[13]
1-(2-Bromoethynyl)-2-, 3-, and 4-iodobenzene (8a–c):
General Procedure
In a nitrogen flushed three-neck round bottom flask, acetone
(25 mL) was added into a mixture of 1-ethynyl-2,3, or 4-iodobenzene
(1.00 g, 4.4 mmol), N-bromosuccinimide (0.94 g, 5.3 mmol) and
silver nitrate (0.12 g). After stirring for 6 h, the reaction mixture was
quenched with water; extracted with dichloromethane, dried with
magnesium sulfate and filtered. The solvent was removed under reduced
pressure and the pure product was isolated by column chromatography.
1-(2-Bromoethynyl)-4-iodobenzene (8a). White solid recrystallized
from methanol (silica gel, 4:1 hexane/dichloromethane, Rf ¼ 0.81, 93%
yield). ꢀH (300 MHz, CDCl3): 7.63 (d, J ¼ 8.3 Hz, 2H), 7.14 (d, J ¼ 8.3 Hz,
2H). ꢀC (75 MHz, CDCl3): 137.52 (CH), 133.44 (CH), 122.09, 94.86,
79.16, 51.77. Elemental Analysis Calculated for C8H4IBr: C, 31.31; H,
1.31. Found: C, 32.05; H, 1.47.
1-(2-Bromoethynyl)-3-iodobenzene (8b). Yellow solid recrystallized
from methanol (silica gel, 4:1 hexane/dichloromethane, Rf ¼ 0.81, 89%
yield). ꢀH (300 MHz, CDCl3): 7.86 (s, 1H), 7.69 (d, J ¼ 8.2 Hz, 1H), 7.46
(d, J ¼ 7.9 Hz, 1H), 7.06, (dd, J ¼ 7.8 Hz, 1H). ꢀC (75 MHz, CDCl3):
140.49 (CH), 137.66 (CH), 131.01 (CH), 129.71 (CH), 124.59, 93.58,
78.37, 51.68. Elemental Analysis Calculated for C8H4IBr: C, 31.31; H,
1.31. Found: C, 31.90; H, 1.34.

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Donor/Acceptor bis(Aryl)diyne Family
2457
1-(2-Bromoethynyl)-2-iodobenzene (8c). Yellow solid recrystallized
from methanol (silica gel, 4:1 hexane/dichloromethane, Rf ¼ 0.81, 87%
yield). ꢀH (300 MHz, CDCl3): 7.79 (d, J ¼ 8.1 Hz, 1H), 7.41 (d, J ¼ 8.0 Hz,
1H), 7.26 (m, 1H), 6.98 (m, 1H). ꢀC (75 MHz, CDCl3): 138.57 (CH),
133.11 (CH), 129.69 (CH), 129.11, 127.66 (CH), 100.54, 82.04, 54.26.
Elemental Analysis Calculated for C8H4IBr: C, 31.31; H, 1.31. Found:
C, 31.73; H, 1.40.
1-[2-, 3-, and 4-Iodophenyl]-4-[2-,3-, and
4-pyridyl]buta-1,3-diyne (1a–i)
In a nitrogen flushed three-neck round bottom flask, methanol
(5 mL) was added into a measured amount of hydroxylamine hydrochlo-
ride (0.007 g, 0.1 mmol) and copper(I) chloride (0.01 g, 0.1 mmol) and
stirred for 5 min. A 70% aqueous solution of ethylamine (1.2 mL) was
then slowly dropped into the solution and allowed to stir for five more
minutes. A solution of 2-, 3-, or 4-ethynylpyridine (0.1 g, 0.97 mmol)
dissolved in a mixture of methanol (2 mL) and dichloromethane (1 mL)
was then slowly added into the flask dropwise. After ten minutes, a
separate solution of 1-(2-bromoethynyl)-2-, 3-, or 4-iodobenzene
(0.33 g, 1.1 mmol) of dissolved in a mixture of methanol (1 mL) and
dichloromethane (2 mL) was slowly added into the flask at 35ꢁC. After
6 h, the reaction mixture was quenched with water; extracted with
dichloromethane, dried with magnesium sulfate and filtered. The solvent
was removed under reduced pressure and the pure solid was isolated by
column chromatography and recrystallized from chloroform/hexane.
1-[4-Iodophenyl]-4-[4-pyridyl]buta-1,3-diyne (1a). White solid (silica
gel, 1:1 hexane/chloroform, Rf ¼ 0.20, 82% yield). ꢀH (300 MHz,
CDCl3):8.62(d,J ¼ 6.0 Hz,2H),7.71(d,J ¼ 8.3 Hz,2H),7.36(d,J ¼ 5.9 Hz,
2H), 7.25 (d, J ¼ 6.3 Hz, 2H). ꢀC (75 MHz, CDCl3): 149.90 (CH), 137.80
(CH), 133.89 (CH), 139.93, 136.01 (CH), 120.87, 96.45, 79.04, 77.89, 76.22,
74.65. Elemental Analysis Calculated for C15H8NI: C, 54.74; H, 2.45; N,
4.26. Found: C, 54.50; H, 2.71; N, 4.15. UV ꢁmax (ethanol): 318.5 nm.
1-[4-Iodophenyl]-4-[3-pyridyl]buta-1,3-diyne (1b). White solid (silica
gel, 1:1 hexane/chloroform, Rf ¼ 0.20, 84% yield). ꢀH (300 MHz,
CDCl3): 8.76 (s, 1H), 8.58 (m, 1H), 7.79–7.81 (m, 1H), 7.68–7.71 (m,
2H), 7.30–7.23 (m, 3H). ꢀC (75 MHz, CDCl3): 153.18 (CH), 149.43
(CH), 139.38 (CH), 137.81 (CH), 133.93 (CH), 123.15 (CH), 120.91,
119.14, 96.04, 81.77, 78.78, 77.13, 74.81. Elemental Analysis Calculated
for C15H8NI: C, 54.74; H, 2.45; N, 4.26. Found: C, 55.01; H, 2.82; N,
4.41. UV ꢁmax (ethanol): 313.5 nm.

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2458
Holmes, Pennington, and Hanks
1-[4-Iodophenyl]-4-[2-pyridyl]buta-1,3-diyne (1c). White solid (silica
gel, 1:1 hexane/chloroform, Rf ¼ 0.20, 70% yield). ꢀH (300 MHz,
CDCl3): 8.63 (m, 1H), 7.65–7.71 (m, 3H), 7.52 (d, J ¼ 7.8 Hz, 1H),
7.24–7.30 (m, 3H). ꢀC (75 MHz, CDCl3): 150.39 (CH), 142.15, 137.70
(CH), 136.15 (CH), 133.94 (CH), 128.11 (CH), 123.58 (CH), 120.83,
95.96, 81.37, 80.90, 74.90, 73.46. Elemental Analysis Calculated for
C15H8NI: C, 54.74; H, 2.45; N, 4.26. Found: C, 54.62; H, 2.81; N,
4.31. UV ꢁmax (ethanol): 238.5 nm.
1-[3-Iodophenyl]-4-[4-pyridyl]buta-1,3-diyne (1d). White solid (silica
gel, 1:1 hexane/chloroform, Rf ¼ 0.20, 88% yield). ꢀH (300 MHz,
CDCl3): 8.61 (m, 2H), 7.87 (s, 1H), 7.72 (d, J ¼ 8.2 Hz, 1H), 7.48 (d,
J ¼ 7.8 Hz, 1H), 7.35 (d, J ¼ 5.1 Hz, 2H), 7.07 (dd, J ¼ 7.8 Hz, 1H). ꢀC
(75 MHz, CDCl3): 149.94 (CH), 141.09 (CH), 138.83 (CH), 131.79 (CH),
130.11, 129.88 (CH), 126.18, 123.26 (CH), 93.78, 81.76, 79.09, 77.92,
74.42. Elemental Analysis Calculated for C15H8NI: C, 54.74; H, 2.45;
N, 4.26. Found: C, 54.83; H, 2.41; N, 4.19. UV ꢁmax (ethanol): 245.0 nm.
1-[3-Iodophenyl]-4-[3-pyridyl]buta-1,3-diyne (1e). White solid (silica
gel, 1:1 hexane/chloroform, Rf ¼ 0.20, 80% yield). ꢀH (300 MHz,
CDCl3): 8.71 (s, 1H), 8.53 (d, J ¼ 4.1 Hz, 1H), 7.82 (s, 1H), 7.74 (d,
J ¼ 6.6 Hz, 1H), 7.65 (d, J ¼ 8.1 Hz, 1H), 7.43 (d, J ¼ 7.7 Hz, 1H), 7.20-
7.24 (m, 1H), 7.02 (dd, J ¼ 7.8 Hz, 1H). ꢀC (75 MHz, CDCl3): 152.99
(CH), 149.24 (CH), 140.83 (CH), 139.21 (CH), 138.40 (CH), 131.52
(CH), 129.82 (CH), 123.31, 122.94 (CH), 118.87, 93.60, 80.67, 78.70,
76.81, 74.59. Elemental Analysis Calculated for C15H8NI: C, 54.74; H,
2.45; N, 4.26. Found: C, 54.72; H, 2.50; N, 4.39. UV ꢁmax (ethanol):
301.5 nm.
1-[3-Iodophenyl]-4-[2-pyridyl]buta-1,3-diyne (1f ). Yellow solid (silica
gel, 1:1 hexane/chloroform, Rf ¼ 0.20, 70% yield). ꢀH (300 MHz, CDCl3):
8.55 (d, J ¼ 4.6 Hz, 1H), 7.81 (s, 1H), 7.58–7.66 (m, 2H), 7.38–7.51 (m,
2H), 7.20–7.24 (m, 1H), 7.01 (dd, J ¼ 7.9 Hz, 1H). ꢀC (75 MHz, CDCl3):
150.23 (CH), 141.88, 140.83 (CH), 138.42 (CH), 136.03 (CH), 131.61
(CH), 129.80 (CH), 128.04 (CH), 123.51 (CH), 123.23, 93.51, 80.87,
80.29, 74.67, 73.18. Elemental Analysis Calculated for C15H8NI: C,
54.74; H, 2.45; N, 4.26. Found: C, 54.80; H, 2.43; N, 4.35. UV ꢁmax
(ethanol): 306.5 nm. **Unstable solid, turns brown/black under ambient
conditions.
1-[2-Iodophenyl]-4-[4-pyridyl]buta-1,3-diyne (1g). Yellow solid (silica
gel, 1:1 hexane/chloroform, Rf ¼ 0.20, 81% yield). ꢀH (300 MHz, CDCl3):
8.60 (d, J ¼ 4.7 Hz, 2H), 7.84 (d, J ¼ 8.1Hz, 1H), 7.51 (d, J ¼ 6.4 Hz, 1H),
7.29–7.37 (m, 3H), 7.03–7.08 (m, 1H). ꢀC (75 MHz, CDCl3): 149.86 (CH),
138.93 (CH), 134.07 (CH), 130.67 (CH), 129.88, 127.92, 127.91 (CH),
126.02 (CH), 100.87, 84.80, 79.77, 77.99, 76.37. Elemental Analysis

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Donor/Acceptor bis(Aryl)diyne Family
2459
Calculated for C15H8NI: C, 54.74; H, 2.45; N, 4.26. Found: C, 55.00; H,
2.45; N, 4.25. UV ꢁmax (ethanol): 241.0 nm.
1-[2-Iodophenyl]-4-[3-pyridyl]buta-1,3-diyne (1h). Yellow solid
(silica gel, 1:1 hexane/chloroform, Rf ¼ 0.20, 79% yield). ꢀH (300 MHz,
CDCl3): 8.74 (s, 1H), 8.56 (d, J ¼ 3.8 Hz, 1H), 7.77–7.83 (m, 2H),
7.48–7.51 (m, 1H), 7.23–7.32 (m, 2H), 7.00–7.05 (m, 1H). ꢀC (75 MHz,
CDCl3): 153.05 (CH), 149.29 (CH), 139.28 (CH), 138.84 (CH), 133.94
(CH), 130.43 (CH), 128.19, 127.84 (CH), 123.01 (CH), 119.02, 100.84,
83.89, 79.54, 77.01, 76.83. Elemental Analysis Calculated for C15H8NI:
C, 54.74; H, 2.45; N, 4.26. Found: C, 54.46; H, 2.80; N, 4.46. UV ꢁmax
(ethanol): 311.5 nm.
1-[2-Iodophenyl]-4-[2-pyridyl]buta-1,3-diyne (1i). Yellow solid (silica
gel, 1:1 hexane/chloroform, Rf ¼ 0.20, 72% yield). ꢀH (300 MHz,
CDCl3): 8.55 (d, J ¼ 4.67 Hz, 1H), 7.78 (d, J ¼ 8.04 Hz, 1H), 7.59–7.65
(m, 1H), 7.40–7.48 (m, 2H), 7.0–7.264 (m, 2H), 7.00 (dd, J ¼ 7.6 Hz, 1H).
ꢀC (75 MHz, CDCl3): 150.19 (CH), 141.88, 138.71 (CH), 136.03 (CH),
133.91 (CH), 131.80, 130.38 (CH), 127.97 (CH), 127.73 (CH), 123.49
(CH), 100.75, 84.44, 81.63, 76.72, 73.36. Elemental Analysis Calculated
for C15H8NI: C, 54.74; H, 2.45; N, 4.26. Found: C, 54.97; H, 2.31; N,
4.40. UV ꢁmax (ethanol): 316.50 nm. **Unstable solid, turns brown/black
under ambientconditions.
ACKNOWLEDGMENT
We thank the donors of the Petroleum Research Fund (Grant No.
35462-B5), the NASA/S.C. Space Grant program and the S.C./EPSCoR
program (Grant No. NCC5-575) for supporting this project.
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2460
Holmes, Pennington, and Hanks
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triques. Hebd.
Received in the USA November 19, 2002

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