Synthesis and photophysical properties of biphenyl and terphenyl arylene-ethynylene macrocycles

Article

pubs.acs.org/joc

Synthesis and Photophysical Properties of Biphenyl and Terphenyl

Arylene−Ethynylene Macrocycles

Andrew L. Korich,^‡Ian A. McBee,^§Jonathan C. Bennion,^†,∥Jenna I. Giﬀord,^†,⊥and Thomas S. Hughes*^,†

^†Siena College, Department of Chemistry and Biochemistry, Morrell Science Center, 515 Loudon Road, Loudonville, New York

12211, United States

^‡Department of Chemistry, Grand Valley State University, 1 Campus Drive, Allendale, Michigan 49401, United States

^§Triton High School, 112 Elm Street, Byﬁeld, Massachusetts 01922, United States

^∥Department of Chemistry, University of Michigan, 930 North University, Ann Arbor, Michigan 48109, United States

^⊥Albany Molecular Research, Inc., 21 Corporate Circle, Albany, New York 12212, United States

S

* Supporting Information

ABSTRACT: A series of single-walled carbon nanotube precursors, C_3h-symmetric cyclotri(ethynylene)(biphenyl-2,4′-diyl) and

cyclotri(ethynylene)(p-terphenyl-2,4″-diyl), have been prepared by a linear stepwise oligomerization−cyclization route and by

statistical intermolecular cyclooligomerization. In addition to producing these members of a novel class of arylene ethynylene

macrocycles, 1 and 2, the latter statistical process produces the smaller cyclic dimer, cyclodi(ethynylene)(p-terphenyl-2,4″-diyl)

and the larger cyclic tetramer cyclotetra(ethynylene)(biphenyl-2,4′-diyl). These macrocycles display large Stokes shifts in their

ﬂuorescence spectra. Their biphenyl or terphenyl connectivity prevents these macrocycles from achieving full planarity in the

ground state, and the ethynylene moieties could provide synthetic access to cyclic arylene oligomers and discrete carbon

nanotube segments.

interactions. AEMs can aggregate into columnar mesophases as

well as vesicles¹²and have the potential to act as model systems

for organic nanotubes.¹³

INTRODUCTION

■

Conjugated shape-persistent macrocycles¹and, in particular,

arylene ethynylene macrocycles (AEMs)²have received much

attention in recent years because advances in synthetic

techniques have made them more accessible, and they have

potential in many applications. AEMs are relatively thermally,

photolytically, and oxidatively stable;³they often have strong

UV absorptions and are often highly ﬂuorescent.⁴Their rigid

shape makes them suitable for host−guest interactions.⁵

Additionally, these macrocycles have been of interest because

their high polarizability makes them desirable as second-order

nonlinear optical materials⁶and as materials for organic

semiconductors⁷and devices.⁸Their unique two-dimensional

structure could potentially allow these materials to circumvent

the trade-oﬀ between eﬃciency and transparency observed in

linear systems, and C₃-symmetric systems can be derivatized to

give noncentrosymmetric materials. Planar AEMs have been

shown to aggregate in solution,⁹in the liquid crystalline

phase,¹⁰and in the solid phase¹¹through weak van der Waals

Arylene ethynylene macrocycles are synthetically accessible

either by statistical cyclization of a single aryl halide ethynyl

monomer^14,15or by the cyclization of a linear oligomer via a

palladium catalyzed cross coupling,¹⁶in either case at low

concentrations. This latter approach requires a linear, stepwise,

and often tedious synthesis of the linear oligomer but usually

gives a single discrete macrocycle as the sole product.

Alternatively, the former methodology employs more syntheti-

cally accessible precursors but often yields various cyclic and

linear oligomers¹⁷unless speciﬁc macrocycle ring sizes are

excluded by ring strain or steric interactions on neighboring

monomer units.¹⁸More recently, alkyne metathesis has proven

to be an eﬃcient synthetic method to prepare the arylene

Received: October 25, 2013

Published: January 7, 2014

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ethynylene scaﬀold.¹⁹Metathesis allows the formation of the

thermodynamically most favored product(s) but may not oﬀer

the functional group tolerance of the palladium-catalyzed

protocols. Derivatization of the monomers should allow the

formation of electron-rich and/or electron-poor ring systems

and thus the tuning of their physical properties. The

incorporation of side chains is often crucial to allow the

solubility of the highly rigid macrocycles.

Despite the recent attention given arylene ethynylene

macrocycles, the incorporation of biphenyl and terphenyl

moieties is rare, and such macrocycles have not been fully

explored. The few reported examples of biphenyl or teraryl

units include bipyridyl,²⁰m-terphenyl,²¹m-terpyridinyl,²²and

11,12-dihydroindolo[2,3-a]carbazole²³(nominal p-terpheny-

lenes) and tetram-phenylene²⁴subunits but no simple biphenyl

or p-terphenylene containing macrocycles have been reported.

The presence of such biphenyl units disrupts the fully planar

geometry of the macrocycle and would therefore be expected to

attenuate any aggregation via stacking of the planar rings. The

deviation from planarity also would aﬀect the conjugation

around the macrocycle, and change their electronic properties

in comparison to their fully planar analogs. The macrocycles

depicted in Figure 1 represent novel classes of arylene

ethynylene macrocycles.

are usually used as rigid spacers that prevent diaryl steric

interactions. However, alkynes are also reactive moieties, and if

the alkynes in the title macrocycles can be incorporated into

ortho-substituted aromatic rings via cycloaddition reactions with

cyclopentadienone synthons, the vertices of the triangular

macrocycles could be folded out of the plane to form the walls

of the nanotube segment.²⁵The phenylene rings in such a

cycloaddition product are geometrically disposed to produce a

fully fused nanotube segment upon oxidative cyclodehydroge-

nation (Figure 2). This synthetic path toward carbon nanotube

segments relies on the title macrocycles as relatively strain-free

templates that are elaborated with additional phenyl rings in a

stepwise increase of strain until the fused tube is achieved.

Alternatively, macrocycles containing cyclopentadienone moi-

eties could be constructed and undergo cycloadditions with

diarylalkynes to give similar cyclooligophenylenes.²⁶

A similar strain strategy pioneered by Bertozzi and Jasti²⁷

converts a more highly curved precursor containing sp³centers

to the all-sp²nanotube segment. Jasti,²⁸Itami,²⁹and others³⁰

have used this route to prepare a variety of [n]-

cycloparaphenylenes, and Jasti³¹and Mullen³²have recently

prepared [n]cycloparaphenylenes that could in principle give

belts of longer length upon oxidative cyclodehydrogenation of

pendant phenyl substituents. Bodwell³³has also prepared

highly curved nanotube segments by incorporating polycyclic

arenes in cyclophanes. Scott has proposed a slightly diﬀerent

approach that uses bowl-shaped templates upon which the

nanotube can be grown.³⁴To further our synthetic proposal,

the synthesis of C₃-symmetric biphenyl and terphenyl arylene

ethynylene macrocycles and their alkyl derivatives, along with

their photophysical properties, are described below.

RESULTS AND DISCUSSION

■

Monomer Synthesis. As discussed above, the construction

of cyclooligomers is usually achieved by one of two means: a

statistical coupling of simple monomer units or a cyclization of

a linear oligomer of appropriate length. The former method

involves a shorter synthetic route and was the ﬁrst one

attempted for the construction of the C₃-symmetric macro-

cycles 1a, 1b, 2a, and 2b. Since both synthetic approaches

require monomers 3a, 3b, 4a, and 4b, they were prepared ﬁrst.

The diethyltriazene and triisopropylsilyl groups on the termini

Figure 1. Biphenyl and terphenyl macrocycles.

More signiﬁcantly, the title C₃macrocycles oﬀer the

possibility to synthesize short segments of single-walled carbon

nanotubes. Ethynylene units in shape-persistent macrocycles

Figure 2. Potential conversion of title macrocycles to nanotube segments.

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Scheme 1. Retrosynthetic Analysis

Scheme 2. Convergent Approach to Biphenyl 3a and Terphenyl 4a Monomers

of 3 and 4 are protecting groups that can be removed under

orthogonal reaction conditions to give the aryl iodide or

terminal alkyne, respectively. A statistical macrocyclization

would require both groups to be deprotected to give the AB

monomer, while the synthesis of a linear trimer which could be

subsequently cyclized could be accomplished using a split-pool

strategy (Scheme 1).

Compound 3a was prepared via a convergent approach

(Scheme 2). Triazene 5 was prepared in 97% yield by

diazotization of 4-iodoaniline followed by quenching with

diethylamine. Boronation of 5 with 1.2 equiv of bis(pinacalato)-

diboron, Cl₂Pd(dppf), and dry KOAc in DMSO gave 6 in 74%

yield. However, this boronation also produced a signiﬁcant

quantity of biphenyl 7 which could only be removed by

recrystallization from 2-propanol. In an attempt to minimize

the formation of this undesired homodimer, a 3-fold excess of

bis(pinacalato)boron was used. No homodimerization was

observed, but the excess diboron proved equally diﬃcult to

remove during puriﬁcation. The most eﬀective puriﬁcation

protocol involves recrystallization from 2-propanol to remove

the homodimer 7 followed by column chromatography to

remove the residual palladium and excess diboron. Alter-

natively, 6 was prepared by diethylamine addition to the

diazotized aminophenylboronic acid pinacol ester in 85% yield.

This second protocol not only provided an overall higher yield

of the phenylene synthon 6 but also a high enough purity after

workup that the crude product could be used in further

reactions without further puriﬁcation, in stark contrast to the

ﬁrst protocol. Alkyne coupling partner 8 was prepared in 99%

yield according to literature procedures from 1-bromo-2-

iodobenzene and triisopropylsilylacetylene.

Suzuki coupling of the boronate ester 6 and alkyne 8 was

performed using Cl₂Pd(dppf) and K₃PO₄in DME to give the

biphenyl monomer 3a in 95% yield. It should be noted that

other palladium catalysts (notably Pd(PPh₄)₃), bases, and

solvents did not give comparable yields. Terphenyl monomer

4a was prepared in 65% yield from triazene 3a by treatment

with iodomethane to give 9 followed by a Suzuki coupling with

triazene 6. Despite the more reactive iodide and lack of

hindering ortho group in 9 compared to 8, the lower yield for

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Scheme 3. Convergent Approach to Alkyl-Substituted Biphenyl 3b and Terphenyl 4b Monomers

the second Suzuki coupling was the result of competitive

protiodeiodination³⁵to give 2-(triisopropylsilylethynyl)-

biphenyl. The terphenyl triazene also undergoes photolytic

decomposition, especially in the presence of silica gel or

Florisil; alumina was used in the chromatography of all

terphenyl triazenes described, and little such decomposition

was observed on this stationary phase.

mixture containing a mixture of linear and cyclic oligomers.

Poor solubility and similar polarities of the reaction products

precluded chromatographic separation or puriﬁcation, but the

presence of 1a was evident by peaks in the ¹H NMR (Figure 3)

that matched those in pure samples of 1a obtained by the

alternate synthesis described below.

Since the macrocycles constructed from 3a and 4a were

anticipated to have low solubility, alkyl-substituted analogues

3b and 4b were also prepared (Scheme 3). Octylaniline 10 was

iodinated with an ammonium dichloroiodate with high

regiospeciﬁcity give iodoarene 11, which was diazotized and

quenched with diethylamine gave triazene 12. The Sonogashira

coupling of 12 with triisopropylsilylacetylene gave 13, which

was then converted to iodoarene 14 in 86% yield over four

steps.

As with the unsubstituted analogues, biphenyl monomer 3b

was obtained by Suzuki−Miyaura coupling of 6 and 14, and

terphenyl monomer 4b was obtained from 3b by deprotection

of the triazene in 3b with methyl iodide to give iodoarene 15

(in 94% yield) which was then coupled with another equivalent

of 6. Initial attempts to couple 6 and 14 produced very poor

yields of 3b along with signiﬁcant quantities of (3-

octylphenylethynyl)triisopropylsilane, the protiodeiodination

product of 14. The concentration of reactants was increased

5-fold in an attempt to make the coupling more competitive

with protiodeiodination, and the yield of the desired biphenyl

3b was increased to 82%. The careful exclusion of water, a

potential source of protons,³⁶did not increase the yield of

coupled product 3b appreciably. Additionally, the yield of the

Suzuki coupling to produce the terphenyl monomer 4b was

68%, lower than that for 3b, presumably for the same reasons

discussed above for 3a.

Statistical Macrocyclization. The doubly deprotected

monomeric iodoalkynes 16a and 17a were obtained by

diethyltriazene removal in methyl iodide followed by ﬂuoride

deprotection of the ethynyl protecting groups (Scheme 2) in

88% and 71% yields over two steps, respectively. The instability

of terphenyl 17a required that this free alkyne be utilized

immediately after preparation and explains the lower yield of its

preparation in comparison to the biphenyl 16a. Biphenyl

monomer 16a was subjected to Sonogashira reaction

conditions using Cl₂Pd(PPh₃)₂at low concentration (18

mM) for 10 days at room temperature to give a product

Figure 3. (Top) statistical macrocyclization of 16a. (Bottom) stepwise

construction of 1a.

Stephens−Castro coupling of terphenyl monomer 17a at 182

mM and Sonogashira coupling at 155 mM with Pd(PPh₃)₂Cl₂

1

gave only an insoluble yellow product, which had an H NMR

spectrum consistent with a mixture of linear and cyclic

oligomers. The Sonogashira coupling of 17a was attempted

again, using Pd(PPh₃)₄and at lower concentration, 18 mM.

After 12 days at room temperature, this reaction yielded a solid

that when washed repeatedly with methylene chloride proved

to be macrocycle 2a. The cyclic trimer was isolated in 20%

crude yield but could not be separated from an impurity of

unknown structure.

Similar protocols were used to convert the alkyl-substituted

monomers 3b and 4b to cyclooligomers. Double deprotection

of 3b and 4b to give 16b and 17b proceeded as with the

unsubstituted analogues in 68% and 98% yields over two steps,

respectively. Compound 16b was subjected to Sonogashira

coupling conditions at 28 mM; four ﬂuorescent compounds

were identiﬁed by TLC, but only two compounds were isolated

by ﬁve iterations of ﬂash chromatography, the cyclic trimer 1b

in 36% yield, and the cyclic tetramer 1c in 24%. In an eﬀort to

improve the yield of the cyclooligomers, the concentration was

lowered to 1.5 mM in the Sonogashira coupling reaction of

17b. A 51% yield of the cyclic trimer 2b was recovered by

column chromatography as well as cyclic dimer 2c in 12% yield.

The yield of the cyclic trimer may also have been higher in the

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Scheme 4. Cyclization of Unsubstituted and Alkyl-Substituted Free Monomers

Scheme 5. Cyclization of Alkyl-Substituted and Alkyl-Substituted Free Monomers

cyclooligomerization of 17b because of the use of Pd(PPh₃)₄

instead of PdCl₂(PPh₃)₂. The isolation of the substituted

macrocycles was greatly facilitated by their much higher

solubility, attributable to their long alkyl side chains.

Macrocyclization of Linear Oligomers. Analytically pure

samples of 1a and 2a were obtained by constructing each

through a linear, stepwise approach (Schemes 4 and 5,

respectively). This split pool approach began with the removal

of the diethyltriazene of 3a to give 18a in 98% yield and the

removal of the ethynyl protecting group of 3a using TBAF to

yield 19a in 90% yield (Scheme 3). Sonogashira coupling of

fragments 18a and 19a gave the protected dimer 20a in 75%

yield. Unmasking the aryl iodide by removal of the

diethyltriazene was followed by a second coupling with

fragment 19a, which led to the linear trimer 22a in 67% yield

over the two steps. Compound 22a was then quantitatively

converted to the iodide 23a. Deprotection of 23a with TBAF

gave an iodoarylethyne which was immediately subjected to

Sonogashira coupling conditions without puriﬁcation. The

cyclization was performed by slowly adding a solution of the

linear trimer iodoarylethyne with a syringe pump to a solution

of the catalysts in triethylamine. The ﬁnal and highest

concentration of the linear trimer was 3.7 mM, and after the

addition was complete, the reaction was stirred for another 12 h

before workup. Column chromatography gave pure 1a in 45%

yield (Scheme 6).

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Scheme 6. Linear Approach to Macrocycle 1a

A split-pool approach to the terphenyl macrocycle 2a also

occurred in a similar sequence, but the additional p-phenylene

unit within the monomer unit contributed to solubility

problems (Scheme 4). Both deprotections of 3b proceeded

in 91% yield to give the iodide 18b and terminal alkyne 19b,

which were coupled under Sonogashira conditions to give

dimer 20b in 76% yield. A signiﬁcant quantity of unreacted 18b

was also recovered, along with a similar amount of a third

organic product which is presumed to be the Hay coupled

dialkyne arising from dimerization of 19b. Conversion of the

triazene to the iodide 21b and Sonogashira coupling with

another 1.3 equiv of 19b gave the trimer 22b in 52% combined

yield. The lower yield compared to the biphenyl system can be

attributed to losses during chromatography of the sparingly

soluble synthons, and the larger excess of the terminal alkyne

was utilized to minimize yield loss due to Hay coupling.

Deprotection of the triazene to give iodide 23b proceeded in

quantitative yield. Removal of the TIPS group gave the

sparingly soluble iodoarylethyne linear trimer; the loss of the

relatively small alkyl groups in the TIPS group signiﬁcantly

lowered its solubility, and its subsequent cyclization was carried

out without further chromatographic puriﬁcation or complete

characterization. As with the biphenyl trimer, the cyclization

was carried out under high dilution Sonogashira conditions (2.1

mM) achieved using a syringe pump. The product mixture was

puriﬁed by removing the solvent and centrifugation of the

residue slurried with dichloromethane. The insoluble organic

products ﬂoated on the chlorinated solvent while the inorganic

catalysts and byproducts thereof formed a solid pellet.

Macrocycle 2b was thus isolated in 21% yield (Scheme 7).

Computational Modeling of Cyclooligomer Strain.

The formation of both linear and cyclic oligomers of various

sizes during cyclooligomerization is not unexpected and has

been shown to occur in various systems under a wide array of

reaction conditions.¹⁴In some of these reports, the cyclo-

trimeric and cyclotetrameric products isolated from o-

iodoethynylenebenzene precursors were relatively unstrained.¹⁵

Other studies have reported the production of strained cyclic

dimeric species along with unstrained cyclotrimers and

cyclotetramers.³⁷

On the basis of the macrocycles described above, the cyclic

dimer, cyclic trimer, and cyclotetramer of the 1,2-phenylene,

1,4′-biphenylene, and 1,4″-terphenylene ethynylene macro-

cycles were computationally modeled. Geometry optimization

and single-point energies were calculated at various levels of

theory using Gaussian 03,³⁸and the alkyl chains were omitted

for computational ease. The structures shown are from the

B3LYP/6-31G(d) geometry optimization, but the structures for

the geometries optimized with every method do not diﬀer

appreciably. The energies tabulated in Table 3 are per repeat

unit and normalized to the cyclotrimer for each analogous

series.

For the o-arylene ethynylene cyclooligomers, it is no surprise

that the D_2hcyclodimer 24c is much higher in energy than

either the D_3hcyclotrimer 24a or D_2dtetramer 24b. The

incomplete treatment of the closed π-system in the molecular

mechanics force ﬁeld is most likely the source of the diﬀerence

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Scheme 7. Linear Synthesis of Macrocycle 2b

in repeat unit strain calculated for the cyclotetramer 24b; the

puckered ring of 24b is predicted to be as nearly strainless as

cyclotrimer 24a by semiempirical, ab initio, and density

functional methods but not by molecular mechanics.

a nearly all-planar system in which only the central p-phenylene

of the terphenyl unit is twisted out of the plane. As a result,

there are three planar diphenylacetylene moieties within 2a, a

structural feature that is shared by the optimized geometry of

C₂symmetric 2e. The lack of angle strain in the alkykyl

moieties in both 2a and 2e is a contributing factor making them

nearly isoenergetic.

In all cases, the cyclodimers have the highest energy per

monomer unit compared to the respective cyclotrimers or

cyclotetramers, which in each case are nearly isoenergetic.

There is a relationship between the number of p-phenylene

units in the macrocycle and the relative strain of the

cyclodimer; presumably, the angle strain of the alkynyl moieties

is shared among additional phenylene units and the overall

strain of the repeat unit is reduced. The average sp carbon bond

angle is 155.4° in 24c, 166.5° in 1d, and 170.0° in 2d, and it is

evident that smaller deviations from the ideal bond angle in the

alkynyl carbons is accompanied by a reduction in the strain

energy. The structural similarities shared between 1a and 1e as

well as 2a and 2e shown in Table 1 reﬂect their isoenergetic

relationships. There is one close nonbonded C−H interaction

present in the biphenyl and terphenyl macrocycles that is as

signiﬁcant in setting the aryl−aryl dihedral as the distance

Calculations on the biphenyl cyclooligomers exhibit similar

energy trends. The C₁₄H₈repeat units in cyclodimer C_2h1d are

∼10 kcal/mol higher in energy than those in C₃1a, and the two

para-substituted rings are predicted to be coplanar with one

another, which gives C₂1d the appearance of an extended

cyclophane. The aryl−aryl dihedral angle decreases from 90° in

1d to 56° in cyclotrimer 1a. Cyclic tetramer 1e shows a similar

aryl−aryl dihedral angle (57°) as well as a similar alkyne bond

angle to that of the cyclic trimer. These structural similarities,

despite the pucker in the cyclotetramer ring, contribute its lack

of strain; the cyclotrimer and cyclotetramer are nearly

isoenergetic on the basis of each repeat unit.

The constrained cyclic array of the terphenyl dimer C₂

symmetric 2d forces the two para-substituted rings to be

nearly coplanar, while being orthogonal to the ortho-substituted

ring. The C₂₀H₁₂repeat units are calculated to be ∼8 kcal/mol

more strained in 2d than in 2a, a smaller diﬀerence than that

calculated in the biphenyl macrocycles. The optimized

geometry of the cyclotrimer 2a is C₃symmetric and features

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cyclotrimer 1b and cyclotetramer 1c in the macrocyclization of

3a.

Table 1. Energies and Geometries of Various Arylene

Ethynylene Macrocycles

a

Optical Properties. The absorption and emission spectra

of the novel macrocycles described above were recorded in a

variety of solvents, since solvent polarity has been shown to

aﬀect the absorption and emission wavelength as well as the

quantum yields (Φ) of organic molecules.³⁹Their poor

solubility in some solvents such as pentane limited full

comparisons of all of the macrocycles, but in benzene, THF

and CHCl₃, their λ_maxand ε_maxwere determined.

Compounds 1a and 2a were not suﬃciently soluble in

pentane to record UV−vis absorption spectra, but the alkyl-

substituted cyclooligomers were. Compound 1b exhibited an

absorption maximum at 296 nm, with shoulders near 264 and

330 nm. Cyclotetramer 2b exhibited two nearly equally intense

absorptions at 282 and 301 nm, and these two maxima were

observed in other solvents as well. Cyclotrimer and cyclodimer

2b and 2c exhibited more similar spectra in pentane, with single

dominant absorption maxima at 312 and 306 nm, respectively.

It should be noted that accurate molar absorptivities were not

obtained for 2b and 2c because of the formation of insoluble

precipitate during the measurement of the spectra in pentane.

All of the macrocycles were more soluble in benzene, and

their absorption spectra are shown in Figure 4. The spectra of

linear trimers 23a and 23b were also obtained in benzene. The

λ_maxof biphenylene linear trimer 23a, 299 nm, does not change

appreciably upon cyclization to 1a, which has a λ_maxof 298 nm.

Alternatively, the λ_maxof terphenylene linear trimer 23b, 295

nm, is shifted bathochromatically by 8 nm upon cyclization to

cyclic trimer 2a (λ_max= 303 nm). This could arise from an

increase in conjugation upon moving from the linear to the

cyclic system.⁴⁰Both 1b and 2b are red-shifted by 5−6 nm

compared to their unsubstituted analogs, 1a and 2a. Cyclic

tetramer 1c is also red-shifted 6 nm compared to cyclic trimer

1b and has a much broader and less intense UV absorption

band. All of the terphenylene macrocycles also showed broad

absorptions, but cyclic dimer 2c and cyclic trimer 2b had very

similar spectra. The absorption spectra of the macrocycles in

THF show similar trends to those seen in the less polar

benzene and pentane.

a

Energies are in kcal mol⁻¹per repeat unit of cyclooligomer and are

referenced to the cyclic trimer repeat unit energy for each set of

cyclooligomers.

between the 2- and 2′-hydrogens; these distances are only

signiﬁcant in the cyclic trimers and tetramers since the cyclic

dimer has a near orthogonal biphenyl dihedral angle (Table 2).

Table 2. Structural Features of Various Arylene Ethynylene

Macrocycles

other Ar−Ar

avg sp C bond H−C

Ar−CC−Ar

dihedral angles

(deg)

angle (deg)

(Å)

dihedral angle (deg)

24c

24a

24b

1d

155.4

179.4

178.0

166.5

177.8

177.6

170.0

177.2

177.4

0.0

60.5

95.0

47.6

47.9

87.4

6.5

3.60

2.72

2.74

3.07

2.72

2.66

1a

1e

2d

29.0, 68.3

39.4, 46.5

38.4, 52.8

2a

2e

18.1

The observation of cyclic dimer 2c in the macrocyclization of

3b suggests that the strain calculated per repeat unit is not great

enough to prevent the irreversible, kinetic formation of 2c. The

larger strain calculated for the biphenyl dimer 1d suggests that

strain may be playing a role in favoring the formation of

Figure 4. UV−vis absorbance spectra of macrocycles in benzene.

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Figure 5. UV−vis absorption spectra of macrocycles in CHCl₃.

Table 3. λ_max(nm) and ε (M⁻¹cm⁻¹) of n-Octyl Terphenyl Cyclodimer and Cyclotrimer

solvent

1a λ_max(ε)

1b λ_max(ε)

1c λ_max(ε)

2a λ_max(ε)

2b λ_max(ε)

312 (−)

2c λ_max(ε)

nC₅H₁₂

296 (20300)

282 (14700)

301 (14500)

309 (7400)

285 (7500)

307 (7500)

285 (12300)

306 (12200)

306 (−)

C₆H₆

THF

298 (19800)

295 (13000)

303 (34100)

302 (15800)

303 (12600)

303 (8200)

309 (11200)

305 (10900)

307 (9800)

305 (4800)

CHCl₃

297 (19900)

302 (21700)

315 (12000)

307 (6200)

All of the terphenylene macrocycles 2a−c exhibit a

bathochromatic shift in their absorption maxima in CHCl₃

compared to THF, while no such shift is observed for the

biphenylene macrocycles 1a−c. Just as was observed in

benzene, the λ_maxof linear trimer 23a, 298 nm, is very similar

to that of cyclic trimer 1a, 297 nm, while terphenylene linear

trimer 23b has a λ_maxof 293, 10 nm blueshifted compared to

the cyclic trimer 2a which has a λ_maxof 303 nm. Alkyl

substitution again redshifts the λ_maxof cyclic trimers, from 297

nm for 1a to 302 nm for 1b and from 303 for 2a to 315 nm for

2b, which was the largest λ_maxobserved in the solvents

examined. As observed in previous solvents, biphenyl cyclo-

tetramer 1c exhibits two λ_maxat 286 and 308 nm, and cyclic

dimer 2c exhibits a broad maximum with a relatively small

molar absorptivity (Figure 5).

There is little to no solvent dependence on absorption for

macrocycles 1a−c and 2a−c. cyclotrimers 1a, 1b and 2a or for

cyclotetramer 1c or cyclodimer 2c. Only substituted

biphenylene cyclotrimer 1b and terphenylene cyclotrimer 2b

exhibited a signiﬁcant solvatochromic shifts, and while

cyclotetramer 1c exhibits two nearly identical λ_maxin pentane,

THF and chloroform, it has only a single broad λ_maxin benzene.

The relationship between the structure of the macrocycle and

its absorption spectrum should depend on the extent of

conjugation around the macrocyclic ring. The three central p-

phenylene aromatic rings of the terphenylene moiety in 2b are

∼47° out of the macrocyclic plane, as are the three p-

phenylenes in 1b. It is possible that the conjugation around the

macrocyclic ring is not interrupted to a signiﬁcant extent, thus

causing 2b to exhibit a more red-shifted λ_maxcompared to 1b

which has a smaller π system. This trend exists in all solvents

tested, although the extent of the shift increases as solvent

polarity decreased. CHCl₃and THF show a shift of 1−2 nm

each, while nonpolar solvents benzene and pentane cause a

larger red shift of 9 and 18 nm, respectively.

Several groups have examined the varying eﬀects of ring

strain on absorption properties of conjugated ethynylic

systems.⁴¹In the case of the biphenylene and terphenylene

systems, ring strain is accompanied with perturbation of the

aryl−aryl dihedral angles. The structures and energies predicted

by the computations described above for cyclic trimer 1a and

cyclic tetramer 1e suggest that all biphenylene macrocycles

synthesized, 1a, 1b, and 1c, are all essentially strain-free. The

aryl−aryl dihedral angle is also nearly identical in 1a and 1e,

and both the planar cyclic trimer and puckered cyclic tetramer

diﬀer only in the disposition of the identical biphenylene−

ethynylene units; these units are coplanar in the cyclic trimer

and are not in the cyclic tetramer. In all solvents examined

excepting benzene where the solvent may have partially

obscured the spectrum, trimer 1b showed a single, broad λ_max

at around 300 nm, and tetramer 1c showed two λ_max, one ∼15

nm shorter and another ∼5 nm longer wavelength (Table 3). It

should be noted that the two-dimensional π-network is

disrupted in the cyclotetramer by the ring pucker, which may

explain the lower molar absorptivities of the cyclic tetramer in

each solvent examined. Cyclic dimer 2c and cyclic trimer 2b

exhibit very similar spectra in benzene and THF, and slightly

shifted spectra in pentane and chloroform. Deformation from

planarity by the ethynyl-substituted p-phenylene ring in the

terphenyl cyclotrimer, 2b is ampliﬁed from 6° to near

orthongonality, 87°, by removing a single repeat unit to form

the terphenyl cyclodimer 2c. Despite this interruption in the

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Figure 6. Fluorescence spectra in benzene of macrocycles and linear trimers.

Figure 7. Concentration-dependent NMR chemical shifts of 1b in C₆D₆; ﬂuorescence spectra were observed at 0.066 mM.

cyclic π-nework, the UV−vis spectra are similar. This suggests

that either π-conjugation is not occurring in both systems and

absorptions are a result of individual subunits or that

delocalization about the macrocycles is not disrupted. In all

cases, 2b exhibits greater molar absorptivity which could be the

result of a larger number of absorbing moieties in the cyclic

trimer versus the cyclic dimer.

phenylene. The dihedral angles of the terphenyl moiety do

not appear to perturb the optical properties of these systems.

While 1a and 1b exhibit Stokes shifts of 120 nm, all of the

other macrocycles exhibit Stokes shifts of ∼80 and 100 nm.

The larger Stokes shifts for the biphenylene cyclic trimers could

indicate a more complete planarization of the macrocycle in 1a

and 1b than the other macrocycles; extending the conjugation

throughout the biphenylene cyclotrimers requires only a single

close H−H and a single close C−H contact, while the

biphenylene cyclotetramer cannot achieve planarity and greater

conjugation without involving a signiﬁcant amount of angle

strain and the terphenylenes would require four close H−H

contacts to achieve full planarity and conjugation.

One possible cause for the Stokes shifts observed could be

aggregation of the macrocycles in solution, which has been

observed for similar structures. To test this hypothesis, we

obtained the NMR spectra of solutions of 1b in benzene at

concentrations higher than those used to obtain the

ﬂuorescence spectrum of 1b (Figure 7). If 1b had been

aggregating in the 0.066 mM solution used in the ﬂuorescence

experiment, it should be doing so at higher concentrations as

well. Since the NMR chemical shifts of all of the aromatic

protons in 1b show no concentration dependence above that

concentration, it seems likely that no aggregation would have

taken place at the lower concentration.

Solutions of all of the macrocycles 1 and 2 as well as the

linear trimers 23a and 23b are highly ﬂuorescent (Figure 6).

The emission properties of these compounds were analyzed in

benzene and their ﬂuorescence quantum yields were

determined using pyrene as a standard. All macrocycles

displayed large Stokes shifts which are indicative of large

conjugated arylene ethynylene macrocycles (see Table 4).⁴⁰

The absorbance spectrum of biphenylene linear trimer 23a

and biphenylene cyclic trimer 1a are very similar, but the single

emission maximum exhibited by linear trimer 23a at 381 nm

shifts to 418 nm upon ring closure to form 1a. No such large

shift is observed upon ring closure of terphenylene linear trimer

23b with an emission maxima of 381 and 399 nm to

terphenylene cyclic trimer 2a with emission maxima of 390

and 406 nm. Comparison of the ﬂuorescence spectra of 1a to

1b and 2a to 2b indicates that n-octyl substitution causes only

small shifts in the emission maxima. Cyclic tetramer 1c displays

two λ_emat 382 and 401 nm, at much shorter wavelengths than

1a and 1b; the puckering of the macrocyclic ring not only

aﬀects the absorbance spectrum of 1c, but its emission

spectrum. All terphenylene macrocycles emit two λ_emat similar

wavelengths to 1c, at ∼390 and ∼405 nm. Cyclic dimer 2c

shows similar emission properties to that of the cyclic trimer

even though the p-phenylenes are orthogonal to the o-

All macrocycles exhibit fairly low quantum yields (Φ) in

benzene compared to larger arylene ethynylene macrocycles

(Table 4).¹³However, these systems do not contain long linear

conjugated pathways which has been correlated to high

quantum yields.²⁸Quantum yields for the biphenyl macrocycles

range from 0.02 for 1b to 0.04 for 1c while the quantum yields

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2974, 2933, 2871, 1475, 1420, 1391, 1341, 1238, 1198, 1108, 1093,

1001, 828; MS (CI-isobutane) [MH⁺] 304.6 m/z.

Table 4. Absorbance and Emission Optical Properties of

Macrocycles and Linear Trimers

(2-(2-Bromophenyl)ethynyl)triisopropylsilane (8).⁴³A 25 mL

round-bottomed ﬂask was charged with 1-bromo-2-iodobenzene

(2.697 g, 9.53 mmol, 1.00 equiv), Cl₂Pd(PPh₃)₂(0.198 g, 0.282

mmol, 0.03 equiv), CuI (0.051 g, 0.267 mmol, 0.03 equiv),

triisopropylsilylethynylene (2.3 mL, 10.25 mmol, 1.07 equiv), and 20

mL of 1:1 THF/Et₃N. The solution was stirred at room temperature

for 24 h before being concentrated in vacuo. The crude residue was

dissolved in diethyl ether and washed with saturated NH₄Cl (aq). The

organic layers were dried over MgSO₄, ﬁltered, and concentrated in

vacuo. Puriﬁcation of the crude material by ﬂash column

chromatography yielded 3.18 g of the product as a yellow oil (99%

λ_abs(nm)

λ_em(nm)

Stokes Shift (nm)

Φ

23a

1a

300

298

303

309

381

418

422

382

401

381

399

390

406

387

405

387

405

81

120

119

73

0.03

0.02

0.04

1b

1c

92

23b

2a

296

303

309

307

85

103

87

0.04

0.06

0.05

1

103

78

yield): H NMR (500 MHz, CDCl₃) δ 7.56 (d, J = 8.2 Hz, 1H), 7.50

(d J = 7.74 Hz, 1H), 7.22 (t, J = 7.74 Hz, 1H), 7.13 (t, J = 7.95 Hz,

1H), 1.13 (br s, 21H); ¹³C NMR (125 MHz, CDCl₃) δ 134.1, 132.6,

129.6, 127.0, 126.0, 125.9, 105.0, 96.4, 18.9, 11.6; IR (cm⁻¹) 2943,

2865, 2161, 1464, 1220, 1047, 908, 883, 834, 753, 678; MS (CI-

isobutane) [MH⁺] 295.5, 296.4 m/z

2b

2c

96

80

98

3,3-Diethyl-1-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-

yl)phenyl)triaz-1-ene (6). Method A: 1,1-Diethyl-3-(4-iodophenyl)-

triazene (1.931 g, 6.370 mmol, 1.00 equiv) was combined with

bis(pinacolato)diboron (1.947 g, 7.667 mmol, 1.20 equiv), Cl₂Pd-

(dppf) (0.143 g, 0.195 mmol, 0.03 equiv), and KOAc that had been

dried under vacuum (1.875 g, 19.11 mmol, 3.00). Deoxygenated

DMSO (52 mL) was added, and the reaction was heated to 80 °C and

monitored by TLC (5% diethyl ether in hexanes). Upon consumption

of triazene starting material, the reaction was diluted with water and

extracted with EtOAc. The organic layers were combined, washed with

satd NH₄Cl (aq), dried over MgSO₄, and concentrated in vacuo.

Crude material was puriﬁed by ﬂash chromatography using 5% diethyl

ether in hexanes as the eluent to aﬀord 1.931 g (74% yield) of the

desired product as a white solid, mp 119−120 °C. The product can

also be puriﬁed by ﬁltration through a silica plug (10% ethyl acetate in

hexanes) followed by recrystallization from 2-propanol: ¹H NMR (500

MHz, CDCl₃) δ 7.77 (d, J = 8.3 Hz, 2H), 7.40 (d, J = 8.3 Hz, 2H),

3.77 (q, J = 7.3, 4H), 1.35 (s, 12H), 1.27 (br t, J = 6.8 Hz, 6H); ¹³C

NMR (125 MHz, CDCl₃) δ 153.6, 135.5, 119.7, 83.5, 24.8; IR (cm⁻¹)

2979, 1602, 1391, 1351, 1320, 1139, 1087, 857, 655; HRMS (ESI) m/

z calc’d for C₁₆H₂₆BN₃O₂H ([M + H⁺]) 304.2196, found 304.2194.

3,3-Diethyl-1-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-

yl)phenyl)triaz-1-ene (6). Method B: 6 N HCl (27.10 mL, 162.51

mmol, 8.9 equiv) was added dropwise to a solution of 4-(4,4,5,5-

tetramethyl-1,3,2-dioxaborolan-2-yl)aniline (4.035 g, 18.42 mmol, 1

equiv) in 62.40 mL of diethyl ether, 48.00 mL of tetrahydrofuran, and

9.60 mL of acetonitrile chilled to −5 °C in an ice−salt bath. A solution

of NaNO₂(4.3255 g, 62.69 mmol, 3.5 equiv) in 21.60 mL of water and

9.69 mL of acetonitrile was added dropwise, and the reaction was

stirred at −5 °C for 30 min before being slowly transferred via cannula

to a ﬂask containing diethylamine (43.45 mL, 419.98 mmol, 23 equiv)

and K₂CO₃(12.640 g, 91.46 mmol, 5 equiv) in 79.20 mL of water and

174.00 mL of acetonitrile at 0 °C. The reaction was stirred for 45 min

while being warmed to room temperature before being diluted with

satd NaCl and extracted with Et₂O. The organics were washed with

H₂O, dried over MgSO₄, ﬁltered, and concentrated in vacuo to give a

brown crystal. Crude material was puriﬁed by extraction with hexanes

and concentration in vacuo to aﬀord 4.7567 g (85% yield) of orange

crystals: ¹H NMR (500 MHz, CDCl₃) δ 7.77 (d, J = 8.3 Hz, 2H), 7.40

(d, J = 8.3 Hz, 2H), 3.77 (q, J = 7.3, 4H), 1.35 (s, 12H), 1.27 (br t, J =

6.8 Hz, 6H); ¹³C NMR (125 MHz, CDCl₃) δ 153.6, 135.5, 119.7, 83.5,

24.8; IR (cm⁻¹) 2979, 1602, 1391, 1351, 1320, 1139, 1087, 857, 655;

HRMS (ESI) m/z calcd for C₁₆H₂₆BN₃O₂H ([M + H⁺]) 304.2196,

found 304.2194.

for terphenyl macrocycles are slightly more eﬃcient ranging

0.04 for both 2a and 23b to 0.06 for 2b.

CONCLUSIONS

■

In an eﬀort to synthesize precursors of short carbon single-

walled nanotubes, cyclic trimers containing biphenylene and p-

terphenylene ethynylene units were constructed via linear, split-

pool approaches to give unsubstituted macrocycles 1a and 2a.

More soluble alkyl-substituted analogues 1b and 2b were also

synthesized, utilizing statistical macrocyclizations of monomers

made possible by the increased solubility. These statistical

macrocyclizations also yielded a cyclotetramer 1c in the

biphenylene system and a cyclodimer 2c in the p-terphenylene

system; these alternative cyclooligomers were separable from

the cyclotrimers by exhaustive column chromatography.

Computational geometry optimizations suggest that the cyclic

dimer is not energetically accessible in the statistical macro-

cyclization of 16b, while a lesser degree of angle strain in the

terphenylene monomer 17b allows formation of cyclodimer 2c.

All of the macrocycles obtained absorb around 300 nm, but the

cyclotrimers 1a and 1b exhibit larger Stokes shifts in their

ﬂuorescence emission spectra than the other macrocycles

observed. Further studies are currently being conducted to

determine if multiple cycloadditions can be carried out on the

alkynes present in these macrocycles to convert them into

arylene cyclooligomers that can be oxidized to make carbon

nanobelts.

EXPERIMENTAL SECTION

■

3,3-Diethyl-1-(4-iodophenyl)triaz-1-ene (5).⁴²4-Iodoaniline

(10.004 g, 45.67 mmol, 1.00 equiv) was dissolved in 380 mL of

acetonitrile, 160 mL of water, and 16.0 mL of concentrated

hydrochloric acid and cooled to 0 °C. A solution of 1.1 equiv of

NaNO₂(3.321 g, 48.14 mmol, 1.05 equiv) in 20 mL water was added

slowly via syringe and the mixture stirred 45 min at 0 °C. The mixture

was transferred to a ﬂask containing K₂CO₃(21.001 g, 151.9 mmol,

3.32 equiv) and diethylamine (9.5 mL, 91.81 mmol, 2.00 equiv) in 250

mL of H₂O at 0 °C. The reaction was allowed to slowly warm to room

temperature and stirred for 2 h before being extracted with diethyl

ether. The combined organic layers washed with brine, dried over

magnesium sulfate, ﬁltered, and concentrated in vacuo. The crude

product was then puriﬁed by ﬂash chromatography using 5% diethyl

ether in hexanes to aﬀord 13.43 g of the desired product as an orange

3,3-Diethyl-1-(4-(2-(2-triisopropylsilyl)ethynyl)phenyl)-

phenyl)triaz-1-ene (3a). (2-Bromophenylethynyl)triisopropylsilane

(2.067 g, 6.13 mmol, 1.00 equiv) was added to a ﬂask ﬁtted with a

sealed reﬂux condenser and charged with 3,3-diethyl-1-(4-(4,4,5,5-

tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)triaz-1-ene (2.787 g, 9.19

mmol, 1.5 equiv), powdered potassium phosphate (tribasic) (6.51 g,

30.65 mmol, 5 equiv), and PdCl₂(dppf) (0.150 g, 0.184 mmol, 0.03

1

oil (97% yield): H NMR (500 MHz, CDCl₃) δ 7.61 (d, J = 8.8 Hz,

2H), 7.16 (d, J = 8.8 Hz, 2H), 3.74 (q, J = 7.3, 4H), 1.25 (br t, 6H);

¹³C NMR (125 MHz, CDCl₃) δ 150.9, 137.6, 122.4, 88.9; IR (cm⁻¹)

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equiv). The ﬂask was purged with nitrogen, and 50 mL of

dexoygenated 1,2-dimethoxyethane was added via syringe. The

reaction was stirred at reﬂux for 6−24 h, until TLC indicated

completion (some side products run at the same R_fas the bromide,

making exact assignment of completion diﬃcult). The reaction

mixture was then cooled, and the DME was removed in vacuo. The

reaction mixture was then extracted with water and diethyl ether. The

combined organic layers were washed with brine, dried over

magnesium sulfate, ﬁltered, and concentrated in vacuo. Puriﬁcation

was eﬀected by ﬂash column chromatography over neutral alumina

with a mobile phase of 5% diethyl ether in hexanes to obtain 2.66 g of

= 8.0 Hz, 1H), 7.59 (d, J = 8.2 Hz, 2H), 7.50 (d, J = 8.2 Hz, 2H),

7.41−7.40 Hz (m, 2H), 7.30−7.27 (m, 1H), 3.80 (q, J = 7.0 Hz, 4H),

3.06 (s, 1H), 1.30 (t, J = 7.0 Hz, 6H); ¹³C NMR (125 MHz, CDCl₃) δ

150.6, 144.4, 136.9, 133.8, 129.7, 129.5, 128.9, 126.6, 120.3, 119.9,

83.3, 80.0. IR (cm⁻¹) 3284, 1330, 1229, 837; HRMS (photospray

ionization) m/z calcd for C₁₈H₂₀N₃([M + H⁺]) 278.1657, found

278.1664.

3,3-Diethyl-1-(4-(2-(2-(4-(2-(2-triisopropylsilyl)ethynyl)-

phenyl)phenyl)ethynyl)phenyl)phenyltriaz-1-ene (20a). A 50

mL round-bottomed ﬂask was charged with 9 (0.223 g, 0.484 mmol,

1.00 equiv), 19a (0.180 g, 0.649 mmol, 1.34 equiv), and Cl₂Pd(PPh₃)₂

(0.020 g, 0.0285 mmol, 0.06 equiv) and ﬂushed with N₂. To this 20

mL of deoxygenated THF/Et₃N (1:1 v/v) was added, and the reaction

ﬂask was sparged with N₂for 5 min. CuI was added and the reaction

stirred at 40 °C for 18 h. Upon completion, the reaction was diluted

with 25 mL of H₂O and extracted with diethyl ether (3 × 25 mL). The

organics were combined, washed with satd NH₄Cl, dried over MgSO₄,

and concentrated in vacuo. The crude material was puriﬁed via ﬂash

chromatography using 5% diethyl ether in hexanes to give 0.226 g

1

the biphenyl product as an orange oil (95% yield): H NMR (500

MHz, CDCl₃) δ 7.59 (d, J = 8.3 Hz, 3H), 7.43 (d, J = 8.3 Hz, 2H),

7.38 (d, J = 7.8 Hz, 1H), 7.33 (t, J = 7.3 Hz, 1H), 7.23 (t, J = 7.8 Hz,

1H), 3.76 (q, J = 7.3 Hz, 4H), 1.27 (t, J = 7.3 Hz, 6H), 1.03 (s, 21H);

¹³C NMR (125 MHz, CDCl₃) δ 150.48, 144.0, 137.1, 133.9, 129.7,

129.3, 128.4, 126.5, 121.7, 119.9, 106.6, 93.9, 18.6, 11.3; IR (cm⁻¹)

2940, 2864, 2151, 1464, 1397, 1330, 1235, 1096, 883, 835, 761, 677;

HRMS (ESI) m/z calcd for C₂₇H₃₉N₃SiH ([M + H⁺]) 434.2992,

found 434.2991.

1

(77%) of the desired product as a yellow oil: H NMR (500 MHz,

1-(4-iodophenyl)-2-(2-triisopropylsilyl)ethynylbenzene (9).

Compound 3a (1.855 g, 4.277 mmol, 1.00 equiv) was dissolved in

10 mL of methyl iodide in a sealable reaction ﬂask, degassed, backﬁlled

with nitrogen, sealed, and heated to 125 °C for 44 h. After cooling, the

methyl iodide was removed by evaporation and the product puriﬁed by

ﬂash chromatography over silica with 5% diethyl ether in hexanes to

CDCl₃) δ 7.72 (d, J = 8.5 Hz, 2H), 7.70 (d, J = 7.9 Hz, 1H), 7.62 (d, J

= 7.8 Hz, 1H), 7.57−7.54 (m, 4H), 7.48 (d, J = 8.0 Hz, 1H), 7.43 (d, J

= 7.9 Hz, 2H), 7.40 (d, J = 8.3 Hz, 1H), 7.38−7.27 (m, 4H), 3.82 (q,

7.2 Hz, 4H), 1.31 (t, J = 7.1 Hz, 6H), 1.05 (s, 21H); ¹³C NMR (125

MHz, CDCl₃) δ 150.6, 143.7, 143.5, 140.2, 137.2, 133.8, 133.0 130.9,

129.8, 129.5, 129.2, 129.1, 128.5, 127.1, 126.7, 122.5, 121.8, 121.4,

119.9, 106.0, 94.4, 92.3, 89.8, 18.55, 11.3; IR (cm⁻¹) 2942, 2860, 2356,

1460, 1334, 1229, 830; HRMS (MALDI) m/z calcd for C₄₁H₄₈N₃Si

([M + H⁺]) 610.3618, found 610.3616.

1

isolate 1.950 g of a yellow oil (99% yield): H NMR (500 MHz,

CDCl₃) δ 7.70 (d, J = 8.3 Hz, 2H), 7.59 (d, J = 7.8 Hz, 1H), 7.27−7.37

(m, 5H), 1.01 (s, 21H); ¹³C NMR (125 MHz, CDCl₃) δ 143.1, 140.1,

137.0, 133.7, 131.2, 129.0, 128.5, 127.2, 121.9, 105.9, 94.6, 93.1, 18.5,

11.3; IR (cm⁻¹) 2940, 2863, 2152, 1469, 1386, 1000, 883, 820, 758,

677; HRMS (EI) m/z calcd for C₂₃H₂₉ISi ([M⁺]) 460.1083, found

460.1091.

2-(2-(4-(2-(2-(4-Iodophenyl)phenyl)ethynyl)phenyl)phenyl)-

ethynyltriisopropylsilane (21a). Compound 20a (0.206 g, 0.338

mmol, 1.00 equiv) and 4 mL of MeI were placed in a sealed tube ﬂask

under an atmosphere of N₂. The reaction was heated to 125 °C for 18

h before being allowed to cool to room temperature. Excess MeI was

allowed to evaporate. The residue was dissolved in 10 mL of CH₂Cl₂,

washed with H₂O, dried over MgSO₄, and concentrated in vacuo. The

crude product was puriﬁed via ﬂash chromatography using 5% EtOAc

in hexanes as the eluent and aﬀorded 0.202 g (94% yield) of the

2-Ethynyl-1-(4-iodophenyl)benzene (16a). TBAF (1 M) in

THF (2.0 mL, 2.00 mmol, 4.35 equiv) was added to a solution of 9

(0.212 g, 0.460 mmol, 1.00 equiv) in 3 mL of THF. The reaction was

stirred at room temperature and monitored by TLC. Upon

disappearance of starting material, the reaction was concentrated to

one-third of its original volume, diluted with 25 mL of H₂O, and

extracted with diethyl ether (3 × 50 mL). The organic layers were

combined, dried over MgSO₄, and concentrated in vacuo. The crude

material was puriﬁed via ﬂash chromatography using 5% diethyl ether

in hexane to aﬀord 0.134 g (96% yield) of a reddish oil: ¹H NMR (500

MHz, CDCl₃) δ 7.78 (d, J = 7.0 Hz, 2H), 7.64 (d, J = 7.5 Hz, 1H),

7.42 (t, J = 6.5 Hz, 1H), 7.37−7.34 (m, 4H), 3.08 (s, 1H); ¹³C NMR

(125 MHz, CDCl₃) δ 143.1, 139.7, 137.1, 133.9, 131.1, 129.2, 129.0,

127.3, 120.3, 93.6, 80.6; IR (neat, cm⁻¹) 3274, 3061, 1583,1472;

HRMS (ESI) m/z calcd for C₁₄H₁₀I ([M + H⁺]) 304.9827, found

304.9821.

Attempted Synthesis of Cyclotri(ethynylene)(biphenyl-2,4′-

diyl) (1a). 16a (0.060 g, 0.197 mmol, 1.00 equiv), Cl₂Pd(PPh₃)₂

(0.007 g, 0.010 mmol, 0.05 equiv), and CuI (0.004 g, 0.020 mmol, 0.11

equiv) were combined and dissolved in 10.6 mL of THF and 0.2 mL

of Et₃N. The reaction was stirred for 10 days at room temperature

before being diluted with H₂O and extracted with Et₂O (3 × 20 mL).

The organics were washed over brine, dried over MgSO₄, ﬁltered, and

concentrated in vacuo. The crude material was run through a ﬂash

column to aﬀord a white solid mixture of cyclic and linear oligomers

that resisted further puriﬁcation.

3,3-Diethyl-1-(4-(2-ethynyl)phenyl)phenyltriaz-1-ene (19a).

Compound 3a (0.655 g, 1.510 mmol, 1 equiv) was dissolved in 5

mL of methanol. A solution of 1 M TBAF in THF (7.6 mL, 7.50

mmol, 4.97 equiv) was added; the reaction was then stirred at room

temperature and monitored by TLC. Upon disappearance of starting

material, the reaction was concentrated to one-third its original

volume, diluted with 50 mL of H₂O, and extracted with diethyl ether

(3 × 50 mL). The organic layers were combined, dried over MgSO₄,

and concentrated in vacuo. The crude material was puriﬁed via ﬂash

chromatography using 5% diethyl ether in hexane to aﬀord 0.376 g

(90% yield) of a yellow oil: ¹H NMR (500 MHz, CDCl₃) δ 7.62 (d, J

1

desired product as a yellow oil: H NMR (500 MHz, CDCl₃) δ 7.81

(d, J = 8.5 Hz, 2H), 7.69 (d, J = 7.7 Hz, 1H), 7.62 (d, J = 7.5 Hz, 1H),

7.59 (d, J = 8.0 Hz, 2H), 7.46 (d, J = 8.0 Hz, 2H), 7.41−7.38 (m, 2H),

7.37−7.35 (m, 5H), 7.32−7.29 (m, 1H) 1.05 (s, 21H); ¹³C NMR (125

MHz, CDCl₃) δ 143.3, 142.5, 140.5, 140.0, 137.0, 133.8, 133.0, 131.3,

130.9, 129.3, 129.2, 128.6, 128.5, 127.4, 127.2, 122.1, 121.8, 121.5,

106.0, 94.5, 93.4, 92.8, 89.1, 18.6, 11.3; IR (cm⁻¹) 2940, 2865, 2148,

1467, 1000, 756; HRMS (ESI) m/z calcd for C₃₇H₃₈ISi ([M + H⁺])

637.1787, found 637.1777.

3,3-Diethyl-1-(4-(2-(2-(4-(2-(2-(4-(2-(2-triisopropylsilyl)-

ethynyl)phenyl)phenyl)ethynyl)phenyl)phenyl)ethynyl)-

phenyl)phenyltriaz-1-ene (22a). Compound 21a (0.091 g, 0.142

mmol, 1.00 equiv), 3,3-diethyl-1-(2′-ethynylbiphenyl-4-yl)triaz-1-ene

(0.035 g, 0.153 mmol, 1.08 equiv), Cl₂Pd(PPh₃)₂(0.005 g, 0.007

mmol, 0.05 equiv), and CuI (0.002 g, 0.010 mmol, 0.07 equiv) were

dissolved in 5 mL of deoxygenated THF and 5 mL of deoxygenated

triethylamine. The solution was heated to 40 °C overnight before

being diluted with satd NH₄Cl and extracted with EtOAc. The

organics were washed with satd NH₄Cl, dried over MgSO₄, ﬁltered,

and concentrated in vacuo. The crude material was puriﬁed by ﬂash

chromatography using 10% EtOAc in hexanes to aﬀord 0.075 g of the

desired product as an oﬀ-white waxy solid (67% yield): ¹H NMR (500

MHz, CDCl₃) δ 7.72−7.66 (m, 5H), 7.62 (d, J = 7.5 Hz, 1H), 7.58−

7.52 (m, 6H), 7.50−7.28 (m, 8H), 3.77 (q, J = 7.2 Hz, 4H), 1.28 (t, J =

7.2 Hz), 1.02 (s, 21H); ¹³C NMR (125 MHz, CDCl₃) δ 143.7, 143.3,

143.1, 140.4, 140.2, 137.2, 133.8, 133.0, 132.9, 131.0, 130.9, 129.85,

129.4, 129.3, 129.27, 128.18, 128.5, 127.2, 127.0, 126.6, 122.7, 122.2,

121.8, 121.5, 121.4, 119.0, 106.0, 94.4, 92.6, 92.2, 90.2, 89.3, 18.5, 11.2;

IR (neat, cm⁻¹): 2932, 2860, 2154, 1473, 1096, 836, 744; HRMS

(ESI) m/z calcd for C₅₅H₅₆N₃Si ([M + H⁺]) 786.4244, found

786.4257.

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Article

2-(2-(4-(2-(2-(4-(2-(2-(4-Iodophenyl)phenyl)ethynyl)phenyl)-

phenyl)ethynyl)phenyl)phenyl)ethynyltriisopropylsilane (23a).

Compound 22a (0.039 g, 0.0478 mmol, 1.0 equiv) was sealed in a ﬂask

with 1 mL of MeI and heated to 120 °C for 48 h. Excess MeI was

allowed to evaporate after the reaction mixture cooled. The crude

residue was puriﬁed by ﬂash chromatography using 10% EtOAc in

hexanes as eluent to aﬀord 0.039 g of the desired product as a light

with 50% methylene chloride in hexanes to aﬀord 0.092 mg of the

product as a yellow solid: mp 81−83 °C (91% yield); H NMR (500

1

MHz, CDCl₃) δ 7.77 (d, J = 8.3 Hz, 2H), 7.64 (d, J = 8.3 Hz, 2H),

7.61 (d, J = 7.8 Hz, 1H), 7.54 (d, J = 8.3 Hz, 2H), 7.27−7.38 (m, 5H),

1.00 (s, 21H); ¹³C NMR (125 MHz, CDCl₃) δ 143.7, 140.5, 140.1,

138.9, 137.9, 137.8, 129.9, 128.91, 128.87, 128.5, 127.0, 126.4, 122.0,

106.2, 95.2, 93.0, 18.6, 11.3. IR (cm⁻¹) 2939, 2862, 2152, 1473, 1384,

1064, 1000, 882, 837, 812, 578, 662; HRMS (photospray ionization)

m/z calcd for C₂₉H₃₃SiI ([M⁺]) 536.1396, found 536.1383.

1

yellow waxy solid (98% yield): H NMR (500 MHz, CDCl₃) δ 7.81

(d, J = 8.0 Hz, 2H), 7.70 −7.67 (m, 4H), 7.61 (d, J = 8.0 Hz, 1H), 7.57

(d, J = 8.5 Hz, 2H), 7.47−7.35 (m, 14H), 7.32−7.27 (m, 1H) 1.05 (s,

21H); ¹³C NMR (125 MHz, CDCl₃) δ 143.3, 142.9, 140.6, 140.5,

140.0, 137.0, 133.8, 133.1, 133.0, 131.2, 130.9, 129.4, 129.4, 129.3,

129.2, 128.7, 128.5, 128.5, 127.4, 127.3, 127.1, 122.3, 122.2, 121.9,

121.6, 121.4, 106.04, 94.4, 93.4, 92.7, 92.6, 89.5, 89.3, 18.5, 11.2; IR

(neat, cm⁻¹) 2802, 2847, 2356, 1726, 1457, 1273, 761; HRMS (ESI)

m/z calcd for C₅₁H₄₆ISi ([M + H⁺]) 813.2413, found 813.2406.

2-(2-(4-(2-(2-(4-(2-(2-(4-Iodophenyl)phenyl)ethynyl)phenyl)-

phenyl)ethynyl)phenyl)phenyl)ethyne (24a). Compound 23a

(0.039 g, 0.0463 mmol, 1.00 equiv) was dissolved in 0.25 mL of

THF before 0.100 mL of 1 M TBAF in THF (0.100 mL, 0.100 mmol,

2.16 equiv) was added. After 5 min, the reaction showed no signs of

starting material by TLC and was diluted with Et₂O. The organics

were washed with satd NH₄Cl (aq), dried over MgSO₄, ﬁltered, and

rotovapped. The crude material was puriﬁed by ﬂash chromatography

using 5% EtOAc in hexanes to aﬀord the desired compound which was

used in the following reaction without further characterization.

Cyclotri(ethynylene)(biphenyl-2,4′-diyl) (1a). Compound 24a

(assuming 100% conversion in previous reaction: 0.032 g, 0.0463

mmol, 1.00 equiv) was dissolved in 1 mL of Et₃N and charged in a

gastight syringe in a syringe pump. Pd(dba)₂(0.039 g 0.068 mmol,

1.42 equiv), CuI (0.015 g, 0.079 mmol, 1.71 equiv), and PPh₃(0.076

g, 0.290 mmol, 6.26 equiv) were dissolved in 11.6 mL of Et₃N. The

iodoalkyne trimer was added at a rate of 0.1 mL per hour, and the

reaction was allowed to stir for an additional 12 h after the addition

was complete. The reaction was diluted with sat NH₄Cl (aq) and

extracted with EtOAc. The organic phases were dried over MgSO₄,

ﬁltered, and concentrated in vacuo. The crude material was puriﬁed

using 15% CH₂Cl₂in hexanes to aﬀord 11 mg (45% yield) of the

1-(4-(4-Iodophenyl)phenyl)-2-ethynylbenzene (17a). Com-

pound 18b (0.229 g, 0.427 mmol, 1.00 equiv) was stirred with

TBAF (1 M in THF) (5.55 mL, 5.55 mmol, 13 equiv) with 4 mL of

THF and 1 mL of methanol for 3 days at room temperature. The

solvent was removed in vacuo, and the organic products were extracted

from water with methylene chloride. The combined organic layers

were dried over magnesium sulfate, ﬁltered, and concentrated to

produce 0.127 g of an orange solid (78% yield): ¹H NMR (500 MHz,

CDCl₃) δ 7.78 (d, J = 8.6 Hz, 2H), 7.68 (d, J = 8.1 Hz, 2H), 7.61−7.65

(m, 3H), 7.38−7.43 (m, 4H), 7.30−7.34 (m, 1H), 3.08 (s, 1H); ¹³C

NMR (125 MHz, CDCl₃) δ 143.7, 140.2, 139.6, 139.1, 137.8, 134.0,

129.7, 129.5, 129.0, 128.9, 127.1, 126.4, 120.3, 93.1, 83.0, 80.4; HRMS

(photospray ionization) m/z calcd for C₂₀H₁₄I ([M + H⁺]) 381.0140,

found 381.0151

3,3-Diethyl-1-(4-(4-(2-ethynyl)phenyl)phenyl)phenyl)triaz-1-

ene (19b). Compound 4a (0.240 g, 0.471 mmol, 1.00 equiv) was

stirred with TBAF (1 M in THF) (1.41 mL, 1.41 mmol, 3.0 equiv)

with 2.0 mL of THF and 6 drops of methanol for 40 h at room

temperature. The organic products were extracted from water with

methylene chloride, dried over magnesium sulfate, ﬁltered, and

concentrated in vacuo. Puriﬁcation over neutral alumina with 50%

methylene chloride in hexanes yielded 0.152 g of 1,1-diethyl-3-(4-(4-

(2-ethynyl)phenyl)phenyl)phenyl)triaz-1-ene as an orange solid: mp

1

117−119 °C (91% yield); H NMR (500 MHz, CDCl₃) δ 7.56−7.68

(m, 7H), 7.51 (d, J = 8.3 Hz, 2H), 7.40 (m, 2H), 7.29 (m, 1H), 3.77

(q, J = 7.3 Hz, 4H), 3.07 (s, 1H), 1.26 (br t, 6H); ¹³C NMR (125

MHz, CDCl₃) δ 150.6, 144.0, 140.1, 138.7, 137.2, 133.9, 129.6, 129.5,

129.0, 127.4, 126.9, 126.8, 126.3, 120.8, 120.3, 83.2, 80.3; IR (cm⁻¹)

3280, 1471, 1427, 1324, 1233, 1098, 1003, 828, 761, 659, 634; HRMS

(APCI) m/z calcd for C₂₄H₂₄N₃([M⁺]) 354.1970, found 354.1965.

3,3-Diethyl-1-(4-(4-(2-(2-(4-(4-(2-(2-(triisopropylsilyl)-

ethynyl)phenyl)phenyl)phenyl)ethynyl)phenyl)phenyl)-

phenyl)triaz-1-ene (20b). Compounds 18b (0.100 g, 0.186 mmol,

1.00 equiv) and 19b (0.069 g, 0.196 mmol, 1.05 equiv) were dissolved

with CuI (0.001 g, 0.0056 mmol, 0.03 equiv) and PdCl₂(Ph₃P)₂(0.006

g, 0.009 mmol, 0.05 equiv) in 0.5 mL of deoxygenated triethylamine

and 2.0 mL of deoxygenated THF. The reaction was stirred at room

temperature, periodically reloading solvent and palladium catalyst as

needed over the course of several days. When TLC failed to show any

further conversion, the solvents were removed in vacuo, and the

products were extracted from saturated ammonium chloride solution

with methylene chloride. The combined organic layers were dried over

sodium sulfate, ﬁltered, and concentrated. Flash chromatography over

neutral alumina provided 0.108 g (76% yield) of 20b as a yellow oil as

1

desired macrocycle as a white solid: mp 282−291 °C; H NMR (500

MHz, CDCl₃) δ 7.75 (d, J = 8.4 Hz, 6H), 7.67 (d, J = 7.4 Hz, 3H),

7.50−7.48 (m, 9H), 7.45 (t, J = 7.8 Hz, 3H), 7.36 (t, J = 7.4 Hz, 3H);

¹³C NMR (125 MHz, CDCl₃) δ 143.7, 140.9, 133.4, 131.5, 130.0,

129.9, 129.5, 128.1, 123.1, 122.2, 93.4, 90.3; HRMS (MALDI) m/z

calcd for C₄₂H₂₄([M⁺]) 528.1872, found 528.1864.

3,3-Diethyl-1-(4-(4-(2-(2-triisopropylsilyl)ethynyl)phenyl)-

phenyl)phenyl)triaz-1-ene (4a). Compound 9 (1.923 g, 4.18 mmol,

1.00 equiv) was added to a ﬂask with 6 (1.90 g, 6.27 mmol, 1.5 equiv),

boronate, K₃PO₄(4.52 g, 21.3 mmol, 5.1 equiv), and PdCl₂(dppf)

(0.10 g, 0.125 mmol, 0.03 equiv). The ﬂask was purged with nitrogen

and 30 mL of deoxygenated DME added. The reaction was reﬂuxed

for 20 h and cooled to room temperature, the solvent was removed in

vacuo, and the organic products were extracted from water with

diethyl ether. The combined organic layers were washed with brine,

dried over magnesium sulfate, ﬁltered, and concentrated in vacuo.

Puriﬁcation over neutral alumina with 25% methylene chloride in

hexanes aﬀorded 1.38 g of the product as a pale yellow solid: mp 110−

1

well as 13% recovery of unreacted iodide 18b: H NMR (500 MHz,

CDCl₃) δ 7.77 (d, J = 8.3 Hz, 2H), 7.73 (d, J = 8.3 Hz, 2H), 7.51−7.69

(m, 12H), 7.48 (d, J = 7.8 Hz, 1H), 7.33−7.45 (m, 6H), 7.28 (t, J = 7.3

Hz, 1H), 3.78 (q, J = 6.8 Hz, 4H), 1.27 (br t, 6H), 1.00 (s, 21H); ¹³C

NMR (125 MHz, CDCl₃) δ 150.7, 143.7, 143.5, 140.1, 139.9, 139.2,

139.1, 137.3, 133.7, 133.0, 131.8, 129.8, 129.7, 129.4, 129.2, 128.8,

128.65, 128.55, 128.4, 127.5, 127.0, 126.9, 126.5, 126.3, 122.3, 120.8,

106.2, 94.2, 92.3, 90.2, 18.5, 11.3; IR (cm⁻¹) 3280, 2978, 2932, 2360,

1471, 1427, 1390, 1322, 1233, 1098, 828, 761, 698, 659; HRMS (EI)

m/z calcd for C₅₃H₅₅N₃Si ([M⁺]) 761.4165, found 761.4160.

2-(2-(4-(4-(2-(2-(4-(4-Iodophenyl)phenyl)phenyl)ethynyl)-

phenyl)phenyl)phenyl)ethynyltriisopropylsilane (21b). Com-

pound 20b (0.096 g, 0.126 mmol, 1.00 equiv) was dissolved in 2.5

mL of methyl iodide in a sealable reaction ﬂask, degassed, backﬁlled

with nitrogen, sealed, and heated to 125 °C for 40 h. After cooling, the

methyl iodide was removed by evaporation and the product puriﬁed by

ﬂash chromatography over silica with 25% methylene chloride in

1

111 °C (65% yield);. H NMR (500 MHz, CDCl₃) δ 7.58−7.65 (m,

7H), 7.51 (d, J = 8.3 Hz, 2H), 7.36−4.42 (m, 2H), 7.29 (t, J = 7.3 Hz,

1H), 3.79 (q, J = 7.3 Hz, 4H), 1.29 (t, J = 7.3 Hz, 6H), 1.01 (s, 21H);

¹³C NMR (125 MHz, CDCl₃) δ 150.6, 144.0, 140.0, 139.1, 137.7,

133.7, 129.7, 129.2, 128.4, 127.5, 126.8, 126.4, 122.0, 120.8, 106.4,

94.1, 18.6, 11.3; IR (cm⁻¹) 2940, 2864, 2361, 2151, 1463, 1329, 1233,

1092, 995, 882, 823, 764, 674, 639; HRMS (ESI) m/z calcd for

C₃₃H₄₃N₃SiH ([M + H⁺]) 510.3305, found 510.3309.

1-(4-(4-Iodophenyl)phenyl)-2-(2-triisopropylsilyl)-

ethynylbenzene (18b). Compound 4a (0.096 g, 0.188 mmol, 1

equiv) was dissolved in 2.5 mL of methyl iodide in a sealable reaction

ﬂask, degassed, backﬁlled with nitrogen, sealed, and heated to 125 °C

for 40 h. After cooling, the methyl iodide was removed by evaporation

and the product puriﬁed by ﬂash chromatography over neutral alumina

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The Journal of Organic Chemistry

Article

hexanes to aﬀord 0.065 mg of a white, crystalline solid: mp 109−112

°C (86% yield); ¹H NMR (500 MHz, CDCl₃) δ 7.78 (m, 4H), 7.51−

7.69 (m, 10H), 7.26−746 (m, 10H), 1.01 (s, 21H); ¹³C NMR (125

MHz, CDCl₃) δ 143.7, 143.1, 140.7, 140.3, 140.0, 139.1, 139.0, 137.9,

137.8, 133.7, 133.0, 131.8, 129.9, 129.8, 129.4, 129.2, 128.93, 128.86,

128.5, 127.2, 127.0, 126.9, 126.5, 126.3, 122.2, 122.0, 121.6, 106.3,

94.2, 93.1, 92.4, 90.1, 18.6, 11.3; IR (cm⁻¹) 2939, 2861, 2151, 1473,

1384, 1064, 1000, 882, 813, 758, 664; HRMS m/z calcd for C₃₇H₃₈ISi

([MH⁺]) 637.1782, found 637.1777.

brine, and concentrated. The solids were then ﬁltered with Whatman

quantitative ﬁlter paper (1 μm pore size) and washed with methylene

chloride; centrifugation in methylene chloride yielded 0.008 g (21%

yield) of a colorless solid ﬂoating on top of the supernatant. No

1

melting transition was observed below 300 °C: H NMR (500 MHz,

CDCl₃) δ 7.81 (d, J = 8.3 Hz, 2H), 7.70 (d, J = 7.8 Hz, 2H), 7.69 (d, J

= 6.3 Hz, 1H)7.64 (d, J = 8.3 Hz, 2H), 7.52 (d, J = 7.8 Hz, 1H), 7.49

(d, J = 7.8 Hz, 2H), 7.44 (t, J = 6.8 Hz, 1H), 7.37 (t, J = 7.3 Hz, 1H);

¹H NMR (500 MHz, C₆D₄Cl₂) δ 7.82 (d, J = 8.0 Hz, 6H), 7.70 (d, J =

7.5 Hz, 3H), 7.67 (d, J = 8.0 Hz, 6H), 7.58 (d, J = 8.5 Hz, 6H), 7.51

(d, J = 8.5 Hz, 6H), 7.47 (d, J = 7.5 Hz, 3H), 7.36 (t, J = 7.3 Hz, 3H),

7.29 (t, J = 7.3 Hz, 3H); COSY (500 MHz, o-C₆D₄Cl₂) δ 7.82 × 7.67,

7.70 × 7.29, 7.58 × 7.51, 7.47 × 7.36, 7.36 × 7.29; HMQC (500 MHz,

o-C₆D₄Cl₂) δ 7.82 × 130.3, 7.70 × 133.0, 7.68 × 126.6, 7.59 × 127.1,

7.52 × 132.0, 7.47 × 129.5, 7.36 × 128.9, 7.29 × 127.5; HMBC (o-500

MHz, C₆D₄Cl₂, selected peaks) δ 7.82 × 143.3, 7.82 × 139.5, 7.70 ×

143.3, 7.70 × 90.7, 7.68 × 140.4, 7.68 × 139.8, 7.59 × 139.5, 7.59 ×

122.6, 7.52 × 140.4, 7.52 × 92.7, 7.47 × 139.8, 7.47 × 121.6, 7.36 ×

143.3, 7.29 × 121.6; IR (cm⁻¹) 3056, 3031, 2217, 1922, 1498, 1473,

1442, 1395, 1104, 1004, 819, 758, 733, 703; HRMS (MALDI) m/z

calcd for C₆₀H₃₆([M⁺]) 756.2817, found 756.2822.

3,3-Diethyl-1-(4-(4-(2-(2-(4-(4-(2-(2-(4-(4-(2-(2-

(triisopropylsilyl)ethynyl)phenyl)phenyl)phenyl)ethynyl)-

phenyl)phenyl)phenyl)ethynyl)phenyl)phenyl)phenyl)triaz-1-

ene (22b). Compound 21b (0.086 g, 0.109 mmol, 1.00 equiv) was

dissolved in 0.5 mL of deoxygenated THF and 0.2 mL of

deoxygenated triethylamine with 19b (0.042 g, 0.120 mmol, 1.10

equiv), PdCl₂(Ph₃P)₂(0.006 g, 0.0087 mmol, 0.08 equiv), and CuI

(0.0006 g, 0.0033 mmol, 0.03 equiv). The reaction was stirred at room

temperature for 24 h, the solvent was removed in vacuo, and the

organic products were extracted from saturated ammonium chloride

solution with methylene chloride. The combined organic layers were

dried over sodium sulfate, ﬁltered, and concentrated. Four rounds of

puriﬁcation by ﬂash column chromatography over alumina with 40%

methylene chloride in hexanes yielded 0.067 g of trimer 22b as a white,

Method B (Sonogashira Cyclotrimerization). Compound 17a

(0.053 g, 0.139 mmol, 1.00 equiv) was dissolved in 0.8 mL of THF

and 0.1 mL of triethylamine (both solvents distilled and

deoxygenated) with CuI (0.3 mg, 0.0016 mmol, 0.01 equiv) and

PdCl₂(Ph₃P)₂(0.005 g, 0.007 mmol, 0.05 equiv) and stirred at room

temperature. The reaction was monitored by TLC and periodically

reloaded with catalysts and solvent until TLC failed to indicate a

signiﬁcant change over a 24 h period. The solid precipitate formed was

ﬁltered from solution and washed with methylene chloride to yield a

solid: ¹H NMR (500 MHz, C₆D₄Cl₂) δ 7.80 (d), 7.26−7.7.2 (m), 3.07

(s).

Method C (Sonogashira Cyclotrimerization). Compound 17a

(0.053 g, 0.139 mmol, 1.00 equiv) was dissolved in 7.5 mL of THF

and 0.1 mL of triethylamine (both solvents were distilled and

deoxygenated) with CuI (0.3 mg, 0.0016 mmol, 0.01 equiv) and

Pd(Ph₃P)₄(0.005 g, 0.007 mmol, 0.05 equiv) and stirred at room

temperature. The reaction was monitored by TLC and periodically

reloaded with catalysts and solvent until TLC failed to indicate a

signiﬁcant change over a 24 h period. The solid precipitate formed was

ﬁltered from solution and washed with methylene chloride to yield

20% yield of macrocycle 2a with slight contamination evidenced by:

¹H NMR (500 MHz, CDCl₃) δ 7.78 (d, J = 7.8 Hz), 7.62 (d, J = 7.8

Hz).

1

crystalline solid: mp 167−171 °C (61% yield); H NMR (500 MHz,

CDCl₃) δ 7.22−7.79 (m, 36H), 3.75 (q, J = 7.3 Hz, 4H), 1.25 (br t,

6H), 1.00 (s, 21H); ¹³C NMR (125 MHz, CDCl₃) δ 150.6, 143.6,

143.4, 143.1, 140.8, 140.6, 140.3, 140.2, 140.1, 139.8, 139.3, 139.1,

139.0, 137.3, 133.6, 133.1, 133.0, 132.9, 131.8, 131.7, 129.8, 129.7,

129.4, 129.1, 128.7, 128.5, 128.4, 127.5, 127.4, 127.1, 127.0, 126.8,

126.4, 126.2, 122.4, 122.3, 122.2, 121.9, 121.5, 120.8, 106.2, 94.1, 92.3,

92.3, 90.3, 90.2, 90.0, 18.5, 11.2; IR (cm⁻¹) 2929, 2862, 1474, 1440,

1343, 1233, 1091, 1003, 882, 821, 760, 665, 553; HRMS (ESI) m/z

calcd for C₆₉H₅₇N₂Si ([M − (C₄H₁₀N)⁺]) 941.4291, found 941.4255.

2-(2-(4-(4-(2-(2-(4-(4-(2-(2-(4-(4-Iodophenyl)phenyl)phenyl)-

ethynyl)phenyl)phenyl)phenyl)ethynyl)phenyl)phenyl)-

phenyl)ethynyltriisopropylsilane (23b). Compound 22b (0.067 g,

0.066 mmol, 1.00 equiv) was dissolved in 2.5 mL of methyl iodide in a

sealable reaction ﬂask, degassed, backﬁlled with nitrogen, sealed, and

heated to 125 °C for 40 h. After cooling, the methyl iodide was

removed by evaporation. The residue was ﬁltered through a silica plug

with methylene chloride to provide 0.068 g of the product iodide (99%

yield) as a colorless waxy solid, which was reacted without further

puriﬁcation since poor solubility precluded further chromatography:

¹H NMR (500 MHz, CDCl₃) δ 7.78 (d, J = 8.8 Hz, 6H), 7.52−7.70

(m, 15H), 7.35−7.48 (m, 14H), 7.29 (m, 1H), 0.99 (s, 21H); ¹³C

NMR (125 MHz, CDCl₃) δ 143.7, 143.1, 140.7, 140.5, 140.3, 139.9,

139.2, 139.1, 139.0, 137.9, 133.7, 133.0, 131.8, 131.7, 129.9, 129.9,

129.8, 129.4, 128.9, 128.6, 127.2, 126.9, 126.8, 126.4, 126.4, 126.3,

122.3, 122.2, 122.0, 121.5, 106.2, 94.1, 93.1, 92.3, 90.1, 18.6, 11.3; IR

(cm⁻¹) 2921, 2860, 2360, 2342, 2155, 1473, 1441, 1384, 1000, 822,

814, 761, 667.

2-Iodo-4-n-octylaniline (11). [BnN(CH₃)₃]·ICl₂(3.535 g, 10.15

mmol, 1.05 equiv) and CaCO₃(3.141 g, 31.38 mmol, 3.21 equiv) were

added to a stirred solution of 4-n-octylaniline (1.995 g, 9.72 mmol, 1

equiv) in 80 mL of dry CH₂Cl₂and 35 mL of anhydrous MeOH. The

reaction stirred at room temperature for 2 h prior to being vacuum

ﬁltered through a pad of Celite. The ﬁltrate was washed with satd

Na₂SO₄(40 mL) followed by satd NH₄Cl (40 mL). The organics were

dried over MgSO₄, ﬁltered, and concentrated in vacuo to give a brown

oil that was puriﬁed by chromatography (10% ethyl acetate in hexane

on silica) to give 3.08 g of a brown oil (96% yield). This product was

Cyclotri(ethynylene)(p-terphenyl-2,4″-diyl) (2a). Method A

(Sonogashira Cyclization). Compound 23b (0.070 g, 0.067 mmol,

1.00 equiv) was stirred with 4.0 mL of THF, 6 drops of methanol, and

TBAF (1 M in THF) (0.20 mL, 0.20 mmol, 3.0 equiv) for 48 h, during

which time a precipitate was observed in the reaction. Extraction from

water with methylene chloride, drying of the organic layers with

magnesium sulfate, ﬁltration, and concentration in vacuo yielded 0.53

g of crude trimer (90% yield), which was used in the next step without

further puriﬁcation or characterization. The crude linear iodoaryle-

thyne trimer was dissolved in 10 mL of deoxygenated THF and placed

in a syringe pump. 1.5 equiv of Pd(dba)₂(0.046 g, 0.080 mmol, 1.5

equiv), 1.3 equiv of CuI (0.013 g, 0.068 mmol, 1.3 equiv), and 5.9

equiv of triphenylphosphine (0.082 g, 0.313 mmol, 5.9 equiv) were

dissolved in 5.0 mL of deoxygenated triethylamine and 10 mL of

deoxygenated THF. The catalyst solution was heated to reﬂux under

nitrogen, and the trimer solution was added at 0.6 mL/h, followed by

continued reﬂuxing overnight. The solvents were then removed in

vacuo and the organic products extracted from saturated ammonium

chloride solution with methylene chloride, washed with water and

1

used in subsequent reactions without further puriﬁcation: H NMR

(500 MHz, CDCl₃) δ 7.43 (d, J = 1.9 Hz, 1H), 6.93 (dd, J = 1.9, 8.3

Hz, 1H), 6.65 (d, J = 8.3 Hz, 1H), 3.93 (br s, 2H), 2.44 (t, J = 7.3 Hz,

2H), 1.52 (m, 2H), 1.23−1.31 (m, 10H), 0.88 (t, J = 7.3 Hz, 3H); ¹³C

NMR (125 MHz, CDCl₃) δ 144.4, 138.4, 134.8, 129.4, 114.6, 84.4,

34.5, 31.8, 31.6, 29.5, 29.4, 29.2, 22.6, 14.0; IR (cm⁻¹) 3407, 3317,

2954, 2916, 2850, 1617, 1496, 1467, 1405, 1306, 1152, 1028, 819, 665;

HRMS (MALDI) m/z calcd for C₁₄H₂₂NI ([M + H]⁺) 332.0870,

found 332.0870.

3,3-Diethyl-1-(2-iodo-4-octyl)phenyltriaz-1-ene (12). HCl

(1.1 mL, 13.2 mmol, 7.8 equiv) was added dropwise to a solution of

11 (0.558 g, 1.68 mmol, 1 equiv) in 10.0 mL of tetrahydrofuran and

0.6 mL of acetonitrile chilled to −5 °C in an ice−salt bath. A solution

of NaNO₂(0.415 g, 6.02 mmol, 3.58 equiv) in 1.8 mL of water and 0.8

mL acetonitrile was added dropwise, and the reaction was stirred at −5

°C for 30 min before being slowly transferred via cannula to a ﬂask

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containing diethylamine (3.5 mL, 42.5 mmol, 25 equiv) and K₂CO₃

(2.32 g, 16.8 mmol, 10 equiv) in 7.0 mL of water at 0 °C. The reaction

was stirred for 45 min while warming to room temperature before

being diluted with satd NaCl and extracted with Et₂O. The organics

were washed with H₂O, dried over MgSO₄, ﬁltered, and concentrated

in vacuo. Crude material was puriﬁed by ﬂash chromatography using

hexanes to aﬀord 0.686 g of an orange oil (98% yield): ¹H NMR (500

MHz, CDCl₃) δ 7.66 (d, J = 1.9 Hz, 1H), 7.25 (d, J = 8.6 Hz, 1H),

7.08 (dd, J = 1.9, 8.2 Hz, 1H), 3.78 (q, J = 7.2 Hz, 4H), 2.52 (t, J = 7.5

Hz, 2H), 1.57 (m, 2H), 1.23−1.33 (m, 12H), 0.88 (t, J = 6.4 Hz, 3H);

¹³C NMR (125 MHz, CDCl₃) δ 148.3, 141.5, 138.6, 128.8, 117.1, 96.5,

1234, 1095, 908, 883, 827, 734, 666; HRMS (ESI) m/z calcd for

C₃₅H₅₅N₃SiH ([M + H⁺]) 546.4244, found 546.4235.

4-Octyl-1-(4-iodophenyl)-2-(2-triisopropylsilyl)-

ethynylbenzene (15). Compound 3b (0.349 g, 0.639 mmol, 1.00

equiv) was dissolved in 5 mL of MeI in a sealed tube. The ﬂask was

evacuated and purged with N₂before being sealed and heated to 125

°C for 44 h. The reaction was cooled to room temperature before

excess MeI was removed by N₂bubbling. The crude residue was

puriﬁed by ﬂash chromatography using 5% Et₂O in hexanes to aﬀord

1

0.336 g of the desired compound as a colorless oil (92% yield): H

NMR (500 MHz, CDCl₃) δ 7.69 (d, J = 8.3 Hz, 2H), 7.39 (s, 1H),

7.30 (d, J = 8.8 Hz, 2H), 7.21 (d, J = 7.8 Hz, 1H), 7.17 (dd, J = 7.8, 1.5

Hz, 1H), 2.60 (t, J = 7.8 Hz, 2H), 1.63 (m, 2H), 1.25−1.37 (m, 10H),

1.01 (s, 21H), 0.88 (t, J = 7.3 Hz, 3H); ¹³C NMR (125 MHz, CDCl₃)

δ 142.3, 140.5, 140.1, 136.9, 133.5, 131.3, 128.9, 128.8, 106.2, 93.9,

92.8, 35.4, 31.9, 31.4, 29.4, 29.3, 29.2, 22.7, 18.6, 14.1, 11.3; IR (cm⁻¹)

2924, 2861, 2366, 2333, 2145, 1464, 1385, 1000, 883, 816, 667;

HRMS (ESI) m/z calcd for C₃₁H₄₅SiI ([M⁺]) 572.2335, found

572.2344.

34.9, 31.8, 31.4, 29.4, 29.22, 29.16, 22.6, 14.1; IR (cm⁻¹) 2923, 2853,

1463, 1432, 1389, 1331, 1266, 1234, 1202, 1105; HRMS (MALDI) m/

z calcd for C₁₈H₃₀N₃I ([M + H]⁺) 416.1563, found 416.1558.

3,3-Diethyl-1-(2-(2-triisopropylsilyl)ethynyl-4-octyl)-

phenyltriaz-1-ene (13). Compound 12 (0.250 g, 0.602 mmol, 1.00

equiv), (triisopropylsilyl)acetylene (0.21 mL, 0.934 mmol, 1.55 equiv),

Cl₂Pd(PPh₃)₂(0.0227 g, 0.0323 mmol, 0.054 equiv), and CuI (0.0039

g, 0.0204 mmol, 0.034 equiv) were combined in a 50 mL round-

bottomed ﬂask and purged with N₂. Ten milliliters of deoxygenated

THF and 10 mL of deoxygenated Et₃N were added by syringe, and the

reaction was stirred at 40 °C for 18 h. The reaction mixture was then

diluted with H₂O (50 mL) and extracted with EtOAc (3 × 50 mL).

The combined organic phases were washed with satd NH₄Cl (2 × 50

mL), dried over MgSO₄, ﬁltered, and concentrated in vacuo. The

crude material was puriﬁed by ﬂash chromatography using 5% Et₂O in

4-Octyl-1-(4-iodophenyl)-2-ethynylbenzene (16b). Com-

pound 15 (0.299 g, 0.522 mmol, 1.00 equiv) was dissolved in 2 mL

of THF before 0.63 mL of 1 M TBAF (in THF containing 5% H₂O)

was added. TLC showed disappearance of starting material within 5

min. The reaction was then concentrated, and the residue was

dissolved in Et₂O and washed with satd NH₄Cl. The organic phase was

dried over MgSO₄, ﬁltered, and concentrated in vacuo. The crude

material was puriﬁed by ﬂash chromatography using hexanes to aﬀord

1

hexanes to give 0.256 g of a brown/orange oil (92% yield): H NMR

1

0.22 g of a colorless oil (74% yield): H NMR: (CDCl₃, 500 MHz) δ

(500 MHz, CDCl₃) δ 7.34 (d, J = 8.3 Hz, 1H), 7.28 (d, J = 1.9 Hz,

1H), 3.77 (q, J = 7.3 Hz, 4H), 2.53 (t, J = 7.3 Hz, 2H), 1.55−1.60 (m,

2H), 1.22−1.32 (m, 18H), 1.13 (s, 21H), 0.88 (t, J = 6.3 Hz, 3H); ¹³C

NMR (125 MHz, CDCl₃) δ 150.5, 139.2, 133.5, 129.2, 118.2, 116.5,

105.9, 35.2, 31.9, 31.5, 29.5, 29.2, 22.7, 18.8, 14.1, 11.4; IR (cm⁻¹)

2925, 2862, 2147, 1463, 1398, 1330, 1242, 1201, 1092, 883; HRMS

(MALDI) m/z calcd for C₂₉H₅₁N₃Si ([M + H]⁺) 470.3930, found

470.3917.

7.90 (d, J = 7.0 Hz, 2H), 7.49 (s, 1H), 7.37 (d, J = 7.0 Hz, 2H), 7.28−

7.24 (m, 2H), 3.07 (s, 1H), 2.64 (t, J = 7.8 Hz, 2H), 1.68 (m, 2H),

1.25−1.37 (m, 10H), 0.88 (t, J = 7.3 Hz, 3H); ¹³C NMR (CDCl₃, 125

MHz) δ 142.3, 140.6, 139.7, 137.1, 133.9, 131.1, 129.4, 129.2, 120.0,

93.4, 83.2, 80.2, 77.1, 35.3, 31.9, 31.2, 29.5, 29.3, 29.2, 22.7, 14.2; IR

(neat, cm⁻¹) 3293, 1479.7, 1384, 1007, 814; HRMS (ESI) m/z calcd

for C₂₂H₂₅IH ([M + H⁺]) 417.1071, found 417.1090.

Cyclooligo(ethynylene)(4-octylbiphenyl-2,4′-diyl) (1b, 1c).

Compound 16b (0.031 g, 0.074 mmol, 1.00 equiv) was dissolved in

2.6 mL of 1:1 PhCH₃/Et₃N. Cl₂Pd(PPh₃)₂(0.002 g, 0.0028 mmol,

0.038 equiv) and CuI (0.001 g, 0.005 mmol, 0.07 equiv) were added

neat. The reaction was stirred at room temperature for 2 h and

monitored by TLC (10% EtOAc in hexanes). It was then diluted with

H₂O and extracted with Et₂O (3 × 20 mL), and the combined organic

phases were washed with satd NaCl before being dried over MgSO₄,

ﬁltered, and concentrated in vacuo. Puriﬁcation required 5× silica gel

ﬂash columns using 5% CH₂Cl₂in hexanes to aﬀord 2.5 mg of the

cyclotrimer 1b and 1.2 mg of the cyclotetramer 1c, both as white waxy

solids (12% and 6% yield, respectively).

4-Octyl-2-(2-triisopropylsilyl)ethynyliodobenzene (14).

Compound 13 (0.485 g, 1.032 mmol, 1 equiv) was dissolved in 5

mL of MeI in a sealed tube. The reaction ﬂask was evacuated and

backﬁlled with N₂before being sealed and heated to 125 °C for 20 h.

The reaction was cooled to room temperature before excess MeI was

evaporated by N₂bubbling. The crude residue was puriﬁed by ﬂash

chromatography using hexanes as eluent to aﬀord 0.51 g of a yellow oil

(99% yield): ¹H NMR (500 MHz, CDCl₃) δ 7.70 (d, J = 8.2 Hz, 1H),

7.29 (d, J = 2.1 Hz, 1H), 6.81 (dd, J = 2.1, 8.0 Hz, 1H), 2.51 (t, J = 7.7

Hz, 2H), 1.23−1.31 (m, 10H), 1.16 (s, 21H), 0.88 (t, J = 7.1, 3H); ¹³C

NMR (125 MHz, CDCl₃) δ 142.8, 138.4, 133.2, 129.9, 129.8, 108.2,

97.1, 94.6, 31.9, 31.2, 29.4, 29.2, 22.6, 18.7, 14.1, 11.4; IR (cm⁻¹) 2923,

2862, 2366, 2150, 1459, 1394, 1017, 883, 765, 735, 665; HRMS

(MALDI) m/z calcd for C₂₅H₄₁ISi ([M + H]⁺) 497.2100, found

497.2098.

1

Cyclic trimer 1b: H NMR (CDCl₃, 500 MHz) δ 7.73 (d, J = 6.5

Hz, 6H), 7.48 (s, 3H), 7.47 (d, J = 8.0 Hz, 6H), 7.39 (d, J = 8.5 Hz,

3H), 7.23 (d, J = 8.0 Hz, 3H), 2.65 (t, J = 7.7 Hz, 6H), 1.67 (quintet, J

= 7.5 Hz, 6H), 1.40−1.26 (m, 30H), 0.89 (t, J = 6.5 Hz, 9H); ¹³C

NMR (125 MHz, CDCl₃) δ 140.55, 140.24, 137.32, 132.75, 130.87,

129.42, 129.35, 129.20, 122.35, 121.33, 92.48, 90.02, 35.56, 32.06,

31.46, 29.64, 29.49, 29.42, 22.84, 14.27; HRMS (MALDI) m/z calcd

for C₆₆H₇₂([M⁺]) 864.5634, found 864.5624.

3,3-Diethyl-1-(4-(2-(2-triisopropylsilyl)ethynyl)-4-

octylphenyl)phenyltriaz-1-ene (3b). Boronic ester 6 (0.620 g, 2.04

mmol, 2.00 equiv) and 14 (0.508 g, 1.02 mmol, 1.00 equiv) were

dissolved in deoxygenated DME and further deoxygenated for 10 min

by N₂bubbling. To this solution were added Cl₂Pd(dppf) (0.061 g,

0.0834 mmol, 0.082 equiv) and dry K₃PO₄(1.045 g, 4.922 mmol, 4.83

equiv), and the reaction was deoxygenated by N₂bubbling for an

additional 10 min. The reaction was heated to 90 °C for 20 h before

being cooled to room temperature and diluted with H₂O. The reaction

was extracted with Et₂O (3 × 30 mL), and organics were washed with

satd NaCl before being dried over MgSO₄, ﬁltered, and concentrated

in vacuo. Puriﬁcation by ﬂash chromatography over neutral alumina

with 5% diethyl ether in hexanes gave 0.56 g of a yellow oil (82%

Cyclic tetramer 1c: ¹H NMR (CDCl₃, 500 MHz) δ 7.65 (d, J = 8.5

Hz, 6H), 7.49 (d, J = 1.5 Hz, 3H), 7.45 (d, J = 8.5 Hz, 6H), 7.31 (d, J

= 8.5 Hz, 3H), 7.20 (dd, J = 8.0 Hz, 1.5 Hz, 3H), 2.64 (t, J = 7.5 Hz,

3H), 1.67 (quintet, J = 7.0 Hz, 6H) 1.40−1.26 (m, 30H), 0.88 (t, J =

7.0 Hz, 9H); ¹³C NMR (125 MHz, CDCl₃) δ 140.56, 137.14, 133.21,

131.40, 129.68, 129.47, 129.25, 122.39, 121.35, 92.20, 89.88, 35.56,

32.05, 31.44, 29.63, 29.52, 29.41, 22.83, 14.27; HRMS (MALDI) m/z

calcd for C₈₈H₉₆([M⁺]) 1152.75065, found 1152.7470.

3,3-Diethyl-3-(4-(4-(2-(2-triisopropylsilyl)ethynyl-4-octyl)-

phenyl)phenyl)phenyltriaz-1-ene (4b). Compound 15 (0.276 g,

0.482 mmol, 1.00 equiv) was added to a round-bottomed ﬂask ﬁtted

with a sealed reﬂux condenser, as were 6 (0.248 g, 0.819 mmol, 1.7

equiv), tribasic potassium phosphate (0.563 g, 2.65 mmol, 5.5 equiv),

and PdCl₂(dppf) (0.018 g, 0.022 mmol, 0.045 equiv). The ﬂask was

purged with nitrogen and 4.0 mL deoxygenated 1,2-dimethoxyethane

1

yield): H NMR (500 MHz, CDCl₃) δ 7.58 (d, J = 8.3 Hz, 2H), 7.41

(d, J = 8.8 Hz, 3H), 7.29 (d, J = 7.8 Hz, 1H), 7.16 (d, J = 7.8 Hz, 1H),

3.77 (q, J = 7.0 Hz, 4H), 2.60 (t, J = 7.8 Hz, 2H), 1.64 (m, 2H), 1.25−

1.38 (m, 16 H), 1.03 (s, 21H), 0.88 (t, J = 6.8 Hz, 3H); ¹³C NMR

(125 MHz, CDCl₃) δ 150.3, 141.5, 141.3, 137.2, 133.7, 129.8, 129.2,

128.8, 121.5, 119.9, 106.9, 93.2, 35.3, 31.9, 31.4, 29.5, 29.4, 29.3, 22.7,

18.7, 14.1, 11.3; IR (cm⁻¹) 2926, 2862, 2363, 2341, 2146, 1463, 1380,

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Article

added. The reaction was heated to reﬂux for 5 h and cooled to room

temperature and the solvent removed under vacuum. The product was

extracted from water with ether, and the combined organic layers

washed with brine, dried over magnesium sulfate, ﬁltered, and

concentrated. Puriﬁcation by ﬂash column chromatography over

neutral alumina with 25% methylene chloride in hexanes aﬀorded

0.204 g of a dark yellow oil (68% yield): ¹H NMR (500 MHz, CDCl₃)

δ 7.63 (d, J = 8.4 Hz, 2H), 7.57−7.61 (m, 4H), 7.50 (d, J = 8.8 Hz,

2H), 7.42 (d, J = 1.5 Hz, 1H), 7.31 (d, J = 8.0 Hz, 1H), 7.19 (dd, J =

1.7, 7.7 Hz, 1H), 3.78 (q, J = 7.1 Hz, 4H), 2.61 (t, J = 7.7 Hz, 2H),

1.65 (m, 2H), 1.25−1.38 (m, 16H), 1.01 (s, 21H), 0.89 (t, J = 6.9 Hz,

3H); ¹³C NMR (125 MHz, CDCl₃) δ 150.5, 141.7, 141.4, 139.8,

139.1, 137.7, 133.5, 129.6, 129.1, 128.7, 127.3, 126.3, 121.7, 120.7,

106.7, 93.4, 35.4, 31.9, 31.4, 29.5, 29.4, 29.3, 22.6, 18.6, 14.1, 11.3; IR

(cm⁻¹) 2926, 2864, 2146, 1462, 1396, 1352, 1235, 1100, 882, 818,

770, 663; HRMS (ESI) m/z calcd for C₃₇H₄₉N₂Si ([M − (C₄H₁₀N)⁺])

549.3665, found 549.3659.

CDCl₃) δ 7.75 × 7.67, 7.60 × 7.41, 7.37 × 7.22, 2.66 × 1.68, 1.68 ×

1.38, 1.30 × 0.89; HMQC (CDCl₃) δ 7.75 × 130.0, 7.67 × 126.3, 7.60

× 126.9, 7.51 × 132.6, 7.41 × 131.8, 7.37 × 129.3, 7.22 × 129.0, 2.66

× 35.5, 1.68 × 31.3, 1.36 × 29.4, 1.31 × 22.6, 1.26 × 31.8, 1.22 × 26.7,

1.21 × 33.5, 0.89 × 14.1; MALDI-TOF (DHB matrix) [M⁺] m/z calcd

for C₅₆₁H₅₆728.4832, found 728.6150.

2b: H NMR (500 MHz, CDCl₃) δ 7.80 (d, J = 8.3 Hz, 6H), 7.68

(d, J = 8.3 Hz, 6H), 7.64 (d, J = 7.8 Hz, 6H), 7.52 (s, 3H), 7.49 (d, J =

7.8 Hz, 6H), 7.42 (d, J = 7.8 Hz, 3H), 7.26 (m, 3H), 2.67 (t, J = 7.8

Hz, 6H), 1.69 (quintet, J = 8.3 Hz, 6H), 1.29−1.42 (m, 30H), 0.90

(quintet, J = 8.3 Hz, 9H); ¹³C NMR (125 MHz, CDCl₃) δ 142.1,

140.7, 140.6, 139.8, 139.3, 132.6, 131.7, 130.0, 129.2, 127.1, 126.4,

122.5, 121.2, 91.8, 90.5, 35.4, 31.9, 31.3, 29.7, 29.5, 29.3, 22.7, 14.1;

HMQC (CDCl₃) δ 7.80 × 130.1, 7.68 × 126.4, 7.64 × 127.1, 7.49 ×

131.7, 7.52 × 132.6, 7.42 × 129.2, 7.26 × 129.9, 2.67 × 35.4, 1.69 ×

31.3, 1.36 × 29.5, 1.29 × 22.7, 0.89 × 14.1; HMBC (CDCl₃, selected

peaks) δ 7.80 × 140.7, 7.80 × 139.3, 7.68 × 140.6, 7.68 × 139.8, 7.64

× 139.3, 7.64 × 122.5, 7.52 × 90.5, 7.52 × 35.4, 7.49 × 140.7, 7.49 ×

91.8, 7.42 × 142.1, 7.42 × 139.8, 7.42 × 121.2, 7.26 × 140.6, 2.67 ×

129.2, 2.67 × 132.6, 2.67 × 142.1, 2.67 × 31.3, 2.67 × 29.3, 1.69 ×

29.3, 1.36 × 29.7, 0.90 × 31.9, 0.90 × 22.7; MALDI-TOF (DHB

matrix) m/z calcd for C₈₄H₈₄([M⁺]) 1092.7, found 1092.7. HRMS

(MALDI) m/z calcd for C₈₄H₈₄([M⁺]) 1092.6573, found 1092.6612.

4-Octyl-1-(4-(4-iodophenyl))phenyl-2-(2-triisopropylsilyl)-

ethynylbenzene (4c). Compound 4b (0.0631 g, 0.101 mmol, 1.00

equiv) was added to 2.5 mL of iodomethane in a ﬂask ﬁtted with a

sealable valve and the ﬂask degassed and backﬁlled with nitrogen. The

ﬂask was sealed and the reaction heated to 125 °C for 44 h. After

cooling, the methyl iodide was evaporated and the product ﬁltered

through a silica plug with 25% dichloromethane in hexanes to aﬀord

1

0.065 g (quantitative yield) of the iodide as a reddish oil: H NMR

ASSOCIATED CONTENT

* Supporting Information

■

(500 MHz, CDCl₃) δ 7.77 (d, J = 8.3 Hz, 2H), 7.64 (d, J = 8.3 Hz,

2H), 7.53 (d, J = 8.3 Hz, 2H), 7.42 (d, J = 1.4 Hz, 1H), 7.33 (d, J = 8.3

Hz, 2H), 7.29 (d, J = 7.8 Hz, 1H), 7.19 (dd, J = 1.4, 7.8 Hz, 1H), 2.60

(t, J = 7.8 Hz, 2H), 1.65 (m, 2H), 1.25−1.39 (m, 10H), 1.00 (s, 21H),

0.89 (t, J = 6.9 Hz, 3H); ¹³C NMR (125 MHz, CDCl₃) δ 141.9, 141.1,

140.6, 140.1, 138.6, 137.8, 133.5, 129.8, 129.1, 128.9, 128.8, 126.3,

121.7, 106.6, 93.5, 92.8, 35.3, 31.8, 31.3, 29.4, 29.3, 29.2, 22.6, 18.5,

14.0, 11.3; IR (cm⁻¹) 2923, 2861, 2363, 2148, 1476, 1382, 1064, 1000,

882, 810, 771, 734, 666; HRMS (EI) m/z calcd for C₃₇H₅₀ISi ([M +

H⁺]) 649.2726, found 649.2714.

S

Complete ref 21. NMR spectra of novel compounds.

Optimized Cartesian coordinates for 1a,d,e, 2a,d,e, and 24a−

c. UV−vis spectra of 1b and 2b in pentane, benzene, THF, and

CHCl₃, 1c and 2c in THF and pentane, and 1a in THF. This

material is available free of charge via the Internet at http://

pubs.acs.org.

AUTHOR INFORMATION

Corresponding Author

*E-mail: thughes@siena.edu.

■

2-Ethynyl-4-octyl-1-(4-(4-iodophenyl))phenylbenzene (17b).

2-(2-Triisopropylsilyl)ethynyl-4-octyl-4″-iodoterphenyl (0.0519 g,

0.080 mmol, 1.00 equiv) was dissolved in 2 mL of THF with 5

drops of methanol, to which TBAF (1 M in THF) (1.05 mL, 1.05

mmol, 13 equiv) was added. The reaction was stirred overnight at

room temperature, and the solvents were evaporated. The crude

product was puriﬁed by column chromatography over silica with 100%

hexanes followed by 25% dichloromethane in hexanes to yield 0.039 g

Notes

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

1

We gratefully acknowledge the National Science Foundation

(CHE 0719231, CHE 1048365) and Vermont EPSCoR (EPS

0236976) for support of this work. We thank Bruce Deker of

the University of Vermont for assistance obtaining 2-D NMR

spectra. Mass spectrometry was provided by the Washington

University Mass Spectrometry Resource with support from the

NIH National Center for Research Resources (Grant No.

P41RR0954).

of white crystals: mp 69−71 °C (98% yield); H NMR (500 MHz,

CDCl₃) δ 7.76 (d, J = 8.6 Hz, 2H), 7.66 (d, J = 8.6 Hz, 2H), 7.60 (d, J

=8.4 Hz, 2H), 7.46 (d, J = 1.7 Hz, 1H), 7.38 (d, J = 8.4 Hz, 2H), 7.31

(d, J = 8.0 Hz, 1H), 7.23 (dd, J = 1.9, 8.0 Hz, 1H), 3.04 (s, 1H), 2.62

(t, J = 7.7 Hz, 2H), 1.65 (m, 2H), 1.25−1.37 (m, 10H), 0.89 (t, J = 7.1

Hz, 3H); ¹³C NMR (125 MHz, CDCl₃) δ 142.0, 141.0, 139.6, 138.8,

137.8, 133.8, 129.7, 129.3, 128.9, 126.4, 120.0, 93.0, 83.4, 79.8, 35.3,

31.8, 31.2, 29.4, 29.2, 29.2, 22.6, 14.0; IR (cm⁻¹) 3288, 2922, 2854,

2360, 2340, 1478, 1386, 1000, 895, 808, 788, 731, 657, 611; HRMS

(EI) m/z calcd for C₂₈H₂₉I ([M⁺]) 492.1314, found 492.1312.

Cyclooligo(ethynylene)(4-octyl-p-terphenyl-2,4″-diyl) (2b

and 2c). Compound 17b (0.0364 g, 0.074 mmol, 1.00 equiv) was

dissolved with CuI (0.0009 g, 0.0047 mmol, 0.06 equiv) and

Pd(Ph₃P)₄(0.0243 g, 0.021 mmol, 0.28 equiv) in 40 mL of dry,

deoxygenated THF and 10 mL of triethylamine. The reaction was

stirred at room temperature under nitrogen for 2 weeks, with periodic

reloading of catalyst (only 3 mol % of Pd at a time). When TLC

indicated the reaction had gone to completion, the solvents were

removed in vacuo, and the reaction was puriﬁed over a silica column

with 15% dichloromethane in hexanes. Two products were recovered,

3.2 mg of cyclodimer 2c (12% yield) and 13.8 mg of cyclotrimer 2b

(51% yield), both as colorless waxy solids.

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dx.doi.org/10.1021/jo4023809 | J. Org. Chem. 2014, 79, 1594−1610

Article Doi

Synthesis and photophysical properties of biphenyl and terphenyl arylene-ethynylene macrocycles

DOI: 10.1021/jo4023809

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