Electronic, spectroscopic, and ion-sensing properties of a dehydro[m]pyrido[14]-and [15]annulene isomer library

Article

pubs.acs.org/joc

Electronic, Spectroscopic, and Ion-Sensing Properties of a

Dehydro[m]pyrido[14]- and [15]annulene Isomer Library

Paul N. W. Baxter,*^,†Abdelaziz Al Ouahabi,^†Jean-Paul Gisselbrecht,^‡Lydia Brelot,^∥

and Alexandre Varnek^§

^†Institut Charles Sadron, UPR 22-CNRS, 23 rue du Loess, Strasbourg, France

§

^‡Laboratoire d’Electrochimie et de Chimie Physique du Corps Solide and Laboratoire d’Infochimie, Universite

UMR 7177-CNRS, 4 rue Blaise Pascal, Strasbourg, France

́

de Strasbourg,

^∥Service de Radiocristallographie, Universite

́

de Strasbourg, UMR 7177-CNRS, 1 rue Blaise Pascal, Strasbourg, France

S

* Supporting Information

ABSTRACT: An isomeric series of dehydro[m]pyrido[n]-

annulenes incorporating strained 1,4-buta-1,3-diyne units have

been synthesized, where m = 2, n = 14 (1a−d); m = 2, n = 15

(2a,b); and m = 3, n = 15 (3). The number of pyridine rings

and annulene ring π-electrons are denoted by m and n,

respectively. The X-ray crystal structures of 1b and 1c

confirmed their cyclic formulation. All macrocycles were

found to be luminescent chromophores with differing isomer-

dependent proton and metal ion-sensory emission responses,

which appear collectively as analyte-specific color patterns. Within the series studied, 1a was singular in displaying the highest

luminescence quantum yield and sharing the strongest emission energy and molar absorption changes upon protonation and Hg^II

binding. Spectroscopic and electrochemical results were supported by density functional theory calculations in showing 1a, 2a,

and 3 to be low bandgap materials with lowest unoccupied molecular orbitals delocalized over the 1,4-di(pyridin-4-yl)buta-1,3-

diyne bridges that provide a pathway for electronic communication between the nitrogens. Overall, the investigations suggest that

1a, 2a, and 3 would be excellent ligands for the construction of novel conjugated hybrid metallosupramolecular nanostructures,

polymers, and ion-sensory systems.

undergo intramolecular rearrangements to give novel poly-

aromatic hydrocarbons^47,50,51and continue to serve as targets

for theoretical modeling, to gain further insight

into their aromaticity and spectroscopic and electronic

properties.^41,52−60

INTRODUCTION

■

Dehydroaryl[n]annulenes¹⁻⁷are a class of cyclically conjugated

hydrocarbons that are currently the focus of considerable

interest within the physical and chemical community. For

example, dehydrotribenzo[12]- and [18]annulenes represent

the elementary structural units of graphyne and graphdiyne,

respectively, which are hypothetical expanded carbon networks

predicted to possess many intriguing mechanical and

physicochemical properties.⁸⁻¹⁵Further structural elaboration

of these dehydrobenzo[n]annulenes may in the future yield

sections or fragmental model systems of such polymers.¹⁶⁻²²

Specific dehydrobenzo[n]annulenes have recently been shown

to act as NLO chromophores with potential two-photon

absorption properties²³⁻²⁵and to function as new types of

photochromic,^26,27high spin magnetic,²⁸⁻³⁰and liquid

crystalline materials,^31,32as well as electronic conductors

when doped.³³They are also high-energy storage substrates,

particular examples serving as precursors for the generation of

carbon buckyonions and nanotubes,³⁴⁻³⁷as well as constituting

interesting novel strained-ring systems.³⁸⁻⁴⁷Within the field of

supramolecular chemistry, they have been reported to function

as assembly units for the generation of pseudorotaxane type

architectures⁴⁸and to form well ordered two-dimensional

crystalline layers on specific interfaces.⁴⁹They may also

We have been particularly interested in exploring the

physicochemical properties of the dehydro[m]pyrido[n]-

annulenes, for example, 4−6 (Chart 1),⁶¹which are nitrogen-

heterocyclic analogues of the dehydrobenzo[n]annulenes that

are capable of binding metal ions directly to the heteroatoms

situated on the outer surface of the macrocyclic ring.⁶²⁻⁶⁸Some

of these and related macrocycles were discovered to function as

luminescence ion sensors^61,69,70and to afford coordination

network polymers with specific metal salts.⁷¹Coordination

polymers incorporating dehydro[m]pyrido[n]annulene repeat

units, which topologically mimic theoretically proposed all-

carbon networks, are attractive synthetic targets because they

may be expected to display a rich variety of exploitable

properties such as electrochemical, photochemical, magnetic,

optical, catalytic, porous, inclusion, sensory, and mechanical

behavior.⁷²⁻⁷⁴

Received: July 31, 2011

Published: December 1, 2011

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Article

Chart 1

In particular, the incorporation of metal ion-binding pyrido-

analogues of the internally strained dehydrotribenzo[14]-

annulenes of type 7⁴⁶and its [15]annulene isomer⁴⁴into

coordination polymers and oligomers may yield materials with

topologically interesting curved pathways for intermetal

electronic communication. The ligands themselves may also

exhibit characteristic spectroscopic perturbations upon metal

ion-binding with potential ion-sensing applications.

With these considerations in mind, however, we first needed

to determine which of the many possible isomers within the

dehydro[m]pyrido[14]- and [15]annulene series would be

optimally suited for the creation of coordination polymers and

ion sensors.

We therefore present below an investigation into the

comparative spectroscopic and ion-binding properties of an

isomer library of dehydro[m]pyrido[14]- and [15]annulenes

1a−d, 2a,b, and 3, supported by electrochemical and density

functional theory (DFT) investigations. These studies predict

that 1a, 2a, and 3 would be best suited for the assembly of

electronically conjugated coordination polymers and oligomers

and suggest that ion-sensory applications would be most

efficiently achieved collectively, involving libraries of macro-

cycles rather than with specific isomers. It may be noted that

the spectroscopic properties of some structurally related

dehydro[m]pyrido[n]annulenes such as, for example, 8, have

been reported⁷⁵⁻⁷⁷but differ electronically in being donor−

acceptor systems with nitrogens more sterically constrained for

metal coordination and for which no metal ion-binding studies

have been reported.

single quantum coherence (HSQC) measurements and spectral

comparisons with their respective precursors. It may be noted

that despite the fact that cycles 1a−d, 2a,b, and 3 were strained

molecules, they were found to be indefinitely stable in the solid

state at ambient temperature as well as in CH₂Cl₂solution over

several months, in the absence of light. Although stable to silica

gel, they were found to be best purified by chromatography on

neutral or basic alumina, as is often the case with polypyridine

ligands, due to their enhanced basicity.

Solution Aggregation of 1a. As planar aromatic macro-

cycles are frequently known to form aggregates in solu-

tion,^61,78−80we investigated the possibility of aggregation

effects in the case of 1a, as it was one of the least soluble

macrocycles within the series studied, and formed a fibrous

microcrystalline solid upon solvent evaporation suggestive of

strong intermolecular association. The ¹H NMR spectrum of 1a

in CDCl₃did indeed exhibit upfield displacements in proton

chemical shifts upon solution concentration, indicative of

aggregation phenomena and supportive of its planar structural

formulation (see the Supporting Information for details).

However, measurement of the hydrodynamic radius using the

diffusion ordered spectroscopy (DOSY) technique⁸¹afforded a

value of 4.3 Å, corresponding to single molecules or weak

associations of no more than two molecules of 1a, suggesting

fast association−dissociation on the NMR time scale.

X-ray Crystal Structural Characterization of 1b and

1c. An X-ray crystal structural analysis of suitable crystals of 1b

and 1c grown from CDCl₃confirmed the macrocyclic identity

and strained nature of these systems and revealed that they

both possess a small triangular internal cavity (Figure 1, upper

left). As expected, 1b is planar; yet, 1c is distinctly nonplanar,

with the benzene ring positioned to one side of the mean plane

through the 1,4-di(pyridin-3-yl)buta-1,3-diyne moiety and

pointing away from it (Figure 1, upper right).

RESULTS AND DISCUSSION

■

The syntheses of 1a−d, 2a,b, and 3 were achieved using

standard Sonogashira and Eglinton−Galbraith coupling meth-

odology, from a series of regiochemically defined mono-

protected ortho-diethynylpyridine isomers, the details of which

are described in the Supporting Information. The structural

formulation of all products was established on the basis of mass

spectroscopic, infrared, ¹H and ¹³C NMR spectroscopic studies,

and, when necessary, correlation spectroscopy, heteronuclear

multiple quantum coherence (HMQC), and/or heteronuclear

In contrast to the hydrocarbon analogue 7,⁴⁶cycles 1b and

1c do not stack into columns with the 1,4-diarylbuta-1,3-diyne

units in parallel overlay optimal for topotactic polymerization.

Instead, the crystal packing of 1b and 1c comprise tilted “head

to tail” rows of macrocycles, which rest upon each other in

alternate directions and collectively form close-packed sheets

(Figure 1, center left and right). The alternate directional

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Figure 1. X-ray crystal structures of 1b and 1c. Plan view of 1b (space-filling representation), upper left; and stick representation of 1c, view through

the 1,4-di(pyridin-3-yl)buta-1,3-diyne mean plane, upper right (the benzene is in the foreground). View of the b−c plane (sheet) of 1b showing

alternate antiparallel rows of macrocycles (center left), and view along the b-axis showing the arrangement of tilted sheets of 1b (lower left). View of the

a−c plane (sheet) of 1c showing alternate antiparallel rows of macrocycles (center right), and view through the c-axis showing zigzag arrangement of tilted

sheets of 1c (lower right). In the center right view, the lowest pair of overlaid rows of 1c is highlighted by enclosure within a rectangle.

packing between the rows of 1b and 1c ensures that the

pyridine ring dipoles avoid parallel alignments, thereby

minimizing intermolecular repulsions. However, the arrange-

ment of the rows of 1c relative to each other differs from 1b in

that the 1,4-di(pyridin-3-yl)buta-1,3-diyne and benzene moi-

eties directly overlay each other only within pairs of rows. Each

pair of overlaid rows is displaced from the next pair such that

the benzenes of one pair lie over the faces of the macrocycles of

the adjoining pair (Figure 1, center right). Indeed, this packing

arrangement appears responsible for the nonplanarity of 1c, as

the benzene rings are bent into the faces of the overlying

macrocycles at the interface between each adjoining pair of

rows.

In 1b and 1c, the shortest interpyridine contacts are,

respectively, 3.380 and 3.324 Å, and in 1c, the shortest

interbenzene contact is 3.372 Å, all of which are within the Van

der Waals radii. Aromatic π−π stacking interactions and dipole

alignments therefore significantly control the packing motifs in

the latter two macrocycles.

metallopolymers incorporating these ligands. To explore this

possibility, we performed electrochemical investigations on 1a,

2a, and 3, the systems anticipated to have the most effective

pathways for internitrogen electronic communication, as well as

acyclic 9⁶¹for comparison.

In the case of the dehydro[m]pyrido[15]annulenes 2a and 3,

at relatively low scan rates (0.1 V s⁻¹), one well-resolved

reversible one-electron reduction step is observed at −1.71 and

−1.70 V vs Fc⁺/Fc as well as a second irreversible reduction at

Epc = −2.05 and −2.03 V vs Fc⁺/Fc, respectively. This second

reduction became reversible at scan rates higher than 1 (2a)

and 2 V s⁻¹(3), with the corresponding redox potentials being

observed at −1.73 and −1.98 V for 2a and −1.69 and −1.93 V

for 3 vs Fc⁺/Fc, respectively (Table 1 and Figure 2), denoting

the chemical instability of the generated dianion.

Qualitatively, cycle 3 would be expected to be more easily

reduced than 2a due to the presence of the three comparatively

electron-withdrawing pyridine rings in the former. However,

the first reversible one-electron reduction and the second

irreversible reduction at 0.1 V s⁻¹of 2a and 3 are very similar,

within the accuracy of potential determination, revealing that

the presence of the central pyridine nitrogen in 3 has a

negligible effect upon the reduction potentials. Within the

dehydro[m]pyrido[15]annulene series, the lowest unoccupied

molecular orbitals (LUMOs) involved in the reductions

Cyclic Voltammetric Studies. In view of the electro-

chemical activity reported for dehydroaryl[n]annulenes and

related systems,^33,82−84we anticipated that our dehydro[m]-

pyrido[14]- and [15]annulenes may also be electrochemically

active, especially toward reduction, a property that would be of

importance for electron transport within hybrid conjugated

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and showed minimal deviation from the Beer and Lambert

law, demonstrating that aggregation was negligible in more

dilute solution. Overall, the spectra comprise two main groups

of absorption envelopes, the first centered around 300 nm

with the greatest molar absorption coefficients, averaging at

higher energies for the [15]annulenes as compared to the

[14]annulenes (Figure 3). The second group of maxima

between 320 and 420 nm are of much lower intensity, with

pronounced absorption edge tailing in the case of 2a and 3.

The optical bandgaps were also determined from the lowest

energy absorption edges of the UV−vis spectra both in solution

and in the solid state,^85,86which show a similar overall trend

(Table 2). Thus, the solution optical bandgaps decrease in the

following order: 1c > 1d > 1b > 2b > 1a > 2a ≅ 3. For a given

N−N isomer, the dehydro[m]pyrido[15]annulenes display

lower energy optical bandgaps than their [14]annulene

congeners, while those possessing the 1,4-di(pyridin-4-yl)-

buta-1,3-diyne unit, that is, 1a, 2a, and 3 exhibit the lowest

energy bandgaps within the series. The solution UV−vis spectra

of all of the macrocycles studied also display absorption edges

of lower energy than their respective uncyclized precur-

sors^61,69,70(Figure 11 in the Supporting Information),

emphasizing the bandgap energy-lowering effect of cyclization.

Luminescence Spectroscopic Studies. The lumines-

cence properties of 1a−d, 2a,b, and 3 were also investigated,

the results of which are summarized in Table 2 and the solution

and thin film luminescence emission spectra in Figure 4.

The luminescence spectra of the dehydrodipyrido[14]-

annulenes 1b−d exhibit relatively little variation in shape and

energy, whereas that of 1a is uniquely red-shifted in

comparison. In the [15]annulene series, the emission spectra

of 2a and 3 are very similar, highlighting the minor effect that

the central pyridine nitrogen of 3 exerts upon the π* excited

state energies, whereas the emission of 2b is significantly blue-

shifted in comparison. The regiochemistry of nitrogen

substitution appears therefore to influence the energy of the

excited states only in particular cases.

Table 1. Electrochemical Data of 1a, 2a, 3, and Precursor 9

Observed by Cyclic Voltammetry (CV) in CH₂Cl₂with 0.1

mol/L [(n-Bu₄)N]PF₆

a

annulene/

precursor

scan rate

b

c

d

e

(V s⁻¹

0.1

)

E° (V/_Fc+/Fc

)

ΔEp (mV) Epc (V)

1a

2a

3

−1.78

−2.14

5

−1.74

−1.71

80

−2.19

80

0.1

5

−2.05

110

130

70

−1.73

−1.98

−1.70

0.1

5

−2.03

80

−1.69

−1.93

85

9

0.1

−2.04

a

b

All potentials are given vs ferrocene, used as internal standard. The

CVs at 5 V s⁻¹scan rate were corrected for Ohmic drop before

c

determination of the redox potential. E° = (Epa + Epc)/2 where Epa

and Epc are the respective anodic and cathodic peak potentials. ΔEp

is the potential difference between the cathodic and the anodic peak

d

e

potentials. Irreversible peak potential.

therefore appear not to involve the central aromatic ring. This

conclusion is further supported by theoretical calculations that

show the LUMOs to be mainly nodal on the 1,3-bridging aryl

rings of 2a and 3 (see later).

In contrast, 1a gave two irreversible reduction peaks at,

respectively, Epc = −1.78 and −2.14 V vs Fc⁺/Fc at low scan

rates. By increasing the scan rates up to 10 V s⁻¹, only the first

reduction became reversible for scan rates higher than 2 V s⁻¹,

with a redox potential of −1.74 V vs Fc⁺/Fc (Table 1 and

Figure 2). Reduction of 1a, an aromatic 14-π electron cycle,

would yield a less stable nonaromatic radical, which may

therefore undergo a follow-up chemical reaction.

Acyclic 9, on the other hand, afforded only an irreversible

reduction peak at Epc = −2.04 V at a scan rate of 0.1 V s⁻¹,

identical to those observed for 2a and 3 (Epc = −2.05 and

−2.03 V, respectively) at the same scan rate. Increasing the scan

rate did not result in reversible behavior, denoting the

generation of a species of high reactivity despite the presence

of the insulating triisopropylsilyl (TIPS) substituents (Figure 2).

Clearly, cyclization results in a relative stabilization of the

monoanion radicals generated upon reduction, a finding

suggesting that cyclic dehydroaryl[n]annulene type ligands

may be superior candidates for achieving electrochemical

reservoir behavior and intermetal communication within

coordination polymers, as compared to the acyclic arylethyny-

lene ligands frequently used in their construction.

The overall stability toward electrochemical reduction is very

similar for 1a, 2a, and 3 (E° = −1.74, −1.73, and −1.69 V for

1a, 2a, and 3, respectively, at 5 V s⁻¹scan rate; Table 1),

although the [14]annulene 1a is marginally more resistant to

reduction than the [15]annulenes 2a and 3. This trend is

reflected in the calculated LUMOs of 1a, 2a, and 3 (Table 3

and Figure 9), which are also of similar energies and

delocalization, yet with that of 1a lying just above and therefore

slightly less reducible than those of 2a and 3.

In contrast, the emission spectra of thin films are particularly

sensitive to the structural characteristics and surrounding

environment of the ligands, showing a continual variation in

emission color over 114 nm on passing from 1c to 3, and with

the [15]annulenes emitting at lower energies than the

[14]annulenes.

Luminescence quantum yields were also estimated (Table 2)

and, with the exception of 1a, are all relatively low, falling

within the range of 0.02−0.1. Uniquely, cycle 1a exhibited a

quantum yield of 0.26, which is much higher than the overall

averaged quantum yield of the other cycles within the

series.⁸⁷

Spectroscopic Study of Hg^IIBinding to 1a−d, 2a,b,

and 3. Previous studies revealed that 4−6 and related cycles

undergo binding to a range of transition metal ions in dilute

solution but in many cases form insoluble precipitates that

hamper measurements.^61,69,70This limitation was not however

encountered with Hg^II, which also afforded clear and easy-to-

follow spectroscopic changes. We therefore decided to evaluate

the metal ion-binding properties of 1a−d, 2a,b, and 3 using

Hg^II, with the additional interest that Hg^IIis an environmental

and biological toxin, for which the discovery of new spectro-

scopic detection methods continues to be in demand.⁸⁸⁻⁹³

Initially, we probed the binding of Hg^IIwith 1a over a [1a]:

[Hg^II] range of 1:4−1:100, as this ligand gave the strongest

UV−vis response to protonation (see below). The titration

UV−Vis Spectroscopic Studies. The UV−vis absorption

spectra of 1a−d, 2a,b, and 3 were recorded in CH₂Cl₂solution at

several concentrations within the range 2 × 10⁻⁶to 2 × 10⁻⁵mol/L

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Figure 2. Cyclic voltammetry of 1a, 2a, 3, and 9. All CVs were recorded in CH₂Cl₂with 0.1 mol/L [(n-Bu₄)N]PF₆, and the voltammograms were

uncorrected for the Ohmic drop. The CV of 2a at 0.1 V s⁻¹scan rate was performed in the absence of ferrocene and then calibrated to the ferrocene

redox wave. All other CVs were recorded in the presence of ferrocene.

Figure 3. UV−vis absorption spectra of dehydrodipyrido[14]annulenes 1a−d (left) and dehydro[m]pyrido[15]annulenes 2a,b and 3 (right)

recorded in CH₂Cl₂solution.

experiment showed most noticeably that the coordination-

induced changes in the UV−vis spectrum of 1a occur over a

large ligand:metal window; yet, a relatively high [Hg^II] is

required to induce a significant perturbation over the whole of

the UV−vis of 1a (Figure 5). On the basis of this latter

experiment, we decided to use a 1:20 ratio of [L]:[Hg^II] for all

subsequent L:Hg^IIbinding studies to ensure a significant

spectroscopic response.

As in 1a, the addition of Hg^IIto 1b−d, 2a,b, and 3 results in

a reduction in the absorption coefficient of the principle λ_maxof

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Table 2. UV−Vis and Luminescence Emission Spectroscopic Data for 1a−d, 2a,b, and 3

a

[m]pyrido[n]-

no. [n]- π-electrons (no. [m]

λ_{em thin film}

optical bandgap E_g^opt(eV)

quantum

annulene

pyridine rings)

λ_{abs solution}(nm) λ_{em solution}(nm)

(nm)

(solution)

yield Φ

b

1a

1b

14 (2)

294, 302, 313

411

443, 457sh

2.857 (3.037)

2.936 (3.157)

0.26

0.03

b

c

300, 311,

389, 407, 422

421, 432

318sh

b

b,d

d

1c

14 (2)

299sh, 309,

318

384, 402, 418

411,

3.100 (3.195)

2.979 (3.169)

0.02

0.06

428

b

1d

299, 309, 318

391, 408,

442

424sh

b

2a

2b

3

15 (2)

15 (3)

284

429sh, 463

501

469

525

2.731 (2.938)

2.877 (3.076)

2.732 (2.945)

0.06

0.10

0.04

b

293

400, 423, 437

b

275, 293, 307

421, 461

a

Optical bandgap extrapolated from the lowest energy absorption edge of drop-cast thin film UV−vis spectrum. Optical bandgap obtained from

b

c

d

lowest energy absorption edge of CH₂Cl₂solution UV−vis spectra in parentheses. Highest intensity peaks. Equal intensity peaks. The relative

intensity and line shape of these peaks vary according to the nature of the thin film and its angle with respect to the incident light. Unless otherwise

stated, all UV−vis and luminescence solution measurements were performed in air-equilibrated CH₂Cl₂at 20−25 °C.

the ligand, with an associated rise and extension to lower

energy of the absorption tail (Figure 12 in the Supporting

Information). Although the spectral response to Hg^IIis

relatively insensitive to isomer variations, it is dependent

upon the number of π-electrons, being most pronounced for

the dehydrodipyrido[14]annulenes 1a−d.

the proton-induced luminescence perturbations of 1a−d, 2a,b,

and 3 are influenced by both the isomeric variations in nitrogen

regiochemistry and the number of π-electrons.⁹⁵However,

further investigations such as, for example, time-resolved

luminescence decay studies will be necessary to clearly

characterize the emitting species generated upon protonation

and Hg^IIbinding.

In all cases, the addition of Hg^IIat an [L]:[Hg^II] ratio of 1:20

(Figure 5) causes the luminescence λ_maxto shift to lower

energy, with the dehydrodipyrido[14]annulenes 1a−c experi-

encing the greatest shifts.⁹⁴The coordination-induced shifts of

the pairs 1b/1c, 1d/2b, and 2a/3 are, however, strikingly

similar, indicating a lower sensitivity to isomer differences. The

similarity in the luminescence shifts of 2a and 3 suggests that

the central pyridine of 3 may have little involvement with Hg^II

ion coordination in the excited state complex.

Finally, the visual distinction between protonation and Hg^II

binding by 1a−d, 2a,b, and 3 is displayed more clearly as the

collective response of all of the ligands in the form of a

luminescence color pattern, rather than by the response of

particular individual ligands. This observation raises the

intriguing possibility that libraries of such ligands may find

applications as luminescence fingerprint color sensors for

particular metal ions.⁹⁶

Spectroscopic Study of Protonation of 1a−d, 2a,b,

and 3. Protonation of 4−6 resulted in a solution optical

bandgap reduction as well as partial quenching and red-shifting

of the luminescence, consistent with emission from aggregated

excited states.⁶¹More recently, some donor-functionalized

dehydrodipyrido[14]annulenes and dehydropyrido[15]-

annulenes have also been shown to undergo various proton-

induced shifts in the UV−vis and luminescence color

changes.^75,76

The effects of protonation on the UV−vis spectra of

solutions of 1a−d, 2a,b, and 3 are shown in Figure 6 and in

all cases show increased tailing of the low-energy absorption

edge into the visible in the presence of 0.1 mol/L TFA. The

proton-induced spectral shifts of the dehydro[m]pyrido[15]-

annulenes 2a−3 involve λ_maxred-shifting and moderate or zero

reduction in molar absorption coefficients. The

dehydrodipyrido[14]annulenes 1a−d on the other hand

experience more line shape rather than energy changes and

significant molar absorption coefficient reductions, especially in

the UV−vis of 1a.

In contrast to the absorption changes, the solution

luminescence spectra of 1a−d, 2a,b, and 3 undergo significant

shifts in the λ_maxto lower energy (by 46−101 nm) in the

presence of 0.1 mol/L TFA (Figure 6). The sensitivity of the

luminescence energy to acid was found to decrease in the

following order: 1d > 1a ≅ 2b > 2a > 1c > 1b ≅ 3 and was

accompanied by a range of visible color changes (Figure 7).

Cycles 1a and 1d are thus singular in their response to

protonation, in both undergoing the largest UV−vis line shape

changes and the strongest luminescence red-shifting. Overall,

Quantum Mechanics Calculations. In contrast to the

hydrocarbon annulenes and dehydroaryl[n]annulenes,

dehydro[m]pyrido[n]annulenes are materials of comparatively

recent existence and have consequently been little studied from

a theoretical standpoint.^75,76,97,98To obtain a deeper under-

standing of the electronic properties of 1a−d, 2a,b, and 3, we

therefore conducted a DFT investigation on these molecules

using the Spartan 08 software⁹⁹at the B3LYP level of theory

and employing the 6-31G* basis set.^100,101

Selected frontier molecular orbital (FMO) surfaces (1a,b, 2a,

and 3) are shown in Figure 8 along with schematics for clarity,

and those of 1c,d and 2b are in Figure 13 of the Supporting

Information.¹⁰²The dehydrodipyrido[14]annulenes 1b−d

exhibit similar highest occupied molecular orbitals

(HOMOs), concentrated principally on the 1,4-di(pyridinyl)-

buta-1,3-diyne units, whereas in 1a, the HOMOs are nodal at

the 1,4-buta-1,3-diyne bridge. However, the HOMOs on the

nitrogens of 1a−c are significantly contracted or nodal,

suggesting that internitrogen electronic communication would

be weak or negligible in the HOMOs of these systems. In

contrast, the LUMOs of 1a, 1c and 1d are almost identical

and, in 1a and 1d, are concentrated on the pyridine nitrogens,

the majority of the pyridine carbons and the 1,4-buta-1,3-

diyne bridges, suggesting efficient internitrogen electronic

communication in these molecules. The LUMO of 1b on the

other hand is located mainly on the nitrogens and 1,2-

bis(pyridin-4-ylethynyl)benzene moiety, affording a “V”-

shaped conjugation pathway suggestive of ortho-internitrogen

electronic communication.

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do we observe complete cyclic conjugation over the core of the

macrocyclic ring.

Overall, 1a, 2a, and 3 exhibit LUMOs with para-connected

orbital overlap between the pyridine nitrogens, which are

additionally optimally positioned for external metal ion

complexation. The generation of electro-reduced species or

complexation to low oxidation state metals capable of electron

donation into the LUMOs of these latter annulenes would thus

be expected to achieve the most effective intermacrocyclic

electronic communication within extended supramolecular

arrays of dehydro[m]pyrido[n]annulenes.

The HOMO−LUMO energies and dipole moments of 1a−

d, 2a,b, and 3 are given in Table 3. The calculated HOMO−

LUMO bandgaps were all higher in energy than the optical

bandgaps, with the closest agreement being between bandgaps

estimated from solution UV−vis spectra and those calculated

from the energy-minimized structures. The trend between

experimental and calculated bandgaps was reasonable and in

overall agreement within the limits of experimental error

(Figure 14 in the Supporting Information).

Separation of the dehydro[m]pyrido[14]- and [15]annulenes

into two groups as shown in Figure 9 revealed that within each

group, the decrease in bandgaps upon passing, respectively,

from 1c to 1a and 2b to 2a results principally from an increased

relative reduction in the LUMO energy.

Thermochemical Properties. As high carbon content

materials with an increased density of triple bonds are well-

known to undergo topotactic¹⁰³and amorphous carbonization

polymerizations when heated,^104,105we therefore considered it

of interest to explore the thermochemical properties of our

macrocycles. The TGA profiles of the dehydrodipyrido[14]-

and [15]annulenes are shown in Figure 10, and all exhibited

explosive decompositions at specific temperatures. However, no

clear overall correlation between structure and thermal stability

was observed. Wider investigations will therefore be necessary

for general predictive structure−property relationships to

emerge for these systems.

CONCLUSIONS

■

The above work discloses the synthesis of a range of isomeric

parent dehydro[m]pyrido[14]- and [15]annulenes 1a−d, 2a,b,

and 3, which were characterized by NMR and mass

spectroscopic techniques as well as crystallography in the case

of 1b,c. The macrocycles were found to function as luminescent

chromophores in solution upon protonation and Hg^II

coordination, with emissions sensitive to the number of π-

electrons and isomeric composition of the macrocyclic ring. In

the solid state, an even greater sensitivity to ligand structural

characteristics as well as surrounding environment was evidenced

by the observation of emission color-tuning. In particular, the

ion-specific luminescence color patterns that collectively result

from the differing spectroscopic isomer responses suggest

potential applications as “fingerprint” analyte sensors.

Ligand 1a afforded a unique spectroscopic profile in being a

relatively low optical bandgap material, which shared the

strongest Hg^IIand proton-induced emission energy changes

and molar absorption coefficient perturbations within the

dehydro[m]pyrido[14]- and [15]annulene series. It also

exhibits the highest luminescence quantum yield.

Figure 4. Normalized solution luminescence emission spectra of

dehydrodipyrido[14]annulenes 1a−d (upper), dehydro[m]pyrido-

[15]annulenes 2a,b and 3 (center), and drop-cast thin films of 1a−

d, 2a,b, and 3 (lower). The solution luminescence emission spectra

were recorded in CH₂Cl₂solution (see the Supporting Information for

experimental details).

The HOMOs of the dehydro[m]pyrido[15]annulenes 2a,b

and 3 are expanded on the pyridine nitrogens, the adjacent

pyridine carbons, and the 1,4-buta-1,3-diyne bridges, indicating

possible internitrogen electronic communication across these

units. The LUMOs of 2a,b and 3 are also similar to those of

1a,c,d in being concentrated principally on the 1,4-di-

(pyridinyl)buta-1,3-diyne units. This finding is in agreement

with the site of reduction as indicated by the electrochemical

measurements and suggestive of efficient internitrogen

electronic communication in 2a,b and 3. However, in none

of the FMOs of the dehydro[m]pyrido[14]- and [15]annulenes

The DFT calculations corroborated the spectroscopic

findings that 1a, 2a, and 3 are the lowest bandgap materials

with LUMOs delocalized over the para-connected pyridine

rings and intervening 1,4-buta-1,3-diyne bridges, a conclusion

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Figure 5. UV−vis absorption spectra of 1a titrated with incremental additions of Hg(CF₃SO₃)₂(upper left), where the [1a]:[Hg^II] ratios are, respectively,

1:0, 1:4, 1:8, 1:12, 1:16, 1:20, 1:30, 1:40, 1:60, and 1:100, recorded 40 h after solution preparation. Normalized luminescence emission spectra of 1b and

1c (L) (upper right), 1a and 1d (L) (lower left), and 2a,b and 3 (L) (lower right) with Hg(CF₃SO₃)₂; [L]:[Hg^II] ratio = 1: 20; spectra recorded 7 days

after solution preparation. All L + Hg^IIspectra were recorded in 10% MeOH/CH₂Cl₂, and those of pure L were recorded in CH₂Cl₂.

cases to achieve optimal product yields and purities. These details are

provided below when necessary for the particular products concerned.

Slow heating of 1a−d, 2a,b, 3, 13a−d, 20a,b, and 23 at 1−2 °C/min

up to 310 °C resulted in a gradual color change to black, with no

visible melting phase.

supported by the electrochemical measurements that showed

reduction to be insensitive to the nature of the 1,3-aromatic

bridge in 2a and 3. Isomeric variation within the dehydro[m]-

pyrido[14]- and [15]annulenes clearly also results in bandgap

fine-tuning. The superior LUMO delocalization between the

pyridine nitrogens along with their para-connectivity and ideal

regiochemistry leads to the anticipation that 1a, 2a, and 3

would be the most suitable candidates for the assembly of

electronically delocalized supramolecular arrays and polymers,

when complexed to low oxidation state metals capable of back-

donation of electrons into the ligand π* LUMOs.

Furthermore, the finding that cyclization of the 1,4-di(pyridin-

4-yl)buta-1,3-diyne unit results in augmented monoanion radical

stabilization upon reduction as well as optical bandgap lowering

and improved electronic delocalization as compared to acyclic

analogues suggests that the development of molecular solenoids

and hybrid nanoelectronic materials with curved electronic

pathways based upon the optimally conjugated para-arylethyny-

lenes is viable.^106,107Work towards this goal along with the

creation of hybrid dehydro[m]pyrido[n]annulene-coordination

polymers based upon 1a are currently in progress.

A. Sonogashira Type Heterocouplings. To the respective

arylalkyne and PdCl₂(PPh₃)₂catalyst under an atmosphere of argon

was added N₂-purged Et₃N followed by the appropriate quantity of

diiodobenzene consecutively by syringe. After it was stirred for 0.2 h, a

solution of CuI in N₂-purged Et₃N (prepared in a separate Schlenk

under argon) was syringed into the reaction, and stirring was

continued for 4−21 days at ambient temperature in the absence of

light. A pale dark gray or brown precipitate slowly formed in all cases,

visually indicating the progress of the reaction. All solvent was then

removed under reduced pressure in a water bath at 70 °C, and the

residue was extracted with 5 × 30 mL of pentane. The combined

extracts were gravity filtered, and the solvent was removed under

reduced pressure on a water bath at ambient temperature. The crude

product was purified as described individually for each compound

below. As the reaction conditions and yields of the Sonogashira

couplings were not optimized, the reactions were run with an emphasis

on longer rather than shorter reaction times to ensure complete

conversion of the starting materials.

B. Fluoride-Mediated Desilylations. To a stirred solution of the

triisopropylsilylalkyne in THF was first added dropwise a small

quantity of distilled water followed by the appropriate quantity of the

[(n-Bu)₄N]F (1.0 M in THF) solution, and stirring was continued at

ambient temperature in the absence of light until TLC sampling

indicated complete deprotection (1−4 days). The reaction was

EXPERIMENTAL SECTION

■

The general experiment is described in the Supporting Information.

Synthetic Procedures and Characterization Data for 1a−d,

2a,b, 3, 12a−d, 13a−d, 15−17, 19a,b, 20a,b, 22, and 23.

Variations in the following procedures A−C were necessary in some

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Figure 6. UV−visible absorption spectra of 1a−d (upper left) and 2a,b and 3 (L) (upper right) in CH₂Cl₂/TFA ([TFA] = 0.1 mol/L) with 2a,b and

3 in pure CH₂Cl₂for comparison in the upper right spectrum. Normalized luminescence emission spectra of 1a−c (lower left) and 2a,b and 3 (lower

right) in CH₂Cl₂/TFA ([TFA] = 0.1 mol/L) and in pure CH₂Cl₂for comparison. [L] = 7−9 × 10⁻⁶mol/L.

of the dialkyne was complete, the reaction was stirred for a further

0.25−1 h, and then, all solvent was removed under reduced pressure

on a water bath at 40 °C. The residue was further dried in a stream of

air and then distilled water (200−300 mL) added, followed by excess

ice, and the mixture vigorously stirred. Excess solid KCN (4−5 g) was

then added in portions with continued stirring, until no further visible

change occurred, at which point the mixture appeared as a brown

suspension. Further workup and purification methods are detailed

separately for each product below.

Macrocycles 1a−d, 2a,b, and 3 were isolated as described below

with ≤1 mol % entrained CH₂Cl₂after air-drying, as judged by the ¹H

NMR integrations. The entrained solvent could be removed upon

heating to 85−95 °C in a gentle stream of argon for 0.5 h.

1,2-Bis((4-((triisopropylsilyl)ethynyl)pyridin-3-yl)ethynyl)-

benzene (12a). According to general procedure A, 10a (0.788 g,

2.78 × 10⁻³mol), 11 (0.400 g, 1.21 × 10⁻³mol), and PdCl₂(PPh₃)₂

Figure 7. From left to right: solutions of 1a−d, 2a,b, and 3 (L) with

(0.068 g, 9.69 × 10⁻⁵mol) in Et₃N (20 mL), to which was added a

[L] = 7−9 × 10⁻⁶mol/L; in CH₂Cl₂(upper), in 10% MeOH/CH₂Cl₂

solution of CuI (0.053 g, 2.78 × 10⁻⁴mol) in Et₃N (10 mL), was

with a 1:20 ratio of [L]:[Hg^II] (center), and in 0.1 mol/L TFA in

stirred for 4 days and worked up to yield crude 12a. The product was

CH₂Cl₂(bottom row), under illumination by a high intensity 312 nm

then chromatographed on a column of neutral alumina (activity II/III)

UV lamp in the dark.

eluting first with CH₂Cl₂to remove some less polar impurities. The

column was subsequently gradient eluted with 1−5% MeOH/CH₂Cl₂

quenched by the addition of distilled water, and all solvent was

to obtain the product, which was isolated as pale honey-colored oil

removed under reduced pressure at ambient temperature. The crude

that solidified into a tacky glass upon standing for several weeks.

product was purified as described individually for each compound

below.

C. Macrocyclizations (Eglinton/Galbraith Protocol). In a well-

ventilated hood, a solution of the dialkyne in toluene was added

dropwise over 0.7−2.5 h to a solution of anhydrous Cu₂OAc₄in

pyridine (400−567 mL) with rapid stirring at 55 °C. After the addition

Further drying under vacuum at 70−80 °C/0.001 mm Hg was

necessary to remove residual CH₂Cl₂to yield pure 12a (0.754 g, 97%).

¹H NMR (CDCl₃, 400.13 MHz, 23 °C): δ 8.710 (d, ⁵J(2,5) = 0.9 Hz,

3

2H; pyH2), 8.454 (d, J(6,5) = 5.1 Hz, 2H; pyH6), 7.567 (m, 2H;

phH3/6), 7.346 (m, 2H; phH4/5), 7.344 (dd, ³J(5,6) = 5.1 Hz,

⁵J(5,2) = 0.8 Hz, 2H; pyH5), 1.091 (m, 42H; CH(CH₃)₂). ¹³C NMR

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Figure 8. FMOs (B3LYP/6-31G*) of 1a,b, 2a, and 3. LUMO (upper) and HOMO (lower) plots, with molecular schematics shown at the bottom.

Table 3. Energy Properties and Dipole Moments Calculated

(B3LYP/6-31G*) for 1a−d, 2a,b, and 3 in the Gas Phase

E (HOMO)

E (LUMO)

ΔE (L−H)

annulene

(eV)

μ (D)

1a

1b

1c

1d

2a

2b

3

−6.014

−5.965

−5.818

−5.894

−5.970

−5.927

−5.976

−2.484

−2.332

−2.112

−2.193

−2.637

−2.425

−2.601

3.529

3.633

3.706

3.701

3.333

3.502

3.374

0.59

5.41

1.46

5.92

0.09

4.35

1.13

Figure 10. TGA thermal decomposition profiles of 1a−d, 2a, and 2b,

heated at a rate of 10 °C/min under an inert atmosphere. The

decomposition temperature ranges are shown in brackets for the

respective dehydrodipyrido[14]- and [15]annulenes.

ambient temperature to yield a dark oil, which was chromatographed on

neutral alumina (activity III), eluting with CH₂Cl₂. Pentane

(15 mL) was added, and the mixture briefly ultrasonicated. The

crystalline solid that formed, was isolated by filtration under vacuum,

washed with pentane (4 × 0.5 mL) and air-dried. This latter solid was

combined with the solid obtained from the methanol washing of the

crude product above and dissolved in boiling heptane (150 mL) to

which 0.1 g of NORIT A had been added. After it was heated for

1 min, the mixture was gravity filtered and left to cool to ambient

temperature in the dark. The crystalline solid that formed was isolated

by filtration under vacuum, washed with heptane (4 × 1 mL), and air-

Figure 9. HOMO and LUMO energies (B3LYP/6-31G*) of 1a−d,

2a,b, and 3 as a function of annulene structure.

1

(CDCl₃, 100.61 MHz, 23 °C): δ 152.8, 148.2, 132.9, 132.0, 128.4,

125.8, 125.5, 121.8, 102.6 (−C), 101.3 (−C), 94.3 (−C), 89.5

(−C), 18.6 (CH(CH₃)₂), 11.2 (CH(CH₃)₂). IR (thin film): 2941

(s), 2891 (m), 2864 (s), 1574 (s), 1488 (s), 1462 (s), 1398 (s), 1164

(m), 996 (s), 882 (s), 865 (s), 828 (s), 802 (s), 755 (s), 677 (s), 663

(s), 641 cm⁻¹(s). High res. ESI MS: m/z (%): 641.3658 (100) [M + H⁺].

Calcd for C₄₂H₅₃N₂Si₂, 641.3742.

1,2-Bis((4-ethynylpyridin-3-yl)ethynyl)benzene (13a). Com-

pound 13a was obtained from the reaction of 12a (0.730 g, 1.14 ×

10⁻³mol) with [(n-Bu)₄N]F (1.0 M in THF; 2.4 mL, 2.4 × 10⁻³mol)

in THF (60 mL) to which 10 drops of H₂O had been added, after 1 day

according to the general deprotection procedure B. Methanol (20 mL)

was added to the residue, the mixture was filtered under vacuum, and

the isolated solid was washed with excess methanol and air-dried. The

solvent was removed from the filtrate under reduced pressure at

dried to afford 13a (0.299 g, 80%) as cream-colored microflakes. H

NMR (CDCl₃, 400.13 MHz, 25 °C): δ 8.802 (d, ⁵J(2,5) = 0.5 Hz, 2H;

pyH2), 8.510 (d, ³J(6,5) = 5.3 Hz, 2H; pyH6), 7.645 (m, 2H; phH3/6),

7.392 (m, 2H; phH4/5), 7.383 (d, ³J(5,6) = 4.8 Hz, 2H; pyH5),

3.421 (s, 2H; −CCH). ¹³C NMR (CDCl₃, 100.61 MHz, 25 °C): δ

152.7, 148.3, 132.5, 131.9, 128.8, 125.8, 125.0, 122.2, 94.7 (−C),

88.8 (−C), 85.9 (−C), 79.6 (−C). UV−vis (CH₂Cl₂): λ_max

(ε) = 239 (5.4 × 10⁴), 280 (2.9 × 10⁴), 313 (2.5 × 10⁴), 326sh (2.3 ×

10⁴), 336 nm; sh (2.1 × 10⁴M⁻¹cm⁻¹). IR (thin film): 3284 (s) (

C−H), 3187 (s) (C−H), 3055 (w), 2106 (s) (CC), 1577 (s),

1487 (s), 1443 (s), 1399 (s), 1049 (s), 849 (s), 837 (vs), 759 (vs), 753

(vs), 694 (s), 641 cm⁻¹(s). High res. ESI MS: m/z (%): 329.1062

(100) [M + H⁺], 335.1159 (27) [M + Li⁺], 351.0906 (4) [M + Na⁺],

663.2068 (9) [2M + Li⁺]. Calcd for C₂₄H₁₃N₂, 329.1073; C₂₄H₁₂LiN₂,

335.1155; C₂₄H₁₂NaN₂, 351.0893; C₄₈H₂₄LiN₄, 663.2156.

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Dehydro[2]pyrido[14]annulene (1a) via Copper-Mediated

Cyclization of 13a. A solution of 13a (0.060 g, 1.83 × 10⁻⁴mol) in

toluene (30 mL) was added to a stirred solution of anhydrous

Cu₂OAc₄(1.330 g, 3.66 × 10⁻³mol) in pyridine (400 mL) at 55 °C

over 2 h. The reaction was stirred at the above temperature for a

further 0.5 h, and then, the reaction worked up as described in the

general macrocyclization procedure C. The straw-colored aqueous

KCN suspension was extracted with CH₂Cl₂(3 × 60 mL), the

combined extracts were dried (anhydrous Na₂SO₄) and gravity

filtered, and the solvent was reduced in volume to 20 mL under

reduced pressure at ambient temperature. The concentrate was

chromatographed first on a column of basic alumina (activity IV) and

then on a short column of neutral alumina (activity III) in complete

darkness, in both cases eluting with CH₂Cl₂. The solvent was removed

under vacuum at ambient temperature in darkness, and the remaining

solid was suspended in MeCN (10 mL), briefly ultrasonicated, isolated

by filtration under vacuum, washed with MeCN (3 × 1 mL), and air-

dried at ambient temperature to constant mass affording 1a (0.040 g,

67%) as a fibrous cream-colored solid. ¹H NMR (CDCl₃, 400.13 MHz,

remained upon removal of the solvent was partitioned between water

(350 mL) and CH₂Cl₂(60 mL) and extracted with a further 60 mL

aliquot of CH₂Cl₂. The combined organic extracts were further

extracted with water, then dried (anhydrous Na₂SO₄), and gravity

filtered, and the solvent was removed under reduced pressure at

ambient temperature. The remaining solid was boiled in 600 mL of

Et₂O and gravity filtered, and the Et₂O was distilled off on a water

bath. The product was finally dissolved in 40 mL of boiling heptane to

which 0.1 g of NORIT A had been added, gravity filtered, and left to

stand in the dark for 1 day. The solid that formed was isolated by

vacuum filtration, washed with heptane, and air-dried to yield 13b

(0.140 g, 68%) as cream microcrystals. ¹H NMR (CDCl₃, 400.13

5

MHz, 25 °C): δ 8.767 (d, J(2,5) = 0.7 Hz, 2H; pyH2), 8.543 (d,

³J(6,5) = 5.1 Hz, 2H; pyH6), 7.661 (m, 2H; phH3/6), 7.427 (m, 2H;

3

5

phH4/5), 7.408 (dd, J(5,6) = 5.2 Hz, J(5,2) = 0.8 Hz, 2H; pyH5),

3.343 (s, 2H; −CCH). ¹³C NMR (CDCl₃, 100.61 MHz, 31 °C): δ

153.2, 148.7, 133.6, 132.8, 129.2, 125.2, 124.8, 120.6, 96.1 (−C),

89.5 (−C), 84.3 (−C), 79.1 (−C). UV−vis (CH₂Cl₂): λ_max

(ε) = 228 (4.9 × 10⁴), 242 (4.8 × 10⁴), 290 (3.6 × 10⁴), 309 (2.4 ×

10⁴), 317sh (2.4 × 10⁴), 330 nm; sh (2.1 × 10⁴M⁻¹cm⁻¹). IR (thin

film): 3301 (m) (C−H), 3155 (m) (C−H), 2222 (m) (CC),

2204 (m) (CC), 2098 (m) (CC), 1577 (vs), 1495 (m), 1442

(m), 1400 (s), 855 (m), 832 (vs), 758 (vs), 708 (s), 673 (s), 646 (s),

624 cm⁻¹(vs). High res. ESI MS: m/z (%): 329.1066 (100) [M + H⁺].

Calcd for C₂₄H₁₃N₂, 329.1073. Anal. (%) calcd for C₂₄H₁₂N₂: C,

87.79; H, 3.68; N, 8.53. Found: C, 87.45; H, 3.65; N, 8.44.

5

3

24 °C): δ 9.129 (d, J(2,5) = 0.8 Hz, 2H; pyH2), 8.669 (d, J(6,5) =

5.1 Hz, 2H; pyH6), 7.972 (m, 2H; phH3/6), 7.541 (m, 2H; phH4/5),

3

5

7.458 (dd, J(5,6) = 5.1 Hz, J(5,2) = 0.7 Hz, 2H; pyH5). ¹³C NMR

(CDCl₃, 100.61 MHz, 26 °C): δ 153.2, 147.9, 136.1, 129.4, 128.7, 125.4,

122.9, 122.1, 96.6 (−C), 89.9 (−C), 84.9 (−C), 83.5 (−C).

UV−vis (CH₂Cl₂): λ_max(ε) = 266 (2.8 × 10⁴), 277 (3.0 × 10⁴), 294 (6.0 ×

10⁴), 302 (5.7 × 10⁴), 313 (8.9 × 10⁴), 323sh (4.1 × 10⁴), 352 (1.2 ×

10⁴), 362 (8.9 × 10³), 394 nm (4.5 × 10³M⁻¹cm⁻¹). IR: 3041 (w),

3025 (w), 2181 (w) (CC), 2162 (w) (CC), 1573 (m), 1476 (m),

1406 (m), 1272 (m), 1255 (m), 878 (m), 829 (s), 792 (m), 754 (vs),

748 (s), 597 cm⁻¹(m). High res. ESI MS: m/z (%): 327.0883 (88) [M +

H⁺], 333.0969 (100) [M + Li⁺], 659.1717 (7) [2M + Li⁺]. Calcd for

C₂₄H₁₁N₂, 327.0917; C₂₄H₁₀LiN₂, 333.0999; C₄₈H₂₀LiN₄, 659.1843.

Dehydro[2]pyrido[14]annulene (1a) via Palladium-Mediated

Cyclization of 13a. A mixture of PdCl₂(dppe) (0.018 g, 3.1 × 10⁻⁵mol),

CuI (0.09 g, 5 × 10⁻⁵mol), and iodine (0.039 g, 3.1 × 10⁻⁴mol)

in 1:1 THF/i-Pr₂NH (600 mL) was homogenized by brief

ultrasonication and stirred at 50 °C for 0.5 h. A solution of 13a

(0.100 g, 3.0 × 10⁻⁴mol) in THF (20 mL) was then added to the

warm catalyst mixture dropwise over 9 h with vigorous stirring. The

reaction was stirred at the above temperature for a further 1 h, and all

solvent subsequently was removed under reduced pressure at 30 °C.

The residue was treated with aqueous KCN as described in the general

procedure C and purified as described above for the copper-mediated

cyclization of 13a to afford 1a (0.023 g, 23%).

Dehydro[2]pyrido[14]annulene (1b). A solution of 13b (0.076 g,

2.31 × 10⁻⁴mol) in toluene (30 mL) was added dropwise to a stirred

solution of anhydrous Cu₂OAc₄(1.682 g, 4.63 × 10⁻³mol) in pyridine

(507 mL) at 55 °C over 2.25 h. The reaction was stirred at the above

temperature for a further 0.3 h, and then, the reaction was worked up

as described in the general macrocyclization procedure C. The

aqueous KCN suspension was filtered under vacuum, and the isolated

straw-colored solid was washed with excess distilled water and air-

dried. The solid was then dissolved in CH₂Cl₂(20 mL) and

chromatographed on a column of basic alumina (activity IV), which

was completely shielded from the light, eluting with CH₂Cl₂. The

solvent was removed under vacuum from the eluate containing 1b, at

ambient temperature in darkness. The remaining solid was suspended

in MeCN (10 mL), briefly ultrasonicated, isolated by filtration under

vacuum, washed with MeCN (4 × 1 mL), and air-dried at ambient

temperature to a constant mass affording 1b (0.070 g, 93%) as a cream

microcrystalline solid. ¹H NMR (CDCl₃, 400.13 MHz, 24 °C): δ 8.866

5

3

(d, J(2,5) = 0.7 Hz, 2H; pyH2), 8.696 (d, J(6,5) = 5.3 Hz, 2H;

pyH6), 7.961 (m, 2H; phH3/6), 7.722 (dd, ³J(5,6) = 5.2 Hz, ⁵J(5,2) =

0.8 Hz, 2H; pyH5), 7.560 (m, 2H; phH4/5). ¹³C NMR (CDCl₃,

100.61 MHz, 25 °C): δ 149.9, 148.6, 136.7, 136.6, 129.2, 126.0, 122.9,

118.5, 97.7 (−C), 90.7 (−C), 84.4 (−C), 83.2 (−C). UV−

vis (CH₂Cl₂): λ_max(ε) = 265 (3.0 × 10⁴), 300 (8.9 × 10⁴), 311 (1.2 ×

10⁵), 318sh (8.5 × 10⁴), 343sh (2.3 × 10⁴), 353 (1.9 × 10⁴), 370

(1.3 × 10⁴), 383 nm (2.7 × 10³M⁻¹cm⁻¹). IR: 3036 (w), 2182 (m)

(CC), 2160 (vw) (CC), 1577 (m), 1518 (m), 1496 (m), 1476

(m), 1418 (m), 1400 (m), 1272 (m), 1165 (m), 954 (m), 882 (m),

838 (s), 753 (vs), 746 (s), 710 (m), 586 (m), 580 (s), 576 cm⁻¹(s).

EI MS m/z (%): 326.0 (100) [M⁺]. High res. ESI MS: m/z (%):

327.0909 (100) [M + H⁺]. Calcd for C₂₄H₁₁N₂, 327.0917.

1,2-Bis((3-((triisopropylsilyl)ethynyl)pyridin-4-yl)ethynyl)-

benzene (12b). According to general procedure A, 10b (0.600 g,

2.12 × 10⁻³mol), 11 (0.350 g, 1.06 × 10⁻³mol), and PdCl₂(PPh₃)₂

(0.100 g, 1.42 × 10⁻⁴mol) in Et₃N (30 mL), to which was added a

solution of CuI (0.100 g, 5.25 × 10⁻⁴mol) in Et₃N (6 mL), were

stirred for 21 days and worked up to yield crude 12b. The product was

then purified by column chromatography three times on neutral

alumina (activity III), eluting with CH₂Cl₂. After the solvent was

removed by distillation on a water bath, the product was air dried to

1

yield pure 12b (0.470 g, 69%) as a pale honey-colored oil. H NMR

5

(CDCl₃, 400.13 MHz, 25 °C): δ 8.735 (d, J(2,5) = 0.7 Hz, 2H;

pyH2), 8.441(d, ³J(6,5) = 5.3 Hz, 2H; pyH6), 7.581 (m, 2H;

phH3/6), 7.382 (m, 2H; phH4/5), 7.320 (dd, ³J(5,6) = 5.2 Hz,

⁵J(5,2) = 0.8 Hz, 2H; pyH5), 1.103 (m, 42H; CH(CH₃)₂). ¹³C NMR

(CDCl₃, 100.61 MHz, 25 °C): δ 153.3, 148.0, 133.0, 132.1, 128.8,

125.3, 125.2, 121.7, 102.0 (−C), 99.2 (−C), 95.8 (−C), 90.1

(−C), 18.6 (CH(CH₃)₂), 11.2 (CH(CH₃)₂). IR (thin film): 2941

(s), 2890 (m), 2863 (s), 2223 (w) (CC), 2155 (w) (CC), 1575

(s), 1462 (s), 1398 (s), 1283 (m), 1185 (m), 996 (m), 882 (s), 826

(s), 803 (s), 756 (s), 669 cm⁻¹(s). High res. ESI MS: m/z (%):

641.3736 (100) [M + H⁺]. Calcd for C₄₂H₅₃N₂Si₂, 641.3742.

1,2-Bis((3-((triisopropylsilyl)ethynyl)pyridin-2-yl)ethynyl)-

benzene (12c). According to general procedure A, 10c (0.729 g,

2.57 × 10⁻³mol), 11 (0.362 g, 1.10 × 10⁻³mol), and PdCl₂(PPh₃)₂

(0.050 g, 7.12 × 10⁻⁵mol) in Et₃N (20 mL), to which was added a

solution of CuI (0.050 g, 2.63 × 10⁻⁴mol) in Et₃N (10 mL), was

stirred for 21 days, and worked up to yield crude 12c. The product was

then chromatographed twice on neutral alumina (activity III), eluting

in both cases with CH₂Cl₂. The product thus obtained was stirred

briefly in 30 mL of Et₂O to which 0.560 g of NORIT A had been

added and then gravity filtered, and the solvent was distilled off at

atmospheric pressure on a water bath. Drying under vacuum at 70 °C/

0.001 mm Hg removed the last traces of Et₂O to yield 12c (0.491 g,

1,2-Bis((3-ethynylpyridin-4-yl)ethynyl)benzene (13b). Com-

pound 13b was obtained from the reaction of 12b (0.400 g, 6.24 ×

10⁻⁴mol) with [(n-Bu)₄N]F (1.0 M in THF; 2.0 mL, 2.0 × 10⁻³mol)

in THF (25 mL) to which 1 mL of H₂O had been added, after 2 days

according to the general deprotection procedure B. The residue that

1

70%) as a pale honey-colored glass. H NMR (CDCl₃, 400.13 MHz,

3

4

28 °C): δ 8.489 (dd, J(6,5) = 4.8 Hz, J(6,4) = 1.7 Hz, 2H; pyH6),

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The Journal of Organic Chemistry

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3

4

7.759 (dd, J(4,5) = 7.9 Hz, J(4,6) = 1.8 Hz, 2H; pyH4), 7.613

(m, 2H; phH3/6), 7.323 (m, 2H; phH4/5), 7.153 (dd, ³J(5,4) =

(−C), 82.0 (−C). UV−vis (CH₂Cl₂): λ_max(ε) = 260 (2.6 × 10⁴),

291sh (5.6 × 10⁴), 299sh (6.5 × 10⁴), 309 (9.2 × 10⁴), 318 (6.8 ×

10⁴), 340sh (2.2 × 10⁴), 352 (2.1 × 10⁴), 366 (1.1 × 10⁴), 380 nm

(1.5 × 10³M⁻¹cm⁻¹). IR: 3075 (vw), 3040 (vw), 2192 (w) (CC),

2177 (w) (CC), 1540 (m), 1488 (m), 1435 (m), 1414 (m), 1404

(s), 1105 (m), 803 (s), 761 (s), 753 (vs), 596 (s), 517 (s), 513 cm⁻¹

(s). High res. ESI MS: m/z (%): 327.0904 (36) [M + H⁺], 333.0985

(13) [M + Li⁺], 349.0720 (100) [M + Na⁺], 365.0494 (8) [M + K⁺],

675.1474 (54) [2M + Na⁺], 691.1218 (8) [2M + K⁺]. Calcd for

C₂₄H₁₁N₂, 327.0917; C₂₄H₁₀LiN₂, 333.0999; C₂₄H₁₀N₂Na, 349.0736;

C₂₄H₁₀KN₂, 365.0476; C₄₈H₂₀N₄Na, 675.1580; C₄₈H₂₀KN₄, 691.1320.

1,2-Bis((2-((triisopropylsilyl)ethynyl)pyridin-3-yl)ethynyl)-

benzene (12d). According to general procedure A, 10d (0.767 g,

2.71 × 10⁻³mol), 11 (0.425 g, 1.29 × 10⁻³mol), and PdCl₂(PPh₃)₂

(0.066 g, 9.40 × 10⁻⁵mol) in Et₃N (20 mL), to which was added a

solution of CuI (0.057 g, 2.99 × 10⁻⁴mol) in Et₃N (5 mL), were

stirred for 14 days and worked up to yield crude 12d. The product was

then chromatographed on a column of neutral alumina (activity III)

and then rechromatographed on a column of silica, eluting with

CH₂Cl₂in both cases. Drying under vacuum at 60 °C/0.001 mm Hg

and air drying yielded 12d (0.736 g, 89%) as a pale honey-colored

7.9 Hz, ³J(5,6) = 4.9 Hz, 2H; pyH5), 1.078 (m, 42H; CH(CH₃)₂). ¹³

C

NMR (CDCl₃, 100.61 MHz, 28 °C): δ 148.6, 144.9, 139.8, 132.9,

128.2, 125.2, 123.1, 121.8, 102.9 (−C), 98.5 (−C), 91.8 (−C),

90.9 (−C), 18.6 (CH(CH₃)₂), 11.3 (CH(CH₃)₂). IR (thin film):

2942 (s), 2891 (m), 2864 (s), 2222 (w) (CC), 2157 (w) (CC),

1462 (m), 1445 (m), 1416 (s), 1199 (m), 1097 (m), 993 (m), 882 (s),

797 (vs), 765 (vs), 752 (s), 678 (vs), 658 (vs), 639 (vs), 637 (vs), 628

cm⁻¹(vs). High res. ESI MS: m/z (%): 641.3782 (100) [M + H⁺],

647.3921 (30) [M + Li⁺], 663.3600 (50) [M + Na⁺], 679.3353 (11)

[M + K⁺]. Calcd for C₄₂H₅₃N₂Si₂, 641.3742; C₄₂H₅₂LiN₂Si₂, 647.3824;

C₄₂H₅₂N₂NaSi₂, 663.3561; C₄₂H₅₂KN₂Si₂, 679.3301.

1,2-Bis((3-ethynylpyridin-2-yl)ethynyl)benzene (13c). Ac-

cording to the general deprotection procedure B, 12c (0.459 g,

7.16 × 10⁻⁴mol) in THF (80 mL) to which 10 drops of H₂O had

been added, with [(n-Bu)₄N]F (1.0 M in THF; 1.5 mL, 1.5 × 10⁻³

mol), was stirred for 1 day at ambient temperature. A second aliquot of

[(n-Bu)₄N]F (1.5 mL) was added, and stirring was continued for a

further 12 h. The residue that remained after removal of the solvent

was partitioned between water (160 mL) and Et₂O (120 mL), and the

aqueous layer was extracted with a further 2 × 40 mL of Et₂O. The

combined organic extracts were further extracted with 4 × 80 mL of

water, then dried (anhydrous Na₂SO₄), and gravity filtered, and the

solvent was removed under reduced pressure at ambient temperature.

The product was then chromatographed on neutral alumina (activity III)

eluting with CH₂Cl₂to yield a pale honey-colored glass after removal

of the solvent by distillation on a water bath and drying under vacuum.

The glass was recrystallized from heptane and air-dried to afford 13c

1

viscous oil. H NMR (CDCl₃, 400.13 MHz, 24 °C): δ 8.522 (dd,

4

3

³J(6,5) = 4.8 Hz, J(6,4) = 1.5 Hz, 2H; pyH6), 7.764 (dd, J(4,5) =

4

7.8 Hz, J(4,6) = 1.6 Hz, 2H; pyH4), 7.560 (m, 2H; phH3/6), 7.351

3

(m, 2H; phH4/5), 7.154 (dd, J(5,4) = 7.9 Hz, J(5,6) = 4.8 Hz, 2H;

pyH5), 1.108 (m, 42H; CH(CH₃)₂). ¹³C NMR (CDCl₃, 100.61 MHz,

25 °C): δ 148.9, 144.3, 139.5, 131.8, 128.4, 125.6, 123.0, 122.1, 104.3

(−C), 96.2 (−C), 94.3 (−C), 90.0 (−C), 18.6 (CH-

(CH₃)₂), 11.3 (CH(CH₃)₂). IR (thin film): 2942 (s), 2889 (m), 2863

(s), 1547 (m), 1455 (s), 1412 (vs), 996 (s), 881 (vs), 875 (vs), 829

(s), 796 (vs), 766 (vs), 756 (vs), 720 (s), 676 (vs), 659 (vs), 636 cm⁻¹

(vs). High res. ESI MS: m/z (%): 641.3672 (100) [M + H⁺], 647.3662

(6) [M + Li⁺], 663.3450 (22) [M + Na⁺]. Calcd for C₄₂H₅₃N₂Si₂,

641.3742; C₄₂H₅₂LiN₂Si₂, 647.3824; C₄₂H₅₂N₂NaSi₂, 663.3561.

1,2-Bis((2-ethynylpyridin-3-yl)ethynyl)benzene (13d). Ac-

cording to the general deprotection procedure B, 12d (0.620 g,

9.67 × 10⁻⁴mol) in THF (80 mL) to which 10 drops of H₂O had

been added, with [(n-Bu)₄N]F (1.0 M in THF; 2.0 mL, 2.0 × 10⁻³

mol), was stirred for 1.5 days at ambient temperature. The residue that

remained after removal of the solvent was partitioned between water

(100 mL) and Et₂O (100 mL), and the aqueous layer was extracted

with a further 60 mL of Et₂O. The combined organic extracts were

further extracted with 3 × 50 mL of water, then dried (anhydrous

Na₂SO₄), and gravity filtered, and the solvent was removed under

reduced pressure at ambient temperature. The product was then

chromatographed on a column of silica, eluting with CH₂Cl₂, to yield a

honey-colored oil after removal of the solvent by distillation on a water

bath and air drying. The product was boiled in heptane (240 mL) to

which 0.1 g of NORIT A had been added and gravity filtered, and the

filtrate was left to stand for 24 h in the dark. The crystals that formed

were isolated by filtration under vacuum, washed with heptane, and

air-dried. The recrystallization procedure was repeated to afford 13d

(0.217 g, 68%). ¹H NMR (CDCl₃, 500.13 MHz, 25 °C): δ 8.546 (dd,

1

(0.200 g, 85%) as colorless needles. H NMR (CDCl₃, 400.13 MHz,

3

4

26 °C): δ 8.571 (dd, J(6,5) = 4.8 Hz, J(6,4) = 1.7 Hz, 2H; pyH6),

3

4

7.788 (dd, J(4,5) = 7.9 Hz, J(4,6) = 1.7 Hz, 2H; pyH4), 7.716 (m,

3

2H; phH3/6), 7.383 (m, 2H; phH4/5), 7.211 (dd, J(5,4) = 7.9 Hz,

³J(5,6) = 4.9 Hz, 2H; pyH5), 3.560 (s, 2H; −CCH). ¹³C NMR

(CDCl₃, 100.61 MHz, 26 °C): δ 149.0, 145.7, 139.5, 133.5, 128.9,

124.8, 122.4, 122.0, 91.7 (−C), 91.3 (−C), 85.0 (−C), 79.7

(−C). UV−vis (CH₂Cl₂): λ_max(ε) = 229 (4.0 × 10⁴), 244 (4.1 ×

10⁴), 287 (2.7 × 10⁴), 306 (2.2 × 10⁴), 328 (2.1 × 10⁴), 349 nm; sh (1.0 ×

10⁴M⁻¹cm⁻¹). IR (thin film): 3274 (s) (C−H), 3170 (s) (C−H),

3053 (m), 2217 (m) (CC), 2102 (m) (CC), 1549 (s), 1489 (s),

1447 (s), 1440 (s), 1414 (vs), 1093 (s), 1090 (s), 801 (vs), 760 (vs), 723

(vs), 671 (vs), 646 cm⁻¹(vs). High res. ESI MS: m/z (%): 329.1059 (100)

[M + H⁺], 335.1138 (74) [M + Li⁺], 351.0874 (13) [M + Na⁺]. Calcd for

C₂₄H₁₃N₂, 329.1073; C₂₄H₁₂LiN₂, 335.1156; C₂₄H₁₂N₂Na, 351.0893.

Anal. (%) calcd for C₂₄H₁₂N₂: C, 87.79; H, 3.68; N, 8.53. Found: C,

87.57; H, 3.65; N, 8.59.

Dehydro[2]pyrido[14]annulene (1c). A solution of 13c (0.085 g,

2.59 × 10⁻⁴mol) in toluene (43 mL) was added dropwise to a stirred

solution of anhydrous Cu₂OAc₄(1.880 g, 5.18 × 10⁻³mol) in pyridine

(567 mL) at 55 °C over 2.5 h. The reaction was stirred at the above

temperature for a further 0.6 h, and then, the reaction worked up as

described in the general macrocyclization procedure C. The aqueous

KCN suspension was extracted with CH₂Cl₂(5 × 30 mL), and the

combined organic extracts were dried (anhydrous Na₂SO₄) and gravity

filtered, and the solvent was removed under reduced pressure at

ambient temperature. The remaining solid was then dissolved in warm

CH₂Cl₂(60 mL) and successively chromatographed three times on

basic alumina (activity IV) in the absence of light, eluting with CH₂Cl₂

in all cases. The solvent was removed under vacuum from the eluate

containing 1c, at ambient temperature in darkness. The remaining

solid was suspended in MeCN (5 mL), briefly ultrasonicated, isolated

by filtration under vacuum, washed with MeCN (4 × 0.5 mL) and

then Et₂O (3 × 0.5 mL), and air-dried at ambient temperature to

constant mass to afford 1c (0.055 g, 65%) as an off-white

4

3

³J(6,5) = 4.9 Hz, J(6,4) = 1.7 Hz, 2H; pyH6), 7.861 (dd, J(4,5) =

4

8.0 Hz, J(4,6) = 1.7 Hz, 2H; pyH4), 7.641 (m, 2H; phH3/6), 7.394

3

(m, 2H; phH4/5), 7.268 (dd, J(5,4) = 8.0 Hz, J(5,6) = 4.8 Hz, 2H;

pyH5), 3.321 (s, 2H; −CCH). ¹³C NMR (CDCl₃, 125.76 MHz,

25 °C): δ 148.9, 143.8, 139.3, 132.5, 128.8, 125.1, 123.3, 122.7,

94.5 (−C), 89.4 (−C), 81.5 (−C), 81.2 (−C). UV−vis

(CH₂Cl₂): λ_max(ε) = 231 (5.5 × 10⁴), 240sh (5.0 × 10⁴), 286 (4.2 ×

10⁴), 306 (2.7 × 10⁴), 315 (2.6 × 10⁴), 326 nm; sh (2.3 × 10⁴M⁻¹

cm⁻¹). IR (thin film): 3276 (s) (C−H), 3231 (s) (C−H), 3044

(w), 2106 (s) (CC), 1548 (s), 1484 (s), 1456 (s), 1412 (vs), 1107

(s), 1093 (s), 808 (s), 797 (vs), 767 (vs), 756 (vs), 683 (s), 669 (s), 645

cm⁻¹(vs). High res. ESI MS: m/z (%): 329.1040 (100) [M + H⁺],

335.1119 (28) [M + Li⁺], 351.0850 (33) [M + Na⁺]. Calcd for

C₂₄H₁₃N₂, 329.1073; C₂₄H₁₂LiN₂, 335.1155; C₂₄H₁₂N₂Na, 351.0893.

Dehydro[2]pyrido[14]annulene (1d). A solution of 13d (0.085 g,

2.59 × 10⁻⁴mol) in toluene (43 mL) was added dropwise to a stirred

solution of anhydrous Cu₂OAc₄(1.880 g, 5.18 × 10⁻³mol) in pyridine

1

microcrystalline powder. H NMR (CDCl₃, 400.13 MHz, 24 °C): δ

3

4

8.768 (dd, J(6,5) = 4.7 Hz, J(6,4) = 1.3 Hz, 2H; pyH6), 8.125 (m,

3

4

2H; phH3/6), 7.916 (dd, J(4,5) = 8.0 Hz, J(4,6) = 1.4 Hz, 2H;

pyH4), 7.528 (m, 2H; phH4/5), 7.366 (dd, ³J(5,4) = 7.9 Hz, ³J(5,6) =

4.9 Hz, 2H; pyH5). ¹³C NMR (CDCl₃, 100.61 MHz, 26 °C): δ 149.5,

147.9, 137.1, 136.6, 129.0, 122.6, 121.9, 119.9, 92.7 (−C), 83.7

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(567 mL) at 55 °C over 2.3 h. The reaction was stirred at the above

temperature for a further 0.4 h, and then, the reaction was worked up

as described in the general macrocyclization procedure C. The

aqueous KCN suspension was filtered under vacuum, and the isolated

solid was washed with excess water and air-dried. The filtrate was

extracted with CH₂Cl₂(2 × 100 mL), and the combined organic

extracts were dried (anhydrous Na₂SO₄) and gravity filtered, and the

solvent was removed under reduced pressure at ambient temperature.

The residue was agitated with MeCN (5 mL), and the solvent was

decanted. The remaining solid was combined with that obtained from

the filtration and chromatographed on a column of basic alumina

(activity IV), which was completely shielded from the light, eluting

with CH₂Cl₂. The solvent was removed under vacuum from the eluate

containing 1d, at ambient temperature in darkness, to yield a solid that

was suspended in MeCN (5 mL). The mixture was briefly

ultrasonicated, isolated by filtration under vacuum, washed with

MeCN (3 × 1 mL), and air-dried at ambient temperature to constant

mass to afford 1d (0.061 g, 72%) as a white powder. ¹H NMR

(CDCl₃, 400.13 MHz, 26 °C): δ 8.687 (dd, ³J(6,5) = 4.7 Hz, ⁴J(6,4) =

1.4 Hz, 2H; pyH6), 8.163 (dd, ³J(4,5) = 8.0 Hz, ⁴J(4,6) = 1.5 Hz, 2H;

pyH4), 7.936 (m, 2H; phH3/6), 7.515 (m, 2H; phH4/5), 7.431 (dd,

reaction at −78 °C. The reaction was stirred at −78 °C for a further 3

h and then allowed to warm to ambient temperature with continued

stirring overnight. The reaction solution was extracted with dilute

aqueous Na₂S₂O₃(150 mL), and then water (2 × 200 mL). The

combined aqueous extracts were shaken with Et₂O (150 mL), and the

combined organic extracts dried (anhydrous Na₂SO₄), gravity filtered,

and the solvent distilled off at atmospheric pressure on a water bath.

The remaining brown oil was dried under vacuum and chromato-

graphed on silica eluting with CH₂Cl₂. The product thus obtained was

further chromatographed on three successive columns of silica, eluting

with 10% Et₂O/heptane to yield 16 (11.537 g, 91%) as a faintly pale

honey-colored oil after drying under vacuum. ¹H NMR (CDCl₃,

400.13 MHz, 25 °C): δ 8.541 (dd, ³J(6,5) = 4.6 Hz, ⁴J(6,4) = 1.5 Hz,

1H; H6), 8.124 (dd, J(4,5) = 8.0 Hz, J(4,6) = 1.5 Hz, 1H; H4),

6.935 (dd, ³J(5,4) = 8.0 Hz, ³J(5,6) = 4.8 Hz, 1H; H5), 1.183

(m, 21H; CH(CH₃)₂). ¹³C NMR (CDCl₃, 100.61 MHz, 25 °C): δ

148.8, 147.4, 146.0, 123.6, 106.4, 98.7, 96.4, 18.7 (CH(CH₃)₂), 11.3

(CH(CH₃)₂). IR (thin film): 2941 (s), 2889 (m), 2863 (s), 1558 (m),

1461 (m), 1406 (vs), 1259 (m), 1062 (m), 1007 (vs), 996 (m), 882

(s), 846 (vs), 788 (s), 752 (s), 674 cm⁻¹(vs). High res. ESI MS: m/z

(%): 386.0761 (100) [M + H⁺], 408.0560 (7) [M + Na⁺], 771.1620

(6) [2M + H⁺]. Calcd for C₁₆H₂₅INSi, 386.0795; C₁₆H₂₄INNaSi,

408.0615; C₃₂H₄₉I₂N₂Si₂, 771.1518.

3

4

3

³J(5,4) = 8.0 Hz, J(5,6) = 4.8 Hz, 2H; pyH5). ¹³C NMR (CDCl₃,

100.61 MHz, 25 °C): δ 148.9, 141.8, 139.8, 136.2, 128.6, 126.6, 122.7,

96.2 (−C), 90.6 (−C), 85.1 (−C), 80.2 (−C). UV−vis

(CH₂Cl₂): λ_max(ε) = 299 (7.7 × 10⁴), 309 (7.8 × 10⁴), 318 (8.8 × 10⁴),

343sh (2.1 × 10⁴), 353 (1.5 × 10⁴), 370 nm (1.4 × 10⁴M⁻¹cm⁻¹). IR:

3068 (w), 3034 (vw), 2182 (vw) (CC), 2154 (w) (CC), 1543

(m), 1492 (m), 1407 (m), 1106 (m), 802 (m), 754 (vs), 650 cm⁻¹(m).

EI MS m/z (%): 326.1 (100) [M⁺]. High res. ESI MS: m/z (%):

327.0954 (100) [M + H⁺]. Calcd for C₂₄H₁₁N₂, 327.0917.

2-((Triisopropylsilyl)ethynyl)-3-((trimethylsilyl)ethynyl)-

pyridine (17). To 16 (8.404 g, 2.18 × 10⁻²mol) and PdCl₂(PPh₃)₂

(0.350 g, 4.99 × 10⁻⁴mol) under argon were added N₂-purged Et₃N

(150 mL) and trimethylsilylacetylene (3.684 g, 3.75 × 10⁻²mol)

consecutively by syringe. In a separate Schlenk filled with argon, a solu-

tion of CuI (0.251 g, 1.32 × 10⁻³mol) in N₂-purged Et₃N (15 mL)

was prepared and syringed into the above reaction, which resulted in

an immediate color change from orange to dark gray. The mixture was

stirred at ambient temperature in the dark for 9 days, and then, all

solvent was removed under reduced pressure on a water bath. The

residue was stirred with pentane (120 mL) and gravity filtered. The

remaining solid was washed with pentane (4 × 40 mL), and the

combined extracts and filtrate were stripped of solvent by distillation

on a water bath at atmospheric pressure. The remaining oil was

chromatographed on silica with CH₂Cl₂, and the product thus

obtained was dissolved in MeCN (30 mL), briefly stirred with NORIT

A (0.2 g), and gravity filtered. The filtrate was evaporated to dryness

under vacuum on a water bath to afford 17 (7.575 g, 98%) as a light

3-Bromo-2-((triisopropylsilyl)ethynyl)pyridine (15). To 14

(5.00 g, 2.11 × 10⁻²mol) and PdCl₂(PPh₃)₂(0.125 g, 1.78 × 10⁻⁴

mol) under argon were added consecutively by syringe N₂-purged

Et₃N (80 mL) and triisopropylsilylacetylene (4.023 g, 2.21 ×

10⁻²mol), and the reaction was stirred for 0.2 h in an ice bath. A

solution of CuI (0.114 g, 5.99 × 10⁻⁴mol) in N₂-purged Et₃N (6 mL)

was prepared in a separate Schlenk under argon and syringed into the

reaction mixture. Stirring was maintained at 0−5 °C for 5 h and then

at ambient temperature in the dark for 7 days. All solvent was then

removed under reduced pressure on a water bath, and the residue was

extracted with pentane (5 × 40 mL). The combined pentane extracts

were gravity filtered, and the solvent was distilled off on a water bath at

atmospheric pressure. The remaining oil was purified by distillation

under vacuum to yield 15 (5.984 g, 84%) as a pale-pink oil, which

distilled at 136−139 °C/0.030 mm Hg. ¹H NMR (CDCl₃, 400.13 MHz,

25 °C): δ 8.514 (dd, ³J(6,5) = 4.6 Hz, ⁴J(6,4) = 1.4 Hz, 1H; H6), 8.891

(dd, ³J(4,5) = 8.2 Hz, ⁴J(4,6) = 1.4 Hz, 1H; H4), 7.100 (dd, ³J(5,4) = 8.2

1

straw-colored oil. H NMR (CDCl₃, 400.13 MHz, 25 °C): δ 8.503

(dd, ³J(6,5) = 4.9 Hz, ⁴J(6,4) = 1.7 Hz, 1H; H6), 7.756 (dd, ³J(4,5) =

4

7.8 Hz, J(4,6) = 1.7 Hz, 1H; H4), 7.161 (dd, ³J(5,4) = 7.9 Hz,

³J(5,6) = 4.9 Hz, 1H; H5), 1.173 (m, 21H; CH(CH₃)₂), 0.250 (s, 9H;

Si(CH₃)₃).

1,3-Bis((4-((triisopropylsilyl)ethynyl)pyridin-3-yl)ethynyl)-

benzene (19a). According to the general procedure A, 10a (0.600 g,

2.12 × 10⁻³mol), 18 (0.350 g, 1.06 × 10⁻³mol), and PdCl₂(PPh₃)₂

(0.100 g, 1.42 × 10⁻⁴mol) in Et₃N (30 mL), to which was added a

solution of CuI (0.100 g, 5.25 × 10⁻⁴mol) in Et₃N (6 mL), was stirred

for 15 days and worked up to yield crude 19a. The product was then

chromatographed on three successive columns of neutral alumina

(activity III), with CH₂Cl₂as the eluant. Removal of the solvent by

distillation on a water bath at atmospheric pressure, drying under

vacuum at 60 °C/0.001 mm Hg, and air drying yielded 19a (0.490 g,

3

Hz, J(5,6) = 4.6 Hz, 1H; H5), 1.169 (m, 21H; CH(CH₃)₂). ¹³C NMR

(CDCl₃, 100.61 MHz, 25 °C): δ 148.0, 143.4, 139.9, 124.1, 123.6, 103.6

(−C), 97.8 (−C), 18.6 (CH(CH₃)₂), 11.2 (CH(CH₃)₂). IR (thin

film): 2942 (s), 2891 (m), 2864 (s), 1564 (m), 1462 (m), 1411 (vs),

1261 (m), 1062 (s), 1019 (s), 996 (s), 882 (vs), 850 (vs), 789 (s), 752

(vs), 694 (vs), 674 (vs), 659 (vs), 629 cm⁻¹(vs). High res. ESI MS: m/z

(%): 338.0948 (100) [M + H⁺], 360.0761 (24) [M + Na⁺]. Calcd for

C₁₆H₂₅BrNSi, 338.0934; C₁₆H₂₄BrNNaSi, 360.0754.

3-Iodo-2-((triisopropylsilyl)ethynyl)pyridine (16). To a dried,

argon-filled 1 L two-necked flask fitted with an alcohol thermometer,

vacuum/argon inlet adaptor, and rubber septum and containing 15

(11.087 g, 3.28 × 10⁻²mol) was added Et₂O (380 mL) via syringe.

The stirred solution was cooled to −78 °C (acetone/CO₂bath), and

1.6 M n-BuLi (23 mL, 3.68 × 10⁻²mol) was added by syringe at a rate

that maintained the internal temperature between −78 and −70 °C,

and the resulting orange solution was stirred at −78 to −75 °C for 1.5

h. In a separate dried Schlenk was prepared a solution of 1,2-

diiodoethane (13.00 g, 4.61 × 10⁻²mol) in Et₂O (50 mL) under

argon, and this was syringed into the lithiopyridine reaction solution at

a rate that ensured that the internal temperature did not rise above

−70 °C, and the reaction was stirred at −78 °C for 2 h. A solution of

iodine (1.00 g, 7.88 × 10⁻³mol) in Et₂O (10 mL) was also prepared in

a dried, argon-filled Schlenk and added dropwise via syringe to the

1

72%) as a pale honey-colored viscous oil. H NMR (CDCl₃, 400.13

3

MHz, 25 °C): δ 8.750 (s, 2H; pyH2), 8.481 (d, J(6,5) = 5.1 Hz, 2H;

pyH6), 7.755 (td, ⁴J(2,4/2,6) = 1.4 Hz, ⁵J(2,5) = 0.5 Hz, 1H; phH2),

3

4

7.519 (dd, J(4,5/6,5) = 7.8 Hz, J(4,2/6,2) = 1.6 Hz, 2H; phH4/6),

3

5

7.364 (dd, J(5,6) = 5.1 Hz, J(5,2) = 0.7 Hz, 2H; pyH5), 7.353 (td,

³J(5,4/5,6) = 7.6 Hz, J(5,2) = 0.6 Hz, 1H; phH5), 1.128 (m, 42H;

5

CH(CH₃)₂). ¹³C NMR (CDCl₃, 100.61 MHz, 26 °C): δ 152.6, 148.1,

135.2, 133.2, 131.8, 128.4, 125.8, 123.0, 121.7, 102.5 (−C), 101.5

(−C), 94.8 (−C), 85.9 (−C), 18.6 (CH(CH₃)₂), 11.2

(CH(CH₃)₂). IR (thin film): 2941 (s), 2891 (m), 2864 (s), 1572

(s), 1485 (s), 1462 (s), 1399 (s), 996 (m), 882 (vs), 863 (vs), 842

(vs), 832 (vs), 794 (vs), 679 (vs), 663 (vs), 641 cm⁻¹(vs). High res.

ESI MS: m/z (%): 641.3666 (100) [M + H⁺]. Calcd for C₄₂H₅₃N₂Si₂,

641.3742.

138

dx.doi.org/10.1021/jo201595s|J. Org. Chem. 2012, 77, 126−142

The Journal of Organic Chemistry

Article

3

1,3-Bis((4-ethynylpyridin-3-yl)ethynyl)benzene (20a). Ac-

cording to the general deprotection procedure B, 19a (0.430 g,

6.71 × 10⁻⁴mol) in THF (25 mL) to which H₂O (1 mL) had been

added, with [(n-Bu)₄N]F (1.0 M in THF; 2.2 mL, 2.2 × 10⁻³mol),

was stirred at ambient temperature for 3 days. The residue that

remained after removal of the solvent was partitioned between water

(150 mL) and CH₂Cl₂(150 mL) and extracted further with CH₂Cl₂

(2 × 150 mL). The combined organic extracts were extracted with

water (100 mL), dried (anhydrous MgSO₄), gravity filtered, and

concentrated to 20 mL by distillation on a water bath. The concentrate

was chromatographed on neutral alumina (activity III), eluting with

CH₂Cl₂, and the product thus isolated was recrystallized from heptane

as described for the purification of 13d above to afford 20a (0.105 g,

7.360 (d, J(5,6) = 5.0 Hz, 2H; pyH5), 1.132 (m, 42H; CH(CH₃)₂).

¹³C NMR (CDCl₃, 100.61 MHz, 24 °C): δ 153.3, 148.0, 135.4, 132.9,

132.3, 128.5, 125.0, 122.7, 122.0, 102.0 (−C), 99.1 (−C), 96.2

(−C), 86.6 (−C), 18.6 (CH(CH₃)₂), 11.3 (CH(CH₃)₂). IR (thin

film): 2942 (s), 2891 (m), 2863 (s), 2218 (m) (CC), 2159 (m)

(CC), 1574 (s), 1488 (s), 1462 (s), 1413 (m), 1399 (m), 1190 (m),

994 (s), 882 (vs), 862 (m), 839 (m), 826 (vs), 797 (vs), 730 (m), 680

(vs), 669 (vs), 656 (vs) cm⁻¹. High res. ESI MS: m/z (%): 641.3727

(100) [M + H⁺]. Calcd for C₄₂H₅₃N₂Si₂, 641.3742.

1,3-Bis((3-ethynylpyridin-4-yl)ethynyl)benzene (20b). Ac-

cording to the general deprotection procedure B, 19b (0.270 g,

4.21 × 10⁻⁴mol) in THF (25 mL) to which H₂O (1 mL) had been

added, with [(n-Bu)₄N]F (1.0 M in THF; 1.4 mL, 1.4 × 10⁻³mol),

was stirred at ambient temperature for 3 days. The residue that

remained after removal of the solvent was partitioned between water

(150 mL) and CH₂Cl₂(150 mL) and extracted further with CH₂Cl₂

(2 × 150 mL). The combined organic extracts were extracted with

water (100 mL), dried (anhydrous Na₂SO₄), gravity filtered, and

concentrated to 20 mL by distillation on a water bath. The concentrate

was chromatographed on neutral alumina (activity III), eluting with

CH₂Cl₂, and the product thus isolated was recrystallized from heptane

as described for the purification of 13d above to afford 20b (0.107 g,

1

48%) as a crystalline cream solid after air drying. H NMR (CDCl₃,

3

400.13 MHz, 23 °C): δ 8.784 (s, 2H; pyH2), 8.518 (d, J(6,5) = 5.1

Hz, 2H; pyH6), 7.777 (t, ⁴J(2,4/2,6) = 1.5 Hz, 1H; phH2), 7.578 (dd,

4

³J(4,5/6,5) = 7.8 Hz, J(4,2/6,2) = 1.4 Hz, 2H; phH4/6), 7.393 (m,

3H; phH5/pyH5), 3.596 (s, 2H; −CCH). ¹³C NMR (CDCl₃,

100.61 MHz, 26 °C): δ 152.4, 148.3, 134.9, 132.2, 132.1, 128.7, 125.7,

123.0, 122.1, 95.3 (−C), 85.8 (−C), 85.5 (−C), 79.7 (−C).

UV−vis (CH₂Cl₂): λ_max(ε) = 242 (5.6 × 10⁴), 280sh (3.4 × 10⁴),

287sh (3.7 × 10⁴), 295 (4.2 × 10⁴), 316 (3.4 × 10⁴), 325 nm (3.4 ×

10⁴M⁻¹cm⁻¹). IR (thin film): 3121 (s) (C−H), 2219 (w) (CC),

2097 (s) (CC), 1579 (s), 1567 (s), 1478 (s), 1399 (s), 1050 (s),

896 (s), 829 (vs), 795 (vs), 754 (vs), 731 (s), 683 cm⁻¹(vs). High res.

ESI MS: m/z (%): 329.1070 (100) [M + H⁺], 351.0911 (11) [M +

Na⁺]. Calcd for C₂₄H₁₃N₂, 329.1073; C₂₄H₁₂N₂Na, 351.0893.

1

77%) as a crystalline cream solid after air drying. H NMR (CDCl₃,

400.13 MHz, 27 °C): δ 8.768 (d, ⁵J(2,5) = 0.7 Hz, 2H; pyH2), 8.554

3

4

(d, J(6,5) = 5.3 Hz, 2H; pyH6), 7.795 (t, J(2,4/2,6) = 1.5 Hz, 1H;

3

4

phH2), 7.613 (dd, J(4,5/6,5) = 7.8 Hz, J(4,2/6,2) = 1.6 Hz, 2H;

phH4/6), 7.421 (t, ³J(5,4/5,6) = 8.0 Hz, 1H; phH5), 7.393 (dd,

³J(5,6) = 5.2 Hz, J(5,2) = 0.8 Hz, 2H; pyH5), 3.499 (s, 2H; −C

5

Dehydro[2]pyrido[15]annulene (2a). A solution of 20a (0.060 g,

1.83 × 10⁻⁴mol) in toluene (30 mL) was added dropwise to a stirred

solution of anhydrous Cu₂OAc₄(1.330 g, 3.66 × 10⁻³mol) in pyridine

(400 mL) at 55 °C over 2 h. The reaction was stirred at the above

temperature for a further 1 h, and then, the reaction worked up as

described in the general macrocyclization procedure C. The aqueous

KCN suspension was extracted with CH₂Cl₂(3 × 250 mL), and the

combined organic extracts were dried (anhydrous Na₂SO₄) and

gravity filtered, and the solvent removed under vacuum at ambient

temperature. The remaining solid was stirred in hot CH₂Cl₂(60 mL)

and twice chromatographed on neutral alumina (activity III) with

CH₂Cl₂as the eluant. The product thus obtained was suspended in

ice-cold CH₂Cl₂(6 mL), briefly ultrasonicated, isolated by filtration

under vacuum, washed with ice-cold CH₂Cl₂(3 × 1 mL), and air-dried

at ambient temperature to constant mass to afford 2a (0.033 g, 55%)

as a pale yellow solid. ¹H NMR (CDCl₃, 400.13 MHz, 25 °C): δ 8.701

CH). ¹³C NMR (CDCl₃, 100.61 MHz, 25 °C): δ 153.2, 148.7, 135.3,

133.4, 132.8, 128.8, 124.9, 122.6, 120.7, 96.7 (−C), 86.2 (−C),

84.2 (−C), 79.2 (−C). UV−vis (CH₂Cl₂): λ_max(ε) = 228 (4.1 ×

10⁴), 246 (4.7 × 10⁴), 300 (4.7 × 10⁴), 313 nm; sh (4.0 × 10⁴M⁻¹cm⁻¹).

IR (thin film): 3219 (m) (C−H), 3148 (m) (C−H), 3032 (w),

2215 (m) (CC), 2097 (m) (CC), 1593 (m), 1578 (s), 1528 (m),

1487 (m), 1404 (m), 1399 (m), 1188 (m), 1049 (m), 943 (s), 904 (s),

836 (vs), 795 (vs), 704 (s), 681 cm⁻¹(vs). High res. ESI MS: m/z

(%): 329.1065 (100) [M + H⁺]. Calcd for C₂₄H₁₃N₂, 329.1073.

Dehydro[2]pyrido[15]annulene (2b). A solution of 20b (0.075 g,

2.28 × 10⁻⁴mol) in toluene (30 mL) was added dropwise to a

stirred solution of anhydrous Cu₂OAc₄(1.680 g, 4.62 × 10⁻³mol) in

pyridine (500 mL) at 55 °C over 1.25 h. The reaction was stirred at

the above temperature for a further 0.25 h and worked up as described

in the general macrocyclization procedure C. The aqueous KCN

suspension was filtered under vacuum, and the isolated solid was

washed with excess distilled water and air-dried. The crude product

was then stirred with warm CH₂Cl₂(30 mL) and chromatographed in

the dark on silica with CH₂Cl₂as the eluant. The solid thus isolated

was washed successively with Et₂O and MeCN, air-dried, and

rechromatographed on silica with CH₂Cl₂. The product was then

chromatographed on a short column of basic alumina (activity III)

completely shielded from the light, eluting with CH₂Cl₂. All solvent

was removed from the eluate containing 2b under vacuum at ambient

temperature in darkness. The remaining solid was suspended in

MeCN (5 mL), briefly ultrasonicated, isolated by filtration under

vacuum, washed with MeCN (4 × 0.5 mL) and then Et₂O (3 ×

0.5 mL), and air-dried at ambient temperature to constant mass to

afford 2b (0.043 g, 58%) as an amorphous white powder. The product

5

(d, J(2,5) = 0.7 Hz, 2H; pyH2), 8.652 (m, 1H; phH2), 8.549 (d,

3

5

³J(6,5) = 5.1 Hz, 2H; pyH6), 7.400 (dd, J(5,6) = 5.1 Hz, J(5,2) =

0.8 Hz, 2H; pyH5), 7.368 (m, 3H; phH4/6, phH5). ¹³C NMR

(CDCl₃, 100.61 MHz, 26 °C): δ 150.4, 148.5, 145.4, 133.1, 129.0,

127.9, 125.5, 123.4, 123.1, 99.5 (−C), 89.1 (−C), 81.4 (−C),

81.2 (−C). UV−vis (CH₂Cl₂): λ_max(ε) = 284 (9.3 × 10⁴), 303sh

(5.4 × 10⁴), 331 (2.1 × 10⁴), 353 (9.0 × 10³), 376 (3.9 × 10³), 401 nm

(2.0 × 10³M⁻¹cm⁻¹). IR: 3045 (vw), 3009 (vw), 2199 (m) (CC),

1569 (s), 1520 (m), 1482 (m), 1409 (s), 1395 (m), 1264 (m), 892

(m), 830 (vs), 803 (s), 789 (vs), 746 (m), 726 (m), 676 cm⁻¹(s). EI

MS m/z (%): 326.1 (100) [M⁺]. High res. ESI MS: m/z (%):

327.0873 (100) [M + H⁺]. Calcd for C₂₄H₁₁N₂, 327.0917.

1,3-Bis((3-((triisopropylsilyl)ethynyl)pyridin-4-yl)ethynyl)-

benzene (19b). According to general procedure A, 10b (0.600 g,

2.12 × 10⁻³mol), 18 (0.350 g, 1.06 × 10⁻³mol), and PdCl₂(PPh₃)₂

(0.140 g, 1.99 × 10⁻⁴mol) in Et₃N (30 mL), to which was added a

solution of CuI (0.140 g, 7.40 × 10⁻⁴mol) in Et₃N (6 mL), were

stirred for 21 days and worked up to yield crude 19b. The product was

then chromatographed on silica, first with CH₂Cl₂as the eluant, and

then, the solvent polarity was increased from 0.5−1% MeOH/CH₂Cl₂

to elute the 19b. Removal of the solvent by distillation on a water bath

at atmospheric pressure, drying under vacuum at 60 °C/0.001 mm Hg,

and air drying yielded 19b (0.316 g, 46%) as a pale honey-colored

1

can be recrystallized from MeCN. H NMR (CDCl₃, 400.13 MHz,

27 °C): δ 8.758 (s, 2H; pyH2), 8.731 (s, 1H; phH2), 8.557 (d, ³J(6,5) =

3

5.1 Hz, 2H; pyH6), 7.406 (m, 3H; phH4/6, phH5), 7.282 (d, J(5,6) =

5.3 Hz, 2H; pyH5). ¹³C NMR (CDCl₃, 100.61 MHz, 23 °C): δ 152.6,

149.2, 146.2, 134.8, 129.1, 129.0, 123.1, 122.8, 122.2, 100.5 (−C),

89.9 (−C), 80.9 (−C), 80.5 (−C). UV−vis (CH₂Cl₂): λ_max

(ε) = 292 (1.1 × 10⁵), 326sh (2.9 × 10⁴), 339 (2.0 × 10⁴), 363 (1.0 ×

10⁴), 374 (9.3 × 10³), 393 nm (9.3 × 10³M⁻¹cm⁻¹). IR: 3050 (m),

3014 (m), 2199 (s) (CC), 2159 (m) (CC), 1582 (vs), 1573 (vs),

1520 (m), 1487 (s), 1411 (s), 1396 (s), 1262 (m), 1186 (m), 898 (s),

828 (s), 785 (s), 747 (m), 679 (s), 672 (m), 576 cm⁻¹(s). EI MS

m/z (%): 326.0 (100) [M⁺]. High res. ESI MS: m/z (%): 327.0909

(100) [M + H⁺], 333.1003 (19) [M + Li⁺], 349.0806 (9) [M + Na⁺].

1

viscous oil. H NMR (CDCl₃, 400.13 MHz, 25 °C): δ 8.742 (s, 2H;

pyH2), 8.503 (d, ³J(6,5) = 5.1 Hz, 2H; pyH6), 7.762 (t, ⁴J(2,4/2,6) =

3

4

1.4 Hz, 1H; phH2), 7.547 (dd, J(4,5/6,5) = 7.7 Hz, J(4,2/6,2) =

3

1.7 Hz, 2H; phH4/6), 7.375 (t, J(5,4/5,6) = 7.7 Hz, 1H; phH5),

139

dx.doi.org/10.1021/jo201595s|J. Org. Chem. 2012, 77, 126−142

The Journal of Organic Chemistry

Article

Calcd for C₂₄H₁₁N₂, 327.0917; C₂₄H₁₀LiN₂, 333.0999; C₂₄H₁₀N₂Na,

349.0736.

Dehydro[3]pyrido[15]annulene (3). A solution of 23 (0.067 g,

2.03 × 10⁻⁴mol) in toluene (30 mL) was added dropwise to a stirred

solution of anhydrous Cu₂OAc₄(1.880 g, 5.18 × 10⁻³mol) in pyridine

(567 mL) at 55 °C over 0.7 h. The reaction was stirred at the above

temperature for a further 0.25 h and worked up as described in the

general macrocyclization procedure C. The aqueous KCN suspension

was filtered under vacuum, and the isolated dark brown/black solid

was washed with excess distilled water and air-dried. The aqueous

filtrate was extracted with CH₂Cl₂(4 × 60 mL). The solid was

ultrasonicated with hot CH₂Cl₂(100 mL) and filtered under gravity.

The CH₂Cl₂extracts and filtrate were combined, and the solvent was

removed under reduced pressure at ambient temperature. The

remaining grayish-colored solid was dissolved in CH₂Cl₂(25 mL)

and chromatographed in the dark on basic alumina (activity IV) with

CH₂Cl₂as the eluant. All solvent was removed from the eluate

containing 3 under vacuum at ambient temperature in darkness. The

remaining solid was suspended in MeCN (5 mL), briefly ultra-

sonicated, isolated by filtration under vacuum, washed with MeCN

(4 × 0.5 mL) and then Et₂O (3 × 0.5 mL), and air-dried at ambient

temperature to constant mass to afford 3 (0.024 g, 36%) as a lemon-

2,6-Bis((4-((triisopropylsilyl)ethynyl)pyridin-3-yl)ethynyl)-

pyridine (22). According to general procedure A, 10a (0.700 g,

2.47 × 10⁻³mol), 21 (0.290 g, 1.22 × 10⁻³mol), and PdCl₂(PPh₃)₂

(0.064 g, 9.12 × 10⁻⁵mol) in Et₃N (25 mL), to which was added a

solution of CuI (0.063 g, 3.31 × 10⁻⁴mol) in Et₃N (7 mL), were

stirred for 21 days. After the solvent was removed, the residue was

extracted with hot heptane (5 × 30 mL), the combined extracts were

gravity filtered, and the solvent was removed under reduced pressure

on a water bath to yield crude 22. The product was then twice

chromatographed on basic alumina (activity IV) and then on a short

column of neutral alumina (activity III) with CH₂Cl₂as the eluant.

Removal of the solvent by distillation on a water bath at atmospheric

pressure, drying under vacuum at 60 °C/0.001 mm Hg, and air drying

yielded 22 (0.608 g, 77%) as a pale honey-colored vitreous semisolid.

¹H NMR (CDCl₃, 400.13 MHz, 25 °C): δ 8.821 (d, ⁵J(2,5) = 0.5 Hz,

3

2H; terminal pyH2), 8.514 (d, J(6,5) = 5.1 Hz, 2H; terminal pyH6),

3

7.688 (t, J(4,3/4,5) = 7.9 Hz, 1H; central pyH4), 7.490 (d, J(3,4/

3

5,4) = 7.9 Hz, 2H; central pyH3/5), 7.370 (dd, J(5,6) = 5.1 Hz,

1

⁵J(5,2) = 0.7 Hz, 2H; terminal pyH5), 1.127 (m, 42H; CH(CH₃)₂).

¹³C NMR (CDCl₃, 100.61 MHz, 25 °C): δ 153.0, 148.7, 143.3, 136.1,

133.5, 126.7, 125.7, 120.9, 102.3 (−C), 101.9 (−C), 94.2

(−C), 85.2 (−C), 18.6 (CH(CH₃)₂), 11.2 (CH(CH₃)₂). IR (thin

film): 2941 (s), 2889 (m), 2863 (s), 1571 (s), 1556 (s), 1479 (s),

1462 (m), 1441 (vs), 1399 (m), 1158 (m), 996 (m), 881 (s), 864 (s),

842 (vs), 806 (s), 797 (s), 752 (m), 677 (vs), 663 (vs), 641 cm⁻¹(s).

High res. ESI MS: m/z (%): 642.3621 (100) [M + H⁺], 648.3700 (79)

[M + Li⁺], 664.3437 (4) [M + Na⁺]. Calcd for C₄₁H₅₂N₃Si₂,

642.3694; C₄₁H₅₁LiN₃Si₂, 648.3777; C₄₁H₅₁N₃NaSi₂, 664.3514.

2,6-Bis((4-ethynylpyridin-3-yl)ethynyl)pyridine (23). Accord-

ing to the general deprotection procedure B, 22 (0.570 g, 8.88 × 10⁻⁴

mol) in THF (40 mL) to which 6 drops of H₂O had been added, with

[(n-Bu)₄N]F (1.0 M in THF; 1.8 mL, 1.8 × 10⁻³mol), was stirred at

ambient temperature for 1 day. The residue that remained after

removal of the solvent was shaken with Et₂O (2 × 80 mL), and the

extracts were decanted off. Distilled water (60 mL) was then added to

the residue, and the suspended solid was isolated by filtration under

vacuum, washed with excess water, and air-dried. The Et₂O extracts

were shaken with water (100 mL), dried (anhydrous Na₂SO₄), and

gravity filtered, and the solvent was removed by distillation on a water

bath. Pentane (60 mL) was then added to the remaining oil, which

caused precipitation of a solid, after which the pentane was decanted

off. All isolated solids were combined and chromatographed on basic

alumina (activity IV) eluting with CH₂Cl₂. The product isolated from

the chromatography was dissolved in boiling methylcyclohexane

(300 mL) and gravity filtered, and all solvent removed under reduced

pressure on a water bath. Decolorizing carbon (NORIT A) and

CH₂Cl₂(10 mL) were added to the product, and the mixture briefly

stirred and gravity filtered, and all solvent removed from the

filtrate by distillation under reduced pressure at ambient temperature.

The product was then suspended in MeCN (5 mL), briefly

ultrasonicated, filtered under vacuum, and washed with MeCN (3 ×

1 mL) to afford 23 (0.161 g, 55%) as a microcrystalline cream powder

yellow micofibrous solid. H NMR (CDCl₃, 400.13 MHz, 26 °C): δ

8.688 (s, 2H; terminal pyH2), 8.556 (d, ³J(6,5) = 5.1 Hz, 2H; terminal

3

pyH6), 7.679 (t, J(4,3/4,5) = 7.8 Hz, 1H; central pyH4), 7.371 (d,

3

³J(5,6) = 5.1 Hz, 2H; terminal pyH5), 7.311 (d, J(3,4/5,4) = 7.8 Hz,

2H; central pyH3/5). ¹³C NMR (CDCl₃, 100.61 MHz, 26 °C): δ 150.5,

149.2, 144.0, 137.3, 134.8, 125.5, 123.5, 122.7, 99.1 (−C), 86.7 (−C),

82.9 (−C), 80.1 (−C). UV−vis (CH₂Cl₂): λ_max(ε) = 275 (6.4 ×

10⁴), 293 (6.1 × 10⁴), 307 (8.3 × 10⁴), 324sh (2.1 × 10⁴), 338 (2.1 × 10⁴),

377 (3.2 × 10³), 405 nm (1.2 × 10³M⁻¹cm⁻¹). IR: 3051 (w), 3008 (vw),

2160 (w) (CC), 2139 (w) (CC), 1586 (m), 1573 (s), 1552 (m),

1474 (s), 1447 (m), 1411 (s), 1269 (m), 1152 (m), 980 (m), 833 (s), 827

(s), 802 (vs), 747 (m), 729 (m), 579 (s), 557 cm⁻¹(s). EI MS m/z (%):

327.1 (100) [M⁺]. High res. ESI MS: m/z (%): 328.0845 (62) [M + H⁺],

334.0927 (66) [M + Li⁺], 350.0661 (100) [M + Na⁺], 677.1476 (18)

[2M + Na⁺]. Calcd for C₂₃H₁₀N₃, 328.0869; C₂₃H₉LiN₃, 334.0951;

C₂₃H₉N₃Na, 350.0689; C₄₆H₁₈N₆Na, 677.1485.

ASSOCIATED CONTENT

* Supporting Information

■

S

Synthesis of dehydro[m]pyrido[14]- and [15]annulenes 1a−d,

2a,b, and 3; general experimental; spectroscopic character-

ization of macrocycles 1a−d, 2a,b, and 3 and precursors 12a−d

1

and 13a−d; H NMR investigation of solution aggregation of

1a; ¹H and ¹³C NMR solution spectra of 1a−d, 2a,b, 3, 12a−d,

13a−d, 15−17, 19a,b, 20a,b, 22, and 23; UV−vis spectroscopic

properties of precursors 13a−d, 20a,b, and 23 and UV−vis

absorption spectra of 1a−d, 2a,b, and 3 with Hg(CF₃SO₃)₂;

general X-ray experimental, crystallographic data, and ORTEP

representations for 1b and 1c; HOMO and LUMO plots of

1c,d and 2b; linear regression through origin of optical bandgap

vs calculated bandgap for 1a−1d, 2a,b, and 3; calculated

structure Cartesian coordinates of 1a−d, 2a,b, and 3; and

references (continued). This material is available free of charge

via the Internet at http://pubs.acs.org.

1

after air drying. H NMR (CDCl₃, 400.13 MHz, 26 °C): δ 8.855 (d,

⁵J(2,5) = 0.5 Hz, 2H; terminal pyH2), 8.558 (d, ³J(6,5) = 5.3 Hz, 2H;

3

pyH6), 7.745 (t, J(4,3/4,5) = 7.8 Hz, 1H; central pyH4), 7.576 (d,

AUTHOR INFORMATION

Corresponding Author

*E-mail: paul.baxter@ics-cnrs.unistra.fr.

³J(3,4/5,4) = 7.7 Hz, 2H; central pyH3/5), 7.412 (d, ³J(5,6) = 5.1 Hz,

2H; terminal pyH5), 3.612 (s, 2H; −CCH). ¹³C NMR (CDCl₃,

100.61 MHz, 26 °C): δ 152.9, 148.9, 143.3, 136.6, 132.6, 127.3, 125.8,

121.2, 94.5 (−C), 86.3 (−C), 84.9 (−C), 79.5 (−C). UV−

vis (CH₂Cl₂): λ_max(ε) = 228 (4.3 × 10⁴), 238 (4.4 × 10⁴), 278 (2.3 ×

10⁴), 321 (2.9 × 10⁴), 330 nm (3.1 × 10⁴M⁻¹cm⁻¹). IR (thin film):

3301 (m) (C−H), 3189 (m) (C−H), 3008 (w), 2102 (m) (C

C), 1570 (s), 1557 (s), 1476 (m), 1440 (s), 1396 (m), 1206 (m), 983

(m), 845 (s), 827 (s), 804 (s), 758 (m), 752 (s), 726 (s), 654 (s), 617

cm⁻¹(s). High res. ESI MS: m/z (%): 330.1007 (100) [M + H⁺],

659.1911 (7) [2M + H⁺]. Calcd for C₂₃H₁₂N₃, 330.1026; C₄₆H₂₃N₆,

659.1979.

■

ACKNOWLEDGMENTS

The Centre National de la Recherche Scientifique and the

Institut Charles Sadron are acknowledged for financial support

■

(P.N.W.B.), along with the Minister

̀

e de l’Enseignement

Superieur et de la Recherche for a Ph.D. fellowship (A.A.).

́

Dr. Raymonde Baltenweck-Guyot and Romain Carriere of the

Service de Spectrometrie de Masse, Inst. de Chimie, UdS, are

140

dx.doi.org/10.1021/jo201595s|J. Org. Chem. 2012, 77, 126−142

The Journal of Organic Chemistry

Article

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E. J. Org. Chem. 1999, 64, 7375−7380.

thanked for the MALDI and ESI mass spectrometric measure-

ments. Dr. Roland Graff and Dr. Lionel Allouche of the Service

de RMN, Inst. de Chimie, UdS, are thanked for the NOESY,

ROESY, HMQC, HSQC, and DOSY NMR measurements, and

Y. Guilbert of the ICS is thanked for the TGA measurements.

Jacques Druz and Marie-France Peguet of the Service de

Microanalyse, ICS, are thanked for the elemental analyses, and

Pascal Disdier (MISHA, CNRS, UdS) is thanked for the

photographic images.

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142

dx.doi.org/10.1021/jo201595s|J. Org. Chem. 2012, 77, 126−142

Article Doi

Electronic, spectroscopic, and ion-sensing properties of a dehydro[m]pyrido[14]-and [15]annulene isomer library

DOI: 10.1021/jo201595s

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