Arrays of Molecular Rotors with Triptycene Stoppers: Surface Inclusion in Hexagonal Tris(o -phenylenedioxy)cyclotriphosphazene

Article

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Arrays of Molecular Rotors with Triptycene Stoppers: Surface

Inclusion in Hexagonal Tris(o‑phenylenedioxy)cyclotriphosphazene

Jirí Kaleta,*^,†Paul I. Dron,^‡Ke Zhao,^⊥Yongqiang Shen,^⊥Ivana Císarova,^§Charles T. Rogers,^⊥

̌

́

and Josef Michl^†,‡

^†Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nam

Czech Republic

́

. 2, 16610 Prague,

^‡Department of Chemistry and Biochemistry and ^⊥Department of Physics, University of Colorado, Boulder, Colorado 80309, United

States

^§Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030, 12840 Prague, Czech Republic

S

* Supporting Information

ABSTRACT: A new generation of rod-shaped dipolar molecular

rotors designed for controlled insertion into channel arrays in the

surface of hexagonal tris(o-phenylenedioxy)cyclotriphosphazene

(TPP) has been designed and synthesized. Triptycene is used as a

stopper intended to prevent complete insertion, forcing the

formation of a surface inclusion. Two widely separated ¹³C NMR

markers are present in the shaft for monitoring the degree of

insertion. The structure of the two-dimensional rotor arrays

contained in these surface inclusions was examined by solid-state

NMR and X-ray powder diﬀraction. The NMR markers and the

triptycene stopper functioned as designed, but half of the guest

molecules were not inserted as deeply into the TPP channels as the

other half. As a result, the dipolar rotators were distributed equally in two planes parallel to the crystal surface instead of being

located in a single plane as would be required for ferroelectricity. Dielectric spectroscopy revealed rotational barriers of ∼4 kcal/

mol but no ferroelectric behavior.

NMR if the guest contains suitable NMR markers. Its

disadvantages are sensitivity to oxygen during long-term storage

in air and the existence of a competing monoclinic form whose

formation needs to be avoided.

INTRODUCTION

■

Artiﬁcial molecular rotors have attracted the unﬂagging

attention of scientists over the last few decades, as documented

by numerous articles, reviews, and book chapters.¹⁻¹⁸We are

interested in the design, preparation, and characterization of

two-dimensional rotor arrays with a well-deﬁned ground state.

The most interesting of these would be ferroelectric with the

dipoles of all of the rotators aligned. This might be achievable at

a low temperature in a planar triangular lattice of strongly

coupled rotors with a very low rotational barrier.¹⁹

Our approach has been to ﬁnd a host crystal with a suitable

facet that contains trigonally arranged channels into which the

axles of the rotors can be tightly included as guests.^10,15For the

host, we chose the hexagonal form of tris-o-(phenylenedioxy)-

cyclotriphosphazene, commonly abbreviated as TPP (Figure 1).

It is a molecular crystal with a layered structure containing

parallel channels with a 4.5−5.0 Å internal diameter oriented

perpendicular to the layers and located in a triangular lattice

∼11.5 Å apart.²⁰TPP is chemically quite inert and is

transparent down to 300 nm. It can be readily prepared from

commercially available chemicals, its ¹³C and ³¹P NMR spectra

are simple, and the ring currents of its benzene rings modify the

chemical shifts of the guest nuclei by several ppm, allowing the

extent of guest inclusion to be readily recognized by solid state

The formation of a two-dimensional array of rotors requires

the production of a surface inclusion in which the guests are

present only at the surface and are unable to penetrate inside

the crystal. Little is known about the design of artiﬁcial surface

inclusions, but it seems reasonable that the inclusion of a fat

“stopper” in the rod to be inserted would lead to the desired

structure. Because TPP is a molecular crystal, it is able to

expand its lattice relatively easily when guests are included,

increasing the channel diameter and interchannel distance by

up to ∼10%.¹⁵This oﬀers a valuable independent method for

recognizing inclusion by X-ray powder diﬀraction (XRD), but

also causes a fair degree of uncertainty in estimates of the

maximum size of an acceptable guest and the necessary

minimum size of a stopper. Admittedly, size is not the only

factor that controls the formation of inclusion compounds, and

the relative lattice energies of the inclusion compound and of

the separate crystals of pure host and guest are critical. After

Received: March 24, 2015

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Chart 1. Structures 1−3: Long Shaft (a), Triptycene Stopper

(b), Axle (c), Dipolar Rotator (d), and Bulky Terminus (e)

Figure 1. Structure of hexagonal TPP. (A) Chemical structure and (B)

space-ﬁlling model of a single TPP molecule. (C) Two successive

layers of the crystal viewed from above. (D) Idealized model of rotor

insertion.

empty TPP channel, is sometimes able to enter.^10,15Presently,

we examine the use of triptycene derivatives and establish that

the equatorial diameter of triptycene is suﬃcient to prevent this

undesirable behavior. Triptycenes are easily accessible from

cheap and commercially available precursors, have high

chemical stability, and are easily provided with substituents at

the bridgehead carbons.²³⁻²⁶

Axle (c). The use of butadiynylene instead of ethynylene as

an axle extends the distance between the rotator and the

triptycene stopper, thus minimizing the rotational barrier, and it

is synthetically convenient. However, it also increases the

ﬂexibility of the axle, whose bending might permit an

undesirable aggregation of neighboring dipoles.

some initial searching,^{10,11,14,15,21}we are now able to report a

host−guest combination that promises to reliably lead to

surface inclusions.

As shown in Figure 1 (cf. Chart 1), rotor guests are designed

to form surface inclusions by inserting a long shaft (a) but

being unable to insert a bulky stopper (b) that separates the

shaft from an axle (c) that carries a dipolar rotator (d). In an

attempt to discourage undesirable aggregation of neighboring

axles and the associated rotators, structure 2 is terminated with

a bulky group (e).

Long Shaft (a). This part of molecules 1 and 2 is similar to

some of the rotor shafts that were used in our previous work

with TPP inclusions and showed high aﬃnity for the

channels.^21,22A recent novelty is the presence of two bulky

saturated groups, tert-butyl at one end and bicyclo[1.1.1]penta-

1,3-diyl, near the center of the segment that is to be included.

These groups are meant to serve three purposes: (i) they

facilitate synthetic manipulations by increasing solubility, (ii)

their bulk helps to ﬁx the shaft ﬁrmly against the channel walls,

limiting its possible wobbling motion,²²and (iii) because their

¹³C NMR shifts are situated in spectral regions that avoid

overlap with signals of other rotor carbons and TPP, they reveal

the inclusion of the shaft in the channel.

Dipolar Rotator (d). The choice of rotators was driven by

the desire to have not only a small barrier to rotation and a

sizable dipole moment, but also a diameter that will be large

enough to discourage entry into the TPP channel, because

otherwise the molecular rotor could prefer to insert its rotator

instead of its shaft. As before, we used 2,3-dichlorophenyl,

whose ∼7.8 Å diameter²⁷signiﬁcantly exceeds the nominal

4.5−5.0 Å internal diameter of the channel. The dipole

moment of o-dichlorobenzene is 2.51 D.²⁸

Bulky Terminus (e). The intended function of this third

modiﬁcation in rotor design is to constrain possible contacts

between neighboring 2,3-dichloro-1,4-phenylene rotators per-

mitted by the ﬂexibility of the butadiyne axle. It also prevents a

“backward” insertion of the rotor into a TPP channel. This

building block thus had to fulﬁll three major criteria: (i) its

diameter had to be larger than that of the rotator, both to keep

the rotators apart and to prevent channel entry, (ii) it had to

avoid mechanical contact with the rotator in order to keep the

Triptycene Stopper (b). Our initial attempts to form a

regular array of dipolar rotors on the surface of TPP were

plagued by uncertainties related to the choice of a reliable

stopper, because even the p-carborane stopper, whose van der

Waals diameter greatly exceeds the internal diameter of an

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Scheme 1. Preparation of the Shaft (10)

rotational barrier small, and (iii) it had to be nonpolar and

preferably trigonally symmetrical. We chose the 3,6,9-

trimethyladamantyl unit.

The guest molecules that were used in this study are listed in

Chart 1. Symmetric structure 3, with two 2,3-dichlorophenyl

rotators, was not expected to form an inclusion compound and

was prepared to check the inability of a 2,3-dichlorophenyl

moiety to enter an empty TPP channel that was not stretched

by another large included guest (this group is known to enter

when attached to p-carborane²¹).

Martin periodinane in CH₂Cl₂at room temperature yielded

dialdehyde 16. Poor solubility of diol 15 in CH₂Cl₂, even at

room temperature, did not allow such transformation using the

standard protocol for Swern oxidation. The reaction of 16 with

CBr₄in the presence of PPh₃aﬀorded tetrabromo derivative 17,

whose dehydrobromination with n-BuLi was followed by

capturing the dilithiated species with TMSCl. The desired

disilylated tetrayne 18 was isolated in high yield. Desymmet-

rization of 18 using MeLi in THF at 10 °C gave a statistical

mixture of 19 and 20 in isolated yields of 48% and 39%,

respectively (Scheme 2).

The next focus was synthesis of the bulky 3,5,7-

trimethyladamantyl unit required for rotor 2 (Scheme 3).

The AlBr₃-catalyzed Friedel−Crafts reaction of commercially

available 1-bromo-3,5,7-trimethyladamantane (21) in liquid

vinyl bromide introduced the 2,2-dibromoethyl moiety and

RESULTS

■

1

We describe the synthesis of 1−3, assignment of H and ¹³C

peaks in their solution NMR spectra, single-crystal X-ray

structures of four related compounds, the formation of

inclusion compounds with TPP, and the characterization of

these inclusions by solid-state NMR spectroscopy, X-ray

powder diﬀraction, and temperature-dependent dielectric

behavior.

Scheme 2. Synthesis of 19 and 20

Synthesis. The synthetic approach to 1 and 2 respected the

expected negligible solubility of the ﬁnal products. The

approach is based on the preparation of two adequately soluble

molecular fragments (the bicyclo[1.1.1]pentane-based shaft 4

and a triptycene derivative with a 2,3-dichlorophenyl or a 2,3-

dichloro-1,4-phenylene rotator 5 or 6) whose Sonogashira

coupling produces the poorly soluble ﬁnal products.

Synthesis of Rotors 1−3. Synthesis of the long shaft (a) of

molecules 1 and 2 (Chart 1) started with Friedel−Crafts

alkylation of 4-bromobiphenyl to 7,²⁹whose Sonogashira

coupling with ((3-ethynylbicyclo[1.1.1]pent-1-yl)ethynyl)-

trimethylsilane^30,31(8) aﬀorded silyl derivative 9 (Scheme 1).

The trimethylsilyl group was removed using TBAF, and

corresponding alkyne 10 was obtained in a nearly quantitative

yield.

The triptycene stopper (b, Chart 1) was made in eight steps

from commercially available 9,10-dibromoanthracene (11). The

known route from 11 to 9,10-diethynyltriptycene (12) was

slightly modiﬁed and scaled up, allowing the preparation of

multigram quantities of 12. Anthracene 11 was coupled with

TMSA in reﬂuxing Et₂NH under PdCl₂(PPh₃)₂/CuI catalysis to

obtain the silylated derivative 13 in excellent yield.³²Diels−

Alder addition of benzyne, generated in situ from anthranilic

acid and isoamyl nitrite, to anthracene 13 aﬀorded the desired

silylated triptycene 14.³³Both trimethylsilyl groups were

removed in an almost quantitative yield using either K₂CO₃

in the mixture of THF and methanol³³or TBAF in THF.

Double lithiation of 12 followed by the reaction with

paraformaldehyde gave diol 15, whose oxidation using Dess−

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Scheme 3. Construction of Rotator 25

yielded 22. A modiﬁcation of the published procedure³⁴

Scheme 5. Final Assembly of Molecular Rotors 1 and 2

allowed us to increase the isolated yield from the original 40%

to 75%. Alkyne 23 was obtained by treatment with t-BuOK.³⁴

A

rapid trans dehydrobromination in the ﬁrst step was followed

by a geometrically disfavored cis elimination and a 3 day

reaction time was required. Sonogashira coupling with excess

1,4-diiodo-2,3-dichlorobenzene (24)³⁵at a slightly elevated

reaction temperature (40 °C, most likely required due to the

high steric demand of the adamantyl unit) gave a mixture

containing 25 as the expected major product and 26 as a minor

side product (Scheme 3).

Rotators 27 and 25 were connected with triptycene stopper

19 using Sonogashira coupling. Terminal alkynes 5 and 6 were

then liberated from their TMS derivatives 28 and 29,

respectively, in almost quantitative yields using TBAF (Scheme

4).

Scheme 4. Preparation of Alkynes 5 and 6

Sonogashira coupling. A double reaction on both terminal

alkynes of 20 resulted in 78% yield of 3.

Unsuccessful Attempts to Prepare Related Rotors. The

benzene ring connecting alkyne 10 with the triptycene stopper

in 5 and 6 is not crucial for the rotor function, and two

attempts were made to reduce the length of the shaft (a, Chart

1) with the expectation that the shorter molecules would be

more soluble. Unfortunately, both attempts failed.

In the ﬁrst approach, simple monosilylated triptycene 30,

obtained by statistical desymmetrization of 14 in an acceptable

isolated yield of 57% (Scheme 6), was used to mimic the

behavior of the less easily accessible alkyne 5 or 6. Cadiot−

Chodkiewicz coupling between alkyne 10 and alkynyl bromide

31, which was made by AgNO₃-catalyzed NBS bromination of

30 (Scheme 6), did not lead to the expected product, and the

¹H NMR spectrum of the crude reaction mixture contained

mostly the product of oxidative homocoupling of alkyne 10.

The last step in the synthesis of the long shaft (4) was the

coupling of alkyne 10 with excess 1,4-diiodobenzene, which

proceeded in 78% yield. The Sonogashira coupling of iodo

derivative 4 with alkynes 5 and 6 aﬀorded the desired molecular

rotors 1 and 2 in 76 and 70% yield, respectively (Scheme 5).

The low solubility of the ﬁnal products simpliﬁed their

puriﬁcation, because both compounds precipitated from the

reaction mixture and were easily isolated using a centrifuge and

ﬁltration.

Symmetric rotor 3 was made from tetrayne 20 and 1,2-

dichloro-3-iodobenzene (27) using standard conditions for

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in a synthetically useless yield of less than 5% (based on H

Scheme 6. Statistical Desymmetrization of 14 and

Bromination of 30

NMR). The failure of the ﬁrst approach and the poor yield of

dibromo derivative 38 during this second approach prompted

us not to pursue additional attempts to reduce the length of the

shaft (a).

The van der Waals diameter of the 3,5,7-trimethyladamantyl

group (∼6.9 Å) should discourage aggregation of neighboring

rotators after the insertion of 2 into TPP but is unlikely to

prevent bending of the butadiyne axle (c). Accordingly, the

sterically more demanding tris(trimethylsilyl)silyl unit, whose

van der Waals diameter is ∼8.0 Å, was chosen as a second

possible candidate. The intended synthesis followed the

reactions shown in Schemes 4 and 5 with an Si(TMS)₃

group in place of the 3,5,7-trimethyladamantyl unit. Because

little is known about the chemical stability of Si(TMS)₃in the

presence of other silyl protecting groups, we synthesized silane

39 containing both TMS and Si(TMS)₃to test for selective

TMS removal.

Alkyne 40 was easily available from ClSi(TMS)₃and

BrMgCCH in THF at room temperature.³⁸Its Sonogashira

coupling with bromo derivative 41 gave desired model structure

39 in 82% yield. An attempted removal of TMS using K₂CO₃in

THF/MeOH failed. Mild conditions that allow selective

cleavage of TMS in the presence of TES even at room

temperature^39,40caused quantitative removal of the Si(TMS)₃

group even though the reaction was run at 0 °C. A reaction of

39 with MeLi in THF clearly demonstrated that the Si(TMS)₃

group is much more labile than TMS, because the same

reaction conditions had been used twice in this work to remove

the TMS group at 5−10 °C (Schemes 2 and 6). Si(TMS)₃was

cleaved preferentially at −78 °C, and compounds 42 and 43

were isolated in almost quantitative yields (Scheme 9). A

combination of the sterically protected triple bond of alkyne 40

with the more sterically demanding tetrahalo derivative 24

prevented the Sonogashira coupling reaction entirely. The

desired product was not formed even at 80 °C, and only the

starting materials were isolated from the crude reaction mixture

(Scheme 9).

The second approach was inspired by the preparation of

conjugated polyynes, where the crucial step is a stepwise

synthesis of an internal triple bond based on the Fritsch−

Buttenberg−Wiechell rearrangement.^36,37At ﬁrst, alkyne 10

was converted to ynone 32 in two steps (Scheme 7, route A).

Lithiation of 10 followed by a reaction with paraformaldehyde

resulted in alcohol 33, which was subsequently oxidized to

ynone 32 by Swern oxidation.

Scheme 7. Possible Routes to Ynone 32

The observation that alkyne 40 does not undergo

Sonogashira coupling with sterically demanding substrate 24,

whereas ClSi(TMS)₃reacts with deprotonated alkynes,

prompted an alternative strategy for reaching the desired

rotator. One iodine atom in 24 was substituted by a triple bond,

and the resulting acetylide was coupled with ClSi(TMS)₃.

Tetrahalo derivative 24 was desymmetrized using Sonogashira

coupling with TMSA. The reaction yielded alkynes 44 and 45

in 69 and 25% yield, respectively, at an elevated temperature

(40 °C). Deprotection of 44 using TBAF in THF gave the

unstable terminal alkyne 46 in 90% yield as a white crystalline

solid that turned black instantly after exposure to air.

Compound 46 was therefore immediately lithiated using

LiHMDS and treated with ClSi(TMS)₃. The triple bond was

indeed silylated, but iodine was surprisingly replaced by

hydrogen at the same time; dichloro derivative 47 was isolated

as the only product in 76% yield (Scheme 10).

A one-step conversion of 10 to 32 based on the formylation

of the lithiated alkyne with anhydrous DMF did not produce

any of the expected 32, and only starting material 10 was

isolated from the crude reaction mixture (Scheme 7, route B).

In contrast, carboxylation of the lithium acetylide derived from

10 by gaseous CO₂gave acid 34 in excellent yield. Subsequent

esteriﬁcation by ethereal diazomethane also aﬀorded methyl

ester 35 in an almost quantitative yield. The following DIBAL

reduction failed, however, and H NMR of the crude reaction

mixture contained starting material 35 and mere traces of the

desired ynone 32 (Scheme 7, route C).

The addition of lithiated 30 to ynone 32 resulted in a nearly

quantitative yield of racemic alcohol 36, whose Swern oxidation

gave ketone 37 in 79% yield (Scheme 8). However, the reaction

with CBr₄in the presence of PPh₃provided desired product 38

The unpredictable reactivity of Si(TMS)₃-substituted de-

rivatives prompted us to give up additional attempts to use the

Si(TMS)₃unit as the bulky group (e, Chart 1).

1

Molecular Rotors. Solution H and ¹³C NMR. Except for

the signals of several triple bond carbons, all ¹H NMR and most

1

of the ¹³C NMR signals of 1−3 were assigned using H−¹H

COSY, ¹³C attached-proton test (APT), HSQC, and HMBC

(Figure 2 and Supporting Information).

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Scheme 8. Attempted Synthesis of Dibromide 38

Scheme 9. Attempted TMS Removal and Coupling with 24

Compound 16 crystallized in the triclinic crystal system and P-1

space group, and 17 and 26 crystallized in the monoclinic

crystal system and C2/c and P2₁/c space groups, respectively.

Tetrayne 20 formed orthorhombic crystals with a Pbca space

group. ORTEP representations of single molecules of 16, 17,

and 20, along with space-ﬁlling models showing two

neighboring molecules and their arrangement in one crystal

layer, are shown in Figure 3. They all crystallize in the same

manner with two paddles of a triptycene core embracing an

ethynyl unit of a neighbor.

Scheme 10. Desymmetrization of 24 and Silylation of 46

Inclusion Compounds. These were prepared by milling

and subsequent extended annealing at 70 °C, sometimes

followed by brief annealing at 235 °C. The samples will be

referred to by symbols such as X%1@TPP-d₁₂(70) or X%1@

TPP-d₁₂(235), respectively, where X equals 5 or 16, and stands

for the molar % of guest 1. These concentrations were chosen

based on analogy with similar previously published inclusion

complexes.^14,21

Solid-State ¹³C and ³¹P NMR. The NMR behavior of the

inclusion compounds was studied by ¹³C cross-polarization

magic-angle spinning (CP MAS), ³¹P CP MAS, and ³¹P single

pulse excitation (SPE).

Crystal Packing. Intermolecular interactions between rotor

molecules codetermine the structures of surface inclusions, and

it would be helpful to understand how the rotors prefer to pack

in a crystal lattice. Attempts to obtain high-quality crystals of

1−3 were unsuccessful, but we were able to grow suitable single

crystals of 16, 17, 20, and 26 by slow evaporation of CH₂Cl₂

solutions and examine their crystal packing by X-ray analysis.

Rotor 1. The solid-state ¹³C CP MAS NMR spectrum of

5%1@TPP-d₁₂(70) shows a similar peak pattern as the ¹³C

solution NMR with peaks shifted upﬁeld or downﬁeld. It also

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Figure 2. H (blue) and ¹³C NMR (black) assignments in 1, 2, and 3; the spectra can be found in the Supporting Information.

contains three additional peaks in the aromatic region that are

due to TPP (Figure 4). In light of the complex structure of 1, it

is understandable that only some of the chemical shifts

identiﬁed in the solid-state ¹³C CP MAS NMR spectrum

have been assigned.

The bicyclo[1.1.1]pentane cage present in the shaft has two

characteristic signals in the ¹³C solution NMR spectrum of

rotor 1 at 32.0 (bridgehead carbons) and 59.8 ppm (bridge

carbons). In the solid-state ¹³C CP MAS NMR spectrum, the

former peak is not obvious and probably overlaps with the tert-

butyl signal at 30.4 ppm. The signal of the bridge carbons is

doubled and appears as two peaks of comparable intensity, at

57.3 and 60.8 ppm.

The terminal tert-butyl moiety of rotor 1 has two signals in

the ¹³C solution NMR, at 31.7 ppm for the methyl carbons and

at 35.3 ppm for the quaternary carbon. Two peaks of nearly

equal intensities also appear in the solid-state ¹³C CP MAS

NMR spectrum of 5%1@TPP-d₁₂(70) but are shifted upﬁeld to

30.4 and 32.3 ppm. It is possible that the signal of the methyl

carbons is doubled similar to the signal of the bridge carbons

discussed above, but it is also possible that one of the peaks

belongs to the methyl carbons and the other to the quaternary

carbon.

The aromatic carbon atom connected to the tert-butyl

moiety, which appears at 151.4 ppm in the ¹³C solution NMR,

is absent in the solid-state ¹³C CP MAS NMR of the inclusion

and probably overlaps with the strong TPP signal at 144.7 ppm.

The quaternary carbon atoms in the triptycene moiety are

equivalent in the ¹³C solution NMR and have a resonance at

54.1 ppm. In the solid-state ¹³C CP MAS NMR spectrum of the

inclusion, these atoms are observed at 53.7. The acetylenic

carbon atoms are characterized by several resonances between

75 and 92 ppm in the ¹³C solution NMR. In the solid-state ¹³

C

CP MAS NMR spectrum of 5%1@TPP-d₁₂(70), only one

broad peak centered at 78.0 ppm is observed.

The ³¹P CP MAS and ³¹P SPE NMR spectra of the

inclusions show peaks characteristic for hexagonal TPP.

However, in the ³¹P SPE NMR, additional peaks characteristic

of the monoclinic form of TPP can be observed.

In an eﬀort to convert all TPP to its hexagonal form, 5%1@

TPP-d₁₂(70) was heated to 235 °C for 2 min. This temperature

lies above the 225 °C transition point at which the guest-free

hexagonal form of TPP becomes more stable than its

monoclinic form⁴¹but is still safely below the 245 °C melting

point of TPP. NMR spectra of the resulting 5%1@TPP-

d₁₂(235) are shown in Figure S1 (Supporting Information).

The ³¹P SPE and ³¹P CP MAS NMR spectra show that TPP is

present only in its hexagonal form, but that partial

decomposition of TPP to other phosphorus-containing species

has occurred.

In the 20−90 ppm region of the spectrum, which contains

the characteristic peaks of the triptycene and bicyclo[1.1.1]-

pentane units, the ¹³C CP MAS NMR spectra of 5%1@TPP-

d₁₂(70) and 5%1@TPP-d₁₂(235) are identical, and we conclude

that rotor 1 survived the heating intact. Between 110 and 150

ppm, additional peaks are observed in the ¹³C CP MAS NMR

spectrum of 5%1@TPP-d₁₂(235) and are attributed to

decomposition products of TPP.

Rotor 2. Molecule 2 shares some structural characteristics

with rotor 1 but is even more complex. Its NMR character-

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Figure 3. X-ray single crystal structure of 16, 17, and 20: ORTEP

representation of a single molecule (A), space-ﬁlling model of two

neighboring molecules (B), and molecular packing in a crystal (C,

hydrogen atoms omitted for clarity). ORTEPs drawn at the 30% level.

For more detail, see the Supporting Information.

ization relies on the identiﬁcation of the same moieties that

were used in the description of rotor 1.

The solid-state ¹³C CP MAS NMR spectrum of neat rotor 2

shows a pattern similar to the ¹³C solution NMR spectrum with

some small variations in the chemical shifts. The solid-state ¹³

C

Figure 4. NMR spectra of 1 ¹³C in THF-d₈(*) solution (A) and of

5%1@TPP-d₁₂(70) ¹³C CP MAS (B), ³¹P CP MAS (C), and ³¹P SPE

(D).

CP MAS NMR spectrum of 5%2@TPP-d₁₂(70) is dominated

by the three peaks characteristic of TPP (Figure S2, Supporting

Information). The methyl carbon atoms of the tert-butyl moiety

of the rotor appear at 32.5 ppm in solution ¹³C NMR, in the

solid state of the neat rotor, and in the ¹³C CP MAS NMR of

the inclusion compound. The only diﬀerence is that, in the

spectrum of the inclusion compound, the peak is much broader,

probably because it also contains the signals of the methyl

carbon atoms of the adamantyl moiety. The quaternary carbon

atom of the tert-butyl group is at almost the same position in

the solution NMR (35.2 ppm) as in the neat rotor (35.5 ppm)

NMR spectra, but it is not observed in the spectrum of the

inclusion compound, most likely due to overlap with

adamantane carbons. Similarly, the aromatic carbon attached

to the tert-butyl moiety appears at 151.5 ppm in the solution

NMR and at 150.9 ppm in the spectrum of the neat solid, but it

is not observed in the spectrum of the inclusion.

The bridge carbon atoms characteristic of the bicyclo[1.1.1]-

pentane cage of 2 have a resonance at 59.8 ppm in solution

NMR. These carbon atoms appear at 59.9 ppm in the spectrum

of the neat rotor, but the peak is broader. In the ¹³C CP MAS

NMR of the inclusion, this peak appears as a broad doublet

located at the same chemical shift. The quaternary carbon

atoms present in the triptycene unit have resonances at 54.17

and 54.19 ppm in solution. These atoms appear at 53.3 ppm in

both the spectrum of the neat rotor and the spectrum of the

inclusion. The acetylenic carbon atoms have chemical shifts

between 76 and 93 ppm in the solution ¹³C NMR spectrum. In

the spectra of the neat rotor and of the inclusion, they appear in

the same range, but the peaks are broad and poorly deﬁned.

In the ³¹P CP MAS spectrum of 5%2@TPP-d₁₂(70), the

main peak lies at 33.6 ppm, indicating inclusion in the TPP

channel, but an additional small peak at −1.8 ppm suggests that

some TPP has decomposed. From the ³¹P SPE NMR spectrum

of the inclusion, it is obvious that ∼45% of the TPP decayed to

the monoclinic form.

The ¹³C CP MAS NMR spectrum of 16%2@TPP-d₁₂(70)

(Figure 5) is identical to that of 5%2@TPP-d₁₂(70). Its ³¹P SPE

NMR spectrum reveals that the 16% loading allows all of the

TPP to stay in its hexagonal form (Figure 4E). The ³¹P CP

MAS NMR spectrum contains two peaks in a 14:1 integrated

intensity ratio. The stronger peak at 33.3 ppm is observed when

a rotor is included in TPP, but the presence of a weak peak at

−83.4 ppm suggests the presence of decomposition products.

Rotor 3. The solid-state ¹³C CP MAS NMR spectrum of

5%3@TPP-d₁₂(70) shows a pattern almost identical to that of

neat solid rotor 3. Only three very weak additional peaks

characteristic of TPP are observed (Figure 6). Besides the very

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Figure 5. NMR spectra of 2 ¹³C in THF-d₈(*) solution (A), of neat 2

¹³C CP MAS (B), and of 16%2@TPP-d₁₂(70) ¹³C CP MAS (C), ³¹P

CP MAS (D), and ³¹P SPE (E).

Figure 6. NMR spectra of 3 ¹³C in CDCl₃(*) solution (A), of neat 3

¹³C CP MAS (B), and of attempted 5%2@TPP-d₁₂(70) ¹³C CP MAS

(C), ³¹P CP MAS (D), and ³¹P SPE (E).

weak peak at 33.6 ppm, characteristic of an inclusion complex,

the ³¹P CP MAS spectrum of the inclusion contains additional

peaks at 12.5, −2.1, and −21.1 ppm. The ³¹P SPE NMR

spectrum of the same sample is dominated by the three

resonances characteristic of monoclinic TPP.

X-ray Powder Diﬀraction. The inclusion compounds 1@

TPP-d₁₂to 3@TPP-d₁₂were characterized by Cu Kα1

wavelength X-ray powder patterns. As an example, Figure 7

shows the powder pattern for 5%1@TPP-d₁₂(70) plotted as X-

ray photon counts versus the scattering wave vector magnitude

q, where q is related to the scattering angle θ and X-ray

wavelength λ by q = (4π/λ) sin θ. The large peaks in the

pattern arise from a hexagonal inclusion phase with an in-plane

lattice parameter of 1.168

0.001 nm and hexagonal layer

spacing of 0.990 0.001 nm. The in-plane lattice parameter

and layer spacing show roughly 2.5% expansion and 1.7%

contraction, respectively, compared to the 1.1454 0.0005 nm

and 1.0160 0.0005 nm reported⁴²for empty hexagonal TPP.

Peak widths allow us to estimate the typical powder particle size

at near 300 nm. In addition to peaks associated with the

hexagonal phase, we ﬁnd additional small peaks that arise from

the monoclinic phase of TPP.

In 5%1@TPP-d₁₂(235), the TPP monoclinic diﬀraction

peaks are absent, and the hexagonal peaks are narrower,

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Figure 8. Dielectric loss of 5%1@TPP-d₁₂(70) between 10 and 280 K.

Black, 140 Hz; red, 1400 Hz; blue, 14000 Hz.

Figure 7. X-ray powder pattern for 5%1@TPP-d₁₂(70). The solid

black line is the diﬀraction data, and the red line is the ﬁt assuming

hexagonal peak positions and a measured background from the sample

capillary tube.

which is consistent with an increase in powder particle size. The

in-plane hexagonal lattice parameter is now 1.167 0.001 nm,

and the hexagonal layer spacing is 0.982

0.001 nm. XRD

powder patterns of the 5%2@TPP-d₁₂(70) and 5%3@TPP-

d₁₂(70) samples show a mixture of hexagonal and monoclinic

TPP. The hexagonal lattice parameters are consistent with

those of empty TPP.

In the XRD pattern of 5%2@TPP-d₁₂(235), peaks of

monoclinic TPP are absent. It contains signals from a hexagonal

inclusion phase with an in-plane lattice parameter of 1.166

0.001 nm, layer spacing of 0.996 0.001 nm, and many small

unassigned peaks.

The XRD powder pattern of 16%2@TPP-d₁₂(70) shows a

mixture of monoclinic TPP and a hexagonal inclusion

compound with an in-plane lattice parameter of 1.164

0.001 nm and layer spacing of 0.999 0.001 nm. Annealing

this sample to 235 °C resulted in the elimination of all

signiﬁcant diﬀraction peaks and apparent decomposition of the

sample.

Figure 9. Dielectric loss of 5%1@TPP-d₁₂(70) at 140 Hz (green),

1400 Hz (orange), and 14000 Hz (purple), and 5%1@TPP-d₁₂(235)

at 140 Hz (black), 1400 Hz (red), and 14000 Hz (blue). The curves

have been shifted vertically for better viewing.

16%2@TPP-d₁₂(70) also has two frequency-dispersing

dielectric loss peaks between 50 and 150 K (Figure 10). One

Dielectric Spectroscopy. Dielectric loss peaks at low

temperatures are indications of dielectric relaxations related

to rotations of dipolar rotators. The rotational barrier and

attempt frequency of a rotational mode can be extracted by

analyzing the positions of the associated dielectric loss peaks for

diﬀerent external ﬁeld frequencies.

Two major dielectric loss peaks in the 100−200 K range that

disperse with frequency are seen for 5%1@TPP-d₁₂(70)

(Figure 8). A peak near 100 K is consistent with a rotational

mode with a barrier of 3.98 kcal/mol and an attempt frequency

of 7.5 × 10¹¹Hz. The other, between 150 and 200 K, is

consistent with a barrier of 9.64 kcal/mol and an attempt

frequency of 9.6 × 10¹⁶Hz. There also is a small dielectric loss

shoulder below 100 K, representing a rotation with a barrier of

2.39 kcal/mol and an attempt frequency of ∼8 × 10¹⁰Hz.

Upon going to 5%1@TPP-d₁₂(235), one of the two major

peaks in the dielectric loss spectrum between 80 K and room

temperature is shifted to higher temperature (Figure 9). The

barrier height of the lower peak increases slightly from 3.98 to

4.36 kcal/mol with an almost unchanged attempt frequency.

The peak is now much smaller, suggesting a reduced population

of rotators active in this rotational mode.

Figure 10. Dielectric loss of 16%2@TPP-d₁₂(70) in the range 10−220

K at 140 Hz (black), 1400 Hz (red), and 14000 Hz (blue).

is consistent with a rotational mode with a barrier of 3.43 kcal/

mol and an attempt frequency of 2.2 × 10¹³Hz. The other has

a barrier of 4.38 kcal/mol and an attempt frequency of 5 × 10¹²

Hz. Both peaks are much smaller than the major peaks of

5%1@TPP-d₁₂(70), indicating that far fewer rotators are active.

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The dielectric spectrum of 5%3@TPP-d₁₂(70) is relatively

featureless in the temperature range of interest, suggesting that

either too few rotators can actually rotate or that rotational

barriers are so high that possible dielectric loss peaks lie at high

temperatures (Figure 11).

channel and their shafts inserted, one-half of them deeper than

the other. Given the trigonal arrangement of the channels, the

insertion pattern cannot be completely regular but we have no

other information on it.

The signal near 78 ppm in the solid-state NMR spectrum can

be assigned to all of the acetylenic carbon atoms present in 1.

The only peak observed in the ³¹P CP MAS spectrum of

5%1@TPP-d₁₂(70) is indicative of an inclusion in the TPP

channel. However, the peaks corresponding to the monoclinic

TPP observed in the ³¹P SPE NMR spectrum suggest that 5%

loading of rotor 1 was not optimal and that ∼25% of the TPP

collapsed from the hexagonal form to the monoclinic one.

The analysis of 5%1@TPP-d₁₂(235) provided three

important pieces of information: (i) rotor 1 survives the high

temperature as revealed by ¹³C CP MAS NMR, (ii) on the basis

of the ³¹P SPE NMR, the TPP is present almost exclusively in

its hexagonal form, and (iii) a signiﬁcant amount of

phosphorus-containing TPP decomposition products were

formed (³¹P CP MAS NMR and ¹³C CP MAS NMR). It is

not clear whether these decomposed structures were formed by

degradation of hexagonal TPP or its monoclinic modiﬁcation,

which was originally present in the sample.

Figure 11. Dielectric loss of 5%3@TPP-d₁₂(70) between 10 and 280

K at 140 Hz (black), 1400 Hz (red), and 14000 Hz (blue).

Rotor 2. From the solid state NMR spectrum of 5%2@TPP-

d₁₂(70) in Figure S2 (Supporting Information), it is obvious

that the general procedure for the preparation of inclusions

does not produce a pure hexagonal inclusion of rotor 2.

Although the ³¹P SPE NMR spectrum indicates that there is

still some free hexagonal TPP in the system, the ³¹P CP MAS

spectrum suggests the existence of an inclusion in the TPP

channel.

DISCUSSION

■

Synthesis. The design concept for a multistep synthesis of

the molecular rotors 1−3 based on the preparation of two key

molecular fragments whose coupling produces the target rotors

in the ﬁnal step worked as we had hoped. This strategy allows

their preparation on a scale of hundreds of milligrams. The

generality of this approach is apparent, because singly protected

alkyne 19 could in principle be coupled with almost any

(hetero)aryl bromide, iodide, or triﬂate, providing access to a

variety of dipolar rotators.

The only other observation that requires comment is the low

chemical stability of the Si(TMS)₃group relative to TMS

(Scheme 9). The reaction of 39 with MeLi in THF at −78 °C

demonstrated that the bulky and electron-poor Si(TMS)₃

group could be selectively cleaved in the presence of TMS in

a nearly quantitative isolated yield.

Inclusion Compounds. The production of inclusion

compounds by milling proceeded as usual. The only novelty

is high temperature annealing, which provided access to

samples that contained only the hexagonal form of TPP.

The X-ray powder patterns indicate that both 1 and 2 form

hexagonal inclusion compounds with TPP, whereas sym-

metrical compound 3 does not. The nearly identical hexagonal

lattice parameters that we ﬁnd for inclusion compounds of both

1 and 2 are entirely consistent with their identical tail structure

and thus with our picture of how these rotor molecules form

surface inclusions on TPP.

Rotor 1. The carbon atoms present in the tert-butyl moiety,

the bicyclo[1.1.1]pentane cage, and the triptycene unit appear

slightly shifted in the ¹³C CP MAS NMR spectrum of the

inclusion compounds. The doubling of the signal of the bridge

carbons of bicyclo[1.1.1]pentane proves the existence of two

distinct environments for this part of the shaft, present at

equilibrium in approximately the same amounts and unchanged

by additional annealing. It is also compatible with the possible

doubling of the signal of the methyl carbons of the tert-butyl

group. The bridgehead carbons of triptycene produce a signal at

53.7 ppm, only 0.4 ppm from their location in solution. We

conclude that all of the rods have their triptycenes outside the

The ¹³C CP MAS NMR spectrum of 5%2@TPP-d₁₂(70) is

very similar to that of 5%1@TPP-d₁₂(70) but contains

additional unresolved peaks attributable to the trimethylada-

mantyl moiety. The signal of the bridge carbons of the

bicyclo[1.1.1]pentane cage again appears as a doublet of peaks

of similar intensity at 60.7 and 57.3 ppm, the same locations as

in 5%1@TPP-d₁₂(70). The signal of the methyls of the tert-

butyl group also appears as an upﬁeld shifted doublet but is so

strongly overlapped with signals of adamantyl carbons that it

does not allow for any ﬁrm conclusions. The signals of the

triptycene bridgeheads again exhibit a minimal shift (0.3 ppm)

from their position in solution. The peak corresponding to the

proximal methylene groups in the adamantyl substituent

appears at the same chemical shift in all of the spectra (48.7

ppm in solution and 48.9 ppm in the solids), nicely compatible

with the notion that the bulky trimethyladamantyl is not

inserted in the channel.

The signal at 75 ppm in the solid-state NMR spectrum can

be assigned to all of the acetylenic carbon atoms present in

rotor 2.

The ¹³C CP MAS NMR spectra of 16%2@TPP-d₁₂(70) and

16%2@TPP-d₁₂(235) are very similar to that of 5%2@TPP-

d₁₂(70). The ³¹P SPE NMR spectrum of 16%2@TPP-d₁₂(70)

shows almost exclusively hexagonal TPP, and its ³¹P CP MAS

NMR spectrum reveals the presence of a minor decomposition

product of TPP. Both ³¹P NMR spectra of 16%2@TPP-

d₁₂(235) show extensive decomposition of TPP.

Overall, we conclude that the rods of 2 form a surface and

not a bulk inclusion, and that half of them are inserted deeper

than that other half. Only the shaft part of the rotor molecule,

separated from the rotator by the triptycene stopper, is capable

of insertion. The surface inclusions of 2 are very similar to

those of 1, and both rotors are thermally very stable. For

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reasons that are unclear, the TPP constituent is thermally less

stable in the former.

more importantly, because the rotating dipoles are not all

located in the same plane.

Rotor 3. The solid-state ¹³C CP MAS NMR spectra of

5%3@TPP-d₁₂(70) are almost identical to those of neat solid

rotor 3. The signals of TPP are detectable but very weak,

indicating that only very little magnetization is transmitted from

proton containing moieties to the carbon atoms of TPP-d₁₂.

Judging by the ³¹P SPE NMR spectrum, the content of

monoclinic TPP in the inclusion sample is almost 85%. The

very weak ³¹P CP MAS signal again shows that no part of rotor

3 is included in the channel.

Rotational Barriers. The dielectric spectra of 1@TPP-d₁₂

and 2@TPP-d₁₂indicate that rotators can rotate with barriers as

low as 3−4 kcal/mol, and a small fraction may have an even

lower barrier in the 2 kcal/mol range. The sizes of the dielectric

loss peaks of 1@TPP-d₁₂are comparable to other surface

inclusions in TPP,¹⁰which is consistent with the conclusion of

solid-state NMR and XRD studies that a surface inclusion has

been formed. Given that half of the rotors 1 and 2 are inserted

deeper than the other half, it is easy to see why the surface

inclusion of 2 contains far fewer active rotators than that of 1.

Instead of keeping the rotor axles apart as intended, the

trimethyladamantyl groups block the rotators of their diﬀer-

ently inserted molecular rotor neighbors (Figure 12). It is likely

CONCLUSIONS

■

The triptycene unit works well as a stopper in TPP channels,

the NMR markers perform as desired, the dichlorophenyl

rotator and the trimethyladamantyl substituent are bulky

enough to prevent undesired backward insertion of the rotor

into the TPP channel, and both compounds 1 and 2 form

surface inclusions in TPP as intended. However, in these

inclusions, half of the rods are inserted deeper than the other

half, apparently imitating the packing found in single crystals of

16, 17, and 20, and likely to be present in the crystals of neat

rotors. The resulting staggering of the rods is probably

responsible for the relatively high observed rotational barriers

of 3.98 and 9.64 kcal/mol for 5%1@TPP-d₁₂and 3.43 and 4.38

kcal/mol for 16%2@TPP-d₁₂as well as the absence of

ferroelectricity. As expected, the presence of the two bulky

1,2-dichlorophenyl groups (whose diameter is larger than the

internal diameter of the TPP channel) in symmetrical

molecular rotor 3 prevents its insertion into the TPP channel.

To achieve a ferroelectric ground state, it would be helpful to

force all guest rotors to penetrate the TPP channels to the same

depth, perhaps by providing the triptycene stoppers with six

peripheral substituents that have high aﬃnity for their

counterparts on neighboring triptycenes, or by modifying the

bulky terminal moieties in a way that would provide them with

aﬃnity for their bulky neighbors, or both. The use of a

hexahalotriptycene as a stopper and C₆₀as a terminal group

may be worth exploring. Using the shorter ethynylene instead

of butadiynylene axles would likely be another improvement.

EXPERIMENTAL SECTION

■

Materials. All reactions were carried out under an argon

atmosphere with dry solvents freshly distilled under anhydrous

conditions unless otherwise noted. Standard Schlenk and vacuum

line techniques were employed for all manipulations with air- or

moisture-sensitive compounds. Yields refer to isolated chromato-

graphically and spectroscopically homogeneous materials unless

otherwise stated.

THF and ether were dried over sodium with benzophenone and

distilled under argon prior to use. Triethylamine and CH₂Cl₂were

dried over CaH₂and distilled under argon prior to use. All other

reagents were used as supplied unless otherwise stated.

Analytical thin-layer chromatography (TLC) was performed using

precoated TLC aluminum sheets (Silica gel 60 F₂₅₄). Spots on TLC

were visualized using either UV light (254 nm) or a 5% solution of

phosphomolybdic acid in ethanol using heat (200 °C) as a developing

agent. Flash chromatography was performed using silica gel (high

purity grade, pore size 60 Å, 70−230 mesh). Melting points reported

are uncorrected. Infrared spectra (IR) were recorded in KBr pellets.

NMR chemical shifts are reported relative to CHCl₃(δ = 7.26 ppm for

¹H NMR), CHCl₃(δ = 77.0 ppm for ¹³C NMR), THF-d₈(δ = 1.72

Figure 12. Side views of proposed structures of surface inclusions 1@

TPP-d₁₂(A) and 2@TPP-d₁₂(B).

1

and 3.58 ppm for H NMR), THF-d₈(δ = 25.40 and 67.50 ppm for

that many neighbor pairs are packed similarly to those in the

single crystals of the triptycene derivatives shown in Figure 3.

The same structural feature is likely responsible for the

diﬀerences between the rotational barriers observed in the

two inclusion compounds, particularly the absence of the 9.64

kcal/mol barrier in the inclusion compounds of 2. Rotor 3 did

not form an inclusion with TPP; thus, the absence of dielectric

losses in 3@TPP-d₁₂spectrum is expected.

1

¹³C NMR), acetone-d₆(δ = 2.05 ppm for H NMR), and acetone-d₆

(δ = 29.8 and 206.3 ppm for ¹³C NMR) as internal references.

Splitting patterns are assigned as s = singlet, d = doublet, t = triplet, m

= multiplet, and br = broad signal.

High-resolution mass spectra (HRMS) using atmospheric pressure

chemical ionization (APCI) and electrospray ionization (ESI) were

obtained on a mass analyzer combining linear ion trap and the

Orbitrap, and those using electron ionization (EI) and chemical

ionization (CI) mode were taken on a time-of-ﬂight mass

spectrometer.

No ferroelectricity is observed at low temperatures, probably

because the barriers to rotation are excessive and, probably

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TPP-d₁₂was synthesized from catechol-d₆⁴³as reported.⁴⁴The code

for designating an inclusion compound is X%Y@TPP-d₁₂(T), where X

is the molar percentage of rotor Y, and T is the annealing temperature.

The previously published procedure¹⁵for preparing the inclusion

compounds from components was modiﬁed as follows. The neat

rotors 1−3 and neat solvent-free hexagonal TPP-d₁₂were mixed, ball

milled for 2 h with a stainless steel disk, and annealed for 2 days at 70

°C under an argon atmosphere. Some samples were annealed for two

more minutes at 235 °C.

Single-Crystal X-ray Diﬀraction. Crystallographic data for 16,

17, 20, and 26 were collected on a Kappa geometry diﬀractometer

with a CCD detector by monochromatized Mo Kα radiation (λ =

0.71073 Å) at a temperature of 150(2) K. The structures were solved

by direct methods (SHELXS)⁴⁵and reﬁned by full matrix least-squares

based on F²(SHELXL97).⁴⁵

X-ray Powder Diﬀraction. The X-ray powder patterns were taken

with a system based on a Rigaku Ultrax18 rotating anode generator. It

uses a curved silicon multilayer monochromator to produce Cu Kα

radiation at a wavelength of λ = 0.15418 nm. Powder samples, loaded

into 1.0 mm diameter borosilicate glass capillaries with a wall thickness

of 10 μm, were mounted on a Huber four-circle goniometer. The

scattered X-rays were measured with a NaI scintillator point detector

that was moved in a horizontal plane by an angle 2θ with respect to

the direction of the incident X-rays to scan the Bragg scattering proﬁle.

degassed THF (8 mL) and triethylamine (8 mL). Molecular rotor 2

was obtained as a white crystalline solid (160 mg, 0.146 mmol, 70%).

1

Mp >260 °C (dec.). H NMR (500 MHz, CDCl₃): δ 0.89 (s, 9H),

1.09−1.12 (m, 3H), 1.17−1.20 (m, 3H), 1.35 (s, 9H), 1.58 (s, 6H),

2.47 (s, 6H), 7.15−7.17 (m, 6H), 7.42−7.44 (m, 2H), 7.44 (d, J = 8.05

Hz, 1H), 7.46−7.47 (m, 4H), 7.55−7.57 (m, 2H), 7.58−7.59 (m, 2H),

7.63−7.65 (m, 2H), 7.67 (d, J = 8.06 Hz, 1H), 7.73−7.74 (m, 6H).

¹³C NMR (125 MHz, CDCl₃): δ 30.4, 31.7, 32.0, 32.5, 34.0, 35.3, 48.7,

50.7, 54.17, 54.19, 59.8, 75.50, 75.54, 77.42, 77.44, 77.9, 78.7, 79.2,

80.2, 80.4, 80.9, 81.1, 89.1, 92.0, 107.9, 121.8, 122.7, 123.06, 123.13,

125.7, 126.6, 127.13, 127.14, 127.3, 127.5, 128.1, 132.0, 132.86,

132.94, 133.2, 133.6, 135.7, 136.5, 138.2, 141.7, 143.8, 144.0, 151.5. IR

(KBr): 3069, 3033, 3017, 2945, 2915, 2891, 2862, 2840, 2225, 1607,

1580, 1494, 1453, 1403, 1394, 1364, 1353, 1303, 1267, 1253, 1210,

1154, 1141, 1113, 1102, 1032, 1013, 1004, 981, 964, 946, 926, 874,

852, 836, 821, 752, 723, 660, 647, 639, 608, 573, 544, 507, 492, 478

cm⁻¹. MS m/z (%): 1093.4 (100, M + H). HRMS (APCI) for

(C₈₀H₆₂Cl₂+ H⁺): calcd 1093.43013, found 1093.43026. Anal. Calcd

for C₈₀H₆₂Cl₂: C, 87.81; H, 5.71. Found: C, 87.71; H, 5.85.

9,10-Bis[2,3-dichlorophenylbuta-1,3-diynyl]triptycene (3). A

ﬂame-dried Schlenk ﬂask was charged with 20 (60 mg, 0.171 mmol),

1,2-dichloro-3-iodobenzene (27) (98 mg, 0.359 mmol), Pd(PPh₃)₄

(16 mg; 0.014 mmol, 8 mol %), and CuI (2 mg, 0.010 mmol, 6 mol

%). After three successive vacuum/argon cycles, dry and degassed

THF (5 mL) and triethylamine (5 mL) were added from a syringe.

The slightly yellowish solution was stirred for 18 h at room

temperature. A dense white solid precipitated. The crude reaction

mixture was diluted with CH₂Cl₂(100 mL), washed with saturated aq

NH₄Cl (2 × 20 mL), and dried over MgSO₄. Column chromatography

on silica gel (hexane/CH₂Cl₂= 4:1) yielded 3 as a white crystalline

solid (86 mg, 0.134 mmol, 78%).

The resolution of the instrument, in its usual conﬁguration, is q_res

≈

0.003 Å⁻¹.

Dielectric Spectroscopy. The powder samples were loaded onto

the surface of coplanar interdigitated electrode capacitators fabricated

by gold metallization on fused silica substrates (each with 50 ﬁngers

separated by ∼10 μm gaps). Nominal capacitor values for the empty

capacitors were near 1 pF and dielectric loss tangents were at or below

10⁻¹⁵level. An Andeen−Hagerling capacitance bridge was used to

measure the dielectric loss and capacitance with sinusoidal alternating

voltage (1.8−5 V and 0.12−12 kHz) applied on the capacitor. Data

were taken continuously with the temperature slowly changing

between 7 K and room temperature. The curves were averaged over

heating and cooling steps and smoothed.

Mp >315 °C (dec.). ¹H NMR (400 MHz, CDCl₃): δ 7.15−7.17 (m,

6H), 7.25 (dd, J₁= 7.65 Hz, J₂= 8.19 Hz, 2H), 7.53 (dd, J₁= 1.47 Hz,

J₂= 8.10 Hz, 2H), 7.62 (dd, J₁= 1.47 Hz, J₂= 7.74 Hz, 2H), 7.78−7.80

(m, 6H). ¹³C NMR (100 MHz, CDCl₃): δ 53.1, 74.5, 76.5, 78.9, 79.4,

122.4, 123.8, 126.1, 127.2, 131.4, 132.8, 133.7, 135.5, 142.7. IR (KBr):

3075, 3061, 3034, 3016, 2954, 2925, 2853, 2243, 2161, 1607, 1577,

1551, 1452, 1412, 1407, 1339, 1303, 1261, 1220, 1191, 1156, 1142,

1112, 1077, 1049, 1032, 983, 949, 842, 796, 782, 749, 703, 639, 570,

530, 491, 474, 455 cm⁻¹. MS m/z (%): 641.1 (100, M + H, center of

isotope cluster). HRMS (APCI) for (C₄₀H₁₈Cl₄+ H⁺): calcd

639.0235, found 639.0226. Anal. Calcd for C₄₀H₁₈Cl₄: C, 75.02; H,

2.83. Found: C, 74.98; H, 3.22.

Synthesis. Rotor 1. A ﬂame-dried Schlenk ﬂask was charged with

5 (150 mg, 0.303 mmol), 4 (153 mg, 0.290 mmol), Pd(PPh₃)₄(14

mg; 0.012 mmol, 4 mol %), and CuI (2 mg, 0.009 mmol, 3 mol %).

After three successive vacuum/argon cycles, degassed dry THF (15

mL) and triethylamine (8 mL) were added from a syringe. The yellow

solution was stirred for 16 h at room temperature. A dense white solid

precipitated. The crude reaction mixture was centrifugated to remove

solvents (10 min, 3000 rpm). The white solid residue was placed on a

frit and washed with 10% aq HCl (2 × 10 mL), concentrated aq

NH₄Cl (2 × 10 mL), water (3 × 10 mL), hexane (4 × 20 mL), CHCl₃

(2 × 10 mL), and ether (2 × 5 mL) and ﬁnally dried using a Kugelrohr

distillation apparatus (60 min, 80 °C, 500 mTorr). Molecular rotor 1

was obtained as a white crystalline solid (196 mg, 0.219 mmol, 76%).

Mp >320 °C (dec.). ¹H NMR (500 MHz, THF-d₈): δ 1.34 (s, 9H),

2.46 (s, 6H), 7.14−7.17 (m, 6H), 7.38 (dd, J₁= 7.72 Hz, J₂= 8.13 Hz,

1H), 7.42−7.43 (m, 2H), 7.45−7.47 (m, 4H), 7.55−7.56 (m, 2H),

7.57−7.59 (m, 2H), 7.63−7.65 (m, 2H), 7.66 (dd, J₁= 1.48 Hz, J₂=

8.13 Hz, 1H), 7.72−7.76 (m, 7H). ¹³C NMR (125 MHz, THF-d₈): δ

31.7, 32.0, 35.3, 54.1, 59.8, 75.4, 75.5, 77.4, 77.9, 78.7, 79.2, 79.3, 80.3,

80.4, 81.0, 89.1, 92.0, 121.8, 122.6, 123.05, 123.11, 124.5, 125.7, 126.6,

127.12, 127.13, 127.3, 127.4, 129.0, 132.83, 132.85, 132.93, 133.6,

134.2, 134.3, 135.9, 138.2, 141.7, 143.8, 144.0, 151.4. IR (KBr): 3069,

3033, 3016, 2988, 2963, 2913, 2876, 2221, 2152, 1607, 1577, 1551,

1494, 1472, 1459, 1453, 1407, 1394, 1362, 1341, 1303, 1267, 1212,

1191, 1174, 1155, 1141, 1113, 1102, 1049, 1033, 1013, 1003, 979, 948,

921, 873, 852, 837, 820, 781, 750, 722, 706, 677, 653, 647, 639, 567,

544, 525, 491, 476 cm⁻¹. MS m/z (%): 893.3 (100, M + H). HRMS

(APCI) for (C₆₅H₄₂Cl₂+ H⁺): calcd, 893.27363; found, 893.27388.

Anal. Calcd for C₆₅H₄₂Cl₂: C, 87.33; H, 4.74. Found: C, 87.28; H,

4.87.

1-((4′-tert-Butylbiphenyl-4-yl)ethynyl)-3-((4-iodophenyl)-

ethynyl)bicyclo[1.1.1]pentane (4). The procedure for 3 was

followed starting with 10 (200 mg, 0.616 mmol), 1,4-diiodobenzene

(1.017 g, 3.082 mmol, 5 equiv), Pd(PPh₃)₄(29 mg, 0.025 mmol, 4 mol

%), and CuI (4 mg, 0.018 mmol, 3 mol %) in dry and degassed THF

(20 mL) and triethylamine (5 mL). Column chromatography on silica

gel (hexane/CH₂Cl₂= 4:1, then hexane/CH₂Cl₂= 1:1) gave 4 as a

white crystalline solid (252 mg, 0.479 mmol, 78%).

1

Mp >275 °C (dec.). H NMR (400 MHz, CDCl₃): δ 1.36 (s, 9H),

2.48 (s, 6H), 7.12−7.14 (m, 2H), 7.45−7.47 (m, 4H), 7.51−7.54 (m,

4H), 7.62−7.64 (m, 2H). ¹³C NMR (100 MHz, CDCl₃): δ 30.7, 31.0,

31.3, 34.6, 59.0, 79.2, 80.1, 88.6, 89.7, 94.0, 121.4, 122.4, 125.8, 126.6,

126.7, 132.1, 133.3, 137.3, 137.4, 140.6, 150.7. IR (KBr): 2986, 2969,

2952, 2907, 2871, 2221, 1494, 1482, 1476, 1445, 1394, 1388, 1366,

1359, 1297, 1280, 1269, 1212, 1201, 1116, 1055, 1031, 1005, 854, 823,

785, 747, 742, 723, 574, 546, 530 cm⁻¹. MS m/z (%): 527.1 (100, M +

H). HRMS (APCI) for (C₃₁H₂₇I + H⁺): calcd 527.12302, found

527.12297. Anal. Calcd for C₃₁H₂₇I: C, 70.72; H, 5.17. Found: C,

70.64; H, 5.17.

9-((2,3-Dichlorophenyl)buta-1,3-diynyl)-10-(buta-1,3-

diynyl)triptycene (5). A solution of TBAF in THF (1.0 M, 0.50 mL,

0.500 mmol) was added to a stirred solution of 28 (236 mg, 0.416

mmol) in wet THF (10 mL) at room temperature. The reddish

reaction mixture was stirred at that temperature for 30 min. The

mixture was then diluted with ether (60 mL), washed with water (2 ×

20 mL), and the organic phase was dried over MgSO₄. Solvents were

removed under reduced pressure and column chromatography on

Rotor 2. The procedure for 1 was followed starting with 6 (150 mg,

0.216 mmol), 4 (111 mg, 0.210 mmol), Pd(PPh₃)₄(10 mg, 0.009

mmol, 4 mol %), and CuI (1 mg, 0.006 mmol, 3 mol %) in dry and

M

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The Journal of Organic Chemistry

Article

silica gel (hexane/CH₂Cl₂= 4:1) aﬀorded 5 as a white crystalline solid

cm⁻¹. MS m/z (%): 419.2 (100, M + Na), 397.2 (42, M + H). HRMS

(ESI+) for (C₂₈H₃₂Si + H⁺): calcd 397.23460, found 397.23461. Anal.

Calcd for C₂₈H₃₂Si: C, 84.79; H, 8.13. Found: C, 84.49; H, 7.96.

1-((4′-tert-Butylbiphenyl-4-yl)ethynyl)-3-ethynylbicyclo-

[1.1.1]pentane (10). To a stirred solution of 9 (580 mg, 1.462

mmol) in wet THF (25 mL) was added a solution of TBAF in THF

(1.0 M, 2.00 mL, 2.000 mmol) at room temperature. The reddish

reaction mixture was stirred for 30 min. The mixture was then diluted

with ether (50 mL) and washed with water (2 × 20 mL), and the clear

yellowish organic phase was dried over MgSO₄. Solvents were

removed under reduced pressure, and column chromatography on

silica gel (hexane/CH₂Cl₂= 4:1) gave 10 as a white crystalline solid

(465 mg, 1.433 mmol, 98%).

(200 mg, 0.404 mmol, 97%).

1

Mp >210 °C (dec.). H NMR (400 MHz, CDCl₃): δ 3.30 (s, 1H),

7.13−7.15 (m, 6H), 7.36 (dd, J₁= 7.64 Hz, J₂= 8.18 Hz, 1H), 7.65

(dd, J₁= 1.45 Hz, J₂= 8.13 Hz, 1H), 7.69−7.75 (m, 7H). ¹³C NMR

(100 MHz, CDCl₃): δ 53.7, 54.1, 67.9, 71.1, 71.6, 75.4, 77.4, 77.9,

79.3, 80.3, 123.01, 123.03, 124.5, 127.10, 127.12, 128.9, 132.8, 134.2,

134.4, 135.9, 143.78, 143.82. IR (KBr): 3298, 3069, 3034, 3015, 2955,

2927, 2869, 2241, 2223, 2162, 2068, 1608, 1579, 1551, 1530, 1454,

1414, 1410, 1340, 1302, 1256, 1228, 1197, 1155, 1141, 1120, 1107,

1078, 1050, 1034, 982, 971, 965, 948, 922, 905, 884, 874, 858, 783,

756, 751, 736, 706, 700, 668, 639, 622, 567, 554, 521, 497, 483, 478,

454 cm⁻¹. MS m/z (%): 495.1 (100, M + H). HRMS (APCI) for

(C₃₄H₁₆Cl₂+ H⁺): calcd 495.07018, found 495.07013. Anal. Calcd for

C₃₄H₁₆Cl₂: C, 82.43; H, 3.26. Found: C, 82.42; H, 3.44.

Mp 216.8−218.1 °C. ¹H NMR (500 MHz, CDCl₃): δ 1.36 (s, 9H),

2.11 (s, 1H), 2.42 (s, 6H), 7.44−7.47 (m, 4H), 7.51−7.54 (m, 4H).

¹³C NMR (125 MHz, CDCl₃): δ 29.9, 30.7, 31.3, 34.6, 58.7, 68.2, 79.9,

Compound 6. The procedure for 5 was followed starting with 29

(200 mg, 0.260 mmol) in wet THF (8 mL) and a solution of TBAF in

THF (1.0 M, 313 μL, 0.313 mmol). Column chromatography on silica

gel (hexane/CH₂Cl₂= 6:1) aﬀorded 6 as a white crystalline solid (176

mg, 0.253 mmol, 97%).

82.6, 88.5, 121.3, 125.8, 126.6, 126.7, 132.1, 137.3, 140.7, 150.7. IR

(KBr): 3280, 3083, 3032, 2963, 2914, 2877, 2219, 2108, 1611, 1507,

1493, 1478, 1463, 1448, 1394, 1364, 1345, 1268, 1251, 1202, 1113,

1029, 1014, 1003, 966, 950, 924, 852, 821, 764, 748, 742, 724, 687,

658, 645, 572, 546, 532, 507 cm⁻¹. MS m/z (%): 347.2 (100, M + Na),

325.2 (47, M + H). HRMS (ESI+) for (C₂₅H₂₄+ H⁺): calcd

325.19508, found 325.19504. Anal. Calcd for C₂₅H₂₄: C, 92.54; H,

7.46. Found: C, 92.27; H, 7.50.

1

Mp >200 °C (dec.). H NMR (500 MHz, CDCl₃): δ 0.89 (s, 9H),

1.08−1.10 (m, 3H), 1.16−1.18 (m, 3H), 1.57 (s, 6H), 2.43 (s, 1H),

7.13−7.15 (m, 6H), 7.34 (d, J = 8.10 Hz, 1H), 7.50 (d, J = 8.10 Hz,

1H), 7.72−7.78 (m, 6H). ¹³C NMR (125 MHz, CDCl₃): δ 29.9, 31.7,

32.9, 47.8, 49.9, 52.6, 53.1, 67.6, 68.6, 71.1, 74.7, 76.5, 76.6, 77.2, 79.6,

79.8, 107.1, 122.0, 122.3, 122.4, 126.10, 126.12, 126.9, 130.6, 131.6,

135.2, 135.9, 142.6, 142.7. IR (KBr): 3310, 3291, 3069, 3034, 2943,

2917, 2890, 2861, 2837, 2226, 1607, 1580, 1453, 1367, 1353, 1303,

1253, 1225, 1154, 1142, 1110, 1032, 1003, 984, 967, 926, 909, 831,

752, 733, 639, 616, 559, 549, 526, 495, 478 cm⁻¹. MS m/z (%): 695.2

(100, M + H). HRMS (APCI) for (C₄₉H₃₆Cl₂+ H⁺): calcd 695.22668,

found 695.22675. Anal. Calcd for C₄₉H₃₆Cl₂+ CDCl₃in a 3:2 ratio: C,

76.94; H, 4.77. Found: C, 76.64; H, 4.86.

9,10-Diethynyltriptycene (12).³³To an ice-cold and well stirred

solution of 14 (7.589 g, 16.988 mmol) in wet THF (40 mL) was

slowly dropwise added a solution of TBAF in THF (1.0 M, 35.68 mL,

35.675 mmol). The brownish-red reaction mixture was stirred at room

temperature for 30 min, diluted with ether (200 mL), and washed with

water (3 × 40 mL), and the organic phase was dried over MgSO₄.

Solvents were removed under reduced pressure, and column

chromatography on silica gel (hexane/CH₂Cl₂= 4:1) aﬀorded 12 as

a white crystalline solid (5.066 g, 16.754 mmol, 99%).

4-Bromo-4′-tert-butylbiphenyl (7).²⁹A previously published

procedure²⁹was adapted as follows: To a solution of 4-bromobiphenyl

(5.00 g, 21.450 mmol) and tert-BuCl (2.39 mL, 22.000 mmol) in dry

CCl₄(30 mL) was added freshly sublimed AlCl₃(267 mg, 2.000

mmol) at 0 °C. The reaction mixture was stirred for an additional 60

min at 0 °C. The solution turned green immediately and massive

evolution of gaseous HCl was observed. The reaction mixture was

diluted with CHCl₃(100 mL), washed with saturated aq NaHCO₃(3

× 20 mL) and water (3 × 20 mL), and ﬁnally dried over MgSO₄.

Solvents were removed under reduced pressure, and a yellowish solid

residue was recrystallized from methanol. Crystals were ﬁltered on a

frit, washed with cold methanol (2 × 20 mL), and dried under reduced

pressure (500 mTorr, 50 °C, 60 min). Compound 7 was obtained as a

white crystalline solid (4.214 g, 14.570 mmol, 68%).

¹H NMR (400 MHz, CDCl₃): δ 3.33 (s, 2H), 7.13−7.15 (m, 6H),

7.79−7.81 (m, 6H). ¹³C NMR (100 MHz, CDCl₃): δ 52.2, 78.0, 80.9,

122.2, 125.8, 142.9, which is in agreement with the literature.³³

9,10-Bis(trimethylsilylethynyl)anthracene (13).³²A previously

published procedure³²was adapted as follows: A ﬂame-dried and

argon-ﬁlled apparatus consisting of a 500 mL two-necked ﬂask

equipped with a gas condenser and a magnetic stirrer was charged with

9,10-dibromoanthracene (11) (30.000 g, 89.280 mmol), PdCl₂(PPh₃)₂

(2.507 g, 3.571 mmol, 4 mol %), and CuI (1.020 g, 5.357 mmol, 6 mol

%). After ﬁve successive vacuum/argon cycles, dry and degassed

Et₂NH (400 mL) was cannulated to the reaction mixture. Finally,

TMSA (37.9 mL, 267.840 mmol) was added via syringe. The reaction

mixture turned black immediately. The dark solution was reﬂuxed for 6

h and then stirred for 16 h at 70 °C. A dense, dark solid precipitated.

All volatiles were removed under reduced pressure, and the black solid

residue was suspended in ether (1 L). The dark organic phase was

extracted with saturated aq NH₄Cl (3 × 300 mL) and combined aq

phases were extracted with ether (3 × 200 mL). Combined ethereal

phases were dried over MgSO₄, and volatiles were removed under

reduced pressure. Column chromatography on silica gel (hexane) gave

13 as a yellow crystalline solid (31.590 g, 85.233 mmol, 95%).

¹H NMR (400 MHz, CDCl₃): δ 0.46 (s, 18H), 7.62−7.64 (m, 4H),

8.59−8.62 (m, 4H). ¹³C NMR (100 MHz, CDCl₃): δ 0.2, 101.5, 108.1,

118.4, 126.8, 127.2, 132.2, which is in agreement with the literature.³²

9,10-Bis(trimethylsilylethynyl)triptycene (14).³³A previously

published procedure³³was adapted as follows: A solution of 13

(31.590 g, 85.233 mmol) in anhydrous DME (400 mL) was canulated

to a ﬂame-dried and argon-ﬁlled 1 L three-necked ﬂask equipped with

a gas condenser, stirrer, and two 250 mL dropping funnels. Isoamyl

nitrite (92.8 mL, 690.712 mmol) was dissolved in DME (100 mL) and

placed into the ﬁrst dropping funnel. The second dropping funnel was

ﬁlled with a solution of anthranilic acid (71.043 g, 518.034 mmol) in

DME (150 mL). The solution in the reaction ﬂask was magnetically

stirred and heated to gentle reﬂux (∼100 °C) using a heating mantle

with a magnetic stirrer. The two solutions in the funnels were slowly

dropped into the reaction vessel at the same rate over 6 h. The

addition of the solutions was accompanied by rapid evolution of gases

¹H NMR (400 MHz, CDCl₃): δ 1.37 (s, 9H), 7.45−7.52 (m, 6H),

7.54−7.56 (m, 2H). ¹³C NMR (100 MHz, CDCl₃): δ 31.3, 34.5, 121.1,

125.8, 126.4, 128.5, 131.8, 137.0, 139.9, 150.7, which is in agreement

with the literature.²⁹

((3-((4′-tert-Butylbiphenyl-4-yl)ethynyl)bicyclo[1.1.1]pent-1-

yl)ethynyl)trimethylsilane (9). A ﬂame-dried Schlenk ﬂask was

charged with 8^30,31(540 mg, 2.867 mmol), 7 (995 mg, 3.441 mmol),

Pd(PPh₃)₄(133 mg, 0.115 mmol, 4 mol %), and CuI (16 mg, 0.086

mmol, 3 mol %). After three successive vacuum/argon cycles, dry and

degassed THF (10 mL) and triethylamine (5 mL) were added from a

syringe. The yellow solution was stirred for 20 h at 55 °C. A dense

white solid precipitated. The crude reaction mixture was diluted with

CH₂Cl₂(150 mL), washed with saturated aq NH₄Cl (2 × 30 mL), and

the clear yellow organic phase was dried over MgSO₄. Column

chromatography on silica gel (hexane/CH₂Cl₂= 4:1) gave 9 as a white

crystalline solid (906 mg, 2.284 mmol, 80%).

Mp 268.4−269.9 °C. ¹H NMR (400 MHz, CDCl₃): δ 0.16 (s, 9H),

1.35 (s, 9H), 2.41 (s, 6H), 7.44−7.47 (m, 4H), 7.50−7.53 (m, 4H).

¹³C NMR (100 MHz, CDCl₃): δ 0.0, 30.6, 30.7, 31.3, 34.6, 59.0, 79.9,

84.7, 88.8, 104.6, 121.4, 125.8, 126.6, 126.7, 132.1, 137.3, 140.6, 150.7.

IR (KBr): 3032, 2990, 2963, 2913, 2876, 2165, 1604, 1493, 1477,

1462, 1446, 1394, 1362, 1318, 1264, 1254, 1201, 1180, 1113, 1082,

1027, 1003, 920, 857, 843, 822, 760, 743, 723, 699, 621, 572, 545, 532

N

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The Journal of Organic Chemistry

Article

(CO₂and N₂). The reaction mixture turned black and was reﬂuxed for

an additional 20 h. All volatiles were removed under reduced pressure

and a dark honey-like residue was triturated with boiling hexane (8 ×

250 mL). Hexane was evaporated, and the remaining high boiling

species were removed under reduced pressure (150 °C, 500 mTorr).

(Note: It is crucial to remove all volatiles, mostly isoamyl nitrite and its

decomposition products, to ensure suﬃcient separation during the

subsequent column chromatography.) A black solid residue was

sorbed on silica gel (20 g) and placed on a column ﬁlled with silica gel

(500 g). Slow elution (hexane) provided 14 as a white or a slightly

yellowish solid (8.638 g, 19.336 mmol, 23%).

the orange reaction mixture was stirred for 30 min at 0 °C and then for

30 min at room temperature. The solution was cooled back to 0 °C,

and a solution of 16 (3.200 g, 8.929 mmol) in dry CH₂Cl₂(70 mL)

was added dropwise. The reaction mixture turned brown immediately.

Cooling was stopped, and the brown solution was stirred for an

additional 3 h at room temperature. Silica gel (25 g) was added

directly to the reaction mixture, and all volatiles were removed under

reduced pressure. Column chromatography on silica gel (hexane/

CH₂Cl₂= 1:1) yielded 17 as a white crystalline solid (3.442 g, 5.137

mmol, 58%).

1

Mp >320 °C (dec.). H NMR (400 MHz, CDCl₃): δ 7.09 (s, 2H),

¹H NMR (400 MHz, CDCl₃): δ 0.47 (s, 18H), 7.09−7.11 (m, 6H),

7.70−7.73 (m, 6H). ¹³C NMR (100 MHz, CDCl₃): δ 0.6, 53.2, 98.3,

99.8, 122.4, 125.9, 143.6, which is in agreement with the literature.³³

9,10-Bis(3-hydroxyprop-1-ynyl)triptycene (15). To a solution

of 12 (4.700 g, 15.544 mmol) in THF (200 mL) at −78 °C was

dropwise added n-BuLi in hexane (2.5 M, 24.87 mL, 62.175 mmol). A

dense white precipitate was formed immediately. The white

suspension was stirred for 20 min at −78 °C, 30 min at room

temperature, and then cooled back to −78 °C. Subsequently, dry solid

paraformaldehyde (2.801 g, 93.264 mmol) was added. Cooling was

stopped, and the reaction mixture was slowly warmed to room

temperature and stirred for 16 h. The suspension turned gray. The

reaction was quenched with saturated aq NH₄Cl (40 mL), and the

solution was stirred for an additional 60 min. The reaction mixture was

diluted with diethyl ether (250 mL) and washed with saturated aq

NH₄Cl (4 × 40 mL), and the clear yellow organic phase was dried

over MgSO₄. Volatiles were removed under reduced pressure. Column

chromatography on silica gel (hexane/acetone = 4:3) provided 15

(4.621 g, 12.750 mmol, 82%) as a white crystalline solid.

7.10−7.13 (m, 6H), 7.75−7.77 (m, 6H). ¹³C NMR (100 MHz,

CDCl₃): δ 53.3, 89.4, 91.7, 103.6, 119.3, 122.4, 125.9, 142.9. IR (KBr):

3069, 3059, 3033, 3017, 2222, 1674, 1650, 1604, 1580, 1456, 1313,

1265, 1247, 1162, 1033, 979, 949, 944, 874, 833, 828, 755, 749, 679,

662, 639, 584, 555 cm⁻¹. MS m/z (%): 669.8 (38, M, center of isotope

cluster), 590.9 (12, center of isotope cluster), 509.9 (39, center of

isotope cluster), 485.9 (35, center of isotope cluster), 459.9 (30, center

of isotope cluster), 430.0 (11, center of isotope cluster), 406.0 (10,

center of isotope cluster), 348.1 (78, center of isotope cluster), 324.1

(100, center of isotope cluster), 300.1 (49), 272.1 (17), 248.1 (20),

174.0 (21), 162.0 (26), 149.0 (10), 137.0 (7), 84.0 (12). HRMS (EI)

+

for (C₂₈H₁₄Br₄): calcd 665.7829, found 665.7826. Anal. Calcd for

C₂₈H₁₄Br₄: C, 50.19; H, 2.11. Found: C, 50.51; H, 2.16.

9,10-Bis((trimethylsilyl)buta-1,3-diynyl)triptycene (18). The

solution of n-BuLi in hexane (2.5 M, 9.67 mL, 24.180 mmol) was

added dropwise to a solution of 17 (2.700 g, 4.030 mmol) in THF (40

mL) cooled to −78 °C. A dense white precipitate was formed

immediately. The suspension was stirred at −78 °C for 90 min, −40

°C for 10 min, and cooled back to −78 °C. Subsequently, TMSCl

(4.09 mL, 32.240 mmol) was added, and the solution was stirred at

−78 °C for 30 min and ﬁnally for 60 min at room temperature. The

reaction mixture was diluted with ether (150 mL) and washed with

saturated aq NH₄Cl (3 × 30 mL). The clear yellowish organic phase

was dried over MgSO₄, and volatiles were removed under reduced

pressure. Column chromatography on silica gel (hexane/CH₂Cl₂=

5:1) gave 18 as a white crystalline solid (1.664 g, 3.363 mmol, 90%).

Mp >350 °C (dec.). ¹H NMR (400 MHz, CDCl₃): δ 0.35 (s, 18H),

7.11−7.13 (m, 6H), 7.72−7.74 (m, 6H). ¹³C NMR (100 MHz,

CDCl₃): δ −0.4, 52.8, 72.2, 77.2, 87.4, 87.7, 122.3, 126.0, 142.8. IR

(KBr): 3071, 3034, 2956, 2897, 2261, 2230, 2106, 1605, 1462, 1454,

1442, 1411, 1304, 1251, 1172, 1155, 1145, 1099, 1032, 1004, 977, 956,

844, 760, 747, 710, 670 cm⁻¹. MS m/z: 495.3 (M + H). HRMS (ESI+)

for (C₃₄H₃₀Si₂+ H⁺): calcd 495.19588, found 495.19577. Anal. Calcd

for C₃₄H₃₀Si₂: C, 82.54; H, 6.11. Found: C, 82.32; H, 6.26.

Desymmetrization of Tetrayne 18. To a solution of 18 (1.600 g,

3.234 mmol) in THF (140 mL) cooled to 0−5 °C in an ice bath was

slowly added (0.05 mL/min) a solution of MeLi in ether (1.6 M, 2.43

mL, 3.881 mmol). The reaction mixture was stirred at this temperature

for an additional 3 h. A dense white solid precipitated. Progress of the

reaction was monitored by TLC (hexane/CH₂Cl₂= 4:1). The solution

was diluted with ether (150 mL) and washed with saturated aq NH₄Cl

(2 × 30 mL), and the clear yellowish organic phase was dried over

MgSO₄. Solvents were removed under reduced pressure, and the

yellowish solid residue was puriﬁed using column chromatography on

silica gel (hexane/CH₂Cl₂= 4:1). Compounds were eluted from the

column in the following order: 18 (210 mg, 0.424 mmol, 13%), 19

(654 mg, 1.548 mmol, 48%), and 20 (440 mg, 1.256 mmol, 39%). All

three compounds were obtained as white crystalline solids.

1

Mp >310 °C (dec.). H NMR (400 MHz, CDCl₃): δ 4.82 (s, 4H),

7.08−7.11 (m, 6H), 7.71−7.73 (m, 6H). ¹H NMR (400 MHz,

acetone-d₆): δ 4.73−4.80 (m, 6H), 7.12−7.15 (m, 6H), 7.77−7.80 (m,

6H). ¹³C NMR (100 MHz, acetone-d₆): δ 51.0, 53.1, 78.3, 94.3, 123.0,

126.6, 144.6. IR (KBr): 3550, 3403, 3306, 3068, 3059, 3034, 3002,

2938, 2917, 2867, 2254, 1704, 1605, 1460, 1455, 1446, 1391, 1373,

1348, 1309, 1241, 1224, 1215, 1163, 1151, 1133, 1077, 1031, 1018,

1012, 985, 970, 945, 922, 890, 859, 771, 766, 757, 752, 714, 692, 673,

639, 590, 572, 550, 493, 488, 483 cm⁻¹. MS m/z: 385.2 (M + Na⁺).

HRMS (ESI+) for (C₂₆H₁₈O₂+ Na⁺): calcd 385.11990, found

385.11989. Anal. Calcd for C₂₆H₁₈O₂: C, 86.16; H, 5.01. Found: C,

86.31; H, 5.16.

9,10-Bis(3-oxoprop-1-ynyl)triptycene (16). To a solution/

suspension of 15 (4.600 g, 12.692 mmol) in dry CH₂Cl₂(150 mL)

was added Dess−Martin periodinane (DMP, 13.458 g, 31.730 mmol)

at room temperature. The solution turned yellow immediately, and the

reaction mixture was stirred for 2.5 h. The suspension dissolved,

leaving a clear yellowish solution. Subsequently, solutions of saturated

aq Na₂S₂O₃(50 mL) and NaHCO₃(50 mL) were added, and the

mixture was stirred for an additional 15 min. The aqueous phase was

removed, and the clear yellowish organic phase was washed with a

saturated aqueous solution of Na₂S₂O₃and NaHCO₃in a 1:1 ratio (2

× 50 mL) and ﬁnally dried over MgSO₄. The solvent was removed

under reduced pressure, and a solid yellow residue was sorbed on silica

gel (6 g). Column chromatography on silica gel (CH₂Cl₂) aﬀorded 16

as a white crystalline solid (3.257 g, 9.088 mmol, 72%).

Mp >335 °C (dec.). ¹H NMR (400 MHz, CDCl₃): δ 7.16−7.18 (m,

6H), 7.71−7.73 (m, 6H), 9.74 (s, 2H). ¹³C NMR (100 MHz, CDCl₃):

δ 52.4, 89.5, 91.6, 122.2, 126.4, 141.6, 176.1. IR (KBr): 3061, 3034,

3005, 2875, 2230, 2196, 1674, 1608, 1458, 1443, 1385, 1309, 1235,

1179, 1163, 1154, 1074, 1032, 945, 858, 760, 753, 725, 685, 648, 638

cm⁻¹. MS m/z (%): 358.1 (68, M), 329.1 (62), 313.1 (11), 300.1

(100), 274.1 (23), 224.1 (12), 150.0 (13), 84.0 (8). HRMS (EI) for

9-((Trimethylsilyl)buta-1,3-diynyl)-10-(buta-1,3-diynyl)-

triptycene (19). Mp >240 °C (dec.). ¹H NMR (400 MHz, CDCl₃): δ

0.35 (s, 9H), 2.43 (s, 1H), 7.12−7.14 (m, 6H), 7.71−7.75 (m, 6H).

¹³C NMR (100 MHz, CDCl₃): δ −0.4, 52.6, 52.8, 67.7, 68.6, 71.2,

72.2, 76.5, 77.3, 87.4, 87.8, 122.2, 122.4, 126.0, 126.1, 142.6, 142.8. IR

(KBr): 3303, 3071, 3034, 2957, 2928, 2254, 2252, 2112, 2119, 1605,

1453, 1442, 1422, 1411, 1304, 1251, 1170, 1153, 1088, 1032, 1008,

950, 906, 880, 843, 750, 735, 705, 639 cm⁻¹. MS m/z (%): 445.2 (100,

M + Na⁺), 423.2 (18, M + H⁺). HRMS (ESI+) for (C₃₁H₂₂Si + Na⁺):

calcd 445.13830, found 445.13824. Anal. Calcd for C₃₁H₂₂Si: C, 88.11;

H, 5.25. Found: C, 88.27; H, 5.12.

+

(C₂₆H₁₄O₂): calcd 358.0994, found 358.0989. Anal. Calcd for

C₂₆H₁₄O₂: C, 87.13; H, 3.94. Found: C, 87.13; H, 3.91.

9,10-Bis(4,4-dibromobut-3-en-1-ynyl)triptycene (17). A

ﬂame-dried and argon-ﬁlled Schlenk ﬂask was charged with PPh₃

(15.223 g, 58.039 mmol) and CBr₄(8.883 g, 26.787 mmol). After

three successive vacuum/argon cycles, the mixture was cooled to 0 °C

using an ice bath, dry and degassed CH₂Cl₂was added (30 mL), and

O

DOI: 10.1021/acs.joc.5b00661

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The Journal of Organic Chemistry

Article

9,10-Di(buta-1,3-diynyl)triptycene (20). Mp >190 °C (dec.).

¹H NMR (400 MHz, CDCl₃): δ 2.44 (s, 2H), 7.13−7.15 (m, 6H),

7.72−7.75 (m, 6H). ¹³C NMR (100 MHz, CDCl₃): δ 52.6, 67.6, 68.6,

71.1, 76.5, 122.3, 126.1, 142.6. IR (KBr): 3285, 3270, 3069, 3060,

3048, 3034, 3020, 3004, 2246, 2217, 2109, 1606, 1581, 1456, 1443,

1311, 1262, 1247, 1168, 1161, 1151, 1144, 1032, 984, 975, 947, 940,

922, 907, 876, 867, 859, 755, 749, 701, 650, 638 cm⁻¹. MS m/z (%):

351.1 (100, M + H). HRMS (APCI) for (C₂₈H₁₄+ H⁺): calcd

351.11683, found 351.11642. Anal. Calcd for C₂₈H₁₄: C, 95.97; H,

4.03. Found: C, 95.60; H, 3.93.

added from a syringe. The slightly yellowish solution was stirred for 5

h at 40 °C. A dense white solid precipitated. The crude reaction

mixture was diluted with ether (80 mL) and washed with saturated aq

NH₄Cl (2 × 30 mL). The clear yellowish organic phase was dried over

MgSO₄, and volatiles were removed under reduced pressure. Column

chromatography repeated four times on silica gel (hexane) provided

25 as a colorless viscous oil (394 mg, 0.833 mmol, 84%).

¹H NMR (400 MHz, CDCl₃): δ 0.86 (s, 9H), 1.04−1.07 (m, 3H),

1.12−1.15 (m, 3H), 1.53 (s, 6H), 7.00 (d, J = 8.29 Hz, 1H), 7.66 (d, J

= 8.29 Hz, 1H). ¹³C NMR (100 MHz, CDCl₃): δ 29.9, 31.7, 32.8,

47.8, 49.9, 76.1, 97.4, 105.3, 126.0, 131.6, 134.1, 137.1, 137.4. IR

(KBr): 2944, 2917, 2891, 2861, 2838, 2230, 1452, 1436, 1414, 1374,

1351, 1285, 1253, 1226, 1167, 1139, 1076, 927, 873, 829, 814, 783,

760, 621, 578, 524 cm⁻¹. MS m/z (%): 472.0 (82, M, center of isotope

cluster), 457.0 (16, M − CH₃, center of isotope cluster), 374.2 (25,

center of isotope cluster), 346.1 (71, M − I), 177.2 (100, 3,5,7-

trimethyladamantyl). HRMS (CI) for (C₂₁H₂₃Cl₂I⁺): calcd 472.0222,

found 472.0211. Anal. Calcd for C₂₁H₂₃Cl₂I: C, 53.30; H, 4.90. Found:

C, 53.37; H, 4.84.

1-(2,2-Dibromoethyl)-3,5,7-trimethyladamantane (22).³⁴

A

previously published procedure³⁴was adapted as follows. A ﬂame-

dried and argon-ﬁlled apparatus consisting of a 50 mL three-necked

ﬂask equipped with a stirrer, septa, L-shaped glass tubing for the

addition of solids, and a connector to the vacuum/argon line was

charged with 1-bromo-3,5,7-trimethyladamantane (21) (1.500 g, 5.832

mmol), and the L-shaped tubing was charged with anhydrous

powdered AlBr₃(621 mg, 2.334 mmol). After three successive

vacuum/argon cycles, an anhydrous vinyl bromide (6.00 mL, 85.554

mmol) was added at −78 °C. Subsequently, the AlBr₃from the L-

shaped tubing was added to the reaction mixture, and the solution was

vigorously stirred at −78 °C for 3 h. A dense white solid precipitated.

The well-stirred reaction mixture was quenched by the dropwise

addition of water (5 mL). Cooling was stopped, and the reaction

mixture was heated to room temperature, allowing spontaneous

evaporation of vinyl bromide. An additional portion of water (10 mL)

was added; the suspension was extracted with ether (3 × 25 mL), and

the combined ethereal phases were dried over MgSO₄. The colorless

ethereal phase was concentrated, and the yellowish oily residue was

distilled using a Kugelrohr distillation apparatus (600 mTorr, 180 °C).

Product 22 was obtained as a clear colorless liquid (1.593 g, 4.374

mmol, 75%).

Bis((3,5,7-trimethyladamantyl)-1-ethynyl)-2,3-dichloroben-

zene (26). The title compound was isolated as a more polar side-

product during the chromatography described above as a white

crystalline solid (33 mg, 0.060 mmol, 12%).

Mp 226.3−227.9 °C. ¹H NMR (400 MHz, CDCl₃): δ 0.86 (s,

18H), 1.04−1.07 (m, 6H), 1.12−1.15 (m, 6H), 1.53 (s, 12H), 7.20 (s,

2H). ¹³C NMR (100 MHz, CDCl₃): δ 30.0, 31.7, 32.8, 47.9, 49.9, 76.5,

105.1, 124.6, 130.2, 134.6. IR (KBr): 2948, 2916, 2863, 2841, 2229,

1454, 1374, 1363, 1350, 1287, 1253, 1226, 1214, 1065, 1054, 938, 920,

910, 884, 830, 807, 774, 686, 612, 569, 551, 528, 511 cm⁻¹. MS m/z

(%): 547.3 (100, M + H). HRMS (APCI) for (C₃₆H₄₄Cl₂+ H⁺): calcd

547.28928, found 547.28927. Anal. Calcd for C₃₆H₄₄Cl₂: C, 78.95; H,

8.10. Found: C, 78.62; H, 8.06.

¹H NMR (400 MHz, CDCl₃): δ 0.82 (s, 9H), 1.04 (s, 6H), 1.18 (s,

6H), 2.57 (d, J = 6.05 Hz, 2H), 5.82 (t, J = 6.05 Hz, 1H). ¹³C NMR

(100 MHz, CDCl₃): δ 30.2, 31.9, 37.2, 40.1, 47.7, 50.2, 59.3. IR (KBr):

2945, 2919, 2894, 2862, 2835, 1454, 1429, 1374, 1355, 1254, 1247,

1225, 1165, 1144, 1028, 936, 915, 872, 799, 691, 585, 562, 439 cm⁻¹.

MS m/z (%): 363.0 (2, M), 177.2 (100, M − CH₂CHBr₂). HRMS

9-((2,3-Dichlorophenyl)buta-1,3-diynyl)-10-((trimethylsilyl)-

buta-1,3-diynyl)triptycene (28). A ﬂame-dried Schlenk ﬂask was

charged with 19 (260 mg, 0.615 mmol), 1,2-dichloro-3-iodobenzene

(27) (201 mg, 0.738 mmol), Pd(PPh₃)₄(29 mg, 0.025 mmol, 4 mol

%) and CuI (3 mg, 0.018 mmol, 3 mol %). After three successive

vacuum/argon cycles, degassed dry THF (8 mL) and triethylamine (5

mL) were added from a syringe. The yellow solution was stirred for 18

h at room temperature. A dense white solid precipitated. The crude

reaction mixture was diluted with CH₂Cl₂(150 mL) and washed with

saturated aq NH₄Cl (2 × 30 mL), and the yellow organic phase was

dried over MgSO₄. Column chromatography on silica gel (hexane/

CH₂Cl₂= 4:1) gave 28 as a white crystalline solid (236 mg, 0.416

mmol, 68%).

+

(CI) for (C₁₅H₂₃Br₂): calcd 361.0166, found 361.0172. Anal. Calcd

for C₁₅H₂₄Br₂: C, 49.47; H, 6.64. Found: C, 49.24; H, 6.56, which is in

agreement with the literature.³⁴

1-Ethynyl-3,5,7-trimethyladamantane (23).³⁴A ﬂame-dried

Schlenk ﬂask was charged with t-BuOK (1.294 g, 11.532 mmol).

After three successive vacuum/argon cycles, THF (5 mL) was added

from a syringe. Subsequently, a solution of 22 (1.400 g, 3.844 mmol)

in THF (10 mL) was added dropwise at 0 °C. Cooling was stopped,

and the reaction mixture was stirred at room temperature for 3 d. A

dense, white solid precipitated. The crude reaction mixture was diluted

with ether (80 mL), and water (10 mL) was slowly added. The slightly

yellowish organic phase was washed with water (2 × 20 mL) and

saturated aq NH₄Cl (1 × 20 mL) and dried over MgSO₄. Solvents

were removed under reduced pressure, and the yellowish solid residue

was puriﬁed using column chromatography on silica gel (hexane) to

give 23 (663 mg, 3.277 mmol, 85%) as a colorless liquid, which

solidiﬁed in the refrigerator.

1

Mp >300 °C (dec.). H NMR (400 MHz, CDCl₃): δ 0.36 (s, 9H),

7.13−7.15 (m, 6H), 7.23 (t, J = 7.93 Hz, 1H), 7.52 (dd, J₁= 1.30 Hz,

J₂= 8.08 Hz, 1H), 7.62 (dd, J₁= 1.33 Hz, J₂= 7.73 Hz, 1H), 7.74−7.79

(m, 6H). ¹³C NMR (100 MHz, CDCl₃): δ −0.4, 52.8, 53.1, 72.2, 74.4,

76.5, 77.3, 78.9, 79.4, 87.4, 87.8, 122.3, 122.4, 123.8, 126.0, 126.1,

127.2, 131.3, 132.7, 133.6, 135.5, 142.7, 142.8. IR (KBr): 3069, 3033,

3015, 3007, 2111, 1606, 1577, 1550, 1453, 1409, 1341, 1304, 1251,

1192, 1166, 1152, 1110, 1050, 1032, 970, 948, 939, 922, 860, 843, 784,

750, 744, 707, 639 cm⁻¹. MS m/z (%): 567.1 (100, M + H, center of

isotope cluster), 495.1 (43, M − TMS, center of isotope cluster).

HRMS (APCI) for (C₃₇H₂₄Cl₂Si + H⁺): calcd 567.10971, found

567.10931. Anal. Calcd for C₃₇H₂₄Cl₂Si: C, 78.30; H, 4.26. Found: C,

78.67; H, 4.47.

Compound 29. A ﬂame-dried Schlenk ﬂask was charged with 25

(200 mg, 0.423 mmol), 19 (197 mg, 0.465 mmol), Pd(PPh₃)₄(20 mg;

0.017 mmol, 4 mol %), and CuI (2 mg, 0.013 mmol, 3 mol %). After

three successive vacuum/argon cycles, degassed dry THF (6 mL) and

triethylamine (6 mL) were added from a syringe. The yellow solution

was stirred for 18 h at room temperature. A dense white solid

precipitated. The crude reaction mixture was diluted with ether (80

mL) and washed with saturated aq NH₄Cl (2 × 30 mL), and the

yellowish organic phase was dried over MgSO₄. Volatiles were

removed under reduced pressure. Column chromatography on silica

gel (hexane/CH₂Cl₂= 6:1) gave 29 as a white foamy solid (238 mg,

0.310 mmol, 73%).

¹H NMR (400 MHz, CDCl₃): δ 0.83 (s, 9H), 1.01−1.04 (m, 3H),

1.08−1.11 (m, 3H), 1.44 (s, 6H), 2.08 (s, 1H). ¹³C NMR (100 MHz,

CDCl₃): δ 29.9, 31.60, 31.63, 48.2, 49.8, 66.7, 92.3. IR (KBr): 3312,

2947, 2894, 2864, 2837, 2106, 1454, 1375, 1354, 1255, 1231, 912, 627,

553, 529 cm⁻¹. MS m/z (%): 203.2 (100, M + H), 187.1 (65), 177.2

(14), 161.1 (8), 147.1 (13), 133.1 (5), 121.1 (12). HRMS (CI) for

(C₁₅H₂₂+ H⁺): calcd 203.1800, found 203.1796. Anal. Calcd for

C₁₅H₂₂: C, 89.04; H, 10.96. Found: C, 88.98; H, 10.96, which is in

agreement with the literature.³⁴

1-(2,3-Dichloro-4-iodophenyl)ethynyl-3,5,7-trimethylada-

mantane (25). A ﬂame-dried Schlenk ﬂask was charged with 23 (200

mg, 0.988 mmol), 1,4-diiodo-2,3-dichlorobenzene (24) (1.970 g, 4.940

mmol, 5 equiv), Pd(PPh₃)₄(46 mg; 0.040 mmol, 4 mol %), and CuI

(6 mg, 0.030 mmol, 3 mol %). After three successive vacuum/argon

cycles, dry and degassed THF (5 mL) and triethylamine (10 mL) were

P

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The Journal of Organic Chemistry

Article

Mp 172.3−174.3 °C. ¹H NMR (400 MHz, CDCl₃): δ 0.35 (s, 9H),

0.89 (s, 9H), 1.08−1.11 (m, 3H), 1.16−1.19 (m, 3H), 1.57 (s, 6H),

7.13−7.15 (m, 6H), 7.34 (d, J = 8.13 Hz, 1H), 7.51 (d, J = 8.12 Hz,

1H), 7.74−7.77 (m, 6H). ¹³C NMR (100 MHz, CDCl₃): δ −0.3, 30.0,

31.7, 32.9, 47.8, 49.9, 52.8, 53.1, 72.2, 74.7, 76.49, 76.53, 77.3, 79.7,

79.9, 87.4, 87.7, 107.1, 122.1, 122.3, 122.4, 126.0, 126.1, 126.9, 130.6,

131.6, 135.2, 135.9, 142.7, 142.8. IR (KBr): 3069, 3034, 2945, 2916,

2891, 2862, 2836, 2225, 2109, 1607, 1579, 1453, 1366, 1353, 1252,

1227, 1211, 1150, 1141, 1084, 1032, 941, 910, 845, 790, 752, 712, 677,

639, 608, 560, 550, 525, 500, 478 cm⁻¹. MS m/z (%): 767.3 (100, M +

H). HRMS (APCI) for (C₅₂H₄₄Cl₂Si + H⁺): calcd 767.26621, found

767.26642. Anal. Calcd for C₅₂H₄₄Cl₂Si: C, 81.33; H, 5.78. Found: C,

81.12; H, 5.86.

9-Trimethylsilylethynyl-10-ethynyltriptycene (30). To a sol-

ution of 14 (5.530 g, 12.379 mmol) in THF (120 mL) cooled to 0−5

°C in an ice bath was slowly (0.05 mL/min) added a solution of MeLi

in ether (1.6 M, 10.06 mL, 16.093 mmol). The reaction mixture was

stirred at this temperature for additional 60 min, during which time a

dense white precipitate was formed. Progress of the reaction was

monitored by TLC (hexane/CH₂Cl₂= 4:1). The solution was diluted

with ether (150 mL) and washed with saturated aq NH₄Cl (2 × 30

mL), and the clear yellowish organic phase was dried over MgSO₄.

Solvents were removed under reduced pressure, and the yellowish

solid residue was puriﬁed using column chromatography on silica gel

(hexane/CH₂Cl₂= 4:1). Compounds were eluted from the column in

following order: 14 (542 mg, 1.213 mmol, 10%), 30 (2.662 g, 7.107

mmol, 57%) and 12 (1.175 g, 3.886 mmol, 31%). All three compounds

were obtained as white crystalline solids.

¹³C NMR (100 MHz, CDCl₃): δ 29.6, 31.3, 31.7, 34.6, 58.9, 79.8, 80.6,

87.7, 94.8, 121.0, 125.8, 126.6, 126.7, 132.1, 137.3, 140.9, 150.8, 176.7.

IR (KBr): 3032, 2991, 2954, 2944, 2914, 2900, 2876, 2225, 2197,

1663, 1492, 1462, 1393, 1376, 1367, 1358, 1271, 1201, 1109, 1004,

951, 907, 852, 837, 821, 749, 725, 671, 573, 547, 532 cm⁻¹. MS m/z

(%): 375.2 (100, M + Na). HRMS (ESI+) for (C₂₆H₂₄O + Na⁺): calcd

375.17194, found 375.17184. Anal. Calcd for C₂₆H₂₄O: C, 88.60; H,

6.86. Found: C, 88.23; H, 6.87.

3-(3-((4′-tert-Butylbiphenyl-4-yl)ethynyl)bicyclo[1.1.1]pent-

1-yl)prop-2-yn-1-ol (33). To a solution of 10 (140 mg, 0.431 mmol)

in ether (8 mL) was added n-BuLi in hexane (2.5 M, 520 μL, 1.300

mmol) dropwise at −78 °C. A dense white precipitate was formed

immediately. The slightly yellowish solution was stirred at −78 °C for

5 min, heated to room temperature, and then cooled back to −78 °C.

Subsequently, dry paraformaldehyde (66 mg, 2.200 mmol) was added,

and the white suspension was stirred for an additional 60 min at −78

°C. Cooling was stopped, and the reaction mixture was slowly warmed

to room temperature and stirred for an additional 16 h. The

suspension turned yellow. The reaction was quenched with saturated

aq NH₄Cl (10 mL), and the solution was stirred for an additional 20

min. The reaction mixture was diluted with ether (80 mL) and washed

with saturated aq NH₄Cl (2 × 20 mL). Combined water phases were

extracted with ether (1 × 30 mL). The clear yellow organic phase was

dried over MgSO₄, and volatiles were removed under reduced

pressure. Column chromatography on silica gel (CH₂Cl₂) gave 33 as a

white crystalline solid (117 mg, 0.330 mmol, 77%).

1

Mp 258−264 °C (dec.). H NMR (400 MHz, CDCl₃): δ 1.35 (s,

9H), 1.54 (br s, 1H), 2.40 (s, 6H), 4.27 (s, 2H), 7.43−7.47 (m, 4H),

7.51−7.53 (m, 4H). ¹³C NMR (100 MHz, CDCl₃): δ 30.1, 30.8, 31.3,

34.6, 51.3, 58.7, 78.2, 80.0, 84.6, 88.5, 121.4, 125.8, 126.6, 126.7, 132.1,

137.3, 140.6, 150.7. IR (KBr): 3334, 3083, 3028, 2994, 2961, 2914,

2877, 1492, 1462, 1447, 1394, 1359, 1275, 1201, 1108, 1020, 1003,

937, 897, 857, 843, 822, 749, 742, 725, 574, 546 cm⁻¹. MS m/z (%):

377.0 (100, M + Na). HRMS (ESI+) for (C₂₆H₂₆O + Na⁺): calcd

377.18759, found 377.18768. Anal. Calcd for C₂₆H₂₆O: C, 88.09; H,

7.39. Found: C, 88.39; H, 7.24.

Mp 213.0−214.2 °C. ¹H NMR (400 MHz, CDCl₃): δ 0.47 (s, 9H),

3.30 (s, 1H), 7.10−7.12 (m, 6H), 7.72−7.76 (m, 6H). ¹³C NMR (100

MHz, CDCl₃): δ 0.3, 52.1, 53.0, 78.1, 80.9, 98.2, 99.4, 122.1, 122.3,

125.7, 125.8, 143.0, 143.2. IR (KBr): 3288, 3068, 3034, 3016, 2958,

2898, 2181, 2149, 2129, 1622, 1608, 1457, 1454, 1448, 1427, 1418,

1409, 1330, 1302, 1252, 1221, 1168, 1158, 1075, 1037, 1032, 1007,

981, 950, 857, 842, 753, 701, 692, 666, 648, 640, 614 cm⁻¹. MS m/z

(%): 375.2 (100, M + H). HRMS (APCI) for (C₂₇H₂₂Si + H⁺): calcd

375.15635, found 375.15651. Anal. Calcd for C₂₇H₂₂Si: C, 86.58; H,

5.92. Found: C, 86.41; H, 5.90.

9-Bromoethynyl-10-(trimethylsilylethynyl)triptycene (31).

Freshly recrystallized NBS (63 mg, 0.353 mmol) and AgNO₃(12

mg, 0.074 mmol) were added to a solution of 30 (110 mg, 0.294

mmol) in dry acetone (10 mL) at 25 °C. The slightly yellowish

solution was stirred at room temperature in the dark for 2.5 h. A white

solid precipitated. Solvent was removed under reduced pressure, and

column chromatography on silica gel (hexane/CH₂Cl₂= 4:1) gave 31

as a white crystalline solid (111 mg, 0.245 mmol, 83%).

3-(3-((4′-tert-Butylbiphenyl-4-yl)ethynyl)bicyclo[1.1.1]pent-

1-yl)propiolic Acid (34). A solution of n-BuLi in hexane (2.5 M, 148

μL, 0.370 mmol) was added dropwise to a stirred solution of 10 (60

mg, 0.185 mmol) in THF (10 mL) at −78 °C. The slightly yellowish

solution was stirred at −78 °C for 15 min, heated to room

temperature, and then cooled back to −78 °C. Gaseous CO₂was

bubbled into the solution through a PTFE cannula at −78 °C for 10

min and at room temperature for an additional 10 min. A dense white

solid precipitated. The white suspension was diluted with water (10

mL), acidiﬁed with concentrated HCl (pH ≈1), and extracted with

ether (4 × 30 mL), and the combined colorless ethereal phases were

dried over MgSO₄. Solvents were removed under reduced pressure,

and the white solid residue was triturated with CH₂Cl₂(3 × 3 mL).

Carboxylic acid 34 was obtained as a white crystalline solid (63 mg,

0.171 mmol, 92%).

Mp 247.7−248.9 °C. ¹H NMR (500 MHz, CDCl₃): δ 0.47 (s, 9H),

7.11−7.12 (m, 6H), 7.69−7.74 (m, 6H). ¹³C NMR (125 MHz,

CDCl₃): δ 0.3, 51.4, 52.9, 53.3, 74.8, 98.2, 99.3, 122.1, 122.3, 125.7,

125.8, 143.1. IR (KBr): 3070, 3034, 3018, 2959, 2897, 2217, 2173,

1608, 1453, 1422, 1409, 1328, 1303, 1262, 1250, 1226, 1168, 1158,

1140, 1090, 1048, 1032, 976, 949, 857, 843, 752, 711, 698, 645, 640,

488 cm⁻¹. MS m/z (%): 477.10 (100, M + H, center of isotope

cluster). HRMS (ESI+) for (C₂₇H₂₁BrSi + Na⁺): calcd 475.04881,

found 475.04866. Anal. Calcd for C₂₇H₂₁BrSi: C, 71.52; H, 4.67.

Found: C, 71.42; H, 4.53.

1

Mp 265 °C (dec). H NMR (400 MHz, THF-d₈): δ 1.33 (s, 9H),

2.43 (s, 6H), 7.40−7.46 (m, 4H), 7.53−7.58 (m, 4H). ¹³C NMR (100

MHz, THF-d₈): δ 30.3, 31.6, 32.2, 35.2, 59.4, 73.6, 81.0, 84.6, 88.5,

122.4, 126.5, 127.2, 127.3, 132.9, 138.1, 141.7, 151.4, 154.2. IR (KBr):

3434, 3083, 3032, 2993, 2960, 2916, 2902, 2879, 2233, 1686, 1493,

1478, 1462, 1448, 1418, 1394, 1364, 1348, 1293, 1238, 1203, 1180,

1113, 1095, 1029, 1004, 926, 876, 851, 820, 753, 748, 724, 657, 636,

601, 572, 547 cm⁻¹. MS m/z (%): 367.1 (38, M − H), 323.1 (100, M

3-(3-((4′-tert-Butylbiphenyl-4-yl)ethynyl)bicyclo[1.1.1]pent-

1-yl)propiolaldehyde (32). To a solution of DMSO (140 μL, 1.974

mmol) in CH₂Cl₂(5 mL) was added (COCl)₂(119 μL, 1.410 mmol)

at −78 °C. After 30 min at this temperature, 33 (100 mg, 0.282 mmol)

in CH₂Cl₂(25 mL) was slowly introduced, and the milky solution was

stirred 90 min at −78 °C. Then, triethylamine (393 μL, 2.820 mmol)

was added, and the reaction mixture was stirred for 60 min and

warmed to room temperature. A white precipitate dissolved, leaving a

clear yellow solution. Volatiles were removed under reduced pressure,

and the yellowish solid residue was sorbed on silica gel (4 g). Column

chromatography on silica gel (hexane/CH₂Cl₂= 1:1) yielded 32 as a

white crystalline solid (81 mg, 0.230 mmol, 82%).

−

− COOH). HRMS (ESI−) for (C₂₆H₂₃O₂): calcd 367.17035, found

367.17052. Anal. Calcd for C₂₆H₂₄O₂: C, 84.75; H, 6.57. Found: C,

84.64; H, 6.55.

Methyl 3-(3-((4′-tert-Butylbiphenyl-4-yl)ethynyl)bicyclo-

[1.1.1]pent-1-yl)propiolate (35). An ethereal solution of CH₂N₂

was added dropwise to a solution of 34 (55 mg, 0.149 mmol) in ether

(10 mL) at room temperature until the reaction mixture turned yellow.

The solution was stirred for 10 min, and volatiles were removed under

reduced pressure. Column chromatography on silica gel (hexane/

CH₂Cl₂= 1:1) yielded 35 as a white crystalline solid (53 mg, 0.139

mmol, 93%).

1

Mp 237−239 °C (dec.). H NMR (400 MHz, CDCl₃): δ 1.36 (s,

9H), 2.51 (s, 6H), 7.44−7.48 (s, 4H), 7.52−7.54 (s, 4H), 9.19 (s, 1H).

Q

DOI: 10.1021/acs.joc.5b00661

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

Article

Mp 233.4−234.9 °C. ¹H NMR (400 MHz, CDCl₃): δ 1.36 (s, 9H),

2.48 (s, 6H), 3.77 (s, 3H), 7.43−7.47 (m, 4H), 7.51−7.53 (m, 4H).

¹³C NMR (100 MHz, CDCl₃): δ 29.3, 31.3, 31.4, 34.5, 52.8, 58.8, 71.6,

80.4, 86.1, 87.9, 121.1, 125.8, 126.6, 126.7, 132.1, 137.3, 140.8, 150.7,

153.9. IR (KBr): 3032, 2994, 2960, 2913, 2876, 2233, 1709, 1675,

1610, 1492, 1457, 1438, 1396, 1360, 1289, 1215, 1178, 1113, 1091,

1030, 1003, 979, 865, 856, 822, 753, 725, 678, 573, 545 cm⁻¹. MS m/z

(%): 405.2 (100, M + Na). HRMS (ESI+) for (C₂₇H₂₆O₂+ Na⁺):

calcd 405.18250, found 405.18245. Anal. Calcd for C₂₇H₂₆O₂: C,

84.78; H, 6.85. Found: C, 84.66; H, 6.90.

Compound 36. To a solution of 30 (127 mg, 0.340 mmol) in

THF (2 mL) was dropwise added n-BuLi in hexane (2.5 M, 102 μL,

0.255 mmol) at −78 °C. A dense white precipitate was formed

immediately. The slightly yellowish suspension was stirred at −78 °C

for 15 min, heated to room temperature, and then cooled to −78 °C

again. Subsequently, a solution of 32 (60 mg, 0.170 mmol) in THF (6

mL) was added, and the reaction mixture was stirred for 60 min at

−78 °C. Cooling was stopped, and the reaction mixture was slowly

warmed to room temperature and stirred for 30 min. The suspension

dissolved, leaving a clear yellow solution. The reaction mixture was

diluted with ether (60 mL) and washed with saturated aq NH₄Cl (2 ×

20 mL), and the clear yellow organic phase was dried over MgSO₄.

Volatiles were removed under reduced pressure, and column

chromatography on silica gel (hexane/CH₂Cl₂= 1:1, then pure

CH₂Cl₂) gave racemic 36 as a white crystalline solid (117 mg, 0.161

mmol, 95%).

degassed THF (10 mL) and triethylamine (5 mL) were added from a

syringe. The yellow solution was stirred for 3 days at 55 °C. A dense

white solid precipitated, and the mixture turned black. The crude

reaction mixture was diluted with ether (80 mL) and washed with

saturated aq NH₄Cl (2 × 30 mL), and a brownish organic phase was

dried over MgSO₄. Column chromatography on silica gel (hexane)

gave 39 as a colorless oil (867 mg, 1.948 mmol, 82%).

¹H NMR (400 MHz, CDCl₃): δ 0.24 (s, 27H), 0.25 (s, 9H), 7.30−

7.37 (m, 4H). ¹³C NMR (100 MHz, CDCl₃): δ −0.05, 0.4, 91.0, 95.8,

104.8, 107.9, 122.2, 124.7, 131.5, 131.7. IR (KBr): 3079, 3037, 2958,

2895, 2828, 2158, 1505, 1494, 1441, 1404, 1246, 1221, 1101, 1018,

866, 836, 788, 759, 747, 691, 645, 623, 550, 434 cm⁻¹. MS m/z (%):

445.2 (82, M + H), 429.2 (100, M - CH₃). HRMS (CI) for (C₂₂H₄₀Si₅

+ H⁺): calcd 445.2055, found 445.2061. Anal. Calcd for C₂₂H₄₀Si₅: C,

59.38; H, 9.06. Found: C, 59.46; H, 9.09.

2-Ethynyl-1,1,1,3,3,3-hexamethyl-2-(trimethylsilyl)trisilane

(40).³⁸A previously published procedure³⁸was adapted as follows. A

solution of HCCMgBr in THF (0.5 M, 23.74 mL, 11.868 mmol) was

added dropwise to a stirred solution of ClSi(TMS)₃(2.800 g, 9.890

mmol) in THF (20 mL) at 0 °C. The clear yellowish reaction mixture

was stirred for 10 min at 0 °C and then for 18 h at room temperature.

The reaction mixture was diluted with hexane (100 mL) and washed

with saturated aq NH₄Cl (2 × 30 mL), and the clear slightly yellowish

organic phase was dried over MgSO₄. Volatiles were removed under

reduced pressure. Sublimation on a Kugelrohr distillation apparatus

(90 °C, 800 mTorr) gave 40 as a white crystalline solid (2.424 g, 8.890

mmol, 90%).

Mp 164.7−165.9 °C. ¹H NMR (400 MHz, CDCl₃): δ 0.48 (s, 9H),

1.36 (s, 9H), 2.50 (s, 6H), 5.62 (s, 1H), 7.11−7.13 (m, 6H), 7.46−

7.48 (m, 4H), 7.52−7.54 (m, 4H), 7.71−7.75 (m, 6H). ¹³C NMR

(100 MHz, CDCl₃): δ 0.3, 30.1, 31.1, 31.3, 34.6, 52.0, 52.8, 53.0, 58.8,

77.6, 79.3, 80.2, 83.9, 88.4, 90.5, 98.2, 99.4, 121.3, 122.1, 122.3, 125.7,

125.78, 125.83, 126.6, 126.7, 132.1, 137.3, 140.7, 143.1, 143.2, 150.7.

IR (KBr): 3549, 3293, 3069, 3032, 2962, 2914, 2878, 2245, 2216,

2180, 1608, 1494, 1454, 1446, 1394, 1363, 1309, 1297, 1271, 1251,

1230, 1166, 1155, 1141, 1113, 1055, 1032, 1004, 975, 853, 843, 821,

753, 692, 649, 640, 611, 573, 545, 486 cm⁻¹. MS m/z (%): 749.3 (100,

M + Na). HRMS (ESI+) for (C₅₃H₄₆OSi + Na⁺): calcd 749.32101,

found 749.32071. Anal. Calcd for C₅₃H₄₆OSi: C, 87.56; H, 6.38.

Found: C, 87.57; H, 6.15.

Mp 100.3−101.5 °C. ¹H NMR (400 MHz, CDCl₃): δ 0.21 (s,

27H), 2.30 (s, 1H). ¹³C NMR (100 MHz, CDCl₃): δ 0.2, 84.0, 95.8.

IR (KBr): 3300, 3285, 2952, 2896, 2828, 2787, 2015, 1443, 1399,

1312, 1283, 1258, 1246, 835, 746, 691, 648, 622, 598, 472 cm⁻¹. MS

m/z (%): 273.1 (32, M), 257.1 (100, M − CH₃). HRMS (CI) for

+

(C₁₁H₂₈Si₄): calcd 272.1268, found 272.1273. Anal. Calcd for

C₁₁H₂₈Si₄: C, 48.45; H, 10.35. Found: C, 48.48; H, 10.22, which is

in agreement with the literature.³⁸

Reaction of 39 with MeLi. To a colorless solution of 39 (230 mg,

0.517 mmol) in THF (20 mL) cooled to −78 °C was slowly added a

solution of MeLi in ether (1.6 M, 356 μL, 0.569 mmol). The solution

turned orange-brown immediately. The reaction mixture was stirred at

this temperature for 60 min and then for an additional 60 min at 0 °C.

The solution turned green-brown during this time. Progress of the

reaction was monitored by TLC (hexane). The solution was diluted

with ether (50 mL), washed with saturated aq NH₄Cl (1 × 30 mL),

and the clear yellowish organic phase was dried over MgSO₄. Solvents

were removed under reduced pressure, and the yellowish solid residue

was puriﬁed using column chromatography on silica gel (hexane).

Compounds were eluted from the column in the following order: 42

(130 mg, 0.496 mmol, 96%) and then 43 (95 mg, 0.480 mmol, 93%).

Both compounds were obtained as colorless oils.

Compound 37. To a solution of DMSO (137 μL, 1.932 mmol) in

CH₂Cl₂(2 mL) was added (COCl)₂(117 μL, 1.380 mmol) at −78 °C.

After 30 min at this temperature, 36 (100 mg, 0.138 mmol) in CH₂Cl₂

(4 mL) was slowly introduced, and the milky solution was stirred for

60 min at −78 °C. Then, triethylamine (385 μL, 2.760 mmol) was

added. The mixture was stirred for 10 min, warmed to room

temperature, and stirred for an additional 30 min. The solution turned

yellow and contained a dense white precipitate. Volatiles were

removed under reduced pressure, and the yellowish solid was sorbed

on silica gel (4 g). Column chromatography on silica gel (hexane/

CH₂Cl₂= 1:1) aﬀorded 37 as a white crystalline solid (79 mg, 0.109

mmol, 79%).

1,1,1,2,3,3,3-Heptamethyl-2-(trimethylsilyl)trisilane

(42).^46,47¹H NMR (400 MHz, CDCl₃): δ 0.05 (s, 3H), 0.12 (s, 27H).

¹³C NMR (100 MHz, CDCl₃): δ 0.4. IR (KBr): 2949, 2893, 2855,

1

Mp >245 °C (dec.). H NMR (400 MHz, CDCl₃): δ 0.49 (s, 9H),

2823, 1438, 1416, 1395, 1306, 1246, 835, 782, 744, 730, 687, 623

1.37 (s, 9H), 2.61 (s, 6H), 7.14−7.16 (m, 6H), 7.47−7.49 (m, 4H),

7.53−7.56 (m, 4H), 7.69−7.71 (m, 3H), 7.75−7.77 (m, 3H). ¹³C

NMR (100 MHz, CDCl₃): δ 0.3, 29.7, 31.3, 31.8, 34.6, 52.2, 53.1, 59.0,

80.7, 80.9, 87.4, 87.8, 92.1, 92.5, 98.5, 99.0, 121.0, 121.9, 122.6, 125.8,

125.9, 126.2, 126.6, 126.7, 132.1, 137.3, 140.9, 142.0, 143.0, 150.8,

160.1. IR (KBr): 3070, 3033, 2993, 2958, 2915, 2878, 2222, 2207,

2178, 1645, 1608, 1507, 1493, 1458, 1454, 1445, 1395, 1362, 1309,

1281, 1261, 1251, 1231, 1183, 1159, 1131, 1113, 1057, 1044, 1032,

1024, 1005, 857, 843, 821, 744, 719, 690, 652, 639, 623, 590, 574, 547,

491, 485 cm⁻¹. MS m/z (%): 725.2 (100, M + H). HRMS (ESI+) for

(C₅₃H₄₄OSi + H⁺): calcd 725.32342, found 725.32324. Anal. Calcd for

C₅₃H₄₄OSi: C, 87.80; H, 6.12. Found: C, 87.65; H, 5.95.

cm⁻¹. MS m/z (%): 262.1 (55, M), 247.1 (100, M − CH₃). HRMS

+

(CI) for (C₁₀H₃₀Si₄): calcd 262.1425, found 262.1431. Anal. Calcd

for C₁₀H₃₀Si₄: C, 45.72; H, 11.51. Found: C, 45.94; H, 11.70, which is

in agreement with the literature.^46,47

((4-Ethynylphenyl)ethynyl)trimethylsilane (43).⁴⁸¹H NMR

(400 MHz, CDCl₃): δ 0.25 (s, 9H), 3.16 (s, 1H), 7.41 (s, 4H). ¹³C

NMR (100 MHz, CDCl₃): δ −0.1, 78.9, 83.2, 96.5, 104.3, 122.1, 123.6,

131.8, 131.9, which is in agreement with the literature.⁴⁸

Synthesis of Silanes 44 and 45. A ﬂame-dried Schlenk ﬂask was

charged with 24 (1.994 g, 5.000 mmol), Pd(PPh₃)₄(83 mg, 0.072

mmol, 4 mol %), and CuI (10 mg, 0.054 mmol, 3 mol %). After three

successive vacuum/argon cycles, dry and degassed THF (10 mL) and

triethylamine (5 mL) were added from a syringe. Subsequently, TMSA

(255 μL, 1.800 mmol) was added dropwise at room temperature. The

yellow solution was stirred for 3 h at 40 °C. A dense white solid

precipitated. The crude reaction mixture was diluted with ether (100

mL) and washed with saturated aq NH₄Cl (2 × 30 mL), and the

1,1,1,3,3,3-Hexamethyl-2-(trimethylsilyl)-2-((4-

((trimethylsilyl)ethynyl)phenyl)ethynyl)trisilane (39). A ﬂame-

dried Schlenk ﬂask was charged with 40 (776 mg, 2.844 mmol), ((4-

bromophenyl)ethynyl)trimethylsilane (41) (600 mg, 2.370 mmol),

Pd(PPh₃)₄(110 mg, 0.095 mmol, 4 mol %), and CuI (14 mg, 0.071

mmol, 3 mol %). After three successive vacuum/argon cycles, dry and

R

DOI: 10.1021/acs.joc.5b00661

J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry

Article

yellowish organic phase was dried over MgSO₄. Solvents were

removed under reduced pressure, and the yellowish solid residue was

puriﬁed using column chromatography on silica gel (hexane).

Compounds were eluted from the column in the following order:

24 (1.258 g, 3.154 mmol) as a white crystalline solid, 44 (456 mg,

1.235 mmol, 69%) as a clear colorless oil, and 45 (153 mg, 0.451

mmol, 25%) as a white crystalline solid.

ASSOCIATED CONTENT

* Supporting Information

■

S

¹H and ¹³C NMR spectra of all new compounds, solid state

NMR spectra of 5%1@TPP-d₁₂(235) and 5%2@TPP-d₁₂(70),

and an ORTEP view of a single molecule and packing in

crystals of 16, 17, 20, and 26. The Supporting Information is

available free of charge on the ACS Publications website at

DOI: 10.1021/acs.joc.5b00661.

((2,3-Dichloro-4-iodophenyl)ethynyl)trimethylsilane (44). ¹H

NMR (400 MHz, CDCl₃): δ 0.27 (s, 9H), 7.09 (d, J = 8.28 Hz, 1H),

7.70 (d, J = 8.28 Hz, 1H). ¹³C NMR (100 MHz, CDCl₃): δ −0.3, 99.1,

100.3, 102.6, 125.0, 131.9, 134.4, 137.4, 137.6. IR (KBr): 2959, 2897,

2853, 2173, 2147, 1561, 1449, 1431, 1408, 1350, 1321, 1299, 1250,

1234, 1170, 1160, 1137, 1067, 900, 844, 815, 760, 686, 621, 581 cm⁻¹.

MS m/z (%): 367.9 (12, M + H), 352.9 (14, M − CH₃), 73.0 (100,

TMS). HRMS (CI) for (C₁₁H₁₁Cl₂ISi + H⁺): calcd 368.9130, found

368.9131. Anal. Calcd for C₁₁H₁₁Cl₂ISi: C, 35.79; H, 3.00. Found: C,

36.05; H, 3.26.

(2,3-Dichloro-1,4-phenylene)bis(ethyne-2,1-diyl)bis-

(trimethylsilane) (45). Mp 81.3−82.0 °C. ¹H NMR (400 MHz,

CDCl₃): δ 0.27 (s, 18H), 7.32 (s, 2H). ¹³C NMR (100 MHz, CDCl₃):

δ −0.3, 100.7, 103.0, 124.7, 130.7, 135.1. IR (KBr): 2955, 2926, 2897,

2854, 2162, 1579, 1451, 1409, 1365, 1351, 1250, 1150, 948, 936, 866,

843, 829, 760, 698, 662, 630, 615, 600, 547 cm⁻¹. MS m/z (%): 339.1

(100, M + H), 323.0 (75, M − CH₃), 73.0 (65, TMS). HRMS (CI) for

(C₁₆H₂₀Cl₂Si₂+ H⁺): calcd 339.0559, found 339.0568. Anal. Calcd for

C₁₆H₂₀Cl₂Si₂: C, 56.62; H, 5.94. Found: C, 56.69; H, 6.01.

AUTHOR INFORMATION

Corresponding Author

*E-mail: kaleta@uochb.cas.cz.

Notes

■

The authors declare no competing ﬁnancial interest.

ACKNOWLEDGMENTS

■

This work was supported by the European Research Council

under the European Community Framework Programme

(FP7/2007-2013), ERC Grant 227756, and by the Institute

of Organic Chemistry and Biochemistry, Academy of Sciences

of the Czech Republic (RVO 61388963). Y.S., K.Z., and C.T.R.

gratefully acknowledge ﬁnancial support from the US National

Science Foundation Division of Materials Research through

Grant DMR-1409981. We are grateful to Dr. Lucie Bednarova

́ ̌ ́

and Dr. Radek Pohl for help with IR and NMR spectra,

respectively.

2,3-Dichloro-1-ethynyl-4-iodobenzene (46). To a stirred

solution of 44 (400 mg, 1.084 mmol) in wet THF (5 mL) was

added a solution of TBAF in THF (1.0 M, 1.30 mL, 1.300 mmol) at

room temperature. The yellowish reaction mixture was stirred for 30

min. The mixture was then diluted with ether (50 mL) and washed

with water (1 × 20 mL), and the organic phase was dried over MgSO₄.

Solvents were removed under reduced pressure, and column

chromatography on silica gel (hexane) aﬀorded 46 as a light and air

sensitive white crystalline solid (290 mg, 0.977 mmol, 90%).

REFERENCES

■

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additional 18 h. The purple reaction mixture was diluted with ether

(50 mL), washed with 5% aq HCl (1 × 25 mL), water (1 × 25 mL),

and saturated aq NH₄Cl (2 × 25 mL), and the clear yellowish organic

phase was dried over MgSO₄. Volatiles were removed under reduced

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¹H NMR (400 MHz, CDCl₃): δ 0.26 (s, 27H), 7.10 (dd, J₁= 7.67

Hz, J₂= 8.14 Hz, 1H), 7.34 (dd, J₁= 1.54 Hz, J₂= 8.19 Hz, 1H), 7.35

(dd, J₁= 1.54 Hz, J₂= 7.61 Hz, 1H). ¹³C NMR (100 MHz, CDCl₃): δ

0.4, 96.9, 104.0, 126.4, 126.7, 129.4, 131.5, 133.1, 134.4. IR (KBr):

3067, 2950, 2894, 1577, 1554, 1448, 1432, 1407, 1349, 1258, 1245,

1188, 1155, 1049, 895, 866, 836, 780, 746, 709, 691, 652, 623, 483

cm⁻¹. MS m/z (%): 417.1 (55, M + H), 384.1 (100). HRMS (APCI)

for (C₁₇H₃₀Cl₂Si₄+ H⁺): calcd 417.08744, found 417.08747. Anal.

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Arrays of Molecular Rotors with Triptycene Stoppers: Surface Inclusion in Hexagonal Tris(o -phenylenedioxy)cyclotriphosphazene

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