Insulated molecular wires: Dendritic encapsulation of poly(triacetylene) oligomers, attempted dendritic stabilization of novel poly(pentaacetylene) oligomers, and an organometallic approach to dendritic rods

Article abstract of DOI:10.1002/1522-2675(20010228)84:2<296::AID-HLCA296>3.0.CO;2-X

Multinanometer-long end-capped poly(triacetylene) (PTA) and poly(pentaacetylene) (PPA) oligomers with dendritic side chains were synthesized as insulated molecular wires. PTA Oligomers with laterally appended Frechet-type dendrons of first to third generation were prepared by attaching the dendrons (8, 13, and 17, respectively. Scheme 1) to (E)-enediyne 18 by a Mitsunobu reaction and subsequent Glaser-Hay oligomerization under end-capping conditions (Scheme 2). Whereas first-generation oligomers up to the pentamer were isolated (1a-e), for reasons of steric overcrowding, only oligomers up to the trimer (2a-c) were formed at the second-generation level, and only the end-capped monomer and dimer (3a.b) were isolated at the third-generation level. By repetitive sequences of hydrosilylation (with the Karstedt catalyst), followed by allylation or vinylation, a series of carbosilane dendrons were also prepared (Schemes 3 and 4). Attachment of the second-generation wedge 40 to (E)-enediyne 18, followed by deprotection and subsequent end-capping Hay oligomerization, provided PTA oligomers 4a-d with lateral carbosilane dendrons (Scheme 5). UV/VIS Studies (Figs. 5-10) demonstrated that the insulating dendritic layers did not alter the electronic characteristics of the PTA backbone, even at the higher-generation levels. Despite distortion from planarity due to the bulky dendritic wedges, no loss of π-electron conjugation along the PTA backbone was detected. A surprising (E)-(Z) isomerization of the diethynylethene (DEE) core in the third generation derivative 3a was observed, possibly photosensitized by the bulky Frechet-type dendritic wedge. Electrochemical investigations by steady-state voltammetry and cyclic voltammetry showed that the first reduction potential of the PTA oligomer with Frechet-type dendrons is shifted to more negative values as the dendritic coverage increases. With compounds 5a-c, the first oligomers with a poly(pentaacetylene) backbone were obtained by oxidative Hay oligomerization under end-capping conditions (Scheme 6). The synthesis of dendritic PPA oligomers by oxidative coupling of (E)-enetetrayne 60 under end-capping conditions provided oligomers 61a-d, which were formed as mixtures of stereoisomers due to unexpected thermal (E)-(Z) isomerization (Scheme 8). In another novel approach towards dendritic encapsulation of molecular wires with a Pt-bridged tetraethynylethene (TEE) oligomeric backbone, the trans-dichloroplatinum(II) complex trans-67 with dendritic phosphane ligands (Fig. 14) was coupled under Hagihara conditions to mono-deprotected 69 under formation of the extended monomer 65 (Scheme 12). Again, an unexpected thermal (E)-(Z) isomerization, possibly induced by steric strain between TEE moieties and dendritic phosphane ligands in the unstable complex, led to the isolation of 65 as an isomeric mixture only.

Full text of DOI:10.1002/1522-2675(20010228)84:2<296::AID-HLCA296>3.0.CO;2-X

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Insulated Molecular Wires: Dendritic Encapsulation
of Poly(triacetylene) Oligomers, Attempted Dendritic Stabilization
of Novel Poly(pentaacetylene) Oligomers, and an Organometallic Approach
to Dendritic Rods
by Albertus P. H. J. Schenninga), Jan-Dirk Arndta), Masato Itoa), Alison Stoddarta), Martin Schreibera),
Peter Siemsena), Rainer E. Martina), Corinne Boudonb), Jean-Paul Gisselbrechtb), Maurice Grossb),
Volker Gramlichc), and François Diederich*a)
a) Laboratorium für Organische Chemie, ETH-Zentrum, Universitätstrasse 16, CH-8092 Zürich
b) Laboratoire dꢀElectrochimie et de Chimie Physique du Corps Solide, U. M. R. au CNRS, no 7512,
Â
Â
Faculte de Chimie, Universite Louis Pasteur, 1 et 4, rue Blaise Pascal, F-67008 Strasbourg Cedex
c) Laboratorium für Kristallographie, Eidgenössische Technische Hochschule, ETH-Zentrum,
Sonneggstrasse 5, CH-8092 Zürich
Multinanometer-long end-capped poly(triacetylene) (PTA) and poly(pentaacetylene) (PPA) oligomers
with dendritic side chains were synthesized as insulated molecular wires. PTA Oligomers with laterally
Â
appended Frechet-type dendrons of first to third generation were prepared by attaching the dendrons (8, 13, and
17, respectively, Scheme 1) to (E)-enediyne 18 by Mitsunobu reaction and subsequent Glaser-Hay
a
oligomerization under end-capping conditions (Scheme 2). Whereas first-generation oligomers up to the
pentamer were isolated (1a ± e), for reasons of steric overcrowding, only oligomers up to the trimer (2a ± c) were
formed at the second-generation level, and only the end-capped monomer and dimer (3a,b) were isolated at the
third-generation level. By repetitive sequences of hydrosilylation (with the Karstedt catalyst), followed by
allylation or vinylation, a series of carbosilane dendrons were also prepared (Schemes 3 and 4). Attachment of
the second-generation wedge 40 to (E)-enediyne 18, followed by deprotection and subsequent end-capping Hay
oligomerization, provided PTA oligomers 4a ± d with lateral carbosilane dendrons (Scheme 5). UV/VIS Studies
(Figs. 5 ± 10) demonstrated that the insulating dendritic layers did not alter the electronic characteristics of the
PTA backbone, even at the higher-generation levels. Despite distortion from planarity due to the bulky dendritic
wedges, no loss of p-electron conjugation along the PTA backbone was detected. A surprising (E) ! (Z)
isomerization of the diethynylethene (DEE) core in the third generation derivative 3a was observed, possibly
Â
photosensitized by the bulky Frechet-type dendritic wedge. Electrochemical investigations by steady-state
Â
voltammetry and cyclic voltammetry showed that the first reduction potential of the PTA oligomer with Frechet-
type dendrons is shifted to more negative values as the dendritic coverage increases. With compounds 5a ± c, the
first oligomers with a poly(pentaacetylene) backbone were obtained by oxidative Hay oligomerization under
end-capping conditions (Scheme 6). The synthesis of dendritic PPA oligomers by oxidative coupling of (E)-
enetetrayne 60 under end-capping conditions provided oligomers 61a ± d, which were formed as mixtures of
stereoisomers due to unexpected thermal (E) ! (Z) isomerization (Scheme 8). In another novel approach
towards dendritic encapsulation of molecular wires with a Pt-bridged tetraethynylethene (TEE) oligomeric
backbone, the trans-dichloroplatinum(II) complex trans-67 with dendritic phosphane ligands (Fig. 14) was
coupled under Hagihara conditions to mono-deprotected 69 under formation of the extended monomer 65
(Scheme 12). Again, an unexpected thermal (E) ! (Z) isomerization, possibly induced by steric strain between
TEE moieties and dendritic phosphane ligands in the unstable complex, led to the isolation of 65 as an isomeric
mixture only.
1. Introduction. ± Among the various classes of monodisperse, rod-like oligomers
with a linearly p-conjugated backbone [1][2], poly(triacetylene) (PTA) oligomers are
attracting increasing interest for their electronic, nonlinear optical, and mesomorphic

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properties [3 ± 7]. On the other hand, dendrimer technology (for recent reviews, see
[8]) has provided in recent years a fascinating tool for modulating optoelectronic
properties through encapsulation of chromophores inside dendritic branches [9]. We
now describe a merger of dendrimer chemistry with our ongoing development of
monodisperse-functionalized PTA oligomers to generate insulated molecular wires, as
schematically shown in Fig. 1.
Fig. 1. Schematic representation of PTA oligomers insulated inside a dendritic shell
Dendritic modification of p-conjugated polymers has been increasingly inves-
tigated, and these studies were recently summarized in a review by Schlüter and Rabe
[10]. Three types of modification have been reported: p-conjugated oligomers and
polymers with dendritic side chains [11][12] or dendritic end groups [13] and
dendrimers with p-conjugated oligomers/polymers at the periphery [14]. We were
interested in exploring how encapsulation of the linearly p-conjugated backbone by
laterally attached, sterically shielding dendritic wedges influences the processability
and stability of PTA oligomers and polymers. At the same time, we wished to explore to
what extent steric hindrance between adjacent dendritic wedges of higher generation
could possibly cause nonplanarity and deconjugation of the backbone. Here, we report
the synthesis of monodisperse, multinanometer-long dendritic PTA rods bearing
Â
Frechet-type dendrons [15] of first to third generation (1 ± 3) (for a preliminary
communication of this part of the work, see [11]) or carbosilane dendrons [8b] [16 ± 20]
of second generation (4) (Fig. 2). We show that p-electron conjugation in these tubular
macromolecules is fully maintained at all generation levels. In addition, we report the
first series of poly(pentaacetylene) (PPA) oligomers (5, Fig. 3) as well as attempts to
Â
stabilize these more delicate unsaturated backbones by lateral attachment of Frechet-
type dendrons. Poly(pentaacetylene)s [ (CꢀC CꢀC CRˆCR CꢀC CꢀC)n
]
are the fourth class of linearly conjugated polymers with a nonaromatic all-
carbon backbone in the progression that starts with poly(acetylene)
[
[
(CRˆCR)n ], poly(diacetylene) [ (CꢀC CRˆCR)n ], and poly(triacetylene)
(CꢀC CRˆCR CꢀC)n ], and ultimately leads to carbyne [ (CꢀC)n ]. Also,
preliminary results in an organometallic approach towards dendritic rods are described.
2. Results and Discussion. ± 2.1. Synthesis of Poly(triacetylene) Oligomers
Â
Encapsulated with Frechet-Type Dendrons. The dendrons required for the synthesis
of 1 ± 3 (Fig. 2) were prepared as shown in Scheme 1 [15]. Etherification of methyl 3,5-
dihydroxybenzoate (6) gave 7, and subsequent ester hydrolysis yielded the first-
generation dendritic branch 8. Etherification of 3,5-dihydroxybenzyl alcohol (9)
provided 10, which was transformed into benzyl bromide 11. Etherification of 6 with 11
gave ester 12, which was hydrolyzed to the second-generation dendron 13. Similar
sequences (9 ! 14 ! 15 and 6 ! 16 ! 17) provided the third-generation dendron 17.

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Fig. 2. Dendritically encapsulated PTA oligomers 1 ± 4

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299
Fig. 3. First series of poly(pentaacetylene) (PPA) oligomers 5a ± c
Dendrons 8, 13, and 17 were subsequently attached to (E)-2,3-bis[(triisopropylsi-
lyl)ethynyl]but-2-ene-1,4-diol (18) [4][21] using the Mitsunobu reaction [22] to give the
dendritic silyl-protected monomers 19 ± 21, respectively (Scheme 2). The yield of the
third-generation compound 21 was very low (4%), possibly due to steric hindrance of
the reacting COOH group by the bulky dendritic wedges in dendron 17. After
deprotection with Bu4NF in wet THF, the free (E)-enediynes 22 ± 24 were obtained.
The dendritic wedges substantially stabilize the usually rather unstable free (E)-
enediynes [23], and compounds 22 ± 24 can be stored in the air at ambient temperature
for months without decomposition. Oxidative Hay coupling [24] of 22 ± 24 in the
presence of PhCꢀCH as an end-capping reagent [21] provided the oligomeric PTAs as
solids. The first-generation compound 22 afforded separable oligomers up to the
pentamer (1a ± e), which extend in length from 19.4 Š (1a) to 49.4 Š (1e) [11][21]. For
steric reasons, the second-generation derivative 23 yielded isolable oligomers only up
to the trimer (2a ± c). Finally, due to severe steric overcrowding, conversion of the third
generation enediyne 24 gave only end-capped monomer and dimer (3a,b) in pure form
and sufficient yields.
Analytical gel-permeation chromatography (GPC) proved to be extremely useful
for monitoring the purification of our compounds. The separation of the oligomers was
achieved by preparative GPC (Bio-Beads S-X1; CH2Cl2), and the purity of the
fractions was determined by analytical GPC because, specifically for the higher
oligomers, thin-layer chromatography (TLC) was useless. With other techniques such
1
as H- and 13C-NMR spectroscopy, we could not detect impurities (lower and higher
oligomers) with less than 10% abundance, while analytical GPC was sensitive for
impurities with an abundance of less than 1%. The analytical GPC traces of the first-
generation dendritic oligomers 1a ± e are shown in Fig. 4. Optical detection occurred at
300 nm in the absorption region of the aromatic wedges. GPC Separations of the
higher-generation compounds were equally efficient.
The molecular constitution of the dendritic rods was confirmed by matrix-assisted
laser-desorption-ionization mass spectra (MALDI-TOF-MS; matrix: 9-nitroanthra-
‡
‡
cene), which depicted either the [M ‡ Na] or [M ‡ K] ions as base peaks, and NMR
spectra. In the 1H-NMR spectra of the centrosymmetrical oligomers, the number of the
t-Bu resonances increases with the number of monomeric units (Table 1). Similar
behavior was observed for the aromatic protons positioned between the two alkoxy
substituents of the central benzene rings that serve as linkers between PTA backbone
and dendritic wedges.

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Fig. 4. Analytical GPC traces (Bio-Beads S-X1; CH2Cl2) for the first-generation dendritic rods 1a ± e (UV
detection at 300 nm)
In the 13C-NMR spectra, the number of C(sp) resonances, which appear as clearly
discernable signals between 73 and 90 ppm, increases by 2 ‡ 2n, where n is the number
of monomeric units in the oligomers. The spectra did not display a significant difference
in chemical shift between these resonances in oligomers of same length but different
dendritic generation (Table 1) [25]. Force-field calculations [26] showed clearly that
the conformation of the PTA backbone, including the two end-capping Ph groups, is not
planar in the higher-generation dendritic rods ± in particular in the third-generation
dimer 3b ± due to the steric hindrance of the bulky dendritic wedges. Only the first
generation derivatives 1a ± e, similar to previous PTA oligomers [3 ± 5], should have a
planar conjugated backbone. The activation barriers for rotation of the backbone about
C(sp) C(sp) and C(sp) C(sp2) single bonds, however, are very small [27]; therefore,
symmetrical averaged NMR spectra are observed at all generation levels.
An interesting observation was made during purification of the end-capped third-
generation monomer 3a by preparative GPC [28]. Instead of the expected single
1
resonance, two t-Bu resonances were observed in the H-NMR spectrum and TLC of
the solution showed two spots. After column chromatography (SiO2; hexane/CH2Cl2
1:1) in the dark, 3a was obtained as a pure substance, and only one t-Bu resonance was
observed. When a solution of isomerically pure 3a was irradiated with sunlight, two t-
Bu resonances were observed again, indicating that 3a underwent a (E) ! (Z)
photoisomerization of the central CˆC bond [29]. This phenomenon was not
encountered with the end-capped monomers of first and second generation (1a and
Â
2a, resp.) and resembles observations made with dendrimers also containing Frechet-
type dendritic wedges around a photoisomerizable azobenzene core, in which IR
excitation of the aromatic wedges, followed by energy transfer, induced a (Z) ! (E)
isomerization of the core [30].

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Table 1. Characteristic NMR (500 MHz) Resonances of the Dendritic PTA Oligomers in CHCl3
Oligomer
1H-NMR (d [ppm])
Me3C
ArHa)
1a
1b
1c
1d
1e
2a
2b
2c
3a
3b
1.33
1.31; 1.32
1.29; 1.30; 1.31
1.27; 1.28; 1.29; 1.30
1.26; 1.27; 1.28; 1.29; 1.30
1.32
1.29; 1.31
1.26; 1.27; 1.31
1.29
6.85
6.76; 6.81
6.72; 6.75; 6.81
6.71; 6.72; 6.74; 6.80
6.71 ± 6.72 (m); 6.73; 6.80
6.84
6.73; 6.79
6.69; 6.70; 6.77
6.82
b
1.23; 1.26
)
Oligomer
13C-NMR (d [ppm])
CꢀC
1a
1b
1c
1d
1e
2a
2b
2c
3a
3b
73.41; 76.52; 87.67; 88.75
73.41; 76.37; 82.45; 87.53; 88.23; 89.68
73.46; 76.43; 82.34; 83.06; 87.37; 88.29; 88.33; 89.81
73.47; 76.41; 82.28; 82.83; 83.11; 87.35; 88.12; 88.29; 88.45;
73.42; 76.35; 82.23; 82.73; 82.82; 83.07; 87.32; 88.08; 88.20;
73.41; 76.52; 87.79; 88.87
89.84
88.29; 88.45; 89.85
73.46; 76.39; 82.61; 87.71; 88.31; 89.77
73.46; 76.43; 82.46; 83.15; 87.54; 88.29; 88.35; 89.86
73.44; 76.51; 87.83; 88.94
c
)
a) Resonance of the proton positioned between the two alkoxy substituents in the central benzene ring bridging
the dendrons to the PTA backbone. b) Masked in a multiplet. c) Not determined.
2.2. Synthesis of Poly(triacetylene) Oligomers Encapsulated in Carbosilane Den-
drons. Several considerations led to the preparation of the second class of PTA
Â
oligomers (4a ± d, Fig. 2) bearing ꢁcarbosilaneꢀ wedges. Frechet-type dendrons of
generations 1 ± 3 are not spherical but rather flat. In contrast, we expected ꢁcarbosilaneꢀ
wedges to generate a more spherical encapsulation already at low generation numbers.
Also, we expected enhanced stability of the ꢁcarbosilaneꢀ dendrons and hoped to avoid
Â
the (E) ! (Z) photoisomerization that apparently is promoted by the Frechet-type
dendrons as described in Sect. 2.1. We also wished to enhance the length of the spacers
connecting the dendrons to the PTA monomer in order to reduce the steric hindrance
in the oxidative acetylenic oligomerization.
In analogy to the synthesis of 1 ± 3, we adopted for the preparation of 4a ± d a
strategy in which ꢁcarbosilaneꢀ dendrons are attached to (E)-enediyne 18 (Scheme 2)
by the Mitsunobu reaction. Dendron synthesis was pursued via two routes, either
repetitive hydrosilylation/allylation or repetitive hydrosilylation/vinylation. The for-
mer approach started from 4-allylanisole (25) or from the corresponding tert-butyl ether
26, which was prepared by demethylation of 25 with Br3B [31] to give 27, followed by
acid-catalyzed etherification with isobutene [32] (Scheme 3). The two aromatic ethers
25 and 26 were subsequently reacted with HSiCl3 in the presence of Karstedt catalyst (a
(divinyltetramethylsiloxane)platinum complex in xylene) [33] to yield the hydro-

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silylated products 28 and 29, respectively, with complete regioselectivity (1H-NMR).
Subsequent conversion with allylmagnesium bromide afforded the first-generation
ꢁcarbosilaneꢀ dendrons 30 and 31. The hydrosilylation reaction was conducted in pure
HSiCl3 on the multigram scale, and the excess reagent was readily removed by vacuum
distillation. The isomerized styrene derivatives 32 and 33 were formed as minor side
products (yields < 5%) and were readily separated by bulb-to-bulb distillation.
Scheme 3. ꢀCarbosilaneꢁ Dendrons by Repetitive Hydrosilylation/Allylation
a) Br3B, CH2Cl2, 788 ! 158, 2 h; 70%. b) Isobutene, CF3SO3H (cat.), 788, 3 h; 96%. c) HSiCl3, Karstedt
catalyst, 208, 2 h. d) Allylmagnesium bromide, THF, 208, 6 h; 61% (30), 49% (31), less than 5% 32 or 33 formed
(yields starting from 25 and 26, respectively). e) HSiCl3, Karstedt catalyst, THF, 208, 3 h; then allylmagnesium
bromide, THF, 208, 48 h; 26%.
Hydrosilylation in pure HSiCl3 was quite advantageous at the first-generation level,
since it provided, after allylation, good yields of products that were readily purified. At
the second-generation level, however, the conversion in neat reagent proceeded much
too slowly, and a cosolvent (THF) was added to accelerate the reaction. In this way,
anisole 30 was hydrosilylated in the presence of Karstedt catalyst to provide, after
allylation, the second-generation dendron 34 in 26% yield. The modest yield was a
result of the tedious efforts required to separate by multiple preparative GPC runs the
desired product from a small impurity with similar retention time. Since the 1H-NMR
monitoring of the hydrosilylation step indicated a clean conversion, we presume that
this side product was formed in the allylation step. The yield of the desired product was

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305
even more disappointing in the hydrosilylation/allylation starting from tert-butyl ether
1
31. In this case, H-NMR monitoring showed that the tert-butyl ether was readily
cleaved during hydrosilylation.
The purity of the dendrons of first and second generations was readily revealed by
29Si-NMR spectroscopy, which showed a single 29Si resonance for 30 and two for 34.
In the second approach, 25 was hydrosilylated, and the crude product was reacted
with vinylmagnesium bromide to give 35 in 66% yield (Scheme 4). Again, 32 was
formed as a side-product in less then 5% yield but was readily removed by bulb-to-bulb
distillation. In comparison to allyl derivative 30, vinylated first-generation dendron 35
was much more reactive, and hydrosilylation was successful in neat HSiCl3. After
vinylation, the second-generation dendron 36 was conveniently purified by column
chromatography (CC), followed by one preparative GPC run. A comparison of the
yields of the second generation wedges (34: 26%, 36: 67%) shows substantial
advantages of the hydrosilylation/vinylation over the hydrosilylation/allylation route.
ꢁCarbosilaneꢀ dendrons with an aliphatic periphery were prepared by catalytic
hydrogenation of the terminal double bond in 35, yielding 37, which was demethylated
Scheme 4. ꢀCarbosilaneꢁ Dendrons by Repetitive Hydrosilylation/Vinylation
a) HSiCl3, Karstedt catalyst, 208, 2 h. b) Vinylmagnesium bromide, THF, 208, 12 h; 66% (35 from 25), 67% (36
from 35). c) H2, Pd/C (10%), pentane, 208, 2 h; 90%. d) Br3B, CH2Cl2, 788 ! 158, 2 h; 99% (38); 71% (40);
70% (43). e) Et3SiH, Karstedt catalyst, THF, D, 48 h; 97% (39), 82% (41). f) Ph3SiH, Karstedt catalyst, THF, D,
7 h; 27%.

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with Br3B to provide the phenolic wedge 38. Alternatively, hydrosilylation of 35 with
Et3SiH gave 39, which was demethylated to the second-generation wedge 40. A third-
generation dendron with aliphatic periphery, 41, was obtained in very high yield (82%)
by hydrosilylation of 36 with Et3SiH. With Ph3SiH, we also prepared derivative 42,
which was transformed by demethylation into the phenolic wedge 43 bearing nine Ph
groups in its periphery.
On the way to PTA oligomers bearing ꢁcarbosilaneꢀ dendrons, the first-generation
phenolic wedge 38 was reacted with (E)-enediyne 18 under classical Mitsunobu
conditions (Ph3P, diethyl azodicarboxylate (DEAD)) [22a] to give protected monomer
44, which was converted to 45 with Bu4NF (Scheme 5). In contrast, the second-
generation wedge 40 did not react with 18 under these conditions. However, application
of the redox system (Bu3P, 1, 1'-(azodicarbonyl)piperidine (ADDP)) introduced by
Tsunoda et al. [22b] provided the desired product 46 in 65% yield. For the success of
this reaction, it was essential to add ADDP slowly, over a period of 24 h, to the stirred
mixture. Deprotection with Bu4NF afforded the second generation dendritic monomer
47, which was isolated as a stable, clear oil. In contrast, the first-generation counterpart
45 was much less stable and could only be isolated as a deep-red oil, due to slow
decomposition during workup. Oligomerization of 47 was achieved under Hay
conditions in the presence of PhCꢀCH as end-capping reagent and afforded the
desired oligomers 4a ± d, which were separated by preparative GPC, first at ambient,
then at high pressure. The sensitivity of the Mitsunobu reaction of 18 to steric
hindrance was further demonstrated in the attempted conversion of the phenolic
ꢁcarbosilaneꢀ wedge 43 with nine Ph rings in the periphery. Both protocols (Ph3P,
DEAD or Bu3P, ADDP) failed to give the desired monomer 48 (Scheme 5).
The nature and length of the oligomers 4a ± d was readily revealed by MALDI-
1
TOF-MS, the number of resolved resonances in the H- and 13C-NMR spectra, and
1
comparison of the H-NMR integrals of the monomeric repeat units in the PTA
Â
backbone with those of the end-capping groups. In contrast to the rods with Frechet-
type dendrons (Sect. 2.1), no (E) ! (Z) isomerization was observed with the
ꢁcarbosilaneꢀ derivatives.
2.3. UV/VIS and Electrochemical Characterization of the Dendritic PTA Rods. As
mentioned in Sect. 2.1, force-field calculations of the higher-generation dendritic rods
showed clearly that the conformation of the PTA backbone, including the two end-
capping Ph groups, is not planar due to severe steric hindrance of the bulky dendritic
wedges. A resulting decrease or even complete loss of the p-electron conjugation along
the PTA backbone in the higher-generation compounds should be readily observable
by means of electronic absorption spectroscopy.
Â
The UV/VIS spectra of the dendritic molecular wires with Frechet-type dendrons,
1 ± 3, were measured in CHCl3 (Figs. 5 ± 7) at 298 K. All compounds, except the
monomers, are yellow solids. At all generation levels, the longest-wavelength
absorption maximum (lmax) is bathochromically shifted with increasing rod length,
and no saturation was observed. The latter was expected from other work, which had
shown that saturation of the optical properties in PTA oligomers occurs only at a length
of 8 ± 10 monomeric units [4][5].
A comparison of the spectra of dimers 1b, 2b, and 3b revealed that, independent of
the dendritic generation number, the longer-wavelength absorptions, which originate

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Scheme 5. Preparation of PTA Oligomers Bearing Carbosilane Dendrons
a) Ph3P, DEAD, 208, 6 h; 68%. b) Bu4NF, THF, 08, 2 min; 88% (45), 82% (47). c) Bu3P, ADDP, 208, 34 h, 65%.
d) CuCl, TMEDA, air, PhCꢀCH, CH2Cl2, 208, 4 h, 13% (4a), 7% (4b), 2% (4c), 1% (4d).

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Fig. 5. Electronic absorption spectra of 1a ± e in CHCl3 (Tˆ 298 K)
from electronic transitions within the conjugated PTA backbone, appear at almost the
same positions (around l ˆ 400 nm) with nearly identical fine structure and molar
extinction coefficients (Fig. 8). Similarly, position, fine structure, and molar extinction
coefficients of the longer-wavelength absorption bands in the spectra of trimers 1c (first
generation) and 2c (second generation) are nearly identical (Fig. 9). A precise
determination of lmax required deconvolution of the UV/VIS spectra [34]. The values
obtained for the dimers (Fig. 8) showed a minimal bathochromic shift in changing from
Fig. 6. Electronic absorption spectra of 2a ± c in CHCl3 (Tˆ 298 K)

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Fig. 7. Electronic absorption spectra of 3a,b in CHCl3 (Tˆ 298 K)
Fig. 8. Comparison of the electronic absorption spectra of dimers 1b, 2b, and 3b in CHCl3

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Fig. 9. Comparison of the electronic absorption spectra of trimers 1c and 2c in CHCl3
generation one to three: lmax ˆ 428.0 Æ 0.2 nm (1b), 430.0 Æ 0.3 (2b), and 431.1 Æ
0.2 nm (3b). For all dendritic rods, the lmax values were converted into energies (Emax
[eV]), which were then plotted against the reciprocal number of monomeric units
(1/n). These plots revealed for all three oligomeric series straight lines intersecting the
ordinate at nearly identical Emax ˆ 2.57 Æ 0.06 eV. This value corresponds well to the
optical gap determined for other PTA oligomers lacking dendritic wedges [4][5].
All these data provide impressive support that p-electron delocalization and
effective conjugation length of the PTA backbone are not affected by distortions out of
planarity due to steric compression of the bulky dendritic wedges at higher generations.
Apparently, p-electron conjugation involving the acetylenic fragments in the PTA
backbone is best described as being cylindrical rather than resulting from orbital
overlap within a distinct plane and is, therefore, fully maintained upon rotation about
C(sp) C(sp2) and C(sp) C(sp) single bonds.
The position, shape, and molar extinction coefficients of the longest wavelength
absorptions in the dendritic rods, which result from p-electron conjugation in the PTA
backbone, are nearly independent of the nature of the dendritic coverage. This is nicely
Â
shown by a comparison of the spectra of derivatives 1a ± e with Frechet-type dendrons
(Fig. 5) with those recorded for the carbosilane derivatives 4a ± d (Fig. 10). The only
major difference between the two series is the strong increase in absorptivity below
320 nm in 1a ± e, due to the large increase in aromatic rings at higher dendritic
generation number.

Helvetica Chimica Acta ± Vol. 84 (2001)
311
Fig. 10. Electronic absorption spectra of 4a ± d in CHCl3 (Tˆ 298 K)
The electrochemical properties of the dendritic rods 1a ± c and 2a ± c were studied
by steady-state voltammetry and cyclic voltammetry in CH2Cl2 (‡0.1m Bu4NPF6) on a
glassy carbon electrode. All oligomers could not be oxidized in the accessible potential
range but were reduced in several irreversible steps, the electrons being transferred to
the conjugated PTA backbone [4][5] (Table 2). The irreversibility increases with the
dendritic generation, due probably to steric hindrance [35]. Interestingly, the first
reduction potential is shifted to more negative values as the dendritic coverage
‡
increases (e.g., 1.79 V (1a) and 1.84 V (2a); vs. Fc/Fc ). We tentatively explain
Table 2. Electrochemical Data for the Dendritic Rods 1a ± c and 2a ± c Measured by Steady-State Voltammetry on
a Glassy Carbon Electrode
Oligomer
E11=2 [V]a)
E21=2 [V]
E31=2 [V]
1a
1b
1c
2a
2b
2c
1.79 (98)b)
1.60 (90)
1.54 (140)
1.84 (135)
1.62 (105)
1.56 (145)
2.30 (120)
1.76 (90)
1.76 (110)
2.35 (114)
1.82 (110)
1.78 (100)
±
±
2.21 (100)
±
2.30 (75)
2.22 (105)
a) Half-wave potentials in CH2Cl2 ‡ 0.1m Bu4NPF6 vs. Fc/Fc (ferrocene/ferricinium couple). b) The slopes of
the waves (given in parentheses in mV/log unit) were obtained by plotting the potential E vs. log[i(id i)] (i is
the current and id is the limiting current).
‡

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Â
these data by pointing out that the encapsulating Frechet-type dendrons provide an
electron-rich environment in which it becomes more difficult ± with increasing
coverage ± to inject an electron into the PTA backbone. As the oligomeric length
increased, the first reduction step occurred at increasingly less-negative potential; plots
of E1/2 vs. 1/n (n ˆ number of monomeric units in the oligomer) gave a straight line in
both series.
2.4. Poly(pentaacetylene) Oligomers and Attempted Dendritic Encapsulation. In our
efforts to further extend the progression leading from polyacetylene to carbyne (see
Introduction), we prepared the first series of oligomeric poly(pentaacetylene)s (PPAs)
5a ± c (Scheme 6). PPAs were hitherto unknown, and we were interested to explore i)
whether oxidative acetylenic coupling could be employed for oligomerization, as in the
case of PTA materials (see above), and ii) whether the conjugated PPA backbone, with
its high acetylenic content, would still display sufficient environmental stability for
isolation and characterization of the new materials and study of their physical
properties.
The first series of PPA oligomers 5a ± c was prepared starting from (E)-enetetrayne
49 [36], which was selectively bis-deprotected, with a catalytic amount of Bu4NF
adsorbed on SiO2, to give 50 as an unstable yellow oil (Scheme 6). All attempts to
remove the Me3Si groups of 49 under basic conditions (K2CO3/MeOH or 45% KOH)
failed due to the instability of product or starting material. Possible degrading reactions
of 50 with base may involve deprotonation in the initial step, in view of the enhanced
acidity of the terminal H-atoms [37], or nucleophilic attack at the extended
unsaturated chromophore [38]. Oligomerization of 50 under Hay conditions in the
presence of 3,5-di(tert-butyl)phenylacetylene 51 [39] as end-capping reagent led to a
Scheme 6. Synthesis of the PPA Oligomers 5a ± c
a) Bu4NF/SiO2, THF/H2O, 208, 5 min; 90%. b) CuCl, TMEDA, air, CH2Cl2, 208, 2 h; 10% (5a), 6% (5b),
3% (5c).

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313
mixture of the oligo(pentaacetylene)s 5a ± c in a total yield of 19%, which was
separated by preparative GPC (PhMe). Analysis of the crude oligomerization mixture
by MALDI-TOF-MS (matrix: a-cyano-4-hydroxycinnamic acid) revealed that oligo-
mers up to the heptamer had been formed. The material quantities of the higher
oligomers beyond trimeric 5c were, however, too small to allow isolation and
characterization; furthermore, workup was severely hampered by insolubility of the
compounds.
A comparison of the UV/VIS spectra of PPA oligomers 5a ± c (Fig. 11) with those of
the corresponding PTA oligomers 52a ± c (neglecting the influence of the t-Bu groups in
the former series) [40] shows that the extension of the p-conjugated backbone ±
expectedly ± leads to a substantial bathochromic shift of both the longest wavelength
absorption maximum lmax and the optical end-absorption, while the overall spectral
shape is similar in both series. Thus, lmax in CHCl3 increases from 422 (52a) to 458
(5a) nm, from 478 (52b) to 508 (5b) nm, and from 506 (52c) to 519 nm (5c). The
pronounced vibrational fine structure in the spectra of 5a ± c is indicative of a rigid
backbone, as was previously found for the PTA oligomers [40].
To prepare more soluble oligomers with the PPA backbone, (E)-hex-3-ene-1,5-
diyne 53 with appended Me2(t-Bu)SiOCH2 groups [41] was subjected to [Pd/Cu]-
catalyzed C(sp) C(sp) heterocoupling [24b] with 1-bromo-2-(trimethylsilyl)acety-
lene (54) [42] to give the Me3Si-protected monomer 55a, which was isolated in 21%
yield, in addition to dimeric 55b (18%) and trimeric 55c (3%) (Scheme 7). Removal of
the Me3Si groups in 55a was accomplished with K2CO3 in MeOH to give PPA
Fig. 11. Electronic absorption spectra of 5a ± c in CHCl3 (Tˆ 298 K)

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monomer 56, which proved to be very unstable. In contrast to PPA monomer 50,
enetetrayne 56 could not be isolated as a neat solid due to its instability. Oxidative
oligomerization under Hay conditions in the presence of end-capping reagent 51,
however, was successful, leading to the dark-red unstable solid oligomeric mixture 57
with a degree of polymerization Xn ꢁ 9, as determined by end-group analysis. In this
1
analysis, the H-NMR integral of the t-Bu resonance of the end-capping moieties was
compared to the integrals of the resonances in the lateral (t-Bu)Me2SiOCH2 side chains
of the monomeric repeat units. The low isolated yield of 57 (11%) presumably was
again a result of the instability of starting monomer 56, since an insoluble, dark-red
precipitate immediately formed after addition of CuCl and TMEDA.
Scheme 7. Synthesis of the PPA Polymer 57
a) [PdCl2(PPh3)2], CuI, (i-Pr)2NH, THF, 08, 2 h; 21% (55a), 18% (55b), 3% (55c). b) K2CO3, MeOH, 208,
30 min; 90%. c) CuCl, TMEDA, air, CH2Cl2, 208, 2 h; 11%.

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315
PPA Oligomer 57 was found to be highly light-sensitive. Irradiation of a solution of
57 at l ˆ 366 nm led to a significant hypochromic effect already after 5 min. After
15 min, all characteristic absorption bands had disappeared. The nature of the chemical
processes leading to this photo-bleaching remains to be investigated.
To circumvent the stability and solubility problems encountered in these first series
of PPA oligomers, we decided to encapsulate these delicate chromophores into
dendritic shells. For this purpose, (E)-enediyne 23, which bears second-generation
Â
Frechet-type dendrons, was transformed by Cadiot-Chodkiewicz heterocoupling with
1-bromo-3-(triisopropylsilyl)acetylene (58) [38] into (E)-enetetrayne 59, which was
deprotected with Bu4NF to give monomer 60 (Scheme 8). The latter proved to be
highly unstable and was used directly ± without isolation ± in the oxidative Hay
oligomerization in the presence of PhCꢀCH as end-capping reagent. According to
GPC analysis, this reaction produced four main products, and analysis by MALDI-
TOF-MS showed that monomeric to tetrameric oligomers 61a ± d had formed.
Scheme 8. Synthesis of the Dendritic PPA Oligomers 61a ± d
a) i-PrNH2, CuCl, NH2OH ´ HCl, air, 208, 1 h; 64%. b) Bu4NF, wet THF, 208, 5 min. c) CuCl, TMEDA,
PhCꢀCH, air, 208, 1 h; yields not determined.
Monomer 61a had a slightly higher retention time than the higher oligomers and
was readily separated by GPC (CH2Cl2). Repeated preparative GPC finally also
1
afforded pure fractions of dimer 61b, as revealed by analytical GPC. The H-NMR
spectra, however, showed that monomer 61a and dimer 61b were present as mixtures of
(E)- and (Z)-isomers: their t-Bu resonances were clearly doubled. Separation of the

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(E)- and (Z)-isomers was achieved chromatographically (SiO2); however, material
quantities were too small to measure their 13C-NMR spectra. It is unclear at present,
whether this isomerization occurs thermally or photochemically, or even under both
conditions. Trimer 61c and tetramer 61d could not be obtained in completely pure
form; their MALDI-TOF-MS (matrix: 9-nitroanthracene) still showed the presence of
compounds with higher molecular masses. In view of the ready (E) ! (Z) isomer-
ization, which again could be promoted by the dendritic branches (see Sect. 2.1), the
Â
preparation of PPA oligomers with Frechet-type dendritic wedges was not further
pursued.
2.5. An Organometallic Approach to Dendritic Rods. Here, we present initial studies
towards the preparation of oligomers consisting of Pt-bridged tetraethynylethenes
(TEEs, 3,4-diethynylhex-3-ene-1,5-diynes) with dendritic phosphane ligands coordi-
nated to the metal centers to provide solubilization and encapsulation (Fig. 12). As
Â
ligands, we intended to use Frechet-type dendritic phosphanes such as 62 and 63
(Fig. 13) introduced by Catalano and Parodi [43] (for P-containing dendrimers, see
[8e][44]). Additionally, we prepared ligand 64 by reacting benzyl bromide 11 with
NaPPh2 (Scheme 9).
Fig. 12. Schematic representation of dendritic oligomers made from Pt-bridged tetraethynylethenes
To test the concept, we chose as the first target compounds trans-65 and trans-66,
two bis(s-acetylene)platinum complexes of tetraethynylethenes [45] with phosphane
dendrons ligated to the metal center (Scheme 10). Selective removal of their Me3Si
alkyne-protecting groups would provide direct monomeric precursors for oxidative
oligomerization under formation of dendritically encapsulated molecular wires of the
type shown in Fig. 12. For the construction of these systems, we needed the trans-
dichloroplatinum(II) complexes trans-67 and trans-68 (Scheme 11), respectively, which
were expected to react with mono-deprotected TEE 69 [46] according the Hagihara
coupling [47].
For the synthesis of trans-65 and trans-66, trans-[Pt(NCPh)2Cl2] was prepared by
heating PtCl2 in PhCN to 1008 [48], and subsequent ligand exchange with 62 or 64

Helvetica Chimica Acta ± Vol. 84 (2001)
317
Fig. 13. Dendritic phosphane ligands 62 and 63 introduced by Catalano and Parodi [43]
Scheme 9. Synthesis of the Dendritic Phosphane Ligand 64
a) Na, NH3, ClPPh2, THF, 788 ! 208, 3 h; 72%.
afforded 67 and 68, respectively, as mixtures of cis- and trans-isomers (Scheme 11).
While chromatographic separation of the isomers failed in both cases, fractional
crystallization (CH2Cl2/EtOH 2 :1; 208) was successful for 67 and provided isomeri-
cally pure trans-67. Expectedly, the 31P-NMR spectrum (202.5 MHz, CHCl3) displayed
only one resonance at 16.01 ppm (1J(195Pt,31P) ˆ 2576 Hz), whereas the 195Pt-NMR
spectrum (107.5 MHz, CDCl3) showed one triplet at
2582 Hz).
4007.8 ppm (1J(195Pt, 31P) ˆ
The structure of trans-67 was unambiguously revealed by X-ray structure analysis
(Fig. 14) of crystals obtained at 208 from CH2Cl2/EtOH 4 :1. The complex crystallized
Å
in the triclinic space group P1 with Pt as the inversion center.
Scheme 10. Projected Synthesis of the Dendritic Bis(s-acetylene)platinum Complexes 65 and 66

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Scheme 11. Synthesis of the Dichloroplatinum(II) Complexes 67 and 68
a) 62 or 64, CHCl3, D, 45 min, 30% (trans-67); 60% (68).
We subsequently undertook the Hagihara coupling of trans-67 with mono-
deprotected TEE 69 under the conditions described by Harriman et al. and obtained
the bis(s-acetylene)platinum complex 65 in 41% yield (Scheme 12) [49]. However, the
31P-NMR spectrum (121.5 MHz, CDCl3) displayed two close resonances at 14.46 ppm
Fig. 14. X-Ray crystal structure of trans-67. Arbitrary numbering. Atomic displacement parameters obtained at
293 K are drawn at the 30% probability level. Selected bond lengths [Š] and angles [8]: Pt P 2.319(3), Pt Cl
2.343(3), P C(1) 1.840(7), P C(22) 1.821(7), P C(28) 1.816(8), P Pt P 180.0, P Pt Cl 90.33(11),
Cl Pt Cl 180.0, C(28)
P
Pt 108.7(2), C(22)
P
Pt 118.6(2), C(1)
P Pt 118.4(3), C(28) P C(22)
104.1(3), C(28)
P
C(1) 104.7(3), C(22)
P
C(1) 100.6(3)

Helvetica Chimica Acta ± Vol. 84 (2001)
319
Scheme 12. The Synthesis of the Dendritic Bis(s-acetylene)platinum Complex 65 Proceeds with (Z)/(E)-
Isomerization of the TEE Moieties
a) trans-67, CuI, (i-Pr)2NH, THF, 208, 20 h; 41%.
(1J(195Pt,31P) ˆ 2540 Hz) and 14.81 ppm (1J(195Pt,31P) ˆ 2514 Hz), indicating that isom-
erization had occurred during the coupling. The similar values of the chemical shifts
and the coupling constants clearly indicated that both compounds had the same (trans)
coordination geometry at the Pt center [50]. Indeed, we never had observed trans !
cis isomerization during Hagihara couplings at Pt; furthermore, the trans-isomers are
usually the thermodynamically more stable ones. To explain the formation of two
isomers, we, therefore, had to assume that (E) ! (Z) isomerization at one of the
coordinating TEE moieties had occurred.
Photochemical [29][51] and electrochemical [52] (E) ! (Z) isomerization of TEE
and DEE (1,2-diethynylethene) derivatives coupled directly to substituted Ph or other
aromatic rings has been well-established in our recent work. In some studies, we also
observed this isomerization as an undesired side reaction in the presence of proton
sources [23a]. Since we rigorously excluded light and proton sources in the Hagihara
coupling of 69, we must conclude that the observed TEE isomerization is a hitherto
unobserved process, possibly induced by steric interactions between TEE and
phosphane dendrons in 65. Further investigations to shed light into this process are
now underway.
3. Conclusions. ± In this paper, the first comprehensive approach towards dendritic
encapsulation of monodisperse oligomers with a p-conjugated backbone is described.
Â
Poly(triacetylene) (PTA) oligomers were laterally functionalized either with Frechet-
type dendrons of generation one (1a ± e), two (2a ± c), or three (3a,b) or with second-
generation carbosilane dendrons (4a ± d). During the course of this investigation, we
also synthesized the first series of poly(pentaacetylene) (PPA) oligomers (5a ± c) but
found these compounds to be quite insoluble as well as rather unstable. To enhance
solubility and stability, we prepared a series of dendritic PPA oligomers 61a ± d
Â
with laterally appended second-generation Frechet-type wedges; these interesting
novel oligomers, however, were not formed in isomerically pure form (see below).

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In yet another approach towards dendritic encapsulation of chromophoric molecular
rods, we explored the formation of Pt-bridged tetraethynylethene oligomers
(Fig. 12) bearing solubilizing dendritic phosphane ligands at the metal centers. Our
preliminary work demonstrated the synthetic feasibility, but again, isomerization of
the monomeric precursor 65 to such rods caused problems that require further
investigation.
Physical studies (UV/VIS, electrochemistry) with the PTA oligomers 1 ± 4
demonstrated that, in these tubular macromolecules, the insulating layers created by
the dendritic wedges protect and stabilize the central conjugated backbone, but do not
alter its electronic properties. UV/VIS Spectroscopic measurements indicated that
there is no loss of p-electron conjugation along the PTA backbone in the higher-
generation compounds, despite their distortion from planarity due to steric over-
crowding of the bulky dendritic wedges. Independent of the dendritic generation
number, the longer-wavelength absorptions, which originate from electronic transitions
within the conjugated PTA backbone, appear at almost the same positions, with nearly
identical vibrational fine structure and molar extinction coefficients. p-Electron
conjugation involving the acetylenic fragments in the PTA backbone is presumably best
described as being cylindrical rather than resulting from orbital overlap within a
distinct plane and is therefore fully maintained upon rotation about C(sp) C(sp2) and
C(sp) C(sp) single bonds. The observation that effective p-electron conjugation does
not require full planarity of the molecule is an important finding for the rich field of
acetylenic scaffolding [24b].
This study also raised challenging new questions concerning the (E) ! (Z)
isomerization of tetraethynylethenes (TEEs) and diethynylethenes (DEEs). While
this isomerization under photochemical or electrochemical control is quite established
through other work from this program [29][51][52], and while some members of these
classes of molecules have been shown to undergo proton-induced isomerization [23a],
the present study has revealed additional, potentially quite different mechanisms for
Â
this isomerization. First, we found that the Frechet-type dendrons of generation three
induce (E) ! (Z) isomerization within the PTA backbone, possibly through photo-
sensitization [30]. Subsequently, we found that the dendritic PPA oligomers 61a ± d
readily underwent (E) ! (Z) isomerization within the conjugated backbone, presum-
ably in a thermal process. Finally, monomer 65 for the preparation of dendritic Pt-
bridged tetraethynylethene oligomers surprisingly underwent isomerization within the
TEE moieties during its preparation by Hagihara coupling. Possibly, steric interactions
between the TEE moieties and the dendritic phosphane ligands at the Pt center are
promoting this thermal process, the exact nature of which remains to be determined in
future work. From one viewpoint, these isomerization processes hampered progress in
some aspects of the described work, from another viewpoint, however, they could
provide the basis for new molecular switches for use in molecular electronics and
optical devices [51][53].
We thank the ETH Research Council (TEMA grant), the Fonds der Chemischen Industrie, Germany, the
Japan Society for the Promotion of Science (JSPS postdoctoral fellowship to M. I.), and the Deutsche
Forschungsgemeinschaft (postdoctoral fellowship to J.-D. A.) for generous support of this work. We also thank
Dr. C. Thilgen for help with the nomenclature.

Helvetica Chimica Acta ± Vol. 84 (2001)
321
Experimental Part
General. Solvents and reagents were reagent-grade and commercially available and used without further
purification unless otherwise stated. Compounds 18 [4][21], 51 [39], 53 [41], 62 [43], and 69 [46] were prepared
according to literature procedures. Karstedt catalyst ((divinyltetramethyldisiloxane)platinum complex in
xylene) was obtained from United Chemical Technologies, Inc. 2731 Bartram Road, Bristol, PA 19007. CuI
(99.999%) was purchased from Aldrich; Bu3P (85%) from Fluka. THF and Et2O were freshly distilled from
sodium benzophenone ketyl. CH2Cl2 and CHCl3 were distilled over CaH2. All reactions were carried out under
N2 or Ar unless otherwise noted. Degassing of solvents for Pd- and Pt-mediated reactions as well as for
conversions with three-valent phosphorus derivatives was done by three freeze-pump-thaw cycles. Evaporation
in vacuo was conducted at H2O-aspirator pressure. For anal. and spectroscopic characterization, compounds
were dried at 10 2 Torr. Column chromatography (CC) and flash chromatography (FC): SiO2 60 (230 ±
400 mesh, 0.040 ± 0.063 mm) from E. Merck, SiO2 (70 ± 230 mesh, 0.05 ± 0.2 mm) from Macherey-Nagel, or
SiO2-H (0.005 ± 0.040 mm) from Fluka. TLC: glass sheets coated with SiO2 60 F254 from E. Merck or Macherey-
Nagel glass plates DURASIL-25 UV254; visualization by UV light or staining with KMnO4 (0.5 g KMnO4 in
100 ml 1m NaOH) or with a ꢁmostainꢀ soln. (400 ml 10% aq. H2SO4, 20 g (NH4)6Mo7O24 ´ 6 H2O, 0.6 g Ce(SO4)2).
Prep. GPC: Bio-Beads S-X1 (styrene-divinylbenzene copolymer, pore size 200 ± 400 mm) from BIO-RAD at
ambient pressure and temp.; mobile phase: PhMe or CH2Cl2; flow rate 5 ± 10 drops min 1. High-performance
prep. and anal. GPC: Merck-Hitachi HPLC pump L-7100, UV detector L-7400, RI detector L-7490, and
Chromointegrator D-2500. Anal. separations: two sequential NovoGrom columns (GROM-SDV gel 1000, 2 Â
60 cm, pore diameter: 10 mm) from GROM Analytik und HPLC; or two Shodex GPC KF-802.5 and Shodex
GPC KF-803L columns, or two TSK gel G2500 HR columns (7.8 Â 300 mm) from TosoHaas; eluent: PhMe, flow
rate 0.5 ml min 1. Anal. GPC for oligomeric mass determination: Knauer GP chromatograph with KMX-6-
LAALS (Low Angle Laser Light Scattering) detector from Chromatix and Viscotek H-502 differential
viscosimeter; data sampling and evaluation with TriSEC GPC-Software V. 2.7; column PL-Gel mixed-C5 from
Polymer Laboratories (7.5 Â 600 mm); calibration with polystyrene standards from Polymer Laboratories;
eluent: THF, flow rate 1 ml min 1. M.p.: Büchi B-510 or Büchi B-540, uncorrected. UV/VIS Spectra: Varian-
CARY 5 spectrometer; e [l mol 1 cm 1]. IR Spectra (cm 1): Perkin-Elmer 1600-FT-IR. NMR Spectra: Bruker
AMX-500 and Varian Gemini-300 or -200 at 293 K, with solvent peak (1H, 13C) or Na2PtCl6 (195Pt) as reference.
31P-NMR Spectra were measured with 1H- and 13C-broad-band decoupling. All NMR spectra were recorded in
CDCl3 unless noted otherwise. MS (m/z (%)); EI-MS: VG TRIBRID spectrometer at 70 eV; FAB-MS: VG
ZAB2-SEQ spectrometer with 3-nitrobenzyl alcohol (NOBA) as matrix. MALDI-TOF-MS: Bruker REFLEX
spectrometer; matrices: 9-nitroanthracene and 2,5-dihydroxybenzoic acid (DHB); positive-ion mode at 20-kV
acceleration voltage, reflector mode. ESI-MS: Finnigan TSQ 7000. High-resolution (HR) MALDI-TOF-MS:
Ion Spec Ultima FT-ICR mass spectrometer (DHB matrix, 4.7 Tesla) by the two-layer technique (analyte in
CH2Cl2 is added via capillary to the matrix in MeOH/H2O). Elemental analyses were performed by the
Mikrolabor at the Laboratorium für Organische Chemie, ETH-Zürich.
Electrochemistry. The electrochemical experiments were carried out at 20 Æ 28 in CH2Cl2 containing 0.1m
Bu4NPF6 in a classical three-electrode cell. The working electrode was a glassy C disk electrode used either
motionlessly for CV (10 mV s 1 to 10 V s 1) or as a rotating disk electrode (RDE). All potentials in the present
‡
study are referenced to the ferrocene/ferricinium (Fc/Fc ) couple used as an internal standard. The auxiliary
electrode was a Pt wire, and a Ag wire was used as a pseudo-reference electrode. The accessible range of
‡
potentials on the glassy carbon electrode in CH2Cl2 was ‡ 1.4 to 2.4 V vs. Fc/Fc .
Methyl 3,5-Bis{[4-(tert-butyl)benzyl]oxy}benzoate (7). K2CO3 (9.4 g, 68.0 mmol) was added to 4-(tert-
butyl)benzyl bromide (10 ml, 54.4 mmol), 6 (4.57 g, 27.2 mmol), and [18]crown-6 (1.44 g, 5.4 mmol) in acetone
(800 ml). After stirring at reflux for 2 d, filtration of insoluble materials, drying (MgSO4), evaporation in vacuo,
and recrystallization (PhMe/hexane) afforded 7 (11.38 g, 91%). White needles. M.p. 1218. IR (KBr): 2963, 1717,
1596, 1161, 1158. 1H-NMR (200 MHz): 1.36 (s, 18 H); 3.94 (s, 3 H); 5.06 (s, 4 H); 6.84 (t, J ˆ 2.3, 1 H); 7.34 (d, J ˆ
2.3, 2 H); 7.39 (d, J ˆ 8.7, 4 H); 7.46 (d, J ˆ 8.7, 4 H). 13C-NMR (50.8 MHz): 31.26; 34.53; 52.18; 70.18; 107.28;
‡
‡
108.33; 125.63; 127.63; 132.07; 133.50; 151.31; 160.04; 166.96. EI-MS: 460 (2, M ), 429 (1, [M OMe] ), 313 (16,
‡
‡
[M ((t-Bu)C6H4CH2)] ), 147 (100, [(t-Bu)C6H4CH2] ). Anal. calc. for C30H36O4 (460.62): C 78.23, H 7.88;
found: C 78.29, H 8.15.
3,5-Bis{[4-(tert-butyl)benzyl]oxy}benzoic Acid (8). A soln. of 7 (8.72 g, 18.9 mmol) in EtOH (370 ml) was
stirred with solid KOH (2.01 g, 35.8 mmol) at reflux for 2 h. After concentration by half and acidification to pH
of ca. 1 with 1n HCl, the resulting emulsion was extracted with CH2Cl2 (3Â), and the combined org. layers were
washed with sat. aq. NaCl soln. Drying (MgSO4) and evaporation in vacuo provided 8 (8.45 g, 99%). White

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solid. M.p. 1958. IR (KBr): 2963, 1694, 1595, 1162. 1H-NMR (500 MHz): 1.37 (s, 18 H); 5.09 (s, 4 H); 6.90 ± 6.91
(m, 1 H); 7.32 ± 7.52 (m, 10 H); 11.8 (br. s, 1 H). 13C-NMR (125.8 MHz): 31.33; 34.61; 70.24; 108.19; 108.82;
‡
‡
125.59; 127.58; 131.08; 133.33; 151.25; 159.98; 171.76. EI-MS: 446 (2, M ), 299 (1, [M ((t-Bu)C6H4CH2)] , 147
‡
(100, [(t-Bu)C6H4CH2] ). Anal. calc. for C29H34O4 (446.59): C 78.00, H 7.67; found: C 77.79, H 7.81.
(3,5-Bis{[4-(tert-butyl)benzyl]oxy}phenyl)methanol (10). K2CO3 (17.3 g, 125 mmol) was added to 4-(tert-
butyl)benzyl bromide (18.5 ml, 0.100 mmol), 9 (7.00 g, 50.0 mmol), and [18]crown-6 (2.64 g, 10.0 mmol) in
acetone (800 ml), and the mixture was heated to reflux for 2 d. Filtration through a plug (SiO2) and washing
with CH2Cl2, drying (MgSO4), evaporation in vacuo, and recrystallization (EtOH/hexane) afforded 10 (14.48 g,
67%). White needles. M.p. 116 ± 1178. IR (CHCl3): 2967, 1594, 1156. 1H-NMR (300 MHz): 1.38 (s, 18 H); 1.98 (t,
J ˆ 5.6, 1 H); 4.64 (d, J ˆ 5.6, 2 H); 5.03 (s, 4 H); 6.61 (t, J ˆ 2.2, 1 H); 6.67 (d, J ˆ 2.2, 2 H); 7.40 (d, J ˆ 8.4, 4 H);
7.46 (d, J ˆ 8.4, 4 H). 13C-NMR (75.5 MHz): 31.20; 34.45; 65.19; 69.97; 101.23; 105.60; 125.57; 127.57; 133.83;
‡
143.49; 151.14; 160.37. EI-MS: 432 (M ). Anal. calc. for C29H36O3 (432.61): C 80.52, H 8.39; found: C 80.65, H
8.49.
5-(Bromomethyl)-1,3-bis{[4-(tert-butyl)benzyl]oxy}benzene (11). Ph3P (5.38 g, 20.5 mmol) was added to
10 (7.09 g, 16.4 mmol) and CBr4 (6.80 g, 20.5 mmol) in THF (20 ml), and the mixture was stirred for 30 min
while a precipitate formed. After dilution with hexane (60 ml), the mixture was filtered through a plug (SiO2;
hexane), and evaporation in vacuo yielded a colorless oil that crystallized upon standing to give 11 (8.10 g,
99%). White needles. M.p. 100 ± 1018. IR (CHCl3): 2967, 1594, 1161. 1H-NMR (200 MHz): 1.38 (s, 18 H); 4.46 (s,
2 H); 5.03 (s, 4 H); 6.60 (t, J ˆ 2.2, 1 H); 6.69 (d, J ˆ 2.2, 2 H); 7.42 (d, J ˆ 8.1, 4 H); 7.46 (d, J ˆ 8.1, 4 H).
13C-NMR (75.5 MHz): 31.22; 33.51; 34.49; 70.01; 102.14; 108.05; 125.63; 127.64; 133.64; 139.79; 151.26; 160.30.
‡
EI-MS: 46 (M ). Anal. calc. for C29H35O2Br: C 70.30, H 7.12, Br 16.13; found: C 70.23, H 7.20, Br 15.89.
Methyl 3,5-Bis[(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzyl)oxy]benzoate (12). According to the procedure
for 7, 11 (3.18 g, 6.42 mmol), 6 (540 mg, 3.21 mmol), [18]crown-6 (170 mg, 0.64 mmol), and K2CO3 (1.11 g,
8.03 mmol) were reacted in acetone (100 ml) to give, after filtration (SiO2 plug) and recrystallization (hexane),
1
12 (3.07 g, 96%). White needles. M.p. 1208. IR (KBr): 2961, 1723, 1597, 1158. H-NMR (200 MHz): 1.39 (s, 36
H); 3.97 (br. s, 3 H); 5.06 (br. s, 12 H); 6.66 ± 6.67 (m, 2 H); 6.76 ± 6.77 (m, 6 H); 6.87 ± 6.88 (m, 1 H); 7.34 ± 7.49
(m, 16 H). 13C-NMR (75.5 MHz): 31.26; 34.50; 52.21; 69.99; 70.18; 101.66; 106.33; 107.25; 108.46; 125.60; 127.66;
‡
132.17; 133.79; 138.90; 151.18; 159.85; 160.45; 166.86. FAB-MS: 995 (7, [M 1] ), 849 (9, [M ((t-
‡
‡
‡
Bu)C6H4CH2)] ), 581 (17, [M ((t-Bu)C6H4CH2O)2C6H3CH2] ), 415 (11, [(t-Bu)C6H4CH2O)2C6H3CH2] ),
‡
147 (100, [(t-Bu)C6H4CH2] ). Anal. calc. for C66H76O8 (997.34): C 79.49, H 7.68; found: C 79.51, H 8.01.
3,5-Bis[(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzyl)oxy]benzoic Acid (13). According to the procedure for
8, 12 (505 mg, 0.51 mmol) and KOH (56 mg, 1.00 mmol) were reacted in EtOH (10 ml), and recrystallization
(PhMe/hexane) gave 13 (487 mg, 97%). White needles. M.p. 1728. IR (KBr): 2961, 1692, 1597, 1161. 1H-NMR
(500 MHz): 1.33 (s, 36 H); 5.01 (s, 8 H); 5.03 (s, 4 H); 6.60 (t, J ˆ 2.2, 2 H); 6.70 (d, J ˆ 2.2, 4 H); 6.86 (t, J ˆ 2.2, 1
H); 7.36 ± 7.42 (m, 18 H). 13C-NMR (125.8 MHz): 31.3; 34.6; 70.0; 70.2; 101.7; 106.3; 108.0; 108.9; 125.5; 127.5;
‡
131.2; 133.7; 138.7; 151.1; 159.8; 160.3 (CˆO resonance not observed). FAB-MS: 1005 (21, [M ‡ Na] );
‡
‡
835 (16, [M ((t-Bu)C6H4CH2)] ), 567 (34, [M ((t-Bu)C6H4CH2O)2C6H3CH2] ), 415 (22, [((t-
‡
‡
Bu)C6H4O)2C6H3CH2] ), 147 (100, [(t-Bu)C6H5CH2] ). Anal. calc. for C65H74O8 (983.31): C 79.40, H 7.59;
found: C 79.43, H 7.69.
{3,5-Bis[(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzyl)oxy]phenyl}methanol (14). According to the procedure
for 10, 11 (1.43 g, 2.89 mmol), 9 (203 mg, 1.45 mmol), K2CO3 (501 mg, 3.62 mmol), and [18]crown-6 (77 mg,
0.29 mmol) were reacted in acetone (45 ml) to give, after plug filtration (SiO2; Et2O) and recrystallization
(PhMe/hexane), 14 (1.22 g, 87%). White solid. M.p. 1428. IR (KBr): 3550, 2961, 1597, 1162. 1H-NMR
(500 MHz): 1.35 (s, 36 H); 4.64 (d, J ˆ 6.1, 2 H); 5.00 (s, 4 H); 5.01 (s, 8 H); 6.57 (t, J ˆ 2.2, 1 H); 6.60 (t, J ˆ 2.2, 2
H); 6.64 (d, J ˆ 2.2, 2 H); 6.71 (d, J ˆ 2.2, 4 H); 7.38 (d, J ˆ 8.4, 8 H); 7.43 (d, J ˆ 8.4, 8 H). 13C-NMR
(125.8 MHz): 31.34; 34.58; 65.31; 70.00; 101.35; 101.50; 105.75; 106.27; 125.53; 127.58; 133.71; 139.20; 143.43;
‡
‡
151.08; 160.12; 160.29. FAB-MS: 968 (19, M ), 821 (12, [M ((t-Bu)C6H4CH2)] ), 553 (48, [((t-
‡
‡
‡
Bu)C6H4CH2O)2C6H3CH2] ), 415 (30, [((t-Bu)C6H4CH2O)2C6H3CH2] ), 147 (100, [(t-Bu)C6H4CH2] ). Anal.
calc. for C65H76O7 (969.33): C 80.54, H 7.90; found: C 80.25, H 8.09.
1,3-Bis[(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzyl)oxy]-5-(bromomethyl)benzene (15). According to the
procedure for 11, 14 (9.80 g, 10.11 mmol), CBr4 (4.36 g, 13.15 mmol), and Ph3P (3.45 g, 13.15 mmol) were
reacted in THF (15 ml) to provide, after CC (SiO2; CH2Cl2), 15 (10.34 g, 99%). White solid. M.p. 1718. IR
(KBr): 2961, 1596, 1158. 1H-NMR (200 MHz): 1.37 (s, 36 H); 4.45 (s, 2 H); 5.01 (s, 4 H); 5.04 (s, 8 H); 6.59 ± 6.73
(m, 9 H); 7.40 (d, J ˆ 8.5, 8 H); 7.46 (d, J ˆ 8.5, 8 H). 13C-NMR (50.3 MHz): 31.32; 33.66; 34.56; 69.95; 70.05;
101.54; 102.21; 106.27; 108.14; 125.55; 127.57; 133.67; 138.94; 139.76; 151.06; 159.98; 161.30. FAB-MS: 415 (7, [(t-

Helvetica Chimica Acta ± Vol. 84 (2001)
323
‡
‡
Bu)C6H4CH2O)2C6H3CH2] ), 147 (100, [(t-Bu)C6H4CH2] ). Anal. calc. for C65H75O6Br´ H2O (1050.24): C
74.34, H 7.39; found: C 74.25, H 7.43.
Methyl 3,5-Bis({3,5-bis[(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzyl)oxy]benzyl}oxy)benzoate (16). Accord-
ing to the procedure for 7, 15 (4.041 g, 3.91 mmol), 6 (329 mg, 1.96 mmol), K2CO3 (676 mg, 4.89 mmol), and
[18]crown-6 (103 mg, 0.39 mmol) were reacted in acetone (390 ml) to give, after filtration (SiO2 plug; CH2Cl2)
and CC (SiO2; CH2Cl2/hexane 7 :3), 16 (3.03 g, 74%). White solid. M.p. 778. IR (KBr): 2960, 1723, 1596, 1156.
1H-NMR (200 MHz): 1.37 (s, 72 H); 3.90 (s, 3 H); 5.00 (br. s, 28 H); 6.60 (m, 6 H); 6.70 (br. s, 12 H); 6.82 ± 6.83
(m, 1 H); 7.32 (d, J ˆ 2.1, 2 H); 7.37 (d, J ˆ 8.5, 16 H); 7.43 (d, J ˆ 8.5, 16 H). 13C-NMR (50.3 MHz): 31.17; 34.31;
51.96; 69.74; 101.45; 106.17; 125.41; 127.54; 132.01; 133.75; 138.93; 130.19; 150.87; 159.69; 160.10; 160.26; 166.55.
‡
‡
‡
FAB-MS: 2068 (<1, [M 1] , 1922 (<2, [M ((t-Bu)C6H4CH2)] , 147 (100, [(t-Bu)C6H4CH2] ). Anal. calc.
for C138H156O16 (2070.77): C 80.04, H 7.59; found: C 80.07, H 7.67.
3,5-Bis({3,5-bis[(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzyl)oxy]benzyl}oxy)benzoic Acid (17). According
to the procedure for 8, 16 (609 mg, 0.29 mmol) and KOH (33 mg, 0.59 mmol) were reacted in EtOH/THF 1:1
(12 ml) containing one drop of H2O to give 17 (605 mg, 99%). Slightly yellow solid. M.p. 1038. IR (KBr): 2961,
1714, 1596, 1157. 1H-NMR (300 MHz): 1.30 (br. s, 72 H); 4.97 (br. s, 28 H); 6.57 (br. s, 6 H); 6.68 (br. s, 12 H);
6.84 ± 6.85 (m, 1 H); 7.24 ± 7.38 (m, 34 H). 13C-NMR (50.3 MHz): 31.26; 34.50; 69.99; 101.60; 106.36; 125.60;
127.66; 133.79; 138.86; 139.18; 151.15; 159.10; 160.26; 160.42 (CˆO resonance not observed). FAB-MS: 2078 (9,
‡
‡
[MH ‡ Na] ), 147 (100, [(t-Bu)C6H4CH2] ). Anal. calc. for C137H154O16 ´ H2O (2074.76): C 79.31, H 7.58; found:
C 79.46, H 7.49.
[(E)-1,6-Bis(triisopropylsilyl)hex-3-ene-1,5-diyne-3,4-diyl]dimethylene Bis(3,5-bis{[4-(tert-butyl)benzyl]-
oxy}benzoate) (19). Bu3P (2.4 ml, 8.29 mmol) and TMAD (1.42 g, 8.22 mmol) were sequentially added to a
degassed soln. of 18 (1.47 g, 3.28 mmol) and 8 (3.67 g, 8.22 mmol) in THF (20 ml), and the mixture was heated
to reflux under N2 for 1 d. Evaporation in vacuo and CC (SiO2; CH2Cl2/hexane 1:1) afforded 19 (3.49 g, 81%).
White solid. M.p. 1848. FT-IR (KBr): 2960, 2143, 1725, 1596, 1161. 1H-NMR (200 MHz): 1.00 (s, 42 H); 1.34 (s, 36
H); 5.03 (s, 8 H); 5.24 (s, 4 H); 6.82 ± 6.83 (m, 2 H); 7.27 ± 7.46 (m, 20 H). 13C-NMR (50.3 MHz): 11.00; 18.43;
31.25; 34.52; 64.39; 70.17; 101.34; 107.07; 107.21; 108.67; 125.59; 127.62; 127.66; 131.87; 133.56; 151.27; 159.97;
‡
‡
165.90. FAB-MS: 859 (6, [M ((t-Bu)C6H4CH2O)2C6H3CO2] ), 429 (100, [((t-Bu)C6H4CH2O)2C6H3CO] ),
‡
147 (97, [(t-Bu)C6H4CH2] ). Anal. calc. for C84H112O8Si2 (1306.00): C 77.25, H 8.64; found: C 77.21, H 8.74.
[(E)-1,6-Bis(triisopropylsilyl)hex-3-ene-1,5-diyne-3,4-diyl]dimethylene Bis{3,5-bis[(3,5-bis{[4-(tert-butyl)-
benzyl]oxy}benzyl)oxy]benzoate} (20). According to the procedure for 19, 18 (1.01 g, 2.23 mmol), 13 (5.49 g,
5.58 mmol), PBu3 (1.6 ml, 5.64 mmol), and TMAD (0.966 g, 5.59 mmol) were reacted in THF (20 ml) to give,
after CC (SiO2; CH2Cl2/hexane 1 :1), 20 (3.25 g, 61%). White solid. M.p. 1398. IR (KBr): 2958, 2143, 1728, 1596,
1160. 1H-NMR (200 MHz): 0.97 (s, 42 H); 1.31 (s, 72 H); 4.99 (s, 24 H); 5.23 (s, 4 H); 6.58 (t, J ˆ 2.3, 4 H); 6.70 (d,
J ˆ 2.3, 8 H); 6.80 ± 6.81 (m, 2 H); 7.33 ± 7.44 (m, 36 H). 13C-NMR (50.3 MHz): 11.09; 18.55; 31.32; 34.59; 64.49;
70.05; 70.27; 101.66; 106.40; 106.84; 107.19; 108.77; 125.54; 127.57; 127.85; 131.92; 133.76; 138.84; 151.09; 159.76;
‡
160.36. MALDI-TOF-MS (9-nitroanthracene): 2403 ([M ‡ Na] ). Anal. calc. for C156H192O16Si2 (2379.43): C
78.75, H 8.13; found: C 78.77, H 8.02.
[(E)-1,6-Bis(triisopropylsilyl)hex-3-ene-1,5-diyne-3,4-diyl]dimethylene Bis(3,5-bis({3,5-bis[(3,5-bis{[4-
(tert-butyl)benzyl]oxy}benzyl)oxy]benzyl}oxy)benzoate) (21). According to the procedure for 19, 18 (0.10 g,
0.223 mmol), 17 (1.23 g, 0.599 mmol), Bu3P (0.16 ml, 0.553 mmol), and TMAD (0.098 g, 0.569 mmol) were
reacted in THF (20 ml) to give, after GPC (CH2Cl2), 21 (39 mg, 4%). White solid. M.p. 948. IR (KBr): 2952,
2369, 1726, 1596, 1157. 1H-NMR (300 MHz): 0.98 (br. s, 42 H); 1.32 (br. s, 144 H); 4.98 (br. s, 56 H); 5.24 (s, 4 H);
6.58 (br. s, 12 H); 6.70 (m, 24 H); 6.82 ± 6.83 (m, 2 H); 7.24 ± 7.38 (m, 68 H). 13C-NMR (75.5 MHz): 10.96; 18.45;
31.20; 31.25; 34.47; 64.55; 69.96; 70.24; 101.30; 101.67; 106.35; 106.56; 106.91; 108.84; 125.13; 125.58; 125.64;
127.86; 132.02; 133.83; 138.98; 139.22; 151.16; 159.88; 160.30; 160.45; 165.82. MALDI-TOF-MS (9-nitro-
‡
‡
anthracene): 4564 (70, [M ‡ K] ), 4549 (100, [M ‡ Na] ). Anal. calc. for C300H352O32Si2 (4526.30): C 79.61, H
7.84; found: C 79.90, H 7.64.
[(E)-Hex-3-ene-1,5-diyne-3,4-diyl]dimethylene Bis(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzoate) (22). A
soln. of 19 (2.10 g, 1.61 mmol) and Bu4NF (2 ml of a 1m soln. in THF, 2.0 mmol) in wet THF was stirred for
1 h. CH2Cl2 was added, and the mixture was washed with sat. aq. NH4Cl soln. and dried (MgSO4). Evaporation
in vacuo and recrystallization (Et2O) provided 22 (1.75 g, 99%). Off-white crystals. M.p. 1628. IR (KBr): 3258,
2962, 1717, 1592, 1159. 1H-NMR (300 MHz): 1.33 (s, 36 H); 3.59 (s, 2 H); 5.03 (s, 8 H); 5.17 (s, 4 H); 6.82 (t, J ˆ
2.4, 2 H); 7.35 ± 7.44 (m, 20 H). 13C-NMR (75.5 MHz): 32.21; 34.52; 64.20; 70.17; 78.42; 90.85; 107.43; 108.56;
‡
122.66; 127.67; 128.16; 131.67; 133.48; 151.35; 160.06; 166.01. FAB-MS: 992 (<2, M ), 429 (100, [((t-
‡
‡
Bu)C6H4CH2O)2C6H3CO] ), 147 (87, [(t-Bu)C6H4CH2] ). Anal. calc. for C66H72O8 ´ 0.5 H2O (1002.31): C 79.09,
H 7.34; found: C 79.12, H 7.35.

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Helvetica Chimica Acta ± Vol. 84 (2001)
[(E)-Hex-3-ene-1,5-diyne-3,4-diyl]dimethylene Bis{3,5-bis[(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzyl)oxy]-
benzoate} (23). According to the procedure for 22, 20 (2.02 g, 0.849 mmol) and Bu4NF (2.0 ml of a 1m soln. in
THF, 2.0 mmol) were reacted in wet THF to give, after precipitation from Et2O, 23 (1.70 g, 97%). White solid.
M.p. 1078. IR (KBr): 3286, 2961, 1726, 1597, 1158. 1H-NMR (200 MHz): 1.30 (s, 72 H); 3.58 (s, 2 H); 4.96 (s, 24
H); 5.16 (s, 4 H); 6.58 ± 6.59 (m, 4 H); 6.68 (d, J ˆ 2.2, 8 H); 6.80 ± 6.81 (m, 2 H); 7.24 ± 7.44 (m, 36 H). 13C-NMR
(50.3 MHz): 31.27; 34.48; 64.09; 69.91; 70.10; 78.38; 90.95; 101.59; 106.28; 107.42; 108.61; 125.46; 127.52; 127.97;
128.16; 129.03; 131.62; 133.65; 138.76; 150.95; 159.71; 160.25; 165.65. MALDI-TOF-MS (9-nitroanthracene):
‡
2091 ([M ‡ Na] ). Anal. calc. for C138H154O16 (2066.74): C 80.20, H 7.41; found: C 79.86, H 7.46.
[(E)-Hex-3-ene-1,5-diyne-3,4-diyl]dimethylene Bis[3,5-bis({3,5-bis[(3,5-bis{[4-(tert-butyl)benzyl]oxy}ben-
zyl)oxy]benzyl}oxy)benzoate] (24). According to the protocol for 22, 21 (0.2 g, 0.04 mmol) and Bu4NF (0.1 ml
of a 1m soln. in THF, 0.1 mmol) were reacted in wet THF (20 ml) to give, after precipitation from Et2O, 24
(152 mg, 90%). White solid. M.p. 898. IR (KBr): 3286, 2961, 1726, 1596, 1156. 1H-NMR (200 MHz): 1.33 (br. s,
144 H); 3.62 (s, 2 H); 4.98 (br. s, 56 H); 5.16 (s, 4 H); 6.62 (t, J ˆ 2.2, 12 H); 6.73 (d, J ˆ 2.2, 24 H); 6.86 (t, J ˆ 2.2,
2 H); 7.24 ± 7.45 (m, 68 H). 13C-NMR (75.5 MHz): 29.58; 30.23; 31.22; 34.11; 34.45; 64.20; 69.46; 70.04; 70.17;
78.41; 90.78; 101.62; 101.75; 106.36; 106.56; 107.45; 108.73; 125.57; 127.64; 133.78; 133.82; 138.96; 139.20; 151.14;
‡
159.86; 160.28; 160.43; 165.85. MALDI-TOF-MS (9-nitroanthracene): 4238 ([M ‡ Na] ). Anal. calc. for
C
282H312O32 (4213.61): C 80.21, H 7.66; found: C 79.92, H 7.70.
Oxidative Oligomerization of 22. TMEDA (80 mg, 0.10 ml, 0.69 mmol) and CuCl (22 mg, 0.02 mmol) were
added to 22 (200 mg, 0.202 mmol) and PhCꢀCH (41 mg, 0.402 mmol) in dry CH2Cl2 (10 ml) over molecular
sieves (4 Š), and the mixture was stirred in air for 2 h. After addition of sat. aq. NH4Cl soln., the mixture was
exhaustively extracted with CH2Cl2. The combined org. phases were washed with sat. aq. NaCl soln. and dried
(MgSO4). GPC (CH2Cl2) and FC (SiO2; CH2Cl2/hexane 1:1), followed by precipitation from MeOH, gave the
pure oligomers 1a ± e.
[(E)-1,10-Diphenyldec-5-ene-1,3,7,9-tetrayne-5,6-diyl]dimethylene Bis(3,5-bis{[4-(tert-butyl)benzyl]oxy}-
benzoate) (1a). Yield: 41 mg (17%). M.p. 1998. UV/VIS (CHCl3): 259 (68 000), 324 (29 600), 361 (46 500),
388 (35 400). IR (KBr): 2956, 2200, 1722, 1594, 1161. 1H-NMR (200 MHz): 1.33 (s, 36 H); 5.06 (s, 8 H); 5.25 (s, 4
H); 6.85 (t, J ˆ 2.4, 2 H); 7.26 ± 7.44 (m, 30 H). 13C-NMR (50.3 MHz): 31.19; 34.56; 64.40; 70.17; 73.41; 76.52;
87.67; 88.75; 107.76; 108.43; 121.06; 125.54; 127.63; 128.43; 129.22; 129.67; 131.51; 132.56; 133.35; 151.13; 159.92;
‡
165.82. MALDI-TOF-MS (9-nitroanthracene): 1216 ([M ‡ Na] ). Anal. calc. for C82H80O8 (1193.55): C 82.52,
H 6.76; found: C 82.66, H 6.73.
[(5E,11E)-1,16-Diphenylhexadeca-5,11-diene-1,3,7,9,13,15-hexayne-5,6,11,12-tetrayl]tetramethylene Tetra-
kis(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzoate) (1b). Yield: 26 mg (6%). M.p. 988. UV/VIS (CHCl3): 264
(143 000), 362 (60 000), 387 (72000), 422 (51500). IR (KBr): 2960, 2200, 1728, 1595, 1158. 1H-NMR (300 MHz):
1.31 (s, 36 H); 1.32 (s, 36 H); 4.98 (s, 12 H); 5.01 (s, 8 H); 5.09 (s, 4 H); 6.76 (t, J ˆ 2.4, 2 H); 6.81 (t, J ˆ 2.4, 2 H);
7.26 ± 7.43 (m, 50 H). 13C-NMR (75.5 MHz): 31.22; 34.47; 63.94; 64.06; 70.14; 73.41; 76.37; 82.45; 87.53; 88.23;
89.68; 107.72; 108.26; 108.43; 121.10; 125.58; 125.61; 127.70; 127.81; 128.53; 129.82; 130.32; 131.44; 132.54;
132.67; 133.38; 133.43; 151.22; 152.29; 160.03; 160.06; 165.67; 165.77. MALDI-TOF-MS (9-nitroanthracene):
‡
2209 ([M ‡ Na] ). Anal. calc. for C148H150O16 (2184.84): C 81.36, H 6.92; found: C 81.17, H 6.78.
[(5E,11E,17E)-1,22-Diphenyldocosa-5,11,17-triene-1,3,7,9,13,15,19,21-octayne-5,6,11,12,17,18-hexayl]hexa-
methylene Hexakis(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzoate) (1c). Yield: 19 mg (3%). M.p. 968. UV/VIS
(CHCl3): 266 (164 500), 397 (71 300), 420 (71 200). IR (KBr): 2960, 2203, 1724, 1595, 1159. 1H-NMR
(500 MHz): 1.29 (s, 36 H); 1.30 (s, 36 H); 1.31 (s, 36 H); 4.87 (s, 4 H); 4.94 (s, 8 H); 4.96 (s, 8 H); 4.98 (s, 4 H); 5.00
(s, 8 H); 5.08 (s, 4 H); 6.72 (t, J ˆ 2.3, 2 H); 6.75 (t, J ˆ 2.3, 2 H); 6.81 (t, J ˆ 2.3, 2 H); 7.26 ± 7.43 (m, 70 H).
13C-NMR (125.8 MHz): 29.69; 31.32; 34.56; 63.78; 64.06; 70.22; 73.46; 76.43; 82.34; 83.06; 87.37; 88.29; 88.33;
89.81; 107.72; 107.84; 108.37; 108.42; 108.52; 121.10; 125.49; 125.51; 127.59; 127.66; 128.08; 128.43; 128.85; 129.54;
129.71; 130.86; 130.99; 131.35; 131.40; 131.56; 132.59; 133.38; 133.42; 151.11; 151.12; 151.15; 159.96; 159.99;
‡
165.35; 165.56. MALDI-TOF-MS (9-nitroanthracene): 3199 ([M ‡ Na] ). Anal. calc. for C214H220O24 (3176.13):
C 80.93, H 6.98; found: C 80.92, H 6.97.
[(5E,11E,17E,23E)-1,28-Diphenyloctacosa-5,11,17,23-tetraene-1,3,7,9,13,15,19,21,25,27-decayne-5,6,11,12,17,
18,23,24-octayl]octamethylene Octakis(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzoate) (1d). Yield: 8 mg (1%).
M.p. 948. UV/VIS (CHCl3): 269 (278000), 397 (85900), 423 (89000). IR (KBr): 2955, 2200, 1728, 1594, 1156.
1H-NMR (500 MHz): 1.27 (s, 36 H); 1.28 (s, 36 H); 1.29 (s, 36 H); 1.30 (s, 36 H); 4.87 (s, 8 H); 4.92 (s, 8 H); 4.93
(s, 12 H); 4.95 (s, 12 H); 5.06 (s, 8 H); 6.71 (t, J ˆ 2.4, 2 H); 6.72 (t, J ˆ 2.4, 2 H); 6.74 (t, J ˆ 2.4, 2 H); 6.80
(t, J ˆ 2.4, 2 H); 7.24 ± 7.41 (m, 90 H). 13C-NMR (125.8 MHz): 29.70; 31.32; 31.58; 34.55; 34.56; 63.76; 63.85;
64.04; 70.20; 70.24; 73.47; 76.41; 82.28; 82.83; 83.11; 87.35; 88.12; 88.29; 88.45; 89.84; 107.71; 107.84; 108.42;
108.51; 121.10; 125.49; 125.51; 127.60; 127.66; 128.02; 128.43; 129.17; 129.71; 130.16; 131.09; 131.31; 131.36;

Helvetica Chimica Acta ± Vol. 84 (2001)
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131.39; 131.56; 132.59; 133.38; 133.42; 151.11; 141.15; 159.96; 159.99; 165.33; 165.39; 165.56. MALDI-TOF-MS
‡
(9-nitroanthracene): 4189.6 ([M ‡ Na] ). Anal. calc. for C280H290O32 ´ 4 H2O (4239.48): C 79.33, H 7.09; found: C
79.48, H 7.38.
[(5E,11E,17E,23E,29E)-1,34-Diphenyltetratriaconta-5,11,17,23,29-pentaene-1,3,7,9,13,15,19,21,25,27,31,33-
dodecayne-5,6,11,12,17,18,23,24,29,30-decayl]decamethylene Decakis(3,5-bis{[4-(tert-butyl)benzyl]oxy}ben-
zoate) (1e). Yield: 4 mg (0.4%). M.p. 938. UV/VIS (CHCl3): 272 (320000), 397 (80800), 462 (95000). IR
(KBr): 2957, 2199, 1726, 1594, 1156. 1H-NMR (500 MHz): 1.26 (s, 36 H); 1.27 (s, 36 H); 1.28 (s, 36 H); 1.29 (s, 36
H); 1.30 (s, 36 H); 4.85 (s, 8 H); 4.90 (s, 16 H); 4.92 (s, 8 H); 4.94 (s, 12 H); 4.98 (s, 12 H); 5.05 (s, 4 H); 6.71 ± 6.72
(m, 6 H); 6.73 (t, J ˆ 2.4, 2 H); 6.80 (t, J ˆ 2.4, 2 H); 7.24 ± 7.47 (m, 110 H). 13C-NMR (75.5 MHz): 29.60; 31.22;
34.45; 63.78: 64.01; 70.12; 73.42; 76.35; 82.23; 82.73; 82.82; 83.07; 87.32; 88.08; 88.20; 88.29; 88.45; 89.85; 107.69;
107.82; 108.39; 108.48; 121.11; 125.58; 127.70; 127.77; 128.06; 128.53; 129.14; 129.84; 130.32; 131.16; 131.34;
131.41; 131.60; 132.68; 133.41; 133.46; 151.24; 160.06; 165.48; 165.72. MALDI-TOF-MS (9-nitroanthracene):
‡
‡
5198 ([M ‡ K] ), 5182 ([M ‡ Na] ). Anal. calc. for C346H360O40 (5158.70): C 80.56, H 7.03; found: C 80.33, H
7.28.
Oxidative Oligomerization of 23. According to the procedure for 1a ± e, 23 (200 mg, 0.097 mmol),
PhCꢀCH (20 mg, 0.196 mmol), CuCl (1 mg, 0,01 mmol), and TMEDA (4 mg, 0.005 ml, 0.035 mmol) were
reacted in dry CH2Cl2 over molecular sieves (4 Š) in the air to give, after GPC (CH2Cl2), FC (SiO2; CH2Cl2/
hexane 1:1), and precipitation from MeOH, the pure oligomers 2a ± c.
[(E)-1,10-Diphenyldec-5-ene-1,3,7,9-tetrayne-5,6-diyl]dimethylene Bis{3,5-bis[(3,5-bis{[4-(tert-butyl)benzyl]-
oxy}benzyl)oxy]benzoate} (2a). Yield: 20 mg (9%). M.p. 988. UV/VIS (CHCl3): 260 (56000), 323 (28100), 361
1
(45800), 390 (37200). IR (KBr): 2956, 2204, 1729, 1594, 1158. H-NMR (200 MHz): 1.32 (s, 72 H); 4.98 (s, 16
H); 5.04 (s, 8 H); 5.24 (s, 4 H); 6.58 (t, J ˆ 2.4, 4 H); 6.70 (d, J ˆ 2.4, 8 H); 6.84 (t, J ˆ 2.4, 2 H); 7.24 ± 7.41 (m, 46
H). 13C-NMR (50.3 MHz): 29.61; 31.23; 34.47; 64.34; 69.92; 70.24; 73.41; 76.52; 87.79; 88.87; 101.76; 106.43;
107.82; 108.55; 121.03; 125.56; 127.63; 128.46; 129.22; 129.72; 131.69; 132.58; 133.79; 138.77; 151.15; 159.91;
‡
160.39; 165.85. MALDI-TOF-MS (9-nitroanthracene): 2290 ([M ‡ Na] ). Anal. calc. for C154H160O16 (2266.98):
C 81.59, H 7.11; found: C 81.32, H 6.87.
[(5E,11E)-1,16-Diphenylhexadeca-5,11-diene-1,3,7,9,13,15-hexayne-5,6,11,12-tetrayl]tetramethylene Tetra-
kis{3,5-bis[(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzyl)oxy]benzoate} (2b). Yield: 25 mg (6%). M.p. 798. UV/
VIS (CHCl3): 314 (83000), 361 (50800), 390 (69000), 423 (52500). IR (KBr): 2952, 2214, 1738, 1596, 1158.
1H-NMR (300 MHz): 1.29 (s, 72 H); 1.31 (s, 72 H); 4.93 (s, 48 H); 5.09 (s, 8 H); 6.54 ± 6.56 (m, 8 H); 6.64 ± 6.66
(m, 16 H); 6.73 (t, J ˆ 2.3, 2 H); 6.79 (t, J ˆ 2.3, 2 H); 7.20 ± 7.40 (m, 82 H). 13C-NMR (50.8 MHz): 29.57; 31.18;
31.25; 34.41; 34.44; 64.02; 69.88; 70.14; 73.46; 76.39; 82.61; 87.71; 88.31; 89.77; 101.70; 106.40; 108.45; 120.97;
125.53; 127.65; 128.33; 128.48; 129.77; 130.50; 131.49; 131.63; 132.62; 133.82; 133.83; 151.03; 151.11; 159.86;
‡
159.90; 160.38; 165.62; 165.67. MALDI-TOF-MS (9-nitroanthracene): 4353 ([M ‡ Na] ). Anal. calc. for
C
292H310O32 (4331.71): C 80.97, H 7.21; found: C 80.71, H 7.13.
[(5E,11E,17E)-1,22-Diphenyldocosa-5,11,17-triene-1,3,7,9,13,15,19,21-octayne-5,6,11,12,17,18-hexayl]hexa-
methylene Hexakis{3,5-bis[(3,5-bis{[4-(tert-butyl)benzyl]oxy}benzyl)oxy]benzoate} (2c). Yield: 12 mg (2%).
M.p. 808. UV/VIS (CHCl3): 313 (60200), 397 (69700), 420 (69500). IR (KBr): 2956, 2200, 1728, 1594, 1156.
1H-NMR (500 MHz): 1.26 (s, 72 H); 1.27 (s, 72 H); 1.31 (s, 72 H); 4.86 (s, 8 H); 4.87 (s, 8 H); 4.88 (s, 16 H); 4.90
(s, 16 H); 4.91 (s, 8 H); 4.92 (s, 16 H); 5.00 (s, 4 H); 5.01 (s, 4 H); 5.03 (s, 4 H); 6.51 (t, J ˆ 2.3, 4 H); 6.53 (t, J ˆ 2.3,
4 H); 6.55 (t, J ˆ 2.3, 4 H); 6.60 ± 6.64 (m, 24 H); 6.69 (t, J ˆ 2.3, 2 H); 6.70 (t, J ˆ 2.3, 2 H); 6.77 (t, J ˆ 2.3, 2 H);
7.23 ± 7.38 (m, 118 H). 13C-NMR (100.6 MHz): 29.68; 31.29; 34.47; 34.49; 34.52; 64.02; 69.85; 70.08; 70.57; 73.46;
76.43; 82.46; 83.15; 87.54; 88.29; 88.35; 89.86; 101.69; 106.30; 106.39; 107.56; 108.36; 120.99; 125.40; 125.42;
125.45; 127.54; 128.34; 128.48; 129.74; 130.53; 131.32; 131.56; 132.50; 133.72; 138.69; 150.82; 150.87; 150.95;
‡
159.68; 160.19; 165.33. MALDI-TOF-MS (9-nitroanthracene): 6415 ([M ‡ Na] ). Anal. calc. for C430H460O48
(6396.43): C 80.75, H 7.25; found: C 80.73, H 7.29.
Oxidative Oligomerization of 24. According to the procedure for 1a ± e, 24 (100 mg, 0.024 mmol),
PhCꢀCH (5.1 mg, 0.050 mmol), CuCl (1 mg, 0.01 mmol), and TMEDA (2.5 mg, 0.02 mmol) were reacted in
dry CH2Cl2 over molecular sieves (4 Š) in the air to give, after GPC (CH2Cl2), FC (SiO2; CH2Cl2/hexane 1 :1),
and precipitation from MeOH, the pure oligomers 3a,b.
[(E)-1,10-Diphenyldec-5-ene-1,3,7,9-tetrayne-5,6-diyl]dimethylene Bis(3,5-bis({3,5-bis[(3,5-bis{[4-(tert-bu-
tyl)benzyl]oxy}benzyl)oxy]benzyl}oxy)benzoate) (3a). Yield: 14 mg (13%). M.p. 918. UV/VIS (CHCl3): 323
(25800), 363 (45200), 389 (38100). IR (KBr): 2955, 2211, 1728, 1594, 1156. 1H-NMR (200 MHz): 1.29 (br. s, 144
H); 4.91 (s, 16 H); 4.96 (br. s, 32 H); 4.99 (br. s, 8 H); 5.19 (s, 4 H); 6.55 (t, J ˆ 2.1, 12 H); 6.66 (d, J ˆ 2.1, 24 H);
6.82 (t, J ˆ 2.1, 2 H); 7.15 ± 7.41 (m, 78 H). 13C-NMR (100.6 MHz): 29.69; 30.91; 31.12; 31.32; 34.55; 64.31; 69.96;
70.02; 70.24; 73.44; 76.51; 87.83; 88.94; 101.56; 101.79; 106.30; 106.55; 107.69; 108.51; 120.90; 125.50; 127.24;