Dendritic encapsulation - "postsynthetic" functionalizations of a single benzophenone shielded by shape-persistent polyphenylene dendrons

Article abstract of DOI:10.1002/ejoc.200500773

First- and second-generation polyphenylene dendrimers were synthesized starting from benzophenone as core. Variation of the size and the density of the dendrimer shell resulted in different isolation of the cores. To investigate the effect of shielding up

Full text of DOI:10.1002/ejoc.200500773

FULL PAPER
DOI: 10.1002/ejoc.200500773
Dendritic Encapsulation – “Postsynthetic” Functionalizations of a Single
Benzophenone Shielded by Shape-Persistent Polyphenylene Dendrons
Stefan Bernhardt,[a] Martin Baumgarten,[a] and Klaus Müllen*[a]
Keywords: Dendrimer / Encapsulation / Polyphenylene / Benzophenone / Steric hindrance
First- and second-generation polyphenylene dendrimers
were synthesized starting from benzophenone as core. Varia-
tion of the size and the density of the dendrimer shell re-
sulted in different isolation of the cores. To investigate the
effect of shielding upon the reactivity of the core, chemical
functionalizations as well as the alkali-metal reduction of the
encapsulated benzophenone core were performed. The
herein presented synthetic concept opens the way to spa-
tially well-defined spherical nanoparticles bearing a single
isolated function in the center.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
the level of incorporation was strongly influenced by the
size of the reagent.[7] However, the core of polyphenylene
dendrimers has not yet been the subject of such a “postsyn-
thetic” functionalization.
Introduction
Dendrimers represent a class of organic materials that
can be obtained in a monodisperse way on the nanometer
scale. In the last decade, the introduction of functionalities,
either in the core, in the dendritic backbone, or on the sur-
face of dendrimers has been a main focus of research.[1]
Beyond a certain molecular weight, a dendrimer core is ex-
pected to be shielded from the surrounding medium by a
close-packed shell. The degree of branching, the structure
and chemical nature of the repeating unit, and the spatial
orientation of the dendrons are the main factors, that deter-
mine the shielding of a central core.[2] Almost all knowledge
about dendritic encapsulation has been derived from the
investigation of the effect that the dendrimer shell has on
the physical properties of an internal photoactive[3] and/or
redox-active probe.[4] In this regard, Gorman et al. demon-
strated, that a rigid dendritic backbone blocked the electron
transfer from an electrode to an iron–sulfur core more ef-
ficiently than a flexible one.[4c,4e] Furthermore, computa-
tionally derived models indicated a highly mobile core in
the flexible dendrimers and a more immobilized core in the
rigid dendrimers. Polyphenylene dendrimers with their stiff
and shape-persistent dendrons have shown to be very ef-
ficient in the encapsulation of chromophores. The pre-
vented aggregation of a dye, as, for example, perylene, led
to improved optical properties of the chromophore, such
as an increased fluorescence quantum yield.[5] Recently, we
reported the “postsynthetic” functionalization of polyphen-
ylene dendrimers bearing multiple benzophenones in their
scaffold.[6] Twyman et al. presented the modification at the
focal point of a hyperbranched polymer and observed that
In this paper, we present the synthesis and characteriza-
tion of polyphenylene dendrimers with a single benzophe-
none core. Placing the benzophenone in the core was ex-
pected to significantly increase the shielding as compared
to the benzophenones in the dendrimer scaffold.[6] To inves-
tigate the influence of the dendrimer shell upon the reactiv-
ity of the benzophenone core, chemical functionalizations
of the core were tested by reacting the encapsulated benzo-
phenone with aryl-/alkyl-lithium and Grignard reagents of
various sizes. Furthermore, the alkali-metal reduction of
the dendrimers was carried out and yielded the correspond-
ing benzophenone radical anions. Their biradical formation
was used to further investigate the shielding of the core.
Results and Discussion
Synthesis of the Dendrimers: For the synthesis of poly-
phenylene dendrimers with a benzophenone core, its corre-
sponding ethynyl-substituted derivative must be available.
After monolithiation of 1,3,5-tribromobenzene (1), the re-
action was quenched with 3,5-dibromobenzaldehyde (2) to
give the tetrabromo-substituted diphenylmethanol deriva-
tive 3 (Scheme 1). The subsequent Swern oxidation[8] gener-
ated 3,3Ј,5,5Ј-(tetrabromo)benzophenone (4), which, after
subsequent Hagihara–Sonogashira cross-coupling reac-
tion[9] with (triisopropysilyl)ethyne, yielded the benzophe-
none derivative 5, possessing four triisopropylsilyl (TIPS)
protected ethynyl groups. Deprotection of the TIPS protect-
ing groups with tetrabutylammonium fluoride (TBAF) fur-
nished the desired core 3,3Ј,5,5Ј-(tetraethynyl)benzophe-
[a] Max-Planck-Institut für Polymerforschung,
Ackermannweg 10, 55128 Mainz, Germany
Fax: +49-6131-379350
E-mail: muellen@mpip-mainz.mpg.de
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S. Bernhardt, M. Baumgarten, K. Müllen
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none (6). The synthesis of monodisperse, structurally well- protecting groups in dendrimer 10 generated the first-gener-
defined polyphenylene dendrimers consisted of two steps. ation dendrimer 11 with 16 peripheral ethynyl groups. The
Firstly, the [4+2] cycloaddition of a (tetraphenyl)cyclopen- Diels–Alder cycloaddition of 11 with (tetraphenyl)cyclo-
tadienone branching unit to an ethynyl-substituted core or pentadienone (7) yielded the second-generation dendrimer
dendrimer, and secondly, the deprotection of the TIPS pro- 12, where the benzophenone core is surrounded already by
tecting groups, which activates the molecule for further 100 benzene rings.
growth.[10] The first-generation dendrimer 8 was obtained
The monodispersity of the dendrimers 8 and 12 was
from the Diels–Alder cycloaddition of (tetraphenyl)cyclo- proven by MALDI-TOF mass spectrometry showing single
pentadienone (7) with the benzophenone core 6 (Scheme 2). distinctive signals for the product mass. The NMR spec-
To increase the isolation of the benzophenone core, the troscopy displayed generation-dependent chemical shifts of
branching unit 9 was used for the synthesis of the second- the protons on the pentaphenyl repeating units (Scheme 2).
generation dendrimer 12. This building block possesses four To derive some knowledge about the shape and size of the
active sites for further dendrimer growth (A4B) and there- synthesized dendrimers, force-field calculations were carried
fore provides a significantly denser dendrimer shell than the out.[11] Figure 1 shows the three-dimensional structures of
parent branching unit 13, which carries only two protected (a) the first- and (b) the second-generation dendrimers 8
ethynyl groups (A2B).[10b] Subsequent cleavage of the TIPS and 12, respectively.
Scheme 1. Synthesis of the benzophenone core 3,3Ј,5,5Ј-(tetraethynyl)benzophenone (6). (i) n-butyllithium, –78 °C, 80%; (ii) oxalyl chlo-
ride, DMSO, triethylamine, CH2Cl2, –78 °C, 85%; (iii) 6 equiv. (triisopropylsilyl)ethyne, [Pd(PPh3)2]Cl2, PPh3, CuI, toluene/triethylamine,
80 °C, 60%; (iv) TBAF, THF, 67%.
Scheme 2. Synthesis of the first- and second-generation dendrimers 8 and 12, (i) 6 equiv. 7, o-xylene, 150 °C, 77%. (ii) 6 equiv. 9, o-xylene,
160 °C, 76%; (iii) TBAF, THF, 78%; (iv) 48 equiv. 7, o-xylene, 170 °C, 85 %.
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Polyphenylene Dendrimers with a Single Benzophenone Core
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the halogen–lithium exchange of 3-bromobiphenyl, were
treated with 8, only the starting material 8 was recovered.
Likewise as for 8, the reaction of phenyllithium with the
second-generation dendrimer 12 yielded starting material
and alcoholic product. No side-product, coming from the
possible Grignard reduction, could be detected. Due to the
small difference in polarity, the second-generation alcoholic
product could not be separated from the mixture, however,
NMR spectra suggested less than 10% of unreacted 12.
Also in the case of 12, no product was formed during the
reaction with biphenyllithium. To extend the postsynthetic
concept to alkyllithium reagents, 8 was treated with n-butyl-
lithium to give the alcoholic product 14c. Surprisingly, even
in that case, residual starting material was obtained.
The functionalization of the benzophenone core was ob-
viously possible only with reagents smaller than biphenyl.
Furthermore, contrary to polyphenylene dendrimers
possessing multiple benzophenones in their scaffold
(Scheme 3c),[6] no quantitative conversion could be
achieved for both dendrimers, 8 and 12. An explanation
for these results is the different substitution pattern of the
benzophenones. The benzophenones in the dendritic scaf-
fold were connected to the dendrimer backbone by their
para-positions. This allowed the introduction of even large
nucleophiles like pyrene. The herein presented dendrimers
8 and 12 were grown from a fourfold meta-substituted
benzophenone core. This substitution pattern obviously
produced an enhanced spatial shielding, thus only reagents
of the size of benzene or smaller could react with the car-
bonyl function.
Figure 1. Molecular model of (a) the first-generation dendrimer 8
and (b) the second-generation dendrimer 12. For reasons of clarity,
the hydrogen atoms have been omitted. Radii were measured as
largest carbon–carbon distances between the carbonyl carbon and
peripheral benzene rings.
The shape of 8 is strongly influenced by the substitution
pattern of the benzophenone core, resulting in a bent
dumb-bell-like structure. Contrary, in the second-genera-
tion dendrimer 12, the high number of branching points
arising from the A4B branching unit 9, and the additional
dendrimer layer produced an increased encapsulation of the
core. Additionally, due to the dense polyphenylene shell
provided by the A4B branching unit 9, compound 12 pos-
sesses a more spherical shape. From the models, the radii
were determined to be 2.2 nm for 8 and 3.6 nm for 12
(largest carbon–carbon distance between the carbonyl car-
bon and peripheral benzene rings).
Chemical Functionalizations: Applying the synthetic con-
cept recently presented,[6] aryl- and alkyllithium reagents
were used for the functionalization of the dendrimer core.
When the first-generation dendrimer 8 was treated with
phenyllithium, the alcoholic product 14a could be obtained
in good yield (Scheme 3). The reaction of 8 with the
Grignard reagent (4-methoxyphenyl)magnesium bromide
yielded the dendrimer 14b. Residual amounts of starting
material had to be separated from the product in both cases.
When larger reagents, e.g. biphenyllithium, obtained from
Further proof for the encapsulation of the benzophenone
core was derived from the alkali-metal reduction of 8 and
12. The reduction of dendrimers 8 and 12 was performed
on a potassium mirror under high vacuum in THF solu-
tion.[12] UV/Vis and EPR spectroscopy were used to follow
the state of reduction.
Upon contact of a solution of dendrimer 8 with the po-
tassium mirror, two increasing absorption bands at λ Ϸ 350
Scheme 3. (a) Chemical functionalizations of the first-generation dendrimer 8 with aryl- and alkyllithium and Grignard reagents. (b)
Potassium-bridged biradical of benzophenone. (c) Schematic draw of a polyphenylene dendrimer functionalized with eight benzophenones
in the scaffold.[6] One arm is drawn out fully. The three other arms are identical with the one shown but are abbreviated as a circled-D
for ease of visualization. (i) 14a: 60 equiv. phenyllithium, THF, 70 °C, 70 %. 14b: 25 equiv. (4-methoxyphenyl)magnesium bromide, THF,
70 °C, 66 %. 14c: 100 equiv. n-butyllithium, THF, 70 °C, 70 %.
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Figure 2. (a) UV/Vis absorption spectra of dendrimer 8 in THF in the order of further reduction. (K, THF, room temp.) Inset: EPR
spectrum of dendrimer 8 at the maximum amount of radical monoanion. (b) EPR spectra of the radical anion of 8 in THF at ca. 120 K,
zero-field splittings and half-field transition (inset).
and 825 nm were observed in the UV/Vis spectra (Fig- ing the radical centers separate. Secondly, using the A4B
ure 2a). They can be assigned to the formation of the radi- branching-unit 9 during the synthesis of dendrimer 12 af-
cal anion of the phenyl-substituted benzophenone core, forded a dense polyphenylene shell, which efficiently encap-
with the absorption maxima bathochromically shifted as sulated the core. For both dendrimers 8 and 12, continued
compared to those of the parent benzophenone radical reduction on the potassium mirror resulted in the decrease
monoanion (λmax = 336 and 560 nm).[13] The bathochromic of the absorption band of the radical monoanion (λ Ϸ 350
shift (∆λmax Ϸ 14 nm, first absorption maximum) was and 825 nm). A new absorption band at λ Ϸ 575 nm in-
smaller than the shift observed for the radical anions of creased in intensity (Figure 2a) and can be attributed to the
para-phenyl-substituted
benzophenones
(Scheme 3c, absorption of the benzophenone dianion.[13] EPR showed
∆λmax Ϸ 75 nm).[6] Reason for this is the less efficient delo- a signal of very low intensity, however, the signal did not
calization of the charge/spin into the neighboring phenyl disappear even after longer reaction time. Upon further re-
rings in the case of the meta-phenyl-substituted benzophe- duction, the increase of an intense sharp EPR signal was
none core 6. At a maximum intensity of the radical anion observed due to highly mobile extra charges in the poly-
bands, the solution EPR spectra (inset in Figure 2a) dis- phenylene shell.[6]
played a somewhat resolved signal with several lines. The
computer simulation of experimental spectra yielded the
proton hyperfine couplings of aH (para) = 0.35 mT and
Conclusions
aH (ortho) = 0.25 mT very close to those of known benzo-
phenones.[14] Thus, the detected hyperfine couplings can be
First- and second-generation polyphenylene dendrimers
assigned to the four ortho-protons and the two para-protons with a single active carbonyl group in the core were pre-
carrying the largest spin-density, whereas further phenyl pared by the divergent approach. Chemical functionaliza-
rings block the meta-positions of the benzophenone radical tions of the core with aryl-/alkyllithium and Grignard rea-
monoanion. The frozen-state EPR spectra (T Ϸ 120 K) sur- gents were limited to molecules smaller than biphenyl due
prisingly showed characteristic zero-field splittings of 2D Ϸ to spatial shielding. The alkali-metal reduction of the
16 mT (Figure 2b), which are of similar size as usually benzophenone core produced the corresponding radical
found for potassium-bridged benzophenone anions monoanion species. Potassium-bridged benzophenone
(Scheme 3b, 2D Ϸ 18–20 mT).[13,15] In addition to the typi- anions could only be detected for the first-generation den-
cal ∆ms = 1 signals for the zero-field splittings, also a rela- drimer 8, due to the larger and denser dendrimer shell of
tively strong half-field transition at g Ϸ 4 was found (∆ms the second-generation dendrimer 12, that led to an isolation
= 2), further demonstrating the triplet character of these of the radical anion species. Molecular modelling showed
biradicals (inset in Figure 2b). For the second-generation an efficient encapsulation of the core for the second-genera-
dendrimer 12, reduction experiments have been performed tion dendrimer, supporting the results obtained from the
under the same conditions. The UV/Vis and EPR spectra reduction and the postsynthetic functionalization of the
in solution were similar to those of the first-generation den- benzophenone core.
drimer 8. Contrary to 8, the EPR spectra of a frozen solu-
The herein presented approach enables the synthesis of
tion of 12 displayed no zero-field splittings and half-field shape-persistent and monodisperse nanoparticles with a
transition, ruling out the formation of potassium-bridged single isolated active site in the interior. With the postsyn-
biradicals from two anions of 12.
thetic concept, the introduction of functional groups in the
The different results from the frozen-state EPR measure- core of polyphenylene dendrimers is simplified, however the
ments can be attributed to two reasons: Firstly, the dia- size of the nucleophile was found to be a limiting factor.
meter of 12 is significantly larger than that of 8, thus keep- This concept should also allow the introduction of tempera-
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2 H, 4-H, 4Ј-H) ppm. 13C NMR (175 MHz, C2D2Cl4, 353 K): δ =
190.8 (C=O), 139.7 (C-1, C-1Ј), 138.6 (C-4, C-4Ј), 131.4 (C-2, C-
2Ј, C-6, C-6Ј), 123.8 (C–Br) ppm. FD mass (8 kV): m/z (%) = 497.9
(100) [M]+. C13H6Br4O (497.8): calcd. C 31.37, H 1.21; found C
31.38, H 1.26.
ture-labile functions, which are not stable under the condi-
tions of the Diels–Alder cycloaddition (Ϸ 150 °C), and rep-
resents therefore a significant step forward in the synthesis
of monofunctional well-defined nanoobjects.
3,3Ј,5,5Ј-Tetrakis(triisopropylsilanylethynyl)benzophenone (5): Com-
pound 4 (3.6 g, 7.23 mmol) was suspended in triethylamine (60 mL)
and toluene (20 mL). Bis(triphenylphosphane)palladium() dichlo-
ride (1.02 g, 1.45 mmol), copper() iodide (550 mg, 2.89 mmol), and
triphenylphosphane (1.02 g, 1.45 mmol) were added, and the flask
evacuated and flushed with argon for several times. Under stirring
the reaction mixture was heated to 60 °C and triisopropylsilyle-
thyne (9.65 mL, 43.4 mmol) was injected through a septum. After
15 min stirring at this temperature the reaction was heated to 80 °C
and stirred overnight under argon. After cooling the reaction mix-
ture was diluted with CH2Cl2 and extracted with H2O. The organic
phase was dried with MgSO4, and the solvent was removed under
reduced pressure. The crude product was purified by column
chromatography (petroleum ether/CH2Cl2) to afford 5 as a white
solid. Yield: 3.87 g (4.3 mmol), 60%. 1H NMR (500 MHz, CD2Cl2,
300 K): δ = 7.78–7.79 (m, 6 H, Harom.), 1.14 (s, 84 H, -CH,
-CH3) ppm. 13C NMR (175 MHz, CD2Cl2, 300 K): δ = 193.9
(C=O), 139.1 (C-4, C-4Ј), 137.8 (C-1, C-1Ј), 133.0 (C-2, C-2Ј, C-6,
C-6Ј), 124.8 (C–Cϵ), 105.2 (CϵC–Si), 93.6 (CϵC–Si), 18.9 (CH3),
11.8 (CH) ppm. FD mass (8 kV): m/z (%) = 902.8 (100) [M]+).
C57H90OSi4 (903.7): calcd. C 75.76, H 10.04; found C 76.07, H
10.08.
Experimental Section
General Remarks. General Procedures: All starting materials were
obtained from commercial suppliers (Aldrich, Fluka, Fischer,
Strem, Acros) and were used without purification. Solvents were
used in HPLC-grade purity as purchased. All atmosphere-sensitive
reactions were performed under argon using Schlenk techniques.
Column chromatography was carried out with silica gel 60 (230–
400 mesh) from E. Merck. 1H and 13C NMR spectra were recorded
with a Bruker AMX250 spectrometer, a Bruker AC300 spectrome-
ter, a Bruker AMX500 NMR spectrometer and a Bruker 700Ultra-
shield NMR spectrometer by using residual proton resonance of
the solvent or the carbon signal of the deuterated solvent as the
internal standard. Abbreviation Bp = benzophenone. FD mass
spectra were performed with a VG-Instruments ZAB 2-SE-FDP.
MALDI-TOF mass spectra were measured with a Bruker Reflex II
and dithranol as matrix (molar ratio dithranol/sample, 250:1). EPR
spectra were recorded with a CW X-band ESP 300 equipped with
an NMR gauss meter (Bruker ER 035), a frequency counter
(Bruker ER 041 XK) and a variable-temperature-control con-
tinuous-flow N2 cryostat (Bruker B-VT 2000). The elemental analy-
sis was carried out by the Microanalytical Laboratory of the Uni-
versity of Mainz, Mainz, Germany. Because of the high carbon
content in some molecules, the combustion may have been incom-
plete (sooting) resulting in lower values than expected for the car-
bon content.
3,3Ј,5,5Ј-(Tetraethynyl)benzophenone (6): Compound 5 (500 mg,
0.55 mmol) was dissolved in dry THF (10 mL) and reacted with
TBAF (175 mg, 0.5 mmol) under argon for 5 min. The reaction
was quenched with H2O. Purification was performed by column
chromatography (petroleum ether/CH2Cl2) to afford 6 as a white
solid. Yield: 103 mg (0.37 mmol), 67%. 1H NMR (250 MHz,
CD2Cl2, 300 K): δ = 7.82 (s, 6 H, 2-H, 2Ј-H, 4-H, 4Ј-H, 6-H, 6Ј-H),
3.77 (s, 4 H, ϵCH) ppm. 13C NMR (175 MHz, CD2Cl2, 300 K): δ
= 192.9 (C=O), 139.3 (C-4, C-4Ј), 138.6 (C-1, C-1Ј), 133.5 (C2, C-
2Ј, C-6, C-6Ј), 124.3 (C–Cϵ), 82.1 (CϵCH), 81.0 (ϵCH) ppm. FD
mass (8 kV): m/z (%) = 278.4 (100) [M]+). C21H10O (278.3): calcd.
C 90.63, H 3.62; found C 90.70, H 3.89.
Bis(3,5-dibromophenyl)methanol (3): 1,3,5-Tribromobenzene (2.6 g,
8.3 mmol) was placed in dry diethyl ether (150 mL) at –78 °C under
argon. Within 60 min n-butyllithium (5.07 mL, 8.3 mmol, 1.6  in
hexane) was added dropwise, and the solution stirred for 2 h at
this temperature. 3,5-Dibromobenzaldehyde (2.4 g, 9.1 mmol) was
dissolved in diethyl ether (30 mL) and added to the solution within
5 min. The reaction mixture was stirred for another 2 h at –78 °C
and then allowed to reach room temperature. Methanol (100 mL)
was added and the solution stirred for 30 min. The organic layer
was concentrated under reduced pressure and the crude product
purified by column chromatography (petroleum ether/CH2Cl2) to
afford 3 as a white solid. Yield: 3.3 g (6.6 mmol) 80%. 1H NMR
(700 MHz, C2D2Cl4, 353 K): δ = 7.88 (s, 2 H, 4-H, 4Ј-H), 7.69 (s,
4 H, 2-H, 2Ј-H, 6-H, 6Ј-H) ppm. 13C NMR (175 MHz, C2D2Cl4,
353 K): δ = 146.5 (C-1, C-1Ј), 134.1 (C-4, C-4Ј), 128.6 (C-2, C-2Ј,
C-6, C-6Ј), 123.7 (C–Br), 74.2 (C–OH) ppm. FD mass (8 kV):
m/z (%) = 499.8 (100) [M]+. C13H8Br4O (499.8): calcd. C 31.24, H
1.61; found C 31.33, H 1.62.
8: A mixture of 6 (75 mg, 0.27 mmol) and 7 (620 mg, 1.61 mmol)
was dissolved in o-xylene (6 mL) and refluxed at 150 °C for 16 h
under argon. The solvent was removed under reduced pressure and
the crude product purified by column chromatography (petroleum
ether/CH2Cl2) to afford 8 as a white solid. Yield: 0.35 g (0.2 mmol),
77%. 1H NMR (500 MHz, CD2Cl2, 300 K): δ = 7.25 (s, 2 H, 4-
HBp, 4Ј-HBp), 7.20–7.17 (m, 22 H, Harom.), 7.04 (s, 4 H, 2-HBp, 2Ј-
HBp, 6-HBp, 6Ј-HBp), 6.95–6.70 (m, 62 H, Harom.) ppm. 13C NMR
(175 MHz, CD2Cl2, 300 K): δ = 196.5 (C=O) 142.2, 142.0, 141.6,
141.3, 140.7, 140.4, 140.1, 134.0, 139.6, 137.4, 135.6, 131.8, 131.8,
131.6, 130.3, 129.0, 127.4, 127.2, 127.0, 126.7, 126.2, 126.0,
125.8 ppm. FD mass (8 kV): m/z (%) = 1704 (100) [M]+. C133H90O
(1704): calcd. C 93.74, H 5.32; found C 93.84, H 5.34.
3,3Ј,5,5Ј-(Tetrabromo)benzophenone (4): Dry CH2Cl2 (25 mL) was
placed in a flask under argon and cooled to –78 °C. Oxalyl chloride
(1.1 mL, 2.15 mmol) was added through a septum and the solution
was stirred for 15 min. Afterwards DMSO (0.31 mL, 4.41 mmol),
dissolved in CH2Cl2 (2 mL), was added and after 15 min of stirring,
compound 3 (1 g, 2.0 mmol), dissolved in CH2Cl2 (2 mL), was
added and the solution stirred for another 15 min. Thereafter, tri-
ethylamine (1.41 mL, 10.0 mmol) was added and the solution al-
lowed to reach room temperature. Subsequent extraction with
brine, 1% H2SO4, H2O and 5% NaHCO3 gave the crude product
which could be purified by recrystallisation from EtOH to give 4 as
a white solid. Yield: 846 mg (1.7 mmol), 85%. 1H NMR (700 MHz,
C2D2Cl4, 353 K): δ = 7.89 (s, 4 H, 2-H, 2Ј-H, 6-H, 6Ј-H), 7.74 (s,
10: A mixture of 6 (50 mg, 0.18 mmol) and 9 (1.2 g, 1.09 mmol)
was dissolved in o-xylene (6 mL) and refluxed at 160 °C for 20 h
under argon. The solvent was removed under reduced pressure and
the crude product purified by column chromatography (petroleum
ether/CH2Cl2). Precipitation from methanol afforded 10 as a white
solid. Yield: 625 mg (136 µmol), 76%. 1H NMR (500 MHz,
CD2Cl2, 300 K): δ = 7.33–7.06 (m, 50 H, Harom.), 6.80–6.64 (m,
24 H, Harom.), 1.14–1.09 (m, 336 H, -CH, -CH3) ppm. 13C NMR
(175 MHz, CD2Cl2, 300 K): δ = 194.5 (C=O), 141.6, 141.5, 141.4,
140.8, 140.5, 140.3, 140.2, 140.0, 139.4, 139.3, 137.1, 133.8, 131.9,
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S. Bernhardt, M. Baumgarten, K. Müllen
131.8, 131.6, 131.4, 131.1, 130.2, 129.4 (all Carom.), 122.3, 121.8, gave the crude product, which was further purified by column
FULL PAPER
121.7, 121.5 (all C–Cϵ), 107.3, 107.2 (all CϵC–Si), 91.3, 91.2 (all
ϵC–Si), 19.0, 18.9, 18.9 (all CH3), 11.2 (CH) ppm. MALDI TOF
chromatography (petroleum ether/CH2Cl2) and precipitation from
methanol to afford 14b as a white solid. Yield: 70 mg (39 µmol),
mass: m/z (%) = 4552 (50), [M – 43, isopropyl]+, 4595 (100), [M]+, 66%. 1H NMR (700 MHz, CD2Cl2, 300 K): δ = 7.21 (s, 4 H,
4618 (20), [M + Na]+, 4633 (40) [M + K]+. C309H410OSi16 (4590):
calcd. C 80.86, H 9.00; found C 80.94, H 7.11.
H1st generation), 7.18–7.11 (m, 20 H, Harom.), 6.99 (s, 2 H, 4-HBp, 4Ј-
HBp), 6.93–6.92 (m, 12 H, Harom.), 6.86–6.83 (m, 22 H, Harom.),
6.78–6.75 (m, 16 H, Harom.), 6.68–6.67 (m, 4 H, Harom.), 6.63–6.61
(m, 8 H, Harom.), 6.53–6.52 (2s, 4 H, 2-HBp, 2Ј-HBp, 6-HBp, 6Ј-HBp),
11: Compound 10 (350 mg, 76.2 µmol) was dissolved in dry THF
(10 mL) and treated with TBAF (385 mg, 1.22 mmol) under argon
for 5 min. The reaction was quenched with H2O. Purification was
performed by precipitation from methanol/H2O to afford 11 as a
white solid. Yield: 125 mg (60 µmol), 78%. 1H NMR (500 MHz,
3
6.35–6.34 (d, JH,H = 8.8 Hz, 2 H, Harom), 3.80 (s, 3 H, CH3), 1.87
(s, 1 H, OH) ppm. 13C NMR (175 MHz, CD2Cl2, 300 K): δ =
158.6, 146.8, 142.1, 142.0, 141.2, 141.1, 141.0, 140.8, 140.5, 140.4,
139.7, 139.6, 138.1, 132.0, 131.9, 131.8, 131.4, 130.6, 130.3, 129.8,
128.2, 127.9, 127.8, 127.2, 126.9, 126.7, 126.0, 125.9, 125.7, 113.3,
81.3 (C–OH), 55.6 (CH3) ppm. FD mass (8 kV): m/z (%) = 1815.2
(100) [M]+, 1797.8 (30) [M – 17 = OH]+. C140H98O2 (1812.3): calcd.
C 92.78, H 5.45; found C 92.43, H 5.38.
CD2Cl2, 300 K): δ = 7.33–7.31 (m, 12 H, Harom.), 7.17 (s, 2 H, 4-
3
H
Bp, 4Ј-HBp), 7.11–7.03 (m, 28 H, Harom.), 6.98–6.96 (d, JH,H
=
3
8.2 Hz, 8 H, Harom.), 6.79–6.77 (d, JH,H = 8.2 Hz, 8 H, Harom.),
3
3
6.71–6.70 (d. JH,H = 8.2 Hz, 8 H, Harom.), 6.67–6.65 (d, JH,H
=
8.2 Hz, 8 H, Harom.), 3.13–2.99 (4s, 16 H, ϵCH) ppm. 13C NMR
(175 MHz, CD2Cl2, 300 K): δ = 195.3 (C=O), 141.9, 141.3, 141.3,
140.8, 140.6, 140.4, 140.4, 140.3, 139.3, 139.2, 137.3, 135.3, 132.0,
131.7, 131.6, 131.5, 131.4, 131.3, 131.2, 130.2, 129.2 (all Carom.),
120.9 120.3, 120.1 (all C–Cϵ), 83.5, 83.6, (all CϵCH) 78.1, 78.0,
77.7, 77.7 (all ϵCH) ppm. MALDI TOF mass: m/z (%) = 2090
(100) [M]+, 4182 (10) [2 M]+ (C165H90O calcd. 2089).
14c: Compound 8 (96 mg, 56.3 µmol) was dissolved in dry THF
(5 mL) under argon. A solution of n-butyllithium (2 mL, 3.2 mmol,
1.6 ) in hexane was added through a septum and the mixture
heated at 70 °C for 16 h. Afterwards H2O (5 mL) was added, the
mixture extracted with CH2Cl2/H2O and the organic solvent re-
moved under reduced pressure. The crude product was purified by
column-chromatographie (petroleum ether/CH2Cl2) and precipi-
tation from methanol to afford 14c as a white solid. Yield: 70 mg
12: A mixture of 11 (60 mg, 28.7 µmol) and 7 (530 mg, 1.38 mmol)
was dissolved in o-xylene (4 mL) and refluxed at 170 °C for 3 days
under argon. The solvent was removed under reduced pressure and
the crude product purified by column chromatography (petroleum
ether/CH2Cl2). Precipitation from methanol afforded 12 as a white
solid. Yield: 190 mg (24.4 µmol), 85%. 1H NMR (500 MHz,
CD2Cl2, 300 K): δ = 7.43–7.39 (m, 20 H, H1st+2nd generation), 7.26 (s,
1
(39 µmol), 70%. H NMR (500 MHz, CD2Cl2, 300 K): δ = 7.24 (s,
4 H, H1st generation), 7.17–7.12 (m, 20 H, Harom.), 6.96–6.69 (m, 63
H, Harom.), 6.61 (s, 4 H, 2-HBp, 2Ј-HBp, 6-HBp, 6Ј-HBp), 1.28–1.24
3
(m, 4 H, α-CH2, β-CH2), 1.15–1.06 (sept, 2 H, JH,H = 7.4 Hz, γ-
3
CH2), 0.81 (t, JH,H = 7.2 Hz, 3 H, CH3) ppm. 13C NMR
(125 MHz, CD2Cl2, 300 K): δ = 146.5 (CBp-1, CBp-1Ј), 142.0, 141.9,
141.1, 141.0, 140.9, 140.8, 140.4, 139.6, 139.5, 131.9, 131.8, 131.7,
131.3, 130.3, 129.9, 127.8, 127.2, 127.1, 126.8, 126.6, 125.9, 125.6,
77.5 (C–OH), 40.9 (α-CH2), 25.4 (β-CH2), 23.3 (γ-CH2), 14.2
(CH3) ppm. FD mass (8 kV): m/z (%) = 1761.5 (100) [M]+.
C137H100O (1762.3): calcd. C 93.37, H 5.72; found C 93.04, H 5.61.
4 H, Harom.), 7.13 (m, 370 H, Harom.), 6.54–6.34 (s, 16 H, Harom.
)
ppm. 13C NMR (175 MHz, CD2Cl2, 300 K): δ = 196.4 (C=O),
142.2, 142.2, 142.1, 142.1, 142.0, 142.0, 141.2, 141.1, 141.0, 141.0,
140.8, 140.6, 140.6, 140.5, 140.4, 139.7, 139.6, 139.6, 139.4, 139.3,
131.9, 131.5, 131.5, 131.4, 130.3, 130.3, 130.2, 130.2, 129.7, 129.6,
127.9, 127.8, 127.8, 127.2, 127.1, 127.1, 126.9, 126.9, 126.5, 126.5,
126.0, 125.9, 125.6, 125.5 ppm. MALDI TOF mass: m/z = 7792
(100) [M]+, 7819 (40) [M + Na]+, 7898 (45) [M + Ag]+. C613H410
(7792): calcd. C 94.49, H 5.30; found C 94.46, H 5.33.
O
Acknowledgments
14a: Compound 8 (110 mg, 64.5 µmol) was dissolved in dry THF
(5 mL) under argon. A solution of phenyllithium (2 mL, 3.8 mmol,
1.8–2.1 ) in cyclohexane/ether (70:30) was added through a sep-
tum and the mixture heated at 70 °C for 16 h. Then H2O (5 mL)
was added, the mixture extracted with CH2Cl2/H2O and the or-
ganic solvent removed under reduced pressure. The crude product
was purified by column chromatography (petroleum ether/CH2Cl2)
and precipitation from methanol to afford 14a as a white solid.
Yield: 80 mg (45 µmol), 70%. 1H NMR (500 MHz, CD2Cl2,
300 K): δ = 7.21 (s, 4 H, H1st generation), 7.16–7.11 (m, 20 H, Harom.),
Financial support by the Deutsche Forschungsgemeinschaft (SFB
625) is gratefully acknowledged. We thank C. Beer for synthetic
support.
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6ЈHBp), 6.47–6.46 (d, JH,H = 8.5 Hz, 2 H, 4-HBp, 4Ј-HBp), 1.89 (s,
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tube under argon. (4-Methoxyphenyl)magnesium bromide (3 mL,
1.5 mmol, 0.5  in THF) was added and the reaction mixture re-
fluxed at 70 °C for 24 h. After cooling, H2O (5 mL) was added and
the solution stirred for another 30 min. Extraction with CH2Cl2/
H2O and concentration of the organic layer under reduced pressure
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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