Synthesis of light-harvesting dendrimers focally anchored with crown ethers or terpyridine ligands.

Article abstract of DOI:10.1039/b307507a

Crown ethers and terpyridine ligands have been successfully attached to the focal point of light harvesting phenylacetylene monodendrons through Pd-catalyzed coupling reactions. The structures of these functional monodendrons were characterized by 1H and

Full text of DOI:10.1039/b307507a

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Synthesis of light-harvesting dendrimers focally anchored with
crown ethers or terpyridine ligands
Yongchun Pan,a Meng Lu,a Zhonghua Peng*a and Joseph S. Melingerb
a Department of Chemistry, University of Missouri-Kansas City, 5100 Rockhill Road,
Kansas City, MO 64110, USA. E-mail: pengz@umkc.edu
b Naval Research Laboratory, Electronics Science and Technology Division, Code 6812,
Washington, DC 20375, USA
Received 2nd July 2003, Accepted 10th October 2003
First published as an Advance Article on the web 31st October 2003
Crown ethers and terpyridine ligands have been successfully attached to the focal point of light harvesting
phenylacetylene monodendrons through Pd-catalyzed coupling reactions. The structures of these functional
monodendrons were characterized by 1H and 13C NMR spectroscopy, mass spectrometry and elemental analysis.
Such binding-ligand anchored dendrons exhibit broad absorption, large molar extenction coefficients and high
fluoresence quantum yields. Coordination of crown ethers with alkali ions results in a significant increase in
absorption strength in the UV range, but little alteration in either intensity or position of fluorescence emission.
Coordination of terpyridine ligands with Ru2ϩ, however, does efficiently quench the fluorescence from the dendrons,
albeit only the smallest dendron exhibits efficient binding.
Introduction
Dendrimers have been extensively studied for well over a dec-
ade.1 Not only have a great number of dendritic molecules been
prepared through well-developed synthetic methodologies,
interesting properties associated with the unique dendritic
structures have been explored as well.2 One particular appli-
cation involves using dendrimers as synthetic light-harvesting
antennae,3–5 which can serve as a model system for mimicking
the energy transduction events in natural photosynthetic
systems. A variety of light-harvesting dendrimers have been
synthesized and their efficient energy transfer properties dem-
onstrated.3–5 In light-harvesting dendrimers, the energy that is
collected at the periphery over a broad range of irradiation is
transferred convergently to an energy acceptor at the focal
point and emitted as fluorescence in a narrow wavelength range.
Both the intensity and the wavelength of the fluorescence emis-
sion at the locus may be designed to be responsive to environ-
mental changes, making such dendrimers good candidates for
fluorescence sensors.6
Chart 1 Structures of crown ether and terpyridine anchored mono-
dendrons.
Synthesis of crown-ether terminated monodendrons (GnCr)
The synthesis of unsymmetrical conjugated monodendrons
with a triflate functional group at the locus GnOTf (X = OTf
in Chart 1, n = 1–3) has been reported previously.7,10 Crown
ether functionalized monodendrons were synthesized by the
Sonogashira coupling reaction of acetylene compound 2 with
GnOTf.11 As shown in Scheme 1, compound 2 was synthesized
by the coupling reaction of bromobenzocrown ether 1 with tri-
(isopropy)silyl acetylene at 80 ЊC, followed by desilylation with
tetrabutylammonium fluoride. The overall yield is 60%. When
trimethylsilylacetylene, a compound with a much lower boiling
point, is used, however, the coupling reaction was slow and
incomplete. The reaction of compound 2 with GnOTf went
smoothly. While the yields decrease gradually from lower
generation to higher generation dendrons, good yields were
obtained even for the third generation dendron. Unreacted
triflates were easily removed by chromatography due to their
We have recently described a novel unsymmetrical phenyl-
acetylene (PA) monodendron that exhibits broad absorption,
large molar extinction coefficients, high fluorescence quantum
yields, and high energy transfer efficiencies, making the unsym-
metrical dendrimers efficient light-harvesting antennas.7,8 In
addition, the presence of a phenolic hydroxy group at the focal
point allows site-specific functionalization with a wide variety
of structural units to realize functional dendrimers. Herein
we report the detailed synthesis and optical properties of
unsymmetrical dendrimers functionalized with crown ethers or
terpyridine ligands at the locus. It is envisioned that binding of
crown ethers or the terpyridine ligands with metal ions will alter
the fluorescence from the dendron segments, thus making them
fluorescence-based ion-sensors. In addition to their applications
as sensors, these dendrimers are also interesting systems for
self-assembly studies relating to nanoscale materials.9
Results and discussion
Chart 1 shows the structures of the two sets of dendrons, one
focally anchored with benzo-crown ethers and the other with
terpyridine units. The dendritic skeleton is based on para- and
meta-branched phenylacetylenes.7
Scheme 1 Synthesis of crown ether functionalized monodendrons.
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 4 6 5 – 4 4 7 0
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significantly lower polarity than the crown ether anchored
fields (δ > 7.7 ppm). MALDI-TOF mass spectrometry gives the
products.
correct masses for G1Cr and G2Cr. But for G3Cr, it gives a
mass 23 units higher than the theoretical value, likely due to salt
ions such as Naϩ introduced either from the sample or the
matrix.
Synthesis of GnTp
To attach a terpyridine ligand to the dendron core, an acetyl-
ene-functionalized terpyridine compound 4 was prepared
according to Scheme 2. The Sonogashira coupling reaction of 4
with GnOTf was not successful when Pd(PPh3)2Cl2 was used as
the catalyst. However, the reaction can be promoted by simply
switching the palladium catalyst to Pd(PPh3)4.12 It was found
that, in the coupling reactions of triflates, it was beneficial to
use DMF as the solvent and a minimum amount of triethyl-
amine as the base.10 In DMF with about 10–20 equivalents of
amine relative to reactants, the reaction of triflates GnOTf and
acetylene terminated terpyridine 4 behaved quite well and the
target functional dendrons were obtained in moderate to good
yields.
Terpyridine-functionalized monodendrons show good solu-
bility in common organic solvents as well. A stacked plot of
aromatic regions of the 1H NMR spectra of G1Tp, G2Tp,
G3Tp and the ethynyl-substituted terpyridine compound 4, is
shown in Fig. 1. The signals can be grouped into four regions.
Chemical shifts above 8.6 ppm are due to protons 1, 4, and 5 in
the terpyridine segment (see Chart 1 and Scheme 2 for the label-
ing). These signals are well separated from those associated
with protons in the PA dendrons. It is interesting to note that a
significant downfield shift is observed for protons in the central
pyridine ring (proton 5) when the PA dendrons are attached to
the terpyridine segment, indicating a deshielding effect due to
the electron delocalization from the central pyridine ring to the
PA dendrons. The second region shows peaks with chemical
shifts at 7.7–8.0 ppm. The triplet at 7.88 pm is attributed to
proton 2 in the two side pyridine rings. The aromatic protons
ortho to both ethynyl groups (labeled as b, bЈ, bЉ in Chart 1)
appear as singlets in this region. For G1Tp and G2Tp, these
singlets are separated from the triplet. For higher-generation
dendrons, however, they are severely overlapped. The third
region shows chemical shifts at 7.30–7.40 ppm. Aromatic pro-
tons in the peripheral phenyl rings (labeled a, aЈ in Chart 1) give
broad signals in this region. Proton 3 in the side pyridine rings
also appears in this region. The fourth region includes signals
with chemical shifts between 7.0–7.2 ppm, which are due to
aromatic protons associated with the PA dendrons (protons
labeled c, cЈ, cЉ in Chart 1). The structures of GnTp are also
confirmed by mass spectrometry and elemental analysis.
Scheme 2 Synthesis of terpyridine functionalized monodendrons.
An alternative route to terpyridine functionalization mono-
dendrons uses the reaction of terpyridine triflate 3 and the
acetylene terminated monodendrons GnA (X is ethynyl in
Chart 1). GnA can be readily synthesized by converting the
focal triflate functional group in GnOTf to the ethynyl group.10
The presence of electron-withdrawing pyridine groups makes 3
more reactive than triflates of monodendrons, such as G1OTf.
The reaction of G1A and 3 at 76 ЊC in triethylamine finished in
two days and the product G1Tp was isolated in 71% yield after
chromatography. Under the same conditions, however, the reac-
tion of G2A and 3 took much longer. While the desired product
G2Tp was obtained in 42% yield, a significant amount (17%) of
self-coupling side product, 2G2A was isolated. It appears that
this alternative route works well only for the first generation
dendron.
Structural characterizations of GnCr and GnTp
All GnCr were soluble in common organic solvents such as
chloroform, methylene chloride, THF, etc. They were character-
ized by 1H NMR, 13C NMR, and MALDI-TOF mass spectro-
1
Fig. 1 Aromatic regions of H NMR spectra of 4, G1Tp, G2Tp and
G3Tp.
1
metry. In the H NMR, characteristics of both benzo crown
Optical properties of GnCr and GnTp
ether functionality and monodendrons can be easily identified.
In the aromatic region, a well-isolated doublet at 6.84 ppm,
corresponding to proton 1 (see Chart 1 for labeling), can be
clearly seen even for G3Cr. The protons ortho to both acetylene
groups (labeled as b, bЈ, bЉ in Chart 1) appear as singlets at low
Fig. 2 shows the absorption spectra of G3OH, G3Cr, and
G3Cr with excess KBr in methylene chloride solutions. The
UV/Vis absorption spectra of GnCr resemble those of GnOH
(X = OH in Chart 1). Compared to G3OH, G3Cr shows
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Table 1 Optical properties of dendritic compounds
ab
ab
em
λ edge a/nm
λ max b/nm
εmax c/MϪ1 cmϪ1
λ max d/nm
ꢀfl
τf/ns
e
Compound
4
338
403
438
452
376
422
356
416
440
453
242
290
322
324
276
304
283
299
310
321
47000
79000
111000
213000
48000
110000
48000
82500
351
423
439
451
392
425
360, 374 (sh)
417, 438 (sh)
440, 466 (sh)
452, 479 (sh)
—
—
G1Tp
G2Tp
G3Tp
G1A
0.77
0.65
0.49
0.66
0.84
0.40
0.81
0.70
0.65
2.1
2.1
1.7
2.7
2.4
1.7
2.0
1.9
1.7
G2A
G1OH
G2OH
G3OH
G4OH
171000
330000
a Absorption band edge. b Maximum absorption wavelengths. c Molar extinction coefficients at the absorption maximum. d Fluorescence emission
wavelengths. e Fluorescence quantum yields. f Fluorescence lifetimes.
G3Tp are 403, 438, and 452 nm, respectively. Compared to G1A
and G2A, the absorption band edges of G1Tp and G2Tp are
red-shifted by 27 and 15 nm, respectively, indicating that the π
conjugation extends from the main PA branch to the central
1
pyridine ring, consistent with the H NMR results. It is worth
noting that the absorption band edges of GnTp approach those
of Gn 1OH, except for the smallest dendron (n = 1). For
ϩ
example, G3Tp has an absorption band edge of 452 nm, nearly
identical to that of G4OH.7
These terpyridine-anchored monodendrons exhibit relatively
strong fluorescence. Their steady-state fluorescence emission
spectra in methylene chloride solution are shown in Fig. 4. The
emission spectra were obtained using an excitation wave-
Fig. 2 UV/Vis absorption spectra of G3OH, G3Cr and G3Cr ϩ Kϩ.
length of 350 nm. It should be pointed out that the emission
maxima and shape of all these monodendrons do not change
stronger absorptions in the shorter wavelength region. The
absorptions in the longer wavelength range (350–440 nm) are
nearly identical to those of G3OH. Even though the longest
para conjugated segment in G3Cr is one phenyl acetylene unit
longer that that of G3OH, the absorption edge is only slightly
red shifted. Addition of KBr into the G3Cr solution results in a
significant increase in the absorption strength at around 275
nm. However, little change is obeserved for the absorption at
longer wavelengths. As a result, both the fluorescence intensity
and wavelengths show no obvious change after Kϩ co-
ordination. This could result from either inefficient binding due
to the steric crowding at the focal point or insufficient conform-
ational change caused by binding of those ions due to the
rigidity of the dendrons.
with variations of excitation wavelengths within their absorp-
tion profiles. As the size of the monodendron increases, the
maximum emission wavelengths shift to the red, while the
quantum yield decreases. As shown in Table 1, the fluorescence
quantum yields for G1TP, G2Tp and G3Tp are 77, 65, 49%,
respectively. A similar trend is also observed for the Gn 1OH
ϩ
monodendrons. The decreased quantum yields for higher-
generation monodendrons are likely due to the stronger inter-
actions between the different branches, which may also account
for the slightly decreased fluorescence lifetimes with higher-
generation dendrons.
The optical properties of GnTp in dilute methylene chloride
solutions were studied by UV/Vis absorption, steady-state and
time-resolved fluorescence measurements. The photophysical
properties of these compounds are collected in Table 1. For
comparison, the optical properties of GnA and GnOH, which
have been reported previously,8,10 are also listed in the same
table.
Fig. 3 shows the absorption spectra of GnTp and the ethynyl
substituted terpyridine 4 in methylene chloride. Clearly, the
lowest excitation energy of GnTp shifts to the red with increas-
ing generations. The absorption edges for G1Tp, G2Tp, and
Fig. 4 Fluorescence emission spectra of GnTp.
Coordination with Ru-complexes
Coordination of the PA dendron-attached terpyridine ligands
with Ru-complexes was investigated. The ruthenium complex
of G1Tp was prepared according to a reported procedure.13 As
shown in Scheme 3, a mixture of G1Tp, terpyridine ruthenium
trichloride and a drop of 4-ethylmorpholine was refluxed in
methanol for 21 h to give a dark red solution, which was then
treated with excess ammonium hexafluorophosphate to afford
G1TpRu as a red solid after chromatography. Using the same
procedure, however, we were not able to obtain the ruthenium
complexes for G2Tp and G3Tp. Although the reason is
not known, the steric hindrance at the focal point of these
Fig. 3 Absorption spectra of 4, G1Tp, G2Tp and G3Tp in methylene
chloride.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 4 6 5 – 4 4 7 0
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Experimental
All reagents and solvents were obtained from either Aldrich or
Fisher and were used as received unless otherwise stated.
Anhydrous THF and acetonitrile were distilled prior to use
from sodium metal/benzophenone. Triethylamine was distilled
from calcium hydride prior to use. All air- and moisture-sensi-
tive reactions were carried out under a N2 atmosphere.
Scheme 3 Synthesis of ruthenium complex G1TpRu.
1H NMR spectra were recorded on a Varian Unity 400 MHz
spectrometer. UV/Vis absorption spectra were recorded using
a Hewlett-Packard 8452A diode array spectrophotometer. The
fluorescence emission spectra were measured using a Shimadzu
RF-5301PC spectrofluorimeter. Fluorescence quantum yields
were determined using quinine sulfate in 1 N H2SO4 (ꢀfl ≈ 0.55)
as the standard.14 Time-dependent fluorescence measurements
were performed using the technique of time-correlated single-
photon counting (TCSPC).
monodendrons may play a role. It is possible that the steric
effect limits the bond angles of the terpyridine so that the
desired bite angles for terpyridine with ruthenium could not be
achieved. To overcome this problem, bipyridine ligands are
being attached to the locus.
The structure of G1TpRu was confirmed by NMR, MS, and
elemental analysis. The FAB mass spectrum shows observed
masses of m/z 1267 and 1123, corresponding to the loss of one
Ϫ
and two PF6 ions, respectively. No molecular ion was
1
observed. H NMR spectra of G1TpRu in CDCl3 show well-
Synthesis
resolved signals. The existence of two terpyridine groups is
manifested by the appearance of many signals in pairs in
the aromatic region. For example, there are two pairs of well-
separated triplets, one at around 7.2 ppm and the other at 7.8
ppm, which can be assigned to protons 2/2Ј and 3/3Ј, respect-
ively. There is also one doublet, at around 7.3 ppm which is
assigned to protons 4/4Ј. A lone triplet at 8.2 ppm is attributed
to proton 6. The two protons (b and c) in the central phenyl ring
give two singlets at 7.17 and 7.92 ppm. The protons in the two
phenyl rings with tert-butyl substituents appear as two broad
signals at 7.40 and 7.42 ppm.
After coordination of terpyridine with metal ion, the UV/Vis
absorption spectrum reveals a new band at 498 nm, which is
assigned to the MLCT band (Fig. 5).15 While G1Tp is highly
fluorescent, the fluorescence of G1TpRu at room temperature is
barely detectable. The quenching efficiency is greater than 99%.
These results suggest that terpyridine-anchored dendrons GnTp
would be highly efficient fluorescence sensors had GnTp been
able to bind with transition metal ions. To facilitate metal–
ligand binding and to enhance emission from the MLCT state
after coordination, efforts are being made to link bipyridine
ligands, whose Ru- and Os-complexes are known to exhibit a
strong and long-lived luminescence at room temperature in
fluid solution,16 to the dendron locus.
The preparations of compounds GnOH (n = 1–3) and GnOTf
(n = 1–3) were reported previously.7
4Ј-Ethynylbenzo-18-crown-6 (2). An oven-dried flask was
charged with 4Ј-bromobenzo-18-crown-6 (2.48 g, 6.332 mmol),
triisopropylsilylacetylene (8.0 cm3, 35.66 mmol), Pd(PPh3)2Cl2
(0.147 g, 0.209 mmol), copper() iodide (0.0243 g, 0.128 mmol),
triethylamine (3.0 cm3) and DMF (15.0 cm3). The mixture was
stirred at 80 ЊC overnight. The reaction mixture was then
poured into 3 M hydrochloric acid (20 cm3) and extracted with
methylene chloride (3 × 20 cm3). The combined organic extracts
were washed with water (3 × 20 cm3), brine (20 cm3), dried over
anhydrous sodium sulfate and evaporated in vacuo. The residue
was then purified by chromatography, eluting with hexanes/
ethyl acetate (3 : 1), followed by methylene chloride/methanol
(20 : 1) to give trisopropylsilyl-protected precursor (2.59 g, 83%)
as white crystals. δH (250 MHz; CDCl3) 7.06 (1 H, d, J 8.6), 6.97
(1 H, s), 6.77 (1H d, J 8.6), 4.15–4.12 (4 H, m), 3.92–3.89 (4 H,
m), 3.74–3.67 (12 H, m) and 1.12 (21 H, s). δC(62.5 MHz,
CDCl3) 149.6, 148.4, 125.9, 117.4, 116.2, 113.4, 107.2, 88.6,
70.9, 70.7, 69.5, 69.2, 69.0, 18.7 and 11.4. The precursor com-
pound was desilylated by adding a sample of Bu4NF (1.93 g,
6.10 mmol) to its THF solution (2.59 g, 5.27 mmol in 25 cm3 of
THF). The solution was stirred at room temperature for 30 min
and poured into water. It was extracted with methylene chlor-
ide. The organic extracts were washed with water, dried over
anhydrous sodium sulfate and evaporated in vacuo to give a
yellow solid. It was then purified by passing through a short
silica gel column, eluting with hexanes/ethyl acetate (3 : 1), fol-
lowed by methylene chloride/methanol (25 : 1) to afford the title
compound (1.28 g, 72%) as a white solid. δH (250 MHz, CDCl3)
7.08 (1 H, dd, J 8.6 and 2.5), 6.99 (1 H, d, J 2.5), 6.79 (1 H, d,
J 8.6), 4.17–4.12 (4 H, m), 3.94–3.89 (4 H, m), 3.78–3.68 (12 H,
m) and 3.00 (1 H, s). δC (62.5 MHz, CDCl3) 150.1, 148.6, 126.1,
117.5, 114.7, 113.5, 83.9, 75.9, 71.1, 70.9, 69.7, 69.2 and 69.1.
Fig. 5 Absorption spectra of G1Tp and G1TpRu.
4Ј-Ethynyl-2,2Ј:6Ј,2Љ-terpyridine (4). A solution of compound
3 (1.008 g, 2.64 mmol), trimethylsilylacetylene (0.80 cm3,
5.62 mmol), Pd(PPh3)2Cl2 (0.123 g, 0.176 mmol), copper()
iodide (0.0209 g, 0.110 mmol), triethylamine (2.0 cm3) in DMF
(5.0 cm3) was stirred at 55 ЊC for 3 h and was then poured into
water. The resulting aqueous solution was extracted with
methylene chloride. The combined organic extracts were
collected and dried over magnesium sulfate. After removal of
the solvent, the crude product was purified by chromatography
on aluminium oxide to give 4Ј-[(trimethylsilyl)ethynyl]-2,2Ј:6Ј,
2Љ-terpyridine as a white solid. δH (400 MHz, CDCl3) 8.73 (2 H,
ddd, J 4.8, 1.6 and 1.2), 8.63 (2 H, dt, J 7.6 and 1.2), 8.58 (2 H,
s), 7.88 (2 H, td, J 7.6 and 1.6), 7.36 (2 H, ddd, J 7.6, 4.8 and
1.2), 0.28 (9 H, s). δC (100 MHz, CDCl3) 155.9, 155.7, 149.4,
137.1, 133.7, 132.2, 129.3, 128.7, 124.2, 123.1, 122.7, 121.5, 94.0
Conclusions
Taking advantage of the phenolic group at the PA dendron
locus, crown ethers and terpyridine ligands have been success-
fully attached to the core of light-harvesting PA mono-
dendrons. While coordination of crown ethers with alkali ions
does not lead to significant alteration in either intensity or pos-
ition of their fluorescence emission, coordination of terpyrine
ligands with Ru2ϩ does efficiently quench the fluorescence from
the dendrons, albeit only the smallest dendron exhibits efficient
binding. The same synthetic approach can be applied to attach
a variety of other units to the dendron locus to generate func-
tional dendrimers.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 4 6 5 – 4 4 7 0
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and 87.7. Compound 4 was prepared by the desilylation of
4Ј-[(trimethylsilyl)ethynyl]-2,2Ј:6Ј,2Љ-terpyridine using the same
procedure as previously described. The overall yield for the two
steps was 81%. δH (400 MHz, CDCl3) 8.73 (2 H, ddd, J 4.8, 1.6
and 1.2), 8.63 (2 H, dt, J 7.6 and 1.2), 8.58 (2 H, s), 7.88 (2 H, td,
J 7.6 and 1.6) and 7.36 (2 H, ddd, J 7.6, 4.8 and 1.2). δC (100
MHz, CDCl3) 155.9, 155.7, 149.4, 137.1, 133.7, 132.2, 129.3,
128.7, 124.2, 123.1, 122.7, 121.5, 94.0 and 87.7.
G2Tp. 78% using G2OTf as the reactant and 42% using G2A
as the reactant. δH (400 MHz, CDCl3) 8.74 (2 H, ddd, J 4.8, 1.6
and 1.2), 8.63 (2 H, dt, J 7.6 and 1.2), 8.62 (2 H, s,), 7.88 (2 H,
td, J 7.6 and 1.6), 7.85 (1 H, s), 7.83 (1 H, s), 7.79 (1 H, s), 7.40–
7.34 (14 H, m), 7.13 (1 H, s), 7.10 (1 H, s), 7.09 (1 H, s), 4.01
(3 H, s), 3.93 (3 H, s), 3.92 (3 H, s) and 1.27–1.25 (72 H, m).
δC (100 MHz, CDCl3) 159.8, 159.5, 159.4, 156.0, 155.8, 151.1,
151.0, 151.0, 151.0, 149.4, 137.8, 137.5, 137.2, 137.1, 133.6,
127.9, 127.8, 127.3, 126.2, 126.0, 124.2, 123.4, 123.3, 123.2,
123.0, 122.9, 122.6, 122.6, 122.3, 122.2, 121.5, 119.0, 118.9,
118.7, 114.2, 113.9, 113.9, 113.5, 113.1, 113.0, 112.8, 96.9, 96.5,
94.0, 94.0, 93.8, 93.5, 93.2, 91.4, 89.5, 89.4, 88.5, 87.4, 87.3,
86.5, 86.3, 56.5, 56.4, 56.4, 35.0, 34.9 and 31.5. Found: C, 86.07;
H, 7.74; N, 2.78%; (M ϩ 1)ϩ (MALDI) m/z 1473.5. Calc. for
C106H109N3O3: C, 86.43; H, 7.46; N, 2.85%; M, 1471.8.
G1Cr. A mixture containing G1OTf (0.149 g, 0.218 mmol),
4Ј-ethynylbenzo-18-crown-6 (0.0973 g, 0.289 mmol), Pd(PPh3)2-
Cl2 (0.0072 g, 0.0103 mmol), and copper() iodide (0.0046 g,
0.0242 mmol) in triethylamine (0.5 cm3) and DMF (2.0 cm3)
was stirred at 60 ЊC for 6 h. After cooling to room temperature,
the mixture was poured into water and extracted with CH2Cl2.
The organic layer was washed with an aqueous HCl solution
and then dried over MgSO4. The crude product was purified by
chromatography using silica gel eluting with 5 : 1 hexane/ethyl
acetate to afford G1Cr (0.15 g, 81%) as a white solid. δH (250
MHz, CDCl3) 7.70 (1 H, s), 7.39–7.37 (6 H, m), 7.14 (1 H, dd,
J 8.6 and 2.5), 7.09 (1 H, s), 7.06 (1 H, d, J 2.5), 6.83 (1 H, d,
J 8.6), 4.19–4.16 (4 H, m), 3.95–3.93 (7 H, m), 3.76–3.69 (12 H,
m) and 1.28 (36 H, s). δC(62.5 MHz, CDCl3) 159.1, 151.0, 150.9,
149.8, 148.6, 136.8, 132.3, 132.2, 128.8, 128.6, 127.0, 126.1,
126.0, 125.7, 123.3, 123.0, 122.5, 122.1, 118.9, 116.9, 115.8,
113.7, 113.4, 96.4, 95.6, 93.7, 87.3, 86.3, 83.6, 77.9, 77.4, 76.8,
71.1, 70.9, 70.8, 69.7, 69.1, 69.0, 56.3, 34.9 and 31.5. Found: Mϩ
(MALDI) m/z 866.8. C57H70O7 requires 867.1.
G3Tp. 60%, a brown powder. δH (400 MHz, CDCl3) 8.73 (2
H, ddd, J 4.8, 1.6 and 1.2), 8.634 (2 H, dt, J 7.6 and 1.2), 8.629
(2 H, s), 7.89 (1 H, s), 7.88 (2 H, td, J 7.6 and 1.6), 7.87 (1 H, s),
7.85 (2 H, s), 7.82 (1 H, s), 7.810 (1 H, s), 7.808 (1 H, s), 7.40–
7.32 (26 H, m), 7.15 (1 H, s), 7.13 (1 H, s), 7.12 (1 H, s), 7.08
(2 H, s), 7.07 (2 H, s), 4.03 (3 H, s), 3.93–3.90 (18 H, m) and
1.27–1.23 (144 H, m). δC (100 MHz, CDCl3) 159.8, 159.8, 159.7,
159.5, 159.5, 159.4, 159.4, 156.0, 155.8, 151.0, 151.0, 150.9,
149.4, 137.8, 137.8, 137.5, 137.5, 137.3, 137.2, 137.1, 133.6,
127.9, 127.8, 127.8, 127.5, 127.3, 127.2, 126.9, 126.2, 126.0,
124.2, 123.3, 123.3, 123.3, 123.2, 122.9, 122.9, 122.6, 122.6,
122.6, 122.6, 122.3, 122.2, 122.2, 122.2, 121.5, 119.0, 118.9,
118.9, 118.7, 118.6, 118.5, 114.2, 114.1, 113.9, 113.9, 113.6,
113.5, 113.3, 113.0, 112.9, 112.8, 96.8, 96.7, 96.5, 96.4, 94.2,
94.1, 94.0, 93.9, 93.8, 93.5, 93.4, 93.3, 91.4, 91.3, 91.0, 89.5,
88.6, 88.5, 88.4, 87.4, 87.4, 87.3, 87.3, 86.5, 86.5, 86.4, 86.3,
56.6, 56.5, 56.5, 56.4, 35.0, 34.9 and 31.5. Found: C, 86.92;
H, 7.63; N, 1.42%; (M ϩ 1)ϩ (MALDI) m/z 2841.6. Calc. for
C206H213N3O7: C, 87.03; H, 7.55; N, 1.48%; M, 2840.6.
The synthetic procedure used for G2Cr, G3Cr, G1Tp, G2Tp,
and G3Tp was similar to that for G1Cr.
G2Cr. 67%, a yellow solid. δH (250 MHz, CDCl3) 7.88 (1 H,
s), 7.83 (1 H, s), 7.77 (1 H, s), 7.42–7.39 (12 H, m), 7.17 (1 H, d,
J 8.6), 7.12–7.10 (4 H, m), 6.84 (1 H, d, J 8.6), 4.20–4.16 (4 H,
m), 3.99–3.93 (13 H, m), 3.76–3.69 (12 H, m) and 1.29 (72 H, s).
δC (62.5 MHz, CDCl3) 159.4, 159.3, 151.0, 149.9, 148.6, 137.43,
137.2, 132.4, 132.2, 128.8, 128.6, 127.8, 127.2, 126.5, 126.1,
126.0, 125.8, 123.4, 123.3, 123.0, 122.5, 122.5, 122.1, 122.1,
118.9, 118.8, 118.5, 117.0, 115.8, 114.0, 113.8, 113.5, 112.9,
96.8, 96.5, 95.9, 94.1, 93.9, 93.4, 90.8, 88.3, 87.3, 87.2, 86.4,
86.3, 83.6, 71.1, 70.9, 70.9, 69.7, 69.2, 69.1, 56.4, 34.9 and 31.5.
Found: (M ϩ 1)ϩ (MALDI) m/z 1552.1. C107H122O9 requires
1552.0.
2G2A
This compound was isolated as a side product in the reaction of
compound 3 (0.0519 g, 0.136 mmol) with G2A (0.204 g, 0.165
mmol). Yield 17%. δH (400 MHz, CDCl3) 7.84 (2 H, s), 7.81
(2 H, s), 7.74 (2 H, s), 7.39–7.36 (24 H, m), 7.09–7.08 (6 H, m),
3.97 (6 H, s), 3.91 (12 H, m) and 1.27–1.26 (144 H, m). δC (100
MHz, CDCl3) 160.8, 159.5, 159.4, 151.0, 151.0, 151.0, 151.0,
138.1, 137.5, 137.2, 128.0, 126.2, 126.0, 123.4, 123.3, 123.0,
122.9, 122.6, 122.5, 122.2, 122.1, 119.0, 118.9, 118.8, 118.7,
114.1, 113.9, 113.8, 113.4, 112.9, 112.2, 96.9, 96.8, 96.5, 94.0,
94.0, 93.9, 93.0, 91.7, 88.5, 87.3, 87.2, 86.4, 86.3, 80.0, 78.9,
56.4, 56.4, 56.4, 35.0, 34.9 and 31.5. Mϩ (MALDI) m/z 2479.7.
C182H198O6 requires 2479.5.
G3Cr. 59%, a brown solid. δH (250 MHz, CDCl3) 8.02–7.77
(7 H, m), 7.39–7.36 (24 H, m), 7.20–7.08 (9 H, m), 6.85 (1 H, d,
J 8.6), 4.20 (4 H, m), 4.01–3.92 (25 H, m), 3.78–3.62 (12 H, m)
and 1.27–1.26 (144 H, m). δC (62.5 MHz, CDCl3) 159.6, 159.6,
159.4, 159.3, 150.9, 149.6, 148.4, 137.7, 137.4, 137.2, 132.4,
132.2, 128.8, 128.6, 127.8, 127.7, 127.3, 127.2, 126.8, 126.1,
125.9, 125.8, 123.3, 122.9, 122.5, 122.1, 118.9, 118.8, 118.5,
118.4, 118.3, 116.6, 115.9, 114.0, 113.8, 113.4, 113.3, 113.2,
112.9, 112.8, 96.7, 96.4, 95.8, 94.3, 94.1, 94.0, 93.9, 93.8, 93.6,
93.4, 93.3, 91.2, 90.9, 90.7, 88.5, 88.3, 88.2, 87.3, 87.2, 86.4,
86.3, 83.6, 70.8, 69.5, 68.7, 56.4, 34.9 and 31.5. Found: Mϩ
(MALDI) m/z 2945.3. C207H226O13 requires 2921.9.
G1TpRu
A mixture containing G1Tp (0.0371 g, 0.0471 mmol), terpyrid-
ine ruthenium trichloride (0.0208 g, 4.7198 mmol), 4-ethylmor-
pholine (4 drops) and methanol (15 cm3) was refluxed for 21 h.
The resulting dark red solution was cooled to room tem-
perature. After filtration, to the filtrate was added 1.0 g of
ammonium hexafluorophosphate and the resulting solution
was stirred at room temperature for half an hour. Methanol
was then removed in vacuo. To the residue was then added water
(20 cm3) and methylene chloride (20 cm3). The organic layer was
separated and washed with water (3 × 20 cm3) and the solvent
was then evaporated. The deep red residue, which was essen-
tially pure product, was further purified by chromatography on
basic aluminium oxide, eluting with methylene chloride and
then methylene chloride/methanol (30 : 1) to yield the title
compound (0.0539 g, 81%) as red solids. δH (400 MHz, CDCl3)
8.64 (2 H, s), 8.61 (2 H, d, J 8.0), 8.36 (2 H, d, J 8.0), 8.20 (1 H,
t, J 8.0), 7.92 (1 H, s), 7.80 (2 H, t, J 8.0), 7.70 (2 H, t, J 8.0),
7.42–7.40 (6 H, m), 7.33 (2 H, d, J 5.2), 7.25 (2 H, d, J 5.2),
G1Tp. Whether using G1OTf or G1A (the alternative route)
as the reactant, the synthetic procedure is similar to that of
G1Cr. The yields were 39 and 71%, respectively. δH (400 MHz,
CDCl3) 8.73 (2 H, ddd, J 4.8, 1.6 and 1.2), 8.62 (2 H, dt, J 7.6
and 1.2), 8.61 (2 H, s), 7.87 (2 H, td, J 7.6 and 1.6), 7.76 (1 H, s),
7.40 (6 H, m), 7.35 (2 H, ddd, J 7.6, 4.8 and 1.2), 7.12 (1 H, s),
3.98 (3 H, s) and 1.27–1.25 (36 H, m). δC (100 MHz, CDCl3)
159.6, 155.9, 155.7, 151.1, 150.9, 149.4, 137.4, 137.1, 133.6,
128.2, 126.2, 126.1, 124.2, 123.5, 123.1, 123.0, 122.5, 122.0,
121.5, 119.0, 113.9, 112.3, 96.9, 93.9, 93.2, 89.6, 87.2, 86.1, 56.3,
35.0, 31.5 and 31.5. Found: C, 85.03; H, 7.53; N, 5.04%. Found:
(M ϩ 1)ϩ (LRFAB) m/z 789. C56H57N3O requires C, 85.35; H,
7.29; N, 5.33%; M, 787.5.
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 4 4 6 5 – 4 4 7 0
4469

View Article Online
S. Campagna, G. Denti, A. Juris, S. Serroni and M. Venturi,
7.1685 (2 H, t, J 6.6), 7.168 (1 H, s), 7.09 (2 H, t, J 6.6), 3.98
(3 H, s) and 1.27–1.25 (36 H, m). Found: C, 60.58; H, 5.20%;
Acc. Chem. Res., 1998, 31, 26–34; (d ) T. Sato, D.-L. Jiang and
T. Aida, J. Am. Chem. Soc., 1999, 121, 10658–10659; (e) A. R. H. J.
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Ϫ
ϩ
Ϫ ϩ
(M Ϫ PF6
) (LRFAB), m/z 1267; (M Ϫ 2PF6 ) (LRFAB),
1123. C71H68F12N6OP2Ru requires C, 60.38; H, 4.85%; M,
1412.4.
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Acknowledgements
Financial support from the Office of Naval Research (ONR)
and the Defense Advanced Research Project Agency (DARPA)
are gratefully acknowledged.
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