Construction of regulated nanospace around a porphyrin core

Article abstract of DOI:10.1021/ja004312d

A series of 1,3,5-phenylene-based rigid dendritic porphyrins were synthesized by Suzuki coupling between a porphyrin core and dendron units. The intramolecular energy transfer was studied by absorption and fluorescence spectroscopies. The encapsulation of the porphyrin core within the 1,3,5-phenylene dendron units was found to provide highly efficient energy transfer from the dendron units to the porphyrin core. The dendritic wedge structure affected the energy transfer efficiency. The 1,3,5-phenylene-based rigid dendron units act as highly efficient light-harvesting antennae. These dendritic porphyrins have also been examined as C₆₀ hosts and substrate-selective oxidation catalysts. The attachment of the second generation of 1,3,5-phenylene-based dendron units with the porphyrin core enabled a stable inclusion of C₆₀ in toluene. Furthermore, the size and shape of the nanospace in the rigid dendritic porphyrins were found to affect the selectivity of substrates in the catalytic olefin oxidations.

Full text of DOI:10.1021/ja004312d

5636
J. Am. Chem. Soc. 2001, 123, 5636-5642
Construction of Regulated Nanospace around a Porphyrin Core
Mutsumi Kimura,*,† Tetsuo Shiba,† Megumi Yamazaki,† Kenji Hanabusa,†
Hirofusa Shirai,*,† and Nagao Kobayashi‡
Contribution from the Department of Functional Polymer Science, Faculty of Textile Science and
Technology, Shinshu UniVersity, Ueda 386-8567, Japan, and Department of Chemistry,
Graduate School of Science, Tohoku UniVersity, Sendai 980-8587, Japan
ReceiVed December 20, 2000
Abstract: A series of 1,3,5-phenylene-based rigid dendritic porphyrins were synthesized by Suzuki coupling
between a porphyrin core and dendron units. The intramolecular energy transfer was studied by absorption
and fluorescence spectroscopies. The encapsulation of the porphyrin core within the 1,3,5-phenylene dendron
units was found to provide highly efficient energy transfer from the dendron units to the porphyrin core. The
dendritic wedge structure affected the energy transfer efficiency. The 1,3,5-phenylene-based rigid dendron
units act as highly efficient light-harvesting antennae. These dendritic porphyrins have also been examined as
C60 hosts and substrate-selective oxidation catalysts. The attachment of the second generation of 1,3,5-phenylene-
based dendron units with the porphyrin core enabled a stable inclusion of C60 in toluene. Furthermore, the size
and shape of the nanospace in the rigid dendritic porphyrins were found to affect the selectivity of substrates
in the catalytic olefin oxidations.
Introduction
dendritic porphyrin possessing forth generation dendron units
due to the accumulation effect of aryl ether dendrons.5 Moore,
Suslick, et al. reported regioselective and shape-selective
catalytic abilities in dendritic porphyrins.6 These dendritic
porphyrins were also shown to serve as synthetic models of
biological systems: light-harvesting antennas in a photosynthetic
process, electron-carrying proteins, and enzymes. The molecular
design of a three-dimensional dendritic structure around a
porphyrin core could tune the functionalities of porphyrins and
metalloporphyrins.
The focus of these previous works on dendritic porphyrins
was on encapsulation in flexible dendron units. The mobility
of flexible linkages in dendron units significantly affects the
overall shapes of dendrimers. In contrast, rigid all-hydrocarbon
dendrimers based on polyphenylene and polyphenylacetylene
have also been synthesized. Moore et al. reported a convergent
synthesis of rigid dendrimers based on 1,3,5-trisubstituted
phenylacetylene repeating units.7 Polyphenylene-based den-
drimers have been synthesized through divergent and convergent
methods as reported by Miller, Neenan, et al.,8 Webster and
Kim,9 and Mu¨llen et al.10 These rigid linkages can control the
mobility of dendron units, and the shapes and sizes of the rigid
Dendrimers were well-defined, three-dimensional, and nano-
scopic macromolecules constructed from an interior core with
a regular array of branching units.1 When photo- and electro-
active functional units are incorporated into the interior core of
the dendrimers, the regular branching arrays of the dendrimers
affect several functionalities through the control of the microen-
vironment around functional units.2 Accordingly, the modifica-
tion of functionalities with dendritic structures can possibly
generate new nanoscopic materials with desirable properties.
Dendritic porphyrins have been synthesized by attaching
dendrimers to porphyrins and metalloporphyrins. Aida et al. have
reported dendritic effects on photochemical events and ligand
bindings as dioxygen and dendritic ligands in dendritic por-
phyrins bearing aryl ether dendrons.3 Diederich et al. investi-
gated electrochemical properties of metalloporphyrins encap-
sulated within dendrimers.4 They reported that dendrimers
influenced the redox potentials of metalloporphyrins and steri-
cally inhibited electron transfer from the electrode surface to
the redox center. Fre´chet et al. prepared the zinc porphyrin-
cored dendrimers up to the forth generation and found that
quenching efficiency with benzyl viologen was increased at the
† Shinshu University.
(4) (a) Dandliker, P. J.; Diederich, F.; Gross, M.; Knobler, C. B.; Louati,
A.; Sanford, E. M. Angew. Chem., Int. Ed. Engl. 1994, 33, 1739. (b)
Dandliker, P. J.; Diederich, F.; Gisselbrecht, J.-P.; Louati, A.; Gross, M.
Angew. Chem., Int. Ed. Engl. 1995, 34, 2725. (c) Weyermann, P.;
Gisselbrecht, J.-P.; Boudon, C.; Diederich, F.; Gross, M. Angew. Chem.,
Int. Ed. 1999, 38, 3215.
(5) (a) Pollak, K. W.; Sanford, E. M.; Fre´chet, J. M. J. J. Mater. Chem.
1998, 8, 519. (b) Pollak, K. W.; Leon, J. W.; Fre´chet J. M. J.; Maskus, M.;
Abrun˜a, H. D. Chem. Mater. 1998, 10, 30. (c) Matos, M. S.; Hofkens, J.;
De Schryver, F. C.; Hecht, S.; Pollak, K. W.; Fre´chet J. M. J.; Forier, B.;
Dehaen, W. Macromolecules 2000, 33, 2967.
(6) (a) Bhyrappa, P.; Young, J. K.; Moore, J. S.; Suslick, K. S. J. Am.
Chem. Soc. 1996, 118, 5708. (b) Bhyrappa, P.; Vaijayanthimala, G.; Suslick,
K. S. J. Am. Chem. Soc. 1999, 121, 262.
(7) (a) Xu, Z.; Kahr, M.; Walker, K. L.; Wilkins, C. L. Moore, J. S. J.
Am. Chem. Soc. 1994, 116, 4537. (b) Pesak, D. J.; Moore, J. S. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1636. (c) Devadoss, C.; Bharathi, P.; Moore,
J. S. Macromolecules 1998, 31, 8091. (d) Pesak, D. J.; Moore, J. S.; Wheat,
T. E. Macromolecules 1997, 30, 6467.
‡ Tohoku University.
(1) (a) Tomalia, D. A.; Dupont Durst, H. Top. Curr. Chem. 1993, 165,
193. (b) Newkome, G. R.; Moorefield, C. N. ComprehensiVe Supramo-
lecular Chemistry; Pergamon: New York, 1996; Vol. 10, pp 777-832. (c)
Fre´chet, J. M. J. Science 1994, 263, 1710. (d) van Genderen, M. H. P.;
Meijer, E. W. Supramolecular Technology; Wiley: New York, 1999;
Chapter 2, pp 47-88.
(2) (a) Gorman, C. AdV. Mater. 1998, 10, 295. (b) Fischer, M.; Vo¨gtle,
F. Angew. Chem., Int. Ed. 1999, 38, 884. (c) Bosman, A. W.; Janssen, H.
M.; Meijer, E. W. Chem. ReV. 1999, 99, 1665. (d) Newkome, G. R.; He,
E.; Moorefield, C. N. Chem. ReV. 1999, 99, 1689.
(3) (a) Jin, R.-H.; Aida, T.; Inoue, S. J. Chem. Soc., Chem. Commun.
1993, 1260. (b) Sadamoto, R.; Tomioka, N.; Aida, T. J. Am. Chem. Soc.
1996, 118, 3978. (c) Tomoyose, Y.; Jiang, D.-L.; Jin, R.-H.; Aida, T.;
Yamashita, T.; Horie, K.; Yashima, E.; Okamoto, Y. Macormolecules 1996,
29, 5236. (d) Jiang, D.-L.; Aida, T. Chem. Commun. 1996, 1523. (e)
Tomioka, N.; Takasu, D.; Takahashi, T.; Aida, T. Angew. Chem., Int. Ed.
1998, 37, 1531.
10.1021/ja004312d CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/24/2001

Regulated Nanospace around a Porphyrin Core
J. Am. Chem. Soc., Vol. 123, No. 24, 2001 5637
Scheme 1. Synthetic Approach to a Series of Dendritic Porphyrins
dendrimers persist in all physical environments. Such stiff and
shape-persistent rigid dendrimers can create a regulated nano-
space within a dendritic structure. The creation of a regulated
nanospace around functional molecules might provide some
unique properties, e.g., sizes, shapes, or chemical selectivities
for guest molecules.
The effects of rigid dendron units on porphyrin functionalities
have not been as extensively explored. Constructing a rigid
dendrimer around a porphyrin core may enhance the porphyrin
functionalities. Here, we describe the synthesis and characteriza-
tion of a series of 1,3,5-phenylene-based dendritic porphyrins
possessing a porphyrin central core. In this paper, we also
discuss a structural dependence of the intramolecular singlet-
singlet energy transfer from the rigid dendrons to the porphyrin
core and the selective recognitions in the regulated nanospace
constructed around the porphyrin core.
(trimethylsilyl)benzene. Purification of the first-generation
3-TMS was accomplished by column chromatography followed
by recrystallization. The trimethylsilyl group at the focal point
was then converted to the corresponding boronic acid by
treatment with BBr3. Dendron 4-B(OH)2 was synthesized from
3-B(OH)2 and 4-bromo-(1-trimethylsilyl)benzene through the
same procedure as that for 3-TMS. Finally, the coupling of
dendrons 2-B(OH)2, 3-B(OH)2, and 4-B(OH)2 to the porphyrin
core 1 using Pd(PPh3)4 as a catalyst proceeded to yield dendritic
porphyrins H2P3, H2P4, and H2P5. The third-generation por-
phyrin dendrimer could not be prepared from the coupling
between 1 and a higher generation of phenylboronic acid
5-B(OH)2. Matrix-assisted laser desorption/ionization time-of-
flight mass spectra (MALDI-TOF-MS) of the resulting products
showed a mixture of defect structures (Figure 1), suggesting
that it becomes more difficult to carry out a complete coupling
reaction of a focal point of a dendron unit 5-B(OH)2 with a
porphyrin core. Dendritic porphyrin H2P7, in which the tri-
phenylene dendron units were linked with the porphyrin core
through ether bonds, was synthesized by an alkaline-mediated
coupling reaction between 5,10,15,20-tetrakis(3′,5′-dihydroxy-
phenyl)porphyrin3a and dendritic bromide 7-Br.11 The synthe-
sized dendritic porphyrins were fully characterized by UV-
visible spectroscopy, size-exclusion chromatography (SEC),
high-performance liquid chromatography (HPLC), MALDI-TOF
mass spectroscopy, and 1H and 13C NMR spectroscopy.
Results and Discussion
Synthesis of Rigid Dendritic Porphyrins. A series of 1,3,5-
phenylene-based dendritic porphyrins H2P3-H2P7 were syn-
thesized by using the convergent methodology developed by
Miller, Neenan, et al. (Scheme 1).8 The dendron construction
began by palladium-catalyzed cross coupling (Suzuki coupling)
between 4-tert-butylphenylboronic acid and 3,5-dibromo-1-
(8) Miller, T. M.; Neeman, T. X.; Zayas, R.; Bair, H. E. J. Am. Chem.
Soc. 1992, 114, 1018.
(9) Kim, Y. H.; Webster, O. W. J. Am. Chem. Soc. 1990, 112, 4592.
(10) Berresheim, A. J.; Mu¨ller, M.; Mu¨llen, K. Chem. ReV. 1999, 99,
1747 and related references therein.
(11) (a) Hawker, C. J.; Fre´chet, J. M. J. J. Am. Chem. Soc. 1990, 112,
7638. (b) Wooley, K. L.; Hawker, C. J.; Fe´chet, J. M. J. J. Am. Chem. Soc.
1991, 113, 4252.

5638 J. Am. Chem. Soc., Vol. 123, No. 24, 2001
Kimura et al.
Figure 2. 1H NMR spectra of dendritic porphyrins H2P3, H2P4, and
H2P6 in CDCl3.
Table 1. Spectroscopic and Photophysical Data for the Dendritic
Porphyrins and Dendrons
absorption,a λmax, nm
emission,b
max, nm (τ, ns)
(log ꢀ, M-1 cm-1
)
λ
φET
c
3-TMS
5-TMS
6-TMS
H2P3
H2P4
H2P6
262 (4.30)
264 (4.76)
270 (4.77)
256 (4.90), 424 (5.38)
262 (5.36), 424 (5.38)
270 (5.37), 424 (5.38)
256 (5.24), 424 (5.38)
354
360
370
652, 719 (8.2)
651, 717 (8.3)
650, 717 (8.2)
652, 718 (8.3)
0.66
0.98
0.74
0.42
Figure 1. MALDI-TOF mass spectra of (a) H2P3, (b) H2P4, (c) H2P6,
(d) H2P7, and (e) defect products after cross coupling between 1 and
5-B(OH)2.
H2P7
a In CH2Cl2 solution. b In degassed CH2Cl2 solution. c Quantum yield
of energy transfer (φET) in dendritic porphyrins estimated by comparing
the absorption spectrum and excitation spectrum by monitoring the
emission of the porphyrin moiety in degassed CH2Cl2.
Examinations of SEC showed that the observed molecular
weight rose with each generation and that all products have sharp
and symmetrical elution patterns with polydispersities (Mw/Mn)
less than 1.02. With HPLC, it was possible to resolve fully
substituted and partially substituted dendritic porphyrins, provid-
ing confirmation that dendron substitution in H2P3, H2P4, H2P6,
and H2P7 is complete. Figure 2 shows 1H NMR spectra of H2P3,
H2P4, and H2P6 in CDCl3 at 25 °C, which provides the structural
information. As shown in Figure 2, proton resonances in the
aromatic region of all dendritic porphyrins are distinguishable
and assignable. The proton resonances of benzene units nearer
the porphyrin core shift downfield compared with those of the
exterior benzene units, indicating the successive generation of
a highly symmetric layered structure.
Light-Harvesting Properties of 1,3,5-Phenylene-Based
Dendrons. The absorption spectra of the dendritic porphyrins
H2P3, H2P4, H2P5, and H2P6, along with trimethylsilyl-
terminated dendrons, were measured in CH2Cl2. The absorption
maxima (λmax) and molar extinction coefficient (ꢀ) of the
porphyrins are summarized in Table 1. Figure 3 illustrates the
absorption spectra of the dendritic porphyrins in CH2Cl2. These
absorption spectra are the sum of a porphyrin moiety (400-
Figure 3. UV-vis absorption spectra of H2P3, H2P4, H2P6, and H2P7
in CH2Cl2. The spectra were normalized to 5.0 µM concentration.
650 nm) and 1,3,5-phenylene-based dendron units (260-270
nm). The Soret bands and Q-bands of the porphyrin core
remained unaltered in H2P3, H2P4, H2P6, and H2P7 with
different structures of the dendron units, suggesting that the
electronic conditions in all dendritic porphyrins are similar to

Regulated Nanospace around a Porphyrin Core
J. Am. Chem. Soc., Vol. 123, No. 24, 2001 5639
dendron units was very weak (Figure 4B). A mixture of the
porphyrin core 1 and 5-TMS showed no emission peaks from
the porphyrin moiety with excitation at 262 nm. This result
indicated the efficient intramolecular singlet-singlet energy
transfer from the phenylene-based dendron units to the porphyrin
core.
The efficiency of energy transfer (φET) can be estimated by
comparing the UV-vis spectrum and excitation spectrum of
the dendron units (Table 1). When the absorption and excitation
spectra are normalized at the Soret band of the porphyrin core,
the ratio of the normalized excitation and absorption spectrum
at λmax of the dendron unit represents the total energy transfer
efficiency (φET). The similarity of the band shape and intensity
of these two spectra for H2P4 indicates a high transfer efficiency.
The φET values in H2P3 and H2P4 were estimated to be 66 and
98%, respectively. With increasing branching layers, more
photons can be harvested by the phenylene-based dendron units,
and the absorbed photons are transduced to the fluorescence
emission from the porphyrin core through the highly efficient
energy transfer. The other dendritic porphyrins H2P6 and H2P7
exhibited a residual fluorescence in the range of 350-400 nm
from the phenylene dendron units together with the fluorescence
from the porphyrin core as shown in Figure 4B. Clearly, H2P6
and H2P7 have lower energy transfer efficiencies than H2P4.
Recently, chromophore-containing dendrimers have attracted
significant attention as artificial light-harvesting antennae due
to their morphological similarities to architectures of natural
light-harvesting complexes.12 The uniform three-dimensional
structures of dendrimers allow the precise placement of chro-
mophores by the introduction of chromophores at the core,
branching, and peripheral positions of the dendritic structure.
There has been much work on the light-harvesting properties
of the designed chromophore-containing dendrimers as dendritic
polynuclear Ru and Os polypyridine complexes,13 lanthanide-
cored dendrimers,14 rigid acceptor-terminated phenylacetylene
dendrimers,15 dendritic porphyrins,16 and acceptor/donor dye-
labeled dendrimers.17 Among them, Jiang and Aida found that
the dendritic porphyrins having a continuous array of flexible
aryl ether dendron units exhibit highly efficient intramolecular
energy transfer, and the energy transfer efficiency depends on
the generation number and morphology of the dendritic por-
phyrins.16 The intramolecular energy transfer within dendritic
architectures has been explained by the Fo¨rster mechanism.12
According to this, the energy transfer efficiency depends on
the distance between donor and acceptor molecules and the
spectral overlap between donor emission and acceptor absorption
spectra. With increasing dendrimer size, the φET value increases.
The spectral overlap is better for H2P6 than for H2P4. However,
the φET value in H2P6 is lower than that in H2P4. Our attempt
to apply the Fo¨rster mechanism fails to explain the highly
Figure 4. (A) Steady-state fluorescence spectra of 5-TMS and H2P4
upon excitation at the absorption maximum of 5-TMS (262 nm) and
the Soret band of H2P4 (424 nm), respectively. (B) Fluorescence spectra
of H2P4, H2P6, and H2P7 upon excitation at the absorption maximum
of the each dendron components. The measurements were carried out
in degassed CH2Cl2 at room temperature. All spectra are normalized
to a constant absorbance at the excitation wavelength.
each other. In contrast, the absorption bands corresponding to
the dendron units around 260 nm dramatically differed with
the different structures of the dendron units. As the dendrimer
generation increased, the ꢀ value of the dendron units in the
second-generation H2P4 nearly doubled from that of the first-
generation H2P3. The cross-conjugated structures of the 1,3,5-
phenylene-based dendron units in H2P4 exhibited a strong UV
absorption characteristic. The absorption intensity corresponding
to the dendron units in the larger dendrimer H2P6, in which a
benzene spacer was inserted between the porphyrin core and
the outer branching units, did not significantly change compared
with that for H2P4. However, the absorption band was red
shifted and broadened, since H2P6 contained linear triphenylene
units in addition to the cross conjugation of the 1,3,5-phenylene
branching system. Despite the number of benzene rings being
the same in H2P4 and H2P7, the absorption intensity of the
dendron units for H2P7 was two-thirds of that for H2P4. The
ether linkage in H2P7 led to a decrease in the electronic
interaction among benzene components in the dendron units.
Figure 4A shows steady-state fluorescence spectra of H2P4
and trimethylsilyl-terminated dendron 5-TMS in degassed CH2-
Cl2 upon excitation at the Soret band of the porphyrin core and
λmax of 5-TMS, respectively. The fluorescence parameters for
all of the dendritic porphyrins and dendrons are summarized in
Table 1. The dendritic porphyrins emitted fluorescence at 650
and 717 nm and exhibited nearly the same intensities in different
generations. The fluorescence of all of the dendritic porphyrins
showed a normal decay profile, and the fluorescence lifetime
of the porphyrin core was independent of the structural
differences of the dendron units. These results suggested that
the 1,3,5-phenylene-based dendritic structure hardly affected the
fluorescence properties of the porphyrin core. The dendron
5-TMS emitted strong fluorescence at 360 nm with excitation
at 264 nm. By the excitation at the absorption band of 1,3,5-
phenylene dendron units in H2P4, the emission was mostly from
the porphyrin core, and the residual fluorescence from the
(12) (a) Adronov, A.; Fre´chet, J. M. J. Chem. Commun. 2000, 1701. (b)
Stewart, G. M.; Fox, M. A. J. Am. Chem. Soc. 1996, 118, 4354. (c) Hu,
Q.-S.; Pugh, V.; Sabat, M.; Pu, L. J. Org. Chem. 1999, 64, 7528. (d) Sato,
T.; Jiang, D.-L.; Aida, T. J. Am. Chem. Soc. 1999, 121, 10658. (e) Li, J.;
Diers, J. R.; Yang, S. I.; Bocian, D. F.; Holten, D.; Lindsey, J. S. J. Org.
Chem. 1999, 64, 9090.
(13) Balzani, V.; Campagna, S.; Denti, G.; Juris, A.; Serroni, S.; Venturi,
M. Acc. Chem. Res. 1998, 31, 26 and related references therein.
(14) (a) Kawa, M.; Fre´chet, J. M. J. Thin Solid Films 1998, 331, 259.
(b) Kawa, M.; Fre´chet, J. M. J. Chem. Mater. 1998, 10, 286.
(15) Devadoss, C.; Bharathi, P.; Moore, J. S. J. Am. Chem. Soc. 1996,
118, 9635.
(16) Jiang, D.-L.; Aida, T. J. Am. Chem. Soc. 1998, 120, 10895.
(17) (a) Gilat, S. L.; Adronov, A.; Fre´chet, J. M. J. Angew. Chem., Int.
Ed. 1999, 38, 1422. (b) Chrisstoffels, L. A. J.; Adronov, A.; Fre´chet, J. M.
J. Angew. Chem., Int. Ed. 2000, 39, 2163. (c) Adronov, A.; Gilat, S. L.;
Fre´chet, J. M. J.; Ohta, K.; Neuwahl, F. V. R.; Fleming, G. R. J. Am. Chem.
Soc. 2000, 122, 1175.

5640 J. Am. Chem. Soc., Vol. 123, No. 24, 2001
Kimura et al.
efficient energy transfer phenomena in these 1,3,5-phenylene-
based dendritic porphyrins. Moreover, the decrease in the φET
value in H2P7 compared with that in H2P4 provided clear
evidence of the presence of a through-bond pathway of energy
transfer within the cross-conjugated dendritic porphyrins. A
similar observation was noted in the perylene-terminated
phenylacetylene dendrimers reported by Moore et al.15 There-
fore, we concluded that the high efficiency of the energy transfer
from the phenylene-based dendron units to the porphyrin core
can be ascribed to the efficient energy flow through the cross
conjugation of the 1,3,5-phenylene dendron units (through-bond)
as well as the larger overlap between the emission of the dendron
units and the absorption of the porphyrin core (through-space).
Figure 5. Effect of C60 concentration on the absorption spectrum of
H2P4 in toluene at room temperature: [H2P4] ) 3.0 µM; [C60]/[H2P4]
) 0, 0.33, 0.67, 1.0, 2.0, 3.3, 5.0, 6.0, 7.0, 8.3, 10.0, 16.7.
Complexation of C60 with Rigid Dendritic Porphyrins. The
inclusion of fullerenes into organic hosts through noncovalent
bonds has attracted considerable interest due to the modification
of fullerene functionalities as well as their purification.18 Several
organic hosts for fullerenes have been designed and synthe-
sized.19 Atwood et al. and Shinkai et al. discovered that p-tert-
buthylcalix[8]arene selectively includes C60 in organic solvents
and forms a precipitate with 1:1 stoichiometry.20 Very recently,
porphyrin dimers have also shown a selective fullerene binding
with a high binding constant (>105 M-1).21 In these supramo-
lecular hosts for fullerenes, the conformity of the C60 size with
the host cavity enables stable complexation between the organic
hosts and C60.
The absorption spectrum of H2P4 in toluene solution changed
upon the addition of C60, and the Soret band was red shifted
from 424 to 428 nm with decreasing absorption intensity,
indicating electronic interaction between the porphyrin core
within H2P4 and C60 (Figure 5). A similar spectral change was
observed in the porphyrin dimers.21 However, the other dendritic
porphyrins, H2P3, H2P6, and H2P7, showed no spectral changes
in the absorption spectra after the addition of a large excess of
C60. We could not measure the 1H and 13C NMR spectra of the
complex of H2P4 with C60 because of the formation of
precipitate. When the equimolar toluene solution of C60 was
admixed with the H2P4 solution, a red-brown precipitate was
formed. Filtration of the precipitate recovered above 85% yield
of the initial amount of H2P4 and C60. Elemental analysis of
the precipitate indicated a 1:1 complex of H2P4 and C60. (Anal.
Calcd for C312H254N4: C, 92.31; H, 6.31; N, 1.38. Found: C,
92.02; H, 6.38; N, 1.37.) Furthermore, the MALDI-TOF mass
spectrum of the precipitate clearly shows the mass ion peak at
m/z 4059 corresponding to the 1:1 complex between H2P4 and
C60. The precipitate dissociated into each component after the
addition of CHCl3. In contrast, no precipitation was observed
in the other dendritic porphyrins after the addition of C60. The
mixing of C60 with the dendritic porphyrins H2P3, H2P6, or H2P7
The synthesized 1,3,5-phenylene-based dendritic porphyrins
possess a regulated nanospace with different sizes. These well-
defined nanospaces within the 1,3,5-phenylene-based dendrimers
can provide cavities for inclusion of C60. Furthermore, the
porphyrin core in the dendritic porphyrins can interact strongly
with C60 via a π-donor-π-acceptor interaction. In this context,
we expect stable complexation of C60 with 1,3,5-phenylene-
based dendritic porphyrins.
(18) Diederich, F.; Effing, J.; Janas, U.; Jullien, L.; Plesnivy, T.;
Ringsdorf, H.; Thilgen, C.; Weinsterin, D. Angew. Chem., Int. Ed. Engl.
1992, 31, 1599. Andersson, T.; Nilsson, K.; Sundahl, M.; Westman, G.;
Wennerstro¨m, O. J. Chem. Soc. Chem. Commun. 1992, 604. Izuoka, A.;
Tachikawa, T.; Sugawara, T.; Saito, Y.; Shinohara, H. Chem. Lett. 1992,
1049. Steed, J. W.; Junk, P. C.; Atwood, J. L.; Barnes, M. J.; Raston, C. L.
J. Am. Chem. Soc. 1994, 116, 10346. Yoshida, Z.; Takekuma, H.; Takekuma,
S.; Matsubara, Y. Angew. Chem., Int. Ed. Engl. 1994, 33, 1597. Haino, T.;
Yanase, M.; Fukazawa, Y. Angew. Chem., Int. Ed. 1998, 37, 997.
(19) Covalently bonded dendrimer-fullerene and porphyrin-fullerene
hybrids have been reported. (a) Dendrimer-fullerrene hybrid: Wooley, K.
L.; Hawker, C. J.; Fre´chet, J. M. J.; Wudl, F.; Srdanov, G.; Shi, S.; Li, C.;
Kao, M. J. Am. Chem. Soc. 1993, 115, 9836. Hawker, C. J.; Wooley, K.
L.; Fre´chet, J. M. J. J. Chem. Soc., Chem. Commun. 1994, 925. Cloutet,
E.; Gnanou, Y.; Fillaut, J.-L.; Astruc, D. Chem. Commun. 1996, 1565.
Catalano, V. J.; Parodi, N. Inorg. Chem. 1997, 36, 537. Camps, X.; Hirsch,
A. J. Chem. Soc., Perkin Trans. 1 1997, 1595. Armaroli, N.; Boudon, C.;
Felder, D.; Gisselbrecht, J.-P.; Gross, M.; Marconi, G.; Nicoud, J.-F.;
Nierengarten, J. F.; Vicinelli, V. Angew. Chem., Int. Ed. 1999, 38, 3730.
Felder, D.; Gallani, J.-L.; Guillon, D.; Heinrich, B.; Nicoud, J.-F.;
Nierengarten, J.-F. Angew. Chem., Int. Ed. 2000, 39, 201. Brettreich, M.;
Burghardt, S.; Bo¨ttcher, C.; Bayerl, T.; Bayerl, S.; Hirsch, A. Angew. Chem.,
Int. Ed. 2000, 39, 1845. (b) Porphyrin-fullerene hybrids: Imahori, H.;
Hagiwara, K.; Aoki, M.; Akiyama, T.; Taniguchi, S.; Okada, T.; Shirakawa,
M.; Sakata, Y. J. Am. Chem. Soc. 1996, 118, 11771. Baran, P. S.; Monaco,
R. R.; Khan, A. U.; Schuster, D. I.; Wilson, S. R. J. Am. Chem. Soc. 1997,
119, 8363. Carbonera, D.; Di Valentin, M.; Corvaja, C.; Agostini, G.;
Giacometti, G.; Liddell, P. A.; Kuciauskas, D.; Moore, A. L.; Moore, T.
A.; Gust, D. J. Am. Chem. Soc. 1998, 120, 4398. Dietel, E.; Hirsch, A.;
Zhou, J.; Riker, A. J. Chem. Soc., Perkin Trans. 2 1998, 1357. Cheng, P.;
Wilson, S. R.; Schuster, D. I. Chem. Commun. 1999, 89.
1
showed no spectral changes in the H NMR spectra of the
dendritic porphyrins and the 13C NMR spectra of C60. Accord-
ingly, we judged that only H2P4 possessing the second genera-
tion of 1,3,5-phenylene-based dendron units can form a stable
complex with C60. The regulated nanospace constructed from
the regulated branching system of 27 benzene rings around the
porphyrin core is exactly fitted to the C60 size, and the multipoint
interaction among the curved π surface of C60, the planar π
surface of the porphyrin core, and the benzene rings of the
branching units work to stabilize the complex between H2P4
and C60 in toluene.
Shape-Selective Oxidation of Olefins within the Regulated
Nanospace. A number of synthetic metalloporphyrins have been
employed to catalyze olefin epoxidation and alkane hydroxy-
lation with a view toward mimicking the enzymatic activity of
cytochrome P-450.22 The shape-selectivities, regioselectivities,
and enantioselectivities in these catalytic reactions have also
been investigated using a variety of metalloporphyrins possess-
ing substrate recognition sites or sterically bulky substituents.
The encapsulation of a metalloporphyrin core with bulky
(20) (a) Atwood, J. L.; Koutsantonis, G. A.; Raston, C. L. Nature 1994,
368, 229. (b) Suzuki, T.; Nakashima, K.; Shinkai, S. Chem. Lett. 1994,
699. (c) Ikada, A.; Shinaki, S. Chem. ReV. 1997, 97, 1713.
(21) (a) Tashiro, K.; Aida, T.; Zheng, J.-Y.; Kinbara, K.; Saigo, K.;
Sakamoto, S.; Yamaguchi, K. J. Am. Chem. Soc. 1999, 121, 9477. (b) Sun,
D.; Tham, F. S.; Reed, C. A.; Chaker, L.; Burgess, M.; Boyd, P. D. W. J.
Am. Chem. Soc. 2000, 122, 10704.
(22) (a) Cook, B. R.; Reinert, T. J.; Suslick, K. S. J. Am. Chem. Soc.
1986, 108, 7281 and related references therein. (b) Groves, J. T.; Nemo, T.
E. J. Am. Chem. Soc. 1987, 109, 5045. (c) Ostovic, D.; Bruice, T. C. J.
Am. Chem. Soc. 1989, 111, 6511. (d) Collman, J. P.; Brauman, J. I.;
Fitzgerald, J. P.; Hampton, P. D.; Naruta, Y.; Michida, T. Bull. Chem. Soc.
Jpn. 1988, 61, 47. (e) Collman, J. P.; Wang, Z.; Straumanis, A.; Quelquejeu,
M.; Rose, E. J. Am. Chem. Soc. 1999, 121, 460.

Regulated Nanospace around a Porphyrin Core
J. Am. Chem. Soc., Vol. 123, No. 24, 2001 5641
of 4-vinyl-1-hexene decreases as the generation of dendrimers
increases. While Fe(P3)(Cl), Fe(P6)(Cl), and Fe(P7)(Cl) show
little selectivity ([4-epoxyethyl-1-cyclohexene]/[4-vinyl-1-cy-
clohexene 1,2-epoxide] ) ca. 1.026), Fe(P4)(Cl) exhibits regio-
selectivity for the epoxidation of 4-vinyl-1-cyclohexene at the
least hindered double bond ([4-epoxyethyl-1-cyclohexene]/
[4-vinyl-1-cyclohexene 1,2- epoxide] ) 1.426). The substrate
selectivity was examined using the epoxidation of a 1:1 mixture
of 1-octene and cis-cyclooctene. The high intermolecular
selectivity in the epoxidation of 1-octene over that of cis-
cyclooctene was also observed in Fe(P4)(Cl) ([1,2-epoxyoctane]/
[cyclooctene oxide] ) 2.826). This observation agreed with the
result reported by Suslick et al. for flexible dendritic manganese
porphyrins.6 The size and shape of the nanospace around the
reaction center were found to affect the selectivity of the
substrate in catalytic reactions.
Figure 6. Epoxidation results for cis-cyclohexene, 1-octene, and
4-vinyl-1-cyclohexene using Fe(TPP)(Cl), Fe(P3)(Cl), Fe(P4)(Cl), Fe-
(P6)(Cl), and Fe(P7)(Cl) in the presence of iodosylbenzene at 25 °C.
The ratios of the epoxides are normalized with respect to the
corresponding Fe(TPP)(Cl) values.
Conclusion
In summary, novel rigid 1,3,5-phenylene-based dendrimers
containing porphyrin and iron porphyrin complexes have been
synthesized and characterized. Absorption and fluorescence
spectroscopic studies demonstrated that the energy harvested
by the cross-conjugated dendron units can be efficiently
transferred to the porphyrin core through space and through
bond. In addition, the rigid dendritic porphyrins were examined
as hosts for C60 and shape-selective epoxidation catalysts. We
found that the sizes and structures of the dendron units strongly
affected the efficiency of the intramolecular energy transfer,
interaction with C60, and shape selectivity in the catalytic
reactions of olefin epoxidation. The construction of a 1,3,5-
phenylene-based regular branching array around the porphyrin
core allowed the creation of a regulated nanospace within the
dendrimers. The design of the nanospace could control the
functionalities of the functional core. These attempts can, in
principle, be applied to many nanoscopic functional materials,
in which functionalities are developed by the combination of
functional molecules and the designed nanospace within a single
molecule.
polyester dendritic wedges has been found to induce regio-
selectivity and shape-selectivity in the catalytic reaction of olefin
epoxidation.6 The regulated nanospace around the metallopor-
phyrin core constructed from 1,3,5-phenylene-based dendrimers
may also affect the shape selectivity in olefin epoxidation.23
For the preparation of dendritic iron(III) complexes, free-
base H2P3, H2P4, H2P6, and H2P7 were reacted with FeCl2 in
THF. After purification, the complete metalations in Fe(P3)-
(Cl), Fe(P4)(Cl), Fe(P6)(Cl), and Fe(P7)(Cl) were confirmed
by UV-vis and MALDI-TOF mass spectra. It is well known
that iron(III) tetraphenylporphyrin (Fe(TPP)(Cl)) forms an
unreactive µ-oxo-dimer.24 When CH2Cl2 solutions of dendritic
porphyrins were mixed with basic aqueous solutions at pH 12.0,
the MALDI-TOF mass spectra showed only a monomeric
molecular ion peak, indicating no formation of µ-oxo dimers.
The steric hindrance of dendritic wedges in all of the dendritic
iron porphyrins was enough to prevent the formation of µ-oxo
dimers.
Experimental Section
The epoxidation of olefins with the dendritic iron porphyrins
was performed in degassed CH2Cl2 in the presence of iodosyl-
benzene as the oxygen donor. Figure 6 shows results for the
epoxidation of 1-octene, cis-cyclooctene, and 4-vinyl-1-hexene
with different shapes and sizes. We can see that the rigid
dendritic iron porphyrins exhibit remarkable selectivities com-
pared with unsubstituted Fe(TPP)(Cl) and the catalytic activity
strongly depends on the structures of the dendron units and
substrates.25 The catalytic activity for the epoxidation of cyclic
cis-cyclooctene is comparable for all dendritic iron porphyrins.
On the other hand, the second-generation dendrimers Fe(P4)-
(Cl) and Fe(P7)(Cl) show ca. 3-fold higher catalytic activity in
linear 1-octene relative to Fe(TPP)(Cl) and the other dendritic
iron porphyrins.
General. NMR spectra were recorded on a Bruker AVANCE 400
FT-NMR spectrometer operating at 399.65 MHz for 1H in CDCl3
solution. Chemical shifts are reported relative to internal TMS. IR
spectra were obtained on a JASCO FS-420 spectrometer as KBr pellets.
UV-vis spectra and fluorescence spectra were measured on a JASCO
V-570 and a JASCO FP-750. MALDI-TOF mass spectra were obtained
on a PerSeptive Biosystems Voyager-DE-Pro spectrometer with dithra-
nol as matrix. GPC analyses were carried out with a JASCO HPLC
system (pump 1580, UV detector 1575, refractive index detector 930)
and a Showa Denko GPC KF-804L column (8.0 × 300 mm, polystyrene
standards, M ) 900-400 000 g/mol) in THF as an eluent at 35 °C
(1.0 mL min-1). Melting points were recorded using a Shibata MEL-
270 melting point apparatus and are corrected.
Materials. All chemicals were purchased from commercial suppliers
and used without purification. Solvents, such as toluene, THF, and CH2-
Cl2, were freshly distilled. Column chromatography was performed with
activated alumina (Wako, 200 mesh) or Wakogel C-200. Analytical
thin-layer chromatography was performed with commercial Merck
The diene 4-vinyl-1-hexene was oxidized into two products
(4-vinyl-1-cyclohexene 1,2-epoxide and 4-epoxyethyl-1 cyclo-
hexene) through the epoxidation of two different intramolecular
double bonds. The total catalytic activity for the epoxidation
plates coated with silica gel 60 F254 or aluminum oxide 60 F254
.
Porphyrin Core 1. A mixture of pyrrole (2.0 mL, 1.59 × 10-2 mol)
and 3,5-dibromobenzaldehyde (4.2 g, 1.59 × 10-2 mol) in 25 mL of
propionic acid was refluxed for 48 h. The residue resulting from
evaporation was purified using column chromatography on activated
alumina by eluting with CHCl3. Yield: 11%. MALDI-TOF-MS
(Dithranol): m/z ) 1238 ([M + H]+, 100), calcd for C44H22N4Br8
1237.5.
(23) (a) Knapen, J. W. J.; van der Made, A. W.; de Wilde, J. C.; van,
Leeuwen, P. W. N. M.; Wijkens, P.; Grove, D. M.; van Koten, G. Nature
1994, 372, 659. (b) Miedaner, A.; Curtis, C. J.; Barkley, R. M.; DuBois,
D. L. Inorg. Chem. 1994, 33, 5482. (c) Brunner, H. J. Organomet. Chem.
1995, 500, 39. (d) Chow, H.-F.; Mak, C. C. J. Org. Chem. 1997, 62, 5116.
(e) Kimura, M.; Sugihara, Y.; Muto, T.; Hanabusa, K.; Shirai, H.; Kobayashi,
N. Chem. Eur. J. 1999, 5, 3495.
(24) Cheng, B.; Hobbs, J. D.; Debrunner, P. G.; Erlebacher, J.; Shelnutt,
H. A.; Scheidt, W. R. Inorg. Chem. 1995, 34, 102.
(25) During catalytic reaction, less than 10% degradation of dendritic
porphyrins had occurred as analyzed by UV-vis spectral change.
(26) The distribution of epoxide products for 4-vinyl-1-hexene and the
ratio of the epoxide products for 1-octene and cis-cyclooctene are normalized
with respect to the value for nondendritic Fe(TPP)(Cl).

5642 J. Am. Chem. Soc., Vol. 123, No. 24, 2001
Kimura et al.
3-TMS. Yield: 93%. 1H NMR (CDCl3, 400 MHz): δ ) 7.76 (2H,
s, Ph), 7.67 (1H, s, Ph), 7.57 (4H, d, J ) 8.1 Hz, Ph), 7.47 (4H, d, J
) 8.3 Hz, Ph), 1.37 (18H, s, -C(CH3)3), 0.33-0.34 (9H, s, -Si(CH3)3).
4-TMS. Synthesized from 3-B(OH)2 and 4-bromo-1-(trimethylsilyl)-
benzene. Yield: 82%. 1H NMR (CDCl3, 400 MHz): δ ) 7.77 (1H, s,
Ph), 7.75(2H, s, Ph), 7.67 (2H, d, J ) 8.1 Hz, Ph), 7.63 (2H, d, J )
8.3 Hz, Ph), 7.59 (4H, d, J ) 8.3 Hz, Ph), 7.49 (4H, d, J ) 8.3 Hz,
Ph), 1.38 (18H, s, -C(CH3)3), 0.31 (9H, s, -Si(CH3)3). MALDI-TOF-
MS (Dithranol): m/z ) 489 ([M + H]+, 100), calcd for C35H42Si 490.
5-TMS. Synthesized from 3-B(OH)2 and 3,5-dibromo-1-(trimeth-
ylsilyl)benzene. Yield: 74%. 1H NMR (CDCl3, 400 MHz): δ ) 7.92
(1H, s, Ph), 7.79 (8H, m, Ph), 7.63 (8H, d, J ) 8.1 Hz, Ph), 7.49 (8H,
d, J ) 8.4 Hz, Ph), 1.48 (36H, s, -C(CH3)3), 0.33-0.34 (9H, s, -Si-
(CH3)3). MALDI-TOF-MS (Dithranol): m/z ) 830 ([M + H]+, 100),
calcd for C61H70Si 831.
1,3,5-Phenylene-Based Dendritic Porphyrin H2P3. A Schlenk flask
was charged with 1 (0.18 g, 4.32 × 10-4 mol) and Pd(PPh3)4 (0.03 g,
2.60 × 10-5 mol) under an Ar atmosphere. Solutions of 2-B(OH)2 (1.35
g, 1.44 × 10-3 mol) in THF (6 mL) and Na2CO3 (2.0 M, 7 mL) in
H2O were prepared and deoxygenated with a stream of Ar. These
solutions and deoxygenated toluene were added to the reaction vessel,
and the mixture was refluxed under Ar for 72 h. The reaction mixture
was poured into a mixture of H2O and diethyl ether. The aqueous phase
was washed with ether, and the organic phases were combined and
washed with 1 M NaOH aqueous solution and brine. The crude product
was purified using column chromatography on activated alumina by
eluting with CH2Cl2/n-hexane (1:9 v/v), and the resulting material was
recrystallized from 2-methoxyethanol. Yield: 57%. 1H NMR (CDCl3,
400 MHz): δ ) 9.04 (8H, s, pyrrole), 8.48 (8H, s, Ph), 8.25 (4H, s,
Ph), 7.86 (16H, d, J ) 8.2 Hz, Ph), 7.54 (16H, d, J ) 8.3 Hz, Ph),
1.37 (36H, s, -C(CH3)3), -2.58 (2H, s, -NH). MALDI-TOF-MS
(Dithranol): m/z ) 1672 ([M + H]+, 100), calcd for C124H126N4 1670.9.
The synthetic procedure for H2P4 and H2P5 is similar to that for
H2P3.
mixture was filtered, and the filtrate was evaporated to dryness. The
crude product was purified by column chromatography (silica gel,
eluting with n-hexane gradually increasing to CH2Cl2/n-hexane (9:1
v/v)). Yield: 95%. FT-IR (KBr): disappearance of peak at 1720 cm-1
.
1H NMR (CDCl3, 400 MHz): δ ) 7.72 (1H, s, Ph), 7.53 (6H, m, Ph),
7.45 (4H, d, J ) 8.3 Hz, Ph), 4.73 (2H, s, CH2OH), 1.52 (18H, s,
-C(CH3)3).
7-Br. To a solution of 7-OH (1.00 g, 2.68 × 10-3 mol) in 5.0 mL
dry THF were added CBr4 (2.22 g, 6.70 × 10-3 mol) and tri-
phenylphosphine (1.75 g, 6.70 × 10-3 mol) with stirring for 15 min at
room temperature. The reaction mixture was poured into a mixture of
H2O and CH2Cl2. The aqueous phase was washed with CH2Cl2, and
the organic phases were combined and evaporated to dryness. The crude
product was purified using column chromatography (silica gel, eluting
with n-hexane gradually increasing to CH2Cl2/n-hexane (1:2 v/v)).
Yield: 78%. 1H NMR (CDCl3, 400 MHz): δ ) 7.71 (1H, s, Ph), 7.55
(6H, m, Ph), 7.46 (4H, d, J ) 8.3 Hz, Ph), 4.53 (2H, s, CH2Br), 1.52
(18H, s, -C(CH3)3).
H2P7. 5,10,15,20-Tetrakis(3′,5′-dihydroxyphenyl)porphyrin (32.8
mg, 4.59 × 10-5mol) and 7-Br (0.20 g, 4.59 × 10-4 mol) were dissolved
in acetone (10 mL) containing K2CO3 (0.10 g) and 18-crown-6 (catalytic
amount), and the reaction mixture was refluxed for 5 days with stirring.
The mixture was filtered, and the filtrate was evaporated to dryness.
The crude product was purified by column chromatography (activated
alumina, eluting with n-hexane gradually increasing to CH2Cl2).
Yield: 32%. 1H NMR (CDCl3, 400 MHz): δ ) 8.91 (8H, s, pyrrole),
7.73 (8H, s, Ph), 7.66 (16H, s, Ph), 7.56 (32H, d, J ) 8.4 Hz, Ph),
7.36 (32H, d, J ) 8.1 Hz, Ph), 5.31 (16H, m, -CH2O-), 1.48 (144H,
s, -C(CH3)3), -2.53 (2H, s, -NH). MALDI-TOF-MS (Dithranol): m/z
) 3579 ([M + H]+, 100), calcd for C260H270N4Cl 3578.
Dendritic Iron Porphyrin Fe(H2P3)(Cl). FeCl2 (10.0 mg, 7.89 ×
10-5 mol) and H2P3 (30.0 mg, 1.79 × 10-5 mol) were dissolved in 20
mL of THF, and the reaction mixture was refluxed under Ar. During
the reaction, the UV-vis spectrum of the reaction mixture was
monitored. The mixture was refluxed until no change in the Soret band
was observed. The resulting iron complex was purified by column
chromatography (activated alumina, CH2Cl2) and treatment with
methanoic HCl. Yield: 59%. UV-vis (CH2Cl2): λmax (log ꢀ) ) 424
(5.04), 258 (5.16). MALDI-TOF-MS (Dithranol): m/z ) 1725 ([M -
Cl]), calcd for C124H124N4FeCl 1761.
H2P4. Prepared from 1 and 3-B(OH)2 and purified by column
chromatography (activated alumina, CH2Cl2/n-hexane (1:9 v/v)) and
recrystallization from 2-methoxyethanol. Yield: 24%. 1H NMR (CDCl3,
400 MHz): δ ) 9.11 (8H, s, pyrrole), 8.62 (8H, s, Ph), 8.42 (4H, s,
Ph), 8.03 (16H, s, Ph), 7.80 (8H, s, Ph), 7.61 (32H, d, J ) 8.3 Hz, Ph),
7.40 (32H, d, J ) 8.3 Hz, Ph), 1.37 (144H, s, -C(CH3)3), -2.58 (2H,
s, -NH). 13C NMR (CDCl3): δ ) 150.5, 142.7, 142.4, 142.0, 141.7,
140.6, 138.3,132.5, 129.1, 127.1, 126.9, 125.7, 125.4, 125.2, 34.5, 31.3.
MALDI-TOF-MS (Dithranol): m/z ) 3337 ([M + H]+, 100). Anal.
Calcd for C252H254N4: C, 90.65; H, 7.67; N, 1.68. Found: C, 90.70;
H, 7.65; N, 1.66.
The synthetic procedure for Fe(H2P4)(Cl), Fe(H2P5)(Cl), and Fe-
(H2P6)(Cl) is similar to that for Fe(H2P3)(Cl).
Fe(H2P4)(Cl). Yield: 76%. UV-vis (CH2Cl2): λmax (log ꢀ) ) 424
(5.04), 260 (5.37). MALDI-TOF-MS (Dithranol): m/z ) 3391 ([M -
Cl]), calcd for C252H254N4FeCl 3427.
H2P5. Prepared from 1 and 4-B(OH)2 and purified by column
chromatography (activated alumina, CH2Cl2/n-hexane (1:9 v/v)) and
recrystallization from 2-methoxyethanol. Yield: 11%. 1H NMR (CDCl3,
400 MHz): δ ) 9.15 (8H, s, pyrrole), 8.60 (8H, s, Ph), 8.40 (4H, s,
Ph), 8.05 (16H, m, Ph), 7.76-7.86 (40H, m, Ph), 7.64 (32H, d, J )
8.3 Hz, Ph), 7.45 (32H, d, J ) 8.3 Hz, Ph), 1.48 (144H, s, -C(CH3)3),
-2.57 (2H, s, -NH). MALDI-TOF-MS (Dithranol): m/z ) 3947 ([M
+ H]+, 100), calcd for C300H286N4 3947.
Partially Flexible Dendritic Porphyrin H2P7. The dendritic
bromide 7-Br was synthesized from 3,5-dibromobenzoic acid methyl
ester and 4-tert-butylphenylboronic acid. Cross coupling between 3,5-
dibromobenzoic acid methyl ester and 4-tert-butylphenylboronic acid
in the presence of Pd(PPh3)4 (7-COOCH3), reduction of methyl ester
(7-OH), and bromination with CBr4 and triphenylphosphine gave the
dendritic bromide 7-Br.11
Fe(H2P5)(Cl). Yield: 68%. UV-vis (CH2Cl2): λmax (log ꢀ) ) 424
(5.04), 270 (5.37). MALDI-TOF-MS (Dithranol): m/z ) 4000 ([M -
Cl]), calcd for C300H284N4FeCl 4036.
Fe(H2P6)(Cl). Yield: 88%. UV-vis (CH2Cl2): λmax (log ꢀ) ) 424
(5.04), 258 (5.24). MALDI-TOF-MS (Dithranol): m/z ) 3634 ([M -
Cl]), calcd for C260H268O8N4FeCl 3668.
Catalytic Reactions. Epoxidations of alkenes were performed in
degassed CH2Cl2 using iodosylbenzene as an oxygen atom transfer
reagent. A solution of iodosylbenzene (10.0 µmol) in CH2Cl2 was added
to the mixed solution of alkene (500.0 µmol) and iron complex (1.0
µmol). After addition, the mixture was stirred at 25 °C under Ar for
30 min. After 30 min, the internal standard (n-decane) was added to
the reaction mixture, and all oxidation products were identified by GC,
GC-MS, and 1H NMR. Standard epoxides were purchased from
commercial chemical suppliers. The yields of the oxidation products
were determined by GC using the internal standard method. No reaction
occurred in the absence of the catalysts in the reaction examined under
the same experimental conditions.
7-COOCH3. The synthetic procedure for 7-COOCH3 is similar to
that for 3-TMS. Yield: 95%. FT-IR (KBr): 1720 cm-1 1H NMR
.
(CDCl3, 400 MHz): δ ) 8.22 (2H, s, Ph), 7.98 (1H, s, Ph), 7.60 (4H,
d, J ) 8.4 Hz, Ph), 7.48 (4H, d, J ) 8.3 Hz, Ph), 3.96 (3H, s, COOCH3),
1.41 (18H, s, -C(CH3)3).
7-OH. To a stirred suspension of lithium aluminum hydride (0.25
g, 6.20 × 10-3 mol) in dry THF (30 mL) was added a solution of
7-COOCH3 (1.24 g, 3.1 × 10-3 mol) in dry THF (10 mL) dropwise
under nitrogen. After addition was complete, the reaction mixture was
stirred for 2 h at room temperature. Water (2 mL) and 1.0 M NaOH
aqueous solution (2 mL) were added to the reaction mixture. The
Acknowledgment. This research was partially supported by
a Grant-in-Aid for COE Research “Advanced Fiber/Textile
Science and Technology” (No. 10CE2003) and Scientific
Research (No. 11450366) from the Ministry of Education,
Science, Sports, and Culture of Japan.
JA004312D