Oxidation chemistry of poly(ethylene glycol)-supported carbonylruthenium(ii) and dioxoruthenium(vi) meso-tetrakis(pentafluorophenyl) porphyrin

Article abstract of DOI:10.1002/chem.200501510

[Ru¹¹(F₂₀-tpp)(CO)] (1, F₂₀-tpp = meso-tetrakis(pentafluorophenyl)porphyrinato dianion) was covalently attached to poly(ethylene glycol) (PEG) through the reaction of 1 with PEG and sodium hydride in DMF. The water-soluble PEG-supported ruthenium porphyrin (PEG-1) is an efficient catalyst for 2,6-Cl₂pyNO oxidation and PhI=NTs aziridination/amidation of hydrocarbons, and intramolecular amidation of sulfamate esters with PhI (OAc)₂. Oxidation of PEG-1 by m-CPBA in CH₂C1₂, dioxane, or water afforded a water-soluble PEG-supported dioxoruthenium(VI) porphyrin (PEG-2), which could react with hydrocarbons to give oxidation products in up to 80 % yield. The behavior of the two PEG-supported ruthenium porphyrin complexes in water was probed by NMR spectroscopy and dynamic light-scattering measurements. PEG-2 is remarkably stable to water. The secondorder rate constants (k₂) for the oxidation of styrene and ethylbenzene by PEG-2 in dioxane-water increase with water content, and the k₂ values at a water content of 70% or 80% are up to 188 times that obtained in ClCH₂CH₂Cl.

Full text of DOI:10.1002/chem.200501510

DOI: 10.1002/chem.200501510
Oxidation Chemistry of Poly(ethylene glycol)-Supported
Carbonylruthenium(ii) and Dioxoruthenium(vi) meso-
Tetrakis(pentafluorophenyl)porphyrin
Jun-Long Zhang, Jie-Sheng Huang, and Chi-Ming Che*[a]
Abstract: [RuII(F20-tpp)(CO)] (1, F20-
tpp=meso-tetrakis(pentafluorophe-
nyl)porphyrinato dianion) was cova-
lently attached to poly(ethylene glycol)
(PEG) through the reaction of 1 with
PEG and sodium hydride in DMF. The
water-soluble PEG-supported rutheni-
um porphyrin (PEG-1) is an efficient
catalyst for 2,6-Cl2pyNO oxidation and
PhI=NTs aziridination/amidation of hy-
drocarbons, and intramolecular amida-
tion of sulfamate esters with PhI-
(OAc)2. Oxidation of PEG-1 by m-
CPBA in CH2Cl2, dioxane, or water af-
forded a water-soluble PEG-supported
dioxoruthenium(vi) porphyrin (PEG-
2), which could react with hydrocar-
bons to give oxidation products in up
to 80% yield. The behavior of the two
PEG-supported ruthenium porphyrin
complexes in water was probed by
NMR spectroscopy and dynamic light-
scattering measurements. PEG-2 is re-
markably stable to water. The second-
order rate constants (k2) for the oxida-
tion of styrene and ethylbenzene by
PEG-2 in dioxane–water increase with
water content, and the k2 values at a
water content of 70% or 80% are up
to 188 times that obtained in
ClCH2CH2Cl.
Keywords: homogeneous catalysis ·
oxidation · porphyrinoids · rutheni-
um · supported catalysts
Introduction
dendrimers have also demonstrated high reactivity and se-
lectivity.
The importance of metalloporphyrin-mediated hydrocarbon
functionalization in organic catalysis[1–4] is well documented,
and oxygen[1a–d,h,j]/nitrogen[1e,f]/carbon[1g–i]-atom transfer reac-
tions catalyzed by metalloporphyrins have begun to emerge
as useful reactions that have found applications in organic
synthesis.[1] An appealing approach to practical metallopor-
phyrin catalysts is to attach a metalloporphyrin to a polymer
or mesoporous silica material;[2–4] this method facilitates
product separation and catalyst recovery/reuse. Interestingly,
the heterogenization of a ruthenium porphyrin catalyst by
covalent attachment to Merrifieldꢀs peptide resin was found
to result in excellent reactivity, selectivity, and versatility in
alkene epoxidation.[2a] Homogeneous epoxidation and cyclo-
Metalloporphyrin-mediated hydrocarbon functionalization
is important in biomimetic studies as well.[1d,5–11] Notable ex-
amples include 1) regioselective oxidation of steroids by
manganese porphyrin complexes that have b-cyclodex-
trins[6a,b,d] or by manganese/iron porphyrin complexes with
appending cholenic acid moieties in vesicle bilayer assem-
blies,[7] 2) regioselective C=C bond cleavage of carotenoids
by a ruthenium porphyrin complex containing b-cyclodex-
trins,[8] and 3) progressive epoxidation of polybutadiene by a
topologically linked manganese porphyrin.[9] These catalytic
systems mimic the activities of cytochrome P-450 enzymes,
carotene dioxygenases, and toroidal enzymes (such as exo-
and endonucleases), respectively.
It has been proposed that hydrocarbon oxidation reac-
tions mediated by metalloporphyrins involve reactive oxo-
metalloporphyrin intermediates.[1a–d] Investigation on the re-
activity of oxometalloporphyrins attached to macromole-
cules is important for understanding the mechanism of hy-
drocarbon oxidation catalyzed by polymer-supported metal-
loporphyrins or by related native enzymes (the
metalloporphyrin active sites of which are attached to pro-
tein chains), and could provide useful information for design
of both new catalysts and enzyme mimics. Up to now, a
series of oxometalloporphyrins containing FeIV=O,[12a–d] CrV=
propanation of alkenes catalyzed by manganese[4a]/iron[4b]
/
ruthenium[4c] porphyrin complexes covalently attached to
[a] J.-L. Zhang, Dr. J.-S. Huang, Prof. C.-M. Che
Department of Chemistry and
Open Laboratory of Chemical Biology of the
Institute of Molecular Technology for Drug Discovery and Synthesis
The University of Hong Kong, Pokfulam Road, Hong Kong (China)
Fax : (+852)2857-1586
E-mail: cmche@hku.hk
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
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FULL PAPER
O,[12f] MnIV/V=O,[12e,i,j] and RuVI=O[13] groups that are reactive
toward hydrocarbon oxidation are known; an in situ gener-
ated MnIV=O porphyrin encapsulated into a polymer dendri-
graft was reported recently,[12j] but, to the best of our knowl-
edge, covalent attachment of these oxometalloporphyrins to
synthetic macromolecules remains unrealized.
Results
Synthesis and characterization of PEG-supported ruthenium
porphyrins PEG-1 and PEG-2: The carbonylruthenium(ii)
porphyrin 1 has previously been reported to be an active
and robust catalyst for oxidation of C H bonds.[14] This com-
ꢀ
We are interested in constructing a soluble macromole-
cule-supported oxometalloporphyrin by covalently linking a
reactive hydrophobic dioxoruthenium(vi) porphyrin [RuVI-
(por)O2][13] to hydrophilic poly(ethylene glycol) (PEG). This
was prompted by the reports that [RuVI(por)O2] are reactive
toward hydrocarbon oxidation[13] and could be isolated, and
several soluble PEG-supported manganese[4f,10]/ruthenium[4d]
porphyrins are active hydrocarbon oxidation catalysts. The
amphiphilic PEG-supported dioxoruthenium(vi) porphyrin
is expected to dissolve in water through, for example, mi-
celle formation, providing a unique opportunity of develop-
ing hitherto rarely explored oxidation chemistry of oxome-
talloporphyrins in aqueous media.
In this work, we report the covalent attachment of oxida-
tively robust [RuII(F20-tpp)(CO)] (1, F20-tpp=meso-tetra-
kis(pentafluorophenyl)porphyrinato(2-))[14] to PEG to form
a polymer-supported ruthenium porphyrin (PEG-1) and the
preparation of a PEG-supported dioxoruthenium(vi) por-
phyrin (PEG-2; Figure 1), by oxidation of PEG-1 with m-
chloroperoxybenzoic acid (m-CPBA), along with PEG-1-
catalyzed oxidation/amidation of hydrocarbons. Kinetic
studies on the oxidation of a series of hydrocarbons by
PEG-2 in organic solvents (such as ClCH2CH2Cl, benzene,
and dioxane) and in aqueous solutions are described.
plex could be functionalized through substitution reaction of
the para-F atom of the perfluorophenyl ring with nucleophil-
ic reagents, such as primary/secondary amines and alkoxide
ions.[15] In the present work, PEG-1 was obtained by treating
excess 1 with a solution of sodium PEG salt generated in
situ from sodium hydride and PEG in DMF. The progress of
the reaction was followed by thin-layer chromatography
(TLC). After purification, PEG-1 was obtained in 70%
yield based on the amount of PEG used. PEG-2 was pre-
pared by addition of m-CPBA to a solution of PEG-1 in
CH2Cl2. Both PEG-1 and PEG-2 are red hygroscopic solids,
soluble in CH2Cl2, CHCl3, ethanol, dioxane, and water, but
insoluble in acetone and diethyl ether. A control experiment
was performed by adding 1 (1 mmol, 1.1 mg) to a solution of
PEG (0.1 mmol, 0.5 g) in water (100 mL); the ruthenium
porphyrin complex was rapidly precipitated out, revealing
that a physical mixture of 1 and PEG could not solubilize
the former in water.
1
The H NMR spectrum of PEG-1 in CDCl3 shows a broad
signal at d=8.82 ppm which is assigned to the pyrrolic pro-
tons (b-H) of the porphyrin macrocycle; a similar b-H
chemical shift (d=8.78 ppm) was found for 1. In the case of
PEG-2, the b-H signal appears as a broad peak at d=
9.20 ppm, similar to the b-H chemical shift of [RuII(F20-
tpp)O2] (2, d=9.18 ppm).
The 19F NMR spectrum of PEG-1 in CDCl3 at room tem-
perature reveals three sets of signals at d=ꢀ136.7 to
ꢀ141.5, ꢀ151.9 to ꢀ152.6, and ꢀ157.0 to ꢀ163.0 ppm, which
are assigned to the ortho-, para-, and meta-F atoms by com-
parison with the related 19F NMR signals of 1 (dF ꢀ136.1,
ꢀ138.1 (ortho-F), ꢀ152.2 (para-F), ꢀ161.5, ꢀ162.2 ppm
(meta-F)). PEG-2 shows broad signals at d=ꢀ135.6 to
ꢀ139.0 (ortho-F), ꢀ150.4 (para-F), and ꢀ157.6 to
ꢀ161.5 ppm (meta-F) in CDCl3, while the related 19F signals
of 2 are at d=ꢀ136.8 (ortho-F), ꢀ149.2 (para-F), and
ꢀ161.2 ppm (meta-F).
The IR spectrum of PEG-1 shows an intense n(CO) band
at 1954 cmꢀ1; such a band is absent in the IR spectrum of
PEG-2, the latter displays a weak band at 830 cmꢀ1 assigna-
ble to the n(RuO2) stretch.[13] The UV/Vis spectrum of
PEG-1 in CH2Cl2 features Soret band at 406 nm and b band
at 526 nm, similar to those of 1. For PEG-2, the absorption
bands at 413 (Soret) and 508 nm (b) are similar to those of
2 at 412 and 506 nm, respectively. The slightly red-shifted
Soret and b bands of PEG-1 and PEG-2 relative to those of
1 and 2, respectively, could be due to the substitution of the
para-F of a perfluorophenyl ring by the alkoxy group of the
PEG chain.
For PEG-1, the integration ratio of the porphyrin b-H
signal to the PEG methoxy signal gave a loading of 1 of
0.10 mmolgꢀ1. Based on the absorbance of the Soret band at
Figure 1. Schematic structure of PEG-1 and PEG-2.
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3021

C.-M. Che et al.
406 nm and assuming that the e values of PEG-1 and 1 at
406 nm are the same (with 10% error), the loading of 1 in
PEG-1 was also estimated to be 0.10 mmolgꢀ1. For PEG-2,
the integration of the b-H and the PEG methoxy signals re-
vealed that the loading of 2 was about 0.10 mmolgꢀ1, sug-
gesting that no appreciable ruthenium porphyrin leaching
occurred during oxidation of PEG-1 to PEG-2 by m-CPBA
in CH2Cl2.
Two-dimensional nuclear Overhauser effect NMR spec-
troscopy (NOESY) was employed to probe the interaction
of PEG-1 with styrene (a substrate in the oxidation reac-
tions described below) in a mixture of PEG-1 and styrene in
CDCl3 or D2O (Figure 3). In CDCl3, the signals of styrene in
Behavior of PEG-1 in aqueous solution
NMR studies: In NMR spectroscopy, signal broadening
(which is often accompanied by change in relaxation time
and decreased intensity, and reflects a change in microenvir-
onment of the nuclei) has been taken as an indication for ag-
gregation of amphiphilic polymers[16] or restriction of inter-
nal nuclei mobility in water.[17] We found that while the
1H NMR spectrum of PEG-1 in CDCl3 shows well-resolved
signals of the PEG chain (d=3.35–4.78 ppm) and the por-
phyrin ring b-H protons (d=8.82 ppm), in D2O the signal of
the porphyrin ring b-H proton (d=8.80 ppm) is markedly
broadened (although the signals of the PEG chain are only
slightly affected). The 19F NMR spectrum of PEG-1 in D2O
is almost featureless, in contrast to the well-resolved signals
in CDCl3.
To further investigate the solvent effect on the microen-
vironment of ruthenium porphyrin core supported by PEG
chain, we measured the 19F NMR spectra of PEG-1 in
[D8]dioxane–D2O with water content increasing from 0 to
100% at 10% or 20% intervals (Figure 2). Upon increasing
Figure 3. 2D 1H NMR spectra (NOESY) of a mixture of PEG-1 (1.2”
10ꢀ3 m) and styrene (2.0”10ꢀ3 m) in CDCl3 (upper) and D2O (lower).
the mixture are similar to those of free styrene and no NOE
between styrene and the PEG-chain/porphyrin was ob-
served. However, in D2O, the spectrum of the mixture fea-
tures broad, poorly resolved, and upfield shifted (Dd
ꢂ0.30 ppm) signals of styrene and there is an NOE between
the styrene and the PEG chain (but not between styrene
and the porphyrin ring). A control experiment using a mix-
ture of styrene and PEG in D2O under the same conditions
showed similar 1H NMR chemical shifts to those of the
PEG-1/styrene mixture, suggesting that styrene molecules
were encapsulated by the PEG chains in water.
Figure 2. 19F NMR spectra of PEG-1 (2.4”10ꢀ3 m) in [D8]dioxane–D2O at
different water contents (v/v).
the water content from 0 to 30%, the signals were broad-
ened and slightly changed. As the water content increased
to 40–60%, the signals were further broadened and became
more complicated. At water contents of ꢁ70%, the signals
were very broad or even hard to be observed.
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Homogeneous Catalysis
FULL PAPER
The effect of water content on the interaction between
styrene and PEG-1 was examined by measuring the
1H NMR spectra of a mixture of PEG-1 and styrene in
[D8]dioxane–D2O at different water contents; these experi-
ments revealed a dependence of the chemical shift changes
(Dd) of styrene on the water content as shown in Figure 4
Figure 5. Average particle sizes of PEG-1 in dioxane–water solution at
different water contents.
As listed in Table S3 (see Supporting Information), m-
CPBA, PhIO, and TBHP could oxidize PEG-1 and 1 to
PEG-2 and 2, respectively, in CH2Cl2. The oxidation by
TBHP was much slower (2 h, entry 10) than by m-CPBA
and PhIO (several minutes, entries 1 and 4). m-CPBA was
found to be a suitable oxidant for generation of PEG-2
from PEG-1 in water (entry 2) and in dioxane–water (50%
v/v) (entry 3). Conversion of PEG-1 to PEG-2 in dioxane–
water (50% v/v) could also be effected by using PhIO and
TBHP, but a 2 h reaction time was needed (entries 6 and
12). In water, neither PhIO nor TBHP was observed to oxi-
dize PEG-1 to PEG-2 (entries 5 and 11). Complex 1 is in-
soluble in water and no reaction was found with the above
oxidants in this solvent (entries 5, 8, 11, and 14). Even in the
mixed solvent dioxane–water (50% v/v), PhIO and m-
CPBA could not oxidize 1 to 2 (the reaction shifted the
Soret band to 398 nm and the b band to 540 nm, which are
substantially different from those of 2) (entries 3 and 6). 2,6-
Cl2pyNO was not an effective oxidant for conversion of
PEG-1 and 1 to PEG-2 and 2, respectively (entries 7–9). In
the case of H2O2, its reaction with 1 and PEG-1 showed sim-
ilar spectral changes in CH2Cl2 and dioxane–water: the
Soret band blue shifted to 406 nm, the b band red shifted to
560 nm, and a new band at 600 nm developed; such spectral
features do not correspond to the formation of 2 (entries 13
and 15). In water, no reaction was observed between PEG-1
and H2O2 at room temperature even at a reaction time of
4 h.
1
Figure 4. Change of H NMR chemical shifts (Dd) of styrene protons as a
function of water contents observed for a mixture of PEG-1 (1.2”10ꢀ3 m)
and styrene (2.0”10ꢀ3 m) in [D8]dioxane–D2O (Dd=DdXCꢀDd0X, in which
X=a,b,g,d,s,e; DdX =dXꢀdPEG; dPEG is the chemical shift of the most in-
tense signal of PEG; DdCX and DdX0 are the values at water contents of
C% and 0%, respectively).
(see also Table S1 in Supporting Information). Evidently, for
all the styrene protons, the Dd values increase with increas-
ing water content in a similar manner, suggesting an “iso-
tropic” effect of water content on the styrene proton reso-
nances. The most dramatic increase of Dd occurs at water
contents of 60–80%.
Dynamic light-scattering studies: We measured the size of
the particles in a solution of PEG-1 in water by dynamic
light scattering. The average hydrodynamic diameter of the
particles was observed to be about 34 nm. Reducing the sol-
vent polarity by addition of dioxane led to increase in the
size of the particles. The dependence of particle size on
water content for the dioxane–water solution of PEG-1 is
depicted in Figure 5 (see also Table S2 in Supporting Infor-
mation).
1H NMR spectroscopy was used to monitor the reaction
between PEG-1 (1 mm) and m-CPBA (10 equiv) in D2O.
This reaction was found to shift the b-H signal of the por-
phyrin ring at d=8.82 ppm to d=9.20 ppm within 5 minutes,
indicating the formation of PEG-2.
Oxidation to PEG-2: Previous studies showed that dioxoru-
thenium(vi) porphyrins [RuVI(por)O2] could be obtained by
oxidation of [RuII(por)(CO)] with m-CPBA or PhIO in
CH2Cl2 and alcohol.[13] However, there has been no report
on the generation of dioxoruthenium(vi) porphyrin in aque-
ous medium. In this work, we examined the reaction of
PEG-1 with H2O2, TBHP (tert-butyl hydroperoxide), 2,6-
Cl2pyNO (2,6-dichloropyridine N-oxide), PhIO, or m-CPBA
in aqueous solutions at room temperature by UV/Vis spec-
troscopy.
Catalytic properties of PEG-1
Oxygen-atom transfer reactions: In a previous report, we
demonstrated the activity of PEG-supported ruthenium por-
phyrin catalysts in epoxidation of alkenes with 2,6-
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C.-M. Che et al.
Table 1. Epoxidation of alkenes (3–12) with 2,6-Cl2pyNO catalyzed by PEG-1.[a]
porphyrinato(2-)) and “dendrit-
ic ruthenium porphyrin + 2,6-
Cl2pyNO” protocols.[4c]
Groves and co-workers re-
ported that 1 is an efficient and
robust catalyst for 2,6-Cl2pyNO
ꢀ
oxidation of saturated C H
bonds.[14] To test the catalytic
ꢀ
activity of PEG-1 toward C H
bond oxidation, we examined
oxidation of ethylbenzene (23)
with the “PEG-1
+
2,6-
Cl2pyNO” protocol in CH2Cl2.
At 408C for 24 h, acetophenone
(28) was obtained in 99% yield
and the conversion of ethylben-
Entry
Substrate
Product
t [h]
Conv. [%][b]
Yield [%] (TON)[c]
Config.[d]
n.d.[e]
cis
zene
was
52%
(entry 1,
1
2
3
4
5
6
7
8
9
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
24
24
24
24
24
24
24
24
24
24
82
86
88
90
90
82
72
82
68
95
76 (620)
88 (750)
82 (720)
92 (820)
99 (880)
99 (820)
88 (630)
99 (810)
99 (670)
99 (940)
Table 2), which is lower than
the conversion of 70% ob-
tained for catalyst 1 (entry 2,
cis
n.d.
n.d.
n.d.
trans
n.d.
a:b=9:1
b
Table 2),
but
considerably
higher than the conversion of
22% obtained by using a previ-
ously reported PEG-supported
ruthenium porphyrin catalyst.[4d]
Severin and Nestler reported
that a cross-linked polymer-sup-
ported ruthenium porphyrin
could catalyze oxidation of 23
to 28 in a high conversion of
10
[a] All reactions were carried out in CH2Cl2 at 508C in a sealed flask (unless otherwise noted) with catalyst/
2,6-Cl2pyNO/alkene molar ratio of 1:1100:1000. [b] Determined by GC or 1H NMR spectroscopy by using in-
ternal standard method (1,4-dichlorobenzene or 1,3,5-tribromobenzene). [c] Based on the amount of consumed
alkenes. TON=turnover number. [d] Determined by comparison with the 1H NMR data or GC spectra of
standard products. [e] n.d.=not determined.
Cl2pyNO.[4d] In this work, PEG-1 was found to be a more re-
active and robust oxidation catalyst.
74%.[2b] For the substrates ethylnaphthalene, 1,2,3,4-tetrahy-
dronaphthalene, indane, and adamantane (24–27), the con-
versions obtained for PEG-1 (entries 3–6, Table 2) are com-
As depicted in Table 1, PEG-1 is an efficient catalyst for
epoxidation of a wide variety of alkenes with 2,6-Cl2pyNO.
In the cases of styrene, cis-stilbene, cis-b-methylstyrene, 1,2-
dihydronaphthalene, cyclooctene, and 1-octene (substrates
3–8, entries 1–6), the yields and selectivity of the epoxides
(13–18) are comparable to those obtained with the reported
PEG-, MCM-41-, and Merrifieldꢀs resin-supported rutheni-
um porphyrin catalysts.[2a,3c,f,4d] For reactions with trans-b-
methylstyrene (9), the trans-epoxide 19 was obtained in high
yield (88%, entry 7). The applicability of the “PEG-1 +
2,6-Cl2pyNO” protocol in the synthesis of organic building
blocks has been examined. By using 1-phenethynyl cyclo-
hexene (10) as substrate, the reaction afforded the corre-
sponding epoxide 20, which could be used for the synthesis
of bioactive enedyne antitumor agents,[18] in high yield
(99%, entry 8). 3,4,6-Tri-O-acetyl-D-glycal (11) was convert-
ed to the epoxide derivative 21[19] in 99% yield with a:b
ratio of 9:1. This a-selectivity is comparable to that obtained
for [RuII(2,6-Cl2tpp)(CO)] (2,6-Cl2tpp=meso-tetrakis(2,6-di-
chlorophenyl)porphyrinato(2-)),[3c] dendritic ruthenium por-
phyrins,[4c] and for the ruthenium porphyrins immobilized on
MCM-41[3c] and Merrifieldꢀs peptide resin.[2a] Cholesteryl
acetate 12 was epoxidized to 22 in 99% yield with complete
b-selectivity, similar to the previously reported epoxidation
using the “[RuVI(tmp)O2] + air” (tmp=meso-tetramesityl-
Table 2. Oxidation of hydrocarbons (23–27) with 2,6-Cl2pyNO catalyzed
by PEG-1.[a]
Entry Catalyst Substrate Product t [h] Conv. [%][b] Yield [%]
(TON)[c]
1
2
3
4
5
6
PEG-1
1
PEG-1
PEG-1
PEG-1
PEG-1
23
23
24
25
26
27
28
28
29
30
31
32
24
24
24
24
24
24
52
70
46
60
70
65
99 (50)
99 (70)
99 (40)
99 (60)
99 (70)
80 (50)
[a] All reactions were carried out in CH2Cl2 at 658C in a sealed flask,
with catalyst/2,6-Cl2pyNO/substrate molar ratio of 1:220:100 for en-
tries 1–5 and 1:110:100 for entry 6. [b] Determined by GC or 1H NMR
spectroscopy by using internal standard method (1,4-dichlorobenzene or
1,3,5-tribromobenzene). [c] Based on the amount of consumed substrates.
TON=turnover number.
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Homogeneous Catalysis
FULL PAPER
parable to those obtained for 1. No reaction was found with
benzene and naphthalene.
of a series of benzylic hydrocarbons 6, 23, 24, 26, 27, and 33
to give N-tosylamides 37–42 in 80–90% yields with 20–94%
conversions (entries 4–6 and 8–10, Table 3). These results
are comparable to those obtained for catalyst 1[20b,d] and
better than those obtained for previously reported PEG-
supported ruthenium porphyrin catalysts.[4d] Under a low
catalyst loading of 0.1 mol% (1/PhI=NTs/26 molar ratio=
1:2000:1000), the PEG-1-catalyzed amidation of 26 afforded
39 in 73% yield with 36% substrate conversion (entry 7,
Table 3), corresponding to a turnover number of 190.
In the presence of catalyst PEG-1 and Al2O3 with a cata-
lyst/PhI(OAc)2/substrate/Al2O3 molar ratio of 1:150:75:180,
the reaction of sulfamate esters 43–46 with PhI(OAc)2 in
CH2Cl2 at 408C for 6 h afforded cyclic sulfamidates 47–50 in
86–90% yields (entries 1–4, Table 4) with retention of con-
We also examined the epoxidation of styrene (0.1 mmol)
with 2,6-Cl2pyNO (0.15 mmol) in water (5 mL) by using cat-
alyst PEG-1 (0.01 mmol). The reaction was conducted at
room temperature for 24 h, affording benzaldehyde as main
product with a styrene conversion of 5%. When PhIO was
used as oxidant, no conversion of styrene was observed.
Nitrogen-atom-transfer reactions: Metal-mediated nitrogen-
atom transfer to hydrocarbons is an appealing route to aziri-
dines and amides.[1e,f] Both ruthenium[20] and manganese por-
phyrins[21] were reported to be efficient catalysts for these
reactions. However, there are few studies on supported
ꢀ
metal catalysts for C N bond formation reactions. Recently,
we reported that the PEG-supported carbonylruthenium(ii)
porphyrin bearing para-chloro substitutents on the porphyr-
in meso-phenyl groups exhibited moderate reactivity in cata-
lyzing aziridination of alkenes.[4d] We envisioned that replac-
ing this carbonylruthenium(ii) porphyrin core by 1 would
lead to an efficient and robust PEG-supported ruthenium
porphyrin catalyst for aziridination/amidation reactions.
Reactions of alkenes 3, 7, and 8 with PhI=NTs in CH2Cl2
at 408C for 4 h in the presence of a catalytic amount of
Table 4. Intramolecular amidation of sulfamate esters (43–46) with PhI-
(OAc)2 catalyzed by PEG-1.[a]
PEG-1 at
a catalyst/PhI=NTs/substrate molar ratio of
1:150:75 afforded aziridines 34–36 in 70–86% yields with
38–82% substrate conversions (entries 1–3, Table 3). Under
similar conditions, PEG-1 catalyzed the PhI=NTs amidation
Entry
Substrate
Product
t [h]
Conv. [%][b]
Yield [%][c]
1
2
3
4
43
44
45
46
47
48
49
50
6
6
6
6
60
62
72
80
90
86
90
88
Table 3. Aziridination or amidation of hydrocarbons (3, 6–8, 23–24, 26–
27, and 33) with PhI=NTs catalyzed by PEG-1.[a]
[a] All reactions were carried out in CH2Cl2 at 408C at a catalyst/PhI-
(OAc)2/substrate/Al2O3 molar ratio of 1:150:75:180. [b] Determined by
1H NMR spectroscopy by using the reaction mixture. [c] Based on the
amount of consumed substrate.
figuration. The regioselectivity of these PEG-1-catalyzed in-
tramolecular amidation reactions is similar to that for cata-
lyst 1[20e] and dirhodium catalysts.[22] Prior to this work, no
polymer-supported catalyst has been reported to be efficient
catalyst for intramolecular amidation of sulfamate esters.
Entry
Substrate
Product
t [h]
Conv. [%][b]
Yield [%][c]
Oxidation chemistry of PEG-2
1
2
3
4
5
3
7
8
23
24
26
26
27
33
6
34
35
36
37
38
39
39
40
41
42
4
4
4
4
4
4
8
4
4
4
82
40
38
20
21
92
36
90
45
94
86
70
80
82
84
80
73
80
90
80
Stability of PEG-2: We found that PEG-2 is rather stable in
CH2Cl2 and dioxane. When these solutions were left stand-
ing for 4 h, less than 5% of PEG-2 was decomposed as re-
vealed by UV/Vis spectroscopy. In dioxane–water, contain-
ing pyrazole (<2% w/w, relative to the amount of dioxane)
and with a water content of ꢁ 40% (v/v), PEG-2 also dis-
played a remarkably high stability, as shown by the <5%
decrease in the absorbance at 414 nm over 2 h. This con-
trasts with the shift of the Soret (412 nm) and b (506 nm)
bands of 2 to 396 and 545 nm, respectively, within 2 min
under the same conditions (suggesting the formation of a m-
6
7[d]
8
9
10
[a] All reactions were carried out in CH2Cl2 at 408C with a catalyst/PhI=
NTs/substrate molar ratio of 1:150:75 (unless otherwise noted). [b] Deter-
mined by GC by using internal standard method (1,4-dichloro- or 1,3,5-
tribromobenzene). [c] Based on the amount of consumed substrate.
[d] Catalyst/PhI=NTs/substrate molar ratio=1:2000:1000.
Chem. Eur. J. 2006, 12, 3020 – 3031
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3025

C.-M. Che et al.
oxo ruthenium porphyrin dimer). A control experiment
showed that, for a physical mixture of 2 and two equivalents
of PEG in dioxane containing 20% (v/v) water and 2%
(w/w) pyrazole, 2 was rapidly converted to the m-oxo ruthe-
nium porphyrin dimer (as revealed by UV/Vis spectrosco-
py). These observations indicate that covalent attachment of
2 to the hydrophilic PEG chain dramatically enhances its
stability toward water.
The effect of pH on the stability of PEG-2 in water was
examined by UV/Vis spectroscopy. When the pH was varied
from 5 to 9, the Soret band absorbance of PEG-2 decreased
by <5% within 2 h. At pH >9 or <5, significant decompo-
sition of PEG-2 was observed, with the Soret band blue
shifted to 402 nm and the b band red shifted to 520 nm
upon standing for 2 h.
conversion of [RuIV(por)O2] to [RuIV(por)(pz)2] (Hpz=pyr-
azole).[13e,f] In the absence of pyrazole, the kinetic profile for
the RuVI to RuIV transformation was influenced by secon-
dary reactions (possibly by the formation of RuII porphyrin)
and deviated from first-order exponential decay. A similar
phenomenon was observed for the oxidation of styrene by 2
or PEG-2 in ClCH2CH2Cl; in these cases the conversion of
the RuVI to RuIV species in the presence of pyrazole (2%
w/w) is manifested by the decay of the Soret band at
~412 nm with concomitant development of a new absorp-
tion band at 402 nm.
We conducted kinetic studies on the oxidation of hydro-
carbons by PEG-2 or 2 in ClCH2CH2Cl containing pyrazole
(2% w/w) under the condition that [Ru]![substrate]<1m.
For all the substrates employed, the reactions exhibited
pseudo-first-order kinetics and isosbestic spectral changes
over four half-lives. The pseudo-first-order rate constants
(kobs) were determined by monitoring the disappearance of
the Soret band (lmax =414 nm for PEG-2 and 412 nm for 2)
of the dioxoruthenium(vi) porphyrins; the second-order rate
constants (k2) were determined from the plots of kobs versus
[hydrocarbon] (Table 6). The k2
Stoichiometric oxidation of hydrocarbons by PEG-2: Treat-
ment of styrene (1 mmol) with PEG-2 (30 mmol) in CH2Cl2
(5 mL) containing pyrazole (2% w/w) at room temperature
for 2 h afforded styrene oxide in 70% yield, together with
benzaldehyde in 10% yield (entry 1, Table 5). cis-b-Methyl-
values were unaffected by the
Table 5. Stoichiometric oxidation of hydrocarbons by PEG-2 and 2 in CH2Cl2, water, or dioxane–water.[a]
pyrazole loading at 2–10%
(w/w), and no appreciable reac-
tion of PEG-2 or 2 with pyra-
zole was observed within the
timescale of the kinetic studies.
For the reaction of styrene with
PEG-2, the k2 values in differ-
ent solvents have been deter-
mined and are listed in
Table S4 (see Supporting Infor-
mation).
Entry
Substrate
Product
Solvent
Yield[%][b]
PEG-2
2
1
2
3
4
5
6
3
3
5
9
23
23
13
51
15
19
28+52
28
CH2Cl2
70
70
80
62
74
–
86
66
dioxane–water[c]
CH2Cl2
CH2Cl2
CH2Cl2
18 (28), 32 (52)
22 (28), 36 (52)
dioxane–water[c]
22
–
[a] All reactions were performed in the presence of pyrazole (2% w/w) at room temperature. [b] Based on the
amount of PEG-2. [c] Water content: 40–90% v/v.
Kinetic studies on the reactions
of PEG-2 with hydrocarbons in
aqueous solution: UV/Vis spec-
styrene, trans-b-methylstyrene, and ethylbenzene were also
reactive with PEG-2 under similar conditions, giving epox-
ides (15 and 19), ketone (28), or alcohol (52) in up to 80%
yield (entries 3–5, Table 5). The oxidation of cis-b-methyl-
styrene gave a mixture of cis- and trans-b-methylstyrene
oxides in a 10:1 ratio.
Table 6. Second-order rate constants (k2) for oxidation of hydrocarbons
by PEG-2 and 2 in ClCH2CH2Cl containing pyrazole (2% w/w) at
298 K.[a]
Entry
Substrate
k2 ”103 [dm3 molꢀ1 sꢀ1
PEG-2
]
2
In dioxoane–water (5 mL), containing pyrazole (2% w/w),
and with a water content ranging from 40% to 90% v/v, the
reaction of PEG-2 (50 mmol) with styrene (1 mmol) at room
temperature for 2 h afforded benzaldehyde (51) in about
70% yield (entry 2, Table 5); oxidation of ethylbenzene by
PEG-2 under similar conditions gave acetophenone in about
22% yield (entry 6, Table 5).
1
2
3
4
5
6
7
8
styrene
7.7ꢃ0.3
9.0ꢃ0.3
14.0ꢃ0.2
14.9ꢃ0.8
16.8ꢃ0.3
24.2ꢃ1.0
60.4ꢃ1.5
9.7ꢃ0.5
4-fluorostyrene
4-chlorostyrene
4-methylstyrene
4-methoxystyrene
cis-b-methylstyrene
trans-b-methylstyrene
cyclohexene
cis-stilbene
trans-stilbene
cyclooctene
11.5ꢃ0.4
17.8ꢃ0.7
37.4ꢃ1.2
8.6ꢃ0.3
11.4ꢃ0.2
32.8ꢃ1.1
3.8ꢃ0.2
14.0ꢃ0.6
41.2ꢃ1.3
4.3ꢃ0.3
9
10
11
12
13
12.9ꢃ0.3
9.5ꢃ0.3
20.1ꢃ1.2
12.4ꢃ1.3
1.01ꢃ0.06
0.56ꢃ0.03
Kinetic studies on the reactions of PEG-2 with hydrocarbons
in ClCH2CH2Cl: Previous work demonstrated that oxidation
of hydrocarbons by [RuVI(por)O2] in organic solvents (such
as ClCH2CH2Cl) containing pyrazole (2% w/w) features iso-
sbestic UV/Vis spectral changes corresponding to a smooth
ethylbenzene
cumene
0.81ꢃ0.03
0.48ꢃ0.02
[a] Pyrazole was not found to interfere with the rate-limiting step of the
hydrocarbon oxidation reactions.
3026
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ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 3020 – 3031

Homogeneous Catalysis
FULL PAPER
tral changes for the oxidation of styrene or ethylbenzene by
PEG-2 in dioxane containing 40% (v/v) water and 2%
(w/w) pyrazole showed an isosbestic transformation due to
conversion of RuVI to RuIV species (we chose dioxane as an
organic media because this solvent could dissolve the sub-
strates and is less prone to substrate diffusional limitation).
Similar spectral features were also observed for the same re-
action in dioxane–water mixtures with different water con-
tents (40–90%; see, for example, Figure 6). The oxidation of
Discussion
PEG has commonly been used as a support or non-ionic sur-
factant in organic catalysis, combinatorial chemistry, and bi-
ological studies for its good solubility in many solvents (in-
cluding water), easy recovery by simple precipitation or
membrane separation, and biological compatibility.[23] In cat-
alysis, PEG-supported metal catalysts were found to exhibit
comparable reactivity and selectivity to the unsupported
counterparts and could be reused several times with slight
decrease in product yield and selectivity.[4d,f] PEG is a water-
soluble polymer containing hydrophobic moieties; in aque-
ous solution, the hydrophobic moieties could bind (or inter-
act with) nonpolar substrates to form a stable supramole-
cule. For the reactions involving nonpolar substrates and
PEG in aqueous solution, hydrophobic effect[24] might be
important. To probe the formation of hydrophobic microdo-
mains from aggregation of the hydrophobic moieties (to
minimize their exposure to water) and the biomimetic be-
havior of PEG-based polymer systems in aqueous solutions,
a variety of NMR techniques including relaxation time[25a]
/
chemical shift[25b] measurements and pulse gradient spin-
echo (PGSE) NMR[25c] were employed. Some fluorescent
probes sensitive to the surrounding microenvironment have
been used to study micellization of PEG polymers in
water.[26]
The reactivity, stability, and selectivity of metal catalysts
or artificial enzymes and the corresponding reactive oxo in-
termediates in aqueous solution could be significantly differ-
ent from that in organic solvents. So far few reactive oxome-
talloporphyrin intermediates are stable enough for isolation.
The isolable, reactive dioxoruthenium(vi) porphyrins previ-
ously reported in the literature[13] are insoluble in water; it is
not feasible to study their oxidation chemistry in aqueous
solution. In this regard, the water solubility and stability of
the PEG-supported dioxoruthenium(vi) porphyrin PEG-2,
would be of interest.
Figure 6. UV/Vis spectral changes during reaction of PEG-2 with styrene
(0.0036m) in dioxane–water (70% water, v/v) containing pyrazole (2%
w/w) at 298 K (time scan: 3000 s, interval: 45 s). The isosbestic points
were located at 402 and 436 nm.
styrene or ethylbenzene by PEG-2 in dioxane–water exhibit-
ed pseudo-first-order kinetics under the condition [sub-
strate]@[PEG-2], like that in ClCH2CH2Cl. The pseudo-
first-order rate constants (kobs) at different substrate concen-
trations and water contents were determined by monitoring
the disappearance of the Soret band of PEG-2 at lmax
=
414 nm. As styrene or ethylbenzene is virtually insoluble in
water, increasing water content in dioxane–water would
impose limitation on the substrate concentration that could
be used in kinetic studies. Table 7 lists the k2 values for the
oxidation of styrene or ethylbenzene by PEG-2 in dioxane–
water at different water contents.
Effect of solvent on configurations of PEG-1 and PEG-2:
The well-resolved 1H NMR signals of the PEG chain of
PEG-1 in CDCl3 and D2O indicate that the PEG moiety is
well solvated in both solvents. The marked broadening of
the porphyrin ring b-H signal of PEG-1 by changing solvent
from CDCl3 to D2O and the almost featureless 19F NMR
spectrum of PEG-1 in D2O suggest a poor solvation of the
porphyrin core in water. This can be rationalized by the for-
mation of micellar assemblies in a solution of PEG-1 in
water, with the hydrophobic porphyrin cores embedded in
the interior of the micelles, which restricts the motion of
porphyrin H and F nuclei and shortens their relaxation
times. Similar micellar assemblies could be present in aque-
ous solution of PEG-2; the encapsulation of oxometallopor-
phyrin cores by PEG chains in this system somewhat resem-
bles that by protein chains in native enzymes.
Table 7. Second-order rate constants (k2) for oxidation of styrene and
ethylbenzene by PEG-2 in dioxane-water with different water contents at
298 K.[a]
Entry
Water
k2 ”103 [dm3 molꢀ1 sꢀ1
]
content [% v/v]
styrene
ethylbenzene
1
2
3
4
5
6
7
40
50
60
65
70
80
90
34.8ꢃ1.6
54.4ꢃ3.3
2.9ꢃ0.2
7.2ꢃ0.2
89.0ꢃ2.0
15.5ꢃ0.9
39.9ꢃ3.1
99.5ꢃ5.4
152.0ꢃ9.7
161.3ꢃ14.7
304.8ꢃ8.9
479.0ꢃ39.5
548.0ꢃ37.3
570.9ꢃ28.1
As shown in Figure 2, addition of [D8]dioxane to a solu-
tion of PEG-1 in D2O leads to better resolved 19F NMR sig-
nals. Probably, increasing the content of dioxane or decreas-
[a] All reactions were performed in the presence of pyrazole (2% w/w)
(pyrazole was not found to interfere with the rate-limiting step of the hy-
drocarbon oxidation reactions).
Chem. Eur. J. 2006, 12, 3020 – 3031
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3027

C.-M. Che et al.
ing the content of water in the solution renders the micelles
less compact and improves the solvation of the porphyrin
core. This is consistent with the increase in particle size with
decreasing water content as observed by dynamic light scat-
tering measurements (Figure 5). A related phenomenon was
previously observed for a water-soluble dendrimer, which, in
aqueous solution, swells progressively like dried sponges
upon addition of THF.[17]
and “tightly” protected by the PEG chains. This might be a
reason for the remarkable stability of PEG-2 in water.
A “loose” arrangement of the PEG chain is also expected
in CDCl3, in which case there might not be significant inter-
action between styrene and PEG protons, accounting for the
absence of NOE between styrene and PEG protons in the
2D NMR spectrum recorded in this solvent (see Figure 3).
However, in D2O, the interaction of the hydrophilic part of
PEG chain with D2O would cause the hydrophobic part of
PEG and styrene molecules to form a hydrophobic region,
wherein the interaction between styrene and PEG protons
could be sufficiently strong to allow observation of NOE
(Figure 3).
Figure 7 shows a proposed change in the microenviron-
ment of ruthenium porphyrin moiety in PEG-1 as the sol-
vent changes from dioxane to dioxane–water and to water,
Kinetic studies of hydrocarbon oxidation by PEG-2: Inspec-
tion of the data in Table 6 reveals that attachment of 2 to
PEG slightly retards the reaction of dioxoruthenium(vi) por-
phyrin with hydrocarbons (k2(2)/k2(PEG-2)=1.1–1.8) in
ClCH2CH2Cl and the reactions of PEG-2 or 2 with ethyl-
benzene and cumene (entries 12 and 13) are much slower
than those with styrenes (entries 1–7, 9, and 10). The epoxi-
dation by PEG-2 displays a larger k2 value for trans-b-meth-
ylstyrene and trans-stilbene than for cis-b-methylstyrene and
cis-stilbene, respectively, like that by 2. In previous studies
of dioxoruthenium(vi) complexes with sterically bulky por-
phyrin ligands,[13d,f] the k2 value for the epoxidation of trans-
b-methylstyrene or trans-stilbene is smaller than that for cis-
b-methylstyrene or cis-stilbene; this result arises from larger
steric interaction of trans- than cis-alkene with bulky por-
phyrin ligands. This suggests that, in organic solvent, the
porphyrin core of PEG-2 has a similar steric environment to
that of 2.
Our previous work demonstrated that oxidation of styr-
enes p-X-C6H4CH=CH2 (X=H, F, Cl, Me, MeO) with other
dioxoruthenium(vi)
porphyrins,
such
as
[RuVI(2,6-
Cl2tpp)O2], exhibits a linear dual-parameter Hammett corre-
lation log krel =1mbsmb +1CJJsCJJ (in which krel =k2(X)/k2(H)),
with 1mb ranging from ꢀ0.58 to ꢀ0.77 and 1CJJ from 1.01 to
1.67 (j1CJJ/1mb j=1.63–2.17).[13e,f] From the data in Table 6, we
obtained
a
similar Hammett correlation, logkrel
=
ꢀ0.59smb +0.96sCJJ (R=0.98, j1CJJ/1mb j=1.63) for
2
and
logkrel =ꢀ0.56smb +1.20sCJJ (R=0.99, j1CJJ/1mb j=2.07) for
PEG-2. Apparently, the oxidation of styrenes in
ClCH2CH2Cl by these dioxoruthenium(vi) porphyrins pro-
ceeds through a similar mechanism.
From the data in Table 7 it is evident that for the oxida-
tion of styrene by PEG-2 in dioxane–water, when water con-
tent increases from 40% to 60%, the k2 value increases
gradually and reaches (89.0ꢃ2.0)”10ꢀ3 dm3 molꢀ1 sꢀ1, which
is 11.6 times that obtained in ClCH2CH2Cl. As water con-
tent reaches 65%, the k2 value increases to (304.8ꢃ8.9)”
10ꢀ3 dm3 molꢀ1 sꢀ1. At a water content of 70%, k2 increases
dramatically and reaches (479.0ꢃ39.5)”10ꢀ3 dm3 molꢀ1 sꢀ1,
which is 62 times that obtained in ClCH2CH2Cl. With fur-
ther increase in water content to 80% and 90%, the k2
value increases slightly to (548.0ꢃ37.3)”10ꢀ3 and (570.9ꢃ
28.1)”10ꢀ3 dm3 molꢀ1 sꢀ1, respectively.
Figure 7. Schematic diagram showing proposed change in microenviron-
ment of ruthenium porphyrin core in PEG-1 upon changing solvent from
dioxane to dioxane-water and to water.
which should be applicable to the case of PEG-2 as well.
We propose that, in dioxane, the PEG-supported ruthenium
porphyrins exhibit a “loose” structure and are well solvated.
When the solvent polarity is increased by the addition of
water, formation of micellar aggregates occurs. The micelles
become more compact at higher water contents, and in
water, the ruthenium porphyrin cores are probably “frozen”
3028
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Chem. Eur. J. 2006, 12, 3020 – 3031

Homogeneous Catalysis
FULL PAPER
The effect of water content on the reaction of PEG-2 with
ethylbenzene in dioxane–water is similar to, or even larger
than, that observed with styrene. When the water content
increases from 40% to 60%, the k2 value increases gradual-
ly and reaches (15.5ꢃ0.9)”10ꢀ3 dm3 molꢀ1 sꢀ1, which is 19
times that obtained in ClCH2CH2Cl. A faster increase of k2
occurs at a water content of 65%, with the k2 value reaching
(39.9ꢃ3.1)”10ꢀ3 dm3 molꢀ1 sꢀ1. As the water content in-
creases to 80%, the k2 value increases to (152.0ꢃ9.7)”
10ꢀ3 dm3 molꢀ1 sꢀ1, which is 188 times that obtained in
ClCH2CH2Cl! When the water content reaches 90%, there
is a slight increase of k2 to (161.3ꢃ14.7)”10ꢀ3 dm3 molꢀ1 sꢀ1.
Figure 8 shows the k2 versus water content plots for the
oxidation of styrene and ethylbenzene by PEG-2 in diox-
ane–water. Such plots resemble the Dd versus water content
plot (Figure 4) and closely correlate with the particle size
versus water content plot (Figure 5). For example, the most
dramatic changes in k2, Dd, and micelle size all occur at a
change in water content from ~60 to ~70%. Considering
the observed NOE between styrene and PEG chain in D2O
(Figure 3), the above water-induced rate acceleration is at-
tributed to the change in interaction between the hydrocar-
bon substrate and PEG chain upon addition of water. Such
a change in the interaction should result from hydrophobic
effect, the involvement of which in some organic reactions
that exhibit increased rate in water has previously been
demonstrated by Breslow and co-workers.[24a]
It can be seen that PEG plays an important role in the hy-
drocarbon oxidation in aqueous media, which not only pro-
hibits the formation of m-oxoruthenium porphyrin dimers,
but could also serve as a vehicle to facilitate the dissolution
of dioxoruthenium(vi) porphyrin in water and to create a
micellar environment for the reactive dioxoruthenium(vi)
porphyrin species.
Conclusion
Treatment of [RuII(F20-tpp)(CO)] with PEG sodium salt in
DMF results in the covalent attachment of [RuII(F20-
tpp)(CO)] to the PEG chains. The PEG-supported [RuII-
(F20-tpp)(CO)] (PEG-1) could be oxidized to PEG-support-
ed dioxoruthenium(vi) porphyrin PEG-2 by m-CPBA in
CH2Cl2, dioxane, and water. PEG-1 exhibits high catalytic
activity in 2,6-Cl2pyNO oxidation of cholesterol acetate and
glycal as well as styrene, cyclooctene, ethylbenzene, and
indane. In catalytic PhI=NTs aziridination/amidation of hy-
drocarbons, PEG-1 exhibits an efficiency comparable to that
of [RuII(F20-tpp)(CO)]. PEG-1 is also an active catalyst for
intramolecular amidation of sulfamate esters with PhI-
(OAc)2, representing the first efficient polymer-supported
ꢀ
metalloporphyrin catalyst for such a C N bond formation
reaction. The catalytic properties of PEG-1 are superior to
those of previously reported PEG-supported ruthenium por-
phyrin catalysts. Stoichiometric oxidations of hydrocarbons,
such as styrene and ethylbenzene, by PEG-2 in CH2Cl2 gave
oxidation products in up to 80% yield. Kinetic studies on
the oxidation of hydrocarbons by PEG-2 in CH2Cl2, ben-
zene, and ClCH2CH2Cl showed slightly lower reactivity than
that by [RuVI(F20-tpp)O2]. In dioxane–water mixtures con-
taining 40–90% (v/v) water, the reactivity of PEG-2 toward
oxidation of styrene and ethylbenzene increases with water
content. The isolation of reactive PEG-supported dioxoru-
thenium(vi) porphyrin PEG-2 provides a useful model
system for studying the mechanism of oxygen-atom transfer
reactions involving macromolecule-supported oxometallo-
porphyrin intermediates.
Experimental Section
General: PEG (Aldrich, monomethylate, Mw=5000) was used as re-
ceived. The alkene substrates were purified by passing through a column
of activated alumina before use. 2,6-Cl2pyNO,[27] PhI=NTs,[28] sulfamate
esters 43–46,[22a] and complexes 1[14] and 2[14,29] were prepared by the liter-
ature methods. All solvents were of AR grade. 1H NMR and 19F NMR
spectra were measured on a Bruker DPX 300 or 400 spectrometer. Infra-
Figure 8. Variation of k2 with different water contents for oxidation of
styrene and ethylbenzene by PEG-2 in dioxane–water containing pyra-
zole (2% w/w) at 298 K.
Chem. Eur. J. 2006, 12, 3020 – 3031
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3029

C.-M. Che et al.
red spectra (KBr pellets) were recorded on a Bio-Rad FTS-7 FT-IR spec-
trometer. UV/Visible spectra were measured on a Milton Roy Spectronic
3000 diode-array spectrophotometer. Gas chromatography was per-
formed on a Hewlett–Packard 5890 Series II gas chromatograph equip-
ped with a flame ionization detector and a 3396 Series II integrator.
band in the UV/Vis spectrum of the reaction mixture at different reac-
tion time (t) was measured, by using standard 1.0 cm quartz cuvettes, on
a Hewlett–Packard 8453 diode array spectrophotometer interfaced with
an IBM-compatible PC and equipped with a Lauda RM6 circulating
water bath. A nonlinear least-squares fitting of the (AfꢀAt) versus t data
over four half-lives (t1/2) by the equation (AfꢀAt)=(AfꢀAi)exp(ꢀkobst) (in
which Af and Ai are the final and initial absorbance, respectively, and At
is the absorbance measured at time t) gave the pseudo-first order rate
constant kobs of the reaction. Upon determination of the kobs values at
various concentrations of the hydrocarbon substrate, the second-order
rate constant k2 of the reaction was obtained from the linear least-
squares fitting of the kobs versus hydrocarbon concentration plot. No rate
saturation was observed over the hydrocarbon concentrations employed
in this work.
Preparation of PEG-supported carbonyluthenium(ii) porphyrin PEG-1:
NaH (2.3 mg, 60% in oil, 0.06 mmol) was added to a solution of PEG
(200 mg, 0.04 mmol) in DMF (10 mL). The mixture was stirred at room
temperature for 2 h, followed by addition of a solution of 1 (112.5 mg,
0.1 mmol) in DMF (10 mL). The resulting solution was vigorously stirred
at 608C for 3 days under argon and then cooled to room temperature,
poured into water, and extracted with CH2Cl2 (3”30 mL). The organic
layer was dried with anhydrous Na2SO4 for 12 h. Upon removal of sol-
vent in vacuo and subsequent addition of diethyl ether (20 mL), the pre-
cipitate was filtered quickly under argon and dried in vacuo. The crude
red solid was dissolved in distilled water (2 mL) and purified by Sepha-
dex-25 gel. The red band was collected. Removal of water under reduced
pressure gave PEG-1 as a red solid. Yield: 70% (based on the amount of
starting PEG); UV/Vis (CH2Cl2): lmax =406 (Soret), 526 nm (b); IR: n˜ =
1954 cmꢀ1 (CO); 1H NMR (CDCl3): d=8.82 (brs, 8H), 4.78 (m, 2H;
-CH2CH2O-por), 4.06 (m, 2H; -CH2CH2O-por), 3.80–3.45 (m, PEG
CH2), 3.35 ppm (s, PEG MeO); 19F NMR (CDCl3): d=ꢀ136.7 to ꢀ141.5
(m, 8o-F), ꢀ151.9 to ꢀ152.6 (m, 3p-F), ꢀ157.0 to ꢀ158.2 (m, 4m-F),
ꢀ161.3 to ꢀ163.0 ppm (m, 4m-F).
Dynamic light-scattering studies: All measurements were performed at
258C on Zetasizer 3000Hs equipped with a 633 nm He-Ne laser using
back-scattering detection. The sample solutions (1 mgmLꢀ1) were filtered
through 0.20 mm filters. The scattered light of a vertically polarized He-
Ne laser was measured at an angle of 90.08 and was collected on an auto-
correlator. The polydispersity factor of micelles, m2/G2 (in which m2 is the
second cumulant of the decay function and G is the average characteristic
line width), was determined and listed in Table S2. The dependence of G
on K2 (K=4pnsin(q/2)/l, in which n is the refractive index of the solu-
tion, q is the scattering angle, and l is the wavelength of the incident
beam) was used to determine the diffusion coefficient D0 of the micellar
aggregates. The hydrodynamic diameters (dh) of micelles were calculated
using the Stokes–Einstein relationship [Eq. (1)], in which kB is the Boltz-
mann constant, T is the absolute temperature, and h0 is the viscosity of
the solvent at T.
Preparation of PEG-supported dioxoruthenium(vi) porphyrin PEG-2:
Excess m-CPBA (40 mg) was added to a CH2Cl2 (5 mL) solution of
PEG-1 (60 mg). The resulting solution was stirred for 3 min. When the
color of the solution changed to dark purple, anhydrous diethyl ether
(25 mL) was added. The precipitate was quickly collected by filtration
and dried in vacuo at room temperature, affording PEG-2 as a dark
brown hygroscopic solid. Yield: 80%; UV/Vis (CH2Cl2): lmax =414
kBT
ð1Þ
D0
¼
3ph0dh
1
(Soret), 508 nm (b); IR: n˜ =830 cmꢀ1 (RuO2); H NMR (CDCl3): d=9.20
(brs, 8H), 4.76 (m, 2H; -CH2CH2O-por), 4.08 (m, 2H; -CH2CH2O-por),
3.80–3.45 (m, PEG CH2), 3.35 ppm (s, PEG MeO); 19F NMR (CDCl3):
d=ꢀ135.6 to ꢀ139.0 (m, 8o-F), ꢀ150.4 (m, 3p-F), ꢀ157.6 to ꢀ161.5 ppm
(m, 8m-F).
Acknowledgements
Oxidation of hydrocarbons with 2,6-Cl2pyNO catalyzed by PEG-1: A
mixture of hydrocarbon (1 mmol), catalyst PEG-1 (1 mmol), and 2,6-
Cl2pyNO in CH2Cl2 (5 mL) was stirred under argon. The amount of 2,6-
Cl2pyNO and the reaction time and temperature are indicated in Tables 1
and 2. At the end of the reaction, the mixture was evaporated to dryness.
The organic products in the residue were extracted with diethyl ether,
and were identified by GC in the cases in which the corresponding au-
thentic samples were available or by comparison with previously reported
1H NMR spectral data.
This work was supported by The University of Hong Kong (University
Development Fund), the Hong Kong Research Grants Council (HKU
7011/04P), and the University Grants Committee of the Hong Kong SAR
of China (Area of Excellence Scheme, AoE/P-10/01).
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Chem. Eur. J. 2006, 12, 3020 – 3031

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Received: December 3, 2005
Published online: February 21, 2006
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ꢁ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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