Comparative reactivity of hypervalent iodine oxidants in metalloporphyrin-catalyzed oxygenation of hydrocarbons: Iodosylbenzene sulfate and 2-iodylbenzoic acid ester as safe and convenient alternatives to iodosylbenzene

Article abstract of DOI:10.1002/adsc.200800784

A comparative study of the reactivity of 2-iodylbenzoic acid isopropyl ester (IBX-ester), oligomeric iodosylbenzene sulfate [(PhIO)₃· SO₃]_u, and iodosylbenzene in the oxygenation of anthracene in the presence of metal porphyrin or phthalocyanine complexes is reported. Results of this study demonstrate that oligomeric iodosylbenzene sulfate and the IBX-ester are the most reactive oxygenating reagents that can be used as a safe and convenient alternative to the thermally unstable and potentially explosive iodosylbenzene.

Full text of DOI:10.1002/adsc.200800784

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DOI: 10.1002/adsc.200800784
Comparative Reactivity of Hypervalent Iodine Oxidants in
Metalloporphyrin-Catalyzed Oxygenation of Hydrocarbons:
Iodosylbenzene Sulfate and 2-Iodylbenzoic Acid Ester as Safe
and Convenient Alternatives to Iodosylbenzene
a
a
a
a,b
Ivan M. Geraskin, Olga Pavlova, Heather M. Neu, Mekhman S. Yusubov,
a,
a,
Victor N. Nemykin, * and Viktor V. Zhdankin *
Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN 55812, USA
a
Fax : (+1)-218-726-7394; e-mail: vzhdanki@d.umn.edu
Siberian State Medical University and Tomsk Polytechnic University, 2 Moskovsky trakt, 634050 Tomsk, Russia
b
Received: December 17, 2008; Revised: March 2, 2009; Published online: March 17, 2009
Abstract: A comparative study of the reactivity of
-iodylbenzoic acid isopropyl ester (IBX-ester), oli-
gomeric iodosylbenzene sulfate [(PhIO) ·SO ] , and
In this communication, we report preliminary re-
sults on the use of the new and convenient hyperva-
lent iodine reagents 1 and 2 (Figure 1) as terminal ox-
idants in the biomimetic oxidation of anthracene to
anthraquinone catalyzed by Fe AHCUTNGRNENUG( III) phthalocyanine
complex 3 (Figure 2), Co(II) tetraphenylporphyrin (4)
2
3
3 n
iodosylbenzene in the oxygenation of anthracene in
the presence of metal porphyrin or phthalocyanine
complexes is reported. Results of this study demon-
strate that oligomeric iodosylbenzene sulfate and
the IBX-ester are the most reactive oxygenating re-
agents that can be used as a safe and convenient al-
ternative to the thermally unstable and potentially
explosive iodosylbenzene.
or Ru(II) tetraphenylporphyrin (5).
The
oligomeric
iodosylbenzene
sulfate
[(PhIO) ·SO ] (2) was prepared by simple treatment
3
3 n
of commercially available (diacetoxyiodo)benzene
with aqueous hydrogen sulfate and isolated as a ther-
[
5]
mally stable, yellow crystalline solid. The isopropyl
ester of 2-iodylbenzoic acid (IBX-ester) (1) was pre-
pared by the hypochlorite oxidation of the readily
available isopropyl ester of 2-iodobenzoic acid and
isolated in the form of a stable, white, microcrystalline
Keywords: iodine; iodosylbenzene; 2-iodylbenzoic
acid isopropyl ester (IBX-ester); oxygenation; por-
phyrins
[
6a,b]
solid.
Reagent 1 is also commercially available
[6c]
from several chemical companies. Complex 3 was
prepared using the direct high-temperature reaction
Hypervalent iodine compounds are versatile, selective between 4-tert-butylphthalonitrile and iron(II) acetate
[
7]
oxidants that have the added advantage of being bio- as described previously, while Co(II) tetraphenyl-
[
1,2]
degradable and low in toxicity.
Among these re- porphyrin 4 and Ru(II) carbonyl tetraphenylporphyr-
agents, iodosylbenzene, (PhIO) , is particularly impor- in 5 were obtained from commercial sources. The het-
n
tant as an efficient oxygen transfer agent that has erogenized phthalocyanine catalysts similar to com-
found widespread application in various oxygenation plex 3 were previously reported in the CÀH activation
[
2]
reactions. In 1979 Groves and co-workers reported reactions using H O or organic peroxides as source
2
2
[
8]
that iodosylbenzene is the most efficient source of of oxygen. Recently, we have reported the use of
oxygen for the oxygenation of hydrocarbons in the complexes 3–5 in the catalytic oxidations of alco-
[
3a]
[9]
presence of iron
A
H
U
G
E
N
N
(III) porphyrin complexes,
and hols.
since then (PhIO) has been widely used as a terminal
n
oxidant in the reactions mimicking natural oxidations
performed by the heme-containing cytochrome P-450
[
3]
class of enzymes. Despite its usefulness as an oxi-
dant, practical applications of iodosylbenzene are
hampered by its low solubility in non-reactive
[2]
media, as well as low thermal stability and explosive
[
4]
properties upon moderate heating.
Figure 1. Hypervalent iodine oxidants: isopropyl 2-iodylben-
zoate (1) and oligomeric iodosylbenzene sulfate (2).
Adv. Synth. Catal. 2009, 351, 733 – 737
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
733

Ivan M. Geraskin et al.
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Figure 2. Iron ACHTUNGTRENNUNG( III) phthalocyanine (3) and metal porphyrin complexes 4 and 5.
Scheme 1. Catalytic oxidation of anthracene (6) to anthraquinone (7).
We have investigated the catalytic oxidation of an-
The oxidation of anthracene was carried out in dry
thracene (6) to anthraquinone (7) using oxidants 1, 2 dichloromethane or in toluene using a 2.0–2.5-fold
and complexes 3–5 (Scheme 1) in comparison with io- excess (6.0–7.5 mol. equiv. of active oxygen per 1 mol-
dosylbenzene as the common oxygenating reagent. ecule of anthracene 6) with 0.10–0.15 equiv of the ap-
The use of iodosylbenzene in this reaction in the pres- propriate catalyst (Table 1). After the indicated time,
ence of transition metal complexes was previously re- the catalyst was removed by flash chromatography
[
10]
ported in the literature.
and the obtained solution was analyzed by GC-MS to
Table 1. Catalytic oxidations of anthracene (6) to anthraquinone (7) using hypervalent iodine reagents.
Entry
Reagent
Temperature [8C]
Catalyst
(mol%)
Solvent
Conversion [%]
Time [h]
(
mol equiv.)
ACHTUNGTRENNUNG
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
3
3
3
3
3
3
3
3
r.t.
40
none
none
none
none
3
3
4
5
0
0
0
0
toluene
CH Cl
0
0
24
24
3.5
24
24
2.5
3.5
21
0.5
3.5
24
2
2
1
24
5
3
2
2
110
110
r.t.
110
110
110
40
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
toluene
toluene
toluene
toluene
toluene
toluene
CH Cl
14
86
0
100
14
0
100
100
0
100
100
100
0
15
15
15
15
15
10
0
10
10
10
0
3
3
5
5
2
2
2
10
11
12
13
14
15
16
17
18
19
CH Cl
2
2.5
2.5
2.5
2.5
7.5
7.5
7.5
7.5
7.5
none
3
4
5
toluene
toluene
CH Cl
2
2
2
CH Cl
2
PhIO
PhIO
PhIO
PhIO
PhIO
none
toluene
toluene
CH Cl
3
5
5
4
10
15
15
15
100
7
100
26
2
2
2
2
CH Cl
24
2
2
CH Cl
2
734
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ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2009, 351, 733 – 737

Comparative Reactivity of Hypervalent Iodine Oxidants
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determine the conversion of anthracene (6) to anthra- this oxidation under the same reaction conditions
quinone (7). According to the GC-MS and NMR (1108C, toluene) leads to a significantly lower conver-
data, 7 and the appropriate iodides resulting from the sion (14%, entry 7 and 0%, entry 8, respectively),
reduction of hypervalent iodine reagents were the which is even lower than the conversion in the ab-
only products formed under these reaction conditions. sense of a catalyst (entries 3 and 4). This result is
Dichloromethane was found to be the best solvent for probably explained by the low thermal stability of the
the oxidations in the presence of metal porphyrins 4 intermediate high-valent oxo-metal complexes gener-
and 5. Toluene was used for the reactions catalyzed ated from the initial interaction of metal porphyrins 4
by Fe
complex 3 in dichloromethane solutions. The results ature leads to a fast and efficient oxidation in the
of the oxidations are summarized in Table 1. presence of catalyst 5 (entry 9: 100% conversion in
ACHTUNGTRENNUNG( III) phthalocyanine 3 due to the instability of and 5 and the oxidant. Lowering the reaction temper-
First of all, we have found that the oxidation of an- 0.5 h at 408C; entry 10: 100% conversion in 3.5 h at
thracene with hypervalent iodine reagents 1 and 2 in room temperature). It should be emphasized that
the absence of catalysts at room temperature in tolu- IBX-ester 1 is more reactive in this reaction than the
ene or at 408C in dichloromethane proceeds extreme- commonly used iodosylbenzene, which shows only
ly slowly and does not show any measurable conver- 7% conversion after 3 h and 100% conversion only
sion to anthraquinone after 24 h (entries 1, 2, and 11). afer 24 hour of the reaction in the presence of Ru(II)
Reagent 1, however, slowly oxidizes anthracene in porphyrin 5 (entries 17 and 18, respectively). The
toluene under reflux conditions (1108C) with a 14% Co(II) porphyrin 4 shows slightly lower catalytic ac-
conversion after 3.5 h and 86% conversion after 24 h tivity in these oxidations (entries 13 and 19).
(
entries 3 and 4). The addition of 0.15 mol equiv of
In contrast to IBX-ester 1, the oligomeric iodosyl-
Fe(III) phthalocyanine 3 leads to a significant in- benzene sulfate 2 shows high reactivity in catalytic ox-
ACHTUNGTRENNUNG
crease in the reaction rate with a 100% conversion idations at room temperature in the presence of any
being reached in 2.5 h at 1108C (entry 6). The graphi- of the catalysts 3–5 (10 mol%), while the reaction in
cal representation of the conversion in this reaction the absence of catalysts at room temperature does not
vs. time is shown in Figure 3. Lowering the reaction occur (entry 11). The best catalytic effect is observed
temperature leads to a slower conversion rate in the in the presence of Ru(II) porphyrin 5 (entry 14;
reaction in the presence of Fe
entry 5).
The use of Co(II) tetraphenylporphyrin 4 and (entries 12 and 13; 100% conversion in 2 h). The
ACHTUNGTRENNUNG
(
Ru(II) carbonyl tetraphenylporphyrin 5 as catalysts in graphical representation of the conversion in the oxi-
dations using reagents 1 and 2 catalyzed by the Fe-
AHCTUNGTRENNGNU( III) phthalocyanine complex 3 vs. time is shown in
Figure 3 in comparison with the analogous oxidation
using iodosylbenzene.
The data presented in Table 1 and Figure 3 clearly
indicate that the oligomeric iodosylbenzene sulfate 2
is the best oxidant, significantly more reactive than
the commonly used iodosylbenzene. The slower reac-
tion with iodosylbenzene can partially be explained
by its polymeric structure, (PhIO) , requiring initial
n
depolymerization, while the structure of sulfate 2 con-
sists of smaller trimeric units of PhIO. The presence
of the initial period of activation in the reaction of
(
PhIO)n is clearly observed on its reactivity curve
(
Figure 3). The reaction of IBX-ester 1 in the pres-
ence of the Fe ACHTUNGRNENUG( III) phthalocyanine complex 3 requires
heating to 1108C; the need for higher temperature
can be explained by the low solubility of reagent 1 in
toluene, which is the preferable solvent for the reac-
tions involving catalyst 3. The reactivity of both oxi-
dants 1 and 2 is similar when a more stable Ru(II)
complex 5 is used in dichloromethane solution (en-
tries 9, 10 and 14). Overall, ruthenium(II) complex 5
shows the highest catalytic activity; however, the
Figure 3. Conversion in catalytic oxidation of anthracene (6)
to anthraquinone (7) using oxidants 1, 2 and iodosylbenzene
in the presence of the Fe
ACHTUNGTRNENUNG( III) phthalocyanine complex 3.
Oxidations using IBX-ester 1 were performed at 1108C in
toluene, while oxidant 2 and PhIO were used in dichlorome- availability and low cost of iron
ACHTUNGTRENNUNG
thane at room temperature.
Adv. Synth. Catal. 2009, 351, 733 – 737
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asc.wiley-vch.de
735

Ivan M. Geraskin et al.
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Scheme 2. Catalytic oxidation of 2-tert-butylanthracene (8) to 2-tert-butylanthraquinone (9) using oligomeric iodosylbenzene
sulfate 2 as the oxidant.
analysis was carried out with an HP 5890 A Gas Chromato-
tentially useful reagent for biomimetic catalytic trans-
graph using a 5970 Series mass selective detector.
formations.
In order to demonstrate the general character of
the optimized reaction conditions, we performed the
oxidation of 2-tert-butylanthracene (8) using oxidant 2
Typical Pocedure for Catalytic Oxidation of
Anthracene
in the presence of the Fe
ACHTUNGTNERNUNG( III) phthalocyanine complex
A solution of anthracene (6; 0.10–0.15 mmol) in toluene or
3
(Scheme 2). Compared to the oxidation of anthra- dichloromethane (3–5 mL) was mixed with the appropriate
cene (6) the reaction of 2-tert-butylanthracene (8) was catalyst (0.010–0.015 mmol) and the hypervalent iodine oxi-
slower, probably due to steric hindrance caused by dant (6–7.5 equiv. of O), with stirring, at indicated tempera-
ture (see Table 1). Samples of the reaction mixture (50 mL)
the tert-butyl group, with a 100% conversion reached
were collected every 30 min, filtered through 2–3 cm of
only after 20 h at room temperature. The GC analysis
silica gel suspended in a Pasteur pipet, washed with a mix-
ture of ethyl acetate and hexane (2:3 v:v), and analyzed
using GC-MS.
of the reaction mixture indicated the presence of a
single product of oxidation, 2-tert-butylanthraquinone
(
9), along with iodobenzene resulting from the reduc-
tion of reagent 2. 2-tert-Butylanthraquinone (9) was
isolated from the reaction mixture by preparative
column chromatography on silica gel as yellow nee-
dles in 72% yield and identified by comparison with
Catalytic Oxidation of 2-tert-Butylanthracene
A solution of 2-tert-butylanthracene (8; 16 mg, 0.068 mmol)
in toluene (2.5 mL) was mixed with Fe
complex 3 (15 mg, 0.0094 mmol) and reagent 2 (110 mg,
.15 mmol) and was stirred 24 h at room temperature. The
ACHTUNGTRENNUNG( III) phthalocyanine
[
11]
an authentic sample.
0
In summary, the results of our study show that
IBX-ester 1 and oligomeric iodosylbenzene sulfate 2
are efficient oxygenating agents in the biomimetic cat-
alytic oxidation of aromatic hydrocarbons in the pres-
ence of metal porphyrin or phthalocyanine complexes.
These two reagents can be used as safe and conven-
ient alternative to the potentially explosive iodosyl-
benzene. Reagents 1 and 2 can be conveniently pre-
pared from common precursors and in contrast to the
thermally unstable iodosylbenzene, they can be stored
solvent was removed and the residue was separated by
column chromatography on silica gel (ethyl acetate/hexane,
1
:20) to give 2-tert-butylanthraquinone 9 as yellow needles;
[11]
yield:13 mg (72%); mp 101–102.58C (Lit. mp 103–1048C).
Acknowledgements
This work was supported by a research grant from the Na-
for extended periods at room temperature and are tional Science Foundation (grant CHE-0702734) and Petrole-
not explosive.
um Research Fund, administered by the American Chemical
Society (grant PRF-45510-GB-3).
Experimental Section
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Adv. Synth. Catal. 2009, 351, 733 – 737

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Adv. Synth. Catal. 2009, 351, 733 – 737
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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