Iodine(V)/ruthenium(III)-cocatalyzed oxidations: A highly efficient tandem catalytic system for the oxidation of alcohols and hydrocarbons with oxone

Article abstract of DOI:10.1002/chem.200901953

An extremely mild and efficient tandem catalytic system for the oxidation of alcohols and hydrocarbons based on Ru(III)-catalyzed reoxidation of ArIO to ArIO₂ was reported, by using Oxone as a stoichiometric oxidant. Oxone was added to a mixture of propylbenzene, PhI, and RuCl₃ in acetonitrile and water in five portions over 22 h under stirring at room temperature. The reaction mixture was stirred for an additional 4 h and was monitored by TLC by the disappearance of propylbenzene. Then ethyl acetate and water were added and the mixture was stirred for 5 mm. The organic solution was separated and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, washed with NaCl, and dried over Na₂SO ₄. The oxidation of the other hydrocarbons was performed by using a similar procedure. The use of smaller amounts of Oxone led to incomplete conversion owing to its noticeable decomposition with loss of oxygen gas under reaction conditions.

Full text of DOI:10.1002/chem.200901953

COMMUNICATION
DOI: 10.1002/chem.200901953
Iodine(V)/RutheniumACTHNUTRGNE(NUG III)-Cocatalyzed Oxidations: A Highly Efficient
Tandem Catalytic System for the Oxidation of Alcohols and Hydrocarbons
with Oxone
Mekhman S. Yusubov,*[b] Aleksandra A. Zagulyaeva,[a] and Viktor V. Zhdankin*[a]
Hypervalent iodine compounds have found wide applica-
tion as versatile and environmentally friendly oxidizing re-
agents in synthetic organic chemistry.[1,2] One of the most
impressive recent achievements in the field of organoiodine
chemistry is the development of catalytic systems based on
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
which proceeds relatively slowly even at temperatures
above 708C.[4]
Recently we reported a facile experimental procedure for
the preparation of iodylarenes through the RuCl3-catalyzed
oxidation of iodoarenes with peracetic acid.[5] Further stud-
ies have demonstrated that the use of Oxone as the oxidant
instead of peracetic acid leads to even milder reaction con-
ditions. In a typical procedure, treatment of iodobenzene
with Oxone in aqueous acetonitrile at room temperature in
the presence of RuCl3 (0.16 mol%) results in the formation
of iodylbenzene, which can be isolated from the reaction
mixture in a 59% preparative yield (Scheme 2).
hypervalent iodine.[2–4] In particular, the iodine(I)/iodine
ACTHNUTRGNE(NUG III)
catalytic cycle based on the oxidation of ArI in situ by using
peracids has been utilized for the a functionalization of car-
bonyl compounds,[3a–d] the oxidative cleavage of alkenes and
alkynes,[3e] the TEMPO-mediated oxidation of benzylic alco-
hols (TEMPO=2,2,6,6-tetramethylpiperidine-1-oxyl),[3f] as
well as for various intramolecular cyclizations.[3 gÀn] Like-
wise, the iodine(V)-based catalytic cycles that employ
Oxone as a stoichiometric oxidant have been used for the
oxidation of alcohols,[4a–c] the oxidation of p-alkoxyphenols
to quinones,[4d] and the oxidation of benzylic C H bonds
À
(Scheme 1).[4e] However, the synthetic value of the io-
Scheme 2. RuCl3-catalyzed preparation of iodylbenzene.
Taking into account that the RuACTHNUGRTNEUNG(III)-catalyzed oxidation
of alcohols usually occurs only at temperatures above
808C,[6] whereas iodylarenes are effective oxidants at room
temperature,[1f,h] we investigated the oxidation of alcohols by
using an ArI/RuCl3 tandem catalytic system. The reaction
was optimized by using 1-phenylethanol (1) as a model sub-
strate (Table 1). As expected, in the absence of PhI and in
the presence of RuCl3 (0.16 mol%), or in the presence of
PhI without RuCl3, the oxidation of substrate 1 at room
temperature proceeded very slowly (Table 1, entries 1 and
2). The combined application of PhI and RuCl3 resulted in
almost instantaneous oxidation of 1 to acetophenone (2)
with a 100% conversion reached in less than 20 min
(Table 1, entry 3). The optimized reaction required at least
1 molequiv of Oxone (2 equiv of active oxygen); the use of
smaller amounts of Oxone led to incomplete conversion
owing to its noticeable decomposition with loss of oxygen
gas under reaction conditions (Table 1, entry 4). Several
Scheme 1. Iodine(V)-catalyzed oxidations by using Oxone.[4]
[a] A. A. Zagulyaeva, Prof. Dr. V. V. Zhdankin
Department of Chemistry and Biochemistry
University of Minnesota Duluth
Duluth, MN 55812 (USA)
Fax : (+1)218-726-7394
E-mail: vzhdanki@d.umn.edu
[b] Prof. Dr. M. S. Yusubov
Department of Chemistry
Siberian State Medical University and
Tomsk Polytechnic University, 634050 Tomsk (Russia)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200901953.
Chem. Eur. J. 2009, 15, 11091 – 11094
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11091

Table 1. Effect of ArI and RuCl3 on the oxidation of 1-phenylethanol to
acetophenone with Oxone.[a]
Table 2. PhI/RuCl3-cocatalyzed oxidation of alcohols.[a]
Entry Alcohol 3
Oxone [molequiv] T [h] Yield of 4 [%][b]
Entry ArI
Oxone [molequiv] T [h] Conversion [%][b]
1
2
3
4
5
6
7
8
none
1.5
1.0
1.0
0.67
1.25
1.15
0.3
1.0
0.3
1.0
0.3
0.3
0.6
1.0
12[c]
0
100
83
100
100
100
99
1
1.2
1.2
0.3
10
100
96
PhI[d]
PhI
PhI
2
3
2-IC6H4SO3H
4-IC6H4SO3H
4-IC6H4SO3Na 1.25
3-IC6H4CO2H 1.22
2.0
7
100
[a] All reactions were performed at room temperature by using 1-phenyl-
ethanol (0.1 mmol), RuCl3 (0.16 mol%), and ArI (5 mol%) in MeCN/
H2O (1:1 v/v) unless otherwise noted. [b] The conversion was determined
by GC analysis. [c] Also contains styrene (8%) and unreacted alcohol
(80%). [d] No RuCl3 added.
4
5
1.0
1.2
2
92
0.8
100
other iodoarenes tested in this reaction showed high catalyt-
ic activity that was comparable to PhI (Table 1, entries 5–8).
A variety of alcohols 3 were smoothly oxidized under op-
timized reaction conditions to afford the respective oxida-
tion products 4 in excellent isolated yields at room tempera-
ture (Table 2). Similar to the high-temperature ArI/Oxone
procedure,[4a] our protocol afforded ketones from the secon-
dary alcohols (Table 2, entries 1–9) and mainly carboxylic
acids from primary alcohols (Table 2, entries 10 and 11).
Shorter reaction times, however, allowed the oxidation of
benzyl alcohol predominantly to benzaldehyde (Table 2,
entry 12). The use of smaller quantities of Oxone and de-
creasing the reaction time in the oxidation of other primary
alcohols (Table 2, entries 10 and 11) also led to the predomi-
nant formation of aldehydes.
6
1.0
0.5
100
100
7
8
1.05
1.0
0.5
0.8
99
9
1.0
2.4
0.8
4
100
À
Selective oxidation of activated and unactivated C H
10
96[c]
bonds is of particular interest for organic chemists. The pen-
tavalent iodine reagent, IBX, has been demonstrated to be a
[7]
11
12
1.1
16
100[d]
80[e]
À
reagent of choice for the oxidation of benzylic C H bonds.
À
Recently, the oxidation of benzylic C H bonds has been
1.25
1.5
performed under catalytic conditions by the IBX formed in
[a] All reactions were performed at room temperature by using alcohol
(1 mmol), RuCl3 (0.16 mol%), and PhI (5 mol%) in MeCN/H2O
AHCTUNGTRENNUNG
situ by using Oxone as a terminal oxidant at 70–808C for 8–
48 h.[4e] We investigated the oxidation of C H bonds by
À
using the ArI/RuCl3 tandem catalytic system. The reaction
was optimized by using ethylbenzene (5) as a model sub-
strate (Table 3). As expected, in the absence of PhI and in
the presence of RuCl3, or in the presence of PhI and in the
absence of RuCl3 the oxidation of substrate 5 at room tem-
perature did not occur or proceeded very slowly (Table 3,
entries 1, 2, and 11). The combined application of PhI and
RuCl3 resulted in a 27% conversion of 5 to 2 (Table 3,
entry 3). The optimized reaction conditions that led to 80%
conversion of substrate 5 to product 2 required the addition
of 4.2 molequiv of Oxone in small portions over 11 h and
the use of PhI (10 mol%; Table 3, entry 12). Out of several
other iodoarenes tested in this reaction, 2-iodosulfonic acid
and 2-iodobenzoic acid showed slightly better catalytic ef-
CTHUNGTRENNUNG
[e] Isolated yield of 2,4-dinitrophenylhydrazone of benzaldehyde.
fects than iodobenzene (Table 3, entries 4–9), however, a
AHCTUNGTRENNUNG
under optimized catalytic conditions are summarized in
Table 4. In general, moderate to high isolated yields of aro-
matic ketones were obtained in these oxidations under very
mild reaction conditions (Table 4, entries 1–6). Compared
with the high-temperature IBX/Oxone procedure,[4e] our
protocol was much more selective and generally did not
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Chem. Eur. J. 2009, 15, 11091 – 11094

Oxidation of Alcohols and Hydrocarbons with Oxone
COMMUNICATION
Table 3. Effect of ArI and RuCl3 on the oxidation of 5 with Oxone.[a]
Table 4. PhI/RuCl3-cocatalyzed oxidation of hydrocarbons.[a]
Entry Substrate Oxone Products
[molequiv] [h]
T
Yield
[%][b]
1
6.1[c]
26
80
77
Entry ArI
Oxone [molequiv] T [h] Products (yield [%])[b]
1
2
3
4
5
6
7
8
none
1.05
1.05
1.05
3.3 1 (1), 2 (8)
PhI[c]
PhI
24
1 (0), 2 (0)
3.3 1 (0.5), 2 (27)
3.3 1 (1), 2 (31)
3.3 1 (0.5), 2 (17)
3.3 1 (1), 2 (30)
3.3 1 (0), 2 (18)
3.3 1 (0), 2 (13)
3.3 1 (0), 2 (21)
4.0 1 (0), 2 (50)
4.0 1 (0), 2 (14)
11.5 1 (0), 2 (80)
2-IC6H4SO3H 1.05
4-IC6H4SO3H 1.05
2-IC6H4CO2H 1.05
3-IC6H4CO2H 1.03
4-IC6H4CF3
4-IC6H4Br
PhI
2
2.06
3
1.05
1.05
11
9
10
11
12
2.10[d]
2.10[d]
4.2[f]
none
PhI[e]
[a] All reactions were performed at room temperature by using
5
3
4
5
1.2
6
1
1
23
95
69
(0.1 mmol), ArI (5 mol%), and of RuCl3 (0.16 mol%) in MeCN/H2O
(1:1 v/v) unless otherwise noted. [b] Product yields were determined by
GC analysis. Unreacted 5 was also present in all entries. [c] No RuCl3
added. [d] Oxone (1.05 molequiv) was initially added and the second
portion (1.05 molequiv) was added after 2 h. [e] PhI (10 mol%) was
used. [f] Oxone (0.9 molequiv) was initially added, the second portion
(1.1 mol equiv) was added after 2 h, the third portion (1.1 molequiv) was
added 4 h later, and the final portion (1.1 molequiv) was added 3 h later.
2.0[c,d]
1.2[d]
À
afford products of C C bond cleavage and carboxylic acids.
6
7
8.2[d]
2.5[d]
20
8
72
À
The oxidation of an unactivated C H bond in adamantane
under these conditions proceeded with a low conversion, af-
fording 1-adamantanol in only 1.5% yield (Table 4, entry 7).
A plausible, simplified mechanism for these catalytic oxi-
dations is shown in Scheme 3, which includes two catalytic
1.5[e]
[a] All reactions were performed at room temperature by using a hydro-
carbon (1.0 mmol), RuCl3 (0.16 mol%), and PhI (5 mol%) in MeCN/
H2O (1:1 v/v) unless otherwise noted. [b] Yields of isolated products are
shown. Unreacted hydrocarbons were also present in all entries.
[c] Oxone was added in small portions during the indicated time period.
[d] PhI (10 mol%) was used. [e] The yield of 1-adamantanol was deter-
mined by GC analysis.
Scheme 3. Tandem catalytic system for the oxidation of organic substrates
with Oxone.
tion-metal complex to the iodine atom of the starting
AHCTUNGTREGiNNNU odoarene, has previously been observed in the reaction of
redox cycles. The reaction starts with the initial oxidation of
oxoiron(IV) porphyrin and iodobenzene.[9]
ArI to ArIO and then to ArIO2 by the Oxone/Ru
(III,V)
In summary, we have reported an extremely mild and effi-
cient tandem catalytic system for the oxidation of alcohols
and hydrocarbons based on a RuACTHNUTRGENUGN(III)-catalyzed reoxidation
of ArIO to ArIO2 by using Oxone as a stoichiometric oxi-
dant. Owing to the mild reaction conditions, our protocol is
highly selective and generally does not afford products of
system as inferred from Schemes 1 and 2. The in situ gener-
ated, highly active monomeric ArIO2 species are responsible
for the actual oxidation of organic substrates by known
mechanisms.[7a] We propose that the intermediate oxoruthe-
nium complexes are responsible for the reoxidation of the
initially formed ArIO to ArIO2 (Scheme 3). Experimental
evidence towards catalytic oxidation of PhIO to PhIO2
mediated by the oxoruthenium species has previously been
documented,[8a] and the generation and identification of
highly reactive ruthenium(V)-oxo species was reported in
the literature.[8b–d] The initiation step of this catalytic mecha-
nism, that is, an oxygen atom transfer from an oxo transi-
À
C C bond cleavage.
Experimental Section
Typical procedure of the PhI/RuCl3-cocatalyzed oxidation of propylben-
zene: Oxone (3.74 g; 6.1 mmol) was added to a mixture of propylbenzene
Chem. Eur. J. 2009, 15, 11091 – 11094
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
11093

V. V. Zhdankin, M. S. Yusubov et al.
(120 mg, 1 mmol), PhI (0.5 mL of a 0.1m solution in MeCN, 0.05 mmol, 5
mol%), and RuCl3 (10 mL of 0.16m solution in water, 0.0016 mmol, 0.16
mol%) in acetonitrile (3 mL) and water (3 mL) in five portions over 22 h
under stirring at room temperature. The reaction mixture was stirred for
an additional 4 h (the reaction was monitored by TLC by the disappear-
ance of propylbenzene). Then ethyl acetate (15 mL) and water (20 mL)
were added and the mixture was stirred for 5 min. The organic solution
was separated and the aqueous phase was extracted with ethyl acetate
(2ꢁ15 mL). The organic phases were combined, washed with NaCl (satu-
rated solution, 20 mL), and dried over Na2SO4 (anhydrous). Removal of
the solvent under vacuum afforded propiophenone (107 mg, 80%). The
oxidation of the other hydrocarbons (Table 4) was performed by using a
similar procedure.
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Acknowledgements
This work was supported by a research grant from the National Science
Foundation (CHE-0702734).
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Keywords: catalysis · hypervalent compounds · oxidation ·
Oxone · ruthenium
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Received: July 15, 2009
Published online: September 16, 2009
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Chem. Eur. J. 2009, 15, 11091 – 11094