Benzyltributylammonium periodate as a novel and safe oxygen source for Mn-porphyrin catalyzed practical and highly selective oxygenation of hydrocarbons

Article abstract of DOI:10.1016/j.poly.2011.06.025

Benzyltributylammonium periodate (BzBu₃NIO₄) was prepared easily in high yield in neat water. The compound crystallized with two cations and two anions per asymmetric unit and a space group of Pna2₁ was determined by single-crystal X-ray diffraction. It was used practically in the clean and selective epoxidation of olefins and oxygenation of saturated hydrocarbons catalyzed by manganese (III) porphyrins in water/ethanol as a green media. The catalyst could be reused without noticeable loss of activity, and the oxidant's by-product (BzBu₃NIO₃) could also be reused. The efficiency of the oxidation system depends critically upon the steric hindrances and electronic structures of both the nitrogen donors and Mn-catalysts. Some evidences suggest the involvement of a high valent Mn-oxo species as well as a six-coordinate [(L)(Por)Mn-OIO₃] complex in the oxidation reactions.

Full text of DOI:10.1016/j.poly.2011.06.025

Polyhedron 30 (2011) 2303–2309
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Benzyltributylammonium periodate as a novel and safe oxygen source
for Mn-porphyrin catalyzed practical and highly selective oxygenation
of hydrocarbons
a,
a
Abdolreza Rezaeifard a, , Maasoumeh Jafarpour , Hossein Kavousi ,
⇑
⇑
Mahboubeh Alipour a, Helen Stoeckli-Evans b
a Catalysis Research Laboratory, Department of Chemistry, Faculty of Science, University of Birjand, Birjand 97179-414, Iran
b Institute of Physics, University of Neuchâtel, Rue Emile-Argand 11, CH-2009 Neuchâtel, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
Benzyltributylammonium periodate (BzBu3NIO4) was prepared easily in high yield in neat water. The
compound crystallized with two cations and two anions per asymmetric unit and a space group of
Pna21 was determined by single-crystal X-ray diffraction. It was used practically in the clean and selec-
tive epoxidation of olefins and oxygenation of saturated hydrocarbons catalyzed by manganese (III) por-
phyrins in water/ethanol as a green media. The catalyst could be reused without noticeable loss of
activity, and the oxidant’s by-product (BzBu3NIO3) could also be reused. The efficiency of the oxidation
system depends critically upon the steric hindrances and electronic structures of both the nitrogen
donors and Mn-catalysts. Some evidences suggest the involvement of a high valent Mn-oxo species as
well as a six-coordinate [(L)(Por)Mn–OIO3] complex in the oxidation reactions.
Received 17 April 2011
Accepted 15 June 2011
Available online 1 July 2011
Keywords:
Porphyrins
Periodate
Oxygenation
Epoxidation
Catalyst
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
solvents, in particularly aqueous media [10–12]. Additionally, the
accessibility of the oxidant in terms of their price and availability
The development of selective hydrocarbon oxidation, which is
of fundamental importance in both nature and organic synthesis,
is a goal that has long been pursued [1,2]. Metalloporphyrins mim-
icking cytochrome P-450 monooxygenase enzymes have been
vastly employed for this invaluable transformation, using a variety
of oxygen donors during the past decades [3,4].
Periodates have drawn considerable attention as mild and effi-
cient single oxygen donors for Mn-porphyrin, and salens catalyzed
various oxidation reactions in recent decades [5–9]. Nevertheless,
the extensive use of toxic and volatile organic solvents in many
oxidation systems, including periodates [5–9], mediated by metal-
loporphyrins has reduced considerably the importance of biologi-
cally inspired oxidation catalysis [3]. Furthermore, during recent
years, increasingly demanding legislation as well as public and
economic pressure has led to increased interest in new, ‘‘clean’’
methods for the production of chemical compounds. Discarding of
harmful organic solvents is the major problem in chemical indus-
tries, which accounts for around 80% of their wastes. Thus, a new
challenge is to make such processes cleaner by using non-toxic
at a large scale alongside the stability of the catalyst under oxidiz-
ing conditions, providing recycling of the reaction, play important
roles for economical viability of the processes [10].
In continuation of our ongoing research on the development of
new biomimetic methods for the oxidation of organic compounds
[13–22], we explored that benzyltributylammonium periodate
(BzBu3NIO4), which is synthesized easily in high yield in water
without recourse to any organic solvents for isolation, is a safe
and efficient oxygen source for the clean and selective epoxidation
of olefins and oxygenation of saturated hydrocarbons to the related
alcohols and ketones, catalyzed by Mn(TPP)OAc in H2O/EtOH as a
sustainable media (Scheme 1). Moreover, the catalyst could be re-
used without noticeable loss of activity. We also report the crystal
structure of this novel oxidant, as determined by single-crystal X-
ray diffraction.
2. Experimental
2.1. General remarks
All chemicals were purchased from Merck or Fluka. The free
base porphyrins: TPPH2 [23], T(4-OMeP)PH2 [23], T(4-NO2P)PH2
[24], TMPH2 [25] and TDCPPH2 [25] were prepared and purified
⇑
Corresponding authors. Tel.: +98 0561 2502516; fax: +98 0561 2502515.
E-mail
addresses:
rrezaeifard@birjand.ac.ir,
rrezaeifard@gmail.com
(A. Rezaeifard), mjafarpour@birjand.ac.ir (M. Jafarpour).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.06.025

2304
A. Rezaeifard et al. / Polyhedron 30 (2011) 2303–2309
chromatography eluting with n-hexane/ethyl acetate (10/2). Then,
the aqueous phase was centrifuged and the solid catalyst was sep-
arated, dried under air and reused for a similar reaction [22].
N
N
N
Mn
O
N
2.5. Crystallographic data collection and structure refinement
Suitable X-ray quality crystals of BzBu3NIO4 were obtained as
colorless plates by slow evaporation of solvent from a 1:2 metha-
nol/acetonitrile solution of the compound at room temperature.
The intensity data were collected at 173 K with a Stoe Image Plate
BzBu3NIO4,
Water/EtOH,
60oC
R
R
R
Diffraction System [27] using Mo K
radiation. The image plate distance was 70 mm,
0–200°, step = 1.0°, exposures of 3 min, 2h range 3.27–52.1°,
a
graphite monochromated
OH
O
+
x
oscillation scans
D
x
R'
R'
R'
dmin–dmax = 12.45–0.81 Å. The structure was solved by direct
methods using SHELXS-97 [28]. The refinement and all further calcu-
lations were carried out using SHELXL-97 [28]. The H atoms were in-
cluded in calculated positions and treated as riding atoms using
SHELXL default parameters. The non-H atoms were refined aniso-
Scheme 1. Oxygenation of hydrocarbons with BzBu3NIO4 catalyzed by Mn-
porphyrins in H2O/EtOH.
tropically, using weighted full-matrix least-squares on F2.
A
by the methods reported previously. The Mn(Por)OAc complexes
were obtained using Mn(OAc)2Á4H2O, according to the procedure
of Adler et al. [26].
semi-empirical absorption correction was applied using the MUL-
scanABS routine in PLATON [29]. The compound crystallized in the
non-centrosymmetric orthorhombic space group Pna21, with two
cations and two anions per asymmetric unit (Z = 8). The structure
was refined as an inversion twin and gave as the final refined Flack
parameter, or BASF, a value of 0.11(3). Two of the alkyl chains are
disordered; they were refined with restraints on the C–C bond dis-
tances, given as values close to those found in the non-disordered
alkyl chains, with large standard uncertainties and with PARTs.
Their occupancies were also refined. Data collection and refine-
ment processes are summarized in Table 1.
2.2. Instrumentation
Purity determinations of the products were accomplished by GC
on a Shimadzu GC-16A instrument equipped with a 25 m CBP1-
S25 (0.32 mm ID, 0.5 lm coating) capillary column and a flame
ionization detector. IR spectra were recorded on a Perkin Elmer
780 instrument. UV–vis spectra were recorded on a 160 Shimadzu
spectrophotometer. NMR spectra were recorded in CDCl3 solutions
with a Brucker Avance DPX FT-NMR 250 MHz instrument. The
residual CHCl3 in conventional 99.8 atom% CDCl3 gives a signal at
d = 7.26 ppm, which was used for calibration of the chemical shift
Table 1
Crystal data and structure refinement for BzBu3NIO4.
scale. Mass spectra were recorded on
QP5050A.
a Shimadzu GC–MS-
Compound (BzBu3NIO4)
Empirical formula
Formula weight
T (K)
C19H34NIO4
467.37
173
2.3. Synthesis of benzyltributylammonium periodate
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
0.71073
orthorhombic
Pna21
Benzyltributylammonium periodate was prepared by addition
of an aqueous solution of benzyltributylammonium chloride
(10 mmol, 3.12 g in 30 mL distilled water) to a solution of NaIO4
(10 mmol, 2.14 g) in distilled water (50 mL), followed by simple fil-
tration. The white solid was eluted by distilled water and dried un-
der air. A solid colorless powder was obtained in 90% yield (4.2 g).
16.5662(10)
10.0028(6)
25.5308(17)
90.00
90.00
90.00
4230.7(5)
8
1.468
1.535
1920
0.19 Â 0.30 Â 0.38
2.19–26.04
À20 ꢀ h ꢀ 20
À12 ꢀ k ꢀ 12
À31 ꢀ l ꢀ 31
32,084
8300 [Rint = 0.044]
Nnnn [I > 2r (I)]
multi-scan
b (Å)
c (Å)
a
(°)
b (°)
M.p. 106.6 °C, IR (KBr) 2956, 2865, 1474, 1372, 839, 725 cmÀ1 1H
;
c
(°)
V (Å3)
NMR (250 MHz, CDCl3, 25 °C) dppm: 0.87 (t, J = 7.25 Hz 9H, alkyl
protons), 1.23 (m, 6H, alkyl protons), 1.66 (m, 6H, alkyl protons),
3.01 (t, J = 8 Hz, 6H, alkyl protons), 4.33 (s, 2H, benzyl protons),
7.29–7.36 (m, 5H, aromatic protons); 13C NMR (63 MHz, CDCl3,
25 °C) dppm: 13.56, 19.55, 24.02, 58.25, 62.37, 126.62, 129.48,
130.95, 132.15. Anal. Calc. for C19H34INO4 (467): C, 48.83; H,
7.33; N, 3.0. Found: C, 48.80; H, 7.35; N, 3.00%.
Z
Dcalc (Mg/m3)
Absorption coefficient (mmÀ1
F(0 0 0)
)
Crystal size (mm3)
h range for data collection (°)
Index ranges
2.4. General oxidation procedure and recycling
Reflections collected
Independent reflections
Observed reflections
Absorption correction
Maximum and minimum transmission
Refinement method
To a mixture of olefin (1 mmol), Mn(por)OAc (0.01 mmol) and
nitrogen donors (0.1 mmol) in H2O/EtOH (2 mL/3 mL) was added
BzBu3NIO4 (2 mmol, 0.93 g). The reaction mixture was stirred at
60 °C for the appropriate reaction time, which was monitored by
GC. After completion of the reaction, ethanol was removed from
the mixture and then petroleum ether (3 Â 2 mL) was added to
the aqueous phase and cooled. The BzBu3NIO3 from the oxidant
was precipitated and removed by filtration. The organic phase con-
taining product was separated and evaporated. If the conversion
was not complete, further purification was achieved by silica
1.000 and 0.9049
full-matrix least-squares on F2
8300/25/453
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
0.924
Final R indices [I > 2
R indices (all data)
Flack parameter
r
(I)]
6079 (R1a = 0.0399, wR2b = 0.0953)
R1a = 0.0586, wR2b = 0.1031
0.11(3)
P
P
a
R1
=
||Fo| À |Fc||/ |Fo|.
P
P
w[(Fo2 À F2c )2/ w[(F2c 2)2]]1/2
.
b
wR2
=

A. Rezaeifard et al. / Polyhedron 30 (2011) 2303–2309
2305
make it potentially useful for oxidation reactions and therefore an
expedient substitute for n-Bu4NIO4. However, the reaction media
should be sustainable for practical goals requiring scale-up proce-
dures. Accordingly, we tried to carry out our oxidation method in a
clean media. Initially, water and ethanol as neat solvents have been
3. Results and discussion
3.1. Properties and structural discussion of BzBu3NIO4
BzBu3NIO4 was prepared immediately by mixing aqueous solu-
tions of NaIO4 and BzBu3NCl at room temperature in 90% yield,
without recourse to any organic solvents for isolation. When we
carried out this procedure by using n-tetrabutylammonium
hydrogensulfate or bromide in place of BzBu3NCl, the yield of the
precipitated product (n-Bu4NIO4) was only 40–43%. The solubility
properties of BzBu3NCl in some traditional solvents were first
investigated. It is completely soluble in methanol, ethanol, acetone,
dichloromethane, chloroform, acetonitrile, nitromethane, tetrahy-
drofuran, N,N-dimethylformamide and dimethylsulfoxide. Other
solvents such as ethylacetate, benzene, CCl4, n-hexane, toluene,
ether and water are not able to dissolve BzBu3NIO4.
The compound was characterized by elemental analysis, IR,
NMR and single-crystal X-ray diffraction. The ORTEP plot of BzBu3-
NIO4 is given in Fig. 1. The compound crystallized with two cations
and two anions per asymmetric unit (Z = 8) and a space group of
Pna21 was determined by single-crystal X-ray diffraction. Two of
the alkyl chains are disordered. The O–I–O angles are 105.9–
111.9° and the I–O distances are 1.693–1.764 Å. The C–N–C angles
are 106.2–111.5° and the N–C distances are 1.508–1.538 Å for the
alkyl chains and 1.540–1.543 Å for the benzyl groups.
examined as green media for the oxidation of
a-methylstyrene,
which led to the isolation of the starting olefin at room tempera-
ture (Table 2, entries 1 and 2). Nevertheless, the reaction was trig-
gered by using a mixture of H2O/EtOH at room temperature (entry
3) and a quantitative yield of epoxide product was obtained with a
2:3 ratio of H2O/EtOH within 2.5 h under these conditions (entry
5). It was observed that the reaction proceeded most rapidly and
gave the optimal yield of epoxide (92%/5 min) at 60 °C (entry 8).
Our results also showed that for complete conversion of the start-
ing olefin in the desired time, a 2:1 M ratio of oxidant to substrate
(Fig. 2) and 1 mol% of the catalyst are sufficient (Fig. 3). It is worthy
to mention that under these conditions a poorer oxidation activity
was observed for NaIO4 and n-Bu4NIO4 than that of BzBu3NIO4
(Fig. 4).
3.3. Co-catalytic effect of the nitrogen donors
The efficient catalytic epoxidation, which takes place only when
both catalyst and nitrogen base are present, may be taken as an
indication of that a nitrogen donor coordinates to the manganese
center and makes it prone to oxidation by the periodate [30]. Ini-
tially we investigated the effect of the co-catalyst concentration
3.2. Oxidation activity of BzBu3NIO4
on the oxidation of
Im/Mn(TPP)OAc molar ratio up to 10:1 improved the yield of epox-
ide. However a further increase in this ratio led to a decrease in the
a-methylstyrene (Fig. 5). An increase in the
To evaluate the oxidation activity of BzBu3NIO4, blank experi-
ments were performed using
a-methylstyrene as a model sub-
strate. In the absence of Mn(TPP)OAc as a catalyst and also
imidazole (Im) as a co-catalyst in different organic solvents, no oxi-
dation of the substrate was observed, indicating the use of both
catalyst and co-catalyst are essential. The addition of BzBu3NIO4
(2 mmol) to the solution of Mn(TPP)OAc (0.01 mmol) in CH2Cl2
Table 2
The effect of the H2O/EtOH ratio and temperature on the epoxidation of
a-
methylstyrene with BzBu3NIO4 catalyzed by Mn(TPP)OAc in the presence of Im.a
containing Im (0.1 mmol) and a-methylstyrene (1 mmol) afforded
Entry
Solvent
Temperature (°C)
Epoxide yield %b (time/min)
to the related epoxide in 87% yield after 5 h at room temperature.
Also, the full conversion of cyclooctene was observed using this
catalytic system. A comparison of these results with those obtained
using n-Bu4NIO4 as an oxidant under the same conditions indicates
the same oxidation activity of both oxidants under the catalytic
influence of Mn(TPP)OAc [8]. Nevertheless, the high yielding and
safe procedure for the preparation of BzBu3NIO4 by using BzBu3NCl
as a cheap compound with respect to n-tetrabutylammonium salts
1
2
3
4
5
6
7
8
H2O
EtOH
25
25
25
60
25
40
50
60
–
–
4.5 (300)
7 (300)
76(180)
100(30)
100(150)
25(15)
H2O/EtOH (1:1)
H2O/EtOH (1:1)
H2O/EtOH (2:3)
H2O/EtOH (2:3)
H2O/EtOH (2:3)
H2O/EtOH (2:3)
30(60)
75(5)
45(60)
20(5)
40(5)
92(5)
81(15)
100(15)
a
The reactions were run under air with the molar ratio of 100:200:10:1 for
a-
methylstyrene:BzBu3NIO4:Im:Mn(TPP)OAc.
b
GC yield based on the starting olefin.
5 min
15 min
100
80
60
40
20
0
100
92
88
84
85
63
30
28
1
1.5
2
2.5
Oxidant/Olefin Molar Ratio
Fig. 1. The molecular structure of BzBu3NIO4, with the atomic numbering and
displacement ellipsoids drawn at the 50% probability level. (The disordered parts of
the alkyl chains are drawn with dashed lines.)
Fig. 2. The effect of various oxidant/olefin molar ratios on the epoxidation of
styrene by BzBu3NIO4 in H2O/EtOH (2:3) at 60 °C after 5 min.
a-Me-

2306
A. Rezaeifard et al. / Polyhedron 30 (2011) 2303–2309
Table 3
100
100
100
100
80
60
40
20
0
The effect of different axial ligands on the epoxidation of
a-methylstyrene with
BzBu3NIO4 catalyzed by Mn(TPP)OAc in H2O/EtOH.a
Entry
Axial ligand
pKa
Epoxide yield (%)b
5 min
15 min
58
1
2
3
4
5
6
7
8
9
Im
BzIm
6.953
5.53
6.95
5.25
5.99
1.86
11.12
10.75
–
92
45
20
45
39
15
14
25
0
100
76
32
65
45
25
25
38
0
45
1-MeIm
Py
4-t-BuPy
4-CNPy
Piperidine
Et3N
None
0.25
5
0.5
1
3
ImH, imidazole; 1-MeIm, 1-methylimidazole; BzImH, benzimidazole; Py, pyridine;
4-t-BuPy, 4-tert-butylpyridine; 4-CNPy, 4-cyanopyridine; Et3N, triethylamine.
Mol% Catalyst
a
The reactions were run under air at 60 °C with a molar ratio of 100:200:10:1 for
Fig. 3. The effect of the catalyst concentration on the epoxidation of
rene with BzBu3NIO4 in H2O/EtOH (2:3) at 60 °C after 5 min.
a-methylsty-
a
-methylstyrene:BzBu3NIO4:Im:Mn(TPP)OAc.
GC yield.
b
Table 3. The general order of the co-catalytic activities of the vari-
ous classes of nitrogen donors was amines < pyridines < imida-
zoles. Nevertheless, a significant decrease in conversion rates in
combination with bulky BzIm and 4-t-BuPy indicate that the steric
effects are quite pronounced. The sluggish co-catalytic activity of
1-MeIm, lacking the N–HÁ Á ÁB (B = nitrogen donor or anionic spe-
cies) hydrogen bonding, and also the weak base 4-CNPy (pKa =
1.86), containing an electron-withdrawing CN group, demonstrate
the crucial importance of electronic factors upon their donor
abilities toward the Mn-por catalyst [21,30]. The much lower co-
100
100
80
72
45
60
40
20
0
80
25
5
60ºC (15 min)
25ºC (120 min)
catalytic activity of pure
r-donor amines (entries 7 and 8) than
those of the N–H imidazoles clearly confirm that the
p-donation
of the axial base is considerably dominant in the present catalytic
system.
3.4. Catalytic epoxidation and hydroxylation reactions
Oxidant
To establish the general applicability of the method, various ole-
fins were subjected to the oxidation protocol using BzBu3NIO4 un-
der the catalytic influence of Mn(TPP)OAc at 60 °C (Table 4). As
summarized in Table 4, different olefins were generally excellent
substrates for this catalyst. It led to high/excellent conversion of
cyclohexenes, cyclooctene and norbornene, with the formation of
the corresponding epoxides as the sole products (entries 1–4).
The conversion and selectivity of indene was 100% (entry 5). The
epoxidation of 1-octene as a less reactive terminal olefin proceeded
with moderate yield (60%) and excellent selectivity (entry 6). It
seems that the efficiency of epoxidation in this catalytic system
is very dependent on the electronic and steric requirements of
the substrate. Electron-donating and electron-withdrawing sub-
stituents on the styrene have a pronounced effect on the rate of
Fig. 4. Comparison of the oxidation activity of NaIO4, n-Bu4NIO4, and BzBu3NIO4 in
the epoxidation of a-methylstyrene catalyzed by Mn(TPP)OAc in H2O/EtOH.
100
80
60
40
20
0
0
oxygenation. The conversion and yield of
a-methylstyrene were
1
10
15
20
50
100%, whereas the epoxidation yield of electron-deficient 3-Cl
and 4-Cl styrenes were 75% and 60%, respectively (entries 6–10).
trans-Stilbene, having great phenyl–phenyl non-bonded interac-
tions, oxidized slowly (54%) with the catalyst, with absolute ste-
reospecificity (entry 12). Nevertheless, a quantitative conversion
occurred for cis-stilbene with the formation of a mixture of cis-
(83%) and trans-stilbene oxide (12%) with the same period (entry
11). Formation of trans-stilbene oxide in the oxidation of cis-
stilbene suggests competition between closure of the epoxide ring
and rotation around the C–C bond during the oxygen transfer step
from the active oxidizing species to the olefin [31].
Im/Mn(TPP)OAc Molar Ratio
Fig. 5. The effect of various Im/Mn(TPP)OAC molar ratios on the epoxidation of
-methylstyrene by BzBu3NIO4 in H2O/EtOH (2:3) at 60 °C after 5 min.
a
olefin conversion, confirming the formation of catalytically inac-
tive six coordinate species, i.e., Mn(TPP)(Im)2 [21,30].
It was also found that the efficiency of the reaction was dramat-
ically dependent upon the nature of the co-catalyst (Table 3). The
results for the Mn(TPP)OAc catalyzed oxidation of
using BzBu3NIO4 in association with three classes of nitrogen do-
nors as co-catalysts, including the strong pure -donor amines
(pKa = 10.75–11.12), the strong -donor imidazoles (pKa = 5.53–
7.86) and weak -donor pyridines (pKa = 1.86–6.65), are given in
a-methylstyrene
When we applied the present catalytic system to the oxygena-
tion of C–H bonds, a mixture of alcohols and ketones with com-
bined yields of 21–84% and excellent selectivities in desired
times (20 min) were obtained (Table 5).
r
p
p

A. Rezaeifard et al. / Polyhedron 30 (2011) 2303–2309
2307
Table 4
Epoxidation of different olefins with BzBu3NIO4 catalyzed by Mn(TPP)OAc in the presence of Im in H2O/EtOH.a
Entry
Alkene
Conversion %b (isolated yield %)c
Product
Selectivity %b
1
100
100
100
O
O
2
3
100
98 (90)
97 (89)
100
100
O
4
O
100 (92)
100
O
5
6
60
100
100
O
O
100 (90)
7
8
93 (85)d
100
O
63
O
9
100
100
Cl
Cl
O
10
75 (64)d
Cl
Cl
95e
O
11
12
Ph
Ph
Ph
87e
Ph
Ph
Ph
13e
Ph
O
O
Ph
54e
100e
Ph
Ph
a
b
c
The reactions were run under air at 60 °C with a molar ratio of 100:200:10:1 for Olefin:BzBu3NIO4:Im:Mn(TPP)OAc.
GC yields based on the starting olefins. All products were identified by authentic samples [19,22].
Yields of isolated products after evaporation of petroleum ether.
d
e
Yields of isolated products after plate chromatography.
Determined by 1H NMR.
3.5. Stability and reusability of catalyst
the oxidizing conditions and in the absence of olefin, was followed
by measuring the percentage decrease of the absorbance at 478 nm
(Soret band of Mn(TPP)OAc, referred to the sample taken at zero
time of reaction) (Fig. 6). The slow reduction of the absorption with
time is indicative of the stability of the catalyst in this oxidation
system. It is noteworthy that Mn-por is reasonably stable even in
the absence of any substrate (Fig. 6).
These results encouraged us to evaluate the reusability of the
catalyst. After isolation of the products, the solid catalyst was sep-
arated from the aqueous solution by centrifuging and was reused
for a subsequent reaction under similar reaction conditions. The
catalyst has been observed to be reusable for at least three times.
Moreover, the oxidant’s by-product (BzBu3NIO3) was separated,
which can be reused as a valuable compound. Therefore, from
The high/excellent yields of the oxidation products, especially
in the oxidation of the less reactive substrates such as 1-octene
(Table 1, entry 6) and saturated hydrocarbons (Table 1, entry 9–
12), obtained using this new biomimetic method in desired times
demonstrate the high catalytic activity and relative stability of
the simple Mn(TPP)OAc complex in association with BzBu3NIO4.
More evidences in this matter have been achieved by the impres-
sive turnover numbers obtained in the oxidation of norbornene
(6800) and a-methylstyrene (6200) using a 10,000:20,000:1 M ra-
tio for substrate/BzBu3NIO4/catalyst. This was further supported by
the study of the electronic spectra of the complex in the oxidation
of
a-methylstyrene. The Mn-catalyst decomposition, both under

2308
A. Rezaeifard et al. / Polyhedron 30 (2011) 2303–2309
Table 5
Oxygenation of different hydrocarbons with BzBu3NIO4 catalyzed by Mn(TPP)OAc in
the presence of Im in H2O/EtOH.a
Substrate
Conversion
%
Alcohol
Yield
%
Ketone
Yield
%
b
b
b
OH
OH
O
21
48
14
7
O
23
30
25
36
OH
O
66
84
X
H
Y
H
Z
OH
O
70
14
H
TPP
(65)c
(12)c
T(4-OMeP)P
H
H
H
H
H
H
OMe
NO2
a
The reactions were run under air at 60 °C with a molar ratio of 100:200:10:1 for
substrate:BzBu3NIO4:Im:Mn(TPP)OAc.
T(4-NO2P)P
b
GC yields based on the starting materials. All products were identified by
authentic samples [22].
Me
Cl
Me
H
TMP
c
Yields of isolated products after plate chromatography.
TDCPP
Olefin
Fig. 7. The Mn-porphyrins utilized in this study.
100
present
80
Im
100
100
80
60
40
20
0
95
60
Py
81
Olefin
absent
79
78
40
64
54
20
0
34
30
5
0
5
10
15
20
30
Time/min
T(4-OMePP) TPP
TMP
T(4-NO2PP) TDCPP
Mn-Por
Fig. 6. Change of the percent absorption at 478 nm in the electronic spectra of
Mn(TPP)OAc in the presence of Im and BzBu3NIO4 at 60 °C.
Fig. 8. The effect of the electronic and steric requirements of the porphyrin ligands
on the catalytic activity of the Mn-catalysts in the epoxidation of
with BzBu3NIO4 in the presence of Im and Py.
a-methylstyrene
the stand point of greener chemical processes, the present method
does not lead to the three major sources of waste: toxic organic
solvents, catalysts and harmful by-products. These advantages for
this high yielding oxidation method offer ready scalability. In the
of the Mn-catalyst in the presence of both co-catalysts. When
hindered catalysts such as Mn(TMP)OAc and particularly
Mn(TDCPP)OAc, with a large electrophilicity at the Mn center, were
employed, the steric factors became dominant in the presence of
both co-catalysts. Nevertheless, a more significant steric effect ap-
peared in the presence of Py rather than Im, confirming the
involvement of a bulky and weak electrophilic six coordinate
adduct [(Py)(TPP)Mn–OIO3)] during the reaction under the co-
catalytic effect of Py [21]. On the other hand, the pronounced
catalytic performance of electron-rich porphyrins in the presence
oxidation of
a-methylstyrene as a substrate, in a semi scale-up
procedure (25 mmol), the related epoxide was secured in 93%
yield.
3.6. The electronic and steric effects of the porphyrin ligand
The catalytic activity of different electronic and structural Mn-
porphyrins (Fig. 7) in combination with both Im and Py have been
of strong
p-donor Im is due to the formation of a less hindered
compared in the oxidation of
a-methylstyrene as an electron-
and high valent Mn-oxo species.
deficient olefin with some steric hindrances around the double
bond (Fig. 8). The extent of the catalytic activity of the Mn(Por)s
was found to follow the order: Mn(TDCPP)OAc < Mn[T(4-NO2P)-
P]OAc < Mn(TMP)OAc < Mn(TPP)OAc < Mn[T(4-OMeP)P]OAc. The
lower activity of Mn[T(4-NO2P)P]OAc, containing an electron-
withdrawing –NO2 group, compared to the simple Mn(TPP)OAc
and electron-rich Mn[T(4-OMeP)P]OAc, with very similar steric
environments at their Mn centers, reflects the reducing influence
of the electron-deficient substituent upon the catalytic activity
This was further supported by monitoring the UV–vis spectral
changes by addition of BzBu3NIO4 to a solution of Mn(TMP)OAc
(0.1 mM) in water/EtOH containing Im and Py (10 mM). When Py
was employed as the co-catalyst, the spectrum displayed no
change. In the presence of Im, an intense Soret band, (kmax = 418
nm) appeared after addition of the oxidant (Fig. 9), confirming
the formation of MnTMP(Im)(O) species [32]. Addition of an excess
amount of
a-methylstyrene immediately gave the original Soret

A. Rezaeifard et al. / Polyhedron 30 (2011) 2303–2309
2309
Appendix A. Supplementary data
CCDC 775581 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223 336 033; or e-mail: deposit@ccdc.cam.ac.uk.
References
[1] R.A. Sheldon, J.K. Kochi, Metal-Catalyzed Oxidation of Organic Compounds,
Academic Press, New York, 1981.
[2] M. Hudlicky, Oxidations in Organic Chemistry, ACS, Washington, DC, 1990.
[3] B. Meunier, Biomimetic Oxidation Mediated by Metal Complexes, Imperial
College Press, London, 2000.
[4] K.M. Kadish, K.M. Smith, R. Guilard (Eds.), The porphyrin handbook, in:
Biochemistry and Binding: Activation of Small Molecules, vol. 4, Academic
Press, 2000.
[5] D. Mohajer, S. Tangestaninejad, J. Chem. Soc., Chem. Commun. (1993) 240.
[6] D. Mohajer, S. Tangestaninejad, Tetrahedron Lett. 35 (1994) 945.
[7] V. Mirkhani, M. Moghadam, S. Tangestaninejad, I. Mohammdpoor-Baltork, H.
Kargar, M. di Araghi, Appl. Catal. A: Gen. 323 (2009) 61. and references cited
there.
[8] S. Tangestaninejad, M. Moghadam, V. Mirkhani, I. Mohammadpoor-Baltork,
M.S. Saeedi, Appl. Catal. A: Gen. 381 (2010) 231. and references cited there.
[9] Q.-G. Ren, S.-Y. Chen, X.-T. Zhou, H.-B. Ji, Bioorg. Med. Chem. 18 (2010) 8144.
[10] A. Lubineau, Chem. Ind. (1996) 123.
[11] A. Lubineau, J. Auge, Topics in Current Chemistry, vol. 206, Springer-Verlag,
Berlin, 1999.
[12] B. Cornils, W.A. Hermann, Aqueous Phase Organometallic Chemistry: Concepts
and Applications, Wiley-Interscience, Weinheim, 1998.
[13] D. Mohajer, A. Rezaeifard, Tetrahedron Lett. 43 (2002) 1881.
[14] N. Iranpoor, D. Mohajer, A.-R. Rezaeifard, Tetrahedron Lett. 45 (2004) 3811.
[15] A. Rezaeifard, M. Jafarpour, G. Kardan Moghaddam, F. Amini, Bioorg. Med.
Chem. 15 (2007) 3097.
Fig. 9. The UV–vis spectra of Mn(TPP)OAc (0.1 mM) in the presence of Im (10 mM)
before (kmax = 478 nm) and after (kmax = 418 nm) the addition of BzBu3NIO4
(20 mM) in H2O/EtOH (2:3) at 60 °C.
band (kmax = 478 nm), clearly indicating that the new species
formed after addition of the oxidant is kinetically competent for
performing substrate oxidation. It is worth mentioning that the
spectrum displayed no change when the electron-deficient
Mn[T(4-NO2P)P]OAc and Mn(TDCPP)OAc were used in association
with both the Im and Py.
The scope and synthetic and industrial applications of the oxi-
dation procedure using different catalysts are currently under
investigation.
4. Conclusion
[16] A. Rezaeifard, M. Jafarpour, S. Rayati, R. Shariati, Dyes Pig. 80 (2009) 80.
[17] I. Sheikhshoaie, A. Rezaeifard, N. Monadi, S. Kaafi, Polyhedron 28 (2009) 733.
[18] A. Rezaeifard, I. Sheikhshoaie, N. Monadi, H. Stoeckli-Evans, Eur. J. Inorg. Chem.
(2010) 799.
[19] A. Rezaeifard, I. Sheikhshoaie, N. Monadi, M. Alipour, Polyhedron 29 (2010)
2703.
[20] A. Rezaeifard, M. Jafarpour, M.A. Nasseri, R. Haddad, Helv. Chim. Acta 93 (2010)
711.
[21] A. Rezaeifard, M. Jafarpour, H. Raissi, E. Ghiamati, A. Tootoonchi, Polyhedron
30 (2011) 592.
In conclusion, a biomimetic catalytic method for the selective
epoxidation of olefins and oxygenation of saturated hydrocarbons
to alcohols and ketones using BzBu3NIO4 as a novel and safe oxi-
dant in the presence of the Mn(TPP)OAc/Im system in H2O/EtOH
has been developed. The employment of H2O/EtOH as a ‘green’
media in this high yielding oxidation method as well as the reus-
ability of the catalyst, providing ready scalability, makes it more
attractive for a practical goal. Our findings show that the strong
[22] A. Rezaeifard, M. Jafarpour, A. Naeimi, S. Kaafi, Catal. Commun. 12 (2011) 761.
[23] A.D. Adler, F.R. Longo, J.D. Finarelli, J. Goldmacher, J. Assour, L. Korsakoff, J. Org.
Chem. 32 (1967) 476.
p-donating N–H imidazoles demonstrate higher co-catalytic activ-
ity than pyridines and amines. The low activity of the electron-
deficient Mn[T(4-NO2P)P]OAc and Mn(TDCPP)OAc catalysts reflect
the diminishing effect of the electron-withdrawing substitute upon
the catalytic activity of the Mn-catalyst. The experimental results
and spectroscopic evidences suggest the involvement of a high va-
lent Mn-oxo species as well as a six-coordinate [(L)(Por)Mn–OIO3]
complex.
[24] A. Bettelheim, B.A. White, S.A. Raybuck, R.W. Murray, Inorg. Chem. 26 (1987)
1009.
[25] P. Hoffmann, A. Robert, B. Meunier, Bull. Soc. Chim. Fr. 129 (1992) 85.
[26] A.D. Adler, F.R. Longo, F. Kampas, J. Kim, J. Inorg. Nucl. Chem. 32 (1970) 2443.
[27] Stoe
& Cie, IPDS-I Bedienungshandbuch, Stoe & Cie GmbH, Darmstadt,
Germany, 2000.
[28] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112.
[29] A.L. Spek, Acta Crystallogr., Sect. D 65 (2009) 148.
[30] D. Mohajer, G. Karimipour, M. Bagherzadeh, New J. Chem. 28 (2004) 740.
[31] J.T. Groves, T.E. Nemo, R.S. Myers, J. Am. Chem. Soc. 101 (1979) 1032.
[32] D. Mohajer, L. Sadeghian, J. Mol. Catal. A Chem. 272 (2007) 191.
Acknowledgment
Support for this work by the Research Councils of the University
of Birjand is highly appreciated.