Oxoperoxo molybdenum(VI)- and tungsten(VI) complexes with 1-(2′-hydroxyphenyl) ethanone oxime: Synthesis, structure and catalytic uses in the oxidation of olefins, alcohols, sulfides and amines using H2O2 as a terminal oxidant

Article abstract of DOI:10.1016/j.ica.2008.05.017

High yield synthesis of two new oxodiperoxo-molybdate, PPh₄[MoO(O₂)₂(HPEOH)] (1), and -tungstate, PPh₄[WO(O₂)₂(HPEOH)] (2), complexes with 1-(2′-hydroxyphenyl) ethanone oxime (HPEOH₂

Full text of DOI:10.1016/j.ica.2008.05.017

Inorganica Chimica Acta 362 (2009) 1089–1100
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Inorganica Chimica Acta
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Oxoperoxo molybdenum(VI)- and tungsten(VI) complexes with
1-(20-hydroxyphenyl) ethanone oxime: Synthesis, structure and catalytic
uses in the oxidation of olefins, alcohols, sulfides and amines
using H2O2 as a terminal oxidant
Narottam Gharah a, Santu Chakraborty b, Alok K. Mukherjee b, Ramgopal Bhattacharyya a,
*
a Department of Chemistry, Jadavpur University, Kolkata, West Bengal 700 032, India
b Department of Physics, Jadavpur University, Kolkata, West Bengal 700 032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
High yield synthesis of two new oxodiperoxo-molybdate, PPh4[MoO(O2)2(HPEOH)] (1), and -tungstate,
PPh4[WO(O2)2(HPEOH)] (2), complexes with 1-(20-hydroxyphenyl) ethanone oxime (HPEOH2) as organic
ligand has been achieved by adding methanol solution of the ligand to the pale-yellow solution obtained
by dissolving molybdic-/tungstic-acid (freshly prepared) in hydrogen peroxide and precipitating the
complexes using tetraphenylphosphonium chloride. The orange-yellow complexes have been character-
ized by elemental analysis, IR, 1H NMR, UV–Vis spectroscopy and finally by X-ray structure analysis. Both
the complexes function as facile olefin epoxidation catalysts with hydrogen peroxide as terminal oxidant
and bicarbonate as a co-catalyst at room temperature. Catalytic potentiality of 1 and 2 is also exhibited in
the case of oxidation of alcohols, amines and sulfides. The catalysts are very much efficient especially in
olefin epoxidation giving high yield, TON (turnover number) and TOF (turnover frequency). The method
described is environmentally benign and cost-effective in all the cases.
Received 29 September 2007
Received in revised form 11 April 2008
Accepted 17 May 2008
Available online 23 May 2008
Keywords:
Synthesis
Crystal structure
Catalysis
Epoxidation
Oxoperoxo molybdenum and tungsten
Alcohol, amine and sulfide oxidation
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
with non-deprotonated a-amino acid ligands having the general
composition [MoO(O2)2(L–L0H)], where L–L0H = glycine, alanine,
proline, valine, leucine or serine, were found to be stable at ambi-
ent temperature and behaved as stoichiometric reagents for sub-
strate oxidation, themselves being converted to their respective
mono peroxo species [23]. However, the catalytic activities of these
compounds have not yet been examined [24]. Although recently it
has been shown that the MO(O2)2 cores ligated with bidentate li-
gands are known to be extremely useful catalysts in the epoxida-
tion of olefins [25–27] and oxidation of alcohols [22,28–31].
Epoxidation of olefins and arenes is an outstanding transforma-
tion in organic synthesis since the epoxy compounds are widely
used as they are or used for the manufacturing of a wide variety
of high demand commodity chemicals such as polyurethanes,
unsaturated resins, glycols, surfactants and other products [32].
Out of the many ways to accomplish olefin epoxidation using tran-
sition metal compounds as catalysts [1e,33], H2O2 is probably the
best ecologically sustainable ‘‘green” terminal oxidant [34] after
dioxygen. Indeed, in certain circumstances it is better than
dioxygen insofar as O2 – organic mixtures sometimes spontane-
ously ignite [35]. The inaugural report of Na2WO4-catalyzed epox-
idation of olefins with H2O2 as oxidant was made by Payne and
Williams [36]. Venturello and coworkers [37] used their catalysts,
namely, (R4N)3[PO4{W(O)(O2)2}4] for epoxidation of olefins with
A coordinated metal center activates hydrogen peroxide render-
ing peroxometal complexes, which are important as intermediates
in the substrate oxidation catalysis in homogeneous as well as het-
erogeneous mode [1]. A variety of synthesis of peroxocomplexes of
various metals are known [2–4] to catalyze the oxidation of olefins,
arenes, phenols, alcohols, phosphines and sulfides [5–9]. The cata-
lytic activity of peroxometal complexes is influenced by the type of
metal atom, the number of peroxo ligands attached to the catalyst
and the nature of the remaining ligands in the co-ordination
sphere [10–20]. In oxoperoxo chemistry of Mo and W, an impor-
tant structural motif, in which two peroxo groups and a doubly
bonded oxo ligand create the median M(O2)2O (M = Mo, W) plane,
is well known [21]. This core, although recognized as most stable
[21] and a common motif in oxoperoxo-molybdenum and -tung-
sten systems, has in our experience [22], a high formation ten-
dency no doubt, but is also a rather reactive species, which
readily performs substrate oxidation, converting itself into a
MO(O2)2+ core, which gives more stable compounds than its diper-
oxo analogue. A group of compounds containing an MO(O2)2 core
* Corresponding author. Tel.: +91 33 2432 7159; fax: +91 33 2414 6584.
E-mail address: aargibhatta@yahoo.com (R. Bhattacharyya).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.05.017

1090
N. Gharah et al. / Inorganica Chimica Acta 362 (2009) 1089–1100
H2O2 economy in biphasic system often involving chlorinated sol-
vents. Efficiency of the system is not very high but is higher than
the corresponding Mo catalysts, which give lower turnovers and
selectivities [38]. BASF patents [39] using Mimoun-type [40] diper-
oxo-tungsten and -molybdenum complexes further encouraged
the studies on the Mo and W catalysts in the area of olefin epoxi-
dation. Noyori and coworkers [41] reported that a ternary system
consisting of Na2WO4, amino methyl phosphoric acid and n-octy-
lammonium hydrogen sulfate in the presence of H2O2 in a sol-
vent-free medium behaved as a much efficient catalyst for alkene
epoxidation including 1-dodecene. Kamata et al. [42] recently re-
plexes with another aldoxime ligand, namely, 1-(20-hydroxy-
phenyl) ethanone oxime, HPEOH2, which is introduced by us for
the first time as a ligand. In this ligand a steric bulk is imposed
by introducing a methyl group by substituting the C–H proton of
the aldoxime ligand used earlier [27a] to examine the comparative
efficiency of the present complexes as catalysts with that of the
former [27a]. The complexes isolated herein are Ph4P[MoO(O2)2(H-
PEOH)] (1) and Ph4P[WO(O2)2(HPEOH)] (2). Besides olefin epoxida-
tion we also describe here the catalytic properties of 1 and 2in the
field of oxidation of alcohols, amines and sulfides using H2O2 as a
terminal oxidant. However, for the olefin epoxidation reaction
we have used NaHCO3 as a co-catalyst as in the previous cases.
Varieties of substrates of aromatic, carbocyclic and aliphatic ori-
gins have been used for the catalytic oxidation mentioned above.
ported a silicotungstate compound (Bu4N)4[c-SiW10O34(H2O)] as
catalyst with H2O2 as oxidant in the CH3CN medium and claimed
that their catalyst showed the highest efficiency among the known
epoxidation catalysts [42]. In case of homogeneous molybdenum-
catalyzed epoxidations alkyl hydro-peroxide is generally used
since many catalysts reportedly failed to activate H2O2 [43]. Inspite
of the high cost component of the ARCO-Halcon process for using
TBHP (tert-butyl hydroperoxide) oxidant [44,45], the process is still
in use in industries. Besides the cost factor, since alkyl hydroperox-
ides generate environment pollutants and global warming agents
(CO2) at slightly high temperature, replacement of TBHP by H2O2
as oxidant is very much warranted [46].
Reports of metal complexes in the catalytic oxidation of alcohol
[47] to aldehyde/ketone and carboxylic acid, sulfide [48] to sulfox-
ide and sulfones, and amine [49] to nitro, nitroso and hydroxamate
have appeared in the literature. Jacobson et al. [50] were one of the
first to report the use of Mo and W complexes as catalysts in the
oxidation of alcohols. The yields were moderate to poor with poor
turnovers. Mo(VI)-peroxo compounds also catalyze the oxidation
of alcohols to carbonyl compounds [51] and amides to hydroxamic
acids [52,53]. Anionic Mo-peroxo complexes were used as catalysts
in the oxidation of alcohols by Trost et al. [54]. The Modena group
reported a series of methods in the catalytic oxidations of primary
and secondary alcohols [55] and sulfides [56] using Mo-peroxo
complexes of picolinic acid and picolinic acid-N-oxide with moder-
ate to good yields. Peroxidic catalytic oxidation [57] of sulfides was
also performed using heteropolyacids of Mo and W. Ishii and co
workers studied the catalytic oxidation of alcohols and diols [58]
as well as aromatic amines [59] using the peroxotungstatophos-
phate (PCWP) in the presence of 35% H2O2 at room temperature.
2. Experimental
2.1. Materials
All synthetic works were carried out open to atmosphere. The
chemicals, MoO3, Na2WO4 ꢁ 2H2O, hydroxylamine hydrochloride
were of extra pure quality and obtained from Loba Chemie (India).
Hydrogen peroxide (30%, w/v), dichloromethane, n-hexane, aceto-
nitrile, diethylether, isopropanol, butanol, 1-octanol, 1-dodecanol,
acetone, cyclohexanol, benzaldehyde, cinnamaldehyde, p-pheny-
lene diamine, 1,4-diaminobenzene and methanol were of analyti-
cal grade and procured from E. Marck (India). Cyclopentene,
cyclohexene, cyclooctene, norbornene, 1-hexene, 2-hexen-1-ol,
1-heptene, 1-octene, 1-decene, trans-5-decene and 1-dodecene were
the products of Sigma–Aldrich Chemie GmbH, Germany, and were
directly used. Styrene, dimethyl sulfide, cinnamyl alcohol and allyl
alcohol were obtained from E. Merck (Germany). The epoxides of
the corresponding olefins and tetraphenylphosphonium chloride
were the products of Aldrich, Germany. Sodium hydrogen carbon-
ate, 1-(20-hydroxyphenyl) ethanone, benzyl alcohol, phenol and so-
dium acetate were from Sisco research laboratories (SRL, India).
Acetonitille, dichloromethane, acetone and methanol were further
purified prior to use following the literature methods [63]. Ethanol
(95%) was obtained from Bengal Chemical and pharmaceutical
works (Calcutta) and was lime distilled before use. IOLAR II grade
dioxygen, dihydrogen, zero air and dinitrogen gas used for chro-
matographic analysis were obtained from Indian Refrigeration
Stores, Calcutta. All the solvents used for chromatographic analysis
were either of HPLC-, spectroscopic-, or GR-grade.
Hetero
and
isopolytungstato
lanthates
(III),
namely,
[LnIII{PW11O39}2]11ꢀ and [LnW10O36
]
9ꢀ, respectively, and the sim-
7ꢀ
ple heteropolytungstatophosphates [PW11O39
]
have been used
for the oxidation of alcohols, tertiary amines and sulfides by Grif-
fith and co workers [60]. The same group also studied [61] the oxi-
dation of alcohols using the polyoxotungstatothorate (IV)
Na8[ThW10O36] ꢁ 28H2O. A molybdenum–copper system [30] has
been demonstrated to efficiently catalyze the oxidation of alcohols
in aerobic conditions with high selectivity. Recently, bis-quater-
nary phosphonium salts of peroxo complexes of molybdate and
tungstate have been used [62] in the oxidation of alcohols in the
presence of 30% H2O2. In all previous attempts to oxidize the alco-
hols, sulfides and amines to their respective oxidation products in
the presence of metal complex as catalyst, the turnover numbers
were moderate to poor.
With this background we recently reported highly efficient
methods for epoxidation of olefins with H2O2 as oxidant and NaH-
CO3 as co-catalyst [27] and the oxidation of alcohols, sulfides,
amines with H2O2 [22] as oxidant involving Mo and W-based cat-
alysts. Notably, the organic ligand used by us showed almost
matchless efficiency of the catalyst with respect to the yield, TON
and TOF, compared to all the existing methods of olefin epoxida-
tion was an aldoxime ligand [27a]. So in this paper we report the
synthesis, spectroscopic and X-ray crystallographic structure
determination of oxodiperoxo-molybdenum and -tungsten com-
2.2. Physical measurements
Infrared spectra were recorded as KBr pellets on Perkin–Elmer
FT IR RXI spectrometer and electronic spectra on Hitachi U-3410
UV–Vis NIR spectrophotometer. Elemental analyses were per-
formed using Carlo Erba 1108 Elemental Analyzer. W and Mo were
estimated gravimetrically as WO3 and [MoO2(QO)2], respectively,
where QOH = 8-hydroxy quinoline. Triply distilled (all glass) water
was used throughout whenever necessary. GC measurements were
done on an Agilent 6890N gas chromatograph using HP-1 and
INNOWAX capillary column in the FID mode with dinitrogen as
carrier gas.
2.3. Preparation of the ligand, 1-(20-hydroxyphenyl) ethanone oxime
Five milliliters of 1-(20-hydroxyphenyl) ethanone (5.65 g,
41.50 mmol) dissolved in 20 mL of methanol was added to an
aqueous solution (15 mL) of hydroxylaminehydrochloride (4.33 g;
62.25 mmol). Sodium acetate (6.81 g; 83 mmol) dissolved in
20 mL of water was then added to the resulting solution and the

N. Gharah et al. / Inorganica Chimica Acta 362 (2009) 1089–1100
1091
reaction mixture was refluxed for 2 h. The solution was then cooled
2.6. X-ray crystallographic data collection and refinement
to room temperature and poured in a beaker containing ice and
stirred vigorously to get a white precipitate. The solid obtained
was filtered off and washed with ice-cold water. The same was dis-
solved in dichloromethane and passed through anhydrous sodium
sulfate to remove traces of water. The solid was then crystallized
by slow evaporation of its dichloromethane solution. Yield:
4.68 g (80%). Anal. Calc. for C8H9O2N: C, 63.57; H, 5.96; N, 9.27.
Found: C, 63.48; H, 6.00; N, 9.29%. IR (KBr, cmꢀ1): 3686(s),
2246(s), 1640(m), 1591(s), 1441(s), 1405(s), 1293(s), 1237(s),
1159(m), 1127(m), 1009(m), 937(m), 830(m), 742(s), 637(s),
559(w), 507(w), 438(w). 1H NMR (CDCl3, d ppm): 2.366 (s, 3H,
CH3); 6.888–7.458 (m, 4H, aromatic protons of HPEOH2); 7.769
(s, 1H from C@N–OH); 11.364 (s, 1H from phenolic OH). UV–Vis
Single crystals of 1 and 2 suitable for X-ray structure analyses
were obtained from dichloromethane and hexane (1:1) solvent
mixture. Their diffraction data for 1 and 2 were collected at
295 K on a Bruker SMART-CCD diffractometer (graphite monochro-
mated MoKa-radiation). Relevant crystal data, data collection, and
structure refinement parameters are summarized in Table 1. The
structures of both complexes were solved by Direct methods with
SHELXS-97 [64] and refined using full-matrix least squares on F2 by
SHELXL-97 [64]. All non-hydrogen atoms were refined anisotropi-
cally and the hydrogen atoms were placed geometrically and trea-
ted as riding.
(kmax/nm): 305 (
e
= 4405 Mꢀ1 cmꢀ1).
2.7. Experimental procedure of epoxidation and isolation of products
2.4. Preparation of PPh4[MoO(O2)2(HPEOH)] (1)
The experimental procedure for the epoxidation of olefins
involving a wide variety of substrates is described as follows: an
acetonitrile (ꢂ10 mL) solution {in some cases, namely, the entries
16–18, a solution of acetonitrile and acetone (3:2 volume ratio)
was used} containing a given substrate (ca. 10 mmol), NaHCO3
(2.50 mmol), catalyst 1 or 2 (0.01–0.001 mmol; see Table 2) and
30% H2O2 (3.4–6.8 mL; 30–60 mmol) was taken in a flat-bottomed
two-neck reaction flask with one neck fitted with a reflux conden-
sor (to check evaporation), the other neck being closed with a sep-
tum. The resulting reaction mixture was stirred at 25 °C (in some
cases at 40 °C) for a definite period as quoted in Table 2. As and
when required an aliquot of the reaction solution was withdrawn
from, and H2O2 added to, the contents of the flask with the help
of a syringe through the septum. Periodically 0.5 mL of the reaction
solution was pipetted out (micro pipette) and then subjected to
multiple ether extraction, and the extract was also concentrated
MoO3 (1.44 g, 10 mmol) was dissolved in 30 mL of H2O2 (30%,
w/v) by stirring at room temperature (25 °C) to get a pale yellow
solution. Addition of 10 mL of a methanolic solution of 1-(20-
hydroxyphenyl) ethanone oxime (1.51 g, 10 mmol) to the above
solution on stirring for 1 h produced an orange-red solution. This
on treatment with PPh4Cl (3.75 g, 10 mmol) dissolved in 10 mL of
methanol yielded an orange-yellow solid. The solid was filtered
off and washed with water under suction and finally washed with
diethyl ether, and dried in vacuo. Yield: 5.98 g (90%). The com-
pound is soluble in acetonitrile, acetone, dichloromethane, chloro-
form, methanol and ethanol, but insoluble in water, diethyl ether,
benzene and toluene. The crude (1 g, 1.5 mmol) was crystallized
from dichloromethane–hexane (1:1) mixture to get 1 (0.95 g) as
an orange-yellow crystal (Yield: 95% of the crude). Anal. Calc. for
C32H28O7NPMo: C, 57.74; H, 4.21; N, 2.11; Mo, 14.43; P, 4.66.
Found: C, 57.57; H, 4.41; N, 2.34; Mo, 14.23; P, 4.46%. IR (KBr,
cmꢀ1) 3240(b), 1650(w), 1600(m) 1470(m), 1445(s), 1300(m),
1250(m), 1110(s), 1000(m), 945(s), 845(s), 755(m), 720(s),
690(m), 640(m), 570(w), 520(s). UV–Vis (kmax/nm): 310
up to 0.5 mL from which 1 lL solution was withdrawn with the
Table 1
Crystallographic data and structure refinement details for 1 and 2
(e
= 4538 Mꢀ1 cmꢀ1). 1H NMR (CDCl3, d ppm): 2.08 (s, 3H, CH3);
Compound
1
2
6.77–7.89 (m, 20H, PPh4 and 4H, aromatic protons of HPEOH);
9.04 (s, 1H from C@N–OH).
Empirical formula
Molecular weight (g molꢀ1
Crystal colour
Crystal system
T (K)
C32H28NO7PMo
665.46
orange–yellow
Triclinic
C32H28NO7PW
753.37
orange–yellow
Triclinic
)
2.5. Preparation of PPh4[WO(O2)2(HPEOH)] (2)
293(2)
293(2)
Wavelength
Space group
a (Å)
b (Å)
c (Å)
0.71073
P1
10.010(2)
10.416(3)
14.439(5)
83.70(3)
79.83(2)
82.06(2)
1462(1)
2
1.512
680
multi-scan
2.88–49.94
5090
0.71073
P1
10.033(2)
10.416(2)
14.385(3)
83.55(2)
80.11(2)
81.99(2)
1461(1)
2
1.713
744
multi-scan
2.88–49.98
5120
ꢀ
ꢀ
Na2WO4.2H2O (3.30 g, 10 mmol), dissolved in 2 mL of water,
was acidified with 6(M) HCl until a complete white precipitate of
H2WO4 was obtained. It was filtered off and washed several times
with water. The precipitate was dissolved in 30 mL of H2O2 (30%,
w/v) by stirring at room temperature (25 °C) until a clear and col-
ourless solution was obtained. 1-(20-hydroxyphenyl) ethanone
oxime (1.51 g; 10 mmol) was added to the above solution and stir-
red until an orange-red colour developed. PPh4Cl (3.75 g, 10 mmol)
dissolved in 10 mL of methanol was added to the above solution
when an orange-yellow solid separated, which was filtered off
and washed with water under suction, and finally washed with
diethyl ether, and dried in vacuo. Yield: 6.85 g (91%) The solubility
of this compound is the same as that of 1. The crude (1 g,
1.3 mmol) was crystallized from dichloromethane–hexane (1:1)
mixture to get orange-yellow crystals. Yield: 0.96 g (96% of the
crude). Anal. Calc. for C32H28O7NPW: C, 50.90; H, 3.70; N, 1.80;
W, 24.42; P, 4.11. Found: C, 51.05; H, 3.79; N, 1.53; W, 24.32; P,
a
(°)
b (°)
c
(°)
V (Å3)
Z
DCalc (mg mꢀ3
F(000)
)
Scan type
2h Range (°)
Reflections collected
Reflections unique
Refinement method
3945
4586
full-matrix least-
squares on F2
0 6 h6 11
ꢀ12 6 k 6 12
ꢀ16 6 1 6 17
R1 = 0.0448;
WR2 = 0.0984
R1 = 0.0665;
WR2 = 0.1075
1.034
full-matrix least-
squares on F2
0 6 h 6 11
ꢀ12 6 k 6 12
ꢀ16 6 1 6 17
R1 = 0.0307;
WR2 = 0.0724
R1 = 0.0384;
WR2 = 0.0872
1.114
hkl Range
Final R indices [I > 2
r(I)]
4.10%. IR (KBr, cmꢀ1
) 3260(b), 1600(m) 1470(w), 1445(s),
1300(m), 1260(m), 1120(s), 1000(m), 955(s), 830(s), 760(m),
R indices (all data)
720(s), 670(m), 630(m), 560(w), 520(s). UV–Vis (kmax/nm): 309
Goodness-of-fit (GOF) on F2
(e
= 3304 Mꢀ1 cmꢀ1). 1H NMR (CDCl3, d ppm): 2.22 (s, 3H, CH3);
Largest difference peak and
1.36 and ꢀ0.45
1.43 and ꢀ0.85
6.79–7.86 (m, 20H, PPh4 and 4H, due to aromatic protons of
HPEOH); 9.35 (s, H from C@N–OH).
hole (e Åꢀ3
)

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N. Gharah et al. / Inorganica Chimica Acta 362 (2009) 1089–1100
Table 2
Details of the catalytic epoxidation of olefinic compounds using the Mo- and W-catalysts
Entry
1
Substrate
Productb
Time
Percentage conversionc,d
Percentage yield
Yield percentagef
TONg (TOF)h
GCe
isolated
10 min
[10 min
91
91
91
91
30
30
4550 (27300)i
4550 (27300)]i,j
O
2
3
4
1 h
[1 h
99
96
99
96
27
27
1980(1980)
O
1920 (1920)]j
O
70 min
[70 min
96
95
96
95
88
85
50
50
3840 (3291)
3800 (3257)]j
30 min
[30 min
98
96
98
96
92
89
41
41
9800 (19600)i
o
9600 (19200)]i,j
o
5
5 h
[4 h
90
90
90
90
36
29
1800 (360)
1800 (450)]j
O
OH
6
7
8
9
5 h
[4.5 h
70
67
70
67
62
57
40
35
2800 (560)
OH
2680 (595)]j
O
HO
3 h
[2.25 h
90
90
90
90
70
44
3600 (1200)
HO
3600 (1600)]j
O
3 h
[3 h
87
80
87
80
55
55
3480(1160)
3200 (1066)]j
HO
HO
HO
HO
3.25 h
[3 h
97
98
97
98
60
50
3880(1193)
O
3920 (1306)]j
HO
10
HO
90 min
[70 min
75 min
[45 min
99
98
91
95
99
98
91
95
50
35
45
45
3960 (2640)
3920 (3360)]j
1820(1456)
o
O
a11
85
88
OH
OH
1900 (2533)]i,j
HO
HO
a12
2.25 h
[2 h
97
95
97
95
45
36
1940 (862)
1900 (950)]j
O
13
3 h
[3 h
96
99
96
98
95
99
91
99
90
96
99
95
96
99
96
98
95
99
91
99
90
96
99
95
45
45
50
42
45
40
40
34
20
16
22
16
1920 (640)
1980 (660)]j
1920 (768)
1960(1120)]j
1900 (760)
1980 (880)]j
910(303)
O
a14
a15
a16
a17
a18
2.5 h
[1.75 h
2.5 h
[2.25 h
3 h
[2.5 h
3 h
[2.5 h
1.5 h
[80 min
O
a14
a15
a16
a17
a18
O
O
990 (396)]j
900 (300)
O
82
90
86
84
960[(384)]j
990 (660)
O
950(712)]j
a
For entries 11, 12, 14–18, the reaction temperature is 40 °C.
Selectivity = 100%.
b
c
d
e
f
A control experiments (omission of catalysts 1 and 2 as well as HCO3ꢀÞ does not show any conversion to epoxide or other probable products.
Omission of only the bicarbonate shows a gross conversion of the 60–70% in each case in the same condition.
The detailed calculation of GC yield is given as Supplementary material.
This is the yield of control experiment, excluding the catalysts, but not NaHCO3 which remains in the reaction solution at the same 25 mol% concentration. When the
control experiment uses NaHCO3 at a catalytic concentration the conversion and yield percentage become negligible.
g
TON = ratio of moles of product (here epoxide) obtained to the moles of catalyst used.
h
The corresponding TOFs (TON hꢀ1) are shown in parentheses.
i
Values extrapolated.
j
The results for M = W are included within [ ]. The mole ratio of catalyst: substrate = 1:10000 (for entry 4), 5000 (for entry 1), 4000 (for entries 3 and 6–10), 2000 (for
entries 2, 5, 11–15), 1000 (for entries 16–18). For entries 16, 17 and 18, acetonitrile and acetone solvent mixtures were used in 2:1 volume ratio.
help of a gas syringe and injected into the GC port. The retention
times of the peaks were compared with those of commercial stan-
dards and for GC yield calculation nitrobenzene was used as an
internal standard. For few cases, especially for olefinic alcohols,
the identity of the product was confirmed by GC–MS analysis.
The isolated yield for selected substrates (Table 2) was obtained
by multiple ether extraction of the reaction solution after the reac-
tion was over (known from GC results) and then evaporating the
ether and acetonitrile by distilling at a mildly reduced pressure
(using water aspirator) and kept over P2O5 in a desiccator and
weighed in a micro-balance. The identity of the products was con-
firmed by IR and NMR probing. This method is applicable only
when the yield of the product is 98–100%, but for lower yield per-
centage the reaction solution was subjected to preparative TLC and
the highly intense spot was cut out and plunged in CH2Cl2 which
serves as an eluant, and then the resulting solution was dried
over MgSO4, filtered through a short silica gel pad and finally
evaporated to dryness to yield only the epoxide as residue. The res-
idue was kept over P2O5 for 15 min and weighed. In cases where
the epoxide separated as solid during concentration, the same

N. Gharah et al. / Inorganica Chimica Acta 362 (2009) 1089–1100
1093
Table 3
Catalytic oxidation of various alcohols, sulfides and amines in refluxing acetonitrile (78 °C) using 1 and 2 as catalysts and H2O2 as oxidant
Entry
1
Substrate
Time (h)
24
Product
Percentage yielda
TONb
1
1
2
2
81
85
810
850
OH
O
O
OH
2
24
63
65
630
650
H
OH
O
3
4
24
5
89
98
92
99
890
980
920
990
OH
O
O
5
6
CH3OH
16
20
HCHO (5a) + HCOOH (5b)
44 + 35
93
46 + 33
97
440 + 350
930
460 + 330
970
OH
O
O
(7a)
H
+
7
15
60 + 20
67 + 24
600 + 200
570 + 240
OH
O
(7b)
OH
( )
(8a)
(8b)
O
4
OH
+
8
9
22
22
46 + 25
48 + 28
460 + 250
480 + 280
( )
OH
4
( )
O
4
(
)
(9a)
(9b)
5
o
+
(
OH
62 + 15
64 + 16
620 + 150
640 + 160
)
OH
5
(
)
O
5
( )
O(10a)
9
OH
+
10
11
( )
30
11
80 + 2
83 + 3
800 + 20
830 + 30
OH
9
( )
(10b)
O
9
HO
O
88
91
880
910
OH
O
O
S
+
O
12
1
4 + 96
5 + 95
40 + 960
50 + 950
S
S
O
(continued on next page)

1094
N. Gharah et al. / Inorganica Chimica Acta 362 (2009) 1089–1100
Table 3 (continued)
Entry
Substrate
Time (h)
1
Product
Percentage yielda
TONb
1
1
2
2
13
4 + 96
3 + 97
40 +960
30 + 970
O
S
(13a)
S
+
O
S
(13b)
O
O
S
(14a)
(14b)
14
1
96 + 4
94 + 6
960 + 40
940 + 60
+
S
O
S
O
(15a)
(15b)
O
O
15
6
54 + 30
60 + 32
540 + 300
600 + 320
H
N
NH
+
2
2
H
N
N
O
2
2
O
(16a)
(16b)
N
16
7
78 + 18
79 + 19
780 + 180
790 + 190
+
H2N
-O
N+
O
a
Based on substrate concentration.
Turnover number (TON) is defined as a ratio of the moles of product obtained to the moles of catalyst used.
b
was filtered off, washed, vacuum dried and weighed in
microbalance.
a
was extracted with ether. From the ether extract the respective
oxidized products were isolated and characterized as described
below.
2.8. Experimental procedure for the oxidation of alcohols, amines and
sulfides
(1) Carbonyl compounds were isolated as their respective yel-
low-orange 2,4-dinitrophenyl hydrazone derivatives and the
respective carbonyl compounds were generated from the deriva-
tives by acid hydrolysis. The purity of the DNP derivatives was
checked by the integration of the respective 1H NMR spectrum
in each case. (2) The reaction solutions supposed to contain car-
boxylic acid were treated with aqueous NaHCO3, and the aque-
ous layer was concentrated and allowed to stand for 30 min.
when the corresponding acids were isolated as their colourless
Na-salts. (3) The sulfones were crystallized out as solids on con-
centrating the aqueous layer while the unreacted sulfides and
sulfoxides remained in the CH2Cl2 layer. The materials in the
CH2Cl2 layer were separated by fractional distillation. (4) 1,4-
Benzoquinone (from phenol) (see Table 3) was extracted out
from the reaction solution by diethylether and evaporation of
ether deposits the off-white material. (5) The mixture of prod-
ucts, 1,4-benzoquinone and 4-nitroaniline obtained from 1,4-
diaminobenzene, was separated by steam distillation since the
quinone is steam volatile. (6) Other amines and their oxidized
products were separated by column chromatography and their
identities were checked by NMR spectroscopy. It may be men-
tioned that for all the above procedures the amount of products
Alcohols, amines and sulfides (25.0 mmol) were separately
weighed and put in a 50 mL two-neck flask and dissolved in
10 mL CH3CN and catalyst 1 or 2 (0.025 mmol, 0.1 mol%) was
added separately to each and every substrate. The resulting
solutions were then separately treated with 30% H2O2 (in total
11.3 mL; 100 mmol; 400 mol%; 4 equiv. with respect to sub-
strates) portion-wise throughout the entire time span and the
reaction mixtures were separately refluxed for a period given
in Table 3. The refluxing solutions were periodically cooled
and an aliquot was taken out and treated as in the case of
olefin substrates for gas chromatographic analysis at regular
intervals.
For the isolated yield, the solvent (CH3CN) was distilled out and
the residual liquid (water from H2O2) was shaken with CH2Cl2
(5 mL) in a separatory funnel when the aqueous and organic layers
separated and the latter was taken out with the help of a dropper
and the aqueous layer was repeatedly (3–4 times) washed with
CH2Cl2. The washings were mixed with the organic extract and
the solution mixture (organic) was distilled out and the left residue

N. Gharah et al. / Inorganica Chimica Acta 362 (2009) 1089–1100
1095
separated corresponds with the GC results (see also Table 3), but
with slightly lower yield.
methanol, followed by addition of methanol solution of tetraphen-
ylphosphonium chloride. The complexes are air stable. The molar
conductance of complexes 1 and 2 are 123 and 125 Ohmꢀ1
cm2 molꢀ1 indicating that the complexes behave as 1:1 electrolyte
[65]. The vibration arising at 3686 cmꢀ1 is due to the presence of
the OH function in –C@N–OH moiety, in the case of free ligand.
In the case of 1 and 2, the said vibration undergoes a downward
shift to 3240 of 1 and to 3260 of 2 after complexation. The peak
arising at 2246 cmꢀ1, due to the presence of phenolic OH, in
HPEOH2 disappears in 1 and 2 due to deprotonation of phenolic
OH before the O ? M bond formation. The peak arising at
1600 cmꢀ1 in both 1 and 2 is due to the coordinated C@N vibration,
arising from downshifting of the 1640 cmꢀ1 vibration in the free li-
2.9. Recovery of catalyst
The residue left after distilling ether and acetonitrile at mildly
reduced pressure was thoroughly shaken with diethyl ether
repeatedly in which each of the substrates and the products was
almost quantitatively extracted. The orange-yellow solid residue
left was the catalyst as verified by IR spectroscopy.
3. Results and discussion
gand. The
m (M@O) vibration appears as a strong bond at 945 and
3.1. Synthetic aspect and general characterization
955 cmꢀ1 in 1 and 2, respectively. The
m
(O–O) vibration appears as
an intense band at 845 (1) and 830 cmꢀ1 (2). A medium to weak
intensity band in the region of 640 and 570 cmꢀ1 in case of 1
and 630 and 560 cmꢀ1 in case of 2 are assignable to asymmetric
Complexes 1 and 2 were synthesized by dissolving MoO3 or
H2WO4 (freshly precipitated) in H2O2 and treating the resulting
solution with 1-(20-hydroxyphenyl) ethanone oxime dissolved in
and symmetric vibrations, respectively of the MO2 triangle formed
2ꢀ
from terminally coordinated O2
ligand [66]. The vibration
appearing at 1445, 1110, 1000, 755, 720, 690 and 520 cmꢀ1 in case
Table 4
Selected bond lengths (Å) and angles (°) for 1 and 2
Bond lengths
M–O7
M–O4
M–O3
M–O2
M–O1
M–O5
M–N1
1 (M = Mo)
1.979 (3)
1.967 (3)
1.941 (3)
1.916 (3)
1.944 (3)
1.673 (3)
2.396 (3)
2 (M=W)
1.968(4)
1.962(4)
1.937(5)
1.907(4)
1.941(5)
1.694(4)
2.377 (5)
Bond angles
O7–M–O4
O7–M–O3
O7–M–O2
O7–M–O1
O7–M–O5
O7–M–N1
O4–M–O3
O4–M–O2
O4–M–O1
O4–M–O5
O4–M–N1
O3–M–O2
O3–M–O1
O3–M–O5
O3–M–N1
O2–M–O1
O2–M–O5
O2–M–N1
O1–M–O5
O1–M–N1
O5–M–N1
1
2
89.2 (1)
130.7 (1)
128.5 (1)
85.5 (1)
100.1 (1)
74.8 (1)
44.4 (1)
131.0 (1)
158.0 (1)
98.8 (1)
77.1 (1)
87.8 (1)
129.7 (1)
102.6 (1)
78.3 (1)
44.5 (1)
102.7 (1)
83.9 (1)
103.2 (1)
80.9 (1)
173.3 (1)
89.1 (2)
131.4 (2)
129.0 (2)
85.5 (2)
99.8 (2)
75.1 (2)
45.0 (2)
131.4 (2)
158.4 (2)
98.7 (2)
77.0 (2)
87.6 (2)
129.9 (2)
102.0 (2)
78.7 (2)
44.9 (2)
102.2 (2)
84.6 (2)
102.8 (2)
81.5 (2)
173.2 (2)
Fig. 1. An ORTEP view of anionic part of complex 1.
Table 5
Hydrogen bonding geometry (Å, °) in 1
D–Hꢁ ꢁ ꢁA
D–H
Hꢁ ꢁ ꢁA
Dꢁ ꢁ ꢁA
D–Hꢁ ꢁ ꢁA
O6–H6Aꢁ ꢁ ꢁO3
0.82
0.93
0.93
0.93
0.93
0.93
0.93
0.93
2.06
2.53
2.49
2.63
2.53
2.60
2.67
2.55
2.709(5)
3.438(6)
3.416(7)
3.235(5)
3.346(6)
3.236(7)
3.387(7)
3.408(6)
135.2(3)
163.4(3)
171.9(3)
123.4(3)
147.1(3)
126.1(3)
134.2(3)
154.0(3)
C5–H5ꢁ ꢁ ꢁO1i
C3–H3ꢁ ꢁ ꢁO3ii
C12–H12ꢁ ꢁ ꢁO7iii
C19–H19ꢁ ꢁ ꢁO4iv
C23–H23ꢁ ꢁ ꢁO5v
C25–H25ꢁ ꢁ ꢁO4vi
C29–H29ꢁ ꢁ ꢁO2vii
Symmetry codes: (i) ꢀx + 1, ꢀy, ꢀz; (ii) x + 1, +y, +z; (iii) ꢀx, ꢀy, ꢀz + 1; (iv) x ꢀ 1,
+y + 1, +z; (v) ꢀx, ꢀy + 1, ꢀz + 1; (vi) x, +y + 1, +z; (vii) ꢀx, ꢀy + 1, ꢀz.
Fig. 2. An ORTEP view of anionic part of complex 2.

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N. Gharah et al. / Inorganica Chimica Acta 362 (2009) 1089–1100
Fig. 3. Packing diagram of complex (1) showing the formation of two-dimensional network.
Table 6
1-hexene
100
90
Hydrogen bonding geometry (Å, °) in 2
D–Hꢁ ꢁ ꢁA
Dꢁ ꢁ ꢁH
Hꢁ ꢁ ꢁA
Dꢁ ꢁ ꢁA
D–Hꢁ ꢁ ꢁA
80
70
60
50
40
30
20
10
0
O6–H6Aꢁ ꢁ ꢁO3
0.82
0.93
0.93
0.93
0.93
0.93
0.93
2.07
2.48
2.50
2.52
2.53
2.58
2.62
2.700(5)
3.409(5)
3.406(4)
3.339(6)
3.393(5)
3.237(5)
3.363(4)
134.4(4)
175.0(5)
163.6(4)
146.3(5)
153.9(5)
128.3(5)
136.6(5)
C3–H3ꢁ ꢁ ꢁO3i
C5–H5ꢁ ꢁ ꢁO1ii
1-octene
1-decene
C19–H19ꢁ ꢁ ꢁO4iii
C29–H29ꢁ ꢁ ꢁO2iv
C23–H23ꢁ ꢁ ꢁO5v
C25–H25ꢁ ꢁ ꢁO4vi
3-butenol
styrene
Symmetry codes: (i) x + 1, +y, +z; (ii) ꢀx + 1, ꢀy, ꢀz; (iii) ꢀx + 1, ꢀy ꢀ 1, ꢀz + 1; (iv)
x,y ꢀ 1,z + 1; (v) x,y ꢀ 1,z; (vi) ꢀx, ꢀy ꢀ 1, ꢀz + 1.
1octene
1-hexene
0
10
20
30
40
50
60
100
80
60
40
20
0
1-decene
3-butenol
Time (min)
styrene
Fig. 5. Plot of percentage yield vs. time selecting the linear portions of each of the
corresponding curve shown in Fig. 4.
of 1 and 1445, 1120, 1000, 760, 720, 690 and 520 cmꢀ1 in case of 2
are due to the Ph4P+ ion. The HPEOHꢀ ? M (VI) LMCT transition in
1 (310 nm) as well as in 2 (309 nm) occurs almost at the same
wavelength. No other peak appears in the UV–Vis spectrum in both
the complexes. The 1H NMR signals arising at 9.04 and 9.35 ppm in
1 and 2, respectively, is assignable to the N-coordinated C@N–OH
proton. In the case of free ligand this peak arises at 7.76 ppm. This
large positional shift of the OH protons of the C@N–OH moiety on
coordination is due to the high order of deshielding of the proton
owing to the combined effect of metal complexation and hydrogen
binding between the OH proton and peroxo moiety present in the
metal complexes. The peak at 11.36 ppm is observed in the free li-
gands, but disappears in both 1 and 2. This is due to the deproto-
0
20 40 60 80 100 120 140 160 180 200 220 240 260
Time (min)
Fig. 4. Plot of percentage yield vs. time using 2 as catalyst keeping all other
parameters same as in Table 2 for the oxidation of styrene, 3- butenol, 1-octene,
1- decene and 1-hexene.

N. Gharah et al. / Inorganica Chimica Acta 362 (2009) 1089–1100
1097
sible isostructurality between them. Three isostructural parameters
i.e. (cell parameters isostructurality index), Ii(n) (coordinates iso-
structurality index) and Iv (volume isostructurality index) were cal-
culated for the structures 1 and 2 following the procedure described
by Fábián et al. [70]. The obtained parameters [p = 0.003; Ii = 85.5%,
100
80
60
40
20
0
d
p
c
a
Iv = 97.6] reveal a high degree of isostructurality between the
complexes.
b
The crystal packing arrangements in the structures exhibit sev-
eral intermolecular C–Hꢁ ꢁ ꢁO hydrogen bonds between the anions,
and the cations and the anions (Table 5). The 1-(20-hydroxyphenyl)
ethanone oxime carbon atom C3 at (x, y, z) is hydrogen bonded to
peroxo O3 atom at (1 + x, y, z) producing infinite one-dimensional
parallel chains propagating along [100] direction. Adjacent anionic
chains are further linked, where C5 atom at (x, y, z) is hydrogen
bonded to peroxo O1 atom (1 ꢀ x, ꢀy, ꢀz) generating a two-dimen-
sional network in the (101) plane (Fig. 3). Additional intermolecu-
lar C–Hꢁ ꢁ ꢁO hydrogen bonds involving the carbon atoms of the
tetraphenylphosphonium cations and oxygen atoms of the anions
stabilize the molecular structures for both complexes (Table 6).
0
5
10
15
20
25
30
Time(h)
Fig. 6. Plot of yield (based on amount of substrate) versus time for the conversion of
(a) cyclohexanol to cyclohexanone, (b) benzyl alcohol to benzaldehyde, (c)
cinnamyl alcohol to cinnamaldehyde, (d) isopropanol to isopropanone using 2 as
catalyst.
3.3. Summary of the results of catalytic oxidation by 1 and 2
The complexes show good catalytic activities in peroxidic oxi-
dation of various olefins, alcohols, sulfides to their corresponding
epoxides (Table 2), aldehydes or ketones, sulfoxides and sulfones
(Table 3). Table 3 also shows the mixture of oxidized products ob-
tained by amine oxidation.
nation of the phenolic OH group on coordination. (All the three
UV–Vis and NMR spectra are included as Fig. S1 as supplementary
material.)
Using 2 as a representative catalyst, NaHCO3 (0.25 equiv.) as co-
catalyst and H2O2 as terminal oxidant, a plot of percentage yield
versus time for the oxidation of some representative substrates,
namely, 1-hexene (entry 13), 1-octene (entry 15), styrene (entry
5), 3-buten-2-ol (entry 8), 1-decene (entry 16) is presented in
Fig. 4, where each curve maintains a gross linearity up to 1 h time
span but thereafter deviate from linearity showing a slow reaction
rate. Plot of percentage yield versus time selecting the linear por-
tions of the corresponding curves is presented in Fig. 5, which
shows that the initial rate of the reaction (up to 1 h) follows a
first-order kinetics and hence the TOF rightly has the unit, hꢀ1, in
the case of olefin epoxidation. However, the selectivity in olefin
oxidation is not shown for alcohol oxidation especially in the cases
of aliphatic alcohols. Lack of selectivity in the case of aliphatic alco-
hols is due to the fact that only in the aromatic case resonance sta-
bilization of C@O bond makes it reasonably immune against attack
by necleophiles [71,72] (here O22ꢀ). Actually, so long as there is a
remarkable concentration of H2O2, the aromatic aldehydes formed
are not oxidized to their corresponding acids. It is observed that
with increase in chain length of the aliphatic alcohols the rate of
catalytic oxidation decreases and the aldehyde is exclusively ob-
tained from n-dodecanol (entry 10). The conversion of
CH3OH ? HCHO is very much important for the industrial and
pharmacological use of formaldehyde.
Notably, oxidation of 1,4-diaminobenzene (entry 15) to quinone
is industrially important, though the simultaneous production of p-
nitroaniline is interesting from reactivity standpoint. A reduction
in the time of reflux increases the proportion of p-nitroaniline pro-
duced. The same was found to occur in case of aniline (entry 16)
where also a reduction in the time of reflux increases the propor-
tion of nitroso benzene. The oxidation of dimethyl sulfide (entry
13) to dimethyl sulfone goes via a dimethyl sulfoxide intermediate.
If the time of reflux and amount of peroxide are reduced, it is pos-
sible to get a selective and quantitative yield of DMSO and the
same observations were noticed for the other two sulfides (entries
12 and 14). Among the three sulfides, dimethyl sulfide and methyl
benzyl sulfide rapidly convert to sulfone. So in these two cases if
time and peroxide concentration are reduced, it is possible to get
their sulfoxide products with high yield.
3.2. Description of the molecular structure of complex 1 and complex 2
Crystal structures of complexes 1 and 2 consist of discrete
monomeric anions, [MO(O2)2(HPEOH)]ꢀ, (M = Mo in 1 and W in
2, HPEOH = 1-(20-hydroxyphenyl) ethanone oximate), and tetra-
phenylphosphonium, [PPh4]+ cations (see Figs. 1 and 2 for the OR-
TEP [67] view). The close similarity between the crystallographic
parameters, e.g., unit cell dimensions, space group, atomic coordi-
nates, crystal packing of 1 and 2 indicates that the complexes are
isostructural and subsequent discussions relating to complex 1
are also applicable to complex 2. The coordination geometry
around the metal atom can be best described as pentagonal bipy-
ramidal with the axial sites being occupied by the nitrogen (N1)
and the oxo (O5) ligands. The phenolate oxygen (O7) and the per-
oxo moieties (O1, O2 and O3, O4) define the equatorial plane with
the Mo atom displaced by ꢀ0.374(1) Å [ꢀ0.369(1) Å for the W
atom in 2] from the equatorial plane towards the oxo-oxygen
(O5). This is consistent with the observations in oxodiperoxo
molybdenum(VI)- and tungsten(VI) complexes which generally
feature the metal atom coordinated to the oxo-group in the axial
position and the two peroxide ligands bound in the equatorial
positions [3]. The chelated 1-(20-hydroxyphenyl) ethanone oxime
ligand fragment (C1–C7, N1, O6, O7), excluding the methyl group
(C8), is essentially planar (r. m. s. deviation 0.110 Å for complex
1 and 0.106 Å for complex 2) and is approximately orthogonal to
the equatorial plane (O1–O4, O7); the dihedral angle between
the two planes is 86.6(1)° in 1 [87.3(1)° in 2]. Selected bond dis-
tances and angles for 1 and 2 (Table 4) correspond well to those
of other seven coordinate Mo and W oxoperoxo complexes [31].
The lengthening of the Mo–N1 [2.397(3) Å] and W–N1 [2.377
(5) Å] distances in 1 and 2 compared to the Mo–N [2.194(3)–
2.269(3) Å] and W–N [2.264(6)–2.273(6) Å] bond lengths in com-
plexes [68] where the ligand nitrogen atoms coordinate the metal
center equatorially reflects the strong trans influence of the oxo li-
gand [69].
Similarity of the crystallographic parameters, i.e. unit cell, space
group, and closely related crystal packing of 1 and 2 indicates pos-

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N. Gharah et al. / Inorganica Chimica Acta 362 (2009) 1089–1100
Adding (1) and (8) we get Eq. (9)
As shown in Table 4 it is apparent that tungsten complex 2 is
more efficient catalyst than that of the analogous molybdenum
complex 1. A plot of percentage yield versus time for the oxidation
of some representative substrates, namely, cyclohexanol (entry 1),
benzyl alcohol (entry 2), cinnamyl alcohol (entry 3) and isopropa-
nol (entry 6) is shown in Fig. 6 using 2 as a representative catalyst
and H2O2 as oxidant.
½MOðO2Þ ðHPEOHÞꢃꢀ þ R1SðOÞR2
2
! ½MðOÞ ðO2ÞðHPEOHÞꢃꢀ þ R1SðOÞ2R2
ð9Þ
2
D. Amine oxidation
C6H5NH2 þ 2O2ꢀ ! C6H5NO þ H2O þ 4eꢀ
Multiplying Eq. (1) by (2) we get Eq. (11)
2½MOðO2Þ ðHPEOHÞꢃꢀ þ 4eꢀ ! 2½MðOÞ ðO2ÞðHPEOHÞꢃꢀ þ 2O2ꢀ
ð10Þ
3.4. Comparison of the catalytic properties of the complexes
2
2
The result of catalytic studies using these two catalysts reveals
that the proactive olefins such as cyclic olefins (reported in Table 2)
show similar behaviour towards epoxidation. On the other hand,
the tungsten compound shows higher reactivity toward the less
reactive substrates like alcohol-functionalized olefins than that
achieved from the molybdenum compound. The entries in which
time requirement for obtaining higher yield is long and the entries
where high temperature is required to get the optimum yield, H2O2
should be added intermittently because with decreasing concen-
tration of H2O2, the produced epoxides start to decompose to diols.
Considering yields of the oxidation products of alcohols, sulfides
and amines reported in Table 3 it can be stated that tungsten com-
plex 2 is a more efficient catalyst than that of the corresponding
molybdenum complex 1.
ð11Þ
Adding Eqs. (10) and (11) we get Eq. (12)
C6H5NH2 þ 2½MOðO2Þ ðHPEOHÞꢃꢀ
2
! 2½MðOÞ ðO2ÞðHPEOHÞꢃꢀ þ C6H5NO þ H2O
ð12Þ
2
Catalytic:
A. Olefin epoxidation – Role of bicarbonate
When H2O2 is used as a sole oxidant the catalytic efficiency is
rather poor, but when NaHCO3 is added as an additive (a co-
catalyst) the efficiency of the catalysis system increases many
fold. The key aspect [73,74] of such reaction is that H2O2 and
bicarbonate react in an equilibrium process to produce per-
oxymonocarbonate (HCO4ꢀ), which is a more reactive nucle-
ophile than H2O2 and speeds up the reaction. Eq. (13) shows
the conversion of bicarbonate to peroxymonocarbonate
4. Rationalization of stoichiometric and catalytic reactivity of 1
and 2
The complexes are capable of furnishing the stoichiometric oxi-
dation by transferring one of the peroxo oxygens to the substrates.
The stoichiometric oxidation can be represented by the equations
shown below, where [MO(O2)2(HPEOH)]ꢀ, (M = Mo or W) repre-
sents the complex anions of 1 and 2. Also in each case a represen-
tative substrate is taken into account.
HCO3ꢀ þ H2O2 ! HCO4ꢀ þ H2O
ð13Þ
The basic principle of the catalytic reaction is the conversion
of diperoxo-complexes to monoperoxo-complexes transfer-
ring oxo species to the substrates and the conversion of
monoperoxo complexes to the diperoxo complexes reacting
ꢀ
with HCO4 to regain the catalytic activity. This principle is
explained by Eqs. (14)–(17)
Stoichiometric:
½MOðO2Þ ðHPEOHÞꢃꢀ þ R1CH@CHR2
2
A. Olefin epoxidation
! ½MðOÞ ðO2ÞðHPEOHÞꢃꢀ þ R1CHðOÞCHR2
ð14Þ
2
½MOðO2Þ ðHPEOHÞꢃꢀ þ 2eꢀ ! ½MðOÞ ðO2ÞðHPEOHÞꢃꢀ þ O2ꢀ
ð1Þ
ð2Þ
ꢀ
2
2
½MO2ðO2ÞðHPEOHÞꢃꢀ þ HCO4
R1CH@CHR2 þ O2ꢀ ! R1CHðOÞCHR2 þ 2eꢀ
! ½MOðO2Þ ðHPEOHÞꢃꢀ þ HCO3
ð15Þ
ð16Þ
ꢀ
2
HCO3ꢀ þ H2O2 ! HCO4ꢀ þ H2O
Adding (1) and (2) we get Eq. (3)
½MOðO2Þ ðHPEOHÞꢃꢀ þ R1CH@ CHR2
Adding Eqs. (14)–(16) we have Eq. (17)
2
R1CH@CHR2 þ H2O2 þ f½MOðO2Þ ðHPEOHÞꢃꢀg
! ½MðOÞ ðO2ÞðHPEOHÞꢃꢀ þ R1CHðOÞCHR2
ð3Þ
ð4Þ
2
2
! R1CHðOÞCHR2 þ H2O þ f½MOðO2Þ ðHPEOHÞꢃꢀg
ð17Þ
ð18Þ
2
B. Alcohol oxidation
C6H5CH2OH þ O2ꢀ ! C6H5CHO þ H2O þ 2eꢀ
Adding (1) and (4) we get Eq. (5)
B. Alcohol oxidation
½MOðO2Þ ðHPEOHÞꢃꢀ þ C6H5CH2OH
2
! ½MðOÞ ðO2ÞðHPEOHÞꢃꢀ þ C6H5CHO þ H2O:
½MOðO2Þ ðHPEOHÞꢃꢀ þ C6H5CH2OH
2
2
½MðOÞ ðO2ÞðHPEOHÞꢃꢀ þ H2 O2 ! ½MOðO2Þ ðHPEOHÞꢃꢀ þ H2O
! ½MðOÞ ðO2ÞðHPEOHÞꢃꢀ þ C6H5CHO þ H2O
ð5Þ
ð6Þ
2
2
2
ð19Þ
C. Sulfide oxidation
(i) Sulfoxide
Adding Eqs. (18) and (19) we get,
C6H5CH2OH þ H2O2 þ f½MOðO2Þ ðHPEOHÞꢃꢀg
R1SR2 þ O2ꢀ ! R1SðOÞR2 þ 2eꢀ
Adding (1) and (6) we get Eq. (7)
2
! C6H5CHO þ 2H2O þ f½MOðO2Þ ðHPEOHÞꢃꢀg
ð20Þ
2
C. Sulfide oxidation
(i) Sulfoxide
½MOðO2Þ ðHPEOHÞꢃꢀ þ R1SR2 ! ½MðOÞ ðO2ÞðHPEOHÞꢃꢀ
2
2
þ R1SðOÞR2
ð7Þ
ð8Þ
R1SR2 þ ½MOðO2Þ ðHPEOHÞꢃꢀ ! R1SðOÞR2
2
þ ½MðOÞ ðO2ÞðHPEOHÞꢃꢀ
(ii) Sulfone
2
R1SðOÞR2 þ O2ꢀ ! R1SðOÞ2R2 þ 2eꢀ
ð21Þ

N. Gharah et al. / Inorganica Chimica Acta 362 (2009) 1089–1100
Angew. Chem., Int. Ed. 43 (2004) 5255;
1099
Adding Eqs. (19) and (21) we get,
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Chem. Commun. (2004) 608.
R1SR2 þ H2O2 þ f½MOðO2Þ ðHPEOHÞꢃꢀg
2
! R1SðOÞR2 þ H2O þ f½MOðO2Þ ðHPEOHÞꢃꢀg
ð22Þ
ð23Þ
ð24Þ
2
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(ii) Sulfone
R1SðOÞR2 þ ½MOðO2Þ ðHPEOHÞꢃꢀ
2
! R1SðOÞ R2 þ ½MðOÞ ðO2ÞðHPEOHÞꢃꢀ
2
2
Adding Eqs. (19) and (23) we get,
R1SðOÞR2 þ H2O2 þ f½MOðO2Þ ðHPEOHÞꢃꢀg
2
! R1SðOÞ R2 þ H2O þ f½MOðO2Þ ðHPEOHÞꢃꢀg
2
2
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Multiplying Eq. (19) by 2 we get
2½MðOÞ ðO2ÞðHPEOHÞꢃꢀ þ 2H2O2
2
! 2½MOðO2Þ ðHPEOHÞꢃꢀ þ 2H2O
ð25Þ
ð26Þ
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2½MOðO2Þ ðHPEOHÞꢃꢀ þ C6H5NH2
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! 2½MðOÞ ðO2ÞðHPEOHÞꢃꢀ þ C6H5NO þ H2O
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C6H5NH2 þ 2H2O2 þ 2f½MOðO2Þ ðHPEOHÞꢃꢀg
2
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ð27Þ
2
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In this work we have arrived at a situation that both Mo and W
complexes are almost equally effective olefin epoxidation catalysts
where H2O2 is the oxidant. In the cases of alcohol, sulfide and
amine oxidation, however, the tungsten catalysts are slightly more
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Acknowledgements
We acknowledge CSIR, New Delhi, for financial assistance under
the Project [01 (1818)/02/EMR-II] and DST, Government of India,
for financing the purchase of Agilent 6890N gas chromatograph.
S.C. thanks UGC, India, for a research fellowship.
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