Novel heterotetranuclear V2Mo2 or V2W 2 complexes with 4,4′-Di- tert -butyl-2,2′-bipyridine: Syntheses, crystal structures, and catalytic activities

Article abstract of DOI:10.1021/ic2009094

Two novel heterotetranuclear complexes [V₂O₂(μ- MeO)₂(μ-WO₄)₂(4,4′- ^tBubpy)₂] (1) and [V₂O₂(μ-MeO) ₂(μ-MoO₄)₂(4,4′-^tBubpy) ₂] (2) were synthesized, and the solid state structures of these complexes were revealed by single crystal X-ray crystallography. The heterotetranuclear complexes 1 and 2 are centrosymmetric building blocks, considered as consisting of two [VO(4,4′-^tBubpy)]³⁺ units bridged by μ-MO₄^2- (M = W or Mo) anions connected with methoxy groups. Furthermore, catalytic activities of 1 and 2 in the alcohol oxidation with hydrogen peroxide as terminal oxidants in water as solvent were investigated.

Full text of DOI:10.1021/ic2009094

ARTICLE
pubs.acs.org/IC
Novel Heterotetranuclear V2Mo2 or V2W2 Complexes with 4,40-Di-tert-
butyl-2,20-bipyridine: Syntheses, Crystal Structures, and Catalytic
Activities
Shintaro Kodama,† Akihiro Nomoto,† Shigenobu Yano,‡ Michio Ueshima,† and Akiya Ogawa*,†
†Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku,
Sakai, Osaka 599-8531, Japan
‡Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara 630-0192, Japan
S Supporting Information
b
ABSTRACT: Two novel heterotetranuclear complexes [V2O2-
(μ-MeO)2(μ-WO4)2(4,40-tBubpy)2] (1) and [V2O2(μ-MeO)2-
(μ-MoO4)2(4,40-tBubpy)2] (2) were synthesized, and the solid
state structures of these complexes were revealed by single crystal
X-ray crystallography. The heterotetranuclear complexes 1 and 2
are centrosymmetric building blocks, considered as consisting of
two [VO(4,40-tBubpy)]3+ units bridged by μ-MO42ꢀ (M = W or
Mo) anions connected with methoxy groups. Furthermore,
catalytic activities of 1 and 2 in the alcohol oxidation with
hydrogen peroxide as terminal oxidants in water as solvent were investigated.
’ INTRODUCTION
stirred at ambient temperature to form a brown precipitate.
A heterotetranuclear V2W2 complex (vanadium(V)ꢀtungsten(VI)
complex), [V2O2(μ-MeO)2(μ-WO4)2(4,40-tBubpy)2] (1), was
obtained as a yellow crystal by recrystallization of the precipitate
from a mixture of methanol and chloroform. A heterotetra-
nuclear V2Mo2 complex (vanadium(V)ꢀmolybdenum(VI)
complex), [V2O2(μ-MeO)2(μ-MoO4)2(4,40-tBubpy)2] (2) was
also obtained by the reaction of [VO(4,40-tBubpy)2]SO4 with
Na2MoO4.6 The use of 4,40-tBubpy as a bipyridyl ligand was
necessary for the syntheses of this type of heterotetranuclear
V2W2 or V2Mo2 complexes.7 The structures of these complexes 1
and 2 were characterized by NMR, IR, ESI-MS, and elemental
analysis (see Experimental Section). The solid state structures of
1 and 2 were determined by single crystal X-ray crystallography.
Crystal data for complexes 1 and 2 are summarized in Table 1.
The crystal structures of 1 and 2 are shown in Figures 1ꢀ3. They
have similar structures. Vanadium, tungsten, and molybdenum
atoms in 1 and 2 are present in octahedral coordination. The
heterotetranuclear complexes 1 and 2 are centrosymmetric build-
ing blocks, considered as consisting of two [VO(4,40-tBubpy)]3+
units bridged by μ-MO42ꢀ (M = W or Mo) anions connected with
methoxy groups. Selected bond lengths (Å) and angles (deg) for 1
and 2 are listed in Table 2. The VdO distances in 1 and 2 are
almost the same (1.60 Å). The WdO distances in 1 and the
ModO distances in 2 are 1.73 Å and 1.71 Å, respectively. The
cyclic tetranuclear eight-membered structures exist in these com-
plexes 1 and 2. The VꢀO distances within the eight-membered
Development of new heteropolynuclear complexes is of great
importance in many fields of catalysis and materials chemistry
because complexes with different metals are known to modify the
properties of the individual metals.1 The heteropolynuclear
complexes as catalysts are known to have potential to exhibit
distinct activity different from the one shown by mononuclear
complexes.2 However, it is often difficult to combine different
metals together in a single molecule without controlling their
individual chemical properties. Complexation of the cationic
2ꢀ
metal complexes by metal oxyanions, such as WO4 and
MoO42ꢀ, is an attractive method for the synthesis of heteropoly-
nuclear complexes, but the examples of such simple anions used
as ligands to the cationic metal complexes are still limited,
compared with those of complexation by polyoxoanions.3 Also,
most of heterometallic complexes bridged by metal oxyanions
are used for the investigation of their magnetic properties,4 and
the catalysis of those complexes is not investigated sufficiently.
Here, we report the development of new heterotetranuclear
complexes from a cationic vanadium complex bearing appropriate
organic ligands and metal oxyanions (WO42ꢀ or MoO42ꢀ). In
addition, the catalytic activity of these heterotetranuclear complexes
was investigated.
’ RESULTS AND DISCUSSION
In a typical procedure, to an aqueous suspension of the
vanadium(IV) complex, [VO(4,40-tBubpy)2]SO4, prepared from
VOSO4 and 4,40-di-tert-butyl-2,20-bipyridyl (4,40-tBubpy),5 an
aqueous solution of Na2WO4 was added, and the mixture was
Received: February 8, 2011
Published: September 09, 2011
r
2011 American Chemical Society
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|

Inorganic Chemistry
ARTICLE
Table 1. Crystallographic Data and Structure Refinement of
Complexes 1 and 2
1
2
formula
T (K)
C38H54N4O12V2W2
113
C38H54N4O12V2Mo2
123
cryst syst
space group
a (Å)
triclinic
P1
triclinic
P1
10.1338(3)
15.6779(5)
19.7520(6)
72.9803(9)
80.3509(9)
88.1885(9)
2957.75(15)
1
10.2163(2)
16.2648(4)
19.0493(4)
105.0638(7)
97.1994(7)
93.2327(7)
3019.4(1)
1
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Figure 1. Crystal structure of 1 (symmetry-expanded structures).
Ellipsoids are shown at the 50% probability level.
Z
Dcalcd (g/cm3)
μ (MoKα) (cmꢀ1
F(000)
2θ max (deg)
Nmeasured
Nunique
1.644
1.672
)
44.149
12.911
1434.50
50.6
1516.00
55.0
24398
52629
10737
13821
GOF
1.05
1.03
R1
0.0335
0.0597
wR2
0.0960
0.1651
ring are longer (1.78ꢀ1.79 Å) compared with the VdO distances.
The WꢀO distances within the eight-membered ring are in the
range 1.95ꢀ1.96 Å, and the MoꢀO distances within the eight-
membered ring are in the range 1.95ꢀ1.97 Å, which are longer
than the MdO (M = W or Mo) distances. In 1, the O2ꢀ
V1ꢀO4#1 angle and the O2ꢀW1ꢀO4 angle are 102.34(17)°
and153.56(16)°, respectively. Also, in 2, theO2ꢀV1ꢀO4#1angle
and the O2ꢀMo1ꢀO4 angle are 102.77(14)° and 153.71(13)°,
respectively. These complexes also have the four-membered ring
structure (M2(μ-MeO)2 (M = W or Mo)) and two kinds of six-
membered ring structures (VM2O2(μ-MeO) (M = W or Mo)).
The tungsten or molybdenum centers are connected through
methoxy groups. The W1ꢀO3 and W1ꢀO3#1 distances are 2.26
Å and 2.24 Å, respectively, and the Mo1ꢀO3 and Mo1ꢀO3#1
distances are almost the same (2.25 Å). In 1, the O3ꢀW1ꢀO3#1
angle, the W1ꢀO3ꢀW1#1 angle, the O3ꢀW1ꢀO4angle, andthe
O3#1ꢀW1ꢀO4 angle are 70.64(12)°, 109.36(13)°, 82.38(13)°,
and 75.66(15)°, respectively. In 2, the O3ꢀMo1ꢀO3#1 angle,
the Mo1ꢀO3ꢀMo1#1 angle, the O3ꢀMo1ꢀO4 angle, and the
O3#1ꢀMo1ꢀO4 angle are 70.85(11)°, 109.15(12)°, 81.88(11)°,
and 75.38(12)°, respectively.
Figure 2. Crystal structure of 2 (symmetry-expanded structures).
Ellipsoids are shown at the 50% probability level.
precatalyst for the oxidation reaction in Table 3, and 4a was
produced selectively in a good yield (entry 6).10,11
Furthermore, when the oxidation of 3a (1.5 mmol) was
conducted using H2O2 (1.57 mmol) at 90 °C for 24 h in the
presence of 1 (0.1 mol %), the turnover number (TON) of 1
increased from 292 (see, Table 3, entry 6) to 630 (eq 1).12,13
V2Mo2 complex 2 could also be employed as a precatalyst for the
oxidation of 3a, but the yield of 4a and TON were lower
compared with the case using 1 as a precatalyst (eq 2).
Oxoperoxo vanadium(V), molybdenum(VI), and tungsten-
(VI) complexes are known to serve as useful oxidation catalysts.8
Therefore, we next investigated the catalytic activity of these
heterotetranuclear complexes, 1 and 2, for the oxidation of
alcohols with hydrogen peroxide as terminal oxidants.
Oxidation of 1-phenylethanol (3a) was examined with hydro-
gen peroxide in the presence of 1 or other metal complexes using
water as solvent. The results are shown in Table 3. VOSO4 and
VO(Hhpic)29 exhibited moderate catalytic activity in the oxida-
tion of 3a (entries 1 and 2). 4,40-Di-tert-butyl-2,20-bipyridyl
(4,40-tBubpy) was not effective as an additional ligand to VOSO4
(entry 3). Na2WO4 was not effective as catalysts for the oxidation
(entries 4 and 5). The complex 1 was found to be an effective
The results of the oxidation of various secondary alcohols
using 1 are shown in Table 4. Diphenylmethanol (3b) was
oxidized under the reaction condition to afford benzophenone
(4b) in a moderate yield (entry 2). The oxidation of cyclohexyl-
(phenyl)methanol (3c) proceeded very slowly (entry 3). From
these results, steric hindrance may influence the reactivity of
1. Oxidations of 1-(p-substituted phenyl)ethanols 3d and 3e
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ARTICLE
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1
and 2
1 (M = W)a
2 (M = Mo)b
V1ꢀO1
V1ꢀO2
V1ꢀO4#1
V1ꢀN1
V1ꢀN2
M1ꢀO2
M1ꢀO3
M1ꢀO3#1
M1ꢀO4
M1ꢀO5
M1ꢀO6
O3ꢀC1
1.602(3)
1.783(3)
1.784(4)
2.153(3)
2.139(4)
1.947(3)
2.259(3)
2.238(4)
1.957(3)
1.730(3)
1.731(4)
1.440(5)
1.602(4)
1.787(3)
1.783(4)
2.165(3)
2.150(4)
1.948(3)
2.254(3)
2.247(4)
1.972(3)
1.714(3)
1.709(4)
1.437(5)
Figure 3. Numbering of selected atoms of heterotetranuclear V2M2
(M = W or Mo) complexes 1 or 2.
proceeded selectively to afford the corresponding ketones 4d and
4e, respectively (entries 4 and 5). Furthermore, 4-tert-butylcy-
clohexanol (3f) could be oxidized by prolonging the reaction
time (entry 6).14
The examples of metal-complex-catalyzed oxidation of alco-
hols with H2O2 using water as solvent are still limited,15 although
oxidations using water as solvent could be cheaper, more eco-
friendly, and safer than current oxidation processes in organic
solvents.16 Also, oxidation of alcohols using water as solvent
often proceeds in an organicꢀaqueous biphasic system, and
therefore, phase transfer catalysts are often required. In our
reaction system, however, the oxidation of alcohols with 1
proceeded without the addition of any phase transfer catalyst.
The result suggests that affinity of 1 to organic substrates was
improved by the selection of appropriate organic ligands, that is,
4,40-tBubpy. In addition, from the result of Table 3, we believe
that preparation of heteropolynuclear complexes enables us to
develop new oxidation catalysts with improved catalytic activity
to realize efficient oxidation reactions.17
O1ꢀV1ꢀO2
103.27(17)
104.84(19)
95.34(17)
96.24(18)
102.34(17)
155.91(17)
89.33(17)
87.24(16)
152.62(15)
73.39(17)
75.20(13)
83.73(15)
153.56(16)
97.14(16)
99.15(17)
70.64(12)
82.38(13)
160.79(18)
93.15(16)
75.66(15)
91.22(17)
162.38(14)
99.64(15)
95.85(17)
105.6(2)
102.86(14)
104.95(16)
93.16(14)
96.74(16)
102.77(14)
158.29(15)
90.48(14)
86.82(14)
151.12(12)
72.97(14)
74.61(11)
85.78(12)
153.71(13)
98.19(14)
99.39(15)
70.85(11)
81.88(11)
159.81(15)
94.19(13)
75.38(12)
90.03(14)
162.43(12)
99.97(14)
93.83(15)
105.68(16)
119.58(14)
117.68(17)
109.15(12)
117.3(3)
O1ꢀV1ꢀO4#1
O1ꢀV1ꢀN1
O1ꢀV1ꢀN2
O2ꢀV1ꢀO4#1
O2ꢀV1ꢀN1
O2ꢀV1ꢀN2
O4#1ꢀV1ꢀN1
O4#1ꢀV1ꢀN2
N1ꢀV1ꢀN2
O2ꢀ M1ꢀO3
O2ꢀ M1ꢀO3#1
O2ꢀ M1ꢀO4
O2ꢀ M1ꢀO5
O2ꢀ M1ꢀO6
O3ꢀ M1ꢀO3#1
O3ꢀ M1ꢀO4
O3ꢀ M1ꢀO5
O3ꢀ M1ꢀO6
O3#1ꢀ M1ꢀO4
O3#1ꢀ M1ꢀO5
O3#1ꢀ M1ꢀO6
O4ꢀ M1ꢀO5
O4ꢀ M1ꢀO6
O5ꢀ M1ꢀO6
M1ꢀO2ꢀV1
’ CONCLUSIONS
Two new heterotetranuclear complexes 1 and 2 were synthe-
sized, and the solid state structures of 1 and 2 were revealed by
single crystal X-ray crystallography. These complexes had unique
2ꢀ
structures linked through μ-MO4 (M = W or Mo) and
μ-MeOꢀ bridges, and contained two different metals known to
have a potential to act as useful oxidants. Preliminary results of
alcohol oxidation with H2O2 using water as solvent in the
presence of 1 as a precatalyst suggest that polynucleation of
the complex with appropriate organic ligands leads to the
development of new catalysts for environmentally friendly
oxidation systems.
’ EXPERIMENTAL SECTION
General Procedures. 1H NMR spectra were recorded on a JEOL
JNMꢀALꢀ300 (300 MHz) spectrometer using CDCl3 as the solvent
with tetramethylsilane (TMS) as an internal standard. 13C NMR spectra
were obtained on a JEOL JNMꢀALꢀ400 (100 MHz) spectrometer
using CDCl3 as the solvent. Chemical shifts in 13C NMR were measured
relative to CDCl3 by using δ 77.0 ppm. 51V NMR spectra were obtained on
a JEOL ECXꢀ400 (105 MHz) spectrometer using CDCl3 as the solvent
with VOCl3 (ꢀ4 ppm) as an external standard. IR spectra were determined
on a Shimadzu FTIR 8400 infrared spectrometer. Substrates 3c,18 3d,19 and
3e20 were prepared by reduction of the corresponding ketones with NaBH4.
Unless otherwise noted, other reactants and reagents were purchased from
commercial source and used without further purification.
120.12(16)
119.1(2)
M1ꢀO4ꢀV1#1
M1ꢀO3ꢀ M1#1
M1ꢀO3ꢀC1
M1#1ꢀO3ꢀC1
109.36(13)
118.3(3)
116.9(3)
116.8(3)
a Symmetry operators: (#1) ꢀX+1, ꢀY+1, ꢀZ+1. b Symmetry opera-
tors: (#1) ꢀX+1, ꢀY, ꢀZ.
Synthesis of [V2O2(μ-MeO)2(μ-WO4)2(4,40-tBubpy)2] (1).
To a solution of 4,40-di-tert-butyl-2,20-bipyridyl (4,40-tBubpy) (930.4 mg,
X-ray Crystallography. Crystals of 1 or 2 were mounted on a glass fiber
and cooled in the cold stream of nitrogen gas. All measurements were
made on aRigakuRAXISRAPIDimaging plate areadetectorwithgraphite
monochromated Mo-Kα radiation. The structure was solved by direct
methods (SHELX97). For 1, the tert-butyl group was found disordered.
3.5 mmol) in EtOH (40 mL) was added a solution of VOSO4 5H2O (437.6
3
mg, 1.7 mmol) in EtOH (20 mL). After stirring for 2.5 h at 40 °C, the solution
was concentrated under reduced pressure, and the precipitate was filtered
using diethyl ether and dried in vacuo to afford [VO(4,40-tBubpy)2]SO4 as a
green powder (700.6 mg). HR-ESI MS (MeOH) calcd for C36H49N4O5SV
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ARTICLE
Table 3. Catalytic Activities for Oxidation of 1-Phenylethanol with 1 and Other Metal Complexes
entry
catalyst (mol %)
ligand (mol %)
yield (%)a
selectivity (%)b
conversion (%)c
TONd
1
2
3
4
5
6
VOSO4 (1)
VO(Hhpic)2 (1)
VOSO4 (1)
Na2WO4 (1)
Na2WO4 (1)
1 (0.25)
none
44
43
33
7
66
65
50
70
42
82
67
66
66
10
19
89
44
43
33
7
none
4,40-tBubpy (2)
none
4,40-tBubpy (2)
none
8
8
73
c
292
a Determined by H NMR. b Selectivity = (formed 4a)/(converted 3a). Conversion of 3a to 4a. d The turnover number (TON) of the catalyst =
1
(mmol of 4a)/(mmol of catalyst).
Table 4. Oxidation of Various Secondary Alcohols in the Presence of 1
a Determined by 1H NMR. b Selectivity = (formed 4)/(converted 3). c The turnover number (TON) of the catalyst = (mmol of 4)/(mmol of catalyst).
[M + H]+ 700.2863, found 700.2881. Next, water (10 mL) was added to the
green powder to form a suspension in a glass vessel. After addition of an
concentrated under reduced pressure to afford [VO(4,40-tBubpy)2]SO4 as a
green powder, andwater (10 mL) was added to the green powder to form a
suspension in a glass vessel. After addition of an aqueous solution of
aqueous solution of Na2WO4 2H2O (494.3 mg, 1.5 mmol) in water
3
(10 mL) to the suspension, the reaction mixture was stirred for 3 h at
ambient temperature. After the reaction, the precipitate was filtered using
wateranddriedinvacuotoaffordabrownpowder.Next,methanolwasadded
to the brown powder, forming a brown suspension, followed by filtration of
the suspension to give a yellow solution. Chloroform was added to the yellow
solution, and the resulting mixture was let stand for recrystallization at room
temperature for 2 weeks, affording 1 (428.4 mg, yield = 40% based on
vanadium) as a yellow crystal. 1HNMR(CDCl3, 300MHz) δ9.15 (d, J=6.1
Hz, 4H), 8.05 (d, J=1.7 Hz, 4H), 7.70(dd, J= 6.3, 1.7 Hz, 4H), 3.18 (s, 6H),
1.46 (s, 36H); 13C NMR (CDCl3, 100 MHz) δ 166.82, 154.01, 152.21,
124.78, 117.15, 57.38, 35.87, 30.34; 51V NMR (CDCl3, 105 MHz) δ ꢀ544;
IR (KBr, cmꢀ1) 3442, 2964, 1618, 1413, 977, 906, 758; HR-ESI MS
(CHCl3) calcd for C38H54N4O12V2W2Na [M + Na]+ 1251.153, found
1251.150. Anal. Calcd for C38.5H54.5Cl1.5N4O12V2W2: C, 35.90; H, 4.26; N,
4.35. Found: C, 35.82; H, 4.18; N, 4.29.
Na2MoO4 2H2O (366.7 mg, 1.5 mmol) in water (10 mL) to the
3
suspension, the reaction mixture was stirred for 3 h at ambient tempera-
ture. After the reaction, the precipitate was filtered using water and dried in
vacuo to afford a brown powder. Next, methanol was added to the brown
powder, forming a brown suspension, followed by filtration of the
suspension to give a yellow solution. Chloroform was added to the yellow
solution, and the resulting mixture was let stand for recrystallization at
room temperature for 2 weeks, affording 2 (192.2 mg, yield = 37% based
on vanadium) as a yellow crystal. 1H NMR (CDCl3, 300 MHz) δ 9.04 (d,
J = 5.9 Hz, 4H), 8.05 (d, J = 1.7 Hz, 4H), 7.65 (dd, J = 6.0, 1.8 Hz, 4H),
3.10 (s, 6H), 1.45 (s, 36H); 13C NMR (CDCl3, 100 MHz) δ 166.34,
153.40, 152.20, 124.52, 117.06, 57.38, 35.80, 30.36; 51V NMR (CDCl3,
105 MHz) δ ꢀ533; IR (KBr, cmꢀ1) 3442, 2962, 1618, 1411, 968, 904,
742; HR-ESI MS (CHCl3) calcd for C38H54N4O12V2Mo2Na [M + Na]+
1079.062, found 1079.058. Anal. Calcd for C38.8H54.8Cl2.4N4O12V2Mo2:
C, 40.70; H, 4.72; N, 4.98. Found: C, 40.59; H, 4.81; N, 4.88.
Synthesis of [V2O2(μ-MeO)2(μ-MoO4)2(4,40-tBubpy)2] (2). To
asolutionof4,40-di-tert-butyl-2,20-bipyridyl (4,40-tBubpy) (539.5 mg, 2.0 mmol)
General Procedure for Oxidation of Alcohols with Hydro-
gen Peroxide in the Presence of 1 (Table 4). The V2W2 complex
1 (1.8 mg, 0.0015 mmol) and alcohols 3 (1.5 mmol) were placed in a
in MeOH (20 mL) was added a solution of VOSO4 5H2O (253.6 mg, 1.0
3
mmol) in MeOH (20 mL). After stirring for 2.5 h at 40 °C, the solution was
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ARTICLE
25 mL two necked flask, and then water (3.0 mL) was added. The
mixture was heated to 90 °C, 30% H2O2 aq. (0.16 mL, 1.57 mmol) was
added to the mixture, and then the reaction was conducted with
magnetic stirring for the appropriate time. After the reaction, the mixture
was diluted with diethyl ether, and the organic phase was evaporated.
The crude product was dissolved in CDCl3, and an appropriate amount
of 1,3,5-trioxane was added as an internal standard to determine the yield
of the product by 1H NMR spectroscopy.
for the syntheses of heterotetranuclear V2W2 or V2Mo2 complexes.
However, the materials obtained in the reaction of the vanadium(IV)
complexes with Na2WO4 or Na2MoO4 in water have low solubility to
organic solvents such as methanol, and therefore, recrystallization using
methanol have been so far unsuccessful. We feel that the selection of the
appropriate ligands to increase the solubility to organic solvents is
important to obtain heterotetranuclear V2W2 or V2Mo2 complexes in
the present synthetic method.
(8) (a) Johnson, M. K.; Rees, D. C.; Adams, M. W. W. Chem. Rev.
1996, 96, 2817. (b) Ligtenbarg, A. G. J.; Hage, R.; Feringa, B. L. Coord.
Chem. Rev. 2003, 237, 89.
’ ASSOCIATED CONTENT
(9) (a) Nakai, M.; Obata, M.; Sekiguchi, F.; Kato, M.; Shiro, M.;
Ichimura, A.; Kinoshita, I.; Mikuriya, M.; Inohara, T.; Kawabe, K.; Sakurai,
H.; Orvig, C.; Yano, S. J. Inorg. Biochem. 2004, 98, 105. (b) Kodama, S.; Ueta,
Y.; Yoshida, J.; Nomoto, A.; Yano, S.; Ueshima, M.; Ogawa, A. Dalton Trans.
2009, 9708. (c) Kodama, S.; Yoshida, J.; Nomoto, A.; Ueta, Y.; Yano, S.;
Ueshima, M.; Ogawa, A. Tetrahedron Lett. 2010, 51, 2450.
S
Supporting Information. X-ray crystallographic data in
b
CIF format, NMR spectra, and IR spectra. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
(10) The oxidation of 3a was examined using both metal precursors
(VOSO4 and Na2WO4) with and without the ligand (4,40-tBubpy) accord-
ing to the reaction conditions of Table 3. As a result, the product of 4a was
formed in moderate yields, respectively (eq 3). Although the real active
species is still unknown, we believe that the structure of 1 (Figure 1) is
important as a precatalyst for the present oxidation reaction.
Corresponding Author
*Phone: +81-72-254-9290. Fax: +81-72-254-9290. E-mail: ogawa@
chem.osakafu-u.ac.jp.
’ ACKNOWLEDGMENT
This research was supported by JST Research Seeds Quest
Program (Lower Carbon Society), from the Ministry of Educa-
tion, Culture, Sports, Science and Technology, Japan, and Kansai
Research Foundation for Technology Promotion (KRF). S.K.
acknowledges Research Fellowships of the Japan Society for the
Promotion of Science (JSPS) for Young Scientists. We acknowl-
edge Mr. Shouhei Katao, Ms. Mika Yamamura, and Professor
Kiyomi Kakiuchi of Nara Institute of Science and Technology in
Kyoto-Advanced Nanotechnology Network for their help with
X-ray crystallography and mass spectrometry. We also thank Mr.
Suguru Hashidate and Mr. Kuniaki Marui of Osaka Prefecture
University for their experimental support.
(11) When hydrogen peroxide was added to the reaction mixture of
1 and 1-phenylethanol (3a) at 90 °C, the color of the mixture turned
from pale yellow to orange. This suggests that a peroxo complex was
formed immediately by the addition of hydrogen peroxide. In addition,
no significant induction period was observed in the oxidation of 3a with
1 (Table 3, entry 6) varying the reaction time: the yield of 4a (time) =
16% (2 h); 44% (6 h); 73% (17 h). Hydrogen peroxide was completely
consumed after the reaction time of 17 h.
(12) Hydrogen peroxide was completely consumed after the reaction.
(13) Additional hydrogen peroxide (1.57 mmol) was added to the
reaction mixture after 24 h, and the mixture was stirred at 90 °C for 24 h.
As a result, the turnover number (TON) of 1 increased from 630 (see,
eq 1) to 710, but the unchanged substrate 3a (13%) was recovered and
hydrogen peroxide was left at the end of the reaction (eq 4). We assume
that the high concentration of substrate 3 in the reaction mixture is
effective in the present oxidation reaction.14
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Inorganic Chemistry
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