Novel vanadium(III) complexes with rigid phenylpolycarboxylate ligands: Synthesis, structures and application in C-H bond activation

Article abstract of DOI:10.1039/c3dt32472a

Two novel vanadium(iii) complexes: V(dipic)(Hbdc)(H₂O) ₂ (1) and [V₂(dipic)₂(H₂btec)(H ₂O)₄]·2H₂O (2) (H₂dipic = 2,6-pyridinedicarboxylic acid, H₂bdc = 1,3-benzene-dicarboxylic acid, H₄btec = 1,2,4,5-benzenetetracarboxylic acid) are synthesized by the reaction of V₂(SO₄)₃, 2,6-pyridinedicarboxylic acid and 1,3-benzene-dicarboxylic acid (for 1) or 1,2,4,5- benzenetetracarboxylic acid (for 2) under hydrothermal condition at 120 °C for 3 days. They were characterized by elemental analysis, IR, UV-Vis, single crystal X-ray diffraction analysis and thermogravimetric analyses (TG). Structural analyses show that the vanadium atoms in the complexes 1 and 2 are both in a pentagonal-bipyramidal coordination environment with the NO6 donor set, and there is intermolecular hydrogen bonding in each complex. Research results found that the complexes exhibited bromination catalytic activity in the single-pot reaction of the conversion of phenol red to bromophenol blue in the mixed solution of H₂O-DMF at the constant temperature of 30 ± 0.5 °C with pH = 5.8, and catalytic C-H bond cleavage activity for the peroxidative oxidation (with hydrogen peroxide) of cyclohexane to cyclohexanol and cyclohexanone (the maximum total turnover number is 395) under the mild conditions.

Full text of DOI:10.1039/c3dt32472a

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PAPER
Novel vanadium(III) complexes with rigid phenylpolycarboxylate
ligands: synthesis, structures and application in C-H bond activation
Dong Xue Ren, Na Xing, Hui Shan, Chen Chen,Yun Zhu Cao, Yong Heng Xing*
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
Two novel vanadium(III) complexes: V(dipic)(Hbdc)(H2O)2 (1) and [V2(dipic)2(H2btec)(H2O)4]ꢀ2H2O (2)
(H2dipic=2,6ꢁpyridinedicarboxylic acid, H2bdc=1,3ꢁbenzeneꢁdicarboxylic acid, H4btec=1,2,4,5ꢁ
benzenetetracarboxylic acid) are synthesized by the reaction of V2(SO4)3, 2,6ꢁpyridinedicarboxylic acid
and 1,3ꢁbenzeneꢁdicarboxylic acid (for 1) or 1,2,4,5ꢁbenzenetetracarboxylic acid (for 2) under
10 hydrothermal condition with 120°C for 3 days. They were characterized by elemental analysis, IR, UV–
Vis, single crystal Xꢁray diffraction analysis and thermo gravimetric analyses (TG). Structural analyses
show that the vanadium atoms in the complexes 1 and 2 are both in a pentagonalꢁbipyramidal
coordination environment with the NO6 donor set, and there are intermolecular hydrogen bonding in each
complex. Research results found that the complexes exhibited bromination catalytic activity in the singleꢁ
15 pot reaction of the conversion of phenol red to bromophenol blue in the mixed solution of H2O–DMF at
the constant temperature of 30 ± 0.5 °C with pH=5.8, and catalytic CꢁH bond cleavage activity for the
peroxidative oxidation (with hydrogen peroxide) of cyclohexane to cyclohexanol and cyclohexanone (the
maximum total turnover number is 395) under the mild conditions.
green catalysts with more new environment friendly catalytic
processes for industrial use. We explored a homogeneous
catalytic reaction with various transition metal complexes as
50 catalyst and fortunately found that vanadium complexes as
catalysts yielded excited results and displayed good catalytic
properties in the oxidation reaction of the cyclohexane.
Introduction
20 To be in the face of increasing global crisis of energy,
diminishing petroleum reserves and rising emissions of CO2, nonꢁ
edible lignocellulose has received great interest recently as a
renewable source of fuel and chemicals.1 For the rich reserve and
lowꢁcost of lignocellulose (cellulose, hemicellulose and lignin),
25 we will possess an exhaustless energy storehouse if they can be
fully used. However, breaking down the highly functionalized
polymers lignin and cellulose for using is a major challenge, and
the main problem is how to active the inert CꢁC/CꢁO or CꢁH bond
in lignocellulosic biomass.
Functionlization reactions of saturated hydrocarbons of
lignocellulosic biomass, in particular oxidation reactions, provide
rather promising methods towards the reuse of unreactive
compounds. A typical example is the oxidation of cyclohexane,
with the main products as cyclohexanol and cyclohexanone that
35 are important raw materials for the production of adipic acid and
caprolactam used in the manufacture of nylonꢁ6,6 and nylonꢁ6,
respectively.2 To the best of our knowledge, precious metals
zirconium, ruthenium, rhodium, and iridium complexes were
usually used as catalysts for the activation of CꢁH.3ꢁ7 In addition,
40 the transition metals such as nickel and iron complexes as
catalysts have also received intensive attention with the
development of technology.8ꢁ10 However, they were not applied
widely in industrial production, this is because whatever precious
metals or transitional metal complexes have a limitation of
45 themselves, such as stability of catalyst, catalyst life,
environmental pollution, etc. which stimulates researchers to seek
Besides the cyclohexane oxidation, the oxidation of bromide
by H2O2 catalyzed by vanadate(V)ꢁdependent bromoperoxidase
55 and functional enzyme mimics attracted considerable attention
owing to the ability in predicting selectivity for biomimetic
synthesis of organobromines. Although molecular bromine is a
favorable agent for the synthesis of organobromines, it is
corrosive and toxic. So, it is necessary that how to choose better
60 bromine source for the green bromiding reaction. We think that
the common bromine source should be bromide, such as
bromocarnallite (MgBr2, KBr) and bromosylvinite [K(Cl, Br)]. In
addition, the use of organobromines in life and society is
attributed to the unique properties of the carbon–bromine bond. A
65 bromoꢁsubstituent is able to raise lipophilicity of an organic
molecule, which improves a substance in physical and chemical
properties to serve as emulsifier, insecticide, orbiologically active
compound.11,12 Arylꢁbound bromosubstituents lower the rate of
oxidative arene metabolism, which is important to increase the
70 stability of pharmaceuticals in vivo. In the mean time,
conjugation between an aromatic πꢁsystem and a pair of
nonbonding electrons at bromine shifts electronic excitation
energies of chromophors and thus induces auxochromic effects.
In other arenes, the carbon bromine bond is a key structural
75 element to achieve flame retarding properties of material
30
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(videinfra).13–16 The aliphatic carbon–bromine bond, on the other
hand, combines in a unique manner stability and chemical
reactivity. This bond can be selectively broken in heterolytic or
of 3257−3467 cm–1 were assigned to ν(O–H) of the coordinated
or uncoordinated water. The bands due to ν(=CꢁH) of benzene
ring or pyridine ring were appeared in the range of 3056ꢁ3075
homolytic reactions, which to serve as progenitor of carbocations, 60 cm–1. The bands attributed to asymmetric νas(COOꢁ) and
5
carbanions, or free carbon radicals.17 In recent decades,
oxidovanadium(IV) and dioxovanadium(V) complexes have been
studied for their synthesis, structures and properties. For example,
D. Rehder et al. have reported the mechanism that vanadium
symmetric νs(COOꢁ) vibrations of the carboxyl group are at 1652
and 1395 cmꢁ1 for 1, 1672 and 1379 cmꢁ1 for 2. Band of ν(V–
Owater) is at 512 cmꢁ1 for 1 and 539 cmꢁ1 for 2, while those at 475
cmꢁ1 for 1 and 491 cmꢁ1 for 2 are assigned to ν(V–Ocarboxyl) and
haloperoxidase catalyzed the oxidation of halides;18 C. J. Carrano 65 the bands due to ν(V–N) are in the range of 449ꢁ455 cmꢁ1.33
10 et al. reported the reactions of vanadium on various oxidation
states (III/IV/V) with hydridotris(pyrazoly1)borate ligands and
discussed their spectroscopic properties in detail;19 A. J. L.
Pombeiro, et. al. reported novel scorpionate and pyrazole
dioxovanadium complexes, catalysts for carboxylation and
15 peroxidative oxidation of alkanes.20 However, the studies of
V(III) complexes were obviously less than that of V(IV) or V(V)
complexes reported and metal centre of concerning V(III)
complexes was sixꢁcoordinate mode, while studies on V(III)
complexes with sevenꢁcoordinate were relatively rare.21ꢁ27
UV–Vis spectra
The UV–Vis absorption spectra of the complexes 1 and 2 (Fig. S3
and S4) are recorded in the form of solid sample and their
characteristic UVꢁVis bands are listed in Table S2. The highꢁ
70 frequency absorption bands at 262 nm for 1 and 268 nm for 2 are
assigned to πꢁπ* transition of the aromaticꢁlike chromophore from
the bdc, btec or dipic ligands. The absorption bands at 420 nm for
1 and 456 nm for 2 are attributed to the LMCT (charge transfer
from ligand to metal) transition. While the broad bands at 742,
75 1040 nm for 1 and 742, 1100 nm for 2 are assigned to dꢁd
transition of vanadium atom.34, 24 The absorption bands of the
complex 2 relative to 1 happened slightly redꢁshift, which may be
attributed to different ligands and coordination environment.
20 Although our group has
a longꢁstanding interest in the
investigation of vanadium complexes with poly(pyrazolyl)borate
ligands,28 schiffꢁbase ligands29 and dicarboxylic acid ligands,30 in
order to further extend structural variety and investigate
relationship between structure and function of the vanadium
25 complexes, here, we firstly designed and synthesized two novel
Structural description of complexes 1 and 2
80 The molecular structures of the complexes 1 and 2 are depicted in
sevenꢁcoordinate
vanadium(III)
complexes
with
rigid
polycarboxylate as ligands, V(dipic)(Hbdc)(H2O)2 (1) and
[V2(dipic)2(H2btec)(H2O)4]ꢀ2H2O (2), and studied the catalytic
properties in the aspect of arylꢁbound bromosubstituent and
30 oxidation of cyclohexane. It was rather surprising that high
catalytic efficiency with total turnover number (TON) value of
395 was reached in the cyclohexane oxidation under mild
conditions, which is much higher than 19, 167 or 308 that have
been reported in previous reports.20b,31,32
85
a
90
35 Results and Discussion
Synthesis
Two
novel vanadium (III) coordination
complexes
[V(dipic)(Hbdc)(H2O)2] (1) and [V2(dipic)2(H2btec)(H2O)4]ꢀ2H2O
(2) were successfully synthesized for the first time via the
40 reaction of V2(SO4)3 with mixed ligands of dipic and bdc or btec,
together with vitamin C as antioxidant at 120 °C for three days
(Scheme 1). It was surprise to found that vitamin C affect the
reaction results to some extent owing to the easily oxidization of
V2(SO4)3 in the reaction based on our previous experience.
95
100
OH
O
45
2
COOH
O
O
C
N
C
O
O
1)
(
b
O
O
V
OH
OH
V (SO )
O
O
OH
2
4 3
Fig. 1 (a) The molecular structure of the complex 1 (All H atoms are
omitted for clarity). (b) A view of 2D hydrogen bonding network on abꢁ
105 face in the complex 1. (All H atoms except for the hydrogen bonds are
omitted for clarity.)
2
+
N COOH
120oC
HOOC
OH
OH
OH
O
O
OH
OH
2
2
COOH
O
O
O
C
N
C
O
O
O
O
C
N
C
O
O
2
( )
V
O
V
O
O
HOOC
OH
OH
OH
2
2
O
50
Scheme 1 The reaction processes of the complexes.
IR spectra
110
The IR spectral data of the complexes 1 and 2 are listed in Table
Fig. 2 The molecular structure of the complex 2 (All H atoms are omitted
55 S1 and the corresponding spectra are shown in Fig. S1 and S2.
For the two complexes, the broad absorption bands in the region
for clarity)
2
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Table 1 Selected bond distances (Å) and angles (°) of the complexes 1 and 2
Selected bond lengths (Å) and angles (°) of complex 1
V1–O1
2.086(2)
2.142(2)
1.268(3)
89.49(8)
90.61(8)
73.43(6)
90.08(8)
76.14(6)
V1–O2
2.057(2)
2.090(2)
1.212(3)
178.35(8)
137.41(6)
149.34(7)
149.39(7)
146.62(6)
V1–O3
2.062(2)
2.107(2)
1.323(3)
89.74(8)
92.07(7)
89.85(8)
137.21(7)
89.21(7)
V1–O5
2.038(2)
1.270(3)
88.66(7)
75.97(6)
90.29(9)
73.20(7)
90.01(7)
61.27(6)
V1–O7
V1–O8
V1–N
C8–O7
C8–O8
C14–O10
O2–V1–O1
O3–V1–O8
N–V1–O7
O8–V1–N
O5–V1–O3
C14–O9
O2–V1–O3
O5–V1–O8
O1–V1–O8
O3–V1–N
O2–V1–O7
O8–V1–O7
O5–V1–O1
O2–V1–O8
O5–V1–N
O1–V1–N
O3–V1–O7
O3–V1–O1
O5–V1–O2
O2–V1–N
O5–V1–O7
O1–V1–O7
Selected bond lengths (Å) and angles (°) of complex 2
V1–O1
2.062(1)
2.117(1)
1.257(2)
87.62(6)
90.03(6)
73.40(6)
95.32(5)
136.13(5)
V1–O2
2.046(1)
2.129(2)
1.207(2)
175.69(5)
74.96(5)
150.42(5)
147.81(5)
145.98(5)
V1–O3
2.041(1)
2.110(2)
1.303(2)
90.51(5)
91.79(6)
88.60(6)
77.87(6)
90.36(5)
V1–O5
2.049(1)
1.267(2)
92.36(6)
138.79(5)
87.61(6)
72.97(6)
85.34(5)
61.26(5)
V1–O7
V1–O8
V1–N
C8–O7
C8–O8
C11–O17
O2–V1–O1
O5–V1–O8
O7–V1–N
O8–V1–N
O5–V1–O3
C11–O18
O5–V1–O1
O3–V1–O2
O2–V1–N
O3–V1–O7
O1–V1–O7
O2–V1–O3
O3–V1–O8
O1–V1–O8
O5–V1–N
O2–V1–O7
O8–V1–O7
O3–V1–O1
O2–V1–O8
O3–V1–N
O1–V1–N
O5–V1–O7
5
Table 2 Hydrogen bonds (Å) and angles (°) of the complexes 1 and 2.
D–HꢀꢀꢀA
d(D–H)
d(HꢀꢀꢀA)
d(DꢀꢀꢀA)
∠D–HꢀꢀꢀA
Complex 1
O1#1–H1AꢀꢀꢀO7
O1#1–H1BꢀꢀꢀO9#2
O2#3–H2AꢀꢀꢀO6#4
O2#3–H2BꢀꢀꢀO10#2
O9–H9ꢀꢀꢀO4#2
0.7225
0.7871
0.8513
0.8422
0.9034
0.9144
0.9549
2.1304
2.1715
1.8156
1.8903
1.6778
2.2650
2.4828
2.8523
2.9548
2.6587
2.7184
2.5587
3.1679
3.4229
177.32
173.46
170.34
167.42
164.12
169.22
168.12
C3–H3ꢀꢀꢀO6#4
C4–H4ꢀꢀꢀO8#4
Complex 2
O1W#5–H1WAꢀꢀꢀO7#6
O1–H1AꢀꢀꢀO6#7
O1–H1BꢀꢀꢀO3#8
O1W#5–H1WBꢀꢀꢀO5#6
O2–H2AꢀꢀꢀO4#9
O2–H2BꢀꢀꢀO9#10
O10–H20ꢀꢀꢀO1W#5
0.7407
1.0160
0.8726
0.7067
0.8193
0.8506
0.7915
2.2357
1.6580
1.9675
2.2892
1.8186
1.9140
1.8169
2.8393
2.6670
2.8040
2.9070
2.6316
2.7628
2.5947
139.39
171.44
160.14
146.91
171.47
175.45
167.21
Symmetry transformation used to generate equivalent atoms: #1: ꢁx, 1ꢁy, ꢁz; #2: ꢁ1ꢁx, 1ꢁy, ꢁz; #3: ꢁx, 0.5+y, 0.5ꢁz; #4:1ꢁx, 0.5+y, 0.5ꢁz; #5: 2ꢁx, 2ꢁy, 1ꢁz;
#6 : x, 1+y, z; #7: 2ꢁx, ꢁy, ꢁz; #8: 2ꢁx, 1ꢁy, ꢁz; #9: 1ꢁx, 1ꢁy, ꢁz; #10: 2ꢁx, 1ꢁy, 1ꢁz.
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Fig. 1a and 2, and some selected bond distances and angles are
summarized in Table 1. Singleꢁcrystal Xꢁray structure analyses
revealed that each vanadium atom of the two complexes posses a
distorted pentagonal–bipyramidal geometry defined by the NO6
donor set.
For the complex 1, the vanadium atom is coordinated by two
oxygen atoms (O1, O2) from coordinated water, two oxygen
atoms and one nitrogen atom (O3, O5, N) from a 2,6ꢁ
pyridinedicarboxylic acid (dipic) ligand and two oxygen atoms
a 3D supramolecular structure.
For the complex 2, the molecule contains two vanadium
atoms, two 2,6ꢁpyridineꢁdicarboxylic ligands, four coordinated
water molecules and one 1,2,4,5ꢁbenzeneꢁtetracarboxylic acid
55 (btec). Each vanadium atom is coordinated by two oxygen atoms
(O1, O2) from two coordinated water, two oxygen atoms and one
nitrogen atom (O3, O5, N) from a 2,6ꢁpyridinedicarboxylic acid
(dipic) ligand and two oxygen atoms (O7, O8) from the carboxyl
group of the btec ligand. The coordination mode of dipic ligand is
5
10 (O7, O8) from the carboxyl group of a 1,3ꢁbenzeneꢁdicarboxylic 60 the same as complex 1, and the btec ligand shows a ꢂ2ꢁbridging
acid (bdc), forming a slightly distorted pentagonal–bipyramidal
vanadium center, with O3, N, O5, O7 and O8 in the equatorial
plane, O1 and O2 in the axial positions. Dipic ligand adopts a k3–
O, N, O coordination mode to coordinate with vanadium atom,
linkage with 1ꢁ and 4ꢁpositions coordinated to carboxylate group,
respectively in ꢂ1–η1–η1ꢁbidentate mode, and another two
carboxylate groups are uncoordinated and protonated. Adjacent
two vanadium atoms are connected via the btec ligand. VꢁOwater
15 namely, O, N, O atoms of dipic ligand are coordinated only one 65 distances are 2.062(2) Å and 2.046(2) Å, V–Ocarboxyl distances are
metal atom; for bdc ligand, one carboxyl group is coordinated to
vanadium with ꢂ1–η1–η1ꢁbidentate chelated mode, while another
is uncoordinated and protonated. It is found that VꢁOwater
distances are 2.086(2) Å and 2.057(2) Å, VꢁOcarboxyl distances are
20 in the range of 2.038(2)ꢁ2.142(2) Å, VꢁNdipic distance is 2.107(2)
Å.
in the range of 2.041(2)–2.129(2) Å, V–Ndipic distance is 2.110(2)
Å.
70
It is worthy to note that there is obvious difference on the
bond length of C–O between coordinated and uncoordinated
carboxyl groups of bdc ligand, C14–O9 and C14–O10 distances
25 of uncoordinated carboxyl are 1.323(3) Å and 1.212(3) Å,
respectively, which indicates that C14–O9 is a single bond and
C14–O10 is a double bond. However, C8–O7 and C8–O8
distances of coordinated carboxyl are 1.270(3) Å and 1.268(3) Å,
respectively. Their bond length are between the single bond and
30 double bond, indicating that the presence of the coordinated
carboxyl group make electron cloud distribution uniformly,
which led to the closer of the two C–O bond lengths.
As illustrated in Fig. 1b, there are two kinds of hydrogen
bonds O–HꢀꢀꢀO and C–HꢀꢀꢀO in the complex 1. The relevant Hꢁ
35 bond parameters are listed in Table 2. Thereinto, hydrogen bond
of O–HꢀꢀꢀO comes from among coordinated water molecules,
coordinated carboxyl groups and uncoordinated carboxyl groups:
O1#1–H1AꢀꢀꢀO7 (2.8523 Å, #1: ꢁx, 1ꢁy, ꢁz), O1#1–H1BꢀꢀꢀO9#2
(2.9548 Å, #2: ꢁ1ꢁx, 1ꢁy, ꢁz), O2#3–H2AꢀꢀꢀO6#4 (2.6587 Å, #3:ꢁx,
40 0.5+y, 0.5ꢁz; #4: 1ꢁx, 0.5+y, 0.5ꢁz) and O2#3–H2BꢀꢀꢀO10#2
(2.7184 Å), and between carboxyl of bdc ligand and carboxyl of
dipic ligand: O9–H9ꢀꢀꢀO4#2 (2.5587 Å); hydrogen bonds of C–
HꢀꢀꢀO are from among carbon atom of dipic ring, coordinated
carboxyl groups and uncoordinated carboxyl groups: C3–
45 H3ꢀꢀꢀO6#4 (3.1679 Å) and C4–H4ꢀꢀꢀO8#4 (3.4229 Å). Through the
hydrogen bonding interaction of O9–H9ꢀꢀꢀO4#2, C3–H3ꢀꢀꢀO6#4
and C4–H4ꢀꢀꢀO8#4, a twoꢁdimensional hydrogen bonding network
on the abꢁplane is formed, the 2D network is further connected
via hydrogen bonding interaction of O1#1–H1AꢀꢀꢀO7, O1#1–
50 H1BꢀꢀꢀO9#2, O2#3–H2AꢀꢀꢀO6#4 and O2#3–H2BꢀꢀꢀO10#2, to generate
75
Fig. 3 (a) An infinite 1D chain of the complex 2. (b) A view of 3D
hydrogen bond network in the complex 2. (All H atoms except for the
hydrogen bonds are omitted for clarity.)
80
Similarly, there are abundant hydrogen bonds of O–HꢀꢀꢀO in
the complex 2 (listed in Table 2). As illustrated in Fig. 3,
according to oxygen atoms from different groups, which can be
divided into two types: (1) lattice water molecule and coordinated
85 carboxyl groups or uncoordinated carboxyl groups: O1W#5–
H1WAꢀꢀꢀO7#6 (2.8393 Å, #5: 2ꢁx, 2ꢁy,1ꢁz; #6: x, 1+y, z), O1W#5–
H1WBꢀꢀꢀO5#6 (2.9070 Å) and O10–H20ꢀꢀꢀO1W#5 (2.5947 Å); (2)
coordinated water molecules and coordinated or uncoordinated
carboxyl groups: O1–H1AꢀꢀꢀO6#7 (2.6670 Å, #7:2ꢁx, ꢁy, ꢁz), O1–
90 H1BꢀꢀꢀO3#8 (2.8040 Å, #8: 2ꢁx, 1ꢁy, ꢁz ), O2–H2AꢀꢀꢀO4#9 (2.6316
Å, #9: 1ꢁx, 1ꢁy, ꢁz) and O2–H2BꢀꢀꢀO9#10 (2.7628 Å, #10: 2ꢁx, 1ꢁy,
1ꢁz). Each independent molecule form a 1D chain by the
hydrogen bonding interaction of O10–H20ꢀꢀꢀO1W#5, O1W#5–
H1WAꢀꢀꢀO7#6 and O1W#5–H1WBꢀꢀꢀO5#6. The chains are further
95 linked through the hydrogen bonds O1–H1AꢀꢀꢀO6#7, O1–
H1BꢀꢀꢀO3#8, O2–H2AꢀꢀꢀO4#9 and O2–H2BꢀꢀꢀO9#10 to generate a
3D hydrogen bond network (shown in Fig. 3b).
Table 3 A comparison of key bond lengths (Å) for the complexes reported previously.
Number
Complexes
VꢁNdipic
VꢁOdipic
References
V(III)
1
2
V(dipic)(Hbdc)( H2O)2
[V2(dipic)2(H2btec)(H2O)4]ꢀ2H2O
V(IV)
2.107(2)
2.110(2)
2.062(2), 2.038(2)
2.041(1), 2.049(1)
This work
This work
3
[(CH3CH2)4N][VO(dipic)(HMDCl)]
2.031(1)
2.014(1), 2.027(1)
35
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4
5
6
VO(dipicꢁCl)(Me2NO)(H2O)
VO(dipic)(Me2NO)(H2O)
VO(dipic)(H2NO)(H2O)
V(V)
2.077(3)
2.067(3)
2.064(3)
2.027(2), 2.027(2)
2.026(3), 2.008(3)
2.031(3), 2.039(3)
36
37
38
7
8
9
K[VO2(dipicꢁOH)]ꢀH2O
C(NH2)3[VO2(dipic)]ꢀ2H2O
NH4[VO2(dipic)]
2.089(6)
2.086(2)
2.091(2)
2.033(5), 1.990(5)
1.983(2),1.988(2)
1.974(2), 1.988(2)
39
38
40
producing the halogenated product by the reaction of oxidized
halogen species with the organic substrate, and the reactive
process is as follows (Scheme 2).
It is found that average bond length of VꢁOwater of the
complex 1 is slightly longer than that of the complex 2. The
average bond length of VꢁOdipic of the complex 1 is close to that
of the complex 2 as well as the distance of VꢁNdipic. While
average bond length of VꢁObdc of the complex 1 is slightly shorter
than that of VꢁObtec in the complex 2. Furthermore, for the dipic
ligand coordinated to vanadium, a comparison of key bond
lenghs(Å) reported previously are listed in Table 3. The average
5
55
10 distance of V(III)ꢁNdipic, V(IV)ꢁNdipic and V(V)ꢁNdipic are 2.109(2), 60 Scheme 2 The reactive process of the bromination reaction for the
2.060(3) and 2.089(3) Å, respectively. The bond lengths of
V(III)ꢁOdipic, V(IV)ꢁOdipic and V(V)ꢁOdipic are in the range of
2.038(2) ꢁ2.062(2) Å, 2.014(1) ꢁ2.039(3) Å and 1.974(2) ꢁ2.033(5)
Å, respectively. It indicates that different oxidation states of
15 center vanadium atom indeed influence the bonding characteristic
of the complexes.
complexes
65
Thermal properties
To examine the thermal stability of the complexes, thermo
gravimetric analyses (TG) were carried out in the range of 30–
20 1000 °C. For the complex 1, the TG curve indicated three steps
(Fig. S5): the first step in the temperature range of 230–330 °C
with mass loss of 19.06% accords with a loss of two coordinated
water molecules and a uncoordinated carboxyl of bdc (calcd:
19.17%). The second step of decomposition occurred within the
25 range of 330–565 °C with a percentage weight loss of 31.62%,
which was due to the loss of three coordinated carboxyl (calcd:
31.65%). The last step of decomposition occurred within the
range of 565–1000 °C, which is considered the loss of framework
of the ligands. The TG curve of 2 (Fig. S6) is different from 1,
30 which shows four stages: the first stage occurs in the temperature
region of 115–150 °C with a mass loss of 4.63% corresponding to
the loss of two lattice water (calcd: 4.54%). The second stage in
the temperature region of 150–230 °C with mass loss of 9.22%
accords with a loss of four coordinated water molecules (calcd:
35 9.09%). For the third stage in the temperature region of 230–400
°C, 11.31% weight loss is observed, which due to the release of
two uncoordinated carboxyl of btec (calcd: 11.36%). And the last
step is observed in 400–1000 °C, which is similar to the complex
1 that considered the gradual decomposition of framework of the
40 ligands.
70
Fig. 4 Oxidative bromination of phenol red catalyzed by the complex 2.
Spectral changes at 10 min intervals, c(phosphate buffer) = 50 mmol/L,
75 pH = 5.8, c(KBr) = 0.4 mol/L, c(phenol red) = 10ꢁ4 mol/L
Addition of the solution of the complex 2 to the standard
reaction of bromide in phosphate buffer with phenol red as a trap
for oxidized bromine resulted in the visible color change of the
80 solution from yellow to blue. As is shown in Fig. 4, the electronic
absorption spectra are collected during such a color change
catalyzed by 2. It shows that a decrease in absorbance of the peak
at 443 nm due to the loss of phenol red and a increase in the
absorbance of the peak at 592 nm characteristic of the
85 bromophenol blue product, showing that the complex 2 performs
significant catalytic activity. The result of the mimic catalytic
activities for 1 (Fig. S7) is similar to that of 2.
Kinetic studies of mimicking bromination reaction
As vanadateꢁdependent haloperoxidases catalyze the visible
90 conversion of phenol red to bromophenol blue under peroxide
conditions, the role of the oxidovanadium complexes in the
bromide oxidation reaction was investigated in the mixed solution
of H2O–DMF under the constant temperature of 30 ± 0.5 °C.
Solutions used for kinetic measurements were maintained at a
95 constant concentration of H+ by the addition of the buffer solution
with NaH2PO4–Na2HPO4. Reactions were initiated in the
presence of H2O2 and KBr.
Mimicking bromination reaction of the complexes
To our knowledge, oxidovanadium complexes are able to mimic
the reaction in which vanadium haloperoxidases catalyze the
bromination of organic substrates in the presence of H2O2 and
45 bromide. For example, the bromination of trimethoxybenzene,41
+
benzene, salicylaldehyde and phenol catalyzed by the VO2
moiety.42,43 Herein, we investigated the bromination reaction
activities of the complexes 1 and 2 using phenol red as an organic
substrate which is shown by the conversion of phenol red to
50 bromophenol blue. The reaction is rapid and stoichiometric,
100
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which the two “cores” active site is in favor of forming a
intermediate species of the peroxidovanadium(VO(O2)+) and
accelerating of the catalytic reaction. This shows that the
intermediate species could be influenced by different molecular
60 structures of the complexes.45a The catalytic bromination
activities of the complexes (III) are similar to those of the
oxovandium complexes (IV)45b,c, furthermore, it is found that
related vanadium complexes also present different catalytic
activity, which may be due to the diffence of the nature, the
5
Fig. 5 The measurable absorbance(592 nm) dependence of time for the
10 complex 2. Conditions used: pH = 5.8, c(KBr) = 0.4 mol/L, c(H2O2) = 1 65 electronic and steric effects of Nꢁ, and Oꢁ donor chelating
mmol/L, c(phenol red)
=
10ꢁ4 mol/L. c(complex 2/mmol/L)
=
a:
aromatic ligands. In addition, for comparison, we are carried out
some reactions with other transition metal complexes as catalyst
(e.g. Cu, Ni, Co, Zn compounds, etc.), the results found that the
compounds not exhibited obviously the catalytic bromination
1.1359×10ꢁ5; b: 3.4077×10ꢁ5; c: 4.5436×10ꢁ5; d: 5.6795×10ꢁ5; e:
6.8154×10ꢁ5
15
20
25
Taking the complex 2 as an example, a series of dA/dt data 70 activities in our experiment system except the copper compound,
were obtained (Fig. 5) by changing the concentration of the
oxidovanadium complex (the measurable absorbance dependence
of time for complex 1 is shown in Fig. S8).
catalytic activity of which is close to those of the vanadium
complexes.
To our knowledge, their detailed catalytic reaction
mechanism is not clear up to now. Further catalytic reaction
75 mechanistic studies are underway. In general, the two complexes
exhibit different catalytic activity and they can be considered as
potential functional model vanadiumꢁdependent haloperoxidases.
Catalytic activity studies
To screen and evaluate the catalytic oxidative activity of the
80 synthesized complexes, all of them were applied in the oxidation
of cyclohexane with H2O2 as primary oxidant. The formation of
the main products is outlined in Scheme 3. In search of suitable
reaction conditions to achieve the best results in terms of
maximum products formation, the effect of oxidant concentration
85 (moles of H2O2 per mole of catalyst), acid concentration (moles
of HNO3 per mole of catalyst), nature of solvent and temperature
were studied in detail.
Fig. 6 –log(dC/dt) dependence of –logc for the complex 2 in DMF–H2O
30 at 30 ± 0.5 °C (c is the concentration of the complex 2; Conditions used:
c(phosphate buffer) = 50 mmol/L, pH 5.8, c(KBr) = 0.4 mol/L, c(phenol
red) = 10ꢁ4 mol/L.
And then as is shown in Fig. 6, the plot of ꢀlog(dc/dt) versus
35 (ꢀlog c) for complex 2 gives a straight line with a slope of 1.0381
and b=ꢁ1.0857, the former confirms the firstꢁorder dependence on
vanadium. Basing on the equation of “b=log k + ylog c2 + zlog
c3”, the reaction rate constant, k, is determined by the
concentrations of KBr and phenol red (c2 and c3), the reaction
40 orders of KBr and phenol red (y and z), as well as b. While in the
experiment, considering that the reaction orders of KBr and
phenol red (y and z) are 1 according to the literature;44 c2 and c3
are known as 0.4 mol/L and 10ꢁ4 mol/L, respectively, so the
reaction rate constant (k) for complex 2 can be calculated as
45 2.054×103 (mol/L)ꢁ2 sꢁ1.
90
Scheme 3 Main products observed during the catalytic oxidation of
95 cyclohexane
100
Table 4. Kinetic data for the complexes in DMF–H2O at 30 ± 0.5 °C.a
Complexes
m
b
k(mol/L)2s1
1.174×103
2.054×103
1
2
1.0495 ꢁ1.3284
1.0381 ꢁ1.0857
105
Similar plot for the complex 1 (Fig. S9) was generated in the
same way. Kinetic data for the complexes 1 and 2 in DMF–H2O
50 at 30 ± 0.5 °C are shown in Table 4. It is found that: (i) the
reaction orders of the oxidovanadium complex in bromination
reaction are all close to 1, confirming the firstꢁorder dependence
on vanadium; (ii) the order of the reaction rate constant is 1<2,
which is probably due to the two “core” active site of the
55 complex 2, while mono “core” active site of the complex 1, in
Fig. 7 Effect of H2O2 concentration on the cyclohexane oxidation with
catalyst 2. Reaction conditions: cyclohexane (0.34 g, 4 mmol), H2O2
110 (H2O2×10ꢁ5/catalyst molar ratio = 1, 2, 4 and 6), HNO3 (0.1 g, 1.5 mmol),
catalyst (0.0004 g, 0.0005 mmol), acetonitrile (3 mL), 40 oC
As shown in Fig. 7, the amount of hydrogen peroxide has an
6
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interesting effect on the catalytic activity. All the TON values
Fig. 9 Effect of solvent on the cyclohexane oxidation with catalyst 2.
displayed volcano shape curves, which may be caused by the 60 Reaction conditions: cyclohexane (0.34 g, 4 mmol), HNO3 (0.188 g, 3
further oxidation of cyclohexanol and cyclohexanone to
cyclhexylhydroperoxide by H2O2,46 which led to the decrease of
main products conversion. The maximum TON value was 20 or
44 upon 4 h when the H2O2×10ꢁ5/catalyst molar ratio was 1:1 or
mmol), H2O2 (2.59 g, 0.8 mol), catalyst (0.0004 g, 0.005 mmol), solvent
(3 mL), 40 oC
5
A deep evaluation devoted to select the best solvent for our
2:1. And it was 59 upon 3 h with the ratio of 4:1. When the 65 catalytic reactions, has been carried out by comparing the results
H2O2×10ꢁ5/catalyst molar ratio was higher to 6:1, the maximum
TON reached to 177 and the time was shorted to 2 h. It means
10 that more H2O2 led to higher TON value and shorter time to get it,
i.e. the participation of H2O2 can not only increase the conversion
obtained in 3 mL of five different solvents as acetonitrile
(CH3CN), methanol (MeOH), ethanol (EtOH), chloroform
(CHCl3) and petroleum ether (PE), while keeping fixed the
amount of cyclohexane (0.34 g, 4 mmol), HNO3 (0.188 g, 3
of the aimed products (cyclohexanol and cyclohexanone), but 70 mmol), H2O2 (2.59 g, 0.08 mol) and catalyst (0.0004 g, 0.0005
also increase the reaction rate. So, 2.59 g H2O2 was chosen to
make the H2O2×10ꢁ5/catalyst molar ratio equals to 6:1 in the
15 following experiments.
mmol), at 40 oC, running for 5 h. (shown in Fig. 9). All the curves
display a volcano shape, which is in good accordance with the
influence of H2O2 existing in the reaction solution on the TON
value (Fig. 8). The complex almost has no catalytic activity in
75 chloroform, little in methanol and ethanol (maximum TON of 15
and 34, respectively), good in acetonitrile (maximum TON of 213)
and best in petroleum ether (maximum TON of 297). This may be
the first finding that in petroleum ether with low solvent polarity,
a catalyst shows such high catalytic activity in cyclohexane
80 oxidation.
20
To our the best knowledge, acetonitrile usually be used as
solvent in the catalytic oxidation of cyclohexane,20b
cyclohexene,47 methyl phenyl sulfide,48 diphenyl sulfide,48
styrene47 and its derivatives,49 and epoxidation of cyclooctene32
25
Fig. 8 Effect of HNO3 concentration on the cyclohexane oxidation with
catalyst 2. Reaction conditions: cyclohexane (0.34 g, 4 mmol), H2O2 (2.59 85 catalyzed by vanadium(IV) or vanadium(V) complex due to its
g, 0.08 mol), HNO3 (HNO3/catalyst molar ratio = 0, 1000, 2000 and 4000),
catalyst (0.0004 g, 0.0005 mmol), CH3CN (3 mL), 40 oC, 4 h
high solvent polarity. In our previous study, we also found that,
vanadium(IV) complex shown the best catalytic activity in
acetonitrile and almost had no activity in petroleum ether for the
oxidation of cyclohexane.50 However, herein, acetonitrile is no
30
Similarly, four different molar ratios of HNO3/catalyst i.e. 0,
1000:1, 2000:1 and 4000:1 were considered to evaluate the effect 90 longer the best solvent for the oxidation catalyzed by
of nitric acid concentration on the oxidation of cyclohexane
catalyzed by the complex 2, while keeping fixed the amount of
vanadium(III) complex, but petroleum ether. We could not been
clear that why vanadium complex(III) is higher catalytic activity
in petroleum up to now. In order to further confirm higher
catalytic activity of vanadium complex(III), So, we have designed
35 cyclohexane (0.34 g, 4 mmol), H2O2 (2.59 g, 0.08 mol), catalyst
o
(0.0004 g, 0.0005 mmol) and CH3CN (3 mL) at 40 C, running
for 4 h. As shown in Fig. 8, the complex displayed no catalytic 95 a catalytic reaction experiment with starting materal V2(SO4)3(III)
activities in the absence of nitric acid. It indicates that H+ displays
a significant role in the reaction of cyclohexane oxidation. The
40 complex shows its catalytic activity with TON value of 21 when
the HNO3/catalyst molar ratio was 1000:1. And the overall TON
as a catalytst under the same conditions. The result shown that the
TON value of 75 was obtained in the solvent of petroleum ether,
which was also higher than those found by the oxidovanadium
complexes with +4 or +5 oxidation state as a catalytst in the same
increased sharply to 214 with a higher HNO3/catalyst molar ratio 100 nonꢁpolar solvent.32,50a
of 2000:1 (HNO3, 0.188 g, 3 mmol). However, it decreased
unexpectively to 17 with the ratio further increasing to 4000:1.
45 This indicates that excess acid is not good at the formation of the
aimed products, which may be due to the large amount of water
Under the optimal conditions: 2.59 g H2O2 (molar ratio of
H2O2×10ꢁ5/catalyst=6:1); 0.188
HNO3 (molar ratio of
HNO3/catalyst=2000:1); 3 mL petroleum ether; 40 C; 3 h, the
catalytic activity of the complex in the oxidation of
g
o
1
in the acid solution (68% HNO3), which has a block effect on the 105 cyclohexane was also studied. TON value of 395 was achieved,
catalytic activity.
which is higher than that of the complex 2.
The experimental results show that the catalytic oxidative
activities of the vanadium (III or IV) complexes are higher than
those of other metal complexes, such as Zn complexes (TON
110 =1.07ꢁ9.31) and Mo complexes (TON=36 and 18), etc. in the
oxidation of cyclohexane50b,c. This is probably because that metal
vanadium present variable oxidation states, form different activity
intermediate oxide species. In addition, the related vanadium
complexes also present different catalytic activity, samely, this is
115 also due to the infulence of the different Nꢁ, and Oꢁ donor
chelating aromatic ligands.50aꢁe
50
55
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Experimental Section
Formula
C15H12NO10V
417.20
C24H22N2O22V2
M (g mol−1)
792.32
Materials and methods
Crystal system
Monoclinic
P2(1)/c
Triclinic
P1
All the chemicals used were of analytical grade and without
further purification. V2(SO4)3 was synthesized according to the
literature method.51 A 30% aqueous solution of hydrogen
peroxide was used as primary oxidant in the cyclohexane
oxidation reaction. The synthetic manipulations were carried out
by hydrothermal reaction. The elemental analyses for C, H, and N
were carried out on a Perkin Elmer 240C automatic analyzer. IR
10 spectra was recorded on a JASCO FT/IRꢁ480 PLUS Fourier
Transform spectrometer with pressed KBr pellets in the range
200–4000 cm–1. UV–Vis absorption spectra diffuse reflection was
recorded with a JASCO V–570 UV/VIS/NIR spectrophotometer
in the 200–2500 nm. The cyclohexane oxidation products were
15 determined and analyzed by Shimadzu GCꢁ16A series gas
chromatograph equipped with a FID detector and a capillary
column (PG20000, column length: 30 m; internal diameter: 0.25
mm).
Space group
a ( Å )
7.1920(6)
15.4368(12)
14.2060(12)
90
8.1031(2)
9.7398(2)
10.142(2)
103.42(3)
109.89(3)
90.08(3)
729.3(2)
1
5
b ( Å )
c ( Å )
α
β
( ° )
( ° )
91.894(5)
90
γ ( ° )
V ( Å3 )
1576.3(2)
4
Z
Dcalc (Mg m−3)
Crystal size (mm3)
F(000)
1.758
1.804
0.07 × 0.141 × 0.121
848
0.188 × 0.209× 0.226
402
ꢀ
(MoꢁKα) (cm−1)
6.91
7.47
Reflections collected
Independent
reflections
11312
7242
3916 (2512)
5476 (4732)
Synthesis of V(dipic)(Hbdc)(H2O)2 (1). V2(SO4)3 (0.09 g, 0.25
20 mmol), 2,6ꢁpyridinedicarboxylic acid (H2dipic, 0.08 g, 0.5 mmol),
1, 3ꢁbenzeneꢁdicarboxylic acid (H2bdc, 0.08 g, 0.5 mmol),
vitamin C (0.02 g, 0.1 mmol) and H2O (10 mL) were mixed in a
25 mL glass beaker. After stirring for 3 h, the mixture was sealed
in a Teflonꢁlined autoclave and heated at 120 °C for three days,
25 followed by slowly cooling to room temperature. Yellowꢁgreen
crystals suitable for Xꢁray diffraction were obtained. Yield (based
on V): 0.12 g, 57.53%. Anal. Calc. for C15H12NO10V: C, 43.22; H,
2.81; N, 3.42. Found: C, 43.14; H, 2.88; N, 3.36%. IR (KBr, ν,
cmꢁ1): 3467, 3292, 3075, 3056, 1652, 1395, 512, 475, 449. UV–
30 Vis (λmax, nm): 262, 420, 742, 1040.
Synthesis of [V2(dipic)2(H2btec)(H2O)4]·2H2O (2). Complex 2
was synthesized by a similar method of 1 except that 1,3ꢁ
benzeneꢁdicarboxylic acid was replaced by 1,2,4,5ꢁ
benzenetetracarboxylic acid (H4btec, 0.06 g, 0.25 mmol). Yield
35 (based on V): 0.13 g, 65.63%. Anal. Calc. for C24H22N2O22V2: C,
36.45; H, 2.68; N, 3.63. Found: C, 36.35; H, 2.78; N, 3.53%. IR
(KBr, ν, cmꢁ1): 3439, 3257, 3060, 1672, 1379, 539, 491, 455.
UV–Vis (λmax, nm): 268, 456, 742, 1100.
(I > 2σ(I) )
Parameters
ꢃ(ρ) (e Å−3)
292
535
0.453 and ꢁ0.292
0.937
0.256 and ꢁ0.324
1.105
Goodnessꢁofꢁfit
a
R1
0.0413 (0.0766)b
0.0904 (0.1033)b
0.0266 (0.0330)b
0.0685 (0.0772)b
a
wR2
*a R = Σ Fo − Fc / Σ  Fo , wR2 = {Σ[w(Fo2−Fc2)2] / Σ[w(Fo2)2]}1/2
[Fo> 4σ(Fo)].
b Based on all data
;
Fourier map. All calculations were performed using the
60 SHELXSꢁ97 program.53 Crystal data, details of the data
collection and the structure refinement were given in Table 5.
Thermal analysis
Thermogravimetric analyses (TG) experiments were carried out
on a Perkin Elmer Diamond TG/DTA instrument. The samples
65 are initially heated for 1 h at 50 °C to remove the rudimental air.
During the simple ramping experiment, weight changes were
recorded as a function of temperature for a 10 °C minꢁ1
temperature gradient between 30 and 1000 °C in nitrogen
environments.
X-ray crystallographic determination
40 Suitable single crystals of the two complexes were mounted on
glass fibers for Xꢁray measurement, respectively. Reflection data
were collected at room temperature on a Bruker AXS SMART
APEX II CCD diffractometer with graphite monochromatized
Mo Kα radiation (λ=0.71073 Å) and a ω scan mode. All the
45 measured independent reflections (I > 2σ(I)) were used in the
structural analyses, and semiꢁempirical absorption corrections
were applied using SADABS program.52 Crystal structures were
solved by the direct method. All nonꢁhydrogen atoms were
refined anisotropically. All hydrogen atoms on organic
50 frameworks were fixed at calculated positions with isotropic
thermal parameters. while the oxygen atoms of coordinated water
molecules or lattice water molecules were located by different
70 Experimental set up for bromination reaction
Bromination reaction activity tests were carried out in the mixed
solution of H2O–DMF at the constant temperature of 30 ± 0.5°C.
Vanadium complexes were dissolved in a 25 mL H2O–DMF
mixed solution with the volume ratio of 4:1. Solutions used for
75 kinetic measurements were maintained at
a
constant
concentration of H+ (pH 5.8) by the addition of KBr, H2O2 and
NaH2PO4–Na2HPO4 buffer solution.54 Reactions were initiated by
the addition of the phenol red solution. The oxidovanadium
complexes in five different concentrations were confected in five
80 cuvettes, respectively. Then the cuvettes were put in the constant
temperature of water to heat 10 min and spectral changes were
recorded using a 721 UV–Vis spectrophotometer every interval 5
min. Finally, the resulting data were collected of the reaction and
fitted using the curveꢁfitting software in the program of Microsoft
85 Excel.
Table 5 Crystallographic data and structure refinement for complexes 1
55 and 2*
Complexes
1
2
It is assumed that the rate of this reaction is described by the
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x
y
z
rate equation: dc/dt=kc1 c2 c3 , then the equation of “log(dc/dt)=
logk xlogc1 ylogc2 zlogc3” was obtained, it is
corresponding to “ꢀlog(dc/dt)=ꢀxlogc1 ꢀ b (b=logk + ylogc2
concentration of vanadium(III) complexes, the reaction rate
constant (k) were obtained finally (k of 1.174×103 and 2.054
×103, respectively), which indicated that they can be considered
+
+
+
+
zlogc3)” where k is the reaction rate constant; c1, c2, c3 are the 60 as a potential functional model of VHPO. In addition, the
5
concentrations of oxidovanadium complexes, KBr and phenol red,
respectively; while x, y, z are the corresponding reaction orders.
According to LambertꢁBeer’s law, A=εꢁdꢁc, which is differential,
namely, dA/dt=εꢁdꢁ(dc/dt), where A is the measurable absorbance
catalytic abilities of the vanadium(III) complexes were evaluated
in the oxidation of cyclohexane. Various parameters as solvent,
temperature, acid and oxidant concentration have been tested in
order to optimize both activity and selectivity of the oxidative
of the resultant; ε is molar absorption coefficient, which of 65 process. Under optimized conditions, cyclohexanol and
10 bromophenol blue is measured as 14500 Mꢁ1cmꢁ1 at 592 nm; d is
light path length of sample cell(d=1). When the measurable
absorbance data were plotted versus reaction time, a line was
obtained and the reaction rate of oxidovanadium complexes
cyclohexanone were obtained with good to excellent conversion
catalyzed by the complexes 1 and 2 (TON of 395 for 1 and 279
for 2, respectively).
It is found that vanadium complexes with Nꢁ, and Oꢁ donor
(dA/dt) was given by the slope of this line. By changing the 70 chelating aromatic ligands exhibited better catalytic activity by
15 concentration of oxidovanadium complexes, a series of dA/dt data
can be obtained. The reaction rate constant (k) can be obtained
from a plot of ꢀlog (dc/dt) versus ꢁlog c1 and were fitted using the
curveꢁfitting software in the program Microsoft Excel by
generating a least squares fit to a general equation of the form
20 “y=mx – b”, in which “m” is the reaction order of the
oxidovanadium complexes in this reaction and “b” is the intercept
of the line. In the experiment, considering that the reaction orders
of KBr and phenol red (y and z) are 1 according to the literature;55
c2 and c3 are known as 0.4 mol/L and 10ꢁ4 mol/L, respectively.
25 Based on the equation of “b=logk + ylogc2 + zlogc3”, so the
reaction rate constant (k) can be obtained. Bromination of phenol
red was monitored by measurement of the absorbance at 592 nm
for reaction aliquots which were extracted at specific time points
and diluted into phosphate buffer of pH=5.8.
studying on the reactions of catalytic bromination and catalytic
oxidation. Our group will investigate deeply the application of the
vanadium complexes as catalysts in the future.
Acknowledgements
75 This work was supported by the grants of the National Natural
Science Foundation of China (No.21071071) and Dr. start
Foundation of Liaoning province in China (No.20111067) for
financial assistance and State Key Laboratory of Inorganic
Synthesis and Preparative Chemistry, College of Chemistry, Jilin
80 University, Changchun 130012, P. R. China (Grant No.
2013−05).
Supporting information paragraph
Tables of atomic coordinates, isotropic thermal parameters, and
complete bond distances and angles have been deposited with the
85 Cambridge Crystallographic Data Center. Copies of this
information may be obtained free of charge, by quoting the
publication citation and deposition numbers CCDC 858688 (1)
and 858689 (2) from the Director, CCDC, 12 Union Road.
Cambridge, CB2 1EZ, UK (fax+44ꢁ1223ꢁ336033; eꢁmail
90 deposit@ccdc.cam.ac.uk; http://www.ccdc.cam.ac.uk).
30 Experimental set up for catalytic oxidation
The oxidation reactions were carried out under air condition
(atmospheric pressure) in a twoꢁnecked glass flask, fitted with a
water condenser. In a typical experiment, 0.0004 g of the catalyst
(complexes 1 or 2) was dissolved in 3 mL of desired solvent.
35 Then the required amounts of H2O2 (in a 30% H2O solution) and
HNO3 were added in this order, followed by 0.34 g of
cyclohexane. The reaction solution was stirred at chosen
temperature for selected times.
Notes and references
For the products analysis, 0.05 g of methylbenzene (internal
40 standard) and 3 mL of diethyl ether (to extract the substrate and
the organic products from the reaction mixture) were added. The
obtained mixture was stirred for 10 min and then a sample (1.0
ꢂL) was taken from the organic phase and analyzed by a GC
equipped with a capillary column and a flame ionization detector
45 by the internal standard method. TON is moles of products
(cyclohexanol and cyclohexanone)/mole of catalyst. Blank
experiments confirmed that no cyclohexanol or cyclohexanone
was formed in the absence of the metal catalyst under the same
conditions.
College of Chemistry and Chemical engineering, Liaoning Normal
University, Dalian, 116029, P.R. China. Fax: 86ꢀ0411ꢀ82156987; Tel:
86ꢀ0411ꢀ82156987; Corresponding author: Y. H. Xing; Eꢀmail:
95 xingyongheng2000@163.com
.
† Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/b000000x/
1
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presence of H2O2, KBr and phosphate buffer. By changing the
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10 | Journal Name, [year], [vol], 00–00
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For Table of Contents Use only
Novel vanadium(III) complexes with rigid
phenylpolycarboxylate ligands: synthesis, structures and
application in C-H bond activation
Dong Xue Ren, Na Xing, Hui Shan, Chen Chen, Yun Zhu Cao, Yong Heng Xing*
College of Chemistry and Chemical Engineering, Liaoning Normal University, Huanghe Road 850#,
Dalian 116029, P. R. China
*Corresponding author: E-mail: xingyongheng2000@163.com
Two vanadium(III) complexes: V(dipic)(Hbdc)(H2O)2 (1) and [V2(dipic)2(H2btec)(H2O)4]·2H2O (2) are
synthesized and characterized. They exhibited catalytic bromination and cyclohexane oxidation activity.
1