КООРДИНАЦИОННАЯ ХИМИЯ, 2015, том 41, № 6, с. 342-345
УДК 541.49
SYNTHESIS, CRYSTAL STRUCTURE, AND CATALYTIC PROPERTY OF A VANADIUM(V) COMPLEX WITH MIXED LIGANDS
© 2015 X. H. Shen*, Z. W. Zhang, L. J. Shao, Q. Lian, and C. Liu
Department of Chemistry, Hebei Normal University of Science & Technology, Qinhuangdao, 066600 P.R. China
*E-mail: xihai_shen@163.com Received October 20, 2014
With a tridentate hydrazone ligand N'-(3-bromo-2-hydroxybenzylidene)-2-methylbenzohydrazide (H2L) and a bidentate ligand benzohydroxamic acid (HL') with VO(Acac)2, a mononuclear vanadium(V) complex was prepared and characterized by elemental analysis, IR spectroscopy and X-ray structure determination (CIF file CCDC no. 1029909). The complex crystallizes in the monoclinic space group C2/c with unit cell dimensions a = 27.870(2), b = 11.4893(5), c = 18.467(2) А, в = 131.444(1)°, V = 4432.6(6) A3, Z = 8, R1 = = 0.0350, and wR2 = 0.0749. Single crystal X-ray diffraction analysis reveals that the V atom is coordinated by the phenolate O, imino N and enolate O atoms of the hydrazone ligand, and the carbonyl O and hydroxy O atoms of benzohydroxamate ligand, and one oxo O group, in an octahedral coordination. Catalytic oxidation of the complex on some olefins was performed.
DOI: 10.7868/S0132344X15050060
INTRODUCTION
In recent years, the catalytic oxidation of olefins has aroused much attention in the production of chemicals and fine chemicals since epoxides are key starting materials for a wide variety ofoily products [1—5]. Because of the environment friendly nature, H2O2 has been regarded as the first selected oxidant in the oxidation of olefins. Transition metal complexes with various ligands have presented interesting catalytic properties [6—10]. Among the complexes, vanadium species show efficient catalytic oxidation properties [11—16]. In this paper, a new vanadium(V) complex with mixed ligands N'- (3-bromo-2-hydroxybenzylidene)- 2-me-thylbenzohydrazide (H2L) and a bidentate ligand ben-zohydroxamic acid (HL') was prepared and its catalytic oxidation property was performed.
EXPERIMENTAL
Materials and methods. 3-Bromosalicylaldehyde, 2-methylbenzohydrazide and benzohydroxamic acid were purchased from Alfa Aesar. VO(Acac)2 and solvents are commercially available and were used without further purification. Elemental analyses for carbon, hydrogen, and nitrogen were carried out with an Elementar Vario EL. Infrared spectra were measured on KBr disks with a Hitachi I-5040 FT-IR spectrophotometer. XH NMR data were recorded on a Bruker NMR 300 MHz instrument.
Synthesis of H2L. 3-Bromosalicylaldehyde (2.01 g, 10 mmol) and 2-methylbenzohydrazide (1.50 g, 10 mmol) were dissolved in methanol (30 mL). The mixture was refluxed for 30 min and the solvent was evaporated by
distillation. Colorless solid was recrysallized from methanol to give pure product of H2L. The yield was 83%.
For C15H13BrN2O2
anal. calcd., %: C, 54.07; H, 3.93; N, 8.41. Found, %: C, 53.89; H, 4.02; N, 8.50.
IR (KBr; v, cm-1): 3440 v(O-H); 3241 v(N-H); 1646 v(C=O); 1608 v(C=N); 1175 v(C-OH). 1H NMR (300 MHz; DMSO-d6): 8 12.71 (s., 1H), 12.22 (s., 1H), 8.63 (s., 1H), 7.2-7.7 (m., 5H), 6.93 (t., 1H), 2.51 (s., 3H).
Synthesis of the complex. Equimolar quantities (1.0 mmol each) of H2L (0.333 g), HL' (0.137 g) and VO(Acac)2 (0.265 g) were dissolved in methanol (20 mL). The mixture was refluxed for 30 min and cooled to room temperature to give a deep brown solution. The solution was kept still in air for a week to slow evaporate to give brown block-shaped single crystals of the complex. The yield was 61%.
For C22H17BrN3O5V
anal. calcd., %: Found, %:
C, 49.46; C, 49.32;
H, 3.21; H, 3.15;
N, 7.87. N, 8.02.
IR (KBr; v, cm-1): 3445 v(O-H); 3196 v(N-H); 1602 v(C=N); 976 v(VO).
Catalytic oxidation experiment was carried out in a 50 mL glass round-bottom flask fitted with a reflux condenser and placed in an oil bath at prearranged temperature under continuous stirring. The oxidation
SYNTHESIS, CRYSTAL STRUCTURE, AND CATALYTIC PROPERTY
343
Table 1. Crystallographic data ment for the complex
and and structure refine-
Parameter Value
Formula weight 534.2
Crystal system Monoclinic
Space group C2/c
a, Â 27.870(2)
b, Â 11.4893(5)
c, Â 18.467(2)
ß, deg 131.444(1)
V, Â3 4432.6(6)
Z 8
Pcalcd g cm-3 1.601
/(000) 2144
p., mm-1 2.289
9 Range, deg 2.86-26.06
Index ranges hkl -32 < h < 34
-13 < k < 14
-22 < l < 22
Reflections collected/unique 18693/4373
Rint 0.0279
Observed with I > 2o(I) 3500
Parameters 293
Rastraints refined 1
Final R index (I > 2a(I)) 0.0350, 0.0749
R index (all data) 0.0506, 0.0835
Goodness-of-fit on F2 1.040
APmaxMPmirn « Â~3 0.442/-0.361
was carried out as follows: the complex (0.032 mmol) was dissolved in 10 mL 1,2-dichloroethane. Then 10 mmol alkene was added to the reaction mixture and 30 mmol TBHP was added. The reaction mixture was refluxed for 1 h. The reaction products were monitored at periodic time intervals using gas chromatography. The oxidation products were identified by comparison with authentic samples (retention times in GC).
X-ray structure determination. Data collection for the complex was performed with a Bruker Apex II CCD diffractometer at 298 K. The structure was solved by direct methods with SHELXS-97 and refined by full-matrix least squares (SHELXL-97) on F 2 [17]. All non-hydrogens were refined anisotropically. The hydrogen atom of N(3) was located from a difference Fourier map and refined isotropically, with N—H distance restrained to 0.90(1) A. The remaining hydrogens were placed geometrically and refined with a riding model, with isotropic displacement coefficients U(H) = 1.2 U(C) or 1.5 U(C). Crystallographic data for the complex are summarized in Table 1. Selected bond lengths and angles are listed in Table 2.
Supplementary material for complex has been deposited with the Cambridge Crystallographic Data Centre (no. 1029909; deposit@ccdc.cam.ac.uk or http:// www.ccdc.cam.ac.uk).
RESULTS AND DISCUSSION
The vanadium complex was prepared by reaction of equimolar quantities of the hydrazone ligand, benzo-hydroxamic acid and VO(Acac)2 in methanol. Crystals of the complex are stable in air, and soluble in methanol, ethanol, DMF and DMSO, insoluble in water. The hydrazone ligand and the complex have been characterized by infrared spectroscopy. In the spectra of both H2L and the complex, the broad bands centered at about 3440 cm-1 are assigned to the O—H vi-
Table 2. Selected bond distances (A) and angles (deg) for the complex
Bond d, Â Bond d, Â
V(1)-O(1) 1.8697(18) V(1)-O(2) 1.9755(17)
V(1)-O(3) 2.1904(19) V(1)-O(4) 1.8655(17)
V(1)-O(5) 1.5855(19) V(1)-N(1) 2.057(2)
Angle ro, deg Angle ro, deg
O(5)V(1)O(4) 95.00(9) O(5)V(1)O(1) 98.99(9)
O(4)V(1)O(1) 107.93(8) O(5)V(1)O(2) 100.76(9)
O(4)V(1)O(2) 88.95(7) O(1)V(1)O(2) 152.70(8)
O(5)V(1)N(1) 96.27(9) O(4)V(1)N(1) 161.51(8)
O(1)V(1)N(1) 84.72(8) O(2)V(1)N(1) 74.58(8)
O(5)V(1)O(3) 170.93(9) O(4)V(1)O(3) 76.16(7)
O(1)V(1)O(3) 82.16(8) O(2)V(1)O(3) 81.30(7)
N(1)V(1)O(3) 92.79(8)
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C(5)
Fig. 1. The molecular structure of the complex with 30% probability thermal ellipsoids.
Fig. 2. Molecular packing structure of the complex, viewed along the y axis. Hydrogen bonds are shown as dashed lines.
brations of the water molecules. In the spectra of H2L bands appear attributed to N—H, C=O, C=N, and
and the complex, the typical bands due to the N—H vi- C—OH at 3241, 1646, 1608, and 1175 cm-1, respec-
brations are observed at 3241 and 3196 cm-1, respec- tively. As a comparison, in the spectrum of the com-
tively. In the infrared spectrum of H2L, absorption plex, the strong band indicative of the C=N group is
Table 3. Catalytic oxidation results*
Substrate Product Conversion, %**
69
77
O
86
XT Jf] 93
XT* JC^ 82
* The molar ratio of catalyst : substrate : TBHP is 1 : 300 : 1000. The reactions were performed in mixture of CH^OH-CH^C^ (V: V = 6 : 4; 1.5 mL).
** The GC conversion (%) was measured relative to the starting substrate after 1 h.
KOOP^HH^HOHHAtf XHMH3 TOM 41 № 6 2015
SYNTHESIS, CRYSTAL STRUCTURE, AND CATALYTIC PROPERTY
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observed at 1602 cm-1 [18], and the C=O absorption in the spectrum of H2L is disappeared in that of the complex. The V=O stretching mode occur as a single sharp band at 976 cm-1 [19].
The molecular structure of the complex is shown in Fig. 1. The coordination geometry around vanadium can be described as octahedral with the phenolate O, imine N and enolate O atoms of the hydrazone ligand, and the hydroxy O atom of the benzohydroxamate ligand in the equatorial plane, and with the carbonyl O atom of the benzohydroxamate ligand and one oxo O group in the axial positions. The O(5)=V(1)-O(3) axis is almost linear with bond angle of 170.93(9)°. Because of the trans influence of the oxo O group, the distance of V(1)-O(3) is much longer than the other bonds. Such elongation has previously been observed in other complexes with similar structures [20, 21]. The V atom deviates from the equatorial plane by 0.255(1) Á. All the bond values are in good agreement with those observed in vanadium(V) complexes with hydrazone ligands [20-23].
In the crystal structure of the complex, molecules are linked through intermolecular hydrogen bonds of N(3)-H(3)---O(2)i (N(3)-H(3) 0.90(1), H(3)-O(2) 2.05(2), N(3)---O(2)i 2.915(3) Á, N(3)-H(3)-O(2) 160(3)°; symmetry code: 1 -x, 1 - y, -z) and C(4)-H(4)-O(5)ü (C(4)-H(4) 0.93, H(4)-O(5)u 2.56(2), C(4)-O(5)11 3.253(3) Á, C(4)-H(4)-O(5)11 131(3)°; symmetry code: 11 -1/2 - x, -1/2 + y, -1/2 - z) to form 1D chains, as shown in Fig. 2.
The catalytic results are given in Table 3. Effective epoxide yields and 100% selectivity were observed for all aliphatic and aromatic substrates. In general, oxidation of aromatic substrates gave the corresponding epoxides in over 82% yields, while in the oxidation of aliphatic substrates, the conversion is lower than 7
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