Synthesis, characterization, crystal structure determination and catalytic activity in epoxidation reaction of two new oxidovanadium(IV) Schiff base complexes

Article abstract of DOI:10.1016/j.molstruc.2016.06.038

The five coordinated vanadium(IV) Schiff base complexes of VOL¹ (1) and VOL² (2), HL¹?=?2-{(E)-[2-bromoethyl)imino]methyl}-2- naphthol, HL²?=?2-{(E)-[2-chloroethyl)imino]methyl}-2- naphthol, have been synthesized and they were characterized by using single-crystal X-ray crystallography, elemental analysis (CHN) and FT-IR spectroscopy. Crystal structure determination of these complexes shows that the Schiff base ligands (L¹ and L²) act as bidentate ligands with two phenolato oxygen atoms and two imine nitrogen atoms in the trans geometry. The coordination geometry around the vanadium(IV) is distorted square pyramidal in which vanadium(IV) is coordinated by two nitrogen and two oxygen atoms of two independent ligands in the basal plane and by one oxygen atom in the apical position. The catalytic activity of the Schiff base complexes of 1 and 2 in the epoxidation of alkenes were investigated using different reaction parameters such as solvent effect, oxidant, alkene/oxidant ratio and the catalyst amount. The results showed that in the presence of TBHP as oxidant in 1: 4 and 1:3 ratio of the cyclooctene/oxidant ratio, high epoxide yield was obtained for 1 (76%) and 2 (80%) with TON(= mole of substrate/mole of catalyst) of 27 and 28.5, respectively, in epoxidation of cyclooctene.

Full text of DOI:10.1016/j.molstruc.2016.06.038

Accepted Manuscript
Synthesis, characterization, crystal structure determination and catalytic activity in
epoxidation reaction of two new oxidovanadium(IV) Schiff base complexes
Vida Tahmasebi, Gholamhossein Grivani, Giuseppe Bruno
PII:
S0022-2860(16)30614-7
10.1016/j.molstruc.2016.06.038
MOLSTR 22657
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 17 April 2016
Revised Date: 9 June 2016
Accepted Date: 13 June 2016
Please cite this article as: V. Tahmasebi, G. Grivani, G. Bruno, Synthesis, characterization, crystal
structure determination and catalytic activity in epoxidation reaction of two new oxidovanadium(IV) Schiff
base complexes, Journal of Molecular Structure (2016), doi: 10.1016/j.molstruc.2016.06.038.
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Synthesis, characterization, crystal structure determination and catalytic activity in
epoxidation reaction of two new oxidovanadium(IV) Schiff base complexes
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Vida Tahmasebia. Gholamhossein Grivania,* . Giuseppe Brunob
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aSchool of Chemistry, Damghan University, Damghan, 36715-364, Iran
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bUniversità degli Studi di Messina, dip. Scienze Chimiche, Viale Ferdinando S.
d’Alcontres, 98166 Messina, Italy
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*Corresponding author:
E-mail address: grivani@du.ac.ir
Tel/fax.: +98 2335220095
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Abstract
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The five coordinated vanadium(IV) Schiff base complexes of VOL1 (1) and VOL2 (2), HL1=2-
{(E)-[2-bromoethyl)imino]methyl}-2- naphthol, HL2=2-{(E)-[2-chloroethyl)imino]methyl}-2-
naphthol, have been synthesized and they were characterized by using single-crystal X-ray
crystallography, elemental analysis (CHN) and FT-IR spectroscopy. Crystal structure
determination of these complexes shows that the Schiff base ligands (L1 and L2) act as bidentate
ligands with two phenolato oxygen atoms and two imine nitrogen atoms in the trans geometry.
The coordination geometry around the vanadium(IV) is distorted square pyramidal in which
vanadium(IV) is coordinated by two nitrogen and two oxygen atoms of two independent ligands
in the basal plane and by one oxygen atom in the apical position. The catalytic activity of the
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Schiff base complexes of 1 and 2 in the epoxidation of alkenes were investigated using different
reaction parameters such as solvent effect, oxidant, alkene/oxidant ratio and the catalyst amount.
The results showed that in the presence of TBHP as oxidant in 1: 4 and 1:3 ratio of the
cyclooctene/oxidant ratio, high epoxide yield was obtained for 1 (76% ) and 2 (80% ) with
TON(= mole of substrate /mole of catalyst) of 27 and 28.5, respectively, in epoxidation of
cyclooctene.
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Keywords: Oxidovanadium(IV) ; Schiff base; X-ray crystallography; Catalysis; Epoxidation;
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Introduction
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The Schiff base compounds, derived from condensation reaction of primary amines and
aldehydes or ketones, are important class of ligands and played central role in the development
of coordination chemistry [1-3] as they readily form stable complexes with most transition
metals with interesting and important properties in different oxidation states [4-7]. Recently
many researchers have been concentrating on the coordination chemistry of vanadium
complexes. Interest in the coordination chemistry of vanadium complexes has grown enormously
due to:(i) multifaceted biological activity observed in some low-order living systems like
mushrooms[8-10], terrestrial fungi, algae [11, 12] and sea squirts [13]; (ii) involvement in active
site of several enzymes such as vanadium-dependent nitrogenases, haloperoxidases [14, 15] as
well as its involvement in phosphate metabolizing enzymes [16] and phosphomutases [17]; (iii)
widely used as catalysts for many organic reactions[18-24]; (iv) exhibition of insulin mimesis by
certain vanadium complexes [25–27] and, (v) exhibition anticancer properties
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by some oxidovanadium(IV) complexes [28, 29] as well as antibacterial and antimicrobial [30,
31] activity. Recently we reported the synthesis, characterization, crystal structure determination
and catalytic activity of some oxidovanadium(IV) Schiff base complexes[ 32] derived from
salicylaldehyde derivatives and 2-halo(chloro and bromo) ethyl amines [33–35]. In this research
we describe the synthesis, characterization, crystal structure determination of two new
oxidovanadium Schiff base complexes of 1 and 2 derived from 2-Hydroxy-naphthaldehyde and
2-bromo ethyl ammonium hydrobromide and 2-chloro ethyl ammonium hydrochloride,
respectively. In addition the catalytic activity of synthesized vanadyl complexes in epoxidation
of alkenes was investigated (scheme 1).
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<Scheme 1>
Experimental
Materials
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All reagents and solvents for synthesis and analysis were commercially available and purchased
from Merck and used as received without further purifications. Infrared spectra were recorded
using KBr disks on a FT-IR PerkinElmer RXI spectrophotometer. Elemental analyses were
carried out using a Heraeus CHN–O-Rapid analyzer. X-ray diffraction pattern of the freshly
calcined sample was recorded in a Bruker AXS diffractometer D8 ADVANCE with Cu Ka
radiation filtered by a nickel monochromator and operated at 40 kV and 30 mA. Diffraction
pattern was recorded in the range of 2θ = 10–80 and the results agreed with calculated values.
All GC yields base on starting materials were obtained by using Varian CP-3800 instrument with
silicon-DC 200 column.
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Synthesis of the 2-{(E)-[2-bromoethyl)imino]methyl}2- naphthol (HL1)
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To a 250 ml round bottom flask containing 100 ml absolute methanol were added 10 mmol 2-
hydroxy-naphthaldehyde, 10 mmol of 2-bromo ammonium hydrobromide. Then 10 mmol of
NaOH, dissolved in 5 ml of H2O, was added to the above solution and the content was refluxed
for 4 h. After evaporating the solvent by a rotary evaporator at 90 °C, the yellow precipitate was
collected and washed with slightly cooled water and filtered ( 89%). The yellow crystals were
obtained by the crystallization of precipitate in 1:1 mixture of chloroform and methanol. M.p.:
106°C. Anal. Calc. for C13H12BrNO: C, 56.63; H, 4.18; N,5.25 %. Found: C, 56.33; H, 3.97, N,
5.05 %. IR (KBr pellet, cm-1): 3300-3520 (b1, O-H, phenolic), 2800-3070 (w2, C-H aliphatic and
aromatic), 1630 (s3, C=N), 1490, 1538, (m4, C=C).
Synthesis of the 2-{(E)-[2-chloroethyl)imino]methyl}2- naphthol (HL2)
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The Schiff base compound of HL2 was synthesized in similar to the preparation of the Schiff
base compound of HL1 except 2-chloroethyl ammonium hydrochloride was used instead of 2-
bromo ammonium hydrobromide (84%). M.p.: 104°C. Anal. Calc. for C13H12ClNO: C, 66.54; H,
5.04; N,6.03 %. Found: C, 67.09; H, 4.73, N, 6.02 %. IR (KBr pellet, cm-1): 3300-3525 (b, O-H,
phenolic), 2800-3060 (w, C-H aliphatic and aromatic), 1624 (s, C=N), 1430-1550, 1534(m,
C=C).
Synthesis of the 1
1 broad
2 weak
3 strong
4 medium
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In a 100 ml round bottom flask, 5 mmol of HL1 was dissolved in 40 ml of MeOH and to this
solution was added 2.5 mmol of VO(acac)2 dissolved in 20 ml of MeOH and the content was
refluxed with stirring for 2 h. After evaporating of the solvent by a rotary evaporator at 90 °C,
the content was crystallized in the solvent mixture of n-Hexane/CHCl3 (1/1 v/v) Then the
greenish crystals were filtered off and washed with n-hexane and dried in an oven (62%). M.p
270.oC. Anal. Calc. for C26H20Br2N2O3V: C, 50.40; H, 3.43; N, 4.67%. Found: C,50.42; H, 3.23;
N, 4.52% IR (KBr pellet, cm-1): 2880-3080, (w, C-H aliphatic and aromatic), 1610 (s, C=N),
1508, 1540 (m, C=C) and 970 (s, V=O).
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Synthesis of the 2
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The Schiff base complex of 2 was synthesized in similar to the preparation of the 1 Schiff base
complex except 2-{(E)-[2-chloroethyl)imino]methyl}2- naphthol (HL2) was used instead of 2-
{(E)-[2-bromoethyl)imino]methyl}2- naphthol (HL1)(72%). M.p 265.oC. Anal. Calc. for
C26H20Cl2N2O3V: C, 58.67; H, 3.99; N, 5.50%. Found: C,58.87; H, 3.77; N, 5.28% IR (KBr
pellet, cm-1): 2880-3080, (w, C-H aliphatic and aromatic), 1604 (s, C=N), 1508, 1540 (m, C=C)
and 970 (s, V=O).
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X-ray structure determination
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Green single crystals with dimensions of 0.22 mm × 0.15 mm × 0.34 mm for 1 and the
dimensions 0.35 mm × 0.18 mm × 0.40 mm for 2 were chosen for X-ray diffraction study.
Crystallographic measurements were done at 296 K with four circle CCD diffractometer Gemini
of Oxford diffraction, Ltd., with mirrors-collimated Mo Kα radiation (λ = 0.71073Å). The crystal
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structures were solved by direct methods with program SIR2002 [36] and refined with the
Jana2006 program package [37] by full-matrix least-squares technique on F2. The molecular
structure plots were prepared by ORTEP III [38]. Hydrogen atoms were mostly discernible in
difference Fourier maps and could be refined to reasonable geometry. According to common
practice they were nevertheless kept in ideal positions during the refinement. Crystallographic
data and details of the data collection and structure solution and refinements are listed in Table 1.
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<Table 1>
General procedures of the epoxidation reaction
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In a 10 ml round bottom flask equipped with a magnetic stirring bar 0.5 mmol of alkene was
reacted with different amounts of oxidant and vanadyl Schiff base complex in the 5 ml of solvent
and the reaction mixture was refluxed. The progress of the reaction was monitored by GLC.
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Results and discussion
Synthesis and Characterization
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Scheme 1 shows the synthetic procedures of the bidentate Schiff base ligands of HL1, HL2 and
their vanadyl Schiff base complexes of 1 and 2. The Schiff base ligands of HL1, HL2 were
prepared by the simple reaction of 2-hydroxy-naphthaldehyde with 2-bromo ammonium
hyrobromide(HL1) and 2-chloro ammonium hydrochloride (HL2) in the presence of NaOH in the
methanol as a solvent in the reflux conditions. Subsequently, by reaction of the synthesized
Schiff base ligands (HL1, HL2) with VO(acac)2 in the molar ratio of 2:1 in methanol in the reflux
conditions, the vanadyl Schiff base complexes of 1 and 2, were prepared. The two vanadyl Schiff
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base complexes of 1 and 2 are soluble in common organic solvents such as CH3OH, CHCl3 and
(CH3)2S=O (dimethyl sulfoxe) but insoluble in H2O. The HL1, HL2 Schiff base ligands and their
vanadyl Schiff base complexes were characterized by CHN analysis, FT-IR spectra. The
structures of the oxovanadium(IV) Schiff base complexes of 1 and 2 were determined by single
crystal X-ray analysis while the FT-IR spectra of HL1, HL2, 1 and 2 provided the data regarding
to the nature of their functional groups. The FT-IR spectra of the Schiff base ligands (HL1, HL2)
show a broad band in the region of 3300-3520 cm-1 indicating the presence of the phenolic O-H.
This band is disappeared in the FT-IR spectrum of the 1 and 2 Schiff base complexes indicating
the coordination of the ligand via phenolato dentate. The fundamental stretching mode of the
azomethine moiety, vC=N, for the free ligands(HL1, HL2) are appeared at 1630 cm-1 and 1624 cm-
1 respectively which are shifted to the lower frequencies by 20 cm-1 and appeared at 1610 cm-1 in
the FT-IR spectra of the 1 and 2 vanadium Schiff base complexes(S1 and S2 in Supplementary
materials). These changes are attributed to the involvement of the azomethine nitrogen of the
Schiff base ligands (HL1, HL2) in coordination to the vanadium(IV) center. The
oxovanadium(IV) complexes generally show vV= O around 860 cm-1 for polynuclear linear chain
structures (V=O…V=O…) with orange color but in solution they are green and around 970 cm-1
for monomeric form with green color in the solution and solid state [39, 40]. Thus the sharp band
in 970 cm-1 in the FT-IR spectra of the oxidovanadium Schiff base complexes of 1 and 2,
attributed to the V=O vibration frequencies approves the monomeric form of (L1)2V=O and
(L2)2V=O Schiff base complexes in the solid state as confirmed by the single crystal X-ray
diffraction ( Figs 1, 2). In comparison to similar complexes [33-35, 41,42], the two characteristic
bands (vC=N, vV= O) in the synthesized ligands (HL1, HL2) and complexes (1, 2) are located in the
same region as it was seen in Table 2.
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<Table 2>
Crystal and molecular structure
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An ORTEP view of 1 and 2 Schiff base complexes with the atoms numbering scheme is given in
Figs. 1 and 2, respectively. Tables 3 and 4 list the selected bond lengths and angles. In these
complexes, the Schiff base ligands are anionic and N, O-bidentate. Vanadium(IV) is coordinated
by two nitrogen and two oxygen atoms of two independent ligands in the basal plane and by one
oxygen atom in the apical position. The square pyramidal geometry around the vanadium (IV)
ion in these complexes is distorted because of the different bond distances and angles. The
largest angular distortion from an ideal square pyramidal geometry (90 & 180°) occurs in the
angles of O3-V1-O1 [110.70(2), 110.75(6)], O3-V1-O2 [112.50 (7), 112.42(5)], O2-V1-O1
[136.80(2), 136.83(5)] and N1-V1-N2 [156.30(2), 156.30(5)] for 1 and 2 respectively. The V=O,
V-O and V-N distances are similar to those found in other oxidovanadium(IV) complexes with
bidentate Schiff base ligands [43-47].
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<Figs. 1, 2> & <Tables 3, 4>
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These complexes contain several intra- and inter-molecular non-classical hydrogen bonds
of the type C–H…X (X = O, Br, Cl), as well as C–H···O intermolecular hydrogen bonds linking
the monomeric units to each other (Figs. 3, 4 and Tables 5, 6).
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<Figs. 3, 4> & <Table 5, 6>
Catalytic activity
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In order to investigate the catalytic activity of the oxidovanadium Schiff base complexes of 1 and
2 in epoxidation reaction, the cyclooctene was used as a model substrate and different reaction
parameters such as solvent, oxidant, alkene /oxidant ratio and the amount of the catalyst were
optimized. Fig. 5 illustrates the results of the epoxidation of the cyclooctene in the presence of
the tert-butyl hydroperoxide( TBHP) as an oxidant in different solvents with the catalytic amount
of the oxidovanadium(IV) Schiff base complexes (1 and 2). The trend of the observed solvent
effect was CHCl3>CH3CN>CCl4>CH2Cl2>MeOH>CH3CN/H2O>THF. It seems that in the
aprotic solvents such as CHCl3, CH3CN and CCl4 the high epoxidation yield is observed. By
addition of the H2O (as a protic solvent) to the CH3CN the conversion was decreased
dramatically (Fig. 5). We also tested the different reaction media to obtain the suitable oxidant
media for epoxidation of the cyclooctene (Table 7). The results show that the high conversion is
only obtained in the presence of the TBHP in CHCl3. This may be related to the ability of the
TBHP and inability of the H2O2 and NaIO4 to mix with the organic substrate phase. Table 8
shows the cyclooctene/oxidant ratio and the effect of amount of the catalyst in epoxidation
reaction of the cyclooctene by the Schiff base complexes of 1 and 2. According to this table the
1:4 and 1:3 ratio of cyclooctene/oxidant and the 0.014 mmol of the catalysts can be chosen as the
optimal amounts providing the highest epoxide yields for 1 and 2, respectively. Table 9 shows
the effect of catalyst concentration in epoxidation of cyclooctene in CHCl3 as a solvent and in the
presence of TBHP as an oxidant. The epoxidation reaction was carried out by using three
amounts of catalysts of 1 and 2 ( 0.01, 0.014 and 0.02 mmol) with keeping of other conditions.
According to this table it was clear that in the case of 0.014 mmol of both of catalysts the highest
conversion were obtained. In this work, the stability of the vanadyl Schiff base complexes of 1
and 2 has not been studied in the optimum conditions. Thus the epoxidation of different alkenes
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were investigated in optimized conditions (0.014 mmol of catalysts, TBHP as an oxidant, 1:4 and
1:3 ratio of alkene/oxidant for 1 and 2 respectively and CHCl3 as a solvent). The obtained results
were showed in Table 10. As seen from these tables cyclic alkenes were more efficiently
converted to their epoxides than linear alkenes and all alkenes selectively converted to their
epoxides by 1 and 2. In comparison, the activity of the vanadyl Schiff base complexes of 1 and 2
is lower than those vanadyl complexes that recently were reported [33, 41, 42]. Thus the
naphtolate moiety have been decreased the activity of the vanadyl complexes respect to other
substituted (H and OMe) salicylate moieties.
<Fig. 5 > & <Tables 7, 8, 9, 10>
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Conclusion
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In conclusion we readily synthesized two new oxovanadium(IV) Schiff base
complexes and characterized them by spectroscopic methods as well as single crystal
X-ray diffraction. The catalytic activity of the 1 and 2 complexes was investigated in
the epoxidation of the alkenes. The reaction conditions were optimized and the results
showed that the 1 and 2 complexes can be used as active and selective homogeneous
catalysts in the epoxidation of alkenes. It seems that the naphtalate moiety decreases
the activity of the vanadium center respect to the substituted salicylate (with H and
OMe groups).
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Appendix A. Supplementary
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Crystallographic data (excluding structure factors) for the structures reported in this paper have
been deposited with the Cambridge Crystallographic Center. CCDC of 1440825 & 1440826
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contains the supplementary crystallographic data for 1 and 2. Copies of the data can be obtained
free of charge on application to The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK,
fax: +44 1223 336 033, e-mail: deposit@ccdc.cam.ac.uk or http:www.ccdc.cam.ac.uk.
Acknowledgements
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We acknowledge Damghan University (DU) for partial support of this work.
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Scheme 1. Preparation procedure of the new bidentate O, N Schiff base ligands, HL1, HL2, and
their vanadyl Schiff base complexes of 1 and 2.
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Fig. 1. An ORTEP view of the 1, showing 50% probability displacement ellipsoids and the atom-
numbering. Dashed lines indicate intramolecular C–H···O hydrogen bond.
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Fig. 2. An ORTEP view of the 2, showing 50% probability displacement ellipsoids and the
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atom-numbering. Dashed lines indicate intramolecular C–H···O hydrogen bond.
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Fig. 3. Packing arrangement and hydrogen bonding for the 1.
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Fig. 4. Packing arrangement and hydrogen bonding for the 2.
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Fig 5. The catalytic epoxidation of the cyclooctene in different solvents in the presence of the
TBHP by the 1 and 2 vanadyl Schiff base complexes. Reaction conditions: (5 ml) solvent, (0.5
mmol) cyclooctene, (1.5 mmol) TBHP and (0.014 mmol or 2.8× 10-3 M) catalyst; in neural PH .
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Table 1. Crystallographic data and structure refinement for the 1 and 2
(1)
(2)
C26H22Cl2N2O3V
532.29
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C26H22Br2N2O3V
617.18
Monoclinic
P21/n
Monoclinic
P21/c
15.6158 (6)
9.6941 (4)
17.6582 (7)
115.616 (2)
2410.4 (2)
4
15.5068 (4)
9.7128 (3)
17.6047 (4)
115.919 (10)
2384.8 (1)
4
b (Å)
c (Å)
β
(°)
V (Å3)
Z
ꢀ
(mm-1)
3.76
0.67
Rint
S
0.053
0.040
1.01
1.02
1220
1092
F000
Dx(Mg m−3)
1.701
2.3, 28.00
296(2)
1.483
2.60, 29.0
296 (2)
θmin
,
θmax
T (K)
Independent
reflections
5809
177339
4650
6334
95703
5141
Measured reflections
reflections with
I>2
σ(I)
Parameters
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308
R[F2>2
wR(F2)
σ
(F2)]
0.037
0.1233
0.033
0.097
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ꢀρmax, ꢀρmin (eÅ−3)
0.79, −0.78
h;-23(23),
k;-14(14),
l;-26(26)
0.49, −0.47
h;-21(21),
k;-13(13),
l;-24(24)
Index range
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Table 2. The comparison of the two characteristic bands of vC=N and vV=O in the synthesized
complexes(1, 2) and similar vanadyl Schiff base complexes
Complex
vC=N(cm-1)
Free Ligand
vV=O(cm-1)
Ref
Complex
1618
Br
1636
1632
1634
984
N
O
(
(
(
)2V=O
34
33
35
Br
Br
1612
1622
982
984
N
)2V=O
O
OCH
3
Cl
N
)V=O
2
O
OCH
3
Br
1631
1640
1620
1620
993
984
N
N
(
(
)2V=O
41
42
O
O
Cl
)2V=O
1630
1624
1610
1604
970
970
This research
This research
1
2
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Table 3. Selected bond distances (Å) and angles (º) for the 1.
V1-O1
V1-O2
V1-O3
V1-N1
1.913(5)
1.893(5)
1.600(5)
2.113(5)
V1-N2
N1-C11
N1-C12
O1-C1
2.093(5)
1.264(9)
1.494(8)
1.321(8)
O3-V1-O1
O3-V1-N1
O1-V1-N1
C10-C11-N1
C11-N1-C12
110.70(2)
101.82(2)
85.00(2)
O1-V1-O2
N1-V1-N2
V1-O1-C1
V1-N1-C11
C1-C10-C11
136.80(2)
156.30(2)
131.30(4)
125.22(5)
119.92(6)
127.51(6)
115.90(5)
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Table 4. Selected bond distances (Å) and angles (º) for the 2.
V1—O3
V1—O1
V1—O2
V1—N1
1.5965 (11)
1.9051 (10)
1.9163 (11)
2.1005 (12)
V1—N2
N1—C11
N1—C12
O1—C1
2.1071 (12)
1.2912 (19)
1.4721 (19)
1.3155 (16)
O3—V1—O1
O3—V1—N1
O1—V1—N1
C10-C11-N1
112.42 (5)
101.66 (5)
85.63 (4)
127.77(6)
136.83 (5)
156.73 (5)
134.25 (9)
125.74 (10)
120.46 (12)
O1-V1-O2
N1-V1-N2
V1-O1-C1
V1-N1-C11
C1-C10-C11
115.87 (12)
C11-N1-C12
276
277
Table 5. Geometric parameters of hydrogen bond for the 1
D–H···A
Distance, Å
D–HꢁꢁꢁA, deg
D–H
HꢁꢁꢁA
DꢁꢁꢁA
C26-H26aꢁꢁꢁO3
C26i-H26biꢁꢁꢁBr1
C2i-H2iꢁꢁꢁ Br1
0.971
0.971
0.930
0.930
0.970
2.632
3.207
3.085
2.770
2.507
3.339
4.011
3.980
3.659
3.471
129.95
141.27
162.17
160.24
172.96
C11ii-H11iiꢁꢁꢁO3
C12ii-H12aiiꢁꢁꢁO3
278
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279
280
281
282
283
284
285
Table 6. Geometric parameters of hydrogen bond for the 2
D–H···A
Distance, Å
D–HꢁꢁꢁA, deg
D–H
HꢁꢁꢁA
DꢁꢁꢁA
C26-H26aꢁꢁꢁO3
C13-H4ꢁꢁꢁ O3
C13-H4ꢁꢁꢁCl1
C11i-H11iꢁꢁꢁO3
C12i-H12aiꢁꢁꢁO3
0.970
0.970
0.970
0.930
0.971
2.836
2.640
3.158
2.776
2.494
3.468
3.351
3.925
3.658
3.460
123.60
130.36
137.23
158.76
173.41
286
287
288
289
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290
291
292 Table 7. Epoxidation of the cyclooctene in different reaction media by the oxovanadium Schiff
293
base complexes, 1a and 2a
Solvent
Oxidant
Time(min)
Conversion(%)
(1)
(2)
CHCl3
CHCl3
TBHP
H2O2
NaIO4
H2O2
H2O2
H2O2
H2O2
H2O2
140
140
140
140
140
140
140
140
76
80
6
8
3
3
12
CH3CN/H2O(3:2)
THF
12
6
CH3CN
6
MeOH
No Reaction
No Reaction
No Reaction
No Reaction
No Reaction
No Reaction
CCl4
CH3CN/H2O(3:2)
294
295
aReaction conditions: (5 ml) solvent, (0.5 mmol) cyclooctene, (1.5 mmol) Oxidant and (0.014
mmol or 2.8× 0-3M) 1 and 2 complexes; in neutral PH.
296
297
298
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299
300
Table 8. The effect of the alkene/oxidant ratio in the epoxidation of the cyclooctene in CHCl3 as
solvent by the vanadyl Schiff base complexes of 1 and 2a.
Time
(min)
Yield%
Alkene/Oxidant
1:1.2
Alkene/Oxidant
1: 2
Alkene/Oxidant
1: 3
Alkene/Oxidant
1:4
1
12
20
25
33
38
40
43
48
51
54
58
59
60
60
60.5
60.5
2
1
2
1
2
12
21
34
42
52
56
62
67
72
75
76
77
79
80
80
80.5
1
2
10
20
17
25
32
40
42
45
48
52
54
57
59
60
62
62
63
63
8
12
25
31
34
36
40
45
48
56
58
65
67
68
71
72
72
9
10
20
25
38
48
51
56
61
68
72
75
78
79
81
81
81
13
26
34
47
58
63
69
73
76
80
80
81
81
81
80
78
15
23
28
32
35
45
49
56
61
65
67
68
70
71
70
17
26
36
45
51
58
63
65
68
70
72
74
76
76
76
30
40
50
60
70
80
90
100
110
120
130
140
150
160
301
302
303
a Reaction conditions: (5 ml) solvent, (0.5 mmol) cyclooctene, (2 mmol, 1.5 mmol, 1 mmol and 0.6 mmol
for 1:4, 1:3, 1:2 and 1: 1.2 ratios, respectively) TBHP and (0.014 mmol or 2.8× 10-3 M) complex (1); in
neural PH.
304
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305
306
Table 9. The effect of the amounts of the vanadyl Schiff base complexes of 1 and 2 in
epoxidation of the cyclooctene in CHCl3 as solvent in the presence of the TBHPa
Time(min)
Yeild(%)
Amount of 1 catalyst (mmol)
Amount of 2 catalyst (mmol)
0.01
10
0.014
12
0.02
0.01
10
13
18
27
34
42
47
52
60
63
67
71
72
73
73.5
73
0.014
12
0.02
18
10
20
14
20
25
32
46
51
62
65
68
71
75
75
74
74.5
75
75
20
21
21
26
30
30
34
34
32
40
40
42
42
38
50
50
52
52
52
60
60
56
56
58
70
70
62
62
68
80
80
67
67
73
90
90
72
72
74
100
110
120
130
140
150
160
100
110
120
130
140
150
160
75
75
76
76
76
78
77
77
77
79
79
76
80
80
76.8
75.6
75
80
80
80.3
80.3
307
308
a Reaction conditions: (5 ml) solvent, (0.5 mmol) cyclooctene, (2 mmol) TBHP and (0.01, 0.014 and 0.02
mmol or 2×10-3, 2.8×10-3 and 4×10-3 M) complex (1) in neutral PH.
309
310
26

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311
312
313
Table 10. The epoxidation of alkenes in optimal conditionsa in the presence of vanadyl Schiff
base complexes of 1 and 2
%Conversion
Alkene
Time(min)
140
(1)*
(2) **
76
80
300
300
35
42
38
45
140
300
320
70
32
25
74
35
30
314
315
aReaction conditions: CHCl3(5 ml), alkene (0.5 mmol), TBHP (2 mmol)*, (1.5 mmol)**,
vanadium(IV) Schiff base catalyst (0.014 mmol or 2.8× 0-3M); in neural PH.
316
317
318
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319
320
References:
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333
Garner, Angew. Chem. Int. Ed. Engl. 38 (1999) 795-798.
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