Oxido-bridged dinuclear vanadium(V) Schiff base complexes derived from 1R,2S(-)-norephedrine: Synthesis, structure, characterization and catalytic studies

Article abstract of DOI:10.1016/j.poly.2012.10.053

A series of vanadium(V) complexes with chiral tridentate Schiff base ligands, obtained by a single condensation of 1R,2S(-)-norephedrine with salicylaldehyde and its derivatives, were prepared. The complexes were characterized by elemental analysis and by

Full text of DOI:10.1016/j.poly.2012.10.053

Polyhedron 50 (2013) 179–186
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Oxido-bridged dinuclear vanadium(V) Schiff base complexes derived from
1
R,2S(ꢀ)-norephedrine: Synthesis, structure, characterization and catalytic studies
⇑
Grzegorz Romanowski , Michał Wera
Faculty of Chemistry, University of Gda n´ sk, Sobieskiego 18/19, PL-80952 Gda n´ sk, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of vanadium(V) complexes with chiral tridentate Schiff base ligands, obtained by a single con-
Received 28 April 2012
Accepted 11 October 2012
Available online 16 November 2012
densation of 1R,2S(ꢀ)-norephedrine with salicylaldehyde and its derivatives, were prepared. The com-
1
51
plexes were characterized by elemental analysis and by their IR, CD, UV–Vis, 1D ( H, V) and 2D
(
COSY, gHSQC) NMR spectra. The X-ray analysis of
l
-oxido-bis({1R,2S(ꢀ)-2-[(1-oxido-1-phenylpro-
3
0
pyl)iminomethyl]-3,5-dimethoxyphenolato-
j
N,O,O }oxidovanadium(V)), V (C18 19NO , 4, revealed
2
O
3
H
4 2
)
Keywords:
oxido-bridged dinuclear structure with, unexpectedly, two five-coordinate square-pyramidal geometries
Vanadium(V)
Schiff base
Complex
Amino alcohol
Sulfoxidation
about metal atoms. The two O-bonded oxidovanadium units are in the twist-angular configuration with
V
V
the V –O–V angle of 108.75(8)° and V–O distances of 1.802(2) and 1.818(2) Å. The vanadium(V) com-
plexes have ability to catalyze the oxidation of sulfides [PhSR (R = Me, Bz)] in good yields and enantio-
meric excesses, utilizing aqueous 30% H
O
2 2
or cumene hydroperoxide (CHP) as oxidant.
Ó 2012 Elsevier Ltd. All rights reserved.
1
. Introduction
tained Schiff base ligands derived from achiral amino alcohols
-aminoethanol [9] and 2-methyl-2-aminopropanol [8], whereas
2
The structurally characterized vanadate dependent haloperox-
the amine constituents of Schiff base ligands in the mononuclear
complexes were chiral amino alcohols: 2-amino-3,3-dimethyl-
butanol [10], 2-amino-3-methylbutanol [11], 2-benzylo-2-
amino-1,1-diphenylethanol, 2-phenyl-2-amino-1-phenylethanol,
aminoindanol and aminoisoborneol [12].
idases isolated from fungi (Curvularia inaequalis) [1], brown algae
Ascophyllum nodosum) [2] and red algae (Corallina officinalis) [3]
contain in their active centers vanadate covalently linked to N of
imidazolyl moieties, i.e. vanadium(V) in NO environment. These
(
e
4
enzymes catalyze the two electron oxidation of halide to hypoha-
lous acid [4] and the oxido transfer from peroxide to organic sul-
fides [5]. The sulfide oxidation activity can be modeled by
vanadium(V) coordination compounds with vanadium(V) in a
coordination environments similar to those found in the native en-
The excellent catalytic activity of mononuclear oxidovanadi-
um(V) complexes incorporating tridentate ligands has been already
reported by Mimoun et al. [13]. Ten years later the formation of sul-
fide adduct with dinuclear vanadium(V) complex derived from ami-
no alcohol has been documented [9]. Finally, isolation and X-ray
characterization of two catalyst precursors in asymmetric oxida-
tions of organic disulfides has been discussed by Blum et al. [11]. Till
now vanadium(V) complexes with tridentate Schiff base ligands
derived from chiral and achiral amino alcohols have been used suc-
cessfully as catalysts in the enantioselective oxidation of organic
sulfides [14,15], the asymmetric alkynylation of aldehydes [15],
the epoxidation of cyclooctene [16], the oxidation of bromide [17]
and the stereoselective synthesis of functionalized tetrahydrofu-
rans [12,17].
In continuation of our studies on synthesis, structure, spectro-
scopic and catalytic properties of vanadium(V) complexes incorpo-
rating chiral tridentate Schiff base ligands [18–20], we prepared a
series of new oxidovanadium(V) complexes comprising coordi-
nated single condensation products of 1R,2S(ꢀ)-norephedrine with
aromatic o-hydroxyaldehydes presented in Fig. 1. We examined
their spectroscopic (1D and 2D NMR, UV–Vis, CD and IR) and cat-
alytic properties in the asymmetric oxidation, i.e. enantioselective
4
zymes [6]. Vanadium in NO environment contained in vana-
dium(V) Schiff base complexes with chiral amino alcohols as
amine constituents catalyzes the oxidation of organic sulfides to
sulfoxides enantioselectively [7]. These complexes were prepared
2
either by the aerobic or pure oxygen oxidation of VO(acac) in
the presence of Schiff base ligand [8–10] or by mixing equimolar
amounts of tris(ethoxy) or tris(isopropoxy)vanadate and Schiff
bases in anhydrous ethanol [11,12]. The X-ray crystallographic
structural data show that the former synthetic procedure produced
dinuclear oxido-bridged complexes [8,9] and a mononuclear 2:1 li-
gand to vanadium complex [10], while the latter one resulted in
formation of mononuclear mixed ligand complexes incorporating
dibasic tridentate Schiff base ligands and alcoholate as a co-ligand
[
11,12]. The reported oxido-bridged dinuclear complexes con-
⇑
Corresponding author. Fax: +48 585235472.
E-mail address: greg@chem.univ.gda.pl (G. Romanowski).
0
277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.10.053

1
80
G. Romanowski, M. Wera / Polyhedron 50 (2013) 179–186
Table 1
R2
R4
R1
Crystal data and structure refinement.
Compound
4
R3
O
V
O
N
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C
36 38 2 11 2
H N O V
O-V=O(L)
O
776.56
295(2)
0.71073
triclinic
P1
8.8351(3)
b (Å)
c (Å)
10.5497(4)
10.7460(4)
95.908(3)
111.240(3)
106.429(3)
871.50(6)
1
1.480
0.601
402
a
(°)
b (°)
(°)
R1
R2
R3
R4
c
3
Volume (Å )
1
2
3
4
5
6
H
OCH
H
H
H
H
H
H
H
H
Z
D
calc (g cm 3
ꢀ
)
3
Absorption coefficient (mmꢀ1)
F(000)
OCH
H
3
H
Crystal size (mm)
h range for data collection (°)
Limiting indices
0.4 ꢁ 0.4 ꢁ 0.1
3.05 to 25.05
ꢀ10 6 h 6 10,
H
H
H
H
H
OCH
H
3
OCH
H
3
CH
Br
3
ꢀ
ꢀ
12 6 k 6 12,
12 6 l 6 12
H
H
Reflections collected/unique
Completeness to 2h (%)
7434/4815 [Rint = 0.0177]
99.7
4815/3/466
1.063
7
8
9
0
H
OH
H
NO2
H
H
Data/restraints/parameters
H
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R
R
1
= 0.0235, wR
= 0.0252, wR
2
2
= 0.0617
= 0.0632
C(CH3)3
H
H
H
1
1
H
(CH)
4
Absolute structure parameter
0.018(13)
0.253 and ꢀ0.189
Largest difference in peak and hole (e Åꢀ3)
Fig. 1. Structural formulae of vanadium(V) complexes.
sulfoxidation of methyl phenyl sulfide (PhSMe) and benzyl phenyl
sulfide (PhSBz) utilizing aqueous 30% H or cumene hydroperox-
ide (CHP) as an oxidant. Crystal and molecular structures of
oxido-bridged dinuclear complex,
-oxido-bis({1R,2S(ꢀ)-2-[(1-oxi-
do-1-phenylpropyl)iminomethyl]-3,5-dimethoxyphenolato-
oxidovanadium(V)), is also reported.
anisotropically. The positions of hydrogen atoms were calculated
and treated as riding atoms with fixed thermal parameters.
2 2
O
l
3
0
2.3. Catalytic activity
j
N,O,O }
In typical procedure, to a solution of vanadium(V) complex
(
2 2
0.010 mmol) in 3 ml of CH Cl /MeOH solution (7:3, v/v), sulfide
2
. Experimental
.1. Measurements
All chemicals and reagents were obtained from commercial
(1.00 mmol) was added at room temperature or ꢀ20 °C, together
with 1,3,5-trimethoxybenzene as internal standard. Aqueous 30%
H O or cumene hydroperoxide (CHP) as oxidant was added
2
2
2
(
1.10 mmol) by small portions and the resulting mixture was stir-
red. After the appropriate reaction time, the solution was quenched
with 2 ml of sodium sulfite solution (0.1 M) and extracted with
CH Cl (3 ꢁ 5 ml). The combined organic layers were evaporated
sources and used without further purification unless stated other-
wise. Carbon, hydrogen and nitrogen contents were determined on
a Carlo Erba MOD 1106 elemental analyzer. IR spectra of solid sam-
ples (KBr pellets) were run on a Bruker IFS 66, and electronic spec-
tra on the Perkin-Elmer LAMBDA 18 spectrophotometer. Circular
dichroism spectra were measured with a Jasco J-815 spectropolar-
2
2
to dryness. The solid product dissolved in CDCl was analyzed
3
1
(yield and ee – enantiomeric excess value) by H NMR spectra in
the presence of chiral shift reagent Eu(hfc) (where Hhfc is 3-(hep-
tafluoropropylhydroxymethylene)-(+)-camphoric acid) [22].
3
imeter. NMR spectra were obtained in CD
3
OD solutions with a Var-
1
ian Mercury-400BB (400 MHz) spectrometer using TMS ( H) and
2.4. Complexes
5
1
3
VOCl ( V) as reference compounds.
The complexes were obtained in
a following example
2.2. X-ray investigations
procedure. A solution of 5 mmol of 1R,2S(ꢀ)-norephedrine in
1
0 ml absolute ethanol was added with stirring to 5 mmol of an
Diffraction measurements were made on a Oxford Diffraction
Gemini R Ultra Ruby CCD, using graphite-monochromatized Mo
radiation (k = 0.71073 Å) at 295(2) K and determination of the
aromatic o-hydroxyaldehyde (salicylaldehyde, 3-methoxysalicylal-
dehyde, 5-methoxysalicylaldehyde, 4,6-dimethoxysalicylaldehyde,
5-methylsalicylaldehyde, 5-bromosalicylaldehyde, 5-nitrosalicyl-
aldehyde, 2,4-dihydroxybenzaldehyde, 3-tert-butylsalicylaldehyde,
2-hydroxy-1-naphthaldehyde) in 20 ml absolute EtOH and heated
under reflux for 1 h. Then a vanadium(V) oxytriethoxide (5 mmol)
in 10 ml of absolute EtOH was added and stirred at room tempera-
ture for 2 h. After cooling in a fridge a solid was separated and
Ka
crystal class, orientation matrix, and accurate unit cell parameters
was performed according to established procedures. Data collec-
tion and processing parameters are summarized in Table 1. The
structure was solved by direct methods and refined with all data
2
on F with SHELXTL [21]. All non-hydrogen atoms were refined

G. Romanowski, M. Wera / Polyhedron 50 (2013) 179–186
181
filtered off, washed several times and recrystallized from absolute
EtOH.
2.4.5.
iminomethyl]-4-methylphenolato-
Yield 83%. Anal. Calc. for C34
l
-Oxido-bis({1R,2S(ꢀ)-2-[(1-oxido-1-phenylpropyl)
3
0
j
N,O,O }oxidovanadium(V)) (5)
H N O V : C, 59.7; H, 5.0; N, 4.1.
34 2 7 2
ꢀ1
2
.4.1.
iminomethyl]phenolato-
Yield 80%. Anal. Calc. for C32
Found: C, 58.4; H, 4.7; N, 4.4%. IR (KBr, cm ): 1624
l
-Oxido-bis({1R,2S(ꢀ)-2-[(1-oxido-1-phenylpropyl)
Found: C, 59.8; H, 5.1; N, 4.0%. IR (KBr, cm ): 1626
m
C@N); 981
3
0
ꢀ1
ꢀ1
j
N,O,O }oxidovanadium(V)) (1)
: C, 58.5; H, 4.6; N, 4.3.
(mV@O). UV–Vis spectrum in MeOH [kmax (nm), e (M cm )]: 279
ꢀ
1
30
H N
2
O
V
7 2
(7840), 331 (3380). CD spectrum in MeOH [kmax (nm),
D
e (M
OD,
ꢀ
1
ꢀ1
1
m
C@N); 975
cm )]: 276 (ꢀ1.69), 296 (1.38), 362 (ꢀ6.61). H NMR (CD
3
ꢀ1
ꢀ1
(m
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (M cm )]: 278
ppm) major (60%): 8.67 (1H, s) (azomethine); 7.30–7.39 (5H, m),
ꢀ1
7.25–7.32 (2H, ov), 6.87 (1H, t) (aromatic); 6.34 (1H, d, 3J = 8 Hz),
(
9770), 350 (3590). CD spectrum in MeOH [kmax (nm),
D
e (M
OD,
ppm) major (60%): 8.72 (1H, s) (azomethine); 7.32–7.41 (5H, m),
ꢀ1
1
3
cm )]: 274 (ꢀ1.50), 297 (1.21), 358 (ꢀ6.69). H NMR (CD
3
4.88 (1H, ov) (methine); 2.35 (3H, s), 0.94 (3H, d, J = 8 Hz)
(methyl); minor (40%): 8.77 (1H, s) (azomethine); 7.48 (2H, m),
7.40 (2H, ov), 7.27 (3H, ov), 6.86 (1H, ov) (aromatic); 6.17 (1H, d,
3
7
(
8
.57 (2H, m), 6.95 (2H, m) (aromatic); 6.37 (1H, d, J = 8 Hz), 4.83
1H, ov) (methine); 0.94 (3H, d, 3J = 8 Hz) (methyl); minor (40%):
.77 (1H, s) (azomethine); 7.46 (2H, m), 7.37 (3H, m), 7.27 (2H,
3
J = 8 Hz), 4.51 (1H, br s) (methine); 2.34 (3H, s), 1.32 (3H, d,
3
51
J = 8 Hz) (methyl). V NMR (CD
3
OD, ppm): ꢀ531.4, ꢀ532.5.
3
m), 6.97 (1H, ov) (aromatic); 6.17 (1H, d, J = 8 Hz), 4.49 (1H, br
s) (methine); 1.31 (3H, d, 3J = 8 Hz) (methyl). V NMR (CD
51
2.4.6.
iminomethyl]-4-bromophenolato- N,O,O }oxidovanadium(V)) (6)
2 32 28 2 7 2
Yield 85%. Anal. Calc. for Br C H N O V : C, 47.2; H, 3.5; N, 3.4.
l
-Oxido-bis({1R,2S(ꢀ)-2-[(1-oxido-1-phenylpropyl)
3
OD,
3
0
ppm): ꢀ533.4, ꢀ534.9.
j
ꢀ1
2
.4.2.
iminomethyl]-6-methoxyphenolato-
Yield 82%. Anal. Calc. for C34
Found: C, 56.9; H, 4.7; N, 4.0%. IR (KBr, cm ): 1625
l
-Oxido-bis({1R,2S(ꢀ)-2-[(1-oxido-1-phenylpropyl)
Found: C, 47.3; H, 3.6; N, 3.3%. IR (KBr, cm ): 1630
m
C@N); 966
3
0
ꢀ1
ꢀ1
j
N,O,O }oxidovanadium(V)) (2)
: C, 57.0; H, 4.8; N, 3.9.
(mV@O). UV–Vis spectrum in MeOH [kmax (nm), e (M cm )]: 288
ꢀ1
34
H N
2
O
V
9 2
(9850), 336 (4400). CD spectrum in MeOH [kmax (nm),
D
e (M
cm )]: 283 (ꢀ1.20), 310 (1.72), 366 (ꢀ6.40). H NMR (CD OD,
ppm) major (60%): 8.68 (1H, s) (azomethine); 7.70 (1H, s), 7.57
ꢀ1
ꢀ1
1
m
C@N); 981
3
ꢀ1
ꢀ1
(m
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (M cm )]: 286
ꢀ1
3
4
(
8920), 355 (4440). CD spectrum in MeOH [kmax (nm),
D
e (M
OD,
ppm) major (60%): 8.72 (1H, s) (azomethine); 7.33–7.42 (5H, m),
.17–7.23 (2H, m), 6.87–6.94 (1H, m) (aromatic); 6.35 (1H, d,
(1H, dd, J = 8 Hz, J = 3 Hz), 7.32–7.42 (5H, m), 6.90 (1H, d,
ꢀ1
1
3
3
cm )]: 278 (ꢀ2.16), 308 (1.17), 359 (ꢀ5.31). H NMR (CD
3
J = 8 Hz) (aromatic); 6.43 (1H, d, J = 8 Hz), 4.88 (1H, ov)
(methine); 0.94 (3H, d, J = 8 Hz) (methyl); minor (40%): 8.73
3
3
7
(1H, s) (azomethine); 7.59 (1H, ov), 7.48 (1H, d, J = 8 Hz), 7.41
3
3
J = 8 Hz), 4.83 (1H, ov) (methine); 0.93 (3H, d, J = 8 Hz) (methyl);
(2H, ov), 7.28 (3H, ov), 6.78 (1H, ov) (aromatic); 6.13 (1H, d,
3
5
3
3
7
6
.95 (3H, s) (methoxy); minor (40%): 8.77 (1H, s) (azomethine);
.47 (2H, m), 7.28 (3H, m), 7.23 (2H, ov), 6.95 (1H, ov) (aromatic);
J = 8 Hz), 4.47 (1H, br s) (methine); 1.32 (3H, d, J = 8 Hz) (methyl).
1
V NMR (CD
3
OD, ppm): ꢀ535.2, ꢀ535.9.
3
.17 (1H, d, J = 8 Hz), 4.51 (1H, br s) (methine); 1.31 (3H, d,
3
51
J = 8 Hz) (methyl); 3.94 (3H, ov) (methoxy). V NMR (CD
3
OD,
2.4.7.
l
-Oxido-bis({1R,2S(ꢀ)-2-[(1-oxido-1-phenylpropyl)
3
0
ppm): ꢀ530.7, ꢀ531.9.
iminomethyl]-4-nitrophenolato-
j
N,O,O }oxidovanadium(V)) (7)
Yield 78%. Anal. Calc. for C32H N O V : C, 51.0; H, 3.8; N, 7.5.
Found: C, 50.9; H, 3.8; N, 7.5%. IR (KBr, cm ): 1635
28 4 11 2
ꢀ1
2
.4.3.
l
-Oxido-bis({1R,2S(ꢀ)-2-[(1-oxido-1-phenylpropyl)
m
C@N); 987
3
0
ꢀ1
ꢀ1
iminomethyl]-4-methoxyphenolato-
Yield 79%. Anal. Calc. for C34
Found: C, 57.1; H, 4.8; N, 4.0%. IR (KBr, cm ): 1628
j
N,O,O }oxidovanadium(V)) (3)
(mV@O). UV–Vis spectrum in MeOH [kmax (nm), e (M cm )]: 348
ꢀ
1
ꢀ1
34
H N
2
O
V
9 2
: C, 57.0; H, 4.8; N, 3.9.
(12890). CD spectrum in MeOH [kmax (nm),
D
e (M cm )]: 353
ꢀ1
1
m
C@N); 980
(ꢀ6.24). H NMR (CD
3
OD, ppm) major (60%): 8.88 (1H, s) (azome-
ꢀ1
ꢀ1
3
4
(m
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (M cm )]: 283
thine); 8.55 (1H, s), 8.34 (1H, dd, J = 8 Hz, J = 3 Hz), 7.34–7.48 (5H,
m), 7.04 (1H, d, J = 8 Hz) (aromatic); 6.51 (1H, d, J = 8 Hz), 4.75
ꢀ
1
3
3
(
9230), 337 (4560). CD spectrum in MeOH [kmax (nm),
D
e (M
OD,
ppm) major (60%): 8.70 (1H, s) (azomethine); 7.32–7.41 (5H, m),
.17–7.23 (1H, m), 7.12 (1H, d), 6.94 (1H, t) (aromatic); 6.36 (1H,
ꢀ1
1
3
cm )]: 274 (ꢀ2.23), 293 (1.44), 356 (ꢀ6.15). H NMR (CD
3
(1H, m) (methine); 0.95 (3H, d, J = 8 Hz) (methyl); minor (40%):
8.93 (1H, s) (azomethine); 8.36 (1H, ov), 7.47 (1H, d, 3J = 8 Hz),
7
7.40 (2H, ov), 7.28 (3H, m), 7.05 (1H, ov) (aromatic); 6.10 (1H, d,
3
3
3
5
3
d, J = 8 Hz), 4.82 (1H, ov) (methine); 0.94 (3H, d, J = 8 Hz)
methyl); 3.83 (3H, s) (methoxy); minor (40%): 8.77 (1H, s) (azo-
methine); 7.47 (2H, m), 7.28 (3H, m), 7.22 (1H, ov), 7.12 (1H, ov),
J = 8 Hz), 4.51 (1H, m) (methine); 1.32 (3H, d, J = 8 Hz) (methyl).
1
(
V NMR (CD
3
OD, ppm): ꢀ532.7, ꢀ534.0.
3
6
.94 (1H, ov) (aromatic); 6.18 (1H, d, J = 8 Hz), 4.50 (1H, br s)
2.4.8.
iminomethyl]-5-hydroxyphenolato-
Yield 81%. Anal. Calc. for C32
Found: C, 55.7; H, 4.3; N, 4.1%. IR (KBr, cm ): 1616
l
-Oxido-bis({1R,2S(ꢀ)-2-[(1-oxido-1-phenylpropyl)
3
3
0
(
methine); 1.31 (3H, d, J = 8 Hz) (methyl), 3.82 (3H, ov) (methoxy).
j
N,O,O }oxidovanadium(V)) (8)
5
1
V NMR (CD
3
OD, ppm): ꢀ529.1, ꢀ530.8.
H N O V : C, 55.8; H, 4.4; N, 4.1.
30 2 9 2
ꢀ1
m
C@N); 960
ꢀ1
ꢀ1
2
.4.4.
iminomethyl]-3,5-dimethoxyphenolato-
4)
l
-Oxido-bis({1R,2S(ꢀ)-2-[(1-oxido-1-phenylpropyl)
(mV@O). UV–Vis spectrum in MeOH [kmax (nm), e (M cm )]: 297
3
0
ꢀ1
j
N,O,O }oxidovanadium(V))
(10620), 360 (4220). CD spectrum in MeOH [kmax (nm), De (M
ꢀ1
1
(
cm )]: 268 (ꢀ1.84), 294 (1.45), 353 (ꢀ6.93). H NMR (CD
3
OD,
Yield 84%. Anal. Calc. for C36
Found: C, 55.8; H, 4.8; N, 3.5%. IR (KBr, cm ): 1606
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (M cm )]: 316
H
38
N
2
O
11
V
2
: C, 55.7; H, 4.9; N, 3.6.
ppm) major (60%): 8.54 (1H, s) (azomethine); 7.40 (1H, m), 7.28–
ꢀ1
3
m
C@N); 978
7.37 (5H, m), 6.47 (1H, m), 6.38 (1H, d, J = 3 Hz) (aromatic); 6.31
ꢀ1
ꢀ1
(1H, d, J = 8 Hz), 4.82 (1H, ov) (methine); 0.91 (3H, d, 3J = 8 Hz)
3
(
(
(
m
ꢀ
1
ꢀ1
16100). CD spectrum in MeOH [kmax (nm),
D
e (M cm )]: 350
(methyl); minor (40%): 8.59 (1H, s) (azomethine); 7.45 (1H, m),
1
3
ꢀ6.32). H NMR (CD
3
OD, ppm) major (60%): 8.92 (1H, s) (azome-
7.23–7.30 (5H, m), 6.44 (1H, ov), 6.35 (1H, d, J = 3 Hz) (aromatic);
4
3
thine); 7.40 (2H, m) 7.36 (3H, m), 6.16 (1H, d, J = 3 Hz), 6.10 (1H, d,
6.18 (1H, d, J = 8 Hz), 4.43 (1H, br s) (methine); 1.28 (3H, d,
4
3
3
51
J = 3 Hz) (aromatic); 6.33 (1H, d, J = 8 Hz), 4.81 (1H, ov)
J = 8 Hz) (methyl). V NMR (CD
3
OD, ppm): ꢀ530.1, ꢀ530.9.
3
(
methine); 0.95 (3H, d, J = 8 Hz) (methyl); 3.91 (3H, s), 3.87 (3H,
s) (methoxy); minor (40%): 8.97 (1H, s) (azomethine); 7.46 (2H,
m), 7.27 (3H, m), 6.19 (1H, d, J = 3 Hz), 6.15 (1H, d, J = 3 Hz) (aro-
2.4.9.
iminomethyl]-6-tert-butylphenolato-
Yield 74%. Anal. Calc. for C40
Found: C, 62.4; H, 6.1; N, 3.5%. IR (KBr, cm ): 1626
(mV@O). UV–Vis spectrum in MeOH [kmax (nm), e (M cm )]: 286
l
-Oxido-bis({1R,2S(ꢀ)-2-[(1-oxido-1-phenylpropyl)
4
4
3
0
j N,O,O }oxidovanadium(V)) (9)
matic); 6.33 (1H, ov), 4.49 (1H, br s) (methine); 1.32 (3H, d,
46
H N
2
O
V
7 2
: C, 62.5; H, 6.0; N, 3.6.
3
J = 8 Hz) (methyl); 3.91 (3H, ov), 3.86 (3H, ov) (methoxy). 51
ꢀ1
V
m
C@N); 985
ꢀ1
ꢀ1
NMR (CD
3
OD, ppm): ꢀ531.1, ꢀ533.2.

1
82
G. Romanowski, M. Wera / Polyhedron 50 (2013) 179–186
(
(
10230), 341 (4920). CD spectrum in MeOH [kmax (nm),
D
e
[VO(NAE)]
no)ethanol) and [VO(SAMP)]
2
O [9] (where NAE is 2-(2-hydroxynaphthalideneami-
O [8,13] (where SAMP is 1,1-di-
ꢀ1
ꢀ1
1
M
cm )]: 278 (ꢀ0.76), 298 (0.72), 345 (ꢀ6.78). H NMR (CD
3
2
OD, ppm) major (60%): 8.74 (1H, s) (azomethine); 7.60 (1H, m),
7
methyl-2-(salicylideneamino)ethanol). In these compounds, one
of the vanadium(V) atoms adopts a five-coordinate square-pyrami-
dal geometry, but the other one forms a weak bridge with alkoxide
oxygen of the adjacent Schiff base ligand adopting a distorted six-
coordinate octahedral structure.
In contrast to abovementioned complexes, X-ray analysis of 4
showed that it is an asymmetric oxido-bridged dinuclear com-
pound with the two vanadium(V) atoms adopting a five-coordinate
square-pyramidal geometry (Fig. 2). The coordination spheres of
both vanadium atoms are composed of phenolate oxygens
(V23A–O24A = 1.871(2) and V23B–O24B = 1.866(2) Å), azomethine
nitrogens (V23A–N12A = 2.077(2) and V23B–N12B = 2.071(2) Å)
and deprotonated alkoxide oxygens (V23A–O22A = 1.875(1) and
V23B–O22B = 1.890(2) Å) from the Schiff base ligands, oxido
groups in the apex (V23A–O25A = 1.587(2) and V23B–
O25B = 1.588(2) Å), and
O26 = 1.802(2) Å) that forms a strong bridge to second vanadium
atom (V23B–O26 = 1.818(2) Å).
There are also a few distinct differences in the observed param-
eters for the two halves of the molecule such as distances and an-
gles. The V23A and V23B atoms are displaced toward its terminal
oxido atom O25A and O25B by 0.445(2) and 0.440(2) Å, respec-
tively, from the mean plane of O26, O24, O22, N12, while in related
3
.38 (1H, d, J = 3 Hz), 7.32–7.37 (5H, m), 6.96 (1H, m), (aromatic);
3
6
.28 (1H, d, J = 8 Hz), 4.82 (1H, ov) (methine); 0.95 (3H, d,
3
J = 8 Hz) (methyl); 1.52 (9H, s) (tert-butyl); minor (40%): 8.79
(
7
4
1H, s) (azomethine); 7.48 (1H, d, 3J = 3 Hz), 7.44 (1H, m), 7.27–
3
.33 (5H, m), 6.92 (1H, ov) (aromatic); 6.21 (1H, d, J = 8 Hz),
3
.49 (1H, br s) (methine); 1.30 (3H, d, J = 8 Hz) (methyl); 1.53
5
1
(
9H, ov) (tert-butyl). V NMR (CD
3
OD, ppm): ꢀ544.5, ꢀ545.6.
2
.4.10.
iminomethyl]naphtholato-
Yield 77%. Anal. Calc. for C40
Found: C, 63.4; H, 4.6; N, 3.6%. IR (KBr, cm ): 1623
l
-Oxido-bis({1R,2S(ꢀ)-2-[(1-oxido-1-phenylpropyl)
3
0
j
N,O,O }oxidovanadium(V) (10)
: C, 63.5; H, 4.5; N, 3.7.
34 2 7 2
H N O V
ꢀ1
m
C@N); 972
ꢀ
1
ꢀ1
(m
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (M cm )]: 310
ꢀ1
(
9650), 397 (5610). CD spectrum in MeOH [kmax (nm),
D
e (M
OD,
ꢀ
1
1
cm )]: 264 (ꢀ1.16), 294 (1.40), 351 (ꢀ6.24). H NMR (CD
3
a
second oxido atom (V23A–
ppm) major (60%): 8.64 (1H, s) (azomethine); 8.33 (1H, d,
3
J = 8 Hz), 8.03 (1H, d, J = 8 Hz), 7.83 (1H, d, 3J = 8 Hz), 7.60 (1H,
3
t, J = 8 Hz), 7.49 (1H, t, 3J = 8 Hz), 7.34–7.42 (5H, m), 7.20 (1H, d,
3
3
3
J = 8 Hz) (aromatic); 6.44 (1H, d, J = 8 Hz), 4.98 (1H, m)
3
(
(
7
methine); 0.95 (3H, d, J = 8 Hz) (methyl); minor (40%): 8.69
1H, s) (azomethine); 8.35 (1H, ov), 8.04 (1H, ov), 7.84 (1H, ov),
.61 (1H, ov), 7.50 (1H, ov), 7.26–7.32 (5H, m), 7.18 (1H, ov) (aro-
3
matic); 6.28 (1H, d, J = 8 Hz), 4.30 (1H, br s) (methine); 1.39 (3H, d,
2 2
[VO(SAE)] O and [VO(NAE)] O deviation is just 0.365 and 0.369 Å,
3
J = 8 Hz) (methyl). 51V NMR (CD
. Results and discussion
.1. Crystal and molecular structure
The crystallographic data of 4 are summarized in Table 1 and
OD, ppm): ꢀ532.6; ꢀ537.9.
respectively, due to weakly bridging alkoxide oxygen. On the other
hand, the abovementioned displacements are about normal for a
vanadium center in a square-pyramidal coordination sphere with
3
3
2 2
comparison to [VO(SAE)] O (0.469 Å) and [VO(NAE)] O (0.490 Å).
3
Distances between vanadium atom and the alkoxide oxygen
coordinated by the other vanadium atom are different
(V23Bꢂ ꢂ ꢂO22A = 2.645(2) Å and V23Aꢂ ꢂ ꢂO22B = 2.751(2) Å). The
shorter separation, 2.645(2) Å, is however distinctly longer than
the selected bond distances and angles are given in Table 2. Similar
results have been obtained for the other compounds.
Despite extensive studies, so far three crystal structures of
vanadium(V) Schiff base complexes derived from only achiral ami-
no alcohols involving the OV (
i.e. [VO(SAE)] O [13] (where SAE is 2-(salicylideneamino)ethanol),
the Vꢂ ꢂ ꢂO(alkoxide) separations in related [VO(SAE)]
2
O,
[VO(NAE)] O and [VO(SAMP)] O complexes (2.401, 2.404 and
2
2
2.459 Å, respectively). Assuming for that reason that the V23B
and O22A separation represents a non-bonding distance the
V23B atom was considered to be unassociated with O22A.
V
V
2
l -O)V O unit have been reported,
2
Table 2
Selected bond lengths (Å) and angles (°) and hydrogen bonding parameters (Å, °) for 4.
V23A–O25A
V23A–O26
V23A–O22A
V23A–N12A
1.5867(18)
1.8018(17)
1.8750(14)
2.0766(19)
1.8409(17)
106.36(9)
103.45(9)
86.92(7)
1.5877(17)
1.8177(16)
1.8903(15)
2.0709(19)
1.8659(17)
105.85(9)
102.26(9)
87.69(7)
O25A–V23A–N12A
O26–V23A–N12A
O22A–V23A–N12A
O25A–V23A–O24A
O26–V23A–O24A
O22A–V23A–O24A
N12A–V23A–O24A
V23A–O26–V23B
O25B–V23B–N12B
O26–V23B–N12B
O22B–V23B–N12B
O25B–V23B–O24B
O26–V23B–O24B
O22B–V23B–O24B
N12B–V23B–O24B
104.52(10)
147.43(8)
76.02(7)
100.38(9)
100.67(8)
151.80(8)
83.62(8)
108.75(8)
106.49(9)
146.37(8)
76.69(7)
V23A–O24A
O25A–V23A–O26
O25A–V23A–O22A
O26–V23A–O22A
V23B–O25B
V23B–O26
V23B–O22B
V23B–N12B
V23B–O24B
O25B–V23B–O26
O25B–V23B–O22B
O26–V23B–O22B
99.27(9)
100.37(8)
153.97(7)
83.32(8)
DHꢂ ꢂ ꢂA
C11B–H11Bꢂ ꢂ ꢂO25A
D–H
Hꢂ ꢂ ꢂA
2.38
Dꢂ ꢂ ꢂA
3.265(3)
DHꢂ ꢂ ꢂA
159
i
0.93
CgI
CgJ
Cgꢂ ꢂ ꢂCg
3.953(2)
3.953(2)
Dihedral angle
Interplanar distance
Offset
Cg1
Cg2
Cg2ii
Cg1
9.32
9.32
3.758(1)
3.510(1)
5.454
5.286
iii
Symmetry code: (i) x ꢀ 1, y, z; (ii) x + 1, y, z + 1; (iii) x ꢀ 1, y, z ꢀ 1.
Notes: Cg1 is the centroid of ring A (C1–C6), Cg2 is the centroid of ring B (C1–C6). Cgꢂ ꢂ ꢂCg is the distance between ring centroids. The dihedral
angle is that between the planes of the rings CgI and CgJ. The interplanar distance is the perpendicular distance of CgI from ring J. The offset is the
perpendicular distance of ring I from ring J.

G. Romanowski, M. Wera / Polyhedron 50 (2013) 179–186
183
Fig. 2. The molecular structure of 4, with displacement ellipsoids drawn at the 25% probability level and H atoms are shown as small spheres of arbitrary radius.
The O25A@V23A/V23B@O25B pseudo torsion angle of 90.15(2)°
in 4 shows an intermediate disposition of the two V@O units in the
3.2. Spectroscopic studies
4
+
(
V@O)
than angle of 79.7° reported for the related [VO(NAE)]
105°) than in [VO(SAMP)] O, which may be brought about by the
2
O
core between cis and trans, and is considerably higher
The electronic, circular dichroism, NMR and selected solid-state
IR spectral data are listed in Section 2.
2
O and lower
(
2
The IR spectra of solid complexes display strong C@N stretch
ꢀ1
sterically more demanding amino alcohol fragment in the latter.
The bridging angle V23A–O26–V23B of 108.75(8)° and the
V23Aꢂ ꢂ ꢂV23B separation of 2.942(2) Å are almost the same as these
(around 1620 cm ) which indicates the C@N group of the coordi-
nated Schiff base ligands [23,24]. For all vanadium(V) complexes a
ꢀ1
strong absorption band is observed at around 980 cm assigned as
stretching vibration of the V@O moiety, which are close to values
reported for related oxidovanadium(V) Schiff base complexes
2 2
in [VO(SAE)] O (107.62°, 2.942 Å), [VO(NAE)] O (109.3°, 2.94 Å), but
distinctly smaller than these structural parameters in [VO(SAMP)]
2
ꢀ1
O (113°, 3.06 Å). Moreover, the distinct difference in bond lengths
[12,16]. The appearance of weak/medium band near 2800 cm
between the O26 oxygen and V23A or V23B of only 0.0159 and
separate from other C–H stretching vibrations in 2, 3, 4 complexes
indicated the presence of the methoxy substituents [25].
0
.035 Å in [VO(NAE)]
metric in these cases, but in contrast to much greater the V–O–V
bridge asymmetry in [VO(SAE)] O and [VO(SAMP)] O, i.e. 0.096
2
O indicates that the bridge is slightly asym-
The electronic and circular dichroism spectra of all complexes
were recorded in methanol. Strong intense bands, emax = 7840–
2
2
3
ꢀ1
ꢀ1
and 0.098 Å, respectively. There are also significant differences in
V–O(alkoxide) distances and O(alkoxide)–V–O(phenolate) angles
between six-coordinated vanadium centers (1.811 Å, 155.99° in
10620 dm mol cm , with kmax in region 278–310 nm are con-
⁄
sidered to arise from intraligand
p
–p
transitions. The low energy
bands, recorded for 1–3, 5, 6, 8–10 complexes, between 331 and
3
ꢀ1
ꢀ1
[
VO(SAE)]
coordinated vanadium centers (1.893 Å, 143.24° in [VO(SAE)]
and 1.828 Å, 137.2° in [VO(SAMP)] O), in contrast to 4 where these
parameters are very similar, i.e. V–O(alkoxide) bond lengths of
.8750(18) and 1.8903(15) Å, and O(alkoxide)–V–O(phenolate)
2
O and 1.805 Å, 156.5° in [VO(SAMP)]
2
O) and five-
397 nm (emax = 3380–5610 dm mol cm ) may be assigned as
2
O
a ligand-to-metal charge transfer (LMCT) transition originating
from the p orbital on the phenolate oxygen to the empty d orbital
p
at the vanadium(V) center [26,27]. The spectra of 4 and 7 com-
plexes examined in the same spectral region display only one very
2
1
bond angles of 151.80(8)° and 153.97(7)°.
strong bands at 316 (emax = 16100) and 348 (emax = 12890) nm,
Coordination of tridentate ligands by vanadium atoms resulted
in formation of four chelate rings. Six-membered rings formed by
V23A, O24A, C1A, C2A, C11A, N12A and by V23B, O24B, C1B, C2B,
C11B, N12B are planar (deviations of atoms defining the plane from
the mean plane in both cases do not exceed 0.197 Å). The two five-
membered chelate rings adopt different conformations. The ring de-
fined by V23A, O22A, C15A, C13A, N12A atoms chooses an envelope
conformation on N12A, while the other, formed by V23B, O22B,
C15B, C13B, N12B atoms, takes a twisted conformation on C13B
and N12B.
respectively, similar to the same strong bands at around 320 and
350 nm for complexes derived from 4,6-dimethoxysalicylaldehyde
and 5-nitrosalicylaldehyde [18–20]. The circular dichroism spectra
revealed an additional band in the 293–310 nm range with oppo-
site sign of the Cotton effect to the bands at around 280 and
350 nm. And as in the case of the electronic spectra, 4 and 7 com-
pounds, exhibit only one absorption with strong negative Cotton
effect at 350 and 348 nm, respectively.
1
H NMR signals were assigned on the basis of intensity,
spin–spin coupling pattern, chemical shifts, COSY and gHSQC
techniques. Single condensation of salicylaldehyde and its deriva-
tives with 2-amino-1-phenyl-1-propanol is confirmed by the pres-
ence of azomethine proton signals in the spectra of all complexes.
Signals of the methyl and methine protons in all compounds have
been readily recognized. For this purpose 2D (COSY, gHSQC) NMR
spectroscopy was performed for all complexes and allow to
unambiguously establish the attachment of carbon atoms in the
Molecules of 4 are assembled via weak intermolecular C–Hꢂ ꢂ ꢂO
short contacts (see Table 2). The structure of the complex also
shows
mine moiety, the centroid–centroid distances of the rings being
.953 Å. The planes are almost parallel, forming an dihedral angle
p–p interactions between phenyl rings of the salicylaldi-
3
of 9.32°. These intermolecular interactions are continuous through
the crystal lattice (Fig. 3).

1
84
G. Romanowski, M. Wera / Polyhedron 50 (2013) 179–186
Fig. 3. The arrangement of the molecules of 4 in the crystal structure. The C–Hꢂ ꢂ ꢂO contacts are represented by dashed lines and the
p–p interactions are represented by
dotted lines. H atoms not involved in interactions were omitted.
2
-amino-1-phenyl-1-propanolate fragment. For example, in case of
complexes or flexibility with respect to the coordination geometry
and the arrangement of the ligands. When dimers or oligomers are
formed temperature dependence of chemical shift and the increas-
ing intensity of signals with an increase of the concentration of
COSY spectrum of 8, cross-peaks between the methine proton
signal (major species signal at 4.82 ppm) and the methyl proton
signal at 0.91 ppm, and also, second methine proton doublet at
5
1
6
.31 ppm are observed. Moreover, NOESY spectra exhibit cross-
complexes should be observed in V NMR spectra. These rather
high-field resonances are present in chloroform solution [29] and
disappear when methanol is used as solvent, due to an additional
coordination of methanol leading to six-coordinated vanadium
species. We assume that in our case the existence of two diastereo-
mers (ARS and CRS), caused by chiral R and S methine carbon atoms
in the 2-amino-1-phenyl-1-propanolate moiety and two possible
(clockwise – C and anti-clockwise – A) absolute configurations at
vanadium atom (Fig. 4), is the most likely explanation for presence
peaks between the signals of the azomethine proton and the
methyl protons, and also between the signals of the azomethine
proton and the methine proton at 4.81 ppm. As expected, there is
lack of any cross-peak between the signals of the azomethine pro-
ton and second methine proton at 6.31 ppm.
1
In the H NMR spectra in CD
3
OD, two sets of signals are ob-
served to suggest the presence of two species in solution. Chemical
shifts for the two species are listed separately and designated as
major and minor. In all cases, the major:minor ratios are about
5
1
of two V NMR signals [30,31].
6
0:40, in contrast to similar vanadium(V) Schiff base complexes
derived from different amino alcohols, where contribution of major
3.3. Sulfoxidation
species varies from 53% to 95%. The 51V NMR spectra exhibit two
1
signals with the same major:minor ratios as the signals in the
H
In this study, the oxidovanadium(V) complexes 1–10 for their
ability to catalyze the oxidation of prochiral sulfides using methyl
phenyl sulfide (thioanisol) and phenyl benzyl sulfide as model
NMR spectra. According to Rehder and co-workers [28], possible
reasons for presence of two species in solution could be diastereo-
mers, equilibria between monomeric and dimeric (or oligomeric)
2 2
substrates have been tested. Aqueous 30% H O or cumene

G. Romanowski, M. Wera / Polyhedron 50 (2013) 179–186
185
R
R
reaction, catalyst and sulfide, but employing CHP as oxidant, sim-
ilar yield (82–87%) and much lower ee’s values (21–33%) of the
S-configured sulfoxide were obtained (Table 3, entries 21–30).
When benzyl phenyl sulfide was used as substrate, possessing
more bulky substituent, with hydrogen peroxide as oxidant, the
overall yield of sulfoxide is still comparable to previous reactions
O
V
O
N
O
N
O-V=O(L)
O
O-V=O(L)
O
V
O
(
84–90%) but enantioselectivity decreases to value of 16% and
smaller (Table 3, entry 11–20). With the reaction carried out at
20 °C with 30% H as oxidant, for 2, 3, 5, 6 and 8 as catalysts,
ꢀ
2 2
O
ARS
CRS
enantioselectivities improve significantly to 44–49% ee and a con-
version of over 90% of the substrate is observed after 3 h (Table 3,
entries 31–35). Mimoun et al. [32] pointed out the importance of
sufficiently nucleophilic center for the oxidative catalysis of organ-
ic substances by peroxidovanadium(V) compounds. Better enanti-
oselectivities for 2, 3, 5, 6 and 8 as compared to other catalysts may
be result of a higher electron density on the phenolato oxygen, e.g.
due to the effects of substituents in ortho-, meta- and para- posi-
tions, contributing to an attainment of sufficient nucleophilicity
by the vanadium center.
Fig. 4. Visualization of ARS and CRS diastereomers caused by dissymmetric
vanadium(V) ions.
hydroperoxide (CHP) were used as oxidants in a slight excess of
.10 equivalents based on the sulfide substrate. Reactions were
run with 1 mol% of catalyst based on the model substrate. The re-
sults of catalytic studies are listed in Table 3.
1
The best results have been obtained for complexes 2, 3, 5, 6 and
8
as catalysts in the oxidation of methyl phenyl sulfide with aque-
ous 30% H as oxidant (Table 3, entries 2, 3, 5, 6 and 8). An over-
all yields for all catalysts were in the range of 87–91% within
0 min reaction time and enantiomeric excess (ee’s) of 38–42% of
2 2
O
In general, the best results have been obtained in the oxidation
reactions of methyl phenyl sulfide with 30% H O as oxidant. Sig-
2 2
3
nificant decrease in reactivity is observed, i.e. enantioselectivity
as well as the overall yield of the oxidation of PhSMe, when the
bulkier oxidant cumene hydroperoxide as oxidant has been em-
ployed. Moreover, increasing the steric demand of the substrate
on going from methyl phenyl sulfide to benzyl phenyl sulfide leads
to a decrease in both the overall yield and enantioselectivity of cor-
responding sulfoxide. In contrast to chiral oxidovanadium(V) Schiff
base complexes derived from optically active diamines used as cat-
alysts in the sulfoxidation reactions significantly shorter reaction
times and much higher values of enantiomeric excesses of corre-
sponding sulfoxides employing 1–10 as catalysts were observed
the S-configured sulfoxide was obtained. For the same time of
Table 3
Catalytic oxidation of PhSMe and PhSBz by hydrogen peroxide or cumene hydroper-
oxide (CHP) as oxidant in presence of 1 mol% vanadium(V) Schiff base complexes as
catalysts.
[
18–20].
Entry Catalyst Substrate Oxidant Yield
%)
T
(°C)
t
ee
(%)
a
(
(min)
4. Conclusion
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
1
2
3
4
5
6
7
8
9
10
2
3
5
6
8
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSBz
PhSBz
PhSBz
PhSBz
PhSBz
PhSBz
PhSBz
PhSBz
PhSBz
PhSBz
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
PhSMe
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
CHP
CHP
CHP
CHP
CHP
CHP
CHP
CHP
CHP
CHP
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
90
87
91
90
88
91
87
89
92
90
86
85
87
89
90
86
84
87
86
87
83
84
86
83
85
84
83
87
85
82
94
92
93
92
91
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
rt
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
180
180
180
180
180
32
42
40
31
38
39
33
40
28
29
8
15
13
10
14
16
7
To the best of our knowledge, it is the first report on crystal and
molecular structure of oxido-bridged dinuclear vanadium(V) com-
plex incorporating tridentate Schiff base ligand derived from chiral
amino alcohol.
We have characterized ten chiral vanadium(V) complexes de-
rived from Schiff base ligands, monocondensation products of o-
hydroxycarbonyl compounds with 1R,2S(ꢀ)-norephedrine. We
have also tested their catalytic properties towards the oxidation
of sulfides. Enantioselectivity of vanadium(V) complexes is better
and the reaction times are much shorter than for other vana-
dium(V) complexes with Schiff bases derived from optically active
diamines. The results show that the observed yield and enantio-
meric excess significantly depend on the nature of the catalyst,
substrate and peroxide used, especially in the aspect of bulky sub-
stituent leading to large steric demand, and finally depend on the
temperature in which the reaction is carried out.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
16
6
8
25
31
30
24
32
29
25
33
21
23
49
45
46
44
47
Acknowledgment
This scientific work was supported by the Polish Ministry of Sci-
ence and Higher Education (DS/8210-4-0177-11).
Appendix A. Supplementary data
H
H
H
H
H
2
O
2
O
2
O
2
O
2
O
2
2
2
2
2
ꢀ20
ꢀ20
ꢀ20
ꢀ20
ꢀ20
CCDC 876824 contains the supplementary crystallographic data
for 4. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
a
All sulfoxides are in S configuration.

1
86
G. Romanowski, M. Wera / Polyhedron 50 (2013) 179–186
[
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