Chiral oxidovanadium(V) complexes with tridentate Schiff bases derived from S(+)-2-amino-1-propanol: Synthesis, structure, characterization and catalytic activity

Article abstract of DOI:10.1016/j.ica.2012.09.030

A series of vanadium(V) complexes with chiral tridentate Schiff base ligands, obtained by a single condensation of S(+)-2-amino-1-propanol with salicylaldehyde and its derivatives, were prepared. The complexes were characterized by elemental analysis and by their IR, CD, UV-Vis, 1D ( ¹H, ⁵¹V) and 2D (COSY, gHSQC) NMR spectra. The X-ray analysis of μ-oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]-4- nitrophenolato-κ³N,O,O′}oxidovanadium(V)), V ₂O₃(C₁₀H₁₀N₂O ₄)₂, 7, revealed oxido-bridged dinuclear structure with, unexpectedly, two five-coordinate square-pyramidal geometries about metal atoms. The two O-bonded oxidovanadium units are in the twist-angular configuration with the V^V-O-V^V angle of 107.05(11)° and V-O distances of 1.794(2) and 1.826(2) A?. The vanadium(V) complexes have ability to catalyze the oxidation of sulfides [PhSR (R = Me, Bz)] in good yields and enantiomeric excesses, utilizing aqueous 30% hydrogen peroxide or cumene hydroperoxide (CHP) as oxidant.

Full text of DOI:10.1016/j.ica.2012.09.030

Inorganica Chimica Acta 394 (2013) 627–634
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Inorganica Chimica Acta
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Chiral oxidovanadium(V) complexes with tridentate Schiff bases derived from
S(+)-2-amino-1-propanol: Synthesis, structure, characterization and catalytic
activity
b
Grzegorz Romanowski a, , Tadeusz Lis
⇑
a Faculty of Chemistry, University of Gdan´sk, Sobieskiego 18/19, PL-80952 Gdan´sk, Poland
b Institute of Chemistry, University of Wroclaw, F. Joliot-Curie 14, PL-50383 Wroclaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 April 2012
Received in revised form 3 August 2012
Accepted 12 September 2012
Available online 4 October 2012
A series of vanadium(V) complexes with chiral tridentate Schiff base ligands, obtained by a single con-
densation of S(+)-2-amino-1-propanol with salicylaldehyde and its derivatives, were prepared. The com-
plexes were characterized by elemental analysis and by their IR, CD, UV–Vis, 1D (1H, 51V) and 2D (COSY,
gHSQC) NMR spectra. The X-ray analysis of
l-oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]-4-nitro-
phenolato-j3N,O,O0}oxidovanadium(V)), V2O3(C10H10N2O4)2, 7, revealed oxido-bridged dinuclear struc-
ture with, unexpectedly, two five-coordinate square-pyramidal geometries about metal atoms. The
two O-bonded oxidovanadium units are in the twist-angular configuration with the VV–O–VV angle of
107.05(11)° and V–O distances of 1.794(2) and 1.826(2) Å. The vanadium(V) complexes have ability to
catalyze the oxidation of sulfides [PhSR (R = Me, Bz)] in good yields and enantiomeric excesses, utilizing
aqueous 30% hydrogen peroxide or cumene hydroperoxide (CHP) as oxidant.
Keywords:
Vanadium(V)
Schiff base
Complex
Amino alcohol
Sulfoxidation
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
um(V) complexes with dibasic tridentate Schiff base ligands and
alcoholate as a co-ligand [14,15].
Vanadium is a bioelement involved in various catalytic and
inhibitory processes [1,2]. Vanadium-containing peroxidases cata-
lyze the oxidation of halides in the presence of hydrogen peroxide
to highly reactive intermediate, a hypohalous acid, which may re-
act either with suitable nucleophilic acceptor, if present, forming a
halogenated compound [3,4] or with hydrogen peroxide yielding
1O2 [4,5]. It has been also established that such enzymes are able
to catalyze the oxidation of organic sulfides to the corresponding
sulfoxides in the presence of hydrogen peroxide [6,7].
Recently, an increasing interest has been focused on the vana-
dium(V) Schiff base complexes derived from chiral amino alcohols
and its catalytic activity. These complexes were prepared either by
the aerobic or pure oxygen oxidation of VO(acac)2 in the presence
of Schiff base ligand [8–13] or by mixing equimolar amounts of
tris(ethoxy) or tris(isopropoxy)vanadate with Schiff bases ligand
[14,15]. The X-ray crystallographic structural data show that the
former synthetic procedure produced dinuclear oxido-bridged
complexes [8–10], mononuclear ones as anionic dioxidovanadi-
um(V) species [11] or incorporating chelated diols [12], while the
latter one resulted only in formation of mononuclear oxidovanadi-
The excellent catalytic activity of mononuclear oxidovanadi-
um(V) complexes incorporating tridentate ligands has been al-
ready reported by Mimoun et al. [16]. Ten years later the
formation of sulfide adduct with dinuclear vanadium(V) complex
derived from amino alcohol has been documented [9]. Finally, iso-
lation and X-ray characterization of two catalyst precursors in
asymmetric oxidations of organic disulfides has been discussed
by Blum et al. [17]. Till now vanadium(V) complexes with triden-
tate Schiff base ligands derived from chiral and achiral aminoalco-
hols have been used successfully as catalysts in the
enantioselective oxidation of organic sulfides [13,15], the asym-
metric alkynylation of aldehydes [15], the epoxidation of cyclooc-
tene [10], the oxidation of bromide [18] and the stereoselective
synthesis of functionalized tetrahydrofurans [14,18].
In continuation of our studies on synthesis, structure, spectro-
scopic and catalytic properties of vanadium(V) complexes incorpo-
rating chiral tridentate Schiff base ligands [19–21], we prepared a
series of new oxidovanadium(V) complexes comprising coordi-
nated single condensation products of S(+)-2-amino-1-propanol
with aromatic o-hydroxyaldehydes presented in Fig. 1. We exam-
ined their spectroscopic (1D and 2D NMR, UV–Vis, CD and IR)
and catalytic properties in the asymmetric oxidation, i.e. enantio-
selective sulfoxidation of methyl phenyl sulfide (PhSMe) and ben-
zyl phenyl sulfide (PhSBz) utilizing aqueous 30% hydrogen
⇑
Corresponding author.
E-mail address: greg@chem.univ.gda.pl (G. Romanowski).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.09.030

628
G. Romanowski, T. Lis / Inorganica Chimica Acta 394 (2013) 627–634
Table 1
R1
2
R
Crystal data and structure refinement.
Compound
7
R3
O
N
O
V
Empirical formula
Formula weight
T (K)
k (Å)
Crystal system
Space group
C
20H20N4O11V2
O-V=O(L)
594.28
100(2)
1.54180
monoclinic
P21
R4
O
Unit cell dimensions
H3C
a (Å)
b (Å)
c (Å)
8.568(3)
11.384(4)
11.696(4)
90.00
1
2
3
4
R
H
R
R
R
a
(°)
b (°)
96.06(4)
90.00
1134.4(7)
2
1.740
7.554
604
0.14 ꢁ 0.12 ꢁ 0.04
3.80 to 76.53
ꢀ10 6 h 6 5
ꢀ12 6 k 6 13
ꢀ13 6 l 6 14
10762/4002 [Rint = 0.0294]
98.5
4002/1/336
1.001
R1 = 0.0290, wR2 = 0.0731
R1 = 0.0321, wR2 = 0.0743
0.004(5)
c
(°)
H
H
H
H
H
H
1
V (Å3)
Z
OCH3
H
2
3
4
5
6
Dcalc (g cmꢀ3
)
Absorption coefficient (mmꢀ1
F(000)
)
H
OCH3
H
H
H
OCH3
H
OCH3
H
Crystal size (mm)
h Range for data collection (°)
Limiting indices
H
CH3
Br
H
H
H
H
Reflections collected/unique
Completeness to 2h (%)
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
H
OH
H
NO
2
H
7
8
H
H
H
H
C(CH )
H
9
r(I)]
3 3
H
H
(CH)4
10
Absolute structure parameter
Largest difference in peak and hole (e Åꢀ3
)
0.25 and ꢀ0.43
Fig. 1. Structural formulae of vanadium(V) complexes.
2.3. Catalytic activity
peroxide or cumene hydroperoxide (CHP) as oxidant. Crystal
and molecular structure of oxido-bridged dinuclear complex,
l
-
In typical procedure, to a solution of vanadium(V) complex
(0.010 mmol) in 3 ml of CH2Cl2/MeOH solution (7:3, v/v), sulfide
(1.00 mmol) was added at room temperature or ꢀ20 °C, together
with 1,3,5-trimethoxybenzene as internal standard. Hydrogen per-
oxide (30% aqueous) or cumene hydroperoxide (CHP) as oxidants
were added (1.10 mmol) by small portions and the resulting mix-
ture was stirred. After the appropriate reaction time, the solution
was quenched with 2 ml of sodium sulfite solution (0.1 M) and ex-
tracted with CH2Cl2 (3 ꢁ 5 ml). The combined organic layers were
evaporated to dryness. The solid product dissolved in CDCl3 was
analyzed (yield and ee value) by 1H NMR spectra in the presence
of chiral shift reagent Eu(hfc)3 (where Hhfc is 3-(hepta-
fluoropropylhydroxymethylene)-(+)-camphoric acid) [23].
oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]-4-nitrophenolato-
j3N,O,O0}oxidovanadium(V)), is also reported.
2. Experimental
2.1. Measurements
All chemicals and reagents were obtained from commercial
sources and used without further purification unless stated other-
wise. Carbon, hydrogen and nitrogen contents were determined on
a Carlo Erba MOD 1106 elemental analyser. 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-
imeter. NMR spectra were obtained in CD3OD solutions with a Var-
ian Mercury-400BB (400 MHz) spectrometer using TMS (1H) and
2.4. Complexes
The complexes were obtained in a following example procedure.
A solution of 5 mmol of S(+)-2-amino-1-propanol in 10 ml absolute
ethanol was added with stirring to 5 mmol of an aromatic
o-hydroxyaldehyde (salicylaldehyde, 3-methoxysalicylaldehyde,
VOCl3 (
51V) as reference compounds.
2.2. X-ray investigations
5-methoxysalicylaldehyde,
4,6-dimethoxysalicylaldehyde,
5-
methylsalicylaldehyde, 5-bromosalicylaldehyde, 5-nitrosalicylal-
dehyde, 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 filtered
off, washed several times and recrystallized from absolute EtOH.
Diffraction measurements were made on a Xcalibur PX j-geom-
etry diffractometer with CCD Onyx camera, using graphite-mono-
chromatized Cu K radiation (k = 1.54180 Å) at 100(2) K and
a
determination of the crystal class, orientation matrix, and accurate
unit cell parameters was performed according to established pro-
cedures. Data collection and processing parameters are summa-
rized in Table 1. The structure was solved by direct methods
using and refined with all data on F2 with SHELXTL [22]. All non-
hydrogen atoms were refined anisotropically. The positions of
hydrogen atoms were calculated and treated as riding atoms with
fixed thermal parameters.
2.4.1. l-Oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]phenolato-
j3N,O,O0}oxidovanadium(V)) (1)
Yield 74%. Anal. Calc. for C20H22N2O7V2: C, 47.6; H, 4.4; N, 5.6.
Found: C, 47.4; H, 4.3; N, 5.5%. IR (KBr, cmꢀ1): 1633 (
mC@N); 981

G. Romanowski, T. Lis / Inorganica Chimica Acta 394 (2013) 627–634
629
(
m
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (Mꢀ1 cmꢀ1)]: 274
(10560), 330 (4860). CD spectrum in MeOH [kmax (nm),
e (Mꢀ1
286 (10150), 334 (4580). CD spectrum in MeOH [kmax (nm), De
D
(Mꢀ1 cmꢀ1)]: 277 (ꢀ0.79), 297 (0.28), 340 (ꢀ1.69). 1H NMR (CD3-
OD, ppm) major (60%): 8.64 (1H, s) (azomethine); 7.37 (2H, s),
6.84 (1H, t, 3J = 8 Hz) (aromatic); 4.78 (1H, br s), 4.49 (1H, dd,
3J = 8 Hz, 4J = 6 Hz), (methylene); 4.13 (1H, m) (methine); 2.34
(3H, s), 1.61 (3H, d, 3J = 8 Hz) (methyl); minor (40%): 8.67 (1H, s)
(azomethine); 7.35 (2H, s), 6.86 (1H, ov) (aromatic); 5.02 (1H, dd,
3J = 8 Hz, 4J = 6 Hz), 4.36 (1H, br s) (methylene); 4.63 (1H, m)
(methine); 2.34 (3H, ov), 1.34 (3H, d, 3J = 8 Hz) (methyl). 51V
NMR (CD3OD, ppm): ꢀ532.7, ꢀ533.8.
cmꢀ1)]: 276 (ꢀ0.67), 294 (0.39), 334 (ꢀ2.06). 1H NMR major
(60%): 8.68 (1H, s) (azomethine); 7.57 (1H, dd, 3J = 8 Hz,
4J = 3 Hz), 7.50 (1H, t, 3J = 8 Hz), 6.96 (1H, t, 3J = 8 Hz), 6.93 (1H,
ov) (aromatic); 4.79 (1H, br s), 4.52 (1H, dd, 3J = 8 Hz, 4J = 6 Hz)
(methylene); 4.16 (1H, m) (methine); 1.62 (3H, d, 3J = 8 Hz)
(methyl); minor (40%): 8.71 (1H, s) (azomethine); 7.57 (1H, dd,
3J = 8 Hz, 4J = 3 Hz), 7.50 (1H, t, 3J = 8 Hz), 6.96 (1H, t, 3J = 8 Hz),
6.93 (1H, ov) (aromatic); 5.04 (1H, dd, 3J = 8 Hz, 4J = 6 Hz), 4.38
(1H, br s) (methylene); 4.64 (1H, m) (methine); 1.37 (3H, d,
3J = 8 Hz) (methyl). 51V NMR (CD3OD, ppm): ꢀ534.9, ꢀ536.0.
2.4.6. l-Oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]-4-
bromophenolato-j3N,O,O0}oxidovanadium(V)) (6)
2.4.2.
l
-Oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]-6-
Yield 76%. Anal. Calc. for Br2C20H20N2O7V2: C, 36.3; H, 3.0; N, 4.2.
methoxyphenolato-j3N,O,O0}oxidovanadium(V)) (2)
Found: C, 36.4; H, 3.1; N, 4.1%. IR (KBr, cmꢀ1): 1631 (
(m
m
C@N); 962
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (Mꢀ1 cmꢀ1)]:
288 (10230), 336 (4650). CD spectrum in MeOH [kmax (nm),
Yield 77%. Anal. Calc. for C22H26N2O9V2: C, 46.8; H, 4.6; N, 5.0.
Found: C, 46.7; H, 4.6; N, 4.9%. IR (KBr, cmꢀ1): 1631 (
m
C@N); 983
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (Mꢀ1 cmꢀ1)]:
284 (10070), 345 (4510). CD spectrum in MeOH [kmax (nm),
De
(m
(Mꢀ1 cmꢀ1)]: 277 (ꢀ0.63), 292 (0.35), 335 (ꢀ1.24). 1H NMR (CD3-
OD, ppm) major (60%): 8.61 (1H, s) (azomethine); 7.71 (1H, s),
7.57 (1H, d, 3J = 8 Hz), 6.86 (1H, d, 3J = 8 Hz) (aromatic); 4.81 (1H,
br s), 4.54 (1H, dd, 3J = 8 Hz, 4J = 6 Hz) (methylene); 4.22 (1H, m)
(methine); 1.58 (3H, d, 3J = 8 Hz) (methyl); minor (40%): 8.65
(1H, s) (azomethine); 7.71 (1H, ov), 7.54 (1H, d, 3J = 8 Hz), 6.83
(1H, d, 3J = 8 Hz) (aromatic); 5.07 (1H, dd, 3J = 8 Hz, 4J = 6 Hz),
4.38 (1H, br s) (methylene); 4.73 (1H, m) (methine); 1.34 (3H, d,
3J = 8 Hz) (methyl). 51V NMR (CD3OD, ppm): ꢀ534.1, ꢀ535.0.
D
e
(Mꢀ1 cmꢀ1)]: 284 (ꢀ0.65), 304 (0.34), 341 (ꢀ1.28). 1H NMR (CD3-
OD, ppm) major (60%): 8.68 (1H, s) (azomethine); 7.18 (2H, s),
6.89 (1H, t, 3J = 8 Hz) (aromatic); 4.79 (1H, br s), 4.51 (1H, dd,
3J = 8 Hz, 4J = 6 Hz) (methylene); 4.16 (1H, m) (methine); 1.62
(3H, d, 3J = 8 Hz) (methyl); 3.92 (3H, s) (methoxy); minor (40%):
8.73 (1H, s) (azomethine); 7.20 (2H, s), 6.92 (1H, t, 3J = 8 Hz) (aro-
matic); 5.04 (1H, dd, 3J = 8 Hz, 4J = 6 Hz), 4.38 (1H, br s) (methy-
lene); 4.65 (1H, m) (methine); 1.37 (3H, d, 3J = 8 Hz) (methyl);
3.91 (3H, ov) (methoxy). 51V NMR (CD3OD, ppm): ꢀ531.6, ꢀ532.4.
2.4.7. l-Oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]-4-
nitrophenolato-j3N,O,O0}oxidovanadium(V)) (7)
2.4.3.
l
-Oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]-4-
Yield 72%. Anal. Calc. for C20H20N4O11V2: C, 40.4; H, 3.4; N, 9.4.
methoxyphenolato-j3N,O,O0}oxidovanadium(V)) (3)
Found: C, 40.3; H, 3.5; N, 9.4%. IR (KBr, cmꢀ1): 1632 (
(m
m
C@N); 986
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (Mꢀ1 cmꢀ1)]:
343 (14930). CD spectrum in MeOH [kmax (nm),
e (Mꢀ1 cmꢀ1)]:
Yield 71%. Anal. Calc. for C22H26N2O9V2: C, 46.8; H, 4.6; N, 5.0.
Found: C, 46.7; H, 4.7; N, 4.9%. IR (KBr, cmꢀ1): 1630 (
m
C@N); 982
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (Mꢀ1 cmꢀ1)]:
284 (10280), 341 (4450). CD spectrum in MeOH [kmax (nm),
D
(m
324 (ꢀ2.33). 1H NMR (CD3OD, ppm) major (60%): 8.64 (1H, s) (azo-
methine); 8.58 (1H, d, 4J = 3 Hz), 8.32 (1H, dd, 3J = 8 Hz, 4J = 3 Hz),
7.01 (1H, d, 3J = 8 Hz) (aromatic); 4.80 (1H, br s), 4.68 (1H, dd,
3J = 8 Hz, 4J = 6 Hz) (methylene); 4.18 (1H, m) (methine); 1.61
(3H, d, 3J = 8 Hz) (methyl); minor (40%): 8.67 (1H, s) (azomethine);
8.55 (1H, d, 4J = 3 Hz), 8.32 (1H, dd, 3J = 8 Hz, 4J = 3 Hz), 7.01 (1H, d,
3J = 8 Hz) (aromatic); 5.21 (1H, dd, 3J = 8 Hz, 4J = 6 Hz), 4.45 (1H, br
s) (methylene); 4.68 (1H, m) (methine); 1.41 (3H, d, 3J = 8 Hz)
(methyl). 51V NMR (CD3OD, ppm): ꢀ531.8, ꢀ532.9.
D
e
(Mꢀ1 cmꢀ1)]: 280 (ꢀ0.66), 298 (0.35), 344 (ꢀ1.31). 1H NMR (CD3-
OD, ppm) major (60%): 8.68 (1H, s) (azomethine); 7.15 (2H, m),
6.88 (1H, t, 3J = 8 Hz) (aromatic); 4.80 (1H, br s), 4.50 (1H, dd,
3J = 8 Hz, 4J = 6 Hz) (methylene); 4.15 (1H, m) (methine); 1.63
(3H, d, 3J = 8 Hz) (methyl); 3.82 (3H, s) (methoxy); minor (40%):
8.72 (1H, s) (azomethine); 7.15 (2H, m), 6.91 (1H, t, 3J = 8 Hz) (aro-
matic); 4.99 (1H, dd, 3J = 8 Hz, 4J = 6 Hz), 4.37 (1H, br s) (methy-
lene); 4.64 (1H, m) (methine); 1.37 (3H, d, 3J = 8 Hz) (methyl),
3.81 (3H, ov) (methoxy). 51V NMR (CD3OD, ppm): ꢀ530.1, ꢀ530.9.
2.4.8. l-Oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]-5-
hydroxyphenolato-j3N,O,O0}oxidovanadium(V)) (8)
2.4.4.
l
-Oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]-3,5-
Yield 74%. Anal. Calc. for C20H22N2O9V2: C, 44.8; H, 4.1; N, 5.2.
dimethoxyphenolato-j3N,O,O0}oxidovanadium(V)) (4)
Found: C, 44.6; H, 4.1; N, 5.1%. IR (KBr, cmꢀ1): 1621 (
(m
m
C@N); 980
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (Mꢀ1 cmꢀ1)]:
295 (14610), 364 (5470). CD spectrum in MeOH [kmax (nm),
Yield 70%. Anal. Calc. for C24H30N2O11V2: C, 46.2; H, 4.8; N, 4.5.
Found: C, 46.1; H, 4.9; N, 4.6%. IR (KBr, cmꢀ1): 1622 (
m
C@N); 978
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (Mꢀ1 cmꢀ1)]:
314 (20040). CD spectrum in MeOH [kmax (nm),
e (Mꢀ1 cmꢀ1)]:
De
(m
(Mꢀ1 cmꢀ1)]: 281 (-0.70), 306 (0.39), 335 (-2.08). 1H NMR (CD3OD,
ppm) major (60%): 8.50 (1H, s) (azomethine); 7.49 (1H, t, 3J = 8 Hz),
6.45 (1H, t, 3J = 8 Hz), 6.33 (1H, dd, 3J = 8 Hz, 4J = 3 Hz) (aromatic);
4.79 (1H, br s), 4.47 (1H, dd, 3J = 8 Hz, 4J = 6 Hz) (methylene);
4.14 (1H, m) (methine); 1.60 (3H, d, 3J = 8 Hz) (methyl); minor
(40%): 8.53 (1H, s) (azomethine); 7.47 (1H, ov), 6.43 (1H, ov),
6.35 (1H, ov) (aromatic); 5.00 (1H, dd, 3J = 8 Hz, 4J = 6 Hz), 4.34
(1H, br s) (methylene); 4.61 (1H, m) (methine); 1.34 (3H, d,
3J = 8 Hz) (methyl). 51V NMR (CD3OD, ppm): ꢀ530.9, ꢀ531.8.
D
334 (ꢀ1.80). 1H NMR (CD3OD, ppm) major (60%): 8.88 (1H, s) (azo-
methine); 6.10 (1H, d, 4J = 3 Hz), 6.06 (1H, d, 4J = 3 Hz) (aromatic);
4.77 (1H, br s), 4.45 (1H, dd, 3J = 8 Hz, 4J = 6 Hz) (methylene); 4.17
(1H, m) (methine); 1.62 (3H, d, 3J = 8 Hz) (methyl); 3.91 (3H, s),
3.86 (3H, s) (methoxy); minor (40%): 8.93 (1H, s) (azomethine);
6.15 (1H, d, 4J = 3 Hz), 6.12 (1H, ov) (aromatic); 5.02 (1H, dd,
3J = 8 Hz, 4J = 6 Hz), 4.33 (1H, br s) (methylene); 4.63 (1H, m)
(methine); 1.34 (3H, d, 3J = 8 Hz) (methyl); 3.91 (3H, ov), 3.86
(3H, ov) (methoxy). 51V NMR (CD3OD, ppm): ꢀ532.4, ꢀ533.8.
2.4.9. l-Oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]-6-tert-
butylphenolato-j3N,O,O0}oxidovanadium(V)) (9)
2.4.5.
l
-Oxido-bis({S(+)-2-[(1-oxidopropyl)iminomethyl]-4-
Yield 75%. Anal. Calc. for C28H38N2O7V2: C, 54.6; H, 6.2; N, 4.5.
methylphenolato-j3N,O,O0}oxidovanadium(V)) (5)
Found: C, 54.7; H, 6.1; N, 4.6%. IR (KBr, cmꢀ1): 1624 (
m
C@N); 977 (mV-
Yield 73%. Anal. Calc. for C22H26N2O7V2: C, 49.6; H, 4.9; N, 5.3.
@O). UV–Vis spectrum in MeOH [kmax (nm), e (Mꢀ1 cmꢀ1)]: 281
Found: C, 49.5; H, 5.0; N, 5.4%. IR (KBr, cmꢀ1): 1626 (
mC@N); 982
(10540), 331 (5150). CD spectrum in MeOH [kmax (nm), D
e (Mꢀ1
(m
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (Mꢀ1 cmꢀ1)]:
cmꢀ1)]: 278 (ꢀ0.61), 297 (0.25), 333 (ꢀ2.26). 1H NMR (CD3OD,

630
G. Romanowski, T. Lis / Inorganica Chimica Acta 394 (2013) 627–634
ppm) major (60%): 8.69 (1H, s) (azomethine); 7.56 (1H, d, 3J = 8 Hz),
7.43 (1H, d, 3J = 8 Hz), 6.91 (1H, t, 3J = 8 Hz) (aromatic); 4.82 (1H, br
s), 4.46 (1H, dd, 3J = 8 Hz, 4J = 6 Hz) (methylene); 4.14 (1H, m)
(methine); 1.63 (3H, d, 3J = 8 Hz) (methyl); 1.48 (9H, s) (tert-butyl);
minor (40%): 8.74 (1H, s) (azomethine); 7.58 (1H, ov), 7.45 (1H, ov),
6.95 (1H, t, 3J = 8 Hz) (aromatic); 4.98 (1H, dd, 3J = 8 Hz, 4J = 6 Hz),
4.37 (1H, br s) (methylene); 4.64 (1H, m) (methine); 1.37 (3H, d,
3J = 8 Hz) (methyl); 1.48 (9H, ov) (tert-butyl). 51V NMR (CD3OD,
ppm): ꢀ546.0, ꢀ546.8.
Table 2
Selected bond lengths (Å) and angles (°) and hydrogen bonding parameters (Å, °) for 7.
V17–O18
V17–O19
V17–O16
V17–N12
1.590(2)
1.826(2)
1.862(2)
2.095(2)
1.874(2)
104.60(11)
101.67(10)
89.94(9)
1.581(2)
1.794(2)
1.864(2)
2.098(2)
1.882(2)
107.10(11)
104.04(10)
88.36(10)
O18–V17–N12
O19–V17–N12
O16–V17–N12
O18–V17–O7
O19–V17–O7
O16–V17–O7
104.00(10)
150.61(9)
77.79(9)
99.98(10)
97.68(9)
154.40(9)
83.87(9)
107.05(11)
104.64(11)
147.37(10)
76.75(9)
V17–O7
O18–V17–O19
O18–V17–O16
O19–V17–O16
V17A–O18A
V17A–O19
V17A–O16A
V17A–N12A
V17A–O7A
N12–V17–O7
V17–O19–V17A
O18A–V17A–N12A
O19–V17A–N12A
O16A–V17A–N12A
O18A–V17A–O7A
O19–V17A–O7A
O16A–V17A–O7A
N12A–V17A–O7A
2.4.10. l-Oxido-bis({S(+)-2-[(1-
oxidopropyl)iminomethyl]naphtholato-j3N,O,O0}oxidovanadium(V)
(10)
100.90(10)
97.38(10)
151.48(9)
83.87(9)
O18A–V17A–O19
O18A–V17A–O16A
O19–V17A–O16A
Yield 73%. Anal. Calc. for C28H26N2O7V2: C, 55.6; H, 4.3; N, 4.6.
Found: C, 55.4; H, 4.4; N, 4.6%. IR (KBr, cmꢀ1): 1621 (
m
C@N); 981
V@O). UV–Vis spectrum in MeOH [kmax (nm), e (Mꢀ1 cmꢀ1)]:
308 (8900), 396 (5640). CD spectrum in MeOH [kmax (nm),
(m
DHꢂ ꢂ ꢂA
D–H
Hꢂ ꢂ ꢂA
Dꢂ ꢂ ꢂA
DHꢂ ꢂ ꢂA
D
e
C13–H13ꢂ ꢂ ꢂO18(i)
C13–H13ꢂ ꢂ ꢂO19(i)
C14–H14Aꢂ ꢂ ꢂO18(i)
C11–H11ꢂ ꢂ ꢂO16(i)
C11A–H11Aꢂ ꢂ ꢂO9A(ii)
C15A–H15Eꢂ ꢂ ꢂO7(iii)
1.00
1.00
0.99
0.95
0.95
0.98
2.53
2.42
2.59
2.60
2.25
2.56
3.259(4)
3.385(4)
3.308(4)
3.483(3)
3.040(4)
3.519(4)
130
161
130
155
139
165
(Mꢀ1 cmꢀ1)]: 281 (ꢀ0.93), 315 (0.27), 349 (ꢀ1.95). 1H NMR (CD3-
OD, ppm) major (60%): 8.53 (1H, s) (azomethine); 8.28 (1H, d,
3J = 8 Hz), 8.01 (1H, d, 3J = 8 Hz), 7.83 (1H, d, 3J = 8 Hz), 7.62 (1H,
t, 3J = 8 Hz), 7.47 (1H, t, 3J = 8 Hz), 7.13 (1H, d, 3J = 8 Hz) (aromatic);
4.89 (1H, br s), 4.55 (1H, dd, 3J = 8 Hz, 4J = 6 Hz) (methylene); 4.33
(1H, m) (methine); 1.74 (3H, d, 3J = 8 Hz) (methyl); minor (40%):
8.61 (1H, s) (azomethine); 8.32 (1H, d, 3J = 8 Hz), 8.04 (1H, d,
3J = 8 Hz), 7.86 (1H, d, 3J = 8 Hz), 7.64 (1H, ov), 7.49 (1H, ov), 7.17
(1H, d, 3J = 8 Hz) (aromatic); 5.13 (1H, dd, 3J = 8 Hz, 4J = 6 Hz),
4.42 (1H, br s) (methylene); 4.83 (1H, m) (methine); 1.42 (3H, d,
3J = 8 Hz) (methyl). 51V NMR (CD3OD, ppm): ꢀ534.9; ꢀ538.0.
Symmetry code: (i) 2 ꢀ x, ½ + y, 1 ꢀ z; (ii) 2 ꢀ x, ½ + y, ꢀz; (iii) 1ꢀx, ½ + y, 1 ꢀ z.
V17A toward O18A from the plane of O7A, O16A, O19, N12A,
0.465(2) Å, is about normal for a vanadium center in a square-
pyramidal coordination sphere with comparison to [VO(SAE)]2O
(0.469 Å) and [VO(NAE)]2O (0.490 Å). Distances between vanadium
atom and the alkoxide oxygen coordinated by the other vanadium
atom are different (V17ꢂ ꢂ ꢂO16A = 2.585(2) Å and V17Aꢂ ꢂ ꢂO16 =
2.801(2) Å). The shorter separation, 2.585(2) Å, is however dis-
tinctly longer than the Vꢂ ꢂ ꢂO(alkoxide) separations in related
[VO(SAE)]2O, [VO(NAE)]2O and [VO(SAMP)]2O complexes (2.401,
2.404 and 2.459 Å, respectively).
The O18 = V17/V17A = O18A pseudo torsion angle of 91.82(2)°
in 7 shows an intermediate disposition of the two V = O units in
the (V = O)2O4+ core between cis and trans, and is considerably
higher than angle of 79.7° reported for the related [VO(NAE)]2O
and lower (105°) than in [VO(SAMP)]2O, which may be brought
about by the sterically more demanding aminoalcohol fragment
in the latter. The bridging angle V17–O19–V17A of 107.05(11)°
and the V17ꢂ ꢂ ꢂV17A separation of 2.9115(14) Å are a little smaller
than these structural parameters in [VO(SAE)]2O (107.62°,
2.9422 Å), [VO(NAE)]2O (109.3°, 2.94 Å) and [VO(SAMP)]2O (113°,
3.06 Å). Moreover, the difference in bond lengths between the
O19 oxygen and V17 or V17A of only 0.032 Å and 0.035 Å in
[VO(NAE)]2O indicates that the bridge is slightly asymmetric in
these cases, but in contrast to much greater the V–O–V bridge
asymmetry in [VO(SAE)]2O and [VO(SAMP)]2O, i.e. 0.096 Å and
0.098 Å, respectively. There are also significant differences in V–
O(alkoxide) distances and O(alkoxide)–V–O(phenolate) angles be-
tween six-coordinated vanadium centres (1.811 Å, 155.99° in
[VO(SAE)]2O and 1.805 Å, 156.5° in [VO(SAMP)]2O) and five-
coordinated vanadium centres (1.893 Å, 143.24° in [VO(SAE)]2O
and 1.828 Å, 137.2° in [VO(SAMP)]2O), in contrast to 7 where these
parameters are very similar, i.e. V–O(alkoxide) bond lengths of
1.862(2) and 1.864(2) Å, and O(alkoxide)–V–O(phenolate) bond
angles of 154.40(9) and 151.48(9)°.
3. Results and discussion
3.1. Crystal and molecular structure
The crystallographic data of 7 are summarized in Table 1 and
the selected bond distances and angles are given in Table 2.
So far, three crystal structures of vanadium(V) Schiff base com-
plexes derived from only achiral amino alcohols involving the
OVV( 2–O)VVO unit have been reported, i.e. [VO(SAE)]2O [10]
l
(where SAE is 2-(salicylideneamino)ethanol), [VO(NAE)]2O [9]
(where NAE is 2-(2-hydroxynaphthalideneamino)ethanol) and
[VO(SAMP)]2O [8,10] (where SAMP is 1,1-dimethyl-2-(salicylide-
neamino)ethanol). In these compounds, one of the vanadium(V)
atoms adopts a five-coordinate square-pyramidal 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 7
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 (V17–
O7 = 1.874(2) and V17A–O7A = 1.882(2) Å), azomethine nitrogens
(V17–N12 = 2.095(2) and V17A–N12A = 2.098(2) Å) and deproto-
nated alkoxide oxygens (V17–O16 = 1.862(2) and V17A–
O16A = 1.864(2) Å) from the Schiff base ligands, oxido groups in
the apex (V17–O18 = 1.590(2) and V17A–O18A = 1.581(2) Å), and
a second oxido atom (V17–O19 = 1.826(2) Å) that forms a strong
bridge to second vanadium atom (V17A–O19 = 1.794(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 V17 atom is displaced toward the terminal oxido group
O18 by 0.414(2) Å from the mean plane of O7, O16, O19, N12,
while in related [VO(SAE)]2O and [VO(NAE)]2O deviation is just
0.365 and 0.369 Å, respectively, due to weakly bridging alkoxide
oxygen. On the other hand, the corresponding displacement of
Coordination of tridentate ligands by vanadium atoms resulted
in formation of four chelate rings. Six-membered rings formed by
V17, O7, C1, C6, C11, N12 and by V17A, O7A, C1A, C6A, C11A,
N12A are planar (deviations of atoms defining the plane from the
mean plane in both cases do not exceed 0.13 Å). Both five-
membered rings containing V17, O16, C14, C13, N12 and C17A,
O16A, C14A, C13A, N12A atoms assumed half-chair conformations

G. Romanowski, T. Lis / Inorganica Chimica Acta 394 (2013) 627–634
631
Fig. 2. An ORTEP drawing of 7 molecule with atom-numbering scheme. Thermal ellipsoids drawn at the 10% probability level. H atoms are shown as small spheres of
arbitrary radius.
the former one twisted on C13 and N12, the latter twisted on C13A
and N12A.
hydrogen bonds, to the two-dimensional hydrogen-bonded chains
along b axis (Fig. 3).
The compound 7 has four centers of symmetry (both vanadium
atoms and asymmetric carbon atoms of both S(+)-2-amino-1-pro-
panol moieties). Setting the priority sequence of atoms coordinated
in the basal plane O(bridging) > O(phenolate) > O(alkox-
ide) > N(enamine) and viewing of the two metal centers down
the V = O (terminal oxido) axis the absolute configuration is found
to be of clockwise type in the cases of both V17 and V17A. Of three
possible diastereomers AASS, ACSS and CCSS of 7, where A and C
correspond to the chirality of a vanadium center, the latter one
(CCSS) is represented in the asymmetric unit.
3.2. Spectroscopic properties
The electronic, circular dichroism, NMR and selected solid-state
IR spectral data are listed in Section 2.
The IR spectra of solid complexes display strong C@N stretch
(around 1630 cmꢀ1) which indicates the C@N group of the coordi-
nated Schiff base ligands [24,25]. For all vanadium(V) complexes a
strong absorption band is observed at around 980 cmꢀ1 assigned as
stretching vibration of the V@O moiety, which are close to values
reported for related oxidovanadium(V)–Schiff base complexes
[10,14]. The appearance of weak/medium band near 2800 cmꢀ1
Molecules of 7 are assembled via weak intermolecular C–Hꢂ ꢂ ꢂO
short contacts (see Table 2), which can be considered as weak
Fig. 3. The arrangement of the molecules of 7 in the crystal structure viewed approximately along b-axis. The C–Hꢂ ꢂ ꢂO intermolecular contacts are represented by dashed
lines.

632
G. Romanowski, T. Lis / Inorganica Chimica Acta 394 (2013) 627–634
separate from other C–H stretching vibrations in 2, 3, 4 complexes
indicated the presence of the methoxy substituents [26].
R
R
O
V
O
N
O
N
O-V=O(L)
O
O-V=O(L)
O
The electronic and circular dichroism spectra of all complexes
were recorded in methanol. Strong intense bands, emax = 8900–
14610 dm3 molꢀ1 cmꢀ1, with kmax in region 274–308 nm are con-
V
O
sidered to arise from intraligand p–
p⁄ transitions. The low energy
bands, recorded for 1–3, 5, 6, 8–10 complexes, between 330 and
396 nm (emax = 4450–5640 dm3 molꢀ1 cmꢀ1) may be assigned as
a ligand-to-metal charge transfer (LMCT) transition originating
H3C
H3C
AS
CS
from the p orbital on the phenolate oxygen to the empty d orbital
p
Fig. 4. Visualization of AS and CS diastereomers caused by dissymmetric vana-
at the vanadium(V) center [27,28]. The spectra of 4 and 7 com-
plexes examined in the same spectral region display only one very
dium(V) ions.
strong bands at 314 (emax = 20040) and 343 (emax = 14930) nm,
respectively, similar to the same strong bands at around 320 and
350 nm for complexes derived from 4,6-dimethoxysalicylaldehyde
and 5-nitrosalicylaldehyde [19–21]. The circular dichroism spectra
revealed an additional band in the 292–315 nm range with oppo-
site sign of the Cotton effect to the bands at around 280 and
340 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 334 and 324 nm, respectively.
3.3. Sulfoxidation
In this study, the oxovanadium(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 sub-
strates have been tested. Aqueous 30% H2O2 or cumene hydroper-
oxide (CHP) were used as oxidants in a slight excess of 1.10
equivalents based on the sulfide substrate. Reactions were run
with 1 mol% of catalyst based on the model substrate. The results
of catalytic studies are listed in Table 3.
1H NMR signals were assigned on the basis of intensity, spin–spin
coupling pattern, chemical shifts, COSY and gHSQC techniques. Sin-
gle condensation of salicylaldehyde and its derivatives with 2-ami-
no-1-propanol is confirmed by the presence of azomethine proton
signalsinthespectraofall complexes. Signalsofthemethyl, methine
and methylene protons in all compounds have been readily recog-
nized. 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 2-amino-1-propanolate frag-
ment. For example, in case of COSY spectrum of 8, cross-peaks be-
tween the methine proton signal (major species signal at
4.17 ppm) and the methyl proton signal at 1.34 ppm, and also, one
of methylene protons signal at 4.47 ppm are observed. Further, there
are cross-peak between the methylene proton signal at 4.47 ppm
and the second methylene proton signal at 4.79 ppm. Moreover,
NOESY spectra exhibit cross-peaks between the signals of the azo-
methine proton and the methyl protons, and also between the sig-
nals of the azomethine proton and the methine proton. As
expected, there is lack of any cross-peaks between the signals of
the azomethine proton and each of the methylene protons.
The best results have been obtained for complexes 2, 3, 5, 6 and
8 as catalysts in the oxidation of methyl phenyl sulfide with hydro-
gen peroxide as oxidant (Table 3, entries 2, 3, 5, 6 and 8). In this
case an overall yield in the range of 90–95% within 30 min reaction
time and enantiomeric excess (ee’s) of 22–27% of the S-configured
sulfoxide was obtained. For the same time of reaction, catalyst and
sulfide, but employing CHP as oxidant, similar yield (82–89%) and
much lower ee’s values (10–16%) of the S-configured sulfoxide
were obtained (Table 3, entries 21–30). When benzyl phenyl sul-
fide was used as substrate, possessing more bulky substituent,
with hydrogen peroxide as oxidant, the overall yield of sulfoxide
is still comparable to previous reactions (85–91%) but enantiose-
lectivity decreases to value of 9% and smaller or even resulting in
a racemic product (Table 3, entry 11–20). With the reaction carried
out at ꢀ20°C with hydrogen peroxide as oxidant, for 2, 3, 5, 6 and 8
as catalysts, enantioselectivities improve significantly to 29–34%
ee and a conversion of over 90% of the substrate is observed after
3 h (Table 3, entries 31–35). Mimoun et al. [33] pointed out the
importance of sufficiently nucleophilic centre for the oxidative
catalysis of organic substances by peroxidovanadium(V) com-
pounds. Better enantioselectivities 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-positions, contributing to an attainment of suffi-
cient nucleophilicity by the vanadium centre.
Zeng et al. [13] have performed sulfoxidation reactions employ-
ing methyl phenyl sulfoxide as model substrate, 30% hydrogen per-
oxide as oxidant and similar vanadium(V) Schiff base complexes
derived from 2-amino-1-propanol but containing VO(OH) frag-
ment. They observed that in ice-water bath (about 4 °C) after 4 h
using catalysts derived from salicylaldehyde and 3,5-di-tert-butyl-
salicyaldehyde obtained enantioselectivities are much smaller,
6.7% and 2.9%, respectively. A much longer reaction time and lower
ee values, in contrast to 1–10 catalysts, may be the result of
employing only apolar dichloromethane as solvent. It is well
known that sulfoxidation in aprotic solvents tend to give better re-
sults concerning the enantioselectivity of the reaction [17], but
such catalysts are very poorly soluble in dichloromethane. When
we have conducted sulfoxidation reactions with addition of meth-
anol to CH2Cl2 in 3:7 ratio the solubility of vanadium catalysts has
been dramatically improved. Change of the solvent may be the
important reason of better enantioselectivity and shorter reaction
time in case of using 1–10 complexes as catalysts. Nevertheless,
In the 1H NMR spectra in CD3OD, 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
60:40, in contrast to similar vanadium(V) Schiff base complexes
derived from different aminoalcohols, where contribution of major
species varies from 53% to 95%. The 51V NMR spectra exhibit two
signals with the same major: minor ratios as the signals in the
1H NMR spectra. According to Rehder and co-workers [29], possible
reasons for presence of two species in solution could be diastereo-
mers, equilibria between monomeric and dimeric (or oligomeric)
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
complexes should be observed in 51V NMR spectra. These rather
high-field resonances are present in chloroform solution [30] 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 (AS and CS), caused by chiral S methine carbon atom in the 2-
amino-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 of two 51V
NMR signals [31,32].

G. Romanowski, T. Lis / Inorganica Chimica Acta 394 (2013) 627–634
633
Table 3
Catalytic oxidation of PhSMe and PhSBz by hydrogen peroxide or cumene hydroperoxide (CHP) as oxidant in presence of 1 mol% vanadium(V) Schiff base complexes as catalysts.
O
S
S
1 mol% catalyst
R
R
H O or CHP
2
2
a
b
c
Entry
Catalyst
Substrate
Oxidant
Yield (%)
T (°C)
t (min)
TON
ee (%)
1
2
3
4
5
6
7
8
9
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
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
H2O2
CHP
94
92
95
92
90
94
90
92
94
93
88
87
91
90
87
88
85
89
91
88
84
84
88
83
85
89
83
87
88
82
96
97
94
95
93
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
94
92
95
92
90
94
90
92
94
93
88
87
91
90
87
88
85
89
91
88
84
84
88
83
85
89
83
87
88
82
96
97
94
95
93
17
27
25
16
22
23
19
24
16
14
0
9
9
3
5
5
0
8
0
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
0
10
16
15
11
13
14
12
16
11
10
34
30
31
29
32
CHP
CHP
CHP
CHP
CHP
CHP
CHP
CHP
CHP
H2O2
H2O2
H2O2
H2O2
H2O2
ꢀ20
ꢀ20
ꢀ20
ꢀ20
ꢀ20
a
b
c
Solvent, methylene chloride/methanol (7:3).
Turnover numbers.
All sulfoxides are in S configuration.
this comparison is disputable due to dinuclear nature of described
complexes.
We have characterized ten chiral vanadium(V) complexes de-
rived from Schiff base ligands, monocondensation products of o-
hydroxycarbonyl compounds with S(+)-2-amino-1-propanol. 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 1,2-diamino-
propane or 2-amino-1-propanol. The results show that the
observed yield and enantiomeric excess significantly depend on
the nature of the catalyst, substrate and peroxide used, especially
in the aspect of bulky substituent leading to large steric demand,
and finally depend on the temperature in which the reaction is car-
ried out.
In general, the best results have been obtained in the oxidation
reactions of methyl phenyl sulfide with hydrogen peroxide as oxi-
dant. Significant decrease in reactivity is observed, i.e. enantiose-
lectivity as well as the overall yield of the oxidation of PhSMe,
when the bulkier oxidant cumene hydroperoxide as oxidant has
been employed. 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 were observed [19–21]. Moreover, much higher values of
enantiomeric excesses of corresponding sulfoxides employing 1–
10 as catalysts have been recorded than in compounds possessing
1,2-diaminopropane [21] or 2-amino-1-propanol [13] moieties.
Acknowledgement
This scientific work was supported by the Polish Ministry of Sci-
ence and Higher Education (DS/8210-4-0177-11).
4. Conclusion
Appendix A. Supplementary material
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.
CCDC 876825 contains the supplementary crystallographic data
for this article. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/

634
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