Synthesis, characterization, and structures of oxovanadium(v) complexes of Schiff bases of β-amino alcohols as tunable catalysts for the asymmetric oxidation of organic sulfides and asymmetric alkynylation of aldehydes

Article abstract of DOI:10.1039/b613212j

Oxovanadium(v) complexes 3a-3k and 4a-4d with general formula VO(L ₃*)(OR⁵) were prepared in quantitative yields in alcohol (R⁵OH) from reactions of VO(O-i-Pr)₃ and tridentate Schiff bases of β-amino alcohols having one or two stereogenic centers, (HO)C*(R¹)(R²)C*H(R ³)NCH(2-OH-3,5-R⁴₂-C₆H₂) (H₂L₃*). The alkoxy OR⁵ ligand exchanges readily with the alcoholic molecule in the solvent. Crystal structures of 3b, 3f, 3i, and 4a were determined to be five-coordinate square pyramidal monomers. However, ¹H NMR spectra of the complexes reveal two sets of signals, indicating the presence of two isomers in solution. The two isomers are suggested to be the endo/exo pair or the monomer/dimer pair. Asymmetric oxidations of methyl phenyl sulfide catalyzed by catalyst precursors 3 were demonstrated to afford the chiral sulfoxide in yields and ee values similar to those obtained from the in situ-formed catalytic systems of VO(acac)₂ and corresponding Schiff base ligands. Complexes 3 and 4 are also good catalysts for asymmetric alkynyl additions to aldehydes. Structural differences between the oxovanadium complexes, for inducing high stereoselectivities in the asymmetric oxidation of organic sulfides and the asymmetric alkynyl addition to aldehydes, are rationalized. This journal is The Royal Society of Chemistry.

Full text of DOI:10.1039/b613212j

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PAPER
www.rsc.org/dalton | Dalton Transactions
Synthesis, characterization, and structures of oxovanadium(V) complexes of
Schiff bases of b-amino alcohols as tunable catalysts for the asymmetric
oxidation of organic sulfides and asymmetric alkynylation of aldehydes
Sheng-Hsiung Hsieh, Ya-Pei Kuo and Han-Mou Gau*
Received 12th September 2006, Accepted 26th October 2006
First published as an Advance Article on the web 3rd November 2006
DOI: 10.1039/b613212j
Oxovanadium(V) complexes 3a–3k and 4a–4d with general formula VO(L3*)(OR5) were prepared in
quantitative yields in alcohol (R5OH) from reactions of VO(O-i-Pr)3 and tridentate Schiff bases of
1
2
3
=
b-amino alcohols having one or two stereogenic centers, (HO)C*(R )(R )C*H(R )N CH(2-OH-
3,5-R4 –C6H2) (H2L3*). The alkoxy OR5 ligand exchanges readily with the alcoholic molecule in the
2
solvent. Crystal structures of 3b, 3f, 3i, and 4a were determined to be five-coordinate square pyramidal
monomers. However, 1H NMR spectra of the complexes reveal two sets of signals, indicating the
presence of two isomers in solution. The two isomers are suggested to be the endo/exo pair or the
monomer/dimer pair. Asymmetric oxidations of methyl phenyl sulfide catalyzed by catalyst precursors
3 were demonstrated to afford the chiral sulfoxide in yields and ee values similar to those obtained from
the in situ-formed catalytic systems of VO(acac)2 and corresponding Schiff base ligands. Complexes 3
and 4 are also good catalysts for asymmetric alkynyl additions to aldehydes. Structural differences
between the oxovanadium complexes, for inducing high stereoselectivities in the asymmetric oxidation
of organic sulfides and the asymmetric alkynyl addition to aldehydes, are rationalized.
disulfides13 and complexes prepared by Hartung and coworkers
successfully catalyze oxidation of bis(homoallylic) alcohols to
afford functionalized tetrahydrofurans.14
Introduction
Ever since the vanadium metal center was recognized at the active
site in biological systems of nitrogenase1 and bromoperoxidase,2
many vanadium complexes with ligands bearing oxygen and
nitrogen donors have been developed for mimicking biological
activity in natural systems.3 Structurally, both monomeric and
dimeric oxovanadium complexes having five-coordinate4 or six-
coordinate5 geometries were documented. Meanwhile, oxovana-
dium complexes were illustrated to be catalysts6 in a variety
of asymmetric reactions such as the cyanation reaction,7 the
epoxidation of allyl alcohols,6a,8 the oxidative coupling of 2-
naphthol,9 the oxidation of organic sulfides,6a,10 alkynyl addition
to aldehydes,11 and others.12 The asymmetric oxidation of organic
sulfides catalyzed by oxovanadium complexes of Schiff bases of
chiral b-amino alcohols 1 is the reaction which has attracted the
most attention since the catalytic system is highly effective with a
catalyst loading of ≤1 mol% for achieving chiral sulfoxides in
good yields and good to excellent enantioselectivities. Despite
extensive studies, only two papers13,14 report crystal structures
of oxovanadium(V) complexes of Schiff bases of chiral amino
alcohols. The complexes reported by Ellman et al. were shown
to be catalyst precursors in asymmetric oxidations of organic
To continue exploring structural and electronic effects of chiral
metal complexes applied to asymmetric catalysis,15 we report
here the synthesis of a series of oxovanadium(V) complexes
VO(L3*)(OR) (3a–3k, 4a–4d) from reactions of VO(O-i-Pr)3
with Schiff bases 1 (H2L3*). Solid-state structures of 3b, 3f, 3i,
and 4a were determined to be five-coordinate square pyramidal
monomers. However, two isomers are observed in solution ac-
1
cording to H NMR spectroscopy and solution structures of the
complexes are discussed. Complexes 3 and 4 are catalyst precursors
or catalysts for asymmetric oxidations of methyl phenyl sulfide and
asymmetric alkynyl additions to aldehydes. Structural differences
between the catalysts for these two asymmetric reactions are
rationalized.
Results and discussion
Synthesis of tridentate Schiff bases of b-amino alcohols and their
V(V) complexes
Eleven tridentate Schiff bases 1a–1k were prepared in quantitative
yields in methanol according to standard synthetic procedures
from reactions of b-amino alcohols 2a–2g with 2-hydroxy arylalde-
hydes in the presence of Na2SO4 under reflux conditions for 12 h
(Scheme 1). The Schiff bases synthesized include species having
one stereogenic center with R1 = R2 = Ph groups (1a and 1b) or
with R1 = R2 = H (1c–1g) and species with two stereogenic centers
(1h–1k).
Department of Chemistry, National Chung-Hsing University, Taichung,
402, Taiwan. E-mail: hmgau@dragon.nchu.edu.tw; Fax: +886-4-22862547;
Tel: +886-4-22878615
According to synthetic procedures by Hartung et al.,14 oxovana-
dium(V) complexes 3a–3k were prepared in quantitative yields
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Table 1 Crystallographic data for 3b, 3f, 3i, and 4a
Complex
3b
3f
3i
4a
˚
Bond lengths/A
V–O
V–OEt (i-Pr)
V–OR*
1.586(3)
1.788(3)
1.846(2)
1.843(2)
2.134(3)
0.486
1.595(3)
1.763(3)
1.839(3)
1.844(2)
2.117(3)
0.469
1.584(2)
1.777(2)
1.826(2)
1.889(2)
2.117(2)
0.471
1.576(2)
1.775(2)
1.833(2)
1.865(2)
2.118(2)
0.484
V–OAr
V–N
V–basal
Bond angles/◦
O–V–OEt(i-Pr)
O–V–OR
O–V–OAr
O–V–N
103.55(15) 102.09(16) 105.70(9)
111.67(14) 112.84(13) 107.21(8)
109.60(14) 110.13(13) 106.27(8)
105.08(10)
107.20(9)
106.66(11)
100.33(10)
94.68(13)
92.71(12)
97.92(8)
of Schiff bases of amino acids, both five-coordinate square
pyramidal structure and six-coordinate octahedral structure were
reported and two diastereomeric structures, i.e., the exo-17 and the
endo-structures18 are observed. In contrast, for oxovanadium(V)
complexes of Schiff bases of amino alcohols13,14 including the four
structures reported in this work, only the five-coordinate square
pyramidal geometry is observed. The solid state structures of 3b,
3i, and 4a with R3 = Bn adopt the endo-structure, in which the
Bn group and the oxo ligand are on the same side of the basal
plane defined by the donor atoms of the Schiff base ligand and the
terminal alkoxy ligand. However, the complex 3f adopts the exo-
structure with the t-butyl R3 group trans to the oxo ligand. The
exo-structure is also observed for the complex with R3 = i-Pr.14
Scheme 1 Synthesis of tridentate Schiff bases of amino alcohols 1a–1k.
in a reaction time of 1 h from reactions of 1a–1k and 1 molar
equiv. of VO(O-i-Pr)3 in ethanol and, similarly, complexes 4a–4d
were prepared in 2-propanol, i-butanol, or t-butanol (Scheme 2).
Elemental analyses reveal that the complexes have a 1 : 1
composition ratio of the vanadium metal relative to the Schiff base
ligand. The alkoxy OR5 ligand in complexes readily exchanges with
the alcoholic solvent molecule. For example, recrystallization of
the ethoxy complex 3a in 2-propanol affords a crystalline material
of 2-propoxy complex 4a and vice versa. These oxovanadium
complexes are considerably stable and can be stored under a
nitrogen atmosphere for months.
For either the exo-structure 3f or the endo-structures 3b, 3i, and
4a, the basal donor atoms are bent away from the oxo ligand.
Variations of the distance from the vanadium metal center to the
˚
basal plane are minimal from 0.469 to 0.486 A. However, larger
variations in the O(oxo)–V–L angles are observed and differences
in the O(oxo)–V–N angles are up to ∼8◦ between 3f at 92.71(12)◦
and 4a at 100.33(10)◦.
Scheme 2 Synthesis of oxovanadium(V) complexes of Schiff bases of
b-amino alcohols.
Solid state structures of 3b, 3f, 3i, and 4a
NMR study of complexes 3a–3k and 4a–4d
1
Suitable crystals of 3b, 3f, 3i, and 4a were subjected to X-ray
diffraction analyses. Selected bond lengths and bond angles are
listed in Table 1 and molecular structures are shown in Fig. 1. In
the solid state, all four structures are square pyramidal monomers.
The V–O(oxo) bonds are strong with short bond lengths ranged
Complexes 3a–3k and 4a–4d were characterized by H and 13C
1
NMR spectroscopy and the H NMR spectra clearly reveal two
sets of signals, suggesting the presence of two isomers in solution.
Since the co-existence of both the endo- and the exo-structures in
solid state oxovanadium complexes of Schiff bases of amino acids
have been observed previously,17a the two isomers in solution can
be rationalized as the endo/exo pair. However, in the study of
the VO(cyclo-C5H9O)3 complex, a monomer/dimer equilibrium
was suggested based on the concentration-difference 51V NMR
study.19 In addition, six-coordinate dimeric oxovanadium com-
plexes bridging through the alkoxy or the oxo donors are known.20
˚
from 1.576(2) to 1.595(3) A which are shorter than the terminal V–
˚
O(Et or i-Pr) bond distances by ∼0.2 A. In comparison with
the chelating V–OR* and the V–OAr bonds, the V–O(oxo) bond
˚
lengths are shorter by ∼0.25 A. The strong V–O(oxo) bonding
causes the coordination site trans to it to be rather labile16 or
even unfavorable for coordination. For oxovanadium complexes
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Fig. 1 Molecular structures of (a) 3b (R1 = R2 = Ph, R3 = Bn, R4 = t-Bu, R5 = Et), (b) 3f (R1 = R2 = H, R3 = t-Bu, R4 = H, R5 = Et), (c) 3i (R1 = Ph,
R2 = H, R3 = Bn, R4 = t-Bu, R5 = Et), and (d) 4a (R1 = R2 = Ph, R3 = Bn, R4 = H, R5 = i-Pr). Ellipsoids of the atoms are 20% probability.
It seems that the possibility of the monomer/dimer pair can not
be ruled out completely. In this study, concentration-difference
1H NMR experiments in CDCl3 were conducted. For 3c at 6.04 ×
10−2 M and 21.9 × 10−2 M, the major : minor ratios vary from 1.78
to 1.33 : 1 and, for 3f at 1.51 × 10−2 M and 6.04 × 10−2 M, the ratios
increase about 10% from 3.55 to 4.00 : 1. For 4b with the Schiff base
ligand bearing two stereogenic centers, the ratios change from 2.44
(6.04 × 10−2 M) to 2.22 : 1 (17.8 × 10−2 M). Due to small changes
in the ratios of the two sets of signals, results from concentration-
difference 1H NMR experiments do not fully support the argument
of the monomer/dimer pair in solution. It is worth noting that
additional minor signals are observed for complexes 3g–3j and
4a–4d. Yet, it is not clear whether these additional signals are due
to isomers in solution or are just minor impurities.
b-amino alcohols have been extensively studied.10 Although the
oxovanadium(IV) species VO(acac)2 is used as the metallic reagent,
the active oxovanadium(V) catalytic species have been illustrated
using evidence from 51V NMR studies. Further evidence to
support the active oxovanadium(V) catalytic species is from the
work by Ellman and coworkers. In their work, oxovanadium(V)
complexes 5 and 6 were demonstrated to be catalyst precursors
for asymmetric oxidation of organic disulfides.13 In addition,
the hydroxyl oxovanadium(V) complexes 7 also catalyze the
asymmetric oxidation of methyl phenyl sulfide.21
Asymmetric oxidation of methyl phenyl sulfide by catalyst
precursors 3a–3g
Asymmetric oxidations of organic sulfides by the H2O2 oxidant
employing catalytic systems of VO(acac)2 and Schiff bases of
In this study, asymmetric oxidations of methyl phenyl sul-
fide were conducted employing 1 mol% catalyst precursors
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Table 2 Asymmetric oxidation of methyl phenyl sulfide with H2O2 catalyzed by vanadium(V) complexes of Schiff basesa
Entry
Complex
R
T/◦C
Yield (%)
ee (%) (S)
1
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3f
3g
3g
3g
3g
R1 = R2 = Ph, R3 = Bn, R4 = H
R1 = R2 = Ph, R3 = Bn, R4 = t-Bu
R1 = R2 = H, R3 = Bn, R4 = H
R1 = R2 = H, R3 = Ph, R4 = H
R1 = R2 = H, R3 = i-Bu, R4 = H
R1 = R2 = H, R3 = t-Bu, R4 = H
R1 = R2 = H, R3 = t-Bu, R4 = I
R1 = R2 = H, R3 = t-Bu, R4 = I
R1 = R2 = H, R3 = t-Bu, R4 = I
R1 = R2 = H, R3 = t-Bu, R4 = I
rt
rt
rt
rt
rt
rt
rt
70
67
72
76
62
74
79
80
75
61
rac
rac
56
26
58
60
83
87
90
98
0
9
−20
10b
−20
a Methyl phenyl sulfide : 30% H2O2 : catalyst precursor = 1.0 mmol : 1.1 mmol : 0.010 mmol; solvent: CH2Cl2 (2 mL); reaction time, 16 h. b Solvent,
toluene–CH2Cl2 = 2 : 1, 2 mL.
3a–3g (eqn (1))
to 9. In order to achieve the chiral sulfoxide in the observed
S-configuration, the methyl phenyl sulfide should attach to the
peroxy oxygen in an orientation with the phenyl group pointing
away from the ortho iodo substituent to afford an intermediate or
a transition state 11. Detachment of the sulfoxide product from
11 affords the hydroxyl complex having a structure similar to 7 for
next cycle of asymmetric reaction.
(1)
and results are listed in Table 2. For 3a or 3b having R1 = R2 = Ph
and R3 = Bn, the reactions gave the racemic sulfoxide in 70 and
67% yield (entries 1 and 2), respectively. For 3c of both R1 and R2 of
the smaller H substituent and R3 also Bn, the enantioselectivity of
the product improves dramatically to 56% ee (entry 3). For 3d with
R3 = Ph, the product was obtained in a lower enantioselectivity
of 26% ee (entry 4). For 3e of R3 = i-Bu or 3f of R3 = t-Bu,
enantioselectivities of the product in 58% and 60% ee (entries 5
and 6) were obtained. When the catalyst precursor 3g (having
an iodo group as R4) was used, the enantioselectivity improves
significantly to 83% ee (entry 7). With the reaction carried out at
0 or at −20 ◦C, enantioselectivities further increase to 87 and 90%
ee (entries 8 and 9), respectively. Yet, the best enantioselectivity
of 98% ee (entry 10) was obtained with the reaction conducted in
1 : 1 mixed solvents of toluene–CH2Cl2.
Asymmetric alkynyl additions to aldehydes catalyzed by complexes
3 and 4
Our recent paper demonstrates that oxovanadium complexes of
Schiff bases of amino alcohol also catalyze asymmetric alkynyl
additions to aldehydes (eqn (2))
Results obtained in this work are comparable to those obtained
by employing the in situ-formed catalytic systems of VO(acac)2
and corresponding Schiff bases, indicating that the same active
species is involved for both catalytic systems. For the in situ-formed
catalytic system, Bolm and Bienewald proposed possible active
V(V) complex species of either exo-VO(HL3*)(OO) (8a) or endo-
VO(HL3*)(OO) (8b).22 A recent computational study by Maseras
et al.23 using the structural data of complexes 5 and 6 suggests an
active catalytic species of complex 9.
(2)
and extracted results are listed in Table 3.11 This study shows that,
for catalysts bearing both R1 and R2 = Ph, a racemic mixture of
propargyl alcohol is obtained (entry 1). For catalysts with R1 =
R2 = H, the product is obtained with a low enantioselectivity of
12% ee (entry 2). However, the enantioselectivity improves to 43%
ee for catalyst 3h (R1 = Ph, entry 3) having the Schiff base ligand
with two stereogenic centers and to 75% ee for catalyst 3j (R1 =
t-Bu, entry 4). However, the enantioselectivity drops to 32% ee for
catalyst 3k having R4 of a bulkier t-Bu substituent (entry 5). This
study also demonstrates that enantioselectivities of the product
are sensitive to variations of the terminal alkoxy OR5 ligand. For
catalyst 4b with R5 of i-Bu instead of Et as in 3j, a 20% increase
In this study, the best performing catalyst precursor 3g is reacted
with H2O2 to afford the active species 10 having a structure similar
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Table 3 Asymmetric alkynylation of benzaldehyde catalyzed by oxovana-
dium(V) complexes of Schiff bases of b-amino alcoholsab
the vanadium metal center as the zinc alkoxide ZnR(OR*) for
regenerating the catalyst for the next cycle of the catalytic reaction.
Entry Complex R1
R2
R4
R5
Yieldc (%) eed (%)
1
2
3
4
5
6
7
8
3a
3c
3h
3j
3k
4b
4c
4d
Ph
H
Ph
t-Bu
t-Bu
t-Bu
t-Bu
t-Bu
Ph
H
H
H
H
H
H
H
H
H
H
H
Et
Et
Et
Et
100
100
100
95
78
98
rac
12
43
75
32
96
84
69
t-Bu Et
H
H
H
i-Bu
i-Pr
t-Bu 100
100
a Benzaldehyde–ZnEt2–phenylacetylene–catalyst
=
0.5
:
1.5
:
1.5 :
Conclusions
0.05 mmol; toluene, 5 ml; CH2Cl2, 2.5 mL. b ZnEt2 and phenylacetylene
were refluxed in toluene for 6 h and the resulting solution cooled to room
temperature. The resulting mixture was transferred to the solution of
catalyst in CH2Cl2 at −20 ◦C followed by addition of benzaldehyde. c Yields
were calculated based on 1H NMR spectra. d ee values were determined by
HPLC using an OD column from Daicel.
A series of oxovanadium(V) complexes 3 and 4 of Schiff bases of
amino alcohols were prepared easily in quantitative yields. The
complex with R3 of t-Bu has the exo-structure and the complexes
having R3 = Bn adopt the endo structures. 1H NMR studies of the
complexes reveal two isomers in solution and the two isomers are
suggested to be either the endo/exo pair or the monomer/dimer
pair. The complexes 3 were demonstrated to be catalyst precursors
for the asymmetric oxidation of organic sulfides. For asymmetric
oxidations of organic sulfides and disulfides, catalyst precursors
with smaller R1 = R2 = H and larger R4 = I or t-Bu induce
higher enantioselectivities for the sulfoxide products. In contrast,
vanadium catalysts having R1 of a group other than the H atom
and R2 and R4 of small H substituents afford better stereocontrol
for asymmetric alkynyl addition reactions to aldehydes. Our
studies demonstrate that oxovanadium(V) complexes of Schiff
bases of amino alcohols are highly tunable catalytic systems
through adjustments of R1, R2, R3, and R4 substituents of the
Schiff base ligands and also through adjustment of the terminal
alkoxy OR5 ligand. Further studies of the oxovanadium complexes
in asymmetric catalysis are currently underway.
in enantioselectivity to 96% ee is obtained (entry 6). However,
increasing steric size of R5 to i-Pr (4c) or to t-Bu (4d) results in
decreasing enantioselectivities of 84% and 69% ee (entries 7 and
8), respectively. For comparison, alkynyl additions to aromatic
aldehydes catalyzed by the best performing oxovanadium complex
4b afford products in comparable enantioselectivities to products
obtained by zinc-,24 titanium-,25 or indium-catalytic systems.26
Structural requirements of oxovanadium complexes for asymmetric
oxidations of organic sulfides and for asymmetric alkynyl additions
to aldehydes
Though oxovanadium(V) complexes of Schiff bases of amino alco-
hols are catalyst precursors for asymmetric oxidations of organic
sulfides or catalysts for asymmetric alkynyl additions to aldehydes,
structural requirements to induce high stereoselectivities are quite
different for the two reactions. In asymmetric oxidations of organic
sulfides, the Schiff base ligands with one stereogenic center having
small R1 = R2 = H substituents and large R4 = I or t-Bu are
essential for directing organic sulfides in the best orientation for
achieving good stereoselectivities. The terminal alkoxy OR5 ligand
plays no role in the oxidation reaction since, under the catalytic
reaction conditions, the alkoxy ligand is replaced by the peroxy
O2H group to afford the active peroxy catalytic species.
In contrast, catalysts having Schiff base ligands with two
stereogenic centers, i.e. having R1 other than the H atom and
both R2 and R4 of H substituents provide good stereoselectivities
for the asymmetric alkynyl additions to aldehydes. In this reaction,
the OR5 ligand plays a key role in stereoselectivities probably due
to the size of the OR5 ligand which strongly affects the orientation
of the aldehyde substrate and the alkynyl reagent accessing the
vanadium metal center from the open site trans to the strong oxo
ligand. To achieve the desired (R)-propargyl alcohol, the aldehyde
attaches to the catalyst from the empty site trans to the oxo ligand
with the larger Ph group oriented under the open edge defined
by the phenoxy and the terminal alkoxy. Then, the zinc alkynyl
reagent accesses the complex through weak interactions of the
zinc metal and the two alkoxy oxygen donors to afford a likely
intermediate or transition state 12. After transferring the alkynyl
group to the aldehyde ligand, the resulting product detaches from
Experimental
Reagents and general techniques
b-Amino alcohols with one stereogenic centre were prepared
according to standard synthetic procedures and (1R,2S)-b-amino
alcohols were synthesized based on modified procedures reported
by Reetz et al.27 2-Hydroxy arylaldehydes and VO(O-i-Pr)3
(Aldrich) were used without further purification. H2O2 (30%)
was used directly. Methanol, absolute ethanol, and 2-propanol
were dried over CaH2 and were freshly distilled prior to use.
Other solvents were dried by refluxing for at least 24 h over
P2O5 (dichloromethane) or sodium–benzophenone (n-hexane or
toluene) and were freshly distilled prior to use. Deuterated solvents
were dried over molecular sieves. All syntheses and manipulations
were carried out under a dry nitrogen atmosphere.
Physical measurements
1H NMR spectra were obtained with a Varian Mercury-400
(400 MHz) spectrometer and chemical shifts were measured
relative to tetramethylsilane as the internal reference. 13C NMR
spectra were recorded with the Varian Mercury-400 (100 MHz)
spectrometer and chemical shifts are relative to TMS as the
internal reference. Elemental analyses were performed using a
Heraeus CHN-OS-RAPID instrument.
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General procedures for the synthesis of Schiff bases of amino
alcohols
35.03, 34.91, 33.92, 31.51, 31.43, 29.48, 26.95 ppm. Anal. calcd.
C28H41NO2: C, 79.39; H, 9.76; N, 3.31%. Found: C, 79.58; H,
9.57; N, 3.12%.
2-Hydroxy arylaldehyde (3.0 mmol) was added to a solution of an
amino alcohol (3.0 mmol) and sodium sulfate (1.28 g, 9.00 mmol)
in 50 mL methanol at room temperature. The mixture was refluxed
for 12 h and was filtered. The solvent was removed under reduced
pressure to furnish a quantitative yield of product.
General procedures for synthesis of oxovanadium(V) complexes of
Schiff bases
To a solution of a Schiff base (1.00 mmol) in 10 mL alcohol,
VO(O-i-Pr)3 (0.24 mL, 1.0 mmol) was added at room temperature.
The mixture was stirred for 1 h and the solvent was removed
under reduced pressure to give a quantitative yield of the product.
Analytically pure samples and crystals for X-ray structural
2-Hydroxy-benzaldehyde 2S-(1,1,3-triphenylpropanol) imine
1
(1a). Yellow solid. H NMR (CDCl3): d 7.66–6.85 (m, 19H),
4.35 (d, J = 9.2 Hz, CHN), 3.04 (d, J = 13.6 Hz, 1H, PhCHAHB),
2.95 (br, 1H, OH), 2.84 (dd, J = 10.4, 13.6 Hz, 1H, PhCHAHB)
1
determination were recrystallized from the alcohol solvent. H
1
ppm. 13C{ H} NMR (CDCl3): d 166.40, 160.52, 145.15, 144.06,
NMR spectra in CDCl3 were measured to suggest the presence of
two isomers in solution. Chemical shifts for the two isomers are
listed separately and designated as major and minor. Resonances
of minor aromatic hydrogens are included in the major resonances
due to overlapping of these signals. In a few complexes, extra minor
peaks are observed. NMR and elemental analysis data of 3h and
4b have already been reported.11
138.80, 132.27, 131.37, 129.61, 128.30, 128.22, 128.10, 126.97,
126.81, 126.21, 126.16, 126.00, 118.47, 118.22, 116.68, 79.69,
78.62, 37.35 ppm. Anal. calcd. C28H25NO2: C, 82.53; H, 6.18; N,
3.44%. Found: C, 82.84; H, 5.86; N, 3.77%.
2-Hydroxy-3,5-di-tert-butyl-benzaldehyde 2S-(1,1,3-triphenyl-
1
propanol) imine (1b). Yellow solid. H NMR (CDCl3): d 7.67–
6.67 (m, 19H), 4.36 (dd, J = 2.0, 9.6 Hz, 1H, CHN), 3.05 (d,
Ethoxo[2-oxobenzaldehyde 2S-(1,1,3-triphenylpropoxo) imine]-
oxovanadium(V) (3a). Yellowish-brown solid. 1H NMR
(400 MHz, CDCl3): major (95%): d 7.90–6.74 (m), 5.30–5.22 (m,
OCH2), 4.88 (dd, J = 2.4, 11.2 Hz, CHN), 3.71 (dd, J = 11.6,
13.2 Hz, CHAHBPh), 2.86 (dd, J = 2.4, 13.2 Hz, CHAHBPh),
1.58 (t, J = 6.8 Hz, 3H, CH3) ppm; minor (5%): d 5.43–5.38
(m, OCH2), 5.10–5.03 (m, CHN), 3.98–3.88 (m, CHAHBPh),
3.14–3.06 (m, CHAHBPh), 2.68–2.60 (m, CHAHBPh), 2.50–2.42
(m, CHAHBPh), 1.73 (t, J = 6.8 Hz, CH3), 1.24 (t, J = 6.8 Hz,
J = 13.2 Hz, 1H, PhCHAHB), 2.86 (dd, J = 10.4, 13.6 Hz, 1H,
1
PhCHAHB), 1.40 (s, 9H, t-Bu), 1.22 (s, 9H, t-Bu) ppm. 13C{ H}
NMR (CDCl3): d 167.71, 157.53, 145.55, 144.23, 139.88, 139.13,
136.28, 129.72, 128.65, 128.37, 128.28, 128.21, 127.07, 126.94,
126.79, 126.25, 126.16, 126.09, 126.01, 117.57, 79.82, 78.39, 37.52,
34.92, 33.97, 31.38, 29.39 ppm. Anal. calcd. C36H41NO2: C, 83.20;
H, 7.95; N, 2.70%. Found: C, 83.20; H, 8.18; N, 2.72%.
2-Hydroxy-3,5-di-tert-butyl-benzaldehyde
2S-(1,3-diphenyl-
1
propanol) imine (1i). Yellow solid. 1H NMR (CDCl3): d 7.82
CH3) ppm. 13C{ H} NMR (100 MHz, CDCl3): d 163.86, 162.87,
=
(s, 1H, CH N), 7.40–6.82 (m, 12H, ArH), 4.93–4.91 (m, 1H,
147.39, 144.88, 138.15, 135.63, 132.20, 130.35, 130.26, 128.62,
128.49, 128.42, 128.35, 128.16, 126.99, 126.87, 126.80, 126.73,
126.63, 126.55, 126.23, 125.91, 119.61, 119.26, 118.60, 96.13,
86.13, 77.97, 38.08, 17.69 ppm. Anal. calcd. C30H28NO4V: C,
69.63; H, 5.45; N, 2.71%. Found: C, 69.55; H, 4.97; N, 2.73%.
CHO), 3.63 (m, 1H, CHN), 3.14 (dd, J = 3.2, 13.6 Hz, 1H,
PhCHAHB), 2.86 (dd, J = 9.6, 13.8 Hz, 1H, PhCHAHB), 2.21
1
(br, 1H, OH), 1.44 (s, 9H, t-Bu), 1.24 (s, 9H, t-Bu) ppm. 13C{ H}
NMR (CDCl3): d 166.79, 158.03, 140.80, 139.73, 138.52, 136.45,
129.62, 128.27, 128.23, 127.90, 127.07, 126.95, 126.15, 126.05,
117.60, 76.78, 76.78, 38.26, 34.98, 34.01, 31.42, 29.39 ppm. Anal.
calcd. C30H37NO2: C, 81.22; H, 8.41; N, 3.16%. Found: C, 81.15;
H, 8.57; N, 3.35%.
Ethoxo[2-oxo-3,5-di-tert-butylbenzaldehyde 2S-(1,1,3-triphenyl-
propoxo) imine]oxovanadium(V) (3b). Green solid. 1H NMR
(400 MHz, CDCl3): major (87%): d 7.90–6.58 (m), 5.23–5.11 (m,
OCH2), 4.85 (dd, J = 2.0, 8.8 Hz, CHN), 3.66 (dd, J = 11.6,
13.6 Hz, CHAHBPh), 2.81 (dd, J = 2.0, 13.6 Hz, CHAHBPh),
1.48 (t, J = 11.2 Hz, CH3), 1.41 (s, t-Bu), 1.23 (s, t-Bu) ppm; minor
(13%): d 5.50–5.30 (m, OCH2), 5.06–4.94 (m, CHN), 3.80–3.72 (m,
CHAHBPh), 3.00–2.92 (m, CHAHBPh), 2.64 (dd, J = 2.0, 10.4 Hz,
CHAHBPh), 2.50–2.40 (m, CHAHBPh), 1.68 (t, J = 6.8 Hz, CH3),
2-Hydroxy-benzaldehyde
imine (1j). Yellow solid. H NMR(400 MHz, CDCl3): d 7.58
2S-(1-tert-butyl-3-phenylpropanol)
1
=
(s, 1H, CH N), 7.30–6.77 (m, 9H, ArH), 3.59 (d, J = 5.6 Hz,
1H, CHO), 3.49–3.44 (m, 1H, CHN), 3.40 (dd, J = 2.4, 13.6 Hz,
1H, CHAHBPh), 2.82 (dd, J = 10.4, 13.6 Hz, 1H, CHAHBPh),
1.01 (s, 9H, t-Bu) ppm. 13C{ H} NMR (100 MHz, CDCl3): d
1.51 (s, t-Bu), 1.46 (s, t-Bu), 1.33 (s, t-Bu) ppm. 13C{ H} NMR
1
1
164.16, 161.05, 138.85, 132.18, 131.27, 129.90, 128.24, 126.18,
118.48, 116.91, 81.36, 74.06, 39.13, 35.77, 26.84 ppm. Anal. calcd.
C20H25NO2: C, 77.14; H, 8.09; N, 4.50%. Found: C, 77.25; H,
8.23; N, 4.39%.
(100 MHz, CDCl3): d 163.46, 161.31, 147.88, 145.45, 141.74,
138.48, 137.99, 130.49, 130.39, 130.19, 128.47, 128.41, 128.05,
126.83, 126.73, 126.58, 126.54, 126.50, 126.36, 126.29, 126.05,
126.02, 125.85, 119.32, 95.84, 85.46, 76.18, 38.07, 35.26, 35.17,
34.11, 34.08, 31.25, 29.71, 29.58, 19.13, 18.17 ppm. Anal. calcd.
C38H44NO4V: C, 72.48; H, 7.04; N, 2.22%. Found: C, 72.33; H,
7.43; N, 2.21%.
2-Hydroxy-3,5-di-tert-butyl-benzaldehyde 2S-(1-tert-butyl-3-
1
phenylpropanol) imine (1k). Yellow solid. H NMR (400 MHz,
=
CDCl3): d 7.69 (s, 1H, CH N), 7.38–6.76 (m, 7H, ArH), 3.56
(d, J = 4.4 Hz, 1H, CHO), 3.51–3.44 (m, 1H, CHN), 3.33 (dd,
J = 2.4, 13.6 Hz, 1H, CHAHBPh), 2.88 (dd, J = 10.0, 13.6 Hz,
1H, CHAHBPh), 1.94 (br, 1H, OH), 1.45 (s, 9H, t-Bu), 1.25 (s,
Ethoxo[2-oxo-benzaldehyde 2S-(3-phenylpropoxo) imine]oxo-
vanadium(V) (3c). Red solid. 1H NMR (400 MHz, CDCl3):
=
major (57%): d 7.55 (s, CH N), 7.54–6.82 (m), 5.28 (q, J =
1
9H, t-Bu), 1.02 (s, 9H, t-Bu) ppm. 13C{ H} NMR (100 MHz,
6.8 Hz, OCH2), 5.17 (dd, J = 4.8, 9.2 Hz, CHAHBO), 4.77 (d,
br, CHAHBO), 4.12 (m, CHN), 3.87 (dd, J = 10.0, 14.0 Hz,
CHAHBPh), 3.33 (dd, J = 4.8, 13.2 Hz, CHAHBPh), 1.55
CDCl3): d 165.10, 158.14, 139.58, 139.04, 136.36, 129.80, 128.14,
126.73, 125.97, 125.79, 117.57, 81.39, 73.70, 38.93, 35.96, 35.64,
102 | Dalton Trans., 2007, 97–106
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=
(t, J = 6.8 Hz, CH3) ppm; minor (43%): d 7.80 (s, CH N),
(m), 3.90–3.82 (m, CHN), 3.73 (br), 1.63 (d, J = 6.4 Hz), 1.59
(t, J = 6.8 Hz, CH3), 1.49 (br), 1.28 (s), 1.16 (s, t-Bu), 0.84 (d,
5.35 (q, J = 6.8 Hz, OCH2), 4.63 (br, CHAHBO), 4.50 (m, 1H,
CHAHBO), 3.05 (dd, J = 6.4, 13.2 Hz, CHAHBPh), 2.87 (dd, J =
1
J = 10.4 Hz) ppm. 13C{ H} NMR (100 MHz, CDCl3): d 164.61,
1
4.8, 13.2 Hz, CHAHBPh), 1.65, (t, J = 6.8 Hz, CH3) ppm. 13C{ H}
163.99, 163.03, 151.38, 151.30, 141.28, 141.05, 121.66, 120.39,
91.77, 85.77, 84.11, 83.84, 79.82, 79.70, 79.66, 79.57, 79.45, 78.48,
77.20, 75.91, 75.71, 36.34, 35.62, 27.27, 27.10, 26.96, 25.52, 25.10,
24.97, 19.08, 18.45, 18.27 ppm. Anal. calcd. C15H20NO4I2V: C,
30.90; H, 3.46; N, 2.40%. Found: C, 30.82; H, 3.59; N, 2.14%.
NMR (100 MHz, CDCl3): d 165.02, 163.77, 163.26, 162.83, 137.30,
136.80, 135.71, 135.54, 132.46, 132.34, 129.88, 129.83, 128.64,
128.58, 126.92, 126.85, 119.99, 119.58, 119.39, 119.21, 118.73,
81.89, 79.16, 78.77, 78.17, 78.09, 77.21, 75.58, 41.59, 40.87, 17.97,
17.65 ppm. Anal. calcd. C18H20NO4V: C, 59.18; H, 5.52; N, 3.83%.
Found: C, 58.95; H, 5.76; N, 4.23%.
Ethoxo[2-oxo-3,5-di-tert-butylbenzaldehyde 2S-(1R,3-diphenyl-
propoxo) imine]oxovanadium(V) (3i). Red solid. 1H NMR
(400 MHz, CDCl3): major (80%): d 7.56–6.64 (m), 6.38 (d, J =
4.4 Hz, CHO), 5.34–5.20 (m, OCH2), 4.18–4.10 (m, CHN), 3.62–
3.50 (m, CHAHBPh), 2.60 (dd, J = 2.8, 13.6 Hz, CHAHBPh), 1.51
(t, J = 6.8 Hz, CH3), 1.49 (s, t-Bu), 1.25 (s, t-Bu) ppm; minor (20%):
d 6.54 (d, J = 4.8 Hz, 1H, CHO), 5.37 (q, J = 7.2 Hz, OCH2),
4.58–4.50 (m, CHN), 3.76–3.58 (m, CHAHBPh), 2.54–2.42 (m,
CHAHBPh), 1.69 (br), 1.63 (t, J = 7.2 Hz, CH3), 1.53 (s, t-Bu)
Ethoxo[2-oxo-benzaldehyde 2S-(2-phenyethoxo) imine]oxovana-
dium(V) (3d). Dark brown solid. H NMR (400 MHz, CDCl3):
major (60%): d 8.28 (s, CH N), 7.54–6.84 (m), 5.48–5.39 (m,
1
=
CHN), 5.39–5.26 (m, OCH2), 5.02–4.88 (m, CH2O), 1.63 (t, J =
=
7.2 Hz, CH3) ppm; minor (40%): d 8.20 (s, CH N), 5.86–5.78 (m,
CHN), 1.59 (t, J = 6.8 Hz, CH3) ppm. 13C{ H} NMR (100 MHz,
1
CDCl3): d 164.57, 164.25, 163.83. 138.43, 138.22, 135.90, 135.77,
132.87, 132.83, 129.26, 129.16, 128.95. 128.76, 128.71, 128.13,
120.14, 119.56, 119.36, 118.81, 82.68, 82.41, 78.58, 77.87, 17.85,
17.78 ppm. Anal. calcd. C17H18NO4V: C, 58.13; H, 5.16; N, 3.99%.
Found: C, 57.85; H, 5.31; N, 4.11%.
1
ppm. 13C{ H} NMR (100 MHz, CDCl3): d 163.53, 163.29, 162.17,
161.05, 141.85, 141.34, 141.05, 140.41, 138.11, 138.07, 137.86,
137.33, 130.55, 130.38, 130.14, 130.06, 128.44, 128.36, 128.32,
127.37, 127.22, 126.68, 126.44, 126.36, 126.06, 125.91, 119.62,
119.16, 90.73, 86.75, 83.90, 78.89, 77.25, 76.93, 36.45, 35.91, 35.27,
35.21, 34.10, 31.27, 31.24, 29.59, 18.33, 18.20 ppm. Anal. calcd.
C32H40NO4V: C, 69.43; H, 7.28; N, 2.53%. Found: C, 69.28; H,
7.28; N, 2.57%.
Ethoxo[2-oxo-benzaldehyde 2S-(2-isobutylethoxo) imine]oxo-
vanadium(V) (3e). Black solid. 1H NMR (600 MHz, CDCl3):
major (53%): d 8.44 (s, CH N), 7.56–7.36 (m, 4H), 7.10–6.90
=
(m), 5.25 (q, J = 6.6 Hz, OCH2), 4.62–4.44 (m), 4.16–4.06 (m,
CHN), 1.80–1.76 (m, CHAHB), 1.64–1.58 (m, CH3), 1.50–1.40
(m), 1.03 (d, J = 10.8 Hz, CH(CH3)2), 0.99 (d, J = 10.8 Hz,
Ethoxo[2-oxo-benzaldehyde 2S-(1R-tert-butyl-3-phenylpropoxo)
1
imine]oxovanadium(V) (3j). Brown solid. H NMR (400 MHz,
=
CH(CH3)2) ppm; minor (47%): d 8.51 (s, CH N), 5.36–5.26 (m,
CDCl3): major (66%): d 7.48–6.72 (m), 5.16–5.00 (m, OCH2), 4.93
(d, J = 4.0 Hz, CHO), 4.18–4.00 (m, CHN), 3.82 (dd, J = 12.4,
12.4 Hz, CHAHBPh), 3.44 (dd, J = 3.2, 13.2 Hz, CHAHBPh), 1.49
(t, J = 7.2 Hz, CH2CH3), 1.19 (s, t-Bu) ppm; minor (34%): d 5.34–
5.20 (m, OCH2, CHO), 4.38–4.30 (m, CHN), 3.76–3.66 (m), 3.28
(dd, J = 3.2, 13.2 Hz, CHAHBPh), 2.63 (dd, J = 13.2, 13.6 Hz),
1.66 (t, J = 7.2 Hz, CH2CH3), 1.22 (s, t-Bu), 1.09 (s), 1.06 (s)
OCH2), 5.08–4.90 (m, OCHAHB), 4.74 (dd, J = 3.6, 8.0 Hz), 2.20–
2.02 (m, CHAHB), 1.56–1.51 (m), 1.36–1.18 (m), 0.97 (d, J = 6.6,
1
Hz, CH(CH3)2), 0.96 (d, J = 6.6 Hz, CH(CH3)2) ppm. 13C{ H}
NMR (100 MHz, CDCl3): d 164.66, 163.60, 162.52. 162.44, 162.21,
135.95, 135.63, 135.47, 132.76, 132.63, 120.26, 119.55, 119.48,
119.39, 118.65, 117.92, 81.54, 78.37, 78.23, 77.67, 74.59, 72.39,
43.99, 43.39, 43.20, 24.73, 24.61, 23.02, 22.76, 22.41, 21.89, 17.86,
17.62 ppm. Anal. calcd. C15H22NO4V: C, 54.38; H, 6.69; N, 4.23%.
Found: C, 54.54; H, 6.40; N, 4.54%.
1
ppm. 13C{ H}NMR (100 MHz, CDCl3): d 165.13, 163.73, 162.00,
161.92, 137.92, 137.14, 135.45, 135.14, 132.28, 132.19, 130.20,
130.03, 128.46, 128.40, 126.69, 126.63, 119.95, 119.39, 119.06,
118.98, 118.60, 118.51, 98.17, 94.79, 83.47, 78.24, 77.92, 76.40,
36.76, 36.33, 35.85, 27.56, 27.13, 17.91, 17.48 ppm. Anal. calcd.
C22H28NO4V: C, 62.70; H, 6.70; N, 3.32%. Found: C, 62.21; H,
6.40; N, 3.11%.
Ethoxo[2-oxo-benzaldehyde 2S-(2-tert-butylethoxo) imine]oxo-
vanadium(V) (3f). Brown solid. H NMR (400 MHz, CDCl3):
major (75%): d 8.53 (s, CH N), 7.58–7.38 (m), 7.12–6.90 (m), 5.27
1
=
(q, J = 6.8 Hz, OCH2), 5.23 (m, 1H, CHAHBO), 4.92–4.82 (m, br,
CHAHBO), 3.99 (d, J = 5.6 Hz, CHN), 1.62 (t, J = 6.8 Hz, CH3),
Ethoxo[2-oxo-3,5-di-tert-butyl-benzaldehyde 2S-(1R-tert-butyl-
3-phenylpropoxo) imine]oxovanadium(V) (3k). Greenish-brown
=
0.93 (s, t-Bu) ppm; minor (25%): d 8.45 (s, 1H, CH N), 5.26–5.18
1
(m. OCH2), 5.14–5.04 (m, CHAHBO), 3.88–3.82 (m, CHN), 1.51
solid. H NMR (400 MHz, CDCl3): too complicated for assign-
(t, J = 6.8 Hz, CH3), 1.18 (s, t-Bu) ppm. 13C{ H} NMR (100 MHz,
ment. 13C{ H} NMR (100 MHz, CDCl3): d 162.69, 162.58, 161.06,
1
1
CDCl3): d 166.21, 165.83, 164.05, 135.99, 135.87, 132.91, 132.71,
120.50, 119.46, 119.36, 118.76, 85.85, 83.89, 78.23, 75.69, 36.19,
35.56, 27.16, 27.00, 17.92, 17.71 ppm. Anal. calcd. C15H22NO4V:
C, 54.38; H, 6.69; N, 4.23%. Found: C, 54.01; H, 6.39; N, 4.28%.
141.59, 140.91, 138.38, 138.09, 137.62, 130.28, 129.93, 128.50,
126.64, 126.47, 126.32, 119.07, 98.12, 94.18, 82.94, 77.75, 75.20,
37.04, 36.74, 36.31, 35.90, 35.26, 35.21, 34.11, 31.31, 31.28, 30.01,
29.78, 29.63, 29.59, 27.66, 27.24, 27.11, 19.10, 18.34, 18.06 ppm.
Anal. calcd. C30H44NO4V: C, 67.52; H, 8.31; N, 2.62%. Found C,
67.56; H, 7.95; N, 2.43%.
Ethoxo[2-oxo-3,5-diiodo-benzaldehyde 2S-(2-tert-butylethoxo)-
imine]oxovanadium(V) (3g). Brown solid. H NMR (400 MHz,
1
=
CDCl3): major (76%): d 8.39 (s, CH N), 8.27 (d, J = 2.4 Hz), 7.70
2-Propoxo[2-oxo-3,5-di-tert-butylbenzaldehyde
2S-(1,1,3-tri-
(d, J = 2.4 Hz), 5.54–5.38 (m, OCH2), 5.31 (dd, J = 6.0, 7.2 Hz,
CHAHBO), 4.87 (br, CHAHBO), 4.02 (d, J = 5.6 Hz, CHN), 1.69
(t, J = 6.8 Hz, CH3), 0.93 (s, t-Bu) ppm; minor (24%): d 8.31 (s,
phenylpropoxo) imine]oxovanadium(V) (4a). Orange solid. 1H
NMR (400 MHz, CDCl3): major (90%): d 7.92–6.66 (m), 5.61
(sept, OCH), 4.87 (dd, J = 2.0, 9.6 Hz, CHN), 3.71 (dd, J = 12.0,
13.4 Hz, CHAHBPh), 2.87 (dd, J = 2.4, 13.6 Hz, CHAHBPh),
1.60 (d, J = 6.4 Hz, CH(CH3)2), 1.57 (d, J = 6.4 Hz, CH(CH3)2)
=
CH N), 8.12–8.02 (m), 7.86–7.78 (m), 7.63 (d, J = 2.0 Hz), 7.46
(d, J = 2.0 Hz), 5.17 (dd, J = 2.8, 10.8 Hz, CHAHBO), 5.12–5.00
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Dalton Trans., 2007, 97–106 | 103
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ppm; minor (10%): d 5.71 (sept, OCH), 5.47 (m), 5.14 (dd, J =
2.8, 8.8 Hz, CHN), 5.06 (dd, J = 2.0, 9.6 Hz), 3.93 (dd, J =
12.4, 13.6 Hz, CHAHBPh), 3.09 (dd, J = 2.0, 9.6 Hz, CHAHBPh),
2.62 (dd, J = 2.4, 13.6 Hz), 2.46 (dd, J = 11.2, 13.6 Hz), 1.72
(d, J = 6.4 Hz, CH(CH3)2), 1.69 (d, J = 6.4 Hz, CH(CH3)2),
24.63, 24.08, 24.01 ppm. Anal. calcd. C23H30NO4V: C, 63.44; H,
6.94; N, 3.22%. Found: C, 63.46; H, 6.58; N, 3.09%.
tert-Butoxo[2-oxo-benzaldehyde
propoxo) imine]oxovanadium(V) (4d). Brown solid. 1H
NMR(400 MHz, CDCl3): major (56%): 7.44–6.70 (m),
2S-(1R-tert-butyl-3-phenyl-
1
1.42 (d, J = 6.0 Hz, CH(CH3)2) ppm. 13C{ H}NMR (100 MHz,
d
CDCl3): d 162.69, 162.58, 161.06, 141.59, 140.91, 138.38, 138.09,
137.62, 130.28, 129.93, 128.50, 126.64, 126.47, 126.32, 119.07,
98.12, 94.18, 82.94, 77.75, 75.20, 37.04, 36.74, 36.31, 35.90,
35.26, 35.21, 34.11, 31.31, 31.28, 30.01, 29.78, 29.63, 29.59, 27.66,
27.24, 27.11, 19.10, 18.34, 18.06 ppm. Anal. calcd. C31H30NO4V:.
C, 70.05; H, 5.69; N, 2.64%. Found: C, 69.95; H, 5.77;
N, 2.73%.
5.26 (m, OCH), 4.78 (d, J = 4.0 Hz, CHO), 4.08–4.00 (m, CHN),
3.82 (dd, J = 13.6, 13.6 Hz, CHAHBPh), 3.43 (dd, J = 2.8,
13.0 Hz, CHAHBPh), 1.59 (s, t-Bu), 1.17 (s, t-Bu) ppm; minor
(44%): d 5.33 (d, J = 4.0 Hz), 5.19 (d, J = 4.0 Hz, CHO), 5.08 (d,
J = 3.6 Hz), 4.34–4.24 (m, CHN), 4.16–4.08 (m), 3.25 (dd, J =
2.8, 13.2 Hz, CHAHBPh), 2.63 (t, J = 13.2, 13.2 Hz, CHAHBPh),
1.69 (s, t-Bu), 1.47 (s), 1.28 (s), 1.20 (s, t-Bu), 1.09 (s), 1.07 (s)
1
ppm. 13C{ H}NMR (100 MHz, CDCl3): d 165.47, 162.00, 161.82,
138.33, 137.55, 135.25, 134.90, 132.25, 132.15, 130.38, 130.21,
128.50, 128.46, 126.69, 126.63, 120.12, 118.96, 118.84, 118.73,
96.81, 94.25, 83.14, 77.94, 36.82, 36.63, 36.04, 31.25, 30.65, 30.22,
26.67, 27.32 ppm. Anal. calcd. C24H32NO4V: C, 64.13; H, 7.18; N,
3.12%. Found C, 64.18; H, 7.36; N, 3.06%.
2-Propoxo[2-oxo-benzaldehyde 2S-(1R-tert-butyl-3-phenylprop-
oxo)
imine]oxovanadium(V)
(4c). Brown
solid.
7.46–6.70 (m),
1H
NMR(400 MHz, CDCl3): major (58%):
d
5.43 (sept, OCH(CH3)2), 4.86 (d, J = 2.8 Hz, CHO), 4.10–4.00
(m, CHN), 3.82 (dd, J = 12.8, 12.8 Hz, CHAHBPh), 3.43 (d,
J = 12.4 Hz, CHAHBPh), 1.47 (d, J = 6.0 Hz, CH(CH3)2), 1.45
(d, J = 6.0 Hz, CH(CH3)2), 1.17 (s, t-Bu) ppm; minor (42%): d
5.56 (sept, OCH(CH3)2), 5.22 (d, J = 3.6 Hz, CHO), 5.33 (br),
5.17 (br), 5.08 (br), 4.97 (br), 4.38–4.26 (m, CHN), 3.27 (d, J =
12.8 Hz, CHBHAPh), 2.62 (dd, J = 12.0, 12.0 Hz, CHAHBPh),
1.64 (d, J = 6.0 Hz, CH(CH3)2), 1.61 (d, J = 6.4 Hz, CH(CH3)2),
1.42 (d, J = 6.0 Hz, CH(CH3)2), 1.37 (s), 1.21 (s, t-Bu), 1.10 (d,
General procedures for asymmetric oxidation of methyl phenyl
sulfide
To a solution of complex 3 (0.010 mmol) in 2.0 mL CH2Cl2,
methyl phenyl sulfide (1.0 mmol, 0.12 mL) was added at room
temperature. 30% H2O2 (1.1 mmol, 0.13 mL) was added over 2 h
using a syringe pump and the resulting mixture was stirred for 16 h.
The reaction was quenched with 2.0 mL H2O and the solution was
extracted with ethyl acetate (3 × 10 mL). The organic phase was
dried with anhydrous MgSO4 and concentrated to give a colorless
oil. The product was separated by column chromatography with an
eluent of EtOAc. Enantioselectivities were determined by HPLC
1
J = 6.0 Hz), 1.07 (s), 1.01 (s) ppm. 13C{ H}NMR (100 MHz,
CDCl3): d 165.34, 163.95, 162.04, 161.87, 138.18, 137.43, 135.64,
135.40, 135.06, 132.29, 132.18, 130.35, 130.17, 129.98, 128.70,
128.66, 128.53, 128.48, 126.90, 126.73, 126.68, 120.09, 119.27,
119.07, 118.94, 118.77, 97.79, 94.58, 84.20, 83.31, 82.96, 78.06,
77.20, 36.84, 36.49, 36.01, 27.66, 27.26, 25.66, 25.55, 25.36, 24.69,
Table 4 Crystal and structure refinement data
3b
3f
3i
4a
Empirical formula
M/g mol−1
C38H44NO4V
629.68
Orthorhombic
P212121
9.8460(8)
11.2520(9)
31.761(3)
90
90
90
3518.8(5)
4
1.189
C15H22NO4V
331.28
Monoclinic
P21
8.2505(7)
11.0013(10)
9.4013(8)
90
109.720(2)
90
803.28(12)
2
C32H40NO4V
553.69
Orthorhombic
P212121
6.3509(4)
19.3947(12)
25.8562(16)
90
90
90
3184.8(3)
4
1.155
C31H30NO4V
531.50
Orthorhombic
P212121
10.9280(8)
12.6932(10)
19.5875(15)
90
90
90
2717.0(4)
4
1.299
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
3
˚
V/A
Z
D
calc/g cm−3
1.370
0.631
l(Mo-Ka)/mm−1
0.320
0.344
0.401
F(000)
1336
19900
6877
348
4478
3054
1176
18010
6243
1112
15500
5334
Reflections collected
Independent reflections
Observed reflections [I > 2r(I)]
5504
0.0354
397
2973
0.0143
190
4547
0.0353
343
3483
0.0373
334
Rint
Parameter refined
R1
0.0556
0.1556
1.059
−0.01(3)
−0.411
0.789
0.0265
0.0733
1.025
0.053(17)
−0.175
0.266
0.0530
0.1367
1.018
−0.01(3)
−0.475
0.819
0.0369
0.0807
0.920
0.07(3)
−0.263
0.163
wR2
S
Absolute structure parameter
−3
˚
˚
Dqmin/e A
Dqmax/e A
−3
104 | Dalton Trans., 2007, 97–106
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using chiral OD column (i-PrOH–hexane = 10 : 90, flow rate =
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0.5 mL min−1) from Diacel.
Crystal structure determinations
A green crystal of 3b of size 0.68 × 0.46 × 0.25 mm, a red crystal
of 3f of size 0.80 × 0.26 × 0.24 mm, a brown crystal of 3i of size
0.60 × 0.44 × 0.32 mm, and a dark red crystal of 4a of size 0.63 ×
0.60 × 0.39 mm in sealed capillaries under nitrogen atmosphere
were used for X-ray diffraction studies. Diffraction intensities were
collected on a Bruker CCD Smart-1000 diffractometer equipped
˚
with graphite-monochromated Mo-Ka radiation (k = 0.71073 A).
All refinements and calculations were carried out with the Bruker
AXS SHELXTL software package on a P4 2.4 GHz computer.
Positions of heavy atoms were determined by direct methods
and remaining non-hydrogen atoms were located from successive
difference Fourier map calculations. Refinements were carried
out using full-matrix least-squares techniques. All non-hydrogen
atoms were refined as individual anisotropic atoms. Hydrogen
atoms were considered as the riding atoms on carbon atoms with
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˚
a C–H bond length of 0.96 A and hydrogen atom temperature
˚
factors were fixed at 0.08 A. Crystal and structure refinement data
are listed in Table 4.
CCDC reference numbers 620539–620542.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b613212j
Acknowledgements
We would like to thank the National Science Council of Republic
of China for financial support (NSC 94-2113-M-005-012).
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