Stereoselective oxidation of linalool with tert-butyl hydroperoxide, catalyzed by a vanadium(V) complex with a chiral terpenoid ligand

Article abstract of DOI:10.1016/S1381-1169(02)00527-7

Stereoselective epoxidation of (-)-(R)-linalool by tert-butylhydroperoxide (TBHP) catalyzed by a V complex formed by interaction of [VO(acac)₂] or [VO(On-Bu)₃] with a new chiral terpenoid ligand was presented. The oxidation of (-)-(R)-linalool with TBHP in the presence of [VO(acac)₂] in toluene led to the formation of two diastereomeric monoepoxides, (2S,3R) and (2R,3R), with a poor diastereomeric excess (de 4%, Run 1). The use of CH₂Cl₂ and CCl₄ instead of toluene resulted in the de decrease, while in the presence of MeCN as a solvent, the reaction did not proceed. The oxidation of racemic linalool revealed that a kinetic resolution of the allylic alcohol takes place: at 70% conversion the yield of the (2R,3S)+( 2S,3S) diastromers was 5-fold higher than the yield of the (2S, 2R) + (2R, 3R) diastereomeric pair. Thus, (+)-(S)-linalool oxidation rate was higher as compared to (-)-(R)-linalool. The ⁵¹V chemical shift of complex 1 in CH₂Cl₂ was affected by the presence of TBHP, indicating fast exchange between at least two forms existing in solution. When the concentration of TBHP increased, the ⁵¹V signal shifted upfield monotonically.

Full text of DOI:10.1016/S1381-1169(02)00527-7

Journal of Molecular Catalysis A: Chemical 194 (2003) 79–88
Stereoselective oxidation of linalool with tert-butyl hydroperoxide,
catalyzed by a vanadium(V) complex with a chiral terpenoid ligand
K.P. Bryliakova,∗, E.P. Talsia, S.N. Stas’koa, O.A. Kholdeevaa,
S.A. Popovb, A.V. Tkachevb,1
Boreskov Institute of Catalysis, Prospekt Akafamika Lavrentieva 5, Novosibirsk 630090, Russia
a
b
Novosibirsk Institute of Organic Chemistry, Pr. Ac. Lavrentieva 9, Novosibirsk 630090, Russia
Accepted 5 September 2002
Abstract
Stereoselective epoxidation of (−)-(R)-linalool by tert-butylhydroperoxide (TBHP) catalyzed by a vanadium(V) complex
formed by interaction of [VO(acac)2] or [VO(On-Bu)3] with a new chiral terpenoid ligand (L) is reported. Moderate diastere-
omeric excess (de 56%) was attained in toluene at 20 ◦C. 51V, 13C and 17O NMR spectroscopic monitoring of the studied
catalytic system showed that a new complex 1 forms quantitatively upon interaction of [VO(On-Bu)3] with L in CH2Cl2. Com-
=
pound 1 is a mononuclear complex of vanadium(V), which incorporates the tridentate chiral ligand L, as well as V O moieties.
It has been shown that TBHP binds to 1 giving a 1·TBHP adduct with the association constant K = 1.36 0.11 l mol−1
at room temperature and enthalpy ∆rH2098 = −6.5 2.0 kJ mol−1 and entropy ∆rS2098 = −20 6 J mol−1 K−1. These
thermodynamic parameters are typical for outer sphere complexes (OSCs). Adduct 1·TBHP is suggested to be a precursor of
the active intermediate of the stereoselective epoxidation process.
© 2002 Elsevier Science B.V. All rights reserved.
Keywords: Stereoselective epoxidation; Linalool; Terpenoid ligand; TBHP; NMR; Intermediates; Outer sphere complex
1. Introduction
tem [2]. Since that time, a variety of transition metal
based catalytic systems for stereoselective epoxida-
tion appeared. A great number of Katsuki–Sharpless
type systems are still dominating over others ([3,4]).
However, the main disadvantage of these systems, a
low turnover number, stimulates the search for new
efficient catalysts.
Vanadium-based epoxidation of allylic alcohols
with TBHP is well-known [5–7]. A number of asym-
metric epoxidations based on the use of vanadium chi-
ral complexes and TBHP have been reported [8–13].
Vanadium(V) alkylperoxo complexes were widely
accepted as intermediates in the [VO(acac)2]/TBHP
[5,14–16] and [VO(acac)2]/ligand/TBHP [12,17,18]
catalytic systems. The X-ray structure of the alkylper-
Efforts to perform stereoselective epoxidation of
olefins commenced in 1965 with the report by Henbest
that a low level of enantiomeric excess (10%) could
be achieved using percamphoric acid [1]. A useful
level of enantioselectivity remained an elusive goal
for 15 years and was reported by Katsuki and Sharp-
less to be achieved for epoxidation of allylic alcohols
using titanium–tartrate complex/TBHP catalytic sys-
∗
Corresponding author. Tel.: +7-3832-341877;
fax: +7-3832-343766.
E-mail addresses: bryliako@catalysis.nsk.su (K.P. Bryliakov),
atkachev@nioch.nsc.ru (A.V. Tkachev).
1
Tel.: +7-3832-344855; fax: +7-3832-344752.
1381-1169/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S1381-1169(02)00527-7

80
K.P. Bryliakov et al. / Journal of Molecular Catalysis A: Chemical 194 (2003) 79–88
oxo complex [VO(OOtert-Bu)(dipic)(H2O)] has been
established [19].
2.1.2. Synthesis of tris alkyl ortho-vanadates
[VO(On-Bu)3] and [VO(Otert-Bu)3]
In this work, we have studied a catalytic system,
generated in situ from [VO(acac)2] or [VO(On-Bu)3],
the new chiral terpenoid ligand L, and TBHP.
(−)-R-linalool was used as a model substrate to es-
timate the synthetic utility of the above system, and
multinuclear NMR techniques were used to penetrate
the reaction mechanism.
The procedure described in [24] was used with
minor modifications: 30–50 mg of powdered V2O5
was placed into a 50 ml flask, and 40 ml of the
respective alcohol (n-BuOH or tert-BuOH) was
added. The mixture was subject to azeotropic dis-
tillation (typically, 6–8 h) until the volume reduced
twice. The residual solid was filtered off, and excess
alcohol was removed in vacuo to give the desired alkyl
ortho-vanadates as yellowish liquids.
2. Experimental
2.1. Materials
(−)-(R)-Linalool [(3R)-3,7-dimetyl-1,6-octadiene-
3-ol], methylene chloride, tert-butyl alcohol, tert-butyl
hydroperoxide (2.6 M solution in toluene), were
purchased from Aldrich and used as received.
[VO(acac)2] was synthesized according to reference
[20]. tert-Butyl hydroperoxide (100%) was synthe-
sised as described in references [21,22].
2.2. General epoxidation procedure
Typically, a mixture containing 0.004–0.1 mmol
of [VO(acac)2], 0.2 mmol of (−)-(R)-linalool,
0.025–0.1 mmol of L and 2 ml of a solvent was cooled
down to −18 ◦C and then 0.3 mmol of TBHP (2.6 M
toluene solution) was added. Then the reaction was
carried out at −18, 0, 20 or 40 ◦C during 8–120 h until
the substantial conversion of linalool was attained.
2.1.1. Synthesis of ligand L
(3bR,4aR)-2-(3,4,4-Trimethyl-3b,4,4a,5-tetrahydr-
ocyclopropa[3,4]cyclopenta[1,2-c]pyrazol-1-yl)-etha-
nol (L) with mp 84–86 ◦C (MeCN) and [α]51768 + 97.8
(c: 1.9, CHCl3) was prepared as described before [23].
2.3. Analysis of oxidation products
Oxidation products were identified by 1H NMR.
Linalool conversion was determined using GC
(glass capillary column 35 mm × 0.3 mm filled
with SE-54, Ar). Linalool monoepoxides were sep-
arated from the reaction mixture by using column
chromatography on a silica gel, and the de values,
|(2S, 3R) − (2R, 3R)|/(2S, 3R) + (2R, 3R), were de-
termined by GC (Hydrodex-␤-PM, 50 m × 0.25 mm
i.d. × 0.25 ␮m film; He, 110 ◦C).
2.4. NMR measurements
1
13C{ H}, 51V and 17O NMR spectra were recorded
on a Bruker MSL-400 spectrometer at 100.614,

K.P. Bryliakov et al. / Journal of Molecular Catalysis A: Chemical 194 (2003) 79–88
81
105.191 and 54.245 MHz, respectively, using 5 mm
or 10 mm cylindrical tubes. For 17O NMR spectra,
high-power probehead was used to increase the sensi-
tivity. Chemical shifts were measured with respect to
residual CH2Cl2 carbons (δ: 55.0 ppm) for 13C, ex-
ternal reference VOCl3 for 51V spectra, and external
reference H2O for 17O spectra, with positive values in
the low-field direction. Typical operation conditions
for 51V measurements were as follows: sweep widths
125,000 Hz, spectrum accumulation frequency 20 Hz,
number of scans 4096, 10 ␮s radio-frequency pulse,
2 K data points. Typical operation conditions for
17O measurements were the following: sweep widths
125,000 Hz, spectrum accumulation frequency 40 Hz,
number of scans 4096, 45◦ pulse at 10 ␮s, 2 K data
points. 1H-decoupled 13C NMR measurements: sweep
widths 30,000 Hz, spectrum accumulation frequency
0.2 Hz, number of scans 1000, 10 ␮s radio-frequency
pulse. 13C NMR data were collected with 32 K points
and zero filled to 64 K.
Samples for NMR measurements were prepared as
follows: an appropriate amount (60–600 ␮mol) of the
vanadium catalyst precursor (either [VO(On-Bu)3] or
[VO(acac)2]) was dissolved in 3 ml of CH2Cl2 in a
10 mm glass NMR tube. Then the ligand, L, was added
as a solid to obtain the desired L/V ratio (1:1 to 6:1).
If necessary, tert-BuOOH, linalool, etc. were added.
Samples were kept at an appropriate temperature in
the probehead, and 51V and 13C spectra were run with
the parameters stated above. To record 17O NMR,
0.003 ml of H217O (4.6% in 17O) was added to the
sample containing the solution of [VO(On-Bu)3] and
L in 2 ml of CH2Cl2.
absence and in the presence of the chiral ligand L
are given in Table 1. We have found that the oxida-
tion of (−)-(R)-linalool with TBHP in the presence
of [VO(acac)2] in toluene resulted in the formation
of two diastereomeric monoepoxides, (2S,3R) and
(2R,3R), with a poor diastereomeric excess (de 4%,
Run 1).
The reaction proceeded slowly at room temperature
(55% conversion in 49 h). At the same time, the addi-
tion of the chiral ligand L considerably enhanced the
reaction rate, while the diastereoselectivity increased
(Table 1). The use of CH2Cl2 and CCl4 instead of
toluene resulted in the de decrease, while in the pres-
ence of MeCN as a solvent, the reaction did not pro-
ceed. The stereoselectivity increased with increasing
concentration of L up to L/[VO(acac)2] molar ratio
equal to 6/1 and then remained constant (Table 1). A
similar optimum ligand/[VO(acac)2] molar ratio (5/1)
has been previously found for the chiral hydroxamic
acid ligands [8]. At a constant L/[VO(acac)2] ratio,
both the reaction rate and stereoselectivity raised with
decreasing vanadium precursor concentration down to
[VO(acac)2] = 0.002 M (compare Runs 5, 12 and 13).
This is a quite unusual phenomenon because ordinar-
ily the lower the chiral catalyst turnover number, the
higher the asymmetric induction level [3]. The rea-
son for this is unclear yet and further investigation is
needed to explain this phenomenon. We may tenta-
tively suppose that low association constants between
the vanadium(V) chiral complex (see later) and the
reactants (TBHP, linalool) might be responsible for
this. The maximal de values were observed at 20 ◦C
in toluene and attained 56% in optimal reaction con-
ditions.
3. Results and discussion
3.1. Stereoselective epoxidation of (−)-R-linalool in
[VO(acac)2]/L/TBHP catalytic system
The oxidation of linalool with TBHP in the pres-
ence of catalytic amounts of [VO(acac)2] was first de-
scribed by Sharpless and Michaelson in 1973 [5]. The
reaction was found to give nearly quantitatively the
previously unknown 1,2-monoepoxide. The epoxide
diastereomeric ratios were not reported in [5].
The results on the [VO(acac)2]-catalyzed oxi-
dation of (−)-(R)-linalool with TBHP both in the
The oxidation of racemic linalool has revealed that
a kinetic resolution of the allylic alcohol takes place:
at 70% conversion the yield of the (2R, 3S)+(2S, 3S)
diastereomers was 5-fold higher than the yield of the
(2S, 3R) + (2R, 3R) diastereomeric pair. Thus, we
may conclude that (+)-(S)-linalool oxidation rate is
higher as compared to (−)-(R)-linalool. All these facts

82
K.P. Bryliakov et al. / Journal of Molecular Catalysis A: Chemical 194 (2003) 79–88
Table 1
Stereoselective epoxidation of (−)-(R)-linalool with TBHP in the presence of the chiral catalyst generated in situ from VO(acac)2 and La
Run
[VO(acac)2] × 103 (M)
[L] × 103 (M)
Solvent
T (◦C)
Time (h)
de (%)b
(−)-(R)-Linalool
conversion (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
2
2
2
2
2
2
2
2
2
2
2
5
20
50
–
12.5
12.5
12.5
12.5
12.5
12.5
12.5
5
18
25
31
125
125
CH3C6H5
CH3CN
CCl4
20
20
20
20
20
40
0
−18
20
20
20
20
20
20
49
120
24
24
24
8
72
120
24
24
4
3
55
4
18
26
56
40
42
39
36
55
56
41
8
90
92
97
97
95
95
96
97
97
95
48
37
CH2Cl2
CH3C6H5
CH3C6H5
CH3C6H5
CH3C6H5
CH3C6H5
CH3C6H5
CH3C6H5
CH3C6H5
CH3C6H5
CH3C6H5
24
51
120
120
3
a Reaction conditions: 0.004–0.1 mmol of [VO(acac)2], 0.2 mmol of (−)-(R)-linalool, 0.025–0.1 mmol of L and 2 ml of a solvent was
cooled down to −18 ◦C and then 0.3 mmol of TBHP (2.6 M toluene solution) was added. Then the reaction was carried out at −18, 0, 20
or 40 ◦C during 8–120 h.
b de = |(2S, 3R) − (2R, 3R)|/(2S, 3R) + (2R, 3R).
collectively show that an asymmetric induction does
arise in the L/[VO(acac)2]/TBHP/linalool system.
3.2. 51V , 13C and 17O NMR spectroscopic
monitoring of vanadium(V) species formed in the
catalytic systems studied
Fig. 1 demonstrates the 51V NMR spectra of
the major vanadium species present in the catalytic
system [VO(acac)2] + L + TBHP. When an ex-
cess of TBHP (5 ␮l, 50 ␮mol) was added to the
sample containing 11.4 ␮mol of [VO(acac)2] and
14.4 ␮mol of L in 600 ␮l CH2Cl2, various vana-
dium(V) signals appeared (Fig. 1a). An earlier study
has shown that vanadium(IV) present completely
oxidized to vanadium(V) upon the interaction of
TBHP with [VO(acac)2] [25]. In the 51V NMR spec-
tra (Fig. 1a and b), two of the peaks observed be-
long to the well-characterized VO(acac)2OOtert-Bu
(δ = −350 ppm) and VO(acac)2Otert-Bu (δ
=
−489 ppm) complexes [25]. VO(acac)2OOtert-Bu
and VO(acac)2Otert-Bu species were shown to form
in toluene and C6D6 as solvents, too. The broad sig-
nal at −517 ppm (ꢀν1/2 = 1.0 kHz) can be assigned
to a new complex 1 incorporating the chiral ligand
L. Its chemical shift is in the field typical for vana-
dium(V) complexes with O,N-donor ligands [26]. The
Fig. 1. 51V NMR spectra of the vanadium(V) complexes formed
in the system studied in CH2Cl2 at 20 ◦C: (a) [VO(acac)2]
=
0.019 M, [L]
=
0.024 M, [tert-BuOOH]
=
0.083 M; (b)
[VO(acac)2] = 0.019 M, [L] = 0.10 M, [tert-BuOOH] = 0.33 M;
(c) [VO(On-Bu)3] = 0.01 M, [L] = 0.025 M. The asterisk is to
mark signals of the residual VO(On-Bu)3 (δ = −591 ppm). For
notation 1 see text.

K.P. Bryliakov et al. / Journal of Molecular Catalysis A: Chemical 194 (2003) 79–88
83
Fig. 3. 51V NMR spectra of the vanadium species formed in 600 ␮l
of CH2Cl2 solution of VO(On-Bu)3 (0.016 M) and L (0.016 M):
complex 1 (a); 10 ␮l of linalool added (b); 30 ␮l of linalool added
(c); additional amount of L added to make [L] = 0.052 M (d).
Fig. 2. 51V NMR spectra of the vanadium species
([VO(On-Bu)3] = 0.18 M) in dry, degassed toluene (a); the
same sample after the addition of L (CL = 0.27 M) and H2O
(CH O = 0.063 M) (b); CH O = 0.10 M (c); CH O = 0.15 M (d);
2
2
2
CH O = 0.18 M (e). When [VO(On-Bu)3] = CH O = 0.18 M, 96%
2
2
high-resolution 13C{ H} NMR spectra of 1. It has
1
of the vanadium present in the form of 1. Special injecting of wa-
ter is only needed when dried solvent and ligand are used and the
samples are handled under argon. When no moisture protection is
practised, complex 1 forms without addition of water.
been found that to convert [VO(OAlk)3] into 1 quanti-
tatively, L/V ratio equal or higher than 1:1 is required
(Figs. 1–3). This means that complex 1 incorporates
one ligand L per vanadium atom. Possible reason why
higher than 1:1 L/V ratio is needed to form 1 when
one starts from [VO(acac)2], is that acetylacetone is
a bidentate ligand and high excess of L is required to
substitute two acetylacetonate ligands.
nature of other signals is unclear yet (Fig. 1a). With
the increase of the concentration of L (48.5 ␮mol,
L/V = 4), complex 1 becomes the predominant
species in the solution (Fig. 1b).
Complex 1 can be obtained quantitatively using
[VO(Otert-Bu)3] or [VO(On-Bu)3] as catalyst pre-
cursors (Fig. 1c). This approach allows to record
13C NMR chemical shifts of complex 1 along with
those of the free ligand L in CH2Cl2 are presented in
Table 2. One can see that chemical shifts of the first,
Table 2
The 13C NMR chemical shifts in ppm for ligand L and vanadium(V) complexes 1 and 1·TBHP in CH2Cl2
Carbon speciesa
1
2
3
4
5
6
7
8
9
10
11
12
L
62.8
73.7
73.6
52.7
52.4
52.3
143.6
148.6
148.0
126.3
127.9
127.5
152.9
155.4
155.1
13.4
14.3
14.4
24.6
25.2
24.9
14.6
14.8
14.7
35.5
35.2
35.0
23.5
23.9
23.7
27.3
27.3
27.4
27.6
27.8
27.6
1b
1·TBHPc
a For carbons numbering in L see Section 2.
b Complex 1 ([1] = 0.010 M) was generated by interaction of VO(On-Bu)3 with L (L/V = 1 : 1) in 3 ml of CH2Cl2.
c Complex 1 ([1] = 0.024 M) was generated by interaction of VO(On-Bu)3 with L (L/V = 1 : 1) in 3 ml of CH2Cl2, and 60 ␮l of TBHP
was added at −5 ◦C [TBHP] = 0.2 M. Spectra were recorded at this temperature. Signals of TBHP were found at 26.5 ppm (C(CH3)3)
and 81.5 ppm (C(CH3)3).

84
K.P. Bryliakov et al. / Journal of Molecular Catalysis A: Chemical 194 (2003) 79–88
third and fifth carbons of L in complex 1 are most of all
perturbed by coordination to vanadium. This tendency
could be interpreted in favor of tridentate coordination
of L so that those carbon atoms that are distant by two
bonds from the metal should be most perturbed by
coordination to vanadium. The similar approach was
previously used to determine the solution structure of
various vanadium(V) complexes [27,28].
by [VO(On-Bu)3] to give 1 upon binding L. Most
probably, formation of 1 follows the equation:
It should be particularly emphasized that there were
no 13C NMR signals other than those of coordinated L
and free n-BuOH observed in L/[VO(On-Bu)3] (1:1)
system. Thus, remaining coordination sites of 1 can be
occupied by some inorganic ligands or n-BuOH (on
assumption of fast exchange between coordinated and
free n-BuOH).
Possible structure of complex 1 is shown below:
The 17O NMR spectrum of 1 exhibits a single
peak at 1175 ppm (ꢀν1/2 = 800 Hz). It is charac-
teristic of O2− and OH− groups in six-coordinated
vanadium(V) complex [29–32]. According to the lit-
erature, 17O NMR peaks of O2− and OH− groups are
not observed separately because of rapid proton ex-
change between oxygen atoms [31]. The typical range
of chemical shifts for V–O–V bridging oxygen atoms
is 500–600 ppm [31]. There were no peaks observed
in this region, so dinuclear structure of 1 seems im-
probable. Thus, based on 17O NMR data, 1 may be a
mononuclear vanadium(V) complex with one triden-
The facts that there is a single 17O resonance for ter-
minal oxygens of 1 as well as a single 13C resonance
for n-BuOH can be explained by fast exchange pro-
cesses: (1) proton transfer between V–O moieties and
(2) exchange of the axial (n-BuOH) ligand (Scheme 1).
After the addition of linalool to the sample contain-
ing 1, a set of new sharp resonances appears in the
range of −570 to −690 ppm in the 51V spectrum at the
expense of the intensity of the resonance at −517 ppm
(Fig. 3a–c). Probably, these sharp peaks belong to
vanadium species of the type VO(OR)n(OR1)3−n
,
=
tate chiral ligand L and V O and V–OH moieties.
where n = 1–3, R: On-Bu, HOR1: linalool. By adding
extra amount of L, the formation of vanadium species
with sharp resonances can be suppressed, and the
original concentration of 1 can be restored (Fig. 3d).
Thus, we may conclude that when added in high
excess, linalool can reversibly replace L in the first
It was found that to form 1 starting from the ligand
L and [VO(OAlk)3], some water is needed (Fig. 2).
Experiments carried out in dry solvents (CH2Cl2,
toluene) with addition of appropriate amounts of wa-
ter showed that 1 equivalent of water was consumed
Scheme 1. The structures proposed for vanadium(V) complexes existing in solution. The facts that there is a single 17O resonance for
terminal oxygens of 1 and a single 13C resonance for n-BuOH can be explained by fast exchange processes: (1) proton transfer between
=
V–OH and V O moieties and (2) exchange of the axial ligand (n-BuOH).

K.P. Bryliakov et al. / Journal of Molecular Catalysis A: Chemical 194 (2003) 79–88
85
coordination sphere of vanadium. Note that binding
of allylic alcohols to vanadium is well precedented
and is believed to be responsible for high regioselec-
tivity in the vanadium-catalyzed oxidation of these
compounds with alkylhydroperoxides [5,25]. Based
on these data, simultaneous coordination of allylic al-
cohol and ligand L to vanadium is expected to provide
the observed stereoselectivity. One can expect that
linalool could substitute n-BuOH as the axial ligand.
However, we obtained no direct spectral evidences in
favor of the formation of such complexes yet.
3.3. 51V and 13C NMR study of the interaction
of 1 with TBHP
The 51V chemical shift of 1 in CH2Cl2 was found
to be affected by the presence of TBHP, indicating
fast exchange between at least two forms existing in
solution. Actually, when the concentration of TBHP
increased, the 51V signal shifted upfield monotoni-
cally (Fig. 4). This effect was not observed when equal
amounts of tert-BuOH instead of TBHP were added.
On the contrary, the addition of tert-BuOH caused
changes in the 51V spectrum analogous to those ob-
served in 1/linalool system: L was ejected from the
first vanadium coordination sphere, concentration of 1
decreased, and the signal assigned to [VO(Otert-Bu)3]
species (δ = −670 pm) grew up at the expense of that
of 1. The identity of [VO(Otert-Bu)3] was confirmed
by synthesizing it independently [20]. As we men-
tioned already, the ejection of L from the vanadium
coordination sphere is reversible, and the formation of
[VO(Otert-Bu)3] can be suppressed by adding extra
amounts of L.
Fig. 4. 51V NMR spectra of the vanadium species formed in 600 ␮l
of CH2Cl2 solution of VO(On-Bu)3 (0.01 M) and L (0.02 M) at
258 K (a); 10 ␮l of TBHP added (b); 20 ␮l of TBHP added (c);
30 ␮l of TBHP added (d). Plot of 1/(δa − δobs) vs. 1/[TBHP],
where δobs is the 51V chemical shift of the [1·TBHP] OSC in
CH2Cl2 solution, at different temperatures: at 233 K (᭿), at 291 K
(᭢). Solid lines represent least-square fit to the data (e).
According to the 13C NMR spectra, TBHP con-
centration in the sample containing 1 and TBHP was
constant at −5 ◦C in the absence of organic substrates.
Addition of allylic alcohol (linalool) to the solution
of 1 and TBHP resulted in a rapid conversion of the
former into the corresponding monoepoxides and de-
crease of TBHP concentration, while concentration
of tert-BuOH increased. At [1] = [L] = 0.024 M,
[TBHP] = 0.4 M and [linalool] = 0.2 M, complete
alkene transformation occurred within 10–15 min.
When linalool (0.05 M) was added into the sample
containing 1·TBHP (0.010 M solution in CH2Cl2)
generated from [VO(On-Bu)3], L and H2O (1:1) and
0.27 M of TBHP, the corresponding monoepoxide
formed with de 28%. This demonstrates the reactiv-
ity of the observed vanadium(V) species, 1·TBHP,
It was found that the 13C NMR spectrum of 1 was
virtually unaffected by TBHP coordination (Table 2).
No 13C NMR signals of tert-BuOO− groups coor-
dinated to vanadium were observed in the temper-
ature range of −90 to 0 ◦C. This might indicate a
very short lifetime of 1·TBHP complex even at low
temperature or (/and) a small coordination induced
shift. Thus, in contrast to [VO(acac)2] + TBHP and
[VO(On-Bu)3] + TBHP catalytic systems and the
[VO(OOtert-Bu)(dipic)(H2O)] complex where the
formation of alkylperoxo complexes with VOOtert-Bu
moieties is well documented [19,25,29], unexpectedly
weak complex and labile 1·TBHP was observed in
the 1 + TBHP system.

86
K.P. Bryliakov et al. / Journal of Molecular Catalysis A: Chemical 194 (2003) 79–88
Table 3
towards allylic alcohols and its ability to induce
diastereoselectivity.
The association constant K values for the 1·TBHP OSC at differing
temperatures in CH2Cl2
Complex
T (K)
K (mol−1
)
3.4. The stability constant for 1·TBHP and its
temperature dependence: 51V NMR spectroscopic
measurement
1·TBHP
203
233
258
291
313
2.35
2.00
1.75
1.36
1.04
0.50a
0.10
0.05
0.11
0.10
To explain (1) the short lifetime of the 1·TBHP com-
plex so that the condition of fast (on NMR timescale)
exchange between 1 and 1·TBHP is always fulfilled,
(2) the absence of the 13C NMR signals of tert-BuOO−
groups coordinated to vanadium and (3) the fact that
the addition of tert-BuOH results in the formation
of [VO(Otert-Bu)3] rather than 1·tert-BuOH, we sup-
posed that formation of the 1·TBHP outer sphere com-
plex (OSC) is the case. Monotonic dependence of the
1·TBHP 51V chemical shift on the TBHP concentra-
tion is in favor of the formation of a 1:1 OSC [33,34].
This dependence can be used to estimate the associa-
a At 203 K, accuracy of the measurement of 51V chemical
shifts is low because of high linewidth of 1·TBHP resonance.
where ∆ = δb − δa. Taking into account that
[TBHP] ꢀ [1], we can apply [TBHP] ≈ [TBHP]0.
So, our equation for δobs should be linear in the
following form:
1
1
1
1
=
+
K∆ [TBHP]0
(6)
δobs − δa
∆
tion constant for 1·TBHP formation. The observed 51
V
Fig. 4e represents the dependence of 1/(δa − δobs
)
chemical shift of 1·TBHP involved in a two-position
rapid exchange between 1 and 1·TBHP can be ex-
pressed by
versus 1/[TBHP] which appeared to be linear. This lin-
earity is in favor of our hypothesis that TBHP interac-
tion with 1 leads to the formation of the 1:1 complex.
Measurements of K at different temperatures gave the
values collected in Table 3. All of them fall in the
interval 0.1–10 mol−1 that is typical for outer sphere
complexes formation processes [34].
δobs = (1 − p)δa + pδb
(1)
where δa is the 51V NMR shift of 1 in the absence of
TBHP, δb the 51V NMR shift of the individual complex
1·TBHP that could be observed if concentration of
TBHP, [TBHP], tended to infinity, p the probability
of 1 being in the coordinated state [33]. In our case,
1·TBHP forms via reaction:
One can obtain ꢀrH0 for 1·TBHP formation using
van’t Hoff’s equation [35]:
d lnK
dT
∆rH0
RT 2
=
(7)
K
1 + TBHPꢀ1 · TBHP
(2)
Assuming that the enthalpy temperature dependence
is
where K is the stability constant for 1·TBHP. The prob-
∆rHT0 = ∆rH2098 + ∆rCp0(T − 298)
(8)
ability p can be obtained as
[1 · TBHP]
p =
(3)
(i.e. ∆rCp is regarded as temperature-independent, cf.
[35]), substitution of (8) in (7) and subsequent inte-
gration gives
[1 · TBHP][1]
Applying the relationship [1]·K = [1·TBHP]/[TBHP]
one obtains p as
A
ln K = − + B lnT + C
(9)
1
T
p =
(4)
1 + 1/K[TBHP]
Substituting expression (4) for p in Eq. (1), we obtain
δobs
where A = (∆rH0 − 298∆rCp0)/R, B = ∆rCp0/R,
C is an integratio2n98constant. In Fig. 5, experimental
points ln K versus 1/T together with their theoretical
simulation according to (9) are presented. ∆rH2098 ob-
tained is −6.5 2.0 kJ mol−1 and ∆rS2098 is estimated
:
∆
δobs = δa +
(5)
1 + 1/K[TBHP]

K.P. Bryliakov et al. / Journal of Molecular Catalysis A: Chemical 194 (2003) 79–88
87
sociation constant K = 1.36 0.11 l mol−1 at room
temperature, enthalpy ∆rH2098 = −6.5 2.0 kJ mol−1
and entropy ∆rS2098 = −20 6 J mol−1 K−1. The
outer sphere complex 1·TBHP is reactive towards
linalool and is believed to be a precursor of the true
reactive intermediate in the vanadium catalyzed di-
astereoselective epoxidation of allylic alcohols. The
true intermediate is expected to be formed upon
interaction of 1·TBHP with the substrate.
Acknowledgements
This work was supported in part by Russian Foun-
dation for Basic Research, grant 00-03-32438.
Fig. 5. Plot of ln K vs. 1/T (᭿). Solid line represents the
least-square fit to the data according to Eq. (9).
References
as −20 6 J mol−1 K−1 that is close to the values typ-
ically observed for binding one outer sphere ligand
[1] H.B. Henbest, Chem. Soc. Spec. Publ. 19 (1965) 83.
[2] T. Katsuki, K.B. Sharpless, J. Am. Chem. Soc. 102 (1980)
5974.
[3] R.A. Johnson, K.B. Sharpless, Catalytic asymmetric
epoxidation of allylic alcohols, in: Ojima (Ed.), Catalytic
Asymmetric Synthesis, 2nd ed., VCH Publishers, New York,
2000, pp. 231–280.
[4] T. Katsuki, V.S. Martin, Org. React. 48 (1996) 1.
[5] K.B. Sharpless, R.C. Michaelson, J. Am. Chem. Soc. 95
(1973) 6136.
[6] A. Butler, M.J. Clague, G.E. Meister, Chem. Rev. 94 (1994)
625.
(−8 to −20 kJ mol−1 and −20 to −60 J mol−1 K−1
,
respectively) [33,34].
Thus, the association constants and the thermo-
dynamic parameters for the formation of complex
1·TBHP are close to those accepted for outer sphere
complexes that confirms our hypothesis. 1·TBHP
OSC is the last observable intermediate in 1 + TBHP
catalytic system and is probably the precursor of the
actual reactive intermediate in the vanadium catalyzed
diastereoselective epoxidation of allylic alcohols in
the presence of L.
[7] V. Conte, F. Di Furia, G. Licini, Appl. Catal. A: Gen. 157
(1997) 335.
[8] R.C. Michaelson, R.E. Palermo, K.B. Sharpless, J. Am. Chem.
Soc. 99 (1977) 1990.
[9] H. Glas, E. Herdtweck, G.R.J. Artus, W.R. Thiel, Inorg.
Chem. 37 (1998) 3644.
[10] N. Murase, Y. Hoshino, M. Oishi, H. Yamamoto, J. Org.
Chem. 64 (1999) 338.
[11] C. Bolm, T. Kuhn, Synletters (2000) 899.
[12] Y. Hoshino, H. Yamamoto, J. Am. Chem. Soc. 122 (2000)
10452.
[13] T. Katsuki, Epoxidation of Allylic Alcohols, in: E.N.
Jacobsen, A. Pfaltz, H. Yamamoto (Eds.), Comprehensive
Asymmetric Catalysis, Parts I–III, vol. 2, Springer, Berlin,
1999, p. 621.
[14] K.B. Sharpless, T.R. Verhoeven, Aldrichim. Acta 12 (1979)
63.
[15] R. Curci, F. Di Furia, R. Testi, G. Modena, J. Chem. Soc.
Perkin Trans. 2 (1974) 752.
[16] E.S. Gould, R.R. Hiatt, K.C. Irwin, J. Am. Chem. Soc. 90
(1968) 4573.
[17] H. Mimoun, M. Mignard, P. Brechot, L. Saussine, J. Am.
Chem. Soc. 108 (1986) 3711.
4. Conclusions
The oxidation of (−)-(R)-linalool by TBHP in the
presence of the vanadium(V) complex formed by inter-
action of [VO(acac)2] or [VO(On-Bu)3] with the new
chiral pyrazolylethanol ligand L, affords (2S,3R) and
(2R,3R) monoepoxides with moderate diastereomeric
excess. 51V and 13C{ H} spectra provided insight into
1
solution structure, stability and reactivity of the vana-
dium(V) species that operates in the catalytic system
studied. It has been shown that the mononuclear
vanadium(V) complex 1 is the predominant species
in the reaction mixture. It incorporates the tridentate
terpenoid ligand L and O2− moieties. TBHP binds to
1 to give an outer sphere complex 1·TBHP with as-

88
K.P. Bryliakov et al. / Journal of Molecular Catalysis A: Chemical 194 (2003) 79–88
[18] H. Mimoun, Catal. Today 1 (1987) 281.
[19] H. Mimoun, P. Chaumette, M. Mignard, L. Saussine, J.
Fischer, R. Weiss, Nouv. J. Chim. 7 (1983) 467.
[20] T. Moeller (Ed.), Inorganic Synthesis, New York, 1957, vol.
5, p. 114.
[27] D. Crans, P. Shin, J. Am. Chem. Soc. 116 (1994) 1305.
[28] K.P. Bryliakov, N.N. Karpyshev, S.A. Fominsky, A.G.
Tolstikov, E.P. Talsi, J. Mol. Catal. A: Chem. 171 (2001) 73.
[29] D.E. Babushkin, E.P. Talsi, React. Kinet. Catal. Lett. 71
(2000) 115.
[21] N.A. Milas, D.M. Surgenor, J. Am. Chem. Soc. 68 (1946)
205.
[30] M. Postel, C. Brevard, H. Arzoumanian, J.G. Riess, J. Am.
Chem. Soc. 105 (1983) 4922.
[22] P.D. Bartlett, J.M. McBride, J. Am. Chem. Soc. 87 (1965)
1727.
[31] A.T. Harrison, O.W. Howarth, J. Chem. Soc. Dalton Trans.
(1985) 1173.
[23] S.A. Popov, M.M. Shakirov, A.V. Tkachev, N. De Kimpe,
Tetrahedron 53 (1997) 17735.
[24] N.F. Orlov, M.G. Voronkov, Izv. Acad. Nauk SSSR, Ser.
Khim. (1959) 933.
[25] E.P. Talsi, V.D. Chinakov, V.P. Babenko, K.I. Zamaraev, J.
Mol. Catal. 81 (1993) 235.
[26] O.W. Howarth, Progr. Nucl. Magn. Res. Spectrosc. 22 (1991)
453.
[32] W.J. Ray Jr., D.C. Crans, J. Zheng, J.W. Burgner II, H. Deng,
M. Mahroof-Tahir, J. Am. Chem. Soc. 117 (1995) 6015.
[33] K. Zamaraev, New J. Chem. 18 (1994) 3.
[34] V.M. Nekipelov, K.I. Zamaraev, Coord. Chem. Rev. 61 (1985)
185.
[35] K. Denbigh, The Principles of Chemical Equilibrium,
Cambridge University Press, Cambridge, 1971, pp. 144–145.