Chiral bis(oxazoline) and pyridyl alcoholate dioxo-molybdenum(VI) complexes: Synthesis, characterization and catalytic examinations

Article abstract of DOI:10.1016/S0022-328X(00)00774-9

A group of chiral molybdenum(VI) complexes comprising MoO₂Cl₂L^**, MoO₂Cl(THF)L^* and MoO₂L^*₂ [L^** = chiral bis(oxazoline) and L^* = chiral 2′-pyridyl alcoholate] have been prepared in good yields by reaction of the solvent substituted complex MoO₂Cl₂(THF)₂ with one or two equivalents of chiral ligand. Optically active aminoalcohols (L^*) were obtained by reaction of the appropriate organolithium compound with (-)-menthone, (+)-8-phenylisomenthone, (-)-8-phenylmenthone, (+)-camphor and (-)-thujone. The molybdenum complexes were characterized by multinuclear NMR (¹H, ¹³C, ¹⁷O, ⁹⁵Mo) spectroscopy, IR spectroscopy and elemental analysis. ⁹⁵Mo-NMR data reflected the donor capability of the organic ligands, whereas ¹H-NMR and IR data were comparatively indifferent to the changes in the Lewis base ligand. The complexes were evaluated as catalysts for the asymmetric epoxidation of trans-β-methylstyrene by tert-butylhydroperoxide. The bis(oxazoline) complexes showed good catalytic activity but had low optical yields. Complexes of the type MoO₂Cl(THF)L^* (L^* = chiral 2′-pyridyl alcoholate) also exhibited high catalytic activity and enantiomeric excesses of up to 23%. The corresponding MoO₂L^*₂ alcoholate complexes were considerably less active with comparable optical yields.

Full text of DOI:10.1016/S0022-328X(00)00774-9

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Journal of Organometallic Chemistry 621 (2001) 207–217
Chiral bis(oxazoline) and pyridyl alcoholate
dioxo-molybdenum(VI) complexes: synthesis, characterization and
catalytic examinations
Fritz E. Ku¨hn a,*1, Ana M. Santos a, Andre´ D. Lopes b, Isabel S. Gonc¸alves b,c,
Jose´ E. Rodr´ıguez-Borges b,d, Martyn Pillinger c, Carlos C. Roma˜o b,*2
a Anorganisch-chemisches Institut der Technischen Uni6ersita¨t Mu¨nchen, Lichtenbergstraße 4, D-85747 Garching bei Mu¨nchen, Germany
b Instituto de Tecnologia Qu´ımica e Biolo´gica da Uni6ersidade No6a de Lisboa, Quinta do Marqueˆs, EAN, Apt 127, 2781-901 Oeiras, Portugal
c Departamento de Qu´ımica, Uni6ersidade de A6eiro, Campus de Santiago, 3810-193 A6eiro, Portugal
d Departamento de Qu´ımica Orga´nica, Facultade de Farmacia, Uni6ersidade de Santiago de Compostela, E-15706 Santiago de Compostela, Spain
Received 15 June 2000; received in revised form 28 July 2000
Dedicated to Professor Dr Henri Brunner on the occasion of his 65th birthday
Abstract
A group of chiral molybdenum(VI) complexes comprising MoO2Cl2L**, MoO2Cl(THF)L* and MoO2L*2 [L**=chiral
bis(oxazoline) and L*=chiral 2%-pyridyl alcoholate] have been prepared in good yields by reaction of the solvent substituted
complex MoO2Cl2(THF)2 with one or two equivalents of chiral ligand. Optically active aminoalcohols (L*) were obtained by
reaction of the appropriate organolithium compound with (−)-menthone, (+)-8-phenylisomenthone, (−)-8-phenylmenthone,
(+)-camphor and (−)-thujone. The molybdenum complexes were characterized by multinuclear NMR (1H, 13C, 17O, 95Mo)
spectroscopy, IR spectroscopy and elemental analysis. 95Mo-NMR data reflected the donor capability of the organic ligands,
whereas 1H-NMR and IR data were comparatively indifferent to the changes in the Lewis base ligand. The complexes were
evaluated as catalysts for the asymmetric epoxidation of trans-b-methylstyrene by tert-butylhydroperoxide. The bis(oxazoline)
complexes showed good catalytic activity but had low optical yields. Complexes of the type MoO2Cl(THF)L* (L*=chiral
2%-pyridyl alcoholate) also exhibited high catalytic activity and enantiomeric excesses of up to 23%. The corresponding MoO2L2*
alcoholate complexes were considerably less active with comparable optical yields. © 2001 Elsevier Science B.V. All rights
reserved.
Keywords: Chiral ligands; Epoxidation; Molybdenum; Oxazoline; Oxide complexes; 2%-Pyridyl alcoholate
methylprolinols [2b] or diisopropyl tartrates [2d]. One
of the difficulties in this area is the development of
suitable chiral ligands that are stable to oxidation and
straightforward to synthesize, with the possibility of
changing electronic and steric characteristics by simple
variation of the starting material. One class of ligands
that meets these pre-requisites are 2%-pyridyl alcohols,
which are readily accessible by the reaction of 2-
lithiopyridine with either symmetrical or unsymmetrical
ketones [3], yielding chiral or achiral molecules, respec-
tively. Herrmann and coworkers prepared complexes of
the type MO2L2 (M=Mo, W, L=achiral 2%-pyridyl
alcoholate) and tested them as catalysts for the selective
oxidation of olefins with molecular oxygen or TBHP
1. Introduction
Currently, there is considerable interest in the synthe-
sis of chiral oxometallate complexes and their use as
catalysts for asymmetric olefin epoxidation [1]. In the
field of oxomolybdenum chemistry, several approaches
have been reported [2]. The catalytically active species is
normally prepared in situ from MoO2(acac)2, tert-
butylhydroperoxide (TBHP) and an excess of chiral
N/O or O/O-ligands, e.g. N-alkyl ephedrines [2a], N-
1 *Corresponding author. Tel.: +49-89-28913080; fax: +49-89-
28913473; e-mail: fritz.kuehn@ch.tum.de
2 *Corresponding author.
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00774-9

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F.E. Ku¨hn et al. / Journal of Organometallic Chemistry 621 (2001) 207–217
[4]. In a recent development of this work, chiral 2%-
pyridyl alcohols were prepared and the resulting chiral
dioxomolybdenum complexes exhibited good catalytic
activity and substantial optical induction [5].
2.2. Synthesis of chiral dioxomolybdenum(VI)
compounds 1a–13a
As a consequence of our interest in asymmetric chiral
molybdenum complexes, we have been evaluating the
potential utility of chiral 4,4%-disubstituted bis(oxazo-
lines) such as 1–3 as bidentate ligands. These organic
ligands with donor functionalities, such as nitrogen,
react readily with complexes of the type
MoO2Cl2(THF)2 [9] to form the octahedrally coordi-
nated complexes MoO2Cl2L** [L**=bis(oxazoline)]
1a–3a at room temperature in good isolated yields
(Scheme 2). The product complexes are soluble in
dichloromethane and precipitate from the reaction mix-
ture upon addition of diethyl ether. They are stable at
room temperature but decompose rapidly in the pres-
ence of air.
By reacting one equivalent of the chiral 2%-pyridyl
alcohol ligands 4–9 with MoO2Cl2(THF)2 in a similar
fashion, a variety of other chiral complexes of the type
MoO2Cl(THF)L* (L*=chiral 2%-pyridyl alcoholate)
are accessible in nearly quantitative yields according to
Scheme 3.
Another class of chiral chelating ligands that seems
to meet the requirements outlined above are the C2-
symmetric bis(oxazolines). They are easily prepared
from readily available amino alcohols [6]. The most
extensively studied ligand of this series is that where the
two oxazolines are separated by a methylene bridge and
thereby form a six-membered chelate with the metal.
Bis(oxazoline) metal complexes have emerged as effi-
cient enantioselective catalysts for a variety of organic
transformations, including carbon–carbon bond form-
ing reactions, aziridinations, cyclopropanations, hy-
drosilylation, Diels–Alder and hetero Diels–Alder
reactions [7]. To our knowledge, the synthesis and
catalytic potential of dioxomolybdenum–bis(oxazoline)
complexes has not been reported. We recently reported
the synthesis of cis-MoO22+ complexes of the type
MoO2X2Ln (X=Cl, Br, CH3) with mono- and bi-den-
tate nitrogen and oxygen ligands [8a–d]. The activity of
the dissolved complexes as catalysts in olefin epoxida-
tion with TBHP was also tested. We have extended this
synthetic methodology to include chiral ligands L and
now wish to report on the preparation and characteri-
zation of a series of complexes with chiral 2%-pyridyl
alcoholates and methylenebis(oxazolines). Their cata-
lytic potential has been evaluated in the asymmetric
epoxidation of trans-b-methylstyrene using TBHP as
oxidant.
The complexes belonging to this family (4a–9a) are
more soluble in organic solvents than compounds 1a–
3a, or other similar complexes of the type MoO2Cl2L
[8], and do not precipitate from the reaction mixtures
(they are significantly soluble in diethyl ether). They
can be purified by washing with n-hexane. Dissolution
and recrystallizaton of the product complexes 4a–9a of
the composition MoO2Cl(THF)L* from NCCH3 gave
the NCCH3 adducts of the type MoO2Cl(NCCH3)L*.
Likewise, if the complexes were dissolved in
dichloromethane and pyridine added, the pyridine-sub-
stituted compounds, MoO2Cl(pyridine)L*, were ob-
tained. The composition has been confirmed by
2. Results and discussion
1
2.1. Chiral ligand synthesis
elemental analysis and H-NMR spectroscopy.
Dioxomolybdenum(VI) 2%-pyridyl alcoholate com-
plexes, MoO2L2* 10a–13a, were prepared by two differ-
ent methods, both starting from MoO2Cl2(THF)2. The
first, method (a) Section 4.5, involved the addition of
two equivalents of ligand and subsequent reflux to force
the reaction to completion. The driving force for this
reaction is the formation and liberation of HCl (Scheme
4). The second, method (b) Section 4.5, involved the
addition of two equivalents of ligand and two equiva-
lents of TlOEt. The corresponding molybdenum com-
plexes were obtained in high yields.
The complexes 10a–13a do not decompose readily in
laboratory atmosphere, and all of them can be handled
in air for brief periods of time. This is a remarkable
difference to 1a–9a, all of which are air and moisture
sensitive and can only be handled and stored under
moisture-free inert gas atmosphere. Another notewor-
thy aspect is the difference in solubility. Complexes
10a–13a are significantly less soluble than either
The chiral bis 1,3-oxazolinyl-propanes 1–3 were pre-
pared according to a literature procedure (see Section
4). The 2%-pyridyl alcohol ligands 4–9 are accessible by
reaction of 2-pyridyl-lithium with appropriate prochiral
ketone precursors (Scheme 1). As expected, ligands 4–7
were obtained as single diastereoisomers (diastereospe-
cific) [1b,3a]. In the case of (−)-menthone, (+)-8-
phenylisomenthone,
(−)-8-phenylmenthone,
and
(+)-camphor, the carbonyl group is only accessible
from one stereo side. However, lithiopyridine can at-
tack the carbonyl group of (−)-thujone on either the a
or b face, resulting in the synthesis of two diastereoiso-
mers, 8 and 9, in a ratio of 73:27 (by NMR), which
were separated by chromatography. The two forms of
the (−)-thujone-derivatives (8 and 9), as well as the
other desired ligands 4–7, were fully characterized, and
the absolute stereochemistry of the ligands was con-
firmed (see Section 4.2).

F.E. Ku¨hn et al. / Journal of Organometallic Chemistry 621 (2001) 207–217
209
MoO2Cl2L**,
[L**=bis(oxazoline)]
1a–3a,
or
2.3. NMR spectroscopy
MoO2Cl(Solv)L* (L*=chiral 2%-pyridyl alcoholate).
However, all of the complexes are sufficiently soluble in
polar organic solvents to obtain solution (1H/13C/95Mo)
NMR spectra of good quality (see below). The com-
plexes 1a–13a display their MoꢀO stretching vibrations
in the expected IR range [8a–d]. The symmetric and
asymmetric vibrations are observed at ca. 9409
20 cm−1 and ca. 910910 cm−1, respectively.
The 1H-NMR spectra of the molybdenum(VI) bis(ox-
azoline) complexes 1a–3a do not differ substantially
from those of the respective free bis(oxazoline) ligands.
In contrast, the molybdenum(VI) 2%-pyridyl alcoholate
complexes 4a–9a show broader signals compared with
the free ligands, and the sets change their appearance
significantly upon heating or cooling the solution. This
Scheme 1.

210
F.E. Ku¨hn et al. / Journal of Organometallic Chemistry 621 (2001) 207–217
Scheme 2.
is comparable to the Lewis-base adducts of RRe(VII)O3
complexes, which have also been applied successfully as
oxidation catalysts [8c,10]. These complexes usually
undergo rapid temperature-dependent ligand-exchange
processes [10a,b]. This is of special importance in the
case of chiral ligands, since these Re(VII) systems do
not show significant enantioselectivity if applied in
Scheme 4.
Table 1
95Mo-NMR data of the complexes (CD2Cl2, room temperature)
Compound
l(95Mo) (ppm)
Dw1/2 (Hz)
1a
2a
139.9
138.8
137.4
308.5
289.0
287.2
277.0
283.7
278.0
230.7
239.5
233.3
51.0
60
60
40
1
asymmetric epoxidation processes [10]. The H-NMR
3a
spectra of complexes 10a–13a with two 2%-pyridyl alco-
holate ligands do not show noteworthy thermal changes
and are not significantly different from the spectra of
the free ligands.
4aa
190
300
200
300
200
290
670
600
620
110
250
120
120
120
120
4a
5aa
5a
In complexes 4a–13a the 13C-NMR signals for the
quaternary alcoholate carbon atom (C2%) and also C1
(Scheme 1) are shifted downfield, which indicates coor-
dination of the ligand to the metal center. However, for
the complexes MoO2L2*, 10a–13a, the downfield shifts
for C1 are considerably more pronounced than the
complexes of the type MoO2Cl(THF)L*, 4a–9a, e.g.
l(13C)=77.17 ppm for 4, 79.38 ppm for 4a and
92.82 ppm for 10a. This indicates a more significant
shift of electron density towards the molybdenum cen-
ter in the MoO2L2* family than in the MoO2Cl(THF)L*
family.
6aa
6a
7a
8a
9a
10aa
10a
11a
12a
13a
41.1
53.4
48.3
49.8
MoO2Cl2(DMF)2 (14)
171.5
a Recorded in NCCH3.
95Mo-NMR spectra for all the complexes were avail-
able in good quality. The bis(oxazoline) complexes
1a–3a provide very well defined signals around
l(95Mo):138 ppm, the 2%-pyridyl alcoholate com-
plexes 4a–9a display their 95Mo signal between ca. 310
and 230 ppm, and the 2%-pyridyl alcoholate complexes
10a–13a give their 95Mo signals around 50 ppm (Table
1). These observed chemical shift values are in good
agreement with both the literature values of related
complexes [8] and that expected based on the donor
capabilities of the L and X ligands involved.
Solvent effects were not observed for the
MoO2Cl2L** complexes 1a–3a [L**=bis(oxazoline)]
and the MoO2L*2 complexes 10a–13a (L*=2%-pyridyl
alcoholate). However, NMR analysis of the
MoO2Cl(THF)L* complexes 4a–9a (L*=2%-pyridyl al-
coholate) in two different solvents (CD2Cl2 and
NCCD3) gave, not unexpectedly, slightly different re-
Scheme 3.

F.E. Ku¨hn et al. / Journal of Organometallic Chemistry 621 (2001) 207–217
211
sults (Table 1). This observation indicates that the
ligand surrounding of the metal center is influenced by
the solvent. In the coordinating solvent NCCD3, the
THF in MoO2Cl(THF)L* is substituted by NCCD3,
giving MoO2Cl(NCCD3)L*. The 95Mo-NMR shift of
the complexes 4a–9a is similar to that of the acetoni-
trile-substituted complex [l(95Mo)=278 ppm] [8].
17O enrichment of the oxo group in the complex
MoO2Cl2(DMF)2 (14) was carried out by treatment of a
solution of the unlabeled complex in CH2Cl2 with
excess H217O, in a manner analogous to that previously
reported for 18O enrichment of 14 using H218O [11]. The
labeled complexes Mo17O2Cl2(NCCH3)2 (15) and
Mo17O2Cl2(THF)2 (16) were then obtained by recrystal-
lization of Mo17O2Cl2(DMF)2 from NCCH3 and THF,
respectively. All three complexes displayed their 17O
chemical shifts for the MoꢀO group at about 1016 ppm,
which is at the high-field end of the expected range for
transition-metal oxo-complexes in high oxidation states,
indicating a comparatively electron-deficient molybde-
num(VI) center (Table 2). Reaction of labeled
Mo17O2Cl2(THF)2 with two equivalents of the chiral
2%-pyridyl alcohols 4–6 and 8 (method (a), Section 4.5)
gave the 17O-enriched complexes 10a–13a. The 17O-
NMR signal for the oxo groups of these complexes
appeared as a single sharp line at about 900 ppm,
shifted by about 120 ppm upfield compared with the
solvent-substituted complexes MoO2Cl2(S)2 (Table 2).
This shift reflects the higher electron density in the
complexes due to the donor capability of the N/O
ligands. The complexes of the type MoO2X2L2 [8a]
(X=Cl, Br, L=4-methyl-amino-pent-3-ene-2-one, 4-
anilino-pent-3-ene-2-one) show their 17O chemical shifts
at slightly lower field (930–970 ppm).
2.4. Chiral dioxomolybdenum(VI) complexes in
asymmetric epoxidation catalysis
The design of new metal catalysts for enantioselective
epoxidation of unfunctionalized trans-disubstituted
alkenes remains a challenge in the field of asymmetric
oxidation [12]. Two of the best reported enantiomeric
excesses (ee) for the catalytic oxidation of trans-b-
methylstyrene are 77 and 59% using chiral Cr-salen [13]
and chiral trans-dioxoruthenium(VI) porphyrin [12b]
catalysts, respectively. These catalysts have a limitation,
which is their modest catalytic activity, usually below
120 turnovers/h [14]. Several molybdenum(VI) com-
plexes have proven to be very active catalysts for the
epoxidation of olefins with hydroperoxides [8,15]. As
far as asymmetric epoxidation is concerned, enan-
tiomeric excesses of up to 53% are known with func-
tionalized olefins as substrate, e.g. allylic alcohols or
amides [2b], whereas for unfunctionalized olefins only
one catalyst was known until recently, yielding 14% ee
[16].
Table 2
17O-NMR chemical shifts for the MoꢀO group of 17O-enriched
complexes (CD2Cl2, room temperature)
Compound
l(17O) (ppm)
10a
11a
898
899
Complexes 1a–13a were evaluated as potential cata-
lysts for the asymmetric epoxidation of trans-b-methyl-
styrene using TBHP as oxidant in toluene as solvent at
55°C. The ratio of substrate:oxidant:catalyst used was
100:200:1. Conversions and enantiomeric excesses are
given in Table 3. The methylenebis(oxazoline) com-
plexes 1a–3a catalyzed the oxidation of trans-b-methyl-
styrene with moderate to good activity, complete
stereoretention, but low asymmetric induction. A gen-
eral observation is that catalyst activity increases in the
order 1a (R=isopropyl)B2a (R=isobutyl)B3a (R=
Ph) and, therefore, clearly depends on the nature of the
substituent at the C(4) position on the oxazoline ring.
For complex 3a the reaction proceeded smoothly, and
conversion of the substrate reached 80% after 4 h.
Complete conversion was achieved within 24 h. For all
three complexes, (1R, 2R)-trans-b-methylstyrene oxide
was formed in very slight excess (4–6% ee) at the
beginning of the reaction, but as the reaction proceeded
the ee values decreased to almost zero. This may be due
in part to deleterious effects from tert-butanol, which is
inevitably formed in excess during the reaction from
TBHP [5]. This results in an increase of the polarity of
the solvent (toluene). Since for unfunctionalized olefins
only non-covalent interactions between the catalytically
12a
13a
890
902
1017
1016
1014
Mo17O2Cl2(DMF)2 (14)
Mo17O2Cl2(NCCH3)2 (15)
Mo17O2Cl2(THF)2 (16)
Table 3
Results after 4 h reacting in the catalytic epoxidation of trans-b-
methylstyrene by TBHP at 55°C in the presence of methylenebis(oxa-
zoline) complexes 1a–3a and 2%-pyridyl alcoholate complexes 4a–13a.
See text and Section 4 for reaction details
Compound
Conversion (%)
ee (%)
1a
2a
3a
4a
10a
5a
11a
6a
7a
12a
8a
59
72
86
76
47
66
46
75
59
23
69
51
81
–
–
–
2 (S,S)
5 (S,S)
2 (S,S)
1 (S,S)
16 (R,R)
12 (S,S)
3 (S,S)
18 (S,S)
23 (S,S)
11 (R,R)
13a
9a

212
F.E. Ku¨hn et al. / Journal of Organometallic Chemistry 621 (2001) 207–217
active species and the substrate can contribute to opti-
cal induction, it is clear that polar solvent molecules
impair these interactions leading to a lower ee Alterna-
tively, tert-butanol may act as a competitive achiral
monodentate ligand. These effects have already been
discussed in the literature.
from the catalysts or the oxidant. The shift to higher
fields of the resonances of the MoꢀO group point
toward coordination of (CH3)3COO to the d0 Lewis
acid molybdenum(VI) center. This would be in line with
the current assumptions concerning the mechanism of
catalytic epoxidations with oxomolybdenum(VI) com-
plexes and TBHP as oxidant. Studies with peroxo-
molybdenum complexes established that the oxygen
transferred to the olefin derives from TBHP and not
from the peroxo ligand [15b]. Herrmann et al. sug-
gested that an ‘oxenoid’ oxygen is generated and that
this is subsequently transferred to the olefin. They
proposed that since complexes of the type MoO2L2
(L=bidentate N/O ligand, e.g. 2%-pyridyl alcoholate)
are coordinatively saturated by an octahedral coordina-
tion sphere and the oxo ligands are ‘chemically inert’,
the reaction mechanism must involve a dissociative step
with respect to the chelating ligand [5]. The stereodiffer-
entiation should then be produced by the chiral centers
through weak p–p interactions between the ligand and
the aromatic olefin. However, the experimental evi-
dence for these assumptions is not yet completely
convincing.
Better enantioselectivities were obtained for the 2%-
pyridyl alcoholate complexes 4a–13a. In all cases, the
epoxidation of trans-b-methylstyrene proceeded with
complete retention of configuration. A survey of the
catalytic activity after 4 h reaction reveals good conver-
sions of around 70% for complexes of the type
MoO2Cl(THF) L*, i.e. with one equivalent of chiral
ligand (Table 3). Complexes with two equivalents of
ligand, MoO2L*2 , gave considerably lower conversions
of substrate (ca. 50%). The ee depends on the type of
chiral ligand employed and much less on the number of
equivalents. The highest optical inductions were
achieved with complexes containing the ligand 8
(Scheme 3). Thus, the (S,S)-epoxide was obtained in
18% ee for complex 8a (one equivalent of ligand) and
23% for complex 13a (two equivalents of ligand). How-
ever, when complex 9a was used there was an inversion
of the optical induction compared with 8a and the
(R,R)-epoxide was obtained in 11% ee. The same effect
is evident when comparing complexes 5a and 6a. This
clearly indicates that the stereochemical outcome of
these reactions is primarily determined by the type of
ligand enantiomer employed. Comparison of the com-
plexes with ligands derived from menthone (4a and 5a,
10a and 11a) reveals that changing the substituent at
the C(2) position on the cyclohexan-1-ol ring from
isopropyl to 1-methyl-1-phenylethyl did not have a
noticeable effect on either the resulting conversions or
ee values. Complexes 10a and 12a have already been
reported by Herrmann et al., who carried out similar
catalytic experiments to ours with trans-b-methyl-
styrene as substrate and TBHP as oxidant (chloroform
as solvent) [5].
Considering the spectroscopic results obtained for the
catalyst precursors 1a–13a, and the catalytic activity of
the three types of catalyst precursor (MoO2X2L2 (1a–
3a), MoO2X(THF)L (4a–9a), and MoO2L2 (10a–13a))
under examination, we can at least give some explana-
tions for their differences in activity and chiral induc-
tion. Complexes of the type MoO2X2L2 are of moderate
catalytic activity (TOFs ca. 150 h−1), moderate Lewis
acidity (l(17O):950 ppm, l(95Mo):140 ppm) and do
not show any chiral induction, probably due to the
coordinative lability of the oxazoline ligands. This co-
ordinative lability can be seen by comparing the (tem-
1
perature-dependent) H-NMR-spectra of the complexes
1a–3a to the spectra of the free ligands 1–3. Com-
pounds of the type MoO2X(THF)L are more Lewis
acidic (l(95Mo):250 ppm), less sterically crowded (the
ligand sphere contains a weakly coordinated, easy to
replace solvent molecule) and display turnover frequen-
cies usually significantly higher than 150 h−1. The lig-
ands are coordinated more strongly to the metal center
(one bond is covalent). Therefore, enantiomeric induc-
tion can be achieved. However, since alcohols and
water can react with the coordinatively unsaturated
complexes, their original activity is not maintained for
very long and the ee diminishes after some time. The
complexes of the type MoO2L2 are the least Lewis
acidic of the complexes described in this work
(l(17O):900 ppm, l(95Mo):50 ppm) and contain
two strongly bound ligands (two covalent interactions).
Accordingly, they are not very active (TOFsB
100 h−1). The ee is low because of the significant steric
crowding of the chiral ligands. In general, it has to be
noted that ligands containing a bulky group in a-posi-
17O-NMR was used to study the reaction of the
17O-labeled complexes 10a and 13a with TBHP and
cyclohexene (25°C, CD2Cl2). Upon addition of TBHP
to a solution of 13a (catalyst:oxidant, 1:200) the 17O-
NMR signal for the oxo group shifted from 904 ppm to
894 ppm. In the case of complex 10a the resonance
shifted from 898 to 884 ppm. In both cases, two addi-
tional weak broad peaks appeared at 254 ppm and
205 ppm, attributed to the (CH3)3CO and OH groups,
respectively, of TBHP [17a]. Subsequent addition of
cyclohexene (catalyst:oxidant:substrate=1:200:100) re-
sulted in the appearance of a new sharp line at
−7.3 ppm that grew in intensity with time relative to
the other peaks in the spectrum. This was attributed to
cyclohexene oxide, which increased in concentration
with time [17b]. Addition of the olefin did not result in
significant changes to the signals in the spectrum arising

F.E. Ku¨hn et al. / Journal of Organometallic Chemistry 621 (2001) 207–217
213
tion to the connecting oxygen atom (4–6) are signifi-
cantly less active than molecules with only hydrogen
atoms or methyl ligands in this position (8).
measured at 26.07 MHz on a Bruker Avance DPX-400.
IR spectra were measured on a Unican Mattson Mod
7000 FTIR spectrometer and a Perkin–Elmer FT-IR
spectrometer using KBr pellets. Catalytic runs were
monitored by chiral GC methods on a Hewlett-Packard
(HP5970 B) instrument equipped with a Chiraldex g-
TA column (Alltech) and integration unit (HP 3394).
3. Conclusions
The
precursor
materials
MoO2Cl2
[18],
Chiral oxomolybdenum(VI) derivatives of the general
formulae MoO2Cl2L**, MoO2Cl(THF)L* and MoO2L2
[L**=chiral bis(oxazoline) and L*=chiral 2%-pyridyl
alcoholate] have been prepared and characterized. Con-
siderable activity differences have been found in the
asymmetric catalytic epoxidation of trans-b-methyl-
styrene with TBHP. Although optical yields, in general,
were low, the results with 2%-pyridyl alcoholate ligands
are promising in the context of asymmetric epoxidation
of unfunctionalized olefins by molybdenum complexes.
A clear ligand dependence on enantioselectivity was
observed, which suggests that further optimization of
the appropriate chiral ligands and/or use of alternative
oxidants could lead to more effective epoxidation sys-
tems. This, together with the study of the nature of the
catalytically active species, is currently under investiga-
tion in our laboratories.
The most promising way of achieving significant
enantioselectivity in catalytic oxidations with molecules
of the type MoO2X2L currently appears to be the
replacement of the ligand Cl by a chiral organic sub-
stituent R*. This substituent R* would be stable to
ligand exchange reactions, which always and unavoid-
ably influence the ligands L*, so that the ee in chiral
olefin epoxidations should be significantly higher than
in the cases examined to date.
MoO2Cl2(THF)2 and MoO2Cl2(NCCH3)2 [9] were pre-
pared as described previously. (−)-Menthone, (−)-8-
phenylmenthol, (+)-camphor and (−)-thujone were
purchased from Aldrich and used as received. (+)-8-
Phenylisomenthone [19] and (−)-8-phenylmenthone
[20] were prepared as published or with minor changes.
2,2-Bis[(4S)-4-isopropyl-1,3-oxazolin-2-yl]propane (1),
2,2-bis[(4S)-4-isobutyl-1,3-oxazolin-2-yl)]propane
(2)
and 2,2-bis[4(S)-4-phenyl-1,3-oxazolin-2-yl)]propane (3)
were prepared according to literature procedures
[7a,21].
4.2. Synthesis of the chiral 2%-pyridyl alcohols 4–9
4.2.1. General procedure
A solution of 2-bromopyridine (70.0 mmol) in diethyl
ether (6.0 ml) was added to a solution of nBuLi
(44.0 ml, 1.6 M/n-hexane, 70.4 mmol) in diethyl ether
(100 ml) at −70°C. The red solution was stirred for
30 min at −70°C and then treated with a solution of
the appropriate ketone (65.0 mmol) in diethyl ether
(20 ml). After stirring for 3 h at room temperature (r.t.),
the mixture was filtered (Celite) and the residue washed
several times with diethyl ether (150 ml). The combined
filtrate and washings were concentrated and washed
with 10% NaOH (2×60 ml) and brine (100 ml). The
combined organic layers were then dried over Na2SO4
and the solvent removed to give an oil or a brown
residue, which was purified by flash chromatography.
4. Experimental
4.1. Materials and methods
4.2.2. (1S,2S,5R)-5-Methyl-2-isopropyl-1-(2%-pyridyl)-
cyclohexan-1-ol (4)
All preparations and manipulations were carried out
using standard Schlenk techniques under an atmo-
sphere of nitrogen. Solvents were dried by standard
procedures (THF, n-hexane and Et2O over Na–ben-
zophenone ketyl; CH2Cl2 and NCCH3 over CaH2),
Eluent, n-hexane:EtOAc; 9:1. Yield: 92%. M.p. 58–
1
60°C. [h]2D0 −22.3° (c 1, CHCl3). EA, IR (KBr), H-
and 13C-NMR data were in agreement with Refs. [1b,5].
,
distilled under argon and kept over 4 A molecular
4.2.3. (1S,2S,5R)-5-Methyl-2-(1-methyl-1-phenylethyl)-
1-(2%-pyridyl)cyclohexan-1-ol (5)
,
sieves (3 A for NCCH3).
Microanalyses were performed at the ITQB and the
Mikroanalytische Labor of the Technical University of
Munich (M. Barth). H-NMR spectra were recorded at
300 MHz and 400 MHz on Bruker CXP 300 and
Bruker Avance DPX-400 spectrometers, respectively.
13C-NMR spectra were measured at 100.28 MHz on a
JEOL JNM GX-400 and a Bruker Avance DPX-400,
17O-NMR spectra were measured at 54.14 MHz on a
JEOL JNM GX-400, and 95Mo-NMR spectra were
Eluent, n-hexane:EtOAc; 9:1. Yield: 94% (white
solid). Anal. Found: C, 81.52; H, 8.81; N, 4.55. Calc.
for C21H27NO (309.45): C, 81.51; H, 8.79; N, 4.53%.
M.p. 63–64°C. [h]2D0 +49.6° (c 1, CHCl3). IR (KBr, w
cm−1): 3338 vs (OH), 3061 s, 2945 vs, 2930 vs, 1591 vs,
1398 vs, 769 vs, 702 vs, 575 s. 1H-NMR (CDCl3,
300 MHz, r.t., l ppm): 8.40 (d, 1H, H6%); 7.38 (br, 1H,
H4%); 7.08–7.01 (m, 7H, Ph and H3%/5%); 5.84 (br, 1H,
OH); 2.21–2.17 (m, 1H); 1.94–1.80 (m, 2H); 1.57–1.53
1

214
F.E. Ku¨hn et al. / Journal of Organometallic Chemistry 621 (2001) 207–217
(m, 2H); 1.38–1.34 (m, 1H); 1.28 (s, 3H, CH3); 0.97–
0.82 (m, 2H); 0.77 (d, 3H, CH3); 0.73 (s, 3H, CH3).
13C-NMR (CD2Cl2, 300 MHz, r.t., l ppm): 165.22
(C2%); 152.68 (Ph); 146.53 (C6%); 136.27 (C4%); 127.98 (Ph);
126.41 (Ph); 125.09 (C3%); 121.70 (C5%); 76.26 (C1); 53.52;
53.25; 42.17; 36.01; 28.51; 27.24; 25.30; 22.28 (see
Scheme 1 for numbering).
vs, 2928 vs, 1593 vs, 1464 vs, 1433 vs, 1402 vs, 1066 vs,
781 vs, 752 vs. 1H-NMR (CDCl3, 300 MHz, r.t.,
l ppm): 8.44 (d, 1H, H6%); 7.73 (br, 1H, H4%); 7.39 (d,
1H, H3%); 7.15 (t, 1H, H5%); 5.44 (s, 1H, OH); 2.55–2.51
(br, 1H); 2.36 (d, 1H); 2.00 (d, 1H); 1.50–1.43 (m, 1H);
1.22 (br, 1H); 1.03 (d, 3H, CH3); 0.90 (d, 3H, CH3);
0.79 (d, 3H, CH3); 0.43 (s, 1H); 0.30 (br, 1H). 13C-
NMR (CD2Cl2, 300 MHz, r.t., l ppm): 165.08 (C2%);
146.53 (C6%); 137.22 (C4%); 121.81 (C3%); 129.98 (C5%);
81.16 (C1%); 49.65; 46.56; 33.26; 32.67; 29.32; 19.91;
12.86; 11.20.
4.2.4. (1R,2R,5R)-5-Methyl-2-(1-methyl-1-
phenylethyl)-1-(2%-pyridyl)cyclohexan-1-ol (6)
Eluent, n-hexane:EtOAc; 9:1. Yield: 92% (white
solid). Anal. Found: C, 81.52; H, 8.81; N, 4.55. Calc.
for C21H27NO (309.45): C, 81.51; H, 8.79; N, 4.53%.
M.p. 91–92°C. [h]2D0 −78.1° (c 1, CHCl3). IR (KBr, w
cm−1): 3333 vs (OH), 3060 s, 2943 vs, 2930 vs, 1593 vs,
1398 vs, 769 vs, 771 vs, 704 vs. 1H-NMR (CDCl3,
300 MHz, r.t., l ppm): 8.42 (d, 1H, H6%); 7.47 (br, 1H,
H4%); 7.26–7.03 (m, 7H, Ph and H3%/5%); 5.40 (s, 1H, OH);
2.31–2.27 (m, 1H); 2.07–1.85 (m, 3H); 1.59–1.37 (m,
4H); 1.20 (s, 3H, CH3); 0.90 (d, 3H, CH3); 0.73 (s, 3H,
CH3). 13C-NMR (CD2Cl2, 300 MHz, r.t., l ppm):
166.85 (C2%); 152.61 (Ph); 146.64 (C6%); 136.36 (C4%);
127.97 (Ph); 126.41 (Ph); 125.19 (C3%); 121.60 (C5%);
77.97 (C1); 53.52; 50.09; 42.58; 32.99; 29.13; 28.41;
26.29; 20.30 (see Scheme 1 for numbering).
4.3. Preparation of complexes of the type MoO2Cl2L**
[L**=2,2-bis[2-(4(S)-isopropyl-1,3-oxazolinyl)]propane
(1), 2,2-bis[2-(4(S)-isobutyl-1,3-oxazolinyl)]propane (2)
and 2,2-bis[2-(4(S)-phenyl-1,3-oxazolinyl)]propane (3)]
4.3.1. General procedure
A solution of MoO2Cl2(THF)2 (0.77 g, 2.24 mmol) in
CH2Cl2 (15 ml) was treated with bis(oxazoline) L**
[L**=1, 2, and 3, 2.24 mmol]. The color of the solu-
tion changed to yellow. After 60 min, the solution was
filtered, evaporated to dryness and washed with diethyl
ether–n-hexane.
4.3.2. MoO2Cl2(2,2-bis[2-(4(S)-isopropyl-1,3-
oxazolinyl)]propane) (1a)
Yield: 93%. Anal. Found: C, 38.87; H, 5.50; N, 5.97.
Calc. for C15H26Cl2MoN2O4 (465.22): C, 38.73; H, 5.63;
N, 6.02%. Selected IR data (KBr, w cm–1): 2958 s, 2871
4.2.5. (1R,2R,4R)-1,7,7-Trimethyl-2-(2%-pyridyl)-
bicyclo[2.2.1]heptan-2-ol (7)
Eluent, n-hexane:EtOAc; 9:1. Yield: 83%. M.p. 56–
57°C. [h]2D0 −32.1° (c 1, CHCl3). EA, IR (KBr), H-
1
and 13C-NMR data were in agreement with Refs.
[1b,3,5].
m, 952 m, 912 vs (MoꢀO), 910 vs (MoꢀO). H-NMR
1
(CD2Cl2, 400 MHz, r.t., l ppm): 5.19 (d, 2H); 4.73 (d,
2H); 4.64 (br, 1H); 4.13 (s, 2H); 2.95 (br, 1H); 1.95 (s,
6H, CH3); 1.19 (d, 6H, CH3); 1.08 (d, 6H, CH3).
13C-NMR (CD2Cl2, 300 MHz, r.t., l ppm): 171.6;
73.40; 69.64; 31.96; 29.43; 24.89; 19.54; 14.00.
4.2.6. (1S,3R,4S,5R)-1-Isopropyl-4-methyl-3-
(2-pyridyl)bicyclo[3.1.0]hexane-3-ol (8)
Eluent, n-hexane:EtOAc; 9:1. Yield: 70.0%. Anal.
Found: C, 77.68; H, 9.02; N, 5.98. Calc. for C15H21NO
(231.34): C, 77.88; H, 9.15; N, 6.05%. [h]2D0 +49.5° (c 1,
CHCl3). IR (KBr, w cm–1): 3403 vs (OH), 3049 s, 2959
vs, 2930 vs, 1593 vs, 1470 vs, 1433 vs, 1384 vs, 779 vs,
4.3.3. MoO2Cl2(2,2-bis[2-(4(S)-isobutyl-1,3-
oxazolinyl)]propane) (2a)
Yield: 91%. Anal. Found: C, 41.20; H, 5.97; N, 5.57.
Calc. for C17H30Cl2MoN2O4 (492.27): C, 41.39; H, 6.13;
N, 5.68%. Selected IR data (KBr, w cm–1): 2958 s, 2871
1
750 vs. H-NMR (CDCl3, 300 MHz, r.t., l ppm): 8.48
(d, 1H, H6%); 7.64 (br, 1H, H4%); 7.36 (d, 1H, H3%); 7.14
(t, 1H, H5%); 4.53 (s, 1H, OH); 2.18–2.01 (comp, 3H);
1.55–1.43 (m, 2H); 1.04 (d, 3H, CH3); 0.91 (d, 3H,
CH3); 0.84 (d, 3H, CH3); 0.51 (br, 2H). 13C-NMR
(CD2Cl2, 300 MHz, r.t., l ppm): 162.86 (C2%); 144.58
(C6%); 136.75 (C4%); 121.88 (C3%); 119.62 (C5%); 85.84 (C1%);
52.11; 48.57; 36.69; 33.59; 30.83; 26.73; 20.56; 19.87;
13.00.
1
m, 952 m, 912 vs (MoꢀO), 910 vs (MoꢀO). H-NMR
(CD2Cl2, 400 MHz, r.t., l ppm): 5.57 (dd, 2H); 4.75
(dd, 2H); 4.58 (t, 2H); 2.57 (m, 2H); 1.93–1.39 (m, 10H,
CH3); 1.19 (d, 6H, CH3); 1.08 (s, 6H, CH3). 13C-NMR
(CD2Cl2, 300 MHz, r.t., l ppm): 171.1; 73.90; 69.23;
25.92; 25.93; 19.24; 14.26.
4.3.4. MoO2Cl2(2,2-bis[2-(4(S)-phenyl-1,3-
4.2.7. (1S,3S,4S,5R)-1-Isopropyl-4-methyl-3-
oxazolinyl)]propane) (3a)
(2-pyridyl)bicyclo[3.1.0]hexane-3-ol (9)
Yield: 97%. Anal. Found: C, 47.52; H, 4.28; N, 4.99.
Calc. for C21H22Cl2MoN2O4 (533.25): C, 47.30; H, 4.16;
N, 5.25%. Selected IR data (KBr, w cm–1): 3032 m, 2987
m, 2910 m, 1474 s, 1456 s, 1383 s, 1230 vs, 1123 vs, 943
m (MoꢀO), 917 vs (MoꢀO), 766 s, 698 s, 541 m.
Eluent, n-hexane:EtOAc; 9:1. Yield: 25.0%. Anal.
Found: C, 77.68; H, 9.02; N, 5.98. Calc. for C15H21NO
(231.34): C, 77.88; H, 9.15; N, 6.05%. [h]2D0 +6.3° (c 1,
CHCl3). IR (KBr, w cm–1): 3398 vs (OH), 3005 s, 2957

F.E. Ku¨hn et al. / Journal of Organometallic Chemistry 621 (2001) 207–217
215
1H-NMR (CD2Cl2, 400 MHz, r.t., l ppm): 7.37–7.27
4.4.4. MoO2Cl(THF){(1R,2R,5R)-5-methyl-2-
(1-methyl-1-phenylethyl)-1-(2%-pyridyl)cyclohexan-1-
olato} (6a)
(m, 10H, Ph); 5.94 (dd, 2H); 4.84 (t, 2H); 4.12 (dd, 2H);
1.87 (s, 6H, CH3). 13C-NMR (CD2Cl2, 300 MHz, r.t.,
l ppm): 172.7; 139.9; 128.90; 127.81; 76.61; 71.99;
40.86; 25.96.
Yield: 91%. Anal. Found: C, 54.93; H, 6.00; N, 2.40.
Calc. for C25H34ClMoNO4 (543.95): C, 55.20; H, 6.30;
N, 2.58%. IR (KBr, w cm–1): 3057 m, 2970 s, 2933,
2878, 1604 s, 1475 m, 1454 s, 1388 m, 1298 m, 1031 m,
1
4.4. Preparation of complexes of the type MoO2Cl(S)L*
(L*=chiral 2%-pyridyl alcoholate)
941 vs, 920 vs (MoꢀO), 875 m, 785 s, 702 s. H-NMR
(CD2Cl2, 300 MHz, r.t., l ppm): 8.22 (d, 1H, H6%); 7.45
(t, 1H, H4%); 7.15–6.84 (m, 7H, H5%/3%+Ph); 4.09 (s,
THF); 2.46–2.44 (m, 2H); 2.12–1.99 (m, 2H); 1.95 (s,
THF); 1.77–1.68 (m, 2H); 1.45–1.39 (m, 2H); 1.42 (s,
3H, CH3); 1.29 (s, 3H, CH3); 1.18 (d, 3H, CH3).
13C-NMR (CD2Cl2, 300 MHz, r.t., l ppm): 168.67;
150.98; 147.56; 139.90; 128.29; 126.21; 125.49; 123.90;
79.10 (C1); 70.90 (THF); 50.34; 41.68; 32.29; 31.61;
30.32; 27.96; 25.55 (THF); 19.23.
4.4.1. General procedure
A solution of MoO2Cl2(THF)2 (0.68 g, 2.00 mmol) in
CH2Cl2 (10 ml) was treated with one equivalent of
ligand. The resulting turbid solution was stirred for a
further 30 min. The solvent was evaporated, and the
product washed with n-hexane and dried under
vacuum.
4.4.5. MoO2Cl(THF){(1R,2R,4R)-1,7,7-
4.4.2. MoO2Cl(THF){(1S,2S,5R)-5-methyl-2-
trimethyl-2-(2%-pyridyl)bicyclo[2.2.1]heptan-2-olato} (7a)
Yield: 93%. Anal. Found: C, 48.65; H, 5.76; N, 2.80.
Calc. for C19H28ClMoNO4 (465.83): C, 48.99; H, 6.06;
N, 3.01%. IR (KBr, w cm–1): 2961 s, 2876, 1603 s, 1523
s 1456 s, 1392 m, 1298 m, 1072 m, 959 vs, 918 vs
(MoꢀO), 866 m, 771 s, 682 m, 570 m. 13C-NMR
(CD2Cl2, 300 MHz, r.t., l ppm): 164.56; 147.69; 139.63;
124.78; 123.54; 81.78 (C1); 69.61 (THF); 55.93; 50.00;
47.27; 44.39; 29.08; 26.15 (THF); 24.34; 20.00; 10.17.
isopropyl-1-(2%-pyridyl)cyclohexan-1-olato} (4a)
Yield: 92%. Anal. Found: C, 48.47; H, 6.48; N, 3.07.
Calc. for C19H30ClMoNO4 (467.85): C, 48.78; H, 6.46;
N, 2.99%. IR (KBr, w cm–1): 3099 m, 2953 s, 2872 m,
1605 s, 1516 m, 1454 s, 1386 m, 1298 m, 1058 m, 941 vs
(MoꢀO), 918 vs (MoꢀO), 870 m, 775 s, 756 m, 687 m,
1
648 m. H-NMR (CD2Cl2, 300 MHz, r.t., l ppm): 8.49
(br, 1H, H6%); 8.05 (t, 1H, H4%); 7.52–7.45 (m, 2H,
H5%/3%); 3.90 (s, THF); 2.12–1.81 (m, 4H+THF); 1.74–
1.69 (m, 2H); 1.49 (d, 1H); 1.35–1.26 (m, 1H); 1.12–
1.04 (m, 1H); 1.00 (d, 3H, CH3); 0.93 (d, 3H, CH3);
0.77 (d, 3H, CH3). 13C-NMR (CD2Cl2, 300 MHz, r.t.,
l ppm): 163.13 (C2%); 148.92 (C6%); 142.20 (C4%); 125.21
(C3%); 122.24 (C5%); 79.38 (C1); 69.64 (THF); 51.32 (C6);
50.65 (C2); 34.99 (C4); 28.85 (C5); 28.37 (C10); 25.91
(THF); 23.90 (C5); 22.49 (C8); 21.90 (C3); 18.63 (C9).
4.4.6. MoO2Cl(THF){(1S,3R,4S,5R)-1-
isopropyl-4-methyl-3-(2-pyridyl)bicyclo[3.1.0]
hexane-3-olato} (8a)
Yield: 96.0%. Anal. Found: C, 48.58; H, 5.83; N,
2.90. Calc. for C19H28ClMoNO4 (465.83): C, 48.99; H,
6.06; N, 3.01%. IR (KBr, w cm–1): 2959 s, 2930 m, 2874,
1608 s, 1521 m 1456 s, 1385 m, 1298 m, 1087 m, 941 vs
(MoꢀO), 916 vs (MoꢀO), 771 s, 579 m. 13C-NMR
(CD2Cl2, 300 MHz, r.t., l ppm): 157.63 (C2%); 145.57
(C6%); 140.32 (C4%); 123.72 (C3%); 120.55 (C5%); 87.65(C1);
68.22 (THF); 52.88; 48.06; 36.45; 31.99; 29.14; 24.35
(THF); 19.17; 18.35; 11.80.
4.4.3. MoO2Cl(THF){(1S,2S,5R)-5-methyl-2-
(1-methyl-1-phenylethyl)-1-(2%-pyridyl)cyclohexan-1-
olato} (5a)
Yield: 88%. Anal. Found: C, 54.86; H, 5.98; N, 2.50.
Calc. for C25H34ClMoNO4 (543.95): C, 55.20; H, 6.30;
N, 2.58%. IR (KBr, w cm–1): 3048 m, 2983 s, 1605 s,
1518 m, 1454 s, 1382 m, 1298 m, 1049 m, 941 vs
(MoꢀO), 918 vs (MoꢀO), 889 m, 796 s, 702 s, 572 m,
4.4.7. MoO2Cl(THF){(1S,3S,4S,5R)-1-isopropyl-
4-methyl-3-(2-pyridyl)bicyclo[3.1.0]hexane-3-olato} (9a)
Yield: 91.0%. Anal. Found: C, 48.58; H, 5.83; N,
2.90. Calc. for C19H28ClMoNO4 (465.83): C, 48.99; H,
6.06; N, 3.01%. IR (KBr, w cm–1): 2957 s, 2926 m, 2872,
1606 s, 1456 s, 1398 m, 1298 m, 1067 m, 937 vs
(MoꢀO), 920 vs (MoꢀO), 839 m, 773 s, 651m. 13C-
NMR (CD2Cl2, 300 MHz, r.t., l ppm): 158.03 (C2%);
147.07 (C6%); 140.93 (C4%); 124.74 (C3%); 121.33 (C5%);
86.85 (C1); 68.62 (THF); 51.98; 49.44; 40.62; 31.40;
30.08; 27.40 (THF); 23.14; 18.61; 11.33.
1
553 m. H-NMR (CD2Cl2, 300 MHz, r.t., l ppm): 8.18
(d, 1H, H6%); 7.71 (t, 1H, H4%); 7.37 (t, 1H, H5%); 7.13–
6.91 (m, 5H, Ph); 6.72 (d, 1H, H3%); 3.90 (s, THF);
2.46–2.15 (m, 2H); 1.99–1.93 (m, 2H); 1.90 (s, THF);
1.76–1.69 (m, 2H); 1.45–1.39 (m, 2H); 1.35 (d, 3H,
CH3); 1.25 (s, 3H, CH3); 0.91 (d, 3H, CH3). 13C-NMR
(CD2Cl2, 300 MHz, r.t., l ppm): 168.40; 151.49; 147.70;
139.81; 128.49; 126.25; 125.45; 124.06; 78.34 (C1); 69.92
(THF); 56.26; 51.29; 41.53; 35.55; 31.14; 29.29; 25.92
(THF); 23.83; 21.90.

216
F.E. Ku¨hn et al. / Journal of Organometallic Chemistry 621 (2001) 207–217
4.5. Preparation of complexes of the type MoO2L*
(L*=chiral 2%-pyridyl alcoholate)
l ppm): 165.36; 147.45 (d, C6%); 139.29; 122.29; 119.72;
103.5 (C1); 50.91; 44.48; 37.54; 33.93; 30.92; 28.67;
21.12; 20.16; 15.38.
2
Method (a). A solution of MoO2Cl2(THF)2 (0.38 g,
1.11 mmol) in CH2Cl2 (10 ml) was treated with two
equivalents of ligand. The solution became milky and a
precipitate formed. After 6 h in reflux, the suspension
was evaporated to dryness to yield a powder, which was
washed with diethyl ether–n-hexane.
4.6. O-labeling studies
The labeled complex Mo17O2Cl2(DMF)2 (14) was
prepared according to the published procedure using
H217O [12]. IR (KBr, w cm–1): 941 s, 928 vs, 904 vs, 891
Method (b). A solution of MoO2Cl2(THF)2 (0.38 g,
1.00 mmol) in CH2Cl2 (10 ml) was treated with two
equivalents of ligand and two equivalents of TlEOt.
The turbid reaction mixture was left stirring for 2 h and
then the suspension was evaporated to dryness. After
washing with n-hexane, the residue was extracted with
dichloromethane and the solution taken to dryness to
yield a powder, which was washed with diethyl ether–
n-hexane several times.
s, 870 vs, 860
s
(MoꢀO). Labeled complexes
Mo17O2Cl2(NCCH3)2 (15) and Mo17O2Cl2(THF)2 (16)
were prepared by recrystallization of 14 from NCCH3
and THF, respectively.
Labeled complexes Mo17O2L2* were prepared using
method (a) (Section 4.5) with starting material
Mo17O2Cl2(THF)2 (16).
Mo17O2{(1S,2S,5R) - 5 - methyl - 2 - isopropyl - 1 - (2%-
pyridyl)cyclohexan-1-olato}2 (10a). IR (KBr, w cm–1):
957 s, 948 vs, 916 vs, 895 vs, 864 s (MoꢀO).
Mo17O2{(1S,2S,5R)-5-methyl-2-(1-methyl-1-phenyl-
4.5.1. MoO2{(1S,2S,5R)-5-methyl-2-isopropyl-
1-(2%-pyridyl)cyclohexan-1-olato}2 (10a)
EA, IR (KBr), 1H- and 13C-NMR data were in
agreement with Refs. [1b,5].
ethyl)-1-(2%-pyridyl)cyclohexan-1-olato}2
(11a).
IR
(KBr, w cm–1): 957 s, 946 m, 917 vs, 895 vs, 862 s
(MoꢀO).
Mo17O2{(1R,2R,4R)-1,7,7-trimethyl-2-(2%-pyridyl)-
bicyclo[2.2.1]heptan-2-olato}2 (12a). IR (KBr, w cm–1):
970 s, 946 m, 912 vs, 896 m (MoꢀO).
4.5.2. MoO2{(1S,2S,5R)-5-methyl-2-(1-methyl-
1-phenylethyl)-1-(2%-pyridyl)cyclohexan-1-ol}2 (11a)
Yield: 86.0%. Anal. Found: C, 67.82; H, 6.94; N,
3.78. Calc. for C42H52MoN2O4 (744.83): C, 67.73; H,
7.04; N, 3.76%. IR (KBr, w cm–1): 3055 m, 2945 s, 2920,
2868, 1599, 1474 s, 1435 s, 1390 m, 1368, 1068 m, 916
s (MoꢀO), 895 vs (MoꢀO), 769 vs, 701 vs, 643 m, 580
m, 559m, 482s. 1H NMR (CD2Cl2, 300 MHz, r.t.,
l ppm): 8.76 (br, 1H, H6%); 7.70 (br, 1H, H4%); 7.41–6.99
(m, 7H, Ph and H3%/5%); 2.38–2.29 (m, 1H); 1.89–1.78
(m, 2H); 1.52–1.33 (m, 2H); 1.31–1.29 (m, 1H); 1.25 (s,
3H, CH3); 1.12–0.99 (m, 1H); 0.85 (d, 6H, CH3); 0.70
(s, 6H, CH3).
Mo17O2{(1S,3R,4S,5R)-1-isopropyl-4-methyl-3-(3%-
pyridyl)bicyclo[3.1.0]hexane-3-olato}2 (13a). IR (KBr, w
cm–1): 976 s, 952 m, 923 vs, 906 vs, 854 m (MoꢀO).
4.7. Catalytic epoxidation reactions with compounds
1a–13a
200 mg of trans-b-methylstyrene (1.7 mmol), 100 mg
of mesitylene (internal standard) and 1.0 mol% of 1a–
13a as catalyst (17 mmol) were dissolved in 2 ml of dry
toluene. After addition of 615 ml of TBHP solution
(5.5 M) the reaction mixture was stirred for up to 16 h
at 55°C.
The course of the reaction was monitored by quanti-
tative GC-analysis. Samples were taken every 30 min,
diluted with dichloromethane, and chilled in an ice
bath. For the destruction of hydroperoxide and re-
moval of water a catalytic amount of manganese diox-
ide and magnesium sulfate was added. The ee and
conversion was determined on a chiral GC column. The
conversion was calculated from a calibration curve
(r2=0.999) recorded prior to use. The products were
identified by GC–MS and co-injection of reference
substances.
4.5.3. MoO2{(1R,2R,4R)-1,7,7-trimethyl-2-(2%-pyridyl)-
bicyclo[2.2.1]heptan-2-olato}2 (12a)
EA, IR (KBr), 1H- and 13C-NMR data were in
agreement with Refs. [1b,5].
4.5.4. MoO2{(1S,3R,4S,5R)-1-isopropyl-4-methyl-3-
(2-pyridyl)bicyclo[3.1.0]hexane-3-olato}2 (13a)
Yield: 81.0%. Anal. Found: C, 61.56; H, 6.95; N,
4.68. Calc. for C40H30MoN2O4 (588.50): C, 61.22; H,
6.85; N, 4.76%. IR (KBr, w cm–1): 3046 m, 2948 s, 2871,
1602, 1473 s, 1437 s, 1365 m, 1292, 1159 m, 1088 m,
1053 m, 1020 m, 923 vs (MoꢀO), 906 vs (MoꢀO), 781 s,
1
764 s, 696 m, 642 m, 570m, 534 m. H-NMR (CD2Cl2,
300 MHz, r.t., l ppm): 8.60 (d, 2H, H6%); 7.73 (t, 2H,
H4%); 7.36 (d, 2H, H3%); 7.15 (t, 2H, H5%); 3.04–3.00 (m,
4H); 2.43 (br, 4H); 2.28–1.98 (m, 4H); 1.46–1.18 (m,
6H); 1.12 (d, 6H, CH3); 0.85 (d, 6H, CH3); 0.84 (d, 6H,
CH3); 0.57 (s, 2H). 13C-NMR (CD2Cl2, 300 MHz, r.t.,
Acknowledgements
This work was supported by PRAXIS XXI, Project
(2/2.1/QUI/419/94). These authors are grateful to

F.E. Ku¨hn et al. / Journal of Organometallic Chemistry 621 (2001) 207–217
217
ITQB/Universidade Nova de Lisboa, 1999. (d) F.E. Ku¨hn, A.M.
Santos, A.D. Lopes, I.S. Gonc¸alves, E. Herdtweck, C.C. Roma˜o,
J. Mol. Cat. A: Chem. (2000) in press. (e) M.D. Capparelli, B.
Pigott, S.D. Thorpe, S.F. Wong, R.M. Sheppard, Inorg. Chim.
Acta 106 (1985) 19.
DAAD and CRUP (INIDA and Acc¸o˜es Integradas
Programme) for generous support. A.D.L. and J.E.B.
thank PRAXIS XXI, and A.M.S. acknowledges the
Bayerische Forschungsstiftung for a fellowship. The
authors wish to thank Professor W.A. Herrmann for
continuous support.
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