Studies on olefin epoxidation with t-BuOOH catalysed by dioxomolybdenum(VI) complexes of a novel chiral pyridyl alcoholate ligand

Article abstract of DOI:10.1039/b102523f

The chiral dioxomolybdenum(VI) complexes [MoCl{(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)mentholato}(O)₂ (THF)] and [Mo{(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)mentholato}₂(O) ₂] have been prepared in good yields by reaction of the solvent substituted complex [MoCl₂O₂(THF)₂] with one or two equivalents of chiral 2′-pyridyl alcohol. The optically active aminoalcohol was obtained by reaction of 2-pyridyllithium with (-)-(2S,5S)-8-trimethylsilyloxymenthone. The complexes are active catalysts in the homogeneous epoxidation of cyclic and linear olefins, dienes and terpenes by t-BuOOH. They present remarkable activity and excellent product selectivity in cyclooctene epoxidation (cyclooctene oxide was obtained in quantitative yield). In the case of limonene, regioselectivity is high in favour of the epoxidation of the internal cyclic double bond. Ring opening activity was also observed for α-pinene oxide, producing campholenic aldehyde and epoxy campholenic aldehyde.

Full text of DOI:10.1039/b102523f

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Studies on oleÐn epoxidation with t-BuOOH catalysed by dioxo-
molybdenum(VI) complexes of a novel chiral pyridyl alcoholate ligand
Anabela A. Valente,a Isabel S. Gonc
Ó
alves,*a Andre

D. Lopes,a Jose

E. Rodr•
a-Merad

guez-Borges,b
Martyn Pillinger,a Carlos C. Romao,*c Joa
8
8
o Rochaa and Xerardo Garc•

a Departamento de Qu•
E-mail: igoncalves=dq.ua.pt; Fax: ]351 234 270084
b Departamento de Qu•mica da Faculdade de Ciencias do Porto, Rua do Campo Alegre,
87-4169007 Porto, Portugal
c Instituto de T ecnologia Qu•mica e Biolo
Quinta do Marques, EAN, Apt 127, 2781-901 Oeiras, Portugal
d Departamento de Qu•mica Organica, Facultade de Farmacia, Universidade de Santiago de

mica, Universidade de Aveiro, 3810-193 Aveiro, Portugal.

ü
6


gica da Universidade Nova de L isboa,
ü


Compostela, 15706 Santiago de Compostela, Spain
Received (in Montpellier, France) 19th March 2001, Accepted 27th April 2001
First published as an Advance Article on the web 8th June 2001
The chiral dioxomolybdenum(VI) complexes [MoClM(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)mentholatoN(O) -
2
(
THF)] and [MoM(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)mentholatoN (O) ] have been prepared in good yields
2
2
by reaction of the solvent substituted complex [MoCl O (THF) ] with one or two equivalents of chiral 2@-pyridyl
2
2
2
alcohol. The optically active aminoalcohol was obtained by reaction of 2-pyridyllithium with ([)-(2S,5S)-8-trimethyl-
silyloxymenthone. The complexes are active catalysts in the homogeneous epoxidation of cyclic and linear oleÐns,
dienes and terpenes by t-BuOOH. They present remarkable activity and excellent product selectivity in cyclooctene
epoxidation (cyclooctene oxide was obtained in quantitative yield). In the case of limonene, regioselectivity is high
in favour of the epoxidation of the internal cyclic double bond. Ring opening activity was also observed for
a-pinene oxide, producing campholenic aldehyde and epoxy campholenic aldehyde.
Epoxides are important organic intermediates since they
undergo ring-opening reactions with a variety of reagents to
give mono- or bi-functional organic products.1 In general,
epoxides can be prepared by oxidation using hydrogen per-
oxide or alkylhydroperoxides in the presence of high-valent
early transition-metal catalysts.2 Dioxomolybdenum(VI)
complexes have proven to be particularly e†ective catalysts
or catalyst precursors for the epoxidation of oleÐns. Rep-
resentative general formulae include [MoX O (L1) ],
[MoCl(L*)(O) (S)] and [Mo(L*) (O) ] (L* \ bidentate chiral
2
2
2
2@-pyridyl alcoholate, S \ monodentate neutral solvent
molecule) have recently been described.6 These homogeneous
catalysts showed good activity in the epoxidation of trans-
methylstyrene using t-butyl hydroperoxide (t-BuOOH), but
the enantiomeric excesses were no higher than 25%.6a,d The
present work concerns the synthesis and characterisation of
new chiral dioxomolybdenum(VI) pyridyl alcoholate complex-
es of the type [MoCl(L*)(O) (THF)] and [Mo(L*) (O) ], and
2
2
n
2
2
2
[
MoX(L2) (O) (L1) ] and [Mo(L2) (O) (L1) ]. The ligand sur-
an evaluation of their catalytic activity in the epoxidation of
oleÐns other than trans-methylstyrene, namely 1-octene, 2-
octene, cyclooctene, limonene, a-pinene and styrene.
m
2
n
m
2
n
rounding of the molybdenum(VI) centre can be Ðne-tuned by
either variation of X (Cl, Br, CH ) or L [mono- or bidentate
3
neutral (L1) or anionic (L2) N,O,S-ligand].3 Oxo complexes
with nitrogen, oxygen and/or sulfur donor ligands are of
special interest due to their relevance to the active sites of
certain molybdoenzymes. Asymmetric catalysis is made pos-
sible by the presence of chiral chelating ligands.4 One of the
difficulties in this area is the development of ligands that are
stable to oxidation and straightforward to synthesise, with the
possibility of changing electronic and steric characteristics by
simple variation of the starting material.
Dioxomolybdenum(VI) complexes containing achiral 2@-
pyridyl alcoholate ligands have been shown to have great
potential in the oxidation of terminal oleÐns with molecular
oxygen.5 The anionic ligand complexes the metal centre with
a coordinative bond to the nitrogen of the pyridine ring and a
covalent single bond to the alcoholate oxygen. A broad
variety of the parent alcohol ligands are generally accessible
by the reaction of 2-lithiopyridine with either symmetrical or
unsymmetrical ketones, yielding achiral or chiral molecules,
respectively. Dioxomolybdenum(VI) complexes of the type
Results and discussion
Synthesis of dioxomolybdenum(VI) complexes
The starting material used for the synthesis of the chiral
ligand was cis-p-menthane-3,8-diol, a commercially available
natural product. Oxidation of this diol with CrO gives the
3
ketone derivative (])-(2R,5S)-2-(1-hydroxy-1-methylethyl)-5-
methylcyclohexanone (1).7 Treatment of 1 with (CH ) SiCl in
3
3
CH Cl gives ([)-(2S,5S)-8-trimethylsilyloxymenthone (2).
2
2
The 2@-pyridyl alcohol ligand 3 can then obtained as the sole
diastereomer (100% diastereoselectivity) by a method involv-
ing condensation of 2-pyridyllithium with the chiral ketone 2
(Scheme 1).5,6a,d,8
Reaction of the chiral 2@-pyridyl alcohol ligand 3 with
[MoCl O (THF) ] in CH Cl , in a 1 : 1 molar ratio, gives the
2
2
2
2 2
chiral complex [MoClM(1R,2S,5S)-8-trimethylsilyloxy-1-(2-
pyridyl)mentholatoN(O) (THF)] (4) in nearly quantitative yield
2
DOI: 10.1039/b102523f
New J. Chem., 2001, 25, 959È963
959
This journal is ( The Royal Society of Chemistry and the Centre National de la Recherche ScientiÐque 2001

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free ligand (d 160.11). This indicates a shift of electron density
from the aromatic ring to the molybdenum centre. Unfor-
tunately, in CDCl it is not possible to observe the signals for
3
the quaternary alcoholate carbon atoms (C1) because they are
hidden under the solvent peak.
Catalysis of oxidation reactions
The catalytic performance of [MoClM(1R,2S,5S)-8-trimethyl-
Scheme 1
silyloxy-1-(2-pyridyl)mentholatoN(O) (THF)] (4) was studied
2
for the epoxidation of a variety of oleÐns using t-BuOOH as
after evaporation of the reaction mixture and washing with
hexane. The driving force for this reaction is most likely the
formation of a stable Ðve-membered ring chelate (Scheme 2).
Complex 4 is more soluble in organic solvents than other
related complexes of the type [MoCl O L],3 and does not
oxidant at 55 ¡C under air atmosphere (1 atm), without
solvent. The catalyst is active in the oxidation of all these sub-
strates. The conversion vs. time proÐles are shown in Fig. 1
and reveal the di†erent reactivity of 4 towards the various
cyclic oleÐns. We were unable to detect any induction period
2
2
precipitate from the reaction mixture (it is signiÐcantly soluble
in diethyl ether). It can only be puriÐed by washing with
hexane or pentane. When the reaction is performed in
dichloromethane or THF, complexes of the type
in all cases. Initial activities varied between 7.2 mol mol ~1
Mo
h~1 for styrene and 229.6 mol mol ~1 h~1 for cyclooctene
Mo
(Table 1). With the exception of a-pinene, the main reaction
product was the corresponding epoxide. In the absence of
catalyst (under identical reaction conditions) no reaction was
observed.
[
MoCl(L*)(O) (THF)] are produced but, for example, disso-
2
lution and recrystallisation of 4 from acetonitrile gives the ace-
tonitrile adduct [MoClM(1R,2S,5S)-8-trimethylsilyloxy-1-(2-
The selectivity to epoxide vs. conversion proÐles are shown
pyridyl)mentholatoN(O) (NCMe)], as evidenced by 1H NMR
in Fig. 2. The complex [MoCl(L*)(O) (THF)] (4) is very e†ec-
2
2
and elemental analysis.
tive for the epoxidation of cyclooctene. Within 24 h the reac-
tion was complete and selectivity towards the epoxide was
98.8% (Table 1). The corresponding diol was formed as a
minor byproduct. Catalytic activity was very high during the
Ðrst 15 min but then decreased signiÐcantly (Fig. 1). Similar
autoretardation e†ects were reported for other dioxomolyb-
denum(VI) complexes used as catalysts under identical reaction
conditions.10 These e†ects were attributed to the reaction of
the active Mo complex with t-butyl alcohol, which is inevita-
bly formed during the epoxidation reaction by decomposition
of t-BuOOH (used in excess).
Styrene oxidation in the presence of complex 4 produced
styrene epoxide as the only product up to 29% conversion (at
7 h, Fig. 1 and 2). At 24 h styrene conversion was 49.8% and
the selectivity to the epoxide dropped to 54.0% due to the
formation of the corresponding diol (28.1% selectivity) and
smaller amounts of other unidentiÐed products (Table 1).
Styrene oxide yields (ca. 25% at 24 h) are comparable to
those reported for other octahedrally coordinated dioxo-
molybdenum(VI) complexes, under identical reaction condi-
tions.3c The lower reactivity of styrene to epoxide formation
compared to aliphatic cyclic oleÐns such as cyclooctene may
be due in part to the presence of the electron attracting aro-
Scheme 2
The
dioxomolybdenum(VI)
complex 5 was prepared by three di†erent processes: (a) treat-
ment of [MoCl O (THF) ] with 2 equiv. of the ligand under
bis-2@-pyridyl
alcoholate
2
2
2
reÑux; (b) treatment of [MoCl O (THF) ] with 2 equiv. of the
2
2
2
ligand and 2 equiv. of TlOEt at room temperature; (c) treat-
ment of [Mo(acac) O ] (a common starting material for
2
2
ligand exchange reactions5,6a,b) with 2 equiv. of the ligand
under reÑux. In all three cases the corresponding molybdenum
complex was obtained in high yield. Complexes 4 and 5 are
air and moisture sensitive and must be handled and stored
under a moisture-free inert gas atmosphere.
Complexes 4 and 5 display symmetric and asymmetric IR
stretching vibrations for the cis-dioxo unit in the expected
range (940È910 cm~1).3,9 The other bands in the IR spectra
are assigned to the vibrational signals of the bound ligands.
The 1H NMR spectrum of complex 4 shows the peaks corre-
sponding to the coordinated THF and the chiral ligand. The
1
3C NMR spectra demonstrate that the ligand is bound to the
dioxomolybdenum core. Thus, the signal for the 2@-carbon
atom of the pyridine ring is found at d 168.32 for 4 and d
1
66.63 for 5, both shifted downÐeld compared to that for the
Fig. 1 Conversion proÐles for the di†erent oleÐns in the presence of
4
: cyclooctene (L); styrene (]); a-pinene (|); (R)-(])-limonene (]).
960
New J. Chem., 2001, 25, 959È963

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Table 1 OleÐn oxidations using t-BuOOH in the presence of 4
Substrate
Initial activitya/mol mol ~1 h~1
Conversionb (%)
Product
Selectivityc (%)
Mo
229.6
100.0
98.8
1
.2
42.0
63.0
11.7
6
6
.5
3.2
2
4.1
90.4
(89.5)
71.2
(82.6)
(
20.6)d
9
.4
(
6.2)
7.2
49.8
54.0
2
8.1
a Calculated as mmol converted substrate/(mmol catalyst ] 0.25 h). b Converted substrate after 24 h of reaction. c With the exception of cyclo-
octene oxidation, other unidentiÐed products were formed during the reaction. d Results in parentheses are for the corresponding reaction with
(S)-([)-limonene.
matic ring, which decreases the electron density at the oleÐnic
double bond, making it less susceptible to electrophilic attack.
A comparison of turnover frequencies of oleÐn epoxidation
with complex 4 shows that it is less reactive towards the ter-
minal carbonÈcarbon double bond of 1-octene (which has a
lower electronic density) than a more substituted oleÐn such
as 2-octene: turnover frequencies (during 4 h of reaction) were
oxide on a Lewis or Bronsted acidic centre, involving ring
Ž
opening of the epoxide.11 A similar mechanism may be
involved for complex 4, since molybdenum is in its highest
oxidation state (6]) and has Lewis acid character. Further-
more, a preliminary experiment using a-pinene oxide as the
substrate, under identical reaction conditions, produced cam-
pholenic aldehyde and epoxy campholenic aldehyde (20 and
39% selectivity, respectively, at 65% a-pinene oxide
conversion).
The reactivity of complex 4 (which has a stereogenic center)
towards the oxidation of (1R)-(])-a-pinene or (1S)-([)-a-
pinene was similar. These stereoisomeric oleÐns were used as
starting materials in separate reactions and the results are
roughly the same as those obtained for racemic a-pinene: 57.7
and 54.6% conversion for (1R)-(])-a-pinene and (1S)-([)-a-
pinene, respectively, at 24 h. These results suggest that both
stereoisomers of a-pinene react at the same rate with complex
4. The product distribution (not including stereochemistry)
remained practically unchanged. Thus, after 24 h, selectivities
1
.4 mol mol ~1 h~1 and 10.6 mol mol ~1 h~1 for 1-
oct
Mo
oct
Mo
octene and 2-octene, respectively. In both systems, the corre-
sponding epoxide was the only observed product.
The oxidation of a-pinene in the presence of complex 4 gave
a broad product spectrum, including a-pinene oxide, cam-
pholenic aldehyde and epoxy campholenic aldehyde, and
small amounts of other unidentiÐed products (Table 1). Selec-
tivity to a-pinene oxide reached a maximum of ca. 53% at
25% conversion (Fig. 2), and after 24 h it decreased to 11.7%
at 63.0% conversion (Table 1). Campholenic aldehyde, an
important intermediate used in the synthesis of sandalwood
fragrances, may be formed by the rearrangement of a-pinene
New J. Chem., 2001, 25, 959È963
961

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substituted complex 4 is more active than 5. Activity and
selectivity are highest in cyclooctene epoxidation (cyclooctene
oxide was obtained in quantitative yield). Regioselective epox-
idation of the more substituted internal, or cyclic, double
bonds is observed. In spite of being chiral, complexes 4 and 5
do not discriminate signiÐcantly between both enantio-
merically pure forms of the substrates a-pinene and limonene.
Ring opening activity was also observed for a-pinene oxide,
producing campholenic aldehyde and epoxy campholenic
aldehyde.
Experimental
General
All preparations and manipulations were carried out using
standard Schlenk techniques under an atmosphere of nitro-
gen. Solvents were dried by standard procedures (THF, n-
hexane and Et O over Na/benzophenone ketyl; CH Cl and
2
2 2
NCCH over CaH ), distilled under nitrogen and kept over 4
3
2
Fig. 2 Selectivity to epoxide vs. conversion for the di†erent oleÐns in
the presence of 4: cyclooctene oxide (]); styrene oxide (L); a-pinene
oxide (]); limonene oxide (K).
A
Ž
molecular sieves (3 A
Ž
for NCCH ). Microanalyses were per-
3
formed at the ITQB by Mrs Zara Tavares. 1H and 13C NMR
spectra were recorded at 300 and 75.4 MHz, respectively, on a
Bruker CXP 300 spectrometer. IR spectra were measured on a
Unican Mattson Mod 7000 FTIR spectrometer using KBr
pellets or Nujol mulls.
to a-pinene oxide, campholenic aldehyde and epoxy cam-
pholenic aldehyde were 15.3, 8.6 and 50.2%, respectively, for
The precursor materials MoCl O 12 and [MoCl O -
2
2
2 2
(
1R)-(])-a-pinene oxidation, and 11.5, 9.8 and 58.1%, respec-
(THF) ]13 were prepared as described previously. Oxidation
2
tively, for (1S)-([)-a-pinene oxidation. It was not possible to
identify the stereochemical nature of the di†erent products to
check if these reactions are stereospeciÐc.
of (])-cis-p-menthane-3,8-diol (Aldrich) with CrO gave (])-
3
(2R,5S)-2-(1-hydroxy-1-methylethyl)-5-methylcyclohexanone
(1).7 1-Octene (98%), 2-octene (97%), cyclooctene (95%),
styrene (99%), a-pinene (98%), (1R)-(])-a-pinene (98%), (1S)-
([)-a-pinene (98%), (R)-(])-limonene (97%, 98% ee) and (S)-
([)-limonene (96%) were obtained from Aldrich.
The catalytic activity of complex 4 in the oxidation of (R)-
])-limonene or (S)-([)-limonene was similar (ca. 90% con-
(
version at 24 h, Table 1). Limonene oxide was always the
main product and 8,9-epoxy-p-menth-1-ene was formed as a
side product. For both substrates, maximum selectivity to
limonene oxide was ca. 86% at 59% conversion (Fig. 2), which
decreased to 71.2 and 82.6% for (R)-(])-limonene and (S)-([)
Synthesis of ligands
(
Ô)-(2S,5S)-8-Trimethylsilyloxymenthone (2). (CH ) SiCl
3 3
(
2.24 g, 20.5 mmol) was added dropwise via syringe to a solu-
-
limonene oxidation, respectively (at ca. 90% conversion after
tion of (])-(2R,5S)-2-(1-hydroxy-1-methylethyl)-5-methyl-
cyclohexanone (1) (2.34 g, 13.7 mmol), DMAP (1.68 g, 13.7
mmol) and Et N (1.39 g, 13.7 mmol) in CH Cl (15 mL) at
24 h, Table 1).
The catalytic performance of [MoM(1R,2S,5S)-8-trimethyl-
silyloxy-1-(2-pyridyl)mentholatoN (O) ] (5) was compared to
3
2 2
2
2
0 ¡C. The reaction mixture was stirred for 2 h at room tem-
perature. The mixture was diluted with water (50 mL) and
extracted with diethyl ether (3 ] 80 mL). The combined
that of [MoClM(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)
mentholatoN(O) (THF)] (4) for the oxidation of cyclooctene
2
and (R)-(])-limonene. The initial activity of 5 (54.2 and 6.7
organic layers were washed with H O (100 mL) and brine (100
mL). The organic solution was dried over Na SO and the
solvent removed to give a colourless oil (3.6 g), this was puri-
mol mol ~1 h~1 for cyclooctene and limonene, respectively)
2
Mo
was signiÐcantly lower than that observed for 4 (Table 1). This
2
4
may be accounted for by the fact that compound 5 has a more
rigid coordination sphere with two bulky bidentate N,O-
ligands. In the case of 4, the presence of a labile coordinated
THF molecule may facilitate the formation of the catalytically
active species either by activation of the t-BuOOH or the
oleÐn. Despite the slower initial reaction rate, within 24 h the
oleÐn conversion in the presence of 5 was similar to that
obtained in the presence of 4: 100% for cyclooctene and
Ðed by Ñash chromatography (SiO ; hexaneÈAcOEt 8 : 2) to
2
a†ord the pure oil compound 2 (3.31 g, 99%). Anal. calc. for
C
1
H O Si (242.43): C, 64.40; H, 10.81; found: C, 64.38; H,
13 26 2
0.76%. [a]20 [ 25.1¡ (c 1, CHCl ). IR (Nujol, l/cm~1): 2958
D
3
vs, 2928 vs, 2873 s, 2850 m, 1711 vs, 1456 s, 1378 s, 1362 s,
260 vs, 1249 vs, 1206 m, 1182 s, 1151 vs, 1122 s, 1091 s, 1038
1
vs, 839 vs, 755 vs, 712 m, 685 m, 542 s, 491 m. 1H NMR
(
3
1
CDCl , 300 MHz, r.t., d): 2.36È2.28 (m, 3H); 2.04È1.90 (m,
8
8.4% for (R)-(])-limonene. Product selectivity was roughly
3
H); 1.60È1.44 (m, 2H); 1.37 (s, 3H, CH ); 1.27 (s, 3H, CH );
the same for both catalysts. Cyclooctene oxidation in the pres-
3
3
.02 (d, 3H, CH ); 0.11 (s, 9H, CH ).
ence of 5 gave a quantitative yield of cyclooctene oxide while
3
3
(
R)-(])-limonene oxidation produced limonene oxide and 8,9-
(
+ )-(1R,2S,5S)-8-Trimethylsilyloxy-1-(2-pyridyl)menthol
3). A solution of 2-bromopyridine (1.83 g, 11.6 mmol) in
diethyl ether (4 mL) was added to a solution of nBuLi (6.7 mL,
.6 M in hexane, 10.7 mmol) in diethyl ether (100 mL) at
70 ¡C. The red solution was stirred for 30 min at [70 ¡C
epoxy-p-menth-1-ene with 79.7 and 7.1% selectivity, respec-
(
tively, at 88.4% conversion.
1
[
Conclusions
and then treated with a solution of 2 (2.16 g, 8.9 mmol) in
diethyl ether (6 mL). The reaction mixture was stirred for 30
min at [70 ¡C. The mixture was diluted with water (50 mL)
and extracted with diethyl ether (3 ] 80 mL). The combined
The chiral oxomolybdenum(VI) derivatives [MoClM(1R,2S,5S)-
8
-trimethylsilyloxy-1-(2-pyridyl)mentholatoN(O) (THF)]
(4)
2
and [MoM(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)mentho-
latoN (O) ] (5), prepared from [MoCl O (THF) ] and the
organic layers were washed with H O (100 mL) and brine (100
2
2
2 2
2
2
chiral ligand, are active catalysts in the homogeneous epoxi-
mL). The organic solution was dried over Na SO and the
2
4
dation of cyclic and linear oleÐns by t-BuOOH. The mono-
solvent removed to give an oil (3.28 g), this was puriÐed by
962
New J. Chem., 2001, 25, 959È963

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Ñash chromatography (SiO ; hexaneÈAcOEt 9 : 1) to a†ord
the pure colourless oil compound 3 (2.43 g, 85%). Anal. calc.
0.61 (s, 6H, CH ); 0.06 (s, 18H, CH ). 13C NMR (CDCl , 300
2
3
3
3
MHz, r.t., d): 166.63 (C2{+); 146.58; 137.26; 121.18; 54.62;
for C
H
NO Si (321.53): C, 67.24; H, 9.72; N, 4.35; found:
52.44; 34.21; 30.53; 27.30; 26.51; 26.29; 20.91; 1.49
1
8 31
2
C, 67.19; H, 9.68; N, 4.25%. [a]20 ] 0.9¡ (c 1, CHCl ). IR
D
3
(
Nujol, l/cm~1): 3441 vs, 3052 s, 3001 s, 2951 vs, 2868 s, 2843
Catalytic reactions with the molybdenum compounds
m, 1587 vs, 1568 s, 1455 s, 1431 s, 1398 s, 1384 s, 1366 m, 1287
m, 1251 s, 1213 m, 1173 s, 1163 s, 1141 m, 1121 m, 1092 m,
The catalytic reactions were performed under an air atmo-
sphere, in a reaction vessel equipped with a magnetic stirrer,
immersed into a thermostated oil bath (55 ¡C). A 1% molar
ratio of catalyst/substrate was used (7.3 mmol oleÐn and 73
lmol complex 4 or 5) and 5.5 M t-butyl hydroperoxide in
decane (2 mL, 11 mmol) was used as oxidant. Samples were
withdrawn periodically and analysed using a gas chromato-
graph (Varian 3350) equipped with a capillary column (SPB-5,
20 m ] 0.25 mm ] 0.25 lm) and a Ñame ionisation detector.
The products were quantiÐed using calibration curves and n-
nonane or undecane as internal standard (added after the
reaction), and identiÐed by GC-MS (HP 5890 Series II GC;
HP 5970 Series Mass Selective Detector) using He as carrier
gas.
1001 vs, 956 m, 922 m, 891 vs, 841 vs, 781 s, 752 vs, 734 m, 559
m. 1H NMR (CDCl , 300 MHz, r.t., d, see Scheme 1 for atom
3
numbering): 8.48 (d, 1H, H6{); 7.81 (d, 1H, H4{); 7.67È7.62 (m,
1
H, H5{); 7.10È7.06 (m, 1H, H3{); 5.51 (s, 1H, OH); 2.31È2.25
(
m, 1H); 1.91È1.77 (m, 4H); 1.52È1.37 (m, 2H); 1.21 (s, 3H,
CH ); 1.19È1.09 (m, 1H); 0.85 (d, 3H, CH ); 0.63 (s, 3H, CH ),
3
3
3
0
1
5
.07 (s, 9H, CH ). 13C NMR (CDCl , 300 MHz, r.t., d):
3
3
60.11 (C2{); 148.00; 136.97; 121.28; 119.93; 80.09 (C1); 78.95,
2.23; 50.03; 34.98; 32.19; 27.99; 24.07; 22.29; 2.75.
Synthesis of dioxomolybdenum(VI) complexes
MoCl{(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)menth-
[
olato}(O) (THF)] (4). A solution of [MoCl O (THF) ] (0.53
2
2 2
2
g, 1.54 mmol) in CH Cl (10 mL) was treated with the amino-
Acknowledgements
The authors are grateful to FCT, POCTI and FEDER for
Ðnancial support (Project PCTI/1999/QUI/32889). The
8
authors also thank DAAD and CRUP (INIDA and AccÓ oes
Integradas Programme) for generous support.
2
2
alcohol ligand 3 (0.50 g, 1.54 mmol). The resulting turbid solu-
tion was stirred for a further 30 min. The solvent was
evaporated and the product washed with hexane, then dried
under vacuum (0.80 g, 93%). Anal. calc. for
C
H
ClMoNO Si (556.03): C, 47.52; H, 6.89; N, 2.52;
2
2 38
5
found: C, 47.48; H, 6.75; N, 2.45%. IR (KBr, l/cm~1): 3105
m, 2956 s, 2924 m, 2868 m, 1620 s, 1476 m, 1455 s, 1440 s,
References
1370 m, 1296 m, 1253 s, 1167 m, 1055 s, 940 vs, 916 vs
1
J. W. Schwesinger and T. Bauer, in Stereoselective Synthesis, ed.
G. Helmchen, R. W. Ho†mann, J. Mulzer and E. Schaumann,
Houben Weyl Thieme, New York, 1995, vol. E21e, pp. 4599È
(
(
7
1
3
Mo2O), 881 m, 844 s, 753 s, 687 s, 647 m, 583 m. 1H NMR
CDCl , 300 MHz, r.t., d): 8.91 (br, 1H, H6{); 7.94 (t, 1H, H4{);
3
.47È7.45 (m, 2H, H5{@3{); 3.83 (s, THF); 2.03È2.01 (br, 3H);
4
648.
.90È1.81 (m, 2H); 1.86 (s, THF); 1.63È1.57 (m, 1H); 1.33 (s,
2
3
(a) K. A. Jorgensen, Chem. Rev., 1989, 89, 431; (b) P. Chaumette,
H. Mimoun and L. Saussine, J. Organomet. Chem., 1983, 250, 291,
and references therein.
H, CH ); 1.26È1.24 (m, 1H); 1.02È0.99 (m, 1H); 0.88 (d, 3H,
3
CH ); 0.53 (s, 3H, CH ); 0.10 (s, 9H, CH ). 13C NMR
(
1
3
3
3
3
(a) F. E. Ku
Goncalves, A. D. Lopes and C. C. Roma
999, 583, 3; (b) F. E. Ku
tweck, J. J. Haider, C. C. Roma
Ž
hn, E. Herdtweck, J. J. Haider, W. A. Herrmann, I. S.
CDCl , 300 MHz, r.t., d): 168.32 (C2{); 151.30; 137.97;
23.22; 123.11; 120.51; 67.60 (THF); 51.23; 50.96; 47.79;
3.53; 31.02; 29.56; 25.83; 24.66 (THF); 24.53; 20.69; 0.86.
3
Ó
8
o, J. Organomet. Chem.,
1
Ž
hn, A. D. Lopes, A. M. Santos, E. Herd-
8
o and A. G. Santos, J. Mol. Catal.
A: Chem., 2000, 151, 147; (c) F. E. Ku
Ž
hn, A. M. Santos, A. D.
[
Mo{(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)menth-
Lopes, I. S. GoncÓ alves, E. Herdtweck and C. C. Romao, J. Mol.
Catal A: Chem., 2000, 164, 25; (d) A. D. Lopes, PhD thesis,
ITQB/Universidade Nova de Lisboa, Portugal, 1999; (e) J. J.
Haider, PhD thesis, Technischen Universita
Germany, 1999; ( f ) F. E. Kuhn, A. M. Santos, I. S. Gonc
C. Romao and A. D. Lopes, Appl. Organomet. Chem., 2001, 15,
43.
S.-I. Yamada, T. Mashiko and S. Terashima, J. Am. Chem. Soc.,
8
olato} (O) ] (5). Method (a). A solution of [MoCl O (THF) ]
0.32 g, 0.93 mmol) in CH Cl (10 mL) was treated with 2
equiv. of the aminoalcohol ligand 3. The solution became
milky and after 2 h at reÑux, the mixture was evaporated to
dryness to yield a powder, which was washed with hexane
2
2
2 2
2
(
2
2
Ž
t
Mu
Ó
Ž
nchen,
alves, C.
Ž
8
(
0.67 g, 94%).
4
5
6
1
977, 99, 1988.
Method (b). A solution of [MoCl O (THF) ] (0.32 g, 0.93
2
2
2
W. A. Herrmann, G. M. Lobmaier, T. Priermeier, M. R. Mattner
and B. Scharbert, J. Mol. Catal., 1997, 117, 455.
mmol) in CH Cl (10 mL) was treated with 2 equiv. of the
2
2
alcohol ligand 3 and 2 equiv. of TlOEt. The reaction mixture
was left stirring for 4 h and then the suspension was evapo-
rated to dryness. After washing with hexane, the residue was
extracted with dichloromethane and the solution taken to
dryness to yield a powder, which was washed with hexane
several times (0.63 g, 88%).
(a) W. A. Herrmann, J. J. Haider, J. Fridgen, G. M. Lobmaier
and M. Spiegler, J. Organomet. Chem., 2000, 603, 69; (b) S.
Bellemin-Laponnaz, K. S. Coleman and J. A. Osborn, Poly-
hedron, 1999, 18, 2533; (c) S. Bellemin-Laponnaz, K. S. Coleman,
P. Dierkes, J.-P. Masson and J. A. Osborn, Eur. J. Inorg. Chem.,
2
000, 1645; (d) F. E. Ku
Goncalves, J. E. Rodr•guez-Borges, M. Pillinger and C. C.
Romao, J. Organomet. Chem., 2001, 621, 207.
Ž
hn, A. M. Santos, A. D. Lopes, I. S.
Ó

Method (c). A solution of [Mo(acac) O ] (0.25 g, 0.77
2
2
8
mmol) in THF (10 mL) was treated with 2 equiv. of the
aminoalcohol ligand 3 (0.49 g, 1.53 mmol). The reaction
mixture was reÑuxed for 2 h and then the solution was evapo-
rated to dryness. The oily solid was washed several times with
hexane and dried to yield a white powder (0.54 g, 92%). Anal.
7
(a) H. E. Ensley, C. A. Parnell and E. J. Corey, J. Org. Chem.,
1978, 43, 1610; (b) R. Ratcli†e and R. Rodehorst, J. Org. Chem.,
1970, 35, 4000.
8
9
W. A. Herrmann, J. Fridgen, G. M. Lobmaier and M. Spiegler,
New J. Chem., 1999, 23, 5.
W. P. Griffith, J. Chem. Soc. A, 1969, 211.
calc. for C
H
MoN O Si (769.00): C, 56.23; H, 7.86; N,
3
6 60
2 6 2
10 P. Ferreira, I. S. Gonc
Ó
alves, F. E. Ku
Ž
hn, A. D. Lopes, M. A.
3.64; found: C, 56.12; H, 7.75; N, 3.58%. IR (KBr, m/cm~1):
Martins, M. Pillinger, A. Pina, J. Rocha, C. C. Roma
8
o, A. M.
3071 m, 2949 s, 2868 m, 2846 m, 1569 s, 1519 s, 1476 m, 1455
Santos, T. M. Santos and A. A. Valente, Eur. J. Inorg. Chem.,
s, 1434 s, 1385 s, 1367 m, 1290 m, 1249 vs, 1202 m, 1160 s,
021 s, 959 vs, 922 vs, 907 vs (Mo2O), 856 m, 838 s, 776 s, 684
2000, 2263.
1
1
P. J. Kunkeler, J. C. Van der Waal, J. Bremmer, B. J. Zuurdeeg,
R. S. Dowing and H. Van Bekkum, Catal. L ett., 1998, 53, 135,
and references therein.
1
s, 644 m, 551 m. 1H NMR (CDCl , 300 MHz, r.t., d): 8.56 (br,
3
2
(
H, H6{); 7.72 (t, 2H, H4@); 7.26È7.24 (m, 4H, H5{@3{); 2.18È2.02
1
1
2
3
R. Colton and I. B. Tomkins, Aust. J. Chem., 1965, 18, 447.
W. M. Carmichael, D. A. Edwards, G. W. A. Fowles and P. R.
Marshall, Inorg. Chim. Acta, 1967, 1, 93.
m, 2H); 1.95È1.77 (m, 4H); 1.67È1.58 (m, 2H); 1.46È1.40 (m,
4
H); 1.16 (s, 6H, CH ); 1.04È0.97 (m, 4H); 0.84 (d, 6H, CH );
3
3
New J. Chem., 2001, 25, 959È963
963