Dioxomolybdenum(VI) complexes with naphtholate-oxazoline ligands in catalytic epoxidation of olefins

Article abstract of DOI:10.1016/j.molcata.2014.01.009

Synthesis, characterization and catalytic epoxidation experiments of two new dioxomolybdenum(VI) complexes [MoO₂(L)₂] (3a-b) equipped with O,N-bidentate naphtholate-oxazoline ligands L = 2a-b are described. Ligands 2a-b (2a = 2-(4,5-dihydrooxazol-2-yl)naphthalen-1-ol, 2b = 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)naphthalen-1-ol) were obtained via a two-step synthesis starting from 1-hydroxy-naphthoic acid. Complexes 3a-b were synthesized starting from [MoO₂(acac)₂] and obtained in good yields as air and moisture stable solids. The molecular structure of both complexes 3a-b were determined by single crystal X-ray diffraction analysis, showing the expected octahedral coordination of the Mo center by two bidentate ligands of 2a or 2b and two terminal oxo ligands. Interestingly, for complex 3b two different coordination isomers with regards to the orientation of the bidentate ligands (N,N-trans 3b and N,N-cis 3b'), were obtained in the solid state. Both complexes 3a-b show high catalytic activities and selectivities in the epoxidation of various terminal and internal olefins at low catalyst loadings of 0.05 mol% with tert-butylhydroperoxide. With cyclooctene TON of 5000 could be reached, for styrene selectivities of >90% were achieved.

Full text of DOI:10.1016/j.molcata.2014.01.009

Journal of Molecular Catalysis A: Chemical 385 (2014) 54–60
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Dioxomolybdenum(VI) complexes with naphtholate-oxazoline
ligands in catalytic epoxidation of olefins
Pedro Traar, Jörg A. Schachner, Bernhard Stanje, Ferdinand Belaj, Nadia C. Mösch-Zanetti∗
Institute of Chemistry, Karl–Franzens–University Graz, Stremayrgasse 16, Graz 8010, Austria
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 August 2013
Received in revised form 9 January 2014
Accepted 11 January 2014
Available online 21 January 2014
Synthesis, characterization and catalytic epoxidation experiments of two new dioxomolybdenum(VI)
complexes [MoO2(L)2] (3a-b) equipped with O,N-bidentate naphtholate-oxazoline ligands L = 2a-b
are described. Ligands 2a-b (2a = 2-(4,5-dihydrooxazol-2-yl)naphthalen-1-ol, 2b = 2-(4,4-dimethyl-
4,5-dihydrooxazol-2-yl)naphthalen-1-ol) were obtained via
a two-step synthesis starting from
1-hydroxy-naphthoic acid. Complexes 3a-b were synthesized starting from [MoO2(acac)2] and obtained
in good yields as air and moisture stable solids. The molecular structure of both complexes 3a-b were
determined by single crystal X-ray diffraction analysis, showing the expected octahedral coordination
of the Mo center by two bidentate ligands of 2a or 2b and two terminal oxo ligands. Interestingly, for
complex 3b two different coordination isomers with regards to the orientation of the bidentate ligands
(N,N-trans 3b and N,N-cis 3b’), were obtained in the solid state. Both complexes 3a-b show high catalytic
activities and selectivities in the epoxidation of various terminal and internal olefins at low catalyst load-
ings of 0.05 mol% with tert-butylhydroperoxide. With cyclooctene TON of 5000 could be reached, for
styrene selectivities of >90% were achieved.
Keywords:
Dioxomolybdenum(VI) complex
Epoxidation
Oxazoline
Homogeneous catalysis
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
developed [14–16]. One of the industrially used heterogeneous
epoxidation catalyst is formed by the reaction [Mo(CO)6] and alkyl-
The propensity of oxomolybdenum species to perform oxy-
gen atom transfer (OAT) reactions has been observed in the
realm of biology and has been exploited in industrial chem-
istry. Several Mo containing enzymes are known that take part
in various metabolic OAT reactions in the living cell [1–3]. The
mechanism of these molybdoenzymes is still under investiga-
tion; therefore several research groups including us have been
studying synthetic, functional or structural analogous molybde-
num complexes to further elucidate mechanistical details [4–12].
OAT reactions on an industrial scale include the epoxidation of
olefins. Epoxides are very important intermediates in the chem-
ical industry, in particular for the synthesis of various polymers
(polyglycols, polyamides, polyurethanes etc.) [13]. Production of
propylene oxide makes up for the biggest share on the market,
with a global capacity of eight million tons per year [14]. In order
to avoid the non-economical use of stoichiometric amounts of
oxidants like peracids, NaOCl or iodosobenzene, many different
transition metal catalysts, also containing molybdenum, have been
hydroperoxides, and many homogeneous molybdenum catalysts
have been investigated in order to improve this important reac-
tion [17–22]. Phenolate–oxazoline ligands were amongst the first
reported examples of active molybdenum(VI) epoxidation catalysts
and have been further investigated since [19,23–26].
We have an ongoing interest in the chemistry of dioxo-
molybdenum(VI) and oxorhenium(V) complexes using different
O,N-bidentate ligands. With
a phenolate–pyrazole ligand we
obtained very active molybdenum and rhenium epoxidation cat-
alysts for a range of substrates [27,28]. Employing O,N-Schiff base
ligands in dioxomolybdenum(VI) complexes we could selectively
epoxidize the challenging substrate styrene [29]. Also dimeric
Mo(V) complexes equipped with Schiff base ligands are active
epoxidation catalysts [30]. We are furthermore interested in
mechanistic aspects of OAT reactions relevant to metalloenzymes
[31–33]. Therefore, we would like to report on the synthe-
sis and characterization of two new entries into the family of
aryloxide–oxazoline ligands, namely naphtholate–oxazoline lig-
ands 2a-b and the dioxomolybdenum(VI) complexes 3a-b thereof.
Furthermore, complexes 3a-b were tested as potential catalysts in
the epoxidation of various challenging olefins. Thereby the influ-
ence of the aromatic moiety of the O,N-bidentate ligand can be
∗
Corresponding author. Tel.: +433163805286.
E-mail address: nadia.moesch@uni-graz.at (N.C. Mösch-Zanetti).
1381-1169/$ – see front matter © 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2014.01.009

P. Traar et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 54–60
55
Scheme 1. Synthesis of benzamides 1a-b and oxazoline ligands 2a-b (isolated yields in brackets).
Scheme 2. Synthesis of complexes 3a and 3b.
Table 1
studied and compared to the published phenolate–oxazoline com-
Selected IR bond stretching frequencies of ligands 2a-b and complexes 3a-b.
plexes.
Bond stretching frequencies, ꢀ (cm−1
)
2a
2b
3a
3b
2. Results and discussion
ꢀC
ꢀMo
1626
–
1620
–
1572
878, 866
1573
885, 867
N
Ligands 2a-b were synthesized via
a modified two step
O
reaction in analogy to published procedures [34,35]. There, the
authors started from 1-methoxynaphthalene in order to obtain
2-(1-methoxynaphthalen-2-yl)-4,4-dimethyl-4,5-dihydrooxazole,
which represents the methyl ether of ligand 2b [34,35]. In order
to obtain the free naphtholate–oxazoline ligands we started
from commercially available 1-hydroxy-2-naphthoic acid and the
respective aminoalcohol and synthesized the benzamides 1a-b
via a Steglich condensation in refluxing tetrahydrofuran (THF)
(Scheme 1). Optimal conditions for the condensation reaction of
1a-b were found using dicyclohexylcarbodiimid (DCC), 1-hydroxy-
2-naphthoic acid and the respective aminoalcohol in the ratio of
1/1.5/1.1 molar equivalents in the presence of a catalytic amount of
dimethylaminopyridine (5 mol%, DMAP). Amides 1a-b can be iso-
lated and purified by column chromatography or used directly in
a one pot synthesis for the next step (see Supporting Information).
The cyclization to obtain the respective oxazoline ligands 2a-b was
achieved in analogy to a published procedure with thionyl chloride
[36]. Compounds 2a-b represent bidentate O,N-coordinating
ligands, where the hydroxyl group is easily deprotonated by bases
like NEt3, whereby they become mono-anionic (Scheme 2).
Dioxomolybdenum(VI) complexes 3a-b were obtained by stir-
ring a mixture of [MoO2(acac)2] and two equivalents of the
corresponding ligand 2a or 2b in methanol for 1 h [23]. The so
obtained precipitates were filtered and washed with small amounts
of MeOH to give 3a-b in analytically pure form as orange–yellowish
solids (yield: 3a 78%; 3b 63%).
one N-donor and one naphthoxy group trans to the terminal oxo lig-
ands (N,O-isomer). The asymmetric coordination of the bidentate
ligands 2a-b creates a chiral environment around the Mo atom, so
that each of the three possible isomers forms a pair of diastereomers
ꢁ and ꢂ [23]. The occurrence of only one set of ligand resonances
in the proton spectrum of 3a-b evidences the formation of a C2-
symmetric isomer, either the N,N-isomer or O,O-isomer (Fig. 1).
The formation of complexes 3a-b was also apparent by IR spec-
troscopy (Table 1). Upon coordination of the respective ligand 2a-b
a shift to lower wave numbers of the ꢀC
vibration is observed
N
as well as the appearance of two diagnostic ꢀMo
vibrations
O
between 850 and 950 cm−1 [23,25,37–39]. Mass spectrometry as
well as elemental analysis are also consistent with the formula of
dioxomolybdenum(VI) complexes 3a-b.
Single crystals of 3a-b were obtained from concentrated solu-
tions of methanol. The C2-symmetric structures were confirmed
by single crystal X-ray diffraction analysis for both complex 3a-
b. Complex 3a displayed the O,O-isomer in the solid state (vide
infra). For compound 3b single crystals of two different colors were
obtained, with a majority of orange crystals and a small amount of
Both complexes are barely soluble in polar solvents like
methanol, chloroform or dichloroethane. For this reason 1H NMR
spectra of 3a-b had to be measured in deuterated methanol at
50 ◦C. Because of their low solubility we were unable to obtain
meaningful 13C NMR spectra. Due to the bidentate nature of lig-
ands 2a-b a total of three geometric isomers are possible for
disubstituted cis-dioxomolybdenum(VI) complexes, depending on
the coordinating atoms in trans position to the terminal oxo groups:
both N-donors trans to the terminal oxo ligands (N,N-isomer), both
naphthoxy groups trans to the terminal oxo ligands (O,O-isomer) or
Fig. 1. Possible geometrical and optical isomers of complexes 3a-b.

56
P. Traar et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 54–60
Scheme 3. Catalytic epoxidation of various olefins.
2008 [25]. In contrast to 3a, complex [MoO2(oz)2] displayed the
N,N-isomer in the solid state. Also, the related phenolate complex
to 3b [MoO2(ozMe2)], containing two methyl groups on each oxa-
zoline ligand, was fully structurally characterized [37]. In contrast
to 3b the N,N-isomer was described as the only observed isomer in
the solid state. Also a diasteromeric complex [MoO2(oz*)2] contain-
ing the chiral ligand (R)-2-(4-ethyl-4,5-dihydrooxazol-2-yl)phenol
was obtained with a published yield of 80% (Fig. 4) [23]. For the
complex [MoO2(oz*)2] single crystals could be grown containing
both the N,N- and the O,O-isomer [23]. Thus exact factors leading
to one over the other isomer are still not known.
2.1. Epoxidation of olefins
Complexes 3a and 3b were tested as catalysts for the
epoxidation of various terminal and internal olefins with tert-
butylhydroperoxide (TBHP) as oxidant (Scheme 3). Initially the
optimal conditions regarding solvent, catalyst and oxidant loading
were determined using the substrate cyclooctene. At first, the opti-
mal solvent at different temperatures was determined (Table 4). As
an example, the results for 3b are shown, which are also consistent
for 3a.
The best solvent found for epoxidations was 1,2-dichloroethane
(DCE) at 80 ◦C, where cyclooctene was converted to its epoxide in
>95% after 30 min. Next, the optimal catalyst and oxidant load-
ing were tested. The results for 3a are shown in Fig. 5, the same
conditions were found to be optimal for 3b.
The optimal conditions with regards to atom economy and reac-
tion time were found with 0.05 mol% of catalyst and 2 equiv. of
TBHP in DCE at 80 ◦C. Under these conditions a conversion of >95%
of cyclooctene was achieved within 90 min. A similar result was
obtained for 3b under the same conditions. With the optimized
reaction conditions a set of ten different terminal and internal
olefins were tested to further explore the reactivity profile of 3a-b.
Full details for the catalytic experiments are given in the Section 4.
Complexes 3a and 3b are catalytically active in the epoxida-
tion of various internal as well as terminal olefins. Internal olefins
(Table 1, Table 3, Table 5 entries 1, 3 and 5) are converted with
high yields and selectivities to their respective epoxides. For the
standard substrate cyclooctene, TOF of 9500 h−1 can be achieved.
Even with an electron poor terminal olefin like allylphenylether
(entry 6) complexes 3a-b show activity. Styrene (entry 4), which
is prone to further unwanted ring-opening reactions after epoxi-
dation, is converted with high selectivities of >90%. The sterically
demanding substrates cis- and trans-stilbene (entries 7 and 8) are
also epoxidized in good yields and high selectivities. ␣-Terpineol
and R-(+)-limonene are epoxidized unselectively at 80 ◦C in DCE
(entries 9 and 11). However, if the reaction temperature is low-
ered to 55 ◦C, both substrates are converted with high selectivities
(entries 10 and 12).
Fig. 2. Molecular structures of 3a showing the atomic numbering scheme. Proba-
bility ellipsoids are drawn at the 50% level; H atoms are omitted for clarity.
yellow plates. The crystals could be separated under the microscope
and analyzed individually. The major orange crystalline fraction
thereby displayed the O,O-isomer, which is the same isomer as in
3a, whereas the yellow crystals displayed the N,N-isomer (3b’).
Since 3b’ only formed in traces, we were not able to isolate a
significantamountof3b’in orderto obtainfullanalyticalandexper-
imental data on 3b’. Therefore all the epoxidation experiments
were done with complex 3b. In the 1H NMR spectrum of 3b no
signals for 3b’ could be detected. This is possible due to the general
low solubility of the complexes. However, isomerisation in solution
might be occurring, but again the low solubility prevented further
investigations by e.g. VT-NMR spectroscopy.
The crystal structure analysis of 3a confirmed the formation
of cis-dioxomolybdenum(VI) complex with the two oxazoline N
atoms N(13) and N(33) trans to each other and the two naphtholate
oxygen atoms O(21) and O(41) trans to two terminal oxo ligands
O(2) and O(4) (O,O-isomer) (Fig. 2).
All bond lengths and angles in 3a fall within the expected
range for an octahedral dioxomolybdenum(VI) complex (Table 2)
[23,25,28,37]. The distorted octahedral coordination is most likely
a result of the small bite angle of bidentate ligand 2a, which is
reflected for example by the smaller than 90◦ angle of O(41)-Mo(1)-
N(33) of 78.96(5)◦. For complex 3b single >crystals of both the
O,O-isomer (3b) as well as the N,N-isomer (3b’) could be obtained
and characterized by X-ray crystallography. The asymmetric unit
cell of 3b consists of two half molecules, each one arranged around
two-fold rotation axes parallel to the monoclinic b axis through the
Mo atoms (for full details see SI). Also for 3b’, the asymmetric unit
cell contains half a molecule arranged around a two-fold rotation
axis parallel to the short b axis through Mo(1).
Both complexes of 3b and 3b’ are distorted octahedral dioxo-
molybdenum(VI) complexes. The most striking structural feature
of 3b’ is the very long Mo-N(oxazoline) distance Mo(1)-N(13)
Finally we investigated the stability of the catalysts 3a-b by
performing a repeated addition experiment. Under the optimized
conditions for epoxidation of cyclooctene (0.05 mol% 3a or 3b/2
equiv. TBHP in DCE at 80 ◦C) aliquots for GC–MS were withdrawn
after 60 min and new substrate and TBHP were added. This was
repeated three times.
As shown in Fig. 6 the catalyst activity decreases after the second
addition and drops further after the third addition of cyclooctene.
This could possibly be due to thermal instability of complexes
˚
˚
of 2.3570(13) A compared to only 2.144(10) A in 3b. This can be
explained by the strong trans-effect of the terminal oxo ligands
(Fig. 3 and Table 3).
Our results should be compared to the previously published
dioxomolybdenum(VI) complex equipped with the oxazoline
ligand (Fig. 4). Interestingly, the related phenolate-oxazoline com-
plex to 3a, [MoO2(oz)2] (oz = 2-(4,5-dihydrooxazol-2-yl)phenol),
had been isolated and characterized by X-ray crystallography in

P. Traar et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 54–60
57
Table 2
Selected bond distances and angles of 3a.
Bond distances
(Å)
Bond angles
(◦)
Mo(1)-O(4)
Mo(1)-O(2)
Mo(1)-O(21)
Mo(1)-O(41)
Mo(1)-N(33)
Mo(1)-N(13)
1.7088(12)
1.7140(11)
2.0630(11)
2.0651(12)
2.1408(14)
2.1478(13)
O(4)-Mo(1)-O(2)
101.51(6)
162.87(5)
161.35(5)
165.93(5)
78.96(5)
79.34(5)
O(2)-Mo(1)-O(21)
O(4)-Mo(1)-O(41)
N(33)-Mo(1)-N(13)
O(41)-Mo(1)-N(33)
O(21)-Mo(1)-N(13)
Fig. 3. Molecular structures of 3b (left) and 3b’ (right) showing the atomic numbering scheme. Probability ellipsoids are drawn at the 50% level; H atoms are omitted for
clarity.
Table 3
Selected bond distances and angles of 3b and 3b’.
Bond distances (Å)
3b
3b’
Bond angles (◦)
3b
3b’
Mo(1)-O(1)
Mo(1)-O(21)
Mo(1)-N(13)
1.695(8)
2.078(8)
2.144(10)
1.7061(11)
1.9519(11)
2.3570(13)
O(1)-Mo(1)-O(1)a
O(1)-Mo(1)-O(21)
N(13)-Mo(1)-N(13)a
O(21)-Mo(1)-O(21)a
103.3(5)
164.5(3)
165.0(5)
78.5(4)
106.16(8)
95.80(5)
79.67(6)
157.90(7)
a
Symmetry transformations used to generate equivalent atoms: 3/2-x, y, 3/2-z
Fig. 4. Previously published and structurally characterized dioxomolybdenum(VI) complexes [23,25,37].
3a-b at 80 ◦C or as the increasing concentration of tert-butanol in
the reaction mixture inhibits catalysis.
Overall both complexes 3a-b show a very similar catalytic activ-
ity in the epoxidation of various olefins. Apparently the four methyl
groups on the oxazoline moieties in 3b compared to 3a have
negligible influence on the catalysis. Also with regard to previously
published aryloxide–oxazoline complexes the results obtained in
our study are comparable. For example, very similar activities for
the same substrates were obtained for the phenolate–oxazoline
complex [MoO2(oz)2]. It is feasible that the steric influence of
Table 4
Conversion of cyclooctene to cyclooctane oxide in different solvents.
Benzene, 55 ◦
(%)b
C
Toluene, 55 ◦
(%)b
C
CHCl3, 55 ◦
(%)b
C
DCEa, 55 ◦
(%)b
C
DCEa,80 ◦
(%)b
C
(min)
30
60
90
80
94
>99
77
87
89
88
96
>99
84
94
97
>95
Conditions: 0.5 mol% 3b, 2 equiv. TBHP; conversions were determined via GC–MS using mesitylene as internal standard.
a
1,2-Dichloroethane.
Conversion of cyclooctene to cyclooctane oxide.
b

58
P. Traar et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 54–60
Catalyst loading [mol%]/TBHP [equiv.]
100
90
80
70
60
50
40
30
20
10
0
0.05/2
0.05/1
0.02/2
0.02/1
0.01/2
0.01/1
0
20
40
60
80
100
t [min]
Fig. 5. Testing of different catalyst (3a) and oxidant (TBHP) loading in the conversion of cyclooctene in 1,2-dichloroethane at 80 ◦C.
the ligand coordinated to Mo (naphtholate vs. phenolate) is small.
According to the generally accepted mechanism the peroxide coor-
dinates under proton transfer to a terminal oxo ligand to the
dioxo-Mo core from the sterically less hindered side [40]. The bulky
naphthyl backbone however is located on the opposite side of
the Mo atom. Therefore the steric influence of the ligand should
be negligible. From an electronic point of view, naphtholate and
phenolate substituents are very similar, explaining the overall very
Table 5
Results of epoxidation of various olefins catalyzed by 3a and 3b.
3a
t (h)
3b
(%)a
>95
Sel.b
>99
TON
(%)a
Sel.b
>99
TON
1
2
1.5
5000
>95
5000
21
5
74
88
>99
>99
3700
4400
78
88
>99
>99
3900
4400
3
4
5
6
76
76
92
95
3500
3600
83
64
90
89
3730
2840
18
6
7
18
5
19
37
>99
>99
950
20
44
>99
>99
1000
2200
1850
8
5
42
>99
2100
38
>99
1900
9
5
5
1
5
74
66
60
78
76
>99
64
2800
3300
1920
3900
71
68
58
87
71
>99
60
2520
3400
1740
4350
10c
11
12c
>99
>99
Conditions: 0.05 mol% catalyst, 2 equiv. TBHP, 1,2-dichloroethane at 80 ◦C (except entry 10 and 12 at 55 ◦C).
a
Conversions determined by GC–MS via peak integration referenced to internal standard mesitylene.
b
Selectivity towards epoxide product, determined by GC–MS.
Reaction temperature was 55 ◦C.
c

P. Traar et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 54–60
59
Repeated addiꢀon of cyclooctene
100
90
80
70
60
50
40
30
20
10
0
3a
3b
1st run
2nd run
3rd run
catalyꢀc cycles
Fig. 6. Repeated addition of cyclooctene and TBHP to catalysts 3a and 3b. Conditions used were 0.05 mol% catalyst, 2 equiv. TBHP in DCE at 80 ◦C.
similar catalytic activities. In contrast, the related chiral complex
[MoO2(oz*)2] displayed a rather sluggish behavior as epoxidation
catalyst, albeit under different conditions than reported here [24].
Complex [MoO2(ozMe2)2] was tested in the epoxidation of styrene
at room temperature, but showed no activity at all [37].
Chemistry. Deviations from calculated elemental compositions are
due to residual solvent in the sample.
4.2. Single crystal X-ray diffraction analyses
All the measurements were performed using graphite-
monochromatized
Mo
K␣
radiation
at
100 K.
3a:
3. Conclusions
C26H20MoN2O6, Mr 552.38, triclinic, space group P-1,
◦
˚
˚
˚
a = 7.2205(3) A, b = 11.0269(4) A, c = 13.9798(5) A, ˛ = 86.8539(14) ,
ˇ = 80.1179(13)◦,
ꢃ = 76.5620(12)◦,
V = 1066.40(7) A ,
Z = 2,
3
˚
Within this paper we present the synthesis and characterization
of two new dioxomolybdenum(VI) complexes 3a-b equipped with
the bidentate monoanionic naphtholate-oxazoline ligands 2a-b. All
analytical data is consistent with the formation of asymmetrically
disubstituted complexes. Complexes 3a-b were also characterized
by single crystal X-ray diffraction analysis. In the case of 3b, both
the O,O-isomer (3b) as well as the N,N-isomer (3b’) could be char-
acterized, although 3b’ was only formed in traces. Furthermore
complexes 3a-b were tested in the catalytic epoxidation of various
olefinic substrates. In all cases they showed good to high activity
with acceptable selectivities comparable or higher to other pub-
lished dioxomolybdenum(VI) complexes.
dcalc = 1.720 g cm−3
,
ꢄ = 0.665 mm−1
.
A
total of 14358 reflec-
tions were collected (ꢅmax = 30.0◦), from which 6212 were unique
(Rint = 0.0253), with 5671 having I > 2ꢆ(I). For 322 parameters
final R indices of R1 = 0.0263 and wR2 = 0.0669 (GOF = 1.041) were
obtained. 3b: C30H28MoN2O6, Mr 608.48, monoclinic, space group
˚
˚
˚
P 2/n, a = 15.890(3) A, b = 10.632(2) A, c = 16.039(3) A, ˇ = 96.191(8)(,
V = 2693.9(9) A3, Z = 4, dcalc = 1.500 g cm−3, ꢄ = 0.534 mm−1. A total
˚
of 10725 reflections were collected (ꢅmax = 26.0◦), from which
5256 were unique (Rint = 0.0717), with 3092 having I > 2ꢆ(I). For
363 parameters final R indices of R1 = 0.0855 and wR2 = 0.2388
(GOF = 1.081) were obtained. 3b’: C30H28MoN2O6, Mr 608.48,
˚
˚
orthorhombic, space group P b c n, a = 17.4070(6) A, b = 7.6439(3) A,
c = 19.8304(7) A, V = 2638.58(17) A , Z = 4, dcalc = 1.532 g cm−3
,
3
˚
˚
4. Experimental
ꢄ = 0.545 mm−1
. A total of 27367 reflections were collected
(ꢅmax = 30.0◦), from which 3851 were unique (Rint = 0.0353),
with 2990 having I > 2ꢆ(I). For 183 parameters final R indices
of R1 = 0.0244 and wR2 = 0.0659 (GOF = 1.060) were obtained.
For full details on data collection and refinement please refer
to the Supporting Information. Crystallographic data (excluding
structure factors) for the structure of 3a, 3b and 3b’ reported in this
paper have been deposited with the Cambridge Crystallographic
Data Center as supplementary publication no. CCDC-940630 (3a),
CCDC-945467 (3b) and CCDC-945466 (3b’). Copies of the data
can be obtained free of charge on application to: The Director,
CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: (int.) +44
1223/336 033; E-mail: deposit@ccdc.cam.ac.uk]. A summary of the
crystallographic data can be found in the Supporting Information
which is available online free of charge.
Synthesis of 2a: a suspension of 1a (2.31 g, 10 mmol, 1 equiv.)
in dichloromethane (50 mL) was cooled to 0 ◦C. Thionyl chloride
(1.79 g, 15 mmol, 1.5 equiv.) was added under Ar slowly over a
period of 15 min resulting in a brown solution. The solution was
allowed to slowly warm up to room temperature over night. After
12 h stirring at room temperature a suspension was obtained con-
taining crude 2a·HCl as an off-white solid. The off-white solid was
4.1. General remarks
Unless otherwise specified, all experiments were performed
under atmospheric conditions with standard laboratory equipment
at the Institute of Chemistry, University of Graz. For the synthesis of
1a-b please refer to the Supporting Information. All other chemicals
and solvents were purchased from commercial sources and used
as received. 1H and 13C NMR spectra were recorded on a Bruker
Optics Instrument. Chemical shifts are reported in parts per million
(ppm) and referenced to residual protons or carbons in the deuter-
ated solvent. Electron impact mass spectroscopy measurements
(EI-MS) were recorded with an Agilent 5973 MSD mass spectrom-
eter with Direct Probe. Gas chromatography mass spectroscopy
measurements (GC–MS) have been performed with an Agilent
7890 A (column type Agilent 19091J-433), coupled to a mass spec-
trometer type Agilent 5975 C. Samples for infrared spectroscopy
were measured on a Bruker Optics ALPHA ATR FT-IR Spectrome-
ter. IR bands are reported with wave number (cm−1). Elemental
analyses were measured on a Heraeus Vario Elementar automatic
analyzer at the Graz University of Technology, Institute of Inorganic

60
P. Traar et al. / Journal of Molecular Catalysis A: Chemical 385 (2014) 54–60
filtered off, subjected to aqueous work-up with saturated NaHCO3
and dried in vacuo to yield 1.4 g (6.5 mmol, 65%) of 2a as a pale
white solid. 1H NMR (DMSO-d6, ppm): ␦ 13.51(s, 1H), 8.29–7.34
(m, 6H), 4.52 (t, J = 9.4 Hz, 2H), 4.09 (t, J = 9.4 Hz, 2H). 13C NMR
(DMSO-d6, ppm): ␦ 166.40, 158.76, 135.70, 128.60, 127.55, 125.61,
124.30, 123.06, 117.49, 102.68, 67.25, 51.94, 1 C obscured. Selected
IR frequencies (cm−1): ∼3100 (C H, aromatic), 1628 (ꢀC N). EI-MS:
m/z = 213.1 [M+]. Anal. calcd. for C13H11NO2 (213.23): C 73.23, H
5.20, N 6.57; found: C 72.46, H 5.12, N 6.70
(1.5 mL), at which time TBHP (363 ␮l, 2.0 mmol, 2 equiv.) was
added. Aliquots for GC–MS (10 ␮L) were withdrawn, quenched
with MnO2 and diluted with HPLC grade ethyl acetate. The reac-
tion products were analyzed by GC–MS, and quantified via peak
integration vs. mesitylene (internal standard).
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In a typical experiment, the respective dioxomolybdenum(VI)
complex (0.05 mol%) and olefin (1 mmol, 1 equiv.) were mixed and
heated in a Mininert® vial to 55 or 80 ◦C in 1,2-dichloroethane