Oxidorhenium(V) complexes with oxazolinylmethoxido ligands-structure and catalytic epoxidation

Article abstract of DOI:10.1002/ejic.201100538

Reaction of [ReOCl₃(PPh₃)₂] with (4,5-dihydrooxazol-2-yl)methanol and three methyl-substituted derivatives thereof (2a-2d) in boiling acetone or tetrahydrofuran gave oxidorhenium(V) complexes of the type [ReOCl₂(PPh₃)(2a-2d)] (3a-3d) as blue crystalline materials in good yields. The complexes were characterized by ¹H, ¹³C, ³¹P NMR and IR spectroscopy, mass spectrometry, elemental analysis and single-crystal X-ray diffraction analysis. All the complexes showed distorted octahedral geometries and were found to contain only one oxazolyl ligand displacing one PPh₃ molecule and one chloride ion from the precursor complex [ReOCl₃(PPh ₃)₂]. The complexes were tested as catalysts for the epoxidation of cyclooctene with 3 equiv. of tert-butyl hydroperoxide (TBHP). Complex 3a containing (4,5-dihydrooxazol-2-yl)methanol showed the highest yield of epoxide (79 %), whereas the complex with the tetramethyl-substituted ligand 3d exhibited the lowest catalytic activity. Copyright

Full text of DOI:10.1002/ejic.201100538

FULL PAPER
DOI: 10.1002/ejic.201100538
Oxidorhenium(V) Complexes with Oxazolinylmethoxido Ligands – Structure
and Catalytic Epoxidation
Belina Terfassa,[a,b] Pedro Traar, Manuel Volpe, Nadia C. Mösch-Zanetti,*
[a]
[a]
[a]
[b]
[b]
[b]
V. J. T. Raju, Negussie Megersa, and Negussie Retta
Keywords: Rhenium / Oxazoline / Epoxidation / Oxidation
Reaction of [ReOCl
methanol and three methyl-substituted derivatives thereof
2a–2d) in boiling acetone or tetrahydrofuran gave oxidorhe-
nium(V) complexes of the type [ReOCl (PPh )(2a–2d)] (3a–
3
(PPh
3
)
2
] with (4,5-dihydrooxazol-2-yl)-
only one oxazolyl ligand displacing one PPh
one chloride ion from the precursor complex [ReOCl
3
molecule and
3
-
(
(PPh ]. The complexes were tested as catalysts for the epox-
3 2
)
2
3
idation of cyclooctene with 3 equiv. of tert-butyl hydroperox-
3
d) as blue crystalline materials in good yields. The com- ide (TBHP). Complex 3a containing (4,5-dihydrooxazol-2-yl)-
1
13
31
plexes were characterized by H, C, P NMR and IR spec-
troscopy, mass spectrometry, elemental analysis and single-
crystal X-ray diffraction analysis. All the complexes showed
distorted octahedral geometries and were found to contain
methanol showed the highest yield of epoxide (79%),
whereas the complex with the tetramethyl-substituted ligand
3d exhibited the lowest catalytic activity.
Introduction
complexes have been reported. No rhenium complexes with
2-(2Ј-hydroxymethyl)-2-oxazoline-type ligands have as yet
Oxazoline derivatives are known in a wide variety as li-
gands in transition metal complexes.[1] Upon coordination
they are highly robust under many reaction conditions.
Furthermore, they are synthetically accessible by conve-
nient organic reactions. Many examples are known includ-
been described in the literature.
Rhenium(VII) compounds are known to be highly active
[21–23]
epoxidation catalysts,
methyltrioxidorhenium being
[24]
the most prominent among them.
However, a pro-
nounced sensitivity towards hydrolysis sometimes decreases
[
1,2]
ing bi-, tri- and polydentate ligands and chiral versions.
An extensively investigated ligand is 2-(2Ј-hydroxyphenyl)-
[25]
turnover numbers.
Rhenium(V) complexes are usually
less prone towards hydrolysis, which explains the recent in-
vestigations of oxidorhenium(V) complexes as catalysts in
epoxidation reactions of olefins.
2
-oxazoline, in particular coordinated to rhenium centres in
[3–7]
high oxidation states.
Abu-Omar et al. demonstrated
[12–14,26–30]
However, all the
that oxidorhenium(V) complexes containing 2-(2Ј-hy-
systems reported do not yet reach the activity of rheni-
um(VII) compounds as they usually suffer from oxidative
degradation. For this reason it is a worthwhile goal to fur-
ther investigate oxidorhenium(V) complexes with ligands
exhibiting higher stability towards oxidation, such as (4,5-
dihydrooxazol-2-yl)methanol.
Therefore, we report the synthesis and structural charac-
terization of oxidorhenium(V) complexes with several (4,5-
dihydrooxazol-2-yl)methanol-type ligands and their cata-
lytic applications in the epoxidation of cyclooctene.
droxyphenyl)-2-oxazoline exhibit interesting catalytic be-
haviour for oxygen atom transfer reactions.[
4,8,9]
Most inter-
estingly, they were found to successfully catalyze the re-
–
[4,8]
duction of perchlorate (ClO ) to chloride ions,
a reac-
4
tion that is environmentally interesting (waste water clean-
ing) but kinetically hindered.[
10]
The success of oxazoline ligands as stabilizing agents in
catalysis as well as our ongoing interest in rhenium-cata-
lyzed epoxidations[
11–15]
prompted us to investigate a largely
unexplored oxazoline ligand in oxidorhenium(V) chemistry.
We were surprised to find that 2-(hydroxymethyl)-2-oxazol-
ine and derivatives thereof have, in general, limited used
incoordinationchemistry.Thus,with(4,5-dihydrooxazol-2-yl)-
Results and Discussion
III [16]
II [17,18]
IV[19]
IV[20]
methanol only a few Cr , Ni ,
Zr
and Hf
Synthesis of Ligands
[
[
a] Institute of Chemistry, Karl-Franzens-University Graz,
Schubertstrasse 1, 8010 Graz, Austria
E-mail: nadia.moesch@uni-graz.at
The 2-oxazoline ligands were obtained according to lit-
b] Department of Chemistry, Addis Ababa University,
Ethiopia
[17,31,32]
erature procedures
in a two-step method. Amides
were formed in the first step from the respective organic
acid and β-amino alcohols by heating neat melts or by re-
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100538.
4434
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 4434–4440

Oxidorhenium(V) Complexes with Oxazolinylmethoxido Ligands
Scheme 1. Synthesis of the 2-oxazoline ligands 2a–2d.
fluxing in a suitable high-boiling solvent. Subsequent subli- ligands 2b–2d are the two methyl groups at the ring carbon
mation of the resulting amides under high vacuum yielded atom adjacent to the nitrogen atom. The six protons appear
1
the respective oxazoline (Scheme 1).
as one singlet resonance in the H NMR spectra of the free
ligands, whereas two resonances are observed upon coordi-
nation due to the different chemical environments. The
same is true for the resonance of the two ring protons, the
Synthesis of Oxidorhenium(V) Complexes
The desired complexes of the type [ReOCl (PPh )(2)] signal of which splits into two characteristic doublets upon
2
3
(
1
3a–3d) were prepared by metathesis reactions between coordination. NMR spectra of 3c reveal the existence of
equiv. of [ReOCl (PPh ) ] and the respective ligand 2a–2d two isomers in solution in contrast to 3a, 3b and 3d, which
3
3 2
(
Scheme 2). Interestingly, even when 2 equiv. of the ligands were found to be isomerically pure. Ligand 2c contains a
were used, only the monosubstituted complexes were ob- chiral centre at the alcoholic carbon atom. Thus, upon co-
tained. Use of NEt as a base to accept the proton removed ordination of the racemic mixture, two diastereomers are
3
from the oxazoline resulted in decomposition of the starting formed as 3c contains an additional chiral centre at the rhe-
material. Stronger bases such as NaH also resulted in de- nium atom. The isolated material showed the two isomers
1
composition. As a result, all attempts to obtain disubsti- in a ratio of 2:1 evidenced by the H NMR spectrum, which
tuted rhenium complexes of the type [ReOCl(2) ] were not displays two sets of resonances in this ratio as indicated in
2
successful. In all cases, stable [ReOCl (PPh )(2)] complexes the Experimental Section. The 13C NMR spectrum showed
2
3
were obtained in agreement with similar work reported in one set of resonances for a coordinated ligand and, unfortu-
[
33]
the literature.
nately, the second set was barely visible due to background
Complexes 3a–3d are air-stable, blue solids. They are noise. Extended measurement times did not improve the
moderately soluble in strongly polar solvents such as thf, quality of the spectrum. However, consistent with two iso-
acetonitrile, acetone, chloroform, methanol and ethanol, mers, the 31P NMR spectrum of 3c in CDCl
and are completely insoluble in medium polar (toluene, di- resonances for a coordinated PPh
revealed two
molecule at δ = –16.20
3
3
ethyl ether) and apolar solvents (benzene, hexane). Analyti- and –17.30 ppm, which is diagnostic of triphenylphosphane
V[15,34–37]
cally pure samples were obtained at the end of the synthesis in the coordination sphere of Re .
upon cooling of the boiling thf solution, from which 3a–
The IR spectra of 3a–3d exhibit characteristic ν(Re=O)
3
d precipitated as blue powders. Further concentration and bands at 965.00 (3a), 974.62 (3b), 973.43 (3c) and 965.72
–1
cooling of the solution increased the yield.
cm (3d), which are in good agreement with those of sim-
[
8,15,34,36]
The oxidorhenium complexes 3a–3d were characterized ilar oxidorhenium compounds.
The bands at
1
13
31
–1
by H, C and P NMR spectroscopy. However, 3a was 1670.05 (3a), 1644.63 (3b), 1644.59 (3c) and 1648.17 cm
13
not soluble enough for the recording of a meaningful
C
(3d) are assigned to the ν(C=N) mode of the oxazoline ring,
NMR spectrum. All spectra show respective resonances in which represents a shift of 4–25 cm–1 to a lower frequency
the aromatic region for phenyl protons and carbon atoms, compared to the free ligands, indicating that the imine ni-
consistent with the coordination of one molecule of PPh3 trogen atom of the oxazoline ring is strongly coordinated
[
8,38]
in the complexes. Particularly characteristic for coordinated to the metal centre.
Scheme 2. Synthesis of 3a–3d.
Eur. J. Inorg. Chem. 2011, 4434–4440
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4435

N. C. Mösch-Zanetti et al.
FULL PAPER
Molecular Structures of the Complexes
The structures of 3a, 3b and 3d were determined by sin-
gle-crystal X-ray diffraction analysis. The high residual den-
sity for 3b is located in close proximity to the Re atom. For
3c the crystal quality from several crystallization experi-
ments was not high enough, so only a low-quality data set
was obtained that could not be refined satisfactorily. Never-
theless, it proves the connectivity of 3c (see Supporting In-
formation). The perspective molecular views of the com-
plexes are shown in Figures 1, 2 and 3; crystallographic
data are presented in Table 1, and selected bond lengths and
angles are given in Table 2.
Figure 2. Molecular view of 3b with selected atom numbering. Hy-
drogen atoms and a molecule of lattice MeCN are omitted for clar-
ity.
Figure 3. Molecular view of 3d with selected atom numbering. Hy-
drogen atoms are omitted for clarity.
Figure 1. Molecular view of 3a with selected atom numbering. Hy-
drogen atoms are omitted for clarity.
Table 1. Crystallographic data for 3a, 3b and 3d.
[
ReOCl
2
PPh
3
(2a)] (3a)
PRe
[ReOCl
2
PPh
3
(2b)] (3b)
PRe·CH
[ReOCl
2
PPh
3
(2d)] (3d)
PRe
Empirical formula
Formula mass
Color/habit
Crystal size [mm]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C
22
H21Cl
2
NO
3
C
24
H25Cl
2
NO
3
3
CN
C
26
H29Cl
2
NO
3
635.47
blue/column
0.17ϫ0.80ϫ0.13
704.57
blue/tablet
0.71ϫ0.60ϫ0.13
691.57
blue/tablet
0.51ϫ0.22ϫ0.05
monoclinic
1
P2 /n
14.5598(8)
9.4533(5)
19.5256(10)
90
95.729(2)
90
triclinic
triclinic
¯
¯
P1
P1
7.4525(3)
7.9206(3)
18.6652(8)
96.4690(10)
91.715(2)
93.9960(10)
1091.30(8)
2
9.3914(7)
11.7438(9)
10.6840(10)
95.886(2)
96.464(2)
98.804(2)
1363.43(18)
2
γ [°] 3
V [Å ]
2674.0(2)
4
Z
T [K]
100(2)
1.934
5.910
100(2)
1.716
4.741
100(2)
1.718
4.832
–3
Dcalcd. [dcm ]
–1
μ [mm ]
F(000)
θ range [°]
Limiting indices
616
2.45–30.06
–10 Յ h Յ 10
692
1360
2.55–31.40
–13 Յ h Յ 13
–17 Յ k Յ 17
–18 Յ l Յ 18
30071
2.39–36.92
–23 Յ h Յ 23
–15 Յ k Յ 15
–32 Յ l Յ 32
53707
–
–
11 Յ k Յ 11
26 Յ l Յ 26
No. refections collected
46059
No. independent reflections, Rint
No. observed reflections [F Ͼ 4σ(F)]
No. data/restraints/parameters
6345, 0.0329
6182
6345/0/271
0.0159/0.0405
0.0167/0.0408
1.182
8726, 0.0481
8219
8726/0/314
0.0413/0.1219
0.0434/0.1229
1.099
11568, 0.0573
9990
11568/0/312
0.0393/0.0969
0.0448/0.1061
1.044
R
R
F
/wRF2 [F Ն4σ(F)]
[
a]
F
/wRF2 (all data)
2
[a]
GOF (on F )
Largest difference peak/hole [eÅ ]
–3
1.084/–1.310
4.931/–4.514
3.576/– 4.396
a] R = Σ(||F | – |F ||)/Σ|F
|. wR2 = {Σ[w(F 2
– F
2)2]/Σ[w(F
2)2]}1/2. GOF = {Σ[w(F
2
– F
2)2]/(n – p)}1/2
.
[
o
c
o
o
c
o
o
c
4436
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Eur. J. Inorg. Chem. 2011, 4434–4440

Oxidorhenium(V) Complexes with Oxazolinylmethoxido Ligands
Table 2. Selected bond lengths [Å] and angles [°] for 3a, 3b and 3d.
The complexes show Re=O bond lengths between
.688(6) and 1.694(2) Å, which are in the expected range
1
3a
3b
3d
[
3,14,34,40,41]
for monooxidorhenium(V) complexes;
Re1–O2
Re1–O1
Re1–O2
Re1–N1
Re1–Cl2
Re1–Cl1
Re1–P1
O1–Re1–O2
O1–Re1–N1
O2–Re1–N1
O1–Re1–Cl2
O2–Re1–Cl2
N1–Re1–Cl2
O1–Re1–Cl1
O2–Re1–Cl1
N1–Re1–Cl1
Cl2–Re1–Cl1
O1–Re1–P1
O2–Re1–P1
N1–Re1–P1
Cl2–Re1–P1
Cl1–Re1–P1
1.6878(16)
1.9751(15)
2.1216(18)
2.3438(5)
2.4230(5)
2.4449(5)
161.37(7)
88.35(7)
74.67(7)
101.25(6)
96.29(5)
169.59(5)
98.96(6)
87.36(5)
85.04(5)
89.47(2)
93.76(6)
80.33(5)
94.79(5)
88.62(2)1
167.27(2)
1.690(3)
1.963(3)
2.141(3)
1.694(2)
1.953(2)
2.147(2)
2.3497(7)
2.4255(7)
2.4703(7)
163.5(1)
88.9(1)
75.25(9)
102.96(8)
93.11(6)
167.87(6)
96.30(8)
87.87(7)
88.14(7)
87.99(3)
88.99(8)
87.74(7)
94.50(7)
88.36(2)
174.14(2)
distances are 1.953(2)–1.9751(15) Å, which are longer than
V
that of Re =O as expected. The Re1–N1 distances are
2.3486(10)
2.4202(10)
2.4599(10)
163.34(14)
90.20(14)
74.90(13)
103.95(11)
91.28(9)
165.72(10)
97.21(11)
89.97(9)
88.60(9)
87.78(4)
2.1216(18)–2.147(2) Å, which are within the normal range
of Re–N single bonds for oxidorhenium(V) complexes
(
2.11–2.18 Å). The Re1–Cl1 bond trans to the PPh phos-
3
phorus atom at 2.4202(10)–2.4255(7) Å is slightly longer
than the Re1–Cl2 bond [2.3438(5)–2.3497(7) Å], trans to the
oxazoline ring nitrogen atom. This seems to be due to the
trans influence of the phosphorus atom.
The O1–Re1–O2 angles [161.37(7)–163.5(1)°] deviate
V
from 180° for an ideal octahedral structure. The Re =O
linkage significantly expands the angles to the equatorial
chloride ions; the O1–Re1–Cl1 [96.30(8)–98.96(6)°] and
O1–Re1–Cl2 [101.25(6)–103.95(11)°] angles deviate signifi-
cantly from 90°.
87.80(11)
85.87(9)
93.95(9)
88.54(4)
174.38(3)
Epoxidation of Cyclooctene
Isostructural 3a and 3b are triclinic and crystallize in the
Compounds 3a–3d were examined as catalysts for the
¯
space group P1, whereas 3c and 3d are monoclinic and crys- epoxidation of cyclooctene with TBHP as an oxidant. Typi-
tallize in P2 /c and P2 /n, respectively. cally 1 mol-% of catalyst and 3 equiv. of TBHP were used.
1
1
The X-ray structures show that in each complex, the rhe- Details of the catalytic reaction are given in the Experimen-
nium centre is coordinated in an octahedral coordination tal Section. Blank reactions showed that no significant
sphere to one oxido ligand, two chlorido ligands, a phos- amounts of epoxide are formed in the absence of the cata-
phorus atom from PPh and a nitrogen and an oxygen atom lyst.
3
V
from the oxazoline ligand. The oxido (Re =O) ligand along
All four catalysts 3a–3d showed activity in the epoxid-
the axial direction lies trans to the oxazolinylmethoxido ation of cyclooctene with TBHP with similar reactivity pat-
oxygen atom (O2). This is due to a strong trans effect of the terns (Figures 4 and 5). Furthermore, all four catalysts
oxido group, forcing the harder oxygen atom of the N,O reached their maximum conversion of cyclooctene after 5 h.
ligand into a trans position.[
12,13]
The high electron density The best yield obtained was 79.3% for 3a, and the lowest
along the Re–O axis strongly influences the positions of the was 46.8% for 3d (Figure 5). However, complete conversion
adjacent halogen atoms, which are pushed away.[ The ni- to cyclooctene epoxide was not observed with any of the
trogen atom in the heterocyclic oxazoline ring is trans to catalysts. In the case of 3a at prolonged reaction times, com-
one of the cis-chloride ions, and the second chloride ion is plete consumption of the substrate cyclooctene was ob-
trans to the phosphorus atom. The two cis-chloride ions, served with concomitant consumption of the product, cy-
the nitrogen atom of the oxazoline ring and the phosphorus clooctene epoxide, to yet unidentified products. This could
39]
atom occupy the equatorial plane.
be due to further oxidation or hydrolysis of the epoxide. In
Figure 4. Reaction progress in the epoxidation of cyclooctene by using catalysts 3a–3d.
Eur. J. Inorg. Chem. 2011, 4434–4440
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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4437

N. C. Mösch-Zanetti et al.
FULL PAPER
Figure 5. Comparative catalytic conversion of cyclooctene to cyclooctene oxide by catalysts 3a–3d.
the case of 3d there were no side products observed during yl)methanol (2a),[31] (4,4-dimethyl-4,5-dihydrooxazol-2-yl)meth-
anol (2b),[17,32] 1-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)ethanol
the reaction, but reaction progress stalled after 5 h, and nei-
2c),[32] 2-(4,4-dimethyl-4,5-dihydrooxazol-2-yl)propan-2-ol (2d)
[17]
(
ther a significant consumption of substrate nor product was
observed. We attribute this to a possible decomposition or
inhibition of the catalyst. Further investigations to clarify
[43,44]
and [ReOCl
3
(PPh
3
)
2
]
were prepared according to previously
published methods.
these issues are needed. We were also interested in how the Instrumentation: H, 13C and 31P NMR spectra were recorded at
1
300, 75 and 121 MHz, respectively, with a Bruker AC300 instru-
introduction of electron-donating substituents such as
methyl groups affects the catalytic activity. However, there
was no clear trend observed regarding the degree of methyl-
ation and catalytic activity. For example, 3a bearing the
parent oxazoline ligand with no methyl groups showed the
highest catalytic activity of all four complexes, and 3d bear-
ing four methyl groups showed the lowest catalytic activity.
ment. Chemical shifts are reported in ppm and referenced to resid-
3
1
ual solvent peaks. P NMR shifts are referenced against external
PO . EI mass spectra were measured with an Agilent 5973 MSD
H
3
4
direct-probe. Elemental analysis was carried out by using a Heraeus
Vario Elemental Automatic Analyzer. IR spectra were recorded
with a Bruker Alpha FTIR spectrometer in the range of 4000–
–1
4
00 cm . Melting points were recorded in glass capillary tubes with
However, the trend is reversed for 3b with two methyl a Büchi Melting Point B-540 apparatus and are uncorrected. Sin-
groups and chiral 3c with three methyl groups (Figure 5), gle-crystal X-ray measurements were performed by using Mo-K (λ
= 0.71073 Å) radiation with a Bruker SMART APEX II dif-
α
where 3c was more active than 3b.
fractometer equipped with a CCD area detector at 100(2) K. The
APEX II program[ was used for collecting frames of data, in-
dexing reflections and determinations of lattice parameters; data-
The average performance of complexes 3a–d in the epox-
45]
idation of cyclooctene has also been observed with other
oxidorhenium(V) systems.[12,13,29,42]
The structure of the
[46]
sets were integrated and scaled with SAINT
and corrected for
active species is as yet unidentified. One possible deactiva-
tion of the catalyst could be an irreversible oxidation to a
colourless perrhenate(VII) ion, which has been observed in
other epoxidation reactions.[ Another possible inhibition
absorption and Lp effects with SADABS.[ Structures were solved
47]
[48]
either by Patterson synthesis (SHELXL-97)
or direct methods
[49]
[50]
(
SIR-92) using the WinGX suite of programs. The other non-
29]
hydrogen atoms were located in successive difference Fourier syn-
of catalysis is the formation of tert-butyl alcohol, the re- theses. The final refinements were performed by full-matrix least-
2
duction product of TBHP, which could compete with squares analysis on F . Hydrogen atoms were fixed in calculated
TBHP for empty coordination sites on the Re centre.
positions with a riding model (Uiso = 1.5 Uiso of the parent carbon
atom). Graphical plots of the structures were made by using
ORTEP-3.[ CCDC-826465 (for 3a), -826464 (for 3b) and -826466
51]
Conclusions
(
for 3d) contain the supplementary crystallographic data for this
paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Oxidorhenium complexes of 2-(hydroxymethyl)-2-
oxazoline-based ligands have been prepared and charac-
terized. The crystal structures of the rhenium complexes
show that one oxazoline ligand displaces one PPh and one Synthesis of Oxidorhenium(V) Complexes
3
chlorido ligand in the precursor. The complexes show cata-
lytic activities in the epoxidation of cyclooctene.
[
ReOCl
OCl (PPh
0.202 g, 2 mmol) dropwise with vigorous stirring. The resulting
2
(PPh
3
)(2a)] (3a): To a greenish-yellow suspension of [Re-
3
3 2
)
] (0.833 g, 1 mmol) in acetone (300 mL) was added 2a
(
deep blue solution was heated to reflux for 24 h. Blue needle-
shaped crystals were obtained by slow evaporation of the solvent
Experimental Section
Materials: All chemicals were purchased from commercial sources at room temperature. Collection by filtration and washing with
and were used without further purification. (4,5-Dihydrooxazol-2- methanol and diethyl ether afforded 3a (0.43 g, 71%). Blue single
4438
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Oxidorhenium(V) Complexes with Oxazolinylmethoxido Ligands
crystals suitable for X-ray diffraction were grown by slow solvent
7.71 (m, 15 H) ppm. 13C NMR (CDCl
(CH ), 25.0 (CH ), 26.1 (CH ), 69.4 (CMe
(ring CH ), 128.3–135.1 (C atoms of PPh ), 174.7 (C=N) ppm.
H), 4.19 (m, 2 H), 4.57 (m, 1 H), 4.98 (m, 1 H), 7.55–7.71 (m, 15 NMR (CDCl , 121 MHz): δ = –17.96 ppm. IR: ν˜ = 3062.36,
H) ppm. 31P NMR (CD
CN): δ = –15.79 ppm. IR: ν˜ = 3052.39 (w, 2987.16, 2962.78, 1648.17, 1433.22, 1371.98, 1359.38, 1259.47,
C–H), 2888.00 (w, νC–H), 1670.05 (s, νC=N), 1480.70 (νC=C), 1425.89 1092.17, 1016.19, 989.09, 965.72, 952.00, 936.23, 795.56, 757.54,
C=C), 1251.65, 1202.77, 1185.71, 1099.90, 1077.44, 1065.42, 742.62, 691.16, 658.15, 524.21, 501.98 cm . EI-MS: m/z = 692.1
): δ = 21.6 (CH
) 24.5
2
), 85.7
3
3
evaporation from
a
concentrated acetonitrile solution. M.p.
3
3
3
2
), 80.6 (OCMe
1
31
220.0 °C (dec.). H NMR (CD CN): δ = 3.44 (m, 1 H), 3.80 (m, 1
3
2
3
P
3
3
ν
–
1
(ν
+
1
7
025.55, 998.07, 964.86 (νRe=O), 952.69, 906.02, 757.28, 743.45,
2 3
[M ]. C26H29Cl NO PRe (691.30): calcd. C 45.15, H 4.23, N 2.03;
found C 42.79, H 4.48, N 1.74.
–1
00.85, 689.60 (s), 530.41, 501.75 (s) cm . EI-MS: m/z = 373.0
+
[M
– PPh
3 3 2 3
], 262.1 [PPh ]. C22H26Cl NO PRe (640.28): cacld. C
Catalytic Reactions: In a typical experiment, cyclooctene (100 mg,
41.58, H 3.33, N 2.20; found C 41.59, H 3.28, N 2.18.
0.91 mmol, 1 equiv.), TBHP (246.03 mg, 2.73 mmol, 3 equiv.) and
chloroform (1.5 mL) were heated to 50 °C, and the respective ox-
idorhenium(V) complexes (1 mol-%) were added (Scheme 3). Sam-
ples for GC–MS (10 μL) from each mixture were withdrawn every
[
(
ReOCl
2
(PPh )(2b)] (3b): suspension of [ReOCl
3
A
3
(PPh
3 2
) ]
0.416 g, 0.5 mmol) in THF (50 mL) was slowly added to a solution
of 2b (0.129 g, 1 mmol) in THF (20 mL) with vigorous stirring to
give a purple solution, which changed to brown on heating to 55 °C
and finally to blue after heating to reflux for 9 h. Slow evaporation
of the solvent yielded blue crystalline material of 3b, which was
recrystallized from dichloromethane to give blue blocks suitable for
X-ray analysis. M.p. 138.0 °C (dec.). H NMR ([D
10 min with a micropipette over 8 h, and the last sample was taken
after stirring at the same temperature for 12 h, diluted with HPLC
grade ethyl acetate. The reaction products were analyzed by using
GC–MS (Agilent Technologies 7890 GC System), and the epoxide
produced from each reaction mixture was quantified vs. n-decane
as the internal standard.
1
6
]acetone): δ =
0
(
8
=
.61 (s, 3 H), 1.58 (s, 3 H), 4.34 (dd, J = 19.2, 3.8 Hz, 1 H), 4.41
d, J = 8.8 Hz, 1 H), 4.67 (dd, J = 19.2, 3.8 Hz, 1 H), 4.81 (d, J =
.8 Hz, 1 H), 7.53–7.68 (m, 15 H) ppm. 13C NMR ([D
]acetone): δ
23.3 (CH ), 28.9 (CH ), 68.1 (CH ORe), 70.1 (CMe ), 87.2 (ring
CH ), 130.0–135.9 (C’s of PPh ), 174.1 (C=N) ppm. P NMR
[D ]acetone): δ = –18.95 ppm. IR: ν˜ = 3055.83, 2985.80, 2929.03,
644.63, 1433.73, 1107.18, 1092.32, 974.62, 959.21, 933.50, 916.14,
6
3
3
2
2
3
1
2
3
(
1
7
6
Scheme 3. Epoxidation of cyclooctene.
–1
+
44.68, 690.79, 561.69, 529.92 cm . EI-MS: m/z = 400.9 [M
], 277.1 [OPPh ], 262.1 [PPh ]. C24 NO PRe (663.27):
calcd. C 43.44, H 3.80, N 2.11; found C 43.83, H 4.24, N 2.25.
–
PPh
3
3
3
H25Cl
2
3
Supporting Information (see footnote on the first page of this arti-
cle): Non-refinable crystal structure of complex 3c proving the cor-
rect connectivity.
2
3
A
3
3 2
[ReOCl (PPh )(2c)] (3c): suspension of [ReOCl (PPh ) ]
(0.833 g, 1.0 mmol) in THF (50 mL) was slowly added to a solution
of 2c (0.286 g, 2 mmol) in THF (10 mL). The mixture was heated
to reflux for 48 h to yield a deep blue solution. Slow evaporation
of the solvent yielded a blue precipitate, which was washed with
methanol (4ϫ3 mL) and dried under vacuo to afford 3c (408 mg,
Acknowledgments
B. T. thanks the Vice President Office for Research and Graduate
Programs, Addis Ababa Univesity, Ethiopia for granting a fellow-
ship. We thank Dr. Jörg Schachner for help in preparing this manu-
script.
71.4%). Single crystals suitable for X-ray crystallography were ob-
tained from a concentrated solution of dichloromethane and etha-
1
nol (3:1) at room temperature. M.p. 190.0 °C (dec.). H NMR
[
CDCl
isomer B), 0.53 (s, 3 H, major isomer A), 0.70 (d, 3 H, B), 1.25 (d,
H, B), 1.59 (s, 3 H, B), 1.61 (s, 3 H, A), 4.22 (d, 1 H, A), 4.32
m, overlap A + B), 4.56 (d, 1 H, A), 4.59 (d, 1 H, B), 4.66–4.77
3
, two diastereomers A and B (2:1)]: δ = 0.49 (s, 3 H, minor
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(
(
13
3
m, overlap A + B), 7.40–7.75 (m, 15 H) ppm. C NMR (CDCl ,
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): δ = –16.20, –17.30 ppm. IR: ν˜
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06.67 cm . EI-MS: m/z = 429.1 [M – PPh
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ReOCl (PPh )(2d)] (3d):
2
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8 h. The resulting deep blue solution was concentrated to give a
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X-ray crystallography were obtained by slow solvent evaporation
1
of a concentrated acetonitrile solution. M.p. 196.0 °C (dec.).
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H
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4440
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 4434–4440