Synthesis, Characterization, X-Ray Crystal Structures, and Catalytic Epoxidation Activity of cis-Dioxomolybdenum(VI) and Oxovanadium(V) Complexes With N'-(2-Hydroxy-4-methoxybenzylidene)-4-trifluoromethylbenzohydrazide

Article abstract of DOI:10.1080/15533174.2015.1137075

A new cis-dioxomolybdenum(VI) complex, [MoO₂LMeOH] (1) and a new oxovanadium(V) complex, [VOL(OMe)MeOH] (2), with potentially tridentate ONO aroylhydrazone Schiff base derived from 4-methoxysalicylaldehyde with 4-trifluoromethylbenzohydrazide, have been synthesized and fully characterized on the basis of elemental analysis, FT-IR, molar conductivity, and electronic spectra. Structures of the complexes have been accomplished by single-crystal X-ray diffraction. The complexes have distorted octahedral structures in which the aroylhydrazones behave as binegative ligands. It is also revealed from the crystal structures that the Mo(VI) and V(V) centers adopt NO₅ donor environment, and the octahedral coordination is furnished by oxido groups and oxygen atoms of methanol or deprotonated methanol molecules. The catalytic properties were investigated for epoxidation of cyclooctene using aqueous tert-butyl hydroperoxide as the oxidant.

Full text of DOI:10.1080/15533174.2015.1137075

Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry
ISSN: 1553-3174 (Print) 1553-3182 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt20
Synthesis, Characterization, X-Ray Crystal
Structures, and Catalytic Epoxidation
Activity of cis-Dioxomolybdenum(VI) and
Oxovanadium(V) Complexes With N’-
(2-Hydroxy-4-methoxybenzylidene)-4-
trifluoromethylbenzohydrazide
Qing Liu, Jiahui Lin, Juan Liu, Wu Chen & Yongming Cui
To cite this article: Qing Liu, Jiahui Lin, Juan Liu, Wu Chen & Yongming Cui (2016):
Synthesis, Characterization, X-Ray Crystal Structures, and Catalytic Epoxidation Activity
of cis-Dioxomolybdenum(VI) and Oxovanadium(V) Complexes With N’-(2-Hydroxy-4-
methoxybenzylidene)-4-trifluoromethylbenzohydrazide, Synthesis and Reactivity in Inorganic,
Metal-Organic, and Nano-Metal Chemistry, DOI: 10.1080/15533174.2015.1137075
To link to this article: http://dx.doi.org/10.1080/15533174.2015.1137075
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Synthesis, Characterization, X-Ray Crystal Structures, and Catalytic Epoxidation Activity of
cis-Dioxomolybdenum(VI) and Oxovanadium(V) Complexes With
N’-(2-Hydroxy-4-methoxybenzylidene)-4-trifluoromethylbenzohydrazide
QING LIU1, JIAHUI LIN1, JUAN LIU1, WU CHEN1,2, YONGMING CUI3,*
1School of Textile Science and Engineering, Wuhan Textile University, Wuhan 430073, P.R.
China
2Ministry of Education Key Laboratory for Textile Fibers and Products, Wuhan Textile
University, Wuhan 430073, P.R. China
3School of Environmetal Engineering, Wuhan Textile University, Wuhan 430073, P.R. China
*Correspondence author. E-mail: cym981248@sohu.com
Abstract
A new cis-dioxomolybdenum(VI) complex, [MoO2LMeOH] (1) and a new oxovanadium(V)
complex, [VOL(OMe)MeOH] (2), with potentially tridentate ONO aroylhydrazone Schiff base
derived from 4-methoxysalicylaldehyde with 4-trifluoromethylbenzohydrazide, have been
synthesized and fully characterized on the basis of elemental analysis, FT-IR, molar conductivity,
and electronic spectra. Structures of the complexes have been accomplished by single crystal
X-ray diffraction. The complexes have distorted octahedral structures in which the
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aroylhydrazones behave as binegative ligands. It is also revealed from the crystal structures that
the Mo(VI) and V(V) centers adopt NO5 donor environment, and the octahedral coordination is
furnished by oxido groups and oxygen atoms of methanol or deprotonated methanol molecules.
The catalytic properties were investigated for epoxidation of cyclooctene using aqueous tert-butyl
hydroperoxide as the oxidant.
Keywords
Dioxomolybdenum(VI); Oxovanadium(V); Aroylhydrazone; Schiff base; X-ray crystal structure;
Catalytic epoxidation activity
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Introduction
In recent years, Schiff base ligands and their transition metal complexes have attracted
considerable attention, not only for their facile synthesis, but also for potential biological, catalytic
and industrial applications.[1-5] As we know, catalytic epoxidation of olefins is an important
reaction in organic synthesis. Many transition metal complexes are active catalysts for this
process.[6-10] Yet, among the complexes, molybdenum and vanadium complexes have a unique
place in coordination chemistry and have displayed very high catalytic activities in the oxidation
of olefins and sulfides.[11-16] To date, the relationship between structures and catalytic epoxidation
activity of the molybdenum and vanadium complexes is still less studied. In the present work, a
new aroylhydrazone Schiff base,
N’-(2-hydroxy-4-methoxybenzylidene)-4-trifluoromethylbenzohydrazide (H2L), was prepared
and used to prepare dioxomolybdemum(VI) and oxovanadium(V) complexes with MoO2(acac)2
and VO(acac)2, respectively, in methanol. The catalytic properties were investigated for
epoxidation of cyclooctene using aqueous tert-butyl hydroperoxide as the oxidant.
Experimental
Materials and Methods
4-Trifluoromethylbenzohydrazide was prepared as described in the literature.[17]
4-Methoxysalicylaldehyde and VO(acac)2 were purchased from Alfa Aesar and used as received.
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MoO2(acac)2 was prepared as described in the literature.[18] Reagent grade solvents were used as
received. Microanalyses of the complexes were performed with a Vario EL III CHNOS elemental
analyzer. Infrared spectra were recorded as KBr pellets with an FTS-40 spectrophotometer.
Electronic spectra were recorded on a Lambda 900 spectrometer. The catalytic reactions were
followed by gas chromatography on an Agilent 6890A chromatograph equipped with an FID
detector and a DB5-MS capillary column (30 m × 0.32 mm × 0.25 μm). Molar conductance
measurements were made by means of a Metrohm 712 conductometer in acetonitrile.
Synthesis of the Aroylhydrazone Schiff Base H2L
The aroylhydrazone Schiff base H2Lwas synthesized by refluxing a methanolic solution (30 mL)
of 4-methoxysalicylaldehyde (10 mmol, 1.52 g) with 4-trifluoromethylbenzohydrazide (10 mmol,
2.04 g). Reflux was continued for 1 h at oily bath during which a solid compound separated. It was
filtered and washed with cold methanol. The crude product was recrystallized from methanol and
dried over anhydrous CaCl2. Yield: 2.87 g (85%). Elemental analysis: Anal. Calc. for
C16H13F3N2O3: C, 56.81; H, 3.87; N, 8.28. Found: C, 56.72; H, 3.95; N, 8.16%. IR data (KBr
pellet, cm1): 3413 ν(O--H), 3218 ν(N--H), 1645 ν(C = O), 1611 ν(C = N). UV-Vis data in
methanol (nm): 289, 353, 421.
Preparation of the Complexes
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The complexes [MoO2LMeOH] (1) and [VOL(OMe)MeOH] (2) were prepared in a similar way
by refluxing a methanolic solution (30 ml) of H2L(1.0 mmol, 0.34 g) with methanolic solutions of
MoO2(acac)2 (1.0 mmol, 0.33 g) and VO(acac)2 (1.0 mmol, 0.27 g), respectively. Initially on
mixing the two components immediately an orange yellow color for molybdenum complex and a
deep brown color for vanadium complex were observed. The mixture was refluxed for 1 h. The
respective complex separated as single crystals during slow evaporation of the reaction mixture. It
was filtered, washed with cold methanol and dried over anhydrous CaCl2. [MoO2LMeOH] (1):
Yield: 0.28 g (56%). Elemental analysis: Anal. Calc. for C17H15F3MoN2O6: C, 41.15; H, 3.05; N,
5.65. Found: C, 41.02; H, 3.12; N, 5.75%. IR data (KBr pellet, cm1): 3445 ν(O--H), 1606 ν(C =
N), 1355 ν(C--Ophenolate), 1158 ν(N--N), 950 νsym(cis-MoO2), 851 νasym(cis-MoO2). UV-Vis data in
acetonitrile (nm): 270, 326, 405. Molar conductance (103 M, acetonitrile): 36 Ω1·cm2·mol1.
[VOL(OMe)MeOH] (2): Yield: 0.32 g (69%). Elemental analysis: Anal. Calc. for
C18H18F3N2O6V: C, 46.37; H, 3.89; N, 6.01. Found: C, 46.50; H, 3.95; N, 5.89%. IR data (KBr
pellet, cm1): 3453 ν(O--H), 1605 ν(C = N), 1366 ν(C--Ophenolate), 1159 ν(N--N), 955 ν(V = O).
UV-Vis data in acetonitrile (nm): 278, 340, 415. Molar conductance (103 M, acetonitrile): 28
Ω1·cm2·mol1.
Crystal Structure Determination
Data were collected on a Bruker SMART 1000 CCD area diffractometer using a graphite
monochromator Mo Kα radiation (λ = 0.71073 Å) at 298(2) K. The data were corrected with
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SADABS programs and refined on F2 with Siemens SHELXL software.[19, 20] The structures were
solved by direct methods and difference Fourier syntheses. All non-hydrogen atoms were refined
anisotropically. The methanol hydrogen atoms were located from difference Fourier maps and
refined isotropically, with O‒H distances restrained to 0.85(1) Å. The remaining hydrogen atoms
were placed in calculated positions and included in the last cycles of refinement. Crystal data and
details of the data collection and refinement are listed in Table 1. Selected coordinate bond lengths
and angles are listed in Table 2.
Catalytic Epoxidation Process
A mixture of cyclooctene (2.76 mL, 20 mmol), acetophenone (internal reference) and the
complexes as catalysts (0.05 mmol) was stirred and heated up to 80 ºC before addition of aqueous
tert-butyl hydroperoxide (TBHP; 70% w/w, 5.48 mL, 40 mmol). The mixture is initially an
emulsion, but two phases become clearly visible as the reaction progresses, a colorless aqueous
one and a yellowish organic one. The reaction was monitored for 5 h with withdrawal and analysis
of organic phase aliquots (0.1 mL) at required times. Each withdrawn sample was mixed with 2
mL of diethylether, treated with a small quantity of MnO2 and then filtered through silica and
analyzed by GC.
Results and Discussion
Synthesis
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The aroylhydrazone Schiff base and its molybdenum and vanadium complexes were synthesized
in a facile and essentially identical way (Scheme 1).
The aroylhydrazone Schiff base acts as a tridentate dianionic ONO donor ligand towards the
MoO22+ and VO3+ cores. Both Mo(VI) and V(V) complexes were obtained from a refluxing
mixture of the aroylhydrazone ligand with MoO2(acac)2 and VO(acac)2, respectively, in 1:1 molar
proportion in methanol. The complexes were isolated as single crystals from the reaction mixture
by slow evaporation at room temperature. The complexes are stable in room temperature and are
found to be fairly soluble in most of the common organic solvents such as methanol, ethanol,
acetonitrile, DMF and DMSO. The low molar solution conductance of the complexes in
acetonitrile, indicating the complexes have non-electrolyte behavior.
IR and Electronic Spectra
IR spectra of the aroylhydrazone Schiff base shows bands at 3251 cm1 for ν(N--H), 3370--3440
cm1 for ν(O--H), and 1650 cm1 for ν(C = O).[21] The peaks attributed to ν(N--H) and ν(C = O) are
absent in the spectra of the complexes as the ligand binds in binegative form losing proton from
carbohydrazide group. Strong bands observed at 1606 cm1 for (1) and 1605 cm1 for (2) are
attributed to ν(C = N), which are located at lower frequencies as compared to the free
aroylhydrazone Schiff base, viz. 1613 cm1.[22] The molybdenum complex exhibits two
characteristic bands at 950 cm1 and 851 cm1 for symmetric and asymmetric stretching of
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cis-MoO22+ core, respectively.[23,24] The vanadium complex exhibits characteristic band at 955
cm1 for the stretching of V = O bond.[25]
Electronic spectra of the complexes recorded in acetonitrile solution display strong absorption
bands centered at 421 nm for (1) and 415 nm for (2), which are assigned as charge transfer
transitions of N(pπ)--Mo(dπ) LMCT. The medium absorption bands centered at 353 nm for (1) and
340 nm for (2) are assigned as charge transfer transitions of O(pπ)--Mo(dπ) LMCT.[26,27] The slight
change of λmax values within each set of peaks may be due to the difference of electron donating
capacity of the aroylhydrazone ligands induced by the metal atoms.
Structure Description of Complex (1)
The perspective view of complex (1) together with the atom numbering scheme is shown in Figure
1. The coordination geometry around the molybdenum(VI) atom in the complex reveals a distorted
octahedral environment with NO5 chromophore. The aroylhydrazone Schiff base behaves as
dianionic tridentate ligand binding through the phenolate oxygen, the enolate oxygen and the
imine nitrogen, and occupies three positions in the equatorial plane. One oxo group is located trans
to the imine nitrogen in the equatorial plane. The other oxo group and the methanol oxygen are
located at the axial positions. The two terminal oxo groups are hence cis to each other and exhibit
typical Mo = O double bond distances.[28,29] The molybdenum is found to be deviated from the
mean equatorial plane defined by the four donor atoms by 0.338(1) Å. The Mo--Omethanol bond
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length in the complex is longer than the normal single bond lengths (2.37 Å against 1.9--2.0 Å).
This shows that the methanol molecule is loosely attached to the Mo(VI) center.[27] The remaining
Mo--O bond lengths are similar to other molybdenum(VI) complexes.[30,31] The bond between Mo
and the azomethine nitrogen in the complex is about 2.24 Å which is comparatively longer than the
normal Mo--N single bonds. This is due to the trans effect generated by the oxo group trans to the
Mo--N bond.[27] The C(9)--O(2) bond length in the complex is 1.31 Å, which is closer to single
bond length rather than C = O double bond length. However, the shorter length compared to C--O
single bond may be attributed to extended electron delocalization in the ligand.[27] Similarly
shortening of C(9)--N(2) bond length (1.30 Å instead of normal 1.38 Å) together with the
elongation of N(1)--N(2) bond length also supports the electron cloud delocalization in the ligand
system.[27] The aroylhydrazone Schiff base ligand forms a five-membered and a six-membered
chelate rings with the Mo center. The five-membered metallacycle ring is thus rather planar, but
the six-membered metallacycle ring is clearly distorted. The dihedral angle between the two
benzene rings is 5.0(3)º. The trans angle between the donor atom of the methanol ligand and the
oxo atom is 170.89(7)º, indicating considerable distortion of the coordination octahedron around
the Mo(VI) center.
The crystal packing diagram of the complex is shown in Figure 2. The adjacent two complex
molecules are linked by two O--H···N hydrogen bonds [O(6)--H(6) = 0.85(1) Å, H(6)···N(2)i =
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1.97(1) Å, O(6)···N(2)i = 2.808(2) Å, O(6)--H(6)···N(2)i = 171(3)º; symmetry code for i: -- x, -- y,
-- z], to form dimer.
Structure Description of Complex (2)
The perspective view of complex (2) together with the atom numbering scheme is shown in Figure
3. The asymmetric unit of the compound contains two independent vanadium complex molecules.
The coordination geometry around each vanadium(V) atom in the complex reveals a distorted
octahedral environment with NO5 chromophore. The aroylhydrazone Schiff base behaves as
dianionic tridentate ligand binding through the phenolate oxygen, the enolate oxygen and the
imine nitrogen, and occupies three positions in the equatorial plane. One deprotonated methanol
oxygen is located trans to the imine nitrogen in the equatorial plane. One oxo group and one
methanol oxygen are located at the axial positions. The vanadium atoms are found to be deviated
from the mean equatorial planes defined by the four donor atoms by 0.344(1) Å for V1 and
0.320(1) Å for V2. The V--Omethanol bond lengths in the complex are longer than the normal single
bond lengths (2.37--2.38 Å against 1.9--2.0 Å). This shows that the methanol molecule is loosely
attached to the V(V) center as that observed for complex (1). This is due to the trans effect
generated by the oxo group trans to the V--Omethanol bond. The remaining V--O and V--N bond
lengths are similar to other vanadium(V) complexes.[32,33] The C(9)--O(2) and C(27)--O(8) bond
lengths in the complex are 1.30--1.31 Å, which are closer to single bond length rather than C = O
double bond length. However, the shorter length compared to C--O single bond may be attributed
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to extended electron delocalization in the ligand.[27] Similarly shortening of C(9)--N(2) and
C(27)--N(4) bond lengths (1.29--1.32 Å instead of normal 1.38 Å) together with the elongation of
N(1)--N(2) and N(3)--N(4) bond lengths also supports the electron cloud delocalization in the
ligand system. The aroylhydrazone Schiff base ligand forms a five-membered and a six-membered
chelate rings with the V center. The five-membered metallacycle ring is thus rather planar, but the
six-membered metallacycle ring is clearly distorted. The dihedral angles between the two benzene
rings are 7.6(5)º for V1 molecule and 10.3(5)º for V2 molecule. The trans angles between the
donor atom of the methanol ligand and the oxo atom are 175.4(2)º for V1 molecule and 175.2(2)º
for V2 molecule, indicating considerable distortion of the coordination octahedron around the
V(V) center.
The crystal packing diagram of the complex is shown in Figure 4. The adjacent complex
molecules are linked by methanol molecules through O--H···N hydrogen bonds [O(6)--H(6) =
0.85(1) Å, H(6)···N(2)ii = 2.02(3) Å, O(6)···N(2)ii = 2.836(6) Å, O(6)--H(6)···N(2)ii = 161(8)º;
O(12)--H(12) = 0.85(1) Å, H(12)···N(4)iii = 1.99(2) Å, O(12)···N(4)iii = 2.833(5) Å,
O(12)--H(12)···N(4)iii = 171(9)º; symmetry codes: ii: --1/2 + x, -- y, z; iii: --1/2 + x, 1 -- y, z], to
form one-dimensional chains.
Catalytic Epoxidation Results
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After addition of aqueous TBHP at 80 ºC, the molybdenum and vanadium complexes dissolve
completely in the organic phase. The aqueous phase of the complexes was colorless and the
organic one yellowish for molybdenum complex and brown for vanadium complex, indicating that
the catalyst is mainly confined in the organic phase. TBHP is mainly transferred into the organic
phase under those conditions, and for that reason the reactant and products in the organic layer
were analyzed. Cyclooctene and cyclooctene oxide are not significantly soluble in water, therefore
the determination of the epoxide selectivity (epoxide formation/cyclooctene conversion) is
expected to be accurate. The obtained results are given in Table 3. For the cyclooctene epoxidation
by using aqueous TBHP, with no extra addition of organic solvents, the present study shows
effective activity. Kinetic profiles of the complexes as catalysts are presented in Figure 5. No
induction time was observed. The cyclooctene conversion for the complexes is high after 5 h, viz.
87% for (1) and 83% for (2).
Possible mechanistic consideration involves coordination of TBHP as a neutral molecule, with
the hydrogen bond O--H···O (Schemes 2 and 3). Even though high conversion of cyclooctene is
observed, selectivity towards cyclooctene oxide is not high, 55% for (1) and 63% for (2).
Conclusion
In summary, the present paper reports a very common but facile way to synthesize new Mo(VI)
and V(V) complexes with aroylhydrazone Schiff base. In the complexes, the aroylhydrazone
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Schiff base ligands coordinate to the metal atoms through phenolate oxygen, imine nitrogen and
enolate oxygen. The complexes are efficient catalysts for the epoxidation of cyclooctene.
Acknowledgments
This work was financed by the National Technology Support Project (2012BAD36B03), the Open
Foundation of Zhejiang Provincial Top Key Academic Discipline of Chemical Engineering and
Technology（YR2015004）and the Foundation of Wuhan Textile University.
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29. Dinda, R.; Sengupta, P.; Ghosh, S.; Mayer-Figge, H.; Sheldrick, W. S. A family of
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Table 1. Crystallographic data for the complexes
(1)
(2)
Empirical formula
Formula weight
Crystal system
Space group
a [Å]
C17H15F3MoN2O6
496.25
C18H18F3N2O6V
466.28
monoclinic
P21/n
orthorhombic
Pca21
8.1408(7)
12.286(1)
18.929(2)
91.136(1)
1892.8(3)
4
11.192(2)
8.599(1)
43.024(2)
b [Å]
c [Å]
β [º]
V [Å3]
4141.0(8)
8
Z
T [K]
298(2)
298(2)
0.71073
λ [Å]
0.71073
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ρcalcd. [g cm--3]
μ [mm--1]
F(000)
1.741
0.759
992
1.496
0.542
1904
θ range for data collection 1.98--25.49
2.37--25.49
--13 ≤ h ≤ 13
--10 ≤ k ≤ 9
--43 ≤ l ≤ 41
11022
Index ranges
--9 ≤ h ≤ 9
--14 ≤ k ≤ 13
--22 ≤ l ≤ 17
9695
Measured reflections
Independent reflections
3510
4756
Observed reflections (I >
2σ(I))
3150
4039
Parameters
266
1
553
3
Restraints
Data completeness
1.046
1.067
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Maximum and minimum
transmission
0.8212 and 0.8447
0.8542 and 0.8674
Final R indices [I > 2σ(I)] 0.0233, 0.0623
0.0436, 0.0928
0.0559, 0.0991
1.067
R indices (all data)
0.0271, 0.0657
1.046
Goodness-of-fit on F2
Largest difference in peak 0.427 and --0.335
and hole (e Å3)
0.429 and --0.252
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Table 2. Selected bond lengths (Å) and angles (º) for the complexes
(1)
Mo1-O1
1.9217(15)
1.7000(15)
2.3710(17)
105.98(8)
102.51(7)
97.80(7)
Mo1-O2
2.0203(15)
1.6947(18)
2.2423(17)
98.79(8)
Mo1-O4
Mo1-O5
Mo1-O6
Mo1-N1
O5-Mo1-O4
O4-Mo1-O1
O4-Mo1-O2
O5-Mo1-N1
O1-Mo1-N1
O5-Mo1-O6
O1-Mo1-O6
N1-Mo1-O6
(2)
O5-Mo1-O1
O5-Mo1-O2
O1-Mo1-O2
O4-Mo1-N1
O2-Mo1-N1
O4-Mo1-O6
O2-Mo1-O6
97.18(8)
149.50(6)
156.22(7)
71.27(6)
96.49(7)
81.22(6)
170.89(7)
82.63(7)
82.36(7)
77.75(6)
74.78(6)
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V1-O1
1.852(4)
1.775(4)
2.370(5)
1.852(4)
1.768(3)
2.381(5)
103.3(2)
101.29(17)
92.95(18)
95.6(2)
V1-O2
1.941(4)
1.573(5)
2.120(5)
1.933(4)
1.586(5)
2.103(4)
102.3(3)
98.9(2)
V1-O4
V1-O5
V1-O6
V1-N1
V2-O7
V2-O8
V2-O10
V2-O11
V2-O12
V2-N3
O5-V1-O4
O4-V1-O1
O4-V1-O2
O5-V1-N1
O1-V1-N1
O5-V1-O6
O1-V1-O6
N1-V1-O6
O5-V1-O1
O5-V1-O2
O1-V1-O2
O4-V1-N1
O2-V1-N1
O4-V1-O6
O2-V1-O6
O11-V2-O10
150.81(19)
158.7(3)
74.43(19)
80.77(18)
78.53(17)
102.8(2)
83.73(18)
175.4(2)
78.79(19)
79.99(19)
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O11-V2-O7
O11-V2-O8
O7-V2-O8
O10-V2-N3
O8-V2-N3
O10-V2-O12
O8-V2-O12
100.6(2)
99.6(2)
O10-V2-O7
O10-V2-O8
O11-V2-N3
O7-V2-N3
101.33(16)
93.83(18)
94.4(2)
151.2(2)
160.7(3)
74.55(19)
81.83(18)
78.90(17)
83.67(18)
175.22(19)
79.19(19)
80.83(19)
O11-V2-O12
O7-V2-O12
N3-V2-O12
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Table 3. Catalytic results for the cyclooctene epoxidation by aqueous TBHPa
Complex
(1)
Conversion (%)b
Selectivity (%)c
TONe
362
TOF (h1)d
351
87
83
55
63
(2)
278
296
aReaction conditions: time, 5 h; temperature, 80 ºC. Metal complex/cyclooctene/TBHP molar
ratio: 0.25/100/200.
bFor cyclooctene, calculated after 5 h.
cFormed epoxide per converted olefin after 5 h.
dn(cyclooctene transformed)/n(catalyst)/time at 20 minutes.
en(cyclooctene transformed)/n(catalyst at 5 h).
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Fig. 1. ORTEP plots (30% probability level) and numbering scheme for (1).
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Fig. 2. Hydrogen bond (dashed lines) linked structure of (1), viewed down the c axis.
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Fig. 3. ORTEP plots (30% probability level) and numbering scheme for (2).
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