Designing chiral amido-oxazolines as new chelating ligands devoted to direct Cu-catalyzed oxidation of allylic C–H bonds in cyclic olefins

Article abstract of DOI:10.1016/j.tet.2018.12.062

A new type of amido-oxazoline ligands was conveniently synthesized from inexpensive and commercially available materials in high yields and enantiomeric excesses. The corresponding chiral copper complexes with this class of ligands [C₂ symmetric S,S-bis(amido-oxazoline-Cu(II) complex] were synthesized accordingly. The ORTEP diagram of ligand 6a and complex 6a-copper were compared and characterization of the complex confirmed the involvement of both dentate parts of the ligands, the oxygen and nitrogen atoms, in complexation with copper. The utilization of this amido-oxazoline ligands in the copper-catalyzed enantioselective esterification of allylic C–H bonds of cyclic olefins with tert-butyl-4-nitrobenzoperoxoate resulted in the highest activities, yields (up to 95%) and enantioselectivities (up to 96%) in the presence of HZSM-5 zeolite. These new findings highlight the protocol as one of the most attractive and useful methods for the oxidation of the asymmetric allylic C–H bond of cycloalkenes compared to other methodologies reported in the literature.

Full text of DOI:10.1016/j.tet.2018.12.062

Tetrahedron 75 (2019) 862e867
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Tetrahedron
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Designing chiral amido-oxazolines as new chelating ligands devoted
to direct Cu-catalyzed oxidation of allylic CeH bonds in cyclic olefins
,
Saadi Samadi a *, Khosrow Jadidi b, Mojgan Samadi a, Akram Ashouri a, Behrouz Notash b
a Laboratory of Asymmetric Synthesis, Department of Chemistry, Faculty of Science, University of Kurdistan,Sanandaj, Iran
b Department of Chemistry, Shahid Beheshti University, G.C., Tehran, 1983963113, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
A new type of amido-oxazoline ligands was conveniently synthesized from inexpensive and commer-
cially available materials in high yields and enantiomeric excesses. The corresponding chiral copper
complexes with this class of ligands [C2 symmetric S,S-bis(amido-oxazoline-Cu(II) complex] were syn-
thesized accordingly. The ORTEP diagram of ligand 6a and complex 6a-copper were compared and
characterization of the complex confirmed the involvement of both dentate parts of the ligands, the
oxygen and nitrogen atoms, in complexation with copper. The utilization of this amido-oxazoline ligands
in the copper-catalyzed enantioselective esterification of allylic CeH bonds of cyclic olefins with tert-
butyl-4-nitrobenzoperoxoate resulted in the highest activities, yields (up to 95%) and enantioselectivities
(up to 96%) in the presence of HZSM-5 zeolite. These new findings highlight the protocol as one of the
most attractive and useful methods for the oxidation of the asymmetric allylic CeH bond of cycloalkenes
compared to other methodologies reported in the literature.
Received 9 October 2018
Received in revised form
9 December 2018
Accepted 28 December 2018
Available online 30 December 2018
Keywords:
Chiral amido-oxazoline ligands
Enantioselective allylic CeH bonds
oxidation
Chiral allylic ester
Chiral copper complex
© 2019 Elsevier Ltd. All rights reserved.
1. Introduction
chiral allylic alcohols is considered one of the most important re-
actions in organic chemistry, in which, unlike hydroxylation and
Transferring the chirality from an optically active catalyst to the
reaction product can meet the concept of atom economy perfectly,
as one of the key requirements of the twelve principles of green
chemistry [1]. During the last decades, the role of chirality trans-
formation in chiral oxazoline ligands have been confirmed in
numerous transition-metal-catalyzed asymmetric transformations.
Although chiral bisoxazolines ligands can be extensively used in
catalytic asymmetric synthesis, chiral mono oxazoline versions
have rarely presented comparable impacts [2e5]. However, based
on some examples, metal complexes of chiral mono oxazolines
have been applied to a variety of catalytic asymmetric reactions and
have provided better enantioselectivities, compared to other
famous chiral bis oxazolines. Regarding the activity, yield and
enantioselectivity, highly valuable catalysts are often designed
based on chiral amido-oxazoline ligands, which are widely imple-
mented in the catalytic asymmetric synthesis, compared to mono-
and multi-dentate mono oxazoline ligands [6e8]. Asymmetric
allylic CeH bonds oxidation of olefins to chiral allylic esters and
epoxidation, a second functional group is formed while the double
bond remains unchanged [9e28]. In addition, the olefins can be
more functionalized to produce a variety of products such as
leukotriene B4 [29], chrysanthemic acid [30], amyrin [31] and
brevetoxin [32] (Scheme 1).
Using ligated copper complexes, allylic oxidation reaction was
performed in higher chemical yield and rate of reaction in com-
parison to those with unligated copper. Nevertheless, the literature
survey shows that all reported asymmetric allylic oxidations were
done in the presence of Cu - complexes containing chiral mono
oxazoline, bisoxazoline or tris oxazoline ligand in different condi-
tion which suffers from long reaction times, moderate yields and
enantiomeric excesses [9e19,21e26,28,33e47]. In 2013, our group
disclosed the use of chiral biarylbisoxazoline ligands for allylic CeH
bond oxidation of cyclic olefins [21e23]. Although the
Cu(CH3CN)4PF6 complexes of those ligands induced the chirality,
the reactions time were too long. Moreover, the synthesis of biaryl
bisoxazoline ligands (including several steps) was somehow diffi-
cult. Other hand, in continue of our laboratory purposes, in order to
approach to improving the obtained results and increasing the ef-
ficiency of this reaction, herein we report the easy preparation and
characterization of new chiral amido-oxazolines, and the use of
* Corresponding author.
E-mail address: s.samadi@uok.ac.ir (S. Samadi).
https://doi.org/10.1016/j.tet.2018.12.062
0040-4020/© 2019 Elsevier Ltd. All rights reserved.

S. Samadi et al. / Tetrahedron 75 (2019) 862e867
863
single-crystal diffraction study, without any desired chiral product
7 (Fig. 1) (see S62eS65 in the electronic supplementary material)
[61,62]. In the crystal structure, the determination of hydrogen
atom attached to nitrogen was found in a different Fourier map.
Most probably, an intramolecular hydrogen bonding between the
NH and carbonyl groups, and the long conjugation of the newly
formed double bond with the carbonyl group, phenyl group, and
lone pairs of oxygen and nitrogen atoms of oxazoline ring could
provide the driving force for this condensation process so as to
stabilize the product and control the selectivity.
As illustrated in Fig. 2, the treatment of two equivalents of 6a
with one equivalent of Cu(CH3CN)4PF6 in acetonitrile produced
suitable crystals for the single-crystal X-ray analysis [62,63]. Its be
noted oxidation state of copper was changed (Cu(I) to Cu(II)) in
during the complex formation process [64]. According to the liter-
ature survey, Cu(II) complexes with two bisoxazoline ligands have
not been reported since two ligands cannot be easily accommo-
dated by Cu(II) for steric reasons. However, the chiral amido-
oxazolines ligands are sterically less hindered, which enable the
preparation of the Cu(II) complex (see S66eS69 in the electronic
supplementary material) [23,24,65].
Scheme 1. The synthesis of leukotriene B4 by asymmetric allylic CeH bond oxidation
of cyclohexene.
chiral copper complexes of these ligands which was evaluated in
the allylic CeH bonds oxidation of cyclic olefins with perester in the
presence of different additives such as HZSM-5 zeolite [48], mes-
oporous SBA-15 and MCM-41 silica [49,50] for the first time.
Both crystal structures of 6a and 8a demonstrated that the chiral
centers remained unchanged. In addition, this analysis confirmed
that these chiral ligands are bidentate when they are associated
with copper. Further, the structure of the oxazoline ring in this
complex changed into the expected structure due to the coordi-
nation of the carbonyl group and lone pair of nitrogen atom on
copper.
2. Results and discussion
2.1. Synthesis of chiral amido-oxazolines ligands 6aed
Synthesizing of chiral amido-oxazolines 6aed can be performed
in excellent yields and enantiomeric excess from inexpensive and
available starting material (S)-amino acids 1 and 4-nitrobenzoic
acid 3 (Scheme 2). First, the chiral amino acids 1 were easily
reduced with NaBH4 and I2 in tetrahydrofuran which resulted in
producing the corresponding amino alcohols 2 cleanly (Meyers
method) [51]. The main synthesis was started by preparing amino
oxazolines 5 from amino alcohols 2, bromine and sodium cyanide
reagents in methanol [52e60]. Then, 4-nitrobenzoic acid 3 was
treated with oxalyl chloride in a separate pot and produced the
required acid chloride 4 in the presence of a catalytic amount of
dimethylformamide. Base on the obtained results, the treatment of
acid chloride 4 with four individual S-amino oxazoline 5 led to the
formation of chiral amido-oxazolines ligands 6 as shown in the
2.2. Catalytic and induced asymmetric effects of chiral copper
complexes in asymmetric allylic CeH bonds oxidation of cyclic
olefins
2.2.1. Optimization of the model reaction
On the basis of a typical experimental procedure, the allylic
oxidation of cyclic olefins was carried out by using cyclohexene
(n ¼ 2) as the model substrate in the presence of Cu(OTf),
Cu(CH3CN)4PF6 or other copper salts in order to study the optimi-
zation of the reaction conditions (Scheme 3). The nature of the
chiral ligand, metal salt, perester oxidant and reaction conditions,
such as solvent and temperature, can substantially influence the
reaction. The use of additives such as molecular sieves (MS) and
phenylhydrazine is necessary for obtaining the optimized condi-
tions in the asymmetric allylic CeH bonds oxidation of cycloolefins
as well [9e26]. Hence, the effect of different solvents, Cu salts,
temperature, chiral ligands 6aed, chiral ligands loading, additives,
and additive loading were examined to attain the optimized reac-
tion conditions based on the model reaction [21e23].
First, the effect of solvent on the model reaction was investi-
gated. Among the tested solvents, acetone and acetonitrile with
high polarity were regarded as the most effective solvents. Analo-
gously to some previous studies, phenylhydrazine (acts as reducing
agents) [23,46] improved the reactivity, enantioselectivity, and
Scheme 2. Synthesis of chiral Cu-oxazoline benzamide complexes 8aed.
Fig. 1. ORTEP diagram of ligand 6a. Thermal ellipsoids are at the 30% probability level.

864
S. Samadi et al. / Tetrahedron 75 (2019) 862e867
The effect of different Cu salts was also examined in the pres-
ence of ligand 6a using HZSM-5 zeolite as an additive at different
temperatures in order to achieve optimal reaction conditions. The
best results were obtained in all cases with CuOTf as the copper
source at 0 ꢀC (entry 4, Table 2). When the reaction was catalyzed
by different copper (I) and copper (II) salts, variation was observed
in the obtained results. A low-efficiency reaction was achieved
especially for the copper (II) nitrate (entry 7). In order to investigate
the influence of other peresters on the efficiency of the reaction at
hand,
tert-butylbenzoperoxoate,
tert-butyl-4-
methylbenzoperoxoate and tert-butyl 4-chlorobenzoperoxoate
were also examined. However, the isolated yield, enantiose-
lectivity and rate of reaction were decreased in comparison with
tert-butyl 4-nitrobenzoperoxoate 9 (entry 4 vs. 9 and 11, Table 2).
The effect of HZSM-5 zeolite loading is summarized in Table S2.
The best results were obtained using 5 mg loading of HZSM-5. In
addition, the reaction was not completed with less than 5 mg of
HZSM-5 such that an increase in the amount of this additive led to a
decrease in the reaction results (See Table S2 in the electronic
supplementary material).
Fig. 2. ORTEP diagram of complex 6a-Cu(II). Thermal ellipsoids are at the 30% prob-
ability level.
In the next procedure, other ligands (6bed) were examined
under the optimized reaction conditions. As displayed in Table 3,
the substitution on the oxazoline ring, especially the aryl sub-
stituents play an important role in increasing the efficiency of the
ligand. The phenyl or benzyl substituted oxazolines 6a and 6b led to
higher enantioselectivities, yields and reactivities compared to the
other two ligands, 6c and 6d [22]. In addition to the nitro group on
the ligand, we had checked the reaction with some substitutions
such as H, Br, OMe and NH2 on ligand in a typical optimized
experimental procedure, but we did not obtain better results
(reactivity and enantioselectivity) in comparison (Table S3 in the
electronic supplementary material). Its be noted, the chemical yield
for preparation of ligand with the nitro group was better than
others.
Scheme 3. Enantioselective allylic oxidation of cycloolefins.
yields (See Table S1 in the electronic supplementary material).
Furthermore, the effects of different inorganic additives such as
molecular sieve MS(4 Å), mesoporous SBA-15 silica, mesoporous
MCM-41 silica and HZSM-5 zeolite in the presence of ligand 6a
were evaluated in the selected solvent (Table 1). Based on the re-
sults, the HZSM-5 zeolite (5 mg/mmol) indicated the greatest effect
among these additives. The enantioselectivity of the reaction was
enhanced considerably (up to 47%) and the reaction was completed
in only 7 h while providing the chiral allylic ester 11 in 94% yield
(entry 5). In addition, the simultaneous use of molecular sieves and
phenylhydrazine resulted in an enhancement of the enantiomeric
excess, yield, and reactivity (compare the entries 1 and 2 with 3,
Table 1).
Furthermore, regarding the effect of chiral ligand loading, the
results indicated that the enantioselectivity, yield and time of re-
action varies by changing the active species of the reaction medium
at various ratios of chiral amido-oxazoline ligand to copper.
Although, in our previous study, the best stereospecificity was
Table 2
Effect of copper salts on the enantioselectivity, yield and reactivity of the reaction at
different temperatures.
Table 1
Effect of different additives on yield, reactivity, and enantioselectivity of the reaction
at room temperature.
Entry
Cu salt
T (ꢀC)
Time (h)
Yield (%)
Ee (%)
1
2
3
4
5
6
7
8
Cu(OTf)
Cu(OTf)
CuPF6
25
10
0
0
0
4
95
90
87
95
73
78
75
70
80
72
85
52
66
72
88
66
54
43
96
80
65
83
20
75
45
95
150
150
90
82
110
65
Cu(OTf)
Cu(OTf)2
Cu(OAc)2
Cu(NO3)2
Cu(OTf)
Cu(OTf)
Cu(OTf)
Cu(OTf)
0
0
Entry
Additives
Time (h)
Yield (%)
Ee (%)
1
e
31
36
22
18
7
70
71
83
90
94
86
21
25
34
40
47
32
ꢁ10
2a
3
MS(4 Å)
MS(4 Å)
SBA-15
HZSM-5
MCM-41
9a
10b
11c
0
0
0
4
5
6
a
In the presence of tert-butylbenzoperoxoate.
In the presence of tert-butyl 4-methylbenzoperoxoate.
In the presence of tert-butyl 4-chlorobenzoperoxoate.
30
b
c
a
In the absence of PhNHNH2.

S. Samadi et al. / Tetrahedron 75 (2019) 862e867
865
Table 3
enantioselective allylic esterification of the CeH bond of cyclo-
hexene by using tert-butyl-4-nitrobenzoperoxoate, CuOTf, and
chiral ligand 6a. Based on a literature review on the chemistry of
the reaction [21,27,66e72], the reaction proceeds via a radical in-
termediate. Thus, in the present study, the homolysis of the oxygen-
oxygen bond in perester by CuOTf is proposed to form copper (II)
benzoate and tert-butoxy radical. Due to the C2 symmetry of S,S-
bis(chiral amido-oxazolines) Cu(I) complex, which creates a chiral
environment, the two phenyl groups of the oxazoline ligand can
occupy one of the two faces available for the complexation, and the
remaining face provides a space for perester. Then, tert-butoxy
radical abstracts a prochiral hydrogen atom at the allylic position of
the cyclohexene, thus resulting in the allylic radical and tert
-butanol. In the next step, the allylic radical is quickly added to
copper (II) carboxylate, such that the favored transition state can be
depicted with the allyl and benzoate ligands positioned in a manner
to minimize the interactions with the flanking phenyl groups of the
oxazolines, as the copper (III) intermediate [73e75] adopts pref-
erably an octahedral geometry. So the mechanism flows by an
attack of the carboxyl group from the Si-face to the cyclohexnyl,
followed by a pericyclic rearrangement and a reductive elimination
to yield the chiral allylic ester as the product and the Cu(I) catalyst
regenerated [21,27,66e72] (Scheme 4).
Effects of chiral ligands 6aed on yield, reactivity and enantioselectivity of the re-
action.
Entry
Catalyst
Time (h)
Yield (%)
ee (%)
1
2
3
4
5
6
7
8
6a-CuPF6
75
45
67
50
82
75
55
70
87
95
67
88
60
75
50
65
74
88
62
75
22
37
20
24
6a-Cu(OTf)
6b-CuPF6
6b-Cu(OTf)
6c-CuPF6
6c-Cu(OTf)
6d-CuPF6
6d-Cu(OTf)
obtained by using complexes containing a ratio of ligand to copper
1:1 [22, 23], in the case of chiral amido -oxazolines ligands, the
single-crystal X-ray analysis indicated that this ratio should be 2:1
(Fig. 2). The best result was achieved when the amounts of 6a and
CuOTf were 5 and 2.5 mol%, respectively (See entry 2, Table S4 in
the electronic supplementary material).
3. Conclusion
In conclusion, we have reported the design and synthesis of a
new class of chiral amido-oxazolines ligands from inexpensive and
commercially available materials in high yields and enantiomeric
excesses. The copper complexes of these ligands demonstrated
positive impacts on the catalytic enantioselective allylic esterifica-
tion of the CeH bonds in cycloolefins and afforded the product with
promising enantioselectivities (up to 96%) and yields (up to 95%).
Further investigation of the potential applications of this series of
ligands in other reactions is underway in our laboratory.
2.2.2. Evaluation of the scope of the reaction
Table 4 demonstrates the results of the generality of these chiral
ligands by preparing various chiral allylic esters from different
cycloalkenes under optimized conditions. Based on the results,
using larger cycloalkenes (cycloheptene or cyclooctene) led to some
products with lower enantiomeric excesses than cyclohexene and
cyclopentene, which can be explained by the fact that the bigger
ring systems than six members may be too bulky to be fit to the
catalyst complex cavity which is determined by the substituent on
the amido-oxazoline ligand. It is worth noting that almost the same
results could be observed for 1, 5-cyclooctadiene as cyclohexene in
the presence of these chiral catalysts. We also applied the optimal
conditions to prepared allylic esters from acyclic olefins, the
oxidation delivered a mixture of regioselective isomers in long time
reaction with very low yield and enantiomeric excess.
4. Experimental section
4.1. Typical procedure for the synthesis of amino oxazolines 5aed
To a solution of (33 mmol) bromine in anhydrous methanol
(40 mL), sodium cyanide (1.62 g, 33.0 mmol) was added slowly
while stirring over 1 h at 0 ꢀC. Then a solution of (S)-amino alcohols
2aed [51] (30.0 mmol) in anhydrous methanol (70 mL) was added
over 20 min. The solution was allowed to warm slowly to room
temperature by stirring for 1 h under N2. Next, a 25% ammonia
2.3. Proposed mechanism
Scheme 4 represents the related mechanism for the catalytic
Table 4
Synthesis of chiral allylic esters 10, 12, 13 and 14 by allylic CeH bonds oxidation of various cycloolefins in the presence of chiral ligands under optimized conditions.
Starting material
Product
Ligand
Time (h)
Yield (%)
ee (%)
Time (h)
Yield (%)
ee (%)
Time (h)
Yield (%)
ee (%)
Time (h)
Yield (%)
ee (%)
6a
6b
6c
6d
50
70
65
81
80
90
75
82
84
77
32
25
58
77
60
50
85
80
85
74
71
63
18
23
60
73
57
75
80
59
75
80
74
77
12
20
30
76
58
71
85
90
90
80
90
94
33
20

866
S. Samadi et al. / Tetrahedron 75 (2019) 862e867
Scheme 4. Proposed pathway for the catalytic esterification of the allylic CeH bonds of cyclohexene using tert-butyl- 4-nitrobenzoperoxoate, chiral ligand 6a and CuOTf.
solution (15 mL) was added and was stirred for 10 min. After that,
most of the solvent was evaporated under vacuum. Under vigorous
stirring, 30 mL of NaOH (20%) was added subsequently. The mixture
was extracted with ethyl acetate (4 ꢂ 40 mL), the organic layer
washed with saturated brine (5 mL), dried over magnesium sulfate
and concentrated. The pure products 5aed were achieved by
recrystallization from ethyl acetate. The total yields for compounds
5aed were 70%, 85%, 75%, and 75% respectively [52,53,55e60] (see
S2-3, S20-28 in the electronic supplementary material).
separated by flash chromatography (5e25% EtOAc/hexanes) as
yellow solids. The total yields for compounds 6bed were 90%, 95%,
85%, and 87% respectively [22,23] (see S3-5, S29-42 in the electronic
supplementary material).
4.3. Typical procedure for enantioselective allylic CeH bonds
oxidation of cycloolefins
A light yellow solution of the chiral amido-oxazolines ligands
6aed (0.043 mmol), copper salt (0.022 mmol) and anhydrous
acetone (2 mL) were added to a flame-dried schlenk tube and
stirred for 3 h at ambient temperature. In this case, TLC analysis
indicated the formation of a single spot (Rf ¼ 0.0 in 50% EtOAc/n-
4.2. Typical procedure for the synthesis of amido-oxazoline ligands
6aed
To a solution of p-nitrobenzoic acid 1 (0.5 g, 3.0 mmol) in 10 mL
of anhydrous methylene chloride (10 mL) were added 0.62 mL
(6 mmol) of oxalyl chloride and 3 drops of dimethylformamide at
0 ꢀC. The reaction mixture was stirred for 8 h at 0 ꢀC under N2. The
solvent was removed under reduced pressure to afford the p-
nitrobenzoyl chloride 4 as a light yellow solid (0.56 g, quantitative).
Then, the solid was dissolved in 10 mL of anhydrous methylene
chloride and cooled to 0 ꢀC, and was added to a solution of (S)-
amino oxazoline (3.3 mmol) 5aed and triethylamine (0.5 mL,
3.3 mmol) in 10 mL anhydrous methylene chloride at 0 ꢀC over 1 h.
Next, the solution was allowed to warm slowly to room tempera-
ture while stirring for 6 h under N2. TLC analysis of the reaction
(10%/90% EtOAc/n-hexane) confirmed the formation of the new
compounds 6aed. The mixture was extracted with ethyl acetate;
the organic layer was washed with saturated brine, dried with
magnesium sulfate and concentrated. Products 6aed were
hexane). After the addition of phenyl hydrazine (2 mL, 0.02 mmol)
the color of the solution was changed from blue-green to red. Then
5 mg of HZSM-5 (or other additives) was added. After a few mi-
nutes, cycloolefin (2.5 mmol) was added. The reaction mixture was
cooled to 0 ꢀC and then tert-butyl-p-nitrobenzoperoxoate
9
(0.203 g, 0.85 mmol) was added to the reaction solution under
argon atmosphere. The mixture was kept at 0 ꢀC until TLC showed
the complete disappearance of perester. The reaction mixture was
dissolved in 5 mL of NH4OH (%10), extracted with EtOAc (3e5 mL)
and dried over MgSO4. Removal of the solvent under vacuum
afforded a yellow residue that was chromatographed over silica gel
to provide the pure white solid product 10e14 (yields up to 95%)
and recovered chiral amido-oxazoline ligands in 74e88% yields
[20e23,28] (see S6-10, S43eS58 in the electronic supplementary
material).

S. Samadi et al. / Tetrahedron 75 (2019) 862e867
867
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We are grateful to the University of Kurdistan Research Councils,
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support of this work.
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P21, a ¼ 6.2041(12), b ¼ 10.247(2), c ¼ 11.602(2) Å;
b
¼ 90.14(3)ꢀ , V ¼
ꢀ
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737.6(2) Å3, Z ¼ 2, Dcalcd ¼ 1.402 g cm-3
,
m
(Mo-K
a
)¼ 0.103 mm-1, crystal
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dimension of 0.45ꢂ0.35ꢂ0.22 mm; T ¼ 298(2) K; F(000) ¼ 324; reflections
collected ¼ 3412; reflections independent ¼ 2188;
q range 2.65 to 25.00; h, k, l
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range: -6ꢃhꢃ7, -10ꢃkꢃ12, -13ꢃlꢃ13; parameters ¼ 213; restraints ¼ 2,
largest difference in peak and hole, Drmax and Drmin ¼ 0.702 and -0.724 e.Å3.
The X-ray diffraction measurement was made on a STOE IPDS-II diffractom-
eter with graphite monochromated Mo-K
a radiation. The structure was
solved by using SHELXS. The Data reduction and structure refinement was
carried out with SHELXL using the X-STEP32 crystallographic software
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matrix least-squares on F2 values to final R1 ¼ 0.0894, wR2 ¼ 0.2399[I>2sig-
ma(I)] and S ¼ 1.135. Hydrogen atom attached to nitrogen atom was found in
a difference Fourier map and refined isotropically. All other hydrogen atoms
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been deposited with the Cambridge Data Centre, CCDC 1813681.
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space group P212121, a ¼ 10.990(2), b ¼ 13.104(3), c ¼ 21.732(4) Å; V ¼
3129.6(11) Å3, Z ¼ 4, Dcalcd ¼ 1.539 g cm-3
,
m
(Mo-K
a
)¼ 0.765 mm-1, crystal
dimension of 0.50ꢂ0.18ꢂ0.15 mm; T ¼ 120(2) K; F(000) ¼ 1492; reflections
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q range 2.08 to 25.00; h, k,
l range: -13ꢃhꢃ13, -15ꢃkꢃ15, -25ꢃlꢃ25; parameters ¼ 453; restraints ¼ 0,
largest difference in peak and hole, Drmax and Drmin ¼ 2.535 and -1.344 e.Å3.
The X-ray diffraction measurement was made on a STOE IPDS-II diffractom-
eter with graphite monochromated Mo-K
a radiation. The structure was
solved by using SHELXS. The Data reduction and structure refinement was
carried out with SHELXL using the X-STEP32 crystallographic software
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matrix least-squares on F2 values to final R1 ¼ 0.1141, wR2 ¼ 0.2768[I>2sig-
ma(I)] and S ¼ 1.105. All hydrogen atoms were added in idealized positions.
The crystallographic information file has been deposited with the Cambridge
Data Centre, CCDC 1813680.
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