Solvent-Dependent Oxime-Azide and Oxime-Nitrile Coupling: Crystallographic and Catalytic Studies

Article abstract of DOI:10.1002/cplu.201402178

This study describes the solvent-dependent conversion of an oxime under identical reaction conditions ([Cu(bipy)Cl₂]/NaN₃/5-Br-H₂salox/TEA=1:2:1:2 molar ratio; bipy=2,2′-bipyridyl, 5-Br-H₂salox=5-bromosalicylaldoxime, TEA=triethylamine), but in different solvents. In DMSO/CH₂Cl₂ (2:1v/v) only tetrazole is formed, whereas iminoacylation in MeCN and simple complexation takes place in MeOH. The formed tetrazole and iminoacylated ligands further undergo complexation with metal ions, as evidenced from single-crystal X-ray diffraction studies and ESI-MS analyses. Mechanistic models have been proposed in which coordination-assisted bonding of sodium azide across the -C=N-OH double bond occurs to form a tetrazole and oxime-MeCN coupling forms an iminoacylated ligand. The former is a catalytic reaction, as evidenced from a turnover number of approximately 50, whereas the latter is stoichiometric in nature. This is the first report to demonstrate the dependence of solvent polarity on oxime transformation reactions through structural elucidation.

Full text of DOI:10.1002/cplu.201402178

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DOI: 10.1002/cplu.201402178
Solvent-Dependent Oxime–Azide and Oxime–Nitrile
Coupling: Crystallographic and Catalytic Studies
Malay Dolai,[a] Tarun Mistri,[a] Surajit Biswas,[a] Guillaume Rogez,[b] and Mahammad Ali*[a]
This study describes the solvent-dependent conversion of an
oxime under identical reaction conditions ([Cu(bipy)Cl2]/NaN3/
5-Br-H2salox/TEA=1:2:1:2 molar ratio; bipy=2,2’-bipyridyl, 5-
Br-H2salox=5-bromosalicylaldoxime, TEA=triethylamine), but
in different solvents. In DMSO/CH2Cl2 (2:1 v/v) only tetrazole is
formed, whereas iminoacylation in MeCN and simple complex-
ation takes place in MeOH. The formed tetrazole and iminoacy-
lated ligands further undergo complexation with metal ions, as
evidenced from single-crystal X-ray diffraction studies and ESI-
MS analyses. Mechanistic models have been proposed in
which coordination-assisted bonding of sodium azide across
the ꢀC=NꢀOH double bond occurs to form a tetrazole and
oxime–MeCN coupling forms an iminoacylated ligand. The
former is a catalytic reaction, as evidenced from a turnover
number of approximately 50, whereas the latter is stoichiomet-
ric in nature. This is the first report to demonstrate the de-
pendence of solvent polarity on oxime transformation reac-
tions through structural elucidation.
Introduction
Tetrazoles are popular N-heterocycles[1] with potential applica-
tions in pharmaceuticals as lipophilic spacers[2] and carboxylic
acid surrogates,[3] in special explosives, in photography,[4] in in-
formation storage technology,[5] and finally as precursors for
a variety of N-heterocycles.[6] The formal [2+3] cycloaddition of
azides and nitriles are the most popular synthetic route to
form tetrazoles. However, evidence in the literature indicates
that the mechanism of the reaction is different for different
azide species. When an organic azide is used as the dipole, it
reacts only with highly activated nitriles as dipolarophiles[7] to
give 1-alkylated tetrazole.[8]
best solvent for such transformations, giving high yields.[12–14]
Hence, replacement of nitriles by oximes and investigating the
influence of the nature of the solvent on its direct conversion
to tetrazoles are the two motives that prompted us to perform
this study.
On the other hand, the reactions of aldoximes or ketoximes
as nucleophiles towards electrophilically activated ligands con-
taining double and triple bonds are limited, but have been
known for some time.[15,16] This intriguing addition of oxime
species to coordinated organonitriles in platinum(IV) and rhe-
nium(IV) complexes results in stable monodentate iminoacylat-
ed ligands (Scheme 1A) that simultaneously coordinate to the
metal center[17–20] (Scheme 1B). So far, these reactions were fa-
vored by the coordinatively activated organonitriles. Another
interesting feature of phenolate oximes is that they can simply
Although the nitrile–azide click reaction does not occur only
with heat, the copper catalyst is used to promote the electro-
cyclization of the intermediate alkynyl azide,[9] but the impor-
tance of the copper(I/II)–azide interaction has been relatively
understated.[10,11] Interestingly, there are very few reports in
which the conversion of oxime derivatives into tetrazoles are
discussed.[12] Tetrazole formation from oxime occurs in a step-
wise fashion in which dehydration of aldoximes afford nitriles
(RCH=NOH!RꢀCꢁN+H2O), which then react with an azide to
give the tetrazole.[12,13] Recently, the effects of different sol-
vents and reaction temperature on nitrile–azide coupling reac-
tions have been investigated and DMSO was found to be the
[a] M. Dolai, T. Mistri, S. Biswas, Prof. M. Ali
Department of Chemistry, Jadavpur University
Kolkata 700 032 (India)
Fax: (+91)33-2414-6223
E-mail: mali@chemistry.jdvu.ac.in
[b] Prof. G. Rogez
IPCMS-UMR 7504 CNRS-Universitꢀ de Strasbourg
23, rue du Loess, B.P. 43
67034 Strasbourg cedex 2 (France)
Scheme 1. Addition of oxime species to coordinated organonitriles in plati-
num(IV) and rhenium(IV) complexes to give stable monodentate iminoacy-
lated ligands (A) that simultaneously coordinate to the metal center (B).
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cplu.201402178.
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Scheme 3. A catalytic conversion of oxime ligand to tetrazole.
cacy of this transformation (Scheme 3) through quantification
1
and analysis of the products by HRMS and H NMR spectrosco-
py studies.
Results and Discussion
Structural description of 1–3
Dimeric CuII complex 1 was prepared by a one-pot transforma-
tion of oxime to tetrazole. Thus, 5-bromosalicylaldoxime (5-Br-
H2salox) undergoes a single-step cyclization reaction with an
azide ion in the presence of [Cu(bipy)Cl2] as a catalyst to give
a tetrazole, which subsequently coordinates to the metal
center to give phenoxo-bridged dimeric complex 1 under stoi-
chiometric reaction conditions. Single-crystal X-ray diffraction
Scheme 2. A schematic representation of the strategies for the formation of
complexes 1–3. TEA=triethylamine.
coordinate to a metal center such as CuII to give a pseudo-
macrocyclic monomer complex.[21]
Herein, we report the solvent-dependent conversion of
oxime in the presence of [Cu(bipy)Cl2] (bipy=2,2’-bipyridyl),
thereby forming three different complexes, 1, 2, and 3, in
three different solvents (Scheme 2). These complexes have
been characterized by single-crystal X-ray diffraction tech-
niques. The conversion of oxime to tetrazole can be catalyzed
by [Cu(bipy)Cl2]; this occurs only in a DMSO/CH2Cl2 (2:1 v/v)
solvent system. On the other hand, in MeCN, iminoacylation
and concomitant coordination to the metal center occurs in
a concerted way, whereas in MeOH simple coordination to the
metal center occurs. We have also examined the catalytic effi-
studies show that complex 1 crystallizes in the triclinic system
II
¯
with space group P1. Both Cu atoms are penta-coordinated;
each is coordinated by N1 and O1 atoms of 5-bromo-2-(tetra-
zolato-5-yl)phenolate, ligand L2ꢀ, and atoms N5 and N6 from
a neutral bipyridyl ligand to form the equatorial plane (Fig-
ure 1i), while the sole axial position is occupied by the bridg-
ing phenoxo oxygen atom (O1; symmetry code: a=x,y,z; b=
x,ꢀy,ꢀz). In the unit cell, there are two crystallographically in-
dependent dimeric units A and B and one molecule of water
of crystallization (Figure S1 in the Supporting Information).
Both units are isostructural, but with small differences in bond
Figure 1. Coordination environment of a) 1, b) 2, and c) 3. All hydrogen (except NꢀH) atoms are omitted for clarity.
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Table 1. Selected bond lengths and angles of complex 1.
Table 2. Selected bond lengths and angles of complex 2.
Bond lengths [ꢁ]
unit A
Bond angles [8]
Bond lengths [ꢁ]
unit A
Bond angles [8]
Cu1ꢀO1
Cu1ꢀN5
Cu1ꢀN6
Cu1ꢀN1
Cu1ꢀO1[a]
2.325(3)
2.020(4)
2.007(3)
1.951(3)
1.923(3)
O1-Cu1-N1
O2[b]-Cu2-N9
Cu1-O1-Cu1[a]
O1-Cu1-N5
O1-Cu1-N6
O1-Cu1-N6
O1-Cu1-O1[a]
N1-Cu1-N5
N1-Cu1-N6
O1[a]-Cu1-N1
N5-Cu1-N6
O1[a]-Cu1-N5
O1[a]-Cu1-N6
99.67(12)
89.58(12)
93.89(10)
88.68(12)
95.56(12)
95.56(12)
86.11(10)
102.89(15)
164.43(15)
88.74(13)
80.60(14)
167.92(13)
89.05(13)
Cu1ꢀN1
Cu1ꢀO1
Cu1ꢀN1[a]
Cu1ꢀO1[a]
1.931(4)
1.903(3)
1.931(4)
1.903(3)
O1-Cu1-N1
91.69(14)
91.87(14)
180.00
88.31(14)
88.31(14)
O1-Cu1-O1[a]
O1-Cu1-N1[a]
O1i-Cu1-N1
N1-Cu1-N1[a]
unit B
Cu2ꢀO3
Cu2ꢀN2
Cu2ꢀO3[b]
Cu2ꢀN2[b]
1.895(3)
1.935(4)
1.895(3)
1.935(4)
O3-Cu2-N2
180.00
88.14(14)
91.87(14)
O3[b]-Cu2-N2
O3[b]-Cu2 N2[b]
[a] 2ꢀx, 1ꢀy,ꢀz. [b] 1ꢀx, 2ꢀy,1ꢀz.
unit B
Cu2ꢀO2
Cu2ꢀN14
Cu2ꢀO2[b]
Cu2ꢀN8
Cu2ꢀN9
2.437(3)
1.954(4)
1.924(3)
2.024(3)
1.999(4)
O2-Cu2-N14
O2-Cu2-O2b
N8-Cu2-N9
N8-Cu2-N14
O2[b]-Cu2-N8
O2-Cu2-N8
98.96(11)
86.29(10)
80.79(14)
101.36(14)
169.48(13)
89.77(11)
93.71(10)
168.93(14)
91.88(11)
88.90(12)
Table 3. Selected bond lengths and angles of complex 3.
Bond lengths [ꢁ] Bond angles [8]
Cu1ꢀCl1
2.2242(17)
1.902(4)
2.846(4)
1.936(5)
1.939(5)
Cl1-Cu1-O1
Cl1-Cu1-O2
Cl1-Cu1-N1
Cl1-Cu1-N2
O1-Cu1-O2
O1-Cu1-N1
O1-Cu1-N2
O2-Cu1-N1
O2-Cu1-N2
N1-Cu1-N2
94.36(13)
148.37(11)
168.50(18)
98.03(17)
116.37(15)
89.72(19)
166.9(2)
Cu1ꢀO1
Cu1ꢀO2
Cu1ꢀN1
Cu1ꢀN2
Cu2-O2-Cu2[b]
N9-Cu2-N14
O2-Cu2-N9
O2[b]-Cu2-N14
[a] 1ꢀx, 2ꢀy, 1ꢀz. [b] 1ꢀx, 1ꢀy, 2ꢀz.
126.80(17)
52.12(18)
78.9(2)
lengths and angles (Table 1). In unit A, CuꢀO/N bond lengths
fall in the range 1.931–2.232 ꢁ and Cu···Cu distances of 3.112 ꢁ;
in unit B, CuꢀO/N bond lengths fall in the range 1.926–2.428 ꢁ
and Cu···Cu distances of 3.20 ꢁ. The hydrogen-bonding interac-
tions in complex 1 are given in Figure S2a in the Supporting
Information.
Catalytic studies and mechanistic details
During a systematic investigation of ternary ([CuII(bipy)Cl2], 5-
ꢀ
Br-H2salox+N3 ) reactions, we examined the influence of sol-
The reaction between [Cu(bipy)Cl2] and 5-Br-H2salox in the
presence of NaN3 in MeOH and TEA as a base does not lead to
the formation of tetrazole, but rather to the formation of com-
plex 2, which takes place in quantitative yield. Single-crystal X-
vent polarity on the chemical and structural identity of the
products. Scheme 2 displays the various combinations of sol-
vents and products thus obtained in each case.
An initial attempt involved the reaction between equimolar
quantities of [Cu(bipy)2Cl2] and 5-Br-H2salox in the presence of
two equivalents of NaN3 and TEA in DMSO/CH2Cl2 (2:1 v/v);
this resulted in a light-green reaction solution that finally yield-
ed 1. The structure of 1 was confirmed by single-crystal X-ray
diffraction studies and also by ESI-MS+ analysis (Figure S6 in
the Supporting Information). The molecular structure of
1 (Figure 1) reveals the presence of a deprotonated 4-bromo-
2-(1H-tetrazol-5-yl)phenol in the form of a CuII complex.
ray diffraction studies reveal that complex 2 (Figure 1ii) crystal-
II
¯
lizes in the triclinic space group P1. The Cu atom is tetra-coor-
dinated with two bidentate NO donor ligands, namely, through
N1 and O1, and their symmetry-related counter atoms in
a square-planar geometry. In the unit cell, there are also two
crystallographically independent asymmetric units A and B
with some differences in bond lengths and angles (Table 2). In
the asymmetric units, both monomers are intramolecularly hy-
drogen bonded through the phenolate oxygen and oxime
proton (ꢀC=NOH) to form a pseudo-macrocyclic framework
(Figure S2b in the Supporting Information).
In another set of reactions, the catalytic behavior of [Cu-
(bipy)Cl2] was explored under the following reaction condi-
tions: [Cu(bipy)Cl2] (0.01 mmol), 5-Br-H2salox (1 mmol), and
NaN3 (2 mmol) in DMSO/CH2Cl2 (10 mL; 2:1 v/v) at approxi-
mately 708C for 20 h. The product thereby formed was extract-
ed with diethyl ether, dried over anhydrous Na2SO4, and finally
the solvent was removed to give the solid product, which was
Complex 3 is a mononuclear CuII species (Figure 1), which
II
¯
crystallizes in the triclinic space group P1. The Cu atom here is
also tetra-coordinated with one tridentate iminoacylated
ligand through N1, O1, and N2 and one chloride ion (Cl1) to
give a square-planar geometry. Important bond lengths and
angles are listed in Table 3. The hydrogen-bonding interactions
of complex 3 are given in Figure S2c in the Supporting Infor-
mation.
1
characterized by HRMS (positive mode) and H NMR spectros-
copy (Figure 2); these results clearly demonstrated the forma-
tion of tetrazole as the sole product. Within this time, the turn-
over number (TON) was calculated to be 38 with approximate-
ly 100% selectivity. It was also noted that, when this reaction
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1
Figure 2. ESI-MS (positive) spectrum of the catalytic reaction product (tetrazole ligand) and the corresponding H NMR spectrum (inset).
was performed without external base (TEA), the conversion in-
creased and led to a TON of approximately 50.
coordination of ꢀC=NꢀOH to copper(II) through the oxime
oxygen atom will favor removal of oxime OH group, making
It was further noted that the yield of tetrazole was lower
when the reaction was performed at room tempera-
ture; this may be due to trapping of the catalyst as
complex 1, which may be unstable at high tempera-
ture and favor the catalytic cycles proceeding.
the attack of the azide ion across the C=N bond more facile. If
A tentative mechanism for the catalytic transforma-
ꢀ
tion of oxime to tetrazole by coupling with N3 in
the presence of [Cu(bipy)Cl2] in DMSO/CH2Cl2 (2:1 v/
v) is given in Scheme 4. We propose that nitrile for-
mation does not occur in an intervening step, but
rather it proceeds in a concerted way. It is proposed
that direct nucleophilic attack of an azide ion onto
the electron-deficient carbon atom of the ꢀC=NꢀOH
moiety with concomitant cycloaddition occurs to
give tetrazoles. Here, coordination of the oxime
oxygen atom to the metal ion in [Cu(bipy)Cl2] acti-
vates the oxime moiety by facilitating the cycloaddi-
tion of NaN3 across the C=N bond. Thus, the two-
step conversion of oxime to tetrazole (ꢀC=NꢀOH!ꢀ
CN!tetrazole) can be replaced by a single-step, con-
certed process.[12] The dehydration of oxime to nitrile
requires specific reagents and high temperature;
Scheme 4. Proposed mechanism for the copper-mediated oxime–azide coupling to form
these are absent from our reaction medium.[12,13] The a tetrazole.
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[Cu(bipy)Cl2] is coordinated by a nitrogen atom and a pheno-
late oxygen atom to form a chelate ring, removal of the OH
group might be more difficult and the catalyst, [Cu(bipy)Cl2],
will be trapped permanently, which will terminate the catalytic
cycle. Thus, we propose coordination of ꢀC=NꢀOH to the CuII
center by the O atom to give an unstable intermediate, which
subsequently undergoes attack by NaN3 across the C=N bond
and removal of the oxime OH group.[14] However, when the re-
action is performed in stoichiometric proportions, the formed
tetrazole reacts immediately with [Cu(bipy)Cl2] to give com-
plex 1 in quantitative yield. Parallel reactions under identical
reaction conditions, but in the absence of [Cu(bipy)Cl2], do not
lead to the formation of trace amounts of tetrazoles (Figure S7
in the Supporting Information); this, on the other hand, firmly
establishes the metal ion/complex catalyzed transformation of
oxime to tetrazole in the presence of sodium azide.
in the range of n˜ =40–130 cmꢀ1 [19]
. To confirm the involvement
of the metal ion/complex in the formation of the iminoacylat-
ed product we performed parallel reactions under identical
conditions, but in the absence of [Cu(bipy)Cl2], and it was ob-
served that the oxime remained unreacted during the entire
course of the reaction without any sign of the formation of
iminoacylated product, as evidenced from ESI-MS (ꢀ) analysis
(Figure S7 in the Supporting Information). Similar observations
were made by Raptopoulou et al.,[22] who used simple copper(-
II) ions and proposed that oxime–MeCN coupling occurred
with bulk MeCN. Herein, we observed that activation of MeCN
through metal coordination was a prerequisite for the reaction.
In the transformation of the oxime to the tetrazole, in the
presence of an azide ion, the solvent played a vital role. DMSO,
which is a polar aprotic solvent (Na+), is heavily solvated and
makes the anion (N3ꢀ) free and like a ‘naked ion’, thereby in-
creasing its nucleophilicity to attack the electron-deficient
carbon center in ꢀC=NꢀOH. On the other hand, when using
When we performed this reaction in MeOH, THF, acetone, or
other low-boiling solvents alone, no tetrazole formation took
place; rather simple, mononuclear, pseudo-macrocyclic com-
plex 2 formed. This was confirmed by single-crystal X-ray dif-
fraction studies and also by ESI-MS+ analysis (Figure S6 in the
Supporting Information). On the other hand, when we per-
formed the same reaction in MeCN, traditional oxime–nitrile
coupling was favored over cycloaddition to give the tetrazole.
The in situ formation of iminoacylated ligand Lꢀ is best de-
scribed by nucleophilic attack of the oximato oxygen atom of
5-Br-H2salox to the unsaturated carbon atom of the nitrile
group of MeCN (Figure S6 in the Supporting Information). The
question now arises as to whether the oximato oxygen attacks
the carbon atom of MeCN present in the bulk or in the coordi-
nated state (Scheme 5). To check these possibilities, we record-
ed the IR spectrum of [Cu(bipy)Cl2] in MeCN, and it was ob-
served that MeCN did coordinate to the metal center because
there were two IR stretching frequencies at n˜ =2294 and
2252 cmꢀ1, which corresponded to coordinated and free
MeCN, respectively. The shift in the IR frequency by 42 cmꢀ1
(Figure S8 in the Supporting Information) is normal and occurs
ꢀ
methanol as a polar solvent, both Na+ and N3 become solvat-
ed simultaneously within the solvent cage through ion–dipole
interactions (MeOH can form hydrogen bond with the azide),
ꢀ
which reduce the nucleophilicity of N3 to such an extent that
it cannot promote the cycloaddition reaction of oxime for tet-
razole formation.
Magnetic properties
The cT value for 1 at 300 K is 0.94 cm3 molꢀ1 K, and is in accord-
ance with the expected value for two uncoupled copper(II)
ions (0.91 cm3 molꢀ1 K, considering g=2.2; Figure 3). The cT
product remains constant as the temperature decreases, until
approximately 50.0 K. It then decreases faster and finally reach-
es 0.67 cm3 molꢀ1 K at 1.8 K. This overall behavior is characteris-
tic of a very weak, antiferromagnetically coupled copper(II)
dimer.
The data were fitted by using the spin Hamiltonian given in
Equation (1), in which the spin operator, S, is defined[23] as S=
SCu1 +SCu2
:
H ¼ ꢀJSCu1SCu2 þ gbHS
ð1Þ
The best fit parameters were found for J=ꢀ1.3(1) cmꢀ1 and
g=2.23(1), with a very good agreement factor R=2ꢂ10ꢀ5; R is
defined by Equation (2):
ꢀ
ꢁ
P
2
cTexp tl ꢀ cTcalcd
P
ð2Þ
R ¼
cTe2xp tl
The sign and magnitude of J=ꢀ1.3(1) cmꢀ1 reveals that the
two copper(II) centers in complex 1 are very weakly antiferro-
magnetically coupled. The EPR spectra of all complexes are
given in Figure S9 in the Supporting Information.
Conclusion
The main objective of this study was to explore the effect of
solvent polarity on the single-step transformation of oxime to
Scheme 5. Proposed mechanism for the copper-mediated oxime–nitrile cou-
pling.
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Crystallography
Single-crystal X-ray data for 1–3 were collected at room tempera-
ture on a Bruker SMART APEX-II CCD diffractometer by using
graphite monochromated MoKa radiation (l=0.71073 ꢁ). Data inte-
gration and reductions were processed with SAINT+ software.[24]
Structures were solved by direct methods and then refined on F2
by the full-matrix least-squares technique with SHELX-97[25] and
SHELXTL[26] crystallographic software packages. The molecular
views and hydrogen-bonding patterns were drawn by using DIA-
MOND-3.2 and Mercury 3.0 software packages. The crystallographic
data for 1–3 are given in Table 4.
CCDC 900536 (1), 984812 (2), and 914811 (3) contain the supple-
mentary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
Magnetic measurements
&
*
Figure 3. Temperature dependence of c ( ) and cT ( ) for 1. The full lines
correspond to the best fit of the data.
Magnetic measurements were performed by using a Quantum
Design squid-vibrating sample magnetometer (SVSM). The static
susceptibility measurements were performed in the 300–1.8 K tem-
perature range with an applied field of 5 kOe. Magnetization meas-
urements at different fields at a given temperature confirmed the
absence of ferromagnetic impurities. Data were corrected for the
sample holder and diamagnetism was estimated from Pascal con-
stants.
tetrazole in the presence of [Cu(bipy)Cl2] as a catalyst. For this
purpose, we performed the same reaction ([Cu(bipy)2Cl2]+
H2Br-salox+NaN3 in a 1:1:2 molar ratio in the presence of TEA
(2.0 equiv) as a base) in different solvents, namely, DMSO/
CH2Cl2, MeOH, THF, and MeCN, which varied widely with re-
spect to their dielectric constants. It was interesting to note
that in DMSO/CH2Cl2 medium tetrazole formation occurred
smoothly and immediately reacted with [Cu(bipy)Cl2] to give
dinuclear complex 1. Under catalytic conditions and at 708C,
the TON of tetrazole was 38 with approximately 100% selectiv-
ity, whereas in the absence of TEA this transformation is in-
creased to give a TON of approximately 50. On the other hand,
in solvent (MeOH/MeCN) different products are formed.
Preparation of the 5-Br-H2salox (H2L)
NH2OH·HCl (2.76 g, 40 mmol) in water (20 mL) was added to a solu-
tion of 5-bromosalicylaldehyde (4.02 g, 20 mmol) in ethanol
(60 mL) with stirring. Na2CO3 (4.00 g, 40 mmol) in water (20 mL)
was then added and the resulting mixture was heated at 808C.
The progress of the reaction was monitored by TLC (solvent: 1/
1 hexanes/EtOAc) and found to be completed within 3–5 h. The re-
action mixture was filtered through a pad of Celite and a solid pre-
cipitated upon subsequent concentration; this precipitate was col-
lected by filtration and washed with cold water. Recrystallization
from methanol gave the product as a needle-like crystalline materi-
Experimental Section
1
al (2.55 g, 59%). M.p. 133–134.58C; H NMR (300 MHz, [D6]DMSO):
d=6.87 (d, J=8.75 Hz, 1H), 7.36 (dd, J=9 Hz, 2H), 7.65 (brs, 1H;
phenolic OH), 8.15 (s, 1H; methyne), 9.84 ppm (s, 1H; NꢀOH).
Materials and reagents
Starting materials such as 5-bromosalicylaldehyde (Lancaster), hy-
droxylamine hydrochloride (Merck, India), anhydrous Na2SO4
(Merck), triethylamine (Merck, India), and sodium azide (Merck,
India) were of reagent grade and used as received. CuCl2·2H2O
(Merck, Germany) and bipy (Spectrochem, India) were used for the
preparation of [Cu(bipy)Cl2]. Solvents such as methanol, diethyl
ether, acetonitrile, CH2Cl2, and DMSO (Merck, India) were of reagent
grade and dried before use.
Metal precursor [Cu(bipy)Cl2]
[Cu(bipy)Cl2] was prepared by following a method reported in the
literature.[27]
Preparation of 1
The one-pot reaction between 5-Br-H2salox and NaN3 in the pres-
ence of [Cu(bipy)Cl2] and TEA in DMSO/CH2Cl2 gave 5-bromo-2-(tet-
razolato-5-yl)phenol, which subsequently coordinated to [Cu-
(bipy)Cl2] to give 1. In a typical procedure, [Cu(bipy)Cl2] (0.290 g,
1.0 mmol) was added to a pale-yellow solution of 5-Br-H2salox
(0.216 g, 1.0 mmol) in DMSO/CH2Cl2 (30 mL; 2:1 v/v). The addition
of TEA (0.202 g, 2.0 mmol) resulted in a green solution, which was
stirred for an additional 20 min. Then sodium azide (0.13 g,
2.0 mmol) was added and stirring was continued for an additional
2 h at room temperature. The reaction mixture was then filtered
and the filtrate was set aside undisturbed for slow evaporation.
Physical measurements
Elemental analyses were performed by using a PerkinElmer 240 el-
emental analyzer. IR spectra (n˜ =400–4000 cmꢀ1) were recorded as
KBr pellets on a Nickolet Magna IR 750 series-II FTIR spectropho-
1
tometer. H NMR spectra were recorded in [D6]DMSO on a Bruker
300 MHz NMR spectrophotometer by using tetramethylsilane (d=
0) as an internal standard. EPR spectra were recorded as solid sam-
ples on an X-band EPR spectrometer (Model: JEOL, JES-FA 200).
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ChemPlusChem 2014, 79, 1649 – 1656 1654

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product, which was characterized
by HRMS (positive mode) and
1H NMR spectroscopy (Figure 2).
Table 4. Crystallographic data and details of the structure determination for 1–3.
1
2
3
formula
Mw
crystal system
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
a [8]
b [8]
C34H22Br2Cu2N12O3
933.54
triclinic
C14H10Br2CuN2O4
493.59
triclinic
C9H8BrClCuN2O2
355.07
triclinic
Acknowledgements
¯
¯
¯
P1 (no. 2)
P1 (no. 2)
P1 (no. 2)
8.0981(4)
11.8943(5)
19.2588(7)
105.530(2)
101.767(2)
95.953(2)
1724.92(13)
2
4.3940(2)
8.1448(4)
21.3588(10)
82.121(2)
89.994(2)
89.995(2)
757.18(6)
2
7.4794(8)
7.7956(8)
10.7861(12)
88.665(7)
81.377(7)
65.790(7)
566.59(11)
2
Financial support from the CSIR
(Ref. 02(2490)/11/EMR-II) and DST
(Ref. SR/S1/IC-35/2006),
New
Delhi, are gratefully acknowl-
edged. M.D. gratefully acknowl-
edges SRF-UGC for a fellowship
(direct).
g [8]
V [ꢁꢀ3
]
Z
1calcd [gcmꢀ3
]
1.797
3.606
924
2.165
6.740
478
2.081
5.673
346
m(MoKa) [mmꢀ1
F(000)
]
Keywords: heterocycles
homogeneous catalysis
·
·
absorption correction
index ranges
reflns collected
independent reflns (Rint
no. of parameters
GOF
ꢀ10:10;ꢀ15:15;ꢀ25:25
27190
7957(0.052)
478
ꢀ5:5;ꢀ10:10;ꢀ28:28
11807
3677(0.131)
213
ꢀ9:9;ꢀ9:9;ꢀ13:13
8010
2466 (0.063)
146
magnetic properties · structure
elucidation · synthesis design
)
1.01
0.83
0.86
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R1/wR2 (I>2s(I))
R1/wR2 (all data)
min and max residual density [eꢁꢀ3
0.0454(5151)
0.1336
ꢀ1.31, 1.15
0.0348(1924)
0.0883
ꢀ0.68, 0.49
0.0553 (1755)
0.1762
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The reactants and their proportions were the same as those used
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system. MeOH was used instead of a mixture of DMSO/CH2Cl2
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elemental analysis calcd (%) for C14H10Br2CuN2O4 (493.59): C 34.06,
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Preparation of 3
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C9H8BrClCuN2O2 (355.07): C 30.44, H 2.27, N 7.88; found: C 30.61, H
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Published online on September 8, 2014
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ChemPlusChem 2014, 79, 1649 – 1656 1656