Synthesis, crystal structure, optical and electrochemical properties of novel diphenylether-based formazan derivatives

Article abstract of DOI:10.1039/c4nj02353f

In this study, formazans 5a-5h were synthesized by coupling the reactions of substituted phenylhydrazone compounds 3a-3h with diazonium salt of 4-chloro-2-phenoxybenzenamine (4). The substituted phenylhydrazones 3a-3h were obtained from the condensation o

Full text of DOI:10.1039/c4nj02353f

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Synthesis, crystal structure, optical and
electrochemical properties of novel
Cite this:DOI: 10.1039/c4nj02353f
diphenylether-based formazan derivatives†
Gulsen Turkoglu, Halil Berber* and Ibrahim Kani
In this study, formazans 5a–5h were synthesized by coupling the reactions of substituted phenylhydra-
zone compounds 3a–3h with diazonium salt of 4-chloro-2-phenoxybenzenamine (4). The substituted
phenylhydrazones 3a–3h were obtained from the condensation of substituted phenylhydrazines 1a–1h
with 4-methoxybenzaldehyde (2). The structures of the formazans were characterized by using elemental
1
analysis, FTIR, H NMR, 13C NMR, LC-MS and the crystal structure of compound 5e was determined by X-ray
crystallography. The absorption spectra of all compounds were investigated in various solvents. Although
their absorption bands are only slightly dependent on the polarities of solvents, the significant change was
observed by altering the electronic characteristics of the substituents. The fluorescence quantum yield
properties and Stokes shifts of compounds 5a–5h in DMSO were also explored. Electrochemical properties
of the new products were studied by CV measurements. In addition, computational studies were conducted
at the PBE1PBE/6-311g (2d,2p) level to shed light on the structures of possible tautomers and intramolecular
H-bonds.
Received (in Montpellier, France)
19th December 2014,
Accepted 16th January 2015
DOI: 10.1039/c4nj02353f
www.rsc.org/njc
for electronic structural properties, molecular modelization tech-
niques allow a solution for the interpretation of experimental
Introduction
Formazans were first synthesized more than a century ago but data. For the calculation of large molecular electronic structures,
still attract the attention of chemists, biologists, technologists the most widely used method is the density functional theory
and other specialists.1 Numerous studies have been under- (DFT).26,28 Tautomerism, which is extremely important in the
taken related to their syntheses, structural and spectroscopic structure and properties of formazans, and intramolecular
properties,2–5 photochemical transformations,6,7 tautomer forma- hydrogen bridges in some formazans were studied by means
tion,8,9 the synthesis of crown formazans10 and the broad spec- of DFT.28,29
trum of biological activities.11–15 In addition, formazan derivatives
Diphenylether derivatives find applications in many areas.
were reported to be used for the synthesis, optical properties, and They have been used as biocides, flame retardants, functional
the electrochemical behaviours of metal16–20 and boron com- fluids and motifs in many natural products. Among biocides,
plexes as functional materials.21–23
they have been used as herbicides with antibacterial and anti-
Formazans form tetrazolium salt upon oxidation. The tetra- tubercular properties, and also as copolymers.30–32 Formazans
zolium/formazan couple is a special redox system acting as containing diphenylether are anticipated to be intriguing
proton acceptor or oxidant; this system is now widely applied organic compounds in medicinal and material applications.
in different branches of biological science, including medicine,
In our previous work, a new formazan derivative was synthe-
pharmacology, immunology, and botany, but especially in bio- sized and used for the modification of pencil graphite electro-
chemistry and histochemistry.24,25 These features cause growing des for the determination of paracetamol in electrochemical
interest particularly in the electrochemical and spectral pro- sensor applications.33 Herein, we synthesized eight new com-
perties of tetrazolium/formazan systems.26,27 As a predictive tool pounds 5a–5h by coupling the reactions of phenylhydrazones
(3a–3h) with appropriate diphenylether-substituted aryldiazo-
Chemistry Department, Faculty of Science, Anadolu University, 26470 Eskis-ehir,
Turkey. E-mail: hlberber@nadolu.edu.tr
nium chlorides in pyridine (Scheme 1) in order to shed light on
the physical and chemical properties of formazan derivatives.
The structures of all synthesized molecules were characterized
using elemental analysis, various spectroscopic methods and the
structure of the representative compound 5e was unambiguously
confirmed based on X-ray crystallography. The absorptions of
† Electronic supplementary information (ESI) available: Experimental procedures
and characterization data of compounds (3a–3h), crystallographic data, absorp-
tion spectra data and NMR spectra of final compounds (5a–5h). CCDC 912620
(5e). For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c4nj02353f
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with 3a possessing an unsubstituted phenyl group gave a corres-
ponding product of 5a in 82% yield, halogenated ones (Cl, Br
and F) resulted in good to excellent yields (70–86%). The other
compounds 5b and 5f–5h gave rise to moderate yields (49–62%).
Analytical and spectral data fully supported the structure of all
compounds.
Characterizations
The FTIR spectra of all synthesized formazans 5a–5h were
recorded using the solid KBr pellet technique in the 400–
4000 cmꢀ1 range. The characteristic IR frequency bands are given
in the Experimental section. The absence of N–H absorption
bands between 3100 and 3500 cmꢀ1 verify the six-membered
pseudo-aromatic ring with the intramolecular hydrogen bond
Ph1–NHꢁꢁꢁN–Ph5 in a formazan skeleton.35,36 The observation of
weak bands in the range of 3055–3093 cmꢀ1 for all compounds
indicated the existing of intramolecular hydrogen bond in
formazans. The sharp characteristic –CQN– tension vibration
bands were observed between 1589–1610 cmꢀ1 pointing out the
existence of intramolecular hydrogen bonds (Scheme 2).37,38 The
observation of intense bands between 1461–1496 cmꢀ1 indicated
the –NQN– group, which was in good agreement with the reported
FTIR values.2,4
Scheme 1 Synthetic route for the formation of formazan derivatives 5a–5h.
the compounds were investigated in solvents with different
polarities. The dependence of their absorption spectra on the
substituents was studied. The fluorescence quantum yield pro-
perties and Stokes shifts of compounds 5a–5h in DMSO were
explored. The electrochemical properties of the new products
were investigated by cyclic voltammetry. In addition, the results
of the calculations at the PBE1PBE/6-311g (2d,2p) level were
taken into consideration to determine the possible tautomer
structures and intramolecular hydrogen bonds of all synthesized
compounds.
1H NMR spectrum data and the calculated coupling con-
stants for 5a–5h were given in the Experimental section. The
downfield –NH peak of formazans was characteristic and
indicated the presence of an intramolecular hydrogen bond.39
Due to the existence of hydrogen bonds inside the molecule, an
NH proton is detected as a singlet in the downfield 5a–5g
between 14.87–15.38 ppm.9,10 However, the weakening of the
intramolecular hydrogen bonds, likely emerging from the
electronic effect of the attached NO2 group, points out the
upfield shift of –NH proton (5h, 13.95 ppm).13,17,40 The obser-
vation of these values confirm the presence of pseudo aromatic
–NH–N molecular hydrogen bond in a formazan skeleton
(–NH–NQC–NQN–) (Scheme 2). The chemical shifts of the
aromatic protons were recorded between 8.88 and 6.83 ppm as
expected. Methoxy protons (–OCH3) were observed as a singlet
between 3.86–3.80 ppm, whereas methyl groups (–CH3) in com-
pound 5g were detected in the upfield (2.20–2.30 ppm).
Results and discussion
Synthesis
The substituted phenylhydrazones used as the initial substances
were obtained via condensation reactions of substituted phenyl-
hydrazines with 4-methoxybenzaldehyde resulting in good to
excellent yields (75–98%). 3a–3h were characterized using FTIR,
1H NMR, 13C NMR and elemental analysis (see ESI†).
In this work, formazans 5a–5h were synthesized according to the
first method reported by Nineham,34 in particular, the coupling of
substituted phenylhydrazones with a 4-chloro-2-phenoxybenzen-
amine diazonium cation in a basic media at 0 1C (Scheme 1).
Although pyridine was characteristic of a strong catalyst,
which abstracts proton,34 the improvement of the reaction
condition was achieved by the addition of a solution of NaOH
with pyridine because the coupling step was also largely governed
by the pH of the medium. The optimum level was found to be pH
Z 12, whereas at pH r 9, the product formed a sticky material
that clung to the stirring bar, which left the reaction incomplete.
Moreover, the position and steric effects of the substituents
located at the phenyl group of the benzaldehyde unit of the
starting material significantly affect the coupling reactions. There-
fore, para-substituted phenyl was chosen to avoid the steric
effects. Synthesized compounds were purified by recrystallization
from methanol. Although a coupling reaction of diazonium salt
13C NMR spectra of formazans 5a–5h are given in the
Experimental section. The obtained peaks belonging to carbon
atoms in –N–CQN– units of 5a–5h were recorded in downfield
between 165.37 and 159.69 ppm, which are in good agreement
with reported literature values.38,41 Aliphatic –OCH3 carbon
atoms were observed in the range of 55.42–55.37 ppm, whereas
Scheme 2 Intramolecular hydrogen bonding and tautomerisation of the
formazan system.
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Table 1 Dihedral angles between the least-squares planes of rings
methyl groups attached to 5g were observed in the range of
19.92–19.67 ppm. 1H NMR and 13C NMR spectra confirmed the
validity of the structures given in Scheme 1.
Ring no.
Ring no.
Dihedral angle (1)
R1
R1
R1
R1
R2
R2
R2
R3
R3
R4
R2
R3
R4
R5
R3
R4
R5
R4
R5
R5
7.38(1)
8.81(1)
72.46(2)
5.47(1)
3.41(1)
62.94(2)
2.96(1)
77.04(2)
6.05(1)
74.08(2)
The mass spectral data of the formazans 5a–5h are given in
the Experimental section. In the mass spectrum of compound
5a (C26H21ClN4O2, M = 456.92 g molꢀ1), the molecular ion peak
was observed to be MS (ESI)+: m/z = 456.1 (18%, M+), and the
fragmentation of 1-position phenyl and 5-position unsubsti-
tuted phenyl radical cations led to the residual molecule having
+
a mass of 304.3 (87%, M-C14H11N4ClO2 ). All synthesized
compounds were evaluated in the same manner, and the
results obtained from the mass spectra confirmed the validity
of the structures given in Scheme 1.
between the least squares planes of the phenyl rings R1
[C2–C3–C4–C5–C6–C7], R2 [C9–C10–C11–C12–C13–C14], R3
[C15–C16–C17–C18–C19–C20], R4 [C21–C22–C23–C24–C25–C26]
and the pseudo six-membered aromatic ring R5 [C8–N1–N2–N3–
N4–H2] are given in Table 1 (see Fig. 2a).
The shortest intermolecular p-ring distance of 4.035 Å is
observed between R2 and R3. Moreover, weak intermolecular
interactions exist between C4–F1i, C10–F1i, C25–O2ii and
C1–O2iii. The distances are 3.609(3), 3.260(3), 3.732(3) and
3.580(4) Å, respectively (symmetry codes i: ꢀx + 1/2 + 1, ꢀy + 2,
+z + 1/2, ii: ꢀx + 1/2 + 1, ꢀy + 2, +z ꢀ 1/2, iii: x + 1/2, +y, ꢀz + 1/2).
The molecules in the crystal structure are stacked along the
b-axis through the hydrogen bonding of C10–F1 as shown Fig. 2b.
Crystal structure
The molecular view of 5e is shown in Fig. 1 and some selected
bond lengths and angles are given in Table S1 (ESI†). 5e
(red needles) crystallizes in an orthorhombic system with Z = 8
in the space group Pbca. All bond lengths and angles were
within the normal ranges. X-ray investigation of compound 5e
showed that tautomer 2 structure was favoured in the solid state
(see Fig. 1). The molecule of 5e has –CQN– and –NQN– double
bonds [C8–N1 = 1.307(3), N3–N4 = 1.277(3) Å]. The exocyclic
C–C–N bond angles around the C15 atom are asymmetrical.
The C16–C15–N4 angle (114.1(2)1) is significantly smaller than
that of the C20–C15–N4 (125.7(2)1). C8–N3–N4 (114.8(2)1) and
C8–N1–N2 (120.1(2)1) angles around the N1, N3 atoms are not
equal to each other. The aromatic rings in the molecule have
the usual bond lengths and angles. 5e has a strong intra-
molecular N2–H2ꢁ ꢁ ꢁN4 hydrogen bond with D–H, Dꢁ ꢁ ꢁA and
Hꢁ ꢁ ꢁA distances of 0.89(3), 2.549(3) and 1.87(3) Å, respectively,
and the D–Hꢁ ꢁ ꢁA angle of 132.3(3)1 as shown Fig. 1.
Absorption spectra
The UV-vis studies of the synthesized formazans 5a–5h were
carried out in solvents with 14 different polarities, and the
results are listed in Table S2 (see ESI†). The stock solutions of
the compounds were prepared in a 1 ꢂ 10ꢀ5 mol Lꢀ1 concen-
tration. The UV-vis spectra of compound 5a within various
solvents are given in Fig. 3. The observed visible band in
formazans was a result of p–p* transition of the N,N-diaryl-
hydrazone conjugated system.42,43 Because the formazan skeleton
has a structure showing tautomerization, the characteristic bands
belong to the p–p* transitions (Fig. 3).1
The compounds 5a–5g, in accordance with the figures in
literature, produced wide bands between lmax1 of 494–554 nm
in various polarity solvents, which belong to the characteristic
p–p* transitions in the formazan skeleton and demonstrated
the existence of a six-membered ring in the formazan skeleton
due to the inner-molecular hydrogen transfer (Scheme 2).44
Contrary to the other compounds, 5h (lmax1 = 366–400 nm)
showed the blue shift in solvents due to the fact that it forms
the equilibrium structure possessing hydrogen bonding
between oxygen of the ortho-NO2 group with Ph1–NH, and as
a result, suppressed the formation of hydrogen bonds in the
formazan skeleton (Scheme 3).45,46
This bond indicated the formation of a six-membered pseudo
aromatic ring in the molecule due to the inner-molecular
hydrogen transfer, which is also responsible for its tautomers,
and the molecule has almost planar conformation. The torsion
angle is 4.3(4)1 for N3–N4–C15–C20 and ꢀ3.1(4)1 for N1–N2–C9–C10.
In the asymmetric unit of the molecule, the dihedral angle
The second band lmax2 appearing in the range of 294–
335 nm emerged from the p–p* transitions within the hydrogen
bond formed by the azo and hydrazo groups and the tautomer-
ization in Scheme 2.36 In accordance with the literature values,
for the compounds 5a–5e and 5g, the inner-molecular hydrogen
bonds were seen in the lmax2 of 294–303 nm belonging to the
p–p* electronic transitions of the chelate rings. Formazan 5f
Fig. 1 Molecular structure of compound 5e.
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Fig. 2 (a) View of the center of the rings in 5e. (b) Chain formation in the crystal structure along the b-axis through hydrogen bonding.
Scheme 3 Formation of hydrogen bonds between –NO2 and N–H and
NHꢁ ꢁ ꢁNQN groups in compound 5h (red dashed line = H-bond).
interaction in the form of hydrogen bonding or bulk solvent
properties. These values in the absorption spectra of formazan
derivatives have supported the presence of an intramolecular
Fig. 3 Electronic absorption bands of compound 5a in various solvents.
hydrogen transfer over a formazan skeleton.
Effect of solvent on the absorption spectra. The effects of
solvent polarity on the absorption of these formazans are
demonstrated this band in between 358–393 nm, which might summarized in Table S2 (ESI†). The absorption properties of
arise from an intramolecular charge transfer from solute–solvent formazans have shown some dependence on the polarity of the
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solvents (Fig. 3). With an increase in the polarity of the solvents,
the absorption peak position of formazans 5a–5d and 5g
generally exhibited a red shift up to 28 nm, in addition to that
of 5h, which depicted an obvious red shift between 10 and
34 nm. This can be mainly attributed to the fact that solvation by
polar solvents stabilizes p and p* orbitals.36 As a result, the
decrease of p–p* transition energy concerning an intramolecular
charge transfer (ICT) band within the entire molecule was
observed.47 Compound 5e demonstrated a bathochromic shift
of 4 to 10 nm in non-polar solvents, such as toluene, cyclohexane
and n-hexane. With an increase in solvent polarity, the absorp-
tion peak of compound 5f (lmax = 24–79 nm) was shifted to a
shorter wavelength, thus exhibiting a negative solvatochromism
because the ground state was more stabilized in a solvent cage of
already partially oriented solvent molecules with stronger polar-
ity. Compounds 5a–5d and 5g–5h showed a slight positive
solvatochromism, whereas compounds 5e and 5f demonstrated
negative solvatochromism in polar solvents. The longest wave-
Fig. 4 Electronic absorption bands of all compounds in toluene.
length maximum was found at 554 nm in toluene, whereas the smallest bathochromic shifts in THF and toluene (for compound
highest hypsochromic shift was observed at 366 nm in cyclo- 5e Dlmax = 2–7 nm relative to compound 5a in methanol). The
hexane. These changes were attributed to the hydrogen-bonding lmax1 value of the compound 5f, which included the para-NO2
interaction between the solute and solvent molecules or the group on the 1-phenyl ring with its strong electron withdrawing
intramolecular charge transfer within the whole molecule.
effect, showed bathochromic shifts (Dlmax = 28–40 nm), com-
Substituent effect on the absorption spectra. The substitu- pared with 5a. lmax1 value of the compound 5g substituted by the
ent effects on characteristic lmax1 values of formazans 5a–5h –CH3 group, which is inductive as electron donating at meta- and
were examined in methanol, THF and toluene (Table 2). The para-positions, showed little hypsochromic shift (Dlmax
=
peak shift values (Dlmax) were determined according to the 1–5 nm). The fact that lmax1 value of the compound 5h sub-
difference between the lmax1 value of parent compound 5a and stituted with a strong electron attractive –NO2 group at posi-
the lmax1 values of substituted formazans 5b–5h.45,46 The UV- tions ortho- and para- in a 1-phenyl ring introduced shift
vis spectra of all compounds are given in toluene (Fig. 4).
towards lower wavelength (Dlmax = 116 nm), compared with
5a. This phenomenon can only be explained by the formation
As seen in methanol in Table 2, the absorption value (lmax1
)
of compound 5b possessing an electron donating –OCH3 sub- of a possible hydrogen bond between an N–H proton with
unit at para position was recorded 13 nm lower than the parent oxygen of a –NO2 group attached to the ortho-position of the
molecule in methanol. In both –Cl and –Br substituted com- 1-phenyl ring (Scheme 3).45,46 Therefore, the electron attrac-
pounds 5c and 5d, the lmax1 values exhibited bathochromic tive quality of the ortho–NO2 group decreases progressively,
shifts of 19 nm and 15 nm, respectively. Under these circum- and the resonance effect disappears.45,46 According to these
stances, the –Cl and –Br atoms, acting as inductive electron results, electron donating groups generally lead to hypso-
withdrawing and resonance electron donating effects, ended up chromic shifts, whereas the electron withdrawing units result
with two opposite effects. It can be seen that they acted as weak in bathochromic shifts.
electron withdrawing groups. The high electronegativity of the
fluorine group attached to the 1-phenyl ring resulted in the
Fluorescence spectra
Fluorescence spectra of the target materials under excitation at
470 nm are depicted in Fig. 5b. Excitation at the lmax of most
formazans showed either no fluorescence or fluorescence of
Table 2 UV-vis spectra of compounds 5a–5h lmax1 (nm) and peak shift
(Dlmax) values (1 ꢂ 10ꢀ5 M)
Methanol
THF
Toluene
lmax
lmax
(nm) Dlmax
lmax
(nm) Dlmax
a
a
a
Comp. Substituent (nm) Dlmax
5a
5b
5c
5d
5e
5f
4-H
4-OCH3
4-Cl
4-Br
4-F
4-NO2
3,4-(CH3)2
2,4-(NO2)2
506
493
525
521
504
546
501
390
—
13
ꢀ19
ꢀ15
2
ꢀ40
509
505
534
530
511
537
508
380
—
515
518
538
535
522
554
516
378
—
4
ꢀ3
ꢀ25
ꢀ21
ꢀ2
ꢀ23
ꢀ20
ꢀ7
ꢀ28
1
ꢀ39
ꢀ1
5g
5h
5
116
129
137
Fig. 5 (a) Absorption and (b) normalized fluorescence spectra of 5a–5h in
DMSO.
a
Dlmax = lmax1(unsubstituted formazan (5a)) ꢀ lmax1(substituted formazan (5b–5h))
.
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Table
3
Absorption and fluorescence characteristics of compounds
Fluorescence quantum yields. The relative fluorescence
quantum yields (Fx) were calculated by the comparative
method (eqn (1)),50 expressed as
5a–5h in DMSO solution
log ea
labs (nm)
lem (nm)
Fx
S d (nm)
b
b
c
Compound
À
Á
2
As ꢂ Fx ꢂ nx ꢂ Fs
5a
5b
5c
5d
5e
5f
4.603
4.732
4.599
4.637
4.665
4.740
4.764
4.885
513
521
540
533
512
475
513
400
570
526, 566
556
553
564
532
512, 561
510
0.045
0.046
0.041
0.043
0.047
0.092
0.046
0.038
100
96
86
83
94
62
91
40
Fx ¼
(1)
2
ðAx ꢂ Fs ꢂ ns Þ
where A is the absorbance at the excitation wavelength; F, the
area under the fluorescence curve; and n, the refraction index.
Subscripts s and x refer to the standard and the sample of
unknown quantum yield, respectively.
The fluorescence quantum yields (Fx) of 5a–5h were deter-
mined in the DMSO using rhodamine 6G (Fs = 0.95 in ethanol)
as a standard (Table 3).51 The emission efficiency in dilute
solution largely depends on the molecular structure. Com-
pound 5f provided the highest quantum yield of 0.092, which
was unexpected for electron withdrawing NO2 substituent on
5g
5h
a
b
Extinction coefficient (1 Mꢀ1 cmꢀ1). Wavelengths of maximum
c
absorbance (labs) and emission intensity (lem). Fx was determined
by using rhodamine 6G in ethanol (F = 0.95) as the standard. Stokes
shift is calculated as the difference between emission maxima and
excitation wavelength (470 nm).
d
very low intensity, which suggested that fluorescence does not the 1-phenyl ring, compared with 5a–5e. Although –Cl and –Br
come from the species responsible for lmax absorption. Fluores- atoms were known to show mesomeric effect, the obtained low
cence was measured at low concentrations to avoid aggrega- quantum yields (Fx = 0.041 and 0.043, respectively) rationalized
tion, self-absorption effects, excimers, and emission spectrum with a heavy atom effect. The mesomeric effect of the fluorine
distortion.48,49 The 470 nm excitation wavelength provided the unit located at the para-position of the 1-phenyl in compound
highest fluorescence level and was a useful wavelength for 5e was observed with high quantum yield (Fx = 0.047), com-
quantum yield comparison.
pared with other compounds. The lowest quantum yield
Compounds (5a–5h) afforded a green to yellow emission (Fx = 0.038) was observed for compound 5h possessing
with the maxima varying from 510 to 570 nm in DMSO electron-withdrawing nitro-substituents at 2- and 4-positions
(Table 3). Compound 5a exhibited a yellow fluorescence with on the 1-phenyl ring.52 These Fx values indicated that a low
the emission maximum of 570 nm, which is highest among number of photons were emitted relative to the number of
the other compounds (Fig. 5b). Due to strong electron photons that were deactivated by non-radiative transitions
withdrawing ability of the NO2 group on the 1-phenyl (internal conversion or intersystem crossing), which are favour-
ring, compounds 5f and 5h were blue-shifted by 57 and able if the photons underwent intersystem crossing to the
110 nm, respectively, compared with 5a. These were consis- triplet excited state. Based on the outcome of fluorescence
tent with the results recorded from the UV-vis absorption investigations, quantum yields are not dependent on the pro-
spectra of these compounds. Compound 5g, which has a 3,4- perties of electron-donating and withdrawing substituents.
dimethyl group on the 1-phenyl ring, also exhibited green
Electrochemical properties
fluorescence with a maximum at 561 nm. The emission
maximum of 5b, having a methoxy substitution on the The electrochemical behaviour of the target compounds was
1-phenyl ring, was blue-shifted by 4 nm, compared with 5a. probed by cyclic voltammetry in 1 mmol Lꢀ1 of dichloro-
Compared with that of compound 5c (lem = 556 nm), the methane solution with 0.1 M tetrabutylammonium hexafluoro-
emission maxima of compounds 5d (lem = 553 nm) and 5e phosphate. The reduction and oxidation curves of 5a–5h are
(lem = 564 nm) were red shifted by about 8 and 11 nm, shown in Fig. 6, and the corresponding electrochemical data
respectively. The difference of electron withdrawing and are summarized in Table 4. Cyclic voltammetric experiments
donating capabilities of the substituents on the 1-phenyl ring, showed the presence of quasi-reversible oxidation potentials for
and the difference in the degree of conjugation caused the all of the compounds. Although the reduction processes were
aforementioned phenomenon.
found to be reversible for compounds 5b–5d, irreversible
The Stokes shifts of compounds 5a–5h were calculated from characteristics for compounds 5a, 5e and 5f were recorded. In
the difference between lem and the excitation wavelength of addition, compounds 5g and 5h provided quasi-reversible
470 nm (Table 3). Stokes shifts of formazans were also depen- reduction potential (Fig. 6).
dent on the groups bonded to the 1-phenyl ring. Although
Formazans were generally oxidized in two steps and reduced in
compound 5a with no substitute on the 1-phenyl ring exhibited one step.17 Formazans 5c, 5d, 5g and 5h were oxidized by means
a large Stokes shift of 100 nm, those of the other compounds of a quasi-reversible, two-electron transfer process giving the
were obtained between 40 and 96 nm. The Stokes shifts corresponding cation radical. This was followed by the second
detected in the emission spectra were attributed to electronic step in which their tetrazolium cations were formed by giving one
transitions and an intramolecular charge transfer (ICT) from eꢀ and –H+ from the radicals (Scheme 4a).53 The charge delocali-
the Ph1–NH donor to the N–Ph5 acceptor (Scheme 2). The zation within systems showing an extended p conjugation
intramolecular CT resulted in the incremental charge density further stabilizes the cation radical intermediate.54 Formazans
on Ph1–NH.
5a, 5b, 5e and 5f were oxidized in a single two-electron process.
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anionic and cationic particles.53 There is also agreement between
these results and the data given in literature.55–58
The effect of electron withdrawing and electron donating
groups at the N-aryl substituents was investigated by cyclic
voltammetry. The highest first oxidation potential peaks were
observed for the compounds 5f and 5h, having strong electron
withdrawing NO2 groups. Due to the electronegativity of Cl, Br
and F atoms, the first oxidation potentials were recorded
relatively higher for the compounds 5c, 5d and 5e, compared
to 5a. Electron donating groups, such as methoxy and methyl
units, reduced the first oxidation potentials. Compound 5b
containing electron-donating –OMe group at para-position
provided the lowest first oxidation potential, whereas com-
pound 5h containing electron withdrawing –NO2 groups at
ortho- and para-positions has the highest first oxidation
potential.
The HOMO–LUMO energy gaps, as well as the HOMO and
LUMO energies, were calculated in order to correlate them
with the oxidation and reduction potentials of the investigated
5a–5h. On the basis of the onset potentials, whereas the HOMO
energy levels of 5a–5h were estimated to be between ꢀ5.19 and
ꢀ5.57 eV, the LUMO energy levels were calculated between
ꢀ3.23 and ꢀ4.26 eV, respectively. The cyclic voltammograms of
5a–5h should correlate not with electronic excitation energies
but with the electron-acceptor capacity of the substituents,
which characterized by the LUMO energies. In addition, the
electronic band gaps of the new formazans varied between 1.13
and 2.14 eV, respectively (Table 4).
Theoretical calculations
The geometry optimizations of all synthesized compounds in
the gas phase were carried out at the DFT level of theory using
PBE1PBE/6-311g (2d,2p)-level basis set.59–61 Relative Gibbs free
energies and possible tautomeric forms of each molecule were
calculated using the same level of basis set. The results are
listed in Tables 5 and 6.
It was believed that the tautomerism of aryl formazans
contained in the HN–Ph1 and N–Ph5 atoms is an intramolecular
process occurring between two degenerate forms.1,29,34,62,63
According to the calculation results, synthesized formazan
derivatives were found in two tautomeric equilibrium due
to the proton transfer between the hydrazone nitrogen atom
(N4–H1) and the azo group (N2–H2) atoms, which was labelled
as tautomer 1 and tautomer 2 in the formazan frame. Possible
tautomeric forms of 5h are depicted as a representative example
in Fig. 7.
Fig. 6 Cyclic voltammograms of 5a–5e (up) and 5f–5h (down) in 0.1 M
Bu4NPF6 in dry dichloromethane run at a sweep rate of 100 mV sꢀ1
showing oxidation and reduction potentials.
,
According to the calculation results, the molecular stability
This electrochemical process coupled with H+ transfer, directly order and the possible tautomeric forms’ Gibbs free energy
yields their tetrazolium cations due to a very fast follow-up based stabilities are 5d 4 5c 4 5h 4 5f 4 5b 4 5e 4 5g 4 5a
chemical reaction (Scheme 4b).27,55,56 The reduction of the tetra- (Table 5). These changes observed in the molecular stabili-
zolium cation occurred with a peak potential between of ꢀ0.29 to zation energy may be explained with electronic characteristics
ꢀ0.85 V.17,33 On reducing the formazans, an anion radical prob- of substituent groups in the aromatic ring. This situation can
ably formed the negative charge on which all four nitrogen atoms be explained by considering the volume of the bromine atom,
were distributed. The formazan structure, which consists of four which is greater than that of hydrogen. Therefore, the steric effect
nitrogen atoms and one carbon atom conjugated with three of bromine was greater than other substituents (–F and –Cl).
aromatic rings, leads to ready electrochemical formation of stable Electron withdrawing units increased molecular stabilization,
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Table 4 Electrochemical properties of compounds 5a–5h
ECgV (eV)
a
a
onset b
ox
onset b
red
c
Comp.
Eox1/Eox2 (V)
Ered1/Ered2 (V)
E
(V)
E
(V)
EHOMO/LUMO (eV)
5a
5b
5c
5d
5e
5f
1.28
1.27
1.34/1.83
1.30/1.77
1.31
1.41
1.29/1.82
1.56/1.78
ꢀ0.80
1.03
0.96
1.13
0.97
0.99
0.79
1.04
1.09
ꢀ0.54
ꢀ0.21
ꢀ0.67
ꢀ1.17
ꢀ0.14
ꢀ0.43
ꢀ0.16
ꢀ0.44
ꢀ5.43/ꢀ3.86
ꢀ5.36/ꢀ4.19
ꢀ5.57/ꢀ3.73
ꢀ5.37/ꢀ3.23
ꢀ5.39/ꢀ4.26
ꢀ5.19/ꢀ3.97
ꢀ5.44/ꢀ4.24
ꢀ5.49/ꢀ3.96
1.58
1.17
1.84
2.14
1.13
1.22
1.20
1.53
ꢀ0.35/ꢀ0.97
ꢀ0.85
ꢀ0.31/ꢀ0.92
ꢀ0.29/ꢀ0.88
ꢀ0.61
5g
5h
ꢀ0.34/ꢀ0.88
ꢀ0.58/ꢀ0.91/ꢀ1.11
a
b
c
Oxidation and reduction potentials from cyclic voltammograms. Onsets of oxidation and reduction. HOMO = ꢀ(Eonset (ox) + 4.4) (eV), LUMO =
ꢀ(Eonset (red) + 4.4).
Scheme 4 (a) Schematic representation of the structure of 5c for possible oxidation mechanisms of 5c, 5d, 5g and 5h; (b) structure of 5a for possible
oxidation mechanism of 5a, 5b, 5e and 5f.
Table 5 Calculated Gibbs free energies (GFEs) and selected H-bond values of compounds 5a–5h and their tautomers by PBE1PBE/6-311G(2d,2p)
calculations
H-bond (Å)
Comp.
Substituents
-H
GFE (Hartree)
H1ꢁ ꢁ ꢁN2
1.7601
H2ꢁ ꢁ ꢁN4
H1ꢁ ꢁ ꢁO2
—
H2ꢁ ꢁ ꢁO2
—
—
H1ꢁ ꢁ ꢁO1
2.7274
H2ꢁ ꢁ ꢁO1
5a1
5a2
5b1
5b2
5c1
5c2
5d1
5d2
5e1
5e2
5f1
ꢀ1371.7337
ꢀ1371.7333
ꢀ1486.1311
ꢀ1486.1369
ꢀ1831.1717
ꢀ1831.177
ꢀ3944.8858
ꢀ3944.8849
ꢀ1470.9251
ꢀ1470.9256
ꢀ1576.1263
ꢀ1576.122
ꢀ1450.2286
ꢀ1450.2226
ꢀ1780.5003
ꢀ1780.4909
1.8180
1.8203
1.8081
1.8071
1.8142
1.7868
2.3124
2.3108
2.2984
2.2981
2.3043
2.2852
4-OMe
4-Cl
1.6314
1.6312
1.7522
1.7478
1.7679
2.6061
2.5801
2.6947
2.7029
2.6797
4-Br
4-F
4-NO2
3,4-(CH3)2
2,4-(NO2)2
5f2
5g1
5g2
5h1
5h2
2.7309
3.4258
1.6825
1.7893
2.3144
3.9855
1.9217
2.1160
whereas electron-donating groups decreased the stabilization and 5e were stable in tautomer 2 form, whereas molecules 5a, 5d
energy of molecules. and 5g were also stable in tautomer 1 (Table 6). X-ray structural
In formazans, the equilibrium was fully shifted towards the analysis of compound 5e determined tautomer 2 to be a stable
form where the proton was localised at the nitrogen atom linked tautomer in the solid state. This experimental result has been
to the substituent, according to the electronic characteristics.1 confirmed by theoretical calculations (Fig. 1 and 2).
Compounds 5f and 5h, which have strong electron-withdrawing
Intramolecular H-bonds (H1ꢁꢁꢁN2, H2ꢁꢁꢁN4, H1ꢁꢁꢁO1, H2ꢁꢁꢁO1,
aryl substituents at the Ph–N4 leads to co-existence of tautomer 2 H1ꢁ ꢁ ꢁO2 and H2ꢁ ꢁ ꢁO2) belonging to possible tautomeric forms
with a considerable amount of tautomer 1.1,34 Molecules 5b, 5c of the molecules were investigated (Fig. 7 and Table 5).
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Table 6 Total tautomer stable (DKT) and differential DH bond between
tautomer forms (5a–5h)
Gibbs free energy and selected H-bonds of the molecules
5a–5h calculated theoretically in the gas phase are listed in
Table 6. The results of the calculation indicated two different
tautomeric forms of the molecules generated by their intra-
molecular hydrogen bonds in the gas phase.
DHb
a
Comp.
DKT
Ac
Bd
Ce
5a1 ! 5a2
5b1 ! 5b2
5c1 ! 5c2
5d1 ! 5d2
5e1 ! 5e2
5f1 ! 5f2
5g1 ! 5g2
5h1 ! 5h2
0.0004
0.058
0.189
0.177
0.055
0.066
ꢀ0.415
ꢀ0.295
ꢀ0.282
ꢀ0.397
ꢀ0.399
ꢀ0.395
ꢀ0.417
0.560
ꢀ0.0058
ꢀ0.0053
0.0009
Conclusions
ꢀ0.0005
0.0043
0.019
In this work, a series of novel formazans 5a–5h were synthe-
sized in overall yields of 49–86%, which required minimal
purification. The structures of the formazans were characterized
by using elemental analysis, various spectroscopic methods and
the structure of a representative compound 5e was confirmed
based on X-ray crystallography. UV-vis measurements indicated
that lmax values were somewhat dependent on the solvent
polarities. Although compounds 5a–5d and 5g–5h showed slight
positive solvatochromism, compounds 5e and 5f demonstrated
negative solvatochromism in polar solvents. The substituent
effects were examined in various solvents, which pointed out a
bathochromic shift for electron withdrawing units and a hypso-
chromic shift for electron donating groups. Fluorescence spec-
tral characteristics of the compounds were investigated in DMSO
solution. Among all of the synthesized derivatives, compound 5a
exhibited yellow fluorescence with the highest emission maxi-
mum of 570 nm, whereas compounds 5h exhibited a green
fluorescence with lowest emission maxima of 510 nm. The
results showed that emission maximum mainly varied depend-
ing on the substituent on 1-phenyl ring. In addition, the
fluorescence quantum yield and Stokes shifts of all compounds
were calculated. Electrochemical measurements supported the
proposed structures of the target compounds. According to the
computational results, the stability order of the molecules and
0.0059
0.0094
ꢀ0.071
ꢀ0.227
0.194
a
DKT = Gtautomer form 2 ꢀ Gtautomer form 1, DKT, and constant stable between
tautomer forms. b DH, the differential hydrogen bond between tautomer
forms. c A, DH = H-bond(H2ꢁꢁꢁN4) ꢀ H-bond(H1ꢁꢁꢁN2)
.
d B, DH = H-bond(H2ꢁꢁꢁO1)
ꢀ
H-bond(H1ꢁꢁꢁO1)
.
e C, DH = H-bond(H2ꢁꢁꢁO2) ꢀ H-bond(H1ꢁꢁꢁO2)
.
The differential DH were calculated by taking the difference
between selected H-bonds of tautomers 1 and 2 (Table 6).
H-bonds between H1ꢁ ꢁ ꢁN2, which belong to tautomer 1 struc-
ture of the molecules 5a1–5f1, were determined to be shorter
and stronger than H-bonds between H2ꢁ ꢁ ꢁN4 belonging to
tautomer 2. According to the different hydrogen bonds in
molecules 5g2 and 5h2, tautomeric form 2 was found to be
more stable. When the H-bonds between H2ꢁ ꢁ ꢁO1 in tauto-
meric forms 2 of the molecules 5a–5g were compared with the
H-bonds between H1ꢁ ꢁ ꢁO1 in tautomeric form 1, H-bonds
between H2ꢁ ꢁ ꢁO1 were determined to be shorter and stronger.
Likewise, tautomeric form 1 appeared to be more stable in the
case of molecule 5h1, owing to the fact that molecule 5h1
possesses possible H-bonds between oxygen O2 in the ortho-
NO2 substituent with H1 and H2. Based on the computations,
the H bond between H1–O2 was shorter and stronger with
respect to that appearing between H2–O2.
Fig. 7 Molecular structures of the possible tautomeric forms of 5h with atomic numbering.
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Gibbs free energy based stabilities of the possible tautomeric at 296(2) K using graphite monochromated Mo Ka radiation at
forms are 5d 4 5c 4 5h 4 5f 4 5b 4 5e 4 5g 4 5a. l = 0.71073 Å. Diffraction data were collected over the entire
Spectroscopic explorations and quantum chemical calculations sphere and were corrected for absorption. The data reduction
confirmed that the existence of a six-membered pseudo aro- was performed with the Bruker SMART program package. The
matic ring hydrogen bond in a formazan skeleton and its structure solution was determined with a SHELXS-97 package
tautomers due to the inner-molecular hydrogen transfer is using direct methods and was refined with SHELXL-97 against
consistent with literature. These structural isomers are promis- F 2 using first isotropic and later anisotropic thermal para-
ing candidates as ligands for coordination chemistry. Based on meters for all non-hydrogen atoms. Hydrogen atoms were
these factors, we envision this new class of compounds to be of added to the structure model at calculated positions. Geometric
significant interest in the field of functional materials.
calculations were performed with PLATON.
A specimen of C34.67H26.67Cl1.33F1.33N5.33O2.67, approximate
dimensions of 0.07 ꢂ 0.19 ꢂ 0.76 mm3, was used for X-ray
crystallographic analysis, and the X-ray intensity data were
measured. The integration of the data using an orthorhombic
unit cell yielded a total of 105 204 reflections to a maximum y
angle of 28.461 (minimum y angle of 1.501) (0.75 Å resolution),
of which 5570 were independent (average redundancy 18.888,
completeness = 99.3%, Rint = 14.67%, and Rsig = 10.85%) and
2799 (50.25%) were greater than 2s(F2). The final cell constants
of a = 7.8846(3) Å, b = 27.1172(12) Å, c = 20.7714(9) Å, and
volume = 4441.1(3) Å3 are based upon the refinement of the
XYZ-centroids of the reflections above 20s(I). The calculated
minimum and maximum transmission coefficients (based on
crystal size) are 0.8547 and 0.9852. The structure was solved
and refined using the Bruker SHELXTL Software Package using
the space group Pbca with Z = 6 for the formula unit
Experimental section
Materials and instruments
4-Chloro-2-phenoxybenzenamine, substituted phenylhydra-
zines, 4-methoxybenzaldehyde, NaOH and high-grade organic
solvents for UV-vis and fluorescence measurements were pur-
chased from Sigma-Aldrich and used without further purifica-
tion. Thin layer chromatography plates (DC-Alufolien Kieselgel
60 F254) were purchased from Merck (Darmstadt, Germany).
Isolation of the compounds was performed by using column
chromatography over Sigma silica gel 60 (63–200 mm).
Microanalyses were carried out using a Leco CHNS-932 elemental
analyser. The melting points were measured on a Gallenkamp
1
apparatus using a capillary tube. H NMR and 13C NMR spectra
were recorded on a Bruker DPX FT-NMR (500 MHz) spectrometer
(SiMe4 as an internal standard) and chemical shifts (d) are
given in ppm. The spectrometer was equipped with a 5 mm
PABBO BB-inverse gradient probe. The concentration of the
solute compounds was 10–15 mg in 1.0 mL of CDCl3 and DMSO-d6.
The FTIR spectra were recorded as KBr pellets using a Bruker IFS
66 v/S FTIR Spectrophotometer in a 4000–400 cmꢀ1 range at room
temperature. The electronic spectra of formazans (10ꢀ5 mol Lꢀ1) in
different solvents were measured using a SHIMADZU UV-3150
UV-VIS-NIR spectrophotometer. The fluorescence spectra of the
compounds were recorded on a Cary Eclipse Fluorescence Spectro-
photometer (Varian). LC-MS studies of formazans were carried out
with an Agilent 1100 Series LC/MSD Trap VL&SL using atmospheric
pressure chemical ionization and electrospray with positive and
negative ion detection.
C
34.67H26.67Cl1.33F1.33N5.33O2.67. The final anisotropic, full-
matrix, least-squares refinement on F2 with 312 variables con-
verged at R1 = 5.22% for the observed data and wR2 = 15.06% for
all data. The goodness-of-fit was 1.018. The largest peak in the
final difference electron density synthesis was 0.469 eꢀ ꢀ3, and
Å
the largest hole was ꢀ0.505 eꢀ Åꢀ3 with an RMS deviation of
0.170 eꢀ ꢀ3. On the basis of the final model, the calculated
Å
density was 1.421 g cmꢀ3 and F(000), 1968 eꢀ.
Computational method
In the calculations, CS Chem Office Pro 12.0 for Microsoft
Windows64 and the Gaussian0965 software package with a
2 ꢂ 6-core Intel Core i7 980X processor, 3.33 GHz, 12 MB L3
Cache, LGA 1366 socket, and X58 chipset workstation were
used. Quantum chemical calculations at the DFT Perdew, Burke
and Ernzerhof (PBE) functional were done with basis sets
6-311g (2d,2p).59,60
Electrochemical measurements were made using a CH-
Instruments Model 400A as a potentiostat. A conventional
three-electrode configuration consisting of a platinum working
electrode, a Pt-wire counter electrode and an Ag-wire reference
electrode was employed. All measurements were run in dichloro-
methane with 0.1 M tetrabutylammonium hexafluorophosphate
([Bu4N]PF6) as the supporting electrolyte at room temperature
under a nitrogen atmosphere. Ferrocene was added as a calibrant
after each set of measurements, and all potentials reported were
quoted with reference to the ferrocene/ferrocenium (Fc/Fc+) couple
Synthesis
Synthesis of substituted phenylhydrazones 3a–3h. The
substituted phenylhydrazones 3a–3h were synthesized by the
condensation of 4-methoxybenzaldehyde with substituted phenyl-
hydrazine compounds (see ESI†).
General synthesis of formazans 5a–5h. A diazonium salt
solution was first obtained. To a solution of 4-chloro-2-
phenoxybenzenamine in 10 mL of HCl(aq) (50%, v/v), was
dropped a solution of NaNO2 in 5 mL of water at 0–5 1C for
1 h. The reaction mixture was allowed to stir for an additional
at a scan rate of 100 mV sꢀ1
.
X-ray crystallographic study
Diffraction data for the complex were collected with a Bruker 1 h. The completion of diazotization was checked using starch
AXS APEX CCD diffractometer equipped with a rotation anode iodide paper. 10 mL of 20% NaOH (1.00 g) was added to a
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solution of 3a–3h in 20 mL of pyridine at 0 1C. Diazonium salt 7.49 (d, J = 7.57 Hz, 2H), 7.47 (d, J = 8.82 Hz, 2H), 7.43
of 4-chloro-2-phenoxybenzenamine (4) was added dropwise (t, J = 7.93 Hz, 2H), 7.21 (t, J = 7.37 Hz, 1H), 7.11 (d, J = 7.83
with continuous stirring over 1 h, maintaining the temperature Hz, 2H), 7.04 (d, J = 8.79 Hz, 2H), 7.03 (d, J = 8.45 Hz, 1H), 6.87
below 5 1C. The reaction mixture was allowed to stir for another (d, J = 8.62 Hz, 1H), 3.81 (s, 3H). 13C NMR (126 MHz, CDCl3): d
3 h and then poured into 250 mL of ice-cold water with 159.81, 156.54, 149.98, 143.94, 142.64, 137.36, 132.42, 130.36,
continuous stirring. The resulting violet-coloured viscous solid 130.17, 129.61, 127.47, 124.49, 124.11, 124.04, 122.85, 119.85,
was filtered off, washed with water and recrystallized from 118.15, 114.98, 113.90, 55.38. ESI-MS m/z: 491.0 ((M + H)ꢀ, 70%);
methanol.
490.0 ((M)ꢀ, 70%); 489.0 ((M ꢀ H)ꢀ, 35%). ESI-MS/MS m/z: 395.9
(20%); 284.9 (7%); 250.8 (21%); 202.8 (100%); 174.9 (22%).
Preparation of 5-(4-chloro-2-phenoxyphenyl)-3-(4-methoxyphenyl)-
1-phenylformazans (5a). This compound was obtained from 3a
5-(4-Chloro-2-phenoxyphenyl)-3-(4-methoxyphenyl)-1-(4-bromo-
(1.0 g, 4.40 mmol) and diazonium salt 4 (0.96 g, 4.40 mmol). phenyl)formazan (5d). This compound was obtained from 3d
Formazan 5a (1.65 g, 82%) was obtained as a light violet powder (1.20 g, 3.90 mmol) and diazonium salt 4 (0.86 g, 3.90 mmol) as
with a melting point of 176–177 1C. Rf: 0.63 (n-hexane/ethyl a dark violet solid. Anal. calcd for C26H20BrClN4O2 (%): C, 58.28;
acetate, 5 : 1). Anal. calcd for C26H21ClN4O2 (%): C, 68.34; H, H, 3.76; N, 10.46; found: C, 58.15; H, 3.84; N, 10.43. Yield: 1.81 g
4.63; N, 12.26; found: C, 68.12; H, 4.75; N, 11.97. FT-IR (86%); Rf: 0.75 (n-hexane/ethyl acetate, 5 : 1); m.p. 177–178 1C;
(KBr, cmꢀ1) nmax: 3055 (w), 1361 (s), 1587 (s), 3010 (s), 1596 FT-IR (KBr, cmꢀ1) nmax: 3066 (w), 1352 (s), 1587 (s), 3012 (s),
1
(s), 1492 (s), 1249–1211 (m). 1H NMR (500 MHz, CDCl3): d 15.23 1598 (s), 1490 (m), 1247–1215 (m). H NMR (500 MHz, CDCl3):
(s, 1H), 8.12 (d, J = 8.73 Hz, 2H), 8.04 (d, J = 2.39 Hz, 1H), 7.67 d 15.25 (s, 1H), 8.07 (d, J = 8.78 Hz, 2H), 8.02 (d, J = 2.26 Hz, 1H),
(t, J = 7.57 Hz, 2H), 7.43 (d, J = 7.73 Hz, 2H), 7.40 (m, 3H), 7.19 7.55 (d, J = 8.65 Hz, 2H), 7.42 (t, J = 7.92 Hz, 2H), 7.34 (d, J = 8.68 Hz,
(t, J = 7.42 Hz, 1H), 7.13 (d, J = 8.40 Hz, 2H), 7.03 (d, J = 8.73 Hz, 2H), 7.20 (t, J = 7.39 Hz, 1H), 7.10 (d, J = 8.00 Hz, 2H), 7.01
2H), 6.98 (dd, J = 8.54 and 2.45 Hz, 1H), 6.87 (d, J = 8.61 Hz, 1H), (d, J = 8.76 Hz, 2H), 6.98 (d, J = 2.23 Hz, 1H), 6.86 (d, J = 8.65 Hz,
3.90 (s, 3H). 13C NMR (126 MHz, CDCl3): d 159.75, 156.66, 1H), 3.89 (s, 3H). 13C NMR (126 MHz, CDCl3): d 159.80, 156.56,
151.36, 143.63, 142.49, 137.44, 130.64, 130.30, 130.09, 129.84, 149.78, 143.71, 142.60, 137.23, 136.29, 130.36, 130.16, 129.63,
129.21, 127.53, 123.89, 123.53, 121.73, 119.83, 118.18, 114.89, 129.45, 127.48, 124.02, 123.88, 122.76, 119.83, 118.13, 114.95,
113.88, 55.39. ESI-MS m/z: 457.1 ((M + H)+, 18%); 456.1 ((M)+, 113.90, 55.38. ESI-MS m/z: 536.1 ((M + 2H)ꢀ, 28%); 535.1 ((M + H)ꢀ,
13%); 455.1 ((M ꢀ H)+, 50%). ESI-MS/MS m/z: 318.2 (100%); 23%); 534.0 ((M)ꢀ, 100%). ESI-MS/MS m/z: 294.8 (19%); 255.1
304.3 (87%); 244.3 (6%).
(18%); 202.8 (100%).
5-(4-Chloro-2-phenoxyphenyl)-1,3-bis(4-methoxyphenyl)formazan
5-(4-Chloro-2-phenoxyphenyl)-3-(4-methoxyphenyl)-1-(4-fluoro-
(5b). This compound was obtained from 3b (1.50 g, 5.90 mmol) phenyl)formazan (5e). This compound was obtained from 3e
and diazonium salt 4 (1.29 g, 5.90 mmol) as a red solid. Anal. (1.20 g, 3.90 mmol) and diazonium salt 4 (0.86 g, 4.90 mmol) as
calcd for C27H23ClN4O3 (%): C, 66.60; H, 4.76; N, 11.51; found: C, a red solid. Anal. calcd for C26H20ClFN4O2 (%): C, 65.75; H,
66.85; H, 4.89; N, 11.24. Yield: 1.68 g (59%); Rf: 0.48 (n-hexane/ 4.24; N, 11.80; found: C, 65.45; H, 4.33; N, 11.83. Yield: 2.18 g
ethyl acetate, 5 : 1); m.p. 164–166 1C; FT-IR (KBr, cmꢀ1) nmax: 3068 (70%); Rf: 0.71 (n-hexane/ethyl acetate, 5 : 1); m.p. 158–160 1C;
(w), 1352 (s), 1583 (s), 3004 (s), 1596 (s), 1461 (s), 1253–1215 (m). FT-IR (KBr, cmꢀ1) nmax: 3068 (w), 1359 (s), 1508 (s), 3005 (s),
1
1H NMR (500 MHz, CDCl3): d 14.87 (s, 1H), 8.10 (d, J = 8.56 Hz, 1589 (s), 1494 (m), 1245–1211 (m). H NMR (500 MHz, CDCl3):
2H), 8.00 (d, J = 2.03 Hz, 1H), 7.69 (d, J = 8.64 Hz, 2H), 7.42 d 15.09 (s, 1H), 8.08 (d, J = 8.83 Hz, 2H), 8.01 (d, J = 2.40 Hz,
(t, J = 7.65 Hz, 2H), 7.18 (t, J = 7.33 Hz, 1H), 7.12 (d, J = 8.35 Hz, 1H), 7.66 (dd, J = 8.84, 5.25 Hz, 2H), 7.43 (t, J = 7.96 Hz, 2H),
2H), 7.02 (d, J = 8.55 Hz, 2H), 6.91 (d, J = 8.45 Hz, 3H), 6.83 7.19 (t, J = 7.40 Hz, 1H), 7.10 (d, J = 7.64 Hz, 2H), 7.07
(d, J = 8.56 Hz, 1H), 3.88 (s, 6H). 13C NMR (126 MHz, CDCl3): (d, J = 8.44 Hz, 2H), 7.01 (d, J = 8.84 Hz, 2H), 6.95 (dd, J = 8.60
d 162.54, 159.70, 156.78, 146.65, 142.42, 142.37, 137.02, 130.35, and 2.42 Hz, 1H), 6.84 (d, J = 8.59 Hz, 1H), 3.92 (s, 3H). 13C NMR
130.26, 130.05, 129.94, 129.48, 128.81, 127.67, 126.51, 124.31, (126 MHz, CDCl3): d 165.37, 163.36, 159.78, 156.63, 148.49,
123.75, 122.00, 119.72, 118.07, 114.53, 114.43, 114.09, 113.98, 148.47, 142.92, 142.41, 136.88, 130.38, 130.12, 129.67, 127.52,
55.65, 55.38 (2C). ESI-MS m/z: 487.1 ((M + H)+, 34%); 486.1 ((M)+, 124.04, 123.97, 123.93, 123.01, 119.77, 118.07, 116.34, 116.15,
28%); 485.1 ((M ꢀ H)+, 100%). ESI-MS/MS m/z: 350.0 (4%); 230.9 114.80, 113.87, 55.37. ESI-MS m/z: 475.0 ((M + H)ꢀ, 34%); 474.0
(5%); 168.0 (32%).
((M)ꢀ, 28%); 473.1 ((M ꢀ H)ꢀ, 100%). ESI-MS/MS m/z: 268.9
(47%); 234.8 (28%); 202.8 (100%).
5-(4-Chloro-2-phenoxyphenyl)-3-(4-methoxyphenyl)-1-(4-chloro-
phenyl)formazan (5c). This compound was obtained from 3c
5-(4-Chloro-2-phenoxyphenyl)-3-(4-methoxyphenyl)-1-(4-nitro-
(1.20 g, 4.60 mmol) and diazonium salt 4 (1.01 g, 4.60 mmol) as phenyl)formazan (5f). This compound was obtained from 3f
a claret solid. Anal. calcd for C26H20Cl2N4O2 (%): C, 63.55; H, (1.50 g, 5.50 mmol) and diazonium salt 4 (1.22 g, 5.50 mmol)
4.10; N, 11.40; found: C, 63.36; H, 4.25; N, 11.18. Yield: 1.64 g as a darkish solid. Anal. calcd for C26H20ClN5O4 (%): C, 62.22;
(73%); Rf: 0.80 (n-hexane/ethyl acetate, 5 : 1); m.p. 164–166 1C; H, 4.02; N, 13.95; found: C, 61.95; H, 4.09; N, 13.92. Yield:
FT-IR (KBr, cmꢀ1) nmax: 3074 (w), 1353 (s), 1587 (s), 3010 (s), 1.60 g (58%); Rf: 0.86 (n-hexane/ethyl acetate, 5 : 1); m.p. 211–
1598 (s), 1490 (m), 1249–1215 (m). 1H NMR (500 MHz, CDCl3): d 213 1C; FT-IR (KBr, cmꢀ1) nmax: 3076 (w), 1371 (s), 1502 (s),
15.20 (s, 1H), 8.07 (d, J = 8.81 Hz, 2H), 8.03 (d, J = 2.31 Hz, 1H), 3004 (s), 1591 (s), 1471 (m), 1249–1213 (m). 1H NMR
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(500 MHz, CDCl3): d 15.38 (s, 1H), 8.15 (d, 2H), 8.09 (d, 2H), Notes and references
7.99 (s, 1H), 7.46 (d, 2H), 7.34 (s, 1H), 7.26 (s, 1H), 7.23
(m, 3H), 7.16 (d, 2H), 7.00 (s, 2H), 3.82 (s, 3H). 13C NMR
(126 MHz, CDCl3): d 160.23, 156.25, 151.81, 150.19, 143.70,
143.43, 141.96, 131.70, 130.53, 130.11, 129.07, 127.71, 126.21,
125.54, 124.76, 120.51, 118.88, 115.99, 115.48, 114.06, 55.42.
ESI-MS m/z: 502.0 ((M + H)+, 35%); 501.1 ((M)+, 28%); 500.1
((M ꢀ H)+, 100%). ESI-MS/MS m/z: 350.0 (15%); 230.9 (20%);
168.0 (100%).
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(1.50 g, 5.90 mmol) and diazonium salt 4 (1.30 g, 5.90 mmol) as
a red solid. Anal. calcd for C28H25ClN4O2 (%): C, 69.34; H, 5.20;
N, 11.55; found: C, 69.11; H, 5.28; N, 11.27. Yield: 1.78 g (62%);
Rf: 0.70 (n-hexane/ethyl acetate, 5 : 1); m.p. 173–175 1C; FT-IR
(KBr, cmꢀ1) nmax: 3074 (w), 1363 (s), 1587 (s), 3041 (s), 1598 (s),
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Synthesis, 1995, 577.
1
1490 (m), 1249–1217 (m). H NMR (500 MHz, CDCl3): d 15.27
(s, 1H), 8.12 (d, J = 8.03 Hz, 2H), 8.02 (s, 1H), 7.48 (s, 1H), 7.43
(t, J = 7.51 Hz, 2H), 7.20 (d, J = 7.34 Hz, 2H), 7.16 (d, J = 8.20 Hz,
3H), 7.02 (d, J = 8.13 Hz, 2H), 6.93 (d, J = 8.60 Hz, 1H), 6.85 (d, J =
8.55 Hz, 1H), 3.90 (s, 3H), 2.20–2.30 (s, 6H). 13C NMR (126 MHz,
CDCl3): d 159.69, 156.71, 150.30, 142.98, 142.40, 140.71, 137.60,
137.14, 130.42, 130.22, 130.06, 130.02, 127.57, 124.45, 123.83,
122.53, 119.50, 118.55, 118.28, 114.59, 113.83, 55.37, 19.92,
19.67 (2C). ESI-MS m/z: 485.1 ((M + H)ꢀ, 41%); 484.1 ((M)ꢀ,
30%); 483.1 ((M ꢀ H)ꢀ, 100%). ESI-MS/MS m/z: 377.0 (6%);
270.8 (4%); 216.8 (34%); 202.8 (100%).
´
´
´
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FT-IR (KBr, cmꢀ1) nmax: 3093 (w), 1332 (s), 1591 (s), 3014 (s),
1610 (s), 1496 (m), 1253–1207 (m). 1H NMR (500 MHz, CDCl3): d
13.95 (s, 1H), 9.25 (s, 1H), 8.88 (s, 2H), 8.38 (s, 2H), 8.01 (s, 1H),
7.85 (m, 2H), 7.43 (m, 1H), 7.15 (m, 4H), 7.10 (m, 2H), 3.85
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100%). ESI-MS/MS m/z: 485.1 (100%); 391.9 (27%); 167.9 (41%).
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