Novel phenyl-substituted pyrazinoporphyrazine complexes of rare-earth elements: optimized synthetic protocols and physicochemical properties

Article abstract of DOI:10.1039/c8nj05939j

Novel synthetic protocols based on both template and multi-step methods were developed for phenyl-substituted pyrazinoporphyrazine complexes of rare-earth elements (Y, Eu, Gd, Dy, Er and Lu). p-Hydroquinone was employed as a reaction medium and as a reducing agent in the process of porphyrazine macrocycle formation. Both thermal and microwave irradiation techniques were successfully applied for activation of the template macrocyclization process. An alternative multi-step approach involving the initial stage of free-base ligand formation was realized for the lutetium compound. The target complexes were identified by high-resolution mass spectrometry, infrared spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. Electrochemical behavior in solution and UV-vis absorbance in solutions and films were studied as well. Shifts in the position of the Q band and oxidation-reduction potentials in comparison with corresponding phthalocyanine analogues were noticed. Using the IR absorption spectra recorded in the temperature range of 170-300 K, the position of the Fermi level of ?4.7 ± 0.1 eV and a characteristic energy diagram were obtained for the erbium complex.

Full text of DOI:10.1039/c8nj05939j

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Novel phenyl-substituted pyrazinoporphyrazine
complexes of rare-earth elements: optimized
synthetic protocols and physicochemical
properties†
Cite this:DOI: 10.1039/c8nj05939j
a
ab
ac
a
a
A. D. Kosov, T. V. Dubinina,
*
N. E. Borisova,
A. V. Ivanov, K. A. Drozdov,
d
d
a
ab
S. A. Trashin, K. De Wael, M. S. Kotova and L. G. Tomilova
Novel synthetic protocols based on both template and multi-step methods were developed for phenyl-
substituted pyrazinoporphyrazine complexes of rare-earth elements (Y, Eu, Gd, Dy, Er and Lu).
p-Hydroquinone was employed as a reaction medium and as a reducing agent in the process of
porphyrazine macrocycle formation. Both thermal and microwave irradiation techniques were
successfully applied for activation of the template macrocyclization process. An alternative multi-step
approach involving the initial stage of free-base ligand formation was realized for the lutetium compound.
The target complexes were identified by high-resolution mass spectrometry, infrared spectroscopy and
nuclear magnetic resonance (NMR) spectroscopy. Electrochemical behavior in solution and UV-vis
absorbance in solutions and films were studied as well. Shifts in the position of the Q band and oxidation–
reduction potentials in comparison with corresponding phthalocyanine analogues were noticed. Using the
IR absorption spectra recorded in the temperature range of 170–300 K, the position of the Fermi level of
ꢀ4.7 ꢁ 0.1 eV and a characteristic energy diagram were obtained for the erbium complex.
Received 22nd November 2018,
Accepted 22nd January 2019
DOI: 10.1039/c8nj05939j
rsc.li/njc
properties and unique structural features, only little attention
has been paid to pyrazinoporphyrazine complexes of rare-earth
Introduction
Annelation of the porphyrazine macrocycle by four electron- elements (REE). Kobayashi et al. described tert-butyl substituted
18
deficient pyrazine moieties leads to the appearance of single- and double-decker lutetium pyrazinoporphyrazines. Their
1
,2
3
enhanced nonlinear optical properties, n-type conductivity,
octa-substituted analogues were synthesized by two other groups,
but the complexes were identified only by IR spectroscopy and
4
–6
and interesting photochemical and photophysical properties.
Similar to phthalocyanine complexes, the structure of pyrazino- elemental analysis.
19,20
Thus, developing an effective synthesis and
porphyrazines can be modified by incorporation of peripheral characterization of new pyrazinoporphyrazine complexes of REE is
substituents and variation of the central metal. Porphyrazine an important task.
and phthalocyanine single-decker complexes of lanthanides
The present paper focuses on the development of effective
can be used as building blocks in the synthesis of sandwich- techniques to synthesize substituted REE tetrapyrazinoporphyr-
7
–15
type architectures,
materials.
as well as for the creation of hybrid azine complexes. 5,6-Diphenylpyrazine-2,3-dicarbonitrile was
In addition, lanthanide(III) monophthalocyaninates chosen herein as a model compound for the development of
usually show good solubility and decreased aggregation tendency synthetic approaches to pyrazinoporphyrazines due to its high
1
6,17
2
1,22
due to the steric effect of an axial ligand and high accessibility of availability. Additionally, we previously showed
that the
the central lanthanide ion to solvation. Despite the promising incorporation of phenyl-groups onto the macrocycle periphery
can increase intramolecular interactions and improve the
a
b
c
conductivity of the target complexes in films.
Department of chemistry, Lomonosov Moscow State University, 119991 Moscow,
Russian Federation. E-mail: dubinina.t.vid@gmail.com
Institiute of physiologically Active Compounds, Russian Academy of Science,
1
42432 Chernogolovka, Moscow Region, Russian Federation
Results and discussion
A.N. Nesmeyanov Institute of Organoelement Compounds Russian Academy of
Science, 28 Vavilov Str., 119334 Moscow, Russian Federation
d
The most convenient synthetic approach to initial 5,6-diphenyl-
pyrazine-2,3-dicarbonitrile 1 includes the reaction between
benzil and diaminomaleonitrile in the presence of different
AXES research group, University of Antwerp, 2020 Antwerp, Belgium
Electronic supplementary information (ESI) available. See DOI: 10.1039/
†
c8nj05939j
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Scheme 1 Synthesis of phenyl-substituted pyrazinoporphyrazine complexes 2a–f.
5
,23,24
acids and ethanol.
obtained, using ethanol as a solvent (Scheme 1).
In the current work, compound 1 was Table 1 High-resolution MALDI TOF/TOF mass spectrometry data
Compound
Molecular formula)
Mass
calculated
Mass
found
2
0
It was earlier demonstrated that template synthesis of
unsubstituted and tetra-tert-butylsubstituted pyrazinoporphyr-
azine complexes of lanthanides in a melt of the initial nitrile
gives the target compounds in 10–30% yield. Our attempts to 2c (C72
obtain octaphenyl-substituted porphyrazine REE complexes 2
from nitrile 1 in melt or in solutions of high-boiling alcohols
(
Ion
+
2
a (C79
H
H
46
40EuN16
40GdN16
54DyN18
N
16
O
4
Y)
)
)
[M-OAc + DHB]
1371.2946
1281.2834
1286.2863
1670.3765
1672.3777
1457.3296
1371.2944
1281.2746
1286.2749
1670.3651
1672.2586
1457.3768
+
2b (C72
[M-OAc]+
H
[M-OAc]
+
2
2
2
d (C92
e (C92
f (C79
H
O
6
)
)
)
[M-OAc + 2CHCA]+
H
H
54ErN18
O
6
[M-OAc + 2CHCA]
+
46LuN16
O
4
[M-OAc + DHB]
(isoamyl alcohol, and n-octanol) were unsuccessful. Instead, we
found that formation of compounds 2a–f takes place in a melt
of p-hydroquinone. Since macrocyclization of 1 includes the In the case of REE complexes 2a–f, ionization is accompanied by
reduction stage, we decided to use p-hydroquinone as a reducing cleavage of axial acetate. Moreover, in the case of more rigid small
3+
3+
3+
3+
agent and at the same time the reaction medium. p-Hydroquinone ions (Dy , Er , Lu and Y ) the further formation of adducts
25,26
was earlier utilized in the synthesis of phthalocyanines.
ever, the target phthalocyanines were synthesized in low yields
about 20%). In the present study, p-hydroquinone was used for 2c is shown in Fig. 1. The isotopic pattern of the molecular ion
the first time in the synthesis of porphyrazines. Noteworthily, the agrees well with the calculated pattern.
How- with the matrices (O-ligands) was observed under laser ionization.
As an example, the mass-spectrum of gadolinium complex
(
yields of the target complexes were high, sometimes reaching 75%.
In FT-IR spectra of complexes 2a–f (Fig. 2 shows the spectrum
On the example of lutetium complex 2f, we also showed that both of dysprosium complex 2d as a representative example), skeletal
thermal and microwave energy can be successfully employed for vibrations of the pyrrole and pyrazine fragments occupy the region
ꢀ1
heating the reaction mixture with nearly equal effectiveness from 1375 to 1635 cm . Stretching vibrations of CH from
ꢀ
ꢀ
1
(Scheme 1).
phenyl groups are observed at 3054–3066 cm and those for
1
For comparison, a multi-step approach through the intermediate the axial acetate can be seen at 2850–2981 cm . The bands at
ꢀ
1
ꢀ1
formation of the porphyrazine ligand was applied on the example of 1282–1446 cm and 1512–1635 cm were assigned to C–O
compound 2f (Scheme 1). In order to avoid harsh demetallation by a and CQO vibrations, respectively. The same values were
2
8
strong (sulfuric) acid in the synthesis of porphyrazine ligand 4 as reported for acetates in the literature and for perchlorinated
commonly used in demetallation of Mg phthalocyanines and their phthalocyaninates of lanthanides bearing acetate counter-ions,
8,16,21,23,27
16
analogues,
we used dilithium salt 3, which was further which were reported by us earlier.
demetallated by freshly obtained polyphosphoric acid. The
following insertion of lutetium was performed in boiling NH groups are observed at 3288 cm (Fig. S2, ESI†). The same
o-DCB in the presence of DBU as a base. The total yield of the values were observed for phthalocyanine ligands.
three stages (lithium salt formation, demetallation, and metal- In this work, pyridine-d5 was chosen as a solvent for the
lation) of the multi-step approach is similar to that of the one- NMR measurements due to its ability to coordinate with a
step procedure (Scheme 1). central metal ion, which allows the suppression of the aggrega-
In the case of porphyrazine ligand 4, stretching vibrations of
ꢀ1
1
6,29
All the obtained compounds were characterized by MALDI TOF tion of the target complexes and improves their solubility. In
mass spectrometry, including high-resolution spectra (Table 1). the case of diamagnetic complexes of yttrium 2a and lutetium
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Fig. 1 MALDI-TOF mass spectrum of 2c, isotopic pattern of the molecular
ion (inset A) and simulated MS pattern of the molecular ion (inset B).
1
5
Fig. 3 H NMR spectra of complexes 2b (A) and 2e (B) in [D ]Py.
3
0
lie near ꢀ20 ppm. In our case, a weaker effect of the para-
magnetic REE apparently results from a larger distance
between peripheral phenyl groups and the central REE ion in
comparison to the reported data for a-protons of REE phthalo-
cyaninates. As expected, the Gd analogue is NMR silent in
5 8
[D ]Py and [D ]THF due to the strong paramagnetic nature of
3
+
33,34
the Gd ion.
In the UV-vis spectra of target lanthanide complexes 2a–f,
two absorption bands are observed: B band (348–358 nm) and
Q band (663–665 nm). Due to the lower orbital symmetry and
Fig. 2 FT-IR spectra of dysprosium complex 2d in ZnSe.
3
5
corresponding splitting of the LUMO, the porphyrazine
ligand 4 possesses two Q bands at 639 and 672 nm (Fig. 4A).
2f, the signals of phenyl protons occupy the same region of the As it was presented earlier for lanthanide(III) monophthalo-
spectra as it is observed for their precursor – 5,6-diphenyl- cyaninates, the lanthanide ion’s nature does not influence the
2
1
pyrazine-2,3-dicarbonitrile.
Q band position. In comparison with phenyl-substituted
The NMR data of compounds 2 with paramagnetic REE are phthalocyanine complexes a hypsochromic shift of the Q band
3
6
of special note. Despite the fact that the lanthanide induced of about 30 nm is observed.
shifts in paramagnetic REE monophthalocyanines have been
The UV-vis spectra were measured for erbium complex 2e, in a
2
5,30–32
studied widely,
the NMR spectra of porphyrazine com- thin film and in poly(methyl acrylate) film, that were deposited from
plexes with paramagnetic REE have not been investigated a pyridine solution on a glass substrate by the drop casting method
previously. The effect of the paramagnetic nature of europium (Fig. 4B). Due to the aggregation effect, an increase of absorption
and erbium ions manifests in a downfield shift of the phenyl intensity in the vibrational satellite area (582 nm) was observed
proton signals for compounds 2b and 2e, respectively, com- indicating H-type aggregation, while a shoulder appeared near
pared to analogues with diamagnetic REE (2a and 2f) (Fig. 3 740 nm implying formation of J-type aggregates. In poly(methyl
and Fig. S1, ESI†). The largest chemical shift value (21.70 ppm) acrylate) film, a polymeric matrix prevents strong aggregation of the
was detected for erbium complex 2e (Fig. 3B). The assignment porphyrazine molecules. It resulted in almost similar Q band
1
of signals in the H NMR spectrum of europium complex 2b positions for the dilute solution (663 nm) and polymeric film
was made using the COSY technique (Fig. S1, ESI†). It was (665 nm) and the absence of intensive absorption at 582 nm.
shown, that the most downfield shifted signals at 7.96 and
Information regarding the energy spectrum for erbium
.88 ppm most likely can be assigned to ortho protons of phenyl complex 2e was obtained from the current–voltage (I–V) char-
7
groups.
acteristics and temperature evolution of the IR spectra.
For the 2e film the I–V dependence for the Ag–active layer–Ag
structure is linear (Fig. 5, inset), which indicates the absence of
The opposite upfield shift of the signals of aromatic protons
up to ꢀ26.88 ppm was observed for dysprosium complex 2d.
For example, a-protons of the phthalocyanine macrocycle an energy barrier at the boundary of the active layer and Ag
25,30,32
in erbium phthalocyaninate lie at 20–40 ppm,
while the signals contact. This is possible when the positions of the Fermi levels
of a-protons for unsubstituted dysprosium monophthalocyaninate in both materials are close and while the Fermi level in the
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Fig. 5 I–V curves for the ITO–active layer (2e)–Ag sandwich structure in
the dark (closed symbols) and under illumination with the wavelengths
corresponding to the B band and Q band in the optical absorption spectra
(
open symbols). The inset shows the I–V curve for the Ag–active layer
2e)–Ag coplanar structure.
(
For 2e film the temperature evolution of the IR transmittance in
ꢀ
1
the 2000–8000 cm wavenumber interval demonstrates significant
ꢀ1
changes only for 3100–3600 cm (Fig. 6).
This behavior can be attributed to a change in the popula-
tion of the energy levels. With temperature decrease the elec-
tron population at the LUMO level decreases substantially; the
increase in absorption is due to the optical excitation of
electrons to the LUMO from the lower-lying levels. To obtain the
exact position of the LUMO level a simple model was used, where
transmittance is calculated as C ꢀ A ꢂ f(E,T) ꢂ (1 ꢀ f(E + dE,T)),
where constants C and A were considered temperature-
independent, and f(E,T) and f(E + dE,T) followed the Fermi–Dirac
Fig. 4 UV-vis spectra of erbium complex 2e (solid line) and porphyrazine
ligand 4 (dashed line) in CHCl
a thin film (solid line) and erbium complex 2e in poly(methyl acrylate) film
dashed line) (B).
3
(A). UV-vis spectra of erbium complex 2e, in
(
38
distribution. The value of dE was obtained from the position of
the local minimum in Fig. 6 and amounted to 0.4 eV. These
3
7
active layer lies close to the LUMO level. It is established that estimations show that the LUMO level in 2e film lies 0.3 eV above
the Fermi level in erbium complex 2e film lies at ꢀ4.3 ꢁ 0.1 eV; the Fermi level. In addition, the presence of an additional level,
the LUMO level lies at or within 0.5 eV above the Fermi level.
lying 0.1 eV below the Fermi level and not seen in the absorbance
The I–V curve for the ITO–active layer (2e)–Ag structure in in the UV-vis spectral range is acknowledged. The obtained results
the dark is non-linear with the activation barrier determined by are in good agreement with the data known from the literature.
the ITO–active layer boundary (Fig. 5). Illumination at wave-
lengths corresponding to the B and Q band in the absorption
spectra (Fig. 4B) leads to the higher current values and lineari-
zation of the I–V curves. Since the Ag-ITO contact does not
demonstrate such a behavior, the observed change in the
curves should be associated with the active layer. It can be
explained by the change in the activation energy to the mobility
threshold due to the generation of photoexcited charge carriers
and change in the position of the Fermi level in the active
layer. Thus, the B and Q band absorption (Fig. 4) should be
associated with the photoexcitation of electrons to the LUMO
level from the levels lying 3.5 and 1.9 eV below the LUMO.
Together with the absence of other absorption peaks besides
the B and Q bands (Fig. 4), this result suggests the existence
of a single energy level lying at or within 1 eV interval above
the Fermi level. This level is already determined as the
LUMO level.
Fig. 6 Temperature evolution of the IR spectrum for thin film of erbium
complex 2e.
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Fig. 7 Temperature evolution of the IR spectrum for erbium complex 2e
in poly(methyl acrylate) film.
For example, from the concentration of charge carriers for similar
39
materials, it follows that the LUMO should lie 0.2–0.4 eV above
the Fermi level.
For erbium complex 2e in poly(methyl acrylate) film the tem-
ꢀ1
perature evolution of the IR transmittance in the 2000–8000 cm
wavenumber interval demonstrates significant changes for
ꢀ
1
3
700–4200 cm (Fig. 7).
In order to analyze the curves, the same model was used Fig. 8 CV (A) and SWV (B) of complex 2e (1.2 mM) recorded at room
temperature in pyridine containing 0.1 M TBABF
4
. Dashed lines depict
with the transition of electrons from the lower-lying level to the
higher-lying level and the evolution of the population of these
levels with a change in temperature. These estimations show
that the LUMO level for erbium complex 2e in poly(methyl
acrylate) film lies 0.6 eV above the Fermi level. The excitation of
voltammograms of the background. Pt disk working electrode; CV scan
ꢀ1
rate, 0.1 V s ; SW modulation amplitude, 50 mV; frequency, 10 Hz; step
potential, 5 mV.
electrons to the LUMO level is carried out from the level lying previously introduced error of 0.1 eV. This allows construction
0
.14 eV above the Fermi level.
The qualitative difference in the temperature dependence of
of a characteristic energy diagram for the erbium complex 2e.
The redox properties of erbium complex 2e were investigated by
the transmittance (Fig. 6 and 7) can be explained from the cyclic (CV) and square wave (SWV) voltammetry (Fig. 8). Table 2
position of the levels relative to the Fermi level. For the 2e film summarizes the found formal oxidation–reduction potentials.
3
+
(
Fig. 6), electron excitation occurs from a level lying below the Since the central lanthanide ion in phthalocyanines (except Ce )
41,42
Fermi level. Its population varies little with temperature. does not change its oxidation state,
all found redox processes
The main contribution is provided by a decrease in the popula- for 2e were referred to the pyrazinoporphyrazine macrocycle.
tion of the LUMO level with temperature decrease. As a result, In total, three reductions and two oxidations were observed
the excitation of electrons to the LUMO level proceeds more within the available potential window (ꢀ1.6 to+1.6 V). In the
+
intensively and the transmittance decreases. For the erbium same conditions Fc /Fc shows the formal potential of +0.610 V.
0
complex 2e in poly(methyl acrylate) film (Fig. 7), both levels lie
An additional peak (Red
1
) at ꢀ0.51 V was attributed to
above the Fermi level. In this case, the main contribution is strongly adsorbed one-electron reduced 2e because of its peculiar
provided by a decrease in the population of the lower level with behavior in CV at different scan rates (Fig. S3, ESI†).
temperature decrease. The excitation of electrons from this
1
The peak current of Red was linearly proportional to the
level proceeds less intensively and the transmittance increases. square root of the scan rate as expected for a diffusion con-
0
A significant difference in the spectral characteristics of trolled electrochemical process, while the peak Red
1
was
pure film of 2e and 2e in poly(methyl acrylate) film is due to noticeable only at the backward scan, and it became more
the aggregation effect. For the B and Q bands in the UV-vis pronounced at higher scan rates as expected for electrochemical
spectral range (Fig. 4B), aggregation in the film leads to a shift processes complicated by adsorption. Moreover, electrochemistry
of the local absorption maxima towards higher energies by of pyrazinoporphyrazines can be complicated by aggregation and
43
0
.17 and 0.07 eV, respectively. This shift must be correlated coordination of pyridine. Oxidation of analogous pyridiniumyl-
with the simultaneous distortion of the LUMO level in k-space substituted pyrazinoporphyrazines in pyridine was not observed
44
and the displacement of the LUMO position in terms of energy. previously, but two oxidations were found for analogous phenyl-
45
The HOMO levels are significantly less affected and their energy substituted diazepinoporphyrazines in pyridine at slightly lower
4
0
values can be taken as aggregation independent with the potentials compared to 2e (Table S1, ESI†).
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+
Table 2 The oxidation–reduction potentials E1/2 (V) for complex 2e in pyridine. E1/2(Fc /Fc) = +0.610 V
a
Red
3
Red
2
Red
1
Ox
1
Ox
2
Ph
8
2ꢀ/3ꢀ
b
Ph
8
1ꢀ /2ꢀ Ph
8
0/1ꢀ
Ph
8
1+ /0 Ph
8
2+/1+
[
TPyzPzLnOAc]
*
[
TPyzPzLnOAc]
*
[
TPyzPzLnOAc]
* [ TPyzPzLnOAc]
*
[
TPyzPzLnOAc]
* DERed1–Ox1
E
E
1/2
ꢀ1.24
ꢀ0.98
ꢀ1.59
ꢀ0.74
ꢀ1.35
+0.86
+0.25
+1.20
+0.59
1.60
1.60
+
1/2 vs. Fc /Fc ꢀ1.85
a
0
+
b Ph
8
An additional peak Red
1
at ꢀ0.51 V (ꢀ1.12 V vs. Fc /Fc) was observed.
TPyzPz = phenyl-substituted pyrazinoporphyrazine.
In comparison to phenyl-substituted phthalocyanines acid (CHCA) as the matrix. High-resolution MALDI mass spectra
Ph
8
21
(
PcLuOAc, Table S1, ESI†) in o-DCB, the oxidation and were obtained using a Bruker ULTRAFLEX II TOF/TOF instrument.
1
1
1
reduction processes in 2e are shifted towards higher potentials
H and H– H COSY NMR spectra were recorded on Bruker Avance
due to the electron-withdrawing effects of the four pyrazine 400 and Bruker Avance 600 spectrometers (400.13 and 600.13 MHz).
4
6,47
fragments fused to the porphyrazine macrocycle.
As a Chemical shifts are given in ppm relative to SiMe
was FT-IR spectra were obtained using an IR 200 ThermoNicolet
PcLuOAc in spectrometer with a spectral resolution Dl = 4 cm
the potential window of o-DCB. Similar to phthalocyanines, Temperature evolution of the IR spectrum was investigated
electron withdrawing and donating peripheral substituents can using a Bruker Vertex 70v spectrometer (spectral resolution,
4
.
consequence of the anodic shift, the third reduction Red
3
Ph
8
ꢀ1
observed for 2e but it was not detected for
.
ꢀ
1
strongly affect the oxidation–reduction potentials as it is seen Dl = 4 cm ) with an Oxford cryostat in a temperature range
from comparison of octachloro- and octadodecyl-substituted 300–170 K. I–V characteristics were measured using a Keithley
4
8,49
pyrazinoporphyrazines.
In this view, the eight phenyl 6430 Source Meter. Samples were fabricated in coplanar and
groups should result in a strong electron donating effect that sandwich geometry. An active layer was deposited on the
explains a cathodic shift in the reduction potentials compared substrates by drop casting from the solution in pyridine. The
to octa(2-(N-methyl)pyridiniumyl)- and octa(2-pyridyl)-substituted thickness of the active layer was about 2 mm (estimated by
4
4,50
pyrazinoporphyrazines.
The HOMO–LUMO gap calculated optical microscopy). For the coplanar geometry, a pair of silver
and Ox contacts with a contact gap of 200 mm was used. For the
.60 V for 2e) is rather the same as that for PcLuOAc in o-DCB sandwich geometry an ITO conducting layer on the glass
from the difference in the potentials of Red
1
1
(DERed1–Ox1 =
Ph
8
1
21
(
Table S1, ESI†), although about 10% increase in the band gap was substrate (lower contact) and a silver layer (upper contact)
previously predicted by DFT calculations for unsubstituted were used. The upper silver layer was formed using silver paste
4
7
pyrazinoporphyrazines compared to phthalocyanines.
‘‘Kontaktol’’. Illumination of samples in the sandwich geo-
Taking into account all uncertainty factors, the experimental metry was carried out from the ITO contact side (transparent
finding rather agrees with the theoretical prediction that the band in the visible spectral range) using a white light lamp and a
gaps should lie close together for pyrazinoporphyrazines and MDR-206 monochromator.
phthalocyanines. Noteworthily, the bandgap of 2e is about
Electrochemical measurements were performed using a
0
.24 V larger than the bandgap of phenyl-substituted diazepino- Metrohm-Autolab 302N instrument. A platinum rod and double
45
porphyrazines studied in the same solvent (DERed1–Ox1 = 1.36 V).
junction Ag/AgCl (1 M LiCl in ethanol) were used as a counter
electrode and a reference electrode, respectively. A Pt disk
electrode (BASi MF-2013, 1.6 mm in diameter) was used as a
working electrode. Prior to use, the working electrodes were
polished with abrasive paper (grit 400), cleaned in ultrapure water in
Experimental
Materials and methods
an ultrasound bath and dried with compressed air. Ferrocene was
s
All reagents and solvents were obtained or distilled according used as an internal reference. Pyridine (dehydrated, SeccoSolv ,
to standard procedures. All reactions were monitored by TLC Merck Millipore) containing 0.1 M tetrabutylammonium tetra-
and UV/vis until complete disappearance of the starting fluoroborate (TBABF , Sigma-Aldrich, for electrochemical analysis,
4
reagents if not additionally specified. Thin-layer chromatography Z99.0%) was used as background electrolyte.
was performed using Merck Aluminium Oxide F254 neutral flexible
Synthetic procedures
plates. The salts Y(OAc)
O, Dy(OAc) O, Er(OAc)
ꢂ 4H
were dried immediately before use for 4 h at 70 1C.
3
ꢂ 4H
2
O, Eu(OAc)
3
ꢂ 3H
2
O, Gd(OAc)
ꢂ 4H
3
ꢂ
4
H
2
3
2
3
ꢂ 4H O and Lu(OAc)
2
3
2
O
5,6-Diphenylpyrazine-2,3-dicarbonitrile (1). Benzil (1.06 g,
5.00 mmol) and diaminomaleonitrile (0.54 g, 5.00 mmol) were
2
The synthesis under microwave irradiation was performed refluxed in 100 mL ethanol for 6 h (TLC-control: SiO , ethyl
using a Samsung microwave oven. UV-vis absorption spectra acetate : hexane (1 : 2)). Then the reaction mixture was cooled to
were recorded on a ThermoSpectronic Helios-a spectrophoto- room temperature. The resulting residue was filtered off,
meter using quartz cells (1 ꢂ 1 cm). Matrix assisted laser washed with cold C H OH (3 ꢂ 30 mL) and dried at room
2
5
desorption/ionization time-of-flight (MALDI-TOF) mass-spectra temperature to give compound 1 (1.24 g, 88%). M.p. 244–246 1C
5
1
1
5
were taken on a Bruker Autoflex II mass spectrometer with (lit. 246 1C ). H NMR (400.13 MHz, [D ]Py) d H ppm: 7.35–
2,5-dihydroxybenzoic acid (DHB) or a-cyano-4-hydroxycinnamic 7.39, 7.43–7.47 and 7.65–7.67 (m, Ph).
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Paper
Synthesis of phenyl-substituted pyrazinoporphyrazine a MeOH–H
2
O (20 : 1 v/v) mixture was added. The precipitate was
complexes of rare-earth elements 2a–e
filtered and washed with water, MeOH, and acetone. This
General procedure. 5,6-Diphenylpyrazine-2,3-dicarbonitrile 1 yielded complex 2f (0.13 g, 54%). MS (MALDI-TOF) m/z: 1457
+
(
0.20 g, 0.71 mmol), Ln(OAc)3 ꢂ nH O (0.36 mmol) and ([M-OAc + DHB] , 100%). UV-vis l
(Py)/nm 354 (lg e 4.69) and 665
2
max
1
p-hydroquinone (0.16 g, 1.45 mmol) were taken in a glass tube. (4.56). H NMR (400.13 MHz, [D ]Py) d H ppm: 7.66–7.69 (16H, m,
5
The resulting mixture was irradiated in a microwave oven
600 W) for 15 min. Then the reaction mixture was cooled to room n (cm ): 1321–1446 (C–O), 1377–1633 (g pyrrole and pyrazine),
temperature and a MeOH–H O (20 : 1 v/v) mixture was added. The 1512–1633 (CQO), 2850–2933 (st CH CH COO–), 3054 (st CHPh).
precipitate was filtered and washed with H O, MeOH, and acetone.
2,3,9,10,16,17,23,24-Octaphenyl-1,4,8,11,15,18,22,25-octaaza-
phthalocyaninato]yttrium acetate (2a). Yield 0.13 g (57%). MS
HPh), 7.71–7.74 (16H, m, HPh) and 7.78 (8H, br., HPh). IR (KBr):
ꢀ1
(
2
3
2
Approach A (ii). A mixture of compound 1 (0.050 g,
[
0
.18 mmol), Lu(OAc)3 ꢂ 4H O (0.031 g, 0,08 mmol) and
2
+
p-hydroquinone (0.040 g, 0,018 mmol) was heated at 200 1C in a
glass tube, equipped with an air cooled condenser, for 15 min.
Then the reaction mixture was cooled to room temperature and a
MeOH–H
filtered and washed with H
(
MALDI-TOF) m/z: 1354 ([M-OAc + DHB-OH] , 100%), 1371
+
([M-OAc + DHB] , 90%). UV-vis l
(Py)/nm 350 (lg e 4.43) and
5
]Py) d H ppm: 7.71 (16H, m,
Ph), 7.76–7.79 (16H, m, HPh) and 7.86–7.92 (8H, m, HPh). IR (KBr):
n (cm ): 1319–1446 (C–O), 1375–1635 (g pyrrole and pyrazine),
512–1635 (CQO), 2833–2981 (st CH CH COO–), 3062 (st CHPh).
2,3,9,10,16,17,23,24-Octaphenyl-1,4,8,11,15,18,22,25-octaaza-
phthalocyaninato]europium acetate (2b). Yield 0.17 g (71%). MS
MALDI-TOF) m/z: 1281 ([M-OAc] , 85%), 1551 ([M-OAc + CCA +
Na], 100%). UV-vis l (Py)/nm 348 (lg e 4.77) and 665 (4.54).
max
1
6
H
63 (3.90). H NMR (600.13 MHz, [D
2
O (20 : 1 v/v) mixture was added. The precipitate was
O, MeOH, and acetone. This yielded
ꢀ1
2
complex 2f (0.037 g, 60%). The characteristics were identical with
those obtained by Approach A (i).
1
3
[
+
Approach B. Compound 4 (0.050 g, 0.044 mmol) and
(
Lu(OAc)
3
ꢂ 4H
2
O (0.038 g, 0,088 mmol) were refluxed in
max
1
3 mL o-dichlorobenzene (o-DCB) in the presence DBU (0.2 mmol)
for 2 h. Then the reaction mixture was cooled to room temperature
and a MeOH–H O (20 : 1, v/v) mixture was added. The precipitate
2
was filtered and washed with water, MeOH, and acetone. This
yielded complex 2f (0.056 g, 91%). The characteristics were
identical with those obtained by Approach A (i).
[2,3,9,10,16,17,23,24-Octaphenyl-1,4,8,11,15,18,22,25-
octaazaphthalocyaninato]dilithium (3). A mixture of compound
H NMR (600.13 MHz, [D
Ph) and 7.88–7.96 (16H, m, HPh). IR (KBr): n (cm ): 1282–1381
C–O), 1381–1539 (g pyrrole and pyrazine), 1539–1630 (CQO),
854–2931 (st CH CH COO–), 3055 (st CHPh).
2,3,9,10,16,17,23,24-Octaphenyl-1,4,8,11,15,18,22,25-octaaza-
phthalocyaninato]gadolinium acetate (2c). Yield 0.15 g, (63%).
7
]DMF) d H ppm: 7.39–7.67 (24H, m,
ꢀ1
H
(
2
3
[
+
MS (MALDI-TOF) m/z: 1286 ([M-OAc] , 100%). UV-vis l
(Py)/
max
ꢀ1
nm 349 (lg e 4.41) and 665 (4.23). IR (KBr): n (cm ): 1319–1446
C–O), 1377–1626 (g pyrrole and pyrazine), 1512–1626 (CQO),
854–2924 (st CH CH COO–), 3066 (st CHPh).
2,3,9,10,16,17,23,24-Octaphenyl-1,4,8,11,15,18,22,25-octaaza-
phthalocyaninato]dysprosium acetate (2d). Yield 0.12 g (50%).
MS (MALDI-TOF) m/z: 1670 ([M-OAc + 2CHCA] , 10%), 1774
1
(0.40 g, 1.42 mmol), MeOLi (0.11 g, 2.89 mmol) and
(
2
p-hydroquinone (0.080 g, 0.73 mmol) was placed into a glass
tube. The resulting mixture was irradiated in a microwave oven
3
[
(
600 W) for 15 min. Then the reaction mixture was cooled to
room temperature and a MeOH–H O (20 : 1 v/v) mixture was
added. The precipitate was filtered and washed with H O,
+
2
+
2
(
(
[
[M-OAc + 2CHCA + p-hydroquinone] , 100%). UV-vis l
max
1
MeOH, and acetone. This yielded complex 3 (0.31 g, 76%).
MS (MALDI-TOF) m/z: 1132 ([M-2Li + 3H] , 30%), 1154 ([M-2Li +
Na + 2H] , 100%), 1176 ([M-2Li + 2Na + H] ). UV-vis lmax (Py)/
Py)/nm 358 (lg e 4.70) and 665 (4.61). H NMR (600.13 MHz,
D ]Py) d H ppm: ꢀ26.88–23.21 (8H, m, H ), ꢀ20.96–12.11 (16H,
+
5
Ph
+
+
ꢀ
1
m, HPh) and ꢀ10.40–4.30 (16H, m, HPh). IR (ZnSe): n (cm ):
323–1446 (C–O), 1381–1626 (g pyrrole and pyrazine), 1514–1626
CQO), 3056 (stCHPh), 2854–2925 (st CH CH COO–), 3056 (st CHPh).
2,3,9,10,16,17,23,24-Octaphenyl-1,4,8,11,15,18,22,25-octaaza-
phthalocyaninato]erbium acetate (2e). Yield 0.18 g (75%). m/z
ꢀ1
nm 370 (lg e 4.56) and 660 (4.66). IR (ZnSe): n (cm ): 1377–1612
g pyrrole and pyrazine), 3062 (st CHPh).
,3,9,10,16,17,23,24-Octaphenyl-1,4,8,11,15,18,22,25-
1
(
(
3
2
[
octaazaphthalocyanine (4). Complex 3 (0.31 g. 0.27 mmol) was
dissolved in polyphosphoric acid (30 ml) and stirred at 110 1C
for 2 h. Then the mixture was cooled to room temperature, and
distilled H
until neutral pH of the reaction mixture was reached. The
precipitate was filtered and washed with H O, MeOH, and
acetone. This yielded compound 4 (0.25 g, 82%). MS (MALDI-
+
(
1
(
MALDI TOF) (%): 1407 ([M-OAc + p-hydroquinone] , 80%),
(Py)/nm 356
max
lg e 4.74) and 663 (4.64). H NMR (600.13 MHz, [D ]Py) d H
ppm: 15.57–16.32 (16H, m, HPh), 17.52–18.11 (16H, m, HPh) and
9.29–21.70 (8H, m, HPh). IR (KBr): n (cm ): 1282–1379 (C–O),
379–1633 (g pyrrole and pyrazine), 1513–1633 (CQO), 2850–
+
672 ([M-OAc + 2CHCA] , 100%). UV-vis l
1
2
O was added. Ammonium carbonate was added
5
ꢀ
1
2
1
1
2
+
3
TOF) m/z: 1131 ([M + H] , 100%). UV-vis lmax (CHCl )/nm 363
935 (st CH CH
3
COO–), 3057 (st CHPh).
ꢀ1
(lg e 3.98), 639 (4.56) and 672 (4.63). IR (ZnSe): n (cm ): 1346–
[
2,3,9,10,16,17,23,24-Octaphenyl-1,4,8,11,15,18,22,25-octaaza-
1637 (g pyrrole and pyrazine), 3059 (st CHPh), 3288 (st NH).
phthalocyaninato]lutetium acetate (2f):
Approach A (i). A mixture of compound 1 (0.20 g, 0.71 mmol),
Lu(OAc)3 ꢂ 4H O (0.15 g, 0.36 mmol) and p-hydroquinone
2
Conclusions
(
0.16 g, 1.45 mmol) was taken in a glass tube. The resulting
mixture was irradiated in a microwave oven (600 W) for 15 min. Novel phenyl-substituted pyrazinoporphyrazine complexes of
Then the reaction mixture was cooled to room temperature and rare-earth elements (Y, Eu, Gd, Dy, Er, and Lu) were obtained in
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high yields using a modified template approach and a multi-
step synthesis involving formation of the porphyrazine ligand.
The main feature of our protocol for the template synthesis was the
use of p-hydroquinone as a reducing agent and the reaction
medium at the same time. Target complexes were identified by
high resolution MALDI-TOF mass-spectrometry, IR and NMR
spectroscopy. The impact of the paramagnetic nature of lanthanide
2 M. Villano, V. Amendola, G. Sandon `a , M. P. Donzello,
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1
ions on the H NMR spectra of the porphyrazine complexes was
investigated for the first time. A downfield shift of the signals of
phenyl protons for the europium and erbium complexes compared
to diamagnetic ones has been demonstrated. An upfield shift of the
signals of aromatic protons up to ꢀ26.88 ppm was observed for the
dysprosium complex. Redox transitions in pyridine and UV-vis
absorption spectra in solutions and films were characterized. In
comparison with phenyl-substituted phthalocyanine complexes, a
hypsochromic shift of the Q band of about 30 nm was observed.
The electrochemical measurements revealed the strong electron 10 W. Cao, H. Wang, X. Wang, H. K. Lee, D. K. P. Ng and
withdrawing nature of the pyrazine fragments in octaphenyl-
J. Jiang, Inorg. Chem., 2012, 51, 9265–9272.
substituted pyrazinoporphyrazines compared to phthalocyanine 11 W. Cao, C. Gao, Y.-Q. Zhang, D. Qi, T. Liu, K. Wang,
analogues. A characteristic energy diagram was obtained for the
C. Duan, S. Gao and J. Jiang, Chem. Sci., 2015, 6, 5947–5954.
erbium complex 2e in a thin film and in poly(methyl acrylate) 12 H. Pan, L. Gong, W. Liu, C. Lin, Q. Ma, G. Lu, D. Qi, K. Wang
matrix. In poly(methyl acrylate) film, a polymeric matrix prevents
and J. Jiang, Dyes Pigm., 2018, 156, 167–174.
strong aggregation of the porphyrazine molecules and allows 13 W. Liu, H. Pan, Z. Wang, K. Wang, D. Qi and J. Jiang, Chem.
energy levels for the monomeric form to be obtained. The results
Commun., 2017, 53, 3765–3768.
for erbium complex 2e in poly(methyl acrylate) film are as follows: 14 K. Wang, F. Ma, D. Qi, X. Chen, Y. Chen, Y.-C. Chen,
ꢀ
4.1 eV for the LUMO level; ꢀ4.7 eV for the Fermi level; ꢀ4.5, ꢀ5.9,
H.-L. Sun, M.-L. Tong and J. Jiang, Inorg. Chem. Front.,
2018, 5, 939–943.
15 C. Yuxiang, L. Chao, M. Fang, Q. Dongdong, L. Qingyun,
S. Hao-Ling and J. Jianzhuang, Chem. – Eur. J., 2018, 24,
and ꢀ7.5 eV for additional energy levels. The accuracy of determi-
nation is at or below 0.1 eV.
8
066–8070.
Conflicts of interest
1
6 E. A. Kuzmina, T. V. Dubinina, A. V. Zasedatelev, A. V.
Baranikov, M. I. Makedonskaya, T. B. Egorova and L. G.
Tomilova, Polyhedron, 2017, 135, 41–48.
There are no conflicts to declare.
1
1
1
2
7 H. Wang, W. Cao, T. Liu, C. Duan and J. Jiang, Chem. – Eur. J.,
2013, 19, 2266–2270.
8 N. Kobayashi, J. Rizhen, S.-I. Nakajima, T. Osa and H. Hino,
Chem. Lett., 1993, 185–188.
9 S. Tomachynskyi, S. Korobko, L. Tomachynski and
V. Pavlenko, Opt. Mater., 2011, 33, 1553–1556.
0 T. A. Lebedeva, V. P. Kulinich, G. P. Shaposhnikov, S. V.
Efimova, A. B. Korzhenevskii and O. I. Koifman, Russ. J. Gen.
Chem., 2007, 77, 1944–1950.
1 T. V. Dubinina, K. V. Paramonova, S. A. Trashin,
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2 T. V. Dubinina, A. D. Kosov, E. F. Petrusevich, S. S.
Maklakov, N. E. Borisova, L. G. Tomilova and N. S. Zefirov,
Dalton Trans., 2015, 44, 7973–7981.
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Acknowledgements
We are grateful for main financial support from the Russian
Foundation for Basic Research (Grant No. 16-33-60005 and
18-33-00519). Investigation of optical properties was supported by
the Russian Science Foundation (Grant 17-13-01197). Electrochemi-
cal investigations were supported by ERA.Net RUS Plus Plasmon
Electrolight and FWO funding (RFBR No. 18-53-76006 ERA). We also
thank the Council under the President of the Russian Federation for
State Support of Young Scientists and Leading Scientific Schools
2
2
(Grants MK-3115.2018.3) and partial support from the framework of
the State Assignment of 2019 (Theme 45.5 Creation of compounds
with given physicochemical properties). Investigation of electro-
physical properties was supported by the RFBR (Grant 16-07-
00961). K. A. Drozdov and M. S. Kotova thank Prof. L. I. Ryabova
2
2
2
for productive discussion of the electrophysical data.
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