Synthesis and spectral and electrochemical properties of hexadecamethyl-substituted diphthalocyanines of rare-earth metals

Article abstract of DOI:10.1023/A:1014083529199

A new method for the preparation of 3,5-dimethyl-o-phthalodinitrile was proposed, and the substituted diphthalocyanine complexes of Lu^III, Tm^III, Er^III, and Dy^III were synthesized. The spectral and electrochemical characteristics of the complexes were found. The complexes can be used as materials for electrochromic devices with high contrast.

Full text of DOI:10.1023/A:1014083529199

Russian Chemical Bulletin, International Edition, Vol. 50, No. 7, pp. 1299—1302, July, 2001
1299
Synthesis and spectral and electrochemical properties of
hexadecamethyl-substituted diphthalocyanines of
rare-earth metals
I. P. Kalashnikova,a I. V. Zhukov,b T. V. Magdesieva,b K. P. Butin,b L. G. Tomilova,a«
and N. S. Zefirova
aInstitute of Physiologically Active Compounds,
142432 Chernogolovka, Moscow Region, Russian Federation.
Fax: +7 (095) 913 2113
bDepartment of Chemistry, M. V. Lomonosov Moscow State University,
Leninskie Gory, 119899 Moscow, Russian Federation.
Fax: +7 (095) 939 0290. E-mail: tom@org.chem.msu.su
A new method for the preparation of 3,5-dimethyl-î-phthalodinitrile was proposed, and
the substituted diphthalocyanine complexes of LuIII, TmIII, ErIII, and DyIII were synthesized.
The spectral and electrochemical characteristics of the complexes were found. The complexes
can be used as materials for electrochromic devices with high contrast.
Key word: diphthalocyanines, rare-earth metals, electrochemistry, electronic absorption
spectra.
An active search for the procedures for synthesis of
substituted phthalocyanines with practically significant
properties have recently being performed.1—4
sized for the first time from dinitrile 1. Since the
starting phthalodinitrile 1 has a nonsymmetric structure,
a mixture of isomers can be formed, and they, as in the
case of the earlier obtained 4-tert-butyl-substituted
diphthalocyanine complexes10 cannot be separated ei-
ther on a chromatographic column or by TLC.
Diphthalocyanines of LuIII, TmIII, ErIII, and DyIII were
synthesized in n-hexanol in the presence of diazabi-
The yield of phthalocyanine metal complexes can be
increased when î-phthalodinitriles are used as the start-
ing compounds instead of acids and anhydrides.5
Cyanation of î-dibromobenzenes with copper cyanide
in DMF (see, e.g., Refs. 6 and 7) is the common
method for the synthesis of substituted phthalocyanines.
Other approaches to the synthesis of phthalodinitriles
containing functional substituents at different positions
of the benzene ring have been proposed in recent years.8,9
In this work, we synthesized 3,5-dimethyl-î-phtha-
lodinitrile (1) with the purpose for preparation of 3,5-sub-
stituted diphthalocyanine complexes of rare-earth met-
als that possess simultaneously the photochromic prop-
erties and sufficient solubility to isolate them in the
individual state.
ꢀꢀ
cycloundecene (DBU) in high yields (Scheme 1).
The electronic absorption spectra of the obtained
complexes contains bands in the region of 680—700 nm
and the band at 450 nm characteristic of diphthalo-
cyanines (Fig. 1). With an increase in the ion radius of
D
2
1
2
Results and Discussion
1
Since the orientation effect of substituents in the
aromatic ring of m-xylene does not allow the prepara-
tion of î-dibromo derivatives and, hence, 3,5-dimethyl-
phthalodinitrile by bromination, it was necessary to
search for another synthetic approach. 1-Amino-2-cy-
ano-3,5-dimethylbenzene (2) prepared from compound
1 by Sandmeyer´s reaction was chosen as the starting
compound.
3
300
400
500
600
700
λ/nm
Fig. 1. Electronic absorption spectra of the neutral (1), reduced
(2), and oxidized (3) redox forms of 3,5-MePc2Tm generated at
potentials of –0.3 and +0.5 V (vs. Ag|AgCl|KCl) on the Pt
Several 3,5-methyl-substituted diphthalocyanine com-
plexes of rare-earth metals (3,5-MePc2Ln) were synthe-
electrode in DMF against 0.05 Ì Bun NBF4.
4
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1238—1241, July, 2001.
1066-5285/01/5007-1299 $25.00 ©ꢀ2001 Plenum Publishing Corporation

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Russ.Chem.Bull., Int.Ed., Vol. 50, No. 7, July, 2001
Kalashnikova et al.
Scheme 1
Table 1. Potentials of redox transitionsa of 3,5-MePc2Ln
(Ln = Lu, Tm, Er)
1. HCl
2. NaNO2
Me
Me
CN
Me
Me
CN
Compound
Å b/V
3. Na[Cu(CN)2]
Oxidation
Reduction
3,5-MePc2Lu
3,5-MePc2Lu c
3,5-MePc2Tm
3,5-MePc2Er
0.46
0.42
0.46
0.47
–0.06, –0.81, –1.23, –1.62
–0.01, –0.78, –1.21, –1.61
–0.07, –0.76
NH2
CN
ꢀ
LnX3
–0.07, –0.75, –1.19, –1.58
DBU,
C6H13OH
a Graphite electrode; DMF; 0.05 Ì Bun NBF4; Ag|AgCl|KCl;
4
Me
v = 200 mV s–1; 20 °C.
Me
N
Me
b Arithmetic mean of the potentials of the direct and inverse
peaks in CVA.
c Pt electrode.
Me
N
N
N
N
Me
N
N
The electrochemical properties of 3,5-dimethyl-sub-
stituted diphthalocyanine complexes of LuIII, TmIII
,
N
Me
Me
and ErIII were studied by cyclic voltammetry in DMF.
Five reversible redox transitions were detected in the
accessible potential interval (from –2.0 to +1.1 V)
(Fig. 2). The first anodic peak exists in the region of
0.42—0.47 V (vs. Ag|AgCl|KCl) (Table 1) and corre-
sponds to the transition
Me
Ln
Me
Me
Me
N
N
N
N
Me
N
Me
N
N
–e
N
3,5-Me
Pc2Ln
(
3,5-MePc2Ln)+(Ln = Lu, Tm, Er).
Me
+e
Me
Four peaks are present in the cathodic region of
potentials (see Table 1), which correspond to the suc-
cessive transfer of four electrons to 3,5-MePc2Ln
Me
!—$
+e
–e
+e
–e
–
3,5-MePc2Ln
(
3,5-MePc2Ln)
Ln = Lu (!), Tm ("), Er (#), Dy ($)
+e
–e
+e
–e
(
(
3,5-MePc2Ln)2–
3,5-MePc2Ln)4–
(
3,5-MePc2Ln)3–
the metal atom, the main absorption maximum is insig-
nificantly shifted to the long-wave region (bathochromic
shift) from 682 nm (for complex 3) to 690 nm (6).
Compounds 3—6 are well soluble in chloroform and
benzene, which differs them from symmetric analogs,
4,5-dimethyl-substituted diphthalocyanines,12 and makes
it possible to extent the possibilities of their chromato-
graphic purification and application.
.
It is difficult to study the electrochemical properties
of diphthalocyanine complexes of rare-earth metals due
to their low solubility in most organic solvents suitable
for electrochemical measurements. In the case of com-
plexes 3—6, DMF solutions with a maximum concen-
–4
–1
tration of 1•10 mol L can be obtained. This con-
centration is not sufficient for the reliable detection of
redox transitions by smooth platinum electrodes. Hence,
we used the working electrode prepared from a graphite
material (pyrolyzed polyacrilonitrile) with the highly
developed surface (∼7•103 mm2).
–5
2•10
A
The potentials measured with this electrode and
smooth platinum are very close (see Table 1), which
enables a comparison of the data detected by these
electrodes.
Redox processes were studied in a special cell, which
allows the detection of spectral changes directly during
electrolysis. Absorption maxima in the electronic spec-
tra of the neutral, oxidized, and reduced forms of
3,5-MePc2Ln are presented in Table 2. Figure 1 presents
the electronic absorption spectra of the neutral, re-
duced, and oxidized forms of 3,5-MePc2Tm obtained
0.5
–0.5
–1.5 E/V
Fig. 2. Cyclic voltammogram of 3,5-MePc2Er (graphite electrode;
DMF; 0.05 Ì Bun NBF4; Ag|AgCl|KCl; v = 200 mV s–1; 20 °C).
4

Russ.Chem.Bull., Int.Ed., Vol. 50, No. 7, July, 2001
1301
Diphthalocyanines of rare-earth metals
Table 2. Electronic absorption spectra of the neutral, reduced, and oxidized forms of 3,5-MePc2Ln (Ln = Lu, Tm,
Er) in DMF
CompooxundRed form
λ
max*/nm
Color of solution
3,5-MePc2Lu
3,5-MePc2Tm
3,5-MePc2Er
Neutral
330, 343 sh, 492 sh, 600 sh, 616, 653 sh, 685
295, 326, 358, 510, 611, 730
300 sh, 322, 336, 580 sh, 637, 708
296, 330, 350 sh, 494 sh, 602 sh, 619, 652 sh, 687
296, 324, 346 sh, 514, 612, 734
296, 337, 586 sh, 639, 704
300, 328, 348 sh, 500 sh, 603 sh, 618, 651, 689
297, 324, 352 sh, 515, 617, 736
Green
Pink
Bluish-green
Green
Pink
Bluish-green
Green
Pink
Oxidized
Reduced
Neutral
Oxidized
Reduced
Neutral
Oxidized
Reduced
298, 338, 588 sh, 640, 703
Bluish-green
* The most intense absorption bands are underlined.
after preparative electrolysis at the potentials corre-
sponding to the first reduction and first oxidation peaks.
It is seen in Table 2 that the redox species differ strongly
in color in each case, i.e., 3,5-dimethyl-substituted
diphthalocyanine complexes of rare-earth metals can be
used as materials for electrochromic devices with high
contrast.
Since direct electrochemical measurements of the
number of electrons participating in redox processes of
the diphthalocyanine complexes often give underesti-
mated results,13 spectral measurements can serve as the
most adequate estimation of the number of electrons.
The shape of electronic spectra of the neutral, reduced,
and oxidized forms of the complexes studied is typical
of diphthalocyanine complexes14 and indicates that elec-
trons are localized on the phthalocyanine rings. A com-
parison of the peak heights corresponding to the first
anodic and first cathodic redox transitions and the peak
heights for deeper reduction (see Fig. 2) suggests that all
observed redox transitions are one-electron.
than the nature of the central metal atom. In the case of
the 3,5-dimethyl-substituted and 4-tert-butyl-substituted
LuII diphthalocyanine complexes, the oxidation poten-
tials are shifted to the cathodic region compared to the
nonsubstituted diphthalocyanine (Table 3). This is ex-
plained by the donor nature of alkyl substituents and
agrees with electron localization on the phthalocyanine
ligand. The potentials of the deeper reduction of the
3,5-dimethyl-substituted complex, unlike those of the
4-tert-butyl-substituted complex, are substantially shifted
to the anodic region compared to the nonsubstituted
derivative. Additional studies are required to explain
these facts.
Experimental
Absorption spectra were recorded on a Specord M-800 UV
spectrometer in the region of 200—800 nm. Spectra of the
electrochemically generated forms of the diphthalocyanine com-
plexes were obtained directly in a quartz cell on a Hitachi 124
spectrophotometer in the 200—800 nm region using 0.05 Ì
For this series of complexes (see Table 1), the metal
nature only insignificantly affects the potential of the
electrochemical transitions. We observed the same for
the series of diamagnetic and paramagnetic octa-tert-
butyl-substituted diphthalocyanine complexes of lan-
thanides.13
Bun NBF4 in the same solvent as the reference solution.
4
1Í NMR spectra were recorded on a Bruker AC-200 instru-
ment (200 MHz, vs. Me4Si).
1-Amino-2-cyano-3,5-dimethylbenzene (2) was prepared
from mesityl oxide and malononitrile using a previously de-
scribed procedure15 in 80% yield (m.p. 60 °C). Compounds
Bun NBF4 (Merck) and DMF (Aldrich) were used as received.
Substituents in the phthalocyanine ring have a much
stronger effect on the potentials of redox transitions
4
Formates or acetates of the corresponding lanthanides (analyti-
cally pure grade) were used for the synthesis of phthalocya-
nines.
Table 3. Potentials of the redox transitionsa of Pc2Lu,
3,5-MePc2Lu, and Pct2Lu
3,5-Dimethyl-î-phthalodinitrile (1). Concentrated HCl
(12 mL) was slowly added with stirring and cooling with ice-
cold water to a solution of benzonitrile 2 (5.0 g, 0.034 mol) in
water (30 mL). The reaction mixture was diazotized at 0—5 °C
by adding dropwise a solution of NaNO2 (3.44 g, 0.05 mol) in
water (15 mL). The resulting solution of the diazonium salt was
treated with stirring and cooling to 0 °C with a solution of
Na[Cu(CN)2] prepared from CuCl (6.2 g, 0.062 mol) and
NaCN (9.36 g, 0.15 mol). The reaction mixture was stirred for
2 h and stored for 12 h, and the precipitate that formed was
filtered off. The solid residue was extracted with hot benzene,
and the filtrate was extracted with chloroform. The organic
extracts were combined and dried with MgSO4. After removal
of solvents, the combined crystalline product was recrystallized
from CCl4 and additionally purified by sublimation. Compound
Com-
pound
Åb/V
Oxidation
Reduction
Pc2Lu
3,5-MePc2Lu c
Pct2Lu
0.53
0.42
0.35
0.14, –1.02, –1.37, –1.71
0.01, –0.78, –1.21, –1.61
0.01, –1.10, –1.41, –1.85
a Pt electrode; î-dichlorobenzene—MeCN (1 : 1); 0.05 Ì
Bun NBF4; Ag|AgCl|KCl; v = 200 mV s–1; 20 °C.
4
b Arithmetic mean of the potentials of the direct and inverse
peaks in CVA.
c Solution in DMF.

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Russ.Chem.Bull., Int.Ed., Vol. 50, No. 7, July, 2001
Kalashnikova et al.
1 was obtained as colorless crystals with m.p. 122 °C in 43%
yield (2.30 g). Found (%): C, 76.39; H, 5.14; N, 17.88.
Calculated (%): C, 76.89; H, 5.17; N, 17.94. C12H8N2. 1Í NMR
(DMSO-d6), δ: 2.39, 2.49 (both s, 3 H each, Ìå); 7.65, 7.78
(both s, 1 H each, Ñ6H2).
tial values were measured vs. saturated Ag|AgCl electrode.
DMF was used as the solvent. The concentration of solutions
–5
was 3.5•10 mol L–1. A solution was stirred during electroly-
sis and dissolved oxygen was removed during preparation using
a flow of dry argon.
Bis(octamethylphthalocyanine)lutetium(III) (3). A mixture
of compound 1 (500 mg, 3.2 mmol), (HCOO)3Lu•2H2O
(111 mg, 0.32 mmol), DBU (290 mg, 1.92 mmol), and n-hexanol
(5 mL) was refluxed in an argon atmosphere. The solution was
cooled, n-hexanol was distilled off in vacuo, and the residue
was washed with MeOH and twice chromatographed on a
column packed with SiO2 (eluent CHCl3). Compound 3 was
obtained as a dark-green powder in 66% yield (310 mg),
Rf = 0.84 (Alufol® plates, eluent CHCl3), λmax = 682 nm.
Found (%): Ñ, 67.54; H, 4.66; N, 15.58. C80H64N16Lu. Calcu-
lated (%): Ñ, 67.46; H, 4.53; N, 15.73.
Bis(octamethylphthalocyanine)thulium(III) (4) was prepared
similarly to compound 3, yield 68%, Rf = 0.80 (Alufol® plates,
eluent CHCl3), λmax = 683 nm. Found (%): Ñ, 67.92; H, 4.68;
N, 15.63. C80H64N16Tm. Calculated (%): Ñ, 67.74; H, 4.55;
N, 15.80.
This work was financially supported by the Russian
Foundation for Basic Research (Project Nos. 97-03-
33229 and 00-03-32658).
References
1. M. M. Nicholson, in Phthalocyanines: Properties and Appli-
cation, Eds. C. C. Leznoff and A. B. P. Lever, VCH, New
York, 1993, 3, 71.
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5. V. D. Berezin, Koordinatsionnye soedineniya porfirinov i
ftalotsianinov [Coordination Compounds of Porphyrins and
Phthalocyanines], Nauka, Moscow, 1978, 280 pp. (in
Russian).
Bis(octamethylphthalocyanine)erbium(III) (5) was prepared
similarly to compound 3, yield 72%, Rf = 0.71 (Alufol® plates,
eluent CHCl3), λmax = 685 nm. Found (%): Ñ, 67.94; H, 4.62;
N, 15.65. C80H64N16Er. Calculated (%): Ñ, 67.82; H, 4.55;
N, 15.82.
6. E. A. Cuellar and T. J. Marks, Inorg. Chem., 1981, 20, 3766.
7. R. Dieing, G. Schmid, E. Witke, G. Feucht, N. Dreben,
J. Pohmer, and M. Hanack, Chem. Ber., 1995, 128, 589.
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land, M. J. Heeney, K. Welford, J. Porphyrins and Phthalo-
cyanines, 1997, 1, 77.
9. D. S. Tereknov, K. J. Nolan, C. R. McArthur, and C. C.
Leznoff, J. Org. Chem., 1996, 61, 3034.
10. L. G. Tomilova, E. V. Chernykh, N. T. Ioffe, and E. A.
Luk´yanets, Zh. Obshch. Khim., 1983, 53, 2594 [J. Gen.
Chem. USSR, 1983, 53 (Engl. Transl.)].
11. J. Jiang, R. C. W. Liu, T. C. W. Mak, T. W. D. Chan, and
D. K. P. Ng, Polyhedron, 1997, 16, 515.
12. M. A. Ovseevich, L. G. Tomilova, E. G. Kogan, and N. S.
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13. T. V. Magdesieva, I. V. Zhukov, L. G. Tomilova, E. V.
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14. C. C. Leznoff and A. B. P. Lever, in Phthalocyanines:
Properties and Application, Eds. C. C. Leznoff, A. B. P.
Lever, VCH, New York, 1993, 3, 85.
Bis(octamethylphthalocyanine)dysprosium(III) (6) was pre-
pared similarly to compound 3, yield 70%, Rf = 0.68 (Alufol®
plates, eluent CHCl3), λmax = 690 nm. Found (%): Ñ, 68.14;
H, 4.65; N, 15.55. C80H64N16Dy. Calculated (%): Ñ, 68.05;
H, 4.57; N, 15.87.
Electrochemical measurements were carried out on a
PI-50-1.1 potentiostat, PR-8 programmator, and PDA-1 two-
coordinate detecting instrument using the three-electrode scheme
on a graphite electrode (pyrolyzed polyacrilonitrile) and on a
disk platinum electrode with a working surface of 20.7 mm2
against 0.05 Ì Bun NBF4 at 20 °C. A Pt wire served as an
4
auxiliary electrode, and a saturated Ag|AgCl electrode was used
as the reference electrode. Dissolved oxygen was removed from
the cell with a flow of dry argon. Voltammetric curves were
detected by cyclic voltammetry at a sweep of 200 mV s–1. The
electrode was thoroughly polished after obtaining each curve.
The measured potential values were recalculated taking into
account ohmic losses. DMF was used as the solvent. The
concentration of solutions of the compounds under study was
–4
–1
1•10 mol L
.
Spectroelectrochemical studies were carried out at 20 °C in
the potentiostatic regime in a special quartz cell connected to a
P-5827Ì potentiostat using the three-electrode scheme. A Pt
wire with a surface area of 120 mm2 served as the working
15. J. Sepiol, J. Mirek, and R. L. Soulen, Pol. J. Chem., 1978,
52, 1389.
electrode, and 0.02 Ì Bun NBF4 was used as the supporting
4
electrolyte. The spaces of the auxiliary, working, and Pt elec-
trodes were separated by a glass porous membrane. The poten-
Received July 21, 2000;
in revised form February 27, 2001