Mendeleev Commun., 2002, 12(2), 54–55
Synthesis of mono- and bisphthalocyanine complexes using microwave irradiation
Evgeniya G. Kogan,a Aleksey V. Ivanov,a Larisa G. Tomilova*b and Nikolai S. Zefirovb
a Institute of Physiologically Active Compounds, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region,
Russian Federation. Fax: +7 095 785 7024
b Department of Chemistry, M. V. Lomonosov Moscow State University, 119992 Moscow, Russian Federation.
Fax: +7 095 939 0290; e-mail: tom@org.chem.msu.su
10.1070/MC2002v012n02ABEH001558
Starting with phthalic and 4-tert-butylphthalic acid derivatives, the bisphthalocyanines of rare earth elements and hafnium and
zirconium were prepared using microwave irradiation.
Phthalocyanines are of interest not only as model compounds
for biologically important porphyrins but also because of their
outstanding physical properties, including semiconductive, liquid
crystalline and non-linear optical behaviour.1–4
Generally, the published methods of phthalocyanine synthesis,
rely on the interaction of phthalogens (anhydrides of phthalic
acids or phthalodinitriles) with metals or their salts at high
temperatures.5–8 These methods require long-term heating (for
2.5–5 h) of a reaction mixture in a melt (fusion) or high-boiling
solvent. In more recent publications,9,10 it was proposed to use
alcohols as solvents and 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU) as the base in order to decrease the temperature of the
synthesis. However, the synthesis takes 12–14 h, and the range
of phthalogens is limited to phthalodinitrile.
Recently, the synthesis of metal-containing (Cu, Co, Ni and
Fe) phthalocyanines has been reported using microwave irradia-
tion,11 which simplified the synthesis in the absence of solvents
and shortened its duration from several hours to few minutes.
However, Shaabani11 restricted his studies to complex forma-
tion from phthalic anhydride in the presence of urea.
cyanines. Therewith, phthalimide and phthalodinitrile have some
advantages for the synthesis of Cr and Mn phthalocyanines,
respectively.
As the described for the divalent metals studied, tert-substi-
tuted phthalocyanines of Cr and Mn were produced in greater
yield (52% and 30%, respectively) than their unsubstituted ana-
logues after 6–10 min exposure to microwave irradiation (650–
700 W).
Of particular interest was the synthesis of the phthalocyanines
of rare-earth elements, which are capable of forming both planar
and sandwich-like complexes.13 In our work, rare-earth elements
phthalocyanines were produced from tetrahydrated Tb, Dy and
Lu acetates and different phthalogens.
Inasmuch as we found previously14 that the formation of bis-
phthalocyanines proceeds via planar phthalocyanines, our attempts
were focused on the production of individual mono- and bis-
phthalocyanines by varying the phthalogen : salt ratio (4:1, 8:1,
12:1) and the time of synthesis. Indeed, with increasing time of
synthesis, the proportion between mono- and bisphthalocyanine
yields was shifted toward the bisphthalocyanine.
We investigated the synthesis of phthalocyanine complexes
using microwave irradiation with different phthalogens: phthalo-
dinitrile 1a, phthalimide 1b, phthalic anhydride 1c, and phthalic
acid 1d. tert-Butyl-substituted phthalocyanines were synthesised
from 4-tert-butyl phthalodinitrile 2a or 4-tert-butyl phthalimide 2b.
The reaction mixtures were irradiated in a microwave oven
(Samsung, model 1714R) for 5–10 min at 450–850 W. Following
these experiments, we were able to select optimal conditions for
the production of planar and sandwich-like complexes, depending
on the nature of starting reagents and their ratio.
The interaction of phthalodinitrile or 4-tert-butyl phthalo-
dinitrile with lithium methylate (taken in a 2:1 ratio of nitrile to
lithium methylate) for 3–5 min at the irradiation power 700 W
resulted in the formation of di-lithium complexes of the corre-
sponding phthalocyanines in yields of as high as 70%. Treating
the reaction mass with a 3% HCl solution gave the quantitative
yields of free phthalocyanines, since the complexes of alkali
metals are unstable and lithium is rapidly removed from com-
plexes even with trace water.12 The other phthalogens used for
the synthesis of lithium phthalocyanines and free phthalocyanine
were found to be less active in the complex formation reactions.
When we carried out the synthesis of divalent metal (Co, Zn,
Cu and Ni) phthalocyanines, we observed that the activity of
phthalogens increased in the order phthalic acid < phthalic
anhydride < phthalimide < phthalodinitrile; tert-butyl phthalo-
cyanines were produced in better yields than unsubstituted
phthalocyanines. The highest yield (70–80%) was attained with
the use of 4-tert-butyl phthalodinitrile as the initial reagent under
microwave irradiation at 650–700 W for 6–10 min.
The activity of 1b–d as phthalogens slightly increased in the
order: phthalic acid < phthalic anhydride < phthalimide, but the
main final product was mono-phthalocyanine even if the reagents
were taken in the ratio optimal for bisphthalocyanine synthesis.
However, the reaction with 1a as a precursor gave bisphthalo-
cyanine as the main final product, which was formed even at
the phthalodinitrile : salt ratio equal to 4:1. Thus, depending
upon the nature of the phthalogen, its proportion to the metal
salt, and the duration of microwave irradiation, it was possible
to control the yield of final products. Unexpectedly, the yield of
the tert-butyl-substituted phthalocyanines of rare earth elements
under microwave irradiation was much smaller than that of un-
substituted phthalocyanine analogues. Thus, the yield of unsub-
stituted bisphthalocyanines synthesised from rare-earth acetates
was 7–10 times higher than that of tert-butyl phthalocyanines
and accounted for more than 70%.
Earlier, we found that the heating of the reaction mixture
consisting of phthalodinitrile and hafnium and zirconium salts
at 250–280 °C for several hours was necessary for the formation
of sandwich-like complexes of these metals.15 In this work, this
reaction was accomplished over a few minutes under exposure
to 650–700 W microwave irradiation and the amount of side
products was lower, which make final purification simpler. Thus,
a single purification procedure with the use of column chroma-
tography gives the individual compounds with a high degree of
purity, as is evident from TLC, elemental analysis and the UV
and visible spectra.
Hence, the proposed method of phthalocyanine synthesis allows
one to avoid lengthy heating of the reaction mass at high tem-
peratures, which is undesirable for some of phthalodinitriles in
view of their possible destruction.
To synthesise manganese and chromium phthalocyanines, MnCl2
or Mn(OAc)2 and chromium hexacarbonyl Cr(CO)6 served as
the initial reagents. Unsubstituted Mn- and Cr-containing phthalo-
cyanines were produced from precursors 1a–b. As in the case
of divalent metals, the yield of phthalocyanines was lowest after
synthesis from phthalic acid, while the use the other phthalogens
ensured similarly good production of metal-containing phthalo-
This work was supported by the Russian Foundation for Basic
Research (grant no. 00-03-32658) and the International Science
and Technology Centre (grant no. 1526).
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Tomita et al.
