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Y.B. Platonova et al. / Journal of Catalysis 373 (2019) 222–227
NMR spectroscopy. The m/z value in the MALDI spectrum confirms
the structure of the complex and the isotopic distribution, which is
typical for such palladium complexes is in accordance with the cal-
culated data. Moreover, the stability of prepared compound was
determined by thermogravimetric analysis and it was found that
palladium phthalocyanine complex are thermally stable until up
300 °C both in argon atmosphere and in air.
4,5-Diphenoxyphthalonitrile 2 was prepared by Wohrle’s method
[46], which based on nucleophilic displacement reaction from 4,5-
dichlorophthalonitrile 1 through treatment with phenol under basic
conditions in DMSO at 90 °C. 4,5-Dichlorophthalonitrile 1 was syn-
thetized from inexpensive commercially available 4,5-
dichlorophthalic acid as starting material by reported three step
approach including sequence anhydride-imide-amide-nitrile with
overall yield 49% [46].
essary use only stoichiometric quantities of brominating agent to
avoid the formation of tri-bromo-substituted by-products. At the
next step 1,2-dibromo-4,5-dialkoxybenzenes 7–9 were converted
to corresponding phthalonitrile via palladium-catalysed cyanation
reaction with use of Pd2(dba)3–1,10-bis(diphenylphosphinoferro
cene) catalytic system and zinc(II) cyanide. It was determined that
this combination of catalyst and cyanation reagent is the most
effective and lead to desired products with excellent yields without
formation of by-products. 4,5-Dialkoxyphthalonitriles 10–12 were
prepared in three-step protocol with high overall yield and their
structure was confirmed by 1H, 13C NMR, IR spectroscopy and mass
spectrometry. Then we synthesized palladium complexes 13–15
from corresponding nitriles 10–12 with good yields. Target com-
pounds were characterized by MALDI-TOF/TOF mass spectrometry,
HRMS ESI, UV–Vis, and 1H NMR spectroscopy.
The final step was preparation of palladium(II) 2,3,9, 10,16,17,
23,24-octaphenoxyphthalocyanine 3 from 4,5-diphenoxyphthalo-
nitrile 2 by template synthesis. Target compound was character-
ized by MALDI-TOF/TOF mass spectrometry, HRMS ESI, UV–Vis,
and 1H NMR spectroscopy. Since this method was so effective we
have chosen it for synthesis of 4,5-alkoxyphthalonitriles but it
was found that nucleophilic substitution reaction with aliphatic
alcohols (methanol, ethanol, n-butanol) proceeded at these condi-
tions with minor yields that is explained by their unstability in
these conditions. Thus, we have chosen three-step protocol, which
was published in literature [47] and is effective for synthesis of 4,5-
dialkoxybenzenes. It should be noted that we have slightly modi-
fied this approach by changing the order of stages of alkylation
and bromination of catechol, which made it possible to improve
total yields of target products 13–15. This protocol uses catechol
as inexpensive, commercially available starting material, which
was successfully alkylated by alkyl iodides at basic conditions in
refluxing dry acetone that yielded 1,2-dialkoxybenzenes
(Scheme 2.). The reactions were carried out in mild conditions
and advantages of this procedure were short time (up to 8 h in
accordance with alcohol) and easy work up. Preparing 1,2-
dialkoxybenzenes were brominated by bromine in dry tetra-
chloromethane at room temperature and it was found that is nec-
Palladium complex of 5,10,15,20-tetraphenylporphyrin was
prepared by a method based on the reaction of Pd(MeCN)2Cl2 with
porphyrin free base (3:1) in refluxing acetonitrile similarly earlier
reported method of synthesizing palladium(II) coproporphyrinates
[48]. The formation of palladium complex was confirmed by UV–
Vis spectroscopy, MALDI-TOF mass spectrometry and 1H NMR
spectroscopy.
After successful synthesis of palladium complexes of
octaphenoxy-,
octaalkoxysubstituted
phthalocyanines
and
5,10,15,20-tetraphenylporphyrin we have begun investigations
aimed at evaluation of it’s catalytic activities in Pd-catalysed Sono-
gashira cross-coupling reaction of phenylacetylene with various p-
substituted aryl bromides. First, we have investigated Pd/Cu-
catalyzed Sonogashira reaction of bromobenzene with pheny-
lacetylene under various conditions. The reactions were performed
in the presence of palladium catalyst, CuI as a co-catalyst, various
bases (Et3N, i-Pr2NEt, Cs2CO3) and solvents in test tubes of Radleys
Carousel 6 plus at 25 °C during 8 h and yields of products were
determined by GC/MS. The reaction conditions explored are sum-
marized in Table 1.
The task of our investigation was to further estimate of the
effects of different reaction parameters and nature of substituent
in macrocycles on the catalytic activity in order to optimize the
Scheme 2. The synthesis scheme for 1,2-alkoxyphthalonitriles and corresponding PdPc.