F. Rigodanza, E. Tenori, A. Bonasera, Z. Syrgiannis, M. Prato
SHORT COMMUNICATION
sisting in dispersing PBA in sulfolane, water, THF and even amines, without detectable substitution at bay-positions.
neat conditions (no solvent). DMF is the only medium that The yields were comparable to non-bay-halogenated PBIs,
gives sufficiently high yields and reproducible results for the almost quantitative.
chosen amines (Table 1). The procedure is reproducible also
after scaling-up the quantities of the reagents (2 g of PBA
instead of 100 mg). We developed two different work-up Conclusions
procedures depending on the nature of the amine. The
A fast and versatile microwave-assisted method for the
products 1–8, 12–17 of uncharged amines were suspended
synthesis of a broad library of perylenebisimide derivatives
in 50 mL of 10% KOH aqueous solution and stirred for 2
has been developed. Imidation reactions of the perylenebis-
hours. The precipitate was filtered and washed thoroughly
anhydride (PBA) were performed using a large variety of
with water until neutralization of the filtrate. On the other
amines, such as alkylamines 1, 2, 3, 6, amino alcohols 4, 5,
hand, products 9–12 of amino acids were dissolved in basic
8
, heteroarylamines 7 and amino acids 9–11. This strategy
solution at pH 10 and filtered. The solution was then acidi-
fied with concentrated HCl to pH 1, filtered and washed
until neutralization.
The starting PBA is insoluble in common deuterated
solvents and is not detected in the NMR spectra. Conse-
quently, reactions were monitored by IR spectroscopy to
turned out to be compatible also with bay-halogenated
PBAs, functionalizing selectively the imide position without
affecting the aromatic core. Different efficient work-up pro-
cedures gave highly pure products in short times. Despite
of mild conditions, weak nucleophiles like aromatic amines
and amino acids efficiently provided functionalized per-
ylenebisimides, with some novel entries not previously re-
ported in the literature.
check the absence of unreacted anhydride. All the final
compounds exhibited strong peaks at 1690 and 1650 cm–1
related to the C=O stretching of imide groups, while typical
–
1
peaks related to C=O stretching of anhydride at 1765 cm
–
1
and 1730 cm were not detected, in accordance with data
reported in literature.[
10]
Experimental Section
Moreover, we observed that the presence of unreacted General Information: All solvents used were of reagent quality and
PBA in the crude affected the solubility of the final com- purchased commercially. All purchased starting materials were
pounds. In fact, the addition of a small amount of PBA to used without further purification. The microwave reactor used for
this study (CEM Discover) was purchased from CEM Corp.
a PBI solution caused precipitation of the latter, especially
for those bearing amino acid groups (9–12). This experi-
The pressure-resistant, tightly sealed quartz tubes were 3 mm thick
mental evidence confirmed the hypothesis that traces of the with a volume of 10 mL.
perylene anhydride in solution facilitate the aggregation of
NMR spectra were recorded on 400 MHz instruments and refer-
enced to the solvent. All spectra were recorded at 298 K.
the PBIs. Thus, appropriate work-up procedures appeared
instrumental to obtain the final compounds in high purity
and to collect characterization data of derivatives such as
1H NMR spectroscopic data are reported as follows: chemical shift
in parts per million (ppm) on the δ scale, integration, multiplicity,
[
11]
PBIs 4, 5, 7, 11, not reported in the literature to date.
1
3
coupling constants (Hz), and assignments. C NMR spectroscopic
data are reported as follows: chemical shifts in parts per million on
the δ scale and carbon environments determined from DEPT spec-
This study highlights that the main factors influencing
the reactions were the steric hindrance and the polarity of
[
12]
amines. In the experiments, the steric bulkiness at the α- tra. The 1,6,7,12-tetrabromo- and 1,6,7,12-tetrachloroperylene-
carbon influenced the outcome of the reaction. Amines 3,4,9,10-tetracarboxylic bisanhydride were prepared according to
with a small linear structure (1–6, 12–17) gave higher yields the literature.[13]
in shorter time. To compensate the lower reactivity of some
reagents (7, 8), the number of cycles of irradiation was in-
Synthesis of Perylenebisimides with Alkylamine. General Procedure
for 1–6: 100 mg of perylene-3,4,9,10-tetracarboxylic bisanhydride
creased and both conditions and work-up procedures were were suspended in dry DMF (5 mL) with 2 equiv. of the corre-
sponding amine in a pressure tight microwave tube. The suspension
slightly modified as reported in the Experimental Section.
In addition, amino acids reacted faster than nonpolar was sonicated for few minutes before heating under microwave irra-
diation at 50 W for 10 min. 5 cycles. Max T was set at 200 °C. After
amines. On similar steric hindrance, derivative 9 was
cooling, the colour turned to dark red and the mixture appeared
more homogeneous. 50 mL of NaOH 1 m were added to the start-
ing material and stirred for 20 min. The precipitate was filtered and
washed abundantly with water until pH neutralization and dried
using a vacuum pump.
obtained in shorter time and higher yields than compound
7. Indeed, the presence of carboxylic groups on the
isophthalic amine promoted the reaction, enhancing the po-
larity.
On the other hand, the basicity of the amine does not
particularly influence the outcome of reactions. Indeed,
weak nucleophiles, such as isophthalic amine and 4-amino-
pyridine, showed reaction times comparable to the ones of
stronger nucleophiles, such as dopamine and β-alanine.
Bay-halogenated PBIs are very reactive species due to the
Synthesis of Perylenebisimides with Aromatic Amines. General Pro-
cedure for 7–8: 100 mg of perylene-3,4,9,10-tetracarboxylic bi-
sanhydride were suspended in dry DMF (5 mL) with 4 equiv. of
the corresponding amine and 50 uL of Et N in a pressure tight
3
microwave tube. The suspension was sonicated for few minutes be-
fore heating under microwave irradiation at 80 W for 10 min. 10
higher solubility of the related anhydride in DMF. Reac- cycles. Max T was set at 200 °C. After cooling, the colour turned
tions took place in only 6–10 minutes. with all the tested to dark red and the mixture appeared more homogeneous. To the
5062
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Eur. J. Org. Chem. 2015, 5060–5063