N-Alkylated and N,N-dialkylated 1,6-diaminoperylene diimides synthesized via copper catalyzed direct aromatic amination

Article abstract of DOI:10.1039/c4cc02124j

Perylene diimides (PDIs) and naphthalene diimides (NDIs) can be efficiently aminated with primary or secondary amines under mild conditions using Cu(ii) salts as catalysts and air as an oxidant. Depending on the substrate and the amine, yields over 80% ca

Full text of DOI:10.1039/c4cc02124j

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ARTICLE TYPE
N-Alkylated and N,N-Dialkylated 1,6-Diaminoperylene Diimides via
Copper Catalyzed Direct Aromatic Amination
Gesche Rauch and Sigurd Höger*
Dedicated to Professor Fritz Vögtle on the occasion of his 75th birthday
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
and N,N-dialkylated 1-amino and 1,6-diamino PDIs in one step
starting from the unsubstituted PDIs (in the following we will
50 describe the products simply as 1-amino- and 1,6-diamino PDIs
and ignore the alkyl groups at the amino group).20 The reaction is
achieved by simply stirring the corresponding PDI in the amine
with copper(II) salts as catalysts and oxygen (air) as oxidant
(Scheme 1). PDIs react with primary amines, secondary amines,
55 morpholine and 1-methylpiperazine in moderate to excellent
yields to 1-amino PDIs or to 1,6-diamino PDIs. In contrast to
previous protocols by which the diamino substituted compounds
are obtained via bromination/nucleophilic substitution as a
mixture of the 1,6- and 1,7-regioisomers (in a ratio of 1:3 to
60 1:4),12, 13 we obtain the twofold amination selectively in the 1,6-
position. We investigated three different PDIs with branched
alkyl (1) and aromatic (1´, 1´´) substituents at the imide nitrogen
(compound numbers without apostrophe bear the alkyl
substituents, compounds with one apostrophe the dibromo-tert-
65 butyl phenyl groups and compounds with two apostrophes the di-
tert-butyl phenyl groups).
In all cases are either the 1-substituted products (denoted as a) or
the 1,6-disubstituted products (denoted as b), or mixtures of them
are formed. No other regioisomers could be identified. The
70 product structure is unambiguously proven by spectroscopic and
spectrometric methods and comparison of the spectra of 1,7 and
1,6 disubstituted PDIs that were independently synthesized
according to literature procedures (see SI).
The high interest in direct aryl aminations prompted us to
75 investigate if other metal salts also catalyze the reaction.
However, neither iron (Fe(acac)3) nor palladium (Pd(PPh3)2Cl2)
salts lead under our conditions to an observable conversion. Best
results are achieved with Cu(II) salts, although the reaction
worked with Cu(I) salts and copper powder, too, in all cases in
80 the presence of air. The counter ion has no effect on the reaction,
as different Cu(II) salts gave similar yields (Table 1, product 2b).
The yields, reaction times and reaction temperatures depend on
the PDI derivative and the specific amines (see Table 1). Cyclic
secondary amines like pyrrolidine and piperdine gave the highest
85 yields of disubstituted products. For example, pyrrolidine lead to
the formation of the corresponding 1,6-diamino substituted PDI
3b at room temperature within one hour in very good yields up to
82 %.
Perylene diimides (PDIs) and naphthylene diimides (NDIs)
can be efficiently aminated with primary or secondary amines
under mild conditions using Cu(II) salts as catalysts and air
10 as oxidant. Depending on the substrate and the amine, yields
over 80 % can be obtained by simply stirring the reaction
mixture at room temperature for one hour.
Perylene diimides (PDIs) have outstanding physical properties
such as strong absorption, high fluorescent yields and thermal as
15 well as photochemical stability and are important chromophores
in dye chemistry and electronic devices like photovoltaic cells
and light emitting diodes (OLEDS).1-4 Variations of the perylene,
e.g. by core expansion along or perpendicular to the molecule
axes,5 or introduction of oxy or amino substituents at the core
20 alter the physicochemical properties and the aggregation behavior
of the dyes, thus expanding possible application.6-10 Core
substitutions are usually performed in two steps; the halogenation
of the bay position is followed by a nucleophilic substitution with
N or O nucleophiles.11 If only two bay positions are substituted,
25 the separation of regioisomers (1,6 and 1,7 disubstituted products
are generally obtained in a 1:3 to 1:4 ratio) is sometimes tedious.
Nevertheless, e. g. green 1,7-bis-(dialkylamino) PDIs and blue
1,6-bis-(dialkylamino) PDIs can be obtained in pure form.12, 13 An
alternative route is a nitration in the first step followed by an
30 ipso-substitution of the nitro group.14 In this case also a twofold
amination in 1- and 6-position starting from a mono nitro PDI
was reported, although in low yield. Depending on the reaction
conditions, or alternatively by reduction of the nitro group and
subsequent alkylation, also mono(dialkylamino) PDIs are
35 accessible. The high interest in PDI derivatives lead also to
increased activities in the search for direct core functionalization
via C-H activation to circumvent the halogenation or nitration
step. The tetra borolation,15 tetra arylation16 and tetra alkylation17
of PDIs with Ru-complexes as catalyst are described in the
40 2,5,8,11-positions. Furthermore,
a mono alkylation in bay
position of PDIs is reported via catalytic C-H activation with Pd-
complexes18 and a catalyst-free mono- and diamination at the 2-
and 2,11-position, respectively, was proposed recently.19
However, to the best of our knowledge, aminations of PDIs in the
45 bay position without prior functionalization have not been
described so far.
Herein, we describe a new synthetic route towards N-alkylated
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only moderate yields.21 In all cases, the compounds were purified
15 by column chromatography and subsequently by recycling GPC
(recGPC), when necessary. Although only a limitedVaiemwoAurtinctle oOfnline
DOI: 10.1039/C4CC02124J
different compounds were prepared, it became clear that PDIs
with aromatic substituents at the imide nitrogen seem to be more
reactive towards the formation of disubstituted products and that
20 pyrrolidine and piperidine are favorable amines for that
transformation.
1 R=
T [°C]
Amine
T [°C]
24 h
A
-
B
2b
95 °C
(49 %, CuCl2)
(52 %, Cu(OAc)2)
60 °C
60 °C
24 h
48 h
24 h
24 h
3a (60 %)
4a (9 %)
3b (28 %)
H2N
-
-
-
5
N
O
NH
NH
110 °C
110 °C
5a (25 %)
6a (18 %)
Scheme 2 Proposed simplified mechanism for the perylene amination.
At present, the exact mechanism for this transformation is not
25 clear. After our initial experiments we first speculated that the
Cu(II) might be coordinated to the imide oxygen and activate the
nearby CH-bond. However, this assumption does not agree with
the substitution pattern in the products. At present we propose a
non-coordinative mechanism at the less electron deficient bay
30 positions. Cu(II) is coordinated by the amine22 and oxidizes it to
the ammonium radical which is acidic enough to be deprotonated
in the amine solvent.23 Addition of the amino radical to the
1´ R=
Amine
T [°C]
T [°C]
A
-
B
HN
rt
rt
1 h
2´b (82 %)
3´b (89 %)
PDIs24 followed by a proton coupled electron transfer (PCET)
24 h
-
leads to the aminoperylene.25,
35 Cu(II) is performed by oxygene.
Reoxidation of the Cu(I) to
26
1´´ R=
We also tried to expand the protocol to other substrates. Electron
deficient aromatics as N-butylphthalimide and benzophenone did
not give any detectable reaction under the condition we used so
far. Also toluene and naphthalenes (2,7-dimethylnaphthaline) did
40 not react. However, our protocol allows the functionalization of
naphthalene diimids (NDI) with secondary amines in core
position in one synthetic step (Scheme 4). NDIs are also of
significant interest, e.g. for organic electronics2 and in
Amine
HN
T [°C]
rt
T [°C]
3 h
A
-
B
2´´b (68 %)
80 °C
14 h
3´´a (56 %) 3´´b (7 %)
28
supramolecular chemistry.27, As for the perylene dyes, core-
Scheme 1 and Table 1 N-alkylated (denoted without prime) PDIs (1) and
N-arylated PDIs (denoted with one or two primes, respectively; e.g. 1´,
1´´) give the mono (denoted as a) or diamino (denoted as b) PDIs,
5 depending on the PDI and the respective amine.
45 substituted NDIs are mostly obtained in a two-step synthesis,
either after chlorination29 or bromination.30 Only few examples of
aminated NDIs are described,19, 31-35 and the products of the two-
step synthesis are generally substituted in the 2 and 6 position.
Contrary, 2,7-diamino substituted NDIs are just briefly
50 explored.36 By applying the previous protocol, mono and
disubstituted NDIs are obtainable in which the disubstitution
leads exclusively to the 2,7-diamino compounds. An optimization
of the reaction conditions has not been performed so far and
reaction yields are yet only moderate (12 % and 36 % for double
55 amination). However, the simple reaction conditions already give
access to dyes which are otherwise difficult to prepare. The lower
With piperidine we obtained a mixture of mono and diamino
DPIs, depending on the substrate.
1 gave mainly the
monosubstituted product 3a. 1´ leads selectively to the 1,6-
diamino substituted PDI in excellent yield. 1´´ gave the 1-amino
10 PDI 3´´a as main product and the 1,6-diamino PDI 3´´c in only
small
amounts.
1-hexylamine,
morpholine
and
1-
methylpiperazine did not give clean reactions with either of the
PDIs, and the monoamino substituted products were obtained in
2
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Page 3 of 3
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60 °C
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-
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75
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G. Rauch, Prof. Dr. S. Höger, Kekulé-Institut für Organische Chemie und
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Financial Support by the Volkswagenstiftung is gratefully acknowledged.
30
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† Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/b000000x/
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