Published on the web September 5, 2011
931
Facile Preparation of Macrocycles with Triphenylamine Backbone
via C-N Coupling Reaction
Kousuke Tsuchiya,* Hiroko Miyaishi, and Kenji Ogino
Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology,
2-24-16 Nakacho, Koganei, Tokyo 184-8588
(Received April 15, 2011; CL-110321; E-mail: ktsuchiy@cc.tuat.ac.jp)
Cyclic oligomers composed of triphenylamine backbone
were conveniently prepared via palladium-catalyzed one-pot
synthesis. The condition for the preparation was optimized to
give the cyclic oligomers with large ring sizes in good yield up to
73.7%. The type of base for the reaction dramatically influenced
the yield of cyclic oligomers, and potassium tert-butoxide was
the most effective for the cyclization. The composition of the
cyclic oligomers was determined by high-performance liquid
chromatography (HPLC) as a mixture of pentamer, hexamer,
and heptamer. The cyclic pentamer was easily isolated by only
recrystallization from tert-butyl methyl ether.
Pd(OAc)2
P(t-Bu)3
t-BuONa
H
Br
N
n-Bu
toluene
reflux, 24 h
1
n-Bu
N
n-Bu
n-Bu
N
N
Arylamine derivatives have been widely applied to organic
light-emitting diodes, photoconductors, and photovoltaic de-
vices because of their excellent electrical properties.1 Recently,
we have reported that poly(4-n-butyltriphenylamine) (PTPA)
was prepared via palladium-catalyzed C-N coupling polymer-
ization, and that the resulting product involved a trace amount
of cyclic oligomers which were proven to be a mixture of
pentamer, hexamer, and heptamer by mass spectrometry.2 High
hole mobility and high photoconductivity of PTPA backbone
offers the possibility of being applied to organic photovoltaic
devices.3 In addition, because of electron-donating ability of the
triphenylamine moiety, charge-transfer (CT) interaction with an
electron acceptor can be a driving force for the cyclic oligomers
to form inclusion complex.
Macrocyclic compounds such as calixarene and cyclodex-
trin have lead many researchers toward designing and synthesiz-
ing new chemical backbones because of their fascinating ability
to form inclusion complexes in supramolecular chemistry.
Aromatic compounds containing heteroatoms such as aniline,4
pyridine,5 and thiophene6 are introduced into macrocyclic
structures so as to exploit strong ³-³ interaction with fullerenes
for the complexation. Among them, azacalix[n]pyridines have
been reported to show stronger affinity for C60 and C70 than
calixarene derivatives, probably because of introduction of
electron-donating heteroatoms.5b-5d However, the variety of the
structure as well as the sizes of ring were limited in a few
instances due to the difficulty of synthesis, especially for large
ring size. Wang’s group has prepared azacalixpyridines with up
to 10 aromatic rings, which possess thermodynamically unfavor-
able ring size, via elaborate stepwise reactions.5b-5d
n
N
N
n-Bu
CTPA
n = 1 ~ 3
n-Bu
Scheme 1. Synthesis of CTPA via C-N coupling reaction.
A
self-condensing monomer, 4-(4¤-bromophenyl)-4¤¤-n-
butyldiphenylamine (1), was synthesized from 4,4¤-dibromobi-
phenyl and 4-n-butylaniline using palladium catalyst. In a
similar manner to polymerization but in diluted conditions,
cyclic oligomers were prepared from 1 via C-N coupling
reaction (Scheme 1).2 The general synthetic procedure for CTPA
is as follows; To a solution of 1 (0.25 g, 0.66 mmol), sodium
tert-butoxide (0.0695 g, 0.72 mmol), and palladium(II) acetate
(2.95 mg, 0.013 mmol) in dry toluene (25 mL) was added tri-tert-
butylphosphane (12.7 ¯L, 0.10 mmol) under nitrogen atmo-
sphere. The mixture was stirred under reflux for 24 h. After
the reaction, the resulting solution was poured into methanol,
and the mixture of polymer and oligomers was filtered as the
precipitate. The collected mixture was subjected to Soxhlet
extraction with acetone to separate the oligomers from the
polymer. The resulting acetone solution was concentrated by
rotary evaporator and the crude product was purified by silica
gel column chromatography with toluene/hexane (2/3 in
volume ratio) to remove linear oligomers.
Table 1 summarizes the results of the formation of cyclic
oligomers under various conditions. All the products contained
the linear polymer and oligomers which were easily removed by
Soxhlet extraction and column chromatography, respectively.
When the reaction was performed under diluted conditions
without changing any parameters, the yield of cyclic oligomers
is improved up to 9.4% (Runs 2 and 3) compared with that at
tenfold concentration (Run 1, same condition as the polymer-
From a practical point of view, inclusion complexes of
cyclic oligotriphenylamine (CTPA) with an electron acceptor,
such as fullerene and perylenetetracarboxydiimide allow us to
fabricate a new type of donor-acceptor complex which probably
creates effective charge separation necessary for organic photo-
voltaic cells. In this communication, our interest is focused on
effective methods to prepare the cyclic oligomer.
Chem. Lett. 2011, 40, 931-933
© 2011 The Chemical Society of Japan
Tsuchiya, Kousuke
