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Published on the web April 3, 2010
Microwave-assisted One-pot Synthesis of Luminescent OrganicInorganic Hybrids
via Simultaneous Process of SolGel and SuzukiMiyaura Coupling Reactions
Yuichi Kajiwara,1,2 Atsushi Nagai, and Yoshiki Chujo*
1
1
1
Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University,
Katsura, Nishikyo-ku, Kyoto 615-8510
2
Matsumoto Yushi-Seiyaku Co., Ltd., 2-1-3 Shibukawa-cho, Yao, Osaka 581-0075
(
Received February 1, 2010; CL-100096; E-mail: chujo@chujo.synchem.kyoto-u.ac.jp)
In order to disperse luminescent compounds with low
Generally, the SuzukiMiyaura coupling is carried out using
bases such as sodium carbonate or potassium carbonate.
Therefore, the solgel reaction must be conducted under basic
conditions to perform the SuzukiMiyaura homocoupling of 1-
pyreneboronic acid together. Prior to preparation of luminescent
hybrid, we examined hybridization of CPTMS without 1-
pyreneboronic acid in the absence of palladium catalyst under
microwave irradiation and basic conditions. However, the
obtained hybrids formed viscous gel due to poor condensation
of CPTMS. To improve the condensation of CPTMS, CPTMS
was hybridized under acidic conditions to provide the complete
formation of (3-chloropyropyl)silanetriol, and then added
aqueous potassium carbonate solution. Further, the mixture
was exposed to microwave. Accordingly, the obtained hybrid
showed high transparency, implying the possibility for one-pot
processing of the SuzukiMiyaura homocoupling and solgel
reaction. Although the role of the chloropropyl groups has not
been cleared yet, they may affect the film formability of silica
matrices. Next, optimization of the SuzukiMiyaura homocou-
pling was carried out using several palladium catalysts such as
palladium acetate (Pd(OAc)2), tetrakis(triphenylphosphine)pal-
ladium(0) [Pd(PPh ) ], and acid-stabilized palladium stock
solubility or high crystallinity into silica matrices, we demon-
strate here facile one-pot synthesis of organicinorganic
luminescent hybrids via simultaneous process of solgel
reaction of 3-(chloropropyl)trimethoxysilane (CPTMS) and the
SuzukiMiyaura homocoupling of 1-pyreneboronic acid under
microwave irradiation. Highly luminescent hybrid without
aggregates of the pyrene dimer, which was efficiently generated
in situ, was obtained by microwave irradiation due to rapid
formation of silica matrices, whereas huge aggregates were
observed in the hybrid prepared under conventional heating.
The SuzukiMiyaura coupling has emerged as an extremely
powerful carboncarbon bond-forming protocol available to
practitioners of ³-conjugated architectures. Numerous interests
have been devoted to synthesis of conjugated biaryl compounds
1
that are applicable as organic light-emitting diodes (OLEDs),
polymer LEDs, and nonlinear optical materials.3 Simple
scaffolds of the conjugated compounds, i.e., nonsubstituted
biaryl compounds, usually lead to low solubility and high
crystallinity originating from the intermolecular ³³ stacking
interaction. Therefore, the introduction of long alkyl chains into
the conjugated compounds is required to increase the solubility
of them. Recently, the utility of microwave irradiation for the
Suzuki coupling has been widely reported. In particular,
Leadbeater et al. have demonstrated that the microwave-assisted
SuzukiMiyaura coupling can be performed using low levels of
ligandless palladium salts as the catalyst and water/ethanol
mixtures as the solvent, and the coupling reaction can proceed
efficiently in either sealed or open vessels.4 Furthermore,
microwave irradiation has been applied to the preparation of
some organicinorganic polymer hybrids, in which solgel
reaction of alkoxysilanes is highly accelerated.8 In this paper,
we demonstrate a facile one-pot synthesis of luminescent
hybrids via the simultaneous SuzukiMiyaura coupling reaction
and solgel process under microwave irradiation. Two con-
ceivable advantages of one-pot synthesis of the hybrids under
microwave irradiation are as follows; (1) the objective emissive
compounds can be facilely prepared without individually
multistage reaction and (2) it is possible to share both
dispersion and incorporation of the molecules with low
solubility and high crystallinity, which were generated by the
SuzukiMiyaura coupling in situ, into solgel matrices,
providing the enhancement of photoproperties such as fluo-
rescence quantum yield. Herein, 3-(chloropropyl)trimethoxy-
silane (CPTMS) and 1-pyreneboronic acid were used as an
alkoxysilane and a substrate of SuzukiMiyaura homocoupling,
respectively.
2
3
4
solution. Consequently, it was found that a palladium hydro-
chloric acid solution was the most efficient catalyst for the
11
homocoupling. As shown in Scheme 1, transparent and
homogeneous luminescent hybrids were obtained under micro-
wave irradiation (200 W 10 min, 500 W 10 min, and 800 W
10 min, sequentially). The yield of the in situ SuzukiMiyaura
homocoupling of 1-pyreneboronic acid was estimated by
7
B(OH)2
OCH3
OH
K2CO3, 1-pyreneboronic acid
10
Cl
Hydrolysis Cl
HCl
Si OCH3
Si OH
OCH3
OH
(3-chloropropyl)silanetriol
CPTMS
R
R
O
O
O
R
O
R
OH
R
O
Si
O
O
Si
OH
Si
Si Si
R
O
R
HO
HO
OH
Si
O
O
Si
O
R
Si
O
Si
O
O
OH
Si
R
O
R
OH
R
O
Si
HO
R
R
OH B(OH)2
OH
R
Si
Si
O
HO
R
OH
Si
O
R
Si
O
O
R
O
Si
Si
(HO)2B
OH
HO
OH OH
Pd
HO
O
Si
O
Si
R
HO
OH
R
Si
R
HO
Si
OH
Microwave
O
O
Si
R
O
O Si
Si
O
Si
O
R
HO
O
O
Si
O
R
R
OH
B(OH)2
O
Si
O
O
R
HO
R
OH
O
Si
R
R
R
R
OH
Si
Si
R
Si
O
(HO)2B
HO
OH OH
O
HO
R
R
O
HO
OH
HO
R
O
Si
O
O
OH
Si
OH
O
O
Si
O
Si
R
O
Si
Si
Si
Si
O
R
HO
O
OH
OH
R
R
R
R: CH CH CH Cl
2
2
2
Physical entrapment
of pyrene dimer
Scheme 1. Reaction scheme of the SuzukiMiyaura homocou-
pling and solgel reaction.
Chem. Lett. 2010, 39, 480481
© 2010 The Chemical Society of Japan