Reactive and Functional Polymers
DMAP-based flexible polymer networks formed via Heck coupling as
efficient heterogeneous organocatalysts
Wei Xu a,b, Wu Xia a,b, Yukun Guan c, Yiming Wang a,b, Cuifen Lu a,b, Guichun Yang a,b
,
Junqi Nie a,b, Zuxing Chen a,b,
⁎
a
Hubei Collaborative Innovation Center for Advanced Organochemical Materials, Hubei University, Wuhan 430062, China
b
c
Ministry-of-Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Hubei University, Wuhan 430062, China
School of Pharmacy, Yantai University, Yantai 264005, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two DMAP-based flexible polymer networks TPB-DMAP and TPA-DMAP have been successfully synthesized via
palladium catalyzed Heck cross-coupling. The structures of these polymers were confirmed by solid state 13C CP/
MAS and Fourier transform infrared spectroscopy (FTIR). Although both polymers have negligible surface areas,
they exhibit excellent catalytic efficiency for the acylation of 1-phenylethanol with acetic anhydride due to their
good swelling capacities. Utilized as a typical catalyst, the polymer TPA-DMAP shows high activities for acylation
of a variety of alcohols to the corresponding esters. Moreover, the catalyst can be recycled at least ten times with-
out obvious loss of catalytic activity.
Received 20 January 2016
Received in revised form 31 March 2016
Accepted 17 April 2016
Available online 22 April 2016
Keywords:
Flexible polymer
Heterogeneous catalyst
Organocatalysis
Acylation
© 2016 Elsevier B.V. All rights reserved.
DMAP
1. Introduction
heterogeneous catalysts due to their excellent stability, low framework
density and various structural features [9–14]. These networks usually
During the past few decades, organocatalysis has received continu-
ous attention in organic transformations [1–3]. A variety of small organ-
ic molecular catalysts have been developed and applied in a wide range
of organic processes, providing efficient access to fine chemicals and
pharmaceuticals. Their practical applications, however, suffered from
some limitations such as difficulties in separating the catalyst from the
product and catalyst recovery and reuse. From these perspectives,
heterogenization of the existing homogeneous catalysts seems to be
an attractive way to the problems. The classical approach to obtaining
heterogeneous catalysts is immobilization of catalysts on solid supports
such as polymers, silica and magnetic particles [4–6]. In this case, the
active sites are usually not well distributed and pendent into the pore
volume, which may make it difficult for substrates to access the catalytic
centers or even cause pore blocking, thus eventually deactivate the cat-
alytic system [7,8].
have robust structure and permanent porosity because of the rigid
building blocks and the specific polymerization methods, which
facilitate the mass transfer and improve the reaction efficiency [15]. In
addition to the rigid hypercrosslinked networks, there are also flexible
polymer networks disclosed very recently which contain flexible link-
ages [16]. The flexible polymers do not have the permanent porosities
and high surface areas prevalent in robust analogues due to the rotation
and twisting of linkers, however, these flexible networks can swell in
organic solvents [17–19] and may exhibit superior catalytic activities
because the swelling behavior of flexible polymers in solvents makes
contact between the substrates and active sites in polymers more fre-
quent [20]. Nevertheless, the examples of promotion of catalytic reac-
tions by using flexible polymers are still rare [16].
4-(N,N-dimethylamino)pyridine (DMAP) is a very effective acyla-
tion catalyst [21–23] and has been extensively studied [24]. Due to the
acute dermal toxicity of DMAP and some of its derivatives, many strat-
egies for recycling of DMAP were developed [25–34]. Notably, Zhang
et al. prepared a DMAP-based conjugated nanoporous polymer
(DMAP-CNP) which has a robust structure and BET surface area of
508 m2 g−1 [34]. This catalyst, however, exhibited poor efficiency in
the acylation reaction of alcohols with acetic anhydride.
In order to overcome the shortcomings brought by the traditional
immobilization methods, a new class of highly crosslinked materials,
which are prepared by strong covalent bonds between functional moi-
eties and structural linkers through a bottom-up methodology, have
been developed and become a promising platform for recyclable
As a continuation of efforts to explore efficient heterogeneous cata-
lytic system [35], herein we report the synthesis of two DMAP-based
flexible polymers (TPB-DMAP and TPA-DMAP) via the Heck coupling
⁎
Corresponding author at: Hubei Collaborative Innovation Center for Advanced
Organochemical Materials, Hubei University, Wuhan 430062, China.
1381-5148/© 2016 Elsevier B.V. All rights reserved.