Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short communication
Heterogeneous heck coupling in multivariate metal–organic frameworks
for enhanced selectivity
Jonathan W. Brown, Nanette N. Jarenwattananon, Trenton Otto, James L. Wang,
Stefan Glöggler, Louis-S. Bouchard ⁎
Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Highly selective heterogeneous Heck coupling has been demonstrated inside a series of metal–organic frame-
Received 12 November 2014
Received in revised form 4 February 2015
Accepted 5 March 2015
works (MOFs). These MOFs, Zn
have been synthesized with different amounts of 1,4-benzenedicarboxylate (BDC) and 2-amino-1,4-
benzenedicarboxylate (BDC-NH ) incorporated into their structure. The BDC-NH is functionalized by covalent
postmodification with salicylic aldehyde for binding catalytically active Pd(II) ions. The catalytic activity of the
embedded Pd(II) ions was tested via heterogeneous Heck coupling to produce resveratrol trimethyl ether, a
pharmaceutically relevant precursor. It is also found during catalytic testing that a trade-off exists between
amount of metalation and pore blocking.
4 2 n
O(BDC-NH ) (BDC)(3 − n) (n = 3, 2.4, 1.8, 1.2, 0.9, 0.75, 0.6, 0.3, and 0.15),
2
2
Available online 7 March 2015
Keywords:
Metal–organic framework
Heterogeneous catalyst
Heck coupling
© 2015 Elsevier B.V. All rights reserved.
Resveratrol
1
. Introduction
Multivariate metal–organic frameworks (termed MTV-MOFs) are
to play a role in the cardioprotective effects of red wine and is of great
interest for possible use in cancer treatment [24]. It is found that MOFs
with higher porosity and lower density of metal binding sites achieve
higher catalytic turnover and selectivity than MOFs with maximal den-
sity of metal binding sites.
porous crystalline solids in which the pores are lined with multiple
organic functional groups [1–5]. This report describes heterogeneous
Heck coupling reactions in a series of MTV-MOFs where postsynthetic
modification is used to adjust and embed specific amounts of catalyti-
cally active Pd(II) ions while avoiding pore blockage [6–9]. MOFs as het-
erogeneous catalysts have been studied because of their high porosity
and their ability to incorporate different catalytic units [10–13]. A dis-
tinct advantage of the MTV platform [14,15] is the ability to control
the density of the active sites and the porosity of a catalytic MOF [16].
Varying the percentage of functionalized links, in this case amino-
The MOF-5 structure with 1,4-benzenedicarboxylate (BDC) was
assembled with varying amounts of BDC-NH
2
to give five MOFs,
Zn O(BDC-NH (BDC)(3 − n) (n = 3, 2.4, 1.8, 1.2, 0.9, 0.75, 0.6, 0.3,
4
2 n
)
and 0.15) [see Supporting information (SI) for detailed synthetic
procedure] [25,26]. Each compound was postsynthetically modified
by reaction with salicylic aldehyde to give the imine derivative and
metalated with Pd to give the palladium functionalized framework
(Scheme 1). The structural integrity of the framework was confirmed
by a powder X-ray diffraction pattern (PXRD), which was coincident
to that of simulated structures (see SI). The presence of the imine
moiety was confirmed by a resonance at 255 ppm in the 15N cross-
polarization magic angle spinning nuclear magnetic resonance (CP/MAS
2
functionalized benzene dicarboxylate (BDC-NH ) in the original synthe-
sis of the MOF provides a means of tuning the amount of metal catalyst
lining the pores and optimization of its activity.
Heck coupling reactions to form aromatic carbon–carbon bonds are
one of the most important and useful ways to prepare complex organic
molecules [17]. Due to its outstanding stereoselectivity, Heck coupling is
of particular interest in the pharmaceutical chemistry [18] and has been
demonstrated in both homogeneous and heterogeneous systems previ-
ously, including other MOFs [19–23]. To highlight the advantage of
combining the MTV approach with postmodification, we investigated
the Heck coupling reaction for the synthesis of resveratrol trimethyl
ether, a pharmaceutically relevant precursor. Resveratrol is suspected
2
NMR) spectrum. The MOF was digested in DCl/D O and analyzed
1
with H solution-state NMR to ascertain the yield of the imine reaction
(See SI).
After fully characterizing our frameworks, the catalytic activity of
our MOFs in heterogeneous Heck coupling reaction to form resvera-
trol trimethyl ether was investigated (Fig. 1A). While Heck coupling
has been demonstrated in heterogeneous systems previously, con-
cerns of recyclability [27], selectivity [28], and catalyst leaching
[
29] continue to plague current systems and led us to investigate
the effect of catalyst loading and porosity on yield and selectivity. Our
reaction conditions were selected based on a previously published
⁎
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1