Angewandte
Communications
Chemie
Heterogeneous Catalysis
Highly Efficient Cooperative Catalysis by CoIII(Porphyrin) Pairs in
Interpenetrating Metal–Organic Frameworks
Zekai Lin+, Zhi-Ming Zhang+, Yu-Sheng Chen, and Wenbin Lin*
Abstract: A series of porous twofold interpenetrated In-
CoIII(porphyrin) metal–organic frameworks (MOFs) were
constructed by in situ metalation of porphyrin bridging ligands
and used as efficient cooperative catalysts for the hydration of
terminal alkynes. The twofold interpenetrating structure brings
adjacent CoIII(porphyrins) in the two networks parallel to each
other with a distance of about 8.8 ꢀ, an ideal distance for the
simultaneous activation of both substrates in alkyne hydration
reactions. As a result, the In-CoIII(porphyrin) MOFs exhibit
much higher (up to 38 times) catalytic activity than either
homogeneous catalysts or MOF controls with isolated
CoIII(porphyrin) centers, thus highlighting the potential appli-
cation of MOFs in cooperative catalysis.
traditional homogeneous catalysis. Because MOFs can be
designed with multiple, precisely spaced catalytic sites at very
high local concentrations, they are an ideal platform to
engineer recyclable and reusable solid catalysts for coopera-
tive catalysis. Herein we report the design of porous and
interpenetrating
MOFs
with
strategically
placed
CoIII(porphyrin) active sites for efficient cooperative hydra-
tion of terminal alkynes by dual substrate activation.
The new In-TBP MOF with the framework formula
In(TBP)x[In(TBP)(H2O)](1Àx)[DMA]x, (DMA = dimethylam-
monium; x > 0.9), was synthesized by heating indium nitrate
and tetrakis(4-benzoic acid)porphyrine (H4TBP) in a mixture
of DEF, DMF, and H2O, to result in purple crystals in 40%
yield. The TBP ligand was partially metallated with indium
during the reaction. The porphyrin in the In-TBP MOF could
be metallated with CoIII ions in situ by adding Co2+ salts to the
reaction mixtures to afford In-Co(TBP) in a similar yield. The
extent of TBP metallation can be tuned by varying the
amounts of metal salts. For example, the presence of 0 to
38.8 equivalents of Co2+ ions, with respect to H4TBP, led to
the formation of 0 to 93.8% Co(TBP) in the resulting MOF,
as quantified by inductively coupled plasma-mass spectrom-
etry (ICP-MS; see Table S1 in the Supporting Information)
and UV/Vis spectra analysis (see Table S5). The addition of
HfOCl2·8H2O improved the crystallinity of the MOFs,
although no Hf was detected in the MOFs by ICP-MS. The
In-Co(TBP)-MOF could also be synthesized by using the
premetallated ligand CoIII-TBP (see the Supporting Informa-
tion).
M
etal–organic frameworks (MOFs) are a class of highly
tunable, porous molecular materials with properties suitable
for a wide variety of applications, including gas storage[1]
separation,[2] catalysis,[3] nonlinear optics,[4] sensing[5] and
imaging,[6] drug delivery,[7] and others.[8,9] In particular,
MOFs have shown great promise as effective heterogeneous
catalysts because of the large channels and cavities that make
the catalytic sites readily accessible to substrates. Although
MOFs with isolated catalytic sites have been used to effect
a variety of organic transformations,[10,11] MOF catalysts with
multiple active sites are far less explored. We surmized that
MOFs with active sites in close proximity can be used for
cooperative catalysis by synergistic substrate activations or
for tandem/cascade catalysis.[12]
Cooperative catalysis, in which multiple catalytic sites
work synergistically to effect an organic transformation, is
prevalent in nature[13] and has emerged as a powerful strategy
in synthetic chemistry.[14] Cooperative catalysis can afford
improved efficiency and specificity over monocatalytic sys-
tems but is not operative at the low catalyst loading typical of
Single-crystal X-ray crystallographic[15] study of the In-
Co(TBP)-MOF revealed that each four-connected Co(TBP)
ligand links four four-connected [In(COOÀ)4] secondary
building units (SBUs), thus forming a twofold interpenetrated
three-dimensional (3D) framework of pts (PtS) topology (the
[In(COOÀ)4] tetrahedral node has a vertex symbol of
4·4·82·82·88·88 and the CoTBP square planar node has
a vertex symbol of 4·4·87·87·87·87). The void space was
54.8%, as calculated by PLATON. However, a low surface
area of (186.0 Æ 10.2) m2 gÀ1 was obtained by nitrogen adsorp-
tion studies, which is likely due to the severe distortion of the
MOF framework during the drying process (see Figure S9).
This drying process was not needed for the MOF catalysts
used in liquid-phase catalytic reactions. Within each Co(TBP)
unit, the cobalt cation has a pentacoordinated environment
completed by the four N atoms of the TBP and an axial aqua
[*] Z. Lin,[+] Dr. Z.-M. Zhang,[+] Prof. W. Lin
Department of Chemistry, University of Chicago
929 East 57th Street, Chicago, Illinois, 60637 (USA)
E-mail: webinlin@uchicago.edu
Dr. Z.-M. Zhang,[+] Prof. W. Lin
Collaborative Innovation Center of Chemistry for Energy Materials
College of Chemistry and Chemical Engineering, Xiamen University
Xiamen 361005 (P.R. China)
Dr. Y.-S. Chen
ChemMatCARS, Center for Advanced Radiation Sources
University of Chicago
9700 South Cass Avenue, Argonne, Illinois 60439 (USA)
À
group to form a [Co(TBP)(OH2)] unit. The Co N bond
À
[+] These authors contributed equally to this work.
lengths ranged from 1.94 to 1.97 ꢀ, and the Co O bond
length was 2.05 ꢀ. In one 3D unit of the twofold inter-
penetrated framework, the Co(TBP) functional units were
parallel to each other, with distances of 1.72 and 1.44 nm,
Supporting information and the ORCID identification number(s) for
Angew. Chem. Int. Ed. 2016, 55, 1 – 6
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1
These are not the final page numbers!