Photophysical Properties and Heterogeneous Photoredox Catalytic Activities of Ru(bpy)3@InBTB Metal–Organic Framework (MOF)

Article abstract of DOI:10.1002/chem.202003743

Metal–organic frameworks (MOFs) with negatively charged frameworks are suitable for selectively encapsulating cationic guest ions via a cation-exchange process. Encapsulating photoactive [RuL₃]²⁺ polypyridine complexes into the preorganized mesoscale channels of a MOF is a good method for stabilizing the excited states of the complexes. Three new RuL₃@InBTB MOFs were prepared by encapsulating cationic [Ru(bpy)₃]²⁺ (bpy=2,2′-bipyridine), [Ru(phen)₃]²⁺ (phen=1,10-phenanthroline), and [Ru(bpz)₃]²⁺ (bpz=2,2′-bipyrazine) into the mesopores of a three-dimensional (3D) InBTB MOF (H₃BTB=1,3,5-benzenetribenzoic acid). The photophysical properties of the resulting materials were investigated by photoluminescence (PL) analysis. The photoredox catalytic activities were also investigated for the aza-Henry reaction, hydrogenation of dimethyl maleate, and decomposition of methyl orange under visible light irradiation at room temperature. RuL₃@InBTB MOFs were found to be very stable and highly recyclable photoredox catalytic systems.

Full text of DOI:10.1002/chem.202003743

Accepted Article
Accepted Article
Title: Photophysical Properties and Heterogeneous Photoredox
Catalytic Activities of Ru(bpy)3@InBTB MOF
Authors: In-Hwan Choi, Sukbin Yoon, SEONG HUH, Sung-Jin Kim,
and Youngmee Kim
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
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To be cited as: Chem. Eur. J. 10.1002/chem.202003743
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0
1/2020

Chemistry - A European Journal
10.1002/chem.202003743
COMMUNICATION
Photophysical Properties and Heterogeneous Photoredox
Catalytic Activities of Ru(bpy)
3
@InBTB MOF
[a]
[a]
[a]
[b]
[b]
In-Hwan Choi, Sukbin Yoon, Seong Huh,* Sung-Jin Kim, and Youngmee Kim*
[
a]
I.-H. Choi, S. Yoon, Prof. Dr. S. Huh
Department of Chemistry and Protein Research Center for Bio-Industry
Hankuk University of Foreign Studies, Yongin, Korea 17035
E-mail: shuh@hufs.ac.kr
[
b]
Prof. Dr. S.-J. Kim, Dr. Y. Kim
Institute of Nano-Bio Technology and Department of Chemistry and Nano Science
Ewha Womans University, Seoul, Korea 03760
E-mail: ymeekim@ewha.ac.kr
Supporting information for this article is given via a link at the end of the document.
Abstract: Metal-organic frameworks (MOFs) with negatively
charged frameworks are suitable for selectively encapsulating
cationic guest ions via a cation-exchange process. Encapsulating
free RD in the solid state. In the case of rhodamine 6G (Rh6G)
encapsulated InBTB, Rh6G@InBTB exhibited quite distinct
fluorescence properties compared to free Rh6G crystals in the
solid state.[14] Thus, this simple encapsulation method can be a
good way of capturing guest ions, and guiding the molecular
ordering of guests and systematically altering or enhancing their
optical properties.
Meanwhile, there is active development of photoredox
catalytic systems for various organic transformations.[17,18] For
instance, several [RuL
3
]2+ polypyridine complexes were
2+
photoactive [RuL
mesoscale channels of an MOF is a good method for stabilizing the
excited states of the complexes. Three new RuL @InBTB MOFs
3
]
polypyridine complexes into the preorganized
3
2+
were prepared by encapsulating cationic [Ru(bpy)
3
]
(bpy = 2,2'-
1,10-phenanthroline), and
(bpz = 2,2'-bipyrazine) into the mesopores of a three-
dimensional (3D) InBTB MOF (H BTB = 1,3,5-benzenetribenzoic
2+
bipyridine), [Ru(phen)
3
]
(phen
=
2+
[
3
Ru(bpz) ]
3
acid). The photophysical properties of the resulting materials were
investigated by photoluminescence (PL) analysis. The photoredox
catalytic activities were also investigated for the aza-Henry reaction,
hydrogenation of dimethyl maleate, and decomposition of methyl
orange under visible light irradiation at room temperature.
successfully employed as visible light-driven photoredox
catalysts for a wide range of reactions, such as reductive
dehalogenation, radical cyclization, aza-Henry reaction,
oxidative biaryl coupling, and so on. Despite their cost-
effectiveness, the limitation of [RuL
3
]2+ polypyridine complex-
RuL
3
@InBTB MOFs were found to be very stable and highly
based photoredox catalysis is the relatively short-lived
photoexcited state compared to the cyclometalated Ir(III)
complex-based systems. Furthermore, only a limited number
of catalyst immobilization trials using MOFs have been reported
recyclable photoredox catalytic systems.
[
17]
Metal-organic
frameworks
(MOFs)
are
multifunctional
organic/inorganic hybrid materials with diverse framework
structures.[ Almost an infinite number of MOFs are possible via
simple variation of metal ions and bridging linkers.[2,3] Solvent-
free MOFs can often be employed for a wide range of chemical
applications including selective gas sorption,[4,5] heterogeneous
catalysis,[6,7] and biomedical applications.[8] Additionally, MOFs
with well-defined large open channels can be ideal host
materials for the encapsulation of various functional guest
molecules or ions.[9] Catalytically active metal-based
nanoparticles (NPs), metal complexes, and organometallic
1]
[
10-
compounds can be captured and stabilized in MOF channels.
1
2]
Especially, MOFs with negatively charged frameworks are
suitable for selectively encapsulating cationic guest ions via a
simple cation-exchange process with countercations present in
the MOF channels.[13-16] For example, the InBTB framework with
In3+
Et
ions
[In
and
(BTB) ]·10DEF·14H
BTB3-
linkers
(H
formulated
BTB
as
1,3,5-
[
2
NH
2
]
3
3
4
2
O
3
=
benzenetribenzoic acid; DEF = N,N-diethylformamide) contains
both a negatively charged 3D framework and large mesoscale
channels, with
containing 71.0% void volume of cation- and solvent-free InBTB
Figure S1).[13] A very large photoactive Reichardt's dye (RD)
a 2-fold interpenetrated network structure
(
was successfully encapsulated into the mesopores of a 3D
InBTB MOF. The captured RD cations showed unusual
absorption properties due to a confinement effect compared to
Figure 1. Photo images of colorless as-prepared InBTB and color-changed
2+
2+
RuL
3
@InBTB MOFs. The chemical structures of [Ru(bpy)
3
]
(a), [Ru(phen) ]
3
2+
(
b), and [Ru(bpz)
3
]
(c) are shown together.
1
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Chemistry - A European Journal
10.1002/chem.202003743
COMMUNICATION
investigated by PL techniques. We selected this Ru(II) series
because it exhibits an excellent metal-to-ligand charge transfer
(
MCLT) transition under visible light irradiation.[23] These Ru(II)
polypyridine complexes are being currently utilized as efficient
photoredox catalytic systems for a wide range of organic
transformations.[17,24] Once the excited state lifetime for the
encapsulated redox-active [RuL
3
]2+ complexes becomes longer
complexes, RuL @InBTB MOFs
2
+
than that for the free [RuL
3
]
3
can behave as efficient heterogenized photoredox catalytic
systems for recycling.
Each Ru(II) derivative was encapsulated into the
mesoscale channels of InBTB through cation-exchange with
+
Et
2
NH
2
counterions in ethanol or acetonitrile solution (2 mM
concentration) for 7 d (see Experimental Procedures in the SI).
The color change observed for all three RuL -encapsulating
crystals indicates clear encapsulation of [RuL
]2+ in InBTB, as
3
3
shown in Figure 1. The color-changed InBTB crystals were
investigated by X-ray crystallography. The crystal structures for
the three RuL @InBTBs are depicted in Figure 2. The
3
mesoscale channels in InBTB are sufficiently large enough to
accommodate all three [RuL
3
]2+ ions. The dimensions of the
2
+
3
free [RuL
3
2
]
ions are approximately 9.60 × 9.56 × 9.48 Å for
+
3
]2+, and 9.65
[
Ru(bpy)
3
] , 10.07 × 9.72 × 9.67 Å for [Ru(phen)
3
9.63 × 9.54 Å3 for [Ru(bpz)
] . To study the interaction
2+
×
3
between the framework and [RuL
crystal structure of each RuL @InBTB was analyzed, and the
occupancies of all [RuL
3
]2+ cation atoms were fixed to obtain
]2+ cation complexes, the
3
3
3 3
Figure 2. Crystal structures of Ru(bpy) @InBTB (a), Ru(phen) @InBTB (b),
the best fit with the largest residual peaks (Table S1). The real
occupancies were estimated using adsorption data obtained
from UV/Vis spectroscopy. The 3-fold rotation axis exists in the
center of the BTB3− ligands alternatively along the c-axis in
and Ru(bpz)
shown using a green and blue stick model, while [RuL
using a CPK model. The spatial distributions for the [RuL
3
@InBTB (c). 2-fold interpenetrated InBTB frameworks are
2+
3
]
ions are shown
]2+ ions and their
3
interactions with InBTB framework are shown together. Black dashed lines
indicate π•••π interactions and red dashed lines indicate hydrogen bonding.
Ru(bpy)
occupied [Ru(bpy)
to the framework through π•••π interactions (separation
distances of 3.66 Å and 4.14 Å for Ru(bpy) @InBTB and 3.71 Å
for Ru(phen) @InBTB) with C rotational symmetry alternatively
along the c-axis (Figure 2a and 2b). Partially occupied pairs of
Ru(bpz) rotational
]2+ cations exist in the framework with C
symmetry alternatively along the c-axis, and there are
electrostatic interactions between [Ru(bpz)
]2+ cations and the
anionic framework (Figure 2c). In contrast to the [Ru(bpy)
]2+
cation, two [Ru(bpz)
]2+ cations are paired through π•••π
3
@InBTB and Ru(phen)
3
@InBTB, and partially
]2+ cations were attracted
3
]2+ and [Ru(phen)
3
in the literature. Amara et al. immobilized [Ru(bpy)
3
]2+ onto the
3
surface of nonporous silica for realizing enhanced
photochemical oxidation.[19] There are previous reports on the
heterogeneous visible light-driven photoredox aza-Henry
catalytic systems.[19,20] Lin et al. directly coupled dibrominated
3
3
[
3
3
3 2
Ru(bpy) = 2-phenylpyridine)
]2+ and [Ir(ppy) (bpy)]+ (ppy
[
3
moieties with tetra(p-ethynylphenyl)methane to prepare
polymeric heterogeneous catalysts.[19] Xi and Xie et al.
prepared active heterogeneous photocatalysts based on the
covalent organic frameworks (COFs) composed of
tetraphenylethylene(TPE)-based electron donor and triazine-
based electron acceptor.[20] Since most photoredox active
polypyridine complex-based catalysts are cations, MOFs with
negatively charged frameworks can encapsulate these
catalysts through simple cation-exchange on the condition that
MOF channels are sufficiently large. Relatively strong
electrostatic interactions between the anionic framework and
metal complex ions will be beneficial for recycling of catalyst.
Very recently, Zhou et al. demonstrated a similar recyclable
photoredox catalytic system for the aza-Henry reaction using
3
3
interaction (separation distance of 4.08 Å) and nonclassical
hydrogen bonding interactions (C-H•••N 2.61 Å, 139.3°). The N
atoms of the bpz ligand may play an important role in the
formation of pairs of cations inside the channels. The unit cell
dimensions of RuL @InBTB deviated to be longer on the a- and
3
b-axes and shorter on the c-axis compared to the dimensions of
as-prepared InBTB (Table S1). The cation- and solvent-free
3
RuL @InBTBs possess smaller void volumes than the 71.0%
void volume based on PLATON analysis: 53.4% for
Ru(bpy)
Ru(bpz)
3
3
@InBTB, 53.9% for Ru(phen)
@InBTB. These results indicate that RuL
3
@InBTB, and 58.1% for
2+
3
cations
were encapsulated by 12.9 - 17.6% of the original void volume
of InBTB.
Ru(bpy)
3
@PCN-608-SBDC (H
3
SBDC
=
2-sulfoterephthalic
acid).[ However, the Ru(bpy)
22]
@PCN-608-SBDC catalyst was
3
]2+ ion by InBTB was
The uptake amount for each [RuL
estimated through periodic measurement of the concentration
of [RuL
]2+ ions remaining in the solution by UV/Vis
spectroscopy (Figure 3a). The uptake amount of [Ru(bpy)
3
recycled only three times.
To prepare an efficient heterogenized photoredox
catalytic system, we attempted to prepare new RuL @InBTB
MOFs by encapsulating a series of cationic Ru(II) polypyridine
3
3
2
+
3
] ,
]2+, was found to be 0.33 mmol/10
mg-solids, 0.42 mmol/10 mg-solids, and
2
+
[
3 3
Ru(phen) ] , and [Ru(bpz)
2
+
2+
derivatives (Figure 1): [Ru(bpy)
3
] , [Ru(phen)
3
] , and
2
+
[
Ru(bpz) ] . Their photophysical properties were also
3
2
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Chemistry - A European Journal
10.1002/chem.202003743
COMMUNICATION
and Ru(bpz) 2
+
ions and distinct nanoscale environments in the
3
InBTB channels dramatically altered the PL properties.
The time-resolved photoluminescence (TRPL) decay
curves for the solid samples were also measured to compare
the excited state lifetimes of bulk [Ru(bpy)
Ru(bpy) @InBTB, as depicted in Figure 3b. Interestingly, the
fitted curves indicate that the amplitude average lifetime of
3
]2+ and
3
2
+
[
Ru(bpy)
3
]
3
captured in Ru(bpy) @InBTB (τ = 420 ± 2.8 ns) is
much longer than the control bulk sample (τ = 114 ± 0.11 ns).
This means that the captured [Ru(bpy)
3
]2+ ions maintain a triplet
3
excited state ( MLCT) more effectively than the bulk sample
through retarding nonradiative decay.[
26]
Ru(bpz)
S4). Contrarily,
@InBTB is an exceptional case. Ru(phen) @InBTB
3
@InBTB
showed
Ru(phen)
similar
behavior
(Figure
3
3
showed an unusually shorter decay lifetime than that for bulk
Ru(phen) ]Cl The fluorescence lifetime imaging (FLIM)
images shown in Figure 3c-3e also clearly indicate that the
captured [Ru(bpy)
]2+ and [Ru(bpz) ]2+ ions exhibit longer
[
3
2
.
3
3
luminescence lifetimes than the bulk samples. These results
suggest that encapsulation of Ru(II) polypyridine complexes
into MOF channels is a good method to enhance their PL
lifetimes.[26,27]
Ru(bpz) @InBTB with long-lived excited states can be
employed as efficient photoredox catalytic systems for organic
transformations and other optical applications. The redox
Furthermore,
Ru(bpy)
@InBTB
and
3
Figure 3. [RuL
(
3
]2+ adsorption kinetic curves measured for as-prepared InBTB
a), normalized TRPL decay curves measured for bulk [Ru(bpy) ]Cl and
@InBTB upon excitation at 470 nm (b), Fluorescence lifetime
]Cl vs. Ru(bpy) @InBTB (c), bulk
@InBTB (d), and bulk [Ru(bpz) ][PF vs.
3
3
2
Ru(bpy)
3
imaging (FLIM) images of bulk [Ru(bpy)
Ru(phen) ]Cl vs. Ru(phen)
Ru(bpz) @InBTB (e).
3
2
3
potentials of Ru(bpy)
3
@InBTB were estimated from the cyclic
[
3
2
3
3
6 2
]
3
voltammogram as shown in Table S2. The values are
2
+
[17]
comparable to those of the free [Ru(bpy)
Encouraged by these promising results, the catalytic
activities of RuL @InBTB were investigated for the photoredox
3
]
ion.
0
.42 mmol/10 mg-solids, respectively. Thus, the encapsulation
amount for the [Ru(bpy)
]2+ ion is slightly smaller than that for
the [Ru(phen)
]2+ and [Ru(bpz) ]2+ ions. A fluorescence confocal
laser scanning microscopy (CLSM) investigation of the
RuL @InBTB crystals indicated uniform distribution of
phosphorescent [RuL
]2+ ions over the entire crystal (Figure S2).
However, the central part of the crystal indicates less intense
emission, and this implies that the penetration of [RuL
]2+ ions
into the mesopores was not completely achieved. Pore blocking
3
3
aza-Henry reaction of 2-phenyl-1,2,3,4-tetrahydroisoquinoline
(THIQ) with nitromethane under visible light irradiation using a
commercial fluorescent lamp (20 W), as shown in Figure 4a
and Figure S5. In the aza-Henry reaction, the tertiary amine
substrate is oxidized to an iminium ion via an aminium radical
cation in the aerobic condition, which further reacts with
nitromethane to give the desired coupled product.[17,28] Thus,
3
3
3
3
3
photoactivated [RuL
3
]2+* species can act as an oxidant for the
by initially exchanged [RuL
exchange.
3
]2+ ions may prevent complete
THIQ substrate in the first step of the previously proposed
reaction pathway (Figure S6).[ In the screening experiments,
17]
We investigated the PL properties of Ru(bpy)
3
@InBTB
ion in acetonitrile
absorbs the visible range of light centered at a wavelength of
4
1
3
Ru(bpy) @InBTB displayed a slightly higher product selectivity
(S = 71%; the selectivity S is defined by the ratio of the desired
C-C coupled product to the conversion of the substrate) despite
2
+
crystals in the solid state. The [Ru(bpy)
3
]
52 nm due to an efficient 1MLCT transition.[23] The excited
its lower conversion than Ru(phen)
Ru(bpz) @InBTB (S = 68%) (Figure S5). The product yield for
the desired product increases in the order of Ru(bpy) @InBTB
(46%) < Ru(phen) @InBTB (56%) < Ru(bpz) @InBTB (63%). A
3
@InBTB (S = 67%) and
MLCT state quickly relaxes to a lowest-energy 3MLCT state
through the intersystem crossing (ISC) process. Thus, an
intense 3MLCT emission band centered at 620 nm was
observed upon excitation by visible light. The same band was
seen at 607 nm in aqueous solution.[25] Interestingly, the solid-
3
3
3
3
control experiment under visible light without catalysts showed
that the reaction can also give the product with a much lower
selectivity (S = 53%). Another control experiment using as-
prepared InBTB alone under visible light showed a very similar
result with a low selectivity (S = 50%). Thus, as-prepared
InBTB cannot itself catalyze the reaction. We chose
state PL spectrum of Ru(bpy)
3
@InBTB revealed a strong
3
MLCT emission band centered at 598 nm (λex = 450 nm)
Figure S3). Therefore, the encapsulation of the [Ru(bpy)
]2+ ion
induced blueshifted PL emission band. Contrarily, the
emission band position for Ru(phen) @InBTB is very similar to
that for the free Ru(phen) 2+
ion in aqueous solution, 604 nm vs.
10 nm (λex = 422 nm).[17] In stark contrast, Ru(bpz)
@InBTB
displayed a redshifted emission band at 619 nm (λex = 443 nm),
(
3
a
3
Ru(bpy)
3
@InBTB catalyst for recycling experiments because it
@InBTB can
3
showed the highest product selectivity. Ru(bpy)
3
6
3
be recycled up to nine times without significant loss of activity
and product selectivity (Figure 4b). This capacity illustrates that
Ru(bpy) @InBTB is a stable recyclable photoredox catalytic
3
system for the aza-Henry reaction. Notably, both the conversion
and product yield gradually increased upon recycling. We did
not expect these gradual increases of activities because the
2
+
while the free Ru(bpz)
3
ion in acetonitrile showed a band
centered at 591 nm.[25] The origin of this difference can be
attributed to the dimeric form of Ru(bpz) 2+
Ru(bpz)
ions in
3
@InBTB. The unique spatial orientations of Ru(bpy) 2
+
3
3
3
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Chemistry - A European Journal
10.1002/chem.202003743
COMMUNICATION
colorless InBTB crystals showed a color change to a reddish
color after the control reaction, indicating the possible
encapsulation of the iminium intermediate (Figure S8). Although
the X-ray analysis of the used InBTB containing iminium ions
was not successful, these results clearly confirm the formation
of an iminium species during the reaction.
To further demonstrate the versatility of the
Ru(bpy) @InBTB catalyst, its activity for the hydrogenation of
3
electron-deficient dimethyl maleate to dimethyl succinate in the
presence of 1-benzyl-1,4-dihydronicotinamide (BNAH) as a
hydrogen source was tested by using a blue LED (7 W) as a
2
+
light source at room temperature (Figure 4c). [Ru(bpy)
reported to effectively catalyze this hydrogenation.[
3
]
was
This
30]
hydrogenation is a good model reaction for a photoredox
hydrogenation catalyst. Ru(bpy) @InBTB serves as an oxidant
3
in the first reductive quenching cycle of BNAH during the
proposed reaction pathway (Figure S9).[17,30] The photoexcited
[
Ru(bpy)
3
]2+* accepts an electron from BNAH to generate a
+
BNAH cation radical, BNAH· , in the proposed catalytic cycle.
In deoxygenated DMF, Ru(bpy)
catalyzed the reaction up to nine times without loss of activity
Figure 4d). While the reaction conversions are ~100% for each
3
@InBTB successfully
(
reaction, the product yields are in the range 68~81%. The initial
product yield (68%) is slightly different from that of the ninth
reaction (78%). Unwanted byproducts were usually observed in
this two-electron reduction process, and they are the coupled
product of a BNA· radical with dimethyl maleate or the dimeric
form of BNA· radicals.[ These results clearly confirm that the
30]
3
heterogeneous Ru(bpy) @InBTB is a good heterogeneous
photoredox hydrogenation catalyst with high recyclability.
We further explored the visible light-driven photocatalytic
decomposition of methyl orange (MO) in the presence of
2 2 8 3
potassium persulfate, K S O , by using Ru(bpy) @InBTB as a
photocatalyst and a solar simulator (150 W) as a visible light
source (Figure 4e). Since the reaction solvent is deionized
water, this reaction also presents a good method to investigate
Figure 4. (a) Catalytic aza-Henry reaction of THIQ. (b) Recycling results for
the aza-Henry reaction by Ru(bpy) @InBTB. Photographic images of the
3
retrieved catalyst after the 1st, 3rd, and 7th runs are shown together. (c)
Catalytic hydrogenation of dimethyl maleate in the presence of BNAH. (d)
Recycling results obtained for the corresponding hydrogenation. (e)
the stability of the Ru(bpy)
*Ru(bpy)
3
@InBTB system. The photoexcited
[
3
]2+ ions tend to cleave the S
2
O
8
2-
ion into two SO
4
·-
Photodecomposition of methyl orange by Ru(bpy)
of K
3
@InBTB in the presence
2
S
2 8
O .
radical anions, which further react with water to generate HO·.
-
Both SO
4
· and HO· radicals are likely to be responsible for the
decomposition of MO (Figure S10).[ The Ru(bpy)
31]
@InBTB
3
recovery of the used catalyst for recycling could not be perfect.
Generally, the activity may gradually decrease due to small loss
of catalyst. We speculate that there were iminium ions derived
from the substrate in the reaction mixture for aza-Henry
reaction, and these ions could replace some of the remaining
photoredox catalyst efficiently generated reactive radicals and
successfully decomposed MO. Interestingly, the
Ru(bpy) @InBTB catalyst could be recycled at least five times
(Figure S11). The catalytic activities for all five runs were
maintained at similar levels.
3
diethylammonium ions in Ru(bpy)
3
@InBTB. This process could
The PXRD patterns of each recovered catalyst after
recycling experiments indicated relatively weak and broad
diffraction signals as shown in Figure S12. The diffraction
enhance the activity upon recycling. The doubly charged
2
+
[
Ru(bpy)
3
]
ions should be more resistant to this cation
exchange.
signals of Ru(bpy)
showed very broad signals indicating partial loss of crystallinity.
Nonetheless, the microscopic image of Ru(bpy) @InBTB
crystals before catalytic reaction did not show any significant
change of crystal shapes as depicted Figure S13. More
3
@InBTB before catalytic reactions also
From a mechanistic point of view, the cationic iminium
intermediate can be captured in the channels of as-prepared
InBTB during the reaction, thus the FT-IR spectra for as-
prepared InBTB and the retrieved InBTB after the control
experiment were collected to probe distinct features (Figure S7).
The InBTB used showed a new signal attributable to the
iminium moiety (C=N ) derived from THIQ at 1698 cm , while
this signal was absent in the spectrum measured for the as-
prepared InBTB.[29] Concomitantly, the characteristic C=O
3
3
importantly, the Ru(bpy) @InBTB crystals after nine times of
hydrogenation of dimethyl maleate performed in DMF solvent
exhibited much enhanced diffraction peaks. These observations
suggest that the residual DEF and water solvate molecules in
InBTB might be exchanged with EtOH or nitromethane used for
Ru(II) complex encapsulation and catalytic reactions to show
broad and weak diffraction signals. Therefore, despite the
+
-1
-1
signal due to DEF solvates at 1657 cm in the as-prepared
InBTB completely disappeared. Additionally, the initially
4
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Chemistry - A European Journal
10.1002/chem.202003743
COMMUNICATION
partial loss of crystallinity due to exchange of solvate molecules,
the metal-ligand connectivities and 3D framework were well
preserved.
In summary, we successfully prepared new optical
materials containing luminescent Ru(II) polypyridine complexes
using a mesoporous InBTB MOF through a simple cation-
[17] C. K. Prier, D. A. Rankic, D. W. C. MacMillan, Chem. Rev. 2013, 113,
5322-5363.
[
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Conflict of interest
The authors declare no conflict of interest.
Keywords: metal-organic framework • ruthenium complex •
photoredox catalysis • aza-Henry reaction • hydrogenation
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Chemistry - A European Journal
10.1002/chem.202003743
COMMUNICATION
Entry for the Table of Contents
Photoactive cationic Ru(II) polypyridine complexes can be
effectively encapsulated into mesoscale channels of an InBTB
metal-organic framework to afford heterogenized photoredox
3 3
catalytic systems, RuL @InBTB. Ru(bpy) @InBTB showed a
longer excited state lifetime compared to the free ion and
displayed highly recyclable catalytic activities for the aza-Henry
reaction, hydrogenation of methyl maleate, and decomposition
of methyl orange under visible light irradiation.
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