Efficient Rare-Earth-Based Coordination Polymers as Green Photocatalysts for the Synthesis of Imines at Room Temperature

Article abstract of DOI:10.1021/acs.inorgchem.8b00465

Five new rare-earth coordination polymers (CPs) were designed in order to offer a remarkable platform that contains light-harvesting antennas and catalytic active centers to achieve solar-energy conversion as green alternatives in the synthesis of imines. These five new spirobifluorene-containing Ln-CPs, named [Er₃(Hsfdc)₃(sfdc)₃(H₂O)]·xH₂O (RPF-30-Er), [Ln(Hsfdc)(sfdc)(EtOH)]·S (RPF-31-Ln, where Ln = La, Nd, and Sm and S = H₂O or EtOH), and [Ho(Hsfdc)(sfdc)(H₂O)] (RPF-32-Ho) (RPF = rare-earth polymeric framework and H₂sfdc = 9,9′-spirobi[9H-fluorene]-2,2′-dicarboxylic acid), have been solvothermally synthesized, and their structural features can be described as follows: (i) RPF-30-Er shows a 3D framework in which the inorganic trimers (secondary building units) are cross-linked by Hsfdc^- and sfdc^2- linkers displaying a pcu topology. (ii) The isostructural RPF-31-Ln series of materials, together with RPF-32-Ho, exhibit a 1D network of chains growing along the a axis with a ribbon-of-rings topology type. The photocatalytic activity of the RPF-n materials was tested in the oxidative coupling of amines using molecular oxygen and air as oxidizing agents under warm light. Among the materials investigated, RPF-31-Nd was chosen to further investigate the approach in the selectivity of different amine derivates.

Full text of DOI:10.1021/acs.inorgchem.8b00465

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Efficient Rare-Earth-Based Coordination Polymers as Green
Photocatalysts for the Synthesis of Imines at Room Temperature
Lina M. Aguirre-Díaz,*,† Natalia Snejko,† Marta Iglesias,† Felix Sanchez,‡ Enrique Gutierrez-Puebla,†
́
́
́
,†
́
and M. Angeles Monge*
†Departamento de Nuevas Arquitecturas en Química de Materiales, Materials Science Factory, Instituto de Ciencia de Materiales de
Madrid, Consejo Superior de Investigaciones Científicas, Sor Juana Ines de la Cruz 3, Cantoblanco, Madrid 28049, Spain
‡Departamento de Síntesis, Estructura y Propiedades de Compuestos Organ
icos, Instituto de Química Organica General, Juan de la
́
́
́
Cierva 3, Madrid 28006, Spain
S
* Supporting Information
ABSTRACT: Five new rare-earth coordination polymers
(CPs) were designed in order to offer a remarkable platform
that contains light-harvesting antennas and catalytic active
centers to achieve solar-energy conversion as green alternatives
in the synthesis of imines. These five new spirobifluorene-
containing Ln-CPs, named [Er3(Hsfdc)3(sfdc)3(H2O)]·xH2O
(RPF-30-Er), [Ln(Hsfdc)(sfdc)(EtOH)]·S (RPF-31-Ln,
where Ln = La, Nd, and Sm and S = H2O or EtOH), and
[Ho(Hsfdc)(sfdc)(H2O)] (RPF-32-Ho) (RPF = rare-earth polymeric framework and H2sfdc = 9,9′-spirobi[9H-fluorene]-2,2′-
dicarboxylic acid), have been solvothermally synthesized, and their structural features can be described as follows: (i) RPF-30-Er
shows a 3D framework in which the inorganic trimers (secondary building units) are cross-linked by Hsfdc− and sfdc2− linkers
displaying a pcu topology. (ii) The isostructural RPF-31-Ln series of materials, together with RPF-32-Ho, exhibit a 1D network
of chains growing along the a axis with a ribbon-of-rings topology type. The photocatalytic activity of the RPF-n materials was
tested in the oxidative coupling of amines using molecular oxygen and air as oxidizing agents under warm light. Among the
materials investigated, RPF-31-Nd was chosen to further investigate the approach in the selectivity of different amine derivates.
heterocyclic compounds, α-amino acids, and α-amino alco-
hols,27,28 great research efforts have been dedicated to finding
different environmentally friendly alternatives to achieve the
selective synthesis of imines.29−31 Recently, several studies
based on transition-metal-mediated catalytic routes have been
developed.32−38
In the event of the selective oxidation of amines using light as
a clean and renewable energy resource, some advances has been
achieved using heterogeneous catalysts,39−42 but for the direct
synthesis of imines from benzylamines, the use of CPs and
MOFs as catalysts appears to have been rarely studied.43−49
However, it seems important to highlight the advantage of
using CPs in photocatalytic processes because of their ability to
integrate both light-harvesting and catalytic active sites in a
single solid platform, allowing the conversion of solar energy to
chemical energy.13 In this respect, lanthanide CPs (Ln-CPs) are
interesting candidates because of their stability in water, their
strong Lewis acid properties, and their higher stability in front
of their transition-metal-based analogues.
1. INTRODUCTION
Rare-earth-based coordination polymers (CPs) have been
extensively studied for their diversified structures and promising
applications, such as gas storage/separation,1,2 information
storage,3−5 chemical sensing,6−8 and heterogeneous cataly-
sis,9−13 among others.14−16 Our work always being focused on
control of the material properties, from both the compositional
and structural points of view, has proved that catalysis17−20 and
photoluminescence10,21−24 are the fields where the route to
improve the properties is more straightforward. In this context,
we had previously designed and synthesized several rare-earth-
based metal−organic frameworks (MOFs), with high catalytic
activity in several organic transformations including multi-
component (one-pot or cascade) catalytic reactions. These
materials were conceptually planned to contain catalytic active
sites in both the organic linkers and metal centers.10,11,25,26 The
development of new and selective heterogeneous catalysts is
crucial for the advancement in new catalytic processes,
particularly in the oxidation of organic compounds. This type
of reaction usually undergoes the generation of considerable
amounts of byproducts and waste, which can be avoided with
higher selectivity and recyclability of the catalyst, combined
with the use of molecular oxygen or air as oxidizing agents
instead of the traditional organic peroxides.
Herein, we present five new Ln-CP materials obtained by
solvothermal synthesis using La, Nd, Sm, Ho, and Er as metal
sources, together with the quite rigid dipodal ligand 9,9′-
spirobi[9H-fluorene]-2,2′-dicarboxylic acid (H2sfdc; Scheme
In the case of imines, which are well-known for being
important intermediates in the synthesis of biologically active
Received: February 22, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b00465
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
water, ethanol, and acetone. Yield: 0.025 g (68% La), 0.064 g (83%
Nd), and 0.020 g (83% Sm). RPF-31-La. Elem anal. Found (calcd for
C56H35LaO9·0.5H2O): C, 67.25 (67.21); H, 3.99 (3.63). IRKBr (cm−1):
3589, 3428, 3061−2922, 1924, 1682, 1608−1590, 1539, 1490, 1425−
1393, 1303, 1265, 1239, 1156, 1126−1109, 1077, 1006, 910, 876, 848,
799−794, 756, 730, 680, 655, 638, 552, 503, 497. TG (N2, 10 °C/
min): the framework loses its solvent-encapsulated molecules (∼0.5%)
under 100 °C, and then the framework is stable up to 420 °C, and
between 430 and 490 °C, the loss of 95% of the material content is
observed, which corresponds to the rest of the framework material.
RPF-31-Nd. Elem anal. Found (calcd for C56H35NdO9·EtOH): C,
66.51 (66.67); H, 3.86 (3.95). IRKBr (cm−1): 3616, 3419, 3065−2925,
2648−2609, 2499, 1953−1918, 1692, 1609−1588, 1535, 1491, 1464−
1455, 1422−1395, 1344, 1303, 1265, 1238, 1155, 1124, 1109, 1077,
1046, 1028, 1006, 908, 876, 849, 820, 800−794, 756, 727, 680, 652−
638, 553, 501−497. TG (N2, 10 °C/min): the framework loses its
solvent-encapsulated molecules (∼1%) under 100 °C, and then the
framework is stable up to 400 °C, and between 440 and 490 °C, the
loss of 98% of the material content is observed, which corresponds to
the rest of the framework material. RPF-31-Sm. Elem anal. Found
(calcd for C56H35SmO9·1.5H2O): C, 65.43 (65.41); H, 3.68 (3.72).
IRKBr (cm−1): 3428, 3064−2923, 1685, 1609−1589, 1532, 1491,
1463−1454, 1422, 1395, 1344, 1301, 1265, 1233, 1156, 1125−1109,
1006, 908, 849, 800−794, 755, 729, 679, 653, 638, 554, 503. TG (N2,
10 °C/min): the framework loses its solvent-encapsulated molecules
(∼2%) at 100 °C, and then the framework is stable up to 400 °C, and
between 430 and 500 °C, the loss of 98% of the material content is
observed, which corresponds to the rest of the framework material.
RPF-32-Ho. [Ho(Hsfdc)(sfdc)(H2O)] was synthesized as follows:
0.019 g (0.047 mmol) of H2sfdc was added to a solution of
Ho(NO3)3·5H2O (0.025 g, 0.057 mmol) in water (9 mL); the mixture
was then magnetically stirred at room temperature for 15 min in a
Teflon-lined stainless steel autoclave and heated at 200 °C for 96 h.
After cooling to room temperature, the crystalline product was filtered
and washed with water, ethanol, and acetone. Yield: 0.010 g (43%).
Elem anal. Found (calcd for C56H35HoO9·1.5H2O): C, 64.12 (64.37);
H, 3.60 (3.67). IRKBr (cm−1): 3428, 3064−2923, 1685, 1609−1589,
1532, 1491, 1463−1454, 1422, 1395, 1344, 1301, 1265, 1233, 1156,
1125−1109, 1006, 908, 849, 800−794, 755, 729, 679, 653, 638, 554,
503. TG (N2, 10 °C/min): the framework loses its solvent-
encapsulated molecules (∼8%) at 150 °C, and then between 200
and 300 °C, the framework loses the coordinated water molecule. The
framework remains stable up to 400 °C, and between 430 and 500 °C,
the loss of 92% of the material content is observed, which corresponds
to the rest of the framework material.
1). The photocatalytic activities of all materials have been
explored, and the true heterogeneous nature of the catalyst is
demonstrated.
Scheme 1. Organic Ligand H2sfdc Reacting with Several
Lanthanide Metals To Form a Series of New Ln-CPs
2. EXPERIMENTAL SECTION
2.1. Materials. The following reagents were commercially available
and were used as supplied without further purification: Ln(NO3)3·
xH2O (Ln = La, Nd, Sm, Ho, and Er; all 99% Strem Chemicals).
2.2. Preparation and Characterization of the Organic Linker
(H2sfdc) and RPF Materials. 2.2.1. Preparation and Character-
ization of 9,9′-Spirobi[9H-fluorene]-2,2′-dicarboxylic acid (H2sfdc).
H2sfdc was easily prepared in two successive steps; selective 2,2′-
diacetylation of 9,9-spirobi[9H-fluorene] by acetyl chloride in
nitromethane (2,2′-diacetyl-9,9′-spirobi[9H-fluorene]), followed by a
treatment with sodium hypobromite (NaOHBr2) and acidification.
Characterization by NMR spectroscopy and mass spectrometry (MS)
and a comparison with published data confirmed its chemical structure
(see the Supporting Information).50−52
2.2.2. Preparation and Characterization of RPF Materials. RPF-
30-Er with the formula [Er3(Hsfdc)3(sfdc)3(H2O)] was synthesized as
follows: 0.019 g (0.047 mmol) of H2sfdc was added to a solution of
Er(NO3)3·5H2O (0.028 g, 0.063 mmol) in water (9 mL). The mixture
was then magnetically stirred at room temperature for 15 min in a
Teflon-lined stainless steel autoclave and heated at 200 °C for 72 h.
After cooling to room temperature, the crystalline product was filtered
and washed with water, ethanol, and acetone. Yield: 0.017 g (72%).
Elem anal. Found (calcd for C162H97Er3O29): C, 64.95 (64.66); H, 3.47
(3.25). IRKB (cm−1): 3589, 3428, 3061−2922, 1924, 1682, 1608−
1590, 1539, 1490, 1425−1393, 1303, 1265, 1239, 1156, 1126−1109,
1077, 1006, 910, 876, 848, 799−794, 756, 730, 680, 655, 638, 552,
503, 497. TG (N2, 10 °C/min): the framework loses its solvent-
encapsulated molecules (∼0.5%) under 100 °C; between 200 and 350
°C, the structure loses 5% of the material content, which corresponds
to the coordinated water molecule and the third part of a protonated
linker. Then the framework is stable up to 420 °C, and between 430
and 490 °C, the loss of 94% of the material content is observed, which
corresponds to the rest of the framework material.
2.3. Visible-Light-Induced Oxidation of Amine Catalysis. In a
3 mL Pyrex reactor was placed 5 mg (∼0.005 mmol) of RPF-n
material and benzylamine (5 μL, 0.048 mmol) in acetonitrile (ACN; 1
mL). The mixture was stirred and irradiated with a 100 W warming
lamp for 18 h. The temperature of the reaction system was precisely
controlled at 25 °C. The reaction product was analyzed by mass-
coupled gas chromatography (GC−MS).
3. CHARACTERIZATION TECHNIQUES
The Fourier transform infrared (FT-IR) spectra were recorded
from KBr pellets in the range 4000−250 cm−1 on a Bruker IFS
66 V/S spectrometer. Thermogravimetric (TG) and differential
thermal (DTA) analyses were performed using a Seiko TG/
DTA 320U equipment in a temperature range between 25 and
1000 °C in air and N2 (100 mL/min flow) with a heating rate
of 10 °C/min. A PerkinElmer CNHS Analyzer 2400 was
employed for elemental analysis. Powder X-ray diffraction
analysis was performed using a Bruker D8 diffractometer, with
step size = 0.02° and exposure time = 0.5 s/step. Powder X-ray
diffraction measurements were used to check the purity of the
obtained microcrystalline products by a comparison of the
experimental results with the simulated patterns obtained from
single-crystal X-ray diffraction data. UV−visible studies were
Materials RPF-31-Ln with the formula [Ln(Hsfdc)(sfdc)(EtOH)]·
xS [Ln = La, Nd, and Sm and S = solvent (H2O or EtOH)] were
synthesized under the same reaction conditions, as follows: A
lanthanum compound (0.032 g, 0.079 mmol) of H2sfdc was added
to a solution of La(NO3)3·6H2O (0.016 g, 0.037 mmol) in a mixture
of water and ethanol (1 and 8 mL, respectively). The mixture first was
stirred at room temperature for 15 min in a Teflon-lined stainless steel
autoclave and then heated at 200 °C for 96 h. After cooling to room
temperature, the crystalline product was filtered and washed with
B
DOI: 10.1021/acs.inorgchem.8b00465
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 1. Main Crystallographic and Refinement Data for the Compounds H2sfdc, RPF-30, RPF-31, and RPF-32
H2sfdc
C27H16O4
RPF-30-Er
C162H87Er3O25
RPF-31-Nd
C56H35NdO9
RPF-31-Sm
C56H35SmO9
RPF-32-Ho
C54H31HoO9
formula
mol wt/(g/mol)
temperature/K
404.40
200
2935.09
296
996.08
200
1002.19
200
988.72
296
́
wavelength/Å
1.54178
monoclinic
C2/c
1.54184
triclinic
P1
1.54178
triclinic
1.54178
triclinic
1.54178
triclinic
cryst syst
space group
P1
̅
P1
̅
P1
̅
́
́
a/Å
36.035(5)
14.3544(19)
8.3818(10)
90
14.3779(6)
14.6340(6)
14.7237(7)
91.940(3)
94.008(3)
91.914(3)
3086.6(2)
1
11.6558(4)
14.3929(5)
15.0469(5)
111.891(2)
109.916(2)
96.232(2)
2120.38(13)
2
11.7296(5)
14.4538(7)
15.1994(7)
112.026(2)
109.758(3)
96.449(3)
2162.08(18)
2
11.6105(4)
14.6839(5)
14.8117(5)
65.450(2)
89.574(2)
68.298(2)
2101.94(13)
2
b/Å
́
c/Å
α/deg
β/deg
γ/deg
102.630(9)
90
3
́
V/Å
4230.6(9)
8
Z
Dx/(g/cm3)
μ/mm−1
F(000)
GOF of F2
1.270
1.579
1.557
1.539
1.562
0.691
4.287
9.865
10.711
4.026
1680
1463
1002
1010
988
0.962
1.010
1.090
1.108
1.157
final R indexes [I >
2σ(I)]
R1 = 0.0801, wR2 =
0.1808
R1 = 0.0611, wR2 =
0.1598
R1 = 0.0533, wR2 =
0.1521
R1 = 0.0450, wR2 =
0.1295
R1 = 0.0591, wR2 =
0.1759
R indices (all data)
R1 = 0.1666, wR2 =
0.2265
R1 = 0.0908, wR2 =
0.2004
R1 = 0.0667, wR2 =
0.1819
R1 = 0.0501, wR2 =
0.1411
R1 = 0.0851, wR2 =
0.2442
carried out on a PerkinElmer Lambda XLS+ spectrometer.
Fluorescence spectra were recorded on an Aminco SLM 8000
spectrophotometer.
Scheme 2. Different Coordination Modes of the Half-
Protonated (Hsfdc−) and Fully Deprotonated (sfdc2−)
Organic Linkers in RPF-n
3.1. Single-Crystal Structure Determination. Crystals
were selected under a polarizing optical microscope for a single-
crystal X-ray diffraction experiment. Single-crystal X-ray data
were obtained on a Bruker four-circle κ diffractometer equipped
with a Cu INCOATED microsource, operated at 30 W power
(45 kV, 0.60 mA) to generate Cu Kα radiation (λ = 1.54178 Å),
and a Bruker VANTEC 500 area detector (microgap
technology). Diffraction data were collected by exploring over
a hemisphere of the reciprocal space in a combination of φ and
ω scans to reach a resolution of 0.85 Å, using a Bruker APEX2
software suite (each exposure, depending on ω, was of 56, 90,
or 140 s covering 1° in ω or φ). Unit cell dimensions were
determined for a least-squares fit of the reflections with I > 4σ.
The structures were solved by intrinsic phase methods. The
hydrogen atoms were fixed at their calculated positions using
distances and angle constraints. All calculations were performed
using APEX2 software for data collection and OLEX2-1.2 and
SHELXTL for resolution and refinement of the structure.
dimethylformamide.54 In our work, we were able to obtain
colorless plate-shaped single crystals (see Figure S1) of this
organic ligand without any cosolvent from recrystallization of
the freshly synthesized H2sfdc using a microwave treatment
(Table 1).
Only one work with sfdc2− as the organic linker in a CP has
been reported.52 In such a case, calcium is the metal center
selected and the corresponding CP (named SHU-1) consists of
2D layers built by square-planar Ca4O clusters connected by
the sfdc2− linker. The existence of rhombic windows is a
common attribute observed in our materials and in the reported
SHU-1, which is a consequence of the linker geometry.
R P F - 3 0 - E r m a t e r i a l w i t h t h e f o r m u l a
[Er3(Hsfdc)3(sfdc)3(H2O)] crystallizes in the triclinic P1
space group. Although reflection statistics (Wilson plot)
indicate a centrosymmetric cell with Er2 in the inversion
center, it is the asymmetric coordination of this atom in the
ErO6 octahedron that makes it acentric. The asymmetric unit of
RPF-30 consists of three different crystallographic Er3+ ions,
three molecules of the half-deprotonated linker Hsfdc−, three
anions of the fully deprotonated sfdc2− linker, and a
coordinated water molecule (Figure 1). The sfdc2− linker
shows two different coordination modes: (i) L1 with η2μ-η2 and
4. RESULTS AND DISCUSSION
4.1. Crystal Structures. The crystal structure for each
compound was determined using single crystal X-ray
diffraction; crystals of suitable size were obtained through the
solvothermal synthesis using conventional heating. Details of
data collection, refinement, and crystallographic data for the
compounds H2sfdc, RPF-30, RPF-31, and RPF-32 are
summarized in Table 1.
4.2. Structural Description. The dipodal ligand H2sfdc
presents several alternatives of the ligand coordination to metal
centers. In the present work, three different coordination
modes can be appreciated for the fully deprotonated sfdc−2
linker and three for the protonated Hsfdc−1 species (Scheme
2).
In the CCDC database,53 we found that in 1983 the organic
ligand H2sfdc was reported as a solvate with N,N-
C
DOI: 10.1021/acs.inorgchem.8b00465
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 1. (Top) Atomic and polyhedral representation of a RPF-30 3D structure, showing the asymmetric unit (left) and a (111) view of one of the
3D frameworks (right). (Bottom) SBU and view of the pcu topological representation (left) using the ToposPro program.55
(ii) L2 with η2-η2. Meanwhile, the Hsfdc− linker displays only a
η1-η2μ coordination mode, named L4 from now on (Scheme 2).
There are three crystallographically independent erbium metal
centers, two of them in an ErO8 coordination environment and
one in an ErO6 octahedral environment. As a result, the
formation of two −[ErO8]− primary building units (PBUs) of
eight-coordinated erbium centers and one −[ErO6]− PBU of
an octahedral erbium center is observed.
crystallizes in the triclinic P1 space group. The asymmetric unit
̅
consists of one Ln3+ ion, half-deprotonated linker molecules
Hsfdc−, one molecule of the fully deprotonated sfdc2− linker,
and one coordinated ethanol molecule (Figure 2). The sfdc2−
linker shows the coordination mode L3 with η2μ-η3μ, and in the
case of the Hsfdc− linker, a η1-η2 coordination mode (L5) is
observed (Scheme 2).
The lanthanide cation is nine-coordinated to one ethanol
molecule and eight oxygen atoms from the linker, forming
−[LnO9]− PBUs. The carboxylate groups of the linker
exhibited different coordination behaviors in both Hsfdc− and
sfdc2− species. In RPF-31-Ln, the SBU is formed by two face-
sharing −[LnO9]− polyhedra (Ln1 and Ln1′) related by
symmetry, forming a dimer in the [010] direction, which are
connected through Hsfdc− and sfdc2− linkers, giving rise to a
1D framework that grows along the a axis and presents a
chainlike topology with the RoR type (Figure 2).
The supramolecular network is built up through two types of
weak interactions, which increase the dimensionality of the
framework, connecting the 1D covalent chains: (i) Ar−H···Ar
interaction from two neighboring chains (C11−H11···π, D =
3.576 Å, d = 2.688 Å, and θ = 155.85°) displaying a T
geometry; (ii) several Ar−H···CAr weak interactions (C36−
H36···C11, D = 3.624 Å, d = 2.684 Å, and θ = 172.01°; C3−
H3···C45, D = 3.490 Å, d = 2.699 Å, and θ = 141.22°; C5−
H5···C47, D = 3.526 Å, d = 2.786 Å, and θ = 135.36°; C4−
H4···C23, D = 3.582 Å, d = 2.796 Å, and θ = 140.72°); (iii)
C55−H55AEtOH···C23Ar, D = 3.670 Å, d = 2.891 Å, and θ =
136.26°; all of these interactions allow the RoR chains to be
aligned along the [001] direction as a hexagonal rod packing
(Figure 2).
The environment of the first erbium metallic center (Er1) is
built by four Er−O bonds in a chelate way from the L1 and L2
modes of the fully deprotonated linker, one Er−O bond from
the monodentate part of the L4 coordination mode of the
Hsfdc−linker, and three Er−O bonds from the bridging part of
the L4 coordination mode of the Hsfdc− linker. The
environment of the second erbium metallic center (Er2) is
formed by five Er−O bonds from the bridging O−C−O groups
−
of the sfdc2− and Hsfdc linkers (L1 and L4, respectively) and
one Er−O from a coordinated water molecule. It is precisely
this coordinated water molecule that breaks the octahedron
symmetry and thus avoids the P1 space group. The third
̅
erbium (Er3) environment consists of three Er−O bonds from
the bridging part of the L1 linker type, one Er−O bond from
the monodentate part of the L4 linker type, and four Er−O
bonds from the chelating part of the L1 and L2 linker types.
In RPF-30-Er, the secondary building unit (SBU) is formed
by three different PBUs joined through the binding of O−C−O
groups, giving rise to a trimer that grows in the [111] direction.
−
2−
These trimers are connected through the Hsfdc and sfdc
linkers in all directions. The result is a 3D structure with pcu
topology of a 6-connected uninodal net (Figure 1).
RPF-31-Ln material with the formula [Ln(Hsfdc)(sfdc)-
(EtOH)]·nS (Ln = La, Sm and Nd and S = H2O or EtOH)
D
DOI: 10.1021/acs.inorgchem.8b00465
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 2. (Top) Atomic and polyhedral representation of a RPF-31 1D structure, showing the dimer SBU (left) and the (001) view of the 1D
framework (right). (Middle) View of different supramolecular weak interactions between neighboring chains in RPF-31-Nd. (Bottom) Parallel
alignment in the [100] direction of chains showing the supramolecular hexagonal rod packing.
RPF-32-Ho material with the formula [Ho(Hsfdc)(sfdc)-
and sfdc2− linkers, give rise to a 1D framework that grows along
the a axis and presents a chainlike topology with the RoR type
(Figure 3).
(H O)] crystallizes in the triclinic P1 space group. The
̅
2
asymmetric unit consists of one Ho3+ ion, one half-
deprotonated linker molecule Hsfdc−, one molecule of the
fully deprotonated sfdc2− linker, and one coordinated water
molecule (Figure 3).
Two intramolecular hydrogen bonds are observed for RPF-
32-Ho: (i) O8−H8Aw···O1L (1.757 Å, 2.649 Å, and 150.66°);
(ii) O9−H9L···O3L (1.919 Å, 2.718 Å, and 164.32°). The
supramolecular network is built up through two types of weak
interactions, which increase the dimensionality of the frame-
work, connecting the 1D covalent chains along the b and c axes:
(i) Ar−H···Ar from two neighboring chains with distances of
2.683 and 3.612 Å displaying a T geometry (82.97°) with an
angle of 175.49°; (ii) several C−H···O weak interactions
[dD−A(C−H···O1) = 3.219 Å and 175.61°; dD−A(C−H···O5) =
3.569 Å and 163.79°]. Like RPF-31, these weak interactions
connect the RoR chains along the [100] direction as a
hexagonal rod packing.
The structural difference between RPF-31 and RPF-32 relies
in the coordination mode of the organic linker. Whereas for
RPF-32-Ho, it is L3 and L6, in RPF-31, it is L3 and L5 for sfdc2−
and Hsfdc−, respectively. Therefore, nine- and eight-coordi-
nated holmium centers are formed for RPF-31 and RPF-32
correspondingly.
The −[HoO8]− PBU is formed with one Ho−O bond from
the coordinated water molecule and seven Ho−O bonds from
the linker (Hsfdc− and sfdc2− species). In RPF-32-Ho, the SBU
is formed by two face-sharing −[HoO8]− polyhedra (Ho and
Ho′) related by symmetry. These dimeric units (that run along
the [001] direction), which are connected through the Hsfdc−
4.3. Photocatalytic Activity of RPF-n Materials. In order
to evaluate the stability and capacity of these novel RPF
E
DOI: 10.1021/acs.inorgchem.8b00465
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Figure 3. (Top) View in the (001) direction of the atomic and polyhedral representation of a RPF-32 1D structure. (Bottom) Augmentation of the
small cages of RPF-32 (left) and a close-up in the SBU dimer showing the coordination linker types and an intramolecular O−H···O hydrogen bond
(right).
Scheme 3. (Top) Oxidative Condensation of Benzylamine Catalyzed by RPF-n Materials and (Bottom) Cross-Condensation of
Benzylamine with Aniline
materials as heterogeneous photocatalysts, the oxidative
coupling of amines to imines was chosen as a model organic
transformation. Furthermore, cross-condensation between
different amines was studied to analyze the selectivity scope
of the best catalyst (Scheme 3).
For the initial trials, the self-coupling of benzylamine (∼5 μL,
0.05 mmol) was selected as a model reaction at room
temperature (25 °C) using a commercial 100 W warm light
lamp under an oxygen atmosphere purged with balloon using
ACN (1 mL) as the solvent (Table 2, entries 1−5). Given that
the H2sfdc linker has an extinction coefficient several orders of
magnitude higher than the corresponding the metal, the
samples had to be diluted (5 μg/mL) to observe the absorption
band in the visible region (Figure S12).
The progress of the reaction was monitored by GC−MS.
Blanks run in the absence of catalyst and without light gave
nonrepresentative reactivity under the same conditions (Table
2, entries 17 and 18, respectively). The use of RPF materials as
catalysts (10%mol) provided good conversion in the 60−76%
range of the 1a product with high selectivity (Table 2, entries
1−5). Although several MOFs have been used as catalysts in
the oxidation of amines (entries 6−16), in some cases higher
temperatures were used in order to afford good conversions
with high selectivity (Table 2, entries 7−13). Only a few of the
MOFs explored so far in this reaction used light as an energy
source (Table 2, entries 14−16). However, in the case of Zn-
PDI and NH2-MIL-125(Ti) catalysts, the use of high-power
light sources was necessary to achieve high conversions without
F
DOI: 10.1021/acs.inorgchem.8b00465
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Table 2. Screening of RPF-n Materials as Photocatalysts in the Oxidation of Benzylamine
entry
catalyst
RPF-30-Er
metal CN, dimensionality
time (h)
conversion (%)
selectivity to 1a (%)
ref
1
6 and 8, 3D
9, 1D
9, 1D
9, 1D
8, 1D
6, 3D
6, 3D
6, 3D
6, 3D
6, 3D
4, 3D
6, 3D
6, 3D
4, 2D
6, 3D
8, 3D
18
18
18
18
18
6
76
71
>99
>99
>99
>99
>99
>99
38
this work
this work
this work
this work
this work
46
2
RPF-31-La
3
RPF-31-Nd
RPF-31-Sm
RPF-32-Ho
MOF-253 (Al)
60
4
65
5
74
b
6
>99
38
b
7
ZrMOF-BIPY
6
46
b
8
DUT-5
6
46
c
9
NHPI/Fe(BTC)
24
24
24
24
4
98
67
17
61
92
74
73
>99
7
90
43
c
10
11
12
13
14
15
16
17
18
19
MIL-100(Fe)
97
43
c
Cu3(BTC)2
98
43
c
Al2(BDC)3
97
43
d
Mn/Co-MOF
92
45
e
Zn-PDI
4
unspecified
47
f
NH2-MIL-125(Ti)
12
2
86
>99
95
48
g
UNLPF-12
49
without catalyst
without light
H2L
18
18
18
this work
this work
this work
22
15
96
74
a
Reaction conditions: benzylamine (0.05 mmol); catalyst (10 mol %); ACN as the solvent (1 mL); an oxygen atmosphere purged with balloon at 25
b
°C; 3000K LED 14 W (100 W) of warm light (distance ≈ 8 cm). Yields by GC−MS. Reaction conditions: benzylamine (10 mmol); catalyst (1.5
c
mol %); 1 bar of oxygen; T = 100 °C; without light. Yields by GC−MS. Reaction conditions: benzylamine (0.5 mL); an oxygen atmosphere purged
d
with balloon, T = 100 °C, without light. Yields by GC−MS. Reaction conditions: benzylamine (1 mmol); tert-butyl hydroperoxide (2 mmol); Mn/
e
Co-MOF (10 mg) in ACN (2 mL) at room temperature; without light. Reaction conditions: benzylamine (1 mmol); catalyst (1 mol %); ACN (5
f
mL); in air; 500 W xenon lamp with a cut filter below 420 nm. Reaction conditions: benzylamine (0.1 mmol); NH2-MIL-125(Ti) (5 mg); ACN
(2.0 mL); an oxygen atmosphere; irradiated for 12 h with a 300 W xenon lamp with a UV-cut filter to remove all wavelengths of less than 420 nm; an
g
IR-cut filter to remove all wavelengths larger than 800 nm. Reaction conditions: catalyst (1.0 μmol; 0.4 mol % based on porphyrin moiety);
benzylamine (0.27 mmol); 1 mL of dry ACN; 14 W white compact fluorescent lamp (distance ≈ 8 cm).
complete selectivity to the desired product (1a). The UNLPF-
12 material, although it seems to have incredible conversion
and selectivity at shorter time, owes its activity to the doping of
porphyrin present in the MOF with tin(IV), and the activity
does not proceed from the indium-based MOF itself.
The RPF-30, RPF-31, and RPF-32 materials show good
activity (around 70%) and excellent selectivity (>99%) in the
oxidation of the benzylamine reaction. From the small
differences among their activities, we can infer the following:
(i) The nature of the metal source itself does not seem to have
much influence on the reactivity and/or selectivity of the
catalyst. (ii) The amount and accessibility of the active catalytic
sites (Ln3+) in the structure, together with the Ln3+
coordination number (CN), and the presence of easily
displaced labile ligands, make the reactivity order displayed
by these RPF-n materials perfectly understandable. For
example, the small upper conversion displayed by RPF-30 is
related to its higher number of metal centers, or the lower CN
(8) in RPF-32 favors better conversions in front of RPF-31
with a CN of 9.
Figure 4. SEM images of the synthesized RPF-31-Nd material before
(600× magnification, left) and after (75× magnification, right)
photocatalysis.
reaction times are needed to obtain the same conversion,
although the selectivity is kept at >99% (Table 3, entries 3 and
4). Thus, the chosen conditions to perform the oxidative
coupling of amines were 10 mol % (based on metal), ACN as
the solvent, and an oxygen atmosphere purged with balloon at
25 °C.
After these tests, additional trials were performed using RPF-
31-Nd (Figure 4) as the catalyst (Table 3, entries 1−4). This
material was chosen because of its high yield in its synthesis
preparation, which allowed the performance of several
experiments. On the other hand, we assumed that the above-
described characteristics make the results obtained for RPF-31
scalable to the other catalysts RPF-n. The reactions were
performed under both molecular oxygen and air.
The results show that when using air instead of molecular
oxygen (Table 3, entry 2), the selectivity remains at >99% but
the conversion drops considerably from 60% to only 30% after
48 h. When the catalyst amount decreases to 5% and 1%, longer
The oxidation of several amines was examined, and when 1-
phenylethan-1-amine was used (Table 3, entry 5), the rate of
reaction was lower and was attributed to the large size of this
reactant, reaching only 22% conversion with 96% of the
selectivity. In the case of anilines (without a hydrogen atom at
the α carbon atom), a small rate of conversion to the
diphenylamine product was observed to be <10%, still with
high selectivity (Table 3, entries 6 and 7). A primary aliphatic
amine such as butan-1-amine was also transformed toward the
corresponding imine (Table 3, entry 8).
Having determined the relative ability of amines to undergo
catalytic aerobic oxidation in the presence of RPF-31-Nd, we
G
DOI: 10.1021/acs.inorgchem.8b00465
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
a
Table 3. Screening of RPF-31-Nd as the Photocatalyst in the Oxidation of Several Amines with Molecular Oxygen
entry
amine
t (h)
product
conversion (%)
selectivity (%)
1
2
3
4
5
6
7
8
1
1
1
1
18
18
36
18
24
24
24
18
1a
1a
1a
1a
2a
3a
4a
5a
60
30
58
28
22
6
>99
>99
>99
>99
96
b
c
d
1-phenylethan-1-amine
aniline
>99
>99
>99
p-chloroaniline
2
e
butan-1-amine
99
a
Reaction conditions: amine (0.05 mmol); catalyst (10 mol %, based on metal); ACN as the solvent; an oxygen atmosphere purged with balloon at
b
c
25 °C. Reaction conditions: benzylamine (0.05 mmol); catalyst (10 mol %); ACN as the solvent; in air; at 25 °C. Reaction conditions:
benzylamine (0.52 mmol); catalyst (5 mol %); ACN as the solvent; an oxygen atmopshere at 25 °C. Reaction conditions: benzylamine (5.2 mmol);
catalyst (1 mol %); ACN as the solvent; an oxygen atmosphere purged with balloon; T = 25 °C. Conversion by GC−MS. Reaction conditions:
biphenyl as the internal standard.
d
e
tested the reaction of a mixture of benzylamine and aniline
(Table 4).
filtered and then washed with water and ethanol. This process
of reuse was then repeated five times. The efficiency of RPF-
31-Nd was reached even after five cycles of repetition.
Moreover, the powder X-ray diffraction analysis of RPF-31-
Nd after the recycling events showed that the material
crystalline structure remained unchanged (Figure S19). To
verify that no leaching from the catalyst occurs during the
photocatalytic reaction, the reaction was carried out under
optimized conditions and the solid was removed by hot
filtration after 3 h; after removal, the mixture is again exposed
to light and oxygen for the next 16 h. As expected, no
significant conversion to the product 1a was observed.
Table 4. Cross-Condensation of Benzylamine with Aniline
a
Using RPF-31-Nd as the Photocatalyst
selectivity (%)
entry
ratio of 1:3
time (h)
conversion (%)
1a
6a
1
2
3
1:1
1:3
36
36
36
55
60
63
85
92
36
15
8
5. CONCLUSIONS
b
5:1 (5)
41 (7a)
Herein we report five new rare-earth CPs that contain light-
harvesting antennas and catalytic active centers and represent
green alternatives in the synthesis of imines. RPF-30-Er shows
a 3D framework in which the inorganic trimers (SBUs) are
cross-linked by the Hsfdc− and sfdc2− linkers, displaying a pcu
topology. The isostructural RPF-31-Ln series and RPF-32-Ho
compound exhibit 1D networks of chains with a RoR topology
type. The photocatalytic activity of the RPF-n materials was
tested in the oxidative coupling of amines using molecular
oxygen and air as oxidizing agents under warm light.
The first example of 1D rare-earth-based CPs RPF-n as
efficient photocatalysts for the oxidation of amines is reported.
Reactions have been performed under both oxygen and air
atmospheres, using mild conditions without any cosolvent. The
catalysts can be reused without loss in selectivity toward the
desired product.
From this study, it can be inferred that the nature of the
metal source itself does not seem to have much influence in the
reactivity and/or selectivity of the catalyst. The experimental
data (Table 2 and Figure S12) show that the metals act as
connectors among the organic antennas through what seems to
be a ligand-to-metal charge-transfer mechanism in the visible
range. However, the results obtained for the lanthanum (f0)
compound and the multiple CH3−π interactions all over the
structures do not allow one to rule out a cooperative ligand-to-
ligand charge-transfer mechanism. To further investigate this
point, more research with this ligand and no rare-earth metal is
being carried out.
a
Reaction conditions: benzylamine (0.05−0.10 mmol); aniline (0.05−
0.15 mmol); catalyst (10 mol %); ACN as the solvent; an oxygen
atmosphere purged with balloon; at 25 °C. Reaction conditions:
benzylamine (0.05 mmol); butylamine (0.01 mmol); catalyst (10 mol
%); ACN as the solvent, an oxygen atmosphere purged with balloon;
at 25 °C. Conversion by GC−MS. The values inside parentheses are
the corresponding yields for each product.
b
When the reaction was carried out with equal stoichiometry
of amines, we obtain a mixture of products in 85/15 yield (1a/
6a)because of the lack of aniline oxidation (Table 4, entry 1).
We tried to increase the selectivity toward N-benzylideneaniline
by performing the reaction with 3 equiv of aniline, although the
selectivity toward N-benzylideneaniline does not augment.
When the reaction was performed between benzylamine and
butan-1-amine, we obtained a mixture 36/41 for 1a and the
cross-condensation product N-butyl-1-phenylmethanimine
(Table 4, entry 3).
4.4. Recyclability and Leaching Test. To meet the
practical applicability and to improve the process economy, the
photocatalytic activity of RPF-n materials must be enhanced;
therefore, we next investigated the recyclability of the RPF-31-
Nd catalyst using the standard reaction. To verify this, the
catalytic activity of the material (10 mol % loading) was
analyzed after stirring with benzylamine (5 μL in 1 mL of
ACN) for 18 h using 100 W of warm light. The product
reaction was then analyzed by GC−MS, and the catalyst was
H
DOI: 10.1021/acs.inorgchem.8b00465
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(8) Muller-Buschbaum, K.; Beuerle, F.; Feldmann, C. MOF based
̈
ASSOCIATED CONTENT
■
luminescence tuning and chemical/physical sensing. Microporous
Mesoporous Mater. 2015, 216, 171−199.
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b00465.
́
(9) Corma, A.; García, H.; Llabres i Xamena, F. X. Engineering Metal
Organic Frameworks for Heterogeneous Catalysis. Chem. Rev. 2010,
110, 4606−4655.
(10) D’Vries, R. F.; Iglesias, M.; Snejko, N.; Alvarez-Garcia, S.;
Gutierrez-Puebla, E.; Monge, M. A. Mixed lanthanide succinate-sulfate
3D MOFs: catalysts in nitroaromatic reduction reactions and emitting
materials. J. Mater. Chem. 2012, 22, 1191−1198.
Structural determination of 9,9′-spirobi[9H-fluorene]-
2,2′-dicarboxylic acid, experimental data for all RPF-n
materials, and heterogeneous photocatalytic activities for
RPF-n materials (PDF)
́
(11) Gandara, F.; Puebla, E. G.; Iglesias, M.; Proserpio, D. M.;
́
Snejko, N.; Monge, M. A. Controlling the Structure of Arenedisul-
fonates toward Catalytically Active Materials. Chem. Mater. 2009, 21,
655−661.
Accession Codes
CCDC 1810728−1810730 and 1811714−1811716 contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.ac.
uk, or by contacting The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336033.
(12) Pagis, C.; Ferbinteanu, M.; Rothenberg, G.; Tanase, S.
Lanthanide-Based Metal Organic Frameworks: Synthetic Strategies
and Catalytic Applications. ACS Catal. 2016, 6, 6063−6072.
(13) Zhang, T.; Lin, W. Metal-organic frameworks for artificial
photosynthesis and photocatalysis. Chem. Soc. Rev. 2014, 43, 5982−
5993.
(14) Feng, J.; Zhang, H. Hybrid materials based on lanthanide
organic complexes: a review. Chem. Soc. Rev. 2013, 42, 387−410.
AUTHOR INFORMATION
(15) Bunzli, J.-C. G. Review: Lanthanide coordination chemistry:
̈
■
from old concepts to coordination polymers. J. Coord. Chem. 2014, 67,
3706−3733.
Corresponding Authors
*E-mail: Lina.Aguirre@csic.es.
*E-mail: amonge@icmm.csic.es.
(16) Rocha, J.; Carlos, L. D.; Paz, F. A. A.; Ananias, D. Luminescent
multifunctional lanthanides-based metal-organic frameworks. Chem.
Soc. Rev. 2011, 40, 926−940.
ORCID
́
(17) Aguirre-Díaz, L. M.; Gandara, F.; Iglesias, M.; Snejko, N.;
Marta Iglesias: 0000-0001-7373-4927
́
́
Gutierrez-Puebla, E.; Monge, M. A. Tunable Catalytic Activity of Solid
Felix Sanchez: 0000-0003-4069-1291
́
́
Solution Metal−Organic Frameworks in One-Pot Multicomponent
Reactions. J. Am. Chem. Soc. 2015, 137, 6132−6135.
́
M. Angeles Monge: 0000-0003-2242-7593
(18) Aguirre-Diaz, L. M.; Iglesias, M.; Snejko, N.; Gutierrez-Puebla,
E.; Monge, M. A. Toward understanding the structure-catalyst activity
relationship of new indium MOFs as catalysts for solvent-free ketone
cyanosilylation. RSC Adv. 2015, 5, 7058−7065.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
́
(19) Aguirre-Díaz, L. M.; Iglesias, M.; Snejko, N.; Gutierrez-Puebla,
́
E.; Monge, M. A. Synchronizing Substrate Activation Rates in
Multicomponent Reactions with Metal−Organic Framework Catalysts.
Chem. - Eur. J. 2016, 22, 6654−6665.
We gratefully acknowledge the Spanish Ministry of Economy,
Industry and Competitiveness (MINECO-Spain; Projects
MAT2014-52085-C2-2-P and MAT2016-78465-R), and
Fondo Social Europeo from the European Union, Comunidad
Autonoma de Madrid (Grant S2013/MIT-2740; PHAMA 2.0).
L.M.A-D wants to thank S. Jimenez Aguirre for his help.
(20) Aguirre-Díaz, L. M.; Reinares-Fisac, D.; Iglesias, M.; Gutier
́
rez-
́
Puebla, E.; Gan
́
dara, F.; Snejko, N.; Monge, M. A. Group 13th metal-
organic frameworks and their role in heterogeneous catalysis. Coord.
Chem. Rev. 2017, 335, 1−27.
(21) D’Vries, R. F.; Alvarez-Garcia, S.; Snejko, N.; Bausa, L. E.;
Gutierrez-Puebla, E.; de Andres, A.; Monge, M. A. Multimetal rare
earth MOFs for lighting and thermometry: tailoring color and optimal
temperature range through enhanced disulfobenzoic triplet phosphor-
escence. J. Mater. Chem. C 2013, 1, 6316−6324.
REFERENCES
(1) Devic, T.; Serre, C.; Audebrand, N.; Marrot, J.; Fer
Lanthanide-Based Metal Organic Framework with Large One-
Dimensional Tunnels and a High Surface Area. J. Am. Chem. Soc.
2005, 127, 12788−12789.
■
́
ey, G. 3-D
(22) Gomez, G. E.; Kaczmarek, A. M.; Van Deun, R.; Brusau, E. V.;
Narda, G. E.; Vega, D.; Iglesias, M.; Gutierrez-Puebla, E.; Monge, M.
(2) Roy, S.; Chakraborty, A.; Maji, T. K. Lanthanide−organic
frameworks for gas storage and as magneto-luminescent materials.
Coord. Chem. Rev. 2014, 273−274, 139−164.
(3) Sorace, L.; Benelli, C.; Gatteschi, D. Lanthanides in molecular
magnetism: old tools in a new field. Chem. Soc. Rev. 2011, 40, 3092−
3104.
(4) Woodruff, D. N.; Winpenny, R. E. P.; Layfield, R. A. Lanthanide
Single-Molecule Magnets. Chem. Rev. 2013, 113, 5110−5148.
(5) Liu, K.; Zhang, X.; Meng, X.; Shi, W.; Cheng, P.; Powell, A. K.
Constraining the coordination geometries of lanthanide centers and
magnetic building blocks in frameworks: a new strategy for molecular
nanomagnets. Chem. Soc. Rev. 2016, 45, 2423−2439.
(6) Dang, S.; Ma, E.; Sun, Z.-M.; Zhang, H. A layer-structured Eu-
MOF as a highly selective fluorescent probe for Fe3+ detection
through a cation-exchange approach. J. Mater. Chem. 2012, 22, 16920−
16926.
́
A. Photoluminescence, Unconventional-Range Temperature Sensing,
and Efficient Catalytic Activities of Lanthanide Metal−Organic
Frameworks. Eur. J. Inorg. Chem. 2016, 2016, 1577−1588.
(23) Godoy, A. A.; Gomez, G. E.; Kaczmarek, A. M.; Van Deun, R.;
Furlong, O. J.; Gandara, F.; Monge, M. A.; Bernini, M. C.; Narda, G. E.
Sensing properties, energy transfer mechanism and tuneable particle
size processing of luminescent two-dimensional rare earth coordina-
tion networks. J. Mater. Chem. C 2017, 5, 12409−12421.
́ ́ ́ ́
(24) Gandara, F.; Andres, A. d.; Gomez-Lor, B.; Gutierrez-Puebla, E.;
Iglesias, M.; Monge, M. A.; Proserpio, D. M.; Snejko, N. A Rare-Earth
MOF Series: Fascinating Structure, Efficient Light Emitters, and
Promising Catalysts. Cryst. Growth Des. 2008, 8, 378−380.
(25) Gan
́
dara, F.; Perles, J.; Snejko, N.; Iglesias, M.; Gom
́
ez-Lor, B.;
́
Gutier
́
rez-Puebla, E.; Monge, M. A. Layered Rare-Earth Hydroxides: A
Class of Pillared Crystalline Compounds for Intercalation Chemistry.
(7) Cui, Y.; Chen, B.; Qian, G. Lanthanide metal-organic frameworks
for luminescent sensing and light-emitting applications. Coord. Chem.
Rev. 2014, 273−274, 76−86.
Angew. Chem., Int. Ed. 2006, 45, 7998−8001.
́
(26) D’Vries, R. F.; Snejko, N.; Iglesias, M.; Gutierrez-Puebla, E.;
Monge, M. A. Ln-MOF Pseudo-Merohedral Twinned Crystalline
I
DOI: 10.1021/acs.inorgchem.8b00465
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Family as Solvent-Free Heterogeneous Catalysts. Cryst. Growth Des.
2014, 14, 2516−2521.
(27) Kobayashi, S.; Mori, Y.; Fossey, J. S.; Salter, M. M. Catalytic
Enantioselective Formation of C−C Bonds by Addition to Imines and
Hydrazones: A Ten-Year Update. Chem. Rev. 2011, 111, 2626−2704.
(28) Adams, J. P. Imines, enamines and oximes. Journal of the
Chemical Society, Perkin Transactions 1 2000, 125−139.
(29) Orito, K.; Hatakeyama, T.; Takeo, M.; Uchiito, S.; Tokuda, M.;
Suginome, H. Dimerization of anilines and benzylamines with
mercury(II) oxide-iodine reagent. Tetrahedron 1998, 54, 8403−8410.
(30) Nicolaou, K. C.; Mathison, C. J. N.; Montagnon, T. New
Reactions of IBX: Oxidation of Nitrogen- and Sulfur-Containing
Substrates To Afford Useful Synthetic Intermediates. Angew. Chem.,
Int. Ed. 2003, 42, 4077−4082.
(46) Qiu, X.; Len, C.; Luque, R.; Li, Y. Solventless Oxidative
Coupling of Amines to Imines by Using Transition-Metal-Free Metal−
Organic Frameworks. ChemSusChem 2014, 7, 1684−1688.
(47) Zeng, L.; Liu, T.; He, C.; Shi, D.; Zhang, F.; Duan, C. Organized
Aggregation Makes Insoluble Perylene Diimide Efficient for the
Reduction of Aryl Halides via Consecutive Visible Light-Induced
Electron-Transfer Processes. J. Am. Chem. Soc. 2016, 138, 3958−3961.
(48) Sun, D.; Ye, L.; Li, Z. Visible-light-assisted aerobic photo-
catalytic oxidation of amines to imines over NH2-MIL-125(Ti). Appl.
Catal., B 2015, 164, 428−432.
(49) Johnson, J. A.; Luo, J.; Zhang, X.; Chen, Y.-S.; Morton, M. D.;
Echeverría, E.; Torres, F. E.; Zhang, J. Porphyrin-Metalation-Mediated
Tuning of Photoredox Catalytic Properties in Metal−Organic
Frameworks. ACS Catal. 2015, 5, 5283−5291.
(50) Stobe, C.; Seto, R.; Schneider, A.; Lutzen, A. Synthesis, Chiral
̈
(31) Zhao, S.; Liu, C.; Guo, Y.; Xiao, J.-C.; Chen, Q.-Y. Oxidative
Coupling of Benzylamines to Imines by Molecular Oxygen Catalyzed
by Cobalt(II) β-Tetrakis(trifluoromethyl)-meso-tetraphenylporphyrin.
J. Org. Chem. 2014, 79, 8926−8931.
Resolution, and Absolute Configuration of C2-Symmetric, Chiral 9,9′-
Spirobifluorenes. Eur. J. Org. Chem. 2014, 2014, 6513−6518.
(51) Haas, G.; Prelog, V. Optisch aktive 9,9′-Spirobifluoren-Derivate.
Helv. Chim. Acta 1969, 52, 1202−1218.
́
(32) Esteruelas, M. A.; Honczek, N.; Olivan, M.; Onate, E.; Valencia,
̃
(52) Li, H.; Fang, X.; Ma, S.; Niu, Y.; Zhao, X.; Xu, J.; Duan, Z. A
two-dimensional porous framework: solvent-induced structural trans-
formation and selective adsorption towards malachite green. Dalton
Transactions 2017, 46, 8350−8353.
(53) Groom, C. R.; Bruno, I. J.; Lightfoot, M. P.; Ward, S. C. The
Cambridge Structural Database. Acta Crystallogr., Sect. B: Struct. Sci.,
Cryst. Eng. Mater. 2016, 72, 171−179.
(54) Czugler, M.; Stezowski, J. J.; Weber, E. Co-ordination-assisted
inclusion of neutral molecules by the racemic 9,9[prime or minute]-
spirobifluorene-2,2[prime or minute]-dicarboxylic acid host lattice. X-
Ray crystal structure of the dimethylformamide clathrate at 170 K. J.
Chem. Soc., Chem. Commun. 1983, 154−155.
(55) Blatov, B. A.; Shevchenko, A.; Proserpio, D. M. Applied
topological analysis of crystal structures with the program package
ToposPro. Cryst. Growth Des. 2014, 14, 3576−3586.
M. Direct Access to POP-Type Osmium(II) and Osmium(IV)
Complexes: Osmium a Promising Alternative to Ruthenium for the
Synthesis of Imines from Alcohols and Amines. Organometallics 2011,
30, 2468−2471.
(33) Ell, A. H.; Samec, J. S. M.; Brasse, C.; Backvall, J.-E.
Dehydrogenation of aromatic amines to imines via ruthenium-
catalyzed hydrogen transfer. Chem. Commun. 2002, 1144−1145.
(34) Hamid, M. H. S. A.; Slatford, P. A.; Williams, J. M. J. Borrowing
Hydrogen in the Activation of Alcohols. Adv. Synth. Catal. 2007, 349,
1555−1575.
(35) Jiang, L.; Jin, L.; Tian, H.; Yuan, X.; Yu, X.; Xu, Q. Direct and
mild palladium-catalyzed aerobic oxidative synthesis of imines from
alcohols and amines under ambient conditions. Chem. Commun. 2011,
47, 10833−10835.
́
(36) Samec, J. S. M.; Ell, A. H.; Backvall, J.-E. Efficient Ruthenium-
̈
Catalyzed Aerobic Oxidation of Amines by Using a Biomimetic
Coupled Catalytic System. Chem. - Eur. J. 2005, 11, 2327−2334.
(37) Zhu, B.; Lazar, M.; Trewyn, B. G.; Angelici, R. J. Aerobic
oxidation of amines to imines catalyzed by bulk gold powder and by
alumina-supported gold. J. Catal. 2008, 260, 1−6.
(38) Yamaguchi, K.; Mizuno, N. Efficient Heterogeneous Aerobic
Oxidation of Amines by a Supported Ruthenium Catalyst. Angew.
Chem., Int. Ed. 2003, 42, 1480−1483.
(39) Su, F.; Mathew, S. C.; Mohlmann, L.; Antonietti, M.; Wang, X.;
̈
Blechert, S. Aerobic Oxidative Coupling of Amines by Carbon Nitride
Photocatalysis with Visible Light. Angew. Chem., Int. Ed. 2011, 50,
657−660.
(40) Huang, H.; Huang, J.; Liu, Y.-M.; He, H.-Y.; Cao, Y.; Fan, K.-N.
Graphite oxide as an efficient and durable metal-free catalyst for
aerobic oxidative coupling of amines to imines. Green Chem. 2012, 14,
930−934.
́
(41) Perez, Y.; Aprile, C.; Corma, A.; Garcia, H. Comparison of the
Catalytic Activity of Gold Nanoparticles Supported in Ceria and
Incarcerated in Styrene Copolymer. Catal. Lett. 2010, 134, 204−209.
(42) Zhu, B.; Angelici, R. J. Non-nanogold catalyzed aerobic
oxidation of secondary amines to imines. Chem. Commun. 2007,
2157−2159.
(43) Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. Aerobic
Oxidation of Benzyl Amines to Benzyl Imines Catalyzed by Metal−
Organic Framework Solids. ChemCatChem 2010, 2, 1438−1443.
(44) Bermudez, J. M.; Menendez, J. A.; Arenillas, A.; Martinez-Palou,
R.; Romero, A. A.; Luque, R. Selectivity matters: Graphene oxide-
mediated oxidative coupling of benzylamine to N-benzylidine-1-
phenylmethanamine under microwave irradiation. J. Mol. Catal. A:
Chem. 2015, 406, 19−22.
(45) Ge, D.; Qu, G.; Li, X.; Geng, K.; Cao, X.; Gu, H. Novel
transition bimetal-organic frameworks: recyclable catalyst for the
oxidative coupling of primary amines to imines at mild conditions.
New J. Chem. 2016, 40, 5531−5536.
J
DOI: 10.1021/acs.inorgchem.8b00465
Inorg. Chem. XXXX, XXX, XXX−XXX