A palladium-carbon-connected organometallic framework and its catalytic application

Article abstract of DOI:10.1039/c9cc07829k

Herein, we report an organometallic framework (OMF) generated from a divergent tridentate arylisocyanide ligand and PdI₂ under solvothermal conditions. The obtained Pd-C bond-connected two-dimensional Pd-OMF was crystalline and porous. Moreover, it could be a highly active catalyst to promote the Suzuki-Miyaura cross-coupling reaction in a heterogeneous manner.

Full text of DOI:10.1039/c9cc07829k

Showcasing research from Yu-Bin Dong’s laboratory,
Department of Chemistry, Shandong Normal University,
Jinan, China.
As featured in:
Volume 55 Number 96 14 December 2019 Pages 14393–14544
A palladium–carbon-connected organometallic framework and
its catalytic application
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An organometallic framework (OMF) can be readily prepared via
self-assembly of PdI2 and a divergent tridentate arylisocyanide
ligand under solvothermal conditions. The obtained Pd–C
bond connected 2D Pd-OMF can act as a highly active catalyst
to promote the Suzuki–Miyaura cross-coupling reaction in a
heterogeneous way.
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A palladium–carbon-connected organometallic
framework and its catalytic application†
Cite this: Chem. Commun., 2019,
55, 14414
b
Ying Dong,a Jing-Jing Jv,a Xiao-Wei Wu,
Jing-Lan Kan,a Ting Lina and
a
Received 5th October 2019,
Accepted 17th October 2019
Yu-Bin Dong
*
DOI: 10.1039/c9cc07829k
rsc.li/chemcomm
Herein, we report an organometallic framework (OMF) generated from
In this contribution, we report an OMF which is generated from
a divergent tridentate arylisocyanide ligand and PdI2 under solvother- a divergent tridentate arylisocyanide ligand L and PdI2 under
mal conditions. The obtained Pd–C bond-connected two-dimensional solvothermal conditions. The obtained Pd-OMF (Pd1.5I3L) featured
Pd-OMF was crystalline and porous. Moreover, it could be a highly an extended two-dimensional (2D) OMF network that was driven
active catalyst to promote the Suzuki–Miyaura cross-coupling reaction by the Pd–C bond. Furthermore, it could be a highly active catalyst
in a heterogeneous manner.
to promote the Suzuki–Miyaura cross-coupling reaction under
mild conditions in a heterogeneous manner.
As two well-known types of porous polymeric materials, metal–
As shown in Scheme 1, the tridentate arylisocyanide ligand L
organic frameworks (MOFs)1 and covalent organic frameworks was prepared by POCl3-assisted dehydration of the triformamide
(COFs),2 have been garnering intense attention due to their intermediate A (ESI†). Upon mixing with PdI2 in dry CH3CN,
fascinating structures and potential applications in gas adsorp- Pd-OMF was obtained as micro-sized light-yellow crystals under
tion–separation,3 catalysis,4 medicine,5 and sensing.6
solvothermal conditions (100 1C, 72 h) in 76% yield (Scheme 1
By analogy with molecular chemistry,7 metal–carbon (M–C) and ESI†).
bond-driven polymeric porous species should also be present
widely, but such species are rare.8 Different from conventional
metal–heteroatom-driven MOFs, organometallic frameworks
(OMFs) are connected via metal–carbon linkages, although they
are all driven by metal–ligand interaction. In doing so, the
inherent functionalities shown by the porous polymeric mate-
rials derived from the inorganic, organometallic, and organic
building blocks will be displayed fully.
Isocyanide is a typical organometallic coordination group that
can bind various transition metal ions via strong s-donating and
weak p-back bonds, giving rise to various stable organometallic
complexes.9 It is similar to heteroatom ligands; isocyanide ligands
can also accommodate most metal coordination geometries and,
furthermore, propagate their geometry codes in a reversible way to
form regular structures.
a College of Chemistry, Chemical Engineering and Materials Science, Collaborative
Innovation Centre of Functionalized Probes for Chemical Imaging in Universities
of Shandong, Key Laboratory of Molecular and Nano Probes, Ministry of
Education, Shandong Normal University, Jinan 250014, P. R. China.
E-mail: yubindong@sdnu.edu.cn
b School of Chemical Engineering, Nanjing University of Science and Technology,
Nanjing, Jiangsu 210094, P. R. China
† Electronic supplementary information (ESI) available: The synthesis and addi-
tional characterization of L and Pd-OMF; catalytic procedures, GC analysis, the
Scheme 1 The synthesis of L and Pd-OMF. The Pd-OMF crystal structure
proposed mechanism, and crystallographic information for Pd-OMF. See DOI:
generated using Materials Studio and a sample photograph are also shown.
10.1039/c9cc07829k
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As indicated in the infrared (IR) spectra (Fig. 1a), the char- of Pd-OMF showed no obvious weight loss r350 1C in air,
acteristic sharp peak of –NRC at 2110 cmꢀ1 in L moved to indicating its good thermal stability (ESI†).
2183 cmꢀ1 after reaction with PdI2, indicating that the isocya-
Alternatively, structural modeling has been carried out with
nide donors coordinated with Pd(II) and the Pd–C-bonded Materials Studio v2018.12 The crystal structure of Pd-OMF was
Pd-OMF was formed.10 Evidence that Pd-OMF had been formed established based on powder X-ray diffraction (PXRD) data with
was further supported by 13C cross-polarization magic-angle Cu Ka radiation. As shown in Fig. 2, Pd-OMF was highly
spinning (CP/MAS) nuclear magnetic resonance (NMR) spectro- crystalline, and displayed prominent diffraction peaks at 2.31,
scopy. As shown in Fig. 1b, the peaks associated with the 4.71, 6.01, 6.91, 7.91, 8.71, and 9.61 in its PXRD pattern, which
aliphatic carbons of –CH3 and –CH(CH3)2 groups were located could be assigned to (100), (200), (210), (310), (101), (201), and
at 25.4 and 31.1 ppm, respectively. The signal at 170.4 ppm in L (211) facets, respectively (Fig. 2, black curve). The obtained
assignable to –NRC carbon was upfield-shifted to 120.1 ppm as PXRD pattern from Pd-OMF was completely different from its
a shoulder peak in Pd-OMF.10 This spectroscopic change corro- L and PdI2 precursors (ESI†), implying the formation of new
borated well with formation of the Pd–C bond. Besides, the crystalline species. To elucidate the structure of Pd-OMF and
broad low-intensity peak at B92.4 ppm was ascribed to acetylene to calculate the unit-cell parameters, two types of possible
carbons, and the broad signals at ca. 126.4, 136.0, 144.9 and 2D structures were generated. That is, eclipsed (AA) (Fig. 2a)
148.3 ppm were assigned unambiguously to aromatic carbons.
and staggered stacking (AB) models (Fig. 2b) were built and
The oxidation state of the Pd species in Pd-OMF was deter- optimized by the Forcite molecular dynamics module within
mined by X-ray photoelectron spectroscopy (XPS). As shown in Materials Studio. Different from the AA stacking model, the
Fig. 1c, the binding energies for Pd 3d5/2 and 3d3/2 were 338.0 experimental PXRD pattern for Pd-OMF matched well with the
and 343.1 eV respectively, suggesting that the Pd valence in simulated pattern of the staggered stacking (AB) model in the
Pd-OMF was bivalent.11 Elemental analysis confirmed the for- hexagonal P63/mmc space group. Pawley refinement showed a
mation of Pd-OMF with a formula of (C51H54I3N3Pd1.5)n (ESI†). In negligible difference between the simulated PXRD pattern
addition, inductively coupled plasma (ICP) analyses showed that and experimental patterns, and gave the optimized parameters
the Pd content in Pd-OMF was 12.46 wt% (calcd 12.78 wt% based a = b = 44.6 Å, c = 11.8 Å, a = b = 901, and g = 1201 (residuals
on C51H54I3N3Pd1.5).
Rwp = 4.52% and Rp = 3.17%, ESI†).
Scanning electron microscopy (SEM) showed that the as-
Structural analyses revealed that the PdI2 in Pd-OMF was
synthesized sample featured lamellar morphology (ESI†). SEM- linked together by L via a trans-diiodobis(isocyanide)–Pd link-
energy dispersive X-ray (EDX) mapping showed that the C, N, I age into a 2D OMF net extended in the crystallographic ab
and Pd were distributed evenly in the OMF matrix (ESI†). Notably, plane with a honeycomb-like cavity in which the opposite
attempts have been made by varying the synthetic conditions Pdꢁ ꢁ ꢁPd distance was B45 Å (Scheme 1). As shown in Fig. 2b,
(including different reaction temperatures, solvents, and metal :
ligand ratio) to grow single crystals of Pd-OMF of suitable size for
X-ray single-crystal analyses, but they have all failed. As indicated
in Scheme 1, the obtained crystals were too small to be used for
X-ray single-crystal analyses. Thermogravimetric analysis (TGA)
Fig. 2 The PXRD patterns of Pd-OMF: a comparison between the experi-
mental (black curves) and Pawley-refined (red curves) profiles, simulated
patterns for AA (a) and AB (b) stacking modes (blue curves) and refinement
differences (green curves). The insets are structural models of Pd-OMF
with AA (a) and AB (b) stacking styles. For the staggered structure,
Fig. 1 (a) IR spectra of L and Pd-OMF. (b) The 13C NMR spectrum of
Pd-OMF. (c) The XPS spectrum for Pd species in Pd-OMF.
alternating yellow layers with undefined atoms are presented for better
visibility.
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structural AB-modeling revealed that these 2D nets stacked out the reaction. K2CO3 was better than the other inorganic and
together along the crystallographic c axis in an AB-fashion to organic bases (Table 1, entries 8–13). Furthermore, when the
generate rhombic channels with a reduced pore size (opposite reaction was carried out with less catalyst loading, 0.1 (Table 1,
Pdꢁ ꢁ ꢁPd distance at B28 Å) due to their staggered arrangement. entry 14) or 0.5 (Table 1, entry 15) instead of 0.7 mol%, the coupled
Transmission electron microscopy (TEM) also showed product was obtained at lower (75% and 93%) yields. Conversely, the
Pd-OMF possessing a 2D layered structure with an interlayer reaction temperature appeared to be crucial for catalytic efficiency.
distance of 5.9 Å (ESI†), which was consistent with its structural As indicated in Table 1, the catalytic activity of Pd-OMF was largely
modeling.
diminished at lower temperature (Table 1, entries 16 and 17). In
N2 sorption undertaken at 77 K provided a Brunauer–Emmett– addition, shortening the reaction time led to reduced (75–86%)
Teller (BET) surface area of 205.80 m2 gꢀ1 for Pd-OMF. The yields under the given conditions (Table 1, entries 18 and 19). We
observed type-IV isotherm was indicative of its mesoporous did not observe any desired product in the absence of Pd-OMF even
characteristics. Pore-size distribution based on nonlocal density at 70 1C at 8 h (Table 1, entry 20). Based on these observations, the
functional theory (NLDFT) was done. It revealed that Pd-OMF optimal conditions for the model cross-coupling reaction were set
displayed a pore-size-distribution centered at B19 ꢂ 1 Å, which as 0.7 mol% of Pd, K2CO3 (base), MeOH (solvent), 70 1C, and 8 h
was in good agreement with its simulated structure (ESI†).
(reaction time) (Table 1, entry 8).
Molecular isocyanide–Pd complexes have been reported to
As shown in Fig. 3a, no further reaction occurred after
be a highly efficient class of catalyst in various C–C coupling ignition of the reaction at 4.0 h when it reached B75% yield.
reactions, but in a homogeneous way.13 By means of an OMF Gas chromatography (GC) monitoring indicated that the yield
platform, the isocyanide–Pd species herein was loaded and was unaltered during the prolonged reaction time. This sug-
fixed in an orderly manner within the polymeric OMF. There- gested that Pd-OMF was a typical heterogeneous catalyst and,
fore, its heterogeneous catalysis for recyclable C–C coupling as such, it could be reused, and its catalytic yield was r92%
should be feasible.
after five runs (Fig. 3b and ESI†). After multiple catalytic cycles,
The catalytic activity of Pd-OMF for the Suzuki–Miyaura cross- no valence change of the Pd species was detected based on the
coupling reaction was examined, in which the coupling between XPS spectrum (ESI†). Inductively coupled plasma (ICP) analyses
bromobenzene and phenylboronic acid was chosen as the model showed that the Pd amount in Pd-OMF was 12.33 wt%, suggest-
reaction. As shown in Table 1, solvent screening revealed MeOH to ing that only B1 wt% Pd leached after five runs. Hence, the
be the best solvent among toluene, THF, dioxane, DMF, isopropyl arylisocyanide is an ideal class of organic ligand that can firmly
alcohol (IPA), acetone, and MeCN (Table 1, entries 1–8). In addi- bind Pd(II) ions via M–C bonds and, furthermore, incorporate
tion, the bases K2CO3, K3PO4, Na2CO3, KOH, triethylamine (TEA), them into the extended OMFs. The measured PXRD pattern,
and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), were used to carry SEM, and energy-dispersive X-ray-SEM spectra demonstrated
that the structural integrity, crystallinity, morphology, and uni-
form elemental distribution of Pd-OMF were well maintained
after multiple catalytic use (ESI†).
Table 1 Optimization of the model Suzuki–Miyaura coupling reaction
between bromobenzene and phenylboronic acida
Notably, Pd-OMF was tolerant to a wide range of substrates
with different functional groups (–NO2, –COCH3, –OCH3, –OH,
–CH3, –CO2Me, –CN) at different substituted positions. As shown
in Table 2, phenyl bromides with electron-donating and electron-
withdrawing groups afforded cross-coupling products with excel-
lent yields (97–99%, entries 1–9). Compared with phenyl bromides,
phenyl iodides were more active. For example, the coupling yield
Entry Pd (mol%) Base
Sol.
T (1C) t (h) Yieldb (%)
1
2
3
4
5
6
7
8
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.1
0.5
0.7
0.7
0.7
0.7
—
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K3PO4
Na2CO3 MeOH
KOH
TEA
DBU
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Toluene 70
THF 70
Dioxane 70
DMF
IPA
Acetone 70
MeCN
MeOH
MeOH
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
8
4
6
8
75
65
20
86
83
23
24
499
97
95
94
33
23
64
93
43
83
75
86
—
70
70
70
70
70
70
70
70
70
70
70
rt
50
70
70
70
9
10
11
12
13
14
15
16
17
18
19
20
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
Fig. 3 (a) Leaching test for the model Suzuki–Miyaura cross-coupling
reaction. (b) Yields of diphenyl over repeated runs for the model Suzuki–
Miyaura cross-coupling reaction. After each run, Pd-OMF was recollected
via centrifugation, washed with MeCN (3 ꢃ 2 mL) and CHCl3 (3 ꢃ 2 mL),
and dried at 110 1C for 24 h under vacuum, and then reused for the next
catalytic run under identical reaction conditions.
a
Reaction conditions: bromobenzene (1.0 mmol), phenylboronic acid
b
(1.1 mmol), base (2.0 mmol), solvent (2 mL), in N2. Yields were
determined by gas chromatography (ESI).
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Table 2 Cross-coupling reactions of various PhX and PhB(OH)2 mole-
cules catalyzed by Pd-OMFa
In summary, we prepared a Pd–C bond-connected OMF and,
furthermore, introduced the Pd–isocyanide species into an
OMF network. The obtained Pd-OMF exhibited high catalytic
activity to promote the Suzuki–Miyaura cross-coupling reaction
in a heterogeneous way. We have expanded the research field of
polymeric porous materials driven by metal–carbon bonding
interactions.
We are grateful for financial support from NSFC (21971153,
21671122, 21802091), Taishan Scholar’s Construction Project,
and Changjiang Scholar Project at SDNU.
Entry
R1
X
R2
t (h)
Yieldb (%)
1
H
Br
Br
Br
Br
Br
Br
Br
Br
Br
I
I
I
I
I
I
I
I
I
I
I
I
H
H
H
H
H
H
H
H
8
8
8
8
8
8
8
8
8
7
7
7
7
7
7
7
7
8
8
8
8
8
8
8
8
99
99
99
99
99
97
99
99
99
99
99
99
99
99
99
99
99
99
499
499
96
6
2
4-NO2
4-COCH3
4-OCH3
3-OH
2-CN
2-CH3
3-NO2
H
3c
4
5
6
7
8
Conflicts of interest
9
4-OCH3
H
H
H
H
H
H
H
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
H
There are no conflicts of interest to declare.
2-OCH3
2-CF3
3-CH3
3-NO2
4-OCH3
4-CN
4-CO2CH3
H
Notes and references
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H
2-OCH3
4-F
3-OCH3
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H
H
3-NO2
4-CN
H
H
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Cl
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(2 mmol, 0.276 g), Pd-OMF (0.7 mol% Pd equiv.), methanol (2 mL), 70 1C,
c
in N2. b Yields were determined by GC (ESI). 40-Bromoacetophenone and
phenylboric acid coupling gave 76% yield in the presence of molecular
(AdNC)2PdCl2 catalyst (PhX, 1 mmol; PhB(OH)2, 1.2 mmol; Cs2CO3,
2.2 mmol; (AdNC)2PdCl2, 0.05 mmol; refluxed in dioxane for 18 h).14
based on iodobenzene and 2-, 4- or 3-substituted phenyl iodides
was 99% even at 7 h (Table 2, entries 10–17). For coupling with
substituted phenylboronic acids, phenyl iodides also afforded
excellent yields of 96% to 499% but in 8 h (Table 2, entries 18–21).
In contrast, Pd-OMF could not effectively activate ArCl-based
Suzuki–Miyaura reactions. For example, the coupling of phenyl-
boronic acid with chlorobenzene or trifluoromethylchloroben-
zene only gave 6% or 9% yield under given conditions (Table 2,
entries 22 and 23). The coupling of nitro- or cyano-substituted
phenyl chlorine with phenylboronic acid, however, provided
moderate (55% or 45%) yields (Table 2, entries 24 and 25).
The possible mechanism of the Pd-OMF-catalysed Suzuki–
Miyaura coupling reaction was believed to be the same as that of
molecular isocyanide–Pd-promoted coupling reactions in solution
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4191–4193.
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