Pd(II)-Metalated and l-Proline-Decorated Multivariate UiO-67 as Bifunctional Catalyst for Asymmetric Sequential Reactions

Article abstract of DOI:10.1007/s10562-021-03719-0

The construction of a multifunctional catalyst for multistep sequentialtandem reactions at the molecular level faces a formidable challenge. Multivariate (MTV)-MOFs can provide a facile and tunable platform for rationally designing such multifunctional catalysts via grafting different catalytic groups on the bridging ligands. However, the related investigations are still limited. Here, Pd(II) and l-proline are metalated and decorated to organic linkers, respectively, to build a MTV-MOF, which is then successfully applied to sequential Suzuki Coupling/asymmetric Aldol reactions with satisfied coupling performance (yields up to 99%) and good enantioselectivities (ee_anti up to 98%). Inductively coupled plasma optical emission spectrometer (ICP-OES) measurements of the supernatant and hot leaching test suggest the heterogeneous nature of the catalyst. Macrosubstrate tests verify that the reaction occurs inside the pores of the MOF. The heterogeneous catalyst can maintain structural stability and catalytic activity within three cycles. Graphic Abstract: Versatile Pd(II) and l-proline were metalated and decorated, respectively, into stable UiO-67 to construct bifunctional and heterogeneous multivariate MOF catalyst, which displayed efficient and recyclable catalytic activity in sequential Suzuki Coupling/asymmetric Aldol reactions.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-021-03719-0

Catalysis Letters
https://doi.org/10.1007/s10562-021-03719-0
Pd(II)‑Metalated and l‑Proline‑Decorated Multivariate UiO‑67
as Bifunctional Catalyst for Asymmetric Sequential Reactions
Lin Cheng1 · Liumei Cao · Hao Ren · Qiaoqiao Guo · Huifang Deng · Yiming Li
1
1
1
1
1
Received: 26 May 2021 / Accepted: 20 June 2021
©
The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2021
Abstract
The construction of a multifunctional catalyst for multistep sequential\tandem reactions at the molecular level faces a
formidable challenge. Multivariate (MTV)-MOFs can provide a facile and tunable platform for rationally designing such
multifunctional catalysts via grafting diꢀerent catalytic groups on the bridging ligands. However, the related investigations
are still limited. Here, Pd(II) and l-proline are metalated and decorated to organic linkers, respectively, to build a MTV-
MOF, which is then successfully applied to sequential Suzuki Coupling/asymmetric Aldol reactions with satisꢁed coupling
performance (yields up to 99%) and good enantioselectivities (ee up to 98%). Inductively coupled plasma optical emission
anti
spectrometer (ICP-OES) measurements of the supernatant and hot leaching test suggest the heterogeneous nature of the
catalyst. Macrosubstrate tests verify that the reaction occurs inside the pores of the MOF. The heterogeneous catalyst can
maintain structural stability and catalytic activity within three cycles.
Graphic Abstract
Versatile Pd(II) and l-proline were metalated and decorated, respectively, into stable UiO-67 to construct bifunctional and
heterogeneous multivariate MOF catalyst, which displayed eꢂcient and recyclable catalytic activity in sequential Suzuki
Coupling/asymmetric Aldol reactions.
Keywords Chiral proline · UiO-67 · Heterogeneous catalyst · Bifunctional catalyst · Asymmetric sequential reactions
*
Lin Cheng
lcheng@seu.edu.cn
1
School of Chemistry and Chemical Engineering, Southeast
University, Nanjing 210009, People’s Republic of China
Vol.:(0
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L. Cheng et al.
1
Introduction
Unfortunately, the investigation of multifunctional MTV-
MOFs with mixed ligands on sequential/tandem catalysis
has seldom reported [45–48, 69–74], and the rare exam-
ples were mainly focused on the cascade reactions cata-
lyzed via mixed metallosalen linkers with diꢀerent metal
central sites [45–48].
Sequential reactions, combining multi-step organic syn-
thetic procedures into one with a single catalyst, have
aroused considerable interest because they can minimize
chemical wastes, lower operation time, and avoid the isola-
tion and puriꢁcation of reaction intermediates [1, 2]. The
single catalyst usually needs to own multifunctional active
sites, achieving each step in sequence. However, the design
and construction of such a multifunctional catalyst with
two or more active sites at the molecular level is still a
huge challenge owing to rapidly increased molecular com-
plexity [3–5], high stability requirements of active sites
under the reaction conditions of each catalytic step and
the avoidance of the deactivation between incompatible
active sites, such as acid–base [5–13]. Thus, looking for a
universal strategy to unit diꢀerent catalytic sites into a sta-
ble platform becomes particular important. Metal–organic
frameworks (MOFs) can be regarded as an ideal and tun-
able platform for rationally designing heterogeneous
multi-functional catalysts via precisely functionalizing
metal nodes, organic linkers and encapsulated active spe-
cies [14–23]. Compared with versatile and diverse organic
ligands, the selection of open metal sites and encapsulated
catalysts is always limited. Coordinately unsaturated metal
sites are usually only used as Lewis acid catalysts [24–28],
and immobilized species are often restricted to stable or
large-size catalysts, such as metal and metal oxide nano-
particles, polymers, enzymes, etc., which are diꢂcult to
escape from the channels/holes of MOFs during the cata-
lytic process [17]. For soluble or small molecules, such as
metal salts and organic small molecules, which are widely
applied as homogeneous catalysts in various reactions, it’s
hard to be introduced into MOFs as open metal sites or
encapsulated catalysts. Fortunately, these organic small
molecules can be easily decorated to the desired linkers of
MOFs via multifarious organic synthetic methods [24–28],
and metal ions can also be metalated into programmed
coordinated sites of organic ligands [29–39]. Besides, the
linkers can be easily modiꢁed via tailored chiral groups to
construct chiral MOF catalysts and yet they have seldom
been applied in asymmetric sequential/tandem reactions
Pd(II) salts, including PdCl2 and Pd(OAC)2, are a kind of
famous catalysts for organic transformation. Because of their
high price and limited resource, the full utilization of each
Pd(II) catalytic site becomes a signiꢁcant yet challenging
task [9, 71]. The immobilization of isolated active single-
site Pd(II) into the bipyridyl-containing ligands of MOFs via
metalation interaction has oꢀered a promising solution [9,
36, 75–77]. However, to our knowledge, Pd(II)-metalated
MOFs have yet to be employed in asymmetric sequential/
tandem reactions. Meanwhile, l-proline, a well-known privi-
lege catalyst, has been successfully decorated to MOFs via
coordination to open metal sites or grafting to organic link-
ers to construct chiral heterogeneous catalysts [44, 78–94].
Herein, UiO-67 with excellent chemical and thermal sta-
bility was selected as the parent MOF. PdCl2 and l-proline
were metalated and decorated, respectively, to UiO-67 via
mixed-ligand strategy, resulting in a MTV-MOF (Scheme 1).
The heterogeneous bifunctional catalyst was further applied
in sequential Suzuki Coupling/asymmetric Aldol reactions,
achieving satisꢁed coupling performance (yield up to 99%)
and enantioselectivities (eeanti up to 98%). To our knowl-
edge, this was the ꢁrst example of MTV-MOFs, dual-func-
tionalized by metal salts and organic catalysts via mixed
ligand strategy, which was applied in asymmetric sequential
reactions.
2 Results and Discussion
2.1 Synthesis and Characterization
of the Bifunctional Catalyst
Three organic ligands with similar length and coordination
modes, were employed to construct the MTV-MOF, UiO-67-
Pd-pro (Scheme 1), in which l-proline decorated ligand was
fabricated via four-step process (Scheme S1), and Pd(II)-
metalated ligand was synthesized by a bipyridine-based
ligand, 2,2’-bipyridine-5,5’-dicarboxylic acid, with PdCl2,
via three-step synthesis (Scheme S2). UiO-67-Pd and UiO-
67-pro, used in controlled experiments, were synthesized via
the similar procedure to that of UiO-67-Pd-pro.
[
40–48].
Multivariate (MTV)-MOFs, containing more than one
organic linker with similar length, geometry and connec-
tivity within a single framework, have been extensively
investigated [49–74] since Yaghi and co-workers success-
fully introduced eight distinct functionalities in a single
MOF via mixed-linker strategy [49]. The combination
of two or more functional groups, grafted onto diꢀerent
bridging ligands, promotes MTV-MOFs to be reliable
candidates for catalyzing multistep sequential reactions.
Powder X-ray diꢀraction (XRD) pattern of UiO-67-
Pd-pro was identical to that of parent UiO-67 (Fig. 1),
1
indicating that it was isostructural to UiO-67. H-NMR
spectroscopy of UiO-67-Pd-pro, after treated by dilute
HF acidlysis, was performed to examine the ratio of
three ligands. The ratio of l-proline decorated ligand,
1
3

Pd(II)-Metalated and l-Proline-Decorated Multivariate UiO-67 as Bifunctional Catalyst…
Scheme 1 Construction of multivariate UiO-67-Pd-pro via mixed-linker strategy and its application in sequential Suzuki Coupling/asymmetric
Aldol reactions
7
6
5
4
3
2
1
00
00
00
00
00
00
00
0
recycled UiO-67-Pd-pro after 3 times
activated UiO-67-Pd-pro
UiO-67-Pd-pro
2
.0
1.5
.0
0.5
.0
UiO-67-Pd
1
UiO-67-pro
UiO-67
UiO-67-Pd-pro
synthesized UiO-67
0
0
2
4
6
8
10
Pore diameter (Å)
-
100
simulated UiO-67
0
.0
0.2
0.4
0.6
0.8
1.0
P/P
0
5
10
15
20
25
30
35
2
Theta (degree)
Fig. 2 N adsorption–desorption isotherms of UiO-67 and UiO-67-
2
Pd-pro
Fig. 1 PXRD patterns of the synthesized samples
In IR spectra of UiO-67-Pd-pro (Fig. S3), the peaks at
−
1
Pd(II)-metalated linker and 1,1’-biphenyl-4,4’-dicarbo-
xylic acid was 1:1.4:2.75 (Fig. S2), suggesting the suc-
cessful synthesis of multivariate UiO-67 via mixed-linker
strategy.
650 and 769 cm can be ascribed to stretching vibration of
−
1
Zr–O bonds [44]. Two strong peaks at 1260 and 1590 cm
corresponded to the characteristic of C–N and C=O bonds,
respectively [95]. Moreover, the characteristic peak at
−
1
The N adsorption–desorption isotherms of UiO-67 and
3400 cm belonged to the vibration of N–H bond [96]. CD
spectrum of UiO-67-Pd-pro was also measured, in which
there was a negative Cotton eꢀect at 222 nm and a positive
cotton eꢀect at 252 nm (Fig. S4), exhibiting the structural
chirality of bulk samples [97–100].
2
UiO-67-Pd-pro displayed typical Type I gas adsorption
behaviour (Fig. 2). The BET speciꢁc surface area and pore
2
−1
volume of UiO-67-Pd-pro were, respectively, 1207.6 m g
3
−1
and 0.58 cm g , lower than those of pure UiO-67 (2244.8
2
−1
3
−1
m g and 1.07 cm g ). Meanwhile, compared with the
parent UiO-67, the pore size distribution of UiO-67-Pd-pro
slightly decreased from 4.04 to 4.01 Å. These phenomena
signiꢁed that the cavities of UiO-67-Pd-pro were partially
blocked by large l-proline decorated and Pd(II)-metalated
ligands [36].
X-ray photoelectron spectroscopy (XPS) spectra sug-
2
+
gested the Pd element in UiO-67-Pd-pro was Pd with two
obvious peaks at 337.5 and 342.8 eV [101, 102], and no
0
Pd peaks were found (Fig. S5). Scanning electron micros-
copy (SEM) revealed that the as-prepared UiO-67-Pd-pro
exhibited a uniform and regular octahedral morphology with
1
3

L. Cheng et al.
crystal size of 600–800 nm (Fig. S6). Transmission Elec-
tron Microscope (TEM) was further utilized to investigate
the detailed structure information of the catalyst (Fig. 3).
The results showed that no aggregated Pd particles were
distinctly observed (Fig. 3a, b), which was in accordance
with the conclusion of XPS. Moreover, in EDS mapping of
UiO-67-Pd-pro, Cl, Pd and Zr displayed a consistent and
even distribution (Fig. 3d–f), which further suggested the
existence of Pd(II)-metalated ligands. Thermal stability of
UiO-67-Pd-pro was tested via TGA and the sample remained
intact till 280 °C (Fig. S7).
(Table 1, entries 1–4). Thus, K CO was used as the inor-
2
3
ganic base. When the reaction temperature decreased from
90 to 50 °C, the yield was obviously reduced from 99 to 51%
(Table 1, entries 2 and 5). Besides, the yield was only 45%
and 87%, when the reaction was stopped after 8 and 12 h,
respectively (Table 1, entries 6 and 7). The catalyst amount
was reduced by half to 10 mg, and the yield was decreased
to 82% (Table 1, entry 8). Comparison tests were performed,
using UiO-67, UiO-67-pro or none as the catalyst (Table 1,
entry 9–11), and there was no signs of conversion, suggest-
ing that the metalated PdCl in the MTV-MOF acted as the
2
active sites.
2
.2 Sequential Suzuki Coupling/Asymmetric Aldol
Homogeneous PdCl and Pd(OAC) , with the same
2
2
Reactions
amounts of Pd(II) sites, were employed as comparative
catalysts, resulting in lower yields with 63% and 84%,
respectively (Table 1, entries 12, 13), which may be attrib-
The coexistence of Pd(II) and l-proline in UiO-67-Pd-pro
made it have the potential in Suzuki Coupling/asymmetric
Aldol sequential reactions as a bifunctional catalyst. The
catalytic sequence can be divided into two steps: Suzuki
Coupling (step I) and asymmetric Aldol reaction (step II).
We then explored the optimal conditions of each step in
sequence.
2
+
uted to the site-isolation of Pd centers in UiO-67-Pd-pro
2
+
and protection of MOF to avoid Pd deactivation under air
atmosphere [36].
As a result, UiO-67-Pd-pro exhibited outstanding cata-
lytic yield of Suzuki coupling (99%) with K CO as inor-
2
3
ganic base at 90 °C for 16 h.
For Suzuki Coupling, the reaction of bromobenzene and
For asymmetric Aldol reaction, 4-phenylbenzaldehyde
and cyclopentanone were selected as model substrates. The
eꢀect of solvent, catalyst amount and reaction temperature
was investigated. Firstly, toluene, EtOH, CH Cl , DMSO
4
-formylphenylboronic acid was selected as the template
reaction to investigate the optimal catalytic conditions, such
as base, temperature, reaction time and catalyst amount.
As shown in Table 1, we ꢁrst studied the eꢀect of inor-
ganic base on the catalytic activity. Compared to Na CO ,
2
2
and solvent-free, were employed as the reaction solvent,
suggesting that DMSO was the optimal solvent with the
2
3
KF and CsF, K CO was the best inorganic base (99%)
higher yield and ee value (Table 2, entries 1–5). When
2
3
anti
Fig. 3 a–c TEM images, d Cl, e Pd, f Zr distribution in EDX elemental mapping images of UiO-67-Pd-pro
1
3

Pd(II)-Metalated and l-Proline-Decorated Multivariate UiO-67 as Bifunctional Catalyst…
Table 1 Exploration on reaction conditions of Suzuki cross-coupling reaction
o
Yield (%)a
Entry
Catalyst
mg
Base
T ( C)
t (h)
1
2
3
4
5
6
7
8
9
1
1
1
1
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67
20
20
20
20
20
20
20
10
20
20
0
Na CO
90
90
90
90
50
90
90
90
90
90
90
90
90
16
16
16
16
16
8
12
16
16
16
16
16
16
85
99
80
59
51
45
87
82
n.d
n.d
n.d
63
84
2
3
K CO
2
3
KF
CsF
K CO
2
3
3
3
3
3
3
3
3
3
K CO
2
K CO
2
K CO
2
K CO
2
0
1
2
3
UiO-67-pro
none
PdCl2
K CO
2
b
K CO
2
1.8
2.2
K CO
2
Pd(OAc)2
K CO
2
Reaction conditions: 4-bromobenzaldehyde (1 mmol), phenylboronic acid (1.5 mmol), base (2 mmol), toluene (8 mL) and catalyst
a
Isolate yield
No catalyst
b
Table 2 Exploration on reaction conditions of asymmetric Aldol reaction
Entry
Catalyst
mg
Solvent
T (°C)
Yield (%)a
syn:antib
eeanti (%)b
1
2
3
4
5
6
7
8
9
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67-Pd-pro
UiO-67
20
20
20
20
20
10
20
20
20
20
Toluene
EtOH
Free
20
20
20
20
20
20
40
-20
20
20
67
75
59
83
87
63
92
79
n.d
n.d
52:48
68:32
55:45
66:34
66:34
64:36
77:23
53:47
n.d
1
1
4
10
13
23
4
69
n.d
n.d
CH Cl
2
2
DMSO
DMSO
DMSO
CH Cl
2
2
CH Cl
2
2
2
1
0
UiO-67-Pd
CH Cl
n.d
2
Reaction conditions: biphenyl-4-carbaldehyde (1 mmol), cyclopentanone (0.88 mL), solvent (2 mL), 4 days and catalyst
a
Isolate yield
b
Determined by chiral HPLC (chiral AD-H column, 1 mL min−1, n-hexane: isopropanol=90:10)
1
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L. Cheng et al.
CH Cl was utilized as the solvent, the yield and ee value
The optimal conditions were ꢁnally popularized to other
substituted substrates for asymmetrical sequential reactions
(Table 3). It can be easily seen that regardless of the sub-
stituents, UiO-67-Pd-pro showed excellent catalytic activ-
ity (94–99%) in the Suzuki coupling reaction. Although the
yield of Aldol reaction was moderate, the catalyst exhibited
2
2
anti
were slightly lower than those of DMSO (Table 2, entries
4
, 5). Secondly, while the catalyst amount was reduced by
half to 10 mg, the yield was only 63%, signiꢁcantly lower
than that of 20 mg catalyst (87%) (Table 2, entries 5 and 6).
Finally, considering the important inꢃuence of temperature
on diastereoselectivity and enantioselectivity of asymmetric
catalysis, the reaction was performed at 40 °C. The yield was
satisꢁed enantioselectivities with ee values up to 98%.
anti
increased to 92%, but the ee value was only 4% (Table 2,
2.3 Heterogeneous and Recycling Experiments
anti
entry 7). Thus, we tried to low the temperature. Because
of high freezing point of DMSO (18.4 °C), CH Cl with
In order to verify the heterogeneous nature of the catalyst,
two experiments were performed. First, after the model
sequential reaction was ꢁnished, the supernatant was meas-
ured via ICP-OES and the results showed that only Zr and
Pd traces (<0.20 ppm) were found, hinting that there was
2
2
the second best catalytic performances was selected as the
solvent at -20 °C, resulting in slightly lower yield (79%)
but greatly improved ee value (69%). Therefore, CH Cl ,
anti
2
2
−
20 °C, 20 mg catalyst were chosen as the optimal condi-
tions for the asymmetric Aldol condensation reaction.
As UiO-67 and UiO-67-Pd were, respectively, used to
replace UiO-67-Pd-pro as the catalyst, there was no product
observed (Table 2, entries 9, 10), indicating that l-proline
in the MTV-MOF acted as the catalytic sites of asymmetric
Aldol reactions.
No Filtrating
1
00
Filtrating experiment
8
6
4
2
0
0
0
0
0
Remarkably, compared with other l-proline functional-
ized MOFs, UiO-67-Pd-pro exhibited superior performances
for catalyzing asymmetric Aldol reactions (Table S1).
After the optimal conditions of Suzuki Coupling (step I)
and asymmetric Aldol reaction (step II) were conꢁrmed, the
model sequential reaction was further performed. Consider-
ing the negative eꢀect of inorganic base (K CO ) and solvent
2
3
(
toluene) in step I, on the performance of step II, the residual
K CO was neutralized with diluted HCl and the solvent
0
4
8
12
16
2
3
was also removed via rotary vacuum evaporation after the
Time (h)
coupling was over.
Fig. 4 Hot leaching test of Suzuki coupling reaction
Table 3 Substrate exploration of sequential Suzuki coupling/asymmetric Aldol reactions
a
a
syn:antib
eeantib (%)
Entry
R
X
RCHO yield (%)
Aldol Yield (%)
1
2
3
4
5
H
4-CH3
4-CH O
4-CN
Br
I
I
I
Br
99
96
94
98
99
79
65
69
83
88
56:44
89:11
83:17
50:50
2:98
68
75
86
56
98
3
4-NO2
a
Isolate yield
b
Determined by chiral HPLC (chiral AD-H column, 1 mL min−1, n-hexane: isopropanol=90:10)
1
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Pd(II)-Metalated and l-Proline-Decorated Multivariate UiO-67 as Bifunctional Catalyst…
almost no leaching of Zr and Pd elements from UiO-67-
Pd-pro during the catalysis process. Second, a hot leach-
ing test was investigated (Fig. 4). After the model Suzuki
coupling reaction was carried out for 4 h, the solid catalyst
was separated by hot ꢁltration, and then the reaction was
continued. It was found that the yield of coupling reaction
did not increase with the increase of reaction time, while
the reaction continued to proceed when the catalyst wasn’t
separated from the system.
In order to ꢁnd out whether the reaction occurred on the
surfaces or inside the pores of the catalyst, macrosubstrate
experiments were performed (Table S2). A bulk aldehyde
with the size of 9 Å×14 Å, far larger than the pore size of
UiO-67-Pd-pro (4 Å), was used to Aldol reaction. No cor-
Fig. 6 Compare the catalytic performances of two diꢀerent Pd cata-
responding microaldol product was observed via HPLC test
after 2 weeks of reaction, while the aldol product achieved
lysts
5
1% yield for 48 h by the use of the homogeneous catalyst,
l-proline. This result suggested that the reaction took place
inside the pores with the use of UiO-67-Pd as the catalyst.
Recycling experiments showed that the catalytic activity
and enantioselectivity of the catalyst did not have a signiꢁ-
cant decrease within three catalytic cycles (Fig. 5). Moreo-
ver, the catalyst maintained structural stability after three
cycles, measured via XRD (Fig. 1a). Thus, the UiO-67-Pd-
pro catalyst had excellent cycle stability.
it can be clearly observed that the catalytic performance of
UiO-67-Pd-pro was obviously superior to that of Pd@NH -
2
UiO-66(pro)-1 when the reaction time reached 16 h. With the
increase of time, the catalytic performance of UiO-67-Pd-pro
was in equilibrium, which was mainly attributed to the high
utilization rate of UiO-67-Pd-pro for Pd ion coordination.
Pd@NH -UiO-66(pro)-1 has a slight increase, mainly due
2
to Pd nanoparticles aggregation resulting in less active sites
exposure.
2.4 Comparison of Catalytic Performance Between
UiO‑67‑Pd‑pro and Pd@NH ‑UiO‑66(pro)‑1
3 Conclusions
2
In order to prove that Pd2+ in synthetic catalyst UiO-67-Pd-pro
has better catalytic performance in Suzuki cross-coupling reac-
tion, we compared it with the previously reported elemental
In summary, we have successfully designed and fabricated
a Pd(II)-metalated and l-proline-decorated chiral MTV-
MOF via mixed-linker strategy. The combination of Pd(II)
and l-proline bifunctional active sites promoted the MOF
to be an eꢀective heterogeneous catalyst for Suzuki Cou-
pling/asymmetric Aldol sequential reactions. The catalyst
exhibited remarkably higher performance than its homoge-
Pd catalyst Pd@NH -UiO-66(pro)-1 [44]. As shown in Fig. 6,
2
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
Yield (%)
ee
value (%)
anti
neous counterpart, PdCl . ICP-OES measurements of the
2
supernatant and hot leaching test showed the heterogene-
ous nature of the catalyst. Macrosubstrate tests also veriꢁed
that the reaction occurred inside the pores of the MOF. The
catalyst can be recycled for 3 times without obvious struc-
tural change and loss of catalytic activity. This work may
provide a simple but eꢂcient strategy to design multifunc-
tional MTV-MOF catalysts for sequential/tandem reactions
via mixed-linker strategy.
4
Experimental
1
2
3
4.1 Materials
Recycling Number
4
-Methoxyphenylboronic acid, Pd(PPh ) , N-Boc-
3 4
Fig. 5 Recycling experiments of UiO-67-Pd-pro about sequential
Suzuki Coupling/asymmetric Aldol reactions
l-proline, 2,2’-bipyridine-5,5’-dicarboxylic acid, ZrCl ,
4
1
3

L. Cheng et al.
PdCl (CH CN) , ethyl 4-bromo-3-aminobenzoate and
0.026 mmol) were added in 4 mL DMF. The subsequent
steps of reaction and washing were the same as the prepara-
tion of UiO-67.
2
3
2
2
,2’-biphenyl-5,5’-dicarboxylic acid (H bpdc) were obtained
2
from Sinopharm Chemical Reagent Co. Ltd. Catalytic sub-
strates were bought from Aladdin. Isopropyl alcohol and
n-hexane for HPLC were acquired from Tedia and Merck,
respectively. All the reagents were directly used as received
without further puriꢁcation.
4.4 General Catalytic Procedures
4
.4.1 General Procedure for Suzuki Coupling Reaction
Catalyzed by UiO‑67‑Pd‑pro
4.2 Synthesis of the Ligands
In a round-bottom ꢃask, aryl halide (1 mmol), 4-formyl-
phenylboronic acid (225 mg, 1.5 mmol), UiO-67-Pd-pro
l-proline decorated ligand, R-2-(pyrrolidine-
-carboxamido)-[1,1’-biphenyl]-4,4’-dicarboxylic acid
2
(
20 mg), and K CO (276 mg, 2 mmol) were added into
2 3
[
79], and Pd(II)-metalated ligand, Pd(2,2’-bipyridine-5,5’-
toluene (8 mL). The reaction mixture was stirred in air
atmosphere at 90 °C for 16 h. The reaction products were
monitored by TLC to determine whether the substrate was
completely consumed. After centrifugation, the solvent was
removed by rotary evaporation and puriꢁcation by chroma-
tography column, giving a white solid product.
dicarboxylic acid)Cl [75], were synthesized according to
2
the similar procedures previously reported and the detailed
processes were shown in supporting information.
4.3 Synthesis of the MOFs
4.3.1 Synthesis of UiO‑67
4
.4.2 General Procedure for Asymmetric Aldol Reaction
Catalyzed by UiO‑67‑Pd‑pro
ZrCl (24.5 mg, 0.105 mmol), H bpdc (25.4 mg,
4
2
0
.105 mmol) were added in 4 mL DMF. The mixture was
evenly dispersed by sonication for about 10 min, then trans-
ferred to a reaction kettle and kept at 100 °C for 36 h. The
solid was collected by centrifugation and washed with DMF
A mixture of biphenyl formaldehyde (1 mmol), cyclopen-
tanone (0.88 mL, 10 mmol), dichloromethane (2 mL) and
the catalyst UiO-67-Pd-pro (20 mg) was stirred at the certain
temperature in Table 2 for 5 days. The solid catalyst was
removed by ꢁltration and the organic phase was concentrated
in vacuo, and puriꢁed by ꢃash column chromatography.
The ee value and dr value of the product were calculated
by HPLC spectra (chiral column AD-H, n-hexane: isopro-
(
3×10 mL) and methanol (3×10 mL). Before catalyzed the
Suzuki/Aaymmetric Aldol sequential reaction, the synthe-
sized catalyst was immersed in 10 mL methanol solution
for 3 days. Fresh solvent was replaced for 24 h, and then the
activated catalyst was dried via vacuum.
−
1
panol=90:10, ꢃow rate: 1 mL min ).
4.3.2 Synthesis of UiO‑67‑pro
ZrCl (24.5 mg, 0.105 mmol), H bpdc (19.1 mg,
4.4.3 General Procedure for Suzuki/Asymmetric Aldol
Sequential Reactions Catalyzed by UiO‑67‑Pd‑pro
4
2
0
0
.079 mmol) and chiral l-proline decorated ligand (9.3 mg,
.026 mmol) were added in 4 mL DMF. The subsequent
steps of reaction and washing were the same as the prepara-
tion of UiO-67.
In a toluene (8 mL) solution, aryl halide (1 mmol), 4-for-
mylphenylboronic acid (225 mg, 1.5 mmol), UiO-67-Pd-pro
(
20 mg), and K CO (276 mg, 2 mmol) were reacted under
2 3
4.3.3 Synthesis of UiO‑67‑Pd
speciꢁc conditions. After the coupling procedure was com-
pleted, the reaction mixture was cooled to room tempera-
ture. Considering the inꢃuence of K CO and toluene on
ZrCl (24.5 mg, 0.105 mmol), H bpdc (19.1 mg,
4
2
2
3
0
0
.079 mmol) and Pd(II)-metalated ligand (11.1 mg,
asymmetric aldol reactions, after the coupling procedure was
completed, the reaction mixture was cooled to room tem-
perature and then neutralized with 1 M HCl. The solvent was
also evaporated under reduced pressure. Cyclopentanone
.026 mmol) were added in 4 mL DMF. The subsequent
steps of reaction and washing were the same as the prepara-
tion of UiO-67.
(
0.88 mL, 10 mmol) and CH Cl (2 mL) were added into
2 2
4.3.4 Synthesis of UiO‑67‑Pd‑pro
the above residue, followed by applied ultrasonic treatment
for 10 min. Then the mixture was stirred at − 20 °C. The
product was collected by fast column chromatography and
analyzed by HPLC spectra (chiral AD-H column, n-hexane:
ZrCl (24.5 mg, 0.105 mmol), H bpdc (12.7 mg,
4
2
0
0
.052 mmol), chiral l-proline decorated ligand (9.3 mg,
−
1
.026 mmol) and Pd(II)-metalated ligand (11.1 mg,
isopropanol=90: 10, 1 mL min ).
1
3

Pd(II)-Metalated and l-Proline-Decorated Multivariate UiO-67 as Bifunctional Catalyst…
Supplementary Information The online version contains supplemen-
28. Song Y, Feng XY, Chen JS, Brzezinski C, Xu ZW, Lin WB
tary material available at https://doi.org/10.1007/s10562-021-03719-0.
(2020) J Am Chem Soc 142:4872–4882
2
3
3
3
3
9. Zeng LZ, Wang ZY, Wang YK, Wang J, Guo Y, Hu HH, He XF,
Wang C, Lin WB (2020) J Am Chem Soc 142:75–79
0. Kobayashi A, Ohba T, Saitoh E, Suzuki Y, Noro S, Chang HC,
Kato M (2014) Inorg Chem 53:2910–2921
Acknowledgements This work was supported by the Priority Aca-
demic Program Development of Jiangsu Higher Education Institutions,
National Natural Science Foundation of China (No. 21471031) and
Fundamental Research Funds for the Central Universities.
1. Kim D, Whang DR, Park SY (2016) J Am Chem Soc
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2. Miera GG, Gόmez AB, Chupas PJ, Martín-Matute B, Chapman
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Declarations
3. Marshall RJ, Lennon CT, Tao A, Senn HM, Wilson C, Fairen-
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Conflict of interest The authors declare that there is no conꢃict of in-
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34. Wang XN, Zhang P, Kirchon A, Li JL, Chen WM, Zhao YM, Li
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