Synthesis tricyanovinyl derivatives via one-pot tandem reactions with heterogeneous catalyst Au@Cu(II)-MOF

Article abstract of DOI:10.1016/j.catcom.2018.04.006

In this article, the heterogeneous catalyst of Au@Cu(II)-MOF was prepared with high performance catalytic activities. By adding 5% mol Au@Cu(II)-MOF, the substrate of 2,6-di-tert-butylphenol (1) was oxidized to 2,6-di-tert-butyl-p-benzoquinone (2) with the yield of 99% using H₂O₂ as an oxidizing reagent. Moreover, treating the catalytic reaction mixture with malononitrile, one new product of 2-(3,5-di-tert-butyl-4-hydroxyphenyl)ethane-1,1,2,-tricarbonitrile (3) was obtained with the isolated yield of 87%. However, in the absence of the catalyst of Au@Cu(II)-MOF, the intermedia of 2 and malononitrile react to form a product not 3 but its isomer 2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)ethane-1,1,2,-tricarbonitrile (4). At the meanwhile, in the presence of Au@Cu(II)-MOF and H₂O₂, the product of 3 with comparable isolated yield of 86% was isolated when 1 and malononitrile directly reacted during one pot tandem reaction. Furthermore, the tautomerization of 3 and 4 was also observed in CH₂Cl₂ solution driven by trimethylamine and acetic acid.

Full text of DOI:10.1016/j.catcom.2018.04.006

Accepted Manuscript
Synthesis tricyanovinyl derivatives via one-pot tandem reactions
with heterogeneous catalyst Au@Cu(II)-MOF
Fa-Zheng Jin, Chao-Qun Chen, Qun Zhao, Jing-Lan Kan, Yang
Zhou, Gong-Jun Chen
PII:
DOI:
Reference:
S1566-7367(18)30137-7
doi:10.1016/j.catcom.2018.04.006
CATCOM 5379
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Catalysis Communications
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Accepted date:
8 January 2018
29 March 2018
8 April 2018
Please cite this article as: Fa-Zheng Jin, Chao-Qun Chen, Qun Zhao, Jing-Lan Kan, Yang
Zhou, Gong-Jun Chen , Synthesis tricyanovinyl derivatives via one-pot tandem reactions
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ACCEPTED MANUSCRIPT
Synthesis tricyanovinyl derivatives via one-pot tandem
reactions with heterogeneous catalyst Au@Cu(II)-MOF
Fa-Zheng Jin, Chao-Qun Chen, Qun Zhao, Jing-Lan Kan, Yang Zhou* and Gong-Jun
Chen*
College of Chemistry, Chemical Engineering and Materials Science, Collaborative
Innovation Center 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:
zhouyang0404@sdnu.edu.cn, gongjchen@126.com

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Abstract
In this article, the heterogeneous catalyst of Au@Cu(II)-MOF was prepared with high
performance catalytic activities. By adding 5% mol Au@Cu(II)-MOF, the substrate of
2,6-di-tert-butylphenol (1) was oxidized to 2,6-di-tert-butyl-p-benzoquinone (2) with
the yield of 99% using H2O2 as an oxidizing reagent. Moreover, treating the catalytic
reaction
mixture
with
malononitrile,
one
new
product
of
2-(3,5-di-tert-butyl-4-hydroxyphenyl)ethane-1,1,2,-tricarbonitrile (3) was obtained
with the isolated yield of 87%. However, in the absence of the catalyst of
Au@Cu(II)-MOF, the intermedia of 2 and malononitrile react to form a product not 3
but
its
isomer
2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)ethane-1,1,2,-tricarbonitrile
(4). At the meanwhile, in the presence of Au@Cu(II)-MOF and H2O2, the product of
3 with comparable isolated yield of 86% was isolated when 1 and malononitrile
directly reacted during one pot tandem reaction. Furthermore, the tautomerization of 3
and 4 was also observed in CH2Cl2 solution driven by trimethylamine and acetic acid.
Keywords: Heterogeneous catalyst; Tandem reaction; Proton tautomerism

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1 Introduction
The development of heterogeneous catalysts is one of the major subjects in
modern synthetic chemistry and industry. Owing to the features of economic,
simplified and catalysts recycling [1-3], heterogeneous catalysis has received
much attention in the past few decades. Inside the heterogeneous catalysis
domain, Metal-organic framework (MOF) materials are relatively novel to
other well-recognized porous materials like zeolites. The rational design of
extended frameworks with thermal stabilities, controlled pore size and
coordinative unsaturated metal sites for selective catalytic properties offers an
advantageous platform to develop heterogeneous systems [4-7]. Au
Nanoparticles (Au NPs) have been recognized as very active and effective
catalysts and widely used in promoting many types of organic reactions such as
oxidation of alcohols, reduction of nitro-aromatic compounds and so on [8-10].
Therefore, the incorporation of MOF-supports with the Au NPs would lead to
an enhanced or even novel catalytic property compared to their pristine
counterparts [11-12]. On the other side, tandem reactions provide incomparable
opportunities for the expeditious increase of complexity and diversity. This
strategy offers significant advantages over classical stepwise approaches, such
as tandem cost and time timesaving, eco-friendliness, and simplified processes
and low cost [13-14]. As a continuation of our work with the Au NPs-loaded
Cu-MOF materials, namely Au@Cu(II)-MOF, we report herein its
heterogeneous
catalytic
nature.
Au@Cu(II)-MOF
catalyzes

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2,6-di-tert-butylphenol (1) to 2,6-di-tert-butyl-p-benzoquinone (2) using H2O2
as oxidizing reagent, malononitrile reactions in a successive manner, and
furthermore, 1 with malononitrile reactions using one-pot tandem synthesis of
tricyanovinyl
2-(3,5-di-tert-butyl-4-hydroxyphenyl)ethane-1,1,2,-tricarbonitrile (3). However,
and malononitrile react without Au@Cu(II)-MOF to form
derivatives
2
2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)ethane-1,1,2,-tricarboni
trile (4). The synthesis of 3 and 4 is discussed in detail and the spectroscopic
characteristics and proton tautomerism of the 3 and 4 are investigated.
2 Experimental
2.1. Materials
The reagents and solvents employed were commercially available and used
without
further
purification.
Ligand
4,4,4-trifluoro-1-(4-(pyridin-4-yl)phenyl)butane-1,3-dione (L) was synthesized
according to a previous reported procedure [15-16].
2.2. Instrumentation
The powder diffractometer (XRD) patterns were collected by a D8
ADVANCEX-ray with Cu Kα radiation (λ = 1.5405 Å). ICP-LC was performed
on an IRIS InterpidII XSP and NU AttoM. HRTEM (High resolution
transmission electron microscopy) analysis was performed on a JEOL 2100

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1
13
Electron Microscope at an operating voltage of 200 kV. H NMR and C NMR
spectra were recorded on Bruker Avance 400 MHz spectrometer in CDCl3.
Mass spectra analysis was performed on API 200 LC/MS system (Applied
Biosystems Co. Ltd). Gas chromatography (GC) analysis was performed on an
Agilent 7890B GC. XPS spectra were obtained from PHI Versaprobe II.
2.3. X-ray Crystallography
Diffraction data for the complex was collected at 293 (2) K, with Agilent
SuperNova X-Ray single crystal diffractometer using Cu-Kα radiation (λ =
1.54178 Å) with the ω-2θ scan technique. An empirical absorption correction
was applied to raw intensities [17]. The structure was solved by direct methods
(SHELX-97) and refined with full- matrix least-squares technique on F2 using
the SHELX-97 [18]. The hydrogen atoms were added theoretically, and riding
on the concerned atoms and refined with fixed thermal factors.
2.4. Synthesis of Cu(II)-MOF and Au@Cu(II)-MOF
Cu(II)-MOF and Au@Cu(II)-MOF were synthesized according to previous
reported procedures [15-16].
Synthesis of Cu(II)-MOF. A solution of Cu(OAc)2 (2.4 mg, 0.01 mmol) in MeOH (1
mL) was layered onto a solution of L (4.8 mg, 0.02 mmol) in CH2Cl2 (2 mL). The
solutions were left for about 3 days at room temperature, and then Cu(II)-MOF
(Cu3L6) was obtained as bright green crystal.

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Synthesis of Au@Cu(II)-MOF. Cu(II)-MOF (15 mg, 0.003 mmol) was added to a
CH3OH (10 mL) solution of chloroauric acid (20 mg, 0.2 mmol). The mixture
was stirred for 1 h at room temperature. The resulting solid was isolated by
centrifugation and washed with CH2Cl2. The obtained green-yellow crystalline
solid was mixed with NaBH4 (50 mg, 1.3 mmol) in water (4 mL) and the
mixture was stirred for additional 5 h to afford a dark brown solid. This
obtained crystalline solid, Au@Cu(II)-MOF, was washed with CH3CN and
EtOH and dried in air.
2.5.
Synthesis
of
2,
6-di-tert-butyl-1,4-benzoquinone
(2)
from
2,6-di-tert-butylphenol (1)
1 (21 mg, 0.1 mmol) was added to 2 mL acetonitrile solution of H2O2 (50 μL,
0.5 mmol). After addition of Au@Cu(II)-MOF (5 mg, 5% mol Au), the mixture
was stirred at 75°C for 2 h and 25 min to afford 2 with (monitored by GC on
DB-1701 column) conversion (100%) and selectivity (99%), respectively.
Leaching test: Au@Cu(II)-MOF was separated from the solution by
centrifugation, and the reaction solution was transferred to another reaction vial
under the same conditions.
2.6.
Synthesis
of
2-(3,5-di-tert-butyl-4-hydroxyphenyl)ethane-1,1,2,-tricarbonitrile (3) from 2
and malononitrile
1 (105 mg, 0.5 mmol) and H2O2 (250 μL, 2.5 mmol) were added to 5 mL
acetonitrile solution. After addition of Au@Cu(II)-MOF (25 mg, 5 % mol Au),

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the mixture was stirred at 75°C for 2 h in air. Acetonitrile solution (5 mL) of
malononitrile (115 mg, 1.75 mmol) was added to above system and then stirred
for additional 8h at 75°C being monitored by TLC before cooling down to
room temperature and concentrated. The crude product was purified by silica
gel column chromatography (CH2Cl2/THF 25: 1) as eluent to give a light
yellow solid 3 158 mg with yield 87 %.
2.7.
Synthesis
of
2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)ethane-1,1,2,-tricarboni
trile (4) from 2 and malononitrile
1 (105 mg, 0.5 mmol) was added to acetonitrile (5 mL) solution of H2O2 (250
μL, 2.5 mmol). After addition of Au@Cu(II)-MOF (25 mg, 5 % mol Au), the
mixture was stirred at 75°C for 2h in air. After filtering Au@Cu(II)-MOF, the
acetonitrile solution (5 mL) of malononitrile (115 mg, 1.75 mmol) was added to
above system. The mixture was stirred for additional 12h at 75°C monitored by
TLC and then cooled to room temperature and concentrated. The crude product
was purified by silica gel column chromatography (CH2Cl2/THF 25: 1) as
eluent to give a red solid 4 36 mg with yield 20 %.
2.8. One-pot tandem 3 from 2,6-di-tert-butylphenol and malononitrile
A mixture of 1 (105 mg, 0.5 mmol), H2O2 (250 μL, 2.5 mmol), malononitrile
(115 mg, 1.75 mmol) and Au@Cu(II)-MOF (25 mg, 5 % mol Au) in acetonitrile
(10 mL) was stirred at 75°C for 8 h (monitored by TLC). The mixture after
being cooled and concentrated, the product of 3 was purified by column

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chromatography on silica gel (CH2Cl2/THF 25: 1) with yield 86 %.
2.9. Recycle and activation of Au@Cu(II)-MOF
Au@Cu(II)-MOF was recovered by centrifugation, washed with ethanol (3.0
mL) and dichloromethane (3.0 mL) (3 times), and then dried at 90°C in vacuum
for the next run reaction under the same reaction conditions.
3 Results and Discussion
3.1. Characterization of Cu(II)-MOF and Au@Cu(II)-MOF
Cu(II)-MOF is 3D NbO network. The opposite Cu(II)···Cu(II) distance in MOF
is 26.6139(4) Å. All the fluorine atoms on the framework face toward the center
of the channels and the opposite F···F distance is 14.4423 (3) Å.
Au@Cu(II)-MOF was prepared via the HAuCl4 solution impregnation in
Cu(II)-MOF (Scheme 1). The Au NPs-embedded Cu(II)-MOF was synthesized
by the reduction of Au(III)@Cu(II)-MOF with NaBH4 in aqueous solution. The
uploaded amount of Au, as determined by inductively coupled plasma (ICP)
measurement, is up to 9.3 wt. %. HRTEM was shown Au NPs highly dispersed
in Cu(II)-MOF and the average particle size of ca. 2 nm. The atomic lattice
with spacing of 0.23 nm fringes corresponding to Au (111) planes was
observed. The oxidation state of Nano Au after reduction was checked by X-ray
photoelectron spectroscopy (XPS). The observation of Au 4f7/2 and 4f5/2 peak at
83.86 and 87.46ev in XPS of Au@Cu(II)-MOF demonstrated the reduction
from Au(III) to Au(0) (Fig S1). The XRPD of Au@Cu(II)-MOF is well

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agreement with Cu(II)-MOF, which indicates that the structural integrity of the
Cu(II)-MOF is well preserved (Fig. 1).
3.2.
Synthesis
of
2,6-di-tert-butyl-1,4-benzoquinone
(2)
from
2,6-di-tert-butylphenol (1).
We firstly examine the catalytic behavior of Au@Cu(II)-MOF for catalyzing 1 to 2,
which is an important class of compounds in organic synthesis, biomedicine and
materials science [19-20]. This oxidation reaction (with Au@Cu(II)-MOF, 5 % Au)
was carried out using more environmentally-friendly H2O2 as oxidant (monitored by
GC) in acetonitrile solution. As shown in Fig. 2, upon increasing the reaction time
from 20 min to 2h the yield of 2 significantly is enhanced. It should be noted that an
excellent yield of 99 % was achieved when the reaction was carried out at 2h, which
was confirmed by GC analysis (Fig. S2 and S3). It therefore, appears that 2h is the
optimum reaction time for the maximum yield of 2. The total number (TON)
and turnover frequency (TOF) are 2.45 and 5.88 h-1, respectively. When using
tert-butyl hydroperoxid (TBHP) as the oxidant agent, the optimum reaction time
for achieving the maximum yield is largely shortened to 25 minutes (Fig. S4). In
order to gain insight into the heterogeneous nature of Au@Cu(II)-MOF, the hot
leaching test was carried out. As indicated in Fig. 2, the yield slightly increases
without Au@Cu(II)-MOF after ignition of the oxidation reaction at 60min,
indicating Au@Cu(II)-MOF exhibits a typical heterogeneous catalyst nature.
The ICP measurement indicated that the amount of Au NPs in
Au@Cu(II)-MOF have no changes after leaching test, the amount of Au species
still keep 9.3 wt. %. The catalytic activity of this oxidation reaction with only
H2O2 (the amount five times of 1), Cu(II)-MOF (the amount two times of
Au@Cu(II)-MOF) or Au@Cu(II)-MOF for was also examined under 2h,

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however, 1 conversion are 20 %, 6 % and 53 %, respectively, which suggests
that Nano Au is the main catalytic site (Fig. S5). The scope of the oxidation
catalytic system was explored by performing the oxidation reaction. Phenol, 2,
6-Dimethylphenol and 2, 3, 5-Trimethylphenol gave 95 %, 82 % and 74 %
conversion, respectively (Fig. S6). The recyclability of Au@Cu(II)-MOF was
also examined. After an initial reaction, the solid catalyst was isolated from the
reaction system by centrifugation and reused in additional runs. The
Au@Cu(II)-MOF was be recycled for five times (Fig. 2). After each run, the
solid catalyst was collected by centrifugation, washed with ethanol, dried at
90°C and reused in next run under the same conditions. The reaction yields still
keep 98 % (Fig. S7), indicating almost no change of the catalytic activity of
recycled Au@Cu(II)-MOF. The XRPD patterns of Au@Cu(II)-MOF and that
after reused for five cycles indicated that the structural integrity of
Au@Cu(II)-MOF was well preserved (Fig. S8).
3.3.
Knoevenagel-Substitution
reaction
synthesis
(3)
of
2-(3,5-di-tert-butyl-4-hydroxyphenyl)ethane-1,1,2,-tricarbonitrile
and
2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)ethane-1,1,2,-tricarboni
trile (4) from 1 and malononitrile
As one of the most prominent classes of compounds, the tricyanovinyl (TCV)
compounds are strong organic electron acceptors for creating reduced band gap
materials, and tricyanovinyl derivatives are also key structural motifs in
photochromic active compounds and useful building blocks in the synthesis of
semiconducting [21-23], as well as in intriguing nonlinear optical properties
(NLO) material [24-25]. Usually, tricyanovinyl compounds are prepared by
tetracyanoethylene (TCNE) with activated aromatic rings [26-27].

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The catalytic behavior of Au@Cu(II)-MOF for the Knoevenagel reaction was
tested. After oxidation of 1, malononitrile was added to the above system. The
mixture was stirred for an additional 8 h at 75°C monitored by TLC, the
product
of
2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)malononitrile did not
generate from 2 with malononitrile (even reduce the amount of malononitrile)
catalysis with Au@Cu(II)-MOF. But yellow production 3 with yield 87% was
1
found (Scheme 2.). The structure of 3 was assigned on the basis of ESI-MS, H
13
and C NMR. In addition, the structure of 3 is further supported by the X-ray
diffraction analysis, which unambiguously confirmed its structure (Fig. S9.).
Molecules of 3 are planar all atoms (excluding the butyl groups), the structure
consists of one malononitrile and one cyano in the molecule of 3, Furthermore,
molecule 3 forms π-stacks distance of 3.637 Å along the c-axis (CIF of 3 in
Supplementary material, CCDC: 1546189). Noteworthy, after the completion of
the catalytic oxidation reaction of 1 to form 2, Au@Cu(II)-MOF was filtered
before malononitrile was added to the filtrate, and then a red production of
2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)ethane-1,1,2,-tricarboni
trile (4) (Scheme 2.) was obtained with yield 20 % (monitored by TLC) (Fig.
S10). For the exclusion the influence of acetonitrile in the reaction process,
using methanol instead of acetonitrile, the product is still 3 (Fig. S11). After the
catalytic oxidation reactions of 1 to 2, Au@Cu(II)-MOF was filtered before
Cu(II)-MOF and malononitrile were added to the filtrate, the red production 4
was also been synthesized (Fig. S12). A proposed mechanism for the reaction
comprises initial oxidation of 1 to form 2, subsequent Knoevenagel reaction
malononitrile attack keto group of 2 to form intermediate product 2-(3,

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5-di-tert-butyl-4-oxocyclohexa-2, 5-dien-1-ylidene) malononitrile (Fig. S13). At
the third stage of substitution reaction, another malononitrile molecule attacks
the malononitrile middle carbon atom of intermediate product of
2-(3,5-di-tert-butyl-4-oxocyclohexa-2,5-dien-1-ylidene)malononitrile, and
cyano leave to form 3 or 4 (Scheme 3.).
a
3.4. The one-pot tandem synthesis of 3 from 1 and malononitrile
To further investigate the catalytic behaviour of Au@Cu(II)-MOF, the tandem
reaction was expanded to 1 and malononitrile. A mixture of 1, H2O2,
malononitrile and Au@Cu(II)-MOF (5 % mol Au) in acetonitrile was stirred at
75°C monitored by TLC for 8 h. The product of 3 was purified by column
chromatography on silica gel with yield 86 % (Fig. 3). The hot leaching test
was carried out to show the heterogeneous nature of Au@Cu(II)-MOF. The
yield of 3 is 48 % with Au@Cu(II)-MOF after reaction 4 hours and the yield no
further increases by filtering Au@Cu(II)-MOF after 2 hours. Reusability of
catalysts is very important for heterogeneous catalytic reaction. The
recyclability of Au@Cu(II)-MOF was also examined. After an initial reaction,
the solid catalyst was isolated from the reaction system by centrifugation and
reused in additional runs. The Au@Cu(II)-MOF was be recycled five times
(Fig. 3). After each run, the solid catalyst was collected by centrifugation,
washed with acetonitrile, dried at 90°C and reused in next run under the same
conditions. Interestingly, the reaction yield decrease slightly, as shown in Fig. 3
the XRPD patterns of Au@Cu(II)-MOF and that after reused for five cycles
indicated that the structural integrity of Au@Cu(II)-MOF was well preserved.
The scope of the one-pot tandem catalytic system was explored by performing
the reaction phenol, 2, 6-Dimethylphenol and 2, 3, 5-Trimethylphenol with

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malononitrile. Unfortunately, the reaction selectivity and the yield is very poor,
the products are difficult to isolate by column chromatography, respectively.
3.5. Proton tautomerism 3 and 4
Proton tautomerism has been of sustained interest because of its importance for
understanding various chemical and biochemical phenomena [28-29], many
reaction mechanisms are explained by the proton tautomerism such as a
keto-enol tautomerism. From physicochemical point of view, proton
tautomerism can be described by an intramolecular proton transfer reaction.
This implies that proton tautomerism has potential for switching the molecular
properties compounds by external stimuli such as light, heat, and solvent
polarity [30-35]. Initially CH2Cl2 solution of 3 has a light yellow color, which
turns dark red upon the addition of triethylamine because of the generation of 4.
After adding acetate to the solution, the color change from dark red to yellow
again. Compound 3 with a hydroxyl group shows yellow color, after the
addition of triethylamine, the hydrogen of hydroxyl group transfer to
malononitrile group to form 4, resulting this color variation. Besides naked-eye
detectable color change, the reaction progress was monitored by UV-vis spectra.
As indicated in Fig. 4, the adsorption of 3 at 335 and 510 nm rapidly decreased
while a concomitant increase of the peak at 425 nm. The remarkable color
change of the solutions implies a presence of a proton tautomeric between
keto-enol tautomer, which is further confirmed by ESI-MS data (Fig. S14 and
S15).

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4. Conclusions
Here we report a new one-pot tandem route for preparing the tricyanovinyl
compound from 2,6-di-tert-butylphenol and malononitrile using
3
Au@Cu(II)-MOF as the catalyst in the presence of H2O2 oxidizing reagent,
including the described highly efficient and convenient synthetic protocols,
broaden the synthetic chemistry scope, as well as existed proton tautomerism
between 3 and 4. Furthermore, the distinguishingly catalytic behaviour of
Au@Cu(II)-MOF in this new one-pot tandem route is successfully investigated
as a heterogeneous catalyst.
Acknowledgements
We are grateful for financial support from NSFC (Grant Nos. 21301109 and
21401118), Shandong Provincial Natural Science Foundation (No.
ZR2014BP011) and Jinan Science and Technology Bureau (OUT_06623).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the online version.

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Figure Captions
Scheme 1: Schematic representation of synthesis of Au@Cu(II)-MOF.
Fig. 1. Left: HRTEM image of Au@Cu(II)-MOF. Right: XRPD patterns of
Cu(II)-MOF and Au@Cu(II)-MOF.
Fig. 2. Left: Reaction time examination and leaching test for the synthesis of 2
catalysed by Au@Cu(II)-MOF. Right: catalytic cycles. Reaction conditions: 1
(21mg, 0.1 mmol), H2O2 (50 μL, 0.5 mmol) and Au@Cu(II)-MOF (5 mg, 5%
mol Au) in acetonitrile (2 mL) solution. The mixture was stirred at 75°C.
Au@Cu(II)-MOF was recovered by centrifugation, washed with EtOH and dried
at 90°C.
Scheme 2: After oxidation of 1, malononitrile was added to the above system to
synthesis of 3 and synthesis of 4.
Scheme 3: A proposed mechanism for the reactions of 3 and 4
Fig. 3. Recycling test: The yield obtained at 8 h in repeated runs of 3 (left) and
corresponding XRPD patterns (right).
Fig. 4. The UV−vis absorption spectra for the solution of 3 (1×10-3 mol in 2 ml
CH2Cl2, yellow line) in the presence of different quantity of triethylamine
(0.2×10-3, 0.4×10-3, 0.5×10-3, 0.8×10-3, 1×10-3, 1.2×10-3 ,1.4×10-3 mol) was
added. The insert shows the color change of triethylamine and acetic acid
-driven 3 and 4 tautomerism. 3 (1×10-3 mol), triethylamine in order to add
(0.2×10-3, 0.4×10-3, 0.5×10-3, 0.8×10-3, 1×10-3, 1.2×10-3 ,1.4×10-3 mol) and
(0.2×10-3, 0.4×10-3, 0.5×10-3, 0.8×10-3, 1×10-3, 1.2×10-3 ,1.4×10-3 mol)
acetic acid was added again.

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Scheme 1
Fig. 1.
conversion
selectivety
100
80
100
80
60
60
40
40
20
20
20
40
60
80
100 120
0
1
2
3
4
5
Time/h
cycle
Fig. 2.

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Scheme 2.
Scheme 3.
Fig. 3.

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Fig. 4.

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Graphical abstract:

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Highlights




The catalyst Au@Cu(II)-MOF exhibits a heterogeneous catalytic nature.
Au@Cu(II)-MOF is able to catalyze one-pot tandem synthesis of compounds 3.
Without loading the catalyst, intermedia 2 and malononitrile can form product of 4.
The products 3 and 4 exist proton tautomerism.