Ni/Pd-catalyzed Suzuki-Miyaura cross-coupling of alcohols and aldehydes and C-N cross-coupling of nitro and amines: via domino redox reactions: base-free, hydride acceptor-free

Article abstract of DOI:10.1039/d0ra08344e

Domino oxidation-Suzuki-Miyaura cross-coupling of benzyl alcohols with phenylboronic acid and domino reduction-C-N cross-coupling of the nitro compounds with aryl halides were carried out using a strong Ni/Pd bimetallic redox catalyst. The catalyst bearing a copolymer with two Ni/Pd coordinated metals in porphyrin (derived from demetalated chlorophyll b) and salen-type ligands, and pyridine moiety as a base functionality all immobilized on magnetite NPs was synthesised and characterized. The domino oxidation cross-coupling reaction was accomplished under molecular O2 in the absence of any hydride acceptor or/and base. Also, the domino reduction C-N cross-coupling reaction was performed in the presence of NaBH4 without the need for any base and co-reductant. This multifunctional catalyst gave moderate to good yields for both coupling reactions with high chemoselectivity. A wide investigation was conducted to determine its mechanism and chemoselectivity.

Full text of DOI:10.1039/d0ra08344e

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Ni/Pd-catalyzed Suzuki–Miyaura cross-coupling of
alcohols and aldehydes and C–N cross-coupling of
nitro and amines via domino redox reactions: base-
free, hydride acceptor-free†
Cite this: RSC Adv., 2020, 10, 43962
a
Rebin Omer Ahmedb and Boshra Mahmoudic
*
Milad Kazemnejadi,
Domino oxidation-Suzuki–Miyaura cross-coupling of benzyl alcohols with phenylboronic acid and domino
reduction-C–N cross-coupling of the nitro compounds with aryl halides were carried out using a strong Ni/
Pd bimetallic redox catalyst. The catalyst bearing a copolymer with two Ni/Pd coordinated metals in
porphyrin (derived from demetalated chlorophyll b) and salen-type ligands, and pyridine moiety as a base
functionality all immobilized on magnetite NPs was synthesised and characterized. The domino oxidation
cross-coupling reaction was accomplished under molecular O2 in the absence of any hydride acceptor
or/and base. Also, the domino reduction C–N cross-coupling reaction was performed in the presence of
NaBH4 without the need for any base and co-reductant. This multifunctional catalyst gave moderate to
good yields for both coupling reactions with high chemoselectivity. A wide investigation was conducted
to determine its mechanism and chemoselectivity.
Received 29th September 2020
Accepted 18th November 2020
DOI: 10.1039/d0ra08344e
rsc.li/rsc-advances
reaction,5 Cu-catalyzed aryl-I bond thiolation for the switchable
synthesis of 2,3-dihydrobenzothiazinones and benzoisothiazo-
lones,6 Cu-catalyzed one-pot synthesis of C-4 sulfonated iso-
quinolin-1(2H)-ones,7 and Co-catalyzed diastereoselective
diuoroalkylation/Giese addition domino reactions8 are some
of the recently reported applications of the domino approach in
organic synthesis. Previously, Chandra et al. reviewed the
application of domino reactions in catalytic C–C bond
formation.1
An intelligent strategy for the synthesis of multistep
compounds is the use of multifunctional catalysts. Climent
et al. showed that the one-pot domino reactions catalyzed by
multifunctional catalysts provide higher selectivity by adjusting
the relative rates of the various successive steps in some cases.9
Different catalytic sites can be combined into a single cata-
lyst for a specic purpose, and like a machine, perform a multi-
step synthesis in one step. One of the best examples of these
systems was reported by Ke et al. recently,10 where a multistep
auto-tandem reaction was performed by an integrated-
trifunctional single catalyst with acid, base and anchored Pd
sites (Scheme 1). As shown in Scheme 1, the synthesis required
three different types of catalysts with different nature in the
stepwise traditional system; however they performed the
synthesis using a multifunctional single catalyst.
Introduction
Cascade or domino reactions are one of the most applicable
organic reactions, wherein consecutive C–C bond formation
occurs in one step to prepare a complex molecule, and thus
multiple chemical transformations are catalyzed by a single
catalyst. Thus, they save energy, eliminate the troublesome
work-up, reduce the generation of waste, increase synthetic
efficiency, and are environmentally friendly and atom
economical in most cases.1 These systems have prominent
application in total synthesis, especially for the preparation of
complex molecular structures and chiral cyclic derivatives from
simple and readily available starting materials.2 For example,
very recently, Chen et al. developed the domino 10-step total
synthesis of FR252921 (complex macrocyclic immunosuppres-
sants), and based on this domino synthesis, 14 biologically
active compounds were synthesized.3 This is a good example of
the preparation of very complex multi-step compounds that are
very difficult or impossible to prepare through step-by-step and
conventional methods.
The construction of eight-membered cyclic diaryl suldes via
the domino reaction of arynes with thioaurone analogues,4
toluene
oxidation–Knoevenagel-condensation
domino
In the last decade, multifunctional catalytic systems have
been widely developed in organic synthesis11,12 as follows: (1)
Pd-DTP@ZIF-8 in one-pot synthesis of 3-phenyl propyl
aDepartment of Chemistry, College of Science, Shiraz University, Shiraz 7194684795,
Iran. E-mail: miladkazemnejad@yahoo.com
bAnwar Shekha Medical City, Sulaymaniyah, Zip code 46024, Iraq
cResearch Center, Sulaimani Polytechnic University, Sulaimani, Iraq
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d0ra08344e
benzoate,13
Mg1ꢀxAlx(OH2)x+(CO3
(2)
HRh(CO)(PPh3)3
impregnated
on
2ꢀ
)
x/n$mH2O for the one-pot multistep
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Conventional C–C cross-coupling reactions such as Suzuki,
Heck, and Sonogashira couplings utilize aryl halides as the
electrophile, which in most cases is limited to aryl iodide and
aryl bromide, and undesirable efficiency is obtained for aryl
chlorides. In addition, these compounds are expensive, and
their variety is limited due to their low availability. Therefore,
using more affordable, inexpensive, and highly diversied
alternatives to aryl halides as electrophiles will be benecial to
develop these reactions.
Scheme 1 Development of a trifunctional catalytic system for an
auto-tandem reaction by Ke et al.10
Recently, Guo et al. developed an Ni-catalyzed decarbon-
ylative arylation reaction of aldehydes with boronic esters
(Scheme 2).20 The use of the inexpensive, more accessible, and
high diversity aldehydes than aryl halides was the prominent
advantage of their work. Accordingly, the development of these
unconventional coupling electrophiles can be a revolution in
the synthesis of medicinal and biological compounds and the
study and discovery of new compounds.
We went a step further, using nitro and alcohol raw materials
to develop this by designing a redox multifunctional bimetallic
catalytic system. In this work, for the rst time, the domino
coupling of benzyl alcohols (or aldehydes) was performed by
developing a three-functional catalyst including Pd/Ni centers
and Py moieties (as a base functionality), with redox activity.
Due to the different nature of oxidation and reduction reactions
with coupling reactions, the most challenging part of this work
was the design of the catalyst. Using two different ligand
systems, Pd and Ni were coordinated to the ligands in two
different steps. The base character was also given to the catalyst
by graing vinyl pyridine to the copolymer chain, and all these
functionalities were combined on a single catalyst. The catalyst
was designed in such a way that all reactions were performed
using a very small amount of catalyst in the absence of any
additives and base.
synthesis of C8 aldehydes and alcohol from propene,14 (3) Pd-
supported alkaline earth oxides and mixed oxides for the
production of a series of ne chemicals involving one-pot multi-
step reactions,9 (4) Au/Hap for the direct tandem synthesis of
imines and oximes,15 (5) Fe3O4@MS–NH2@Pd for the direct
synthesis of a-alkylated nitriles through facile one-pot multistep
domino reaction sequences,16 and (6) Cs–Pr–Me–Cu(II)–Fe3O4
for the cascade oxidation of benzyl alcohols/Knoevenagel
condensation.17 The development of these catalytic systems
creates milder conditions, reduces the synthesis steps in multi-
step syntheses, synergistic effects in reactions, removes some
additives, uses less catalyst, etc. Recently, bimetallic catalytic
systems with different functions have attracted much attention.
Nasseri et al. reported a Co–Cu bimetallic nanocatalyst with
a synergistic and bifunctional performance for base-free Suzuki,
Sonogashira, and C–N cross-coupling reactions.11
C–C and C–N cross-coupling reactions are of great impor-
tance due to their application in the construction of applicable
biologically active molecules, functional materials, and phar-
maceuticals.18,19 Thus, due to their inevitable application in the
synthesis of organic and pharmaceutical molecules, the
construction of these bonds is very important.11,19
Scheme 2 Comparison between the present work with the classical and previously (decarbonylative arylation reaction) reported protocol for
C–C cross-coupling reactions.
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The presence of oxidation and reduction reagents did not immobilized on Fe3O4@SiO2–NH2 magnetic nanoparticles by
disrupt the domino one-pot coupling reactions. In addition, forming an iminium bond. The resulting catalyst possessed
due to the nature of the catalyst and the presence of Ni centers, a salen-like ligand position, which could be used to coordinate
the domino reaction of reduction-coupling of nitro compounds another metal, and thus, catalyst 11 was produced by coordi-
with aryl halides was also performed using this catalytic system nating Ni ions to these groups. Catalyst 11 was well character-
in the presence of NaBH4.
ized by some analyses (ESI, Fig. S6–S9 and Table S1†). The
average molecular weight of the copolymer was studied by GPC
analysis.6,21 According to the GPC results, the average molecular
weight of compound 4 was found to be 12 580.
Results and discussion
The multifunctional catalyst was prepared in several steps. As
shown in Scheme 3, aer extraction of chlorophyll b, it was
demetalated by HCl (ESI, Fig. S1–S5†) and then allylated by
allylamine for the subsequent copolymerization reaction, which
was performed in the presence of 4-vinyl pyridine. Initially, Pd
metal was coordinated to porphyrin groups in the chlorophyll.
Due to the presence of a vinyl group and coordinated Pd in the
structure of 5, it was auto-catalytically coupled to 4-iodo-
salicylaldehyde by autocatalytic coupling reaction in the
absence of any base. The resulting copolymer was then
Table 1 shows the results of the EDX elemental analysis and
GPC for all the prepared compounds.
The degree of polymerization (DP) of pyridine in copolymer 4
was determined by titration with acetic acid. This observed
acidic property is related to the Py groups plus the pyrrole
groups in the porphyrin ring. Therefore, to relate the degree of
polymerization to the acidic nature of the Py groups, a homo-
logue of 12 (Scheme 4) was prepared using the same procedure
and almost the same degree of polymerization, and an acid test
Scheme 3 Step-by-step schematic showing the preparation of the Fe3O4@SiO2/(Py)-copolymer-(chlorophyll b) Ni/Pd (11) catalyst.
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Table 1 Elemental and GPC analyses of compounds 1–11
EDX analysis (wt%)
a
Compound
C
O
N
Mg
Fe
Si
Pd
Ni
AMw
1
2
3
4
5
6
10
11
12
13
78.60
80.75
81.39
81.09
79.88
80.00
26.54
26.11
81.45
79.87
10.76
11.74
9.35
8.80
7.64
6.66
3.98
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
22.84
22.55
—
—
—
—
—
—
—
11.55
11.30
—
—
—
—
—
3.40
3.04
1.73
1.41
—
—
—
—
—
—
—
—
2.02
—
—
—
7.51
9.26
10.11
9.08
9.08
6.22
6.08
9.12
8.06
884
924
12 580
—
—
—
—
11 440
—
7.88
31.12
30.53
9.43
8.91
—
—
3.16
a
Average molecular weight based on GPC analysis.
was performed on it. Thus, the results obtained from the acidic for the domino Suzuki and C–N coupling reactions, respectively
nature of compound 4 were subtracted from compound 12. It (Table 2, entry 11). DMSO2 has previously been identied as
should be noted that this is only an approximation of the degree a green solvent in coupling reactions.21 Toluene, glycerol and
of polymerization for the catalyst since some of the acid may be DMSO also provided satisfactory efficiencies for both reactions,
used to hydrolyze the ester groups in the chlorophyll groups of but due to environmental considerations and availability,
11 or 12. According to the titration results, the degree of poly- DMSO2 was used as the optimal solvent for the coupling reac-
merization for the pyridine in 4 is 19.
tions. The optimum catalyst loading for the domino Suzuki C–C
Thus, by correlating the GPC and acid-titration test results and C–N coupling reactions were 1.0 and 2.0 mg, respectively.
(as well as the EDX results), it can be concluded that the average Larger amounts of catalyst had no effect on the efficiency of the
degree of polymerization for chlorophyll in the copolymer reactions, and at lower values, the efficiency decreased linearly
loaded on the catalyst is equal to 11 (12 580 ꢀ 19(105) ¼ 10 048/ (Table 2, entries 15–18).
907 ¼ 11). On the other hand, the acid titration test was
The oxidation-coupling reaction was performed in the pres-
reasonable proof for the successful graing of Py monomer to ence of molecular oxygen. The reaction under an air atmo-
the copolymer chain by the radical polymerization. sphere produced only 30% efficiency for 33 h, indicating the
ICP analyses of catalyst 11 shows that 1.46 wt% Pd and importance of molecular O2 in the reaction. In addition, the
2.08 wt% Ni were present in its framework, completely in catalyst showed excellent activity and selectivity for the oxida-
agreement with the EDX analysis.
tion of 1ꢁ-type alcohols to aldehydes in the presence of molec-
ular oxygen, and thus can also be used as an effective catalyst for
the selective oxidation of alcohol (ESI, Table S2†).
A reduction-coupling reaction was performed in the pres-
ence of 2 mmol NaBH4 (optimal value) (Table 2, entry 11). The
reaction did not progress in the absence of NaBH4 (Table 2,
entry 19), which shows that: (1) the coupling reaction occurs
only through the amine precursor and (2) the reduction reaction
is well performed by the catalyst in the presence of 2 mmol
NaBH4.
The catalytic activity of 11 was evaluated for domino-Suzuki
and C–N coupling reactions. The results of the domino Suzuki
coupling reactions using alcohol or aldehyde in the presence of
phenylboronic acid catalyzed by 11 are summarized in Table 3.
The prominent advantages of the catalyst are the in situ oxida-
tion of alcohol to aldehyde and its coupling with the phenyl
ring.
Optimization of reaction parameters
To perform coupling reactions through nitro and alcohol
substrates, rst the reaction parameters were studied to the
achieve optimal conditions. The reaction parameters were
studied for two reactions: (1) the oxidation-coupling reaction of
benzyl alcohol with phenylboronic acid and (2) reduction-
coupling reaction of nitrobenzene with iodobenzene, as
model reactions. The results are summarized in Table 2, and
entry 11 shows the optimal conditions for both reactions.
The best solvent for both reactions was dimethyl sulfone
ꢁ
(DMSO2), which at 120 C produced 84% and 90% efficiencies
All the alcohol and aldehyde substrates were successfully
coupled to the phenyl ring. Similar efficiencies were obtained
for both the alcohol and aldehyde substrates, but longer times
(between 2 and 5 h) were necessary for alcohols, which can be
attributed to the time required for alcohol oxidation to
aldehyde.
Scheme 4 Preparation of polyvinyl chlorophyll-Pd complex (13).
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Table 2 Optimization of the catalytic oxidation of benzyl alcohol and reduction of nitrobenzene using 10 and 11, respectively
C–C Suzuki couplinga
C–N couplingb
Entry
Solvent
T (ꢁC)
Cat. 11 (mg)
Yield (%)
T (ꢁC)
NaBH4 (mmol)
Cat. 11 (mg)
Yield (%)
1
2
3
4
5
6
7
8
EtOH
MeOH
THF
CH3CN
DMF
Glycerol
Dioxane
Toluene
H2O
DMSO
DMSO2
DMSO2
DMSO2
DMSO2
DMSO2
DMSO2
DMSO2
DMSO2
DMSO2
Ref.
Ref.
Ref.
Ref.
Ref.
120
Ref.
Ref.
Ref.
Ref.
120
80
160
R.T.
Ref.
Ref.
Ref.
Ref.
120
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.001
0.05
1.5
2.0
1.0
55
60
N.R.
55
80
84
30
55
45
80
84
44
85
N.R.
50
68
80
84
30
Ref.
Ref.
Ref.
Ref.
Ref.
160
Ref.
Ref.
Ref.
Ref.
120c
80
160
Ref.
Ref.
Ref.
Ref.
Ref.
120
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
1.0
1.5
2.0
2.0
2.0
0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
0.5
1.0
2.5
2.0
50
50
N.R.
40
88
85
45
60
30
9
10
11
12
13
14
15
16
17
18
19e
90
90d
60
90
33
55
65
80
90
N.R.
a
Reaction conditions: benzyl alcohol (1.0 mmol), catalyst 11, temperature, solvent (2.0 mL, DMSO2: 3.36 g), O2 balloon (ꢂ1.0 atm). For a better
b
comparison, a constant time of 33 h was reported for all entries. Reaction conditions: nitrobenzene (1.0 mmol), NaBH4 (2.0 mmol), catalyst
11, solvent (2.0 mL, DMSO2: 3.36 g). For the better comparison, a constant time of 4.2 h was reported for all entries. No improvement was
observed until 40 h. No improvement was observed until 8 h. The reaction was performed under air conditions.
c
d
e
In general, aryl halides with electron withdrawing groups hand, electron donor substituents on the amines increased the
produced better efficiency (in terms of time and efficiency) than coupling reaction efficiency. For example, 19f with similar
aryl halides with electron donor groups (for example, compare hydroxyl substitution produced better efficiency than 19b, also
19b with 19e, 19j with 19m, and 19s with 19u). On the other 19c with 19g, and 19e with 19h. The leaving group also had an
Table 3 Ni/Pd-catalyzed C–C cross-coupling reaction from phenylboronic acid and aldehydesa
Time (h)
Yieldb (%)
Entry
R (alcohol or aldehyde)
Product
From alcohola,c
From aldehyde
From alcohol
From aldehyde
1
2
3
4
5
6
7
8
H
4-MeO
4-Me
2-Me
4-CN
4-NO2
1-Naphthyl
4-Cl
2-MeO
4-NO2, 2-Me
Nicotine
Picoline
2-Furfuryl
15a
15b
15c
15d
15e
15f
15g
15h
15i
33
36
36
32
28
30
40
35
36
40
28
28
40
30
34
34
30
28
30
36
33
35
36
24
26
35
84
77
73
75
66
74
70
25d
70
78
80
82
65
84
79
75
75
60
77
74
35e
70
75
82
80
80
9
10
11
12
13
15j
15k
15l
15m
a
Reaction conditions: aldehyde or benzyl alcohol (1.0 mmol), phenylboronic acid (1.0 mmol), catalyst 11 (1.0 mg, 0.013 mol% Pd, 0.034 mol% Ni),
b
c
d
DMSO2 (3.36 g, 35.7 mmol), and 120 ꢁC. Isolated yield. O2 balloon (ꢂ1.0 atm). 45% coupling product was takes place through Cl (major
product). e 33% coupling product was takes place through Cl (major product).
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Table 4 Ni/Pd-catalyzed C–N cross-coupling reaction of aryl halides with amine and nitro precursorsa
Time (h)
Yieldb (%)
Entry
R1
X
R2 (amine or nitro)
Product
From amine
From nitroa,c
From amine
From nitro
1
2
3
4
5
6
7
8
H
I
I
I
I
I
I
I
I
Br
Br
Br
Br
Br
Br
Br
Br
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
H
H
H
H
19a
19b
19c
19d
19e
19b
19c
19e
19a
19b
19c
19d
19e
19b
19c
19e
19a
19b
19c
19d
19e
19b
19c
19e
3
5
6
3.5
2.2
2.6
5.5
2
5
6.5
7
5
3
3
6.5
4
8.5
9
12
9
8.5
8
7
4.2
6.5
7
4.8
3.5
4
6.5
3.5
6.2
7.7
8
90
90
94
92
96
95
94
98
88
80
82
85
90
92
88
80
75
80
66
75
70
76
75
75
90
92
96
96
96
97
95
98
90
80
85
85
86
92
92
85
80
76
60
75
65
80
80
84
4-OH
4-MeO
4-Me
4-CN
H
H
H
H
4-OH
4-MeO
4-Me
4-CN
H
H
H
H
H
4-OH
4-MeO
4-CN
H
H
H
H
H
4-OH
4-MeO
4-CN
H
H
H
H
H
4-OH
4-MeO
4-CN
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
6.5
4
4.5
7.9
5.4
10
10.5
14
11
10
9
4-OH
4-MeO
4-Me
4-CN
H
H
H
8.5
9
8
a
Reaction conditions: amine or nitro (1.0 mmol), aryl halide (1.0 mmol), catalyst 11 (2.0 mg, 0.026 mol% Pd, 0.068 mol% Ni), DMSO2 (3.36 g, 35.7
mmol), and 120 ꢁC. b Isolated yield. c NaBH4 (2.0 mmol).
undeniable role in the productivity of the coupling reactions, reactions (preparation of 15a) and domino reduction-C–N
and thus that the order of I > Br > Cl activity was quite evident coupling (preparation of 19a). The results are summarized in
for all the substrates (Table 4).
Table 5. For a better comparison, the reaction time was
The results suggest a mechanism based on oxidative- considered constant. Catalyst 10 produced very low efficiencies
addition and reductive-elimination stages, which is for 15a (45%) during the same time, while the efficiency of 80%
completely consistent with the mechanism proposed in the next was achieved for 19a (Table 5, entry 1). According to these
section. Coupling reactions with a nitro precursor also pro- results, it can be deduced that a synergistic and cooperative
ceeded well in the presence of 2 mmol NaBH4 in the reaction effect occurs due to the second metal (Ni). In addition, since the
mixture. The results in Table 4 show that coupling through reaction requires initial oxidation by alcohol, catalyst 10 showed
nitro precursors takes longer, but similar and even higher effi- lower selectivity than 11 (ESI, Table S3†), which can be
ciencies were produced than amines. This can be due to the in responsible for the low efficiency observed for the preparation
situ production of amine (via the reduction of nitro compounds) of 15a. Considering this, the presence of the second metal (Ni)
and the effect of concentration. In addition, according to the controls the selectivity for the oxidation of alcohol to aldehydes.
obtained efficiencies, it can be concluded that the reduction of The effect of pyridine groups on the catalyst was also clearly
the nitro group to amine (for all the substrates) occurred identied by the negligible catalyst activity observed for 13. As
completely with high selectivity.
shown in Table 5 (entry 2), very low efficiency was observed for
19a, and no efficiency was observed for 15a.
These results not only show the vital role of the base in the
reactions, but also show that the presence of Ni in the catalyst
provides the required electron transitions (between Pd and Ni)
for the oxidation-coupling and reduction-coupling reactions,
completely in accordance with the proposed mechanism.
Control experiments
To elucidate the unique catalytic activity of 11, the catalytic
activity of different species (homologues) was studied by per-
forming several control reactions for domino oxidation-Suzuki
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Table 5 The control experiments for the domino oxidation Suzuki–
Miyaura cross-coupling of benzyl alcohol with phenylboronic acida
and domino reduction C–N cross-coupling of nitrobenzene with
iodobenzeneb
For this, a mixture of 5/Fe3O4@SiO2–NH2/Ni(OAc)4$H2O was
evaluated for the preparation of 15a and 19a (Table 5, entry 11).
The efficiency was found to be 35% for 15a, which was higher
than that for compound 5 (Entry 7). This slight increase can be
attributed to the catalytic effect of nickel salt in the reaction
mixture. However, the efficiency of the catalytic mixture for the
preparation of 19a (30%) was less than that of compound 5. The
results show the effect of Ni metal coordination on the catalytic
structure for its reducing activity. In addition, these results
indicate the unique catalytic activity of 11 relative to its
components alone, suggesting a consistent correlation between
the various components with a potential synergistic effect.
15a
19a
Conversion Conversion
Entry Catalyst
(%)
(%)
1
Catalyst 10
40
80
2
3
4
5
6
7
Polyvinyl chlorophyll-Pd(II) (13)
Chlorophyll b
Fe3O4
Fe3O4@SiO2
Fe3O4@SiO2–NH2
Compound 5
Catalyst 10-poisoned
Catalyst 11-poisoned
Catalyst 11
5/Fe3O4@SiO2–NH2/
Ni(OAc)4$H2O
N.R.
N.R.
N.R.
N.R.
N.R.
25
Trace
N.R.
N.R.
N.R.
N.R.
65
N.R.
N.R.
—
Chemoselectivity
8c
9c
10
11e
N.R.
5
Chemoselectivity studies give useful information regarding the
selectivity and activity of a catalyst. Five different combinations
of alcohols and amines were selected for the domino oxidation-
C–C coupling and domino-reduction C–N coupling reactions.
Table 6 shows the corresponding results. The combination of
phenyl boronic acid, 4-NO2-benzyl alcohol, and benzaldehyde,
gave 15a selectively; i.e. decarbonylative coupling with benzal-
dehyde instead domino oxidation-coupling (Table 6, entry 1).
The catalyst did not show satisfactory selectivity in the
presence of iodobenzene, wherein the C–C coupling reaction
was performed at 1.5 h with 25% conversion for 15a (entry 2).
However, 66% selectivity was obtained for 4-NO2-benzaldehyde
for this combination. On the other hand, 4-NO2-benzyl alcohol
selectively coupled with phenylboronic acid in the presence of
butyraldehyde and the oxidation product was also found,
reecting the selectivity of the catalyst towards aromatic alde-
hyde (entry 3). Two combinations were also performed for the
domino reduction-C–N coupling, where in rst, the combina-
tion of iodobenzene, 4-CN-nitrobenzene, and aniline, selectively
gave 19a with 94% conversion (Table 6, entry 4). Similarly, the
aromatic 4-CN-nitrobenzene was selectively coupled without
interference from the aliphatic amine present in the mixture
(Table 6, entry 5).
4d
35
30
a
Reaction conditions: benzyl alcohol (1.0 mmol), phenylboronic acid
(1.0 mmol), catalyst (1.0 mg), DMSO2 (3.36 g, 35.7 mmol), 120 ꢁC, O2
b
balloon (ꢂ1.0 atm), 33 min. Reaction conditions: nitrobenzene (1.0
mmol), iodobenzene (1.0 mmol), catalyst (2.0 mg), NaBH4 (2.0 mmol),
c
DMSO2 (3.36 g, 35.7 mmol), 120 ꢁC, 4.2 h. Hg(0) was added equal to
d
320 molar equivalents vs. Pd content. The preparation of 15a was
performed under an N2 (sealed) atmosphere.
e
5
(1.0 mg),
Fe3O4@SiO2–NH2 (2.0 mg), Ni(OAc)4$H2O (0.1 mg).
Chlorophyll, Fe3O4, Fe3O4@SiO2, and Fe3O4@SiO2–NH2 did not
produce any observable efficiencies for any of the products 15a
and 19a for 32 min and 4.2 respectively (Table 5, entries 3–6).
As shown in entry 7, compound 5 showed less efficiency than
10 (which was only immobilized on the surface of nano-
particles). Considering that 10 and 5 are heterogeneous, this
difference can be attributed to the immobilization of the
copolymer on the surface of the nanoparticles and the increase
in the surface-to-volume ratio, and consequently the increase in
catalytic activity.
In conclusion, the cross-coupling with aldehyde and amine
is superior to the domino oxidation- and reduction coupling,
and the coupling of aromatic substrates can be selectively
coupled compared to the aliphatic type.
The catalytic activity of the metal complex moieties as active
sites in the catalyst was determined by performing two
mercury(0) poisoning control tests for two catalysts, 10 and 11
(Table 5, entries 8 and 9). The reactions with both 15a (from
benzyl alcohol) and 19a (from nitrobenzene) stopped, and do
detectable efficiency was produced. These results not only
indicate the nature and heterogeneity of catalysts 10 and 11 in
the reaction medium, but also indicate that the Pd and Ni active
sites are responsible for the observed catalytic activity for the
oxidation and reduction reactions.
To investigate the reaction mechanism, 15a was prepared
using catalyst 11 under a nitrogen atmosphere. For this, the
reactor was degassed for 5 min and then the catalyst was added
to the reaction mixture simultaneously. Aer 33 minutes, only
4% conversion was observed (Table 5, entry 10). This result well
demonstrates the effect of molecular oxygen (as a source of
oxygen) and the subsequent coupling reaction through the
aldehyde intermediate. Finally, the catalytic activity of the single
components of catalyst 11 was studied in a control experiment.
Mechanism studies
According to the mechanism reported by Guo et al.20 for the
nickel-catalyzed decarbonylative arylation reaction of aldehydes
with boronic esters, and based on our observations, a general
reaction mechanism was proposed for the Fe3O4@SiO2/(Py)-
copolymer-(chlorophyll b) Ni/Pd-catalyzed C–C cross-coupling
reactions. Previously, alcohol oxidation to the corresponding
carbonyl group could be performed using any Pd or Ni active
site. However, it is not possible to determine with certainty
which metal exhibits the desired catalytic activity, and it may be
done either alone or in collaboration with a synergistic effect, as
reported by Nasseri et al. for the Co–Cu bimetallic catalytic
system for coupling reactions.11 Therefore, the oxidation
mechanism of alcohols is selectively sketched for Pd. According
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Table 6 Chemoselectivity behavior of catalyst 11 over the domino oxidation-C–C coupling and domino-reduction C–N coupling reactions in
various combinationsa,b
Selectivityc (%)
Entry
Combination
15a
15f
BB
OxP
19a
19e
RP
Time (h)
Conversionc,d (%)
1
2
3
4
5
PB + NBA + B
PB + NBA + I
PB + NBA + BA
I + NN + An
92
34
—
—
—
0
0
99
—
—
—
—
0
—
—
7
66
0
—
—
—
—
—
96
99
—
—
—
4
—
—
—
0
30
1.5
30
3
79
25
98
94
94
I + NN + BAm
0
0
3
a
Denition: BB: butyl benzene; OxP: oxidation products; RP: reduction products; PB: phenylboronic acid; NBA: 4-NO2-benzyl alcohol; B:
b
benzaldehyde; I: iodobenzene; BA: n-butanol; NN: 4-CN-nitrobenzene; An: aniline; and BAm: n-butyl amine. Reaction conditions: for each
combination, 1.0 mmol of each reactant was used. For entries 1–3: see Table 3 footnote (O2 balloon ꢂ1.0 atm). For entries 4 and 5 see Table 4
footnote (NaBH4: 2.0 mmol). c GC analysis. d For major coupling product.
to this proposed mechanism (Scheme 5a), the alcohol is initially Pd(II) to Pd(0) seems probable (in the case of direct the coupling
approached by the oxygen groups to the Pd sites and a possible of arylamines with aryl halides, this process can also be per-
hydrogen bond forms between the Py and oxygen groups. In the formed by amine groups33,34). Then, by an oxidative-addition
next step, with the abstraction of protons by the Py groups, the reaction, aryl halide is added to Pd and the Pd centers are
alcohol is coordinated to the Pd centers. b-Hydride elimination oxidized to +2. In the next step, the amine group is attached to
leads to the carbonyl product. The protons adsorbed by the Pd the Pd centers via a nitrogen electron pair, and the amino group
and Py centers are received by molecular oxygen and converted proton is taken by the Py group present in the catalyst.
to water, and the catalyst returns to the cycle. It has been shown
Finally, the C–N coupling product is formed, and the Pd
that the simultaneous presence of two coordinated metals in centers are regenerated to the zero oxidation state. Finally, the
a catalytic structure allows the transfer of electrons between
centers.22–26
Here, again, the electron exchange between the Pd and Ni
centers creates the 0 and IV oxidation states for Ni and Pd,
respectively, and prepares the catalyst for the coupling reaction.
The proposed mechanism is completely consistent with these
results. The aldehyde group approaches the Ni(0) centers
through the C]O bond and acylates it, and the corresponding
proton is taken up by the Py group (V).20 Then, phenylboronic
acid approaches to catalyst surface with the help of the Pd
centers and through intermediate VI, leading to the phenyl
coordination and formation of Pd(IV)–B(OH)2 groups. The
coupling product is formed aer several intermediates and the
catalyst returns to the cycle by removing B(OH)2(CH2OH).27–29
Control experiments (Table 5) were performed to help under-
stand this mechanism. Elimination of any of the catalytic
centers (Table 5, entries 1, 2, 8 and 9) and removal of oxygen
(Table 5, entry 10) caused the catalytic activity to stop. This
indicates that all parts of the catalyst, including the Pd, Ni
centers and Py groups are involved in the reaction and suggests
a synergistic effect according to the mechanism shown in the
scheme. Subsequently, a possible mechanism for the reduction
of nitro compounds to amine and subsequent C–N coupling
was proposed in accordance with the observations obtained
from the control experiments and the reported mechanisms
(Scheme 6).30,31
According to this mechanism, NaBH4 and the nitro groups
on the surface of the catalyst are coordinated/linked through
the Ni and Pd centers, respectively, and in several steps of
hydride transfer from the BH4 groups to nitro (intermediates I,
II, III, and IV),30–32 are reduced to an arylamine. Due to the
presence of NaBH4 groups in the medium, the reduction of
Scheme
5 Plausible reaction mechanism for (a) Ni/Pd-catalyzed
oxidation of alcohol and (b) domino oxidation Suzuki–Miyaura cross-
coupling of alcohols.
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normal kinetics for both reactions. The reaction rate was
monitored at different times. According to Fig. S10a and b,†
hydroquinone had no effect on the efficiency and subsequent
kinetics of the reaction, which reects the absence of any
radical (and radical mechanism) in both reactions, in full
agreement with the proposed mechanism.
Due to the presence of multiple catalytic centers in the Ni/Pd
catalyst, the recoverability, metal leaching, and heterogeneity of
the catalyst were studied. For this purpose, the catalyst recovery
was performed in two coupling reactions of domino C–C
coupling of benzyl alcohol with iodobenzene in the presence of
molecular O2 and also domino C–N coupling of nitrobenzene
with iodobenzene in the presence of NaBH4. Both reactions
were performed under the optimal conditions for the appro-
priate times according to Tables 3 and 4.
Leaching experiments for the domino preparation of 15a and
19a in each cycle from the residual mixture were studied by ICP
analysis for both Ni and Pd metals. The results are shown as
curves in Fig. 1. The amount of leaching in each cycle was very
small and at the end of the seventh cycle. A total of 2.35% and
2.77% were observed for Pd and 2.66% and 2.4% for Ni for
products 15a and 19a, respectively. This slight leaching caused
a slight decrease in catalytic activity for the preparation of
compounds 15a and 19a, and thus the efficiency declined to
95% and 94%, respectively, aer 7 consecutive runs. Interest-
ingly, the drop rate was zero for Pd up to the third cycle for both
reactions. This stability can be directly attributed to the better
coordination of Pd ions in the rigid structure of porphyrins than
the salen ligand for Ni ions. In addition, the results showed the
good stability for the catalyst in successive cycles (Fig. 1). The
heterogeneous performance of the catalyst in the reaction
medium was shown previously by mercury poisoning experi-
ments (Table 5, entries 8 and 9) for catalysts 10 and 11 for the
Suzuki–Miyaura domino oxidation cross-coupling of benzyl
alcohol with phenylboronic acid and domino reduction C–N
cross-coupling of nitrobenzene with iodobenzene, respectively.
In addition, the hot ltration test for catalyst 11 in the reaction
for the Suzuki–Miyaura domino oxidation cross-coupling of
benzyl alcohol with phenylboronic acid was studied. For this,
the catalyst was magnetically ltered from the reaction medium
aer 15 h. The reaction progress was 48% at this time, aer
which the reaction proceeded for another 15 h in the absence of
the catalyst. Subsequently, the efficiency reached to 50% (with
negligence). Therefore, the results once again conrmed the
Scheme 6 Plausible reaction mechanism for the Ni/Pd-catalyzed
reduction of nitro to amine and domino reduction C–N cross-
coupling of nitro compounds with aryl halides.
protonated Py groups are treated with NaBO2 (formed in the
previous step), and the catalyst is returned to the cycle.
In addition, to conrm the absence of radical species in the
reaction mixture, and subsequently conrm the non-radical
mechanism in the coupling reactions, the preparation of 15a
and 19a in the presence of hydroquinone, as an electron capture
agent, was performed from the beginning. Fig. S10† shows the
effect of the presence of hydroquinone in comparison with the
Fig. 1 Recyclability and leaching studies of the catalyst over the reaction of (a) benzyl alcohol with phenylboronic acid and (b) nitrobenzene with
iodobenzene.
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Fig. 2 (a) EDX spectrum and (b) TEM image of the recovered catalyst after the 7th recycling of the domino oxidation-coupling reaction of benzyl
alcohol with phenylboronic acid.
heterogeneity of the catalyst and showed that the amount of the aliphatic type. The catalyst could be recycled for at least 7
metal leaching in the reaction medium is very small and consecutive runs with an insignicant loss in its reactivity for
unlikely.
In addition, the recovered catalyst was characterized by TEM
both the C–C and C–N coupling reactions.
and EDX analyses aer the end of the seventh cycle in the
domino C–C coupling of benzyl alcohol with phenylboronic
acid. As shown in Fig. 2, the EDX analysis showed the presence
of all elements at exactly the same percentages as that of the
freshly prepared catalyst. However, the decrease in the
percentages of Ni and Pd can be directly attributed to the metal
leaching, which is completely consistent with the results of the
leaching study (Fig. 2). The TEM image also showed the same
morphology and particle size as that of the freshly prepared
catalyst. Thus, the results showed the good stability of the
catalyst in terms of structure and morphology during successive
cycles.
Experimental
Materials and instruments
All chemicals were obtained from Sigma and Fluka and used
without further purication. All solvents were distilled and
dried before use. All other reagents were of analytical grade.
Dimethyl sulfone (DMSO2) crystals were prepared according to
a previously reported procedure11 and used as the solvent in the
reactions. Reaction progress was monitored by thin layer
chromatography (TLC) on silica gel (Polygram SILG/UV 254
plates) or gas chromatography (GC) using a Shimadzu-14B gas
chromatography equipped with an HP-1 capillary column and
N2 as the carrier gas and anisole as an internal standard. FTIR
spectra were recorded using a JASCO FT/IR 4600 spectropho-
tometer using KBr discs. 1H NMR (250 MHz) and 13CNMR (62.9
Conclusion
Herein, a stable multifunctional catalyst bearing a hetero- MHz) spectra were recorded on a Bruker Avance DPX-250
magnetic solid support, base functionality, and coordinated spectrometer in deuterated solvents, CDCl3 and DMSO-d6,
metal sites (including Ni and Pd) with redox catalytic property with TMS as an internal standard. X-ray diffraction (XRD)
was successfully synthesized as a single catalytic system for the analyses were performed with a Bruker D8/Advance powder X-
domino oxidation-C–C and reduction-C–N cross-coupling reac- ray diffractometer. The cell temperature was maintained at
ꢁ
tions. The catalyst was characterized using various analytical 25.0 ꢃ 0.1 C using a HAAKE D8 recirculating bath. Elemental
and spectroscopic techniques including GPC, FTIR, UV-Vis, analyses were performed on a PerkinElmer-2004 instrument.
EDX, FE-SEM, TEM, NMR, XPS, DLS, VSM, DET, and ICP anal- Field emission scanning electron microscopy (FE-SEM) images
yses. Domino C–C coupling of alcohols with aryl halides and were obtained on a HITACHI S-4160 and TESCAN MIRA3
domino C–N cross-coupling of nitro compounds with aryl instrument. Elemental analysis (EDX) spectroscopy was per-
halides were performed in the presence of the Ni/Pd catalyst, formed using a eld emission scanning electron microscope,
and moderate efficiency and high selectivity were achieved FESEM, JEOL 7600F, equipped with an energy dispersive X-ray
toward a variety of substrates. The cooperative performance of spectrometer from Oxford Instruments. Transmission electron
the catalyst between the Ni sites, Pd sites, and pyridine moieties microscopy (TEM) was performed on a Philips EM208 micro-
was responsible for this excellent activity, which was conrmed scope operated at 100 kV. The size distribution of the nano-
by various control experiments. The results also conrmed the particles was measured by dynamic light scattering (DLS) on
synergistic effect of Ni and Pd sites for domino oxidation– a HORIBA-LB550 apparatus. The magnetic behavior of the
reduction reactions, which promoted the efficiency and selec- samples was measured on a Lake Shore vibrating sample
tivity. The chemoselectivity studies demonstrated that the magnetometer (VSM) at room temperature. ICP experiments
cross-coupling with aldehyde and amine is superior to the were performed using a VARIAN VISTA-PRO CCD simultaneous
domino oxidation- or reduction coupling, and the coupling of ICP-OES instrument. The average molecular weight of the
aromatic substrates could be selectively coupled compared to samples was measured by the gel permeation chromatography
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(GPC) using a Knauer Advanced Scientic Instrument, Ger- and then dried under vacuum at room temperature for a day
many, with an RI detector (Smartline 2300) PL gel 10 mm, 10 ꢄ (Scheme 3).
3
˚
10 A column with 20 mL injected volume. Monodispersed pol-
y(methyl methacrylate), PMMA, standards were used for cali- Preparation of (Py)-graed-(chlorophyll b)-Pd(II) complex (5)
bration. The average molar mass was determined using the
Coordination of Pd ions to 4 (as a ligand) was performed as
follows: copolymer 4 (0.5 g) was added to 25 mL EtOH at 50 C,
and then PdCl2$2H2O (0.04 g, 0.2 mmol) was added to the
mixture. The mixture was stirred for 2 h, and then ltered, washed
with dry toluene (2 ꢄ 10 mL), and dried in an oven (60 ꢁC).
Millennium 2010 soware. The surface area, pore volume, and
pore diameter of the obtained NPs were measured by N2 phys-
isorption at ꢀ196 ꢁC with a surface area and pore size analyzer
(Micromeritics ASAP 2000 instrument) using the BET method.
X-ray photoelectron spectroscopy (XPS) investigations were
conducted on an XR3E2 (VG Microtech) twin anode X-ray source
with Al-Ka ¼ 1486.6 eV.
ꢁ
Self-catalytic cross-coupling of (Py)-copolymer-(chlorophyll b)-
Pd(II) complex with 4-iodo salicylaldehyde (6)
The self-catalytic base-free coupling of (Py)-graed-(chlorophyll
b)-Pd(II) complex with 4-iodo salicylaldehyde was performed in
DMF (10 mL) in the absence of any base. Compound 5 (0.5 g)
was added to 10 mL DMF under reux conditions. Then, 4-iodo
salicylaldehyde (20.0 mmol) dissolved in 10 mL DMSO was
added to the above mixture. Then, the mixture was stirred for
24 h. Subsequently, the mixture was poured in excess 50 mL
cold EtOH. The precipitate was ltered, washed with acetone
and DEE (each 2 ꢄ 10 mL). The product was dried in an oven
and isolated at a refrigerator.
Demetalation of chlorophyll b (2)
Chlorophyll b was extracted from Heliotropium europaeum plant
by simply extracting 1.0 g of dried plant powder in 30 mL of 80%
acetone, and then ltered.35 The chlorophyll b was puried by
silica gel column chromatography.36–38 The following mobile
phases were applied with the order of: 60% n-hexane, 16%
cyclohexane, 10% ethyl acetate, 10% acetone, and 4% meth-
anol. The elution order using this elution solvent system was b-
carotene, chlorophyll b, and xanthophyll (from top to bottom).
Commercial puried samples of b-carotene and chlorophyll
b were used as controls. For the demetalation of chlorophyll b,
an acetone solution of the chlorophyll (5.0 mM) was prepared
according to previous works. Then, 1.0 mL of 0.5 M HCl was
added to 3.0 mL of acetone solution of chlorophyll in a round-
bottom ask. The reaction was stirred for 2 h at room temper-
ature. Then, the mixture was extracted by n-BuOH (3 ꢄ 10 mL).
Finally, the solvent was removed under reduced pressure and
Preparation of Fe3O4@SiO2–NH2 NPs (9)
Fe3O4@SiO2–NH2 (9) was prepared through three steps
according to a procedure described elsewhere.40
Immobilization of (Py)-copolymer-(chlorophyll b)-Pd(II)-
epoxide on Fe3O4@SiO2–NH2 (10)
the resulting product was completely dried in a vacuum oven at (Py)-copolymer-(Chlorophyll b)-Pd(II) epoxide (6) was immobi-
ꢁ
50 C for 12 h (Scheme 3).
lized on Fe3O4@SiO2–NH2 magnetic NPs in one step. Fe3O4@-
SiO2–NH2 (1.0 g) was dispersed ultrasonically in 10 mL DMSO
for 20 min at room temperature. Then, 0.5 g (Py)-copolymer-
(chlorophyll b)-Pd(II) (6) in 15 mL DMSO was added dropwise to
the mixture under ultrasonic conditions. The addition took
30 min, and then the mixture was reuxed for 24 h. The
resulting product was collected by an external magnetic eld,
washed with deionized water and EtOH (each 2ꢄ 15 mL), an
then dried in a vacuum oven (Scheme 3).
Preparation of chlorophyll-allyl (3)
The extracted chlorophyll b (1.0 g, 1.0 mmol) was dissolved in
20.0 mL of absolute methanol. A methanolic solution of allyl-
amine (3.0 mmol in 20 mL methanol) was added dropwise for
30 min to the chlorophyll solution. The color immediately
changed to green-yellow and the mixture was stirred at room
temperature for 2 h. Subsequently, the pale green solid was
ltered, washed with deionized water and dried at room
temperature in a vacuum desiccator.
Preparation of Fe3O4@SiO2/(Py)-copolymer-(chlorophyll b)-
Pd(II) (11) by coordination of Ni ions to 10
Preparation of (Py)-co-(chlorophyll b) polymer (4)
For the coordination of Ni ions to the catalyst framework, 0.5 of
10 was dispersed in 25 mL absolute EtOH at room temperature
for 20 min. Then Ni(OAc)2$4H2O (0.05 g, 0.2 mmol) was added
to the mixture. The mixture was reuxed with stirring for 4 h.
Then, the resulting product was ltered using an external
magnetic eld and washed with deionized water and ethanol
several times to remove of any metal salt, and then dried in an
oven.
Copolymerization/graing 4-vinylpyridine to chlorophyll-allyl
was performed according to a previously reported procedure.39
Typically, 4-vinylpyridine (0.15 g) and chlorophyll-allyl (3) were
added to a dried round-bottom ask. The ask was nitrogen-
purged for two minutes, and then 6.0 mL dioxane, 6.0 mg
AIBN was added to the ask. The system was sealed and
equipped with an N2 inlet and then immersed in an oil bath.
The mixture was stirred at 85 ꢁC for 24 h. Then, the solution was
allowed to cool to room temperature and added to excess MeOH
as a precipitating solvent in one step. Copolymer 4 was obtained
Acid titration test for the determination of the content of Py
monomer in the catalyst
aer the removal of the solvent under reduced pressure. The An acid titration assay was used to prove and quantify the
product was puried by treatment with diethyl ether (25 mL), graing of the Py moieties in copolymer 4. In this test, 1.2 g of 4
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was added to 50 mL of distilled water and sonicated for 10 min.
The copolymer was titrated with 0.2 M acetic acid in the pres-
ence of phenolphthalein indicator under ultrasonic conditions.
About 9.5 mL acetic acid was consumed at the end point.
Simultaneously, a blank was also titrated, and the total volume
of acetic acid was recorded.
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General procedure for Ni/Pd-catalyzed domino oxidation
Suzuki–Miyaura cross-coupling from alcohols
Generally,
a 10 mL round-bottom ask equipped with
a magnetic stirrer bar and condenser was charged with alcohol
(1.0 mmol), phenylboronic acid (1.0 mmol), catalyst 11
(0.013 mol% Pd), and DMSO2 (3.36 g, 35.7 mmol). An O2 balloon
(ꢂ1.0 atm) was installed and the mixture temperature was
adjusted to 120 ꢁC. The reaction progress was monitored by
TLC. Upon completion of the reaction, the catalyst was removed
magnetically aer cooling the mixture to room temperature,
washed with deionized water and EtOH (each 3 ꢄ 5.0 mL), and
then dried and stored for the next run. For the extraction of the
product, EtOAc (5.0 mL) and H2O (5.0 mL) were added to the
residue. The resulting aqueous phase was further extracted in
EtOAc (2 ꢄ 5.0 mL). The organic layers were combined and
dried over Na2SO4, and EtOAc was removed under reduced
pressure. The pure coupling product was obtained by ash
chromatography of the crude product.
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19 M. Kazemnejadi, A. R. Sardarian and M. Esmaeilpour, J.
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21 S. Cheng, W. Wei, X. Zhang, H. Yu, M. Huang and
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167–172.
In a 10 mL round-bottom ask, nitroarene (1.0 mmol), aryl
halide (1.0 mmol, in the case of C–N coupling), catalyst 11
(2.0 mg, 0.026 mol% Pd, 0.068 mol% Ni), DMSO2 (3.36 g, 35.7
mmol), and NaBH4 (2.0 mmol) were mixed and the reaction
temperature was adjusted to 120 ꢁC. The reaction was stirred at
constant temperature and the progress was monitored by TLC
based on aryl halide consumption. The catalyst separation and
isolation of the desired C–N coupling product was the same as
the aforementioned procedure for the domino oxidation C–C
coupling.
Conflicts of interest
23 A. Alshammari, V. N. Kalevaru and A. Martin, Catalysts, 2016,
6, 97.
24 S. Hamid, M. A. Kumar and W. Lee, Appl. Catal., 2016, 187,
37–46.
There are no conicts to declare.
25 Z. Shah, P. Kumam and W. Deebani, Sci. Rep., 2020, 10, 1–14.
26 C. Chen, N. Jia, K. Song, X. Zheng, Y. Lan and Y. Li, Sep. Purif.
Technol., 2020, 236, 116248.
27 T. Zhou, P. P. Xie, C. L. Ji, X. Hong and M. Szostak, Org. Lett.,
2020, 22, 6434–6440.
Acknowledgements
Authors gratefully acknowledge the nancial support of this
work by the Research Council of Shiraz University and Anwar
Shekha Medical City, Sulaymaniyah.
28 C. Liu, C. L. Ji, Z. X. Qin, X. Hong and M. Szostak, iScience,
2019, 19, 749–759.
29 Z. Wang, X. Wang and Y. Nishihara, Chem.–Asian J., 2020, 15,
1234–1247.
30 Z. Li, X. Xu, X. Jiang, Y. Li, Z. Yu and X. Zhang, RSC Adv.,
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This journal is © The Royal Society of Chemistry 2020
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