Pd- and Ni-Pyridyl Complexes Deposited as Films for Suzuki-Miyaura and Mizoroki-Heck Cross Coupling Reactions

Article abstract of DOI:10.1007/s10562-015-1614-4

A pyridyl fluorene ligand, 2,7-bis(4-pyridyl)-9,9-diethylfluorene (1), has been synthesized by a simple route. The ability of the two linearly terminal pyridyl nitrogen atoms of 1 to coordinate with the Pd(II) or Ni(II) ions has enabled the use of 1 as a linking ligand in the preparation of (PdCl₂/1) _n, (Ni(NO₃)₂/1) _n films, PdCl₂/1 and Ni(NO₃)₂/1 complex. The resulting films and complexes were characterized by UV-vis spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectrometer. The application of films and complexes as catalysts for Suzuki-Miyaura and Mizoroki-Heck reactions was carried out. (PdCl₂/1) _n films show high catalytic activity in the reactions with the Pd loading of ppm. (Ni(NO₃)₂/1) _n multilayers as the active catalytic moieties for these reactions were investigated with very low Ni(II)-loading. Graphical Abstract: The (Pd or Ni/1) _n multilayer films were used as high active catalysts for the C-C formation with extremely low M(II)-loading in ppm level.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-015-1614-4

Catal Lett
DOI 10.1007/s10562-015-1614-4
Pd- and Ni-Pyridyl Complexes Deposited as Films for Suzuki–
Miyaura and Mizoroki–Heck Cross Coupling Reactions
1
2
2
2
Xiuhua Zhao
•
Jie Zhang
•
Yayun Zhao
•
Xing Li
Received: 28 June 2015 / Accepted: 26 August 2015
Ó Springer Science+Business Media New York 2015
Abstract A pyridyl fluorene ligand, 2,7-bis(4-pyridyl)-
,9-diethylfluorene (1), has been synthesized by a simple
Graphical Abstract The (Pd or Ni/1) multilayer films
n
9
were used as high active catalysts for the C-C formation
with extremely low M(II)-loading in ppm level.
route. The ability of the two linearly terminal pyridyl
nitrogen atoms of 1 to coordinate with the Pd(II) or Ni(II)
ions has enabled the use of 1 as a linking ligand in the
preparation of (PdCl /1) , (Ni(NO ) /1) films, PdCl /1 and
2
n
3 2
n
2
Ni(NO ) /1 complex. The resulting films and complexes
3
2
were characterized by UV–vis spectroscopy, atomic force
microscopy, X-ray photoelectron spectroscopy, scanning
electron microscopy, transmission electron microscopy and
energy dispersive X-ray spectrometer. The application of
films and complexes as catalysts for Suzuki–Miyaura and
Mizoroki–Heck reactions was carried out. (PdCl /1) films
2
n
show high catalytic activity in the reactions with the Pd
Keywords Palladium Á Nickel Á Multilayer films Á
loading of ppm. (Ni(NO ) /1) multilayers as the active
3
2
n
Catalysis Á Suzuki–Miyaura and Mizoroki–Heck reactions
catalytic moieties for these reactions were investigated
with very low Ni(II)-loading.
1
Introduction
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-015-1614-4) contains supplementary
material, which is available to authorized users.
The transition-metal-catalyzed cross-coupling reactions
such as Suzuki–Miyaura [1], Mizoroki–Heck [2], Stille [3–
5], Kumada [6], Negishi [7, 8], Hiyama [9] and Sono-
gashira [10] reactions are very powerful tools for the C–C
bonds formation. These methods have been extensively
used in a wide range of academic areas including biological
materials and medicinal product synthesis. Among the
powerful transformations, the traditional palladium-cat-
alyzed Suzuki–Miyaura and Mizoroki–Heck reactions
represent the important ones with phosphine ligand in the
presence of a suitable base under an insert atmosphere [11–
&
Xing Li
lixing@nbu.edu.cn; lix905@126.com
Xiuhua Zhao
1
017027635@qq.com
Jie Zhang
347582628@qq.com
Yayun Zhao
390617347@qq.com
1
1
1
2
Faculty of Science, Ningbo University,
Ningbo 315211, Zhejiang, People’s Republic of China
15]. However, phosphine ligands are toxic and air-sensitive
[16, 17]. Therefore, large-scale industrial application is
limited for Pd-P catalysts, and the development of phos-
phine-free catalysts for C–C bond formation reactions has
Faculty of Materials Science and Chemical Engineering,
Ningbo University, Ningbo 315211, Zhejiang,
People’s Republic of China
123

X. Zhao et al.
¨
become a current focus [18, 19]. Yu [20] and Ozdemir
21] reported that bidentate 1,10-phenanthroline and
(GC–MS) was performed on a 430 GC (Varian, USA). UV–
vis absorption spectra were recorded on a quartz slide using a
Lambda35 spectrophoto-meter (Perkin Elmer, USA). High-
resolution X-ray photoelectron spectra (XPS) were collected
at a takeoff angle of 45° using PHI Quantum 2000 scanning
ESCA microprobe (Physical Electronics, USA) with an Ala
X-ray line (1486.6 eV). Atomic force microscope (AFM)
images were taken on a single-crystal silicon slide using a
Veeco Multimode NS3A-02NanoscopeIII atomic force
microscope with silicon tips. Height images of the films were
recorded using tapping-mode AFM. Analysis of Pd content
was measured by inductively coupled plasma-atomic emis-
sion spectroscopy (ICP-AES) using Ultima. Transmission
electron microscopy (TEM) images were carried out by
Tecnai G2 F20 S-TWIN. Scanning electron microscopy
(SEM) images were taken with SU-70 field-emission scan-
ning electron microscope. Energy dispersive X-ray spec-
trometer (EDS) was carried out on a Carl Zeiss model Ultra
55 microscope. The solid state fluorescence spectra were
measured on F-4600 fluorescence spectrophotometer. Pow-
der X-ray diffraction (PXRD) data were collected on a
Bruker D8 Focus X-ray diffractometer using Cu Ka
radiation.
[
dialkylimidazolinium were used as the ligand to activate
the Pd(II)-catalysts, respectively. The phosphine-free Pd-
catalyst is a luxurious case in the industrial organic syn-
thesis since Pd and its complexes are very expensive
materials, even which show high catalytic activity with a
high Pd-loading of 3–10 mol%. Subsequently, Pd–Pt
multilayer films were successfully assembled with the
extra-low Pd loading, which as catalysts in the Suzuki–
Miyaura coupling reaction showed considerable high cat-
alytic activity [22, 23]. However, the application of Pd–Pt-
organometallic catalysts was greatly restricted in the
organic synthesis because of its high cost and strict
preparation process. Wang [24] and Monteiro [25]
demonstrated that the Ni(TFA) with b-diketone and PPh
2
3
ligands, or the ligand-free NiCl Á6H O could be used to
2
2
catalyze the coupling reactions of a certain scope of aryl
bromides and iodides with aryl boronic acids, but it’s a pity
that the Ni(II)-loading is up to 10 mol% in those reaction
above. In this report, we synthesized a new pyridyl fluorene
ligand, namely, 2,7-bis(4-pyridyl)-9,9-diethylfluorene (1,
Scheme 1), which was used to assemble the multilayer
films by alternating adsorption metal ions (Pd or Ni) and 1
onto the quartz slide [26–32]. The (PdCl /1) , (Ni(NO ) /
2.2 Synthesis of 2,7-Bis(4-pyridyl)-9,9-
diethylfluorene (1)
2
n
3 2
1
)n films catalysts showed high catalytic activity in the
Suzuki–Miyaura and Mizoroki–Heck reactions with the
metal loading in ppm level.
0
The samples of 2,7-dibromo-9,9 -diethylfluorene (3.0 mmol),
4-pyridine boronic acid (7.5 mmol), Na CO (12.0 mmol)
2 3
and Pd(PPh ) (0.1 mmol) were added to the 250 mL three-
3
4
2
Experimental Section
necked flask and dissolved in a mixture of 1,2-dimethoxy
ethane (abbreviated as DME) and distilled water (80/40 mL).
2
.1 Materials and Methods
The resulting mixture was refluxed under N atmosphere at
2
95 °C for 48 h, cooled to the room temperature, and extracted
All catalysis coupling reactions were carried out under air
atmosphere. All other synthetic reactions were performed by
using standard Schlenk techniques utilizing a double-mani-
fold vacuum system with high purity nitrogen flow.
Poly(ethylenimine) (abbreviated as PEI) was purchased
from Aldrich Chemical Company. All solutions were pre-
pared with doubly-distilled water. All reagents were of
analytical grade and used as received without further
purification. Infra-red spectra were recorded on a Nicolet
Avatar FTIR spectrophotometer in the range 4,000–
with dichloromethane for three times. Then the organic phase
was dried over anhydrous magnesium sulfate, concentrated
and purified by column chromatography on silica gel eluting
with petroleum ether/ethyl acetate (1: 2) to give compound 1
-1
as a faint yellow solid (yield: 71 %). IR (KBr, v/cm ): 3478
(m), 3398 (w), 3028 (w), 2959 (w), 2931 (w), 2870 (vw), 2853
(vw), 1592 (vs), 1463 (s), 1408 (s), 1190 (w), 1121 (w), 1005
-1 1
(w), 807 (s), 721 (w), 713 (m), 617 (w), 543 (m) cm . H
NMR (CDCl , 400 MHz) d: 8.69 (d, J = 4.8 Hz, 4H, PhH),
3
7.84 (d, J = 8.0 Hz, 2H, PhH), 7.59 * 7.70 (m, 8H, PhH),
2.11 (q, J = 56.4 Hz, 4H, CH ), 0.40 (t, J = 14.4 Hz, 6H,
-
1
-1
4
00 cm (1 cm resolution, 16 scans). NMR spectra were
2
obtained from solutions in CDCl using Bruker DRX-400
3
CH ) ppm. ESI(?)-MS (m/z) for [M ? H]?: Calc. = 377.5,
3
spectrometers. Gas chromatography-mass spectrometry
Obs. = 377.3.
Scheme 1 Synthesis schematic
diagram of complex 1
1
23

Pd- and Ni-Pyridyl Complexes Deposited as Films for Suzuki–Miyaura and Mizoroki–Heck Cross…
2
.3 Layer-by-Layer Assembly of Multilayer Films
dried over anhydrous Na SO , concentrated and purified by
2 4
silica gel column chromatography with the eluent of pet-
roleum ether.
The quartz slides were cleaned with ‘‘a piranha solution’’
(
98 % H SO /30 % H O = 8:3, V/V) at 80 °C for
2
4
2 2
4
0 min, and thoroughly washed with distilled water.
2.6 Recycling Experiments
Further purification was carried out by immersion in a
H O/H O /NH OH (5:2:1, V/V/V) bath at 70 °C for
In the first catalytic cycle, the quartz slide coated with
multilayer films was immersed into a solution of aryl
halides (1.0 mmol), arylboronic acid (1.2 mmol), K CO
2
2
2
4
3
0 min. Then the clean slides were first immersed in PEI
solution for 20 min. Then the pre-coated PEI slides were
alternatively immersed in the aqueous solution of PdCl2
2
3
(3.0 mmol) in EtOH (3.0 mL) and H O (4.0 mL). After the
2
(
5 mM) and ethanol solution of complex 1 (5 mM) for
0 min. The substrates were washed with water and
mixture was stirred for 20 min at 50 °C, the quartz slide
was removed and the resulting solution was heated at reflux
for a further 20 h at 50 °C. Afterward, the mixture was
extracted with ethyl acetate (3 9 15 mL). The water phase
was collected and recharged with aryl halides (1.0 mmol),
arylboronic acid (1.2 mmol), K CO (3.0 mmol). EtOH
3
dried after each immersion at room temperature. By
repeating the above-mentioned steps, the (PdCl /1)
2
n
multilayer films were prepared. The (Ni(NO ) /1) films
2
3
n
were assembled using the same method with the con-
2
3
centration of (Ni(NO ) and complex 1 corresponding to
3
(3.0 mL) and sufficient H O were added to make the
2
2
3
0 mM.
solution volume to 7.0 mL. The coated quartz slide was re-
immersed into the new reaction mixture. After the mixture
was stirred for 20 min, the quartz slide was again removed
from the mixture and the released metal–ligand complex
was used to catalyze the second Suzuki–Miyaura reaction.
By repeating these steps, the catalytic behavior of the film
was investigated over several cycles.
2
.4 Preparation of Metal–Organic Complexes
The aqueous solution of PdCl was quickly added to the
2
EtOH solution compound 1 (Pd: 1 = 1: 1, mol), and the
resulting mixture was stirred at 50 °C for 10 h. Then the
PdCl /1 complex was obtained and collected by centrifugal
separation, washed alternatively with H O and EtOH, and
2
2
3
Results and Discussion
dried in the air. The (Ni(NO ) /1 complex was prepared by
3
2
the similar method with the temperature of 90 °C.
3.1 UV–Vis Spectroscopy of the Multilayer Films
2
.5 General Procedure for the Suzuki–Miyaura
and Mizoroki–Heck Cross-Coupling Reactions
Through the layer-by-layer (LbL) self-assembly technique,
the multilayer film is prepared by alternating adsorption of
metal ion and complex 1 layers onto solid substrate pre-
coated with PEI, resulting in the metal-1 complexes loaded
within multilayer films. The method is based on the coor-
dination bond between metal ions and pyridyl N atoms
from compound 1. UV–vis spectroscopy is used to monitor
the growth process of the multilayer films. The UV–vis
spectra of (PdCl /1) and (Ni(NO ) /1) films are shown in
A general procedure for the couplingreactionof an arylhalide
with arylboronic acid is as follows: aryl halide (1.0 mmol),
arylboronic acid (1.2 mmol), K CO (3.0 mmol), ten layers
2
3
films loaded on quartz slides as catalysts, 4.0 mL H O and
2
3
.0 mL EtOH were added to an flask. The reaction mixture
was heated to a certain temperature in air. After the end of the
reaction, the reaction system was cooled to room temperature,
and extracted with ethyl acetate for three times. Then the
combined organic phase was dried over anhydrous Na SO .
2
n
3 2
n
Figs. 1 and 2, respectively. The absorption peaks at 220
and 358 nm (Fig. 1) were observed, which could be
attributed to the p–p* transitions and n-p* transitions of
the aromatic ring, respectively. The high-energy peak at
358 nm were red-shifted compared with the one of com-
plex 1 (Fig. S6, 330 nm), which was probably due to the
charge transfer between metal and ligand or solvent effect
[33]. The (PdCl /1) film growth shows a relatively fine
2
4
After removal of the solvent, the crude product was purified
bysilica gel column chromatographyusing petroleum ether to
obtain the product with high purity.
For Mizoroki–Heck cross-coupling reaction, aryl halide
(
1.0 mmol), styrene (or t-butyl acrylate) (1.5 mmol), Na2
2
n
2
CO (2.0 mmol), 6.0 mL N,N-dimethylformamide (DMF)
3
linear correction with R = 0.9900 between the optical
absorption at kmax = 358 nm and the number of ligand
layers, suggesting that the ligand is incorporated into the
films with a regular growth. However, the (Ni(NO ) /1)
n
and ten layers films loaded on quartz slides as catalysts
were added to the flask. Then the resulting mixture was
stirred at 140 °C for 24 h under ambient atmosphere,
cooled to room temperature, and extracted with ethyl
acetate for three times. The combined organic phase was
3
2
film growth shows a relatively bad linear correction with
2
R = 0.9790 between the optical absorption at
123

X. Zhao et al.
Fig. 1 UV–vis spectra of the PEI-(PdCl
increase in the absorbance at 358 nm as a function of the number of
bilayers of PEI-(PdCl /1)
2
/1)
n
(n = 1–10) films. Inset:
Fig. 3 XPS spectra of PEI-(PdCl
crystal silicon substrate. Inset: Pd3d
2
/1)10 film deposited on a single-
2
n
change of the coated quartz slide. When the coated quartz
slide exhibited no absorbance, the aqueous solution
(25 mL) was used for analysis of Pd content by the ICP-
AES. The amount of Pd in the (PdCl /1) films is deter-
2
10
-
4
-8
mined as 9.7 9 10 wt % (6.3 9 10 mol Pd). Under
similar conditions, aqueous solution of HNO was used to
3
determine the Ni content in (Ni(NO ) /1) films, and the
3
2
10
-
amount of Ni in the film is 7.3 9 10 wt % (8.5 9 10
4
-8
mol Ni).
XPS measurements were carried out to identify the
element composition of the multilayer films deposited on
the single crystal silicon substrates. As expected, the sur-
vey spectra (Fig. 3) of the (PdCl /1) films showed the
2
10
existence of C1s (285.0 eV), Cl2p (199.0 eV), N1s
401.7 eV), O1s (532.9 eV), OKLL (979.4 eV) and Pd3d
(
Fig. 2 UV–vis spectra of the PEI-(Ni(NO
Inset: increase in the absorbance at 344 nm as a function of the
number of bilayers of PEI-(Ni(NO /1)
3
)
2
/1)
n
(n = 1–10) films.
(337.8 eV), which were consistent with characteristic
peaks of the corresponding elements. The shoulders of the
Pd3d peak on the low binding energy region were ascribed
to satellite peak. Photoelectrons with energies of 338.3 eV
and 343.6 eV were observed in the Inset of Fig. 3, indi-
cating the Pd(II) oxidation state in the (PdCl /1) films.
3
)
2
n
kmax = 344 nm and the number of ligand layers, which
indicates that the complex 1 merged into the films with a
relatively irregular growth.
2
10
Figure S8 also confirms the existence of Pd(II) in PdCl /1
2
complex.
3
.2 Analysis of Metal Content in the Multilayer
Films
The XPS spectra of (Ni(NO ) /1) film was also
3
2
10
investigated. As shown in Fig. 4, the survey spectra dis-
played the presence of C1s (285.0 eV), N1s (399.2 eV), O1s
(532.9 eV), OKLL (981.0 eV), Ni2p (856.7 eV), Si2s
(152.1 eV) and Si2p (99.3 eV), indicating that all the
expected elements were loaded in the film. The peaks of
855.3 eV and 872.9 eV on the high binding energy region
were attributed to Ni2p3/2 and Ni2p1/2, respectively, indi-
cating the presence of Ni(II) oxidation state in the
(Ni(NO ) /1) film. Figure S9 also shows that the Ni
It is necessary for cross-couplings reactions to ascertain the
metal content in multilayer films as catalysts. The on-line
detection of the metal concentration can not be performed
during the catalytic reaction process in our lab. A substi-
tuted method was selected to determine the amount of
metal: The quartz slide coated with (PdCl /1) was
2
10
immersed into a NaOH aqueous solution (25 mL, 1.0 M)
and UV–vis spectra were used to monitor the absorbance
3
2
10
oxidation state in the Ni(NO ) /1 complex is ?2.
3
2
1
23

Pd- and Ni-Pyridyl Complexes Deposited as Films for Suzuki–Miyaura and Mizoroki–Heck Cross…
Fig. 6 AFM images of the films on the single-crystal silicon
2
substrate (scan area is 3.0 9 3.0 lm ); a and b are the height images
of PEI-(Ni(NO /1) (Rrms = 2.11 nm) and PEI-(Ni(NO /1)10
rms = 6.17 nm), respectively
)
3 2
5
3 2
)
(
R
3.4 Scanning Electron Microscope of the Multilayer
Films
3 2
Fig. 4 XPS spectra of PEI-(Ni(NO ) /1)10 film deposited on a single-
crystal silicon substrate. Inset: Ni2p
3.4.1 Scanning Electron Microscope of the (PdCl /1)
2
n
Films
The SEM image of (PdCl /1) film confirmed the rough
2
10
surface texture. As shown in Fig. 7a, the colloid-like parti-
cles are distributed in the film, and the holes with different
size and depth are presented on the film surface, which are
consistent with the AFM discussed above. Statistic calcu-
lations in SEM showed that the particle sizes ranged from
25.0 to 61.1 nm with average size of 37.8 nm (Fig. 7b).
EDS spectrum confirmed all the expected elements (Pd, Cl,
C and N) on the film (Fig. 7a, inset), which indicated PdCl2
and complex 1 were adsorbed on the substrates. It should be
noted that the presence of Si, O and Pt are most likely from
single-crystal silicon substrate and platinum spray used in
this procedure. Besides, FT-IR spectrum of (PdCl /1) film
Fig. 5 AFM images of the films on the single-crystal silicon
2
substrate (scan area is 1.0 9 1.0 lm ); a and b are the height images
of PEI-(PdCl
1
2
/1)
5 2
(Rrms = 2.16 nm) and PEI-(PdCl /1)10 (Rrms =
1.20 nm), respectively
2
n
3
.3 Atomic Force Microscopy Images
of the Multilayer Films
was also investigated. As shown in Fig. S10, a strong broad
1
-
absorption band centred at 3,400 cm can be assigned to
the O–H stretching vibrations of water molecules stemming
-
from air. The shoulder peak at 2,922 cm and sharp band at
1
AFM is a powerful technique for the measurement of three-
dimensional surface topography at the nanoscale. Here the
AFM images of the films were used to provide detailed
information of the surface morphology and homogeneity.
As shown in Fig. 5a, the five-layer film of (PdCl /1) was
-
1
1,567 cm
are attributed to C–H and C=C (or C=N)
stretching vibrations in-plane on the aromatic ring, respec-
-
1
-1
tively. The peaks at 1,409 cm and 650 cm correspond
to C–H bending vibrations on ethyl group and aromatic ring,
respectively. The FT-IR spectrum of (PdCl /1) film indi-
2
5
relatively uniform with the root-mean-square (RMS)
roughness of 2.16 nm. As the number of deposited bilayers
increases, large particle aggregates were observed and the
island-shaped nanostructures were distributed on the sur-
face of the (PdCl /1) film with the RMS roughness of
2
n
cates the existence of complex 1.
The PdCl /1 complexes were prepared by mixing pre-
determined quantificational homogeneous solutions of
2
PdCl and complex 1, and characterized by SEM, TEM and
2
2
10
1
1.20 nm, in which the average diameter of the nanopar-
EDS to better understand the nature, size and structure of
the composite. SEM showed that the particles are relatively
uniform in size (Fig. 8a). Statistic calculations in SEM
ticulate was about 60 nm (Fig. 5b). Similarly, the RMS
roughness of (Ni(NO ) /1) and (Ni(NO ) /1) films was
3
2
5
3 2 10
2
.11 and 6.17 nm (Fig. 6), respectively. And the mean
showed the diameters of PdCl /1 complex particles ranged
2
diameters of nanoparticulate of five-layer and ten-layer
films were 58.822 and 68.844 nm, respectively. Obviously,
the RMS roughness and diameter of the films increase with
the film growth in the substrate.
from 34.8 to 71.6 nm with average size of 47.5 nm
(Fig. 8b). EDS spectrum analysis of the complex reveals
the presence of all the expected elements Pd, Cl, C, N (see
inset of Fig. 8c), indicating that the complexes in the film
123

X. Zhao et al.
Fig. 7 a The SEM image of
PEI-(PdCl /1)10 film (Inset:
EDS spectrum); b particle size
2
distribution
2
Fig. 8 a SEM and c TEM images of the PdCl /1 complex (Inset: EDS spectrum); b particle size distribution
consist of PdCl and complex 1. The morphologies of
2
the islanded-like particles were distributed in the film with
different size and depth, indicating the rough surface tex-
ture, which were consistent with the AFM discussed above.
EDS spectrum confirmed all the expected elements (Ni, C,
N and O) on the film (Fig. 9a, inset), which proved
Ni(NO ) and complex 1 were adsorbed on the substrates.
PdCl /1 complex particles were confirmed by TEM
2
(
Fig. 8c).
PdCl /1 complex was also characterized by UV–vis
2
absorption spectroscopy, fluorescence spectroscopy, FT-IR
spectroscopy and PXRD. The UV–vis absorption spectra
3
2
(
Fig. S11) analysis reveals that compound 1 exhibits
absorption peaks at 228 and 330 nm in the solution of
The peaks of Si, Al and Pt are derived from the single-
crystal silicon substrate and platinum spray used in this
procedure, respectively. Statistic calculations indicated that
the particle size in the films ranged from 35.9 to 63.7 nm
with mean size of 49.7 nm (Fig. 9b). Besides, IR absorp-
tion peaks (Fig. S15) of (Ni(NO ) /1) film are as follows:
EtOH, corresponding to the p ? p* and n ? p* transi-
tions, respectively; PdCl /1 complex shows a broad
absorption band centered at 375 nm with a red shift of
2
2
5 nm stemming from MLCT transitions, which confirms
3
2
n
that PdCl /1 complex is composed of PdCl and 1. The
2
3446 (O–H), 2920 (C–H), 1652 (C=C, C=N), 1385 (C–H),
2
-
669 (C–H) cm , indicating the presence of complex 1.
1
fluorescence emission spectra (Fig. S12) analysis of free 1
and PdCl /1 complex also confirms that. IR absorption
Correspondingly, the Ni(NO ) /1 complexes were
3 2
2
peaks (Fig. S13) of PdCl /1 complex are as follows: 3450
2
characterized by SEM, TEM and EDS. As shown in
Fig. 10, the complexes were rod-like in shape, which were
different ones from the film. The element map gave all the
expected elements Ni, C, N and O measured by EDS
(
(
O–H), 2924 (C–H), 1611 (C=C, C=N), 1218 (C–N), 1154
-
C–H), 814 (C–H) cm , indicating the presence of com-
1
plex 1. Besides, PXRD patterns of PdCl /1 complex are
2
likely a mix of PdCl and free 1 (Fig. S14), indicating that
2
spectrum (Fig. 10b, inset), indicating that the Ni(NO ) /1
3 2
the complex is composed of PdCl and 1.
2
complex should be composed of Ni(NO ) and complex 1.
3 2
Besides, the UV–vis absorption spectroscopy, fluores-
cence spectroscopy, FT-IR spectroscopy and PXRD could
also give some evidences concerning the nature of
Ni(NO ) /1 complex. The UV–vis absorption spectra
3
.4.2 Scanning Electron Microscope of the (Ni(NO ) /1)
3 2 n
Films
3
2
The SEM images of (Ni(NO ) /1) film were recorded to
3
(Fig. S11) analysis reveals that Ni(NO ) /1 complexes
3 2
2
10
understand the surface morphology. As shown in Fig. 9a,
show two absorption peaks at 212 and 332 nm, which are
1
23

Pd- and Ni-Pyridyl Complexes Deposited as Films for Suzuki–Miyaura and Mizoroki–Heck Cross…
Fig. 9 a The SEM image of
PEI-(Ni(NO ) /1)10 film (Inset:
3 2
EDS spectrum); b particle size
distribution
Fig. 10 a SEM and b TEM
images of Ni(NO
3 2
) /1 complex
(
Inset: EDS spectrum)
similar with the corresponding peaks of complex 1. The
shift of the highest absorption peak between Ni(NO ) /1
carried out with K CO as base in H O/EtOH at 50 °C for
2
3
2
4 h. As shown in Table 1, the para-substituted aryl bro-
3
2
complexes and free 1 may be attributed to MLCT transi-
tions. This inference is also tested and proved by fluores-
cence emission spectra of the relevant samples in the same
solution of EtOH (Fig. S12). Besides, IR absorption peaks
mides with electron-withdrawing (e.g., 4-CF , 4-CN,
3
4-COMe) and electron-donating groups (e.g., 4-OMe) give
the corresponding biaryls in high yields. However, the
ortho substituents offer the low yield due to the steric
hindrance effect (Table 1, entry 7). Longer reaction time
and higher temperature were required for complete con-
version (Table 1, entry 8). The para-substituted aryl-
boronic acids bearing electron-donating substituents (e.g.,
4-Me, 4-OMe) also favor the coupling reactions (Table 1,
entries 9–10). Even for the ortho-substituted arylboronic
acid (e.g., 2-MeO), it also gives high yield (Table 1, entry
(
Fig. S16) of Ni(NO ) /1 complex are as follows: 3419 (O–
3 2
H), 2963 (C–H), 1612 (C=C, C=N), 1384 (C–H), 814 (C–
-
1
H) cm , indicating the presence of complex 1. PXRD
patterns of Ni(NO ) , complex 1 and Ni(NO ) /1 complex
were also recorded (Fig. S17), which clearly showed that
3
2
3 2
the pattern of Ni(NO ) /1 complex was the stack of
3
2
Ni(NO ) and free 1.
3
2
11), indicating that the steric hindrance effect from the
3
.5 Catalytic Application of the (PdCl /1)10 Films
2
ortho substituents hardly affects the yield of the reactions.
In order to further investigate the catalytic activity of the
(PdCl /1) films, a series of parallel experiments were
Loaded Quartz Slide for the Suzuki–Miyaura
Cross-Coupling Reaction
2
10
performed in the similar conditions. It was observed that
complex 1 as a catalyst was inactive in the reaction of
4-methoxy-aryl bromide and phenylboronic acid without
the palladium source (Table S2, entry 1). Contrarily, PdCl2
displayed moderate catalytic activity with the yield of
In order to optimize the efficiency of (PdCl /1) multilayer
2
10
film as catalysts, the Suzuki–Miyaura reaction of 4-bro-
moanisole with phenylboronic acid was carried out under a
variety of time conditions, and the results are presented in
Table S1. Among the time employed, 1 h gives the very
low yield (18 %). 2 h offers moderate yield (56 %). When
the time increased to 4 h, the high yield (96 %) was
obtained.
55 % (Table S2, entry 2). Reaction of PdCl with 1 formed
2
a precipitate, which was collected and fully characterized.
The PdCl /1 complex exhibited relatively higher catalytic
2
activity than PdCl , but less than the (PdCl /1) films
2
2
10
To explore the scope of the catalytic reactions, the cross-
couplings between aryl halides and arylboronic acid were
(Table S2, entries 3 and 4). Besides, this film as catalyst
can be successfully re-used for several times, and high
123

X. Zhao et al.
Table 1 Suzuki-Miyaura cross-coupling reactions of aryl halides with arylboronic acid using (PdCl
catalysts
2
/1)10 films loaded on quartz slides as
H O/EtOH
2
X
+
B(OH)2
R1
R
2
Catalyst, K CO3
R
1
R
2
2
a
Entry
R
1
R
2
X
T/ °C, timer/h
Yield (%)
1
2
3
4
5
6
7
8
9
4-OEt
H
Me
H
I
50, 4
50, 4
50, 4
50, 4
50, 4
50, 4
50, 4
100, 24
50, 4
50, 4
50, 4
97
89
87
95
93
96
55
86
95
95
90
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
4-CF
3
H
4-CN
4-COMe
4-OMe
2-OMe
2-OMe
H
H
H
H
H
H
4-Me
1
1
0
1
H
4-OMe
2-OMe
H
2 3 2
General procedure: 1.0 mmol of aryl halide, 1.2 mmol of arylboronic acid, 3 mmol of K CO , in H O/EtOH (4:3, V/V) under ambient
atmosphere
a
1
Isolated yield. H NMR data of the products in Supplementary Materials
yields of the coupled products were obtained under similar
conditions (Fig. 11, or Table S3, entries 1–5). After five
cycles, the yield decreased rapidly (Table S3, entries 6–7),
indicating that the catalytic active species into the solution
were gradually used up in the reactions [15, 17]. Con-
trastively, (PdCl /1) films as catalyst for the reaction of
3.6 Catalytic Application of the (Ni(NO ) /1)10
3 2
Films Loaded Quartz Slide for the Suzuki–
Miyaura Cross-Coupling Reaction
The Suzuki–Miyaura cross-coupling reactions were carried
out by employing the (Ni(NO ) /1)10 multilayer film loa-
3 2
2
10
4
-iodophenetole with 4-methylphenylboronic acid can be
ded on the solid slides as catalysts. As shown in Table 2,
for aryl iodide, the reaction gives the high yield (entry 1).
The aryl bromide offers the low yield of 30 % (Table 2,
entry 2), even though longer time and higher temperature
are executed in the reaction system, and it is very difficult
to reach considerably high yield (Table 2, entry 3), which
could be attributed to the low activity of aryl bromide and
the low loading of Ni(II) on the film. The Suzuki–Miyaura
recycled six times (Fig. 12, or Table S4, entries 1–6).
Afterword, it sharply lost catalytic activity. After each
cycle step, a certain amount of metal–ligand complexes
were desorbed from films into reaction mixture, so it is
very important to recycle the solvent for the yield and
environmental protection.
Fig. 11 Yields obtained in recycles catalysis runs of reaction of
4
Fig. 12 Yields obtained in recycles catalysis runs of reaction of
-bromoanisole with phenylboronic acid using (PdCl
2
/1)
n
and
4-iodophenetole with 4-methylphenylboronic acid using (PdCl
2 n
/1)
(
Ni(NO /1) films as catalysts
n
3
)
2
and (Ni(NO /1) films as catalysts
n
3
)
2
1
23

Pd- and Ni-Pyridyl Complexes Deposited as Films for Suzuki–Miyaura and Mizoroki–Heck Cross…
Table 2 Suzuki-Miyaura cross-coupling reactions of aryl halides with arylboronic acid using Ni(NO
loaded on quartz slides as catalysts
3
)
2
/1 complex and (Ni(NO
3
)
2
/1)10 films
H O/EtOH
2
X
+
B(OH)2
R1
R
2
Catalyst, K CO3
R
1
R
2
2
a
Entry
R
1
R
2
X
Catalysts
T/ °C, time/h
Yield (%)
b
1
2
3
4
5
6
4-OEt
4-Me
H
I
(Ni(NO
(Ni(NO
(Ni(NO
3
3
3
)
)
)
2
/1)10 film
90, 10
90, 10
110, 24
90, 10
90, 10
90, 10
87
b
4-OMe
4-OMe
4-OEt
Br
Br
I
2
2
/1)10 film
30
b
H
/1)10 film
60
c
85
4-Me
H
Ni(NO
Ni(NO
Ni(NO
3
)
)
)
2
2
2
/1 complex
/1 complex
/1 complex
c
81
4-OMe
Br
Br
3
3
c
80
4-CF
3
H
2 3 2
General procedure: 1.0 mmol of aryl halide, 1.2 mmol of arylboronic acid, 3 mmol of K CO , in H O/EtOH (3:4, V/V) under ambient
atmosphere
a
Isolated yield
b,c
-5 1
Catalyst loading was 8.5 9 10 and 0.03 mmol, respectively. H NMR data of the products in Supplementary Materials
Table 3 Mizoroki-Heck cross-coupling reactions of aryl halides with olefins using (PdCl
as catalysts
2
/1)10 and (Ni(NO
3
)
2
/1)10 films loaded on quartz slides
DMF
Catalyst, Na CO
R2
X
+
R1
R1
2
3
R2
a
Entry
R
1
R
2
X
Catalyst
Yield (%)
1
2
3
4
5
6
7
8
9
H
Ph
Ph
Ph
Ph
Ph
t
COO Bu
t
COO Bu
Br
Br
Br
Br
Br
Br
I
(PdCl
(PdCl
(PdCl
(PdCl
(PdCl
(PdCl
(PdCl
(PdCl
2
2
2
2
2
2
2
2
/1)10 films
/1)10 films
/1)10 films
/1)10 films
/1)10 films
/1)10 films
/1)10 films
/1)10 films
67
94
70
73
78
49
98
96
4-CN
4-COMe
4-CF
3
4-OMe
H
H
H
Ph
Ph
Ph
I
4-CN
4-COMe
Br
I
(Ni(NO
(Ni(NO
3
)
)
2
/1)10 films
/1)10 films
42
68
1
0
3
2
General procedure: the mixture of aryl halide (1.0 mmol), olefins (1.5 mmol), Na
2
2
CO
3
(2 mmol) and DMF (6 mL) were stirred at 140 °C for
4 h under ambient atmosphere
a
1
Isolated yield. H NMR data of the products in Supplementary Materials
reaction catalyzed by Ni(NO ) /1 complex performs well.
2
(Ni(NO ) /1) films can be re-used five times for the
3 2 10
3
The aryl iodide gives the high yield of 85 % (Table 2,
reaction of 4-iodophenetole with 4-methylphenylboronic
acid (Fig. 12 or Table S4, entries 10–14). After five cycles,
the yield decreased rapidly (Table S4, entries 15–16),
indicating that the Ni(II) species into the solution were
gradually used up in the reactions.
entry 4); the para-substituted aryl bromides bearing elec-
tron-withdrawing (e.g., CF ) and electron-donating sub-
3
stituents such as OMe offer the well-pleasing yields
(
Table 2, entries 5–6).
As we all know, recycling experiment is very important
for a successful and potential catalytic system. The recy-
3.7 Catalytic Application of the Films Loaded
Quartz Slides for the Mizoroki–Heck Reaction
cling behaviour of (Ni(NO ) /1) films was investigated.
3
2
10
As shown in Fig. 11 or Table S3, entries 11, this film gives
extremely low yield (4 %) in the second run, indicating
that it could not be effectively multi-used in the reaction of
The Mizoroki–Heck reaction was carried out employing
the solid slide coated with multilayer films as catalysts. In
order to optimize the efficiency of films, the effect of time
4
-bromoanisole with phenylboronic acid. However,
123

X. Zhao et al.
for the reaction between 4-bromobenzonitrile and styrene
(2013R405068) and sponsored K. C. Wong Magna Fund in Ningbo
University.
is investigated using (PdCl /1)10 films as catalyst. As
2
shown in Table S5, the reaction gives the highest yield
under 24 h among all the time used.
References
To further explore the scope of the catalytic reactions,
the Mizoroki–Heck cross-coupling reaction between
aryl halides and terminal olefins with (PdCl /1) and
1
2
3
4
. Suzuki A (1985) Pure Appl Chem 57:1749
. Heck RF (1982) Org React 27:345
. Milstein D, Stille JK (1979) J Am Chem Soc 101:4981
. Milstein D, Stille JK (1979) J Am Chem Soc 101:4992
2
10
(
(
Ni(NO ) /1) films as catalysts were performed. For
3 2 10
PdCl /1) films, it is evident in Table 3 that aryl bromides
2
5. Milstein D, Stille JK (1979) J Org Chem 44:1613
10
6
7
8
9
. Yang LM, Huang LF, Luh TY (2004) Org Lett 6:1461
. Negishi E (1982) Acc Chem Res 15:340
. Erdik E (1992) Tetrahedron 48:9577
containing electron-withdrawing/donating groups (e.g.,
CN, COMe, CF , OMe) give moderate yields (Table 3,
3
entries 2–5). However, in the reaction of bromobenzene
t
and terminal olefins (e.g., COO Bu), the reaction offers low
. Nakao Y, Hiyama T (2011) Chem Soc Rev 40:4893
10. Sonogashira K, Tohda Y, Hagihara N (1975) Tetrahedron Lett
6:4467
11. Lipshutz BH, Taft BR (2008) Org Lett 10:1329
2. Moore LR, Shaughnessy KH (2004) Org Lett 6:225
3. Liu S, Berry N, Thomson N, Pettman A, Hyder Z, Mo J, Xiao L
(2006) J Org Chem 71:7467
1
yield (Table 3, entry 6). The reactions between aryl iodides
t
and olefins (e.g., Ph, COO Bu) present high yield under the
1
1
same conditions (Table 3, entries 7). In 2002, Kawano
0
et al. reported that dichloro-(2,2 -bipyridine) palladium(II)
1
1
4. Battace A, Zair T, Doucet H, Santelli M (2006) Synthesis 3495
5. Gao SY, Huang YB, Cao MN, Liu TF, Cao R (2011) J Mater
Chem 21:16467
complex is not suitable for the Mizoroki–Heck reaction of
aryl bromides [34]. However, in our work, the (PdCl /1)
2
n
catalyst with very low loading (ppm level) is proved to be
high active for the Mizoroki–Heck reaction of aryl
bromides and terminal olefins. Correspondingly, the
1
17. Gao SY, Zheng ZL, Lu J, Cao R (2010) Chem Commun 46:7584
6. Tucker CE, de Vries JG (2002) Top Catal 19:111
1
8. Sigeev AS, Peregudov AS, Cheprakov AV, Beletskaya IP (2015)
Adv Synth Catal 357:417
(
Ni(NO ) /1) films-catalyzed Mizoroki–Heck reaction
3 2 10
1
2
9. Basu B, Paul S (2013) Appl Organometal Chem 27:588
0. Ye M, Gao GL, Yu JQ (2011) J Am Chem Soc 133:6964
were also performed in this report. The coupling of aryl
iodides with styrene gave desired product in moderate yield
21. O¨ zdemir I˙ , Cetinkaya B, Demir S, G u¨ rb u¨ z N (2004) Catal Lett
9
7:37
(
Table 3, entry 10), while aryl bromides showed low yield
Table 3, entry 9), because aryl bromides is less active than
2
2. Li X, Zhao XH, Gao SY, Marqu e´ s-Gonz a´ lez S, Yufit DS, Howard
JAK, Low PJ, Zhao YY, Gan N, Guo ZY (2013) J Mater Chem A
(
aryl iodides.
1
:9164
3. Li X, Zhao XH, Zhang J, Zhao YY (2013) Chem Commun
9:10004
4. Wang M, Yuan XB, Li HY, Ren LM, Sun ZZ, Hou YJ, Chu WY
2015) Catal Commun 58:154
5. Zim D, Monteiro AL (2002) Tetrahedron Lett 43:4009
2
2
2
4
4
Conclusions
(
Compound 1 was successfully prepared and used in the
LbL self-assembly of multilayer films through a sequential
reaction with metal ions Pd(II) or Ni(II). The resulting
26. Altman M, Shukla AD, Zubkov T, Evmenenko G, Dutta P, van
der Boom ME (2006) J Am Chem Soc 128:7374
2
2
2
3
7. Altman M, Zenkina OV, Ichiki T, Iron MA, Evmenenko G, Dutta
P, van der Boom ME (2009) Chem Mater 21:4676
8. Motiei L, Altman M, Gupta T, Lupo F, Gulino A, Evmenenko G,
Dutta P, van der Boom ME (2008) J Am Chem Soc 130:8913
9. Altman M, Zenkina O, Evmenenko G, Dutta P, van der Boom
ME (2008) J Am Chem Soc 130:5040
0. Choudhury J, Kaminker R, Motiei L, de Ruiter G, Morozov M,
Lupo F, Guilino A, van der Boom ME (2010) J Am Chem Soc
132:9295
(
PdCl /1) multilayers were used as high active catalysts
2 n
for the Suzuki–Miyaura and Mizoroki–Heck reactions with
extremely low Pd(II)-loading in ppm level. Interestingly,
the (Ni(NO ) /1) multilayers as the active catalytic moi-
3
2
n
eties can be re-used five times in Suzuki–Miyaura reaction
of 4-iodophenetole with 4-methylphenylboronic acid,
which is attractive for industrial syntheses in the view of
the low costs.
3
3
3
3
1. Milie TN, Chi N, Yablon DG, Flynn GW, Batteas JD, Drain CM
2002) Angew Chem Int Ed 41:2117
2. Milic T, Garno JC, Batteas JD, Smeureanu G, Drain CM (2004)
Langmuir 20:3974
3. Li X, Zha MQ, Wang XW, Cao R (2009) Inorg Chim Acta
(
Acknowledgments Authors acknowledge the financial support by
the NSFC (21571110), the Ningbo Foundation (2014C50037 and
2014A610106), the Ningbo University Foundation (py2013001, and
G14034), the Youth Talent programs of Zhejiang Province
362:3357
4. Kawano T, Shinomaru T, Ueda I (2002) Org Lett 4:2545
1
23