Iminophosphine palladium catalysts for Suzuki carbonylative coupling reaction

Article abstract of DOI:10.1002/aoc.4002

Three iminophosphine ligands having soft phosphorus and hard nitrogen atoms and their Pd(II) complexes were synthesized and characterized using ¹H NMR, ¹³C NMR, ³¹P NMR and Fourier transform infrared spectroscopic techniques. Also, electrochemical properties of the iminophosphines and their Pd(II) complexes were investigated in acetonitrile–tetrabutylammonium perchlorate solution with cyclic and square wave voltammetry techniques. All Pd(II) complexes were evaluated as catalysts for carbonylative cross-coupling reactions of aryl iodides with phenylboronic acid. The Suzuki carbonylation of aryl iodides at 80?°C under balloon pressure of carbon monoxide in the presence of K₂CO₃ as a base was examined, and good to high conversions and excellent selectivities were obtained.

Full text of DOI:10.1002/aoc.4002

Received: 10 May 2017
DOI: 10.1002/aoc.4002
Revised: 28 June 2017
Accepted: 29 June 2017
F U L L P A P E R
Iminophosphine palladium catalysts for Suzuki
carbonylative coupling reaction
Mustafa Kemal Yılmaz1
| Hülya Keleş2
| Simay İnce2
| Mustafa Keleş2
1 Mersin University, Faculty of Arts and
Sciences, Department of Chemistry, 33343
Mersin, Turkey
2 Osmaniye Korkut Ata University, Faculty
of Arts and Sciences, Department of
Chemistry, 80000 Osmaniye, Turkey
Three iminophosphine ligands having soft phosphorus and hard nitrogen
atoms and their Pd(II) complexes were synthesized and characterized using
1H NMR, 13C NMR, 31P NMR and Fourier transform infrared spectroscopic
techniques. Also, electrochemical properties of the iminophosphines and their
Pd(II) complexes were investigated in acetonitrile–tetrabutylammonium per-
chlorate solution with cyclic and square wave voltammetry techniques. All Pd
(II) complexes were evaluated as catalysts for carbonylative cross‐coupling reac-
tions of aryl iodides with phenylboronic acid. The Suzuki carbonylation of aryl
iodides at 80 °C under balloon pressure of carbon monoxide in the presence of
K2CO3 as a base was examined, and good to high conversions and excellent
selectivities were obtained.
Correspondence
Mustafa Keleş, Osmaniye Korkut Ata
University, Faculty of Arts and Sciences,
Department of Chemistry, 80000
Osmaniye, Turkey.
Email: mkeles@osmaniye.edu.tr
Funding information
The Scientific and Technological Research
Council of Turkey, Grant/Award Number:
115Z829
KEYWORDS
electrochemistry, iminophosphines, palladium, Suzuki carbonylation
1 | INTRODUCTION
available palladium complexes,[7,12–15] palladium on
carbon,[16] palladium nanoparticles immobilized on
Palladium‐catalysed
carbonylative
cross‐coupling
supported ionic liquid‐like phases,[6] palladium
reactions of aryl halides with organoboron compounds
play an important role in modern chemical transforma-
tions, and these types of reactions are widely applied for
the synthesis of pharmaceuticals, agrochemicals and
advanced materials.[1–3] While carbonyl compounds
have been traditionally synthesized by multi‐step
syntheses, biologically important symmetric or
unsymmetric diaryl ketones such as benzophenones
can be obtained in one‐step procedures using
carbonylative cross‐coupling reactions.[4,5] In such cases,
these coupling reactions typically proceed in organic
solvents, but they have also been applied successfully
in green solvents such as water and ionic liquids.[6–9]
Carbonylative Suzuki cross‐coupling reactions are
generally catalysed by palladium nanoparticles,[10,11] in
situ generated palladium complexes with phosphines or
N‐heterocyclic carbene ligands or various commercially
supported on hollow magnetic mesoporous spheres,[17]
palladium
nanoparticles
supported
on
nickel
pyrazolate[18] or palladacycles.[19] However, to the best
of our knowledge, there has been no study of
carbonylative cross‐coupling reactions of arylboronic
acids with aryl iodides catalysed by PN‐type bidentate
iminophosphine ligand‐based palladium complexes.[20]
In the study reported in this paper, we prepared,
characterized and investigated the electrochemical
behaviour of PN‐type iminophosphine ligands and their
Pd(II) complexes. All the Pd(II) complexes were also
applied as catalysts for the carbonylative Suzuki
cross‐coupling reactions of aryl iodides with arylboronic
acids under an atmospheric pressure of carbon
monoxide. The results show that the iminophosphine
palladium complexes can catalyse the carbonylative
coupling reactions of aryl iodides with arylboronic acids
Appl Organometal Chem. 2017;e4002.
wileyonlinelibrary.com/journal/aoc
Copyright © 2017 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4002

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YILMAZ ET AL.
with good to high selectivity even under an atmospheric
pressure of carbon monoxide.
μm particle size. The cleaning procedure was followed
by sonication with an isopropyl alcohol–water mixture
for 10 min and rinsing with acetone.
Electrochemical measurements were performed with
mM Pd(II) complexes. CV measurements were
2 | EXPERIMENTAL
1
performed with a 100 mV s−1 scan rate between −1.5
and 1.5 V potential window starting from negative. SWV
settings were: step potential, 4 mV; amplitude, 25 mV;
frequency, 15 Hz.
2.1 | Materials and methods
All manipulations were carried out under argon atmo-
sphere using standard Schlenk techniques. Solvents were
dried using established procedures and then immediately
distilled under nitrogen atmosphere prior to use.[21] (S)‐α‐
Methylbenzylamine, (S)‐α,4‐dimethylbenzylamine, (R)‐α‐
methyl‐4‐nitrobenzylamine hydrochloride and Pd(cod)
Cl2 were purchased from Sigma‐Aldrich Chemie GmbH
(Steinheim, Germany) and were used without further
purification. 2‐(Diphenylphosphino)benzaldehyde[22] and
1‐(2‐(diphenylphosphinyl)phenyl)‐N‐(1‐phenylethyl)
methaneimine[23] were prepared according to literature
methods.
2.2 | Preparation of ligands and complexes
2.2.1 | Preparation of (o‐PPh2)
C6H4CH═NCH(CH3)C6H5 (1)
Ligand 1 was prepared (Scheme 1) according to a litera-
ture procedure.[24]
Microanalysis (C, H and N) was performed using a
LECO CHNS 932 instrument. Fourier transform infra-
red (FT‐IR) spectra of synthesized compounds were
recorded with a PerkinElmer RX1 spectrophotometer
2.2.2 | Preparation of (o‐PPh2)
C6H4CH═NCH(CH3)C6H4(p‐CH3) (2)
1
in the range 650–4000 cm−1. All H NMR (400.1 MHz)
2‐(Diphenylphosphino)benzaldehyde (0.25 g, 0.86 mmol)
with (S)‐α,4‐dimethylbenzylamine (0.13 mL, 0.86 mmol)
were stirred for 12 h in dry toluene and in the presence
of molecular sieves (4 Å) at 70 °C. The reaction was
monitored by TLC (hexane–ethyl acetate, 3:1). Filtration
and drying in vacuum afforded the desired yellow oily
product (Scheme 2).
and 31P{1H} NMR (162.0 MHz) spectra were recorded
at 25 °C with deuterated DMSO or CDCl3 with a Bruker
NMR spectrometer. 13C NMR spectra were obtained
with
a Varian Mercury 100.6 MHz spectrometer.
31P{1H} NMR spectra were recorded with complete
proton decoupling using 85% H3PO4 as external
standard. The Suzuki carbonylative cross‐coupling
products were analysed using GC/MS with an Agilent
7890A GC System 5975C MSD series gas chromatograph
equipped with a flame ionization detector and a
30 m × 0.25 mm × 0.25 μm film thickness β‐Dex
capillary column and an Agilent 1200 (HPLC). TLC
was used for monitoring the reactions.
Yield 282 mg (81%). FT‐IR (KBr, cm−1): 1434, 1634,
3052. 1H NMR (400.2 MHz, CDCl3, δ, ppm): 8.83 (d,
J = 4.8 Hz, 1H, H7), 7.90 (m, 1H), 7.42 (m, 1H),
7.27–7.16 (m, 11H), 6.99 (m, 4H), 6.78 (m, 1H), 4.37 (q,
J = 6.6 Hz, 1H, H10), 2.30 (s, 3H, H18), 1.32 (d,
J = 6.6 Hz, 3H, H12). 13C NMR (100.6 MHz, CDCl3, δ,
ppm): 158.0 (d, J = 20.4 Hz, C7), 141.9 (s, C11), 139.7 (d,
J = 17.0 Hz, C4), 137.4 (d, J = 19.5 Hz, Ci), 134.2 (d,
J = 5.7 Hz, Co), 134.0 (d, J = 5.6 Hz, Cm), 133.2 (s, C1),
132.0 (s), 130.10 (s, C2), 129.0 (s), 128.8 (s, Cp), 128.6 (d,
J = 7.0 Hz), 128.1 (d, J = 4.2 Hz), 126.6 (s, C6), 69.4 (s,
C10), 24.4 (s, C12), 21.1 (s, C18). 31P NMR (162.0 MHz,
CDCl3, δ, ppm): −12.46 (s). Anal. Calcd for C28H26NP
(%): C, 82.53; H, 6.43; N, 3.44. Found (%): C, 82.64; H,
6.59; N, 3.49.
Cyclic voltammetry (CV) and square wave voltamme-
try (SWV) techniques were performed using a CHI 6094D
electrochemical analyser equipped with a three‐electrode
electrochemical cell system. An Ag/Ag+ (10 mM Ag+/
ACN) reference electrode, a Pt wire as counter electrode
and a glassy carbon electrode (3.0 mm in diameter) as
working electrode were employed for the electrochemical
studies.
Voltammetric experiments were performed at room
temperature in acetonitrile (ACN) solution with 0.1 M
tetrabutylammonium perchlorate (TBAP) as the
supporting electrolyte. High‐purity argon was purged to
the solution for 15 min to maintain deoxygenated condi-
tion and the passage of argon was also continued during
the experiment. The working electrode was polished with
alumina paste on a felt pad in order of 1.0, 0.3 and 0.05
SCHEME 1 Preparation of ligand 1[24]

YILMAZ ET AL.
3 of 8
was filtered off and dried to afford the title compound
2a (Scheme 4).
Yield 575 mg (85%); m.p. 228 °C. FT‐IR (KBr, cm−1):
1436, 1632, 3056. 1H NMR (400.2 MHz, DMSO‐d6, δ,
ppm): 7.72 (d, J = 7.7 Hz, 1H), 7.69 (s, 1H, H25),
7.62–7.44 (m, 1H), 7.44–7.38 (m, 2H), 7.34–7.23 (m, 2H),
7.20 (s, 1H), 6.82 (d, J = 7.7 Hz, 1H), 6.62 (q,
J = 6.8 Hz, 1H), 3.41 (q, J = 7.02 Hz, 1H, H30), 2.24 (s,
3H, H18), 1.45 (d, J = 7.0 Hz, 3H, H12). 13C NMR
(100.6 MHz, CDCl3, δ, ppm): 161.9 (d, J = 8.6 Hz, C7),
152.4 (s, C11), 138.3 (d, J = 16.8 Hz, C4), 137.6 (d,
J = 20.4 Hz, Ci), 136.3 (dd, J = 9.5, 4.8 Hz, Co), 134.4
(s), 133.7 (d, J = 7.3 Hz, Cm), 133.2 (s, C1), 131.7 (s),
129.8 (s, C2), 129.4 (dd, J = 7.0, 5.9 Hz), 128.5 (d,
J = 4.0 Hz), 128.3 (s), 124.4 (s, C6), 69.7 (s, C10), 21. 4
(s, C18), 21.2 (s, C12). 31P NMR (162.0 MHz, CDCl3, δ,
ppm): 31.44 (s). Anal. Calcd for C28H26Cl2NPPd (%): C,
57.51 H, 4.48; N, 2.40. Found (%): C, 57.88; H, 4.69; N,
2.66. HRMS: calcd for C28H26Cl2NPPd (M+) m/z
584.0292, found 584.0298.
SCHEME 2 Preparation of ligand 2
2.2.3 | Preparation of (o‐PPh2)
C6H4CH═NCH(CH3)C6H4(p‐NO2) (3)
2‐(Diphenylphosphino)benzaldehyde (0.25 g, 0.86 mmol)
with (R)‐α‐methyl‐4‐nitrobenzylamine hydrochloride
(0.18 g, 0.86 mmol) were stirred for 12 h in dry
toluene, in the presence of molecular sieves (4 Å) and
Et3N (0.12 ml, 0.86 mmol) at 70 °C (Scheme 3). The
reaction was monitored by TLC (hexane–ethyl acetate,
3:1). The solvent was evaporated under reduced pressure
until dryness and diluted with CH2Cl2. The solution was
washed with NaHCO3 solution and water and combined
organic phases were dried (Na2SO4) and the solvent
evaporated. The residue was crystallized at −20 °C in
methanol.
Yield 300 mg (80%). FT‐IR (KBr, cm−1): 1432, 1645,
3052. 1H NMR (400.2 MHz, CDCl3, δ, ppm): 8.90 (d,
J = 4.7 Hz, 1H, H25), 8.07 (d, J = 8.76 Hz, 2H, H34,36),
7.96 (m, 1H, H24), 7.35 (m, 14H), 6.89 (m, 1H), 4.48 (q,
J = 6.6 Hz, 1H, H30), 1.35 (d, J = 6.7 Hz, 3H, H32). 13C
NMR (100.6 MHz, CDCl3, δ, ppm): 159.4 (d, J = 18.6 Hz,
C25), 152.4 (s, C31), 139.1 (d, J = 16.8 Hz, C22), 137.7 (d,
J = 20.4 Hz, Ci), 136.7 (dd, J = 9.5, 4.8 Hz, Co), 134.2 (s),
134.08 (d, J = 7.3 Hz, Cm), 133.9 (s, C19), 133.5 (s), 130.5
(s, C20), 128.7 (dd, J = 7.0, 5.9 Hz), 128.5 (d, J = 4.0 Hz),
127.4 (s), 123.6 (s, C24), 69.1 (s, C30), 24.7 (s, C32). 31P
NMR (162.0 MHz, CDCl3, δ, ppm): −12.36 (s). Anal. Calcd
for C27H23N2O2P (%): C, 73.96 H, 5.29; N, 6.39. Found (%):
C, 74.12; H, 5.32; N, 6.43.
2.2.5 | Preparation of [PdCl2(o‐PPh2)
C6H4CH═NCH(CH3)C6H4(p‐NO2)] (3a)
Compound 3a was prepared using a procedure similar
to that described for 2a. Yield 560 mg (78%); m.p.
113 °C (decomp.). FT‐IR (KBr, cm−1): 1436, 1632,
1
3059. H NMR (400.2 MHz, DMSO‐d6, δ, ppm): 8.23 (s,
1H, H25), 7.90–7.19 (s, 16H, ar‐CH), 7.05 (q, 1H), 6.88
(dd, 1H), 6.62 (q, J = 6.8 Hz, 1H), 3.48 (m, 1H, H30),
1.63 (d, J = 7.0 Hz, 3H, H32). 13C NMR (100.6 MHz,
CDCl3, δ, ppm): 162.0 (d, J = 18.6 Hz, C25), 147.6 (s,
C31), 146.4 (d, J = 16.8 Hz, C22), 137.1 (d, J = 20.4 Hz,
Ci), 136.4 (dd, J = 9.5, 4.8 Hz, Co), 134.3 (s), 133.9 (d,
J = 7.3 Hz, Cm), 133.6 (s, C19), 133.0 (s), 132.4 (s, C20),
129.1 (dd, J = 7.0, 5.9 Hz), 128.9 (d, J = 4.0 Hz), 128.9
(s), 124.1 (s, C24), 68.5 (s, C30), 20.8 (s, C32). 31P NMR
(162.0 MHz, CDCl3, δ, ppm): 31.29 (s). Anal. Calcd for
C27H23Cl2N2O2PPd (%): C, 52.66 H, 3.76; N, 4.55.
Found (%): C, 52.98; H, 3.92; N, 4.77. HRMS: calcd
for C27H23Cl2N2O2PPd (M+) m/z 614.9987, found
614.9992.
2.2.4 | Preparation of [PdCl2(o‐PPh2)
C6H4CH═NCH(CH3)C6H4(p‐CH3)] (2a)
To a solution of Pd(cod)Cl2 (0.28 g, 1.00 mmol) in dry
CH2Cl2 (10 mL) was added 2 (0.40 g, 1.00 mmol). The
mixture was stirred for 6 h at room temperature. Then,
addition of diethyl ether caused a yellow solid which
SCHEME 4 Preparation of complexes 1a, 2a and 3a[24]
SCHEME 3 Preparation of ligand 3

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YILMAZ ET AL.
13C NMR spectra, the methylene carbon appears as a
doublet signal in the region 162.0–158.0 ppm (158.0
(20.4 Hz) (2), 159.4 (18.6) (3), 161.9 (8.6 Hz) (2a) and
162.0 ppm (8.8 Hz) (3a)) as expected. The coordination
of the phosphorus donor to the metal centre is clear from
the downfield shift of the 31P{1H} NMR signal compared
to that of the free ligand which is approximately 40 ppm
for the palladium complexes. From FT‐IR analysis, the
displacement of C═N stretching frequencies from 1634
(2) and 1645 (3) cm−1 for the free iminophosphine ligands
to lower values of 1632 (2a) and 1632 (3a) cm−1 for the
palladium complexes indicates the coordination of
azomethine nitrogen to the Pd(II) centre. Microanalytical
data for C, H and N of the Pd(II) complexes indicate that
the metal‐to‐ligand ratio of the complexes is 1:1. Based on
2.3 | General procedure for Carbonylative
Suzuki coupling reaction
The desired Pd(II) complex (0.01 mmol), base (1.2 mmol),
phenylboronic acid (1.2 mmol), iodobenzene (1.0 mmol)
and solvent (4.0 mL) were placed under argon atmosphere
into a Schlenk tube and then pressurized with carbon
monoxide at a pressure of 1 atm. Next the reaction was
conducted for 4 h at 80 °C. After completion of the
reaction, the Schlenk tube was cooled to room tempera-
ture, and the mixture was diluted with diethyl ether
(8 mL) and then filtered through a pad of silica gel. Then
the mixture was analysed using GC–MS with mesitylene
as an internal standard to determine the conversion of
iodobenzene.
1
the elemental CHN analysis and FT‐IR, H NMR, 13C
NMR and 31P NMR spectral analysis, we suggest that
the iminophosphine ligands act as PN‐bidentate ligands
and bond to the palladium atom through the azomethine
nitrogen atom (C═N) and the phosphorus atom.
3 | RESULTS AND DISCUSSION
3.1 | Characterization
Ligands 1, 2 and 3 and Pd(II) complexes 1a, 2a and 3a
were synthesized by treating 2‐(diphenylphosphino)benz-
aldehyde with the appropriate primary amine under
argon atmosphere using a literature procedure.[24] All
compounds are very soluble in dichloromethane,
chloroform, ethanol and acetone, and insoluble in n‐hex-
ane and diethyl ether.
3.2 | Electrochemical characterization of
synthesized complexes
Electrochemical characterization of the synthesized
iminophosphine ligands (1, 2, 3) and their Pd(II)
complexes (1a, 2a, 3a) was done using CV and SWV in
an ACN–0.1 M TBAP solution system within the potential
range − 1.5 to 1.5 V.
Figure 1 shows CV responses of ligand 1 and its Pd(II)
complex 1a on glassy carbon electrode with a 100 mV s−1
scan rate. The voltammogram of 1a exhibited a wide
oxidation peak and two reduction peaks. The anodic peak
observed at anodic potentials was also observed in the CV
curve of 1. So these peaks were evaluated as ligand‐based
electrochemical processes and only cathodic side of the
potential range is shown in the SWV plot (inset). Complex
1a showed two cathodic peaks at −0.748 and −1.055 V,
corresponding to the redox pairs Pd(II)/Pd(I) and Pd(I)/
1
From the H NMR spectra, displacement of doublet
signal of azomethine proton from upfield in non‐coordi-
nated ligands (2: 8.58 ppm; 3: 9.12 ppm as a doublet) to
downfield in palladium complexes (2a: 7.69 ppm; 3a:
8.23 ppm) as a singlet, due to back‐bonding from the
palladium centre, suggest the coordination of azomethine
nitrogen to palladium metal.[25–27] The ligands show
phosphorus coupling from the imine proton of the ligand
in 1H NMR spectra (4.6 Hz in 1, 4.8 Hz in 2, and 4.7 Hz in
3), which points to a through‐space coupling, indicating
that the CH═N atom (C(7)H and C(25)H) is directed
towards the lone pair of the phosphorus atom. In the
FIGURE 1 CV curves of 1 mM Schiff
base ligand 1 and Pd(II) complex 1a in
0.1 M TBAP–ACN on glassy carbon
electrode with 0.1 V s−1 scan rate (inset:
SWV of 1 and 1a; amplitude = 25 mV;
frequency = 15 Hz; step potential = 4 mV)

YILMAZ ET AL.
5 of 8
Pd(0), respectively.[28,29] The second reduction peak was
also related to the ligand‐based reduction process in 1a.
There were no anodic reversible peaks on the reverse scan
except a small oxidation peak at −0.041 V which is
assigned to oxidation of Pd(I) to Pd(II). This process is the
resultant of unstable Pd(II) + Pd(0) → 2Pd(I) reaction.[30]
The data obtained from the CV traces of the Schiff base
ligands and metal complexes are presented in Table 1.
The CV curves of 2a (Figure 2) showed two
irreversible redox processes during the negative scan. A
comparison of the voltammetric responses of 2a and 2
under the same potential region establishes that the first
cathodic reduction peak at −1.030 V corresponds to 2.
The second reductive response at Epc = −1.241 V and oxi-
dation at Epa = −1.139 V can be assigned to Pd(II) → Pd(I)
reduction process. The observed E1/2 value of the Pd(II)/
Pd(I) redox pair is comparable to the value reported
earlier.[31] The reduction of Pd(II) → Pd(I) is clearly
observed from the SWV results at the inset.
Epc = −1.190 V. A weak peak observed at −0.231 V is
related to Pd(I) → Pd(II) redox process. Formation of Pd
(I) is explained with a subsequent proportionation pro-
cess, Pd(0) + Pd(II) → 2Pd(I), in aprotic solvents. This
behaviour is similar to that reported previously in CV
studies of Pd(II) complexes.[32]
3.3 | Suzuki Carbonylation
The carbonylative cross‐coupling reaction of iodobenzene
with phenylboronic acid under an atmospheric pressure
of carbon monoxide was chosen as a model reaction.
The influences of various reaction parameters, such as
solvent, catalyst loading, CO pressure and base, on the
reaction were investigated.
Initially, the reaction was performed at 80 °C for 2 h in
the presence of 1 mol% of catalyst (1a) with various bases
(1.2 equiv.). The influence of base in the reaction was first
examined and a significant effect of the base on the
catalytic activity and yield was observed. Thus, when the
reaction was carried out with K2CO3 as a base, 85% selec-
tivity and 80% conversion were observed (Table 2, entry
5). Preliminary experiments showed that highly polar
solvents, such as tetrahydrofuran (THF), 1,4‐dioxane and
ethanol, were required in order to obtain high reaction
rates and yields (Table 2). The highest activity was
obtained in 1,4‐dioxane with K2CO3 as a base (Table 2,
entry 5).
Entries 5, 6 and 7 of Table 2 show the effect of cat-
alyst loading on the catalytic activity of complex 1a.
When 1 mol% of 1a is used, 80% conversion and 85%
selectivity are reached within 2 h of the reaction, while
75% conversion and 76% selectivity, and 74% conversion
and 61% selectivity are reached in the same time when
0.4% and 0.2 mol%, respectively, are used. Comparing
entries 5–7 of Table 2, substrate‐to‐catalyst ratio did
not significantly decrease the conversion and selectivity
when using 0.2% and 0.4 mol% catalyst. We also inves-
tigated the effect of the pressure of CO with pressures
The CV curves of Schiff base ligand 3 and Pd(II)
complex 3a are presented in Figure 3. The peaks in the
negative potential region (0.0 to −1.5 V) related to 3 were
also observed in the CV curve of 3a. The inset shows the
SWV curves of 3 and 3a. The peak at −1.109 V is assigned
to a quasi‐reversible electrochemical response of Pd(II)/
Pd(0) couple of 3a, with potentials Epa = −1.027 V and
TABLE 1 Electrochemical parameters for Pd(II) complexes in
0.1 M TBAP–ACN solution
Redox
Compound couple
Epc
(V)
Epa
(V)
ΔEp
E1/2
(mV)a (V)b
1a
Pd(II)/Pd(I) −0.748 −0.041 707
Pd(I)/Pd(0) −1.055
−0.395
—
—
—
2a
3a
Pd(II)/Pd(I) −1.241 −1.139 102
−1.190
Pd(II)/Pd(0) −1.190 −1.027 163
−1.109
Pd(I)/Pd(II)
—
−0.231
—
—
aΔEp = Epa − Epc
.
bE1/2 = (Epa + Epc)/2, v = 100 mV s−1
.
FIGURE 2 CV curves of 1 mM Schiff
base ligand 2 and Pd(II) complex 2a in
0.1 M TBAP–ACN on glassy carbon
electrode with 0.1 V s−1 scan rate (inset:
SWV of 2 and 2a; amplitude = 25 mV;
frequency = 15 Hz; step potential = 4 mV)

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YILMAZ ET AL.
FIGURE 3 CV curves of 1 mM Schiff
base ligand 3 and Pd(II) complex 3a in
TBAP–ACN on glassy carbon electrode
with 0.1 V s−1 scan rate (inset: SWV of 3
and 3a; amplitude = 25 mV;
frequency = 15 Hz; step potential = 4 mV)
TABLE 2 Effect of base, solvent and catalyst loading on Suzuki carbonylative coupling reaction of iodobenzenea
Entry
Solvent
Base
Conversion (%)b
Yield (A) (%)b
Yield (B) (%)b
Selectivity (A) (%)c
1
THF
Et3N
63
4
5
45
2
1,4‐Dioxane
Ethanol
Et3N
64
5
‐
100
3
Et3N
79
4
4
50
4
THF
K2CO3
67
4
14
22
5
1,4‐Dioxane
1,4‐Dioxane
1,4‐Dioxane
Ethanol
K2CO3
80
22
4
85
6
K2CO3 (S:C = 250)
K2CO3 (S:C = 500)
K2CO3
75
19
6
76
7
74 (75d, 78e)
17 (9d, 8e)
11 (3d, 4e)
61 (71d, 68e)
8
100
61
60
97
58
69
64
4
40
—
—
34
—
5
9
9
THF
Na2CO3
Na2CO3
Na2CO3
K3PO4
—
5
—
100
11
—
45
—
10
11
12
13
14
1,4‐Dioxane
Ethanol
4
THF
—
4
1,4‐Dioxane
Ethanol
K3PO4
K3PO4
—
—
aIodobenzene (1.0 mmol), phenylboronic acid (1.2 mmol), base (1.2 mmol), solvent (4 mL), 1a (0.01 mmol), 80 °C, 2 h.
bMesitylene used as internal standard and coupled products analysed by GC–MS.
cSelectivity (A) (%) = 100 × Yield (A)/Yield (A + B).
dCO (5 bar).
eCO (10 bar).
of 5 and 10 atm. However, when the CO pressure
increased from 1 to 5 and 10 atm, the conversion of
the reaction and the desired product selectivity did not
increase obviously. Therefore, the Suzuki carbonylative
coupling reaction was carried out with atmospheric
pressure of CO, 0.2 mol% catalyst and K2CO3 in
1,4‐dioxane at 80 °C.
because water is a cheap, readily available nontoxic
solvent and is environmentally friendly.[9] Therefore, we
used water and water–1,4‐dioxane solvent system for the
Suzuki carbonlylative coupling reaction of iodobenzene
and we also studied the effect of catalyst loading on the
reaction (Table 3). It can be seen that both water and
water–1,4‐dioxane solvent system gave very poor selectiv-
ity of product compared to 1,4‐dioxane. In addition,
increasing the catalyst loading from 0.2 to 1.0 mol% did
To extend the scope of the reaction, water was also
used for the Suzuki carbonylative coupling reaction,

YILMAZ ET AL.
7 of 8
TABLE 3 Effect of water on Suzuki carbonylative coupling reactiona
Entry
Solvent
S:C
Conversion (%)b
Yield (A) (%)b
Yield (B) (%)b
Selectivity (A) (%)c
1
H2O
500
95
13
23
36
2
3
H2O/1,4‐dioxane
500
100
100
97
—
43
20
—
H2O
13
40
aIodobenzene (1.0 mmol), phenylboronic acid (1.2 mmol), base (1.2 mmol), solvent (4 mL), catalyst (1a), 80 °C, 2 h.
bMesitylene used as internal standard and coupled products analysed by GC–MS.
cSelectivity (A) (%) = 100 × Yield (A)/Yield (A + B).
not improve the selectivity of the Suzuki carbonylative
coupling product. As a result, we performed the coupling
reaction of substituted aryl iodides in 1,4‐dioxane as
solvent.
After the optimized reaction conditions were
identified for base and solvent, we also investigated the
Suzuki carbonylative coupling of substituted aryl iodides
with phenylboronic acid at 80 °C under balloon pressure
of CO in 1,4‐dioxane with the palladium catalysts
(1a–3a). We found that when using 2a as a catalyst it
was possible to obtain 82% conversion and 89% selectivity
with 4‐fluoroiodobenzene after 2 h of the reaction
(Table 4, entry 13). But the use of 4‐iodotoluene as a
substrate gave moderate conversion (64%) and 27%
selectivity (entry 4). Similarly, the electron‐rich aryl
iodide 4‐iodoanisole gave acceptable yield (60%) but with
full selectivity (entry 11) in the presence of 3a catalyst.
However, when 4‐nitroiodobenzene was used as a
substrate no selectivity was found with any of the catalysts
(entries 6–8). Moreover, the reaction of iodobenzene and
phenylboronic acid catalysed by 2a resulted in full
selectivity in 2 h (entry 1).
TABLE 4 Suzuki carbonylative coupling reaction of substituted aryl iodides with catalysts 1a–3a
Entry
R
Catalyst
2a
Conversion (%)b
Yield (A) (%)b
Yield (B) (%)b
Selectivity (A) (%)c
1
H
76
26
—
100
2
H
3a
1a
2a
3a
1a
2a
3a
1a
2a
3a
1a
2a
3a
72
35
64
44
76
73
75
57
56
60
72
82
77
5
22
26
24
26
29
34
32
5
19
—
27
—
—
—
—
78
68
100
78
89
89
3
4‐CH3
4‐CH3
4‐CH3
4‐NO2
4‐NO2
4‐NO2
4‐OCH3
4‐OCH3
4‐OCH3
4‐F
—
9
4
5
—
—
—
—
18
19
32
18
33
32
6
7
8
9
10
11
12
13
14
9
—
5
4‐F
4
4‐F
4
aAryl iodide (1.0 mmol), phenylboronic acid (1.2 mmol), catalyst (0.002 mmol), K2CO3 (1.2 mmol), 1,4‐dioxane (4 mL), 80 °C, 2 h.
bMesitylene as internal standard and coupled product analysed by GC–MS.
cSelectivity (A) (%) = 100 × Yield (A)/Yield (A + B).

8 of 8
YILMAZ ET AL.
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4 | CONCLUSIONS
[14] B. M. Okeefe, N. Simmons, S. F. Martin, Org. Lett. 2008, 10, 5301.
We have synthesized new iminophosphine–Pd(II)
complexes and then characterized using NMR (1H, 13C,
31P) and FT‐IR techniques. Also, the electrochemical
behaviour of the complexes was investigated and E1/2
values of reversible redox processes were determined. Ep
values of irreversible processes have also been reported.
We report the catalytic activity of the complexes in the
carbonylative Suzuki coupling reaction of common aryl
iodides with phenylboronic acid. Under our reaction
conditions, we obtained good conversion and excellent
selectivity when iodobenzene and 4‐iodoanisole were
used as substrates. It is noteworthy that these activities
were observed with 0.02 mol% catalyst and under atmo-
spheric pressure of carbon monoxide.
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ACKNOWLEDGEMENTS
[23] R. Frauenlob, M. M. Cormack, M. C. Walsh, E. Bergin, Org.
Biomol. Chem. 2011, 9, 6934.
We thank Osmaniye Korkut Ata University for financial
support and the Scientific and Technological Research
Council of Turkey (project no. 115Z829) for a grant.
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A. Bansleben, M. W. Day, Organometallics 1998, 17, 3149.
Mustafa Kemal Yılmaz
http://orcid.org/0000-0002-9969-
3956
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Hülya Keleş http://orcid.org/0000-0002-2450-7290
Simay İnce http://orcid.org/0000-0002-9941-7281
Mustafa Keleş http://orcid.org/0000-0003-2669-1818
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How to cite this article: Yılmaz MK, Keleş H,
İnce S, Keleş M. Iminophosphine palladium
catalysts for Suzuki carbonylative coupling
reaction. Appl Organometal Chem. 2017;e4002.
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