Synthesis, characterization and catalytic activity of new bis(N-2,6-diphenylphenol-R-salicylaldiminato)Pd(II) complexes in Suzuki-Miyaura and CO2 fixation reactions

Article abstract of DOI:10.1016/j.jorganchem.2016.03.024

A series of bulky N-2,6-diphenylphenol-R-salicylaldimines (HL^x) and their corresponding bis(N-2,6-diphenylphenol-R-salicylaldiminato)Pd(II) complexes (X), where R = H (1), 3-OCH₃ (2), 4-OCH₃ (3), 5-OCH₃ (4), 3-Me (5), 5-Me (6), 5-C(CH₃)₃ (7), 3-C(CH₃)₃ (8) and 3,5-di-C(CH₃)₃ (9) have been synthesized. Their structures characterized by elemental analyses, IR, UV/vis, ¹H NMR and ¹³C NMR spectroscopic techniques. X-ray crystallography shows that complex 3 crystallizes in the triclinic P-1space group with one trans-[PdL³₂] molecule and two acetic acid (C₂H₄O₂) molecules in the unit cell. All X compounds are proved to be as efficient homogeneous catalysts for both Suzuki-Miyaura cross-coupling reactions of various aryl bromides and cyclic carbonates synthesis from CO₂ and epoxides are reported under appropriate conditions (2 h, 100 °C and 1.6 MPa pressure) without use of phosphine ligands.

Full text of DOI:10.1016/j.jorganchem.2016.03.024

Journal of Organometallic Chemistry 811 (2016) 81e90
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, characterization and catalytic activity of new bis(N-2,6-
diphenylphenol-R-salicylaldiminato)Pd(II) complexes in Suzuki-
Miyaura and CO2 fixation reactions
,
Nurdal Oncel a, Veli T. Kasumov a *, Ertan Sahin b, Mahmut Ulusoy a
a Chemistry Department, Harran University, 630190 Sanliurfa, Turkey
b Chemistry Department, Ataturk University, TR-25240 Erzurum, Turkey
a r t i c l e i n f o
a b s t r a c t
A series of bulky N-2,6-diphenylphenol-R-salicylaldimines (HLx) and their corresponding bis(N-2,6-
diphenylphenol-R-salicylaldiminato)Pd(II) complexes (X), where R ¼ H (1), 3-OCH3 (2), 4-OCH3 (3), 5-
OCH3 (4), 3-Me (5), 5-Me (6), 5-C(CH3)3 (7), 3-C(CH3)3 (8) and 3,5-di-C(CH3)3 (9) have been synthe-
sized. Their structures characterized by elemental analyses, IR, UV/vis, 1H NMR and 13C NMR spectro-
scopic techniques. X-ray crystallography shows that complex 3 crystallizes in the triclinic P-1space group
with one trans-[PdL32] molecule and two acetic acid (C2H4O2) molecules in the unit cell. All X compounds
are proved to be as efficient homogeneous catalysts for both Suzuki-Miyaura cross-coupling reactions of
various aryl bromides and cyclic carbonates synthesis from CO2 and epoxides are reported under
appropriate conditions (2 h, 100 ꢀC and 1.6 MPa pressure) without use of phosphine ligands.
© 2016 Elsevier B.V. All rights reserved.
Article history:
Received 24 August 2015
Received in revised form
23 February 2016
Accepted 21 March 2016
Available online 23 March 2016
Keywords:
Bis(N-2,6-diphenylphenol-R-
salicylideneiminato)Pd
Catalytic activity
Suzuki reaction
CO2 fixation
Cyclic carbonate
1. Introduction
mostly used as catalysts in the palladium catalyzed SM cross-
coupling reaction [10e14]. However, many phosphines are air and
The coordination chemistry of transition metal complexes with
salicyladimine ligands on the basis of bulky tert-butylphenol moi-
eties has achieved a considerable attention in the last decades,
because of their unusual structural, magnetic properties, redox-
chemistry and their usage as models for metalloproteins [1e6], as
catalysts for the polymerization, copolymerization, epoxidation
and hydrogenation of simple olefins and CeC cross-coupling re-
actions [7e11]. The steric and electronic effects of substituent on
the salicylaldimine ligands are the key factors in catalytic and redox
reactivity [1,6]. Among metal-catalyzed CeC coupling reactions the
Pd-catalyzed SuzukieMiyaura (SM) coupling reaction is one of the
most widely used methods for the designing of CeC coupling bonds
formation reactions. The SM cross-coupling reaction of aryl halides
with organoboron reagents is becoming one of the most important
methods for the construction of biaryls, which are present in a wide
range of natural products [10], pharmaceuticals, agrochemicals and
functional polymer materials [7e11]. Bulky phosphine ligands are
moisture sensitive, toxic and therefore difficult to handle. Recently,
alternative ligands such as N-heterocyclic carbenes [15], as well as
ligand-free systems [16], have been employed in Suzuki coupling
reactions. Various nitrogen bearing ligands, such as amines [17],
diazabutadienes [18] and salicylaldimines [19], have attracted
considerable interest due to their stability and excellent activity. In
addition, nitrogen-based ligands are generally non-toxic, robust in
nature, insensitive to air/moisture, easy-to-handle, and have the
potentiality to overcome some of the drawbacks faced by tradi-
tional phosphine ligands [20]. Moreover, electronic and steric
properties of salicylaldimine ligands could be easily tuned by
properly selecting the condensing partners. Indeed, there have
been few reports about employment of sterically hindered phenol
bearing ligands in palladium-catalyzed SM reactions [21].
Carbon dioxide is an attractive C1 feedstock as it is renewable,
inexpensive from the viewpoint of green chemistry and atom
economy, and can replace commonly used toxic C1 building blocks,
such as phosgene [22,23]. One of the way of the conversion of
carbon dioxide and epoxides to afford five-membered cyclic car-
bonates under appropriate conditions represents encouraging
technologies for CO2 utilization (Scheme 1).
* Corresponding author. Tel.: þ90 4143183000 3588.
E-mail address: vkasumov@harran.edu.tr (V.T. Kasumov).
http://dx.doi.org/10.1016/j.jorganchem.2016.03.024
0022-328X/© 2016 Elsevier B.V. All rights reserved.

82
N. Oncel et al. / Journal of Organometallic Chemistry 811 (2016) 81e90
K. Catalytic CO2 transformation reactions were performed in a PARR
4591 25 ml stainless pressure reactor. The mixture was separated
by centrifugation, and the liquid phase was subjected to GC (Agilent
7820A) analysis with ethylene glycol di-butyl ether as internal
standard and hydrogen as the carrier gas.
2.3. Synthesis of 1e9 complexes
Scheme 1. Atom economic synthesis of cyclic carbonates from various epoxides and
CO2.
The ligands were synthesized by refluxing of the 2,6-diphenyl-
4-aminopenol with corresponding salicylaldehyde derivatives in a
1:1 M ratio in ethanol solutions as recently described [25]. The
Pd(Lx)2 complexes were prepared as fellows. Pd(II) acetate (0.122 g,
0.5 mmol) was added as a solid to stirring warm solution of HLx
(1 mmol) in acetic acid (10 ml) and CHCl3 (25e30 ml). The resulting
mixture was heated at ca. 45e50 ꢀC on water bath for about 2 h. In
most cases after 3e5 min stirring, the appearance of orange or red
precipitates was observed. The volume of the reaction mixture was
reduced to 2e3 ml and precipitated solids were collected by vac-
uum filtration, washed with cold water/methanol solution and
dried in air. The obtained compounds were recystallized from
methanol/CHCl3 mixture (2:3). Slow evaporation of a solution of 3
in CH3CN/CHCl3 mixture (1:1) at room temperature afforded or-
ange crystals suitable for X-ray diffraction analysis. Unlike of our all
efforts, we were not able to grow crystals suitable for X-ray analysis
for 1, 2, 4e9 complexes. Some physicochemical characteristics of
1e9 are given in Table 1.
As part of our interest in designing new, easily prepared steri-
cally hindered redox active ligands and studying their coordination
behavior and catalytic applications, we report herein the synthesis
and characterization of a series of palladium complexes with
bidentate salicylaldimine ligands derived from X-salicylaldehydes
(X ¼ H, CH3, CH3O and C(CH3)3) and 4-amino-2,6-di-phenylphenol
and examined their structure and catalytic activity both SM cross-
coupling and chemical fixation reactions of CO2 to yield cyclic
carbonates.
2. Experimental
2.1. Materials
R-salicylaldehyde derivatives, R ¼ H, 3-OCH3, 4-OCH3 5-OCH3,
3-CH3, 5-CH3, 3-C(CH3)3, 5-C(CH3)3, 3,5-di-C(CH3)3, 2,6-diphenyl-
4-aminopenol,
2,4-di-tert-butylphenol,
Pd(OAc)2,
4-
2.3.1. Bis[N-(2,6-diphenylphenol)salicylaldiminato]Pd(II) (1)
bromoacetophenone, bromobenzene, 4-bromoanisole, 1-bromo-
4-nitrobenzene, phenylboronic acid, epichlorohydrin (ECH),1,2-
epoxybutane(EB), propylene oxide (PO), styrene oxide (SO), dime-
thylaminopyridine (DMAP) and cyclohexeneoxide and all solvents,
were purchased from Sigma-Aldrich, and Merck. All reagents were
used without further purification. The 3,5-di-tert-butylsalicylalde-
hyde was prepared according to the Jacobsen method [24].
Yield: 65%. 1H NMR (VNMRS-400 MHz, CDCl3)
d: 8.5 (s, 2H, CH]
N), 8.2 (s, 2H, CH]N), 7.60 (d, J ¼ 8.0 Hz, 6H), 7.42(t, J ¼ 8 Hz 8 H,
Ph), 7.32 (d, J ¼ 7.2 Hz, 7.05 (td, J1 ¼ 8.8 Hz, J2 ¼ 1.6 Hz, 2H, Ph), 6.47
(t, J ¼ 7.2 Hz, 2H, Ph), 6.07 (d, J ¼ 8.8 Hz, 2H, Ph), 5.46 (s, 2H, OH). 13
C
NMR (VNMRS-400 MHz, CDCl3) d: 162.62 (CH]N), 149.62 (C1aniline-
OH),146.48 (C2sal-O),143.59(C4aniline-N),138.10 (C1sal),135.74(C3 sal),
132.48 (Ph-C4 sal), 129.89 (Ph-C5 sal), 128.93 (Ph-C), 128.0 (Ph-C),
127.64 (Ph-C), 124.92 (Ph-C), 120.57 (Ph-C), 119.66 (Ph-C).
2.2. Measurements
The C, H, N elemental analyses were performed on a LECO
CHNS-932 model analyzer at the Scientific and Technological
Research Center, Inonu University of Turkey. UV-Visible spectra
were measured on a Perkin-Elmer Lambda 25 spectrometer oper-
ating between 200 and 1100 nm. The IR spectra (without KBr pellet)
were recorded on a Perkin-Elmer FT-IR spectrometer in the
450e4000 cmꢁ1 region. The 1H {13C} NMR spectra were recorded in
CDCl3with a VNMRS-400 “Agilent-NMR” spectrometer at 400 and
100 MHz respectively, without internal standard. Single-crystal
structure data were collected with a four-circle Rigaku R-AXIS
2.3.2. Bis[N-(2,6-diphenylphenol)-3-CH3O-salicylaldiminato]
Pd(II)(2)
Yield: 78%.1H NMR (VNMRS-400 MHz, CDCl3)
d: 7.70 (s, 2H,
CH]N), 7.63 (d, J ¼ 6.8 Hz, 6H), 7. 47(t, J ¼ 7.2 Hz 6 H, Ph), 7.39 (d,
J ¼ 6.0 Hz, 2H, Ph), 7.25 (d, J ¼ 6.0 Hz, 4H, Ph), 7.05 (d, J ¼ 8.8 Hz, 2H,
Ph), 5.76 (s, 2H, OH), 3.5 (s, 6H, CH3O). 13C{1H} NMR (100 MHz,
CDCl3)
d: 166.19 (CH]N), 165.39(CH]N), 162.50 (C1aniline-OH),
148.98 (C2sal-O), 142.98 (C4aniline-N), 138.87 (C3sal-OCH3), 136.86
(C4sal), 130.69 (C3anilime), 129.83 (Ph-C), 127.47 (Ph-C), 126.47 (Ph-
C), 114.92 (Ph-C), 106.05 (Ph-C), 101.08 (Ph-C), 55.31 (OCH3), 21.49
(OCH3).
RAPID-S diffractometer using Mo Ka (0.71073 Å) radiation at 293(2)
Table 1
Physical properties of the 1e9 complexes.
Com- pound
Color
M.p. ꢀ
C
Empirical formula
Found(Calcd.) (%)
C
H
N
1
2
3
4
5
6
7
8
9
green
orange
orange
orange
orange
orange
red
>280
C50H36N2O4Pd
C52H40N2O6Pd
72.19 (72.15)
69.26(69.76)
66.36(66.24)
69.36(69.76)
72.46(72.34)
72.26(72.34)
73.43(73.52)
71.16(71.11)
74.66(74.81)
4.75(4.85)
4.52(4.51)
4.68(4.76)
4.32(4.51)
4.82(4.68)
4.52(4.68)
5.42(5.54)
5.62(5.31)
6.32(6.48)
3.26(3.36)
3.26(3.13)
2.56(2.76)
3.21(3.13)
3.36(3.24)
3.34(3.24)
3.06(2.96)
3.06(2.86)
2.58(2.64)
>282a
>280
>278a
>280
>280
>253a
>280
>292
C56H48N2O10Pd
C52H40N2O6Pd
C
C
52H40N2O4Pd
52H40N2O4Pd
C58H52N2O4Pd
red
green
C
C
58H52N2O4Pd
66H68N2O4Pd
a
Decomposition.

N. Oncel et al. / Journal of Organometallic Chemistry 811 (2016) 81e90
83
2.3.3. Bis[N-(2,6-diphenylphenol)-4-CH3O-salicylaldiminato]Pd(II)
(3)
2.3.8. Bis[N-(2,6-diphenylphenol)-3-tert-butylsalicylaldiminato]
Pd(II)(8)
Yield: 65%.1H NMR (VNMRS-400 MHz, CDCl3)
Yield: 75%. 1H NMR (VNMRS-400 MHz, CDCl3)
d: 13.4 (s, 2H,
d
: 7.82 (s, 2H, CH]
COOH), 7.80 (s, 2H, CH]N), 7.61 (d, J ¼ 7.2 Hz, 6H), 7.47 (t, J ¼ 7.2 Hz,
4H), 7.39(d, J ¼ 6.8 Hz 4 H, Ph-H), 7.27 (d, J ¼ 20.8 Hz, 6H, Ph-H), 6.8
(d, J ¼ 6 Hz, 2H, Ph-H), 6.26 (d, J ¼ 9.2 Hz, 2H, Ph-H), 5.5 (s, 2H, OH),
N), 7.6 (d, J ¼ 6.8 Hz, 6H, Ph), 7.51 (t, J ¼ 7.2 Hz, 6H, Ph), 7.43 (t,
J ¼ 7.2 Hz, 2H, Ph), 7.15 (d,d, J1 ¼ 6.8 Hz, J2 ¼ 1.2 Hz, 2H, Ph), 7.0 (d,d,
J1 ¼7.6 Hz, J2 ¼ 1.6 Hz, 2H, Ph), 6.47 (t, J ¼ 7.2 Hz, 2H, Ph), 5.4 (s, 2H,
OH), 0.95 (s, 18 H, C(CH3)3). 13C NMR (VNMRS-100 MHz, CDCl3)
3.6 (s, 6H, CH3O). 1C NMR (VNMRS-100 MHz, CDCl3)
d:172.63
(COOH), 168.25 (C]N), 164.53 (CH]N), 153.38 (C-OH), 153 (C4sal
-
d:165.11(CH]N), 163.64 (C1aniline-OH), 148.54 (C2sal-O), 144.22
OCH3), 147.0 (C4aniline-N), 143.6 (C3sal), 135.5 (C3sal), 134.60 (C5sal-
C), 133.44 (C5sal-C), 132.24 (Ph-C), 130.99 (Ph-C), 125.7 (Ph-C) (Ph-
C), 124.2 (CH3eC]O), 119.88(CH3eC]O), 60.64(OCH3).
(C4aniline-N), 140.37 (C3sal), 132.92(C3aniline), 131.86(Ph-C),
129.38(Ph-C), 129.01 (Ph-C), 128.99 (Ph-C), 127.97 (Ph-C), 125.93
(Ph-C), 122.17(Ph-C), 114.83 (Ph-C), 34.68 (C(CH3)3), 28.69
(C(CH3)3).
2.3.4. Bis[N-(2,6-diphenylphenol)-5-CH3O-salicylaldiminato]Pd(II)
2.3.9. Bis[N-(2,6-diphenylphenol)-3,5-di-tert-
(4)
butylsalicylaldiminato]Pd(II)(9)
Yield: 75%. 1H NMR (VNMRS-400 MHz, CDCl3)
d: 7.80 (s, 2H,
Yield:65 4%. 1H NMR (VNMRS-400 MHz, CDCl3)
d: 7.80 (s, 2H,
CH]N), 7.59(t, J ¼ 5.4 Hz, 6-4H), 7.6 (t, J ¼ 7.6 Hz, 6H), 7.42 (s, 2H),
7.39 (t, J ¼ 4 Hz, 4H), 7.02 (d, J ¼ 7.6 Hz, 2H, Ph), 6.4 (t, J ¼ 7.4 Hz, 2H,
Ph), 5.46 (s, 2H, OH), 2.49 (s, 6H, CH3O). 13C NMR (VNMRS-400 MHz,
CH]N), 7.3 (t, J ¼ 6.8 Hz, 6H, Ph), 7.51 (t, J ¼ 7.2 Hz, 4H, Ph), 7.43 (t,
J ¼ 7.2 Hz, 2H, Ph), 7.23 (d, J1 ¼ 6.8 Hz, J2 ¼ 1.2 Hz, 2H, Ph), 7.0 (d,
J ¼ 2.0 Hz, 2H, Ph), 6.9 (d, J ¼ 2 Hz, 2H, Ph), 5.4 (s, 2H, OH), 1.55 (s,
18 H, C(CH3)3), 0.96 (s, 18 H, C(CH3)3). 13C NMR (VNMRS-100 MHz,
CDCl3)
d:163.84 (CH]N), 163.38(C4aniline-OH), 156.89 (C2sal-O),
147.89 (C4aniline-N), 143.51(C3sal), 137.01(C3aniline), 135.14(C6sal),
132.35 (Ph-C), 129.72 (Ph-C), 129.30 (Ph-C), 128.99 (Ph-C), 128.90
(Ph-C), 127.94 (Ph-C), 125.0 (Ph-C), 119.18 (Ph-C), 114.83 (Ph-C),
15.60 (CH3O).
CDCl3) d:163.5 (CH]N), 162.9 (CH]N), 156.6 (C1aniline-OH), 151.3
(C2sal-O), 147.6(C2sal-O), 142.95 (C4aniline-N), 142.68 (C4aniline-N),
137.41(C3sal), 137.34 (C5sal), 137.17 (C6sal), 127.74 (Ph-C), 125.76
(Ph-C), 120.51(Ph-C), 119.90 (Ph-C), (Ph-C), 114.60 (Ph-C), 114.19
(Ph-C), 33.58 (5-OCH3), 29.71(5-OCH3).
2.3.5. Bis[N-(2,6-diphenylphenol)-3-CH3-salicylaldiminato]Pd(II)
2.4. X-ray crystallographic data
(5)
Yield: 68%.1H NMR (VNMRS-400 MHz, CDCl3)
d: 7.80 (s, 2H,
For the crystal structure determination, the single-crystals of
the complexes trans-[PdL32]$2C2H4O2 were used for data collection
on a four-circle Rigaku R-AXIS RAPID-S diffractometer (equipped
CH]N), 7.62 (d, J ¼ 7.2 Hz, 8H Ph), 7.48 (t, J ¼ 7.2 Hz, 8H), 7.39 (t,
J ¼ 7.2 Hz, 4H, Ph), 7.26 (d, J ¼ 5.6 Hz, 6H), 6.93 (d, J ¼ 8.4 Hz, 4H),
6.26 (d, J ¼ 5.6 Hz, 2H), 5.5 (s, 2H, OH), 2.2 (s, 6H, CH3). 13C NMR
with
a two-dimensional area IP detector). The graphite-
(VNMRS-400 MHz, CDCl3)
d:163.42 (CH]N), 162.62 (CH]N),
monochromatized Mo Ka radiation (
l
¼ 0.71073 Å) and oscilla-
149.62 (C1aniline-OH), 147.58(C2sal-O), 142.59(C4aniline-N), 137.10
(C1sal-CHimine), 136.84(C3 sal), 133.38 (Ph-C4 sal), 129.39 (Ph-C5 sal),
128.93 (Ph-C), 128.17 (Ph-C), 127.84 (Ph-C), 125.92 (Ph-C), 123.83
(Ph-C), 120.57 (Ph-C), 119.66 (Ph-C), 19.99 (CH3).
tion scans technique with Du ¼ 5ꢀ for one image were used for data
collection. The lattice parameters were determined by the least-
squares methods on the basis of all reflections with F2 > 2 (F2).
s
Integration of the intensities, correction for Lorentz and polariza-
tion effects and cell refinement was performed using Crystal Clear
(Rigaku/MSC Inc., 2005) software [26]. The structures were solved
by direct methods using SHELXS-97 [27] and refined by a full-
matrix least-squares procedure using the program SHELXL-97
[27]. H atoms were positioned geometrically and refined using a
riding model. The final difference Fourier maps showed no peaks of
chemical significance.
2.3.6. Bis[N-(2,6-diphenylphenol)-5-CH3-salicylaldiminato]Pd(II)
(6)
Yield: 55%.1H NMR (VNMRS-400 MHz, CDCl3)
d: 8.7 (s, 2H, CH]
N), 7.8 (s, 2H, CH]N), 7.61e7.60 (dd, J ¼ 7.2 Hz, 2H), 7.5 (t, J ¼ 8.2 Hz,
6H), 7.44(d, J ¼ 1.2 Hz, 4), 7.38 (d, J ¼ 1.2 Hz, 2H), 7.22 (d, J ¼ 1.2 Hz,
2H), 7.14 (d, J ¼ 1.6 Hz, 2 H, Ph), 7.03 (d, J ¼ 6.8 Hz, 2H, Ph), 6.87 (t,
J ¼ 7.6 Hz, 2H, Ph), 6.46 (t, J ¼ 7.6 Hz, 2H, Ph), 5.46 (s, 2H, OH), 5.40
(s, 2H, OH), 1.46 (s, 3H, CH3), 0.95 (s, 3H, CH3). 13C NMR (VNMRS-
2.5. Catalytic activity measurements
100 MHz, CDCl3)d:164.3 (CH]N), 152(CPh-OH), 149 (CPh-O), 146.4
Two different types of catalytic studies (SM and CO2-epoxide
coupling reactions) were performed.
(CPh-N), 144.5 (CPh-N), 141.6 (Csal-CHimine), 137.4 (Csal-CHimine), 132.7
(Csal), 129.39 (Csal), 129.29 (Csal), 129.02(Csal), 128.99 (Csal), 128.03
(Csal-C), 122.59(Ph-C), 117.23 (Ph-C), 114.45(Ph-C), 110.78(Ph-C),
66.89(Ph-C), 64.08(Ph-C), 29.32(CH3), 28.93(CH3).
2.5.1. SM coupling reactions
All reactions were performed using Schlenk-type flask under
nitrogen gas. Pd(II) complex (1.5% mmol), phenylboronic acid
(1.5 mmol), aryl halides (1 mmol), base (1.5 mmol) and solvent
(3 ml) were added in to a Schlenk tube under nitrogen atmosphere.
The Schlenk tube was stirred at 80 ꢀC for desired hours. The reac-
tion mixture was then cooled to room temperature, diluted with
CH2CI2 and filtered through on celite. The yield of reaction was
determined by GC (Agilent 7820A).
2.3.7. Bis[N-(2,6-diphenylphenol)-5-tert-butylsalicylaldiminato]
Pd(II) (7)
Yield: 65%.1H NMR (VNMRS-400 MHz, CDCl3)
d: 7.85 (s, 2H,
CH]N), 7.61e7.26 (m), 6.81 (d, J ¼ 7.6 Hz, 2H, Ph), 6.63 (d,
J ¼ 6.8 Hz, 2H, Ph), 6.57 (d, J ¼ 6.8 Hz, 2H, Ph), 6.47 (d, J ¼ 6.0 Hz, 2H,
Ph), 6.2 (t, 2H, J ¼ 6.8 Hz, 2H, Ph), 6.1 (d, J ¼ 7.2 Hz, 2H, Ph), 5.52 (s,
2H, OH), 5.45 (s, 2H, OH), 2.1 (s, 9 H, C(CH3)3,1.38 (s, 9 H, C(CH3)3. 13
C
NMR (VNMRS-100 MHz, CDCl3)
d:163.5 (CH]N), 162.9 (CH]N),
2.5.2. CO2-epoxide coupling reactions
156.6 (C1aniline-OH), 151.3 (C2sal-O), 147.6 (C4aniline-N), 142.95(C3sal),
142.68 (C4sal),137.41(C6sal),137.34 (Ph-C),137.17 (Ph-C),127.74 (Ph-
C), 125.76 (Ph-C), 120.51(Ph-C), 119.90 (Ph-C), 114.60 (Ph-C), 114.19
(Ph-C), 55.51 (Ph-C), 33.58 (5-OCH3), 29.71(5-OCH3).
A 25 ml stainless pressure reactor was charged with complex
(4.5
ꢂ
10ꢁ5 mol), epoxide (4.5
ꢂ
10ꢁ2 mol), and DMAP
(9 ꢂ 10ꢁ5 mol). The reaction vessel was placed under a constant
pressure of carbon dioxide for 2 min to allow the system to

84
N. Oncel et al. / Journal of Organometallic Chemistry 811 (2016) 81e90
reaction. The pressure was released, then, the excess gases were
vented. The yields of epoxides to corresponding cyclic carbonates
were determined by GC (Agilent 7820A).
Ph
Ph
Ph
HO
R
R
Reflux
EtOH
CHO
+
H2N
OH
CH
N
OH
Ph
HO
HLx
3. Results and discussion
Pd(OAC)2 HOAC / CHCl3
Ph
The synthesizes of salicylaldimine ligands, HL1-HL9, and their
analytical, IR, UV/Vis, 1H and 13C NMR spectroscopic characteristics
were described in a previous report [25]. While the synthesis,
characterization and redox reactivity behaviors of Pd(II) complexes
with HL1 and HL9 ligands were previously reported [28], their 1H,
13C NMR spectral characterization and catalytic activity properties
have not reported, therefore for comparative purposes, their some
spectral and physicochemical data are also included in present
work. The synthetic procedure of complexes was shown as below
(Scheme 2).
R
HO
N
CH
Ph
O
Pd
2
Pd(Lx)2
R = H (HL ), 3-OCH (HL ), 4-OCH (HL ), 5-OCH (HL ), 3-CH (HL ),
5-CH (HL ), 5-C(CH ) (HL ), 3-C(CH ) (HL ) and 3,5-di-C(CH )
(HL ). Corresponding complexes Pd(L ) abbreviated as 1-9.
Scheme 2. Synthetic procedure of complexes 1e9.
equilibrate and CO2 was charged into the autoclave with desired
pressure then heated to the desired temperature. The pressure was
kept constant during the reaction. The vessel was then cooled to
5e10 ꢀC in ice bath after the expiration of the desired time of
3.1. IR spectra
Some characteristic FT-IR data of 1e9 are presented in Table 2.
The stretching vibrations of the n(CH]N) group in the IR spectra of
Table 2
IR and electronic spectral data of 1e9 complexes in CHCl3.
Com-pound
Characteristic IR spectral data
C ¼ N, C ¼ O
Electronic spectra (l/nm) (logε)
n
n
nC ¼ C-O
nOH
1
2
3
4
5
6
7
8
9
1605
1604
1602, 1750
1601
1603
1613
1614
1608
1606
1536
1543
1534
1538
1543
1531
1526
1542
1528
3514, 3356
3538
3537, 3498
3449
3538
3523
3538
3533
3538, 3407
290(4.93), 350a, 380a, 417(4.54)
250(4.7), 303(4.26), 424(4.43)
254(3.92), 303(4.83), 402(4.44)
244(4.64), 320(4.56), 451(4.11)
248(4.83), 300a, 412(3.74)
253(4.77), 310(4.33), 430(3.91)
244(5.11), 262(4.80), 313(4.78), 353a, 425(4.2)
246(4.8), 260a, 307(4.49), 406(4.1)
233(4.8), 260(3.9), 307(4.4), 406(4.1)
a
Shoulder.
Fig. 1. Molecular structure of trans-[PdL32](C2H4O2); thermal ellipsoids were drawn at the 40% probability level. Selected bond lengths (Å) and bond angles (ꢀ): PdeO2 1.981(7),
PdeN1 2.029(12), N1-PdeO291.25(1), N1eC191.291(9), PdeN1-C19 123.10(4), O1eC12 1.368(4), C25eO2ePd1 27.75(5), C23-O31.356(4), N1-C9 1.443(4), O4-C281.218(4), C28-O5
1.491.

N. Oncel et al. / Journal of Organometallic Chemistry 811 (2016) 81e90
85
Table 3
Crystal data and structure refinement.
Empirical formula
Formula weight
Temperature
C52H40N2O6Pd$2(C2H4O2)
1015.36
293(2) K
Wavelength
0.71073 Å
Crystal system
Space group
Unit cell dimensions
triclinic
P-1
a ¼ 10.2045(4) Å
b ¼ 11.1654(4) Å
c ¼ 12.2134(5) Å
1216.30(9) Å3
a
b
g
¼ 76.593(3)ꢀ
¼ 86.689(2)ꢀ
¼ 64.112(2)ꢀ
Volume
Z
1
Density (calculated)
Absorption coefficient
F(000)
1.386 Mg/m3
0.444 mmꢁ1
524
1.7e28.5ꢀ
q
range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to
Refinement method
ꢁ13 ꢃ h ꢃ 13, ꢁ14 ꢃ k ꢃ 14, ꢁ14 ꢃ l ꢃ 16
29706
5751 [Rint ¼ 0.043]
98.7%
q
¼ 28.50ꢀ
Full-matrixleast-squares on F2
5104/3/315
Data/restraints/parameters
Goodness-of-fit on F2
1.210
Final Rindices [F2 > 2
Rindices (all data)
s
(F2)]
R1 ¼ 0.063, wR2 ¼ 0.134
R1 ¼ 0.082, wR2 ¼ 0.146
1.799 and ꢁ1.052 e Åꢁ3
Largest difference in peak and hole
Table 4
Suzuki coupling reaction of 4-bromoacetophenone with phenylboronic acid.
Entry
Catalysts
Solvent
Time (h)
Yielda(%)
1
2
3
4
5
6
7
8
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
9
9
9
9
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
DMF/H2O(4:1)
dioxane
2
4
2
4
2
4
2
4
2
4
2
4
2
4
2
4
2
4
2
4
96
91
96
91
98.7
98.3
98.9
98
98.1
98
9
10
11
12
13
14
15
16
17
18
19
20
98.4
98
99.7
97.4
98.8
97.9
90
95
99.2
99
dioxane
DMF/H2O(4:1)
DMF/H2O(4:1)
Reaction conditions: 1.5 mmol % Pd, 1 mmol 4-bromoacetophenone, 1.5 mmol phenylboronic acid, 3 mL solvent (DMF(4)/H2O(1)-dioxane), heat (80 ꢀC), base (Cs2CO3).
a
The yields checked by GC analysis.
1e9 were detected in the 1601e1614 cmꢁ1 region and shifted to
lower frequencies relative to corresponding free HLx
(1613e1619 cmꢁ1), indicating that the coordination has taken place
through the azomethine nitrogen atom of the ligands to palladium
metal ion. A weak broad feature centered at 2500e2800 cmꢁ1, due
the 1, 2 and 4e9 complexes. In the IR spectrum of 3 unlike of other
complexes along with intense broad peak at 1750 cmꢁ1 assignable
to
middle intensity very broad band centered at 3449e3537 cmꢁ1
were observed (Table 2). These peaks are assigned to OH of the
n
(C]O) of CH3COOH, an intense narrow band at 3498 cmꢁ1 and a
n
to
n
(OH) of the intramolecularly H-bonded OH,,,N in HLx, disap-
sterically hindered OH of 3 and intermolecular OH/O between
CH3COOH and 3 molecules, respectively. A sharp strong peak
pears in the spectra of all the complexes, suggesting their coordi-
nation via deprotonated phenolic oxygen atom to Pd(II). The sharp
strong band appeared in the 3514e3538 cmꢁ1 range has been
observed at 3449 cmꢁ1 in the IR spectrum of 4 is assigned to
nOH of
the intermolecularly bonded OH groups. A new bands appeared
assigned to stretching frequency of the sterically hindered
n
OH in
within ranges of 1526e1543, 530e562 and 479e505 cmꢁ1 detected

86
N. Oncel et al. / Journal of Organometallic Chemistry 811 (2016) 81e90
Table 5
Suzuki coupling reactions of aryl halides with phenylboronic acid.
Entry
Catalysts
Arylhalide
Product
Time (h)
1
Yielda(%)
98.8
1
7
4-bromoacetophenone
2
3
4
5
7
7
7
7
4-bromoacetophenone
bromobenzene
2
1
2
1
97.9
99.3
100
bromobenzene
1-bromo-4-nitrobenzene
99.4
6
7
8
7
7
7
1-bromo-4-nitrobenzene
4-bromoanisole
2
1
2
100
94.6
99.7
4-bromoanisole
Reaction conditions: 1.5 mmol % 7, 1 mmol arylhalide, 1.5 mmol phenylboronic acid, 3 mL solvent (DMF(4)/H2O(1)), heat (80 ꢀC), base (Cs2CO3).
a
The yields checked by GC analysis.
Table 6
Suzuki coupling reactions of 1-bromo-4-nitrobenzene with phenylboronic acid in the presence of inorganic bases.
Entry
Catalysts
Base
Time (h)
Yielda(%)
1
2
3
4
5
6
7
7
7
7
7
7
Na2CO3
Na2CO3
K2CO3
K2CO3
Cs2CO3
Cs2CO3
1
2
1
2
1
2
99.7
100
100
100
99.4
100
Reaction conditions: 1.5 mmol % 7, 1 mmol 1-bromo-4-nitrobenzene, 1.5 mmol phenylboronic acid, 3 ml solvent (DMF(4)/H2O(1)), heat (80 ꢀC).
a
The yields checked by GC analysis.
in the spectra of all 1e9 compounds are assigned to
N and Pd-O vibrations, respectively [29].
n
C ¼ CeO,
nPd-
were described in the Experimental section. The 1H NMR and 13C
NMR spectral parameters of 1e9 complexes shows that their aro-
matic, azomethine and CH3 groups protons signals were shifted to
high field positions comparing to those in the uncomplexed free
HL1-HL9 ligands.
n
3.2. Electronic absorption spectra
The UV/vis spectral data for all 1e9 complexes were obtained
using 10ꢁ3 10ꢁ5 M solutions in the CHCl3 in the 200e1100 nm
range (Table 2). The electronic spectra of 1e9 in CHCl3 (Table 2)
exhibit very intense similar bands at 245e380 nm region and were
3.4. Molecular structure description
3.4.1. Single crystal X-ray diffraction studies of complex 3
assigned to intraligand n /
p* and p / p* transitions. The very
Single crystals of complex 3 suitable for X-ray crystallographic
analysis were grown from a saturated acetonitrile/chloroform so-
lution at room temperature over a period of two days through slow
evaporation of the solvent. The complex crystallizes in a triclinic
system with a P-1space group, with one trans-[PdL32] molecule and
two acetic acid (trans-PdL32$2C2H4O2) molecules in the unit cell.
The asymmetric unit of this compound consists of one half-
molecule of trans-[PdL32] and one acetic acid molecule. The mo-
lecular structure is depicted in Fig. 1 and the crystal data are given
intense bands appeared within 390e440 nm region according to
their
higher
molar
coefficient
extinctions
(logε ¼ 3.91e4.54 Mꢁ1 cmꢁ1) were assigned to a spin allowed
charge transfer (MLCT) transitions [30,31].
3.3. 1H and 13C NMR spectra
The 1H and 13C NMR spectroscopic data and their interpretation

N. Oncel et al. / Journal of Organometallic Chemistry 811 (2016) 81e90
87
Table 7
Suzuki coupling reactions of 1 mmol 1-bromo-4-nitrobenzene with phenylboronic acid under various temperature and times.
Entry
Catalysts
Heat (0C)
Time (h)
Yielda(%)
99.4
100
4
7.5
12
13
20
1
2
3
4
5
6
7
7
7
7
7
7
7
7
80
80
25
25
25
25
25
1
2
1
2
4
6
24
Reaction conditions: 1.5 mmol % 7, 1 mmol 1-bromo-4-nitrobenzene, 1.5 mmol phenylboronic acid, 3 ml solvent (DMF(4)/H2O(1)), base (Cs2CO3).
a
The yields checked by GC analysis.
in Table 3. In this complex, each Schiff base ligand (HL3) is bonded
to the Pd(II) center through nitrogen atom and oxygen atom,
providing two equivalent six-member N-Pd-O-C-chelate rings. The
geometry at the Pd(II) center in 3 is square planar, with the two
cyclometalated ligands in a trans arrangement. The PdeO and
PdeN distances are 1.980(3) and 2.028(4) Å, similar to those seen in
related complexes [20,32,33].
most reactive aryl halide, while 4-bromoanisole exhibited the
lowest activity of the epoxides surveyed. According to Tables 4 and
5, the yield was increased with increasing time.
Effect on the reactions of the bases (Cs2CO3, K2CO3, Na2CO3) has
been investigated and it has been found that these bases nearly
exhibit the same effect (Table 6). In addition, reaction temperature
had positively affected to the reaction yield (Table 7).
The bite angle [N1ePdeO2 ¼ 91.26(4)ꢀ] is in good agreement
with those found in a structurally related mononuclear complex
with salicylaldiminato ligands as bridging ligands [32e35]. The
imine C]N bonds in complex 3 retain their double bond character,
being 1.292(6) Å (C19 ¼ N1)) in length.
3.5.2. CO2-epoxide coupling
Since the sterically hindered salen-type transition metal com-
plexes exhibits excellent catalysts in the coupling reactions of CO2
and epoxides, which provide formation of polycarbonates or cyclic
carbonates [36], we have interested to study the catalytic efficiency
of the 1e9 complexes in the coupling of CO2 with epoxides as
shown in Scheme 3. To the best of our knowledge this study is the
first study of using bidentate sterically hindered salicylaldimine
palladium complexes as catalysts for CO2 transformations into the
cyclic carbonates.
The square-planar trans-[PdL32] complex did not display any
close metal-metal or p-p interactions in the crystal lattice. Instead,
it showed 1D polymeric stacking of turned sheets consisting of C-
H/O hydrogen bonds along the b-axis and the acetic acid molecule
was stacked between trans-[PdL32] complex units via O-H/O
hydrogen bonds (See Supplementary Data).
The square-planar trans-[PdL32] complex did not display any
We have carried out catalytic reactions changing the tempera-
ture, time, base, pressure and epoxide to find the best reaction
conditions. Firstly, the experiments of other epoxides with CO2 to
synthesize the corresponding cyclic carbonates were investigated.
The epichlorohydrin (ECH), 1,2-epoxybutane(EB), propylene oxide
(PO), styrene oxide (SO), and cyclohexeneoxide (CHO) were tested
as substrates. As can be seen from Table 8 among 1e9 complexes,
compound 2 exhibits higher value for parameters such as yield,
selectivity, TON and TOF. Therefore, the effects of temperature, time
and pressure on the above parameters have been tested on the
samples of 2. The comparison of catalysts (1e9) on the cycloaddi-
tion of CO2 with epoxide ECH at the same catalytic conditions
revealed that all complexes exhibit higher yield and selectivity with
the formation of cyclic carbonate (Fig. 2).
close metal-metal or p-p interactions in the crystal lattice. Instead,
it showed 1D polymeric stacking of turned sheets consisting of C-
H/O hydrogen bonds along the b-axis and the acetic acid molecule
was stacked between trans-[PdL32] complex units via O-H/O
hydrogen bonds (See Supplementary Data).
3.5. Catalytic activity studies
3.5.1. SM coupling reactions
The palladium complexes (1e9) were tested as catalysts for the
Suzuki coupling reactions to give the biaryl derivative compounds.
We initially studied the reaction of phenylboronic acid with 4-
bromoacetophenone in DMF/H2O as a model reaction under
heating to 80 ꢀC in the presence of 1.5 mmol% of Pd(II) metal
catalysts and 1.5 mmol of bases. The results are summarized in
Table 4. All catalytic reactions were carried out in inert
atmosphere.
As can be seen from Table 4, among 1e9 compounds
salicylaldiminato-palladium complexes having 5-tert-butyl (7) and
3,5-di-tert-butyl substituent (9) were found to be most active cat-
alysts for the SM cross-coupling reactions. In order to find optimum
conditions different substrates (4-bromoacetophenone, bromo-
benzene, 1-bromo-4-nitrobenzene, 4-bromoanisole) has been
performed with phenylboronic acid as model compounds. As
shown in Table 5, 1-bromo-4-nitrobenzene was found to be the
Scheme 3. Cycloaddition reaction of CO2with various epoxides catalyzed by 1e9
catalysts.

88
N. Oncel et al. / Journal of Organometallic Chemistry 811 (2016) 81e90
Table 8
The comparison of synthesized complexes in catalytic transformation of CO2 into cyclic carbonate.
Entry
Cat.
Yield a(%)
Selectivitya
%
TONb
TOFc(h1)
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
88.1
89.8
80.5
88.2
83.4
85.0
81.0
76.2
79.0
99.9
98.0
98.6
98.8
99.0
99.0
98.4
99.0
99.5
881
898
805
882
834
850
810
762
790
440
449
403
441
417
425
405
381
395
Reaction conditions: Cat (4.5 ꢂ 10ꢁ5 mol), epichlorohydrin (4.5 ꢂ 10ꢁ2 mol), DMAP (4.5 ꢂ 10ꢁ5 mol),CO2(1.6 MPa), 100 ꢀC, 2 h.
a
Yield and selectivity of epichlorhydrin to corresponding cyclic carbonate were determined by GC.
b
Moles of cyclic carbonate produced perm ole of catalyst.
c
The rate is expressed in terms of the turnover frequency {TOF [mol of product (mol of catalyst h)ꢁ1] ¼ turnovers/h}.
Fig. 2. The comparison of catalysts on the cycloaddition of CO2 with epichlorohydrin at the same catalytic conditions.
Fig. 3. The comparison of bases on the cycloaddition of CO2 with ECH at the same catalytic conditions with Pd (II) salicylaldimine complex (2) catalyst.
As shown in Fig. 3, the activity order of epoxides was found to
be as epichlorohydrin (ECH) > styrene oxide (SO) > cyclohexene
oxide (CHO) > 1,2-epoxybutane (EB) > propylene oxide (PO). This
result may be due to the more electron donating substituents
linked to C2-atom of these which could be coordinately bonded to
the metal center and could be responsible for the catalyst
poisoning [37]. Similar effect was observed in our previous studies
[35e39].
Fig. 4 shows that the ECHC yield increased with reaction time up
to a period 4 h. The cycloaddition reaction proceeds rapidly within

N. Oncel et al. / Journal of Organometallic Chemistry 811 (2016) 81e90
89
Fig. 4. Conversion and selectivity of ECH as a function of time with 2 as catalyst.
Fig. 5. Conversion and selectivity of ECH as function of temprature using Pd (II) salicylaldimine complex (2) as catalyst.
Fig. 6. Conversion and selectivity of ECH as function of pressure using Pd (II) salicylaldimine complex (2) as catalyst.
the first 2 h, reaching a ECHC yield of 89.8%. With increase of time
4. Conclusion
from 0.5 to 4 h, ECHC yield increased sharply from 58 to 97.5%. On
this basis, the experiments to assess other reaction parameters
were performed for 4 h. The results shown in Fig. 5 clearly show
that temperature has a strong effect on the ECH conversion. When
catalytic reactions were conducted at 75, 100, and 125 ꢀC, the ECH
conversions were 99.5, 100.0, and 100.0%, respectively. This tem-
perature and conversion relationship is attributed to higher reac-
tivity at a higher temperature.
As shown in Fig. 6, in the low-pressure range (0.5e2.5 MPa),
there is rise of yield (from 71.0% to 90.0%) with increase of initial
CO2 pressure, but further rise of pressure to 4 MPa results in
moderate decrease of ECHC yield.
In this research, sterically hindered novel palladium(II) salicy-
laldimine complexes have been successfully synthesized and
characterized based on the elemental CHN analysis, spectroscopic
techniques and X-ray crystallographic analysis. While all complexes
have been prepared in the identical conditions in CH3COOH/CHCl3,
as supported by X-ray, FTIR and 1H NMR techniques, only complex 3
was crystallized as trans-PdL32$2C2H4O2 solvate molecules. All 1e9
compounds are proved to be as an efficient homogeneous catalyst
for both Suzuki-Miyaura cross-coupling reactions of various aryl
bromides and cyclic carbonates synthesis from CO2 and epoxides
are reported under appropriate conditions. To the best of our

90
N. Oncel et al. / Journal of Organometallic Chemistry 811 (2016) 81e90
b) B.J. Bennett, J.C. Smith, S.J. Duffy, C.M. Vogels, A. Decken, S.A. Westcott,
Canad. J. Chem. 85 (2007) 392e399;
c) J. Yorke, C. Dent, A. Xia, Inorg. Chem. Commun. 13 (2010) 54e57;
d) E. Tas, A. Kilic, M. Durgun, I. Yilmaz, I. Ozdemir, N. Gurbuz, J. Organomet.
Chem. 694 (2009) 446e454;
knowledge this study is the first study of using bidentate sterically
hindered salicylaldimine palladium complexes as catalysts for atom
economic CO2 fixation into the cyclic carbonates.
e) N. Shahnaz, B. Bank, P. Das, Tetrahedron Lett. 54 (2013) 2886e2889.
[20] E.G. Bowes, G.M. Lee, C.M. Vogels, A. Decken, S.A. Westcott, Inorg. Chim. Acta
377 (2011) 84e90.
Acknowledgements
[21] a) Z.Z. Zhou, F.S. Liu, D. Shen, Ch. Tan, L.-Y. Luo, Inorg. Chem. Commun. 14
(2011) 659;
This work was supported by the HUBAK (Project No: 14084).
Appendix A. Supplementary data
b) D.F. Braton, T.M. Larkin, D.A. Vicic, O. Navarro, J. Organomet, Chem. 694
(2009) 3008;
c) S.R. Barhade, S.B. Waghmode, Tetrahedron Lett. 49 (2008) 3423.
[22] M. Aresta, A. Dibenedetto, Dalton Trans. (2007) 2975.
[23] S.N. Riduan, Y. Zhang, Dalton Trans. 39 (2010) 3347.
[24] J.F. Larrow, E.N. Jacobsen, Y. Gao, Y. Hong, X. Nie, C.M. Zeppe, J. Org. Chem. 59
(1994) 1939.
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2016.03.024.
[25] V.T. Kasumov, H. Türkmen, I. Uçar, A. Bulut, N. Yaylı, Spectrochim. Acta Part A
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