Polyfluorinated Pd(II)-3,5-di-tert-butylsalicylaldimenes complexes: Synthesis, structure, spectroscopy, redox behaviors and catalytic activity

Article abstract of DOI:10.1016/j.saa.2013.01.015

A series of new polyfluorinated palladium(II) complexes (7-12) of N-polyfluorophenyl-3,5-di-tert-butylsalicylaldimines (1-6) have been synthesized. They were characterized by analytical, spectroscopic (UV/Vis, IR, ¹H NMR, and ESR), electrochemi

Full text of DOI:10.1016/j.saa.2013.01.015

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 107 (2013) 31–38
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Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Polyfluorinated Pd(II)-3,5-di-tert-butylsalicylaldimenes complexes: Synthesis,
structure, spectroscopy, redox behaviors and catalytic activity
b
Veli T. Kasumov a, , Ertan Sahin
⇑
a Department of Chemistry, Harran University, Fac. Arts & Sci., 63300 Sßanlıurfa, Turkey
b Department of Chemistry, Ataturk University, Fac. Sci., TR-25240 Erzurum, Turkey
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
"
"
New bis(N-polyfluorophenyl-3,5-
But2-salicylaldiminato)palladium(II)
complexes.
Spectroscopic, redox reactivity and
catalytic activity of the above
complexes are reported.
Bis-[N-(3,5-di-tert-
butylsalicylidene)-2,3,4,5,6-
pentafluoroaniline]Pd(II) has been
structurally characterized.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 July 2012
Received in revised form 29 December 2012
Accepted 10 January 2013
Available online 23 January 2013
A series of new polyfluorinated palladium(II) complexes (7–12) of N-polyfluorophenyl-3,5-di-tert-butyl-
salicylaldimines (1–6) have been synthesized. They were characterized by analytical, spectroscopic (UV/
Vis, IR, 1H NMR, and ESR), electrochemical methods and their chemical oxidation and hydrogenation cat-
alytic activity were studied. The X-ray crystal structure analysis of bis[N-(3,5-di-tert-butylsalicylidene)-
F5Ph]Pd(II) (12) revealed a slightly distorted square-planar trans-PdN2O2 geometry around the palladium
center. The UV/Vis and EPR results indicate that chemical oxidation of 7–10 by Ce(IV) in CHCl3 generates
relatively stable Pd(II)–phenoxyl radical complexes (g = 2.0044–2.0062). The results of chemical and elec-
trochemical oxidation of 1–12, as well as the catalytic activity of 7–10 complexes in the hydrogenation of
PhNO2 were presented.
Keywords:
Bis[(N-3,5-di-tbusalicylidene)-
polyfluorophenyl]Pd
X-ray structure
Ó 2013 Elsevier B.V. All rights reserved.
Redox reactivity
PdII-phenoxyl radicals
Introduction
have ability to form the directly coordinated MII,III–phenoxyl radi-
cal complexes [3–7].
The design, synthesis and structural characterization of salicyl-
aldimine complexes bearing sterically hindered tert-butyl groups
are a subject of current interest due to their interesting structural,
magnetic, spectral, catalytic and redox properties, use as models
for enzymes and various theoretical interests [1–4]. The discovery
of Cu(II)–phenoxyl radical centers in the active site of CuII-contain-
ing enzymes (galactose and glyoxal oxidases and others) has stim-
ulated the development of various transition metal chelates that
One of the unique properties of first row-transition metal com-
plexes with phenoxyimine ligands bearing bulky tert-butylated
phenol fragments is their ability to form stable metal(II/III)–phe-
noxyl type radical complexes [2–4]. 4- and 5-group transition me-
tal complexes with above mentioned ligands have been widely
used as olefin polymerization catalysts [8–15]. Among these cata-
lysts, the use of perfluorinated phenoxyimine ligands with transi-
tion metal complexes (fluorinated MAFI catalysts) to catalyze the
ethylene and propylene living polymerization reactions has be-
come one of the most widely used compounds in highly controlled
living olefin polymerization catalysts [8–15]. Fujita and co-workers
⇑
Corresponding author. Tel.: +90 414 318 3588; fax: +90 414 3440051.
E-mail address: vkasumov@harran.edu.tr (V.T. Kasumov).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.01.015

32
V.T. Kasumov, E. Sahin / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 107 (2013) 31–38
demonstrated that bulky substituents ortho to the phenoxy–oxy-
gen in these complexes play a key role in achieving both living
and isospecific polymerization and increase their catalytic activity
[12–14]. Calculations demonstrate that the ortho-F interacts elec-
tronically with a b-H on a growing polymer chain (ortho-F/b-H dis-
tance: 2.276 Å) [14–16]. This indicates that the presence of an
attractive interaction between the ortho-F and the b-H for all
ortho-fluorinated TiAFI independent of the phenoxy–imine ligand
structures, confirming the generality of the unusual attractive
interaction for ortho-F in TiAFI catalysts.
In continuation, in our studies on the chemistry of bulky phen-
oxyimine ligands bearing di-tert-butylated phenol fragments we
report the synthesis, crystal structure, spectroscopic characteriza-
tion, chemical oxidation and catalytic activity of the N-perfluor-
ophenyl-3,5-di-tert-butylsalicylaldimine ligands Pd(II) complexes
[17–20]. The aim of this work is to investigate the influence of
the strong electron-withdrawing fluorine atoms in the aniline ring
on the formation of Pd(II)-phenoxyl radicals and catalytic activity
in the hydrogenation of nitro compounds. Here we describe the
synthesis, crystal structure, spectroscopic characterization as well
as chemical and electrochemical redox behaviors and catalytic
activity of some N-polyfluorophenyl-3,5-di-tert-butylsalicylidene
ligands (1–6) Pd(II) complexes (7–12) (Scheme 1). The crystal
structure of 2 and 3 ligands [21] and some spectral and redox
behavior of complex 10 [22], as well as the synthesis and some
IR and 1H NMR characteristics of 1–6 ligands [8–13] have been
early reported.
Instrumentation
The C, H, N elemental analyses were performed on a LECO
CHNS-932 model analyzer. Electronic spectra were recorded by
using a Perkin Elmer Lambda 25 spectrometer, IR spectra ob-
tained on a Perkin Elmer FT-IR spectrometer using KBr pellet.
1H NMR spectra were measured on a Bruker Spectro spin Avance
DPX-300 Ultra Shield Model NMR with Me4Si as an internal
standard in CDCl3 solutions ESR spectra were taken on a Varian
E109C X-band spectrometer. The field and frequency calibration
were made using DPPH (g = 2.0037). An Eco Chemie Autolab-12
potentiostat with the electrochemical software package GPES
4.9 (Utrecht, The Netherlands) was used for voltammetric mea-
surements. A platinum disk (2 mm o.d.) was employed as a
working electrode, a platinum coil as a counter electrode, and
an Ag/AgCl as reference electrode, respectively. All measure-
ments were performed in MeCN containing 0.05 M Et4NBF4 (TEA-
TFB) as
a
supporting electrolyte under N2 at ambient
temperatures.
Synthesis
General method for the synthesis of N-(3,5-di-tert-butylsali-
cylidene)polyfluoroaniline ligands. The compounds 1–4 were
prepared by the standard method of condensation of 3,5-di-
tert-butyl-2-hydroxybenzaldehyde with corresponding fluoroani-
lines in absolute ethanol in the presence of a few drops of for-
mic acid. The mixture was stirred at reflux for 24–30 h and then
the volume of the solution was reduced to ca. 25 ml. After cool-
ing to room temperature, a yellow solid precipitate was isolated
by vacuum filtration and dried in air to give 1–4 (62–88%) prod-
ucts. The ligands 5 and 6 were prepared by similar manners
using excess of 2,3,5,6-tetrafluoroaniline and 2,3,4,5,6-pentafluo-
roaniline according the literature procedure [24]. The 1H NMR
and elemental analysis data of the 1–6 ligands were found to
be identical with those reported by Fujita and co-workers [8–
15].
Experimental
Materials
Chemicals, reagents, and solvents employed were commercially
available and used as received. All chemicals, reagents, and sol-
vents employed were commercially available and used as received.
N,N-dimethylformamide (DMF), dimethyl-ulfoxide (DMSO), aceto-
nitrile (MeCN), chloroform, ethanol, methanol, 2,4-di-tert-butyl-
phenol, hexamethylenetetramine, nitrobenzene, palladium(II)
acetate, (NH4)2Ce(NO3)6 (CAN), acetic acid and all fluorinated ani-
lines (2,4-difluouroaniline, 2,5-difluouroaniline, 2,6-difluouroani-
line, 2,3,4-trifluouro-aniline, 2,3,5,6-tetrafluouroaniline and
2,3,4,5,6-pentafluouroaniline) were purchased from Sigma–Aldrich
and used without further purification. 3,5-tBu2-salicylaldehyde
was prepared according to a published procedure [23].
Synthesis of palladium(II) complexes
The general method of preparation was as follows. Palladium
acetate (0.25 mmol) was added to
(ꢀ40 °C) containing 0.5 mmol of appropriate ligand (1–4) in
30 ml of acetonitrile. The mixture was heated for about 50 min at
this temperature and left at room temperature for 3–4 h. The
a stirred warm solution
Scheme 1. A general synthetic route for the palladium(II) complexes; HTM = hexamethylenetetramine.

V.T. Kasumov, E. Sahin / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 107 (2013) 31–38
33
precipitated red complex was collected by suction filtration and
washed with water, could methanol and recrystallised from meth-
anol/chloroform mixture. The synthesis of complexes 11 and 12
was carried out in the same way as that described for above com-
plexes, but 10 ml glacial acetic acid was used instead of acetoni-
trile. The crude orange red solid complexes 11 and 12 were
recrystallized in methanol/CHCl3 mixture.
Theelectronic spectra of 1–6(Table 1, Figs. 1 and 2a), unlikemany
other non-fluorinated bidentate arylsalicylaldimines [20,27,28], did
not exhibit absorptions above 370 nm even in the concentrated
strongly H-bonding polar solvents such as ethanol and methanol
solutions. This observation suggests that the perfluorinated 1–6 sal-
icylaldimines exist only in enol-imine tautomer form at room tem-
perature. The higher intense absorption bands observed in the
ranges of 210–330 and 355–362 nm (Table 1) have been assigned
to
p ?
pꢄ and n ? pꢄ transitions for the electrons localized on the
Hydrogenation procedure
aromatic and imine groups, respectively. However, a more intense
band at 355–362 nm, according to their higher extinction coeffi-
The hydrogenation of nitrobenzene was carried out in a thermo-
static reaction flask (100 ml) at 25 °C under 760 Torr H2 with vig-
orous stirring in dry and deoxygenated 25 ml DMF solution.
Catalyst (1.0 ꢁ 10ꢂ5 to 4.0 ꢁ 10ꢂ6 mol) was added into 25 ml
DMF and saturated with H2 for 10–15 min. After addition of NaBH4
(5 ꢁ 10ꢂ6 mol) the mixture was stirred for ca. 5 min and PhNO2 (4–
8 ꢁ 10ꢂ4 mol) was transferred into the vessel. Then the H2 gas was
bubbled again into the flask and the volume of the absorbed H2
was measured periodically.
cients (e
= 10,000–39,000 Mꢂ1cmꢂ1) can be assigned to overlapped
bands originated from low intense n ? pꢄ transitions and higher in-
tense charge transfer absorptions [28]. Thus, UV/Vis study in the dif-
ferent solvents indicates that no tautomerisim takes place in polar
Table 1
Electronic spectral data for 1–12 and their oxidized intermediates.
Compound Solvent
Electronic spectra, k (nm), (loge )
, Mꢂ1 cmꢂ1
1
MeOH
MeCN
207(4.83), 222*, 235*, 277(4.35), 325*, 356(4.21)
222(4.6), 235**, 277(4.4), 309(4.12), 322 (4.1)*,
355(3.98)
X-ray crystallography
MeCN + Ox. 222, 275, 308, 320*, 354, 520*
MeOH
For the crystal structure determination, the single-crystals of
the complexes (12ꢃCHCl3) were used for data collection on a
four-circle Rigaku R-AXIS RAPID-S diffractometer (equipped with
a two-dimensional area IP detector). The graphite-monochroma-
2
208(4.7), 220(4.6), 281(4.5), 314(4.5), 329*,
360(4.3)
EtOH
MeCN
210(4.8), 224(4.8), 237*, 281(4.7), 331*, 362(4.3)
221(4.5), 235*, 280(4.4), 314(4,4), 329*, 358(4.2)
MeCN + Ox. 268, 285*, 315, 328*, 350
tized Mo K
nique with
a
D
radiation (k = 0.71073 Å) and oscillation scans tech-
= 5° for one image were used for data collection.
3
4
MeOH
208(4.9), 227(4.8), 276(4.8), 305(4.4), 321(4.6),
x
356(4.5)
The lattice parameters were determined by the least-squares
EtOH
218*, 233(4.9), 276(4.8), 306(4.7), 320(4.6), 357
(4.5)
methods on the basis of all reflections with F2 > 2 (F2). Integration
r
of the intensities, correction for Lorentz and polarization effects
and cell refinement was performed using Crystal Clear (Rigaku/
MSC Inc., 2005) software [25]. The structures were solved by direct
methods using SHELXS-97 [26] and refined by a full-matrix least-
squares procedure using the program SHELXL-97 [26]. H atoms
were positioned geometrically and refined using a riding model.
The final difference Fourier maps showed no peaks of chemical
significance.
MeCN
MeCN + Ox
MeOH
227(3.3),276(3.2), 305(3.1), 320(3.1), 355(2.9)
272, 308, 320*, 352, 420*, 520*
207(4.8), 222(4.7), 236**, 282(4.6), 306(4.6),
323*, 358(4.6)
MeCN
223(4.6), 333**, 282(4.47), 306(4.5), 322*,
357(4.3)
MeCN + Ox. 278, 305, 320*, 355, 550**
MeOH
MeCN
MeCN + Ox
MeOH
5
6
206(4.6), 231(4.5), 278(4.4), 305(4.3), 361(4.1)
229(4.5), 280(4.4), 306*(4.33), 321**, 360(4.1)
230*, 277, 305*, 322*, 355, 715
206(4.8), 225(4.8), 279(4.7), 300(4.6), 322*,
361(4.4)
224(4.46), 279(4.34), 323*(4.19), 360(4.05)
277, 304*, 322*, 736
Results and discussion
MeCN
MeCN + Ox
EtOH
CHCl3
MeCN
7
8
208(4.6), 239*(45), 263(4.6), 303(4.3), 414(3.7)
263(4.8), 306(4.5), 414(3.9)
IR and UV/visible spectroscopic characterization of 7–12 compounds
241(4.93), 262(4.98), 302(4.65), 409(4.19)
The analytical, IR, 1H NMR spectroscopic characteristics of the
compounds 1–6 were previously reported [8–10,13]. The analyti-
cal, IR, 1H NMR spectroscopic characteristics of the compounds
7–12 is presented in Supplemental part. In order to compare the
spectral properties of the ligands and their 7–12 complexes, also
we have measured the IR and 1H NMR characteristics of 1–6 li-
gands. The IR spectra of all compounds exhibit sharp bands in
the region of 2860–2950 cmꢂ1 due to the asymmetric and sym-
MeCN + Ox
EtOH
235*, 289, 350, 404*, 530**
210(4.5), 237(4.6), 264(4.6), 303(4.3), 353*(4.2),
420(4.2)
CHCl3
MeCN
MeCN + Ox
EtOH
CHCl3
MeCN
MeCN + Ox
EtOH
CHCl3
MeCN
MeCN + Ox
EtOH
CHCl3
MeCN
MeCN + Ox
EtOH
CHCl3
MeCN
MeCN + Ox
261(4.97), 306(4.62), 421(4.08)
238(4.5), 262(4.6), 303(4.28), 416(3.7)
250*, 294, 320*, 378, 405
9
10
11
12
219(4.7), 252(4.0), 301(4.9), 354(3.3), 422(3.4)
259(4.17), 305(3.91), 358*(3.10), 422(3.56)
220(4.5), 262(4.54), 302(4.3), 416(3.72)
237, 261*, 296, 355*, 413, 530**
237*(4.52), 263(4.55), 302(4.26), 417(3.78)
262(4.83), 306(4.76), 420(4.09)
240*(4.1), 262(4.13), 302(3.98), 414(3.47)
234*, 294, 348*, 404* 500**
240(4.77), 260(4.89), 304(4.48), 430(3.98)
258(3.62), 307(4.67), 432(4.03)
240(4.57), 261(4.86), 305(4.57), 426(4.06)
238*, 296, 355*, 419
metric
m(CAH) stretching frequencies of the C(CH3)3 groups. The
m
(C@N) stretching vibrations of 7–12 are blue shifted (1602–
1616 cmꢂ1
) relative to those of free 1–6 ligands (1622–
1630 cmꢂ1), indicating coordination of the imine nitrogen atom
to copper(II) (Section ‘Experimental’). A weak broad feature cen-
tered at 2500–2800 cmꢂ1, due to
m(OH) of the intramolecularly
H-bonded OHꢃ ꢃ ꢃN in 1–6, disappears in the spectra of all the com-
plexes. This suggests their coordination via deprotonated phenolic
oxygen atom to Pd(II). The appearance of new bands at 1526–
208(4.7), 241(4.9), 262(4.9), 306(4.7), 430(4.2)
269(4.9), 308(4.8), 430(4.2)
240(4.8), 261(4.9) 305(4.5), 426(4.0)
231, 299, 355, 419
1530 cmꢂ1, attributable to the coordinated
m(CAO) stretching
mode [27,28] and in the 450–660 cmꢂ1 region assignable to the
PdAO and PdAN bonds, further confirmed the coordination of li-
gands through phenolic O and azomethine N atoms.
*
Shoulder.
Very weak shoulder.
**

34
V.T. Kasumov, E. Sahin / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 107 (2013) 31–38
spectra of the free ligands (d 11.45–14.86 ppm) disappeared in
the complexes indicating that the OH group was deprotonated
and bonded to the metal ion as an oxygen anion (Section ‘Experi-
mental’). Note that the chemical shift of OH proton decreased with
an increase in the number of F atoms on the aniline ring in the or-
der d = 13.42 (1) > 13.35 (3) > 13.32 (2) > 13.18 (4) > 12.84
(5) > 12.76 (6). The higher field shift trends were also detected
for salicylic and aniline rings protons. Similar magnetic shielding
effects have been previously observed in Schiff base complexes of
Pd(II), Zn(II), Co(II) and Cu(II) [20,28]. A plausible explanation up-
field shift of the peripherally bonded CH3 protons is that when
the tert-butyl group is exposed to the anisotropy generated by
close proximity to an aromatic ring, the group is shielded and an
upfield shift is observed [28].
Complexes 7–12 are diamagnetic, suggesting a square-planar
geometry for these complexes. Electronic spectra of these com-
plexes are also indicative of a square-planar geometry [18,20,27].
The electronic spectra of 7–12 in EtOH, MeCN and CHCl3 solutions
exhibit very similar three intense bands in the 260–432 nm region
(Table 1). The intense broad band appeared within 409–432 nm due
to its higher molar extinction coefficients (e = 2512–15,850 Mꢂ1
-
cmꢂ1) is assigned to metal-to-ligand charge-transfer [21,23].
Chemical oxidation of 1–12
Fig. 1. Electronic spectra of 1–4 ligands in EtOH: (a) spectra of 3 and 4. (b) Insert:
spectra of 1 and 2.
Our previous studies demonstrated that the chemical oxidation
of some bis[N-alky(aryl)-3,5-tBu2-salicyilaldiminato] M(II) (M = Cu,
Co, Pd) complexes by (NH4)2[Ce(NO3)6] (CAN) in CHCl3 or MeCN
was accompanied by disappearance of their d–d bands and appear-
ance of the new absorptions typical for radical signals [2–4,19].
The addition of 1.5 equiv. CAN to CHCl3 solution of 7–10 com-
plexes under ambient conditions caused a color change from or-
ange red to dark red and EPR monitoring of these reaction
mixture revealed the appearance of signals at g = 2.0032–2.0062
typical for phenoxyl radical species (Fig. 3). For oxidized 7, 8, 9
and 10 complexes isotropic single line spectra with g = 2.0062
H-bonding solvents for N-perfluorinated 3,5-di-tert-butyl-
salicylaldimines.
1H NMR spectral characterization of 7–12 compounds
The 1H NMR spectral data was obtained for 7–10 complexes in
CDCl3, with their assignments are presented in Section ‘Experimen-
tal’. In order to establish the mode of coordination of the ligands on
the metal center, 1H NMR proved to be very useful. The comparison
of the 1H NMR chemical shifts of 1–6 hydrogen atoms with those in
the corresponding 7–12, shows that all proton signals of the li-
gands were shifted to upfield in the spectra of corresponding com-
plexes. For example, d 8.71–8.88 (CH@N), d 1.50–1.52 [3-C(CH3)3]
and d 1.35–1.37 ppm [5-C(CH3)3] of the free 1–6 ligands groups
protons signals are, respectively, shifted upfield to d 7.53–8.08
(CH@N), d 1,23–1.25 [3-C(CH3)3] and 0.87–0.90 ppm [5-C(CH3)3]
regions, in the spectra of corresponding 7–12 complexes
(Section ‘Experimental’). The OH proton signals in the 1H NMR
(D
Hpp = 6.25 G), g = 2.0059 (DHpp = 6.0 G), g = 2.0044 (DHpp = 6.0
G) and g = 2.0054 ( Hpp = 6.5 G), respectively, were detected
D
(Fig. 3a). These spectral features are similar to other M(II)-phe-
noxyl radicals [3,19]. It is interesting that when 4-fold excess of
CAN was added to CHCl3 solution of 10 instead of single line spec-
trum the six line spectrum (Fig. 3b) with g = 2.0032 and line width
D
Hpp = 23.5 G was detected. It is necessary to note that the above
detected radicals are unstable and upon second scanning the de-
crease about 50% in their peak intensities was observed.
Fig. 2. Spectral changes in the oxidation of 5 with one equiv. Ce(IV). Spectra of ligand 5 (a) and its oxidized species (b and c) in acetonitrile and at r.t.

V.T. Kasumov, E. Sahin / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 107 (2013) 31–38
35
spectroscopy in the range 200–1100 nm. The results of these
experiments show that on mixing of equivalent molar amounts
of the ligands 1–6 and CAN in MeCN, the light yellow color of
the ligands simultaneously turns to greenish-brown and except
2, the appearance of a new broad absorption in the range 520–
736 nm was detected in the spectra of the reaction mixture (Ta-
ble 1). The shoulder patterns at 520–550 nm for oxidized [1–4]Å+
and a broad maximum bands at 715 and 736 nm in the spectra
of the oxidized [5]Å+ and [6]Å+, respectively, confirm the generation
of the phenoxyl radical species, which are relatively stable at r.t.
under aerobic conditions. Similar spectral changes were also ob-
served upon one-electron oxidation for all 7–12 complexes in
MeCN. The comparison of the UV/Vis spectra of 7–12 with those
for oxidized [7–12]Å+ species revealed the appearance new bands
within 355–380 and 500–550 nm regions for oxidized complexes
(Fig. 4, Table 4). These new absorption features along with EPR re-
sults clearly indicate that chemical oxidation of 7–12 complexes
generate Pd(II)-phenoxyl radical species.
Fig. 3. Solution ESR spectra generated by the chemical oxidation of 7 (a) and 10 (b)
complexes with Ce(IV) in CHCl3 at r.t. and aerobic conditions: (a) 7 + 1.5 equiv.
Ce(IV) and (b) 10 + 4 equiv. Ce(IV).
The UV/Vis spectral results of the oxidized compounds along
with non-oxidized 1–12 original compounds in MeCN are collected
in Table 1. The spectral changes followed by the chemical oxidation
of 1–12 with one-electron oxidant, CAN, in CH3CN solutions at r.t.
and under aerobic conditions, were monitored by UV/Vis
Electrochemical oxidation of 7–12 complexes
The electrochemical redox behaviors of 7–12 has been exam-
ined by cyclic voltammetry technique using a Pt working electrode
Fig. 4. The changes in the UV/Vis spectra of 7 (a and e) and 7 + Ce(IV) system (b–d, g) in MeCN solution at r.t. and aerobic conditions; (a) – initial spectrum of 7; (b) –
successive scanned spectra of 7 + Ce(IV) mixture; (c, d, g) – diluted spectrum of (a). The arrow indicates the direction of the increasing absorbance.
Fig. 5. Cyclic voltammograms of 8 and 12 in MeCN containing 0.05 M TEATFB in the potential range 0.0–2.0 V: (a) CV of 8 (0.4 mM) at a scan rate of 0.05 V/s. (b) CV of 12
(0.5 mM) at a scan rate of 0.1–0.5 V/s. Working electrode Pt, Counter electrode Pt wire, reference electrode Ag/AgCl was used in all experiments.

36
V.T. Kasumov, E. Sahin / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 107 (2013) 31–38
Table 2
Crystallographic data of the complex 12ꢃCHCl3.
Empirical formula
Formula weight
Temperature (K)
Crystal size (mm)
Crystal system
Space group
a (Å)
C42H42N2O2F10 Pdꢃ ꢃ ꢃCHCl3
1022.6
293(2)
0.21 ꢁ 0.14 ꢁ 0.11
Monoclinic
P21/n
13.6334(3)
b (Å)
13.1863(4)
c (Å)
25.5649(8)
a
=
c
(°)
90
b (°)
92.114 (3)
4592.56(2)
V (Å3)
Z
4
q
l
calcd. (g/cm3)
(mmꢂ1
1.48
0.656
)
F(000)
2071.8
H
– range (°)
2.2–26.4
Index ranges
Reflections collected
Reflections observed (>2
ꢂ17 < h < 17, ꢂ16 < k < 13, ꢂ31 < l < 31
26364
9231
r)
Data/restrains/parameters
R1 (all)
wR2
4627/0/565
0.089
0.218
GooF
1.033
Table 3
Selected bond lengths (Å) and angles (°) for (12ꢃCHCl3).
Fig. 6. Hydrogenation of PhNO2 with catalysts 7–9 (3 ꢁ 10ꢂ4 M, 6 ꢁ 10ꢂ6 mol) at
298 K, in the presence of a catalytic amount of NaBH4 (2.5 ꢁ 10ꢂ6 mol) in DMF. 2
(10) and 4 (10) were measured in the absence of NaBH4. 4 (10) was measured after
72 h of the 2 (10).
Selected bond lengths (Å)
PdAO(1)
PdAN(1)
F(6)AC(42
F(7)AC(41)
O(1)AC(3)
F(3)AC(19)
N(1)AC(1)
2.004(6)
2.011(7)
1.340(10)
1.339(11)
1.314(9)
1.350(12)
1.289(10)
PdAO(2)
PdAN(2)
1.979(6)
2.008(6)
F(1)AC(17)
F(4)AC(20)
O(2)AC(23)
N(1)AC(16)
F(2)AC(18)
1.312(12)
1.330(13)
1.317(10)
1.425(10)
1.351(14)
Selected Bond angles (°)
O(1)APdAO(2)
O(1)APdAN(2)
O(2)APdAN(2)
PdAO(1)AC(3)
170.1(3)
89.1(3)
91.7(3)
124.6(5)
122.4(5)
115.2(7)
O(1)APdAN(1)
O(2)APdAN(1)
N(1)APdAN(2)
PdAO(2)AC(23)
PdAN(1)AC(1)
PdAN(2)AC(37)
92.0(3)
88.7(3)
170.6(3)
123.3(5)
121.8(6)
119.9(5)
PdAN(1)AC(16)
C(16)AN(1)AC(1)
Table 4
Parameters (Å) for hydrogen bonds and short intramolecular contacts.
DAHꢃ ꢃ ꢃA
Hꢃ ꢃ ꢃA
2.67
2.68
2.49
Dꢃ ꢃ ꢃA
<DAHꢃ ꢃ ꢃA
136
135
C(14)AH(14B)ꢃ ꢃ ꢃCg(4)
C(34)AH(34C)ꢃ ꢃ ꢃCg(2)i
C(43)AH(43)ꢃ ꢃ ꢃCg(1)ii
3.431(11)
3.435(11)
3.449(19)
166
Y–X...Cg(
p
-ring)
X. . .Cg
Y. . .Cg
<Y–Xꢃ ꢃ ꢃCg
118
119
C(43)ACl(3)ꢃ ꢃ ꢃCg(2)iii
C(21)AF(5)ꢃ ꢃ ꢃCg(4)iv
C(41)AF(7)ꢃ ꢃ ꢃCg(3)iv
3.538(8)
3.434(7)
3.181(6)
4.559(7)
4.256(8)
4.380(8)
Fig. 7. Perspective view of the Pd(II) complex (12-CHCl3) with the atom numbering
scheme. Displacement ellipsoids are at the 40% probability level.
148
Symmetry codes: (i) x, y, z; (ii) 3/2 ꢂ x, ꢂ1/2 + y,1/2 ꢂ z; (iii) ꢂ1/2 + x,1/2ꢂy,1/2 + z;
(iv) 1 ꢂ x,1 ꢂ y, ꢂz Cg(1), Cg(2), Cg(3) and Cg(4), are the centroid of the rings
C(2)AC(7), C(16)AC(21), C(22)AC(27),and C(37)A.
in acetonitrile (MeCN) in the potentials ranging from ꢂ2.0 to +2.5 V
versus Ag/AgCl at 293 K under N2 containing Et4NBF4 (0.05 M) as
the background electrolyte. The CV of 7 exhibits three irreversible
ligand centered anodic oxidation processes with anodic peak
potentials (Epa) approximately at 1.08, 1.35, 1.50 V versus Ag/AgCl
indicating the instability of the oxidized species in the CV time
scale. The first oxidation wave of the 8 and 9 complexes are qua-
si-reversible with E1pa=Ep1c of 1.14/1.01 and 1.15/1.08 V, respec-
tively. The second and third waves are irreversible oxidation
processes the respective anodic peak potentials at ca 1.32 and
1.58 V for former and at 1.48 and 1.58 V versus Ag/AgCl for lather
complexes, respectively (Fig. 5a). On the other hand, for complex
10 under above conditions only one quasi-reversible oxidation
wave with E1pa=Ep1c ¼ 1:14=0:32 was detected. It is interesting that
the CV profile of 11 and 12 complexes (Fig. 5b) are very similar
to each other and significantly different from those for 7–10 com-
plexes. The positive slope obtained in the plot of the peak current
(ip) versus the square root of the voltage scan rate (V1/2) within the
range of 100–500 mV/s indicates diffusion controlled electron ex-
change reactions at the first oxidation peak potentials of the 11
and 12 complexes [29].
Analyses of the electrochemical results show that the potentials
of the ligand-centered redox couple do not correlate with the elec-
tron withdrawing ability of the F atoms on the aniline ring substit-
uents. Some voltammograms also exhibit ill-defined low intense

V.T. Kasumov, E. Sahin / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 107 (2013) 31–38
37
Fig. 8. Unit cell packing diagram for 12-CHCl3 along the a-axis.
Fig. 9. CAHꢃ ꢃ ꢃCg(
p-ring) stacking interaction with the chloroform and the C(16)AC(21) aromatic ring along the unit cell diagonal-axis.
minor features, which can be assigned to the Pt-surface adsorbed
phenoxyl radicals or to other secondary decomposition products.
for acceleration their catalytic activity, for complex 10 did not need
any preliminary activation. In order to check whether the catalyst
lost its activity or not, the recycling efficiency of the catalysts was
carried out by conducting some experiments over a period of 36 h.
It was observed that the initial rate of hydrogenation reaction re-
mains almost unchanged even after two weeks for complex 10.
The recycling experiments showed that the catalytic activity of
10 remains unchanged and can be re-used without appearance
any sign of decomposition of complex. Unlike nonflour substituted
Pd(N-X-arylsalicylaldimiato)2 type complexes [20], no evidence of
the palladium metal precipitation was observed in the course of
the hydrogenation of nitrobenzene for a period of two weeks.
The average rate of H2 absorption and the specific catalytic activity
of 7–10 were obtained as 0.5–1.1 ml/min and 3.56–6.58 H2 con-
sumed/mol-cat (min), respectively. While the hydrogenation cata-
lytic activity of the present Pd(II) complexes are lower than those
for some mono-F, Br and CH3 substituted Pd(N-X-arylsalicylaldim-
iato)2 type complexes [20], the catalytic activity of 9 and 10 com-
plexes remains unchanged at least two weeks.
Catalytic reduction of nitrobenzene by complexes 7–10
The present investigation has shown that all of the 7–10 com-
plexes exhibit catalytic activity in the hydrogenation of nitroben-
zene under normal pressure of H2, 760 Torr, in DMF solution at
25 °C. Nitrobenzene, as identified by means of IR scanning, was
completely reduced to aniline. The catalytic studies showed that
complexes 7–10 exhibit a catalytic activity towards the hydroge-
nation of nitrobenzene in DMF solution at 25 and 30 °C, under nor-
mal pressure of H2 gas (760 Torr), without any preliminary
activation. The concentration of nitrobenzene was varied from
0.147 to 1.224 mol/l using
a fixed amount of the catalyst
(4 ꢁ 10ꢂ4 mol/l) Pd(II) content. The course of the hydrogenation
of the PhNO2 with 7–10 catalysts is shown in Fig. 6. Although,
for starting of the hydrogenation of PhNO2 with 7–9 catalysts it
is necessary to add of NaBH4 (1.0 ꢁ 10ꢂ6 mol) to catalysts solution

38
V.T. Kasumov, E. Sahin / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 107 (2013) 31–38
Crystal structure of 12ꢃCHCl3
3,5-di-tert-butylsalicylaldimines exist only in the enol-imine form.
Electron-withdrawing fluorine atoms in FnPh groups increase the
magnetic shielding of all proton atoms in the 7–12 complexes. As
supported by EPR and UV/Vis studies, chemical oxidation of the pre-
sented complexes with Ce(IV) leads to the formation of the relatively
stable Pd(II)-phenoxyl radicals at ambient conditions. It has been
demonstrated that 7–10 complexes exhibit moderate catalytic
activityin the hydrogenation of nitrobenzene withoutlosing activity
at least for two weeks.
In spite of our best efforts, suitable crystals for X-ray diffraction of
7–11 complexes could not be obtained. But our efforts are contin-
ued. The molecular structure of solvated Pd(II) complex 12ꢃCHCl3
including atom-numbering is shown in Fig. 7. Crystal data and addi-
tional data collection parameters and refinement details are pre-
sented in Table 2. Selected bond distances and angles as well as
the data of hydrogen-bonding interactions are given in Tables 3
and 4, respectively. Complex 12ꢃCHCl3 adopts a slightly distorted
square-planar trans-[PdN2O2] coordination geometry with
OAPdAO, NAPdAN and OAPdAN angles ranges of 88.73(8)–
170.56(8)°. The search in the CSD database [30] revealed that for
complexes formed with the similar ligands, most of them have the
trans-N2O2 square-planar geometry around Pd(II) center. The Pd(II)
bonds to the two phenolic oxygen and the two imine nitrogen atoms
of 12-CHCl3 with a PdAO distances of 1.979(2), 2.004(2) Å and PdAN
distances of 2.008(3), 2.0011(3) Å, respectively are close to those
known for Pd(II) salicylaldimine complexes [31–34]. The C36AN2
[1.310(4) Å] and C1AN1 [1.289(4) Å] distances indicate that these
correspond to double bonds. The dihedral angle between the two
coordination planes defined by PdAN1AO1 and PdAN2AO2 is
36.45(15)° (Fig. 7), as well as the trans-O2APdAO1 and trans-
N2APdAN1 bond angles are 170.09(4) Å and 170.56(5) Å, respec-
tively, indicate that the Pd(II) center has a distorted square-planar
geometry. The cis-N1APdAO1 and O2APdAN2 bond angles are
92.03(5)° and 91.74(8)°, respectively. The dihedral angle between
salicylidine ring plane (C2AC7, Ring A) and Pd/N1/O1 plane is
19.2(3)°, while the same angle between the other salicylidine ring
plane (C22AC27, Ring B) and Pd/N2/O2 plane is 20.0(2)°. The angle
between the planes of pentafluorobenzene moieties is 47.2(2)°,
whereas the dihedral angle between the salicylidine planes is
47.8(3) Å. The C3/O1/Pd and C23/O2/Pd angles are 124.6(2)° and
123.3(2)°, respectively, as expected for sp2-hybridized oxygen atom.
Within the layer the shortest non-bridged Pdꢃ ꢃ ꢃPd distance is
8.617 Å. In extended structure, there is non-classical hydrogen
Acknowledgements
Support of this investigation by Harran University Research
Council for Grants under HUBAK-712 and HUBAK-1043 and Ata-
turk University, Erzurum, is gratefully acknowledged.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.01.015.
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Conclusions
A new series of polyfluorinated palladium(II) complexes with N-
perfluorophenyl-3,5-di-tert-butyl-salicylaldimine ligands were
synthesized and characterized by spectroscopic and X-ray crystal-
lography, and examined their chemical and electrochemical oxida-
tion behaviors as well as catalytic activity in hydrogenation
reaction. The X-ray study shows that the geometry around
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palladium(II) atoms is
a slightly distorted square planar.
UV–Vis and 1H NMR spectra revealed that the N-polyfluorophenyl-