Synthesis, structural, spectroscopic and reactivity properties of a new N-2,3,4-trifluorophenyl-3,5-di-tert-butylsalicylaldimine ligand and its Cu(II) and Pd(II) complexes

Article abstract of DOI:10.1016/j.jfluchem.2009.10.005

A new N-2,3,4-trifluorophenyl-3,5-di-tert-butylsalicylaldimine (1) complexes with Cu(II) (2) and Pd(II) (3) have been synthesized and characterized by X-ray crystallography, UV-Vis, IR, ¹H NMR and EPR spectroscopic techniques. The X-ray crystal structure of complex 2 reveals tetrahedrally distorted square-planar coordination geometry around Cu(II). The UV/Vis and EPR results indicate that the solid state geometry of 2 remains unchanged in solutions. Chemical oxidation of 3 with Ce(IV) in CHCl₃ generates relatively stable Pd(II)-phenoxyl radical complex (g = 2.0073). The results related with the chemical oxidation of 2 and 3 as well as the catalytic activity of 3 in the hydrogenation of PhNO₂ are presented.

Full text of DOI:10.1016/j.jfluchem.2009.10.005

Journal of Fluorine Chemistry 131 (2010) 59–65
Contents lists available at ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis, structural, spectroscopic and reactivity properties of a new
N-2,3,4-trifluorophenyl-3,5-di-tert-butylsalicylaldimine ligand and its
Cu(II) and Pd(II) complexes
b
b
Veli T. Kasumov a, , Ibrahim Uc¸ar , Ahmed Bulut
*
a Department of Chemistry, Harran University, Osmanbey, 63300 Sanlıurfa, Turkey
b Department of Physics, Faculty of Arts and Sciences, Ondokuz Mayıs University, 55139 Kurupelit, Samsun, Turkey
A R T I C L E I N F O
A B S T R A C T
Article history:
A new N-2,3,4-trifluorophenyl-3,5-di-tert-butylsalicylaldimine (1) complexes with Cu(II) (2) and Pd(II)
(3) have been synthesized and characterized by X-ray crystallography, UV–Vis, IR, 1H NMR and EPR
spectroscopic techniques. The X-ray crystal structure of complex 2 reveals tetrahedrally distorted
square-planar coordination geometry around Cu(II). The UV/Vis and EPR results indicate that the solid
state geometry of 2 remains unchanged in solutions. Chemical oxidation of 3 with Ce(IV) in CHCl3
generates relatively stable Pd(II)–phenoxyl radical complex (g = 2.0073). The results related with the
chemical oxidation of 2 and 3 as well as the catalytic activity of 3 in the hydrogenation of PhNO2 are
presented.
Received 17 July 2009
Received in revised form 7 October 2009
Accepted 7 October 2009
Keywords:
Trifluorinated-3,5-di-tert-
butylsalicylaldimine
Cu(II) and Pd(II) complexes
X-ray structure
ß 2009 Elsevier B.V. All rights reserved.
Spectroscopy
Chemical oxidation
1. Introduction
complexes in the interaction with tri-arylphosphines [(XC6H5)3P]
were also observed [4–6].
The design, synthesis and structural characterization of
salicylaldimine complexes are a subject of current interest due
to their interesting structural, magnetic, spectral, and catalytic and
redox properties, use as models for enzymes and various
theoretical interests [1–3].
Our recent studies on coordination chemistry of N-X-pheny-
l(alkyl)-3,5-di-tert-butylsalicylaldimines, prepared from 3,5-di-
tert-salicylaldehyde and mono- (F, Cl, Br, CH3, OCH3) and di-
substituted (F, Cl, CH3, OCH3) aniline derivatives or various n-
alkyl(cyclic) amines, demonstrated that they not only easily form
bis-ligand chelates only with Cu(II), Co(II) and Pd(II), but they also
exhibit less complexing ability with respect to Ni(II), VO(II), Mn(II),
Zn(II) and Cd(II) metal ions [8–11]. Our repeated attempts to
prepare complexes of these metals with above salicylaldimnes
were unsuccessful.
It is interesting to note that in the studies of the catalytic
activity of early transition metals complexes (named FI Catalysts)
with ligands similar to above, Fujita and co-workers demonstrated
that bulky substituents ortho to the phenoxy-oxygen in these
complexes to play a key role in achieving both living and isospecific
polymerization and increase their catalytic activity [12]. Further
investigations aimed at developing higher performance FI Cata-
lysts for living ethylene/propylene polymerization led to the
discovery of an exceptional fluorinated Ti-FI Catalyst [13]. In order
to investigate the mechanism of this unusual polymerization
process, complexes which varied in the number and positions of
fluorine atoms in imine nitrogen-phenyl group were synthesized
[14,15]. The results of the investigations indicate that living
Our interest in these type of complexes was associated with
coordination chemistry, electron transfer reactivity and antiox-
idant effectiveness of N-salicylaldimines and other ligands
transition metal(II) complexes bearing bulky 2,6-di-tert-butylated
phenol fragments [4–6]. The unique properties of ligands with
these types of bulky phenols are their capability to form stable
metal(II)–phenoxyl or semiquinone type radical complexes upon
chemical or electrochemical oxidation [3], which are extensively
used for elucidating the chemistry and functionality of enzymatic
and non-enzymatic processes [7]. In addition, along with
unexpected oxidative C–C coupling reactions in the complexation
of N-1-HO-2,6-di-tert-butylphenyl-X-salicylaldimines and other
ligands with Cu(II), the reduction of some Cu(II) and Pd(II)
* Corresponding author. Fax: +90 414 3440051.
E-mail address: vkasumov@harran.edu.tr (V.T. Kasumov).
0022-1139/$ – see front matter ß 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jfluchem.2009.10.005

60
V.T. Kasumov et al. / Journal of Fluorine Chemistry 131 (2010) 59–65
the chemistry of metal complexes of polyfluorinated Schiff bases is
less studied, unlike those of
chelates [17].
b-diketonate and related ligand
2. Results and discussion
2.1. Structural properties
The molecular structure of 2 including atom-numbering is
shown in Fig. 1. Crystal data and additional data collection
parameters and refinement details are presented in Table 1.
Selected bond distances and angles of 2 as well as the data of
hydrogen-bonding interactions are given in Tables 2 and 3,
respectively. Complex 2 adopts a tetrahedrally distorted square-
planar trans-[CuN2O2] coordination geometry with O–Cu–O, N–
Cu–N and O–Cu–N angles ranges of 92.38(11)–155.73(12)8. The
Cu(II) bonds to the two phenolic oxygens and the two imine
Scheme 1. Structural representations of the Cu(L)2 and Pd(L)2.
polymerizations proceed only when at least one fluorine is located
in the 2,6-positions of imine N-phenyl group and the activity
increases with the number of fluorine atoms in both living and
non-living systems. It is reasonable to suggest that electron-
withdrawing fluorine enhances the electrophilicity and conse-
quently the living nature stemmed from the stabilization of the Ti
center by the ortho-F through electronic interaction. However, the
calculations indicate that there is no interaction between the Ti
center and the ortho-F. Instead, the calculations demonstrate that
˚
nitrogens of 1 with a Cu–O distances of 1.894(2), 1.891(2) A and
˚
Cu–N distances of 1.956(3), 1.969(3) A, respectively. The average
˚
Cu–O and Cu–N distances of 1.893(2) and 1.963(3) A fall within the
range reported for other strucurally characterized mononuclear
the ortho-F interacts electronically with a
b-H on a growing
bis-salicylaldimine copper(II) complexes [2,18]. The C7–N1
˚
˚
˚
polymer chain (ortho-F/
that the presence of an attractive interaction between the ortho-F
and the -H for all ortho-fluorinated Ti-FI independent of the
b-H distance: 2.276 A) [15,16] indicating
[1.305(4) A] and C28–N2 [1.301(4) A] distances indicate that these
correspond to double bonds. The dihedral angle between the two
coordination planes defined by Cu1N1O1 and Cu1N2O2 is
36.45(15)8 (Fig. 1), as well as the trans-O2–Cu1–O1 and trans-
N2–Cu1–N1 bond angles which are 151.83(12)8 and 155.73(12)8,
respectively, indicate that the Cu(II) center has a distorted square-
planar geometry. The cis-O1–Cu1–N1 and O2–Cu1–N1 bond angles
are 94.00(11)8 and 92.38(11)8, respectively. The dihedral angle
between salicylidine ring plane (C8/C9/C10/C11/C12/C13, Ring A)
and Cu1/N1/O1 plane is 10.35(15)8, while the same angle between
the other salicylidine ring plane (C29/C30/C31/C32/C33/C34, Ring
B) and Cu1/N2/O2 plane is 31.39(2)8. The planes of 2-, 3-, 4-F-Ph
moieties are approximately perpendicular [81.37(1)8] to each
other, whereas the dihedral angle between the salicylidine planes
b
phenoxy-imine ligand structures, confirming the generality of the
unusual attractive interaction for ortho-F in Ti-FI Catalysts. It
should be noted that a similar, but much weaker, interaction has
been suggested for the corresponding fluorinated Zr- and Hf-FI
Catalysts [12,15].
In continuation, in our studies on the chemistry of sterically
hindered phenoxy-imine systems we report the synthesis, crystal
structure, spectroscopic characterization, chemical oxidation and
catalytic activity of the N-2,3,4-trifluorophenyl-3,5-di-tert-butyl-
salicylaldimine (LH) and its Cu(L)2 and Pd(L)2 complexes (Scheme
1) abbreviated as 1, 2 and 3, respectively. It is necessary to note that
Fig. 1. The molecular structure of 2, showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atom are omitted for clarity.

V.T. Kasumov et al. / Journal of Fluorine Chemistry 131 (2010) 59–65
61
Table 1
Table 2
˚
Crystal data and structure refinement for complex 2.
Selected bond lengths (A) and angles (8) for 2.
˚
Formula
C
42H46F6N2O2Cu
Bond distances (A)
Formula weight
Temperature (K)
Radiation; wavelength
Crystal system
Space group
788.36
298(2)
N1–Cu1
N2–Cu1
O1–Cu1
O2–Cu1
C1–N1
1.956(3)
1.969(3)
1.894(2)
1.891(2)
1.426(4)
C7–N1
1.305(4)
C28–N2
C28–C29
C9–O1
1.301(4)
1.421(5)
1.305(4)
1.308(4)
Mo Ka; 0.71073
Monoclinic
P 21/n
C34–O2
Unit cell dimensions
Bond angles (8)
O2–Cu1–O1
O2–Cu1–N2
O1–Cu1–N2
˚
a, b, c (A)
9.795(6), 17.635(5), 22.778(11)
151.83(12)
92.56(11)
94.00(11)
O2–Cu1–N1
O1–Cu1–N1
N2–Cu1–N1
92.38(11)
94.00(11)
155.73(12)
a
,
b
,
g
(8)
˚
90.00, 90.144(4), 90.00
3
Volume (A )
3935(3)
Z
4
Calculated density (g cmꢁ3
)
1.331
m
(Mo K
F(000), e
Crystal size (mm)
range (8)
h k l ranges
a
) (mmꢁ1
)
0.621
Table 3
1644.0
˚
Hydrogen-bonding interactions (A, 8).
0.35 ꢂ 0.23 ꢂ 0.15
D–Hꢀ ꢀ ꢀA
D–A
Hꢀ ꢀ ꢀA
Dꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA
u
1.46–27.18
ꢁ12 ꢃ h ꢃ 12, ꢁ22 ꢃ k ꢃ 22, ꢁ29 ꢃ l ꢃ 29
C6–H6ꢀ ꢀ ꢀF6ii
0.93
0.96
0.96
0.96
0.96
2.54
2.35
2.38
2.35
2.36
3.317(5)
141
124
123
125
123
Reflections collected/independent
53644/8710
0.109
C19–H19Cꢀ ꢀ ꢀO1
C20–H20Aꢀ ꢀ ꢀO1
C37–H37Aꢀ ꢀ ꢀO2
C38–H38Aꢀ ꢀ ꢀO2
2.987(6)
3.015(6)
3.004(5)
2.987(5)
Rint
Reflections observed [I > 2
Absorption correction
Refinement method
s
(I)]
5092
Integration
Full-matrix least-squares on F2
8710/0/480
0.96
Data/restrains/parameters
Goodness-of-fit on F2
Symmetry code (ii): ꢁ1/2 + x, 1/2 ꢁ y, 1/2 + z.
R1/wR2 [I ꢄ 2
s
(I)]
0.0572/0.1495
0.1029/0.1685
0.057
In extended structure, there are non-classical hydrogen-
bonding interactions. The crystal packing of complex 2, shown
in Fig. 2, is formed via intramolecular (C–Hꢀ ꢀ ꢀO) and intermole-
R1/wR2 (all data)
Final R indices [I > 2s(I)]
Largest diff. peak and hole, e (A
ꢁ3
˚
)
0.93/ꢁ0.65
cular (C–Hꢀ ꢀ ꢀF) hydrogen bonds (see Table 2 for details), weak
p–
p
and p–ring interactions. p–p stacking is observed between the
is 61.14(12)8. The C9O1Cu1 and C34O2Cu1 angles
a
are 128.5(2)8
salicylidine ring B and phenyl (C22/C23/C24/C25/C26/C27; Ring
C) moieties of two symmetry related copper(II) complexes. Ring B
is oriented in such a way that the perpendicular distance from B to
Ci is 3.4529(14) A, the closest interatomic distance being
˚
and 124.1(2)8, respectively, as expected for sp2-hybridized oxygen
atom. Within the layer the shortest non-bridged Cuꢀ ꢀ ꢀCu distance
˚
is 6.94 A (ꢁx + 1, ꢁy, ꢁz).
Fig. 2. Packing diagram of complex 2, showing intermolecular interactions as dashed lines.

62
V.T. Kasumov et al. / Journal of Fluorine Chemistry 131 (2010) 59–65
C23ꢀ ꢀ ꢀC29i [3.466(5) A; symmetry code (i): 1 ꢁ x, ꢁy, ꢁz] are
respectively. The 1H NMR spectrum of 3 showed single resonances
at = 0.96, 1.24, and 7.08 ppm, which are assigned to the C(CH3)3
˚
within the range of the sum of the van der Waals radii of two
˚
d
carbon atoms (3.4–3.6 A) [19], indicating existence
p
–
p
stacking
and CH55N protons. The multiplet pattern at 6.94–7.07 ppm is
assigned to resonances of trifluorophenyl non-equivalent protons.
Two doublet signals centered at 7.26 and 7.54 ppm are assigned to
meta-coupled salicylidine ring protons. The comparison of the 1H
NMR spectrum of 1 with that for 3 indicates that the complexation
of 1 by Pd(II) is accompanied by the high field shifts of the
resonances of protons in the imine (Dd ꢅ 0.9 ppm), trifluorophenyl
interactions between these aromatic rings. The distance between
the ring centroids is 3.988(3) A. In the packing structure of 2 there
˚
is also a weak C–Hꢀ ꢀ ꢀpi interaction between C16–H16b and a ring
A (Fig. 2). The C–Hꢀ ꢀ ꢀCg contact distance between the centroid of a
˚
ring A and the H atoms, nearest that ring A, is 2.84 A. The
perpendicular distance between atom H16b and the center of the
˚
ring
A
is 2.74 A and the C–Hꢀ ꢀ ꢀCg angle is 1388. These
(
Dd ꢅ 0.5 ppm) and tert-butyl (Dd ꢅ 0.27 ppm) groups. On the
intermolecular interactions, namely an extensive network of
non-classical hydrogen bonds, stacking and –ring inter-
other hand, the ring C4H and C6H protons resonances at lower
fields comparing to free ligand protons.
p
–
p
p
actions, are responsible for constructing an infinite three-
dimensional lattice in the crystal structure of 2.
The observed r.t. magnetic moment of 2 (1.83 B.M.) per Cu(II)
ion is consistent with the magnetic moment data reported for
tetrahedrally distorted square-planar Cu(II) complexes [22,23].
The room temperature ESR spectrum of powder samples of 2, is
2.2. Spectroscopic properties
characterized by an axial
g
tensors with
g
(2.223) > g
jj ?
Selected IR and UV/Vis data for 1–3 compounds are given in
Section 4. In the IR spectra of these compounds, there are several
sharp bands in the region 2800–3000 cmꢁ1 due to the asymmetric
(2.072) > ge. The solution ERP spectrum of this complex in CHCl3
displays isotropic (298 K) (giso = 2.116, Aiso = 73.3G) and aniso-
tropic (173 K) (g = 2.232, g = 2.058, A = 168G and A = 26G)
jj
?
jj
?
and symmetric
groups. The IR spectrum of 1 exhibits a characteristic broad weak
band centered in the 2600–2800 cmꢁ1 and
sharp strong
absorption at 1625 cmꢁ1, attributable to intramolecularly H-
bonded phenolic OH and to the (CH55N) stretching mode,
respectively. In the spectra of complexes, the former band
disappears and the latter is shifted to lower frequencies in the
spectra of 2 (1612 cmꢁ1) and 3 (1600 cmꢁ1), suggesting the
coordination of the imine nitrogen and the deprotonated phenolic
oxygen atoms to the metal atom [1].
In the electronic spectrum of 1 in polar hydrogen-bonding
solvents such as methanol or ethanol solutions (Section 4), unlike
many other substituted similar substituted bidentate arylsalicy-
laldimines, no absorption was observed around 400 nm, attribu-
table to the ketoamine tautomer structure [20,21]. The higher
intense absorption bands observed in the range 210–330 nm and
n
(C–H) stretching frequencies of the C(CH3)3
signals, which are typical for monomer copper(II) complexes. The
observed trend, g > g > ge, suggests a d or dxy ground state
2
2
jj
?
x
ꢁy
a
in a distorted copper centers for 2 [22]. The obtained ratio g /A
jj jj
(142 cm) for 2, lying between 140 and 250 cm, again indicates
tetrahedral distorted square-planar environment for Cu(II)
centers in frozen CHCl3 solution [26]. The exchange-coupling
n
parameter, G = (g ꢁ ge)/(g? ꢁ ge), reflects the exchange interac-
jj
tion between the copper(II) centers in polycrystalline solids [22].
According to Hathaway and Billing [22], if G > 4 the exchange
interaction is negligible. A value of G < 4 indicates considerable
exchange interaction in the solid complex. The obtained value
G = 3.17 for powder samples of 2, unlike its frozen glass CHCl3
solution samples which has a G value of 4.12, suggests the
presence of an exchange coupling interaction between Cu(II)
centers in the solid state [22].
at 362 nm are assigned to intraligand
p
!
p
* and n !
p
*, in the
2.3. Chemical oxidation of 2 and 3
aromatic rings and imine groups, respectively. The absence of the
visible absorption band around 400 nm, even in concentrated
strongly hydrogen-bonding solvents such as EtOH and MeOH,
suggests that trifluorinated compound 1 exists only in enol-imine
form at room temperature (r.t.). Complex 2 exhibits a phenolate-
Our recent studies demonstrated that in the chemical
oxidation of some bis(N-X-aryl-(alkyl)-3,5-di-tert-butylsalicylal-
diminato)Cu(II) complexes by (NH4)2Ce(NO3)6 [Ce(IV)] in CHCl3
along with a decrease of the intensity of their EPR spectra, the
appearance of radical signals takes place [8–11]. A similar EPR and
UV/Vis investigation of the oxidative behavior of 1–3 compounds
was performed in the present work. The spectral changes followed
by the chemical oxidation of 2 with Ce(IV) in CH3CN and CHCl3
solutions at r.t. and under aerobic conditions, were monitored by
UV/Vis spectroscopy in the range 200–1100 nm. One-electron
oxidation of 2 (5.5 ꢂ 10ꢁ3 M) in MeCN with one equiv Ce(IV),
along with color change from dark brown to yellowish brown, is
accompanied by the simultaneous disappearance of the d–d
absorption band of the parent complex 2 at 660 nm and the
growth of a new broad band of lower intensity maxima at 708 nm
was observed (Fig. 3a). Upon successive recording of this band
with time interval of 1 min, the shifts of this band to a lower
to-Cu(II)
= 19,500 Mꢁ1 cmꢁ1). A broad band at 665 nm (204 Mꢁ1 cmꢁ1
is assigned to convolution of three allowed d–d transitions
charge-transfer
band
centered
at
415 nm
(
e
)
(dx 2 ! d 2 , d
2 ! dxz;yz and dx 2 ! dxy), in the tetrahedrally
2
2
2
ꢁy
z
x
ꢁy
ꢁy
distorted square-planar geometries [22–24]. A strong bands in UV
region 250 (sh), 292 (66,000 Mꢁ1 cmꢁ1) and 337 (sh) are due to of
the
p
!
p
* and n !
p* transitions, respectively.
Complex 3 is diamagnetic, suggesting a square-planar geome-
try for this complex. Electronic spectra of 3 are also indicative of a
square-planar geometry [25]. The electronic spectra of 3 in EtOH
and CHCl3 solutions exhibit only two intense bands (ca. 300 and
420 nm), which are assigned to metal-to-ligand charge-transfer
transitions [22,23]. The DMF solution of 3 also displays very weak
shoulder around 500 nm (
transition [11].
e
= 275 Mꢁ1 cmꢁ1) attributable to d–d
wavelength with decreased absorbance, lmax(A), from 708 (0.61)
to 695 (0.51) nm within a period 5 min were detected. In the
following repeated scanning, slowly decreases in the intensity and
blue shifts were detected. It is interesting that in the oxidation of
concentrated 2 (1.2 ꢂ 10ꢁ2 M) by one or two equiv Ce(IV),
scanning after 30 s, the appearance of additional band at
The 1H NMR spectral characteristics of 1 and 3 are presented in
Section 4. The 1H NMR spectrum of 1 in CDCl3 showed strong sharp
singlet signals at 1.37 and 1.51 ppm which are assigned to the
C(CH3)3 protons. The trifluorophenyl ring protons signals were
observed as two particularly overlapped doublets pattern at
7.04 ppm. Two doublets, observed at 7.26 and 7.54 ppm, are
assigned to meta-coupled salicylidine ring C4–H and C6–H
hydrogen atoms resonances. The CH55N and OH groups protons
resonances appeared as singlet peaks at 8.88 and 13.18 ppm,
l
> 1100 nm was observed (Fig. 3b). After the second scan this
band was disappeared. This observation suggests that the
generated [2ꢆ]+ or [2ꢆꢆ ++
primer radical cation complexes are
]
unstable and rapidly decompose under experimental conditions,
at 290 K.

V.T. Kasumov et al. / Journal of Fluorine Chemistry 131 (2010) 59–65
63
Fig. 3. UV/Vis spectra of 2: (a) absorption bands of initial complex 2 (1, 2 and 3) in CH3CN; absorption spectral change of 2 (3.8 ꢂ 10ꢁ3 M) after one-electron oxidation by
2 equiv of Ce(IV) at 290 K in CH3CN (4 and 5); (b) Initial spectrum of relatively concentrated 2 (1.12 ꢂ 10ꢁ2 M) (1) in CH3CN; spectrum of 2 + 2 equiv Ce(IV) system (2) scanned
after 30 s at 290 K in CH3CN.
Upon addition of two equiv molar Ce(IV) into CH3CN solution of
3, without appearance of any new bands in the visible region, the
color change from orange to red was observed. At the same time, in
the similar treatment of 3 in CHCl3 solution at r.t., even in the
presence of atmospheric oxygen, the appearance of singlet signal
with g = 2.0073 (DH = 28G) was detected. The relatively stable
behaviors and the increased g-factors of these radicals compared to
that for free 2,4-di-tert-butylphenoxyl radical (g = 2.0045) [27],
suggest significant metal-orbital contribution to the SOMO of
phenoxyl radical and also that the generated radical species can be
assigned to Pd(II)–phenoxyl radical complexes.
2.4. Catalytic reduction of nitrobenzene by 3 complex
Fig. 4. Hydrogenation of PhNO2 with catalyst 3 (3.1 ꢂ 10ꢁ4 M, 6.2 ꢂ 10ꢁ6 mol) in
20 ml DMF at 303 K: (a) CPhNO ¼ 0:147 M; (b) CPhNO ¼ 1:205 M.
2
2
The hydrogenation reaction of nitrobenzene with catalyst 3
was carried out at atmospheric pressure in a magnetically
stirred glass reactor using DMF as solvent. The progress of the
reduction of nitrobenzene was followed by measuring the
uptake of hydrogen gas as a function of the reaction time, at
precipitation was observed in the course of the hydrogenation
of nitrobenzene for a period of 36 h. The average rate of H2
absorption and the specific catalytic activity of
3 were
constant pressure, using
a
glass manometer. The catalytic
obtained as 0.8 ml/min and 6.58 H2 consumed/mol-cat(min),
respectively.
studies showed that complex 3 exhibits a catalytic activity
towards the hydrogenation of nitrobenzene in DMF solution at
20 and 30 8C, under normal pressure of H2 gas (760 Torr),
without any preliminary activation. The concentration of
nitrobenzene was varied from 0.147 to 1.224 mol/l at 30 8C
and 1 atm H2 pressure using a fixed amount of the catalyst
(3.15 ꢂ 10ꢁ4 mol/l) Pd(II) content. 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 24 h. It was observed that the initial rate of
hydrogenation reaction remains almost unchanged even after
36 h (Fig. 4). The recycling experiments showed that the
catalytic activity of 3 remains unchanged and can be reused
without appearance any sign of decomposition of complex.
Unlike mono-fluoro-substituted Pd(N-X-arylsalicylaldimiato)2
type complexes [10], no evidence of the palladium metal
3. Conclusions
New copper(II) and palladium(II) complexes of N-2,3,4-trifluor-
ophenyl-3,5-di-tert-butylsalicylaldimine ligand were synthesized
and characterized by spectroscopic and X-ray crystallography. The
presented ligand possesses lower complexation ability towards
Co(II), Ni(II), Mn(II), VO(II) and Zn(II). The X-ray study shows that the
geometry around copper(II) atoms is tetrahedrally distorted square-
planar. As supported by EPR and UV/Vis studies, their chemical
oxidation with Ce(IV) leads to the formation of the relatively stable
metal(II)–phenoxyl radical complexes. It has been demonstrated
that trifluorinated sterically hindered Pd(II) complex exhibits
catalytic activity in the hydrogenation of nitrobenzene without
losing activity at least for 3 months.

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V.T. Kasumov et al. / Journal of Fluorine Chemistry 131 (2010) 59–65
4. Experimental
4.1. Materials
1 mmol) and stirred at ꢅ40 8C for ca. 45 min. Yield 0.284 g, 68%.
mp > 310 8C. Anal. calcd. for C42H46N2O2F6Pd: C, 60.68; H, 5.57;
N, 3.37. Found: C, 60.07; H, 5.48; N, 3.19. FT-IR (KBr, cmꢁ1):
2868–2958 [C(CH3)3], 1600 (CH55N); UV–Vis [EtOH,
(log
)]: 231(4.66), 261(3.74), 304(3.52), 414(3.17). 1H NMR
(300 MHz, CDCl3): 7.08 (s, 2H, CH55N), 7.555 (d, J = 1.5 Hz, 2H,
meta-coupled 4-ArH), 7.315 (d, J = 2.4 Hz, 2H, meta-coupled 6-
ArH), 7.11–6.94 (m, 4H, 2,3,4-FPhH), 1.24 [s, 18H, C(CH3)3), 0.9
(s, 18H, C(CH3)3].
lmax/nm
All solvents, sulfuric acid, acetic acid, hexamethylenetetramine,
nitrobenzene, 2,4-di-tert-butylphenol, (NH4)2Ce(NO3)6, 2,3,4-tri-
fluoroaniline and acetates of Cu(II) and Pd(II) were purchased from
Sigma–Aldrich and used without further purification. The reagent
3,5-di-tert-butylsalicylaldehyde was prepared according to the
literature procedure [28].
e
d
4.4. X-ray structural determination of 2
4.2. Instrumentation
A suitable single crystal of complex 2 was mounted on a glass
The C, H, N elemental analyses were performed on a LECO
CHNS-932 model analyzer. Electronic spectra were recorded by
using a PerkinElmer Lambda 25 spectrometer, IR spectra obtained
on a PerkinElmer FT-IR spectrometer using KBr pellet. 1H NMR
spectra were recorded on a Bruker Spectro spin Avance DPX-400
Ultra Shield Model NMR with Me4Si as an internal standard in
CDCl3. The room temperature magnetic susceptibility was
measured by using a Sherwood Scientific magnetic balance and
the diamagnetic corrections were evaluated using Pascal’s con-
fiber and data collection were performed on a STOE IPDS(II) image
˚
plate detector using Mo Ka radiation (l = 0.71019 A) at 298 K. Data
collection: Stoe X-AREA [29]. Cell refinement: Stoe X-AREA [29].
Data reduction: Stoe X-RED [29]. The structure was solved by
direct methods using SHELXS-97 [30] and anisotropic displace-
ment parameters were applied to non-hydrogen atoms in a full-
matrix least-squares refinement based on F2 using SHELXL-97 [30].
All hydrogen atoms except H7 and H28 were positioned
geometrically and refined by a riding model with Uiso 1.2 times
that of attached atoms and remaining hydrogen atoms were found
by Fourier difference. Molecular drawings were obtained using
ORTEP-III [31].
stant. ESR spectra were taken on
a Varian E109C X-band
spectrometer. The field and frequency calibration were made
using DPPH (g = 2.0037).
4.3. Synthesis
Acknowledgment
4.3.1. N-2,3,4-trifluorophenyl-3,5-di-tert-butylsalicylaldimine (1)
Ligand 1 was prepared using standard procedures involving the
We are grateful to the Harran University Research Council for
¨
Grant under HUBAK-712.
condensation
of
3,5-di-tert-butyl-2-hydroxybenzaldehyde
(0.936 g, 4 mmol) with 2,3,4-fluoroaniline (0.588 g, 4 mmol) in
absolute ethanol (100 ml) in the presence of a few drops of formic
acid. The mixture was stirred at reflux for 36 h and then
concentrated to ꢅ40 ml. By slow cooling of the reaction mixture
to room temperature, a light yellow crystal of 1 was obtained. Yield
1.277 g, 88%. mp = 102 8C. IR (KBr, cmꢁ1): 1625 (CH55N), 2866–
Appendix A. Supplementary data
Crystallographic data (excluding structure factors) for the
structure in this paper have been deposited with the Cambridge
Crystallographic Data Centre as the supplementary publication no.
CCDC 718000 for 2. These data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge, CB12 1EZ, UK, fax:
+44 1223 366 033, e mail: deposit@ccdc.cam.ac.uk or on the web
www: http://www.ccdc.cam.ac.uk.
2957 [C(CH3)3]; UV/Visible [EtOH,
lmax/nm (log e)]: 225(4.47),
234(sh), 282(4.5), 322(sh), 360(4.1). 1H NMR (300 MHz, CDCl3),
d
:
13.18 (s, 1H, OH), 8.88 (s, 1H, CH55N), 7.537 (d, J = 2.1 Hz, 1H, meta-
coupled 4-ArH), 7.255 (d, J = 2.4 Hz, 1H, meta-coupled 6-ArH),
7.018 (d, J = 5.7 Hz, 1H, 2,3,4-F-Ph C6-H), 7.049 (d, J = 5.4 Hz, 1H,
2,3,4-FPh C5-H), 1.51 (s, 9H), 1.367 (s, 9H). Anal. calcd. for
References
C
4.18.
21H24NOF3: C, 73.02; H, 7.29; N, 4.05. Found: C, 72.74; H, 7.29; N,
[1] R.H. Holm, M.J. O’Connor, Prog. Inorg. Chem. 14 (1971) 241–401.
[2] A.D. Garnovski, A.P. Sadimenko, M.C. Sadimenko, D.A. Garnovski, Coord. Chem.
Rev. 173 (1998) 31–77.
[3] P. Chaudhuri, K. Wieghardt, Prog. Inorg. Chem. 50 (2001) 151–216.
[4] A.A. Medjidov, V.T. Kasumov, H.S. Mamedov, Koord. Khim. 7 (1981) 66–71.
[5] A.A. Medjidov, V.T. Kasumov, M.K. Guseyinova, H.S. Mamedov, V.S. Aliev, Dokl. AN
USSR 259 (1981) 866–869.
[6] V.T. Kasumov, A.A. Medjidov, Koord. Khim. 15 (1989) 1404–1407.
[7] I.J. Rehle, T.F. Markle, H. Nagao, A.G. DiPasquale, O.P. Lam, M.A. Lockwood, K. Rotter,
J.M. Mayer, J. Am. Chem. Soc. 128 (2006) 6075–6088, and references therein.
[8] V.T. Kasumov, F. Ko¨ksal, R. Ko¨seoglu, J. Coord. Chem. 57 (2004) 591–603.
[9] V.T. Kasumov, F. Ko¨ksal, Y. Zeren, Spectrochim. Acta Part A 63 (2006) 330–336.
[10] V.T. Kasumov, F. Ko¨ksal, A. Sezer, Polyhedron 24 (2005) 1203–1211.
4.3.2. Copper bis{2-[(2,3,4-Trifluorophenylimino)methyl-3,5-di-tert-
butylphenolato]} (2)
Complex 2 was prepared by addition of 5 ml methanol solution
of Cu(OAc)2xH2O (0.1 g, 0.5 mmol) to a hot solution of MeOH
(60 ml) containing 1 (0.364 g, 1.0 mmol). The reaction mixture was
refluxed with stirring for ca. 60 min. Then the volume of solution
was reduced to ꢅ30 ml and kept in air at r.t. After one day the dark
green crystals were obtained.
Crystals of 2 suitable for an X-ray crystal structure determina-
tion were grown from a saturated solution of methanol at r.t. Yield
0.295 g, 74.7%. mp > 270 8C. FT-IR (KBr, cmꢁ1): 2868–2952
[C(CH3)], 1612 (CH55N), 3429 (OH, lattice H2O)]. UV–Vis (CHCl3,
¨
[11] V.T. Kasumov, E. Tas¸ , F. Ko¨ksal, S¸. Ozalp-Yaman, Polyhedron 24 (2005) 319–
325.
[12] H. Makio, N. Kashiwa, F. Fujita, Adv. Synth. Catal. 344 (2002) 477–493.
[13] A.F. Mason, J. Tian, P.D. Hustad, E.B. Lobkovsky, G.W. Coates, Isr. J. Chem. 42 (2002)
301–306.
[14] R. Furuyama, J. Saito, S. Ishii, H. Makio, M. Mitani, H. Tanaka, T. Fujita, J.
Organomet. Chem. 690 (2005) 4398–4413.
[15] T. Matsugi, T. Fujita, Chem. Soc. Rev. 37 (2008) 1264–1277.
[16] K. Kawai, T. Fujita, Top. Organomet. Chem. 26 (2009) 3–46.
[17] D.L. Chizhov, D.V. Sevenard, E. Lork, K.I. Pashkevich, G.V. Ro¨schenthaler, J. Fluorine
Chem. 123 (2004) 1137–1141.
l
m
max/nm (log
e): 250(sh), 292(4.82), 337(sh), 415(4.29), 665(2.31),
eff = 1.83 B. Anal. calcd. for C42H46N2O2F6Cu: C, 67.08; H, 6.43; N,
m
3.72; Found: C, 66.81; H, 6.73; N, 3.08.
[18] S. Yamada, Coord. Chem. Rev. 190–192 (1999) 537–555.
[19] A. Bondi, J. Phys. Chem. 68 (1964) 441–451.
[20] M.D. Cohen, G.M.J. Schmidt, J. Phys. Chem. 66 (1962) 2442–2446.
[21] Y.I. Koslov, D.N. Shigorin, R.N. Nurmukametov, V.A. Puchkov, Russ. J. Phys. Chem.
37 (1963) 1315–1319.
4.3.3. Palladium bis{2-[(2,3,4-Trifluorophenylimino)methyl-3,5-di-
tert-butylphenolato]} (3)
Complex 3 was prepared by direct addition of Pd(OAc)2
(0.112 g, 0.5 mmol) to 30 ml hot CH3CN solution of 1 (0.363 g,

V.T. Kasumov et al. / Journal of Fluorine Chemistry 131 (2010) 59–65
65
[22] B.J. Hathaway, D.E. Billing, Coord. Chem. Rev. 6 (1970) 143–207.
[23] L. Sacconi, M. Ciampolini, J. Chem. Soc. (1964) 276–281.
[24] B. Bosnich, J. Am. Chem. Soc. 90 (1968) 627–632.
[25] P.L. Googgin, R.J. Goodfellow, F.J.S. Reed, J. Chem. Soc., Dalton Trans. (1972) 1298–
1303.
[26] U. Sakaguchi, A.W. Addison, J. Chem. Soc., Dalton Trans. (1979) 600–608.
[27] B.A. Jazdzewski, W.B. Tolman, Coord. Chem. Rev. 200–202 (2000) 633–
685.
[28] J.F. Larrow, E.N. Jacobsen, Y. Gao, Y. Hong, X. Nie, C.M. Zeppe, J. Org. Chem. 50
(1994) 50–56.
[29] Stoe & Cie X-AREA (Version 118) and X-RED (Version 104), Stoe & Cie, Darmstadt
(Germany) 2002.
[30] G.M. Sheldrick, SHELXL-97, Program for the Refainment of Crystal Structures,
University of Gottingen, Germany, 1997.
[31] M.N. Burnett, C.K. Johnson, ORTEP III, Report ORNL-6895, Oak Ridge National
Laboratory, TN, USA, 1996.