Effect of ortho-substituents on the stereochemistry of 2-(o-substituted phenyl)-1H-imidazoline-palladium complexes

Article abstract of DOI:10.1016/j.jorganchem.2010.05.007

Palladium complexes composed of [Pd(Ln)₂Cl₂] (n = 1, 2, 3, 4, 6), [L5a]₂[PdCl₄] and [Pd(L5b)₂], where L1 = 4,5-dihydro-2-phenyl-1H-imidazole (=2-phenyl-1H-imidazoline), L2 = 2-(o-fluorophenyl)-1H-imidazoline, L3 = 2-(o-methylphenyl)-1H-imidazoline, L4 = 2-(o-tert-butylphenyl)-1H-imidazoline, L5a = 2-(o-hydroxyphenyl)-1H- imidazolinium, L5b = 2-(1H-imidazolin-2-yl)phenolate, and L6 = 2-(o-methylphenyl)-1H-imidazole, were synthesized. Molecular structures of the isolated palladium complexes were characterized by single crystal X-ray diffraction analysis. The effect of ortho-substituents on the phenyl ring on trans-chlorine geometry was noted for complexes [Pd(L1)₂Cl ₂] 1a and 1b, [Pd(L2)₂Cl₂] 2 and [Pd(L6) ₂Cl₂] 6, whereas cis-chlorine geometry was observed for [Pd(L3)₂Cl₂] 3 and [Pd(L4)₂Cl₂] 4. PdCl₂ reacts with 2-(o-hydroxyphenyl)-1H-imidazoline in DMF to give [L5a]⁺ and [L5b]^- so that [L5a]₂[PdCl ₄] 5a and [Pd(L5b)₂] 5b were obtained. In complex 5b, as an N,O-bidentate ligand, two ligands L5b coordinated with the central Pd(II) ion in the trans-form. The coordination of PdCl₂ with 2-(o-hydroxyphenyl)-1H-imidazolines in solution was investigated by NMR spectroscopy. Palladium complexes composed of [Pd(Ln)2Cl2] (n = 1, 2, 3, 4, 6), [L5a]2[PdCl4] and [Pd(L5b)2], where L1 = 4,5-dihydro-2-phenyl-1H-imidazole (= 2-phenyl-1H-imidazoline), L2 = 2-(o-fluorophenyl)-1H-imidazoline, L3 = 2-(o-methylphenyl)-1H-imidazoline, L4 = 2-(o-tert-butylphenyl)-1H-imidazoline, L5a = 2-(o-hydroxyphenyl)-1H-imidazolinium, L5b = 2-(1H-imidazolin-2-yl) phenolate, and L6 = 2-(o-methylphenyl)-1H-imidazole, were synthesized and characterized by single crystal X-ray diffractometry.

Full text of DOI:10.1016/j.jorganchem.2010.05.007

Journal of Organometallic Chemistry 695 (2010) 2022e2029
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Effect of ortho-substituents on the stereochemistry of 2-(o-substituted
phenyl)-1H-imidazolineepalladium complexes
*
Zhibin Gan, Kenjiro Kawamura, Kazuo Eda, Masahiko Hayashi
Department of Chemistry, Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Palladium complexes composed of [Pd(Ln)2Cl2] (n ¼ 1, 2, 3, 4, 6), [L5a]2[PdCl4] and [Pd(L5b)2], where
L1 ¼ 4,5-dihydro-2-phenyl-1H-imidazole (¼2-phenyl-1H-imidazoline), L2 ¼ 2-(o-fluorophenyl)-1H-
imidazoline, L3 ¼ 2-(o-methylphenyl)-1H-imidazoline, L4 ¼ 2-(o-tert-butylphenyl)-1H-imidazoline,
L5a ¼ 2-(o-hydroxyphenyl)-1H-imidazolinium, L5b ¼ 2-(1H-imidazolin-2-yl)phenolate, and L6 ¼ 2-
(o-methylphenyl)-1H-imidazole, were synthesized. Molecular structures of the isolated palladium
complexes were characterized by single crystal X-ray diffraction analysis. The effect of ortho-substituents
on the phenyl ring on trans-chlorine geometry was noted for complexes [Pd(L1)2Cl2] 1a and 1b, [Pd
(L2)2Cl2] 2 and [Pd(L6)2Cl2] 6, whereas cis-chlorine geometry was observed for [Pd(L3)2Cl2] 3 and [Pd
(L4)2Cl2] 4. PdCl2 reacts with 2-(o-hydroxyphenyl)-1H-imidazoline in DMF to give [L5a]þ and [L5b]e so
that [L5a]2[PdCl4] 5a and [Pd(L5b)2] 5b were obtained. In complex 5b, as an N,O-bidentate ligand, two
ligands L5b coordinated with the central Pd(II) ion in the trans-form. The coordination of PdCl2 with
2-(o-hydroxyphenyl)-1H-imidazolines in solution was investigated by NMR spectroscopy.
Ó 2010 Elsevier B.V. All rights reserved.
Received 23 February 2010
Received in revised form
6 May 2010
Accepted 6 May 2010
Available online 31 May 2010
Keywords:
Palladium complex
Imidazoline
Imidazole
Nitrogen ligand
N,O-bidentate ligand
X-ray diffractometry
1. Introduction
position of the phenyl ring. Here, we report a series of palladium(II)
complexes which were synthesized by mixing one equiv of PdCl2
Recently, imidazole, imidazoline and their related compounds
have received a great deal of attention not only in the field of
organic synthesis [1], but also in the area of pharmaceutical
chemistry [2], supramolecular chemistry [3], and catalysis [4].
There have been many reports concerning structure and catalytic
reactivity on aspects of metal complexes with imidazoles and
imidazolines [5]. We also reported a series of studies on some PdCl2
complexes with imidazole derivatives as catalysts for the Mizor-
okieHeck reaction and SuzukidMiyaura coupling reaction [6].
During the course of this study, we became interested in the
stereochemistry of the Pd(II) complexes upon discovering that two
distortional isomers of dichlorobis[(2-phenyl-1H-imidazoline)]
palladium(II) were isolated in the solid state [6e]. Many challenges
and problems still remain in the determination of stereochemistry
of coordination compounds [7], and in the process of crystallization
itself, which can be regarded as a very complicated process. We
selected 2-(ortho-substituted phenyl)-1H-imidazolines in this
study because conformational changes in the coordination sphere
of the Pd(II) complexes could be expected by tuning properties such
as the steric and electronic effects of the substituents at the ortho-
with 2 equiv of 2-(ortho-substituted phenyl)-1H-imidazolines or
imidazoles in DMF, and the crystal structures obtained by X-ray
diffractometry.
2. Results and discussion
2.1. Synthesis and properties of ligands
Reaction of 2-substituted benzaldehydes with ethylenediamine
gave 2-(o-substituted phenyl)-1H-imidazolines (Scheme 1). Here,
L1 ¼ 4,5-dihydro-2-phenyl-1H-imidazole (¼2-phenyl-1H-imida-
zoline), L2 ¼ 2-(o-fluorophenyl)-1H-imidazoline, L3 ¼ 2-(o-meth-
ylphenyl)-1H-imidazoline, L4
imidazoline, L5
L6 2-(o-methylphenyl)-1H-imidazole. The most common
¼
2-(o-tert-butylphenyl)-1H-
2-(o-hydroxyphenyl)-1H-imidazoline, and
¼
¼
method for transformation of imidazoline into imidazole is oxida-
tion. Recently we reported a method of oxidative aromatization
with molecular oxygen in the presence of activated carbon [8],
which was also adopted for transformation of 2-(o-methylphenyl)-
1H-imidazoline to the corresponding imidazole (Scheme 1) [9].
This simple process is not only environmentally friendly but also
economical and operationally simple. Only oxygen and commer-
cially available and inexpensive activated carbon were used.
Neither metal oxides nor organic peroxides were required. The
* Corresponding author. Tel.: þ81 78 803 5687; fax: þ81 78 803 5688.
E-mail address: mhayashi@kobe-u.ac.jp (M. Hayashi).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.05.007

Z. Gan et al. / Journal of Organometallic Chemistry 695 (2010) 2022e2029
2023
substituent in the phenyl ring on the trans-chlorine geometry was
noticed for complexes [Pd(L1)2Cl2] 1a and 1b and complex 2, in
contrast with the cis-chlorine geometry for complexes 3 and 4. Due
to the different coordination properties of imidazoline and imid-
azole, the cis-chlorine geometry was noted for complex 3 whereas
the trans-chlorine geometry was observed for complex 6. Generally,
only [Pd(L)2Cl2] type palladium complexes were isolated from each
reaction solution. However, the reaction of PdCl2 with 2 equiv of
ligand L5 gave a mixture of palladium coumpounds. After diffusion
of CH2Cl2 into the resulting solution as an ionic salt having lower
solubility in organic solvents, the orange red crystal [L5a]2[PdCl4]
5a was precipitated first, and it was filtered. After one month, the
yellow crystal [Pd(L5b)2] 5b was obtained.
Scheme 1. Preparation of ligands L1eL6.
2.3. Single-crystal X-ray diffractometry (XRD) study
Crystallographic data for the structures of complexes 2, 3, 4, 5a,
5b and 6 are summarized in Table 1.
same method was not adopted for preparation of 2-(o-hydrox-
yphenyl)-1H-imidazoline (L5), which was prepared by reaction of
methyl salicylate and ethylenediamine following the Rogers and
Bruice thermal condensation procedure (Scheme 1) [10]. Excess
ethylenediamine was removed along with methanol and water by
distillation to give the crude product as a yellow crystal. Higher
purity L5 was obtained by crystallization from water/ethanol (2:1).
This method has an advantage due to its large scale applicability
and easy isolation by distillation. Ligand L5 is amphoteric, such that
L5a and bidentate chelate ligand L5b are produced by protonation
and deprotonation of L5, respectively (Scheme 2).
2.3.1. Molecular structure of trans-[Pd(L2)2Cl2] 2
Structural views of palladium complex 2 are shown in Fig. 2. In
the complex, the central Pd(II) cation is four-coordinated in
a slightly distorted square planar environment containing two
chlorine atoms in the trans-position and two 2-arylimidazoline
molecules. Ligands bound to Pd(II) via their Nimine atoms and their
aryl rings are situated cis to each other. The Molecular structure is
similar to that found in trans-dichlorobis(2-phenyl-1H-imidazo-
line) palladium(II) 1a.[6e]
In each 2-(o-substituted phenyl)-1H-imidazoline, the CeC bond
between the aryl and imidazoline rings is freely rotatable. The
2.3.2. Molecular structures of cis-[Pd(L3)2Cl2] 3 and cis-[Pd
(L4)2Cl2] 4
Nimine of the imidazoline ligand usually makes a
s bond with Pd(II)
and this NimineePd bond is also freely rotatable. Introducing an
o-substituent on the phenyl ring creates an obstacle to a freely
rotatable bond in both ligands and complexes. We propose that the
multiaxial rotations are affected by the steric hindrance of a bulky
tert-butyl group in the ortho-position of the phenyl ring after the
ligand coordinates with palladium chloride.
The structural views of palladium complexes 3 and 4, are shown
in Fig. 3. In each palladium complex, the central Pd(II) is coordi-
nated to two 2-arylimidazoline molecules via their unsaturated
Nimine atoms. cis-chlorine geometry, trans-Me and cis- Bu geome-
tries were observed in 3 and 4, respectively. In complex 3, spon-
taneous resolution took place. The combination of the cis-chlorine
and trans-Me geometries, which enables the formation of a simple
network structure due to the hydrogen bonds (NeH$$$Cl), might
allow the formation of the conglomerate [11]. In complex 4, the
tert-butyl group of one ligand molecule L4 shows rotational
disorder in about a 4:1 ratio.
2.2. Preparation of palladium compounds
Palladium(II) dichloride complexes of [Pd(L2)2Cl2] 2, [Pd
(L3)2Cl2] 3, [Pd(L4)2Cl2] 4 and [Pd(L6)2Cl2]$2DMF 6$2DMF were
prepared by the reaction of the corresponding ligands with palla-
dium chloride in a 2:1 M ratio (Fig. 1). All complexes tended to
precipitate from the DMF solution by adding an excessive amount
of a poor solvent such as toluene, hexane or CH2Cl2 to the reaction
solution. By slow diffusion of the solvent into the solution, the
solubilities of the complexes were decreased, continually gener-
ating a low supersaturated solution for crystal growth. X-ray
diffraction and NMR spectroscopic characterization of the palla-
dium complexes were performed, and the structures and complex
numbers are shown in Figs. 2e6. All of the Pd(II) complexes were
crystallized as mononuclear complexes. The effect of the ortho-
2.3.3. Molecular structure of trans-[Pd(L6)2Cl2]∙2DMF 6
The structural views of 6 from different orientations are shown
in Fig. 4. Contrary to the expected cis-chloride as in complex 3, its
molecular structure is similar to that found in 1b.
2.3.4. Structure of the salt of [L5a]2[PdCl4] 5a
The structural view of the ionic salt 5a is shown in Fig. 5.
The asymmetric unit of the ionic crystal structure is comprised
of the bridge-type counter cation and a square planar tetra-
chloropalladate(II) anion where four chlorine atoms as ligands in
Scheme 2. Protonation and deprotonation of L5.

2024
Z. Gan et al. / Journal of Organometallic Chemistry 695 (2010) 2022e2029
Fig. 1. Preparation of various palladium complexes.
the solid state through formation of intermolecular NeH.Cl and
OeH.Cl hydrogen bonds.
suggest that 5c is an isomer of 5b, cis-bis[2-(1H-imidazoline-2-yl)
phenolato-
2N3,O] Palladium (II) (Scheme 3).
k
Intermolecular proton transfer between L5 was promoted by
reaction with PdCl2. We propose that 5d was formed first, passing
through an intramolecular dehydrochloride to give 5b and 5c since
the NePd bond is freely rotatable. In the meantime, an equivalent
amount of L5a and tetrachloropalladate (II) anion were also formed
to give an ionic salt 5a that precipitated first due to its low solu-
bility, promoting completion of the reaction.
2.3.5. Molecular structure of [Pd(L5b)2] 5b
The complex 5b was obtained as a yellow crystal. As shown in
Fig. 6, the Pd(II) ion, on an inversion center, is trans-coordinated by
two bidentate 2-(1H-imidazolin-2-yl)phenolate ligands. This is tha
first example of palladium complex of L5b [12].
2.3.6. 1H NMR study of L5, 5a and 5b
The chemical shifts in the 1H NMR spectra for L5, complex 5a, 5b
and the mixture of PdCl2 with 2.0 equiv of L5 in DMF-d7 are shown
in Fig. 7. 1H NMR spectra indicated that there existed more than
three palladium compounds, resulting from the coordination of
PdCl2 with 2.0 equiv of L5 in DMF-d7, i.e., 5a, 5b and 5c at a molar
ratio of 1:0.5:0.5. From the viewpoint of material balance, we
3. Conclusion
We prepared four novel N-monodentate Pd(II) complexes
[PdL2Cl2] (2, 3, 4 and 6) and two new Pd complexes (5a and 5b), and
Fig. 3. Structural view of complex
3 and 4 showing 50% probability ellipsoids.
Fig. 2. Structural view of 2 showing 50% probability ellipsoids.
Hydrogen atoms are omitted for clarity.

Z. Gan et al. / Journal of Organometallic Chemistry 695 (2010) 2022e2029
2025
Fig. 6. Structural view of 5b showing 50% probability ellipsoids with numbering
scheme.
1-(tert-Butyl)-2-iodobenzene 2-tert-Butylaniline (2.2 g,
14.7 mmol) was added to 3.4 M H2SO4 (2 mL) and cooled to ꢀ10 ꢁC.
A saturated aqueous solution of NaNO2 (1.05 g, 15.2 mmol) was
added with vigorous stirring over 5 min to give a light brown slurry.
After stirring for another hour at ꢀ10 to 0 ꢁC, the slurry of the
diazonium salt was added rapidly to a concentrated ice-cold solu-
tion of KI (7.5 g, 45 mmol/10 g H2O). After stirring at 0 ꢁC for 2 h, the
suspension was extracted with diethyl ether (15 mL). After removal
of solvent, purification by column chromatography (silica, hexane)
gave the product as a colorless liquid. Yield: 1.05 g (27.5%). 1H NMR
Fig. 4. Structural view of 6∙2DMF showing 50% probability ellipsoids. DMF molecules
are omitted for clarity.
determined their molecular structures by single crystal X-ray
analysis. We revealed the following characteristic features of the
effect of ortho-substituents on the stereochemistry of 2-(o-
substituted phenyl)-1H-imidazolineepalladium complexes. i) To
examine the properties of substituents in the ortho-position of the
phenyl ring, such as steric and electronic effects, two novel
cis-[PdL2Cl2] complexes were prepared. ii) A palladium salt 5a and
a palladium chelate 5b were successfully isolated and characterized
by single crystal X-ray analysis. iii) The results obtained from the
NMR coordination studies of PdCl2 with L5 in solution support the
feasibility of an amphoteric ligand. The catalytic behavior of these
complexes toward coupling reactions will be studied in due course.
(400 MHz, CDCl3):
d (ppm) 8.00 (d, J [ 7.6 Hz, 1H), 7.44 (d,
J [ 9.6 Hz, 1H), 7.28 (t, J [ 7.6 Hz, 1H), 6.83 (t, J [ 9.6 Hz, 1H), 1.53
(s, t-Bu); 13C NMR (100.4 MHz, DMF-d7):
d (ppm) 150.2, 143.6, 127.9,
127.5, 127.5, 95.1, 36.7, 29.9.
2-(tert-Butyl) benzaldehyde tert-Butyllithium (7.7 mL,
12 mmol, 1.6 M in pentane) was added to a solution of 1-(tert-
butyl)-2-iodobenzene (1.38 g, 5.6 mmol) in THF (10 mL) at ꢀ78 ꢁC.
After 30 min at this temperature, DMF (2 mL) was added, and the
reaction mixture was allowed to warm to room temperature. HCl
(15 mL, 3 M) was added, and the mixture was extracted with diethyl
ether (40 mL). The combined organic phases were dried over
MgSO4 and concentrated under reduced pressure to yield 2-(tert-
butyl)-benzaldehyde. Yield: 0.81 g (89%). 1H NMR (400 MHz,
4. Experimental
4.1. General remarks
CDCl3):
2H), 7.4e7.3 (m, 1H), 1.53 (s, 9H); 13C NMR (100.4 MHz, CDCl3):
(ppm) 192.8, 152.2, 135.5, 133.3, 130.3, 126.3, 115.5, 35.8, 33.0.
d (ppm) 10.85 (s, 1H), 7.93 (d, J [ 8.4 Hz, 1 H), 7.50e7.48 (m,
All melting points were measured on a Yanaco MP-500D and
were uncorrected. 1H and 13C NMR spectra (400 and 100.4 MHz,
respectively) were recorded on a JEOL JNM-LA 400 using Me4Si as
the internal standard (0 ppm). The following abbreviations are
used: s ¼ singlet, d ¼ doublet, t ¼ triplet, q ¼ quartet, m ¼ multiplet.
IR spectra were measured with a PERKIN ELMER FT-IR Spectrom-
eter SPECTRUM 1000 in the range of 4000e400 cmꢀ1. Elemental
analyses were performed with a Yanaco CHN Corder MT-5. Mass
spectra were measured on a Thermo Quest LCQ DECA plus.
Preparative column chromatography was carried out on Fuji Silysia
d
4.2. General procedures for synthesis of 2-(o-substituted phenyl)-
1H-imidazolines
4.2.1. Method A
A
mixture of0 aldehyde (2 mmol) and ethylenediamine
(2.1 mmol) in dry CH2Cl2 (10 mL) was stirred at 0 ꢁC for 2 h under
argon atmosphere. NBS (2.1 mmol) was added to the mixture and
the resulting solution was stirred overnight at rt. The reaction was
quenched by the addition of 10% aq. NaOH and extracted with
CH2Cl2. The organic layer was dried over Na2SO4, and evaporated
under vacuum. The residue was purified by silica gel column
chromatography to give imidazoline.
BW-820MH or YMC*GEL Silica (6 nm I-40e63
chromatography (TLC) was carried out on Merck 25 TLC aluminum
sheets silica gel 60 F254
mm). Thin layer
.
2-(o-Fluorophenyl)-1H-imidazoline (L2) Yield: 280 mg. (85%).
m.p. 85 ꢁC (lit [9b] 85 ꢁC); 1H NMR (400 MHz, CDCl3):
d
(ppm) 7.97
(dd, J ¼ 7.6, 2.0 Hz, 1H), 7.6e7.5 (m, 1H), 7.3e7.2 (m, 2H), 3.66 (s,
4H); 13C NMR (100.4 MHz, DMF-d7):
d
(ppm) 161.28 (d, J ¼ 3.3 Hz),
159.84, 132.75 (d, J ¼ 8.2 Hz), 131.40 (d, J ¼ 2.5 Hz), 124.96 (d,
J ¼ 3.3 Hz), 119.92 (d, J ¼ 12.4 Hz), 116.96 (d, J ¼ 22.3 Hz), 50.47;
ESI-MS m/z: [M þ H]þ 165.1.
Fig. 5. Structural view of 5a showing 50% probability ellipsoids.

2026
Z. Gan et al. / Journal of Organometallic Chemistry 695 (2010) 2022e2029
Table 1
Crystallographic Data for Complexes 2, 3, 4, 5a, 5b and 6$2DMF.
2
3
4
5a
5b
6$2DMF
Formula
Formula wt
T (K)
Radiation
Cryst syst
Space group
C18H18Cl2F2N4Pd
505.66
193(2)
C20H24N4Cl2Pd
496.73
297(2)
C26H36Cl2N4Pd
581.89
193(2)
C18H22N4 Cl4O2Pd
574.60
296(2)
C18H18N4O2Pd
428.76
198(2)
C26H34N6Cl2O2Pd
639.89
295(2)
ꢀ
Mo-K
Monoclinic
a
(
l
¼ 0.71073 A)
Orthorhombic
P212121
Monoclinic
P21/n
Monoclinic
C2/c
Monoclinic
P21/c
Monoclinic
P21/c
P21/c
Unit cell dimens
ꢀ
a (A)
10.719(3)
13.102(4)
14.059(4)
1903.7(9)
90
105.386(5)
90
4
1.764
1008
1.285
0.30 ꢂ 0.16 ꢂ 0.10
1.97e27.42
ꢀ13 ꢃ h ꢃ 13
ꢀ15 ꢃ k ꢃ 16
ꢀ17 ꢃ l ꢃ 11
9.3055(11)
15.1358(17)
15.3710(18)
2164.9(5)
90
90
90
4
1.527
1008
1.116
0.28 ꢂ 0.19 ꢂ 0.14
1.89e26.65
ꢀ10 ꢃ h ꢃ 11
ꢀ19 ꢃ k ꢃ 10
ꢀ18 ꢃ l ꢃ 18
10.5531(8)
17.6061(13)
14.4758(11)
2668.2(3)
90
97.2360(10)
90
4
1.449
1200
0.917
0.32 ꢂ 0.15 ꢂ 0.15
2.26e27.26
ꢀ11 ꢃ h ꢃ 13
ꢀ20 ꢃ k ꢃ 22
ꢀ18 ꢃ l ꢃ 13
13.570(5)
19.628(7)
8.317(3)
2196.9(13)
90
97.374(6)
90
4
1.731
1144
1.354
0.30 ꢂ 0.15 ꢂ 0.033
1.83e27.47
ꢀ9 ꢃ h ꢃ 17
ꢀ23 ꢃ k ꢃ 22
ꢀ10 ꢃ l ꢃ 9
7.8697817)
5.5209(12)
18.238(4)
788.2(3)
90
95.918(3)
90
2
1.807
432
1.200
0.33 ꢂ 0.11 ꢂ 0.06
2.25e27.24
ꢀ10 ꢃ h ꢃ 9,
ꢀ7 ꢃ k ꢃ 6,
ꢀ17 ꢃ l ꢃ 23
8.264(2)
ꢀ
b (A)
10.245(3)
10.317(3)
724.4(4)
118.675(4)
93.297(4)
104.707(4)
1
1.467
328
0.858
0.25 ꢂ 0.16 ꢂ 0.15
2.30e27.05
ꢀ10 ꢃ h ꢃ 10
ꢀ11 ꢃ k ꢃ 12
ꢀ12 ꢃ l ꢃ 5
ꢀ
c (A)
3
ꢀ
V (A )
a
b
g
Z
(deg)
(deg)
(deg)
Dcalcd (Mg/m3)
F(000)
m
(Mo Ka) (mmꢀ1
)
Cryst size (mm3)
range (deg)
Index ranges
q
No. of reflns measd
Total
Unique
Rint
10661
3932
0.0329
11462
4087
0.0275
15113
5540
0.0187
6147
2242
0.0262
4074
1587
0.0436
3914
2756
0.0174
Structure soln
Refinement
No. of variables
GOF
R1
wR2
Direct method
Full-matrix least squares on F2
316
245
357
316
245
172
1.074
0.0334
0.0883
1.015
0.0238
0.0582
1.050
0.0253
0.0637
1.113
0.0346
0.0852
0.973
0.0263
0.0695
1.074
0.0313
0.0828
2-(o-Methylphenyl)-1H-imidazoline (L3) Yield: 258 mg (80%).
flask under an oxygen atmosphere and stirred at 120 ꢁC. After
confirmation of the completion of the reaction by TLC monitoring,
the mixture was filtered using Celite. The filtrate was then
concentrated, and the product was isolated by silica gel column
chromatography to afford the corresponding 2-(o-methylphenyl)-
1H-imidazole (L6). Yield: 418 mg (53%). m.p. 135e136 ꢁC (lit[13]
138e139 ꢁC); IR (KBr): vmax (cmꢀ1) 3032, 2907, 2802, 1577, 1499,
1468, 1444, 1412, 1382, 1369, 1170, 1109, 958, 904, 771, 750, 730;
m.p. 87 ꢁC (lit [9b] 88 ꢁC); 1H NMR (400 MHz, DMF-d7):
d (ppm) 7.54
(dd, J ¼ 8.0,1.6 Hz,1H), 7.3e7.2 (m, 3H), 3.50 (s, 4H), 2.49 (s, 3H); 13C
NMR (100.4 MHz, DMF-d7):
d 166.0, 137.8, 132.6, 131.4, 129.7, 129.1,
126.0, 21.0; ESI-MS m/z: [M þ H]þ 161.10.
2-(o-tert-Butylphenyl)-1H-imidazoline (L4) m.p. 145e147 ꢁC.
Yield: 164 mg (25%). IR (KBr): vmax (cmꢀ1) 3138, 2949, 2866, 1614,
1588, 1502, 1483, 1341, 1273, 1260, 1078, 980, 763; 1H NMR
(400 MHz, CDCl3):
d
(ppm) 7.49 (d, J ¼ 8.0 Hz, 1H), 7.4e7.3 (m, 1H),
1H NMR (400 MHz, CDCl3):
d
(ppm) 7.54 (d, J ¼ 8.0 Hz, 1H), 7.3e7.2
7.3e7.2 (m, 2H), 3.64 (s, 4H),1.42 (s, 9H); 13C NMR (100.4 MHz, D2O/
(m, 3H), 7.15 (d, J ¼ 2.0 Hz, 2H), 2.54 (s, 3H). 13C NMR (100.4 MHz,
DMF-d7):
d
168.4, 148.7, 132.2, 130.6, 129.4, 127.3, 125.8, 51.9, 38.9,
DMF-d7):
d (ppm) 146.9, 136.4, 130.9, 130.4, 129.1, 128.6, 125.7,
32.0; ESI-MS m/z: [M þ H]þ 203.26.
122.4, 20.6.
4.2.2. Method B
4.3. General procedures for preparation of 2-(o-substituted
A mixture of methyl salicylate (12 g, 80 mmol) and ethyl-
enediamine (14.4 g, 120 mol) was intensively mixed for 3 h under
reflux. The excess ethylenediamine was removed by distillation
giving a yellow crystal product in 12.05 g 93% yield. The higher
purity product was recrystallized from water/ethanol (2:1).
2-(1H-Imidazolin-2-yl)phenol (L5) m.p. 200e203 ꢁC (lit [9b]
phenyl)-1H-imidazolineepalladium complexes [14]
Palladium complexes were prepared by simply mixing the cor-
responding ligands with palladium chloride in a 2:1 M ratio. All
complexes were precipitated from the DMF solution by adding an
excessive amount of a poor solvent such as toluene, hexane or
CH2Cl2 into the reaction solution. By slow diffusion of a solvent into
the solution, the solubility of the complexes decreased, continually
generating a low supersaturated solution for crystal growth.
trans-Dichlorobis[(2-o-fluorophenyl)-1H-imidazoline]
palladium(II) 2. To a suspension of PdCl2 (177.3 mg, 1.0 mmol) in
DMF (5 mL), 2-(o-fluorophenyl)-1H-imidazoline (328.4 mg,
2.0 mmol) was added under argon atmosphere. The mixture was
stirred at 50 ꢁC for 2 h until a clear orange yellow solution was
formed. After dilution of the resulting solution with DMF (10 mL),
toluene (40 mL) was added to precipitate the Pd complex. The Pd
complex was isolated as a light yellow powder by filtration, washed
DMF-d7):
d
(ppm) 200e203 ꢁC; IR (KBr): vmax (cmꢀ1) 3362, 3049,
2959, 2891, 2789, 1609, 1591, 1575, 1530, 1472, 1448, 1350, 1268,
1153, 1029, 991, 836, 774, 688, 558, 536; 1H NMR (400 MHz, DMF-
d7):
d
(ppm) 13.0 (br s, 1H), 7.68 (d, J ¼ 8.0 Hz, 1H), 7.33 (t, J ¼ 8.0 Hz,
1H), 6.87 (d, J ¼ 8.0 Hz,1H), 6.77 (t, J ¼ 8.0 Hz,1H), 3.8 (br s, 4H),12.5
to 13.5 (br s, NH and OH); 13C NMR (100.4 MHz, DMF-d7):
d (ppm)
112.4, 117.6, 118.0, 127.9, 133.0, 162.8, 167.3; MS (ESI) m/z: [M þ H]þ
163.3.
2-(o-Methylphenyl)-1H-imidazole (L6). A mixture of 2-(o-
methylphenyl)-1H-imidazoline (2.90 g, 5 mmol) and Shirasagi KL
(1.45 g) in xylene (20 mL) was placed in a 250-mL three-necked

Z. Gan et al. / Journal of Organometallic Chemistry 695 (2010) 2022e2029
2027
Fig. 7. 1H NMR spectra in DMF-d7. (A) L5, (B) 5a, (C) 5b, (D) A mixture of PdCl2 and 2.0 equiv of L5.
with hexane and dried in air. Yield: 470 mg (93%). Anal. Calcd. for
C18H18Cl2F2N4Pd: C, 42.75; H, 3.59; N, 11.08. Found: C, 42.71; H,
3.71; N, 11.19. A single crystal of complex 2, suitable for X-ray
diffraction analysis, was obtained by slow diffusion of hexane into
(d, J ¼ 9.0 Hz), 132.5, 124.9 (d, J ¼ 3.3 Hz), 118.7, 116.5 (d, J ¼ 21 Hz),
55.18, 44.44; Anal. Calcd. for C18H18Cl2F2N4Pd: C, 42.75; H, 3.59; N,
11.08. Found: C, 42.71; H, 3.71; N, 11.19.
cis-Dichlorobis[2-(o-methylphenyl)-1H-imidazoline] palla-
dium(II) 3. To a suspension of PdCl2 (177.3 mg, 1.0 mmol) in DMF
(5 mL), 2-(o-methylphenyl)-1H-imidazoline (320.4 mg, 2.0 mmol)
was added under argon atmosphere. The mixture was stirred at
50 ꢁC for 2 h until a clear orange yellow solution was formed. After
dilution of the resulting solution with DMF (10 mL), toluene (40 mL)
was added manually to slowly diffuse into the Pd complex solution
of DMF. The palladium complex was isolated as an orange red
a solution of complex 2 in DMF. m.p. > 300 ꢁC. IR (KBr): vmax (cmꢀ1
)
3268, 2962, 2881, 1627, 1604, 1518, 1485, 1451, 1353, 1279, 1236,
1101, 1048, 961, 949, 818, 771, 745, 557, 504, 458; 1H NMR
(400 MHz, DMF-d7):
d
(ppm) 8.82 (t, dd, J ¼ 8.0, 1.2, 0.8, 2.0 Hz, 1H),
7.96 (s, 1H), 7.6e7.5 (m, 1H), 7.39 (t, J ¼ 8.0, 0.8 Hz, 1H), 7.30 (dd,
J ¼ 8, 1.2, 0.8 Hz, 1H), 3.90 (t, J ¼ 10.8 Hz, 2H), 3.65 (t, J ¼ 10.8 Hz,
2H); 13C NMR (100.4 MHz, DMF-d7):
d (ppm) 163.55, 159.63, 133.7
Scheme 3. Proposed structure of PdCl2 with L5.

2028
Z. Gan et al. / Journal of Organometallic Chemistry 695 (2010) 2022e2029
crystal by filtration, washed with toluene and dried in air. The
resulting crystal was suitable for X-ray diffraction analysis. Yield:
323.5 mg (65%). m.p. 228e230 ꢁC. IR (KBr): vmax (cmꢀ1) 3314, 2957,
2889, 1616, 1602, 1590, 1510, 1474, 1457, 1285, 1048, 772, 730, 210;
bis-[2-(1H-Imidazoline-2-yl)phenolato-k
2N3,O] palladium(II)
5b. Yield: 112 mg. IR (KBr): vmax (cmꢀ1) 3238, 2882, 2422, 1608,
1590,1544,1500,1435,1326,1282,1241, 851, 745, 682, 579; 1H NMR
(400 Hz, DMF-d7):
d
(ppm) 7.75 (s, 1H), 7.57 (d, J ¼ 8.0 Hz, 1H), 7.14
1H NMR (400 MHz, DMF-d7):
d
(ppm) 7.95 (d, J ¼ 6.4 Hz, 1H), 7.9 (br
s, 1H), 7.6e7.5 (m, 3H), 3.48 (s, 2H), 3.4 (br s, 2H), 2.68 (s, 3H); 13C
NMR (100.4 MHz, DMF-d7): (ppm) 167.3 (168.3), 137.8 (137.2),
(t, J ¼ 8.0 Hz,1H), 6.81 (d, J ¼ 8.0 Hz,1H), 6.48 (t, J ¼ 8.0 Hz,1H), 4.02
(t, J ¼ 12.0 Hz, 2H), 3.65 (t, J ¼ 12.0 Hz, 2H); 13C NMR (100.4 MHz,
d
DMF-d7): d (ppm) 44.0, 51.4, 112.9, 114.1, 122.2, 129.1, 132.7, 160.8,
131.4 (131.4), 131.3 (131.3), 131.0 (131.2), 129.9 (130.4), 126.5 (125.8),
54.4 (55.1), 44.0 (44.2), 20.5 (20.2); Anal. Calcd. for C20H24N4Cl2Pd:
C, 48.26; H, 4.86; N, 11.26. Found: C, 48.33; H, 4.86; N, 11.22.
cis-Dichlorobis[2-(o-tert-butylphenyl)-1H-imidazoline]
166.9; Anal. Calcd. for C18H18N4O2Pd: C, 50.42; H, 4.23; N, 13.07.
Found: C, 49.89; H, 4.68; N, 12.96.
4.5. X-ray Crystallography
palladium(II) 4. To a suspension of PdCl2 (35.5 mg, 0.2 mmol) in
DMF (2 mL), 2-(o-tert-butylphenyl)-1H-imidazoline (80.8 mg,
0.4 mmol) was added under argon atmosphere. The mixture was
stirred at 50 ꢁC for 2 h until a clear orange yellow solution was
formed. After dilution of the resulting solution with DMF, toluene
(5 mL) was slowly added. The Pd complex was isolated as an orange
red crystal by filtration, washed with toluene and dried in air. Yield:
52.4 mg (45%). m.p. 255e258 ꢁC (dec); 1H NMR (400 MHz, DMF-
Single crystal X-ray diffraction data of the complexes were
collected on a Bruker Smart 1000 CCD diffractometer. An empirical
absorption correction was applied using the SADABS program. The
structure was solved by direct methods and refined by full-matrix
least squares calculations on F2 using the SHELXL-97 program
package [15]. Crystal data and details of the data collection and
structure refinement are summarized in Table 1.
d7):
d
(ppm) 7.97 (s, 1H), 7.85 (d, J ¼ 7.6 Hz), 7.8 (br d), 7.66 (s), 7.58
(t, J ¼ 7.6 Hz), 7.5 (br s), 7.44 (t, J ¼ 7.6 Hz), 7.27, 7.06, 3.77 (m), 3.36
Acknowledgements
(t, J ¼ 10.4 Hz), 1.67 (s), 1.57 (s), 1.3 (br s); 13C NMR (100.4 MHz,
DMF-d7):
d (ppm) 169.6 (170.0), 150.7 (149.1), 132.6, 130.4 (130.3),
This work was supported by a Grant-in-Aid for Scientific
Research on Priority Areas “Advanced Molecular Transformations
of Carbon Resources” and Grant No. B17340020 from the
Ministry of Education, Culture, Sports, Science and Technology of
Japan. Z. G. thanks Rotary Yoneyama Memorial Foundation for
scholarship.
128.7 (128.2), 125.8 (125.3), 101.4, 54.5 (55.2), 43.6 (44.1), 37.9
(37.3), 32.5 (32.2); Anal. Calcd. for C26H36Cl2N4Pd: C, 53.66; H, 6.24;
N, 9.63. Found: C, 53.70; H, 6.25; N, 9.77.
trans-Dichlorobis[(2-o-methylphenyl-1H-imidazole)] palla-
dium(II) bis(dimethylformamide) solvate 6$2 DMF. To a suspen-
sion of PdCl2 (177.3 mg, 1.0 mmol) in DMF (5 mL), 2-o-
methylphenyl-1H-imidazole (316.4 mg, 2.0 mmol) was added
under argon atmosphere. The mixture was stirred at 50 ꢁC for 2 h
until a clear orange yellow solution was formed. After dilution of
the resulting solution with DMF (10 mL), toluene (40 mL) was
slowly added. The Pd complex was isolated as an orange red crystal
by filtration, washed with toluene and dried in air. Yield: 416 mg
(65%). m.p. 268 ꢁC (dec); IR (KBr): vmax (cmꢀ1) 3314, 2957, 2889,
1616, 1602, 1590, 1510, 1474, 1457, 1285, 1048, 772, 730, 210; 1H
Appendix A. Supplementary material
CCDC 751531, 751529, 751530, 741320, 741339 and 751528
contain the supplementary crystallographic data for 2, 3, 4, 5a, 5b
and 6$2DMF respectively. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data-request/cif
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2010.05.007.
NMR (400 MHz, DMF-d7):
d
(ppm) 12.78 (s, 1H), 7.99 (dd, J ¼ 8.8,
1.6 Hz, 1H), 7.47 (dd, J ¼ 7.6, 1.6 Hz, 1H), 7.4e7.3 (m, 3H), 7.14 (t,
J ¼ 1.6, 1H), 2.29 (s, 3H); 13C NMR (100.4 MHz, DMF-d7):
d (ppm)
References
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Found: C, 48.71; H, 5.42; N, 12.96.
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