Synthesis and structural studies of cyclopalladated complexes of secondary benzylamines

Article abstract of DOI:10.1016/j.jorganchem.2012.12.032

Di-nuclear cyclopalladated acetato-bridged complexes derived from secondary benzylamines, [Pd₂{(C,N)-C₆H₄CH ₂NH(R)}₂(μ-OAc)₂] (R = Et (1), R = t-Bu (2)) were obtained by refluxing of corresponding benzylamines and Pd(OAc) ₂ in a 1:1 M ratio. Complex 1 was also prepared by heating the bis-amine complex [Pd(OAc)₂(PhCH₂NH(Et))₂] (3) in toluene at 60 °C. Complex 3 reacted with an excess of NaCl to give [Pd(Cl)₂(PhCH₂NH(Et))₂] (4). Metathetical reaction of 1 and 2 with an excess of NaCl or NaBr afforded the corresponding dimers [Pd₂{(C,N)-C₆H₄CH₂NH(R)} ₂(μ-X)₂] (X = Cl, R = Et (5); X = Cl, R = t-Bu (6); X = Br, R = t-Bu (7)). The cationic complex [Pd(C,N)-C₆H ₄CH₂NH(Et)(phen)]BF₄ (8) can be obtained by reacting chloro bridge dimer 5 with AgBF₄ and 1,10-phenanthroline (phen). Neutral ligands split the halide bridges in 6 and 7 to give monomeric complexes [Pd(C,N)-C₆H₄CH₂NH(t-Bu)X(L)] (X = Cl, L = PPh₃ (9); X = Br, L = Me₃Py (10)). Complexes 1-10 were fully characterized by elemental analysis, IR and NMR spectroscopies. In addition, the crystal structures of 2, 3, 4, 8, 9 and 10 were determined by single-crystal X-ray diffraction analysis. In all these structures, the palladium atom shows a distorted or slightly distorted square-planar geometry.

Full text of DOI:10.1016/j.jorganchem.2012.12.032

Accepted Manuscript
Synthesis and structural studies of cyclopalladated complexes of secondary
benzylamines
Kazem Karami, Mahboubeh Hosseini Kharat, Corrado Rizzoli, Janusz Lipkowski
PII:
S0022-328X(12)00742-5
10.1016/j.jorganchem.2012.12.032
JOM 17839
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 21 October 2012
Revised Date: 25 December 2012
Accepted Date: 27 December 2012
Please cite this article as: K. Karami, M.H. Kharat, C. Rizzoli, J. Lipkowski, Synthesis and structural
studies of cyclopalladated complexes of secondary benzylamines, Journal of Organometallic Chemistry
(2013), doi: 10.1016/j.jorganchem.2012.12.032.
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ACCEPTED MANUSCRIPT
Synthesis and structural studies of cyclopalladated complexes of secondary
benzylamines
Kazem Karamia, , Mahboubeh Hosseini Kharata, Corrado Rizzolib, Janusz Lipkowskic
a Department of Chemistry, Isfahan University of Technology, Isfahan, 84156/83111, Iran
bDepartment of Chemistry, University of Parma, I-43124 Parma, Italy
c Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
Corresponding author: Kazem Karami; Email: karami@cc.iut.ac.ir
Tel: +983113913239; fax: +983113912350

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Synthesis and structural studies of cyclopalladated complexes of secondary
benzylamines
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Kazem Karamia, , Mahboubeh Hosseini Kharata, Corrado Rizzolib, Janusz Lipkowskic
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a Department of Chemistry, Isfahan University of Technology, Isfahan, 84156/83111, Iran
b Department of Chemistry, University of Parma, I-43124 Parma, Italy
c Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
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Abstract
Dinuclear cyclopalladated acetato-bridged complexes derived from secondary benzylamines, [Pd2{(C,N)-
C6H4CH2NH(R)}2(ꢀ-OAc)2] (R = Et (1), R = t-Bu (2)) were obtained by refluxing of corresponding
benzylamines and Pd(OAc)2 in a 1:1 molar ratio. Complex 1 was also prepared by heating the bis-amine
complex [Pd(OAc)2(PhCH2NH(Et))2] (3) in toluene at 60°C. Complex 3 reacted with an excess of NaCl to
give [Pd(Cl)2(PhCH2NH(Et))2] (4). Metathetical reaction of 1 and 2 with an excess of NaCl or NaBr afforded
the corresponding dimers [Pd2{(C,N)-C6H4CH2NH(R)}2(ꢀ-X)2] (X = Cl, R = Et (5); X = Cl, R = t-Bu (6); X
= Br, R = t-Bu (7)). The cationic complex [Pd(C,N)-C6H4CH2NH(Et)(phen)]BF4 (8) can be obtained by
reacting chloro bridge dimer 5 with AgBF4 and 1,10-phenanthroline (phen). Neutral ligands split the halide
bridges in 6 and 7 to give monomeric complexes [Pd(C,N)-C6H4CH2NH(t-Bu)X(L)] (X = Cl, L = PPh3 (9); X
= Br, L = Me3Py (10)). Complexes 1−10 were fully characterized by elemental analysis, IR and NMR
spectroscopies. In addition, the crystal structures of 2, 3, 4, 8, 9 and 10 were determined by single- crystal X-
ray diffraction analysis. In all these structures, the palladium atom shows a distorted or slightly distorted
square-planar geometry.
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Keywords: Secondary benzylamines; Cyclopalladated complexes; Palladium(II) acetate; Crystal structures
Corresponding author: Kazem Karami; Email: karami@cc.iut.ac.ir
Tel: +983113913239; fax: +983113912350
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1. Introduction
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The interest in cyclopalladated complexes derived from N-donor ligands has increased considerably due to
their extremely high catalytic activity in a variety of important C−C coupling reactions including Heck
reactions, Stille coupling and Suzuki coupling [1,2]. Cyclopalladation of amine complexes is governed by a
fundamental rule reported in 1968 by Cope and Friedrich [3]: direct activation of C−H bonds by
palladium(II) species to afford the corresponding palladacycles is the most feasible in the case of tertiary
amines, whereas primary and secondary amines are usually inert toward such activation. However, when
using different palladium reagents and/or experimental reaction conditions, it has been demonstrated that
benzylamine, and some of its secondary amine derivatives, can be orthometalated [4,5]. The mechanism of
orthometalation of benzylamine has been investigated by Ryabov et al. [6], proposed that the
cyclopalladation proceeds mainly via monomeric intermediate [Pd(OAc)2(amine)2]. High concentrations of
amine favor the formation of the monomeric complex. Then the intermediate transforms into orthopalladated
materials. The orthopalladation of secondary amines have been reported by Fuchita et al. [4,7−8], Vicente et
al. [9] and our laboratory [10]. For the first time, Vicente et al. [9] reported the crystal structure of a
cyclopalladated complex of secondary benzylamine. Considering that, palladacycles of secondary amine
have not received due attention than the tertiary amine, as not many crystal structures of them have been
reported and due to our interest in the preparation and application of complexes containing the
orthopalladated fragment of amines [10−12], we have described the synthesis and structural characterization
of mono- and dinuclear complexes from secondary benzylamines. We have also designed the synthesis of the
bis-amine complex 3 to form acetato-bridged palladacycle 1 in order to compare with the case where the
palladium (II) acetate reacts directly with the corresponding amine in a 1:1 molar ratio to give the bridged
palladacycle 1. It should be noted that we have been previously reported the formation of acetato-bridged
dinuclear palladacycles 1 and 2 [10], but herein we describe the details of their synthesis and characterize
them fully. Moreover, the crystal structure of the mononuclear complex 9, which was previously
characterized [10], is reported here.
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2. Result and discussion
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Scheme 1 shows the complexes prepared in this work and the labeling assigned to the methylene and
aromatic protons. The crystal data and structural refinement parameters for complexes 2, 3, 4, 8, 9 and 10 are
listed in Table 1.
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(Scheme 1)
(Figure 1)
(Figure 2)
(Figure 3)
2.1. Synthesis and structure of mono- and dinuclear complexes
The reaction of the secondary benzylamines PhCH2NH(Et) or PhCH2NH(t-Bu) with Pd(OAc)2 in a 1:1
molar ratio have been carried out in toluene at 60°C to produce five-membered palladacycles of general
formula [Pd2{(C,N)-C6H4CH2NH(R)}2(ꢀ-OAc)2] (R = Et (1), R = t-Bu (2)). The reaction of palladium(II)
acetate with PhCH2NH(Et) in a 1:2 molar ratio give also the corresponding bis-amine adduct
[Pd(OAc)2(PhCH2NH(Et))2] (3). It has already been confirmed that if there are bulky groups around the
nitrogen atom of the benzylamine, the formation of the bis-amine adduct is difficult [4]. Addition of NaCl to
a
methanolic solution of
3
allowed the isolation of bis(amino)-dichloro palladium(II)
[Pd(Cl)2(PhCH2NH(Et))2] (4). When the bis-amine complex 3 was heated in toluene at 60°C, the dinuclear
complex 1 was precipitated but the reaction yield was low (22%). Treatment of complexes 1 and 2 with an
excess of NaCl or NaBr in methanol afforded the corresponding chloro and bromo bridging dimers
[Pd2{(C,N)-C6H4CH2NH(R)}2(ꢀ-X)2] (X = Cl, R = Et (5); X = Cl, R = t-Bu (6); X = Br, R = t-Bu (7)) in
good yields. Complex 5 reacted with AgBF4 and 1,10-phenantroline (phen) to give [Pd(C,N)-
C6H4CH2NH(Et)(phen)]BF4 (8). Complexes 6 and 7 reacted with PPh3 and sym−collidine (Me3Py) in a 1:2
molar ratio to give the mononuclear complexes [Pd(C,N)-C6H4CH2NH(t-Bu)X(L)] (X = Cl, L = PPh3 (9); X
= Br, L = Me3Py (10)). The elemental analysis results of the prepared compounds 1−10 are in a good
agreement with the calculated values. The mono- and dinuclear palladacycles 1, 2 and 5−10 were also
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characterized by IR and NMR spectroscopy. The crystal structures of complexes 2, 3, 4, 8, 9 and 10 have
been solved by X-ray diffraction studies.
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The IR spectra of complexes 1 and 2 show characteristic bands due to the bridging acetato ligand at 1566,
1415 cm-1 and 1577, 1455 cm-1, respectively [7]. Concerning the 1H NMR spectrum of 1 we observe signals
from the anti and syn type isomers. Two well-separated sets of signals appear for the methylene protons,
acetato-methyl and N−ethyl protons, while signals due to the four aromatic protons of the two isomers
overlapped with each other. It is confirmed that the syn configurations are less favorable as compared with
the anti configurations, because two amino groups in the syn type are located close to each other and create
steric hindrance [7]. Differently from 1, both the acetato-methyl and N-tert-butyl protons in 2 appeared only
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as one singlet in the H NMR spectrum. Considering that the tert-butyl group in 2 is bulkier than the ethyl
group in 1, it supports that 2 displays an anti configuration.
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The crystal structure of 2 shows that the molecule possesses an approximate (noncrystallographyic) C2
symmetry with the nitrogen atoms mutually trans with respect to the di-ꢀ-acetato bridges. Selected bond
distances and angles are summarized in Figure 1. The coordination around each palladium atoms is
essentially square-planar. Each palladium center deviates very slightly (0.0278(2) Å and 0.0192(2) Å) from
the planes containing O1, C1, O3, N1 and N2, O2, C12, O4, respectively. As a result of Pd1 and Pd2 being
bridged by two mutually cis ꢀ-acetate ligands, the chelating C,N–bonded benzylamines are forced to lie
above one another in the dimeric molecule. The bridging acetato groups force the two palladium planes of
the dimer to have dihedral angles of 26.64(5)º. The nonbonding Pd1…Pd2 distance of 2.9145(2) Å is a little
shorter than those found in [Pd{C6H4CH2N(CH2Ph)2−C,N}(ꢀ-OAc)]2 (I, 3.0621 Å) [4] and
[Pd{C6H3(CH2)2NH2-2-OMe-5-κ2C,N}(ꢀ-OAc)]2 (II, 2.9229 Å) [13] because of the larger steric repulsion of
the benzyl groups in I and II. The Pd−C distances (1.949(2) and 1.955(2) Å) are also shorter than those
reported for I and II. The Pd−N distances (2.1069(18) and 2.0724(18) Å) are shorter and longer than those
found in I and II, respectively. These data suggest that sterically demanding benzyl groups at nitrogen atom
increase the Pd−N length [4].
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The molecular structures of bis-amine complexes 3 and 4 are shown in Figs. 2 and 3, respectively. Complex
3 possesses crystallographically imposed center of symmetry. In both compounds, the palladium metal is
coordinated in an almost regular square planar geometry by two monodentate acetato (in 3) or chloride (in 4)
anions, and by two nitrogen atoms from N-benzylethylamine ligands. The trans configuration assumed by
the amino ligands is the normal geometry observed for bis(amino)-palladium(II) complexes [14]. In 3 the
metal atom lies in plane through the donor atoms for symmetry requirements, while it is displaced by
0.0073(2) Å in 4. As expected, the Pd−O (2.012(2) Å) bond length in 3 is significantly shorter than those
observed in 2 (mean value 2.10(3) Å) and other related benzylamine acetato-bridged complexes [4,13]. In
the crystal structure of 3, two intramolecular N—H···O hydrogen bonds are present. In complex 4, molecules
are linked into zig-zag chains running parallel to the b axis by intermolecular N–H...Cl hydrogen bonds.
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The H NMR spectra of complexes 5−7 show only one set of signals, which indicate that in solution the
cyclopalladated dimers 5−7 consist of only one geometrical isomer which we propose to be the anti type
isomer [15]. In dinuclear complexes 5−7, the methylene protons are diastereotopic resulting in the formation
of two separated signals each integrating for one proton at ~ 4.3 and ~ 3.8 ppm.
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In the H NMR spectra of the mononuclear complexes 8, 9 and 10, the methylene protons are also
nonequivalent and resonate at different places. Moreover, the 1H NMR spectra show similar patterns for the
H3-H5 aromatic protons of amine, but H6 is significantly shifted to lower frequencies for 8 (6.56 ppm), 9
(6.19 ppm) and 10 (5.49 ppm) because of the anisotropic shielding from the phenyl or pyridine ring [7].
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Figure 4 shows the ORTEP plot of complex 8 and selected bond distances and angles. The asymmetric
unit of 8 consists of a complex cation and tetrafluroborate as counter ion. The palladium metal exhibits a
slightly distorted square-planar geometry (maximum deviation 0.096(2) Å for atom C15), as indicated by the
angles subtended by the ligands at Pd(II) varying from 80.01(8) to 101.02(8)° and from 175.01(7) to
176.84(7)°. The summation of the bond angles around the palladium is 360.26°. The metal deviates
0.02320(14) Å from the mean coordination plane. The dihedral angle between the two planes formed by N1,
Pd1, N2 and C15, Pd1, N3 is 6.25(7)°. The Pd−N2 bond distance of 2.1288(17) Å is longer than the Pd−N1
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distance of 2.0568(17) Å, showing that C15 has a larger trans influence than N3 of the amine group. The bite
angle N1−Pd−N2 is 80.16(7)°, which is normal for Pd(II) complexes containing bpy or phen ligands [16,17].
The Pd1−C15 bond distance (1.997(2) Å) is similar to that found in a related orthopalladated complex [17].
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The mononuclear complex 9 crystallizes with two independent molecules (hereafter called molecule A and
B) in the asymmetric unit (Fig 5). Each palladium metal is coordinated in a distorted square-planar geometry
(maximum deviations: 0.088(2) and 0.135(2) Å for atoms C21 and C50 for molecules A and B, respectively)
by a chloride anion, a P atom of a triphenylphosphine ligand and a chelating N-benzyl tert-butylamine-C2,N
moiety forming a five-membered cyclopalladated ring through the N1, C21 atoms for molecule A and N2,
C50 atoms for molecule B. The chelate ring assumes a half-boat conformation, with atoms N1 and N2
displaced by 0.7573(16) and 0.7222(16) Å, respectively, from the Pd1/C19-C21 and Pd2/C48-C50 mean
planes. The Pd−C bond distances (2.0101(18) and 2.0185(18) Å for A and B, respectively) are within the
range usually reported by five- and six-membered palladacycles [18−21]. The phosphine ligand is in trans
position to the amine group, in agreement with what observed in related mononuclear palladacycles, where
the phosphine and aryl ligands have a well-demonstrated tendency not to be trans to each other when
coordinated to palladium [18−21]. In the crystal, molecules A and B are linked by a pair of N–H...Cl
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hydrogen bonds resulting in the formation of a ring of R2 (8) graph-set motif.
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The crystal structure of 10 (Fig 6) shows a significantly tetrahedrally distorted square planar environment
(maximum deviation 0.143(3) Å) with a dihedral angle of 9.53(8)º between the N1, Pd1, C1 and N2, Pd1,
Br1 planes. The angles around palladium deviate from the ideal value of 90° due to the small bite of the
cyclometalated ligand, the C−Pd−N angle being 82.68(10)°. Comparing 9 and 10, the Pd−N distances
(2.1215(15) and 2.1375(16) Å) and the Pd−C distances (2.0101(18) and 2.0185(18) Å) for 9 are longer than
the Pd−N1 distance (2.081(2) Å) and the Pd−C distance (1.983(2) Å) for 10, due to the greater trans influence
of the P and Cl atoms with respect to the N2 and Br1 atoms, respectively [22]. In the crystal, two molecules
of complex 10 are connected through a pair of hydrogen bonds between the bromine atoms and the CH2
groups (Fig 7).
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(Figure 4)
(Figure 5)
(Figure 6)
(Figure 7)
(Table 1)
3. Conclusion
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We present here the preparation and structures of mono- and di-nuclear palladacycles from secondary
benzylamines. We have also successfully showed that the acetato-bridge palladacycle 1 is synthesized by
two methods: the first, a direct reaction of palladium (II) acetate with the corresponding benzylamine and the
second, from heating bis-amine complex 3, which confirms that cyclopalladation proceed through the bis-
amine adduct, although the yield of latter method was low. The structure of complexes 2, 3, 4, 8, 9 and 10
was confirmed by single-crystal X-ray diffraction. The crystal structure of 9 and 10 show the phosphine and
sym-collidine ligands are in trans position to the amine group.
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4. Experimental
4.1. General
Starting materials and solvents were purchased from Sigma-Aldrich or Alfa Aesar and used without
further purification. Infrared spectra were recorded on a FT-IR JASCO 680 spectrophotometer in the spectral
range 4000-400 cm−1 using the KBr pellets technique. NMR spectra were measured on a Bruker
spectrometer at 400.13 MHz (1H), 100.61 MHz (13C) and 161.97 MHz (31P) using standard pulse sequences
at 298 K. Elemental analysis was performed on Leco, CHNS-932 apparatus.
4.2. Synthesis of [Pd2{(C,N)-C6H4CH2NH(Et)}2(ꢀ-OAc)2] (1)
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Method (a). N-benzylethylamine (150 ꢀL, 1 mmol) was added to a toluene (20 mL) solution of
palladium(II) acetate (0.224 g, 1 mmol) and the resulting solution was heated under reflux for 24 h. The
resulting mixture was evaporated to dryness and the residue recrystallized from CH2Cl2 and hexane to give 1.
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Yield: 72%. IR (KBr, cm−1): ν(CO) = 1566, 1413; ν(NH) = 3168. H NMR (DMSO-d6, ppm): δ = 0.73 (t,
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3H, CH3, JHH = 7.2 Hz), 1.19 (t, 3H, CH3, JHH = 7.2 Hz), 1.8 (s, 3H, MeCO2), 1.88 (s, 3H, MeCO2), 2.77
3
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(m, 4H, CH2), 3.33 (br s, 1H, NH), 3.54 (dd, 2H, CH2, JHH = 4.4 Hz), 3.78 (dd, Ha, CHaH, JHH = 15.6 Hz,
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3JHH = 4.4 Hz), 4.24 (dd, Hb, CHbH, JHH = 14.6 Hz, JHH = 5.6 Hz), 5.94 (br s, 1H, NH), 6.73-7.5 (m,
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8H,C6H4 JHH = 7.6 Hz). Anal. calcd. for C22H30N2O4Pd2: C, 44.0; H, 5.04; N, 4.67. Found: C, 43.9; H, 5.04;
N, 4.65%.
Method (b). A toluene (10 mL) solution of [Pd{PhCH2NH(Et)}2(OAc)2] (3) (0.1 g, 0.2 mmol) was heated
at 60°C for 2 days. The precipitated green powder were collected and washed with diethyl ether to give 1
(22%).
4.3. Synthesis of [{Pd2{(C,N)-C6H4CH2NH(t-Bu)}2(ꢀ-OAc)2] (2)
N-benzyl tert-buthylamine (181 ꢀL, 1 mmol) was added to a toluene (20 mL) solution of palladium(II)
acetate (0.224 g, 1 mmol) and the resulting solution was heated under reflux for 24 h. The resulting mixture
was evaporated to dryness and the residue recrystallized from CH2Cl2 and hexane to give 2. Yield: 75%. IR
(KBr, cm−1): ν(CO) = 1577, 1455; ν(NH) = 3218. 1H NMR (DMSO-d6, ppm): δ = 1.11 (m, 9H, t-Bu), 1.8 (br
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s, 3H, MeCO2), 3.9 (d, Ha, CHaH, JHH = 15.6 Hz), 4.34 (d, Hb, CHbH, JHH = 15 Hz), 6.82-7.43 (m, 4H,
C6H4), 7.69 (br s, 1H, NH); 13C{1H} NMR (DMSO-d6, ppm): δ = 25.03 (C, t-Bu), 28.6 (Me), 54.01
(MeCO2), 56.8 (CH2), 120.8, 124.4, 124.7,132.6 (Caromatic). Anal. calcd for C26H38N2O4Pd2: C, 47.6; H, 5.8;
N, 4.27. Found: C, 47.5; H, 5.6; N, 4.2%.
4.4. Synthesis of [Pd{PhCH2NH(Et)}2(OAc)2] (3)
N-benzylethylamine (300 ꢀL, 2 mmol) was added to a toluene (20 mL) solution of palladium(II) acetate
(0.224 g, 1 mmol) and the resulting solution was heated under reflux for 6 h. The resulting mixture was
evaporated to dryness and the residue was precipitated from CH2Cl2 and hexane to give 3. Yield: 85%. IR
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(KBr, cm−1): ν(NH) = 3387. Anal. calcd. for C22H32N2O4 Pd: C, 53.39; H, 6.51; N, 5.66. Found: C, 53.27; H,
6.12; N, 5.61 %.
4.5. Synthesis of [Pd{PhCH2NH(Et)}2(Cl)2] (4)
To a suspension of 1 in methanol was added excess NaCl and the resulting mixture stirred for 8 h at room
temperature. A green precipitate was formed which was filtered and washed with water and then air-dried to
give 4. Yield: 74%. IR (KBr, cm−1): ν(NH) = 3385. Anal. calcd. for C18H26Cl2N2Pd: C, 48.28; H, 5.85; N,
6.25. Found: C, 48.44; H, 5.7; N, 6.35%.
4.6. Synthesis of [Pd2{(C,N)-C6H4CH2NH(Et)}2(ꢀ-Cl)2] (5)
To a suspension of palladacycle 3 in methanol was added excess NaCl and the resulting mixture stirred for
12 h at room temperature. A green precipitate was formed which was filtered and washed with water and
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then air-dried to give 5. Yield: 68%. IR (KBr, cm−1): ν(NH) = 3233, 3194. H NMR (DMSO-d6, ppm): δ =
1.18 (t, 3H, CH3, 3JHH = 6.8 Hz), 2.9 (m, 2H, CH2), 3.78 (dd, Ha, CHaH, 2JHH = 15.2 Hz, 3JHH = 2.8 Hz), 4.23
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(dd, Hb, CHbH, JHH = 14.8 Hz, JHH = 5.2 Hz ), 6.18 (br s, 1H, NH), 6.87-7.03 (m, 3H, C6H4), 7.63 (d, 1H,
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C6H4 JHH = 9.2 Hz). Anal. calcd. for C18H24N2Cl2Pd2: C, 39.15; H, 4.3; N, 5.07. Found: C, 39.17; H, 4.25;
N, 5.02%.
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4.7. Synthesis of [{Pd(C,N)-C6H4CH2NH(t-Bu)}2(ꢀ-Cl)2] (6)
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To a suspension of palladacycle 4 in methanol was added excess NaCl and the resulting mixture stirred for
12 h at room temperature. A green precipitate was formed which was filtered and washed with water and
then air-dried to give 6. Yield: 64%. IR (KBr, cm−1): ν(NH) = 3220. 1H NMR (DMSO-d6, ppm): δ = 1.15 (br
s, 9H, t-Bu), 3.86 (m, Ha, CHaH), 4.33 (m, Hb, CHbH), 5.77 (br s, 1H, NH), 6.79-7 (m, 3H, C6H4), 7.55 (d,
3
1H, C6H4 JHH = 7.6 Hz). 13C{1H} NMR (DMSO-d6, ppm): δ = 29.8, 55.5, 57.6 (Caliphatic), 120.8,124.4, 124.8,
131.9, 148.7, 153.34 (Caromatic). Anal. calcd. for C22H32N2Cl2Pd2: C, 43.44; H, 5.3; N, 4.6. Found: C, 43.23;
H, 5.25; N, 4.45%.
4.8. Synthesis of [{Pd(C,N)-C6H4CH2NH(t-Bu)}2(ꢀ-Br)2] (7)
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To a suspension of palladacycle 4 in methanol was added excess NaBr and the resulting mixture stirred for
12 h at room temperature. A green precipitate was formed which was filtered and washed with water and
then air-dried to give 7. Yield: 66%. IR (KBr, cm−1): ν(NH) = 3203. 1H NMR (DMSO-d6, ppm): δ = 1.16 (br
s, 9H, t-Bu), 3.88 (br s, Ha, CHaH), 4.31 (br s, Hb, CHbH), 5.68 (br s, 1H, NH), 6.92 (m, 3H, C6H4), 7.54 (br
s, 1H, C6H4). 13C{1H} NMR (DMSO-d6, ppm): δ = 30.02, 57.6 (Caliphatic), 120.7, 124.3, 152.8 (Caromatic). Anal.
calcd. for C22H32N2Br2Pd2: C, 37.9; H, 4.62; N, 4.0. Found: C, 37.85; H, 4.5; N, 4.0%.
4.9. Synthesis of [Pd(C,N)-C6H4CH2NH(Et)(phen)]BF4 (8)
AgBF4 (0.035 g, 0.18 mmol) was added to a solution of complex 5 (0.05 g, 0.09 mmol) in THF (15 mL).
The resulting mixture was stirred for 30 min under light protection and then filtered through a plug of
MgSO4 to remove AgCl. 1,10-Phenantroline (0.032 g, 0.18 mmol) was added to the filtrate, and the mixture
was stirred for 5 h and then filtered again through MgSO4. The solvent was removed to ca. 2 mL, and n-
hexane (15 mL) was added to precipitate 8 as a cream solid, which was collected and air-dried. Yield: 63%.
IR (KBr, cm−1): ν(NH) = 3273. 1H NMR (DMSO-d6, ppm): δ = 1.27 (t, 3H, CH3, 3JHH = 7.2 Hz), 2.49−2.51
2
2
(m, 2H, CH2), 3.95 (d, Ha, CHaH, JHH = 16 Hz), 4.82 (d, Hb, CHbH, JHH = 14 Hz), 6.56 (br s, 1H,C6H4),
6.86 (br s, 1H, NH), 7.13−7.90 (m, 3H, C6H4), 8.10 (br s, 1H, phen), 8.25 (t, 1H, phen, 3JHH = 7.4 Hz), 8.29
(br s, 1H, phen), 8.66 (d, 1H, phen, 3JHH = 6 Hz), 8.96−8.99 (m, 2H, phen), 9.14 (d, 1H, phen, 3JHH = 3.5 Hz),
3
9.26 (d, 1H, phen, JHH = 4.8 Hz). Anal. calcd. for C21H20BF4N3Pd: C, 49.68; H, 3.97; N, 8.27. Found: C,
48.85; H, 3.65; N, 8.4%.
4.10. Synthesis of [Pd{(C,N)-C6H4CH2NH(t-Bu)}Cl(PPh3)] (9)
To a suspension of palladacycle 6 (0.182 g, 0.3 mmol) in dichloromethane (15 mL) was added PPh3
(0.157 g, 0.6 mmol). The resulting solution was stirred for 8 h and then filtered through a plug of MgSO4.
The filtrate was concentrated to ca. 2 mL, and n-hexane (15 mL) was added to precipitate 9 as a pale yellow
1
solid, which was collected and air-dried. Yield: 59%. IR (KBr, cm−1): ν(NH) = 3186. H NMR (CDCl3,
ppm): δ = 1.32 (s, 9H, CH3), 4.02 (d, Ha, CHaH, 2JHH = 15 Hz), 4.76 (d, Hb, CHbH, 2JHH = 15 Hz), 4.36 (br s,
3
3
3
1H, NH), 6.19 (d, 1H, C6H4, JHH = 5Hz), 6.35 (t, 1H, C6H4, JHH = 5 Hz), 6.79 (t, 1H, C6H4, JHH = 5 Hz),
6.95 (d, 1H, Ph, 3JHH = 5 Hz), 7.36 (m, 6Hm, PPh3), 7.45 (m, 3Hp, PPh3), 7.74 (m, 6Ho, PPh3). 31P {1H} NMR
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(CDCl3, ppm): δ = 40.24 (s, 1P, Pd–PPh3), 41.19 (s, 1P, Pd–PPh3). Anal. calcd. for C29H31ClNPPd: C, 61.49;
H, 5.51; N, 2.47. Found: C, 61.63; H, 5.6; N, 2.56 %.
4.10. Synthesis of [Pd{(C,N)-C6H4CH2NH(t-Bu)}Br(Me3Py)] (10)
To a suspension of palladacycle 7 (0.348 g, 0.5 mmol) in dichloromethane (15 mL) was added Me3Py
(131 ꢀL, 1 mmol). The resulting solution was stirred for 8 h and then filtered through a plug of MgSO4. The
filtrate was concentrated to ca. 2 mL, and n-hexane (15 mL) was added to precipitate 9 as a pale yellow
1
solid, which was collected and air-dried. Yield: 62%. IR (KBr, cm−1): ν(NH) = 3211, ν(C=N) = 1621. H
NMR (DMSO-d6, ppm): δ = 1.16−1.26 (m, 9H, CH3), 2.35 (m, 3H, CH3), 2.83 (s, 3H, CH3), 3.2 (s, 3H,
2
2
3
CH3), 3.91 (d, Ha, CHaH, JHH = 16 Hz), 4.28-4.33 (dd, Hb, CHbH, JHH = 14.8 Hz, JHH = 5.2 Hz), 5.49 (d,
3
1H,C6H4, JHH = 7.6 Hz ), 5.61 (br s, 1H, NH), 6.54 (t, 1H,C6H4), 6.79-6.94 (m, 2H,C6H4), 7.15 (br s, 1H, py),
7.29 (br s, 1H, py); 13C{1H} NMR (DMSO-d6, ppm): δ = 20.15, 20.29, 26.91, 27.23, 29.83, 56.31, 57.44
(Caliphatic), 120.2, 121.05, 123.6, 123.8, 124.3, 129.4, 152.1, 157.6, 158.2 (Caromatic). Anal. calcd. for
C19H27N2BrPd: C, 48.5; H, 5.79; N, 5.9. Found: C, 48.8; H, 5.65; N, 5.72%.
4.13. X-ray structure determinations
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X-ray diffraction data for 3, 4, 8 and 9 were collected at 100 K with the use of Agilent SuperNova single
crystal diffractometer and corrected for absorption using a multifaceted crystal model based on expressions
derived by Clark & Reid [23]. Data for 2 and 10 were collected at ambient temperature using a Bruker
APEX-II CCD diffractometer and corrected for absorption using the SADABS program [24]. Graphite
monochromatized Mo K(α) radiation was used for all data collections. The structures were solved by direct
methods using the SHELXS97 (for 3, 4, 8 and 9) [25] or SIR97 (for 2 and 10) [26] program and refined with
the use of the SHELXL97 program [25]. Hydrogen atoms were positioned geometrically and refined as
riding on their parent atoms during the refinement. The amine H atom of 2 and 10 were located in a
difference Fourier map and refined freely.
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Acknowledgements
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We are grateful for the financial support from the Department of Chemistry, Isfahan University of
Technology (IUT).
Appendix A. Supplementary material
CCDC 905807−12 contain the supplementary crystallographic data for 10, 2, 3, 4, 8 and, 9 respectively.
These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
033; or e-mail: deposit@ccdc.cam.ac.uk.
References
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(1999) 2683−2693.
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[13] J. Vicente, I. Saura-Llamas, J. Cuadrado, M.C. Ramírez de Arellano, Organometallics, 22 (2003)
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Goubitz, H. J. Schenk, J. Organomet. Chem. 508 (1996) 109−120.
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Organometallics, 16 (1997) 4150−4160.
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Organometallics, 22 (2003) 987−999.
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[21] J.M. Chitanda, J. Wilson Quail, S.R. Foley, J. Organomet. Chem. 694 (2009) 1542−1548.
[22] R.H. Crabtree, The Organometallic Chemistry of the Transition Metals, John Wiley & Sons, New
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[24] G. M. Sheldrick, SADABS (1996) University of Göttingen, Germany.
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Moliterni, G. Polidori, R. Spagna, J. Appl. Cryst. 32 (1999) 115−119.
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Scheme 1. (i) Pd(OAc)2 in toluene at 50°C; (ii) 1/2 Pd(OAc)2 in toluene; (iii) Complex 1 in toluene at 50°C; (iv) Excess
NaCl or NaBr in methanol; (v) Complex 5, AgBF4, 1,10-phenanthroline, THF; (vi) Complex 6, PPh3 , complex 7,
Me3Py, (dichloromethane, room temperature, 6 h).
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Table 1
Crystal data and refinement parameters for complexes 2, 3, 4, 8, 9 and 10.
2
3
4
8
9
10
Empirical Formula
Formula weight
T/K
Crystal system
C26H38N2O4Pd2 C22H30N2O4 Pd
C18H26Cl2N2Pd
447.71
100(1)
Monoclinic
P21/c
C21H20BF4N3Pd C29H31ClNPPd
C19H27BrN2 Pd
469.74
292(2)
Monoclinic
C2/c
655.38
295(2)
Monoclinic
P21/n
494.90
100(1)
Monoclinic
P21/n
507.61
566.37
100(2)
100(1)
Monoclinic
P21/n
Triclinic
P-1
Space group
/Å
b/Å
10.5589(4)
17.9393(8)
15.0885(6)
90
99.3223(6)
90
2820.3(2)
4
1.307
1.544
1328
6.75−24.28
5534
9.6680(10)
13.3890(10)
9.9240(10)
90
118.12(2)
90
1132.98(18)
2
0.847
1.445
508
3.03−27.73
2580
9.9100(1)
17.8080(2)
11.9460(2)
90
113.010(1)
90
1940.46(4)
4
1.232
1.532
912
2.94−28.92
4768
10.7340(2)
11.0010(1)
16.9660(2)
90
99.074(2)
90
1978.35(5)
4
0.989
1.704
1192
3.04−27.24
3351
9.9070(2)
14.1890(3)
20.2120(4)
75.45(2)
78.76(2)
71.23(2)
2583.58(9)
4
0.901
1.456
1160
3.01−28.99
8798
12.1947(6)
20.3995(10)
17.7565(9)
90
114.7415(7)
90
4011.7(3)
8
2.918
1.55539
1888
4.27−22.64
3749
c/Å
α/°
β/°
γ/°
V/Å3
Z
ꢀ (mm-1)
Dcal/Mg m-3
F(000)
Ranges/°
Independent reflections
Data/restraints/parameters 5534/0/323
2580/0/133
2.499
R1= 0.0268
wR2= 0.0640
R1= 0.0316
wR2= 0.0650
4768/0/216
1.323
R1= 0.0272
wR2= 0.0606
R1= 0.0274
wR2= 0.0607
3351/0/283
2.062
R1= 0.0199
wR2= 0.0474
R1= 0.0222
wR2= 0.0481
8798/0/603
0.880
R1= 0.0193
wR2= 0.0471
R1= 0.0215
wR2= 0.0486
3749/0/219
1.028
R1= 0.0242
wR2= 0.0574
R1= 0.0301
wR2= 0.0604
Goodness-of-fit on F2
Final R indices
1.089
R1= 0.0196
wR2= 0.0514
R1= 0.0209
wR2= 0.0522
R indices (all data)
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Fig. 1. X-ray thermal ellipsoid plot of complex 2. The hydrogen atoms have been omitted for clarity. Selected
bond lengths (Å), and angles (°): Pd1−C1 1.949(2), Pd1−O3 2.1725(16), Pd1−N1 2.1069(18), Pd1−O1 2.0413(15),
Pd2−C12 1.955(2), Pd2−N2 2.0724(18), Pd2−O4 2.0568(15), Pd2−O2 2.1628(15), O4−C25 1.263(3), O3−C25
1.242(3), O1−C23 1.254(3), O2−C23 1.243(3), N1−C7 1.487(3), N2−C18 1.496(3), C6−C7 1.479(3), C17−C18
1.499(3), C1−C6 1.400(3), C12−C17 1.401(3), O1—Pd1—O3 83.77(7), N1—Pd1—O3 102.38(7), C1−Pd1−N1
82.62(9), C1−Pd1−O1 91.31(8), C1−Pd1−O3 174.93(8), O1−Pd1−N1 172.69(7), Pd1−O3−C25 125.76(14),
Pd1−O1−C23 123.21(14), O4—Pd2—O2 86.84(7), N2—Pd2—O2 95.30(7), C12−Pd2−N2 83.09(8), C12−Pd2−O4
94.78(8), C12−Pd2−O2 178.35(8), O4−Pd2−N2 177.47(7), Pd2−O2−C23 128.19(14), Pd2−O4−C25 123.97(14),
O2−C23−O1 126.82(19), O3−C25−O4 127.0(2).
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Fig. 2. X-ray thermal ellipsoid plot of complex 3. The hydrogen atoms have been omitted for clarity. The
symmetry transformations used to generate equivalent atoms is (i) -x, -y, 1-z. Selected bond lengths (Å), and angles (°):
Pd1−N2 2.055(2), Pd1−O1 2.012(2), O1−Pd1−N1 83.39(10), O1−Pd1−O1i 180.000, O1−Pd1−N1i 96.61(10),
O1i−Pd1−N1 96.61(10).
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Fig. 3. X-ray thermal ellipsoid plot of complex 4. The hydrogen atoms have been omitted for clarity. Selected
bond lengths (Å) and angles (°): Pd1−N1 2.0572(19), Pd1−Cl1 2.3116(6), Pd1−N2 2.0588(19), N1−Pd1−Cl1 88.26(6),
N1−Pd1−Cl2 90.58(6).
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358
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Fig. 4. X-ray thermal ellipsoid plot of complex 8. The hydrogen atoms have been omitted for clarity. Selected
bond lengths (Å), and angles (°): Pd1−N1 2.0568(17), Pd1−N2 2.1288(17), Pd1−N3 2.0626(18), Pd1−C15 1.997(2),
C14−C15 1.411(3), C14−C13 1.495(3), N3−C13 1.498(3), N1−Pd1−N2 80.16(7), C15−Pd1−N3 80.01(8), N3−Pd1−N2
99.07(7), C15−Pd1−N3 80.01(8) N1−Pd1−N3 175.01(7), C15−Pd1−N2 176.84(7).
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Fig. 5. X-ray thermal ellipsoid plot of the two independent molecules (A and B) of complex 9. The hydrogen atoms
have been omitted for clarity. Selected bond lengths (Å), and angles (°) are given for both independent molecules.
For A: Pd1−C21 2.0101(18), Pd1−N1 2.1215(15), Pd1−Cl1 2.3996(4), Pd1−P1 2.2630(5), C21−Pd1−N1 81.56(7),
N1−Pd1−Cl1 88.84(4), P1−Pd1−Cl1 95.206(16), C21−Pd1−P1 94.19(5). For B: Pd2−C50 2.0185(18), Pd2−N2
2.1375(16), Pd2−Cl2 2.3958(4), Pd2−P2 2.2582(5), C50−Pd2−N2 82.31(7), N2−Pd2−Cl2 89.59(5), P2−Pd2−Cl2
94.600(17), C50−Pd2−P2 93.57(5).
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Fig. 6. X-ray thermal ellipsoid plot of complex 10. The hydrogen atoms have been omitted for clarity. Selected
bond lengths (Å) and angles (°):Pd1−C1 1.983(2), Pd1−N1 2.081(2), Pd1−Br1 2.5574(4), Pd1−N2 2.061(2),
C1−Pd1−N1 82.68(10), N1−Pd1−Br1 94.13(7), N2−Pd1−Br1 90.34(6), C1−Pd1−N2 92.91(9).
386
387
388
Fig. 7. Hydrogen bonding (dashed lines) between the bromine atoms and the CH2 groups of complex 10.
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Highlights:
► Ten Pd(II) complexes from secondary benzylamines were synthesized and fully characterized. ►
Molecular structures of six complexes were determined by X-ray crystallography. ► In all structures, the
palladium atom shows a distorted or slightly distorted square-planar geometry.

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Synthesis and structural studies of cyclopalladated complexes of secondary
benzylamines
Kazem Karamia, , Mahboubeh Hosseini Kharata, Corrado Rizzolib, Janusz Lipkowskic
a Department of Chemistry, Isfahan University of Technology, Isfahan, 84156/83111, Iran
bDepartment of Chemistry, University of Parma, I-43124 Parma, Italy
c Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
A new mono- and dinuclear cyclopalladated complexes derived from secondary benzylamines was
synthesized and characterized. Molecular structures of six complexes were determined by X-ray
crystallography. In all structures, the palladium atom shows a distorted or slightly distorted square-planar
geometry.
Corresponding author: Kazem Karami; Email: karami@cc.iut.ac.ir
Tel: +983113913239; fax: +983113912350

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Fig. 1. The crystal packing of 3. Dotted lines represent the intramolecular hydrogen bonding interaction.
Fig. 2. The crystal packing of 4. The adjacent molecules are linked through intermolecular N—H···Cl hydrogen
bonds (dotted lines).
Fig. 3. Part of the crystal packing of 9 with the intermolecular hydrogen bonding between molecules A and B. H
atoms not involved in hydrogen bonding (dotted lines) have been omitted for clarity.
Fig. 1. The crystal packing of 3. Dotted lines represent the intramolecular hydrogen bonding interaction.

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Fig. 2. The crystal packing of 4. The adjacent molecules are linked through intermolecular N—H···Cl hydrogen
bonds (dotted lines).
Fig. 3. Part of the crystal packing of 9 with the intermolecular hydrogen bonding between molecules A and B. H
atoms not involved in hydrogen bonding (dotted lines) have been omitted for clarity.