Synthesis and structural characterisation of Palladium(ii) complexes with N,N′,N-tridentate N′-substituted N,N-Di(2-picolyl)amines and their application to methyl methacrylate polymerisation

Article abstract of DOI:10.1071/CH13731

The reaction of [Pd(CH₃CN)₂Cl₂] with N′-substituted N,N-di(2-picolyl)amine-based ancillary ligands, for example N,N-di(2-picolyl)cyclohexylmethylamine (L1), N,N-di(2-picolyl)benzylamine (L2), N,N-di(2-picolyl)aniline (L3), and 1,4-bis[bis(2-pyridylmethyl)aminomethyl] benzene (L4), in the presence of NaClO₄ in ethanol yields a new series of [(NN′N)PdCl]X (X≤ClO₄, Cl) complexes, i.e. mononuclear [LnPdCl]ClO₄ (Ln≤L₁, L₂, L ₃) and binuclear [L₄Pd₂Cl₂]Cl ₂. X-Ray crystallographic analysis determined that the Pd atom in complexes [(NN′N)PdCl]X showed a slightly distorted square-planar geometry involving three nitrogen atoms and a chlorido ligand. Moreover, the unit cell included a ClO₄-or Cl-anion as the counterion. The complex [L1PdCl]ClO₄ showed the highest catalytic activity for the polymerisation of methyl methacrylate in the presence of modified methylaluminoxane at 60°C among the mononuclear PdII complexes. Specifically, the activity of binuclear [L₄Pd₂Cl ₂]Cl₂ was 2-fold higher than the corresponding mononuclear [L₂PdCl]ClO₄ per active palladium metal centre. CSIRO 2014.

Full text of DOI:10.1071/CH13731

CSIRO PUBLISHING
Aust. J. Chem. 2014, 67, 953–961
Full Paper
http://dx.doi.org/10.1071/CH13731
Synthesis and Structural Characterisation of Palladium(II)
Complexes with N,N9,N-Tridentate N9-Substituted
N,N-Di(2-picolyl)amines and their Application
to Methyl Methacrylate Polymerisation
A
A
A
B C
,
Sunghoon Kim, Dongil Kim, Yujin Song, Ha-Jin Lee,
A D
,
and Hyosun Lee
A
Department of Chemistry and Green-Nano Materials Research Center, Kyungpook
National University, 1370 Sankyuk-dong, Buk-gu, Daegu-city, 702-701,
Republic of Korea.
B
Jeonju Center, Korea Basic Science Institute (KBSI), 634-18 Keumam-dong, Dukjin-gu,
Jeonju-city, 561-180, Republic of Korea.
C
Department of Chemistry, Chonbuk National University, Dukjin-gu, Jeonju-city,
561-756, Republic of Korea.
D
Corresponding author. Email: hyosunlee@knu.ac.kr
The reaction of [Pd(CH3CN)2Cl2] with N0-substituted N,N-di(2-picolyl)amine-based ancillary ligands, for example N,N-di
(2-picolyl)cyclohexylmethylamine (L1), N,N-di(2-picolyl)benzylamine (L2), N,N-di(2-picolyl)aniline (L3), and 1,4-bis
[bis(2-pyridylmethyl)aminomethyl]benzene (L4), in the presence of NaClO4 in ethanol yields a new series of [(NN0N)
PdCl]X (X ¼ ClO4, Cl) complexes, i.e. mononuclear [LnPdCl]ClO4 (Ln ¼ L1, L2, L3) and binuclear [L4Pd2Cl2]Cl2. X-Ray
crystallographic analysis determined that the Pd atom in complexes [(NN0N)PdCl]X showed a slightly distorted square-
planar geometry involving three nitrogen atoms and a chlorido ligand. Moreover, the unit cell included a ClOꢀ4 or Clꢀ
anion as the counterion. The complex [L1PdCl]ClO4 showed the highest catalytic activity for the polymerisation of methyl
methacrylate in the presence of modified methylaluminoxane at 608C among the mononuclear PdII complexes.
Specifically, the activity of binuclear [L4Pd2Cl2]Cl2 was 2-fold higher than the corresponding mononuclear [L2PdCl]
ClO4 per active palladium metal centre.
Manuscript received: 3 January 2014.
Manuscript accepted: 20 February 2014.
Published online: 31 March 2014.
Introduction
for photoluminescent materials and supramolecular materi-
als,[5,9,21,27,28,37,58,59]
tions,[2,3,16,17,20,25,31,32,46–48,60]
The transition metal complexes involving ligands di(2-picolyl)
amine [bis(2-pyridylmethyl)amine] and its derivatives,
N-substituted di(2-picolyl)amine, have been extensively inves-
tigated.[1–27] This is likely attributable to the diverse structural
variations in co-ordination mode fromN,N-bidentate and N,N0,N-
tridentate to N,N0,N,X-tetradentate, in which co-ordination of
the X atom is derived from substitution on the moiety of the
pyridine ring and amine residue. For example, by introducing
various spacers between 2-picolyls on the amine moiety, poly-
dentated or multinuclear complexes with N,N0,N,X-tetradentate
have been generated.[28–37] In particular, the co-ordination
complexes of PdII and PtII with N,N-bidentate and N,N0,N-
tridentate di(2-picolyl)amine ligands are known to form very
stable mononuclear square-planar complexes,[38–49] although
the NiII complexes appeared to have diverse co-ordination
modes.[50–57] The mentioned complexes can be used for
biological
enzymatic
of
applica-
organic
catalysis
transformations,[14,30] and as catalysts for the polymerisation of
a-olefins and polar olefins.[19]
In previous studies, we reported PdII and PtII complexes with
N0-substituted N,N-di(2-picolyl)amine and their utility in the
polymerisation of methyl methacrylate (MMA).[61] Accor-
dingly, weexploredseveralstructural variationsofN0-substituted
N,N-di(2-picolyl)amine ligands, thus allowing the steric and
electronic properties of the tridentate N-donor ligands and their
PdII complexes to be adjusted, and finally investigated the
N0-substitution effect on MMA polymerisation. To the best of
our knowledge, despite many reports on metal complexes with
N0-substituted N,N-di(2-picolyl)amines and their derivatives, our
previous work was the first to examine PdII and PtII complexes
with these ligands as catalysts for MMA polymerisation.[62–70]
In this study, we extended our research on PdII with N0-
substituted N,N-di(2-picolyl)amine by synthesising, performing
important
synthetic,
kinetic,
and
spectroscopic
applications,[1,4,6–8,10–13,15,18,22–24,29,33–36,38–45,50–56] as well as
Journal compilation Ó CSIRO 2014
www.publish.csiro.au/journals/ajc

954
S. Kim et al.
R
N
R
NH2
R
N
ꢁ
ꢁ
Pd(CH3CN)2Cl2
EtOH, NaClO4
ClOꢀ4
H2O, rt, 100h
Pd
Cl
N
N
N
N
2
.
N
Cl HCl
NaOH
4
L1 (R ꢂ cyclohexylmethyl)
L2 (R ꢂ benzyl)
L3 (R ꢂ phenyl)
[L1PdCl]ClO4 (R ꢂ cyclohexylmethyl)
[L2PdCl]ClO4 (R ꢂ benzyl)
[L3PdCl]ClO4 (R ꢂ phenyl)
Cl
Pd
N
N
N
N
N
N
NH2
H2N
ꢁ
Pd(CH3CN)2Cl2
EtOH
2Clꢀ
H2O, rt, 100h
4
.
N
Cl HCl
N
N
ꢁ
NaOH
N
N
Pd
Cl
N
N
4
L4
Scheme 1. Synthesis of ligands and PdII complexes.
[L4Pd2Cl2]Cl2
X-ray structural characterisation of, and determining the cata-
lytic activities for MMA polymerisation of PdII complexes
[LnPdCl]ClO4 (Ln ¼ L1, L2, L3) and [L4Pd2Cl2]Cl.
NMR peaks for CH2-pyridine were affected by the asymmetrical
location of N0–CH2–(X) (X ¼ cyclohexyl, benzyl, phenyl) with
respect to the plane of the palladium centre. In addition, the N0–
CH2–(X) (X ¼ cyclohexyl, benzyl) proton peaks of PdII com-
plexes moved downfield as a result of binding of the N atom of
the amine to the palladium metal for [L1PdCl]ClO4 (d 2.84),
[L2PdCl]ClO4 (d 4.25), and [L4Pd2Cl2]Cl2 (d 4.33) compared
with the ligands L1 (d 2.32), L2 (d 3.63), and L4 (d 3.67).
A similar pattern for the 13C NMR peaks was observed.
13C NMR peaks for the N–CH2–pyridine carbon of the PdII
complexes shifted downfield around d 5–10 compared with the
corresponding ligands.
Results and Discussion
Synthesis and Chemical Properties
The ligands and PdII complexes were prepared using the syn-
thetic procedure as illustrated in Scheme 1. The previously
reported ligands were obtained in yields of L[11,71] (88 %), L[26]
(92 %), L[37,50] (78 %), and L[41,8] (82 %) from the starting mate-
rials cyclohexylmethylamine, benzylamine, aniline, and
p-xylylenediamine, respectively, and 2-picolylchloride hydro-
chloride in water. The [L1PdCl]ClO4 (88 %), [L2PdCl]ClO4
(95 %), [L3PdCl]ClO4 (88 %), and [L4Pd2Cl2]Cl2 (91 %) com-
plexes were obtained from the corresponding ligands with
[Pd(CH3CN)2Cl2] in anhydrous ethanol (Scheme 1).
Crystal Structures
A single crystal suitable for X-ray crystallography was obtained
from diethyl ether or acetone diffusion into dimethylformamide
or dimethyl sulfoxide (DMSO) solutions of the complexes.
Crystal data and structural refinements for PdII complexes are
summarised in Table 1. The ORTEP drawings of complexes are
shown in Fig. 1 ([L1PdCl]ClO4), Fig. 2 ([L2PdCl]ClO4), Fig. 3
([L3PdCl]ClO4), and Fig. 4 ([L4Pd2Cl2]Cl2). The selected bond
lengths and angles are listed in Table 2. The co-ordination
geometry around the PdII centre can be described as a slightly
distorted square plane consisting of the three N atoms and one Cl
atom, judging from 175.37(10)8 [N(3)–Pd(1)–Cl(1)] and 166.12
(15)8 [N(1)–Pd(1)–N(2)] for [L1PdCl]ClO4. The unit cell of
[LnPdCl]ClO4 (Ln ¼ L1, L2, L3) includes a ClO–4 anion as a
counterion, while that of [L4Pd2Cl2]Cl2 includes not only two
Cl– counterions, but also two DMSO and two water molecules.
1
The results of H NMR, 13C NMR, and elemental analyses
1
were consistent with ligand and PdII complex formulation. H
NMR peaks of the PdII complexes were shifted downfield or
upfield compared with the corresponding ligands. The resonance
ofthe CH2-pyridine protons inthe complexes wereshifted upfield
compared with the ligand as a result of a shielding effect of
the interaction between the palladium metal and N0-substitution,
N0–CH2–(X) (X ¼ cyclohexyl, benzyl, phenyl). For example,
1H NMR peaks for the CH2-pyridine protons in ligands showed
a singlet peak at d 3.78 (L1), 3.71 (L2), 4.83 (L3), and 3.81 (L4).
However, the N0–CH2–pyridine proton peaks for PdII com-
plexes appeared as two doublet peaks, e.g. [L1PdCl]ClO4 at
d 5.53 (2JH-H 16.0) and 4.48 (2JH-H 16.0), indicating that the 1H

PdII Complex Ligated by N,N0,N-Tridentate Ligand
955
Table 1. Crystal data and structural refinement for PdII complexes
Parameter
[L1PdCl]ClO4
[L2PdCl]ClO4
[L3PdCl]ClO4
[L4Pd2Cl2]Cl2
Empirical formula
Formula weight
Temperature
C19H25ClN3Pd
536.72
C19H19ClN3Pd
530.67
C39H40Cl4N6O9Pd2
1091.37
C32H32Cl2N6Pd2
1043.49
200(2) K
˚
0.71073 A
200(2) K
˚
0.71073 A
173(2) K
˚
0.71073 A
200(2) K
˚
0.71073 A
Wavelength
Crystal system
Space group
Orthorhombic
Monoclinic
Monoclinic
Monoclinic
Pccn
˚
a 14.3620(6) A
P21/c
˚
a 11.9385(7) A
I2/a
˚
a 23.1546(12) A
P21/c
˚
a 11.2951(10) A
Unit cell dimensions
˚
b 21.1589(8) A
˚
b 13.5637(8) A
˚
b 7.7596(4) A
˚
b 12.7480(11) A
˚
c 14.30465(8) A
˚
c 13.4082(7) A
˚
c 25.5623(14) A
˚
c 15.4636(13) A
a 908
b 908
g 908
a 908
b 110.1070(10)8
g 908
a 908
b 114.1000(10)8
g 908
a 908
b 105.667(2) 8
g 908
3
3
3
3
˚
˚
˚
˚
Volume, Z
4346.9(3) A , 8
2044.0(2) A , 4
4192.5(4) A , 4
2143.9(3) A , 2
Density (calculated)
Absorption coefficient
F(000)
1.640 Mg mꢀ3
1.130 mmꢀ1
2176
1.724 Mg mꢀ3
1.201 mmꢀ1
1064
1.729 Mg mꢀ3
1.175 mmꢀ1
2192
1.616 Mg mꢀ3
1.230 mmꢀ1
1052
Crystal size
0.25 ꢁ 0.24 ꢁ 0.19 mm3
1.718 to 28.308
ꢀ19 # h # 16
ꢀ28 # k # 22
ꢀ19 # l # 18
30800
0.21 ꢁ 0.16 ꢁ 0.09 mm3
1.978 to 28.298
ꢀ15 # h # 15
ꢀ18 # k # 7
ꢀ17 # l # 17
14592
0.18 ꢁ 0.09 ꢁ 0.05 mm3
1.758 to 28.308
ꢀ30 # h # 20
ꢀ10 # k # 10
ꢀ33 # l # 34
14739
0.25 ꢁ 0.19 ꢁ 0.14 mm3
2.008 to 28.318
ꢀ9 # h # 15
ꢀ16 # k # 16
ꢀ20 # l # 20
15504
y range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to y ¼ 28.308
Absorption correction
Refinement method
5400 [R(int) ¼ 0.0799]
99.9 %
5054 [R(int) ¼ 0.0358]
99.6 %
5187 [R(int) ¼ 0.0315]
99.8 %
5318 [R(int) ¼ 0.0552]
99.6 %
None
None
None
None
Full-matrix least-
squares on F2
5400/0/273
0.937
Full-matrix least-
squares on F2
5054/0/262
1.170
Semi-empirical from
equivalents
5187/0/273
Full-matrix least-
squares on F2
5318/0/246
Data/restraints/parameters
Goodness-of-fit on F2
1.187
1.163
Final R indices [I . 2s(I)]
R1 0.0427
R1 0.0413
R1 0.0516
R1 0.0670
wR2 0.0886
R1 0.0963
wR2 0.0783
R1 0.0844
wR2 0.1086
R1 0.0849
wR2 0.1645
R1 0.1250
R indices (all data)
wR2 0.1160
0.998 and ꢀ1.138
wR2 0.1365
1.640 and ꢀ2.039
wR2 0.1750
1.668 and ꢀ2.530
wR2 0.2325
1.480 and ꢀ2.047
ꢀ3
˚
Largest diff. peak and hole [e A
]
C18
C16
C19
C17
C16
C17
C18
C15
C14
C13
C15
C5
C14
C4
C6
N3
C19
C9
C7
C8
C13
C9
C3
C2
C8
N2
C10
C7
C6
N1
C10
N3
Pd1
N2
C11
C1
C5
C4
C12
C11
C12
Pd1
Cl1
N1
C3
Fig. 2. ORTEP drawing of [L2PdCl]ClO4 with thermal ellipsoids at 50 %
probability. Counter anion ClO–4 is not presented. All hydrogen atoms are
omitted for clarity.
C1
Cl1
C2
Fig. 1. ORTEP drawing of [L1PdCl]ClO4 with thermal ellipsoids at 50 %
probability. Counter anion ClO–4 is not presented. All hydrogen atoms are
omitted for clarity.
complexes, which show bond length ranges of 1.966(3)–
˚
˚
2.087(7) A for Pd–Namine and 1.995(6)–2.068(6) A for Pd–
Npyridine
[38–41,43,46–48] Although the sp3 hybridised Namine atom
The bond lengths of Pd–Namine and Pd–Npyridine for PdII
˚
complexes range from 2.023(5) to 2.037(4) A and 2.006(5) to
.
connected to three carbon atoms and a Pd atom is a stronger base
than the sp2 hybridised Npyridine, the Pd–Namine bond lengths are
˚
only 0.01 A longer than that of Pd–Npyridine and virtually no
˚
2.019(7) A, respectively. These values are in good agreement
with the bond lengths for related N,N-di(2-picolyl)amine–PdII

956
S. Kim et al.
discrimination of the two bonds is observed. Moreover, the
Namine atom is coordinated to palladium solely by a s-bond, but
the Npyridine atoms are coordinated by both a s-bond and a weak
p-back bond.
[L4Pd2Cl2]Cl2. However, the bond angles of Npyridine–Pd(1)–
Npyridine showed a slightly bent form with angles of 166.12(15)8
for [L1PdCl]ClO4, 165.7(2)8 for [L2PdCl]ClO4, 167.0(2)8 for
[L3PdCl]ClO4, and 166.2(3)8 for [L4Pd2Cl2]Cl2, which occurred
mainly because of five-membered fused ring strain, but was also
affected by the ligand environment. The average bond angles
of Namine–C(13)–C(14) in [L1PdCl]ClO4, [L2PdCl]ClO4, and
[L4Pd2Cl2]Cl2 were 113.2–116.38, which was larger than those
of Namine–C(6)–C(5) with 109.1–110.88 and Namine–C(7)–C(8)
with 108.1–111.48 because of steric repulsion between the
cyclohexyl or phenyl on the amine moiety and the palladium
plane. In addition, the bond angles of C(7)–N(3)–Pd(1) and
C(6)–N(3)–Pd(1) were 104.6(4)–107.6(2)8 and 102.4(4)–
107.2(4)8, which were significantly smaller than that of ideal
sp3 hybridisation because of ring strain caused by two two-
membered chelate rings.
The mean plane of the cyclohexyl group in [L1PdCl]ClO4
was perpendicular to the mean plane of the PdII metal in a chair
form. Also, the mean plane of the phenyl group in [L3PdCl]ClO4
was perpendicular to the mean plane of the PdII metal and two
five-membered chelate rings. However, the planes of the phenyl
group in [L2PdCl]ClO4 and [L4Pd2Cl2]Cl2 were almost parallel
to the mean plane of the two pyridine rings and PdII metal,
judging from the dihedral angle between the two planes of ,288
in [L2PdCl]ClO4 and ,268 [L4Pd2Cl2]Cl2. This is probably
attributable to p-electron interactions between the phenyl and
pyridine ring. The N(3)–C(13)–C(14) angles of [L2PdCl]ClO4
and [L4Pd2Cl2]Cl2 were 113.2(5)8 and 114.7(7)8; thus, deviation
from the parallel was ,248. The PdII complexes showed average
Namine–Pd(1)–Npyridine bond angles similar to other square-
planar PdII complexes containing two five-membered chelate
rings, with 83.68 for [L1PdCl]ClO4, 83.38 for [L2PdCl]ClO4,
84.48 for [L3PdCl]ClO4, and 83.58 for [L4Pd2Cl2]Cl2. The
Namine–Pd(1)–Cl(1) angles for the complexes were nearly linear,
at 175.37(10)8 for [L1PdCl]ClO4, 175.79(15)8 for [L2PdCl]
ClO4, 176.46(16)8 for [L3PdCl]ClO4, and 178.3(2)8 for
MMA Polymerisation
All PdII complexes could be activated with modified methyla-
luminoxane (MMAO) to polymerise MMA. Since PdII com-
plexes are cationic, their polymerisation of MMA also occurred
in the absence of MMAO. However, a traceable amount of poly
(methyl methacrylate) (PMMA) was obtained. All PdII com-
plexes yielded PMMA, with glass transition temperatures (Tgs)
ranging from 129 to 1328C. A higher Tg represents a higher
optical quality and mainly syndiotacticity of PMMA. Isotactic
PMMA, which is commercially produced by radical processes,
has a Tg of around 658C.[69] However, non-radical mediated
polymerisation of MMA is not available at this time. In this
report, the polymers were isolated as white solids and char-
acterised by gel permeation chromatography (GPC) in THF
using polystyrene standards as a reference. The molecular
weight (Mw) ranged from 61000 to 325000 g molꢀ1, with a
polydispersity index (PDI), which is defined as the Mw over the
number-average of molecular weight (Mn), value of around 3.
The tacticity of PMMA, specifically, the triad microstructure,
was identified in the range around syndiotactic (rr, d 0.85),
heterotactic (mr, d 1.02) and isotactic (mm, d 1.21) for the
C16
C17
C15
C18
C13
C14
C6
C9
C7
C10
C8
N2
C4
C5
N3
C3
Pd1
C11
C12
N1
1
C1
Cl1
methyl groups of the backbone based on H NMR spectro-
C2
scopy.[72] The results of polymerisation, including tacticity and
PDI as the average degree of polymerisation in terms of the
numbers of structural units and of molecules,[73,74] are sum-
marised in Table 3.
Fig. 3. ORTEP drawing of [L3PdCl]ClO4 with thermal ellipsoids at 50 %
probability. Counter anion ClO–4 is not presented. All hydrogen atoms are
omitted for clarity.
C9
C10
C8
C7
C13
C11
C14
N3
C15
C16
C12
N2
C6
C5
Pd1
C4
N1
Cl1
C3
C1
C2
Fig. 4. ORTEP drawing of [L4Pd2Cl2]Cl2 with thermal ellipsoids at 50 % probability. Counter anions Cl–, and
DMSO and water molecules are not presented. All hydrogen atoms are omitted for clarity.

PdII Complex Ligated by N,N0,N-Tridentate Ligand
957
To confirm the catalytic activity for MMA polymerisation of
the PdII complexes, blank polymerisation of MMA was per-
formed with [Pd(CH3CN)2Cl2] or MMAO alone at a specific
temperature. As the mononuclear complex [L1PdCl]ClO4
(4.80 ꢁ 104 g (mol Pd)ꢀ1 hꢀ1) had the highest activity and
provided PMMA with the narrowest PDI and highest Mw at
608C. The other two mononuclear complexes [L2PdCl]ClO4 and
[L3PdCl]ClO4 showed activities of 2.60 ꢁ 104 and 3.23 ꢁ 104 g
Table 2. Selected bond lengths (A) and angles (deg) of all PdII complexes
˚
[L1PdCl]ClO4
[L2PdCl]ClO4 [L3PdCl]ClO4
[L4Pd2Cl2]Cl2
Bond lengths
2.015(5) Pd(1)–N(1)
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–N(3)
Pd(1)–Cl(1)
N(3)–C(6)
N(3)–C(7)
N(3)–C(13)
2.016(3)
2.015(3)
2.025(3)
2.3011(11)
1.511(5)
1.498(5)
1.503(5)
Pd(1)–N(1)
Pd(1)–N(2)
Pd(1)–N(3)
2.007(5)
2.008(5)
2.037(4)
2.2762(17)
1.497(8)
1.511(8)
1.473(8)
Pd(1)–N(1)
2.015(8)
2.019(7)
2.031(6)
2.292(2)
1.475(11)
1.502(10)
1.513(10)
2.006(5)
2.023(5)
2.3045(16)
1.506(7)
1.506(7)
1.508(7)
Pd(1)–N(2)
Pd(1)–N(3)
Pd(1)–Cl(1)
N(3)–C(6)
N(3)–C(7)
N(3)–C(13)
Pd(1)–N(2)
Pd(1)–N(3)
Pd(1)–Cl(1)
N(3)–C(6)
N(3)–C(7)
N(3)–C(13)
Pd(1)–Cl(1)
N(3)–C(6)
N(3)–C(7)
N(3)–C(13)
Bond angles
N(1)–Pd(1)–N(3)
N(3)– Pd(1)–N(2)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
N(1)–Pd(1)–N(2)
N(3)–Pd(1)–Cl(1)
C(7)–N(3)–C(6)
C(7)–N(3)–C(13)
C(6)–N(3)–C(13)
C(7)–N(3)–Pd(1)
C(6)–N(3)–Pd(1)
C(13)–N(3)–Pd(1)
N(3)–C(13)–C(14)
N(3)–C(6)–C(5)
N(3)–C(7)–C(8)
83.16(14)
84.07(14)
96.11(11)
97.06(10)
166.12(15)
175.37(10)
112.4(3)
111.8(3)
108.3(3)
107.6(2)
103.8(2)
112.8(3)
116.3(3)
109.1(3)
111.4(3)
N(1)–Pd(1)–N(3)
N(3)– Pd(1)–N(2)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
N(1)–Pd(1)–N(2)
N(3)–Pd(1)–Cl(1)
C(7)–N(3)–C(6)
C(6)–N(3)–C(13)
C(7)–N(3)–C(13)
C(7)–N(3)–Pd(1)
C(6)–N(3)–Pd(1)
C(13)–N(3)–Pd(1)
N(3)–C(13)–C(14)
N(3)–C(6)–C(5)
N(3)–C(7)–C(8)
84.4(2)
82.2(2)
N(1)–Pd(1)–N(3)
N(3)– Pd(1)–N(2)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
N(1)–Pd(1)–N(2)
N(3)–Pd(1)–Cl(1)
C(7)–N(3)–C(6)
C(6)–N(3)–C(13)
C(7)–N(3)–C(13)
C(7)–N(3)–Pd(1)
C(6)–N(3)–Pd(1)
C(13)–N(3)–Pd(1)
C(13)–N(3)–C(6)
C(13)–N(3)–C(7)
C(6)–N(3)–C(7)
83.9(2)
84.9(2)
N(1)–Pd(1)–N(3)
N(3)– Pd(1)–N(2)
N(1)–Pd(1)–Cl(1)
N(2)–Pd(1)–Cl(1)
N(1)–Pd(1)–N(2)
N(3)–Pd(1)–Cl(1)
C(7)–N(3)–C(6)
C(6)–N(3)–C(13)
C(7)–N(3)–C(13)
C(7)–N(3)–Pd(1)
C(6)–N(3)–Pd(1)
C(13)–N(3)–Pd(1)
N(3)–C(13)–C(14)
N(3)–C(6)–C(5)
N(3)–C(7)–C(8)
83.6(3)
83.3(3)
96.97(16)
96.75(15)
165.7(2)
175.79(15)
112.7(5)
111.7(5)
108.6(4)
105.0(3)
107.2(4)
111.5(4)
113.2(5)
110.5(5)
108.1(5)
95.68(16)
95.87(17)
167.0(2)
176.46(16)
111.5(5)
112.1(5)
113.8(5)
106.6(4)
102.4(4)
109.6(3)
113.8(5)
112.1(5)
111.5(5)
96.7(2)
96.55(19)
166.2(3)
178.3(2)
112.9(6)
111.9(6)
108.7(6)
104.6(4)
105.8(5)
112.8(5)
114.7(7)
110.8(7)
110.1(6)
Table 3. Polymerisation of methyl methacrylate (MMA) by PdII complexes in the presence of modified methylaluminoxane (MMAO)
Entry CatalystA
Temp. [8C] Time [h] Yield [g]B
ActivityC (ꢁ 104)
TDg [8C]
Tacticity [%]
mm mr
MEw (ꢁ 105) Mw/MFn
[g (mol cat.)ꢀ1 hꢀ1
]
[g molꢀ1
]
rr
1
[Pd(CH3CN)2Cl2]G
60
60
60
60
60
60
25
25
25
25
25
25
0
2
0.88
0.42
1.44
0.78
0.97
0.53
0.55
0.14
0.47
0.59
0.44
0.39
0.38
0.12
0.07
0.15
0.10
0.19
2.93
1.40
4.80
2.60
3.23
10.6
1.83
0.47
1.57
1.97
1.47
1.30
1.27
0.40
0.23
0.50
0.33
0.63
131
120
129
129
128
129
130
125
131
132
128
130
129
130
123
127
128
129
7.60 22.8 69.6
0.66
0.61
8.77
4.45
2.35
9.94
0.72
1.45
0.25
1.98
0.61
1.52
9.93
3.25
0.61
1.50
3.23
0.93
2.90
2.20
1.77
1.93
1.26
1.97
2.97
1.10
1.26
2.69
1.72
1.11
1.70
2.56
2.41
1.10
2.94
1.94
2
MMAOF
2
37.2
10.9 51.9
7.40 22.3 70.3
7.00 19.9 73.1
7.70 22.3 70.0
7.30 21.3 71.4
8.80 19.7 71.5
3
[L1PdCl]ClO4
[L2PdCl]ClO4
[L3PdCl]ClO4
[L4Pd2Cl2]Cl2
[Pd(CH3CN)2Cl2]G
MMAOH
2
4
2
5
2
6
20 min
7
2
2
2
2
2
2
2
2
2
2
2
2
8
15.5
28.4 56.1
7.90 18.9 73.2
7.30 20.3 72.4
9
[L1PdCl]ClO4
[L2PdCl]ClO4
[L3PdCl]ClO4
[L4Pd2Cl2]Cl2
[Pd(CH3CN)2Cl2]G
MMAOF
10
11
12
13
14
15
16
17
18
10.1
25.3 64.6
9.00 16.8 74.2
9.20 18.9 71.9
0
11.6
28.8 59.6
29.6 59.9
20.7 66.9
[L1PdCl]ClO4
[L2PdCl]ClO4
[L3PdCl]ClO4
[L4Pd2Cl2]Cl2
0
10.5
12.4
0
0
8.10 30.9 61.0
9.50 20.6 69.9
0
A[PdII catalyst]0 ¼ 15 mmol, and [MMA]0/[MMAO]0/[PdII catalyst]0 ¼ 3100 : 500 : 1.
BYield defined as mass of dried polymer recovered.
CActivity represents g of poly(methyl methacrylate) (PMMA) (mol Pd)ꢀ1 hꢀ1
.
DTg is glass transition temperature which is determined by a thermal analyser.
EDetermined by gel permeation chromatography eluted with THF at room temperature by filtration with polystyrene calibration.
FMn refers the number-average of molecular weights of PMMA.
GBlank polymerisation, in which [Pd(CH3CN)2Cl2] was also activated by MMAO.
HBlank polymerisation accomplished solely by MMAO.

958
S. Kim et al.
(mol Pd)ꢀ1 hꢀ1, at 608C. In addition, the activity of binuclear
[L4Pd2Cl2]Cl2 (1.06 ꢁ 105 g (mol Pd)ꢀ1 hꢀ1) resulted in a 2-fold
increase in activity compared with the corresponding mononu-
clear [L2PdCl]ClO4 at 608C, based on the number of active
palladium metal centres in an equivalent molar amount of PdII
complexes. However, this activity trend was not maintained at
25 and 08C. For comparison, copper complexes with ligand
N-(2-furanylmethyl)-N-(1–3,5-dimethyl-1H-pyrazolylmethyl)-
N-(phenylmethyl)amine[69] were reported to be catalysts for
the polymerisation of MMA to yield syndiotactic PMMA with
an rr value up to 0.78. However, the conversion of MMA into
PMMA was only 30 %. Note that the conversion of [(NN0N)
PdCl]X (X ¼ ClO4, Cl) complexes, which is defined as the
mass of dried polymer recovered/mass of monomer used,
reaches up to 95 %. NiII complexes with ligands such as
pentane-2,4-diol and phenoxy-imine showed syndiotacticity
ranging from 0.73 to 0.82 with activity of 4.20 ꢁ 104 g PMMA
imine[63] and FeII complexes with pyridylmethylamine[79] were
also used as catalysts for MMA polymerisation with moderate
activity and syndiotacticity. Regarding tacticity, about the same
value of syndiotacticity in the case of using the reference
catalyst [Pd(CH3CN)2Cl2] at 60 and 258C was observed, imply-
ing that the steric or electronic effect of the ligand in PdII
complexes was not sufficient to induce non-radical-mediated
polymerisation of MMA by transition metal complexes through
a co-ordination polymerisation mechanism. However, some
contribution of a co-ordination polymerisation mechanism
may occur at 608C, and the activity and syndiotacticity was
only slightly affected by the location of the N0-substituent on the
amine moiety. The y–z plane of the cyclohexyl group in
[L1PdCl]ClO4 is perpendicular to the x–y plane of the PdII
metal. Thus, steric crowding around PdII is induced to accom-
modate a co-ordination polymerisation mechanism. Note that
this is comparable to previously reported PdII complexes con-
taining the bispyridylamine ligand, N,N-di(2-picolyl)cyclo-
heptylamine, which clearly showed the steric and electronic
effects of PdII complexes during MMA polymerisation.[61]
6.9 % weight aluminium of a toluene solution and used without
further purification. Elemental analyses (C, H, N) of the pre-
pared complexes were carried out on an elemental analyser (EA
1
1108; Carlo-Erba, Milan, Italy). H NMR (400 MHz) and 13C
NMR (100 MHz) were recorded on a Bruker Advance Digital
400 NMR spectrometer and chemical shifts were recorded in
ppm units using SiMe4 as an internal standard. The molecular
weight and molecular weight distribution of the obtained
PMMA were carried out using GPC (CHCl3, Alliance e2695;
Waters Corp., Milford, MA). Tgs were determined using a
thermal analyser (Q2000; TA Instruments, New Castle, DE).
Preparation of Ligands and PdII Complexes
N,N-Di(2-picolyl)cyclohexylmethylamine (L1),[1,71] N,N-di(2-
picolyl)benzylamine (L2),[6] N,N-di(2-picolyl)aniline (L3),[7,50]
and 1,4-bis[bis(2-pyridylmethyl)aminomethyl]benzene (L4)[1,8]
were prepared by a similar procedure as described in the indi-
cated literature. The chemical composition of the ligands was
confirmed by 1H NMR spectroscopy.
(mol Ni)ꢀ1 hꢀ1 [62,65,75–78] CoII complexes with phenoxy-
.
N,N-Di(2-picolyl)cyclohexylmethylamine(chloro)PdII
Perchlorate ([L1PdCl]ClO4)
A solution of L1 (0.15 g, 0.50 mmol) and NaClO4ꢂH2O (0.071 g,
0.50 mmol) in dried ethanol (10.0 mL) was added to a solution of
prepared anhydrous [Pd(CH3CN)2Cl2] (0.13 g, 0.50 mmol) in
dried ethanol (10.0 mL) at room temperature. Precipitation of a
yellow material occurred while stirring at room temperature for
12 h. A yellow powder was filtered off and washed with ethanol
(20.0 mL ꢁ 2), followed by washing with diethyl ether
(25.0 mL ꢁ 2) (yield 0.24 g, 89.4 %). Crystals of [L1PdCl]ClO4
suitable for X-ray analysis were obtained within 3 days from
diethyl ether diffusion into an DMF solution of [L1PdCl]ClO4.
n
max (neat)/cmꢀ1 3138(w), 3039(s), 2967(s), 1896(w), 1797(s),
1779(s), 1678(s), 1576(s), 1343(s), 1268(s), 1196(s), 1158(s),
1063(s), 996(s), 876(s), 823(s), 774(s), 693(s). dH (DMSO-d6,
400 MHz) 8.58 (d, 2H, J 8.0, –NC5H4–), 8.22 (t, 2H, J 8.0,
–NC5H4–), 7.76 (d, 2H, J 8.0, –NC5H4–), 7.64 (t, 2H, J 8.0,
–NC5H4–), 5.53(d, 2H, J 16.0, –NCH2–NC5H4–), 4.48 (d, 2H,
J 16.0, –NCH2–NC5H4–), 2.84 (d, 2H, J 5.2, –NCH2–C6H11–),
2.36 (m, 3H, –C6H11–), 1.17 (m, 2H, –C6H11–), 1.01 (m, 5H,
–C6H11–). dC (DMSO-d6, 100 MHz) 165.31 (s, 2C, ipso-
NC5H4–), 150.50 (s, 2C, –NC5H4–), 142.03 (s, 2C, –NC5H4–),
125.57 (s, 2C, –NC5H4–), 123.75 (s, 2C, –NC5H4–), 70.33
(s, 2C, –NCH2–NC5H4–), 67.63 (s, 1C, –NCH2–C6H11–), 35.16
(s, 1C, ipso-C6H11–), 32.57 (s, 2C, m-C6H11–), 25.76 (s, 1C,
p-C6H11–), 25.60 (s, 2C, o-C6H11–). Found: C 42.22, H 4.66,
N 7.81 %. Anal. calc. for [C19H25ClN3Pd]ClO4: C 42.52, H 4.69,
N 7.83 %.
Conclusion
We investigated the synthesis and X-ray crystallographic
structures of mononuclear [LnPdCl]ClO4 (Ln ¼ L1, L2, L3) and
binuclear [L4Pd2Cl2]Cl2, which were prepared by the substitu-
tion reaction of [Pd(CH3CN)2Cl2] with N0-substituted N,N-di(2-
picolyl)amino ligands. The co-ordination geometry around the
PdII centre was slightly distorted square planar. The complex
[L1PdCl]ClO4 showed the highest catalytic activity for MMA
polymerisation at 608C among the mononuclear PdII complexes.
Moreover, the activity of binuclear [L4Pd2Cl2]Cl2 was 2-fold
higher than the corresponding mononuclear [L2PdCl]ClO4.
N,N-Di(2-picolyl)benzylamine(chloro)PdII Perchlorate
([L2PdCl]ClO4)
Experimental
The complex [L2PdCl]ClO4 was prepared according to a similar
procedure described for complex [L1PdCl]ClO4 except using L2
(0.15 g, 0.50 mmol). A yellow powder was filtered off and
washed with ethanol (20.0 mL ꢁ 2), followed by washing with
diethyl ether (25.0 mL ꢁ 2) (yield 0.25 g, 94.2 %). Crystals of
[L2PdCl]ClO4 suitable for X-ray analysis were obtained within
5 days from diethyl ether diffusion into a DMF solution of the
complex [L2PdCl]ClO4. nmax (neat)/cmꢀ1 3134(w), 3011(s),
2865(s), 1885(w), 1783(s), 1639(s), 1599(s), 1469(s), 1393(s),
1366(s), 1253(s), 1236(s), 1039(s), 994(s), 893(s), 816(s),
768(s), 743(s), 713(s). dH (DMSO-d6, 400 MHz) 8.40 (d, 2H,
Physical Measurement
PdCl2,
2-picolylchloride
hydrochloride,
cyclohex-
ylmethylamine, benzylamine, aniline, p-xylylenediamine,
NaClO4ꢂH2O, NaOH, and MMA were purchased from Aldrich
and anhydrous solvents such as ethanol, DMF, diethyl ether,
acetonitrile, and dichloromethane were purchased from Merck
and used without further purification. [Pd(CH3CN)2Cl2] was
prepared by the literature method.[80] Deionised water was
purified using a Millipore Milli-Q water system (Bedford, MA).
MMAO was purchased from Tosoh Finechem Corporation as a

PdII Complex Ligated by N,N0,N-Tridentate Ligand
959
J 7.8, –NC5H4–), 8.05 (t, 2H, J 8.0, –NC5H4–), 7.81 (m, 2H,
o-C6H5–), 7.61 (d, 2H, J 8.0, –NC5H4–), 7.47 (t, 2H, J 7.4,
–NC5H4–), 7.14 (m, 3H, m–, p–C6H5–), 5.54 (d, 2H, J 16.0,
–NCH2–NC5H4–), 4.64 (d, 2H, J 16.0, –NCH2–NC5H4–), 4.25
(s, 2H, –NCH2–C6H5). dC (DMSO-d6, 100 MHz) 165.27 (s, 2C,
–NC5H4–), 150.28 (s, 2C, –NC5H4–), 141.35 (s, 2C, –NC5H4–),
132.74 (s, 1C, ipso-C6H5–), 132.39 (s, 2C, o-C6H5–), 129.45
(s, 2C, m-C6H5–), 128.79 (s, 1C, p-C6H5–), 124.88 (s, 2C,
–NC5H4–), 123.64 (s, 2C, –NC5H4–), 67.37 (s, 2C, –NCH2–
NC5H4–), 66.45 (s, 1C, –NCH2–C6H5). Found: C 42.81, H 3.65,
N 8.11 %. Anal. Calc. for [C19H19ClN3Pd]ClO4: C 43.00,
H 3.61, N 7.92 %.
X-Ray Crystallographic Studies
The crystal for analysis was picked up with paraffin oil and
mounted on a Bruker SMART CCD diffractometer equipped
with a graphite-monochromated MoKa (l 0.71073 A) radiation
˚
source and a nitrogen cold stream. Data collection and inte-
gration were performed with SMART (Bruker, 2000) and
SAINT-Plus (Bruker, 2001) software.[81] Semiempirical
absorption corrections based on equivalent reflections were
applied by SADABS.[82] The structure was solved by direct
methods and refined by full-matrix least-squares on F2 using
SHELXTL.[83] All non-hydrogen atoms were refined aniso-
tropically, and hydrogen atoms were added to their geometri-
cally ideal positions. The crystal and structure refinement data
for all of the structures are summarised in Table 1. CCDC
979076–979079 contains the supplementary crystallographic
data for complexes [L1PdCl]ClO4, [L2PdCl]ClO4, [L3PdCl]
ClO4, and [L4Pd2Cl2]Cl2. 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: (þ44) 1223-336-033; or
email: deposit@ccdc.cam.ac.uk.
N,N-Di(2-picolyl)aniline(chloro)PdII Perchlorate
([L3PdCl]ClO4)
The complex [L3PdCl]ClO4 was prepared according to a similar
procedure described for complex [L1PdCl]ClO4 using L3
(0.14 g, 0.50 mmol). A yellow powder was filtered and washed
with ethanol (20.0 mL ꢁ 2), followed by washing with diethyl
ether (25.0 mL ꢁ 2) (0.25 g, 96.8 %). Crystals of [L3PdCl]ClO4
suitable for X-ray analysis were obtained within 5 days from
diethyl ether diffusion into a DMF solution of the complex. nmax
(neat)/cmꢀ1 3147(w), 3126(s), 2956(s), 1876(w), 1565(s), 1432
(s), 1416(s), 1321(s), 1235(s), 1211(s), 1179(s), 1083(s), 988(s),
893(s), 879(s), 798(s), 769(s), 716(s). dH (DMSO-d6, 400 MHz)
8.58 (d, 2H, J 7.8, –NC5H4–), 8.27 (t, 2H, J 8.0, –NC5H4–), 7.99
(m, 2H, m–C6H5–), 7.75 (d, 2H, J 8.0, –NC5H4–), 7.63 (t, 2H,
J 7.4, –NC5H4–), 7.22 (m, 3H, o-, p-C6H5–), 5.36 (d, 2H, J 16.0,
–NCH2–NC5H4–), 4.48 (d, 2H, J 16.0, –NCH2–NC5H4–), 4.33
(s, 2H, –NCH2–C6H5). dC (DMSO-d6, 100 MHz) 167.39 (s, 2C,
ipso-NC5H4–), 156.67 (s, 2C, –NC5H4–), 148.39 (s, 2C,
–NC5H4–), 138.11 (s, 1C, ipso-C6H5–), 135.44 (s, 2C, m-C6H5–),
130.23 (s, 1C, p-C6H5–), 129.01 (s, 2C, o-C6H5–), 125.38 (s, 2C,
–NC5H4–), 124.88 (s, 2C, –NC5H4–), 67.49 (s, 2C, –NCH2–
NC5H4–). Found: C 41.69, H 3.59, N 8.01 %. Anal. Calc. for
[C18H17ClN3Pd]ClO4: C 41.84, H 3.32, N 8.13 %.
Catalytic Activity
In a Schlenk line, the complex (15 mmol, 8.4 mg for [L1PdCl]
ClO4, 8.0 mg for [L2PdCl]ClO4, 7.8 mg for [L3PdCl]ClO4, and
12.8 mg for [L4Pd2Cl2]Cl2) was dissolved in dried toluene
(10.0 mL) followed by the addition of MMAO (3.25 mL,
7.50 mmol) as a co-catalyst. The solution was stirred for 20 min
at 0–608C. MMA (5.0 mL, 47.1 mmol) was added to the above
reaction mixture and stirred for 20–120 min to obtain a viscous
solution. Methanol (3.0 mL) was added to terminate the poly-
merisation. The reaction mixture was poured into a large
quantity of MeOH (500 mL), and 35 % HCl (5.0 mL) was
injected to remove the remaining co-catalyst. PMMA was
obtained by filtration and was dried under vacuum at mild
temperature for 24 h.
Acknowledgements
1,4-Bis[bis(2-pyridylmethyl)aminomethyl]benzene(chloro)
PdII Chloride ([L4Pd2Cl2]Cl2)
This research was supported by the National Research Foundation of Korea
(NRF), funded by the Ministry of the Education, Science, and Technology
(MEST) (Grant No. 2012-R1A2A2A01045730).
The complex [L4Pd2Cl2]Cl2 was prepared according to a similar
procedure described for complex [L1PdCl]ClO4 except not
adding NaClO4 and using L4 (0.25 g, 0.50 mmol). A yellow
powder was filtered off and washed with ethanol (20.0 mL ꢁ 2),
followed by washing with diethyl ether (25.0 mL ꢁ 2) (yield
0.19 g, 43.0 %). Crystals of [L4Pd2Cl2]Cl2 suitable for X-ray
analysis were obtained within 5 days from acetone diffusion into
a DMSO solution of the complex. nmax (neat)/cmꢀ1 3111(w),
2996(s), 2863(s), 1877(w), 1681(s), 1623(s), 1551(s), 1480(s),
1296(s), 1244(s), 1178(s), 1041(s), 993(s), 893(s), 844(s), 789(s),
687(s), 655(s). dH (DMSO-d6, 400 MHz) 8.38 (d, 4H, J 7.6,
–NC5H4–), 8.04 (t, 4H, J 8.0, –NC5H4–), 7.60 (d, 4H, J 8.0,
–NC5H4–), 7.59 (s, 4H, –C6H4–), 7.45 (t, 4H, J 6.0, –NC5H4–),
5.50 (d, 4H, J 16.0, –NCH2–NC5H4–), 4.49 (d, 4H, J 16.0,
–NCH2–NC5H4–), 4.13 (s, 4H, –NCH2–C6H4–). dC (DMSO-d6,
100 MHz) 164.93 (s, 4C, –NC5H4–), 150.38 (s, 4C, –NC5H4–),
141.41 (s, 4C, –NC5H4–), 132.90 (s, 2C, ipso-C6H4–), 132.69
(s, 4C, o-, m-C6H4–), 124.96 (s, 4C, –NC5H4–), 123.79
(s, 4C, –NC5H4–), 66.83 (s, 2C, –NCH2–NC5H4–), 64.98 (s, 1C,
–NCH2–C6H4–). Found: C 41.85, H 3.98, N 8.28 %. Anal.
Calc. for [C32H32Cl2N6Pd2]Cl2ꢂDMSOꢂH2O: C 42.21, H 4.17,
N 8.69 %.
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