Palladium(II) complexes with N,N′-bidentate N-methyl-N-(pyridin-2-ylmethyl)aniline and its derivatives: Synthesis, characterization, and methyl methacrylate polymerization

Article abstract of DOI:10.1002/bkcs.10119

The N,N′-bidentate [(N,N′)PdCl₂] complexes [i.e., [L_nPdCl₂] (L_n = L₁-L₅)] were synthesized by the reaction of [Pd(CH₃CN)₂Cl₂] with N-methyl-N-(pyridin-2-ylmethyl)aniline (L₁) and its derivatives (L₂-L₅) in ethanol. The molecular structures of [L_nPdCl₂] (L_n = L₁-L₃) were characterized using X-ray crystallography, which showed that the Pd atom in the Pd(II) complexes had a square planar geometry involving two nitrogen atoms of N,N′-bidentate and two chlorido ligands. The complexes [L_nPdCl₂] (L_n = L₁-L₅) were investigated for methyl methacrylate (MMA) polymerization in the presence of modified methylaluminoxane (MMAO) at 60°C. Specifically, complex [L₁PdCl₂] showed moderate catalytic activity toward MMA polymerization with an activity of 3.03 × 10⁴ g poly(methylmethacrylate) (PMMA)/mol Pd·h and PMMA syndiotacticity (characterized by ¹H NMR spectroscopy) of ～0.68.

Full text of DOI:10.1002/bkcs.10119

Article
DOI: 10.1002/bkcs.10119
BULLETIN OF THE
S. Kim et al.
KOREAN CHEMICAL SOCIETY
Palladium(II) Complexes with N,N0-Bidentate N-Methyl-N-(pyridin-2-
ylmethyl)aniline and its Derivatives: Synthesis, Characterization, and
Methyl Methacrylate Polymerization
†,
Sunghoon Kim,† Yujin Song,† Ha-Jin Lee,‡ Jongho Jeon,§ Sang Hyun Park,§, and Hyosun Lee
*
*
†Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National University,
Daegu-city 702-701, Republic of Korea. *E-mail: hyosunlee@knu.ac.kr
‡Jeonju Center, Korea Basic Science Institute (KBSI), Jeonju-city 561-180, Republic of Korea
§Research Division for Biotechnology, Advanced Radiation Technology Institute, Korea Atomic Energy
Research Institute (KAERI), Jeonbuk 580-185, Republic of Korea. *E-mail: parksh@kaeri.re.kr
Received October 1, 2014, Accepted November 27, 2014, Published online January 23, 2015
The N,N0-bidentate [(N,N0)PdCl2] complexes [i.e., [LnPdCl2] (Ln = L1–L5)] were synthesized by the reaction
of [Pd(CH3CN)2Cl2] with N-methyl-N-(pyridin-2-ylmethyl)aniline (L1) and its derivatives (L2–L5) in etha-
nol. The molecular structures of [LnPdCl2] (Ln = L1–L3) were characterized using X-ray crystallography,
which showed that the Pd atom in the Pd(II) complexes had a square planar geometry involving two nitrogen
atoms of N,N0-bidentate and two chlorido ligands. The complexes [LnPdCl2] (Ln = L1–L5) were investigated
for methyl methacrylate (MMA) polymerization in the presence of modified methylaluminoxane (MMAO) at
60 ꢀC. Specifically, complex [L1PdCl2]showed moderate catalytic activitytoward MMA polymerization with
an activity of 3.03 × 104 g poly(methylmethacrylate) (PMMA)/mol Pdꢁh and PMMA syndiotacticity (charac-
terized by 1H NMR spectroscopy) of ~0.68.
Keywords: N-Methyl-N-(pyridin-2-ylmethyl)aniline, Palladium(II) complex, Induced chirality, MMA
polymerization, Syndiotacticity
Introduction
pyridylmethyl units. At the same time, another chirality ori-
ginates from the nonplanar chelating ring of pyridine and
five-membered metallocycle, adopting two conformations
of δ and λ.
Transition-metal complexes with pyridylmethylamines
have been extensively studied in the areas of synthesis,
structure, and spectroscopy1–16 as catalysts for organic
transformation,17–24 biological applications,25–28 and olefin
polymerization.29–32 These ligands are popular because of
their easy synthesis and versatile modification through the
introduction of substituents on the amine residue on either
pyridyl unit. Specifically, structural variations have been
observed in group 10 [nickel (Ni), palladium (Pd), platinum
(Pt)] with pyridylmethylamines and their derivatives. For
example, Ni complexes exist as tetrahedral to octahedral
monomers or dimers, each of which has two ligand units
coordinated to Ni metal, achieving a five- or six-coordinated
geometry.31,33–40 In contrast, Pd and Pt complexes mainly
appear with a monomeric square-planar geometry.32,41–47
These variations result in abundant pyridylmethylamines
and analogs in the transition-metal complexes having chem-
ical applications. For N-methyl-N-(pyridin-2-ylmethyl)ani-
line, its derivative ligands, and their Pd(II) complexes, the
diastereotopic methylene unit in the Pd(II) complexes is
more distinguished from the ligands. Moreover, Pd(II) com-
plexation with these ligands induced chirality (i.e., R or S
configuration) on the amine nitrogen atom bonded to four
different substituents, such as methyl, phenyl, Pd, and
To the best of our knowledge, despite abundant previous
reports on group 10 metals with pyridylmethylamines and
their derivatives, little is known regarding Pd(II) complexes
with specific N,N0-bidentate N-methyl-substituted pyridyl-
methylamines29,43,48 as catalysts for methyl methacrylate
(MMA) polymerization. Regarding coordination polymeriza-
tion of MMA mediated by transition-metal complexes, few
reports have explored Pd(II) and Pt(II) complexes as catalysts
for MMA polymerization.49,50 In addition, we explored the
effect of a chiral environment of Pd(II) complexes with N-
methyl-N-(pyridin-2-ylmethyl)aniline derivatives on control-
ling the tacticity of poly(methylmethacrylate) (PMMA).
Thus, we report the preparation of N,N0-bidentate N0-
methyl-substituted pyridylmethylaniline ligands, i.e.,
N-methyl-N-(pyridin-2-ylmethyl)aniline (L1), N,4-dimethyl-
N-(pyridin-2-ylmethyl)aniline (L2), 4-fluoro-N-methyl-N-
(pyridin-2-ylmethyl)aniline (L3), 2,6-diethyl-N-methyl-N-
(pyridin-2-ylmethyl)aniline (L4), 2,4,6-tetramethyl-N-(pyri-
din-2-ylmethyl)aniline (L5), and their Pd(II) complexes, as
well as their molecular structures. Moreover, the catalytic
activity of Pd(II) complexes for MMA polymerization in tol-
uene are investigated at 60 ꢀC.
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Experimental
KOREAN CHEMICAL SOCIETY
140.86, 135.86, 133.84, 132.84, 128.44, 49.86, 45.81. IR (liq-
uid neat; cm−1): 3033 (w), 2988 (s), 2863 (s), 1657 (w), 1569
(s), 1561 (s), 1522 (s), 1436 (s), 1384 (s), 1344 (s), 1258 (s),
1264 (s), 1189 (s), 1033 (s), 1024 (s), 991 (s), 899 (s), 831 (s),
822 (s), 756 (s), 667 (s).
Materials and Instrumentation. [PdCl2], 2-pyridinecar-
boxaldehyde, aniline, 2,4,6-trimethylaniline, 2,6-diethylani-
line, 4-fluoroaniline, p-toluidine, magnesium sulfate, and
methyl methacrylate (MMA) were purchased from Aldrich
(St. Louis, MO, U.S.A.), and anhydrous solvents such
as C2H5OH, DMF, diethyl ether, dichloromethane were
purchased from Merck (Frankfurter Straße 250, 64293
Darmstadt, Deutschland), and used without further purifica-
tion. Modified methylaluminoxane (MMAO) was purchased
from Tosoh Finechem Corporation (Shiba, Minato-Ku,
Tokyo, JAPAN) as 6.9% weight aluminum of a toluene solu-
tion. Elemental analyses (C, H, N) of complexes were carried
out on an elemental analyzer (EA 1108; Carlo-Erba, Milan,
Italy). 1H NMR (operating at 400 MHz) and 13C NMR (operat-
ing at 100 MHz) spectra were recorded on a Bruker Advance
Digital 400 NMR spectrometer (Billerica, MA 01821-3991,
USA); chemical shifts were recorded in ppm units (δ) relative
to SiMe4 as the internal standard. Infrared (IR) spectra were
recorded on Bruker FT/IR-Alpha as neat, and the data are
reported in reciprocal centimeters. The molecular weight and
molecular weight distribution of the poly(methylmethacrylate)
(PMMA) were carried out using gel permeation chromatogra-
phy (GPC) (CHCl3, Alliance e2695; Waters Corp., Milford,
MA, USA). Glass transition temperature (Tg) was determined
by differential scanning calorimetry (DSC, Q2000; TA
Instruments, New Castle, DE, USA).
N-Methyl-N-(pyridin-2-ylmethyl)aniline (L1): To ani-
line (2.49 mL, 0.0200 mol) in dichloromethane (20.0 mL)
was added 2-pyridinecarboxaldehyde (1.90 mL, 0.0200 mol)
in dichloromethane (20.0 mL). After 24 h of stirring at room
temperature, the dichloromethane solution was dried over
the MgSO4. Then, MgSO4 was filtered and the solvent was
removed under reduced pressure. Crude N-phenyl-1-(pyri-
din-2-yl)methanimine was reduced by sodium borohydride
(2.0 equiv, 1.51 g, 0.0400 mol) in anhydrous methanol
(30.0 mL). The reaction mixture was stirred at room tempera-
ture for 24 h and the solvent was removed under reduced pres-
sure. Iodomethane (1.1 equiv, 1.36 mL, 0.0220 mol) was
added to crude N-(pyridin-2-ylmethyl)aniline in dichloro-
methane (30.0 mL) by a syringe. The reaction mixture was
stirred at room temperature for 24 h, and lithium hydroxide
(1.1 equiv, 0.530 g, 0.0220 mol) was added to the reaction
solution. The reaction mixture was stirred at room temperature
for 4 h and the solid residue was filtered off. The solvent was
removed under reduced pressure and vacuum distilled to
obtain a light red oil (3.14 g, 79.2%). Analysis calculated
for C13H14N2: C, 78.8%; H, 7.12%; N, 14.1%. Found: C,
N,4-Dimethyl-N-(pyridin-2-ylmethyl)aniline (L2): L2
was prepared by a method analogous to that described for
L1 except for utilizing p-toluidine (2.14 g, 0.0200 mol) and
2-pyridinecarboxaldehyde (1.90 mL, 0.0200 mol). The prod-
uct was obtained as a light red oil (2.98 g, 70.2%). Analysis
calculated for C14H16N2: C, 79.2%; H, 7.60%; N, 13.2%.
1
Found: C, 79.4%; H, 7.29%; N, 12.8%. H NMR (CDCl3,
400 MHz): δ 8.53 (d, 1H, J = 7.6 Hz, NC5H4 ), 7.77 (d,
1H, J = 7.6 Hz, −NC5H4 ), 7.59 (d, 1H, J = 7.7 Hz,
NC5H4 ), 7.54 (t, 1H, J = 7.7 Hz, NC5H4 ), 7.03 (d,
2H, J = 7.5 Hz o CH3C6H4 ), 6.83 (d, 2H, J = 7.7 Hz, m-
CH3C6H4 ), 4.41 (s, 3H, CH3NC6H4CH3 ), 3.94 (s, 2H,
CH2NC5H4 ), 2.94 (s, 3H, CH3C6H4 ). 13C NMR
(CDCl3, 100 MHz): δ 159.88, 157.23, 151.59, 133.86,
132.88, 130.65, 129.70, 128.44, 118.84, 50.88, 49.90,
23.81. IR (liquid neat; cm−1): 3035 (w), 2999 (s), 2853 (s),
1657 (w), 1534 (s), 1513 (s), 1491 (s), 1461 (s), 1355 (s),
1376 (s), 1191 (s), 1147 (s), 1139 (s), 1021 (s), 1011 (s),
996 (s), 889 (s), 843 (s), 821 (s), 757 (s), 669 (s).
4-Fluoro-N-methyl-N-(pyridin-2-ylmethyl)aniline (L3):
L3 was prepared by a method analogous to that described
for L1 except for utilizing 4-fluoroaniline (1.89 mL, 0.0200
mol) and 2-pyridinecarboxaldehyde (1.90 mL, 0.0200 mol).
The product was obtained as a light red oil (2.66 g, 61.5%).
Analysis calculated for C13H13FN2: C, 72.2%; H, 6.06%; N,
1
13.0%. Found: C, 71.7%; H, 6.04%; N, 12.7%. H NMR
(CDCl3, 400 MHz): δ 8.51 (d, 1H, J = 7.6 Hz, NC5H4 ),
7.97 (d, 1H, J = 7.6 Hz, NC5H4 ), 7.69 (d, 1H, J = 7.7
Hz, NC5H4 ), 7.49 (t, 1H, J = 7.7 Hz, NC5H4 ), 7.13
(d, 2H, J = 7.6 Hz, o-C6H4F ), 6.94 (d, 2H, J = 7.5 Hz, m-
C6H4F ), 4.41 (s, 3H, CH3NC6H4F ), 3.94 (s, 2H,
CH2NC5H4 ). 13C NMR (CDCl3, 100 MHz): δ 161.74,
159.33, 156.59, 133.99, 132.88, 130.65, 129.70, 127.44,
118.84, 51.38, 48.96. IR (liquid neat; cm−1): 3057 (w),
3011 (s), 2969 (s), 1718 (w), 1695 (s), 1654 (s), 1500 (s),
1464 (s), 1416 (s), 1291 (s), 1236 (s), 1146 (s), 1012 (s),
976 (s), 897 (s), 833 (s), 761 (s), 619 (s).
2,6-Diethyl-N-methyl-N-(pyridin-2-ylmethyl)aniline (L4):
L4 was prepared by a method analogous to that described for
L1 except for utilizing 2,6-diethylaniline (2.81 mL, 0.0200
mol) and 2-pyridinecarboxaldehyde (1.90 mL, 0.0200 mol).
The product was obtained as light red oil (2.88 g, 56.6%).
Analysis calculated for C17H22N2: C, 80.3%; H, 8.72%; N,
1
11.0%. Found: C, 79.8%; H, 8.37%; N, 11.4%. H NMR
1
78.5%; H, 7.09%; N, 14.3%. H NMR (CDCl3, 400 MHz):
(CDCl3, 400 MHz): δ 8.56 (d, 1H, J = 7.6 Hz, NC5H4 ),
8.16 (d, 1H, J = 7.8 Hz, NC5H4 ), 8.11 (t, 1H, J = 7.8 Hz,
NC5H4 ), 7.82 (d, 1H, J = 7.8 Hz, NC5H4 ), 6.58 (m,
δ 8.55 (d, 1H, J = 7.8 Hz, NC5H4 ), 7.77 (d, 1H, J = 7.8
Hz, NC5H4 ), 7.63 (t, 1H, J = 7.6 Hz, NC5H4 ), 7.12
(t, 1H, J = 7.8 Hz, NC5H4 ), 6.74 (t, 4H, J = 7.8 Hz, o-,
m-C6H5 ), 6.58 (s, 1H, p-C6H5 ), 4.31 (s, 3H,
CH3NC6H5 ), 3.94 (s, 2H, −CH2NC5H4 ). 13C NMR
(CDCl3, 100 MHz): δ 161.11, 158.31, 153.55, 153.89,
3H,
(CH3CH2)2C6H3 ), 4.94 (s, 3H,
CH3N
(CH3CH2)2C6H3 ), 4.64 (s, 2H, CH2NC5H4 ), 1.94 (q,
4H, J = 11.0 Hz (CH3CH2)2C6H3 ), 1.72 (t, 6H, J = 11.5
Hz, (CH3CH2)2C6H3 ). 13C NMR (CDCl3, 100 MHz):
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KOREAN CHEMICAL SOCIETY
δ 159.12, 155.33, 152.55, 138.89, 137.86, 136.86, 132.84,
131.74, 128.44, 52.86, 49.86, 23.00, 21.81. IR (liquid neat;
cm−1): 3057 (w), 3031 (s), 2966 (s), 1659 (s), 1533 (s), 1521
(s), 1470 (s), 1406 (s), 1281 (s), 1246 (s), 1046 (s), 1012 (s),
972 (s), 960 (s), 897 (s), 838 (s), 833 (s), 761 (s), 619 (s).
2,4,6-Tetramethyl-N-(pyridin-2-ylmethyl)aniline (L5):
L5 was prepared by a method analogous to that described
for L1 except for utilizing 2,4,6-trimethylaniline (2.81 mL,
0.0200 mol) and 2-pyridinecarboxaldehyde (1.90 mL,
0.0200 mol). The product was obtained as a light red oil
(3.12 g, 64.9%). Analysis calculated for C16H20N2: C,
80.0%; H, 8.39%; N, 11.7%. Found: C, 79.1%; H, 8.27%;
by diethyl ether (10.0 mL × 2) to give a yellow solid (150 mg,
77.0%). Crystals for X-ray analysis of [L2PdCl2] were
obtained within 5 days from diethyl ether (10.0 mL) diffusion
into a DMF solution (10.0 mL) of [L2PdCl2] (50.0 mg). Anal-
ysis calculated for C14H16Cl2N2Pd : C, 43.2%; H, 4.14%; N,
1
7.19%. Found: C, 43.1%; H, 4.11%; N, 7.00%. H NMR
(DMSO-d6, 400 MHz): δ 8.55 (d, 1H, J = 7.6 Hz, NC5H4 ),
7.87 (d, 1H, J = 7.6 Hz, NC5H4 ), 7.60 (d, 1H, J = 7.7 Hz,
NC5H4 ), 7.44 (t, 1H, J = 7.7 Hz, NC5H4 ), 7.13 (d, 2H,
J = 7.6 Hz o-CH3C6H4 ), 6.93 (d, 2H, J = 7.4 Hz, m-
CH3C6H4 ), 4.31 (s, 3H, CH3NC6H4 CH3 ), 4.14 (d,
2
2
1H, J = 15.2 Hz, CH2-NC5H4 ), 4.01 (d, 1H, J = 15.6
Hz, CH2 NC5H4 ), 2.93 (s, 3H, CH3C6H4 ). 13C
NMR (DMSO-d6, 100 MHz): δ 161.34, 158.11, 153.59,
134.89, 133.48, 131.65, 128.67, 126.44, 117.84, 51.01,
48.91, 22.99. IR (solid neat; cm−1): 3034 (w), 2993 (s),
2854 (s), 1655 (w), 1541 (s), 1512 (s), 1489 (s), 1462 (s),
1354 (s), 1374 (s), 1193 (s), 1148 (s), 1134 (s), 1022 (s),
1019 (s), 995 (s), 890 (s), 844 (s), 823 (s), 756 (s), 668 (s).
4-Fluoro-N-methyl-N-(pyridin-2-ylmethyl)aniline
(dichloro)palladium(II) ([L3PdCl2]): [L3PdCl2] was pre-
pared according to a procedure similar to that described for
[L1PdCl2] except for utilizing L3 (108 mg, 0.500 mmol)
and [Pd(CH3CN)2Cl2] (130 mg, 0.500 mmol). The solid res-
idue was filtered and washed with ethanol (10.0 mL × 2) fol-
lowed by diethyl ether (10.0 mL × 2) to give a yellow solid
(139 mg, 70.6%). Crystals for X-ray analysis of [L3PdCl2]
were obtained within 5 days from diethyl ether (10.0 mL) dif-
fusion into a DMF solution (10.0 mL) of [L3PdCl2] (50 mg).
Analysis calculated for C13H13Cl2FN2Pd: C, 39.7%; H,
3.33%; N, 7.12%. Found: C, 39.5%; H, 3.30%; N, 7.01%.
1H NMR (DMSO-d6, 400 MHz): δ 8.61 (d, 1H, J = 7.6 Hz,
NC5H4 ), 8.01 (d, 1H, J = 7.6 Hz, NC5H4 ), 7.79 (d,
1
N, 11.5%. H NMR (CDCl3, 400 MHz): δ 8.49 (d, 1H, J =
7.6 Hz, NC5H4 ), 8.17 (d, 1H, J = 7.8 Hz, NC5H4 ),
8.13 (t, 1H, J = 7.8 Hz, NC5H4 ), 7.82 (d, 1H, J = 7.8 Hz,
NC5H4 ), 6.58 (s, 2H, (CH3)3C6H2 ), 4.89 (s, 2H,
CH2NC5H4 ), 4.64 (s, 3H, CH3N(CH3)3C6H2 ), 1.94
(s, 3H, (CH3)3C6H2 ), 1.72 (s, 6H, (CH3)3C6H2 ). 13C
NMR (CDCl3, 100 MHz): δ 159.12, 155.33, 152.55,
138.89, 137.86, 136.86, 132.84, 131.74, 128.44, 52.86,
50.66, 23.00, 21.81. IR (liquid neat; cm−1): 3066 (w), 3031
(w), 1708 (w), 1696 (s), 1658 (s), 1533 (s), 1521 (s), 1470
(s), 1406 (s), 1281 (s), 1246 (s), 1046 (s), 1012 (s), 972 (s),
960 (s), 897 (s), 838 (s), 833 (s), 761 (s), 619 (s).
N-Methyl-N-(pyridin-2-ylmethyl)aniline(dichloro)pal-
ladium(II) ([L1PdCl2]): A solution of L1 (99.0 mg, 0.500
mmol) inanhydrous ethanol(10.0 mL) wasaddedtoasolution
of anhydrous [Pd(CH3CN)2Cl2]51,52 (130 mg, 0.500 mmol)
in anhydrous ethanol (10.0 mL). The reaction mixture was
stirred for 12 h at room temperature, and the solid residue
was filtered. The solid was washed with ethanol (10.0 mL ×
2) followed by diethyl ether (10.0 mL × 2) to give a yellow
solid (140 mg, 74.5%). Crystals for X-ray analysis of
[L1PdCl2] were obtained within 3 days from diethyl ether
(10.0 mL) diffusion into a DMF solution (10.0 mL) of
1H, J = 7.7 Hz,
NC5H4 ), 7.54 (t, 1H, J = 7.7 Hz,
NC5H4 ), 7.22 (d, 2H, J = 7.6 Hz, o-C6H4F ), 6.92 (d,
2H, J = 7.6 Hz, m-C6H4F ), 4.43 (s, 3H, CH3NC6H4F ),
4.01 (d, 1H, 2J = 16.4 Hz, CH2-NC5H4 ), 3.91 (d, 1H, 2J
= 16.4 Hz, CH2 NC5H4 ). 13C NMR (DMSO-d6, 100
MHz): δ 161.09, 158.11, 154.44, 135.11, 133.81, 131.66,
129.69, 126.44, 118.86, 50.38, 47.96. IR (solid neat; cm−1):
3053 (w), 3010 (s), 2963 (s), 1708 (w), 1696 (s), 1655 (s),
1501 (s), 1463 (s), 1412 (s), 1290 (s), 1234 (s), 1147 (s),
1013 (s), 975 (s), 899 (s), 832 (s), 763 (s), 610 (s).
[L1PdCl2]
(50.0 mg).
Analysis
calculated
for
C13H14Cl2N2Pd: C, 41.6%; H, 3.76%; N, 7.46%. Found: C,
1
41.4%; H, 3.75%; N, 7.44%. H NMR (DMSO-d6, 400
MHz): δ 8.59 (d, 1H, J = 7.8 Hz, NC5H4 ), 7.96 (d, 1H,
J = 7.8 Hz, NC5H4 ), 7.73 (t, 1H, J = 7.6 Hz, NC5H4 ),
7.10 (t, 1H, J = 7.8 Hz, NC5H4 ), 6.94 (t, 3H, J = 7.8 Hz, o-
,m-C6H5 ), 6.66 (s, 2H, p-C6H5 ), 4.11 (s, 3H,
CH3NC6H5 ), 4.04 (d, 1H, 2J = 16.0 Hz, CH2NC5H4 ),
3.74 (d, 1H, 2J = 16.4 Hz, CH2-NC5H4 ). 13C NMR
(DMSO-d6, 100 MHz): δ 162.33, 157.37, 152.95, 153.89,
141.16, 134.56, 131.64, 130.84, 127.44, 50.16, 47.71. IR
(solid neat; cm−1): 3032 (w), 2983 (s), 2859 (s), 1666 (w),
1577 (s), 1554 (s), 1523 (s), 1441 (s), 1394 (s), 1339 (s),
1264 (s), 1243 (s), 1179 (s), 1039 (s), 1026 (s), 992 (s), 899
(s), 834 (s), 831 (s), 759 (s), 670 (s).
N,4-Dimethyl-N-(pyridin-2-ylmethyl)aniline(dichloro)
palladium(II) ([L2PdCl2]): [L2PdCl2] was prepared accord-
ing to a procedure similar to that described for [L1PdCl2]
except for utilizing L2 (106 mg, 0.500 mmol) and [Pd
(CH3CN)2Cl2] (130 mg, 0.500 mmol). The solid residue
was filtered and washed with ethanol (10.0 mL × 2) followed
2,6-Diethyl-N-methyl-N-(pyridin-2-ylmethyl)aniline
(dichloro)palladium(II) ([L4PdCl2]): [L4PdCl2] was pre-
pared according to a procedure similar to that described for
[L1PdCl2] except for utilizing L4 (123 mg, 0.500 mmol) and
[Pd(CH3CN)2Cl2] (130 mg, 0.500 mmol). The solid residue
was filtered and washed with ethanol (10.0 mL × 2)
followed by diethyl ether (10.0 mL × 2) to give a yellow
solid (161 mg, 77.1%). Crystals for X-ray analysis of
[L4PdCl2] were obtained within 5 days from diethyl ether
(10.0 mL) diffusion into a DMF solution (10.0 mL) of
[L4PdCl2] (50.0 mg). Analysis calculated for C17H22Cl2N2Pd:
C, 47.3%; H, 5.14%; N, 6.49%. Found: C, 47.1%; H,
1
5.05%; N, 6.46%. H NMR (DMSO-d6, 400 MHz): δ 8.51
Bull. Korean Chem. Soc. 2015, Vol. 36, 609–617
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KOREAN CHEMICAL SOCIETY
(d, 1H, J = 7.6 Hz, NC5H4 ), 8.11 (d, 1H, J = 7.8 Hz,
−NC5H4-), 8.01 (t, 1H, J = 7.8 Hz, NC5H4 ), 7.83 (d, 1H,
J = 7.8 Hz, NC5H4 ), 6.68 (m, 3H, (CH2CH3)2C6H3 ),
PMMA was obtained by filtration and repeated washing with
methanol and dried under vacuum for 24 h.
X-Ray Crystallographic Studies. A colorless cubic-shaped
crystal was picked up with paratone-N oil and mounted on a
Bruker SMART CCD diffractometer equipped with a graph-
ite-monochromatized Mo Kα (λ = 0.71073 Å) radiation
source and a nitrogen cold stream (200 K). Data collection
and integration were performed with SMART (Bruker,
2000) and SAINT-Plus (Bruker, 2001).53 Semiempirical
absorption corrections based on equivalent reflections were
applied by SADABS.54 The structure was solved by direct
methods and refined by full-matrix least squares on F2 using
SHELXTL.55 All the nonhydrogen atoms were refined aniso-
tropically, and hydrogen atoms were added to their geometri-
cally ideal positions. Crystal and structure refinement data for
all structures are summarized in Table 1.
2
4.64 (s, 3H, CH3 N (CH2CH3)2C6H3 ), 4.14 (d, 1H, J
= 16.0 Hz, CH2 NC5H4 ), 4.00 (d, 1H, 2J = 16.0 Hz,
CH2 NC5H4 ), 2.01 (m, 4H, (CH2CH3)2C6H3 ), 1.92
(t, 6H, J = 11 Hz, (CH2CH3)2C6H3 ). 13C NMR (DMSO-
d6, 100 MHz): δ 160.12 (s, 1C, ipso-NC5H4 ), 154.55 (s, 1C,
NC5H4 ), 153.33 (s, 1C, ipso-(CH2CH3)2C6H3 ), 139.11
(s, 1C, NC5H4 ), 136.83 (s, 2C, o-(CH2CH3)2C6H3-),
134.88 (s, 2C, m-(CH2CH3)2C6H3-), 131.96 (s, 1C,
NC5H4 ), 131.61 (s, 1C, −NC5H4 ), 128.36 (s, 1C,
p-(CH2CH3)2C6H3 ), 51.99 (s, 1C, CH2 NC5H4 ), 50.11
(s, 1C,
CH3 N (CH2CH3)2C6H3 ), 22.96 (s, 2C,
(CH2CH3)2C6H3 ), 21.83 (s, 2C, (CH2CH3)2C6H3 ). IR
(solid neat; cm−1): 3059 (w), 2951 (s), 2858 (s), 1836 (w),
1746 (s), 1695 (s), 1649 (s), 1517 (s), 1462 (s), 1365 (s), 1209
(s), 1148 (s), 1100 (s), 1049 (s), 976 (s), 925 (s), 868 (s), 819
(s), 757 (s), 707 (s), 656 (s).
Results and Discussion
2,4,6-Tetramethyl-N-(pyridin-2-ylmethyl)aniline
(dichloro)palladium(II) ([L5PdCl2]): [L5PdCl2] was pre-
pared according to a method similar to that described for
[L1PdCl2] except for utilizing L5 (120 mg, 0.500 mmol)
and [Pd(CH3CN)2Cl2] (130 mg, 0.500 mmol). The solid res-
idue was filtered and washed with ethanol (10.0 mL × 2) fol-
lowed by diethyl ether (10.0 mL × 2) to give a yellow solid
(151 mg, 70.0%). Crystals for X-ray analysis of [L5PdCl2]
were obtained within 5 days from diethyl ether (10.0 mL) dif-
fusionintoaDMFsolution(10.0 mL)of[L5PdCl2](50.0 mg).
Analysis calculated for C16H20Cl2N2Pd: C, 46.0%; H, 4.83%;
N, 6.71%. Found: C, 45.9%; H, 4.84%; N, 6.72%.1H NMR
(DMSO-d6, 400 MHz): δ 8.53 (d, 1H, J = 7.6 Hz, NC5H4 ),
8.18 (d, 1H, J = 7.8 Hz, NC5H4 ), 8.10 (t, 1H, J = 7.8 Hz,
NC5H4 ), 7.91 (d, 1H, J = 7.8 Hz, NC5H4 ), 6.56 (s,
2H, (CH3)3C6H2 ), 4.88 (d, 1H, 2J = 17.2 Hz, CH2-
Synthesis of N-methyl-substituted pyridylmethylaniline
ligands, Ln (Ln = L1–L5), was achieved through the condensa-
tion reaction between 2-pyridinecarboxaldehyde and the
appropriate aniline, followed by reduction of the imine residue
in anhydrous methanol by sodium borohydride. Final ligands
were obtained and subsequently methylated by MeI at yields
ranging from 57 to 80% (Scheme 1). Ligand L1 has been
recently described.56,57 Complexes [LnPdCl2] (Ln = L1–L5)
were obtained from the corresponding ligands with [Pd
1
(CH3CN)2Cl2] in anhydrous ethanol. H NMR, 13C NMR,
and elemental analyses were consistent with the ligand and
1
Pd(II) complex formulation. The H NMR characterization
of complexes [LnPdCl2] (Ln = L1–L5) was performed in d6-
dimethyl sulfoxide (DMSO) solution because of the low sol-
1
ubility in solvents less polar than DMSO. H NMR spectra
showed a well-resolved AB spin system for the hydrogen
atoms of the diastereotopic methylene group of the chelating
ring (HA and HB) in [LnPdCl2] (Ln = L1–L5) (Table 1). For
example, signals corresponding to these diastereotopic AB
nuclei in the complexes were separated by a maximum value
of δ 0.30 for [L1PdCl2] and a minimum value of δ 0.10 for
[L3PdCl2]. The coupling constant between these two nuclei,
2JAB, ranged from 15.6 to 16.8 Hz. In contrast, chemical shifts
2
NC5H4 ), 4.76 (d, 1H, J = 16.8 Hz, CH2NC5H4 ), 4.63
(s, 3H, CH3N(CH3)3C6H2 ), 2.01 (s, 3H, (CH3)3C6H2 ),
1.71 (s, 6H, (CH3)3C6H2 ). 13C NMR (DMSO-d6, 100
MHz): δ 160.11, 156.41, 153.93, 138.11, 136.81, 136.11,
133.71, 130.76, 128.41, 51.86, 49.76, 23.11, 20.73. IR (solid
neat; cm−1): 3059 (w), 2951 (s), 2858 (s), 1836 (w), 1746 (s),
1695 (s), 1649 (s), 1517 (s), 1462 (s), 1365 (s), 1209 (s), 1148
(s), 1100 (s), 1049 (s), 976 (s), 925 (s), 868 (s), 819 (s), 757 (s),
707 (s), 656 (s).
Table 1. Chemical shift and coupling constant for the diastereotopic
Catalytic Activity for MMA Polymerization. In a Schlenk
line, the complex (15.0 μmol, 5.60 mg for [L1PdCl2], 5.80 mg
for [L2PdCl2], 5.90 mg for [L3PdCl2], 6.20 mg for
[L4PdCl2], and6.50 mg for[L5PdCl2])wasdissolved indried
toluene (10.0 mL) followed by the addition of MMAO (3.25
mL, 7.50 mmol) as a cocatalyst. The solution was stirred for
20 min at 60 ꢀC. Then, MMA (5.0 mL, 47.1 mmol) was added
to the above reaction mixture and stirred for 2 h to obtain a vis-
cous solution. Methanol (2.00 mL) was added to terminate
polymerization. The reaction mixture was poured into a large
quantity of MeOH (500 mL), and 35% HCl (5.00 mL) was
injected to remove the remaining cocatalyst (MMAO).
methylene hydrogens (Ha and Hb).
δ Ha
(PyCH2 NHR)
δ Hb
2J
(HaHb)
Complexes
(PyCH2 NHR)
[L1PdCl2]
[L2PdCl2]
[L3PdCl2]
[L4PdCl2]
[L5PdCl2]
4.04 (3.94)a
4.14 (3.94)
4.01 (3.94)
4.14 (4.64)
4.88 (4.89)
3.74
4.01
3.91
4.00
4.76
16.0
15.6
16.4
16.0
16.8
a Chemical shifts of diastereotopic methylene hydrogens on the pyridine
amine moiety in ligands Ln (Ln = L1–L5) are shown in parentheses. The
peak was not resolved and appeared broad.
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of the diastereotopic methylene group in ligands showed only
one broad peak ranging from δ 3.94 to δ 4.89.
bond distances of the complexes ranged from 1.509 (10) to
1.510(9) Å, which were in the range of accepted carbon–
nitrogen single bonds. The C(5) C(6) bond distances of the
complexes ranged from 1.481 (11) to 1.512(11) Å, reflecting
the lack of delocalized π-electrons in the pyridine ring.32,43,46
All complexes [LnPdCl2] (Ln = L1–L3) showed similar square
planarity, based on the N(1) Pd(1) Cl(2) and N(2) Pd(1)
Cl(1) angles of 174.88(9)ꢀ and 174.67(18)ꢀ in [L1PdCl2],
respectively. The average N(1) Pd(1) N(2) bond angle of
five-membered rings ranged from 81.7(3)ꢀ to 82.5(2)ꢀ and
were slightly affected by the aniline rings. The Cl(1) Pd
(1) Cl(2) angles in [LnPdCl2] (Ln = L1–L3) ranged between
90.27(9)ꢀ and 91.69(8)ꢀ, which were traditional angles for
square-planar coordination complexes.
ORTEP drawings of the complexes are shown in Figure 1
([L1PdCl2]), Figure 2 ([L2PdCl2]), and Figure 3 ([L3PdCl2]).
Crystal data and structural refinementfor Pd(II) complexes are
shown in Table 2. Selected bond lengths and angles are listed
in Table 3. A single crystal suitable for X-ray crystallography
was obtained from diethyl ether (10.0 mL) diffusion into DMF
solution (10.0 mL). The coordination geometry around the
Pd(II) center of the synthesized complexes could be described
as square-planar, consisting of two nitrogen atoms and two
chloride atoms. The bond lengths of Pd Npyridine [Pd(1) N
(1)] in [LnPdCl2] (Ln = L1–L3) ranged from 2.028(6) to
2.044(6) Å, while those of Pd Naniline [Pd(1) N(2)] ranged
from 2.089(7) to 2.111(6) Å. The Pd Cl bond lengths ranged
from 2.288(2) to 2.297(2) Å. Naniline Cmethylene [N(2) C(6)]
Compared to the interlocation on the plane of the aniline
group and the plane of the Pd and pyridine in [L1PdCl2],
Scheme 1. Synthesis of ligands and [LnPdCl2] (Ln = L1–L5) complexes.
Figure 1. Molecular structure of [L1PdCl2] with thermal ellipsoids at
Figure 2. Molecular structure of [L2PdCl2] with thermal ellipsoids at
50% probability. The hydrogen atom is omitted for clarity.
50% probability. The hydrogen atom is omitted for clarity.
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the plane of the aniline group and the plane of Pd and pyridine
in [L2PdCl2] were slightly twisted by ~20ꢀ rather than being
exactlyperpendicular(90ꢀ), asobservedfor[L1PdCl2]. More-
over, both the plane of the aniline group and the plane of Pd
and pyridine were located in the same plane in [L3PdCl2].
Alternatively, the plane of the aniline group and the plane of
Pd and pyridine in [L2PdCl2] were perfectly twisted by 90ꢀ
rather than being perpendicular (90ꢀ) for [L1PdCl2].
[LnPdCl2] (Ln = L1–L5) had two sources of chirality, resulting
in four different isomers.
The coordinated aniline nitrogen atom contained four dif-
ferent substituents, leading to a chiral center that could adopt
R and S configurations. The second induced chirality origi-
nated from the deviation of coplanarity when the Pd chelated
to the pyridine ring and the five-membered metallocycle ring,
which caused two conformations δ and λ (Scheme 2).
Although dynamic isomerization behavior may occur in solu-
tion, [LnPdCl2] (Ln = L1–L3) represents two chiralities show-
ing an enantiomeric relationship of diastereomers Sλ, Rδ , and
Sδ, respectively, in the solid state.43,58–61
In general, a higher glass transition temperature (Tg) of
PMMA represents higher optical quality and syndiotacticity
content of PMMA. The Tg of isotactic PMMA that is produced
by commercial radical processes, is ~65 ꢀC. Thus, studies on
nonradical-mediated MMA polymerization have been per-
formed, and some transition-metal complexes have been gen-
erated.62–74 All Pd(II) complexes were activated by MMAO to
polymerize MMA, yielding PMMA with Tg values ranging
from 127 to 130 ꢀC. The polymers were isolated as white
solids and characterized by GPC in tetrahydrofuran using
standard polystyrene as a reference. The triad microstructure
Figure 3. Molecular structure of [L3PdCl2] with thermal ellipsoids at
50% probability. The hydrogen atom is omitted for clarity.
Table 2. Crystal data and structural refinement of [LnPdCl2] (Ln = L1–L3) complexes.
[L1PdCl2] [L2PdCl2]
C13H14Cl2N2Pd
[L3PdCl2]
C13H13Cl2N2Pd
393.55
200(2)
Empirical formula
Formula weight (amu)
Temperature (K)
C14H16Cl2N2Pd
389.59
375.56
200(2)
200(2)
Wavelength (Å)
0.71073
0.71073
0.71073
Crystal system, space group
Unit cell dimensions
a (Å) and α (ꢀ)
Tetragonal, P43
Monoclinic, P21/n
Monoclinic, P21/c
8.5205(2)
8.5205(2)
18.9050(9)
137248(8)
4, 1.818
1.723
744
10.1805(7)
11.3095(7) and 91.989(1)
12.7540(9)
1467.6(2)
4, 1.763
10.0460(7)
9.9490(7) and 102.248(1)
14.000(1)
1367.4(2)
4, 1.912
b (Å) and β (ꢀ)
c (Å) and γ (ꢀ)
Volume (Å3)
Z, Calculated density (Mg/m3)
μ (mm−1
F(000)
)
1.615
776
1.745
776
Crystal size (mm)
θ range (ꢀ)
0.30 × 0.29 × 0.23
2.39–28.27
0.24 × 0.18 × 0.17
2.41–28.31
0.26 × 0.21 × 0.20
2.07–26.04
Limiting indices
−11 ≤ h ≤ 11
−12 ≤ h ≤ 13
−11 ≤ h ≤ 12
−11 ≤ k ≤ 5
−15 ≤ k ≤ 14
−12 ≤ k ≤ 12
−24 ≤ l ≤ 25
−11 ≤ l ≤ 17
−17 ≤ l ≤ 16
Reflections collected/unique
Refinement method
9758/3261 [R(int) = 0.0277]
Full-matrix least-squares on F2
3261/1/164
10350/3605 [R(int) = 0.0273]
Full-matrix least-squares on F2
3650/0/174
8322/2697 [R(int) = 0.0354]
Full-matrix least-squares on F2
2697/0/173
Data/restraints/parameters
Goodness of fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
1.271
1.198
1.260
R1 = 0.0286, wR2 = 0.0584
R1 = 0.0433, wR2 = 0.1014
1.018 and −1.281
R1 = 0.0356, wR2 = 0.0626
R1 = 0.0700, wR2 = 0.1043
2.137 and −3.078
R1 = 0.0361, wR2 = 0.0710
R1 = 0.0709, wR2 = 0.1399
1.588 and −2.404
Δρmax and Δρmin (e Å−3
)
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Table 3. Selected bond lengths (Å) and angles (ꢀ) of [LnPdCl2] (Ln = L1–L3) complexes.
[L1PdCl2] [L2PdCl2]
Bond lengths (Å)
[L3PdCl2]
Pd(1) N(1)
Pd(1) N(2)
Pd(1) Cl(1)
Pd(1) Cl(2)
N(1) N(5)
N(2) N(6)
N(2) N(7)
C(5) C(6)
2.044(6)
2.111(6)
2.300(2)
2.297(2)
1.335(9)
1.520(9)
1.485(9)
1.48(1)
Pd(1) N(1)
Pd(1) N(2)
Pd(1) Cl(1)
Pd(1) Cl(2)
N(1) N(5)
N(2) N(6)
N(2) N(7)
C(5) C(6)
2.028(6)
2.090(6)
2.289(2)
2.293(2)
1.36(1)
1.51(1)
1.49(1)
1.48(1)
Pd(1) N(1)
Pd(1) N(2)
Pd(1) Cl(1)
Pd(1) Cl(2)
N(1) N(5)
N(2) N(6)
N(2) N(7)
C(5) C(6)
2.044(6)
2.089(7)
2.297(2)
2.288(2)
1.36(1)
1.51(1)
1.48(1)
1.51(1)
Bond angles (ꢀ)
N(1) Pd(1) N(2)
N(1) Pd(1) Cl(2)
N(2) Pd(1) Cl(2)
N(1) Pd(1) Cl(1)
N(2) Pd(1) Cl(1)
Cl(1) Pd(1) Cl(2)
C(6) N(2) C(7)
C(6) N(2) Pd(1)
81.2(2)
175.9(2)
94.9(2)
N(1) Pd(1) N(2)
N(1) Pd(1) Cl(2)
N(2) Pd(1) Cl(2)
N(1) Pd(1) Cl(1)
N(2) Pd(1) Cl(1)
Cl(1) Pd(1) Cl(2)
C(6) N(2) C(7)
C(6) N(2) Pd(1)
81.7(3)
176.2(2)
94.8(2)
N(1) Pd(1) N(2)
N(1) Pd(1) Cl(2)
N(2) Pd(1) Cl(2)
N(1) Pd(1) Cl(1)
N(2) Pd(1) Cl(1)
Cl(1) Pd(1) Cl(2)
C(6) N(2) C(7)
C(6) N(2) Pd(1)
82.5(2)
172.0(2)
92.1(2)
93.9(2)
176.1(2)
91.69(8)
108.8(7)
106(5)
93.5(2)
93.3(1)
174.7(2)
90.45(8)
107.2(6)
101.2(4)
174.7(2)
90.27(9)
107.3(6)
103.4(4)
of PMMA was ~0.70, which was similar to all [LnPdCl2] (Ln
= L1–L5) and to the reference material [PdCl2], regardless of
the polymerization temperature. For comparison, copper(II)
[Cu(II)] complexes with ligand N-(2-furanylmethyl)-N-(1-
3,5-dimethyl-1H-pyrazolylmethyl)-N-(phenylmethyl)
amines69 were reported to be active catalysts for MMA polym-
erization to yield syndiotactic PMMA with an rr value of up to
0.78. However, the conversion of MMA to PMMA was only
30%. In addition, Ni(II) complexes62,65,71–73 with ligands
such as pentane-2,4-diol and phenoxy-imine showed syndio-
tacticity ranging from 0.73 to 0.82 with an activity of 4.20 ×
104 g PMMA/molNiꢁh. Cobalt(II) [Co(II)] complexes with
phenoxy-imine63 were also used as catalysts for MMA polym-
erization with moderate activity and syndiotacticity. Thus, the
moderate syndiotacticity of [LnPdCl2] (Ln = L1–L5) com-
plexes was not sufficient to confer a mechanism of coordina-
tion polymerization, and the chirality in [LnPdCl2] (Ln = L1–
L5) did not play a role during MMA polymerization. In
addition, the presence of 5 equiv of radical inhibitor 2,2,6,6-
tetramethylpiperidinyloxy (TEMPO) during MMA polymer-
ization did not significantly reduce the yield of PMMA (~5%
yield), supporting that the mechanism of coordination polym-
erization is not a radical mechanism.63 These results were
comparable to previously reported Pd(II) complexes contain-
ing the bispyridylamine ligand, namely N,N-di(2-picolyl)
Scheme 2. Representation of the conformation δ and λ. C∗ refers to
the asymmetric carbon.
1
of PMMA was analyzed using H NMR spectroscopy.75,76
The polymerization results, including tacticity based on the
isotactic (mm), heterotactic (mr), and syndiotactic (rr), and
the polydispersity index (PDI), which represents the average
degree of polymerization in terms of the number of structural
units and molecules, are summarized in Table 4. To confirm
the catalytic activity of MMA polymerization, blank polymer-
ization of MMA was performed with anhydrous [PdCl2] and
MMAO at specific temperatures. The tacticity of PMMA was
determined in the range around syndiotactic (δ 0.85), hetero-
tactic (δ 1.02), and isotactic (δ 1.21) based on 1H NMR. The
syndiotacticity of PMMA was ~70%, which was similar to all
[LnPdCl2] (Ln = L1–L5) at a 60 ꢀC polymerization tempera-
ture. The catalytic activities of the Pd(II) complexes were
not significantly affected by the steric effects of ligands and
local chirality around the metal center.
This is supported by the fact that the MMA polymerization
activity of complex [LnPdCl2] (Ln = L1–L5) was similar to
that of the reference complex [PdCl2] (2.73 × 104 g PMMA/
mol Pdꢁh), indicating that N-methyl-substituted pyridyl-
methylaniline ligands did not result in any steric and electronic
effects to confer a mechanism of coordination polymerization.
Moreover, the local chirality in Pd(II) complexesdoes notplay
a role in governing the tacticity of PMMA. The syndiotacticity
cycloheptylamine,49 N-cycloalkyl
2-iminomethylpyridine
ligand,50 and N-(pyridin-2-ylmethyl)aniline and its
derivatives,50 which clearly showed steric and electronic
effects of Pd(II) complexes during MMA polymerization.
However, structural differences caused by the phenyl ring
of the aniline moiety in [LnPdCl2] (Ln = L1–L5) with N-
methyl-N-(pyridin-2-ylmethyl)aniline and its derivatives did
not sufficiently induce steric hindrance or electronic effects
Bull. Korean Chem. Soc. 2015, Vol. 36, 609–617
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Table 4. Polymerization of MMA by [LnPdCl2] (Ln = L1–L5) complexes in the presence of MMAO.
Tacticity
Yieldb
(%)
Activityc (g/
molCat h)
Tg
(%
mm)
(%
mr)
(%
rr)
Mwe (g/
Mw/
Mn
d
Temperature
(ꢀC)
Entry Catalysta
(ꢀC)
mol) × 105
f
1
4
5
6
7
8
9
[PdCl2]
60
60
60
60
60
60
60
12.6
8.97
19.4
19.0
17.7
17.9
13.7
1.97
1.40
3.03
2.98
2.77
2.81
2.12
129
120
129
130
129
129
127
10.2
37.2
7.90
7.40
7.60
6.70
6.80
23.5
10.9
24.1
25.3
24.1
23.7
22.7
66.3
51.9
68.0
67.3
68.3
69.6
70.5
7.52
0.61
1.49
1.13
1.21
1.73
7.42
1.63
2.20
1.21
1.09
1.33
1.11
1.84
MMAOg
[L1PdCl2]
[L2PdCl2]
[L3PdCl2]
[L4PdCl2]
[L5PdCl2]
a [Pd(II) catalyst]0 = 15 μmol and [MMA]0/[MMAO]0/[Pd(II) catalyst]0 = 3100:500:1.
b Yield defined as the mass of dried polymer recovered/mass of monomer used.
c Activity represents (gPMMA)/(molPd h).
d Tg is the glass transition temperature determined using a thermal analyzer.
e Determined using GPC eluted with tetrahydrofuran at room temperature by filtration with polystyrene calibration.
f Mn refers to the number average molecular weight of PMMA.
g Blank polymerization performed with MMAO alone.
on the Pd metal center to improve the activity and syndiotac-
ticity during MMA polymerization.
References
1. D. J. Ayres, D. A. House, W. T. Robinson, Inorg. Chim. Acta
1998, 277, 177.
Conclusions
2. H. M. Helis, W. H. Goodman, R. B. Wilson, J. A. Morgan,
D. J. Hodgson, Inorg. Chem. 1977, 16, 2412.
3. T. Zhu, Z. Guang-Yi, L. Xue-Qiang, X. Sai-Feng, Z. Qian-Jiang,
W. G. Jackson, W. Zhan-Bing, L. La-Sheng, Inorg. Chim. Acta
2004, 357, 953.
4. C. J. O'Connor, E. E. Eduok, F. R. Fronczek, O. Kahn,
Inorg. Chim. Acta 1985, 105, 107.
5. L. Toma, R. Lescouëzec, J. Vaissermann, P. Herson, V.
Marvaud, F. Lloreta, M. Julve, New J. Chem. 2005, 29, 210.
6. A. T. Çolak, O. Z. Yes¸ilel, O. Büyükgüngör, Polyhedron 2010,
29, 2127.
7. M. Shukla, N. Srivastava, S. Saha, T. R. Rao, S. Sunkari,
Polyhedron 2011, 30, 754.
8. L. Wiehl, G. Kiel, C. P. Kohler, H. Spiering, P. Giitlich, Inorg.
Chem. 1986, 25, 1565.
9. S. K. Kang, H. W. Lee, N. Sengottuvelan, Y.-I. Kim, Bull.
Korean Chem. Soc. 2012, 33, 95.
10. P. Maslak, J. J. J. Sczepanski, M. Parvez, J. Am. Chem. Soc.
1991, 213, 1062.
11. A. Mondal, S. Sarkar, D. Chopra, T. N. G. Row, K. K. Rajak,
Dalton Trans. 2004, 3244.
12. J.-X. Li, Y.-M. Jiang, B.-R. Lian, J. Chem. Crystallogr. 2008,
38, 711.
13. Y.-L. Wong, J.-F. Ma, F. Xue, T. C. W. Mak, D. K. P. Ng, Orga-
nometallics 1999, 18, 5075.
14. J. A. Driscoll, M. M. Allard, L. Wu, M. J. Heeg, S. R. P. da
Rocha, C. N. Verani, Chem. Eur. J. 2008, 14, 9665.
15. J. Gómez, G. García-Herbosa, J. V. Cuevas, A. Arnáiz, A. Carbayo,
A. Muñoz, L. Falvello, P. E. Fanwick, Inorg. Chem. 2006,45, 2483.
16. S. Park, H.-J. Jang, S. S. Lee, Bull. Korean Chem. Soc. 2012,
33, 301.
17. M. N. Kopylovich, J. Lasri, M. F. C. Guedes da Silva, A. J. L.
Pombeiro, Dalton Trans. 2009, 3074.
18. K. Fiore, G. Martelli, M. Monari, D. Savoia, Tetrahedron:Asym-
metry 1999, 10, 4803.
We investigated the synthesis and X-ray crystallographic
structures of [LnPdCl2] (Ln = L1–L5), which were prepared
by the substitution reaction of [Pd(CH3CN)2Cl2] with thecor-
responding N0-methyl substituted pyridylmethylamine
ligands. The coordination geometries around the Pd(II) cen-
tersinthesecomplexesweresquare planar. Thecatalytic activ-
ity of [LnPdCl2] (Ln = L1–L5) toward the MMA
polymerization resulted in moderate activity (3.03 × 104 g
PMMA/mol Pdꢁh for [L1PdCl2]) with PMMA syndiotacticity
of ~0.68 compared to the reference complex [PdCl2] (1.97 ×
104 g PMMA/mol Pdꢁh), indicating that N0-methyl substituted
pyridylmethylamine ligands were not effectively coordinated
to the Pd metal to exert high MMA polymerization activity.
Moreover, the induced chirality in Pd(II) complexes did not
control the tacticity of PMMA.
Acknowledgment. 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) and also by
the Korea Atomic Energy Research Institute (KAERI) grant
(grant no. 79085-13) funded by Korea government
(Ministry of Science, ICT and Future Planning).
Supporting Information. CCDC 1001593–1001595 con-
tains the supplementary crystallographic data for [L1PdCl2],
[L2PdCl2], and [L3PdCl2], respectively. These data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallo-
graphic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.
cam.ac.uk.
Bull. Korean Chem. Soc. 2015, Vol. 36, 609–617
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de
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BULLETIN OF THE
Article
Palladium(II) Complexes with N,N0-Bidentate Ligands
KOREAN CHEMICAL SOCIETY
19. S. J. A. Guieu, A. Mari, M. Lanfredi, C. Massera, L. D. Pachón,
P. Gamez, J. Reedijk, Catal. Today 2004, 96, 259.
20. K. Abdur-Rashid, R. Abbel, A. Hadzovic, A. Lough, R. H.
Morris, Inorg. Chem. 2005, 44, 2483.
21. M. K. Panda, M. M. Shaikh, R. J. Butcher, P. Ghosh, Inorg.
Chim. Acta 2011, 372, 145.
46. J. V. Cuevas, G. García-Herbosa, A. Muñoz, S. García-Granda,
D. Miguel, Organometallics 1997, 16, 2220.
47. H. Chen, J. A. Sweet, K.-C. Lam, A. L. Rheingold, D. V.
McGrath, Tetrahedron: Asymmetry 2009, 20, 1672.
48. S. Schouteeten, O. R. Allen, A. D. Haley, G. L. Ong, G. D. Jones,
D. A. Vicic, J. Organomet. Chem. 2006, 691, 4975.
49. D. Kim, S. Kim, E. Kim, H.-J. Lee, H. Lee, Polyhedron 2013,
63, 139.
22. R. Singh, A. Banerjee, K. K. Rajak, Inorg. Chim. Acta 2010,
363, 3131.
23. V. Terrasson, D. Prim, J. Marrot, Eur. J. Inorg. Chem.
2008, 2739.
50. S. Kim, E. Kim, H.-J. Lee, H. Lee, Polyhedron 2014, 69, 149.
51. B. B. Wayland, R. F. Schrammz, Inorg. Chem. 1969, 8, 971.
52. R. A. Walton, Can. J. Chem. 1968, 46, 2347.
53. Bruker AXS Inc., SMART and SAINT-Plus v 6.22, Bruker AXS
Inc., Madison, WI, 2000.
ꢀ
ꢁ
ꢀ
ꢀ
24. M. Juribašic, K. Molcanov, B. Kojic-Prodic, L. Bellotto,
ꢀ
M. Kralj, F. Zani, L. Tušek-Božic, J. Inorg. Biochem. 2011,
105, 867.
25. V. P. Munk, C. I. Diakos, L. T. Ellis, R. R. Fenton, B. A. Mes-
serle, T. W. Hambley, Inorg. Chem. 2003, 42, 3582.
26. R. Alberto, R. Schibli, A. P. Schubiger, J. Am. Chem. Soc. 1999,
121, 6076.
54. G. M. Sheldrick, SADABS v 2.03, University of Göttingen,
Göttingen, 2002.
55. Bruker AXS, Inc., SHELXTL v 6.10, Bruker AXS, Inc.,
Madison, Wisconsin, USA, 2000.
27. X. Wang, J. D. Ranford, J. J. Vittal, J. Mol. Struct. 2006, 796, 28.
28. A. Raja, V. Rajendiran, P. U. Maheswari, R. Balamurugan,
C. A. Kilner, M. A. Halcrow, M. Palaniandavar, J. Inorg. Bio-
chem. 2005, 99, 1717.
29. V. C. Gibson, R. K. O'Reilly, D. F. Wass, A. J. P. White,
D. J. Williams, Dalton Trans. 2003, 2824.
30. R. Cowdell, C. J. Davies, S. J. Hilton, J.-D. Maréchal,
G. A. Solan, O. Thomas, J. Fawcett, Dalton Trans. 2004, 3231.
31. P. Ai, L. Chen, Y. Guo, S. Jie, B.-G. Li, J. Organomet. Chem.
2012, 705, 51.
32. Y.-C. Lin, K.-H. Yu, S.-L. Huang, Y.-H. Liu, Y. Wang, S.-T.
Liu, J.-T. Chen, Dalton Trans. 2009, 9058.
56. J. R. Bernardo, S. C. A. Sousa, P. R. Florindo, M. Wolff,
B. Machura, A. C. Fernandes, Tetrahedron 2013, 69, 9145.
57. F. I. McGonagle, D. S. MacMillan, J. Murray, H. F. Sneddon,
C. Jamiesona, A. J. B. Watson, Green Chem. 2013, 15, 1159.
58. G. M. Kapteijn, M. P. R. Spee, D. M. Grove, H. Kooijman,
A. L. Spek, G. van Koten, Organometallics 1996, 15, 1405.
59. J. A. Casares, P. Espinet, K. Soulantica, I. Pascual, A. G. Orpen,
Inorg. Chem. 1997, 36, 5251.
60. A. Frick, V. Schulz, G. Huttner, Eur. J. Inorg. Chem. 2002, 3129.
61. V. Schulz, A. Frick, G. Huttner, Eur. J. Inorg. Chem. 2002, 3111.
62. X. He, Y. Yao, X. Luo, J. Zhang, Y. Liu, L. Zhang, Q. Wu, Orga-
nometallics 2003, 22, 4952.
33. S. Bruda, M. M. Turnbull, C. P. Landee, Q. Xu, Inorg. Chim.
Acta 2006, 359, 298.
63. B. K. Bahuleyan, D. Chandran, C. H. Kwak, C.-S. Ha, I. Kim,
Macromol. Res. 2008, 18, 745.
34. T. Chattopadhyay, N. Podder, K. S. Banu, A. Banerjee, G. Man-
ami, E. Suresh, M. Nethaji, D. Das, J. Mol. Struct. 2007, 839, 69.
35. S. Tanase, M. Ferbinteanu, M. Andruh, C. Mathonière, I. Stren-
ger, G. Rombaut, Polyhedron 2000, 19, 1967.
36. A. Malassa, H. Görls, M. Westerhausen, Inorg. Chem. Commun.
2008, 11, 612.
64. B. Lian, C. M. Thomas, O. L. Casagrande Jr.. , C. W. Lehmann,
T. Roisnel, J.-F. Carpentier, Inorg. Chem. 2007, 46, 328.
65. J. Li, H. Song, C. Cui, Appl. Organomet. Chem. 2010, 24, 82.
66. W. Wang, P. A. Stenson, A. Marin-Becerra, J. McMaster,
M. Schroder, D. J. Irvine, D. Freeman, S. M. Howdle, Macromo-
lecules 2004, 37, 6667.
37. J.-X. Li, Y.-M. Jiang, M.-J. Chen, J. Coord. Chem. 2008,
61, 1765.
67. M. Yang, E. Kim, J. H. Jeong, K. S. Min, H. Lee, Inorg. Chim.
Acta 2013, 394, 501.
38. H.-W. Kuai, X.-C. Cheng, L.-D. Feng, X.-H. Zhu, Z. Anorg.
Allg. Chem. 2011, 637, 1560.
68. Z. Zhang, D. Cui, A. A. Trifonov, Eur. J. Inorg. Chem.
2010, 2861.
39. F. D. Lesh, S. S. Hindo, M. J. Heeg, M. M. Allard, P. Jain,
B. Peng, L. Hryhorczuk, C. N. Verani, Eur. J. Inorg. Chem.
2009, 345.
40. S. K. Dey, N. Mondal, M. S. E. Fallah, R. Vicente, A. Escuer,
X. Solans, M. Font-Bardía, T. Matsushita, V. Gramlich, S. Mitra,
Inorg. Chem. 2004, 43, 2427.
69. C. Lansalot-Matras, F. Bonnette, E. Mignard, O. Lavastre,
J. Organomet. Chem. 2008, 693, 393.
70. E. Kim, H. Y. Woo, S. Kim, H. Lee, D. Kim, H. Lee, Polyhedron
2012, 42, 135.
71. Y.-J. Hu, H. H. Zou, M.-H. Zeng, N. S. Weng, J. Organomet.
Chem. 2009, 694, 366.
41. S. Iwatsuki, T. Suzuki, T. Yajima, T. Shiraiwa, O. Yamauchi,
Y. Shimazaki, Inorg. Chim. Acta 2011, 377, 111.
42. M. W. Davies, A. J. Clarke, G. J. Clarkson, M. Shipman, J. H. R.
Tucker, Chem. Commun. 2007, 5078.
43. V. Diez, J. V. Cuevas, G. García-Herbosa, G. Aullón, J. P. H.
Charmant, A. Carbayo, A. Muñoz, Inorg. Chem. 2007, 46, 568.
44. M. B. Smith, A. M. Z. Slawin, Polyhedron 2000, 19, 695.
45. T. AI-Allaf, P. Castan, R. Turpin, S. Wimmer, G. Bernardinelli,
Transit. Met. Chem. 1992, 17, 579.
72. C. Carlini, M. Martinelli, E. Passaglia, A. M. R. Galletti,
G. Sbrana, Macromol. Rapid Commun. 2001, 22, 664.
73. G. Tang, G.-X. Jin, Dalton Trans. 2007, 3840.
74. Y.-B. Huang, G.-R. Tang, G.-Y. Jin, G.-X. Jin, Organometallics
2008, 27, 259.
75. R. Chûjû, K. Hatada, R. Kitamaru, T. Kitayama, H. Sato,
Y. Tanaka, Polymer J. 1987, 19, 413.
76. T. Kitaura, T. Kitayama, Macromol. Rapid Commun. 2007,
28, 1889.
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