X-ray crystal structures and MMA polymerization of cadmium(II) complexes with bidentate pyrazole ligands: The formation of monomers or dimers as a function of a methyl substituent on the pyrazole and aniline rings

Article abstract of DOI:10.1002/aoc.3148

The reaction of CdBr₂·4H₂O with ancillary ligands, N,N-bis(1H-pyrazolyl-1-methyl)aniline (L₁), N,N-bis(1H-pyrazolyl-1-methyl)-p-methylaniline (L₂), N,N-bis(1H-pyrazolyl-1-methyl)-3,5-dimethylaniline (L₃), N,N-bis(3,5-dimethyl-1H-pyrazolyl-1-methyl)aniline (L₄) and N,N-bis(1H-pyrazolyl-1-methyl)-2,6-dimethylaniline (L₅) in ethanol yields novel Cd(II) bromide complexes, [L₁CdBr₂] ₂, [L₂CdBr₂]₂, [L ₃CdBr₂]₂, [L₄CdBr₂] and [L₅CdBr₂]. The X-ray crystal structures of [L ₁CdBr₂]₂, [L₂CdBr₂] ₂ and [L₃CdBr₂]₂ reveal a bromo-bridged dimeric species with crystallographic inversion symmetry. Conversely, [L₄CdBr₂] and [L₅CdBr₂] exist as monomeric complexes, presumably due to the steric hindrance between the methyl substituents of the two pyrazole groups in the ligand and cadmium centre for [L₄CdBr₂], and crowding around the cadmium metal by methyl substituents on the aniline residue in the ligand for [L ₅CdBr₂]. The geometry at each Cd(II) centre for [L ₁CdBr₂]₂, [L₂CdBr₂] ₂ and [L₃CdBr₂]₂ is best described as a distorted trigonal bipyramid. A distorted trigonal bipyramid is achieved in [L₄CdBr₂] by coordinative interaction of the nitrogen atom of the aniline unit and the cadmium atom with a σ plane of symmetry, based on the bond length of Cd-N_aniline (2.759(7) A). [L ₅CdBr₂] exists with a distorted tetrahedral geometry involving non-coordination of the nitrogen atom of aniline and the Cd centre, resulting in the formation of an eight-membered chelate ring. The catalytic activity of monomeric, five-coordinated [L₄CdBr₂] in the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at 60°C resulted in a higher molecular weight and a narrower polydispersity index (PDI) than those obtained with dimeric [L _nCdBr₂]₂ (L_n=L₁, L ₂, L₃) or monomeric tetrahedral [L₅CdBr ₂]. Copyright

Full text of DOI:10.1002/aoc.3148

Full Paper
Received: 14 October 2013
Revised: 23 February 2014
Accepted: 24 February 2014
Published online in Wiley Online Library: 28 April 2014
(wileyonlinelibrary.com) DOI 10.1002/aoc.3148
X-ray crystal structures and MMA polymerization
of cadmium(II) complexes with bidentate pyrazole
ligands: the formation of monomers or dimers as a
function of a methyl substituent on the pyrazole
and aniline rings
Dongil Kima, Sunghoon Kima, Hyun Yul Wooa, Ha-Jin Leeb and Hyosun Leea*
The reaction of CdBr2·4H2O with ancillary ligands, N,N-bis(1H-pyrazolyl-1-methyl)aniline (L1), N,N-bis(1H-pyrazolyl-1-methyl)-p-
methylaniline (L2), N,N-bis(1H-pyrazolyl-1-methyl)-3,5-dimethylaniline (L3), N,N-bis(3,5-dimethyl-1H-pyrazolyl-1-methyl)aniline
(L4) and N,N-bis(1H-pyrazolyl-1-methyl)-2,6-dimethylaniline (L5) in ethanol yields novel Cd(II) bromide complexes, [L1CdBr2]2,
[L2CdBr2]2, [L3CdBr2]2, [L4CdBr2] and [L5CdBr2]. The X-ray crystal structures of [L1CdBr2]2, [L2CdBr2]2 and [L3CdBr2]2 reveal a
bromo-bridged dimeric species with crystallographic inversion symmetry. Conversely, [L4CdBr2] and [L5CdBr2] exist as mono-
meric complexes, presumably due to the steric hindrance between the methyl substituents of the two pyrazole groups in the
ligand and cadmium centre for [L4CdBr2], and crowding around the cadmium metal by methyl substituents on the aniline residue
in the ligand for [L5CdBr2]. The geometry at each Cd(II) centre for [L1CdBr2]2, [L2CdBr2]2 and [L3CdBr2]2 is best described as a
distorted trigonal bipyramid. A distorted trigonal bipyramid is achieved in [L4CdBr2] by coordinative interaction of the nitrogen
atom of the aniline unit and the cadmium atom with a σ plane of symmetry, based on the bond length of Cd―Naniline (2.759(7)
Å). [L5CdBr2] exists with a distorted tetrahedral geometry involving non-coordination of the nitrogen atom of aniline and the Cd
centre, resulting in the formation of an eight-membered chelate ring. The catalytic activity of monomeric, five-coordinated
[L4CdBr2] in the polymerization of methyl methacrylate (MMA) in the presence of modified methylaluminoxane (MMAO) at
60°C resulted in a higher molecular weight and a narrower polydispersity index (PDI) than those obtained with dimeric
[LnCdBr2]2 (Ln = L1, L2, L3) or monomeric tetrahedral [L5CdBr2]. Copyright © 2014 John Wiley & Sons, Ltd.
Keywords: bispyrazolyl; dimeric Cd(II) complex; methyl methacrylate polymerization; syndiotacticity
The current study describes the synthesis and characterization of
monomeric and dimeric Cd(II) complexes with the bidentate ligand
Introduction
Transition metal complexes with pyrazole-based ligands, namely poly
(pyrazoyl) ligands, have attracted considerable attention because of
their catalytic activity. Specifically, their structural properties often
meet specific stereochemical requirements for a particular metal
binding site.[1–5] Pyrazolyl-based chelating ligands were first reported
by Driessen in 1982.[6] Since then, due to their structural stability and
catalytic ability, a variety of pyrazolyl complexes have been synthe-
sized as cancer sensors and as hydrolysis and oxidation agents.[7–11]
For example, Driessen et al.[12,13] have synthesized and characterized
bi- and tridentate pyrazole ligands such as 1-[2-ethylamino]ethyl]-
3,5-dimethylpyrazole(deae), bis-[3,5-dimethylpyrazolyl]methyl]ethyla
mine (bdmae), and bis-[(3,5-diemtylpyrazolyl)ethyl]ethylamine (ddae).
Metal complexes with N-alkylaminopyrazole ligands,[14] including Rh
(I), Ru(II), Pd(II), Pt(II), Zn(II), and Co(II) complexes, have exhibited a
variety of potentially useful chemical properties.[15–23] Although there
have been many reports describing transition metal complexes
ligated to chelating pyrazolyl ligands, some recent studies have
documented the use of transition metals, specifically cadmium,[24,25]
catalysts for olefin polymerization[26–28] and methyl methacrylate
(MMA) polymerization.[29–35] Previously, we described Co(II), Zn(II)
and Pd(II) complexes with N,N-bis(1H-pyrazolyl-1-methyl)aniline and
their derivatives in MMA polymerizations.[36–38]
N,N-bis(1H-pyrazolyl-1-methyl)aniline and its derivatives, which
contain two pyrazole groups that act as N-donor atoms. We also in-
vestigated the structural aspects of these Cd(II) complexes and the
effects of substituents attached to the aniline moiety (H, CH3, 2CH3)
or pyrazole ring (2CH3) on catalytic activity in MMA polymerization.
Results and Discussion
Synthesis and Chemical Properties
Scheme 1 shows the synthesis of the ligands and Cd(II) complexes.
The ligands were obtained in yields of approximately 68–85% from
the aniline derivatives and 1H-pyrazolyl-1-methanol or 3,5-di-
*
Correspondence to: Hyosun Lee, Department of Chemistry and Green-Nano
Materials Research Center, Kyungpook National University, 1370 Sankyuk-dong,
Buk-gu, Daegu City 702-701, Republic of Korea. E-mail: hyosunlee@knu.ac.kr
a Department of Chemistry and Green-Nano Materials Research Center,
Kyungpook National University, Daegu City, 702-701, Republic of Korea
b Jeonju Center, Korea Basic Science Institute (KBSI), Jeonju, 561-180, Republic of Korea
Appl. Organometal. Chem. 2014, 28, 445–453
Copyright © 2014 John Wiley & Sons, Ltd.

D. Kim et al.
ligand and bridged μ2-bromo group, are sparse. Al-
though trigonal bipyramidal dinuclear cadmium
complexes that depend on a flexible bipyrazole li-
gand are known,[39] cadmium complexes with four,
five or six coordinations were achieved by the use
of less flexible bispyrazole ligands. In these cases,
the geometry at each cadmium centre is best de-
scribed as a distorted trigonal bipyramid with two
equivalent half-molecules providing an overall C2h
symmetry for [L1CdBr2]2, [L2CdBr2]2 and [L3CdBr2]
2. It is worth noting that the geometry of [L4CdBr2]
is a distorted trigonal bypyramid with a σ plane of
symmetry and that [L5CdBr2] has a distorted tetrahe-
dral structure. In dimeric [LnCdBr2]2 (Ln = L1, L2, L3)
(Figs. 1–3), the Cd(II) is coordinated with two pyrazole
nitrogen atoms, two bridged bromine atoms and a
terminal bromine atom, achieving a five-coordinated
geometry. In addition, the aniline unit and the two
pyrazole rings of [LnCdBr2]2 (Ln = L1, L2, L3) resemble
the back of a chair and elbow rests, respectively. The
phenyl rings in [LnCdBr2]2 (Ln = L1, L2, L3) are approx-
imately perpendicular. The planes of the phenyl ring
and pyrazole rings are virtually parallel in monomeric
[L4CdBr2] and [L5CdBr2], which have four bulky
methyl groups on two pyrazole rings and two methyl
groups on the aniline ring, respectively. Therefore, the
parallel or perpendicular orientation of the plane of
the aniline ring with respect to the plane of the pyrazole
ring depends on the substituents attached to the
aniline ring and pyrazole ring. For example, in [N,N-
bis(3,5-dimethyl-1H-pyrazolyl-1-methyl)aniline]zinc(II)
chloride, ([Zn(bdmpab)Cl2])[40] or cobalt(II) chloride
([Co(bdmpab)Cl2]),[37] the aniline ring exhibits an ap-
proximately 90° orientation with respect to the plane
of the pyrazole moiety. This result indicates that in
Cd(II) complexes the relatively large cadmium atom
has a reduced steric effect compared with that which
a smaller cobalt or zinc atom would have. Thus [LnCdBr2]2 (Ln =L1,
L2, L3) complexes with ligands that produce relatively less steric hin-
drance exist in a distorted trigonal bipyramid by adopting a dimeric
structure. However, monomeric [L4CdBr2], in which the L4 ligand
produces more steric hindrance than L5, exists as a distorted trigonal
bipyramid resulting from weak interactions between the Cd metal
and the N atom of the aniline ring. Monomeric [L5CdBr2] complexes
exhibited only distorted tetrahedral structures.
Scheme 1. Synthesis of ligands and Cd(II) complexes.
methyl-1H-pyrazolyl-1-methanol in methylene chloride. The Cd(II)
bromide complexes [LnCdBr2]m (Ln = L1, L2, L3, L4, L5; m= 1 or 2)
(approximately 72–82% yields) were obtained from Cd(II) bromide
with the corresponding ligands in anhydrous ethanol. The results
of 1H NMR, 13C NMR and elemental analyses were consistent with
the ligands and the molecular formulae of the Cd(II) complexes.
Resonances in the 1H NMR and 13C NMR spectra of the Cd(II)
complexes were only slightly shifted relative to those in the
associated ligands due to resonance effects of the N and C atoms
of the pyrazole group.
The N atom of the aniline ring does not take part in a coordina-
tive bond to the Cd atom in dimeric [LnCdBr2]2 (Ln = L1, L2, L3) as
determined from the bond lengths between the N of the aniline ring
and the Cd atom, which range from 4.104(7) to 4.263(7) Å. However,
monomeric [L4CdBr2] adopted a five-coordinated geometry due to
weak interactions between the N of the aniline ring and the Cd
metal atom, based on the Cd―Naniline bond length of 2.759(7) Å.
Although [L5CdBr2] exhibits a monomeric, four-coordinated
geometry due to the steric effect of the ligand, as in [L4CdBr2],
the bond length of Cd―Naniline in [L5CdBr2] is 3.762(4) Å, which
indicates a non-coordinative interaction between the N of the
aniline ring and the Cd atom.
Discussion of the X-Ray Crystal Structures
Crystallographic data and refinement parameters are listed in
Table 1. The molecular structures of [L1CdBr2]2, [L2CdBr2]2,
[L3CdBr2]2, [L4CdBr2] and [L5CdBr2] are given in Figs. 1–5,
respectively. The selected bond distances and angles are
presented in Table 2.
Colourless, cube-shaped crystals of Cd(II) complexes were
obtained from diethyl ether diffusion into an acetone solution.
Structural determination by X-ray diffraction revealed a bromo-
bridged dimeric species with crystallographic inversion symmetry
for [L1CdBr2]2, [L2CdBr2]2, [L3CdBr2]2 and monomeric structures
for [L4CdBr2] and [L5CdBr2]. Trigonal bipyramidal dicadmium
complexes, especially those containing the bis-pyrazole chelate
The Npyrazole―Cd―Npyrazole angles were 80.9(3)°, 80.3(2)° and
79.5(4)°, the Brbridge―Cd―Brbridge angles were 84.01(4)°, 86.42
(16)° and 85.91(5)°, and the Brterminal―Cd―Brbridge were 120.90
(5)°, 107.07(4)° and 96.84(5)° for [L1CdBr2]2, [L2CdBr2]2 and
[L3CdBr2]2, respectively. The
Npyrazole―Cd―Npyrazole and
wileyonlinelibrary.com/journal/aoc
Copyright © 2014 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 445–453

Cd(II) complexes form monomers/dimers depending on bispyrazolyl ligand
Appl. Organometal. Chem. 2014, 28, 445–453
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

D. Kim et al.
Figure 1. ORTEP drawing of [L1CdBr2]2 with displacement parameters
at the 30% probability level. All hydrogen atoms are omitted for clarity.
Symmetry code: #: -x+1, -y+1, -z+2.
Figure 5. ORTEP drawing of [L5CdBr2] with displacement ellipsoids at
the 30% probability level. All hydrogen atoms are omitted for clarity.
Npyrazole―Cd―Npyrazole angle of [L5CdBr2] approached that of a
tetrahedron at 96.0(2)° due to the substituents on the pyrazole
rings and the bulky, eight-membered chelate ring. Therefore,
[L4CdBr2] and [L5CdBr2] have difficulty in forming dimeric com-
plexes due to steric hindrance around the metal and large
Figure 2. ORTEP drawing of [L2CdBr2]2 with displacement ellipsoids at
the 30% probability level. All hydrogen atoms are omitted for clarity. Sym-
metry code: #: -x+1, -y, -z.
Npyrazole―Cd―Npyrazole angles.
Discussion of MMA Polymerization
All of the Cd(II) complexes could be activated with MMAO to
polymerize MMA, yielding PMMA with glass transition tempera-
tures from 129 to 132°C.[41–43] The polymers were isolated as
white solids and characterized by gel permeation chromatogra-
phy (GPC) in THF using standard polystyrene as the reference.
The microstructure of the PMMA was analysed by 1H NMR
spectroscopy. The resulting polymer characteristics are summa-
rized in Table 3.[44]
To confirm the catalytic activity of the Cd(II) complexes in MMA
polymerization, blank polymerization of MMA was performed
with CdBr2.4H2O and MMAO at a specified temperature, respec-
tively. The tacticity of this PMMA was syndiotactic (rr, δ 0.85),
heterotactic (mr, δ 1.02) and isotactic (mm, δ 1.21) as determined
by 1H NMR.[45,46] Relative to previously reported cobalt com-
plexes with N,N-bis(1H-pyrazolyl-1-methyl)aniline,[36] the Cd(II)
complexes exhibited higher molecular weights (1.29 × 106
g molÀ1 for [L4CdBr2]) of syndiotactic PMMA, narrower polydis-
persity indexes (PDIs) and slightly lower catalytic activities
(4.67 × 104 g PMMA/(mol Cd)(h) for [L4CdBr2]) at 60°C. The PDIs
of the Cd(II) complexes ranged from 1.23 to 3.07. In general, the
PDI range narrowed with increasing molecular weight of
PMMA.[47,48] For comparison, copper complexes with ligand
N-(2-furanylmethyl)-N-(1-3,5-dimethyl-1H-pyrazolylmethyl)-N-
(phenylmethyl)amine[32] were reported as catalysts for the poly-
merization of MMA to give syndiotactic PMMA with rr value up
to 78%; however, the conversion of MMA to PMMA was just
30%. All Cd(II) complexes have shown 100% conversion on MMA
polymerization. In addition, Ni(II) complexes with ligands such as
pentane-2,4-diol and phenoxy-imine were reported to have
syndiotacticity ranging from 73% to 82% with activity of
4.20 × 104 g PMMA/(mol Ni)(h).[41,43,49–52] The Co(II) complex with
phenoxy-imine[42] and Fe(II) complex with pyridylmethylamine[53]
were also used as catalysts for MMA polymerization with moderate
activity and syndiotacticity. For example, the lanthanide metal Sm
(II) complex with bispyrrolylaldiminato ligand is known for producing
isotactic PMMA with an mm value of 98%.[54] Monomeric, five-
coordinated [L4CdBr2] yielded the narrowest PDI and the highest
molecular weight of PMMA. This is due to the substituent on the
Figure 3. ORTEP drawing of [L3CdBr2]2 with displacement ellipsoids at the
30% probability level. All hydrogen atoms are omitted for clarity. Symmetry
code: #: -x+1, -y+1, -z.
Figure 4. ORTEP drawing of [L4CdBr2] with displacement ellipsoids at
the 30% probability level. All hydrogen atoms are omitted for clarity. Sym-
metry code: #: x, -y+1/2, z.
Brbridge―Cd―Brbridge angles were hardly affected by substituents
on the aniline ring. However, Brterminal―Cd―Brbridge angles de-
creased with the size of the substituents on the aniline ring (H>
CH3 > 2CH3). The steric influence of the bromide ligand is affected
by the pyrazole rings. In addition, ―CH2―Naniline―CH2― angles
decreased as substituents on the aniline ring increased in steric
bulk (H > CH3 > 2CH3). However,
Npyrazole―Cd―Npyrazole in
[L4CdBr2] was relatively large
(137.24(19)°). The
wileyonlinelibrary.com/journal/aoc
Copyright © 2014 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 445–453

Cd(II) complexes form monomers/dimers depending on bispyrazolyl ligand
Appl. Organometal. Chem. 2014, 28, 445–453
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

D. Kim et al.
pyrazole ring moiety, which is located near the Cd metal.
Syndiotacticity was not sufficiently high to offer a mechanism of
coordination polymerization but was similar for all of the synthe-
sized Cd(II) complexes. This also indicates that syndiotacticity
was only slightly affected by the substituents on the ligand.
Catalytic activity was affected more by the substituents on the
pyrazole ring than by those on the phenyl ring, as determined
by the relative amounts of PMMA product yielded. The MMA
polymerization activity of Cd complexes should be considered
a function of the electron density about the metal centre.
elsewhere.[6] The CH2Cl2 solution (100 ml) of pyrazole (20.4 g,
0.30 mol) or 3,5-dimethylpyrazole (28.8 g, 0.30 mol) was added
to a CH2Cl2 solution (100 ml) of para-formaldehyde (9.00 g,
0.30 mol). The solution was refluxed for 5 days and the filtrate sol-
vent was removed under reduced pressure to give a white pow-
der: 28.5 g, 96.8% for 1H-pyrazolyl-1-methanol and 36.3 g, 95.9%
for 3,5-dimethyl-1H-pyrazolyl-1-methanol).
N,N-Bis(1H-pyrazolyl-1-methyl)aniline (L1)
L1 was prepared by a similar procedure as described in the liter-
ature.[10,55,56] The CH2Cl2 solution (10.0 ml) of aniline (1.86 g,
0.020 mol) was added to a CH2Cl2 solution (30.0 ml) of 1H-1-
pyrazolyl-1-methanol (3.92 g, 0.040 mol). The reaction solution
was dried over MgSO4 after stirring the reaction mixture at room
temperature for 3 days. The filtrate solvent was removed under
reduced pressure to give a bright-yellow oil (3.54 g, 70.0%). Anal-
ysis. Calcd for C14H15N5: C, 66.38; H, 5.97; N, 27.65%. Found: C,
66.49; H, 6.09; N, 27.77%. 1H NMR (CDCl3, 400 MHz): δ 7.55
(d, 2H, J = 2.4 Hz, ―N CH―CH CH―N―), 7.42 (d, 2H, J = 2.4 Hz,
―N CH―CH CH―N―), 7.25 (dd, 2H, J = 7.8 Hz, J = 7.2 Hz, m-
NC6H5―), 7.10 (d, 2H, J = 7.8 Hz, o-NC6H5―), 6.91 (t, 1H,
J = 7.2 Hz, p-NC6H5―), 6.23 (dd, 2H, J = 2.4 Hz, 2.4 Hz,
―N CH―CH CH―N―), 5.68 (s, 4H, ―CH2―). 13C NMR (CDCl3,
Conclusion
Novel Cd(II) complexes were prepared by reactions between N,N-
bis(1-pyrazolyl)methyl ligands and CdBr2.4H2O and their struc-
tures determined by X-ray crystallography. The coordination of
these ligands to the Cd(II) metal revealed the formation of dimers
in the case of [LnCd(μ-Br)Br]2 (Ln = L1, L2, L3) or monomers in the
case of [L4CdBr2] and [L5CdBr2]. Dimer or monomer formation
was determined by steric effects of substituents on the pyrazole
and aniline rings. Monomeric [L4CdBr2] and [L5CdBr2] exist in
five- and four-coordinated geometries, respectively, depending
on the existence of interactions between the nitrogen atom of
the aniline ring and the metal centre. This indicates that steric ef-
fects of substituents on the pyrazole ring are more important in
determining structural geometry than are those of substituents
on the aniline ring. This is the first bis-pyrazole-containing
binuclear and five-coordinated cadmium complex to have been
structurally characterized. Although the PDI for MMA polymeriza-
tion depended little on the substituent, the molecular weight and
catalytic activity of PMMA were affected by the steric influences
of substituents on both the pyrazole and aniline rings.
100 MHz):
δ
145.57 (1C, ipso-NC6H5―), 139.33 (2C,
―N CH―CH CH―N―), 129.80 (2C, ―N CH―CH CH―N―),
129.29 (2C, m-NC6H5―), 119.65 (1C, p-NC6H5―), 114.35 (2C, o-
NC6H5―), 105.97 (2C, ―N CH―CH CH―N―), 66.23 (s, 2C,
―CH2―). IR (liquid neat; cmÀ1): 3114 (w), 1598 (s), 1503 (s),
1450 (s), 1381 (w), 1312 (w), 1263 (w), 1172 (w), 1084 (s), 1042
(s), 956 (w), 883 (w), 741 (w), 690 (s), 611 (s).
N,N-Bis(1H-pyrazolyl-1-methyl)-p-methylaniline (L2)
L2 was prepared by an analogous method as described for L1 ex-
cept that p-methylaniline was utilized. A white solid product was
obtained (4.54 g, 84.9%). Analysis. Calcd for C15H17N5: C, 67.39; H,
6.41; N, 26.20%. Found: C, 67.47; H, 6.42; N, 26.19%. 1H NMR (CDCl3,
400 MHz): δ 7.82 (d, 2H, J= 2.0Hz, ―N CH―CH CH―N―), 7.50
(d, 2H, J=2.0Hz, ―N CH―CH CH―N―), 7.05 (d, 2H, J=8.4Hz, m-
NC6H4CH3―), 6.98 (d, 2H, J=8.4Hz, o-NC6H4CH3―), 6.26 (dd, 2H,
J = 2.0 Hz, 2.0Hz, ―N CH―CH CH―N―), 5.84 (s, 4H, ―CH2―),
2.11 (s, 3H, ―NC6H4CH3―). 13C NMR (CDCl3, 100 MHz): δ 143.22
(1C, ipso-NC6H4CH3―), 139.38 (2C, ―N CH―CH CH―N―),
129.92 (2C, ―N CH―CH CH―N―), 129.71 (1C, p-NC6H4CH3―),
128.42 (2C, m-NC6H4CH3―), 114.62 (2C, o-NC6H4CH3―), 105.89
(2C, ―N CH―CH CH―N―), 66.42 (2C, ―CH2―), 20.43 (1C,
―NC6H4CH3―). IR (solid neat; cmÀ1): 3113 (w), 2919 (w), 1618
(s), 1516 (s), 1467 (s), 1371 (w), 1306 (s), 1257 (s), 1187 (w), 1154
(s), 1085 (s), 1040 (s), 945 (w), 878 (w), 802 (s), 742 (w), 647 (s),
604 (s).
Experimental
Chemicals and Physical Measurement
CdBr2·4H2O, pyrazole, 3,5-dimethylpyrazole, para-formaldehyde,
(X)aniline (X = H, para-CH3, 3,5-dimethyl) and MMA were pur-
chased from Aldrich. Anhydrous solvents, such as ethanol, DMF,
diethyl ether, acetonitrile (AN) and dichloromethane, were pur-
chased from Merck and used without further purification. Modi-
fied methylaluminoxane (MMAO) was purchased from Tosoh
Finechem Corporation as 6.9% weight aluminum in a toluene so-
lution and used without further purification. Elemental analyses
(C, H, N) of the prepared complexes were carried out on an ele-
mental analyser (EA 1108; Carlo-Erba, Milan, Italy). 1H NMR
(400.01 MHz) and 13C NMR (100.61 MHz) spectra were recorded
on a Bruker Advance Digital 400 NMR spectrometer and chemical
shifts were recorded in parts per million (ppm) using SiMe4 as an
internal standard. The molecular weight and molecular weight
distribution of the obtained PMMA were determined by GPC
(CHCl3, Alliance e2695; Waters Corp., Milford, MA, USA). Glass
transition temperatures (Tg) were determined using a thermal
analyser (Q2000; TA Instruments, New Castle, DE, USA).
N,N-Bis(1H-pyrazolyl-1-methyl)-3,5-dimethylaniline (L3)
L3 was prepared by an analogous method as described for L1 except
that 3,5-dimethylaniline was utilized. A white solid product was
obtained (4.54 g, 80.7%). Analysis. Calcd for C16H19N5: C, 68.30; H,
6.81; N, 24.89%. Found: C, 69.83; H, 7.48; N, 23.67%. 1H NMR (CDCl3,
400 MHz): δ 7.60 (d, 2H, J=2.0Hz, ―N―CHCH―CH N―), 7.45 (d,
2H, J=2.0Hz, ―NCH―CH CH―N―), 6.72 (s, 2H, o-NC6H3(CH3)2―),
6.45(s, 1H, p-NC6H3(CH3)2―), 6.26 (dd, 2H, J=2.0Hz, J=2.0Hz,
―N CH―CH CH―N―), 5.71 (s, 4H, ―CH2―), 2.30 (s, 6H, ―NC6H3
(CH3)2―). 13C NMR (CDCl3, 100 MHz): δ 145.88 (1C, ipso-NC6H3
(CH3)2―), 139.85 (2C, ―N CH―CH CH―N―), 139.12 (2C, m-
NC6H3(CH3)2―), 128.77 (2C, ―N―CH CH―CH N―), 123.12 (1C, p-
Preparation of Ligands and Cd(II) Complexes
1H-Pyrazolyl-1-methanol and 3,5-dimethyl-1H-pyrazolyl-1-methanol
The starting materials 1H-pyrazolyl-1-methanol and 3,5-dimethyl-
1H-pyrazolyl-1-methanol were prepared by processes described
wileyonlinelibrary.com/journal/aoc
Copyright © 2014 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 445–453

Cd(II) complexes form monomers/dimers depending on bispyrazolyl ligand
NC6H3(CH3)2―), 113.75 (2C, o-NC6H3(CH3)2―), 106.17 (2C,
―N―CH CH―CH N―), 66.32 (2C, ―CH2―), 21.65 (2C, ―NC6H3
(CH3)2―). IR (solid neat; cmÀ1): 3124 (w), 2915 (w), 1595 (s), 1475
(w), 1387 (s), 1323 (w), 1278 (w), 1160 (s), 1082 (w), 1038 (s), 955
(s), 882 (s), 827 (w),744 (s), 612 (s).
105.94 (2C, ―N CH―CH CH―N―), 66.22 (s, 2C, ―CH2―). IR (solid
neat; cmÀ1): 3838 (w), 3739 (w), 3616 (w), 1751 (s), 1700 (s), 1591
(w), 1502 (w), 1409 (s), 1363 (s), 1328 (w), 1255 (w), 1187 (w), 1155
(s), 1099 (s), 1058 (s), 981 (s), 940 (w), 757 (s), 646 (s), 609 (s).
[N,N-Bis(1H-pyrazolyl-1-methyl)-p-methylaniline(μ-bromo)Cd(II) bromide]2
([L2CdBr2]2)
N,N-Bis(3,5-dimethyl-1H-pyrazolyl-1-methyl)aniline (L4)
[L2CdBr2]2 was prepared according to a similar procedure as de-
scribed for [L1CdBr2]2. The white powder was filtered and
washed with ethanol (50.0 ml × 2), followed by washing with
diethyl ether (50.0 ml × 2) (0.41 g, 38.0%). Analysis. Calcd for
C30H34Br4Cd2N10: C, 33.39; H, 3.18; N, 12.98%. Found: C, 33.17;
L4 was prepared by an analogous method as described for L1
except that 3,5-dimethyl-1H-pyrazolyl-1-methanol was utilized.
The white solid product was obtained (4.20 g, 67.9%). Analysis.
Calcd for C18H23N5: C, 69.87; H, 7.49; N, 22.63%. Found: C, 69.86;
H, 7.51; N, 22.64%. 1H NMR (CDCl3, 400 MHz): δ 7.20 (dd, 2H,
J = 7.8 Hz, J = 7.2 Hz, m-NC6H5―), 7.12 (d, 2H, J = 7.8 Hz, o-
NC6H5―), 6.82 (t, 1H, J = 7.2 Hz, p-NC6H5―), 5.78 (s, 2H, ―N―C
(CH3) CH―C(CH3) N―), 5.64 (s, 4H, ―CH2―), 2.16 (s, 6H,
―N―C(CH3) CH―C(CH3) N―), 2.08 (s, 6H, ―N―C(CH3)
CH―C(CH3) N―). 13C NMR (CDCl3, 100 MHz): δ 146.58 (1C,
ipso-NC6H5―), 146.13 (2C, m-NC6H5―) 139.43 (2C, ―N―C(CH3)
CH―C(CH3) N―), 129.19 (2C, ―N―C(CH3) CH―C(CH3) N―),
120.50(1C, p-NC6H5―), 117.28 (s, 2C, o-NC6H5―), 105.76 (2C,
―N―C(CH3) CH―C(CH3) N―), 63.67 (2C, ―CH2―), 13.63 (2C,
―N―C(CH3) CH―C(CH3) N―), 11.07 (2C, ―N―C(CH3) CH―C
(CH3) N―). IR (solid neat; cmÀ1): 3289 (w), 2921 (w), 1598 (s),
1549 (s), 1506 (s), 1454 (s), 1387 (w), 1254 (s), 1211 (w), 1153
(w), 1028 (s), 953 (s), 816 (s), 748 (w), 683 (s), 623 (s).
1
H, 3.16; N, 13.07%. H NMR (DMSO-d6, 400 MHz): δ 7.82 (d, 2H,
J = 2.2 Hz, ―N CH―CH CH―N―), 7.50 (d, 2H, J = 1.2 Hz,
―N CH―CH CH―N―), 7.04 (d, 2H, J = 8.8 Hz, o-NC6H4CH3―),
6.98 (d, 2H, J = 8.6 Hz, m-NC6H4CH3―), 6.25 (dd, 2H, J = 2.2 Hz,
J = 1.2 Hz, ―N CH―CH CH―N―), 5.88 (s, 4H, ―CH2―), 2.16 (s,
3H, ―NC6H4CH3―). 13C NMR (DMSO-d6, 100 MHz): δ 143.18 (1C,
ipso-NC6H4CH3―), 139.38 (2C, ―N CH―CH CH―N―), 129.94
(2C, ―N CH―CH CH―N―), 129.79(1C, p-NC6H4CH3―), 128.41
(2C, m-NC6H4CH3―), 114.61 (2C, o-NC6H4CH3―), 105.88 (2C,
―N CH―CH CH―N―), 66.41 (2C, ―CH2―), 20.27 (1C,
―NC6H4CH3―). IR (solid neat; cmÀ1): 3847 (w), 3742 (w), 3619
(w), 1753 (s), 1695 (s), 1647 (s), 1516 (s), 1405 (w), 1318 (w),
1253 (w), 1169 (s), 1098 (s), 1055 (s), 948 (w), 774 (s), 610 (s).
N,N-Bis(1H-pyrazolyl-1-methyl)-2,6-dimethylaniline (L5)
[N,N-Bis(1H-pyrazolyl-1-methyl)-3,5-dimethylaniline(μ-bromo)Cd(II) bromide]
([L3CdBr2]2)
2
L5 was prepared by an analogous method as described for L1 ex-
cept that 2,6-dimethyl-1H-pyrazolyl-1-methanol was utilized. A
white solid product was obtained (4.35 g, 77.3%). Analysis. Calcd
for C16H19N5: C, 68.30; H, 6.81; N, 24.89%. Found: C, 68.12; H, 6.82; N,
25.05%. 1H NMR (CDCl3, 400MHz): δ 7.54 (d, 2H, J=2.0Hz,
―NCH―CH CH―N―), 7.28 (d, 2H, J=2.0Hz, ―NCH―CH CH―N―),
7.00 (m, 3H, m,o-NC6H3(CH3)2―), 6.22 (dd, 2H, J=2.0Hz, J=J=2.0Hz,
―NCH―CHCH―N―), 5.36 (s, 4H, ―CH2―), 1.78 (s, 6H, ―NC6H3
(CH3)2―). 13C NMR (CDCl3, 100 MHz): δ 143.48 (1C, ipso-NC6H3
[L3CdBr2]2 was prepared according to a similar procedure de-
scribed for [L1CdBr2]2. The white powder was filtered and
washed with ethanol (50.0 ml × 2), followed by washing with
diethyl ether (50.0 ml × 2) (0.45 g, 40.6%). Analysis. Calcd for
C32H38Br4Cd2N10: C, 34.71; H, 3.46; N, 12.65%. Found: C, 35.56;
1
H, 3.48; N, 12.92%. H NMR (DMSO-d6, 400 MHz): δ 7.83 (d, 2H,
J = 2.0 Hz, ―N CH―CH CH―N―), 7.51 (d, 2H, J = 2.0 Hz,
―N CH―CH CH―N―), 6.78 (s, 2H, o-NC6H3(CH3)2―), 6.44 (s,
1H, p-NC6H3(CH3)2―), 6.26 (dd, 2H, J = 2.0 Hz, J = 2.0 Hz,
―N CH―CH CH―N―), 5.88 (s, 4H, ―CH2―), 2.20 (s, 6H,
―NC6H3(CH3)2―). 13C NMR (DMSO-d6, 100 MHz): δ 145.53 (1C,
ipso-NC6H3(CH3)2―), 139.39 (2C, ―N CH―CH CH―N―), 138.30
(2C, m-NC6H3(CH3)2―), 129.93 (2C, ―N CH―CH CH―N―),
121.45 (1C, p-NC6H3(CH3)2―), 112.39 (2C, o-NC6H3(CH3)2―),
105.88 (2C, ―N CH―CH CH―N―), 66.17 (2C, ―CH2―), 21.71
(2C, ―NC6H3(CH3)2―). IR (solid neat; cmÀ1): 3871 (w), 3741 (w),
3619 (w), 1697 (s), 1595 (s), 1514 (s), 1463 (s), 1409 (s), 1335 (s),
1246 (w), 1172 (w), 1063 (s), 965 (w), 885 (s), 833 (s), 750 (s), 695
(s), 609 (s).
(CH3)2―),
139.91 (2C,
―N CH―CH CH―N―)
137.16
(2C, ―N CH―CH CH―N―), 129.29 (2C, m-NC6H3(CH3)2―),
128.88 (2C, o-NC6H3(CH3)2―), 126.78 (1C, p-NC6H3(CH3)2―),
106.02 (2C, ―N CH―CH CH―N―), 67.96 (2C, ―CH2―), 17.79
(2C, ―NC6H3(CH3)2―). IR (solid neat; cmÀ1): 3317 (w), 2947 (w),
1836 (s), 1745 (w), 1699 (s), 1550 (w), 1266 (s), 1106 (s), 1070 (s),
1030 (s), 980 (w), 943 (w), 771 (w), 630 (s), 582 (s).
[N,N-Bis(1H-pyrazolyl-1-methyl)aniline(μ-bromo)Cd(II) bromide]2 ([L1CdBr2]2)
A solution of L1 (0.253 g, 25.3 mg, 1.00 mmol) in dried ethanol
(10.0 ml) was added to a solution of CdBr2.4H2O (0.334 g,
33.4 mg, 1.00 mmol) in dried ethanol (10.0 ml) at room tempera-
ture. Precipitation of white material occurred while stirring at
room temperature for 12 h. The white powder was filtered and
washed with ethanol (50.0 ml × 2), followed by washing with
diethyl ether (50.0 ml × 2) (0.41 g, 78.0%). Analysis. Calcd for
C28H30Br4Cd2N10: C, 32.00; H, 2.88; N, 13.33%. Found: C, 32.02;
N,N-Bis(3,5-dimethyl-1H-pyrazolyl-1-methyl)anilineCd(II) bromide ([L4CdBr2])
[L4CdBr2] was prepared according to a similar procedure de-
scribed for [L1CdBr2]2. The white powder was filtered and
washed with ethanol (50.0 ml × 2), followed by washing with
diethyl ether (50.0 ml × 2) (0.43 g, 73.9%). Analysis. Calcd for
C18H23Br2CdN5: C, 37.17; H, 3.99; N, 12.04%. Found: C, 37.28; H,
4.04; N, 12.18%. 1H NMR (DMSO-d6, 400 MHz): δ 7.19 (dd, 2H,
J = 7.8 Hz, J = 7.2 Hz, m-NC6H5―), 7.11 (d, 2H, J = 7.8 Hz, o-
NC6H5―), 6.82 (t, 1H, J = 7.2 Hz, p-NC6H5―), 5.79 (s, 2H, ―N―C
(CH3) CH―C(CH3) N―), 5.63 (s, 4H, ―CH2―), 2.15 (s, 6H,
―N―C(CH3) CH―C(CH3) N―), 2.09 (s, 6H, ―N―C(CH3)
CH―C(CH3) N―). 13C NMR (DMSO-d6, 100 MHz): δ 146.58 (1C,
ipso-NC6H5―), 146.10 (2C, o-NC6H5―) 139.48 (2C, ―N―C(CH3)
CH―C(CH3) N―), 129.26 (2C, ―N―C(CH3) CH―C(CH3) N―),
1
H, 2.87; N, 13.71%. H NMR (DMSO-d6, 400 MHz): δ 7.84 (d, 2H,
J=2.4Hz, ―N CH―CH CH―N―), 7.51 (d, 2H, J=1.2Hz,
―N CH―CH CH―N―), 7.20 (d, 2H, J=9.0Hz, o-NC6H5―), 7.17
(dd, 2H, J=9.0Hz, J=6.6Hz, m-NC6H5―), 6.79 (t, 1H, J=6.6Hz,
p-NC6H5―),
―N CH―CH CH―N―), 5.92 (s, 4H, ―CH2―). 13C NMR (DMSO-d6,
100 MHz): 145.55 (1C, ipso-NC6H5―), 139.44 (2C,
6.26
(dd,
2H,
J=2.4Hz,
J=1.2Hz,
δ
―N CH―CH CH―N―), 130.00 (2C, ―N CH―CH CH―N―), 129.37
(2C, m-NC6H5―), 119.65 (1C, p-NC6H5―), 114.36 (2C, o-NC6H5―),
Appl. Organometal. Chem. 2014, 28, 445–453
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

D. Kim et al.
120.57 (1C, p-NC6H5―), 117.36 (2C, m-NC6H5―), 105.79 (2C,
―N―C(CH3) CH―C(CH3) N―), 63.67 (2C, ―CH2―), 13.82 (2C,
―N―C(CH3) CH―C(CH3) N―), 11.08 (2C, ―N―C(CH3) CH―C
(CH3) N―). IR (solid neat; cmÀ1): 3860 (w), 3742 (w), 3677 (w),
3617 (w), 1744 (s), 1695 (s), 1649 (s), 1600 (s), 1547 (w), 1474
(w), 1387 (w), 1290 (s), 1213 (s), 1160 (s), 1111 (s), 1042 (w), 972
(s), 851 (s), 815 (s), 779 (s), 703 (s), 614 (s).
methanol (250 ml × 2) and dried under vacuum at a mild temper-
ature for 24 h.
Supplementary Materials
CCDC 954827–954829 contains the supplementary crystallographic
data for [L1CdBr2]2, [L2CdBr2]2 and [L3CdBr2]2, respectively. CCDC
9864199 and CCDC 54831 contain the supplementary crystallo-
graphic data for [L4CdBr2] and [L5CdBr2], respectively. These data
can be obtained free of charge at 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.
[N,N-Bis(1H-pyrazolyl-1-methyl)-2,6-dimethylanilineCd(II) bromide ([L5CdBr2])
[L5CdBr2] was prepared according to a similar procedure described
for [L1CdBr2]2. The white powder was filtered and washed with etha-
nol (50.0 ml × 2), followed by washing with diethyl ether (50.0 ml × 2)
(0.43 g, 73.9%). Analysis. Calcd for C16H19Br2CdN5: C, 34.71; H, 3.46;
1
N, 12.65%. Found: C, 34.68; H, 3.46; N, 12.65%. H NMR (DMSO-d6,
400 MHz) : δ 7.64 (d, 2H, J=2.4Hz, ―NCH―CH―CH―N―), 7.51 (d,
2H, J = 1.4 Hz, ―N CH―CH CH―N―), 7.00 (m, 3H, m,o-NC6H3
(CH3)2―), 6.27 (dd, 2H, J = 2.4Hz, J = 1.4Hz, ―N CH―CH CH―N―),
5.43 (s, 4H, ―CH2―), 1.69 (s, 6H, ―NC6H3(CH3)2―). 13C NMR
(CDCl3, 100 MHz): δ 143.09 (1C, ipso-NC6H3(CH3)2―), 141.20 (2C,
―N CH―CH CH―N―) 132.64 (2C, ―N CH―CH CH―N―),
129.43 (2C, m-NC6H3(CH3)2―), 128.49 (2C, o-NC6H3(CH3)2―),
126.88 (1C, p-NC6H3(CH3)2―), 106.42 (2C, ―N CH―CH CH―N―),
71.41 (2C, ―CH2―), 19.82 (2C, ―NC6H3(CH3)2―). IR (solid neat;
cmÀ1): 3858 (w), 3742 (w), 3676 (w), 3617 (w), 1743 (s), 1695 (s),
1546 (s), 1461 (s), 1381 (s), 1303 (w), 1261 (w), 1197 (s), 1113 (s),
1037 (s), 981 (s), 802 (s), 682 (s).
Acknowledgements
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).
References
[1] M. A. Halcrow, Dalton Trans. 2009, 2059.
[2] H. R. Bigmore, S. C. Lawrence, P. Mountford, C. S. Tredget, Dalton
Trans. 2005, 635.
[3] D. L. Reger, E. A. Foley, M. D. Smith, Inorg. Chem. 2009, 48, 936.
[4] M. Guerrero, J. Pons, T. Parella, M. Font-Bardia, T. Calvet, J. Ros, Inorg.
Chem. 2009, 48, 8736.
[5] F. Calderazzo, U. Englert, C. Hu, F. Marchetti, G. Pampaloni,
V. Passarelli, A. Romano, R. Santi, Inorg. Chim. Acta 2003, 344, 197.
[6] W. L. Driessen, Recl. Trav. Chim. Pays-Bas 1982, 101, 441.
[7] M. E. Kodadi, F. Malek, R. Touzani, A. Ramdani, Catal. Comm. 2008,
9, 966.
[8] Z. Chen, N. Karasek, D. C. Craig, S. B. Colbran, J. Chem. Soc. Dalton
Trans. 2000, 3445.
[9] J. Gätjens, C. S. Mullins, J. W. Kampf, P. Thuéryb, V. L. Pecoraro, Dalton
Trans. 2009, 51.
[10] S.-C. Sheu, M.-J. Tien, M.-C. Cheng, T.-I. Ho, S.-M. Peng, Y.-C. Lin,
J. Chem. Soc. Dalton Trans. 1995, 3503.
[11] A. John, M. M. Shaikh, R. J. Butcherc, P. Ghosh, Dalton Trans. 2010, 39,
7353.
[12] W. G. Haanstra, W. L. Driessen, R. A. G. de Graaff, G. C. Sebregts,
J. Suriano, J. Reedijk, U. Turpeinen, R. Himallinen, J. S. Wood, Inorg.
Chim. Acta 1991, 189, 243.
[13] W. L. Driessen, R. M. deVos, A. Etz, J. Reedijk, Inorg. Chim. Acta 1995,
235, 127.
X-Ray Crystallographic Studies
Crystals suitable for the X-ray study of each compound were
obtained within 5 days from diethyl ether (10.0 ml) diffusion into
an acetone solution (10.0 ml) of the respective compound
(0.10 g). For data collection, a colourless crystal was picked up
with paratone oil and mounted on a Bruker SMART CCD diffrac-
tometer equipped with
a graphite-monochromated Mo-Kα
(λ = 0.71073 Å) radiation source under a nitrogen cold stream
(200 K). Data collection and integration were performed with
SMART and SAINT-Plus software packages.[57] Semi-empirical
absorption corrections based on equivalent reflections were
applied by SADABS.[58] Structures were solved by direct methods
and refined using a full-matrix least-squares method on F2 using
SHELXTL.[59] All non-hydrogen atoms were refined anisotropi-
cally. Hydrogen atoms were added to their geometrically ideal
positions. Crystallographic and structural data are summarized
in Table 1. With the exception of the positive residual electron
density peak in the structure of [L1CdBr2]2, which was located
near a bromide atom, all other residuals greater than 1 e ÅÀ3
were located in the vicinity of a cadmium atom.
[14] R. Touzani, A. Ramdani, T. Ben-Hadda, S. E. Kadiri, O. Maury, H. L.
Bozec, P. H. Dixneuf, Synth. Commun. 2001, 31, 1315.
[15] K.-B. Shiu, K.-S. Liou, C. P. Cheng, B.-R. Fang, Y. Wang, G.-H. Lee, W.-J.
Vong, Organometallics 1989, 8, 1219.
[16] R. Mathieu, G. Esquius, N. Lugan, J. Pons, J. Ros, Eur. J. Inorg. Chem.
2001, 2683.
[17] E. Bouwman, W. L. Driessen, J. Reedijk, Inorg. Chem. 1985, 24, 4130.
[18] S. Bhattacharyya, S. B. Kumar, S. K. Dutta, E. R. T. Tiekink,
M. Chaudhury, Inorg. Chem. 1996, 35, 1967.
[19] G. Zamora, J. Pons, J. Ros, Inorg. Chim. Acta 2004, 357, 2899.
[20] A. Panélla, J. Pons, J. García-Antón, X. Solans, M. Font-Bardia, J. Ros,
Inorg. Chim. Acta 2006, 359, 4477.
Polymerization of Methyl Methacrylate
In a Schlenk line, the complex (15.0 μmol, 7.9 mg for [L1CdBr2]2,
8.1 mg for [L2CdBr2]2, 8.3 mg for [L3CdBr2]2, 8.7 mg for [L4CdBr2]
or 6.3 mg for [L5CdBr2]) 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 60°C. MMA
(5.0 ml, 47.1 mmol) was added to the above reaction mixture
and stirred for 2 h at 60°C to obtain a viscous solution. Methanol
(2.0 ml) was added to terminate the polymerization. The reaction
mixture was poured into a large quantity of MeOH (500 ml) and
35% HCl (5 ml) was injected to remove the remaining co-catalyst
(MMAO). White PMMA was obtained by filtration, washed with
[21] M. d. C. Castellano, J. Pons, J. García-Antón, X. Solans, M. Font-Bardia,
J. Ros, Inorg. Chim. Acta 2008, 361, 2491.
[22] G. Esquius, J. Pons, R. Yánéz, J. Ros, J. Organomet. Chem. 2001,
619, 14.
[23] M. Espinal, J. Pons, J. García-Antón, X. Solans, M. Font-Bardia, J. Ros,
Inorg. Chim. Acta 2008, 361, 2648.
[24] J. Pons, J. Garcia-Anton, M. Font-Bardia, T. Calvet, J. Ros, Inorg. Chim.
Acta 2009, 362, 2698.
[25] C. Hopa, M. Alkan, C. Kazak, N. B. Arslan, R. Kurtaran, J. Chem.
Crystallogr. 2010, 40, 160.
[26] K. Li, J. Darkwa, I. A. Guzei, S. F. Mapolie, J. Organomet. Chem. 2002,
660, 108.
wileyonlinelibrary.com/journal/aoc
Copyright © 2014 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2014, 28, 445–453

Cd(II) complexes form monomers/dimers depending on bispyrazolyl ligand
[27] S. Tsuji, D. C. Swenson, R. F. Jordan, Organometallics 1999, 18, 4758.
[28] L. L. de Oliveira, R. R. Campedelli, M. C. A. Kuhn, J.-F. Carpentier, O. L.
Casagrande Jr., J. Mol. Catal. A: Chem. 2008, 288, 58.
[29] G.-F. Liu, L.-L. Li, Z.-G. Ren, H.-X. Li, Z.-P. Cheng, J. Zhu, X.-L. Zhu, J.-P.
Lang, Macromol. Chem. Phys. 2009, 210, 1654.
[43] X. He, Y. Yao, X. Luo, J. Zhang, Y. Liu, L. Zhang, Q. Wu, Organometal-
lics 2003, 22, 4952.
[44] W. Wang, P. A. Stenson, A. Marin-Becerra, J. McMaster, M. Schroder,
D. J. Irvine, D. Freeman, S. M. Howdle, Macromolecules 2004, 37,
6667.
[30] B. Lian, C. M. Thomas, O. L. Casagrande Jr., C. W. Lehmann, T. Roisnel,
[45] T. Kitaura, T. Kitayama, Macromol. Rapid Comm. 2007, 28, 1889.
[46] I. A. Opeida, M. A. Kompanets, O. V. Kushch, E. S. Papayanina, Theor.
Exp. Chem. 2011, 47, 30.
[47] J. Llorens, E. Rudé, R. M. Marcos, Polymer 2003, 44, 1741.
[48] G. T. Lewis, V. Nguyen, Y. Cohen, J. Polymer Sci. Polymer Chem. 2007,
45, 5748.
J.-F. Carpentier, Inorg. Chem. 2007, 46, 328.
[31] Z. Zhang, D. Cui, A. A. Trifonov, Eur. J. Inorg. Chem. 2010, 2861.
[32] C. Lansalot-Matras, F. Bonnette, E. Mignard, O. Lavastre,
J. Organomet. Chem. 2008, 693, 393.
[33] H.-X. Li, Z.-G. Ren, D. Liu, Y. Chen, J.-P. Lang, Z.-P. Cheng, X.-L. Zhu,
B. F. Abrahams, Chem. Commun. 2010, 46, 8430.
[49] Y.-J. Hu, H. H. Zou, M.-H. Zeng, N. S. Weng, J. Organomet. Chem.
[34] L.-L. Miao, H.-X. Li, M. Yu, W. Zhao, W.-J. Gong, J. Gao, Z.-G. Ren, H.-F.
Wang, J.-P. Lang, Dalton Trans. 2012, 41, 3424.
[35] H.-Y. Ding, H.-J. Cheng, F. Wang, D.-X. Liu, H.-X. Li, Y.-Y. Fang,
W. Zhao, J.-P. Lang, J. Organomet. Chem. 2013, 741–742, 1.
[36] M. Yang, W. J. Park, K. B. Yoon, J. H. Jeong, H. Lee, Inorg. Chem.
Comm. 2011, 14, 189.
2009, 694, 366.
[50] C. Carlini, M. Martinelli, E. Passaglia, A. M. R. Galletti, G. Sbrana,
Macromol. Rapid Comm. 2001, 22, 664.
[51] G. Tang, G.-X. Jin, Dalton Trans. 2007, 3840.
[52] Y.-B. Huang, G.-R. Tang, G.-Y. Jin, G.-X. Jin, Organometallics
2008, 27, 259.
[37] E. Kim, H. Y. Woo, S. Kim, H. Lee, D. Kim, H. Lee, Polyhedron 2012, 42,
135.
[53] T. V. Laine, U. Piironen, K. Lappalainen, M. Klinga, E. Aitola, M. Leskela,
J. Organomet. Chem. 2000, 606, 112.
[38] D. Kim, S. Kim, E. Kim, H.-J. Lee, H. Lee, Polyhedron 2013, 63, 139.
[39] J.-H. Liu, X.-Y. Wu, Q.-Z. Zhang, X. He, W.-B. Yang, C.-Z. Lu, J. Coord.
Chem. 2007, 60, 1373.
[54] C. Cui, A. Shafir, C. L. Reeder, J. Arnold, Organometallics 2003, 22, 3357.
[55] P. M. van Berkel, W. L. Driessen, R. Hamalainen, J. Reedijk,
U. Turpeinen, Inorg. Chem. 1994, 33, 5920.
[40] H. L. Blonk, W. L. Driessen, J. Reedijk, Chem. Soc., Dalton Trans.
[56] C. Dowling, V. J. Murphy, G. Parkin, Inorg. Chem. 1996, 35, 2415.
[57] SMART and SAINT-Plus v. 6.22, Bruker AXS Inc, Madison, WI, 2000.
[58] G. M. Sheldrick, SADABS v. 2.03, University of Göttingen,
Germany, 2002.
1985, 1699.
[41] J. Li, H. Song, C. Cui, Appl. Organomet. Chem. 2010, 24, 82.
[42] B. K. Bahuleyan, D. Chandran, C. H. Kwak, C.-S. Ha, I. Kim, Macromol.
Res. 2008, 18, 745.
[59] G. M. Sheldrick, Acta Crystallogr., Sect A 2008, 64, 112.
Appl. Organometal. Chem. 2014, 28, 445–453
Copyright © 2014 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc