Acetamidine complexes as catalysts for ethylene polymerization

Article abstract of DOI:10.1016/j.jorganchem.2008.11.066

The reaction of (2,6-diisopropyl-phenyl)-acetimidoyl chloride or (2,6-dimethyl-phenyl)-acetimidoyl chloride with 2,6-dimethylaniline in the presence of triethylamine yields a mixture of isomers N′-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino

Full text of DOI:10.1016/j.jorganchem.2008.11.066

Journal of Organometallic Chemistry 694 (2009) 717–725
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Acetamidine complexes as catalysts for ethylene polymerization
Carolina Valdebenito a, María Teresa Garland b,d, Raul Quijada a,d, Rene Rojas c,d,
*
a Departamento de Ingeniería Química, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile
b Departamento de Física, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile
c Departamento de Química Inorgánica, Facultad de Química, Pontificia Universidad Católica de Chile, Casilla 306, Santiago-22, Chile
d Centro para la Investigación Interdisciplinaria Avanzada en Ciencias de Materiales (CIMAT), Chile
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 October 2008
Received in revised form 27 November 2008
Accepted 28 November 2008
Available online 10 December 2008
The reaction of (2,6-diisopropyl-phenyl)-acetimidoyl chloride or (2,6-dimethyl-phenyl)-acetimidoyl
chloride with 2,6-dimethylaniline in the presence of triethylamine yields a mixture of isomers N0-(2,6-
diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N-(2,6-dimethyl)-acetamidine (1a) and
N-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N0-(2,6-dimethyl)-acetamidine (1b),
and N,N0-bis-(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-phenylimino)ethyl)]-acetamidine (2), respec-
tively. The addition of isomers (1a + 1b) to nickel (II) dibromide 2-methoxyethyl ether, (NiBr2
[O-(C2H4OMe)2]) gives a mixture of new nickel complexes, [NiBr2{N0-(2,6-diisopropyl-phenyl)-N-[1-
(2,6-diisopropyl-phenylimino)-ethyl]-N-(2,6-dimethyl)-acetamidine}] (3a) and [NiBr2{N-(2,6-diisopro-
pyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N0-(2,6-dimethyl)-acetamidine}] (3b). Similarly,
Keywords:
(N)-imidoylamidine
Nickel
Polyethylene
Polymerization
´
ligand 2 reacts with nickel (II) dibromide 2-methoxyethyl ether to afford the complex [NiBr2{N,N-bis-
(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-phenylimino)ethyl)]-acetamidine}] (4). The structures of the
ligands and nickel complexes have been determined by single crystal X-ray diffraction.
The addition of MAO to these complexes generates catalytically active species for the homopolymeriza-
tion of ethylene. The polymer products are high molecular weight (80–169 K). At temperatures of up to
60 °C both catalysts are a single site giving a monomodal molecular weight distribution. However, at
70 °C the mixture (3a + 3b) shows a bimodal molecular weight distribution.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
have pronounced effects on the molecular weight and chain distri-
bution of the product. Subsequently, a number of research groups
The tailoring of polyolefin bulk properties by synthetic control
is a major focus of many industrial and academic research groups
[1]. After the development of metalocene catalysts, and the discov-
ery of their activation with MAO and other alkylaluminums in the
1980s many groups began to focus on alternatives to the tradi-
tional group 4 metal complexes [2]. Design of the catalyst structure
enables control over the polymer microstructure and therefore of
important bulk properties [3]. The sensitivity of the group 4 metals
such as zirconium and titanium led to the development of late
transition metals such as iron, nickel and palladium [4,1c,1d].
The SHOP process for the production of higher olefins from ethyl-
ene has a long history, and familiarity with the molecular weight
distributions dependance on steric effects on led to the develop-
ment of the Keim oligomerization catalysts nearly 30 years ago
[5]. In these systems it was observed that the ligand bulk could
began investigating ligand structures for the use with late transi-
tion metal polymerization catalysts. A large number and varieties
of ligands (bi, tri and tetra dentate organic molecules) available
for use in the production of these post-metallocene catalysts have
been reported [4a]. The bidentate molecules typically bind in a NN
[6], NO [7], NP, [8,10d] PO [9] or PP [10] coordination modes, either
neutrally or monoanionically coordinated to late transition metals
[4c]. While the possibilities of ligand structures are nearly endless,
a few general categories have emerged which describe the struc-
ture of the catalyst. Brookhart catalyst [11] offer a simplicity of
synthesis and an unconfined 5-member ring structure, Bazan
a-iminocarboxamide ligands allow for the remote coordination
of Lewis acid activators [12].
Substantial variation in geometry and electronics of the ligand
and have been explored in both late and early transition metals
in the Grubbs salicylaldiminato and FI Catalysts [13]. Brookhart–
Gibson catalysts represent a departure from these catalysts in that
they are tridentate, sharing the bisimino structure of the Brookhart
* Corresponding author. Address: Departamento de Química Inorgánica, Facultad
de Química, Pontificia Universidad Católica de Chile, Casilla 306, Santiago-22, Chile.
Tel.: +56 2 3547557; fax: +56 2 3544744.
systems but containing an additional interaction through
a
backbone integrated pyridine. This leads to a more planar and rigid
ligand geometry in addition to substantial changes to the
E-mail address: rrojasg@uc.cl (R. Rojas).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.11.066

718
C. Valdebenito et al. / Journal of Organometallic Chemistry 694 (2009) 717–725
electronics of the metal center. In addition to the N,N,N interaction
for the Gibson style ligands [14] other tridentate molecules (neu-
tral or monoanionic), which bind through NNO [15] and NPN
[16] coordination modes have been reported. The reactivity, in
these type of complexes is mostly dependent on the atoms which
are bound to the metal center and how sterically closed the metal
center is.
The simplicity and symmetry of the Brookhart and Gibson cat-
alysts structures was striking and led us to design a family of cat-
alysts which we suspect will allow for great flexibility in ligand
design and synthesis. While the systems described in this contribu-
tion share some structural similarities to the Brookhart and Gibson
systems, they possess an additional location from which to incor-
porate steric and electronic modifications, which has previously
demonstrated to be practical [5e,17]. In addition these heteroat-
oms may potentially allow for the Lewis acid activation of the cat-
alysts, through remote locations [12,18,19]. In this contribution we
report on the progress in the synthesis of new (N)-imidoylamidine
ligands and their use in the formation of nickel complexes which
are active for the polymerization of ethylene. The activity of
3a + 3b and 4 in presence of MAO towards the homopolymeriza-
tion of ethylene is described along with the characterization of
the products.
The suspension was allowed to cool to room temperature, was
filtered, and extracted three times with H2O. The organic layer
was dried with Na2SO4, filtered and the solvent removed under
vacuum which provided a white solid. Compound 1 was isolated
in 85% yield after purification by crystallization from methanol.
Two isomers of 1 in a 10:1 ratio were observed by 1H and 13C
NMR spectroscopy. Particularly diagnostic peaks are those as-
signed to the isopropyl groups on the phenyl ring, which in the
more symmetric isomer 1a appear at 2.92 ppm, while the minor
and less symmetric isomer has two peaks for the isopropyl groups,
one of which is shifted downfield to 3.41 ppm and the second ap-
pears at 2.86 ppm.
Single crystals of both isomers suitable for X-ray analysis
were separated by slow crystallization from methanol followed
by physical separation based upon crystal size (the major isomer
forms larger crystals). 1H and 13C NMR studies were performed
on the isolated compounds and the structures of the isomers
correspond to those shown in Scheme 1. We suspect that the
two isomers (Schemes 1, 1a and 1b) are formed by the transposi-
tion of the hydrogen in the intermediate, N-(2,6-diisopropyl-
phenyl)-N0-(2,6-dimethyl-phenyl)-acetamidine. When the hydrogen
atom is located over the less crowded nitrogen the more
symmetric ligand 1a is generated, while when the hydrogen is
located on the more crowded nitrogen the less symmetric ligand
is produced 1b.
The ORTEP structures of the isomers are shown in Fig. 1. In solid
state the ligands adopt a non planar arrangement similar to 2,6-i-
PrC6H3N(C(Me)NC6H3-2,6-i-Pr)2 recently reported [21].
2. Results and discussion
2.1. Synthesis and characterization of ligands
In the minor isomer, Fig. 1, (right) two of nitrogen atoms, N(2)
and N(3) occupy a common plane with C(13) and C(27), while
the third, N(1), is twisted out of this plane and is nearly perpendic-
ular. The N(3)–C(27) and N(2)–C(27) bond distances are 1.273(2),
consistent with a double bond, and 1.386(2), with single bond
character, respectively, Table 1. The N(1)–C(13) distance of the
The (N)-imidoylamidine ligand isomers, 2,6-MeC6H3N(C(Me)-
NC6H3-2,6-i-Pr)2 (1a) and 2,6-i-PrC6H3N(C(Me)NC6H3-2,6-i-Pr)-
(C(Me)NC6H3-2,6-Me) (1b) were synthesized by reacting 2 equiv.
of imidoyl chloride [20] with 2,6-dimethylaniline in presence of
Et3N in toluene and heating at reflux for 3 h.
N
NH
N
N
N
NH2
(1b)
NEt3,Toluene
2
+
N
- NEt3HCl
Cl
H3C
N
N
N
NH
N
(1a)
Scheme 1. Synthesis of (N)-imidoylamidine ligands.

C. Valdebenito et al. / Journal of Organometallic Chemistry 694 (2009) 717–725
719
Fig. 1. ORTEP of 1a and 1b drawn at 50% probability. Hydrogen atoms are omitted for clarity.
Table 1
With the goal of accessing a wide variety of (N)-imidoylamidine
ligands, we prepared 2,6-dimethylphenylimidoyl chloride follow-
ing literature procedures [20,21]. Subsequently, a fully symmetric
(N)-imidoylamidine, N,N0-bis-(2,6-dimetyl-phenyl)-N-[1-(2,6-di-
methyl-phenylimino)ethyl)]-acetamidine 2 was synthesized by
reacting 2 equiv. of 2,6-dimethylphenylimidoyl chloride with 2,6-
dimethylaniline in presence of Et3N in toluene and heating at re-
flux for 3 h (Eq. (1)). Compound 2 was isolated in 87% yield by crys-
tallization from ethanol. The 1H NMR and 13C NMR show only a
single isomer. Characteristic signals include: 2.46 ppm (s, 6H, Ph-
CH3), 2.19 (s, 12H, Ph-CH3), 1.95 (s, 6H, (C@N)CH3).
Selected bond distance (Å) and angle (°) for (N)-imidoylamidine ligand.
1a
1b
N(1)–C(13)
N(2)–C(13)
N(2)–C(27)
N(2)–C(23)
N(3)–C(27)
N(3)–C(23)
N(1)–C(13)–N(2)
C(13)–N(2)–C(27)
C(13)–N(2)–C(23)
N(3)–C(27)–N(2)
N(3)–C(23)–N(2)
1.2690(19)
1.4197(19)
1.258(2)
1.446(2)
1.386(2)
1.3945(19)
1.273(2)
1.2689(19)
117.19(13)
116.73(16)
117.67(14)
120.74(12)
118.48(13)
118.42(16)
ð1Þ
out of plane imine is 1.2690(19), slightly shorter than the one in
the plane which could be due more sterically crowded environ-
ment around N(3) and C(27).
Full details of the crystal structure parameters of the ligand 2 are
available in the supporting information.
A significant difference is observed in the N(2)–C(13) bond dis-
tance which is 0.06 Å longer than N(2)–C(27). This is consistent
with conjugation in the direction of the N(3) atoms, likely with
the assistance of the lone pare of N(2). The ORTEP structure of
the more symmetric ligand (Fig. 1 left) shows that the ligand
shares a similar planar arrangement but in this instance the N(1)
is less twisted out of the plane, and is nearly coplanar with the rest
of the backbone. The bond distances observed in the more sym-
metric ligand are similar to those observed in 1b and are in agree-
ment with what would be expected in a conjugated bond, between
N(2)–C(23)–N(3).
2.2. Synthesis of nickel complexes
Eq. (2) depicts the synthesis of [NiBr2{N0-(2,6-diisopropyl-phe-
nyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N-(2,6-dimethyl)-
acetamidine}] (3a) and [NiBr2{N-(2,6-diisopropyl-phenyl)-N-[1-(2,
6-diisopropyl-phenylimino)-ethyl]-N0-(2,6-dimethyl)-acetamidine}]
(3b) by the addition of 1 as a mixture of isomers to nickel (II)
dibromide 2-methoxyethyl ether in THF at room temperature for
4 days. Crystallization from THF–Ether allows isolation of 3a and
3b isomers as air and thermally stable dark purple crystals in
70% yield.

720
C. Valdebenito et al. / Journal of Organometallic Chemistry 694 (2009) 717–725
ð2Þ
Single crystals of 3a and 3b suitable for X-ray diffraction studies
Table 2
Selected bond distance (Å) and angle (°) for (N)-imidoylamidine nickel complexes.
were obtained by diffusion of ether into a THF solution at room
temperature. The results are shown in Fig. 2. The molecular struc-
tures show a six member chelate ring formed by the ligand in a
N,N-binding mode to the nickel dibromide as expected. In both iso-
mers the tetrahedral geometry around nickel is slightly distorted.
For example in complex 3a (the most symmetric), Br(2) is almost
perpendicular to the plane of the ring. This can be observed in
the corresponding angle N(1)–Ni–Br(2) (101.32(9)°) while the an-
gle of N(1)–Ni–Br(1) is 122,18(9)°. The N(3)–C(27), N(1)–C(13)
and N(2)–C(27), N(2)–C(13) bond distances are 1.293(5), 1.279(5)
and 1.392(5), 1.405(5), respectively, Table 2. The second isomer
3b shows nearly the same bond distances for N(3)–C(23), N(1)–
C(9) and N(2)–C(23), N(2)–C(9); 1.283(3), 1.287(3) and 1.411(3),
1.402(3), respectively. If we compare the 3b distances with those
of the pure ligand 1b, we find that the N–C distances of the amine
fragment (N(2)–C(23), N(2)–C(9)) become similar in length, due to
the coordination of the ligand to the nickel center.
3a
3b
4
Ni–Br(1)
Ni–Br(2a)
Ni–Br(2b)
Ni–N(1)
2.3428(6)
2.3660(7)
2.3218(4)
2.3862(4)
2.473(7)
1.9764(17)
1.9759(17)
1.283(3)
2.3874(10)
2.3543(9)
1.979(3)
1.981(3)
1.984(4)
1.977(4)
Ni–N(3)
N(3)–C(23)
N(3)–C(27)
N(3)–C(19)
N(1)–C(9)
N(1)–C(13)
N(2)–C(23)
N(2)–C(27)
N(2)–C(9)
N(2)–C(13)
N(2)–C(19)
N(3)–Ni–N(1)
Br(1)–Ni–Br(2a)
N(3)–Ni–Br(1)
N(1)–Ni–Br(1)
1.293(5)
1.294(6)
1.284(6)
1.287(3)
1.411(3)
1.402(3)
1.280(5)
1.293(5)
1.405(5)
1.403(6)
1.399(6)
90.30(13)
119.12(3)
115.91(10)
122.18(9)
89.76(7)
90.06(16)
118.98(3)
108.92(13)
104.69(12)
122.473(15)
115.83(5)
115.57(5)
The amine bound phenyl ring rests orthogonal to the plane of
the chelated ring with distances of the N(2)–C(15), 1.444(4) Å sim-
ilar to that of the complex N(2)–C(11), 1.470(3) Å.
Another noticeable characteristic of this type of ligand frame-
works bound to the nickel is the planar line configuration of the
chelated ring, which it not observed in the case of
(CH2(C(Me)NC6H3-2,6-i-Pr)2)NiBr2 [6b].
The synthesis of the less crowded and more symmetric complex
was prepared by reaction of N,N-(2,6-dimethyl-phenyl)-N-[1-(2,6-
dimethyl-phenylimino)-ethyl]-acetamidine with nickel (II) dibro-
mide 2-methoxyethyl ether in dichloromethane (DCM) at 75 °C
for 48 h , Eq. (3). Compound 4 is obtained in near quantitative
yields, after filtration, solvent evaporation and recrystallization
from DCM.
Fig. 2. ORTEP drawing of 3a and 3b drawn at 50% probability. Hydrogen atoms are omitted for clarity.

C. Valdebenito et al. / Journal of Organometallic Chemistry 694 (2009) 717–725
721
vated with MAO, 2000 equiv. of Al, were carried out, and the
results are summarized in Table 3. Reactions were performed
inside a 500 mL glass reactor in toluene (100 mL) at an ethyl-
ene pressure of 2–4 bar. The reactions used an external water
bath to maintain the temperature constant at 60–70 °C. Entry 1
corresponds to the reactivity previously reported for CH2(C(Me)-
NC6H3-2,6-i-Pr)2NiBr2/ MAO [6b] and is provided for comparison.
Entries 2 and 3 show the results obtained at different reaction
pressure for 3a + 3b precatalyst. Comparison of these entries
shows that the ethylene consumption increases at higher
pressure.
The results obtained with 4/MAO, entries 6 and 7 demonstrate
that this combination also yields ethylene polymerization sites. A
comparison of these results with catalyst 3a + 3b under the same
reaction conditions (entries 2, 5 and 3, 6) shows that the polymer-
ization activity decreases with a reduction of the steric bulk on the
N-imidoylamidine ligand.
Fig. 3. ORTEP drawing of 4, drawn at 50% probability. Hydrogen atoms are omitted
for clarity.
ð3Þ
Single crystals of 4 suitable for X-ray diffraction studies were
obtained by diffusion of ether into a DCM solution at room temper-
ature. The results of this study are shown in Fig. 3. The molecular
structure shows a six-member chelate ring. The reduction in steric
bulk around the nickel center allows for a more tetrahedral geom-
etry compared to the more crowded nickel complexes Fig. 2. The
imine N(1)–C(9) and N(3)–C(19) bond lengths are 1.284(6) and
1.294(6), respectively similar to the corresponding distances in
complexes 3a and 3b, Table 2.
Thermal analysis was performed using differential scanning
calorimetry (DSC). Results are shown in Table 3. Samples were
scanned from 0 °C to 160 °C at 10 °C/min (taking the data from
the second cycle). One sharp thermal transitions at 132 °C are
observed for the PE obtained from compound 3a and 3b when
the reaction are performed at 60 °C, increasing 4° when the reac-
tion temperature was increased to 70 °C, indicating the produc-
tion of linear PE. The polymer obtained with complexes 4/MAO
yield also unbranched PE with a melting transition of 137 °C
(average).
2.3. Activation with MAO and reactivity towards ethylene
Comparison of the entries 2 and 3 with 5 and 6 shows that the
molecular weight of the resulting polymers decreases with a
reduction of the steric bulk on the N-imidoylamidine ligand, while
the PDIs (Mw/Mn ratios) are approximately 1.8. However, both
Polymerization studies with the family of N-imidoylamidine
nickel complexes ([Ni-(N)-imidoylamidine] = 8.0 ꢀ 10ꢁ5 M) acti-
Table 3
Ethylene polymerization reactions.a
Entry
Precatalyst
Temperature (°C)
Pressure (bar)
Activityb
Mw (g/mol)
Mw/Mn
Tm (°C)
1
2
3
4
5
6
Ref. Catalystc
60
60
60
70
60
60
2
2
4
4
2
4
119
141
547
540
45
–
–
1.9
1.7
–
132
132
136
138
136
3a + 3b
3a + 3b
3a + 3b
4
160.000
169.000
87.000, 21.000
98.000
1.7, 1.04d
1.8
4
95
112.000
1.9
a
Polymerizations were carried out in 500 mL autoclave reactor with 8
controlled by thermo bath.
lmol of precatalyst, Al/Ni ratio, 2000 in 100 mL of toluene; reaction time, 30 min.; temperature
b
kg polymer/(mol Ni)(h).
Catalysts prepared as a reference.
Bimodal distribution.
c
d

722
C. Valdebenito et al. / Journal of Organometallic Chemistry 694 (2009) 717–725
2.0
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
a
b
Entry 2
Entry 3
Entry 4
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Entry 5
Entry 6
3.5
4.0
4.5
5.0
Log MW
5.5
6.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
Log MW
Fig. 4. GPC analysis of the polyethylene isolated from: (a) catalysts 3a + 3b and (b) catalyst 4, Table 3, relative to polystyrene standards at 135 °C.
systems show a slightly increase in the molecular weights when the
ethylene pressure was varied from 2 to 4 bar, Table 3 and Fig. 4a
trace red1 and black for catalyst 3a + 3b and Fig. 4b for catalyst 4.
This behavior can be associated with an increased propagation rate
at higher ethylene concentration. Under these conditions the PDI of
the polyethylene obtained remained constant. When the tempera-
ture was increased at 70 °C the systems which are composed of iso-
mers, shows a bimodal molecular weight distribution, indicating a
second site generate polymers, giving a low molecular weight frac-
tion (Mw = 21 K). The deconvolution of the trace in Fig. 4a (blue
trace), shows that the second reactive site behaves as a living cat-
alyst (PDI = 1.04). Work in progress, involves isolating the isomers
to determine the identity of living site in these systems.
spectra were obtained using Varian Unity 200 and 400 Bruker
spectrometers using deuterated solvent with TMS as internal stan-
dard. Polymers were dried overnight under vacuum, and the poly-
merization activities were calculated from the mass of product
obtained. These values were to within 5% of the calculated mass
by measuring the ethylene consumed by use of a mass flow con-
troller. The polymers were characterized by GPC analysis at
135 °C in trichlorobenzene (in a Polymers Laboratories, high-tem-
perature chromatograph, Pl-GPC 200). Polymer melting points
were measured on a TA Instruments differential scanning calorim-
eter (model DSC 290 modulate TA Instruments) at a rate of 10 °C/
min for two cycles using a temperature range of 0–160 °C. Elemen-
tal analysis was performed on a Leeman Labs Inc. CE440 elemental
analyzer and a Control Equipment Corporation 440 elemental ana-
lyzer. Electron impact (EI) mass spectra were obtained at 70 eV on
a Thermo-Finnigan MAT95 XP High Resolution Mass Spectrometer
using perfluorokerosene (PFK) as reference FTIR spectra were re-
corded on a Bruker Vector-22 spectrophotometer using KBr pellets
and in solution using C6D6 as solvent.
3. Conclusion
In conclusion, we have described the synthesis and character-
ization of stable symmetrical and non-symmetrical (N)-imidoy-
lamidine ligands and the nickel complexes produced through
reaction with nickel (II) dibromide 2-methoxyethyl ether. This syn-
thetic route represents a general pathway into a wide variety of li-
gand and NiBr2{(N)-imidoylamidine} complexes. Separation of the
complexes (3a + 3b) was achieved by crystallization and the phys-
ical separation of the isomers. The catalytic activity for the poly-
merization of ethylene in the presence of MAO has also been
investigated. The polymers properties indicate that the product is
a linear and high molecular weight (80–169 K) polyethylene.
4.2. Synthesis and characterization of compounds
4.2.1. N0-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-
phenylimino)-ethyl]-N-(2,6-dimethyl)-acetamidine (1a)
(2,6-diisopropylphenyl)acetimidoyl [20] (2 g, 8.4 mmol) was
added to a solution of 2,6-dimethylaniline (0.51 g, 4.2 mmol), tri-
ethylamine (0.85 g, 8.4 mmol) in 60 ml of toluene. The reaction
mixture was heated at reflux for 3 h. The slightly cloudy mixture
was washed three times with water, and dried over Na2SO4. The
solvent was removed under vacuum to yield a yellow solid. Crys-
tallization from ethanol gives a white solid in 85% of yield. The
1H NMR spectrum shows two isomers in a 10:1 ratio, N0-(2,6-diiso-
propyl-phenyl)-N-[1-(2,6-diisopropyl-phenylimino)-ethyl]-N-(2,6-
dimethyl)-acetamidine (1a) and N-(2,6-diisopropyl-phenyl)-N-[1-
(2,6-diisopropyl-phenylimino)-ethyl]-N0-(2,6-dimethyl)-acetamidine
(1b), respectively. 1H NMR (399.95 MHz, [d3]-chloroform, 298 K):
Major isomer 1a, d = 7.26–7.00 (m, 9H, H-Ph), 2.92 (sep, 4H,
3JHH = 6.8 Hz, CH-iPr), 2.42 (s, 6H, CH3), 1.92 (s, 6H, CH3), 1.19 (d,
4. Experimental
4.1. General remarks
All manipulations were performed under an inert atmosphere
using standard glovebox and Schlenk-line techniques. All reagents
were used as received from Aldrich unless otherwise specified. Eth-
ylene was purchased from Matheson Tri-Gas (research grade,
99.99% pure) and was further purified by passage through an oxy-
gen/moisture trap BASF R3-11 and 4 Å molecular sieves. Toluene,
THF, hexane, and pentane were distilled from benzophenone ketyl.
All polymerization reactions were carried out in a Parr autoclave
reactor as described below. Toluene for polymerization was dis-
tilled from sodium-benzophenone ketyl. The synthesis of com-
pounds 1a, b and 2 used procedures similar to the literature
procedure [20,21] and were purified by recrystallization. NMR
3
3
12H, JHH = 6.8 Hz, CH3-iPr), 1.06 (d, 12H, JHH = 6.8 Hz, CH3-iPr).
Minor isomer 1b, d 7.34–6.84 (m, 6H, H-Ph), 3.41 (sep, 2H,
3JHH = 6.8 Hz, CH-iPr), 2.86 (sep, 2H, JHH = 6.8 Hz CH-iPr) 2.08 (s,
3
6H, CH3), 2.01 (s, 3H, CH3), 1.82 (s, 3H, CH3), 1.28 (d, 6H,
3
3JHH = 6.4 Hz, CH3-iPr), 1.27 (d, 6H, JHH = 6.4 Hz, CH3-iPr) 1.18 (d,
3
3
6H, JHH = 6.8 Hz. CH3-iPr), 0.94 (d, 6H, JHH = 6.8 Hz, CH3-iPr). 13C
NMR (125.7 MHz, [d3]-chloroform, 298 K): Major isomer 1a,
156.47, 147.86, 137.32, 137.22, 128.38, 127.23, 122.87, 122.78,
28.10, 24.43, 22.94, 19.18, 18.40; Minor isomer 1b, 158, 147.89,
1
For interpretation of color in Fig. 4, the reader is referred to the web version of
this article.

C. Valdebenito et al. / Journal of Organometallic Chemistry 694 (2009) 717–725
723
137.00, 128.58, 127.88, 127.25, 124.06, 122.86, 122.82, 29.06,
27.94, 24.67, 24.45, 23.53, 22.58,18.15.
4.2.4. [NiBr2{N,N0-bis-(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-
phenylimino)ethyl)]-acetamidine}] (4)
One equivalent of nickel (II) dibromide 2-methoxyethyl ether
(0.070 g, 2.3 mmol) was added to solution of 2, (0.10 g,
4.2.2. N,N0-bis-(2,6-dimethyl-phenyl)-N-[1-(2,6-dimethyl-
a
phenylimino)ethyl)]-acetamidine (2)
2.43 mmol) in DCM was added. The mixture was stirred at room
temperature for 48 h. The reaction showed a progressive change
of color from green to purple. The resulting solution was filtered,
the solvent evaporated and the solid extracted with ether. The
product was a purple solid and obtained in a 86% yield. NMR char-
acterization was not possible because the compound is paramag-
netic. FT-IR (KBr Pellet, cmꢁ1): 3422(s), 3060(w), 2962(s),
2926(m), 2867(m), 1632(s). EI-MS(+): m/z = 629.10.
To a solution of 2,6-dimethylaniline (0.38 g, 3.2 mmol), triethyl-
amine (0.64 g, 6.4 mmol) in 60 ml of toluene was added (2,6-
dimethylphenyl)acetimidoyl (1 g, 6.4 mmol). The reaction was
heated at reflux for 3 h. The slightly cloudy mixture was washed
three times with water, and dried over Na2SO4. The solvent was re-
moved under vacuum to yield a yellow solid. Crystallization from
ethanol gives a white solid in 87% of yield. 1H NMR (399.95 MHz,
[d3]-chloroform, 298 K):
d 7.18 (m, 3H, H-Ph), 7.04 (d, 4H,
3
3JHH = 7.6 Hz, H-Ph), 6.87 (t, 2H, JHH = 7.6 Hz, H-Ph) 2.46 (s, 6H,
Ph-CH3), 2.19 (s, 12H, Ph-CH3), 1.95 (s, 6H, (C@N)CH3). 13C NMR
(125.7 MHz, [d3]-chloroform, 298 K): 156.78, 147.53, 141.01,
137.08, 128.58, 127.99, 127.87, 127.05, 122.31, 18.96, 18.59, 18.52.
4.3. Typical procedure for polymerization of ethylene
Toluene, (N)-imidoylamidine complex (8 lmol) dissolved in
DCM and MAO solution in toluene (Al/Ni = 2000), were added to
a 500 mL glass parr reactor such that the final volume of the tolu-
ene solution was 100 mL under nitrogen. The reactor was attached
to an ethylene line, and the gas fed continuously into the reactor at
the specified pressure. The pressurized reaction mixture was stir-
red at a temperature controlled by an external bath. After a specific
reaction time, the ethylene was vented and HCl–MeOH (10%) was
added to quench the excess of MAO in the polymerization. The pre-
cipitated polymer was collected by filtration and dried overnight
under vacuum.
4.2.3. [NiBr2{N0-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-
phenylimino)-ethyl]-N-(2,6-dimethyl)-acetamidine}] (3a) and
[NiBr2{N-(2,6-diisopropyl-phenyl)-N-[1-(2,6-diisopropyl-
phenylimino)-ethyl]-N0-(2,6-dimethyl)-acetamidine}] (3b)
One equivalent of nickel (II) dibromide 2-methoxyethyl ether
(0.041 g, 1.34 mmol) was added to a solution of isomers mixture
1a and 1b, (0.07 g, 1.34 mmol) in THF was added. The mixture
was stirred at room temperature for 4 days. The reaction showed
a progressive change of color from green to purple. The resulting
solution was filtered, the solvent evaporated and the solid ex-
tracted with ether. The product was a purple solid and obtained
in a 70% yield. NMR characterization was not possible because
the compound is paramagnetic. FT-IR (KBr Pellet, cmꢁ1):
3439(m), 3063(w), 3021(w), 2961(s), 2925(m), 2867(m), 1644(s).
EI-MS(+): m/z = 662.31 (M+ꢁBr).
4.4. Crystallography characterization
The monocrystal was mounted on a glass fiber and transferred
to a Bruker CCD platform diffractometer. The SMART [22] program
package was used to determine the unit-cell parameters and for
data collection (25 s/frame scan time for a sphere of diffraction
Table 4
Crystal data and structure refinement for (N)-imidoylamidine ligand.
1a
1b
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C36H49N3
523.78
150(2)
0.71073
Monoclinic
P2(1)/c
C36H49N3
523.78
150(2)
0.71073
Triclinic
ꢀ
P1
10.8098(4)
13.8640(5)
22.6187(7)
90
10.2414(11)
10.6912(12)
16.2338(18)
82.350(2)
b (Å)
c (Å)
a
(°)
b (°)
95.2900(10)
90
3375.4(2)
74.429(2)
73.118(2)
1635.5(3)
2
1.064
0.062
572
c
(°)
Volume(Å3)
Z
4
Dcalc (Mg mꢁ3
)
1.031
0.060
1144
0.59 ꢀ 0.55 ꢀ 0.46
1.89–27.90
ꢁ14 6 h 6 13
ꢁ18 6 k 6 18
ꢁ29 6 l 6 28
27470
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm3)
h Range (°)
0.19 ꢀ 0.09 ꢀ 0.08
1.99–27.77
ꢁ12 6 h 6 13
ꢁ13 6 k 6 13
0 6 l 6 21
Index ranges
Reflections collected
6711
independent reflections
7647 [Rint = 0.0229]
100.0
7647/3/364
1.193
6711 [Rint = 0.0529]
96.9
6711/0/364
1.226
Completeness to h = 26.48° (%) (for 1) and 28.52° (%) (for 10, 2)
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0662, wR2 = 0.2044
R1 = 0.0904, wR2 = 0.2233
0.337 and ꢁ0.221
R1 = 0.0632, wR2 = 0.1042
R1 = 0.1193, wR2 = 0.1220
0.262 and ꢁ0.226
Largest difference in peak and hole (e Åꢁ3
)
P
P
P
P
P
2
2
2
Definitions: R1
¼
kFoj ꢁ jFckꢂ= ½jFoj; wR2 ¼ ½ ðF2o ꢁ Fc2Þ ꢂ= ½wðF2oÞ ꢂꢂ1=2; GOF ¼ ½ ½wðFo2 ꢁ F2c Þ ꢂ=ðn ꢁ pÞꢂ1=2, where n is the number of the reflections and p is the total
number of the parameters refined. *min/max.

724
C. Valdebenito et al. / Journal of Organometallic Chemistry 694 (2009) 717–725
Table 5
Crystal data and structure refinement for (N)-imidoylamidine nickel complexes.
3a
3b
4
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C36H49N3Br2Ni
742.31
150(2)
C36H49N3Br2Ni
742.31
150(2)
0.71073
Monoclinic
P2(1)/n
C28H33N3NiBr2ꢀCCl2H2
715.03
150(2)
0.71073
Monoclinic
P2(1)/c
0.71073
Triclinic
ꢀ
P1
10.0112(9)
11.1804(10)
16.9769(15)
90.3390(10)
99.7510(10)
108.0690(10)
1776.9(3)
11.2211(8)
17.8539(13)
18.2779(14)
90
102.3690(10)
90
3576.8(5)
4
1.378
2.804
13.631(2)
3.0323(19)
18.203(3)
b (Å)
c (Å)
a
(°)
b (°)
(°)
90
107.422(2)
90
3085.3(8)
c
Volume (Å3)
Z
2
4
Dcalc (Mg mꢁ3
)
1.387
2.822
768
1.539
3.415
1448
0.25 ꢀ 0.25 ꢀ 0.09
1.57–26.55
ꢁ14 6 h 6 17
ꢁ15 6 k 6 16
ꢁ22 6 l 6 22
19492
Absorption coefficient (mmꢁ1
F(000)
)
1536
Crystal size (mm3)
h Range(°)
0.36 ꢀ 0.32 ꢀ 0.05
1.92–27.69
ꢁ12 6 h 6 13
4 6 k 6 14
0.64 ꢀ 0.41 ꢀ 0.35
1.96–27.83
ꢁ14 6 h 6 14
ꢁ23 6 k 6 23
ꢁ23 6 l 6 23
25610
Index ranges
ꢁ22 6 l 6 21
Reflections collected
17808
Independent reflections
7596 [Rint = 0.0298]
98.8
7596/0/392
1.059
7905 [Rint = 0.0245]
99.9
7905/0/395
1.059
612 [Rint = 0.0656]
95.2
6112/0/342
1.260
Completeness to h = 26.48° (%)(for 1) and 28.52° (%)(for 10, 2)
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0521, wR2 = 0.1290
R1 = 0.0718, wR2 = 0.1386
1.457 and ꢁ0.602
R1 = 0.0335, wR2 = 0.0800
R1 = 0.0443, wR2 = 0.0838
0.860 and ꢁ0.415
R1 = 0.0552, wR2 = 0.1184
R1 = 0.1029, wR2 = 0.1409
1.357 and ꢁ0.543
Largest difference in peak and hole (e Åꢁ3
)
P
P
P
P
P
2
2
2
Definitions: R1
¼
kFoj ꢁ jFckꢂ= ½jFoj; wR2 ¼ ½ ðF2o ꢁ Fc2Þ ꢂ= ½wðF2oÞ ꢂꢂ1=2; GOF ¼ ½ ½wðFo2 ꢁ F2c Þ ꢂ=ðn ꢁ pÞꢂ1=2, where n is the number of the reflections and p is the total
number of the parameters refined. *min/max.
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Acknowledgments
The authors are grateful for financial support of this work CON-
ICYT PhD Grant and projects AT-24071084 to C. Valdebenito and
projects FONDECYT 11060384, FONDAP 11980002. The authors
are grateful for useful discussions to Dr. Brian People and Professor
Mauricio Valderrama.
(e) F. Auriemma, C. De Rosa, S. Esposito, G.W. Coates, M. Fujita,
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Appendix A. Supplementary material
CCDC 705306, 705307, 705308, 705309, 705310, and 705311
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge Crys-
tallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in the
online version, at doi:10.1016/j.jorganchem.2008. 11.066.
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