Nickel pre-catalysts bearing [(N)-imidoylamidine] ligands; Influence of the presence of pyridine and pentafluorophenyl groups in ligand backbone on the reactivity in ethylene polymerizations

Article abstract of DOI:10.1016/j.jorganchem.2011.11.035

In this contribution the synthesis and polymerization activity of the nickel complexes [NiBr₂{N′-(2,6-diisopropylphenyl)-N-[1-(2,6- diisopropylphenylimine)ethyl]-N-(2,3,4,5,6-pentafluorophenyl)acetamidine}] (2), [NiBr₂{N′-(2,6-diisop

Full text of DOI:10.1016/j.jorganchem.2011.11.035

Journal of Organometallic Chemistry 700 (2012) 147e153
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Nickel pre-catalysts bearing [(N)-imidoylamidine] ligands; influence of the
presence of pyridine and pentafluorophenyl groups in ligand backbone on the
reactivity in ethylene polymerizations
,
Brian C. Peoples a b, Gala De la Vega c, Carolina Valdebenito b, Raul Quijada b, Andrés Ibañez b,
,
Mauricio Valderrama a, René Rojas a
*
a Departamento de Química Inorgánica, Facultad de Química, Pontificia Universidad Católica de Chile, Casilla 306, Santiago-22, Chile
b Departamento de Ingeniería Química, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile
c Departamento de Química, Facultad de Ciencias Naturales y Exactas, Universidad del Valle, Calle 13 No 100-00, Cali, Colombia
a r t i c l e i n f o
a b s t r a c t
In this contribution the synthesis and polymerization activity of the nickel complexes [NiBr2{N0-(2,6-
diisopropylphenyl)-N-[1-(2,6-diisopropylphenylimine)ethyl]-N-(2,3,4,5,6-pentafluorophenyl)acetam
idine}] (2), [NiBr2{N0-(2,6-diisopropylphenyl)-N-[1-(2,6-diisopropylphenylimine)ethyl]-N-(2,3,4,5,6-
pentafluorophenylimine)ethylacetamidine}] (2a) and [NiBr2{N-(2,6-diisopropylphenyl)-N-[1-(2,6-
diisopropylphenylimine)]-N-(pyridin-4-yl)acetamidine}] (3) are reported. The variation of the
Article history:
Received 24 March 2011
Received in revised form
25 November 2011
Accepted 28 November 2011
phenyl substituents on the
b amine was found to influence the polymerization activity of the
Keywords:
Ni polymerization catalysts
Imidoyl chloride
Late transition metal catalyst
Ethylene polymerization
Catalysts
complexes. The electron withdrawing/donating capacity of the substituted ring was found to
be correlated with the polymerization activity, with the pentafluoro substituted ring increasing the
polymerization activity and the pyridine ring decreasing the activity. The ligands and complexes
were characterized using standard techniques and the polymer properties analyzed.
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
properties facilitate the synthesis of new materials with previously
unattained structures and properties [5e7].
The
b
-diketiminate class of ligands, generally denoted as “nac-
Due to the influence of the ligand framework on the reactivity of
the metal center, the design of the ligand is a key step in the
development of new catalyst systems. For example the existence of
a basic functionality on the ligand framework makes it susceptible
to coordination by Lewis acids, which in some cases can be used to
activate the metal center [8e12]. This can also have an electronic
and steric effect over the metal center influencing the properties of
the catalyst systems.
Recently, we discussed that the activation of [(N)-imidoylami-
dine]NiBr2 with MAO (MAO ¼ methylaluminoxane) generates an
active site that is capable of polymerizing ethylene (Fig. 1) [13]. As
expected, the polymerization reaction shows an increase in
molecular weight with increasing pseudo-axial bulk around the
nickel center, however, the reactivity was moderate.
The imidoylamidine based systems also offer the potential for
ligand variation via the modification of the backbone amine [14]. It
is well known that pseudo-axial bulk around the nickel center is
necessary to produce high molecular weight polymers [5,15]. As
demonstrated by the activity of similar complexes which do not
bear a phenyl ring in the backbone, this steric bulk is not necessary
to achieve high molecular weight materials [16]. The presence of
nac”, or {ArNC(R)}2CH (where Ar ¼ aryl and R ¼ CH3 or bulkier
group), rightfully occupies a place alongside a narrow list of
popular ancillary supports, given its ability to stabilize or generate
unique coordination environments and to support reactive organ-
ometallic reagents [1]. The popularity of nacnac and derivatives
amongst synthetic chemists is driven by the mono-anionic nature
of the
capacity of the neutral species [2]. As is well known with neutral
imine ligands, including and diimines and acetamidines, the
substituent at the nitrogen donor atom can provide steric protec-
tion and electronic influence at the metal center, something which
is not possible in many other compounds [1,3,4]. Recently there has
been a great deal of interest focused on late transition metal
complexes as polymerization catalysts. This is justified by the
properties of the polymers produced, the ability to control and
adapt the ligand base, and the functional group tolerance, these
b-diketiminate group and also in the strong coordination
a
b
* Corresponding author. Tel.: þ56 2 354 7557; fax: þ56 2 686 4714.
E-mail address: rrojasg@uc.cl (R. Rojas).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.11.035

148
B.C. Peoples et al. / Journal of Organometallic Chemistry 700 (2012) 147e153
compound include (in ppm): 1H NMR 7.11e7.02 (m, 6H, H-Ph), 2.84
(sep, 4H, CH-i-Pr), 2.00 (s, 6H, CH3), 1.21 (d, 12H, CH3-i-Pr), 19F
NMR ꢀ147.29, ꢀ156.66, ꢀ160.35.
The ORTEP structure of compound 2Ls (Fig. 3), shows that in the
solid state the ligand adopts a non-planar arrangement similar to
the previously reported 2,6-MeC6H3N(C(Me)NC6H3-2,6-i-Pr)2 [13].
A notable difference in the solid state between compound 2Ls
and 2,6-MeC6H3N(C(Me)NC6H3-2,6-i-Pr)2, is that the nitrogen
atoms, N(1), N(2) and N(3) nearly occupy a common plane and only
a minimal distortion was observed (Table 1). The N(1)eC(1) and
C(2)eN(3) bond distances of 1.267(3) Å and 1.262(3) Å are consis-
tent with double bonds. The C(1)eN(2) and N(2)eC(2) bond
distances of 1.422(3) Å and 1.422(3) Å, respectively, are consistent
with an amine N(2).
Fig. 1. In the presence of ethylene and MAO, [(N)-imidoylamidine]NiBr2 produces
polyethylene of high molecular weight.
It was previously observed that the use of imidoyl chloride in
the synthesis of these types of ligands can result in the formation of
distinct compounds depending on the conditions used for the
reaction, in particular the order of addition and base selection were
found to be critical [18]. In the course of preparing 2Ls it was found
that the intermediate could be isolated by carefully selecting the
reaction conditions. The intermediate, N-1-(2,6-diisopro
pylphenyl)-N0-(2,3,4,5,6-pentafluorophenyl)acetamidine (2I) was
generated by reaction of 1 equiv of (2,6-diisopropylphenyl)aceti-
midoyl chloride with pentafluoroaniline (Scheme 2).
this group however offers the opportunity to modify the electronics
at the transition metal center without significantly altering the
steric environment. It is suspected that the modification of the
electronic properties at the metal center will increase the activity
while maintaining the high molecular weight of the polymer.
Therefore, in this contribution, the synthesis, characterization and
reactivity of ligandemetal combinations which are structurally
similar to compound 1 are discussed. The activity of the compounds
in the presence of MAO toward ethylene is described along with the
characterization of the products.
The pentafluoroaniline was added to a toluene solution of (2,6-
diisopropylphenyl)acetimidoyl chloride at room temperature then
the reaction was heated at reflux for 4 h to afford crude 2IꢁHCl. The
crude material was treated with aqueous NH3 (25%) in dichloro-
methane (DCM), the organic phase dried over Na2SO4, followed by
solvent evaporation and crystallization from methanol which
provided a white solid of (2I) in 70% yield. 1H NMR spectroscopy
confirmed the structure of intermediate. Diagnostic peaks include
(in ppm): 3.22 (CH-i-Pr), 2.04 (CH3C¼N), and 5.96 (NH).
2. Results and discussion
2.1. Synthesis of ligands
The general synthesis of the ligands and nickel complexes has
previously been discussed in detail and only a general discussion
will be presented here [17]. Two synthetic targets for ligands were
pursued (Fig. 2), and were selected on the basis of how it was
thought the metal center once ligated would be affected. It was
thought that the pentafluorophenyl ring in compound 2 would
reduce the charge at the metal center in comparison to the diiso-
methylphenyl group present in compound 1, which was previously
reported by our group, whereas the use of the pyridinyl group in
compound 3 would increase the electron density at the metal
center due to the basicity of the substituent, thus producing
changes in the ethylene polymerization activity and polymer
properties.
The 19F NMR presented three peaks at ꢀ146.60, ꢀ153.99, ꢀ
162.61 ppm. Single crystals of 2I suitable for X-ray diffraction were
obtained by crystallization from methanol at room temperature.
The resulting structure is shown in Fig. 4.
The structure shows that both nitrogen atoms and the carbon of
the methyl are sharing a plane, in a trigonal-planar geometry
around the C(7) carbon, while the two substituted phenyl rings are
perpendicular to that plane. The trigonal-planar geometry around
C(7) is slightly distorted. The N(2)eC(7)eN(1), C(8)eC(7)eN(1) and
N(2)eC(8)eC(7) angles are 120.0(2)ꢂ, 124.5(2)ꢂ and 115.5(2)ꢂ
respectively. The bond distances around the C(7); C(7)eN(1), C(7)e
N(2) and C(7)eC(8) are 1.298(2) Å, 1.339(2) Å and 1.502(2) Å,
respectively, indicating that the C(7)eN(1) and C(7)eN(2) bonds
have a great deal of double bond character due to the level of
conjugation. As expected the C(7)eC(8) bond (Table 1) is of single
bond character.
The synthesis of the supporting ligand for compound
2
(symmetric ligand 2Ls) proceeds through the addition of 2 equiv of
(2,6-diisopropylphenyl)acetimidoyl chloride to pentafluoroaniline
in the presence of triethylamine (Scheme 1). A pure white powder
was obtained after crystallization from ethanol, the 1H, 13C and 19
F
The addition of a second equivalent of (2,6-diisopropylphenyl)
acetimidoyl chloride to 2I in toluene solution produced 2La
NMR analysis reveal that the synthesis was clean and only a single,
pure compound was produced. The characteristic signals of the
Fig. 2. Synthetic targets in this contribution.

B.C. Peoples et al. / Journal of Organometallic Chemistry 700 (2012) 147e153
149
Scheme 1. Synthesis of compound 2Ls.
(Scheme 2), which was isolated as a yellow solid in 60% yield
following crystallization from ethanol. The 1H, 13C and 19F NMR
analysis reveal that the synthesis was clean and only a single
compound was produced. The characteristic signals of the
compound include (in ppm): 7.38e7.22 (m, 3H, H-Ph), 3.26 (sep,
2H, CH-i-Pr), 2.79 (sep, 2H, CH-i-Pr), 2.18 (s, 3H, CH3), 1.91 (s, 3H,
CH3), 1.25 (dd, 12H, CH3-i-Pr), 1.17 (d, 12H, CH3-i-Pr), 0.94 (d, 12H,
CH3-i-Pr), 19F NMR ꢀ146.16, ꢀ157.55, ꢀ156.65. Single crystals of 2La
suitable for X-ray diffraction were obtained by crystallization from
ethanol at room temperature. The resulting structure is shown in
Fig. 5. EI-MS [2La þ H]þ analysis revealed a mass of 586.2 which is
consistent with the structure.
Fig. 3. ORTEP drawing of 2Ls drawn at 50% probability. Hydrogen atoms were omitted
for clarity.
In isomer 2La (Fig. 5) two of the nitrogen atoms, N(1) and N(2)
occupy a common plane with C(7), C(9) and C(8) while the third,
N(3), is slightly twisted out of this plane, more similar to 2,6-
MeC6H3N(C(Me)NC6H3-2,6-i-Pr)2 [13] than the 2Ls isomer. The
distances between the atoms N(1)eC(7) and N(3)eC(9) are
1.285(2) Å and 1.264(2) Å, which are consistent with a double bond
and the distances between N(2)eC(7) and N(2)eC(9) are 1.383(2) Å
and 1.437(2) Å which are consistent with a single bond (Table 1).
In a comparison with complex 2Ls where the distances C(2)e
N(2) and C(1)eN(2) are the same (1.422(3) Å) we can find a signif-
icant difference in the C(9)eN(2) bond distance which is 0.054 Å
longer than C(7)eN(2). This is consistent with asymmetry of the
ligand and the less steric hindrance exerted by the penta-
fluoroaniline group in the asymmetric compound. The ORTEP
structure of the more symmetric ligand (Fig. 3) shows that the
substituted phenyl ring in the ligand shares a similar planar
arrangement, but in 2La it is observed that the planes in the
molecule are not completely orthogonal (Fig. 5).
and 1H NMR are consistent with a single product. The characteristic
3
signals include (in ppm) 1H NMR:
d
8.69 (d, 2H, JHH ¼ 6.8 Hz, H-
3
pyridine), 7.25 (d, 2H, JHH ¼ 6.8 Hz, H-pyridine), 7.12 (d, 4H,
3JHH ¼ 6.8 Hz, p-H-Ph), 7.04 (m, 2H, JHH ¼ 6.8 Hz, m-H-Ph), 2.90
3
3
(sep, 4H, JHH ¼ 6.8 Hz, CH-i-Pr), 1.97 (s, 6H, CH3), 1.23 (d, 12H,
3JHH ¼ 6.8 Hz, CH3-i-Pr), 1,09 (d, 12H, JHH ¼ 6.8 Hz, CH3-i-Pr).
3
Attempts to isolate the intermediate compound, as was accom-
plished in the synthesis of 2La (Scheme 2) were not successful.
2.2. Synthesis of nickel complexes
The
[NiBr2{N0-(2,6-diisopropylphenyl)-N-[1-(2,6-diisopropyl
phenylimine)ethyl]-N-(2,3,4,5,6-pentafluorophenyl)acetamidine}]
(2), [NiBr2{N0-(2,6-diisopropylphenyl)-N-[1-(2,6-diisopropylpheny
limine)ethyl]-N-(2,3,4,5,6-pentafluorophenylimine)ethylacetamidi
ne}] (2a) and [NiBr2{N-(2,6-diisopropylphenyl)-N-[1-(2,6-diisopro
pylphenylimine)]-N-(pyridin-4-yl)acetamidine}] (3) were ob-
tained by the addition of 2Ls, 2La or 3Ls to a suspension of nickel
(II) dibromide 2-methoxyethyl ether in DCM and stirring at 60 ꢂC
for 4 days. The resulting purple (for 2Ls and 2La) and blue (for 3Ls)
The symmetric ligand 3Ls, precursor of complex 3 (Fig. 2) was
produced using a similar synthetic pathway as compound 2Ls with
1 equiv of 4-aminopyridine being added to 2 equiv of (2,6-
diisopropylphenyl)acetimidoyl chloride in toluene in the presence
of triethylamine. The product was washed and purified via column
chromatography. A yellow solid was recovered in 50% yield. The 13C
Table 1
Selected bond distance (Å) and angles (deg) for N-imidoylamidine ligands 2Ls and 2La and intermediate 2I.
2I
2Ls
2La
N(1)eC(6)
N(1)eC(7)
N(2)eC(7)
N(2)eC(9)
1.401(2)
1.298(2)
1.339(2)
1.430(2)
1.502(2)
120.0(2)
124.5(2)
115.5(2)
118.2(2)
124.9(2)
C(1)eN(1)
C(1)eC(3)
C(1)eN(2)
C(2)eN(2)
C(2)eC(4)
C(2)eN(3)
N(1)eC(1)eN(2)
N(1)eC(1)eC(3)
N(3)eC(2)eN(2)
N(2)eC(2)eC(4)
C(2)eN(2)eC(1)
1.267(3)
1.483(3)
1.422(3)
1.422(3)
1.498(3)
1.262(3)
114.3(2)
126.2(2)
119.0(2)
114.1(2)
126.8(2)
C(7)eN(1)
C(7)eC(8)
C(7)eN(2)
C(9)eN(2)
C(9)eC(10)
C(9)eN(3)
N(1)eC(7)eN(2)
N(1)eC(7)eC(8)
N(3)eC(9)eN(2)
N(2)eC(9)eC(10)
C(9)eN(2)eC(7)
1.285(2)
1.503(2)
1.383(2)
1.437(2)
1.500(2)
1.264(2)
117.1(1)
125.7(1)
116.5(1)
117.4(1)
119.7(1)
C(7)eC(8)
N(1)eC(7)eN(2)
N(1)eC(7)eC(8)
N(2)eC(7)eC(8)
C(7)eN(1)eC(6)
C(7)eN(2)eC(9)

150
B.C. Peoples et al. / Journal of Organometallic Chemistry 700 (2012) 147e153
Scheme 2. Asymmetric ligand synthesis (2La). (a) Toluene, reflux 4 h. (b) Toluene, reflux 24 h.
complexes can be isolated after filtration, solvent evaporation and
recrystallization from DCMeEther in 77%, 70%, and 73% yields
respectively.
and 1.413(3) Å respectively, indicating the double and single
bond character around the imines and amine nitrogen respec-
tively (Table 2).
NMR characterization of the complexes was poor due to the
paramagnetic nature of the pseudo-tetrahedral nickel centers, and
structural identification inconclusive. Monocrystals of all three of
the complexes were obtained, however, only the structure of 2a
was resolvable, due to twinning in complexes 2 and 3. Crystals of
compound 2a were successfully obtained via the slow evaporation
of a dilute DCM solution. X-ray analysis of the crystals revealed the
molecular structure shown in Fig. 6. Bond angles and distances are
given in Table 2.
The molecular structure confirms a six member chelate ring
formed by the ligand in a N,N binding mode to the nickel
dibromide. The tetrahedral geometry around nickel is distorted.
For example, Br(1) is almost perpendicular to the plane of the
metal containing ring. This can be observed in the corresponding
angle N(3)eNieBr(1), 103.1(5)ꢂ while the angle of N(3)e
NieBr(1) is 122.0(5)ꢂ. The N(1)eC(7), N(3)eC(9), N(2)eC(7) and
N(2)eC(9) bond distances are 1.294(3) Å, 1.286(3) Å, 1.397(3) Å
It was noticed in the synthesis of the ligands and the corre-
sponding nickel complexes, that the production of single crystals
for X-ray analysis was a great deal more difficult than similar
ligands and complexes, in particular the nacnac complexes. It is
thought that the presence of the nitrogen in the
a position relative
to the imines in these ligands causes a disruption in the planarity of
the ligand backbone, making the isolation of crystals suitable for X-
ray crystallization more difficult. In addition, the crystallization
behavior of the complexes 2 and 2a was interesting as one of the
complexes (2a) crystallized after a relatively short time, however,
the other symmetric complex required substantially longer periods
of time to form crystals even under various solvent pairs/condi-
tions. Even when crystals were obtained the structures were
unresolvable due to twinning. FT-IR and elemental analysis were
consistent with the proposed structures.
2.3. Activation with MAO and reactivity toward ethylene
polymerization
Polymerization studies using the nickel complexes 2, 2a and 3
activated with MAO were carried out and the results summarized
Fig. 4. ORTEP drawing of 2I drawn at 50% probability. Hydrogen atoms are omitted for
Fig. 5. ORTEP drawing of 2La drawn at 50% probability. Hydrogen atoms are omitted
clarity.
for clarity.

B.C. Peoples et al. / Journal of Organometallic Chemistry 700 (2012) 147e153
151
Table 3
Ethylene polymerization reactions.a
Entry Precatalyst Temp. (ꢂC) Activityb Mw (kg/mol) Mw/Mn Tm (ꢂC)
1
2
3
4
5
6
7
1
2
2
2a
2a
3
60
60
70
60
70
60
70
95
468
70
387
145
68
112
84
1.9
2.1
1.5
2.5
1.6
1.8
2.0
136
133
135
134
134
126
129
184
162
122
102
98
3
110
a
Polymerizations were carried out in 500 mL autoclave reactor with 8 mmol of
precatalyst, Al/Ni ratio of 2000 in 100 mL of toluene; reaction time, 30 min; ethylene
pressure 4 bar; temperature controlled by external bath.
b
kg polymer/(mol Ni)(h).
3. Conclusions
The ability to remotely modify the electronic properties of
a metal center without significantly altering the steric environment
is particularly important in late transition metal catalyst systems.
As the ligand, variation in the complexes described in this contri-
bution occur remotely, in the ligand backbone, and uses groups
which are about the same size, there is little effect on the steric
environment around the metal center. Thus the changes in the
polymerization activity and polymer properties are due to varia-
tions in the electronic environment of the metal center. This
provides access to a convenient method to explore the relationship
between electronic properties and polymerization activities.
Comparison of the dimethylphenyl substituted [(N)-imidoylami-
dine] (compound 1) with compounds 2 and 3, shows that the
activity of the catalyst system is very dependent on the electronic
effects of the ligand. Compound 2, in which the nickel center is
more electron deficient, shows a greatly increased polymerization
activity, whereas compound 3, which bears a pyridine substituted
[(N)-imidoylamidine] ligand, and should be slightly more electro-
positive than compound 1, shows a reduced polymerization
activity. This is consistent with previously observed results in
exocyclically activated compounds, in which reduction of the
electron density at the metal center resulted in an increased
polymerization activity.
Fig. 6. ORTEP structure of complex 2a drawn at 50% probability.
in Table 3. The results for compound 1 were previously reported
and are used for comparison purposes. In each case, the formation
of high molecular weight linear polyethylene was observed.
Catalysts which bear more negatively charged ligands (meaning
that the metal center has a greater positive charge) 2 and 2a,
entries 2 and 4, show an increase in activity compared to
compound 1, entry 1.
This is likely due to the decreased insertion barriers, similar to
those predicted theoretically in NiDAB systems by Ziegler et al. [19].
The melting points of the polymers produced by 2 and 2a decrease
by 1e2 ꢂC compared to 1, indicating that the polymers are less
linear. Increasing the relative charge on the Ni center, compound 3,
results in a large reduction, ca. 85%, in activity compared to
complex 2. The melting temperature of the material produced by 3,
entry 7, decreased by 6 ꢂC compared to those produced by 2. This
indicates that not only does the presence of the pyridinyl group on
the ligand backbone reduce the activity, but that the reduced
charge increases chain branching. When the polymerization
temperature is increased to 70 ꢂC the activities of both 2 and 2a
decrease substantially, entries 3 and 5, while the activity of 3
actually increases by ca. 50%. This is likely due to the decomposition
of the complexes 2 and 2a at elevated temperatures.
4. Experimental section
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.
Ethylene was purchased from Matheson Tri-Gas (research grade,
99.99% pure) and was further purified by passage through an
oxygen/moisture trap BASF R3-11 and 4 Å molecular sieves.
Toluene, THF, hexane, and pentane were distilled from benzophe-
none ketyl and DCM was distilled from calcium hydride. The
synthesis of compounds 1e3 used recently reported procedures.
NMR spectra were obtained using Varian Unity 200 and Bruker
Avance-400 spectrometers using deuterated solvents and TMS as
internal standard. Polymers were dried overnight under vacuum,
and the polymerization 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
controller. The polymers were characterized by GPC analysis at
135 ꢂC in trichlorobenzene (in a Waters Alliance 2000 GPC). Poly-
mer melting points were measured on a TA Instruments model DSC
2920 modulated differential scanning calorimeter at a rate of 10 ꢂC/
min for two cycles using a temperature range of 0e160 ꢂC.
Table 2
Selected bond distances (Å) and angles (deg) for the N-
imidoylamidine nickel complex 2a.
2a
N(1)eC(7)
N(2)eC(7)
N(2)eC(9)
N(3)eC(9)
NieN(1)
NieN(3)
NieBr(1)
NieBr(2)
N(1)eNieN(3)
N(3)eNieBr(1)
N(3)eNieBr(2)
N(1)eNieBr(1)
N(1)eNieBr(2)
C(7)eN(2)eC(9)
1.294(3)
1.397(3)
1.413(3)
1.286(3)
1.976(2)
1.965(2)
2.371(4)
2.316(4)
88.13(7)
100.10(5)
122.00(5)
110.10(5)
113.21(5)
126.09(2)

152
B.C. Peoples et al. / Journal of Organometallic Chemistry 700 (2012) 147e153
Elemental analysis was performed on a Leeman Labs Inc. CE440
elemental analyzer and a Control Equipment Corporation 440
elemental analyzer. Electron impact (EI) mass spectra were ob-
tained at 70 eV on a Thermo-Finnigan MAT95 XP High Resolution
Mass Spectrometer using perfluorokerosene (PFK) as reference. FT-
IR spectra were recorded on a Bruker Vector-22 spectrophotometer
using KBr pellets and in solution using C6D6 as solvent.
137.26, 123.81, 123.26, 29.92, 28.36, 23.44, 22.89, 18.99. 19F NMR
(200 MHz, CDCl3, 298 K):
d
/ppm ¼ ꢀ147.29, ꢀ156.66, ꢀ160.35. FT-IR
(KBr Pellet, cmꢀ1): 3402(s), 2968(s), 2929(m), 2869(m), 1638(s). EI-
MS[2Ls þ H]þ: m/z ¼ 586.32.
4.2.4. N-(2,6-Diisopropylphenyl)-N-1-(2,6-diisopropylphenylimine)-
N-(pyridine-4-yl)acetamide (3Ls)
(2,6-Dimethylphenyl)acetimidoyl chloride (1.00 g, 4.2 mmol)
was added to a solution of 4-aminopyridine (0.20 g, 2.1 mmol) and
triethylamine (0.42 g, 4.2 mmol) in 60 ml of toluene. The reaction
was heated at reflux with stirring for 6 h. The resulting solution was
washed three times with distilled water and dried with Na2SO4. The
solvent was removed under vacuum and a brown solid was ob-
tained. The product was purified using column chromatography
(ether/hexanes) and a yellow solid obtained (after solvent evapo-
ration) in a 50% yield.
4.2. Synthesis and characterization of compounds
4.2.1. N-1-(2,6-Diisopropylphenyl)-N0-(2,3,4,5,6-pentafluorophenyl)
acetamidine (2I)
(2,6-Diisopropylphenyl)acetimidoyl chloride [18] (1.00 g,
4.2 mmol) was added to
a solution of 2,3,4,5,6-pentafluoro
phenylaniline (0.77 g, 4.2 mmol), in 20 ml of toluene and stirred for
4 h under reflux. A white solid (2IꢁHCl) was collected by filtration
washed with toluene (5 ml). The solid 2IꢁHCl was dissolved in DCM
and washed three times with 25% of aqueous NH3 solution. The
organic phase was dried over Na2SO4. The solvent was removed
under vacuum to yield a white solid. Crystallization from methanol
gives white crystals in 73% of yield.
1H NMR (399.95 MHz, CDCl3, 298 K):
d
/ppm ¼ 8.69 (d, 2H,
3
3JHH ¼ 6.8 Hz, H-pyridine), 7.25 (d, 2H, JHH ¼ 6.8 Hz, H-pyridine),
7.12 (d, 4H, 3JHH ¼ 6,8 Hz, p-H-Ph), 7.04 (m, 2H, 3JHH ¼ 6.8 Hz, m-H-
3
Ph), 2.90 (sep, 4H, JHH ¼ 6.8 Hz, CH-i-Pr), 1.97 (s, 6H, CH3), 1.23 (d,
3
3
12H, JHH ¼ 6.8 Hz, CH3-i-Pr), 1.09 (d, 12H, JHH ¼ 6.8 Hz, CH3-i-Pr).
1H NMR (399.95 MHz, CDCl3, 298 K):
d
/ppm ¼ 7.33e7.20 (m, 3H,
13C NMR (399.95 MHz, CDCl3, 298 K):
d
/ppm ¼ 157.82; 151.31;
H-Ph), 5.95 (s,1H, NH), 3.22 (m, 2H, CH-i-Pr), 2.04 (s, 3H, CH3),1.29 (d,
151.25; 144.64; 137.15; 123.86; 123.69; 123.23; 28.44; 23.68; 23.03;
19.77. FT-IR (KBr Pellet, cmꢀ1): 2959(s), 2930(w), 2867(w), 1652(s),
1239(s).
6H, 3JHH ¼ 6.4 Hz, CH3-i-Pr), 1.23 (d, 6H, 3JHH ¼ 6.8 Hz, CH3-i-Pr). 13
C
NMR (399.95 MHz, CDCl3, 298 K):
d
/ppm ¼ 159.78, 146.08, 132.27,
128.95, 124.16, 123.85, 29.05, 28.65, 24.44, 23.46, 23.04, 18.51. 19F
NMR (200 MHz, CDCl3, 298 K):
d
/ppm ¼ ꢀ146.60, ꢀ153.99, ꢀ162.61.
4.2.5. [NiBr2{N0-(2,6-diisopropylphenyl)-N-[1-(2,6-diisopropylphen
ylimine)ethyl]-N-(2,3,4,5,6-pentafluorophenylimine)acetamidine}] (2)
1 equiv of nickel (II) dibromide 2-methoxyethyl ether (0.14 g,
4.17 mmol) was added to a solution of compound 2Ls, (0.16 g,
4.17 mmol) in DCM. The mixture was stirred under reflux for 4 days.
The reaction showed a progressive change of color from light to
dark purple. The resulting solution was filtered, the solvent evap-
orated and the solid extracted with ether. The product was a purple
solid and obtained in a 67% yield. NMR characterization was not
possible because the compound is paramagnetic. Elemental anal-
ysis (%) C34H40Br2F5N3Ni (M ¼ 803.09 g/mol): calculated C 50.78, H
5.01, N 5.23; found. C 60.14, H 5.21, N 4.93.
FT-IR (KBr Pellet, cmꢀ1): 3402(s), 3061(w), 2968(s), 2929(m),
2869(m), 1638(s). EI-MS(þ): m/z ¼ 385.16.
4.2.2. N0-(2,6-Diisopropylphenyl)-N-[1-(2,6-diisopropylphenylimine)
ethyl]-N-(2,3,4,5,6-pentafluorophenylimine)ethylacetamidine (2La)
(2,6-Diisopropylphenyl)acetimidoyl chloride (0.5 g, 2.1 mmol)
was added to
a
solution of N-1-(2,6-diisopropylphenyl)-N0-
(2,3,4,5,6-pentafluorophenyl)acetamidine (2I) (0.8 g, 2.1 mmol) in
20 mL of toluene. The reaction mixture was heated at reflux for
24 h. The slightly cloudy mixture was filtered and the filtrate was
washed three times with 25% of aqueous NH3 solution and dried
over Na2SO4. The solvent was removed under vacuum to yield
a yellow oil. Crystallization from ethanol gives a white solid in 68%
4.2.6. [NiBr2{[N0-(2,6-diisopropylphenyl)-N-[1-(2,6-diisopropylph
enylimine)ethyl]-N-(2,3,4,5,6-pentafluorophenylimine)ethyl]
acetamidine}] (2a)
yield. 1H NMR (399.95 MHz, CDCl3, 298 K):
d/ppm ¼ 7.38e7.22 (m,
3H, H-Ph), 7.09e6.99 (m, 3H, H-Ph), 3.26 (sep, 2H, 3JHH ¼ 6.8 Hz, CH-
i-Pr), 2.79 (sep, 2H, 3JHH ¼ 6.8 Hz, CH-i-Pr), 2.12 (s, 3H, CH3), 1.91 (s,
1 equiv of nickel (II) dibromide 2-methoxyethyl ether (0.14 g,
4.17 mmol) was added to a solution of compound 2La, (0.16 g,
4.17 mmol) in DCM. The mixture was stirred at reflux for 4 days. The
reaction showed a progressive change of color from light to dark
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 77% yield. NMR characterization was not possible
because the compound is paramagnetic. FT-IR (KBr Pellet, cmꢀ1):
3047(w), 2968(s), 2928(s), 2870(w), 1635(s), 1300(s). Elemental
analysis (%) C34H40Br2F5N3Ni (M ¼ 803.09 g/mol): calculated C
50.78, H 5.01, N 5.23; found. C 49.84, H 5.46, N 5.33.
3
3H, CH3), 1.26 (dd, 12H, JHH ¼ 6.8 Hz, CH3-i-Pr), 1.17 (d, 12H,
3JHH ¼ 6.8 Hz, CH3-i-Pr), 0.96 (d, 12H, JHH ¼ 6.8 Hz, CH3-i-Pr). 13C
3
NMR (399.95 MHz, CDCl3, 298 K):
d/ppm ¼ 163.25, 157.78, 147.59,
144.25, 137.09, 136.79, 129.34, 124.53, 123.49, 123.14, 29.12, 28.20,
24.69, 24.41, 23.62, 22.66, 20.23, 19.52. 19F NMR (200 MHz, CDCl3,
298 K):
z ¼ 586.2.
d
/ppm ¼ ꢀ146.16, ꢀ157.56, ꢀ158.64. EI-MS[2La þ H]þ: m/
4.2.3. N0-(2,6-Diisopropylphenyl)-N-[1-(2,6-diisopropylphenylimine)
ethyl]-N-(2,3,4,5,6-pentafluorophenyl)acetamidine (2Ls)
(2,6-Diisopropylphenyl)acetimidoyl chloride (2.00 g, 8.4 mmol)
was added to a solution of 2,3,4,5,6-pentafluorophenylaniline
(0.77 g, 4.2 mmol), triethylamine (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. Crystallization from methanol gives a white solid in
82% yield.
4.2.7. [NiBr2{N-(2,6-diisopropylphenyl)-N-[1-(2,6-diisopropylp
henylimine)]-N-(pyridine-4-yl)acetamide}] (3)
1 equiv of nickel (II) dibromide 2-methoxyethyl ether (0.11 g,
3.1 mmol) was added to a solution of compound 3L, (0.15 g,
3.1 mmol) in DCM. The mixture was stirred at room temperature
for 4 h. The reaction showed a progressive change of color from
green to blue. The resulting solution was filtered, the solvent
evaporated and the solid extracted with ether. The product was
a purple solid and obtained in a 73% yield. NMR characterization
was not possible because the compound is paramagnetic. EI-
MS(þ): m/z ¼ 715.3(Mþ). Elemental analysis (%) C33H44Br2N4Ni
1H NMR (399.95 MHz, CDCl3, 298 K):
d
/ppm ¼ 7.11e7.02 (m, 6H,
3
H-Ph), 2.84 (sep, 4H, JHH ¼ 6.8 Hz, CH-i-Pr), 2.00 (s, 6H, CH3), 2.21
3
3
(d, 12H, JHH ¼ 7.2 Hz, CH3-i-Pr), 1.08 (d, 12H, JHH ¼ 6.8 Hz, CH3-i-
Pr). 13C NMR (399.95 MHz, CDCl3, 298 K):
/ppm ¼ 155.99, 144.03,
d

B.C. Peoples et al. / Journal of Organometallic Chemistry 700 (2012) 147e153
153
(M ¼ 715.23 g/mol): calculated C 55.42, H 6.20, N 7.83; found. C
Appendix. Supplementary material
55.92, H 5.90, N 7.43.
Additional details about the study for compound 2a are avail-
able in the supporting material. Supplementary material associated
with this article can be found, in the online version, at doi:10.1016/j.
jorganchem.2011.11.035.
4.3. Typical reaction with ethylene
A solution of (N)-imidoylamidine complex (8
mmol) in DCM and
MAO solution in toluene (Al/Ni ¼ 2000), were added to a 500 mL
glass Parr reactor such that the final volume of the toluene solution
was 100 mL. The solution was stirred under nitrogen and brought
to temperature. The reactor was then attached to an ethylene line,
and the gas fed continuously into the reactor at the specified
pressure. After the specified reaction time, the ethylene was vented
and acidified methanol (10 wt% HCl) was added to quench any
residual MAO in the polymerization. The precipitated polymer was
collected by filtration and dried overnight under vacuum.
References
[1] S.D. Ittel, L.K. Johnson, M. Brookhart, Chem. Rev. 100 (2000) 1169e1204.
[2] L. Bourget-Merle, M.F. Lappert, J.R. Severn, Chem. Rev. 102 (2002) 3031e3066.
[3] G.W. Coates, Chem. Rev. 100 (2000) 1223e1252.
[4] V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283e316.
[5] L.K. Johnson, C.M. Killian, M. Brookhart, J. Am. Chem. Soc. 117 (1995)
6414e6415.
[6] S. Mecking, L.K. Johnson, L. Wang, M. Brookhart, J. Am. Chem. Soc. 120 (1998)
888e899.
[7] P. Kuhn, D. Semeril, D. Matt, M.J. Chetcuti, P. Lutz, Dalton Trans. (2007)
515e528.
[8] Z.J.A. Komon, G.M. Diamond, M.K. Leclerc, V. Murphy, M. Okazaki, G.C. Bazan,
J. Am. Chem. Soc. 124 (2002) 15280e15285.
4.4. Crystallographic characterization
The monocrystal was mounted on a glass fiber and transferred to
a Bruker CCD platform diffractometer. The SMART program package
was used to determine the unit-cell parameters and for data
collection (25 s/frame scan time for a sphere of diffraction data) [20].
The raw frame data was processed using SAINT and SADABS to yield
the reflection data file. Subsequent calculations were carried out
using the SHELXTL program. The structure was solved by direct
methods and refined on F2 by full-matrix least-squares techniques.
The analytical scattering factors for neutral atoms were used
throughout the analysis [21]. Hydrogen atoms were located from
a difference-Fourier map and refined (x,y,z and Uiso).
[9] Y. Chen, G. Wu, G.C. Bazan, Angew. Chem., Int. Ed. 44 (2005) 1108e1112.
[10] D.J. Parks, W.E. Piers, M. Parvez, R. Atencio, M.J. Zaworotko, Organometallics
17 (1998) 1369e1377.
[11] A.R. Cabrera, Y. Schneider, M. Valderrama, R. Frohlich, G. Kehr, G. Erker,
R.S. Rojas, Organometallics 29 (2010) 6104e6110.
[12] R.S. Rojas, B.C. Peoples, A.R. Cabrera, M. Valderrama, R. Fröhlich, G. Erker,
G. Kehr, T. Weigand, H. Eckert, Organometallics (2011). doi:10.1021/
om200536z.
[13] C. Valdebenito, M.T. Garland, R. Quijada, R. Rojas, J. Organomet. Chem. 694
(2009) 717e725.
[14] M.N. Kopylovich, A.J.L. Pombeiro, Coord. Chem. Rev. 255 (2011) 339e355.
[15] L.K. Johnson, S. Mecking, M. Brookhart, J. Am. Chem. Soc. 118 (1996) 267e268.
[16] J.D. Azoulay, R.S. Rojas, A.V. Serrano, H. Ohtaki, G.B. Galland, G. Wu, G.C. Basan,
Angew. Chem., Int. Ed. 48 (2009) 1089e1092.
[17] R.T. Boere, V. Klassen, G. Wolmershauser, Dalton Trans. (1998) 4147e4154.
[18] R. Caris, B.C. Peoples, M. Valderrama, G. Wu, R. Rojas, J. Organomet. Chem. 694
(2009) 1795e1801.
Acknowledgments
[19] M.J. Szabo, N.M. Galea, A. Michalak, S.-Y. Yang, L.F. Groux, W.E. Piers, T. Ziegler,
J. Am. Chem. Soc. 127 (2005) 14692e14703.
[20] SMART Software Users Guide, Version 5.1, Bruker Analytical X-Ray Systems,
Inc, Madison, WI, 1999.
[21] International Tables for X-Ray Crystallography, Kluwer Academic Publishers,
Dordrecht, 1992.
The authors are grateful for financial support of projects FON-
DECYT 11060384 and 1100286. B. Peoples is grateful for Post-
doctoral funding from Pontificia Universidad Católica de Chile
Vicerrectoría de Investigación (VRI) No 2/2010.