Mono and bimetallic nickel bromide complexes bearing azolate-imine ligands: Synthesis, structural characterization and ethylene polymerization studies

Article abstract of DOI:10.1016/j.jorganchem.2009.01.005

The synthesis of N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-diisopropylaniline (1) and N-(1-(indazol-2-yl)ethylidene)-2,6-diisopropylaniline (2) allowed access to new transition metal complexes. When reacted with dibromo(2,2′-dimethoxyethylether)nicke

Full text of DOI:10.1016/j.jorganchem.2009.01.005

Journal of Organometallic Chemistry 694 (2009) 1795–1801
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Mono and bimetallic nickel bromide complexes bearing azolate-imine ligands:
Synthesis, structural characterization and ethylene polymerization studies
Rodrigo Caris a, Brian C. Peoples b, Mauricio Valderrama a, Guang Wu c, Rene Rojas a,b,
*
a Departamento de Química Inorgánica, Facultad de Química, Pontificia Universidad Católica de Chile, Casilla 306, Santiago-22, Chile
b Centro para la Investigación Interdisciplinaria Avanzada en Ciencias de Materiales (CIMAT), Chile
c Departments of Chemistry and Materials, University of California, Santa Barbara, CA 93106, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-diisopropylaniline (1) and N-(1-(inda-
zol-2-yl)ethylidene)-2,6-diisopropylaniline (2) allowed access to new transition metal complexes. When
reacted with dibromo(2,20-dimethoxyethylether)nickel(II) the complexes [NiBr2{N-(1-(3,5-dimethyl-
Received 13 November 2008
Received in revised form 7 January 2009
Accepted 8 January 2009
pyrazol-1-yl)ethylidene)-2,6-diisopropylaniline}] (3) and [Ni2Br2(l-Br)2{N-(1-(indazol-1-yl)ethylidene)-
Available online 14 January 2009
2,6-diisopropylaniline}2] (4) are yielded, respectively. The addition of MAO generates catalytically active
species for the homopolymerization of ethylene. The polymer products were low molecular weight
(3–6 K) and a monomodal molecular weight distribution, consistent with the presence of a single active
site. In addition, the catalyst was found to efficiently oligomerize higher olefins to high molecular weights
with narrow PDIs.
Keywords:
Nickel
Azolate-imine ligands
Ethylene polymerization
Branching PE
Ó 2009 Elsevier B.V. All rights reserved.
Late transition metal catalysts
1. Introduction
temperature), but also new materials with well defined molecular
characteristics, including a variety of functionalities [20–27]. A
Synthetic control and tailoring of bulk polyolefin properties is a
major focus of many industrial and academic research groups.
Advances in the design of single site catalysts provide an ever-
increasing array of metal–ligand combinations suitable for catalyz-
ing the polymerization of olefins [1–6]. A substantial body of
mechanistic work exists which provides insight into how the active
site structure influences the polymerization process. General
trends have emerged in the design of catalyst structure, which al-
low for the production of a specific polymer microstructure and
also of important bulk properties of the resulting polymer through
catalyst design. Single site catalyst systems have made a consider-
able impact on the commercial processes that produce these com-
modity products [7,8]. While polyolefin research initially focused
on early transition metals, such as zirconium and titanium, there
has been a shift over the last 20 years to an increased emphasis
on the late transition metals such as iron, nickel and palladium
[9–19]. This shift is based largely on the reduced oxophilicity of
the late transition metals and the ease with which large ligand
libraries and catalysts can be generated. With the late transition
metal system it was not only feasible to prepare known poly-
olefinic materials under gentle conditions (i.e. low pressure and
majority of these late transition metal complexes are based on bi,
tri and tetra dentate organic molecules coordinated to a metal cen-
ter. These systems are based on catalytic oligomerization (a major
industrial process) [27–29] processes, in which Ni or Pd metal cen-
ters chelated by PN or PP ligands are used [30–33]. It was realized
that the size and structure of the ligands could change the product
distribution of the process to produce higher molecular weight
polymers. The bonding versatility and the relative ease with which
the electronic and steric properties of the P and N atoms can be
modified make them attractive as the basis for these ligands. In
theory, the reactivity, selectivity and the ability to oligomerize or
polymerize monomers is defined by the electronic, steric and geo-
metric (chelate ring size) effects of the ligand. In the case of N,N or
N,O bidentate ligands [34–37], the size of the aromatic substitu-
ents on the imine or imide and carboxamide nitrogens would influ-
ence ligand coordination mode (i.e., N,N versus N,O) [38–40], the
reactivity and the propagation and termination ratio, allowing
access to a variety of new materials.
Considerable efforts have been focused on understanding the
role of co-activators on mediating these polymerization processes
[41]. Zwitterionic complexes, where a partial positive charge
formally resides at the metal center, constitute a smaller class of
initiators [42–51]. In many instances, Lewis acids are used to
activate the metal center upon coordination to a basic functionality
on the ligand framework at a site removed from the metal center
[52–56]. This type of activation places the Lewis acid away from
* 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.
E-mail address: rrojasg@uc.cl (R. Rojas).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.01.005

1796
R. Caris et al. / Journal of Organometallic Chemistry 694 (2009) 1795–1801
the trajectory of monomer insertion and eliminates the complexi-
ties associated with the use of alkylaluminoxanes in which anion
de-coordination or displacement is required for monomer inser-
tion [57]. Bidentate or tridentate ligand frameworks which have
additional peripheral heteroaromatic subtituents have been re-
ported, in particular N-hetaryl 1,2-diimine or N,N,N-bis(imino)pyr-
idine ligands [35,58]. These types of ligands were reported to easily
complex the appropriate transition metal halide but the influence
of the heteroaromatic substituent on the reactivity and polymers
properties was not discussed.
In an effort to better understand the effects of heteroaromatic
substituents on the reactivity and polymer properties, the synthe-
sis of N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-diisopropyl-
aniline and N-(1-(indazol-2-yl)ethylidene)-2,6-diisopropylaniline
ligands and subsequent metalation by nickel dibromide complexes
was pursued. During the preparation of this manuscript, similar
ligands and complexes where reported by Wu and co-workers
[59]. The activity of such complexes and their catalytic behavior
is described along with the characterization of the products.
with the formation of a single isomer of compound 1. Diagnostic
peaks include (in ppm): 6.01 (s, 1H, H-3,5-Me2Pz) 2.8–2.9, (hept,
2H, CH-iPr), 2.66 (s, 3H, CH3), 2.29 (s, 3H, Me-Pz) and 2.28 (s, 3H,
Me-Pz).
The addition of imidoyl chloride to indazol can result in the for-
mation of two isomers. While both are isolable, an effort was made
to isolate 2 rather than 20 as this isomer is more desired as it main-
tains the geometry produced in 1. Compound 2 was isolated by fil-
tering the suspension and removing the solvent to provide a crude
white powder. As shown in Scheme 1, the nature of the base de-
fines the regiochemistry of the reaction. When a depronating base
is used it is thought that two regioisomers can be obtained from
this reaction; the N-1(20) and N-2(2) substituted indazoles,
(Scheme 1, right). The reaction can be directed to the desired iso-
mer 2, depending on the base used [61]. In this particular case,
using non-deprotonating bases such as NEt3, the synthesis is direc-
ted towards the formation of isomer 2 only, since the electron pair
at N-2 becomes more reactive than the corresponding one on N-1,
which forms part of the aromatic system. It is also possible that the
electron pair at N-2 facilitates the nucleophilic reaction over the
imine carbon on the imidoyl chloride.
2. Results and discussion
The pure product was isolated by recrystallization from metha-
nol, and obtained as white crystals in 64% yield. The 1H and 13C
NMR spectra are consistent with the formation of a single isomer.
Diagnostic peaks include 2.82 (hept, 2H, CH-iPr), 2.48 (s, 3H, CH3)
and 1.15 (d, 12H, CH3-iPr). The synthesis of [NiBr2{N-(1-(3,5-di-
methylpyrazol-1-yl)ethylidene)-2,6-diisopropylaniline}] (3) by
the addition of N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-
diisopropylaniline (1) to [NiBr2{O(C2H4OMe)2}] in THF at room
temperature is depicted in Eq. (2). Crystallization from dichloro-
methane-ether allows isolation of 3 as air and thermally stable
dark purple crystals in 95% yield.
The ligands N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-di-
isopropylaniline (1) and N-(1-(indazol-2-yl)ethylidene)-2,6-diiso-
propylaniline (2) were synthesized by reacting imidoyl chloride
[60] with a 10% excess of 3,5-dimethylpyrazole or indazole in pres-
ence of Et3N in toluene at reflux. This reaction path yields ligands 1
and 2, respectively, (Eq. (1) and Scheme 1).
N
NEt ,Toluene
3
HN
+
N
N
N
- NEt3HCl
Cl
N
H3C
H3C
Br
Br
O
O
Ni
THF
(1)
NiBr2
O
N
+
N
N
N
RT, 1h
ð1Þ
N
N
To isolate compound 1, after 24 h refluxing in toluene the sus-
pension was filtered and the solvent was removed providing light
brown oil in 89% yield. The 1H and 13C NMR spectra are consistent
(3)
95 %
ð2Þ
B
H
N
N
N
Deprotonating
Base
Non-Deprotonating
Base
N
N
N
HN
N
(a)
(b)
Cl
N
N
Cl
N
N
N
N
N
N
N
N
N
2
2
2'
Scheme 1. Reaction of imidoyl chloride over indazol in the presence of depronating bases (i.e. NaH) and non-deprotonating bases (i.e. NEt3).

R. Caris et al. / Journal of Organometallic Chemistry 694 (2009) 1795–1801
1797
Single crystals of 3 suitable for X-ray diffraction studies were
obtained by diffusion of pentane into a toluene solution of the
compound at room temperature. The results of these studies are
shown in Fig. 1 and the crystallographic parameters in Table 1.
The molecular structure, shows an N,N-binding mode for the N-
(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-diisopropylaniline
and two bromides coordinated to the nickel. The tetrahedral
geometry around nickel is distorted: for example, the angle
N(1)–Ni–Br(1) (135.43 (5)°) is 34.61° longer than N(1)–Ni–Br(2)
(100.82(5)°). Additionally as depicted in Fig. 1, the Br(1) atom is
nearly perpendicular to the plane containing the five membered
chelate ring.
N(1)–C(13), N(2)–C(13) and N(3)–N(2) bond distances of 1.280(3),
1.402(3) and 1.380(3), respectively, which are consistent with
same degree of conjugation in the chelate ring through the pyrazol.
The N(3)–C(17) and N(2)–C(15) bond distances are 1.330(3) and
1.383(3), respectively, which are similar to those of the chelate
ring. The plane of the chelate ring is extended through the pyrazole
fragment while the 2,6-iPr phenyl fragment is perpendicular to the
rest of the molecule, Fig. 1.
Br
Br
O
O
Ni
DCM
RT, 3h
NiBr
2
N
N
+
N
N
N
N
The Ni–N(1), Ni–N(3), Ni–Br(1) and Ni–Br(2) bond distances are
2.0113(16), 1.9618(18), 2.3251(4) and 2.3590(4), respectively. The
O
H3C
(4)
H
3C
95 %
(2)
ð3Þ
The synthesis of [NiBr2{N-(1-(indazol-1-yl)ethylidene)-2,6-
diisopropylaniline}] (4) was carried out following the same proce-
dure of compound 3. Adding equimolar amounts of N-(1-(indazol-
2-yl)ethylidene)-2,6-diisopropylaniline (2) to [NiBr2{(O(C2H4O-
Me)2}] in dichloromethane at room temperature results in the
formation of 4, which was purified via crystallization from a
pentane/diethyl ether mixture. Orange crystals were isolated in
80% yield (Eq. (3)).
The 1H NMR spectrum of the product did not provide sufficient
information to elucidate the purity of the reaction yield as 3 and 4
produce broad NMR signals which are associated with the para-
magnetic nature of the tetrahedral geometry of these compounds.
Single crystals of 4, however, were easily obtained from an ether/
pentane mixture and the resulting molecular structure is shown
in Fig. 2 and the crystallographic parameters in Table 1.
The most significant feature of this structure is an unexpected
bimetallic ligand arrangement around the two nickel centers,
(dimer) without a central inversion center. The two molecules of
4 are bridged by two bromine atoms, leaving an unshared bromide
ligand at each five-coordinate Ni center, resulting in a shared
square pyramidal geometry with the apex of the pyramid oriented
in the same direction while the Ni centers, ligand framework and
Fig. 1. ORTEP drawing of 3, at 50% probability. Hydrogen atoms are omitted for
clarity.
Table 1
Selected bond lengths (Å) and bond angles (°) of complexes 3 and 4.
3
4
Bond distances
Ni–Br(1)
Ni–Br(2)
Ni–N(1)
Ni–N(3)
N(3)–N(2)
N(2)–C(13)
N(1)–C(13)
N(1)–C(1)
N(2)–C(15)
N(3)–C(17)
2.3251(4)
2.3590(4)
2.0113(16)
1.9618(18)
1.380(3)
1.402(3)
1.280(3)
1.451(3)
1.383(3)
1.330(3)
Ni(1)–Br(1)
Ni(1)–Br(2)
Ni(1)–N(1)
Ni(1)–N(3)
N(2)–N(3)
N(1)–C(1)
N(2)–C(1)
N(2)–C(3)
N(3)–C(9)
N(1)–C(10)
2.4831(16)
2.4335(16)
2.065(7)
2.025(6)
1.341(10)
1.248(9)
1.421(11)
1.361(10)
1.382(9)
1.525(11)
Bond angles
Br(1)–Ni–Br(2)
N(3)–Ni–N(1)
N(3)–Ni–Br(1)
N(1)–Ni–Br(1)
N(3)–Ni–Br(2)
N(1)–Ni–Br(2)
N(2)–N(3)–Ni
N(1)–C(13)–N(2)
C(13)–N(1)–C(1)
C(13)–N(1)–Ni
N(3)–N(2)–C(15)
N(3)–N(2)–C(13)
C(17)–N(3)–N(2)
113.536(14)
80.04(7)
Br(1)–Ni–Br(1)*
N(3)–Ni–N(1)
N(3)–Ni–Br(1)
N(1)-Ni–Br(1)
Br(1)*–Ni–N(1)
Br(1)*–Ni–Br(2)
N(1)–Ni–Br(2)
N(3)–Ni–Br(2)
Br(1)–Ni–Br(2)
Ni–Br(1)–Ni*
86.26(5)
77.4(3)
115.46(6)
135.43(5)
104.52(5)
100.82(5)
112.69(13)
115.28(19)
120.01(17)
115.53(14)
110.1(2)
96.1(29)
154.6(2)
94.16(18)
102.44(6)
154.6(2)
91.0(2)
107.96(6)
92.58(5)
110.0(5)
115.8(6)
113.6(8)
118.2(7)
N(2)–N(3)–Ni
Ni–N(1)–C(1)
N(1)–C(1)–N(2)
C(1)–N(2)–N(3)
115.89(17)
106.44(19)
Fig. 2. ORTEP drawing of 4, drawn at 50% probability. Hydrogen atoms were
omitted for clarity.

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R. Caris et al. / Journal of Organometallic Chemistry 694 (2009) 1795–1801
The bond distances in the X-ray structure of 4 reveal interesting
bond characteristics. As the framework of the ligand is planar we
suspected that there would be substantial overlap of the p orbitals
and that conjugation along the ligand framework (through the
indazole ring and including the imine) would be observed. The
length of N(1)–C(1), C(1)–N(2) and N(3)–N(2) bond distances in
the chelate ring, 1.248(9), 1.421(11) and 1.341(10), respectively,
indicate however that the conjugation is not extended over the
chelate ring. The bond distances in the indazole ring, N(2)–C(3)
and N(3)–C(9) measuring 1.361(10) and 1.382(9) Å, are indicative
of conjugation. Similar distances are observed in 3 as well.
Studies of the homopolymerization of ethylene using com-
pounds 3 and 4 activated with methylaluminoxane (MAO) were
carried out and the results are summarized in Table 2. These
polymerization reactions were performed in a 100 mL autoclave
reactor in 30 mL of toluene. Entries 1 and 2 show the results ob-
tained at 20 and 40 °C reaction temperature with compound 3/
MAO. Comparison of these entries shows that while the ethylene
consumption is higher at 40 °C. The molecular weights of the poly-
mers decrease with higher polymerization temperatures. The PDIs
(Mw/Mn ratio) are approximately 2, slightly narrower than that of
the polyethylene obtained at 20 °C. Entries 3–7 show the results
obtain with compounds 4/MAO at different reaction condition
and demonstrate that these combinations also yield ethylene
polymerization sites. Analysis of the polymerization solutions by
GC–MS did not reveal the presence of ethylene dimers, trimers or
tetramers.
Fig. 3. Stick ORTEP drawing of 4.
two of the bromides occupying, for intensive purposes, a shared
plane. As can be seen in Fig. 3, the ligands are not coplanar but
rather assume a gauche configuration. This distortion relieves
steric crowding and separates the two iPr groups from the indazol
ring.
Table 2
Ethylene polymerization reactions.a
A comparison of entries 3, and 4, with 1 and 2, respectively,
under similar reaction conditions show that the polymerization
activity is higher with 4/MAO systems. However, there is a de-
crease in the molecular weight of the polyethylene product proba-
bly associated with the reduction of the steric bulk on the ligand,
particularly in the proximity of the nickel center; interestingly
the PDIs do not change. Additionally for 4/MAO systems there
was a change in the ethylene consumption rate when the ethylene
pressure was varied between 100 and 300 psi. Entries 3 and 5 show
that an increase in the ethylene pressure provides higher activity,
and results in high molecular weight products without increases
to the PDI. Entries 5–7 show the results obtained at different reac-
tion times with 4/MAO systems. Comparison of these entries
shows that the yield of the reaction increases proportionally over
time, but the molecular weight remains fairly constant. The PDIs
Entry
Precatalysta
mol)
Timeb
T
(°C)
Pc
Yieldd
Ae
Mw
PDI
(l
1
2
3
4
5
6
7
3 (9.6)
3 (9.6)
4 (7.8)
4 (7.8)
4 (2.2)
4 (2.2)
4 (2.2)
10
10
10
10
10
20
40
20
40
20
40
20
20
20
100
100
100
100
300
300
300
0.7
1.3
2.8
3.8
2.9
5.8
12.0
435
807
6500
3600
2750
1900
4000
5000
4300
1.9
2.2
2.0
1.9
2.0
1.6
1.7
2231
2890
7634
7400
8000
a
Polymerizations were carried out in 100 mL autoclave reactors in 30 mL toluene
at 20 °C, the internal temperature was measured by using a thermocouple and was
controlled using an external cooling bath, ratio Al/Ni, 1000.
b
Time in minutes.
Ethylene pressure in psi.
Grams.
c
d
e
Activity in g polymer/(mmol Ni) (h).
Fig. 4. 1H NMR spectra of product (Entry 4, Table 1).

R. Caris et al. / Journal of Organometallic Chemistry 694 (2009) 1795–1801
1799
Table 3
In the solid state, compound 4 exists as a dimer without an inver-
sion center and unexpectedly exists in a cis ligand configuration.
The reaction of 3 and 4 with 1000 equiv. of MAO yields ethylene
polymerization sites. Under the same reaction conditions com-
pound 4 has a higher polymerization activity, but due to the less
crowded nickel center, this compound generates low molecular
weight materials. In terms of polymers properties, the resulting
materials are waxes with monomodal molecular weight distribu-
tions, consistent with the presence of a single active metal site. In
addition, compound 4 was demonstrated to be efficient in the olig-
omerization of higher olefins to high molecular weights with nar-
row polydispersity.
1-Decene polymerization reactions.a
Entry
Precatalysta
mol)
Timeb
T (°C)
Yieldc
Conversiond (%)
Mw
PDI
(
l
1
2
4 (10.8)
4 (10.8)
4 (10.8)
4 (10.8)
60
60
60
60
20
40
60
40
–
–
–
–
0.55
0.60
0.50
11
24
10
2027
2209
<500
1.03
1.05
–
3
4e
a
Polymerizations were carried out in Schlenk tubes in 15 g toluene at the tem-
perature indicated. The internal temperature was maintained by an external water
bath. A solution of the catalyst, 10.8 lmol in 5 g toluene, was injected through a
rubber septa into a Schlenk tube containing a solution of 1-decene (5 g) in 10 g
toluene and 0.035 mg of MAO, ratio Al/Ni, 30.
b
Time in minutes.
Grams.
Conversion = grams isolated product/grams monomer injected.
1 g MAO solution was used, ratio Al/Ni 860.
c
d
4. Experimental
e
4.1. General remarks
(Mw/Mn ratios) of the polyethylene obtained are more narrow (1.6
and 1.7) for longer reaction times than for those with shorter dura-
tions (2.0).
The products obtained from polymerizations with 3 and 4/MAO
were surprisingly not solids, but rather waxy materials, which in
our experience is an indication of highly branched materials. In or-
der to elucidate the polymer structure the materials were analyzed
by 1H NMR and 13C NMR techniques. Fig. 4 shows the 1H NMR
while the 13C NMR spectra is available in the supplementary
information.
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
oxygen/moisture trap (Matheson model 6427-4S). Toluene, THF,
hexane, and pentane were distilled from benzophenone ketyl.
NEt3 was dried over KOH. The starting compound N-(2,6-diisopro-
pylphenyl)acetimidoylchloride was synthesized according to liter-
ature procedures [14]. NiBr2(O(C2H4OMe)2 was purchased from
Aldrich and used as received. Polymerization reactions were car-
ried out in a Parr autoclave reactor as described below. Toluene
for polymerization was distilled from sodium/potassium alloy.
NMR spectra were obtained using Varian Unity 200 and 400 Bruker
spectrometers using deuterated solvent with TMS as internal stan-
dard. Polymers (waxes) 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 °C in o-dichlorobenzene (in a Polymer Laboratories, high-
temperature chromatograph, Pl-GPC 200). 1H NMR spectra of the
polymers were obtained in solution (C6D6) at RT. Elemental
analyses (C, H, N) were performed on a Fisons EA 1108 CHNS-O
microanalyzer. 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 recorded on a Bruker Vector-22 spectrophotometer
using KBr pellets. Melting point was determined using an Electro-
thermal melting point apparatus in open capillary tubes and are
uncorrected.
Of particular interest is the peaks assigned to internal olefins at
d 5.5 ppm. The integration of the peak, is ca. 3.6 times larger than
the peaks observed for
a-olefins [62,63]. This indicates that in
addition to oligomerizing ethylene, the catalyst system is undergo-
ing extensive chainwalking followed by b-hydrogen elimination
[9]. The chain walking is confirmed by the 13C NMR of the polymer
which indicates that the polymers are highly branched as 11.2 car-
bons per hundred are branch points. The majority, 61.9%, of these
branch points result in methyl branching while ethyl, propyl and
butyl and longer branches constitute 19.1%, 7.6% and 11.26% of
the totals, respectively. The highly branched structure and rela-
tively low molecular weight of the polymers are consistent with
previous studies of nickel transition metal ethylene polymerization
catalysts [64]. The 13C NMR spectra of the same product reveals
that the oligomer possesses a mixtures of branches, composed of
methyl, ethyl and chains of four or more carbon atoms.
The production of oligomers led us to believe that the catalyst
system would be particularly useful in the oligomerization of high-
er olefins to high molecular weight products. Indeed, when 4/MAO
was added to 1-decene in toluene the system produces waxy olig-
omers of 1-decene with molecular weights greater than 2000 g/
mol. What was surprising was that these materials possess narrow
PDIs of less than 1.1, indicating that the oligomerization of 1-de-
cene proceeds without chain termination. At higher concentrations
of MAO (Table 3, entry 4) the oligomerization produces materials
of very low molecular weight (<500 g/mol) indicating that the
MAO is either acting as a transfer agent, or at higher concentrations
hinders the activity of the system. We suspect that the reduced PDI
is due to the low number of insertions per metal site and the larger
steric bulk of the olefin in comparison to ethylene.
4.2. Synthesis of ligands
4.2.1. N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-
diisopropylaniline (1)
A mixture of 3,5-dimethylpyrazole (0.89 g; 9.26 mmol), N-(2,6-
diisopropylphenyl)acetimidoylchloride (2 g; 8.42 mmol) and NEt3
(2 mL) in toluene (30 mL) was refluxed for 21 h with vigorous
stirring. A white precipitate, Et3NHCl, was formed and removed
by filtration. The yellow solution was evaporated to dryness and
gave a brown oil. This residue was dissolved in diethyl ether and
purified by chromatography on Silica gel type 60. The compound
was eluted with a mixture of dichloromethane-hexane (4:1) to
give a brown oil. Yield 2.249 g (89%). NMR (CDCl3, 295 K): 1H, d
7.14 (d, 2H, JHH = 8 Hz, m-H-Ph), 7.07 (t, 1H, JHH = 8 Hz, p-H-Ph),
6.05 (s, 1H, H (pirazole), 2.84 (hept, 2H, JHH = 8 Hz, CH-iPr), 2.66
(s, 3H, CH3), 2.29 (s, 3H, CH3-pirazole), 2.28 (s, 3H, CH3-pirazole),
3. Conclusions
In summary, the synthesis and characterization of two new
nickel complexes was demonstrated. The reaction of N-(1-
(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-diisopropylaniline
or
N-(1-(indazol-1-yl)ethylidene)-2,6-diisopropylaniline ligands and
[NiBr2{(O(C2H4OMe)2}] gives 3 and 4, respectively, in good yields.

1800
R. Caris et al. / Journal of Organometallic Chemistry 694 (2009) 1795–1801
Table 4
1.17 (d, 6H, JHH = 8 Hz, CH3-iPr) and 1.13 (d, 6H, JHH = 8 Hz, CH3-iPr)
ppm. 13C, d 155.0, 149.0, 142.0, 123.53, 123.17, 123.08, 110.04,
22.25, 17.40, 15.82 and 13.73 ppm. IR (KBr, cmꢀ1): 1672 (s), 1573
(w), 1461 (w), 1438 (w), 1412 (m), 1385 (s), 1354 (s), 1326 (m),
1246 (w), 1087 (m), 966 (m), 775 (m), 755 (m). Anal. Calc. for
C19H27N3: C, 76.72; H, 14.15; N, 9.15. Found: C, 76.00; H, 13.93;
N, 10.07%.
Crystal data and structure refinement for complexes 3 and 4.
3
4
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
C19H27N3Br2Ni
515.97
150 (2)
0.71073
Monoclinic
P2(1)/n
C42H50N6Br4Ni2
1075.94
150(2)
0.71073
Tetragonal
P4(3)2(1)2
4.2.2. N-(1-(indazol-1-yl)ethylidene)-2,6-diisopropylaniline (2)
A suspension of indazole (1.094 g; 9.26 mmol), N-(2,6-diisopro-
pylphenyl)acetimidoylchloride (2 g; 8.42 mmol) and NEt3 (2 mL) in
toluene (30 mL) was refluxed for 21 h with vigorous stirring. The
white precipitate Et3NHCl formed was removed by filtration and
the yellow solution evaporated to dryness to give a white solid res-
idue. The desired compound was isolated as white crystals from
methanol. Yield 1.73 g (64.3%). M.p.: 112–114 °C. NMR (CDCl3,
295 K): 1H, d 9.07 (s, 1H, H–C@N (indazole)), 7.71 (t, 2H, JHH = 8 Hz,
CH–CH (indazole)), 7.33 (t, 1H, JHH = 8 Hz, p-H-Ph (ArNH2)), 7.1–7.2
(m, 4H, H–C–C@N (indazole), H–C–N (indazole), 2m-H-Ph (Ar-
NH2)), 2.82 (hept, 2H, JHH = 8 Hz, CH-iPr), 2.48 (s, 3H, CH3), 1.16
(d, 6H, JHH = 8 Hz, CH3-iPr), and 1.14 (d, 6H, JHH = 8 Hz, CH3-iPr)
ppm. 13C, d 150.0, 142.91, 124.0, 123.4, 123.31, 122.0, 121.0,
120.0, 118.0, 23.27, 22.91 and 16.28 ppm. IR (KBr, cmꢀ1): 1673
(s), 1630 (w), 1520 (m), 1467 (m), 1406 (m), 1385 (s), 1334 (m),
1216 (s), 1147 (w), 1072 (w), 950 (w), 812 (m), 760 (s), 698 (m).
Anal. Calc. for C21H25N3: C, 78.96; H, 13.15; N, 7.89. Found: C,
78.97; H, 13.20; N, 7.83%.
9.7927(3)
17.0553(5)
13.0366(4)
90
93.0730(10)
90
2174.21(11)
4
1.576
14.811(3)
14.811(3)
21.296(4)
90
90
90
4671.5(11)
8
1.530
4.262
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
Volume (Å3)
Z
Dcalc (Mg/m3)
Absorption coefficient
4.574
(mmꢀ1
)
F(000)
1040
2160
Crystal size (mm3)
h Range (°)
0.35 ꢁ 0.22 ꢁ 0.14
1.97–27.80
ꢀ12 6 h 6 12
ꢀ21 6 k 6 21
ꢀ17 6 l 6 17
29226
0.2 ꢁ 0.2 ꢁ 0.15
1.67–26.92
ꢀ18 6 h 6 16
ꢀ18 6 k 6 18
ꢀ26 6 l 6 26
36920
Index ranges
Reflections collected
Independent reflections
Completeness to h = 26.48°
(%) (for 1) and 28.52° (%)
(for 10, 2)
4862 [Rint = 0.0246]
99.8
4874 [Rint = 0.1481]
97.2
Data/restraints/parameters
4862/0/233
1.068
4874/0/255
1.090
Goodness-of-fit on F2
4.3. Synthesis of complexes
Final R indices [I > 2
r
(I)]
R1 = 0.0281,
wR2 = 0.0672
R1 = 0.0359,
wR2 = 0.0708
0.872 and ꢀ0.474
R1 = 0.0540,
wR2 = 0.1272
R1 = 0.1571,
wR2 = 0.1532
1.510 and ꢀ0.573
4.3.1. [NiBr2{N-(1-(3,5-dimethylpyrazol-1-yl)ethylidene)-2,6-
diisopropylaniline-N,N}] (3)
R indices (all data)
Largest difference peak and
hole (e Åꢀ3
To a solution of [NiBr2{O(C2H4OMe)2}] (0.050 g; 0.142 mmol) in
THF (15 mL), ligand 1 (0.042 g; 0.142 mmol) was slowly added. The
solution was stirred at room temperature for 2 h. During this time
the color of the solution changes slowly from orange to red. The
solution was filtered through Celite and the solvent removed under
vacuum to give an orange solid. The solid residue was washed two
times with diethyl ether to afford a violet solid that was crystal-
lized from dichloromethane-diethyl ether. Yield 0.066 g (90%). IR
(KBr, cmꢀ1): 1633 (s), 1578 (s), 1460 (m), 1392 (s), 1364 (s),
1330 (s), 1196 (m), 1115 (m), 1052 (m), 1007 (m), 788 (m). EI-
MS(+): m/z = 355.09 (M+ꢀ2Br). Anal. Calc. for C19H27Br2N3Ni: C,
44.23; H, 5.27; N, 8.14. Found: C, 45.01; H, 5.67; N, 7.97%.
)
(Fo ꢀ Fc2)2]/
R , GOF =
[w(Fo2)2]]1/2
2
Definitions: R1
=
R
||Fo| ꢀ |Fc||]/
R
[|Fo|, wR2 = [
R
2
[R
[w(Fo ꢀ Fc2)2]/(n ꢀ p)]1/2, where n is the number of the reflections and p is the
total number of the parameters refined. *Min/max.
and transferred to a Bruker CCD platform diffractometer. The SMART
[65] program package was used to determine the unit-cell param-
eters and for data collection (25 s/frame scan time for a sphere of
diffraction data). The raw frame data was processed using SAINT
[66] and SADABS [67] to yield the reflection data file. Subsequent cal-
culations were carried out using the SHELXTL [68] program. The
structure was solved by direct methods and refined on F2 by full-
matrix least-squares techniques. The analytical scattering factors
[69] for neutral atoms were used throughout the analysis. Hydro-
gen atoms were located from a difference Fourier map and refined
(x, y, z and Uiso) [70]. The crystal data and refinement are summa-
rized in Table 4.
4.3.2. [Ni2Br2(l-Br)2{N-(1-(indazol-1-yl)ethylidene)-2,6-
diisopropylaniline-N,N}2] (4)
To a solution of NiBr2{O(C2H4OMe)2} (0.050 g; 0.142 mmol) in
dichloromethane (15 mL), ligand 2 (0.042 g; 0.142 mmol) was
slowly added. The resulting orange solution was stirred at room
temperature for 2 h then filtered through Celite. The solution was
evaporated to dryness and the residue washed several times with
diethyl ether to afford an orange solid. The complex was crystal-
lized from a mixture of diethyl ether–pentane. Yield 0.061 g
(80%). IR (KBr, cmꢀ1): 1628 (s, br), 1526 (s), 1468 (s), 1384 (m),
1366 (m), 1317 (s), 1224 (m), 1184 (w), 1134 (w), 1094 (s), 1008
(m), 974 (m), 825 (w), 800 (m), 760 (s). Anal. Calc. for
C42H50Br4N6Ni2: C, 46.74; H, 5.00; N, 7.77. Found: C, 46.89; H,
4.68; N, 7.81%.
Acknowledgments
The work was funded by FONDECYT Grant Nos. 11060384 and
1060597 and FONDAP Grant No. 11980002.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2009.01.005.
4.4. X-ray crystallography
Crystals suitable for X-ray structure determination were
obtained from a slow diffusion of pentane into a solution of
complex 3 in toluene and from a mixture diethyl ether–pentane
for complex 4. The single crystals were mounted on a glass fiber
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