Substituted tridentate pyrazolyl ligands for chromium and nickel-catalyzed ethylene oligomerization reactions. Effect of auxiliary ligand on activity and selectivity

Article abstract of DOI:10.1590/s0103-50532010000700019

Two new chromium(III) complexes [CrCl₃(L)] based on tridentate ligands (1a, L = bis[2-(3-phenyl-1-pyrazolyl)ethyl)]amine; 2a, L = bis[2-(3-methyl-5-phenyl-l-pyrazolyl)ethyl]sulfide) have been prepared and characterized by elemental analysis. Upon activation with methylaluminoxane (MAO), these pre-catalysts showed high turnover frequencies for ethylene oligomerization under optimized conditions (TOFs = 22.9-36.4×10 ³ mol C₂H₄ (mol Cr^III)^-1 h^-1, [Cr] = 10.0 μmol, 80 °C, 20 bar ethylene, MAO:Cr = 300, oligomerization time = 20 min), producing α-olefins in the range C ₄-C₁₄₊ with high selectively (67.71-73.47%). The catalytic performances are substantially affected by the ligand environment, especially the substituents at the 3- and 5-positions of the pyrazolyl rings. In parallel, the use of nickel complexes such as NiCl₂{bis[2-(3,5-dimethyl-1- pyrazolyl)methyl]benzylamine} (3) and NiCl₂{bis[2-(3,5-dimethyl-1- pyrazolyl)ethyl)]ether} (5) in oligomerization reactions carried out in the presence of triphenylphosphine (PPh₃) afforded highly active catalytic systems with turnover frequencies (TOFs) varying from 36.4 to 154.2×10³ mol C₂H₄ (mol Ni ^II)^-1 h^-1. The presence of this auxiliary ligand has a strong impact on the selectivity towards the production of α-olefins, decreasing substantially the amount of 1-butene with a concominat increase of the 2-butene fractions. Attempts to crystallize the nickel complex 3 afforded the tetrametallic [{(L)(μ₃-Cl)NiCl} ₄] (4, L = 1-anilinomethyl-3,5-dimethylpyrazole) which was characterized by X-ray diffraction analysis.

Full text of DOI:10.1590/s0103-50532010000700019

J. Braz. Chem. Soc., Vol. 21, No. 7, 1318-1328, 2010.
Printed in Brazil - ©2010 Sociedade Brasileira de Química
0103 - 5053 $6.00+0.00
Substituted Tridentate Pyrazolyl Ligands for Chromium and Nickel-Catalyzed
Ethylene Oligomerization Reactions. Effect of Auxiliary Ligand on Activity and
Selectivity
Lucilene L. de Oliveira, Roberta R. Campedelli, Adão L. Bergamo,
Ana H. D. P dos Santos and Osvaldo L. Casagrande*
Laboratório de Catálise Molecular, Instituto de Química, Universidade Federal do Rio Grande do Sul,
Av. Bento Gonçalves, 9500, 90501-970 Porto Alegre-RS, Brazil
Dois novos complexos de cromo(III) contendo ligantes tridentados [CrCl3(L)] (1a, L = bis[2-(3-
fenil-1-pirazol)etil)]amina; 2a, L = bis[2-(3-metil-5-fenil-l-pirazol)etil]sulfeto) foram preparados
e caracterizados por análise elementar. Após ativação com metilaluminoxano (MAO), estes pré-
catalisadores mostraram altas frequências de rotação nas reações de oligomerização do etileno sob
condições otimizadas (FRs = 22,9-36,4×103 mol C2H4 (mol CrIII)-1 h-1, [Cr] = 10,0 mmol, 80 °C,
20 bar de etileno, [Al]/[Cr] = 300, tempo de oligomerização = 20 min), produzindo olefinas-a no
intervalo de C4-C14+ com alta seletividade (67,71-73,47%). Os desempenhos catalíticos são afetados
substancialmente pelos grupos presentes nos ligantes, especialmente os substituintes nas posições
3 e 5 dos anéis pirazol. Em paralelo, o emprego de complexos de níquel(II) tais como NiCl2{bis[2-
(3,5-dimetil-1-pirazol)metil]benzilamina} (3) e NiCl2{bis[2-(3,5-dimetil-1-pirazol)etil)]éter} (5)
em reações de oligomerização conduzidas na presença de trifenilfosfina (PPh3) resultou em sistemas
catalíticos altamente ativos com frequências de rotação (FRs) variando de 36,4 a 154,2×103 mol
C2H4 (mol NiII)-1 h-1. A presença deste ligante auxiliar tem um impacto significativo na produção
seletiva de olefinas-a, diminuindo substancialmente a quantidade de buteno-1 com concomitante
aumento da quantidade das frações de butenos-2. Tentativas de cristalização do complexo de
níquel 3 resultaram na formação de um composto de níquel tetrametálico [{(L)(μ3-Cl)NiCl}4]
(4, L = 1-anilinometil-3,5-dimetil-1-pirazol) o qual foi caracterizado por difratometria de raios X.
Two new chromium(III) complexes [CrCl3(L)] based on tridentate ligands (1a, L = bis[2-(3-
phenyl-1-pyrazolyl)ethyl)]amine; 2a, L = bis[2-(3-methyl-5-phenyl-l-pyrazolyl)ethyl]sulfide) have
been prepared and characterized by elemental analysis. Upon activation with methylaluminoxane
(MAO), these pre-catalysts showed high turnover frequencies for ethylene oligomerization under
optimized conditions (TOFs = 22.9-36.4×103 mol C2H4 (mol CrIII)-1 h-1, [Cr] = 10.0 mmol, 80 °C,
20 bar ethylene, MAO:Cr = 300, oligomerization time = 20 min), producing a-olefins in the range
C4-C14+ with high selectively (67.71-73.47%). The catalytic performances are substantially affected
by the ligand environment, especially the substituents at the 3- and 5-positions of the pyrazolyl rings.
In parallel, the use of nickel complexes such as NiCl2{bis[2-(3,5-dimethyl-1-pyrazolyl)methyl]
benzylamine} (3) and NiCl2{bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl)]ether} (5) in oligomerization
reactions carried out in the presence of triphenylphosphine (PPh3) afforded highly active catalytic
systems with turnover frequencies (TOFs) varying from 36.4 to 154.2×103 mol C2H4 (mol NiII)-1 h-1.
The presence of this auxiliary ligand has a strong impact on the selectivity towards the production
of a-olefins, decreasing substantially the amount of 1-butene with a concominat increase of
the 2-butene fractions. Attempts to crystallize the nickel complex 3 afforded the tetrametallic
[{(L)(μ3-Cl)NiCl}4] (4, L = 1-anilinomethyl-3,5-dimethylpyrazole) which was characterized by
X-ray diffraction analysis.
Keywords: ethylene oligomerization, tridentate bis(pyrazolyl) ligands, nickel complexes,
chromium complexes
*e-mail: osvaldo.casagrande@ufrgs.br

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Oliveira et al.
1319
Introduction
NiCl2·6H2O and triphenylphosphine (PPh3), both from
Aldrich, were used as received. Ethylene (White Martins
Co.) and argon were deoxygenated and dried through
columns of BTS (BASF) and activated molecular sieves
(3A) prior to use. PMAO-IP (methylaluminoxane, Akzo,
12.9 wt.% Al solution in toluene) and diethylaluminum
chloride (DEAC) (Aldrich, 1.8 mol L-1, 25 wt.% toluene
solution) were used as received. Elemental analyses were
performed by theAnalytical Central Service of the Institute
of Chemistry-UFRGS (Brazil) and are the average of two
independent determinations. 1H and 13C{1H} NMR spectra
were recorded on aVarian Inova 300 spectrometer operating
at 25 °C. Chemical shifts are reported in ppm vs. SiMe4 and
were determined by reference to the residual solvent peaks.
Infrared spectra were performed on a FTIR Bruker Alpha
Spectrometer. Quantitative gas chromatographic analysis
of ethylene oligomerization products was performed on a
Varian 3400CX instrument with a Petrocol HD capillary
column (methyl silicone, 100 m length, 0.25 mm i.d., and
film thickness of 0.5 mm) operating at 36 °C for 15 min
followed by heating at 5 °C min-1 until 250 °C; cyclohexane
was used as internal standard.
The pursuit of ethylene oligomerization catalysts
capable of producing selectively a-olefins has been a major
focus of research in recent decades, due to their importance
in a variety of industrial processes. Depending on the chain
length of the alkene, they can be used for production of
various materials. The most important ones are linear low-
density polyethylene (LLDPE) (C4-C10), poly-a-olefins
(C4, C10), plasticizers (C6-C10), lubricants (C8-C10), lube
oil additives (C12-C18), and surfactants (C12-C20).1 For this
purpose, several oligomerization catalyst systems have
been developed, most of which are based on nickel2 and
chromium catalysts3 bearing bi- and tridentate ligands.
In recent years we have been interested in studying
the potential applications of tridentate ligands in the
oligomerization catalysis field. We have thus previously
communicated new classes of NiII 4,5 and CrIII 6,7 complexes
based on these tridentate pyrazolyl ligands, which act as
highly selective and highly active pre-catalysts for ethylene
oligomerization in the presence of methylaluminoxane
(MAO) as co-activator. More recently, we have
introduced a new set of NiII complexes based on NZN
ligands that form stable 5-membered chelate rings and
which, in association with an alkylaluminum (MAO or
AlEt2Cl), show high activity in ethylene oligomerization
(TOF = 1.7-104.5×103 mol(ethylene) mol(Ni)-1 h-1),
giving predominantly 1-butene (70-94% yield).8 Herein,
we report the synthesis and characterization of two new
CrIII complexes, CrCl3{bis[2-(3-phenyl-1-pyrazolyl)
ethyl)]amine} (1a), and CrCl3{bis[2-(3-methyl-5-phenyl-
l-pyrazolyl)ethyl]sulfide} (2a), which, in association with
MAO, afford active catalysts for the selective production of
a-olefins in the range C4-C14+. Furthermore, studies on the
influence of the auxiliary ligand triphenylphosphine (PPh3)
on turnover frequency (TOF), selectivity for a-olefins,
and product distribution using 5- and 6-membered ring
nickel complexes NiCl2{bis[2-(3,5-dimethyl-1-pyrazolyl)
methyl]benzylamine} (3) and NiCl2{bis[2-(3,5-dimethyl-
1-pyrazolyl)ethyl)]ether} (5) are also reported.
Synthesis and characterization of tridentate pyrazolyl
ligands
1-(2-hydroxyethyl)-3-methyl-5-phenylpyrazole
A solution of 2-hydroxyethylhydrazine (4.64 g,
60.9 mmol) in absolute ethanol (10 mL) was added dropwise
to a stirred solution of 1-phenyl-1,3-butanedione (10.01 g,
61.7 mmol) in absolute ethanol (30 mL). The temperature
of the reaction mixture was kept below 10 °C. After the
addition of the hydrazine, the reaction mixture was allowed
to warm to room temperature and stirred for another 2 h. The
solvent was then evaporated under reduced pressure to give a
white solid composed by a mixture of two different isomers:
1-(2-hydroxyethyl)-3-methyl-5-phenylpyrazole (isomer A)
and 1-(2-hydroxyethyl)-3-phenyl-5-methylpyrazole (isomer
B). The pure form of isomer A was obtained after several
washingswithdiethylether(4×15mL)(6.36g,52%).1HNMR
(CDCl3):d2.47(s,3H,CH3),3.93(t,2H,3JHH4.8Hz,2H,CH2),
4.26 (t, 3JHH 4.7 Hz, 2H, CH2), 6.22 (s, 1H, CH), 7.24-7.79
(m, 5H, CHar). 13C NMR (CDCl3): d (ppm) 13.4, 50.4, 61.9,
105.6, 128.5, 130.5, 144.9, 148.2. IR (KBr) nmax/cm-1:
3390s, 2947m, 2813w2788w, 1955w, 1903w, 1890w, 1664s,
1620s, 1595s, 1504s, 1460s, 1427s, 1380s, 1307m, 1236w,
1070m, 929w, 869w, 781m and 707s. mp 91°C.
Experimental
General procedures
All manipulations were performed using standard
vacuum line and Schlenk techniques under a purified argon
atmosphere. Et2O, thf and toluene were distilled from
sodium-benzophenone ketyl under argon and degassed by
freeze-thaw-vacuum cycles prior to use. 3-Phenylpyrazole9
and [CrCl3(thf)3]10 were prepared by literature procedures.
1-(2-chloroethyl)-3-methyl-5-phenylpyrazole hydrochloride
A solution of 1-(2-hydroxyethy1)-3-methyl-5-
phenylpyrazole (4.4 g, 19.8 mmol) and thionyl chloride

1320
Substituted Tridentate Pyrazolyl Ligands for Chromium and Nickel-Catalyzed
J. Braz. Chem. Soc.
(2.90 mL, 39.9 mmol) in chloroform (25 mL) was allowed
to reflux for 4 h. The volatiles were then evaporated under
reduced pressure, and the resulting residue was washed
with sodium bicarbonate solution (5%) to give a yellow
128.8, 129.2, 129.8, 130.7 144.0, 148.5. IR (KBr) nmax/cm-1:
3060m, 2960m, 2925s, 2864m, 1955w, 1892w, 1814w,
1764w, 1606m, 1548s, 1496s, 1454s, 1423s, 1303s, 1278m,
1218m, 1180w, 1118w, 1074m, 1035m, 993s, 954w, 919w,
794m, 767s, 700s, 675m, 635w and 549m.
1
oil (3.87, 89%). H NMR (CDCl3): d 2.61 (s, 3H, CH3),
4.13 (t, 3JHH 6.6 Hz, 2H, CH2), 4.75 (t, 3JHH 6.6 Hz, 2H,
CH2), 6.3 (s, 1H, CH), 7.22-7.74 (m, 5H, CHar). 13C NMR
(CDCl3): d (ppm) 13.2, 42.1, 49.8, 105.8, 128.5, 130.3,
144.9, 148.3. IR (KBr) nmax/cm-1:3060w, 2960m, 2928m,
2862w, 1967w, 1892w, 1824w, 1770w, 1602w, 1548m,
1494s, 1454s, 1425m, 1384m, 1307m, 1271m, 1166w,
1122w, 1072w, 1035w, 997m, 916w, 796m, 763s, 698s
and 663s.
CrCl3{bis[2-(3-phenyl-1-pyrazolyl)ethyl)]amine} (1a)
To a solution of bis[2-(3-phenyl-pyrazol)ethyl)]
amine (0.32 g, 0.90 mmol) in thf (10 mL), a solution of
[CrCl3(thf)3] (0.30 mg, 0.80 mmol) in thf (15 mL) was
added, and the resulting mixture was stirred for 30 min at
room temperature. The solvent was removed until ca. 1/3
remained and 10 mL of pentane was added to complete
precipitation. The product was collected by filtration,
washed with pentane and dried in vacuo. Complex 1a was
obtained as a green solid.Yield: 0.38 g (92%). Compound
1a, elemental analysis: Found C, 50.71; H, 4.33; N, 12.96.
Calc. for C22H23Cl3CrN5: C, 51.23; H, 4.49; N, 13.58%.
Bis[2-(3-phenyl-1-pyrazolyl)ethyl]amine (1)
Under an argon atmosphere, 3-phenylpyrazole (2.71 g,
18.7 mmol) was slowly added to a suspension of NaH
(1.2 g, 50 mmol) in dry dmf (50 mL). The mixture was
stirred at room temperature for 2 h. To the resulting solution,
a solution of bis(2-chloroethyl)amine (1.66 g, 9.3 mmol)
in dry dmf (10 mL) was added dropwise under stirring.
The mixture was allowed to stir for 2 h at 70 °C, cooled
and treated cautiously with H2O (15 mL) to decompose
excess NaH. The solvents were then evaporated under
reduced pressure. The residue was extracted with ethyl
acetate (4×40 mL), washed with 10% NaOH (2×30 mL),
H2O (2×30 mL), and then dried over MgSO4. The solvent
was evaporated to give a yellow oil (2.60 g, 77%). 1H NMR
CrCl3[bis[2-(3-methyl-5-phenyl-l-pyrazolyl)ethyl]sulfide]
(2a)
This compound was prepared according to the method
described for 1a using [CrCl3(thf)3] (0.26 g, 0.70 mmol)
and bis[2-(3-methyl-5-phenyl-1-pyrazolyl)ethyl]sulfide
(0.33 g, 0.80 mmol). Complex 2a was obtained as a light
red wine coloured solid (0.36 g, 90%). Compound 2a,
elemental analysis: Found: C, 50.88; H, 4.25; N, 9.76. Calc.
for C24H26Cl3CrN4S: C, 51.39; H, 4.67; N, 9.99%.
3
(CDCl3): d 3.12 (t, JHH 5.7 Hz, 4H, CH2), 4.36 (t, 3JHH
5.7 Hz, 4H, CH2), 6.52 (d, 2JHH 2.3 Hz, 2H, CH), 7.40-7.85
NiCl2{bis[2-(3,5-dimethyl-1-pyrazolyl)methyl]
benzylamine} (3)8
13
(m, 12 H, CHar). C NMR (CDCl3): d (ppm) 48.2, 51.9,
102.4, 125.3, 127.8, 128.3, 131.0, 133.3, 151.4. IR (KBr)
n
1664w, 1604m, 1525m, 1504s, 1461s, 1409s, 1355s,
1326m, 1226s, 1134m, 1076s, 1049m, 948m, 919m, 846w,
756s, 698s), 659w, 626w and 509w.
To a solution of NiCl2·6H2O (130 mg, 0.56 mmol) in
thf (10 mL), a solution of bis[2-(3,5-dimethyl-1-pyrazolyl)
methyl)]benzylamine (200 mg, 0.62 mmol) in thf (10 mL)
was added, and the resulting mixture was stirred for 24 h at
room temperature. Volatiles were removed under reduced
pressure, and the resulting green solid residue was washed
with Et2O (2×10 mL) to afford 3 as a green solid (189 mg,
75%). Compound 3, elemental analysis: Found C, 46.51;
H, 5.90; N, 14.07. Calc. for C19H25Cl2N5Ni·2H2O: C, 46.66;
H, 5.98; N, 14.32%.
max/cm-1: 2948s, 2852s, 1957w, 1884w, 1812w, 1753w,
Bis[2-(3-phenyl-5-methyl-1-pyrazolyl)ethyl]sulfide (2)
A solution of l-(2-chloroethyl)-3-methyl-5-phenyl
pyrazole hydrochloride (5.07 g, 19.8 mmol) and sodium
hydroxide (0.5 g, 12.5 mmol) in aqueous ethanol (50%,
100 mL) was treated with Na2S·9H2O (2.98 g, 12.4 mmol).
The solution was allowed to reflux for 3 h, cooled and
evaporated under reduced pressure. Water was added
(20 mL), the product was extracted with dichloromethane
(4×15 mL), and the organic extracts were dried over Na2SO4.
The volatiles were evaporated under reduced pressure to
give a yellow oil (2.98 g, 75%). 1H NMR (CDCl3): d 2.32
(s, 6 H, CH3), 3.84 (t, 3JHH 7.2 Hz, 4H, CH2), 4.23 (t, 3JHH
7.2 Hz, 4H, CH2), 6.17 (s, 2H, CH), 7.25-7.67 (m, 10 H,
CHar).13C NMR (CDCl3): d (ppm) 13.5, 31.8, 48.5, 105.9,
[{(1-anilinomethyl-3,5-dimethylpyrazole)(μ -Cl)NiCl}4] (4)
3
A solution of 3 (18 mg) in CH2Cl2 (7 mL) was kept at
room temperature for five days, resulting in a few green
crystals of 4, which were separated from the solution and
proved suitable for X-ray diffraction analysis.
NiCl2{bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl)]ether} (5)4
To a solution of NiCl2·6H2O (116 mg, 0.49 mmol) in thf
(10 mL), a solution of bis[2-(3,5-dimethyl-pyrazol)ethyl)]

Vol. 21, No. 7, 2010
Oliveira et al.
1321
ether (128 mg, 0.49 mmol) in thf (10 mL) was added, and the
resulting mixture was stirred for 3 h at room temperature.
Volatiles were removed under reduced pressure, and the
resulting turquoise solid residue was washed with Et2O
(2×10 mL) to afford a turquoise blue solid (175 mg, 91%).
Compound 5, elemental analysis: Found C, 39.98; H, 6.00;
N, 12.83. Calc. for C14H22Cl2N4NiO·2H2O: C, 39.29; H,
6.12; N, 13.09%.
were collected at 100 K using an APEXII Bruker-AXS
diffractometer with graphite-monochromatized Mo-Ka
radiation (l = 0.71073Å).A combination of o- and j-scans
was carried out to obtain at least a unique data set. The
structure was solved by direct methods using the SIR97
program,11 and then refined with full-matrix least-square
methods based on F2 (SHELX-97)12 with the aid of the
WINGX program.13 Many hydrogen atoms could be found
from the Fourier difference map. Carbon-bound hydrogen
atoms were placed at calculated positions and forced to
ride on the attached carbon atom. The hydrogen atom
contributions were calculated but not refined. All non-
hydrogen atoms were refined with anisotropic displacement
parameters.
General oligomerization procedure
A 100 mL double-walled stainless Parr reactor equipped
with mechanical stirring and internal control of temperature
was evacuated and filled three times with argon and twice
with ethylene. Freshly distilled toluene (30 mL) and the
proper amount of MAO or DEAC were added into the
vessel under a stream of ethylene.After 15 min, the toluene
catalyst solution (10 mL) was injected. The reactor pressure
was kept constant throughout the oligomerization process
(20 bar) by manually controlled addition of ethylene.After
the desired time, the reaction was stopped by cooling the
system to -20 °C, depressurizing, and introducing 1 mL of
ethanol. An exact amount of cyclohexane was introduced
(as internal standard) and the mixture was analyzed by
quantitative GLC.
Results and Discussion
Synthesis, characterization of substituted bis(pyrazolyl)-
CrIII complexes and their use in oligomerization reactions
The substituted tridentate nitrogen-bridged
bis(pyrazolyl) ligand (1) used in this study was readily
prepared in high yield through adaptation of literature
procedures (see Experimental). The synthesis of tridentate
ligand 2 was achieved starting from commercially available
1-phenyl-1,3-butanedione and 2-hydroxyethylhydrazine.
The initial step procedure promotes the formation of two
different isomers (Scheme 1) whereas the isomer A was
obtained in pure form (52% yield) after workup.The identity
of isomer A was established on the basis of multinuclear
X-ray crystallographic studies
A suitable single crystal of 2 was mounted onto a
glass fiber using the ‘‘oil-drop’’ method. Diffraction data
H
O
O
ethanol
N
+
+
NH2
OH
N N
N N
OH
OH
isomer B
isomer A
(52 % of isolated product)
CHCl3
SOCl2
S
Na2S.9H2O
N
N
Ph
Ph
N
N
H2O/ethanol
NaOH
N N
HCl
Cl
2
Scheme 1.

1322
Substituted Tridentate Pyrazolyl Ligands for Chromium and Nickel-Catalyzed
J. Braz. Chem. Soc.
Z
Z
Cl
CrCl3(thf)3
N
R2
N
R2
N
R2
N
R2
N
Cr
Cl
N
N
N
Cl
R1
thf, 30 min, RT
R1
R1
R1
1-2
1a: Z = NH; R1 = Ph; R2 = H
2a: Z = S; R1 = Me; R2 = Ph
Scheme 2.
nuclear magnetic resonance (NMR) and heteronuclear
multiple bond correlation (HMBC) experiments (see
HMBC spectra in supporting information). Chlorination
of the isomer A with thionyl chloride in CHCl3 gave l-(2-
chloroethyl)-3-methyl-5-phenyl pyrazole in 77% yield. The
latter compound reacted with Na2S·9H2O in H2O/ethanol
to give the substituted sulfur-bridged tridentate ligand (2)
in 75% yield.
The reaction of [CrCl3(thf)3] with 1.1 equivalent
of tridentate nitrogen-, or sulfur-bridged bis(pyrazoyl)
ligands (1 and 2) in thf at room temperature affords the
corresponding [CrCl3(NZN)] complexes 1a and 2a (Scheme
2), which were isolated, respectively, as green or red wine-
colored solids in high yields (typically 90-92%). These
complexes show moderate solubility at room temperature
in dichloromethane, thf and ethyl acetate, and are readily
soluble in acetonitrile. Due to the paramagnetic nature of
these [CrCl3(NZN)] complexes, 1H NMR spectra featured
very broad resonances and proved to be uninformative.
The identity of 1a and 2a was established on the basis of
elemental analysis.
systems show similar behaviour for production of a-olefins
as shown in Figure 1. This indicates that the central donor
atoms and also the pyrazolyl R1 and R2 substituents play no
significant influence in this series on product distribution.
However, enriched fractions in a-C4 (16.2 wt.%), a-C6
(18.1 wt.%) and a-C12 (9.7 wt.%) are obtained using the
catalyst system derived from2a.This result is consistent with
those ones found for MAO-activated nickel and chromium
complexes bearing analogous tridentate ligands.4,6
The ethylene oligomerization behavior of chromium
complexes 1a and 2a has been evaluated using optimized
conditions recently established for related 6-membered
chelate chromium catalysts,7 i.e., toluene as solvent at
80 ºC under 20 bar of ethylene and Al:Cr ratios of 300.
Representative results are summarized in Table 1.
When activated with MAO, all catalytic systems proved
to be active for oligomerization of ethylene. A moderate
turnover frequency (TOF) of 22,900 mol(ethylene)
mol(Cr)-1 h-1 was obtained with 1a while the catalyst
system derived from 2a, which contains a sulfur-bridged
ligand bearing methyl and phenyl substituents at the 3-
and 5-positions of the pyrazolyl rings, gave a high TOF
of 36,400 mol(ethylene) mol(Cr)-1 h-1. These results are
consistent with those observed in 6-membered ring nickel
and chromium catalysts bearing an analogous tridentate
sulfur-bridged ligand.4,6
Figure 1. Selectivity of 1a, 2a and 2b/MAO oligomerization systems for
a-olefins (80 °C, 20 bar, MAO-to-Cr = 300).
It is interesting to note that the presence of
phenyl groups at 3-position of the pyrazolyl rings in
CrCl3{bis[2-(3-diphenyl-1-pyrazolyl)ethyl)]amine} (1a)
determines a dramatic effect on activity and selectivity
as compared to the similar complex CrCl3{bis[2-(3,5-
dimethyl-1-pyrazolyl)ethyl)]amine} (1b)6 (compare
entries 1 and 3, Table 1). For instance, catalyst 1a
(22,900mol(ethylene)mol(Cr)-1 h-1)is2.2timesmoreactive
than 1b (10,400 mol(ethylene) mol(Cr)-1 h-1). Furthermore,
the amount of PE produced by 1a represents only
3.2% of the total amount of products (oligomers + PE),
while the use of 1b leads exclusively the formation of
polyethylene (PE).
The chromium complexes 1a and 2a produce oligomers
ranging from C4 to C14+ with a high selectivity for a-olefins
attaining 67.71 and 73.47%, respectively. Both catalyst
On the other hand, the introduction of relatively bulky
phenyl substituents at 5-position of the pyrazolyl rings in 2a

Vol. 21, No. 7, 2010
Oliveira et al.
1323
Table 1. Ethylene oligomerization with complexes 1a-b and 2a-ba
Oligomer distribution (wt.%)c
TOFb
(103)
Oligomers
(wt.%)
PE
(wt.%)
Total product
Entry
Cat.
C14+
(mg)
C4 (a-C4) C6 (a-C6) C8 (a-C8) C10 (a-C10) C12 (a-C12)
15.2 (93.5) 17.9 (92.9) 18.5 (88.0) 14.9 (89.1) 8.2 (89.3)
16.9 (96.1) 19.2 (94.3) 17.6 (92.0) 14.3 (92.3) 11.7 (83.3)
1
1a
2a
1b
2b
22.9
36.4
10.4
66.2
19.3
18.4
-
94.0
98.1
-
6.0
1.9
1600
2600
2200
5400
2
3d
4d
-
-
-
-
-
100
14.7
18.0 (94.3) 18.8 (95.8) 16.4 (93.7) 12.8 (92.0) 10.4 (65.5)
8.9
85.3
a Reaction conditions: toluene = 40 mL, oligomerization time = 15 min, p(ethylene) = 20 bar, T = 80 °C, [Cr] = 10 mmol, [Al]/[Cr] = 300. The results shown
are representative of at least duplicated experiments. b mol of ethylene converted (mol of Cr)-1 h-1 as determined by quantitative GLC. c Cn, percentage of
olefin with n carbon atoms in oligomers; a-Cn, percentage of terminal alkene in the Cn fraction, as determined by quantitative GLC. d reference 6.
as compared to methyl groups in CrCl3{bis[2-(3,5-dimethyl-
1-pyrazolyl)ethyl)]sulfide} (2b)6 leads to a noticeable
decrease in catalytic activity in (NSN)CrIII systems (compare
entries 2 and 4, Table 1) which can be associated to the
electronic effects of these phenyl groups to the chromium
metal center. The selectivity for C4-C12 fractions remains
almost unchanged (compare entries 2 and 4).
nickel center is crystallographically distinct and presents
a slightly different distorted octahedral environment. The
NiII atoms are bound to three m3-chloro ligands, a chelating
anilinomethyl-3,5-dimethylpyrazole and one terminal
chloride.
The Ni–Npyrazolyl distances lie in the range of
2.033-2.045 Å, while Ni–Nanilino bonds are 2.105-2.124 Å.
The m3-chloro ligand in the coordination sphere of each
nickel atom yields a Ni–Cl bonding distance lying in the
range of 2.447-2.506Å, while the Ni–Clterminal bonds fall in
the range of 2.3449(8)-2.3799(8)Å. All these values are in
agremeent with those disclosed in the literature.15
The Cl–Ni–Cl angles involving the bridging chlorine
ligands are systematically lower than 90°, ranging from
82.73(2) to 86.4(2)°. On the other hand, Ni–Cl–Ni angles are
significantly higher, tipically in the range of 93.17-97.40°.
Geometric constraints imposed by the cubane core reduce
Ni–Cl–Ni angles from the ideal tetrahedral value of 109.5°,
a reduction often associated with ferromagnetic coupling
of nickel centers.16 The distances varying from 3.588 to
3.726Å between the nickel atoms in the cluster are beyond
significant interactions.
Synthesisandstructuralcharacterizationofthetetrametallic
nickel complex 4 derived from NiCl2{bis[2-(3,5-dimethyl-
1-pyrazolyl)methyl]benzylamine} (1)
The 5-membered-ring nickel catalyst NiCl2{bis[2-
(3,5-dimethyl-1-pyrazolyl)methyl]benzylamine} (3) was
readily prepared in high yield via literature procedures.8
Recrystallization of 3 in methylene chloride at room
temperature afforded a few green crystals of an unexpected
tetrametallic nickel complex [{(L)(μ3-Cl)NiCl}4] (4,
L = 1-anilinomethyl-3,5-dimethylpyrazole) (ca. 8%
yield) (Scheme 3), and a large amount of unidentified
products. The formation of tetranuclear nickel complex
4 can be rationalized in terms of a ligand redistribution/
disproportionation reaction.
Crystal data and structure refinement for 4 are
summarized in Table 2, and selected bond distances and
angles are listed in Table 3. The molecular geometry and
atom-labeling scheme are shown in Figure 2. Complex 4
has a cubane-type {Ni4(m3-Cl)4} core with four NiII and
four chloro ligands occupying alternate vertices. Each
Effect of the auxiliary ligand on catalyst activity and
selectivity using nickel(II) complexes bearing chelating
NZN ligands
Previous studies on nickel-based catalysts have
demonstrated that the incorporation of PPh3 into catalytic
LClNi
Cl
Cl
CH2Cl2, 25 °C
N
N
N
N
N
NiClL
Cl
+ unidentified
compounds
Cl
NiClL
several days
Ni
LClNi
Cl
Cl
3
4
Scheme 3.

1324
Substituted Tridentate Pyrazolyl Ligands for Chromium and Nickel-Catalyzed
J. Braz. Chem. Soc.
Figure 2. Molecular structure of [{(L)(μ3-Cl)NiCl}4] (4). Thermal ellipsoids are drawn at the 30% probability level; hydrogen atoms are omitted for clarity.
systems leads to higher activity and longer catalyst
lifetime.17 We were curious whether such effects would
apply to our nickel catalyst systems. For verifying that,
we have chosen the 5- and 6-membered ring nickel
complexes NiCl2{bis[2-(3,5-dimethyl-1-pyrazolyl)methyl]
benzylamine} (3)8 and NiCl2{bis[2-(3,5-dimethyl-1-
pyrazolyl)ethyl)]ether} (5)7 (Figure 3).
Table 2. Crystal data and structure refinement for 4
Empirical formula
C52H68Cl8N12Ni4
Formula weight / g mol-1
1379.62
100 (2)
0.71073
Triclinic
P-1
Temperature / K
Wavelength / Å
Crystal system
Space group
Unit cell dimensions
Table 3. Selected bond lengths (Å) and angles (°) for 4
a / Å
13.5355 (18)
13.9534 (19)
19.208 (2)
82.961(6)
82.944(7)
77.142(6)
3493.0(8)
2
b / Å
Ni(1)-N(14)
Ni(1)-N(24)
Ni(1)-Cl(5)
Ni(1)-Cl(8)
Ni(1)-Cl(9)
Ni(1)-Cl(11)
Ni(2)-N(15)
Ni(2)-N(22)
Ni(2)-Cl(6)
Ni(2)-Cl(11)
Ni(2)-Cl(7)
Ni(2)-Cl(9)
2.033(2)
2.114(2)
Ni(3)-N(17)
Ni(3)-N(21)
2.037(2)
2.105(2)
2.3449(8)
2.4508(7)
2.4897(8)
2.4926(8)
2.034(2)
2.123(2)
2.3457(8)
2.4636(7)
2.4661(8)
c / Å
a / °
b / °
g / °
Volume / Å3
2.3799(8) Ni(3)-Cl(12)
2.4471(7) Ni(3)-Cl(11)
2.4683(7) Ni(3)-Cl(8)
2.4950(8) Ni(3)-Cl(7)
Z
calculated density / g cm-3
Absorption coefficient / mm-1
F(000)
1.312
2.045(2)
2.124(2)
Ni(4)-N(18)
Ni(4)-N(16)
1.407
1424
2.3530(8) Ni(4)-Cl(1)
2.4640(8) Ni(4)-Cl(9)
2.4676(7) Ni(4)-Cl(7)
2.5057(8)
Crystal size / mm
Theta range for data collection / °
Index ranges
0.37×0.21×0.08
3.01 to 27.48
-17 ≤ h ≤ 17, -18 ≤ k ≤ 18,
-24 ≤ l ≤ 24
Reflections collected / unique
Completeness to q max
Data / restraints / parameters
Goodness-of-fit on F2
50765 / 15824 [R(int) = 0.0461]
Ni(4)-Cl(7)-Ni(2)
Ni(4)-Cl(7)-Ni(3)
Ni(2)-Cl(7)-Ni(3)
Ni(1)-Cl(8)-Ni(4)
Ni(1)-Cl(8)-Ni(3)
Ni(4)-Cl(8)-Ni(3)
94.05(3)
97.41(3)
92.67(3)
93.88(2)
93.44(2)
96.89(3)
Ni(4)-Cl(9)-Ni(1)
93.98(2)
93.17(3)
97.01(3)
93.78(3)
93.21(2)
97.40(3)
0.988
Ni(4)-Cl(9)-Ni(2)
Ni(1)-Cl(9)-Ni(2)
Ni(3)-Cl(11)-Ni(2)
Ni(3)-Cl(11)-Ni(1)
Ni(2)-Cl(11)-Ni(1)
15824 / 0 / 733
1.038
Final R indices [I > 2 s(I)]
R indices (all data)
Largest diff. peak and hole / e Å-3
R1 = 0.0427, wR2 = 0.0944
R1 = 0.0685, wR2 = 0.1021
0.856 and -0.431

Vol. 21, No. 7, 2010
Oliveira et al.
1325
be also considered. However, in both cases, the presence
of PPh3 promotes the formation of more stable catalytic
species and at the same time prevents deactivation by
impurities of active reactants in the catalytic species.18
The presence of this auxiliary ligand in the
oligomerization medium plays no significant influence
on the total C4 production with selectivities varying from
99.8 to 100% (compare entries 1/2, and 4/6). On the
other hand, the PPh3 ligand has a strong impact in the
selectivity towards the production of a-olefins, decreasing
substantially the amount of 1-butene (16.2-20.0%) with a
concomitant increase of internal olefins fractions (cis-C4:
25.7-36.0%; trans-C4 fractions: 54.3-47.6%) as can be
better visualized in Figure 4. We may reasonably assume
that the favored formation of butenes-2 rather than butene-1
O
N
N
N
N
N
N
N
N
N
Ni
Ni
Cl Cl
Cl
Cl
3
5
Figure 3. Nickel complexes NiCl2{bis[2-(3,5-dimethyl-1-pyrazolyl)
methyl]benzylamine} (3), and NiCl2{bis[2-(3,5-dimethyl-1-pyrazolyl)
ethyl)]ether} (5) used in ethylene dimerization reactions in presence
of PPh3.
The ethylene oligomerization behavior of complexes
3 and 5 was investigated in toluene with MAO activation.
Representative results are summarized in Table 4. Under
optimized conditions (toluene as solvent at 30 ºC under
20 bar of ethylene,Al:Ni ratios of 250) the nickel catalysts 3
and 5 are active for dimerization of ethylene in the absence
of PPh3 (3, TOF = 11,300 mol(ethylene) mol(Ni)-1 h-1; 5,
TOF = 7,100 mol(ethylene) mol(Ni)-1 h-1) with selectivity
for 1-butene attaining 84.4 and 87.5%, respectively
(Table 4, entries 1 and 4).
The oligomerization reactions performed in the presence
of 1 equiv of PPh3 resulted in much higher TOFs mainly
in the case of catalyst system 5/MAO (compare entries 4
and 6). One reasonable explanation for this phenomenon
can be associated to the partial substitution of the tridentate
NZN ligand by PPh3 to afford a bidentate NZ/N-Ni-PPh3
complex. On the other hand, the fact that the active nickel
species are coordinated with auxiliary PPh3 on the vacant
coordination sites when lacking ethylene monomers should
Figure 4. Influence of auxiliary ligand (PPh3) on selectivity for butenes
(30 °C, 20 bar, [Al]/[Ni] = 250, [Ni]/[PPh3] = 1).
Table 4. Ethylene oligomerization with nickel complexes 3 and 5a
Selectivity (%)c
Entry
Cat. (mmol) PPh3 (equiv.)
Oligomers (mg)
TOFb (103)
C4
C4 (a-C4)
84.4
20.0
61.0
87.5
24.1
16.2
24.4
31.5
41.6
20.4
32.1
C4 (cis-C4) C4 (trans-C4)
C6 (a-C6)
1
3 (10.0)
3 (10.0)
3 (3.0)
-
1054
3379
1301
680
11.3
36.4
45.1
7.1
96.3
100
8.5
6.5
3.7
-
2
1.0
1.0
-
25.7
16.2
7.3
54.3
22.8
3.9
3
100
4
5 (10.0)
5 (10.0)
5 (10.0)
5 (3.0)
98.7
99.3
99.8
100.0
99.7
99.7
99.7
100.0
1.3
0.7
0.2
-
5
0.5
1.0
1.0
10.0
1.0
1.0
1.0
7770
12420
4410
7950
1860
8280
11940
81.4
113.4
154.2
83.5
77.9
43.3
125.4
23.7
36.0
27.1
27.9
20.4
26.5
43.1
51.6
47.6
48.5
40.5
37.7
52.8
24.8
6
7
8
5 (10.0)
5 (10.0)
5 (10.0)
5 (10.0)
0.3
0.3
0.3
-
9d
10e
11f
a Reaction conditions: toluene = 40 mL, p(ethylene) = 20 bar, oligomerization time = 20 min, MAO [Al]/[Ni] = 250. The results are representative of at
least duplicated experiments. b mol of ethylene converted (mol of Ni)-1 h-1, as determined by quantitative GLC. c Cn, amount of olefin with n carbon atoms
in the oligomers; a-Cn, amount of terminal alkene in the Cn fraction, as determined by quantitative GLC. d Oligomerization time = 5 min. e Oligomerization
time = 40 min. f Oligomerization reaction using DEAC [Al]/[Ni] = 250.

1326
Substituted Tridentate Pyrazolyl Ligands for Chromium and Nickel-Catalyzed
J. Braz. Chem. Soc.
+
+
O
5 min
1 equiv PPh3
N
N
N
N
Ni
isomerization
MAO, ethylene
Cl
Cl
time 5 min → 40 min
5
40 min
+
Scheme 4.
is a consequence of the presence of PPh3 in the milieu,
which would block coordination of incoming ethylene
and lead to isomerisation rather than b-H elimination of R.
When the quantity of precatalysts 3 and 5 was
decreased, very high activities were observed. For
instance, with 3.0 mmol of nickel complexes 3 and 5,
high TOFs of 45,100 mol(ethylene) mol(Ni)-1 h-1 and
154,200 mol(ethylene) mol(Ni)-1 h-1 were obtained,
respectively (entries 3 and 7). This effect can be primarly
associated to (i) an easier solubilization of the precatalyst
in toluene solution, and (ii) increase of molar ratio [ethylene]/
[Ni]; however, a decrease of excessive exotherms during
the oligomerization reactions, which would induce catalyst
decay, cannot be ruled out.
(i.e., chain isomerization transfer is favored relative to
chain propagation). It should be pointed out that the ability
of NiII complexes to isomerize a-olefins is a well-known
process.19 In particular, it was found that increasing the
reaction time results in higher quantity of trans-C4 owing
to the isomerization process involving 1-butene and cis-C4
(Scheme 4).
Based on these preliminary results, complex 5 was
selectedforfurtheroptimization,investigatingthe[Ni]/[PPh3]
ratio, oligomerization reaction time, and cocatalyst type.
As demonstrated in Table 4, when a minor quantity of
PPh3 was used ([Ni]/[PPh3] = 0.5), complex 5 gave a high
activity (TOF = 81,400 mol(ethylene) mol(Ni)-1 h-1, entry
5), which was increased upon using 1.0 equivalent of PPh3
(TOF = 113,400 mol(ethylene) mol(Ni)-1 h-1, entry 6). A
greater loading of PPh3 (10 equivalents) led to lower activity
(TOF = 83,500 mol(ethylene) mol(Ni)-1 h-1, entry 8). At
the same time, increasing the amount of PPh3 from 0.5 to
10.0 equivalents led to slightly improved selectivities for
1-butene (24.1 to 31.5%).
Figure 5. Monitoring of selectivities in the ethylene oligomerization
reaction promoted by the 5/MAO/PPh3 system ([Ni]/[PPh3] = 1.0, [MAO]/
[Ni] = 250; T = 30 ºC; 20 atm ethylene):  C4 products,  1-butene,
 cis-2-butene,  trans-2-butene. Hexenes, mostly 1-hexene, were also
produced in 0.2-0.3% selectivity and are not shown in this figure.
The reaction time can have a significant effect on TOFs,
and the selectivity. It was found that the activity at 5 min
of reaction (Table 4, entry 9) was about 1.5 times lower
than at 20 min (Table 4, entry 6), suggesting that this type
of catalyst needs a long pre-activation time (up to 5 min)
to promote the formation of a higher amount of catalytic
species. Increasing the reaction time to 40 min led to a lower
TOF value (43,300 mol(ethylene) mol(Ni)-1 h-1, entry 10),
indicating that a partial catalyst deactivation took place.
The reaction time affects significantly the selectivity for
1-butene. As can be seen in Figure 5, the selectivity for C4
olefins remains high and constant over time (99.7-99.8%).
However, varying the reaction time from 5 to 40 min,
a larger amount of 2-butenes (from 58.1 to 79.3%) is
produced in consequence of the isomerization process
Activation of nickel complex 5 with diethylaluminum-
chloride (DEAC) instead of MAO resulted in a more active
system (TOF 125,400 mol(ethylene) mol(Ni)-1 h-1). This
observation could reflect a better stabilization of active
species with DEAC than with MAO, possibly thanks to the
chlorine atom. At the same time, the use of DEAC led to
slightly improved selectivity for 1-butene (32.1 %), with
production of lower amounts of 2-butenes (67.9%).
Conclusions
Anewsetofchromium(III)complexesbasedontridentate
ligands has been prepared and evaluated for ethylene
oligomerization under MAO activation. Replacement of the

Vol. 21, No. 7, 2010
Oliveira et al.
1327
central bridging nitrogen with a sulfur donor atom affords a
catalyst that exhibits higher TOF and higher selectivity for
a-C4, a-C6, and a-C8. The presence of phenyl groups at 3-
or 5-position of the pyrazolyl rings determines a pronouced
effect on activity and selectivity owing to the steric/electronic
effects of these phenyl groups on the chromium metal center.
In parallel, the use of triphenylphosphine (PPh3)
in the oligomerization reactions using nickel catalysts
(3 and 5) resulted in much higher TOFs. However, the
presence of this auxiliary ligand has a strong impact
in the selectivity towards the production of a-olefins,
decreasing substantially the amount of 1-butene with a
concomitant increase of the 2-butene fractions. Under
optimized conditions ([Ni]/[PPh3] = 1.0, [Ni] = 3.0 mmol,
30 °C, 20 bar ethylene, MAO-to-Ni = 250, oligomerization
time = 20 min), pre-catalyst 5 leads to TOF = 154.2×103
mol(ethylene) mol(Ni)-1 h-1 and selectivities for C4 and
a-C4 are 100.0 and 24.4%, respectively.
2. Dennett, J. N. L.; Gillon, A. L.; Heslop, K.; Hyett, D. J.;
Fleming, J. S.; Lloyd-Jones, C. E.; Orpen, A. G.; Pringle, P.
G.; Wass, D. F.; Organometallics 2004, 23, 6077; Speiser, F.;
Braunstein, P.; Saussine, L.; Organometallics 2004, 23, 2625;
Speiser, F.; Braunstein, P.; Saussine, L.; Organometallics 2004,
23, 2633; Speiser, F.; Braunstein, P.; Saussine, L.; Welter, R.;
Inorg. Chem. 2004, 43, 1649; Tang, X.; Zhang, D.; Jie, S.;
Sun, W. H.; Chen J.; J. Organomet. Chem. 2005, 690, 3918;
Speiser, F.; Braunstein, P.; Saussine, L.; Acc. Chem. Res. 2005,
38, 784; Malinoski, J. M.; Brookhart, M.; Organometallics
2003, 22, 5324; Braunstein, P.; Chauvin, Y.; Mercier, S.;
Saussine, L.; Fischer, J.; de Cian. A.; J. Chem. Soc., Chem.
Commun. 1994, 2203; Nelkenbaum, E.; Kapon, M.; Eisen, M.
S.; Organometallics 2005, 24, 2645; Speiser, F.; Braunstein, P.;
Saussine, L.; Inorg. Chem. 2004, 43, 4234; Chen, Y.; Wu, G.;
Bazan, G. C.; Angew. Chem. Int. Ed. 2005, 1108; Buchard, A.;
Auffrant, A.; Klemps, C.; Vu-Do, L.; Boubekeur, L.; Le Goff,
X. F.; Le Floch, L.; Chem. Comm. 2007, 1502; Mora, G.; van
Zutphen, S.; Klemps, C.; Ricard, L.; Jean, Y.; Le Floch, P.;
Inorg. Chem. 2007, 46, 10365; Hao, P.; Sun, W.-H.; Shi, Q.;
Adewuyi, S.; Lu, X.; Li, P.; Organometallics 2007, 26, 2439;
Sun, W.-H.; Jie, S.; Zhang, S.; Zhang, W.; Song, Y.; Ma, H.;
Chen, J.; Wedeking, K.; Fröhlich, R.; Organometallics 2006,
25, 666; Hou, J.; Sun, W.-H.; Zhang, S.; Ma, H.; Deng, Y.; Lu,
X.; Organometallics 2006, 25, 236.
Supplementary Information
CCDC746569containsthesupplementarycrystallographic
datafor4.Thesedatacanbeobtainedfreeofchargeviahttp://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or
e-mail:deposit@ccdc.cam.ac.uk.Heteronuclearmultiplebond
correlation (HMBC) data for 1-(2-hydroxyethyl)-3-methyl-
5-phenylpyrazole (isomer A) are available free of charge at
http://jbcs.sbq.org.br, as PDF file.
3. Tomov, A. K.; Chirinos, J. J.; Long, R. J.; Gibson, V. C.;
Elsegood, M. R. J.; J. Am. Chem. Soc. 2006, 128, 7704;
Carney, M. J.; Robertson, N. J.; Halfen, J. A.; Zakharov, L. N.;
Rheingold, A. L.; Organometallics 2004, 23, 6184; Killian,
E.; Blann, K.; Bollmann, A.; Dixon, J. T.; Kuhlmann, S.;
Maumela, M. C.; Maumela, H.; Morgan, D. H.; Nongodlwana,
P.; Overett, M. J.; Pretorius, M.; Höfener, K.; Wasserscheid,
P.; J. Mol. Catal. A: Chem. 2007, 270, 214; Killian, E.; Blann,
K.; Bollmann, K.; Dixon, J. T.; Kuhlmann, S.; Maumela, M.
C.; Maumela, H.; Morgan, D. H.; Taccardi, N.; Pretorius, M.;
Wasserscheid, P.; J. Catal. 2007, 245, 277; McGuinness, D.
S.; Overett, M.; Tooze, R. P.; Blann, K.; Dixon, J. T.; Slawin,
A. M. Z.; Organometallics. 2007, 26, 1108; Elowe, P. R.;
McCann, C.; Pringle, P. G.; Spitzmesser, S. K.; Bercaw, J. E.;
Organometallics 2006, 25, 5255; Bowen, L. E.; Haddow, M.
F.; Orpen,A. G.;Wass, D. F.; DaltonTrans. 2007, 1160;Walsh,
R.; Morgan, D. H.; Bollmann, A.; Dixon, J. T.; Appl. Catal. A:
Gen. 2006, 306, 184; McGuinness, D. S.; Wasserscheid, P.;
Keim, W.; Morgan, D.; Dixon, J. T.; Bollmann, A.; Maumela,
H.; Hess, F.; Englert, U.; J. Am. Chem. Soc. 2003, 125,
5272; Jabri, A.; Temple, C.; Crewdson, P.; Gambarotta, S.;
Korobkov, I.; Duchateau, R.; J. Am. Chem. Soc. 2006, 128,
9238; McGuinness, D. S.; Brown, D. B.; Tooze, R. P.; Hess, F.
M.; Dixon, J. T.; Slawin, A. M. Z.; Organometallics 2006, 25,
3605; Agapie, T.; Schofer, S. J.; Labinger, J. A.; Bercaw, J. E.;
J. Am. Chem. Soc. 2004, 126, 1304; Kuhlmann, S.; Dixon, J.
Acknowledgments
This research was financially supported by CNPq,
Petrobrás and INCT-Catálise. L. L. de Oliveira, R.
Campadelli, A. L. Bergamo and A. H. D. P. dos Santos
gratefully acknowledge CAPES, CNPq and FAPERGS
for fellowships. The X-ray diffraction analysis of 4 was
performed by Thierry Roisnel at the Laboratoire de Chimie
du Solide et Inorganique Moléculaire, Institut de Chimie,
Université de Rennes.
References
1. Skupinska, J.; Chem. Rev. 1991, 91, 613; Al-Jarallah, A.
M.; Anabtawi, J. A.; Siddiqui, M. A. B.; Aitani, A. M.; Al-
Sadoun, A. W.; Catal. Today 1992, 14, 1; Vogt, D. In Applied
Homogeneous Catalysis with Organometallic Compounds;
Cornils, B.; Herrmann, W. A.; eds., Wiley: Weinheim, 1996,
vol. 1, pp. 245-258; Speiser, F.; Braunstein, P.; Saussine, L.;
Acc. Chem. Res. 2005, 38, 784.

1328
Substituted Tridentate Pyrazolyl Ligands for Chromium and Nickel-Catalyzed
J. Braz. Chem. Soc.
T.; Haumann, M.; Morgan, D. H.; Ofili, J.; Spuhl, O.; Taccardi,
N.; Wasserscheid, P.; Adv. Synth. Catal. 2006, 348, 1200; Wass,
D. F.; Dalton Trans. 2007, 816.
20, 2390; Ballester, L.; Coronado, E.; Gutiérrez, A.; Monge,
A.; Perpinán, M. F.; Pinilla, E.; Rico, T.; Inorg. Chem. 1992,
31, 2053; Atkins, A. J.; Blake, A. J.; Schröder, M.; J. Chem.
Soc., Chem. Commun. 1993, 1662; Blake,A. J.; Brechin, E. K.;
Codron,A.; Gould, R. O.; Grant, C. M.; Parsons, S.; Rawson, J.
M.; Winpenny, R. E. P.; Chem. Commun. 1995, 1983; Halcrow,
M. A.; Sun, J.-S.; Huffman, J. C.; Christou, G.; Inorg. Chem.
1995, 34, 4167; Fallah, M. S. E.; Rentschler, E.; Caneschi, A.;
Gatteschi, D.; Inorg. Chim. Acta 1996, 247, 231; Clemente-
Juan, J. M.; Chansou, B.; Donnadieu, B.; Tuchagues, J.-P.;
Inorg. Chem. 2000, 39, 5515; Mukherjee, S.; Weyhermüller, T.;
Bothe, E.; Wieghardt, K.; Chaudhuri, P.; Eur. J. Inorg. Chem.
2003, 863; Paine, T. K.; Rentschler, E.; Weyhermüller, T.;
Chaudhuri, P.; Eur. J. Inorg. Chem. 2003, 3167; Papaefstathiou,
G. S.; Escuer, A.; Mautner, F. A.; Raptopoulou, C.; Terzis, A.;
Perlepes, S. P.; Vicente, R.; Eur. J. Inorg. Chem. 2005, 879;
Efthymiou, C. G.; Raptopoulou, C. P.; Terzis, A.; Boca, R.;
Korabic, M.; Mrozinski, J.; Perlepes, S. P.; Bakalbassis, E.G.;
Eur. J. Inorg. Chem. 2006, 2236.
4. Ajellal, N.; Kuhn, M. C. A.; Boff, A. D. G.; Hoerner,
M.; Thomas, C. M.; Carpentier, J-F.; Casagrande, O. L.;
Organometallics 2006, 25, 1213.
5. Kunrath, F. A.; De Souza, R. F.; Casagrande, O. L.; Brooks, N.
R.; Young, V. G.; Organometallics 2003, 22, 4739.
6. Junges, F.; Kuhn, M. C. A.; Santos, A. H. P.; Rabello, C. R.
K.; Thomas, C. M.; Carpentier, J.-F.; Casagrande Jr, O. L.;
Organometallics 2007, 26, 4010.
7. Junges, F.; Kuhn, M. C. A.; Boff, A. D. G.; Rabello, C. R. K.;
Kokitsu, I.; Casagrande Jr, O. L.; Br Patent 0600702-3, 2006.
8. de Oliveira, L. L.; Campedelli, R. R.; Kuhn, M. C. A.;
Carpentier, J.-F.; Casagrande Jr, O. L.; J. Mol. Catal. 2008,
288, 58.
9. Trofimenko, S.; Calabresi, J. C.; Thompson, J. S.; Inorg. Chem.
1987, 26, 1507.
10. Boudjouk, P.; So, J.-H.; Inorg. Synth. 1992, 29, 108.
11. Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori
G.; Spagna, R.; J. Appl. Crystallogr. 1999, 32, 115.
12. Sheldrick, G.M.; SHELXS-97, Program for the Determination
of Crystal Structures, University of Goettingen, Germany, 1997;
Sheldrick, G.M.; SHELXL-97, Program for the Refinement of
Crystal Structures, University of Goettingen, Germany, 1997.
13. Farrugia, L. J.; J. Appl. Crystallogr.1999, 32, 837.
14. Sorrell, T. N.; Malachowski, M. R.; Inorg. Chem. 1983, 22,
1883; Martens, C. F.; Schenning, A. P. H. J.; Feiters, M. C.;
Berens, H.W.; van der Linden, J. G. M,Admiraal G.; Beurskens,
P. T.; Kooijman, H.; Spek,A. L.; Noltela R. J. M.; Inorg. Chem.
1995, 34, 4135.
16. Ribas, J.; Monfort, M.; Costa, R.; Solam, X.; Inorg. Chem.
1993, 32, 695.
17. Sun, W.-H.; Zhang, W.; Gao, T.; Tang, X.; Chen, L.; Li,Y.; Jin,
X.; J. Organomet. Chem. 2004, 689, 917; Carlini, C.; Isola, M.;
Liuzzo, V.; Galletti, A. M. P.; Sbrana, G.; Appl. Catal. A: Gen.
2002, 231, 307; Jenkins, J. C.; Brookhart, M.; Organometallics
2003, 22, 250; Sun, W.-H.; Tang, X.; Gao, T.; Wu, B.; Zhang,
W.; Ma, H.; Organometallics 2004, 23, 5037.
18. Wang, L.; Sun, W.-H.; Han, L.; Yang, H.; Hu, Y.; Jin, X.;
J. Organomet. Chem. 2002, 658, 62.
19. Birdwhistell, K. R.; Lanza, J.; J. Chem. Educ. 1997, 74, 579;
Chen, H.-P.; Liu,Y.-H.; Peng, S.-M.; Liu, S.-T.; Organometallics
2003, 22, 4893.
15. Bertrand, J. A.; Marabella, C.; Vanderveer, D. G.; Inorg. Chim.
Acta 1978, 26, 13; Gladfelter, W. L.; Lynch, M. W.; Schaefer,
W. P.; Hendrickson, D. N.; Gray, H. B.; Inorg. Chem. 1981,
Received: September 24, 2009
Web Release Date: April 22, 2010

J. Braz. Chem. Soc., Vol. 21, No. 7, S1, 2010.
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Substituted Tridentate Pyrazolyl Ligands for Chromium and Nickel-Catalyzed
Ethylene Oligomerization Reactions. Effect of Auxiliary Ligand on Activity and
Selectivity
Lucilene L. de Oliveira, Roberta R. Campedelli, Adão L. Bergamo,
Ana H. D. P dos Santos and Osvaldo L. Casagrande*
Laboratório de Catálise Molecular, Instituto de Química, Universidade Federal do Rio Grande do Sul,
Av. Bento Gonçalves, 9500, 90501-970 Porto Alegre-RS, Brazil
Figura S1. HMBC spectra of 1-(2-hydroxyethyl)-3-methyl-5-phenylpyrazole (isomer A).
*e-mail: osvaldo.casagrande@ufrgs.br