Furoyl and thiophene carbonyl linker pyrazolyl palladium(II) complexes - Synthesis, characterization, and evaluation as ethylene oligomerization catalysts

Article abstract of DOI:10.1139/v05-092

Reactions of 2-furoyl chloride and 2-thiophene carbonyl chloride with substituted pyrazoles produced the modified pyrazolyl compounds: {(3,5-Me ₂pzCO)-2-C₄H₃O} (L1), {(3,5-Me ₂pzCO)-2-C₄H₃S

Full text of DOI:10.1139/v05-092

843
Furoyl and thiophene carbonyl linker pyrazolyl
palladium(II) complexes — Synthesis,
characterization, and evaluation as ethylene
oligomerization catalysts1
Stephen O. Ojwach, Mmboneni G. Tshivhase, Ilia A. Guzei, James Darkwa, and
Selwyn F. Mapolie
Abstract: Reactions of 2-furoyl chloride and 2-thiophene carbonyl chloride with substituted pyrazoles produced the
modified pyrazolyl compounds: {(3,5-Me2pzCO)-2-C4H3O} (L1), {(3,5-Me2pzCO)-2-C4H3S} (L2), {(3,5-t-Bu2pzCO)-2-
C4H3O} (L3), {(3,5-t-Bu2pzCO)-2-C4H3S} (L4), {(3,5-Ph2pzCO)-2-C4H3S} (L5), and {(pzCO)-2-C4H3O} (L6) in good
yields. Reactions of these synthons with [Pd(NCMe)2Cl2] afforded the corresponding mononuclear palladium(II) com-
plexes: [Pd(L1)2Cl2] (1), [Pd(L2)2Cl2] (2), [Pd(L3)2Cl2] (3), [Pd(L4)2Cl2] (4), [Pd(L5)2Cl2] (5), and [Pd(L6)2Cl2] (6) in
1
moderate to high yields. All compounds synthesized were characterized by a combination of H NMR, 13C NMR, and
IR spectroscopy. Compounds L1, 1, and 2 were examined by single crystal X-ray crystallography. DFT theoretical
studies at the B3LYP/6-31+G(d) level of theory with GAUSSIAN98 have been used to rationalize some of the results.
When the complexes were activated with ethylaluminium dichloride (EtAlCl2), they catalysed the oligomerization of
ethylene to mostly C10 and C12 oligomers. Oligomer distribution greatly depends on the oligomerization conditions; for
example, an increase in temperature and pressure produced a higher percentage of C12 compared to C10.
Key words: furoyl and thiophene carbonyl linker pyrazolyl compounds, palladium complexes, ethylene oligomerization.
Résumé : Les réactions du chlorure de 2-furoyle et le chlorure de thiophène-2-carbonyle avec des pyrazoles substitués
conduisent avec de bons rendements aux composés pyrazolyles modifiés: {(3,5-Me2pzCO)-2-C4H3O} (L1), {(3,5-
Me2pzCO)-2-C4H3S} (L2), {(3,5-t-Bu2pzCO)-2-C4H3O} (L3), {(3,5-t-Bu2pzCO)-2-C4H3S} (L4), {(3,5-Ph2pzCO)-2-
C4H3S} (L5) et {(pzCO)-2-C4H3O} (L6). Les réactions de ces synthons avec du [Pd(NCMe)2Cl2] conduisent avec des
rendements allants de modérés à élevés aux complexes mononucléaires correspondants du palladium(II): [Pd(L1)2Cl2]
(1), [Pd(L2)2Cl2] (2), [Pd(L3)2Cl2] (3), [Pd(L4)2Cl2] (4), [Pd(L5)2Cl2] (5) et [Pd(L6)2Cl2] (6). Tous les composés syn-
1
thétisés ont été caractérisés par une combinaison de spectroscopie infrarouge et RMN du H et du 13C. Les composés
L1, 1 et 2 ont été examinés par diffraction des rayons X. Des études selon la théorie de la densité fonctionnelle au ni-
veau B3LYP/6-31+G(d) de la théorie avec une GAUSSIAN98 ont été utilisées pour rationaliser un certain nombre de
résultats. Lorsqu’ils sont activés par du dichlorure d’éthylaluminium (EtAlCl2), ils catalysent l’oligomérisation de
l’éthylène, principalement en oligomères en C10 et en C12. La distribution des oligomères dépend fortement des condi-
tions d’oligomérisation; par exemple, une augmentation de la température et de la pression conduit à des pourcentages
plus élevés de produit en C12 par rapport à celui en C10.
Mots clés : furoyle et thiophène carbonyle, lieur, composés pyrazolyles, complexes du palladium, oligomérisation de l’éthylène.
[Traduit par la Rédaction] Ojwach et al. 853
Introduction
ligands in coordination chemistry (1). Indeed, the chemistry
of pyrazole and pyrazolyl complexes with transition metals
has been extensively reviewed (2), but despite the numerous
reports on the synthesis and properties of pyrazolyl late
transition metal complexes, very little is known about their
catalytic activity in olefin oligomerization. Olefin oligomeri-
Nitrogen donor compounds represent an important class
of ligands in coordination chemistry. In particular, pyrazoles
and pyrazolyl ligands have been widely used as terminal and
bridging ligands and as precursors for various multidentate
Received 9 December 2004. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 22 July 2005.
S.O. Ojwach, M.G. Tshivhase, J. Darkwa,2 and S.F. Mapolie.3 Department of Chemistry, University of the Western Cape,
Private Bag X17, Bellville 7535, South Africa.
I.A. Guzei. Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, WI 53706, USA.
1This article is part of a Special Issue dedicated to Professor Howard Alper.
2Corresponding author (e-mail: jdarkwa@uwc.ac.za).
3Corresponding author (e-mail: smapolie@uwc.ac.za).
Can. J. Chem. 83: 843–853 (2005)
doi: 10.1139/V05-092
© 2005 NRC Canada

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Can. J. Chem. Vol. 83, 2005
Scheme 1.
R
R
R
N
N
O
Toluene
+
X
N
N
-Et3NHCl
Cl
H
X
R
O
Compound
X
O
R
Compound
X
S
R
L1
L2
L3
L4
L5
L6
tBu
Ph
H
Me
Me
tBu
S
S
O
O
zation is typically catalysed by late transition metal com-
plexes, particularly those of Ni(II) with P, N, and O ligands
(3) because of the propensity of such reactions to undergo β-
hydride elimination.
we have used mainly methylaluminoxane (MAO), but gener-
ally ethylaluminium halides can also activate precatalysts to
polymerize ethylene (3).
In this report we describe the preparation and character-
ization of new furoyl and thiophene carbonyl Pd(II) com-
plexes and their ability to catalyse ethylene oligomerization
when activated by ethylaluminium dichloride (EtAlCl2) as
the co-catalyst. The potential for controlling the catalytic
properties by varying substituents on the ligands is demon-
strated by using different substituted pyrazolyl compounds.
The influence of various conditions such as reaction time
and temperature on the catalyst activity and selectivity in
ethylene oligomerization is described.
However, in the last decade it has become clear that care-
ful tuning of ligand properties and choice of appropriate co-
catalysts can lead to either oligomers or polymers after this
phenomenon was first observed by Keim (4). For example,
reports by Brookhart and co-workers (5) clearly demonstrate
the effect of bulky substituents in pseudo axial sites in nickel
catalysts. Bulky ligands block these axial sites and reduce
chain transfer, whereas less bulky ligands form catalysts that
produce oligomers. Another example of the role of bulky
substituents on catalysts is provided by diimine–pyridine lig-
ands. Gibson and co-workers (6) have used Fe(II) and Co(II)
complexes of this ligand system, with bulky ligands, as cata-
lysts to polymerize ethylene. However, by reducing the
steric bulk of the ligand backbone, the Brookhart group
found the Fe(II) catalyst to oligomerize ethylene to linear α-
olefins with remarkable activity and selectivity (7).
Recently, pyrazolyl nitrogen donor ligands have been
found to be tunable to produce electronic and steric effects
that have resulted in the use of their late transition metal
complexes as catalysts for the transformation of unsaturated
hydrocarbons. The report on the polymerization of ethylene
by [{R2C(3-t-Bu2pz)2}PdCl2] (R = Me, Ph) represents one
of the first examples of the use of pyrazolyl late-transition
metal complexes in olefin polymerization catalysis (8). Re-
ports by our group clearly indicate that electrophilicity of
the catalyst plays a crucial role in polymer formation. We
have found simple pyrazole Ni(II) and Pd(II) complexes that
are good catalysts for ethylene polymerization (9), and by
introducing carbonyl linkers to form benzenedicarbonyl and
benzenetricarbonyl linker pyrazolyl palladium(II) com-
plexes, catalytic activities for ethylene polymerization are
significantly higher than for the analogous simple pyrazole
systems (10). Steric factors also play a role (11). Our calcu-
lations of the steric encumbrance about the central metals in-
dicate that in complex [(3,5-t-Bu2pz)2PdCl2] the ligands
shield 92.1(3)% of the Pd surface while in [(3,5-
Mepz)2PdCl2] only 83.5(6)% of the central Pd is shielded by
the coordinated moieties (12). In producing polyethylene,
Results and discussion
Synthesis and characterization of 2-furoyl and
thiophene carbonyl pyrazolyl compounds and their
palladium(II) complexes
The compounds L1–L6 were readily prepared from either
2-furoyl chloride or 2-thiophene carbonyl chloride and an
equivalent amount of the appropriate pyrazole (Scheme 1)
following the procedure previously described by us (10).
The yields were moderate to high (53%–85%).
Reactions of L1–L6 with [Pd(NCMe)2Cl2] in a 2:1 ratio
produced the corresponding complexes 1–6 (Scheme 2).
While 1–5 were soluble in dichloromethane and could be
purified by recrystallization from dichloromethane and hex-
ane (1:1), 6 was insoluble in common organic solvents like
dichloromethane, toluene, and acetonitrile. Complex 6 pre-
cipitated from the reaction mixture essentially as an analyti-
cally pure solid.
All compounds were characterized by a combination of
1
IR, H NMR, and 13C NMR spectroscopy and elemental
analyses. Structures for L1, 1, and 2 were confirmed by X-
ray crystallography. 1H NMR spectroscopy, however, offered
signals that allowed easy identification of both ligands and
complexes. For example, the 3,5-disubstituted alkyl pyrazolyl
compounds typically have two upfield signals for the alkyl
substituents, a signal at about 6 ppm and three doublets of
doublets with an AMX splitting pattern (13). As expected,
the heteroatom in the linker affected the chemical shift, par-
© 2005 NRC Canada

Ojwach et al.
845
Scheme 2.
R
R
R
N
N
N
Cl
X
N
O
CH2Cl2
Pd
R
Pd(NCMe)2Cl2
+
X
R
O
O
N
X
Cl
N
R
Complex
X
O
R
Complex
X
S
R
1
2
3
4
5
6
tBu
Ph
H
Me
S
Me
tBu
S
O
O
ticularly those close to these atoms. Complexation of
pyrazolyl compounds with Pd resulted in slight changes of
the ligands NMR chemical shifts, but there were essentially
no changes in the signals in the splitting patterns.
607 bonds in 229 relevant complexes reported to the Cam-
bridge Structural Database (CSD, (15)). The Pd—Cl bond
distances in 1 and 2 (2.306(9) and 2.306(3) Å, respectively)
are in good agreement with the distance of 2.33(5) Å ob-
tained by averaging 2055 Pd—Cl bonds in 1268 relevant
complexes reported to the CSD.
Molecular structure determination by single crystal X-
ray analysis
An interesting structural aspect was revealed by examin-
ing the ligand conformations in complexes 1 and 2. The lig-
ands differ only by the nature of the heteroatom (sulfur vs.
oxygen) in their non-pyrazole five-membered rings and one
could have reasonably expected to observe very similar
structures. Indeed, in both cases the heteroatom (S or O) is
located on the same side of the C—C bond of the X-C-C=O
link in each ligand. Recall that in free L1 (Fig. 1), the two
oxygen atoms reside on the same side of the O-C-C=O link-
age. This logical result is in line with expectations, however,
DFT theoretical studies of simplified analogues of the com-
pounds L1 and L2 (Figs. 4 and 5) at the B3LYP/6-
31+G(d) level of theory with GAUSSIAN98 (16) indicate
that a different outcome could have been predicted. The
compounds (L1 and L2) can exist in several stable confor-
mations; the two most stable are shown in Figs. 4 and 5. In
the case of furoyl, the conformation in which the furan oxy-
gen is positioned on the same side as the carbonyl oxygen in
the O-C-C=O sequence is more stable. This conformation (A
in Fig. 4) is observed in the crystal structures of both L1 and
1. On the other hand, in the case of the thiophene carbonyl
compound, the other conformation (D in Fig. 5), in which
the thiophene S atom is on the opposite side from the car-
bonyl ligand in the S-C-C=O sequence is slightly more sta-
ble. Thus, the free compound L2 changes its conformation
upon coordinating to the Pd metal centre during the forma-
tion of 2. The activation energies for the rotation about the
C—C bond of the X-C-C=O linkage are calculated to be
13.4 kcal mol–1 for the A to B and 7.1 kcal/mol for C to D
transitions.
Single crystals suitable for X-ray analysis for compound
L1, complexes 1 and 2 were grown by slow diffusion of hex-
ane into dichloromethane at –4 °C and used to determine
their molecular structures. Crystallographic data for L1, 1,
and 2 are presented in Table 1 while selected bond distances
and angles are tabulated in Tables 2–4, respectively. The mo-
lecular diagrams are presented in Figs. 1–3, respectively.
The solid-state conformation of L1 is consistent with the
results of the DFT studies (vide infra) of its simplified ana-
logue pz-C(O)-C4H3O. In the structure of L1, atoms N(1)
and O(1) are on the opposite sides of the N(2)—C(6) bond
owing to electrostatic interactions (14) and atoms O(1) and
O(2) are on the same side of the C(6)—C(7) bond. This spa-
tial arrangement is also observed in the structure of 1, re-
vealing that the preferred orientation is not altered upon
coordination.
The two palladium complexes 1 and 2 contain the central
metal in slightly distorted square-planar arrangements. In
both cases, the pyrazolyl ligands are trans to each other
rendering Ci molecular symmetry. This is in line with our
density functional theory studies of trans-(pzH)2PdCl2 (sym-
metry C2h) and cis-(pzH)2PdCl2 (symmetry C2) at the
B3LYP/LANL2DZ level of theory that indicate that the
trans-complex is 12.82 kcal mol–1 (1 cal = 4.184 J) more sta-
ble. Compounds L1 and L2 are not planar in their respective
complexes and are monodentate with the heteroatoms sulfur
and oxygen pointing away from the metal centres.
The average Pd—N bond lengths of 2.032(2) and
2.025(7) Å in complexes 1 and 2, respectively, are statisti-
cally indistinguishable and agree well with the average Pd—
N(pz) bond length of 2.06(9) Å determined by averaging
We have also examined the steric crowding around the Pd
centres in 1 and 2 with the program SOLID-G to determine
© 2005 NRC Canada

846
Can. J. Chem. Vol. 83, 2005
Table 1. Crystal data and details of structure refinement for L1, 1, and 2.
Parameter
L1
1
2
Empirical formula
C10H10N2O2
C20H20Cl2N4O4Pd
C21H22Cl4N4O2PdS2
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
190.2
294(2)
0.710 73
Monoclinic
P21/n
557.7
674.75
100(2)
0.710 73
Monoclinic
P21
273(2)
0.710 73
Triclinic
P1
a (Å)
b (Å)
c (Å)
8.005 7(10)
17.761(2)
13.808 3(15)
90
97.148(2)
90
1948.2(4)
8
1.297
0.093
800
0.40 × 0.20 × 0.10
1.88–26.38
–10 ≤ h ≤ 9,
7.442 2(8)
9.209 7(10)
15.742 2(17)
88.898(2)
88.049(2)
86.608(2)
1948.2(4)
2
1.721
1.146
560
0.43 × 0.32 × 0.26
2.22–26.39
–9 ≤ h ≤ 9,
10.696(2)
13.332(3)
18.015(4)
90
96.345(4)
90
2553.1(9)
4
1.755
1.337
1352
0.30 × 0.20 × 0.20
1.90–28.31
–14 ≤ h ≤ 12,
α (°)
β (°)
γ (°)
Volume (Å3)
Z
Density (calculated, Mg m–3)
Absorption coefficient (mm–1)
F(000)
Crystal size (mm3)
θ Range for data collection (°)
Index ranges
–22 ≤ k ≤ 20,
–11 ≤ k ≤ 11,
–16 ≤ k ≤ 17,
–16 ≤ l ≤ 7
–19 ≤ l ≤ 19
–23 ≤ l ≤ 20
Reflections collected
Independent collections
Completeness to θ (%)
Absorption corrections
Max and min transmissions
Refinement method
9077
8891
16 039
3753 (R(int) = 0.029 6)
94.2
Empirical with SADABS
0.990 8 and 0.963 9
4401 (R(int) = 0.020 7)
99.1
Empirical with SADABS
0.754 9 and 0.638 6
10 824 (R(int) = 0.051 2)
92.8
Empirical with SADABS
0.754 9 and 0.638 6
Full-matrix least-squares on F2 Full-matrix least-squares on F2 Full-matrix least-squares on F2
Data/restraints/parameters
Goodness of fit on F2
Final R indices
R indices (all data)
Largest diff. peak and hole (e Å–3) 0.174 and –0.245
3753/0/313
1.025
R1 = 0.051 3, wR2 = 0.126 4
R1 = 0.094 8, wR2 = 0.145 7
4401/0/287
1.063
R1 = 0.027 1, wR2 = 0.073 7
R1 = 0.028 8, wR2 = 0.075 0
1.011 and –0.529
10 829/409/622
1.045
R1 = 0.061 2, wR2 = 0.139 9
R1 = 0.069 6, wR2 = 0.147 9
3.060 and –0.849
that the metal centres are shielded by the ligands to the ex-
tent of 93.1(3)% and 92.3(5)%, respectively. Since the dif-
ference between these values, determined from the crystal
structures reported herein, is not statistically significant, any
variation in the reactivity of these complexes towards the
same reagents ought to be attributed to the differences in the
electronic properties of the ligands and their conformations.
than the analogous complex 3 with tert-butyl substituents
(TON = 70 kg mol–1 Pd h–1) (Table 5, entries 1 and 3). A
similar trend was observed for the thiophene carbonyl ana-
logue (Table 5, entries 2 and 5). Catalyst 5, with the phenyl
substituent on the pyrazolyl ring, was the most active.
A report by Guan and Marshall (17) on the catalytic
behaviour of phosphine–imine Pd(II) complexes shows
that the phenyl analogue has higher activity (TON =
17 200 kg mol–1 Pd h–1) compared to that of the tert-butyl
(TON = 1670 kg mol–1 Pd h–1) and the methyl (TON =
960 kg mol–1 Pd h–1) systems. The observed trend could be
ascribed to the difference in the electronic structure of the
complexes (18) where the less electron-donating phenyl
group produces a more electrophilic metal centre in the cata-
lyst. This could explain why complex 5 is the best catalyst in
our study.
Evaluation of the complexes as catalysts for ethylene
oligomerization
When complexes 1–5 were activated with EtAlCl2, they
were found to oligomerize ethylene to mainly C10 and C12.
No oligomers were obtained when controlled reactions were
carried out at 25 °C and 5 atm (1 atm = 101.325 kPa) with
the co-catalyst and ethylene in the absence of the complexes.
Complex 6 was not evaluated because it is insoluble in tolu-
ene, the oligomerization solvent. There were a number of
factors that influenced the oligomerization: First, the nature
of the ligands influenced both the catalyst activity and prod-
uct distribution. Complex 1, with the furoyl linker and
methyl groups, was less active (TON = 60 kg mol–1 Pd h–1)
The nature of the linker in the ligand systems appears to
have some effect on the oligomer distribution. For example,
the catalysts with furoyl linkers gave higher percentages of
the C12 than C10 oligomers (Table 5, entries 1 and 3) whereas
the thiophene carbonyl analogues gave higher percentages of
© 2005 NRC Canada

Ojwach et al.
Table 2. Selected bond lengths and angles for
847
Table 4. Selected bond lengths and angles for 2.
L1.
Bond lengths (Å)
Pd(1)—N(1A)
Pd(1)—Cl(1)
Pd(2)—N(1B)
Pd(1)—Cl(2)
S(14A)—C(13A)
O(9A)—C(8A)
N(1A)—C(2A)
Bond lengths (Å)
O(1)—C(6)
O(2)—C(10)
O(2)—C(7)
N(1)—C(2)
N(1)—N(2)
N(2)—C(6)
2.026(6)
1.209(2)
1.355(3)
1.377(2)
1.311(3)
1.379(2)
1.405(2)
2.3029(19)
2.035(6)
2.3101(19)
1.694(8)
1.202(8)
1.363(8)
Bond angles (°)
C(10)-O(2)-C(7)
N(1)-N(2)-C(4)
N(1)-N(2)-C(6)
O(2)-C(7)-C(6)
O(1)-C(6)-C(7)
N(2)-C(6)-C(7)
Bond angles (°)
105.82(18)
111.88(16)
120.58(16)
112.40(17)
122.49(18)
117.53(17)
N(1A)-Pd(1)-N-(1B)
N(1A)-Pd(1)-Cl(1)
N(1B)-Pd(1)-Cl(1)
N(1A)-Pd(1)-Cl(2)
N(1C)-Pd(2)-N(1D)
O(9A)-C(8A)-N(7A)
O(9A)-C(8A)-C(10A)
178.7(3)
88.47(5)
90.93(5)
91.29(17)
179.5(3)
119.5(7)
123.4(7)
Table 3. Selected bond lengths and angles for 1.
Fig. 1. ORTEP diagram of a single moiety of L1. Atoms are
shown with 50% thermal probability ellipsoids.
Bond lengths (Å)
Pd(1)—N(1)
Pd(1)—Cl(1)
Pd(2)—N(3)
Pd(2)—Cl(2)
N(1)—C(2)
N(1)—N(2)
O(1)—C(6)
2.0332(15)
2.2993(5)
2.0300(17)
2.3125(5)
1.327(2)
1.388(2)
1.203(2)
Bond angles (°)
N(1)-Pd(1)-N(1)
N(1)-Pd(1)-Cl(1)
N(1)-Pd(1)-Cl(1)
N(1)-Pd(1)-Cl(1)
N(3)-Pd(2)-Cl(2)
N(3)-Pd(2)-Cl(2)
N(2)-C(6)-C(7)
180.00(8)
91.84(5)
88.16(5)
91.84
88.84(5)
91.16(5)
116.36(16)
C10 than C12 (Table 5, entries 2 and 4). There was, however,
no clear trend in oligomer distribution as the steric bulk of
the ligands in the catalysts changed.
while an Al:Pd of 1000 gave 66% C10 and 30% C12. It is not
clear why the changes in co-catalyst to catalyst ratio affect
product distribution.
The co-catalyst to catalyst ratio was found to be crucial in
determining activity. Complex 2 was used to establish the ef-
fective ratio for optimum activity. No activity was observed
for an Al:Pd ratio below 20. This indicates that not much ac-
tivation occurs below this ratio. An increase in the Al:Pd
from 20 to 2000 resulted in a general increase in oligomer
yield to give an optimum ratio of 1000. Above this ratio, the
yield decreased (Table 6, entry 6). Catalyst 1 showed a similar
trend (Table 6, entries 7–9). The co-catalyst to catalyst ratio
in ethylene oligomerization catalysed by phosphinitooxazo-
line and pyridine Ni(II) complexes is known to increase turn-
over frequency from 11 600 to 49 000 mol C2H4 mol–1 Ni h–1
when the EtAlCl2:Ni ratio is increased from 1.3 to 6 (19).
Our catalyst requires much higher co-catalyst to catalyst ra-
tio. This is probably due to the ability of the co-catalyst to
interact with both the carbonyl oxygen and the heteroatom in
the ligands. We found a higher Al:Pd ratio, however, re-
sulted in an increase in the percentage of C10 oligomers. For
instance, an Al:Pd of 50 gave 49% of C10 and 45% of C12,
The effects of time, temperature, and pressure on ethylene
oligomerization were mainly investigated using catalysts 1
and 5. The effect of time on ethylene oligomerization activ-
ity using catalyst 1 at 25 °C, 5 atm, and an Al:Pd ratio of
500 was investigated. Longer reaction times resulted in a
significant decrease in activity (Table 7). The maximum
turnover number (177 kg mol–1 Pd h–1) was obtained at
30 min (Table 7, entry 2), but at 15 min, it was evident that
the process to produce the active species was still incomplete,
resulting in lower yields (120 kg mol–1 Pd h–1). The same trend
was observed for catalyst 5 (Table 7, entries 5 and 6). Gen-
erally, reaction time is known to affect catalyst activity. This
is usually the result of catalyst decomposition. Our catalysts
appear to be stable up to about 30 min and thereafter begin
to decompose, even at room temperature. A similar phenom-
enon is seen for ethylene oligomerization using cationic
Ni(II) and Pd(II) complexes containing bidentate phen-
© 2005 NRC Canada

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Can. J. Chem. Vol. 83, 2005
Fig. 2. ORTEP diagram of 1 shown with 50% probability ellipsoids. The hydrogen atoms are omitted for clarity. The complex resides
on a crystallographic inversion centre.
Fig. 3. ORTEP diagram of 2 drawn with 50% thermal probability ellipsoids. The hydrogen atoms have been omitted for clarity.
acyldiarylphosphine ligands (20), where TOF increases for
the Pd(II) catalyst from 1.2 × 103 h–1 in 15 min to 5.3 ×
104 h–1 of ethylene consumed in 1 h, but after 3 h of activity
dropped to 3.3 × 104 h–1, signifying some catalyst decompo-
sition.
the nature of the oligomers produced. A higher percentage
of C10 (77%) was obtained for the 15 min run as compared
to 38% for the 2 h run (Table 7, entries 1 and 4). This indi-
cates that oligomer molecular weight increases with time, a
result of co-oligomerization of the released matured oligo-
mers, hence, production of higher oligomers. An opposite
Reaction time was also found to have a profound effect on
© 2005 NRC Canada

Ojwach et al.
849
Table 5. Effect of the catalyst on ethylene oligomerization.a
Oligomers (%)b
Entry
Catalyst
C10
C12
C14+
Yieldc (g)
TON (kg mol–1 Pd h–1)
62
54
70
56
73
1
2
3
4
5
6
1
2
3
4
38
66
45
54
34
30
59
30
52
41
61
64
3
4
3
5
5
6
1.15
1.00
1.29
1.05
1.36
2.97
5
5d
124
aReaction conditions: solvent, toluene (50 mL); pressure 5 atm (1 atm = 101.325 kPa); temperature, 25 °C; time
2 h; amount of catalyst 9.00 µm; Al:Pd, 500; co-catalyst, EtAlCl2.
bProduct distribution determined by GC–MS.
cYield of products determined by the total mass of oligomers produced after the solvent was evaporated.
dAl:Pd = 1000.
Table 6. Effect of co-catalyst concentration on ethylene oligomerization.a
Oligomers (%)b
Entry
Al:Pd
C10
C12
C14+
Yieldc (g)
TON (kg mol–1 Pd h–1)
20
50
100
1
2
3
4
5
6
7
8
9
—
49
57
66
65
66
31
38
50
—
45
38
30
30
29
65
59
45
—
6
5
4
5
5
4
3
5
Trace
0.21
0.41
1.00
1.66
1.19
1.79
1.15
2.10
—
10
21
54
94
64
30
62
110
500
1000
2000
100d
500d
1000d
aReaction conditions: solvent, toluene (50 mL); pressure 5 atm (1 atm = 101.325 kPa); temperature, 25 °C; time,
2 h; amount of catalyst, 9.00 µm; co-catalyst, EtAlCl2; catalyst 2 unless stated otherwise.
bProduct distribution determined by GC–MS.
cYield of products determined by the total mass of oligomers produced after the solvent was evaporated.
dCatalyst 1.
Fig. 5. The DFT studies (at the B3LYP/6-31+G(d) level of the-
Fig. 4. The DFT studies (at the B3LYP/6-31+G(d) level of the-
ory) of simplified analogues of L1 (A and B). The more stable
conformation is also observed in the solid-state structures of L1
and 1 (1 cal = 4.184 J).
ory) of simplified analogues of L2 (C and D). The less stable
conformation is observed when L2 serves as a ligand in 2
(1 cal = 4.184 J).
O
O
O
O
S
O
N
N
N
N
N
N
N
N
S
O
A, -2.23 kcal/mol
B, 0 kcal/mol
C, 0 kcal/mol
D, -0.43 kcal/mol
trend is seen with phosphinidine Pd(II) complexes where
prolonged reaction time from 3 to 15 h resulted in reduced
oligomer molecular weight from 215 to 180 (18).
fect of ethylene concentration on oligomerization using cata-
lyst 1 was studied by varying the ethylene pressure from 5 to
35 atm (Table 7, entries 2, 10–12). An increase in ethylene
concentration resulted in a significant increase in oligomer
yield. We also observed selectivity towards higher oligomers
with an increase in pressure (Table 7, entries 2 and 12). For
instance, at 5 atm, 71% of C10 and 23% of C12 were pro-
duced, respectively, while at 35 atm, 48% of C10 and 41% of
C12 were obtained. At high pressures, it has been postulated
that ethylene co-oligomerizes with the preformed olefins re-
sulting in a significant increase in oligomer molecular
weight (3). A report on bis(salicylaldiminate)nickel catalysed
An increase in temperature was found to increase the ac-
tivity of catalyst 1 and a maximum activity was obtained at
60 °C (Table 7). Above 60 °C, the activity of the catalyst
dropped (Table 7, entries 8 and 9), usually an indication of
catalyst decomposition. This observation is consistent with
Pd(II) α-diimine catalysts, which are known to decompose
rapidly above 50 °C (21), and that of Guan and Salo (22)
that uses bisazaferrocene Pd(II) complexes.
The influence of pressure on ethylene oligomerization is
well-established, especially on catalytic activity (21). The ef-
© 2005 NRC Canada

850
Can. J. Chem. Vol. 83, 2005
Table 7. Effect of reaction conditions on ethylene oligomerization.a
Oligomers (%)b
Yieldc (g)
TON (kg mol–1 Pd h–1)
P
(atm)
C10
C12
C14+
Entry
Temp (°C)
Time (min)
C2H4
1
2
3
4
5
6
7
8
9
5
5
5
5
5
5
5
5
5
15
30
60
120
30d
60d
30
30
30
30
30
3
4
4
3
6
5
3
4
5
120
177
137
70
200
151
345
1050
680
216
276
542
25
25
25
25
25
25
40
60
70
25
25
25
77
71
58
38
70
54
36
32
33
61
51
48
20
25
38
59
24
41
61
64
62
36
44
41
0.28
0.82
1.27
1.30
0.93
1.40
1.60
4.86
3.15
1.00
1.28
2.56
10
11
12
10
20
35
3
5
11
30
Note: 1 atm = 101.325 kPa.
aReaction conditions: solvent, toluene (50 mL); amount of catalyst, 9.00 µm; catalyst 1 used unless stated otherwise; co-catalyst, EtAlCl2; Al:Pd = 500.
bProduct distribution determined by GC–MS.
cYield of products determined by the total mass of oligomers produced after the solvent was evaporated.
dCatalyst 5.
ethylene oligomerization found the C6–C12 yield go up from
23% to 70% when the ethylene pressure was increased from
1 to 20 atm, but the butene content of the oligomerization
product dropped from 76% to 30% (23). Our result is in line
with this observation, though not as drastic.
50.3 MHz) at room temperature. The chemical shifts are re-
ported in δ (ppm) and referenced to the residual CHCl3 in
the NMR solvent. Elemental analyses and IR spectroscopy
were performed on a Carlo Erba NA analyzer and a
PerkinElmer FT-IR Paragon 1000PC, respectively, at the
Chemistry Department, University of the Western Cape.
Conclusions
Synthesis of the ligands and complexes
Furoyl and thiophene carbonyl pyrazolyl ligands form
complexes with palladium(II) that have the same structural
motifs as complexes formed by simple substituted pyrazoles
with palladium(II). X-ray structures of 1 and 2 confirm that
in the solid state of [Pd(L)2Cl2] a trans geometry is preferred
to cis. Activation of these complexes with the alkyl alu-
minium compound, EtAlCl2, results in active catalysts for
the oligomerization of ethylene. The major oligomers pro-
duced are C10 and C12, and no lower oligomers in the C4–C8
range were obtained. This shows that the catalysts favour
chain propagation relative to chain termination. The activi-
ties of these palladium(II) catalysts are lower compared with
the α-diimine Pd(II) complexes, possibly because of the
presence of the noncoordinating donor atoms (sulfur and ox-
ygen), which might cause catalyst deactivation by forming
adducts with the aluminium co-catalyst. Thermal instability
of these catalysts could also contribute to their observed low
catalytic activity, as would weakly bound pyrazolyl ligands
that could lead to ligand dissociation from the metal centre.
2-(3,5-Dimethylpyrazolyl-1-carbonyl)furan (L1)
To a solution of 2-furoyl chloride (2.12 g, 15.60 mmol) in
toluene (40 mL) was added 3,5-dimethylpyrazole (1.49 g,
15.60 mmol) and Et3N (2 mL). The mixture was refluxed for
24 h, filtered to remove the Et3NHCl by-product, and the
solvent removed in vacuo to give a white residue. Purifica-
tion by column chromatography on silica gel with dichloro-
methane–hexane (1:1) as the eluent afforded a white solid.
Recrystallization from CH2Cl2–hexane gave single crystals
suitable for X-ray analysis. Yield: 2.52 g (85%). IR
1
(Nujol, cm–1) ν(C=O): 1702. H NMR (CDCl3) δ: 2.29 (s, 3H,
CH3, pz), 2.62 (s, 3H, CH3, pz), 6.02 (s, 1H, pz), 6.61 (dd,
4
3
1H, furan, JHH = 1.6 Hz, JHH = 3.6 Hz), 7.71 (dd, 1H,
4
3
furan, JHH = 0.8 Hz, JHH = 3.6 Hz), 7.94 (dd, 1H, furan,
4JHH = 0.8 Hz, JHH = 3.8 Hz). 13C{1H} NMR (CDCl3) δ:
3
13.2, 13.8, 110.4, 111.7, 123.4, 144.8, 146.9, 152.1, 156.1,
161.8. EI-MS (70 eV) m/z (%): 190 (20) [M+], 162 (100)
[M+ – C2H4], 95 (40) [M+ – C5N2H7], 67 (5) [M+
–
C6N2H7CO]. Anal. calcd. for C10H10N2O2 (%): C 63.25, H
5.32, N 14.71; found: C 62.76, H 4.88, N 14.49.
Compounds L2–L6 were prepared following the same
procedure as described for L1.
Experimental section
All ligand and complex syntheses were performed under a
nitrogen atmosphere using standard Schlenk techniques. All
solvents were of analytical grade and were dried and dis-
tilled prior to use. Toluene and dichloromethane were dried
and distilled from sodium/benzophenone and P2O5, respec-
tively. The carbonyl linkers (2-furoyl chloride and 2-thiophene
carbonyl chloride) were obtained from Sigma-Aldrich and
used as received. The NMR spectra were recorded on a
Varian Gemini 2000 instrument (1H at 200 MHz, 13C at
2-(3,5-Dimethylpyrazolyl-1-carbonyl)thiophene (L2)
Compound L2 was synthesized using 3,5-dimethyl-
pyrazole (1.50 g, 15.60 mmol) and 2-thiophene carbonyl
chloride (2.28 g, 15.60 mmol). Yield: 2.41 g (75%). IR
1
(Nujol, cm–1) ν(C=O): 1675. H NMR (CDCl3) δ: 2.32 (s, 3H,
CH3, pz), 2.63 (s, 3H, CH3, pz), 6.03 (s, 1H, pz), 7.15 (dd,
4
3
1H, thiophene, JHH = 1.6 Hz, JHH = 4.8 Hz), 7.71 (dd, 1H,
© 2005 NRC Canada

Ojwach et al.
851
4
3
thiophene, JHH = 1.4 Hz, JHH = 4.8 Hz), 8.34 (d, 1H,
8.08 (dd, 1H, furan, 4JHH = 0.8 Hz, 3JHH = 3.8 Hz), 8.44 (dd,
4
3
4
3
thiophene, JHH = 1.4 Hz, JHH = 4.0 Hz). 13C{1H} NMR
(CDCl3) δ: 13.3, 14.0, 110.8, 126.4, 127.9, 137.2, 144.5,
151.5, 156.0, 160.0. EI-MS (70 eV) m/z (%): 206 (100)
[M+], 178 (50) [M+ – C2H4], 111 (50) [M+ – C5N2H7], 83 (5)
[M+ – C6N2H7 CO]. Anal. calcd. for C10H10N2OS (%): C
58.32, H 4.87, N 13.65; found: C 58.15, H 4.26, N 13.68.
1H, furan, JHH = 0.8 Hz, JHH = 3.8 Hz). 13C{1H} NMR
(CDCl3) δ: 111.4, 117.4, 124.3, 132.6, 144.9, 145.9, 147.8,
161.8. EI-MS (70 eV) m/z (%): 162 (20) [M+], 134 (100)
[M+ – CN2H2], 95 (40) [M+ – C3N2H3], 67 (5) [M+
–
C3N2H3CO]. Anal. calcd. for C8H6N2O2 (%): C 59.32, H
3.72, N 17.34; found: C 58.89, H 3.35, N 16.81.
2-(3,5-Di-tert-butylpyrazolyl-1-carbonyl)furan (L3)
Compound L3 was prepared using 2-furoyl chloride
(1.42 g, 10.52 mmol) and 3,5-di-tert-butylpyrazole (2.90 g,
Dichloro{bis-2-(3,5-dimethylpyrazolyl-1-
carbonyl)furan}palladium(II) (1)
To a solution of [Pd(NCMe)2Cl2] (0.20 g, 0.68 mmol) in
dichloromethane (20 mL) was added L1 (0.26 g, 1.43 mmol).
The mixture was stirred at room temperature for 6 h and the
resultant solution was concentrated in vacuo to about 10 mL.
An analytically pure yellow powder was obtained upon addi-
tion of an equal volume of hexane. Yield: 0.28 g (79%). IR
10.52 mmol). Yield: 2.31 g (80%). IR (Nujol, cm–1) ν
:
(C=O)
1
1716. H NMR (CDCl3) δ: 1.35 (s, 9H, CH3, pz), 1.46 (s,
4
9H, CH3, pz), 6.18 (s, 1H, pz), 6.60 (dd, 1H, furan, JHH
=
3
4
1.6 Hz, JHH = 3.4 Hz), 7.71 (dd, 1H, furan, JHH = 0.8 Hz,
3JHH = 1.6 Hz), 7.82 (dd, 1H, furan, JHH = 0.8 Hz, JHH
=
4
3
1
(Nujol, cm–1) ν(C=O): 1694. H NMR (CDCl3) δ: 2.34 (s, 6H,
3.8 Hz). 13C{1H} NMR (CDCl3) δ: 29.0, 29.3, 31.9, 32.8,
105.5, 111.7, 123.1, 146.5, 156.1, 158.0, 161.6. EI-MS
(70 eV) m/z (%): 274 (45) [M+], 244 (30) [M+ – C2H6], 232
(100) [M+ – C3H6], 217 (95) [M+ – C11N2H19], 67 (5) [M+ –
C11N2H19CO]. Anal. calcd. for C16H22N2O2 (%): C 69.82,
H 8.36, N 10.18; found: C 69.77, H 8.26, N 10.02.
CH3, pz), 2.44 (s, 6H, CH3, pz), 6.03 (s, 2H, pz), 6.77 (d,
3
3
2H, furan, JHH = 3.6 Hz), 7.70 (d, 2H, furan, JHH
=
3
3.6 Hz), 7.91 (d, 2H, furan, JHH = 3.6 Hz). 13C{1H} NMR
(CDCl3) δ: 12.8, 15.1, 110.9, 113.3, 126.8, 146.1, 147.1,
149.4, 154.8, 155.9. Anal. calcd. for C20H20N4O4PdCl2 (%):
C 43.09, H 3.59, N 10.05; found: C 42.57, H 3.20, N 9.65.
Complexes 2–4 and 6 were prepared in a similar manner
as described for 1.
2-(3,5-Di-tert-butylpyrazolyl-1carbonyl)thiophene (L4)
Compound L4 was prepared by reacting 3,5-di-tert-
butylpyrazole (1.82 g, 10.34 mmol) with 2-thiophene car-
bonyl chloride (1.37 g, 9.35 mmol). Yield: 1.50 g (52%). IR
Dichloro{bis-2-(3,5-dimethylpyrazolyl-1-carbonyl)thio-
phene}palladium(II) (2)
1
(Nujol, cm–1) ν(C=O): 1686. H NMR (CDCl3) δ: 1.37 (s, 9H,
CH3, pz), 1.46 (s, 9H, CH3, pz), 6.17 (s, 1H, pz), 7.12 (dd,
Complex 2 was prepared using ligand L2 (0.50 g,
3.42 mmol) and [PdCl2(NCMe)2] (0.45 g, 1.71 mmol).
Recrystallization from dichloromethane–hexane gave yellow
single crystals suitable for X-ray analysis. Yield: 0.61 g
4
3
1H, thiophene, JHH = 1.8 Hz, JHH = 5.2 Hz), 7.71 (dd, 1H,
4
3
thiophene, JHH = 1.4 Hz, JHH = 5.2 Hz), 8.83 (dd, 1H,
thiophene, JHH = 1.6 Hz, JHH = 4.0 Hz). 13C{1H} NMR
(CDCl3) δ: 28.9, 29.4, 32.1, 32.8, 106.0, 125.8, 137.2, 157.4,
159.7, 169.8. EI-MS (70 eV) m/z (%): 290 (63) [M+], 275
(20) [M+ – CH3], 233 (65) [M+ – C4H9], 191 (30) [M+ –
4
3
1
(62%). IR (Nujol, cm–1) ν(C=O): 1688. H NMR (CDCl3) δ:
2.30 (s, 6H, CH3, pz), 2.32 (s, 6H, CH3, pz), 6.00 (s, 2H,
4
3
pz), 7.29 (dd, 2H, thiophene, JHH = 1.6 Hz, JHH = 3.8 Hz),
C7H15], 111 (100) [M+ – C11N2H19], 83 (5) [M+
–
4
3
7.73 (dd, 2H, thiophene, JHH = 1.6 Hz, JHH = 3.8 Hz), 8.02
(dd, 2H, thiophene, JHH = 6 Hz, JHH = 3.8 Hz). 13C{1H}
NMR (CDCl3) δ: 12.6, 14.4, 110.1, 126.4, 128.4, 136.2,
136.5, 140.1, 146.1, 155.2, 160.0. Anal. calcd. for
C20H20N4O2S2PdCl2 (%): C 40.83, H 3.43, N 9.51; found: C
40.84, H 2.69, N 9.53.
4
3
C11N2H19CO]. Anal. calcd. for C16H22N2OS (%): C 65.98, H
7.90, N 9.62; found: C 65.86, H 8.32, N 9.34.
2-(3,5-Diphenylpyrazolyl-1-carbonyl)thiophene (L5)
Compound L5 was synthesized by reacting 2-thiophene
carbonyl chloride (1.73 g, 11.85 mmol) and 3,5-
diphenylpyrazole (2.61 g, 11.86 mmol). Yield: 3.07 g (75%).
Dichloro{bis-2-(3,5-di-tert-butylpyrazolyl-1-
carbonyl)furan}palladium(II) (3)
1
IR (Nujol, cm–1) ν(C=O): 1689. H NMR δ: 6.61 (s, 1H, pz),
3
6.98 (d, 1H, thiophene, JHH = 3.6 Hz), 7.32 (m, 8H, ph),
Complex 3 was prepared using ligand L3 (0.37 g,
1.35 mmol) and [Pd(NCMe)2Cl2] (0.18 g, 0.68 mmol).
Yield: 0.25 g (52%). IR (Nujol, cm–1) ν(C=O): 1705. 1H NMR
(CDCl3) δ: 1.32 (s, 18H, CH3, pz), 1.46 (s, 18H, CH3, pz),
3
7.63 (d, 1H, thiophene, JHH = 3.8 Hz), 7.82 (m, 2H, ph),
3
8.14 (d, 1H, thiophene, JHH = 3.8 Hz). 13C{1H} NMR
(CDCl3) δ: 109.2, 125.9, 126.5, 127.5, 128.3, 128.8, 130.6,
131.2, 133.0, 137.1, 137.9, 147.8, 153.1, 159.2. EI-MS
(70 eV) m/z (%): 330 (100) [M+], 302 (85) [M+ – C2H4], 189
(20) [M+ – C13H9], 111 (85) [M+ – C15H11N2], 83 (4) [M+ –
C15H11N2CO]. Anal. calcd. for C20H14N2OS (%): C 72.70, H
4.27, N 8.48; found: C 72.68, H 4.05, N 8.36.
4
3
6.17 (s, 2H, pz), 6.58 (dd, 2H, furan, JHH = 1.7 Hz, JHH
=
4
3
3.6 Hz), 7.71 (dd, 2H, furan, JHH = 1.8 Hz, JHH = 3.4 Hz),
4
3
7.82 (dd, 2H, furan, JHH = 1.8 Hz, JHH = 3.4 Hz). 13C{1H}
NMR (CDCl3) δ: 28.8, 29.7, 30.5, 31.6, 100.1, 111.7, 119.3,
125.8, 137.2, 146.7, 156.1, 157.8. Anal. calcd. for
C34H50N4O4PdCl6·2CH2Cl2 (%): C 45.53, H 5.58, N 6.25;
found: C 46.05, H 5.03, N 6.55.
2-(Pyrazolyl-1-carbonyl) furan (L6)
Compound L6 was prepared by reacting 2-furoyl chloride
Dichloro{bis-2-(3,5-di-tert-butylpyrazolyl-1-
carbonyl)thiophene}palladium(II) (4)
Complex 4 was prepared using ligand L4 (0.44 g,
1.52 mmol) and [Pd(NCMe)2Cl2] (0.20 g, 0.76 mmol).
Yield: 0.32 g (58%). IR (Nujol, cm–1) ν(C=O): 1694. 1H NMR
(2.97 g, 22.12 mmol) and unsubstituted pyrazole (1.50 g,
22.00 mmol). Yield: 2.40 g (75%). IR (Nujol, cm–1) ν
:
(C=O)
1
4
1685. H NMR (CDCl3) δ: 6.50 (dd, 1H, pz, JHH = 1.4 Hz,
4
3
3JHH = 3.0 Hz), 6.65 (dd, 1H, furan, JHH = 1.8 Hz, JHH
=
4
3
3.6 Hz), 7.78 (dd, 2H, pz, JHH = 1.6 Hz, JHH = 3.8 Hz),
© 2005 NRC Canada

852
Can. J. Chem. Vol. 83, 2005
(CDCl3) δ: 1.32 (s, 18H, CH3, pz), 1.46 (s, 18H, CH3, pz),
ization source at 70 eV and a 30 m HP PONA capillary
column with a stationary phase based on 5% poly(methyl-
phenylsiloxane). The rate of increase in oven temperature of
the GC was set at 20 °C min–1 and then increased by
10 °C min–1 until a temperature of 260 °C was reached. Un-
der these conditions, it was possible to separate C4 to C20
olefins. The retention times of the individual components
were determined using standard samples of each olefin.
Quantitative analysis of the olefins was done by the internal
standard reference method using pentadecane as the internal
reference.
4
6.19 (s, 2H, pz), 7.13 (dd, 2H, thiophene, JHH = 1.6 Hz,
4
3JHH = 5.0 Hz), 7.72 (dd, 2H, thiophene, JHH = 1.2 Hz,
4
3JHH = 5.4 Hz), 8.26 (dd, 2H, thiophene, JHH = 1.6 Hz,
3JHH = 4.2 Hz). Anal. calcd. for C32H46N2O2S2PdCl2 (%): C
49.05, H 6.27, N 7.63; found: C 48.75, H 5.06, N 7.66.
Dichloro{bis-2-(3,5-diphenylpyrazolyl-1-carbonyl)thio-
phene}palladium(II) (5)
Complex 5 was synthesized by reacting L5 (0.50 g,
1.53 mmol) and [Pd(NCMe)2Cl2] (0.20 g, 0.77 mmol).
Yield: 0.23 g (37%). IR (Nujol, cm–1) ν(C=O): 1694. 1H NMR
3
(CDCl3) δ: 7.20 (s, 1H, pz), 7.46 (d, 1H, thiophene, JHH
=
X-ray crystallography
4.0 Hz), 8.16 (m, 10H, benzene), 8.37 (d, 1H, thiophene,
Crystal evaluation and data collection for L1, 1, and 2
were performed on a Bruker CCD-1000 diffractometer with
Mo Kα (λ = 0.710 73 Å) radiation and the diffractometer to
crystal distance of 4.9 cm. The initial cell constants were ob-
tained from three series of ω scans at different starting an-
gles. The reflections were successfully indexed by an
automated indexing routine built in the SMART program.
The absorption correction was based on fitting a function to
the empirical transmission surface as sampled by multiple
equivalent measurements (24). The structures were solved
by direct methods and refined by least-squares techniques
using the SHELXTL program (24). All non-hydrogen atoms
were refined with anisotropic displacement coefficients. All
hydrogen atoms were included in the structure factor calcu-
lation at idealized positions and were allowed to ride on the
neighbouring atoms with relative isotropic displacement co-
efficients. Additional crystallographic data for the structures
are deposited with the Cambridge Crystallographic Data
Centre as supplementary publication numbers CCDC
257819 (L1), CCDC 257820 (1), and CCDC 257818 (2).4
3JHH = 3.6 Hz), 8.42 (d, 1H, thiophene, JHH = 3.8 Hz).
3
13C{1H} NMR (CDCl3) δ: 109.2, 125.9, 126.5, 127.5, 127.7,
128.4, 128.7, 130.5, 131.2, 133.0, 137.0, 137.9, 147.8,
153.1, 158.2. Anal. calcd. for C40H28N2O2S2PdCl2 (%): C
57.32, H 4.37, N 6.63; found: C 56.82, H 4.15, N 6.16.
Dichloro{bis-2-(pyrazolyl-1-carbonyl)furan}palladium(II)
(6)
To a solution of compound L6 (0.80, 4.94 mmol) in di-
chloromethane (30 mL), [Pd(NCMe)2Cl2] (0.63 g, 2.47 mmol)
was added. A light brown precipitate formed immediately.
The resultant mixture was stirred for 3 h, filtered, and the
yellow solid dried. Yield: 1.01 g (80%). IR (Nujol, cm–1)
1
ν
(C=O): 1712. H NMR (DMSO-d6) δ: 6.64 (dd, 2H, pz,
4JHH = 1.6 Hz, JHH = 3.0 Hz), 6.78 (dd, 2H, furan, JHH
=
3
4
3
4
1.6 Hz, JHH = 3.6 Hz), 7.79 (dd, 4H, pz, JHH = 0.8 Hz,
3JHH = 3.6 Hz), 8.15 (dd, 2H, furan, JHH = 0.8 Hz, JHH
=
4
3
4
3
3.0 Hz), 8.52 (dd, 2H, furan, JHH = 0.8 Hz, JHH = 1.8 Hz).
13C{1H} NMR (CDCl3) δ: 106.4, 110.1, 112.2, 113.2, 117.8,
125.0, 130.5, 145.3, 147.1, 149.8, 154.3, 159.4. Anal. calcd.
for C16H12N4O4PdCl2 (%): C 38.31, H 2.41, N 11.17; found:
C 38.06, H 2.30, N 10.33.
Acknowledgements
Financial support by the National Research Foundation
(NRF) South Africa is highly appreciated. We thank Profes-
sor Len Barbour, University of Stellenbosch, South Africa,
for solving the structure of compound 2 as a service.
Ethylene oligomerization
Ethylene oligomerization was performed in a 300 mL
stainless steel autoclave loaded with the respective catalyst
and the appropriate amount EtAlCl2 as the co-catalyst. This
was carried out in a nitrogen-purged glovebox. The general
procedure involved charging the autoclave with a palladium
complex and EtAlCl2 (25% in toluene) in 100 mL of dry to-
luene. The Al:Pd ratio used was between 20–2000. The au-
toclave was sealed, removed from the glovebox and loaded
into the reactor chamber. The autoclave was flushed three
times with ethylene and heated to the required temperature.
The desired ethylene pressure was set and a constant flow of
ethylene was maintained throughout the reaction. At the end
of the reaction, an aliquot of the reaction mixture was taken
for the GC analysis. The reaction was quenched by the addi-
tion of ethanol after which the solvent was removed in vacuo
and the mass of the total nonvolatile products determined.
Analysis of the oligomers was performed using a Finnigan-
MAT GCQ GC–MS, equipped with an electron impact ion-
References
1. (a) S. Trofimenko. Prog. Inorg. Chem. 34, 115 (1986); (b) S.
Trofimenko. Chem. Rev. 72, 497 (1972); (c) Y. Sun, X. Chen,
P. Cheng, S. Yan, D. Zheng Liao, and P. Wen Shen. J. Mol.
Struct. 597, 191 (2001).
2. (a) R. Mukherjee. Coord. Chem. Rev. 203, 166 (2000); (b) S.
Mecking. Coord. Chem. Rev. 203, 325 (2000); (c) S.
Trofimenko. Chem. Rev. 93, 943 (1993).
3. (a) J. Skupinska. Chem Rev. 91, 613 (1991); (b) M. Peuckert,
W. Keim, S. Storp, and S.R. Weber. J. Mol. Catal. 20, 115
(1983).
4. W. Keim. J. Mol. Catal. 52, 19 (1989).
5. (a) C.M. Killian, L.K. Johnson, and M. Brookhart. Organo-
metallics, 16, 2005 (1997); (b) L.K. Johnson, C.M. Killian,
and M. Brookhart. J. Am. Chem. Soc. 117, 6414 (1995);
4 Supplementary data for this article are available on the Web site or may be purchased from the Depository of Unpublished Data, Document
Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0S2, Canada. DUD 3687. For more information on obtaining mate-
rial refer to http://cisti-icist.nrc-cnrc.gc.ca/irm/unpub_e.shtml. CCDC 257818–257820 contain the crystallographic data for this manuscript.
These data can be obtained, free of charge, via 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 336033; or deposit@ccdc.cam.ac.uk).
© 2005 NRC Canada

Ojwach et al.
(c) S.A. Svejda, L.K. Johnson, and M. Brookhart. J. Am.
Chem. Soc. 121, 10 634 (1999).
6. G.J.P. Britovsek, S.P.D. Baugh, V.C. Gibson, and D.F. Wass.
Angew. Chem. Int. Ed. 38, 428 (1999).
7. B.L. Small and M. Brookhart. J. Am. Chem. Soc. 120, 7143
(1998).
853
Q. Cui, K. Morokuma, D.K. Malick, A.D. Rabuck, K. Ragha-
vachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, A.G. Baboul,
B.B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi,
R. Gomperts, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-
Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W.
Gill, B. Johnson, W. Chen, M.W. Wong, J.L. Andres, C. Gon-
zalez, M. Head-Gordon, E.S. Replogle, and J.A. Pople.
GAUSSIAN98. Revision A9 [computer program]. Gaussian
Inc., Pittsburgh, Pennsylvania. 1998.
8. S. Tsuji, T.R. Younkin, D.C. Swenson, and R.F. Jordan.
Organometallics, 18, 4758 (1998).
9. (a) K. Li, J. Darkwa, I.A. Guzei, and S.F. Mapolie. J.
Organomet. Chem. 660, 108 (2002); (b) S.M. Nelana, J.
Darkwa, I.A. Guzei, and S.F. Mapolie. J. Organomet. Chem.
689, 1835 (2004).
17. Z. Guan and W.J. Marshall. Organometallics, 21, 3580 (2002).
18. O. Daugulis, M. Brookhart, and P.S. White. Organometallics,
21, 5935 (2002).
10. I.A. Guzei, K. Li, G.A. Bikzhanova, J. Darkwa, and S.F.
19. F. Speiser, P. Braunstein, L. Saussine, and R. Welter. Inorg.
Mapolie. Dalton Trans. 715 (2003).
11. L.K. Johnson, S. Mecking, and M. Brookhart. J. Am. Chem.
Soc. 118, 11 664 (1998).
Chem. 43, 1649 (2004).
20. J.M. Malinoski and M. Brookhart. Organometallics, 22, 5324
(2003).
12. (a) I.A. Guzei and M. Wendt. SOLID-G [computer program].
Madison, Wis. 2004; (b) I.A. Guzei. In 2004 Annual Meeting
of the American Crystallographic Association, 17–22 July
2004, Chicago.
13. W. Kemp. Organic spectroscopy. 3rd ed. Macmillan Education
Ltd., London. 1991. p. 36.
21. S.D. Ittel, M. Brookhart, and L.K. Johnson. Chem. Rev. 100,
1169 (2000).
22. Z. Guan and E.V. Salo. Organometallics, 22, 5033 (2003).
23. C. Carlini, M. Isola, V. Liuzzo, A.M.R. Galletti, and G. Sbrana.
Appl. Catal. A, 231, 307 (2002).
24. Bruker-AXS SADABS. Version 2.05 software reference man-
ual. Bruker-AXS, Madison, Wisconsin. 2000–2004; Bruker-
AXS SAINT. Version 6.22 software reference manual. Bruker-
AXS, Madison, Wisconsin. 2000–2004; Bruker-AXS SHELXTL.
Version 6.10 software reference manual. Bruker-AXS, Madi-
son, Wisconsin. 2000–2004; Bruker-AXS SMART 5.622 soft-
ware reference manual. Bruker-AXS, Madison, Wisconsin.
2000–2004.
14. I.A. Guzei, K. Li, and J. Darkwa. J. Chem. Crystallogr. 35,
197 (2005)
15. F.H. Allen. Acta Crystallogr. Sect. B, B58, 380 (2002).
16. M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A.
Robb, J.R. Cheeseman, V.G. Zakrzewski, J.A. Montgomery,
Jr., R.E. Stratmann, J.C. Burant, S. Dapprich, J.M. Millam,
A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi,
V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C.
Adamo, S. Clifford, J. Ochterski, G.A Petersson, P.Y. Ayala,
© 2005 NRC Canada