(Pyrazol-1-yl)carbonyl palladium complexes as catalysts for ethylene polymerization reaction

Article abstract of DOI:10.1016/j.jorganchem.2012.10.036

Reactions of two equivalents of {3,5-(dimethylpyrazol-1-yl)-4-methoxy-1- carbonyl}benzene (L1), {3,5-(dimethylpyrazol-1-yl)-4-ethoxy-1-carbonyl}benzene (L2), {3,5-(dimethylpyrazol-1-yl)-4-hexyloxy-1-carbonyl}benzene (L3), and {3,5-(dimethylpyrazol-1-yl)-4-dodecycloxy-1-carbonyl}benzene (L4) with one equivalent of [Pd(NCMe)₂Cl₂] produced the corresponding monometallic complexes, [Pd(L1)₂Cl₂) (1), [Pd(L2) ₂Cl₂) (2), [Pd(L3)₂Cl₂) (3) and [Pd(L4)₂Cl₂) (4) in good yields. Solid state structures of 2 and 4 confirmed the monodentate character of L1-L4 and trans configuration of the palladium complexes. Activation of 1-4, and the furanyl and thiophenyl carbonyl pyrazolyl palladium complexes: [Pd(_MepzCOfn) ₂Cl₂] (5), [Pd(_MepzCOth)₂Cl ₂] (6), [Pd(_tBupzCOfn)₂Cl₂] (7) and [Pd(_tBupzCOfn)₂Cl₂] (8) (fn = furan, th = thiophene) with MAO produced catalysts for the polymerization of ethylene with moderate activities; forming linear high density polyethylene. The structure of the complexes had a significant effect on both the activity of the catalysts and nature of the polymers obtained.

Full text of DOI:10.1016/j.jorganchem.2012.10.036

Journal of Organometallic Chemistry 724 (2013) 95e101
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
(Pyrazol-1-yl)carbonyl palladium complexes as catalysts for ethylene
polymerization reaction
,
c,
Hosana D. Mkoyi a, Stephen O. Ojwach b , Ilia A. Guzei d, James Darkwa d
*
a Chemistry Department, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa
b School of Chemistry and Physics, University of KwaZulu-Natal, Pietermaritzburg Campus, Private Bag X01, Scottsville 3209, South Africa
c Department of Chemistry, University of WisconsineMadison, 1101 University Avenue, Madison, WI 53706, USA
d Department of Chemistry, University of Johannesburg, Auckland Park Kingsway Campus, Auckland Park 2006, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
Reactions of two equivalents of {3,5-(dimethylpyrazol-1-yl)-4-methoxy-1-carbonyl}benzene (L1), {3,5-
(dimethylpyrazol-1-yl)-4-ethoxy-1-carbonyl}benzene (L2), {3,5-(dimethylpyrazol-1-yl)-4-hexyloxy-1-
carbonyl}benzene (L3), and {3,5-(dimethylpyrazol-1-yl)-4-dodecycloxy-1-carbonyl}benzene (L4) with
one equivalent of [Pd(NCMe)2Cl2] produced the corresponding monometallic complexes, [Pd(L1)2Cl2) (1),
[Pd(L2)2Cl2) (2), [Pd(L3)2Cl2) (3) and [Pd(L4)2Cl2) (4) in good yields. Solid state structures of 2 and 4
confirmed the monodentate character of L1eL4 and trans configuration of the palladium complexes.
Activation of 1e4, and the furanyl and thiophenyl carbonyl pyrazolyl palladium complexes: [Pd(Mepz-
COfn)2Cl2] (5), [Pd(MepzCOth)2Cl2] (6), [Pd(tBupzCOfn)2Cl2] (7) and [Pd(tBupzCOfn)2Cl2] (8) (fn ¼ furan,
th ¼ thiophene) with MAO produced catalysts for the polymerization of ethylene with moderate
activities; forming linear high density polyethylene. The structure of the complexes had a significant
effect on both the activity of the catalysts and nature of the polymers obtained.
Received 11 August 2012
Received in revised form
12 October 2012
Accepted 19 October 2012
Keywords:
Pyrazolylcarbonyl
Palladium complexes
Catalysts
Polyethylene
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
use of benzene-carbonyl linker pyrazolyl palladium catalysts led to
higher catalytic activities but reduced stability compared to simple
Transition metal-catalyzed alkene polymerization has evolved
as one of the most important reactions both in academic and
industrial arenas [1]. Since the discovery by Brookhart and
pyrazole palladium catalysts in ethylene polymerization reactions
[4b]. The observed higher activity is believed to emanate from an
increase in the electrophilicity of the palladium center and hence
facilitate coordination of the ethylene monomer. In a related work,
a change of benzene linker to pyridine carbonyl linker resulted in
a potential tridentate ligand system which showed good stability
but reduced catalytic activity [6]. This is presumably due to the
tridentate coordination of the ligand; thus blocking ethylene access
to the palladium center. This hypothesis was in deed confirmed in
attempts to use 2,6-bis(pyrazol-1-ylmethyl)pyridine palladium
complexes as catalysts in ethylene polymerization reactions where
chloride abstraction resulted in the formation of stable tridentate
cationic species which were inactive towards ethylene oligomeri-
zation or polymerization reactions [7].
In this current work, we report the use of pyrazol-1-yl palladium
complexes containing alkoxybenzene-carbonyl and heterocylic
carbonyl units, in the polymerization of ethylene (Chart 1). The
furanyl and thiophenyl carbonyl units are expected to display hemi-
lability and hence produce more stable catalysts to compensate for
the weaker donor ability of the pyrazol-1-yl unit in the ligand motif.
The structures of these compounds and the catalytic results
obtained are discussed.
co-workers in 1996 that a-diimine nickel and palladium complexes
give active olefin polymerization catalysts, significant amount of
research has been directed towards the design of other late tran-
sition metal nitrogen-donor catalysts [2]. The success of these
nitrogen-based late transition metal catalysts has largely been
attributed to the ability to control both the steric and electronic
properties of the catalysts. This has led to the development of
a plethora of catalysts containing ligands with different steric and
electronic properties [3].
Over the past decades, pyrazolyl nickel(II) and palladium(II)
complexes have emerged as potential catalysts in olefin oligomer-
ization and polymerization reactions [4]. The ease with which their
electronic and steric properties can be regulated has made it
possible to investigate the structureeactivity relationship of
a series of pyrazolyl metal complexes [5]. In one such design, the
* Corresponding author. Tel.: þ27 33 260 5239; fax: þ27 33 260 5009.
E-mail address: ojwach@ukzn.ac.za (S.O. Ojwach).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.10.036

96
H.D. Mkoyi et al. / Journal of Organometallic Chemistry 724 (2013) 95e101
O
CH3
O
CH3
N
N
X
Cl
N
N
H3C
H2n+1CnO
Cl
H3C
Pd
Pd
CH3
CH3
Cl
X
OCnH2n+1
Cl
N
N
N
N
H3C
O
H3C
O
R = Me, X = O (5); R = Me, X = S (6);
n = 1 (1); n = 2 (2); n = 6 (3); n = 12 (4)
t
R = Bu, X = O (7);R = tBu, X = S (8)
Chart 1. Palladium complexes used in polymerization of ethylene.
2. Results and discussion
appeared as multiplets between 1.27 ppm and 1.85 ppm. Micro-
analyses data of complexes 1e4 were consistent with the struc-
2.1. Synthesis of (pyrazolyl)alkoylbenzene ligands and their
palladium(II) complexes
tures shown in Scheme 2.
2.2. Molecular structures of compounds L2, 2, and 4
Reactions of an appropriate 4-alkoxybenzoyl chloride with 3,5-
dimethylpyrazole in a 1:1 mol ratio gave the corresponding
compounds L1eL4 in moderate to good yields (Scheme 1). While
compounds L2 and L4 did not require any purification, L1 and L3
were purified by column chromatography on silica gel using a 4:1
mixture of dichloromethane:hexane as eluent. Subsequent reac-
tions of L1eL4 with [Pd(NCMe)2Cl2] in a 2:1 mol ratio afforded the
corresponding palladium complexes [Pd(L1)2Cl2] (1), [Pd(L2)2Cl2]
(2), [Pd(L3)2Cl2] (3) and [Pd(L4)2Cl2] (4) in moderate to high yields
(Scheme 2). All the complexes were isolated as air stable yellow
solids.
Single crystals suitable for X-ray analyses for compounds L2
were grown by slow evaporation of a CH2Cl2 solution at RT whereas
those of complexes 2 and 4 were grown by slow diffusion of hexane
into dichloromethane solution at RT for about 3e4 days. Table 1
shows the crystallographic data whereas Table
2 contains
selected bond lengths and bond angles for L2, 2, and 4. The
molecular structures of L2, 2 and 4 are depicted in Figs. 1e3,
respectively.
The bond distances and bond angles in compound L2 are typical.
The conjugated p-system deviates from planarity due to the steric
conflict between the H atom on atom C12 and the lone pair of
electrons on atom N1. Consequently the dihedral angles between
the pz plane and the plane defined by atoms O1, N2, C6, C7 is
33.62(1)ꢁ, and the dihedral angle between the latter plane and the
benzene ring is 16.68(9)ꢁ.
All compounds were characterized by a combination of 1H, 13
C
NMR, IR, mass spectrometry, microanalyses and for L2, complexes 2
and 4 by single X-ray crystallography. IR spectra of L1eL4 showed
characteristic carbonyl peaks between 1689 cmꢀ1 and 1702 cmꢀ1
.
This feature was useful in determining coordination of L1eL4 to
palladium to form the corresponding palladium complexes 1e4.
Generally, shifts towards higher frequencies were observed upon
The Pd atom in both 2 and 4 adopts a slightly distorted square
planar geometry, with the pyrazolyl ligands trans to each other. In
both structures, the Pd atom resides on a crystallographic inversion
center, thus only one half of each complex is symmetry-
independent. The NePdeN and ClePdeCl angles are linear due to
the symmetry, whereas the other angles about the palladium
centers range between 88.34 (4)ꢁ and 91.66(4)ꢁ. The PdeNpz bond
coordination of the ligands. For example, the y(C
]
cmꢀ1 were
O)
found at 1689 cmꢀ1 and 1708 cmꢀ1 for L4 and its corresponding
palladium complex, 4, respectively. This is consistent with electron
flow from the ligand to the palladium atom [8]. 1H NMR spectra of
all the compounds (L1eL4) and palladium complexes (1e4)
showed two characteristic upfield singlets in the range 2.18e
2.61 ppm for the two methyl groups on the pyrazolyl unit and
triplets between 3.86 and 4.16 ppm corresponding to OeCH2 in the
alkoxy chain. The CH2-protons for the longer alkoxy chains
ꢀ
lengths of 2.0301(14) A and 2.025(2) and PdeCl bond distances of
ꢀ
ꢀ
2.3076 (4) A and 2.3036 (6) A in compounds 2 and 4 respectively are
similar and fall within the normal ranges for these types of bonds
ꢀ
[9]. The average PdeNpz bond length of 2.027(2) A correlates well
O
H2n+1CnO
CH3
CH3
H3C
O
N
Et3N
+
H2n+1CnO
N
N
N
Toluene
Cl
H
H3C
n = 1 (L1); n = 2, (L2); n = 6 (L3); n = 12 (L4)
Scheme 1.

H.D. Mkoyi et al. / Journal of Organometallic Chemistry 724 (2013) 95e101
97
O
CH3
N
O
N
H2n+1CnO
H2n+1CnO
CH3
Cl
H3C
1/2[Pd(NCMe)2Cl2]
CH2Cl2
Pd
N
CH3
OCnH2n+1
Cl
N
N
N
H3C
H3C
O
n = 1 (1); n = 2 (2); n = 6 (3); n = 12 (4)
Scheme 2.
with those in the benzenedicarbonyl and benzenetricarbonyl
palladium complexes [2.0332(5) A [5,6]]. This indicates minimal
electronic influence from the alkoxy chains in the ligand structure.
corresponding angle in 4 is 41.70(11)ꢁ. The dihedral angle between
the N2, O1, C6, C7 plane and the benzene ring in 2 is 12.18(7)ꢁ,
whereas the corresponding angle in 4 spans 23.52(10)ꢁ. In all the
three reported structures, the dihedral angles involving the pz
group are larger than the angles formed to the benzene ring, which
indicates that the conjugated system is easier to disturb around the
NeC bond rather than between the carbonyl and benzene ring.
ꢀ
The non-planarity of the conjugated p-system in the ligands in 2
and 4 resembles the conformational behaviour of L2 in the solid
state. Namely, the dihedral angles between the pz plane and the
plane defined by atoms N2, O1, C6, C7 in 2 is 44.96(8)ꢁ, whereas the
2.3. Evaluation of the palladium complexes as catalysts for the
polymerization of ethylene
Table 1
Crystal data and structure refinement for compounds L2, 2 and 4.
Parameters
L2
2
4
All the palladium complexes shown in Chart 1 were investigated
as potential catalysts for the polymerization of ethylene using MAO
as the co-catalyst. This was done to probe the effect of pendant
group with stabilizing atom on the catalytic activities of the
palladium complexes; by comparing the activities of palladium
complexes with no donor atoms (1e4) and those with donor atoms
(5e8) (Table 3). First, we screened all the complexes to establish the
structureeactivity relationship in the polymerization of ethylene
(Table 3). Table 3 reveals that complexes 1 and 2, 5e8 were active in
the polymerization of ethylene, with activities between 130 and
471 kg molꢀ1 hꢀ1. Complexes 3 and 4 bearing longer alkoxy chains
were inactive under similar conditions. 13C{1H} NMR spectra of all
the polymers obtained exhibited one signal around 30 ppm,
indicating the formation of high density linear polyethylene.
Empirical
formula
Formula
weight
C14H16N2O2
C28H32Cl2N4O4Pd C48 H72 Cl2 N4 O4 Pd
244.29
665.88
946.40
Temperature
Wavelength
Crystal system
Space group
100(2) K
100(2) K
100(2) K
ꢀ
ꢀ
ꢀ
0.71073 A
0.71073 A
Monoclinic
P21/c
0.71073 A
Triclinic
P
Orthorhombic
Pna21
ꢀ
a/A
14.8463(13)
7.7038(7)
11.5017(10)
90ꢁ
10.1753(7)
7.6073(5)
17.9819(12)
90ꢁ
8.6703(9)
8.8030(9)
16.5208(17)
ꢀ
b/A
ꢀ
c/A
a
a
b
g
¼ 75.443ꢁ
¼ 76.773ꢁ
¼ 78.202ꢁ
3
ꢀ
b
90ꢁ
90.97ꢁ
g
90ꢁ
90ꢁ
3
ꢀ
3
ꢀ
Volume
Z
Density
1315.5(2) A
4
1391.72(16) A
2
1173.5(2) A
1
1.233 Mg/m3
1.589 Mg/m3
1.339 Mg/m3
(calculated)
Absorption
coefficient
F(000)
Theta range for
data collection
Reflections
collected
Independent
reflections
Completeness
to theta
0.084 mmꢀ1
0.901 mmꢀ1
0.556 mmꢀ1
Table 2
ꢁ
ꢀ
Selected bond lengths [A] and angles [ ] for compound L2, 2 and 4.
520
2.74e26.37ꢁ
680
2.00e26.38ꢁ.
500
2.42e26.45ꢁ.
Angles [ꢁ]
ꢀ
Bond lengths [A]
L2
5492
18,286
9836
O(1)eC(6)
N(1)eC(2)
N(1)eC(4)
N(1)eN(2)
1.203(2)
1.318(2)
1.375(2)
2.373(2)
C(2)eN(1)eN(2)
N(1)eN(2)eC(4)
N(1)eN(2)eC(6)
C(4)eN(2)eC(6)
105.15(17)
112.02(18)
121.53(13)
126.42(18)
2551
2853
4769
[R(int) ¼ 0.0190] [R(int) ¼ 0.0268] [R(int) ¼ 0.0839]
(26.37ꢁ) 98.9%
(26.38ꢁ) 99.9%
(26.45ꢁ) 98.7%
2
Absorption
correction
Data/restraints/
parameters
Goodness-of-fit
on F2
Multi-scan
with SADABS
2551/1/166
Multi-scan
with SADABS
2853/0/181
Multi-scan
with SADABS
4769/0/271
Pd(1)eN(1)
Pd(1)eCl(1)
O(1)eC(6)
N(2)eC(4)
N(1)eN(2)
2.0301(14)
2.3076(4)
1.207(2)
1.370(2)
1.379(2)
N(1)#ePd(1)eN(1)
N(1)ePd(1)eCl(1)
N(1)#ePd(1)eCl(1)
N(1)ePd(1)eCl(1)#
N(1)ePd(1)eCl(1)
180.00(8)
88.34(4)
91.66(4)
91.66(4)
88.34(4)
1.031
1.047
0.901
Final R indices
R1 ¼ 0.0331,
R1 ¼ 0.0210,
wR2 ¼ 0.0506
R1 ¼ 0.0256,
wR2 ¼ 0.0534
0.474 and
R1 ¼ 0.0361,
wR2 ¼ 0.0856
R1 ¼ 0.0471,
wR2 ¼ 0.0912
0.891 and
[I > 2sigma(I)] wR2 ¼ 0.0907
4
R indices
R1 ¼ 0.0397,
wR2 ¼ 0.0969
0.133 and
PdeN(1)
PdeCl(1)
O(1)eC(6)
N(1)eC(2)
N(1)eN(2)
2.025(2)
2.3036(6)
1.205(3)
1.342(3)
1.387(2)
N(1)ePdeN(1)#1
N(1)ePdeCl(1)
N(1)#1ePdeCl(1)
N(1)ePdeCl(1)#1
Cl(1)ePdeCl(1)#1
179.999(1)
88.83(6)
91.17(6)
91.17(6)
180.00(3)
(all data)
Largest diff.
peak
ꢀꢀ3
ꢀꢀ3
ꢀꢀ3
ꢀ0.175 e.A
ꢀ0.259 e.A
ꢀ0.918 e.A
and hole

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H.D. Mkoyi et al. / Journal of Organometallic Chemistry 724 (2013) 95e101
backbone. For instance, replacing methyl groups in 4 with tert-butyl
groups in
7 resulted in a reduction of polymer Mw from
8.41 ꢂ 105 g/mol to 5.74 ꢂ 105 g/mol. This is in sharp in contrast to
the expected trends; where an increase in steric bulk is expected to
hinder b-hydride elimination and produce higher molecular weight
polymers [2,10,11]. Similar observations have been made by Broo-
khart et al. using phosphineeimine palladium complexes [14].
Having established the best catalyst system, the effect of Al:Pd
ratio on the ethylene polymerization was studied using complex 2
(Table 4). This was done by varying the Al:Pd ratio from 500:1 to
6000:1. The optimum Al:Pd ratio was found to be 4000:1 (Table 4,
entry 5). This ratio is quite high compared to those reported for
related nitrogen-donor palladium catalysts [15]. The higher amount
of MAO required to activate complexes 1e8, could result from
coordination of oxygen and sulfur atoms (furanyl, alkoxy and
thiophenyl groups) to the Al centers in the co-catalyst. This
assumption is further reinforced by higher activity reported for
catalyst 6, since sulfur (a soft base) does not form stable complexes
with Al metal (a hard acid) compared to catalyst 5, containing
a harder oxygen donor.
The Lewis acidity of boron compounds has been utilized to
improve the catalytic activities of palladium and nickel catalysts in
olefin polymerization reactions [16e19]. To probe if the addition of
a boron compound, B(C6F5)3, would enhance the activities of our
complexes; two equivalents of B(C6F5)3 was added to complex 6
and MAO (Table 4, entries 8e9). We observed a significant increase
in activity from 62 kg molꢀ1 hꢀ1 to 462 kg molꢀ1 hꢀ1 at Al:Pd ratio
of 500:1 and 1000:1 respectively (Table 4, entries 2 and 9). This is
consistent with increase in electrophilicity of the palladium metal
center thus facilitating ethylene coordination [2,10] and hence
increase in catalytic activity.
Fig. 1. Molecular structure of complex L2 drawn with 50% probability.
The activities found for the active compounds were generally
moderate according tothe Gibson scale (10e100 kg PE mol Pd hꢀ1 barꢀ1
)
[10], but lower compared to the benzene-carbonyl [5] and pyridine
carbonyl [6] linker pyrazolyl palladium catalysts. This is rather inter-
esting as complexes 1e8 are expected to be sufficiently electrophilic to
allow ethylene coordination. In ethylene polymerization mechanism, it
has been shown both experimentally and theoretically that the turn-
over limiting step is the migratory insertion of coordinated ethylene
monomer into the PdeMe bond [2,11e13]. For this insertion to occur,
the coordinated ethylene must be in a cis position relative to the coor-
dinated alkyl group. Considering the steric demands of the pyrazolyl
ligands in 1e8, a cis conformation via a transecis labilization would be
energetically unfavourable. Thus the lower activities of 1e8 could be
attributed to the higher migratory insertion barriers of the coordinated
ethylene. Using this hypothesis, the trends in activities of 1e8 as
depicted in Table 3 would be largely due to steric factors. Catalysts 5e6,
containing the smaller furanyl and thiophenyl carbonyl groups showed
higher catalytic activities than catalysts 1e4, containing the more
sterically demanding alkoxy benzene groups. In deed complexes
3 and 4, containing bulkier hexyl and dodecyl groups were inactive.
Similarly, complexes 7 and 8, bearing tert-butyl groups on the pyrazolyl
unit showed lower catalytic activities of 176 kg molꢀ1 hꢀ1 and
125 kg molꢀ1 hꢀ1 compared to the methyl analogues 5and 6which gave
activities of 301 kg molꢀ1 hꢀ1 and 426 kg molꢀ1 hꢀ1 respectively.
The nature of the catalyst also affected the molecular weight of
the polymers obtained. No determination of the polymer molecular
weight was performed on the polymers obtained from catalysts
1e4 due to higher amounts of palladium black deposits. From
Table 3, entries 5e8, it is evident that the molecular weight of the
polymers decreased with increase in steric bulk in the ligand
The molecular weights of the polyethylene obtained were also
affected by the amount of co-catalyst used. Inspection of Table 4
reveals that an increase in the Al:Pd ratio from 500:1 to 4000:1
resulted in a concomitant increase in Mw from 3.30 ꢂ 105 g/mol to
8.01 ꢂ 105 g/mol. Beyond this ratio, polymer molecular weight
decreases with further increase in the amount of MAO.
3. Conclusions
Several palladium(II) complexes containing (pyrazol-1-yl)-4-
alkoxy-1-benzene ligands have been successfully prepared and
characterized. The ligands are monodentate, forming monometallic
complexes in which the ligands are trans to each other in the solid
state. Activation of these complexes and the furanyl and thiophenyl
carbonyl palladium(II) complexes with MAO produced catalysts for
the polymerization of ethylene with moderate activities. Generally,
the heterocylic carbonyl palladium complexes showed better
catalytic activities than the alkoxy carbonyl benzene palladium
catalysts. The steric bulk imposed by the heterocylic and alkoxy
benzene-carbonyl linkers is largely responsible for the reduced
activities of the resultant catalysts. This has the overall effect of
hindering the formation of the cis-isomers required for the
migratory insertion of ethylene to form polyethylene.
4. Experimental
4.1. Materials and instrumentation
All manipulations were performed under a dry, deoxygenated
nitrogen atmosphere using standard Schlenk tube techniques. All solvents
were analytical grade and were dried and distilled prior to use.
Toluene and dichloromethane were dried over sodium-benzophenone
and P2O5 respectively. The compounds, 4-alkoxybenzoyl chloride
(alkoxy ¼ methoxy, ethoxyand hexyloxy), 4-dodecycloxybenzoicacid and
Fig. 2. Molecular structure of complex 2 drawn with 50% probability.

H.D. Mkoyi et al. / Journal of Organometallic Chemistry 724 (2013) 95e101
99
Fig. 3. Molecular structure of complex 4. Selected atoms are labeled while the H atoms are omitted.
3,5-dimethylpyrazole were purchased from SigmaeAldrich and used
as received. The starting materials [PdCl2(NCMe)2] and 4-
dodecycloxybenzylchloride were prepared following literature proce-
dures [20,21]. The pyrazolyl furoyl and thiophene carbonyl palladium
complexes 5e8 were prepared according to our published methods [22].
IR spectra were recorded as nujol mulls on a PerkineElmer, Paragon1000
PC FTIR spectrometer. NMR spectra were recorded on a Gemini 2000
instrument (1H at 200 MHz, 13C at 50 MHz). Microanalyses were per-
formed on a Carlo Erba NA analyzer.
X-ray analyses. Yield ¼ 1.32 g (86%). 1H NMR (200 MHz, CDCl3)
d
1.12 (t,
3H, 3JHH ¼ 6.6 Hz, CH3(alkoxy)); 2.26 (s, 3H, pz-CH3); 2.61 (s, 3H, pz-CH3);
4.13 (m, 2H, OeCH2(alkoxy)); 6.04 (s, 1H, pz-H); 6.96 (d, 2H, 3JHH ¼ 8.8 Hz,
ph); 8.06 (d, 2H, 3JHH ¼ 8.8 Hz, ph).13C NMR(50MHz, CDCl3)
d13.3; 13.7;
14.2; 63.2; 110.7; 162.1; 167.0. IR (nujol cmꢀ1);
n(C]O) 1691.80. Anal.
calcd for C14H16N2O2: C, 68.83; H, 6.60; N,11.47. Found: C, 68.48; H, 6.68;
N, 12.19.
4.2.3. {3,5-(dimethylpyrazol-1-yl)-4-hexyloxy-1-carbonyl}benzene
(L3)
Compound L3 was prepared in a similar manner to L1 by
reacting 4-(hexyloxy)benzoyl chloride (1.00 g, 3.08 mmol) and 3,5-
dimethylpyrazole (0.30 g, 3.08 mmol). Purification by column
chromatograph on silica gel using CH2Cl2:hexane (4:1) as an eluent
afforded an oily product which solidified to a white solid after 24 h.
4.2. Synthesis of (pyrazolyl)alkoxycarbonyl benzene ligands and
their palladium complexes
4.2.1. {3,5-(dimethylpyrazol-1-yl)-4-methoxy-1-carbonyl}benzene
(L1)
Yield ¼ 0.74 g (80%). 1H NMR (200 MHz, CDCl3)
d 0.94 (t, 3H,
To a solution of 3,5-dimethylpyrazole (1.41 g, 14.70 mmol) in
toluene (50 mL), 4-methoxybenzoyl chloride (2.50 g, 14.70 mmol)
and Et3N (1.00 g, 14.70 mmol) was added. The mixture was refluxed
for 24 h and solvent evaporated in vacuo to give a white residue.
Purification of the crude product using column chromatograph on
silica gel with CH2Cl2:hexane (4:1) as an eluent afforded an oily
product which solidified within 24 h to a white solid. Yield ¼ 2.65 g
3JHH ¼ 6.6 Hz, CH3(alkoxy)); 1.47 (m, 6H, CH2(alkoxy)); 1.84 (m, 2H,
CH2(alkoxy)); 2.26 (s, 3H, pz-CH3); 2.61 (s, 3H, pz-CH3); 4.06 (t, 2H,
3JHH ¼ 6.6 Hz, OeCH2(alkoxy)); 6.04 (s, 1H, pz-H); 6.95 (d, 2H,
3JHH ¼ 8.8 Hz, ph); 8.05 (d, 2H, 3JHH ¼ 8.8 Hz, ph). 13C NMR (50 MHz,
CDCl3) d 14.8; 23.3; 26.3; 29.8; 32.2; 68.9; 111.3; 114.9; 125.7; 132.9;
134.7; 145.7; 152.3; 163.6; 171.0. IR (nujol cmꢀ1);
n(C]O) 1689.14.
Anal. calcd for C18H24N2O2: C, 71.97; H, 8.05; N, 9.33. Found: C,
72.31; H, 8.16; N, 9.04.
(78%). 1H NMR (200 MHz, CDCl3)
d 2.25 (s, 3H, pz-CH3); 2.60 (s, 3H,
pz-CH3); 3.86 (s, 3H, OeCH3(alkoxy)); 6.03 (s, 1H, pz-H); 6.96 (d, 2H,
3JHH ¼ 8.8 Hz, ph); 8.05 (d, 2H, 3JHH ¼ 8.8 Hz, ph). 13C NMR (50 MHz,
4.2.4. 3,5-dimethylpyrazol-1-yl-4-dodecycloxy-1-carbonyl benzene
(L4)
CDCl3) d n(C]
13.8; 14.2; 55.4; 110.7; 163.2; 167.5. IR (nujol cmꢀ1);
O) 1702.05. Anal. calcd for C13H14N2O2: C, 67.81; H, 6.12; N, 12.17.
Found: C, 67.57; H, 6.21; N, 12.18.
Compound L4 was prepared in a similar manner to L1 using
4-(dodecycloxy)benzoylchloride (1.00 g, 3.08 mmol) and 3,5-
dimethylpyrazole (0.30 g, 3.08 mmol). Removal of solvent under
4.2.2. {3,5-(dimethylpyrazol-1-yl)-4-ethoxy-1-carbonyl}benzene
(L2)
Compound L2 was prepared in a similar manner to L1 using
4-ethoxybenzoylchloride (1.06 g, 6.29 mmol) and 3,5-dimethylpyrazole
(0.60 g, 6.29 mmol). Evaporation of the solvent in vacuo gave an oily
product which solidified after 24 h to white single crystals suitable for
vacuum produced L4 as a white solid. Yield ¼ 0.97 g (82%). 1H NMR
3
(200 MHz, CDCl3)
d
0.93 (t, 3H, JHH ¼ 6.6 Hz, CH3(alkoxy)); 1.23 (m,
18H, CH2(alkoxy)); 1.74 (m, 2H, CH2(alkoxy)); 2.26 (s, 3H, pz-CH3); 2.61
Table 4
Effect of Al:Pd ratio on ethylene polymerization activity of complex 2a.
Table 3
TONb
Mw ꢂ 105
Mn ꢂ 105
Mw/Mn
c
c
c
Entry
Al:Pd
Ethylene polymerization data for complexes 1-8a.
1
2
3
4
5
6
500:1
1000:1
2000:1
3000:1
4000:1
5000:1
6000:1
500:1
24
62
3.30
5.53
5.83
7.15
8.01
4.89
5.38
2.73
4.19
1.71
2.85
2.89
3.45
3.98
2.05
1.85
1.34
2.06
1.93
1.94
2.01
2.07
2.01
2.38
2.90
1.94
2.07
TONb
Mw ꢂ 105
Mn ꢂ 105
Mw/Mn
c
c
c
Entry
Catalyst
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
130
123
Trace
Trace
301
426
176
125
n.d.
n.d.
n.d.
n.d.
8.41
8.01
5.74
6.17
n.d.
n.d.
n.d.
n.d.
4.05
3.98
2.88
1.90
n.d.
n.d.
n.d.
n.d.
2.08
2.01
1.99
1.90
104
126
426
471
141
48
7
8d
9d
1000:1
462
a
Conditions: Complex 6; [Pd] ¼ 9.76 ꢂ 10ꢀ6 mol; temperature, 50 ꢁC; time, 2 h;
a
Conditions: [Pd] ¼ 9.76 ꢂ 10ꢀ6 mol Al:Pd, 4000:1; temperature, 50 ꢁC; time, 2 h;
solvent, toluene; pressure, 5 bar.
b
solvent, toluene, 100 mL; pressure, 5 bar.
TON in kg of polymer per mol. Pd per h (kg molꢀ1 hꢀ1).
Determined by GPC using polystyrene standards.
B(C6F5)3 used in addition to MAO.
b
c
TON in kg of polymer per mol. Pd per h (kg molꢀ1 hꢀ1).
Determined by GPC using polystyrene standards. n.d., not determined.
c
d

100
H.D. Mkoyi et al. / Journal of Organometallic Chemistry 724 (2013) 95e101
(s, 3H, pz-CH3); 4.05 (t, 2H, 3JHH ¼ 6.6 Hz, OeCH2(alkoxy)); 6.04 (s, 1H,
pz-H); 6.95 (d, 2H, 3JHH ¼ 8.8 Hz, ph); 8.05 (d, 2H, 3JHH ¼ 8.8 Hz, ph).
0.3ꢁ in a 6ꢁ range about
u with the exposure time of 10 s per frame.
A total of 42 reflections were obtained. The reflections were
successfully indexed by an automated indexing routine built in the
SMART program [23]. The final cell constants were calculated from
a set of 3011 strong reflections from the actual data collection.
The data were collected by using the full sphere data collection
routine to survey the reciprocal space to the extent of a full sphere
13C NMR (50 MHz, CDCl3)
d 13.31; 22.2; 31.4; 67.7; 110.2; 114.4;
124.9; 137.4; 145.7; 152.3; 162.4; 167.6. IR (nujol cmꢀ1);
n(C]O)
1689.14. Anal. calcd for C24H36N2O2: C, 76.96; H, 9.66; N, 7.28.
Found: C, 75.42; H, 10.42; N, 7.30.
ꢀ
4.2.5. Synthesis of [Pd(L1)2Cl2] (1)
to a resolution of 0.80 A. A total of 5429 data were harvested by
To a solution of [Pd(NCMe)2Cl2] (0.15 g, 0.58 mmol) in dichloro-
methane (30 mL), 3,5-dimethylpyrazolyl-4-methoxy-1-carbonyl
benzene, L1 (0.27 g, 1.16 mmol) was added. The resultant orange-
yellow solution was stirred at room temperature for 24 h. The
solution was then concentrated to 15 mL and the product precipi-
tated by addition of hexane to give complex 1 as an analytically pure
collecting three sets of frames with 0.25ꢁ scans in
u with an
exposure time 40 s per frame. These highly redundant datasets
were corrected for Lorentz and polarization effects. The absorption
correction was based on fitting a function to the empirical trans-
mission surface as sampled by multiple equivalent measurements.
The systematic absences in the diffraction data were consistent for
the space groups Pnma and Pna21. The E-statistics strongly
suggested the non-centrosymmetric space group Pna21 that yiel-
ded chemically reasonable and computationally stable results of
refinement. A successful solution by the direct methods provided
most non-hydrogen atoms from the E-map. The remaining non-
hydrogen atoms were located in an alternating series of least-
squares cycles and difference Fourier maps. All non-hydrogen
atoms were refined with anisotropic displacement coefficients.
All hydrogen atoms were included in the structure factor calcula-
tion at idealized positions and were allowed to ride on the neigh-
boring atoms with relative isotropic displacement coefficients. The
final least-squares refinement of 166 parameters against 2551 data
yellowsolid. Yield ¼ 0.20 g (53%).1H NMR (200 MHz, CDCl3)
d 2.18 (s,
3H, pz-CH3); 2.32 (s, 3H, pz-CH3); 3.91 (s, 3H, OeCH3(alkoxy)); 5.95 (s,
1H, pz-H); 7.07 (d, 2H, 3JHH ¼ 8.8 Hz, ph); 7.99 (d, 2H, 3JHH ¼ 8.4 Hz,
ph). IR (nujol cmꢀ1);
n(C]O) 1698.31. Anal. calcd for C13H14
Cl2N2O2Pd: C, 48.90;H, 4.42;N, 8.78. Found:C, 48.58;H, 3.94;N, 8.37.
Complexes 2e4 were prepared following the procedure
described for 1.
4.2.6. Synthesis of [Pd(L2)2Cl2] (2)
Ligand L2 (0.27 g, 1.09 mmol) and [Pd(NCMe)2Cl2] (0.14 g,
0.54 mmol). Slow diffusion of hexane in to a dichloromethane
solution of 2 at ꢀ4 ꢁC produced yellow single crystals suitable X-ray
analysis. Yield ¼ 0.23 g (63%). 1H NMR (200 MHz, CDCl3)
d
1.12 (t,
resulted in residuals R (based on F2 for I ꢃ 2
s
) and wR (based on F2
for all data) of 0.0331 and 0.0969, respectively. The final difference
3H, 3JHH ¼ 6.6 Hz, CH3(alkoxy)); 2.26 (s, 3H, pz-CH3); 2.61 (s, 3H, pz-
CH3); 4.21 (m, 2H, OeCH2(alkoxy)); 5.96 (s, 1H, pz-H); 7.05 (d, 2H,
Fourier map was featureless.
3
3JHH ¼ 8.2 Hz, ph); 7.97 (d, 2H, JHH ¼ 8.8 Hz, ph). IR (nujol cmꢀ1);
n(C]O) 1705.89. Anal. calcd for C14H16Cl2N2O2Pd: C, 50.50; H, 4.42;
4.4. General procedure for ethylene polymerization
N, 8.41. Found: C, 50.37; H, 4.45; N, 8.09.
Ethylene polymerization was performed by loading the required
amount of the respective complex and an equivalent amount of
methylaluminoxane (MAO) in a 300 mL stainless steel autoclave
inside a nitrogen-purged glove box. The autoclave was then sealed,
removed from the glove box and mounted on the reactor. The
autoclave was flushed three times with ethylene and heated to
50 ꢁC. The desired ethylene pressure was set and a constant flow
maintained throughout the reaction time. At the end of the poly-
merization reaction, the ethylene supply was closed, and excess
ethylene vented. The reaction was quenched by addition of ethanol
and the polymer was filtered, and 2 M HCl (40 mL) added to remove
excess Al or Pd. The pure polymeric material was filtered off and
dried in an oven at 60 ꢁC until a constant mass was achieved.
The number- and weight-average molecular weights (Mn and Mw)
and polydispersity (Mw/Mn) of polymers were determined by high
temperature gel permeation chromatography (GPC) (1,2,4-
trichlorobenzene, 160 ꢁC, rate ¼ 1.00 mL/min) on GPC220 instru-
ment using polystyrene standards. High temperature 13C NMR
spectra in 1,2,3-trichlorobenzene/benzene-d6 were performed on
a Varian 2000 Gemini instrument (50.3 MHz).
4.2.7. Synthesis of [Pd(L3)2Cl2] (3)
Compound L3 (0.71 g, 2.35 mmol) and Pd(NCMe)2Cl2 (0.31 g,
1.18 mmol). A yellow solid product was obtained. Yield ¼ 0.38 g
(42%). 1H NMR (200 MHz, CDCl3)
d
0.84 (t, 3H, JHH ¼ 6.6 Hz,
3
CH3(alkoxy)); 1.42 (m, 6H, CH2(alkoxy)); 1.94 (m, 2H, CH2(alkoxy)); 2.17
(s, 3H, pz-CH3); 2.31 (s, 3H, pz-CH3); 4.09 (t, 2H, 3JHH ¼ 6.6 Hz, Oe
3
CH2(alkoxy)); 5.94 (s, 1H, pz-H); 7.05 (d, 2H, JHH ¼ 8.8 Hz, ph); 7.97
3
(d, 2H, JHH ¼ 8.8 Hz, ph). IR (nujol cmꢀ1);
n(C]O) 1705.89. Anal.
calcd for C18H24Cl2N2O2Pd: C, 55.87; H, 6.22; N, 7.20. Found: C,
56.07; H, 5.91; N, 7.20.
4.2.8. Synthesis [Pd(L4)2Cl2] (4)
Compound L4 (0.56 g, 1.45 mmol) and [Pd(NCMe)2Cl2] (0.19 g,
0.73 mmol). A yellow solid product was obtained. Slow diffusion of
hexane in to a dichloromethane solution of 4 at ꢀ4 ꢁC produced
yellow single crystals suitable X-ray analysis. Yield ¼ 0.50 g (73%).
1H NMR (200 MHz, CDCl3)
d
0.97 (t, 3H, 3JHH ¼ 6.6 Hz, CH3(alkoxy));
1.13 (m, 18H, CH2(alkoxy)); 1.71 (m, 2H, CH2(alkoxy)); 2.19 (s, 3H, pz-
CH3); 2.37 (s, 3H, pz-CH3); 4.09 (t, 2H, 3JHH ¼ 6.4 Hz, OeCH2(alkoxy));
3
5.95 (s, 1H, pz-H); 7.05 (d, 2H, JHH ¼ 8.6 Hz, ph); 7.97 (d, 2H,
3JHH ¼ 8.8 Hz, ph). IR (nujol cmꢀ1);
n
(C]O) 1602.28. Anal. calcd for
Acknowledgement
C24H36Cl2N2O2Pd: C, 60.91; H, 7.78; N, 5.92. Found: C, 60.41; H,
7.78; N, 5.97.
The authors would like to thank National Research Foundation
(NRF-South Africa) for financial support.
4.3. X-ray crystallography
Appendix A. Supplementary material
The crystal evaluation and data collection were performed on
ꢀ
a Bruker CCD-1000 diffractometer with Mo Ka
(l
¼ 0.71073 A)
CCDC numbers; 883906, 883908 and 883907, contains the
supplementary crystallographic data for compounds L2, 2 and 4.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Center via www.ccdc.cam.ac.uk/data_
request/cif.
radiation and the diffractometer to crystal distance of 4.9 cm. A
typical description is given here for L2. The initial cell constants
u scans at different starting
angles. Each series consisted of 20 frames collected at intervals of
were obtained from three series of

H.D. Mkoyi et al. / Journal of Organometallic Chemistry 724 (2013) 95e101
101
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