Neutral palladium(II) complexes with P,N Schiff-base ligands: Synthesis, characterization and catalytic oligomerisation of ethylene

Article abstract of DOI:10.1016/j.jorganchem.2011.07.042

New N-functionalised 2-phosphinobenzaldimino (P^N) ligands bearing 3-picolyl, furfuryl, thiophene-2-methyl, thiophene-2-ethyl, and benzyl groups have been prepared in good yield. The 2-phosphinobenzaldimino ligands were reacted with PdCl₂(COD) to give the corresponding metal complexes of the type Pd(L)Cl₂ (L = 2-phosphinobenzaldimino (P^N) ligand). All compounds were fully characterized using spectroscopic and analytical techniques, including ¹H, ¹³C, and ³¹P NMR and IR spectroscopies, mass spectrometry and elemental analysis. Selected neutral palladium complexes were evaluated as catalyst precursors in ethylene oligomerisation reactions, after activation with a co-catalyst (MMAO, EtAlCl₂, or Et₂AlCl).

Full text of DOI:10.1016/j.jorganchem.2011.07.042

Journal of Organometallic Chemistry 696 (2011) 3585e3592
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Neutral palladium(II) complexes with P,N Schiff-base ligands: Synthesis,
characterization and catalytic oligomerisation of ethylene
,
,
Mokgolela M. Mogorosi a, Tebello Mahamo a b, John R. Moss a 1, Selwyn F. Mapolie c, J. Chris Slootweg b,
,
Koop Lammertsma b, Gregory S. Smith a
*
a Department of Chemistry, University of Cape Town, Private Bag, Rondebosch 7701, South Africa
b Department of Chemistry and Pharmaceutical Sciences, Faculty of Sciences, VU University Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
c Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag, Matieland, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
New N-functionalised 2-phosphinobenzaldimino (P^N) ligands bearing 3-picolyl, furfuryl, thiophene-2-
methyl, thiophene-2-ethyl, and benzyl groups have been prepared in good yield. The 2-
phosphinobenzaldimino ligands were reacted with PdCl2(COD) to give the corresponding metal
complexes of the type Pd(L)Cl2 (L ¼ 2-phosphinobenzaldimino (P^N) ligand). All compounds were fully
characterized using spectroscopic and analytical techniques, including 1H, 13C, and 31P NMR and IR
spectroscopies, mass spectrometry and elemental analysis. Selected neutral palladium complexes were
evaluated as catalyst precursors in ethylene oligomerisation reactions, after activation with a co-catalyst
(MMAO, EtAlCl2, or Et2AlCl).
Received 28 May 2011
Received in revised form
29 July 2011
Accepted 29 July 2011
Keywords:
Iminophosphine
Schiff base
Ó 2011 Elsevier B.V. All rights reserved.
Palladium
Ethylene oligomerisation
1. Introduction
system (selected from dimethoxybenzene, monoglyme, diglyme,
triglyme and o-dimethoxybenzene) to give a different kind of
The interest in olefin oligomerisation/polymerisation dates back
to 1952 when Gellert and Ziegler reported the reaction of ethylene
with lithium aluminium hydride (LiAlH4) in ether at 180e200 ꢀC
and observed a rapid drop in the ethylene pressure [1]. Ever since,
the selective ethylene dimerisation, trimerisation and tetramer-
isation have attracted considerable attention and also chemical
companies have made efforts to narrow the broad distribution of
olefins to high value co-monomers (1-hexene and 1-octene). These
attempts have involved increased capital expenditure and opera-
tional complexities. Selective ethylene trimerisation has received
the most attention (compared to ethylene dimerisation and the
recently discovered ethylene tetramerisation) [2,3]. In 1977, Manyik
et al. of Union Carbide reported the first selective ethylene tri-
merisation to 1-hexene [4]. In addition, 1-hexene was found to be
an oligomeric by-product in the ethylene polymerisation catalysed
by a homogeneous chromium-based system [chromium(III)tris(2-
ethylhexanoate)/hydrolyzed triisobutylaluminium]. Later, Briggs
and others developed a catalyst system involving a donor ligand
catalyst
system:
[chromium(III)tris(2-ethylhexanoate)/donor
ligand/hydrolyzed triisobutylaluminium] which produced 1-
hexene as a major product with selectivities of up to 74% as well
as a small amount of polyethylene [5]. These results prompted
companies including Phillips Petroleum Corporation, Mitsubishi
Chemical Corporation and Sumitomo Chemical Company to
investigate this system further, using pyrrole or 2,5-dipyrrole donor
ligands. In particular, the four-component catalyst incorporating
halide promoters were investigated, e.g. [chromium(III)tris(2-
ethylhexanoate)/2,5-dimethylpyrrole/AlEt3/CCl4]. Chromium(III)
complexes containing tridentate ligands have also recently been
shown to be highly active and selective catalysts for ethylene tri-
merisation to 1-hexene when activated with MAO [6e9].
In the 1990s, interest in late transition-metal complexes as
catalysts for ethylene reactivity was renewed by the discovery of
highly active
Gibson [11]. An important observation made by Brookhart and co-
workers was the marked effect that ligand manipulation has on the
product formed. It was observed that by eliminating the steric bulk
a-diimine-based complexes by Brookhart [10] and
of the ortho-substituent on the aryl-substituted a-(diimine) Pd and
Ni complexes, only ethylene oligomers were formed as opposed to
the high molecular weight polyethylene produced when bulky
ortho-substituents were present [10,12,13]. These discoveries
* Corresponding author. Tel.: þ27 21 6505279; fax: þ27 21 6505195.
E-mail address: gregory.smith@uct.ac.za (G.S. Smith).
Deceased.
1
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.07.042

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M.M. Mogorosi et al. / Journal of Organometallic Chemistry 696 (2011) 3585e3592
resulted in many research groups making efforts to design new
ligand systems containing N- and also P-donor ligands, in an effort
to find highly active and selective catalyst systems, particularly
those containing late transition metals (Ni and Pd complexes)
[14e17].
and thus not readily available for coordination. The proposed met-
aleoxygen or metalesulphur interaction should thus be strong
enough to stabilize the catalyst’s vacant site but weak enough to be
displaced by the incoming ethylene. Herein, we report the synthesis
of a series of neutral, P,N-chelating, palladium phosphinobenzaldi-
mino complexes and investigate their activity as ethylene oligo-
merisation catalyst precursors.
To date, there are a relatively small number of reports in the
literature describing ethylene oligomerisation catalysed by palla-
dium catalyst precursors. The main reason is presumably the very
low activity (or inactivity) observed with these catalyst systems.
The interest in the chemistry of ligands containing both ‘hard’
nitrogen and ‘soft’ phosphorus donor atoms [18e20] allows for
a variety of coordination possibilities beyond traditional PeP or
NeN ligands [21]. The P,N ligands show a particular behaviour in
binding to soft metal centres such as palladium(II) and platinum(II)
that make their complexes good precursors in catalytic processes
[22e25]. The choice of the P^N coordinating ligand system relates to
their ability to improve thermal stability [26e28] of the corre-
sponding catalysts, presumably due to the presence of the strong
phosphorus-metal bond [29], thereby curbing rapid catalyst deac-
tivation/decomposition at high temperature. The stability of the
catalysts at high temperatures is particularly important since
ethylene oligomerisation reactions can be highly exothermic [26]. In
addition P^N ligands offer unique trans-effects due to the different
electron donor and acceptorcapabilities of phosphorus and nitrogen
that may improve the catalyst’s performance [26e28]. In polymer-
isation reactions, the active catalysts are commonly stabilized by the
metalehydrogen agostic interactions. For the compounds reported
herein, third donors on the imine nitrogen were also introduced to
study their effect on the stability of the in situ generated catalysts.
The rationale for this is linked to the position of the lone pairs on
oxygen and sulphur of the furyl and thiophenyl groups respectively,
which are nearly perpendicular to the ring, and are more aromatic
2. Results and discussion
2.1. Synthesis and characterization of the iminophosphine ligands
(1ae1f)
The iminophosphine ligands were isolated as off-white powders
via a Schiff-base condensation reaction of 2-(diphenylphosphino)
benzaldehyde with the appropriate amine (Scheme 1), following
modified literature methodologies [30e34]. The iminophosphine
ligand (1e), is a known compound and was prepared using the
reported method [35].
The 31P NMR spectra of the iminophosphine ligands show only
one singlet between ꢁ13.2 and ꢁ13.9 ppm and attest to the
formation of only one product. This signal was shifted slightly
upfield compared to the starting 2-diphenylphosphinobenzalde-
hyde signal, which appears at ꢁ11.7 ppm. The disappearance of the
aldehyde proton signal at 10.5 ppm and appearance of a doublet
(JHP ¼ 4.9e5.8 Hz) for the imine fragment (HC]N) at 8.39e9.02
ppm confirmed condensation of the aldehydes and the respective
amines [33,34]. The coupling of phosphorus with the imine proton
is presumed to be due to a through-space coupling, arising from the
ligand’s conformation in which the imine proton points towards
the phosphorus lone pair. This observation is consistent with that
reported by Rauchfuss and others for related ligands [32,36e38]. IR
CHO
N
R
n
DCM, r.t.
- H2O
+
H2N
R
n
1
PPh2
PPh2
Pd(COD)Cl2
DCM, r.t.
N
R
n
Pd
Cl
P
Cl
Ph2
2
Compound
n
1
1
1
2
1
1
R
Complex
n
1
1
1
2
1
1
R
1a
1b
1c
1d
1e
1f
3-pyridyl
2-furyl
2a
2b
2c
2d
2e
2f
3-pyridyl
2-furyl
2-thiopheneyl
2-thiopheneyl
Ph
2-thiopheneyl
2-thiopheneyl
Ph
4-tolyl
4-tolyl
Scheme 1.

M.M. Mogorosi et al. / Journal of Organometallic Chemistry 696 (2011) 3585e3592
3587
spectroscopy was used to confirm the successful formation of the
imine functionality. Strong absorption bands in the region
1625e1636 cmꢁ1 are observed in the IR spectra for all the imino-
phosphine ligands 1ae1f, in agreement with literature values for
related compounds [32,37,38]. Elemental analysis and mass spec-
troscopic data support and are in agreement with the proposed
structures.
due to the lower Lewis acidity of MMAO or deactivation of the
active catalyst by the Bu3Al impurities in MMAO [42e44]. Low
t
catalytic activities of up to 1.9 ꢂ 102 g molꢁ1 Pd hꢁ1 (Table 1, entry
4) were observed when Et2AlCl was employed as a co-catalyst.
Increasing the Al/Pd ratio from 100 to 300 led to an improvement
in the catalytic activity. Further increasing the Al/Pd ratio to 500
resulted in a decrease in the catalytic activity. This trend was
observed for all catalysts investigated and could be ascribed to the
increased amount of trialkylaluminium impurities present in the
solutions of MMAO and Et2AlCl [42,43]. In addition, increasing the
co-catalyst molar ratio could facilitate dialkylation of the Pd centre,
consequently deactivating the catalyst by rapid reductive elimina-
tion to give inactive Pd(0) species [45]. The same behaviour was
observed when EtAlCl2 was used as a co-catalyst, with catalytic
activities increasing appreciably when the Al/Pd molar ratio was
increased from 10 to 50. No catalytic activity was observed at low
co-catalyst molar ratio (Al/Pd ¼ 4), presumably due to insufficient
activation of the catalyst precursors. When larger molar ratios (Al/
Pd ¼ 10 and 50) were employed, only low catalytic activities were
observed (e.g. 6.8 and 7.5 ꢂ102 g molꢁ1 Pd hꢁ1 respectively with
2b/EtAlCl2, Table 1, entries 7 and 8), while further increasing the Al/
2.2. Synthesis and characterization of the palladium complexes
(2ae2f)
The reaction of the ligands 1ae1f with Pd(COD)Cl2 in DCM at
room temperature resulted in the precipitation of the corre-
sponding palladium dichloride complexes 2ae2f (Scheme 1),
which were isolated by filtration as yellow powders in 64e83%
yield. Spectroscopic and analytical data for these complexes are in
agreement with the proposed structures.
The 1H NMR spectra of complexes 2ae2f show imine protons in
the region between 8.34 and 8.72 ppm that are shifted upfield by
0.27e0.7 ppm with respect to the free ligands, which could be due
to the change in the conformation of the ligand to enable k2eP^N
coordination to the metal centre [39]. In addition, all the imine
protons appeared as singlets as opposed to the doublets observed
Pd ratio to 100 led to
a decline in the catalytic activity
(7.4 ꢂ102 g molꢁ1 Pd hꢁ1, Table 1, entry 9). Of the three co-catalysts
investigated, EtAlCl2 gave the best catalytic activities which could
be attributed to its stronger Lewis acidity compared to MMAO and
Et2AlCl, and was therefore used in subsequent investigations.
All catalysts predominantly produced ethylene dimers and
small quantities of ethylene trimers (<1%; see Table 1). In all cases,
the oligomerisation product distribution (C4 and C6) was not
affected by the Al/Pd molar ratios at lower concentrations (i.e Al/
Pd ¼ 100e300 for Et2AlCl and Al/Pd ¼ 10e50 for EtAlCl2). For
example, only a slight increase in the C4 fraction (99.1 and 99.8% at
Al/Pd ¼ 100 and 300) was observed with catalyst 2b/Et2AlCl
(Table 1, entries 3 and 4). At higher co-catalyst concentrations (Al/
Pd ¼ 500) the selectivity for C4 decreased slightly to 98.1% (Table 1,
entry 5) with the same catalyst.
for the free ligands.
A more significant downfield shift to
31.7e37.3 ppm of the single 31P resonances of complexes 2ae2f,
compared to ꢁ13.2 to ꢁ13.9 ppm for the free ligands, was observed
due to coordination of the phosphine moiety to the palladium
centre. The IR spectroscopic data of complexes 2ae2f revealed
a bathochromic (red) shift of about 8e20 cmꢁ1 with respect to the
free ligands, with nC]N stretching vibration bands appearing in the
region 1626e1630 cmꢁ1, which confirmed the coordination of the
imine nitrogen to the palladium metal centre. The mass spectral
data for these complexes show [MeCl]þ as the highest molecular
weight fragment. This is a common phenomenon in the mass
spectra of analogous palladium complexes.
2.3. Oligomerisation of ethylene
Upon activation with Et2AlCl and EtAlCl2, the palladium cata-
lysts yielded besides 1-butene (1-C4) also 2-butene (2-C4). This
suggests that the palladium catalysts have a dual role, namely the
oligomerisation of ethylene to 1-C4 as well as the isomerization of
the formed product (1-C4) to the corresponding 2-C4 isomers (cis
and trans). The selectivity for 2-C4 increased with increasing co-
catalyst concentration (Table 1, entries 3e5 and 7e9), where in
the case of EtAlCl2, 2-C4 is the major component of the C-4 fraction.
The minor C6 components comprised of a mixture of 3-methyl-1-
pentene, trans-3-methyl-2-pentene, cis-3-methyl-2-pentene, and
Selected neutral iminophosphine palladium complexes (2ae2e)
were investigated as ethylene oligomerisation catalyst precursors
under various reaction conditions. The principle steps (reaction
mechanism) in ethylene oligomerisation entail (i) activation of
a neutral catalyst precursor using a co-catalyst to generate the
cationic active catalyst, (ii) chain propagation through insertion of
ethylene into the metalealkyl bond (Cossee mechanism), and b-
hydride elimination to restore the very active metal hydride species
which catalyses subsequent ethylene reactions. Parameters such as
co-catalyst concentration (Al/Pd molar ratio), reaction time, reac-
tion temperature, and ethylene pressure, have a significant effect
on the type of olefin product distribution and these parameters
were varied in this study to determine the optimal reaction
conditions.
Table 1
Influence of the co-catalyst and the co-catalyst/catalyst precursor ratio on catalytic
activity and product distribution with complex 2b.a
Entry
Co-catalyst
Al/Pd
Activityb
Oligomers
C4
C6
1-C4
2.3.1. The selection of a co-catalyst
1
2
3
4
5
6
7
8
9
MMAO
MMAO
Et2AlCl
Et2AlCl
Et2AlCl
EtAlCl2
EtAlCl2
EtAlCl2
EtAlCl2
100
1000
100
300
500
4
10
50
100
e
e
e
e
To establish the most efficient co-catalyst, various co-catalysts
(MMAO, Et2AlCl and EtAlCl2) were used to activate a representa-
tive palladium catalyst precursor (2b) in the oligomerisation of
ethylene. The co-catalyst molar ratios (Al/Pd) were also varied for
each co-catalyst to determine optimum molar ratios (i.e. Al/
Pd ¼ 100 and 1000 for MMAO, Al/Pd ¼ 100, 300, 500 for Et2AlCl, Al/
Pd ¼ 4, 10, 50, 100 for EtAlCl2). The palladium catalyst generally
displayed only low catalytic activities, which were also observed by
Guan, Rieger and co-workers in their ethylene polymerisation
studies [40,41]. In fact, no catalytic activity was observed when
MMAO was used to activate the catalyst precursor 2b. This could be
e
e
e
e
1.3
1.9
1.8
e
99.1
99.8
98.1
e
0.9
0.2
1.9
e
84
81
67
e
6.8
7.5
7.4
99.0
99.5
96.1
1.0
0.5
2.9
32
21
12
a
General conditions: 10 mmol of catalyst precursor; 50 ml toluene; 15 min,
10 bar, error estimate ¼ ꢃ0.1, 1-C4 component is the proportion within the C4
fraction.
b
Activity ¼ ꢂ102 g(product) molꢁ1 Pd hꢁ1
.

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M.M. Mogorosi et al. / Journal of Organometallic Chemistry 696 (2011) 3585e3592
2-ethylbutene, as well as 1-hexene, trans-2-hexene, and cis-2-
hexene, which presumably are secondary products formed by the
co-dimerisation of butene with ethylene [46e51].
discontinued and the autoclave was rapidly cooled to ꢁ25
to ꢁ35 ꢀC before the residual ethylene was vented. Catalysts 2ae2e/
EtAlCl2 displayed selectivities for C4 up to 99%, but proved to have
rather short lifetimes as in all cases the best catalytic activities were
observed when the catalytic reactions were carried out for 1 min
(see Table 3). Reactions carried out beyond 1 min showed a gradual
decrease in the catalytic activities. For example, catalyst system 2b/
EtAlCl2 afforded 7.6, 7.1, 6.2 and 4.2 ꢂ102 g molꢁ1 Pd hꢁ1 after 1, 5,
15, and 30 min (Table 3, entries 5, 6, 7, 8) respectively. In addition,
increasing the reaction time from 1 to 30 min led to a slight
reduction in the amount of C4 (e.g. 99.5 and 98.5% at 1 and 30 min
respectively for catalyst 2b/EtAlCl2), together with an increase in
the 2-C4 fraction from 64 to 85% (Table 3, entries 5e8). The mode of
catalyst deactivation is not clear at this stage, but the role of
palladium black can be ruled out as this was not observed in any of
the cases investigated.
2.3.2. The influence of temperature
The effect of temperature on ethylene oligomerisation was
explored using catalysts 2ae2e and EtAlCl2 as the co-catalyst (Al/
Pd ¼ 50, at 30 bar ethylene for 15 min). The details of this study are
given in Table 2. Three reaction temperatures (10, 50, 80 ꢀC) were
investigated.
Increasing the reaction temperature proved to have an effect on
the catalytic activity, but very little influence on the product
distribution (i.e. relative amounts of C4 and C6). In all cases,
increasing the reaction temperature from 10 to 50 ꢀC resulted in
a significant improvement in the catalytic activity (e.g. 2.2 to
5.2 ꢂ102 g molꢁ1 Pd hꢁ1 for 2e/EtAlCl2, Table 2, entries 13 and 14).
Further increasing the reaction temperature from 50 to 80 ꢀC led to
a decrease in the catalytic activity (e.g. 3.9 ꢂ 102 g molꢁ1 Pd hꢁ1 for
2e/EtAlCl2, Table 2, entry 15). It is most likely that catalyst deacti-
vation occurs at the elevated temperatures. This behaviour is
2.3.4. The influence of ethylene pressure
As the final parameter, the effect of the ethylene pressure on
catalytic activity and product distribution was studied. It was
observed that increasing the ethylene pressure resulted in the
improvement of both the catalytic activity and the selectivity (for
C4) for all the catalysts investigated (see Table 4). For example,
catalyst 2b/EtAlCl2 provided activities of 2.5, 6.8 and
7.1 ꢂ102 g molꢁ1 Pd hꢁ1 (Table 4, entries 4, 5, 6) when the reactions
were carried out at 10, 30, and 50 bar respectively. The selectivity
for the C4 fraction improved as well with increasing ethylene
pressure (e.g. for 2b/EtAlCl2: 98.6, 99.1, and 99.7% at 10, 30, and
50 bar respectively, Table 4, entries 4, 5, 6). Due to the higher
ethylene concentrations in solution (and thus more availability)
ethylene will out-compete butene and therefore less co-
dimerisation (to make C6) will be observed.
consistent with that of Brookhart’s Pd(II)-a-diimine catalysts [52].
A reason for the drop in the catalytic activity could also be ascribed
to the lower ethylene solubility in toluene at 80 ꢀC (i.e.
0.12 mol kgꢁ1 barꢁ1 at 50 ꢀC and 0.080 mol kgꢁ1 barꢁ1 at 80 ꢀC)
[46e48,53,54].
All of the catalysts investigated showed mainly ethylene
dimerisation (up to 100% C4 with 2e/EtAlCl2, Table 2, entry 13) and
to a minor extent trimerisation to C6. In all cases, high temperatures
favoured 1-C4 double bond isomerization since the selectivity for 1-
C4 gradually decreased with increasing temperature. For instance,
at 10, 50, and 80 ꢀC, the selectivities for 1-C4 were 39, 19, and 11%
respectively, for the iminophosphine catalyst 2b/EtAlCl2 (Table 2,
entries 4, 5, and 6).
The 1-C4 component within the C4 fraction was observed to
increase gradually as the ethylene pressure was increased from 10
to 50 bar (e.g. from 28 to 37% for the 2b/EtAlCl2 catalyst system;
Table 4, entries 4 and 6), which is believed to be due to the
2.3.3. The influence of reaction time
Subsequently, the effect of the reaction time on the catalytic
activity and the product distribution was studied. The start of the
reaction was taken when the autoclave was filled with the appro-
priate pressure of ethylene (working pressure). At the end of
a catalytic run (after 1, 5, 15, and 30 min), the ethylene pressure was
Table 3
Influence of reaction time on the catalytic activity with 2ae2e/EtAlCl2.a
Entry
Complex
Time (min)
Activityb
Oligomerisation (wt %)
C4
C6
1-C4
Table 2
1
2
3
4
2a
1
5
15
30
6.9
6.4
6.0
4.9
99.3
99.3
99.1
98.0
0.7
0.7
1.9
1.8
45
33
20
19
Influence of temperature on ethylene oligomerisation with complexes 2ae2e.a
Entry
Complex
Temp. (ꢀC)
Activityb
Oligomerisation (wt %)
C4
99.3
99.5
98.6
C6
1-C4
5
6
7
8
2b
2c
2d
2e
1
5
15
30
7.6
7.1
6.2
4.2
99.5
99.3
98.7
98.5
0.5
0.7
1.3
1.5
36
29
22
15
1
2
3
2a
10
50
80
5.5
6.9
4.3
0.7
0.5
1.4
48
25
12
4
5
6
2b
2c
2d
2e
10
50
80
6.7
7.4
5.1
99.7
99.0
99.6
0.3
1.0
0.4
39
19
11
9
1
5
15
30
6.9
6.6
5.9
4.0
99.3
98.9
98.7
98.1
0.7
1.1
1.3
1.9
43
38
29
21
10
11
12
7
8
9
10
50
80
5.4
6.3
5.5
99.4
99.2
98.9
0.6
0.8
1.1
41
33
13
13
14
15
16
1
5
15
30
5.6
5.3
4.3
3.4
99.0
99.2
98.6
98.4
1.0
0.8
1.4
1.6
33
27
23
20
10
11
12
10
50
80
4.5
4.8
4.5
99.4
99.8
99.1
0.6
0.2
0.9
46
29
16
17
18
19
20
1
5
15
30
6.0
5.4
4.1
3.6
99.2
99.1
99.2
98.8
0.8
0.9
0.8
1.2
37
32
25
16
13
14
15
10
50
80
2.2
5.2
3.9
100
99.3
99.8
e
50
23
17
0.7
0.2
a
a
General conditions: Time ¼ 15 min; 10
m
mol of catalyst precursor; 50 ml
General conditions: Temp ¼ 50 ꢀC; 10
mmol catalyst precursor; 50 ml toluene;
toluene; co-catalyst: EtAlCl2; Al/Pd ¼ 50; pressure ¼ 30 bar, temperature ¼ 25 ꢀC,
30 bar, error estimate ¼ ꢃ0.1, 1-C4 component is the proportion within the C4
error estimate ¼ ꢃ0.1, 1-C4 component is the proportion within the C4 fraction.
fraction; Al/Pd ¼ 50.
b
b
Activity ¼ ꢂ102 g(product) molꢁ1 Pd hꢁ1
.
Activity ¼ ꢂ102 g(product) molꢁ1 Pd hꢁ1
.

M.M. Mogorosi et al. / Journal of Organometallic Chemistry 696 (2011) 3585e3592
3589
Table 4
hotstage microscope (Reichert Thermovar). Elemental analyses
were carried out on a Fisons EA 1108 CHNS Elemental Analyzer in
the microanalytical laboratory at the University of Cape Town. 1H,
31P and 13C NMR spectra were recorded on a Varian Mercury-
300 MHz (1H: 300 MHz; 13C: 75.5 MHz; 31P: 121 MHz) or Varian
Unity-400 MHz (1H: 400 MHz; 13C: 100.6 MHz) spectrometer. 1H
NMR spectra were referenced internally using the residual protons
Influence of ethylene pressure and catalyst concentration on ethylene oligomer-
isation with complexes 2ae2e.a
Entry
Complex
Pressure
Activityb
Oligomerisation (wt %)
C4
98.1
98.9
99.6
C6
1-C4
1
2
3
2a
10
30
50
3.1
7.3
7.7
1.9
1.1
2.3
33
39
44
in the deuterated solvents (CDCl3:
values reported relative to the internal standard tetramethylsilane
0.00). 13C NMR spectra were referenced internally to the reso-
nance (CDCl3: 77.0; DMSO: 39.4) and the values reported rela-
tive to tetramethylsilane ( 0.0). IR absorptions were measured on
d 7.27; DMSO: d 2.50 ppm) and
4
5
6
2b
2c
2d
2e
10
30
50
2.5
6.8
7.1
98.6
99.1
99.7
1.4
0.9
0.3
28
33
37
(d
d
d
d
7
8
9
10
30
50
5.9
6.2
6.4
98.9
99.4
99.3
1.1
0.6
0.5
36
42
43
a Perkin Elmer Spectrum one FT-IR spectrophotometer. GC analyses
were performed using a Varian 3900 gas chromatograph equipped
with an FID and a 50 m ꢂ 0.20 mm HP-PONA column (0.50
mm film
10
11
12
10
30
50
2.6
6.5
6.8
98.3
98.8
99.6
1.7
1.2
0.4
26
36
42
thickness). The carrier gas was helium at 40 psi. The oven was
programmed to hold the temperature at 32 ꢀC for 4 min and then to
ramp the temperature to 200 ꢀC at 10 ꢀC/min and then to hold it at
200 ꢀC hold for 5 min. The sample in a screw-cap vial was cooled in
liquid nitrogen before being injected into the GC, in an attempt to
minimize the loss of the volatile product.
13
14
15
10
30
50
3.6
5.1
6.5
99.0
99.3
100
1.0
0.7
e
31
39
45
a
General conditions: Temp ¼ 50 ꢀC, time ¼ 5 min, 5
mmol of catalyst precursor,
50 ml toluene, error estimate ¼ ꢃ0.1, 1-C4 component is the proportion within the
C4 fraction; Al/Pd ¼ 50.
4.2. General procedure for preparation of ligands (1aef)
b
Activity ¼ ꢂ102 g(product) molꢁ1 Pd hꢁ1
.
competition between chain transfer and chain isomerization [55].
Thus, at high ethylene concentrations formation of 1-C4 is favoured
due to rapid chain transfer versus chain isomerization.
To
a
dichloromethane
solution
(15 mL)
of
2-
diphenylphosphinobenzaldehyde (ca. 3 mmol) was added an
equimolar amount of the appropriate substituted amine. An excess
of magnesium sulphate was also added to the reaction mixture to
remove the water by-product. The reaction was left to stir at room
temperature for 16 h, after which time the magnesium sulphate
was filtered off and the solvent removed from the filtrate in vacuo to
give a yelloweorange oil. The oily crude products of ligands 1ae1f
were solidified by dissolving the oil in hot hexane, followed by
quick hot filtration of the liquid product. The resultant solution was
then cooled at ꢁ16 ꢀC overnight to give an off-white powder, which
was filtered and dried in vacuo.
3. Conclusions
A series of new bidentate iminophosphine ligands have been
synthesized in good yield and characterized by spectroscopic and
analytical methods. Palladium dichloride complexes were isolated
in high yields by the reaction of the ligands with Pd(COD)Cl2. These
complexes were used as catalyst precursors for ethylene oligo-
merisation and were activated with a variety of co-catalysts
(MMAO, EtAlCl2, and Et2AlCl) in an effort to determine an effi-
cient co-catalyst for each catalyst system. EtAlCl2 was found to be
an efficient co-catalyst for the neutral palladium catalyst precur-
sors. For each catalyst system, reaction conditions such as
temperature, reaction time, and ethylene pressure were investi-
gated in an effort to establish optimum catalytic reaction condi-
tions. The neutral palladium/EtAlCl2 catalyst system performed
best at a temperature of 50 ꢀC with an ethylene pressure of 50 bar.
The palladium catalysts generally gave low catalytic activities (up to
7.7 ꢂ 102 g molꢁ1 Pd hꢁ1). These catalysts also gave ethylene
dimerisation (up to 100%) and trimerisation (up to 2.3%) products,
and within the C4 fraction, selectivities for 1-C4 of up to 50% were
obtained. The catalyst systems bearing P^N ligands employed in
this project proved to be highly stable as no formation of palladium
black was observed implying that the ligand remained bound to the
palladium metal centre throughout the catalytic cycle.
4.2.1. Preparation of (2-diphenylphosphino-benzylidene)-pyridin-
3-ylmethyl-amine (C25H21N2P) (1a)
This compound was prepared from the reaction of 2-
diphenylphosphinobenzaldehyde (1.00 g, 3.50 mmol) and 3-
aminomethylpyridine (0.38 g, 3.5 mmol) using the general proce-
dure. The pure product was obtained as an off-white powder
(1.13 g, 86%). M.p. 79e81 ꢀC. IR (KBr): 1635 cmꢁ1 (vC]N, imine). 1H
NMR (CDCl3):
d
9.02 (d, 1H, JHP ¼ 4.9 Hz, H-imine), 8.45 (dd, 1H,
JHH ¼ 1.7, 4.8 Hz, H-pyridyl), 8.42 (d, 1H, JHH ¼ 1.7 Hz, H-pyridyl),
8.01 (ddd, 1H, JHH ¼ 1.4, 3.9, 7.6 Hz, AreH), 7.24e7.43 (m, 13H,
AreH), 7.12 (ddd, 1H, JHH ¼ 0.8, 4.8, 7.8 Hz, AreH), 6.90 (ddd, 1H,
JHH ¼ 7.7, 4.7, 1.1 Hz, AreH), 4.67 (s, 2H, NeCH2). 13C NMR (CDCl3)
d:
161.4 (d, JCP ¼ 21.0 Hz, C-imine), 149.4 (C-pyridyl), 148.3 (C-pyridyl),
137.8 (d, JCP ¼ 19.6 Hz, AreC), 137.1 (d, JCP ¼ 17.0 Hz, AreC), 136.4 (d,
JCP ¼ 9.4 Hz, AreC), 135.5 (C-pyridyl), 134.6 (C-pyridyl), 134.1 (d,
JCP ¼ 20.0 Hz, AreC), 133.4 (AreC), 130.6 (AreC),129.0 (AreC), 128.7
(d, JCP ¼ 7.2 Hz, AreC), 127.9 (d, JCP ¼ 4.1 Hz, AreC), 123.4 (AreC),
4. Experimental
122.6 (C-pyridyl), 62.34 (NeCH2). 31P NMR (CDCl3):
d
ꢁ13.2 (s).
4.1. General remarks
EIeMS: m/z 379.92 [M]þ. Anal. Calc. for C25H21N2P (380.42): C,
78.93; H, 5.56; N, 7.36. Found: C, 78.91; H, 5.49; N, 7.22.
All reactions were carried out under a nitrogen or argon atmo-
sphere using a dual vacuum/nitrogen line and standard Schlenk
techniques unless stated otherwise. Solvents were dried and puri-
fied by heating at reflux under argon in the presence of a suitable
drying agent. All reagents were purchased from Aldrich and used
without further purification. 2-Diphenylphosphinobenzaldehyde
[56], Pd(COD)Cl2 [57], and ligand 1e [58] were prepared by pub-
lished procedures. Melting points were recorded on a Kofler
4.2.2. Preparation of (2-diphenylphosphino-benzylidene)-furan-2-
ylmethyl-amine (C24H20NOP) (1b)
This compound was prepared from the reaction of 2-
diphenylphosphinobenzaldehyde (1.00 g, 3.44 mmol) and furfur-
ylamine (0.33 g, 3.44 mmol) using the general procedure. The pure
product was obtained as anꢁo1ff-white powder (1.03 g, 81%). M.p.
76e77 ꢀC. IR (KBr): 1634 cm (vC]N). 1H NMR (CDCl3):
d 9.01 (d,

3590
M.M. Mogorosi et al. / Journal of Organometallic Chemistry 696 (2011) 3585e3592
JHH ¼ 5.1 Hz, H-imine), 8.07 (ddd, 1H, JHH ¼ 7.7, 4.0, 1.4 Hz, AreH),
7.25e7.42 (m, 13H, AreH), 6.91 (m, 1H, H-furan), 6.27 (m, 1H, H-
furan), 6.05 (dd, 1H, JHH ¼ 3.3, 0.7 Hz, H-furan), 4.65 (s, 2H, NeCH2).
NeCH2e), 2.34 (3H, s, eCH3). 13C (CDCl3): 161.3 (d, JCP ¼ 22.9 Hz, C-
imine), 143.2 (d, JCP ¼ 18.1 Hz, AreC), 137.9 (d, JCP ¼ 19.5 Hz, AreC),
137.4 (d, JCP ¼ 21.0 Hz, AreC), 134.5 (AreC), 133.9 (d, JCP ¼ 11.3 Hz,
AreC), 133.6 (d, JCP ¼ 19.8 Hz, AreC), 130.5 (AreC), 129.2 (AreC),
128.9 (d, JCP ¼ 8.0 Hz, AreC), 128.7 (AreC), 128.3 (AreC), 127.4 (d,
4.6 Hz, AreC), 60.9 (NeCH2), 21.9 (CH3). 31P NMR (CDCl3): ꢁ13.6.
EIeMS: m/z 392.79 [M]þ. Anal. Calc. for C27H24NP (393.46): C,
82.42; H, 6.15; N, 3.56. Found: C, 81.97; H, 6.61; N, 3.35.
13C NMR (CDCl3)
d
: 161.5 (d, JCP ¼ 23.0 Hz, C-imine), 152.3 (C-furan),
142.0 (C-furan), 139.3 (d, JCP ¼ 17.3 Hz, AreC), 137.7 (d, JCP ¼ 19.8 Hz,
AreC), 136.4 (d, JCP ¼ 9.7 Hz, AreC), 134.1 (d, JCP ¼ 19.9 Hz, AreC),
133.3 (AreC), 130.5 (AreC), 129.0 (AreC), 128.8 (AreC), 128.6 (d,
JCP ¼ 7.1 Hz, AreC), 127.6 (d, JCP ¼ 4.2 Hz, AreC), 110.3 (C-furan),
107.4 (C-furan), 57.0 (N-CH2). 31P NMR (CDCl3):
d
ꢁ13.9 (s). EIeMS:
m/z 369.81 [M þ H]þ. Anal. Calc. for C24H20NOP (369.40): C, 78.03;
4.3. General procedure for the preparation of palladium complexes
(2ae2f)
H, 5.46; N, 3.79. Found: C, 77.79; H, 5.56; N, 3.60.
4.2.3. Preparation of (2-diphenylphosphino-benzylidene)-
thiophen-2-ylmethyl-amine (C24H20NPS) (1c)
To a dichloromethane solution (5 mL) of the appropriate ligand
1ae1f (ca.0.2e0.3 mmol) was added a dichloromethane solution
(15 mL) of Pd(COD)Cl2. A yellow precipitate formed immediately.
The reaction mixture was allowed to stir at room temperature for
6 h and the yellow crude product filtered. The product was then
washed three times with 10 mL dichloromethane and dried in
vacuo to give a yellow powder.
This compound was prepared from the reaction of 2-
diphenylphosphinobenzaldehyde (1.00 g, 3.44 mmol) and 2-
thiophene-methylamine (0.39 g, 3.44 mmol) using the general
procedure. The pure product was obtained as an off-white powder
(0.97 g, 73%). M.p. 70e72 ꢀC. IR (KBr): 1625 cmꢁ1 (vC]N). 1H NMR
(CDCl3):
d
9.02 (br d, 1H, JHP ¼ 4.9 Hz, H-imine), 8.11 (m, 1H, AreH),
7.25e7.45 (m, 12H, AreH), 7.20 (dd, 1H, JHH ¼ 5.1, 1.1 Hz, H-thio-
phene), 6.95 (m, 2H, H-thiophene þ AreH), 6.78 (dd, 1H, JHH ¼ 3.1,
4.3.1. Preparation of [Pd(C25H21NP)Cl2] (2a)
This complex was prepared from a reaction of 1a (0.11 g,
0.29 mmol) and Pd(COD)Cl2 (0.08 g, 0.26 mmol) using the general
procedure, to give a pure product as a yellow powder (0.93 g, 64%).
M.p. 210e212 ꢀC (decomp.). IR (KBr): 1626 cmꢁ1 (vC]N). 1H NMR
1.0 Hz, H-thiophene), 4.86 (s, 2H, NeCH2). 13C NMR (CDCl3)
d: 160.8
(d, JCP ¼ 23.2 Hz, C-imine), 141.8 (C-thiophene), 139.3 (d,
JCP ¼ 17.2 Hz, AreC), 137.7 (d, JCP ¼ 19.3 Hz, AreC), 136.3 (d,
JCP ¼ 9.7 Hz, AreC), 134.1 (d, JCP ¼ 20.8 Hz, AreC), 133.3 (AreC),
130.6 (AreC), 129.1 (AreC), 128.9 (AreC), 128.7 (d, JCP ¼ 7.1 Hz,
AreC), 127.8 (d, JCP ¼ 4.2 Hz, AreC), 126.8 (C-thiophene), 125.1 (C-
thiophene), 124.6 (C-thiophene), 59.9 (NeCH2). 31P NMR (CDCl3):
(DMSO-d6):
d
8.50 (dd, 1H, JHH ¼ 4.8, 1.8 Hz, H-pyridyl), 8.34 (s, 1H,
H-imine), 8.32 (d,1H, JHH ¼ 2.2 Hz, H-pyridyl), 7.96 (dt, 1H, JHH ¼ 1.8,
7.7 Hz, H-pyridyl), 7.78 (m, 2H, AreH), 7.56 (m, 4H, AreH), 7.39 (m,
4H, AreH), 7.16 (m, 4H, AreH), 6.99 (m, 1H, AreH), 5.48 (s, 2H,
d
ꢁ13.99 (s). EIeMS: m/z 385.56 [M]þ. Anal. Calc. for C24H20NPS
NeCH2e). 31P NMR (DMSO-d6):
d 37.3 (s). EIeMS: m/z 522.11
(385.46): C, 74.78; H, 5.23; N, 3.63; S, 8.32. Found: C, 74.29; H, 5.29;
N, 3.35; S, 8.26.
[MeCl]þ. Anal. Calc. for C25H21Cl2NPPd (557.75): C, 53.84; H, 3.80;
N, 5.02. Found: C, 53.51; H, 3.99; N, 4.86.
4.2.4. Preparation of (2-diphenylphosphino-benzylidene)-
thiophen-2-ylethyl-amine (C25H22NPS) (1d)
4.3.2. Preparation of [Pd(C24H20NOP)Cl2] (2b)
This complex was prepared from the reaction of 1b (0.13 g,
0.35 mmol) and Pd(COD)Cl2 (0.10 g, 0.35 mmol) using the general
procedure. The pure product was obtained as a yellow powdꢁe1r
(0.15 g, 69%). M.p. 198e199 ꢀC (decomp.). IR (KBr): 1630 cm
This compound was prepared from the reaction of diphenyl-
phosphinobenzaldehyde
(2.00 g,
6.89 mmol)
and
2-
thiopheneethylamine (0.88 g, 6.89 mmol) using the general
procedure. The pure product was obtained as an off-white powder
(2.54 g, 92%). M.p. 64e65 ꢀC. IR (KBr): 1636 cmꢁ1 (vC]N). 1H NMR
(vC]N). 1H NMR (DMSO-d6):
d 8.72 (s, 1H, H-imine), 8.00 (ddd, 1H,
JHH ¼ 1.2, 4.2, 7.6 Hz, AreH), 7.89 (dt, 1H, JHH ¼ 1.5, 7.7 Hz, AreH),
7.75 (tt,1H, JHH ¼ 1.4, 7.6 Hz, AreH), 7.58 (m, 2H, AreH), 7.45 (td, 4H,
JHH ¼ 2.9, 4.8 Hz, AreH), 7.24 (m, 5H, AreH þ H-pyridyl), 7.05 (dd,
1H, JHH ¼ 7.8, 10.1 Hz, AreH), 6.55 (d, 1H, JHH ¼ 3.2 Hz, H-furan),
6.38 (dd, 1H, JHH ¼ 1.9, 3.2 Hz, H-furan), 5.56 (s, 2H, NeCH2e). 31P
(CDCl3):
d
8.91 (d, 1H, JHP ¼ 4.9 Hz, H-imine), 8.03 (m, 1H, AreH),
7.26e7.45 (m, 12H, AreH), 7.08 (dd, 1H, JHH ¼ 5.1, 1.1 Hz, H-thio-
phene), 6.93 (m, 1H, AreH), 6.88 (m,1H, H-thiophene), 6.77 (dd,1H,
JHH ¼ 3.3, 0.9 Hz, H-thiophene), 3.78 (t, 2H, JHH ¼ 3.2 Hz, NeCH2e),
3.02 (t, 2H, JHH ¼ 3.2 Hz, NeCH2eCH2). 13C NMR (CDCl3):
d
160.6 (d,
NMR (DMSO-d6): d
32.2 (s). EIeMS: m/z 511.43 [MeCl]þ. Anal. Calc.
JCP ¼ 21.3 Hz, C-imine), 142.4 (C-thiophene), 139.6 (d, JCP ¼ 17.3 Hz,
AreC), 137.6 (d, JCP ¼ 19.5 Hz, AreC), 136.7 (d, JCP ¼ 9.6 Hz, AreC),
134.1 (AreC), 134.0 (JCP ¼ 19.9 Hz, AreC), 133.5 (AreC), 130.3
(AreC), 130.0 (AreC), 128.9 (AreC), 127.8 (d, JCP ¼ 4.3 Hz, AreC),
126.7 (C-thiophene),125.0 (C-thiophene),123.5 (C-thiophene), 62.5
for C24H20Cl2NOPPd (546.72): C, 52.72; H, 3.69; N, 2.56. Found: C,
52.60; H, 3.58; N, 2.35.
4.3.3. Preparation of [Pd(C24H20NPS)Cl2] (2c)
This complex was prepared from the reaction of 1c (0.10 g,
0.26 mmol) and Pd(COD)Cl2 (0.07 g, 0.26 mmol) using the general
procedure. The pure product was obtained as a yellow powdꢁe1r
(0.97 g, 66%). M.p. 233e234 ꢀC (decomp.). IR (KBr):1629 cm
(NeCH2e), 31.4 (NeCH2eCH2). 31P NMR (CDCl3):
d
ꢁ13.55 (s).
EIeMS: m/z 400.04 [M]þ. Anal. Calc. for C25H22NPS (399.49): C,
75.16; H, 5.55; N, 3.51; S, 7.75. Found: C, 75.03; H, 5.64; N, 3.05; S,
8.06.
(vC]N). 1H NMR (DMSO-d6):
d 8.81 (s, 1H, H-imine), 7.98 (m, 1H,
AreH), 7.93 (m, 1H, AreH), 7.74 (m, 1H, AreH), 7.55 (m, 2H, AreH),
7.41 (dt, 5H, JHH ¼ 2.9, 4.9 Hz, AreH), 7.91 (dd, 4H, JHH ¼ 7.8, 4.9 Hz,
AreH), 7.18 (m, 2H, H-thiophene), 6.90 (dd, 1H, JHH ¼ 2.9, 2.0 Hz, H-
4.2.5. Preparation of benzyl-(2-diphenylphosphino-benzylidene)-
amine (C27H24NP) (1f)
This compound was prepared from the reaction of 2-
diphenylphosphinobenzaldehyde (1.16 g, 4.0 mmol) and 4-
methylbenzylamine (0.49 g, 4.0 mmol) using the general proce-
dure. The pure product was obtained as a yelloweorange oil (1.28 g,
thiophene), 5.66 (s, 2H, NeCH2e),. 31P NMR (DMSO-d6):
d 31.8 (s).
EIeMS: m/z 526.77 [MeCl]þ. Anal. Calc. For C24H20Cl2NPPdS
(562.79): C, 51.22; H, 3.58; N, 2.49; S, 5.70. Found: C, 51.48; H, 3.44;
N, 2.70; S, 5.97.
81%). IR (CH2Cl2): 1635 cmꢁ1 nC]N). 1H NMR (CDCl3): 9.00 (1H, d,
(
JHH ¼ 5.1, H-imine), 8.05 (1H, ddd, JHH ¼ 1.5 Hz, 4.0 Hz, 7.7 Hz,
AreH), 7.68 (1H, ddd, JHH ¼ 0.9 Hz, 3.9 Hz, 7.7 Hz, AreH), 6.78e7.32
(15H, m, AreH), 6.05 (1H, d, JHH ¼ 5.8 Hz, AreH), 4.64 (2H, s,
4.3.4. Preparation of [Pd(C25H22NPS)Cl2] (2d)
This complex was prepared from the reaction of 1d (0.21 g,
0.50 mmol) and Pd(COD)Cl2 (0.14 g, 0.50 mmol) using the general

M.M. Mogorosi et al. / Journal of Organometallic Chemistry 696 (2011) 3585e3592
3591
procedure. The pure product was obtained as a yellow powdꢁe1r
the AngloPlatinum Corporation and Johnson Matthey for the kind
donation of metal salts. Banothile Makhubela is acknowledged for
help in the preparation of the manuscript.
(0.23 g, 71%). M.p. 203e205 ꢀC (decomp.). IR (KBr): 1629 cm
(vC]N). 1H NMR (DMSO-d6):
d 8.52 (s, 1H, H-imine), 7.93 (dd, 1H,
JHH ¼ 1.3, 7.6 Hz, AreH), 7.87 (m, 1H, AreH), 7.73 (tt, 1H, JHH ¼ 1.4,
7.5 Hz, AreH), 7.65 (m, 2H, AreH), 7.56 (dt, 4H, JHH ¼ 3.0, 7.6 Hz,
AreH), 7.46 (m, 5H, AreH), 7.23 (dd, 1H, JHH ¼ 1.2, 5.1 Hz, H-thio-
phene), 6.91 (dd.1H, JHH ¼ 5.6, 7.7 Hz, AreH), 6.80 (dd,1H, JHH ¼ 3.4,
5.1 Hz, H-thiophene), 6.57 (dd, 1H, JHH ¼ 0.7, 3.4 Hz, H-thiophene),
4.55 (t, 2H, JHH ¼ 7.7 Hz, NeCH2eCH2e), 3.07 (t, 2H, JHH ¼ 7.7 Hz,
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(vC]N). 1H NMR (DMSO-d6):
d 8.83 (s, 1H, H-imine), 8.02 (m, 1H,
AreH), 7.91 (m, 1H, AreH), 7.75 (m, 1H, AreH), 7.56 (m, 2H, AreH),
7.38 (dt, 4H, JHH ¼ 2.7, 7.7 Hz, AreH), 7.25 (dd, 4H, JHH ¼ 1.8, 7.9 Hz,
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d 34.1 (s). EIeMS: m/z 521.02
[MeCl]þ. Anal. Calc. for C26H22Cl2NPPd (556.76): C, 56.09; H, 3.98;
N, 2.54. Found: C, 55.86; H, 3.76; N, 2.48.
4.3.6. Preparation of [Pd(C27H24NP)Cl2] (2f)
This complex was prepared from the reaction of 1f (0.47 g,
1.18 mmol) and Pd(COD)Cl2 (0.34 g, 1.18 mmol) using the general
procedure. The pure product was obtained as a yellow powdꢁe1r
(0.34 g, 50%). M.p. 173e175 ꢀC (decomp.). IR (KBr): 1628 cm
(vC]N). 1H NMR (DMSO-d6): 8.84 (1H, s, H3), 8.17 (1H, m, AreH),
7.92 (1H, m, AreH), 7.69 (1H, m, AreH), 7.60 (2H, m, AreH), 7.41
(2H, m, AreH), 7.30 (6H, m, AreH), 7.19 (4H, m, AreH), 7.11 (1H, m,
AreH), 5.47 (2H, s, H2), 2.26 (3H, s, H1). 31P NMR (DMSO-d6): 30.7
(s). EIeMS: m/z 535.27 [MeCl]þ. Anal. Calc. for C27H24Cl2NPPd
(570.79): C, 56.81; H, 4.24; N, 2.45. Found: C, 55.90; H, 4.31; N, 2.53.
4.4. Catalytic olefin oligomerisation reactions
A 250 mL stainless-steel Parr-type autoclave equipped with an
overhead magnetic stirrer was heated at 100 ꢀC under vacuum for
1 h and then cooled to room temperature. The autoclave was
transferred into the glovebox where anhydrous solvent (toluene or
cyclohexane (40 mL)), the catalyst precursor complexes
(2e5 ꢂ10ꢁ5 mol) and a co-catalyst (EtAlCl2, Et2AlCl, or MMAO),
were introduced at room temperature under an inert atmosphere
of nitrogen. The autoclave was sealed inside the glovebox before
being taken out. The autoclave was then purged three times with
ethylene under stirring (300 rpm) before being brought to
a working ethylene pressure (10e50 bar). The contents of the
autoclave were then stirred for the desired time, while maintaining
the ethylene pressure throughout the experiment. At the end of the
catalytic run the autoclave was cooled to ca. ꢁ30 ꢀC in a liquid
nitrogen cooled acetone bath, at which temperature the excess
ethylene was slowly vented. An internal standard (nonane, ca.
1 mL) was then added and a sample of the cooled reaction mixture
collected in a cooled screw-cap vial for GC analysis.
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We gratefully thank the University of Cape Town, the National
Research Foundation (NRF) of South Africa, the Royal Netherlands
Academy of Arts and Sciences (KNAW) for a Carolina MacGillavry
PhD Fellowship (T.M.), and SASOL for financial support. We thank

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