Pyridinylimine-based nickel(II) and palladium(II) complexes: Preparation, structural characterization and use as alkene polymerization catalysts

Article abstract of DOI:10.1016/S0022-328X(00)00291-6

Preparation of four dimeric nickel(II) complexes and three monomeric palladium(II) complexes bearing didentate pyridinylimine ligands is described. The solid-state structures of these compounds have been determined by single-crystal X-ray diffraction. After activation with methylaluminoxane (MAO) the nickel compounds were used as catalysts in ethylene polymerization producing nearly linear or primarily methyl-branched polymers. The effect of ligand environment was most evident on degree of branching, while catalytic activity and molecular weight of the polymer were more dependent on the general catalyst composition as well as reaction conditions. Activation of the dichloropalladium(II) complexes with MAO yields highly active catalysts for the polymerization of bicyclo[2.2.1]hept-2-ene (norbornene) whereas only low conversions (< 20%) were achieved with cationic compounds obtained from two of the neutral palladium complexes by reaction with AgBF₄.

Full text of DOI:10.1016/S0022-328X(00)00291-6

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Journal of Organometallic Chemistry 606 (2000) 112–124
Pyridinylimine-based nickel(II) and palladium(II) complexes:
preparation, structural characterization and use as alkene
polymerization catalysts
Timo V. Laine *, Ulla Piironen, Kristian Lappalainen, Martti Klinga, Erkki Aitola,
Markku Leskela¨
Laboratory of Inorganic Chemistry, Department of Chemistry, PO Box 55, FIN-00014 Uni6ersity of Helsinki, Finland
Received 1 September 1999; received in revised form 3 April 2000
Abstract
Preparation of four dimeric nickel(II) complexes and three monomeric palladium(II) complexes bearing didentate
pyridinylimine ligands is described. The solid-state structures of these compounds have been determined by single-crystal X-ray
diffraction. After activation with methylaluminoxane (MAO) the nickel compounds were used as catalysts in ethylene polymeriza-
tion producing nearly linear or primarily methyl-branched polymers. The effect of ligand environment was most evident on degree
of branching, while catalytic activity and molecular weight of the polymer were more dependent on the general catalyst
composition as well as reaction conditions. Activation of the dichloropalladium(II) complexes with MAO yields highly active
catalysts for the polymerization of bicyclo[2.2.1]hept-2-ene (norbornene) whereas only low conversions (B20%) were achieved
with cationic compounds obtained from two of the neutral palladium complexes by reaction with AgBF4. © 2000 Elsevier Science
S.A. All rights reserved.
Keywords: Nickel; Palladium; Nitrogen ligand; Crystal structures; Polymerization; Catalysis; Ethylene; Norbornene
chromium [8], iron, and cobalt systems [9,10], late
transition metal compounds have traditionally been
considered as poor polymerization catalysts for simple
alkenes [11], such as ethylene and propylene, leading to
short-chain products due to the highly competitive
chain termination step [12,13]. In 1995 the group of
Brookhart, however, was able to produce high molecu-
lar weight polyethylene with nickel- and palladium-
based catalysts [14,15]. The key discovery here was the
use of sterically demanding 1,4-diazabutadiene ligands,
which effectively block the axial coordination sites thus
impeding chain termination [14,16,17]. When the bulki-
ness of the aryl groups attached to the imino nitrogens
is reduced, the product composition can be shifted
towards linear oligomers [18,19].
1. Introduction
During the past two decades transition-metal-based
catalytic applications in alkene polymerization have
rapidly evolved from the realms of academic laborato-
ries into full-scale industrial processes [1]. Consequently
various highly active catalyst systems, which contain
well-defined active centers and catalyst structures thus
enabling the control of polymer properties by fine-tun-
ing of the catalyst precursor itself [2], have been discov-
ered. Some of these new catalysts, particularly Group 4
metallocenes [3–6], are already utilized by the plastics
industry [2].
Although the group of catalytically applicable metals
is expanding beyond the early transition metals [7], as
exemplified by the recently reported homogeneous
Late transition metals can also be used in the poly-
merization of the strained cycloalkene bicy-
clo[2.2.1]hept-2-ene (norbornene) by addition-type
vinylic polymerization yielding a saturated polymer,
poly(2,3-bicyclo[2.2.1]heptene), which contains intact
bicyclic units [20–22]. Catalyst systems for this reaction
* Corresponding author. Present address: Borealis Polymers Oy,
PO Box 330, FIN-06101 Porvoo, Finland. Tel.: +358-9-19140223;
fax: +358-9-19140198.
E-mail address: timo.laine@borealisgroup.com (T.V. Laine).
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(00)00291-6

T.V. Laine et al. / Journal of Organometallic Chemistry 606 (2000) 112–124
113
are typically based on Group 4 and 10 metals, espe-
cially titanium(IV), zirconium(IV), and palladium(II).
Also some chromium(III) [23] and cobalt(II) [24] com-
pounds have been reported to promote vinylic
polymerization.
activated with MAO for ethylene polymerization [39],
even though some ethylene and propylene oligomeriza-
tion activity has been reported using an ion-pair acti-
vated palladium complex of ligand 4 [43].
Earliest palladium-containing norbornene polymer-
ization catalysts consisted of simple palladium(II) salts
or their nitrile and phosphine adducts [25,26]. These
compounds usually required long polymerization times
and resulted in only low to moderate yields. The devel-
opment of cationic catalyst species in which the Pd2+
center is surrounded by four neutral, weakly coordinat-
ing alkylnitrile ligands [27] established the basis for the
present catalyst generation of sharply increased activity
[20–22,28–31]. In other currently investigated catalytic
systems also allyl [29,32–34], alkyl [33,35] or diamine
[36] ligands are incorporated. Activation of various
palladium-based precursors can be achieved using
methylaluminoxane (MAO) as well producing efficient
catalysts for this reaction [35,37].
Recently we have reported the preparation [38] of
novel nickel-based ethylene polymerization catalysts
[39] bearing an unsymmetrical didentate pyridinylimine
ligand which combines specific features from the
bipyridine-type alkene oligomerization catalyst [18] and
the sterically hindered a-diimine-based polymerization
system [14]. Similar systems have also appeared in
recent patent applications [40–42]. In order to study
the effects of different ligand substitution patterns on
the polymerization behavior of these compounds four
new nickel(II) complexes (6–9), which contain substi-
tuted 2-pyridinylimine ligands (2–5), have been synthe-
sized and used as catalysts in ethylene polymerization
after activation with methylaluminoxane (Scheme 1).
By extending the same basic ligand structure to palladi-
um(II) compounds we have prepared three dichloropal-
ladium complexes (10–12) bearing ligands 1–3 and
investigated the catalytic behavior of both cationic (13,
14) and MAO-activated complexes in norbornene poly-
merization. The palladium compounds could not be
2. Results and discussion
2.1. Synthesis of catalyst precursors
Since pyridine-based aromatic aldehydes readily react
with substituted phenylamines, including sterically hin-
dered 2,6-dialkyl derivatives, to form pyridinylimines
[44], ligands 1–3 could be prepared by simple one-step
condensation of 2-pyridinecarboxaldehydes with the
appropriate phenylamines. The synthesis of analogous
compounds starting from aromatic ketones, however, is
usually less successful [45] requiring more severe reac-
tion conditions and prolonged reaction times. In the
case of ligands 4 and 5 moderate yields (33–34%) were
achieved when a few drops of concentrated H2SO4 was
introduced as catalyst and Na2SO4 was used to remove
the water formed during the reaction. This method is a
modified version of the literature procedure for bulky
benzophenone N-arylimines, in which tetraethyl or-
thosilicate is utilized to eliminate water from the reac-
tion mixture [46]. All attempts to improve yields by
varying the acid catalyst used or the ketone–amine
ratio failed.
Subsequent complex formation was accomplished by
treatment of dibromo(1,2-dimethoxyethane)nickel(II)
or (1,5-cyclooctadiene)palladium(II)chloride with
slight excess of the corresponding ligand affording com-
pounds 6–12 in good yields (55–77%). In all cases
complex formation started within 1 h, which could be
observed when the precipitation of the product com-
menced, but stirring was continued overnight to maxi-
mize product yields. However, conversion of the neutral
dichloropalladium(II) complexes 10–12 into the
a
Scheme 1.

114
T.V. Laine et al. / Journal of Organometallic Chemistry 606 (2000) 112–124
2.2. Solid state structures
cationic species using silver tetrafluoroborate proved
to be somewhat difficult. Long reaction times of up to
3 days were needed in order to reach reasonable
yields, but in the case of the dimethylphenylamine
complex 11 this led to decomposition and, therefore,
the corresponding ion-pair compound could not be
obtained.
Crystallization from dichloromethane (for 9), acetone
(for 12) or a mixture of acetone and pentane (1:1 for 6
and 11, 2:1 for 7, and 3:1 for 8) yielded deep orange or
orange–yellow crystals suitable for crystal structure
determinations. The crystal data, together with the data
collection and structure refinement parameters are pre-
sented in Table 1. Selected bond lengths and angles for
the nickel compounds 6–9 are given in Table 2. Se-
lected bond lengths and angles for the palladium com-
plexes are given in Table 3; the previously reported
related values of complex 10 are included for compari-
son. In each compound the solid-state structures are
stabilized only by van der Waals forces between the
molecules.
All nickel complexes crystallize as centrosymmetric
dimers with two ligand nitrogen atoms (N1 and N8),
one terminal bromine (Br2) and two bridging bromine
atoms (Br1 and Br1a) forming the coordination sphere
around each five-coordinate nickel center. The asym-
metric unit of 7, however, contains the halves of two
independent, nearly identical molecules (Fig. 2) whereas
a half of only one complex molecule can be found in
the asymmetric unit of compounds 6, 8, and 9 (see Fig.
1Figs. 3 and 4, respectively).
For pyridinylimines such as compounds 1–4, which
either are lacking the bridge substituent or contain a
small side group attached to the imino carbon, unam-
1
biguous peak assignment of the H-NMR spectra can
be made [38,47], but for the phenyl substituted ligand
5 the interpretation of signals fails in the aromatic
region of the spectrum. Therefore, the bulky nature of
the associated phenyl group seems to play an impor-
tant role. While the less substituted aromatic imines
have a strong preference towards the E-conformation
for steric reasons [45], in the case of compound 5 the
formation of both isomers should be as favorable,
since the two a-substituents are now nearly equal in
steric bulk and the geometric preference can not be
distinguished any longer, thus, giving rise to a mixture
of E- and Z-isomers, as has been observed with
analogous benzophenone-derived N-aryl imines [45].
1H-NMR spectroscopic analysis of the ligands and
the palladium complexes reveals some changes in
chemical shifts. Separation of the isopropyl methyl
peaks, as in this case of compound 10 [38], is also
observed for complexes 12–14 whereas in compound
11, which contains the smaller methyl groups in the 2-
and 6-positions of the phenyl ring, only one peak for
the methyl groups is detected. On the pyridine side of
the complex the effect of the neighboring chloride is
well displayed. When a chlorine atom is attached to
palladium the chemical shift of the proton (or in com-
plex 12, the protons of the methyl group) in the 6-po-
sition of the pyridine ring is transferred downfield by
0.44–0.51 ppm. This interaction between the pyridine
methyl group and the chloro ligand in complex 12
can be seen also in the solid state structure (for fur-
ther structural analysis, see chapter 2.2). After re-
placement of the chlorides with acetonitrile molecules
in the cationic complexes 13 and 14, the values for
the chemical shifts of the ortho substituent protons
return to the proximity of the values observed for free
ligands. Yet another consequence of complex forma-
tion can be seen when signals from the pyridine ring
are analyzed. In the free ligands the signal of the
hydrogen in the 3-position is shifted to lower field,
but this interaction disappears after incorporation of
metal and the usual order of signals originating from
the pyridine meta and para protons [38,47] is restored.
Due to interference by the associated metal NMR
spectroscopic measurements could not be performed
for the nickel complexes 6–9.
The coordination polyhedra can be regarded as
slightly deformed trigonal bipyramids in which the
equatorial plane includes the nitrogen of the imino
bridge in the ligand (N8), the terminal bromine (Br2)
and one of the two m-Br atoms (Br1a in 7, Br1 in 6, 8,
and 9) while the nickel center is slightly deviated from
,
the triangular plane (values ranging from 0.0371(11) A
,
in 7 to 0.171(2) A in 8). The pyridine nitrogen (N1) and
the other constituent of the bromine bridge (Br1 in 7,
Br1a in 6, 8, and 9) occupy the axial coordination sites.
Complex 9 has the bipyramidal structure most distorted
towards a square-based pyramid with the most acute
angle (166.67(11)°) in the vertical axis (N1ꢀNiꢀBr1a)
and one of the equatorial angles being extended to
145.74(10)°. Nevertheless, in all cases the vertical axis
of the bipyramid is tilted from the position perpendicu-
lar to the equatorial plane due to the narrow nitro-
genꢀnickelꢀnitrogen angle (79.4(2)° in 6, 80.29(13) and
80.55(13)° in 7, 79.61(19)° in 8, and 79.06(14)° in 9)
resulting from the relatively small bite size of the
ligand.
Structural parameters in all four nickel complexes of
this study followed the trends found previously for the
analogous dibromonickel(II) compound bearing
2,6-bis(1-methylethyl)-N-(2-pyridinylmethylene)phenyl-
amine as the ligand [38]. All the relevant bond lengths
were in accord with the earlier report with the excep-
tion that for compounds 6 and 7 the bond to the
pyridine nitrogen (N1) is the shorter of the two
nickelꢀnitrogen bonds connecting the metal center and

T.V. Laine et al. / Journal of Organometallic Chemistry 606 (2000) 112–124
115
Table 1
Crystallographic data for complexes 6–9, 11, and 12
6
7
8
9
11
12
Empirical formula
C28H28Br4N4Ni2
C38H48Br4N4Ni2 C38H48Br4N4Ni2 C48H52Br4N4Ni2·4 C14H14Cl2N2Pd C19H24Cl2N2Pd
CH2Cl2
Formula weight
857.55
997.82
997.82
1461.69
387.60
457.73
Crystal color and form
Orange,
prismatic
Monoclinic
P21/n (no. 14)
12.118(7)
10.425(3)
12.438(7)
90
102.75(4)
90
1532.5(13)
2
Red, prismatic
Red, prismatic
Red, prismatic
Yellow,
prismatic
Triclinic
Orange,
prismatic
Orthorhombic
Crystal system
Space group
Monoclinic
P21/c (no. 14)
10.319(4)
19.802(4)
20.691(6)
90
93.84(3)
90
4218(2)
4
Monoclinic
P21/n (no. 14)
14.311(4)
10.240(4)
14.335(5)
90
110.95(2)
90
1961.8(12)
2
Monoclinic
P21/c (no. 14)
11.971(4)
14.369(3)
18.180(4)
90
107.04(2)
90
2989.9(13)
2
(
P1 (no. 2)
P212121 (no. 19)
,
a (A)
11.813(4)
13.017(5)
9.761(4)
96.67(3)
97.89(3)
93.66(3)
1471.8(10)
4
12.496(6)
16.137(6)
9.996(7)
90
90
90
2015.7(19)
4
1.508
1.188
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
3
,
V (A )
Z
Dcalc (g cm−3
)
1.858
6.467
1.571
4.711
1.689
5.065
1.624
3.698
1.749
1.610
Absorption coefficient v
(mm−1
F(000)
)
840
2000
1000
1464
768
928
Crystal size (mm)
Scan mode
qmax (°)
Number of unique
reflections
0.23×0.11×0.10 0.48×0.40×0.35 0.30×0.25×0.22 0.30×0.26×0.24 0.25×0.20×0.15 0.50×0.20×0.10
ꢀ–2q
26.49
2569
ꢀ–2q
25.00
6833
ꢀ–2q
25.01
3101
ꢀ–2q
25.00
4784
ꢀ–2q
25.00
4933
ꢀ–2q
26.47
2295
Number of observed
reflections [I\2|(I)]
Number of parameters
Goodness-of-fit on F2 a
2011
5625
2512
3952
4442
2163
172
1.030
433
1.033
222
1.027
316
1.021
343
1.033
247
1.045
Final R indices [I\2|(I)] b R=0.0485,
wR=0.0909
R=0.0387,
wR=0.0793
R=0.0546,
wR=0.0839
0.440 and
−0.386
R=0.0479,
wR=0.1060
R=0.0656,
wR=0.1130
0.625 and
−0.572
R=0.0441,
wR=0.0981
R=0.0585,
wR=0.1031
0.591 and
−1.127 c
R=0.0355,
wR=0.0908
R=0.0409,
wR=0.0936
0.469 and
−0.816
R=0.0439,
wR=0.1079
R=0.0471,
wR=0.1097
1.345 d and
−1.265 e
R indices (all data) b
R=0.0713,
wR=0.0980
0.526 and
−0.664
Largest differential peak
−3
,
and hole (e A
)
a S={S[w(Fo2−Fc2)2]/(n−p)}0.5 where n=data and p=parameters.
b R=SꢀꢀFoꢀ−ꢀFcꢀꢀ/SꢀFoꢀ with F\4S(F); function minimized is wR={S[w(Fo2−Fc2)2]/S[w(F2o)2]}0.5
.
c
d
e
−3
,
,
Minimum residual electron density −1.127 e A ; hole coordinates x=0.4818, y=0.9406, z=0.1179; distance to nearest atom (Br1) 0.92 A.
−3
,
,
Maximum residual electron density 1.345 e A ; peak coordinates x=0.0581, y=0.1540, z=0.4013; distance to nearest atom (Pd) 0.99 A.
−3
,
,
Minimum residual electron density −1.265 e A ; hole coordinates x=0.0233, y=0.1580, z=0.4781; distance to nearest atom (Pd) 0.95 A.
metric unit of 11, however, contains two independent,
closely resembling molecules (see Fig. 5) whereas only
one molecule is found in the asymmetric unit of com-
plex 12 (see Fig. 6).
the ligand. Also the intramolecular nickelꢀnickel dis-
,
,
tances (between 3.656(2) A in 6 and 3.7158(17) A in 8)
,
are well corresponding with the value (3.658 A) ob-
tained previously for the analogous complex [38]. Fur-
thermore, similar behavior of the aryl ring attached to
the imino nitrogen of the ligand was observed with the
angles between the pyridine ring and the phenyl group
of the imino side arm varying from 83.99(16)° in the
first molecule of complex 7 to 87.0(2)° in complex 6.
Even the phenyl substituent in complex 9 was found to
adopt a position close to perpendicular (72.9(2)°) to the
CꢁN bond, as has been postulated in the literature [45].
Both palladium compounds, in turn, crystallize as
discrete monomers with the expected square-planar co-
ordination sphere around the palladium center consist-
ing of two chlorine atoms (Cl1 and Cl2) and two
nitrogen atoms of the ligand (N1 and N8). The asym-
In both cases the square structure is again slightly
deformed as
a
result of the narrow nitro-
genꢀpalladiumꢀnitrogen angle (80.19(15) and 80.38(15)°
in 11, 80.8(2)° in 12) as in related pyridinylimine [38,47]
and bipyridine [48–50] complexes. The methyl group in
the pyridine 6-position of compound 12 generates even
greater distortion with the neighboring chlorine atom
,
(Cl1) protruding as much as 0.459(7) A away from the
ligand coordination plane, which can be defined as the
plane of the five-membered metallacycle PdꢀN1ꢀ
C6ꢀC7ꢀN8. In the same process the palladiumꢀpyridine
,
bond (PdꢀN1) is extended (2.114(5) A) compared to the
,
bonding distances (2.025(4)–2.028(3) A) of complexes

116
T.V. Laine et al. / Journal of Organometallic Chemistry 606 (2000) 112–124
10 and 12 (see Table 3), corresponding to the slanting
of the palladium coordination sphere towards the side
of the phenyl ring. The other chloride (Cl2) twists only
2.3. Nickel-catalyzed polymerization of ethylene
Each of the four dimeric catalyst precursor com-
plexes (6–9) could be activated for ethylene polymeriza-
tion by treatment with methylaluminoxane (MAO).
Generally the catalytic behavior of these systems fol-
lows closely the trends observed previously for the
related pyridinylimine complex [39]. In this study the
variation in ligand structure, however, allows us to
analyze, which features are due to reaction conditions
and which result from the catalyst used. The polymer-
ization conditions and results are summarized in Table
4.
,
slightly, 0.143(7) A, to the same side as Cl1. Similar
behavior has been reported also for a palladium com-
plex bearing the unsymmetric 6-methyl-2,2%-bipyridine
ligand [48]. The essentially more planar coordination
sphere in compound 12 bears resemblance to the pub-
lished structures of 10 [38] and dichloro(2,2%-
bipyridine)palladium(II) [49] with all the relevant bond
lengths and angles well corresponding. The only incon-
sistent feature is the slight off-plane deviation of Cl1
,
and Cl21 (0.167(5) and 0.154(5) A, respectively).
Table 2
,
Selected bond lengths (A) and angles (°) for complexes 6–9 *
6
7
8
9
Bond lengths
NiꢀN1
2.069(5)
Ni1ꢀN1
Ni2ꢀN22
Ni1ꢀN8
Ni2ꢀN29
Ni1ꢀBr1
Ni2ꢀBr3
Ni1ꢀBr1ab
Ni2ꢀBr3ac
Ni1ꢀBr2
Ni2ꢀBr4
C6ꢀC7
2.086(3)
2.072(3)
2.042(3)
2.036(3)
2.5411(12)
2.5230(12)
2.4806(9)
2.4876(8)
2.4136(10)
2.4266(8)
1.469(6)
1.454(6)
1.267(5)
1.270(5)
1.461(5)
1.460(5)
NiꢀN1
NiꢀN8
NiꢀBr1
NiꢀBr1ad
NiꢀBr2
C6ꢀC7
C7ꢀN8
N8ꢀC9
2.023(5)
NiꢀN1
NiꢀN8
NiꢀBr1
NiꢀBr1ae
NiꢀBr2
C6ꢀC7
C7ꢀN8
N8ꢀC9
2.029(4)
2.100(3)
2.5337(10)
2.4923(8)
2.4244(9)
1.490(6)
1.277(5)
1.455(5)
NiꢀN8
NiꢀBr1
NiꢀBr1aa
NiꢀBr2
C6ꢀC7
C7ꢀN8
N8ꢀC9
2.042(5)
2.060(5)
2.4759(17)
2.5479(12)
2.4139(18)
1.452(8)
2.5920(12)
2.4643(12)
2.4273(13)
1.474(8)
C27ꢀC28
C7ꢀN8
C28ꢀN29
N8ꢀC9
1.265(8)
1.280(7)
1.446(8)
1.455(7)
N29ꢀC30
Bond angles
N1ꢀNiꢀN8
79.4(2)
N1ꢀNi1ꢀN8
N22ꢀNi2ꢀN29
N1ꢀNi1ꢀBr1
N22ꢀNi2ꢀBr3
N1ꢀNi1ꢀBr1ab
N22ꢀNi2ꢀBr3ac
N1ꢀNi1ꢀBr2
N22ꢀNi2ꢀBr4
N8ꢀNi1ꢀBr1
N29ꢀNi2ꢀBr3
N8ꢀNi1ꢀBr1ab
N29ꢀNi2ꢀBr3ac
N8ꢀNi1ꢀBr2
N29ꢀNi2ꢀBr4
Br1ꢀNi1ꢀBr1ab
Br3ꢀNi2ꢀBr3ac
Br1ꢀNi1ꢀBr2
Br3ꢀNi2ꢀBr4
Br1abꢀNi1ꢀBr2
Br3acꢀNi2ꢀBr4
Ni1ꢀBr1ꢀNi1ab
Ni2ꢀBr3ꢀNi2ac
80.29(13)
80.55(13)
175.99(9)
176.09(10)
91.58(10)
90.74(10)
92.17(9)
90.97(10)
99.32(10)
99.75(10)
107.95(10)
106.33(9)
108.95(10)
107.94(9)
84.73(3)
N1ꢀNiꢀN8
79.61(19)
84.02(14)
169.29(14)
92.66(13)
114.91(12)
103.25(13)
108.57(12)
85.44(3)
N1ꢀNiꢀN8
79.06(14)
91.51(10)
166.67(11)
92.01(11)
145.74(10)
96.37(10)
104.25(10)
85.30(3)
N1ꢀNiꢀBr1
N1ꢀNiꢀBr1aa
N1ꢀNiꢀBr2
N8ꢀNiꢀBr1
N8ꢀNiꢀBr1aa
N8ꢀNiꢀBr2
Br1ꢀNiꢀBr1aa
Br1ꢀNiꢀBr2
Br1aaꢀNiꢀBr2
NiꢀBr1ꢀNiaa
91.05(16)
173.09(16)
91.61(16)
110.48(16)
95.30(14)
117.05(16)
86.63(4)
N1ꢀNiꢀBr1
N1ꢀNiꢀBr1ad
N1ꢀNiꢀBr2
N8ꢀNiꢀBr1
N8ꢀNiꢀBr1ad
N8ꢀNiꢀBr2
Br1ꢀNiꢀBr1ad
Br1ꢀNiꢀBr2
Br1adꢀNiꢀBr2
NiꢀBr1ꢀNiad
N1ꢀNiꢀBr1
N1ꢀNiꢀBr1ae
N1ꢀNiꢀBr2
N8ꢀNiꢀBr1
N8ꢀNiꢀBr1ae
N8ꢀNiꢀBr2
Br1ꢀNiꢀBr1ae
Br1ꢀNiꢀBr2
Br1aeꢀNiꢀBr2
NiꢀBr1ꢀNiae
85.43(3)
91.73(4)
92.64(2)
143.02(3)
145.49(3)
95.27(3)
132.06(6)
94.78(4)
134.89(4)
96.12(3)
108.98(3)
101.27(3)
94.70(3)
93.37(4)
94.56(3)
94.57(3)
* Symmetry transformations used to generate equivalent atoms: a −x, −y, −z+1; b −x+2, −y+1, −z+1; c −x+1, −y+1, −z; d −x+1,
−y, −z+1; e −x+1, −y+1, −z+1.

T.V. Laine et al. / Journal of Organometallic Chemistry 606 (2000) 112–124
117
Table 3
Selected bond lengths (A) and angles (°) for 10 , 11 and 12
chain length was achieved with the 6-methylpyridine-
based catalyst 7/MAO at 20 and 40°C (entries 4 and 5).
Therefore, the dominating factor in controlling the
molecular weight, besides reaction conditions, seems to
be the steric bulk of the ligand, which is still lacking on
the pyridine side despite the different modifications
administered. As a result the blocking of the axial
coordination sites in the nickel center, which according
to theoretical calculations is essential in order to obtain
higher molecular weights [17], remains insufficient and
products with MwB50 000 g mol−1 are isolated.
The effect of ligand environment is most clear when
polymer branching is analyzed. Even in this case polymer-
ization temperature plays an important role, though the
extent of branching can be controlled with the ligand
structure. According to structural analysis by 13C-NMR
spectroscopy predominantly methyl-branched polymers
are obtained. Decreasing the steric bulk in the aryl ring
by replacing the two isopropyl groups with methyls in the
2- and 6-positions gives more linear polymers, as also
theoretical [16] and experimental reports [14,53] on the
diazabutadiene systems indicate, but quite remarkably
the least branching was observed in samples produced
with catalyst 7/MAO, in which the isopropyl groups are
present and the pyridine ring is substituted instead.
Introduction of a methyl or phenyl side group to the imino
carbon of the ligand, in turn, leads to increased branching,
as happens with the diazabutadiene-based catalysts [14].
a
,
10
12
11
Bond lengths
PdꢀN1
2.028(3)
2.022(3)
2.114(5)
2.006(5)
Pd1ꢀN1
Pd2ꢀN21
Pd1ꢀN8
Pd2ꢀN28
2.025(4)
2.026(4)
2.021(4)
2.023(4)
2.2919(14)
2.2897(15)
2.2703(16)
2.2796(15)
1.445(6)
1.447(6)
1.276(6)
1.284(6)
1.444(6)
1.438(5)
PdꢀN8
PdꢀCl1
PdꢀCl2
C6ꢀC7
C7ꢀN8
N8ꢀC9
2.2809(11) 2.2890(19) Pd1ꢀCl1
Pd2ꢀCl21
2.2768(10) 2.260(2)
Pd1ꢀCl2
Pd2ꢀCl22
C6ꢀC7
C26ꢀC27
C7ꢀN8
C27ꢀN28
N8ꢀC9
N28ꢀC29
1.457(5)
1.279(4)
1.448(4)
1.445(9)
1.286(9)
1.436(8)
Bond angles
N1ꢀPdꢀN8
80.08(11) 80.8(2)
N1ꢀPd1ꢀN8
80.19(15)
N21ꢀPd2ꢀN28 80.38(15)
94.33(9) 101.98(16) N1ꢀPd1ꢀCl1 94.92(11)
N21ꢀPd2ꢀCl21 94.08(12)
N1ꢀPdꢀCl2 174.51(9) 171.10(16) N1ꢀPd1ꢀCl2 173.92(11)
N1ꢀPdꢀCl1
N21ꢀPd2ꢀCl22 174.29(11)
N8ꢀPdꢀCl1 172.85(8) 172.66(15) N8ꢀPd1ꢀCl1
174.53(11)
N28ꢀPd2ꢀCl21 174.35(11)
90.35(17) N8ꢀPd1ꢀCl2
N8ꢀPdꢀCl2
Cl1ꢀPdꢀCl2
94.64(8)
91.05(4)
93.81(11)
N28ꢀPd2ꢀCl22 93.93(11)
86.90(7)
Cl1ꢀPd1ꢀCl2
91.12(6)
Cl21ꢀPd2ꢀCl22 91.62(6)
a See Ref. [38].
2.4. Palladium-catalyzed polymerization of norbornene
The palladium-based catalyst precursors 10–12 can
be activated for norbornene polymerization by treat-
ment with methylaluminoxane or by conversion into
All the catalysts lose activity with decreasing reaction
temperature: the highest catalytic activities are obtained
at 20°C (except for catalyst 9/MAO) while lowering the
temperature to 0°C leads to a significant decline in
polymer production. Reduced polymer yields at 40°C
(entries 1, 4, 7, and 10) can be attributed to catalyst
decomposition [51], which is detected as diminishing
ethylene consumption after initially higher activity. Nev-
ertheless, activities for the system 7/MAO, which contains
a methyl substitute in the 6-position of the ligand pyridine
ring, are one order of magnitude lower than for the
unsubstituted complex [39]. This indicates severe interfer-
ence from the protruding methyl group, which obstructs
one of the equatorial coordination sites as can be seen
in the solid-state structure as well (Fig. 2), thus, resulting
in diminished activity. Also the phenyl group in the imino
bridge of complex 9 has a slightly decreasing effect on
the polymerization activity at higher temperatures (en-
tries 11 and 12).
Although highly dependant on the polymerization
temperature, the molecular weights of produced polymers
are in general very similar, also with the values reported
using the analogous catalyst [39], yet remain remarkably
lower than obtained with the diazabutadiene systems
under similar conditions [52]. Only a minor increase in
Fig. 1. Crystal structure of complex 6 with the labeling scheme.
Displacement ellipsoids are drawn at the 40% probability level.
Hydrogen atoms are omitted for clarity.

Table 4
Ethylene polymerization with catalysts 6–9/MAO a
Entry
Catalyst
Tp (°C) b
ncat (mmol) c
p (bar) d
Yield (g)
Activity e
Mw (g mol−1
)
Mw/Mn
Tm (°C) f
Methyls per 1000 carbon atoms g
/
1
2
3
4
5
6
7
8
9
6
6
6
7
7
7
8
8
8
9
9
9
40
20
0
40
20
0
40
20
0
40
20
0
2.5
2.5
5.0
5.0
10
5.5
4.3
3.0
5.5
4.3
3.0
5.5
4.3
3.0
5.5
4.3
3.0
4.44
7.08
3.07
1.20
2.93
0.86
3.80
12.16
3.02
7.12
2.28
4.64
3600
5700
610
480
590
2800
5500
26 000
5600
7900
27 000
3400
5000
22 000
2300
7000
30 000
1.7
2.2
1.9
2.2
2.7
2.0
1.8
2.6
2.4
2.5
2.1
2.9
Wax
43
24
6
28
23
7
83
50
17
67
53
24
113.3 h
127.0
116.7 h
118.0 h
127.0
Wax
20
43
2.5
5.0
5.0
4.6
4.6
4.6
3000
4800
600
3100
990
101.7 h
116.3
Wax
10
11
12
101.3 h
115.7
1000
a [Al]:[M]=2000, tp=30 min (except at 0°C 60 min).
b Polymerization temperature.
6
c Molar amount of the catalyst precursor (in mmol Ni).
(
d Ethylene pressure.
e Activity in kg PE (mol catalyst h)−1
f Peak melting temperature.
.
1
g Determined by 1H-NMR spectroscopy.
h Broad melting peak.
124

T.V. Laine et al. / Journal of Organometallic Chemistry 606 (2000) 112–124
119
the cationic species, except in the case of complex 11
for which only MAO-activation was possible, since the
cationic compound was too unstable to be isolated.
Altogether, the latter method seems to be more compli-
cated requiring long reaction times and removal of the
formed AgCl, which may disturb the polymerization
[54], whereas MAO-activation can be performed in situ
in a convenient manner. Polymerization results and
conditions are summarized in Table 5.
Up to 100% monomer conversion was reached using
MAO-containing catalyst systems (entries 5–10). In
most cases the polymerization medium became highly
Fig. 4. Molecular structure of compound 9. The solvent molecules are
omitted for clarity.
Fig. 2. Molecular structure of compound 7 showing the two crystallo-
graphically independent molecules of the asymmetric unit.
Fig. 5. Molecular structure of compound 11 showing the two crystal-
lographically independent molecules of the asymmetric unit.
Fig. 3. Crystal structure of complex 8.

120
T.V. Laine et al. / Journal of Organometallic Chemistry 606 (2000) 112–124
bond (an analogous step is found in the mechanism of
ethylene polymerization with transition metal catalysts
[16]). The prerequisite palladium alkyl species [20] is
readily generated in the reaction of methylaluminoxane
and the catalyst precursor, thus promoting the insertion
of the first monomer, while in the acetonitrile systems
the initiation of polymerization seems to be less
straightforward [55]. The significance of the direct pal-
ladiumꢀcarbon bond has been further demonstrated by
the use of cationic palladium norbornyl derivatives as
active catalysts [35]. Also the bulky size of the MAO
counter ion, or the resulting weaker interaction with the
metal center, may be beneficial to polymerization activ-
ity as in catalyst systems containing h3-allyl ligands
[32], although contrasting evidence has been described
for the [(RCN)4Pd]2+ species [54].
Fig. 6. Crystal structure of complex 12 with the labeling scheme.
viscous within the first 10 min of the 2 h polymerization
run. Only catalyst 11/MAO (entries 7 and 8) was
unable to produce quantitative polymer yields in 2 h,
which further demonstrates the inability of the dimethyl
ligand (2) to sufficiently stabilize the cationic palladium
center. Polymerizations with the single-component sys-
tems 13 and 14 (entries 1–4), in turn, showed disap-
pointingly low yields (B20%) compared to values
reported for cationic diamine complexes (58–70%) [36]
and traditional tetrakis(nitrile) systems (45–92%)
[21,37] under similar conditions. Molecular weights of
obtained polymers could not be determined by gel
permeation chromatography due to insolubility of
products in organic solvents, including 1,2,4-
trichlorobenzene.
One possible explanation for the drastic difference in
activity between the MAO-activated and single-compo-
nent catalysts can be derived from the proposed poly-
merization mechanism [20,22] according to which the
chain propagation step proceeds by insertion of the
coordinated norbornene molecule into a metalꢀcarbon
3. Experimental
3.1. General
All complex preparations were performed under an
argon atmosphere using standard Schlenk techniques.
Acetone and acetonitrile were dried by storing under
argon with CaSO4 and CaCl2 granules, respectively,
other solvents by refluxing with a drying agent (CaH2
for dichloromethane and sodium/benzophenone for the
non-halogenated solvents) and distillation under argon.
Commercial reagents, namely 6-methyl-2-pyridinecar-
boxaldehyde (Merck, 98%), 1-(2-pyridinyl)ethanone
(Merck, 98%), phenyl-2-pyridinylmethanone (Merck,
98%), 2,6-di(1-methylethyl)phenylamine (Aldrich, 90%),
bicyclo[2.2.1]hept-2-ene (Merck, 98%), methylalumi-
noxane (Witco, 30 wt.% solution in toluene) and silver
tetrafluoroborate (Aldrich, 98%), were used as received.
Dibromo(1,2-dimethoxyethane)nickel(II) [(DME)NiBr2]
[56], dichloro(1,5-cyclooctadiene)palladium(II) [(COD)-
PdCl2] [57], 2,6-dimethyl-N-(2-pyridinylmethylene)-
phenylamine (2) [44], 2,6-bis(1-methylethyl)-N-(2-
Table 5
Norbornene polymerization with catalysts 13, 14 and 10–12/MAO a
c
Entry
Catalyst
mcat (mg) b
nnorbornene:ncat
Yield (g)
Conversion (%)
1
2
3
4
5
6
7
8
9
13
13
14
14
10/MAO
10/MAO
11/MAO
11/MAO
12/MAO
12/MAO
50
50
50
50
25
25
25
25
25
25
400
800
400
800
400
800
400
800
400
800
0.18
0.21
0.55
Trace
2.16
4.22
2.29
4.74
2.10
4.11
6.0
3.5
19
–
100
100
94
98
100
100
10
a Tp=25°C, tp=120 min; in entries 5–10 [Al]:[Pd]=1000.
b Mass of the catalyst precursor.
c Monomer-to-catalyst ratio in mol:mol.

T.V. Laine et al. / Journal of Organometallic Chemistry 606 (2000) 112–124
121
pyridinylmethylene)phenylamine (1) [38], and dichloro-
[2,6-bis(1-methylethyl)-N-(2-pyridinylmethylene)phenyl-
amine]palladium(II) (10) [38] were prepared as reported
earlier. Synthesis products were characterized, when
applicable, using a Varian Gemini 200 spectrometer
(200 MHz) with CDCl3 or acetone-d6 as solvent and
TMS as internal standard. Elemental analyses were
carried out at the University of Ulm, Germany.
(2.75 g, 15.0 mmol) and 2,6-di(1-methylethyl)-
phenylamine (3.29 g, 16.7 mmol) at 120°C. The ligand
was obtained from ethanol as bright yellow microcrys-
talline powder. Yield: 1.68 g (33%). Anal. Calc. for
C24H26N2 (342.48): C, 84.17; H, 7.65; N, 8.18. Found:
1
C, 84.04; H, 7.72; N, 8.37%. H-NMR (CDCl3): l 0.90
(d, 3 H, HMe), 0.97 (d, 3 H, HMe), 1.14 (d, 6 H, HMe),
2.93 (m, 2 H, CHMe2), 6.98–7.23 (m, 6 H, Harom), 7.45
(m, Harom), 7.83 (m, Harom), 8.25 (d, Harom), 8.64 (m,
Harom) ppm.
3.2. Ligand and complex preparation
3.2.1. 2,6-Bis(1-methylethyl)-N-[(6-methyl-2-pyridinyl)-
methylene]phenylamine (3)
3.2.4. Di-v-bromodibromobis[2,6-dimethyl-N-
(2-pyridinylmethylene)phenylamine]dinickel(II) (6)
To a suspension of [(DME)NiBr2] (2.03 g, 6.6 mmol)
in 20 ml of CH2Cl2 was added the solution of ligand 2
(1.42 g, 6.8 mmol) in 20 ml of CH2Cl2. The orange–red
reaction mixture was stirred for 24 h at room tempera-
ture (r.t.), after which the precipitate was collected by
filtration, washed with pentane (2×10 ml), and vac-
uum-dried yielding complex 6 as an orange–yellow
Ligand 3 was synthesized by modifying our recently
reported method [38]. 6-Methyl-2-pyridinecarboxalde-
hyde (9.70 g, 80.1 mmol) was dissolved in 100 ml of
ethanol and 2,6-di(1-methylethyl)phenylamine (15.80 g,
80.2 mmol) was added. This mixture was refluxed for
30 min and after solvent evaporation subjected to
column chromatography on basic alumina with pen-
tane–ethyl acetate (3:1) as eluent. Recrystallization
from a 1:3 mixture of ethanol and pentane at −18°C
afforded pale yellow, needle-like crystals. Yield: 11.84 g
(53%). Anal. Calc. for C19H24N2 (280.41): C, 81.38; H,
8.63; N, 9.99. Found: C, 81.05; H, 8.56; N, 9.95%.
1H-NMR (CDCl3): l 1.09 (d, 12 H, HMe), 2.57 (s, 3 H,
Hpyridine,6-Me), 2.89 (m, 2 H, CHMe2), 7.04–7.13 (m, 3
H, Hphenyl), 7.20 (d, 1 H, Hpyridine,5), 7.66 (t, 1 H,
Hpyridine,4), 8.02 (d, 1 H, Hpyridine,3), 8.20 (s, 1 H, CHꢁN)
ppm.
powder. Yield: 1.55
g
(55%). Anal. Calc. for
C28H28Br4N4Ni2 (857.55): C, 39.22; H, 3.29; N, 6.53.
Found: C, 38.97; H, 3.60; N, 6.39%.
Compounds 7–9 were prepared analogously from
[(DME)NiBr2] and the corresponding ligand in
dichloromethane.
3.2.5. Di-v-bromodibromobis{2,6-bis(1-methylethyl)-
N-[(6-methyl-2-pyridinyl)methylene]phenylamine}-
dinickel(II) (7)
Orange–yellow powder. Yield: 57%. Anal. Calc. for
C38H28Br4N4Ni2 (997.82): C, 45.74; H, 4.85; N, 5.61.
Found: C, 45.56; H, 4.81; N, 5.53%.
3.2.2. 2,6-Bis(1-methylethyl)-N-[1-(2-pyridinyl)-
ethylidene]phenylamine (4)
The ketone 1-(2-pyridinyl)ethanone (1.82 g, 15.0
mmol) was combined with 2,6-di(1-methylethyl)-
phenylamine (3.57 g, 18.1 mmol) and three drops of
concentrated H2SO4 as well as some sodium sulfate was
added. This mixture was heated to 120°C and stirring
was continued at this temperature for 24 h. The dark
brown, oily raw product was dissolved in 50 ml of
dichloromethane, filtered, washed with 50 ml of water
and dried with Na2SO4. After filtration and solvent
evaporation the yellow–brown residue was purified by
crystallization from ethanol affording yellow, cubic
crystals. Yield: 1.41 g (34%). Anal. Calc. for C19H24N2
(280.41): C, 81.38; H, 8.63; N, 9.99. Found: C, 81.36;
H, 8.65; N, 10.21%. 1H-NMR (CDCl3): l 1.15 (d, 12 H,
HMe), 2.21 (s, 3 H, Hbridge-Me), 2.75 (m, 2 H, CHMe2),
7.11–7.20 (m, 3 H, Hphenyl), 7.39 (m, 1 H, Hpyridine,5),
7.82 (t, 1 H, Hpyridine,4), 8.36 (d, 1 H, Hpyridine,3), 8.69 (d,
1 H, Hpyridine,6) ppm.
3.2.6. Di-v-bromodibromobis{2,6-bis(1-methylethyl)-
N-[1-(2-pyridinyl)ethylidene]phenylamine}dinickel(II) (8)
Bright orange powder. Yield: 62%. Anal. Calc. for
C38H28Br4N4Ni2 (997.82): C, 45.74; H, 4.85; N, 5.61.
Found: C, 45.44; H, 4.84; N, 5.69%.
3.2.7. Di-v-bromodibromobis[2,6-bis(1-methylethyl)-
N-(phenyl-2-pyridinylmethylene)phenylamine]dinickel(II)
(9)
Orange–brown powder. Yield: 77%. Anal. Calc. for
C48H52Br4N4Ni2·CH2Cl2 (1206.89): C, 48.76; H, 4.51;
N, 4.64. Found: C, 48.44; H, 5.05; N, 4.55%.
3.2.8. Dichloro[2,6-dimethyl-N-(2-pyridinylmethylene)-
phenylamine]palladium(II) (11)
A solution of [(COD)PdCl2] (0.50 g, 1.8 mmol) in 30
ml of CH2Cl2 was combined with a solution of ligand 2
(0.39 g, 1.9 mmol) in 10 ml of CH2Cl2. The resulting
orange–yellow solution was stirred at ambient tempera-
ture for 24 h at which time a precipitate was observed.
The pale orange powder was recovered by filtration,
washed with diethyl ether (2×20 ml), filtered and
3.2.3. 2,6-Bis(1-methylethyl)-N-(phenyl-2-
pyridinylmethylene)phenylamine (5)
Analogously to the preparation of 4, compound 5
was synthesized from phenyl-2-pyridinylmethanone

122
T.V. Laine et al. / Journal of Organometallic Chemistry 606 (2000) 112–124
vacuum dried. Yield: 0.52 g (75%). Anal. Calc. for
C14H14Cl2N2Pd (387.60): C, 43.38; H, 3.64; N, 7.23.
Found: C, 43.38; H, 3.68; N, 7.21%. H-NMR (ace-
tone-d6): l 2.21 (s, 6 H, HMe), 6.94–7.06 (m, 3 H,
Hphenyl), 7.90 (m, 1 H, Hpyridine,5), 8.16 (d, 1 H,
Hpyridine,3), 8.34 (t, 1 H, Hpyridine,4), 8.57 (s, 1 H,
CHꢁN), 9.16 (d, 1 H, Hpyridine,6) ppm.
3.3. X-ray crystallography
1
The crystals were mounted to a glass fiber using
the oil drop method [58]. Crystal data obtained with
the ꢀ–2q scan mode were collected on an automated
four-circle Rigaku AFC-7S diffractometer using
graphite-monochromatized Mo–Ka radiation (u=
,
0.71073 A) at 193 K (except for complex 8 at 213 K).
Three standard reflections were monitored after every
200 intensity scans. The intensities were corrected for
Lorentz and polarization effects. For all compounds
„-scans were used for absorption correction [59].
Data sets were compressed to reflection files with
TEXSAN single crystal structure analysis software [60].
Structure solution using direct methods and further
refinement with full-matrix least-squares on F2 was
carried out with SHELX-97 [61]. All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms
were introduced to calculated positions (riding model)
with 1.2 times the displacement factors of the host
carbon atoms (see Section 4).
3.2.9. Dichloro{2,6-bis(1-methylethyl)-N-[(6-methyl-2-
pyridinyl)methylene]phenylamine}palladium(II) (12)
The analogous complex 12 was prepared from
[(COD)PdCl2] (0.80 g, 2.8 mmol) and 3 (0.81 g, 2.9
mmol) following the method described above. Yield:
0.76 g (60%). Anal. Calc. for C19H24Cl2N2Pd (457.73):
C, 49.86; H, 5.28; N, 6.12. Found: C, 49.92; H, 5.30;
N, 6.07%. 1H-NMR (acetone-d6): l 1.01 (d, 6 H,
HMe), 1.24 (d, 6 H, HMe), 3.01 (s, 3 H, Hpyridine,6-Me),
3.29 (m, 2 H, CHMe2), 7.05–7.19 (m, 3 H, Hphenyl),
7.70 (d, 1 H, Hpyridine,5), 8.02 (d, 1 H, Hpyridine,3), 8.16
(t, 1 H, Hpyridine,4), 8.59 (s, 1 H, CHꢁN) ppm.
3.2.10. Bis(acetonitrile)[2,6-bis(1-methylethyl)-N-
(2-pyridinylmethylene)phenylamine]palladium(II)-
bis(tetrafluoroborate) (13)
3.4. Polymerization experiments
Ethylene polymerization runs were performed at
constant monomer concentration. The polymerization
procedure and equipment have been described in de-
tail previously [39]. For polymer molecular weights
and molecular weight distributions a Waters 150-C
GPC chromatograph was used operating at 135°C
with 1,2,4-trichlorobenzene solvent and polystyrene
calibration standards. Melting temperatures of pre-
heated and cooled samples were determined by differ-
ential scanning calorimetry using a Perkin–Elmer
DSC-2 calorimeter. Analysis of polymer microstruc-
ture was based on NMR spectra recorded on a
Varian XL-300 spectrometer at 125°C. Samples were
dissolved in 1,1,2,2-tetrachloroethane-d2 and a 10:1
weight ratio mixture of 1,2,4-trichlorobenzene and
benzene-d6 for 1H- and 13C-NMR measurements, re-
spectively.
The neutral dichloropalladium compound 10 (0.22
g, 0.49 mmol in 50 ml of CH3CN) was converted to
the corresponding cationic complex by reacting with
AgBF4 (0.19 g, 0.99 mmol) for 96 h at r.t. The reac-
tion mixture was filtered to remove the precipitated
AgCl and evaporated to dryness leaving a yellow
residue, which was then dissolved in CH2Cl2. After
filtration, solvent evaporation and drying under vac-
uum complex 13 was obtained as pale yellow powder.
1
Yield: 0.28 g (89%). H-NMR (acetone-d6): l 1.10 (d,
6 H, HMe), 1.35 (d, 6 H, HMe), 1.91 (s, 6 H, HMeCN),
3.63 (m, 2 H, CHMe2), 7.26–7.47 (m, 3 H, Hphenyl),
7.95 (m, 1 H, Hpyridine,5), 8.43 (d, 1 H, Hpyridine,3), 8.54
(t, 1 H, Hpyridine,4), 8.84 (s, 1 H, CHꢁN), 8.96 (d, 1
H, Hpyridine,6) ppm.
For the polymerization of norbornene the palla-
dium catalyst was dissolved in the polymerization
medium consisting of dichloromethane (50 ml), 1,2-
dichlorobenzene (5 ml), and nitrobenzene (1 ml) in a
250-ml Schlenk flask. When MAO-activation was
used (Table 5, entries 5–10) the reaction was per-
formed in toluene (80 ml). Polymerization was com-
menced by adding the appropriate amount of
norbornene monomer (and MAO cocatalyst, in en-
tries 5–10). After stirring for 2 h at ambient tempera-
ture the reaction was quenched by addition of
methanol acidified with a small amount of aqueous
HCl. The precipitated polymer was collected by filtra-
tion, washed with methanol and dried under vacuum.
3.2.11. Bis(acetonitrile){2,6-bis(1-methylethyl)-
N-[(6-methyl-2-pyridinyl)methylene]phenylamine}-
palladium(II)bis(tetrafluoroborate) (14)
Analogously to the preparation of 13, complex 14
was synthesized from compound 12 (0.40 g, 0.87
mmol) and AgBF4 (0.34 g, 1.7 mmol) in 50 ml of
acetonitrile and collected as pale yellow powder.
1
Yield: 0.41 g (73%). H-NMR (acetone-d6): l 1.09 (d,
6 H, HMe), 1.35 (d, 6 H, HMe), 1.91 (s, 6 H, HMeCN),
2.61 (s, 3 H, Hpyridine,6-Me), 3.58 (m, 2 H, CHMe2),
7.24–7.49 (m, 3 H, Hphenyl), 7.83 (d, 1 H, Hpyridine,5),
8.23 (d, 1 H, Hpyridine,3), 8.33 (t, 1 H, Hpyridine,4), 8.72
(s, 1 H, CHꢁN) ppm.

T.V. Laine et al. / Journal of Organometallic Chemistry 606 (2000) 112–124
123
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC-133658 (for 6), 133659 (for 7),
133660 (for 8), 133661 (for 9), 127783 (for 11), and
127782 (for 12). Copies of this information can be
obtained free of charge from: The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax: +44-
1223-336-033; e-mail: deposit@ccdc.cam.ac.uk or www:
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Acknowledgements
Financial support from the Academy of Finland and
the Technology Development Center of Finland
(TEKES) is gratefully acknowledged. The authors wish
to thank Alexandra Abele (University of Ulm, Ger-
many) and Kimmo Hakala (Helsinki University of
Technology, Finland) for providing the EA and poly-
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