Highly active/selective and adjustable zirconium polymerization catalysts stabilized by aminopyridinato ligands

Article abstract of DOI:10.1016/j.jorganchem.2007.04.041

This paper describes a substantial enhancement of the aminopyridinato ligand stabilized early transition metal chemistry by introducing the sterically very demanding 2,6-dialkylphenyl substituted aminopyridinato ligands derived from (2,6-diisopropylphenyl)-[6-(2,6-dimethylphenyl)-pyridin-2-yl]-amine (1a-H, ApH) and (2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-pyridin-2-yl]- amine (1b-H, Ap^*H). The corresponding bis aminopyridinato zirconium dichloro complexes, [Ap₂ZrCl₂] (3a) and [Ap₂^*ZrCl₂] (3b) and the dimethyl analogues, [Ap₂ZrMe₂] (4a) and [Ap₂^*ZrMe₂] (4b) (Me = methyl) were synthesized, using standard salt metathesis routes. Single-crystal X-ray diffraction was carried out for the dichloro derivatives. Both zirconium metal centers have a distorted octahedral environment with a cis-orientation of the chloride ligands in 3a and a closer to trans-arrangement in 3b. The dimethyl derivatives are proven to be highly active ethylene polymerization catalysts after activation with [R₂N(Me)H][B(C₆F₅)₄] (R = C₁₆H₃₃-C₁₈H₃₇). During attempted co-polymerizations of α-olefins (propylene) and ethylene high activity and selectivity for ethylene and nearly no co-monomer incorporation was observed. Increasing the steric bulk of the ligand going from (2,6-dimethylphenyl) to (2,4,6-triisopropylphenyl) substituted pyridines, switches the catalyst system from producing long chain α-olefins to polymerization of ethylene in a living fashion. In contrast to the dimethyl complexes only [Ap₂^*ZrCl₂] in the presence of MAO at elevated temperature gave decent polymerization activity. NMR investigations of the reaction of dichloro complexes with 25 equiv. of MAO or AlMe₃ at room temperature revealed, that [Ap₂ZrCl₂] decomposes under ligand transfer to aluminum and formation of [ApAlMe₂], while [Ap₂^*ZrCl₂] remains almost unreacted under the same conditions. The aminopyridinato dimethyl aluminum complexes, [ApAlMe₂] (5a) and [Ap^*AlMe₂] (5b) were synthesized independently and structurally characterized. The aluminum complexes 5a and b show no catalytic activity towards ethylene, when activated with[R₂N(Me)H][B(C₆F₅)₄].

Full text of DOI:10.1016/j.jorganchem.2007.04.041

Journal of Organometallic Chemistry 692 (2007) 4569–4579
www.elsevier.com/locate/jorganchem
Highly active/selective and adjustable zirconium polymerization
catalysts stabilized by aminopyridinato ligands
a,
a
b
b
b,
*
Winfried P. Kretschmer *, Bart Hessen , Awal Noor , Natalie M. Scott , Rhett Kempe
a
Center for Catalytic Olefin Polymerization, Stratingh Institute for Chemistry and Chemical Engineering, University of Groningen,
Nijenborgh 4, NL-9747 AG Groningen, The Netherlands
b
Lehrstuhl Anorganische Chemie II, University of Bayreuth, 95440 Bayreuth, Germany
Received 20 March 2007; received in revised form 18 April 2007; accepted 20 April 2007
Available online 6 May 2007
Dedicated to Prof. Gerhard Erker.
Abstract
This paper describes a substantial enhancement of the aminopyridinato ligand stabilized early transition metal chemistry by introduc-
ing the sterically very demanding 2,6-dialkylphenyl substituted aminopyridinato ligands derived from (2,6-diisopropylphenyl)-[6-(2,6-
dimethylphenyl)-pyridin-2-yl]-amine (1a–H, ApH) and (2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-pyridin-2-yl]- amine
*
(1b–H, Ap*H). The corresponding bis aminopyridinato zirconium dichloro complexes, [Ap2ZrCl2] (3a) and [Ap2 ZrCl2] (3b) and the
*
dimethyl analogues, [Ap2ZrMe2] (4a) and [Ap2 ZrMe2] (4b) (Me = methyl) were synthesized, using standard salt metathesis routes.
Single-crystal X-ray diffraction was carried out for the dichloro derivatives. Both zirconium metal centers have a distorted octahedral
environment with a cis-orientation of the chloride ligands in 3a and a closer to trans-arrangement in 3b. The dimethyl derivatives are
proven to be highly active ethylene polymerization catalysts after activation with [R2N(Me)H][B(C6F5)4] (R = C16H33–C18H37). During
attempted co-polymerizations of a-olefins (propylene) and ethylene high activity and selectivity for ethylene and nearly no co-monomer
incorporation was observed. Increasing the steric bulk of the ligand going from (2,6-dimethylphenyl) to (2,4,6-triisopropylphenyl) substi-
tuted pyridines, switches the catalyst system from producing long chain a-olefins to polymerization of ethylene in a living fashion. In
*
contrast to the dimethyl complexes only [Ap2 ZrCl2] in the presence of MAO at elevated temperature gave decent polymerization activ-
ity. NMR investigations of the reaction of dichloro complexes with 25 equiv. of MAO or AlMe3 at room temperature revealed, that
*
[Ap2ZrCl2] decomposes under ligand transfer to aluminum and formation of [ApAlMe2], while [Ap2 ZrCl2] remains almost unreacted
under the same conditions. The aminopyridinato dimethyl aluminum complexes, [ApAlMe2] (5a) and [Ap*AlMe2] (5b) were synthesized
independently and structurally characterized. The aluminum complexes 5a and b show no catalytic activity towards ethylene, when
‘‘activated’’ with[R2N(Me)H][B(C6F5)4].
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Aluminum; Aminopyridinato ligands; N-ligands; Olefin polymerization; Zirconium
1. Introduction
synthesis, combined with easy modification of steric and
electronic properties of the precursor aminopyridines have
led to a wide variety of mono, bis, tris and tetrakis amino-
pyridinato derivatives. In general, aminopyridinato ligands
are interesting non-symmetric versions of bidentate mono-
anionic N-Ligands suited to stabilize early and late transi-
tion metals and can be considered as related to amidinates
[2] or NacNac [3] ligands (Scheme 1, middle and right,
respectively).
In recent years the organo zirconium chemistry of the
ancillary aminopyridinato ligands (Scheme 1, left) [1] has
been increased rapidly. Relatively simple and high yield
*
Corresponding authors. Tel.: +49 921552540.
E-mail addresses: W.P.Kretschmer@rug.nl (W.P. Kretschmer),
Kempe@Uni-Bayreuth.de (R. Kempe).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.04.041

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W.P. Kretschmer et al. / Journal of Organometallic Chemistry 692 (2007) 4569–4579
2. Results and discussion
R''
R'
R'
R'
R
R'
R
N
N
N
N
R N
N R
2.1. Synthesis and characterization of the zirconium
dichloride and dimethyl complexes
Scheme 1. Aminopyridinato ligands (left) and other related bidentate
monoanionic N-Ligands (R, R0 and R00, for instance, alkyl or aryl
substituents).
The reaction of the potassium salts 2a/b [5a] with ZrCl4
leads to the zirconium dichlorides 3a/b which on reacting
with methyl lithium convert selectively to the bisalkyls
4a/b (Scheme 3).
However, comparing with the literature only a few
aminopyridinato ligand based zirconium olefin polymeriza-
tion catalyst systems, with low or moderate activity have
been reported. It seems that the olefin polymerization
chemistry of the aminopyridinato zirconium complexes
has been limited so far since no ligands were available that
could avoid ligand redistribution to tris or tetrakis amino-
pyridinato complexes independent from the ‘‘remaining’’
ligands [4]. Contributions by Scott and co-workers empha-
size the importance of the introduction of steric bulk at the
pyridine ring [4f,4g]. Thus, we concluded that the bulky
aminopyridinato ligands containing 2,6-disubstituted phe-
nyl substituents at the amido N-atom and at the pyridine
ring introduced by us recently [5] could address this
problem.
The molecular structures of 3a/b were determined via
X-ray crystal structure analysis (for experimental details
see Table 1) and are shown in Fig. 1. The space filling
model clearly indicates a well protected active site of 3b
compared to 3a. The overall coordination environment of
complexes 3a/b can best be described as distorted octahe-
dron with cis orientated chlorides for 3a [96.47(4)ꢁ], while
the Cl–Zr–Cl angle of 3b is significantly closer to a transo-
ide arrangement [123.08(6)ꢁ]. The differences in the Zr–
N
amido/Zr–Npyridine bond lengths indicate a localized bind-
ing mode. The anionic charge of the N ligand is localized at
the Namido atom which means a classic donor functional-
ized amido metal bond rather than an aminopyridinate is
observed [8].
In this contribution, we report the synthesis of
zirconium polymerization catalysts based on sterically very
demanding aminopyridines (2,6-diisopropylphenyl)-[6-
(2,6-dimethylphenyl)-pyridin-2-yl]-amine (1a–H, ApH)
and (2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)-
pyridin-2-yl]- amine (1b–H, Ap*H) (Scheme 2). It is shown
that such zirconium aminopyridinato complexes are ther-
mally robust and highly active ethylene polymerization
catalysts. Furthermore, a selective discrimination of pro-
pylene in ethylene/propylene-copolymerization is observed.
Such monomer selectivity especially in combination with
high temperature stability could be of relevance for
instance in chain shuttling polymerizations [6]. Further-
more, the increase of steric bulk going from Ap to Ap*
switches the catalyst system from producing long chain
a-olefins to polymerization of ethylene in a living fashion,
if no chain transfer agents are present. The introduction
of bulkiness does not necessarily lead to very high polymer-
ization activity of the corresponding metal complexes. For
related, sterically demanding amidinate-based zirconium
catalysts only low activities were observed [7].
Despite the bulk of the ligands and their crowded metal
environment the aminopyridinato complexes 3a/b and 4a/b
1
show a dynamic behaviour in solution. In the H and 13C
NMR spectra at room temperature for all four complexes
only one set of resonances for both ligands is observed
(see for instance Fig. 3a). These together with the splitting
of the methyl resonances for each isopropyl group in a
doublet of doublets indicates, there is a chemically differ-
ence for the upper and lower site of the aromatic rings
while the right and left is equal. This observation indicates
a fast inter-conversion of the ligands on NMR timescale at
room temperature. Reaction of 4b with N,N-dimethylani-
linium-tetra(pentafluorophenyl)borate ([PhNMe2H][B(C6-
F5)4]) in bromobenzene leads to the corresponding
[Ap*2ZrMe]+ cation (Scheme 4).
Despite the increase in space around the metal (abstrac-
tion of one of the alkyl functions) the increase in electro-
static interaction between the cationic metal center and
the pyridine fragment most likely prevents the dissociation
and leads to five chemically unequal isopropyl groups
(Fig. 3b). This observation is indicative of a dissociative
2a/b
3a/b
R
N
ZrCl4
2
K
N
N
R'
N
N
H
N
R
R
R
H
N
N
X
Zr
X
R
R'
R'
N
N
2 LiCH3
4a/b
3a/b
R
1a-H, Ap-H
1b-H, Ap*-H
Scheme 3. Synthesis of 3a/b and 4a/b (3: X = Cl, 4: X = CH3; a: R = Me,
R0 = H; b: R, R0 = i-Pr).
Scheme 2. 2,6-Dialkylphenyl substituted amino pyridines.

W.P. Kretschmer et al. / Journal of Organometallic Chemistry 692 (2007) 4569–4579
4571
Table 1
Details of the X-ray crystal structure analyses of 3a 2C6D6, 3b C6H14, 5a and 5b
*
*
Compound
3a 2C6D6
*
3b C6H14
*
5a
5b
Formula
C
994.29
Triclinic
59H67Cl2N4Zr
C67H93Cl2N4Zr
1116.57
Triclinic
C27H35AlN2
414.55
Orthorhombic
Pbca
C34H49AlN2
512.73
Triclinic
Molecular weight
Crystal system
Space group
ꢀ
ꢀ
ꢀ
P1
P1
P1
˚
a (A)
10.620(1)
12.217(1)
20.789(2)
91.276(5)
97.303(6)
95.911(5)
2659.4(8)
2
0.15 · 0.12 · 0.10
Prism
Yellow
1.242
12.191(1)
13.561(2)
20.431(2)
106.085(5)
91.940(5)
91.558(5)
3241(1)
2
0.24 · 0.09 · 0.06
Needle-like
Yellow
1.144
193(2)
15.3010(12)
17.4760(13)
18.9130(17)
90.000(7)
90.000(7)
90.000(6)
5057.3(7)
8
0.42 · 0.35 · 0.23
Prism
Yellow
1.089
193(2)
10.9320(10)
12.0050(10)
13.4470(11)
75.446(7)
81.462(7)
70.393(7)
1605.1(2)
2
0.45 · 0.36 · 0.25
Prism
Colorless
1.061
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Crystal size (mm3)
Habit
Color
qcalc (g cmꢀ3
T (K)
)
193(2)
193(2)
h Range (ꢁ)
Reflections unique
1.68–25.84
10196
1.56–26.35
12821
1.33–26.03
4813
1.57–26.06
6076
Reflections observation (I > 2r(I))
Number of parameters
wR2 (all data)
6736
595
0.1381
3466
652
0.0918
2908
271
0.1537
3733
334
0.1113
R value (I > 2r(I))
0.0543
0.0414
0.0705
0.0507
of solvent separated cation–anion-pairs through smooth
methyl abstraction was also reflected by the small value
of Dd[(p-F)-(m-F)] of 2.4 ppm [9].
2.2. Olefin polymerization and formation of aluminum
aminopyridinates
Despite the fact that the difference in the aminopyridi-
nato ligands Ap and Ap* is quite small, the influence on
the polymerization activity of their complexes 3a and b if
activated with MAO was found to be huge. As shown in
Table 2 activated 3b polymerizes ethylene highly actively
[10] at elevated temperature. Ethylene consumption was
observed over the whole time period (15 min). Complex
3a was almost inactive after a few minutes under the same
conditions. To gain more insight into this different behav-
iour we studied the stability of 3a and 3b against d-MAO
(‘‘dry methylaluminoxane’’) in NMR tube experiments.
NMR tubes were charged with 10 lmol of dichloride 3a/b
in 0.5 ml of deutero-benzene before 25 equiv. of d-MAO
were added. While 3b reacts smoothly (50% in 24 h) with
MAO to form the corresponding methyl complex, com-
pound 3a shows a fast decomposition to insoluble products
and ligand transfer to aluminum (Scheme 5, Fig. 4). After
5 min an NMR detectable amount of [ApAlMe2] (5a) was
found. After 6 h 5a seems to be the only Ap containing
species present. To prove this observation we independently
synthesized the aminopyridinato containing dimethyl
aluminum complexes [ApAlMe2] (Scheme 6, 5a) and
[Ap*AlMe2] (5b), by reaction of the aminopyridines 1a–H
and 1b–H with TMA (trimethylaluminum) in toluene.
Removal of all volatiles under reduced pressure give the
spectroscopically pure products as colorless oils, which
Fig. 1. Molecular structures of 3a (left) and 3b (right). Selected bond
˚
lengths [A] and angles [ꢁ]: 3a Zr1 N3 2.123(3), Zr1 N1 2.145(3), Zr1 N4
2.348(3), Zr1 N2 2.355(3); N3 Zr1 N4 60.04(11), N1 Zr1 N2 59.44(11), Cl2
Zr1 Cl1 96.47(4); 3b N1 Zr1 2.154(4), N2 Zr1 2.358(4), N3 Zr1 2.184(4),
N4 Zr1 2.338(4); N3 Zr1 N4 59.40(14), N1 Zr1 N2 59.52(14), Cl1 Zr1 Cl2
123.08(6).
mechanism of the exchange process observed for 3a/b and
4a/b (Fig. 2). It is notable that reaction of 4b with tris(pen-
tafluorophenyl)borane give identical 1H and 13C NMR
spectra in bromobenzene except the resonances for the
dimethylaniline and the different anions. The formation

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W.P. Kretschmer et al. / Journal of Organometallic Chemistry 692 (2007) 4569–4579
X
N
N
X
N
N
Zr
N
N
Zr
N
X
X
N
N
N
X
N
Zr
Cl
Cl
Cl
Cl
Cl
Cl
X
N
Fig. 2. Proposed reaction mechanism for the dissociative inter-conversion.
a
b
8
7
6
5
4
3
2
1
ppm
1
Fig. 3. H NMR spectrum of [Ap*2ZrMe2] (a) (C6D6, 20 ꢁC) and after addition of 1 equiv. [PhNMe2H][B(C6F5)4] (b) (C6D5Br, 20 ꢁC).
Table 2
Temperature dependence of the ethylene polymerization catalyzed by 3a/b
(activation with MAO)a
R'
R'
R
N
N
R
N
R
N
R
pre-
T
Activator mPol Activity
Mw
Mw/
Mn
i, ii
R
N
R
N
+
cat. (ꢁC)
(g)
(kgPE molcatꢀ1 hꢀ1 barꢀ1) (g molꢀ1
)
Zr
Zr
R
C6D5Br
R
3a
3a
3b
3b
3b
3b
3bb
a
50 MAO
0.7
0.8
0.4
1.7
6.9
6.7
5.9
280
320
160
790000
675000
890800
835200
535500
392300
541500
35.3
14.6
15.1
3.1
2.0
2.2
N
N
R'
R'
80 MAO
30 MAO
50 MAO
80 MAO
100 MAO
50 MAO
[R"B(C6F5)3]-
680
2760
2680
2360
(R" = Me, C6F5)
4b (R = R' = i-Pr)
1.9
Scheme 4. Formation of the alkyl zirconium cations through reaction
with (i) B(C6F5)3 and (ii) [PhNMe2H][B(C6F5)4].
pre-cat.: 2 lmol, Zr/Al = 1/500, 260 ml toluene, pressure: 5 bar, t:
15 min.
b
Ten minutes of premixing of 3b with 250 equiv. of MAO in 2 ml of
toluene (over all Zr/Al = 1/500).
could be crystallized by very slow evaporation of hexane
solutions. The crystal structures are presented in Fig. 5.
Experimental details of the analyses can be found in
Table 1. Both structures are mononuclear involving a
strained g2 coordination of the Ap ligand. The Al–N bond
distances are quite similar and thus indicative of a binding
mode with a high degree delocalization of the anionic
function of the Ap ligands. g2 coordinated Ap aluminum
complexes are rare [5c,11,12]. The first compound of this
kind was published by Wang and coworkers [12].
The temperature dependence of the polymerization
activity of 3a/b if activated with MAO is shown in
Table 2. Complex 3b activated with MAO gives rise to a
highly active single site catalyst. No ligand redistribution
which can give rise to additional polymerization active
species seems to occur during the polymerization process
as can be seen from the narrow molecular weight

W.P. Kretschmer et al. / Journal of Organometallic Chemistry 692 (2007) 4569–4579
4573
R'
N
N
R
N
Cl
MAO
C6D6
R
N
R
N
Al
+
Zr
?
R
R
Cl
R
N
R'
R'
5a( R' =H,R=Me)
5b(R =R' = i-Pr)
3a( R'= H,R =Me )
3b(R =R' = i-Pr)
Scheme 5. MAO assisted aminopyridinato ligand transfer from Zr to Al.
distributions. The low activity at low temperature results
mainly from a very slow alkylation due to the poor acces-
sibility of the two chloro ligands (Fig. 1) which was also
reflected in the decrease of the induction periods with
increasing temperature. Induction periods (time between
injection of the pre-catalyst and start of the ethylene
uptake) of about 120 s at 30 ꢁC, 75 s at 50 ꢁC and 25 s at
80 ꢁC were observed. The slow alkylation, especially at
low temperatures, is also in accordance with the rather
broad polydispersity observed for the 30 ꢁC run in compar-
ison to the higher temperature runs. A possibility to over-
come the slow alkylation problem is the premixing of 3b
with an excess of MAO prior to injection (Table 2, entry
7). It is also notable that the catalyst system is very robust
at elevated temperatures since a very high activity is
observed even at 100 ꢁC as well. Ethylene consumption
for this run had been observed during the entire polymeri-
zation process (15 min) (Table 2, entry 6).
Since ligand transfer processes seems to interfere while
alkylation seems to be rate limiting, we became interested
in perfluoroarylborate activation protocols. The abstrac-
tion of one of the two methyl groups of 4a/b by ammonium
perfluorotetraphenylborate leads to highly active polymer-
ization catalyst systems. Again a notable difference was
found between the Ap and Ap* containing catalysts. In
contrast to the 3a/MAO catalyst system 4a (after activation
with ammonium perfluorotetraphenylborate) was found to
be highly active in the formation of long chain a-olefins
(Fig. 6) indicating a rather fast b-H-elimination/transfer.
Molecular weight distribution clearly shows the presence
of a single site catalyst, while no ligand transfer to scaven-
ger was observed. The more crowded pre-catalyst 4b [13]
instead gives high molecular weight polyethylene most
likely due to sterically disfavored direct b-H transfer
[14,15]. However, under the applied conditions only multi-
modal distributed polymers were found (Fig. 7). The GPC
data are also indicative of a rather narrowly distributed
main peak. The rapid precipitation of the polymers may
lead to a diffusion controlled process and thus to the broad
molecular weight distribution. This problem could be
addressed by a reduction of the catalyst concentration.
a
b
c
7
6
5
4
3
2
1
-0 ppm
Fig. 4. 1H NMR spectra (C6D6, 20 ꢁC) of [Ap2ZrCl2] + 25 equiv. d-MAO
(a) after 5 min and (b) after 6 h. (c) 1H NMR spectrum (C6D6, 20 ꢁC) of
[ApAlMe2].
N
H
N
toluene
- CH4
N
R
R
N
Al
+
R
R
Me3Al
R'
R'
5a (R' = H, R = Me)
5b (R = R' = i-Pr)
Scheme 6. Synthesis of 5a/b.

4574
W.P. Kretschmer et al. / Journal of Organometallic Chemistry 692 (2007) 4569–4579
˚
Fig. 5. Molecular structures of 5a (left) and 5b (right). Selected bond lengths (A) and angles (ꢁ): 5a Al1 N1 1.922(2), Al1 N2 1.959(2), Al1 C1 1.944(3), Al1
C2 1.954(3); N1 Al1 N2 68.87(10), C1 Al1 C2 120.69(16); 5b Al1 N1 1.9212(18), Al1 N2 1.9855(17), Al1 C1 1.941(2), Al11 C2 1.943(2); N1 Al1 N2
68.63(7), C1 Al1 C2 119.98(12).
7
6
5
4
3
2
1
ppm
Fig. 6. 1H NMR spectrum ( C2D2Cl4, 120 ꢁC) of PE (Table 3, entry 3).
*
Fig. 7. Molecular weight distribution (SEC) of the polymerization
experiments listed in Table 3, entry 6 and Table 4, entry 3.
Fig. 8. Molecular weight distribution (SEC) of the polymerization
experiments listed in Table 4.
Consequently, under a regime which avoids diffusion con-
trolled circumstances a ‘‘living’’ polymerization process
(Table 4, Fig. 8) is observed [16]. As long as the living
chains stay in solution very fast chain growing (for the first
seconds) was evidenced by a high ethylene consumption.
At some stage the polymer precipitates, ethylene consump-
tion drops down and we observe further chain growing of
the precipitated polymer. This part of the chain growing
process is shown in Table 4, Fig. 8.
The catalyst systems based on 3a/b (activation with
MAO) or 4a/b (borate activation) are not active towards
a-olefins (for instance propylene) [17]. Catalysts that poly-
merize ethylene and for which olefin insertion is blocked in
the presence of a-olefins are well documented. Such a
behaviour is observed for instance for lanthanide catalysts
[18]. A variety of transition metal complexes get into a dor-
mant state in the presence of a-olefins. Ethylene is able to
reactivate the catalyst which leads to specific insertion

W.P. Kretschmer et al. / Journal of Organometallic Chemistry 692 (2007) 4569–4579
4575
sequences [19]. Both mechanisms are not valid for the cat-
alysts systems described here as can be seen from experi-
ments in which the catalysts are exposed to a mixture of
ethylene and propylene (Table 3, entry 9 and 10). Even at
relatively high partial propylene pressure ethylene is poly-
merized selectively. NMR spectroscopy of the obtained
polymers revealed a propylene insertion of less than
1 mol%. Polymer data are quite similar if carried out in
the absence or presence of propylene (Table 3, entries 3
and 9). A highly selective polymerization of ethylene out
of an ethylene/propylene mixture seems to be possible.
Such a behaviour can result from steric or electronic char-
acteristics. If steric reasons dominate one could describe it
as shape selectivity as documented for micro porous mate-
rials like zeolites [20]. We concluded that the electronic sit-
uation at the metal centre caused by the Ap ligands is
dominating the responsibility for such a behaviour since
the selectivity is observed for 3/4a and b and not just for
the significantly higher crowded zirconium moieties
(Fig. 1). Steric reasons are most likely responsible for the
product selectivity – the selective formation of either a-ole-
fines (Ap2Zr alkyl cations) or saturated products attached
at the Zr centre in a living fashion or chain transferred to
Al if aluminum alkyls are present (in case of Ap*2Zr alkyl
cations).
3. Conclusions
Several conclusions can be drawn from this study. First,
the ligands used here namely Ap and Ap* are able to avoid
ligand redistribution to tris or tetrakis aminopyridinato zir-
conium complexes independent from the ‘‘remaining’’
ligands due to steric demand. Second, the zirconium com-
plexes are thermally robust, highly active and selective eth-
ylene polymerization catalysts. Out of a mixture of
ethylene and propylene, ethylene is polymerized highly
selectively. Third, slight changes in the steric demand of
the bulky ligand periphery can be used to tune the nature
of the formed polymers by maintaining the selectivity issue.
Fourth, Ap*2Zr alkyl cations can polymerize ethylene in a
living fashion even at 50 ꢁC.
4. Experimental
4.1. General aspects
All reactions were carried out under inert atmosphere
using standard glove box and Schlenk line techniques. The
solvents toluene, pentane, hexane, diethyl ether, and tetra-
hydrofurane were dried by refluxing over sodium/benzophe-
none. Benzene-d6 was dried over sodium/potassium alloy
and bromobenzene-d5 over molecular sieves. Toluene for
polymerization (Aldrich, anhydrous, 99.8%) was passed
over columns of Al2O3 (Fluka), BASF R3-11 supported
Table 3
Temperature dependence of the ethylene polymerization catalyzed by 4a/b
(activation with ammonium perfluorotetraphenylborate)a
pre-
cat.
T
mPol
Activity
Mw
(g molꢀ1
Mw/
Mn
(ꢁC) (g)
(kgPE molcatꢀ1 hꢀ1 barꢀ1
)
)
4a
4a
4a
4a
4b
4b
4b
4b
4ac
4bc
a
30
50
80
100
30
50
80
100
80
1.9
760
1960
4440
2800
1400
12070
10900
9670
2.3
2.1
1.9
˚
4.9
11.1
7.0
3.5
6.3
7.9
9.4
27.0
28.5
Cu oxygen scavenger and molecular sieves (Aldrich, 4 A).
Ethylene (AGA polymer grade) was passed over BASF
R3-11 supported Cu oxygen scavenger and molecular sieves
9000
2.0
1833000
1371000
1063000
1009000
8960
22.5b
29.8b
393.7b
176.7b
2.2
˚
(Aldrich, 4 A). N,N,N-Trialkylammonium(tetrapentafluor-
2520
3160
ophenyl)borate ([R2NMeH][B(C6F5)4], R = C16H33–C18-
ꢀ
3760
H37, 6.2 wt.% B(C6F5)4 in Isopar, DOW Chemicals),
54000d
57000d
trimethyl aluminum (TMA, 2.0 M in toluene, Aldrich),
TIBA (Witco), and polymethylaluminoxane ([MeAlO]n,
PMAO, 4.9 wt.% in Al, Akzo) were used as received.
Tetra-iso-butyl aluminoxane ([i-Bu2Al]2O, TIBAO) and
tetra(2-phenyl-1-propyl) aluminoxane ({[CH3CH(Ph)-
CH2]2Al}2O, TPPAO) were prepared according to published
procedure [21]. d-MAO was prepared by removal of all vol-
atile from PMAO (4.9 wt.% in Al, Akzo). The synthesis of
1a–H, 1b–H, 2a and 2b has been described previously [5a].
NMR spectra were recorded on a Varian Gemini 400
(1H: 400 MHz, 13C: 100.5 MHz) or Varian VXR-300
(1H: 300 MHz, 13C: 75.4 MHz) or a Bruker ARX 250
80
755700
113.1b
pre-cat.: 2 lmol, ammoniumborate: [R2N(CH3)H]+[B(C6F5)4]ꢀ
(R = C16H33–C18H37), Zr/B = 1/1.1, 4 and borate were mixed prior to the
injection, scavenger: TIBAO (tetra-iso-butyl-aluminoxane), Zr/Al = 1/50,
260 ml toluene, pressure: 5 bar, t: 15 min.
b
multimodal.
c
co-polymerization, pressure: 5 bar propylene, 15 bar total.
kgPE molcatꢀ1 hꢀ1
d
.
Table 4
Living ethylene polymerization at 50 ꢁC
Mw (g molꢀ1
)
Mw/Mn
ꢀ1
t (min)
mPol (g)
Activity (kgPE molcat
ꢀ1 barꢀ1
1
(1H: 250 MHz, 13C: 63 MHz) spectrometer. The H and
h
)
13C NMR spectra, measured at 25 ꢁC and 120 ꢁC, were
referenced internally using the residual solvent resonances,
and the chemical shifts (d) reported in ppm. The polymer
samples were prepared by dissolving 15 mg of the polymer
in 0.5 ml C2D2Cl4 at 100 ꢁC for 3 h before measuring.
Gel permeation chromatography (GPC) analysis was car-
ried out on a Polymer Laboratories Ltd. (PL-GPC210)
3
9
15
0.46
0.67
0.88
9200
4467
3520
1745000
1996000
2301000
1.26
1.33
1.30
4b:
200 nmol,
ammoniumborate:
[R2N(CH3)H]+[B(C6F5)4]ꢀ
(R = C16H33–C18H37), Zr/B = 1/1.1, 4b and borate were pre-mixed prior
the injection, scavenger: TPPAO {tetra-(2-phenyl-1-propyl)aluminoxane},
Zr/Al = 1/500, 260 ml toluene, pressure: 5 bar, T: 50 ꢁC.

4576
W.P. Kretschmer et al. / Journal of Organometallic Chemistry 692 (2007) 4569–4579
chromatograph, equipped with a capillary differential vis-
cometer (Viscotek), a refractive index (RI) detector and a
two-angle (15ꢁ and 90ꢁ) light scattering photometer at
150 ꢁC using 1,2,4-trichlorobenzene as the mobile phase.
The samples were prepared by dissolving the polymer
(0.1% weight/volume) in the mobile phase solvent in an
external oven and were run without filtration. The molec-
ture instead of the stock solution to start the reaction. The
catalyst mixture was prepared by successively adding 1 ml
of toluene and 1 ml of a 0.002 M catalyst stock solution
in toluene to 25 mg of [R2NMeH][B(C6F5)4] (R = C16-
H33–C18H37, 6.2 wt.% B(C6F5)4 in Isopar, Zr/B = 1/1.1).
After shaking for 1 min the mixture was injected, to start
the reaction.
ꢀ
ular
weight
was
referenced
to
polyethylene
Alternatively, 1 ml of a 0.05 M solution of TPPAO
(tetra(2-phenyl-1-propyl)aluminoxane, Zr/Al = 1/500) in
toluene instead of TIBAO and a catalyst mixture prepared
by successively adding 1 ml toluene and 100 ll of a 0.002 M
catalyst stock solution toluene to 2.5 mg of [R2NMeH]
(Mw = 50000 g/mol) and polystyrene (Mw = 100000–
500000 g/mole) standards. The reported values are the
average of at least two independent determinations. X-
ray crystal structure analysis was carried out at a STOE
IPDS II diffractometer equipped with an Oxford Cryo-
stream low temperature unit.
ꢀ
[B(C6F5)4] (R = C16H33–C18H37, 6.2 wt.% B(C6F5)4 in
Isopar, Zr/B = 1/1.1) were used.
4.4. Description of ethylene/propylene co-polymerization
experiments
4.2. General description of ethylene polymerization
experiments with MAO
The general procedure and conditions as described
above were followed, using successively 5 bar propylene
and 15 bar ethylene to pressurize the reactor.
The catalytic ethylene polymerization reactions were
performed in a stainless steel 1 L autoclave (Medimex)
in semi-batch mode (ethylene was added by replenishing
flow to keep the pressure constant). The reactor was tem-
perature and pressure controlled and equipped with sepa-
rated toluene, catalyst and co-catalyst injection systems
and a sample outlet for continuous reaction monitoring.
Up to 15 bar of ethylene pressure multiple injections of
the catalyst with a pneumatically operated catalyst injec-
tion system were used. During a polymerization run the
pressure, the ethylene flow, the inner and the outer reac-
tor temperature and the stirrer speed were monitored con-
4.5. Synthesis of the metal complexes
4.5.1. Synthesis of 3a
THF (40 ml) was added to [ZrCl4(THF)2] (0.38 g,
1.00 mmol) and 2a (0.80 g, 2.00 mmol), in a Schlenk vessel
and the mixture was stirred for 15 h. The solvent was
removed in vacuum and hexane (30 ml) was added. The
bright yellow reaction mixture was filtered and the filtrate
was allowed to stand at room temperature for 24 h to
afford yellow crystals. Yield: 0.52 g (54%). Elemental anal-
yses for C50H58Cl2N4Zr (877.15): C, 68.5; H, 6.7; N, 6.4.
Found: C, 68.1; H, 7.1; N, 6.4%.
tinuously. In
a typical semi-batch experiment, the
autoclave was evacuated and heated for 1 h at 125 ꢁC
prior to use. The reactor was then brought to desired tem-
perature, stirred at 600 rpm and charged with 230 ml of
toluene together with PMAO (550 mg of a toluene solu-
tion, 4.9 wt.% Al, 1 mmol), if not mentioned different in
the text. After pressurizing with ethylene to reach 5 bar
total pressure the autoclave was equilibrated for 5 min.
Subsequently 1 ml of a 0.002 M catalyst stock solution
in toluene was injected together with 30 ml of toluene,
to start the reaction. During the run the ethylene pressure
was kept constant to within 0.2 bar of the initial pressure
by replenishing flow. After 15 min reaction time the reac-
tor was vented and the residual aluminum alkyls were
destroyed by addition of 100 ml of ethanol. Polymeric
product was collected, stirred for 30 min in acidified eth-
anol and rinsed with ethanol and acetone on a glass frit.
The polymer was initially dried on air and subsequently in
vacuum at 80 ꢁC.
10
9
8
11
12
13
7
14
6
5
4
N
2
25
N
3
23
21
26
15
22
16
24
20
19
17
18
1
3a: H NMR: (250 MHz, C6D6, 298 K): d = 0.87–1.21
(m, 24H, H24,25,26,27), 2.09 (v br s, 12H, H13,14), 3.28 (br
m, 4H, H21,22), 5.52 (br d, 2H, H3), 5.87 (br d, 2H, H5),
6.67 (t, 2H, H4), 6.98–7.13 (m, 12H, H9,10,11,17,18,19). 13C
NMR (63 MHz, C6D6, 298 K): d = 20.50 (C13,14), 23.83
(C21,22), 28.72 (C23,24/25,26), 30.18 (C23,24/25,26), 103.73
(C3), 114.55 (C5), 124.19 (C9,11), 126.88 (C18/10), 127.78
(C17,19), 134.70 (C8/10), 135.88 (C8,12), 137.86 (C7), 141.85
(C4), 144.84 (C15), 148.03 (C16,20), 159.30 (C6), 159.90 (C2)
ppm.
4.3. Description of ethylene polymerization experiments with
ammonium borate activator
The general procedure and conditions as described above
were followed, using 1 ml of a 0.05 M solution of TIBAO
(tetra-iso-butyl-aluminoxan, Zr/Al = 1/50) in toluene
instead of PMAO to charge the reactor and a catalyst mix-

W.P. Kretschmer et al. / Journal of Organometallic Chemistry 692 (2007) 4569–4579
4577
4.5.2. Synthesis of 3b
analyses for C69H99N4Zr (1075.78): C, 77.0; H, 9.3; N,
5.2. Found: C, 77.1; H, 9.2; N, 5.2%.
This compound was obtained in the same way as 3a,
with 2b (0.99 g, 2.00 mmol) instead of 2a. Yield: 0.60 g
(56%). Elemental analyses for C64H86Cl2N4Zr (1073.52):
C, 71.6; H, 8.1; N, 5.2. Found: C, 71.4; H, 8.2; N, 4.7%.
4b: 1H NMR (250 MHz, C6D6, 298 K): d = 0.57
(s, 6H, CH3), 1.11(d, 24H, H24,25,26,27,28,29,30,31,32,33), 1.32
(d, 24H, H24,25,26,27,28,29,30,31,32,33), 2.80–3.06 (m, 10H,
H13,14,15,22,23), 5.38 (d, 2H, H3), 6.18 (d, 2H, H5), 6.65 (dd,
2H, H4), 7.11–7.19 (m, 10H, H9,11,18,19,20) ppm. 13C NMR
(63 MHz, C6D6, 298 K): d = 23.4 (C22,23), 24.4
(C28,29,32,33), 24.8 (C30,31), 26.6 (C13,14), 31.0 (C24,25,26,27),
34.9 (C15), 55.3 (2 CH3), 105.0 (C3), 114.3 (C5), 120.7
(C9,11), 124.6 (C18,20), 126.2 (C19), 134.8 (C4), 139.8 (C7),
143.5 (C8,12), 144.7 (C17,21), 146.8 (C10), 149.3 (C16), 155.8
(C6), 170.5 (C2) ppm.
15
31
30
10
7
9
8
11
12
13
32
28
14
6
33
29
5
4
N
2
N
16
26
4.5.5. Synthesis of 5a
3
24
22
23
A Schlenk vessel was charged with amino pyridine
ligand 1a–H (0.106 g, 0.3 mmol) in toluene (2 ml) before
trimethylaluminum solution (0.5 ml, 2.0 M Me3Al in
toluene, 1.0 mmol) was added. After stirring for 30 min
all volatile was removed, to yield the corresponding, spec-
troscopic pure [ApAlMe2] (based on 1H NMR) as colorless
oil in almost quantitative yield. For X-ray analysis of 5a
the residue was dissolved in 3 ml hexane. Slow evaporation
of the solvent over a period of 5 days leave colorless
crystals in quantitative yield. Elemental analyses for
C27H35AlN2 (414.6): C, 78.2; H, 8.5; N, 6.8. Found: C,
78.1; H, 8.6; N, 6.6%.
25
21
20
27
17
18
19
1
3b: H NMR (250 MHz, C6D6, 298 K): d = 0.99–1.37
(m, 60H, H24,25,26,27,28,29,30,31,32,33), 2.89–3.05 (m, 6H,
H13,14,15), 3.34 (sep, 4H, H22,23), 5.39 (d, 2H, H3), 6.27 (d,
2H, H5), 6.65 (dd, 2H, H4), 7.10–7.24 (m, 10H,
H9,11,18,19,20) ppm. 13C NMR (63 MHz, C6D6, 298 K):
d = 23.0 (C22,23), 24.5 (C28,29,30,31,32,33), 28.8 (C13,14), 31.2
(C24,25,26,27), 34.9 (C15), 105.5 (C3), 116.6 (C5), 120.8
(C9,11), 125.0 (C19), 127.2 (C18,20), 133.5 (C7), 140.3 (C4),
143.1 (C16), 145.1 (C8,12), 146.8 (C17,21), 149.4 (C10), 155.9
(C6), 169.1 (C2) ppm.
10
9
8
11
12
13
7
14
4.5.3. Synthesis of 4a
6
CH3Li (0.71 ml, 1.6 M, 1.13 mmol) was added slowly to
3a (0.44 g, 0.57 mmol) in hexane (20 ml) at ꢀ30 ꢁC. The
yellow reaction mixture was allowed to warm up to room
temperature and was stirred overnight as color turned into
brown. LiCl was filtered off and volume of the filtrate was
reduced in vacuum. Yellow crystals were obtained at room
temperature after standing for 24 h. Yield: 0.32 g (52%).
Elemental analyses for C52H64N4Zr (836.32): C, 74.7; H,
7.7; N, 6.7. Found: C, 74.0; H, 7.8; N, 6.4%.
5
4
N
2
25
N
15
3
23
21
26
22
16
24
20
19
17
18
1
1
4a: H NMR (250 MHz, C6D6, 298 K): d = 0.47 (s, 6H,
5a: H NMR (400 MHz, C6D6, 298 K): d = ꢀ0.35 (s,
CH3), 0.92 (br d, 12H, H23,24/25,26), 1.21 (d, 12H, H23,24/
25,26), 2.15 (s, 12H, H13,14), 3.29 (br m, 4H, H21,22), 5.39
(d, 2H, H3), 5.89 (d, 2H, H5), 6.67 (dd, 2H, H4), 7.00–7.16
(m, 12H, H9,10,11,17,18,19) ppm. 13C NMR (63 MHz, C6D6,
298 K): d = 20.48 (C13,14), 23.61 (C21,22), 28.80 (C23,24/
25,26), 28.67 (C23,24/25,26), 54.38 (2 CH3), 105.04 (C3),
112.20 (C5), 124.50 (C9,11), 126.10 (C18/10), 127.84 (C17,19),
135.89 (C18/10), 136.30 (C8,12), 139.10 (C7), 140.91 (C4),
143.24 (C15), 144.58 (C16,20), 155.88 (C6), 170.31 (C2) ppm.
6H, HAlMe2), 1.17 (d, 6H, J(H,H) = 6.6 Hz, H23ꢀ26), 1.21
3
(d, 6H, 3J(H,H) = 6.9 Hz, H23ꢀ26), 2.11 (s, 6H, H13,14),
3.48 (sept, 1H, 3J(H,H) = 6.9 Hz, H21,22), 5.58 (dd, 1H,
3J(H,H) = 8.8 Hz,4J(H,H) = 0.8 Hz, H3), 5.73 (dd, 1H,
3J(H,H) = 7.0 Hz,4J(H,H) = 0.8 Hz, H5), 6.80 (dd, 1H,
3J(H,H) = 8.8 Hz, 3J(H,H) = 7.0 Hz, H4), 6.91 (d, 2H,
3J(H,H) = 7.7 Hz, H9,11), 7.03 (t, 1H, 3J(H,H) = 7.7 Hz,
H10), 7.12–7.23 (m, 3H; H17ꢀ19). 13C NMR (100 MHz,
C6D6, 298 K): d = ꢀ10.2 (br, CAlMe2), 19.7 (s, C13,14),
24.2 (s, C23ꢀ26), 24.7 (s, C23ꢀ26), 28.5 (s, C21,22), 104.2 (s,
C3), 108.9 (s, C5), 124.2 (s, C17,19), 126.3 (s, C18), 127.6
(s, C9,11), 129.0 (s, C10), 135.8 (s, C8,12), 137.6 (s, C7),
138.2 (s, C15), 142.5 (s, C4), 145.8 (s, C16,20), 154.6 (s,
C6), 166.9 (s, C2) ppm.
4.5.4. Synthesis of 4b
This compound was obtained in the same way as 4a,
with CH3Li (0.98 ml, 1.6 M, 1.56 mmol) and 3b, (0.84 g,
0.78 mmol) instead of 3a. Yield: 0.49 g (61%). Elemental

4578
W.P. Kretschmer et al. / Journal of Organometallic Chemistry 692 (2007) 4569–4579
4.5.6. Synthesis of 5b
(CH(CH3)2,C-23), 23.1 (CH(CH3)2,C-28), 23.5 (CH(CH3)2,
C-29), 24.1 (CH(CH3)2, C-30), 24.8 (CH(CH3), C-31),
25.8 (CH(CH3)2,C-32,33), 26.2 (CH(CH3), C-13), 28.7
(CH(CH3)2,C-14), 31.1 (CH(CH3)2, C-26,27), 31.3
(CH(CH3)2, C-24,25), 34.7 (CH(CH3)2, C15), 54.0
(N(CH3)2), 73.3 (CH3), 107.1 (CH, C-3/5), 118.6 (CH, C-3/
5), 121.4 (CH, C-9,11), 122.8 (CH, C-18,20), 126.0
(B(C6F5)4), 126.2 (CH, C-19), 135.5 (B(C6F5)4), 136.7 (CH,
C-4), 138.9 (B(C6F5)4), 139.0 (C, C-7), 142.6 (C, C-8,12),
144.6(C, C-17,21), 146.5 (C, C-10), 148.0 (C, C-16), 150.6
(B(C6F5)4), 155.5 (C, C-6), 165.2 (C, C-2) ppm. 19F NMR
(C6D5Br, 298 K): d = 132.1 (o-F), 162.6 (p-F), 166.5 (m-F).
This compound was obtained in the same way as 5a,
with trimethylaluminum (0.2 ml, 2.0 M Me3Al in toluene,
0.4 mmol) and amino pyridine ligand 1b–H (0.046 g,
0.1 mmol) instead of 1a–H. Yield: quantitative. Elemental
analyses for C34H49AlN2 (512.8): C, 79.6; H, 9.6; N, 5.5.
Found: C, 79.4; H, 9.6; N, 5.4%.
15
31
30
10
7
9
8
11
12
13
32
28
(b) Reaction
with
tris(pentafluorophenyl)borane
14
6
(B(C6F5)3): A NMR tube was charged with 4b
(0.022 g, 20 lmol), deutero-benzene (0.5 ml) together
with B(C6F5)3 (0.012 g, 22 lmol) to give a red oil,
which was separated from the solvent and dissolved
in deutero-bromobenzene (0.5 ml) before measured.
33
29
5
4
N
2
N
16
26
3
24
22
23
25
21
20
27
17
18
1H NMR (250 MHz, C6D5Br, 298 K): d = 0.21 (s, 3H, CH3)
0.60-1.40 (m, 63H, CH(CH3)2, CH3B), 2.00–3.20 (m, 10H,
CH(CH3)2), 5.72 (d, 2H, H-3), 6.37 (d, 2H, H-5), 6.96 (dd,
2H, H-4), 7.00–7.20 (m, 10H, H-9,11, 18, 19, 20) ppm. 13C
NMR (C6D5Br, 298 K): d = 11.1 (br, CH3B(C6F5)3), 22.0
19
1
5b: H NMR (400 MHz, C6D6, 298 K): d = ꢀ0.24 (s,
6H, HAlMe2), 1.07 (d, 6H, J(H,H) = 6.6 Hz, H24ꢀ33), 1.14
3
(CH(CH3)2,C-22),
22.5
(CH(CH3)2,C-23),
23.1
(d, 6H, 3J(H,H) = 6.6 Hz, H24ꢀ33), 1.16 (d, 6H,
(CH(CH3)2,C-28), 23.5 (CH(CH3)2,C-29), 24.1 (CH(CH3)2,
C-30), 24.8 (CH(CH3), C-31), 25.8 (CH(CH3)2,C-32,33),
26.2 (CH(CH3), C-13), 28.7 (CH(CH3)2,C-14), 31.1
(CH(CH3)2, C-26,27), 31.3 (CH(CH3)2, C-24,25), 34.7
(CH(CH3)2, C15), 73.3 (CH3), 107.1 (CH, C-3/5), 118.6
(CH, C-3/5), 121.4 (CH, C-9,11), 122.8 (CH, C-18,20),
125.8 (CH3B(C6F5)3), 126.2 (CH, C-19), 135.7
(CH3B(C6F5)3), 136.7 (CH, C-4), 138.6 (CH3B(C6F5)3),
139.0 (C, C-7), 142.6 (C, C-8,12), 144.6(C, C-17,21), 146.5
(C, C-10), 148.0 (C, C-16), 150.1 (CH3B(C6F5)3), 155.5
(C, C-6), 165.2 (C, C-2) ppm. 19F NMR (C6D5Br, 298 K):
d = 132.2 (o-F), 164.9 (t, p-F), 167. 2 (m-F).
3J(H,H) = 6.6 Hz, H24ꢀ33), 1.21 (d, 6H, J(H,H) = 6.6 Hz,
3
H24ꢀ33), 1.39 (d, 6H, J(H,H) = 6.6 Hz, H28,29,32,33), 2.76
3
(sept, 1H, 3J(H,H) = 6.6 Hz, H15), 2.90 (sept, 2H,
3J(H,H) = 6.6 Hz, H13,14), 3.49 (sept, 2H, 3J(H,H) =
6.6 Hz, H22,23), 5.61 (d, 1H, J(H,H) = 8.8 Hz, H3), 6.02
3
(d, 1H, J(H,H) = 7.3 Hz, H5), 6.79 (dd, 1H, J(H,H) =
3
3
8.8 Hz, J(H,H) = 7.3 Hz, H4), 7.16 (br, 2 H, H18,20), 7.19
3
(br, 3H, H9,11,19). 13C NMR (100 MHz, C6D6, 298 K):
d = ꢀ9.6 (br, CAlMe2), 23.1 (C28,29,32,33), 24.1 (br,
C24ꢀ29,32,33), 24.2 (C24,25,26,27), 26.1 (C30,31), 28.5 (C22,23),
30.9 (C13,14), 34.7 (C15), 104.3 (C3), 111.1 (C5), 121.0
(C9,11), 124.2 (C18,20), 126.3 (C19), 133.1 (C7), 138.1 (C4),
141.6 (C17,21), 145.7 (C16), 146.9 (C8,12), 150.1 (C10),
154.9 (C6), 167.0 ppm (C2).
4.7. NMR tube reaction with d-MAO
4.6. Generation of the cationic zirconium alkyl complexes
(a) A NMR tube was charged with 3a (0.020 g, 20 lmol),
deutero-bromobenzene (0.5 ml) together with d-
MAO (0.029 g, 500 lmol). Afterwards the tube was
sealed, shaken for 5 min and measured.
(b) A NMR tube was charged with 3b (0.023 g, 20 lmol),
deutero-bromobenzene (0.5 ml) together with d-
MAO (0.029 g, 500 lmol). Afterwards the tube was
sealed, shaken for 5 min and measured.
(a) Reaction with N,N-dimethylanilinium-tetra(pentaflu-
orophenyl)borate([PhNMe2H][B(C6F5)4]): A NMR
tube was charged with 4b (0.022 g, 20 lmol), deu-
tero-bromobenzene
(0.5 ml)
together
with
[PhNMe2H][B(C6F5)4] (0.016 g, 20 lmol). Afterwards
the tube was sealed and shaken for 5 min to become a
clear solution before measured.
5. Supplementary material
1H NMR (250 MHz, C6D5Br, 298 K): d = 0.21 (s, 3H,
CH3) 0.60–1.40 (m, 63H, CH(CH3)2), 2.00–3.20 (m,
10H, CH(CH3)2), 2.60 (s, 6H, N(CH3)2), 5.72 (d, 2H, H-
3), 6.37 (d, 2H, H-5), 6.59 (d, 2H, PhN), 6.73 (t, 1H,
PhN), 7.00–7.20 (m, 13H, H-9,11, 18, 19, 20) ppm. 13C
NMR (C6D5Br, 298 K): d = 22.0 (CH(CH3)2,C-22), 22.5
CCDC 289175, 289174, 640085, and 640086 contain the
supplementary crystallographic data for 3a, 3b, 5a, and 5b.
These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road,

W.P. Kretschmer et al. / Journal of Organometallic Chemistry 692 (2007) 4569–4579
4579
(d) W.P. Kretschmer, A. Meetsma, B. Hessen, N.M. Scott, S.
Qayyum, R. Kempe, Z. Anorg. Allg. Chem. 632 (2006)
1936–1938.
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or
e-mail: deposit@ccdc.cam.ac.uk.
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Wenzel, Science 312 (2006) 714–719.
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