Investigating the nature of the active species in bis(imino)pyridine cobalt ethylene polymerization catalysts

Article abstract of DOI:10.1021/om900490b

The activation of bis(imino)pyridine cobalt-based catalysts of ethylene polymerization with methylalumoxane (MAO), AlMe₃, and AlMe ₃/[CPh₃][B(C₆F₅)₄] has been studied by ¹H,

Full text of DOI:10.1021/om900490b

Organometallics 2009, 28, 6003–6013 6003
DOI: 10.1021/om900490b
Investigating the Nature of the Active Species in Bis(imino)pyridine
Cobalt Ethylene Polymerization Catalysts
Igor E. Soshnikov,†,‡ Nina V. Semikolenova,† Alexey N. Bushmelev,†,‡
Konstantin P. Bryliakov,†,‡ Oleg Y. Lyakin,†,‡ Carl Redshaw,§ Vladimir A. Zakharov,† and
Evgenii P. Talsi*,†,‡
†Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, 630090, Novosibirsk,
§
Russian Federation, ‡Novosibirsk State University, 630090, Novosibirsk, Russian Federation, and School
of Chemistry, University of East Anglia, Norwich NR4 7TJ, U.K.
Received June 10, 2009
The activation of bis(imino)pyridine cobalt-based catalysts of ethylene polymerization with
1
2
methylalumoxane (MAO), AlMe3, and AlMe3/[CPh3][B(C6F5)4] has been studied by H, H, and
19F NMR and EPR spectroscopy. The nature of the active sites of polymerization is discussed. The
polymerization kinetics and the polymer properties for the different catalyst/activator systems were
correlated with spectroscopic data.
Introduction
ligand, and R=alkyl.1-38 NMR spectroscopic investigations
define the structures of iron species formed in the LFeIICl2/
MAO and LFeIICl2/AlMe3 systems.10,17,38 It was shown that
ion pairs [LFeII(μ-Me)2AlMe2]þ[Me-MAO]- predominate
In the past decade, there has been much interest in iron and
cobalt ethylene polymerization catalysts LMIICl2/MAO and
LMIICl2/AlR3, where M=Fe or Co, L=bis(imino)pyridine
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J. Organomet. Chem. 2005, 690, 1233–1239.
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*Corresponding author. Fax: þ7 383 3308056. E-mail: talsi@
catalysis.ru.
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2009 American Chemical Society
Published on Web 09/23/2009
pubs.acs.org/Organometallics

6004 Organometallics, Vol. 28, No. 20, 2009
Scheme 1. Structures of Cobalt Precatalysts Studied
Soshnikov et al.
in the LFeIICl2/MAO systems at [Al]/[Fe] > 500, whereas
activation of LFeIICl2 with AlMe3 leads to neutral species of
the type L(•-)Fe(þ)(μ-Me)2AlMe2 at [Al]/[Fe]>30, where the
FeII is coordinated to the anion radical of L.38
group was confirmed by 2H NMR spectroscopy, using
deuterated MAO.14 As was mentioned, complex 1 was
previously assigned to a neutral complex of the type
L
2MeCoIIMe(Cl)(MAO).14 However, the following data pro-
As for the LCoIICl2/MAO and LCoIICl2/AlMe3 analogues,
the structures of the intermediates formed in these systems are
more controversial. According to results of Gibson and Gal,
in the LCoIICl2/MAO system, initial cobalt(II) precatalyst
reduction to cobalt(I) halide is followed by conversion to a
cobalt(I) methyl and ultimately to a cobalt(I) cationic species.
Addition of ethylene affords an ethylene adduct [LCoI(η-
C2H4)]þ[Me-MAO]-, which is considered tobe the immediate
precursor to the active species.11,21,30 In contrast, our 1H and
2H NMR studies of the L2MeCoIICl2/MAO system (Scheme1)
showed that a cobalt(II) complex with proposed structure
vide evidence in favor of ionic structures for complexes 2, 20,
and 1.
AlMe3/[CPh3][B(C6F5)4] is a well known ion pair genera-
ting reagent. The 19F spectrum of 20 is typical for an outer-
sphere perfluoroaryl borate anion [B(C6F5)4]- (19F NMR,
-20 °C: δ -134.8 (Δν1/2=40 Hz), -155.0 (Δν1/2=430 Hz),
-165.1 (Δν1/2 = 120 Hz)).39,40 Hence, 20 is the ion pair
[L2iPrCoIIMe(S)]þ[B(C6F5)4]- (S=solvent or vacancy). This
assumption is in agreement with recent publications of
Macchioni and co-workers, demonstrating that for the
post-metallocene precatalysts even with the B(C6F5)3 acti-
vator outer-sphere ion pairs can be formed and that the
vacant coordination site can be substantially unoccupied or
involved in weak interaction with solvent.41,42
L
2MeCoIIMe(Cl)(MAO) (1) strongly predominates in the
reaction solution at 20 °C at least several hours after mixing
L
2MeCoIICl2 and MAO.14
In this paper, we describe 1H, 2H, and 19F NMR characteri-
The [B(C6F5)4]- counteranion of 20 is far from the per-
turbing paramagnetic center, and therefore its 19F chemical
shifts are close to those for diamagnetic ion pairs.
zation of cobalt(II) and cobalt(I) species formed inthe systems
LCoIICl2/MAO, LCoIICl2/AlMe3/[CPh3][B(C6F5)4], and
LCoIICl2/AlMe3, where L = L2iPr, L3Me, LtBu, and LCF3
(Scheme 1). Correlations between the structure of the obser-
ved cobalt species and the structure of the resulting poly-
ethylene are discussed.
Apparently, the related complex
2 is the ion pair
[L2iPrCoIIMe(S)]þ[Me-MAO]-. It is evident that the counter-
anion [Me-MAO]- is placed in the outer coordination
sphere of cobalt, since in the case of the direct contact of the
oligomeric molecule of [Me-MAO]- with cobalt (an
1
Results and Discussion
inner-sphere ion pair), extremely broad H resonances are
expected.43-45 The data presented show that complex 1
Activation of L2iPrCoIICl2 with MAO and AlMe3/[CPh3]-
1
[B(C6F5)4]. The H NMR spectra of the catalyst systems
2iPrCoIICl2/MAO ([Al]:[Co] = 100:1, [Co] = 5 ꢀ 10-3 M,
(39) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1991, 113,
3623.
(40) Yang, X.; Stern, C. L.; Marks, T. J. Organometallics 1991, 10,
840–842.
(41) Zuccaccia, C.; Macchioni, A.; Busico, V.; Cipullo, R.; Talarico,
G.; Alfano, F.; Boone, H. W.; Frazier, K. A.; Hustad, P. D.; Stevens,
J. C.; Vosejpka, P. C.; Abboud, K. A. J. Am. Chem. Soc. 2008, 130,
10354–10368.
(42) Ciancaleoni, G.; Fraldi, N.; Budzelaar, P. H. M.; Busico, V.;
Macchioni,A. Dalton Trans. 2009, available online.
(43) Babushkin, D. E.; Semikolenova, N. V.; Zakharov, V. A.; Talsi,
E. P. Macromol. Chem. Phys. 2000, 201, 558–567.
(44) Bryliakov, K. P.; Bochmann, M.; Talsi, E. P. Organometallics
2004, 23, 149–152.
L
toluene-d8) and L2iPrCoIICl2/AlMe3/[CPh3][B(C6F5)4] ([Al]:
[Co]:[B] = 10:1:2, [Co] = 10-2 M, toluene-d8), recorded at
various times after mixing the reagents at -30 to þ20 °C,
show that the starting cobalt complex L2iPrCoIICl2 quantita-
tively converts to cobalt(II) complexes [L2iPrCoIIMe(S)]þ-
[Me-MAO]- (2) and [L2iPrCoIIMe(S)]þ[B(C6F5)4]- (20),
respectively (S=solvent or vacancy). The 1H NMR spectra
of 2 and 20 are very similar (Figures 1a,b and Table 1). The
broad peak at ca. δ 150 in the 1H NMR spectra of 2 and 20
belongs to a Co-CH3 group. A similar resonance was pre-
viously observed for the related complex 1 formed in the
(45) Bryliakov, K. P.; Semikolenova, N. V.; Yudaev, D. V.; Zakharov,
V. A.; Brintzinger, H. H.; Ystenes, M.; Rytter, E.; Talsi, E. P.
J. Organomet. Chem. 2003, 683, 92–102.
L
2MeCoIICl2/MAO system. Its assignment to the Co-CH3

Article
Organometallics, Vol. 28, No. 20, 2009 6005
previouslyassigned toL2MeCoIIMe(Cl)(MAO) isin realitythe
ion pair [L2MeCoIIMe(S)]þ[Me-MAO]-.
It is worth noting that the structure of the ion pair
1H NMR spectra of this type were previously reported for
the ion pairs [L2iPrCoI(η-C2H4)]þ[MeB(C6F5)3]- (3C2H4
)
and [L2iPrCoI(η-N2)]þ[MeB(C6F5)3]- (3N2) (Table 1).21 The
19F spectrum of 30 is typical for the outer-sphere perfluor-
oaryl borate anion [B(C6F5)4]- (19F NMR, 20 °C: δ -130.2
(Δν1/2=30 Hz), -161.0 (Δν1/2=280 Hz), -164.1 (Δν1/2=120
Hz)).39,40 On the basis of their 1H and 19F NMR spectra, 3
and 30 can be assigned to the ion pairs [L2iPrCoI(S)]þ[Me-
MAO]- and [L2iPrCoI(S)]þ[B(C6F5)4]-, respectively.
The activation of L2iPrCoIICl2 with MAO and AlMe3/
[CPh3][B(C6F5)4] at 20 °C thus results in the quantita-
tive formation of the cobalt(II) ion pairs (2 and 20), which
slowly reduce to the ion pairs of cobalt(I) (3 and 30)
(Scheme 2).
[L2iPrCoIIMe(S)]þ[Me-MAO]- (2), formed in the L2iPr
-
CoIICl2/MAO system, differs from the structure of the ion
pair [L2iPrFeII(μ-Me)2AlMe2]þ[Me-MAO]- formed in the
L
2iPrFeIICl2/MAO analogue.38 In the first case, the vacant
coordination site of the cobalt is unoccupied or bound by
solvent (toluene), whereas in the second case this site is
occupied by AlMe3.
Complexes 2 and 20 are the major cobalt species in the
reaction solution even one day after mixing the reagents
at 20 °C. However, prolonged storing (several days) of
the samples L2iPrCoIICl2/MAO ([Al]:[Co] = 100:1, [Co] =
5
ꢀ
10-3 M, toluene-d8) and L2iPrCoIICl2/AlMe3/
Two weeks after the reaction onset at 20 °C, the sample
[CPh3][B(C6F5)4] ([Al]:[Co]:[B] = 10:1:2, [Co] = 10-2 M,
toluene-d8) at room temperature results in the gradual
decrease of the concentration of complexes 2 and 20 and
the growth of the concentration of diamagnetic cobalt(I)
complexes 3 and 30, respectively.
L
2iPrCoIICl2/MAO ([Al]:[Co] = 100:1, [Co] = 5 ꢀ 10-3 M,
toluene-d8) contains complexes 2 and 3 ([2]:[3] ≈ 1:1). Addi-
tion of ethylene to this sample ([Co]:[C2H4]=1:25, 20 °C)
1H NMR spectra of 3 and 30 (Figure 2, Table 1) display
sharp resonances of the L2iPr ligand in the range typical for
diamagnetic species.
Figure 1. 1H NMR spectra (20 °C) of the samples L2iPrCoIICl2/
MAO ([Al]:[Co] = 100:1, [Co] = 5 ꢀ 10-3 M, toluene-d8) (a)
and L2iPrCoIICl2/AlMe3/[CPh3][B(C6F5)4] ([Al]:[Co]:[B]=10:1:2,
[Co]=10-2 M, toluene-d8) (b), recorded 16 h after mixing the
reagents. The inset of the precatalyst is shown for convenience of
the line assignment.
Figure 2. 1H NMR spectra (20 °C) of the samples L2iPrCoIICl2/
MAO ([Al]:[Co]=100:1, [Co]=5ꢀ10-3 M, toluene-d8) 7 days
after storing at room temperature (a) and L2iPrCoIICl2/
AlMe3/[CPh3][B(C6F5)4] ([Al]:[Co]:[B]=10:1:2, [Co]=10-2 M,
toluene-d8) 7 days after storing at room temperature (b).
Table 1. 1H NMR Data for the Complexes Observed upon Activation of L2iPrCoIICl2 with MAO, AlMe3/[CPh3][B(C6F5)4], and AlMe3
(toluene-d8, 20 °C)
A
B
C
D
E
F
G
H
complex
Py-Hm Py-Hp Ar-Hm Me2CH Ar-Hp NdC(Me) Me2CH Me2CH Co-Me μ-Me
L2iPrCoIICl2
116.5
19.4
19.1
7.71
7.48
NA
7.5
49.4
45.9
44.3
8.35
7.92
8.1
9.7
8.1
7.55
8.00
10.19
9.54
10.0
NA
NA
NA
NA
NA
NA
NA
6.87
6.77
7.37
7.27
-17.8
-2.4
-2.2
1.20
1.15
NA
1.1
1.1
1.05
1.09
1.19
1.18
-8.8
12.4
12.3
NA
NA
NA
NA
NA
7.00
∼7.0
7.49
7.41
4.4
-19.0
-15.2
-14.6
1.03
0.91
0.8
0.6
0.8
0.98
0.76
0.62
1.06
-84.6
-41.5
-40.0
2.44
2.44
3.1
3.1
3.1
2.85
3.02
3.13
3.33
a
[L2iPrCoIIMe(S)]þ[Me-MAO]-
[L2iPrCoIIMe(S)]þ[B(C6F5)4]-
[L2iPrCoI(S)]þ[Me-MAO]-
2
-23.6
-23.3
-0.80
-0.81
-0.07
N/O
0.6
1.11
0.75
-1.14
0.05
∼152
∼143
20
3
30
4a
4b
5
[L2iPrCoI(S)]þ[B(C6F5)4]-
b
L
L
2iPrCoI(μ-Me)(μ-Cl)AlMe2
-1.6
-2.8
2iPrCoI(μ-Me)2AlMe2
b
[L2iPrCoI(η-C2H4)]þ[AlMe3Cl]-b
[L2iPrCoI(η-N2)]þ[MeB(C6F5)3]-c
NA
6.69
3N2
N/O
N/O
[L2iPrCoI(η-C2H4)]þ[MeB(C6F5)3]-c 3C2H4 ∼7.0
L
L
2iPrCoIMe c
2iPrCoICl c
7.86
6.91
N/O
a Solution in CH2Cl2. b Spectra recorded at -10 °C, only broad singlets in the each case. c The data are from ref 21. N/O, not observed. NA, not reliably
assigned.

6006 Organometallics, Vol. 28, No. 20, 2009
Soshnikov et al.
leads to ethylene polymerization, monitored by the decrease
of the ethylene peak at δ 5.2. In addition, the resonances of 2
disappear and only 3 is observed in the sample containing
ethylene. Hence, ethylene induces the rapid reduction of 2
into 3. Thus, in agreement with the previous assumption,11,21
the cobalt(I) species seems to be the active polymerizing
species in the catalyst systems LCoIICl2/MAO. However, the
quantitative conversion of cobalt(II) to cobalt(I) occurs only
in the presence of monomer.
neutral cobalt(I) species of the type L2iPrCoI(μ-Me)( μ-
Cl)AlMe2 and L2iPrCoI(μ-Me)2AlMe2 (Scheme 2).
Complexes 4a and 4b are unstable and rapidly (within
several minutes) decay at 20 °C via transfer of the L2iPr ligand
to aluminum to afford the paramagnetic complex
[L2iPr(•-)Al(þ)Me2], exhibiting an EPR signal at g = 2.003
(Figure 4). This complex was first discovered by Gambarotta
and co-workers.24 It is formulated as a complex of AlIII with
the anion radical of L2iPr(•-) and two Me anions. The EPR
spectrum of Figure 4 displays partially resolved multiline
hyperfine splitting (hfs) from Al, N, and H nuclei (inset). This
Activation of L2iPrCoIICl2 with AlMe3. In contrast to the
L
2iPrCoIICl2/MAO and L2iPrCoIICl2/AlMe3/[CPh3][B(C6F5)4]
systems, where cobalt(II) species predominate in the reaction
solution at least several hours after the reaction onset, the
activation of L2iPrCoIICl2 with AlMe3 ([Al]:[Co]=4:1, [Co]=
10-2 M, toluene-d8) leads to a very rapid and quantitative
reduction of the starting complex L2iPrCoIICl2 to two types of
diamagnetic complexes of cobalt(I), denoted as 4a and 4b
(Figure 3a, Table 1). On the basis of the previous studies of
Gibson and Gal,11,21 one can expect that complexes L2iPr-
CoIMe and/or L2iPrCoICl are formed in the L2iPrCoIICl2/
1
AlMe3 system. However, the H NNR spectra of 4a and 4b
differ from those of L2iPrCoIMe and L2iPrCoICl (Table 1). We
have proposed that 4a and 4b are adducts of the type L2iPrCoI-
(μ-Me)(μ-Cl)AlMe2 (4a) and L2iPrCoI(μ-Me)2AlMe2 (4b). In
agreement with this prediction, only 4b was observed in the
sample L2iPrCoCl2/AlMe3 with a [Al]:[Co] ratio of 50.
The 1H NMR spectrum of Figure 3a displays two low-field
resonances at δ -1.6 and -2.8. The sample containing only
4b exhibits only the one signal at δ -2.8. The latter signal can
be attributed to the μ-Me group of 4b, and the signal at δ
-1.6 to a μ-Me group of 4a. To support this assignment, the
2H NMR spectrum of the system L2iPrCoIICl2/Al(CD3)3
([Al]:[Co]=6:1, [Co]=2ꢀ10-2 M, toluene) was recorded.
This spectrum exhibits resonances at δ -1.7 and -3.0,
identical within accuracy of our measurements to those
Figure 3. 1H NMR spectra of the samples L2iPrCoIICl2/AlMe3
([Al]:[Co] = 4:1) (a) and L2iPrCoIICl2/AlMe3/C2H4 ([Al]:[Co]:
[C2H4]=10:1:50) (b) recorded 10 min after mixing the reagents
([Co]=10-2 M, toluene-d8, -20 °C). Sample in “b” 10 min after
additional storing at -10 °C (c).
1
observed in the H NMR spectrum. Thus, 4a and 4b are
Scheme 2. Interaction of L2iPrCoIICl2 with MAO, AlMe3/[CPh3][B(C6F5)4], and AlMe3

Article
Organometallics, Vol. 28, No. 20, 2009 6007
Figure 4. EPR spectrum (-196 °C) of the sample L2iPrCoIICl2/
AlMe3 ([Al]:[Co] = 4:1, toluene-d8, [Co] = 5ꢀ10-3 M) after
1 day storage at room temperature (asterisk marks signal of an
impurity in the sample tube).
Figure 5. 1H NMR spectra of the L3MeLCoIICl2/MAO
([Al]:[Co]=100:1, [Co]=6 ꢀ 10-3 M, toluene-d8) at -20 °C
(a) and at 20 °C (b). Asterisks mark still unidentified species,
probably outer-sphere ion pairs, containing a Co-Cl instead of a
Co-Me moiety.
splitting has been previously well resolved and interpreted
for the same aluminum complex formed upon reacting the
ligand, L2iPr, with AlMe3.24
Therefore, 7 is the outer-sphere ion pair [L3MeCoII(Me)(S)]þ-
[Me-MAO]-. Complex 6 displays a resonance at δ = 52.5
(6H), characteristic of the AlMe2 moiety in the heterobi-
nuclear ion pairs [LFeII(μ-Me)2AlMe2]þ[Me-MAO]-10
(Figure 5a and Table 2). Hence, 6 is the heterobinuclear
ion pair [L3MeCoII(μ-Me)2AlMe2]þ[Me-MAO]- (Scheme 3).
Thus, the nature of the substituents in the aryl rings of the
bis(imino)pyridine ligand can affect the tendency of the
[LCoIIMe]þ cation to bind the particular donor atom. For
the L2iPrCoIICl2/MAO system, the structure [L2iPrCoIIMe-
(S)]þ[Me-MAO]- (S=solvent or vacancy) is preferable at
The EPR spectrum of Figure 4 also displays a very broad
and intense resonance (ΔH1/2=1700 G) from the ferromag-
netic cobalt(0) species. Apparently, cobalt(I) compounds
reduce at 20 °C to metallic cobalt. The black cobalt(0)
residue was observed in the NMR tube upon storing the
L
2iPrCoIICl2/AlMe3 sample during 1 h at 20 °C.
Interestingly, complexes 4a and 4b predominate in the
sample L2iPrCoIICl2/AlMe3 only in the absence of monomer.
The 1H NMR spectrum of the sample L2iPrCoIICl2/AlMe3/
C2H4 ([Al]:[Co]:[C2H4]=10:1:50) recorded just after mixing
the reagents at -20 °C displays resonances of the new
complex 5 with chemical shifts close to those for the ion pair
[L2iPrCoI(η-C2H4)]þ[MeB(C6F5)3]- (3C2H4). The resonances
of 4a (4b) were also observed (Figure 3b, Table 1). On the
both low and high temperatures, whereas for the L3Me
-
CoIICl2/MAO analogue, the structure [L3MeCoIIMe(S)]þ-
[Me-MAO]- is preferable at high temperatures, and the
structure [L3MeCoII(μ-Me)2AlMe2]þ[Me-MAO]- at low
temperatures.
basis of the similarity of the 1H NMR spectra of 5 and 3C2H4
,
complex 5 can be assigned to the ion pair [L2iPrCoI(η-
C2H4)]þ[AlMe3Cl]- (Scheme 2). According to EPR spin-
trap studies, the Lewis acidity of AlEt2Cl is higher than that
of MAO.46 Therefore, the abstraction of methide anion by in
situ formed AlMe2Cl and formation of the ion pair 5 seem to
be plausible. The decrease of ethylene concentration in the
course of polymerization leads to the decrease in concentra-
tion of 5 and the growth in concentration of 4a (4b)
(Figure 3c).
In the system
L
3MeCoIICl2/AlMe3/[CPh3][B(C6F5)4]
([Al]:[Co]:[B]=10:1:1, [Co]=10-2 M, toluene-d8), the hetero-
binuclear ion pair [L3MeCoII(μ-Me)2AlMe2]þ[B(C6F5)4]-
(60) is the major species in the reaction solution at both
relatively low (-20 °C) and high (20 °C) temperatures
(Figure 6, Table 2). Probably [B(C6F5)4]- is a less bulky
counterion than [Me-MAO]- and favors coordination of
AlMe3 to the [L3MeCoIIMe]þ cation. The minor signals in
Figures 6(a, b) belong to the ion pair [L3MeCoIIMe(S)]þ-
[B(C6F5)4]- (70).
Activation of
L
3MeCoIICl2 with MAO, AlMe3/
1
[CPh3][B(C6F5)4], and AlMe3. The H NMR spectrum of
the catalyst system L3MeCoIICl2/MAO ([Al]:[Co] = 100:1,
[Co]=6ꢀ10-3 M, toluene-d8) recorded 5 min after mixing the
reagents at -20 °C displays resonances of two types of
cobalt(II) complexes (complexes 6 and 7, Figure 5a and
Table 2).
The ion pairs 6 (60) and 7 (70), similar to the ion pairs 2 and
20, reduce at 20 °C to the ion pairs of cobalt(I) (8 and 80,
Table 2). The following structures for these ion pairs can be
suggested: [L3MeCoI(S)]þ[Me-MAO]- (8) and [L3MeCoI-
(S)]þ[B(C6F5)4]- (80). Ion pairs 8 and 80 are stable at room
temperature.
Warming the sample to 20 °C leads to the disappearance of
complex 6, and only complex 7 is observed (Figure 5b). The
1H NMR spectrum of 7 resembles that of 2 (Tables 1 and 2).
The interaction of L3MeCoIICl2 with AlMe3 at -10 °C
leads to reduction of the cobalt(II) and the formation of two
complexes of cobalt(I). On the basis of their 1H NMR
spectra, they can be assigned to the neutral complexes
(46) Talsi, E. P.; Semikolenova, N. V.; Panchenko, V. N.; Sobolev,
A. P.; Babushkin, D. E.; Shubin, A. A.; Zakharov, V. A. J. Mol. Catal. A
1999, 139, 131–137.
L
3MeCoI(μ-Me)(μ-Cl)AlMe2 (9a) and L3MeCoI(μ-Me)2Al-
Me2 (9b). As in the case of the L2iPrCoIICl2/AlMe3 system,

6008 Organometallics, Vol. 28, No. 20, 2009
Soshnikov et al.
Table 2. 1H NMR Data for the Complexes Observed upon Activation of L3MeCoIICl2 with MAO, AlMe3/[CPh3][B(C6F5)4], and AlMe3
(toluene-d8)
A
B
C
D
E
F
complex
T, °C
Py-Hm
Py-Hp
Ar-Hm
Ar-Meo
Ar-Mep
NdC(Me)
Co-Me
AlMe2
L3MeCoIICl2a
þ20
-20
-20
-20
-20
þ20
-20
þ20
þ20
þ10
þ10
þ10
þ20
þ20
110.7
141.5
147.6
147.8
21.7
20.2
21.6
7.61
7.42
7.5
36.3
49.3
37.5
36.3
52.0
46.4
50.4
8.19
7.89
12.2
12.6
8.35
10.08
9.49
6.5
6.5
-26.5
-38.1
-7.9
-8.1
-26.3
-22.5
-25.5
1.88
1.80
1.52
1.41
1.57
17.0
21.5
43.4
43.4
NA
NA
NA
1.86
1.76
2.43
2.43
2.03
2.28
2.18
-0.5
a
L
3MeCoIICl2
-0.5
[L3MeCoII(μ-Me)2AlMe2]þ[Me-MAO]-
[L3MeCoII(μ-Me)2AlMe2]þ[B(C6F5)4]-
[L3MeCoIIMe(S)]þ[Me-MAO]-
6
34.4
35.3
NA
NA
NA
6.71
6.66
6.78
6.82
6.54
6.99
6.93
-5.6
-3.9
N/O
55.2
57.2
60
7
N/O
-31.7
-24.9
-30.6
-0.71
-0.72
-1.64
-1.85
0.36
N/O b
N/O b
N/O
[L3MeCoIIMe(S)]þ[B(C6F5)4]-
[L3MeCoI(S)]þ[Me-MAO]-
[L3MeCoI(S)]þ[B(C6F5)4]-
70
8
80
9a
9b
10
L
L
3MeCoI(μ-Me)(μ-Cl)AlMe2
3MeCoI(μ-Me)2AlMe2
N/O
N/O
N/O
N/O
7.6
7.2
7.88
6.90
[L3MeCoI(η-C2H4)]þ[AlMe3Cl]-
L
L
3MeCoIMe c
3MeCoICl c
1.93
2.19
-1.21
-0.06
0.46
a Solution in CH2Cl2. b A broad singlet (δ ≈ 171, Δν1/2 ≈ 600 Hz) was observed at 0 °C after prolonged 1H NMR spectrum accumulation. c The data
are from ref 21. N/O, not observed. NA, not reliably assigned.
Scheme 3. Interaction of L3MeCoIICl2 with MAO, AlMe3/[CPh3][B(C6F5)4], and AlMe3
in the presence of ethylene, the formation of the new
complex 10, with proposed structure [L3MeCoI(η-C2H4)]þ-
[AlMe3Cl]-, is observed (Table 2, Scheme 3).
attributed to the ion pair [LtBuCoI(η-C2H4)]þ[AlMe3Cl]-
(Table 3).
Activation of LCF3CoCl2 with MAO, AlMe3/[CPh3][B(C6F5)4],
and AlMe3. The 1H NMR spectra of the system LCF3CoIICl2/
MAO show that the ion pair [LCF3CoII(μ-Me)2AlMe2]þ[Me-
MAO]- (15) is formed at the initial stage of activation at low
temperatures (Figure 7a, Table 4). In contrast to the MAO-
based systems considered above, the heterobinuclear ion pair
15 does not convert to an ion pair of the type
[LCoIIMe(S)]þ[Me-MAO]- at room temperature. The half-
Activation of LtBuCoIICl2 with MAO, AlMe3/[CPh3]-
[B(C6F5)4], and AlMe3. Complexes observed in the systems
L
tBuCoIICl2/MAO and LtBuCoIICl2/AlMe3/[CPh3][B(C6F5)4]
are similar to those observed in the systems L3Me
-
CoIICl2/MAO and L3MeCoIICl2/AlMe3/[CPh3][B(C6F5)4].
Their structures are presented in Scheme 4, and the parameters
of their 1H NMR spectra are collected in Table 3.
Activation of LtBuCoIICl2 with AlMe3 affords diamag-
life of 15 amounts to 1 h at 20 °C. Thus, in the case of L=LCF3
,
1
netic complexes of cobalt(I), the H NMR resonances of
coordination of AlMe3 to the cation [LCoIIMe]þ is more
favorable than in the case of L=L2iPr, L3Me, and LtBu. Such
precatalysts activated with MAO display only the resonances
of the ion pairs [LCoIIMe(S)]þ[Me-MAO]- at 20 °C.
which are broadened and less well resolved than in the
case of L2iPrCoIICl2 and L3MeCoIICl2 precatalysts. This
precludes their assignment; however, addition of ethylene
to the sample LtBuCoIICl2/AlMe3 results in the formation
of complex 14 with well-resolved signals, which can be
Cobalt(II) species formed in the LCF3CoIICl2/MAO sys-
tem reduce with time into their cobalt(I) counterparts.

Article
Organometallics, Vol. 28, No. 20, 2009 6009
1
However, the assignment of their H NMR resonances is
complicated by line broadening caused by rapid reduction of
the monovalent cobalt to ferromagnetic cobalt(0). Thus,
cobalt(I) species formed in the LCF3CoIICl2/MAO system
are less stable to degradation than those formed in the case of
the L=L2iPr, L3Me, and LtBu analogues.
Figure 6. 1H NMR spectra of the L3MeCoIICl2/AlMe3/[CPh3]-
[B(C6F5)4] system ([Al]:[Co]:[B]=10:1:1, [Co]=10-2 M, toluene-
d8) at -20 °C (a) and at 20 °C (b). Asterisks mark still unidenti-
fied signals.
Figure 7. 1H NMR spectra (-40 °C) of the samples LCF3CoIICl2/
MAO ([Al]:[Co] = 100:1, [Co] = 5 ꢀ 10-3 M, toluene-d8) (a)
and LCF3CoIICl2/AlMe3/[CPh3][B(C6F5)4] ([Al]:[Co]:[B]=10:1:2,
[Co] = 10-2 M, toluene-d8) (b) 30 min after storing at -40 °C.
Scheme 4. Structures of the Cobalt Species Formed upon Activation of LtBuCoIICl2 with MAO, AlMe3/[CPh3][B(C6F5)4], and AlMe3/
C2H4
Table 3. 1H NMR Data for the Complexes Observed upon LtBuCoIICl2 Activation with MAO, AlMe3, and AlMe3/[CPh3][B(C6F5)4]
(toluene-d8)
A
B
C
D
E
F
G
H
complex
T, °C Py-Hm Py-Hp Ar-H C(CH3)3 Ar-H NdC(Me) Ar-H Ar-H Co-Me AlMe2
[LtBuCoII(μ-Me)2AlMe2]þ[Me-MAO]- 11 -20
138.6
44.1
30.7
-35.8
-14.7
-12.7
-36.4
-28.7
-13.2
-6.0 -10.1
29.8
NA
NA
29.7
25.6
NA
7.23
NA
NA
NA
NA
NA
NA
NA
6.63
NA
N/O
N/O
∼139
N/O
N/O
N/O
48.3
[LtBuCoIIMe(S)]þ[Me-MAO]-
12 -20
þ20
∼17.6 ∼51.4 NA
NA
NA
-32.8
-26.5
16.5
140.2
118.3
16.5
7.64
7.21
44.6
44.6
37.7
44.3
8.27
8.03
NA
31.0
26.9
NA
NA
NA
[LtBuCoII(μ-Me)2AlMe2]þ[B(C6F5)4]-
110 -20
þ20
-6.3 -10.6
-4.8 -8.2
48.9
40.9
[LtBuCoIIMe(S)]þ[B(C6F5)4]-
[LtBuCoI(S)]þ[Me-MAO]-
120 þ20
13 þ20
14 -30
NA
-26.2
-0.70
0.85
1.17/1.14 NA
0.79 NA
[LtBuCoI(η-C2H4)]þ[AlMe3Cl]-a
a The signal of η-C2H4 at δ 4.82 was observed. N/O, not observed. NA, not reliably assigned.

6010 Organometallics, Vol. 28, No. 20, 2009
Soshnikov et al.
Table 4. 1H NMR Data for the Complexes Observed upon Activation of LCF3CoIICl2 with MAO and AlMe3/[CPh3][B(C6F5)4] (toluene-d8)
A
B
C
D
E
F
G
complex
T, °C
Py-Hm
Py-Hp
NdC(Me)
Ar-Hm
Ar-Hm
Ar-H
Ar-H
AlMe2
LCF3CoIICl2
-40
þ20
-40
þ20
-40
158.3
113.8
156.7
114.9
150.3
67.9
47.1
45.8
37.4
43.6
13.6
9.3
-16.1
-8.4
-15.6
17.8
14.4
37.0
24.7
35.8
-4.5;
-4.0
31.0
23.8
29.5
-16.4;
-10.3
-6.3
NA
NA
NA
10.3
NA
a
[LCF3CoII(μ-Me)2AlMe2]þ[Me-MAO]-
[LCF3CoII(μ-Me)2AlMe2]þ[B(C6F5)4]-
15
58.5
38.8
56.7
-5.9
150
-6.2
a Solution in CDCl3. N/O, not observed. NA, not reliably assigned.
Table 5. Ethylene Polymerization Data for LCoIICl2 Complexes with Different Activatorsa
content per PE molecule d
-CH3 -CHdCH2
0.8 1.0
run
complex
activator
MAO
yield b
initial activity c
Mw ꢀ 10-3
18
18
Mw/Mn
1
2
3
4
5
6
7
8
L2iPrCoCl2
1250
750
980
170
140
110
550
300
235
175
480
370
620
430
80
2.0
2.0
2.0
1.8
1.9
2.6
1.7
2.5
3.9
AlMe3
AlMe3/”B” e
MAO
0.8
0.9
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
18
L
3MeCoCl2
5880
2400
1920
1210
4500
2100
2700 f
1600 f
3100
3600
1.7
1.7
1.4
1.2
330
420
MAO (20)
AlMe3
AlMe3/”B”
MAO
AlMe3
L
tBuCoCl2
9
10
11
12 g
13 g
L
CF3CoCl2
MAO
AlMe3
L2MeCoCl2
MAO
AlMe3
1.5
1.6
1.8
1.8
1.0
1.0
1.0
1.0
60
a Polymerization in toluene at 40 °C, ethylene pressure 5 bar (runs 4 and 8, 2 bar), for 30 min, [Co] = 1.4 ꢀ 10-5 M, [Al]:[Co] = 500:1. b kg
PE mol(Co)-1 bar-1 c Initial activity, calculated from the PE yield for 2 min of polymerization, in kg PE mol(Co)-1 bar-1 min-1 d IR spectroscopy
. .
3
3
3
3
3
data (for runs 4-7 13C NMR data). e “B” = [CPh3][B(C6F5)4] (molar ratio [Co]:[Al]:[B] = 1:100:1). f Liquid oligomers were obtained. g Data of ref 47.
The 1H NMR spectrum of the catalyst system
L
CF3CoIICl2/AlMe3/[CPh3][B(C6F5)4] recorded 30 min after
reaction onset at -40 °C is similar to that observed for the
system LCF3CoIICl2/MAO at this temperature and belongs
to the ion pair [LCF3CoII(μ-Me)2AlMe2]þ[B(C6F5)4]- (150)
(Figure 7b, Table 4). This ion pair decays with the half-life of
40 min at 0 °C. The decay is accompanied by the broadening
of NMR peaks due to the appearance of cobalt(0) species.
Hence, the cobalt species formed in the system LCF3CoIICl2/
AlMe3/[CPh3][B(C6F5)4] are more prone to reduction
than their analogues formed in other LCoIICl2/AlMe3/
[CPh3][B(C6F5)4] systems studied. The attempts to identify
cobalt(I) species formed in the systems based on L=LCF3
were unsuccessful due to the line broadening. Any attempts
to study these systems by 19F NMR were unsuccessful.
Correlation of Polymerization and NMR Spectroscopic
Data. Data on the catalyst activity for ethylene polymeriza-
tion by LCoIICl2 (L = L2iPr, LtBu, L3Me) complexes with
different activators and the characteristics of the obtained
PE samples are collected in Table 5 and Figures 8-11. Like
most homogeneous catalysts, the studied systems demon-
strate high initial activity that decreases with the increase in
polymerization time (Figures 8 and 9). It is possible to
distinguish two sections on the kinetic curves: a very sharp
drop of the polymerization rate in the first minute of
polymerization time and a much more gradual decrease with
further duration of the reaction that leads to high yield of the
PE in prolonged (30 min) polymerization runs. The value of
the initial activity (Table 5) and the deactivation rate depend
on the cobalt complex composition (Figure 8). The activator
nature weakly affects the shape of the kinetic curve for
polymerization over the studied catalysts (Figure 9).
Figure 8. Rate of the ethylene polymerization vs time for
L2iPrCoIICl2 (a), L3MeCoIICl2 (b), and LtBuCoIICl2 (c), activated
with MAO (runs 1, 4, and 8 in Table 5).
and one -CHdCH2 group per one PE molecule. The mole-
cular mass of the PE samples obtained with LCoIICl2 depends
on the composition of bis(imino)pyridine ligand: with the
increase of the steric bulk of a substituent at the ortho-aryl
position the MM of the produced PE also increases (Table 5).
The obtained PE samples are characterized with rather
narrow molecular mass distribution (Mw/Mn was close to 2),
depending on the composition of the cobalt complex, the
activator nature, and the polymerization conditions.
Similar results were obtained for earlier14,47 studied cata-
lyst systems, based on LCoIICl2 (L=L2Me). The molecular
structure of the isolated polymers (Table 5, runs 12 and 13)
was close to those obtained with the catalysts based on the
The catalyst systems based on LCoIICl2 (L = L2iPr, LtBu
3Me) produce highly linear PE containing about one -CH3
,
L
3MeCoIICl2 complex (Table 5, runs 4 and 6).
L

Article
Organometallics, Vol. 28, No. 20, 2009 6011
L2MeCoIICl2/MAO were determined.48 It was found that
the Cp value decreases by a factor of 1.6 (from 0.23 to
0.14 mol/mol(Co)) with the increase of the polymerization
time from 5 to 15 min, whereas the values of the propagation
rate constant (kp) were almost independent on the reaction
time. Analysis of the obtained data on the Cp and kp values
and the molecular mass characteristics of the resulted poly-
mers drew the authors of ref 48 to conclude that the catalyst
system L2MeCoIICl2/MAO contains only one type of active
center and the reason for its deactivation with the increase of
the polymerization time is the reduction of the number of
active centers. Similar data on the catalyst behavior of
L
2MeCoIICl2 and L3MeCoIICl2 activated with MAO makes
it possible to assume that similar active centers are formed in
these catalyst systems.
Comparison of NMR and polymerization data obtained
for the catalyst systems based on LCoIICl2 (L=L2iPr, LtBu
L
,
3Me) can provide information about the active centers of
these systems.
Figure 9. Rate of the ethylene polymerization vs time for
L2iPrCoIICl2, activated with MAO (a), AlMe3 (b), and AlMe3/
“B” (c) (runs 1, 2, and 3 in Table 5).
According to the assumption of Gibson et al.,21 the only
active species (or their immediate precursors) of the catalyst
system
L
2iPrCoIICl2/MAO is the cobalt(I) ion pair
[L2iPrCoI(η-C2H4)]þ[Me-MAO]-. Our NMR studies show
that at high [Al]/[Co] ratios (g100) two types of cobalt
species are present in the system LiPrCoIICl2/MAO: an ion
pair of cobalt(II) (2) and an ion pair of cobalt(I) (3)
(Scheme 2). However, in the presence of monomer, complex
2 rapidly converts into 3 ([L2iPrCoI(S)]þ[Me-MAO]-), and,
probably, only cobalt species of the type 3C2H4 ([L2iPrCoI(η-
C2H4)]þ[Me-MAO]-) exist in the system L2iPrCoIICl2/
MAO/C2H4 in conditions approaching real polymerization.
This result is in agreement with the MWD data for the PE
produced by the catalyst system L2iPrCoIICl2/MAO, which
is typical for single-site catalysts (Mw/Mn = 2.0) (Table 5,
run 1).
The polymerization activity of L2iPrCoIICl2/AlMe3 and
the resulting PE MWD value are very similar to that found
for the L2iPrCoIICl2/MAO system (Table 5, run 2). As it was
shown above, in the presence of ethylene, complexes of
cobalt(I) of the type [L2iPrCoI(η-C2H4)]þ[AlMe3Cl]- (5)
were detected in the catalyst system L2iPrCoIICl2/AlMe3.
These complexes can be regarded as the immediate precur-
sors of the polymerization active species formed in this
system. Thus, the active species (or their precursors) of the
Figure 10. GPC curves for PEs prepared with L3Me CoIICl2,
activated with MAO (a) and AlMe3 (b) (runs 4 and 6 in Table 5).
L
2iPrCoIICl2/MAO and L2iPrCoCl2/AlMe3 systems are simi-
lar (ion pairs of cobalt(I), 3C2H4 and 5, respectively), differing
only in the nature of counteranion. Polymerization activity
of the catalyst system L2iPrCoIICl2/AlMe3/[CPh3][B(C6F5)4]
was close to those of the L2iPrCoIICl2/MAO, and the ob-
tained polymers were characterized by their identical GPC
curves and MWD values (Table 5, runs 1 and 3). These
results evidence that the nature of the counteranion has little
effect on the catalyst properties of the cobalt complex.
Hence, the initially different complexes of cobalt formed in
the L2iPrCoIICl2/MAO and L2iPrCoIICl2/AlMe3 systems
convert upon interaction with ethylene into the similar active
site precursors 3 (3C2H4) and 5. This explains the close
activities of the L2iPrCoIICl2/MAO and L2iPrCoIICl2/AlMe3
Figure 11. GPC curves for PEs prepared with LtBuCoIICl2,
activated with MAO (a) and AlMe3 (b) (runs 8 and 9 in Table 5).
(47) Semikolenova, N. V.; Zakharov, V. A.; Echevskaja, L. G.;
Matsko, M. A.; Bryliakov, K. P.; Talsi, E. P. Catal. Today 2009, 144,
334–340.
(48) Barabanov, A. A.; Semikolenova, N. V.; Bukatov, G. D.;
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The polymerization rate for the catalyst systems L2Me
-
CoIICl2/MAO and L2MeCoIICl2/AlMe3 was unstable. The
Cp (active centers concentration) and kp (propagation
rate constant) values for polymerization over the system

6012 Organometallics, Vol. 28, No. 20, 2009
Soshnikov et al.
systems and formation of the polymers with the same Mw
and MWD values.
Polymerization activity of the catalyst systems based on
([A]-=[Me-MAO]- or [B(C6F5)4]-; S=toluene or vacancy),
whereas neutral complexes LCoI(μ-Me)(μ-Cl)AlMe2 and
LCoI(μ-Me)2AlMe2 predominate in the catalyst systems
LCoIICl2/AlMe3. Addition of monomer (C2H4) plays the
key role in formation of the direct precursors of the poly-
merization active centers of the catalyst systems based on
LCoIICl2. In the case of the LCoIICl2/MAO systems, addition
of ethylene results in rapid reduction of cobalt(II) to cobalt(I),
and only the ion pairs of the type [LCoI(S)]þ[A]- are present
in the reaction solution at 20 °C. In the case of the LCoIICl2/
AlMe3 systems, in the presence of ethylene an ion pair with
proposed structure [LCoI(η-C2H4)]þ[AlMe3Cl]- is the major
cobalt species in the reaction solution. Similar intermediates
(ion pairs of cobalt(I)) are present in the systems LCoIICl2/
MAO/C2H4 and LCoIICl2/AlMe3/C2H4. The results obtained
can explain the close polymerization results (similar activity
and PE structure) obtained with the catalyst systems based on
LCoIICl2 complexes activated with MAO and AlMe3.
L
3MeCoIICl2 was noticeably higher than that of the systems
obtained with complex L2iPrCoIICl2 (Table 5, runs 4-7). The
PE samples obtained with L3MeCoIICl2 activated with MAO,
MAO with a reduced content of AlMe3 (MAO (20)), and
AlMe3/[CPh3][B(C6F5)4] are characterized by low MW.
Narrow MWD (Mw/Mn close to 2) of the studied polymers
is characteristic for single-site catalysts. The MWD of the PE
produced with the L3MeCoIICl2/AlMe3 catalyst system was
slightly broadened (Mw/Mn=2.6, Table 5, run 6). Figure 10
shows the presence of a low molecular mass PE fraction,
whereas the position of the peak, corresponding to the main
polymer fraction, is close to that of the PE produced with
MAO and AlMe3/[CPh3][B(C6F5)4] activators. Formation
of the low molecular mass PE is not clear, and, possibly, it
can be attributed to some fluctuations in the course of the
polymerization run or more facile transmetalation in the case
of TMA than MAO. Nevertheless, it is possible to conclude
that upon activation of L3MeCoIICl2 with MAO and AlMe3,
similar cobalt(I) species [L3MeCoI(η-C2H4)]þ[Me-MAO]-
(8C2H4) and [L3MeCoI(η-C2H4)]þ[AlMe3Cl]- (10) dominate
in the reaction solution, determining formation of PE with
close molecular structure.
Experimental Section
General Experimental Details. Toluene was dried over mole-
˚
cular sieves (4 A), purified by refluxing over sodium metal, and
distilled under dry argon. Toluene-d8 was dried over molecular
˚
sieves (4 A), degassed in vacuo, and stored under dry argon. All
experiments were carried out in sealed high-vacuum systems
using break-seal techniques. LCoIICl2 (L=L3Me, L2iPr, LtBu, and
L
tBuCoIICl2/MAO and LtBuCoIICl2/AlMe3 systems pro-
LCF3 6,20
were synthesized as described. Trimethylaluminum
)
duce PE with noticeably higher MW (Mw=(3.3-4.2) ꢀ 105,
Table 5, runs 8 and 9) due to the presence of a bulky t-Bu
substituent in the bis(imino)pyridyl ligand, hindering the
chain transfer reactions. Figure 11 shows that the positions
of a peak corresponding to the main polymer fraction of PEs
produced with LtBuCoIICl2/MAO and LtBuCoIICl2/AlMe3
are close. The moderate increase in the polydispersity value
can be attributed to the formation of a small amount of high
molecular mass PE. Both catalysts have close values of the
initial activities and produce PE in similar yields. These data
suggest that the close catalyst properties of the LtBuCoIICl2/
MAO and LtBuCoIICl2/AlMe3 systems are determined by
close composition of the direct precursors of the active
centers (cobalt(I) species denoted as 13 (13C2H4) and 14
(Scheme 4)), as was shown above for the catalyst systems
LCoIICl2/MAO and LCoIICl2/AlMe3 (L=L2iPr and L3Me).
In contrast to the catalysts described, the systems formed
by activation of LCF3CoIICl2 with MAO and AlMe3 proved
to be highly active catalyst for ethylene oligomerization
(Table 5, runs 10 and 11). These catalysts demonstrated high
initial activity that drops with time more sharply than in the
(AlMe3) and [CPh3][B(C6F5)4] were purchased from Aldrich.
Methylaluminoxane (MAO) was obtained from Crompton
GmbH (Bergkamen) as a toluene solution (total Al concentra-
tion 1.8 M, Al as AlMe3 0.5 M). For the purposes of this paper,
MAO (or MAO(20)) with total Al content of 40 wt % and 10
mol % of Al as AlMe3 was obtained as a solid product by solvent
removal in vacuo at 20 °C from commercial MAO. 1H and 19
F
NMR spectra were recorded at 250.130 and 62.89 MHz, on a
2
Bruker DPX-250 MHz NMR spectrometer. For the H NMR
spectra, a Bruker Avance-400 MHz NMR spectrometer was
used. EPR spectra were measured on a Bruker ER-200D
spectrometer at 9.3 GHz at room temperature.
NMR and EPR Sample Preparation. Sample preparation was
carried out in sealed high-vacuum systems using break-seal
techniques. Calculated quantities of the cobalt complexes were
weighed, evacuated, and transferred into the NMR tube (length
=200 mm, d=5 mm). Toluene-d8, AlMe3, or MAO (20) was
added after LCoIICl2 cooling in liquid nitrogen (77 K). In the
case of [CPh3][B(C6F5)4], this compound was transferred to the
NMR tube (as a solution in the CH2Cl2 with subsequent solvent
removal) before LCoIICl2 addition.
Ethylene Polymerization Procedure. Polymerization was per-
formedin a steel 1 L autoclave. Precatalysts (2.0 ꢀ 10-6 mol) were
introduced into the autoclave in a vacuum-sealed glass ampule.
The reactor was evacuated at 80 °C, cooled to 20 °C, and charged
with the solution of a calculated cocatalyst amount in 150 cm3 of
toluene. After setting up the polymerization temperature (40 °C)
and ethylene pressure (5 bar), the reaction was started by break-
ing the ampule of the complex. During the polymerization time
(30 min), ethylene pressure, stirring speed, and temperature were
maintained constant. The experimental unit was equipped with
an automatic computer-controlled system for ethylene feed and
recording of the ethylene consumption.
case of the catalyst systems based on LCoIICl2 (L=L2iPr
tBu, L3Me) and after 10 min of polymerization were almost
,
L
deactivated. This corresponds to the NMR data, showing
that the intermediates formed in the LCF3CoIICl2/MAO
(AlMe3) system are less stable to degradation than those
formed in the case of the LCoIICl2/MAO (L=L2iPr, LtBu
L
,
3Me) analogues.
Conclusions
The cobalt(II) and cobalt(I) species, formed upon activa-
tion of LCoIICl2 (L=L3Me, L2iPr, LtBu, and LCF3) with MAO,
AlMe3/[CPh3][B(C6F5)4], and AlMe3 were monitored by 1H,
2H, and 19F NMR spectroscopy. It was shown that the ion
pairs [LCoII(μ-Me)2AlMe2]þ[A]-, [LCoIIMe(S)]þ[A]-, and
[LCoI(S)]þ[A]- can be observed in the catalyst systems
LCoIICl2/MAO and LCoIICl2/AlMe3/[CPh3][B(C6F5)4]
Polymer MW and MWD Measurements. Weight-average
(Mw) and number-average (Mn) molecular weights and mole-
cular weight distributions (Mw/Mn) were obtained by the GPC
method with a Waters-150 at 150 °C with trichlorobenzene as a
solvent.
Acknowledgment. This work was supported by the
Russian Fund of Basic Research, Grant 09-03-00485.

Article
Organometallics, Vol. 28, No. 20, 2009 6013
The authors are grateful to A. V. Golovin for help with
NMR spectroscopic studies. We are also grateful to L. G.
Echevskaja and M. A. Matsko for help in the analysis of
polymer MWD.
Supporting Information Available: NMR details for the
complexes observed (JH-H coupling constants, line half-
widths). This material is available free of charge via the Internet
at http://pubs.acs.org.