Chelate bis(imino)pyridine cobalt complexes: Synthesis, reduction, and evidence for the generation of ethene polymerization catalysts by Li+ cation activation

Article abstract of DOI:10.1021/ja052129k

Treatment of the bis(iminobenzyl)pyridine chelate Schiff-base ligand 8 (lig^Ph) with FeCl₂ or CoCl₂ yielded the corresponding (lig^Ph)MCl₂ complexes 9 (Fe) and 10 (Co). The reaction of 10 with methyllithium or "butadiene-magnesium" resulted in reduction to give the corresponding (lig^Ph)Co(I)Cl product 11. Similarly, the bis(aryliminoethyl)pyridine ligand (lig^Me) was reacted with CoCl₂ to yield (lig^Me)CoCl₂ (12). Reduction to (lig^Me)CoCl (13) was effected by treatment with "butadiene-magnesium". Complex 13 reacted with Li[B(C ₆F₅)₄] in toluene followed by treatment with pyridine to yield [(lig^Me)Co⁺-pyridine] (15). The reaction of the Co(II) complexes 10 or 12 with ca. 3 molar equiv of methyllithium gave the cobalt(I) complexes 16 and 17, respectively. Treatment of the (lig ^Me)CoCH³ (17) with Li[B(C₆F₅) ₄] gave a low activity ethene polymerization catalyst. Likewise, complex 16 produced polyethylene (activity = 33 g(PE) mmol(cat)^-1 h^-1 bar^-1 at room temperature) upon treatment with a stoichiometric amount of Li[B(C₆F₅)₄]. A third ligand (lig^OMe) was synthesized featuring methoxy groups in the ligand backbone (22). Coordination to FeCl₂ and CoCl₂ yielded the desired compounds 23 and 24. Reaction with MeLi gave (lig ^OMe)CoMe (25/26). Treatment of 25/26 with excess B(C ₆F₅)₃ gave the η⁶-arene cation complex 27, where one Co-N linkage was cleaved. Activation of 25/26 with Li[B(C₆F₅)₄] again gave a catalytically active species.

Full text of DOI:10.1021/ja052129k

Published on Web 09/20/2005
Chelate Bis(imino)pyridine Cobalt Complexes: Synthesis,
Reduction, and Evidence for the Generation of Ethene
Polymerization Catalysts by Li+ Cation Activation
Nina Kleigrewe,† Winfried Steffen,† Tobias Blo¨mker,† Gerald Kehr,†
Roland Fro¨hlich,†,§ Birgit Wibbeling,†,§ Gerhard Erker,*,† Julia-Christina Wasilke,†,‡
Guang Wu,‡,§ and Guillermo C. Bazan*,‡
Contribution from the Organisch-Chemisches Institut UniVersita¨t Mu¨nster, Corrensstr. 40,
D-48149 Mu¨nster, Germany, and Department of Chemistry and Biochemistry, Institute for
Polymers and Organic Solids, UniVersity of California, Santa Barbara, CA 93106
Received April 27, 2005; E-mail: erker@uni-muenster.de; bazan@chem.ucsb.edu
Abstract: Treatment of the bis(iminobenzyl)pyridine chelate Schiff-base ligand 8 (ligPh) with FeCl2 or CoCl2
yielded the corresponding (ligPh)MCl2 complexes 9 (Fe) and 10 (Co). The reaction of 10 with methyllithium
or “butadiene-magnesium” resulted in reduction to give the corresponding (ligPh)Co(I)Cl product 11. Similarly,
the bis(aryliminoethyl)pyridine ligand (ligMe) was reacted with CoCl2 to yield (ligMe)CoCl2 (12). Reduction to
(ligMe)CoCl (13) was effected by treatment with “butadiene-magnesium”. Complex 13 reacted with Li[B(C6F5)4]
in toluene followed by treatment with pyridine to yield [(ligMe)Co+-pyridine] (15). The reaction of the Co(II)
complexes 10 or 12 with ca. 3 molar equiv of methyllithium gave the cobalt(I) complexes 16 and 17,
respectively. Treatment of the (ligMe)CoCH3 (17) with Li[B(C6F5)4] gave a low activity ethene polymerization
catalyst. Likewise, complex 16 produced polyethylene (activity ) 33 g(PE) mmol(cat)-1 h-1 bar-1 at room
temperature) upon treatment with a stoichiometric amount of Li[B(C6F5)4]. A third ligand (ligOMe) was
synthesized featuring methoxy groups in the ligand backbone (22). Coordination to FeCl2 and CoCl2 yielded
the desired compounds 23 and 24. Reaction with MeLi gave (ligOMe)CoMe (25/26). Treatment of 25/26
with excess B(C6F5)3 gave the η6-arene cation complex 27, where one Co-N linkage was cleaved. Activation
of 25/26 with Li[B(C6F5)4] again gave a catalytically active species.
Scheme 1
Introduction
Homogeneous Ziegler-Natta chemistry has seen a variety
of advancements in the recent years. After the extensive
development of Group 4 bent metallocene-based catalysts1,2
other metal complex types have become increasingly important
in this chemistry. The bridged Cp/amido complexes of the Group
3 and 4 metals (the “constrained geometry catalysts”)3 and
several types of chelate complexes of the late transition metals
represent noteworthy examples of this important development.4
All these systems seem to have in common that the respective
alkyl-metal cation systems are generated in the course of the
activation process and that alkyl-metal cations represent the
active stages of the catalyst systems in the repetitive steps of
the actual catalytic cycle.1
A few systems were recently described that seemed to show
some deviation from the rule. Royo et al.5 observed that the
Me2Si-bridged bis(amido)/Cp zirconium complex (1, see Scheme
1) polymerized ethene upon activation. It was assumed that a
catalyst was formed that initially did apparently not contain a
metal-bound alkyl group. Chen et al.6 have recently described
a bent metallocene system (2) of similar features. He proposed
† Universita¨t Mu¨nster
‡ University of California
§ Contact this author for information regarding X-ray crystal structure
determinations.
(1) (a) Marks, T. J. Acc. Chem. Res. 1992, 25, 57-65. (b) Brintzinger, H. H.;
Fischer, D.; Mu¨lhaupt, R.; Rieger B.; Waymouth, R. M. Angew. Chem.
1995, 107, 1255-1283; Angew. Chem., Int. Ed. Engl. 1995, 34, 1143-
1170. (c) Bochmann, M. J. Chem. Soc., Dalton Trans. 1996, 255-270.
(d) Kaminsky, W. J. Chem. Soc., Dalton Trans. 1998, 1413-1418.
(2) (a) Erker, G. Acc. Chem. Res. 2001, 34, 309-317. (b) Erker, G. Chem.
Commun. 2003, 1469-1476.
(3) Reviews: (a) McKnight, A. L.; Waymouth, R. M. Chem. ReV. 1998, 98,
2587-2598. (b) Okuda, J.; Eberle, T. Half-Sandwich Complexes as
Metallocene Analogues. In Metallocenes - Synthesis, ReactiVity, Applica-
tions; Togni, A., Halterman, R. L., Eds.; Wiley-VCH: Weinheim, 1998;
Vol. 1, pp 415-453. See also: (c) Kunz, K.; Erker, G.; Do¨ring, S.; Fro¨hlich,
R.; Kehr, G. J. Am. Chem. Soc. 2001, 123, 6181-6182. (d) Bredeau, S.;
Altenhoff, G.; Kunz, K.; Do¨ring, S.; Grimme, S.; Kehr, G.; Erker, G.
Organometallics 2004, 23, 1836-1844.
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111, 448-468; Angew. Chem., Int. Ed. 1999, 38, 428-447. (b) Ittel, S.
D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100, 1169-1203. (c)
Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103, 283-315.
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2495-2497.
(6) Jin, J.; Wilson, D. R.; Chen, E. Y.-X. Chem. Commun. 2002, 708-709.
9
10.1021/ja052129k CCC: $30.25 © 2005 American Chemical Society
J. AM. CHEM. SOC. 2005, 127, 13955-13968
13955

A R T I C L E S
Scheme 2
Kleigrewe et al.
that alkyl transfer from the [R-Al(C6F5)3-] counteranion to
coordinated ethene represented the essential carbon-carbon
bond forming step (followed by alkyl transfer from zirconium
to aluminum) at such initially seemingly transition metal alkyl-
free catalyst systems.
A few chelate bis(iminoalkyl)pyridine cobalt systems were
described by Gal et al.7 and Gibson et al.8,9 that showed related
characteristics. The [bis(iminoalkyl-κN,N′)pyridine-κN]Co(II)-
Cl2 complexes reacted with alkyllithium reagents by reduction
to yield the corresponding (lig)Co(I)Cl complexes. Subsequent
activation with, e.g., methylalumoxane (MAO) gave active
ethene polymerization catalysts. Following the commonly
accepted activation mechanisms10,11 the systems derived from
3 are also homogeneous catalysts that might initially be lacking
a metal-carbon σ-bond. Alkyl transfer from an R-[B]- or
R-[Al]--type counteranion could potentially again represent a
mode of catalytic action at these special systems.
We have now observed that the (lig)Co(I)CH3 complexes
gave active ethene polymerization catalysts simply by treatment
with Li[B(C6F5)4]. This shines some light on the potential olefin
polymerization pathways followed at the small group of early
or late metal Ziegler-Natta catalyst that operate under such
apparently “alkyl-free” conditions. In this paper we will describe
the synthesis, some chemical and structural properties of such
systems, and their catalytic olefin polymerization properties upon
activation with Li+ cation.
Results and Discussion
Synthesis of the Metal Complexes. The bis(N-arylimino-
benzyl)pyridine ligand system (8, ligPh) was prepared analo-
gously as described by Esteruelas et al.12 Pyridine-2,6-dicar-
boxylic acid 5 was prepared by KMnO4 oxidation of 2,6-
dimethylpyridine. Subsequent conversion to the acid chloride
(6) followed by phenylcuprate coupling gave 7, which was
converted to the bis(iminobenzyl)pyridine ligand (8) by acid-
catalyzed condensation with 2,6-diisopropylaniline. The ligand
system 8 was treated with iron(II) chloride to yield the
paramagnetic chelate complex 9. Treatment of 8 with CoCl2 in
boiling n-butanol eventually gave the paramagnetic [bis(N-
aryliminobenzyl-κN,N′)-pyridine-κN]cobalt(II) dichloride system
10 (72% isolated) (Scheme 2).
(7) Kooistra, T. M.; Knijnenburg, Q.; Smits, J. M. M.; Horton, A. D.; Budzelaar,
P. H. M.; Gal, A. W. Angew. Chem. 2001, 113, 4855-4858; Angew. Chem.,
Int. Ed. 2001, 40, 4719-4722.
(8) Gibson, V. C.; Humphries, M. J.; Tellmann, K. P.; Wass, D. W.; White,
A. J. P.; Williams, D. J. Chem. Commun. 2001, 2252-2253.
(9) (a) Britovsek, G. J. P.; Bruce, M.; Gibson, V. C.; Kimberley, B. S.; Maddox,
P. J.; Mastroianni, S.; McTavish, S. J.; Redshaw, C.; Solan, G. A.;
Stro¨mberg, S.; White, A. J. P.; Williams, D. J. J. Am. Chem. Soc. 1999,
121, 8728-8740. (b) Britovsek, G. J. P.; Gibson, V. C.; Spitzmesser, S.
K.; Tellmann, K. P.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton
Trans. 2002, 1159-1171. Clentsmith, G. K. B.; Gibson, V. C.; Hitchcock,
P. B.; Kimberley, B. S.; Rees, C. W. Chem. Commun. 2002, 1498-1499.
Bianchini, C.; Mantovani, G.; Meli, A.; Migliacci, F.; Zanobini, F.; Laschi,
F.; Sommazzi, A. Eur. J. Inorg. Chem. 2003, 1620-1631. (c) Dias, E. L.;
Brookhart, M.; White, P. S. Organometallics 2000, 19, 4995-5004.
Britovsek, G. J. P.; Mastroianni, S.; Solan, G. A.; Baugh, S. P. D.; Redshaw,
C.; Gibson, V. C.; White, A. J. P.; Williams, D. J.; Elsegood, M. R. J.
Chem.sEur. J. 2000, 6, 2221-2231. Britovsek, G. J. P.; Gibson, V. C.;
Kimberley, B. S.; Mastroianni, S.; Redshaw, C.; Solan, G. A.; White, A.
J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 2001, 1639-1644.
Gibson, V. C.; Tellmann, K. P.; Humphries, M. J.; Wass, D. F. Chem.
Commun. 2002, 2316-2317. Britovsek, G. J. P.; Gibson, V. C.; Hoarau,
O. D.; Spitzmesser, S. K.; White, A. J. P.; Williams, D. J. Inorg. Chem.
2003, 42, 3454-3465. Small, B. L. Organometallics 2003, 22, 3178-3183.
Chen, Y.; Chen, R.; Quian, C.; Dong, X.; Sun, J. Organometallics 2003,
22, 4312-4321. Tellmann, K. P.; Gibson, V. C.; White, A. J. P.; Williams,
D. J. Organometallics 2005, 24, 280-286. Humphries, M. J.; Tellmann,
K. P.; Gibson, V. C.; White, A. J. P.; Williams, D. J. Organometallics
2005, 24, 2039-2050 and references cited in these recent articles.
(10) (a) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1991, 113,
3623-3625. (b) Chien, J. C. W.; Tsai, W.-M.; Rausch, M. D. J. Am. Chem.
Soc. 1991, 113, 8570-8571. (c) Bochmann, M.; Jaggar, A. J.; Nicholls, J.
C. Angew. Chem. 1990, 102, 830-832; Angew. Chem., Int. Ed. Engl. 1990,
29, 780-782. (d) Yang, X.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc.
1994, 116, 10015-10031. Reviews: (e) Jordan, R. F. AdV. Organomet.
Chem. 1991, 32, 325-387. (f) Sinn, H.; Kaminsky, W. AdV. Organomet.
Chem. 1980, 18, 99-149. (g) Chen, E. Y.-X.; Marks, T. J. Chem. ReV.
2000, 100, 1391-1434.
(11) See also: Strauch, J. W.; Erker, G.; Kehr, G.; Fro¨hlich, R. Angew. Chem.
2002, 114, 2662-2664; Angew. Chem., Int. Ed. 2002, 41, 2543-2546.
(12) Esteruelas, M. A.; Lo´pez, A. M.; Me´ndez, L.; Oliva´n, M.; On˜ate, E.
Organometallics 2003, 22, 395-406 and references therein.
9
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Ethene Polymerization Catalysts by Li+ Activation
A R T I C L E S
Scheme 3
The [bis(N-aryliminobenzyl-κN,N′)pyridine-κN]CoCl2 com-
plex 10 was reacted with ca. 0.5 molar equiv of “butadiene-
magnesium”.13 As in the related cases described in the litera-
ture,7,8 we did not observe the formation of a metal-dialkyl or
metal-butadiene11 products. Instead the cobalt(II) complex 10
was reduced to the corresponding cobalt(I) chloride 11. Complex
11 is diamagnetic. It features the NMR resonances as expected
for a complex with C2V symmetry.
1
Thus, we have observed H NMR signals at δ 9.53 (t, 1H)
and 7.23 (d, 2H) of the central disubstituted pyridine moiety, a
single set of phenyl substituent resonances [δ 7.82 (d, 4H), 7.32
(t, 2H), and 7.04 (t, 4H)] in addition to one set of signals of the
pair of N-(2,6-diisopropylphenyl) substituents [δ 7.46 (t, 2H),
7.25 (d, 4H), and δ 3.66 (sept., 4H), 1.16 (d, 24H, isopropyl)].
The methyl groups of each isopropyl substituent of 11 are
diastereotopic [13C NMR in d6-benzene at ambient tempera-
ture: δ 29.3 (CHMe2), 24.6 and 23.3 (each CH(CH3)2)].
Complex 11 contains a prochiral axis within the dN-(2,6-
diisopropylphenyl) structural subunit.
The related [bis(N-aryliminoethyl-κN,N′)pyridine-κN]CoCl2
complex (12, (ligMe)CoCl2) was prepared analogously as
described by Gibson et al.9a It was treated with 1 molar equiv
of the “butadiene-magnesium” reagent in toluene solution. Quite
differently from a series of related chelate bis(imine)nickel(II)
dichloride complexes,11,14 formation of a stable butadiene
complex was not observed. Instead, reduction from (ligMe)CoCl2
to (ligMe)CoCl again prevailed, and we isolated the cobalt(I)
chloride complex (13) in 56% yield. Again diastereotopic
splitting of the isopropyl methyl signals is observed in both the
Gibson et al. recently reported the synthesis of the ligand
system 22a (see Scheme 4; Ar ) mesityl) and the formation of
its N,N,N-coordinated FeCl2 complex.15 We had prepared the
related 2,6-diisopropylphenyl substituted ligand 22 [(ligOMe)]
by a different route. We treated the pyridine-2,6-diacid chloride
(20) with 2,6-diisopropylaniline and reacted the resulting
carboxylic acid amide (21) with Meerwein’s reagent [Me3O+]-
[BF4-] (19) to obtain 22 (see Scheme 4). Reaction of this ligand
(22) with iron dichloride gave the iron complex 23 as a light
pink powder, which was characterized by elemental analysis
and X-ray diffraction. It deserves mentioning here, since
crystallization from hot toluene by slowly cooling the solution
to room temperature overnight gave single crystals featuring a
different coordination mode than the one reported by Gibson
et al.15 (see below). Reaction of 22 with cobalt dichloride was
immediate with a color change from blue to green. The product
(24) was isolated after 1 h of reaction time as a green solid and
was characterized by elemental analysis and X-ray diffraction.
The reaction of 24 with 1 equiv of methyllithium did not yield
the expected7,8 2,6-bis-[(2,6-diisopropylphenyliminomethoxy-
κN,O)pyridine-κN]cobalt(I) chloride ((ligOMe)CoCl), and the only
new species detected was methyl-2,6-bis-[(2,6-diisopropyl-
phenyliminomethoxy-κN,N′)pyridine-κN]cobalt(I) ((ligOMe)-
CoMe, 26). The ratio of cobalt complex to methyllithium was
increased to 1:2, and the desired methylated Co(I) compound
(26) was obtained in good yields, sometimes accompanied by
a second diamagnetic minor product that was tentatively
assigned the structure of the isomer 25 (see Scheme 4). Upon
addition of 5 equiv of B(C6F5)3, the purple solution turned blue
while the methide is abstracted by B(C6F5)3. This resulted in
the formation of a cationic [(ligOMe)Co+] species (27) with a
[MeB(C6F5)3-] counterion.
3
1H NMR [δ 3.33 (sept., JHH ) 6.9 Hz, 4H, CHMe2), δ 1.17
and 1.05 (each d, 3JHH ) 6.9 Hz, each 12H, CH(CH3)2] and the
13C NMR spectrum [δ 29.1 (CHMe2), 24.0 and 23.8 (CH-
(CH3)2)].
Treatment of the (ligPh)CoCl2 complex 10 with >2 molar
equiv of methyllithium resulted in the formation of the cobalt-
(I) methyl complex 16. The Co-CH3 1H NMR resonance of
16 occurs at δ 1.07 (s). Again, the signals of diastereotopic
isopropyl methyl groups of the N-C6H3(2,6-bis-CHMe2) units
are observed for complex 16 (1H: 1.05, 0.56 (each d, JHH
)
6.8 Hz); 13C: 22.1, 22.5). The corresponding cobalt(I) methyl
complex 17, previously described by Gal et al.,7 was synthesized
analogously. In both cases it may safely be assumed that the
cobalt(I) chloride complexes 11 and 13, respectively, may be
intermediates of this reaction sequence.
Complex 13 was treated with Li[B(C6F5)4] at room temper-
ature in toluene. This resulted in the abstraction of the chloride
ligand from cobalt. Probably, a [(ligMe)Co+] cation was formed.
This was subsequently trapped by the addition of pyridine to
the reaction mixture which led to the formation of the [(ligMe)-
Co+-pyridine] adduct (15, see Scheme 3). Similarly, [(ligPh)-
Co+-pyridine] (14) was formed from 11 by treatment with
Li[B(C6F5)4] followed by the addition of pyridine.
(13) Yasuda, H.; Kajihara, Y.; Mashima, K.; Nagasuna, K.; Lee, K.; Nakamura,
A. Organometallics 1982, 1, 388-396 and references therein.
(14) See also: (a) Erker, G.; Wicher, J.; Engel, K.; Rosenfeldt, F.; Dietrich,
W.; Kru¨ger, C. J. Am. Chem. Soc. 1980, 102, 6344-6346. (b) Erker, G.;
Kru¨ger, C.; Mu¨ller, G. AdV. Organomet. Chem. 1985, 24, 1-39. (c) Yasuda,
H.; Tatsumi, K.; Nakamura, A. Acc. Chem. Res. 1985, 18, 120-126. (d)
Dahlmann, M.; Erker, G.; Fro¨hlich, R.; Meyer O. Organometallics 1999,
18, 4459-4461. (e) Erker, G.; Kehr, G.; Fro¨hlich R. AdV. Organomet.
Chem. 2004, 51, 109-162.
X-ray Crystal Structure Analyses. Several of the com-
pounds synthesized in the course of this study were characterized
(15) (a) Smit, T. M.; Tomov, A. K.; Gibson, V. C.; White, A. J. P.; Williams,
D. J. Inorg. Chem. 2004, 43, 6511-6512. (b) Bennett, A. U.S. Patent Appl.
Publ. U.S. 6,423,848 B2, 2002 (E. I. Du Pont De Nemours and Company,
USA).
9
J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005 13957

A R T I C L E S
Scheme 4
Kleigrewe et al.
by X-ray diffraction. First, we investigated the free ligand system
8 by an X-ray crystal structure analysis (see Figure 1 and Table
1). In the solid state this bulky bis(N-arylimino)pyridine
derivative adopts a conformation that is characterized by a
nonplanar arrangement of the two imino substituents at the
central pyridine unit. The corresponding dihedral angles N4s
C3sC2sN1 (-67.3(2)°) and N4sC8sC9sN10 (-85.5(2)°)
indicate an almost orthogonal orientation of the imino systems
relative to the pyridine core. The compound 8 adopts a chiral,
close to C2-symmetric structure. The CdN bonds of the
substituents are short (both 1.279(2) Å). The planes of the
adjacent phenyl substituents are oriented such to allow for some
π-conjugation with the CdN double bond systems (θ C902s
C901sC9sN10 -4.3(2)° and C202sC201sC2sN1
-17.3(2)°). In contrast, the bulky 2,6-diisopropylphenyl sub-
stituents at the imino nitrogen atoms are rotated away from any
significant π-interaction (θ C112sC111sN10sC9 90.2(2)° and
C12sC11sN1sC2 99.6(2)°). It must be noted that in the free
ligand 8 the 2,6-diisopropylphenyl substituents are Z-oriented
with the pyridine moiety at the central CdN unit (θ C3sC2s
N1sC11: -2.7(2)°, C8sC9sN10sC111: 0.7(2)°). Conse-
quently, the phenyl substituents at the imino-(sp2)-carbon center
are oriented toward the side of the electron lone pair at the
adjacent planar nitrogen center, i.e., E-oriented to the respective
7,6-diisopropylphenyl substituent (θ C201sC2sN1sC11
178.6(1)°, C901sC9sN10sC111: -177.1(1)°). This is op-
posite to the structural orientation of these substituents at the
CdN double bonds in the metal complexes derived from 8,
where this specific configuration would not allow for chelate
complex formation.
Both imino-nitrogen centers of 8 were inverted15 to form the
paramagnetic chelate [bis(imino)pyridine]MCl2 complex 9 (Fe)
and 10 (Co). In both complexes the metal centers are
pentacoordinated,9b featuring a distorted square pyramidal
geometry. The three nitrogen atoms from the chelate ligand and
one chloride form the base, and the remaining chloride ligand
is found in the apical position (see Figures 2 and 3). In the Fe
complex 9 the corresponding bond angles at the base amount
to 142.34(9)° (N1-Fe-N10), 150.69(8)° (N4-Fe-Cl1),
74.64(9)° (N1-Fe-N4), 73.16(9)° (N4-Fe-N10), 100.27(7)°
(N10-Fe-Cl1), and 98.26(7)° (Cl1-Fe-N1). The magnitude
of the distortion is illustrated by the values of the bond angles
of the chelate ligand nitrogens to the apical chloride ligand:
Figure 1. A view of the molecular geometry of the ligand system 8.
Selected bond lengths (Å) and angles (deg): N1-C11 1.428(2), C2-C3
1.506(2), C3-N4 1.338(2), N4-C8 1.341(2), C8-C9 1.501(2), N10-C111
1.428(2); N1-C2-C3 123.3(1), C2-C3-N4 114.9(1), C3-N4-C8
117.7(1), N4-C8-C9 114.5(1), C8-C9-N10 122.7(1). For additional
values see Table 1.
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13958 J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005

Ethene Polymerization Catalysts by Li+ Activation
A R T I C L E S
Table 1. Selected Structural Data of the Chelate Ligand 8 and the Complexes 9-11, 13, and 15
compound
MLn
8
9
10
11
13
15
Co(pyr)+
-
FeCl2
CoCl2
CoCl
CoCl
C2-N1
1.279(2)
1.279(2)
-
-
1.297(4)
1.296(4)
2.210(2)
2.247(2)
2.052(2)
118.7(2)
122.2(2)
-4.3(4)
5.8(5)
-53.0(5)
-49.8(5)
111.2(3)
112.1(3)
-7.4(4)
-4.5(4)
142.34(9)
74.64(9)
73.16(9)
2.233(1)
2.332(1)
91.09(7)
150.69(8)
118.19(4)
1.298(4)
1.288(4)
2.235(3)
2.292(3)
2.044(2)
120.9(3)
119.8(3)
-9.5(5)
6.4(5)
1.321(2)
1.329(2)
1.914(1)
1.912(1)
1.797(1)
121.71(13)
119.06(13)
-1.6(3)
-2.3(2)
-66.9(3)
47.0(2)
103.6(2)
-107.5(2)
-1.5(2)
2.4(2)
1.322(3)
1.326(3)
1.907(2)
1.908(2)
1.797(2)
118.4(2)
119.6(2)
1.9(3)
1.309(4)
1.313(4)
1.918(3)
1.946(3)
1.799(3)
120.2(3)
122.6(3)
-3.8(5)
-1.3(5)
-
C9-N10
M-N1
M-N10
M-N4
-
C11-N1-C2
C111-N10-C9
C11-N1-C2-C201
C111-N10-C9-C901
C202-C201-C2-N1
C902-C901-C9-N10
C12-C11-N1-C2
C112-C111-N10-C9
N4-C3-C2-N1
N4-C8-C9-N10
N1-M-N10
120.7(1)
119.6(1)
178.6(1)
-177.1(1)
0.9(3)
-
-
-17.3(2)
-50.4(5)
63.4(5)
-4.3(2)
-
99.6(2)
106.8(4)
-98.3(4)
-11.0(4)
8.7(5)
145.62(10)
75.09(11)
74.63(10)
2.231(1)
2.294(1)
92.70(8)
145.42(9)
121.87(4)
90.0(3)
-100.6(3)
-1.4(3)
-0.7(3)
162.95(8)
81.37(8)
81.58(8)
2.179(1)
-
-79.1(4)
111.6(4)
-2.7(4)
2.9(4)
162.74(12)
81.52(13)
81.59(13)
1.946(3)a
-
90.2(2)
-67.3(2)
-85.5(2)
-
-
-
-
-
-
-
-
163.34(6)
81.67(6)
81.73(6)
2.176(1)
-
N1-M-N4
N10-M-N4
M-Cl1
M-Cl2
N4-M-Cl2
-
-
-
N4-M-Cl1
173.43(5)
-
179.55(7)
-
171.24(13)a
-
Cl1-M-Cl2
a Co-N(pyridine).
Figure 3. A view of the molecular structure of the cobalt complex 10.
Selected bond lengths (Å) and angles (deg): N1-C11 1.436(5), C2-C3
1.492(5), C3-N4 1.337(4), N4-C8 1.335(4), C8-C9 1.489(5), N10-C111
1.432(4); Cl1-Co-N1 97.40(8), Cl1-Co-N10 98.30(7), Cl2-Co-N1
97.49(8), Cl2-Co-N10 99.81(8), Co-N1-C11 125.3(2), Co-N1-C2
113.5(2), N1-C2-C3 115.3(3), C2-C3-N4 114.6(3), C3-N4-C8
121.1(3), Co-N4-C3 117.4(2), Co-N4-C8 118.3(2), N4-C8-C9
114.9(3), C8-C9-N10 116.7(3), Co-N10-C9 111.9(2), Co-N10-C111
128.3(2).
Figure 2. Molecular structure of the iron complex 9. Selected bond lengths
(Å) and angles (deg): N1-C11 1.452(4), C2-C3 1.483(4), C3-N4
1.348(3), N4-C8 1.349(4), C8-C9 1.487(4), N10-C111 1.448(4); Fe-
N1-C11 125.8(2), Fe-N1-C2 115.3(2), N1-C2-C3 115.6(2), C2-C3-
N4 113.5(3), C3-N4-C8 120.2(3), Fe-N4-C3 119.4(2), Fe-N4-C8
119.6(2), N4-C8-C9 113.4(3), C8-C9-N10 114.7(3), Fe-N10-C9
113.6(2), Fe-N10-C111 122.7(2). For additional values see Table 1 and
the text.
102.68(7)° (N1-Fe-Cl2), 91.09(7)° (N4-Fe-Cl2), 96.96(7)°
(N10-Fe-Cl2), and especially in the characteristic Cl1-Fe-
Cl2 angle of 118.19(4)°. The Fe-N(pyridyl) bond in complex
9 is markedly shorter than the Fe-N1/N10 (imino) linkages
(∆d ∼0.2 Å; see Table 1). The bulky 2,6-diisopropylphenyl
substituents at the imino-nitrogen centers N1 and N10 are rotated
close to normal to the basal plane of the complex, and also the
phenyl substituents at the iminocarbon atoms are markedly
rotated out of the plane of the Schiff-base functional groups,
probably to avoid sterical interaction with the bulky adjacent
aryl substituents but also to avoid contact with the central pyridyl
group. It is noteworthy that the rotation of the phenyl groups at
C9 and at C2 are equal with regard to the resulting chirality
element. Thus, complex 9 adopts a chiral conformational
arrangement in the crystal (for the values of the corresponding
dihedral angles, see Table 1).
The cobalt(I) chloride complexes 11, 13, and 15 all feature
a distorted square-planar coordination of the central metal atom.
In 11 the N1-Co-N10 angle amounts to 163.34(6)° (which is
by ca. 20° larger than that found in 9 or 10), and the
corresponding N4-Co-Cl angle in 11 is even closer to linear
at 173.43(5)°. The “intra-chelate angles” at Co are both close
to 81° (see Table 1), whereas the remaining pair of ligand angles
at cobalt amount to 98.89(4)° (N1-Co-Cl1) and 97.77(4)°
(N10-Co-Cl1) (the sum of “inplane” bonding angles at cobalt
is 360.06°). The central Co-N4 bond to the pyridine moiety is
by ∆δ 0.11 Å shorter than the lateral Co-N1/N2 distances.
Again, the bulky 2,6-diisopropylphenyl moieties at the imino-
nitrogens are rotated close to normal to the chelate ligand plane,
and the phenyl substituents at the CdN carbon atoms are also
rotated markedly (see Table 1 for the respective dihedral angles).
In 11 both these phenyl groups were found to be rotated in
9
J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005 13959

A R T I C L E S
Kleigrewe et al.
Figure 4. Molecular structure of the [bis(N-aryliminobenzyl)pyridine]Co-
(I)Cl complex 11. Selected bond lengths (Å) and angles (deg): N1-C11
1.445(2), C2-C3 1.446(2), C3-N4 1.373(2), N4-C8 1.370(2), C8-C9
1.446(2), N10-C111 1.439(2); Co-N1-C11 122.1(1), Co-N1-C2
115.9(1), N1-C2-C3 112.9(1), C2-C3-N4 109.9(1), C3-N4-C8
120.7(1), Co-N4-C3 119.6(1), Co-N4-C8 119.7(1), N4-C8-C9
110.0(1), C8-C9-N10 112.6(1), Co-N10-C9 115.8(1), Co-N10-C111
125.0(1). For additional values see the text and Table 1.
Figure 6. A projection of the molecular structure of the cation part of
complex 15. Selected bond lengths (Å) and angles (deg): N1-C11
1.440(5), C2-C3 1.446(5), C3-N4 1.372(4), N4-C8 1.365(4), C8-C9
1.463(5), N10-C111 1.447(4); N21A-Co-N1 99.4(1), N21A-Co-N10
97.9(1), Co-N1-C11 123.4(2), Co-N1-C2 116.1(2), N1-C2-C3
113.0(3), C2-C3-N4 109.9(3), C3-N4-C8 120.6(3), Co-N4-C3
119.3(2), Co-N4-C8 120.1(2), N4-C8-C9 109.9(3), C8-C9-N10
113.3(3), Co-N10-C9 115.1(2), Co-N10-C111 122.3(2). Further values
are listed in Table 1.
square-planar coordination geometry with the three nitrogen
atoms of the chelate ligand showing the typical sequence of
bond lengths to cobalt (Figure 6). In the cation 15 the CdN
bonds are slightly shorter than those in the related neutral
Co(I)Cl complex 13 (for details see Table 1). A single pyridine
ligand is coordinated at cobalt trans to the chelate pyridine
moiety (CosN4 1.799(3) Å vs CosN21A 1.946(3) Å). The
plane of the single pyridine ligand is rotated from the central
(N4Co) plane by 64.2°. Again, the bulky 2,6-diisopropylphenyl
groups at the imino nitrogen centers N1 and N10 are oriented
with their aryl planes close to orthogonal to the major coordina-
tion plane.
The structure of the free ligand 22 [(ligOMe)] shows a
conformation that features one CdN nitrogen (N1) oriented to
the inside of the pincer chelate and the other (N3) oriented away
from the pyridine nitrogen (Figure 7).
Figure 5. A view of the molecular structure of complex 13. Selected bond
lengths (Å) and angles (deg): N1-C11 1.442(3), C2-C3 1.435(3), C3-
N4 1.369(3), N4-C8 1.368(3), C8-C9 1.434(3), N10-C111 1.443(3);
Cl1-Co-N1 98.92(6), Cl1-Co-N10 98.12(6), Co-N1-C11 125.7(2),
Co-N1-C2 115.9(2), N1-C2-C3 113.2(2), C2-C3-N4 109.6(2), C3-
N4-C8 120.7(2), Co-N4-C3 119.9(2), Co-N4-C8 119.4(2), N4-C8-
C9 110.4(2), C8-C9-N10 112.6(2), Co-N10-C9 116.0(2), Co-N10-
C111 124.5(2). For additional values, see Table 1.
This structural motive is retained in the complexes 23 (FeCl2)
and 24 (CoCl2). In 23 the ligand is strongly coordinated to iron
through both nitrogen atoms and weakly to the oxygen atom of
the remaining sC(dNAr)sOMe group (FesO1 2.5361(17) Å;
see Figure 8 and Table 2). This deviates from the structure of
the related complex 23a (with Ar ) mesityl) reported by Gibson
et al.15 which features nitrogen coordination exclusively. In 23
the O1sC20 (1.450(3) Å) and O2sC21 (1.457(3) Å) bond
lengths are slightly longer than typical carbon-oxygen single
bonds, whereas the O1-C7 (1.353(3) Å) and O2-C13
(1.324(3) Å) bond lengths are shorter. The N1-C7 bond length
(1.264(3) Å) exhibits a typical value for carbon-nitrogen double
bonds, while the N3sC13 (1.285(3) Å) bond length is slightly
elongated due to the nitrogen atom coordinating to iron. The
geometry at the metal center can best be described as distorted
trigonal bipyramidal. The equatorial plane is formed by the
pyridine nitrogen atom and the two chloride ligands. The axial
positions are occupied by the nitrogen atom N3 and the oxygen
atom O1. The sum of the bond angles within the equatorial plane
is 354.05° (N2sFesCl1 101.55(6)°, N2sFesCl2 131.13(6)°,
Cl1sFesCl2 121.37(3)°). The axial O1sFesN3 angle was
found at 140.06(7)°.
opposite directions. In the crystal complex 11 thus adopts a close
to achiral “meso-like” conformation (see Figure 4), similar to
10 (see Figure 3).
The closely related complex 13 (see Scheme 3) had previously
been prepared by Gal et al.,7 but to the best of our knowledge,
it had not been characterized by X-ray diffraction. In the crystal
it features a distorted square-planar complex geometry with a
rather short CosN4 (1.797(2) Å) bond trans to CosCl
(2.179(1) Å). As already seen in 11 the CdN bond lengths in
13 [N1sC2 1.322(3) Å, C9sN10 1.326(3) Å] are markedly
longer than those in the (lig)CoCl2 complex (10) or its (lig)-
FeCl2 analogue (9) (see above; see Figure 5).
In the [bis(N-aryliminoethyl-κN,N′)pyridine-κN]Co(pyridine)+-
[B(C6F5)4]- salt 15,16 cations and anions are well separated.
The cobalt(I) center in the cationic part features the typical
(16) Kehr, G.; Roesmann, R.; Fro¨hlich, R.; Holst, C.; Erker, G. Eur. J. Inorg.
Chem. 2001, 535-538.
9
13960 J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005

Ethene Polymerization Catalysts by Li+ Activation
A R T I C L E S
Figure 7. View of the molecular structure of the free ligand 22.
Figure 8. A view of the molecular structure of complex 23.
The cobalt complex 24 (Figure 9) again exhibits a distorted
trigonal bipyramidal geometry, featuring O∧N∧N-coordination
with a weak Co-O1 interaction (2.460(4) Å) with equatorial
angels N2-Co-Cl1 101.57(14)°, N2-Co-Cl2 135.32(15)°,
Cl1-Co-Cl2 116.73(8)° (Σ ) 353.62°) and an axial O1-Co-
N3 angle of 143.44(17)°.
Single crystals for the N∧N∧N-coordinated (ligOMe)CoCH3
isomer 26 were grown from a toluene solution by pentane
diffusion at room temperature (Figure 10). Similar as in 11,
13, and 15 (see above) the metal center is coordinated in a
distorted square planar fashion. The metal coordination plane
is spanned from N(3) through the pyridine ring to N(1) and
C(34) with the 2,6-diisopropylphenyl rings perpendicular to the
plane. The Co-C(34) bond length is 1.958(2) Å. Comparison
between the Co(II) chloride species 24 and the Co(I) methyl
species 26 shows a marked difference in the Co-N bond
lengths. A shortening of 0.20 to 0.23 Å was observed with
reduction of cobalt (24: Co-N(2) ) 2.066(5) Å, Co-N(3) )
2.103(5) Å; 26: Co-N(2) ) 1.8359(14) Å, Co-N(1) )
1.9066(14) Å, Co-N(3) ) 1.9057(14) Å).
Figure 11). The metal coordination plane is spanned from the
coordinating iminoester nitrogen through the pyridine ring. The
2,6-diisopropylphenyl rings are perpendicular to the plane. The
Co-N bonds are comparable in lengths to those of the neutral
precursor 26 (Co-N1 ) 1.8904(19) Å, Co-N2 ) 1.8645(19)
Å). The bond distances for the Co-C bonds of the η6-
coordinated aryl ring were found between 2.03 and 2.15 Å.
Attempts to stabilize this Co(I) complex with pyridine were not
successful.
Ethene Polymerization: Preliminary Results. The (lig)-
CoCH3 complexes 16 and 17 themselves were found to be
inactive toward ethene in the absence of a suitable activator.
Treatment of the [bis(iminoethyl)pyridine]CoCH3 complex 17
with B(C6F5)3 gave an active ethene polymerization catalyst.
In a typical experiment 50 mg of 17 were reacted with 1 molar
equiv of B(C6F5)3. The mixture was allowed to react with ethene
(30 min, toluene, room temperature, 2 bar ethene pressure) to
yield ca. 1.4 g of linear polyethylene (average yield from two
experiments), which corresponds to an averaged polymerization
activity of a ) 16 g(PE) mmol(catalyst)-1 h-1 bar-1. Likewise,
polyethylene was formed at the 16/B(C6F5)3 catalyst system. A
similar (rather low) activity was found in this case (a ) 15
g(PE) mmol (catalyst)-1 h-1 bar-1).
The cationic Co(I) complex 27 features a different structure
than the chemically related [(ligMe)Co+-pyridine] complex 15
(see above). In 27 the cobalt center is coordinated by the
pyridine nitrogen, one imine nitrogen, and one η6-aryl ring (see
9
J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005 13961

A R T I C L E S
Kleigrewe et al.
Table 2. Selected Structural Data of the Chelate Ligand 22 and the Complexes 23, 24, 26, and 27
compound
MLn
22
23
24
26
27
Co+
-
FeCl2
CoCl2
CoMe
C7-N1
1.2609(16)
1.2647(15)
1.3543(14)
1.4387(18)
1.3394(14)
1.4420(15)
-
-
-
-
-
-
1.264(3)
1.285(3)
1.353(3)
1.450(3)
1.324(3)
1.457(3)
-
2.147(2)
2.158(2)
2.5361(17)
2.2517(8)
2.2672(8)
-
129.8(2)
120.7(2)
76.95(8)
66.55(7)
140.06(7)
-
101.55(6)
131.13(6)
-
1.249(7)
1.278(7)
1.351(7)
1.458(7)
1.334(7)
1.462(7)
-
2.066(5)
2.103(5)
2.460(4)
2.237(2)
2.2384(19)
-
129.0(5)
120.7(5)
79.16(19)
67.71(17)
143.44(17)
-
101.57(14)
135.32(15)
-
1.318(2)
1.318(2)
1.356(2)
1.427(3)a
1.350(2)
1.422(3)a
1.9057(14)
1.8359(14)
1.9066(14)
-
1.307(3)
1.268(3)
C13-N3
C7-O1
1.394(3)
C20-O1
1.315(6)a
C13-O2
1.343(3)
1.440(3)
1.8904(19)
1.8645(19)
-
-
-
-
C21-O2
M-N1
M-N2
M-N3
M-O1
M-Cl
-
-
M-Cl
M-C
-
1.9580(19)
118.56(14)
119.09(14)
81.33(6)
-
-
C6-N1-C7
C13-N3-C14
N2-M-N3
N2-M-O1
N3-M-O1
N1-M-N3
N2-M-Cl1
N2-M-Cl2
N1-M-C34
N2-M-C-34
N3-M-C34
Cl1-M-Cl2
C1-C6-N1-C7
C15-C14-N3-C13
N2-C8-C7-N1
N2-C12-C13-N3
125.16(10)
121.50(10)
-
-
-
-
-
-
-
-
-
-
121.1(2)
121.5(2)
-
-
-
-
-
-
-
-
-
-
-
162.90(6)
-
-
98.16(8)
174.55(10)
98.81(8)
-
88.7(2)
100.97(18)
3.4(2)
-
-
-
-
121.37(3)
-73.5(3)
110.8(3)
162.3(2)
0.9(3)
116.73(8)
71.7(9)
74.0(8)
-162.9(7)
2.4(9)
113.51(14)
76.09(16)
-22.6(2)
-132.80(14)
-99.3(3)
-98.9(3)
-
-4.3(2)
10.5(4)
a C20 is C32 and C21 is C33 in this compound.
Figure 9. A view of the molecular structure of complex 24.
Treatment of the [bis(iminoethyl)pyridine]CoCH3 complex
17 with 1 molar equivalent of Li[B(C6F5)4] in toluene followed
by exposure of the solution to ethene again resulted in the
formation of polyethylene with a similar activity. Starting from
50 mg (0.090 mmol) of 17 and 62 mg (0.090 mmol) of lithium
tetrakis(pentafluorophenyl) borate resulted in the formation of
1.70 and 2.22 g, respectively, of polyethylene in two independent
experiments (30 min, room temperature, toluene, 2 bar ethene
pressure) which corresponds to an average catalyst activity of
a ) 22 g(PE) mmol(catalyst)-1 h-1 bar-1. A set of similar
experiments was carried out starting from the [bis(iminobenzyl)-
pyridine]CoCH3 complex 16. Treatment with an equimolar
quantity of Li[B(C6F5)4] again gave an active catalyst; starting
from 50 mg of 16 we obtained ca. 2.4 g of PE under the typical
reaction conditions (see above), which corresponds to an
averaged catalyst activity of a ) 33 g(PE) mmol(catalyst)-1
h-1 bar-1. In CH2Cl2 a similar catalyst activity was obtained.
Complex [(ligPh)CoCH3] (16) could even be activated by
treatment with a Brønsted acid, provided that an inert anion
was employed. The reaction of 16 with the H+ acidic 2H-pyrrol-
B(C6F5)3 adduct 2816 also gave an active catalyst for polyeth-
ylene formation (see Scheme 5 and Table 3). In this case the
catalytically active metal cation complex is accompanied by the
poorly nucleophilic [(N-pyrrol)-B(C6F5)3-] counteranion.
Ethene polymerization with compound 23 activated by MAO
resulted in low activity (3 g(PE) mmol(23)-1 h-1 bar-1).
Activation with MAO/B(C6F5)3 did not result in a change of
activity, and activation with MAO/BF3 gave only a slightly more
active catalyst (8 g(PE) mmol(23)-1 h-1 bar-1).
Compounds 25/26 themselves did not show any ethene
9
13962 J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005

Ethene Polymerization Catalysts by Li+ Activation
A R T I C L E S
Figure 10. A view of the molecular structure of the Co(I) complex 26.
Figure 11. A view of the molecular structure of complex 27.
Scheme 5
Table 3. Ethene Polymerization Activities of the Catalysts Derived
from the (ligx)CoLn Complexes and Different Activatorsa
no. (MLn/X)
no activator
Li+
H+
B(C6F5)3
MAO
MAO/BF3
10 (CoCl2/Ph)
12 (CoCl2/Me)
24 (CoCl2/OMe)
11 (CoCl/Ph)
13 (CoCl/Me)
16 (CoMe/Ph)
17 (CoMe/Me)
25/26 (CoMe/OMe)
n.a.
n.a.
n.a.
n.a.c
12
n.a.
n.a.
15b
16b
n.a.
c
-
n.a.
n.a.
n.a.
33
5b
22b
36
7
37
a n.a.: no activity; a ) g(PE) mmol(cat.)-1 h-1 bar-1 b Average value
.
polymerization activity without cocatalyst under the applied
reaction conditions. Activation with B(C6F5)3 or generation of
compound 27 in situ in this case did not result in an active
species for ethene polymerization, and no color change was
observed after the introduction of ethene. Activation of the
isomeric mixture 25/26 with Li[B(C6F5)4] resulted in polyeth-
ylene formation (Scheme 6) with an average activity of a ) 36
g mmol(25/26)-1 h-1 bar-1. The reaction mixture stayed purple
upon the addition of Li[B(C6F5)4] and turned grayish after the
from several polymerization reactions. c See ref. 19.
introduction of ethene. In comparison, compound 25/26 resulted
in a ca. 3-fold more active species upon activation with
Li[B(C6F5)4] than compound 24 activated with MAO/BF3 (see
Table 3). While the catalyst derived from the Co(II) dichloride
complex 24 gave rise to low molecular weight polymer (Mn )
617 g mol-1) with narrow molecular weight distribution (Mw/
Mn ) 1.3), the (ligOMe)Co(I) methyl derived 25/26/Li[B(C6F5)4]
9
J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005 13963

A R T I C L E S
Scheme 6
Kleigrewe et al.
polyethylene potentially indicates that other Lewis acid or
Brønsted acid activators might activate organometallic precur-
sors by some ligand specific reaction pathways (potentially being
operative out of an equilibrium with other cationic species) other
than previously assumed. It needs to be explored whether such
pathways might also be of importance in the more active
homogeneous Ziegler-Natta systems of this general type such
as, e.g., the (lig)FeCl2 derived polymerization catalysts or in
some of the early metal systems depicted in Scheme 1.
Scheme 7
Experimental Section
General Procedures. Reactions with organometallic substrates or
reagents were carried out in an inert atmosphere (Ar) using Schlenk-
type glassware or in a glovebox. Solvents were dried and distilled under
argon prior to use. NMR spectra were recorded with a Varian
UNITYplus 600 (1H: 599.9 MHz. 13C: 150.8 MHz) spectrometer or a
Varian UNITY INOVA 400 MHz (1H: 399.9 MHz. 13C: 100.6 MHz).
An unsystematical atom numbering scheme analogous to that in Table
1 and Figures 1 to 6 is used. Most assignments were based on additional
2D NMR spectra.20 The following instruments were used for additional
physical characterization: IR spectroscopy, Nicolet 5DXC FT-IR
spectrometer; melting points, DSC 2010 TA instruments); elemental
analysis, Elementar Vario ELIII, Leeman Labs Inc. CE440 Elemental
Analyzer or a Control Equipment Corporation 440 Elemental Analyzer.
2,6-Dibenzoylpyridine (7)12 and the [bis(N-aryliminoethyl-κN,N′)-
pyridine-κN]CoCl2 complex (12)9a were prepared according to literature
procedures. Complex 13 had been described previously7 but was
prepared here by a different reducing method. Li[B(C6F5)4] (18) was
prepared by treatment of freshly prepared Li(C6F5) (warning: this
compound is explosive and must be handled with care at low
temperature) with 0.25 equiv of BCl3 at -78 °C. The obtained white
solid was collected and extracted with toluene, followed by two
successive fractional recrystallizations of the crude product from
toluene. The (lig)CoCH3 complexes were usually freshly prepared prior
to their use in the polymerization experiments.
Data sets were collected with Enraf-Nonius CAD4 and Nonius
KappaCCD diffractometers, the later one equipped with a rotating anode
generator Nonius FR591. Programs used: data collection EXPRESS
(Nonius B.V., 1994) and COLLECT (Nonius B.V., 1998), data
reduction MolEN (K. Fair, Enraf-Nonius B.V., 1990) and Denzo-SMN
(Z. Otwinowski, W. Minor, Methods in Enzymology, 1997, 276, 307-
326), absorption correction for CCD data SORTAV (R. H. Blessing,
Acta Cryst. 1995, A51, 33-37; R. H. Blessing, J. Appl. Cryst. 1997,
30, 421-426), structure solution SHELXS-97 (G. M. Sheldrick, Acta
Cryst. 1990, A46, 467-473), structure refinement SHELXL-97 (G. M.
Sheldrick, Universita¨t Go¨ttingen, 1997), graphics Diamond (K. Bran-
denburg, Universita¨t Bonn, 1997). For the structures of 22-24, 26,
and 27, the single crystal was mounted on a glass fiber and transferred
to a Bruker CCD platform diffractometer. The SMART program
package (SMART Software Users Guide, version 5.1; Bruker Analytical
X-ray Systems, Inc.; Madison, WI, 1999) was used to determine the
unit-cell parameters and for data collection (25 s/frame scan time for
catalyst provided slightly higher molecular weight polymers
(>2000), which were mostly bimodal with broader molecular
weight distributions (Mw/Mn ) 1.5 to 7.6).
Conclusions
The 16/17/B(C6F5)3 system could potentially correspond to
the members of the small family of catalyst systems shown in
Scheme 1. The observation that a catalyst system, albeit of rather
low ethene polymerization activity, was formed upon treatment
of the precursors 16,17 or 25/26 with Li+ seems not to be in
accord with the proposed olefin polymerization pathways at such
catalyst systems but indicates the occurrence of a different
activation mode. A clarification of the actual pathway followed
in these (lig)CoCH3/Li[B(C6F5)4]/ethene systems must await
further experimental evidence. Possibly the Li+ cation might
interact with one “arm” of the chelate donor ligand, which would
create an open coordination site at a reactive overall cationic
reactive intermediate (e.g., 29; see Scheme 7). In the system
27 (see Scheme 4) we had already observed that an imino-
nitrogen coordination can easily be “lost” upon metal cation
formation if some suitable ligand is available for additional
stabilization. In a possible Ziegler-Natta reactive intermediate
(29, see Scheme 7) this could possibly be an incoming ethene
monomer. The observation that 16 can be activated by proto-
nation using the special Brønsted acid 28 could potentially be
explained by a similar mechanism where an imine coordination
from the former tridentate ligand system would be removed by
internal iminium ion formation. A variety of mechanistic
alternatives could be discussed at this stage of the investigation
but must await further detailed experimental studies.
(17) Erker, G.; Fro¨mberg, W.; Kru¨ger, C.; Raabe, E. J. Am. Chem. Soc. 1988,
110, 2400-2405.
(18) Steffen, W.; Blo¨mker, T.; Kleigrewe, N.; Kehr, G.; Fro¨hlich, R.; Erker, G.
Chem. Commun. 2004, 1188-1189.
(19) We have carried out a number of additional series of control experiments.
In a series of four experiments using the [bis(2,6-diisopropylphenylimino-
κN,N′-ethyl)pyridine-κN]CoCl system 13, freshly prepared by treatment of
12 with butadiene-magnesium, an average of 177 mg of PE was isolated
(under typical conditions [50 mg (0.087 mmol) of 13, 59.6 mg (0.087 mmol)
of Li[B(C6F5)4], toluene, rt, 2 bar ethene pressure]). An additional
experiment carried out with independently prepared starting materials gave
only 32 mg of PE under the same conditions. A [bis(2,6-diisopropylphen-
ylimino-κN,N′-benzyl)pyridine-κN]CoCl (11) sample, synthesized from 10
by the butadiene-magnesium method, gave no PE under equivalent reaction
conditions after Li[B(C6F5)4] treatment.
In view of these surprising results we cannot rule out that
the very low activity polyethylene formation that we had recently
observed at the (lig)CoCl(11,13)/Li[B(C6F5)4] systems18 was not
intrinsic but may have been caused by some as yet unidentified
cobalt alkyl contaminant.19 With such low polymerization
activities there is always the possibility that the observed reaction
is caused by a minor high activity contamination. However, our
observation that the (lig)CoCH3/Li[B(C6F5)4] systems produce
(20) Braun, S.; Kalinowski, H. O.; Berger, S. 150 and More Basic NMR
Experiments; VCH: Weinheim, 1998 and references therein.
9
13964 J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005

Ethene Polymerization Catalysts by Li+ Activation
A R T I C L E S
a sphere of diffraction data). The raw frame data were processed using
SAINT (SAINT Software Users Guide, version 6.0; Bruker Analytical
X-ray Systems, Inc.: Madison, WI, 1999) and SADABS (Sheldrick,
G. M. SADABS, version 2.05, Bruker Analytical X-ray Systems, Inc.:
Madison, WI, 2001) to yield the reflection data file. Subsequent
calculations were carried out using the SHELXTL (Sheldrick, G. M.
SHELXTL version 6.12, Bruker Analytical X-ray Systems, Inc.:
Madison, WI, 2001) program. The structure was solved by direct
methods and refined on F2 by full-matrix least-squares techniques. The
analytical scattering factors (International Tables for X-ray Crystal-
lography; Kluwer Academic Publishers: Dordrecht, 1992; Vol. C) for
neutral atoms were used throughout the analysis.
group P21/c (No. 14), λ ) 0.710 73 Å, T ) 198 K, ω and æ scans,
14 059 reflections collected ((h, (k, (l), [(sin θ)/λ] ) 0.59 Å-1, 7403
independent (Rint ) 0.058) and 5005 observed reflections [I g 2σ(I)],
484 refined parameters, R ) 0.051, wR2 ) 0.102, max residual electron
density 0.63 (-0.56) e Å-3, disordered toluene solvent molecule refined
with split positions, fixed occupancies (twice 0.25), and geometrical
constraints, hydrogens calculated and refined as riding atoms.
Reaction of 8 with CoCl2. Preparation of Complex 10: A flame-
dried 200 mL Schlenk flask was charged under argon with the Schiff
base 8 (3.12 g, 6.45 mmol) and dry n-butanol (50 mL). To another
flame-dried 50 mL Schlenk flask CoCl2 (0.84 g, 6.45 mmol) and dry
n-butanol (20 mL) were added under inert conditions. Both Schlenk
flasks were heated to 80 °C for 15 min, and then the blue CoCl2/n-
BuOH solution was transferred to the reaction vessel under argon, which
contained the yellow suspension of the chelate ligand. The reaction
mixture was cooled to room temperature during 15 min and then stirred
for 12 h. The volume of the mixture was reduced to ca. 10 mL, and
dry pentane was added. The precipitated product (10) was collected
by filtration and dried in vacuo to give 10 as a yellow-brown amorphous
solid (yield 3.88 g, 98%) that was used in the subsequent reduction
reaction without further characterization. Single crystals were obtained
from acetone.
X-ray crystal structure analysis of 10: formula C43H47Cl2N3Co‚
C3H6O, M ) 793.74, yellow crystal 0.50 × 0.20 × 0.05 mm3, a )
9.439(1) Å, b ) 25.767(1) Å, c ) 9.547(1) Å, â ) 113.02(1)°, V )
2137.1(3) Å3, Fcalcd ) 1.234 g cm-3, µ ) 5.63 cm-1, empirical
absorption correction (0.766 e T e 0.972), Z ) 2, monoclinic, space
group P21 (No. 4), λ ) 0.710 73 Å, T ) 198 K, ω and æ scans, 15 129
reflections collected ((h, (k, (l), [(sin θ)/λ] ) 0.68 Å-1, 8937
independent (Rint ) 0.034) and 7378 observed reflections [I g 2σ(I)],
486 refined parameters, R ) 0.051, wR2 ) 0.122, max residual electron
density 1.07 (-0.46) e Å-3, Flack parameter 0.000(15), hydrogens
calculated and refined as riding atoms.
Reduction of 10 by Treatment with Methyllithium. Synthesis of
Complex 11: The [bis(imino)pyridine]CoCl2 complex 10 (0.70 g, 0.95
mmol) was suspended in 150 mL of dry toluene under argon in a 250
mL Schlenk flask. The suspension was cooled to -78 °C, and a diethyl
ether solution of methyllithium (1.05 mmol, 0.65 mL of a 1.6 M
solution) was added dropwise with stirring. The mixture was then
allowed to slowly warm to room temperature and stirred for 12 h.
Solvent was removed in vacuo from the purple solution. The residue
was dissolved in dry toluene and filtered under argon through
deactivated silica gel (SiO2/Cl2SiMe2). Solvent was removed in vacuo,
and the residue recrystallized at -30 °C from toluene to yield 0.49 g
(74%) of 11. (Slow diffusion of pentane vapor into a saturated toluene
solution of 11 gave single crystals for the X-ray crystal structure
analysis.) Alternatively, complex 11 was prepared by treatment of
complex 10 (300 mg, 0.41 mmol) with butadiene-magnesium (100 mg,
0.45 mmol) in toluene (30 mL). The two components were mixed with
precooled toluene at -78 °C and allowed to warm to room temperature
overnight to yield 137 mg (48%) of complex 11 as a violet-colored
solid.
Condensation of 2,6-Dibenzoylpyridine with 2,6-Diisopropyl-
aniline. Synthesis of the Ligand System 8: 2,6-Dibenzoylpyridine
(5.00 g, 17.4 mmol), 2,6-diisopropylaniline (6.79 g, 38.3 mmol), and
a catalytic quantity of p-toluenesulfonic acid (221 mg, 1.15 mmol) were
dissolved in 50 mL of toluene. The mixture was refluxed for 12 h using
a Dean-Stark trap to remove the water. Solvent was removed in vacuo,
and the residue was purified by colum chromatography (silicagel,
pentane/triethylamine/chloroform: 50/3/3). Two yellow fractions were
obtained that both contained the product. The volume of the first fraction
was reduced in vacuo to ca. 10 mL. Single crystals for the X-ray crystal
structure analysis were formed overnight at ambient temperature. The
product from both fractions was used for the subsequent reactions; yield
of 8: 5.71 g, 54%, mp 142 °C; IR (KBr): ν˜ ) 2960, 1653, 1446,
1315, 937 cm-1. MS (70 eV, EI): m/z ) 605 (100%, M+). MS
(ESI+): m/z ) 606.4 ([M + H]+), 628.5 ([M + Na]+). Anal. Calcd
for C43H47N3 (605.9): C, 85.25; H, 7.82; N, 6.94. Found: C, 85.09;
H, 7.73; N, 6.94%. 1H NMR (CDCl3, 298 K): δ 8.54, 8.12, 8.04, 7.94,
7.66, 7.54-7.31, 7.23-6.99 (each very broad, 19H), 3.05, 2.95, 2.87
(each very broad, 4H), 1.18, 1.02, 0.96 (each very broad, 24H) (The
system is dynamic).
X-ray crystal structure analysis of 8: formula C43H47N3, M ) 605.84,
light yellow crystal 0.35 × 0.25 × 0.25 mm3, a ) 19.736(2) Å b )
11.967(1) Å, c ) 16.077(2) Å, â ) 106.03(1)°, V ) 3649.4(7) Å3,
F
calcd ) 1.103 g cm-3, µ ) 4.84 cm-1, empirical absorption correction
via ψ-scan data (0.849 e T e 0.889), Z ) 4, monoclinic, space group
P21/c (No. 14), λ ) 1.541 78 Å, T ) 223 K, ω/2θ scans, 7632
reflections collected (-h, +k, (l), [(sin θ)/λ] ) 0.62 Å-1, 7413
independent (Rint ) 0.027) and 5524 observed reflections [I g 2σ(I)],
424 refined parameters, R ) 0.049, wR2 ) 0.153, max residual electron
density 0.27 (-0.21) e Å-3, hydrogens calculated and refined as riding
atoms.
Reaction of 8 with FeCl2. Synthesis of Complex 9: A flame-dried
Schlenk flask was charged under argon with iron(II) dichloride (0.24
g, 1.88 mmol) and n-butanol (50 mL). To another Schlenk flask, the
Schiff base 8 (1.14 g, 1.88 mmol) and n-butanol (50 mL) were added
under inert conditions. Both Schlenk flasks were heated to 80 °C for
1 h, and then the green FeCl2/n-BuOH solution was transferred to the
reaction vessel under argon, which contained the yellow suspension of
the chelate ligand. The reaction mixture was heated further for 30 min
at 80 °C, and then it was stirred for 12 h at room temperature.
Subsequently the solvent was removed in vacuo, and the precipitated
crude product 9 was washed with pentane until the solvent is colorless.
The solid was collected by filtration and dried in vacuo to give 9 as a
blue amorphous solid (1.12 g, 1.53 mmol, 81%). Slow crystallization
from a saturated acetone solution gave single crystals of 9 for the X-ray
crystal structure analysis. IR (KBr): ν˜ ) 3055, 2951, 2923, 2863, 1564,
1464, 1441, 1384, 1321, 1269, 1154, 1102, 1054, 1038, 807, 779, 699
cm-1. Anal. Calcd for C43H47N3Cl2Fe (732.6): C, 70.50; H, 6.47; N,
5.74. Found: C, 69.51; H, 6.88; N, 5.04%.
Anal. Calcd for C43H47N3ClCo (700.3): C, 73.76; H, 6.77; N, 6.00.
1
Found: C, 73.40; H, 6.94; N, 5.94. H NMR (d6-benzene): δ 9.53 (t,
1H, 6-H), 7.23 (d, 2H, 5-H, 7-H), 7.82 (d, 4H), 7.32 (t, 2H), 7.04 (t,
4H, Ph), 7.46 (t, 2H), 7.25 (d, 4H), 3.66 (sept., 4H), 1.16 (d, 24H,
2,6-diisopropylphenyl). 13C{1H} NMR (d6-benzene): δ 168.1 (CdN),
155.3 (C3, C8), 123.8 (C5, C7), 117.5 (C6), 140.0, 123.6, 128.3, 128.0
(ipso-, o-, m-, p- of Ph), 152.0, 140.9, 128.6, 127.1 (ipso-, o-, m-, p- of
2,4-diisopropyl-Ph), 29.3 (CHMe2), 24.6 and 23.3 (CH(CH3)2).
X-ray crystal structure analysis of 11: formula C43H47ClN3Co, M
) 700.22, red crystal 0.40 × 0.30 × 0.08 mm3, a ) 9.872(1) Å, b )
27.669(1) Å, c ) 13.890(1) Å, â ) 96.96(1)°, V ) 3766.1(5) Å3, Fcalcd
) 1.235 g cm-3, µ ) 5.60 cm-1, empirical absorption correction (0.807
e T e 0.957), Z ) 4, monoclinic, space group P21/n (No. 14), λ )
0.710 73 Å, T ) 198 K, ω and æ scans, 38 470 reflections collected
X-ray crystal structure analysis of 9: formula C43H47N3Cl2Fe‚
0.5C7H8, M ) 778.65, yellow crystal 0.25 × 0.08 × 0.05 mm3, a )
13.521(1) Å b ) 16.290(1) Å, c ) 19.298(1) Å, â ) 98.26(1)°, V )
4206.4(5) Å3, Fcalcd ) 1.230 g cm-3, µ ) 5.20 cm-1, empirical
absorption correction (0.881 e T e 0.975), Z ) 4, monoclinic, space
9
J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005 13965

A R T I C L E S
Kleigrewe et al.
((h, (k, (l), [(sin θ)/λ] ) 0.68 Å-1, 9330 independent (Rint ) 0.038)
and 7398 observed reflections [I g 2σ(I)], 441 refined parameters, R
) 0.039, wR2 ) 0.082, max residual electron density 0.32 (-0.31) e
Å-3, hydrogens calculated and refined as riding atoms.
Preparation of Complex 12:9a Similarly as described above for the
preparation of 10, the bis(aryliminoethyl)pyridine Schiff base system
(3.12 g, 6.45 mmol) was reacted with CoCl2 (0.84 g, 6.45 mmol) in a
total of 70 mL of n-butanol. Workup analogously as described above
gave 3.88 g (98%) of 12 as a yellow-brown solid, that was subjected
to the subsequent reduction reaction without further characterization.
Calcd for C62H48N4BF20Co (1298.8): C, 57.34; H, 3.73; N, 4.31.
Found: C, 56.75; H, 3.77; N, 3.74. MS (ESI+): m/z ) 619.4 (M+).
X-ray crystal structure analysis of 15: formula C38H48N4Co‚B(C6F5)4‚
C6H5Br, M ) 1455.79, light green crystal 0.45 × 0.15 × 0.03 mm3,
a ) 20.027(1) Å, b ) 12.241(1) Å, c ) 25.895(1) Å, â ) 93.75(1)°,
V ) 6334.6(7) Å3, Fcalc ) 1.526 g cm-3, µ ) 10.07 cm-1, empirical
absorption correction (0.660 e T e 0.970), Z ) 4, monoclinic, space
group P21/c (No. 14), λ ) 0.710 73 Å, T ) 198 K, ω and æ scans,
20 215 reflections collected ((h, (k, (l), [(sin θ)/λ] ) 0.59 Å-1, 11 147
independent (Rint ) 0.063) and 6954 observed reflections [I g 2σ(I)],
866 refined parameters, R ) 0.056, wR2 ) 0.114, max residual electron
density 0.55 (-0.66) e Å-3, hydrogens calculated and refined as riding
atoms.
Reaction of Complex 12 with “Butadiene-Magnesium”: Prepa-
ration of Complex 13: A 250 mL Schlenk flask was charged with
solid 12 (4.88 g, 7.92 mmol) and [{(butadiene-magnesium) 2 THF}]n
(1.94 g, 8.75 mmol). The mixture was cooled to -78 °C, and then
precooled toluene (150 mL) was slowly added with stirring. The
reaction mixture was allowed to slowly warm to room temperature and
then stirred for 12 h. Solvent was removed from the purple reaction
mixture in vacuo, and the residue was taken up in toluene and filtered
through deactivated silica gel (SiO2/Cl2SiMe2). Solvent was evaporated
from the filtrate in vacuo, and the residue recrystallized from toluene
at -30 °C to give 0.92 g (56%) of 13. (Slow crystallization from a
saturated toluene solution at -30 °C gave single crystals of 13 for the
X-ray crystal structure analysis.) Anal. Calcd for C33H43N3ClCo
(576.1): C, 68.80; H, 7.52; N, 7.29. Found: C, 68.50; H, 7.53; N,
Reaction of Complex 10 with Methyllithium. Preparation of
Complex 16: A solution of complex 10 (300 mg, 0.41 mmol) in diethyl
ether (30 mL) was cooled to -78 °C. Methyllithium in ether (0.77
mL, 1.6 M solution, 1.23 mmol, 3 equiv) was added dropwise with
stirring. The mixture was allowed to warm to room temperature
overnight and then stirred for additional 2 d. A precipitate was removed
by filtration and the solvent removed in vacuo to give 252 mg (98%)
1
of 16. H NMR (d6-benzene): δ 10.04 (t, JHH ) 7.8 Hz, 1H, 6-H),
8.25 (pd, 4H, o-Ph), 8.18 (d, JHH ) 7.8 Hz, 2H, 5-H, 7-H), 7.53 (pt,
2H, p-Ph), 7.48 (t, JHH ) 7.9 Hz, 2H, Ar), 7.29 (d, JHH ) 7.9 Hz, 4H,
Ar), 6.97 (pt, 4H, m-Ph), 3.26 (sept., JHH ) 6.8 Hz, 4H, CHMe2), 1.07
(s, 3H, CoMe), 1.05 (d, JHH ) 6.8 Hz, 12H), 0.56 (d, JHH ) 6.8 Hz,
12H, CH(CH3)2 of 2,6-diisopropylphenyl).
Alternative Preparation of Complex 16: A solution of the complex
10 (200 mg, 0.27 mmol) in toluene (30 mL) was reacted with MeLi
(0.18 mL, 1.5 M solution in ether, 0.27 mmol) at 0 °C for 12 h to a red
brown suspension. After removal of the ether in vacuo, MeMgBr (0.43
mL, 1.9 M solution in ether, 0.81 mmol, 3 equiv) was added and the
mixture was stirred for further 4 days at room temperature. The green
suspension was filtered, and dioxane (30 mL) was added to the clear
filtrate. The formed white precipitate was removed by filtration, and
subsequently the solvent was removed in vacuo to give 144 mg (78%)
of 16. (Some dioxane was left in the product.)
Reaction of Complex 12 with Methyllithium. Preparation of
Complex 17:7 Analogously as described above complex 12 (300 mg,
0.49 mmol) was reacted with 3 molar equiv of methyllithium in ether
(0.92 mL, 1.6 M solution, 1.47 mmol) to give 250 mg (92%) of the
previously described 7 complex 17. 1H NMR (d6-benzene): δ 10.19 (t,
JHH ) 7.6 Hz, 1H, 6-H), 7.86 (d, JHH ) 7.6 Hz, 2H, 5-H, 7-H), 7.49
(t, JHH ) 7.7 Hz, 2H), 7.37 (d, JHH ) 7.7 Hz, 4H, Ar), 3.13 (sept., JHH
1
7.19. H NMR (d6-benzene): δ 9.53 (t, 1H, 6-H), 6.91 (d, 2H, 5-H,
7-H), 7.41 (t, 2H), 7.26 (d, 4H), 3.33 (sept., 4H, CHMe2), 1.17 (d,
12H), 1.05 (d, 12H, CH(CH3)2 of 2,6-diisopropylphenyl), 0.05 (s, 6H,
NdC(CH3)). 13C{1H} NMR (d6-benzene): δ 167.3 (NdC), 152.8 (C3,
C8), 125.5 (C5, C7), and 114.9 (C6), 150.9, 140.8, 127.1, 123.8 (o-,
ipso-, p-, m- of 2,4-diisopropylphenyl), 29.1 (CHMe2), 24.0 and 23.8
(CH(CH3)2), 21.2 (NdC(CH3)).
X-ray crystal structure analysis of 13: formula C33H43ClN3Co, M
) 576.08, red-black crystal 0.30 × 0.20 × 0.07 mm3, a ) 8.775(1) Å,
b ) 22.971(1) Å, c ) 15.634(1) Å, â ) 101.20(1)°, V ) 3091.3(4)
Å3, Fcalcd ) 1.238 g cm-3, µ ) 6.67 cm-1, empirical absorption
correction (0.825 e T e 0.955), Z ) 4, monoclinic, space group P21/n
(No. 14), λ ) 0.717 03 Å, T ) 198 K, ω and æ scans, 21 505 reflections
collected ((h, (k, (l), [(sin θ)/λ] ) 0.68 Å-1, 7772 independent (Rint
) 0.053) and 4939 observed reflections [I g 2σ(I)], 353 refined
parameters, R ) 0.050, wR2 ) 0.096, max residual electron density
0.37 (-0.34) e Å-3, hydrogens calculated and refined as riding atoms.
Preparation of Complex 14: Similarly as described above for the
preparation of 15, the cobalt complex 11 (50.0 mg, 71.4 µmol) was
reacted with Li[B(C6F5)4] (58.8 mg, 85.7 µmol) in a total of 5 mL of
toluene. The deep red solution was stirred for 1 h, and subsequently
pyridine (6.77 mg 85.6 µmol) was added. Workup analogously as
described above gave 46.7 mg (46%) of 14 as a deep blue solid. IR
(KBr): ν˜ ) 3065, 2961, 2865, 1639, 1513, 1465, 1260, 1083, 978,
800, cm-1. MS (ESI+): m/z ) 743. 1H NMR (d6-benzene): δ 9.11 (t,
1H, 6-H), 7.54 (d, 4H, 5-H, 7-H), 7.31 (t, 2H), 7.15-6.96 (m, 13H),
2.60 (sept., 4H, CHMe2), 0.69 (d, 12H), 0.67 (d, 12H, CH(CH3)2 of
2,6-diisopropylphenyl). 13C{1H} NMR (d6-benzene): δ 171.8 (NdC),
155.2 (C3, C8), 148.6, 140.5, 136.8, 129.8, 129.6, 129.5, 129.3, 128.5,
128.1, 127.9, 125.6, 125.3, 125.0 (Ar), 29.9 (CHMe2), 23.5, 23.4 (CH-
(CH3)2).
) 6.8 Hz, 4H, CHMe2), 1.19 (d, JHH ) 6.8 Hz, 12H), 0.62 (d, JHH
)
6.8 Hz, 12H, CH(CH3)2 of 2,6-diisopropylphenyl), 0.58 (s, 3H, CoMe),
-1.14 (s, 6H, NdCMe).
Preparation of Pyridine-2,6-dicarboxylic Acid Bis[2,6-diisoprop-
ylphenyl)amide] (21): 2,6-Pyridinedicarbonyl dichloride (500 mg, 2.45
mmol) was dissolved in 15-20 mL of dry THF. Diisopropylaniline
(924 µL, 4.90 mmol) and triethylamine (683 µL, 4.90‚mmol), dried
over molecular sieves (4 Å), were added at 0 °C. The reaction mixture
was allowed to stir at room temperature for 2 h. The precipitated Et3N‚
HCl was filtered off, and the solvent of the filtrate removed in a vacuum.
The crude material was triturated with boiling hexane to provide the
product as a white solid, which was dried in CH2Cl2 (DCM) over
magnesium sulfate. Single crystals were grown from methanol at room
temperature through solvent evaporation. Yield: 1.05 g, 88%, mp )
210 °C, MS-EI (m/z) calcd ) 485.3042, found ) 485.3050. Anal. Calcd
For C31H39N3O2 (485.65 g/mol): C, 76.66; H, 8.09; N, 8.65. Found:
Reaction of 13 with Li[B(C6F5)4] and Pyridine. Formation of
15: The cobalt complex 13 (100 mg, 0.40 mmol) and Li[B(C6F5)4]
(308 mg, 0.45 mmol) were dissolved in 15 mL of toluene. The mixture
was stirred for 1 h, and then dry pyridine (0.03 mL) was added. The
color of the solution changed from purple to deep blue. The mixture
was filtered, and the solvent was removed from the clear filtrate in
vacuo. The residue was dissolved in dry bromobenzene (4 mL), and
pentane vapor was allowed to slowly diffuse into the solution to give
crystalline 15 after 24 h. Repeating the crystallization procedure gave
single crystals of 15 suited for the X-ray crystal structure analysis. Anal.
1
C, 76.56; H, 8.14; N, 8.75. H NMR (d6-benzene): δ 9.12 (br s, 2H,
NH), 9.32 (d, JHH ) 7.6 Hz, 2H, H-3, H-5), 7.23 (t, JHH ) 7.6 Hz, 1H,
H-11), 7.13 (d, JHH ) 7.6 Hz, 4H, H-10), 7.04 (t, JHH ) 7.6 Hz, 1H,
H-4), 3.28 (sept., JHH ) 6.9 Hz, 4H, CH), 1.20 (d, JHH ) 6.9 Hz, 24H,
CH3). 13C{1H} NMR (d6-benzene, 298 K): δ 163.0 (C-7), 149.8 (C-2,
C-6), 146.9 (C-9), 140.0 (C-4), 132.2 (C-8), 129.1 (C-3, C-5), 126.2
(C-10), 124.3 (C-11), 29.9 (C-CH), 24.1 (C-CH3).
9
13966 J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005

Ethene Polymerization Catalysts by Li+ Activation
A R T I C L E S
Preparation of N2,N6-Bis(2,6-diisopropylphenyl)pyridine-2,6-di-
carboximidic Acid Dimethyl Ester (22): Pyridine-2,6-dicarboxylic
acid bis[2,6-diisopropylphenyl) amide] (21) (394 mg, 0.81 mmol) and
trimethyloxonium tetrafluoroborate (300 mg, 2.03 mmol) were sus-
pended in DCM (20 mL) and refluxed at 55 °C for 3 days. The yellow
solution was diluted with DCM and washed with a concentrated solution
of sodium bicarbonate. The organic layer was dried over MgSO4 and
filtered, and all volatiles were removed to yield the crude material as
a yellow oil. Extraction with pentane, filtration, and crystallization at
-35 °C yield the product as a yellow crystalline powder. Yield: 287
mg, 69%, MS-EI (m/z) calcd ) 513.3355, found ) 513.3375. Anal.
Calcd for C33H43N3O2 (513.70 g/mol): C, 77.15; H, 8.44; N, 8.18.
nitrogen. The solution turned purple and was allowed to stir at room
temperature for 12 h. The volume was reduced in a vacuum to remove
diethyl ether and filtered over Celite. All volatiles were removed in a
vacuum to give the product as a purple crystalline solid, consisting of
an isomeric mixture (600 mg, 82%). Single crystals of the N∧N∧N-
isomer 26 were grown from toluene by pentane diffusion at room
temperature. Anal. Calcd for C34H46CoN3O2 (588.7): C, 69.49; H, 7.89;
N, 7.15. Found: C, 69.28; H, 7.54; N, 6.62.1H NMR (d6-benzene): δ
3
3
10.48 (t, 1H, JHH ) 7.7 Hz, para-pyridine-Ph), 7.86 (d, 2H, JHH
)
7.7 Hz, meta-pyridine-Ph), 7.49 (dd, 2H, 3JHH ) 7.4 Hz, para-aniline-
Ph), 7.41 (d, 4H, meta-aniline-Ph), 3.69 (s, 6H, OCH3), 3.33 (p, 4H,
3JHH ) 6.8 Hz, CH), 1.36 (d, 12 H, 3JHH ) 6.8 Hz, CH3), 0.75 (d, 12H,
3JHH ) 6.8 Hz, CH3), 0.34 (s, 3H, CoCH3). 13C{1H} NMR (d6-
benzene): δ 166.8 (COMe), 150.5 (para-pyridine-C), 147.0 (ortho-
aniline-C), 142.2 (ortho-pyridine-C), 126.9 (meta-pyridine-C), 126.0
(para-aniline-C), 124.0 (meta-aniline-C), 113.7 (ipso-aniline-C), 50.9
1
Found: C, 77.14; H, 8.54; N, 8.31. H NMR (d1-chloroform, 298 K):
δ 7.36 (br s, 1H, p-pyridine), 7.13 (br s, 1H, m-pyridine), 7.03 (m, 4H,
m-aryl), 6.97 (dd, JHH ) 5.8 Hz, 2H, p-aryl), 3.91 (br s, 6H, OMe),
2.88 (sept., JHH ) 6.8 Hz, 4H, CH), 1.13 (d, JHH ) 6.8 Hz, 12H, CH3),
0.90 (d, JHH ) 6.8 Hz, 12H, CH3). 13C{1H} NMR (d1-chloroform, 298
K): δ 154.0 (o-pyridine), 149.3 (i-aryl), 142.9 (o-aryl), 137.0 (m-
pyridine), 136.4 (p-pyridine), 124.8 (p-aryl), 123.1 (m-aryl), 54.7 (br
s, OMe), 28.4 (CH3), 23.6 (CH3), 22.6 (CH). A signal for the Os13Cd
N carbon was not observed.
(OCH3), 29.2 (CH), 24.6 (CH3), 23.7 (CH3), 14.6 (CoCH3).
3
[Isomeric mixture: 1H NMR (d6-benzene): δ 10.48 (t, 1H, JHH
)
7.7 Hz, para-pyridine-Ph), 10.31 (t, 1H, 3JHH ) 7.5 Hz, para-pyridine-
Ph), 10.20 (t, 1H, 3JHH ) 7.5 Hz, para-pyridine-Ph), 8.21 (d, 2H, 3JHH
) 7.5 Hz, meta-pyridine-Ph), 7.64 to 6.96 (m, 22H, aniline- and
pyridine-Ph), 3.88 (s, 9H, OCH3), 3.69 (s, 9H, OCH3), 3.33 (p, 4H,
3JHH ) 6.8 Hz, CH), 3.19 (m, 8H, CH), 1.36 (d, 18 H, 3JHH ) 6.8 Hz,
X-ray crystal structure analysis of 22: formula C33H43N3O2, M )
513.70, light yellow crystal 0.25 × 0.2 × 0.2 mm3, a ) 27.093(1) Å,
b ) 27.093 Å, c ) 8.2461(3) Å, R ) 90°, â ) 90°, γ ) 90°, V )
6052.7(3) Å3, Fcalcd ) 1.127 g cm-3, µ ) 0.070 cm-1, Z ) 8, tetragonal,
space group I4h, λ ) 0.710 73 Å, T ) 117(1) K, 20 962 reflections
collected, 7123 independent (Rint ) 0.0208), 515 refined parameters,
R ) 0.0338, wR2 ) 0.0827, max residual electron density 0.206
3
CH3), 1.19 (m, 18 H, CH3), 0.86 (d, 6 H, JHH ) 6.8 Hz, CH3), 0.75
3
3
(d, 12 H, JHH ) 6.8 Hz, CH3), 0.64 (d, 12 H, JHH ) 6.8 Hz, CH3),
3
0.60 (s, 3H, CoMe), 0.54 (d, 6 H, JHH ) 6.8 Hz, CH3), 0.53 (s, 3H,
CoMe), 0.34 (s, 3H, CoMe).]
X-ray crystal structure analysis of 26: formula C34H46CoN3O2, M
) 587.67, red crystal 0.2 × 0.2 × 0.15 mm3, a ) 11.7149(9) Å, b )
13.5659(10) Å, c ) 20.8201(16) Å, R ) 90°, â ) 105.229(2)°, γ )
90°, V ) 3192.6(4) Å3, Fcalcd ) 1.223 g cm-3, µ ) 0.571 mm-1, Z )
4, monoclinic, space group P2(1)/n, λ ) 0.710 73 Å, T ) 117(1) K,
20 654 reflections collected, 7109 independent (Rint ) 0.0309), 545
refined parameters, R ) 0.0390, wR2 ) 0.0950, max residual electron
(-0.139) e Å-3
.
Preparation of Complex 23: The ligand (22) (300 mg, 0.58 mmol)
and iron(II) chloride (74 mg, 0.58 mmol) were combined in THF (40
mL), and the dark red solution was stirred overnight until no iron salt
was detectable anymore. All volatiles were removed in a vacuum to
give the product as light pink powder. Red single crystals were grown
from hot toluene by cooling to room temperature overnight. Yield: 189
mg, 51%, Anal. Calcd for C33H43Cl2FeN3O2 (640.45 g/mol): C, 61.88;
H, 6.77; N, 6.56. Found: C, 62.31; H, 6.69; N, 6.78.
density 0.444 (-0.239) e Å-3
.
Generation of Complex 27: Complex 25/26 (26 mg, 0.044 mmol)
was dissolved in toluene (3 mL), and B(C6F5)3 (113 mg, 0.22 mmol)
in toluene (3 mL) was added. The purple reaction mixture turned blue
immediately. The reaction was stirred for 5 min and filtered over Celite.
Crystallization from chlorobenzene with pentane diffusion at room
temperature provided the product as brown crystals.
X-ray crystal structure analysis of 23: formula C40H51Cl2FeN3O2,
M ) 732.59, red crystal 0.25 × 0.2 × 0.1 mm3, a ) 11.5856(5) Å, b
) 18.9039(10) Å, c ) 34.7620(16) Å, R ) 90°, â ) 90°, γ ) 90°, V
) 7613.3(6) Å3, Fcalcd ) 1.278 g cm-3, µ ) 0.574 mm-1, Z ) 8,
orthorhombic, space group Pbca, λ ) 0.710 73 Å, T ) 117(1) K, 39 192
reflections collected, 8912 independent (Rint ) 0.0334), 456 refined
parameters, R ) 0.0572, wR2 ) 0.1449, max residual electron density
X-ray crystal structure analysis of 27: formula C52H46BCoF15N3O2,
M ) 1099.66, brown crystal 0.25 × 0.2 × 0.15 mm, a ) 18.2816(7),
b ) 13.9935(5), c ) 18.7573(7) Å, R ) 90, â ) 96.3120(10), γ ) 90
°, V ) 4769.5(3) Å3, Fcalc ) 1.531 g cm-3, µ ) 0.465 mm-1, Z ) 4,
monoclinic, space group P2(1)/c, λ ) 0.71073 Å, T ) 117(1)K, 26459
reflections collected, 9376 independent (Rint ) 0.0306), 690 refined
parameters, R ) 0.0456, wR2 ) 0.1112, max. residual electron density
1.627 (-0.730) e Å-3
.
Preparation of Complex 24: The ligand (22) (300 mg, 0.58 mmol)
and cobalt(II) chloride (76 mg, 0.58 mmol) were combined in THF
(40 mL), and the green solution was stirred for several hours until no
cobalt salt was detectable anymore. The reaction volume was reduced
in a vacuum and pentane was layered onto the solution. Crystallization
took place at -35 °C, and the resulting green solid was filtered and
dried in vacuo (315 mg, 84%). Green single crystals were grown from
THF by pentane diffusion at -35 °C. Anal. Calcd for C33H43Cl2CoN3O2
(643.5): C, 61.59; H, 6.73; N, 6.53. Found: C, 61.90; H, 6.52; N,
6.04.
0.361 (-0.673) e Å-3
.
Ethene Polymerization Reactions, General Procedure: In an inert
atmosphere the respective complex was reacted with the activator in
40 mL of toluene in a 100 mL Schlenk flask. The flask was evacuated
and purged with ethene (2 bar) at room temperature. The reaction
mixture was stirred under a constant pressure of 2 bar ethene for 0.5 h
at room temperature. Then the ethene pressure was released, and the
reaction was quenched with methanol (20 mL). The obtained polyeth-
ylene was collected and consecutively washed with acetone, water, and
THF. The remaining polymer was stirred with THF (20 mL) over 8 h
to remove remaining impurities. The polymer was then dried overnight
in vacuo at 50 °C.
To control the polymerization equipment, every time before the
polymerization a standard polymerization reaction was carried out
following the general procedure described above: Cp2ZrMe2 (5 mg,
0.02 mmol), B(C6F5)3 (10 mg, 0.02 mmol) in 40 mL of toluene.
The polymer was characterized by C,H elemental analysis, DSC,
and 13C NMR spectroscopy; the obtained polymer is linear polyethylene.
X-ray crystal structure analysis of 24: formula C39H55Cl2CoN3O3.50
,
M ) 751.69, green crystal 0.2 × 0.1 × 0.1 mm3, a ) 35.520(3) Å, b
) 11.5844(10) Å, c ) 18.7071(16) Å, R ) 90°, â ) 90°, γ ) 90°, V
) 7697.6(11) Å3, Fcalcd ) 1.297 g cm-3, µ ) 0.626 mm-1, Z ) 8,
orthorhombic, space group Pbcn, λ ) 0.710 73 Å, T ) 117(1)K, 25626
reflections collected, 4545 independent (Rint ) 0.0638), 460 refined
parameters, R ) 0.0566, wR2 ) 0.1208, max residual electron density
0.611 (-0.466) e Å-3
.
Preparation of Complex 25/26: Complex 24 (800 mg, 1.24 mmol)
was dissolved in toluene (80 mL), and methyllithium (1.71 mL, 1.6 M
in diethyl ether, 2.48 mmol) was added to the green suspension under
9
J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005 13967

A R T I C L E S
Kleigrewe et al.
Two polymerization reactions starting from 17 (R ) Ph) [each 50 mg
17 / 61.7 mg Li[B(C6F5)4]: 1.701 g; 2.217 g PE] produced polyethylene
with an average activity of a ) 22 g(PE) mmol(cat.)-1 h-1 bar-1. Two
experiments starting from 16 [each 50.0 mg of 16/50.40 mg of
Li[B(C6F5)4]: 2.500 g; 2.340 g] produced polyethylene with a average
polyethylene was obtained with compound 27. Control experiments
using just Li[B(C6F5)4] (1.00 g) or the complexes 16 and 17 or 25/26
without activator components under otherwise analogous conditions
produced no polyethylene.
activity of a ) 33 g(PE) mmol(cat.)-1 h-1 bar-1
.
Acknowledgment. Financial support from the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen Indus-
trie is gratefully acknowledged. G.C.B. and J.-C.W. are grateful
to the DOE (DE-FG03098ER 14910) for financial support.
For compound 24, 25/26, and 27, the respective cobalt compound
(6 mg) was reacted with Li[B(C6F5)4] (34 mg), MAO, or MAO/BF3 if
appropriate in 30 mL of toluene, and the reactor was purged with 100
psi (6.8 bar) of ethene. Polymerization reactions were run for 20 min
at room temperature. The ethene pressure was released, and the reaction
was quenched with methanol. The obtained polyethylene was washed
with acetone and dried in a vacuum. The polymer was characterized
by DSC and GPC. The obtained polymer is linear polyethylene.
Representative polymerization reactions for the isomeric mixture (25/
26) gave activities ranging from 28 to 38 g(PE) mmol(25/26)-1 h-1
bar-1. A single experiment with the isomerically pure crystalline
complex 26 activated with Li[B(C6F5)4] under the same conditions gave
a slightly lower activity (a ) 21 g(PE) mmol(26)-1 h-1 bar-1). No
Supporting Information Available: CIF files giving details
of the X-ray crystal structure analysis (8, 9, 10, 11, 13, 15, 22,
23, 24, 26, and 27) and text giving additional information about
the polymerization experiments, spectroscopic data, and details
of the X-ray crystal structure determinations. This material is
available free of charge via the Internet at http://pubs.acs.org.
JA052129K
9
13968 J. AM. CHEM. SOC. VOL. 127, NO. 40, 2005