Manganese(II) complexes in ethene polymerization

Article abstract of DOI:10.1021/om0608105

A series of manganese(II) dichloro complexes made in situ and bearing mainly various nitrogen ligands was studied with a parallel screening method in order to identify catalytically active complexes for ethene polymerization using methylaluminoxane (MAO) as a cocatalyst. From the series two of the most active octahedral manganese(II) complexes, those bearing tetradentate nitrogen ligands with chiral bridges, [N,N′-bis(quinoline-2-methylene)diiminocyclohexane] MnCl₂ (1) and {N,N′-(6,6′-dimethylbiphenyl-2,2′- diyl)-bis[(2-pyridyl)methyl]diimine}MnCl₂ (2), were selected for more detailed studies. According to their solid-state structures, it is common for these C₂-symmetric manganese complexes to have a distorted-octahedral coordination geometry where chlorides occupy cis positions with wide Cl-Mn-Cl angles (132-135°). The highest activity in ethene polymerization (67 kg of PE/((mol of Mn) h)) was obtained with 1/MAO at 80°C. Furthermore, the alkylation of 1 and 2 with MeMgBr and (benzyl)MgBr was investigated, but only their monobenzyl derivatives were isolable.

Full text of DOI:10.1021/om0608105

980
Organometallics 2007, 26, 980-987
Manganese(II) Complexes in Ethene Polymerization
Katariina Yliheikkila¨, Kirill Axenov, Minna T. Ra¨isa¨nen, Martti Klinga, Mikko P. Lankinen,
Mika Kettunen, Markku Leskela¨, and Timo Repo*
Department of Chemistry, Laboratory of Inorganic Chemistry, UniVersity of Helsinki, P.O. Box 55
(A. I. Virtasen aukio 1), UniVersity of Helsinki FIN-00014, Finland
ReceiVed September 5, 2006
A series of manganese(II) dichloro complexes made in situ and bearing mainly various nitrogen ligands
was studied with a parallel screening method in order to identify catalytically active complexes for ethene
polymerization using methylaluminoxane (MAO) as a cocatalyst. From the series two of the most active
octahedral manganese(II) complexes, those bearing tetradentate nitrogen ligands with chiral bridges, [N,N′-
bis(quinoline-2-methylene)diiminocyclohexane]MnCl2 (1) and {N,N′-(6,6′-dimethylbiphenyl-2,2′-diyl)-
bis[(2-pyridyl)methyl]diimine}MnCl2 (2), were selected for more detailed studies. According to their
solid-state structures, it is common for these C2-symmetric manganese complexes to have a distorted-
octahedral coordination geometry where chlorides occupy cis positions with wide Cl-Mn-Cl angles
(132-135°). The highest activity in ethene polymerization (67 kg of PE/((mol of Mn) h)) was obtained
with 1/MAO at 80 °C. Furthermore, the alkylation of 1 and 2 with MeMgBr and (benzyl)MgBr was
investigated, but only their monobenzyl derivatives were isolable.
efficient ligand framework for Fe(II)- and Co(II)-based polym-
erization catalysts, are unable to polymerize ethene.7 Apparently,
the choice of ligand has a significant role in the manganese-
catalyzed polymerization reactions.
In this study, a parallel screening method was used to access
a large number of Mn/ligand combinations with sufficient steric
and electronic diversity for a rapid evaluation of various catalyst
candidates for ethene polymerization. After identification of the
suitable ligand candidates, the corresponding Mn(II) complexes
were studied in more detail. In this respect, the synthesis and
structures of novel manganese complexes bearing tetradentate
nitrogen ligands, their conversion into alkyl complexes, and their
reactivity in ethene polymerization were investigated.
Introduction
Late transition metal catalyzed olefin polymerization has
attracted a great deal of interest during the past decade, and
new catalyst systems, now covering nearly all late transition
metals, have been reported.1 While manganese compounds
are frequently used as catalyst precursors in many other
reactions, e.g., epoxidation of alkenes,2 oxidation of sulfides3
and hydrocarbons,4 and various asymmetric reactions,5 thus far
only a few manganese catalysts have been reported for olefin
polymerization.6
The capability of the homogeneous manganese complexes
tris(acetylacetonato)manganese ([Mn(acac)3]),6a bis(cyclopen-
tadienyl)manganese ([Cp2Mn]),6a and Mn(salen)Cl6a to polymer-
ize ethene after methylalumoxane (MAO) activation has been
demonstrated, although very low activities have been reported.
In this respect, Mn complexes bearing scorpionate ligands are
conspicuous, as they provide moderate activity in ethene
polymerization when activated with Al(i-Bu)3/[Ph3C][B(C6F5)4].6c
It is worth noting that manganese complexes bearing bis(imino)-
pyridine and related ligands, commonly known as the most
Results and Discussion
Parallel Screening. For an identification of possible Mn-
(II)-based ethene polymerization catalysts, a parallel screening
procedure was utilized, as this method provides a reliable and
straightforward access to a relatively large amount of catalyst
candidates on a reasonable time scale. The ligand library con-
sisted of 16 different ligands, including a series of diimines and
2,6-bis(imino)pyridyl ligands as prototypes for ligand precursors
generally used in olefin polymerization with late transition metal
complexes. In addition, various bulky protonated diamine, tetra-
dentate imine, and mono- and bidentate phosphine ligands were
included in the library (Chart 1). Furthermore, with bidentate
imines, the metal to ligand ratio was varied from 1:1 to 1:2.
Late transition metal complexes are often formed with high
yields simply by stirring the metal salt and a ligand in a proper
solvent.8 Hence, Mn(II) complexes for the parallel screening
* To whom correspondence should be addressed. Tel: +358-9-19150230.
Fax: +358-9-19150198. E-mail: timo.repo@helsinki.fi.
(1) (a) Gibson, V. C.; Spitzmesser, S. K. Chem. ReV. 2003, 103, 283-
315. (b) Ittel, S. D.; Johnson, L. K.; Brookhart, M. Chem. ReV. 2000, 100,
1169-1203.
(2) (a) Murphy, M.; Dubois, G.; Stack, T. D. P. J. Am. Chem. Soc. 2003,
125, 5250-5251. (b) McGarrigle, E. M.; Gilheany, D. G. Chem. ReV. 2005,
105, 1564-1602. (c) Xia, Q.-H.; Ge, H.-Q.; Ye, C.-P.; Liu, Z.-M.; Su, K.-
X. Chem. ReV. 2005, 105, 1603-1662.
(3) (a) Katsuki, T. Coord. Chem. ReV. 1995, 140, 189-214. (b)
Schoumacker, S.; Hamelin, O.; Pe´caut, J.; Fontecave, M. Inorg. Chem. 2003,
42, 8110-8116.
(4) (a) Lee, N. H.; Lee, C. S.; Jung, D. S. Tetrahedron Lett. 1998, 39,
1385-1388. (b) Moreira, R. F.; When, P. M.; Sames, D. Angew. Chem.,
Int. Ed. 2000, 39, 1618-1621.
(5) Canali, L.; Sherrington, D. Chem. Soc. ReV. 1999, 28, 85-93.
(6) (a) Ban, H. T.; Kase, T.; Murata, M. J. Polym. Sci., Part A: Polym.
Chem. 2001, 29, 3733-3738. (b) Vierle, M.; Zhang, Y.; Herdweck, E.;
Bohnenpoll, M.; Nuyken, O.; Ku¨hn, F. Angew. Chem., Int. Ed. 2003, 42,
1307-1310. (c) Nabika, M.; Seki, Y.; Miyatake, T.; Ishikawa, Y.; Okamoto,
K.; Fujisawa, K. Organometallics 2004, 23, 4335-4337.
(7) (a) Reardon, D.; Aharonian, G.; Gambarotta, S.; Yap, G. P. A.
Organometallics 2002, 21, 786-788. (b) Gibson, V. C.; McTavish, S.;
Redshaw, C.; Solan, G. A.; White, J. P.; Wiliams, D. J. Dalton Trans. 2003,
221-226.
(8) (a) Lappalainen, K.; Yliheikkila¨, K.; Abu-Surrah, A. S.; Polamo, M.;
Leskela¨, M.; Repo, T. Z. Anorg. Allg. Chem. 2005, 631, 763-768. (b)
Castro, P. M.; Lappalainen, K.; Ahlgre´n, M.; Leskela¨, M.; Repo, T. J. Polym.
Sci., Part A: Polym. Chem. 2003, 41, 1380-1389.
10.1021/om0608105 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 01/12/2007

Manganese(II) Complexes in Ethene Polymerization
Organometallics, Vol. 26, No. 4, 2007 981
Chart 1. Selected Examples of the Ligands Used in the Primary Screeninga
a Ligands h/i, m/n, s, and t were purchased from commercial sources and used as such. Ligands a, b, f/g, and j-r were synthesized according
to literature procedures,11 and the preparation of ligands c and d/e is described in the Experimental Section.
were synthesized in situ in a glove box under an argon
atmosphere using small glass reactors sealed with septa. Dry
THF appeared to be the most suitable solvent for the complex
preparation. To ensure the complex formation, a long reaction
time, 48 h, was applied and during this period solid MnCl2
disappeared completely.
The primary screening of ethene polymerizations was done
in a 1 L steel autoclave9 containing 10 small glass reactors.
Complexes made in situ, toluene, and MAO were loaded into
the separate glass reactors in a glovebox, and the autoclave was
sealed. After ethene pressure was introduced (5 bar), the
autoclave was kept 1 h at room temperature, followed by heating
to 60 °C. In these experiments complexes based on ligands e,
g, i, o, and p were able to produce polyethene (PE) (Chart 1).10
Apparently, a tetradentate imine ligand or two bis(imine) ligands
are able to create a suitable coordination sphere for Mn(II) to
be active in ethene polymerization.
As was observed for the series of tetradentate ligands o-r,
even minor modifications in the ligand structure can be
detrimental for catalytic properties. While the manganese
complexes bearing chiral ligands o and p are active in ethene
polymerization, q, with a phenyl bridge, is not (Chart 1). As
shown previously, phenyl-bridged tetradentate ligands such as
q prefer a planar coordination with late transition metals and
(11) References to ligand synthesis are as follows; the letters correspond
to the ligands presented in Chart 1: (a) Kettunen, M.; Vedder, C.;
Brintzinger, H.-H.; Mutikainen, I.; Leskela¨, M.; Repo, T. J. Eur. Chem.
2005, 1081-1089. (b) Feldman, J.; McLain, S. J.; Parthasarathy, A.;
Marshall, W. J.; Calabrese, J. C.; Arthur, S. D. Organometallics 1997, 16,
1514-1516. (f/g) tom Dieck, H.; Munz, C.; Mueller, C. Z. Naturforsch.
1981, 36B, 823-832. (j) Small, B. L.; Brookhart, M.; Bennet, A. M. A. J.
Am. Chem. Soc. 1998, 120, 4049-4050. (k) Abu-Surrah, A. S.; Lappalainen,
K.; Piironen, U.; Lehmus, P.; Repo, T.; Leskela¨, M. J. Organomet. Chem.
2002, 648, 55-61. (l) Valkama, S.; Lehtonen, O.; Lappalainen, K.; Kosonen,
H.; Castro, P.; Repo, T.; Torkkeli, M.; Serimaa, R.; ten Brinke, G.; Leskela¨,
M.; Ikkala, O. Macromol. Rapid Commun. 2003, 24, 556-560. (o) Ettunen,
M.; Vedder, C.; Schaper, F.; Leskela¨, M.; Mutikainen, I.; Brintzinger, H.
H. Organometallics 2004, 23, 3800-3807. (p) Abu-Surrah, A.; Laine, T.;
Repo, T.; Fawzi, R.; Steinmann, M.; Rieger, B. Acta Crystallogr. 1997,
C53, 1458-1459. (q) Yliheikkila¨, K.; Lappalainen, K.; Castro, P. M.;
Ibrahim, K.; Lo¨fgren, B.; Leskela¨, M.; Repo, T. Eur. Polym. J. 2006, 42,
92-100. (r) Ibrahim, K.; Yliheikkila¨, K.; Lo¨fgren, B.; Abu-Surrah, A.;
Lappalainen, K.; Leskela¨, M.; Repo, T.; Seppa¨la¨, J. J. Eur. Polym. 2004,
40, 1095-1104.
(9) For a more detailed description of the autoclave setup, see: Lahtinen,
P.; Korpi, H.; Haavisto, E.; Leskela¨, M.; Repo, T. J. Comb. Chem. 2004,
6, 967-973.
(10) Results of the parallel screening: ligands a-d, f, h, j-n, and q-t,
no polymer; ligands g and i, 1-2 mg of polymer; ligands e, o, and p, 3-6
mg of polymer. Melting points of the polymers were 130-135 °C
(determined with a melting point apparatus).

982 Organometallics, Vol. 26, No. 4, 2007
Yliheikkila¨ et al.
Figure 2. ORTEP drawing of the coordination sphere of complex
1 (Mn2), illustrating the extensive rhombic distortion of the
octahedral geometry. The distortion of Mn1 is similar.
Figure 1. ORTEP drawing of [(1R,2R)-(-)-N,N′-bis(quinoline-2-
methylene)diiminocyclohexane]manganese(II) chloride (complex 1).
Two independent molecules are displayed. H atoms and one CH2-
Cl2 solvent molecule are omitted for clarity. Ellipsoids are drawn
at the 50% probability level.
Table 1. Crystallographic Data for Complexes 1 and 2
1
2
formula
C26H24N4MnCl2‚
CH2Cl2
603.26
P21
9.249(2)
27.100(4)
11.653(2)
90.0
107.78(3)
90.0
2781.3(9)
1.441
C26H22N4MnCl2‚
3CH2Cl2
771.09
P1h (No. 2)
9.767(1)
12.913(1)
13.741(1)
84.13
77.98(1)
85.77
1683.7(2)
1.521
fw
thus occupy equatorial sites in the octahedral coordination
sphere, leaving chlorides in the trans orientation.12 Altogether,
the observations made above indicate that a ligand backbone
that distorts the equatorial N4Mn plane is beneficial for the
catalytic activity. In addition, the Mn complex based on the
ethylene-bridged ligand r proved to be inactive in ethene
polymerization. Whether this is due to either structural freedom2a,13
of the ethylene bridge or replacement of the diimine functionality
with diamine still remains indistinguishable. In accordance with
previous reports7 and despite the major modifications of the
imino substituents, the series of Mn(II) complexes with bis-
(imino)pyridine ligands j-l turned out to be inactive. It has
been proposed that the inability of bis(imino)pyridineMn(II)
complexes to catalyze olefin polymerization is due to the high-
spin d5 electronic configuration of manganese, which destabi-
lizes Mn-alkyl bonding.7a
On the basis of these results from the primary screening, three
major requirements for a manganese-based olefin polymerization
catalyst bearing imine ligands can be determined: (1) common
for the active Mn catalysts is the presence of two imine pyridine/
quinoline functionalities separated by two carbon atoms, (2)
active Mn(II) complexes are six-coordinated, and (3) chiral
ligand backbones that distort the planar coordination of the
tetradentate ligands in the octahedral coordination sphere of Mn
are beneficial.
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
d
calcd, g cm-3
Z
4
2
µ, cm-1
λ, Å
T, K
Rb
0.883
0.710 73
173(2)
0.0555
0.0989
0.03(2)
1.054
0.710 73
173(2)
0.0948
0.2289
c
Rw
Flack param
a In complex 2 three methylene dichloride solvent molecules were found
in a disordered state, which is reflected in the final R value. b R ) ∑||Fo|
- |Fc||/∑|Fo| for observed reflections (I > 2σ(I)). b Rw ) {∑[w(Fo
-
2
2
Fc )2]}1/2 for all data.
obtained from CH2Cl2 by slow evaporation of the solvent,
whereas all our attempts to crystallize 3 gave only a microc-
rystalline powder.
X-ray diffraction measurements of the tetradentate complexes
confirmed the assumption made above that a chiral bridging
unit can have a significant role in turning inactive Mn(II)
complexes into catalytically active ones. As shown for 1 in
Figure 1, the chiral cyclohexyl group twists the N4-Mn basal
plane and thus causes a substantial rhombic distortion in the
octahedral geometry of Mn(II) (Figure 2). As a consequence,
chlorine atoms are bent away from their apical positions toward
the cis conformation. For the two independent molecules in the
unit cell, the Cl-Mn-Cl angles were 132 and 135° and the
distorted N4-Mn basal planes were practically perpendicular
to the plane of MnCl2 (Table 2).
Synthesis and Solid-State Structures. On the basis of the
results of the primary screening, the three most active Mn(II)
catalysts were chosen for a more detailed study. Manganese-
(II) complexes 1-3 were prepared in practically quantitative
yield by the reaction of MnCl2 and ligands p,14 o,15 and e,
respectively. Since the complexes were insoluble in THF and
Et2O, the excess ligand was removed easily by washing raw
products with these solvents. Single crystals of 1 and 2 were
In comparison to 1, the biphenyl-bridged 2 has an even more
distorted coordination sphere. The pyridine nitrogen atoms are
shifted away from the N4-Mn basal plane, and planes defined
by N1-Mn-N2 and N3-Mn-N4 bisect each others with a
49.0(2)° angle (Figures 3 and 4). As in the case of 1, due to the
twisted-octahedral geometry the chlorine atoms are shifted away
from their apical positions toward the cis orientation with a
(12) Garoufis, A.; Kasselouri, S.; Mitsopoulou, C. A.; Sletten, J.;
Papadimitriou, C.; Hadjiliadis, N. Polyhedron 1999, 18, 39-47.
(13) Hureau, C.; Blondin, G.; Charlot, M. F.; Philouze, C.; Nierlich, M.;
Ce´sario, M.; Anxolabe´he´re-Mallart, E. Inorg. Chem. 2005, 44, 3669-3683.
(14) Abu-Surrah, A.; Laine, T.; Repo, T.; Fawzi, R.; Steinmann, M.;
Rieger, B. Acta Crystallogr. 1997, C53, 1458-1459.
(15) Kettunen, M.; Vedder, C.; Schaper, F.; Leskela¨, M.; Mutikainen,
I.; Brintzinger, H. H. Organometallics 2004, 23, 3800-3807.

Manganese(II) Complexes in Ethene Polymerization
Organometallics, Vol. 26, No. 4, 2007 983
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1 and 2
1a
1a
2
Mn2-N32(imine)
Mn2-N33(imine)
Mn2-N31(pyridine)
Mn2-N34(pyridine)
Mn2-Cl4
2.288(5)
2.292(5)
2.510(4)
2.495(5)
2.401(2)
2.398(2)
132.46(7)
152.64(18)
70.91(17)
85.33(13)
115.42(14)
102.79(14)
85.24(13)
82.24(13)
102.33(14)
116.65(14)
85.36(13)
Mn1-N2(imine)
Mn1-N3(imine)
Mn1-N1(pyridine)
Mn1-N4(pyridine)
Mn1-Cl2
2.289(5)
2.299(5)
2.508(4)
2.485(5)
2.407(2)
2.403(2)
135.60(7)
151.99(18)
71.29(18)
85.34(13)
103.42(15)
111.41(13)
85.49(13)
82.83(13)
111.63(15)
105.18(14)
85.38(13)
2.317(5)
2.345(5)
2.336(5)
2.323(5)
2.4844(19)
2.4763(19)
133.17(7)
154.72(19)
81.71(17)
83.80(13)
131.60(14)
87.14(13)
85.27(13)
86.11(13)
86.00(13)
131.14(13)
84.88(14)
Mn2-Cl3
Mn1-Cl1
Cl3-Mn2-Cl4
N31-Mn2-N34
N32-Mn2-N33
N31-Mn2-Cl3
N32-Mn2-Cl3
N33-Mn2-Cl3
N34-Mn2-Cl3
N31-Mn2-Cl4
N32-Mn2-Cl4
N33-Mn2-Cl4
N34-Mn2-Cl4
Cl1-Mn1-Cl2
N1-Mn1-N4
N2-Mn1-N3
N1-Mn1-Cl1
N2-Mn1-Cl1
N3-Mn1-Cl1
N4-Mn1-Cl1
N1-Mn1-Cl2
N2-Mn1-Cl2
N3-Mn1-Cl2
N4-Mn1-Cl2
a Data for two independent molecules of complex 1.
analogues.7 In fact, within this ligand framework the coordina-
tion geometry of manganese(II) dichloride is isostructural with
iron(II) dichloride and can be described as a distorted-square-
pyramidal arrangement.7b In comparison, the bis(imino)pyridine
Mn(II) complex has a narrower Cl-Mn-Cl angle (120°) than
1 (132° and 135°) and 2 (133°) and shorter Mn-Cl bond
distances (2.31-2.35 Å) than in 1 (2.40-2.41 Å) and in 2 (2.48
Å). Thus, despite the appropriate coordination parameters,
MAO-activated bis(imino)pyridine Mn(II) complexes are inac-
tive in ethene polymerization. However, another structural
parameter that separates catalyst precursors 1 and 2 from inactive
species can be detected.
While imine N-Mn bond lengths are rather constant for all
of the Mn complexes described above (2.29-2.35 Å), pyridine
NPy-Mn distances deviate noticeably. The NPy-Mn bonding
with the bis(imino)pyridine ligand is rather short (2.20 Å), while
in 1 the quinoline N-Mn distances are remarkably elongated
(2.49-2.51 Å), even when compared to those in 2 (2.32-2.34
Å). This noticeable difference in the coordination strength of
the pyridyl lone pairs, together with the elongated Mn-Cl
bonds, might be significant with regard to the catalytic properties
of these Mn complexes. Interestingly, a distortion of the N-Mn
bond lengths similar to that in 1 and 2 can be also be visualized,
although to a lesser extent, from the previously published solid-
state structures of [bis(pyridine-2-methylene)diiminocyclohexane]-
Figure 3. ORTEP drawing of the coordination sphere of complex
2. H atoms and three CH2Cl2 solvent molecules are omitted for
clarity. Ellipsoids are drawn at the 50% probability level.
rather wide angle, 133°, and the N2-Mn-N3 plane is perpen-
dicular to the plane of MnCl2. Despite the distorted-octahedral
coordination in 1 and 2, both complexes have a molecular C2
symmetry.
3b
MnCl2 and bis(bipyridine)MnCl2,17 which, according to a
preliminary screening, possess some catalytic activity after MAO
activation.
Solid-state structures for iron(II) and cobalt(II) dichloro
complexes bearing the same ligand as 2 have been reported
earlier.16 Due to the rigid biphenyl-bridged ligand, both Fe(II)
and Co(II) complexes have slightly distorted octahedral coor-
dination spheres where the pyridyl moieties occupy the apical
positions and the imine nitrogens together with the chlorides
are, in practice, coplanar and form the basal plane. This
orientation of the ligand framework brings the chlorides clearly
cis to each other, and the Cl-M-Cl angle is substantially
smaller for the iron(II) (111°) and cobalt(II) complexes (109°)
than for 2 (133°). Within these complexes the M-Cl bond
lengths are practically same for Fe and Co (2.40 Å), while the
Mn-Cl bonds are noticeably longer (statistically 2.48 Å for
2). Quite surprisingly, the ability of the Fe complex to catalyze
ethene polymerization after MAO activation is negligible.16
Bis(imino)pyridine Mn(II) complexes have been extensively
studied because of their relevance to highly active Fe(II)
The diimine ligands o and p or bipyridine, while coordinating
to MnCl2, cause distortion in the octahedral coordination sphere,
whose amplitude depends on the structure of the ligand. In
addition, being strong field ligands, they can cause further
splitting of the d orbitals. This is seen as an elongation of Mn-
NPy bonds. Qualitatively, the elongated NPy-Mn bonds leads
to reduced electron donation from the ligand and an increased
Lewis acidity of Mn, which might explain the observed ethene
polymerization activity of 1 and 2 after MAO activation.18 For
(17) (a) Lumme, P. O.; Lindell, E. Acta Crystallogr. 1988, C44, 463-
465. (b) McCann, S.; McCann, M.; Casey, R. M. T.; Jackman, M.;
Devereux, M.; McKee, V. Inorg. Chim. Acta 1998, 279, 24-29.
(18) The ligand r from the primary screening (inactive) has similarities
with N,N′-dimethyl-N,N′-bis(pyridylmethyl)ethane-1,2-diamine, for which
a solid-state structure with MnIICl2 has been reported.12 This ligand provides
a distorted-octahedral coordination sphere for Mn(II), leaving the chloride
anions in mutual cis positions. Despite the replacement of the diimine
functionality with diamine, the Mn-N bond length (2.366(2) Å) is in the
range of the Mn-N(imine) distances considered here. However, the pyridine
N-Mn distance is significantly shorter than in 1 and 2 (see also ref 3b).
(16) Vedder, C.; Schaper, F.; Brintzinger, H. H.; Kettunen, M.; Babik,
S.; Fink, G. J. Eur. Inorg. Chem. 2005, 1071-1080.

984 Organometallics, Vol. 26, No. 4, 2007
Yliheikkila¨ et al.
Scheme 1. Synthesis of Manganese Alkyl Derivatives from
Manganese(II) Dichloro Complexes 1 and 2
Figure 4. ORTEP drawing of the coordination sphere of 2,
illustrating the distortion of the octahedral geometry toward the
antiprismatic organization.
Fe(II) and Co(II) complexes bearing the ligand e, the pyridine
N-M distances are short and (2.21 and 2.18 Å, respectively)
indicate tight coordination. Thus, one possible explanation for
the negligible polymerization activity of Fe and Co complexes
is their reduced Lewis acidity due to extensive electron donation
from the pyridine lone pairs.
Synthesis of Manganese Alkyl Derivatives. It is generally
accepted that in the activation of transition metal complexes
for olefin polymerization, complexes are converted to corre-
sponding alkyl derivatives by the treatment with aluminum
alkyls, most commonly in situ with MAO. Such alkyl complexes
are prerequisites for the formation of metal alkyl cations,
generally considered as catalytically active centers for olefin
polymerization. Consequently, transition metal alkyl com-
plexes,19 including manganese alkyl complexes,7a,20 are of
significant interest.
Although Mn(II) dialkyl species are, in general, well-known,21
dialkyl derivatives of these octahedral complexes turn out to
be highly reactive. Treatment of 1 and 2 with (methyl)MgBr
gave highly air- and moisture-sensitive products, which con-
tained, according to HR ESI-MS measurements, dimethyl
complexes. In particular, these air-sensitive compounds undergo
rapid decomposition during IR and EI-MS measurements,
yielding inaccurate results in analyses. It has been shown
previously that alkylated bis(imino)pyridine manganese com-
plexes undergo reductive decomposition, and as a result, mono-
and zerovalent species are formed.7a In addition, the imine ligand
can be subject to alkylation.19b,22 Accordingly, it has been
concluded that these reactions might be reasons for their
negligible catalytic activity.7a,19b,22
To avoid decomposition and the formation of hydrolysis and
oxidation products, the entire preparation of alkyl complexes
was carried out in a glovebox. The treatment of dichloro
manganese(II) derivatives 1 and 2 with (benzyl)MgBr provided
the monobenzyl manganese complexes 4 and 5 with high yields,
while attempts to synthesize dibenzyl derivatives failed (Scheme
1). It seems that the bulky twisted tetradentate ligands in 1 and
2 are shielding the metal center from further substitution with
a relatively large benzyl group. Though complexes 4 and 5 were
treated afterward with an excess of (benzyl)MgBr, only the
monoalkylated species were isolated. These octahedral mono(ben-
zyl)Mn complexes were adequately stable for EI-MS, micro
TOF-MS, and IR characterization.
(21) For example, see: (a) Andersen, R. A.; Carmona-Guzman, E.;
Gibson, J. F.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1976, 2204-
2211. (b) Andersen, R. A.; Haaland, A.; Rypdal, K.; Volden, H. V. J. Chem.
Soc., Chem. Commun. 1985, 1807-1808. (c) Buttrus, N. H.; Eaborn, C.;
Hitchcock, P. B.; Smith, J. D.; Sullivan, A. C. J. Chem. Soc., Chem.
Commun. 1985, 1380-1381. (d) Gambarotta, S.; Floriani, C.; Chiesi-Villa,
A; Guastini, C. J. Chem. Soc., Chem. Commun. 1983, 1128-1129. (e)
Howard, C. G.; Wilkinson, G.; Thornton-Pett, M.; Hursthouse, M. B. J.
Chem. Soc., Dalton Trans. 1983, 2025-2030.
(19) (a) Scott, J.; Gambarotta, S.; Korobkov, I.; Budzelaar, H. M. J. Am.
Chem. Soc. 2005, 127, 13019-13029. (b) Reardon, D.; Conan, F.;
Gambarotta, S.; Yap, G.; Wang, Q. J. Am. Chem. Soc. 1999, 121, 9318-
9325. (c) Woodman, T. J.; Yann Sarazin, Y.; Garratt, S.; Fink, G.;
Bochmann, M. J. Mol. Catal. A: Chem. 2005, 235, 88-97. (d) Vela, J.;
Vaddadi, S.; Cundari, T. R.; Smith, J. M.; Gregory, E. A.; Lachicotte, R.
J.; Flaschenriem, C. J.; Holland, P. L. Organometallics 2004, 23, 5226-
5239. (e) Kitiachvili, K. D.; Mindiola, D. J.; Hillhouse, G. L. J. Am. Chem.
Soc. 2004, 126, 10554-10555. (f) Gibson, V. C.; Tellmann, K. P.;
Humphries, M. J.; Wass, D. F. Chem. Commun. 2002, 20, 2316-2317.
(20) (a) Bart, S.; Hawrelak, E.; Schmisseur A.; Lobkovsky, E.; Chirik,
P. Organometallics 2004, 23, 237-246. (b) Sugiyama, H.; Aharonian, G.;
Gambarotta, S.; Yap, G. P. A.; Budzelaar, P. H. M. J. Am. Chem. Soc.
2002, 124, 12268-12274. (c) Chai, J.; Zhu, H.; Fan, H.; Roesky, H. W.;
Magull, J. Organometallics 2004, 23, 1177-1179.
(22) (a) Reardon, D.; Conan, F.; Gambarotta, S.; Yap, G.; Wang, Q. J.
Am. Chem. Soc. 1999, 121, 9318-9325. (b) Clentsmith, G. K. B.; Gibson,
V. C.; Hitchcock, P. B.; Kimberley. B. S.; Rees, C. R. Chem. Commun.
2002, 1498-1499. (c) Riollet, V.; Cope´ret, C.; Basset, J.-M.; Rousset, L.;
Bouchu, D.; Grosvalet, L.; Perrin, M. Angew. Chem., Int. Ed. 2002, 41,
3025-3027.
(23) Alkyl complexes were also studied in ethene polymerization. In
general, MAO-activated dichloro complexes were more active than the
corresponding TIBA/B(C6F5)3-activated alkyl complexes. Furthermore,
complex 1/MAO produced polyethene, while the corresponding TIBA/
B(C6F5)3-activated alkyl complexes resulted in oligomers. The activated
alkyl complexes were extremely unstable, and their transfer into the 1 L
polymerization reactor without minor air contact was very complicated.
This might induce the poor polymerization behavior and production of
oligomeric products.

Manganese(II) Complexes in Ethene Polymerization
Organometallics, Vol. 26, No. 4, 2007 985
Table 3. Selected Ethene Polymerization Results Catalyzed
Chart 2. Possible Conformational Isomers of a
Tetradentate Ligand in Octahedral Coordination
Geometrya,25
by MAO-Activated Complexes 1-3a,23
b
e
ncat
[Al]: Tp
Mw/
Tm
d
d
cat. (µmol) cocat. [Mn] (°C) activityc 10-3Mw
Mn
(°C)
1
1
1
2
3
10
10
10
20
20
MAO 1000 60
23
10
67
13
17
1796
1184
527
729
712
6.92 135
5.25 135
28.23f 136
14.75f 136
11.08f 137
MAO
MAO
500 60
500 80
MAO 2000 60
MAO 2000 60
a Polymerization conditions: toluene 220 mL, ethene 5 bar, polymeri-
zation time 90 min. b Polymerization temperature. c Activity in kg of PE/
((mol of cat) h). d Determined by GPC against polystyrene standards. e Onset
melting temperatures of the polyethenes after heating the samples to 230
°C and cooling down again to 30 °C (cooling and heating rate 10 °C/min).
f Bimodal molar mass distribution.
a X can be a chlorine atom or an alkyl or polymer group.
the activation has been reported for Fe(II) derivatives of 2 by
Brintzinger et al.16
Polymerization. Ethene polymerizations with the Mn com-
plexes 1-3 were carried out in toluene solution using 30% MAO
as a cocatalyst. The activation process of these manganese
complexes turned out to be rather sensitive to the applied
temperature. When the complexes were first treated at room
temperature with MAO and then heated to the desired polym-
erization temperatures, reproducible activity levels were achieved.
In contrast, catalysts exhibited no or very poor ethene polym-
erization activities when MAO treatment was done at elevated
temperatures.
Conclusions
Parallel screening is an efficient method to identify new
catalytically active complexes for various reactions, in this case
for Mn(II)-based polymerization catalysts. In this way, a
relatively large amount of catalyst precursors made in situ were
studied on a short time scale. From the screening experiments,
three manganese(II) dichloro complexes, two bearing a chiral
tetradentate ligand and one having two bidentate nitrogen
ligands, were identified to be active in ethene polymerization
and were chosen for further studies. Consequently, on the basis
of these results, three essential requirements for the active
manganese(II) catalyst precursors can summarized: (1) they are
six-coordinated, 17-electron species, (2) ligands with imine
pyridine/quinoline moieties separated by two carbon atoms must
be present, and (3) there must be distortion of the octahedral
configuration of the manganese by the coordination of the ligand
framework. Hence, conjugated nitrogen ligands, particularly a
combination of imino and pyridine or quinoline donors, have
unique properties in the area of manganese-based polymerization
catalysis. After MAO activation their Mn(II) complexes were
proved to be active in ethene polymerization and the activity
level of these polymerizations was high among the known
homogeneous manganese systems. Probably, the high polym-
erization temperature causes intramolecular fluctuation of the
coordination sphere of the activated manganese complexes. The
results above offer an interesting route for the further develop-
ment of Mn-based olefin polymerization catalysts.
From the series of catalysts the highest polymerization
activity, 67 kg of PE/((mol of cat) h), was observed for the
MAO-activated complex 1 at 80 °C and under 5 bar of ethene
pressure (Table 3). Although the average activity level is not
competitive with that of Fe(II) bis(imino)pyridine complexes,1
it can be considered high among the homogeneous manganese
catalyst systems described in the literature.6 At 60 °C, the MAO-
activated complex 1 produced very high molar mass polyethene
(1200-1700 kg/mol) with relative narrow molar mass distribu-
tion, though slight tailing toward the low molar mass region
was observed. A rise in the polymerization temperature to 80
°C led to PE with clear bimodal molar mass distribution and a
decrease in the molar mass of the produced polymer.
Despite variations in the polymerization conditions, the
activity of the biphenyl-bridged 2 remained low, below 15 kg
of PE/((mol of cat) h). Moreover, the unbridged complex 3,
bearing the ligand e, gave activities practically equal with those
of 2. Both 2 and 3 produced high molar mass polyethene with
bimodal molar mass distribution.
Experimental Section
Although the alkylation experiments underline the high
reactivity of the dialkyl-Mn species, and thus formation of
radical species via complex degradation is possible, the bimo-
dality of the polymer strongly suggests the presence of two
different, structurally defined catalytically active centers. Prob-
ably, the high polymerization temperature causes intramolecular
fluctuation of the coordination sphere of the activated manganese
complexes. Intuitively, unbridged 3 has the needed structural
freedom for the isomerization, while for the manganese
complexes 1 and 2 bearing the rigid chiral ligands the structural
fluctuation is more restricted. However, the existence of
structural isomerization of similar manganese complexes has
been verified by crystal structure determination,13,24 and the three
possible conformational isomers for tetradentate ligands in an
octahedral coordination sphere are illustrated in Chart 2. In
addition, a similar fluctuation of the complex geometry during
General Considerations. Complex syntheses and polymerization
experiments were performed under an argon atmosphere using
standard Schlenk techniques or in a glovebox. Solvents (HPLC
grade) were dried over sodium flakes and distilled before use.
Anhydrous manganese(II) chloride (MnCl2) was purchased from
Aldrich and stored under an argon atmosphere. Other reagents of
high purity grade were purchased from commercial sources and
used as received. MAO (30% in toluene) was obtained from
Borealis Polymers Ltd.
The mass spectrum of complex 1 was recorded with a Mariner
electrospray ionization MS (ESI-MS), and the mass spectra of
complexes 2-7 were measured with a Bruker MicrOTOF Esquire
3000Plus instrument. The mass spectra of complexes 4 and 6 were
measured with a JEOL JMS-SX102 EI+ instrument (70 eV), using
a direct inlet method. Infrared spectra were measured on a Perkin-
Elmer SpectrumOne spectrometer using an ATR sampling acces-
sory. NMR spectra were recorded in CDCl3 at 25 °C on a Varian
Gemini 200 spectrometer operating at 200 MHz (1H NMR) and
50.286 MHz (13C NMR). Elemental analyses were performed with
an EA 1110 CHNS-O CE instrument.
(24) Li, Q-X; Luo, Q.-H.; Li, Y.-Z.; Pan, Z.-Q.; Shen, M-C. J. Eur. Inorg.
Chem. 2004, 22, 4447-4456.
(25) Rieger, B.; Abu-Surrah, A. S.; Fawzi, R.; Steinman, M. J. Orga-
nomet. Chem. 1995, 497, 73-79.

986 Organometallics, Vol. 26, No. 4, 2007
Yliheikkila¨ et al.
Molar masses and molar mass distributions of polyethene samples
were determined with a Waters Alliance GPCV 2000 high-
temperature gel chromatographic device. HMW7, 2*HMWGE, and
HMW2 Waters Styrogel columns were used for GPC. Measure-
ments were performed in 1,2,4-trichlorobentzene (TCB) at 160 °C
relative to polyethene standards, and 2,6-di-tert-butyl-4-methylphe-
nol was used as a stabilizer. Chromatograms were calibrated using
linear polystyrene standards. DSC measurements were performed
on a Mettler Toledo Star system. Melting temperatures of PE were
measured from 30 to 230 °C using a heating rate of 10 °C/min.
The melting temperature was determined from the second heating
curve.
Parallel Screening. Small glass reactors (Radleys Discovery
Technologies, carousel reaction station) were loaded with different
ligands and manganese(II) chloride and sealed with septa. Solvent
(THF, 4 mL) was added to each reactor through a septum, and
stirring was continued at room temperature for 48 h to ensure the
complex formation. After this, the solvent (THF) was evaporated.
A mixture of MAO (30%) and toluene was added to each reactor,
and the reactors were then placed in a custom-made steel autoclave.9
After addition of ethene (5 bar), the autoclave was kept at room
temperature for 1 h. Subsequently, the autoclave was placed in the
oil bath (60 °C) for 18 h. The batch polymerizations were stopped
by depressurizing the reactor and by adding acidified methanol (1%
HCl). Precipitated polymer was stirred in methanol overnight and
dried in an oven (60 °C) to constant weight.10 Control reactions
with combinations of THF, MnCl2, and MAO without a ligand were
inactive in polymerization.
Preparation of Complexes. [N,N′-Bis(quinoline-2-methylene)-
diiminocyclohexane]manganese(II) Dichloride (1). Manganese-
(II) chloride (0.18 g, 1.4 mmol) was added to a stirred solution of
(1R,2R)-(-)-N,N′-bis(quinoline-2-methylene)diiminocyclohexane
(DQDEC; 0.73 g, 1.9 mmol)27 in THF (30 mL). The solution slowly
turned yellow, and stirring was continued for 48 h at room
temperature. The yellow product was filtered and washed with THF
(2 × 10 mL) and Et2O (2 × 10 mL) and dried under vacuum (0.73
g, 99%). Crystals suitable for single-crystal diffraction studies were
obtained by slow evaporation of solvent (CH2Cl2). Anal. Found:
C, 59.97; H, 5.16; N, 10.93. Calcd: C, 60.25; H, 4.67; N, 10.81.
ESI-MS: m/z 540.6 ([M + Na] 10%). IR: ν 1641 m (CdN, ligand),
1655 m cm-1 (CdN, complex).
{N,N′-(6,6′-Dimethylbiphenyl-2,2′-diyl)bis[(2-pyridyl)methyl]-
diimine}manganese(II) Dichloride (2). This complex was syn-
thesized as described above for 1. Manganese(II) chloride (0.20 g,
1.6 mmol) and N,N′-(6,6′-dimethylbiphenyl-2,2′-diyl)bis(2-pyridyl-
methyl)diimine15 (0.74 g, 1.9 mmol) were used. Yellow crystals
(0.79 g, 97%) grew, similarly to the path described for complex 1.
Anal. Found: C, 60.07; H, 4.38; N, 11.13. Calcd: C, 60.48; H,
4.29; N, 10.88. HR-MS (ESI): m/z calcd for [C26H22N4MnCl2],
515.059 65; m/z obsd, 515.059 74; error, 0.18 ppm. IR: ν 1632 m,
1585 m, 1567 s (CdN, ligand), 1632 s, 1592 s, 1568 m cm-1 (Cd
N, complex).
Bis{2-[((2,6-diisopropylphenyl)imino)methyl]quinoline}-
manganese(II) Dichloride (3). Manganese(II) chloride (0.13 g, 1.1
mmol) and 2,6-bis(1-methylethyl)-N-(2-quinoline-2-methylene)-
phenylamine (e; 0.70 g, 2.2 mmol) were mixed in toluene (20 mL).
The isolation and purification of complex 3 was analogous to the
methods described above for complex 1. Yield: 0.73 g, 91%. HR-
MS (ESI): m/z calcd for [C44H48N4], 758.2709; m/z observed,
758.2686; error, 3.01 ppm. IR: ν 1634 s (in ligand CdN), 1630 s
cm-1 (in complex CdN).
Preparation of Manganese Alkyl Complexes. [N,N′-Bis-
(quinoline-2-methylene)diiminocyclohexane]benzylmanganese-
(II) Chloride (4). A solution of (benzyl)MgBr in Et2O (1 M, 0.8
mL, 0.8 mmol) was added via a syringe to a solution of complex
1 (0.2 g, 0.4 mmol) in Et2O (10 mL) at -78 °C. Stirring was
continued for 5 h, and the resulting mixture was kept in a freezer
(-20 °C) overnight. All volatiles were then removed under vacuum,
and the brown residue was extracted with THF, followed by
filtration through a PTFE syringe filter in a glovebox. The resulting
solution was evaporated off under vacuum. The brown product (0.19
g, 83%) was crystallized by layering THF and hexane. Despite our
efforts, only the monoalkylated species could be prepared. The
alkylated complex 4 was treated afterward with an excess of
(benzyl)Mg, but no further alkylation occurred. HR-MS (ESI): m/z
calcd for [C33H31N4MnCl + H]+, 574.1695; obsd, m/z 574.1691;
error, 0.25 ppm. EI-MS: m/z 574 ([C33H31N4MnCl] (M+), 3%),
483 (M+ - C7H7, 6%). IR: ν 700.75 s (monosubstituted benzene
ring), 749.90 s (monosubstituted benzene ring), 1565.16 w, 1600.55
w, 1618.25 w cm-1 (aromatic, not present in the corresponding
dichloro complex).
Preparation of Ligands. Ligands h/i, m/n, s, and t were
purchased from commercial sources and used as such. Ligands a,
b, f/g, and j-r were prepared according to earlier published
procedures.10
Ligand c, Bis(2,6-difluorophenyl)-NAcNAc. This ligand was
synthesized from 2,6-difluoroaniline (55 mmol, 7.1 g, 5.92 mL)
and 2,4-pentanedione (25.8 mmol, 2.58 g, 2.70 mL). The starting
materials were dissolved in toluene, and a catalytic amount of
p-toluenesulfonic acid was added. The reaction mixture was refluxed
for 12 h with a Dean-Stark apparatus. Toluene was evaporated,
and subsequently 100 mL of Et2O, 80 mL of H2O, and 10 g of
Na2CO3 were added. After the dissolution of solids, the Et2O phase
was separated and washed with saturated Na2CO3 solution (2 ×
10 mL) and brine (10 mL) and dried over MgSO4. The evaporation
of Et2O gave an off-white crystalline solid as a product. The pure
product (5.1 g, 62%) was obtained by recrystallization from absolute
1
EtOH. H NMR (CDCl3): δ 1.95 (s, 6H, -CH3), 5.11 (s, 1H,
-CHd), 6.88-7.04 (m, 6H, Harom), 12.2 (s, 1H, NH). 13C NMR
(CDCl3): δ 20.75 (s, CH3), 97.71 (s, dCH-), 111.73-158.92
(Carom, multiplets due to the 19F couplings), 163.23 (s, CdN). EI-
MS: m/z 322 ([C17H14N2F4] (M+), 80%), 195 (M+ - C6H3F2,
100%), 154, (M+ - C6H3F2NC2H4, 90%).
Ligand d/e, 2-[(2,6-Diisopropylphenylimino)methyl]quinoline.
This ligand was synthesized by a modified literature procedure,
reported earlier for 2-{[(2,6-diisopropylphenyl)imino]methyl}-
pyridine.26 Ethanol (40 mL), 2,6-diisopropylaniline (1.6 g, 9.1
mmol), and 2-quinolinecarboxaldehyde (1.3 g, 7.8 mmol) were
combined and refluxed for 20 min. The solvent was removed, and
the raw product was purified by column chromatography on basic
alumina using pentane/ethyl acetate (3:1) as an eluent. Recrystal-
lization from n-pentane yielded yellow crystals (2.2 g, 89%, 7.0
{N,N′-(6,6′-Dimethylbiphenyl-2,2′-diyl)bis[(2-pyridyl)methyl]-
diimine}benzylmanganese(II) Chloride (5). A solution of (ben-
zyl)MgBr in Et2O (1 M, 0.8 mL, 0.8 mmol) was added via a syringe
to a solution of complex 2 (0.2 g, 0.4 mmol) in Et2O (10 mL) at
-78 °C. Stirring was continued for 5 h, and the resulting mixture
was kept in a freezer (-20 °C) overnight. After 2 h of stirring at
-20 °C the brown solution and yellow residue turned dark green.
All volatiles were then removed under vacuum, and the solid residue
was extracted with toluene and THF. The reddish brown extracts
were filtrated through a PTFE syringe filter, and solvents were
1
mmol). H NMR (CDCl3): δ 1.21 (d, 12 H, HMe), 3.02 (m, 2H,
CHMe2), 7.0-8.5 (10 H, Harom, Himine). 13C NMR (CDCl3): δ 23.62
(-CH3), 28.19 (-CH-, isopropyl), 118.47, 122.95, 123.24, 124.71,
127.98, 129.26, 130.13, 136.90, 137.28, 148.19, 148.60, 154.72
(Carom), 163.57 (-HCdN). EI-MS: m/z 316 ([C22H24N2] (M+),
40%), 301 (M+ - CH3, 50%), 273 (M+ - C3H7, 45%).
(27) (a) Ibrahim, K.; Yliheikkila¨, K.; Lo¨fgren, B.; Abu-Surrah, A.;
Lappalainen, K.; Leskela¨, M.; Repo, T.; Seppa¨la¨, J. J. Eur. Polym. 2004,
40, 1095-1104. (b) Yliheikkila¨, K.; Lappalainen, K.; Castro, P. M.; Ibrahim,
K.; Lo¨fgren, B.; Leskela¨, M.; Repo, T. J. Eur. Polym. 2006, 42, 92-100.
(26) Laine, T. V.; Klinga, M.; Leskela¨, M. J. Eur. Inorg. Chem. 1999,
959-964.

Manganese(II) Complexes in Ethene Polymerization
Organometallics, Vol. 26, No. 4, 2007 987
evaporated off under vacuum. The brown product was crystallized
by layering THF and hexane. As above, only the monoalkylated
species were observed. Yield: 0.21 g, 92%. HR-MS (ESI): m/z
calcd for [C33H29N4MnCl + H]+, 572.1534; m/z obsd, 572.1522;
error, 2.08 ppm. EI-MS: m/z 572 ([C33H29N4MnCl] (M+), 5%),
487 (M+ - C7H7, 52%), 491 (M+ - C7H7MnCl, 50%). IR: ν 699
and 732 s (monosubstituted benzene ring, not present in the cor-
responding dichloro complex), 2845 and 2921 m cm-1 (-CH2-).
Methylation of Manganese Dichloro Complexes. Reaction of
1 with MeMgBr. Complex 1 (0.1 g, 0.2 mmol) and MeMgBr in
Et2O (3.0 M, 0.2 mL, 0.6 mmol) were mixed in Et2O at -78 °C.
The isolation and purification of the resulting product was analogous
to that described above for alkyl complex 4. Yield of the brown
product: 0.09 g. HR-MS (ESI): m/z calcd for the dimethyl Mn
derivative (C28H31N4Mn), 478.1923; m/z obsd, 478.1925; error, 0.41
ppm. Due to the rapid decomposition of the compound in the air,
EI-MS measurements and IR measurements were not feasible.
Reaction of 2 with MeMgBr. Complex 2 (0.1 g, 0.2 mmol)
and MeMgBr in Et2O (3.0 M, 0.2 mL, 0.6 mmol) were mixed in
Et2O at -78 °C. A procedure identical with that described for alkyl
complex 4 was then carried out. Yield of the brown product: 0.07
g. HR-MS (ESI): m/z calcd for the dimethyl Mn derivative
(C28H28N4Mn + Na), 498.1586; m/z obsd, 498.1569; error, 3.59
ppm. Due to the rapid decomposition of the compound in the air,
EI-MS measurements and IR measurements were not feasible.
Single-Crystal X-ray Diffraction Studies. Crystal data for
complexes 1 and 2 were collected with a Nonius KappaCCD area-
detector diffractometer at 173(2) K using Mo KR radiation (graphite
monochromator); λ ) 0.710 73 Å. Software used: data reduction,
COLLECT;28 absorption correction, SADABS;29 solution and
refinement, SHELX97;30 graphics, SHELXTL/PC.31 All non-
hydrogen atoms were refined anisotropically, and the hydrogen
atoms were refined on calculated positions. The displacement factors
of the H atoms were 1.2× (1.5×) those of the host atom.
Crystallographic data for complexes 1 and 2 are given in Table 1.
Ethene Polymerization. Polymerizations were carried out in a
Bu¨chi 1.0 L stainless steel autoclave equipped with a temperature-
controlling unit. Mechanical stirring (800 rpm) was applied, and
the partial pressure of ethene and the reaction temperature were
kept constant during the polymerization. Ethene consumption was
measured with a calibrated mass flow meter and monitored online
together with the temperature and pressure.
Toluene (200 mL), the cocatalyst (MAO, 30%) and the catalyst
precursor (20 µmol) were introduced into the argon-purged reactor.
Once the polymerization temperature was reached, the reactor was
charged with ethene to the appropriate pressure. The polymerization
was stopped by pouring the contents of the vessel into methanol
that was acidified with concentrated hydrochloric acid (1%). The
solid polyethene was filtered, washed with methanol, and dried
overnight at 60 °C to a constant weight.
When alkylated manganese complexes were used, the catalyst
solutions were prepared in a glovebox. TIBA (2.0 mmol) was
dissolved in toluene (20 mL), and the mixture was stirred for 20
min. An alkyl complex (20 µmol) was added, and after 10 min of
stirring it was activated with B(C6F5)3 (21 µmol). The solution was
transferred immediately from the glovebox into the thermostated
reactor charged with toluene (200 mL) and the appropriate ethene
pressure. The polymerization was stopped as described above.
Acknowledgment. This work was financed by the University
of Helsinki, the Academy of Finland Project Nos. 204408 and
77317 (Centre of Excellence, Bio- and Nanopolymer Research
Group), the Finnish Technology Development Agency (Tekes),
and the Walter and Lisi Wahls Foundation. We are grateful to
Mrs. Eeva Kaija for the GPC and DSC measurements, Mr. Pertti
Elo for the Micro TOF-MS measurements, and Dr. Kristian
Lappalainen for valuable discussions. Special thanks are due
to Dr. Stuart Richardson and Dr. Paula Yliheikkila¨ for their
advice.
(28) Nonius. COLLECT; Nonius BV, Delft, The Netherlands, 2002.
(29) Sheldrick, G. M. SADABS; University of Go¨ttingen, Go¨ttingen,
Germany, 1996.
(30) Sheldrick, G. M. SHELX97; University of Go¨ttingen, Go¨ttingen,
Germany, 1997.
(31) Sheldrick, G. M. SHELXTL, version 5.10; Bruker AXS, Madison,
WI, 1997.
Supporting Information Available: CIF files giving crystal
data for 1 and 2 and GPC chromatograms of PE prepared with
1/MAO at different reaction temperatures. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM0608105