Imine versus amine donors in iron-based ethylene polymerisation catalysts

Article abstract of DOI:10.1002/1099-0682(200102)2001:2<431::AID-EJIC431>3.0.CO;2-Q

The synthesis and characterisation of iron(II) dichloro complexes containing neutral tridentate nitrogen ligands of the type 2-arylaminoalkyl-6-aryliminoalkylpyridine [2-ArNHCR(Me)-6-ArN=CR]C₅H₃N (R = H, Ar = 2,6-iPr₂C

Full text of DOI:10.1002/1099-0682(200102)2001:2<431::AID-EJIC431>3.0.CO;2-Q

FULL PAPER
Imine Versus Amine Donors in Iron-Based Ethylene Polymerisation Catalysts
George J. P. Britovsek,[a] Vernon C. Gibson,*[a] Sergio Mastroianni,[a] Daniel C. H. Oakes,[a]
Carl Redshaw,[a] Gregory A. Solan,[a] Andrew J. P. White,[a] and David J. Williams[a]
Keywords: Alkenes / Polymerizations / Iron / N ligands
The synthesis and characterisation of iron(II) dichloro com- methyl)pyridine [2,6-(ArNHCH2)2]C5H3N (Ar = 2,6-iPr2C6H3)
plexes containing neutral tridentate nitrogen ligands of the
type 2-arylaminoalkyl-6-aryliminoalkylpyridine [2-ArNHCR-
(Me)-6-ArN=CR]C5H3N (R = H, Ar = 2,6-iPr2C6H3 or 2,4,6-
Me3C6H2; R = Me, Ar = 2,6-iPr2C6H3)] and 2,6-bis(arylamino-
are described and their activity in ethylene polymerisation is
compared with their 2,6-bis(aryliminoalkyl)pyridine ana-
logues.
Introduction
anionic tridentate bis(imino)pyrollide,[24] bis(amino)phenyl
and bis(phosphanyl)amide ligands.[25] These variations have
resulted in very low catalyst activities. With a view to ob-
taining a greater understanding of structure-activity rela-
tionships in the [N,N,N]Fe catalyst system, we have targeted
alternative tridentate [N,N,N] chelate ligands. A relatively
straightforward modification to the ligand frame is to re-
place one, or both, of the imine groups by amine donors,
examples being 2-aminoalkyl-6-iminoalkylpyridine com-
plexes of type II and the 2,6-bis(aminoalkyl)pyridine species
of type III (see Figure 1). The synthesis and characteris-
ation of complexes of type II and III are described and their
ethylene polymerisation activity is discussed and compared
to the parent bis(imino)pyridine system I.
Transition metal-catalyzed olefin polymerisation is cur-
rently a subject of intense academic and industrial interest.
The need for greater control over the products of olefin
polymerisation, combined with advances in the understand-
ing of homogeneous polymerisation systems, have resulted
in the development of highly active single-site olefin poly-
merisation catalysts such as Group 4 metallocenes and the
‘‘constrained geometry’’ catalysts’.[1Ϫ5] The development of
non-metallocene early transition metal catalysts, and in par-
ticular the discovery of highly active late transition metal
based systems, have signposted the way forward for further
developments in catalytic olefin polymerisation.[6,7] The dis-
covery by Brookhart and co-workers in 1995 of highly act-
ive nickel and palladium olefin polymerisation catalysts
containing the α-diimine ligand frame[8] has been followed
by extensive studies on variations of the α-diimine
ligand.[9Ϫ11] In addition, many other non-diimine neutral
bidentate ligands have been screened for olefin polymeris-
ation activity, a large number by in situ methods.[7,12] How-
ever, to date, no other donor combinations have matched
the high activities obtained with α-diimine ligands, sug-
gesting a special feature of these systems that has yet to be
fully understood.
Figure 1. Pyridyldiimine (I), pyridylimineamine (II) and pyridyldi-
amine (III) iron complexes
A second family of highly active late transition metal
polymerisation catalysts based on 2,6-bis(imino)pyridine
complexes of iron and cobalt, was reported independently Results and Discussion
by ourselves,[13] Bennett and Brookhart in 1998.[14] The ef-
fects of ligand changes, especially at the aryl (Ar) and imino
carbon (R) substituents, on the activity and product select-
ivity of these bis(imino)pyridine iron and cobalt catalysts
(I) have been studied in detail,[15Ϫ17] as well as the poly-
merisation of propene[18Ϫ20] and applications in reactor
blending.[21,22] Only a few variations on the core bis(imino)-
pyridine skeleton have been reported; for example, a neutral
tridentate bis(oxazolinyl)pyridine ligand[23] and mono-
Synthesis of ligands and complexes
A convenient method of preparing 2-aminoalkyl-6-imino-
alkylpyridines is by exploiting attack by nucleophilic re-
agents at the imine carbon atoms.[26] We have recently
shown that AlMe3 reacts with bis(imino)pyridines to give
products of the type {[2-ArNCR(Me)-6-ArNϭCR]-
C5H3N}AlMe2 (1aϪc, Scheme 1) in which only one of the
imino functionalities is attacked to generate an amide
donor.[27] Hydrolysis of these complexes, followed by ex-
traction with pentane and workup, affords ligands 2a؊c as
pale yellow crystalline solids.
[a]
Department of Chemistry, Imperial College,
South Kensington, London SW7 2AY, U.K.
E-mail: V.Gibson@ic.ac.uk
Eur. J. Inorg. Chem. 2001, 431Ϫ437
WILEY-VCH Verlag GmbH, 69451 Weinheim, 2001
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431

V. C. Gibson et al.
FULL PAPER
Scheme 1
1
The H NMR spectra of 2aϪc confirm the presence of
the amine protons as broad resonances in the range δ ϭ
4.3Ϫ4.5, and the infrared spectra show NϪH stretches in
the region 3355Ϫ3365 cmϪ1. A single crystal X-ray struc-
ture of 2a shows the molecule to possess a transoid relation-
ship between the imine and amine groups (Figure 2), a geo-
metry that is different to the cisoid conformation in the
metal complexes (see 3a, Figure 3). There is only a small
(ca. 7°) out-of-plane rotation of the CϭN double bond rel-
ative to the pyridyl ring, whereas the 2,6-diisopropylphenyl
ring system is oriented essentially orthogonally (ca. 87°).
˚
Figure 3. The molecular structure of 3a; selected bond lengths (A)
and angles (°): FeϪN(1) 2.115(7), FeϪN(7) 2.310(8), FeϪN(9)
2.217(8), FeϪCl(1) 2.311(3), FeϪCl(2) 2.243(2), C(7)ϪN(7)
1.489(12), C(9)ϪN(9) 1.281(12); N(1)ϪFeϪN(9) 75.4(3),
N(1)ϪFeϪCl(2)
148.0(2),
N(9)ϪFeϪCl(2)
102.9(2),
N(1)ϪFeϪN(7) 73.5(3), N(9)ϪFeϪN(7) 148.5(3), Cl(2)ϪFeϪN(7)
101.2(2), N(1)ϪFeϪCl(1) 102.8(2), N(9)ϪFeϪCl(1) 102.3(2),
Cl(2)ϪFeϪCl(1) 108.6(1), N(7)ϪFeϪCl(1) 88.8(2)
The transoid conformation observed here for the pyridyl im- paramagnetic, with µeff typically between 5.4 and 5.6 BM,
ine unit is typical for such species in the solid state,[18,28,29] indicating four unpaired electrons; they were further char-
i.e. there has to be an approximate 180° rotation about the acterized by IR, MS and microanalysis. The IR spectra of
C(2)ϪC(9) bond for chelation of the pyridyl and imino ni- 3aϪc show ν(NϪH) stretches at ca. 3300 cmϪ1. Crystals of
trogen atoms to a metal centre. In contrast to the in-plane 3a suitable for a single crystal structure determination were
conformation of the conjugated imine group, there is a grown from a concentrated acetonitrile solution. The X-ray
marked deviation of the saturated ‘‘amine arm’’ from co- analysis of 3a shows[30] (Figure 3) that the partially satur-
planarity with the pyridyl ring, the N(1)ϪC(6)ϪC(7)ϪN(7) ated ligand (2a) complexes to the iron(II) centre in a similar
torsion angle being 65°. Centrosymmetrically related pairs way
to
its
unsaturated
analogue,[13,14]
the
of molecules pack such that the edge of ring A of one mole- N(7)ϪC(7)ϪpyϪC(9)ϪN(9) component being co-planar to
˚
˚
cule is directed into the face of ring B of another; the within 0.07 A, with the iron atom lying 0.07 A out of this
˚
centroid···centroid distance is 4.94 A, and is consistent with plane. The five-membered chelate ring containing the am-
an aromatic···aromatic edge-to-face interaction.
ino nitrogen atom N(7) is also almost planar, the torsional
Treatment of 2aϪc with FeCl2 in nBuOH at elevated tem- twist about the C(6)ϪC(7) bond being only ca. 6°. The geo-
perature gives complexes 3aϪc as pale blue solids. Analog- metry at iron is distorted square pyramidal with cis angles
ous to the bis(imino)pyridine systems, these complexes are in the range 73.5(3) to 108.6(1)°, the iron atom lying 0.43
˚
Figure 2. The molecular structure of 2a; selected bond lengths (A): C(7)ϪN(7) 1.473(8), C(9)ϪN(9) 1.255(8)
432
Eur. J. Inorg. Chem. 2001, 431Ϫ437

Imine Versus Amine Donors in Iron-Based Ethylene Polymerisation Catalysts
FULL PAPER
˚
A out of the basal plane in the direction of the apical atom
Cl(1). The most noticeable feature in the pattern of bonding
˚
is the weak nature of the FeϪN(7) linkage [2.310(8) A] —
a distance equal to that to the apical chlorine centre Cl(1)
˚
[2.311(3) A] — and a consequent shortening of the
˚
˚
FeϪN(9) bond to 2.217(8) A {cf. 2.238(4) and 2.250(4) A
in the related bis(imino)pyridine iron dichloride
species[13Ϫ15]}. The FeϪN(1) bond length is, as expected,
˚
shorter at 2.115(7) A, as is the distance to the basal chlorine
[2.243(2) A]. Both of the 2,6-diisopropylphenyl substituents
˚
Scheme 2
are oriented approximately orthogonally to the basal coor-
dination plane, the ca. 81° twist about the N(9)ϪC(22)
bond facilitating characteristic CϪH···N(pπ) interactions[31] dentate, binding to the iron centre through the pyridyl and
between the isopropyl methine hydrogen atoms and the im- the two amine nitrogen atoms in a fashion analogous to
ine nitrogen [N(9)]; the H···N distances are 2.41 and 2.44 that seen in the imine/amine complex 3a. The geometry at
3
˚
A. The amine nature (i.e. sp hybridisation) of the N(7) ni- iron is still distorted square pyramidal, but with the iron
˚
trogen precludes any such interaction here, and results in atom lying 0.61 A out of the basal plane; the cis angles are
a distinct folding of the C(10) aryl substituent out of the in the range 74.2(1) to 115.6(1)°. The two five-membered
N(7)ϪC(7)ϪpyϪC(9)ϪN(9) plane — the C(22) phenyl car- chelate rings are nonplanar, there being torsional twists of
bon atom is virtually coplanar with this plane (deviation ca. 26 and 18° about the C(2)ϪC(7) and C(6)ϪC(8) bonds,
˚
˚
ca. 0.03 A) whilst C(10) lies 1.06 A below it, such that the respectively. Interestingly, these twists are in opposite
NϪAr bond is inclined by ca. 42° to this plane. This devi- senses, thus producing δ and λ conformations, respectively,
ation will strongly affect the steric influence of the ligand for the two rings, whereas the configurations at the two am-
on the remaining metal coordination sites. Finally, there are ino centres are the same. As expected, the FeϪN(1) distance
˚
no dominant intermolecular interactions of note, although [2.118(4) A] is significantly shorter than that to the two
there is evidence for a weak CϪH···Cl hydrogen bond be- amine nitrogens, which are the same at 2.313(4) and
˚
tween the imine CϪH group [C(9)] in one molecule and 2.328(4) A for N(7) and N(8), respectively, values essentially
the apical chorine [Cl(1)] in another; the C···Cl and H···Cl the same as that to the amino nitrogen in 3a. Similarly, the
˚
˚
distances are 3.34 and 2.57 A, respectively, with a CϪH···Cl FeϪCl(axial) distance [2.313(2) A] is longer than its basal
angle of 137°.
˚
counterpart [2.269(2) A]. In common with 3a, the two 2,6-
2,6-Bis(2,6-diisopropylphenylaminomethyl)pyridine (5) diisopropylphenyl ring systems are oriented approximately
(see Scheme 2) was readily prepared according to a proced- orthogonally to the basal coordination plane. Although
ure by McConville and co-workers, from the reaction of both the amine nitrogen atoms N(7) and N(8) are pyram-
2,6-bis(bromomethyl)pyridine with LiNHAr (Ar ϭ 2,6-di- idal, as a consequence of the different folds of the five-mem-
isopropylphenyl).[32] However, this potentially tridentate bered chelate rings only one of the 2,6-diisopropylphenyl
chelate does not react with anhydrous FeCl2 in nBuOH, nor rings is folded out of the basal coordination plane, the other
in THF; there is no colour change on mixing and warming having its N(7)ϪC(9) linkage virtually in plane. This results
to 80 °C, and after workup, only starting materials are reco- in an overall geometry very similar to that seen in the imine-
vered. In case this outcome may have been a consequence amine structure 3a. The only intermolecular packing inter-
of the modified disposition of the large aryl groups imposed action of note is a weak π-π stacking of pairs of C(21) con-
by the sp3-hybridised nitrogen centres, we also attempted a taining 2,6-diisopropylphenyl rings of adjacent molecules;
˚
similar reaction between 2,6-bis(diphenylaminomethyl)pyri- the mean interplanar separation is 3.85 A.
dine and FeCl2 but again complexation did not occur. An
The orthorhombic form of the complex (6b) has crystal-
alternative method, recently described by Calderazzo et lographic C2 symmetry about an axis passing along the
al.,[33] was investigated by refluxing a mixture of pyridyldia- Fe···N(1)···C(4) vector. The conformations of the two five-
mine ligand 5 and FeCl2·thf in toluene overnight. This route membered chelate rings are both λ relative to the S config-
leads to the desired complex 6 in high yield as blue/green urations at the amino centres (Figure 5); the torsional twists
crystals (Scheme 2). The compound is air stable and readily about the C(2)ϪC(5) bonds are ca. 17°. Accompanying this
soluble in polar solvents such as dichloromethane or THF, difference in the conformational/configurational relation-
but decomposes in acetone. Satisfactory microanalysis, IR ship (cf. that in 6a) is a change from a square pyramidal to
and magnetic data (µeff ϭ 5.08 BM) as well as X-ray crystal- a trigonal bipyramidal coordination geometry for the iron
lographic analysis confirm the structure of 6 to be the ex- with N(1), Cl and ClA forming the equatorial plane. The
pected five-coordinate [N,N,N]FeCl2 complex.
angles subtended at iron by these three atoms are all, within
Depending upon the method of crystallization, two dif- statistical significance, 120°; the axial bonds [FeϪN(5)] sub-
ferent crystalline forms are produced, one monoclinic (6a, tend an angle of 153.8(2)°. The FeϪN(1) and FeϪN(5)
˚
Figure 4), obtained from a hot saturated toluene solution bond lengths [2.095(5) and 2.322(4) A, respectively] do not
and the other orthorhombic (6b, Figure 5), grown from cold differ significantly from those in 6a. In contrast to the
(Ϫ30 °C) toluene. In the monoclinic form, the ligand is tri- asymmetric FeϪCl bond lengths in 3a and 6a, here they are
Eur. J. Inorg. Chem. 2001, 431Ϫ437
433

V. C. Gibson et al.
FULL PAPER
the other ‘‘down’’. There are no intermolecular packing in-
teractions of consequence.
For bis(imino)pyridine iron complexes we have shown
previously that, depending on the aryl substituents of the
ligand (e.g. 2,6-diisopropylphenyl versus mesityl), either
square based pyramidal or trigonal bipyramidal geometries
are observed in the solid state.[15] Here we see that, in the
case of complex 6, different geometries (6a and 6b) are ob-
tained depending on the method of crystallisation. These
results suggest a small energy difference between the two
geometries, indicating stereochemical nonrigidity of
[N,N,N]FeCl2 complexes, a behaviour that is not uncom-
mon for five-coordinate complexes.[34]
Ethylene Polymerisation Results
The results of ethylene polymerization tests at 1 bar and
10 bar with precatalysts 3a؊c, 4 and 6 with methylalumi-
noxane (MAO) as activator are collected in Table 1. For
comparison, the polymerisation results of the previously re-
ported pyridyldiimine iron precatalysts 7 and 8 are also in-
cluded (Figure 6). Two sets of polymerisation tests are
Figure 4. The molecular structure of the monoclinic form of 6 (6a)
showing also the square pyramidal geometry at iron; selected bond
˚
lengths (A) and angles (°): FeϪN(1) 2.118(4), FeϪN(7) 2.313(4),
FeϪN(8) 2.328(4), FeϪCl(1) 2.313(2), FeϪCl(2) 2.269(2),
C(7)ϪN(7) 1.445(6), C(8)ϪN(8) 1.507(6); N(1)ϪFeϪCl(2)
142.87(12), N(1)ϪFeϪN(7) 74.16(14), Cl(2)ϪFeϪN(7) 91.09(12), shown in Table 1. Tests at 1 bar were carried out in a
N(1)ϪFeϪCl(1)
N(7)ϪFeϪCl(1)
Cl(2)ϪFeϪN(8)
103.32(12),
115.61(14),
101.42(11),
Cl(2)ϪFeϪCl(1)
N(1)ϪFeϪN(8)
N(7)ϪFeϪN(8)
113.75(7),
76.48(14),
145.2(2),
Schlenk flask at room temperature, with no scavenger and
toluene as the solvent. High pressure tests (10 bar) were
performed in a 1 litre autoclave at 35 °C, with triisobutylal-
uminium as a scavenger and isobutane as the solvent.
The results collected in Table 1 show that all of the new
pyridylimine amine (3a؊c) and pyridyldiamine (6) iron
complexes are active ethylene polymerisation catalysts un-
der these conditions. However, it is also apparent that the
activities of these new precatalysts are dramatically reduced
relative to the pyridyldiimine catalysts 7 and 8 (run 10 and
11). The highest activities of 90Ϫ110 g/mmol·h·bar are ob-
tained with complex 3c, which is derived from the pyridyldi-
ketimine ligand (as in complex 8). The precatalysts 3a and
3b, derived from aldimine precursors, generally show lower
activities, around 20 g/mmol·h·bar. This difference in activ-
ity parallels the trends observed for aldimine (7) versus
ketimine (8) precatalysts based on pyridyldiimine ligands
(runs 10 and 11).[15] The very low activity observed for the
pyridylimine amine cobalt precursor 4 (run 7) compared to
the iron analogue 3a (run 1) is equally not surprising, bear-
ing in mind that, in general, for pyridyldiimine systems, co-
balt precatalysts are an order of magnitude less active than
their iron counterparts. Substitution of both imine donors
for amine donors as in precatalyst 6 leads to a further de-
crease in activity, typically to around 10 g/mmol·h·bar. A
similar behaviour of diimine versus diamine donors is ob-
served in nickel ethylene polymerisation systems, where the
saturated bis(2,6-diisopropylphenyl)ethylene diamine ligand
showed only very low activity relative to the α-diimine ana-
logue.[12]
Cl(1)ϪFeϪN(8) 88.94(12)
Figure 5. The molecular structure of the orthorhombic form of 6
(6b) showing also the trigonal bipyramidal geometry at iron; se-
˚
lected bond lengths (A) and angles (°): FeϪN(1) 2.095(5), FeϪN(5)
2.322(4), FeϪCl 2.277(2), C(5)ϪN(5) 1.479(6); N(1)ϪFeϪCl
120.03(5), N(1)ϪFeϪClA 120.03(5), ClϪFeϪClA 119.94(9),
N(1)ϪFeϪN(5A)
ClAϪFeϪN(5A)
ClϪFeϪN(5)
76.91(10),
102.29(12),
102.29(12),
ClϪFeϪN(5A)
N(1)ϪFeϪN(5)
ClAϪFeϪN(5)
90.80(12),
76.91(10),
90.80(12),
N(5A)ϪFeϪN(5) 153.8(2)
˚
symmetric at 2.277(2) A, there being no axial/basal distinc-
Previously we have shown for pyridyldiimine iron poly-
tion. The essentially orthogonal relationship between the merisation catalyst 8, that the rate of propagation is first
2,6-diisopropylphenyl ring systems and the N3Fe coordina- order in ethylene, resulting in a linear increase of the yield
tion plane is retained, but in contrast to 6a, because of the of polyethylene with pressure.[15] Although we have not car-
C2 symmetry and the pyramidalisation at the amine nitro- ried out a systematic study of the effect of pressure on these
gens, one of the 2,6-diisopropylphenyl is directed ‘‘up’’ and new pyridylimine amine systems, the results in Table 1 show
434
Eur. J. Inorg. Chem. 2001, 431Ϫ437

Imine Versus Amine Donors in Iron-Based Ethylene Polymerisation Catalysts
FULL PAPER
Table 1. Results of ethylene polymerization runs using precatalysts 3aϪc, 4, 6؊8
Run
Precatalyst
(µmol)
Activator
(mmol/equiv.)
T
P
(bar)
Yield
(g)
Activity
Mn
Mw
Mw/Mn
(g mmolϪ1
˚
(C)
hϪ1 barϪ1
)
1[a]
2[b]
3[a]
4[b]
5[a]
6[b]
7[a]
8[a]
9[b]
10[c]
11[c]
3a (20)
3a (25)
3b (20)
3b (27)
3c (20)
3c (25)
4 (20)
6 (20)
6 (25)
7 (6)
MAO (8/400)
MAO (10/400)
MAO (8/400)
MAO (10/400)
MAO (8/400)
MAO (10/400)
MAO (8/400)
MAO (8/400)
MAO (10/400)
MAO (1.2/200)
MAO (0.5/1000)
25
35
25
35
25
35
25
25
35
35
50
1
0.4
20
21
18
14
90
110
3
10
1
5.2
30000
21000
161000
210000
177000
896000
7.1
8.4
5.5
0.4
10
1
3.7
2.1
10
1
27.8
0.06
0.21
0.70
18.2
26.9
1
11
3
10
10
10
3000
3400
64000
63000
132000
611000
21.1
38.9
9.5
305
5340
8 (0.5)
[a]
[b]
Schlenk-test conditions: Toluene solvent (40 mL), reaction time 1 hour. Ϫ
High pressure reactor conditions: Isobutane solvent
(0.5 L), reaction time 1 hour, AliBu3 scavenger (2 mL of a 1  solution). Ϫ Results for precatalysts 7 and 8 taken from ref.[15]
[c]
hindering access of monomer to the active site or growth
of the polymer chain.
Experimental Section
General: All manipulations were carried out under an atmosphere
of nitrogen using standard Schlenk and cannula techniques or in a
conventional nitrogen-filled glove-box. Solvents were refluxed over
an appropriate drying agent, and distilled and degassed prior to
Figure 6. 2,6-Bis(imino)pyridine iron precatalysts 7 and 8
use. Elemental analyses were performed by the microanalytical ser-
vices of the Department of Chemistry at Imperial College, Medac
Ltd. or SACS at the University of North London. NMR spectra
were recorded on a Bruker spectrometer at 250 MHz (1H), and
62.9 MHz (13C) at 293 K; chemical shifts are referenced to the re-
sidual protio impurity of the deuterated solvent; coupling constants
are quoted in Hz. Mass spectra were obtained using either Fast
Atom Bombardment (FAB), Electron Impact (EI) or Chemical
Ionization (CI). Magnetic susceptibility studies were performed us-
ing an Evans balance or the Evans NMR method (solvent CD2Cl2;
reference: cyclohexane).
the difference between 1 bar and 10 bar tests. With a tenfold
increase in pressure (similar amount of catalyst in each
case) an approximate tenfold increase in polymer yield is
observed, suggesting that for these systems the rate of pro-
pagation is also first order in ethylene.
Molecular weight data have only been obtained for the
pyridyl imine amine systems which showed moderate activ-
ity (Table 1). The Mw value for the polyethylene obtained
with the ketimine-derived imine amine catalyst 3c is com-
parable to the parent pyridyl diimine catalyst 8. The aldim-
ine-derived analogue 3a gives a lower value for Mn and Mw
than for 3c, but follows the same trend as seen for pyridyl
diimine systems (cf. Runs 2 and 6 versus 10 and 11), includ-
ing a negligible difference between 2,6-diisopropyl and mes-
ityl substituents (3a versus 3b, runs 2 and 4).
Materials: The ligands 2,6-bis[(2,6-diisopropylphenylimino)methyl-
]pyridine,[15] and 2,6-bis[(2,6-diisopropylphenylamino)methyl]pyri-
dine (5),[32] as well as pyridinedicarboxaldehyde,[35] FeCl2·thf[33] and
the aluminium complexes 1aϪc[27] were prepared according to es-
tablished procedures while 2,6-diacetylpyridine, MAO (10% solu-
tion in toluene) and all anilines were purchased from Aldrich
Chemical Co. All other chemicals were obtained commercially and
used as received unless stated otherwise.
In conclusion, we have synthesized and characterized a
series of complexes containing neutral tridentate [N,N,N]
ligands. The 2-aminoalkyl-6-iminoalkyl-pyridine iron com-
plexes of type II (Figure 1) show moderate activity in ethyl-
Synthesis of Ligands and Complexes
6-[(2,6-Diisopropylphenylamino)-1-ethyl]-2-[(2,6-diisopropylphenyl-
imino)methyl]pyridine (2a): Pentane (40 mL) was added to
ene polymerisation, whereas a 2,6-bis(alkylamino)pyridyl [C5NH3{CHϭN(2,6-iPr2-C6H3)}{CHMeN(2,6-iPr2-C6H3)}]AlMe2
(1a; 5.79 g, 11.0 mmol) followed by slow addition of an equal vol-
ume of water. After stirring for a further 3 h the pentane was
stripped off. The aqueous phase was then extracted into chloroform
(3 ϫ 30 mL), filtered, dried over MgSO4 and taken to dryness to
iron complex of type III shows only low activity. Interest-
ingly, although the activities are significantly lower than the
related pyridyldiimine catalysts, similar trends upon ligand
variation, both in activity as well as in polymer properties,
are observed. A possible reason for the lower activity relat-
ive to bis(imino)pyridine systems is the weakness of the
amino-iron interaction, which may lead to dissociation of
the amine arm in these catalysts. However, the lack of con-
jugation through the ligand backbone may also be signific-
give
analytically
pure
[C5NH3{CHϭN(2,6-iPr2-C6H3)}-
{CHMeNH(2,6-iPr2-C6H3)}] (2a; 4.14 g, 80%).
(CDCl3, 293 K): δ ϭ 8.38 (s, 1 H, NϭCH), 8.17 [d, J(HH) ϭ 7.7,
1 H, Py-Hm], 7.73 [app. t, J(HH) ϭ 7.7, 1 H, Py-Hp], 7.3Ϫ7.0 (m,
Ϫ
3
1H NMR
3
3
7 H, Ar-H, Py-Hm), 4.48 [d, J(HH) ϭ 10.4, 1 H, N-H], 4.3Ϫ4.4
(m, 1 H, NϪCHMe), 3.31 [sept, 3J(HH) ϭ 6.8, 2 H, CHMe2], 3.02
ant, as may the orientation of the amino aryl substituent in [sept, 3J(HH) ϭ 6.8, 2 H, CHMe2], 1.49 [d, 3J(HH) ϭ 6.6, 3 H,
Eur. J. Inorg. Chem. 2001, 431Ϫ437
435

V. C. Gibson et al.
FULL PAPER
NϪCHMe], 1.3Ϫ1.2 (m, 18 H, CHMe2), 1.09 (d, 6 H, CHMe2). Ϫ Kα) ϭ 6.30 cmϪ1, F(000) ϭ 1264, T ϭ 293 K; deep red blocks, 0.57
CI MS: m/z ϭ 470 [(M ϩ H)ϩ]. Ϫ IR (Nujol mull): ν˜ ϭ 3356 cmϪ1 ϫ 0.40 ϫ 0.23 mm, Siemens P4/PC diffractometer, ω-scans, 3302
[ν(NϪH)]. Ϫ C32H43N3 (469.71): calcd. C 81.88, H 9.17, N 8.96; independent reflections. The structure was solved by direct
found C 82.21, H 9.30, N 8.71.
methods and the non-hydrogen atoms were refined anisotropically
using full-matrix least-squares based on F2 to give R1 ϭ 0.065,
wR2 ϭ 0.113 for 1968 independent observed absorption corrected
reflections [|Fo| Ͼ 4σ(|Fo|), 2θ Յ 50°] and 347 parameters. The abso-
lute chirality of 3a (which undergoes spontaneous resolution upon
crystallisation) was determined by an R-factor test [R1ϩ ϭ 0.0648,
R1Ϫ ϭ 0.0666].
Crystallographic data (excluding structure factors) for this struc-
ture have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC-149267.
Copies of the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: (in-
ternat.) ϩ 44-1223/336-033; Email: deposit@ccdc.cam.ac.uk].
Crystal Data for 2a: C32H43N3, M ϭ 469.7, monoclinic, space
group P21/c (no. 14), a ϭ 16.208(2), b ϭ 10.364(1), c ϭ 17.664(3)
3
Ϫ3
˚
˚
A, β ϭ 100.67(1)°, V ϭ 2916.1(6) A , Z ϭ 4, Dc ϭ 1.070 g cm
,
µ(Cu-Kα) ϭ 4.70 cmϪ1, F(000) ϭ 1024, T ϭ 293 K; clear plates,
0.23 ϫ 0.07 ϫ 0.02 mm, Siemens P4/RA diffractometer, ω-scans,
4065 independent reflections. The structure was solved by direct
methods and the non-hydrogen atoms were refined anisotropically
using full-matrix least-squares based on F2 to give R1 ϭ 0.096,
wR2 ϭ 0.191 for 1619 independent observed reflections [|Fo| Ͼ
4σ(|Fo|), 2θ Յ 116°] and 317 parameters.
Crystallographic data (excluding structure factors) for this struc-
ture have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC-149266.
Copies of the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax: (in-
ternat.) ϩ 44-1223/336-033; Email: deposit@ccdc.cam.ac.uk].
{6-[(2,4,6-Trimethylphenylamino)-1-ethyl]-2-[(2,4,6-trimethylphenyl-
imino)methyl]pyridine}iron(II) Dichloride (3b): Complex 3b was pre-
pared by an analogous route to that outlined for complex 3a from
FeCl2 (0.15 g, 1.18 mmol) and ligand 2b (0.44 g, 1.18 mmol). Yield:
0.46 g, 80%. Ϫ µeff (Evans Balance): 5.4 BM. Ϫ IR (Nujol): ν˜ ϭ
6-[(2,4,6-Trimethylphenylamino)-1-ethyl]-2-[(2,4,6-trimethylphenyl-
imino)methyl]pyridine (2b): Prepared in the same way as described
for compound 2a, from Al complex 1b. Yield 75%. Ϫ 1H NMR
3307 cmϪ1 [ν(NϪH)]. Ϫ FAB MS: m/z ϭ 511 [Mϩ], 476 [Mϩ
Ϫ
Cl]. Ϫ C26H31Cl2N3Fe (512.30): calcd. C 60.94, H 6.05, N 8.20;
found C 60.11, H 6.12, N 7.98.
3
(CDCl3, 293 K): δ ϭ 8.28 (s, 1 H, NϭCH), 8.07 [d, J(HH) ϭ 7.8,
3
1 H, Py-Hm], 7.64 [app. t, J(HH) ϭ 7.8, 1 H, Py-Hp], 7.14 (d, 1
{6-[2-(2,6-Diisopropylphenylamino)-2-isopropyl]-2-[(2,6-diisopropyl-
phenylimino)ethyl]pyridine}iron(II) Dichloride (3c): Complex 3c was
prepared by an analogous route to that outlined for 3a from FeCl2
(0.15 g, 1.18 mmol) and 2c (0.59 g, 1.18 mmol). Yield: 0.46 g, 62%.
Ϫ µeff (Evans Balance): 5.6 BM. Ϫ IR (Nujol): ν˜ ϭ 3301 cmϪ1
[ν(NϪH)]. Ϫ FAB MS: m/z ϭ 623 [Mϩ], 588 [Mϩ Ϫ Cl]. Ϫ
C34H47Cl2N3Fe (624.52): calcd. C 65.38, H 7.53, N 6.73; found C
65.31, H 7.89, N 7.31.
H, Py-Hm), 6.84 (s, 2 H, Ar-H), 6.70 (s, 2 H, Ar-H), 4.43 [br, q,
3J(HH) ϭ 6.5, 1 H, NϪCHMe], 4.31 (s, br, 1 H, NϪH), 2.23 (s, 3
H, Ar-Mep), 2.18 (s, 6 H, Ar-Meo), 2.13 (s, 3 H, Ar-Mep), 2.07 (s,
6 H, Ar-Meo), 1.36 (d, 3 H, NCHMe). Ϫ CI MS: m/z ϭ 385 [(M
ϩ H)ϩ]. Ϫ IR (Nujol mull): ν˜ ϭ 3359 cmϪ1 [ν(NϪH)]. Ϫ C26H31N3
(385.55): calcd. C 81.04, H 8.05, N 10.91; found C 81.44, H 8.39,
N 10.79.
6-[2-(2,6-Diisopropylphenylamino)-2-isopropyl]-2-[(2,6-diiso-
propylphenylimino)ethyl]pyridine (2c): Prepared in the same way as
described for compound 2a, from Al complex 1c. Yield 71%. Ϫ 1H
{6-[(2,6-Diisopropylphenylamino)-1-ethyl]-2-[(2,6-diisopropylphenyl-
imino)methyl]pyridine}cobalt(II) Dichloride (4): Complex 4[30] was
prepared by an analogous route to that outlined for 3a from CoCl2
(0.15 g, 1.15 mmol) and 2a (0.54 g, 1.15 mmol). Yield: 0.48 g, 70%.
Ϫ µeff(Evans Balance): 4.6 BM. Ϫ IR (Nujol mull): ν˜ ϭ 3304 cmϪ1
[ν(NϪH)]. Ϫ FAB MS: m/z ϭ 599 [Mϩ], 563 [Mϩ Ϫ Cl], 528
[Mϩ Ϫ2Cl].
3
NMR (CDCl3, 293 K): δ ϭ 8.25 [d, J(HH) ϭ 7.7, 1 H, PyϪHm],
7.79 (app. t, 3J(HH) ϭ 7.7, 1 H, Py-Hp), 7.59 (d, 1 H, Py-Hm),
7.2Ϫ7.0 (m, 6 H, Ar-H), 4.47 (s, br, 1 H, NϪH), 3.31 [sept,
3J(HH) ϭ 6.7, 2 H, CHMe2], 2.77 [sept, 3J(HH) ϭ 6.7, 2 H,
CHMe2], 2.24 (s, 3 H, NϭCMe), 1.51 (s, 6 H, NϪCMe2), 1.17 (d,
12 H, CHMe2), 1.07 (d, 12 H, CHMe2). Ϫ EI MS: m/z ϭ 497 [Mϩ].
Ϫ IR (Nujol mull): ν˜ ϭ 3362 cmϪ1 [ν(NϪH)]. Ϫ C34H47N3
(497.77): calcd. C 82.09, H 9.46, N 8.45; found C 82.39, H 9.71,
N 8.30.
[2,6-Bis(2,6-diisopropylphenylaminomethyl)pyridine]iron(II) Dichlor-
ide (6): A suspension of the pyridyldiamine ligand 5 (0.45 g;
1.0 mmol) and FeCl2·thf (1 equiv.) in toluene (50 mL) was refluxed
overnight. Upon cooling to room temperature, the product precip-
itated as blue/green crystals (6a), which were washed with toluene
and pentane and dried in vacuo. Another batch of crystals were
grown from a saturated toluene solution at Ϫ30 °C (6b). Yield:
{6-[(2,6-Diisopropylphenylamino)-1-ethyl]-2-[(2,6-diisopropylphenyl-
imino)methyl]pyridine}iron(II) Dichloride (3a): FeCl2 (0.20 g,
1.57 mmol) was dissolved in hot n-butyl alcohol (10 mL) at 80 °C.
A suspension of 2a (0.72 g, 1.62 mmol) in n-butyl alcohol was ad-
ded dropwise at 80 °C. The reaction mixture turned blue. After
stirring at 80 °C for 15 minutes the reaction was allowed to cool
to room temperature. The reaction volume was then reduced to a
few millilitres and diethyl ether added to precipitate [C5NH3{CHϭ
N(2,6-iPr2-C6H3)}{CHMeNH(2,6-iPr2-C6H3)}]FeCl2 (3a; 0.76 g,
83%) as a blue powder, which was subsequently washed three times
with diethyl ether (10 mL). Ϫ µeff (Evans Balance): 5.6 BM. Ϫ IR
(Nujol): ν˜ ϭ 3303 cmϪ1 [ν(NϪH)]. Ϫ FAB MS: m/z ϭ 596 [Mϩ],
560 [Mϩ Ϫ Cl]. Ϫ C32H43N3FeCl2 (596.46): calcd. C 64.43, H 7.21,
N 7.05; found C 64.70, H 7.19, N 6.99.
0.51 g (87%).
Ϫ µeff (Evans NMR method): 5.08 BM. Ϫ
C31H43N3FeCl2·0.5thf (620.51): calcd. C 63.88, H 7.63, N 6.77;
found C 64.07, H 7.77, N 6.52.
Crystal Data for 6a (monoclinic form): C31H43N3Cl2Fe·0.5C7H8,
M ϭ 630.5, monoclinic, space group P21/n (no. 14), a ϭ 9.789(2),
3
˚
˚
b ϭ 14.750(4), c ϭ 24.757(3) A, β ϭ 95.79(1)°, V ϭ 3556(1) A ,
Z ϭ 4, Dc ϭ 1.178 g cmϪ3, µ(Mo-Kα) ϭ 6.00 cmϪ1, F(000) ϭ 1340,
T ϭ 293 K; blue/straw dichroic needles, 0.77 ϫ 0.17 ϫ 0.17 mm,
Siemens P4/PC diffractometer, ω-scans, 6268 independent
reflections. The structure was solved by the heavy atom method
and all the major occupancy non-hydrogen atoms were refined an-
isotropically using full-matrix least-squares based on F2 to give
R1 ϭ 0.066, wR2 ϭ 0.137 for 3276 independent observed reflections
[|Fo| Ͼ 4σ(|Fo|), 2θ Յ 50°] and 438 parameters.
Crystal Data for 3a: C32H43Cl2N3Fe, M ϭ 596.4, orthorhombic,
space group P212121 (no. 19), a ϭ 13.433(2), b ϭ 13.449(3), c ϭ
3
18.624(3) A, V ϭ 3365(1) A , Z ϭ 4, Dc ϭ 1.177 g cmϪ3, µ(Mo-
˚
˚
436
Eur. J. Inorg. Chem. 2001, 431Ϫ437

Imine Versus Amine Donors in Iron-Based Ethylene Polymerisation Catalysts
FULL PAPER
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Crystallographic data (excluding structure factors) for this struc-
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Data Centre as supplementary publication no. CCDC-149268.
Copies of the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax:
(internat.) ϩ 44-1223/336-033; Email: deposit@ccdc.cam.ac.uk].
[3]
[4]
[5]
[6]
[7]
Crystal Data for 6b (orthorhombic form): C31H43N3Cl2Fe·3C7H8,
[8]
M ϭ 860.8, orthorhombic, space group Pccn (no. 56), a ϭ
3
˚
˚
25.815(2), b ϭ 10.106(1), c ϭ 18.516(1) A, V ϭ 4830.6(5) A , Z ϭ
4 (the complex has crystallographic C2 symmetry), Dc ϭ 1.184 g
cmϪ3, µ(Cu-Kα) ϭ 37.9 cmϪ1, F(000) ϭ 1840, T ϭ 183 K; pale
yellow plates, 0.53 ϫ 0.47 ϫ 0.07 mm, Siemens P4/RA diffracto-
meter, ω-scans, 3564 independent reflections. The structure was
solved by direct methods and all the major occupancy non-hydro-
gen atoms were refined anisotropically using full-matrix least-
squares based on F2 to give R1 ϭ 0.068, wR2 ϭ 0.168 for 2253
independent observed absorption corrected reflections [|Fo| Ͼ
4σ(|Fo|), 2θ Յ 124°] and 288 parameters.
[9]
[10]
[11]
[12]
[13]
Crystallographic data (excluding structure factors) for this struc-
ture have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC-149269.
Copies of the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax:
(internat.) ϩ 44-1223/336-033; Email: deposit@ccdc.cam.ac.uk].
[14]
[15]
General Polymerization Procedures: (a) High Pressure Tests: A 1
litre stainless steel reactor was baked out under a nitrogen flow for
at least 1 h at Ͼ85 °C and subsequently cooled to the temperature
of polymerization. Isobutane (0.5 L) and trialkylaluminum (triiso-
butylaluminum) were introduced into the reactor and stirred at the
reaction temperature for at least 1 hour. Ethylene was introduced
by over-pressure and the difference between the total pressure and
the initial pressure (isobutane and nitrogen: ca. 10 bar) is the pres-
sure quoted in Table 1. The catalyst solution in toluene was then
injected under nitrogen. The reactor pressure was maintained con-
stant throughout the polymerization run by computer controlled
addition of ethylene. The polymerization time was 60 minutes. Runs
were terminated by venting off volatiles and the reactor contents
were isolated, washed with aqueous HCl, methanol and dried in a
vacuum oven at 50 °C.
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B. L. Small, M. Brookhart, J. Am. Chem. Soc. 1998, 120,
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M. S. Brookhart, B. L. Small, (DuPont/UNC), WO 98/30612,
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[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
(b) Schlenk-line 1 bar ethylene Tests: The precatalyst was dissolved
in toluene (40 mL) and MAO (10 wt% in toluene) added to produce
an orange solution. The Schlenk tube was placed in a water bath,
purged with ethylene and the contents magnetically stirred and
maintained under ethylene (1 bar) for the duration of the poly-
merization (60 minutes). The polymerization was terminated by the
addition of aqueous hydrogen chloride. The solid PE was recovered
by filtration, washed with methanol (50 mL) and dried (vacuum
oven at 50 °C).
M. D. Bruce, V. C. Gibson, C. Redshaw, G. A. Solan, A. J. P.
White, D. J. Williams, Chem. Commun. 1998, 2523Ϫ2524.
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The cobalt analogue 4 of 3a, is isomorphous: orthorhombic,
space group P212121 (no. 19), a ϭ 13.426(2), b ϭ 13.441(4),
3
˚
˚
c ϭ 18.455(8) A, V ϭ 3330(2) A .
[31]
[32]
[33]
P. N. Jagg, P. F. Kelly, H. S. Rzepa, D. J. Williams, J. D. Wool-
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and G. Audley are thanked for NMR and GPC measurements, re-
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437