Bis(arylimino)pyridine derivatives of Group 4 metals: Preparation, characterization and activity in ethylene polymerization

Article abstract of DOI:10.1039/b415997g

Titanium tetrachloride reacts with 2,6-bis[(1-phenylimino)ethyl]pyridine, 1, and 2,6-bis[1-(2,6-diisopropyl-phenylimino)ethyl]pyridine, 2, giving the adducts of general formulae [Ti(1)Cl₃]Cl, 3, and [Ti(2)Cl ₃]Cl, 6, the latter through the intermediacy of the covalently bonded [Ti(2)Cl₄], 4. Heating 6 leads to reduction to the titanium(III) derivative [Ti(2)Cl₃], 12, the latter characterized by X-ray diffraction methods. The reaction of [Ti(1)Cl₃]Cl with a toluene solution of MAO proceeds with methylation at the ortho-position of the pyridine ring to give the titanium(IV) derivative [Ti(C₂₂H₂₁N ₃)Cl₃], 8. The reaction of [Ti(2)Cl₃]Cl with MAO gives a mixture of products containing [Ti(2)Cl₂(OAlCl ₃)], 9. Compound 9, which has been prepared independently by reacting 6 with AlOCl, is a rare case of a compound containing the -OAlCl₃ moiety, as shown by a single-crystal X-ray diffraction study. From the tetrachlorides of zirconium and hafnium with 1 or 2, the corresponding adducts [M(L)Cl₄] have been obtained in high yields. These derivatives of Group 4 metals act as ethylene polymerization catalytic precursors: the substitution of the phenyl ring of the imino fragment strongly influences the catalytic activity which is 5,544 kg_PE mol_Ti^-1 h^-1 in the case of 3 and 267 kg_PE mol_Ti ^-1 h^-1 with 6. Catalytic activity has been observed for zirconium and hafnium too, the activity decreasing from zirconium to hafnium, under comparable conditions. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b415997g

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F U L L P A P E R
Bis(arylimino)pyridine derivatives of Group 4 metals: preparation,
characterization and activity in ethylene polymerization
Fausto Calderazzo,a Ulli Englert,b Guido Pampaloni,*a Roberto Santi,†c Anna Sommazzi*c and
Marianna Zinna‡a
a Universita` di Pisa, Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35,
I-56126, Pisa, Italy. E-mail: pampa@dcci.unipi.it; Fax: int. +050-2219-246;
Tel: int. +050-2219-219
b Institut fu¨r Anorganische Chemie der RWTH Aachen, Professor-Pirlet-Strasse 1, D-52074,
Aachen, Germany
c Polimeri Europa, Centro Ricerche Novara-Istituto Guido Donegani, via G. Fauser 4, I-28100,
Novara, Italy
Received 15th October 2004, Accepted 18th January 2005
First published as an Advance Article on the web 1st February 2005
Titanium tetrachloride reacts with 2,6-bis[(1-phenylimino)ethyl]pyridine, 1, and 2,6-bis[1-(2,6-diisopropyl-
phenylimino)ethyl]pyridine, 2, giving the adducts of general formulae [Ti(1)Cl3]Cl, 3, and [Ti(2)Cl3]Cl, 6, the latter
through the intermediacy of the covalently bonded [Ti(2)Cl4], 4. Heating 6 leads to reduction to the titanium(III)
derivative [Ti(2)Cl3], 12, the latter characterized by X-ray diffraction methods. The reaction of [Ti(1)Cl3]Cl with a
toluene solution of MAO proceeds with methylation at the ortho-position of the pyridine ring to give the titanium(IV)
derivative [Ti(C22H21N3)Cl3], 8. The reaction of [Ti(2)Cl3]Cl with MAO gives a mixture of products containing
[Ti(2)Cl2(OAlCl3)], 9. Compound 9, which has been prepared independently by reacting 6 with AlOCl, is a rare case
of a compound containing the –OAlCl3 moiety, as shown by a single-crystal X-ray diffraction study. From the
tetrachlorides of zirconium and hafnium with 1 or 2, the corresponding adducts [M(L)Cl4] have been obtained in
high yields. These derivatives of Group 4 metals act as ethylene polymerization catalytic precursors: the substitution
of the phenyl ring of the imino fragment strongly influences the catalytic activity which is 5,544 kgPE molTi−1 h−1 in the
case of 3 and 267 kgPE molTi h−1 with 6. Catalytic activity has been observed for zirconium and hafnium too, the
−1
activity decreasing from zirconium to hafnium, under comparable conditions.
Introduction
Since the original discovery by Natta and Ziegler of the olefin
polymerization process,1–4 there has been considerable interest
in the study of early transition metal derivatives as catalytic pre-
cursors for this process. Before the mid-1990s, the main interest
was concentrated on the use of Group 4 (titanium, zirconium
and hafnium) metal complexes,5 while middle-to-late transition
metals (Groups 6–10) were recognized to activate the olefin
Scheme 1
polymerization at a later stage.6 An important result was the
discovery7,8 that pentacoordinated iron(II) or cobalt(II) deriva-
ligand may favour its detachment: this fact, together with the
tives containing bis(arylimino)pyridine ligands, see Scheme 1,
generally observed decrease of the metal–nitrogen bond energies
efficiently polymerize ethylene in the presence of methylalumox-
on going to the left in a given transition d series,17 may destabilize
ane (MAO). Additional work has shown that stereochemical
the bis(phenyl)iminopyridine derivatives of Group 4. In this
and electronic factors influence the yield, the molecular weight
paper we will demonstrate the limits of this hypothesis and
and the microstructure of the polymer.9 As a matter of fact, com-
we report the synthesis, the characterization and the catalytic
plexes bearing an unsubstituted bis(arylimino)pyridine ligand,
activity of compounds of bis(phenylimino)pyridine ligands with
R = H, are substantially inactive.10 Further studies have been
the chlorides of titanium, zirconium and hafnium. We also show
performed on several transition metals including noble metals11
that both the stability of the complexes and their activity are
and vanadium.12
related to the steric hindrance of the bis(phenylimino)pyridine
As far as Group 4 elements are concerned, some data on
ligand.
the synthesis and polymerization activity of bis(phenylimino)-
pyridine metal complexes have been reported in the patent
literature,13–16 their chemical and physical properties still re-
quiring further work. This is somewhat surprising due to the
large amount of data available in the literature for Group
4 metal derivatives with chelating amidato, b-diketoiminato,
silicylaldiminato, phenoxyamino and other charged ligands of
this type.11 The uncharged nature of the bis(arylimino)pyridine
Results and discussion
Titanium derivatives
The reactions of the metal chlorides of Group 4 with the
nitrogen-containing ligands were normally carried out in toluene
or in halogenated solvents, due to our prior findings18 on the
preparation of chloro-complexes of iron(II). Compound 1 reacts
with TiCl4 forming 3, see Scheme 2. The IR spectrum of 3 shows
the C N stretching vibration at 1592 cm−1 with a shift of 44 cm−1
=
† Deceased December 25th, 2003.
‡ Present address: Polimeri Europa, Centro Ricerca e Sviluppo Ravenna,
via Baiona 107, I-48100 Ravenna, Italy.
with respect to the uncomplexed ligand absorbing at 1636 cm−1.9
A similar shift of ca. 40 cm−1 is observed in bis(pyrrolyl)imino
9 1 4
D a l t o n T r a n s . , 2 0 0 5 , 9 1 4 – 9 2 2
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

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We have found that formation of the hexacoordinated cation
[Ti(2)Cl3]+ can also be promoted thermally. As a matter of
fact, the reaction of TiCl4 with 2 in refluxing toluene produces
a diamagnetic dark product which has been identified as the
scarcely soluble, moisture–sensitive [Ti(2)Cl3]Cl, 6, see Scheme 2.
Elevated temperatures are required to obtain a pure compound:
in refluxing dichloromethane the reaction is not complete and
the IR spectrum of the solid still shows an absorption at
1657 cm−1 typical of 4 (vide infra).
Compound 6 is not stable in donor solvents such as THF
or Et2O, the ligand being released (vide infra); due to its ionic
nature, 6 has a limited solubility in non-polar solvents. Its 13C
NMR spectrum was therefore measured in the solid state, the
8b
assignment being based on the known solution spectrum of 2.
Scheme 2
The coordination of 2 to titanium produces a low-field shift of
the signals, and as expected the most evident shift occurs for the
complexes of transition metals.19 Compound 3 has a limited
solubility in common organic solvents and is stable in basic
solvents such as THF.
The reaction of TiCl4 with 2 is more complex. Mixing
solutions of the components in toluene or dichloromethane
at 25 ◦C gives a slightly soluble yellow solid which has been
identified as the 1 : 1 adduct, [Ti(2)Cl4], 4. The IR spectrum
of this compound shows a strong absorption at 1657 cm−1,
attributed to the stretching vibration of a non-coordinated
=
C N carbon atom which moves from 166.9 ppm in ligand 2 to
180.2 in compound 6.
Mixtures of uncomplexed 2 and TiCl4(THF)2 have been
obtained by treating 6 with THF. Both the steric hindrance of
the ligand and the high affinity of metal cations of Group 4 for
oxygen donors may be responsible for this observations. In this
connection it is interesting to note that bis(phenylimino)pyridine
derivatives of transition metals are often prepared in polar
solvents such as alcohols. Although Brookhart and Gibson7,8
report that the iron and cobalt compounds of this class are stable
in THF or butyl alcohol, a more recent paper by Gibson and
coworkers29 recommends the use of solvents of low polarity, such
as toluene, for the successful preparation of iron(II) derivatives
of imino or amino compounds with bulky substituents.
=
=
C N bond (the C N stretching vibration of the uncomplexed
molecule is at 1643 cm−1). A similar observation has been made
in the case of the complexes of 1,10-phenanthroline-9,10-dione
with MCl4 (M = Ti, Zr, Hf).20 No additional data could be
obtained on 4 due to low thermal stability (vide infra), low
solubility and instantaneous reaction with loss of 2 in solvents
such as THF or DME. We suggest that compound 4 contains
2 as a bidentate ligand. Although it is possible in principle,
monodentate coordination of 2 through the pyridine nitrogen
atom is considered to be less probable as the bidentate bonding
mode satisfies the generally observed hexa-coordination typical
of titanium(IV) with nitrogen-containing ligands.21 The small
Compound 6 undergoes reduction in boiling toluene: the
paramagnetic (leff = 1.72 lB at 298 K) derivative of titanium(III)
of formula [Ti(2)Cl3], 11 (vide infra), was obtained by heating
compound 6 in toluene. Strictly connected with this observation
are the examples reported in the literature concerning the
oxidation of ligand 2 in some metal complexes of this type.30
When the reaction between TiCl4 and 2 was repeated using
a TiCl4/2 molar ratio of 3, an orange product was obtained at
room temperature whose IR spectrum in the solid state does not
show absorptions above 1600 cm−1. This compound, which has
been identified as [Ti(2)Cl3][Ti2Cl9], 7, can also be obtained by
reacting 6 with two equivalents of TiCl4, see Scheme 2.
ionic radius of hexacoordinated titanium(IV), 0.74 A,22 together
˚
with the steric requirement of the bulky isopropyl substituents,
probably prevents coordination of the third nitrogen atom in
4. It has to be noted that bidentate coordination of 2 has been
observed in rhenium,23 platinum,24 palladium,24a and copper25
derivatives. Moreover, the molecular structures of the complexes
of 2 with vanadium(III),12 chromium(III),26 manganese(II),27
The formation of 7 is consistent with earlier results31 on the
reaction of TiCl4 with hexamethylbenzene forming the ionic
8b
8b
iron(II) and cobalt(II) show a short M–Npy bond (with respect
to the iminic ones) suggesting that such M–N interaction is
stronger than that between the metal and the iminic nitrogen
atoms, probably due to some pyridine-to-metal p-bonding
contribution.
6
[Ti(g -C6Me6)Cl3][Ti2Cl9]. The authors attributed the formation
of this compound to the reaction of the initially formed
6
charge transfer complex [C6Me6·TiCl4] with TiCl4 to give [Ti(g -
C6Me6)Cl3][TiCl5] followed by its further reaction with TiCl4.
A similar reaction sequence, see Scheme 4, may be operative in
our system: in the presence of excess TiCl4, the initially formed
adduct 4 undergoes chloride transfer to TiCl4 to give 7 probably
through the intermediacy of 4ꢀ containing the [TiCl5]− anion.
The reaction of 4 with AlCl3 in sym-tetrachloroethane has
been studied by IR spectroscopy in solution, the absorption
at 1657 cm−1 promptly disappearing upon addition of AlCl3.
When the reaction was repeated on a preparative scale, the
compound [Ti(2)Cl3]AlCl4, 5, see Scheme 3, was obtained, whose
IR spectrum shows the stretching vibration of the coordinated
iminic group at 1582 cm−1. A strong absorption at 493 cm−1
is attributed to the AlCl4 anion.28 Thus, AlCl3 promotes the
−
coordination of the third nitrogen of 2 to the central metal atom
by removing the chloride ion from titanium.
Scheme 4
In the perspective to use these titanium derivatives as promot-
ers in olefin polymerization, we studied the behaviour of 3 with
MAO. As shown in Scheme 5, compound 3 undergoes alkylation
by MAO (Al/Ti molar ratio of 2) affording compound 8
identified as the product of methylation at the ortho-carbon
atom of the pyridine ring. A similar result was obtained by
Gambarotta and coworkers on the [V(2)Cl3]/MAO (MAO/V
molar ratio = 2) system.12
1
The H NMR spectrum of compound 8 is quite informative
with respect to the methylation reaction: the proton resonances
Scheme 3
D a l t o n T r a n s . , 2 0 0 5 , 9 1 4 – 9 2 2
9 1 5

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◦
˚
Table 1 Selected bond distances (A) and angles ( ) of 9, with estimated
standard uncertainties in parentheses referring to the least significant
digit
Ti(1)–O(1)
Ti(1)–N(3)
Ti(1)–Cl(2)
Cl(3)–Al(1)
Cl(5)–Al(1)
N(1)–C(19)
N(2)–C(2)
N(3)–C(20)
1.772(3) Ti(1)–N(1)
2.212(3) Ti(1)–N(2)
2.258(1) Ti(1)–Cl(1)
2.133(2) Cl(4)–Al(1)
2.152(2) Al(1)–O(1)
1.337(5) N(1)–C(1)
1.287(5) N(2)–C(3)
1.287(5) N(3)–C(21)
2.140(3)
2.217(3)
2.341(1)
2.132(2)
1.758(3)
1.346(5)
1.460(5)
1.464(4)
Scheme 5
of the nitrogen-containing ring are at 3.68 ppm (proton H*) and
at 6.70 and 6.58 ppm (vinylic hydrogen H**). The resonance at
1.77 ppm has been assigned to the methyl group derived from the
O(1)–Ti(1)–N(1)
N(1)–Ti(1)–N(3)
N(1)–Ti(1)–N(2)
O(1)–Ti(1)–Cl(2)
N(3)–Ti(1)–Cl(2)
O(1)–Ti(1)–Cl(1)
N(3)–Ti(1)–Cl(1)
Cl(2)–Ti(1)–Cl(1)
O(1)–Al(1)–Cl(3)
O(1)–Al(1)–Cl(5)
Cl(3)–Al(1)–Cl(5)
85.60(11) O(1)–Ti(1)–N(3)
72.36(11) O(1)–Ti(1)–N(2)
73.03(11) N(3)–Ti(1)–N(2)
91.86(11)
91.57(11)
144.83(11)
175.73(9)
107.35(9)
83.76(8)
=
methylating agent, while the two N C–Me methyl groups are
observed at 2.30 ppm, probably due to accidental overlapping.
The reaction of 6 with MAO (molar ratio Al/Ti = 2) in toluene
is more complex and gives a mixture of at least two components.
One of them, compound 9, has also been obtained in good yields
98.62(9)
106.70(9)
169.14(9)
87.05(8)
92.04(5)
N(1)–Ti(1)–Cl(2)
N(2)–Ti(1)–Cl(2)
N(1)–Ti(1)–Cl(1)
N(2)–Ti(1)–Cl(1)
O(1)–Al(1)–Cl(4)
83.20(8)
◦
by reacting 6 with AlOCl34 in sym-tetrachloroethane at 90 C,
112.81(10)
110.63(7)
108.61(7)
108.05(10) Cl(4)–Al(1)–Cl(3)
107.92(10) Cl(4)–Al(1)–Cl(5)
108.71(7)
see Scheme 6.§
[N(1)–Ti–Cl(2) 175.73(9)◦, N(3)–Ti–Cl(2) 106.70(9)◦, N(2)–Ti–
Cl(2) 107.35(9)◦]. The other chlorine and the oxygen of the –
OAlCl3 fragment subtend an angle of 169.14(9)◦. The Ti–Cl
˚
distances amount to 2.258(1) and 2.341(1) A, while the two
Ti–N distances formed by the two iminic functions [Ti(1)–
˚
˚
N(3) 2.212(3) A, Ti(1)–N(2) 2.217(3) A] are longer than those
formed between the metal and the pyridine nitrogen atom
Scheme 6
˚
[Ti(1)–N(1) 2.140(3) A], a situation typical of compounds of
this ligand with transition elements.
8b,12,26
The pyridine ring is
coplanar with the equatorial plane of the molecule whereas
the two aryl groups form dihedral angles C(4)–C(3)–N(2)–Ti
and C(29)–C(21)–N(3)–Ti of 77.09 and 82.53◦, respectively,
at variance with the vanadium(III) derivative [V(2)Cl3], where
the corresponding dihedral angles are 85.4 and 92.0◦.12 The
larger deviation from 90◦ probably arises from the presence of
the –OAlCl3 fragment which forces the aryl groups to rotate
around the C–N bond. This is confirmed by the fact that the
Cl–Al–Cl angles [109.3(7)◦, mean value] are smaller than those
measured [112.1(1)] for [N(C4H9)4][NbCl4(OAlCl3)],35 the only
other example of a transition metal derivative containing the
–OAlCl3 fragment.
The AlCl3 group shows local C3v symmetry [Al–Cl: 2.132(2)–
◦
˚
2.152(2) A; Cl–Al–Cl: 108.6–110.6 ]; these values, together
˚
with the Al–O distance of 1.758(3) A, agree well with the
geometry observed for [C20H48N2Si2][Al2Cl6O]36 [Al–Cl mean
◦
˚
˚
value 2.092 A; Al–O, 1.768 A; Cl–Al–Cl, mean value 113.9 ]
and in [C16H35N2Si]2[Al4Cl10O2]37 [Al–Cl m◦ean value, 2.123 A;
˚
Fig. 1 View of the molecular structure of 9. Thermal ellipsoids are
˚
Al–O, 1.77 A; Cl–Al–Cl, mean value: 110.8 ].
drawn at 50% probability level.
Complexes of ligands 1 and 2 have also been prepared for
titanium in oxidation states lower than four. The reaction
of TiCl3(THF)3 with 1 or 2 affords compounds 10 or 11,
respectively, which have been characterized analytically and
spectroscopically as the hexacoordinated titanium(III) deriva-
tives of Scheme 7.
The titanium(III) derivatives are thermally stable compounds,
slightly soluble in common organic solvents, unstable [with loss
of the bis(arylimino)pyridine ligand] in donor media such as
THF. They are paramagnetic with a leff at room temperature
of 1.67 (10) and 1.72 (11) lB, in agreement with the presence of
titanium(III) of d1 electronic configuration.
Crystals of 9 were grown from dichloromethane and
characterized by X-ray diffraction methods, see Fig. 1, as
[Ti(2)Cl2(OAlCl3)] formally containing the [OAlCl3]2− fragment.
Table 1 reports a selection of bond distances and angles.
The coordination geometry around titanium is distorted
octahedral with the metal bonded to three nitrogen atoms
of 2, to two chlorine atoms and to the oxygen atom of the
–OAlCl3 fragment. The equatorial plane is defined by the three
nitrogen atoms of the ligand [N(1)–Ti–N(3) 72.36(11)◦, N(1)–
Ti–N(2) 73.03(11)◦, N(3)–Ti–N(2) 144.83(11)◦] and one chlorine
The molecular structure of compound 11 is reported in Fig. 2,
while Table 2 lists a selection of bond distances and angles.
Compound 11 crystallizes with two independent molecules per
asymmetric unit, which differ in the orientation of the phenyl
groups [C(22)–C(21)–N(3)–Ti(1) 76.36◦ and C(4)–C(3)–N(2)–
Ti(1) 83.38◦ for one molecule; C(37)–C(36)–N(5)–Ti(2) 86.62◦
and C(55)–C(54)–N(6)–Ti(2) 74.88◦ for the other molecule] with
§ We have not been able to isolate any other compound from the reaction
mixture. Nevertheless, we have collected some 1H NMR evidences
suggesting that one component of the mixture may be the result of
the methylation at one of the two iminic carbon atoms of the ligand,
as observed earlier on compounds resulting from the reaction of
bis(arylimino)pyridine derivatives of aluminium32 and vanadium33 with
AlMe3 and AlEt2Cl.
9 1 6
D a l t o n T r a n s . , 2 0 0 5 , 9 1 4 – 9 2 2

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Scheme 7
present in the unit cell differing in the orientation of the phenyl
groups with respect to the plane defined by the metal and the
nitrogen donor atoms.
Due to the fact that the bond distances and angles are
similar in the two independent molecules, reference will be
made to the molecule identified by Ti(1). Titanium presents a
slightly distorted octahedral arrangement, the equatorial plane
being defined by three nitrogens and by one chlorine [N(1)–
Ti(1)–N(3) 72.01(11)◦, N(1)–Ti(1)–N(2) 72.37(12)◦, N(2)–Ti–
N(3) 143.44(12)◦] [N(1)–Ti(1)–Cl(3) 169.53(10)◦, N(3)–Ti(1)–
Cl(3) 116.07(9)◦, N(2)–Ti(1)–Cl(3) 100.30(9)◦]. The Ti–Cl bond
˚
distances range from 2.298(1) to 2.429(1) A. The Ti–N distances
˚
involving the iminic nitrogen atoms [Ti(1)–N(3) 2.268(3) A,
˚
Ti(1)–N(2) 2.215(3) A] are longer than that involving the
˚
heterocyclic nitrogen atom [Ti(1)–N(1) 2.148(3) A], as generally
8b,12,26
observed in compounds of this class.
The pyridine ring
is coplanar with the equatorial plane of the molecule and the
bond distances within the coordinated ligand do not differ
substantially from those of the uncomplexed species.
Fig. 2 View of the molecular structure of one of the two independent
molecules of 11·1.5PhMe. Thermal ellipsoids are drawn at 50% proba-
bility level.
The diamagnetic titanium(II) derivative 12 has been obtained
starting from TiCl2(THF)2, see Scheme 7, the latter being
prepared by reducing TiCl4(THF)2 with sodium in THF.38
The experimentally verified diamagnetism of compound 12
deserves some comments. Due to the fact that the structurally
characterized complexes of this family [M(2)Cl2], M = Mn,39
◦
˚
Table 2 Selected bond distances (A) and angles ( ) of 11·1.5PhMe,
with estimated standard uncertainties in parentheses referring to the
least significant digit
Molecule A
Molecule B
8b
8b
Ti(1)–N(1)
Ti(1)–N(2)
Ti(1)–N(3)
Ti(1)–Cl(3)
Ti(1)–Cl(1)
Ti(1)–Cl(2)
2.148(3) Ti(2)–N(4)
2.215(3) Ti(2)–N(5)
2.268(3) Ti(2)–N(6)
2.298(1) Ti(2)–Cl(6)
2.344(1) Ti(2)–Cl(4)
2.429(1) Ti(2)–Cl(5)
2.146(3)
2.185(3)
2.242(3)
2.297(1)
2.338(1)
2.399(1)
Fe, Co, show a distorted square-pyramidal geometry, the
same coordination geometry of titanium(II) will be assumed for
12. It can therefore be suggested that we are dealing with a low-
spin complex where the degeneracy of the dxz and dyz orbitals
(typical of a square-pyramidal geometry)40 has been removed.
N(1)–Ti(1)–N(2)
N(1)–Ti(1)–N(3)
N(2)–Ti(1)–N(3)
N(1)–Ti(1)–Cl(3)
N(2)–Ti(1)–Cl(3)
N(3)–Ti(1)–Cl(3)
N(1)–Ti(1)–Cl(1)
N(2)–Ti(1)–Cl(1)
N(3)–Ti(1)–Cl(1)
Cl(3)–Ti(1)–Cl(1)
N(1)–Ti(1)–Cl(2)
N(2)–Ti(1)–Cl(2)
72.37(12) N(4)–Ti(2)–N(5)
72.01(11) N(4)–Ti(2)–N(6)
143.44(12) N(5)–Ti(2)–N(6)
169.53(10) N(4)–Ti(2)–Cl(6)
72.61(12)
72.26(12)
144.27(11)
168.50(9)
99.69(9)
116.01(9)
93.97(9)
92.73(8)
83.39(8)
94.94(5)
79.85(9)
91.35(9)
Zirconium and hafnium derivatives
The reaction of ZrCl4 or HfCl4 with 1 or 2 affords the
scarcely soluble compounds 13–16 (Scheme 8) which have been
characterized analytically and spectroscopically. Compounds
13 and 14 are stable in the presence of Lewis bases, while
compounds 15 and 16 readily undergo ligand displacement, the
steric hindrance of the isopropyl groups being an important
factor of stability.
Due to its limited solubility in hydrocarbons or chlorinated
solvents, a CP-MAS 13C NMR spectrum of 16 has been
recorded in the solid state. A downfield shift of the resonances
with respect to the uncomplexed ligand 2 is observed, the
resonance of the iminic carbon being observed at 174.9 ppm,
as in the uncharged ruthenium(II) derivative [Ru(2)(C2H4)Cl2]
100.30(9)
116.07(9)
92.54(9)
89.83(9)
83.78(9)
94.94(4)
80.79(9)
94.24(9)
N(5)–Ti(2)–Cl(6)
N(6)–Ti(2)–Cl(6)
N(4)–Ti(2)–Cl(4)
N(5)–Ti(2)–Cl(4)
N(6)–Ti(2)–Cl(4)
Cl(6)–Ti(2)–Cl(4)
N(4)–Ti(2)–Cl(5)
N(5)–Ti(2)–Cl(5)
respect to the plane defined by the three nitrogen donor atoms
and titanium. A similar situation is observed in the crystal
structure of [V(2)Cl3],12 where three independent molecules are
Scheme 8
D a l t o n T r a n s . , 2 0 0 5 , 9 1 4 – 9 2 2
9 1 7

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(168.1 ppm).41 By considering that ionic derivatives such as
Probably, this system produces short, unsaturated chains which
are able to act as a “co-monomer”, giving the branched polymer.
Chain transfer or hydrogen transfer phenomena may also occur
producing branching and a low MW polymer, respectively.44
In view of the low stability of the complexes containing ligand
2, the possibility of loss of the ligand under polymerization
conditions has been considered and blank experiments were
carried out with TiCl4, TiCl3 and ZrCl4 in the absence of the
nitrogen ligand. The data reported in Table 3 show that the
polydispersity of the polymer is between 2 and 3 in the case of
TiCl4 and ZrCl4, to be compared to 2.3 and 7.7 in the case of the
polymer obtained with 3 and 6, respectively. This fact suggests
that partial dissociation of the bis(phenyl)iminopyridine ligand
may take place under the polymerization conditions.
=
[Rh(2)Me][OTf]2, and [Ru(2)MeI][BAr4] show C N resonances
at 181.0, and 182.3 ppm, respectively,41 the signal at 174.6 ppm
for 16 confirms that the hafnium derivative (and probably 13,
14 and 15 too) is not ionic. The increased ionic radii on going
˚
from hexacoordinated titanium(IV) (0.74 A) to zirconium(IV)
22
˚
and hafnium(IV) (0.86 and 0.85 A, respectively), accounts for
the increasing of the coordination number of the metal on going
from titanium to zirconium and hafnium.
Ethylene polymerizations
Several metal complexes have been evaluated in ethylene poly-
merization. A preliminary screening showed that the best poly-
merization conditions require the use of methylaluminoxane
(MAO) as co-catalyst (Al/M molar ratio of 500) at 70 ◦C with 7
bar of ethylene. On treatment with MAO, the titanium (3, 6, 7,
10, 11, 12), zirconium (13, 15) and hafnium (14, 16) derivatives
are active polymerization catalysts, see Table 3.
Conclusions
This paper reports the preparation, reactivity, and catalytic
properties of metal complexes of Group 4 with bis(phenyl-
imino)pyridine derivatives filling a blank present in the literature.
We have shown that, especially in the case of titanium(IV), the
interaction between bis(phenylimino)pyridines and the metal
chlorides of Group 4 is more complex with respect to other
transition elements with the same type of ligands, as reported in
the literature for chromium, manganese, iron, cobalt and vana-
dium. Moreover, the steric hindrance of the ortho-substituents
on the phenyl groups controls the nature, the stability and the
catalytic properties of the resulting complexes, especially in the
case of titanium(IV).
With TiCl4, see Scheme 2, 1 behaves as a tridentate ligand, the
ionic compound 3 being obtained at room temperature. On the
other hand, under comparable experimental conditions, TiCl4
and 2 afford compound 4 where the ligand behaves as bidentate,
tridentate coordination being achieved only by addition of a
Lewis acid (AlCl3) or by forcing the reaction conditions.
We have demonstrated that the stability of the titanium(IV)
derivatives decreases on increasing the steric demand of the
ligand: compound 3 is thermally stable at variance to 6 which,
on prolonged heating, undergoes reduction to the paramagnetic
titanium(III) derivative 11. Moreover, basic solvents such as THF
or acetone or DME must be avoided with metal compounds
of 2, due to the high oxophilicity of the metal derivatives
which promptly generate MCl4(solvent)n solvates with loss of
the ligand.
As far as the ethylene polymerization reaction is concerned,
we have observed that the activity of the catalyst depends on
the steric hindrance of the ligand which is also strictly related
to the stability of the overall metal precursor. For example, the
titanium(IV) and the zirconium(IV) derivatives of ligand 2, which
contains the bulky isopropyl groups in the ortho position of the
phenyl rings, show an activity of the same order of magnitude
as TiCl4 or ZrCl4, thus suggesting that some dissociation of 2
may occurs under the polymerization conditions. It has to be
noted that also mono(salicyladiminato)titanium(IV) derivatives
containing bulky isopropyl substituents show a polymerization
activity similar to that of TiCl4 under the same experimental
conditions.45 On the other hand, we observe that the titanium
derivative 3, containing the unsubstituted ligand, is an highly ac-
tive in producing branched polyethylene (5544 kgPE molTi−1 h−1).
Due to the availability of complexes with the same ligand
for the three elements of Group 4, we have observed that the
activity decreases in the order Ti ꢁ Zr > Hf at variance with the
results (Ti ꢂ Zr) reported by Fujita and coworkers in the case
of the M(phenoxyamine)2Cl2 derivatives when used as catalytic
precursors for the ethylene polymerization.46
The most striking evidence is the large difference of activity of
the derivatives containing the unsubstituted bis(phenylimino)-
pyridine (compounds 3, 10, 13, 14) with respect to the cor-
responding isopropyl-substituted ones (compounds 6, 11, 15,
16). This is somehow surprising due to the fact that iron(II)
derivatives without substituents on the ortho aryl position are
generally less catalytically active than the corresponding ortho-
10b
substituted bis(phenylimino)pyridine derivatives. The reverse
trend observed in the case of compounds of Group 4 may be
ascribed to the lower steric hindrance of the unsubstituted ligand
1. In the case of the iron(II) derivatives, it is generally accepted
that sterically demanding ligands reduce the possibility of b-
hydrogen transfer to the metal making these species extremely
active polymerization catalysts. For Group 4 derivatives, it
has been concluded42 that the alkene C–H activation rather
than the b-hydrogen transfer is the most probable termination
process, sterically demanding ligands having consequently a
negative influence on the whole process, in agreement with the
polymerization mechanism proposed by Cossee.42,43 As a matter
of fact, ligand 2 is more steric demanding than 1 and the titanium
derivatives containing 2 are less stable than those containing the
unsubstituted ligand 1.
The absence of substituents on the aryl rings in the catalytic
precursor also affects the nature of the polymer. Independent of
the metal, the derivatives of 2 produce a linear polyethylene char-
acterized by mp around 135 ◦C, whereas the polymers obtained
with compounds of ligand 1 have lower mp’s, between 118.4
(from 13) and 123.7 ◦C (from 3), suggesting that we are dealing
with branched polyethylene. The behaviour of 3 is noteworthy
because it shows the highest activity (5544 kgPE molTi h−1)
−1
together with the narrowest molecular weight distribution
(Mw/Mn = 2.3) and a MW of the polymer of 5200 Da.
Table 3 Ethylene polymerization with catalytic precursors of Group 4a
Metal
Precursor
Activityb
Tf /◦C
10−3MW
Mw/Mn
Ti
Ti
Ti
Ti
Ti
Ti
Zr
Zr
Hf
Hf
3
5544
267
207
4326
128
58
789
139
139
9
123.7
133.3
134.3
123.4
132.4
134.0
118.4
134.0
130.9
134.8
5.2
96.7
270
30.1
105
576
ndc
492
410
ndc
2.3
7.7
9.1
10.0
2.8
12.0
ndc
3.1
6
7
10
11
12
13
15
14
16
2.2
ndc
a Blank experiments, in the absence of the nitrogen ligand, were carried
out with TiCl4, TiCl3 and ZrCl4, with the following results of activity
Experimental
[kgPE molmetal h−1]: TiCl4, 140; TiCl3, 58; ZrCl4, 84. The properties of
−1
the polymer, namely, Tf (◦C), MW (× 10−3), Mw/Mn, were, respec-
General methods
tively: TiCl4, 133; 254; 3; TiCl3, 134; 525; 2; ZrCl4, 134; 302; 2.5.
−1
b kgPE molmetal h−1
.
c Not determined.
All manipulations of air and/or moisture-sensitive compounds
were performed under an atmosphere of argon using standard
9 1 8
D a l t o n T r a n s . , 2 0 0 5 , 9 1 4 – 9 2 2

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Schlenk techniques. The reaction vessels were oven dried at
2.70 mmol), immediate formation of a deep orange suspension
being observed. The mixture was stirred at room temperature
for 20 h and filtered. The yellow solid was washed with toluene
(2 × 5 ml), and dried in vacuo obtaining 1.63 g (89.8% yield)
of 4 as a yellow solid extremely sensitive to moisture. Found: C,
58.8; H, 6.4; N, 6.3; Ti, 6.9. C33H43Cl4N3Ti requires: C, 59.0; H,
6.5; N, 6.3; Ti, 7.1%. IR (Nujol, cm−1): 3066w, 2724w, 2362br–w,
1975br–m, 1657s, 1578s, 1467s, 1321m, 1271m, 1213m, 1199w,
1182w, 1109m, 1056w, 1032s, 995w, 979w, 935w, 885w, 824m,
809s, 734m, 696m.
◦
150 C prior to use, evacuated (10−2 mmHg) and then filled
with dinitrogen or argon.
IR spectra were recorded with a Perkin Elmer model FT
1725X instrument on Nujol mulls prepared under exclusion
of moisture and dioxygen, using KBr windows. Reflectance
IR spectra of the solid samples were recorded by using a
Perkin-Elmer model FTR-Spectrometer equipped with a Perkin
Elmer Universal ATR sampling accessory. NMR spectra (1H,
200 MHz; 13C, 50.31 MHz, with TMS as reference) were
recorded with a Varian Gemini 200BB spectrometer. 13C-
CP/MAS NMR spectra were obtained by using a Bruker MSL
200 NMR instrument working at 50.32 MHz on 13C, using 4 mm
ZrO2 rotors. The acquisition conditions were the following:
contact pulse, 5 ms; acquisition delay, 4 s; 90◦ pulse, 4 ls; spectral
width, 20.000 Hz. No quaternary suppression experiments
were performed. Magnetic measurements were performed with
a Faraday balance, consisting of a Sartorius 4104 balance
and a Varian V 2900 electromagnet calibrated with CuSO4·5
H2O. Differential scanning calorimetry (DSC) measurements
were carried out with a Perkin Elmer Pyris 1 instrument,
typically using ca. 10 mg of polymer, with a scan speed of ca.
10 ◦C min−1 under a dinitrogen◦atmosphere: samples, which were
first heated up to 160 ◦C at 10 C min−1, were kept at 150 ◦C for
1 min, cooled to 30 ◦C at 10 ◦C min−1, and finally heated from
RT to 160 ◦C. The MW of the polymers were measured by using
a Waters Associates 150 C High Temperature gel permeation
chromatography (GPC) instrument equipped with four Waters
Styragel columns: HT3, HT4, HT5, HT6 with pore dimensions
Preparation of [Ti(2)Cl3]AlCl4, 5. A solution of 4 (448 mg,
0.67 mmol) in CH2Cl2 (100 ml) was added of AlCl3 (97 mg,
0.73 mmol). No change of colour was observed. The mixture
was stirred at room temperature for 16 h and heated at the
reflux temperature for 9 h. After removal of the volatiles in
vacuo at room temperature, the residue was added of toluene
and the brown microcrystalline solid was recovered by filtration,
washed with toluene (2 × 5 ml) and dried in vacuo at room
temperature affording 171 mg (32% yield) of 5 as a micro-
crystalline solid very sensitive to moisture. Found: C, 49.0; H,
5.6; N, 5.0. C33H43AlCl7N3Ti requires: C, 49.2; H, 5.4; N, 5.2%.
IR (Nujol, cm−1): 1579m, 1269m, 1208w, 1104w, 1034w, 935w,
874m, 844w, 801m, 776w, 733m, 696w, 668w, 493s, 415m.
Preparation of [Ti(2)Cl3]Cl, 6. To a suspension of 2 (1.00 g,
2.1 mmol) in toluene (100 ml) 0.23 ml (398 mg, 2.1 mmol) of
TiCl4 were added. The colour rapidly changed from yellow to
orange. The mixture was stirred at room temperature for 12 h
and then refluxed for 10 h. The suspension was filtered when
still hot, and the dark green solid was washed with toluene (2 ×
5 ml), dried in vacuo and identified as [Ti(2)Cl3]Cl, 6, (moisture
sensitive; 1.008 g; 74.5% yield). Found: C, 59.2; H, 6.8; N, 6.2;
Ti, 6.6. C33H43Cl4N3Ti requires: C, 59.0; H, 6.5; N, 6.3; Ti, 7.1%.
IR (Nujol mull, cm−1): 2969m, 1577m, 1320w, 1271w, 1213w,
1032w, 808mw, 732mw, 696w, 421m. Magnetic measurement at
298 K, vg, < 0. CP MAS 13C NMR d: 180.2 (Cquat), 148.2 (Cquat),
140.8 (CH), 135.8 (CH), 127.4 (CH), 124.93 (CH), 26.5 (CH3),
24.8 (CH3), 22.8 (CH3).
Compound 6 (250 mg, 0.373 mmol) was treated with THF
(80 ml). The resulting dark green solution was refluxed for 2 h.
The solvent was removed in vacuo and the solid was collected
and identified as a mixture of 2 and TiCl4(THF)2 by IR and 1H
NMR spectra.
In one of the preparations, the reaction mixture was heated
at the reflux temperature for 23 h and filtered when hot. The
diamagnetic dark green solid collected was identified as 6 (36.2%
yield) by elemental analysis and IR spectroscopy. However, after
some days at room temperature, the green crystals isolated from
the filtrate were identified as the titanium(III) adduct 11, vide
infra. Found: C, 62.6; H, 7.1; N, 5.8. C33H43Cl3N3Ti requires: C,
62.4; H, 6.8; N, 6.6%. Magnetic measurement: vcMorr 1.38 × 10−3
cgsu; diamagnetic correction: −399.8 × 10−6 cgsu. leff (298 K) =
1.72 lB.
3
4
5
6
˚
of 10 , 10 , 10 and 10 A, respectively, and a refractive index
detector. All samples were run in 1,2,4-trichlorobenzene at
135 ◦C with a flow-rate of 1 ml min−1. The data obtained were
processed with a Maxima 820 software version 3.30 (Millipore);
for the calculation of the average molecular weights Mn and Mw,
the universal calibration principles were applied, by selecting
polystyrene standards for the calibration with MW in the range
6500000–2000.
Methylalumoxane (10% Al in toluene, MAO, Crompton
GmbH) was used as received. The derivatives AlOCl,34
TiCl3(THF)3,47 and TiCl2(THF)2 were prepared according to
38
literature. Titanium tetrachloride (Aldrich) was distilled by col-
lecting the fraction bp = 136 ◦C. Titanium trichloride (Aldrich)
was purified by washing the commercial product with heptane;
after filtration, the solid was dried in vacuo at room temperature
and stored in sealed tubes. Zirconium tetrachloride (Aldrich)
and hafnium tetrachloride (Cezus Chemie) were treated with
refluxing SOCl2. After partial evaporation of the solvent, the
residue was treated with heptane and the solid was collected by
filtration, washed with heptane (5 × 25 ml) and dried in vacuo
at ca. 200 ◦C.
The derivatives 2,6-bis[(1-phenylimino)ethyl]pyridine, 1,9 C21-
H19N3, and2,6-bis[1-(2,6-diisopropylphenylimino)ethyl]pyridine,
2,7 C33H43N3, were prepared by a slight modification of the
published procedure, essentially consisting in the use of formic
acid as catalyst.
Preparation of [Ti(2)Cl3][Ti2Cl9], 7. To a toluene (150 ml)
solution of 2 (800 mg, 1.66 mmol) TiCl4 (967 mg, 5.1 mmol) was
added. The colour changed from yellow to orange. The mixture
was stirred at room temperature for 3 h and then filtered. The
orange solid was washed with toluene (2 × 10 ml), dried in vacuo
and identified as the diamagnetic air-sensitive [Ti(2)Cl3][Ti2Cl9],
7 (784 mg, 46.6% yield). Found: C, 37.3; H, 4.4; N, 3.8; Cl, 39.4;
Ti, 13.2. C33H43Cl12N3Ti3 requires: C, 37.7; H, 4.1; N, 4.0; Cl,
40.2; Ti, 13.8%. IR (Nujol mull, cm−1): 2970m, 1576ms, 1464m,
1365s, 1319w, 1269m, 1207w, 1181w, 1105m, 1053w, 1034m,
935w, 803s, 776vs, 735vs, 697ms. Compound 7 was unchanged
after treatment with excess 2.
Preparation of [Ti(1)Cl3]Cl, 3. A toluene (100 ml) solution
of 1 (575 mg, 1.8 mmol) was added of TiCl4 (341 mg, 1.8 mmol).
The colour immediately changed from yellow–orange to red.
The mixture was refluxed for 1 h and the colour turned dark
green. After 10 h stirring at room temperature, the suspension
was filtered and the solid was washed with toluene (2 × 5 ml),
dried in vacuo at room temperature and identified as 3 (909 mg,
97.8% yield). Found: C, 50.8; H, 3.4; N, 8.7. C21H19Cl4N3Ti,
requires: C, 50.1; H, 3.8; N, 8.3%. IR (solid state, cm−1):
2953s, 1592m, 1286m, 1075w, 1022w, 871w, 812w, 738m, 696m.
Magnetic measurement at 298 K, vg < 0. Similar results were
obtained in dichloromethane.
Treating compound 6 with two equivalents of TiCl4 in toluene
at room temperature also led to compound 7.
Preparation of [Ti(2)Cl4], 4. A suspension of 2 (1.30 g,
2.70 mmol) in toluene (80 ml) was added of TiCl4 (510 mg,
Preparation of [Ti(C22H21N3)Cl3], 8. A toluene suspension
of 3 (325 mg, 0.65 mmol) in toluene (70 ml) was treated with a
D a l t o n T r a n s . , 2 0 0 5 , 9 1 4 – 9 2 2
9 1 9

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solution of MAO (0.4 ml, 10% Al, 1.3 mmol of Al). The mixture
was stirred at ca. 90 ◦C for 1 h and then overnight at room
temperature. After elimination of some insoluble material by
filtration, the solution was evaporated under reduced pressure
affording a residue which was dissolved in CH2Cl2 (10 ml) and
layered with heptane (25 ml). The crystalline green solid (63 mg,
20% yield) which formed was collected by filtration and dried
2.4 mmol) was added. The mixture was stirred at room
temperature for 12 h and then refluxed for 3 h. The suspension
was filtered, the dark green solid was washed with toluene
(2 × 5 ml), dried in vacuo and identified as 13 (air sensitive,
1.35 g; 90.8% yield). Found: C, 65.5; H, 7.0; N, 6.5; Cl, 11.4.
C33H43Cl2N3Ti requires: C, 66.1; H, 7.2; N, 7.0; Cl, 11.7%. IR
(Nujol mull, cm−1): 3059m, 1577mw, 1324w, 1271mw, 1208w,
1104w, 1056w, 936w, 799mw, 769mw, 730mw, 695w. Magnetic
measurement (298 K): vg< 0.
◦
in vacuo at ca. 50 C for 7 h affording the green 8, sensitive to
moisture. Found: C, 54.3; H, 4.6; N, 8.5. C22H21Cl3N3Ti requires:
C, 54.9; H, 4.4; N, 8.7%. 1H NMR (CDCl3) d: 7.53 (10H, m), 6.70
(1H, d), 6.58 (1H, dd), 3.68 (1H, s), 2.30 (3H, s), 1.77 (3H, s). IR
(solid state, cm−1): 2925w, 1591m, 1484m, 1217m, 1027s, 870s,
812s, 747s, 694s.
Preparation of [M(L)Cl4], L = 1, M = Zr, 13, M = Hf, 14; L =
2, M = Zr, 15, M = Hf, 16. Only the preparation of 15 is
described in detail, the preparation of derivatives 13, 14, and 16
being performed in a similar way. To a suspension of 0.987 g
(2.05 mmol) of 2 in toluene (100 ml) ZrCl4 (478 mg, 2.05 mmol)
was added. The mixture was stirred at room temperature for 12 h
and then heated to 80 ◦C for 3 h. The suspension was filtered, the
pale yellow solid was washed with toluene (2 × 5 ml), dried in
vacuo and identified as 15 (1.47 g; 96% yield). Found: C, 56.1; H,
6.5; N, 5.5. C33H43Cl4N3Zr requires: C, 55.7; H, 6.1; N, 5.9%. IR
(Nujol mull, cm−1): 3048m, 1613w, 1586s, 1364s, 1323w, 1267s,
1202w, 1173w, 1015w, 806mw, 783ms, 730s, 693mw, 467w. The
same compound (IR and analytical data) was obtained from
ZrCl4(THF)2 and 2 in dichloromethane.
Reaction of 6 with MAO. A suspension of 6 (647 mg,
1.0 mmol) in toluene (50 ml) was treated with a toluene solution
of MAO (0.6 ml, 10% Al, 2.0 mmol of aluminium). The colour
promptly changed from deep green to brown. The mixture
was heated at ca. 70 ◦C for 15 min and stirred overnight at
room temperature. After filtration of some insoluble material,
the solution was evaporated to dryness in vacuo at room
temperature, the solid residue was treated with CH2Cl2 (10 ml),
and the system was layered with heptane. The resulting deep
brown solid (0.236 g) was recovered by filtration and dried in
vacuo at room temperature. 1H NMR (CDCl3) d: 8.80 (2 H, m),
8.65 (1 H, t), 8.32 (2H, d), 7.42 (2 H, d), 7.34 (2H, d), 3.70 (1 H,
m), 3.05 (1H, m), 2.8–2.6 (2 H, m), 2.56 (3 H, s), 1.20 (30 H,
m). A qualitative test with alizarine as indicator48 showed the
presence of aluminium in the sample.
[Zr(1)Cl4], 13 (moisture sensitive, pale yellow, from ZrCl4-
(THF)2, 61% yield). Found: C, 46.5; H, 3.8; N, 7.5. 13, C21H19Cl4-
N3Zr requires: C, 46.4; H, 3.5; N, 7.7%. IR (solid, cm−1): 2949m,
1614w, 1587s, 1324w, 1268s, 1203w, 1174w, 1016w, 801mw, 784s,
731s, 694w.
[Hf(1)Cl4], 14 (moisture sensitive, pale yellow, from HfCl4-
(DME), 82% yield). Found: C, 40.1; H, 3.2; N, 6.3. C21H19Cl4-
HfN3 requires: C, 39.8; H, 3.0; N, 6.6%. IR (solid, cm−1): 3020m,
1623m, 1590s, 1486ms, 1270s, 1222ms, 1072w, 1019ms, 820m,
781ms, 723m, 694ms, 576w.
[Hf(2)Cl4], 16 (moisture sensitive; 1.339 g; 88% yield). Found:
C, 49.4; H, 5.7; N, 5.9. C33H43Cl4HfN3 requires: C, 49.4; H, 5.4;
N, 5.2%. IR (Nujol mull, cm−1): 3045w, 1616w, 1590s, 1380s,
1325w, 1270s, 1204w, 1174w, 1017w, 801mw, 784mw, 731s, 694w,
467w. CP-MAS 13C NMR d: 174.6 (Cquat), 148.0 (Cquat), 139.8
(Cquat), 137.1 (Cquat), 128.4 (CH), 124.1 (CH), 27.5 (CH), 24.8
(CH3), 24.8 (CH3), 22.1 (CH3).
Preparation of [Ti(2)Cl2(OAlCl3)], 9. A solution of AlOCl
(130 mg, 1.66 mmol) in sym-tetrachloroethane (150 ml) was
treated with 598 mg (1.66 mmol) of 6 and the mixture was
stirred at room temperature for 2 h and heated at ca. 90 ◦C for
1 h. The dark solid was recovered by filtration, washed with sym-
tetrachloroethane and dried in vacuo at ca. 50 ◦C affording 9 as a
microcrystalline solid sensitive to moisture (0.622 g; 50% yield).
Found: C, 53.1; H, 5.5; N, 5.9; Cl., 23.3. C33H43AlCl5N3OTi
requires: C, 52.9; H, 5.8; N, 5.6; Cl., 23.4%. 1H NMR (THF-d8)
d: 6.52 (2 H, s), 2.87 (2 H, m), 2.23 (2 H, s), 1.05 (24 H, m).
The presence of aluminium in the sample was confirmed by a
qualitative test with alizarine as indicator.48 When dried in vacuo
at room temperature, sym-tetrachloroethane is retained in the
solid. The amount of solvent may be determined by hydrolysis
of the sample, extraction of the aqueous phase with CCl4 and
1H NMR analysis of the organic phase in the presence of FeCp2
as internal standard.
Polymerizations. Polymerizations of ethylene were con-
ducted in a Buchi pressure-resistant 300 ml glass reactor previ-
ously subjected to three vacuum–dinitrogen cycles and equipped
with a propeller stirrer, a thermocouple and a heating jacket
connected to a thermostat for temperature control. A solution
of the catalyst was prepared by dissolving 5.4 × 10−3 mmol of the
complex in 50 ml of toluene. The solution was then aged 30 min
at room temperature with stirring. In the meantime 100 ml of
toluene and 1.72 ml (2.7 mmol of aluminium) of a 10% solution
of MAO in toluene ([Al] = 1.57 M), corresponding to an Al/M
ratio of about 500, were charged into the autoclave, and heated
at 70 ◦C. The aged catalytic solution was introduced into the
reactor, and then the apparatus was pressurized with ethylene
at 7 bar. The polymerization was carried out for 60 min, under
continuous ethylene feed at constant pressure. At the end, the
residual gas was vented, the reactor was purged with dinitrogen
and the polymer was recovered by precipitation with acidified
methanol followed by methanol washings and drying.
Preparation of [Ti(L)Cl3], L = 1, compound 10; L = 2,
compound 11. Only the preparation of 11 is described in
detail, 10 being prepared in a similar way. A suspension of
1.043 g (2.1 mmol) of 2 in toluene (100 ml) was added of
TiCl3(THF)3 (777 mg, 2.1 mmol). The mixture was stirred at
room temperature for 12 h and then heated to 80 ◦C for 5 h.
The suspension was filtered and the dark solid was washed with
toluene (2 × 5 ml), dried in vacuo at ca. 50 ◦C and identified as 11
(air sensitive, 1.158 g, 83% yield). Found: C, 62.8; H, 6.9; N, 6.3;
Cl, 15.7; Ti, 7.7. C33H43Cl3N3Ti requires: C, 62.4; H, 6.8; N, 6.6;
Cl, 16.5; Ti, 7.6%. IR (Nujol mull, cm−1): 3050m, 1574w, 1271w,
1213w, 1209w, 798w, 777mw, 735mw, 696w, 412m. Magnetic
measurement: vcMorr = 1.35 × 10−3 cgsu; diamagnetic correction:
−399.8 × 10−6 cgsu; leff (294 K): 1.71 lB.
Compound 10 (air sensitive, 77% yield). Found: C, 53.8; H,
4.4; N 8.7. C21H19Cl3N3Ti requires: C, 54.1; H, 4.1; N, 9.0%.
IR (Nujol mull, cm−1): 3072w, 1581m, 1484m, 1450w, 1371m,
1271ms, 1094w, 1069w, 1025w, 921w, 813s, 778s, 738s, 728s, 696s.
Magnetic measurement: vcMorr = 1.19 × 10−3 cgsu; diamagnetic
correction: − 255 × 10−6 cgsu; leff (294 K) 1.67 lB.
Crystal structure solutions and refinements
Compound 9. Crystals of 9 were grown from CH2Cl2–
heptane at room temperature. Crystal data and structure refine-
ment are reported in Table 4. Data were collected with a graphite-
˚
monochromated Mo-Ka radiation (k = 0.71073 A) with a
Bruker Smart Apex CCD area detector on a D8 goniometer at
110(2) K on a crystal of approximate dimensions 0.22 × 0.12 ×
0.12 mm. A set of 59704 reflections with indices −15 ≤ h ≤ 15,
Preparation of [Ti(2)Cl2], 12. To a suspension of 1.15 g
(2.4 mmol) of 2 in toluene (80 ml), TiCl2(THF)2 (631 mg,
9 2 0
D a l t o n T r a n s . , 2 0 0 5 , 9 1 4 – 9 2 2

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Table 4 Crystal data and structure refinement for Ti(C33H43N3)Cl2-
(OAlCl3), 9, and Ti(C33H43N3)Cl3, 11·1.5PhMe
References
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Compound
Formula
Formula weight
Crystal system
Space group
9
11·1.5PhMe
C87H110Cl6N6Ti2
1548.3
Monoclinic
P21/c
2 K. Ziegler, Angew. Chem., 1964, 76, 545.
C33H43AlCl5N3OTi
749.8
3 G. Natta, Angew. Chem., 1956, 68, 393.
4 G. Natta, Angew. Chem., 1964, 76, 553.
Monoclinic
P21/c
5 H. H. Brintzinger, D. Fischer, R. Mu¨lhaupt, B. Rieger and R. M.
Waymouth, Angew. Chem., Int. Ed. Engl., 1995, 34, 1143, and
references therein.
Unit cell dimensions:
˚
a/A
12.683(4)
16.674(5)
17.317(5)
96.79(1)
3656(1)
20.761(5)
16.266(4)
31.141(6)
128.19(1)
8266(3)
6 A. S. Abu-Surrah and B. Rieger, Angew. Chem, Int. Ed. Engl., 1996,
35, 2475, and references therein.
7 B. L. Small, M. Brookhart and A. M. A. Bennet, J. Am. Chem. Soc.,
1998, 120, 4049.
˚
b/A
˚
c/A
b/◦
3
˚
V/A
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Z
4
4
Dc/Mg m−3
1.362
0.654
1.244
0.434
l/mm−1
Reflections collected
Independent reflections
Absorption correction
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I >2r(I)]
59704
7002
104563
18429
Empirical
7002/0/407
1.032
R1 = 0.0536
wR2 = 0.1228
R1 = 0.0985
wR2 = 0.1404
Empirical
18429/196/933
1.041
R1 = 0.0695
wR2 = 0.1627
R1 = 0.1146
wR2 = 0.1877
R Indices (all data)
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was applied before averaging symmetry-equivalent data (Rint
=
0.101). After merging, 7002 independent reflections remained
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was completed by Fourier difference syntheses and refined with
full-matrix least-squares on F2.50 Convergence was reached for
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R1 = 0.0536 [observations with I > 2r(I)]. Maxima and minima
from a final Fourier map were 0.616 and −0.391 e A−3.
Crystal structure solution and refinement of 11·1.5 toluene.
Crystals of 11·1.5PhMe were obtained by slowly cooling a
saturated toluene solution of 11. The asymmetric unit contains
two molecules of 11 and three molecules of toluene. Crystal
data and structure refinement are reported in Table 4. Data
were collected with graphite-monochromated Mo-Ka radiation
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˚
(k = 0.71073 A) on a Bruker Smart Apex CCD area detector
on a D8 goniometer at 110(2) K on a crystal of approximate
dimensions 0.40 × 0.27 × 0.16 mm. A set of 104563 reflections
with indices −26 ≤ h ≤ 26, −20 ≤ k ≤ 20, −40 ≤ l ≤ 40
were collected with the x scan method in the range 1.25 ≤ h ≤
27.25◦. An empirical absorption correction (min. transmission
0.85, max. transmission 0.93) was applied before averaging
symmetry equivalent data (Rint = 0.0815). After merging, 18429
independent reflections remained for structure solution by direct
methods.49 The structure model was completed by Fourier
difference syntheses and refined with full-matrix least-squares
on F2.50 Convergence was reached for 18429 reflections and 933
variables at wR2 = 0.1877 (all data), R1 = 0.0695 [observations
with I > 2r(I)]. Maxima and minima from a final Fourier map
were 1.2 and −0.0695 e A−3.
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Acknowledgements
The authors wish to thank the Ministero dell’Istruzione
dell’Universita` e della Ricerca (MIUR, Roma), Programma di
Ricerca Scientifica di Notevole Interesse Nazionale 2002–2003,
for financial support.
D a l t o n T r a n s . , 2 0 0 5 , 9 1 4 – 9 2 2
9 2 1

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9 2 2
D a l t o n T r a n s . , 2 0 0 5 , 9 1 4 – 9 2 2