Mono(aryloxido)titanium(IV) Complexes and their application in the selective dimerization of ethylene

Article abstract of DOI:10.1002/ejic.200900322

We report on the synthesis of mono(aryloxido)titanium(IV) complexes of general formula [Ti[O(o-R)Ar]X₃), with X = OiPr, ArO = 2-ie.rr-but:yl-4-methylphenoxy and. R = CMe₃ (2a), CMe₂Ph (2b) and CH₂NMe₂ (2c). Attempts to reach pure mono(aryloxido) complexes when R = CH₂NMe(CH₂Ph) (2d) or CH₂N(CH₂Ph)₂ (2e) were unsuccessful, When R = CH₂OMe, the analogous mononuclear complex was not obtained, and instead, a dinuclear complex [(2-ieri-butyl-4methyl-6- methoxymethylphenoxy) TiCl(OiPr)(H₂-OiPr)₂TiCl(OiPr) ₂] (3) was formed. Complexes 2b and 3 were characterized by single-crystal X-ray diffraction, The former contains a tetrahedrally coordinated. Ti^IV centre, whereas in the latter the aryloxido ligand behaves as a chelating-bridging ligand between the two, chemically very different metal centres that form two face-sharing octahedra, Different synthetic approaches starting from. [Ti(OiPr)₄] or [TiCl(OiPr) ₃] were evaluated and are discussed, The hemllabile behaviour of the aryloxido ligand. resulting from, reversible coordination of its side arm was studied by variable-temperature 1H NMR spectroscopy for 2c (R = CH ₂NMe₂). Complexes 2a-d were contacted, with ethylene and AlEt₃ as cocatalyst, When activated with AlEt₃ (3 equiv.) at 20 bar and 60 ° C, complex 2c exhibits interesting activity (2100 g/gTi/h) for the selective dimerization of ethylene to 1-butene (92% C ₄"⁼; 99+% C4⁼¹), Noticeable differences in catalyst activity were observed when the R group was modified,

Full text of DOI:10.1002/ejic.200900322

FULL PAPER
DOI: 10.1002/ejic.200900322
Mono(aryloxido)Titanium(IV) Complexes and Their Application in the
Selective Dimerization of Ethylene
Jean-Benoit Cazaux,[a] Pierre Braunstein,[b] Lionel Magna,*[a] Lucien Saussine,*[a] and
Hélène Olivier-Bourbigou[a]
Keywords: Dimerization / O ligands / Hemilability / Titanium / Structure–activity relationships
We report on the synthesis of mono(aryloxido)titanium(IV)
complexes of general formula {Ti[O(o-R)Ar]X3}, with X =
OiPr, ArO = 2-tert-butyl-4-methylphenoxy and R = CMe3
(2a), CMe2Ph (2b) and CH2NMe2 (2c). Attempts to reach
pure mono(aryloxido) complexes when R = CH2NMe(CH2Ph)
(2d) or CH2N(CH2Ph)2 (2e) were unsuccessful. When R =
CH2OMe, the analogous mononuclear complex was not ob-
tained, and instead, a dinuclear complex [(2-tert-butyl-4-
methyl-6-methoxymethylphenoxy) TiCl(OiPr)(µ2-OiPr)2TiCl-
(OiPr)2] (3) was formed. Complexes 2b and 3 were charac-
terized by single-crystal X-ray diffraction. The former con-
tains a tetrahedrally coordinated TiIV centre, whereas in the
latter the aryloxido ligand behaves as a chelating–bridging
ligand between the two, chemically very different metal
centres that form two face-sharing octahedra. Different syn-
thetic approaches starting from [Ti(OiPr)4] or [TiCl(OiPr)3]
were evaluated and are discussed. The hemilabile behaviour
of the aryloxido ligand resulting from reversible coordination
of its side arm was studied by variable-temperature 1H NMR
spectroscopy for 2c (R = CH2NMe2). Complexes 2a–d were
contacted with ethylene and AlEt3 as cocatalyst. When acti-
vated with AlEt3 (3 equiv.) at 20 bar and 60 °C, complex 2c
exhibits interesting activity (2100 g/gTi/h) for the selective
dimerization of ethylene to 1-butene (92% C4=; 99+% C4=1).
Noticeable differences in catalyst activity were observed
when the R group was modified.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
in the C4 fraction have a boiling point very close to that
of 1-butene and separation by superfractionation is almost
impossible. Chemical extraction is industrially used but the
1-butene obtained contains 1,3-butadiene and isobutene im-
purities, which are very detrimental in polyethylene pro-
cesses. On the contrary, selective ethylene dimerization,
which is industrially operated in the IFP Alphabutol pro-
cesses,[26] has the main advantage to provide 1-butene with
a much better quality associated with a low investment. To-
day, 24 Alphabutol units have been licensed, for a cumu-
lated 1-butene production capacity of 500000 t/y, nearly
25% of the world’s 1-butene consumption as co-monomer
in polyethylene.
Another source of 1-butene results from its co-pro-
duction in the ethylene oligomerization processes leading to
higher, linear α-olefins (Ineos, Chevron-Phillips, Idemitsu
processes). However, 1-butene appears as a byproduct in
these processes, and the amount available is directly de-
pendent on the market for the higher linear α-olefins. When
these two sources cannot be envisaged, a polyethylene man-
ufacturer may either import 1-butene, which implies trans-
portation and storage costs, or produce 1-butene on-site by
a dedicated process. Titanium complexes also appeared re-
cently as good catalysts for the selective trimerization of
ethylene to 1-hexene. This new catalyst comprises a tita-
nium cyclopentadienyl (Cp) system with an aromatic side
arm grafted onto the Cp ligand.[27–29] The addition of this
Introduction
The catalytic oligomerization of ethylene represents the
main industrial source of α-olefins.[1] Processes based on
this reaction yield olefins with an even number of carbon
atoms and a more or less tuneable chain length distribution.
Among these products, short-chain linear α-olefins (1-but-
ene, 1-hexene, 1-octene) are of particular interest because of
their use, for example, in the synthesis of linear low-density
polyethylene. The development of efficient catalyst systems
for the selective production of these olefins has recently
triggered intensive research in both academia and industry.
For this purpose, titanium- and chromium-based catalysts
have attracted much attention.[2] Homogeneous chromium
catalysts play a major role in ethylene trimerization[3–13] and
tetramerization reactions.[14–22] Titanium catalysts are pre-
ferred catalysts for the selective dimerization of ethylene to
1-butene.[23–26] The conventional industrial production of 1-
butene is realized by extraction from the C4 fraction of
steam cracker plants. Butadiene and isobutene also present
[a] IFP Lyon, Rond Point de l’échangeur de Solaize,
BP3, 69360, Vernaison, France
E-mail: lionel.magna@ifp.fr
lucien.saussine@ifp.fr
[b] Laboratoire de Chimie de Coordination Institut de Chimie
(UMR 7177 CNRS), Université de Strasbourg,
4 rue Blaise Pascal, 67070 Strasbourg, France
E-mail: braunstein@chimie.u-strasbg.fr
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Mono(aryloxido)TiIV Complexes for Selective Dimerization of Ethylene
functionality to Cp dramatically changes the selectivity of were synthesized by using a Mannich-type condensation, as
the known ethylene polymerization system [CpTiCl3]-MAO. described for 1c[49] [Equation (1)], and they were obtained
DFT studies were conducted on this catalytic system and as white crystalline solids in 85, 76 and 57% yield, respec-
essentially confirmed the role of the arene side arm on this tively, depending on the steric hindrance of the precursor
surprising reactivity.[30–33] In a further modification of this amine.
titanium-based catalyst, Huang et al. replaced the pendant
arene with a thienyl[34] or ether pendant group[35] and ob-
served again selectivity toward 1-hexene. Over the past dec-
ade, there has been much interest for catalysts based on
post-metallocene group 4 complexes.[36–38] In this context,
aryloxido-based ligands[39,40] have proved to be good alter-
natives to the Cp ligand. In particular, ancillary phenoxyim-
ine systems have raised a great deal of interest.[41,42] The use
of other functionalized aryloxido ligands in group 4 metal
complexes remains scarce.[43–46] Most of these aryloxido/
group 4 systems were developed for ethylene polymerization
and contain ligands presenting a constrained geometry for
better polymer selectivity. In comparison with these sys-
tems, complexes containing one aryloxido ligand with a π-
electron donor pendant group remain underrepresented.[47]
Owing to the expected reversible coordination of the pen-
dant group, such ligands could stabilize highly reactive elec-
trophilic metal centres until the substrate coordinates and
replaces the pendant group. The aim of the present work
was to design monoanionic bidentate phenoxido ligands
capable of generating hemilabile behaviour in association
with a titanium complex. This feature should lead to more
flexibility in the ligand-coordinating ability and could affect
both the stability and the reactivity of the complexes for the
selective dimerization of ethylene.
(1)
The synthesis of ligand 1f was achieved in a two-step
reaction involving the synthesis of the chloromethylphenol
intermediate and its reaction with sodium methoxide
[Equation (2)]. Ligand 1f was isolated as a white solid that
melts at room temperature (52% yield).
(2)
Synthesis of the [Ti(OAr)(OiPr)3] Complexes
We used two different approaches to access the mono(ar-
yloxido) complexes shown in Scheme 2. The most suitable
synthetic route (path A, Scheme 2) involved ligand ex-
change between the tetraalkoxide TiIV precursor [Ti(OiPr)
4] and the phenol.[39,50–52] This route led to readily isolable
species, as the only byproduct was an alcohol that could be
easily removed under reduced pressure. These mono(arylox-
ido) complexes could also be obtained by transmetallation,
starting from the metallated phenol (Na, Li) and the
[TiCl(OiPr)3] precursor (path B, Scheme 2).
Results and Discussion
Synthesis of the Substituted Aryloxido Ligands
The ortho position of 2-tert-butyl-4-methylphenol was
functionalized with various R groups (Scheme 1). These
side chains cover a wide panel of coordinating abilities,
ranging from the bulky non-coordinating tert-butyl group
to the stronger donor amine chain, through an aromatic
group able to donate up to 6π electrons to the titanium
centre. The influence of steric factors was also studied by
comparing several aminophenols.
Scheme 2. General synthesis of [Ti{O(o-R)Ar}(OiPr)3].
Scheme 1. o-Functionalized aryloxido ligands.
When 2,6-di-tert-butyl-4-methylphenol was treated with
Ligand 1b was obtained by an acid-catalyzed alkylation [Ti(OiPr)4], expected mono(aryloxido)titanium(IV) com-
reaction by following a procedure described for the synthe- plex 2a was obtained and isolated in good yield after
sis of 2,6-di-tert-butylphenol.[48] The use of ortho/para-sub- crystallization from cold pentane (off white solid, 78%).
stituted phenol as the starting material prevented the for- The same synthetic route applied to the aminophenol series
mation of bisalkylation products and facilitated the isola- gave less satisfactory results. The desired mono(aryloxido)
tion of the desired compound (43% yield after distillation complex was only obtained starting from 1c with neverthe-
and recrystallization from pentane). Aminophenols 1c–e less the presence of residual phenol characterized by 1H
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FULL PAPER
NMR spectroscopy. Owing to the oily nature of 2c and its
high solubility in common organic solvents, we were not
able to isolate this complex pure. Moreover, it became in-
creasingly difficult to obtain pure compounds when the ste-
ric bulk of the N-substituents increased. Benzylmethylami-
nomethyl derivative 2d could only be obtained with in 90%
purity, and bulkier dibenzylaminomethyl derivative 2e was
only observable in a very complex mixture [free phenol 1e,
residual [Ti(OiPr)4], mono- and bis(aryloxido) complexes].
Path B was then evaluated to overcome these difficulties.
The reaction of the sodium phenoxide derived from 1c with
[TiCl(OiPr)3] afforded 2c in high yields as a bright-yellow
oil. None of the various crystallization attempts afforded a
crystalline product. Unfortunately, the reaction of the phen-
oxide derived from 1e with [TiCl(OiPr)3] yielded a compli-
cated mixture of products. The relatively large amount of
bis(aryloxido) complex formed suggests the occurrence of a
ligand redistribution in solution [Equation (3)].
Figure 1. ORTEP view and atom numbering of 2b. H atoms omit-
ted for clarity. Thermal ellipsoids include 50% of the electron den-
sity.
(3)
Following path B, complex 2b was also isolated in high
yield as a pure crystalline compound that easily formed
large, colourless crystals suitable for X-ray diffraction. A
view of the molecular structure of 2b is shown in Figure 1
and selected bond lengths and angles are collected in
Tables 1 and 2, respectively. In complex 2b, the tetrahedral
coordination geometry around the metal centre is slightly
distorted and the bulky aryloxido unit is further away from
the metal than the isopropoxido ligands, Ti–O(3) Ͻ Ti–
O(4) Ͻ Ti–O(2) Ͻ Ti–O(1), indicating a weaker interaction
of the aryloxido oxygen lone pairs with the titanium d or-
bitals. Furthermore, the position of the aromatic side chain
induces a widening of the tetrahedral cone angle Ti-
{O(1),O(2),O(3)}. This results in a relatively short distance
of 0.550 Å between Ti and the {O(1),O(2),O(3)} plane (ma-
terialized by a dashed plane in Figure 1). The distances be-
tween the titanium and the other {O(x),O(y),O(z)} planes
are much longer: Ti-{O(1),O(3),O(4)} = 0.583 Å, Ti-{O(1),
O(2),O(4)} = 0.613 Å and Ti-{O(2),O(3),O(4)} = 0.635 Å.
The titanium atom is not at the centre of the tetrahedron
but slightly displaced towards the aromatic side chain.
However, when considering the interatomic distances, the
aromatic group appears too far from the metal to interfere
significantly with its coordination sphere [C(15)–Ti ≈
3.6 Å].
Table 1. Selected bond lengths for 2b.
Atom 1
Atom 2
Bond length [Å]
Ti
Ti
O1
O2
1.825(1)
1.793(2)
1.754(2)
1.774(2)
1.360(2)
1.423(2)
1.421(3)
1.383(3)
Ti
Ti
O3
O4
O1
O2
O3
O4
C8
C21
C24
C27
Table 2. Selected bond angles for 2b.
Atom 1
Atom 2
Atom 3
Bond angle [°]
O1
O1
O1
O2
O2
O3
C8
C21
C24
C27
Ti
Ti
Ti
Ti
Ti
Ti
O1
O2
O3
O4
O2
O3
O4
O3
O4
O4
Ti
Ti
Ti
Ti
110.77(7)
113.21(7)
108.92(7)
109.04(8)
107.29(7)
107.40(9)
170.3(2)
145.0(2)
158.7(2)
157.8(2)
Difficulties observed for the selective synthesis of analysis (Figure 2). In this compound, the Ti1 atom is at
mono(aryloxido)titanium(IV) complexes 2c–e were also ob- the centre of a distorted octahedron formed by a terminal
served with ether-functionalized phenol ligand 1f. The reac- chloride ion, a terminal alkoxido group, two bridging al-
tion of 1f with [Ti(OiPr)4] and that of the sodium derivative koxido ligands, the terminally bound ether oxygen atom of
of 1f with [TiCl(OiPr)3] led to redistribution of the ligands, the aryloxido group and the bridging oxygen atom of the
and the only isolated product was the bis(aryloxido) species. aryloxido ligand. The Ti2 centre displays a distorted struc-
Another approach (Scheme 3) was attempted with 1f that ture between trigonal-bipyramidal and octahedral when
involved the use of its trimethylsilyl derivative.[40,53]
considering the terminal chloride ion, the two terminal alk-
However, this reaction did not afford the expected com- oxido groups, the two bridging alkoxido groups and the
plex of type 2; instead, binuclear complex 3 was obtained methoxy group of the aryloxido ligand. The structure of
in low yield as red crystals, suitable for X-ray diffraction this dinuclear complex can therefore be viewed as that of
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Mono(aryloxido)TiIV Complexes for Selective Dimerization of Ethylene
not present. It is conceivable that a strong donor group in-
duces ligand redistribution via some dinuclear intermediate,
but if this donor binds tightly to the titanium in the mono-
nuclear species, then this pathway for ligand redistribution
is blocked.
Table 3. Selected bond lengths for 3.
Atom 1
Atom 2
Bond length [Å]
Ti1
Ti1
Ti1
Ti1
Ti1
Ti1
Ti2
Ti2
Ti2
Ti2
Ti2
Ti2
O1
O2
O2
O3
O4
O5
O6
O7
O1
O2
O3
O4
1.842(3)
2.382(3)
1.751(3)
2.028(3)
1.979(2)
2.334(1)
2.346(1)
2.554(2)
1.997(2)
2.055(3)
1.771(3)
1.755(3)
1.361(4)
1.466(5)
1.455(5)
1.428(6)
1.454(5)
1.443(5)
1.389(7)
1.427(5)
O5
Cl1
Cl2
O2
O4
O5
O6
O7
C8
C1
C19
C20
C16
C13
C23
C26
Scheme 3.
two face-sharing octahedra. It clearly illustrates the bending
induced by the coordination of the ether group (Tables 3
and 4). As shown, the selective synthesis of N- or O-func-
tionalized mono(aryloxido)titanium complexes appears
rather difficult. We first thought that steric factors (in the
case of the aminophenol series) were responsible for the li-
gand redistribution reactions. However, we did not observe
them with 2a and 2b, where a strong ortho donor group is
Table 4. Selected bond angles for 3.
Atom 1
Atom 2
Atom 3
Bond angle [°]
O1
O2
O5
O2
O4
O5
C8
C20
C16
C16
C13
C13
C23
C26
Ti1
Ti1
Ti1
Ti2
Ti2
Ti2
O1
O3
O4
O4
O5
O5
O6
O7
O4
O3
Cl1
O7
Cl2
O6
Ti1
Ti1
Ti2
Ti1
Ti1
Ti2
Ti2
Ti2
155.6(1)
172.31(1)
157.5(1)
166.4(1)
153.3(1)
156.8(1)
136.0(2)
169.8(3)
132.6(2)
124.7(2)
133.4(3)
124.0(2)
151.8(5)
147.6(4)
Hemilabile Properties of the –CH2NMe2 Group in Complex
2c
1
The H NMR spectrum of complex 2c in the methylene
region suggests a loose coordination of the amine side chain
to the metal centre. The two CH protons display a very
broad signal at room temperature, which can be explained
by a dynamic exchange involving reversible coordination of
the amine, typical of hemilabile behaviour.[54] The 1H NMR
resonances of the methylene protons are diagnostic for the
formation of metallocycles.[55] Therefore, the variable-tem-
1
perature H NMR study performed in [D8]toluene between
Figure 2. ORTEP views of 3. H atoms omitted for clarity. Thermal
ellipsoids include 50% of the electron density. The bottom view
emphasizes the metal coordination polyhedra forming face-sharing
octahedra.
193 and 353 K allowed us to follow the evolution of the
broad signal observed for the methylene protons at 293 K
(Figure 3).
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J.-B. Cazaux, P. Braunstein, L. Magna, L. Saussine, H. Olivier-Bourbigou
FULL PAPER
was 93% with more than 99% of 1-butene. Under the same
reactions conditions, complex 2c exhibited an activity of
2100 g/gTi/h for the selective dimerization of ethylene to 1-
=
butene (92% C4=; 99+% C4=1). A small amount of C6 by-
products were also obtained, which contained (GC analy-
sis) 3-methyl-1-pentene (30%), 2-ethyl-1-butene (57%) and
linear hexenes (10%). The nature of these products and the
high selectivity for 1-butene can be explained by a metall-
acyclic mechanism, and byproducts result from a codimer-
ization process reported earlier.[57] The influence of the
AlEt3/Ti ratio was also evaluated for complex 2c. By in-
creasing this ratio from 3 to 5, the activity decreased dra-
matically and the amount of polyethylene formed increased
1
Figure 3. H NMR study of complex 2c as a function of tempera-
from ca. 1 to 36 wt.-%, but the selectivity for 1-butene in
the butenes was not affected. This loss of activity can be
related to the presence of free AlEt3, which promotes the
transfer of the aryloxido ligand to aluminum, resulting in
inactive aluminum species.[58] Noticeable differences of ac-
tivity were observed when the side group of the aryloxido
ligand was modified. Substitution of the nitrogen with a
benzyl group in 2d reduced the catalytic activity. A similar
comment can be made for complex 2b, which displays a
somewhat higher activity than 2a. This could result from a
weak coordination of the aromatic side chain to the tita-
nium centre in the activated species. If the catalytic activity
is enhanced by the aromatic side chain, the selectivity for
the dimerization products is lowered. Indeed, this catalyst
ture.
The resonance of the methylene protons at 3.6 ppm
sharpens when the temperature is raised from 293 to 353 K.
On the contrary, the broad signal observed at 293 K pro-
gressively disappears when the sample is cooled down, until
two doublets appear at 2.7 and 4.5 ppm, indicative of the
presence of an AX spin system. This pattern is attributed
to the two geminal protons of the species with the amine
nitrogen coordinated to titanium in a titanaoxoazacy-
clohexane. This reversible “opening–closing” phenomenon
indicates a high stability of the compound over this tem-
perature range. The free energy of activation associated
with this process was calculated to be 50.4 kJ/mol.[56] The
same NMR spectroscopic study was performed for complex
2b. In that case, no evolution of the 1H NMR spectrum was
detected from 203 to 353 K. If thermal stability of complex
2b is then demonstrated, this result indicates the absence of
dynamic equilibrium involving the pendant aromatic ring.
=
yields a mixture of 1-butene and C6 isomers with a lower
selectivity for butenes (less than 70%) than 2c and a distri-
bution of hexene isomers typical of a codimerization pro-
cess (the main products being 2-ethyl-1-butene and 3-
methyl-1-pentene). This observation suggests an increase in
the rate of codimerization reaction. Complementary experi-
ments were conducted with aluminoxane derivatives or
chlorinated aluminum alkyls as cocatalysts.[59] These acti-
vators switch the reactivity from dimerization to polymeri-
zation.
Catalysis
The catalytic properties of complexes 2a–d were investi-
gated for ethylene oligomerization. [Ti(OiPr)4] was used as
a reference for comparison of ligand effects. Experiments
were carried out in heptane at 60 °C in the presence of
AlEt3 as cocatalyst. The ethylene pressure was maintained
Conclusions
New titanium monoanionic aryloxido complexes were
constant at 20 bar throughout the catalytic run (1 h). Re- synthesized and characterized. The interaction of the ary-
sults are summarized in Table 5. loxido ortho-substituent R with titanium could be evi-
With [Ti(OiPr)4], the catalyst activity was estimated at denced, and the resulting hemilabile behaviour demon-
1600 g/gTi/h. The ethylene consumption remained constant strated through variable-temperature 1H NMR spectro-
during the test. The selectivity for dimerization products scopic analyses on complex 2c. When the ortho-substituent
Table 5. Oligomerization of C2H4 with complexes 2a–d and AlEt3 as cocatalyst.[a]
Productivity (g/gTi/h)[b]
Sel. C4=(α[c])
Sel. C6=(α[d]
)
Sel. C8+
PE[e]
=
Catalyst
Al/Ti ratio
[Ti(OiPr)4]
3
3
3
3
5
3
1600
170
380
2100
320
100
93 (99+)
91 (99)
69 (99+)
92 (99+)
53 (98)
91 (98)
6 (13)
2 (5)
27 (2)
7 (11)
9 (16)
8 (1)
Ͻ1
4
3
Ͻ1
2
Ͻ1
≈1
2
≈1
≈1
36
–
2a
2b
2c
2c
2d
[a] Ti precursor (0.15 mmol), heptane (6 mL), 20 bar C2H4, 60 °C, stirring rate: 1000 rpm, reaction time: 1 h. [b] Expressed in grams of
products per gram of Ti per hour. [c] 1-Butene vs. total butenes formed. [d] 1-Hexene vs. total hexenes formed. [e] Calculated from the
solid isolated (insoluble in heptane).
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Mono(aryloxido)TiIV Complexes for Selective Dimerization of Ethylene
CD2Cl2, 298 K): δ = 1.30 [s, 9 H, C(CH3)3], 1.69 [s, 6 H, C(CH3)2],
R was CH2OMe, dinuclear complex 3 was obtained and
characterized by X-ray diffraction. The Ti centres are in
very different coordination environments and only one
mono(aryloxido) ligand is present, which acts as a chelat-
ing–bridging ligand. The activation of these complexes with
AlEt3 as cocatalyst was performed to evaluate their per-
formances as ethylene selective dimerization catalysts. The
donating ability as well as the steric bulk of the R group
have a significant influence on the catalytic performances,
as shown by the dimethylamine-functionalized compound
2c, which selectively dimerizes ethylene with good produc-
tivity, whereas the benzylmethylamine and α,α-dimeth-
ylbenzyl derivatives (2d and 2b, respectively) are less active.
The influence of the aluminum-based cocatalyst was evalu-
ated and appears critical for the type of mechanism in-
volved. Whereas AlEt3 generally implies selective ethylene
dimerization, chlorinated cocatalysts or aluminoxane deriv-
atives systematically lead to polymerization catalysis.
4
2.37 (s, 3 H, CH3), 4.83 (s, 1 H, OH), 7.07 and 7.22 (2 d, JH,H
=
2 Hz, 2 H, CH from ArOH), 7.35 (m, 1 H, p-CHAr), 7.38 (m, 4 H,
o- and m-CHAr) ppm. 13C{1H} NMR (75 MHz, CD2Cl2, 298 K): δ
= 21.31 (s, C-CH3), 29.9 [s, C(CH3)3], 30.1 [s, C(CH3)2], 34.9 [s,
C(CH3)3], 42.2 [s, C(CH3)2], 115.8 (s, p-C from ArOH), 125–130 (s,
5 CH), 135.8 and 138.0 (s, o-C from ArOH), 148.6 (s, C-OH), 150.8
[s, CArOH-C(CH3)2-CAr] ppm. C20H26O (282,42): calcd. C 85.06,
H 9.28, O 5.67; found C 84.81, H 9.52, O 5.46.
2-tert-Butyl-4-methyl-6-(N-dimethylaminomethyl)phenol (1c): This
compound was synthesized following the procedure described in
the literature.[49] A solution of 2-tert-butyl-4-methylphenol (10.6 g,
64.6 mmol) in ethanol (200 mL) was heated at reflux overnight with
paraformaldehyde (3.06 g, 102 mmol) and 40% aqueous dimeth-
ylamine (9.0 g, 78.3 mmol). The volatiles were then removed under
reduced pressure. The viscous residue was purified by crystalli-
zation from cold ethanol, yielding 1c (12.2 g, 85%) as white crys-
tals. MS (CI+): m/z = 221 [M]+. 1H NMR (300 MHz, CD2Cl2,
298 K): δ = 1.28 [s, 9 H, C(CH3)3], 2.12 (s, 3 H, CH3), 2.18 [s, 6 H,
N(CH3)2], 3.46 (s, 2 H, NCH2Ph), 6.55 and 6.87 (2 s, 2 H, aro-
matic), 11 (br. s, 1 H, OH) ppm. 13C{1H} NMR (75 MHz, CD2Cl2,
298 K): δ = 20.8 (s, CH3), 29.07 [s, C(CH3)3], 34.2 [s, C(CH3)3],
44.34 [s, N(CH3)2], 63.45 (s, NCH2Ph), 122.5 (s, 1 C), 126.7 (s, CH),
127.1 (s, 1 C), 127.22 (s, CH), 136.3 (s, 1 C), 155 (s, C-OH) ppm.
C14H23NO (221,34): calcd. C 75.97, H 10.47, N 6.33, O 7.23; found
C 75.79, H 10.63, N 6.08, O 7.48.
Experimental Section
General Methods: All manipulations were performed under an ar-
gon atmosphere by using standard Schlenk techniques. Ethyl ether
and thf were distilled from Na/benzophenone prior to use. Pentane,
heptane, o-xylene and toluene were distilled from a sodium suspen-
sion and dichloromethane over calcium hydride. The water con-
tents of these solvents were periodically controlled by Karl-Fischer
coulometry by using a Methrom 756 KF apparatus. 1H NMR
(300 MHz) and 13C NMR (75 MHz) spectra were recorded with
a Bruker AC 300 MHz instrument. Deuterated solvents (CD2Cl2,
CDCl3, D2O) were purchased from Aldrich or Eurisotop. CD2Cl2
and CDCl3 were degassed by freeze–thaw–vacuum cycles and
stored over 3 Å molecular sieves. Chemical shifts are reported in
ppm vs. SiMe4 and were determined by reference to the residual
solvent peaks. All coupling constants are given in Hertz. Elemental
analyses of the ligands were performed by the Service Central
d’Analyses of the CNRS (Vernaison, France) or by the ICMUB
Université de Bourgogne (Dijon, France). Elemental analyses of
the complexes were performed by Mikroanalitisches Labor Pascher
(Remagen, Germany). Mass spectra analyses were performed by
using an Agilent 5975 B instrument, in a chemical ionization mode
with methane as gas. The samples, liquids or solids, were intro-
duced by using a SIM automated direct inlet probe system with
temperature control. Ion mass (m/z) signals are reported as values
in atomic mass units. Ligand 1a (2,6-di-tert-butyl-3-methylphenol)
2-tert-Butyl-4-methyl-6-(N-benzylmethylaminomethyl)phenol (1d):
This compound was synthesized following the procedure described
for 1c. A solution of 2-tert-butyl-4-methylphenol (4.5 g, 27.4 mmol)
in toluene (100 mL) was heated at 80 °C for 6 h with paraformal-
dehyde (1.0 g, 33 mmol) and methylbenzylamine (3.5 mL,
27.1 mmol). After cooling to room temperature, water (100 mL)
was poured into the reaction mixture. The organic layer was col-
lected, and the aqueous phase was extracted with ethyl acetate
(200 mL). The combined organic phase was dried with MgSO4,
and the volatiles were removed under reduced pressure. The viscous
residue was purified by crystallization from cold methanol, yielding
1
1d (6.14 g, 76%) as white crystals. MS (CI+): m/z = 298 [M]+. H
NMR (300 MHz, CD2Cl2, 298 K): δ = 1.42 [s, 9 H, CC(CH3)3],
2.20–2.24 (2 s, 2ϫ3 H, CH3 and N-CH3), 3.54 (s, 2 H, NCH2Ph),
4
3.70 (s, 2 H, NCH2Ar), 6.71 and 7.00 (2 d, JH,H = 1.9 Hz, 2 H,
CH from ArOH), 7.73 (m, 5 H, CH Ph), 11.0 (br. s, 1 H, OH)
ppm. 13C{1H} NMR (75 MHz, CD2Cl2, 298 K): δ = 20.8 (s, CH3),
29.7 [s, C(CH3)3], 34.8 [s, CC(CH3)3], 41.1 (s, NCH3), 61.1 and 61.8
(s, 2 NCH2), 126.94, 127.6, 127.8, 128.8 and 129.8 (s, CH), 122.5,
127.4, 136.5, 137.7 (s, 1 C), 154.7 (s, C-OH) ppm. C20H27NO
(297.43): calcd. C 80.76, H 9.15, N 4.71; found C 80.3, H 9.14, N
4.89.
and all reagents were obtained from commercial sources and used
as received unless otherwise indicated.
2-tert-Butyl-4-methyl-6-(N-dibenzylaminomethyl)phenol (1e): The
procedure described above for 1c was used, starting from 2-tert-
butyl-4-methylphenol (4.43 g, 27 mmol) in toluene (170 mL), para-
formaldehyde (1.0 g, 33 mmol) and dibenzylamine (5.4 mL,
27.9 mmol). Ligand 1e (5.57 g, 57%) was obtained as white crys-
tals. MS (CI+): m/z = 373 [M + 1]+. 1H NMR (300 MHz, CD2Cl2,
298 K): δ = 1.43 [s, 9 H, CC(CH3)3], 2.24 (s, 3 H, CH3), 2.62 (m,
4 H, CH2), 3.59 (s, 4 H, NCH2Ph), 3.70 (s, 2 H, NCH2Ar), 6.70
2-tert-Butyl-4-methyl-6-(α,α-dimethylbenzyl)phenol (1b): A solution
of triethylaluminum (1.3 mL, 1.16 g, 10 mmol) in n-heptane
(15 mL) was added dropwise to 2-tert-butyl-4-methylphenol
(16.4 g, 198 mmol). The reaction mixture was then heated to 60 °C
before α-methylstyrene (13 mL, 11.8 g, 100 mmol) was added. The
reaction mixture was stirred for 1.5 h at 60 °C and then cooled to
room temperature. The organics were diluted with heptane/ethyl
ether (70:30, 150 mL) and washed with 5% aqueous HCl (20 mL),
distilled water (2ϫ20 mL), 5% NaOH (20 mL) and then water
4
and 6.99 (2 d, JH,H = 1.9 Hz, 2 H, H from Ar), 7.73 (m, 10 H, H
benzyl), 10.6 (s, 1 H, OH) ppm. 13C{1H} NMR (75 MHz, CD2Cl2,
(2ϫ20 mL). The organic phase was then dried with MgSO4 and 298 K): δ = 20.8 (s, CH3), 29.7 [s, CC(CH3)3], 34.8 [s, CC(CH3)3],
filtered, and the solvents were removed under vacuum. Distillation
of the oily residue under reduced pressure (4.10–2 mbar, 80 °C) and
crystallization from n-pentane yielded 1b (12.1 g, 42.7%) as white
cubic crystals. MS (CI+): m/z = 282 [M]+. 1H NMR (300 MHz,
57.8 and 57.9 (s, 3 NCH2), 127.0, 127.86, 127.99, 128.86 and 130.02
(s, CH), 122.6, 127.6, 136.5 and 137.7 (s, 1 C), 154.2 (s, C-OH)
ppm. C26H31NO (373,53): calcd. C 83.60, H 8.37, N 3.75; found C
82.98, H 8.38, N 3.97.
Eur. J. Inorg. Chem. 2009, 2942–2950
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2947

J.-B. Cazaux, P. Braunstein, L. Magna, L. Saussine, H. Olivier-Bourbigou
FULL PAPER
2-tert-Butyl-4-methyl-6-(methoxymethyl)phenol (1f): Gaseous HCl
(Air Liquide, 99+%) was bubbled for 5 min through a cold (0 °C)
solution of 2-tert-butyl-4-methylphenol (15.3 g, 93.2 mmol) in tolu-
ene (60 mL). Paraformaldehyde powder (3.63 g, 121 mmol) was
then added in small portions. Bubbling of gaseous HCl was main-
tained for 1 h at room temperature. The solution was further stirred
for 1 h while a second phase appeared in the flask. The organic
phase was washed three times with cold water (10 mL) and then
dried with K2CO3. After removing the volatiles under vacuum, the
chlorinated intermediate was obtained (18.83 g, 92.4%). Without
further purification, it was treated in methanol (30 mL) with an
excess amount of sodium methoxide in methanol. The temperature
of the mixture was brought to 25 °C and then reflux was main-
tained for 3 h. After addition of distilled water (100 mL), the reac-
tion mixture was extracted with dichloromethane (3ϫ50 mL). The
organic layers were collected, dried with K2CO3, filtered and con-
centrated under vacuum to leave a yellow oily residue. Purification
of this residue by distillation under vacuum (4ϫ10–2 mbar, 60 °C)
yielded 1f (10.21 g, 52.4%) as a colourless viscous oil. 1H NMR
(300 MHz, CD2Cl2, 298 K): δ = 1.45 [s, 9 H, CC(CH3)3], 2.29 (s, 3
H, CH3), 3.47 (s, 3 H, O-CH3), 4.6 (s, 2 H, CH2OMe), 6.76 and
yield 2b (3.63 g, 86.8 %) as white crystals. 1H NMR (300 MHz,
CD2Cl2, 298 K): δ = 1.1 [d, 18 H, OCH(CH3)2], 1.31 [s, 9 H,
C(CH3)3], 1.61 [s, 6 H, CC(CH3)2C], 2.2 (s, 3 H, CH3), 4.35 [m, 3
H, OCH(CH3)2], 6.9 (2 d, 2 H, 2CH ArO), 7.0 (m, 1 H, p-H, Ph),
7.1 (m, 4 H, m- and o-H, Ph) ppm. 13C{1H} NMR (75 MHz,
CD2Cl2, 298 K): δ = 20.2 (s, CH3), 25.3 [s, OCH(CH3)2], 29.8 and
30.4 [s, C(CH3)3, CC(CH3)2C], 33.8 [s, C(CH3)3], 42.0 [s,
C(CH3)2], 77.2 [s, OCH(CH3)2], 124.2, 124.8, 125.3, 125.4, 126.5,
126.9, 136.9, 138.2, 149.7 (10 C, Ph), 160.7 (s, CO). C29H46O4Ti
(506.54): calcd. C 68.76, H 9.15, Ti 9.45; found C 68.93, H 9.42,
Ti 9.69.
[Ti{2-tert-Butyl-4-methyl-6-(N,N-dimethylaminomethyl)phenoxy}-
(OiPr)3] (2c)
Path A: To a cold solution of [Ti(OiPr)4] (0.73 mL, 0.71 g,
2.5 mmol) in Et2O (5 mL) was added a solution of 1c (0.55 g,
2.5 mmol) in Et2O (10 mL). The reaction mixture immediately
turned yellow. After warming the solution to room temperature,
the reaction mixture was vigorously stirred overnight. The volatiles
were then removed under vacuum, yielding 2c (1.02 g, 92%) as a
yellow oil. Attempts to obtain a crystalline compound were unsuc-
cessful. 1H NMR (300 MHz, CD2Cl2, 298 K): δ = 1.27 [d, 18 H,
OCH(CH3)2], 1.44 [s, 9 H, C(CH3)3], 2.24 (s, 3 H, CH3), 2.35 [s, 6
H, N(CH3)2], 3.7 (br. s, 2 H, ArCH2N), 4.9 [m, 3 H, OCH(CH3)2],
4
6.09 (2 d, JH,H = 2 Hz, 2 H, Ar-H), 7.65 (s, 1 H, OH) ppm.
13C{1H} NMR (75 MHz, CD2Cl2, 298 K): δ = 20.8 (s, CH3), 29.8
[s, CC(CH3)3], 34.9 [s, CC(CH3)3], 58.3 (s, OCH3), 75.0 (s,
OCH2Ar), 122.7 (s, CH, Ph), 127.0 (s, CH, Ph), 127.9 (s, CH, Ph),
128.4–136.9 (s, Ph-C), 153.4 (s, C-OH, Ph) ppm. C13H20O2
(208,30): calcd. C 74.96, H 9.68, O 15.36; found C 74.87, H 9.42,
O 15.69.
4
6.67–6.95 (2 d, JH,H = 2 Hz, CH) ppm. 13C{1H} NMR (75 MHz,
CD2Cl2, 298 K): δ = 20.3 (s, CH3), 26.3 [s, OCH(CH3)2], 29.2 [s,
C(CH3 )3 ], 34.4 [s, C(CH3 )3 ], 46.8 [s, N(CH3 )2 ], 62.5 [s,
ArCH2N(CH3)2], 77.0 [s, OCH(CH3)2], 124.9, 126.2, 126.3, 127.6,
135.9 (5 C), 158.3 (s, CO) ppm. C23H43N1O4Ti (445.46): calcd. C
62.01, H 9.73, N 3.14, Ti 10.75; found C 61.87, H 9.66, N 3.30, Ti
11.30.
[Ti(2,6-di-tert-Butyl-4-methylphenoxy)(OiPr)3] (2a): To a cold solu-
tion (–30 °C) of 2,6-bis(tert-butyl)-4-methylphenol (1.10 g,
5.0 mmol) in Et2O (15 mL) was added [Ti(OiPr)4] (1.5 mL, 1.45 g,
5.0 mmol) in Et2O (20 mL). The mixture turned yellow and was
then warmed to 20 °C and stirred overnight. The solvent was then
removed under vacuum, leading to an oily yellow residue (2.26 g,
99% crude yield). This residue was then crystallized from cold pen-
tane (5 mL, –78 °C), yielding 2a (1.77 g, 78%) as an off-white solid.
1H NMR (300 MHz, CD2Cl2, 298 K): δ = 1.28 [d, 18 H,
OCH(CH3)2], 1.49 [s, 9 H, C(CH3)3], 2.29 (s, 3 H, CH3), 4.67 [m,
3 H, OCH(CH3)2], 7.0 (s, 2 H, CH) ppm. 13C{1H} NMR (75 MHz,
CD2Cl2, 298 K): δ = 21.3 (s, CH3), 26.3 [s, OCH(CH3)2], 30.7 [s,
C(CH3)3], 34.8 [s, C(CH3)3], 78.2 [s, OCH(CH3)2], 125.3, 127.6,
138.8 and 162.2 (s, CO) ppm for the aromatics.
Path B: This complex was synthesized following the procedure de-
scribed for 2b. To a solution of 1c (1.1 g, 5.0 mmol) in thf (40 mL)
was added dropwise nBuLi (1.7  in pentane, 4 mL, 6.8 mmol). The
mixture was stirred for 12 h at room temperature. The volatiles
were then removed under reduced pressure, yielding a yellow oil
that was used without further purification. To this crude adduct of
ArOLi·thf was added [TiCl(OiPr)3] (1.3 g, 5.0 mmol) in thf
(10 mL). The resulting yellow slurry was stirred overnight at room
temperature. After the volatiles were removed under reduced pres-
sure, the yellow residue was extracted with pentane (30 mL) and
dried under vacuum to yield the desired compound as a yellow
viscous oil (1.9 g, 85% yield). Characterization data are the same
as for 2c isolated from path A.
[Ti{2-tert-Butyl-4-methyl-6-(α,α-dimethylbenzyl)phenoxy}(OiPr)3]
(2b): A solution of nBuLi (1.7  in pentane, 7 mL, 12 mmol) was
added dropwise to a solution of 1b (2.9 g, 10 mmol) in thf (40 mL).
After the mixture was stirred overnight, a white precipitate was
formed. The volatiles were then removed under reduced pressure,
and the residue was washed twice with pentane (20 mL). After dry-
ing under vacuum, the phenoxide derived from 1b was obtained as
a white solid (3.43 g, 92%). 1H NMR (300 MHz, CD2Cl2): δ = 1.03
[s, 9 H, C(CH3)3], 1.71 [s, 6 H, CC(CH3)2C], 1.85 [m, 4 H,
O(CH2CH2)2, thf], 2.28 (s, 3 H, CH3), 3.71 [m, 4 H, O(CH2CH2)2,
[Ti{2-tert-Butyl-4-methyl-6-(N,N-benzylmethylaminomethyl)phen-
oxy}(OiPr)3] (2d): To a cold solution of [Ti(OiPr)4] (1.0 mL,
3.4 mmol) in Et2O (5 mL, –30 °C) was added ligand 1d (0.51 g,
1.72 mmol) in Et2O (10 mL). The mixture instantly turned yellow
and was then warmed to 20 °C and stirred for 1 h. The volatiles
were removed under vacuum at 40 °C. The resulting yellow oil was
a mixture of desired compound 2d with some residual phenol as
well as unreacted [Ti(OiPr)4]. 1H NMR (300 MHz, CD2Cl2,
298 K): δ = 1.30 [d, 18 H, OCH(CH3)2], 1.45 [s, 9 H, C(CH3)3],
2.22 (s, 3 H, CH3), 2.25 (s, 3 H, NCH3), 3.72 (s, 2 H, ArCH2N),
4.12 (s, 2 H, NCH2Ph), 4.93 [m, 3 H, OCH(CH3)2], 6.57–6.97 (2 d,
4JH,H = 2 Hz, CH), 7.20–7.34 (2 m, 5 H, CH2Ph) ppm. 13C{1H}
NMR (75 MHz, CD2Cl2, 298 K): δ = 20.3 (s, CH3), 26.3 [s,
OCH(CH3)2], 29.2 [s, C(CH3)3], 34.4 [s, C(CH3)3], 41.4 [s, N(CH3)],
56.9 (s, NCH2Ph), 58.4 [s, ArCH2N(CH3)benzyl], 77.2 [s,
OCH(CH3)2], 124.4, 126.2, 126.4, 127.3, 127.6, 128.1, 132.0, 133.5
and 136.1 (C, Ph), 158.6 (s, CO) ppm.
3
3
thf], 6.92–7.1 (2 d, JH,H = 2.3 Hz, 2 H, 2CH ArO), 7.2 (tt, JH,H
4
= 7.18 Hz, JH,H = 1.6 Hz, 1 H, Ph, p-H), 7.33 (m, 4 H, Ph, o-H
and m-H) ppm. 13C{1H} NMR (75 MHz, CD2Cl2): δ = 20.6 (CH3),
25.4 [O(CH2CH2)2, thf], 31.0 [s, C(CH3)3 and C(CH3)2], 33.0
[C(CH3)3], 42.0 [C(CH3)2], 67.5 [O(CH2CH2)2, thf], 125.1 and 125.4
(2 s, CH ArO), 126.4 (p-CH, Ph), 124.3 and 129.2 (m- and o-CH,
Ph), 120.6, 136.3, 137.8, 153.4, 159.6 (5 C, Ph) ppm. To a suspen-
sion of the metallated form of 1b (3.43 g, 9.51 mmol) in thf (25 mL)
was added [TiCl(OiPr)3] (2.4 g, 9.2 mmol) in thf (15 mL). The mix-
ture was stirred overnight and the volatiles were removed under
vacuum. The residue was crystallized from n-pentane at 25 °C to
[Ti{2-tert-Butyl-4-methyl-6-(N,N-dibenzylaminomethyl)phen-
oxy}(OiPr)3] (2e): To a cold solution of [Ti(OiPr)4] (1.0 mL,
2948
www.eurjic.org
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 2942–2950

Mono(aryloxido)TiIV Complexes for Selective Dimerization of Ethylene
3.4 mmol) in Et2O (5 mL, –30 °C) was added ligand 1e (0.51 g,
1.72 mmol) in Et2O (10 mL). The mixture instantly turned yellow
and was then warmed to 20 °C and stirred for 1 h. The volatiles
were removed under vacuum at 40 °C. The resulting yellow oil was
a mixture of desired compound 2e with some residual phenol as
well as unreacted [Ti(OiPr)4].
Table 6. Crystallographic data and structure refinement details for
2b and 3.
2b
3
Formula
C29H46O4Ti
506.56
C28H51Cl2O7Ti2
666.39
monoclinic
Cc
13.7950(3)
17.2200(5)
15.6480(4)
90
108.27
90
3529.88(16)
4
1.254
Formula weight
Crystal system
Space group
a [Å]
b [Å]
c [Å]
triclinic
[(2-tert-Butyl-4-methyl-6-methoxymethylphenoxy)TiCl(OiPr)(µ2-
OiPr)2TiCl(OiPr)2] (3): To a stirred solution of ligand 1f (1.34 g,
6.43 mmol) in thf (30 mL) was added solid Na (0.50 g, 21.7 mmol).
The reaction mixture was heated at reflux for 2 h. Trimethylsilyl
chloride (2.5 mL, 2.17 g, 20 mmol) was then poured into this solu-
tion, and the mixture was heated at reflux for 2 d. After cooling to
room temperature, the volatiles were removed, and the residue was
extracted with pentane (10 mL) and dichloromethane (10 mL). The
organics were collected and concentrated, and the silyl ether de-
rived from 1f was obtained as a yellow viscous oil (1.70 g, 94.2%).
1H NMR (300 MHz, CD2Cl2, 298 K): δ = 0.37 [s, 9 H, Si(CH3)3],
1.4 [s, 9 H, C(CH3)3], 2.29 (s, 3 H, CH3), 3.4 (s, 3 H, OCH3), 4.4
¯
P1
9.8570(4)
10.6790(5)
14.5330(7)
86.633(3)
86.380(3)
73.882(2)
1465.37(12)
2
α [°]
β [°]
γ [°]
V [Å3]
Z
ρcalcd. [gcm–3]
µ (Mo-Kα) [mm–1]
F(000)
1.148
0.321
548
0.641
1412
Temperature [K]
θmin–max
Dataset [h, k, l]
173(2)
2.77–30.06
–13/12
173(2)
2.94–30.04
19/19
4
(s, 2 H, ArCH2OCH3), 7.03–7.1 (2 d, JH,H = 2.3 Hz, CH) ppm.
The silyl ether derivative was then added to a thf solution (20 mL)
of [TiCl(OiPr)3] (1.57 g, 6.0 mmol). The solution instantly turned
red. It was then stirred overnight at room temperature, the solvent
was removed under vacuum, leaving a red oil from which a crystal-
line compound was obtained through crystallization from n-pen-
–15/15
–20/20
13051, 8544,
0.0271
–19/24
–22/22
8607, 8605,
0.0185
Total, unique data, R(int)
Observed data
N reflections, N param-
eters
R1, R(all)
wR2, wR(all)
GOF
5994
6524
1
tane at –18 °C (17% isolated yield). H NMR (300 MHz, CD2Cl2,
8544, 307
8605, 352
298 K): δ = 1.3–1.5 [m, 40 H, C(CH3)3 and 5 OCH(CH3)2], 2.30 (s,
2
3 H, CH3), 3.65 (s, 3 H, OCH3), 4.0 and 5.7 (2 d, JH,H = 12.7 Hz,
0.0586, 0.0917
0.1492, 0.1679
1.070
0.0540, 0.0794
0.1269, 0.1416
1.011
ArCH2OCH3, 0.63H each), 4.78, 5.09 and 5.25 [3 m, ratios 1:2:2,
OCH(CH3)2], 6.83 and 7.14 (2 d, CH) ppm. C28H54Cl2O7Ti2
(669.36): calcd. C 50.24, H 8.13; found C 50.44, H 8.09.
Max. and Av. shift/error 0.001, 0.000
0.016, 0.001
Min, max. resd dens.
–0.946, 1.008
[eÅ–3]
–0.352,0.477
X-ray Data Collection, Structure Solution and Refinement for Com-
pounds 2b and 3: Suitable crystals for X-ray analysis were obtained
as described above. Diffraction data were collected at 173(2) K with
a Kappa CCD diffractometer by using graphite-monochromated
Mo-Kα radiation (λ = 0.71073 Å). Data were collected by using φ Acknowledgments
scans, the structures were solved by direct methods by using the
SHELX97 software,[60,61] and the refinement was by full-matrix le-
ast-squares on F2. No absorption correction was used. All non-
hydrogen atoms were refined anisotropically, with H atoms intro-
duced as fixed contributors (dC–H = 0.95 Å, U11 = 0.04). Crystallo-
graphic and experimental details for the structures are summarized
in Table 6. CCDC-727372 (for 2b) and -727373 (for 3) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
We are grateful to the Association Nationale de la Recherche et de
la Technologie (ANRT), the IFP-Lyon, the Centre National de la
Recherche Scientifique (CNRS) and the Ministère de la Recherche
(Paris) for financial support. We also thank Prof. R. Welter (Uni-
versity of Strasbourg) for the crystal structure determinations.
[1] D. Vogt, “Oligomerization of Ethylene to Higher Linear Alpha
Olefins” in Applied Homogeneous catalysis with Organometallic
Compounds (Eds.: B. Cornils, W. A. Hermann), 1st ed., Wiley-
VCH, Weinheim, Germany, 2002, p. 245.
Oligomerization Studies: All catalytic reactions were carried out in
a magnetically stirred (≈1000 rpm) 120-mL stainless steel autoclave.
The evacuated reactor was charged with 1 atm ethylene and heated
to the reaction temperature. The cocatalyst was introduced before
adding the catalyst precursor. The reactor was then sealed and fed
with ethylene up to the desired pressure. During the catalysis, the
pressure was maintained constant through a continuous feed from
a bottle placed on a balance used to monitor the ethylene uptake.
At the end of the test, the catalyst was quenched in situ by addition
of water or methanol and the reactor rapidly cooled down to 25 °C.
The gaseous effluents were then collected in a 15 L polyethylene
bottle filled with water. The liquid effluents were collected, washed
with H2SO4 (10 vol.-%) and weighted. The polymer formed was
collected, washed with methanol, dried under vacuum and
weighed. Aliquots of gaseous and liquid effluents were then ana-
lyzed by gas chromatography. Catalytic runs were performed for
1 h at 60 °C, 20 bar ethylene in 5 mL heptane (unless otherwise
stated).
[2] J. T. Dixon, M. J. Green, F. M. Hess, D. H. Morgan, J. Or-
ganomet. Chem. 2004, 689, 3641.
[3] W. K. Reagen, B. K. Conroy, Patent US 5,198,563, 1993.
[4] F. J. Wu, Patent EP0537609B1, 1996.
[5] R. Köhn, M. Haufe, G. Kociok-Koehn, S. Grimm, P. Wasser-
scheid, W. Keim, Angew. Chem. Int. Ed. 2000, 39, 4337.
[6] T. Yoshida, T. Yamamoto, H. Okada, H. Murakita, Patent US
20020035029A1, 2002.
[7] F. J. Wu, Patent US 5,811,618, Aug 25, 1995.
[8] A. Carter, S. A. Cohen, N. A. Cooley, A. Murphy, J. Scutt,
D. F. Wass, Chem. Commun. 2002, 858.
[9] D. S. McGuinness, P. Wasserscheid, W. Keim, C. Hu, U. En-
glert, J. T. Dixon, J. J. C. Grove, Chem. Commun. 2003, 334.
[10] D. S. McGuinness, P. Wasserscheid, W. Keim, D. H. Morgan,
J. T. Dixon, A. Bollmann, H. Maumela, F. M. Hess, U. Englert,
J. Am. Chem. Soc. 2003, 125, 5272.
[11] K. Blann, A. Bollmann, J. T. Dixon, F. M. Hess, E. Killian, H.
Maumela, D. H. Morgan, A. Neveling, S. Otto, M. J. Overett,
Chem. Commun. 2005, 620.
Eur. J. Inorg. Chem. 2009, 2942–2950
© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2949

J.-B. Cazaux, P. Braunstein, L. Magna, L. Saussine, H. Olivier-Bourbigou
FULL PAPER
[12] W. J. Van Rensburg, J. J. C. Grove, J. P. Steynberg, K. B. Stark,
J. J. Huyser, P. J. Steynberg, Organometallics 2004, 23, 1207.
[13] T. Agapie, M. W. Day, L. W. Henling, J. A. Labinger, J. E.
Bercaw, Organometallics 2006, 25, 2733.
[14] K. Blann, A. Bollmann, J. T.Dixon, A. Neveling, D. H. Mor-
gan, H. Maumela, E. Killian, F. Hess, S. Otto, L. Pepler, H. A.
Mahomed, M. J. Overett, Patent WO 2004/056479 A1, 2004.
[15] A. Bollmann, K. Blann, J. T. Dixon, F. M. Hess, E. Killian, H.
Maumela, D. S. McGuinness, D. H. Morgan, A. Neveling, S.
Otto, M. Overett, A. M. Z. Slawin, P. Wasserscheid, S.
Kuhlmann, J. Am. Chem. Soc. 2004, 126, 14712.
[16] M. J. Overett, K. Blann, A. Bollmann, J. T. Dixon, D. Haas-
broek, E. Killian, H. Maumela, D. S. McGuinness, D. H. Mor-
gan, J. Am. Chem. Soc. 2005, 127, 10723.
[17] M. J. Overett, K. Blann, A. Bollmann, J. T. Dixon, F. Hess, E.
Killian, H. Maumela, D. H. Morgan, A. Neveling, S. Otto,
Chem. Commun. 2005, 622.
[18] A. Jabri, P. Crewdson, S. Gambarotta, I. Korobkov, R. Duch-
ateau, Organometallics 2006, 25, 715.
[19] S. Kuhlmann, J. T. Dixon, M. Haumann, D. H. Morgan, J. Of-
ili, O. Spuhl, N. Taccardi, P. Wasserscheid, Adv. Synth. Catal.
2006, 348, 1200.
[20] R. Walsh, D. H. Morgan, A. Bollmann, J. T. Dixon, Appl. Ca-
tal A 2006, 306, 184.
[40]
[41]
Y. Suzuki, H. Terao, T. Fujita, Bull. Chem. Soc. Jpn. 2003, 76,
1493.
S. Matsui, T. Fujita, Catal. Today 2001, 66, 63; R. Furayama,
J. Saito, S. Ishii, M. Mitani, S. Matsui, Y. Tohi, H. Makio, N.
Matsukawa, H. Tanaka, T. Fujita, J. Mol. Catal. A 2003, 200,
31; T. Matsugi, T. Fujita, Chem. Soc. Rev. 2008, 37, 1264.
J. Tian, G. W. Coates, Angew. Chem. Int. Ed. 2000, 39, 3626.
D. C. H. Oakes, B. S. Kimberley, V. C. Gibson, D. J. Jones,
A. J. P. White, D. J. Williams, Chem. Commun. 2004, 2174.
A. R. F. Cox, V. C. Gibson, E. L. Marshall, A. J. P. White, D.
Yeldon, Dalton Trans. 2006, 5014.
R. J. Long, V. C. Gibson, A. J. P. White, D. J. Williams, Inorg.
Chem. 2006, 45, 511.
L. Matilainen, M. Klinga, M. Leskela, J. Chem. Soc., Dalton
Trans. 1996, 219.
T. A. Manz, K. Phomphrai, G. Medvedev, B. B. Krishnamur-
thy, S. Sharma, J. Haq, K. A. Novstrup, K. T. Thomson, W. N.
Delgass, J. M. Caruthers, M. M. Abu-Omar, J. Am. Chem. Soc.
2007, 129, 3776–3777.
F.-W. Küpper, Appl. Catal A 2004, 264, 253.
T. Maki, Y. Araki, Y. Ishida, O. Onomura, Y. Matsumura, J.
Am. Chem. Soc. 2001, 123, 3371.
[42]
[43]
[44]
[45]
[46]
[47]
[48]
[49]
[21] S. Kuhlmann, K. Blann, A. Bollmann, J. T. Dixon, E. Killian,
M. C. Maumela, H. Maumela, D. H. Morgan, M. Pretorius,
N. Taccardi, P. Wasserscheid, J. Catal. 2007, 245, 279.
[22] R. L. J. Coetzer, D. H. Morgan, H. Maumela, J. Appl. Statis-
tics 2008, 35, 131.
[50]
S. Fokken, T. P. Spaniol, H. C. Kang, W. Massa, J. Okuda, Or-
ganometallics 1996, 15, 5069.
[51] D. R. Mulford, P. E. Fanwick, I. P. Rothwell, Polyhedron 2000,
19, 35.
[52] S. Groysman, E. Sergeeva, I. Goldberg, M. Kol, Inorg. Chem.
2005, 44, 8188.
[23] J. Skupiñska, Chem. Rev. 1991, 91, 613.
[24] S. M. Pillai, M. Ravindranathan, S. Sivaram, Chem. Rev. 1986,
[53] D. A. Pennington, W. Clegg, S. J. Coles, R. W. Harrington,
M. B. Hursthouse, D. L. Hughes, M. E. Light, M. Schormann,
M. Bochmann, S. J. Lancaster, Dalton Trans. 2005, 561.
[54] P. Braunstein, F. Naud, Angew. Chem. Int. Ed. 2001, 40, 680;
L. Annunziata, D. Pappalardo, C. Tedesco, C. Pellechia, Orga-
nometallics 2009, 28, 688–697.
[55] C. Floriani, F. Corazza, W. Lesueur, A. Chiesi-Villa, C. Guas-
tini, Angew. Chem. Int. Ed. Engl. 1989, 28, 66.
[56] The free energy of activation was calculated by using the Eyr-
86, 353.
[25] A. M. Al-Jarallah, J. A. Anabtawi, M. A. B. Siddiqui, A. M.
Aitani, A. W. Al-SaЈdoun, Catal. Today 1992, 14, 1; A. W. Al-
SaЈdoun, Appl. Catal. A 1993, 105, 1.
[26] N. Le Quan, D. Cruypelinck, D. Commereuc, Y. Chauvin, G.
Léger, Patent EP0135441B1, 1985;D. Commereuc, Y. Chauvin,
J. Gaillard, J. Léonard, J. Andrews, Hydrocarbon Processing
1984, 118.
[27] P. J. W. Deckers, B. Hessen, J. H. Teuben, Angew. Chem. Int.
Ed. 2001, 40, 2516.
[28] P. J. W. Deckers, B. Hessen, J. H. Teuben, Organometallics
2002, 21, 5122.
[29] B. Hessen, J. Mol. Catal. A 2004, 213, 129.
[30] A. N. J. Blok, P. H. M. Budzelaar, A. W. Gal, Organometallics
2003, 22, 2564.
[31] T. J. M. de Bruin, L. Magna, P. Raybaud, H. Toulhoat, Orga-
nometallics 2003, 22, 3404.
[32] S. Tobisch, T. Ziegler, J. Am. Chem. Soc. 2004, 126, 9059.
[33] S. Tobisch, T. Ziegler, Organometallics 2004, 23, 4077.
[34] J. Huang, T. Wu, Y. Qian, Chem. Commun. 2003, 2816.
[35] T. Wu, Y. Qian, J. Huang, J. Mol. Catal. A 2004, 214, 227.
[36] G. J. P. Britovsek, V. C. Gibson, D. F. Wass, Angew. Chem. Int.
Ed. 1999, 38, 428.
϶
ing equation, ∆Gc (J/mol) = RTc[22.96 + ln Tc/∆υ], where Tc
϶
is the coalescence temperature. ∆Gc was determined from the
coalescence of the methylene proton on the 2-position of the
1
phenol in the H NMR spectra (Tc = 273 K).
[57] A. Bre, Y. Chauvin, D. Commereuc, New J. Chem. 1986, 10, 34.
[58] H. Makio, T. Fujita, Macromol. Symp. 2004, 213, 221.
[59] Polymerization tests were performed in the same equipment as
the dimerization reaction: Ti precursor (0.15 mmol), heptane
or xylene (6–35 mL), 20 bar C2H4, 60 °C, 1000 rpm, 1 h. Acti-
vators used were MAO (9.2% in toluene, Al/Ti = 100–300),
Et3Al2Cl2 (Al/Ti = 15–36) and Et2AlCl (Al/Ti = 15). For each
preliminary test, more than 80% of polyethylene was produced.
Results are not presented in detail because of reaction condi-
tions not optimized for polymerization.
[60] Bruker-Nonius, Kappa CCD Reference Manual, Nonius BV,
The Netherlands, 1998.
[61] G. M. Sheldrick, SHELXL-97: Program for Crystal Structure
Refinement, University of Göttingen, Germany, 1997.
Received: April 3, 2009
[37] S. D. Ittel, L. K. Johnnson, M. Brookhart, Chem. Rev. 2000,
100, 1169.
[38] V. C. Gibson, S. K. Spitzmesser, Chem. Rev. 2003, 103, 283.
[39] D. C. Bradley, R. C. Mehrotra, I. P. Rothwell, A. Singh, Alkoxo
and Aryloxo Derivatives of Metals, Academic Press, London,
2001.
Published Online: June 2, 2009
2950
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© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2009, 2942–2950