Alkylmono(cyclopentadienyl)titanium complexes containing the 2,2′-methylenebis(6-tert-butyl-4-methylphenoxido) ligand - Studies on the nature of the catalytic species present in α-olefin polymerisation processes

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DOI: 10.1002/ejic.200600710

Alkylmono(cyclopentadienyl)titanium Complexes Containing the 2,2Ј-

Methylenebis(6-tert-butyl-4-methylphenoxido) Ligand – Studies on the Nature

of the Catalytic Species Present in α-Olefin Polymerisation Processes

Marta González-Maupoey,^[a]Tomás Cuenca,*^[a]Luis Manuel Frutos,^[b]Obis Castaño,^[b]

Eberhardt Herdtweck,^[c]and Bernhard Rieger^[d]

Keywords: Titanium / Chelates / Olefin polymerisation / Density functional calculations

The mono(alkyl)bis(phenoxido)titanium complexes [TiRЈ(η⁵-

C₅R₅)(η²-mbmp)] [R = H, RЈ = Me (4), CH₂Ph (5), Ph (6),

CH₂SiMe₃(7); R = Me, RЈ = Me (8), CH₂Ph (9), CH₂SiMe₃

= 2,2Ј-methylenebis(6-tert-butyl-4-methyl-

phenoxido)] have been prepared in good yields by reaction

of the appropriate alkylating reagent with the corresponding

-alkyltitanium derivatives with Lewis acids were examined.

B(C₆F₅)₃reacts with the neutral complexes [TiRЈ(η⁵-C₅R₅)(η²-

mbmp)] by abstraction of the alkyl group RЈ to give the

highly stable species [Ti(η⁵-C₅H₅)(η²-mbmp)][MeB(C₆F₅)₃]

(12), [Ti(η⁵-C₅H₅)(η²-mbmp)][(PhCH₂)B(C₆F₅)₃] (13), [Ti(η⁵-

C₅Me₅)(η²-mbmp)][MeB(C₆F₅)₃] (14) and [Ti(η⁵-C₅Me₅)(η²-

mbmp)][(PhCH₂)B(C₆F₅)₃] (15), which are inactive in propyl-

ene and styrene polymerisation. In contrast, the reaction be-

tween the neutral alkyl derivatives and [CPh₃][B(C₆F₅)₄] af-

(10); η²-mbmp

chlorido(cyclopentadienyl)bis(phenoxido)titanium

deriva-

tive. Compound 6 reacts in toluene with traces of water to

afford the µ-oxidotitanium complex {Ti(η⁵-C₅H₅)(η²-

mbmp)}₂(µ-O) (11). Compounds 8, 9 and 11 have been char- fords species that are active in α-olefin polymerisation. Treat-

acterised by single-crystal X-ray crystallography, and density

functional calculations have been performed in order to elu-

ment of the mono(chlorido) compound [TiCl(η⁵-C₅H₅)(η²-

mbmp)] with 1 equiv. of AlMe₃affords the methyl derivative

cidate the energetic and structural properties of these com- 4 as essentially the only reaction product. When an excess of

pounds. The activity of these complexes in the presence of

methylaluminoxane (MAO), B(C₆F₅)₃or [Ph₃C][B(C₆F₅)₄] as

co-catalysts in the polymerisation of propylene and styrene

has been studied. In an effort to model the nature of the cata-

lytic species generated from these precursors, the reactions

of the mono(cyclopentadienyl)bis(phenoxido)chlorido- and

AlMe₃is used, transmetallation reactions of the bis(phenox-

ido) ligand from titanium to aluminium are observed. Reac-

tions of the bis(phenol) mbmpH₂with AlMe₃or AlClMe₂

yield [AlMe(mbmp)]₂(16) and [AlCl(mbmp)]₂(17).

Germany, 2007)

rivatives of group 4 elements is very difficult as they are

sensitive to atmospheric moisture and to light. The reaction

of [MR_4–x(OAr)_x] complexes with the Lewis acid B(C₆F₅)₃

has been reported to give the zwitterionic species

[M(CH₂Ph)(OAr)₂][B(η⁶-C₆H₅CH₂)(C₆F₅)₃] for the benzyl

derivatives and a mixture of [Ti(C₆F₅)Me(OAr)₂] and

BMe(C₆F₅)₂for the methyl complexes.^[10]

In a previous paper we reported the synthesis and char-

acterisation of the mono(cyclopentadienyl)titanium com-

plexes [TiClCpЈ(η²-mbmp)] [CpЈ = η⁵-C₅H₅(1), η⁵-C₅Me₅

(2), η⁵-C₅H₄SiMe₂Cl (3)] containing the bis(phenoxido) bi-

dentate dianionic ligand 2,2Ј-methylenebis(6-tert-butyl-4-

methylphenoxido) (η²-mbmp). Density functional calcula-

tions developed for these complexes provide remarkable

conclusions about their structural behaviour, which were

subsequently confirmed by X-ray diffraction studies in the

solid state. After activation with MAO, these mono(cyclo-

pentadienyl)titanium derivatives are suitable catalysts for

olefin (propylene, styrene and isoprene) polymerisation.^[11]

To elucidate the influence of the co-catalyst used in these

studies on the activity of the catalyst, as well as on the poly-

Introduction

Alkoxido derivatives of transition metals are used as cat-

alysts in a wide range of homogeneous reactions, and early

transition metal elements are strongly stabilized in high oxi-

dation states by alkoxido (or phenoxido) ligands.^[1–3]Alkox-

idotitanium and -zirconium compounds combined with a

co-catalyst (MAO) are highly active catalysts in α-olefin

polymerisation.^[4–9]The synthesis of dialkyl(alkoxido) de-

[a] Departamento de Química Inorgánica, Universidad de Alcalá,

Campus Universitario,

28871 Alcalá de Henares, Spain

Fax: +34-91-885-4683

E-mail: tomas.cuenca@uah.es

[b] Departamento de Química Física, Universidad de Alcalá, Cam-

pus Universitario,

28871 Alcalá de Henares, Spain

[c] Anorganisch-chemisches Institut, Technische Universität

München,

Lichtenberstrasse 4, 85747 Garching bei München, Germany

[d] Abteilung Anorganische Chemie II, Universität Ulm,

Albert-Einstein-Allee 11, 89069 Ulm, Germany

Supporting information for this article is available on the

WWW under http://ww w .eurjic.org or from the author.

Eur. J. Inorg. Chem. 2007, 147–161

147

T. Cuenca et al.

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merisation mechanism, we have synthesised new alkyl-

mono(cyclopentadienyl)titanium systems containing the

mbmp ligand. Here we report the synthesis of [TiRЈ(η⁵-

C₅R₅)(η²-mbmp)] (R = H, Me; RЈ = Me, CH₂Ph, Ph,

CH₂SiMe₃) derivatives, their reactions with Lewis acids

{AlMe₃, B(C₆F₅)₃and [CPh₃][B(C₆F₅)₄]} as well as their

catalytic application in α-olefin polymerisation, in which

different co-catalysts and temperature conditions were em-

ployed. The synthesis of a dinuclear µ-oxidotitanium deriv-

ative [{Ti(η⁵-C₅H₅)(η²-mbmp)}₂(µ-O)] and dinuclear alu-

Scheme 2.

Compounds 4–10 are soluble in chlorinated solvents

minium compounds [AlX(mbmp)]₂(X = Cl, Me) with a µ- (chloroform and dichloromethane) and aromatic (benzene,

η¹,η²disposition of the mbmp ligand are also reported. The toluene) and aliphatic hydrocarbons (pentane and hexane),

X-ray molecular structures of [TiRЈ(η⁵-C₅Me₅)(η²-mbmp)] while complex 11 only presents low solubility in toluene

(RЈ = Me, CH₂Ph) and [{Ti(η⁵-C₅R₅)(η²-mbmp)}₂(µ-O)] and chlorinated solvents (chloroform and dichlorometh-

complexes were determined by diffraction methods and ane). They can be stored under an inert gas in solution for

density functional calculations performed for [TiRЈ(η⁵- months and are stable for some weeks in the solid state

C₅H₅)(η²-mbmp)] (RЈ = Me, CH₂Ph, Ph).

without decomposition. They were characterised by ele-

mental analysis and NMR spectroscopy. The elemental

analysis values found for 5 were inaccurate due to the pres-

ence of small amounts of impurities which could not be

removed, although this compound has been characterised

by spectroscopic methods. The analytical composition fits

the proposed formulation exactly. The molecular structures

of 8, 9 and 11 have been determined by X-ray diffraction.

The NMR spectra (C₆D₆and CDCl₃, room temperature)

of complexes 4–10 show patterns for the mbmp fragment

similar to those described for compounds containing the

same bis(phenoxido) ligand.^[11]The two CH₂protons ap-

pear in the ¹H NMR spectra as a pair of doublets; the value

of the chemical shift difference (∆δ, C₆D₆) between their

chemical shifts varies between 2.13 and 0.28 ppm. This dif-

ference seems to be due to changes in the configuration of

the metallacyclic ring in solution.^[11]Both equivalent tert-

butyl groups and the two methyl substituents on the phenyl

rings appear as singlets between δ = 1.49–1.20 and 2.18–

2.07 ppm in C₆D₆, respectively. The protons at the 3- and

5-positions on the phenyl ring give two doublets, corre-

Results and Discussion

Synthesis of Complexes

The reaction of the chlorido derivatives [TiCl(η⁵-

C₅R₅)(η²-mbmp)] [R = H (1), Me (2); η²-mbmp = 2,2Ј-

CH₂-bis(6-tBu-4-CH₃C₆H₂-1-O)],^[11]with 1.2 equiv. of MRЈ

(M = Li, RЈ = Me, CH₂Ph, Ph, CH₂SiMe₃; M = Mg, RЈ =

ClCH₂, ClCH₂Ph), in hexane at –78 °C, affords the alkyl-

mono(cyclopentadienyl) complexes [TiRЈ(η⁵-C₅R₅)(η²-

mbmp)] [R = H, RЈ = Me (4), CH₂Ph (5), Ph (6),

CH₂SiMe₃(7); R = Me, RЈ = Me (8), CH₂Ph (9),

CH₂SiMe₃(10)] containing a bidentate bis(phenoxido) li-

gand (Scheme 1). The compounds were isolated as yellow-

orange solids in 60–80% yield.

4

sponding to AAЈ spin systems, with a J_H,Hcoupling con-

stant of 1.83 Hz. Singlets are observed for the cyclopen-

tadienyl and the methylcyclopentadienyl ring protons in the

expected region of the spectra. For all of these compounds,

structural features similar to those determined by ¹H NMR

spectroscopy can be deduced from the ¹³C{¹H} NMR spec-

tra (C₆D₆, room temperature). These spectroscopic data are

1

consistent with C_s-symmetrical molecules. In the H NMR

spectra, the alkyl substituents at the titanium centre show

the expected behaviour for this kind of group in C_smole-

cules, namely one singlet for the methyl group, two singlets

that integrate for two and nine protons for the CH₂SiMe₃

substituent, one singlet and signals of aromatic protons for

the CH₂Ph group and resonances of aromatic protons for

the phenyl group, with the corresponding resonances in the

¹³C{¹H} NMR spectra.

Scheme 1.

When compound 6 reacts in toluene with traces of water

The ¹H NMR spectrum of 11 shows two doublets for the

at room temperature crystals of a dimetallic complex with methylene protons with a chemical shift difference between

an oxygen atom bridging two titanium atoms and identified them of 1.00 ppm (C₆D₆). The tert-butyl and methyl groups

as [{Ti(η⁵-C₅H₅)(η²-mbmp)}₂(µ-O)] (11) were obtained of each bis(phenoxido) ligand are not equivalent and ap-

(Scheme 2).

pear as two singlets. The protons in the 3- and 5-positions

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Alkylmono(cyclopentadienyl)titanium Complexes

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on the phenyl rings are also not equivalent and appear as to locate the minima involved in the related processes. All

four doublets. However, the molecule is symmetric as a re- the structures were optimised at this level of theory. To

sult of the presence of a C₂axis through the bridging oxy- study the character of the stationary points found, an

gen atom that runs perpendicular to the titanium–oxygen analysis of the approximate Hessian was made, which con-

bonds. As a consequence, each fragment of the phenoxido firmed all these points as minima on the PES. In our search,

ligand of one titanium centre is equivalent to the opposite three different conformers (I, II, and III) were found (Fig-

fragment of the phenoxido ligand of the other titanium cen- ure 1).

tre, as shown in Scheme 2. The molecular structure deter-

The equilibrium Ti–O bond length, the relative electronic

mined by X-ray diffraction confirms this proposed arrange- energies and the relative population based on Boltzmann’s

ment, thus indicating that the solid-state structure is main- equilibrium distribution at 298 K of these three conformers

tained in solution.

for compounds 4–6 and previously reported 1^[11]are listed

1

The H NMR spectra of analytically pure samples of 4, in Table 1.

5 and 7 show only one pattern for the signals discussed.

For almost all of the complexes studied, the most stable

The study of the phenyl derivative 6 showed the presence conformer (I) has a geometry intermediate between a boat

of three different isomers (6a, 6b and 6c). Isomers 6a and and a chair conformation (intermediate between C and B

6b can be separated as pure samples by repeated recrystalli- in Scheme 3, although slightly closer to the boat than to the

sation from toluene because of their different solubility. A chair), with the Cp ligand close to the methylene bridge

solution of 6b in deuterated benzene evolves to a 1:1 molar between the phenyl groups and short Ti–O bond lengths

ratio mixture of 6b and 6c at room temperature in 3 h, while (1.78–1.807 Å).

a solution of 6a under the same conditions remains unal-

The second calculated conformer (II in Figure 1, corre-

tered for a long time. The formation of a single compound sponding to a disposition similar to A in Scheme 3 but in-

was observed spectroscopically for the pentamethylcyclo- termediate between A and D) has a similar arrangement to

1

pentadienyl derivatives 8 and 9, while the H NMR spec- conformer I, with the Cp and alkyl ligands interchanged.

trum of 10 shows two sets of signals, thus indicating that The Ti–O bond lengths are analogous (1.79–1.803 Å) to

this complex is obtained in solution as a mixture of two those found for conformer I. These calculations suggest a

isomers (10a/10b) in a 10:1 molar ratio. Theoretical studies clear degree of multiple bonding in the Ti–O link close to

(see below) permitted us to understand this behaviour.

sp hybridisation for both conformers. For complex 6, we

can see how the high planarity of the C–O–Ti–O–C frag-

ment makes isomers I and II very close in energy.

The third conformer (III in Figure 1, corresponding to a

disposition close to D in Scheme 3) exhibits different behav-

iour to I and II as a result of its geometrical structure. It

presents a closer sp²oxygen angle and a larger Ti–O bond

length (1.81–1.814 Å).

As a result of the calculations, two boat conformers (I

and II) related through a ring-inversion process could be

expected. Conformer III, in which the oxygen atoms move

toward sp²hybridisation, is the most unstable due to Ti–O

bond weakening, which raises the energy by around

13 kcalmol^–1with respect to the most stable conformer for

compounds 1 and 4. The stability of each conformer is re-

flected in the Ti–O bond order in such a way that the

shorter the bond the greater the stability. The preference to

adopt conformation I or II depends on the steric impedi-

ment exerted by the cyclopentadienyl ring and the alkyl

substituent at the titanium centre.

Study of the Molecular Structure – Theoretical and

Conformational Studies and Crystal Structure of [TiMe(η⁵-

C₅Me₅)(η²-mbmp)] (8), [Ti(CH₂Ph)(η⁵-C₅Me₅)(η²-mbmp)]

(9) and [{Ti(η⁵-C₅H₅)(η²-mbmp)}₂(µ-O)] (11)

For the [TiRЈCp(η²-mbmp)] type of compounds the exis-

tence of four possible conformers related by two different

conformational change processes, i.e., by ring inversion and

boat/chair interconversion (Scheme 3) can be proposed.^[11]

As shown in Table 1, I is the most stable conformer for

compounds 1, 4 and 6, in which the Cp ligand is located

towards the methylene bridge. A small difference in stability

between I and II is predicted for compound 6, while for

compounds 1 and 4 higher differences in the related ener-

gies are deduced; only for complex 5 is conformation II

more stable than I due to the high steric hindrance pro-

duced between the tBu groups of the bis(phenoxido) ligand

Scheme 3.

The HF method with B3LYP hybrid exchange-corre- and the ring of the benzyl substituent. The high relative

lation energy functional^[12]implemented in the Gaussian energies of conformations I and III for complex 5 are com-

suite of programs^[13]using a 3-21g* basis set was employed parable as a result of this steric hindrance, which in III is

in order to explore the potential energy surface (PES) and due to the steric hindrance between the cyclopentadienyl

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Figure 1. Optimised structures for [TiRЈCp(η²-mbmp)] [RЈ = Me (4), CH₂Ph (5), Ph (6)] complexes.

Table 1. Ti–O distances, energetics and Boltzmann populations for the calculated isomers.

Ti–O distance [Å]

Relative energy^[a][kcalmol^–1]

Boltzmann equilibrium population^[b]

1

4

5

6

1

4

5

6

1

4

5

6

I

1.78

1.79

1.81

1.797

1.801

1.814

1.807

1.801

1.813

1.799

1.803

–

0.0

2.5

12.1

0.0

4.30

13.68

5.02

0.0

6.06

0.0

0.86

–

98.5

1.5

0.0

99.9

0.1

0.0

ca. 0.0

Ͻ99.9

0.0

81.3

18.7

–

II

III

[a] Energy relative to the most stable conformer. [b] Percent populations of the different conformers at 298 K following a distribution of

the energies according to Boltzman’s distribution law.

ligand and the tBu groups. These theoretical results are in the conformation found in the X-ray structures elucidated

agreement with the NMR experimental data. Although for this type of complex (see below and ref.^[11]), a ∆δ_CH

2

complexes 1, 4 and 5 could exist in three different confor- value of around or below 1.00 ppm points to a boat confor-

mations, the high stability of disposition I for 1 and 4 (or mation. In this sense, conformations I and II would corre-

II for 5) is enough to make these the only preferred confor- spond to isomers 6a and 6b. The third pattern (6c) could

mations, which leads to the formation of one unique isomer, correspond to conformer III, which, although it is not

as observed spectroscopically.

found by the theoretical calculations, is experimentally

For complex 6, the theoretical studies predict the pos- plausible and would explain why a pure solution of 6b in-

sibility of two boat conformations (I and II) with similar terconverts at room temperature to an equimolecular mix-

energies and therefore both species can coexist in solution ture of 6b and 6c.

at room temperature. These theoretical studies explain the

To establish and to confirm the structural details of the

presence of two of the three patterns of signals found in the molecular geometry in the solid state for this type of com-

NMR spectra. In contrast, the value of the chemical shift pound, X-ray crystal structure analyses of 8, 9 and 11 were

difference for the two methylene protons of the bis(phenox- carried out. Single crystals of 8 obtained by slow recrystalli-

ido) ligand in the ¹H NMR spectrum is initially an excellent sation from hexane solution were of good enough quality

probe for the detection of the metallacycle conformation.^[11]to be analysed by X-ray diffraction. The crystal structure

Taking into account the relationship between this value and of 8 is shown in Figure 2. Crystals of 9 were also obtained

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Alkylmono(cyclopentadienyl)titanium Complexes

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Figure 2. ORTEP plot of compound 8 in the solid state. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms are

omitted for clarity.

Figure 3. ORTEP plot of compound 9 in the solid state. The major part (82.1%) of the disordered Cp ligand is shown. Thermal ellipsoids

are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity.

from hexane solution at –20 °C but were not good enough

The mbmp ligand adopts a puckered chelate disposition

for X-ray crystallography. However, it was possible to deter- with the typical boat conformation in the solid state with

mine its molecular structure, which is depicted in Figure 3. the methylene bridge pointing toward the cyclopentadienyl

Table 2 summarises selected bond lengths and angles.

ring.^[9,14,15]The observed structural parameters correlate

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T. Cuenca et al.

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Table 2. Selected bond lengths [Å] and bond angles [°] for 8 and 9. tive 2,^[11]the presence of a less electronegative alkyl group

increases the electronic density at the metal centre, which

leads to longer average Ti–O bonds and a more open O1–

Ti–O2 angle.

8

9

Ti–O1

Ti–O2

Ti–C–C34

O1–C1

O2–C13

Ti–C24

Ti–C25

Ti–C26

Ti–C27

1.840(1)

1.834(1)

1.993(2)

1.364(2)

1.372(2)

2.370(2)

2.404(2)

2.436(2)

2.403(2)

2.373(2)

2.071

101.63(6)

101.39(6)

119.62

101.07(7)

119.37

1.828(2)

1.833(2)

2.154(2)

1.365(2)

1.362(3)

2.373(3)^[a]

2.430(3)^[a]

2.425(3)^[a]

2.364(3)^[a]

2.341(3)^[a]

2.064^[a]

102.96(7)

97.15(7)

120.45^[a]

105.37(8)

118.11^[a]

109.98^[a]

151.3(1)

148.0(1)

117.2(2)

The geometry adopted for these complexes is a compro-

mise situation where the least steric hindrance between the

pentamethylcyclopentadienyl ring and the methylene bridge

is produced and the methyl substituent is located far away

from the tert-butyl groups of the bis(phenoxido) ligand.

Crystals of compound 9 diffracted poorly, as indicated

by the weak diffraction patterns, the high thermal param-

eters and the high R values. The pentamethylcyclopen-

tadienyl ring is disordered but the refinement shows un-

doubtedly that complex 9 is present as described. As can be

seen in Figure 3, complex 9 presents a boat conformation

with the methylene bridge pointing toward the pentameth-

ylcyclopentadienyl ring, in a similar manner to conforma-

tion I obtained in the theoretical study. This study for the

analogous benzylmono(cyclopentadienyl) complex 5 pre-

dicted a boat conformation of type II, with the benzyl sub-

stituent far away from the tert-butyl groups of the bis-

(phenoxido) ligand. Nevertheless, the difference in steric re-

laxation between the benzyl group and the pentamethylcy-

clopentadienyl ring near the tert-butyl groups should not

be significant for compound 9, which prefers to adopt the

most stable type-I conformation, which is the preferred con-

formation for the chlorido-, methyl- and phenyl(cyclopen-

tadienyl) derivatives deduced from the theoretical study.

The structure of compound 11 was confirmed by X-ray

diffraction analysis. A view of the molecular structure is

given in Figure 4 and selected bond lengths and angles are

listed in Table 3.

Ti–C28

Ti···Cg^[b]

O1–Ti–O2

O1–Ti–C/C34

O1–Ti···Cg^[b]

O2–Ti–C/C34

O2–Ti···Cg^[b]

C–C34–Ti···Cg^[b]

Ti–O1–C1

Ti–O2–C13

C2–C12–C14

110.84

148.9(1)

149.1(1)

113.2(1)

[a] Distances and angles to the major part (82.1%) of the disor-

dered Cp ligand. [b] Cg denotes the cyclopentadienyl ring centroid.

well with those calculated for the most stable conformer

determined by density functional calculations. This con-

firms that the preferred structure for these complexes in the

solid state is the boat conformation, in agreement with the

theoretical results, from which a similar boat conformation

is predicted for the analogous complexes bearing an η⁵-

C₅H₅ligand.

The coordination geometry around the titanium atom is

a pseudo-three-legged piano stool, as expected for com-

plexes of the type TiCpL₃.^[16]The metal–oxygen bond

lengths in 8 (av. 1.8367 Å) and 9 (av. 1.8300 Å) are in the

expected range for titanium complexes with a linked bi-

The coordination sphere around the metal centre is a

four-legged piano stool. The bite angles of the bis(phenox-

s(phenoxido) ligand with (σ + π) donor oxygen atoms.^[3,17]ido) ligands [O(1)–Ti(1)–O(2) = 103.23(6)° and O(3)–Ti(2)–

Compared with the related structure of the chlorido deriva- O(4) = 103.97(6)°] are larger than 90° and in the same range

Figure 4. ORTEP plot of compound 11 in the solid state. Thermal ellipsoids are drawn at the 40% probability level. Hydrogen atoms

are omitted for clarity.

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Alkylmono(cyclopentadienyl)titanium Complexes

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Table 3. Selected bond lengths [Å] and bond angles [°] for oxygen atoms to the metal centre.^[20]Finally, the angle at

11·0.75C₆H₁₄.

the oxygen bridge atom is crystallographically restricted to

174.30(8)° and the metal–bridging oxygen bond lengths of

1.826(1) and 1.816(1) Å are typical for bridged titanium ox-

ides.^[22]

Bond lengths [Å]

Bond angles [°]

Ti1–O1

Ti1–O2

Ti2–O3

Ti2–O4

Ti1–O5

1.808(2)

1.843(2)

1.809(2)

1.857(2)

1.826(1)

1.816(1)

2.069

O1–Ti1–O2

103.23(6)

117.85

111.56

O1–Ti1···Cg1^[a]

O2–Ti1···Cg1^[a]

O5–Ti1···Cg1^[a]

O1–Ti1–O5

114.87

102.13(6)

105.80(6)

103.97(6)

116.88

111.83

114.12

102.13(6)

106.76(6)

174.30(8)

115.9(2)

115.5(2)

152.9(1)

134.5(1)

152.3(1)

132.0(1)

Olefin Polymerisation

Ti2–O5

O2–Ti1–O5

Ti1···Cg1^[a]

Ti2···Cg2^[a]

O1–C1

O3–Ti2–O4

2.066

O3–Ti2···Cg2^[a]

O4–Ti2···Cg2^[a]

O5–Ti2···Cg2^[a]

O3–Ti2–O5

Using MAO in excess or B(C₆F₅)₃or [CPh₃][B(C₆F₅)₄]

[1:1 molar ratio with respect to the precursor in the pres-

ence of triisobutylaluminium (TIBA) as scavenger] as co-

catalysts, complexes 4, 5, 8 and 9 were studied as α-olefin

polymerisation catalysts under various conditions.

1.367(3)

1.352(3)

1.363(2)

1.360(3)

O2–C13

O3–C24

O4–C36

O4–Ti2–O5

Ti1–O5–Ti2

C14–C12–C2

C25–C35–C37

Ti1–O1–C1

Propylene polymerisation was investigated by using

27 µmol of catalyst in 150 mL total volume of toluene

with

a 1000:1 Al(MAO)/Ti or 250:1:1 Al(TIBA)/Ti/

Ti1–O2–C13

Ti2–O3–C24

Ti2–O4–C36

[CPh₃][B(C₆F₅)₄] molar ratio at different temperatures and

monomer pressures (conditions and results are summarised

in Tables 4 and 5). Only traces of polymer or no polymeri-

sation was found when the reaction was carried out at 30 °C

with 5 atm of monomer and MAO as co-catalyst (runs 1,

[a] Cg denotes the cyclopentadienyl ring centroid.

as those obtained for complexes containing the mbmp li- 4, 7 and 10). However, polymer was found at 0 °C using

gand, such as [Ti(mbmp)₂] [106.24(7)° and 107.28(8)°],^[3]liquid propylene and MAO as co-catalyst for complexes 4

[TiCl₂(mbmp)] [106.5(2)°],^[18][TiMe₂(mbmp)] [112.7(2)°],^[18]and 5 (runs 2 and 5), while compounds 8 and 9 (runs 8 and

[Ti(mbmp)(BH₄)₂] [103.9(2)°],^[19]and the mono(cyclopenta- 11) showed poor activity. Decomposition of the catalyst

dienyl)bis(phenoxido)titanium complexes [CpTiX(OC₆H₃- system in the presence of the monomer at high tempera-

iPr₂)₂] [X = Cl, tBu and Me; 103.0(3)°, 107.7(9)° and tures could be a possible explanation for this behaviour.

109.0(5)°, respectively].^[20]The dihedral angles between The activity [7.4 kgPP(molTi)^–1h^–1] at 0 °C for the chlor-

both phenyl rings are 115.92(19)° and 115.52(18)°, more ido(cyclopentadienyl) system 1/MAO^[11]is markedly higher

open than those found for analogous ligands with different than that found for the corresponding alkyl derivatives 4

bridging units {S in tmbp and Te in tebp [tmbp = 2,2Ј- and 5. Polymerisation runs at 0 °C resulted in the formation

thiobis(6-tert-butyl-4-methylphenoxido), tebp = 2,2Ј-tellu- of PP with a molecular weight (M_w) of around 10⁵for the

robis(6-tert-butyl-4-methylphenoxido)]; [Ti(mbmp)(BH₄)₂] pentamethylcyclopentadienyl derivatives 8 and 9 (2.5–

=

64.1(2)°,^[19][TiCl₂(mbmp)(thf)]

=

113.4(3)°,^[21]5.6ϫ10⁵), one order of magnitude higher than the corre-

[TiCl₂(tmbp)]₂= 102.9(3)°,^[5][CpTiCl(tmbp)] = 107.3(1)°^[9]sponding non-substituted alkyl(cyclopentadienyl) deriva-

and [TiCl₂(tebp)]₂= 96.0(2)°}.^[15]

tives 4 and 5, probably due to the more electron-donating

The mbmp ligand adopts a typical boat conformation in capability of the η⁵-C₅Me₅ligand, which prevents β-elimi-

the solid state, with one of the methylene bridge protons nation processes.

pointing towards the metal centre and the other away from

When the salt [CPh₃][B(C₆F₅)₄] was used as co-catalyst,

it and with both in the proximity of the cyclopentadienyl complexes 4 and 5 exhibited analogous activity (runs 3 and

ring.^[9,15]The metal–oxygen bond lengths [Ti(1)–O(1) = 6), but the activity was greatly increased for compounds 8

1.808(2), Ti(1)–O(2) = 1.843(2), Ti(2)–O(3) = 1.809(2) and and

9

(runs

9

and 12), producing around 20–

Ti(2)–O(4) = 1.857(2) Å] are short but in the expected range 40 kgPP(molTi)^–1h^–1. A similar behaviour is observed with

for titanium complexes with a linked bis(phenoxido) ligand the molecular weight of the polymer synthesised, and the

with (σ + π) donor oxygen atoms, such as [Ti(mbmp)₂] [av. high value found with systems 8/[CPh₃][B(C₆F₅)₄] and 9/

1.802(6) Å],^[3][TiCl₂(mbmp)(thf)] [av. 1.791(2) Å],^[21][CPh₃][B(C₆F₅)₄] is worthy of mention, with each reaching

[TiCl₂(tmbp)]₂[av. 1.818(4) Å],^[5][TiCl₂(tebp)]₂[av. values of 2–3ϫ10⁶, with similar polydispersity values to

1.801(9) Å],^[15][CpTiCl(tmbp)] [av. 1.827(2) Å]^[9]and those reported in the literature.^[7,15,20,23]For these samples,

[Ti(CH₂Ph)₂{2,2Ј-(4-MeO-6-tBuC₆H₂O)₂}] [av. 1.810(7) values of T_g, T_mand ∆H similar to those found with the 1/

Å],^[7]and slightly larger than those found in analogous MAO system^[11]are observed.

compounds such as [TiCl₂(mbmp)] [av. 1.751(4) Å]^[18]and

The use of the borane salt produces a decrease in the

[TiBr₂(ebmp)] [ethylene-bridged analogue; av. 1.750(9) stereoselectivity of the process, as shown in Table 5 from an

Å].^[17]Similar results were found in titanium complexes analysis of the degree of isotacticity in the samples by ¹³C

with non-linked phenoxido ligands, such as [CpTiX- NMR spectroscopy. The activation of the precursors with

(OC₆H₃iPr₂)₂] [X = Cl, tBu, Me; av. 1.801(5), 1.79(2) and MAO at 0 °C gives isotactic PP with an isotacticity

1.817(9) Å, respectively], due to the presence of a cyclopen- (mmmm) of 24–30% (runs 2 and 5) for the cyclopentadienyl

tadienyl ligand, which decreases the π-donation from the complexes

4

and 5. However, activation with

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153

T. Cuenca et al.

FULL PAPER

Table 4. Polymerisation of propylene with [TiRЈ(η⁵-C₅R₅)(η²-mbmp)] compounds.

Run

Catalyst^[a]

Time

[min]

Yield

[mg]

Activity

10^–4M_w

M_w/M_n

T_g

[°C]

T_m

[°C]

∆H

[kgPP(molTi)^–1h^–1]

[Jg^–1]

1

2

3

4

5

6

7

8

9

4^[b]

4^[c]

4^[d]

5^[b]

5^[c]

5^[d]

8^[b]

8^[c]

8^[d]

9^[b]

9^[c]

9^[d]

120

traces

189

158

traces

256

298

79

63

2067

traces

141

–

3.5

3.0

–

4.7

5.5

1.5

1.2

38.1

–

3.8

–

1.86

–

–9.8

–

–9.0

–

101

–

80

–

5.2

–

5.4

–

2.7

53

25

56

217

–

1.78

3.54

3.57

2.42

47.5

–

10

11

12

2.6

21.5

25

301

1.86

37.0

–

1159

[a] 27 µmol of catalyst. [b] Propylene gas (5 atm), 30 °C, co-catalyst: MAO. [c] Propylene liquid (40 mL), 0 °C, co-catalyst: MAO. [d]

Propylene liquid (40 mL), 0 °C, co-catalyst: [CPh₃][B(C₆F₅)₄].

Table 5. Pentand distributions obtained for PP.

tem^[11]and resemble those reported by Ewen^[24]for PP ob-

tained with the achiral metallocene [TiCp₂Ph₂], which is

very unusual for monocyclopentadienyl compounds. This

analysis permits us to conclude that the polymer obtained

at low temperature with precursors 4 and 5 activated with

MAO contains large isotactic stereoblocks produced by a

chain-end control mechanism with a certain atactic charac-

ter due to 2,1-enchainments. Nevertheless, it is noteworthy

Run

Catalyst % mmmm^[a]Run Catalyst % mmmm^[a]

1

2

3

4

5

6

4

5

–

7

8

9

10

11

12

8

9

–

12.5

insoluble

–

17.9

insoluble

24.1

8.2

–

30.2

5.0

[a] From ¹³C NMR spectra.

that the activation of precursors

8

and

9

with

[CPh₃][B(C₆F₅)₄] co-catalyst produces atactic PP with a

high molecular weight of 10⁶.

[CPh₃][B(C₆F₅)₄] produces atactic PP (runs 3 and 6). The

pentamethylcyclopentadienyl complexes 8 and 9 activated

with either MAO or [CPh₃][B(C₆F₅)₄] afford atactic PP. The

high molecular weights of the samples obtained in runs 9

and 12 impeded the detection of their degree of isotacticity

due to their lack of solubility in the deuterated solvents

used for the spectroscopic analysis.

Styrene polymerisation was studied using 40 mL total

volume of reaction and 5 mL of monomer (conditions and

results are summarised in Table 6). When the precursors are

activated with MAO (runs 3, 7, 11 and 15), the activity of

the cyclopentadienyl complexes 4 and 5 is higher (7–

8ϫ10⁵) than the activity found for the pentamethylcyclo-

pentadienyl compounds 8 and 9 (2–3ϫ10⁵), in all cases

The results obtained at different temperatures and the

microstructures of the polymers synthesised with MAO as leading to syndiotactic PS (Ͼ95% syndiotacticity). In-

co-catalyst are similar to those found with the 1/MAO sys- creased activity can be achieved with donor substituents in

Table 6. Polymerisation of styrene with [TiRЈ(η⁵-C₅R₅)(η²-mbmp)] compounds.

Run

Catalyst

T

[°C]

Time

[min]

Al/Ti

Yield

[g]

Activity

Tacticity

10^–4M_w

M_w/M_n

[kgPS(molTi)^–1h^–1]

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

4^[a]

4^[b]

4^[d]

4^[e]

5^[a]

5^[b]

5^[d]

5^[e]

8^[a]

8^[b]

8^[f]

8^[e]

9^[a]

9^[b]

9^[f]

9^[e]

50

45

12

30

45

20

30

45

15

30

45

10

30

–

20

1000

–

2.82

0.02

3.36

–

3.28

0.03

4.58

–

3.37

0.15

2.00

–

2.77

0.05

2.57

–

190

1.6

840

–

220

2.3

700

–

220

9.5

160

–

180

3.0

308

–

atactic

syndiotactic

–

atactic

syndiotactic

–

atactic

syndiotactic

–

atactic

syndiotactic

–

0.4

1.89

[c]

3.2

–

2.19

–

0.4

1.95

[c]

20

1000

–

2.7

–

0.5

0.9

9.8

–

3.68

–

1.85

1.70

2.15

–

20

1000

–

0.6

1.91

[c]

20

1000

–

12.4

–

1.98

–

[a] 20 µmol of catalyst; co-catalyst: [CPh₃][B(C₆F₅)₄]. [b] 20 µmol of catalyst; co-catalyst: [CPh₃][B(C₆F₅)₄]/TIBA; Al/Ti molar ratio: 20:1.

[c] Not enough sample for analysis. [d] 20 µmol of catalyst; co-catalyst: MAO; Al/Ti molar ratio: 1000:1. [e] 20 µmol of catalyst; co-

catalyst: B(C₆F₅)₃. [f] 50 µmol of catalyst; co-catalyst: MAO; Al/Ti molar ratio: 1000:1.

154

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Alkylmono(cyclopentadienyl)titanium Complexes

FULL PAPER

the cyclopentadienyl ring, while the presence of bulky sub- ture, formation of the ionic species [Ti(η⁵-C₅H₅)(η²-

stituents results in a decrease in activity. The bulky substitu- mbmp)][MeB(C₆F₅)₃] (12) and

[Ti(η⁵-C₅H₅)(η²-

ents would inhibit 2,1-insertion through steric effects and mbmp)][(PhCH₂)B(C₆F₅)₃] (13; Scheme 4) was detected.

simultaneously inhibit the generation of the active species.

For the η⁵-C₅Me₅derivatives it was necessary to heat the

When [CPh₃][B(C₆F₅)₄] is used as co-catalyst (runs 1, 5, reaction mixtures at 100 °C for 24 h to complete the reac-

9 and 13) the activity is of the same order of magnitude as tion and to obtain the ionic compounds [Ti(η⁵-C₅Me₅)(η²-

that obtained with MAO as co-catalyst. However, and in mbmp)][MeB(C₆F₅)₃]

agreement with the results obtained in the propylene poly- mbmp)][(PhCH₂)B(C₆F₅)₃] (15; Scheme 4). However, the

merisation, activation with the borane salt affords atactic reaction of with an equimolecular amount of

(14)

and

[Ti(η⁵-C₅Me₅)(η²-

4

PS (Ͼ92% of atactic microstructure). The similarity in the [CPh₃][B(C₆F₅)₄] at room temperature in C₆D₆gave an in-

activity values found for the four alkyl complexes studied tractable mixture of unidentified products.

when the borane salt is used as co-catalyst is noteworthy

and shows that the nature of the cyclopentadienyl ring has

no influence on the activity. The addition of TIBA as scav-

enger in the precursor/[CPh₃][B(C₆F₅)₄] systems (runs 2, 6,

10 and 14) dramatically decreased the activity. No poly-

merisation was found for the precursor/[B(C₆F₅)₃] system

(runs 4, 8, 12 and 16). The molecular weight of the PS ob-

tained with the precursor/[CPh₃][B(C₆F₅)₄] systems is very

low but increases when MAO is used as co-catalyst, reach-

ing an order of magnitude of 10⁵with the pentamethylcy-

clopentadienyl compounds 8 and 9.

Complexes 12–15 are partially soluble in C₆D₆and are

stable in solution at room temperature over long periods of

1

time (days). The H NMR spectra (C₆D₆, 25 °C) show sig-

nals of equivalent tBu and Me groups and two resonances

for the phenyl protons of the bis(phenoxido) ligand, consis-

tent with a C_ssymmetry. The resonances of the cyclopen-

tadienyl protons are shifted to low field with respect to the

neutral precursors, as expected. The methyl group of the

[MeB(C₆F₅)₄]^–fragment gives signals at δ = 0.84 and

0.91 ppm for derivatives 12 and 14, respectively, suggesting

a certain interaction between the anionic and the cationic

centres.^[25–29]The signals of the methylene protons of the

benzylborate anion [(PhCH₂)B(C₆F₅)₄]^–appear at δ = 3.14

and 2.90 ppm for derivatives 13 and 15, respectively. It is

not easy to establish a limit to determine the coordination

or non-coordination of the anionic and cationic centres by

analysing the methylene benzylborate anion resonances.

Reaction with Lewis Acids

In order to gain a better knowledge of the nature of the

active species and the chemical behaviour of the mono(al-

kyl)bis(phenoxido) precatalyst systems in the α-olefin poly-

merisation processes, the reactions of the methyl and benzyl

derivatives 4, 5, 8 and 9 with Lewis acids such as B(C₆F₅)₃

and [CPh₃][B(C₆F₅)₄] were studied using a stoichiometric

1:1 Ti/B ratio and monitored by ¹H NMR spectroscopy.

Likewise, the reaction of the chloromono(cyclopentadienyl)

derivative 1 with trimethylaluminium was examined. All the

procedures were carried out in NMR tubes fitted with Tef-

lon valves to prevent water and oxygen entry and with C₆D₆

as reaction solvent at room temperature.

After addition of C₆D₆to a mixture of B(C₆F₅)₃and

the corresponding neutral derivative 4, 5, 8 or 9 at room

temperature in an NMR tube in a glovebox, the samples

were quickly introduced into the spectrometer and the spec-

tra recorded at 25 °C over a period of time. The reaction

produces an appreciable change in the solution’s colour

Generally, values of δ_{CH B}Ͻ 3.0 ppm seem to indicate the

2

existence of an anion–cation interaction for the [(PhCH₂)-

B(C₆F₅)₄]^–anion,^{[10,25,30,31]}although exceptions to this rule

have been found.^[8,32]The resonance of the C_ipsophenyl ring

of the benzylborate anion is a good probe to determine the

type of interaction with the metal centre. The ¹³C NMR

spectra (C₆D₆, 25 °C) for derivatives 13 and 15 show signals

at δ = 152.5 and 160.3 ppm assignable to the C_ipsophenyl

ring carbon atom. This indicates a certain degree of η⁶-

coordination of the phenyl ring of the benzylborate anion

to the cationic metal centre (δ = 148.6 ppm in the free

anion).^[33,34]The ¹⁹F NMR spectra of the cationic species

12–15 give ∆δ(p,m-F) values of 3.52, 3.40, 3.41 and

5.10 ppm, respectively, indicating the existence of interac-

tions between the ion pairs that are particularly strong for

from yellow for the methyl derivatives or orange for the the pentamethylcyclopentadienyl ionic species 15 with the

benzyl compounds to dark red. After 1 h at room tempera- benzylborate anion.^[25,35]

Scheme 4.

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155

T. Cuenca et al.

FULL PAPER

These results permit us to conclude that the Lewis acid possess one chlorido group at the metal centre, we were

B(C₆F₅)₃reacts with the neutral complexes [TiRЈ(η⁵- motivated to investigate the reactivity of compound 1 with

C₅R₅)(η²-mbmp)] by abstraction of the alkyl group RЈ to AlMe₃. Thus, a solution of the mono(chlorido) compound

give the highly stable cationic species [Ti(η⁵-C₅R₅)(η²- [Ti(η⁵-C₅H₅)(η²-mbmp)Cl] (1) was treated with 1 equiv. of

1

mbmp)]⁺, which retains the Ti–O bonds and the bidentate AlMe₃in toluene at –78 °C (Scheme 5). H NMR spectro-

bis(phenoxido) ligand bonded to the titanium centre. For- scopic analysis revealed complex 4 to be essentially the only

mation of such a stable species exhibiting strong interac- reaction product, thereby indicating alkylation of the Ti–Cl

tions with the anionic unit prevents coordination of the ole- bond and selective formation of the methyl derivative. The

fin and, as a consequence, these systems are inactive in pro- NMR spectra also show the presence of traces of signals

pylene and styrene polymerisation. With [CPh₃][B(C₆F₅)₄] assignable to secondary products containing the bi-

we could initially assume a similar reactivity. However, the s(phenoxido) ligand. The intensity of these signals increases

[B(C₆F₅)₄]^–unit is a less coordinating anion than [RB- when an excess of AlMe₃is used as reagent, along with

(C₆F₅)₄]^–to afford [Ti(η⁵-C₅R₅)(η²-mbmp)][B(C₆F₅)₄], the disappearance of the signals assignable to compound 4.

which is active in styrene polymerisation. In the absence of Transmetallation reactions of the bis(phenoxido) ligand

olefin, these [B(C₆F₅)₄]^–systems show a lack of stability, from titanium to aluminium could explain the formation of

with fast and immediate decomposition observed in solu- these secondary products.^[20,40]

tion.

In an attempt to identify the nature of these secondary

A new family of compounds containing only one metal– products, we performed the reaction of the bis(phenol)

alkyl bond that are active in olefin polymerisation has been mbmpH₂with AlMe₃or AlClMe₂in a 1:1 molar ratio in

reported recently. Mechanistic pathways to explain the ef- toluene at –78 °C. White solids were obtained in both cases,

ficient α-olefin polymerisation of these compounds acti- which were characterised by elemental analysis and NMR

vated with boron reagents have been proposed.^[36–39]In the spectroscopy as the compounds [AlMe(mbmp)]₂(16) and

absence of TIBA, the olefin polymerisation activity ob- [AlCl(mbmp)]₂(17; Scheme 6). The thf adduct monomer

served for complexes 4, 5, 8 and 9 with [CPh₃][B(C₆F₅)₄] as species [AlCl(mbmp)(thf)] obtained by reaction of mbmpH₂

co-catalyst can be explained by these mechanistic pathways. with AlClEt₂in thf has been described previously, although

Aluminium compounds are normally used as co-catalysts the dimeric species was not characterised.^[41]

(MAO) to generate the active species or as scavenger rea-

Complexes 16 and 17 are insoluble in aliphatic hydro-

gents (TIBA) during olefin polymerisation. The former oc- carbons (hexane, pentane), scarcely soluble in aromatic sol-

curs by replacement of the halo groups in the precursor vents and highly water-sensitive. They can be stored for

1

with alkyl groups and then abstraction of one of these alkyl months under an inert gas without decomposition. The H

groups to give cationic alkyl species, which are considered NMR spectra (C₆D₆and CDCl₃, 25 °C) show AB spin sys-

to be the active species in the process. As our neutral species tems for the methylene protons, indicating coordination of

with general formula [TiCl(η⁵-C₅R₅)(η²-mbmp)] [η⁵-C₅R₅the bis(phenoxido) ligand. The tert-butyl and methyl groups

= η⁵-C₅H₅(1), η⁵-C₅Me₅(2), η⁵-C₅H₄SiMe₂Cl (3)]^[11]only are not equivalent, with each appearing as two singlets. A

Scheme 5.

Scheme 6.

156

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Alkylmono(cyclopentadienyl)titanium Complexes

FULL PAPER

mina and molecular sieves (4 Å). Styrene was distilled at reduced

pressure from calcium hydride and stored in the refrigerator. Meth-

ylaluminoxane (MAO, 10% solution in toluene) was purchased

from WITCO GmbH. C, H and N microanalyses were performed

with a Perkin–Elmer 240B and/or Heraeus CHN-O-Rapid micro-

analyzer. Polymer melt endotherms were determined with a Perkin–

Elmer DSC-4 differential scanning calorimeter. NMR spectra,

measured at 25 °C, were recorded with Varian Unity FT-300 (¹H

NMR at 300 MHz, ¹³C NMR at 75 MHz) or Unity-Plus FT-500

(¹H NMR at 500 MHz, ¹³C NMR at 125 MHz) spectrometers, and

high-field-shifted signal assignable to equivalent Al–Me

groups is also observed for complex 16. The ¹³C{¹H} NMR

spectra show twelve signals for the phenyl rings and a pair

of signals for the tert-butyl and methyl groups. These spec-

troscopic data agree with the structure proposed in

Scheme 6.

Comparison of the spectroscopic data rules out the pres-

ence of complexes 16 and 17 in the final products obtained

in the reaction of 1 with AlMe₃, although transmetallation

reactions of the bis(phenoxido) ligand from titanium to alu- chemical shifts (δ, ppm) are referenced to SiMe₄relative to the

carbon resonances (¹³C) and the residual protons (¹H) of the sol-

minium could produce bis(phenoxido)aluminium deriva-

vent. ¹⁹F NMR spectra were recorded with a Varian Unity FT-500

tives of different composition.

The complexes [TiRЈ(η⁵-C₅R₅)(η²-mbmp)] have only one

and chemical shifts (δ, ppm) are referenced to CFCl₃.

[TiMe(η⁵-C₅H₅)(η²-mbmp)] (4): A 1.5  solution of LiMe in diethyl

ether (0.30 mL, 0.45 mmol) was added at –78 °C to a solution of 1

alkyl ligand coordinated to the metal centre. We therefore

assume that in these polymerisation reactions the alumin-

ium reagents (MAO used as co-catalyst or TIBA used as (0.22 g, 0.45 mmol) in hexane (50 mL). The reaction mixture was

slowly warmed to room temperature and stirred overnight. The sol-

vent was completely removed and after extraction with hexane and

concentration of the combined extracts, a bright yellow solid was

obtained which was recrystallised from cold hexane and character-

ised as 4 (0.16 g, 75% yield). C₂₉H₃₈O₂Ti (466.50): calcd. C 74.70,

H 8.16; found C 74.57, H 8.19. ¹H NMR (300 MHz, C₆D₆, 25 °C):

δ = 7.13, 7.00 (AAЈ spin system, 2ϫ2 H, Ph), 6.13 (s, 5 H, C₅H₅),

scavenger) react with these precursors through transmetal-

lation processes of the bis(phenoxido) ligand from titanium

to aluminium to generate active cationic alkyltitanium spe-

cies in a Ziegler–Natta-type olefin polymerisation.

Concluding Remarks

2

3.83, 3.43 (AB spin system, ∆δ = 0.40 ppm, J_H,H= 13.5 Hz, 2ϫ1

H, CH₂), 2.17 (s, 6 H, CH₃Ph), 1.38 [s, 18 H, C(CH₃)₃], 1.31 (s, 3

H, TiCH₃) ppm. ¹H NMR (300 MHz, CDCl₃, 25 °C): δ = 7.07,

6.89 (AAЈ spin system, 2ϫ2 H, Ph), 6.53 (s, 5 H, C₅H₅), 3.76, 3.40

(AB spin system, 2ϫ1 H, CH₂), 2.25 (s, 6 H, CH₃Ph), 1.28 [s, 18

H, C(CH₃)₃], 1.14 (s, 3 H, TiCH₃) ppm. ¹³C NMR (125 MHz,

C₆D₆, 25 °C): δ = 161.6, 137.3, 136.5, 130.2, 129.3, 126.2 (all Ph),

114.98 (C₅H₅), 52.8 (TiCH₃), 36.0 (CH₂), 35.5 [C(CH₃)₃], 30.9

[C(CH₃)₃], 21.4 (CH₃-Ph) ppm.

We have described the synthesis and characterisation of

mono(alkyl)mono(cyclopentadienyl)titanium

complexes

[TiRЈ(η⁵-C₅R₅)(η²-mbmp)] containing the bis(phenoxido)

bidentate dianionic ligand 2,2Ј-methylenebis(6-tert-butyl-4-

methylphenoxido) (η²-mbmp). The µ-oxido compound

[{Ti(η⁵-C₅H₅)(η²-mbmp)}₂(µ-O)] is also obtained by reac-

tion of [TiPh(η⁵-C₅H₅)(η²-mbmp)] with traces of water in

toluene. Density functional calculations for these complexes

have provided remarkable conclusions about their struc-

tural behaviour, which have been confirmed by X-ray dif-

fraction studies in the solid state. After activation with

MAO or [CPh₃][B(C₆F₅)₄], these alkylmono(cyclopentadi-

enyl)titanium derivatives are suitable for olefin (propylene

and styrene) polymerisation, while reaction with B-

(C₆F₅)₃produces inactive species. Polypropylene containing

large isotactic stereoblocks obtained by a chain-end control

mechanism is produced at low temperature. The nature of

the active species in the olefin polymerisation processes has

been examined spectroscopically.

[Ti(CH₂Ph)(η⁵-C₅H₅)(η²-mbmp)] (5): A 2.0  solution of MgClBz

in thf (0.30 mL, 0.62 mmol) was added at –78 °C to a solution of

1 (0.30 g, 0.62 mmol) in hexane (50 mL). The reaction mixture was

slowly warmed to room temperature and stirred overnight and the

solvent was then completely removed under vacuum. Recrystalli-

sation from hexane gave a light orange solid which was character-

ised as 5 (0.23 g, 70% yield). Correct elemental analysis data could

not be obtained, although satisfactory spectroscopic data were ob-

tained. ¹H NMR (300 MHz, C₆D₆, 25 °C): δ = 7.28 (m, 5 H,

CH₂Ph), 7.11, 7.01 (AAЈ spin system, 2ϫ2 H, Ph), 6.01 (s, 5 H,

C₅H₅), 3.84, 3.36 (AB spin system, ∆δ = 0.48 ppm, ²J_H,H= 13.7 Hz,

2ϫ1 H, CH₂), 3.24 (s, 2 H, TiCH₂Ph), 2.18 (s, 6 H, CH₃Ph), 1.47

1

[s, 18 H, C(CH₃)₃] ppm. H NMR (300 MHz, CDCl₃, 25 °C): δ =

7.07, 6.92 (AAЈ spin system, 2ϫ2 H, Ph), 7.30 (t, J_H,H= 8.0 Hz,

2 H, m-CH₂Ph), 7.17 (d, J_H,H= 7.9 Hz, 2 H, o-CH₂Ph), 7.01 (t,

J_H,H= 8.1 Hz, 1 H, p-CH₂Ph), 6.27 (s, 5 H, C₅H₅), 3.83, 3.38 (AB

spin system, 2ϫ1 H, CH₂), 2.99 (s, 2 H, TiCH₂Ph), 2.25 (s, 6 H,

CH₃Ph), 1.41 [s, 18 H, C(CH₃)₃] ppm. ¹³C NMR (125 MHz, C₆D₆,

25 °C): δ = 161.8, 137.1, 137.0, 130.0, 129.3, 126.4 (all Ph), 152.0

(ipso-CH₂Ph), 128.6 (p-CH₂Ph), 126.0 (m-CH₂Ph), 123.4 (o-

CH₂Ph), 117.0 (C₅H₅), 77.2 (TiCH₂Ph), 36.1 (CH₂), 35.4

[C(CH₃)₃], 30.8 [C(CH₃)₃], 21.0 (CH₃-Ph) ppm.

Experimental Section

General Considerations: All manipulations were performed under

argon using Schlenk and vacuum-line techniques or in a glovebox

(model HE-63). The solvents were purified by distillation under

argon before use in the presence of the appropriate drying/deoxy-

genating agent. Deuterated solvents were stored under an inert gas

over activated molecular sieves (4 Å) and degassed by several

freeze-pump-thaw cycles. LiMe, MgClBz, LiPh, mbmpH₂[2,2Ј-

CH₂-bis(6-tBu-4-CH₃C₆H₂-1-OH)], AlMe₃(2.0  hexane solu-

tion), AlClMe₂(1.0  hexane solution) were purchased (Aldrich)

[TiPh(η⁵-C₅H₅)(η²-mbmp)] (6a, 6b, 6c): A 1.8  solution of LiPh

in diethyl ether (0.35 mL, 0.62 mmol) was added at –78 °C to a

solution of 1 (0.30 g, 0.62 mmol) in hexane (50 mL). The reaction

mixture was slowly warmed to room temperature and stirred for

12 h. The resulting solution was concentrated under vacuum and a

brown oily solid was obtained; spectroscopic analysis revealed a

mixture of three isomers 6a, 6b and 6c. Two isomers were obtained

and used without further purification. Li₂mbmp,^[3][B(C₆F₅)₃],^[42]

[CPh₃][B(C₆F₅)₄]^[43]and LiCH₂SiMe₃

were prepared by known

[44]

procedures. Polymerisation-grade propylene from Aldrich was puri-

fied by passage through two columns packed with activated alu-

Eur. J. Inorg. Chem. 2007, 147–161

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157

T. Cuenca et al.

FULL PAPER

as analytically pure samples after repeated recrystallisation from

toluene. C₃₄H₄₀O₂Ti (528.56): calcd. C 77.29, H 7.58; found C

77.12, H 7.74. ¹H NMR (300 MHz, C₆D₆, 25 °C): 6a: δ = 7.08,

7.00 (AAЈ spin system, 2ϫ2 H, Ph), 7.45, 7.02 (d, J_H,H= 8.0 Hz,

and m, 2 H + 3 H, Ph), 6.26 (s, 5 H, C₅H₅), 4.51, 3.36 (AB spin

system, ∆δ = 1.15 ppm, J_H,H= 13.2 Hz, 2ϫ1 H, CH₂), 2.18 (s, 6

H, CH₃Ph), 1.43 [s, 18 H, C(CH₃)₃] ppm; 6b: δ = 7.19, 7.04 (AAЈ

spin system, 2ϫ2 H, Ph), 7.61, 6.92 (d, J_H,H= 8.0 Hz, and m, 2

1.00 mmol) in hexane (60 mL) at –78 °C. The reaction mixture was

slowly warmed to room temperature and stirred overnight. After

filtration, the solvent was completely removed from the resulting

orange solution. Recrystallisation from hexane gave a light orange

solid, which was again recrystallised from cold hexane and charac-

terised as 9 (0.39 g, 63% yield). C₄₀H₅₂O₂Ti (612.72): calcd. C

2

1

78.43, H 8.50; found C 78.31, H 8.77. H NMR (300 MHz, C₆D₆,

25 °C): δ = 7.02, 7.00 (AAЈ spin system, 2ϫ2 H, Ph), 7.00 (m, 5

2

H + 3 H, Ph), 6.42 (s, 5 H, C₅H₅), 3.95, 3.49 (AB spin system,

H, CH₂Ph), 3.75, 3.44 (AB spin system, ∆δ = 0.31 ppm, J_H,H

=

2

2ϫ1 H, ∆δ = 0.46 ppm, J_H,H= 13.7 Hz, CH₂), 2.18 (s, 6 H, 13.7 Hz, 2ϫ1 H, CH₂), 2.91 (s, 2 H, TiCH₂Ph), 2.17 (s, 6 H,

1

CH₃Ph), 1.20 [s, 18 H, C(CH₃)₃] ppm; 6c: δ = 7.06, 6.95 (AAЈ spin CH₃Ph), 1.89 (s, 15 H, C₅Me₅), 1.34 [s, 18 H, C(CH₃)₃] ppm. H

system, 2ϫ2 H, Ph), 7.35, 7.09 (d, J_H,H= 8.0 Hz, and m, 2 H + 3

H, Ph), 6.55 (s, 5 H, C₅H₅), 5.15, 3.02 (AB spin system, ∆δ =

2.13 ppm, J_H,H= 13.7 Hz, 2ϫ1 H, CH₂), 2.07 (s, 6 H, CH₃Ph),

NMR (300 MHz, CDCl₃, 25 °C): δ = 7.03–6.95 (m, 4 H and 5 H,

Ph and CH₂Ph), 3.64, 3.39 (AB spin system, 2ϫ1 H, CH₂), 2.77

(s, 2 H, TiCH₂Ph), 2.24 (s, 6 H, CH₃Ph), 1.97 (s, 15 H, C₅Me₅),

2

1.45 [s, 18 H, C(CH₃)₃] ppm. ¹³C NMR (125 MHz, C₆D₆, 25 °C): 1.24 [s, 18 H, C(CH₃)₃] ppm. ¹³C NMR (125 MHz, C₆D₆, 25 °C):

6a: δ = 162.6, 136.9, 136.7, 133.9, 128.9, 125.6 (all Ph), 129.2 (p- δ = 160.4, 137.1, 135.1, 129.5, 128.9, 126.6 (all Ph), 148.4 (ipso-

Ph), 129.0 (m-Ph), 127.4 (o-Ph), 115.6 (C₅H₅), 35.1 (CH₂), 35.2

CH₂Ph), 129.4 (p-CH₂Ph), 124.7 (m-CH₂Ph), 123.6 (o-CH₂Ph),

[C(CH₃)₃], 30.8 [C(CH₃)₃], 21.1 (CH₃-Ph) ppm; 6b, δ = 161.7, 127.8 (C₅Me₅), 76.7 (TiCH₂Ph), 35.4 (CH₂), 35.3 [C(CH₃)₃], 31.3

137.0, 135.6, 129.2, 128.0, 126.8 (all Ph), 134.8 (p-Ph), 130.3 (m- [C(CH₃)₃], 21.0 (CH₃-Ph), 12.0 (C₅Me₅) ppm.

Ph), 126.3 (o-Ph), 116.1 (C₅H₅), 35.4 (CH₂), 35.2 [C(CH₃)₃], 31.0

[Ti(CH₂SiMe₃)(η⁵-C₅Me₅)(η²-mbmp)] (10a, 10b): A red solution of

[C(CH₃)₃], 21.1 (CH₃-Ph ppm); 6c: δ = 161.7, 140.6, 134.8, 131.1,

2 (0.52 g, 0.93 mmol) in 50 mL of hexane was treated, at –78 °C,

126.4, 125.4 (all Ph), 134.3 (p-CH₂Ph), 129.7 (m-CH₂Ph), 127.6 (o-

with a solution of LiCH₂SiMe₃(0.09 g, 0.95 mmol) in 20 mL of

diethyl ether. The reaction mixture was warmed to room tempera-

ture, stirred for 12 h and the solvent was completely removed. After

CH₂Ph), 116.5 (C₅H₅), 35.2 (CH₂), 35.1 [C(CH₃)₃], 29.9 [C(CH₃)

₃], 21.0 (CH₃-Ph) ppm.

[Ti(CH₂SiMe₃)(η⁵-C₅H₅)(η²-mbmp)] (7):

A red solution of 1

extraction with hexane and concentration of the combined extracts,

an orange microcrystalline solid was obtained, which was recrystal-

lised from cold hexane and characterised as 10a (0.34 g, 60%) con-

taining a small amount of isomer 10b. C₃₇H₅₆O₂SiTi (608.81):

calcd. C 73.03, H 9.21; found C 72.91, H 9.16. ¹H NMR (300 MHz,

C₆D₆, 25 °C): 10a: δ = 7.11, 7.04 (AAЈ spin system, 2ϫ2 H, Ph),

(0.30 g, 0.62 mmol) in 40 mL of hexane was treated with a solution

of LiCH₂SiMe₃(0.06 g, 0.62 mmol) in diethyl ether (20 mL), at

–78 °C. The reaction mixture was slowly warmed to room tempera-

ture, stirred for 12 h and the solvent completely removed. After

extraction with hexane and concentration of the combined extracts,

an orange microcrystalline solid was obtained, which was recrystal-

lised from a cold mixture of toluene and hexane and characterised

as 7 (0.25 g, 73% yield). C₃₂H₄₆O₂SiTi (538.67): calcd. C 71.38, H

2

3.66, 3.38 (AB spin system, ∆δ = 0.28 ppm, J_H,H= 13.4 Hz, 2ϫ1

H, CH₂), 2.17 (s, 6 H, CH₃Ph), 1.93 (s, 15 H, C₅Me₅), 1.49 [s, 18

H, C(CH₃)₃], 1.16 (s, 2 H, TiCH₂SiMe₃), 0.18 (s, 9 H, TiCH₂SiMe₃)

ppm; 10b: δ = 7.04, 6.96 (AAЈ spin system, 2ϫ2 H, Ph), 4.08, 3.40

1

8.55; found C 71.23, H 8.34. H NMR (300 MHz, C₆D₆, 25 °C): δ

= 7.11, 6.98 (AAЈ spin system, 2ϫ2 H, Ph), 6.32 (s, 5 H, C₅H₅),

2

(AB spin system, ∆δ = 0.68 ppm, J_H,H= 13.4 Hz, 2ϫ1 H, CH₂),

2

4.02, 3.34 (AB spin system, ∆δ = 0.68 ppm, J_H,H= 13.5 Hz, 2ϫ1

2.11 (s, 6 H, CH₃Ph), 2.02 (s, 15 H, C₅Me₅), 1.47 (s, 2 H, TiCH₂S-

iMe₃), 1.44 [s, 18 H, C(CH₃)₃], –0.007 (s, 9 H, TiCH₂SiMe₃) ppm.

¹³C NMR (125 MHz, C₆D₆, 25 °C): 10a: δ = 160.8, 136.6, 134.8,

129.0, 128.3, 124.2 (all Ph), 126.6 (C₅Me₅), 67.9 (TiCH₂SiMe₃),

35.4 (CH₂), 35.7 [C(CH₃)₃], 32.3 [C(CH₃)₃], 21.1 (CH₃-Ph), 12.5

(C₅Me₅), 4.4 (TiCH₂SiMe₃) ppm. The small amount of 10b in the

sample did not allow its ¹³C NMR signals to be assigned accurately.

H, CH₂), 2.17 (s, 6 H, CH₃Ph), 1.80 (s, 2 H, TiCH₂SiMe₃), 1.38 [s,

18 H, C(CH₃)₃], 0.29 (s, 9 H, TiCH₂SiMe₃) ppm. ¹H NMR

(300 MHz, CDCl₃, 25 °C): δ = 7.04, 6.87 (AAЈ spin system, 2ϫ2

H, Ph), 6.57 (s, 5 H, C₅H₅), 3.98, 3.34 (AB spin system, 2ϫ1 H,

CH₂), 2.24 (s, 6 H, CH₃Ph), 1.58 (s, 2 H, TiCH₂SiMe₃), 1.29 [s, 18

H, C(CH₃)₃], 0.16 (s,

9

H, TiCH₂SiMe₃) ppm. ¹³C NMR

(125 MHz, C₆D₆, 25 °C): δ = 161.9, 136.9, 136.5, 129.8, 129.1,

125.8 (all Ph), 114.5 (C₅H₅), 72.5 (TiCH₂SiMe₃), 35.7 (CH₂), 35.3

[C(CH₃)₃], 30.7 [C(CH₃)₃], 21.0 (CH₃-Ph), 3.2 (TiCH₂SiMe₃) ppm.

[{Ti(η⁵-C₅H₅)(η²-mbmp)}₂(µ-O)] (11): Distilled water (6.8 µL,

0.38 mmol) was added at room temperature to a solution of 6

(0.20 g, 0.38 mmol) in toluene (20 mL). The solvent was completely

removed to give a red solid, which was recrystallised from diethyl

ether to afford 11 as a crystalline solid. C₅₆H₇₀O₅Ti₂(918.91):

calcd. C 73.22, H 7.67; found C 73.20, H 7.49. ¹H NMR (300 MHz,

C₆D₆, 25 °C): δ = 7.10, 7.02, 6.83 (two AAЈ spin systems, 1 H, 2ϫ1

H, 1 H, Ph), 6.56 (s, 10 H, C₅H₅), 4.24, 3.24 (AB spin system, ∆δ

[TiMe(η⁵-C₅Me₅)(η²-mbmp)] (8): A 1.5  solution of LiMe in di-

ethyl ether (0.36 mL, 0.54 mmol) was added to a solution of 2

(0.30 g, 0.54 mmol) in hexane (60 mL) at –78 °C. The reaction mix-

ture was slowly warmed to room temperature and stirred for 6 h.

After filtration, the resulting bright yellow solution was concen-

trated to dryness. A bright yellow solid was obtained, which was

recrystallised from cold hexane and characterised as 8 (0.22 g, 77%

yield). C₃₄H₄₈TiO₂(536.63): calcd. C 76.14, H 8.96; found C 76.07,

H 8.91. ¹H NMR (300 MHz, C₆D₆, 25 °C): δ = 7.13, 7.00 (AAЈ

spin system, 2ϫ2 H, Ph), 3.88, 3.47 (AB spin system, ∆δ =

2

= 1.00 ppm, J_H,H= 13.6 Hz, 2ϫ2 H, CH₂), 2.21, 2.18 (s, 2ϫ6 H,

CH₃Ph), 1.69, 0.94 [s, 2ϫ18 H, C(CH₃)₃] ppm. ¹³C NMR

(125 MHz, C₆D₆, 25 °C): δ = 164.1, 163.3, 136.9, 136.6, 136.4,

133.0, 130.6, 129.8, 128.9, 128.5, 125.7, 125.2 (all Ph), 116.4

(C₅H₅), 34.8 (CH₂), 35.3, 35.1 [2ϫC(CH₃)₃], 31.9, 30.0 [2ϫC-

(CH₃)₃], 21.1, 21.0 (2ϫCH₃-Ph) ppm.

2

0.41 ppm, J_H,H= 13.4 Hz, 2ϫ1 H, CH₂), 2.16 (s, 6 H, CH₃Ph),

1.92 (s, 15 H, C₅Me₅), 1.39 [s, 18 H, C(CH₃)₃], 1.10 (s, 3 H, TiCH₃)

ppm. ¹³C NMR (125 MHz, C₆D₆, 25 °C): δ = 160.1, 137.1, 134.9,

129.2, 128.7, 123.6 (all Ph), 126.2 (C₅Me₅), 54.8 (TiCH₃), 35.1

(CH₂), 35.0 [C(CH₃)₃], 30.8 [C(CH₃)₃], 21.0 (CH₃-Ph), 11.9

(C₅Me₅) ppm.

[Ti(η⁵-C₅H₅)(η²-mbmp)][MeB(C₆F₅)₃] (12): C₆D₆was added to a

mixture of

4 (0.018 g, 0.04 mmol) and B(C₆F₅)₃(0.019 g,

0.04 mmol) at room temperature in an NMR tube fitted with a

Teflon valve inside a glovebox. The NMR tube was quickly intro-

[Ti(CH₂Ph)(η⁵-C₅Me₅)(η²-mbmp)] (9): A 2.0  solution of MgClBz duced into the NMR equipment and the spectra were recorded at

in thf (0.50 mL, 1.00 mmol) was added to a solution of 2 (0.56 g, room temperature. The formation of 12 was deduced spectroscopi-

158

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Alkylmono(cyclopentadienyl)titanium Complexes

FULL PAPER

132.7, 130.6, 130.5, 127.8, 127.4, 127.1, 126.3 (all Ph), 35.0 (CH₂),

36.1, 34.5 [C(CH₃)₃], 31.8, 29.7 [C(CH₃)₃], 21.1, 21.0 (CH₃-Ph),

14.2 (AlCH₃) ppm.

1

cally. H NMR (300 MHz, C₆D₆, 25 °C): δ = 7.03, 6.94 (AAЈ spin

system, 2ϫ2 H, Ph), 6.33 (s, 5 H, C₅H₅), 4.05, 3,36 (AB spin sys-

tem, 2ϫ1 H, ∆δ = 0.69 ppm, CH₂), 2.12 (s, 6 H, CH₃Ph), 1.43 [s,

18 H, C(CH₃)₃], 0.84 (br. s, 3 H, BCH₃) ppm. ¹³C NMR (125 MHz,

C₆D₆, 25 °C): δ = 163.6, 137.4, 136.6, 131.2, 129.1, 126.2 (all Ph),

149.8, 147.8, 138.2, 136.5 (all C₆F₅), 118.2 (C₅H₅), 35.5 (CH₂), 35.4

[C(CH₃)₃], 31.2 [C(CH₃)₃], 21.1 (CH₃-Ph), 10.5 (BCH₃) ppm. ¹⁹F

NMR (300 MHz, C₆D₆, 25 °C): δ = –136.5, –160.0, –163.5 ppm.

[AlCl(mbmp)]₂(17): AlClMe₂(0.9 mL of a 1.0  solution in hexane,

0.88 mmol) was added to a solution of mbmpH₂(0.3 g, 0.88 mmol)

in 25 mL of toluene at room temperature. After a few minutes, a

white solid appeared and the reaction mixture was stirred for 3 h.

The solution was filtered and the white solid was washed twice with

hexane and toluene and characterised as 17 (0.37 g, 53% yield).

C₄₆H₆₀Al₂Cl₂O₄(801.85): calcd. C 68.90, H 7.54; found C 68.83,

H 7.49. ¹H NMR (300 MHz, C₆D₆, 25 °C): δ = 7.41, 7.18, 7.05,

6.88 (AAЈ spin systems, 4ϫ2 H, Ph), 4.83, 3.90 (AB spin system,

2ϫ2 H, ∆δ = 0.93 ppm, CH₂), 2.27, 1.79 (s, 2ϫ6 H, CH₃Ph),

1.44, 1.43 [s, 2ϫ18 H, C(CH₃)₃] ppm. ¹H NMR (300 MHz, CDCl₃,

25 °C): δ = 7.09, 7.05, 7.02, 6.97 (AAЈ spin systems, 4ϫ2 H, Ph),

[Ti(η⁵-C₅H₅)(η²-mbmp)][(CH₂Ph)B(C₆F₅)₃] (13): The same pro-

cedure described for 12, using a mixture of 5 (0.020 g, 0.04 mmol)

and B(C₆F₅)₃(0.019 g, 0.04 mmol), resulted in the formation of 13.

¹H NMR (300 MHz, C₆D₆, 25 °C): δ = 7.03, 6.94 (AAЈ spin sys-

tem, 2ϫ2 H, Ph), 6.50, 6.41, 6.26 (o, m, p-CH₂Ph), 6.33 (s, 5 H,

C₅H₅), 4.05, 3.36 (AB spin system, 2ϫ1 H, ∆δ = 0.69 ppm, CH₂),

2.12 (s, 6 H, CH₃Ph), 1.43 [s, 18 H, C(CH₃)₃], 3.14 (br. s, 2 H,

BCH₂Ph) ppm. ¹³C NMR (125 MHz, C₆D₆, 25 °C): δ = 163.6,

137.4, 136.6, 131.2, 129.1, 126.2 (all Ph), 149.8, 147.8, 138.6, 136.4

(all C₆F₅), 152.5 (C_ipso-CH₂Ph), 129.4, 127.4, 122.3 (o-, m-, p-

CH₂Ph), 118.2 (C₅H₅), 38.2 (BCH₂Ph), 35.5 (CH₂), 35.4

[C(CH₃)₃], 31.2 [C(CH₃)₃], 21.1 (CH₃-Ph) ppm. ¹⁹F NMR

(300 MHz, C₆D₆, 25 °C): δ = –132.7, –161.1, –164.5 ppm.

2

4.35, 3.68 (AB sin systems, ∆δ = 0.67 ppm, J_H,H= 14.6 Hz, 2ϫ2

H, CH₂), 2.31, 2.22 (s, 2ϫ6 H, CH₃Ph), 1.40, 1.23 [s, 2ϫ18 H,

C(CH₃)₃] ppm. ¹³C NMR (125 MHz, CDCl₃, 25 °C): δ = 149.9,

140.8, 138.5, 135.9, 132.8, 131.0, 130.2, 129.1, 128.9, 128.2, 128.0,

126.7 (all Ph), 35.2 (CH₂), 36.1, 34.5 [C(CH₃)₃], 32.3, 29.8 [C-

(CH₃)₃], 21.1, 21.0 (CH₃-Ph) ppm.

[Ti(η⁵-C₅Me₅)(η²-mbmp)][MeB(C₆F₅)₃] (14): The same procedure

described for 12, using a mixture of 8 (0.021 g, 0.04 mmol) and

B(C₆F₅)₃(0.019 g, 0.04 mmol), resulted in the formation of 14. H

Polymerisation of Propylene: A 250-mL Büchi reactor equipped

with a mechanical stirrer was first evacuated and then charged with

dried scavenger (MAO) and toluene (150 mL). A 10-mL pressure

tube was charged with the titanium complex solution in toluene

(4 mL). The reactor was purged three times with the monomer by

pressurizing and venting. The monomer was then equilibrated with

the toluene in the reactor for 30 min at the polymerisation tempera-

ture and pressure (kept constant at 1 atm over the run) with con-

stant stirring. In the runs in which liquid propylene was used, the

reactor was first equilibrated at 0 °C with constant stirring and

then fed with the monomer. The reaction was initiated by injecting

the solution containing the catalytic system under argon pressure.

After the desired reaction time, the reactor was vented and the

polymer was precipitated into 10% HCl in methanol, washed with

clean methanol and dried in a vacuum oven at 60 °C to constant

weight.

1

NMR (300 MHz, C₆D₆, 25 °C): δ = 7.04, 6.96 (AAЈ spin system,

2ϫ2 H, Ph), 3.98, 3.40 (AB spin system, 2ϫ1 H, ∆δ = 0.58 ppm,

CH₂), 2.11 (s, 6 H, CH₃Ph), 2.02 (s, 15 H, C₅Me₅), 1.45 [s, 18 H,

C(CH₃)₃], 0.91 (br. s, 3 H, BCH₃) ppm. ¹³C NMR (125 MHz,

C₆D₆, 25 °C): δ = 161.4, 137.6, 134.8, 130.4, 129.4, 126.6 (all Ph),

149.6, 147.8, 138.6, 136.5 (all C₆F₅), 128.3 (C₅Me₅), 35.1 (CH₂),

35.4 [C(CH₃)₃], 31.5 [C(CH₃)₃], 21.1 (CH₃-Ph), 13.1 (C₅Me₅), 10.5

(BCH₃) ppm. ¹⁹F NMR (300 MHz, C₆D₆, 25 °C): δ = –136.1,

–160.5, –163.9 ppm.

[Ti(η⁵-C₅Me₅)(η²-mbmp)][(CH₂Ph)B(C₆F₅)₃] (15): The same pro-

cedure described for 12, using a mixture of 9 (0.024 g, 0.04 mmol)

and B(C₆F₅)₃(0.019 g, 0.04 mmol), resulted in the formation of 15.

¹H NMR (300 MHz, C₆D₆, 25 °C): δ = 7.04, 6.96 (AAЈ spin sys-

tem, 2ϫ2 H, Ph), 7.10–6.70 (o-, m-, p-CH₂Ph), 3.96, 3.40 (AB spin

system, 2ϫ1 H, ∆δ = 0.56 ppm, CH₂), 2.10 (s, 6 H, CH₃Ph), 2.02

(s, 15 H, C₅Me₅), 1.45 [s, 18 H, C(CH₃)₃], 2.90 (br. s, 2 H, BCH₂Ph)

ppm. ¹³C NMR (125 MHz, C₆D₆, 25 °C): δ = 161.5, 137.6, 134.8,

130.5, 129.5, 126.6 (all Ph), 150.4, 147.2, 139.0, 135.6 (all C₆F₅),

160.3 (C_ipso-CH₂Ph), 128.6 (C₅Me₅), 37.3 (BCH₂Ph), 35.1 (CH₂),

35.4 [C(CH₃)₃], 31.5 [C(CH₃)₃], 21.1 (CH₃-Ph), 13.1 (C₅Me₅) ppm;

signals of o-, m-, p-CH₂Ph not found. ¹⁹F NMR (300 MHz, C₆D₆,

25 °C): δ = –135.0, –159.5, –164.6 ppm.

Polymerisation of Styrene: A 100-mL glass pressure bottle with

magnetic stirrer was vented and charged with toluene, MAO and

5 mL of the monomer. The mixture was then equilibrated at the

polymerisation temperature with constant stirring and the reaction

was initiated by injecting the solution of the catalyst in toluene

(4 mL). After the desired reaction time, the reactor was vented and

the polymer was precipitated into 10% HCl in methanol, washed

with clean methanol and dried in a vacuum oven at 40 °C to con-

stant weight. The polymer was extracted with refluxing thf for 5 h

and dried again to constant weight in order to determine the sPS

portion of the polymer obtained.

[AlMe(mbmp)]₂(16): AlMe₃(0.3 mL of a 2.0  solution in hexane,

0.59 mmol) was added to a solution of mbmpH₂(0.2 g, 0.59 mmol)

in 25 mL of toluene at room temperature. After a few minutes, a

white solid appeared and the reaction mixture was stirred for 5 h.

The solution was filtered and the white solid was washed twice with

hexane and characterised as 16 (0.29 g, 65% yield). C₄₈H₆₆Al₂O₄

Polymer Analyses: Molecular weights were determined by high-

temperature gel permeation chromatography using propylene and

polystyrene as GPC calibration standards and 1,2,4-trichloroben-

zene as eluent. The glass transition temperature and melting tem-

1

perature were determined at a heating rate of 20 °Cmin^–1. H and

1

(761.02): calcd. C 75.80, H 8.68; found C 75.67, H 8.90. H NMR

¹³C NMR measurements were performed at 363 K in [D₂]1,1,2,2-

tetrachloroethane and referenced using the solvent peaks. The areas

of the nine peaks in the methyl region determined from spectral

integrations in polypropylene samples were used to characterise the

sample microstructure. Analyses of the polymer properties were

performed at the University of Ulm (Germany), Inorganic Chemis-

try II Department.

(300 MHz, C₆D₆, 25 °C): δ = 7.41, 7.21, 7.04, 6.88 (AAЈ spin sys-

tems, 4ϫ2 H, Ph), 4.70, 3.69 (AB spin system, 2ϫ2 H, ∆δ =

1.01 ppm, CH₂), 2.32, 1.83 (s, 2ϫ6 H, CH₃Ph), 1.40, 1.37 [s, 2ϫ18

H, C(CH₃)₃], 0.15 (s, 6 H, AlCH₃) ppm. ¹H NMR (300 MHz,

CDCl₃, 25 °C): δ = 7.07, 7.03, 6.98, 6.95 (AAЈ spin systems, 4ϫ2

2

H, Ph), 4.33, 3.53 (AB spin system, ∆δ = 0.80 ppm, J_H,H

=

13.7 Hz, 2ϫ2 H, CH₂), 2.30, 2.22 (s, 2ϫ6 H, CH₃Ph), 1.36, 1.21

[s, 2ϫ18 H, C(CH₃)₃], –0.33 (s, 6 H, AlCH₃) ppm. ¹³C NMR

(125 MHz, CDCl₃, 25 °C): δ = 151.2, 144.3, 140.9, 137.7, 134.4,

Single-Crystal X-ray Structure Determination of Compounds 8, 9

and 11·0.75C₆H₁₄: Crystal data and details of the structure deter-

Eur. J. Inorg. Chem. 2007, 147–161

www.eurjic.org

159

T. Cuenca et al.

FULL PAPER

Table 7. Crystallographic data for compounds 8, 9 and 11·0.75C₆H₁₄.

8

9

11·0.75C₆H₁₄

Empirical formula

Formula mass

C₃₄H₄₈O₂Ti

536.59

C₄₀H₅₂O₂Ti

612.69

C₁₂₁H₁₆₁O₁₀Ti₄

1967.10

Colour/habit

Crystal dimensions [mm]

Crystal system

Space group

a [Å]

b [Å]

c [Å]

α [°]

orange/fragment

0.20ϫ0.36ϫ0.61

monoclinic

P2₁/n (no. 14)

11.0192(1)

16.2903(1)

18.7555(2)

90

90.1907(4)

90

3366.71(5)

4

orange/fragment

0.15ϫ0.33ϫ0.64

monoclinic

P2₁/c (no. 14)

11.2375(1)

17.6831(1)

17.9601(1)

90

105.4970(4)

90

3439.17(4)

4

orange/fragment

0.23ϫ0.36ϫ0.56

triclinic

¯

P1 (no. 2)

11.5443(1)

14.4543(1)

18.1492(2)

98.6156(3)

106.9058(4)

91.9242(4)

2855.35(5)

1

β [°]

γ [°]

V [Å³]

Z

T [K]

153

1.059

0.279

173

1.183

0.281

123

1.144

0.324

D_calcd.[gcm^–3]

µ [mm^–1]

F(000)

θ range [°]

1160

1320

1055

2.48–25.35

Ϯ13, Ϯ19, Ϯ22

80030

6157/0.044

4990

6157/0/348

0.0400/0.1202

0.0510/0.1248

1.118

1.65–25.32

Ϯ13, Ϯ21, Ϯ21

62663

6249/0.034

5495

6249/0/405

0.0458/0.1258

0.0521/0.1307

1.032

1.85–25.38

Ϯ13, Ϯ17, Ϯ21

59488

10449/0.042

8948

10449/0/920

0.0431/0.1129

0.0522/0.1205

1.027

Index ranges (h, k, l)

No. of refections collected

No. of independent reflections/R_int

No. of obsd reflections [I Ͼ 2σ(I)]

No. of data/restraints/parameters

R1/wR2 [I Ͼ 2σ(I)]^[a]

R1/wR2 (all data)^[a]

GOF (on F²)^[a]

Largest difference peak/hole [eÅ^–3]

+0.43/–0.36

+0.44/–0.35

+0.52/–0.57

2

2 2

2

2 2

[a] R1 = Σ(||F_o| – |F_c||)/Σ|F_o|; wR2 = {Σ[w(F_o– F_c) ]/Σ[w(F_o²)²]}^1/2; GOF = {Σ[w(F_o– F_c) ]/(n – p)}^1/2

.

mination are presented in Table 7. Suitable single crystals for the

X-ray diffraction study were grown from hexane in all cases. A

clear orange fragment was stored under perfluorinated ether, trans-

ferred into a Lindemann capillary, fixed, and sealed. Preliminary

examination and data collection were carried out with an area de-

tecting system (Nonius, MACH3, κ-CCD) at the window of a rot-

factors for all atoms and anomalous dispersion corrections for the

non-hydrogen atoms were taken from the International Tables for

Crystallography. All calculations were performed with an Intel Pen-

tium II PC, with the STRUX-V system, including the programs

PLATON, SIR92 and SHELXL-97.^[45–50]In 8, a problem with an

unresolvable solvent molecule was resolved with the PLATON^[49]

ating anode (Nonius, FR591) with graphite-monochromated Mo- Calc Squeeze procedure. For 9, a disorder [0.821(4):0.179(4)] of the

K_αradiation (λ = 0.71073 Å). The unit-cell parameters were ob-

tained by full-matrix least-squares refinement of 6411 (6477, 10431)

reflections. Data collection was performed at 153 (173, 123) K (Ox-

ford Cryosystems) in the range 2.48°Ͻ θ Ͻ 25.35° (1.65°Ͻ θ Ͻ

25.32°, 1.85°Ͻ θ Ͻ 25.38°) for a total of nine (nine, seven) data

sets in rotation scan mode with ∆φ/∆ω = 1.0° (1.0°, 1.0°). A total

of 80030 (62663, 59488) intensities were integrated. Raw data were

corrected for Lorentz, polarisation, and, arising from the scaling

procedure, latent decay and absorption effects. After merging [R_int

= 0.044 (0.034, 0.042)] a total of 6157 (6249, 10449) (all data) and

4990 (5495, 8948) [I Ͼ 2σ(I)] reflections remained and all these

data were used in the subsequent refinement. The structures were

solved by a combination of direct methods and difference Fourier

syntheses. All non-hydrogen atoms were refined with anisotropic

displacement parameters. For 8 and 9, all hydrogen atoms were

placed in ideal positions (riding model). For 11·0.75C₆H₁₄, all hy-

drogen atoms located at the titanium complex were found in the

difference map calculated from the model containing all non-hydro-

gen atoms. The hydrogen positions were refined with individual

isotropic displacement parameters. All hydrogen positions located

at the disordered hexane solvent molecule were placed in calculated

positions (riding model). Full-matrix least-squares refinements

with 348 (405, 920) parameters were carried out by minimizing

cyclopentadienyl ring was clearly resolved. For 11·0.75C₆H₁₄, the

solvent molecule appeared to be disordered over three positions

(3:2:1) with an overall occupancy factor of 0.75. CCDC-631035

(8), -631036 (9) and -631037 (11·0.75C₆H₁₄) contain the supple-

mentary 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.

Supporting Information (see footnote on the first page of this arti-

cle): ¹³C NMR spectra for the PP sample obtained in run 2 and

run 6 (Table 5).

Acknowledgments

Financial support for this research by DGICYT (project

MAT2004-02614), CAM (project S-0505-PPQ/0328-02) and the

European Commission (contract no. HPRN-CT2000-00004) is

gratefully acknowledged. M. G.-M. acknowledges the Comunidad

de Madrid (CAM) for the award of a Fellowship.

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160

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Eur. J. Inorg. Chem. 2007, 147–161

Alkylmono(cyclopentadienyl)titanium Complexes

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Received: July 31, 2006

Published Online: November 9, 2006

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161

Article Doi

Alkylmono(cyclopentadienyl)titanium complexes containing the 2,2′-methylenebis(6-tert-butyl-4-methylphenoxido) ligand - Studies on the nature of the catalytic species present in α-olefin polymerisation processes

DOI: 10.1002/ejic.200600710

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