Process for the preparation of titanium complexes

Details Process for the preparation of titanium complexes Process for the preparation of titanium complexes

2001-02-02

2004-08-10

Nazario-Gonzalez, Porfirio (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heavy metal containing

C556S007000, C556S012000, C556S020000, C556S022000, C556S028000, C556S053000, C556S056000, C556S058000, C526S160000, C526S943000, C503S223000, C503S223000

Reexamination Certificate

active

06774253

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a new process, particularly simple, convenient and practical, for the preparation of complexes of titanium, preferably monocyclopentadienyl titanium dihydrocarbyl complexes; more specifically, it relates to a process for the direct synthesis of complexes wherein the titanium atom is linked to two sigma ligands selected from the group consisting of linear or branched, saturated or unsaturated C
1
-C
20
alkyl, C
3
-C
20
cycloalkyl, C
6
-C
20
aryl, C
7
-C
20
alkylaryl and C
7
-C
20
arylalkyl radicals, optionally containing Si or Ge atoms.
These complexes are useful as catalyst components in the polymerization of olefins, in association with suitable activating cocatalysts.
PRIOR ART DISCLOSURE
Homogeneous catalytic systems based on constrained geometry catalysts in association with useful cocatalysts are well known in the state of the art and are widely used in the polymerization reaction of olefins, as described for instance in EP-A-416,815, EP-A-420,436, EP-A-671,404, EP-A-643,066 and WO 91/04257.
These homogeneous catalytic systems are based on mono-cyclopentadienyl metal dihalide coordination complexes, wherein the sigma ligands of the central metal atom are halogen, and usually chlorine.
In known prior art processes, the synthesis of the metal dihalide complexes is often troublesome and much lower than quantitative. Said complexes may be produced by contacting the metal reactant (usually MX
4
) and a group I metal salt (usually the dilithium salt) or a Grignard salt of the cyclopentadienyl compound; while this reaction may be favorably carried out to produce zirconium dihalide complexes, it shows only very poor yields in the production of titanium dihalide complexes, due to the reduction of Ti(IV) to Ti(III).
For instance, M. Waymouth et al. (
Organometallics
16:2879-2885, 1997) prepared indenyl-amido titanium dichloride complexes by treating the dilithium salt of (tert-butylamido)(dimethyl)(indenyl)silane (obtained by reacting the ligand with 2BuLi) with TiCl
4
(THF)
2
; the yields for this synthesis were quite low (<20%).
Besides the very low final yields, said reactions have the disadvantage of requiring very low temperatures (−78° C.). In fact, the dianion of the monocyclopentadienyl ligand compound requires a multi-step, laborious recovery and purification procedure, before being reacted with an halogenating agent.
Another disadvantage resides in the fact that, since the reaction has to be carried out in aprotic polar solvents, in order to facilitate the handling of the metal tetrahalide reactant which is air and moisture sensitive, prior to the reaction step the transition metal tetrahalide compound is typically converted to its ether-adduct in a separate step with THF or diethyl ether. This adduct formation step in itself proceeds with difficulty, requiring low to very low temperatures, and an inert atmosphere. The adduct is usually recovered before it is reacted with the dianionic derivative of the ligand. The yield of the adduct formation steps is less than quantitative.
Furthermore, the reaction mixture of the transition metal tetrahalide compound and the dianion of the bridged cyclopentadienyl ligand compound requires a multi-step, laborious recovery and purification procedure. Typically, after the reaction step, the solvent is removed, the product re-dissolved by adding dichloromethane or toluene or a mixture thereof, the metal halide byproduct (typically lithium chloride) removed by filtration of the mixture, the solvent removed at least partially, followed by re-dissolving the solid product and crystallizing the product, optionally followed by one or more further recrystallization procedures.
In a preferred process known in the state of the art, the dianionic salt of the monocyclopentadienyl ligand is reacted with a metal compound wherein the metal is in a lower oxidation state than in the desired final complex, for instance Ti(III) compounds; thereafter, the resulting complex has to be contacted with an oxidizing agent (such as AgCl or PbCl
2
), in order to raise the oxidation state of the metal to form the desired titanium (IV) dihalide complex.
Apart from requiring an extra reaction step (i.e. the oxidation step), the intermediate monohalide coordination complex of Ti(III) is thermally unstable; therefore, reaction yields are usually unsatisfactory.
For instance, in
Organometallics
16:2879-2885, 1997 is described the preparation of a bridged mono(substituted cyclopentadienyl) titanium dichloride complex by treating the THF-adduct of TiCl
3
with the dimagnesium salt of [(R-amide)dimethylsilyl](tert-butyl)cyclopentadienide (obtained by deprotonation of the ligand with iPrMgCl), followed by PbCl
2
oxidation; the yields were only of 52% in case of R=tBu and 16% in case of R=CHMePh. Moreover, in the case of indenyl-amido titanium complexes, reaction of the indenyl dimagnesium dichloride salts with TiCl
3
(THF)
3
followed by PbCl
2
oxidation was completely unsuccessful.
The corresponding dihydrocarbon derivatives, particularly dimethyl ones, have been developed and are widely used as catalyst components for olefin polymerization reactions, in association with suitable cocatalysts, such as alumoxanes and borate salts, e.g.
[Ph
3
C]
+
[B(C
6
F
5
)
4
]
−
or [HN(n-Bu)
3
]
−
[B(C
6
F
5
)
4
]
−
.
When the sigma ligands of the central metal atom are alkyl or aryl groups, the above metal complexes may not be expediently synthesized by the existing methodology; in fact, prior art processes imply always the synthesis of the metal complex dihalide, that is subsequently hydrocarbylated by ligand exchange with an appropriate hydrocarbylating agent to the target product, thus leading to unsatisfactory total yields and requiring at least the following two process steps:
(1) preparing the halide metal coordination complex, usually the dichloride, by reacting a suitable ligand with MX
4
, wherein X is halogen (usually TiCl
4
(THF)
2
or ZrCl
4
); or alternatively preparing the halide metal coordination complex by reacting a suitable ligand with MX
3
(usually TiCl
3
(THF)
3
) and thereafter contacting the product with an oxidizing agent (usually AgCl or PbCl
2
);
(2) converting the dihalide complex obtained in step (1) into the corresponding dialkyl complex, by substitution of the halogens linked to the metal atom with the desired alkyl or aryl groups, by means of an alkylating agent such as alkyllithium, dialkylmagnesium or the corresponding Grignard reagent.
As already evidenced above, process step (1), leading to the metal monohalide complex, is often troublesome (requiring very low reaction temperatures) and not quantitative; in particular, very poor yields are obtained when TiCl
4
or its adducts are used as reactants, due to the abundant reduction of the metal. On the opposite, in case that Ti(III) derivatives are used as the reactants, more acceptable yields are obtained, but the resulting dihalide complex has to be contacted with an oxidizing agent, in order to raise the oxidation state of the metal to form the desired dihalide complex. Therefore, these preparation processes inherently have the disadvantages associated with the preparations of the metal dihalide complexes.
Finally, in order to achieve the desired dialkyl metal complex, the metal dichloride complex has to be treated with an alkylating agent, such as MeLi (step (2)); therefore, a further reaction step is required thus lowering notably the total reaction yields and rendering the whole process more laborious and time consuming.
According to the literature procedures (Jun Okuda et al.,
Journal of Organometallic Chemistry
, 520:245-248, 1996), dimethylsilandiyl(tert-butylamido)(indenyl) titanium dimethyl can be obtained at best in two reaction steps, in an unsatisfactory total yield. More specifically, in the cited reference, Okuda obtained the above Ti(IV) dichloride complex by the reaction of the dilithium derivative Li
2
[Ind-SiMe
2
-NCMe
3

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