Process for the preparation of cyclopentadienyl compounds...

Details Process for the preparation of cyclopentadienyl compounds... Process for the preparation of cyclopentadienyl compounds...

2000-03-27

2002-05-14

Nazario-Gonzalez, Porfirio (Department: 1621)

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

Organic compounds

Silicon containing

C556S087000, C556S489000, C585S023000, C585S502000, C585S507000, C585S521000, C585S530000, C585S638000, C526S160000, C526S943000, C502S103000, C502S117000

Reexamination Certificate

active

06388118

ABSTRACT:

The present invention relates to a process for preparing cyclopentadienyl compounds. More particularly, it relates to a process for preparing alkylidene-bridged bis-cyclopentadienyl compounds. The invention also relates to a class of compounds obtainable from this process.
Compounds having two cyclopentadienyl rings joined by a structural bridge are known and broadly used in the synthesis of organometallic compounds, mainly for the preparation of ansa-metallocenes which are active as catalyst components in the polymerization of olefins.
From the European application EP 129.368 are known metallocene compounds comprising cyclopentadienyl rings linked each other by a bridge constituted by an alkylene group having 1 to 4 carbon atoms. However, in said application the preparation of such compounds is not disclosed.
The European application EP 416.566 discloses propylene polymer having low molecular weight prepared by bulk polymerization carried out in the presence of a catalyst comprising (A) an alumoxane and (B) a metallocene compound in which the cyclopentadienyl rings, equal or different, are linked with a bridge having formula —R
5
CR
6
— wherein R5 and R6 can have different meanings. The ligands of the metallocene compounds are prepared by reacting a cyclopentadienyl compound, previously treated with an organo lithium compound, with a fulvene compound. If the fulvene is corresponding to the cyclopentadienyl compound, symmetric ligand can be obtained. Nevertheless, this method gives unsatisfactory yields and requires, also for the preparation of symmetric ligands, a previous step in which the fulvene is prepared and separated with consequent lowering of the whole reaction yield.
Isopropylidene-bridged cyclopentadienyl compounds have been prepared by I. E. Nifant'ev et al. in J.Chem. Research 1992, 162 by reacting a substituted cyclopentadienyl compound with 6,6-dimethylfulvene in the presence of a NaOH\THF system. Also in this case the 6,6-dimethylfulvene is separately prepared. Furthermore, since the 6,6-dimethylfulvenes having substituents on the cyclopentadienyl ring do not react in these conditions it is impossible to obtain isopropylidene-bridged bis-cyclopentadienyl compounds having substituents on the cyclopentadienyl ring.
According to the same author in Organometallics 1991, 10, 3739, isopropylidene-bis(cyclopentadiene) is prepared by only one step reacting cyclopentadiene and acetone in the presence of the system NaOH\THF. The yields obtained are about 60%. However, in these conditions substituted cyclopentadienes do not react with acetone.
I. F. Urazowski et al. at the Xth Fechem Conference on Organometallic Chemistry held on Sep. 5-10, 1993 in Agia Pelagia, Crete—Greece, presented metallocene complexes of Ti and Zr obtained from two dicyclopentadienyl-dimethyl-methanes, namely those having an isopropyl or tertbutyl substituent on the 3-position of each cyclopentadienyl ring. However, only mechanisms of the formation of those complexes and their structural features on the basis of X-ray analysis were discussed, whilst the preparation of the corresponding dicyclopentadienyl-dimethyl-methanes was not described.
Therefore, it would be highly desirable to provide an easy and advantageous route to the preparation of the general class of bis-cyclopentadienyl compounds bridged by a single carbon atom.
The applicant has now surprisingly found that, by operating under particular conditions, alkylidene-bridged bis-cyclopentadienyl compounds having substituents on the cyclopentadienyl rings can be prepared by means of an easy one-step process.
Therefore, it is an object of the present invention a process for preparing symmetric bridged bis-cyclopentadienyl compounds having the general formula (I):
wherein the double bonds of the cyclopentadienyl ring can be in any of the allowed positions wherein R
1
, R
2
, R
3
and R
4
, which can be identical or different, are hydrogen atoms or C
1
-C
20
-alkyl, C
3
-C
20
-cycloalkyl, C
2
-C
20
-alkenyl, C
6
-C
20
-aryl, C
7
-C
20
-alkylaryl or C
7
-C
20
-arylalkyl radicals which can contain atoms of Si or Ge, and furthermore two adjacent R
1
, R
2
, R
3
and R
4
substituents on the same cyclopentadienyl ring can form a ring having 5 to 8 carbon atoms;
R
5
is a hydrogen atom or a —CHR
7
R
8
group;
R
6
is a C
6
-C
20
-aryl radical or a —CHR
9
R
10
group;
R
7
, R
8
, R
9
and R
10
, which can be identical or different, are hydrogen atoms or C
1
-C
20
-alkyl, C
3
-C
20
-cycloalkyl, C
2
-C
20
-alkenyl, C
6
-C
20
-aryl, C
7
-C
20
-alkylaryl or C
7
-C
20
-arylalkyl radicals which can contain hetero atoms such as nitrogen, phosphorus, oxygen or sulphur, or two R
7
, R
8
, R
9
and R
10
substituents can form a ring having 3 to 8 carbon atoms, which can also contain hetero atoms;
said process comprising the reaction of a carbonyl compound of formula (II):
wherein R
5
and R
6
have the meaning given above, with a cyclopentadienyl compound of formula (III):
wherein the double bonds in the cyclopentadienyl rings can be in any of the allowed positions wherein R
1
, R
2
, R
3
and R
4
have the meaning given above, said reaction being carried out in the presence of a base and of an oxygen-containing solvent having an atomic ratio carbon/oxygen not higher than 3.
The double bonds of the cyclopentadienyl rings in the compounds of formula (I) and (III) can be in any of the allowed positions.
The choice of the solvent is critical for the invention. Unsuitable solvents will not give the desired final product, or will give it with unsatisfactory yields.
A particularly suitable class of solvents for use in the process of the invention are the polyethers such as, for example:
diethers, such as dimethoxyethane, diethoxyethane,
triethers, such as diglyme,
crown ethers,
mono-, di-, oligo- or polyethyleneglycole.
Examples of bases suitable for use in the process of the present invention are, for instance, the alkali or alkali earth metal hydroxides, such as lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide. Potassium hydroxide is the preferred.
According to a particularly preferred embodiment, the process of the invention is carried out in the presence of the system consisting of potassium hydroxide and dimethoxyethane.
The reaction temperature is generally comprised between −50° C. and the boiling temperature of the solvent.
The time of the reaction can vary in a wide range. Generally it is comprised between 2 minutes and 24 hours, more typically between 30 minutes and 4 hours.
In the above reaction, the molar ratio of the cyclopentadienyl compound (III) to the carbonyl compound (II) can vary in a very wide range and, in dependence of said (III)/(II) molar ratio, different embodiments can be practised which permit to obtain the desired final products. Each of said embodiments permits to obtain a different type of final products. However, the above molar ratio is generally equal to or lower than 2.
According to a preferred embodiments of the process of the invention, the reaction between the cyclopentadienyl compound (III) and the carbonyl compound (II) is conducted with a molar ratio (III)/(II) of about 2:1. When such a ratio is used, in dependence of the choice of the type and the number of the substituents in the formulae (II) and (III), different alkylidene-bridged bis-cyclopentadienyl compounds can be prepared in a single step.
Accordingly, starting from cyclopentadienyl compounds of formula (III) in which at least one of the R
1
, R
2
, R
3
and R
4
substituents is a C
1
-C
10
alkyl group, compounds belonging to the class of the alkylidene-bridged bis(alkyl-substituted-cyclopentadienyl) compounds can be obtained, in yields generally higher than those of the processes of the prior art.
In particular when, operating at a (III)/(II) molar ratio of about 2:1, acetone is employed as the carbonyl compound of formula (II) and an alkyl-substituted cyclopentadienyl compound as the compound of formula (III), bridged bis-alkyl-substituted-cyclopentadienes of formula (IV):
2,2-bis(CpR′
n
H

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