WO2018011156A1

WO2018011156A1 - Catalytic process for diene dimerization

Info

Publication number: WO2018011156A1
Application number: PCT/EP2017/067307
Authority: WO
Inventors: Mostafa Taoufik; Kai Chung Szeto; Cesar Rios Neyra
Original assignee: Total Raffinage Chimie; Centre National De La Recherche Scientifique (Cnrs); Universite Claude Bernard Lyon; Ecole Superieure De Chimie Physique Electronique De Lyon
Priority date: 2016-07-12
Filing date: 2017-07-10
Publication date: 2018-01-18

Abstract

The invention relates to a selective head-to-tail dimerization of conjugated diene compounds by a heterogeneous catalytic process using a supported catalyst comprising ligands and a transition metal selected from titanium and zirconium.

Description

CATALYTIC PROCESS FOR DIENE DIMERIZATION

FIELD OF THE INVENTION

The invention relates to the dimerization of conjugated diene compounds, in particular terminal conjugated diene compounds, by a heterogeneous catalytic process in a reaction medium, in order to provide a majority of head-to-tail dimers among the reaction products. BACKGROUND OF THE FNVENTION

Products obtained by dimerization of conjugated dienes and further hydrogenation may be used in different fields, such as flavors and fragrances, pharmaceutical, cosmetics, solvents and lubricants applications. In cosmetic applications, hydrogenated dimers obtained from conjugated dienes may be used in creams, such as nutrient creams and medicated creams or in toilet or milky lotion, in lipstick or in face powder. In pharmaceutical applications, hydrogenated dimers obtained from conjugated dienes may be used in medical and pharmaceutical preparations such as ointments, and medical lubricating agents. As an example of a useful hydrogenated dimer, special mention can be made to squalane, isosqualane and crocetane.

The dimerization process of conjugated dienes is generally performed using a catalyst in the presence of a solvent.

Document WO 2011/146837 describes the dimerization of farnesene by a homogeneous catalytic process using complex catalysts. This document discloses complexes of titanium or zirconium for the dimerization of farnesene leading to isosqualane after hydrogenation.

Document US 8,669,403 discloses a process for catalytic dimerization of farnesene using a homogeneous catalytic process using complexes. This document discloses a complex of palladium. This document also discloses that heterogeneous catalysts of Pd/C, Pd/alumina or Ru/C type do not provide conversions higher than 5%. Therefore, the transposition of a homogeneous catalytic system into a heterogeneous catalyst system cannot be regarded as obvious or predictable.

There still exists a need for the dimerization of conjugated dienes by an industrial process which would be economical and would present an improved selectivity for the desired dimers. SUMMARY OF THE INVENTION

A first object of the present invention is a process for the dimerization of conjugated diene compounds comprising contacting, in a reaction medium, said conjugated diene compounds with a supported catalyst comprising ligands and a transition metal selected from titanium and zirconium.

The reaction medium can comprise a solvent comprising hydrocarbons or can be solvent free.

According to an embodiment, at least one ligand is selected from alkoxides, halides, amines, imines, phenoxides and hydrocarbon ligands.

According to an embodiment, the ligands are selected from halides and hydrocarbon ligands.

According to an embodiment, the ligands are selected from alkoxides.

According to an embodiment, the reaction medium further comprises one or more additive selected from phosphine based additives, tertiary amines, sulfur compounds, ethers, tetrahydrofurane and dioxane, preferably selected from triphenylphosphine (PPh₃), tritolyl phosphine, tribenzylphosphane (PBn₃), dimethylphenylphosphine (PMe₂Ph).

According to an embodiment, the conjugated diene compounds are terminal conjugated diene compounds.

Preferably, the conjugated diene compounds are asymmetric conjugated diene compounds.

Preferably, the conjugated diene compounds have the following formula (I):

wherein R¹, R², R³, R⁴,

ependently to each other, a hydrogen atom, a halogen atom or a hydrocarbyl radical, linear, branched or cyclic, saturated or unsaturated, optionally comprising one or more heteroatoms, being understood that at least one of the R¹ is different from all the others R¹, i being selected from 1, 2, 3, 4, 5 or 6.

According to an embodiment, the conjugated diene compounds have the following formula (II):

wherein R is a hydrocarbyl radical having 1 to 20 carbon atoms, preferably having 2 to 15 carbon atom, optionally comprising one or more heteroatoms, such as nitrogen, oxygen or sulphur. Preferably, the conjugated diene compounds are selected from myrcene or farnesene.

According to an embodiment, head-to-tail dimers representing at least 40% by weight of the reaction products, preferably at least 45% by weight of the reaction products, more preferably at least 50%> by weight of the reaction products, are obtained.

According to an embodiment, the process further comprises a hydrogenation step, whereby hydrogenated dimers are obtained, preferably saturated dimers are obtained.

Another object of the present invention is a supported catalyst comprising a transition metal selected from titanium and zirconium and ligands selected from alkoxides, halides, amines, imines, phenoxides and hydrocarbon ligands, being understood that if one ligand is a cyclopentadienyl ligand, the metal is linked to at least one halide ligand.

According to an embodiment, the ligands are selected from alkoxides.

A further object of the present invention is the use of the supported catalyst of the invention for the dimerization of conjugated diene compounds.

An advantage of the present invention is a process that involves a supported catalyst, which is more convenient for an industrial application. The supported catalyst used in the present invention is less expensive than other catalysts used for the dimerization of dienes, such as palladium catalysts.

Another advantage of the present invention is its improved selectivity, in particular, the process of the present invention leads in majority to head-to-tail dimers, i.e. the amount of the head-to-tail dimers is higher than the amount of the other reaction products. For example, the head-to-tail dimers may represent at least 40% by weight of the reaction products, preferably at least 45% by weight, more preferably at least 50% by weight of the reaction products.

To be complete, if the head-to-tail dimers represent 40% by weight of the reaction products, the reaction products will not comprise one compound (different from head- to-tail dimers) which alone will represent more than 40% by weight (since the process of the invention leads in majority to head-to-tail dimers).

An advantage of the present invention is that it may be implemented without solvent, leading to a more economic process. Additionally, the absence of solvent facilitates the further separation steps, improving the efficiency of the process.

Further features and advantages of the invention will appear from the following description of embodiments of the invention, given as non-limiting examples, with reference to the accompanying drawing listed hereunder.

BRIEF DESCRIPTION OF THE FIGURE

Fig. 1 represents a general formula of a conjugated diene compound.

DETAILED DESCRIPTION OF THE INVENTION

A first object of the present invention is a process for the dimerization of conjugated diene compounds comprising contacting, in a reaction medium, said conjugated diene compounds with a supported catalyst based on a transition metal selected from titanium and zirconium. Diene compound

By "conjugated diene compounds" according to the present invention, it is to be understood a hydrocarbon molecule, linear, branched or cyclic, comprising at least two conjugated carbon-carbon double bonds. The hydrocarbon molecule may also comprise at least one heteroatom (either in the skeleton of the main hydrocarbon chain or in side substituents or side hydrocarbon chains), such as oxygen, nitrogen or sulfur. Preferably, the hydrocarbon molecule consists in hydrogen and carbon atoms. The hydrocarbon molecule preferably comprises from 4 to 30 carbon atoms, more preferably from 5 to 20 carbon atoms. The hydrocarbon molecule may optionally comprise one or more additional carbon-carbon double bonds, apart from the two conjugated carbon-carbon double bonds.

The conjugated diene compounds used in the present invention are preferably such that the dimerization products of said conjugated diene compounds may lead simultaneously to head-to-head dimers and head-to-tail dimers (isomers). The skilled person well knows which conjugated diene compounds can form both different isomers and which conjugated diene compounds cannot form both different isomers. In particular, the conjugated diene compounds are preferably asymmetric conjugated diene compounds, such that the dimerization reaction may lead to different dimer s.

By "asymmetric conjugated diene compound", it is to be understood a compound wherein the conjugated diene function does not comprise a plane of symmetry. The skilled person well knows what is a conjugated diene function that has a plane of symmetry or what is a conjugated diene function that has not a plane of symmetry. For example, with reference to the formula (I) below, an asymmetric conjugated diene compound is a compound which does not have a plane of symmetry between carbon atoms numbered 2 and 3, the plane of symmetry is represented by the AA' axis in formula (I) in fig. 1.

A conjugated diene compound used in the present invention may be represented by the following formula (I):

wherein R¹, R², R³, R⁴, R⁵ and R⁶ represent, independently to each other, a hydrogen atom, a halogen atom or a hydrocarbyl radical, linear, branched or cyclic, saturated or unsaturated, optionally comprising one or more heteroatoms such as oxygen, nitrogen or sulphur atoms, being understood that at least one of the R¹ (i being 1 , 2, 3, 4, 5 or 6) is different from all the others R¹, in order to obtain an asymmetric conjugated diene compounds.

Preferably, R¹, R², R³, R⁴, R⁵ and R⁶ represent, independently to each other, a hydrogen atom or a hydrocarbyl radical having from 1 to 20 carbon atoms, preferably without heteroatoms, being understood that at least one of the R¹ (i being 1, 2, 3, 4, 5 or 6) is different from all the others R¹.

According to an embodiment, R¹, R², R³ and R⁴ are hydrogen atoms; R⁵ is different from R⁶; and R⁵ and R⁶ are selected from a hydrogen atom or a hydrocarbyl radical having from 1 to 20 carbon atoms, optionally comprising heteroatom(s).

In the above formula (I) also represented in Fig. 1, the four carbon atoms of the conjugated diene function have been numbered from 1 to 4.

A "head-to-head dimer" is well known for the skilled person. For example, with reference to the formula (I) above, a head-to-head dimer is a dimer obtained by reaction between a 1-2 carbon-carbon double bond of one conjugated diene compound and the 1-2 carbon-carbon of another conjugated diene compound. A "head-to-tail dimer" is well known for the skilled person. For example, with reference to formula (I) above, a head-to-tail dimer is a dimer obtained by reaction between a 1-2 carbon-carbon double bond of one conjugated diene compound and the 3-4 carbon-carbon double bond of another conjugated diene compound.

According to an embodiment, the terminal conjugated diene compounds have the following formula (II):

wherein R is a hydrocarbyl radical, linear, branched or cyclic, saturated or unsaturated having 1 to 20 carbon atoms, optionally comprising one or more heteroatoms (either in the skeleton of the main hydrocarbon chain or in side substituents or side hydrocarbon chains), such as nitrogen, oxygen or sulphur. Preferably, R is a hydrocarbyl radical having from 2 to 18 carbon atoms, more preferably having from 4 to 15 carbon atoms. According to an embodiment, the conjugated diene compounds are chosen from terpenes, such as myrcene or beta-farnesene, beta-phellandrene or alpha-terpinene, preferably from myrcene, beta-farnesene or beta-phellandrene, more preferably from myrcene or beta-farnesene.

Myrcene refers to a compound having the following formula (III):

Beta-farnesene refers to a compound having the following formula (IV):

Terpenes are molecules of natural origin, produced by numerous plants, in particular conifers. By definition, terpenes (also known as isoprenoids) are a class of hydrocarbons bearing as the base unit an isoprene moiety (i.e. 2-methyl-buta-l ,3-diene). Isoprene [CH₂=C(CH₃)CH=CH₂] is represented below (V):

Terpenes may be classified according to the number n (integer) of isoprene units of which it is composed, for example:

n = 2: monoterpenes (Cio), such as myrcene;

n = 3 : sesquiterpenes (C₁₅), such as farnesene;

n = 4: diterpenes (C₂₀).

Alpha-terpinene is a cyclic terpene having two conjugated carbon-carbon double bonds and refers to a compound havin the following formula (VI):

According to an embodiment, the dimerization reaction is performed with conjugated dienes of same chemical nature. According to another embodiment, the dimerization reaction is performed with conjugated dienes of different chemical natures. Preferably, the dimerization reaction is performed with conjugated dienes of same chemical nature.

The process according to the present invention is performed in a reaction medium, said reaction medium may comprise a solvent or may be free of solvents.

Indeed, the inventors surprisingly found that the process may be performed without solvent with good results.

According to the present invention, by "solvent", it is to be understood an additional component, different from the conjugated diene compounds and different from the catalyst(s).

Reaction medium

According to an embodiment, the dimerization process according to the invention comprises the reaction between at least two conjugated diene compounds in a reaction medium comprising a solvent based on hydrocarbons. These hydrocarbons are generally non protic compounds. They are solvents for the diene compounds. According to this embodiment of the invention, the selected hydrocarbon for the solvent of the reaction medium is different from the diene compounds described above.

Preferably, the reaction medium comprises at least 50% by weight of hydrocarbons, preferably at least 70%> by weight, more preferably at least 90%> by weight of hydrocarbon solvents, still more preferably at least 99% by weight of hydrocarbon solvents, based on the total weight of the reaction medium.

The hydrocarbon solvents comprised in the reaction medium may be chosen from a linear, a branched or a cyclic hydrocarbon.

For example, the hydrocarbon solvents may be chosen from pentane, heptane, hexane, cyclohexane, toluene and o-xylene.

According to another embodiment, the dimerization process according to the invention comprises the reaction between at least two conjugated diene compounds in a reaction medium free of solvents and in particular free of hydrocarbon solvents.

According to an embodiment of the invention, the reaction medium is substantially free, preferably totally free of protic compounds.

By "substantially free", it is to be understood that the reaction medium comprises less than 1000 ppm by mass, preferably less than 500 ppm by mass, more preferably less than 100 ppm by mass, ideally less than 50 ppm by mass, based on the total mass of the reaction medium.

By "protic compound", it is to be understood a compound that has a labile H⁺. The process of dimerization according to the present invention may be performed in a reaction medium comprising one or more additives, different from the conjugated diene compounds and different from the catalyst(s). Preferably, those additives are not protic.

According to an embodiment, the additive may be selected from phosphine based additives, preferably selected from triphenylphosphine (PPh₃), tritolyl phosphine, tribenzylphosphane (PBn₃), dimethylphenylphosphine (PMe2Ph), and from tertiary amines, sulfurs of type TT'S (T and T' being a hydrocarbyl radical), ethers, tetrahydrofurane or dioxane, and mixture thereof. Phosphine based additives are particularly useful when the catalyst is obtained from complexes of type MCU or M(OtBu)4 in order to reduce or even avoid the polymerization of the conjugated diene, M representing titanium or zirconium. On the contrary, it is preferred not to add phosphine based additives in the reaction medium when the catalyst is obtained from complexes such as titanium phenoxy-imine or Cp-arene in order to increase the selectivity.

Catalyst

The catalyst used in the present invention is a supported catalyst based on a transition metal selected from titanium and zirconium.

According to an embodiment, the supported catalyst may be a monopodal catalyst or a bipodal catalyst.

The mono odal catalyst may be represented by the following structures (VIII):

The bipodal catalyst may be represented by the following formula (IX):

In the above formulas (VIII) and (IX):

M represents titanium or zirconium metal,

X, which is identical or different in each catalyst, represents a neutral or anionic ligand that yields to normal covalent bonds with the metal,

L, which is identical or different in each catalyst, represents a neutral ligand that yields to dative covalent bond (also named coordinate bond or bipolar bond) with the metal,

M' which is identical or different in each catalysts, represents an atom from the support, preferably selected from silicon and aluminum.

It must be appreciated that, in the present invention, be it monopodal or bipodal catalysts, the titanium and the zirconium metals (M) are covalently linked to the support through a real and strong M'-O-M bound. This is significantly different from certain catalysts of the prior art, in which the metals and complexes thereof are simply impregnated and therefore non permanently bound to the support ("floating catalysts"). The silica- supported catalysts may be represented by the following expression:

MX4/S1O2 or LMX3/S1O2, wherein M represents either the titanium metal or the zirconium metal and wherein X and L represent a ligand, preferably as defined above. In the above expression, MX₄ or LMX3 represents the (homogeneous) complex, before grafting onto the support. The ligand X may be identical or different in each catalyst. Indeed, it is possible that the supported catalyst comprises 3 different ligands.

According to an embodiment, the catalysts used in the present invention comprise at least one oxide support selected from silica, alumina, silica-alumina, preferably from silica. In the last embodiment, the supported catalyst is a silica-supported catalyst, and in this case, M' is a silicon atom.

According to an embodiment, X is selected from alkoxides, halides, hydride, aryloxy, sulfur, alkyl or aryl, dialkylaminyl, trihydrocarbylsilyl, or hydrocarbylaminylsilyl. Preferably, X is selected from alkoxides having from 1 to 6 carbon atoms, hydride, aryloxy having from 6 to 12 carbon atoms, sulfur, alkyl having from 1 to 6 carbon atoms, aryl having from 6 to 12 carbon atoms, dialkylaminyl wherein the alkyl groups have from 1 to 6 carbon atoms, trihydrocarbylsilyl comprising from 3 to 18 carbon atoms, or hydrocarbylaminylsilyl having from 1 to 18 carbon atoms. Preferably, X is selected from alkoxides having from 2 to 5 carbon atoms, hydride, alkyl having from 1 to 6 carbon atoms, aryl having from 6 to 10 carbon atoms.

Among alkoxide ligands, mention may be made of tert-butyloxide, iso-propyl oxides, n-propyloxide, ethyloxide, aryloxide, such as phenoxide, and methyl oxide.

Among halide ligands, mention may be made of chloride, fluoride, and iodide.

Phenoxide ligands refer to the following bonds: M-O-Ph wherein M represents Zr or Ti and wherein -Ph represents a phenyl radical. The phenyl radical may optionally be substituted.

According to an embodiment, L is selected from substituted phenoxy-imine, phosphonimide, iminoimidazolidide, hydrocarbon ligands such as cyclopentadienyl or indenyl or fluorenyl group and cyclopentadienyl ligand with pendant ligand such as phenyl, amide, sulfur, ether, phosphine, phosphite.

Within the meaning of the present invention, a "pendant ligand" is a ligand that is linked to the main ligand (such as the ligand L) and which participates to the coordination to the metal and that can also participate to the reaction.

Preferably, the ligand L may be selected from cyclopentadienyl or indenyl or fluorenyl with or without pendant ligand or from phenoxyimine with methoxy group as pendant ligand.

According to an embodiment of the invention, hydrocarbon ligands may be selected from saturated or unsaturated linear, branched or cyclic alkyl groups, and optionally substituted aromatic groups. According to an embodiment, the hydrocarbon ligands comprise from 1 to 40 carbon atoms, preferably from 4 to 30 carbon atoms, more preferably from 5 to 24 carbon atoms. According to a particular embodiment, the hydrocarbon ligands consists in hydrogen and carbon atoms.

Among saturated or unsaturated linear, branched or cyclic alkyl groups, mention may be made of cyclopentadienyl ligands, substituted cyclopentadienyl ligands, such as cyclopentadienyl-arene ligands. Imine ligands refer to the following bonds: M-N=C wherein M represents Zr or

Ti and wherein the carbon atom may be linked to two atoms selected from hydrogen or carbon atoms.

Phosphonimide ligands refer to the following bonds: M-N=PPv3 wherein M represents Zr or Ti and wherein R represents an alkyl or an aromatic radical. The alkyl and phenyl radical may optionally be substituted.

According to a preferred embodiment, the catalyst used in the present invention comprises at least one ligand selected from alkoxides, halides, amines, imines, phenoxides and hydrocarbon ligands, preferably from alkoxides, halides and hydrocarbon ligands, more preferably from halides.

According to a further embodiment, the catalyst used in the present invention comprises at least one halide ligands and at least one ligand selected from saturated or unsaturated linear, branched or cyclic alkyl groups, and optionally substituted aromatic groups.

According to an embodiment of the invention, the catalyst used comprises only alkoxides ligands. According to another embodiment of the invention, when one ligand is a cyclopentadienyl ligand which can be optionally substituted, then at least one ligand is selected from halides, preferably is chloride. The supported catalyst used in the process of the invention may be obtained by grafting the metallic compound of the type MX₄ or MLX3 on a support at room temperature (about 25°C) or by heating at a temperature up to 150°C.

Prior to the grafting stage, the support, based preferably on silica, can be subjected to a preliminary stage of calcination and/or of dehydroxylation.

The support can advantageously have a specific surface area (B.E.T.) chosen from 100 to 1200 m²/g, preferably from 125 to 350 m²/g, more particularly from 150 to 250 m²/g. The specific surface area (B.E.T.) is measured according to the standard ISO 9277: 1995. The support can be predominantly macroporous, microporous and/or mesoporous or a mixture thereof.

The support physically can be a powder, an extrudate or other shapes. The final compound is sufficiently stable to allow moulding or pelletisation of the final catalyst; during this stage a binder may be added.

The preferred silica support is generally chosen from silicon oxide substantially free from any other oxide (or containing less than 2 wt% of one or more other oxides generally present in the form of impurities).

Before use in the preparation process of the silica-supported catalyst, the silica is preferably analyzed in order to determine its hydroxyl content which should preferably be comprised between 0.5 and 3.5 OH/nm², as determined by titration and ^!Η solid state NMR. In order to comply with this preferred requirement, the silica is preferably subjected to a so-called "activation" treatment which can advantageously comprise a thermal (or dehydration) treatment. The said activation treatment makes it possible to remove the water contained in the silica precursor, and also partially the hydroxyl groups, thus allowing some residual hydroxyl groups and a specific porous structure to remain. The choice of the silica precursor will preferably impact the conditions of the activation treatment, e.g. the temperature and the pressure, in order to fulfill the above final silica characteristics; this can obviously be defined on a case by case basis depending on the selection of the silica precursor and its reaction to the activation treatment. For example, the activation treatment can be carried out under a flow of air or another gas, particularly an inert gas, e.g. nitrogen, as well as under reduced pressure (from low vacuum to ultra-high vacuum, preferably under high vacuum), at a temperature chosen from 50 to 1000°C, preferably from 100 to 900°C. According to an embodiment of the present invention, the support is subjected to an activation treatment as defined above at a temperature from 200°C to 1000°C, e.g. chosen from 200 to 700°C.

Specific examples of process for preparing the catalysts used in the invention are given in the experimental part of the present application.

According to an embodiment, the catalyst used in the process of the invention is activated before implementation of the process for dimerization.

The activation may be performed by contacting the catalyst with an activator, preferably selected from aluminum- activators such as trialkylaluminum (Q3AI, Q = methyl, ethyl, propyl, isobutyl, octyl...), ethylaluminum sesquichloride (Et₃Al₂Cl₃), diethylaluminum chloride (Et₂AlCl), diethylaluminumethoxide (Et₂A10Et), methylaluminoxane (MAO) or any combination thereof.

According to an embodiment of the invention, the activation is performed with a molar ratio Al/Ti or Al/Zr ranging from 1 to 500, preferably from 2 to 100, more preferably from 5 to 50.

According to an embodiment, the supported catalyst used in the process of the invention is selected from one of the following catalyst:

- Zr(OtBu)₄/Si0₂ catalyst,

- Ti(OtBu)₄/Si0₂ catalyst,

- TiC Si0₂ catalyst,

- CpTiCl₃/Si0₂ catalyst,

- Cp-areneTiCl₃/Si0₂ catalyst, or

- phenoxy-imineTiCl₃/Si0₂ catalyst.

Preferably, the supported catalyst used in the process of the invention is selected one of the following catalyst:

- Zr(OtBu)₄/Si0₂ catalyst,

- Ti(OtBu)₄/Si0₂ catalyst,

- CpTiCl₃/Si0₂ catalyst,

- Cp-areneTiCl₃/Si0₂ catalyst, or

- phenoxy-imineTiCl₃/Si0₂ catalyst.

According to the present invention:

- "tBu" refers to a tert-butyl group,

- "Cp" refers to a cyclo entadienyl group, -arene" refers to the following structure

- "phenoxy-imine" refers to the following structure:

In the phenoxy-imineTiCb/SiC catalyst, the titanium atom can be linked to the phenoxy imine by the oxygen atom of the OH function and optionally also by the nitrogen atom and/or by the other oxygen atom.

Reaction process

The reaction is preferably performed at a temperature comprised between 25 °C and 150°C, preferably between 25°C and 140°C, preferably from 50°C to 120°C. At higher temperatures, there is a risk that the diene polymerizes.

The reaction is preferably performed in an inert gas atmosphere, for example in argon or nitrogen atmosphere, preferably at atmospheric pressure.

The reaction is preferably performed during at least 5 hours, preferably at least 8 hours, more preferably during from 8 to 36 hours, ideally from 12 to 24 hours.

The reaction is preferably performed with a molar ratio conjugated dienes/catalyst ranging from 200 to 30000, preferably from 500 to 25000, more preferably from 1000 to 20000, even more preferably from 2000 to 10000.

The reaction is preferably performed with a molar ratio PPI13 based additive/catalyst ranging from 1 to 100, preferably from 1 to 20, more preferably from 1 to 5.

The reaction can be a batch reaction, a semi-batch reaction or a continuous reaction and preferably takes place in a stirred reactor. Upon completion of the reaction, which under the said process conditions yields a high selectivity, the resulting dimerization product can be separated off from the reactor stream in a manner known per se, for instance by distillation, absorption, etc. The dimerization product can further be submitted to a hydrogenation reaction in the presence of a hydrogenation catalyst. The step of hydrogenation may be carried out by methods well known for the skilled person. For example, the step of hydrogenation may be performed with hydrogen in the presence of a hydrogenation catalyst, such as Pd/C, Raney nickel or Ni/Al₂0₃.

After hydrogenation, hydrogenated dimers are obtained, such as crocetane, squalane or isosqualane, hydrogenated dimer of alpha-terpinene, hydrogenated dimer o f beta-phellandrene .

Preferably, dimers obtained after the hydrogenation are saturated dimers.

The process of the invention leads to reaction products containing the desired dimers which are mainly composed of head-to-tail dimers. However, a dimerization reaction of conjugated diene compounds may lead to different reaction products. The reaction products may be dimers, trimers, etc... Different dimers may be obtained, such as head-to -head dimers or head-to -tail dimers (isomers).

The process according to the present invention allows improving the selectivity of the process. In particular, the use of the supported catalyst based on titanium or zirconium allows improving the selectivity for the head-to-tail dimer, as compared to the selectivity attached to an unsupported catalyst based on titanium or zirconium complexes.

The "selectivity for compound X" refers to the amount of compound X formed in the dimerization reaction based on the total amount of products formed. The selectivity is expressed as a percentage by weight.

Preferably, the head-to-tail dimer obtained represents at least 40% by weight of the reaction products, preferably at least 45% by weight of the reaction products, more preferably at least 50%> by weight of the reaction products.

In particular, the head-to-tail dimers are generally present in greater proportions than the other reaction products.

The present invention is also directed to the use of a supported catalyst comprising a metal transition selected from titanium and zirconium for the dimerization reaction of conjugated diene compounds, in particular for the selective dimerization reaction of conjugated diene compounds.

According to an embodiment, the supported catalyst is a silica- supported catalyst as defined above in the context of the process for the dimerization. According to an embodiment, the conjugated diene compounds are as defined above in the context of the process for the dimerization.

According to an embodiment, the supported catalyst comprising a metal transition selected from titanium and zirconium are used to provide head-to-tail dimers, in particular to provide head-to-tail dimers representing at least 40% by weight, preferably at least 45% by weight, more preferably at least 50% by weight of the reaction products.

Within the meaning of the present invention, the expression "reaction products" refers to all the products obtained at the end of the reaction (dimers, trimers, etc). The conjugated diene compounds (the reactants of the reaction) are not taken into account when we deal with the reaction products.

The present invention is also directed to a supported catalyst comprising a transition metal selected from titanium and zirconium and ligands.

According to the invention, when one ligand is a cyclopentadienyl ligand which can be optionally substituted, then at least one ligand is selected from halides, preferably is chloride. The activation of the supported catalyst may be improved by the presence of at least one halide ligand, since it is generally easier to alkylate a metal-halide bond than another bond such as a metal-oxygen bond. According to an embodiment, the supported catalyst of the invention may be a monopodal catalyst or a bipodal catalyst.

The monopodal catalyst may be represented by the structures (VIII) or (IX) as defined above in the context of the process of the invention. According to an embodiment, the catalysts of the present invention comprises at least one support oxide selected from silica, alumina, silica-alumina, preferably from silica.

The silica- supported catalysts of the invention may be represented by the following expression:

MX4/S1O2 or LMX3/S1O2, wherein M represents either the titanium metal or the zirconium metal and wherein X and L represent a ligand, preferably as defined above. In the above expression, MX₄ or LMX3 represents the (homogeneous) complex, before contact with the support. The ligand X may be identical or different in each catalyst. Indeed, it is possible that the supported catalyst comprises 3 different ligands.

Among halide ligands, mention may be made of chloride, fluoride, and iodide.

According to an embodiment, L is selected from substituted phenoxy-imine, phosphonimide, iminoimidazolidide, hydrocarbon ligands such as cyclopentadienyl or indenyl or fluorenyl group and cyclopentadienyl ligand with pendant ligand such as phenyl, amide, sulfur, ether.

Preferably, the ligands L may be selected from cyclopentadienyl or indenyl or fluorenyl with or without pendant ligand or from phenoxyimine with methoxy group as pendant ligand.

Ti and wherein the carbon atom may be linked to two atoms selected from hydrogen or carbon atoms. Phosphonimide ligands refer to the following bonds: M-N=PPv3 wherein M represents Zr or Ti and wherein R represents an alkyl or an aromatic radical. The alkyl and phenyl radical may optionally be substituted. According to a preferred embodiment, the catalyst used in of the present invention comprises at least one ligand selected from alkoxides, halides, amines, imines, phenoxides and hydrocarbon ligands, preferably from alkoxides, halides and hydrocarbon ligands, more preferably from halides.

According to a further embodiment, the catalyst of the present invention comprises at least one halide ligands and at least one ligand selected from saturated or unsaturated linear, branched or cyclic alkyl groups, and optionally substituted aromatic groups.

According to an embodiment of the invention, the catalyst comprises only alkoxides ligands.

The supported catalyst of the invention may be obtained by grafting the metallic compound of the type MX₄ or MLX3 on a support at room temperature (about 25°C) or by heating at a temperature up to 150°C.

Prior to the grafting stage, the support, based preferably on silica, can be subjected to a preliminary stage of calcination and/or of dehydroxylation, such as defined above in the context of the catalyst used in the process of the invention

Specific examples of process for preparing the catalysts of the invention are given in the experimental part of the present application.

According to an embodiment, the catalyst of the invention is activated before implementation of the process for dimerization, as defined in the context of the process of the invention.

According to an embodiment, the supported catalyst of the invention is selected from one of the following catalyst:

- Zr(OtBu)₄/Si0₂ catalyst,

- Ti(OtBu)₄/Si0₂ catalyst,

- TiCl₄/Si0₂ catalyst,

- CpTiCl₃/Si0₂ catalyst,

- Cp-areneTiCl₃/Si0₂ catalyst, or - phenoxy-imineTiCl₃/Si0₂ catalyst.

Preferably, the supported catalyst of the invention is selected from one of the following catalyst:

- Zr(OtBu)₄/Si0₂ catalyst,

- Ti(OtBu)₄/Si0₂ catalyst,

- CpTiCl₃/Si0₂ catalyst,

- Cp-areneTiCl₃/Si0₂ catalyst, or

- phenoxy-imineTiCl₃/Si0₂ catalyst.

EXAMPLES

Example 1 : Description of the tests

- Material used:

All materials were, unless stated otherwise, commercially available. In particular: Silica (aerosil® 200) available for example from Evonik Company,

Titanium(IV) tert-butoxide (99.95%), Zirconium(IV) tert-butoxide (99.99%), Titanium(IV) tetrachloride (99%), Titanium(IV) trichloride cyclopentadienyl, Magnesium (99.8%) chips are commercially available for example from Strem.

Diethylaluminium chloride (97%), Palladium on carbon extent of labeling: 10 wt loading matrix activated carbon support, Nonadecane (99%>), Phosphorus trichloride (99%), Triethylamine (99.5%), Deuterium oxide (99.8%), Formic acid (96%), p-Cresol (99%), n-Butyllithium solution (1.6 M in hexane), l-Bromo-3,5-dimethylbenzene (97%), 6,6-Dimethylfulvene (≥97.0%), 1-Adamantanol (99%), Acetic acid (>99.7%), Hexamethylenetetramme (>99.0%), 2-Iodoaniline (98%), 2-Methoxyphenylboronic acid (95%), are available for example from Aldrich.

Beta-farnesene used herein can be prepared as described in U.S. Pat. No. 7,399,323 Bl . Triphenylphosphine (99%) and Sodium isopropoxide (95%>) are available for example from Alfa Aesar.

Sodium Chloride (100%) and Silica 60 M (0.04-0.063 mm) for column chromatography are available for example from VWR chemicals Prolabo and Macherey Nagel respectively.

- Analytical methods

Solution NMR spectra were recorded on a DRX300 Bruker spectrometer, operating at 300 MHz for Ή NMR, 75.4 MHz for ¹³C NMR, 282.2 MHz for ¹⁹F NMR and 121.4 MHz for ³¹P NMR. Chemical shift values for 1H ¹³C and ³¹P NMR spectra are referenced to Me4Si, the residual solvent, and 85% phosphoric acid, respectively. Solid state ^!H MAS, ¹³C CP/MAS and ³¹P HPDEC-NMR studies were recorded on a DSX-300 or a Bruker Avance 500 spectrometer equipped with a standard 4 mm double- bearing probehead. Samples were introduced under argon in a zirconia rotor, which was then tightly closed. For all the experiments the rotation frequency was set to 10 kHz. DRIFT spectra were recorded on a Nicolet 6700 FT-IR spectrophotometer. Typically, 64 scans were accumulated for each spectrum with 4 cm^"1 resolution in an airtight cell with CaF₂ window.

Gas chromatography (GC) analyses were conducted on a Hewlett Packard 5890 Series II gas chromatograph equipped with a flame ionization detector (GC-FID). The analytical column is HP-5 (30 m x 0.32 mm, 0.25 μιη), operating under flow of 1 ml/min. The method used to separate iso-squalane and squalane is based on approximate boiling point and small structure differences using an oven ramp from 150°C to 320°C. The heating rate is controlled at 25°C/min to 300°C and then slowed to 2°C/min to 320°C. The products are identified by their retention time. GC-FID was used for quantification of the conversion after the dimerization reaction using nonadecane as internal standard. Quantification is based on peak area of squalane, identified by matching the GC retention time for a known analytical reference standard of squalane having a purity of 99%. Extensive structural determination and analysis were carried out in an Agilent 6850/5975C GC-MS equipped with HP5-MS column (30 m x 0.25 mm, 0.25 μιη). Assignment of the separated compounds was done by comparing the mass fragment to the NIST08 database and retention time of commercial products, if available.

- General procedure for the tests

Reactions were carried out under argon atmosphere (industrial grade, Air Liquide), using Schlenk and glovebox techniques for organometallic synthesis. Chemicals were obtained from commercial suppliers and used as received unless otherwise noted. All solvents for catalytic reactions were dried under standard procedures (toluene under Na, heptane under Na/K and isopropanol under Mg), distilled and degassed via four freeze- pump-thaw cycles before use.

Feedstocks were purified according to the following method. In case a solvent was used for the reaction, beta-farnesene was first mixed with heptane and purified with activated alumina (at 500 °C under high vacuum) in a stirred Schlenk overnight at room temperature. The solution was then filtered through a bed of silica activated at 500 °C and degassed by four freeze-pump-thaw cycles and stored in the glove box. Example 2: Synthesis of the supported catalysts

Example 2a: Synthesis of supported catalysts of alkoxide Ti or Zr on silica dehydroxylated at 200°C

The silica supported monopodal catalysts of Ti and Zr were obtained by impregnation of the respectively alkoxide catalyst (M(OtBu)4) on a silica dehydroxylated at 200°C (Silica2oo) using a double schlenk technique. The reaction may be illustrated by the following scheme:

M = Ti, Zr

The double schlenk apparatus is divided into two compartments connected via a frit. In the glovebox, the first compartment A is charged with the organometallic species (Titanium(IV) tert-butoxide, 142 mg, 0.4 mmol or Zirconium (IV) tert-butoxide, 153 mg, 0.45 mmol) while the second one is charged with the desired support (Silica2oo, 1 g, 0.8 mmol OH). After evacuation using the high vacuum line, the solvent (ether, 20 mL) is condensed in compartment A by a trap-to-trap process. The complex solution is then transferred to the compartment B and stirred for 2h30 at room temperature. At the end of the reaction, the suspension is filtered through the frit and the solvent condensed back to the compartment B. Washing cycles, namely filtration(x3)/condensation(x2), are repeated until excess of complex on the support in B is totally removed.. The resulting powder is dried under vacuum to remove solvent traces, before being stored in the glovebox (usually at -30°C).

Example 2b: Synthesis of supported catalysts of Titanium chloride on silica dehydroxylated at 200°C

The silica supported catalyst of Ti was obtained by impregnation of the titanium(IV) tetrachloride (TiCU) on a Silica dehydroxylated at 200°C (Silica2oo) using a double schlenk technique. The reaction may be illustrated by the following scheme:

The double schlenk apparatus is divided into two compartments connected via a frit. In the glovebox, the first compartment A is charged with the organometallic species (Titanium Tetrachloride, 171 mg, 1.2 mmol) while the second one is charged with the desired support (Silice2oo, 1 g, 0.8 mmol OH). After evacuation using the high vacuum line, the solvent (toluene, 20 mL) is condensed in compartment A by a trap-to-trap process. The complex solution is then transferred to the compartment B and stirred for 2h30min at room temperature. At the end of the reaction, the suspension is filtered through the frit and the solvent condensed back to the compartment B. Washing cycles, namely filtration(x3)/condensation(x2), are repeated until excess of complex on the support in B is totally removed. The resulting powder is dried under vacuum to remove solvent traces, before being stored in the glovebox (usually at -30°C).

Example 2c: Synthesis of supported catalysts of Titanium on silica dehydroxylated at 700°C

The silica supported monopodal catalysts of titanium were obtained by impregnation of the respectively metallocene and phenoxy-imine complex on a Silica dehydroxylated at 700°C (Silica7oo) using a double schlenk technique. The reaction may be illustrated by the following scheme:

The double schlenk apparatus is divided into two compartments connected via a frit. In the glovebox, the first compartment A is charged with the organometallic species { (CyclopentadienylTitanium Trichloride (IV), 43 mg, 0,2 mmol) or (Cyclopentadienyl- AreneTitanium Trichloride (IV), 71 mg, 0,2 mmol) or (Phenoxy-ImineTitanium Trichloride (IV), 135 mg, 0,2 mmol)} while the second one is charged with the desired support (Silica7oo, 0.5 g, 0.15 mmol OH). After evacuation using the high vacuum line, the solvent (ether, 20 mL) is condensed in compartment A by a trap-to-trap process. The complex solution is then transferred to the compartment B and stirred for 2h30min at room temperature. At the end of the reaction, the suspension is filtered through the frit and the solvent condensed back to the compartment B. Washing cycles, namely filtration(x3)/condensation(x2), is repeated until excess of complex on the support in B is totally removed. The resulting powder is dried under vacuum to remove solvent traces, before being stored in the glovebox (usually at -30°C).

Example 3: Dimerization of farnesene using a homogeneous (complex) catalyst

Example 3a: Homogeneous catalysis with TiiO'Bu)^ or ZriO'Bu)^

In a glove box, the catalyst based on complexes Ti(OT3u)4 or Zr(OT3u)4 (0.048 mmol, 20 mg, 1 eq), triphenylphosphine (0.053 mmol, 14 mg, 1.1 eq,) and toluene (3 mL) were charged in a 20 mL schlenk. Then, to this mixture was added a solution of Et₂AlCl (1 M in heptane, 0.86 mL, 18 eq) and stirred for 20 min. After that, beta-farnesene (0.024 mol, 4.9 g, S/C = 500) was added to this mixture and stirred for 12 h at 110°C. Then, the mixture was cooled, removed from the glovebox and under argon, 1.5 mL of isopropanol was added to quench the reaction. An aliquot of the crude is injected in GC- FID to determine if there is any conversion. Finally, the crude of the dimerization reaction was filtrated through a small neutral alumina path on Buchner fritted disc (N°4) funnel, washed several times with toluene. The solvent was evaporated in the rotavapor and the product was stored in the fridge.

Example 3b: Homogeneous catalysis with CpTiCh

In a glove box, the catalyst CpTiCb (0.016 mmol, 3.5 mg, 1 eq) and toluene (3 mL) were charged in a 20 mL schlenk. Then, to this mixture was added a solution of Et₂AlCl (1 M in heptane, 0.3 mL, 18 eq) and stirred for 20 min. After that, beta-farnesene (8 mmol, 1.6 g, S/C = 500) was added to this mixture and stirred for 12 h at 110°C. Then, the mixture was cooled, removed from the glovebox and under argon, 1.5 mL of isopropanol was added to quench the reaction. An aliquot of the crude is injected in GC- FID to determine if there is any conversion. Finally, the crude of the dimerization reaction was filtrated through a small neutral alumina path on Buchner fritted disc (N°4) funnel, washed several times with toluene. The solvent was evaporated in the rotavapor and the product was stored in the fridge. Example 3c: Homogeneous catalysis with Cp-arene TiCh

In a glove box, the catalyst Cp-arene TiCh (0.016 mmol, 6 mg, 1 eq) and toluene (3 mL) were charged in a 20 mL schlenk. Then, to this mixture was added a solution of Et₂AlCl (1 M in heptane, 0.3 mL, 18 eq) and stirred for 20 min. After that, beta- farnesene (8 mmol, 1.6 g, S/C = 500) was added to this mixture and stirred for 12 h at 110°C. Then, the mixture was cooled, removed from the glovebox and under argon, 1.5 mL of isopropanol was added to quench the reaction. An aliquot of the crude is injected in GC-FID to determine if there is any conversion. Finally, the crude of the dimerization reaction was filtrated through a small neutral alumina path on Buchner fritted disc (N°4) funnel, washed several times with toluene. The solvent was evaporated in the rotavapor and the product was stored in the fridge.

Example 3d: Homogeneous catalysis with Phenoxy-imine TiCh

In a glove box, the Phenoxy-imine TiCh catalyst (0.016 mmol, 10 mg, 1 eq) and toluene (3 mL) were charged in a 20 mL schlenk. Then, to this mixture was added a solution of Et₂AlCl (1 M in heptane, 0.3 mL, 18 eq) and stirred for 20 min. After that, beta- farnesene (8 mmol, 1.6 g, S/C = 500) was added to this mixture and stirred for 12 h at 110°C. Then, the mixture was cooled, removed from the glovebox and under argon, 1.5 mL of isopropanol was added to quench the reaction. An aliquot of the crude is injected in GC-FID to determine if there is any conversion. Finally, the crude of the dimerization reaction was filtrated through a small neutral alumina path on Buchner fritted disc (N°4) funnel, washed several times with toluene. The solvent was evaporated in the rotavapor and the product was stored in the fridge. Example 4: Dimerization of farnesene using a heterogeneous (supported) catalyst

Example 4a: Heterogeneous catalysis with TUO'Bu)^ ZriO'Bu)^ supported on silica dehydroxylated at 200°C (SiOi 200 x1)

In a glove box, the supported catalyst prepared according to the synthesis method of example 2a, based on complexes Ti(OT3u)4 or Zr(OT3u)4 (3 mL), named Ti(OⁱBu)4/Si0_{2 2}oo°c and Zr(OT3u)4/Si0_{2 2}oo°c, were charged in a 20 mL schlenk. Then, to this mixture was added a solution of Et₂AlCl (1 M in heptane, 0.63 mL, 18 eq) and stirred for 20 min. After that, beta- farnesene (1.75 mmol, 355 mg, S/C = 500) was added to this mixture and stirred for 12 h at 110°C. Then, the mixture was cooled, removed from the glovebox and under argon, 1.5 mL of isopropanol was added to quench the reaction. An aliquot of the crude is injected in GC-FID to determine if there's any conversion. Finally, the crude of the dimerization reaction was filtrated through a small neutral alumina path on Buchner fritted disc (N°4) runnel, washed several times with toluene. The solvent was evaporated in the rotavapor and the product was stocked in the fridge. Example 4b: Heterogeneous catalysis with TiCU supported on silica dehydroxylated at

In a glove box, the supported catalyst prepared according to the synthesis method of example 2b, based on a TiCU complex, named TiCU /S1O2-200 °c, (0.0075 mmol, 10 mg, 1 eq), triphenylphosphine (20 mg, 0.076 mmol, 1.1 eq) and toluene (3 mL) were charged in a 20 mL schlenk. Then, to this mixture was added a solution of Et₂AlCl (1 M in heptane, 1.3 mL, 18 eq) and stirred for 20 min. After that, beta-farnesene (3.75 mmol, 766 mg, S/C = 500) was added to this mixture and stirred for 12 h at 110°C. Then, the mixture was cooled, removed from the glovebox and under argon, 1.5 mL of isopropanol was added to quench the reaction. An aliquot of the crude is injected in GC- FID to determine if there's any conversion. Finally, the crude of the dimerization reaction was filtrated through a small neutral alumina path on Buchner fritted disc (N°4) funnel, washed several times with toluene. The solvent was evaporated in the rotavapor and the product was stocked in the fridge. Example 4c: Heterogeneous catalysis with CpTiCh supported on silica dehydroxylated at 700°C (SiQ₂ 700 x)

In a glove box, the supported catalyst prepared according to the synthesis method of example 2c, based on a CpTiCh complex, named CpTiCl3/Si0₂-7oo°c, (0.0035 mmol, 10 mg, 1 eq) and toluene (3 mL) were charged in a 20 mL schlenk. Then, to this mixture was added a solution of Et₂AlCl (1 M in heptane, 0.63 mL, 18 eq) and stirred for 20 min. After that, beta-farnesene (1.75 mmol, 357 mg, S/C = 500) was added to this mixture and stirred for 12 h at 110°C. Then, the mixture was cooled, removed from the glovebox and under argon, 1.5 mL of isopropanol was added to quench the reaction. An aliquot of the crude is injected in GC-FID to determine if there's any conversion. Finally, the crude of the dimerization reaction was filtrated through a small neutral alumina path on Buchner fritted disc (N°4) funnel, washed several times with toluene. The solvent was evaporated in the rotavapor and the product was stocked in the fridge.

Example 4d: Heterogeneous catalysis with Cp-areneTiCli_supported on silica dehydroxylated at 700°C (SiOi 700 x1)

In a glove box, the supported catalyst prepared according to the synthesis method of example 2c, based on a Cp-arene T1CI3 complex, named Cp-arene TiCl3/Si0₂-7oo°c, (0.0035 mmol, 10 mg, 1 eq) and toluene (3 mL) were charged in a 20 mL schlenk. Then, to this mixture was added a solution of Et₂AlCl (1 M in heptane, 0.63 mL, 18 eq) and stirred for 20 min. After that, beta-farnesene (1.75 mmol, 357 mg, S/C = 500) was added to this mixture and stirred for 12 h at 110°C. Then, the mixture was cooled, removed from the glovebox and under argon, 1.5 mL of isopropanol was added to quench the reaction. An aliquot of the crude is injected in GC-FID to determine if there's any conversion. Finally, the crude of the dimerization reaction was filtrated through a small neutral alumina path on Buchner fritted disc (N°4) funnel, washed several times with toluene. The solvent was evaporated in the rotavapor and the product was stocked in the fridge.

Example 4e: Heterogeneous catalysis with phenoxy-imineTiCl ^supported on silica dehydroxylated at 700°C (SiOi wf c)

In a glove box, the supported catalyst phenoxy-imine Titanium-trichloride prepared according to the synthesis method of example 2c, based on a phenoxy-imine T1CI3 complex, named (FI)TiCl3/Si0₂-7oo°c (FI = phenoxyimine), (0.0035 mmol, 10 mg, 1 eq) and toluene (3 mL) were charged in a 20 mL schlenk. Then, to this mixture was added a solution of Et₂AlCl (1 M in heptane, 0.63 mL, 18 eq) and stirred for 20 min. After that, beta-farnesene (1.75 mmol, 357 mg, S/C = 500) was added to this mixture and stirred for 12 h at 110°C. Then, the mixture was cooled, removed from the glovebox and under argon, 1.5 mL of isopropanol was added to quench the reaction. An aliquot of the crude is injected in GC-FID to determine if there's any conversion. Finally, the crude of the dimerization reaction was filtrated through a small neutral alumina path on Buchner fritted disc (N°4) funnel, washed several times with toluene. The solvent was evaporated in the rotavapor and the product was stocked in the fridge.

Example 5: Hydrogenation of the crude dimerization reaction obtained in examples 3 and 4

The crude of the dimerization reaction (0.089 g) was charged in a stainless steel autoclave with 10 wt% Pd/C (150 mg), 5 mL of toluene, 40 bar of H₂ and stirred for 12 h at 85 °C. After that, an internal standard nonadecane (80 mg) was added to the hydrogenated mixture and an aliquot was injected in the GC-FID to obtain the conversion and selectivity on squalane and isosqualane. The conversion was mainly calculated based on the latter method unless further specification. The diene conversion refers to the amount in percentage by weight of diene that has reacted. Example 6: Characterization of the reaction products of the dimerization reactions obtained in example 5

Example 6a: Characterization of example 4a and of example 3a

Comparison of the selectivity obtained with a homogeneous catalysis and a heterogeneous catalysis is detailed in the table 1 below for the Ti(OtBu)₄ based catalyst and the Zr(OtBu)₄ based catalyst.

The conditions of the dimerization reactions are summarized below:

schlenk: 20 mL,

time: 12 hour,

- temperature: 100°C,

molar ratio farnesene/(Zr or Ti): 500,

- mo lar ratio Et₂ AlCl/(Zr or Ti) : 18 ,

molar ratio PPh₃/(Zr or Ti): 1.1,

- toluene (solvent): 5 mL.

Table 1 : conversion and selectivities

As illustrated in table 1 , the heterogeneous catalysts according to the invention provide an improved selectivity towards the head-to-tail dimer (iso-squalane), as compared with the "corresponding" homogeneous catalyst.

Even if the conversion may be lower with the heterogeneous catalyst, from an industrial point of view, improving the selectivity is very useful, for example for the further valorization of the products obtained. Additionally, conversion may be improved for example by increasing the temperature or adjusting another operating parameter. Example 6b: Characterization of examples 4c, 4d and 4e and of examples 3b, 3c and 3d

Comparison of the selectivity obtained with a homogeneous catalysis and a heterogeneous catalysis is detailed in the table 2 below for the CpTiCb based catalyst, for the Cp-arene-TiCb based catalyst and for the phenoxy-imineTiCb based catalyst.

The conditions of the dimerization reactions are summarized below:

schlenk: 20 mL,

- time: 12 hour,

- temperature: 100°C,

molar ratio farnesene/Ti: 500,

- molar ratio Et₂AlCl/Ti: 18,

- toluene (solvent): 5 mL.

Table 2: conversion and selectivities

As illustrated in table 2, the heterogeneous catalysts according to the invention provide an improved selectivity towards the head-to-tail dimer (iso-squalane), as compared with the "corresponding" homogeneous catalyst. Example 7: Influence of ligand X on the activity and selectivity

Comparison of the selectivity obtained with the catalysts of examples 4a and 4b is detailed in table 3 below.

The conditions of the dimerization reactions are summarized below:

schlenk: 20 mL,

time: 12 hour,

- temperature: 100°C,

- molar ratio farnesene/Ti: 500,

- molar ratio Et₂AlCl/Ti: 18,

molar ratio PPh₃/Ti: 1.1,

- toluene (solvent): 5 mL.

Table 3 : conversion and selectivities

As illustrated in table 3, both catalysts TiCl₄/Si0₂_₂oo°c and Ti(OtBu)₄/Si0₂ provide a high conversion in dimerization reaction. The catalyst with alkoxide ligands (Ti(OtBu)₄/Si0₂) provides a very good selectivity, of more than 60%.

Claims

1. A process for the dimerization of conjugated diene compounds comprising contacting, in a reaction medium, said conjugated diene compounds with a supported catalyst comprising ligands and a transition metal selected from titanium and zirconium.

2. The process according to claim 1, wherein the reaction medium comprises a solvent comprising hydrocarbons.

3. The process according to claim 1 , wherein the reaction medium is solvent free.

4. The process according to any one of claims 1 to 3, wherein at least one ligand is selected from alkoxides, halides, amines, imines, phenoxides and hydrocarbon ligands.

5. The process according to any one of claims 1 to 4, wherein the ligands are selected from halides and hydrocarbon ligands.

6. The process according to any one of claims 1 to 4, wherein the ligands are selected from alkoxides.

7. The process according to any one of claims 1 to 6, wherein the reaction medium further comprises one or more additive selected from phosphine based additives, tertiary amines, sulfur compounds, ethers, tetrahydrofurane and dioxane, preferably selected from triphenylphosphine (PPh₃), tritolyl phosphine, tribenzylphosphane (PBn₃), dimethylphenylphosphine (PMe2Ph).

8. The process according to any one of claims 1 to 7, wherein the conjugated diene compounds are terminal conjugated diene compounds.

9. The process according to any one of claims 1 to 8, wherein the conjugated diene compounds are asymmetric conjugated diene compounds.

10. The process according to any one of claims 1 to 9, wherein the conjugated diene compounds have the following formula (I):

wherein R¹, R², R³, R⁴, R⁵ and R⁶ represent, independently to each other, a hydrogen atom, a halogen atom or a hydrocarbyl radical, linear, branched or cyclic, saturated or unsaturated, optionally comprising one or more heteroatoms, being understood that at least one of the R¹ is different from all the others R¹, i being selected from 1, 2, 3, 4, 5 or 6.

11. The process according to any one of claims 1 to 10, wherein the conjugated diene compounds have the following formula (II):

wherein R is a hydrocarbyl radical having 1 to 20 carbon atoms, preferably having 2 to 15 carbon atom, optionally comprising one or more heteroatoms, such as nitrogen, oxygen or sulphur.

12. The process according to any one of claims 1 to 11, wherein the conjugated diene compounds are selected from myrcene or farnesene.

13. The process according to any one of claims 1 to 12, wherein head-to-tail dimers representing at least 40% by weight of the reaction products, preferably at least

45%) by weight of the reaction products, more preferably at least 50%> by weight of the reaction products, are obtained.

14. The process according any one of claim 1 to 13, further comprising a hydrogenation step, whereby hydrogenated dimers are obtained, preferably saturated dimers are obtained.

15. A supported catalyst comprising a transition metal selected from titanium and zirconium and ligands selected from alkoxides, halides, amines, imines, phenoxides and hydrocarbon ligands, being understood that if one ligand is a cyclopentadienyl ligand, the metal is linked to at least one halide ligand.

16. The catalyst according to claim 15, wherein the ligands are selected from halides and hydrocarbon ligands.

17. The catalyst according to claim 15, wherein the ligands are selected from alkoxides.

18. Use of the supported catalyst according to any one of claims 15 to 17 for the dimerization of conjugated diene compounds.