Linear a-olefins represent an important petrochemical material. Their applications, depending on the number of carbon atoms, range from their use as comonomers in the production of polyethylenes, their use as plasticizers and synthetic lubricants, to their use as intermediates in the production of detergent alcohols. In particular, linear a- olefins having from 4 to 8 carbon atoms are widely used as comonomers for the production of polyethylenes with varying degrees of density and crystallinity, particularly suitable for producing end-products by means of filming and injec- tion moulding processes.

The possible oligomerization of ethylene to 1-hexene, 1-octene and also 1-butene, seems to be an interesting syn-

thesis method due to the great demand for these monomers.

According to US-A-3,644, 563 (Shell), homogeneous cata- lysts based on organometallic complexes of nickel compris- ing a bidentate ligand (P-0) on which the catalytic activ- ity and selectivity depend, are used for oligomerizing eth- ylene. The catalytic precursor is prepared at 40°C by the reaction of NiCl2 and said bidentate ligand P-O (such as for example diphenylphosphinoacetic acid and diphenylphos- phinobenzoic acid) in the presence of ethylene and a reduc- ing agent, such as NaBH4.

The oligomerization, on the other hand, is carried out at 120°C and 14 MPa (140 bar). The olefins obtained accord- ing to this process have a high linearity and their molecu- lar weights follow a Shulz Flory distribution.

The process therefore has the disadvantage of requir- ing rather drastic pressure and temperature conditions, and of give a wide distribution of a-olefins.

US-A-4,783, 573 (Idemitsu) describes a process in which ethylene is oligomerized at 3.5 MPa and 120°C, in the pres- ence of a catalytic system which comprises ZrCl4, aluminum alkyls and a Lewis base which can be selected from various groups of organic compounds containing heteroatoms, such as alkyldisulfides, thioethers, thiophenes, phosphines and primary amines. The olefins obtained are mainly C4-C8 but considerable quantities of heavy olefins are still present

(generally C1OF > 40-50%) and their preparation moreover also requires high temperatures and pressures.

EP-A-681,106 (Phillips) describes catalytic systems based on chromium (III) alkanoates, which are generally acti- vated with aluminum alkyl AlEt3 mixed with AlClEt2, in the presence of a pyrrole, or one of its alkaline salts, and a halogenating agent, preferably GeCl4, used at temperatures of about 100°C with ethylene pressures higher than 40 atm.

These chromium catalytic systems only produce 1-hexene with a selectivity of over 99% and a high activity at a high ethylene pressure, as polyethylene is obtained at low pres- sures.

International patent application WO 92/10446 (Institut Francaise du Petrol) describes a process for converting ethylene to linear a-olefins in the presence of a catalyst consisting of a zirconium alcoholate, an aluminum chloro- alkyl and an ether. Although the catalyst is active under relatively bland conditions, neither the selectivity of the process towards olefins having 4,6 and 8 carbon atoms nor the distribution of the product among these compounds, which is too orientated towards the production of 1-butene, are satisfactory.

The Applicant has now found that particular complexes of light transition metals substantially overcome the above drawbacks and allow the preparation of oligomerization

catalysts of ethylene which are advantageously selective towards the production of 1-hexene and 1-octen.

In accordance with this, a first object of the present invention relates to any sulfonic complex of a transition metal included in general formula (I) : [MXiX2X3 (X4) nYjs (I) or a mixture of two or more of said complexes, wherein: M is a metal selected from zirconium or hafnium in oxidation state 3 or 4, preferably zirconium, more preferably zirconium in oxidation state 4; X1, X2, X3 and X4 each independently represent any or- ganic or inorganic ligand of an anionic nature, bonded to the metal M as anion in an ionic couple or with a covalent bond ; each Y independently represents a ligand consisting of a neutral sulfonic compound containing the group (>SOz) bonded to two carbon atoms and coordinated to the metal M by means of at least one oxygen atom, "n"has the values of 0 or 1 respectively, if the oxi- dation state of the metal M is 3 or 4, and is prefera- bly 1 ; "m"represents the number of sulfonic ligands Y coor- dinated to M and can have any decimal value equal to or lower than 2, preferably from 1 to 2, extremes in- cluded, and

"s"has integer values ranging from 1 to 6, preferably from 1 to 2, extremes included, on the condition that when X1 = X2 = X3 = X4 = Cl,"n"is 1 and"s"is 2, Y is different from sulfolane (CAS number [126-33-0]).

Another object of the present invention relates to a process for the preparation of said complexes included in formula (I).

Other objects of the present invention appear evident from the following description and claims.

The sulfonic complex having formula (I) according to the present invention can be of a monomeric (s =1), dimeric (s = 2) or polynuclear (s ranging from 3 to 6) form. It has in fact been found that, depending on the nature of the ligands X, the metal M, the sulfonic compounds Y, as well as the physical state of the compound having formula (I), depending on whether it is liquid, solid or in solution, various molecular aggregation forms such as monomer or di- meric, are possible, comprising, in certain cases, one or more sulfonic ligands bridge-bonded between two metals.

Mixtures of several compounds having the above formula (I) with different"s"indexes ranging from 1 to 6 are also in- cluded in the object of the present invention.

The metal M having formula (I) is a metal of Group 4 of the periodic table of elements (as published in"The IU-

PAC Red Book, Nomenclature of Inorganic Chemistry", Black- well Science Ed., 1990, to which reference is made in the present description with the term"periodic table"), pref- erably having an oxidation state +4, although lower oxida- tion states, especially +3, are also included in the scope of the present invention.

Each of the ligands of the type X (i. e. Xi, X2, X3 or X4) independently represents any group of an anionic nature suitable for at least partially neutralizing the oxidation state of M, and can be organic or inorganic, preferably comprising from 1 to 30 atoms different from hydrogen. When X is organic, it preferably comprises from 1 to 30, more preferably from 1 to 10, carbon atoms.

Typical ligands X (Xl, X2, X3 or X4) are, for example, halides, especially chlorides and bromides, the hydroxide group, hydrogen-carbonate group, nitrates or nitrites, - NRiR2 amide or-PR1R2 phosphide groups, wherein R1 and 3R2 are each hydrogen or an alkyl or aryl group preferably hav- ing from 1 to 20 carbon atoms, optionally bonded to each other to form a cyclic structure comprising the nitrogen or phosphorus atoms, linear or branched alkoxide groups, preferably having from 1 to 10 carbon atoms, groups deriv- ing from organic acids, such as carboxylate, carbamate or xanthate, preferably having from 1 to 10 carbon atoms, lin- ear or branched alkylsulfide groups, linear, cyclic or

branched hydrocarbyl groups, especially alkyl or aryl, preferably having from 1 to 15 carbon atoms, optionally also comprising one or more halogen atoms, especially chlo- rine and fluorine, and all other groups of an anionic na- ture generally suitable, as far as is known in the art, for the formation of compounds and complexes with metals in a positive oxidation state, also including groups bonded to the metal M with bonds of the"X"or mixed"C"and"s" type, such as, for example, cyclopentadienyl or allyl hy- drocarbyl groups, and groups deriving from diketonates or ketoesters, such as, for example, ethylacetylacetate or acetylacetonate groups, all preferably having up to 15 car- bon atoms.

Furthermore, according to the present invention, two or more of the above ligands X1, X2, X3 or X4 can be aggre- gated with each other to represent a polyvalent ligand, es- pecially divalent, or a cyclic structure comprising the metal M and having from 5 to 15 atoms in the cycle, such as, for example, oxide, carbonate, sulfate, phosphate and, among the organic groups (generally preferred among polyva- lent groups), all polyfunctional anionic groups containing two or more suitable functions in the molecule selected from those characteristic of the anionic groups mentioned above, such as, for example, amide, phosphide, alkoxide, carboxylate, carbamate, xanthate, sulfide, carbyl func-

tions, including allyl, cyclopentadienyl, P-ketoesterate and ß-diketonate groups.

Typical examples of X (X1, X2, X3 or X4) groups suit- able for the purposes of the present invention are: fluoride, chloride, bromide, iodide, dimethyl-amide, dibu- tyl-amide, diphenyl-amide, bis (trimethylsilyl) -amide, di- methyl-phosphide, diphenyl-phosphide, methoxide, ethoxide, iso-propoxide, butoxide, ter-butoxide, phenoxide, 2,6-di- ter-butylphenoxide, p-fluorophenoxide, pentafluorophenox- ide, acetate, propionate, 2-ethylhexanoate, versatate, naphthenate, benzoate, N, N-diethyl-carbamate, N, N-dibutyl- carbamate, N, N-di-iso-propyl-carbamate, N, N-dicyclohexyl- carbamate, N, N-diphenylcarbamate, hydride, methyl, ter- butyl, neopentyl, phenyl, benzyl, p-fluorophenyl, pen- tafluorophenyl. Chloride, Ci-Cg alkoxide and C2-Cl2 carboxy- late ligands are particularly preferred for their commer- cial availability and solubility in solvents commonly used in the preparation of the above complexes and processes catalyzed thereby.

Y groups suitable for the purposes of the present in- vention are generally all sulfonic compounds, excluding sulfolane in the cases indicated above. This group of com- pounds is generally known in the art and is characterized by a sulfonic group having the formula >S02 bonded to two carbon atoms.

Preferred sulfonic compounds according to the present invention are those represented by the following formula (II): in cui R3 e R4, uguali o diversi tra loro, rappresentano ciascuno wherein R3 and R4, the same or different, each independ- ently represent a linear or branched, saturated or unsatu- rated, cycloaliphatic or aromatic Cl-C20, preferably Ci-Cio, hydrocarbyl group, or a Cz-C2o, preferably C1-Clo, hydrocar- byl group substituted with one or more halogen atoms, or a Cl-C20, preferably Ci-Cl0, hydrocarbyl group comprising one or more heteroatoms of Groups 14 to 16 of the periodic ta- ble of elements, preferably Si, 0, N, S, P, furthermore, R3 and R4 can be joined to each other to form a saturated or unsaturated, C4-C20, preferably C5-C12, cyclic structure, comprising the sulfur atom of the sulfonic group, said structure optionally containing one or more of the heteroa- toms indicated above.

Sulfonic compounds having formula (II) wherein R3 and R4 are two saturated or unsaturated aliphatic groups, each having from 1 to 6 carbon atoms, or joined to each other to form a saturated or unsaturated cyclic structure, having

from 5 to 8 atoms in the cycle, including the sulfur atom, are preferred according to the present invention.

Typical examples of sulfonic compounds having general formula (II) are: dimethylsulfone, diethylsulfone, dibutyl- sulfone, dicylohexylsulfone, diphenylsulfone, bis (p- methylphenyl) sulfone, bis (p-chlorophenyl) sulfone bis (p- fluorophenyl) sulfone, bis (pentafluorophenyl) sulfone, bis (2,4, 6-trimethylphenyl) sulfone, methylphenylsulfone, bu- tylphenylsulfone, tetrahydrothiophene-1, 1-dioxide (also known as sulfolane), 3-sulfolene (2, 5-dihydrothiophene-1, 1- dioxide), 2,4-dimethyl sulfolane (2,4-dimethyltetra- <BR> <BR> <BR> <BR> <BR> hydrothiophene-1, 1-dioxide), 1-(methylsulfonyl) pyrrole, 2- (methylsulfonyl) benzothioazole, 1- (phenylsulfonyl) indole, 1-(phenylsulfonyl) pyrrole, 2- (phenylsulfonyl) tetrahydro- pyrane.

In the above formula (I) the suffix"n"can have val- ues of 0 or 1. In the preferred case of tetravalent M, "n" has the value of 1. When"n"is 0, the ligand X4 is not present in the complex having formula (I) and the metal M has oxidation state +3.

The suffix"m"in the above formula (I) indicates, on the other hand, the average number of sulfonic ligands Y, also optionally different from each other, bonded to each metallic centre M. As described above, in the case of cer- tain di-or poly-nuclear complexes having formula (I), it

has been found that a sulfonic ligand Y can form a bridge between two metallic centers, thus determining a non- integer"m"index, for example having values of 0.5 to 1.5.

The suffix"s"in the formula (I) represents the mo- lecular aggregation level of the sulfonic complexes accord- ing to the present invention. It can have any integer value up to 6, depending on the nature of the metal and ligands X and Y, on the physical state and, for complexes having for- mula (I) in solution, depending on the solvent. More com- monly, the complexes having formula (I) are in the form of a monomer or dimer, with"s"equal to 1 or 2 respectively.

Within the widest scope of the above formula (I) ac- cording to the present invention, for the case in which each symbol M, Xi, Xz, X3 or X4 and Y can represent two or more elements or ligands in the same molecule, this means that said two or more elements or ligands can have differ- ent and independent meanings with respect to each other.

For example, the complex having the following structure, is included in the above formula (I):

Mixtures of any two or more complexes having formula (I) are included in the scope of the present invention as claimed herein.

The complexes having formula (I) are not generally known in literature. The complex [TiCl4 (sulfolane)] 2 was publicly made known on the occasion of the meeting"Trends in transition metal chemistry: towards the third millen- nium"24-27 February 2000, Pisa (Italy), without mentioning however any industrial use thereof.

Sulfonic complexes having formula (I) can be obtained with the known techniques for the preparation of transition metal complexes and are easily formed by the simple contact in a solution and/or suspension of an inert solvent, pref- erably a hydrocarbon or halogenated hydrocarbon, between the precursor compound having the formula MXlX2X3 (X4) n (in which the various symbols have the same meaning as the cor- responding symbols of formula (I) ) and the desired sulfonic compound, preferably selected from those having general formula (II).

A further object of the present invention therefore relates to a method for the preparation of a sulfonic com- plex having formula (I), which comprises putting a sulfonic compound corresponding to the group Y in said formula (I), pure or diluted in a hydrocarbon solvent, optionally halo- genated, in contact, under reaction conditions, with a pre-

cursor compound having the formula MXlX2X3 (X4) n, wherein the symbols M, Xi, X2x X3, X4 and"n"have the same meaning as the corresponding symbols in said formula (I), and separat- ing the complex having formula (I) thus formed.

According to a typical preparation method of the com- plexes of the present invention, the pre-selected sulfonic compound (II), pure or diluted in a hydrocarbon solvent, optionally halogenated, such as for example, pentane, hex- ane, benzene, toluene, chlorobenzene, methylene chloride, tetrachloroethane, preferably toluene, methylene chloride, even more preferably methylene chloride, is generally slowly added to a stirred mixture, comprising the precursor compound having the formula MX1X2X3 (X4) n and a solvent se- lected from those mentioned above, preferably the same sol- vent in which the sulfonic compound (II) is diluted. There are no particular temperature limitations for carrying out the formation reaction of the complex having formula (I), but it is preferable to use a temperature ranging from-30° to 70°C, even more preferably room temperature, for the ob- vious sake of simplicity. The complexing reaction between the sulfonic compound Y and the precursor MXlX2X3 (x4) n iS weakly exothermic and generally does not create any prob- lems relating to the disposal of the reaction heat. The contact times are not particularly critical and preferably range from 5 minutes to 10 hours.

The stoichiometric ratio between the sulfonic compound Y and the precursor MXiX2Xs (X4) n determines the type of com- plex having formula (I) obtained, for example using a molar ratio [Y3/E MXlX2X3 (x4) n] equal to 1, complexes having for- mula (I) are obtained in which"m"is equal to 1 and"s"is commonly equal to 2; whereas if the same molar ratio is raised to 2, complexes (I) are produced, in which"m"is usually equal to 2 and"s"= 1, even though, especially in the presence of sterically voluminous ligands, "m"can also be limited to 1.

This preparation process of the complexes according to formula (I) or their mixtures can generally be conveniently carried out with [Y]/[ MXX2X3(X4)n] ratios ranging from 0.5 to 5.0, preferably from 1 to 2.5, depending on whether one, two or more sulfonic ligands are to be obtained per M atom.

The possible excess of ligand, or residue of non-reacted ligand can usually be easily separated by precipitation or crystallization, and subsequent filtration, of the desired complex.

The solubility and stability characteristics towards atmospheric agents (humidity, oxygen) strongly depend on the X ligands present in the precursor MXlX2X3 (X4) n/as well as the type of Y sulfone used. This naturally influences the operating techniques and procedures for the separation from the reaction mixture and purification of the various

complexes having formula (I), which experts in the field can adopt according to what is known in the art and which are described in the examples subsequently provided, with- out requiring any further inventive efforts or complexity other than what is normally necessary for the setting up of a usual synthesis process.

Additional non-limiting examples of complexes accord- ing to the present invention are provided hereunder: TiCl4 (Me2SO2) 2, TiCl4 (Et2SO2)2, TiCl4 (Ph2S02) 2, [TiCl4 (Me2SO2)]2, TiBr4 (Me2SO2) 2, Ti (OMe) 4 (Me2SO2) 2, Ti (acac) C13 (Me2SO2), ZrCl4 (Me2SO2) 2, ZrCl4 (Ph2S02) 2, [ZrCl4 (Et2SO2) 2, [ZrCl4 (Ph2SO2)] 2, ZrCl4 [ (Me) (Ph) S02] 2, ZrBr4 (Me2S02) 2, ZrI4 (Me2SO2) 2, Zr (NEt2) 4 (Me2SO2) 2, Zr [N (SiMe3) 2]2Cl2(Me2SO2), Zr (OMe) 4 (Me2SO2) 2, Zr (OPh) 2Cl2 (Me2SO2) 2, Zr (OCOMe) 4 (Me2SO2), HfCl4(Me2SO2)2, [HfCl4 (Ph2SO2)] 2, HfBr4(Me2SO2)2.

Figures 1 and 2 enclosed with the present description indicate, for purely illustrative purposes which in no way limit the scope of the present invention, the molecular structures of two typical sulfonic complexes according to the present invention, obtained by means of X-ray diffrac- tometry.

In particular: figure 1 represents the molecular structure of the complex zirconium tetrachloride bis-dimethylsulfone [ZrCl4 (Me2SO2) 2] obtained according to the subsequent Exam- ple 1 ; figure 2 represents the molecular structure of the complex zirconium tetrachloride diphenylsulfone [ZrCl4 (Ph2S02)] 2 obtained according to the subsequent Exam- ple 3.

In accordance with the present invention, the above complexes having formula (I), and more generally complexes of metals of Group 4 of the period table with sulfonic com- pounds, can be advantageously used as components of a cata- lyst for the oligomerization of ethylene, for the selective production of primary linear olefins having 4,6 and 8 car- bon atoms respectively. In particular, said oligomerization catalysts allow a selectivity to be obtained, under the usual process conditions, particularly oriented towards mixtures of 1-hexene and 1-octene, which are particularly desirable in the preparation of low density linear polyeth- ylenes (LLDPE and VLDPE).

Said catalysts according to the present invention therefore comprise the following two components in contact and/or mixed with each other: A) a sulfonic complex of a metal of Group 4 having the

following formula (III) [MX1X2X3(X4)nYm]s (III) wherein the different symbols M, Xl, X2, X3t X4 and Y, as well as the indexes"n","m"and"s", have the same general and specific meaning as the corresponding sym- bols in the previous formula (I), and, in addition, Y can represent sulfolane when X1=X2= X3=X4=Cl, "n" is 1 and"s"is 2.

B) a hydrocarbyl organic compound of a metal MI selected from the elements of Groups 1,2, 12, 13 or 14 of the periodic table as defined above.

The elements C, Si and Ge are not considered metals according to the definition previously used. In particular, according to the present invention, said metal M'is se- lected from boron, aluminum, zinc, lithium, sodium, magne- sium, gallium and tin. In a preferred embodiment of the present invention, the cocatalyst (B) is an aluminum com- pound represented by the following general formula (IV): Al (R5) pZq (IV) wherein: -each R5 independently represents a linear or branched, saturated or unsaturated, cycloaliphatic or aromatic Cl-C2o hydrocarbyl group, or a Cl-C2o hydrocarbyl group substituted with one or more halogen atoms, preferably fluorine;

each Z independently represents a mono-anionic group containing at least one atom different from carbon di- rectly bonded to the aluminum ; -the indexes"p"and"q"can have any decimal numerical value ranging from 0 to 3 so that (p+q) = 3 and"p"is equal to or higher than 0. 5.

R5 is preferably a hydrocarbyl group having from 1 to 8 carbon atoms, and even more preferably is a linear or branched alkyl group having from 1 to 6 carbon atoms, such as for example, methyl, ethyl, propyl, butyl, isobutyl.

Z is preferably hydride, halide, Cl-C15 alkoxide, Ci-Cis carboxylate, C2-C2o dialkyl-amide, C3-C30 trialkyl-silyl. The case in which Z is halide, especially chlorine, is particu- larly preferred according to the present invention.

Furthermore, two or more groups independently selected from R5 and Z in the compounds having formula (IV) can be joined to each other to form a di-or polyvalent group, such as, for example, the tetramethylene group, or the di- valent oxygen atom in oxygenated oligomeric derivatives of aluminum, generally known as aluminoxanes, which are in- cluded in the scope of component (B) of the catalyst ac- cording to the present invention.

The indexes"p"and"q"preferably fall within the range of 1 to 2, extremes included. As is generally used in the empirical formula, when"s"and"q"do not have integer

values, the compound having formula (IV) consists of a mix- ture of compounds or is in the form of a dimer or trimer, as, for example, in the case of aluminum ethylsesquichlo- ride, having the formula AlEt1. 5CI1. 5.

Other examples of compounds represented by formula (IV) include: AlMe3, AlEt3, Al (i-Bu) 3, AlMe2Cl, AlEt2Cl, AlEtCl2, AlEt15Cll5, AlEt2Br, AlEt2I, AlMe2F, Alli-Bu) 2X, AlEt2H, AlMe2 (OMe), AlEt2 (OBu), AlEt2 (OCOMe), AlEt2 (OCOPh), AlMe2 (NEt2), AlMe2 (NPh2), AlMe2SiMe3.

The compounds having formula (IV) are more preferably those wherein R5 is methyl, ethyl, i-butyl and Z is chlo- rine or bromine ; more preferably the compound (IV) is AlEt2Cl. The compounds having formula (IV) can be used as component (B) alone or in a mixture of any two or more thereof.

The above catalyst can be prepared by simple contact and/or mixing of the two components (A) and (B) as defined above, either outside the oligomerization environment (pre- formed catalyst) or"in situ", i. e. inside the oligomeriza- tion reactor. The order of addition of the two components is not particularly critical. In the case of the preformed catalytic system, component (A) comprising the desired quantity of the complex having general formula (III), ei- ther in pure form, or in the solid or liquid state, or di-

luted in a suitable solvent, preferably the same in which component (B) is diluted, is generally added to a solution of compound (B) in a suitable inert solvent. Said solvent is preferably selected from aromatic hydrocarbons, also partially halogenated, such as benzene, toluene, xylenes, mesitylene, chloro-benzene, fluoro-benzene, aliphatic hy- drocarbons such as pentane, hexane, heptane, octane, alicy- clic hydrocarbons, such as cyclohexane, methyl-cyclohexane, or a mixture of any two or more thereof.

According to the present invention, the two components (A) and (B) may also, each independently, comprise an inert solid material with the function of carrier, preferably se- lected from inert organic and inorganic solids generally used for the purpose in analogous oligomerization or polym- erization processes of olefins such as, for example, alu- mina, silica, silico-aluminas, titania, zirconia, polysty- rene. When used, this inert solid carrier preferably con- sists of from 40 to 99% by weight of the catalyst, exclud- ing the weight of the possible solvent. Supporting methods are known to experts in the field, for example, by means of deposition and adsorption. According to a particular as- pect, said supported catalyst can be obtained by putting said carrier in contact with the two components (A) and (B) contemporaneously during the formation of the catalyst, or with the catalyst already preformed.

In the formation of the catalyst according to the pre- sent invention, the two components (A) and (B) are put in contact with each other and mixed in such quantities that the atomic ratio between the metal M'of component (B) and the metal M of component (A) ranges from 2 to 2000, pref- erably from 5 to 1000, even more preferably from 10 to 300.

The mixture thus obtained is catalytically active and can be used immediately or left to age, without undergoing substantial modifications in its characteristics, for times varying from a few minutes to a week. There are no particu- lar temperature limitations for effecting the contact and reaction between the two components. This preferably ranges from-20° to 130°C, more preferably from 0 to 80°C, even more preferably 25°C is selected.

The oligomerization process of ethylene using the above catalyst according to the present invention is car- ried out by putting ethylene, or a gas containing ethylene, in contact with said catalyst under certain pressure and temperature conditions, preferably in the presence of a solvent and/or diluent. In the preferred embodiment, a sol- vent/diluent is used, selected from aliphatic, aromatic and cycloaliphatic hydrocarbons, preferably having from 3 to 8 carbon atoms. In another preferred embodiment of the pres- ent invention, the solvent/diluent is selected from an a- olefin or a mixture of two or more a-olefins, preferably

having from 4 to 26 carbon atoms, more preferably having an even number of carbon atoms ranging from 4 to 26.

The gas containing ethylene which can be used in the process of the present invention comprises an inert gas containing ethylene, polymerization grade ethylene (for ex- ample high purity ethylene). In the preferred embodiment, the process of the present invention uses high purity eth- ylene.

The process temperature of the present invention can vary from 5 to 200°C, preferably from 20 to 150°C.

As far as the pressure is concerned, this is usually lower than 10 MPa, preferably from 0.05 to 7 MPa, even more preferably from 0.1 to 4 MPa.

In the preferred embodiment, the catalytic system and ethylene are charged at the desired pressure and the pres- sure is kept constant during the oligomerization reaction.

The reaction products prevalently consist of 1-butene, 1-hexene and 1-octene and other higher linear a-olefins having an even number of carbon atoms ; 1-hexene is preva- lently obtained, together with surprisingly high quantities of 1-octene, with respect to what is so far known in the art. The quantity of undesired higher oligomers which in- evitably form a by-product of the process is, in fact, sig- nificantly reduced, even if the process is carried out un- der low production conditions of 1-buten. Under the opti-

mum pressure and temperature conditions (P ranging from 2 to 4 MPa, T ranging from 60° to 140°C) the process carried out in the presence of the catalyst according to the pres- ent invention allows an oligomerization product consisting of over 60% by weight of 1-hexene and 1-octene, to be ob- tained.

The a-olefins thus produced can be separated from the raw reaction product according to methods known to experts in the field, particularly by means of distillation.

The following examples are provide for a better under- standing of the present invention.

EXAMPLES The analytical techniques and characterization methods listed and briefly described below were used in the follow- ing examples.

The characterization by means of FTIR spectroscopy was effected on a Nicolet spectrophotometer mod. 510.

The characterization by means of 1H-NMR spectroscopy, mentioned in the following examples, was effected on a nu- clear magnetic resonance spectrometer mod. Bruker MSL-300.

The characterization by means of X-ray spectroscopy for the determination of the molecular structures of the complexes illustrated was effected on a Bruker diffractome- ter mod. AX SP4.

The quantitative analysis of the a-olefin mixtures was

effected by means of gas chromatography with a Hewlett- Packard"Fisons"instrument mod. 9000 equipped with a "Pona"capillary column [50 m x 0.2 mm x 0.5 microns]. The calculation of the quantities of each single a-olefin was carried out using the coefficients obtained from calibra- tions effected with 1-butene, 1-hexene, 1-octene, 1-decene, 1-dodecene and 1-tetradecene respectively, (all products available on the market with purities > 99%) in the pres- ence of 1,3, 5-trimethylbenzene (>99.8 Fluka) as internal standard.

The characterization of the products present in the reaction mixtures was effected by means of gaschromatogra- phy/mass spectrometry (GC-mass) using a Finnigan TSQ 700 instrument.

The elemental analysis was carried out with an ICP-OES "Thermo Jarrel Ash"IRIS ADVANTAGE instrument.

During the preparations described in the examples, the following commercial reagents were used : zirconium tetrachloride (ZrCl4) FLUKA aluminum triethyl (TEA) (AlEt3) ALDRICH aluminum diethyl chloride (DEAC) (AlEt2Cl) ALDRICH aluminum ethyl dichloride (EADC) (AlEtCl2) ALDRICH dimethyl sulfone (Me2SO2) ALDRICH diethyl sulfone (Et2S02) ALDRICH diphenyl sulfone (Ph2S02) ALDRICH

The reagents and/or solvents used and not mentioned above are those commonly adopted in laboratories and on an industrial scale and can be easily found at the usual com- mercial operators specialized in the field.

EXAMPLE 1 : Synthesis of zirconium tetrachloride bis- dimethylsulfone, ZrCl4 (Me2S02) 2 (V).

3.69 g of ZrCl4 (15. 8 mmoles) and 120 ml of anhydrous CH2C12 are charged, under a nitrogen atmosphere, into a 250 ml tailed test-tube, equipped with a magnetic stirrer. 2.99 g of dimethyl sulfone (31.8 mmoles) dissolved in 40 ml of CH2C12 are added dropwise at room temperature to the sus- pension thus obtained. At the end of the addition over about an hour, the mixture is left under stirring at room temperature for a further 2 hours. In this phase, an abun- dant white microcrystalline solid is formed, which is re- covered by filtration. A further aliquot of product is re- covered by adding 30 ml of hexane to the mother liquor and filtering the white crystalline solid precipitated, which is joined to the product previously obtained. The product thus obtained is washed with two portions (15 ml) of CH2C12 and dried under vacuum (10 Pa) for 6 hours. 5.98 g of a white crystalline solid are thus obtained, which, after analysis and characterization by means of IR and X-ray spectroscopy, proves to be essentially pure ZrCl4 (Me2SO2) 2 (V), with an overall yield of 89%.

Elemental analysis: found (calculated) for C4Hl204Cl4S2Zr : Cl, 33.4 (33.66) ; S, 14. 9 (15.22) ; Zr, 21. 4 (21.65) %. 1H-NMR (C2D2C14, 6 ppm rel. to TMS): 3.43 (6H, s).

The structure of the complex, as determined by means of X-rays is indicated in figure 1 enclosed.

EXAMPLE 2: Synthesis of zirconium tetrachloride bis- diphenylsulfone, ZrCl4 (Ph2S02) 2 (VI).

Following a similar procedure to that described in Ex- ample 1,3. 70 g of ZrCl4 (15.9 mmoles), 100 ml of CH2C12 are charged into a 250 ml tailed flask, and 7.03 g of Ph2SO2 (32.2 mmoles) dissolved in 50 ml of CH2C12 are added to the suspension. At the end of the addition, a slightly turbid pale yellow solution is obtained, which is filtered to re- move all of the insoluble material and 80 ml of hexane are then added. A white crystalline precipitate is thus formed, which is recovered by filtration, washed with two 20 ml portions of hexane and dried at reduced pressure (10 Pa).

Operating in this way, 8.48 g of a white crystalline solid are obtained, which, after analysis and characterization by means of IR spectroscopy, proves to be essentially pure ZrCl4 (Ph2SO2) 2 (VI), with an overall yield of 80%.

Elemental analysis: found (calculated) for C24H2004Cl4S2Zr : C1, 20. 8 (21.18) ; S, 9.1 (9.58) ; Zr, 13.0 (13.62) %. 1H-NMR (C2D2C14, 6 ppm rel. to TMS): 8. 01 (8H, d) ; 7.66 (4H, t) ; 7.54 (8H, t).

EXAMPLE 3: Synthesis of zirconium tetrachloride diphenyl- sulfone, [ZrCl4 (Ph2S02)] 2 (VII).

Following a similar procedure to that described in Ex- ample 1,5. 52 g of ZrCl4 (23.7 mmoles), 120 ml of CH2C12 are charged into a 250 ml tailed flask, and 5.01 g of Ph2S02 (22.9 mmoles) dissolved in 40 ml of CH2C12 are added to the suspension. At the end of the addition, a suspension is ob- tained, containing an abundant white solid, which is left under stirring at room temperature for 2 h and the solvent is then completely removed at reduced pressure. The result- ing solid is transferred to an extractor equipped with a porous septum and bubble cooler, and extracted in continu- ous for 12 h using tetrachloroethane as solvent. At the end of the extraction, a small aliquot of insoluble solid re- mains on the porous septum, whereas the product present in the mother liquor is precipitated by cooling the solution and adding 50 ml of hexane. The product thus obtained is recovered by filtration, washed with two 20 ml portions of hexane and dried under vacuum (10 Pa). 7.91 g of a white crystalline solid are thus obtained, which, after analysis and characterization by means of IR and X-ray spectroscopy, proves to be essentially pure [ZrCl4 (Ph2SO2) 2 (VII), with an overall yield of 74%.

Elemental analysis: found (calculated) for Ci2Hio02Cl4SZr : Cl, 29.8 (31.42) ; S, 6.3 (7.10) ; Zr, 18.8

(20.21) e. 1H-NMR (C2D2C14, 6 ppm rel. to TMS) : 8. 25-7. 45 (unsolved multiplets).

The structure of the complex (VII), as determined by X-rays is indicated in figure 2 enclosed.

EXAMPLE 4: Synthesis of zirconium tetrachloride diethylsul- fone, [ZrCl4 (Et2SO2) 2 (VIII).

Following a similar procedure to that described in Ex- ample 1,3. 57 g of ZrCl4 (15.3 mmoles), 100 ml of CH2Cl2 are charged into a 250 ml tailed flask, and 1.81 g of Et2SO2 (14. 8 mmoles) dissolved in 30 ml of CH2C12 are added to the suspension. At the end of the addition, a suspension is ob- tained, containing an abundant white solid, which is left under stirring at room temperature for 2 h and the reaction mixture is then transferred to an extractor equipped with a porous septum and bubble cooler, and the solid is extracted in continuous for 8 h with the same solvent used for the reaction. At the end of the extraction, a small quantity of insoluble solid remains on the porous septum, whereas the product present in the mother liquor is precipitated by cooling the solution and adding 50 ml of hexane. The solid thus obtained is recovered by filtration, washed with two 20 ml portions of hexane and dried under vacuum (10 Pa).

4.51 g of a white crystalline solid are thus obtained, which, after analysis and characterization by means of IR spectroscopy, proves to be essentially pure [ZrCl4 (Et2SO2) 12

(VIII), with an overall yield of 83%.

Elemental analysis: found (calculated) for C4H1o02Cl4SZr : Cl, 38.9 (39.92) ; S, 8.5 (9. 03); Zr, 25.3 (25.68) e. 1H-NME (C2D2C14, 6 ppm rel. to TMS): 3.58 (4H, s) ; 1.61 (6H, s).

EXAMPLES 5-15: oligomerization of ethylene Examples 5 to 15 below refer to a series of oligomeri- zation tests of ethylene for the preparation of linear a- olefins according to the present invention, carried out us- ing a catalyst comprising one of the complexes obtained as described above in examples 1 to 4 and diethyl aluminum chloride (DEAC) as component (B) (cocatalyst).

The specific conditions in each example and the re- sults obtained are specified in Table I below, which indi- cates in succession, the reference example number, the com- plex used, the quantity of zirconium used, the atomic ratio between the aluminum in the DEAC and zirconium in the com- plex, the activity of the catalytic system expressed as grams of a-olefins per gram of metallic zirconium per hour: (gol/gzrh) the quantity, expressed in weight percent, of the single a-olefins produced.

The oligomerization is carried out in an 0.5 litre pressure reactor, equipped with a magnetic drag anchor stirrer and external jacket connected to a heat exchanger for the temperature control. The reactor is previously

flushed by maintaining under vacuum (0. 1 Pascal) at a tem- perature of 80°C for at least 2 hours.

180 g of anhydrous toluene (or other hydrocarbon sol- vent) are charged into the reactor, at 23°C, and optionally an aluminum alkyl or alkyl chloride in such a quantity as to form a solution having a concentration ranging from 1. 10-4 to 110-3 M, having the function of scavenger. The re- actor is then brought to the desired polymerization tem- perature and"polymerization grade"gaseous ethylene is fed by means of a plunged pipe until the desired total equilib- rium pressure is reached, as specified, for each example in Table (I) below.

The DEAC, generally as an 0.8 M solution (as Al) in toluene, and the desired quantity of one of the above com- plexes, either pure or as a toluene solution/suspension having a concentration generally ranging from 310-3 to SlO-2 M, are charged into a suitable tailed test-tube, maintained under nitrogen. The catalyst solution thus formed is kept at room temperature for a few minutes and is then transferred under a stream of inert gas to a metal container from which, due to an overpressure of nitrogen, it enters the reactor.

The catalyst consisting of the mixture of DEAC/complex having formula (III), can, if necessary, be left to age without losing its activity and selectivity, as described,

for illustrative but non-limiting purposes, in Examples 13 and 14 for a period of 24 hours at room temperature, and in Example 15 for an hour at 60°C.

The polymerization reaction is carried out at the de- sired temperature indicated in Table (I), care being taken to keep the total pressure constant by continuously feeding ethylene to compensate the part which has reacted in the meantime. After 60 minutes, the ethylene feeding is inter- rupted and the polymerization is stopped by the addition of 10 ml of ethyl alcohol. After bringing the temperature of the reaction mixture to 10°C, a sample of the solution is removed, by means of a tap situated at the bottom of the reactor, and gas-chromatographic analyses are effected to determine the quantity and type of olefins formed. After eliminating the overpressure of ethylene, the autoclave is opened and its contents are poured into a suitable glass container, containing 500 ml of ethyl alcohol in order to determine the coagulation of possible polymeric products which, if present, are separated from the liquid phase dried at 60°C, at a reduced pressure of 1000 Pa, for at least 8 hours and finally weighed. The overall results are indicated in Table (I) below.

EXAMPLES 16 to 18 (Comparative) Examples 16 to 18 (comparative) were essentially car- ried out under the same operating conditions as the previ-

ous examples from 5 to 12, but using a catalyst consisting of zirconium compounds and complexes known in the art as catalyst components for the oligomerization of ethylene.

The particular conditions, details and results ob- tained are indicated in Table (I) below.

The complexes zirconium tetrachloride- (dimetho- xyethane) [ZrCl4 (DME)], used in Example 18, and zirconium tetrachloride-bis (tetrahydrofuran) [ZrCl4 (THF) 2], used in Example 17, were obtained in accordance with the procedure described in Comprehensive Coordination Chemistry, Pergamon Press, volume 3 (1997) pages 403-406. Ex. Compl./ [Zr] Al/Zr Activity C4 C6 C8 C10 C12+ Nr. example moles#10-3 mol/mol gol/gZr#h % w. % w % w % w % w 5 (1n/1 0. 25 9. 7 660 22. 4 38. 8 23. 0 9. 7 6. 0 6 fVI)/2 0. 18 10. 0 230 17. 8 39.0 25.9 11. 0 6.4 7 (VIII)/4 0.21 19.2 1291 28. 3 36.3 20.2 8. 9 6. 4 8 (Vlìl)/4 0. 10 54. 2 2687 28. 7 35.8 20.9 8. 9 5. 8 9 (VIII)/4 0.052 108 6600 27. 5 34.8 21. 3 9. 6 6. 9 10 (Vll)/3 0. 11 14. 8 1464 24. 7 33.0 21.5 11.2 9. 7 11 (Vll)/3 0.048 117 4328 29. 1 35.7 21. 3 9. 6 5. 8 12 (VII)/3 0. 024 233 6376 33. 0 37. 6 18. 3 7.2 4. 0 13b (V)/1 0.25 9.9 770 25. 1 36.7 22.3 9. 4 6. 4 14b (VI)/1 0.18 10.0 105 21. 8 37.5 25. 5 10. 7 4.5 15° (9)/1 0.22 17.7 777 24. 0 34.2 22.0 10. 8 9. 0 16 ZrC14 0. 11 14. 6 1839 13. 2 24.8 22.1 15.3 24.6 17 ZrCl4 0. 056 14. 3 8460 12. 5 24.7 22.7 15. 8 24.1 (THF) 2 18 ZrCt4 0.066 14.5 511 14.0 30.0 24.1 13.8 18.2 (DME)

TABLE (I): oligomerization of ethylene according to Exam- ples 5 to 18a.

(a) Each example was effected at a temperature of 80°C and an ethylene pressure equal to 3.0 MPa ; (b) the catalytic system was aged at 25°C for 24 h ;' the catalytic system was aged at 60°C for 1 h.