Borate-activated metallocene catalysts

1. A catalyst system, wherein the catalyst system comprises:

(i) at least one metallocene complex of formula (I)

wherein

Mt1 is Hf,

X is a sigma-donor ligand,

R 1 , R 2 ,R 3 are the same or different from each other and are hydrogen or a saturated linear or branched C 1 -C 10 alkyl group, wherein the alkyl group optionally comprises up to 2 heteroatoms belonging to groups 14-16 of the periodic table, or wherein R 1 and R 2 or R 2 and R 3 form a ring having 4 to 6 C-atoms and 1 to 3 double bonds,

R 4 and R 5 are the same or different from each other and are saturated linear or branched C 1 -C 10 alkyl, C 5 -C 10 aryl, C 6 -C 20 alkylaryl or C 6 -C 20 arylalkyl groups, which optionally comprise up to 2 heteroatoms belonging to groups 14-16 of the periodic table,

n is 1 to 5,

Ar is a C 6 -C 20 -aryl or -heteroarylgroup, which is unsubstituted or substituted by 1 to 5 linear or branched C 1 -C 10 alkyl group(s),

and

(ii) a boron containing cocatalyst;

wherein the catalyst system shows a reactivity ratio C AO /C 2 of at least 0.1, wherein AO is C 4-10 alpha-olefin comonomer, in a high temperature solution process for producing ethylene copolymers.

2. The catalyst system of claim 1 , wherein the catalyst system comprises a mixture of the at least one metallocene complex of formula (I) with a metallocene complex of formula (I′):

wherein Mt2 is Zr,

R 1 to R 5 and Ar are defined as for the at least one metallocene complex of formula (I), and wherein the mixture comprises more than 50% by moles of the at least one metallocene complex of formula (I).

3. The catalyst system of claim 1 , wherein in the formula (I):

X is independently a hydrogen atom, a halogen atom, a R 6 , OR 6 , OSO 2 CF 3 , OCOR 6 , SR 6 , NR 6 2 or PR 6 2 group, wherein R 6 is a linear or branched, cyclic or acyclic, C 1 -C 02 -alkyl, C 2 -C 20 -alkenyl, C 2 -C 20 -alkynyl, C 6 -C 20 -aryl, C 7 -C 20 -alkylaryl or C 7 -C 20 -arylalkyl radical, optionally comprising up to 2 heteroatoms belonging to groups 14-16 of the periodic table, or is SiR 6 3 , SiHR 6 2 or SiH 2 R 6 ,

R 1 , R 2 , R 3 are the same or different from each other and are hydrogen or a saturated linear or branched C 1 -C 6 alkyl group, wherein the alkyl group does not comprise any heteroatom belonging to groups 14-16 of the periodic table, or R 1 is hydrogen and R 2 and R 3 form a ring having 5 to 6 C-atoms and 1 to 3 double bonds,

R 4 and R 5 are the same or different from each other and are a saturated linear or branched C 1 -C 10 alkyl or C 6 -C 10 aryl group, wherein the groups do not comprise any heteroatom belonging to groups 14-16 of the periodic table,

Ar is a C 6 -C 10 -aryl or -heteroarylgroup, which is unsubstituted or substituted by one linear or branched C 1 -C6 alkyl group, and wherein n is 2 to 4.

4. The catalyst system of claim 3 , wherein in the formula (I):

X is independently a halogen atom or a R 6 or OR 6 group, wherein R 6 is a C 1-6 -alkyl, phenyl or benzyl group,

R 1 , R 2 , R 3 are the same or different from each other and are hydrogen, a saturated linear or branched C 1 -C 4 alkyl group, wherein the alkyl group does not comprise any heteroatom belonging to groups 14-16 of the periodic table, or R 1 is hydrogen and R 2 and R 3 form a ring having 6 C-atoms and 3 double bonds,

R 4 and R 5 are the same or different from each other and are a saturated linear or branched C 1 -C 6 alkyl or phenyl, wherein the groups do not comprise any heteroatoms belonging to groups 14-16 of the periodic table,

Ar is an unsubstituted C 6 -C 10 -aryl group, and n is 2 to 4.

5. The catalyst system of claim 4 , wherein in the formula (I):

X is independently a C 1 -C 4 -alkyl or a benzyl group,

R 1 , R 2 , R 3 are the same and are all hydrogen, or R 1 is hydrogen and R 2 and R 3 form a ring having 6 C-atoms and 3 double bonds,

R 4 and R 5 are the same and are a saturated linear or branched C 2 -C 6 alkyl group, and wherein

n is 2 to 4, and Ar is phenyl.

6. The catalyst system of claim 1 , wherein the at least one metallocene complex of formula (I) is selected from:

(phenyl)(but-3-en-1-yl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluoren-9-yl)hafnium dimethyl,

(phenyl)(but-3-en-1-yl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluoren-9-yl)hafnium dibenzyl,

(phenyl)(but-3-en-1-yl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluoren-9-yl)hafnium dichloride,

(phenyl)(4-penten-1-yl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluorenyl)hafnium dimethyl,

(phenyl)(4-penten-1-yl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluorenyl)hafnium dibenzyl,

(phenyl)(4-penten-1-yl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluorenyl)hafnium dichloride,

(phenyl)(5-hexen-1-yl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluoren-9-yl)hafnium dimethyl,

(phenyl)(5-hexen-1-yl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluoren-9-yl)hafnium dibenzyl,

(phenyl)(5-hexen-1-yl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluoren-9-yl)hafnium dichloride,

(phenyl)(3-phenylpropyl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluoren-9-yl)hafnium dimethyl,

(phenyl)(3-phenylpropyl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluoren-9-yl)hafnium dibenzyl, or

(phenyl)(3-phenylpropyl)methylene(cyclopentadienyl)(2,7-di-tert-butylfluoren-9-yl)hafnium dichloride,

and wherein the catalyst system optionally comprises a mixture of the at least one metallocene complex of formula (I) with a metallocene complex of formula (I′):

wherein Mt2 is Zr, R 1 to R 5 and Ar are defined as for the at least one metallocene complex of formula (I), and wherein the mixture comprises more than 50% by moles of the at least one metallocene complex of formula (I).

7. The catalyst system of claim 1 , wherein the catalyst system is homogeneous or non-supported, and wherein

A) the catalyst system is prepared in a solution, by contacting:

ia) the at least one metallocene complex of formula (I); or

ib) a mixture of the at least one metallocene complex of formula (I) with a metallocene complex of formula (I′):

wherein Mt2 is Zr, R 1 to R 5 and Ar are defined as for the at least one metallocene complex of formula (I), and wherein the mixture comprises more than 50% by moles of the at least one metallocene complex of formula (I),

wherein the at least one metallocene complex of formula (I) or the mixture exists as a solid or as a solution;

with

ii) the boron containing cocatalyst, wherein the boron containing catalyst is dissolved in a hydrocarbon diluent or has been previously dissolved in an aromatic solvent,

or

B) wherein the catalyst system is formed by sequentially adding the catalyst system components ia)/ib) and ii) directly into a polymerization reactor.

8. The catalyst system of claim 1 , wherein the boron containing cocatalyst comprises an anion of formula (II):

(Z) 4 B −   (II)

where Z is an optionally substituted phenyl derivative, wherein a substituent in the substituted phenyl derivative is a halo-C 1-6 -alkyl or halo group.

9. The catalyst system of claim 8 , wherein the boron containing cocatalyst is a borate selected from:

triphenylcarbenium tetrakis(pentafluorophenyl) borate,

N,N-dimethylcyclohexylammonium tetrakis(pentafluorophenyl)borate,

N,N- dimethylbenzylammonium tetrakis(pentafluorophenyl)borate, or

N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate.

10. A process for the preparation of an ethylene copolymer comprising polymerizing ethylene and a C 4-10 alpha-olefin comonomer in a high temperature solution process at a temperature greater than 100° C. in the presence of a catalyst comprising:

(i) a metallocene complex of formula (I):

wherein

Mt1 is Hf,

X is a sigma-donor ligand,

R 1 , R 2 ,R 3 are the same or different from each other and are hydrogen or a saturated linear or branched C 1 -C 10 alkyl, wherein the alkyl group optionally comprises up to 2 heteroatoms belonging to groups 14-16 of the periodic table, or wherein R 1 and R 2 or R 2 and R 3 form a ring having 4 to 6 C-atoms and 1 to 3 double bonds,

wherein R 4 and R 5 are the same or different from each other and are saturated linear or branched C 1 -C 10 alkyl, C 5 -C 10 aryl, C 6 -C 20 alkylaryl or C 6 -C 20 arylalkyl groups, which optionally comprises up to 2 heteroatoms belonging to groups 14-16 of the periodic table,

n is 1 to 5, and

Ar is a C 6 -C 20 -aryl or heteroarylgroup, which is unsubstituted or substituted by 1 to 5 linear or branched C 1 - C 10 alkyl group(s), or

a mixture of the metallocene complex of formula (I) and a metallocene complex of formula (I′):

wherein Mt2 is Zr, and wherein

R 1 to R 5 and Ar are defined as for the metallocene complex of formula (I), and wherein the mixture comprises more than 50% by moles of the metallocene complex of formula (I), and

(ii) a boron containing cocatalyst;

wherein the catalyst shows a reactivity ratio C AO /C 2 of at least 0.1, wherein AO is C 4-10 alpha-olefin comonomer, in a high temperature solution process for producing ethylene copolymers.

11. The process of claim 10 , wherein the polymerization is performed:

a) at a polymerization temperature of at least 110° C.,

b) a pressure in a range of 50 to 300 bar, and

c) in a hydrocarbon solvent, wherein the hydrocarbon solvent is selected from the group of C 5-12 -hydrocarbons, which is unsubstituted or substituted by C 1-4 alkyl group and is liquid under the above defined polymerization conditions.