AU2020300124A1

AU2020300124A1 - Title of the invention:a new process for synthesizing C2 bridged cyclopentadienyl ligands and corresponding ansa-metallocene catalysts

Info

Publication number: AU2020300124A1
Application number: AU2020300124A
Authority: AU
Inventors: Koushik ADHIKARY; Ranajit Ghosh; Sandip Kumar KUNDU; Joydeb MANNA; Sumanta PATSA; Soumen Sensarma
Original assignee: Haldia Petrochemicals Ltd
Current assignee: Haldia Petrochemicals Ltd
Priority date: 2019-07-04
Filing date: 2020-07-03
Publication date: 2021-08-26
Also published as: EP3994144A1; CN113574060A; WO2021001855A1; JP2023520744A; KR20220029541A

Abstract

The present invention relates to a new, improved and efficient process for synthesizing C2 (ethylene) bridged cyclopentadienyl ligand having formula I: and eventually forming the corresponding ansa-metallocene catalyst from the same; which find potential applications in various olefin polymerization/ co-polymerization reactions.

Description

Title of the invention:

A NEW PROCESS FOR SYNTHESIZING C2 BRIDGED C Y CLOPENTADIEN YL LIGANDS AND CORRESPONDING ANSA-METALLOCENE CATALYSTS FIELD OF INVENTION

The present invention relates to the development of new process to synthesize C2 bridged metallocene catalyst for the polymerization of ethylene or copolymerization of ethylene or for propylene polymerization. More particularly, the present invention relates to a new, improved and efficient process for synthesizing C2 (ethylene) bridged cyclopentadienyl ligands and eventually forming the corresponding ansa-metallocene catalysts which find potential applications in various olefin polymerization reactions.

BACKGROUND OF THE INVENTION AND PRIOR ART

Metallocene based catalysts for olefin polymerization offers significant advantages over traditional Ziegler- Natta (Z-N) catalysts. Due to their single site characteristics it offers greater co-monomer incorporation (more than 20%) and thus providing products with better flexibility, better film clarity, and improvement in dart and impact properties as compared to the products made from traditional Z-N catalysts. Uniform co-monomer distribution in the polymer backbone leads to sharper and narrow melting point range often require for heat seal packaging applications. Metallocene based catalyst in conjunction with suitable co-catalyst such as methylaluminoxane or MAO (hydrolysis product of TMA and water) or in presence of boron based co-catalyst can produce polymer with improved activity, homogeneous co-monomer distribution in the polymer backbone and better stereo-regulating control. W. Kaminsky et. al.: Angew. Chem., 1980, 92, 396; W. Kaminsky et. ak: Makromol. Chem., Rapid Commun. 5, 225 (1984); W. Kaminsky et. ak: Naturwissenschaften 71, 93(1984); W. Kaminsky et. ak: Angew. Chem. 97, 507 (1985); W. Kaminsky et. ak: Makromol. Chem. 193, 1643 -1651 (1992); and W. Kaminsky et. ak: Macromok Chem. Phys., 1996, 197, 3907 initially disclosed metallocene catalysts in combination with methylaluminoxane (MAO) co- catalysts for polymerization of different olefins. These articles further narrated synthesis of a great number of symmetric and chiral zirconocenes that gave tailored polymers of totally different structures. Moreover, single site catalysts showed capability of permitting the user to control polymer tacticity, molecular weight and molecular weight distribution more efficiently. Moreover, besides the homopolymers of polyethylene and poly (propylene), new kinds of copolymers and elastomers were synthesized.

Prof H. H. Brintzinger et.al: J. Organomet. Chem., 1982, 232, 233 first disclosed synthesis of chiral ethylene (C2) bridged ansa metallocene complexes [ethylene-bridged bis(indenyl) precursors] and their advantageous use in polymerization of propylene with better stereo- regularity control and improved isotacticity. Although the most critical use for ansa-metallocene catalysts currently is for polymerization of olefins, such as ethylene and propylene, they also have significant uses as catalysts or catalyst precursors for other reactions where stereo- selectivity is important. The utility of ansa-metallocene complexes as catalysts for olefin polymerization and other reactions has created a high demand for a practical synthesis of ansa- metallocene compounds, especially for isotactic polypropylene and ethylene a-olefin copolymerization . Prior arts such as EP0754698, US6100416 disclose metallocene compounds with C2 (ethylene) bridged cyclopentadinyl groups that are widely used as homogeneous ansa-metallocene catalysts for polymerization of olefins and more specifically of stereochemical control in the polymerization of propylene. Asymmetric ethylene -bridged metallocenes complex with group 4 metals containing fluorenyl and indenyl fragments have also been proposed by the said prior arts for polymerization of propylene.

Few other prior arts such as US5191132; US006100416A; WO2015147215A1;

W02009081792A1; Rieger et. al.: Organometallics, 1994, 13, 647-653; Walter Kaminsky et. al.: J. Chem. Soc., Dalton Trans., 1998, 0, 1413-1418; Thomas E.J et. al.: Organometallics 1999, 18, 1439-1443; B. Ulf Dietrich et. al.: J. Am. Chem. Soc. 1999, 121, 4348-4355; Richard Lai et. al.: Dalton Trans., 2013, 42, 7980-7990 report some routes for synthesizing ethylene -bridged indenyl or fluorenyl metallocenes based on the following schematic principles:

(a) lithium salts of the indenyl or fluorenyl moieties are reacted with 1,2 dibromoethane (or 2- bromoethane indenyl or fluorenyl) to produce respective ethylene-bridged metallocene precursor:

(b) lithium salts of the indenyl or fluorenyl moieties are made to react with ethylene oxide to form 9-hydroxyethylfluorene type moiety which is next reacted with trifluoromethane sulfonic acid anhydride (or p-toluenesulfonyl chloride) to replace the hydroxyl group by OTf (or OTs) group, such that the said OTf (or OTs) derivative being finally reacted with indenyllithium to produce the ethylene-bridged metallocene precursor:

However, it has been observed that the above reported routes for synthesizing ethylene-bridged indenyl or fluorenyl metallocene precursors suffer from the following drawbacks:

(i) the incorporation of the ethylene bridge in ethylene bis(tetrahydroindene) is reportedly [Ref: R.L. Halterman et ah: Journal of Organometallic Chemistry 604 (2000) 12-19] much more troublesome due to a competing intramolecular cyclization to form the non-essential spiro- cyclopropane side product which is additionally formed as a by-product during the reaction of 1,2-dibromoethane and lithium salts of the indenyl or fluorenyl moieties as shown below:

Such formation of non-essential spiro-cyclopropane by-product disadvantageously results into formation of the final metallocene compounds with considerably lower yields (-14%);

(ii) further noted that such reactions requires excess use of starting material indene rendering the processes expensive; use of ethylene oxide as a reagent is environmentally hazardous; and the fluorenyl / indenyl intermediate (OTf) formed is highly unstable and thus not isolable. [Ref: B. Rieger et. al.: Organometallics 1994, 13, 647-653; Richard Lai et. al.: Dalton Trans., 2013, 42, 7980-7990]

Therefore, there still exists a need in the relevant art to develop a superior process for synthesizing ethylene bridged (C2 bridged) ansa metallocene precursors and in turn C2 bridged ansa metallocene catalysts thereof (hereinafter may also be referred to as“final products”), by means of essentially avoiding formation of the above mentioned unwanted by-product spiro- cyclopropane which consequently would provide better“final products” with higher yields. Accordingly, the inventors of the current invention have developed a new, improved, economical and efficient route for synthesizing the “final products” so as to overcome the above disadvantages of the prior reported processes; and in order to synthesize ethylene bridged (C2 bridged) ansa metallocene precursors and in turn produce industrially scalable C2 bridged ansa metallocene catalysts thereof with excellent quality and quantity.

OBJECTS OF THE INVENTION:

An object of the invention is to overcome the disadvantages of the prior art.

Another object of the present invention is to provide a novel process for the preparation of ethylene bridged (C2 bridged) ansa metallocene precursors (ligands) with 70 to 90 % yield.

Another object of the present invention is to provide a novel process for the preparation of industrially scalable C2 bridged ansa metallocene catalysts with 70 to 85 % yield. Another object of the present invention is to provide a new, improved process for synthesizing C2 bridged ansa metallocene precursors and catalysts thereof, wherein the scope of formation of unwanted impurities such as spiro-cyclopropane is nil. Another object of the present invention is to provide a new process for synthesizing C2 bridged ansa metallocene precursors and catalysts thereof which is also environment friendly.

SUMMARY OF INVENTION

One aspect of the present invention provides a new, improved process for synthesizing C2 (ethylene) bridged cyclopentadienyl ligand having a general formula I:

wherein, R1 to R8 is same or different and in each occurrence is independently selected from H, substituted or unsubstituted C1 -C2 alkyl, substituted or unsubstituted C1-C10 alkenyl, substituted or unsubstituted C1-C10 alkynyl, substituted or unsubstituted C1-C12 heterocyclyl, substituted or unsubstituted C1-

C12 cycloalkyl, substituted or unsubstituted C1-C12 aromatic ring system, silyl, alkylsilyl; wherein any two consecutive groups among R1 to R8 may be taken together to form a substituted or unsubstituted aromatic, partially saturated or saturated fused ring system with or without a heteroatom selected from N, O, S; wherein, the said process comprises steps of:

(a) reacting a halo-ester compound with a substituted or unsubstituted cyclopentadienyl (Cp¹) metal salt to form an ester intermediate;

(b) reducing the said ester intermediate with a reducing agent to form an aldehyde intermediate;

(c) adding another substituted or unsubstituted cyclopentadienyl (Cp²) metal salt to the above aldehyde intermediate of step (b) in presence of a saturated cyclic secondary amine, preferably a saturated secondary N-heterocycle catalyst, forming a fulvene derivative; followed by

(d) reducing the said fulvene derivative with a reducing agent to form a C2 (ethylene) bridged cyclopentadienyl ligand.

such that the said process essentially avoids formation of any unwanted spiro- cyclopropane impurity.

Another aspect of the present invention provides a new, improved process for synthesizing C2 (ethylene) bridged ansa metallocene catalyst comprising the steps of:

(e) reacting a halo-ester compound with a substituted or unsubstituted cyclopentadienyl (Cp¹) metal salt to form an ester intermediate;

(f) reducing the said ester intermediate with a reducing agent to form an aldehyde intermediate;

(g) adding another substituted or unsubstituted cyclopentadienyl (Cp²) metal salt to the above aldehyde intermediate of step (b), essentially in presence of a saturated cyclic secondary amine, preferably a saturated secondary N-heterocycle catalyst, forming fulvene intermediate;

(h) reducing the said fulvene derivative with a reducing agent to form a C2 (ethylene) bridged cyclopentadienyl ligand; followed by

(i) lithiating the said C2 (ethylene) bridged cyclopentadienyl ligand with a lithiating agent; and

(j) reacting the said lithiated ligand with MC14, wherein M is a transition metal preferably selected from Ti, Hf and Zr, preferably Zr, in order to form an ansa metallocene catalyst.

Another aspect of the present invention provides an improved process for synthesizing C2 bridged ansa metallocene catalyst comprising steps of:

(k) reacting a halo-ester compound with a substituted or unsubstituted cyclopentadienyl (Cp¹) metal salt to form an ester intermediate;

(1) reducing the said ester intermediate with a reducing agent to form an aldehyde intermediate;

(m) adding another substituted or unsubstituted cyclopentadienyl (Cp²) metal salt to the above aldehyde intermediate of step (b) in presence of a saturated cyclic secondary amine, preferably, asaturated secondary N-heterocycle catalyst, forming a fulvene intermediate; followed by

(n) directly adding a lithiating agent and MCU to the said fulvene intermediate, wherein M is a transition metal preferably selected from Ti, Hf and Zr, preferably Zr, forming an ansa metallocene catalyst. Yet another aspect of the present invention provides an ansa metallocene catalyst produced by the process as claimed in any of the preceding claims, has a structural formula II:

wherein,

R1 to R8 is same or different and in each occurrence is independently selected from H, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C1-C10 alkenyl, substituted or unsubstituted C1-C10 alkynyl, substituted or unsubstituted C1-C12 heterocyclyl, substituted or unsubstituted C1-C12 cycloalkyl, substituted or unsubstituted C1-C12 aromatic ring system, silyl, alkylsilyl; wherein any two consecutive groups among R1 to R8 may be taken together to form a substituted or unsubstituted aromatic, partially saturated or saturated fused ring system with or without a heteroatom selected from N, O, S;

M represents a transition metal atom selected from one of the Groups 3 to 12 of the Periodic Table of Elements, preferably, Ti, Zr and Hf;

X is independently selected from the group consisting of hydrocarbyl radicals having from 1 to 20 carbon atoms, hydrides, amides, alkoxides, sulfides, phosphides, halides, dienes, amines, phosphines, ethers, and a combination thereof, including that two X's may form a part of an aromatic or non-aromatic fused ring or a ring system; R9 and R10 are same or different and at each occurrence are independently selected from H, Si, alkylsilyl, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C1-C12 cycloalkyl, substituted or unsubstituted C1-C10 alkenyl, substituted or unsubstituted C6-C18 aryl, substituted or unsubstituted C5-C18 heteroaryl.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other aspects, features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which:

Figure 1 illustrates 1H NMR data confirming formation of intermediate 2-(9H-Fluoren-9-yl)- propionic acid ethyl ester;

Figure 2 illustrates 1H NMR data confirming formation of intermediate 2-(9H-Fluoren-9-yl)- propionaldehyde;

Figure 3 illustrates 1H NMR data confirming formation of intermediate 9-(2-Cyclopenta-2,4- dienylidene-Fmethyl-ethyl)-9F[-fluorene;

Figure 4 illustrates 1H NMR data confirming formation of C2 bridged Cp ligand 9-(2- Cyclopenta-1 ,3-dienyl-Fmethyl-ethyl)-9F[-fluorene;

Figure 5 illustrates 1H NMR data confirming formation of desired ansa metallocene catalyst i.e. dichloro-[9-(2-cyclopenta-1,3-dien-Fyl-Fmethyl-ethyl)fluoren-9-yl] -methyl zirconium;

Figure 6 illustrates 1H NMR data confirming formation of intermediate 2-(9H-Fluoren-9-yl)- butyric acid ethyl ester;

Figure 7 illustrates 1H NMR data confirming formation of intermediate 2-(9H-fluoren-9-yl)- butyraldehyde; Figure 8 illustrates 1H NMR data confirming formation of intermediate 9-(1-Cyclopenta-2,4- dienylidenemethyl-propyl)-9H-fluorene,

Figure 9 illustrates 1H NMR data confirming formation of Cp ligand 9 -(1-Cyclopenta-2,4- dienylmethyl-propyl)-9H-fluorene;

Figure 10 illustrates 1H NMR data confirming formation of ansa metallocene catalyst i.e. dichloro-[9- [1-(cyclopenta-1, 3 -dien-1-ylmethyl)propyl]fluoren-9-yl] -methyl-zirconium

DESCRIPTION OF THE INVENTION:

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description of exemplary embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

It is to be understood that the singular forms“a,”“an,” and“the” include plural referents unless the context clearly dictates otherwise. Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

It should be emphasized that the term“comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

The term“ansa metallocene” as used in the specification refers to bridged metallocenes, wherein the cyclopentadienyl (Cp) rings are linked by a chemical bridge such as ethylene, propylene etc. The term“C2 bridged ansa metallocene” as used in the specification refers to metallocenes wherein the cyclopentadienyl (Cp) rings are linked by essentially an ethylene bridge.

The term“improved process” as used in the specification refers to a process for the preparation of C2 bridged ansa metallocene precursors and catalysts thereof without formation of any unwanted by-product like spiro-cyclopropane.

The term“higher/ superior yield” as used in the specification refers to synthesizing C2 bridged ansa metallocene precursors and catalysts thereof with 70 to 85 % yield.

The term“THF” as used in the specification is tetrahydrofuran

The term“Et₂0” as used in the specification is ethyl ether

The term“EtOAc” as used in the specification is ethyl acetate

The term“DCM” as used in the specification is dichloromethane

The term“MeOH” is used in the specification is Methanol

The term“MAO” is used in the specification is methylaluminoxane. The present invention relates to a new, improved, economical process for the preparation of ethylene (C2) bridged ansa metallocene precursors (A) and catalysts (B) thereof, represented by the general formula (I):

Wherein,

R1 to R8 is same or different and in each occurrence is independently selected from H, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C1-C10 alkenyl, substituted or unsubstituted C1-C10 alkynyl, substituted or unsubstituted C1-C12 heterocyclyl, substituted or unsubstituted C1-C12 cycloalkyl, substituted or unsubstituted

C1-C12 aromatic ring system, silyl, alkylsilyl; wherein any two consecutive groups among R1 to R8 may be taken together to form a substituted or unsubstituted aromatic, partially saturated or saturated fused ring system with or without a heteroatom selected from N, O, S;

M represents a transition metal atom selected from one of the Groups 3 to 12 of the

Periodic Table of Elements, preferably, Ti, Zr and Hf;

X is independently selected from the group consisting of hydrocarbyl radicals having from 1 to 20 carbon atoms, hydrides, amides, alkoxides, sulfides, phosphides, halides, dienes, amines, phosphines, ethers, and a combination thereof, including that two X's may form a part of an aromatic or non-aromatic fused ring or a ring system;

R9 and R10 are same or different and at each occurrence are independently selected from H, Si, alkylsilyl, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C1-C12 cycloalkyl, substituted or unsubstituted C1-C10 alkenyl, substituted or unsubstituted C6-C18 aryl, substituted or unsubstituted C5-C18 heteroaryl.

such that the said process essentially avoids formation of any unwanted by-products and/or impurities such as spiro-cyclopropane.

Thus in accordance with the present invention, the overall process for synthesizing C2 bridged ansa metallocene precursor and catalysts thereof has been schematically described in Scheme 1 below:

Scheme 1

The currently developed process has been further embodied in many different forms and should not be construed as being limited to the description set forth herein. An embodiment of the present invention provides a new, improved, economical and easily scalable process for the preparation of C2 bridged ansa metallocene precursor / Cp ligand with 70-90 % yield. In a further specific embodiment, each step of the currently developed process for synthesizing C2 bridged ansa metallocene precursor / Cp ligand and the reaction conditions involved have been narrated in details below:

• Overall Reaction Conditions Involved:

All reactions are carried out under an Argon (Ar) atmosphere using standard techniques such as Schlenk technique. Methylaluminoxane (MAO) is procured as a solution in 7% toluene from external vendor and used as received. All other reagents are purchased from external vendor and used without further purification. Toluene, diethyl ether, tetrahydrofuran (THF), and pentane are distilled from sodium (Na) under Ar. Dichloromethane (DCM) is distilled from calcium hydride (CaH₂) under Ar. 1H NMR spectra are recorded by a commercially known NMR spectrometer.

• Step-wise Procedure:

The currently developed process for synthesizing C2 bridge ansa-metallocene complex essentially comprises of the following steps (a-d):

Step (a): Preparation of ester compounds (X)

In accordance with the present invention, a base selected from butyl lithium (BuLi) or potassium tert-butoxide, in an amount of 1-1.2 eqv is added to stirred solutions of a substituted or unsubstituted cyclopentadienyl (Cp¹) (leqv.) in a solvent such as THF, at a temperature of about -78°C to 0°C under stirring at RT (room temperature) for lh. Then a halo-ester selected from bromo-ester or chloro-ester is dissolved in a solvent such as THF and added to the said reaction mixture drop wise at -78°C to 0°C or. Then the reaction mixture is stirred for around 16-18 hrs at room temperature (RT). After completion of the reaction [as monitored by thin layer chromatography (TLC)], the reaction mixture is quenched with ammonium chloride (NH₄C1) solution and extracted with ethyl acetate. The organic layer is washed with brine, dried over sodium sulphate and evaporated. The resulting crude is purified by column chromatography (0- 10% ethyl acetate/hexane) in order to achieve the desired ester intermediate (X) with 75-85% yield.

Step (b): Preparation of Aldehydes (Y)

In accordance with the present invention, reducing agents selected from diisobutylaluminium hydride (DIBALH)in an amount of 1-1.2 eqv, 25% in toluene is added to stirred solutions of esters (1 eqv) in solvents like DCM or toluene at -78°C and stirred for lh at -78°C. Reactions are quenched with methanol (MeOH) and extracted with DCM . The organic layer is washed with water and brine. The organic layer is next dried over sodium sulphate and evaporated to get the desired aldehyde with 80-90% yield. This aldehyde intermediate (Y) thus formed is used in the next step (c) without further purification. Step (c): Preparation of cyclopenta-1, 3-dienes or‘Compound 1A’-

In accordance with the present invention, another prior substituted or unsubstituted cyclopentadiene (Cp²) (1-3 eqv.) is added to the stirred solution of the aldehyde (1 eqv) in methanol (MeOH) at 0-5°C and stirred for 5 minute at this temperature with a saturated cyclic secondary amine, preferably a saturated secondary N-heterocycle as catalyst selected from Pyrrolidine, Piperidine, Morpholine (0.02 to 0.05 eqv) is added to the reaction mixture at 0-5°C. The reaction mixture is allowed to warm to RT and stirred for another 3-12 hrs. Methanol is evaporated and the residue is dissolved in ethyl acetate and washed with water and brine. The organic part is then dried over sodium sulphate and evaporated. The resulting crude is purified by column chromatography in order to get the desired product“Compound 1A” with 85-90% yield.

Step (d): Preparation of desired Cp ligand or“Compound 1B”-

In accordance with the present invention, lithum aluminium hydride (LAH) (1-1.2 eqv.) is added to stirred solutions of the said fulvene derivative in ether at 0°C and the reaction mixture is stirred for lh at 0°C. Excess LAH is quenched by using sodium sulphate decahydrate. The precipitate hence formed is filtered and washed with ethyl acetate and purified by column chromatography (hexane) to get the desired C2 bridged ansa metallocene precursor / Cp ligand [herein after referred to as“Compound IB”] with 85-90% yield.

The “cyclopentadienyl (Cp) moieties” as used in the present invention is selected from cyclopentadiene, fluorene, indene.

Another embodiment of the present invention provides a process for preparing a C2 bridged ansa metallocene catalyst comprising the steps of:

i. reacting“Compound 1A” (Cp ligand) as synthesized above with a lithiating agent selected from lithium triethylborhydride, at 0°C and stirring for 12 hr at room temperature (rt), in order to form a lithiated salt of Compound 1A (Cp ligand);

ii. filtering the precipitated lithium Cp ligand , then washing with diethyl ether and drying in vacuum in order to give respective lithium Cp ligand as a white powder; followed by iii. reacting the said lithiated salt of Compound 1A (Cp ligand ) with n-butyl lithium (nBuLi) and MC1₄ in toluene, wherein M is a transition metal preferably selected from Ti, Hf, Zr, at -78°C and stirred for additional 12h;

iv. evaporating the said reaction mixture to dryness by taking it up in a reagent like chloroform; then

v. removing the excess solvent lithium chloride (LiCl) by filtration over a pad of cellite; followed by

vi. purifying and re-crystallizing the crude metallocene dichloride thus formed by repeated washing with reagents such as pentane, toluene and/or mixtures thereof, in order to produce a desired ethylene (C2) bridged ansa metallocene catalyst complex (yield: 70-

85%).

The formed metallocene complex is then further analyzed by NMR and other elemental analytical.

Another specific embodiment of the present invention thus provides a process for preparing a C2 bridged ansa metallocene catalyst comprising the steps of:

i. reacting 1 eq. of“Compound 1A” as synthesized above with lithium triethylborhydride [LiEt₃BH] (1.5 eq., 1 M in THF) at 0°C under stirring for 12 hr. at room temperature (rt); ii. filtering the precipitated lithium Cp ligand, then washing with diethyl ether and drying in vacuum in order to give respective lithium Cp ligand as a white powder; followed by iii. slowly reacting the said lithiated salt of Compound 1A (Cp ligand ) and another 1.1 eq of n-butyl lithium (nBuLi) in toluene with 1 eq. of ZrC14.2THF, at -78°C and stirred for additional 12h;

iv. evaporating the said reaction mixture to dryness by taking it up in CH2CI2; then v. removing the excess solvent FiCl removed by filtration over a pad of cellite; followed by vi. purifying the crude metallocene dichloride thus formed by repeated washing with pentane, and re-crystallizing from toluene/pentane mixtures, in order to produce the white solid compound of ethylene (C2) bridged ansa Zr metallocene catalyst complex (yield: 73%).

i. reacting leq. of“Compound IB” as synthesized above with n-butyl lithium in toluene at -78°C under nitrogen (N2) atmosphere;

ii. warming the said reaction mixture to room temperature for over 2 hrs. and subsequently cooling to -78°C; followed by

iii. adding 1 eq. of MC1₄.2THF, wherein M is a transition metal preferably selected from Ti, Hf, Zr, to the above reaction mixture in order to afford the formation of a coloured suspension;

iv. warming the said suspension to room temperature along with overnight stirring and finally passing the same through celite;

v. washing the remaining solid fraction with toluene; followed by

vi. concentrating the remaining filtrate under reduced pressure; and

vii. washing of the sticky solid with hexane, and the hexane layer is syringed out, dried the solid part is reduced under pressure in order to get the desired ethylene (C2) bridged ansa metallocene catalyst complex (yield: 70-85%).

The formed metallocene complex is then further analyzed by NMR and elemental analysis. Another specific embodiment of the present invention thus provides a process for preparing a C2 bridged ansa metallocene catalyst comprising the steps of:

i. adding 2.1 eq. of n-butyl lithium to a to a stirred solution of Compound IB (leq) as synthesized above, in a mixture of toluene and dioxane at -78°C under nitrogen (N2) atmosphere;

ii. warming the said reaction mixture to room temperature for over 2hrs followed by subsequent cooling to -78°C;

iii. adding ZrC14.2THF leq) to the above reaction mixture in order to afford the formation of an orange suspension;

iv. warming the said orange suspension to room temperature along with overnight stirring changes the colour of the suspension to light yellow; and finally

v. passing the said suspension of step (iv) through celite and washing the remaining solid fraction with toluene ; followed by

vi. concentrating the remaining filtrate under reduced pressure; and

vii. washing of the yellow sticky solid formed thus obtained with hexane, in order to get the desired ethylene (C2) bridged Zr ansa metallocene catalyst as off-white solid product (356 mg, Yield- 65-73%).

The invention is now illustrated by way of non-limiting examples. The examples are intended to be purely exemplary of the invention, should therefore not be considered to limit the invention in any way. EXAMPLES:

EXAMPLE 1: Preparation of Dichloro-[9-[l-(cyclopenta-l,3-dien-l- ylmethyl)propyl]fluoren-9-yl]-methyl-zirconium ansa metallocene catalyst

Example 1 illustrates the process for preparing Dichloro-[9-[1-(cyclopenta-1,3-dien-1- ylmethyl)propyl]fluoren-9-yl] -methyl-zirconium ansa metallocene catalyst.

• Experimental Section:

In the present invention, all syntheses are carried out under argon using standard Schlenk techniques. The hydrocarbon and ethereal solvents are purified by standard methods. The deuterated solvents C₆D₆ (Cambridge Isotopes, 99.5%) and CDC13 (Aldrich, 99.8%) are dried over activated 4 A molecular sieves.

Starting materials such as ZrC1₄ (Aldrich), n BuLi (Aldrich, 1.6 M in hexane), Methylaluminoxane (MAO) (Aldrich), The ¹ H-NMR analyses are carried out on a Bruker 400 MHz instrument, at 25°C. All the operations are carried out in a dry nitrogen atmosphere, using the conventional techniques for the handling of compounds which are sensitive to air.

• Step 1- Synthesis of 2-(9H-Fluoren-9- vP-propionic acid ethyl ester

o Procedure:

To a stirred solution of 9H-fluorene (10 g, 60.24 mmol) in THF (100 mL), potassium tertbutoxide (7.43 g 66.26 mmol) is added at 0°C. Keep it stirred for 2h in RT. Then ethyl 2- bromopropanoate (11.99 g 66.26 mmol) in THF (150 ml) is added to the reaction mixture drop wise at 0°C. Keep the reaction mixture stirred for 16 h at room temperature. Then the reaction mixture is extracted with EtOAc (100 ml). The organic layer was washed with water & brine solution. The organic part is dried over sodium sulphate & evaporated to get crude. The crude is purified using column chromatography in order to get pure compound 2-(9H-Fluoren-9-yl)- propionic acid ethyl ester with 81% yield.

o Results:

The accompanying figure 1 shows ¹H NMR (CDC1₃) study results: 7.74 (d, 2H), 7.49 (d, 1H), 7.37-7.25 (m, 5H) 4.53 (s, 1H), 4.31 (d, 2H), 3.28 (m, 1H), 1.34-1.30 (t, 3H), 0.63 (d, 3H), confirming formation of pure compound 2-(9H-Fluoren-9-yl)-propionic acid ethyl ester.

• Step 2- Synthesis of 2-(9H-Fluoren-9-yl)-propionaldehyde

o Procedure:

To a stirred solution of 2-(9H-Fluoren-9-yl)-propionic acid ethyl ester (13.5g 93 mmol) in DCM (300mL), diisobutylaluminium hydride (DIBAL-H) (63.2 ml, 25% in toluene) is added at -78°C. It is stirred for lh at -78°C. Reaction is quenched with MeOH (30ml); and then extracted with DCM (250 ml). The organic layer is washed with water (2x100ml) & brine solution (2x100ml). The organic layer is dried over sodium sulphate & evaporated to get crude. The crude is purified by column chromatography (hexane) to get pure 2-(9H-Fluoren-9-yl)-propionaldehyde with 87% yield.

o Results:

The accompanying figure 2 shows H NMR (CDC1₃) study results: 9.91 (s, 1H), 7.76 (d, 2H), 7.49 (d, 1H), 7.40-7.30 (m, 4H), 7.27 (s, 1H), 4.57 (s, 1H), 3.25-3.19 (m, 1H), 0.72 (d, 3H), confirming formation of pure compound 2-(9H-Fluoren-9-yl)-propionaldehyde .

• Step 3- Synthesis of 9-(2-Cyclopenta-2,4-dienylidene-1-methyl-ethyl)-9H-fluorene o Procedure: To a stirred solution of 2-(9H-Fluoren-9-yl)-propionaldehyde (1.6g, 7.20 mmol) in MeOH (60 mL), cyclopentadiene (1.42 g 21.62 mmol) is added at 0-5 °C; and stirred for 5 minute at this temperature. Then pyrrolidine (0.19 g 1.44 mmol) is added as a catalyst to the reaction mixture at 0-5°C. The reaction mixture is allowed to warm to RT and stirred for another 16h.

The excess pyrrolidine is then quenched with acetic acid. Methanol is evaporated off, residue dissolved in EtOAc (70 ml) and washed with water (2x50ml) and brine solution (2x50 ml). The organic part is dried over sodium sulphate and evaporated it. The resulting crude is purified by column chromatography (hexane) to get the desired product 9-(2-Cyclopenta-2,4- dienylidene-1-methyl-ethyl)-9H-fluorene as yellow sticky liquid with 89% yield.

o Results:

The accompanying figure 3 shows ¹H NMR (CDC1₃) study results: 7.75 (t,2H), 7.60 (d,1H), 7.55 (d,1H), 7.40-7.30 (m,3H),7.26 (d,1H), 6.57 (d,2H), 6.44 (d,1H), 6.37 (d,1H), 6.15 (d, 1H), 4.16 (s, 1H), 3.77-3.72 (m, 1H), 0.92 (d, 3H), confirming formation of the compound 9-(2- Cyclopenta-2,4-dicnylidene-1 -methyl-ethyl)-9H-fluorene.

• Step 4- Synthesis of 9-(2-Cyclopenta-1,3-dienyl-1-methyl-ethyl)- H fluorene (Ethyl

bridged CP ligand)

o Procedure:

To a stirred solution of 9-(2-Cyclopenta-2,4-dicnylidcnc- 1 -methyl-ethyl)-9H-fluorene (1.4g, 0.005 mmol) in Ether (60mL), LAH (10.3 ml) is added at 0°C and the reaction mixture is stirred for lh at 0°C. Excess LAH is quenched with sodium sulphate decahydrate. Then excess ether (100 ml) is added in the reaction mixture and it is washed with water (50 ml) and brine (50 ml). Then the organic part is dried over sodium sulphate and the same is concentrated. The resulting crude is purified by column chromatography (hexane) to get the desired product 9-(2- Cyclopenta-1 ,3-dicnyl- 1 -methyl-ethyl)-9H-fluorene with 83% yield.

o Results:

The accompanying figure 4 shows ¹HNMR (CDC1₃) study results: 7.75 (t,2H),7.59 (t,1H), 7.54 (d,1H), 7.35-7.27 (m,4H), 6.48-6.42 (m,2H), 6.27-6.23 (m,1H), 6.08 (s,1H), 4.01 (s,1H), 2.95

(d,2H), 2.66-2.64 (m,1H), 2.52-2.47 (m,1H), 2.38-2.3 (m,1H), 0.64 (d, 3H), confirming formation of the C2 bridged Cp ligand i.e. 9-(2-Cyclopenta-1,3-dienyl-1-methyl-ethyl)-9H- fluorene. · Step 5- Synthesis of dichloro-[9-(2- Cyclopenta- 1 ,3-dien-1 -yl-1 -methyl-ethyl )fluoren-

9-yl]-methyl -zirconium (ansa metallocene catalyst)

o Procedure:

To a stirred solution of compound 9-(2-Cyclopenta-1 ,3-dienyl-1-methyl-ethyl)-9H-fluorene (250 mg, 0.919 mmol) in a mixture of toluene (17.5 ml) and dioxane (3 ml), n-BuLi (0.77 ml, 2.1eq) is added drop wise at -78°C under N2 atmosphere. The reaction mixture is warmed to room temperature over 2h. Subsequent cooling to -78°C and addition of solid ZrC1₄.2THF (346.5 mg) affords the formation of an orange suspension which is warmed to room temperature and stirred overnight. The colour of the reaction mixture changes to light yellow. The mixture is passed through celite. The remaining solid fraction is washed with toluene until the organic phase remained colourless. The filtrate is concentrated under reduced pressure; a light yellow sticky solid is formed. The sticky solid is washed with hexane (2x15ml) and the hexane layer is syringed out, dried the solid part under reduced pressure to get the desired ansa metallocene catalysts i.e. dichloro-[9-(2-cyclopenta-l,3-dien-l-yl-l-methyl-ethyl)fluoren-9-yl]-methyl zirconium_as light yellow solid with 72% yield. o Results:

The accompanying figure 5 shows ¹HNMR (CDC1₃) study results: 7.74 (t, 2H), 7.59 (d,1H), 7.45 (d,1H), 7.37-7.27 (m,5H), 6.22-6.18 (d,3H), 3.97 (s,1H), 2.91-2.86 (m,1H), 2.72-2.66 (m,1H), 0.59 (t,3H), confirming formation of the desired ansa metallocene catalysts i.e. dichloro-[9-(2- cyclopenta- 1 ,3 -dien-1-yl-1-methyl-ethyl)fluoren-9-yl] -methyl zirconium.

EXAMPLE 2: Polymerization of Ethylene

Example 2 illustrates the process for utilizing the said ansa metallocene catalyst of example 1 i.e. Dichloro-[9- [1 -( cyclopenta- 1, 3 -dien-1-ylmethyl)propyl]fluoren-9-yl] -methyl-zirconium in polymerization of ethylene.

• Procedure:

A dried 600 mL stainless steel parr reactor equipped with a mechanical stirrer, thermometer probe are backfilled with nitrogen for 30 min. Dried hexane is introduced to the reaction flask, followed by 1 mL of MAO, and nitrogen is bubbled through the solvent for 10 min under stirring at 400 rpm. The nitrogen is then replaced by ethylene gas, which is left bubbling through the solvent and released it through vent. After 10 min, the desired amount of MAO (5 mL) and 6 mg of ansa metallocene catalyst of example 1 i.e. Dichloro-[9-[1-(cyclopenta-1,,-dien-1- ylmethyl)propyl]fluoren-9-yl]-methyl-zirconium in toluene are introduced into the reaction flask; and then placed at 70°C temperature. When the requisite temperature is reached, the constant ethylene pressure of 5 bars is applied. Polymerization reaction is thus allowed to proceed for 15 min and then quenched with 10 mL of methanol. The reactor is vented, and the polymers are collected and precipitated into acidified methanol (1% HC1). Polymers are washed with methanol and water and dried in a vacuum oven at 60 °C for overnight to get 2.3 gm of polymer. EXAMPLE 3: Copolymerization of ethylene/1-hexene:

Example 3 illustrates the process for utilizing the said ansa metallocene catalyst of example 1 i.e. Dichloro-[9- [1-(cyclopenta-1, 3 -dien-1-ylmethyl)propyl]fluoren-9-yl] -methyl-zirconium in copolymerization of ethylene/l-hexene.

• Procedure:

A dried 600 ml stainless steel parr reactor equipped with a mechanical stirrer, thermometer probe are backfilled with nitrogen for 30 min. Dried hexane is introduced to the reaction flask, followed by 1 ml of MAO, and nitrogen is bubbled through the solvent for 10 min under stirring at 400 rpm. The nitrogen is then replaced by ethylene gas, which is left bubbling through the solvent and released it through vent. After 10 min, the desired amount of MAO (2.3 ml) and 2 mg of the ansa metallocene catalyst of example 1 i.e. Dichloro-[9-[1-(cyclopenta-1,3-dien-1- ylmethyl)propyl]fluoren-9-yl]-methyl-zirconium in toluene are introduced into the reaction flask; and then placed at 70°C temperature. When the requisite temperature is reached, then 2.5 ml of 1-hexene and subsequently ethylene are fed with the pressure adjusted at the constant ethylene pressure of 5 bars. Polymerization reaction is allowed to proceed for 15 min and then quenched with 10 ml of methanol. The reactor is vented, and the polymers are collected and precipitated into acidified methanol (5% HC1). Polymers are washed with methanol and water and dried in a vacuum oven at 60 °C for overnight to get 1.2 gm of polymer.

EXAMPLE 4: Preparation of Dichloro-[9-[l-(cyclopenta-l,3-dien-1- ylmethyl)propyl]fluoren-9-yl]-methyl-zirconium ansa metallocene catalyst

Example 4 illustrates the process for preparing Dichloro-[9-[1-(cyclopenta-1,3-dien-1- ylmethyl)propyl]fluoren-9-yl] -methyl-zirconium ansa metallocene catalyst. • Experimental Section:

• Step 1- Preparation of 2- H Fluoren-9-yl)-butyric acid ethyl ester:

o Procedure:

To a stirred solution of compound 9H-Fluorene (10 gm, leq) in dry THF (150 ml), butyl lithium (47.5 ml, 1.5eq) is added drop wise at -78°C. The reaction mixture is then allowed to warm to room temperature and stirred for 3h. Then ethyl 2-bromobutanoate (11.22 ml, leq) is dissolved in THF, added slowly to the reaction mixture at -30°C and stirred for lh at 25°C. The reaction mixture is concentrated under reduced pressure. The reaction mixture is diluted with ethyl acetate, washed with water and brine. The organic layer is separated, dried over Na₂SO₄ and concentrated under reduced pressure to get the crude material. The crude material is next purified by flash column chromatography to get the desired yellow liquid compound 2-( 9H-Fluoren-9- yl)-butyric acid ethyl ester with 71% yield. o Results:

The accompanying figure 6 shows ¹H NMR (CDC1₃) study results: 7.74 (d, 2H), 7.52-7.49 (t, 2H), 7.37-7.24 (m, 4H) 4.32 (s, 1H), 4.22 (t, 2H), 3.01 (m, 1H), 1.55 (m, 1H), 1.23 (t, 3H), 0.99 (m, 1H), 0.75 (t, 3H), confirming formation of compound 2-(9H-Fluoren-9-yl (-butyric acid ethyl ester.

• Step 2- Synthesis of 2-(9H-Fluoren-9-yl)-butyraldehyde:

o Procedure:

To a stirred solution of 2-(9H-Fluoren-9-yl)-butyric acid ethyl ester (10.5g, 93 mmol) in DCM (300mL), diisobutylaluminium hydride (DIBAL-H) (49.2 ml, 25% in toluene) is added at -78°C. It is stirred for lh at -78°C. Reaction is quenched with MeOH (30ml); and then extracted with DCM (250 ml). The organic layer is washed with water (2x100ml) & brine solution (2x100ml). The organic layer is dried over sodium sulphate & evaporated to get crude. The crude is then purified by column chromatography (hexane) to get pure 2-(9H-Fluoren-9-yl)-butyraldchydc as off white solid with 86 % yield

o Results:

The accompanying figure 7 shows ¹H NMR (CDC1₃) study results: 9.73 (s, 1H), 7.76 (d, 2H), 7.52 (d, 1H), 7.38 (t, 3H), 7.33-7.24 (m, 2H), 4.46 (s, 1H), 3.01 (m, 1H), 1.66-1.55 (m, 1H), 1.13-1.01(m, 1H), 0.77 (t, 3H), confirming formation of the compound 2-(9H-fluoren-9-yl)- butyraldehyde.

• Step 3- Synthesis of 9-(1-Cvclopenta-2,4-dienvlidenemethyl-propvl)-9H-fluorene o Procedure: To a stirred solution of compound 2-(9H-Fluoren-9-yl)-butyraldehyde (1.5 g, 6.356mmol) in MeOH (25mL), cyclopentadiene (1.6 ml, 19.06 mmol) is added at 0°C and stirred for 5 minute at this temperature. Then pyrrolidine (0.90ml, 12.7mmol) is added to the reaction mixture at 0°C. The reaction mixture is allowed to warm to 25 °C and stirred for another 2h, excess pyrrolidine is quenched with acetic acid. Methanol is concentrated, diluted with ethyl acetate (70 ml) and washed with water (2x50 ml) and brine (2x50 ml). The organic layer is separated, dried over sodium sulphate and concentrated under reduced pressure to get the crude material. The resulting crude material is purified by flash column chromatography (hexane) to get the desired fulvene intermediate 9-(1 -Cyclopenta-2, 4-dicnylidcncmcthyl -propyl )-9H-Fluorene as light yellow liquid with 86% yield.

o Results:

The accompanying figure 8 shows ¹H NMR (CDC1₃) study results: 7.75 (q, 2H), 7.61 (d, 1H), 7.55 (d, 1H), 7.40 (t,1H), 7.32 (t,1H), 7.24 (t, 1H), 6.53 (d,2H), 6.41 (d,1H), 6.21 (d,1H), 6.10 (d, 1H), 4.19 (s, 1H), 3.49-3.42 (m, 1H), 1.44-1.25 (m, 2H), 0.82 (t, 3H), confirming formation of the fulvene intermediate 9-(1-Cyclopenta-2,4-dienylidenemethyl-propyl)-9H-fluorene.

• Step 4- Synthesis of the desired Cp ligand 9-(1-Cyclopenta-2,4-dienylmethyl- propyl )-9H-fluorene:

o Procedure:

To a stirred solution of compound 9-(1-Cyclopenta-2,4-dienylidenemethyl-propyl)-9H-fluorene (1.3g, 4.557mmol) in ether (20mL), LAH (6.8 ml, 1.5eq) is added at 0°C and stirred for lh at 0°C. After total consumption of starting material (monitored by TLC), excess LAH is quenched using Fisher workup and diluted the reaction mixture. The organic layer is washed with water, and brine. The organic layer is separated, dried over sodium sulphate and concentrated under reduced pressure to get the crude material. The crude material is purified by flash column chromatography to get the desired Cp ligand 9-(1-Cyclopenta-2,4-dienylmethyl-propyl)-9H- fluorene as light yellow oil with 84% yield (1g, 76.2%).

o Results:

The accompanying figure 9 shows ¹H NMR (CDC1₃) study results: 7.75 (d,2H), 7.58 (t,1H), 7.50 (d,1H), 7.37-7.24 (m,4H), 6.42-6.22 (m,2H), 6.18-6.02 (s,1H), 4.1 (s, 1H), 2.98 (s, 1H), 2.85 (s, 1H), 2.42-2.37 (m, 1H), 2.28-2.17 (m,2H), 1.3-1.14 (m,2H), 0.89 (t,3H), confirming formation of the desired Cp ligand 9-(1-Cyclopenta-2,4-dienylmethyl-propyl)-9H-fluorene

• Step 5- Synthesis of ansa metallocene catalyst Dichloro-[9-H-(cxcloventa-13-dien-1- ylmethyl) ropyllfluoren-9-yl]-methyl-zirconium: o Procedure:

To a stirred solution of compound 9-(1-Cyclopenta-2,4-dienylmethyl-propyl)-9H-fluorene (300 mg, leq) in a mixture of toluene (21ml) and dioxane (1.8 ml), -BuLi (1.2ml, 2.2eq) is added drop wise at -78°C under N₂ atmosphere. The reaction mixture is warmed to room temperature over 2h. Subsequent cooling to -78°C and addition of solid ZrC1₄.2THF (415.8 mg, leq) afford the formation of an orange suspension which is warmed to room temperature and stirred 4h at room temperature. The colour of the reaction mixture changes to light yellow. The mixture is passed through celite. The remaining solid fraction is washed with toluene until the organic phase remained colourless. The filtrate is concentrated under reduced pressure; a light yellow sticky solid is formed. The sticky solid is washed with hexane (2x15ml) and the hexane layer is syringed out, the solid part is dried under reduced pressure to get the desired ansa metallocene catalyst i.e. dichloro- [9- [1-(cyclopenta- 1,3 -dien-1 -ylmethyl)propyl ]fluoren-9-yl] -methyl- zirconium as light brown solid with 83% yield. o Results:

The accompanying figure 10 shows ¹H NMR (CDC1₃) study results: 7.72-7.24 (m,8H), 6.05 (d,1H), 5.86 (s,1H), 3.96 (s,1H), 2.55 (m,1H), 2.44-2.24 (m,2H), 1.61-1.51 (m,2H), 0.82 (t,3H), confirming formation of the desired ansa metallocene catalyst i.e. dichloro-[9-[1-(cyclopenta- 1,3-dien-1 -ylmethyl)propyl]fluoren-9-yl]-methyl-zirconium

EXAMPLE 5: Polymerization of Ethylene

Example 5 illustrates the process for utilizing the said ansa metallocene catalyst of example 4 i.e. dichloro-[9- [1-(cyclopenta-1, 3 -dien-1-ylmethyl)propyl]fluoren-9-yl] -methyl-zirconium in polymerization of ethylene.

• Procedure:

A dried 600 ml stainless steel parr reactor equipped with a mechanical stirrer, thermometer probe are backfilled with nitrogen for 30 min. Dried hexane is introduced to the reaction flask, followed by 1 ml of MAO, and nitrogen is bubbled through the solvent for 10 min under stirring at 400 rpm. The nitrogen is then replaced by ethylene gas, which is left bubbling through the solvent and released it through vent. After 10 min, the desired amount of MAO (3.7 ml) and 2.5 mg of the ansa metallocene catalyst i.e. dichloro-[9-[1-(cyclopenta-1,3-dien-1- ylmethyl)propyl]fluoren-9-yl]-methyl-zirconium of example 4 in toluene are introduced into the reaction flask; and then placed at the 70°C temperature. When the requisite temperature is reached, the constant ethylene pressure of 5 bar is applied. Polymerization reaction is allowed to proceed for 10 min and then quenched with 10 ml of methanol. The reactor is vented, and the polymers are collected and precipitated into acidified methanol (5% HC1). Polymers are washed with methanol and water and dried in a vacuum oven at 60 °C for overnight to get 1.2 gm of polymer. EXAMPLE 6: A comparative data of the present invention in view of the closest prior arts

Example 6 provides a comparative data of the present invention in view of the closest reported prior art.

The salient features and the results obtained by the present invention have been compared with those reported in the closest prior art (I) as depicted in the following table 1:-

I. US6100416A (hereinafter referred to as‘prior art G) recites a process for producing an ethylene-bridged metallocene comprising the following steps:

a) reacting fluorenyllithium with 1,2-dibromoethane to produce 1-(9-fluorenyl)-2- bromoethane,

b) reacting the said 1-(9-fluorenyl)-2-bromoethane with 2,4,7-trimethylindenyllithium to produce 1-(9-fluorenyl)-2-[1 -(2,4,7 -trimethyl)indenyl] ethane precursor,

c) reacting the said 1-(9-fluorenyl)-2-[1-(2,4,7-trimethyl)indenyl]ethane precursor with butyllithium to produce its dilithium salt and

d) reacting the said dilithium salt with a transition metal halide selected from halides of titanium, zirconium and hafnium to produce the metallocenes.

Table 1: Comparative Data

Therefore, from the comparative data in above table 1, it is evident that prior art I reports formation of Cp ligands with very poor yields i.e. 14-29%, mostly due to formation of impurities such as spiro-cyclopropane. Further, it has been observed that such poor yielded Cp ligand of prior art is not suitable enough to be carried forward for metal complex reactions. On contrary, it is evident from the data in table 1 that the currently developed process is advantageously capable of reducing formation of unwanted impurities, thereby, resulting into formation of the final product i.e. ethylene (C2) bridged ansa metallocene precursor / Cp ligand with superior yields i.e. 70-90%. Consequently, these Cp ligands can easily be used for further metal complex reactions forming ethylene bridged ansa metallocene catalysts with good yields (70-85%).

Claims

CLAIMS:

1. A new, improved process for synthesizing C2 (ethylene) bridged cyclopentadienyl ligand having a general formula I:

wherein, R1 to R8 is same or different and in each occurrence is independently selected from H, substituted or unsubstituted C1 -C12 alkyl, substituted or unsubstituted C1-C10 alkenyl, substituted or unsubstituted C1-C10 alkynyl, substituted or unsubstituted Cl -02 heterocyclyl, substituted or unsubstituted C1- C12 cycloalkyl, substituted or unsubstituted C1 -C12 aromatic ring system, silyl, alkylsilyl; wherein any two consecutive groups among R1 to R8 may be taken together to form a substituted or unsubstituted aromatic, partially saturated or saturated fused ring system with or without a heteroatom selected from N, O, S; wherein, the said process comprises steps of:

a. reacting a halo-ester compound with a substituted or unsubstituted cyclopentadienyl (Cp¹) metal salt to form an ester intermediate;

b. reducing the said ester intermediate with a reducing agent to form an aldehyde intermediate; c. adding another substituted or unsubstituted cyclopentadienyl (Cp²) metal salt to the above aldehyde intermediate of step (b) in presence of a saturated cyclic secondary amine, preferably a saturated secondary N-heterocycle catalyst, forming a fulvene derivative; followed by

d. reducing the said fulvene derivative with a reducing agent to form a C2 (ethylene) bridged cyclopentadienyl ligand.

2. A new, improved process for synthesizing C2 (ethylene) bridged ansa metallocene catalyst comprising the steps of:

b. reducing the said ester intermediate with a reducing agent to form an aldehyde intermediate;

c. adding another substituted or unsubstituted cyclopentadienyl (Cp²) metal salt to the above aldehyde intermediate of step (b), essentially in presence of a saturated cyclic secondary amine, preferably a saturated secondary N-heterocycle catalyst, forming fulvene intermediate;

d. reducing the said fulvene derivative with a reducing agent to form a C2 (ethylene) bridged cyclopentadienyl ligand; followed by

e. lithiating the said C2 (ethylene) bridged cyclopentadienyl ligand with a lithiating agent; and f. reacting the said lithiated ligand with MC14, wherein M is a transition metal preferably selected from Ti, Hf and Zr, preferably Zr, in order to form an ansa metallocene catalyst.

3. An improved process for synthesizing C2 bridged ansa metallocene catalyst comprising steps of:

c. adding another substituted or unsubstituted cyclopentadienyl (Cp²) metal salt to the above aldehyde intermediate of step (b) in presence of a saturated cyclic secondary amine, preferably, asaturated secondary N-heterocycle catalyst, forming a fulvene intermediate; followed by

d. directly adding a lithiating agent and MCU to the said fulvene intermediate, wherein M is a transition metal preferably selected from Ti, Hf and Zr, preferably Zr, forming an ansa metallocene catalyst.

4. The process as claimed in claim 1 or claim 2 or claim 3, wherein the halo-ester is selected from bromo-ester or chloro-ester.

5. The process as claimed in claim 1 or claim 2 or claim 3, wherein Cp¹ or Cp² is selected from cyclopentadienyl, fluorenyl, indenyl..

6. The process as claimed in claim 1 or claim 2 or claim 3, wherein the metal salt of Cp¹ or Cp²is selected from butyl lithium (BuLi) or potassium tert-butoxide.

7. The process as claimed in claim 1 or claim 2 or claim 3, wherein the said reducing agents are selected from a group consisting of diisobutylaluminium hydride

(DIBALH), lithium aluminium hydride (LAH).

8. The process as claimed in claim 1 or claim 2 or claim 3, wherein the said saturated cyclic secondary amine catalystis selected from a group consisting of pyrrolidine, piperidine, morpholine. .

9. The process as claimed in claim 2 or claim 3, wherein the lithiating agent is selected from n-butyl lithium (nBuLi) , lithium triethylborhydride (LiEt3BH).

10. The process as claimed in claim 1 produces C2 (ethylene) bridged cyclopentadienyl ligand having 70-90% yield.

11. The process as claimed in claim 2 or claim 3 produces ansa metallocene catalyst having 70-85% yield.

12. An ansa metallocene catalyst produced by the process as claimed in any of the preceding claims, has a structural formula II:

wherein,

R1 to R8 is same or different and in each occurrence is independently selected from H, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C1-C10 alkenyl, substituted or unsubstituted C1 -C10 alkynyl, substituted or unsubstituted C1-C12 heterocyclyl, substituted or unsubstituted C1-C12 cycloalkyl, substituted or unsubstituted C1-C12 aromatic ring system, silyl, alkylsilyl; wherein any two consecutive groups among R1 to R8 may be taken together to form a substituted or unsubstituted aromatic, partially saturated or saturated fused ring system with or without a heteroatom selected from N, O, S;