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Article

Syntheses of Silylene-Bridged Thiophene-Fused Cyclopentadienyl ansa-Metallocene Complexes for Preparing High-Performance Supported Catalyst

by
Sun Mi Jeong
1,
Ju Yong Park
1,
Yong Bin Hyun
1,
Jun Won Baek
1,
Hagjun Kim
2,
Yeokwon Yoon
2,
Sangchul Chung
2,
Junseong Lee
3 and
Bun Yeoul Lee
1,*
1
Department of Molecular Science and Technology, Ajou University, Suwon 16499, Korea
2
Olefins Technology Team, GS Caltex R&D Center, Daejeon 34122, Korea
3
Department of Chemistry, Chonnam National University, Gwangju 61186, Korea
*
Author to whom correspondence should be addressed.
Catalysts 2022, 12(3), 283; https://doi.org/10.3390/catal12030283
Submission received: 4 February 2022 / Revised: 26 February 2022 / Accepted: 28 February 2022 / Published: 2 March 2022
(This article belongs to the Special Issue Organometallic Homogeneous Catalysis)
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Abstract

:
We synthesized a series of Me2Si-bridged ansa-zirconocene complexes coordinated by thiophene-fused cyclopentadienyl and fluorenyl ligands (Me2Si(2-R1-3-R2-4,5-Me2C7S)(2,7-R32C13H6))ZrMe2 (R1 = Me or H, R2 = H or Me, R3 = H, tBu, or Cl) for the subsequent preparation of supported catalysts. We determined that the fluorenyl ligand adopts an η3-binding mode in 9 (R1 = Me, R2 = H, R3 = H) by X-ray crystallography. Further, we synthesized a derivative 15 by substituting the fluorenyl ligand in 9 with a 2-methyl-4-(4-tert-butylphenyl)indenyl ligand, derivatives 20 and 23 by substituting the Me2Si bridge in 12 (R1 = Me, R2 = H, R3 = tBu) and 15 with a tBuO(CH2)6(Me)Si bridge, and the dinuclear congener 26 by connecting two complexes with a –(Me)Si(CH2)6Si(Me)– spacer. The silica-supported catalysts prepared using 12, 20, and 26 demonstrated up to two times higher productivity in ethylene/1-hexene copolymerization than that prepared with conventional (THI)ZrCl2 (21–26 vs. 12 kg-PE/g-(supported catalyst)), producing polymers with comparable molecular weight (Mw, 330–370 vs. 300 kDa), at a higher 1-hexene content (1.3 vs. 1.0 mol%) but a lower bulk density of polymer particles (0.35 vs. 0.42 g/mL).

1. Introduction

Homogeneous single-site catalysts, such as metallocene and half-metallocene, and post-metallocene catalysts are actively used in the production of polyethylene (PE) and polypropylene (PP), although most PE and PP is still produced by suing heterogeneous Ziegler–Natta catalysts [1,2]. While homogeneous catalysts can be directly used in a solution process where polymers (e.g., polyolefin elastomer (POE) with high α-olefin content) are formed by dissolution in solvent, they should be immobilized on an inorganic support, e.g., silica, in order to be applied in a slurry-process or a gas-phase process, where the morphology of the generated polymer particles is of importance for stable operation [3,4,5,6,7,8,9,10,11]. When a homogeneous catalyst is injected, as dissolved, into a slurry- or gas-phase reactor, the shape and size of the generated polymer particles are irregularly uncontrolled, making stable operation impossible (termed ‘fouling’) as well as causing low productivity due to low bulk density. Because a large portion of PE and PP is produced by the slurry and gas-phase processes, high-performance supported catalysts are essential in the industrial sector [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26].
Recently, we reported the syntheses of ansa-metallocene complexes coordinated by thiophene-fused cyclopentadienyl and tetramethylcyclopentadienyl ligands (I in Scheme 1), the dinuclear congener (II), and its analog attaching the tBuO(CH2)6-tether (III), where we showed that the supported catalysts of II and III outperformed those prepared with I, exhibiting the same activity as when dissolved in the homogeneous phase [27]. Other studies also reported the syntheses of metallocene and half-metallocene complexes with thiophene-fused cyclopentadienyl ligands (some of which have been used for commercial processes with advantageous performance) [28,29,30,31,32,33] and the syntheses of dinuclear complexes, for the purpose of developing new polymerization catalysts [34,35,36,37,38,39,40]. In this work, we synthesized a series of silylene-bridged ansa-metallocene complexes constructed with thiophene-fused cyclopentadienyl ligands for the purpose of preparing high-performance supported catalysts, the successful results of which are reported herein.

2. Results and Discussion

2.1. Preparation of ansa-Metallocene Complexes

First, we discuss the syntheses of Me2Si-bridged ansa-zirconocene complexes coordinated by a thiophene-fused cyclopentadienyl and a fluorenyl ligand (Scheme 2). We substituted the expensive tetramethylcyclopentadienyl ligands in I–III with fluorenyl ligands. We prepared the thiophene-fused cyclopentadiene compounds on a large scale (50 g scale with 1 L glassware) [41,42]. The treatment of nBuLi with thiophene-fused cyclopentadiene compounds in hexane precipitated the corresponding cyclopentadienyl–Li salt in ~90% yield. The addition of excess Me2SiCl2 (3.0 eq) to the Li salts in toluene produced Me2(Cl)Si-attached compounds 1–3. The treatment of 1–3 with fluorenyl–Li produced the target compounds 4–8 in yields ranging from 27% to 58%. We removed all unidentified side products via column chromatography and purified the obtained products via recrystallization in hexane at −30 °C. We performed the metalation according to the following established synthetic protocol: lithiation with 2.0 eq nBuLi in THF, followed by the sequential addition of MeMgBr (2.3 eq) and ZrCl4·(THF)2 (0.98 eq) [43,44]. The target ansa-zirconocene complexes 9–13 were isolated via toluene extraction and purified by precipitation in toluene at −30 °C. Except for the 2,7-di(tert-butyl)fluorenyl ligand-containing 12 (24% yield), the metalation produced all the target complexes with good yields ranging from 60% to 91%. The 1H NMR spectra of 9–13 showed two diastereotopic Zr–CH3 signals at −1.6 and −1.1 ppm as singlets. Small variations in the chemical shifts were caused by different substituents in the thiophene ring and fluorenyl ligand (Figures S9–S13). The 1H NMR spectra also showed two diastereotopic Si-bound methyl group signals at 1.04–1.08 ppm and 0.82–0.84 ppm for 9–11, at 1.16 and 0.98 ppm for 12 (downfield shifts caused by electron-donating tBu groups), and at 0.89 and 0.67 ppm for 13 (upfield shifts caused by electron-withdrawing Cl groups).
Because the solids precipitated in toluene were not suitable for X-ray crystallography, we grew single crystals of 9 in a CH2Cl2 solution via the slow evaporation of CH2Cl2 in a closed chamber containing methylcyclohexane. The bond lengths measured by X-ray crystallography suggested an η3-binding mode for the fluorenyl ligand and an η5-binding mode for the thiophene-fused cyclopentadienyl ligand; the two Zr–C bonds in the fluorenyl ligand (Zr–C3, 2.8122(31) Å and Zr–C4, 2.807(3) Å) were too long to be considered chemical bonds (Figure 1). The closest Zr–C distance in the fluorenyl ligand (i.e., Zr–C1, 2.438(3) Å) was shorter than that in the thiophene-fused cyclopentadienyl ligand (i.e., Zr–C14, 2.485(3) Å). The bridged Si atom was located slightly out of the plane formed by either the fluorenyl ligand or the thiophene-fused cyclopentadienyl ligand (Si–C14-centroid of C14–C15–C16–C17–C18 ring, 159.2°; Si–C1-centroid of C1–C2–C3–C4–C5 ring, 168.2°).
Next, we discuss the syntheses of Me2Si-bridged ansa-zirconocene complexes coordinated by a thiophene-fused cyclopentadienyl ligand and a 2-methyl-4-(4-tert-butylphenyl)indenyl ligand (Scheme 3). The reaction of 2-methyl-4-(4-tert-butylphenyl)indenyl–Li with Me2(Cl)Si-attached thiophene-fused cyclopentadiene compound 1 produced the target ligand precursor 14 in 59% yield. The metalation of 14 afforded the Me2Si-bridged ansa-zirconocene complex 15 coordinated by thiophene-fused cyclopentadienyl and 2-methyl-4-(4-tert-butylphenyl)indenyl ligands in 67% yield (Scheme 3a). The 1H NMR spectrum of 14 showed two sets of signals attributed to the presence of two diastereomers. The intensities of the minor set were low (1.0:0.11), indicating that the formation of one of the diastereomers was not favored. The 1H NMR spectrum of 15 also showed two sets of signals attributed to the presence of two diastereomers—racemic-type and meso-type forms; however, the highly biased ratio (i.e., 1.0:0.11) observed for ligand precursor 14 was lost in the deprotonation steps and it changed to a less biased 1.0:0.54 (or vice versa) after metalation. The singlet Zr–CH3 and Si–CH3 signals were observed at −0.86, −0.37, 0.74, and 0.78 ppm for one diastereomer and at −1.32, 0.17, 0.35, and 0.62 ppm for the other diastereomer (Figure S15). Attempts to separate the two isomers via recrystallization using various methods and conditions were unsuccessful. The 1H NMR spectrum of the toluene extract showed broad signals at 3.77 and 1.37 ppm along with those assigned to the product; we attributed these signals to MgCl2·(THF) byproducts. According to previous studies, these THF signals could be completely removed either by the recrystallization process, as in the synthesis of 9–13, or by the hexane extraction process once the complex dissolved in hexane. However, because 15 could neither be crystallized in toluene nor was soluble in hexane, the complete removal of THF signals was not possible. As they contained MgCl2 impurity, the elemental analysis data of 15 were not in agreement. Even for 9–13, which were purified by crystallization in toluene removing the THF signals almost completely, MgCl2 impurity might not have been thoroughly removed; the carbon contents measured in the elemental analyses were several % less than the calculated values. We prepared the CGC-type titanium complex 17 coordinated by a thiophene-fused cyclopentadienyl ligand according to the routine method (Scheme 3b).
Next, we discuss the syntheses of ansa-metallocene complexes attaching a tBuO(CH2)6-tether (Scheme 4). Metallocene complexes attaching tBuO(CH2)6-tether have been routinely used in the preparation of high-performance supported catalysts with some advantages (proprietary catalysts for LG Chem) [11,45]. In the same way, we prepared ansa-metallocene complexes attaching tBuO(CH2)6-tether by replacing the Me2Si bridge with a tBuO(CH2)6(Me)Si bridge. The reaction of the thiophene-fused cyclopentadienyl–Li ((Me3C7H2S)−Li+) with 1.0 eq tBuO(CH2)6(Me)SiCl2 in THF furnished the target compound tBuO(CH2)6(Me)Si(Cl)(Me3C7H2S); however, the formation of a side product, i.e., dialkylated compound tBuO(CH2)6(Me)Si(Me3C7H2S)2 was observed. Unlike the synthesis of 1 (Me2Si(Cl)(Me3C7H2S), where excess Me2SiCl2 (3.0 eq) could react with (Me3C7H2S)−Li+ to avoid the formation of the dialkylated compound Me2Si(Me3C7H2S)2, excess tBuO(CH2)6(Me)SiCl2 could not be added in the synthesis of tBuO(CH2)6(Me)Si(Cl)(Me3C7H2S) because the removal of the unreacted tBuO(CH2)6(Me)SiCl2 would be difficult. Therefore, the formation of the dialkylated side product tBuO(CH2)6(Me)Si(2,7-tBu2C13H7)2 was inevitable in the reaction of 2,7-di-tert-butylfluorenyl–Li ((2,7-tBu2C13H7)−Li+) with 1.0 eq tBuO(CH2)6(Me)SiCl2 performed in THF. We circumvented this problem by reacting (2,7-tBu2C13H7)−Li+ with 1.0 eq tBuO(CH2)6(Me)SiCl2 in hexane with a small amount of tert-butyl methyl ether (3.3 eq/Li+) and at low temperature (−78 °C). This approach gave the target monoalkylated compound 18 with a negligible amount of dialkylated side product tBuO(CH2)6(Me)Si(2,7-tBu2C13H7)2 (ca., 1 mol%, Figure S18, Scheme 4a) [46]. We noted that this approach did not work for fluorenyl–Li without the bulky tBu substituents (e.g., (C13H9)−Li+), as the dialkylated side product (tBuO(CH2)6(Me)Si(fluorenyl)2) was produced at a substantial amount (10 mol%).
The reaction of the thiophene-fused cyclopentadienyl–K ((Me3C7H2S)−K+) with 18 produced the target compound 19 in 67% yield. The metalation of 19 produced the target ansa-metallocene complex 20 containing tBuO(CH2)6-tether in 94% yield. The presence of this tether rendered 20 soluble in hexane, which enabled the purification via hexane extraction. The 1H NMR spectrum of the purified 20 showed no THF signal (Figure 2), and the compound was used without further purification in the preparation of the supported catalyst. There were two diastereomers in 20 due to a chiral center on Si atom and a plane chirality on thiophene-fused cyclopentadienyl ligand. However, most of signals were not split by the diastereomerism, or were split very narrowly, allowing signal assignment; only Si-CH3 signal was split widely at 1.08 and 1.26 ppm (Figure 2).
The reaction of 2-methyl-4-(4-tert-butylphenyl)indenyl–Li and 1.0 eq tBuO(CH2)6(Me)SiCl2 in hexane in the presence of a small amount of tert-butyl methyl ether (3.3 eq/Li+) at −78 °C produced the target compound 21 without the formation of dialkylated species (Scheme 4b). The 1H NMR spectrum of 21 indicated a 1:0.7 diastereomeric mixture (Figure S20). The reaction of the thiophene-fused cyclopentadienyl–K ((Me3C7H2S)−K+) with 21 in THF afforded the target compound 22 in 90% yield. The 1H NMR spectrum of 22 was too complicated to be clearly assigned due to the presence of three chiral centers (Figure S21). The metalation of 22 gave the target ansa-metallocene complex 23 in 92% yield. The 1H NMR spectrum of 23 purified by hexane extraction could be interpreted as a mixture of racemic-type and meso-type complexes in 1.0:0.40 ratio (or vice versa), each of which was further split into a 1:0.9 and 1:1 ratio, respectively, due to the additional chiral centers on the Si atoms for a total of four diastereomers (Figure 3). The 1H NMR signals of the two methyl groups bonded to Zr (Zr–CH3) were observed at −0.85 ppm (narrowly split by a chirality on the Si atom) and at −0.37 ppm for the racemic-type complex. Another set of Zr–CH3 signals was observed at −1.32 ppm (narrowly split by a chirality on Si atom) and at 0.18 ppm for the minor meso-type complex. For the racemic-type complex, two Si–CH3 signals were observed, at 0.84 and 0.88 ppm (1:0.9 ratio), due to the diastereomerism on the Si atom, while two Si–CH3 signals were observed, at 0.73 and 1.07 ppm (1:1 ratio), for the meso-type complex as well. During the hexane extraction, the MgCl2 impurities seemed to be almost completely removed, and the elemental analysis data of 20 and 23 as forms of hexane extract only were quite in agreement with the calculated values, although the carbon contents were still somewhat deviated by 1.2–1.3%.
Next, we discuss the yield improvement of compounds 4–7 by reaction-sequence reversal (Scheme 5). The yields in the syntheses of 4–7 were lower (27–43%) compared to that in the synthesis of 19 (67%). The difference between the two processes is the respective reaction sequences involving Me2SiCl2 and tBuO(CH2)6(Me)SiCl2. For 4–7, the thiophene-fused cyclopentadienyl–Li first reacted with Me2SiCl2 before reacting with fluorenyl–Li, whereas for 19, the fluorenyl–Li first reacted with tBuO(CH2)6(Me)SiCl2 before reacting with the thiophene-fused cyclopentadienyl–K. We attribute the low yields of 4–7 to the deprotonation of the Me2(Cl)Si-attached thiophene-fused cyclopentadiene compounds 1–3 by the action of the basic fluorenyl anion. By 1H NMR analysis, we determined the following basicity sequence:
Fluorenyl–Li (pKa, 22.6) > thiophene-fused cyclopentadienyl–Li ((Me3C7H2S)−Li+) > indenyl–Li (pKa, 20.1) ≈ tetramethylcyclopentadienyl–Li > 2,7-dichlorofluorenyl–Li (Scheme 5, top panel).
This sequence could be inferred from the observations that in THF-d8, (Me3C7H2S)−Li+ could deprotonate indene, tetramethylcyclopentadiene, and 2,7-dichlorofluorene but not fluorene. Further, while the reaction of 2,7-dichlorofluorene with tetramethylcyclopentadienyl–Li produced 2,7-dichlorofluorenyl–Li, the reaction of indenyl–Li with tetramethylcyclopentadiene produced solid deposits of tetramethylcyclopentadienyl–Li with the formation of indene, reaching an equilibrium at ~60% conversion. Following these observations, we reversed the reaction sequence, first by reacting the more basic fluorenyl–Li with Me2SiCl2, followed by the less basic thiophene-fused cyclopentadienyl–Li. This sequence reversal improved the yield of 7 dramatically from 27% to 81% (Scheme 5, bottom panel).
Next, we discuss the syntheses of dinuclear ansa-zirconocene complexes (Scheme 6). Various dinuclear ansa-metallocene complexes were synthesized with silylene-bridged cyclopentadienyl, indenyl, or fluorenyl ligands in the early 2000s, demonstrating higher activity than the mononuclear congener [47,48]. We also demonstrated that dinuclear complexes of thiophene-fused cyclopentadienyl and tetramethylcyclopentadienyl ligands could be used in the preparation of supported catalysts with some advantages. For example, a higher amount of complexes could be anchored on the support, thus achieving higher activity and obtaining finer polymer particles [27]. We prepared 24, the dinuclear complexes of silylene-bridged ansa-zirconocene complexes coordinated with thiophene-fused cyclopentadienyl and 2,7-di(tert-butyl)fluorenyl ligands with an optimal hexamethylene (–(Me)Si(CH2)6Si(Me)–) spacer (Scheme 6). The reaction of 24 via the reversed sequence mentioned above afforded the ligand precursor 25 in 90% yield. The metalation of 25 gave the target dinuclear complex 26 in 62% yield. Since complex 26 was soluble in hexane, a fairly pure complex was obtained, with the complete removal of the contaminant THF signals in the 1H NMR spectrum. The signals were split due to the chiral centers on the Si atom, but the splitting was so narrow that the peaks could be unambiguously interpreted (Figure S24).

2.2. Preparation of Supported Catalyst and Ethylene/1-Hexene Copolymerization

We prepared the supported catalysts using the complexes discussed in the previous sections; the complexes were reacted at 70 °C for 1.0 h with silica–MAO that was beforehand obtained by treatment of silica with methylaluminoxane (MAO) (150 μmol/g-(silica–MAO); Al/Zr = 53), and the resulting supported catalysts were isolated by filtration. In all cases, the filtrates were almost colorless, indicating that most of the metallocene complexes were anchored on the silica–MAO surface. For silica–MAO with optimal MAO coverage (450 mg MAO/g-silica; 4.8 mmol Al/g-(silica-MAO)), we treated silica (~1.0 mmol OH/g; pore volume, 1.6 cm3/g; surface area, 309 m2/g; pore diameter, 230 nm; mean particle size, 30 μm) with MAO (Me3Al content, 13 mol% Al) at a 1:0.5 weight ratio [27,49,50]. We evaluated the performance of each of the prepared supported catalysts via ethylene/1-hexene copolymerization with 6.0 mg of the supported catalysts in hexane (300 mL) containing 1-hexene (3.0 mL) at 80 °C for 30 min under 20 bar ethylene pressure. The supported catalysts prepared with 9–12 containing fluorenyl ligand showed extremely high productivities (21–26 kg PE/g-(supported catalyst)/h; entries 1–4 in Table 1), although 9–12 were used as they contained a slight amount of MgCl2 impurity. The productivity was higher compared with those of both the supported catalysts prepared using tetramethylcyclopentadienyl analog I (17.5 kg PE/g-(supported catalyst)/h; entry 11) and the conventional (rac-ethylenebis(tetrahydroindenyl))ZrCl2 ((THI)ZrCl2) (12 kg PE/g-(supported catalyst)/h; entry 14). Further, our supported catalysts had productivities comparable to those of the supported catalysts prepared using tetramethylcyclopentadienyl analogs II containing tBuO(CH2)6-tether and dinuclear complex III (25 and 23 kg PE/g-(supported catalyst)/h; entries 12–13).
One advantage of the supported catalysts of 9–12 containing fluorenyl ligand was that they produced high-molecular-weight polymers (Mw, 250–330 kDa), with the Mw values comparable to those of the polymers prepared from the conventional (THI)ZrCl2 (Mw, 300 kDa). The supported catalyst prepared with 12 containing 2,7-di(tert-butyl)fluorenyl ligand furnished the polymer with the highest molecular weight (Mw, 334 kDa) and the lowest molecular weight distribution (Mw/Mn, 2.5, entry 4). Comparatively, the supported catalysts prepared with tetramethylcyclopentadienyl analogs I–III produced polymers with much lower molecular weights (Mw = 110–125 kDa). The supported catalyst prepared with 13 containing electron-withdrawing chloro-substituents on fluorenyl ligand showed low activity (5.6 kg PE/g-(supported catalyst)/h; entry 3), although a high-molecular-weight polymer was produced (Mw, 340 kDa; entry 5).
Another advantage of the complexes containing fluorenyl ligand was the higher 1-hexene incorporation capability of 9–12 (1-hexene content, 1.3 mol%) compared to both the tetramethylcyclopentadienyl analogs I–III (0.80 mol%) and (THI)ZrCl2 (1.0 mol%). A disadvantage of the supported catalysts of 9–12 was the lower bulk density of the generated polymer particles, compared to that of I–III or (THI)ZrCl2 (0.33–0.36 vs. 0.38 or 0.42 g/mL). The supported catalyst prepared with the 2-methyl-4-(4-tert-butylphenyl)indenyl complex 15, for which complete removal of the THF signal was impossible and accordingly contained a substantial amount of MgCl2 impurity, showed low activity (13.2 kg PE/g-(supported catalyst)/h; entry 6). The supported catalyst prepared with the CGC-type complex 17 showed very low activity (0.75 kg PE/g-(supported catalyst)/h).
Further, the advantage in terms of activity and molecular weight realized by attaching a tBuO(CH2)6-tether or constructing a dinuclear congener was marginal in this work (entries 7–9). However, another aspect of the advantage is in the synthesis; dinuclear complex and complexes containing tBuO(CH2)6-tether are much more soluble in hexane than their mononuclear congeners. This facilitates the isolation of fairly pure complexes, even with containing many chiral centers, via a simple hexane extraction (in high yields and with the complete removal of contaminant THF signals). Complexes 20 and 23 attaching tBuO(CH2)6-tether and the dinuclear one 26 are not a single compound but a mixture of stereoisomers, and polymers generated with those complexes exhibited rather broad molecular weight distributions (Mw/Mn, 4.1, 5.2, and 4.1, respectively), which may be an advantage; polymers with broad molecular weight distributions are usually needed in the polyolefin industry.

3. Materials and Methods

3.1. General Remarks

All experiments were performed in an inert atmosphere using a standard glove box and Schlenk techniques. Toluene, hexane, and tetrahydrofuran (THF) were purchased from Thermo Fisher Scientific Korea and distilled from benzophenone ketyl. The hexane (HPLC grade) used for the polymerization reactions was purchased from Thermo Fisher Scientific Korea (Seoul, Korea) and purified over a Na/K alloy. The ethylene gas was purified by contact with molecular sieves and copper for more than 12 h under a pressure of 48 bar. Silica (SYLOPOL-2410) was obtained from GRACE and used as received (Yeosu, South Korea). The 1H NMR (600 MHz) and 13C NMR (150 MHz) spectra were recorded on a JEOL (Tokyo, Japan) ECZ 600 instrument. Gel permeation chromatography (GPC) was performed in 1,2,4-trichlorobenzene at 160 °C using an Agilent PL-GPC 220 system equipped with an RI detector and two columns (PLgel mixed-B 7.5 × 300 mm from Varian (Polymer Lab (Salop, UK)).

3.2. Synthesis of 1

A solution of nBuLi in hexane (8.44 g, 2.5 M, 30.4 mmol) was added dropwise to a solution of thiophene-fused cyclopentadiene compound 2,4,5-Me3C7H3S (5.00 g, 30.4 mmol) in hexane (100 mL) at −78 °C. The resulting solution was slowly warmed to room temperature and then stirred overnight at room temperature to precipitate the corresponding thiophene-fused cyclopentadienyl–Li as a white solid, which was isolated by filtration (4.66 g, 90%). A solution of Me2SiCl2 (1.14 g, 8.81 mmol) in toluene (7.0 mL) was added to the prepared Li compound (1.00 g, 5.88 mmol) dispersed in toluene (5.0 mL) at −30 °C. The solution was slowly warmed to room temperature and stirred overnight at room temperature. After the removal of the solvent using a vacuum line, the product was extracted with hexane (20 mL) via filtration over Celite. The solvent was removed using a vacuum line to obtain the desired compound as a yellowish-brown liquid (1.39 g, 92%). 1H NMR (C6D6): δ 6.49 (q, 4J = 1.2 Hz, 1H), 3.23 (s, 1H), 2.28 (s, 3H, CH3), 1.97 (s, 3H, CH3), 1.92 (q, 4J = 1.2 Hz, 3H, CH3), 0.21 (s, 3H, SiCH3), and 0.02 (s, 3H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 152.5, 141.6, 136.8, 135.6, 131.0, 116.6, 48.8, 16.0, 14.8, 11.7, −0.4, and −0.8 ppm. HRMS(EI): m/z calcd. ((M+) C12H17ClSSi) 256.0509. Found: 256.0509.

3.3. Synthesis of 2

Compound 2 was synthesized using the same conditions and procedure as those for 1, with (Me4C7S)−Li+ (1.08 g, 5.88 mmol). A yellowish-brown liquid compound was obtained in 92% yield (1.46 g). 1H NMR (C6D6): δ 3.20 (s, 1H), 2.15 (s, 3H, CH3), 2.05 (s, 3H, CH3), 2.00 (s, 3H, CH3), 1.99 (s, 3H, CH3), 0.27 (s, 3H, SiCH3), and 0.03 (s, 3H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 151.6, 136.8, 134.6, 134.0, 131.8, 125.4, 48.3, 14.6, 13.6, 12.2, 12.1, −0.2, and −0.9 ppm. HRMS(EI): m/z calcd. ((M+) C13H17ClSSi) 270.0663. Found: 270.0665.

3.4. Synthesis of 3

Compound 3 was synthesized using the same conditions and procedure as those for 1, with (Me3C7H2S)−Li+ (0.92 g, 5.88 mmol). A yellowish-brown liquid compound was obtained in 92% yield (1.31 g). 1H NMR (C6D6): δ 7.00 (d, J = 4.8 Hz, 1H), 6.80 (d, J = 4.8 Hz, 1H), 3.21 (s, 1H), 1.94 (s, 3H, CH3), 1.89 (s, 3H, CH3), 0.16 (s, 3H, SiCH3), and −0.01 (s, 3H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 152.8, 138.2, 137.7, 130.9, 127.0, 117.8, 48.4, 14.8, 11.7, −0.5, and −0.8 ppm. HRMS(EI): m/z calcd. ((M+) C11H15ClSSi) 242.0352. Found: 242.0352.

3.5. Synthesis of 4

A solution of nBuLi in hexane (8.34 g, 2.5 M, 30.1 mmol) was added slowly to a solution of fluorene (5.00 g, 30.1 mmol) in toluene (50 mL) at room temperature. The resulting solution was heated to 80 °C and then stirred for 5 h to precipitate fluorenyl–Li as orange solids, which were isolated by filtration (4.66 g, 90%). The prepared fluorenyl–Li (0.248 g, 1.56 mmol) was added to a solution of 1 (0.400 g, 1.56 mmol) in THF (6.0 mL) at −30 °C, and the mixture was slowly warmed to room temperature. The solution was stirred overnight, and the solvent was removed using a vacuum line. The product was extracted with hexane (20 mL) and collected by filtration over Celite. After removing the solvent using a vacuum line, the product was purified by silica gel column chromatography and eluted with hexane and toluene (30:1, v/v). A yellowish-brown, oily compound was obtained (0.181 g, 30%). 1H NMR (C6D6): δ 7.80 (d, J = 7.6 Hz, 1H), 7.77 (d, J = 7.6 Hz, 1H), 7.74 (d, J = 7.6 Hz, 1H), 7.34 (d, J = 7.6 Hz, 1H), 7.29 (t, J = 7.6 Hz, 1H), 7.26 (t, J = 7.6 Hz, 1H), 7.24 (t, J = 7.6 Hz, 1H), 7.15 (t, J = 7.6 Hz, 1H), 6.62 (s, 1H), 4.47 (s, 1H), 3.60 (s, 1H), 2.34 (s, 3H, CH3), 2.00 (s, 3H, CH3), 1.76 (s, 3H, CH3), −0.28 (s, 3H, SiCH3), and −0.49 (s, 3H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 151.9, 145.5, 141.4, 141.3, 140.7, 138.2, 137.6, 130.1, 126.0, 125.9, 124.7, 124.5, 120.5, 120.4, 116.9, 46.1, 40.8, 16.1, 15.0, 11.9, −6.7, and −7.2 ppm. HRMS(EI): m/z calcd. ((M+) C25H26SSi) 386.1527. Found: 386.1527.

3.6. Synthesis of 5

Compound 5 was synthesized under the same conditions and procedure as 4, using 2 (0.423 g, 1.56 mmol). A yellowish-brown, oily compound was obtained by silica gel column chromatography with hexane and toluene (30:1, v/v) as eluents (0.269 g, 43%). 1H NMR (C6D6): δ 7.79 (d, J = 7.6 Hz, 1H), 7.76 (d, J = 7.6 Hz, 2H), 7.33 (d, J = 7.6 Hz, 1H), 7.29 (t, J = 7.6 Hz, 1H), 7.26 (t, J = 7.6 Hz, 1H), 7.23 (td, 3J = 7.6 Hz, 4J = 1.4 Hz, 1H), 7.13 (td, 3J = 7.6 Hz, 4J = 1.4 Hz, 1H), 4.47 (s, 1H), 3.55 (s, 1H), 2.22 (s, 3H, CH3), 2.14 (s, 3H, CH3), 2.07 (s, 3H, CH3), 1.74 (s, 3H, CH3), −0.23 (s, 3H, SiCH3), and −0.44 (s, 3H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 151.0, 145.6, 145.6, 141.4, 138.1, 136.0, 133.7, 131.0, 126.7, 126.5, 126.0, 125.8, 125.6, 124.7, 124.6, 120.5, 120.3, 45.6, 40.8, 14.7, 13.7, 12.4, 12.2, −6.5, and −6.9 ppm. HRMS(EI): m/z calcd. ((M+) C26H28SSi) 400.1684. Found: 400.1681.

3.7. Synthesis of 6

Compound 6 was synthesized using the same conditions and procedure as those for 4, with 3 (0.379 g, 1.56 mmol). A yellowish-brown, oily compound was obtained by silica gel column chromatography with hexane and toluene (30:1, v/v) as eluents (0.174 g, 30%). 1H NMR (C6D6): δ 7.78 (d, J = 7.6 Hz, 1H), 7.76 (d, J = 7.6 Hz, 1H), 7.69 (d, J = 7.6 Hz, 1H), 7.30 (d, J = 7.6 Hz, 1H), 7.29 (t, J = 7.6 Hz, 1H), 7.25 (t, J = 7.6 Hz, 1H), 7.23 (td, 3J = 7.6 Hz, 4J = 1.4 Hz, 1H), 7.15 (td, 3J = 7.6 Hz, 4J = 1.4 Hz, 1H), 6.97 (d, J = 4.8 Hz, 1H), 6.86 (d, J = 4.8 Hz, 1H), 4.34 (s, 1H), 3.51 (s, 1H), 1.92 (s, 3H, CH3), 1.68 (s, 3H, CH3), and −0.39 (s, 3H, SiCH3), −0.56 (s, 3H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 152.3, 145.5, 145.4, 141.4, 141.3, 140.2, 139.2, 130.0, 126.7, 126.5, 126.2, 126.0, 125.9, 124.7, 124.6, 120.5, 120.4, 118.1, 45.7, 40.7, 15.0, 11.8, −6.7, and −7.2 ppm. HRMS(EI): m/z calcd. ((M+) C24H24SSi) 372.1368. Found: 372.1371.

3.8. Synthesis of 7

A solution of nBuLi in hexane (4.98 g, 2.5 M, 18.0 mmol) was added dropwise to a solution of 2,7-di-tert-butylfluorene (5.00 g, 18.0 mmol) in toluene (50 mL) at room temperature. The resulting solution was heated to 80 °C and then stirred for 5 h to precipitate 2,7-di-tert-butylfluorenyl-Li as a yellow solid, which was isolated by filtration (4.32 g, 85%). Compound 7 was prepared using the same conditions and procedures as those for 4, with the prepared 2,7-di-tert-butylfluorenyl-Li (0.444 g, 1.56 mmol). A yellowish-brown oily compound was obtained via silica gel column chromatography with hexane and toluene (30:1, v/v) as eluents (0.210 g, 27%). 1H NMR (C6D6): δ 8.02 (s, 1H), 7.83 (d, J = 8.3 Hz, 1H), 7.80 (d, J = 8.3 Hz, 1H), 7.54 (s, 1H), 7.43 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 7.34 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 6.64 (q, J = 1.2 Hz, 1H), 4.47 (s, 1H), 3.74 (s, 1H), 2.35 (s, 3H, CH3), 2.02 (s, 3H, CH3), 1.86 (s, 3H, CH3), 1.39 (s, 9H, tBu), 1.32 (s, 9H, tBu), −0.15 (s, 3H, SiCH3), and −0.40 (s, 3H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 152.0, 149.3, 149.1, 145.8, 145.7, 140.8, 139.1, 139.0, 138.2, 137.7, 130.2, 123.2, 123.1, 124.9, 121.6, 121.5, 119.9, 119.8, 117.0, 46.4, 40.6, 35.1, 34.9, 31.9, 31.9, 16.1, 15.1, 11.9, −6.3, and −6.9 ppm. HRMS(EI): m/z calcd. ((M+) C33H42SSi) 498.2774. Found: 498.2776. The yield was improved by reversing the reaction sequence. Thus, tert-butyl methyl ether (0.889 g, 3.3 eq/Li+) was added to a solution of 2,7-di(tert-butyl)fluorenyl–Li (0.766 g, 2.70 mmol) in hexane (27 mL) tert-butyl methyl ether (0.889 g, 3.3 eq/Li+). After cooling to −78 °C, a solution of Me2SiCl2 (0.522 g, 4.04 mmol) in hexane (7.5 mL) was added. After overnight stirring at room temperature, the solvent was removed under vacuum. The product was extracted using hexane (15 mL). The extract was collected by filtration over Celite. The solvent was removed using a vacuum line to obtain 2,7-di(tert-butyl)fluorenyl-Si(Me)Cl (0.90 g, 90%). The prepared 2,7-di(tert-butyl)fluorenyl-Si(Me)Cl was dissolved in THF (10 mL). After cooling to −30 °C, thiophene-fused cyclopentadienyl–Li compound (2,4,5-Me3C7H2S)Li (0.413 g, 2.43 mmol) was added. The solution was stirred overnight, and the solvent was removed using a vacuum line. The product was extracted with hexane (15 mL) and collected by filtration over Celite. After removing the solvent using a vacuum line, the product was purified by silica gel column chromatography with hexane and toluene (30:1, v/v) as eluents. A yellowish-brown, oily compound was obtained in 81% yield (0.98 g).

3.9. Synthesis of 8

A solution of nBuLi in hexane (5.90 g, 2.5 M, 21.3 mmol) was added dropwise to a solution of 2,7-dichlorofluorene (5.00 g, 21.3 mmol) in toluene (50 mL) at −78 °C. The resulting solution was stirred overnight to precipitate 2,7-dichlorofluorenyl–Li as a light-yellow solid, which was isolated by filtration (4.51 g, 88%). Compound 8 was prepared using the same conditions and procedures as those for 4, with the prepared 2,7-dichlorofluorenyl–Li (0.376 g, 1.56 mmol). A yellowish-brown, oily compound was obtained by silica gel column chromatography with hexane and toluene (30:1, v/v) as eluents (0.412 g, 58%). 1H NMR (C6D6): δ 7.58 (s, 1H), 7.28 (d, J = 8.3 Hz, 1H), 7.25 (s, 1H), 7.24 (d, J = 8.3 Hz, 1H), 7.22 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 7.17 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 6.52 (s, 1H), 3.91 (s, 1H), 3.21 (s, 1H), 2.37 (s, 3H, CH3), 1.92 (s, 3H, CH3), 1.62 (s, 3H, CH3), −0.33 (s, 3H, SiCH3), and −0.36 (s, 3H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 151.9, 147.3, 147.1, 141.0, 138.7, 138.5, 137.8, 137.1, 132.6, 132.5, 130.4, 126.4, 126.2, 124.9, 124.9, 121.2, 121.1, 117.0, 45.9, 40.9, 16.1, 14.7, 11.8, −5.4, and −5.9 ppm. HRMS(EI): m/z calcd. ((M+) C25H24Cl2SSi) 454.0741. Found: 454.0745.

3.10. Synthesis of 9

A solution of nBuLi in hexane (1.11 g, 2.5 M, 4.02 mmol) was added dropwise to a solution of 4 (0.777 g, 2.01 mmol) in THF (3.5 mL) at −30 °C. After slowly warming to room temperature, the solution was stirred at room temperature for 1 h. After cooling to −30 °C again, MeMgBr (1.41 mL, 1.37 M solution in THF–toluene, 4.62 mmol) and ZrCl4·(THF)2 (0.743 g, 1.97 mmol) were added successively. After the solution was stirred overnight at room temperature, the solvent was removed using a vacuum line. The product was extracted with toluene (30 mL) and collected by filtration over Celite. The solvent was removed using a vacuum line to obtain a yellowish-brown solid, which was redissolved in toluene (4 mL). Yellow solids were deposited when the solution was stored in a freezer at −30 °C (0.906 g, 91%). 1H NMR (C6D6): δ 7.95 (d, J = 8.3 Hz, 1H), 7.85 (d, J = 8.3 Hz, 1H), 7.73 (d, J = 8.3 Hz, 1H), 7.45 (d, J = 8.3 Hz, 1H), 7.34 (t, J = 8.3 Hz, 1H), 7.24 (t, J = 8.3 Hz, 1H), 7.00 (t, J = 8.3 Hz, 2H), 6.17 (q, 4J = 1.2 Hz, 1H), 2.07 (q, J = 1.2 Hz, 3H, CH3), 2.00 (s, 3H, CH3), 1.75 (s, 3H, CH3), 1.06 (s, 3H, SiCH3), 0.83 (s, 3H, SiCH3), −1.08 (s, 3H, ZrCH3), and −1.57 (s, 3H, ZrCH3) ppm. 13C{1H} NMR (C6D6): δ 145.2, 140.1, 132.4, 131.0, 129.1, 128.7, 127.4, 126.9, 126.7, 126.4, 126.1, 125.4, 124.8, 124.0, 123.5, 123.4, 117.1, 116.0, 77.0, 62.7, 40.8, 38.3, 16.2, 15.5, 12.2, 1.5, and 1.3 ppm.

3.11. Synthesis of 10

Compound 10 was synthesized using the same conditions and procedure as those for 9, with 5 (0.175 g, 0.437 mmol). A yellow solid was obtained in 73% yield (0.166 g). 1H NMR (C6D6): δ 7.95 (d, J = 8.3 Hz, 1H), 7.85 (d, J = 8.3 Hz, 1H), 7.74 (d, J = 8.3 Hz, 1H), 7.45 (d, J = 8.3 Hz, 1H), 7.34 (t, J = 8.3 Hz, 1H), 7.23 (t, J = 8.3 Hz, 1H), 7.01 (td, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 7.00 (td, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 2.06 (s, 3H, CH3), 1.96 (s, 3H, CH3), 1.87 (s, 3H, CH3), 1.76 (s, 3H, CH3), 1.08 (s, 3H, SiCH3), 0.84 (s, 3H, SiCH3), −1.08 (s, 3H, ZrCH3), and −1.60 (s, 3H, ZrCH3) ppm. 13C{1H} NMR (C6D6): δ 140.1, 137.1, 132.6, 131.1, 129.5, 127.7, 127.3, 126.8, 126.7, 126.6, 126.5, 125.4, 124.8, 124.4, 123.9, 123.4, 123.4, 117.6, 76.7, 62.8, 39.7, 38.5, 15.3, 13.5, 12.4, 11.9, 1.7, and 1.2 ppm.

3.12. Synthesis of 11

Compound 11 was synthesized using the same conditions and procedure as those for 9, with 6 (0.233 g, 0.626 mmol). A yellow solid was obtained in 60% yield (0.181 g). 1H NMR (C6D6): δ 7.92 (d, J = 8.3 Hz, 1H), 7.83 (d, J = 8.3 Hz, 1H), 7.70 (d, J = 8.3 Hz, 1H), 7.45 (d, J = 8.3 Hz, 1H), 7.34 (t, J = 8.3 Hz, 1H), 7.23 (t, J = 8.3 Hz, 1H), 7.00 (td, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 6.99 (td, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 6.73 (d, J = 5.4 Hz, 1H), 6.44 (d, J = 5.4 Hz, 1H), 1.97 (s, 3H, CH3), 1.74 (s, 3H, CH3), 1.04 (s, 3H, SiCH3), 0.82 (s, 3H, SiCH3), −1.10 (s, 3H, ZrCH3), and −1.65 (s, 3H, ZrCH3) ppm. 13C{1H} NMR (C6D6): δ 139.5, 132.4, 131.2, 130.5, 129.9, 129.4, 129.3, 127.4, 126.8, 126.6, 126.2, 125.4, 124.8, 124.0, 123.5, 123.5, 118.3, 117.5, 76.9, 62.9, 41.9, 38.6, 15.5, 12.1, 1.6, and 1.3 ppm.

3.13. Synthesis of 12

Compound 12 was synthesized using the same conditions and procedure as those for 9, with 7 (0.295 g, 0.591 mmol). A yellow solid was obtained in 24% yield (0.086 g). The solubility of this compound in C6D6 was too low to record the 13C NMR spectrum. 1H NMR (C6D6): δ 7.96, (d, J = 8.3 Hz, 1H), 7.87 (d, J = 8.3 Hz, 1H), 7.76 (s, 1H), 7.58 (s, 1H), 7.50 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 7.43 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 6.22 (q, 4J = 1.2 Hz, 1H), 2.12 (q, 4J = 1.2 Hz, 3H, CH3), 2.03 (s, 3H, CH3), 1.87 (s, 3H, CH3), 1.35 (s, 9H, tBu), 1.30 (s, 9H, tBu), 1.16 (s, 3H, SiCH3), 0.98 (s, 3H, SiCH3), −1.09 (s, 3H, ZrCH3), and −1.59 (s, 3H, ZrCH3) ppm.

3.14. Synthesis of 13

Compound 13 was synthesized using the same conditions and procedure as those for 9, with 8 (0.200 g, 0.440 mmol). A yellow solid was obtained in 74% yield (0.183 g). 1H NMR (C6D6): δ 7.75 (s, 1H), 7.53 (s, 1H), 7.52 (d, J = 8.3 Hz, 1H), 7.41 (d, J = 8.3 Hz, 1H), 7.31 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 7.21 (dd, 3J = 8.3 Hz, 4J = 1.4 Hz, 1H), 6.09 (q, 4J = 1.2 Hz, 1H), 2.05 (q, 4J = 1.2 Hz, 3H, CH3), 1.93 (s, 3H, CH3), 1.72 (s, 3H, CH3), 0.89 (s, 3H, SiCH3), 0.67 (s, 3H, SiCH3), −1.06 (s, 3H, ZrCH3), and −1.56 (s, 3H, ZrCH3) ppm. 13C{1H} NMR (C6D6): δ 125.9, 140.3, 133.2, 133.0, 133.0, 131.8, 129.7, 129.3, 126.5, 125.8, 125.0, 124.3, 124.2, 124.1, 123.6, 123.2, 117.7, 115.8, 77.2, 63.7, 41.4, 38.8, 16.1, 15.3, 12.1, 0.9, and 0.8 ppm.

3.15. Synthesis of 14

A solution of nBuLi in hexane (3.17 g, 2.5 M, 1.14 mmol) was added dropwise to a solution of 2-methyl-4-(4-tert-butylphenyl)indenene (3.00 g, 1.14 mmol) in hexane (30 mL), and the resulting solution was stirred overnight. A light-yellow solid precipitated was isolated by filtration (2.54 g, 83%). Compound 14 was synthesized using the same conditions and procedures as those for 4, with the prepared 2-methyl-4-(4-tert-butylphenyl)indenyl–Li (0.420 g, 1.56 mmol). A yellowish-brown, oily compound was obtained by silica gel column chromatography with hexane and toluene (30:1, v/v) as eluents (0.445 g, 59%). The product was obtained as a mixture of two diastereomers in a ratio of 1.0:0.10. Signals for minor isomers were not recorded (see Figure S14). 1H NMR (C6D6): δ 7.64 (d, J = 8.3 Hz, 2H), 7.42 (d, J = 7.6 Hz, 1H), 7.41 (d, J = 8.3 Hz, 2H), 7.28 (d, J = 7.6 Hz, 1H), 7.14 (t, J = 7.6 Hz, 1H), 7.00 (s, 1H), 6.62 (s, 1H), 6.96 (s, 1H), 6.62 (s, 1H), 3.99 (s, 1H), 3.49 (s, 1H), 2.33 (s, 3H, CH3), 2.14 (s, 3H, CH3), 2.02 (s, 3H, CH3), 1.89 (s, 3H, CH3), 1.31 (s, 9H, tBu), −0.19 (s, 3H, SiCH3), and −0.26 (s, 3H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 152.1, 149.7, 147.5, 146.1, 143.7, 140.7, 139.3, 138.3, 137.7, 134.7, 130.2, 129.2, 126.7, 126.0, 125.7, 123.6, 122.5, 116.8, 47.6, 46.4, 34.6, 31.6, 18.0, 16.0, 15.1, 11.8, −6.3, and −6.8 ppm.

3.16. Synthesis of 15

Compound 15 was synthesized using the same conditions and procedure as those for 9, with 14 (0.207 g, 0.428 mmol). A yellow solid was obtained in 67% yield (0.178 g), as a mixture of two isomers in a 1.0:0.54 ratio (refer to Figure S15a), which was used for polymerization without separation of the isomers. Solids (0.074 g) were deposited in a toluene solution containing 0.250 g of the isomer mixture and were stored in a freezer at −30 °C. The 1H NMR spectrum of the deposited solids indicated that, mainly, the minor isomer in the crude mixture was deposited, along with a small portion of the major isomer, in a 1.0:0.13 ratio (refer to Figure S15b). Contaminant THF signals (0.5 eq) were detected even after crystallization. 1H NMR (C6D6) of major isomer: δ 7.88 (d, J = 8.3 Hz, 2H), 7.64 (d, J = 8.3 Hz, 1H), 7.41 (d, J = 8.3 Hz, 2H), 7.25 (d, J = 8.3 Hz, 1H), 7.24 (s, 1H), 6.87 (dd, J = 9.0 Hz and 6.9 Hz, 1H), 6.26 (s, 1H), 2.14 (s, 3H, CH3), 2.09 (s, 3H, CH3), 1.98 (s, 3H, CH3), 1.83 (s, 3H, CH3), 1.25 (s, 9H, tBu), 1.00 (s, 3H, SiCH3), 0.65 (s, 3H, SiCH3), 0.12 (s, 3H, ZrCH3), and −1.38 (s, 3H, ZrCH3) ppm. 1H NMR (C6D6) of minor isomer: δ 7.85 (d, J = 8.3 Hz, 2H), 7.36 (d, J = 8.3 Hz, 1H), 7.35 (d, J = 8.3 Hz, 2H), 7.25 (d, J = 8.3 Hz, 1H), 7.24 (s, 1H), 6.90 (dd, J = 9.0 Hz and 6.9 Hz, 1H), 6.38 (s, 1H), 2.20 (s, 3H, CH3), 2.19 (s, 3H, CH3), 2.06 (s, 3H, CH3), 1.76 (s, 3H, CH3), 1.24 (s, 9H, tBu), 0.80 (s, 3H, SiCH3), 0.77 (s, 3H, SiCH3), −0.43 (s, 3H, ZrCH3), and −0.91 (s, 3H, ZrCH3) ppm.

3.17. Synthesis of 16

Compound 16 was synthesized using the same conditions and procedures as those for 4, with tert-BuN(H)Li (0.126 g, 1.59 mmol). A yellowish-brown liquid was obtained (0.423 g, 91%). 1H NMR (C6D6): δ 6.61 (q, 4J = 1.2 Hz, 1H), 3.22 (s, 1H), 2.36 (s, 3H, CH3), 2.04 (s, 3H, CH3), 2.04 (s, 3H, CH3), 1.12 (s, 9H, tBu), 0.63 (s, 1H, NH), 0.12 (s, 3H, SiCH3), and −0.03 (s, 3H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 151.3, 139.7, 138.3, 138.1, 129.0, 116.5, 50.3, 49.6, 33.9, 16.1, 15.2, 11.9, 0.0, and −1.6 ppm. HRMS(EI): m/z calcd. ((M+) C16H27NSSi) 293.1633. Found: 293.1631.

3.18. Synthesis of 17

A measured quantity of nBuLi (0.60 mL, 2.5 M in hexane, 1.51 mmol) was added dropwise at −78 °C to 16 (0.221 g, 0.754 mmol) dissolved in THF (2.0 g). After stirring overnight at room temperature, the solution was cooled to −78 °C. Subsequently, MeMgCl (0.52 mL, 3.1 M in THF, 1.58 mmol) and TiCl4·DME (0.211 g, 0.739 mmol) were added. The resulting solution was stirred overnight at room temperature. After the volatiles were removed using a vacuum line, the product was extracted with hexane (13 mL). The extract was collected by filtration over Celite. The solvent was removed using a vacuum line to obtain a yellowish-brown solid (0.133 g, 47%). 1H NMR (C6D6): δ 6.39 (q, 4J = 1.8 Hz, 1H), 2.20 (s, 3H, CH3), 2.19 (q, 4J = 1.8 Hz, 3H, CH3), 1.89 (s, 3H, CH3), 1.53 (s, 9H, tBu), 0.66 (s, 3H, CH3), 0.56 (s, 3H, CH3), 0.46 (s, 3H, CH3), and 0.25 (s, 3H, CH3) ppm. 13C{1H} NMR (C6D6): δ 147.2, 141.4, 137.2, 136.8, 122.1, 116.4, 88.2, 57.9, 55.8, 52.8, 34.7, 16.4, 15.6, 12.6, 4.6, and 4.2 ppm.

3.19. Synthesis of 18

A measured amount of tert-butyl methyl ether (0.886 g, 3 eq/Li+) was added to a solution of 2,7-di-tert-butylfluorenyl–Li (0.853 g, 3.00 mmol) in hexane (30 mL). After cooling to −78 °C, a solution of tBuO(CH2)6(Me)SiCl2 (0.814 g, 3.00 mmol) in hexane (7.5 mL) was added. After stirring overnight at room temperature, the solvent was removed under vacuum. The product was extracted using hexane (15 mL). The extract was collected by filtration over Celite. The solvent was removed using a vacuum line to obtain the desired compound (1.51 g, 98%). 1H NMR (C6D6): δ 7.89 (s, 1H), 7.81 (s, 1H), 7.77 (s, 1H), 7.76 (s, 1H), 7.42 (t, J = 2.07 Hz, 1H), 7.41 (t, J = 2.07 Hz, 1H), 1.50 (m, 2H), 1.39 and 1.37 (s, 18H, tBu), 1.27–1.02 (m, 6H), 1.13 (s, 9H, OtBu) 0.62–0.42 (m, 2H), and 0.09 (s, 3H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 149.4, 143.5, 139.0, 123.8, 122.3, 119.8, 72.0, 61.5, 43.1, 35.0, 33.2, 31.9, 30.9, 27.8, 26.3, 23.2, 15.7, and −1.5 ppm. HRMS(EI): m/z calcd. ((M+) C32H49ClOSi) 512.3240. Found: 512.3241.

3.20. Synthesis of 19

Thiophene-fused cyclopentadiene 2,4,5-Me3C7H3S (0.325 g, 2.00 mmol) in THF (2.0 mL) was added to a Schlenk flask containing KH (0.104 g, 2.6 mmol) and THF (2.0 mL). After stirring overnight at room temperature, the solution was filtered over Celite to remove the remaining KH, owing to its addition in excess. To the filtrate were added CuCN (1.8 mg, 1 mol%) and a solution of 18 (1.02 g, 2.00 mmol) in THF (15 mL) cooled at −30 °C. The solution was stirred overnight, and the solvent was removed using a vacuum line. The product was extracted with hexane (30 mL) and collected by filtration over Celite. After removing the solvent using a vacuum line, the product was purified by silica gel column chromatography with hexane and diethyl ether (30:1, v/v) as eluents. A yellowish-brown, oily compound was obtained (0.854 g, 67%). The 1H NMR spectrum of the product was too complicated for complete analysis because of the mixture of the four diastereomers (Figure S19). HRMS(EI): m/z calcd. ((M+) C42H60OSSi) 640.4138. Found: 640.4134.

3.21. Synthesis of 20

A solution of nBuLi in hexane (0.300 g, 2.5 M, 1.08 mmol) was added dropwise to a solution of 19 (0.347 g, 0.541 mmol) in THF (2 mL) at −30 °C, and the mixture was slowly warmed to room temperature. After the solution was stirred for 1 h at room temperature, the solution was cooled to −30 °C. MeMgBr (0.91 mL, 1.37 M solution in THF-toluene, 1.24 mmol). Next, ZrCl4·(THF)2 (0.200 g, 0.530 mmol) were successively added, and the solution was slowly warmed to room temperature. After stirring overnight, the solvent was removed under vacuum. The product was extracted with hexane (25 mL) and collected by filtration over Celite. The solvent was removed using a vacuum line to obtain a yellow solid (0.379 g, 94%). 1H NMR (C6D6): δ 7.97 and 7.95 (d, J = 1.4 Hz, 1H), 7.87 (d, J = 8.3 Hz, 1H), 7.79 and 7.78 (s, 1H), 7.64 and 7.62 (s, 1H), 7.51 and 7.50 (dd, 3J = 3.4 Hz, 4J = 1.4 Hz, 1H), 7.44 and 7.42 (dd, 3J = 8.7 Hz, 4J = 1.4 Hz, 1H), 6.23 (q, 4J = 1.4 Hz, 1H), 3.31 and 3.30 (q, J = 6.2 Hz, 2H), 2.13 (d, 4J = 1.4 Hz, 3H, SCCH3), 2.03 (s, 3H, CH3), 1.93 and 1.89 (s, 3H, CH3), 1.39, 1.36, 1.34, and 1.32 (s, 18H, tBu), 1.26 and 1.08 (s, 3H, Si–CH3), 1.15 and 1.14 (s, 9H, OtBu), −1.07 and −1.08 (s, 3H, ZrCH3), and −1.58 (s, 3H, ZrCH3) ppm. Anal. Calcd. (C44H64OSSiZr): C, 69.5; H, 8.48; and S, 4.31%. Found: C, 68.2; H, 8.04; and S, 4.08%.

3.22. Synthesis of 21

Compound 21 was synthesized using the same conditions and procedure as those for 18, with 2-methyl-4-(4-tert-butylphenyl)indenyl-Li (0.805 g, 3.00 mmol). A yellow oily compound was obtained in 98% yield (1.46 g). 1H NMR (C6D6): δ 7.58 (d, J = 2.1 Hz, 1H), 7.56 (d, J = 2.1 Hz, 1H), 7.50 and 7.42 (d, J = 7.6 Hz, 1H), 7.41 (d, J = 2.1 Hz, 1H), 7.40 (d, J = 2.1 Hz, 1H), 7.19 and 7.16 (t, J = 7.6 Hz, 1H), 6.89 (s, 1H), 3.47 and 3.44 (s, 1H), 3.26 and 3.21 (t, J = 6.2 Hz, 2H, OCH2), 2.12 and 2.10 (s, 3H, CH3), 1.57–1.47 (m, 2H, CH2), 1.40–1.20 (m, 6H, CH2), 1.30 (s, 9H, tBu), 1.15 and 1.12 (s, 9H, OtBu), 0.84–0.39 (m, 2H, CH2), 0.28 and 0.02 (s, 3H, SiCH3) ppm. HRMS(EI): m/z calcd. ((M+) C31H45ClOSi) 496.2930. Found: 496.2928.

3.23. Synthesis of 22

Compound 22 was synthesized using the same conditions and procedure as those for 19, with 21 (0.955 g, 2.00 mmol). A yellowish-brown oil was obtained in 90% yield (1.11 g). The 1H NMR spectrum of the product was too complicated for complete analysis because of the mixture of four diastereomers (Figure S21). HRMS(EI): m/z calcd. ((M+) C41H56OSSi) 624.3818. Found: 624.3821.

3.24. Synthesis of 23

Compound 23 was synthesized using the same conditions and procedure as those for 20, with 22 (0.396 g, 0.633 mmol). A yellow oil was obtained in 92% yield (0.427 g). It was isolated as a mixture of four diastereomers owing to the presence of three chiral centers. Signals of racemic-type and meso-type complexes in a 1.0:0.40 (or vice versa) ratio were further split into 1:0.9 and 1:1 ratios, respectively, due to the chiral center on the Si atom. Signals assigned to minor meso-type complexes are indicated in italics. 1H NMR (C6D6): δ 7.90–7.87 and 7.86–7.84 (m, 2H, 4-tBuPh-H), 7.73, 7.70, 7.39, and 7.37 (d, J = 8.7 Hz, 1H), 7.49, 7.42, 7.29, and 7.27 (d, J = 8.3 Hz, 1H), 7.42–7.38 (m, 2H, 4-tBuPh-H), 7.31 and 7.29 (s, 1H, indenyl-H), 6.96-6.89 (m, 1H), 6.37 and 6.25 (m, 1H, thiophene-H), 3.33–3.29 (m, 2H, OCH2), 2.26, 2.24, 2.15, and 2.14 (s, 3 H, CH3), 2.19, 2.18, 2.09, and 2.08 (d, 4J = 1.4 Hz, 3H, SCCH3), 2.07, 2.03, and 2.00 (s, 3H, CH3), 1.88, 1.86, 1.84, and 1.78 (s, 3 H, indenyl-CH3), 1.75–1.25 (m, 10H, CH2), 1.24, 1.23, and 1.23 (s, 9H, tBu), 1.16, 1.16, 1.16, and 1.15 (s, 9H, tBu), 1.08, 0.89, 0.84, and 0.73 (s, 3H, SiCH3), 0.18 and −0.37 (s, 3H, Zr–CH3), −0.84, −0.85, −1.31, and −1.32 (s, 3H, Zr–CH3). Anal. Calcd. (C43H60OSSiZr): C, 69.4; H, 8.13; S, 4.31%. Found: C, 68.2; H, 7.77; and S, 4.47%.

3.25. Synthesis of 24

A measured amount of tert-butyl methyl ether (0.716 g, 3.3 eq/Li+) was added to a suspension of 2,7-di-tert-butylfluorenyl–Li (0.700 g, 2.46 mmol) in hexane (15 mL). After cooling to −78 °C, a solution of Cl2Si(Me)-(CH2)6-(Me)SiCl2 (0.384 g, 1.23 mmol) in hexane (5 mL) was added. After stirring overnight at room temperature, the solvent was removed under vacuum. The product was extracted using hexane (15 mL). The extract was collected by filtration over the Celite. The solvent was removed using a vacuum line to obtain a white solid (0.97 g, 99%). 1H NMR (C6D6): δ 7.88 (s, 2H), 7.79 (s, 2H), 7.77 (s, 2H), 7.76 (s, 2H), 7.42 (t, J = 2.07 Hz, 2H), 7.41 (t, J = 2.07 Hz, 2H), 4.01 (s, 2H), 1.39 and 1.37 (s, 36H, tBu), 1.08–0.91 (m, 4H), 0.85–0.80 (m, 4H), 0.51–0.32 (m, 4H), and 0.11 (s, 6H, SiCH3) ppm. 13C{1H} NMR (C6D6): δ 149.4, 143.4, 138.9, 123.8, 122.2, 119.8, 43.1, 35.1, 32.7, 31.9, 23.0, 15.5, and −1.4 ppm.

3.26. Synthesis of 25

Thiophene-fused cyclopentadiene 2,4,5-Me3C7H3S (0.284 g, 1.7 mmol) in THF (2.0 mL) was added to a Schlenk flask containing KH (0.090 g, 2.2 mmol) and THF (2.0 mL). After stirring overnight at room temperature, the solution was filtered over Celite to remove the remaining KH, because of its addition in excess. To the filtrate were added CuCN (0.8 mg, 1 mol%) and a solution of 24 (0.69 g, 0.87 mmol) in THF (7 mL) cooled at −30 °C. The solution was stirred overnight, and the solvent was removed using a vacuum line. The product was extracted with hexane (20 mL) and collected by filtration over Celite. A yellowish-brown, oily compound was obtained (0.818 g, 90%). 1H NMR (C6D6): δ 7.95 (m, 2H), 7.82 (m, 4H), 7.57 (m, 2H), 7.41 (m, 4H), 6.62 (m, 2H), 4.34 (m, 2H), 3.72 (m, 2H), 2.35 (m, 6H), 2.35 (m, 6H), 2.03 (s, 6H), 1.95 (m, 6H), 1.38 (m, 36H, tBu), 1.27 (m, 6H), 0.50 (m, 6H), −0.05 (m, 3H, SiCH3), and −0.27 (m, 3H, SiCH3) ppm.

3.27. Synthesis of 26

A solution of nBuLi in hexane (0.621 g, 2.5 M, 2.28 mmol) was added dropwise to a solution of 25 (0.600 g, 0.570 mmol) in THF (6 mL) at −30 °C, and the mixture was slowly warmed to room temperature. After the solution was stirred for 1 h at room temperature, the solution was cooled to −30 °C. MeMgBr (1.92 mL, 1.37 M solution in THF–toluene, 2.62 mmol) and ZrCl4·(THF)2 (0.421 g, 1.12 mmol) were successively added, and the solution was slowly warmed to room temperature. After stirring overnight, the solvent was removed under vacuum. The product was extracted with hexane (30 mL) and collected by filtration over Celite. The solvent was removed using a vacuum line to obtain a yellow oily compound (0.456 g, 62%). 1H NMR (C6D6): δ 7.95 (m, 2H), 7.86 (m, 2H), 7.79 (m, 2H), 7.64 (m, 2H), 7.50 (m, 2H), 7.42 (m, 2H), 6.23 (m, 2H), 2.13 (m, 6H), 2.03 (m, 6H), 1.92 (s, 6H), 1.35 (m, 36H, tBu), 1.27 (m, 3H, SiCH3), 1.10 (m, 3H, SiCH3), 1.65 (m, 6H), 1.25 (m, 6H), −1.08 (m, 3H, ZrCH3), and −1.58 (m, 3H, ZrCH3) ppm.

3.28. Preparation of Supported Catalysts

Methylaluminoxane (MAO, 5.0 g, GRACE, 10 wt.% in toluene) was added to a solution of silica (GRACE, SYLOPOL-2410, 1.0 g) in toluene (10 mL) and the solution was stirred at 70 °C for 3 h. The solid was isolated by filtration and washed with toluene (10 mL). The resulting MAO–silica was re-dispersed in toluene (10 m), following which the prepared complex (150 μmol) was added. After stirring at 70 °C for 1 h, the solid was isolated by filtration and washed with toluene (20 mL). The residual solvents were completely removed using a vacuum line to obtain the supported catalyst.

3.29. Ethylene/1-Hexene Polymerization

A bomb reactor (450 mL) was evacuated at 120 °C for 4 h and then purged with nitrogen gas. Hexane (300 mL) containing Et3Al (0.20 mL) was added to the reactor, and the mixture was stirred for 1 h at 80 °C. Subsequently, the solution was removed using a cannula. The reactor was evacuated to remove any residual solvents. Next, the reactor was evacuated again at 120 °C for 4 h and recharged with nitrogen gas at atmospheric pressure. The reactor was then recharged with hexane (300 mL) containing 1-hexene (3.0 mL), and the temperature was set to 80 °C. Et3Al (0.2 mL) dissolved in hexane (3.0 mL) was injected and, subsequently, fine particles of the prepared supported catalyst (6.0 mg) were injected into the reactor using a syringe dispersed in hexane (3.0 mL). Ethylene gas was charged to 20 bar for a few seconds. The polymerization was performed for 30 min while maintaining the temperature at 80 °C and a constant pressure of 20 bar by feeding ethylene gas continuously. After the reactor was cooled to room temperature, the remaining ethylene gas was vented off and the generated polymer particles were collected by filtration.

3.30. X-ray Crystallography

Specimens of suitable quality and size were selected, mounted, and centered in the X-ray beam using a video camera. Reflection data were collected at 100 K on an APEX II CCD area diffractometer (Bruker) using graphite-monochromated Mo Kα radiation (λ = 0.7107 Ǻ). The hemisphere of the reflection data was collected as φ and ω scan frames at 0.5° per frame and an exposure time of 10 s per frame. The cell parameters were determined and refined using the SMART program. Data reduction was performed using the SAINT software. The data were corrected for Lorentz and polarization effects. Empirical absorption correction was applied using the SADABS program. The structure was solved by direct methods and refined by the full matrix least-squares method using the SHELXTL package and the olex2 program with anisotropic thermal parameters for all non-hydrogen atoms. Crystallographic data for 9 (CCDC# 2130400) that were used in all calculations are as follows: C26.88H29.64Cl0.12SSiZr, M = 508.33, triclinic, a = 9.00050(10), b = 10.1721(2), c = 13.1285(2) Å, α = 90.6600(8)°, β = 103.7878(8)°, γ = 95.4360(8), V = 1161.36(3) Å3, space group P-1, Z = 2, and 4421 unique (R(int) = 0.0262). The final wR2 was 0.0799 (I > 2σ(I)).

4. Conclusions

A series of Me2Si-bridged thiophene-fused cyclopentadienyl fluorenyl ansa-zirconocene complexes was prepared, and a complex containing a bulky 2-methyl-4-(4-tert-butylphenyl)indenyl ligand was also synthesized by the substitution of the fluorenyl ligand. Analogues containing tBuO(CH2)6-tether, as well as a dinuclear congener, were also prepared by substituting the Me2Si bridge with a tBuO(CH2)6(Me)Si bridge or by connecting the two ansa-zirconocene units with a –(Me)Si(CH2)6Si(Me)– spacer. Because of their solubility in hexane, the complexes containing tBuO(CH2)6-tether and dinuclear complexes were isolated at high yields with complete removal of contaminant THF signals. The silica-supported catalysts prepared with the newly synthesized complexes containing 2,7-di(tert-butyl)fluorenyl ligand showed up to two times higher productivity compared to that prepared with the conventional (THI)ZrCl2 (21–26 vs. 12 kg PE/g-(supported catalyst)). The as-synthesized supported catalysts also produced polymers with comparable molecular weights (Mw, 330–370 vs. 300 kDa), with increased 1-hexene contents (1.3 vs. 1.0 mol%) but with generated polymer particles with decreased bulk density (0.35 vs. 0.42 g/mL).

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal12030283/s1, Figures S1–S24: 1H and 13C NMR spectra of 1–26.

Author Contributions

Conceptualization, B.Y.L.; validation, H.K. and Y.Y.; formal analysis, J.L.; investigation, S.M.J., J.Y.P., Y.B.H. and J.W.B.; writing—original draft preparation, B.Y.L.; writing—review and editing, S.M.J. and J.W.B.; supervision, B.Y.L.; project administration, S.C.; funding acquisition, S.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by GS Caltex and the Priority Research Centers Program (2019R1A6A1A11051471) through the National Research Foundation of Korea (NRF).

Data Availability Statement

All data are included in this article and supporting information.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Kaminsky, W. Discovery of Methylaluminoxane as Cocatalyst for Olefin Polymerization. Macromolecules 2012, 45, 3289–3297. [Google Scholar] [CrossRef]
  2. Kaminsky, W. Polyolefin-nanocomposites with special properties by in-situ polymerization. Front. Chem. Sci. Eng. 2018, 12, 555–563. [Google Scholar] [CrossRef]
  3. Zhang, H.; Zou, C.; Zhao, H.; Cai, Z.; Chen, C. Hydrogen-Bonding-Induced Heterogenization of Nickel and Palladium Catalysts for Copolymerization of Ethylene with Polar Monomers. Angew. Chem. Int. Ed. 2021, 60, 17446–17451. [Google Scholar] [CrossRef] [PubMed]
  4. Kilpatrick, A.F.R.; Geddes, H.S.; Turner, Z.R.; Buffet, J.-C.; Goodwin, A.L.; O’Hare, D. Polymethylaluminoxane organic frameworks (sMAOF)—Highly active supports for slurry phase ethylene polymerisation. Catal. Sci. Technol. 2021, 11, 5472–5483. [Google Scholar] [CrossRef]
  5. Zaccaria, F.; Zuccaccia, C.; Cipullo, R.; Budzelaar, P.H.M.; Vittoria, A.; Macchioni, A.; Busico, V.; Ehm, C. Methylaluminoxane’s Molecular Cousin: A Well-defined and “Complete” Al-Activator for Molecular Olefin Polymerization Catalysts. ACS Catal. 2021, 11, 4464–4475. [Google Scholar] [CrossRef]
  6. Hejazi-Dehaghani, Z.-A.; Arabi, H.; Thalheim, D.; Vidakovic, D.; Nekoomanesh Haghighi, M.; Veith, L.; Klapper, M. Organic Versus Inorganic Supports for Metallocenes: The Influence of Rigidity on the Homogeneity of the Polyolefin Microstructure and Properties. Macromolecules 2021, 54, 2667–2680. [Google Scholar] [CrossRef]
  7. Antonov, A.A.; Bryliakov, K.P. Post-metallocene catalysts for the synthesis of ultrahigh molecular weight polyethylene: Recent advances. Eur. Polym. J. 2021, 142, 110162. [Google Scholar] [CrossRef]
  8. Velthoen, M.E.Z.; Muñoz-Murillo, A.; Bouhmadi, A.; Cecius, M.; Diefenbach, S.; Weckhuysen, B.M. The Multifaceted Role of Methylaluminoxane in Metallocene-Based Olefin Polymerization Catalysis. Macromolecules 2018, 51, 343–355. [Google Scholar] [CrossRef]
  9. Eo, S.C.; Lee, S.; Park, G.H.; Jeon, J.Y.; Lee, B.Y. Anchoring sulfonic acid on silica surface through SiC bond for immobilization of catalyst for polyketone synthesis. Catal. Today 2016, 265, 77–83. [Google Scholar] [CrossRef]
  10. Qi, M.; Fu, Z.; Fan, Z. Immobilization of metallocene catalysts. Prog. Chem. 2014, 26, 737–748. [Google Scholar] [CrossRef]
  11. Lee, B.Y.; Oh, J.S. Preparation of anchored metallocene complexes on dehydroxylated silica and their use in the polymerization of ethylene. Macromolecules 2000, 33, 3194–3195. [Google Scholar] [CrossRef]
  12. Cecílio, D.M.; Fernandes, A.; Lourenço, J.P.; McKenna, T.F.L.; Ribeiro, M.R. Innovative route for the preparation of high-performance polyolefin materials based on unique dendrimeric silica particles. Polym. Chem. 2021, 12, 4546–4556. [Google Scholar] [CrossRef]
  13. Werny, M.J.; Zarupski, J.; ten Have, I.C.; Piovano, A.; Hendriksen, C.; Friederichs, N.H.; Meirer, F.; Groppo, E.; Weckhuysen, B.M. Correlating the Morphological Evolution of Individual Catalyst Particles to the Kinetic Behavior of Metallocene-Based Ethylene Polymerization Catalysts. J. Am. Chem. Soc. 2021, 1, 1996–2008. [Google Scholar] [CrossRef]
  14. Zanoni, S.; Nikolopoulos, N.; Welle, A.; Vantomme, A.; Weckhuysen, B.M. Early-stage particle fragmentation behavior of a commercial silica-supported metallocene catalyst. Catal. Sci. Technol. 2021, 11, 5335–5348. [Google Scholar] [CrossRef]
  15. Yang, Q.; McDaniel, M.P. Comparison of support effects on phillips and metallocene catalysts. Catalysts 2021, 11, 842. [Google Scholar] [CrossRef]
  16. Collins Rice, C.G.; Buffet, J.C.; Turner, Z.R.; O’Hare, D. Supported permethylindenyl titanium catalysts for the synthesis of disentangled ultra-high molecular weight polyethylene (disUHMWPE). Chem. Commun. 2021, 57, 8600–8603. [Google Scholar] [CrossRef]
  17. Mehdiabadi, S.; Lhost, O.; Vantomme, A.; Soares, J.B.P. Ethylene Polymerization Kinetics and Microstructure of Polyethylenes Made with Supported Metallocene Catalysts. Ind. Eng. Chem. Res. 2021, 60, 9739–9754. [Google Scholar] [CrossRef]
  18. Matsko, M.A.; Semikolenova, N.V.; Zakharov, V.A.; Soshnikov, I.E.; Shundrina, I.K.; Sun, W.H. Formation of branched polyethylenes by ethylene homopolymerization using LNiBr2 homo- and heterogeneous precatalysts: Interpretation of the polymer structures in comparison with commercial LLDPE. J. Appl. Polym. Sci. 2021, 138, e50436. [Google Scholar] [CrossRef]
  19. Kenyon, P.; Leung, D.W.J.; Lyu, M.; Chen, C.; Turner, Z.R.; Buffet, J.C.; O’Hare, D. Controlling the activity of an immobilised molecular catalyst by Lewis acidity tuning of the support. J. Catal. 2021, 402, 94–100. [Google Scholar] [CrossRef]
  20. Wang, X.; Kang, W.; Li, G.; Zhang, P.; Jia, H.; Gao, D. Porous organic polymer/MMT hybrid supports for efficient metallocene catalysts. J. Mater. Sci. 2021, 56, 19253–19266. [Google Scholar] [CrossRef]
  21. Brant, P.; Yakovlev, S.; Raney, M.; Narvaez, A. Discovery of Polyolefin Granule Products That Can Be Deconstructed into Individual, Fully Separable Grains Provides New Insights into Grain Growth and Material Design. Macromolecules 2021, 54, 2187–2201. [Google Scholar] [CrossRef]
  22. Lamb, J.V.; Buffet, J.-C.; Turner, Z.R.; O’Hare, D. Ethylene Polymerization Using Zirconocenes Supported on Pentafluorophenyl-Modified Solid Polymethylaluminoxane. Macromolecules 2020, 53, 929–935. [Google Scholar] [CrossRef]
  23. Lamb, J.V.; Buffet, J.C.; Turner, Z.R.; Khamnaen, T.; O’Hare, D. Metallocene Polyethylene Wax Synthesis. Macromolecules 2020, 53, 5847–5856. [Google Scholar] [CrossRef]
  24. Bernardes, A.A.; Scheffler, G.L.; Radtke, C.; Pozebon, D.; dos Santos, J.H.Z.; da Rocha, Z.N. Supported metallocenes produced by a non-hydrolytic sol-gel process: Application in ethylene polymerization. Colloids Surf. A Physicochem. Eng. 2020, 584, 124020. [Google Scholar] [CrossRef]
  25. Groch, P.; Bihun-Kisiel, A.; Piontek, A.; Ochędzan-Siodłak, W. Structural and Thermal Properties of Ethylene-Norbornene Copolymers Obtained Using Vanadium Homogeneous and SIL Catalysts. Polymers 2020, 12, 2433. [Google Scholar] [CrossRef] [PubMed]
  26. Encarnacion, J.D.; Park, S.J.; Ko, Y.S. Polymerization of heterophasic propylene copolymer with Me2Si(2-Me-4-PhInd)2ZrCl2 supported on SiO2 and SiO2-MgCl2 carriers. Korean J. Chem. Eng. 2020, 37, 380–386. [Google Scholar] [CrossRef]
  27. Bae, S.M.; Jeong, S.M.; Baek, J.W.; Lee, H.J.; Kim, H.; Yoon, Y.; Chung, S.; Lee, B.Y. Dinuclear metallocene complexes for high-performance supported catalysts. Eur. Polym. J. 2021, 144, 110243. [Google Scholar] [CrossRef]
  28. Nifant’ev, I.E.; Ivchenko, P.V.; Vinogradov, A.A. Heterocycle-fused cyclopentadienyl metal complexes: Heterocene synthesis, structure and catalytic applications. Coord. Chem. Rev. 2021, 426, 213515. [Google Scholar] [CrossRef]
  29. Nifant’ev, I.E.; Ivchenko, P.V. Synthesis of Heteroarene-Fused Cyclopentadienes and Related Compounds Suitable for Metallocene Preparation. Adv. Synth. Catal. 2020, 362, 3727–3767. [Google Scholar] [CrossRef]
  30. Huang, L.; Liu, Z.; Zhang, Y.; Wu, C.; Cui, D. Ethylene-Triggered Regioselectivity Switch of Dimethylbutadiene in Their Copolymerization: Formation of “Plastic” Rubber and Mechanism. ACS Catal. 2022, 12, 953–962. [Google Scholar] [CrossRef]
  31. Liu, Z.; Liu, B.; Zhao, Z.; Cui, D. Chemo- and Stereoselective Polymerization of Polar Divinyl Monomers by Rare-Earth Complexes. Macromolecules 2021, 54, 3181–3190. [Google Scholar] [CrossRef]
  32. Wang, T.; Wu, C.; Cui, D. cis-1,4 Selective Copolymerization of Butadiene and Functionalized α-Olefins via Polar Group Activation Mechanism. Macromolecules 2020, 53, 6380–6386. [Google Scholar] [CrossRef]
  33. Park, J.H.; Do, S.H.; Cyriac, A.; Yun, H.; Lee, B.Y. Preparation of half-metallocenes of thiophene-fused and tetrahydroquinoline-linked cyclopentadienyl ligands for ethylene/α-olefin copolymerization. Dalton Trans. 2010, 39, 9994–10002. [Google Scholar] [CrossRef]
  34. Sampson, J.; Bruening, M.; Akhtar, M.N.; Jaseer, E.A.; Theravalappil, R.; Garcia, N.; Agapie, T. Copolymerization of Ethylene and Long-Chain Functional α-Olefins by Dinuclear Zirconium Catalysts. Organometallics 2021, 40, 1854–1858. [Google Scholar] [CrossRef]
  35. Liang, T.; Goudari, S.B.; Chen, C. A simple and versatile nickel platform for the generation of branched high molecular weight polyolefins. Nat. Commun. 2020, 11, 372. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  36. Liu, S.; Xing, Y.; Zheng, Q.; Jia, Y.; Li, Z. Synthesis of Anthracene-Bridged Dinuclear Phenoxyiminato Organotitanium Catalysts with Enhanced Activity, Thermal Stability, and Comonomer Incorporation Ability toward Ethylene (Co)polymerization. Organometallics 2020, 39, 3268–3274. [Google Scholar] [CrossRef]
  37. Reinhart, E.D.; Jordan, R.F. Synthesis and Ethylene Reactivity of Dinuclear Iron and Cobalt Complexes Supported by Macrocyclic Bis(pyridine-diimine) Ligands Containing o-Terphenyl Linkers. Organometallics 2020, 39, 2392–2404. [Google Scholar] [CrossRef]
  38. Khoshsefat, M.; Dechal, A.; Ahmadjo, S.; Mortazavi, S.M.M.; Zohuri, G.; Soares, J.B.P. Amorphous to high crystalline PE made by mono and dinuclear Fe-based catalysts. Eur. Polym. J. 2019, 119, 229–238. [Google Scholar] [CrossRef]
  39. Chen, Q.; Suo, H.; Zhang, W.; Zhang, R.; Solan, G.A.; Liang, T.; Sun, W.H. 1,5-Naphthyl-linked bis(imino)pyridines as binucleating scaffolds for dicobalt ethylene oligo-/polymerization catalysts: Exploring temperature and steric effects. Dalton Trans. 2019, 48, 8264–8278. [Google Scholar] [CrossRef]
  40. Khoshsefat, M.; Dechal, A.; Ahmadjo, S.; Mortazavi, M.M.; Zohuri, G.H.; Soares, J.B.P. Zn-assisted cooperative effect for copolymers made by heterodinuclear Fe–Ni catalyst. ChemCatChem 2020, 12, 5809–5818. [Google Scholar] [CrossRef]
  41. Ryabov, A.N.; Voskoboynikov, A.Z. Constrained geometry complexes of titanium (IV) and zirconium (IV) involving cyclopentadienyl fused to thiophene ring. J. Organomet. Chem. 2005, 690, 4213–4221. [Google Scholar] [CrossRef]
  42. Kim, S.; Park, J.; Song, B.; Yoon, S.-W.; Go, M.; Lee, J.; Lee, B. Preparation of Thiophene-Fused and Tetrahydroquinoline-Linked Cyclopentadienyl Titanium Complexes for Ethylene/α-Olefin Copolymerization. Catalysts 2013, 3, 104–124. [Google Scholar] [CrossRef] [Green Version]
  43. Lee, S.; Park, S.S.; Kim, J.G.; Kim, C.S.; Lee, B.Y. Preparation of “Constrained Geometry” Titanium Complexes of [1,2]Azasilinane Framework for Ethylene/1-Octene Copolymerization. Molecules 2017, 22, 258. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  44. Park, J.T.; Woo, B.W.; Yoon, S.C.; Shim, S.C. An efficient synthetic method of ansa-zirconocene dimethyl complexes via Me2ZrCl2. J. Organomet. Chem. 1997, 535, 29–32. [Google Scholar] [CrossRef]
  45. Hong, B.K.; Lee, Y.H.; Han, C.W.; Choi, Y.Y.; Lee, K.S. Transition Metal Compound, Catalyst Composition Comprising the Same, and Method of Preparing Polyolefin. U.S. Patent 9963527B2, 8 May 2018. [Google Scholar]
  46. Cho, K.J.; Lee, K.S.; Lee, S.M.; Hong, B.K.; Cho, M.S.; Kim, S.Y.; Han, C.W. Metallocene Compound. W.O. Patent 2016195423A1, 8 December 2016. [Google Scholar]
  47. Alt, H.G.; Ernst, R. Dinuclear ansa zirconocene complexes as dual-site catalysts for the polymerization of ethylene. J. Mol. Catal. A Chem. 2003, 195, 11–27. [Google Scholar] [CrossRef]
  48. Alt, H.G.; Ernst, R. Asymmetric dinuclear ansa zirconocene complexes with methyl and phenyl substituted bridging silicon atoms as dual site catalysts for the polymerization of ethylene. Inorg. Chim. Acta 2003, 350, 1–11. [Google Scholar] [CrossRef]
  49. Bashir, M.A.; Vancompernolle, T.; Gauvin, R.M.; Delevoye, L.; Merle, N.; Monteil, V.; Taoufik, M.; McKenna, T.F.L.; Boisson, C. Silica/MAO/(n-BuCp)2ZrCl2 catalyst: Effect of support dehydroxylation temperature on the grafting of MAO and ethylene polymerization. Catal. Sci. Technol. 2016, 6, 2962–2974. [Google Scholar] [CrossRef]
  50. Tanaka, R.; Kawahara, T.; Shinto, Y.; Nakayama, Y.; Shiono, T. An Alternative Method for the Preparation of Trialkylaluminum-Depleted Modified Methylaluminoxane (dMMAO). Macromolecules 2017, 50, 5989–5993. [Google Scholar] [CrossRef]
Catalysts 12 00283 sch001 550
Scheme 1. Mononuclear (I), dinuclear (II), and tBuO(CH2)6-tether containing (III) ansa-metallocene complexes synthesized with thiophene-fused cyclopentadienyl ligands.
Scheme 1. Mononuclear (I), dinuclear (II), and tBuO(CH2)6-tether containing (III) ansa-metallocene complexes synthesized with thiophene-fused cyclopentadienyl ligands.
Catalysts 12 00283 sch001
Catalysts 12 00283 sch002 550
Scheme 2. Syntheses of Me2Si-bridged ansa-zirconocene complexes coordinated by thiophene-fused cyclopentadienyl and fluorenyl ligands: (i) Me2SiCl2 in toluene, (ii) 2,7-R32-fluorenyl-Li in THF, (iii) nBuLi (2.0 eq) in THF and then addition of MeMgBr (2.3 eq) and ZrCl4·(THF)2.
Scheme 2. Syntheses of Me2Si-bridged ansa-zirconocene complexes coordinated by thiophene-fused cyclopentadienyl and fluorenyl ligands: (i) Me2SiCl2 in toluene, (ii) 2,7-R32-fluorenyl-Li in THF, (iii) nBuLi (2.0 eq) in THF and then addition of MeMgBr (2.3 eq) and ZrCl4·(THF)2.
Catalysts 12 00283 sch002
Catalysts 12 00283 g001 550
Figure 1. Thermal ellipsoid plot (30% probability level) of 9. Selected bond distances (Å) and angles (°): Zr–C1, 2.438(3); Zr–C2, 2.587(3); Zr–C3, 2.812(31); Zr–C4, 2.807(3); Zr–C5, 2.571(3); Zr–C14, 2.485(3); Zr–C15, 2.513(3); Zr–C16, 2.614(3); Zr–C17, 2.589(3); Zr–C18, 2.502(3); Zr–C26, 2.261(10); Zr–C27, 2.336(3); C1–C2, 1.461(4); C1–C5, 1.445(4); C2–C3, 1.434(4); C4–C5, 1.435(4); C3–C4, 1.439(4); C14–C15, 1.432(4); C14–C18, 1.443(4); C15–C16, 1.420(4); C17–C18, 1.429(4); C16–C17, 1.421(4); C1–Si–C14, 97.05(12); Si–C1–Zr, 97.51(11); Si–C14–Zr, 95.72(11); C26–Zr–C27, 93.90(3).
Figure 1. Thermal ellipsoid plot (30% probability level) of 9. Selected bond distances (Å) and angles (°): Zr–C1, 2.438(3); Zr–C2, 2.587(3); Zr–C3, 2.812(31); Zr–C4, 2.807(3); Zr–C5, 2.571(3); Zr–C14, 2.485(3); Zr–C15, 2.513(3); Zr–C16, 2.614(3); Zr–C17, 2.589(3); Zr–C18, 2.502(3); Zr–C26, 2.261(10); Zr–C27, 2.336(3); C1–C2, 1.461(4); C1–C5, 1.445(4); C2–C3, 1.434(4); C4–C5, 1.435(4); C3–C4, 1.439(4); C14–C15, 1.432(4); C14–C18, 1.443(4); C15–C16, 1.420(4); C17–C18, 1.429(4); C16–C17, 1.421(4); C1–Si–C14, 97.05(12); Si–C1–Zr, 97.51(11); Si–C14–Zr, 95.72(11); C26–Zr–C27, 93.90(3).
Catalysts 12 00283 g001
Catalysts 12 00283 sch003 550
Scheme 3. Syntheses of ansa-zirconocene complex coordinated by thiophene-fused cyclopentadienyl and a 2-methyl-4-(4-tert-butylphenyl)indenyl ligand (a) (asterisks for chiral centers) or a CGC-type titanium complex (b): (i) 2-Methyl-4-(4-tert-butylphenyl)indenyl–Li in THF, (ii) nBuLi (2.0 eq) in THF and then addition of MeMgBr (2.3 eq) and ZrCl4·(THF)2, (iii) tert-BuN(H)Li in THF, (iv) nBuLi (2.0 eq) in THF and then addition of MeMgBr (2.1 eq) and TiCl4·DME.
Scheme 3. Syntheses of ansa-zirconocene complex coordinated by thiophene-fused cyclopentadienyl and a 2-methyl-4-(4-tert-butylphenyl)indenyl ligand (a) (asterisks for chiral centers) or a CGC-type titanium complex (b): (i) 2-Methyl-4-(4-tert-butylphenyl)indenyl–Li in THF, (ii) nBuLi (2.0 eq) in THF and then addition of MeMgBr (2.3 eq) and ZrCl4·(THF)2, (iii) tert-BuN(H)Li in THF, (iv) nBuLi (2.0 eq) in THF and then addition of MeMgBr (2.1 eq) and TiCl4·DME.
Catalysts 12 00283 sch003
Catalysts 12 00283 sch004 550
Scheme 4. Syntheses of 2,7-di-tert-butylfluorenyl ansa-metallocene complex attaching tBuO(CH2)6-tether (a) and 2-methyl-4-(4-tert-butylphenyl)indenyl ansa-metallocene complex attaching tBuO(CH2)6-tether (b): (i) 2,7-(tBu)2-fluorenyl-Li in THF, (ii) nBuLi (2.0 eq) in THF and then addition of MeMgBr (2.3 eq) and ZrCl4·(THF)2, (iii) 2-methyl-4-(4-tert-butylphenyl)indenyl–Li in THF, (iv) nBuLi (2.0 eq) in THF and then addition of MeMgBr (2.3 eq) and ZrCl4·(THF)2.
Scheme 4. Syntheses of 2,7-di-tert-butylfluorenyl ansa-metallocene complex attaching tBuO(CH2)6-tether (a) and 2-methyl-4-(4-tert-butylphenyl)indenyl ansa-metallocene complex attaching tBuO(CH2)6-tether (b): (i) 2,7-(tBu)2-fluorenyl-Li in THF, (ii) nBuLi (2.0 eq) in THF and then addition of MeMgBr (2.3 eq) and ZrCl4·(THF)2, (iii) 2-methyl-4-(4-tert-butylphenyl)indenyl–Li in THF, (iv) nBuLi (2.0 eq) in THF and then addition of MeMgBr (2.3 eq) and ZrCl4·(THF)2.
Catalysts 12 00283 sch004
Catalysts 12 00283 g002 550
Figure 2. 1H NMR spectrum of 20 (asterisk for chiral center).
Figure 2. 1H NMR spectrum of 20 (asterisk for chiral center).
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Catalysts 12 00283 g003 550
Figure 3. 1H NMR spectrum of 23. Racemic-type and meso-type complexes in 1:0.4 ratio (or vice versa) are further split in 1:0.9 and 1:1 ratios, respectively, which are assigned as o, o′, o, and o′, for example, for Si–CH3 signals. Signals for unidentified impurities are marked with # and the chiral centers are marked with asterisks.
Figure 3. 1H NMR spectrum of 23. Racemic-type and meso-type complexes in 1:0.4 ratio (or vice versa) are further split in 1:0.9 and 1:1 ratios, respectively, which are assigned as o, o′, o, and o′, for example, for Si–CH3 signals. Signals for unidentified impurities are marked with # and the chiral centers are marked with asterisks.
Catalysts 12 00283 g003
Catalysts 12 00283 sch005 550
Scheme 5. Basicity order derived from 1H NMR studies (top) and the yield improvement by reversing the reaction sequence (bottom).
Scheme 5. Basicity order derived from 1H NMR studies (top) and the yield improvement by reversing the reaction sequence (bottom).
Catalysts 12 00283 sch005
Catalysts 12 00283 sch006 550
Scheme 6. Syntheses of dinuclear ansa-zirconocene complexes: (i) (2,4,5-Me3C7H2S)K in THF, (ii) nBuLi (4.0 eq) in THF and then addition of MeMgBr (4.6 eq) and ZrCl4·(THF)2 (2.0 eq).
Scheme 6. Syntheses of dinuclear ansa-zirconocene complexes: (i) (2,4,5-Me3C7H2S)K in THF, (ii) nBuLi (4.0 eq) in THF and then addition of MeMgBr (4.6 eq) and ZrCl4·(THF)2 (2.0 eq).
Catalysts 12 00283 sch006
Table
Table 1. Ethylene/1-hexene copolymerization results for the supported catalysts prepared with ansa-zirconocene complexes a,b.
Table 1. Ethylene/1-hexene copolymerization results for the supported catalysts prepared with ansa-zirconocene complexes a,b.
EntryMetallocene ComplexesProductivity
(kg − PE/g − (Supported Catalyst)/h)		Bulk Density
(g/mL)		1-Hexene Content
(mol%)		Mw c
(kDa)		Mw/Mn
19 (Me, H, H)23.00.331.82502.7
210 (Me, Me, H)25.70.351.32983.6
311 (H, H, H)25.80.351.32625.2
412 (Me, H, tBu)20.70.361.33342.5
513 (Me, H, Cl)5.60.371.13404.1
615 (tBuPh-indenyl)13.20.351.82463.5
720 (tBuO–, tBu2fluorenyl)19.60.350.793734.1
823 (tBuO–, tBuPh-indenyl)23.20.361.11965.2
926 (dinuclear, tBu2fluorenyl)24.50.351.23574.1
10I (Me4C5)17.50.380.791253.2
11II (dinuclear, Me4C5)24.80.380.801103.0
12III (tBuO, Me4C5)22.80.380.801143.0
13(THI)ZrCl2 d12.00.421.03003.2
a Supported catalyst preparation conditions: Silica–MAO (1.0 g, 4.8 mmol Al/g-(silica–MAO)), metallocene complex (120 μmol Zr), 70 °C, 1.0 h. b Polymerization conditions: supported catalyst (6.0 mg), hexane (300 mL), 1-hexene (3.0 mL), Et3Al (0.20 mmol) as a scavenger, ethylene (20 bar), 80 °C, 30 min. c Measured by GPC at 160 °C using trichlorobenzene with PS standards. d (rac-ethylenebis(tetrahydroindenyl))ZrCl2.
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Jeong, S.M.; Park, J.Y.; Hyun, Y.B.; Baek, J.W.; Kim, H.; Yoon, Y.; Chung, S.; Lee, J.; Lee, B.Y. Syntheses of Silylene-Bridged Thiophene-Fused Cyclopentadienyl ansa-Metallocene Complexes for Preparing High-Performance Supported Catalyst. Catalysts 2022, 12, 283. https://doi.org/10.3390/catal12030283

AMA Style

Jeong SM, Park JY, Hyun YB, Baek JW, Kim H, Yoon Y, Chung S, Lee J, Lee BY. Syntheses of Silylene-Bridged Thiophene-Fused Cyclopentadienyl ansa-Metallocene Complexes for Preparing High-Performance Supported Catalyst. Catalysts. 2022; 12(3):283. https://doi.org/10.3390/catal12030283

Chicago/Turabian Style

Jeong, Sun Mi, Ju Yong Park, Yong Bin Hyun, Jun Won Baek, Hagjun Kim, Yeokwon Yoon, Sangchul Chung, Junseong Lee, and Bun Yeoul Lee. 2022. "Syntheses of Silylene-Bridged Thiophene-Fused Cyclopentadienyl ansa-Metallocene Complexes for Preparing High-Performance Supported Catalyst" Catalysts 12, no. 3: 283. https://doi.org/10.3390/catal12030283

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