Substituted Indenyl Ligands Research Articles

In-Reactor Polypropylene Functionalization─The Influence of Catalyst Structures and Reaction Conditions on the Catalytic Performance

To unravel the relationship between silylene-bridged metallocene catalyst structures and polymerization conditions and their effect on the performance in in-reactor functionalization of polypropylene, the behaviors of rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO, rac-Me2Si(Ind)2ZrCl2, rac-Me2Si(2-Me-4-Ph-Ind)2HfCl2, and rac-Me2Si(Ind)2HfCl2 in propylene/aluminum alkyl-passivated 10-undecen-1-ol copolymerization were compared. Kinetic analysis revealed higher catalytic activities for zirconocenes compared to analogous hafnocenes. Both the zirconocene and hafnocene with substituted indenyl ligands afforded a higher molecular weight capability, improved stereo-selectivity, and enhanced ability to incorporate functionalized comonomers compared to their non-substituted congeners. An in-depth study of polypropylene functionalization using the best performing catalyst system, rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO, at temperatures ranging from 40 to 100 °C, revealed a linear inversely proportional correlation of polymerization temperature with functionalized comonomer reactivity (↑Tp → ↓ r1), copolymer molecular weight (↑Tp → ↓Mn), and melting temperature (↑Tp → ↓Tm). While performing well under standard laboratory polymerization conditions, rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO showed limited molecular weight and stereo-selectivity capabilities under high-temperature (130–150 °C) solution process conditions. Although immobilization of rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 onto silica, allowing it to be used under industrially relevant slurry and gas-phase conditions, led to an active catalyst, it failed to incorporate any functionalized comonomer.

Group (IV) Metallocene Complexes with Bulky ω-aryloxyalkyl-Substituted Indenyl Ligands as Catalyst Precursors for Homogeneous Ethylene Polymerization

A series of seven new complexes of zirconium and hafnium with bulky ω-aryloxyalkyl substituted indenyl ligands were synthesized and characterized by NMR spectroscopy and elemental analysis. These complexes were activated with methylaluminoxane and tested for homogeneous ethylene polymerization. The zirconium catalysts showed higher activities than their hafnium analogues. The effects of increasing separation between the indenyl and the aryloxy substituent and the introduction of an extra methyl group on the indenyl moiety were also investigated. Catalyst 6 bearing a spacer chain of three methylene groups between the indenyl and aryloxy substituents showed the highest activity (15500 kg PE/mol cat. h). The increase in the spacer chain length resulted in the decrease in catalyst activities.

Syntheses, structures and catalytic activity for Friedel-Crafts reactions of substituted indenyl rhenium carbonyl complexes

The complexes [(η5-C9H6R)Re(CO)3] [R = nBu (8), tBu (9), CH(CH2)4 (10), Ph (11), Bz (12), 4-methoxyphenyl (13), 4-chlorophenyl (14)] were synthesized by refluxing substituted indenyl ligands [C9H7R] [R = nBu (1), tBu (2), CH(CH2)4 (3), Ph (4), Bz (5), 4-methoxyphenyl (6), 4-chlorophenyl (7)], and Re2(CO)10 in decalin. The molecular structures of 9, 10, 12, and 13 were determined by X-ray diffraction analysis. These four crystals have similar molecular structures of the mononuclear carbonyl complex. In each of these molecules, Re is η5-coordinated to the five-membered ring of the indenyl group. Complexes 8–14 have catalytic activity for Friedel-Crafts reactions of aromatic compounds with a variety of alkylation and acylation reagents. Compared with traditional catalysts, these mononuclear metal carbonyl complexes have obvious advantages such as high activities, mild reaction conditions, high selectivity, and environmentally friendly chemistry.

Zirconium dichloride complexes with bulky ω-9-methylfluorenylalkyl substituted indenyl ligands as catalysts for homogeneous ethylene polymerization

The synthesis and characterization of four new zirconium complexes with bulky ω-9-methylfluorenylalkyl substituted indenyl ligands are reported. After activation with methylaluminoxane (MAO) they can be applied as highly active catalysts for ethylene polymerization. The activities of the catalysts depend on the length of the CH2-spacer chain between the indenyl and the 9-methylfluorenyl moieties. The best results were obtained with four CH2 groups. This speaks for a comparatively free catalyst cation allowing easy coordination of the monomer to the active site and unhindered growth of the polymer chain.

Comparing propene polymerization with 1-butene polymerization catalyzed by MAO-activated C2- and C1-symmetric zirconocenes: An experimental and computational study on the influence of olefin size on stereoselectivity

Polypropene and poly(1-butene) have been synthesized under very similar experimental conditions with a series of MAO-activated C 2-symmetric and C 1-symmetric ansa-zirconocenes. The C 1-symmetric zirconocenes bearing the bilaterally symmetric fluorenyl or bis(2-methylthieno)cyclopentadienyl ligand connected through a dimethylsilyl bridge to substituted indenyl ligands produce isotactic polybutene of similar or higher molecular mass and with noticeably higher isotacticity, compared to isotactic polypropene prepared with the same catalysts under comparable conditions. Structural and mechanistic reasons for such behavior are discussed on the basis of QM/MM calculations.

Methylene‐Bridged Metallocenes with 2,2′‐Methylenebis[1H‐inden‐1‐yl] Ligands: Synthesis, Characterization, and Polymerization Catalysis of a Synthetically Simple Class of C2‐ and C2v‐Symmetric ansa‐Metallocenes

AbstractThe acid‐catalyzed reaction between formaldehyde and 1H‐indene, 3‐alkyl‐ and 3‐aryl‐1H‐indenes, and six‐membered‐ring substituted 1H‐indenes, with the 1H‐indene/CH2O ratio of 2 : 1, at temperatures above 60° in hydrocarbon solvents, yields 2,2′‐methylenebis[1H‐indenes] 1–8 in 50–100% yield. These 2,2′‐methylenebis[1H‐indenes] are easily deprotonated by 2 equiv. of BuLi or MeLi to yield the corresponding dilithium salts, which are efficiently converted into ansa‐metallocenes of Zr and Hf. The unsubstituted dichloro{(1,1′,2,2′,3,3′,3a,3′a,7a,7′a‐η)‐2,2′‐methylenebis[1H‐inden‐1‐yl]}zirconium ([ZrCl2(1′)]) is the least soluble in organic solvents. Substitution of the 1H‐indenyl moieties by hydrocarbyl substituents increases the hydrocarbon solubility of the complexes, and the presence of a substituent larger than a Me group at the 1,1′ positions of the ligand imparts a high diastereoselectivity to the metallation step, since only the racemic isomers are obtained. Methylene‐bridged ‘ansa‐zirconocenes’ show a noticeable open arrangement of the bis[1H‐inden‐1‐yl] moiety, as measured by the angle between the planes defined by the two π‐ligands (the ‘bite angle’). In particular, of the ‘zirconocenes’ structurally characterized so far, the dichloro{(1,1′,2,2′,3,3′,3a,3′a,7a,7′a‐η)‐2,2′‐methylenebis[4,7‐dimethyl‐1H‐inden‐1‐yl]}zirconium ([ZrCl2(5′)] is the most open. The mixture [ZrCl2(1′)]/methylalumoxane (MAO) is inactive in the polymerization of both ethylene and propylene, while the metallocenes with substituted indenyl ligands polymerize propylene to atactic polypropylene of a molecular mass that depends on the size of the alkyl or aryl groups at the 1,1′ positions of the ligand. Ethene is polymerized by rac‐dichloro{(1,1′,2,2′,3,3′,3a,3′a,7a,7′a‐η)‐2,2′‐methylenebis[1‐methyl‐1H‐inden‐1‐yl]}zirconium ([ZrCl2(2′)])/MAO to polyethylene waxes (average degree of polymerization ca. 100), which are terminated almost exclusively by ethenyl end groups. Polyethylene with a high molecular mass could be obtained by increasing the size of the 1‐alkyl substituent.

Control of Ultrahigh Molecular Weight Polypropene Microstructures via Asymmetric “Dual‐Side” Catalysts

AbstractAsymmetric ansa‐metallocene catalysts based on fluorenyl and specifically substituted indenyl ligands allow a continuous change of the properties of isotactic polypropene and thus generate a new portfolio of polypropene materials, ranging from excellent thermoplastic elastic to stiff plastomers. Controlling the length of the crystallizable, isotactic segments by means of isolated stereoerrors introduced into the isotactic enchainment made this possible. The combination of synthetic, structural and polymerization studies of a series of ansa‐asymmetric catalysts has provided much insight into the effectiveness of the substitution patterns on tailoring the polymer microstructures. Ligand substitution, temperature and concentration of the propene monomer in the reaction medium can influence stereoerrors distribution, and therefore the crystallinity of the materials. Ultrahigh molecular weight polypropenes with tacticities varying in a broad range (20% < [mmmm] < 80%) are available via (Ind‐Flu)‐based asymmetric hafnocenes.

Synthesis and Characterization of Zirconium and Iron Complexes Containing Substituted Indenyl Ligands: Evaluation of Steric and Electronic Parameters

Evaluation of the steric and electronic influence of a family of silyl- and alkyl-substituted indenyl ligands on zirconium and iron centers has been accomplished by a combination of X-ray diffraction, IR spectroscopy, solution NMR dynamics, and electrochemical measurements. Three tetrasubstituted, bis-indenyl zirconocene dichloride complexes have been characterized by X-ray diffraction and adopt a gauche ligand conformation such that the interactions between tertiary substituents on adjacent rings are minimized. Similar solid state conformations were also observed in two of the corresponding iron compounds. Evaluation of the electronic environment about each zirconium center was achieved by measurement of the CO stretching frequencies of the dicarbonyl derivatives. Simple inductive effects govern the electronic properties of each zirconocene where silyl groups are relatively electron withdrawing and alkyl groups electron donating. For the most hindered zirconocene dicarbonyl derivatives, population of thr...

Indenyl-amido titanium and zirconium dimethyl complexes: improved synthesis and use in propylene polymerization

The synthesis of a series of indenyl amido titanium dimethyl complexes, by means of the direct synthesis from the ligand, a 2-fold excess of MeLi, and TiCl 4 is reported. The 1H NMR spectra of the complexes show a quartet structure for the metal-bound methyl groups, due to through-metal proton–proton coupling. Coupling of Ti-methyl protons with protons on the Cp ring is also revealed by COSY 2D-NMR. The performance of the Ti complexes in propylene polymerization, including [Me 2Si(Me 4C 5)( t-BuN)]TiMe 2 ( 1-TiMe 2 ), [Me 2Si(Ind)( t-BuN)]TiMe 2 ( 2-TiMe 2 ) and six other methyl titanium complexes bearing substituted indenyl ligands, has been investigated with different cocatalysts and at different polymerization temperatures and propylene concentrations. All complexes produce amorphous polypropylene ( am-PP). The catalytic activity and molecular weight strongly depend on the substitution of the Cp ring: 2-TiMe 2 gives polymers of lower molecular weight, while the presence of a methyl group in position 2 (as in 3-TiMe 2 ) determines up to 4-fold increase in molecular weight. The type of cocatalyst influences mainly the catalytic activity, the borates being better activators than MAO, but also molecular weight, with again the borates giving higher molecular weights than MAO. 5-TiMe 2 –Ph 3CB(C 6F 5) 4 shows an overall activation energy of polymerization of 7.35 kcal mol −1. The rate of chain release is first order in monomer. The following activation energies for overall chain release have been calculated: ΔΔ E ‡ 2-TiMe 2 =3.4 kcal mol −1, ΔΔE ‡ 5-TiMe 2 =3.8 kcal mol −1, ΔΔ E ‡ 3-TiMe 2 =6.3 kcal mol −1. Even if all the polymers produced are amorphous, 2-TiMe 2 and 5-TiMe 2 show a microstructure unbalanced towards isotacticity, while 3-TiMe 2 , 6-TiMe 2 and 8-TiMe 2 are syndiotactic-enriched. Chiral induction comes mainly from a weak enantiomorphic site control.

Racemo-Selective Synthesis of ansa-Zirconocene Derivates from Zirconium Biphenolate Complexes

Stereoselective reactions of zirconium biphenolate complexes of the general formula (BIP)ZrCl2(THF)2 (1a−c), where BIP = 3,3‘-iPr2-6,6‘-Me2-1,1‘-bi-2-phenolate (a), 3,3‘-tBu2-5,5‘-Me2-1,1‘-bi-2-phenolate (b), or 3,3‘,5,5‘-tBu4-1,1‘-bi-2-phenolate (c), with 1 equiv of the lithium or magnesium salts of various ansa-bis(indenyl) ligands give the ansa-zirconocenes rac-C2H4(Ind)2Zr(BIP) (2b), rac-Me2Si(Ind)2Zr(BIP) (3c), rac-Me2Si(2-Me-Ind)2Zr(BIP) (4c), rac-Me2Si(2-Me-4-Ph-Ind)2Zr(BIP) (5c), and rac-Me2Si(2-Me-Benz[e]Ind)2Zr(BIP) (6c) in isolated yields of 60−75%. Reactions of C2H4(Ind)2Mg(THF)2 with 1a and 1b and of Me2Si(Ind)2Li2 with 1c give directly the pure diastereomers rac-2a, rac-2b, and rac-3c, respectively. More highly substituted indenyl ligands, on the other hand, give initially kinetically controlled mixtures of the rac- and meso-zirconocene BIP derivatives 4c, 5c, and 6c, from which the pure rac-derivatives are obtained as thermodynamically favored products by heating the reaction mixtures to 75...

Synthesis and polymerization behavior of various substituted indenyl titanium complexes as catalysts for syndiotactic polystyrene

Five substituted indenyltrichlorotitanium compounds have been synthesized and characterized by spectroscopic methods and their catalytic behavior for the polymerization of styrene was studied in the presence of methylaluminoxane (MAO) as a cocatalyst. Substituted indenyl ligands include 1,3-dimethyl, 1-methyl, 1-ethyl, 1-isopropyl and 1-(trimethylsilyl)indenyl groups. All five compounds gave extremely pure syndiotactic polystyrene, with conversion rates of at least 95%, and their catalytic properties were compared with the data obtained from the ( η 5-indenyl)trichlorotitanium-MAO system. The catalytic activity is enhanced by less bulky and better electron-releasing substituents of the indenyl ligand.