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Methylene‐Bridged Metallocenes with 2,2′‐Methylenebis[1 H ‐inden‐1‐yl] Ligands: Synthesis, Characterization, and Polymerization Catalysis of a Synthetically Simple Class of C 2 ‐ and C 2v ‐Symmetric ansa ‐Metallocenes
Author(s) -
Resconi Luigi,
Camurati Isabella,
Fiori Cristina,
Balboni Davide,
Mercandelli Pierluigi,
Sironi Angelo
Publication year - 2006
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200690154
Subject(s) - chemistry , methylene bridge , indene , dilithium , deprotonation , medicinal chemistry , methylene , substituent , ligand (biochemistry) , moiety , yield (engineering) , polymerization , aryl , zirconium , catalysis , alkyl , stereochemistry , organic chemistry , ion , biochemistry , receptor , polymer , materials science , metallurgy
The acid‐catalyzed reaction between formaldehyde and 1 H ‐indene, 3‐alkyl‐ and 3‐aryl‐1 H ‐indenes, and six‐membered‐ring substituted 1 H ‐indenes, with the 1 H ‐indene/CH 2 O ratio of 2 : 1, at temperatures above 60° in hydrocarbon solvents, yields 2,2′‐methylenebis[1 H ‐indenes] 1 – 8 in 50–100% yield. These 2,2′‐methylenebis[1 H ‐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[1 H ‐inden‐1‐yl]}zirconium ([ZrCl 2 ( 1′ )]) is the least soluble in organic solvents. Substitution of the 1 H ‐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[1 H ‐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‐1 H ‐inden‐1‐yl]}zirconium ([ZrCl 2 ( 5′ )] is the most open. The mixture [ZrCl 2 ( 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‐1 H ‐inden‐1‐yl]}zirconium ([ZrCl 2 ( 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.