Half-Sandwich Rare Earth Metal Complexes as Novel Catalysts for Olefin Polymerization and Other Chemical Transformations

Abstract

This article describes our recent studies on the synthesis and chemistry of mono(cyclopentadienyl)-ligated rare earth metal alkyl and hydride complexes. The half-sandwich mono-and dialkyl rare earth metal complexes are prepared either by alkane elimination reactions between trialkyl rare earth complexes and the neutral cyclopentadiene derivatives or by metathetical reactions of rare earth trichlorides with the alkali metal salts of the corresponding ligands. 4 ] generates easily the corresponding cationic monoalkyl species, which serve as excellent catalysts for the polymerization and copolymerization of a variety of olefins to yield a new family of polymer materials that show novel properties but are difficult to prepare by other catalysts. The half-sandwich monoalkyl rare earth complexes bearing the silylene-linked cyclopentadienylarylamido ligands act as excellent catalysts for the catalytic dimerization of terminal alkynes, cross coupling of terminal alkynes with isocyanides, and the catalytic addition of terminal alkyne CH, amine NH, and phosphine PH bonds to carbodiimides. The hydrogenolysis of the dialkyl rare earth complexes with H 2 affords a new class of polynuclear rare earth metal polyhydride complexes, which show unique features in both structure and reactivity.

Rare Earth Metal Boryl Complexes: Synthesis, Structure, and Insertion of a Carbodiimide and Carbon Monoxide

“…The reaction of 2‐Sc with 2 equiv of N , N ′‐diisopropylcarbodiimide in [D 8 ]toluene at room temperature took place rapidly, and the starting materials disappeared within 30 min, as monitored by 1 H NMR. Bis(amidinate)‐ligated boryl complex 3 , formed through carbodiimide insertion into the two ScCH 2 SiMe 3 bonds in 2‐Sc ,7d,e, 8c,g–i was isolated as a pale yellow microcrystalline solid in 30 % yield from a concentrated solution of the reaction mixture in THF/hexane. A certain amount of tris(amidinate) complex 4 , formed by carbodiimide insertion into both ScC bonds and the ScB bond, was also observed in the mother liquor.…”

Recent progress in the chemical modification of syndiotactic polystyrene

“…[48][49][50][51][52][53][54] In this respect, single-site catalysts based on group 3 metals (yttrium, scandium, and the lanthanide series) have been developed for the syndiotactic copolymerization of styrene with dienes and a-olens. 55,56 Binary group 3 metal catalyst systems have been developed by Hou's group. 57,58 These systems are very active and can be compared in this respect to the "classic" CpTiCl 3 /MAO catalyst system.…”

Fluorenyl Half-Sandwich Bis(tetramethylaluminate) Complexes of the Rare-Earth Metals: Synthesis, Structure, and Isoprene Polymerization

“…Coordinative 1,3-diene polymerization has developed into a lucrative market for rare-earth metal (Ln)-based catalysts, which are arguably the most efficient initiators concerning joint activity and selectivity issues. ,,, Regarding this, the ubiquitous cyclopentadienyl (Cp) ligand has played a pivotal role in synthesizing the first single-component catalysts. − The polymerization performance has been assessed for various subsets of Cp derivatives, including half-sandwich, ,,− ( ansa -)­metallocene, − or constrained geometry complexes . Far less attention has been paid to fluorenyl derivatives, possibly because of the favorable occurrence of haptotropic rearrangements (η 5 -to-η 6 ) or (η 5 -to-η 3 -to-η 1 ). , However, such haptotropic shifts might considerably affect the appearance of the initiating species and hence the stereoregularity of the polymer.…”