Catalytic Trimerization of Ethene with Highly Active Cyclopentadienyl−Arene Titanium Catalysts

Abstract

Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. The mono(cyclopentadienyl-arene)titanium complexes [η 5 -C 5 H 3 R-(bridge)-Ar]TiCl 3 , activated by methylalumoxane (MAO) cocatalyst, form a family of highly active catalysts for the trimerization of ethene, giving 1-hexene as the main product. Concomitant cotrimerization of ethene and 1-hexene, to give mainly 5-methylnon-1-ene, is also observed. The selectivity for trimerization depends on the presence of a pendant arene group on the cyclopentadienyl ligand and the nature of the bridge between these two ligand moieties. In the absence of a pendant arene, polyethene is the main product. The highest activity and selectivity for trimerization was observed for catalysts with a disubstituted C 1 bridge between the cyclopentadienyl and arene ligand moieties. A SiMe 3 substituent on the cyclopentadienyl ligand improves catalyst activity and selectivity, whereas methyl substitution of the arene decreases activity. Nevertheless, combining cyclopentadienyl SiMe 3 substitution with arene Me substitution gives rise to a catalyst with the highest activity and selectivity, evidence of the strongly nonlinear additivity of ligand substituent effects in this system. The cyclopentadienyl-arene ligand is likely to exhibit hemilabile behavior during catalysis, stabilizing intermediates by η 6 coordination and dissociating or slipping to make room for the incoming substrate. The presence of two pendant arene groups on the cyclopentadienyl ligand diminishes the activity of the catalyst but greatly enhances its stability.

(nBuCp)2ZrCl2‐catalyzed ethylene‐4M1P copolymerization: Copolymer backbone structure, melt behavior, and crystallization

“…See Scheme 2 which has been extracted from a review of the relevant literature. [68][69][70][71] The mechanism of ethylene trimerization, as shown in Scheme 2, follows a metallacyclic route. Accordingly, two ethylene molecules are added to the metal, followed by insertion of another ethylene unit, which yields a higher order metallacycle (zirconacycloheptane).…”

“…The resulting 1-hexene gets incorporated into the growing polyethylene chain through 1, 2 insertion and synthesizes the branched polyethylene. [68][69][70][71] The literature mostly reports a typical tandem process that involves two different transition metal precatalysts with one cocatalyst [68][69][70][71] as well as one zirconocene precatalyst with two different cocatalysts. 72 2 shows that a tandem copolymerization can also be achieved using a single precatalyst-cocatalyst ion pair.…”

Catalytic Trimerization of Ethylene with Highly Active Half‐sandwich Titanium Complexes Bearing Pendant p‐Fluorophenyl Groups

“…To evaluate the activities and selectivities of the new catalysts, the catalytic system 3/MAO reported by Hessen 10 was used as reference. The oligomerization products were analyzed by GC.…”

“…The reason that [η 5 -C 5 H 4 -(bridge)-(p-fluorophenyl)]-TiCl 3 /MAO system can prompt the trimerization of ethylene, according to the mechanism proposed by Hessen, 10 is that the pendant aryl group can exhibit hemilabile behaviour. In the course of formation of active species, the arene coordination can provide additional stabilization to the Ti(II) state.…”

“…Although most catalytic trimerization systems are based on chromium compounds, 8,9 the research on non-chromium based trimerization systems is still in process, not only for potential productivity, but also for pollution reasons. 10 In 2002, Hessen and co-workers 10 reported that the half-sandwich titanium complexes [η 5 -C 5 H 4 -(bridge)-Ar]-TiCl 3 , activated by methylalumoxane (MAO), formed a family of highly active catalysts for the trimerization of ethylene, giving 1-hexene as main product. This discovery has triggered chemist's interest in developing group 4 metal complexes used in ethylene trimerization.…”