Synthesis, structure, and ethene polymerisation catalysis of 1- or 2-silyl substituted bis[indenyl]zirconium(iv) dichlorides

Abstract

The systematic syntheses of 1- and 2-substituted silylindenes, with a wide variety of substitution patterns on the silyl moiety, and their corresponding zirconocene dichlorides are presented. The rac- and meso-diastereomers of the 1-substituted zirconocene dichlorides can in most cases be separated. Instable zirconocenes were observed for certain substitution patterns. Two of the obtained zirconocene dichlorides, bis[2-(dimethylsilyl)indenyl]zirconium dichloride (4a) and bis[2-(trimethylsilyl)indenyl]zirconium dichloride (4b), were characterised by single crystal X-ray diffraction. On the basis of DFT results, the two compounds are geometrically similar, i.e. the additional methyl group on the silyl moiety only affects the conformational energy profile. Differences in their catalyst performance in the homopolymerisation studies with ethane are thus attributed to conformational control. For the remaining complexes, sterically less demanding silyl groups seem to be favoured with respect to the catalyst performance. All the 2-isomers have lower polymerisation activities than the unsubstituted bis[indenyl]zirconium dichloride/MAO system. Curiously, the rac-bis[1-(dimethylphenylsilyl)indenyl]zirconium dichloride/MAO system is found to be the most active catalyst in ethene homopolymerisations.

Indenyl Complexes of Manganese(II). Conformational Flexibility of the Manganese(II)−(RnC9H7−n) Bond

“…1,3-Diisopropylindene (HInd 2i-1,3 ), 2-(trimethylsilyl)indene (HInd Si-2 ), 1,3-bis(trimethylsilyl)indene (HInd 2Si-1,3 ), 4,7-dimethylindene (HInd 2Me-4,7 ), and 2,4,7-dimethylindene (Hind 3Me-2,4,7 ) were prepared by following literature procedures; along with indene, all were converted into their potassium salts by reaction with K[N(SiMe 3 ) 2 ]. Hexanes, toluene, and diethyl ether were distilled under nitrogen from potassium benzophenone ketyl.…”

Synthetic Explorations Towards Sterically Crowded 1,2,3‐Substituted Bis(indenyl)zirconium(IV) Dichlorides

“…As we have seen in earlier work, the presence of hydrogen on the silyl groups in 2 position does not seem to be favored for the zirconocene synthesis. [3] In contrast, the syntheses of bis[1-methyl-2-TMS-indenyl]zirconium(iv) dichloride (12) and bis[1,3-dimethyl-2-TMS-indenyl]zirconium(iv) dichloride (13b) were achieved without undue difficulty, although the separation of the rac and meso diastereomers of 12 failed. The (basic) polymerization studies presented herein suggest that the activity in ethene polymerizations decreases with an increasing degree of substitution.…”

“…The rac and meso diastereomers were assigned according to relative chemical shifts, as published elsewhere. [3] Reaction of 11a with zirconium tetrachloride in diethyl ether at 0°C provided a yellow oil upon filtration through magnesium sulfate and subsequent solvent removal. Crystallization from diethyl ether was only limitedly successful, and we were not able to obtain an analytically pure sample due to the low yield.…”

“…[2] Previous work from our laboratory addressed unbridged zirconocene dichloride with silyl substituents in the 1 or 2 position. [3] Reports on trisubstituted indenyl ligands, i.e. substituents in the 1, 2, and 3 positions, are still quite uncommon.…”

tert-Butyldimethylsilyl Trifluoromethanesulfonate

“…Trialkylsilyl chlorides generally give the product of O-silylation 47. A range of carbanions have been silylated with TBDMS triflate, including allylic, 48 alkynyl,49 and indenyl systems 50. Functionalized TBDMS-substituted diazoacetates are prepared by C-silylation of unsubstituted diazoacetates using TBDMS triflate in combination with Hünig's base (eq 47) 51.…”