Modification of Methylaluminoxane‐Activated ansa‐Zirconocene Catalysts with Triisobutylaluminum—Transformations of Reactive Cations Studied by NMR Spectroscopy

Abstract

When triisobutylaluminum (AliBu(3)) is added to solutions containing methylaluminoxane (MAO) and rac-[Me(2)Si(ind)(2)ZrCl(2)] (ind: indenyl) in C(6)D(6), NMR spectra show that methyl-bridged mixed-alkylaluminum dimers Al(mu-Me)(2)Me(4-x)iBu(x) predominate. These dimers react with MAO under partial transfer of isobutyl groups and induce a conversion of the initially prevailing cationic trimethylaluminum adduct rac-[Me(2)Si(ind)(2)Zr(mu-Me)(2)AlMe(2) (+)] to rac-[Me(2)Si(ind)(2)Zr(mu-Me)(2)AlMeiBu(+)] and rac-[Me(2)Si(ind)(2)Zr(mu-Me)(2)AliBu(2) (+)]. These species are unstable and release isobutene under formation of zirconocene hydrides.

Heterobi‐ and ‐trimetallic Ion Pairs of Zirconocene‐Based Isoselective Olefin Polymerization Catalysts with AlMe3

“…to be a result of an α‐hydrogen transfer reaction of the metallocene ZrMe bonds with those AlMe of MAO, leading to catalytically inactive Zr‐CH 2 ‐Al(Me)‐O‐ species; 2) based on limited 1 H NMR spectroscopic data, Britzinger et al. surmised that, upon activation of 1 b with MAO, formation of the putative methylidene species [ rac ‐{Me 2 Si‐(2‐Me‐4‐Ph‐Ind) 2 }Zr(μ‐CH 2 )(μ‐Me)AlMe 2 ] + [“Me‐MAO”] − takes place from the corresponding parent { rac ‐[{Me 2 Si‐(2‐Me‐4‐Ph‐Ind) 2 }Zr(μ‐Me) 2 AlMe 2 ] + [“Me‐MAO”] − , accompanied by concomitant evolution of methane 7b. 16 This is also reminescent to Anwander’s work on the formation of Ln(μ‐CH 2 )Al species via CH activation of aminomethyl group in neutral lanthanoid alkylaluminate complexes 2c…”

Methylalumoxane – History, Production, Properties, and Applications

“…The direct interactions between MMAO and several catalysts have also been studied 153,154. The Me 3 Al separated ion pair ( 32 ) formed during activation with regular MAO now becomes a i Bu n AlMe 3– n separated ion pair.…”

EPR Identification of Zr(III) Complexes Formed upon Interaction of (2‐PhInd)2ZrCl2 and rac‐Me2Si(1‐Ind)2ZrCl2 with MAO and MMAO

“…[25] No EPR signals of Zr III were observed for the 2/MAO system before and after the addition of pyridine. Thus, the heterobinuclear ion pair [(rac-Me 2 Si(1-Ind) 2 Zr IV (m-Me) 2 [26] Again no EPR signals were observed for the sample 2/ MMAO. However, the addition of pyridine to this sample results in the appearance of an EPR signal at g ¼ 1. .…”