Catalyst Speciation During -Zirconocene-Catalyzed Polymerization of 1-Hexene Studied by UV-vis Spectroscopy-Formation and Partial Re-Activation of Zr-Allyl Intermediates.

Catalyst speciation during polymerization of 1-hexene in benzene or toluene solutions of the catalyst precursor SBIZr(μ-Me)AlMe B(CF)(SBI = -dimethylsilyl-bis(1-indenyl)) at 23 °C is studied by following the accompanying UV-vis-spectral changes. These indicate that the onset of polymerization catalysis is associated with the concurrent formation of two distinct zirconocene species. One of these is proposed to consist of SBIZr-σ-polyhexenyl cations arising from SBIZr-Me (formed from SBIZr(μ-Me)AlMe by release of AlMe) by repeated olefin insertions, while the other one is proposed to consist of SBIZr-η-allyl cations of composition SBIZr-η-(1-R-CH) (R = npropyl), [.

Zirconium-allyl complexes as resting states in zirconocene-catalyzed α-olefin polymerization.

UV-vis spectroscopic data indicate that zirconocene cations with Zr-bound allylic chain ends are generally formed during olefin polymerization with zirconocene catalysts. The rates and extent of their formation and of their re-conversion to the initial pre-catalyst cations depend on the types of zirconocene complexes and activators used.

Formation of trivalent zirconocene complexes from ansa-zirconocene-based olefin-polymerization precatalysts: an EPR- and NMR-spectroscopic study.

Reduction of Zr(IV) metallocenium cations with sodium amalgam (NaHg) produces EPR signals assignable to Zr(III) metallocene complexes. The chloro-bridged heterodinuclear ansa-zirconocenium cation [(SBI)Zr(μ-Cl)2AlMe2](+) (SBI = rac-dimethylsilylbis(1-indenyl)), present in toluene solution as its B(C6F5)4(-) salt, thus gives rise to an EPR signal assignable to the complex (SBI)Zr(III)(μ-Cl)2AlMe2, while (SBI)Zr(III)-Me and (SBI)Zr(III)(μ-H)2Al(i)Bu2 are formed by reduction of [(SBI)Zr(μ-Me)2AlMe2](+) B(C6F5)4(-) and [(SBI)Zr(μ-H)3(Al(i)Bu2)2](+) B(C6F5)4(-), respectively. These products can also be accessed, along with (SBI)Zr(III)-(i)Bu and [(SBI)Zr(III)](+) AlR4(-), when (SBI)ZrMe2 is allowed to react with HAl(i)Bu2, eliminating isobutane en route to the Zr(III) complex.

Cationic alkylaluminum-complexed zirconocene hydrides: NMR-spectroscopic identification, crystallographic structure determination, and interconversion with other zirconocene cations.

The ansa-zirconocene complex rac-Me(2)Si(1-indenyl)(2)ZrCl(2) ((SBI)ZrCl(2)) reacts with diisobutylaluminum hydride and trityl tetrakis(perfluorophenyl)borate in hydrocarbon solutions to give the cation [(SBI)Zr(μ-H)(3)(Al(i)Bu(2))(2)](+), the identity of which is derived from NMR data and supported by a crystallographic structure determination. Analogous reactions proceed with many other zirconocene dichloride complexes. [(SBI)Zr(μ-H)(3)(Al(i)Bu(2))(2)](+) reacts reversibly with ClAl(i)Bu(2) to give the dichloro-bridged cation [(SBI)Zr(μ-Cl)(2)Al(i)Bu(2)](+).

Cationic alkylaluminum-complexed zirconocene hydrides as participants in olefin polymerization catalysis.

The alkylaluminum-complexed zirconocene trihydride cation [(SBI)Zr(μ-H)(3)(Al(i)Bu(2))(2)](+), which is obtained by reaction of (SBI)ZrCl(2) with [Ph(3)C][B(C(6)F(5))(4)] and excess HAl(i)Bu(2) in toluene solution, catalyzes the formation of isotactic polypropene when exposed to propene at -30 °C. This cation remains the sole observable species in catalyst systems free of AlMe compounds. In the presence of AlMe(3), however, exposure to propene causes the trihydride cation to be completely converted, under concurrent consumption of all hydride species by propene hydroalumination, to the doubly Me-bridged cation [(SBI)Zr(μ-Me)(2)AlMe(2)](+).

Reactive intermediates formed during olefin polymerization by methylalumoxane-activated ansa-zirconocene catalysts: identification of a chain-carrying intermediate by NMR methods.

Addition of 1-hexene to methylalumoxane-activated catalyst systems based on rac-Me(2)Si(ind)(2)ZrMe(2) causes, concurrent with polyhexene formation and diminution of the otherwise prevalent cation [rac-Me(2)Si(ind)(2)Zr(mu-Me)(2)AlMe(2)](+), formation of a hitherto unobserved species [rac-Me(2)Si(ind)(2)Zr(mu-R)(mu-Me)AlMe(2)](+), where R is a Zr-bound polyhexyl chain. As hexene is increasingly consumed, this cation decays, mainly back to [rac-Me(2)Si(ind)(2)Zr(mu-Me)(2)AlMe(2)](+) and, in part, to some species containing a Zr-bound allylic chain end.

Alkylaluminum-complexed zirconocene hydrides: identification of hydride-bridged species by NMR spectroscopy.

Reactions of unbridged zirconocene dichlorides, (R(n)C(5)H(5-n))(2)ZrCl(2) (n = 0, 1, or 2), with diisobutylaluminum hydride (HAl(i)Bu(2)) result in the formation of tetranuclear trihydride clusters of the type (R(n)C(5)H(5-n))(2)Zr(mu-H)(3)(Al(i)Bu(2))(3)(mu-Cl)(2), which contain three [Al(i)Bu(2)] units. Ring-bridged ansa-zirconocene dichlorides, Me(2)E(R(n)C(5)H(4-n))(2)ZrCl(2) with E = C or Si, on the other hand, are found to form binuclear dihydride complexes of the type Me(2)E(R(n)C(5)H(4-n))(2)Zr(Cl)(mu-H)(2)Al(i)Bu(2) with only one [Al(i)Bu(2)] unit. The dichotomy between unbridged and bridged zirconocene derivatives with regard to tetranuclear versus binuclear product formation is proposed to be connected to different degrees of rotational freedom of their C(5)-ring ligands.

Modification of methylaluminoxane-activated ansa-zirconocene catalysts with triisobutylaluminum-transformations of reactive cations studied by NMR spectroscopy.

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.

Distinct methylalumoxane(MAO)-derived Me-MAO- anions in contact with a zirconocenium cation--a 13C-NMR study.

Zirconocenium cations of the type [(MeC5H4)2ZrMe]+, formed by excess methylalumoxane (MAO) from (MeC5H4)2ZrCl2 or (MeC5H4)2ZrMe2 with 13C-labelled ring ligands, are found to form ion pairs with two types of anions, Me-MAO(A)- and Me-MAO(B)-, which differ in their coordinative strengths: More strongly coherent ion pairs [(MeC5H4)2ZrMe+...

[{Me(4)C(2)(C(5)H(4))(2)}Zr(BH(4))(2)], a bis(tetrahydroborate) complex of a bridged zirconocene.

Bis(tetrahydroborato)[1,1,2,2-tetramethyl-1,2-ethylenebis(eta(5)-cyclopentadienyl)]zirconium, (I), was synthesized by the reaction of the zirconocene dichloride with lithium tetrahydroborate. Crystals suitable for X-ray structure analysis were obtained by recrystallization from toluene. The molecule adopts an appproximate C(2v) symmetry.

Synthesis of an ansa-Zirconocene via a Novel S -Symmetric Spirobis(silastannaindacene) Compound.

A stereoselective reaction of Sn(NMe ) with the silyl-bridged bis(cyclopentadienyl) derivative 1 generates the novel spiro compound 2, in which two C -symmetric six-membered rings of opposite configuration are joined at a tin center: One ring is R,R-, and the other S,S-configured. Subsequent reaction with two equivalents of ZrCl affords, by stereoselective Sn/Zr exchange, exclusively the C -symmetric isomer of the ansa-zirconocene rac-3.