1H and 13C NMR Studies of Cationic Intermediates Formed upon Activation of “Oscillating” Catalyst (2-PhInd)2ZrCl2 with MAO, MMAO, and AlMe3/[CPh3]+[B(C6F5)4]-

The conformationally dynamic unbridged metallocene (2-PhInd)2ZrCl2 (1-Cl) was activated with methylaluminoxane (MAO), modified methylaluminoxane (MMAO), and AlMe3/[CPh3]+[B(C6F5)4]-. The following ion pairs were characterized by 1H and 13C NMR:  [(2-PhInd)2Zr(μ-Me)2AlMe2]+[Me-MAO]- (III), [(2-PhInd)2Zr(μ-Me)2AlMe2]+[B(C6F5)4]- (III‘), [(2-PhInd)2Zr(μ-Me)2AlMeiBu]+[Me-MAO]- (IIIMeiBu), [(2-PhInd)2Zr(μ-Me)2AliBu2]+[Me-MAO]- (IIIiBuiBu), and [(2-PhInd)2ZrMe+···Me-MAO-] (IV). In the temperature range −50 to 20 °C, the rotation of indenyl ligands of complexes III, III‘, and IIIMeiBu is faster than the evaluated rate of propylene insertion, whereas for IIIiBuiBu the rate of indenyl ligand rotation is comparable to or slower than the rate of propylene insertion. The ion pair IIIiBuiBu demonstrates the fundamental possibility of the existence of intermediates with the “locked” conformation of 2-PhInd ligands in 1-Cl/MAO or 1-Cl/MMAO systems. For the catalytic system 1-Cl/MAO, both outer sphere ion pair III and in...

[1]  H. Brintzinger,et al.  Distinct methylalumoxane(MAO)-derived Me-MAO- anions in contact with a zirconocenium cation--a 13C-NMR study. , 2006, Dalton transactions.

[2]  M. H. Lee,et al.  Endowing aspecific, unbridged-metallocene propylene-polymerization catalysts with isospecificity: the unprecedented role of MAO. , 2006, Angewandte Chemie.

[3]  E. P. Talsi,et al.  Activation of rac‐Me2Si(ind)2ZrCl2 by Methylalumoxane Modified by Aluminum Alkyls: An EPR Spin‐Probe, 1H NMR, and Polymerization Study , 2006 .

[4]  R. Waymouth,et al.  Dynamic NMR Studies of Cationic Bis(2-phenylindenyl)zirconium Pyridyl Complexes: Evidence for syn Conformers in Solution , 2005 .

[5]  R. Waymouth,et al.  Effects of ligand substitutions on the rotation rate of indenyl ligands in bis(2-arylindenyl)zirconocenes by NMR line-shape analysis and relaxation in the rotating frame , 2004 .

[6]  E. P. Talsi,et al.  1H and 13C NMR Spectroscopic Study of Titanium(IV) Species Formed by Activation of Cp2TiCl2 and [(Me4C5)SiMe2NtBu]TiCl2 with Methylaluminoxane (MAO) , 2004 .

[7]  E. Rytter,et al.  1H-, 13C-NMR and ethylene polymerization studies of zirconocene/MAO catalysts: effect of the ligand structure on the formation of active intermediates and polymerization kinetics , 2003 .

[8]  A. Segre,et al.  "Oscillating" metallocene catalysts: what stops the oscillation? , 2003, Journal of the American Chemical Society.

[9]  R. Waymouth,et al.  Influence of cocatalyst on the stereoselectivity of unbridged 2-phenylindenyl metallocene catalysts , 2002 .

[10]  R. Waymouth,et al.  2-Arylindene metallocenes: conformationally dynamic catalysts to control the structure and properties of polypropylenes. , 2002, Accounts of chemical research.

[11]  L. Cavallo,et al.  Selectivity in propene polymerization with metallocene catalysts. , 2000, Chemical reviews.

[12]  E. P. Talsi,et al.  Mechanism of dimethylzirconocene activation with methylaluminoxane: NMR monitoring of intermediates at high Al/Zr ratios , 2000 .

[13]  M. D. Fryzuk,et al.  Preparation and Reactivity of Zirconium(III), Niobium(III), and Molybdenum(III) Complexes Stabilized by a Cyclopentadienyl Unit with Pendant Phosphine Donors , 1999 .

[14]  E. P. Talsi,et al.  Multinuclear NMR investigation of methylaluminoxane , 1997 .

[15]  M. C. Sacchi,et al.  Dimethylzirconocene-methylaluminoxane catalyst for olefin polymerization : NMR study of reaction equilibria , 1997 .

[16]  G. Coates,et al.  Oscillating Stereocontrol: A Strategy for the Synthesis of Thermoplastic Elastomeric Polypropylene , 1995, Science.

[17]  M. Bochmann,et al.  Base-free cationic 14-electron alkyls of Ti, Zr and Hf as polymerisation catalysts : a comparison , 1992 .

[18]  A. Winter,et al.  The First Example of an Ethylene-Selective Soluble Ziegler Catalyst of the Zirconocene Class† , 1989 .

[19]  J. Schwartz,et al.  Direct observation of metal-centered radicals in an oxidative-addition reaction , 1982 .