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]^-

Abstract

The conformationally dynamic unbridged metallocene (2-PhInd) 2 ZrCl 2 (1-Cl) was activated with methylaluminoxane (MAO), modified methylaluminoxane (MMAO), and AlMe 3 /[CPh 3 ] + [B(C 6 F 5 ) 4 ] -. The following ion pairs were characterized by 1 H and 13 C NMR:In the temperature range -50 to 20 °C, the rotation of indenyl ligands of complexes III, III′, and III MeiBu is faster than the evaluated rate of propylene insertion, whereas for III iBuiBu the rate of indenyl ligand rotation is comparable to or slower than the rate of propylene insertion. The ion pair III iBuiBu 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 inner sphere ion pair IV are present in the reaction solution at high [Al] MAO /[Zr] ratios. For the catalytic system 1-Cl/MMAO, the concentration of inner sphere ion pairs of type IV is much smaller (below the NMR detection limit), and only outer sphere ion pairs III MeiBu and III iBuiBu are observed.

Multi-Alkenylsilsesquioxanes as Comonomers and Active Species Modifiers of Metallocene Catalyst in Copolymerization with Ethylene

“…In turn, the complex 1 gradually disappeared at high Al/Zr molar ratios which was confirmed by the decrease in the intensity of the µ -Me resonance at −1.2 ppm (Figure 4b: 3-6). The cationic complexes 2 and 3 turned out to be the major species at high Al/Zr ratios (500 and 1000 mol/mol) (Figure 4b: 6, 7) which was consistent with the published research reports (complexes b and c, respectively) [33][34][35][36][37][38][39][40][41][42].…”

“…This phenomenon is associated with the influence of the POSS comonomer on transformation of the bimetallic metallocene species 1 (inactive form) into 2 or 3 complexes (precursors of the active form). However, the observed metallocene species 2 and 3 were dominant in the catalytic system in this case, even at the low Al/Zr ratio of 50 mol/mol, which is unusual for this group of catalysts [33][34][35][36][37][38][39][40][41][42]. It is probable that the modification of the catalytic system by the POSS compound resulted in much higher activity of the catalytic system in ethylene copolymerization with the POSS-6-3 comonomer as compared to homopolymerization of ethylene ( Figure 2).…”

“…The NMR spectroscopy was successfully applied to investigate the intermolecular structure of the ionic species relevant to the catalytic homogeneous polymerization [33][34][35][36][37][38][39][40][41][42]. These literature data provided important information on the structures of intermediates formed upon the activation of metallocene with MAO in toluene.…”

Conformationally dynamic titanium and zirconium cationic complexes of bis(naphthoxy)pyridine ligands: structure, “oscillation” and olefin polymerization catalysis

“…8,132.7,131.9,131.4,131.3,131.2,131.1,129.9,129.5,128.9,128.5,128.1,127.0,126.7,125.0,122.5,117.7,96.0 (PhCH2B) 5,133.7,129.4,128.9,128.2,127.8,127.0,123.5,123.3,118.3,71.8 (CH2OCH3,DME), 58.6 (CH2OCH3, DME), 39.5 (br s, NCH3), 27.10 (CCH3), 17.8 (CCH3), -3.7 (SiMe2).…”

“…1 Pioneering studies by Waymouth 2 and others 3 on the atropisomeric metallocenium cations [(2-Ph-(R-Ind))2ZrMe] + indicated that those species presumably exist under rac and meso conformational states in a "quasi-controlled" equilibrium; yet, further studies by Busico et al 4 and others 5 revealed a more complicated nature of such interconversion in metallocene catalysts. More recently, several post-metallocene systems were designed with the aim to gain a better control over the "oscillation" process.…”