Structure and Dynamics in Solution of Bis(phenoxy-amine)Zirconium Catalysts for Olefin Polymerization

Abstract

The activity of two bis(phenoxy-amine)ZrR2 precatalysts (bis(phenoxy-amine) = N,N′-(3-tBu-5-OMe-2-C6H2OCH2)2-N,N′-Me2-(NCH2CH2N); R = Me (1), Bn (2, benzyl)) toward propene polymerization has been evaluated using different activators and cocatalysts: MAO, MAO/TBP, B(C6F5)3/TIBA, and [CPh3][B(C6F5)4]/TIBA (MAO = methylalumoxane, TBP = 2,6-di-tert-butylphenol, TIBA = triisobutylaluminum). It was found that the nature of the activator affects the activity only to a small extent. NMR studies in solution and DFT calculations on the 3a–c and 4a–c (a, MeB(C6F5)3 –; b, BnB(C6F5)3 –; c, B(C6F5)4 –) ion pairs deriving from the activation processes of 1 and 2, respectively, showed that three isomers can form. All of them have the anion in the second coordination sphere, whereas the binding modality of the ligand leads to the mer-mer most stable isomer, fac-mer isomer of intermediate stability, and fac-fac least stable isomer. Notably, the energy of the fac-fac isomer, which is supposed to be the active species in the polymerization process, depends more on the R group and not much on X–, in agreement with the small influence of the activators on the polymerization activity.

Selectively Measuring π Back‐Donation in Gold(I) Complexes by NMR Spectroscopy

“…The rotation rate constant (k r ) of the pyrrolidine, which is related to the CÀN bond order, [39] was obtained using the VT-1 H-EXSY NMR technique, which already proved to be effective in the measurement of activation parameters. [40][41][42] The measurement of k r is based on the exchange of the nonequivalent protons A and B of the pyrrolidine ring, due to the rotation around the CÀN bond. This gives two off-diagonal peaks in the 2D spectra ( Figure 3 a and b, example for complex 9), the volume of which is related to the rotation rate (see the Experimental Section and Supporting Information).…”

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

“…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.…”

Tridentate ligands and beyond in group IV metal α-olefin homo-/co-polymerization catalysis

“…The energy of the fac-fac isomer was found to be influenced much more by the R group which, given that the active centre was proposed to be of the fac-fac form, was consistent with the lack of fluctuation of activity on changing the co-catalyst/activator. 88 Salophan ligands bearing secondary N-methyl groups (see XXXIIIH 2 , Fig. 61, top) were prepared via nucleophilic substitution of bromomethylated phenols with the N,N 0 0methylated diaminobenzene (prepared in situ).…”