Improving the Behavior of Bis(phenoxyamine) Group 4 Metal Catalysts for Controlled Alkene Polymerization

Improving the Behavior of Bis(phenoxyamine) Group 4 Metal Catalysts for Controlled Alkene Polymerizatio

Improving the Behavior of Bis(phenoxyamine) Group 4 Metal Catalysts for Controlled Alkene Polymerization

Improving the Behavior of Bis(phenoxyamine) Group 4 Metal Catalysts for Controlled Alkene Polymerizatio

Binuclear Complexes of Bis-Chelating Ligands Based on [1,4]Dioxocino[6,5-<i>b</i>:7,8-<i>b</i>′]dipyridine Moieties

Ligands based on a [1,4]dioxocino[6,5-b:7,8-b′]dipyridine (doxpy) core were prepared and characterized. They all present two equal chelating moieties each one including one N, O, or S donor in addition to a pyridinic nitrogen. These ligands displayed high selectivity for the formation of binuclear complexes. At least one d8 ion (PdII or PtII) complex was prepared for each type of ligand. The stereochemical behavior of the ligands is discussed on the basis of NMR spectra. Stable atropoisomers were obtained in the case of N-oxides or in case chiral centers were introduced in the ethereal bridge. As for the complexes, stable enantiomers appear to be in principle attainable for all the new compounds. A test on the cooperative ability of two PdII centers has been grounded on the microstructure of the styrene/CO copolymer catalytically produced by a binuclear pyridine-imino complex. In fact, comparison with the microstructure of the copolymers produced by related single-site mono- and (open-chain) binuclear catalysts reveals significant difference, thus giving indication of possible synergic metal activity

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

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

Structure−Activity Relationship in Olefin Polymerization Catalysis: Is Entropy the Key?

Activation parameters for propene polymerization mediated by a bis(phenoxyamine)Zr-dibenzyl catalyst in combination with MAO have been measured experimentally and calculated by DFT; experiment and calculation consistently indicate that the entropic term is the most important reason for the low chain propagation rate with this system. Based on this finding and a review of literature data on a variety of olefin polymerization catalysts, we propose a strong correlation between the propagation rate and how catalysts deal with the entropy loss of monomer capture

Structure/Properties Relationship for Bis(phenoxyamine)Zr(IV)-Based Olefin Polymerization Catalysts: A Simple DFT Model To Predict Catalytic Activity

The productivity of a number of bis­(phenoxyamine)­Zr­(IV)-based catalysts (bis­(phenoxyamine) = <i>N,N</i>′-bis­(3-R₁-5-R₂-2-O-C₆H₂CH₂)-<i>N,N</i>′-(R₃)₂-(NCH₂CH₂N)) in ethene and propene polymerization was evaluated for different R₁/R₂/R₃ combinations. In previous studies on this class we demonstrated that the cations that form upon precatalyst activation (e.g., by methylalumoxane) adopt a “dormant” <i>mer-mer</i> geometry, and an endothermic isomerization to the active <i>fac-fac</i> geometry is the necessary first step of the catalytic cycle. Herewith we report a clear correlation between catalyst activity and the DFT-calculated energy difference Δ<i>E</i>_<i>i</i> between the active and dormant state. The correlation only holds when the calculations are run on ion pairs, which is less obvious than it may appear because the anion in these systems is not at the catalyst front. This finding provides a comparatively simple and fast method to predict the activity of new catalysts of the same class

Structure/Properties Relationship for Bis(phenoxyamine)Zr(IV)-Based Olefin Polymerization Catalysts: A Simple DFT Model To Predict Catalytic Activity

The productivity of a number of bis­(phenoxyamine)­Zr­(IV)-based catalysts (bis­(phenoxyamine) = <i>N,N</i>′-bis­(3-R₁-5-R₂-2-O-C₆H₂CH₂)-<i>N,N</i>′-(R₃)₂-(NCH₂CH₂N)) in ethene and propene polymerization was evaluated for different R₁/R₂/R₃ combinations. In previous studies on this class we demonstrated that the cations that form upon precatalyst activation (e.g., by methylalumoxane) adopt a “dormant” <i>mer-mer</i> geometry, and an endothermic isomerization to the active <i>fac-fac</i> geometry is the necessary first step of the catalytic cycle. Herewith we report a clear correlation between catalyst activity and the DFT-calculated energy difference Δ<i>E</i>_<i>i</i> between the active and dormant state. The correlation only holds when the calculations are run on ion pairs, which is less obvious than it may appear because the anion in these systems is not at the catalyst front. This finding provides a comparatively simple and fast method to predict the activity of new catalysts of the same class