A screening DFT study of the para-substituent effect on local hyper-softness in bis(phenoxy-imine) titanium complexes to get insights about their catalytic activity in ethylene polymerization

Sergey V. Nikitin, Jesús Sánchez-Márquez, Ivan I. Oleynik, Irina Oleynik, Elena G. Bagryanskaya

Результат исследования: Научные публикации в периодических изданияхстатья

Аннотация

Quantum chemical calculations of substituted α-Cumyl and t Bu bis(phenoxy-imine) titanium catalysts were performed at the RBP86/SVP level. The impact of para-substitution in the phenoxy-imine ligands on the electronic structure of the titanium complexes was studied within the framework of the Conceptual density functional theory. We found that such a reactivity descriptor as local hyper-softness on titanium correlates well with the Hammett constant for a series of substituents. The effect of the substitution in three para-positions of the phenoxy-imine ligand for the Cumyl catalysts weakens while passing from the α-Cumyl through the salicylic and further to the aniline moiety. By contrast, in the t Bu complexes the presence of a substituent in the salicylic part has similar influence on the local hyper-softness on titanium as compared with the aniline moiety. Moreover, placement of the groups with opposite electronic effects at the termini of the phenoxy-imine framework was shown to provide electronic flexibility in both the α -Cumyl and the t Bu complexes. Within the framework of the “ligand-oriented” concept, such flexibility increases the activity of a bis(phenoxy-imine) catalyst. In addition, we demonstrated that the hyper-conjugation between the π-system of the phenoxy-imine ligand and the α-Cumyl group raises the energy of the highest occupied molecular orbital keeping the lowest unoccupied orbital almost unchanged. This makes the α-Cumyl complexes chemically softer than their t Bu analogs and thereby more active in ethylene polymerization.

Язык оригиналаанглийский
Страницы (с-по)57-67
Число страниц11
ЖурналMolecular Catalysis
Том469
DOI
СостояниеОпубликовано - 1 мая 2019

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