TY - JOUR

T1 - 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

AU - Nikitin, Sergey V.

AU - Sánchez-Márquez, Jesús

AU - Oleynik, Ivan I.

AU - Oleynik, Irina

AU - Bagryanskaya, Elena G.

N1 - Publisher Copyright: © 2019 Elsevier B.V.

PY - 2019/5/1

Y1 - 2019/5/1

N2 - 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.

AB - 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.

KW - Catalytic activity

KW - Conceptual density functional theory

KW - Degeneracy in frontier molecular orbitals

KW - Ethylene polymerization

KW - FI catalysts

KW - Hammett constant

KW - Local hyper-softness

KW - Substituent effect

KW - IMINE CHELATE LIGANDS

KW - DUAL DESCRIPTOR

KW - KOHN-SHAM

KW - SITE

KW - NET CHARGES

KW - DENSITY

KW - POPULATION ANALYSIS

KW - ACTIVITY VALUES

KW - BASIS-SETS

KW - MOLECULAR-FORCE FIELD

UR - http://www.scopus.com/inward/record.url?scp=85062641853&partnerID=8YFLogxK

U2 - 10.1016/j.mcat.2019.02.024

DO - 10.1016/j.mcat.2019.02.024

M3 - Article

AN - SCOPUS:85062641853

VL - 469

SP - 57

EP - 67

JO - Molecular Catalysis

JF - Molecular Catalysis

SN - 2468-8231

ER -