Revisiting Benzylidenequinolinylnickel Catalysts through the Electronic Effects on Catalytic Activity by DFT Studies

Abstract

The reaction activities for a series of benzylidenequinolin nickel complex systems are studied by density functional theory methods. The effective net charge values obtained on nickel atoms illustrate the correlation with experimental activities. Catalytic activity increases with the higher effective net charge values. The energy gaps (Δε1) between Ni complex's lowest unoccupied molecular orbita (LUMO) and ethylene's highest occupied molecular orbital (HOMO) orbitals are calculated, regarding both pre‐catalysts and active species. The results show that there are also relationships between Δε1 and catalytic activities. Comparing the pre‐catalysts to the active species, the energy gaps Δε1 decrease dramatically from about 60 kcal mol–1 to about 0 kcal mol–1 for each complex, indicating the important activating role played by the co‐catalyst. Finally, it is found that the energy difference values between different spin states relates to catalytic activities for both pre‐catalyst and active species as well.

The Catalytic Activities of Carbocyclic Fused Pyridineimine Nickel Complexes Analogues in Ethylene Polymerization by Modeling Study

“…With the appearance of R 3 substituent, the energy differences (∆E) slightly decreased in complexes 4 and 5 compared with that of complexes 1 and 2, respectively. The variation of energy difference (∆E) presented regular increases with catalytic activities, which is in accordance to the previous report for Ni complexes [19]. For the HOMO-LUMO energy gap (∆ε 1 ), the values almost keep constant around 66 kcal/mol, except the slightly bigger values in complexes 4 and 5 compared with complexes 1-3.…”

“…Energy difference (∆E) can be explained in terms of different optimized energy of Ni complex between singlet and triplet states [19]. The values of Hammett constant (F) were taken from literature [29], and depended on the type of substituents.…”

“…The electron donating and withdrawing ability of substituents describes the electronic effect [11,12], while the steric effect is actually associated with bond length, bond angle, size of the substituents, and atomic radii of transition metal [13][14][15]. In preceding reports, the catalytic activities for Fe, Co and Ni complex systems are investigated quantitatively from the perspective of the electronic effect by the correlation with effective net charge on the central metal atom (Q eff ) [16][17][18], activities for Fe, Co and Ni complex systems are investigated quantitatively from the perspective of the electronic effect by the correlation with effective net charge on the central metal atom (Qeff) [16][17][18], Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy gaps (Δε) between complex and ethylene [19], and the energy difference between the two spin states (ΔE) [19], respectively.…”

Substantially enhancing the catalytic performance of bis(imino)pyridylcobaltous chloride pre‐catalysts adorned with benzhydryl and nitro groups for ethylene polymerization

“…In the presence of MMAO, when 4‐R is Cl (Figure ), the highest activity reported under similar conditions is lower than when 4‐R is NO 2 in the current work. It is assumed that the nitro moiety in the title complexes enhances the electrophilic character of the metal center owing to its strong electron‐withdrawing effect, which in turn increases the coordination and insertion of the ethylene, affording higher activities …”

Quantitative Structure-Thermostability Relationship of Late Transition Metal Catalysts in Ethylene Oligo/Polymerization

“…As a result, the quantitative structure-property relationship (QSPR) approach has proven to be useful. In our previous studies, the relationship between the structure of a catalyst and its catalytic activity was investigated by molecular modeling, which successfully predicted the catalytic activities of late transition metal complex precatalysts toward ethylene oligo/polymerization, through electronic effects [38][39][40][41] or both from electronic and steric effects [42,43]. Regarding the influence of the catalyst structure on its thermal stability, several possible factors were proposed by previous experimental research [19,[24][25][26][29][30][31][32][33][34][35][36].…”