The effect of counterion on the kinetics and mechanism of ethylene polymerization by the zirconocene−boron catalytic system was examined using the density functional theory approach. A comparative study of three model catalytic species, namely, ethylzirconocene cation, Cp2ZrEt+, and two ion pairs of composition Cp2ZrEt+A- (A- = CH3B(C6F5)3 -, B(C6F5) 4 -) was carried out. It was shown that the nature of counterion affects mainly the ratio between the most stable β-agostic and nonagostic Cp2ZrEt+A- isomers, the thermodynamic and kinetic characteristics of ethylene addition to the Cp2ZrEt+A- ion pairs, and the chain propagation kinetics. The weaker the nucleophilicity of the counterion, the higher the fraction of the β-agostic isomer, the higher the exotermicity, and the lower the activation barrier to ethylene addition to Cp2ZrEt+A-, and the lower the activation energy of chain propagation. All possible pathways of the interaction between Cp2ZrEt+CH3B(C6F5)3 - and ethylene molecule were examined and compared. Among all species of composition Cp2ZrEt+CH3B(C6F5)3 -, the nonagostic isomer was found to be the most reactive toward ethylene.

The model reactions of ethylene polymerization and hydrogenolysis of linear alkanes (propane, n-butane, and n-pentane) on the silica-supported zirconium hydrides (BSiAO) 3 Zr IV H, (BSiAO) 2 Zr IV H 2 , and (BSiAO) 2 Zr III H were studied using the DFT approach. Catalytic processes under study were shown to occur involving different surface hydrides. The ethylene polymerization was found to proceed at comparable rates on the zirconium monohydrides, (BSiAO) 3 ZrH, and dihydrides, (BSiAO) 2 ZrH 2 . Cleavage of linear alkanes on the monohydrides (BSiAO) 3 ZrH is thermodynamically unfavorable; however, the dihydrides (BSiAO) 2 ZrH 2 can act as catalysts of the process under mild conditions. Hydrides of the trivalent zirconium, (BSiAO) 2 Zr III H, can also contribute to the hydrogenolysis reaction. A feature of all the systems studied is low regioselectivity of the corresponding processes.

Imidazoline-based nitroxide radicals are often used as spin probes for medium acidity and polarity in different systems. In this work, using the density functional theory (DFT) approach, we have studied how physico-chemical characteristics (geometry, atomic charges and electron spin density distribution) of pH-sensitive spin label 4-amino-2,2,5,5-tetramethyl-3-imidazoline-N-oxyl

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