Studies on metal charge density and band gap characteristics produced by the (nBuCp)2ZrCl2 compound and its reaction mechanism

Abstract

The charge density of the central metal atoms and band gap of the compounds were investigated by the Dmol³ software package in Density functional theory (DFT). The band gap of the (ⁿBuCp)₂ZrCl₂ compound was the smallest among the listed metallocene compounds, however, its reactivity reached 11.88 kg (mol h)⁻¹ × 10⁴ at the time of slurry polymerization, which was the most active among the catalysts enumerated by the compounds and also verified the Frontier orbital theory. The polymerization of the (ⁿBuCp)₂ZrCl₂ compound with olefins proceeded according to the α-agostic mechanism of the ground state and the transition state. Hydrogen molecules were released during the transition state and led to (ⁿBuCp)₂Zr(Cyclopropyl)⁺ as the final product. The authenticity of the presence of hydrogen in the olefin polymerization gas was confirmed. The aggregation of hydrogen led to a decrease in the activity of the metallocene catalyst, and that was why the energy barrier caused by the first polymerization was much lower than the second polymerization. The present work would provide valuable insight into the characteristics of metallocene catalysts with high activity and low hydrogen evolution.