The effect of substituents on dimer formation and cation–anion interaction in silicon bridged bisindenyl zirconocene propylene polymerization catalysts

Synthesis, Characterization, Interionic Structure, and Self-Aggregation Tendency of Zirconaaziridinium Salts Bearing Long Alkyl Chains

“…Consequently, the enhanced dimension of the cation in the active species may lead to an increase of ion pair separation and self-aggregation tendency. For example, an increase of the dipole moment as a function of the isotactic propylene chain length, in a silicon-bridged zirconocene ion pair, was predicted by Klesing and Bettonville through DFT (density functional theory) calculations . An additional layer of complexity is faced when solvents with relative permittivity (ε r ) lower than that of benzene are taken into account.…”

Self‐Aggregation Tendency of Zirconocenium Ion Pairs Which Model Polymer‐Chain‐Carrying Species in Aromatic and Aliphatic Solvents with Low Polarity

“…An increase of the dipole moment as a function of the isotactic propylene chain length in a silicon-bridged zirconocene ion pairs was predicted by Klesing and Bettonville through DFT calculations. [10] With the aim of obtaining information about the position of the counterion during the growth of the polymer chain and the tendency of ion pairs bearing a polymer chain to self-aggregate, we decided to synthesize model zirconocenium ion pairs with alkylic chains of variable length and investigate them through advanced NMR techniques. The presence of long chains made zirconocenium ion pairs soluble in aliphatic solvents with relative permittivity (e r ) values lower than benzene.…”

DFT study of formation and properties of dinuclear zirconocene cations: Effects of ligand structure, solvent, and metal on the dimerization process

“…Substituent effects on the feasibility of the dimer formation can be predicted with the aid of DFT calculations, as was pointed out by Klesing et al [23]. However, that work focused on a limited number of substituents and did not study ancillary ligand and/or bridge effects on the process.…”

“…Although the dimer structures have been measured experimentally, detailed theoretical investigations on the dimer formation occurring in the metallocene/cocatalyst polymerization are rather limited, especially how ligand structure influences this process. Klesing et al was the first to point out that it is possible to predict the substituent pattern that favors complexation of monomers or reduce coordination of any adduct to cationic sites [23]. In particular, they showed that appropriate substituents in 4-and 6-position can minimize the formation of the dimer of a silicon-bridged bisindenyl zirconocene.…”