Influence of the Ligand Structure of Hafnocene Polymerization Catalysts: A Theoretical Study on Ethene Insertion and Chain Propagation

Abstract

The influence of the ligand structures of hafnocene polymerization catalysts on ethene insertion and chain propagation was systematically studied by quantum chemical methods. Altogether 54 hafnocenes were studied as a function of the ligand structures. Two consecutive ethene insertions and chain propagations were performed for the catalysts, giving rise to 15 intermediate structures along the reaction pathway. The behavior of the catalysts was analyzed as a function of ancillary ligands, ligand substituents, and bridging units. The differences along the reaction pathway are dominated by the changes in relative stabilities of the catalytic intermediate products. Large aromatic ancillary ligands and electron-donating ligand substituents strongly stabilize the catalyst cations. Steric effects introduced by the ligand framework mostly affect the feasibility of ethene π-coordination and the activation energy for chain propagation. The dominant effect of the relative stabilities of the catalyst intermediates sheds light on the catalytic performance of metallocenes, which may turn out to be useful in further catalyst development.

Catalyst Activation and Chain Transfer Agents in Metallocene Catalysts for Ethylene Polymerization: A Computational Investigation

“…Metallocenes are industrially relevant chemical catalysts for polyolefin production. In the past, numerous efforts [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] have been made to understand the behavior of group 4 metallocenes in olefin polymerization. Metallocenes require cocatalysts to make active catalyst species (ion pair formation), [20][21][22][23] and modification in and/or changing cocatalysts lead to significant changes in catalyst performance.…”

DFT Studies on Styrene Polymerization Catalyzed by Cationic Rare-Earth-Metal Complexes: Origin of Ligand-Dependent Activities

“…However, to the best of our knowledge, there are few systematic theoretical studies on the origin of ligand-induced catalytic performance for styrene polymerization. 22,33,34 The aim of the present contribution on styrene polymerization initiated by the five complexes 1−5 was to explore the molecular origin of their activity discrepancy. We employed the complexes 1, 2, and 3, which have the same side arm moiety, to explore the effect of electron donating of the aromatic ligands during styrene polymerization.…”

Data on electronic structures for the study of ligand effects on the zirconocene-mediated trimethylene carbonate polymerization

“…The effective core potential double-ζ basis set (LANL2DZ) [6] was used for Zr atom, while a double-ζ basis set (6–31G(d)) for all non-metal atoms (C, H, O, F, Si, and Ge). This DFT/mixed basis set method has been shown to reproduce the X-ray structure [7] and has been widely applied in the field of transition metal complexes [7] , [8] , [9] , [10] , [11] , [12] , [13] , [14] , [15] , [16] . Frequency calculations were performed on all optimized structures to confirm the nature of stationary points as minima or transition states.…”