Influence of Ligands on the Activity and Specificity of Soluble Transition Metal Catalysts

Abstract

The reaction of a covalently a-bonded Iigand (alkyl group, hydrogen)

Study on the Activity of Constrained Geometry Metallocenes

“…This result indicates that the activity of CGMs decreases with an increasing net charge on the central atom. This supports Olive's idea [35] that the stronger the electron donating ability of a ligand connected to the central metal atom of the catalyst is, the less the net charge on the metal atom, and the higher the activity of the polymerization are. It appears that the activity does not evenly respond to the amount of the net charge.…”

“…[35] It was pointed out that there are four factors which are most important in terms of affecting the catalyst performance: the transition metal-olefin interaction, the metal-alkyl bond stability, the influence of other ligands and substituents attached to the rings, and the steric effect. If the ligand is a good electron donor, it will reduce the positive charge on the metal and thus weaken the bonding between the metal and other ligands, particularly the unstable M-R bond, which will become more reactive.…”

“…If the ligand is a good electron donor, it will reduce the positive charge on the metal and thus weaken the bonding between the metal and other ligands, particularly the unstable M-R bond, which will become more reactive. [6,35] Concerning the non-bridged metallocenes, it was concluded that for the polymerization of not too larger a-olefins the ligands of the metallocene with electron donating groups enhance the catalytic activity, and that the steric effect plays only a minor role. [6] In the copolymerization of ethylene and octene with Ti-based CGMs, ethylene will be mainly incorporated in the resulting copolymer as it is a quite small molecule.…”

Addition of Lewis bases and acids. Effect on α-olefins polymerization with soluble metallocenes, 1 Ethylene

“…A polymerization mechanism, which avoids the ion pair separation, was proposed by Olivé et al [38] as early as 1970 assuming olefin coordination to a bimetallic Cp 2 TiCH 3 d+ Al(CH 3 ) 2 Cl 2 d-adduct. Hoffmann [39] confirmed this situation if a pentacoordinated Ti atom is assumed.…”

Catalytic activity correlation of Ni(II), Co(II) and Pd(II) complexes to metal atom net charge

“…For example, Olivé [10] concluded that there are four factors affecting the catalyst activity the most: the transition metal-olefin interaction, the metal-alkyl bond stability, the influence of other ligands and substituents attached to the rings, and the steric effect. By studying the influence of central metal atom charge and steric effect on catalytic activity of Zr-based metallocenes, Möhring and Coville [11] pointed out that the electronic effect can contribute as much as 80% of the change in polymerization activity.…”