The Mechanism of the Action of Organometallic Catalysts

Abstract

Kinetic investigations of the polyreaction of isoprene with organolithium compounds as initiators in n-heptane as solvent indicate the following sequence of reactions: I . formation of an adduct between a monomeric form of the organolithium compound and the isoprene and 2. reaction of this adduct with an associated form of the organolithium compound with insertion of the isoprene. The adduct formation is considered to be due to chemisorption, andproof of such chemisorption of a monomer (ethylene) is also demonstrated for a homogeneous Ziegler-type catalyst. All the reactions can be formulated in the form of cyclic structures with electron-deficient character. Postulation of such ring structures explains the surprising values obtained for the frequency factors and equilibrium constants.[Za] This nomenclature is in accordance with the proposals presented in Makromolekulare Chern. 38, 1 (1960). Angew. Chem. intertiat. Edit.[*] In this and the following equations, the point of extension of the molecule.Vol. 3 (I964) 1 No. 2 the asterisk designates

ESR studies on oxidation state of titanocene and zirconocene catalysts

“…According to the study of the homogeneous Ziegler-Natta catalyst system Cp 2 TiCl 2 /Al x RCl 3Ϫx , the catalyst activation process included a series of equilibrium alkylation and reduction steps. 6,15 Chien et al 16 proposed a similar process for metallocene systems activated by MAO. The temperature dependence of the equilibrium constants may explain the different patterns of these decay curves.…”