Wellington E. Walker

A soluble chromium-based catalyst for ethylene trimerization and polymerization

Abstract The catalyst formed by the interaction of chromium (III) 2-ethylhexanoate or related compounds with partially hydrolyzed triisobutyl aluminum, in paraffinic solvents, polymerizes ethylene to linear polyethylene at ethylene turnover numbers of the order of 30 sec−1 atm−1. The polyethylene appears to be formed by what has come to be considered a conventional Ziegler olefin polymerization mechanism [Novaro et al., J. Catal. 41, 91 (1976)]. Hexene-1 can also be produced, at rates comparable to those of polyethylene formation. The mechanism of hexene-1 formation differs from that of polyethylene formation, as shown by differences in the pressure and temperature dependence of the two rates and by the inhibition of hexene-1 formation, but not polyethylene formation, by small quantities of dienes. Some mechanistic implications of the hexene-1 formation kinetics are discussed. Information relating to the structure of poly(isobutyl aluminum oxide) is also presented. Some structures for the catalytically active centers are proposed, and reactions by which such structures could be produced are suggested.

Rhodium Carbonyl Clusters with Encapsulated Main-Group Atom(s). Structures and Reactivity

Homogeneous catalysis by transition metal clusters is attracting increasing attention, (1,3) as well as the modeling of some heterogeneous catalysts by these complexes. (4) Cluster catalysis in homogeneous systems has been reported for some technologically relevant reactions such as hydr formylat ion, (5) water-shift, (6) oxidation (7) and Fisher-Tropsch. (8) In addition, rhodium carbonyl clusters are present during the catalytic synthesis of alcohols from carbon monoxide and hydrogen.(9)