Density functional theory study of C₆-selective Cr-PNP catalysts for ethylene trimerization

Industrially important linear alpha-olefins are commonly produced by oligomerization of ethylene or by Fischer-Tropsch synthesis followed by purification. Biggest challenge for the linear alpha olefin industry is a Schultz-Flory distribution of products made by most of the processes. The selective oligomerization of ethylene to 1-hexene is an important cost-effective technology. A highly effective catalyst system based on Cr-PNP type catalysts has been developed. A mechanism involving metallacycle intermediates seems to be working for the reaction. Because of the unpaired electrons in the valence shell of the chromium, it is difficult to examine the characteristics of the Cr catalysts using usual NMR method. The need for open shell calculation also impeded theoreticians from studying the reactions computationally. In the current presentation DFT methods have been employed to explain the highly selective character of the reaction toward 1-hexene catalyzed by Cr-PNP compexes.