Catalysis

Computational Assessment and Understanding of C6 Product Selectivity for Chromium Phosphinoamidine Catalyzed Ethylene Trimerization

Authors

Abstract

One approach to selectively generate 1-hexene is through ethylene trimerization using highly active Cr N-phosphinoamidine catalysts ((P,N)Cr). Depending on the ligand, (P,N)Cr catalysts can either generate nearly pure 1-hexene or form 1-hexene with significant mixtures of other C6 mass products, for example methylenecyclopentane. Here we report DFT transition state modeling examining 1-hexene catalysis pathways as well as pathways that lead to alternative C6 mass products. This provided qualitative and semi-quantitative modeling of the experimental 1-hexene purity values for several (P,N)Cr catalysts. Consistent with previous computational studies, the key 1-hexene purity-determining transition states were determined to be β-hydrogen transfer structures from the metallacycloheptane intermediate. The origin of selectivity for these (P,N)Cr catalysts can be attributed to steric effects in the transition-state structure with coordinated ethylene that leads to C6 impurities.

Content

Thumbnail image of Cr C6 purity msc-20211209.pdf

Supplementary material

Thumbnail image of Cr C6 purity SI-20211209.pdf
Supporting Information
Computational details, additional mechanisms, pressure and temperature corrections, and entropy-scaled energies.