Rationalizing the catalytic performance of Cr(III) complexes stabilized with alkylphosphanyl PNP ligands for selective ethylene tri-/tetramerization: a DFT study

The effect of alkylphosphanyl substitutions on the PNP scaffold toward ethylene tri-/tetramerization has been explained using density functional theory (DFT). Our calculations show that different alkylphosphanyl substitutions considerably influence the catalytic environment and thus affect the catalytic performance of alkylphosphanyl PNP/Cr system. Comparing the rate-determining steps (RDSs) of all precatalysts 1–9, we have rationalized the product selectivity. The reactivity of precatalysts 5–6 {Ph₂PN(cyclopentyl)PR₂, 5, R = Et; 6, R = ⁱPr} based systems was rationalized by frontier orbital theory. In addition, we further calculated the cyclic by-product paths of precatalysts 5–6 based systems, and the results show that the precatalyst 6 based system offers a high energy barrier toward the formation of cyclic C₆ by-products and therefore produce a small amount of these products.