The Origin of Oligomer Formation in Cr/PNP-Catalyzed Ethylene Tetramerization

The concomitant formation of oligomeric byproducts in ethylene tetramerization remains a major concern. Yet, the presence of higher oligomers (≥C 10 ) can provide mechanistic insights to improve the coselectivity of 1-C 6 /1-C 8 . Here, experimental work combined with density functional theory (DFT) calculations on the classical Cr/PNP system is used to explore the origin of these oligomers. A quantitative link between the Schulz−Flory coefficient ( K value) and oligomer formation is established, which allows for the evaluation of different byproduct pathways. Time-resolved analyses show that these oligomers are primary products arising synchronously from parallel competitive pathways within the catalytic cycle. DFT results further suggest that at least part of the ≥C 10 fraction arises from a Schulz−Flory distribution accessed during a catalytic off-cycle. We propose that these oligomers originate from chain propagation by a presumed ethyl-cyclopentyl Cr species, indicating that oligomer formation is an inherent part of ethylene tetramerization and thus challenging to eliminate.