The mechanism of ethylene trimerization and tetramerization with a chromium–diphosphinoamine (Cr–PNP) catalyst system has been studied with combined experimental and theoretical methods. Of the total product output, 1-octene, cyclopentanes, n-alkanes, and higher (C₁₀₊) olefins are formed with a fractional (∼1.4) order response to ethylene concentration, whereas 1-hexene formation is approximately first-order in ethylene. Theoretical studies suggest a mechanism involving a cationic monometallic catalyst in Cr(I) and Cr(III) formal oxidation states. A key feature of the developed model is the occurrence of a double-coordination mechanism in which a bis(ethylene) chromacyclopentane intermediate is responsible for 1-octene formation as well as the other coproducts that have a greater than first-order response to ethylene. In contrast, 1-hexene is formed primarily from a mono(ethylene) chromacyclopentane intermediate. The selectivity of catalysis is governed by the competition between single- and double-coordination pathways. The mechanistic model developed displays excellent correlation with experimental observations and is able to fully explain the formation of all products generated with this catalyst.

Item Type:	Refereed Article
Keywords:	catalysis, olefin, ethylene, tetramerisation, trimerization, oligomerization, chromium, reaction mechanism
Research Division:	Chemical Sciences
Research Group:	Inorganic chemistry
Research Field:	Organometallic chemistry
Objective Division:	Manufacturing
Objective Group:	Industrial chemicals and related products
Objective Field:	Organic industrial chemicals (excl. resins, rubber and plastics)
UTAS Author:	Britovsek, GJP (Dr George Britovsek)
UTAS Author:	McGuinness, DS (Dr David McGuinness)
UTAS Author:	Wierenga, TS (Ms Tanita Wierenga)
ID Code:	105977
Year Published:	2015
Funding Support:	Australian Research Council (FT100100609)
Web of Science® Times Cited:	61
Deposited By:	Chemistry
Deposited On:	2016-01-21
Last Modified:	2017-11-02
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