Ethylene tri- and tetramerization: a steric parameter selectivity switch from X-ray crystallography and computational analysis.

A steric parameter (θN-sub) is introduced to describe the steric bulk at the nitrogen atom on a range of PNP ligands used in ethylene tri- and tetramerization. This parameter was calculated for the free ligands and different metal complexes thereof and compared to catalytic data. A specific tendency is observed for the value of θN-sub and 1-hexene selectivity, and a slight increase in 1-octene selectivity is found with increased bulkiness of the substituents on the nitrogen atom.

Mechanistic investigations of the ethylene tetramerisation reaction.

The unprecedented selective tetramerisation of ethylene to 1-octene was recently reported. In the present study various mechanistic aspects of this novel transformation were investigated. The unusually high 1-octene selectivity in chromium-catalyzed ethylene tetramerisation reactions is caused by the unique extended metallacyclic mechanism in operation.

New iron bis(imino)pyridyl complexes containing dendritic wedges for alkene oligomerisation.

The synthesis, characterisation and catalytic behaviour of new iron bis(imino)pyridyl complexes containing dendritic wedges, as well as the synthesis of bis(para-hydroxyphenylimino)pyridines is described. The hydroxyl functionality of the bis(para-hydroxyphenylimino)pyridines was used to attach dendritic wedges of the carbosilane type as well as the benzylphenyl ether type. After attachment of the dendritic wedges, complexation of these ligands to iron(II) chloride was achieved.

Ethylene trimerisation and tetramerisation catalysts with polar-substituted diphosphinoamine ligands.

Chromium-based catalyst systems with polar-substituted diphosphinoamine ligands are selective for either trimerisation or tetramerisation of ethylene, depending on the position of the polar groups on the aryl rings.

Highly selective chromium-based ethylene trimerisation catalysts with bulky diphosphinoamine ligands.

In situ prepared chromium catalysts containing bulky diphosphinoamine (PNP) ligands, upon activation with MAO, are extremely efficient catalysts for the trimerisation of ethylene to 1-hexene.