Development of chromium compounds supported by chelating multi-aryl ligands for selective ethylene oligomerization

Abstract

1-octene and 1-hexene are valuable monomers in copolymn. with ethylene, for the prodn. of linear low-d. polyethylene. Cr-bisphosphinoamine (PNP) catalysts oligomerize ethylene to 1-octene and 1-hexene via a metallacyclic mechanism. Such systems require large excesses of aluminum-based activators, making it difficult to study the mechanism of catalyst initiation. This has been a significant hindrance to developing selective oligomerization catalysts for industrial applications. Chromium precursors displaying Cr-aryl or Cr-alkyl bonds have previously been employed in mechanistic studies. However, the isolation of similar Cr compds. supported by PNP ligands without pendant donors has proven challenging. In this work, the synthesis of a series of novel Cr(III) multi-aryl compds. is reported. Their reactivity with ethylene is investigated, with particular attention paid to the products of ethylene insertion into these Cr-C aryl bonds. These studies provide insight into the activation mechanism of these compds. toward oligomerization catalysis.