Ethylene Tri-/Tetramerization Catalysts Supported by Phenylene-Bridged Mixed Alkyl/Aryl Diphosphine Ligands

Abstract

Cr­(III) complexes supported by phenylene-bridged diphosphine ligands with P-alkyl substitution were prepared and evaluated in ethylene tri-/tetramerization. The ligand steric and electronic properties have significantly influenced the catalytic activity. The Cr complex 1 based on a bulky PCy2 phosphine ligand L 1 having a stronger σ-donor ability exhibited the highest activity, which is more reactive than its PPh2 counterpart 8. The selectivity toward ethylene tri-/tetramerization is mainly determined by the steric property of ligands. Reducing the ligand steric bulk switched the selectivity from predominant trimerization into mixed tri-/tetramerization. 1 achieved a high 1-hexene selectivity of 82.5 wt % with a 1-octene selectivity of 9.7 wt %, while 4 based on L4 bearing a less bulky PPhCy group gave a considerable 1-octene selectivity of 43.3 wt % with a very high activity of 1874 kg·gCr –1·h–1. 1 also exhibited a high activity even at a relatively low temperature of 40 °C, while both 4 and 5 based on a PPh­(alkyl) diphosphine ligand gave poor activities at 40 °C. More importantly, these Cr complexes showed a very low PE selectivity of ≤0.1 wt %.

Ethylene Oligomerization Catalyzed by Different Homogeneous or Heterogeneous Catalysts

“…With the increasing research on the ethylene trimerization reaction catalyzed by Cr catalysts, researchers have found many types of ligands, such as the PNP [163][164][165], SNS [166][167][168], NNN [169], PNS [170,171], and PN [172] types.…”

Chromium Ethylene Tri-/Tetramerization Catalysts Supported by Iminophosphine Ligands

“…The past two decades have seen an increasing demand for linear α-olefins (LAOs) mainly due to the extensive use of 1-hexene and 1-octene as comonomers with ethylene for the production of linear low-density polyethylene (LLDPE). − Generally, LAOs are produced with a broad range of olefins from C 4 to C 20 based on the Schulz–Flory distributions manufactured by Shell, Ineos, SABIC, and Chevron–Phillips . In order to meet market demand growth by avoiding the production of less valuable or lower-volume LAOs, selective ethylene oligomerization catalysts are highly desirable and have been developed for use on an industrial scale. − Considerable success has been achieved by employing chromium-based catalysts in developing highly active ethylene trimerization systems for manufacturing 1-hexene, − including the Chevron–Phillips’ pyrrole, , the BP diphosphinoamine (PNP), and the Sasol mixed heteroatomic systems …”