Synthesis, Characterization and Ethylene Oligomerization Studies of Chromium Complexes Bearing Imino-Furfural Ligands

Ana H D P S Ulbrich,Paolo R Livotto,Jorge L S Milani,Jean-François Carpentier,Osvaldo L Casagrande Jr

doi:10.5935/0103-5053.20140274

Abstract

A series of chromium(III) complexes bearing imino-furfural ligands (Cr1-Cr4) were synthesized and characterized by high-resolution mass spectrometry (HRMS). All chromium precatalysts, activated with methylaluminoxane (MAO), exhibited moderate to high activities for ethylene oligomerization [turnover frequency (TOF) = 11,008-23,200 mol(ethylene) mol(Cr)-1 h-1)] producing oligomers in the range C4-C12+ with good selectivity for α-olefins. The in situ chromium precatalysts formed by mixing imino-furfural ligand L1 with [CrCl3(THF)3] or [Cr(acac)3] showed low activities, producing oligomers together with varying amounts of polyethylene. The use of different chromium sources and cocatalysts influences the activity as well as the selectivities toward α-olefin production, which suggests that different active species are formed.

Highlights

A considerable amount of research effort has been dedicated both recently and in the past to nonselective ethylene oligomerization with the aim of improving the comprehension of this industrially relevant catalytic process.[1,2,3,4,5,6,7] The mixtures of linear alpha olefins (LAO) produced by this process are valuable commodity chemicals for a range of industrial and household applications depending on their molar mass distribution (detergents, surfactants, cosmetics, synthetic lubricants, etc.).[8,9,10] A nonselective oligomerization is closely reminiscent of a polymerization randomly truncated atAmong the transition-metal-based catalysts, chromium catalysts occupy a unique position, since they provide both selective (commercially viable tri-, and tetramerization catalytic systems)[12,13,14] and nonselective ethylene oligomerization
We report a series of chromium complexes supported by imino-furfural ligands and investigated their catalytic behavior for ethylene oligomerization
These proligands were characterized by Infrared spectra (IR), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, and by an X-ray diffraction study for proligands L1 and L2

Summary

Introduction

A considerable amount of research effort has been dedicated both recently and in the past to nonselective ethylene oligomerization with the aim of improving the comprehension of this industrially relevant catalytic process.[1,2,3,4,5,6,7] The mixtures of linear alpha olefins (LAO) produced by this process are valuable commodity chemicals for a range of industrial and household applications depending on their molar mass distribution (detergents, surfactants, cosmetics, synthetic lubricants, etc.).[8,9,10] A nonselective oligomerization is closely reminiscent of a polymerization randomly truncated atAmong the transition-metal-based catalysts, chromium catalysts occupy a unique position, since they provide both selective (commercially viable tri-, and tetramerization catalytic systems)[12,13,14] and nonselective ethylene oligomerization. Gambarotta and co-workers[51] reported chromium complexes bearing a series of pyridinephosphine ligands and their catalytic behavior in ethylene oligomerization. It has been demonstrated that minor differences in the ligand structure can result in remarkable changes in catalytic activity and in selectivity toward α-olefins vs polyethylene and distribution of oligomeric products.

Results

Conclusion