Abstract
The synthesis and characterization of a novel trinuclear diphosphinoamine ligand 2 are reported. The ligand combined with Cr(III), activated with methylaluminoxane, lead to highly active and long-lifetime catalytic systems for the tetramerization of ethylene to form 1-octene. The effects of reaction temperature, reaction pressure, molar ratio of Al/Cr and bis(diphenylphosphino)amine/Cr on the catalytic activity and product selectivity were studied. Compared with its mononuclear analogue 1, ligand 2 showed a higher catalytic activity and longer lifetime for ethylene tetramerization in the presence of methylaluminoxane as cocatalyst. High molecular weight polyethylene was generated as a by-product with extremely broad molecular weight distributions.
Highlights
The synthesis and characterization of a novel trinuclear diphosphinoamine ligand 2 are reported
Since the first report of ethylene tetramerization to form 1-octene using Cr-bis(diphenylphosphino)amine (PNP) catalysts [9], numerous studies have investigated the relationship between ligand structure and catalytic properties
These include investigations into various single-site PNP ligands, wherein alkyl [10,11,12], cycloalkyl [13], ether [14], thioether, pyridyl tethers [15] and aryl [16,17] substituents attached to the N or P atom of the ligand backbone were synthesized and evaluated
Summary
All manipulations of water and/or moisture sensitive compounds were performed by means of standard high-vacuum Schlenk techniques under a N2 atmosphere. Toluene was refluxed and distilled from sodium/benzophenone under dry nitrogen. The ligand 1 was prepared according to a published procedure [9]. Cis,cis-1,3,5-cyclohexanetricarboxylic acid, diphenylphosphoryl azide(DPPA) and Cr(acac) were purchased from Sigma-Aldrich(Pennsylvania, USA) and used as received. Polymerization grade ethylene was obtained from Daqing Petro-Chemical Ltd. Methylaluminoxane (MAO) solution (1.4 mol/L) in toluene was purchased from Albemarle Corp. Cyclohexane, toluene and ethanol were dehydrated and de-. Jiang T, et al Chin Sci Bull May (2012) Vol.. All other chemicals were obtained commercially and used as received
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