Chromium(iii) catalysed ethylene tetramerization promoted by bis(phosphino)amines with an N-functionalized pendant

Abstract

Several N-functionalized bis(phosphino)amine ligands with ether, thioether and pyridyl tethers [(R″)₂PN(R′)P(R″)₂ = PNP] (1a–1g) have been synthesized. They react with CrCl₃(THF)₃ in CH₂Cl₂ to give dinuclear chloro bridged Cr₂(µ-Cl)₂Cl₄(PNP)₂ (2) which converts to the corresponding mononuclear solvento complexes fac-CrCl₃(PNP)(NCR) (3). The structures of the ligand 1d with R′ = -(CH₂)₃SCH₃ and R″ = Ph, and the complexes with R = CH₃ (3a) and C₂H₅ (3b), R′ = -(CH₂)₃SCH₃ and R″ = Ph) have been established by single-crystal X-ray crystallography. All ligands are active towards ethylene tetramerization in the presence of Cr(III) and excess MAO at 80 °C in toluene. The ligand with thioether pendant Et₂PN(CH₂CH₂CH₂SCH₃)PEt₂ (1c) shows the highest selectivity (55% weight in liquid product distribution) towards 1-octene. Complexes 3a and 3b are active towards ethylene polymerization under thermal conditions.