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(-Cl)2Cl4(PNP)2 (2) which converts to the corresponding mononuclear solvento complexes fac-CrCl 3(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(CH 2CH2CH2SCH3)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. © The Royal Society of Chemistry.