Ligand effect on ethylene trimerisation with [NNN]-heteroscorpionate pyrazolyl Cr(III) catalysts

Abstract

Cr(III) complexes with [NNN]-heteroscorpionate pyrazolyl ligands of the type Pz'2CHX (Pz' = pyrazol-l-yl (Pz), or 3,5-dimethylpyrazol-1-yl (PzMe); X = N-containing heterocyclic ring or amine CH 2NR1R2; R1, R2 = H or alkyl) have been prepared. Upon activation with MAO, they are active for selective ethylene trimerisation to 1-hexene. The effects of the hetero-functional group and chelate ring size on the catalytic performance have been examined. The pre-catalysts with an N-heterocycle substituent show highest activity [32400-53000 g/(g Cr h-1)] and total C6 selectivities (>97.6%) as well as 1-hexene selectivity (>96.0%) among hexenes. The X-ray single-crystal crystallographic analysis of CrCl 3[PzMe 2CH2NCH2Ph] and CrCl3[PzMe 2CH2NCH2Fc] (Fc = ferrocenyl) shows a tridentate coordination on the fac-octahedral Cr(III) sphere with the Cr-N bond length dependent on the N-substituent. © 2009 The Royal Society of Chemistry.