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

Cr(III) complexes with [NNN]-heteroscorpionate pyrazolyl ligands of the type Pz'(2)CHX (Pz' = pyrazol-l-yl (Pz), or 3,5-dimethylpyrazol-1-yl (Pz(Me)); X = N-containing heterocyclic ring or amine CH(2)NR(1)R(2); R(1), R(2) = 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 C(6) selectivities (>97.6%) as well as 1-hexene selectivity (>96.0%) among hexenes. The X-ray single-crystal crystallographic analysis of CrCl(3)[Pz(Me)(2)CH(2)NCH(2)Ph] and CrCl(3)[Pz(Me)(2)CH(2)NCH(2)Fc] (Fc = ferrocenyl) shows a tridentate coordination on the fac-octahedral Cr(III) sphere with the Cr-N bond length dependent on the N-substituent.