Ni(II) complexes bearing pyrrolide-imine ligands with pendant N-, O- and S-donor groups: synthesis, structural characterization and use in ethylene oligomerization

International audienceA series of new Ni(II) complexes of general formula \L\NiCl [Ni1, L = 2-(C4H3N-2'-CH= N)C2H4NHPh; Ni2, L = 5-tert-butyl-2-(C4H2N-2'-CH=N)C2H4NHPh; Ni3, L = 2-(C4H3N-2'- CH=N)C2H4OPh; Ni4, L = 2-(C4H3N-2'-CH=N)C6H4- 2'-OPh; Ni5, L = 2-(C4H3N-2'-CH=N)C6H4-2'-SPh; Ni6, L = 2-(C4H3N-2'-CH=N)CH2C6H4-2'-OMe] were prepared and fully characterized. All nickel precatalysts, activated with methylaluminoxane (MAO), exhibited moderate to good activities for ethylene oligomerization [TOF = 6.1-71.3 x 10(3) mol (C2H4) (mol (Ni)(-1) h(-1))] and producing high selectivities for 1-butene (68.3-94.0 wt%). The catalytic performance was substantially affected by the ligand environment regarding the pendant oxygen- and sulfur-donor groups, and the substituents on the pyrrolide group. Activation of nickel precatalyst Ni3 with ethylaluminum sesquichloride (Et3Al2Cl3, EASC) instead of MAO produced a significantly more productive catalyst system than Ni2/MAO (TOF = 153 700 vs. 43 500 mol (C2H4) (mol (Ni)(-1) h(-1))); however, the 1- butene selectivity was drastically reduced, attaining only 53 wt% with a concomitant production of larger amounts of internal butenes (38 wt%). Under optimized conditions ([Ni] = 10 mu mol, 30 degrees C, oligomerization time = 20 min, 20 bar ethylene, [Al]/[Ni] = 250), precatalyst Ni3 led to a TOF = 55 900 mol (C2H4) (mol (Ni)(-1) h(-1)) and 82.8 wt% selectivity for 1- buten