Oligomerization of ethylene using tridentate nickel catalysts bearing ether-pyrazol ligands with pendant O- and S-donor groups
作者:Ana H.D.P.S. Ulbrich、Adão L. Bergamo、Osvaldo de L. Casagrande
DOI:10.1016/j.catcom.2011.09.006
日期:2011.11
A series of tridentate pyrazol ligands with pendant O- and S-donor groups (L1-L5) and their corresponding nickel (II) chloride complexes (1-5) were synthesized and fully characterized. All nickel precatalysts, activated with methylaluminoxane (MAO), exhibited high activities for ethylene oligomerization [TOF = 17.1-75.8 x 10(3) mol (ethylene)(mol(Ni))(-1) h(-1))] with good selectivities for 1-butene produced (62.9 - 81.3%). The catalytic performance was substantially affected by the ligand environment regarding the pendant oxygen- and sulfur-donor groups, and the substituents on the phenol group. Activation of nickel precatalyst 1 with ethylaluminum sesquichloride (Et3Al2Cl3. EASC) instead of MAO produced a significantly better catalyst system than 1/MAO (TOF = 227,000 vs. 30,900 (mol C2H4).(mol Ni-1 h(-1)); however, the 1-butene selectivity was drastically reduced, attaining only 28% with a concomitant production of larger amounts of internal butenes (51.4%) and hexones (28.2%). Under optimized conditions ([Ni] = 10 mu mol, 30 degrees C, oligomerization time = 20 min, 40 bar ethylene, [Al]/[Ni] = 250), precatalyst 1 led to TOF = 75,800 (mol C2H4).(mol Ni-1 h(-1)) and 76.1% selectivity for 1-butene. (C) 2011 Elsevier B.V. All rights reserved.