Polymer-Free Ethylene Oligomerization Using a Pyridine-Based Pincer PNP-Type of Ligand

Di- and trivalent chromium complexes of the pyridine-based ligand [2,6-(Ph2PCH2)(2) C5H3N]CrCl3 (1) and {[2,6-(Ph2CH2)(2)C5H3N]CrCl2}center dot(THF) (2) and their aluminate aggregates [2,6-(Ph2CH2)(2)C5H3NCrCl(mu-Cl)AlClMe2] (3), {[(2,6-(Ph2CH2)(2)C5H3NCrCl(mu-Cl)AlClEt2]}center dot(toluene)(0.5) (4), {2,6-(Ph2CH2)(2)C5H3NCrEt(mu-Cl)(2)AlEt2}{AlCl3Et} (5), {2,6-(PPh2CH2) C5H3N (PPh2CH)Al(i-Bu)(2)(mu-Cl)Cr(mu-Cl)(2)Al(i-Bu)(2)}center dot(toluene)(1.5) (6), and {[2,6-(PPh2CH2)(2)C5H3 N](2)Cr} {(mu-Cl)[Al(i-Bu)(3)](2)} (7) were prepared, isolated, and their activities toward ethylene oligomerization tested. While complexes 3, 5, and 6 were directly accessible by reacting catalyst precursor 1 with Me3Al, DEAC, and TIBA, respectively, complexes 4 and 7 were prepared using catalyst precursor 2 with DEAC and TIBA, respectively. All these complexes, with the exception of 7, showed good activities for a polymer-free ethylene oligomerization. Complex 7 contains cationic chromium in its monovalent state and its encapsulation in an octahedral ligand field as defined by two ligands is probably responsible for its failure as a catalyst.