Polymer-Free Ethylene Oligomerization Using a Pyridine-Based Pincer PNP-Type of Ligand
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Di- and trivalent chromium complexes of the pyridine-based ligand [2,6-(Ph2PCH2)2 C5H3N]CrCl3 (1) and {[2,6-(Ph2CH2)2C5H3N]CrCl2}.(THF) (2) and their aluminate aggregates [2,6-(Ph2CH2)2C5H3NCrCl(μ-Cl)AlClMe2] (3), {[(2,6-(Ph2CH2)2C5H3NCrCl(μ-Cl)AlClEt2]}. (toluene)0.5 (4), {2,6-(Ph2CH2)2C5H3NCrEt(μ-Cl)2AlEt2}{AlCl3Et} (5), {2,6-(PPh2CH2) C5H3N (PPh2CH)Al(i-Bu)2(μ-Cl)Cr(μ-Cl)2Al(i-Bu)2}.(toluene)1.5 (6), and {[2,6-(PPh2CH2)2C5H3 N]2Cr} {(μ-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.
