Oxygen-Stabilized Organoaluminum Compounds as Highly Active Cocatalysts for Ziegler−Natta Olefin Polymerization

The hydroalumination of the allyl ethers CH 2 CHCH 2 OR with i Bu 2 AlH yields the (3-alkoxypropyl)diisobutylaluminum complexes i Bu 2 Al(CH 2 ) 3 OR (R = Me ( 1 ), Et ( 2 ), Bu ( 3 )). Et 2 AlCl and i Bu 2 AlCl react with (2-(methoxymethyl)phenyl)lithium and (2-methoxybenzyl)magnesium chloride, yielding (2-(methoxymethyl)phenyl)diethylaluminum ( 4 ), (2-(methoxymethyl)phenyl)diisobutylaluminum ( 5 ), and (2-methoxybenzyl)diisobutylaluminum ( 7 ), respectively. The reaction of i Bu 2 AlCl with (2-methoxyphenyl)lithium affords the dimeric bis((2-methoxyphenyl)diisobutylaluminum) ( 6 ). Et 2 AlCl and (8-ethoxynaphthyl)lithium form (8-ethoxynaphthyl)diethylaluminum ( 10 ) along with a few crystals of bis(8-ethoxynaphthyl)aluminum chloride ( 13 ). AlCl 3 reacts with 2 equiv of (2-methoxybenzyl)magnesium chloride, yielding bis(2-methoxybenzyl)aluminum chloride ( 9 ). Ligand redistribution followed by metathesis was observed for the reactions of Me 2 AlCl and Et 2 AlCl with (2-methoxybenzyl)magnesium and (8-methoxynaphthyl)lithium, yielding bis(2-methoxybenzyl)methylaluminum ( 8 ), bis(8-methoxynaphthyl)methylaluminum ( 11 ), and bis(8-methoxynaphthyl)ethylaluminum ( 12 ), respectively. The new compounds have been characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. The solid-state structures of 6, 8, 9, and 11 − 13 were determined by single-crystal X-ray diffraction. The new aluminum alkyls are very active cocatalysts in the TiCl 4 -catalyzed ethylene polymerization. 7 and 10 cause a higher productivity compared to the common cocatalyst Al 2 Et 6 . The activity depends strongly on the structure of the oxygen-stabilized aluminum alkyls and is also influenced by the Al/Ti ratio.