Tris(4-hydroxy-3,5-diisopropylbenzyl)amine as a new bridging ligand for novel trinuclear titanium complexes

Tris(4-hydroxy-3,5-diisopropylbenzyl)amine (LH3) was synthesized by the reaction of 2,6-diisopropylphenol and hexamethylenetetramine in the presence of p-toluenesulfonic acid or paraformaldehyde. Its solid state structure was determined by single crystal X-ray diffraction. Its fully deprotonated specie, (4-O-3,5-i-Pr2PhCH2)3N (L), was used to form novel trinuclear half-sandwich titanocene complexes, namely [(η5-C5Me5)TiCl2]3L (1) and [(η5-C5Me5)Ti(OMe)2]3L (2), which were then tested for the syndiospecific polymerization of styrene in the presence of methylaluminoxane (MAO) cocatalyst. Their catalytic properties were directly compared with those of trichloro(pentamethylcyclopentadienyl)titanium(IV) (3) and dichloro(2,6-diisopropylphenolato)(pentamethylcyclopentadienyl)titanium(IV) (4). 1/MAO and 2/MAO systems showed higher activities towards styrene polymerization than the mononuclear catalytic systems 3/MAO and 4/MAO, giving syndiotactic polystyrene of high molecular weight.

Trinuclear half-sandwich titanocene complexes bridged by fully deprotonated tris(4-hydroxy-3,5-diisopropylbenzyl)amine were prepared. In the presence of MAO cocatalyst, they showed enhanced activity towards the syndiospecific polymerization of styrene compared with monomeric half-sandwich complexes.Figure optionsDownload as PowerPoint slideHighlights
► Tris(4-hydroxy-3,5-diisopropylbenzyl)amine was used as a bridging ligand.
► Cp∗TiCl3 and Cp∗Ti(OMe)3 were used as metal precursors.
► Trinuclear half-sandwich titanocene complexes were prepared.
► Titanium complexes were used as catalysts for the synthesis of syndiotactic polystyrene.