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.