Titanium Ester Enolate Complex Supported by a Tetradentate Bis(phenolato) Ligand: Synthesis, Structure, and Activity in Methacrylate Polymerization

Reaction of the titanium dichloro complex containing a [OSSO]-type bis(phenolate) ligand (edtbp)TiCl 2 ( 1 ) (edtbpH 2 = (HOC 6 H 2 - t Bu 2 -4,6) 2 (SCH 2 CH 2 S)) with 2 equiv of AlMe 3 produces the methylchloro complex (edtbp)TiMeCl ( 2 ) in 77% yield, alternatively prepared from comproportionation of 1 and the dimethyl complex (edtbp)TiMe 2 ( 3 ). The titanium ester enolate complex (edtbp)TiMe{O( i PrO)C=CMe 2 } ( 4 ) was synthesized by reaction of 2 with lithium isopropylisobutyrate, LiO( i PrO)C=CMe 2, in a 1:1 molar ratio. This complex reacted with alcohols ROH (R = i Pr, Ph, Ph 3 C) to give alkoxy complexes (edtbp)TiMe(OR) ( 6 − 8 ) and with acetone under C−C coupling to afford an aldolate complex (edtbp)TiMe(OCMe 2 CMe 2 CO 2 i Pr) ( 9 ). Methyl abstraction from the neutral complexes 4, 7, and 9 using with B(C 6 F 5 ) 3 gave the corresponding cationic species [(edtbp)Ti(OR)(THF) n ][MeB(C 6 F 5 ) 3 ]. All complexes have been characterized by multinuclear NMR spectroscopy and elemental analysis. Single-crystal X-ray diffraction studies were performed for complexes 2, 4, and 9 . Cationic titanium enolate species initiate the polymerization of methyl methacrylate (MMA) at room temperature, producing syndiotactic-enriched poly(methyl methacrylates) (PMMAs). In the presence of the neutral enolate complex, MMA polymerization proceeds in a living fashion. The neutral titanium enolate complex 4 was found to be moderately active in n -butyl acrylate ( n -BA) polymerization.