Stereospecific propylene polymerization using half-sandwich metallocene/MAO systems: a mechanistic insight

Substituent Effects of Phenyl Group on Silylene Bridge in Stereospecific Polymerization of Propylene with C₁-Symmetric Ansa-Silylene(fluorenyl)(amido) Dimethyl Titanium Complexes

A C₁-symmetric (methylphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (1) and (diphenyl)silylene-bridged (fluorenyl)(naphthylamido) titanium complex (2) were synthesized and characterized by ¹H NMR, element analysis, and X-ray crystal analysis. The coordination mode of the fluorenyl ligand to the titanium metal is an η³ manner in each complex. These complexes were applied for propylene polymerization using dried modified methyaluminoxane (dMMAO) as a cocatalyst under different propylene pressures in a semi batch-type method. The catalytic activity was strongly dependent on the structure of the complex and the propylene pressure, where complex 1 exhibited the highest activity (600 kg mol-1·h-1) under a propylene pressure of 8.0 atm to produce high molecular weight polypropylene. The polypropylenes obtained were syndiotactic-rich with an rr value of 0.50, indicating that the silylene bridge was not efficient for the isospecificity of a constrained geometry catalyst (CGC). The mechanical properties of the resulting polymers depended on their microstructure.

Living Polymerization of Propylene with ansa-Dimethylsilylene(fluorenyl)(cumylamido) Titanium Complexes

A series of ansa-silylene(fluorenyl)(amido) titanium complexes (1a–1c, 2a, and 2b) bearing various substituents on the amido and fluorenyl ligands are synthesized and characterized by elemental analysis, ¹H NMR, and single crystal X-ray analysis. The coordination mode of the fluorenyl ligand to the titanium metal is η³ manner in each complex. The propylene polymerization is conducted with these complexes at 0 and 25 °C in a semi batch-type method, respectively. The catalytic activity of 1a–1c bearing cumyl-amido ligand is much higher than that of 2a and 2b bearing naphthyl group in amido ligand. High molecular weight polypropylenes are obtained with narrow molecular weight distribution, suggesting a living nature of these catalytic systems at 0 °C. The polymers produced are statistically atactic, regardless of the structure of the complex and the polymerization temperature.

Homopolymerization of ethylene, 1-hexene, styrene and copolymerization of styrene with 1,3-cyclohexadiene using (η⁵-tetramethylcyclopentadienyl)dimethylsilyl(N-Ar')amido-TiCl₂/MAO (Ar'=6-(2-(diethylboryl)phenyl)pyrid-2-yl, biphen-3-yl)

The propensity of a half-sandwich (η⁵-tetramethylcyclopentadienyl) dimethylsilylamido Ti(IV)-based catalyst bearing an auxiliary diethylboryl-protected pyridyl moiety (Ti-8), activated by methylaluminoxane (MAO) to homopolymerize α-olefins such as ethylene, 1-hexene and styrene as well as to copolymerize styrene with 1,3-cyclo-hexadiene is described. The reactivity of Ti-8 was investigated in comparison to a 6-(2-(diethylboryl)phenyl)pyrid-2-yl-free analogue (Ti-3).