TiCl2 based catalysts

Busico, V. CipuUo, R. Cutillo, R Talarico, G Razavi, A. Syndiotactic poly(propylene) from [Me2Si(3,6-di-fert-butyl-9-fluorenyl)(N-fert-butyl)]TiCl2-based catalysts Chain-end or enantiotopic-sites stereocontrol Macrc>/nc>/. Chem. Phys. 2003, 204, 1269-1274. 

Due to the presence of a high number of site epimerization errors, the microstructure of the syndiotactic polypropylene polymtas prepared with the catalyst system lO/MAO looks deceptively similar to the microstructure of the syndiotactic polypropylene polymers prepared via chain-end control mechanisms cf. [29] on syndiotactic polypropylene from [Me2Si(3,6- Bu2-9-lluoienyl) (N- Bu]TiCl2-based catalysts. 

The relatively weaker Lewis acidic titanium complexes require the use of a stronger nucleophile than allylsilanes, and tributylallyltin (6.81) is the most common aUylating agent employed when using titanium-based catalyst systems. In 1993, Umani-Ronchi and Keck published related results using BINOL/titanium derived catalysts. In the Umani-Ronchi system, BINOL is employed, in combination with TiCl2 (0 Pr)2 and shown to work weU with aliphatic... 

Extensive efforts have also been made to develop olefin polymerisation catalysts based on metallocenes with only one ligand of the cyclopentadienyl type. Ethylene-,dimethylsilylene- or tetramethyldisilylene-bridged mono(l-tetra -methylcyclopentadienyl), mono(l-indenyl) or mono(9-fluorenyl)-amidotita-nium complexes, such as dimethylsilylene(l-tetramethylcyclopentadienyl)(t-butyl)amidotitanium dichloride [Me2Si(Me4Cp)N(/-Bu)TiCl2] (Figure 3.10), have recently attracted both industrial and scientific interest as precursors for methylaluminoxane-activated catalysts, which polymerise ethylene and copolymerise ethylene with 1-butene, 1-hexene and 1-octene [30,105,148-152]. 

The single-crystal X-ray molecular structure of the complex p-(Me2Si) (3,6di- BuFlu)( BuN)TiCl2 10, is depicted in Fig. 17. It shows a striking similarity to crystal structure of complex 9 with respect to its overall symmetry, despite the exchange of one of the aromatic rings, the cyclopentadienyl, in the molecule and its replacement with an amido group. Complex 10 exemplifies one of the rare examples of a titanium-based syndiotactic-specific metallocene catalyst systems. 

Figure 5.1 shows typical NMR spectra (methylene and methine regions) of the copolymers (THF-soluble fraction) prepared by [Me2Si(C5Mc4)(N Bu)] TiCL, (l,2,3-Me3C5H2)TiCl2(0-2,6- Pr2C6H3) catalysts in the presence of a MAO cocatalyst [13b]. Table 5.1 also summarizes the assignments of resonances for poly(ethylene-co-styrene) in the NMR spectrum based on the distortionless enhancement by polarization transfer (DEPT) spectrum and data reported previously [12-18], and monomer sequences in the copolymer are shown in Scheme 5.1. As described below, the naicrostructures for the resultant poly(ethylene-co-styrene)s depend on the catalysts used. As shown in Figure 5.2, the glass transition temperature (Tg) as measured by DSC increased with an increase in the styrene content (-8.1 to 58.3 °C). This is because, as...

Figure 5.4 Plots of [Tpp]/[Ttotai] ratio versus styrene in the copolymer determined by NMR spectra (in CDCI3 at 60 °C, methylene and methine regions, THF-soluble fraction). [Tpp]/[Ttotai] value (in percent) based on Bernoullian mode ( ) could be calculated as (styrene content) x 100. Catalyst Cp TiCl2(0-2,6-Tr2C6H3) [Cp = 1,2,3-Me3C5H2 (6, ), l,3-Me2C5H3 (7, O), tert-BuCsH (8, )] [Me2Si(C5Me4)(N Bu)]TiCl2 (la,4) [13b].

A majority of the reported enantioselective Lewis acid-catalyzed allylation processes employ complexes with chiral ligands based on the 1,1-binaphthyl skeleton. In 1993, Umani-Ronchi and Tagliavini [122] and Keck [123] independently reported enantioselective allylation of aldehydes with BINOL-Ti(IV) catalysts 195 (from BINOL/TiCl2(Oi-Pr)2) and 196 (from BINOL/ Ti(Oi-Pr)4), respectively (Equation 13). Excellent enantioselectivity was observed with both catalyst systems ( 90% ee). 

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