Dimethylanilinium tetrakis

On the other hand, instead of an alumoxane compound as activator, N,N-dimethylanilinium tetrakis-perfluorophenylboron has been used with a metallocene catalysts (29). 

It is generally adopted that the catalytically active species in the metallocene-catalysed polymerization is a 14-electron cation. As an example, the mechanism of activation of an unbridged zirconocene catalyst is presented in Fig. 9.5-4, top. In the first two steps the activation by MAO, resulting in the 14-electron cation, is shown. The same cation can be generated by N,N -dimethylanilinium-tetrakis(pentafluorophenyl)borate and methylated metallocenes. As side-products methane and an amine are formed. TiBA can also be involved in the activation, which is not shown in Fig. 9.5-4, bottom. On the other hand, TiBA acts as a scavenger in the polymerization. The above-mentioned reactions take place in the absence of the monomer and are performed before the catalyst is used in the polymerization process. 

Methylaluminoxane-free catalysts, such as cationic complexes derived from TiBz4 and tris(pentafluorophenyl)borane [B(C6F5)3], appear to be much less active, poorly stereospecific catalysts for the polymerisation of styrene. Under analogous conditions, the use of N, yV-dimethylanilinium tetrakis(pentafluor-ophenyl)borate [Me2N(Ph)H]+[B(C6F5)4]- instead of B(C6F5)3 does not yield active catalysts only traces of syndiotactic polystyrene were obtained [70]. 

Matsumoto generated group 4 metal catalysts by cosupporting bis(cyclopentadienyl)-, mono(cyclopen-tadienyl)-, or cyclopentadienyl-free compounds with ferricinium or dimethylanilinium tetrakis(pentafluo-rophenylborate) on a variety of carriers. Triisobutyl-aluminum can be added in the support step or added to the reactor with the catalyst. Spherical particles with bulk densities as high as 0.36 g/cm are formed using this technique. 

In addition to MAO, boron compounds based on tris(pentafluorophenyl)boron and its derivatives, typically dimethylanilinium tetrakis(pentafluorophenyl) borate, have been used as cocatalysts for sPS polymerizations (40,41). Although MAO has been used in large molar excesses relative to the titanium complex, the boron compounds may be used in roughly equimolar amounts to the titanium catalyst. The boron cocatalyst reacts with a titanium alkyl species, either by protonation in the case of dimethylanilinium tetrakis(pentafluorophenyl)borate or by alkyl group abstraction in the case of tris(pentafluorophenyl)boron, to generate a titanium cationic species with a borate counterion (74-76). The esr spectral evidence has been reported for these systems, supporting a titanium(III) cationic active species (76). 

The polymerization activity of tris(pentafluorophenyl)boron has been reported to be higher than that of dimethylanilinium tetrakis(pentafluorophenyl) borate with [(CHslsCslTiCCHsla as the catalyst (77). It was proposed that the dimethylaniline coordinates to the active site and decreases the polymerization activity. The use of dimethylanilinium tetrakis(pentafluorophenyl)borate with tri-isobutylaluminum (TIBA) and [(CHslsCslTilCHsla as the catalyst has been reported to jdeld high activity for sPS polymerization (74). 

In case of borate as cocatalyst, the catalytic activity of the titanium complex with a pentamethylcyclopentadienyl hgand is high, but a titanium complex with a cyclopentadienyl ligand without any substituents is not active for the syndiospecific styrene polymerization. The reason is that the reaction product of the borate and the cycopentadienyltitanium compound is unstable. The stability of the active site with the borate compound is lower in comparison to that with MAO. The reaction of CH2(Cp)2Ti(Me)2 with dimethylanilinium tetrakis(pentafiuorophenyl)borate or tris(pentafluorophenyl)borane in an equimolar mixture has been examined by Miyashita, Nabika, and Suzuki [11]. Two types of methylene bis(cyclopentadienyl)titanium ion complexes were isolated (see Fig. 3.6). These complexes were active in the polymerization of styrene, but only atactic polystyrene was formed. 

Copolymerization reactions of 27 (Figure 16) with 1-hexene and 4-methyl-pent-1-ene afford good results using rac-Et(THInd)2ZrMe2 and Cp 2ZrMe2 after activation with N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate... 

---