Titanium cationic species

The rate of reduction of the titanium cationic species [scheme (10)] increases when styrene is added to the system [83,90,93]. 

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). 

It was found in this work that the concentration of hydroxyl species on the surface determines the extent of Fe(C0)5 decomposition on Ti02 T e concentration of reduced titanium cations (T 3+) on the surface apparently has no effect on the process. Neither concentration affects the nature of the species formed. 

It is noted that both the micelle and the sol particles modified titanium cations are positively charged. However, the inorganic species can still condense surrounding the micelle through some pathways described by Huo et al (12). 

In contrast, studies on aqueous solutions of titanium(IV) in 2M HCIO4 are consistent with the presence of doubly charged cationic species. However, it is not clear whether the predominant species is [TiO] + or [Ti(OH)2] +. ... 

Bis-phenoxo hydrocarbyl five-coordinated titanium complexes (Scheme 21) have been synthesized and spectroscopically characterized. The molecular structure determined by X-ray diffraction shows the metal to have a distorted trigonal-bipyramidal coordination geometry. Cationic four-coordinate derivatives can be generated by reaction of the methyl derivatives with B(C6F5)3. These cationic species undergo stoichiometric insertions of ethylene and propylene into the Ti-C bond.67... 

Composition of the inorganic framework can be varied just like the surfactant use has been expanded beyond the original cationic species. The number of explored element combinations has been enormous and often driven by specific catalytic needs and prior experience with amorphous or crystalline compositions [37]. One of the leading approaches was doping of silica formulation with appropriate activating clement, such as aluminum (lo impart acidity) and titanium or vanadium for redox potential. Based on analogy of AlPO s and SAPO s to zeolites these compositions were also synthesized in the mesoporous form as were other non-silica inorganic oxides and their combinations [38]. Pure metal mesoporous product was obtained via the pre-formed liquid crystal route 1391. 

Finally, between the TOT layers of a smectite, large cationic species that are polymeric or oligomeric hydroxyl metal cations formed by the hydrolysis of metal salts of aluminum, gallium, chromium(III), silicon, titanium(IV), iron(III), and mixtures of them can be inserted by cation exchange, giving the so-called pillared clays... 

In some microporous solids, framework cations in tetrahedral sites are able to expand their coordination by chemisorbing small molecules while remaining within the framework, so that removal of the adsorbed species permits their return to tetrahedral coordination. The most important example of this is the titanium in titanosilicates such as TS-1. The titanium cations in the framework of ETS-10 are only able to adopt octahedral coordination, and are unable to show this kind of behaviour. 

Scheme 6.13 Polymerisation of yMBL and yMMBL by titanium-based cationic species.

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