Cyclopentadienyls titanium

Figures 5-41 and 5-42 compare CpTiCp (centroid) bond angles in titanium cyclopentadienyl dichloride complexes from PM3 and BP/ 6-31G calculations, respectively, with experimental values for these and other compounds dealt with in this section from X-ray crystallography. Due to practical limitations, the data used for comparison with the density functional calculations are a subset of that used in comparison with PM3. Both models perform well in separating those systems where the cyclopentadienyl rings are spread far apart from those where they are closer together.

To avoid interference from the alkylation of the titanium cyclopentadienyl compound with aluminum alkyl, Cp2Ti(R)Cl has been used in place of Cp2TiCl2 as a catalyst component. Reichert and Meyer 641 made a detailed kinetic study of the polymerization of ethylene with the soluble Cp2Ti(C2H5)Cl/Al(C2H5)Cl2 catalyst in toluene at 10 °C. Figure 3 shows the polymerization rate as a function of time at... 

Titanium cyclopentadienyl derivatives form an extensive series of dinitrogen complexes. However, when the titanium-containing precursors are bound to polymers there is no reactivity with dinitrogen comparable to that observed for the analogous derivatives in solution, and fixation is, at best, marginal (202, 220). 

There has been significant interest in substituting cobalt for other transition metals giving rise to what are known as Pauson-Khand type reactions.60 In 1996, Buchwald and co-workers showed that a titanium -cyclopentadienyl complex (45) could be used sub-substoichiometrically in the reaction (46->47 - Scheme 18).61,62... 

Figure 5 Examples of titanium-cyclopentadienyl oxo-bridged complexes evaluated for anticancer activity.

A new interesting development is the discovery and tailoring by Kaminsky of Z.N. type systems composed of titanium cyclopentadienyl complexes, and aluminoxanes obtained by controlled hydrolysis of aluminum alkyls (see [8] and papers of the corresponding symposium held at Akron in June 1986). These soluble and extremely active systems (for ethylene) are even claimed to exhibit a good stereoselectivity in propylene polymerization under homogeneous conditions (probably due to the hindered environment provided by the alumoxane structure). 

Examples of photothermoplasts include polyacrylates, polyacrylamides, polystyrenes, polycarbonates, and their copolymers (169). An especially well-re searched photothermoplast is poly(methyl methacrylate) (PMMA), which is blended with methyl methacrylate (MMA) or styrene as a monomer, and titanium-bis(cyclopentadienyl) as a photoinitiator (170). 

The chemistry of complexes having achiral ligands is based solely on the geometrical arrangement on titanium. Optically active alcohols are the most favored monodentate ligands. Cyclopentadienyl is also well suited for chiral modification of titanium complexes. 

Sulfur imides with a single NR functionality, S5NR (6.12), SeNR (6.13) (R = Oct), " SgNH (6.14), ° and S9NH (6.15) ° are obtained by a methodology similar to that which has been used for the preparation of unstable sulfur allotropes, e.g., S9 and Sio. Eor example, the metathesis reaction between the bis(cyclopentadienyl)titanium complexes 6.8-6.10 and the appropriate dichlorosulfane yields 6.14 and 6.15 (Eq. 6.4). °... 

Perhaps because of inadequate or non-existent back-bonding (p. 923), the only neutral, binary carbonyl so far reported is Ti(CO)g which has been produced by condensation of titanium metal vapour with CO in a matrix of inert gases at 10-15 K, and identified spectroscopically. By contrast, if MCI4 (M = Ti, Zr) in dimethoxy-ethane is reduced with potassium naphthalenide in the presence of a crown ether (to complex the K+) under an atmosphere of CO, [M(CO)g] salts are produced. These not only involve the metals in the exceptionally low formal oxidation state of —2 but are thermally stable up to 200 and 130°C respectively. However, the majority of their carbonyl compounds are stabilized by n-bonded ligands, usually cyclopentadienyl, as in [M(/j5-C5H5)2(CO)2] (Fig. 21.8). 

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