Titanium cyclopentadienyl compounds

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(IV) complexes, 25 97-101 Titanium(IV) compounds six-coordinated, 25 90 Titanium(IV) cyclopentadienyls, 25 110, 111—112t... 

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.

Breslow (139) discovered a homogeneous system well suited for kinetic analysis. He realized that bis(cyclopentadienyl)titanium(IV) compounds, which are very soluble in aromatic hydrocarbons, could be used instead of titanium tetrachloride as the transition-metal compound together with aluminum alkyls to give Ziegler catalysts. Subsequent research on this and other systems with various alkyl groups has been conducted by Natta et al. (140, 141), Belov el at. (142-144), Patat (145), Patat and Sinn (146) Sinn et al. (119, 147), Shilov and co-workers (148-150), Chien and Hsieh (20), Adema (151), Clauss and Bestian (152), Henrici-Olive and Olive (153), and Reichert and Schoetter (154) and Fink (155). 

Other studies on mixed Ti-Al systems as alkene polymerization catalysts have afforded examples of bridging between these two metals by cyclopentadienyl residues (69), by carbidic carbon atoms (70, 71, 72), " 5 and by methyl groups (74). The carbide systems 70, 71, and 72 were prepared by reactions between phosphinimido-titanium methyl compounds and trimethylaluminum. The coordination at the carbide carbon atoms in 70 and 72 is flattened tetrahedral. However, the coordination in 71 is distorted trigonal bipyramidal, with a near-linear Ti—C—Al vector (178.5°) (cf. 65 and 66) and bonding as in 67. 

Most of the homogeneous Ziegler-type catalysts have been preferentially investigated in order to understand the elementary steps of the polymerization, which is simplified in soluble systems. Bis(cyclopentadienyl)titanium(IV) compounds, which are soluble in aromatic hydrocarbons could be used together with aluminum alkyls to give Ziegler-catalysts. As to the kinetics of polymerization and to side reactions of the catalyst components, this system is probably the best understood. It has not been used in a technical process because of the low activity and short life of systems that contain chloride (see Table 1). 

K. Ziegler catalysed the polymerization of ethylene using an organo-titanium derivative. The first event initiated a systematic study of cyclopentadienyl compounds, and so led to the preparation of the most stable of the organometallic compounds of this group, while the second event provided a strong commercial incentive for the investigation of this field (see Panel). 

The titanium-containing compound is a metallocene. (It has cyclopentadienyl rings as ligands.) With an atomic number of 22, titanium has an electron configuration of As the following... 

In many cases, such as for cyclopentadienyl compounds of titanium, the attachment of the complex to the support prevents polymerization and other side reactions. This additionally increases the activity and lifetime of the heterogenized catalyst. 

Guiducci AE, Boyd CL, Clot E, Mountford P (2009) Reactions of cyclopentadienyl-amidinate titanium imido compounds with CO2 cycloaddition-extnision vs. cycloaddition-insertion. Dalton Trans 5960-5979... 

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). 

Recently some information became available on a new type of highly active one-component ethylene polymerization catalyst. This catalyst is prepared by supporting organometallic compounds of transition metals containing different types of organic ligands [e.g. benzyl compounds of titanium and zirconium 9a, 132), 7r-allyl compounds of various transition metals 8, 9a, 133), 7r-arene 134, 185) and 71-cyclopentadienyl 9, 136) complexes of chromium]. 

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