Titanium tetravalent derivatives

We have observed that the radioactive contamination is practically independent of the temperature A9). We believe that this radioactive contamination is due to the presence of traces of radioactive polyethylene resulting from ethylene polymerization. Ethylene can result, in fact, from the disproportionation of C2Hs radicals released by decomposition of ethyl titanium compounds, which derive from the reaction between ethylalu-minum and traces of titanium tetrachloride or other tetravalent titanium compounds that are sometimes present as impurities in the a-titanium trichloride. 

FIGURE 21.23 Potential-pH equilibrium diagram for the titanium-water system at 25 °C. [Figure established by considering, as derivatives of tri and tetravalent titanium, the anhydrous oxides Ti203 and Ti02 (rutile).] (from Ref. 35). 

In Section 12.7.B, the Stille coupling reaction reacted a vinyl tin compound with a vinyl triflate, in the presence of palladium(O). Tetravalent tin complexes add to aldehydes and ketones, in the presence of a Lewis acid. Allyltin complexes are, by far, the most widely used of these compounds.297 a typical example is taken from the work of Keck, in which a chiral aldehyde (455) was treated with allyltributyltin, in the presence of various Lewis acids. S As shown in Table 12.19, a mixture of syn (456) and anti (457) products was obtained. The ratio of 456/457 was dependent on the structure of the R group in 455, the solvent and the Lewis acid.The anti product (457) was obtained by using the tert-butyldimethylsilyloxy derivative (sec. 7.3.A.i) of 455 with 2 equivalents of boron trifluoride in dichloromethane. The syn product is obtained preferentially when the benzyloxy derivative of 455 is used with titanium tetrachloride in dichloromethane.298... 

Bradley et al pnrified uranium tetra-alkoxides by sublimation under reduced pressure and also tried to correlate the volatility of uranium tetra-alkoxides with those of other tetravalent metal alkoxides as shown in Table 2.6 (which includes for comparison relevant data for tetravalent titanium and zirconium derivatives). 

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