Titanium amides, mixed

Scheme 7 Modification of mixed Cp/Cp titanium amidate complexes to probe ligand effects upon alkene polymerization [1 Ob]...

Note also the stereochemistry. In some cases, two new stereogenic centers are formed. The hydroxyl group and any C(2) substituent on the enolate can be in a syn or anti relationship. For many aldol addition reactions, the stereochemical outcome of the reaction can be predicted and analyzed on the basis of the detailed mechanism of the reaction. Entry 1 is a mixed ketone-aldehyde aldol addition carried out by kinetic formation of the less-substituted ketone enolate. Entries 2 to 4 are similar reactions but with more highly substituted reactants. Entries 5 and 6 involve boron enolates, which are discussed in Section 2.1.2.2. Entry 7 shows the formation of a boron enolate of an amide reactions of this type are considered in Section 2.1.3. Entries 8 to 10 show titanium, tin, and zirconium enolates and are discussed in Section 2.1.2.3. 

The enolates of other carbonyl compounds can be used in mixed aldol reactions. Extensive use has been made of the enolates of esters, thiol esters, amides, and imides, including several that serve as chiral auxiliaries. The methods for formation of these enolates are similar to those for ketones. Lithium, boron, titanium, and tin derivatives have all been widely used. The silyl ethers of ester enolates, which are called silyl ketene acetals, show reactivity that is analogous to silyl enol ethers and are covalent equivalents of ester enolates. The silyl thioketene acetal derivatives of thiol esters are also useful. The reactions of these enolate equivalents are discussed in Section 2.1.4. 

Titanium and zirconium tetrabenzyl and the mixed metal—benzyl halides are soluble in hydrocarbon solvents and will polymerize ethylene and a-olefins, the latter to stereo-specific polymers [64], The structures of the true initiators are not known but they are unlikely to be the simple organo-metal compounds. Catalysts of higher activity are obtained when they are used in combination with aluminium alkyls. It is of interest to note that titanium tetra(dimethyl amide) reacts with acrylonitrile to form an active species, which then forms high molecular weight polymer by coordination polymerization [65]. 

Titanium tetrakis(dialkylamide) compounds, Ti(NR2)4 (R= Me, Et, n-Pr, n-Bu) have been investigated in the CVD of TiN [144, 154-161]. Their decomposition, carried out in the presence of NH3(g), proceeds under relatively mild conditions and yields TiN films of good quality. Other precursors which have been used for the CVD of TiN include cyclopentadienyl-cycloheptatrienyl titanium, CpTi(C7H7) (15) [161], f-BuTi(NMe)3 [156, 161], [Ti(/i-N-r-Bu)(NMe2)2]2 (16) [156, 161] and Ti(f-BuDAD)2, bis(N,N -di-t-butyl-l,4-diaza-l,3-butadiene) titanium (17) [161]. The mixed amide... 

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