Titanium m

A silastannation product bearing an epoxide moiety undergoes titanium(m)-mediated cyclization with the vinyl-stannane moiety (Equation (109)).268... 

Titanium(iv) iodide" " or a combination of a titanium(iv) salt and an iodide source promotes pinacol coupling reactions of aromatic aldehydes. The combination of the reagents is considered to generate titanium(m) species along with U. 

The synthesis of unsymmetrical 1,4-diketones results from the conjugate addition of the nitronate anion (as the acyl anion equivalent) to an a,fi-unsaturated ketone [Method (6)].l47a The intermediate nitroketone is converted into the diketone by reduction with titanium(m) chloride at pH 1, or by ozono-lysis of the nitronate anion147b (cf. Section 5.7.7, p. 599). 

Reduction of nitroketones with titanium(m) chloride at pH 1. The foregoing nitroketone may be converted into the diketone by means of the following general procedure. The nitroketone in solution in tetrahydrofuran (0.2 m) is treated with 4 equivalents of titanium(m) chloride (1) (20% aqueous hydrochloric acid solution) and stirred under nitrogen at room temperature for 24 hours. The reaction mixture is then poured into ether and the phases separated. The aqueous phase is extracted several times with ether the organic extracts are combined, washed with 5 per cent sodium hydrogen carbonate and with brine, and then dried over anhydrous sodium sulphate, concentrated and distilled. The yield of heptane-2,5-dione is 66 per cent p.m.r. spectrum (CC14, TMS) 8 1.00 (t, 3H), 2.10 (s, 3H), 2.60 (s, 4H) and 3.41 (q, 2H). 

Note. (1) A 20 per cent titanium(m) chloride solution in aqueous hydrochloric acid is available commercially. Solid titanium(m) chloride reagent is a flammable solid and should be handled only under an inert atmosphere, and if used in this reaction should be taken from a fresh bottle. 

Evidence for 2 1 complex formation between titanium(m) and L-lysine has been obtained the complex was not isolated because of its instability to air.106... 

Hydrazine is an intermediate in the formation of ammonia from reduction of N2 by titanium(m) in the presence of molybdenum compounds. Hydrogen is also produced by reaction of the titanium(iv) with the methanol solvent. Activation energies were determined for the formation of these three products.120 The preparation and n.m.r. spectra of Mg, Zn, and Cd derivatives of nonahydrohexaboratobis(cyclopenta-dienyl)titanium(m) have been reported.121... 

The organometallic chemistry of titanium is dominated by complexes in the +IV oxidation state and in comparison there are relatively few examples of titanium complexes in the +III oxidation state. For information on organotitanium(iv) see Chapter 4.05. However, examples of titanium(lll) complexes are more common than examples of titanium complexes in lower oxidation states (for information on organotitanium in oxidation states 0 to II see Chapter 4.03) and titanium(m) chemistry is considerably more advanced than the chemistry of the heavier group 4 metals, zirconium and hafnium in the +m oxidation state. For information on organozirconium(m) and organohafnium(m) see Chapter 4.07. 

Furthermore, over the past 15 years, it has also been demonstrated that titanium(m) complexes can be used as catalysts in organic transformations. Complexes containing a Ti(m) center have been shown to be active catalysts for the hydrosilylation of lactones, esters, and ketones and have also been used to reduce both aryl and alkyl halides, ketones, aldehydes, aromatic azo compounds, and epoxides. These organic applications of titanium(m) complexes are beyond the scope of this chapter. 

In the last 10 years, the solid-state structures of the related titanium(m) amido species Cp 2Ti(NH2) 113 (Figure 15) and Cp 2Ti(NMeH) 114 have been determined.58,91 The structures are nearly identical, and in both cases the amido ligand adopts the least sterically favorable conformation in order to maximize Ti-N 7T-bonding. In this conformation... 

The complexes TiXMe(salen) (Scheme 24) are obtained when the dichloro parent compound TiCl2(salen) reacts with AlMe3 by further addition of OEt2 with additional formation of titanium(m) species (salen = N,N -bis(salicyli-dene)ethylenediamine). The reactivity of these compounds has been studied toward magnesium reduction, halide abstraction with SbCl5 and AgBF4, S02 insertion and hydrolysis reactions.73,74... 

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