Titanium tetrahalides

In this procedure cis- [dihalobis(2,4-pentanedionato)titanium(IV)] complexes (halo = F, Cl, Br) are prepared in high yields through the reaction of a titanium tetrahalide with 2,4-pentanedione in dichloromethane. 

Titanium tetrahalides are reduced by LiBH4 in pentane to (BH4)2TiCl2Ti(BH4)2 and Ti(BH4)3. The chlorine-bridged dimer reacted with THF to give Ti(BH4)3,2THF and TiCl3,nTHF.87... 

Synthesis. Titanium alkoxy halides are intermediates in the preparation of alkoxides from a titanium tetrahalide (except the fluoride) and an alcohol or phenol. If TiCl4 is heated with excess primary alcohol, only two chlorine atoms can be replaced and the product is dialkoxydichlorotitanium alcoholate, (RO)2TiCl2 ROH. The yields are poor, and some alcohols, such as allyl, benzyl, and /-butyl alcohols, are converted to chlorides (46). Using excess TiCl4 at 0°C, the trichloride ROTiCl3 is obtained nearly quantitatively, even from sec- and /( alcohols (47,48). 

The melting and boiling points of the titanium tetrahalides are given below. 

Other Lewis acids that complex with thietane are titanium tetrachloride or bromide,boron trifluoride,trimethylaluminum, and tin tetrachloride. The enthalpies of formation of the aluminum complex (— 16.04 kcal/mole) and the tin complex (— 14.2 kcal/mole) and the wavelength of the charge transfer band of the tin complex (270 nm) have been determined. The titanium tetrahalides form both a 1 1 and a 1 2 adduct (titanium halide thietane). °° Treatment of 3-methyl-thietane with aluminum chloride or tin tetrachloride yields a rubbery white soUd." "... 

Emission from electronically excited TiO molecules has been observed by Palmer and co-workers from the reaction of titanium tetrachloride or tetrabromide with potassium vapour in the presence of oxygen [277] and of nitrous oxide [278]. The potassium atoms presumably strip the halogen atoms from the titanium tetrahalide, and the titanium atoms then react with the oxygen or nitrous oxide producing electronically excited TiO molecules. 

Propyl nitrite has been shown to be a poor reagent for nitrosation of aniline derivatives, but the reaction can be catalysed by halide ions the probable mechanism involves rapid equilibrium formation of the nitrosyl halide, which then reacts with aniline. A similar mechanism has been proposed when alkyl nitrites and titanium tetrahalides are used as a nitrosating reagent. ... 

Allyl alcohols have often proved to be excellent initiators in cation-olefin cyclizations and this is once again demonstrated by the clean conversion of nerol (183) into (184) and of (185) into (186) brought about by a titanium tetrahalide-A-methylaniline combination, In contrast, thallic perchlorate converts (183) into (187), indicating that initiation of cyclization had been induced by attack of... 

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