Titanium complexes dichloride

A derivative 5 of the 1,3-dithiolopentathiepin system was obtained by the action of disulfur dichloride on the titanium complex 4 under conditions of high dilution.397... 

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.

Narasaka has reported that TADDOL-Ti dichloride catalyzes the asymmetric addition of trimethylsilylcyanide to aromatic and aliphatic aldehydes (Sch. 63) [148]. The reactions proceed only in the presence of MS 4A. In reactions with aliphatic aldehydes a chiral cyanotitanium species obtained by mixing of the TADDOL-Ti dichloride and trimethylsilylcyanide before addition of the aldehydes acts as a better chiral cyanating agent and affords higher enantiomeric excesses. Chiral titanium complexes obtained from an alcohol ligand and salicylaldehyde-type Schiff bases and a salen ligand have been reported to catalyze the asymmetric addition of hydrogen cyanide or... 

The formation of biphenyl-substituted bis-Gp titanium complexes (Scheme 439) has been detected during the synthesis of -biphenyl-bridged bis-Cp derivatives.1050 The synthesis of the bis(tetrahydroindenyl) dichloride (C9H10)TiCl21051 and of [G5H3(l,2-CH2-)J2TiCl2 (n = 4-6) (Scheme 440)1052 have been reported. 

Arylamido complexes of a general formula of Cp Zr[N(Ar)SiMe3]Cl2 can be obtained in a similar fashion. Thus, the reaction of Cp MCl3 with 1 equiv. of Li[N(Ar)SiMe3] produces complexes 31248 and 313.252 The difluoride 312 was prepared by metathesis reaction of the dichloride and Me3SnF. Upon activation with MAO, all complexes are active for polymerization of ethylene within complexes 312, the zirconium complexes are much more active than the analogous hafnium complexes, whereas within complexes 313, the zirconium complex exhibits poor activity as compared with the analogous titanium complex. 

Previously, Pasini [27] and Colonna [28] had described the use chiral titani-um-Schiff base complexes in asymmetric sulfide oxidations, but only low selec-tivities were observed. Fujita then employed a related chiral salen-titanium complex and was more successful. Starting from titanium tetrachloride, reaction with the optically active C2-symmetrical salen 15 led to a (salen)titani-um(IV) dichloride complex which underwent partial hydrolysis to generate the t]-0x0-bridged bis[(salen)titanium(IV)] catalyst 16 whose structure was confirmed by X-ray analysis. Oxidation of phenyl methyl sulfide with trityl hydroperoxide in the presence of 4 mol % of 16 gave the corresponding sulfoxide with 53% ee [29]. 

Few of the squarate complexes syntheseized to date contain tetravalent metals coordinated in a tetrahedral geometry. The use of bis(cyclopentadienyl)titanium(IV) dichloride (Cp2TiCl2 or titanocene dichloride) as the metal containing ligand provides the opportunity for obtaining such a complex. 

The basic compound of Brintzinger s ansa-titanocene complexes is ethylenebis-(tetrahydroindenyl)titanium dichloride, (EBTHI)TiCl2. Further analogues ((EBTHI)TiH, (EBTHI)Ti(Me)2, and (EBTHI)Ti(CO)2) have been wddely used for asymmetric hydrogenation, hydrosilylation, and Pauson-Khand reaction (121). Novel optically active titanium complexes containing a linked amido-cyclopentadienyl ligand have been developed and used for asymmetric hydrogenation (122). 

Cross-metathesis of the allyl-Cp substituted titanocene dichloride leads to the formation of dinuclear titanium complexes (Scheme 12.25, M = Ti, n= 1) [33]. The composition of the reaction mixture depends on the catalyst used. Treatment of the substrate with Ru-I (3 mol%) in benzene, toluene, or dichloromethane gave a mixture of Z and E isomers in a 1 1 ratio, while application of the Ru-II catalyst resulted with the formation of the pure E isomer. 

Important applications for titanium have been developed in processes involving acetic acid, malic acid, amines, urea, terephthalic acid, vinyl acetate, and ethylene dichloride. Some of these represent large scale use of the material in the form of pipework, heat exchangers, pumps, valves, and vessels of solid, loose lined, or explosion clad construction. In many of these the requirement for titanium is because of corrosion problems arising from the organic chemicals in the process, the use of seawater or polluted cooling waters, or from complex aggressive catalysts in the reaction. 

Dienones, such as 4-[4-(trimethylsilyl)-2-butenyl]-3-vinyl-2-cyclohexenone, are useful precursors for these particular transformations the allylsilane side chain is too short for effective 1,4-addition, but just right for 1,6-addition, resulting in six-ring annulation. Three different Lewis acids can be used titanium(IV) chloride, boron trifluoride diethyl ether complex, and ethylaluminum dichloride. The best chemical yields and complete asymmetric inductions were obtained with ethylaluminum dichloride. 

Tricyclic compounds can be obtained directly by annulation on to cyclic allylsilanes, using either ethylaluminum dichloride or titanium(IV) chloride as Lewis acids57. The stereochemical outcome of this particular cyclization is controlled by the relative configuration of the cyclic allylsilane. The reaction follows the usual anti" SE2 process for reactions of allylsilanes with electrophiles. Thus, the reaction was stereospecific, which makes it very useful for stereocon-trolled syntheses of complex ring systems57. 

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