Organotitanium compounds,

Among organotitanium compounds of greatest practical interest nowadays are ethers of orthotitanium acid fLfTiCL and the products of hydrolytic poly condensation of these ethers, polyalkoxytitaniumoxanes. 

An introduction of small amounts of ethers of orthotitanium acid into solutions or emulsions of waterproofing silicone liquids increases water-repellent properties of these liquids. 

Ethers of orthotitanium acid are also used as catalysts for the polymerisation of unsaturated compounds (as components of the Ziegler-Natta cata- 

Olefines can be polymerised not only with ethers of orthotitanum acid, but also with halogenised cyclopentadienyl titanium compounds, bis(cyclopentadienyl)titaniumdichloride, as well as diphenyl-bis(cyclopentadienyl) titanium compounds combined with aluminumtrial-kyls, or tetrakys(trimethylsiloxy)titanium combined with aluminumtrialkyl and aluminum alkylhalogenides. 

Triorganosiloxyderivatives of titanium have been used to produce thermally stable polymers. 

In collaboration with Freidlina, Nogina and Brainina we started an investigation into titanium organic chemistry, namely, titanium alkoxides. Good methods were worked out for the synthesis of the compounds (RO) TiX4 where n is 1-4, and X is Cl or Br (395-404). The compounds (RO)2Ti(OR )2 and (RO)3TiOR were also obtained and the properties of all compounds studied. For example, tetraalkoxytitanium compounds were found to induce the Tishtshenko condensations of aldehydes (395). 

Trialkoxy derivatives of trivalent titanium were synthesized, and their interesting reactions, e.g., the oxidation to the dialkoxytitanium oxides, studied. For the first time, the low-alkyl polyalkoxy titanoxanes 

A number of facile procedures were developed for the synthesis of mono and bis cyclopentadienyl derivatives of titanium, e.g., the (tt-CsH )-trialkoxytitanium derivatives, (77-C5H5)-titanium trihalides (406, 407-409), (77-C5H5)-titanium internal complexes (409), triaroxytitanium cyclopentadienyls (410), compounds containing different groups (alkoxy, aryloxy. 

The new syntheses and the properties of the compounds mentioned above or obtained in other ways enabled us to study the titanium-cyclo-pentadienyl bond as a function of the ligands. 

In complexing solvents, monocyclopentadienyl derivatives differed in their properties from the bis(cyclopentadienyl) ones (419). The fluorine chemical shift was affected by the nature of the rings in the latter compounds 

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Thus, chiral organotitanium compounds result from the use of (trialkoxy)chlorotitanates derived from chiral alcohols. The transfer of methyl and phenyl groups by chiral titanium... 

High ee values have also been obtained with organometallics," including organotitanium compounds (methyl, aryl, allylic) in which an optically active ligand is coordinated to the titanium," allylic boron compounds, and organozinc compounds. 

Carbometallation Reactions of Organotitanium Compounds 10.06.2.2.1 Controlled monocarbometallation... 

The organotitanium compounds produced by desulfurization of the diphenyl thioacetals of aldehydes 28 with the titanocene(II) species Cp2Ti[P(OEt)3]2 29 react with carbon—carbon double bonds to form the olefin metathesis-type products. Thioacetals 28 may be transformed into terminal olefins by desulfurization with 29 under an ethene atmosphere (Scheme 14.15) [27]. This reaction is believed to proceed through a titanacyclobutane intermediate, formed by cycloaddition of the titanocene-alkylidene with ethene. 

The use of organotitanium compounds in the synthesis of allenes involves mainly Wittig-type olefmation reactions of carbonyl compounds [86] with titanium ylides. The formation of allenes according to the scheme Q + Q + Q was described by... 

A unique titanium(IV)-silica catalyst prepared by impregnating silica with TiCLt or organotitanium compounds exhibits excellent properties with selectivities comparable to the best homogeneous molybdenum catalysts.285 The new zeolite-like catalyst titanium silicalite (TS-1) featuring isomorphous substitution of Si(IV) with Ti(IV) is a very efficient heterogeneous catalyst for selective oxidations with H2C>2.184,185 It exhibits remarkable activities and selectivities in epoxidation of simple olefins.188,304-306 Propylene, for instance, was epoxidized304 with 97% selectivity at 90% conversion at 40°C. Shape-selective epoxidation of 1- and 2-hexenes was observed with this system that failed to catalyze the transformation of cyclohexene.306 Surface peroxotitanate 13 is suggested to be the active spe-... 

Allyltitanium ate complexes.8 In contrast to organotitanium compounds, which are aldehyde selective, the chemoselectivity of allyltitanium ate complexes depends on the ligands attached to titanium. The most aldehyde-selective allyltitanium ate complex prepared to date is CH2=CHCH2Ti[OCH(CH3) >].jMgCl (1) which reacts... 

The reactivity of organotitanium compounds is similar to that of organoaluminum compounds, and attack at the most polarized C-O bond is usually observed (Scheme4.71). The lack of stereoselectivity of the second example in Scheme4.71 suggests the intermediate formation of carbocations or radicals. 

Weidmann, B. Widler, L. Olivero, A. G. May-cock, C. D. Seebach, D. Selectivities in the reactions of alkyl-, aryl-, and heterosubstituted organotitanium compounds. Helv Chim. Acta 1981, 64, 357-361. 

Among widely used organotitanium compounds are tetraalkoxytitaniums, obtained by the etherification of titanium tetrachloride with alcohols ... 

The high enrichment ratio observed for titanium in the deposit is difficult to explain if all the metal in the coal is present in the mineral state. The data can be interpreted as an indirect indication of the presence in the feed slurry of an unstable titanium species which, upon contact with the catalyst surface, codeposits with carbon, boron, and other metals. A plausible explanation for this observation would be that organotitanium compounds exist in the coal and that they thermally or catalytic ally decompose to yield a stable inorganic species. Some recent model compound studies by Treblow and coworkers have indicated that... 

The above transformation has two different goals 21,22) 1) To increase chemo-, regio-, diastereo- and enantioselectivity in the reaction with carbonyl compounds (Sections C-E), and 2) to make certain reaction types amenable which do proceed readily with classical reagents, e.g., methylation of tertiary alkyl halides, alcohols and ethers, and direct geminal dialkylation of ketones (Section F). It turns out that organotitanium compounds are usually complementary to Li, Mg, Zn, Fe, Ni, Cu and Pd reagents. So far, experience in the above two areas points to the following positive aspects ... 

A number of organotitanium compounds are so tempered in their reactivity, that they react sluggishly or not at all. 

B. Synthesis, Structure and Properties of Some Common Organotitanium Compounds... 

Photoelectron spectra of a few organotitanium compounds provide additional insight into the bonding59,60). For example, in CHjTiXj (X = OR, NR2) back-donation of lone electron pairs explains some of the spectral peculiarities 60). 

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