Titanium selenides

Sodium titanium selenide (NaoflsTiSej), 30 167 [158188-82-0], Lithium tantalum sulfide (Lio.7TaS2), 30 167... 

Very little is known about chalcogenide halides of Group IVB elements. Although the existence of sulfide chlorides (45, 274, 329, 365) and of a selenide chloride (329) of titanium was claimed in early publications, their true composition, and even their existence, remains doubtful. They have usually been obtained by the reaction of titanium chlorides with sulfur and selenium, respectively, or with hydrogen sulfide. The synthesis of a pure compound, TiSClj, was published in 1959 (113). It is an intermediate of the reaction of TiCU with HjS. 

Titanium(II) sulfide, TiS titanium(III) sulfide, Ti2S3 titanium(IV) sulfide, TiS2 zirconium sulfide, ZrS2 hafnium selenide, HfSe2 hafnium sulfide, HfS2. 

Selenides and tellurides can be prepared similarly.774 When epoxides are substrates, p-hydroxy sulfides are obtained in a manner analogous to that mentioned in 0-35. Epoxides can also be directly converted to episulfides,775 by treatment with a phosphine sulfide such as PI13PS776 or with thiourea and titanium tetraisopropoxide.777... 

This chapter has been devoted to the coordination chemistry of titanium and has made no attempt to describe the more basic chemistry of this element. References to alloys, to the simple halides and oxyhalides, the oxides, sulfides, selenides, tellurides, nitrides, azides, phosphides, arsenides and antimonides are well reviewed by Clark,14 and the recent text by Greenwood and Earnshaw180 contains a good section on titanium. 

Many examples of this type of reaction are known the decomposition of arsine the decomposition of phosphine on surfaces of glass, f porcelain, J silica the decomposition of formic acid vapour on a variety of different surfaces— glass, platinum, rhodium, titanium oxide, and others the decomposition of nitrous oxide on the surface of gold Tf the decomposition of sulphuryl chloride on the surface of glass the decomposition of hydrogen iodide on the surface of platinum ff the decomposition of hydrogen selenide on the surface of selenium. J J A general discussion... 

The asymmetric oxidation of sulphides to chiral sulphoxides with t-butyl hydroperoxide is catalysed very effectively by a titanium complex, produced in situ from a titanium alkoxide and a chiral binaphthol, with enantioselectivities up to 96%342. The Sharpless oxidation of aryl cinnamyl selenides 217 gave a chiral 1-phenyl-2-propen-l-ol (218) via an asymmetric [2,3] sigmatropic shift (Scheme 4)343. For other titanium-catalysed epoxidations, see Section V.D.l on vanadium catalysis. 

Shimoishi and Toei [766] have described a gas chromatographic determination of selenium in non saline waters based on l,2-diamino-3,5-dibromobenzene with an extraction procedure that is specific for selenium (IV). Total selenium is determined by treatment of non saline water with titanium trichloride and with a bromine-bromide redox buffer to convert selenide, elemental selenium and selenate to selenious acid. After reaction, the 4,6-dibromopiazselenol formed from as little as lng of selenium can be extracted quantitatively into 1 ml of toluene from 500ml of natural water up to 2ng L 1 of selenium(IV) and total selenium can be determined. The percentage of selenium(IV) in the total selenium in river water varies from 35 to 70%. 

Cyclohexyl selenides 162 can be prepared from the 4-substituted cyclohexanones via the selenoketals and upon oxidation with chiral oxidants, compounds 163 were obtained in high yields and with excellent stereoselectivities. Some representative examples are summarized in Table 5 and it is obvious that only the Davies oxidant 158 is leading to high enantiomeric excesses in the product 163 whereas under Sharpless oxidation conditions no selectivity is obtained. The titanium complex formed in the Sharpless oxidant may promote the racemization of the intermediate selenoxide by acting as a Lewis acid catalyst, while the aprotic nature of the Davies oxidant 158 slows down racemization dramatically. 

HOMOALLYLIC ALCOHOLS B-Allyldiisopino-campheylborane. Allyl phenyl selenide. Allyltri-/i-butyltin. Chromium(II) chloride. Crotyltrimethylsilane. Diethylftributyl-stannyl)aluminum. (2R,4R)-Pentanediol. Pinacol chloromethaneboronate. Tin-Aluminum. Titanium(lV) chloride. 

Compounds Bis-dimethylstibinyl oxide Bis(dimethylthallium) acetylide Butyllithium Nonacarbonyldiiron Octacarbonyldicobalt Pentacarbonyliron Tetracarbonylnickel Dibismuth trisulphide Dicaesium selenide Dicerium trisulphide Digold trisulphide Europium (II) sulphide Germanium (II) sulphide Iron disulphide Iron (II) sulphide Manganese (II) sulphide Mercury (II) sulphide Molybdenum (IV) sulphide Potassium sulphide Rhenium (VII) sulphide Silver sulphide Sodium disulphide Sodium polysulphide Sodium sulphide Tin (11) sulphide Tin (IV) sulphide Titanium (IV) sulphide Uranium (IV) sulphide ... 

Until quite recently the isolation of optically active selenoxides has been limited to those contained in steroids (isolated as diastereoisomers). The difficulty in obtaining these compounds was attributed to the racemization through the achiral hydrated intermediates. Simple optically active selenoxides (5-11% ee) were first prepared by kinetic resolution. Direct oxidation of selenides to selenoxides was first reported using optically active oxaziridine derivatives under anhydrous conditions, but the extent of the asymmetric induction was somewhat unsatisfactory with methyl phenyl selenide as substrate (8-9% ee). Recently much improved enantiomeric excesses (45-73%) were achieved with new oxaziridine reagents such as (70). An attempt at the asymmetric oxidation of more bulky selenides was independently carried out using Bu OCl in the presence of (-)-2-octanol (equation 55),2 but resulted in unsatisfactory enantioselectivities (ee 1%). Much better results were obtained by the oxidation of P-oxyalkyl aryl selenides (ee 18-40% equation 56) and alkyl aryl selenides (ee 1-28%) 2S using TBHP in the presence of (+)- or (-)-diisopropyl tartarate (DIPT) and titanium(IV) alkoxide. 

Asymmetric oxidation of ( )-3-phenyl-2-propenyl aryl selenides under Sharpless conditions (tetraisopropoxy titanium/tartrate/ferr-butyl hydroperoxide) afforded optically active alcohols in moderate to high enantiomeric excess (25-92% ee) and with yields of about 40%31b. The enantioselectivity in this reaction was enhanced remarkably by an ortho nitro group in the aryl ring and the use of diisopropyl tartrate ligand in the Sharpless oxidation. 

Thus, when cyclohexyl selenides 1, prepared from the corresponding 4-sub-stituted cyclohexanone via the selenoketals, were oxidized with various Davis and Sharpless oxidants, the chiral alkyl aryl 4-substituted cyclohexylidenemethyl ketones were obtained in excellent chemical yields with high enantiomeric excesses. Typical results are summarized in Table 4. In this asymmetric induction, of the substrate and the chiral oxidant employed were revealed to show a remarkable effect upon the enantioselectivity of the product. The use of a methyl moiety as instead of a phenyl moiety gave a higher ee value, probably due to the steric difference between the two groups bonded to the selenium atom of the substrate. The results indicate that the titanium complex of the Sharpless oxidant may promote the racemization of the chiral selenoxide intermediate by acting as a Lewis acid catalyst, whereas the racemization in the case of the Davis oxidant, which is aprotic in nature, is slow. 

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