Selenium titanium complex

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. 

Attempts to synthesize Gp titanium complexes with a terminal Ti=Te moiety have met with difficulties. One of the principal factors for this is the particularly weak Ti=Te interaction. Ti=E bond energies for Cp2Ti=0 (152.6 kj mol 1) and Cp2Ti=Te (130.3 kj mol-1) have been calculated. The hydrido titanium(m) complex Gp 2TiH reacts with elemental selenium or tellurium to give mono- and diselenido and tellurido complexes. The possible involvement of monomeric terminal chalcogenides Cp 2Ti(E) (E = O, S, Se, Te) in these reactions has been probed experimentally and computationally by means of DFT calculations. 

Stainless Steel There are more than 70 standard types of stainless steel and many special alloys. These steels are produced in the wrought form (AISI types) and as cast alloys [Alloy Casting Institute (ACI) types]. Gener y, all are iron-based, with 12 to 30 percent chromium, 0 to 22 percent nickel, and minor amounts of carbon, niobium (columbium), copper, molybdenum, selenium, tantalum, and titanium. These alloys are veiy popular in the process industries. They are heat- and corrosion-resistant, noncontaminating, and easily fabricated into complex shapes. 

Urea complex with hydrogen peroxide (UHP) seems to be a very useful and convenient oxidation system in nonaqueous medium. The UHP reaction proceeds in methanol and is catalyzed by Mo (VI), W (VI) salts, or SeC>2 (83). Catalytic oxidation in a water-free medium can be carried out with alkylhydroxyperoxides, the catalysts being titanium alkoxides (84) or selenium compounds (85). The reaction appears to proceed quickly and with good selectivity. 

The synthesis of the mixed sulfur-selenium donor BEDS-TTF (BEST) via the tetralithiation of TTF was mentioned above [53]. Bis(ethylenedithio) tetraselenafulvalene (BEDT-TSF, BETS) is obtained in good yield following the sequence outlined in Scheme 14. The synthesis makes use of a titanium-cyclopentadiene complex to stabilize a problematic, unstable synthetic intermediate (35) [7]. 

The homoleptic, bis(trispyrazolylborate)titanium(ll) complex, Tp2Ti (Tp = trispyrazolylborate 203), has been prepared by reaction of 2 equiv. of KTp with TiCl2(TMEDA) (TMEDA = Ar,Ar,Ar, A -tetrarncthylcthylcncdiarninc).122 The dark red, paramagnetic compound has idealized /)v/ symmetry in the solid state and is easily oxidized to the corresponding Ti(m) derivative both electrochemically and chemically with AgPF, 204. Two-electron oxidation to Ti(rv) chalcogenido complexes has been accomplished with pyridine-N-oxide as well as with elemental sulfur and selenium (205, Scheme 31). 

The classical route to many l,3-dichalcogenole-2-thiones starts from a vicinal dihalogenoethene followed by lithiation and reaction with selenium the intermediate diselenate may be isolated as a titanium-biscyclopentadienyl complex (137) as shown in the example in Scheme 31 <93CL1851>. 

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