Titanium alkoxides preparation

Firstly, we examined the asymmetric hydrocyanation of 3-phenylpropanal. When 3-phenylpropanal was treated with cyanotrimethylsilane using the chiral titanium alkoxide prepared from dichlorodiisopropoxytitanium and the chiral 1,4-diol 17b in toluene at room temperature, only a trace amount of the... 

Section 1.1.3.3 Formation of 1-vinyl-2-alkylcyclohexanes from 1,7-dienes. Narasaka demonstrated that the chiral titanium alkoxide prepared from TiCl2(OPr )2 and (213) catalyzes the asynunetric intramolecular ene reaction of oxazolidinone (212) in Freon 113 at 0 °C to give 63% of ene adduct (214) in >98% enantiomeric excess and 25% of the hetero Diels-Alder adduct. ... 

Various triakylaluminum reagents can be obtained on an industrial scale. However, their utilization in asymmetric alkylation is limited, for example, an enantioselective allylation of aldehydes by allyldialkylaluminum [53]. Recently, Chan et al. reported the first example of a catalytic alkylation of aldehyde using triethylaluminum [54]. Asymmetric ethylations of various aromatic aldehydes proceed in very high yields and ees in the presence of a chiral titanium alkoxide prepared from Ti(0-f-Pr)4 and chiral 5,5, 6,6, 7,7, 8,8 -octahydro-l,T-bi-2-naph-thol (Hg-BINOL) (Scheme 19). It is noteworthy that Hg-BINOL is a more efficient chiral catalyst than BINOL. High enantioselectivity can be attained only in the... 

Williams P.A, Jones A.C., Bickley J.F., Steiner A., Davies H.O., Leedham T.J., Impey SA., Garcia J., Allen S., Rougier A., Blyr A. Synthesis and crystal structures ofdimethylaminoethanol adducts of Ni(ll) acetate and Ni(II) acetylacetonate. Precursors for the sol-gel deposition of electrochromic nickel oxide thin films, J. Mater. Chem. 2001, 11 2329 Yanovskaya M.L, Kotova N.M., Golubko N.V., Turova N.Ya. Reactions of magnesium and titanium alkoxides. Preparation and characterization of alkoxy-derived magnesium titanate powders and ceramics, J. Sol-Gel Sci. Tech. 1998 11 23... 

Golubko, N.V., and Turova, N.Y. (1998) Reactions of magnesium and titanium alkoxides. Preparation and characterization of alkoxy-derived magnesium titanate powders and ceramics./. Sol-Gel Sci Technol., 11,... 

In 1995, Sato and co-workers reported that low-valent titanium alkoxide prepared from Ti(0 -Pr)4 and f-PrMgCl (1 2) can readily incorporate alkynes to give a titanacyclopropene complex, hydrolysis of which then leads to Z-alkenes with high efficiency and excellent stereoselectivity (Fig. 13) [35]. 

PZN-PT, and YBa2Cug02 g. For the preparation of PZT thin films, the most frequently used precursors have been lead acetate and 2irconium and titanium alkoxides, especially the propoxides. Short-chain alcohols, such as methanol and propanol, have been used most often as solvents, although there have been several successful investigations of the preparation of PZT films from the methoxyethanol solvent system. The use of acetic acid as a solvent and chemical modifier has also been reported. Whereas PZT thin films with exceUent ferroelectric properties have been prepared by sol-gel deposition, there has been relatively Httle effort directed toward understanding solution chemistry effects on thin-film properties. 

Tridentate amido-amidinate ligands have also been constructed starting from (lR,2R)-diaminocyclohexane (cf. Section IV.D). Scheme 181 illustrates the use of such ligand in the preparation of novel amidinato-titanium alkoxide com-plexes. ... 

Allylic alcohols can be converted to epoxy-alcohols with tert-butylhydroperoxide on molecular sieves, or with peroxy acids. Epoxidation of allylic alcohols can also be done with high enantioselectivity. In the Sharpless asymmetric epoxidation,allylic alcohols are converted to optically active epoxides in better than 90% ee, by treatment with r-BuOOH, titanium tetraisopropoxide and optically active diethyl tartrate. The Ti(OCHMe2)4 and diethyl tartrate can be present in catalytic amounts (15-lOmol %) if molecular sieves are present. Polymer-supported catalysts have also been reported. Since both (-t-) and ( —) diethyl tartrate are readily available, and the reaction is stereospecific, either enantiomer of the product can be prepared. The method has been successful for a wide range of primary allylic alcohols, where the double bond is mono-, di-, tri-, and tetrasubstituted. This procedure, in which an optically active catalyst is used to induce asymmetry, has proved to be one of the most important methods of asymmetric synthesis, and has been used to prepare a large number of optically active natural products and other compounds. The mechanism of the Sharpless epoxidation is believed to involve attack on the substrate by a compound formed from the titanium alkoxide and the diethyl tartrate to produce a complex that also contains the substrate and the r-BuOOH. ... 

In some examples it is not necessary to prepare the organometallic-coupling agent R2MX2 beforehand. Thus coating glass fibres with a heptane or alcohol solution of titanium alkoxide promotes adhesion between the fibre and polymer, e.g., acrylic, polyolefins, polyester, polyamide and other thermoplastic resins. 

A combination of DAT and a metal alkoxide other than titanium alkoxide serves as a poor catalyst for the epoxidation of allylic alcohols. However, the combination of DAT and silica-supported tantalum alkoxides (2a) and (2b) prepared from Ta(=CHCMe3)(CH2Cme3)3 and silica(5oo) shows high enantioselectivity in the epoxidation of E-allylic alcohols, though chemical yields are not very great (Scheme 4).3... 

Titanium alkoxides are also effective and sought-after initiators for the ROP of lactides due to a low toxicity, which minimizes the problems linked to the presence of catalyst residues in commercial PLA products [18, 19]. Despite impressive advancements in the use of Lewis acidic metal initiators in the preparation of PLAs, surprisingly little attention has been paid to the group 4 metal (Ti, Zr, Hf) initiators, probably due to the highly oxophilic nature of M(1V) which has a natural tendency to form aUcoxy-bridged multinuclear complexes. Verkade and coworkers previously demonstrated a series of titanium aUcoxide complexes 118-122 (Fig. 17) that function as moderately efficient initiators in bulk homopolymeization of L-lactide and rac-lactide, some of these initiators displaying a well-controlled polymerization behavior [119]. 

Generation of an Acetylene-Titanium Alkoxide Complex, Preparation of (Z)-1,2-Dideuterio-1 -(trimethylsilyl)-l -hexene. 

The addition of a base, typically ammonia, to mixtures of transition metal halides and alcohols allows the synthesis of homoleptic alkoxides and phenoxides for a wide range of metals. Anhydrous ammonia was first used in the preparation of titanium alkoxides where the reaction is forced to completion by the precipitation of ammonium chloride.41 Although useful for the synthesis of simple alkoxides and phenoxides of Si, Ge, Ti, Zr, Hf, V, Nb, Ta and Fe, as well as a number of lanthanides,42-47 the method fails to produce pure /-butoxides of a number of metals.58 Presumably, secondary reactions between HC1 and Bu OH take place. However, mixing MC14(M = Ti, Zr) with the Bu OH in the presence of pyridine followed by addition of ammonia proves successful, giving excellent yields of the M(OBul)4 complexes.59... 

Chemical and physical vapor deposition technique has been widely applied for the preparation of such photocatalytic thin films. Since these vapor methods need an instrumental setup which enables control of temperature and pressure, their initial and running costs are generally high and the size of substrate is limited. Spray method, in which titanium alkoxide and water is sprayed on a substrate heated at a desired temperature, affords Ti02 thin films.69) However, like the sol-gel route, the physical properties and photocatalytic activity of Ti02 strongly depend on many factors such as temperature of substrate, flow rate of carrier gas, and partial pressure of starting material in the system. 

Modification by acetylacetone is a powerful route, that allows precursor solutions to be stabilized. Interaction of titanium alkoxides with acetylacetone was extensively studied and reviewed in [1391,86]. Study ofreactions, occurring on interaction of Zr(OPrn)4 and Ti-Zr alkoxide mixture with acetylacetone, was performed in [1448] and allowed the authors to simplify the technique for preparation of precursor solution for PZT films application and to overcome the requirement of prolonged refluxing, which certainly decreases reproducibility. After dissolution of titanium and zirconium alkoxides in methoxyethanol, acetylacetone is added to form stable zirconium and titanium stock solutions. The introduction of acetylacetone allowed aqueous lead acetate (and lanthanum acetate for PLZT films) solutions to be added to mixed titanium and zirconium solutions. No reaction steps involving elevated temperatures or distillation or long reaction times are required. The solution could be used both immediately on mixing or after storage for several months. Such solutions were successfully used for application of ferroelectric films. 

Most precursors used for titanium oxide preparation, especially for film production, are based on titanium alkoxides. A variety of mixed enolate-aUcoxide titanium complexes exist, such as 26a-f, 27, 28 and 29a-e, which are typical CVD precursors for titanium oxide. 

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