Di-isopropoxide

To prepare hexaaluminates for ceramic applications a slightly different sol-gel process was proposed by Debsikbar.19 Ba-hexaaluminates were prepared via hydrolysis of Al di(isopropoxide) acetoacetic ester chelate and anhydrous Ba acetate obtained by reaction between BaC03 and glacial acetic acid. The substitution of Al(i-OC3H7)3 with the alkoxy ester was intended to control the chemical polymerization during gel formation. The reaction was performed in 1-butanol. The formation of the gel slowly occurred at room temperature in about 10 h. To obtain the final phase the gel precursor was dried at 70 °C for about 2 weeks, ground and calcined at 1200°C for 2 h. However no data on the morphology of the final materials were reported by the author. 

A similar study was made on various titanium compounds. It was found that titanium dichloride diacetate and titanium dichloride di-isopropoxide produced high amounts of crystalline polyvinylisobutylether. On the other hand, the more acidic titanium tetrachloride produced more amorphous polymers. The insoluble titanium trichloride and titanium dichloride were ineffective as polymerization catalysts. The less acidic tetraisopropyltitanate and diethyltitanium dichloride were completely ineffective as catalysts. 

Diols, chiral s.a. dichlorotitanium di-isopropoxide/diols, chiral under Titanium (IV) alkoxides, halogeno-... 

The catalysts are best prepared in situ by mixing a half-equivalent of the di-chloro-metal aromatic dimer with an equivalent of the ligand in a suitable solvent such as acetonitrile, dichloromethane or isopropanol. A base is used to remove the hydrochloric acid formed (Fig. 35.3). If 1 equiv. of base is used, the inactive pre-catalyst is prepared, and further addition of base activates the catalyst to the 16-electron species. In the IPA system the base is conveniently aqueous sodium hydroxide or sodium isopropoxide in isopropanol, whereas in the TEAF system, triethylamine activates the catalyst. In practice, since the amount of catalyst is tiny, any residual acid in the solvent can neutralize the added base, so a small excess is often used. To prevent the active 16-electron species sitting around, the catalyst is often activated in the presence of the hydrogen donor. The amount of catalyst required for a transformation depends on the desired reaction rate. Typically, it is desirable to achieve complete conversion of the substrate within several hours, and to this extent the catalyst is often used at 0.1 mol.% (with SCR 1000 1). Some substrate-catalyst combinations are less active, requiring more catalyst (e.g., up to 1 mol.% SCR 100 1), in other reactions catalyst TONs of 10000 (SCR 10000 1) have been realized. 

As indicated in Scheme 3-13, replacing the isopropoxide counterions with less basic oxyanions, namely, commercially available 3,5-di-/< r/-butylsalicylic acid, will lead to new catalyst 30, which shows very good results for the asymmetric aldol addition of alkyl acetate to ketene acetals (Scheme 3-13). 

A variety of other anionic initiators promote the polymerization of thio-carbonyl fluoride. Among them are aluminum isopropoxide, di(hydrogenated tal-low)dimethylammonium methoxide and chloride, N-nitrosodimethylamine, diisopropylamine, and triethylamine (59). Combinations of either [(C6H 5)3 P] 3RhCl or... 

Lutetium(III) isopropoxide, 311 Methylaluminum bis(2,6-di-/-butyl-4-methylphenoxide), 203 Methylaluminum bis(2,4,6-tri-t-butyl-phenoxide), 203... 

The living ROP of e-CL is usually initiated by aluminum isopropoxide, [Al(0 Pr)3] in toluene at 0-25 °C. Under these conditions this initiator exists as an aggregate of trimers and tetramers. However, freshly distilled Al(0 Pr)3 consists mainly of trimers, and is a more reactive initiator for ROP. The initiation rate is high compared to the rate of propagation so that a narrow molecular weight distribution is obtained in the polymer. There is no termination reaction and 3 chains grow per Al atom. Block polymers have been prepared by sequential polymerization of e-CL (monomer A) and DXO (monomer B) using Al(0 Pr)3 as an initiator in THF at 0 °C to yield AB or BA di-block copolymers [95]. 

The A-B di-block copolymer of -CL and oxepan-2,7-dione has been synthesized using aluminum isopropoxide as initiator [114] (Scheme 16). In order to prepare the ABA tri-block copolymer, a difunctional initiator [Et2AlO(CH2)4OAlEt2] was used to polymerize B followed by the addition of monomer A. However, the rate of polymerization was lower than in the Al(0 Pr)3-initiated system. Increasing the temperature to 70 °C increased the rate but a broadening of MWD was observed due to intramolecular back-biting reactions and intermolecular transesterification reactions. The addition of 1 equiv. of pyridine with respect to Al increased the polymerization rate and reduced the MWD from 1.95 to 1.25 [95]. 

Oxetane, a four-membered cyclic ether, is highly susceptible to cationic polymerisation [83]. However, this monomer also undergoes coordination polymerisation in the presence of catalysts such as zinc dimethoxide [84], triethylaluminium water acetylacetone [85-87], aluminium isopropoxide zinc chloride and di-ethylzinc water [87,88], as well as tetraphenylporphinatoaluminium chloride methylaluminium di(2,6-di-/-butyl-4-methylphcnoxidc) [89]. Studies of the microstructure of the polymer derived from the polymerisation of 2-methylox-etane with the triethylaluminium-water-acetylacetone (2 1 2) catalyst showed that the polyether obtained consisted of regioregular monomer unit sequences, fairly rich in isotactic triads [87] ... 

Epoxy alcohols. A few years ago Mihelich1 was granted a patent for preparation of epoxy alcohols by photooxygenation of alkenes in the presence of titanium or vanadium catalysts. Adam et al.2 have investigated this reaction in detail and find that Ti(IV) isopropoxide is the catalyst of choice for epoxidation of di-, tri-, and tetrasubstituted alkenes, acyclic and cyclic, to provide epoxy alcohols. When applied to allylic alcohols, the reaction can be diastereo- and enantioselective. The reaction actually proceeds in two steps an ene reaction to provide an allylic hydroperoxide followed by intramolecular transfer of oxygen catalyzed by Ti(0-i-Pr)4. The latter step is a form of Sharpless epoxidation and can be highly stereoselective. 

Preliminary results for asymmetric epoxidations of ( )-cinnamyl alcohol and geraniol using (15,25)-l,2-di(2-methoxyphenyl)ethane-l,2-diol or (15,25)-l,2-di(4-methoxyphenyl)ethane-l,2-diol as chiral auxiliaries with titanium(IV) isopropoxide and TBHP have been described. High enantioselectivity (95% ee) is observed when the 2-methoxyphenyl compound is used, while somewhat lower enantioselectivity (64% ee) and opposite face selectivity is described for the catalyst comprised of the 4-methoxyphenyl analog.Further elaboration of the scope and generality of these observations will be of interest. 

In general, the yields in aluminum isopropoxide reductions range from 80 to 100%. With a few low-boiling ketones difficulty may be experienced in separating the resulting alcohol from isopropyl alcohol thus the yields of reduction products from diethyl ketone and methoxyacetone are reported to be 60% and 40%, respectively. Di-n-propyl ketone, on the other hand, gives a 92% yield of the carbinol. As would be expected, side reactions are more significant and the yields are consequently lower when extremely sensitive compounds, such as unsaturated aldehydes and the carotenoids, are reduced. 

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