Magnesium alkoxides, synthesis

Synthesis of the third-generation catalyst is an intricate process. Two crucial steps are (1) Precipitation of the supported catalyst from a solution of Mg2+ ion in organic solvent by the addition of TiCl4. (2) Catalyst activation by heat treatment with TiCl4 and phthalate esters (third component). The precursors for the support could be magnesium alkoxides, carboxylates, sulhte, or sulfinates. They all give particles of different but well-defined morphologies. 

Intramolecular aUol condensation. In a synthesis of a precursor to epiallogibberic acid, House et al. effected an unfavorable intramolecular aldol condensation by use of a covalent magnesium alkoxide intermediate. Thus treatment of (1) with 2eq. of... 

The strategy of metal alkoxides synthesis is entirely related to the electronegativity of the element concerned. Some electropositive metals, such as alkali metals, alkaline earth metals, and lanthanides, react directly with alcohols. But some less electropositive metals such as magnesium and aluminum require a catalyst (I or HgCy for successful reaction with alcohols. Use of electrochemical synthesis by anodic dissolution of some metals or metalloids (Sc, Y, Ti, Zr, Nb, Ta, Fe, Co, Ni, Cu, Pb, Si, Ge, etc.) in dry alcohol performs a promising procedure because it does not produce any by-products except hydrogen gas. Another applicable method for the synthesis of some alkoxides (B, Si, Ti, Zr, Hf, Nb, Ta, Fe, etc.) is the reaction of their chlorides with alcohols which require a base such as... 

Scheme 26.9 Cooperative effect of magnesium alkoxides in the synthesis of y-lactams catalyzed by NHCs.

Turowa N.Ya., Popovkin B.A., Nowoselowa A.V. Physicochanical studies of magnesium and alkaline earth alcoholates, Z. Anorg. Allg. Chem. 1969 365 100 Vaartstra B.A., Huffman J.C., Streib W.E., Caulton K.G. Incorporation of barium for the synthesis of heterometalhc alkoxides synthesis and structures of [BaZr2(0-MO-Pr)io]2 and Ba Zr2(O-M0-Pr)9 2- Inorg. Chem. 1991 30 3068... 

Cyclopentadienyl compounds of lithium, sodium, potassium, magnesium and thallium are most commonly used. The synthesis of these cyclopentadienyl-transfer agents is described in more detail in Section II.B.2. Organosilicon halides and alkoxides are the most convenient substrates. The synthesis of side-chain functionalized cyclopentadienyl silanes is described in equation 541,42 as a typical example of this strategy. 

In general, terminal alkenes having a hydroxy group in a proximate position show somewhat improved yields as compared to simple 1-alkenes. This likely arises from the stabilization of the intermediate magnesium species by intramolecular coordination with the alkoxide group as depicted in eq. (3.20), preventing the above unfavourable side reaction. Equation (3.20) demonstrates a synthesis... 

For the preparation of double salts and alkoxides, the most popular method involves dissolving the two alkoxides in a mutual solvent, mixing the solutions, and refluxing at elevated temperatures (eg, refluxing an aluminium sec-butoxide and magnesium methoxide in alcohol at 600 K). One can also prepare a double alkoxide by refluxing the oxide of the first element with the alkoxide of the second element in alcohol. Bradley and co-workers (16) provided an excellent summary of available double alkoxides and techniques used in their synthesis. 

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