Organoaluminums transmetallation

Organoaluminum compounds, particularly AlEt3, are commercially very important as activators for olefin polymerization catalysts and are produced on a large scale, in spite of their pyrophoric nature and violent reaction with water. In the laboratory organoaluminum compounds can be made from mercury alkyls by transmetallation ... 

Mi) Supplementary References. The transmetallation reactions of organolithiums and organoaluminums are extensively reviewed. The preparation of organotransitiop-metal compounds via transmetallation is discussed in various monographs dealing with Ti, Zr and Hf Cr Ni Pd and Pt. The preparation of organoactinide compounds via transmetallation is discussed in reviews . ... 

For aliphatic R3AI, transmetallation is useful in the synthesis of optically active organoaluminums, Mild conditions are required to prevent racemization (see 5.3.3.5.3) ° ... 

Heterocyclic organoaluminums are prepared by the transmetallation of the corresponding boron compounds , e.g. for the 3-methyl-l-ethyl-l-aluminaindane ... 

Transmetalation. Carr and Schwartz have found that an organic group bound to zirconium can be transferred to aluminum. Thus reaction of 1, obtained by hydrozirconation of alkenes or alkynes, with AlCln results in a color change from bright yellow to orange as an organoaluminum dichloride is formed. On addition of an acid chloride, a ketone (2) is formed rapidly. This new ketone synthesis proceeds in high yield from alkyl- and alkenylaluminum dichlorides. 

In addition to organoaluminum compounds, organoboron compounds can also be used as Lewis-acid accelerators for the polymerization of 21 initiated with la, where triphe-nylboron and tris(perfluorophenyl)boron are effective accelerators (See Table 6). Tributylboron (Bu B) bearing no particular steric hindrance neither terminates nor accelerates the polymerization of 21, indicating a low transmetalation activity and a rather poor Lewis acidity of Bu B. This is in sharp contrast with the polymerization upon addition of trimethylaluminum (Me Al) as a monomer activator where the chain growth is terminated by the transfer of the enolate moiety from 32 to Me Al, unless the temperature is lowered to —40°C or below. 

Organoaluminum sonochemistry is not yet well developed despite the synthetic and economic interest. Aluminum, a ductile metal, is easily activated by sonication, as evidenced by the use of foils to determine the energy of cleaning baths. Alkyl halides react with aluminum at room temperature in THF to give the sesquihalide, reduced to the trialkyl compound in the presence of magnesium. Examples are known with bromomethane or -ethane.1 2,183 reaction occurs with stirring under similar conditions. Triethylaluminum was used in sonochemical transmetallation reactions leading to zinc and boron alkyls (Eq. 38). 

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