Aluminum sesquihalides

Aluminum sesquihalides " or even mixtures of metallic Al, alkyl halide and trialkoxy-borane, can also be used. Trialkoxyboroxines, from trialkoxyboranes and boron trioxide, are convenient boron substrates ... 

Modifications are possible -. Thus ethylaluminum sesquichloride can be converted quantitatively to Et2AlCl. Another advantage is the precipitation of finely divided and active Al metaU. This can again be utilized in the preparation of aluminum sesquihalides. 

Finally, cross-coupling reactions involving aluminum reagents have primarily been used for alkenyl transfers from the carbo- and hydroalumination products of terminal alkynes. A number of interesting results were published in recent years and will surely broaden the application of alanes and aluminum sesquihalides to these C,C-bond forming reactions. 

An obvious method to investigate the formation and the nature of the catalytically active nickel species is to study the nature of products formed in the reaction of complexes such as 3 or 4 with substrate olefins. This has been investigated in some detail in the case of the catalytic dimerization of cyclooctene to 1-cyclooctylcyclooctene (17) and dicy-clooctylidene (18) [Eq. (4)] using as catalyst 7r-allylnickel acetylacetonate (11) or 7r-allylnickel bromide (1) activated by ethylaluminum sesquihalide or aluminum bromide (4). In a typical experiment, 11 in chlorobenzene was activated with excess ethylaluminum sesquichloride cyclooctene was then added at 0°C and the catalytic reaction followed by removing... 

The catalyst for the reaction between PVC and the high cis-1,4-polybutadiene was a dialkylaluminum halide—e.g., Et2AlCl—or sesquihalide. The catalyst could be added from an external source or could be generated in situ—e.g., by the reaction of an aluminum alkyl with either titanium tetrachloride or a reactive organic halide such as benzyl chloride or tert-butyl chloride. The concentration of Et2AlCl was varied from 0.2-5% by weight based on PVC, although the preferred concentration was between 0.5 and 1.5 wt %. 

No reaction occurs when triethylaluminum, aluminum chloride, stannic chloride, titanium tetrachloride, diethylzinc or triethylboron are used in lieu of an organoaluminum halide or sesquihalide. 

A classic synthetic route to alkylaluminum halides is reaction of aluminum metal with alkyl halides. This procedure affords alkylaluminum sesquihalides, equimolar mixtures of dialkylalu-minum halides and alkylaluminum dihalides (Equation (5)). 

Alkyl derivatives of metals such as aluminum, boron and zinc are fairly active Friedel-Crafts catalysts. However, hyperconjugative effects result in a lowering of the electron deficiency. In the case of metal alkoxides this effect is even stronger, and, as a result, they are fairly weak Lewis acids. Metal alkyls, such as alkylaluminums, alkylaluminum halides and sesquihalides are also vital components of Ziegler-Natta catalyst systems which sometimes are utilized for Friedel-Crafts-type reactions. For example, alkylations of aromatics with alkenes in the presence of a Ziegler-Natta catalyst such as AIR3 -1- TiCU results in lower-chain alkylates. Even alkylaluminum halides and sesquihalides serve as Friedel-Crafts catalysts. 

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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