Aluminum organoaluminums

Organoaluminum Compounds. Apphcation of aluminum compounds in organic chemistry came of age in the 1950s when the direct synthesis of trialkylalurninum compounds, particularly triethylalurninum and triisobutylalurninum from metallic aluminum, hydrogen, and the olefins ethylene and isobutylene, made available economic organoalurninum raw materials for a wide variety of chemical reactions (see a-BONDED alkyls and aryls). 

Tlie amphoteric behavior of aluminum hydroxide, wliich dissolves readily in strong acids and bases, is shown in Figure 4. In the pH range of 4 to 9, a small change in pH towards the neutral value causes rapid and voluminous precipitation of colloidal hydroxide wliich readily fomis a gel. Gels are also fomied by the hydrolysis of organoaluminum compounds such as aluminum alkoxides (see Alkoxides, metal). 

Prepa.ra.tlon, There are several methods described in the Hterature using various cobalt catalysts to prepare syndiotactic polybutadiene (29—41). Many of these methods have been experimentally verified others, for example, soluble organoaluminum compounds with cobalt compounds, are difficult to reproduce (30). A cobalt compound coupled with triphenylphosphine aluminum alkyls water complex was reported byJapan Synthetic Rubber Co., Ltd. (fSR) to give a low melting point (T = 75-90° C), low crystallinity (20—30%) syndiotactic polybutadiene (32). This polymer is commercially available. 

Propargylic alcohols are reduced by reaction with lithium aluminum hydride and subsequent hydrolysis to ( J-allylic alcohols via an organoaluminum intermediate (A) as shown below ... 

Reactions of enamines with aluminum hydrogen dichloride (540,541) (UAIH4 and AICI3) or aluminum hydrogen dialkyl compounds (542) led to organoaluminum intermediates which could be hydrolyzed to tertiary amines or oxidized to aminoalcohols. The formation of olefins by elimination of the tertiary amine group has also been noted in these reactions. 

Group 14 metal halides also undergo metathesis reactions. For instance, organotin compounds are prepared on an industrial scale using organoaluminum reagents. These reactions take place because tin is a softer Lewis acid than aluminum, and carbon (in an alkyl group, represented by R) is a softer Lewis base than chlorine ... 

Because of the polarity of the carbon-aluminum bond, organoaluminum compounds are valuable intermediates in organic synthesis, which exhibit higher reac-... 

Several modifications have been made to organoaluminum-based catalysts. Methylaluminum bis(2,6-di-tert-butyl-4-alkylphenoxide) (MAD) shows high diastereofacial selectivity in carbonyl alkylation (Scheme 72).31 11 Aluminum tris(2,6-diphenylphenoxide) (ATPH) has been developed as a catalyst for conjugate addition reactions. Since a carbonyl group is stabilized by steric effect of ATPH, the 1,4-adduct is obtained selectively.312... 

The best cocatalysts are those derived from organoaluminum or organo-aluminum chlorides. Certain organometallic complexes, e.g., RMgBr... 

Organoaluminum cluster compounds and compounds with low-valent aluminum 3,4,10 Hydrolysis of organoaluminum compounds 11... 

The chiral trialkylaluminum reagent used in the majority of asymmetric reduction studies is (+ )-tris[(S)-2-methylbutyl]aluminum (119) or its etherates. This reagent is readily prepared from (S)-( + )-2-methyl-l-chlorobutane (152,153). Results of the reductions of prochiral ketones with these reagents and other chiral organoaluminum reagents are shown in Table 15. 

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