Trialkyls of Aluminum

Triacetin. See under Acetins A31-R Triacetone Triperoxide. See under Acetone Peroxides A42-R Trialkyls of Aluminum A144-R... 

M, Roesky. H. W. Reactions of trialkyl phosphates with trialkyls of aluminum and gallium New route to alumino- and galtophos-phate compounds via dealkyIsilyfation. Organometallics 1999, 18, 523-52B. 

The /3-lactone dimer of dimethylketene can be prepared by pyrolysis of its polyester, which is formed by the base-catalyzed polymerization of dimethylketene.3"6 In addition to the rearrangement of the normal dimer described above,6 the direct dimerization of dimethylketene in the presence of aluminum chloride3 or trialkyl phosphites7 leads to the /3-lactone dimer. 

Snell et al, "Colorimetric Methods of Analysis," vol II A, Van Nostrand(1959), 156-87 Aluminum Alkyls were prepd in 1865 by tbe action of aluminum on mercury alkyls(Refs 1 6)(see also Note below). Later they were made by the action of "electron metal (alloy of Al and Mg) on a soln of the alkyl halide in ether (Refs 2 6). The Al trialkyls are volatile liquids, violently attacked by air or water. 

Among organoaluminum compounds, trialkyl derivatives of aluminum are of the most practical interest. These compounds can be obtained by several techniques. 

The reaction should be conducted in hydrocarbon rather than ether, since in ether it forms etherates of trialkyl(aryl)aluminum. 

Of the techniques mentioned above, direct synthesis seems the most promising. It is a convenient and economical technique for the industrial production of trialkyl derivatives of aluminum, because the raw stock is not so scarce. Besides, the reaction releases small amounts of by-products. 

Triisobutylaluminum is a colourless transparent liquid (the boiling point is 138 °C at 6.6 GPa), which dissolves well in hydrocarbons. When heated up to 140-160 °C in vacuum (the residual pressure is 35 GPa), triisobutylaluminum disintegrates into isobutene and diisobutylaluminum hydride. Unlike lower trialkyl derivatives of aluminum with the direct carbon chain (e.g. triethylaluminum), aluminumtrialkyls with a branched chain (triisobutylaluminum is one of them) are monomeric. 

Alkylaluminumchlorides can also be obtained by the reaction of aluminum chloride with corresponding trialkyl derivatives of aluminum. E.g., the interaction of triethylaluminum with aluminum chloride can yield both diethylaluminumchloride and ethylaluminumchloride ... 

Aluminum alkyls are stronger Lewis acids than the trialkyls of boron and galUum, and complex formation in the presence of Lewis bases is an important aspect of the reaction chemistry of organoaluminum compounds. The Lewis acidity of organoaluminum compounds accounts for the strong association of aluminum alkyls and hydrides by three-center two-electron bonds, as well as association of organoaluminum... 

Scheme 2 Proposed reaction scheme for hydrolysis of aluminum trialkyls...

CH3)3N A1H3 was first prepared by direct combination of trimethylamine and an ethereal solution of aluminum hydride. An alternate preparation employs lithium tet-rahydroaluminate and trimethylammonium chloride A Both methods have been used to prepare other trialkyl-amine-aluanes as well. The latter method is more convenient in that the starting materials are commercially available and the necessity of obtaining solutions of aluminum hydride in ether is avoided. It is important, however, that an excess of lithium tetrahydroaluminate be used in the reaction with the trialkylammonium chloride otherwise... 

Striking observations during the addition of aluminum trialkyls to the 1 1 complexes of the type M[R3A1-F] led to the discovery of the 1 2 complexes. Particularly remarkable is the great increase in the conductivity of the 1 1 complex melt or solution upon addition of nonconducting aluminum trialkyls [118, 135, 215, 217, 221]. 

An electrolyte containing less than two moles of aluminum trialkyl per mole MX is less useful for technical purposes because of a decrease in the specific conductivity and applicable current density and because of alkali metal codeposition. An aluminum trialkyl content in excess of two moles per mole of MX in toluene leads to deposition of coarser crystalline aluminum, dendritic growth [63, 130, 146], and reduced throwing power. Thus, these types of electrolytes are unsuitable for the deposition of uniform aliuninum layers on workpieces with complicated shapes. 

In 1954, Lehmkuhl in his dissertation discussed two alternative mechanisms for the cathodic deposition and anodic dissolution of aluminum from the new organo-aluminum electrolytes [118]. One possibility is the preliminary deposition of alkali metals as a result of electrolytic dissociation of the 1 2 complex, resulting in alkali metal cations, and subsequent chemical reaction of this alkali metal with free or coordinated aluminum trialkyl, yielding aluminum metal and alkali metal tetraalkyl aluminate (see Scheme 2). 

---