Redistribution reactions aluminum alkyls

The other commercially important routes to alkyltin chloride intermediates utilize an indirect method having a tetraalkjitin intermediate. Tetraalkyltins are made by transmetaHation of stannic chloride with a metal alkyl where the metal is typicaHy magnesium or aluminum. Subsequent redistribution reactions with additional stannic chloride yield the desired mixture of monoalkyl tin trichloride and dialkyltin dichloride. Both / -butjitin and / -octjitin intermediates are manufactured by one of these schemes. 

In addition to the redistributions discussed above which involve exchanges on aluminum atoms only, there is a great deal of literature available on the exchange reactions of aluminum alkyls with halides, oxides, and alkoxides of other elements which undoubtedly are also equilibrium reactions. These, however, have found great interest as methods for the syntheses of organometallic compounds in general 129, 130). It appears that the equilibria in these systems lie almost completely at the side of the alkyl compound of the other element. 

By-product ethylaluminum dichloride (EADC) is soluble in hexane, but is a poor cocatalyst. EADC must be removed (or converted to a more effective cocatalyst) before introduction of monomer. Eor example, ethylaluminum dichloride can be easily converted (as in eq 4.7) to diethylaluminum chloride by redistribution reaction with triethylaluminum (see reference 3 and literature cited therein for discussions of aluminum alkyl redistribution reactions). 

In the current approach to this problem, a choice was made to focus on polymers which were derived from diols. In part, diis decision was based on their potential to form not only linear, possibly soluble polymers, but also their known reactivity towardalkyl alanes. For example, it is well-known that the reaction products of an alcohol and an alkyl alane are an alkoxy alane and a hydrocarbon (eq. 1). Another reaction of importance to this chemistry is the redistribution reaction which can occur between an aluminum alkoxide and an alcohol (eq. 2). In the presence of large excesses of HOR, this reaction will proceed to the right, as written. 

The product undergoes a redistribution to produce R4A1C12 and R2A1C14. The reaction of aluminum with HgR2 results in transfer of alkyl groups,... 

The redistribution and cleavage reaction of mixtures of tetramethylgermane and tetrabutylgermane with excess of aluminum chloride give di- as well as trichlorogermanes having mixed alkyl groups. 

STEP 1 Formation of an electrophile. Reaction of a haloalkane (a Lewis base) with aluminum chloride (a Lewis acid) gives a molecular complex in which aluminum has a negative formal charge and the halogen of the haloalkane has a positive formal charge. Redistribution of electrons in this complex then gives an alkyl carbocation as part of an ion pair ... 

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