Organoaluminum compounds with halogens

In order to get reliable information about the yield of organoaluminum compounds formed in a transition metal-catalyzed hydroalumination reaction it is essential to derivatize the organometallic products by quenching the reaction mixture with electrophiles like D2O, O2 or halogens. It is often observed that hydrogenation... 

Suitable electron donators for organoalanes are amines (especially tertiary amines), ethers, or anions such as, for example, hydride, alkyl, alkoxy, or halogen. When organoaluminum compounds combine with these electron donors, compounds of tetravalent aluminum are formed. Stable anions with higher coordination numbers, i.e., analogs of [AlFe]3-, have not been observed so far among organoaluminum compounds. 

A large number of different types of organoaluminum compounds, either difficult or impossible to prepare by the usual methods, may be made by alkyl exchange with the more readily prepared organoboron compounds. In addition to trialkyl alanes (133) it is possible to obtain in this way cyclopropylalanes (28), halogenated alkyl alanes (27), and various organoaluminum heterocycles (135, 1S6), e.g.,... 

Organoaluminum compounds are sufficiently Lewis acidic to interact with weak Lewis bases such as alkyl halides, although stable and thoroughly characterized examples are few. Instead, many trialkylaluminum compounds react violently with halogenated solvents. The adduct MeaSiF-AlEta, with weak F- -Al donation, has been characterized by NMR spectroscopy and this adduct is thermally stable to 30 °C. Structurally characterized examples of aryl halides forming dative bonds to aluminum have been reported for cationic organoaluminum complexes as will be discussed later. 

Products from reactions of trivalent alkoxy chlorides of transition metals with certain halogen-fi-ee organoaluminum compounds, e.g., triisobutylaluminum. Such catalysts are used without any support. 

Partial hydrolysis of organoaluminum compounds, e.g., AlEt3 or AIBu 3, with water (solvent toluene, 0°C) produces an active catalyst for the polymerization of p-pinene at room temperature (halogen-free conditions). Products are hard poly(p-pinene) resins with a softening point of >100°C [89]. 

Isobutene can be copolymerized with numerous unsaturated compounds via a cationic route [577-586], Table 30 lists various comonomers and copolymerization parameters. The isobutene portion in the copolymers usually exceeds 90%. The use of aluminum organic compounds (e.g., AlEt2Cl) as opposed to aluminum trichloride permits better control of the copolymerization, as they are weaker Lewis acids. Hydrogen chloride or halogens must be added as cocatalysts that are capable of regenerating the carbocations. The organoaluminum catalysts are produced at —78 °C with boron trifluoride. 

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