PREPARATION OF ORGANOALUMINUM COMPOUNDS BY HYDROZIRCONATION-TRANSMETALATION

Organozirconium(IV) complexes produced by hydrozirconation of olefins or acetylenes with Cp2Zr(H)Cl (Cp = η5-C5H5) are precursors of organoaluminum compounds. By stoichiometric transmetalation, the η1 organic ligand can be transferred stereospecifically from zirconium to aluminum by treatment with aluminum halides. Organoaluminum dichlorides can act as mild alkylating agents; they are precursors of ketones through acylation with acid chlorides (this acylation has been found to proceed well for primary, saturated alkyl- and alkenylaluminum dichlorides). Transmetalation from Zr to A1 occurs faster for vinylic substituents than for alkyl ones and proceeds predominantly with retention of configuration at carbon. A mechanism for transmetalation is postulated in which the transition state (or intermediate) involves a transition metal-main group metal complex containing a bridging alkyl (or vinylic) group. This mechanism is analogous to the one reported for electrophilic cleavage of alkylzirconium complexes. Acylaluminum dichlorides have been formed by transmetalation between Cp2Zr(Cl)(acyl) and aluminum chloride. They have been shown to be reactive toward electrophiles at both the carbon and the oxygen of the acyl group. Treatment of an acylaluminum dichloride with D20 results in an aldehyde which is at least 83% -C(O)-D. However, treatment with acetyl chloride gives an a-chloroalkyl acetate as the major product (attack at O) and an a-diketone as a minor product (attack at C). Copyright © 1979, American Chemical Society. All rights reserved.