METAL CATALYSIS IN ORGANIC-REACTIONS .7. ROLE OF NICKEL-COMPLEXES IN THE REACTION OF TRIISOBUTYLALUMINUM WITH TERMINAL ACETYLENES

The mechanism by which nickel(II) complexes catalyze the stoichiometric reaction between terminal aliphatic alkynes and triisobutylaluminum is discussed in the light of previous reports and new experimental findings. At room temperature (E)-2,4-dialkyl-1,3-butadiene along with 1,3,5-trialkyl- and 1,2,4-trialkylbenzenes are generally formed; the yields of the products were found to be dependent on the ligand originally present in the nickel complex. Deuteriolysis experiments have indicated clearly the occurrence of hydride nickel and nickelole species as reaction intermediates. On the basis of the results obtained, the proposed mechanism involves the formation of alkyl, hydride, and zerovalent nickel species, still containing, at least partially, the ligand. These catalytic species should give rise to the products through insertion and oxidative addition processes of the acetylenic substrate, followed by reductive elimination or alkyl exchange reactions with the excess organoaluminum compound. Copyright © 1979, American Chemical Society. All rights reserved.