Acid−Base Reactions of Methylnickel Hydroxo, Alkoxo, and Amide Complexes with Carbon Acids. Studies on the Reactivity of Noncyclic Nickel Enolates

Basic organonickel hydroxo, alkoxo, or amido complexes of composition Ni(Me)(X)(dippe) (X =
OH, t-BuO, cyclo-NC4H8; dippe = i-Pr2PCH2CH2Pi-Pr2) react with enolizable ketones, esters, and nitriles,
producing the corresponding enolate complexes. In the case of the hydroxo and alkoxo complexes, these
reactions may lead to equilibrium mixtures, allowing a comparison of their respective basicities, while
the amido compound reacts clean and quantitatively in all cases, allowing the isolation of the corresponding
enolates. While the ketone derivatives display oxygen-bound enolate ligands, the ester and nitrile enolates
bind the metal center through the carbon atom. The acetophenone enolate complex has strong nucleophilic
properties and rapidly reacts with aldehydes (PhCHO) or CO2, affording the corresponding aldolate and
carboxylate addition products.