Reactions of α-Diimine-Stabilized Zn–Zn-Bonded Compounds with Phenylacetylene

Treatment of the Zn–Zn-bonded compounds [L^2–Zn–ZnL^2–]·[M­(THF)₂]₂ (1a, M = Na; 1b, M = K; L = [(2,6-iPr₂C₆H₃)­NC­(Me)]₂), which contain doubly reduced α-diimine ligands, with 15-crown-5 and 18-crown-6 led to the ion-separated compounds [L^2–Zn–ZnL^2–]·[Na­(15-crown-5)­(THF)₂]₂ (2a), [L^2–Zn–ZnL^2–]·[K­(15-crown-5)₂]₂·4THF (2b), and [L^2–Zn–ZnL^2–]·[K­(18-crown-6)­(THF)₂]₂·2THF (2c). In the products, the alkali metal ions originally bound by the ligands have been captured by the crown ethers. The Zn–Zn bond distances in 2a, 2b, and 2c are longer than those in the corresponding parent compounds 1a and 1b and in an analogous compound, [L^–Zn–ZnL^–] (3), bearing the monoanionic α-diimine ligands. Theoretical computations suggested that the Zn–Zn bonds in 2a–c are less stable than those in 1a and 1b. Reactions of [L^–Zn–ZnL^–] (3) with different amounts of PhCCH afforded the dimeric product [L^–Zn­(μ-CCPh)]₂ (4) and the monomeric [L⁰Zn­(CCPh)₂]·2THF (5), respectively, while the reaction of the crown ether-containing compound 2b with PhCCH gave a homoleptic zinc alkynide, [Zn­(CCPh)₄]·[K­(15-crown-5)₂]₂·THF (6).