Monomere versus dimere Dialkylaluminiumalkinide R2Al‐C≡C‐R′ – dreifach koordinierte Aluminiumatome gebunden an C≡C‐Dreifachbindungen

Monomeric versus Dimeric Dialkylaluminum Alkynides R2Al‐C≡C‐R′ – Tricoordinated Aluminum Atoms Attached to C≡C Triple Bonds Addition of lithium ethynides, Li‐C≡C‐R (R = C6H5, CMe3), to cooled solutions of the chloroalane Cl‐Al[CH(SiMe3)2]2 (1) afforded the corresponding dialkylaluminum alkynides. Caused by the effective steric shielding the products (2 and 3) are monomeric in solution and in the solid state. They possess coordinatively unsaturated, tricoordinated aluminum atoms attached to C≡C triple bonds and relatively short bonds between aluminum and the alkinyl carbon atoms (<191.4 pm). Owing to quantum‐chemical calculations an interaction between the empty p‐orbital at aluminum with the π‐system of the triple bond can clearly be excluded. The sterically less shielded di(tert‐butyl)aluminum chloride yielded the dimeric aluminumalkynide 4 upon treatment with lithium tert‐butylalkynide. Lithium‐trimethylsilylethynide, Li‐C≡C‐SiMe3, and 1 gave always the alanate Li[(Me3Si‐C≡C)2Al{CH(SiMe3)2}2] (5) independently of the stoichiometric ratio of the starting compounds.