The 12-Ethynylmonocarba-<i>closo</i>-dodecaborate Anion: A Ligand for Metal Alkynide Complexes (M = Li, Na, Ca, Zn)

We report the first isolation of metal alkynide complexes (<b>2a</b>-<b>d</b>) incorporating lithium, sodium, calcium and zinc based on the monocarborane <i>endo</i>/<i>exo</i>-dianionic framework [CB₁₁H₁₁-12-C≡C]^2-. These complexes are synthesized via the deprotonation of terminal alkynes and optimized using lithium, sodium, calcium, and zinc hexamethyldisilazide bases to achieve enhanced yields and crystal stability. X-ray crystallography and NMR spectroscopy reveal unique coordination geometries, including a rare chair-shaped Li₄C₂O₂ unit in <b>2a</b>, multinuclear units in <b>2b</b>-<b>c</b>, and a hexagonal Zn₃C₃ unit in <b>2d</b>. Subsequent nucleophilic reactions with benzophenone afford propargylic alcohols (<b>3</b>) with high efficiency, demonstrating their utility in selective synthetic routes for complex molecular assembly. This work not only highlights the reactivity of alkali and alkaline-earth metals in monocarborane metal acetylides but also offers valuable insights into their structural characteristics and potential applications in advanced materials and catalytic systems.