Synthesis and structures of bimetallic (Mg/K) acetylide complexes from terminal alkynes and an Mg–Mg-bonded compound

The reactions of α-diimine-ligated dimagnesium(I) compound [K(THF)₃]₂[LMg−MgL] (1, L = [(2,6-iPr₂C₆H₃)NC(Me)]₂²⁻) and terminal alkynes afford bimetallic (Mg/K) acetylide complexes (2–10). The reactions proceed via reductive dehydrogenation of the alkynes with release of H₂, while the original Mg(I) center is oxidized to Mg(II). In the complexes, Mg atom is σ-coordinated either by one (2 and 3), two (4–9) or four (10) RC[tbnd]C⁻ moieties. The (solvated) K atoms, on the other hand, are π-coordinated by the C[tbnd]C triple bonds and form extensive interactions with the NCCN backbone and aryl rings of the ligand and alkyl substituents of the alkyne. Interestingly, the versatile bonding modes of potassium ions result in three distinct aggregates of the complexes in the solid state, the monomer (2–7), dimer (8, 9), and polymer (10), where the latter two cases benefit from the “intermolecular” interactions of K⁺ ions with the ligands or acetylides.