Organometallic chemistry of Ga⁺: Formation of an unusual gallium dimer in the coordination sphere of ruthenium

New insights into the distinct organometallic chemistry of the Ga ⁺ ion are presented. Ga⁺ reacts as a strong electrophile with the electron rich ligand trismethylene-methane (C(CH₂) ₃^2-) attached at Ru by insertion into a Ru-C bond. The resulting "gallamethylallyl" ligand behaves like strong nucleophile similar to known monovalent GaR species. This donor property leads to the dimeric structure of the product [ (Ru(GaCp*)₃- [η³-(CH₂)₂C{CH₂(μ-Ga)}]} ₂][(BAr^F)₂] (4) (Cp* = C ₅Me₅, [BAr^F] = [B{C₆H ₃-(CF₃)₂}₄]). Very unexpectedly, the two gallium ligands in this dimer are found in close vicinity to each other with a distance in the range of Ga-Ga bonds. Indeed, AIM calculations confirm a weak attractive closed shell Ga-Ga interaction. Finally, a novel example of a complex with substituent-free Ga⁺ as a ligand was found in the compound [Ru(PCy₃)₂(GaCp*)₂(Ga)][BAr ^F] (6) (Cy = C₆H₁₁, cyclohexyl), the very short Ru-Ga bond length confirming the assumption that Ga⁺ represents a pure σ/π-accepting ligand in this case.