Cyclogallanes and metalloaromaticity, synthesis and molecular structure of dipotassium tris((2,6-dimesityphenyl)cyclogallene), K-2[(Mes(2)C(6)H(3))Ga](3) (Mes=2,4,6-Me(3)C(6)H(2)): A structural and theoretical examination

The cyclogallane dipotassium tris((2,6-dimesitylphenyl)cyclogallene), K-2[(Mes(2)C(6)H(3))Ga](3) (Mes=2,4,6-Me(3)C(6)H(2)), has been prepared by either of two distinct synthetic routes. Dispropartionation of gallium(II) chloride, Ga2Cl4, in the presence of (2,6-dimesitylphenyl)lithium, (Mes(2)C(6)H(3))Li, followed by potassium metal reduction in Et(2)O affords the title compound as large ruby red crystals. Alternatively, K-2[(Mes(2)C(6)H(3))Ga](3) may readily be approached by direct alkali metal reduction of(Mes(2)C(6)H(3))GaCl2. The title compound was characterized by H-1 and C-13 NMR, elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction. The cyclogallane resides about the planar Ga-3 triangle constituted by extremely short Ga-Ga bonds: 2.4260(5), 2.4317(5), and 2.4187(5) Angstrom. Theoretical examination of the Ga-3(2-) anionic core in [GaH](2-)(3), Na-2[GaH](3), and K-2[GaH](3) suggests a well-defined pi-molecular orbital. Both experimental and theoretical results strongly support the cyclogallene dianion, [(Mes(2)C(6)H(3))Ga](2-)(3), as a well-defined metalloaromatic system-a metallic ring system exhibiting aromatic behavior.