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 prepare d by either of two distinct synthetic routes. Dispropartionation of ga llium(II) chloride, Ga2Cl4, in the presence of (2,6-dimesitylphenyl)li thium, (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. Alternativ ely, K-2[(Mes(2)C(6)H(3))Ga](3) may readily be approached by direct al kali metal reduction of(Mes(2)C(6)H(3))GaCl2. The title compound was c haracterized 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 o f 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 a nd theoretical results strongly support the cyclogallene dianion, [(Me s(2)C(6)H(3))Ga](2-)(3), as a well-defined metalloaromatic system-a me tallic ring system exhibiting aromatic behavior.