π-Electron−Cesium Interactions in Cesium Triorganofluorometalates

The reaction of MMes3 (M = Ga, In; Mes = 2,4,6-Me3C6H2) with CsF in acetonitrile yields the trimesitylfluorometalates [{Cs(MeCN)2}{Mes3MF}]2·2MeCN ([1]2·6MeCN, M = Ga; [2]2· 6MeCN, M = In). Ga(CH2Ph)3 gives with CsF under the same conditions the salt [Cs{(PhCH2)3GaF}]2·2MeCN ([3]2·2MeCN). The treatment of 1 equiv CsF with 2 equiv of GaMes3 does not lead to Cs[Mes3GaFGaMes3] but to [1]2·6MeCN and the adduct [Mes3Ga(MeCN)] (4). [1]2·6MeCN−4 have been characterized by NMR, IR, and MS techniques as well as by X-ray analyses. [1]2·6MeCN and [2]2·6MeCN are solvated ion pairs in acetonitrile, while [3]2·2MeCN shows a monomer−dimer equilibrium. According to the X-ray structure determinations, [1]2·6MeCN and [2]2·6MeCN are isostructural and contain Cs−F four-membered rings. The fluorine centers at the rings are bound to the metallane groups. Each cesium cation is coordinated by two molecules of acetonitrile and by one mesityl group in a η3-fashion. The basic structural feature of [3]2·2MeCN is also a Cs−F four-mem...