π-Electron−Cesium Interactions in Cesium Triorganofluorometalates

The reaction of MMes 3 (M = Ga, In; Mes = 2,4,6-Me 3 C 6 H 2 ) with CsF in acetonitrile yields the trimesitylfluorometalates [{Cs(MeCN) 2 }{Mes 3 MF}] 2 ·2MeCN ([ 1 ] 2 ·6MeCN, M = Ga; [ 2 ] 2 · 6MeCN, M = In). Ga(CH 2 Ph) 3 gives with CsF under the same conditions the salt [Cs{(PhCH 2 ) 3 GaF}] 2 ·2MeCN ([ 3 ] 2 ·2MeCN). The treatment of 1 equiv CsF with 2 equiv of GaMes 3 does not lead to Cs[Mes 3 GaFGaMes 3 ] but to [ 1 ] 2 ·6MeCN and the adduct [Mes 3 Ga(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 η 3 -fashion. The basic structural feature of [ 3 ] 2 ·2MeCN is also a Cs−F four-membered ring; however, the cations in [ 3 ] 2 ·2MeCN are surrounded by three phenyl groups of the benzyl substituents. The three η 6 -bound phenyl rings are contributed from two different metallane units. 4 possesses a distorted tetrahedral coordination sphere with a low pyramidalization of the Ga center (angular sum: 355°).