Novel 18-crown-6 organometallic rubidium and cesium complexes containing cyclopentadienyl, indenyl, pentamethylcyclopentadienyl, and fluorenyl as carbanions

The synthesis of base-free cyclopentadienyl-, indenyl-, pentamethylcyclopentadienyl-, and fluorenylrubidium and -cesium is described. Reactions of these compounds with the hexadentate Lewis base 18-crown-6 yielded new complexes of the type [MR(18-crown-6)] and [{RbFl(18-crown-6)}2(L)] (M=Rb, Cs; R=Cp, Ind, Cp*, Fl; L=dimethoxyethane, dioxane). All complexes were characterized by NMR spectroscopy and X-ray structure analysis. The dominating structure element in the investigated complexes is an [MR(18-crown-6)] unit in which the alkali metal ion is in close contact with the six oxygen atoms of the crown ether. In addition, a multihapto π-interaction between the cation and carbanion was found. For all isolated complexes containing the fluorenyl ligand, [MFl(18-crown-6)] and [{RbFl(18-crown-6)}2(L)], only a η2 coordination of the aromatic C–C bond between the C5- and C6-ring to the metal ions was observed.