Adding Rubidium and Cesium to the Homologous Series of Alkali Metal Compounds of (Trimethylsilyl)methanides and 2,2,6,6-Tetramethylpiperidides

(Trimethylsilyl)methylrubidium [RbCH2SiMe3] (1) and (trimethylsilyl)methylcesium [CsCH2SiMe3] (2) were prepared by metathesis reactions of (trimethylsilyl)methyllithium [LiCH2SiMe3] with rubidium or cesium tert-butoxide in n-hexane. Both new compounds are pyrophoric powders which were characterised by NMR spectroscopy and elemental analyses. They can be used as deprotonating agents towards secondary amines such as 2,2,6,6-tetramethylpiperidine (TMPH). The resulting amides [RbTMP] (3) and [CsTMP] (4) form temperature-sensitive, n-hexane-insoluble orange solids. Treatment with the bidentate donor N,N,N',N'-tetramethylethylenediamine (TMEDA) produces the corresponding n-hexane-soluble complexes. The crystal structures of [(TMEDA)RbTMP] (3a) and [(TMEDA)CsTMP] (4a) were determined to be closely related to that of [(TMEDA)KTMP]. Thus they are dimers with frameworks that consist of four-membered MNMN rings (M = Rb, Cs or K, N = TMP). The versatility and stability observed should make these (trimethylsilyl)methyl and TMP compounds of rubidium (1, 3a) and cesium (2, 4a) valuable starting points for further exploration of the chemistry of these heavy alkali metals.