Structural Studies of Cesium, Lithium/Cesium, and Sodium/Cesium Bis(trimethylsilyl)amide (HMDS) Complexes

Reacting cesium fluoride with an equimolar n-hexane solution of lithium bis­(trimethylsilyl)­amide (LiHMDS) allows the isolation of CsHMDS (1) in 80% yield (after sublimation). This preparative route to 1 negates the need for pyrophoric Cs metal or organocesium reagents in its synthesis. If a 2:1 LiHMDS:CsF ratio is employed, the heterobimetallic polymer [LiCs­(HMDS)₂]_∞ 2 was isolated (57% yield). By combining equimolar quantities of NaHMDS and CsHMDS in hexane/toluene [toluene·NaCs­(HMDS)]_∞ 3 was isolated (62% yield). Attempts to prepare the corresponding potassium-cesium amide failed and instead yielded the known monometallic polymer [toluene·Cs­(HMDS)]_∞ 4. With the aim of expanding the structural diversity of Cs­(HMDS) species, 1 was reacted with several different Lewis basic donor molecules of varying denticity, namely, (R,R)-N,N,N′,N′-tetramethylcyclohexane-1,2-diamine [(R,R)-TMCDA] and N,N,N′,N′-tetramethylethylenediamine (TMEDA), N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), tris­[2-(dimethylamino)­ethyl]­amine (Me₆-TREN) and tris­[2-(2-methoxyethoxy)­ethyl]­amine (TMEEA). These reactions yielded dimeric [donor·NaCs­(HMDS)₂]₂ 5–7 [where donor is (R,R)-TMCDA, TMEDA and PMDETA respectively], the tetranuclear “open”-dimer [{Me₆-TREN­·Cs­(HMDS)}₂­{Cs­(HMDS)}₂] 8 and the monomeric [TMEEA·Cs­(HMDS)] 9. Complexes 2, 3, and 5–9 were characterized by X-ray crystallography and in solution by multinuclear NMR spectroscopy.