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

摘要

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)](infinity) was isolated (57% yield). By combining equimolar quantities of NaHMDS and CsHMDS in hexane/toluene [toluene center dot NaCs-(HMDS)](infinity) 3 was isolated (62% yield). Attempts to prepare the corresponding potassium cesium amide failed and instead yielded the known monometallic polymer [toluene center dot Cs(HMDS)](infinity) 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'-tetra-methylethylenediamine (TMEDA), N,N,N',N '',N ''-pentamethyldiethylenetriamine (PMDETA), tris[2-(dimethylamino)ethyl]amine (Me-6-TREN) and tris[2-(2-methoxyethoxy)ethyl]amine (TMEEA). These reactions yielded dimeric [donor center dot NaCs-(HMDS)(2)](2) 5-7 [where donor is (R,R)-TMCDA, TMEDA and PMDETA respectively], the tetranuclear "open"-dimer [{Me-6-TREN center dot Cs(HMDS)}(2){Cs(HMDS)}(2)] 8 and the monomeric [TMEEA center dot Cs(HMDS)] 9. Complexes 2, 3, and 5-9 were characterized by X-ray crystallography and in solution by multinuclear NMR spectroscopy.