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

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posted on 2016-05-13, 13:19 authored by Ana I. Ojeda-Amador, Antonio J. Martínez-Martínez, Alan R. Kennedy, Charles T. O’Hara
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 57 [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 59 were characterized by X-ray crystallography and in solution by multinuclear NMR spectroscopy.

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