Structural studies of cesium, lithium/cesium and sodium/cesium bis(trimethylsilyl)amide (HMDS) complexes

Ojeda Amador, Ana I. and Martínez-Martínez, Antonio J. and Kennedy, Alan R. and O'Hara, Charles T. (2016) Structural studies of cesium, lithium/cesium and sodium/cesium bis(trimethylsilyl)amide (HMDS) complexes. Inorganic Chemistry, 55 (11). 5719–5728. ISSN 0020-1669

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    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 [NaCs(HMDS)2(toluene)]∞ 3 was isolated (62% yield). Attempts to prepare the corresponding potassium-cesium amide failed, and instead yielded the known monometallic polymer [Cs(HMDS)(toluene)]∞ 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,Nʹ,Nʹ-tetramethylethylenediamine (TMEDA), N,N,Nʹ,Nʹʹ,Nʹʹ-pentamethyldiethylenetriamine (PMDETA), tris[2-(dimethylamino)ethyl]amine (Me6-TREN) and tris[2-(2-methoxyethoxy)ethyl]amine (TMEEA). These reactions yielded dimeric [Cs(HMDS)·donor]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 Cs(HMDS)·TMEEA 9. Complexes 2,3 and 5-9 were characterized by X-ray crystallography and in solution by multinuclear NMR spectroscopy.