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Synthetic and Structural Studies of Mixed Sodium Bis(trimethylsilyl)amide/Sodium Halide Aggregates in the Presence of η2N,N‑, η3N,N,N/N,O,N‑, and η4N,N,N,N‑Donor Ligands

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journal contribution
posted on 19.10.2015, 00:00 by Ana I. Ojeda-Amador, Antonio J. Martínez-Martínez, Alan R. Kennedy, Charles T. O’Hara
When n-hexane solutions of an excess of sodium bis­(trimethylsilyl)­amide (NaHMDS) are combined with cesium halide (halide = Cl, Br, or I) in the presence of the tetradentate donor molecule [tris­[2-(dimethylamino)­ethyl]­amine] (Me6TREN), the isolation and characterization of a series of sodium amide/sodium halide mixed aggregates was forthcoming. Cesium halide was employed because it efficiently reacted with NaHMDS to produce a molecular, soluble source of sodium halide salt (which was subsequently captured by an excess of NaHMDS) via a methathetical reaction. These mixed sodium amide/sodium halide complexes are formally sodium sodiates, are deficient in halide with respect to the amide, and have the general formula [{Na5(μ-HMDS)55-X)}­{Na­(Me6TREN)}] [where X = Cl (1), Br (2), or I (3)]. The influence of the donor ligand was studied for the NaI/NaHMDS system, and when n-hexane solutions of this composition were treated with tridentate donors such as N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA) or N,N,N′,N′-tetramethyldiaminoethyl ether (TMDAE), solvent-separated ion-pair cocomplexes [Na5(μ-HMDS)55-I)][Na3(μ-HMDS)2(PMDETA)2]+ (4) and [Na5(μ-HMDS)55-I)][Na­(TMDAE)2]+ (5) were isolated. However, upon reaction with bidentate proligands such as the chiral diamine (R,R)-N,N,N′,N′-tetramethylcyclohexane-1,2-diamine [(R,R)-TMCDA] or N,N,N′,N′-tetramethylethylenediamine (TMEDA), neutral complexes [Na4(μ-HMDS)34-I)­(donor)2] [donor = (R,R)-TMCDA (6) and TMEDA (7)] were produced. To illustrate the generality of the latter reaction with other halides, [Na4(μ-HMDS)34-Br)­(TMEDA)2] (8) was also prepared by employing NaBr in the synthesis instead of NaI.