Synthetic and Structural Studies of Mixed Sodium Bis(trimethylsilyl)amide/Sodium Halide Aggregates in the Presence of η²-N,N-, η³-N,N,N/N,O,N-, and η⁴-N,N,N,N-Donor Ligands

Abstract

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)5(μ5-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)5(μ5-I)](-)[Na3(μ-HMDS)2(PMDETA)2](+) (4) and [Na5(μ-HMDS)5(μ5-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)3(μ4-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)3(μ4-Br)(TMEDA)2] (8) was also prepared by employing NaBr in the synthesis instead of NaI.

One-pot aminobenzylation of aldehydes with toluenes

“…This screen led to the identification of NaN(SiMe 3 ) 2 as a promising base, affording the product 3aa in 47% assay yield (entry 2). It is known that K + forms the stronger cation–π interactions in solution in the series Li + , Na + , and K + 39 , 40 ; however, under our conditions the potassium amide was not as successful as NaN(SiMe 3 ) 2 (entry 3 vs. 2). This may be because KN(SiMe 3 ) 2 is less efficient in the formation of the aldimine 37 .…”

“…It can be prepared, of course, but this would make the methods that require its use less attractive. O’Hara and co-workers found that CsN(SiMe 3 ) 2 could be generated by mixing NaN(SiMe 3 ) 2 with CsX (X = Cl, Br, or I) 40 . Furthermore, combining CsN(SiMe 3 ) 2 with equimolar NaN(SiMe 3 ) 2 led to formation of a sodium–cesium amide polymer [toluene•CsNa(N(SiMe 3 ) 2 ) 2 ] ∞ 39 .…”

Aggregation and Solvation of Sodium Hexamethyldisilazide: Across the Solvent Spectrum

“…Its solubility, stability, and commercial availability appeal to synthetic chemists and render NaHMDS an attractive target for studying aggregation and solvation. Aside from NaHMDS crystal structures of potential interest to synthetic chemists (Chart ), there are remarkably few physicochemical studies of NaHMDS in solution. ,− Even the computational community has shown little interest …”

Reactions of Sodium Diisopropylamide: Liquid-Phase and Solid–Liquid Phase-Transfer Catalysis by N,N,N′,N″,N″-Pentamethyldiethylenetriamine

“…Moreover, the reaction becomes homogeneous at approximately 50% conversion. Although, in principle, this could reflect the solubility limit of NaDA solvated by epoxide 15 , we suspect that soluble mixed aggregates are involved …”