The role of the bis-trimethylsilylamido ligand, [N{SiMe3}2]−, in main group chemistry. Part 2: Structural chemistry of the metallic p-block elements

Structural Characterization of Lithium and Sodium Bulky Bis(silyl)amide Complexes

“…As symmetrical bis(silyl)amides have found most synthetic utility to date [4,5,6,7] we also targeted sodium salts of {HN(SiMe 2 t Bu) 2 } and 1 . We found that the reaction of {HN(Si t BuMe 2 ) 2 } with NaH in toluene was sluggish, so adapting a procedure reported by Arnold for the improved synthesis of NaN′′ [23] we added 2 mol % of NaO t Bu and refluxed the reaction mixture for 16 h. Crystals of [Na{μ-N(Si t BuMe 2 ) 2 }(THF)] 2 ( 9-THF ) were obtained following treatment with THF and recrystallization from pentane.…”

“…In the case of 7 no desolvation was observed, for 4 and 10 approximately half of the solvent was removed and for 9-THF complete desolvation occurred when the sample was heated in vacuo to give 9 . Variable solvent coordination was previously seen in the 1 H and 13 C{ 1 H}-NMR spectra of [K{μ-N(Si t BuMe 2 )(SiMe 3 )}] 2 [13] and [K{μ-N(Si t BuMe 2 )(SiMe 3 )}(C 7 H 8 )] 2 [14] and the desolvation of strongly bound solvent molecules under vacuum is commonly seen in alkali metal bis(silyl)amide chemistry [4,5,6]. Only one signal is observed for each methine and methyl group in the 1 H-NMR spectra of 2 – 4 , 7 , 9 and 10 in C 6 D 6 at 298 K, indicating that any asymmetry observed in the solid state (see below) is not maintained in solution.…”

“…Only one signal is observed for each methine and methyl group in the 1 H-NMR spectra of 2 – 4 , 7 , 9 and 10 in C 6 D 6 at 298 K, indicating that any asymmetry observed in the solid state (see below) is not maintained in solution. Variable degrees of aggregation in non-coordinating solvents is a general feature of s-block N′′ chemistry [4,5,6]; approximate sizes of such aggregates have routinely been studied by 1 H-DOSY-NMR spectroscopy but an investigation of the solution dynamics of the complexes herein are beyond the scope of this study, which focuses on solid state structural characterization.…”

“…The elimination of potassium iodide is advantageous as it is insoluble in most organic solvents. We envisaged that lithium and sodium ligand transfer agents may provide improved yields of products with metal chloride precursors, as had been seen previously in N′′ chemistry [4,5,6,7]. Whilst these lithium and sodium bulky bis(silyl)amides can be used in situ in future, we report their synthesis, isolation and structural characterization herein.…”

“…The bulky bis(silyl)amide {N(SiMe 3 ) 2 } (N′′) is relatively soft due to negative hyperconjugation provided by Si atoms and its alkali metal salts have been used extensively as ligand transfer reagents in the preparation of landmark low-coordinate s-, p-, d- and f-block complexes by salt metathesis reactions with metal/metalloid halide precursors [4,5,6,7]. Although these reagents are often used in situ, the solvent-free solid-state structures of the lighter group 1 salts LiN′′ [8,9], NaN′′ [10] and KN′′ [11] have been reported previously.…”