Structural characterization of lithium and sodium bulky bis(silyl)amide complexes

Abstract

Alkali metal amides are vital reagents in synthetic chemistry and the bis(silyl)amide (N(SiMe3)2) (N) is one of the most widely-utilized examples. Given that N has provided landmark complexes, we have investigated synthetic routes to lithium and sodium bis(silyl)amides with increased steric bulk to analyse the effects of R-group substitution on structural features. To perform this study, the bulky bis(silyl)amines (HN(SitBuMe2)(SiMe3)), (HN(SiiPr3)(SiMe3)), (HN(SitBuMe2)2), (HN(SiiPr3)(SitBuMe2)) and (HN(SiiPr3)2) (1) were prepared by literature procedures as colourless oils; on one occasion crystals of 1 were obtained. These were treated separately withnBuLi to afford the respective lithium bis(silyl)amides [Li(µ-N(SitBuMe2)(SiMe3))]2 (2), [Li(µ-N(SiiPr3)(SiMe3))]2 (3), [Li(N(SitBuMe2)2)(µ-N(SitBuMe2)2)Li(THF)] (4), [Li(N(SiiPr3)(SitBuMe2))(DME)] (6) and [Li(N(SiiPr3)2)(THF)] (7) following workup and recrystallization. On one occasion during the synthesis of 4 several crystals of the ‘ate’ complex [Li2(µ-N(SitBuMe2)2)(µ-nBu)]2 (5) formed and a trace amount of [Li(N(SiiPr3)2)(THF)2] (8) was identified during the recrystallization of 7. The reaction of (HN(SitBuMe2)2) with NaH in the presence of 2 mol % of NaOtBu gave crystals of [Na(µ-N(SitBuMe2)2)(THF)]2 (9-THF), whilst [Na(N(SiiPr3)2)(C7H8)] (10) was prepared by deprotonation of 1 withnBuNa. The solid-state structures of 1–10 were determined by single crystal X-ray crystallography, whilst 2–4, 7, 9 and 10 were additionally characterized by NMR and FTIR spectroscopy and elemental microanalysis.