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

Alkali metal amides are vital reagents in synthetic chemistry and the bis(silyl)amide {N(SiMe(3))(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(Si(t)BuMe(2))(SiMe(3))}, {HN(Si(i)Pr(3))(SiMe(3))}, {HN(Si(t)BuMe(2))(2)}, {HN(Si(i)Pr(3))(Si(t)BuMe(2))} and {HN(Si(i)Pr(3))(2)} (1) were prepared by literature procedures as colourless oils; on one occasion crystals of 1 were obtained. These were treated separately with (n)BuLi to afford the respective lithium bis(silyl)amides [Li{μ-N(Si(t)BuMe(2))(SiMe(3))}](2) (2), [Li{μ-N(Si(i)Pr(3))(SiMe(3))}](2) (3), [Li{N(Si(t)BuMe(2))(2)}{μ-N(Si(t)BuMe(2))(2)}Li(THF)] (4), [Li{N(Si(i)Pr(3))(Si(t)BuMe(2))}(DME)] (6) and [Li{N(Si(i)Pr(3))(2)}(THF)] (7) following workup and recrystallization. On one occasion during the synthesis of 4 several crystals of the ‘ate’ complex [Li(2){μ-N(Si(t)BuMe(2))(2)}(μ-(n)Bu)](2) (5) formed and a trace amount of [Li{N(Si(i)Pr(3))(2)}(THF)(2)] (8) was identified during the recrystallization of 7. The reaction of {HN(Si(t)BuMe(2))(2)} with NaH in the presence of 2 mol % of NaO(t)Bu gave crystals of [Na{μ-N(Si(t)BuMe(2))(2)}(THF)](2) (9-THF), whilst [Na{N(Si(i)Pr(3))(2)}(C(7)H(8))] (10) was prepared by deprotonation of 1 with (n)BuNa. 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.