Structurally diverse organoamides and organoamido-, organometallic-lithium aggregates from reactions of N-(2-phenoxyphenyl)-N-(trimethylsilyl)amine with LiBun

Abstract

Deprotonation of N-(2-phenoxyphenyl)-N-(trimethylsilyl)amine (L¹H) with a slight excess of LiBuⁿ in tetrahydrofuran (thf) or 1,2-dimethoxyethane (dme) yielded the solvated lithium organoamide complexes [Li(L¹)(thf)]_n (1) and [Li(L¹)(dme)] (2) (L¹ = N(C₆H₄OPh-2)(SiMe₃)), respectively. Reaction of L¹H with LiBuⁿ in hexane gave the solvent free lithium organoamide [Li(L¹)]_n (3). Monomeric 2 was shown to have a four-coordinate lithium centre surrounded by chelating L¹ and dme ligands in a distorted tetrahedral environment. Utilisation of diethyl ether as the reaction solvent, followed by work up in hexane containing a trace of bis(2-methoxyethyl) ether (diglyme), gave a low yield of colourless crystals, shown by X-ray crystallography to be [{Li(OEt₂)(L¹)Li₂(L¹¹)}₂(μ-η³-O,O′,O″-diglyme)] (4) (L¹¹ = N(C₆H₄(OC₆H₄-2′)-2)(SiMe₃)), a hexalithium cluster having both singly deprotonated (L¹) and doubly deprotonated (L¹¹) ligands. In L¹¹, the proton of the phenyl substituent ortho to the oxygen has been removed in addition to the amine hydrogen. Deliberate attempts to prepare a pure double lithiated product by reaction of L¹H with 2 equivalents of LiBuⁿ in diethyl ether yielded two different Li₂(L¹¹) complexes depending upon the crystallisation solvent. From hexane, a hexalithium aggregate [Li₂(L¹¹)(OEt₂)Li(Buⁿ)]₂ (5) was obtained. The structure of 5 showed the presence of two doubly deprotonated Li₂(L¹¹) units but, surprisingly, also incorporation of two molecules of LiBuⁿ. Alternatively, a Li₂(L¹¹) complex free of LiBuⁿ, [Li₂(L¹¹)(dme)]₂ (6) was obtained by crystallisation of the product, prepared in diethyl ether, from a hexane/dme mixture. Variable temperature solution NMR (¹H, ⁷Li) data for 4–6 indicated the occurrence of dynamic exchange processes at room temperature, but 4 and 5 have the same number of lithium environments at −90 °C as in the solid state structures.