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

G. B. Deacon, C. M. Forsyth, N. M. Scott

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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)(SiMe 3)), 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.

Original languageEnglish
Pages (from-to)2494-2501
Number of pages8
JournalJournal of the Chemical Society, Dalton Transactions
Issue number17
Publication statusPublished - 29 Sep 2001

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