High-field lithium-7 nuclear magnetic resonance spectroscopic and cryoscopic relative molecular mass studies on solutions of amido- and imido-lithium compounds

REED, D and BARR, D and Mulvey, Robert and SNAITH, R (1986) High-field lithium-7 nuclear magnetic resonance spectroscopic and cryoscopic relative molecular mass studies on solutions of amido- and imido-lithium compounds. Journal of the Chemical Society, Dalton Transactions (3). pp. 557-564. ISSN 0300-9246 (https://doi.org/10.1039/DT9860000557)

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Abstract

High-field lithium-7 n.m.r. spectroscopy and molecular mass measurements are shown to provide an important guideline into the nature of the species present in benzene and toluene solutions of a representative selection of amido- and imido-lithium derivatives. The compounds have solid-state structures ranging from hexameric to tetrameric clusters {[Ph(But)CNLi]6(3), [(Me2N)2CNLi]6(4), [Ph(Me2N)CNLi]6(5), to (Ph2CNLi·NC5H5)4(2)(NC5H5= pyridine)}, to trimeric and dimeric rings {[(PhCH2)2NLi]3(6) and (But2CNLi·hmpa)2(1)(hmpa = hexamethylphosphoramide), [(PhCH2)2NLi·OEt3]2(7), with probably n= 2 for [PhN(H)Li·hmpa]n(8), and [(C6H11)2NLi·hmpa]n(10)}, and to a likely monomer {[(Bun)(C5H5N)Li·2(NC5H8)]n(9)}, yet even more diverse behaviour has been detected in solution. Thus while some of the compounds essentially retain their solid association states [hexameric (3), (4), (5), dimeric (8), and monomeric (9)], others engage in concentration-dependent equilibria also involving monomeric species [tetrameric (2), trimeric (6), dimeric (1) and (10)], and one complex [dimeric (7)] loses donor on dissolution before rearranging to a trimer and a monomer.

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