Complexity in seemingly simple sodium magnesiate systems

Francos, J. and Fleming, B. J. and García-Álvarez, P. and Kennedy, A. R. and Reilly, K. and Robertson, G. M. and Robertson, S. D. and O'Hara, C. T. (2014) Complexity in seemingly simple sodium magnesiate systems. Dalton Transactions, 43 (38). pp. 14424-14431. ISSN 1477-9234

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Abstract

A systematic study both in the solid- and solution-state, was carried out for a series of sodium magnesiates containing the utility amide ligand 1,1,1,3,3,3-hexamethyldisilazide (HMDS). The first complex considered is the donor-free bisamido monoalkyl polymeric complex [Na(μ-HMDS)2Mg(nBu)]∞1. The reactivity of 1 with common tertiary bidentate donors including N,N,N′,N′-tetramethylethylenediamine (TMEDA) or its chiral relative (1R,2R)-tetramethylcyclohexyldiamine [(R,R)-TMCDA] is detailed. Surprisingly, the products of these reactions are not simple diamine adducts but are solvent separated sodium magnesiate systems [(TMEDA)2·Na]+[Mg(HMDS)3]-2 and [{(R,R)-TMCDA}2·Na]+[Mg(HMDS)3]-3. By concentrating on the likely equilibria which may give rise to formation of 2, a potential intermediate complexed ion pair [{(TMEDA)2·Na}(μ-nBu)Mg(HMDS)2] 4 was isolated. Additionally, the novel "inverse magnesiates" [{Na(μ-HMDS)}2Mg(μ-nBu)2·(TMEDA)]∞5 and [{Na(μ-HMDS)}2Mg(μ-nBu)2·{(R,R)-TMCDA}]∞6, were obtained by reacting solutions of composition "NaMg(HMDS)(nBu)2" (a likely by-product in the formation of 2 from 1), with TMEDA or (R,R)-TMCDA. The structure and nature of these bimetallic complexes have been determined using a combination of X-ray crystallographic studies and multinuclear NMR spectroscopy.