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Issue 2, 2014
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Pre-inverse-crowns: synthetic, structural and reactivity studies of alkali metal magnesiates primed for inverse crown formation

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Abstract

Two new alkali metal monoalkyl-bisamido magnesiates, the potassium compound [KMg(TMP)2nBu] and its sodium congener [NaMg(TMP)2nBu] have been synthesised in crystalline form (TMP = 2,2,6,6-tetramethylpiperidide). Devoid of solvating ligands and possessing excellent solubility in hydrocarbon solvents, these compounds open up a new gateway for the synthesis of inverse crowns. X-ray crystallography established that [KMg(TMP)2nBu] exists in three polymorphic forms, namely a helical polymer with an infinite KNMgN chain, a hexamer with a 24-atom (KNMgN)6 ring having endo-disposed alkyl substituents, and a tetramer with a 16-atom (KNMgN)4 ring also having endo-disposed alkyl substituents. Proving their validity as pre-inverse-crowns, both magnesiates react with benzene and toluene to generate known inverse crowns in syntheses much improved from the original, supporting the idea that the metallations take place via a template effect. [KMg(TMP)2nBu] reacts with naphthalene to generate the new inverse crown [KMg(TMP)2(2–C10H7)]6, the molecular structure of which shows a 24-atom (KNMgN)6 host ring with six naphthalene guest anions regioselectively magnesiated at the 2-position. An alternative unprecedented 1,4-dimagnesiation of naphthalene was accomplished via [NaMg(TMP)2nBu] and its NaTMP co-complex “[NaMg(TMP)2nBu]·NaTMP”, manifested in [{Na4Mg2(TMP)4(2,2,6-trimethyl-1,2,3,4-tetrahydropyridide)2}(1,4-C10H6)]. Adding to its novelty, this 12-atom (NaNNaNMgN)2 inverse crown structure contains two demethylated TMP ligands as well as four intact ones. Reactivity studies show that the naphthalen-ide and -di-ide inverse crowns can be regioselectively iodinated to 2-iodo and 1,4-diiodonaphthalene respectively.

Graphical abstract: Pre-inverse-crowns: synthetic, structural and reactivity studies of alkali metal magnesiates primed for inverse crown formation

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Publication details

The article was received on 10 Oct 2013, accepted on 25 Nov 2013 and first published on 26 Nov 2013


Article type: Edge Article
DOI: 10.1039/C3SC52816B
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Citation: Chem. Sci., 2014,5, 771-781
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    Pre-inverse-crowns: synthetic, structural and reactivity studies of alkali metal magnesiates primed for inverse crown formation

    A. J. Martínez-Martínez, D. R. Armstrong, B. Conway, B. J. Fleming, J. Klett, A. R. Kennedy, R. E. Mulvey, S. D. Robertson and C. T. O'Hara, Chem. Sci., 2014, 5, 771
    DOI: 10.1039/C3SC52816B

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