Issue 2, 2014

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

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

Supplementary files

Article information

Article type
Edge Article
Submitted
10 Oct 2013
Accepted
25 Nov 2013
First published
26 Nov 2013
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2014,5, 771-781

Author version available

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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