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Synthesis and structural chemistry of alkali metal tris(HMDS) magnesiates containing chiral diamine donor ligands

Garcia-Alvarez, Pablo and Kennedy, Alan R. and O'Hara, Charles T. and Reilly, Kieran and Robertson, Gemma M. (2011) Synthesis and structural chemistry of alkali metal tris(HMDS) magnesiates containing chiral diamine donor ligands. Dalton Transactions, 40 (19). pp. 5332-5341. ISSN 1472-7773

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Abstract

Six alkali metal tris(HMDS) magnesiate complexes (HMDS, 1,1,1,3,3,3,-hexamethyldisilazide) containing chiral diamine ligands have been prepared and characterised in both the solid- and solution-state. Four of the complexes have a solvent-separated ion pair composition of the form [{M∙(chiral diamine)2}+{Mg(HMDS)3}−] [M = Li for 1 and 3, Na for 2 and 4; chiral diamine = (−)-sparteine for 1 and 2, (R,R)-TMCDA for 3 and 4, (where (R,R)-TMCDA is N,N,N′,N'-(1R,2R)-tetramethylcyclohexane-1,2-diamine)] and two have a contacted ion pair composition of the form [{K∙chiral diamine}+{Mg(HMDS)3}−]n [chiral diamine = (−)-sparteine for 5 and (R,R)-TMCDA for 6]. In the solid-state, complexes 1–4 are essentially isostructural, with the lithium or sodium cation sequestered by the respective chiral diamine and the previously reported anion consisting of three HMDS ligands coordinated to a magnesium centre. As such, complexes 1–4 are the first structurally characterised complexes in which the alkali metal is sequestered by two molecules of either of the chiral diamines (–)-sparteine (1 and 2) or (R,R)-TMCDA (3 and 4). In addition, complex 4 is a rare (R,R)-TMCDA adduct of sodium. In the solid state, complexes 5 and 6 exist as polymeric arrays of dimeric [{K∙chiral diamine}+{Mg(HMDS)3}−]2 subunits, with 5 adopting a two-dimensional net arrangement and 6 a linear arrangement. As such, complexes 5 and 6 appear to be the only structurally characterised complexes in which the chiral diamines (–)-sparteine (5) or (R,R)-TMCDA (6) have been incorporated within a polymeric framework. In addition, prior to this work, no (−)-sparteine or (R,R)-TMCDA adducts of potassium had been reported.

Item type: Article
ID code: 33108
Keywords: sparteine-mediated deprotonation , inverse crown-ether, enantioselective lithiation-substitution , carbon bond formations , cation-pi interactions, asymmetric-synthesis , crystal-structures, conjugate additions, amide chemistry, n-boc-pyrrolidine, Chemistry
Subjects: Science > Chemistry
Department: Faculty of Science > Pure and Applied Chemistry
Related URLs:
    Depositing user: Pure Administrator
    Date Deposited: 05 Sep 2011 16:07
    Last modified: 17 Jul 2013 10:49
    URI: http://strathprints.strath.ac.uk/id/eprint/33108

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