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

Pablo Garcia-Alvarez, Alan R. Kennedy, Charles T. O'Hara, Kieran Reilly, Gemma M. Robertson

Research output: Contribution to journalArticle

15 Citations (Scopus)

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.
Original languageEnglish
Pages (from-to)5332-5341
Number of pages10
JournalDalton Transactions
Volume40
Issue number19
DOIs
Publication statusPublished - 31 Mar 2011

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

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