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Title: Novel synthetic and structural advances in magnesiate and zincate chemistry
Author: Baillie, Sharon E.
ISNI:       0000 0004 2744 0065
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2012
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Building on recent successes in mixed-metal chemistry, this research project aims to enhance the understanding of the complicated correlations existing between structural patterns and reactivities of alkali metal magnesiates and zincates together with exploring their applications in a number of fundamental organic transformation reactions such as metallation, alkyl addition and metal-halogen exchange reactions. Elucidating the effect that donor solvents can exert on the overall constitution of organometallic reagents, a series of novel solvated [(donor)MMgR3] and [(donor)2M2MgR4] (donor = THF, dioxane, TMEDA, PMDETA; M = Li, Na, K; R = CH2SiMe3) compounds have been prepared and fully characterised both in the solidstate and in solution using multinuclear NMR (including 1H-DOSY NMR) studies. A rich variety of structural motifs has been disclosed which range from simple monomers when polydentate ligands such as PMDETA are employed, such as [(PMDETA)LiMgR3] (6) and [(PMDETA )2MMgR4] (M = Na (9), K (11)), to much more complex polymeric structures using oxygen donor ligands dioxane or THF, such as [{(dioxane)2LiMgR3}8] (3), [{(dioxane)Li2Mg2R6}8] (4) and [{(THF)LiMgR3}8] (2). The first examples of unsolvated trisalkyl magnesiates [{NaMgR3}8] (12) and [{KMgR3}8] (16) have been unveiled which exhibit distinct 2D supramolecular structures in the solid-state constructed exclusively of electron deficient M-C bonds. The ability of novel potassium magnesiates to participate in direct magnesium-hydrogen exchange reactions was assessed with several aromatic and heteroaromatic substrates. In addition, key reaction intermediates have been structurally defined from metallation, alkyl addition and metal-halogen exchange reactions which provide compelling evidence that the outcome of these reactions are reliant on subtle changes in the coordination sphere of the bimetallic reagent employed. Thus, the reactivity of heteroleptic zincate [(T HF)LiZn(TMP)(tBu)2] (22) towards pyrazine has demonstrated that despite the presence of two nucleophilic tBu groups the selective two-fold deprotonation of the heterocycle pyrazine is preferred to form the unprecedented 2,5-di-zincated pyrazine molecule. These results are in contrast with those observed when pyrazine is confronted by the homoleptic alkyl zincate [(PMDETA)LiZn(tBu)3] (23) where the chemoselective addition of a tBu group to the (Sa(B-C of the heterocycle takes place under mild reaction conditions. Focussing on metal-halogen exchange reactions, the addition of LiOtBu has proved to greatly activate ZnEt2 towards zinc-iodine exchange reactions with 2-iodoanisole under mild conditions. Novel bimetallic approaches which allow the selective C4 functionalisation of unsaturated N-heterocyclic carbene IPr have been developed. Thus, the first direct zincation of an NHC was achieved by reacting sodium zincate [(TMEDA)Na(TMP)(tBu)Zn(tBu)] with IPr to form [(THF)3Na(IPr *)Zn(tBu)2] (41). 41 exhibits a unique chemical profile and can react efficiently with [ClAu(PPh3)] to form an unprecedented bis-gold [ClAu(IPr*)Au(PPh3)] (47) species. Extension of these reactivity studies to Na/Mg combinations allows the isolation of the first sodium magnesiate containing a deprotonated carbene molecule [(THF)3Na(IPr*)Mg(CH2SiMe3)2(THF)] (50).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available