Alkali-metal-mediated cleave and capture chemistry

Student thesis: Doctoral Thesis

Abstract

Whilst metallation, a fundamental reaction in synthetic chemistry, is well established with mono-metallic organolithium reagents, recently a second generation of bimetallic reagents has been gathering momentum, evading some of the limitations associated with organolithium reagents. This study extends the current research in this area of synergic bimetallic chemistry and reports the synthesis and characterisation of new compounds from reactions of bases with different substrates, as well as detailed studies of the starting reagents. A new method for synthesising the utility organoamidolithium reagent LiTMP by way of a transmetallation reaction between tBuLi and Zn(TMP)₂ is described. This realised a new crystalline polymorph of LiTMP in the cyclotrimer (LiTMP)₃ 2.1. Remarkably an interrogation of the two most popular aluminating reagents “LiTMP·Al(iBu)₃” 3.1 and “LiTMP·Al(TMP)(iBu)₂” 3.2 established that 3.1 is not a single species as previously reported but in fact a complex mixture of five distinct species all in equilibria with each other. Additionally it was discovered that the modus operandi of both reagents is a two-step lithiation - trans-metaltrapping protocol, and not by direct alumination. The pharmacologically relevant amine DMPEA was studied with a range of bimetallic base mixtures. Post metallation and subsequent β-elimination the NMe₂ fragment was captured in three different crystalline compounds: [TMEDA·Na(TMP)(NMe₂)Zn(tBu)] 4.2, [PMDETA·Li(NMe₂)Zn(tBu)₂] 4.3 and [THF·Li(TMP)(NMe₂)Al(iBu)₂] 4.4. The first crystal structure where DMPEA is bonded to a metal has also been revealed in [DMPEA·Li(TMP)Zn(Me)₂] 4.5.Probing ferrocene with bimetallic mixtures afforded a range of mono- and dideprotonated products depending on the stoichiometry used. Both zincations in TMEDA·Na(μ-TMP)[μ-(C₅H₄)Fe(C₅H₅)]Zn(tBu) 5.1 and [TMEDA·Na(μ-TMP)Zn(tBu)]₂(C₅H₄)₂Fe 5.2 and aluminations in THF·Li(μ-TMP)[μ- (C5H4)Fe(C5H5)]Al(iBu)2 5.4, [THF·Li(μ-TMP)Al(iBu)2]2(C5H4)2Fe 5.5, [TMP(H)·Li(μ-TMP)Al(iBu)2]2(C5H4)2Fe 5.6 and TMP(H)·Li(TMP)[(C5H4)Fe(C5H5)]Al(iBu)2 5.7 were possible. The zinc system also provided the novel ferrocenophane type structure [{Fe(C₅H₄)₂}₂{Na₂Zn₂(tBu)₂·(THF)₆}] 5.8, as well as hints of a possible polymetallated product.
Date of Award1 Apr 2015
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council) & University of Strathclyde
SupervisorRobert Mulvey (Supervisor) & Eva Hevia (Supervisor)

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