Thesis

Alkali-metal-mediated alumination : development of bis-TMP chemistry of [(THF)AM(TMP)₂Al(iBu)₂] with emphasis on lithium

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Awarding institution
  • University of Strathclyde
Date of award
  • 2013
Thesis identifier
  • T13601
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Abstract
  • Deprotonation, the exchange of an inert carbon-hydrogen bond for a more chemically useful carbon-metal bond, has long been one of the methods of choice for constructing substituted aromatic and heteroaromatic compounds. Organolithium reagents have been the standard for this purpose for many years; however, their many limitations mean that new reagents for deprotonative metallation are sought. Alkali-Metal-Mediated Metallation (AMMM) was developed as an alternative vehicle to functionalising a plethora of substrates. This project focuses on the synergic alumination chemistry generated by combining lithium amide LiTMP with low polarity aluminium reagent iBu₂AlTMP exhibiting the reaction concept of Alkali-Metal-Mediated Alumination (AMMAl). AMMAl reactions of lithium bis-TMP aluminate [(THF)Li(TMP)Deprotonation, the exchange of an inert carbon-hydrogen bond for a more chemically useful carbon-metal bond, has long been one of the methods of choice for constructing substituted aromatic and heteroaromatic compounds. Organolithium reagents have been the standard for this purpose for many years; however, their many limitations mean that new reagents for deprotonative metallation are sought. Alkali-Metal-Mediated Metallation (AMMM) was developed as an alternative vehicle to functionalising a plethora of substrates. This project focuses on the synergic alumination chemistry generated by combining lithium amide LiTMP with low polarity aluminium reagent iBu₂AlTMP exhibiting the reaction concept of Alkali-Metal-Mediated Alumination (AMMAl). AMMAl reactions of lithium bis-TMP aluminate [(THF)Li(TMP)₂Al(iBu)₂] were explored to learn more about the reactivity of this bis-amido base. Several functionalised aromatic substrates including anisole and N,N-diisopropylbenzamide were effectively ortho-aluminated in hexane solution at ambient temperature and quenched with iodine to generate the corresponding metal-free products in excellent yield. DFT calculations and DOSY NMR experiments were conducted to elucidate a possible structure for the base as it could not be isolated. A mechanism was proposed showing an open-structure with a pseudo-terminal TMP. This allowed a rationale for the intramolecular reactivity observed with a series of donor molecules including THF which could be deprotonated and the resulting anion trapped without ring opening. Several key differences were observed between our bis-amido base [Li(TMP)₂Al(iBu)₂] and Uchiyama's mono-amido base [Li(TMP)Al(iBu)₃]. THF was deprotonated and its anion captured with the former; whereas the latter was found to be more stable in THF solution. Other donor molecules such as 1-methoxy-2-dimethylaminoethane (MDAE) and bis-[2-(N,N-dimethylamino)ethyl]ether (Me₄AEE) were deprotonated with the bis-amido base; whereas they were found to merely solvate lithium when the mono-amido base was employed. An investigation into the mono-amido base in THF solution revealed some interesting facts concluding us to believe that this base disproportionates to give our mono-amido base in THF solution.
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DOI
Date Created
  • 2013
Former identifier
  • 1002018

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