Thesis

Towards understanding synergic s-block chemistry : new insights from zincate and magnesiate reactions

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Awarding institution
  • University of Strathclyde
Date of award
  • 2012
Thesis identifier
  • T13096
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • Metallation, in which an inert carbon-hydrogen bond is transformed into a labile carbonmetal bond, is a useful tool for constructing substituted aromatic compounds. Routinely, highly polar organolithium reagents are employed for this purpose; however, there are limitations to their use. This project was based on further developing an alternative metallation strategy, namely Alkali-Metal-Mediated Metallation (AMMM), with emphasis on zincation by exploiting the synergic chemistry that can be generated when pairing a group 1 metal amide with a low polarity dialkyl zinc reagent. AMMM reactions of the sodium TMP-zincate [(TMEDA)Na(μ-TMP)(μ-tBu)Zn(tBu)] (1) were explored leading to the development of a new concept within Directed-ortho- Metallation (DoM) chemistry with three electron-rich aromatic substrates cleanly zincated ortho to the directing metallation group (DMG) under ambient temperatures; while reaction with benzyl methyl ether produced an ortho-zincated intermediate instead of the thermodynamic α-metallated product. Additionally, a remarkable structural variety was observed when investigating the competition between a DMG and a heteroatom in the N,N-diethyl thiophene-2-carboxamide ring for the site of metallation. Through structurally mapping these reactions and subsequent electrophilic quenches, these studies established reagent 1 as a powerful metallating agent. A case study of the metallation of N,N-dimethylaniline offers complementary insight into the selectivity and mechanism of the base underlining how the cooperative action of the bi-metal partnership promotes special reactions beyond the scope of homometallic reagents. Outwith metallation, some unexpected highlights were the product of this research. Courtesy of a novel four-step domino sequence, a series of unique zwitterionic zincabicyclic complexes were prepared from the reaction of synergic reagents and chlorobenzene. Complementing its Brønsted basicity, zincate 1 underwent single electron transfer with the radical TEMPO; while, treating TEMPO with sodium metal and crystallisation from a hexane/TMEDA mixture produced a ladder structure which represents a rare example of elemental-metal single electron reduction of the radical.
Resource Type
DOI
Date Created
  • 2012
Former identifier
  • 943811

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