Exploiting cooperative effects in s-Block organometallics for new applications in synthesis and catalysis

  • Laia Davin Cardona

Student thesis: Doctoral Thesis

Abstract

Focussing on group 1 and group 2 metals, this thesis advances the use of polar organometallics in catalysis, in particular intermolecular hydroamination processes; as well as other key stoichiometric transformations, namely deprotonative metallation and C-F bond activation.Group 1 alkyl compounds MCH2SiMe3 (M = Li, Na or K) have proved to be efficient catalysts for intermolecular hydroamination of a wide range of substituted vinylarenes and alkynes at room temperature and with short timescales. Similarly,advancing in the concept of s-block cooperative bimetallic catalysis, alkali-metal magnesiate complexes [MMg(CH2SiMe3)3] and [(donor)2M2Mg(CH2SiMe3)4] (M = Li,Na or K) have shown that they can also act as catalysts for these hydroamination processes, although longer times and high temperature conditions are required in some cases. Reactivity studies show an alkali-metal effect with potassium being significally more reactive than lithium. New insights into the constitution of the potential organometallic intermediates involved in these processes have also been gained by combining X-Ray crystallographic and NMR studies (including DOSY NMR).The second part of this thesis assesses cooperative effects of single-metal organomagnesium complexes in deprotonation and C-F bond activation processes.Using a specially designed metallating base, which combines within the same molecule a sterically demanding β-diketiminate ligand with a kinetically activatedTMP base [DippNacnacMg(TMP)], regioselective magnesiation of heterocyclic and aromatic molecules, including pyrazine or 1,2,4,5-tetrafluorobenzene, can be achieved at room temperature. Structural studies of these metallated intermediates have revealed a crucial stabilising role of the β-diketiminate ligand, which facilitates the trapping of the sensitive anions formed.Additionally, they have provided important clues to rationalise the stability of these species in solution. Contrastingly [DippNacnacMg(THF)Bu] complex is a much more kinetically retarded base, which fails to metallate these substrates promoting in some cases, when confronted with fluoroarenes, C-F bond activation process via nucleophilic aromatic substitution.
Date of Award1 Oct 2016
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorEva Hevia (Supervisor) & Charles O'Hara (Supervisor)

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