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Investigations toward the catalytic application of low-oxidation state, low-coordinate heavier group 14 element complexes
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posted on 24.02.2017by Hadlington, Terrance John
Chapter 1 gives a brief overview of the concepts key to low-oxidation state main-group
chemistry. This covers oxidation state and electronic configuration, bonding in the heavier
alkenes and alkynes, kinetic stabilisation, and reductive routes to low-oxidation state element
Chapter 2 summarises bulky ligands commonly used in the kinetic stabilisation of low-oxidation
state element species, and the synthesis of group 14 element(II) halide complexes, which act as
precursors to further low-oxidation state chemistry. Following from this, the synthesis of novel
bulky monodentate amide ligands is discussed, as is their utilisation in the synthesis of group 14 element(II) halide precursors.
Chapter 3 investigates the use of the aforementioned group 14 element(II) halide precursors in
the synthesis of amido-substituted heavier alkyne analogues (i.e. LEEL, E = Ge and Sn), and the
reactivity thereof. These reactivity studies cover H₂ activation, CO₂ reduction, and
cycloaddition/insertion reactions, involving reversible processes and CH-activation. The
activation of H₂ led to the isolation of group 14 element(II) hydride species, which have been
shown to be in equilibrium with monomeric hydride species in solution (i.e. hydrido tetrelenes).
Further increasing the ligand’s bulk led to the solid-state characterisation of two examples of
monomeric amido Ge(II) hydride species.
Chapter 4 presents the further reactivity of the aforementioned group 14 element(II) hydride
species. This culminated in the synthesis of numerous amido alkyl and amido alkoxy germylenes
and stannylenes through hydroelementation of aldehydes, ketones, and alkenes. The addition to
alkenes was found, in some cases, to be reversible, and led to examples of alkene isomerisation
at a Ge(II) centre.
Chapter 5 addresses the use of group 14 element(II) species in catalysis, initially through
stoichiometric studies involving germylenes and stannylenes discussed in Chapter 4. The
efficient hydroboration of aldehydes and ketones is described, catalysed by Ge(II) and Sn(II)
hydride complexes (i.e. those described in Chapter 3), with the mechanism of reaction studied
through in depth kinetic experiments and DFT analyses. The efficient hydroboration of CO₂ was
also achieved, with rates comparable to those achieved for transition-metal systems. The
mechanism of this reaction has been elucidated to some degree through stoichiometric reactivity
Chapter 6 describes the synthesis of a novel boryl amide ligand, and its use in the stabilisation of
low-oxidation state group 14 compounds. This largely acts as a comparison between the
electronics and sterics of this ligand and those seen in Chapters 2-5, and as such highlights the importance in understanding how reactivities involved in this thesis can be affected through
Awards: Vice-Chancellor's Commendation for Doctoral Thesis in Excellence in 2016.