Ligand variations in low oxidation state group 13 and group 14 compounds

: synthesis, characterisation, and novel reactivity

Abstract

Low-oxidation state main group species have emerged as sustainable and versatile alternatives to transition metal reagents, demonstrating remarkable capability in bond activation and catalytic transformations. This thesis aims to advance the field through innovative ligand modification, developing novel group 13 and 14 complexes with tailored reactivity.

Chapter 1 provides an overview of main group chemistry, emphasising the synthesis, bonding and advanced reactivity of low-oxidation state group 13 and 14 element complexes with various ligand systems.

Chapters 2 and 3 focus on the synthesis of new aluminium(I) and gallium(I) complexes, stabilised by backbone-modified β-diketiminate ligands. Notably, (^EtDipnacnac)Al (^EtDipnacnac = [HC(C(Et)N(Dip))₂]), was synthesised efficiently within one hour alongside structurally unique side products. Further reactivity studies yielded unusual Al-Mg and Al-Al bonded species. The gallium analogues (^EtDipnacnac)Ga and (^iPrDipnacnac)Ga mediated unprecedented C-H activation of azobenzene, yielding stable dearomatised spirocyclic compounds that undergo rearomatisation and nucleophilic addition with benzaldehyde. Bimetallic Ga-Mg and Ga-Al complexes were also synthesised and characterised.

Chapter 4 employs a newly introduced N-heterocyclic carbene, ^EtIDip (IDip = {HC(NDip)}₂C), to stabilise robust group 13 element(III) complexes. The oxidative reactions of ^EtIDip with several small substrates, including C₂Cl₆ and CsF, generated new imidazolium halide complexes that can be used in various substitution reactions.

Chapters 5 and 6 establish a versatile synthetic method for iminophosphorane proligands and building blocks, enabling the isolation of reactive heavier group 14 metallylenes. Notably, the silylene exhibits an unprecedented dimeric structure in the solid state and readily reacts with C-C unsaturated bonds as a monomer.

This thesis explores how subtle ligand modifications influence the synthesis, structure, properties and reactivity in low-oxidation state group 13 and 14 complexes, advancing the understanding of this emerging class and providing valuable information for constructing unusual main group complexes with tailored properties in the future.

Date of Award	3 Dec 2025
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Andreas Stasch (Supervisor)