Santoni, Leonardo; (2024) Synthetic and Structural Studies of Aluminium(III) Complexes with β-ketoiminate and Disubstituted Ethanolamine Ligands as Precursors for Metal-Organic Deposition. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Aluminium has garnered significant interest in the printed electronics industry for its earth abundance, high conductivity, and low cost. While aluminium-based complexes have been extensively studied for catalytic applications and polymerisation, their use for direct metal deposition remains unexplored due to handling challenges caused by high reactivity with moisture and air. The use of β-ketoiminate and N,N-disubstituted ethanolamines as ligands offers great flexibility in precursor design and have been previously explored by the Knapp group. Herein, these ligands have been developed further by varying substituent bulkiness and employing them in novel applications. The design, synthesis, and characterisation of aluminium and lithium-oxo compounds, with these two classes of ligands has been explored. Compounds of the type [AlL3] were synthesised (L = Me-acnac and Ph-acnac); firstly, through the reaction with trimethylamine alane (TMAA), and secondly, from the reaction with LiAlH4, eliminating the need for TMAA and reducing the reaction steps. In Chapter 3, the synthesis of chelated aluminates (alumanyl), represented by the generic formula [L2Al]Li(OEt2)2, was achieved using monoanionic β-ketoiminate ligands. The electronic and steric properties of these ligands were found to play a critical role in the formation and stability of aluminium(III) complexes, with detailed structural analyses revealing the unique geometric configurations that these ligands can induce. Chapter 4 explores the synthesis of tricyclic aluminium hydrides using N,N-disubstituted ethanolamines, which offer distinct coordination chemistry compared to β-ketoiminates. These ligands led to the formation of aluminium hydrides with the general structure [(CH3)2NCH2CH2O]6Al4H6, which exhibited remarkable thermal stability and a unique geometry containing six Al–H bonds. Moreover, novel synthetic routes were explored utilizing LiAlH4 in place of TMAA. Chapter 5 delves into the structural diversity of lithium-oxo cages, focusing on how ligand bulkiness impacts the formation of hexameric [Li6O6] and tetrameric [Li4O4] cores. These complexes were synthesized and characterized, with TGA confirming their thermal stability at elevated temperatures, highlighting their potential in metal deposition and materials science. The Chapter also underscores the significance of ligand design in influencing structural outcomes and stability. This study not only enhances the understanding of organometallic chemistry but also offers practical insights for developing metal deposition precursors. As the demand for efficient and scalable materials grows, the insights from this thesis will play a crucial role in advancing aluminium-based deposition technologies.

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