Syntheses and structural characterisations of amidinates, diaminates and phenolates antimony (I and III) and aluminium (III) complexes

Abstract

This thesis focuses on the synthesis and characterisation of antimony(III) and aluminium(III) amidates with an emphasis on structural characterisation, presenting the isolation of 22 new complexes. In addition, some chemistry of (2,6-di–tert-butyl-4-methyl) antimony and aluminium (III) complexes is added in the appendix of this thesis. Below is a general outline for each chapter of original research (2-4), showing the diverse range of compounds obtained from the following formamidinate and polyfluorophenylamidate ligands. Chapter 1 gives an overall introduction to antimony and aluminium (III) chemistry. This chapter describes the general aspects and overview of the relevant literature highlighting the most common synthetic methods used to synthesis antimony and aluminium compounds, particularly formamidinates, amidates, phenolates and their applications. Chapter 2 describes the metathesis reactions employed for the preparation of a range of mono- and bis-substituted formamidinato antimony (III) complexes. The bissubstituted complexes include [Sb(DippForm)₂Cl] (2.2), [Sb(DippForm)₂Br] (2.3) and [Sb(DippForm)₂I] (2.4) and mono-substituted products include [Sb(DippForm)Br₂] (2.5) and [Sb(DippForm)I₂] (2.6). Other complexes have been prepared as dimers [Sb(DippForm)(NSiMe₃)]₂ (2.8) and [Sb(DippForm)Cl(C₆F₅)]₂.(THF)₂ (2.12), also the formamidinato-bridged distibane [Sb₂{μ-(DippForm}₂].(THF)₈ (2.1) that represents an example of monovalent antimony. Fundamentally, the synthesis of antimony (I) and (III) formamidinate complexes was accomplished through deprotonation of N,N'-2,6-diisopropylphenylformamidine (DippFormH) by a metal alkyl/amide reagent (n-BuLi, LiN(SiMe₃)₂, NaN(SiMe₃)₂) in a donor solvent THF or in PhMe and then combined with SbX₃ in THF and/or PhMe. The unexpected [(DippForm)ClSb(μ-O)SbCl₂(Me₂NC₂H₄NMe₂)]₂.(C₆D₆) (2.11) was the only type of halogenated hetero dinuclear complex isolated in this study. Chapter 3 details the synthesis and characterisation of a series of heteroleptic and homoleptic N,N-dimethyl-N'-2,3,5,6-tetrafluorophenylethane-1,2-diaminate antimony (III) complexes. [Sb(p-HC₆F₄NC₂H₄NMe₂)₂Cl] (3.2) and [Sb(p-HC₆F₄NC₂H₄NMe₂)3] (3.3) complexes were isolated by metathesis reactions between SbCl3 and Li(p-HC₆F₄N(CH₂)₂NMe₂), a common synthetic route to antimony complexes; while the direct reaction between SbCl3 and p-HC₆F₄NH(CH₂)₂NMe₂ was used to synthesise [Sb(p-HC₆F₄NC₂H₄NMe₂)Cl₂] (3.1). Halo- and nonhalo-polyfluorophenylamido antimony (III) complexes were gained as monomers in the solid state. Chapter 4 Extending this chemistry to formamidinate aluminium resulted in the isolation of a group of new and interesting formamidinato aluminium (III) complexes ranging from mono- to bis-substituted, involving different bonding modes. Metathesis reactions between AlX₃ (X = Cl, Br, I) and two different deprotonated N,N'-chelating ligands (XylForm) and (DippForm) of varying steric bulk and functionality were used to increase the range of the haloorgano(formamidinato) aluminium (III) system. These complexes are [Al(XylForm)₂Cl] (4.1), [Al(XylForm)₂I].PhMe (4.2), [Al(XylFormH)Br₃] (4.3), [Al(DippFormH)Br₃] (4.5) and [Al(DippForm)₂Cl] (4.8). Using the bulkier formamidinate ligand (DippForm) allowed the isolation of [Al(DippForm)Cl₂(thf)] (4.6) and [Al(DippForm)ClBr(thf)] (4.7). The heteroleptic [Al₃(XylForm)₂(μ₃-O)(OH)Cl₄]₂.PhMe (4.4) was isolated as a monomer and represents a compound contained three aluminium atoms bridged by an oxygen atom. In a different approach, a chlorine/methyl exchange reaction was used for forming bimetallic Al/Sb (III) ionic complexes [Me₃Sb-SbMe₂][AlCl₄] (4.9) and [Br₃Sb-μBr-SbBr₃][AlCl₂(thf)₄] (4.10), showing relatively rare coordination modes. Overall, the knowledge regarding amidato antimony and aluminium (III) complexes has been enhanced and more information has been obtained regarding their structural motifs and bonding modes. The N,N'-bis(aryl)formamidinate ligands can form stable and structurally interesting mono/trivalent antimony and trivalent aluminium species using metathesis route, due to their ease of steric variability. In addition, this thesis demonstrates the ability of N,N-dimethyl-N'-2,3,5,6-tetrafluorophenylethane-1,2-diaminate ligand to stabilise antimony in its most common and stable oxidation state (III). Many of these compounds, particularly the compounds with M-X bonds, are now well set for potential reduction to low valent species. Reaction with KC₈ should form isolable low valent Sb or Al complexes and this work could be performed in future work. There are also many other formamidinate, guanidinate and amidinate ligands that could be used to extend this work.