Advancing Aluminyl Anions: Synthesis of Acyclic and Four-Membered Metallocyclic Aluminium Nucleophiles

Abstract

Chapter 1 presents a general introduction to modern organometallic chemistry and its subsequent paradigm shift encompassing the developing roles of the main group elements, their fundamental considerations and challenges in low oxidation state element synthesis. It includes an overview of the frontiers of research interests and the pursuit of transition-metal metallomimetic species for small molecule activation. Finally, the focus of the chapter shifts to group 13, highlighting its elemental members, and a chronological summary of research discoveries in developing a new class of group 13 anionic nucleophiles.

Chapter 2 focuses on the preparation of bulky silylamido aluminium(III) halide complexes incorporating both monodentate and bidentate chelating ligand scaffolds. The rationalisation and role of ligand design in modern organometallic chemistry, and previous applications of the utilised ligand scaffolds are discussed. The necessitated synthetic routes, isolation and structure of prepared species are explored and compared with related aluminium(III) halide complexes. The complexes reported in the chapter will serve as precursors for the novel aluminyl anions presented in Chapters 3 and 4.

Chapter 3 discusses the preparation and isolation of low oxidation state, aluminium(I) nucleophiles. These include the isolation and characterisation of the first acyclic aluminyl anion [K2(Al{N(Dipp)SiMe3}2)2], synthesised by the reduction of [AlI{N(Dipp)SiMe3}2] with potassium graphite. The reduction of the bulkier analogue, [AlI{N(Dipp)Si(iPr)3}2], yielded intramolecular activation products consistent with the transient generation of an aluminyl anion. The reactivity of the resulting acyclic aluminyl anion was explored briefly towards a range a small molecules, and applied in the preparation of the magnesium aluminyl complexes [(ArNanac)Mg-Al{N(Dipp)SiMe3}2] ([ArNacnac]- = [(ArNCMe)2CH]-, Ar = mesityl, 2,6-diisopropylphenyl). Structural classifications of related aluminyl anions are explored from the conversion of the parent acyclic aluminyl anion contact dimeric pair toward both monomeric and charge-separated ion pairs.

Chapter 4 further expands on the isolated examples of low oxidation state aluminium(I) nucleophiles. This includes the isolation and characterisation of the first aluminyl anion contained within a four-membered metallocycle. This anion was synthesised by the reduction of the aluminium(III) iodide precursor [AlI(DAS)] ([DAS]2- = [Ph2Si(NDipp)2]2-) with potassium graphite under short timeframes, [K{Al(DAS)}] was isolated as a 1-dimensional coordination polymer in the solid state. Synthesis and characterisation of the corresponding iron aluminyl coordination complex [(CO)2CpFe-Al(DAS)] (Cp = cyclopentadienyl) is also discussed. The reactivity of [K{Al(DAS)}] was briefly explored and utilised in the preparation of complexes featuring unsupported bonds of Mg-Al [(ArNanac)Mg-Al(DAS)] and Al-Al [{Al(DAS)}2]. The published library and presented aluminyl anions [K2(Al{N(Dipp)SiMe3}2)2] and [K{Al(DAS)}] are compared, concerning their ligand scaffolds and the imparted electronic and nucleophilic effects present in reactivity is reported.

Chapter 5 concentrates on research investigations undertaken on exchange at the University of Stuttgart. Huckel antiaromatic group 13 metalloles incorporating boron and aluminium, and their reduction to give aromatic and radical species are discussed. The redox applications of the acyclic aluminyl anion [K2(Al{N(Dipp)SiMe3}2)2] with 2,5-disilyl-3,4-diaryl boroles is presented through reductions to analogous boroldiide and borole radical anions, and coinciding oxidation yielding an acyclic dialane [(Al{N(Dipp)SiMe3}2)2]. A catalogue of new 2,5-disilyl-3,4-diaryl alumole complexes are reported, their synthesis, structure and reactivity are explored, and investigations undertaken toward new NHC-stabilised alumole cations are discussed. Show more