Alkali metal chemistry in solution and solid-state

Abstract

Alkali metal organometallic and electride chemistry are essential tools in synthetic chemistry. Alkali metal organometallic reagents aggregate in both solution and solid-state forming clusters and polymers. Electrides, usually formed in situ, via the dissolving of alkali metals in liquid ammonia forming a solution of solvated electrons, have been utilised throughout academia and industry in the Birch reduction. Chapter 1 explores the strategies that have been employed to isolate low aggregates and, in particular, monomeric complexes of the most relevant alkali metal alkyls to this thesis. Furthermore, an overview of organic and inorganic electrides, and the closely related alkalides is provided. Chapter 2 discusses the synthesis and reactivity of organolithium/sodium monomeric complexes. A novel hexadentate neutral amine ligand, DETAN, was utilised to isolate the first monomeric complex of the parent organolithium, methyllithium. Following this, monomeric complexes of trimethylsilylmethyl lithium/sodium were synthesised using the Me6Tren ligand. The reaction of the trimethylsilylmethylsodium monomer towards a variety of ketones, aldehydes and amides resulted in methylenation. In contrast, nucleophilic addition resulted with both the trimethylsilylmethylsodium aggregate and trimethylsilylmethyllithium monomer. A ligand-catalysis strategy was developed to conduct ketone/aldehyde methylenations, using [NaCH2SiMe3]∞ as the CH2 feedstock and Me6Tren as the catalyst (5 mol%). The work was expanded to produce tri-substituted internal alkenes, using monomeric trimethylsilylbenzyl lithium/sodium complexes. In chapter 3, the diverse coordination modes of the DETAN ligand are comprehensively investigated, along with the Me6Tren and Me3TACN ligands, towards lithium/sodium iodide and tetraphenylborate compounds. SCXRD, DOSY NMR and variable-temperature NMR were used investigate the solid and solutionstate structures and dynamic behaviour. Chapter 4 details the use of mechanochemistry to synthesise a Li/K heterobimetallic electride, K+(LiHMDS)e- (HMDS: hexamethyldisilazide). The electride nature was confirmed experimentally via EPR and SQUID. This electride was utilised to promote benzene and pyridine coupling and the first solvent-free Birch-type reductions.