Synthesis, characterisation and application of main group metal amides

2017-01-16T22:44:13Z (GMT) by Koutsaplis, Magdalini
The work presented in this thesis describes the synthesis, characterisation and application of main group metal amides. Metal complexes of the alkali metal series (group 1), lithium, sodium and potassium were primarily investigated. In addition, metal complexes of the p block series, which include aluminium and tin, were investigated to a lesser extent. Chapter one commences with a discussion on the synthesis and characterisation of group 1 metal amides leading to a more specific focus on chiral alkali metal amides. Chiral lithium amides based on α-methylbenzylamine have found application in the asymmetric synthesis, with a high degree of selectivity being of paramount importance. Metallation of the chiral amine (S)-N-(α-methylbenzyl)allylamine with nBuM (M = Li, Na and K) leads to the formation of complexes with three distinct isomeric anion forms: [(PhC(H)Me)(CH2CH=CH2)N]-, 1-aza-allyl [(PhC(H)Me)(CH=CHMe)N]- and aza-enolate [(PhC=CH2)(CH2CH2Me)N]-. The aza-enolate anionic form was also evident in the potassium complex formation of the chiral amine (S)-N-(α-methylbenzyl)phenylallylamine. The anionic form is dependent on the metal, the Lewis donor and thermal history of the complex. Full chemical characterisation, including single crystal X-ray structure determination where possible, was obtained on all new compounds. Chapter two describes the synthesis and characterisation of a chiral aminoalane and chiral aminoalane adduct. Salt elimination of dilithiated (S)-N-(α-methylbenzyl)allylamine with Me2AlCl proved to be a successful synthetic method. The attempted synthesis of mixed metal complexes of the chiral amines (S)-N-(α-methylbenzyl)allylamine and (S) N (α methylbenzyl)phenylallylamine was not successful, but led to the isolation and characterisation of some equally interesting complexes. Full chemical characterisation, including single crystal X-ray structure determination where possible, was obtained on all new compounds. Chapter three describes the synthesis and characterisation of the intermediate formed following metallation of the lactim ether, o-methylvalerolactim with nBuM (M = Li, Na and K). The lactim ether rearranges to form an aza-enolate complex following deprotonation at the α-carbon and coordination of the metal to the nitrogen centre. However, in the absence of a Lewis donor solvent, the rate of deprotonation decreases substantially and nucleophilic substitution of the methoxy group predominates. Full chemical characterisation, including single crystal X-ray structure determination where possible, was obtained on all new compounds Chapter four describes the application of a chiral sodium amide complex in synthesis. Reaction of the sodium anion of (S) N (α methylbenzyl)allylamine with two equivalents of tBu-cinnamate results in a remarkable domino reaction sequence that involves an aza-allyl conjugate, Michael addition, ring closure reaction. This leads to the formation of a chiral aminocyclohexane containing six new vicinal stereogenic centres, with excellent level of stereocontrol. In addition to the formation of the initial aminocyclohexane, a second product isolated from the reaction results from the formation of an N-protected β-lactam fused to the cyclohexane, forming an aza-bicyclo[4.2.0] octane. Preliminary reactivity studies provide a promise of greater scope and application for the domino reaction sequence. Full chemical characterisation, including single crystal X-ray structure determination where possible, was obtained on all new compounds.