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Title: An exploration of alkali metal ferrate chemistry : synthesis and exploitation for N-heterocyclic carbene and fluoroarene functionalisation
Author: Maddock, Lewis Caradoc Huw
ISNI:       0000 0004 6061 3730
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2016
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Building on previous developments on cooperative heterobimetallic reagents, this thesis aims to advance the understanding of the preparation and synthetic exploitation of alkali metal ferrates of Fe(II). Using bis(amide) Fe{N(SiMe3)2}2 as a precursor, here we report the syntheses and structures of a variety of sodium ferrates that have been prepared via direct co-complexation, where the single metal components NaN(SiMe3)2 and Fe{N(SiMe3)2}2 self-assemble in the presence of a range of Lewis donors with different electronic properties and denticities. Furthermore, in some cases the presence of these donors is not required and the isolation and structural elucidation of two novel unsolvated sodium ferrates has been accomplished which display unique polymeric arrangements in the solid state. The ability of sodium ferrates to functionalise NHC ligands has also been assessed, finding that when unsaturated NHC IPr (IPr = 1,3-bis(diisopropylphenyl)-imidazol-2-ylidene) is treated sequentially with NaCH2SiMe3 and Fe{N(SiMe3)2}2, sodium ferrate (THF)3·Na[:C{[N(2,6-iPr2C6H3)]2CHCFe(HMDS)2}] (15) is formed, containing an anionic NHC which binds to Fe via its C4 position and to Na through its C2 site. Interestingly, this complex was found to be an excellent precursor for Fe-abnormal NHC complexes and when treated with MeOTf afforded [CH3C{[N(2,6-iPr2C6H3)]2CHCFe(HMDS)2}] (16). 1,4-dioxane solvate [dioxane·NaFe(HMDS)3] (17a) has been found to be an efficient chemoselective base to promote the direct ferration at room temperature of a wide range of fluoroaromatic molecules. Structural elucidation of key organometallic intermediates has revealed the synergic bonding of the metals with Fe occupying the position previously filled by an H atom forming a strong Fe-C sigma bond, whereas the Na atom forms a dative bond with the F atom. These studies have revealed an important alkali metal effect, thus when the Na atom in 17a is replaced by Li or K, the ferration processes are inhibited. Remarkably, by using two molar equivalents of 17a, it is possible to di-ferrate tri-and tetrafluoro-substituted aromatics. These reactions take place at ambient temperature with excellent yields. Reaction of 1,3,5-trifluorobenzene with three molar equivalents of 17a, led to the isolation of [1,3-bis(FeHMDS)-2,4,6-tris(HMDS)-C6H] (38) resulting from the unprecedented two-fold C-H metallation/three-fold C-F activation of the substrate. Mechanistic studies suggest the reaction is partly driven by the formation of NaF. Magnetic studies using have revealed that this new compound displays single-molecule magnet behaviour.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral