New lithium cuprates for the promotion of directed organic transformations
Harford, Philip James
Wheatley, Andrew E. H.
University of Cambridge
Department of Chemistry
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Harford, P. J. (2014). New lithium cuprates for the promotion of directed organic transformations (doctoral thesis).
The use of bimetallic bases to effect highly stereoselective organic transformations via Directed ortho Metalation (DoM) is an important synthetic tool and requires thorough investigation to maximise efficiency and develop a mechanistic understanding. This thesis begins with a discussion of the history of DoM covering firstly monometallic lithium bases before moving to bimetallic magnesiate, zincate, aluminate, manganate bases and finally covering cuprate bases, which are the focus of this thesis. A description of the techniques employed in this project, which focuses on X-ray crystallography as the primary characterisation tool, follows. The experimental procedures and the associated characterisation data are also presented. These demonstrate that the addition of 2 equivalents of an amido or phosphido lithium to a copper(I) salt results in the crystallisation of a series of bis(amido)- and bis(phosphido)cuprates, and phosphidocopper compounds, many of which are suitable Directed ortho Cupration (DoCu) reagents. Syntheses involving phosphido ligands lead to the isolation of only one lithium cuprate species, Gilman-type [(Cy2P)2CuLi • 2THF], 11, which forms a polymer in the solid-state and is an ineffective DoCu agent. Alternative pathways which yield interesting novel phosphidocopper compounds [(Ph2P)6Cu4][Li • 4THF]2, 9, and Ph2PCu(CN)Li • 2THF, 10, are also investigated. The solid-state structures of all three species are discussed in detail. In situ preparations of bis(amido)cuprate bases from CuICl are shown to be effective in the deprotocupration of halopyridines. Reactions carried out with and without LiCl present in the mixture demonstrate that Lipshutz-type formulation bases are the active species. Analogous preparations from CuIBr are also effective in ortho deprotonation although do not provide consistently high-yields. In the solid-state, both bases are shown to form Lipshutz-type cuprates, [(TMP)2Cu(X)Li2 • THF]2 (X = Cl, Br). The effects of changing the donor solvent to the weaker Lewis base diethyl ether on the syntheses of Lipshutz-type cuprates are investigated, resulting in the isolation of [(TMP)2Cu(X)Li2 • Et2O]2 (X = CN, Hal). The results show that the solid-state structures are very similar to the analogous THF-solvated species. However, when the recrystallisation step is carried in bulk Et2O Lipshutz-type cuprates form, unlike when THF is employed which results in the formation of the Gilman-type cuprate [(TMP)2CuLi]2, 2. Changing the amido ligand to the less sterically demanding cis-2,6-dimethylpiperidine (HDMP) results in the formation of a remarkable new pentametallic structural motif, [(DMP)2CuLi • OEt2]2LiX (X = Hal), which can be viewed as an adduct between monomeric Lipshutz- and Gilman-type cuprates. The isolation of [(DMP)2CuLi • 2THF]2LiBr, 23 shows that adduct-type cuprates form regardless of the nature of the donor solvent and plausible explanations for the preference of DMP-based cuprates to form adduct-type species rather than Lipshutz-type species are presented. Reactivity studies demonstrate that 23 is an effective DoCu agent and theoretical studies explore possible mechanisms as well as the relative energies of the three cuprate structure types. The thesis is completed with a summary of the conclusions drawn and suggestions for further work. Ideas for further solid-state (including extensive investigations into the effects of sterics on the formation of cuprates), solution-state, reactivity and theoretical studies are put forward along with the rationale behind them.
Inorganic Chemistry, Organometallics, Lithium, Copper
This record's URL: http://www.repository.cam.ac.uk/handle/1810/246262