Group 11 'Ate Bases: Towards an Understanding of Solid- and Solution-State Structures
Peel, Andrew James
Wheatley, Andrew E. H.
University of Cambridge
Doctor of Philosophy (PhD)
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Peel, A. J. (2017). Group 11 'Ate Bases: Towards an Understanding of Solid- and Solution-State Structures (Doctoral thesis). https://doi.org/10.17863/CAM.13846
Lithium bis(amido)cuprates are an important class of bimetallic base, which can chemo- and regioselectively metalate aromatic compounds, via directed ortho cupration (DoCu). This thesis begins with an introduction to aspects of the chemistry of organolithium compounds, group 11 organometallic compounds and their lithium 'ate complexes. Examples of such synergic bases are presented and the introduction is concluded with a discussion of lithium bis(amido)cuprate bases, which along with their silver congeners, are the subject of this dissertation. In general, syntheses involve the addition of a lithium amide to a group 11 salt, resulting in the formation of a lithium bis(amido)cuprate or argentate. Structurally focussed work commences with the use of new amide ligands to develop heteroleptic bis(amido)cuprate systems. The reaction of mixtures of lithium amides with CuBr provides a series of novel Lipshutz-type and Gilman cuprates. Interesting structural features are uncovered, which are rationalised in terms of altered steric demands in the newly introduced amide ligands in these systems. CuSCN and CuOCN are investigated as inexpensive and safer alternatives to CuCN in cuprate formation. In the solid state, a series of Lipshutz-type cuprates (TMP)2Cu(SCN)Li2(L) (L = Et2O, THF, THP) are revealed, whose molecular conformations are infuenced by the identity of the Lewis base. However, in benzene solution, in situ conversion of Lipshutz-type to Gilman cuprate is found to occur. Moving to the synthetic setting, derivatisation of chloropyridines is attempted and gives functionalised halopyridines in 51-71 % yield. CuOCN is found to behave quite differently when reacted in the same way as CuSCN, whereby X-ray crystallography reveals structures in which Cu-Li substitution is apparent. The unique reactivity of CuOCN is interpreted with the aid of multinuclear NMR spectroscopy. A new route to Lipshutz-type cuprates is explored by the synthesis of (TMP)2Cu(OCN)Li2(THF) from Gilman cuprate and LiOCN. This avoids Cu-Li substitution. Meanwhile, reaction of lithium N,N-diisopropylamide with CuOCN also avoids metal disorder, to give a novel lithium cuprate-lithium amide adduct. Further advances in our understanding of group 11 'ate complexes are made by introducing silver as a spectroscopically active nucleus in the lithium argentates (TMP)2AgLi and (TMP)2Ag(CN)Li2(THF). In the solid state, these parallel the structures known for Gilman cuprate (TMP)2CuLi and Lipshutz cuprate (TMP)2Cu(CN)Li2(THF), respectively. In solution, NMR spectroscopy reveals features consistent with retention of these structures. Lastly, the formation of mixed Cu-Li aggregates from combining TMPLi and TMPCu in aromatic solvent are investigated. Surprising reactivity is uncovered, in which the aromatic solvent is metalated and incorporated into mixed-metal aggregates. This thesis concludes with a summary of the findings and suggestions for future work, including how the findings presented herein may be transformed into practical improvements to cuprate systems. In particular, the possibility that Gilman cuprate may be activated towards the metalation of aromatic substrates by the addition of sub-stoichiometric or catalytic amounts of a lithium salt additive is explored.
X-ray crystallography, NMR spectroscopy, heterobimetallic, synergic base, lithium, cuprate, argentate, directed ortho metalation
EPSRC grant EP/J500380/1
This record's DOI: https://doi.org/10.17863/CAM.13846
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