Switchable π-coordination and C–H metallation in small-cavity macrocyclic uranium and thorium complexes

Arnold, P. L., Farnaby, J. H. , White, R. C., Kaltsoyannis, N., Gardiner, M. G. and Love, J. B. (2014) Switchable π-coordination and C–H metallation in small-cavity macrocyclic uranium and thorium complexes. Chemical Science, 5(2), pp. 756-765. (doi: 10.1039/C3SC52072B)

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New, conformationally restricted ThIV and UIV complexes, [ThCl2(L)] and [UI2(L)], of the small-cavity, dipyrrolide, dianionic macrocycle trans-calix[2]benzene[2]pyrrolide (L)2− are reported and are shown to have unusual κ5:κ5 binding in a bent metallocene-type structure. Single-electron reduction of [UI2(L)] affords [UI(THF)(L)] and results in a switch in ligand binding from κ5-pyrrolide to η6-arene sandwich coordination, demonstrating the preference for arene binding by the electron-rich UIII ion. Facile loss of THF from [UI(THF)(L)] further increases the amount of U–arene back donation. [UI(L)] can incorporate a further UIII equivalent, UI3, to form the very unusual dinuclear complex [U2I4(L)] in which the single macrocycle adopts both κ5:κ5 and η6:κ1:η6:κ1 binding modes in the same complex. Hybrid density functional theory calculations carried out to compare the electronic structures and bonding of [UIIII(L)] and [UIII2I4(L)] indicate increased contributions to the covalent bonding in [U2I4(L)] than in [UI(L)], and similar U–arene interactions in both. MO analysis and QTAIM calculations find minimal U–U interaction in [U2I4(L)]. In contrast to the reducible U complex, treatment of [ThCl2(L)] with either a reductant or non-nucleophilic base results in metallation of the aryl rings of the macrocycle to form the (L−2H)4− tetraanion and two new and robust Th–C bonds in the –ate complexes [K(THF)2ThIV(μ-Cl)(L−2H)]2 and K[ThIV{N(SiMe3)2}(L−2H)].

Item Type:Articles (Editorial)
Glasgow Author(s) Enlighten ID:Farnaby, Dr Joy
Authors: Arnold, P. L., Farnaby, J. H., White, R. C., Kaltsoyannis, N., Gardiner, M. G., and Love, J. B.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Chemical Science
Publisher:Royal Society of Chemistry
ISSN (Online):2041-6539
Published Online:02 December 2013
Copyright Holders:Copyright © 2014 The Royal Society of Chemistry
First Published:First published in Chemical Science 5(2): 756-765
Publisher Policy:Reproduced under a Creative Commons License

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