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Rhenium calix[4]arenes: precursors to novel imaging and cancer therapy agents

journal contribution
posted on 15.08.2014, 10:47 authored by Carl Redshaw, Xiaoming Liu, Shuzong Zhan, David L. Hughes, Hugo Baillie-Johnson, Mark ElsegoodMark Elsegood, Sophie H. Dale
Interaction of [ReOCl3(PPh3)2] with tert-butylcalix[4]areneH4, Cax(OH)4, in the presence of MOtBu (M = Na, K), or MH, under anaerobic conditions affords the isostructural rhenium(V) oxo complexes [Re(O)(PPh3)Cax(O)4M(NCMe)2] · 4MeCN [M = Na, (1); K, (2)] containing an alkali-metal cation within an elliptical ligand conformation. In the presence of air, the same reaction affords dioxo rhenium(VII) complexes of the form [Re(O)2Cax(O)4M(NCMe)2] [M = Na, · ca. 2.8MeCN (3); K, · 3MeCN (4)]. Prolonged heating also led to the isolation of the first examples of rhenium–rhenium bonding supported by calixarene ligands, viz. [ReCax(O)4M(NCMe)2(μ-O)]2 · 4MeCN [M = Na, (5); K, (6)], and in one case to {ReCax(O)4K(NCMe)2[μ-OK(NCMe)2]}2Cax(O)2(OH)2 · 7MeCN (7). The use of 2 as starting material led to the isolation of the complex {[Re(O)Cax(O)4K(NCMe)2]2(μ-O)} · 2MeCN (8). Given the diversity and complexity of the products arising from these “oxo” reactions, attention was switched to the isoelectronic organoimido [NR] group, and given its synthetic utility, the tert-butylimido group [NtBu] was chosen as our entry point. Reaction of [Re(NtBu)2Cl3] with Cax(OH)4 in a 1:1 ratio afforded the orange [Re(NtBu)2ClCax(O)2(OH)2]· MeCN (9), containing both a linear and a bent imido group. Increasing the amount of Cax(OH)4 (2:3 ratio) afforded both 9 together with the dark red complex [Re(NtBu)Cax(O)4Cax(O)(OH)3]· 6MeCN (10), which contains both mono- and tetra-dentate calixarene ligands. In the presence of adventitious oxygen, the complex {[Re(NtBu)Cax(O)4]2(μ-O)} · 3MeCN (11) was formed. To favour monomeric complex formation, the lithium salt of the monomethoxycalix[4]arene, namely Cax(OLi)3(OMe), was treated with [Re(NtBu)2Cl3] affording the mono- and bisacetonitrile-ligated species [Re(NtBu)2Cax(O)4Li(NCMe)2][Re(NtBu)2Cax(O)4Li(NCMe)] · MeCN (12). To avoid the lithium incorporation of 12, Cax(OH)3(OMe) was treated with [Re(NtBu)3(OSiMe3)] affording [Re(NtBu)2Cax(O)3(OMe)] (13), for which the methoxy ether group protudes into the calixarene cavity. The compounds 1–13 have been structurally characterised by single-crystal X-ray diffraction (synchrotron radiation was used for 4, 6, 7, 9, 11–13).

Funding

This work was supported by the Bryan Gunn Leukaemia Trust (Norwich, U. K.). The Engineering and Physical Sciences Research Council (EPSRC) is thanked for the award of beam-time at Daresbury Laboratory and a studentship (S. H. D.).

History

School

  • Science

Department

  • Chemistry

Published in

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

Issue

17

Pages

2698 - 2712 (15)

Citation

REDSHAW, C. ... et al., 2008. Rhenium calix[4]arenes: precursors to novel imaging and cancer therapy agents. European Journal of Inorganic Chemistry, 2008(17), pp.2698-2712.

Publisher

© Wiley-VCH Verlag GmbH 72 & Co.

Version

NA (Not Applicable or Unknown)

Publication date

2008

Notes

This item is Closed Access.

ISSN

1434-1948

Language

en