Rotaxane-Based Transition Metal Complexes: Effect of the Mechanical Bond on Structure and Electronic Properties

Martina Cirulli, Amanpreet Kaur, James E.M. Lewis, Zhihui Zhang, Jonathan A. Kitchen, Stephen M. Goldup*, Maxie M. Roessler

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)

Abstract

Early work by Sauvage revealed that mechanical bonding alters the stability and redox properties of their original catenane metal complexes. However, despite the importance of controlling metal ion properties for a range of applications, these effects have received relatively little attention since. Here we present a series of tri-, tetra-, and pentadentate rotaxane-based ligands and a detailed study of their metal binding behavior and, where possible, compare their redox and electronic properties with their noninterlocked counterparts. The rotaxane ligands form complexes with most of the metal ions investigated, and X-ray diffraction revealed that in some cases the mechanical bond enforces unusual coordination numbers and distorted arrangements as a result of the exclusion of exogenous ligands driven by the sterically crowded binding sites. In contrast, only the noninterlocked equivalent of the pentadentate rotaxane Cu II complex could be formed selectively, and this exhibited compromised redox stability compared to its interlocked counterpart. Frozen-solution EPR data demonstrate the formation of an interesting biomimetic state for the tetradentate Cu II rotaxane, as well as the formation of stable Ni I species and the unusual coexistence of high- and low-spin Co II in the pentadentate framework. Our results demonstrate that readily available mechanically chelating rotaxanes give rise to complexes the noninterlocked equivalent of which are inaccessible, and that the mechanical bond augments the redox behavior of the bound metal ion in a manner analogous to the carefully tuned amino acid framework in metalloproteins.

Original languageEnglish
Pages (from-to)879-889
Number of pages11
JournalJournal of the American Chemical Society
Volume141
Issue number2
DOIs
Publication statusPublished - 16 Jan 2019

Bibliographical note

Funding Information:
The authors thank Graham Tizzard of the UK National Crystallographic Service at the University of Southampton for assistance with SCXRD. Fluorochem is gratefully acknowledged for the gift of reagents. This work was supported financially by the Royal Society (Research Fellowship to S.M.G.; SERB cofunded Newton International Fellowship to A.K.C.), the European Union (Marie Skłodowska-Curie Fellowship to J.E.M.L., agreement No 660731), European Research Council (Consolidator Grant, agreement no. 724987), and the EPSRC (EP/J01981X/1). M.C. and M.M.R. thank the Materials Research Institute (QMUL) for a studentship.

Publisher Copyright:
Copyright © 2018 American Chemical Society.

ASJC Scopus subject areas

  • Catalysis
  • General Chemistry
  • Biochemistry
  • Colloid and Surface Chemistry

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