Anion directed synthesis of a hydrogensulfate selective luminescent rotaxane

Article abstract of DOI:10.1039/b418878k

A new photo-active rhenium(I) bipyridyl based rotaxane has been synthesised which by virtue of the unique interlocked structural cavity selectively senses hydrogensulfate using luminescence spectroscopy. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b418878k

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Anion directed synthesis of a hydrogensulfate selective luminescent
rotaxane{
David Curiel and Paul D. Beer*
Received (in Cambridge, UK) 16th December 2004, Accepted 25th January 2005
First published as an Advance Article on the web 8th February 2005
DOI: 10.1039/b418878k
A new photo-active rhenium(I) bipyridyl based rotaxane has
been synthesised which by virtue of the unique interlocked
structural cavity selectively senses hydrogensulfate using lumi-
nescence spectroscopy.
In an effort to fabricate innovative molecular switches, sensors and
machines, imaginative template methodologies are increasingly
being used in the construction of interlocked supramolecular
assemblies such as rotaxanes, catenanes and knots.1 Cationic and
neutral species have dominated the templated synthetic strategies
reported to date by employing metal–ligand coordination,2
electron donor–acceptor interactions,3 hydrogen bonding4 and
solvophobic effects5 to bring about assembly between two or more
components. The challenge of using anions to direct supramole-
cular assembly remains largely underexploited, which may be
attributed to their diffuse nature, pH-dependence and relatively
high solvation energy as compared to cations.6 Although various
serendipitous discoveries of cases where anions have templated the
formation of, in particular, inorganic-based polymetallic cage
complexes7 and circular double helicates8 have now appeared,
Scheme 1 (i) Et3N, CH2Cl2 (98%); (ii) Re(CO)5Cl, THF, reflux (90%);
(iii) Grubbs’ catalyst Ru[PCy3]2Cl2CHPh, CH2Cl2 (40%).
strategic anion-templated syntheses and assemblies are rare.9 This
is especially the case when employing anions in the construction of
interpenetrated compounds.10 We have recently reported a general
3,5-bis(chlorocarbonyl)pyridine produced bis-calix[4]arene 8.
method of using anions to template the formation of a range of
[2]pseudorotaxanes,11 a [2]rotaxane12 and [2]catenane.13 The
Reaction of 8 with methyl iodide followed by anion exchange
with ammonium chloride gave the pyridinium chloride bis-
assembly process is based on a coordinatively unsaturated chloride
anion of a tight ion-pair threading component,11b facilitating the
calixarene stoppered thread 9 (Scheme 2). The target rotaxane
was prepared via mixing 4 and 9 in dichloromethane solution
interpenetration of a pyridinium, imidazolium or guanidinium
followed by ring closing metathesis reaction with Grubbs’ catalyst
thread through the annulus of an isophtalamide macrocycle. As a
to produce [2]rotaxane 10 in 21% yield which was characterised by
rare example of using a rotaxane topological cavity as a potential
1H-NMR, 13C-NMR and electrospray mass spectrometry
binding site domain, we describe here the anion directed synthesis
(Scheme 3).
of a novel photo-active rhenium(I) bipyridyl based [2]rotaxane
1
In particular a comparison of the H-NMR spectra of starting
which selectively senses hydrogensulfate using luminescence
materials 4, 9, intermediate adduct 4?9 and 10 clearly shows a
spectroscopy.
correlation of respective chemical shift values (Fig. 1). Also of note
is the observation from H and 13C-NMR spectra of 10 that the
The bis-vinyl appended rhenium(I) bipyridyl derivative 4 was
1
prepared in two high yielding synthetic steps via a condensation of
calix[4]arene stoppers are magnetically inequivalent. Presumably
4,49-bis(chlorocarbonyl)-2,29-bipyridine 1 and two equivalents of
amine 212 to afford 3 followed by complexation with Re(CO)5Cl
this is a consequence of the Re(CO)3Cl-bipyridine moiety and the
possible lack of planarity of the macrocycle which creates different
(Scheme 1). Ring closing metathesis reaction of 4 with Grubbs’
catalyst produced macrocycle 5 in 40% yield (Scheme 1).14 The
calixarene environments on both sides of the macrocycle plane of
the rotaxane. Interestingly this magnetic inequivalence is not
new calix[4]arene stoppered pyridinium chloride axle component 9
observed in the 4?9 assembly which provides further evidence for
was synthesised in five steps via mononitration of tetrapropoxy-
calix[4]arene 6,15 to give 7 which on reduction and reaction with
rotaxane formation. Exchanging the chloride anion template for
the non-coordinating hexafluorophosphate anion to afford
rotaxane 11 was achieved by addition of AgPF6 to a dichloro-
methane solution of 10 (Scheme 3). 1H-NMR titrations of 11 with
{ Electronic supplementary information (ESI) available: synthetic and
characterisation details for 11 and additional fluorescence anion titration
isotherms. See http://www.rsc.org/suppdata/cc/b4/b418878k/
*paul.beer@chem.ox.ac.uk
tetrabutylammonium (TBA) chloride in acetone-d6 confirmed that
anion recognition takes place in the rotaxane binding pocket,
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Fig. 1 Comparison of the 1H-NMR spectra of 4, 9, intermediate
ensemble 4?9 (1 : 1 ratio) and 10 in CDCl3.
(Fig. 2) which may be a consequence of anion complexation in the
rotaxane recognition site increasing the rigidity of the rotaxane
superstructure, disfavouring non-radiative decay processes.16
Specfit/3217 analysis of the resulting titration curves (Fig. 3) gave
anion association constant values for the 1 : 1 complexes shown in
Table 1 along with determined values with acyclic 4 and
macrocyclic 5 rhenium(I) bipyridyl derivatives. It is noteworthy
that Table 1 reveals rotaxane 11 exhibits selectivity for hydro-
gensulfate18 in preference to chloride and nitrate. This contrasts
with acyclic 4 and macrocycle 5 receptors preferentially binding
chloride which suggests the rotaxane cavity of 11 is of
complementary topology and dimensions for the tetrahedral
hydrogensulfate anion.19
Scheme 2 (i) HNO3 (conc.), H2SO4 (fuming) (58%); (ii) NH2NH2; (iii)
3,5-(COCl)2-Py, Et3N, CH2Cl2 (38%); (iv) MeI, acetone, reflux (98%); (v)
NH4Cl, CHCl3, H2O (96%).
where in particular significant downfield shifts of the respective
amide protons were observed. As a consequence of overlapping
peaks, however, difficulties were encountered in obtaining anion
titration binding isotherms which thwarted quantitative associa-
tion constant data being obtained.
In summary a novel photo-active rhenium(I) bipyridyl [2]rotax-
ane has been constructed and shown to selectively sense
hydrogensulfate using luminescence spectroscopy. This rotaxane
receptor system serves to illustrate the potential such interlocked
molecular receptors have in future chemical sensor design and
fabrication.
Preliminary absorption and emission investigations reveal 4, 5
and rotaxane 11 behave like the parent Re(bipy)(CO)3Cl complex.
Fluorescence spectroscopy anion binding studies were under-
taken in order to evaluate the ability of rotaxane 11 to operate as a
luminescent anion sensor. The addition of chloride, nitrate and
especially hydrogensulfate tetrabutylammonium salts to acetone
solutions of 11 led to significant enhancement in emission intensity
We gratefully acknowledge the financial support of a post-
doctoral Marie Curie Fellowship of the European Union and a
EPSRC postdoctoral fellowship.
Scheme 3 (i) Grubbs’ catalyst Ru[PCy3]2Cl2CHPh, CH2Cl2 (21%); (ii) AgPF6, CH2Cl2 (91%).
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Notes and references
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Fig. 2 Fluorescence enhancement upon titration of 11 (1025 M in
acetone) (lexc = 390 nm) with TBAHSO4: 0, 0.2, 0.4, 0.6, 0.8, 1, 2, 4, 10
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Fig. 3 Fluorescence titration curves in acetone at room temperature
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TBAHSO4.
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Table 1 Association constantsa of 4, 5 and 11 with a series of
anions determined by fluorescence titration at room temperature
(lexc = 390 nm)
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17 R. A. Binstead, B. Jung and A. D. Zuberbu¨hler, Specfit/32, E 2000,
Spectrum Software Associates, Marlborough, MA, USA.
Cl2
HSO4
NO3
2
2
4
5
3.10 6 105
8.67 6 104
1.81 6 105
3.52 6 103
4.65 6 103
.106
1.82 6 103
3.87 6 103
5.13 6 104
11
a
[Host] = 1025 M in acetone; error ,10%
18 J. L. Sessler, E. Katayev, G. Dan Pantos and Y. A. Ustynyuk, Chem.
Commun., 2004, 1276.
David Curiel and Paul D. Beer*
19 Fluorescence titrations experiments of 11 with TBA dihydrogenphos-
phate also caused significant enhancement of emission intensity
suggesting strong complexation of this tetrahedral anion guest. Specfit
analysis of the resulting titration curves however failed to give an
association constant value.
Department of Chemistry, Inorganic Chemistry Laboratory, University
of Oxford, South Parks Road, Oxford, UK OX1 3QR.
E-mail: paul.beer@chem.ox.ac.uk; Fax: +44 1865 272690;
Tel: +44 1865 285142
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Chem. Commun., 2005, 1909–1911 | 1911