Luminescent Anion Sensing by Transition-Metal Dipyridylbenzene Complexes Incorporated into Acyclic, Macrocyclic and Interlocked Hosts

Article abstract of DOI:10.1002/chem.202000661

A series of novel acyclic, macrocyclic and mechanically interlocked luminescent anion sensors have been prepared by incorporation of the isophthalamide motif into dipyridylbenzene to obtain cyclometallated complexes of platinum(II) and ruthenium(II). Both

Full text of DOI:10.1002/chem.202000661

A Journal of
Accepted Article
Title: Luminescent Anion Sensing by Transition Metal Dipyridylbenzene
Complexes Incorporated into Acyclic, Macrocyclic and Interlocked
Hosts
Authors: Richard Charles Knighton, Sophie Dapin, and PD D. Beer
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Luminescent Anion Sensing by Transition Metal Dipyridylbenzene
Complexes Incorporated into Acyclic, Macrocyclic and Interlocked
Hosts
Richard C. Knighton,*[a] Sophie Dapin,[a] and Paul D. Beer*[a]
Dedication ((optional))
[a]
Dr. R. C. Knighton, S. Dapin, Prof. P. D. Beer
Department of Chemistry
University of Oxford
Mansfield Road, Oxford, OX1 3TA, UK
E-mail: paul.beer@chem.ox.ac.uk; knighton@unistra.fr
Supporting information for this article is given via a link at the end of the document.
Abstract A series of novel acyclic, macrocyclic and mechanically stimulated the growth of abiotic anion receptor design, and
interlocked luminescent anion sensors have been prepared via importantly the need for the development of anion sensor
incorporation of the isophthalamide motif into dipyridylbenzene to materials. We[7] and others[8] have utilised the unique, three
obtain cyclometallated complexes of platinum (II) and ruthenium (II). dimensional topological cavities of mechamically interlocked
Both the acyclic and macrocyclic derivatives 7·Pt, 7·Ru·PF6, 10·Pt molecules (MIMs) for anion recognition applications. The
and 10·Ru·PF6 are effective sensors for a range of halides and integration of photo-active reporter groups into MIM structural
oxoanions. The near-infra red emitting ruthenium congeners exhibited host frameworks enables such systems to selectively sense
an increased binding strength compared to platinum due to the anions via optical luminescent methodologies.[9] However, there
cationic charge and thus additional electrostatic interactions. is
a
paucity of such interlocked sensors incorporating
Intramolecular hydrogen-bonding between the dipyridylbenzene luminophores which combine long lifetimes and efficient
ligand and the amide carbonyls increases the preorganisation of both photosensitisation, such as cyclometallated transition-metal
acyclic and macrocyclic metal derivatives resulting in no discernible complexes. Herein we incorporate an anion binding
macrocyclic effect. Interlocked analogues were also prepared, and isophthalamide group into the dipyridylbenzene ligand structure
preliminary luminescent chloride anion spectrometric titrations with to produce a range of acyclic, macrocyclic and rotaxane PtII and
12·Ru·(PF6)2 demonstrate a marked increase in halide binding affinity RuII transition metal based hosts and investigate their anion
due to the complementary chloride binding pocket of the [2]rotaxane. binding and sensing capabilities.
1H NMR binding titrations indicate the interlocked dicationic receptor
is capable of chloride recognition even in competitive 30% aqueous
mixtures.
Results and Discussion
Synthesis
The synthetic strategy devised involved the initial preparation of
Introduction
PtII and RuII cyclometallated complexes which contained
carboxylic acid functionalities which would then facilitate
integration into acyclic, macrocyclic and interlocked receptor
structural frameworks via acid chloride-amine condensation
reactions, contrasting previous strategies of post-synthetic
modification of macrocyclic precursors or interlocked
architectures.[10] The synthesis of the dimethyl 4,6-
dipyridylisophthalate ligand 4 was accomplished using a 3-step
sequence (Scheme 1). Dibromo-m-xylene 1[11] was oxidised using
aqueous KMnO4 to afford 2 which was transformed to the methyl
ester 3 via reaction in acidic methanol solution. The target ligand
4 was then obtained in 58% yield by PdII catalysed Stille coupling
between 3 and 2-tributylstannyl pyridine and combined with the
appropriate metal-halide precursor (M = Pt, K2[PtCl4]; M = Ru,
The 1,3-di(2-pyridyl)benzene ligand has been used to produce a
diverse range transition metal complexes with widespread utility
in research areas such as catalysis,[1] organic light emitting diodes
(OLEDs)[2] and energy transfer.[3] Related to well-known tridentate
terpyridine transition metal complexes, they display a planar
N^C^N coordination geometry, and transition metal complexes of
dipyridylbenzene are typically extremely stable due to the
synergistic combination of σ-donating nitrogen and carbon atoms,
and π-accepting aromatic rings.
Complexes containing the dipyridylbenzene ligand have been
reported for a range of late second and third row transition metals
(M = PtII, RuII, OsII, IrIII, and PdII).[4] The strong field imparted by
the ligand produces photo-active complexes which typically emit
in the visible and near-infrared region.[5] In contrast to the
ubiquitous terpyridine motif, the luminescence sensing properties
of such systems is largely unexplored, and has been confined to
volatile analytes.[6] Anions are ubiquitous and their importance in
biological systems and the environment, in particular from
anthropogenic industrial activities, has over the past few decades
[Ru(4-tolylterpyridine)Cl3][12]
) to obtain 5·Pt and 5·Ru·PF6
cyclometallated esters. De-esterification using basic conditions
produced the target isophthalic acid functionalised synthons 6·Pt
and 6·Ru·PF6.
The acyclic and macrocyclic isophthalamide receptors were
prepared via acid chloride intermediates using oxalyl chloride
before condensation with the appropriate amine (Scheme 2). In
1
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the case of the acyclic receptors n-hexylamine was utilised to
afford n-hexylamide compounds, 7·Pt and 7·Ru ·PF6. Macrocyclic
targets were obtained via reaction with bis-amine 8[13] under high-
dilution conditions in the presence of an equimolar amount of 3,5-
bis-hexylamide pyridinium chloride 9·Cl[14] template to obtain
10·Pt and 10·Pt·PF6 in 24% and 48% respective yields.
The target interlocked [2]rotaxane receptors were prepared using
a chloride anion template clipping rotaxanation method,[13],[15]
utilising pyridinium chloride axle 11·Cl[7c] in place of the template
9·Cl (Scheme 3). After challenging extensive size-exclusion
chromatography and preparative TLC purification, the target
mechanically interlocked receptors 12·Pt·Cl and 12·Ru·Cl2 were
obtained in modest respective yields of 3% and 8%. Anion
exchange of the mechanically interlocked ruthenium complex with
aqueous NH4PF6 resulted in the formation of 12·Ru·(PF6)2. All
novel acyclic, macrocyclic and interlocked receptors were
characterised by 1H NMR, 13C NMR and high-resolution mass
spectrometry (ESI-HRMS or MALDI-TOF-MS), with the
interlocked topology of the interlocked receptors determined by
1H-1H ROESY NMR spectroscopy (See Electronic Supplementary
Information).
X-ray Crystallography
Single-crystal X-ray structural analysis was performed on
7·Ru·PF6, which was crystallised in the presence of excess tetra-
n-butylammonium chloride. The crystal structure (Figure 1),
reveals the chloride counteranion is bound within the
isophthalamide cleft of the receptor which adopts a syn- geometry
in the solid state, exhibiting mean N-Cl bond lengths of 3.41 Å.
The chloride is bound out of the plane of the bis-amide motif,
satisfying electrostatic interactions between the anion and the
positively charged complex, as well as the two-hydrogen bonding
interactions with the amide protons. Additionally, there are
secondary hydrogen-bonding interactions between the
dipyridylbenzene ligand and the isophthalamide carbonyl
oxygens with mean C-O distances of 3.21 Å, giving rise to an
additional stabilising effect of the out-of-plane geometry.
Scheme 1. Synthesis of isophthalic acid functionalised complexes; (i) KMnO4,
H2O/Pyridine, 89%, (ii) MeOH/H2SO4, 89%, (iii) PdCl2(PPh3)2, toluene, 58%, (iv)
M = Pt, K2PtCl4, 64%; M = Ru, Ru(ttpy)Cl3, AgBF4, acetone, n-butanol, 76%, (v)
M = Pt, KOH, MeOH, 99%; M = Ru, NaOH, MeOH/1,4-dioxane, 52%.
Scheme 2. Synthesis of acyclic and macrocyclic Pt and Ru receptors; (i) (a) oxalyl chloride, CH2Cl2, (b) CH2Cl2, Et3N, hexylamine, M = Pt, 6%; M = Ru, (c)
NH4PF6(aq)/CH2Cl2, 81%, (ii) (a) oxalyl chloride, CH2Cl2, (b) CH2Cl2, Et3N, 3,5-bis-hexylamide pyridinium chloride 9·Cl, bisamine 8, M = Pt, 24%; M = Ru, (c)
NH4PF6(aq)/CH2Cl2, 48%
2
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Scheme 3. Synthesis of [2]rotaxane Pt and Ru receptors; (i) (a) oxalyl chloride, CH2Cl2, (b) CH2Cl2, Et3N, bisamine 8, pyridinium axle 11·Cl, M = Pt, 3%; M = Ru,
8%, (ii) NH4PF6(aq)/CH2Cl2, 81%
Figure 1. Single crystal X-ray structure of syn-7·Ru·Cl (ellipsoids are plotted at
the 50% probability level; non-hydrogen-bonding hydrogens are omitted for
clarity)
Figure 2. Absorption (dashed) and emission (solid lines) data for 7·Pt (orange;
λex = 320 nm) and 7·Ru.PF6 (purple; λex = 530 nm); intensity in arbitrary units
Crystals suitable for analysis by X-ray diffraction were also
obtained for the macrocyclic ruthenium receptor 10·Ru·PF6 in
both the syn- and anti- geometry (Figure 3). Examination of the
bonding in the solid state reveals that in both cases the
supplementary hydrogen bonding interaction is present, despite
the absence of a coordinating anion in the receptor cavity. The
average C-O bond distance between the isopthamide oxygens
and the dipyridylbenzene ligand backbone are 3.20 Å and 3.11 Å
for the syn- and anti- conformations respectively.
previously reported dipyridylbenzene complexes. In the case of
the ruthenium complexes this is significantly reduced (Δλem = 2
nm), which can be rationalised by considering that the π* orbital
– the MLCT acceptor – is located on the tolylterpyridine ligand
rather than the dipyridylbenzene ligand, which is ancillary with
respect to the emission.[3c] This contrasts the 3π-π emission of the
platinum receptors which occur from the dipyridylbenzene moiety.
Table 1. Absorption and emission data for novel Pt and Ru receptors at 293 K;
Photophysical Characterisation
values are quoted in nm, extinction coefficients are displayed in parentheses;
The photophysical absorption and luminescent emissive
properties of the novel receptors 7·Pt, 7·Ru·PF6 (Figure 2), 10·Pt,
10·Ru·PF6 and 12·Ru·(PF6)2 were investigated in aerated organic
solvent media at 293 K (Table 1). The data shows that acyclic,
macrocyclic and interlocked compounds generally retain the
emissive properties of the corresponding parent unfunctionalised
dipyridylbenzene complexes. The platinum receptors display a
greater deviation of the emission to longer wavelength (Δλem = 13
nm) in the isophthalamide functionalised receptors compared to
Compound
Absorption (nm, ε/104 M-1 cm-1)
Emission (nm)
7·Pt[a]
10·Pt[a]
379 (0.86), 416 (0.90)
380 (0.90), 419 (1.00)
380 (0.87), 401 (0.70)
504
504
491
[Pt(dpyb)Cl][a]
[b]
7·Ru·PF6
516 (1.42), 549 (1.28)
516 (1.28), 554 (1.17)
516 (1.42), 557 (1.21)
504 (1.08), 550 (0.83)
782
782
782
784
[b]
10·Ru·PF6
[b]
12·Ru·(PF6)2
[Ru(dpyb)(ttpy)]
[c]
(PF6)2
[a] CH2Cl2[4a] [b] CH2Cl2/MeOH 95:5. [c] MeCN.[16]
3
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Luminescent Anion Binding Titrations
diminution of emission, which can be attributed to heavy atom
quenching. The large decrease in emission intensity upon
addition of dihydrogenphosphate ions can be tentatively attributed
to photoinduced electron transfer which is common among basic
oxoanions.[17] Again, it is noteworthy that the macrocyclic
analogue displayed much smaller changes upon addition of
anionic substrates. For the acyclic and macrocyclic ruthenium
receptors 7·Ru·PF6 and 10·Ru·PF6 quenching behavior was
exhibited for all anions. Furthermore, the percentage changes are
much more modest compared with the platinum hosts, which is a
consequence of the distal 3MLCT terpyridine moiety and
dipyridylbenzene anion-binding fragment.
Luminescent anion titrations of the acyclic and macrocyclic
receptors were conducted for a range of halides and oxoanions
(Figure 4). The acyclic platinum receptor 7·Pt displayed the
greatest change in emission across the chosen guests, exhibiting
a ca. 60% increase in emission in the presence of chloride and
sulphate, and modest enhancement in the presence of bromide,
which can be rationalised by rigidification of the receptor upon
halide guest binding, thus disfavouring non-radiative decay
pathways. This was less prominent for the macrocyclic congener
10·Pt which is clearly more conformationally restricted. In the
case of iodide both receptors exhibited a significant (ca. 70%)
Figure 3. Single crystal X-ray structure of (top) syn-10·Ru·PF6 and (bottom) anti-10·Ru·PF6 (ellipsoids are plotted at the 50% probability level; counteranions,
solvent and non-hydrogen bonding hydrogen atoms omitted for clarity)
Figure 4. Percentage changes in luminescence emission intensity of (a) Pt receptors 7·Pt and 10·Pt (CH2Cl2, λem = 504 nm, λex =320 nm, 0–100 equivalents of
anion) and (b) Ru receptors 7·Ru·PF6 and 10·Ru·PF6 (CH2Cl2, λem = 782 nm, λex = 530 nm, 0–30 equivalents of anion) at 293 K.
4
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Table 2. Anion association constants determined by global fitting analysis; anions added as their tetra-n-butyl ammonium salts
7·Pt[a]
10·Pt[a]
7·Ru·PF6
10·Ru·PF6
12·Ru·(PF6)2
[b]
[b]
[b]
Cl-
Br-
3.43 (0.04)
3.83 (0.09)
3.43 (0.14)
3.13 (0.48)
3.90 (0.06)
2.27 (0.79)
2.57 (0.56)
2.72 (0.54)
3.89 (0.07)
4.16 (0.14)
3.90 (0.08)
3.25 (0.16)
3.34 (0.17)
4.82 (0.14)
3.65 (0.08)
4.09 (0.12)
3.77 (0.08)
3.34 (0.13)
3.41 (0.07)
4.08 (0.06)
4.61 (0.6), 2.84 (0.5)
[d]
-
[d]
I-
3.39 (0.03)
-
AcO-
H2PO4
SO4
-
[d]
[c]
[d]
-
4.12 (0.04)
3.28 (0.04)
-
2-
[d]
-
[a] CH2Cl2. [b] CH2Cl2/MeOH 95:5 (v/v). [c] data could not be fitted to a simple binding model. [d] not performed
Anion association constants for the acyclic and macrocyclic
receptors were determined using global SPECFIT analysis of the
titration data (Table 2).[18] All systems displayed formation of 1:1
stoichiometric host-guest complexes. The association constant
values for 7·Pt and 10·Pt in CH2Cl2 show that all halides are
bound with comparable strength, with the acyclic receptor
exhibiting the highest affinity for the dihydrogenphosphate anion.
Comparison between the two platinum hosts shows the
magnitude of halide binding is similar in the acyclic and
macrocyclic congeners. It is thought that supplementary
secondary hydrogen-bonding interactions evident in the solid-
state structures gives rise to a highly preorganised isophthamide
motif. This intramolecular interaction increases the degree of
preorganisation in the receptors to such an extent that little or no
macrocyclic effect is observed. For both ruthenium receptors
7·Ru·PF6 and 10·Ru·PF6 the determined association constants
for all anions studied were logKa > 5 in CH2Cl2 and were repeated
in more competitive media (CH2Cl2/MeOH 95:5). The stronger
association for the ruthenium host systems is a result of the
inherent positive charge and consequent additional electrostatic
contributions between host and guest. In the more competitive
solvent system both receptors display a modest preference for
bromide amongst the halides. The sulphate anion has the
strongest association, particularly for the acyclic ruthenium
receptor, which can be rationalised on electrostatic grounds. In
analogy with the platinum systems, there is again little evidence
for a discernible macrocyclic effect which may be attributed to the
high degree of preorganisation of the acyclic receptor.
and likely occurs via association in a peripheral fashion to the
positively charged metal centre.
Rotaxane 1H NMR Anion Binding Titration
To elucidate the binding mode of chloride with the mechanically
1
interlocked host 12·Ru·(PF6)2, a H NMR anion binding titration
was conducted in a competitive aqueous solvent mixture
((CD3)2CO/D2O 7:3) (Figure 5). The observed downfield shifts of
the pyridinium axle protons a and b are indicative of the halide
binding within the [2]rotaxane cavity. However, the shifts of the
internal macrocycle resonance μ are perturbed upfield which
suggests little interaction of this proton with the chloride anion.
Likewise, upfield shifts of the macrocycle hydroquinone protons ζ
and ο are observed upon addition of chloride. This behaviour, in
addition to the X-ray single crystal analysis suggests that chloride
is bound only partially within the rotaxane cavity to maximise the
electrostatic interactions with the cationic ruthenium complex,
although time-averaged C2v symmetry persists throughout the
titration. The titration data for chloride was analysed using
WinEQNMR2 by monitoring the internal axle proton a to
determine a 1:1 stoichiometric association constant of 196 ± 13
M-1,[19] demonstrating 12·Ru·(PF6)2 rotaxane is capable of binding
chloride in a highly competitive aqueous solvent system that
contains 30% water.
Conclusion
An analogous titration with chloride was also performed for the
interlocked ruthenium receptor 12·Ru·(PF6)2 and fitted to a 1:2
host-guest stoichiometric binding model. The first anion binding
event is presumed to occur within the interlocked [2]rotaxane
cavity, resulting in an association constant which is greater by an
order of magnitude than either the acyclic or macrocyclic
ruthenium receptors. The second binding event is relatively weak
Through the integration of the isophthalamide group into the
dipyridylbenzene ligand structure, a series of novel acyclic,
macrocyclic and interlocked rotaxane anion receptors
incorporating luminescent cyclometallated platinum (II) and
ruthenium (II) dipyridylbenzene complexes were prepared.
Figure 5. 1H NMR (500 MHz, (CD3)2CO/D2O (7:3)), 298 K) spectra of [2]rotaxane 12·Ru·(PF6)2 in the presence of increasing amounts of tetra-n-butylammonium
chloride (left); anion binding curve of chemcal shift change of proton a; symbols represent experimental data, continuous line represent calculated binding curve
(right).
5
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Oxalyl chloride (0.110 mL, 1.37 mmol) was added dropwise to a
suspension of PtII(dpb-acid)Cl 6·Pt (0.189 g, 0.343 mmol, ) in anhydrous
CH2Cl2 (100 mL) and anhydrous degassed catalytic DMF (1 drop). The
reaction mixture was stirred under N2 at ambient temperature until
homogenous (ca. 6 hours). The solvent was removed in vacuo and dried
under high vacuum. Anhydrous, distilled Et3N (0.384 mL, 2.75 mmol) and
hexylamine (0.270 mL, 2.06 mmol) were added to the acid chloride
intermediate dissolved in CH2Cl2 (100 mL) at 0 °C. The reaction mixture
was stirred for two hours at ambient temperature. The resulting solution
was washed with sat. NaHCO3(aq) (50 mL), 10 % w/w citric acid (50 mL)
and sat. brine (50 mL) and dried over anhydrous MgSO4. The solvent was
removed in vacuo. Purification by preparative thin-layer chromatography
(SiO2; CH2Cl2/MeOH; 90:10) gave a yellow solid (15.2 mg, 6%, 22 µmol).
The acyclic and macrocyclic derivatives 7·Pt, 7·Ru·PF6, 10·Pt
and 10·Ru·PF6 were demonstrated to be effective luminescent
sensors for a range of anions. In the case of the ruthenium
receptors emission was observed in the near-infrared region (λem
= 782 nm), which is interesting from a biological standpoint. By
virtue of additional favourable electrostatic interactions, the
cationic ruthenium receptors displayed an enhanced affinity for
anionic guests compared to the neutral platinum analogues. With
both metal receptor systems, there was no discernable increase
in anion binding affinity with the macrocyclic derivatives in
comparison to the acyclic analogues which may be due to
preorganising secondary hydrogen-bonding interactions between
the amide carbonyls and the dipyridylbenzene ligand backbone.
Two mechanically interlocked rotaxane congeners were also
synthesised. Preliminary luminescence spectroscopy anion
binding titrations with rotaxane 12·Ru·(PF6)2 revealed a significant
increase in chloride binding affinity compared to the non-
interlocked acyclic and macrocyclic receptors, owing to the
complementary binding cavity of the interlocked host. 1H NMR
titration experiments demonstrated 12·Ru·(PF6)2 to be capable of
binding chloride even in competitive 30% aqueous solvent
mixtures.
4
1H NMR (500 MHz, CDCl3) δH 9.55 (2H, d, JHH = 5.8, ArH), 9.13 (2H, t,
3JHH = 5.6, NH), 8.47 (2H, app. t, Japp = 8.0, ArH), 8.10 (2H, d, 3JHH = 8.3,
ArH), 7.87 (2H, app. t, Japp = 6.6, ArH), 1.45 – 1.56 (4H, m, NHCH2), 1.20
– 1.38 (16H, m, CH2), 0.69 – 0.86 (6H, m, CH3);13C NMR (76 MHz, CDCl3)
δC 168.6, 164.3, 151.3, 137.7, 136.8, 134.2, 123.7, 122.4, 122.0, 40.1, 31.7,
29.6, 27.0, 22.8, 14.3; EI-HRMS m/z calcd. for [C30H37ClN4O4Pt - Cl]+
680.2564, found 680.2791; UV-Vis λmax(CH2Cl2)/nm; ε/dm3 mol-1 cm-1: 251
(48,100) 295 (29,700) 364 (5,800) 379 (8,600) 416 (9,000).
Synthesis
tolylterpyridine) ruthenium(II)
hexyl)(ttpy)PF6]) 7·Ru·PF6
of
(dihexyl
2,4-di-2-pyridyl-isophthalamide)(4-
hexafluorophosphate ([RuII(dpb-
Oxalyl chloride (0.00400 mL, 0.0520 mmol) was added dropwise to a
solution of [RuII(dpb-acid)(ttpy)PF6] 6·Ru·PF6 (9.6 mg, 0.0130 mmol) in
anhydrous CH2Cl2 (50 mL) and anhydrous degassed catalytic DMF (1
drop). The reaction mixture was stirred under N2 at ambient temperature
until homogenous. The solvent was removed in vacuo and dried under
high vacuum. Anhydrous, distilled Et3N (0.0140 mL, 0.104 mmol) and
hexylamine (0.0100 mL, 0.0780 mmol) were added to the acid chloride
intermediate dissolved in anhydrous CH2Cl2 (50 mL) at 0 °C. The reaction
mixture was stirred for two hours at ambient temperature under N2. The
solvent was then removed in vacuo and the solid was dissolved in CH2Cl2
(15 mL) and washed with 0.1 M NH4PF6(aq) (10 × 10 mL) and H2O (2 × 10
mL). The organic layer was dried over MgSO4, and the solvent removed in
vacuo. Purification by preparative thin-layer chromatography (SiO2;
CH2Cl2/MeOH; 90:10) gave a purple solid (9.24 mg, 81 %). 1H NMR (500
MHz, CD2Cl2) δH 8.77 (2H, s, ArH), 8.35 (2H, app. dt, Japp = 8.1, 1.2, ArH),
8.28 (2H, app. dd, Japp = 8.4, 1.1, ArH), 8.01 – 7.93 (2H, m, ArH), 7.65 (2H,
app. td, Japp = 7.8, 1.5, ArH), 7.58 – 7.47 (4H, m, ArH), 7.29 (1H, s, ArH),
7.28 – 7.23 (2H, m, ArH), 7.09 – 7.05 (2H, m, ArH), 6.99 (2H, app. ddd,
Japp = 7.3, 5.6, 1.4, ArH), 6.83 (2H, t, 3JHH = 5.8, ArH), 6.63 (2H, app. ddd,
Japp = 7.2, 5.7, 1.4, ArH), 3.58 (4H, app. td, Japp = 7.3, 5.8, NCH2), 2.54
(3H, s, CH3), 1.77 – 1.68 (4H, m, CH2), 1.52 – 1.43 (4H, m, CH2), 1.33 –
1.39 (8H, m CH2), 0.92 – 0.88 (6H, m, CH3); 13C NMR (126 MHz, CDCl3)
δC 171.6, 167.6, 157.9, 156.6, 153.1, 150.2, 135.2, 134.5, 130.7, 127.2,
123.6, 122.5, 121.6, 119.2, 53.6, 46.0, 40.5, 31.7, 29.9, 29.4, 26.9, 22.8,
21.6, 15.4, 14.2, remaining quaternary carbons undetected; 19F NMR (283
MHz, CDCl3) δF -72.5 (d, 1J = 713 Hz, PF6); 31P NMR (121 MHz, CDCl3)
Experimental Section
General Considerations
Commercial grade chemicals and solvents were used without further
purification. Where anhydrous solvents were used, they were degassed
with N2 and passed through an MBraun MPSP-800 column Where
degassed solvents were used, they were degassed via bubbling of N2 gas
through the solution unless stated otherwise. Triethylamine was distilled
from and stored over potassium hydroxide. De-ionised water dispensed
from a Millipore Milli-Q purification system was used in all cases.
Tetrabutylammonium (TBA) salts were stored under vacuum in
a
desiccator. Microwave reactions were carried out using a Biotage Initiator
2.0 microwave. All synthetic procedures have been reliably repeated
multiple times. Routine 300 MHz NMR spectra were recorded on a Varian
Mercury 300 spectrometer, 1H NMR operating at 300 MHz, 13C{1H} at 76
MHz, 19F at 283 MHz and 31P at 121 MHz. Where the solubility of the
compounds were too low, or not enough compound existed, a Bruker
AVII500 with 13C Cryoprobe spectrometer was used for obtaining 13C{1H}
at 126 MHz, however in some cases a complete 13C{1H} spectrum could
1
1
not be obtained. All 500 MHz H Spectra and all H NMR titrations were
recorded on a Varian Unity Plus 500 spectrometer. All chemical shift (δ)
values are given in parts per million and are referenced to the solvent. In
cases where solvent mixtures are used, the main solvent is used as the
reference. Where an apparent multiplet (e.g. app. t.) is quoted, Japp is given.
Low resolution ESI mass spectra were recorded on a Micromass LCT
Premier XE spectrometer. Accurate masses were determined to four
decimal places using Bruker μTOF and Micromass GCT spectrometers.
UV/visible experiments were carried out on a PG instruments T60U
spectrometer at 293 K. Steady-state fluorescence spectra were recorded
on JobinYvon-Horiba Fluorolog-3 spectrophotometer or a Varian Cary-
Eclipse spectrometer. 2,4-dibromo-1,5-dimethylbenzene 1,[11] 2-
tributylstannylpyridine,[20] 4-tolyl-2,2′:6′,2′′-terpyridine,[21] 4-tolyl-2,2′:6′,2′′-
terpyridine ruthenium trichloride,[12] diamine 8,[10b] 3,5-bis-hexylamide
pyridinium chloride 9·Cl[14] and pyridinium axle·Cl 11·Cl,[7c] were
synthesised as previously described.
δP -144.53 (sept., 1J
[C52H54F6N7O2PRu
= 713 Hz, PF6); ESI-HRMS m/z calcd. for
–
PF6]+ 910.3391, found 910.3390; UV-Vis
λmax(CH2Cl2)/nm; ε/dm3 mol-1 cm-1: 241 (39,900) 289 (64,800) 374 (9,600)
616 (14,200) 549 (12,800)
Synthesis
of
(2,4-di-2-pyridyl-isophthalamide
macrocycle)
platinum(II) chloride ([PtII(dpb-macrocycle)Cl]) 10·Pt
Oxalyl chloride (11 µL, 0.138 mmol) was added dropwise to a solution of
PtII(dpbacid)Cl 6·Pt (19.0 mg, 0.0346 mmol) in anhydrous CH2Cl2 (100 mL)
and anhydrous degassed catalytic DMF (1 drop). The reaction mixture was
stirred under N2 at ambient temperature until homogenous (ca. 6 hours).
The solvent was removed in vacuo and dried under high vacuum. Bis-
amine (0.0160 g, 0.0346 mmol), pyridinium thread 9·Cl (0.0130 g,
0.0346 mmol) and anhydrous, distilled Et3N (0.0120 mL, 0.0865 mmol)
were dissolved in anhydrous CH2Cl2 (100 mL) and stirred until
Synthesis of (dihexyl-2,4-di-2-pyridyl-isophthalamide) platinum(II)
chloride ([PtII(dpb-hexyl)Cl]) 7·Pt
6
This article is protected by copyright. All rights reserved.

10.1002/chem.202000661
Chemistry - A European Journal
FULL PAPER
homogenous. The acid chloride in anhydrous CH2Cl2 (100 mL) was added
dropwise, and the reaction mixture stirred for three hours at ambient
temperature under N2. The solvent was removed in vacuo and the resulting
solid was purified by preparative thin-layer chromatography (SiO2;
CH2Cl2/MeOH; 98:2) to give a yellow solid (8.1 mg, 24%, 8.2 µmol). 1H
chromatography (SiO2; CH2Cl2/MeOH 99:1→95:5), preparative thin-layer
chromatography (SiO2; CH2Cl2/MeOH 99:1→95:5) and size-exclusion
chromatography (Bio-Beads S-X1/ CHCl3) gave the compound as a yellow
solid (7.6 mg, 3 %, 3.7 µmol). 1H NMR (500 MHz, CDCl3/CD3OD 9:1) 9.58
(1H, s, PyH), 9.32 (2H, d, 3JHH = 5.8, ArH), 9.13 (1H, s, ArH), 8.75 (2H, s,
PyH), 8.04 (1H, s, ArH), 7.79 (2H, d, 3JHH = 8.3, ArH), 7.67 (6H, app. dd,
Japp = 20.6, 8.3, ArH + StH), 7.51 – 7.46 (1H, m, ArH), 7.39 (1H, s, ArH),
7.33 – 7.07 (20H, m, ArH + StH), 7.04 (8H, d, 3JHH = 8.5, StH), 6.64 (4H,
d, JHH = 8.5, HQH), 6.28 (4H, d, JHH = 8.6, HQH), 4.09 (4H, s, OCH2),
3.92 (4H, s, OCH2), 3.75 (4H, s, OCH2), 3.65 – 3.56 (8H, m, OCH2), 3.48
– 3.42 (4H, m, NCH2), 3.30 (3H, s, NCH3), 1.22 (36H, s, C(CH3)3); 13C
NMR (126 MHz, CDCl3/CD3OD 9:1) δc 169.1, 164.7, 158.7, 152.9, 151.9,
148.7, 146.9, 144.8, 143.5, 139.3, 134.9, 133.9, 133.6, 131.9, 131.0,
130.6, 128.8, 127.4, 125.9, 124.3, 123.6, 123.1, 119.6, 115.5, 115.0, 70.7,
70.6, 70.2, 68.3, 67.5, 66.2, 63.9, 57.8, 40.2, 38.7, 34.3, 31.3, 30.4, 29.7,
28.9, 23.7, 23.0, 22.7, 17.9, 14.0, 10.9; MALDI-TOF MS m/z calcd. for
[C116H121Cl2N7O11Pt – Cl]+ 2018.32, found 2018.89.
3
NMR (500 MHz, DMSO-d6) δH 9.35 (2H, d, JHH = 5.6, ArH), 9.17 (2H, t,
3JHH = 5.6 Hz, NH), 8.28 (2H, app. t, Japp = 7.6, ArH), 7.95 (2H, d, 3JHH
=
7.4, ArH), 7.67 (2H, app. t, Japp = 7.5, ArH), 7.12 (1H, s, ArH), 6.91 (4H, d,
3JHH = 9.0, ArH), 6.84 (4H, d, 3JHH = 9.0, ArH), 4.11 (4H, t, 3JHH = 5.4, CH2),
3.97 (4H, t, 3JHH = 4.8, CH2), 3.65 – 3.75 (8H, m, CH2), 3.48 – 3.59 (8H, m,
CH2);13C NMR (126 MHz, DMSO-d6) δC 167.9, 164.4, 152.8, 152.4, 140.6,
136.7, 135.3, 124.9, 123.1, 122.5, 115.6, 115.3, 70.0, 69.0, 69.0, 67.7,
66.5, 30.7; MALDI-TOF MS m/z calcd. for [C42H43ClN4O9Pt - Cl]+ 942.27,
found 942.02; UV-Vis λmax(CH2Cl2)/nm; ε/dm3 mol-1 cm-1: 234 (69,000) 253
(60,600), 295 (49,600) 361 (8,400) 380 (9,000) 419 (10,000).
3
3
Synthesis
tolylterpyridine) ruthenium(II)
macrocycle)(ttpy)PF6]) 10·Ru·PF6
of
(2,4-di-2-pyridyl-isophthalamide
macrocycle)(4-
hexafluorophosphate ([RuII(dpb-
Synthesis
tolylterpyridine) ruthenium(II)
of
[2]rotaxane
(2,4-di-2-pyridyl-isophthalamide)(4-
hexafluorophosphate ([RuII(dpb-
macrocycle)(ttpy)PF6] [2]rotaxane) 12·Ru·(PF6)2
Oxalyl chloride (0.0400 mL, 0.450 mmol) was added dropwise to a solution
of [RuII(dpb-acid)(ttpy)PF6] 6·Ru·PF6 (0.100 g, 0.112 mmol) in anhydrous
CH2Cl2 (100 mL) and anhydrous degassed catalytic DMF (1 drop). The
reaction mixture was stirred under N2 at ambient temperature until
homogenous (ca. 6 hours). The solvent was removed in vacuo and dried
under high vacuum. Bis-amine 8 (0.0521 g, 0.112 mmol), pyridinium
thread 9·Cl (0.0430 g, 0.112 mmol) and anhydrous, distilled Et3N (0.0400
mL, 0.281 mmol) were dissolved in anhydrous CH2Cl2 (100 mL) and stirred
until homogenous. The acid chloride, in anhydrous CH2Cl2 (100 mL), was
added dropwise, and the reaction mixture stirred for three hours at ambient
temperature under N2. The solvent was removed in vacuo. The resulting
solid was dissolved in CH2Cl2 (15 mL) and washed with 0.1 M NH4PF6(aq)
(10 × 10 mL) and H2O (2 × 10 mL). The organic layer was dried over
MgSO4, and the solvent removed in vacuo. The resulting solid was purified
by column chromatography (SiO2; CH2Cl2/MeOH; 96:4) and preparative
thin-layer chromatography (SiO2; CH2Cl2/MeOH; 98:2) to give a purple
solid (71.5 mg, 48%, 54.2 µmol). 1H NMR (500 MHz, CDCl3) δH 9.47 (2H,
Oxalyl chloride (0.08 mL, 0.1 mmol) was added dropwise to a solution of
[RuII(dpb-acid)(ttpy)PF6] 6·Ru·PF6 (0.023 g, 0.025 mmol) in anhydrous
CH2Cl2 (10 mL) and anhydrous degassed catalytic DMF (1 drop). The
reaction mixture was stirred under N2 at 40oC until homogenous (ca. 6
hours). The solvent was removed in vacuo and dried under high vacuum.
Bis-amine 8 (0.012 g, 0.025 mmol), pyridinium axle 11·Cl (0.027 g, 0.025
mmol) and anhydrous, distilled Et3N (0.008 mL, 0.0625 mmol) were
dissolved in anhydrous CH2Cl2 (10 mL) and stirred until homogenous. The
acid chloride in anhydrous CH2Cl2 (10 mL) was added dropwise, and the
reaction mixture stirred for three hours at ambient temperature under N2.
The solvent was removed in vacuo. Purification by column
chromatography (SiO2; CH2Cl2/MeOH; 95:5) and by preparative thin-layer
chromatography (SiO2; EtOAc/MeOH; 100:0→98:2). This was dissolved in
CH2Cl2 (15 mL) and washed with 0.1 M NH4PF6(aq) (10 × 10 mL) and H2O
(2 × 10 mL). The organic layer was dried over MgSO4, and the solvent
removed in vacuo to give the compound as a purple solid (4.9 mg, 6.5%
over two-steps, 1.95 µmol); 1H NMR (500 MHz, CD2Cl2) δH 9.47 (1H, br.s,
ArH), 9.37 (1H, br.s, ArH),8.78 (2H, s, ArH), 8.67 (1H, s, ArH + StH), 8.32
3
3
t, JHH = 5.6, ArH), 8.76 (2H, s, ArH), 8.55 (2H, d, JHH = 8.5, ArH), 8.35
3
3
(2H, d, JHH = 8.1, ArH), 7.97 (2H, d, JHH = 7.8, ArH), 7.59 (1H, s, ArH),
7.55 (2H, t, 3JHH = 7.9, ArH), 7.50 (2H, d, 3JHH = 7.9, ArH), 7.44 (2H, d, 3JHH
= 5.5, ArH), 7.37 (2H, t, 3JHH = 8.0, ArH), 7.00 (2H, t, 3JHH = 6.7, ArH), 6.91
– 6.84 (6H, m, ArH), 6.62 (4H, d, 3JHH = 8.6, ArH), 6.50 (2H, t, 3JHH = 6.6,
ArH), 4.27 (4H, t, 3JHH = 6.1, CH2), 3.94 (4H, app. q, Japp = 6.0, CH2), 3.84
3
3
(4H, d, JHH = 8.2, ArH + StH), 8.00 (4H, d, JHH = 7.9, ArH + StH), 7.79
(4H, s, ArH), 7.55 (5H, app. dd, Japp = 15.0, 8.2, ArH), 7.38 (4H, d, 3JHH
=
8.5, StH), 7.30 (11H, d, 3JHH = 7.5, ArH + StH), 7.23 – 7.20 (9H, m, ArH +
StH), 7.06 (4H, d, 3JHH = 5.9, StH), 6.79 (4H, d, 3JHH = 8.0, HQH), 6.62 (2H,
t, 3JHH = 6.6, ArH), 6.33 (4H, d, 3JHH = 8.6, HQH), 4.10 (4H, s, OCH2), 3.93
(4H, s, OCH2), 3.77 (4H, s, OCH2), 3.70 (4H, s, OCH2), 3.63 (4H, s, OCH2),
3.44 (4H, s, NCH2), 2.53 (3H, s, ArCH3), 1.24 (36H, s, C(CH3)3); 13C NMR
(126 MHz, CDCl3/CD3OD 9:1) δc 165.2, 165.1, 164.5, 164.4, 158.4, 158.3,
153.2, 152.2, 152.1, 148.7, 147.0, 146.0, 144.6, 144.5, 143.6, 143.5,
138.0, 136.6, 135.5, 134.8, 133.4, 131.8, 131.0, 130.6, 129.3, 128.9,
127.4, 127.3, 127.0, 125.8, 125.8, 124.4, 124.3, 123.8, 121.6, 120.6,
120.4, 114.9, 70.7, 70.6, 70.0, 68.3, 65.5, 63.8, 41.1, 41.0, 39.2, 34.3,
3
3
(4H, t, JHH = 5.0, CH2), 3.77 (4H, t, JHH = 4.9, CH2), 3.71 (8H s, CH2),
2.50 (3H, s, CH3); 13C NMR (126 MHz, CDCl3) δc 165.5, 158.3, 153.9,
151.9, 148.6, 147.0, 145.5, 145.0, 143.6, 136.7, 135.2, 134.9, 133.9,
132.0, 131.2, 130.8, 127.5, 126.0, 124.5, 120.6, 116.3, 115.0, 114.9, 70.9,
70.7, 70.2, 68.5, 65.9, 64.0, 34.5, 31.6; 19F NMR (283 MHz, CDCl3) δF -
72.0 (d, 1J = 713 Hz, PF6); 31P NMR (121 MHz, CDCl3) δP -144.3 (sept.,
1JPF = 714 Hz, PF6); ESI-HRMS m/z calcd. for [C64H60F6N7O9PRu – PF6]+
1172.3508, found 1172.3528; UV-Vis λmax(CH2Cl2)/nm; ε/dm3 mol-1 cm-1:
233 (40,400) 288 (64,300) 373 (9,300) 516 (12,900) 554 (11,700)
31.3, 29.7; 19F NMR (472 MHz, CD2Cl2) δF -70.9 (d, 1J = 742 Hz, PF6); 31
NMR (121 MHz, CDCl3) δP -144.35 (sept., 1JPF = 714 Hz, PF6); ESI-HRMS
m/z calcd. for [C138H138F6N10O11PRu
1106.4795; UV-Vis λmax(CH2Cl2)/nm; ε/dm3 mol-1 cm-1: 251 (96,300) 289
P
Synthesis
macrocycle)
[2]rotaxane) 12·Pt·Cl
of
[2]rotaxane
(2,4-di-2-pyridyl-isophthalamide
([PtII(dpb-macrocycle)Cl]
–
2PF6]2+ 1106.4793, found
platinum(II)
chloride
(64,000) 371 (9,800) 516 (14,200) 557 (12,100).
Oxalyl chloride (0.0400 mL, 0.496 mmol) was added dropwise to a solution
of PtII(dpb-acid)Cl 6·Pt (0.0682 g, 0.124 mmol) in anhydrous CH2Cl2 (100
mL) and anhydrous degassed catalytic DMF (1 drop). The reaction mixture
was stirred under N2 at 40 °C until homogenous (ca. 6 hours). The solvent
was removed in vacuo and dried under high vacuum. Bis-amine 8 (0.0576
g, 0.124 mmol), pyridinium axle 11·Cl (0.133 g, 0.124 mmol) and
anhydrous, distilled Et3N (0.043 mL, 0.310 mmol) were dissolved in
anhydrous CH2Cl2 (100 mL) and stirred until homogenous. The acid
chloride in anhydrous CH2Cl2 (100 mL) was added dropwise, and the
reaction mixture stirred for three hours at ambient temperature under N2.
The solvent was removed in vacuo. Purification by column
Luminescent Anion binding titrations
Luminescence experiments were carried out on a Varian Cary-Eclipse
spectrometer for the platinum (II) receptors using an excitation wavelength
of 320 nm at 293 K. To a 2.5 mL, 1 × 10-5 M solution of each receptor was
added aliquots of the tetrabutylammonium salts dissolved in a stock
solution made up with the receptor, such that the same concentration of
the host was maintained throughout the titration experiments.
Luminescence experiments were carried out on a Horiba Fluorolog
spectrometer for the ruthenium (II) receptors using an excitation
wavelength of 530 nm at 293 K. To a 1 mL, 1 × 10-4 M solution of each
7
This article is protected by copyright. All rights reserved.

10.1002/chem.202000661
Chemistry - A European Journal
FULL PAPER
receptor was added aliquots of the tetrabutylammonium salts dissolved in
a stock solution made up with the receptor, such that the same
concentration of the host was maintained throughout the titration
experiments. In both cases the titration data was analysed and association
constants determined using the SPECFIT program.[18]
Kwok, C.-M. Che, Adv. Opt. Mater. 2019, 7, 1801452; c) V. N.
Kozhevnikov, B. Donnio, B. Heinrich, D. W. Bruce, Chem. Commun.
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1H NMR anion titration data
Initial NMR sample volumes and concentrations were 500 μL and 2.0 mM
respectively. Solutions (100 mM) of anion were added as their
tetrabutylammonium salts. Spectra were recorded at 0, 0.2, 0.4, 0.6, 0.8,
1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.5, 3.0, 4.0, 5.0, 7.0 and 10 equivalents. In all
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investigated by visual analysis of the titration data, and using
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parameters were refined by non-linear least-squares analysis using
WINEQNMR2 to achieve the best fit between observed and calculated
chemical shifts. The input parameters for the final chemical shift and
association constant were adjusted based on the program output until
convergence was reached. Comparison of the calculated and
experimental binding isotherms demonstrated that an appropriate model
with an appropriate stoichiometry were used.
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R.C.K. thanks a Helmore Award for a DPhil studentship and
Diamond Light Source for the award of beam time on I19
(MT1858).
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Entry for the Table of Contents
Insert graphic for Table of Contents here.
Insert text for Table of Contents here. A series of novel acyclic, macrocyclic and mechanically interlocked luminescent anion sensors
have been prepared via incorporation of the isophthalamide motif into dipyridylbenzene to obtain cyclometallated complexes of PtII
and RuII. Anion titrations with the ruthenium [2]rotaxane demonstrate a marked increase in chloride binding affinity and indicate the
interlocked receptor is capable of chloride recognition even in competitive 30% aqueous mixtures.
10
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