Triazole- and triazolium-containing porphyrin-cages for optical anion sensing

Article abstract of DOI:10.1039/c2dt30124e

Triazole and triazolium groups have been integrated into a zinc(ii) metalloporphyrin-based structural framework to produce two porphyrin-cages for anion sensing applications. UV/visible spectroscopic titration investigations reveal both host systems exhibit strong anion binding affinities, with the positively-charged triazolium-porphyrin cage capable of colorimetric sensing halides, fluoride and chloride, and oxoanions in acetone-water solvent mixtures.

Full text of DOI:10.1039/c2dt30124e

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PAPER
Triazole- and triazolium-containing porphyrin-cages for optical
anion sensing†
Lydia C. Gilday, Nicholas G. White and Paul D. Beer*
Received 18th January 2012, Accepted 3rd April 2012
DOI: 10.1039/c2dt30124e
Triazole and triazolium groups have been integrated into a zinc(II) metalloporphyrin-based structural
framework to produce two porphyrin-cages for anion sensing applications. UV/visible spectroscopic
titration investigations reveal both host systems exhibit strong anion binding affinities, with the
positively-charged triazolium-porphyrin cage capable of colorimetric sensing halides, fluoride and
chloride, and oxoanions in acetone–water solvent mixtures.
triazolium-containing zinc(II) metalloporphyrin-cage systems
Introduction
which combine C–H⋯anion hydrogen bonding and Lewis
acidity for the optical colorimetric sensing of anions in polar
organic and organic–aqueous solvent mixtures.
The fundamental importance of negatively-charged species in
biological processes and medical diseases as well as the detri-
mental environmental impact of anions such as nitrate and phos-
phate is well-known. The need for suitable methods of anion
detection and extraction is therefore acute and as a consequence,
the field of anion supramolecular chemistry has grown rapidly
over recent decades.1 In particular, examples of anion receptor
molecular frameworks with integrated optical and redox reporter
groups for sensing applications is ever increasing.
The porphyrin macrocycle is endowed with inherent optical
and redox properties that can be exploited for signalling anion
recognition via a measurable physical response.2 Indeed, we3
and others4 have reported several porphyrin-based host systems
containing integrated amide, urea, pyrrole, ammonium and
imidazolium hydrogen-bond donor groups capable of recognis-
ing and sensing anions via spectro- and/or electrochemical
methodologies.
Results and discussion
Syntheses
The target triazole-containing zinc(II) metalloporphyrin-cage
receptor 5 was prepared via modification of Crossley’s synthetic
procedure8 which involves a copper(I)-catalysed azide-alkyne
cycloaddition (CuAAC) reaction9 between a tetra-meso-substi-
tuted azide-functionalised porphyrin and a capping aryl-alkyne
(Scheme 1).
Recently, the capability of neutral triazole units to bind anions
in organic solvents by C–H⋯anion type hydrogen bonding
has been demonstrated.5 In particular, Flood has incorporated
multiple triazole groups into a macrocycle leading to strong
chloride anion recognition in dichloromethane.6
With one notable recent exception of a tetra-triazole-appended
“picket-fence” zinc(II) porphyrin receptor which senses halide
anions in organic solvents,7 porphyrin molecules incorporating
triazole and triazolium groups for anion recognition are unprece-
dented. Herein we describe the first examples of triazole- and
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
†Electronic supplementary information (ESI) available: 1H and 13C
NMR spectra and ESI mass spectra of porphyrins 5 and 6·(PF6)4 and
1H–1H TOCSY and 1H–1H ROESY spectra for compound 5; titration
protocols and UV/visible binding curves. CCDC reference number
863074. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c2dt30124e
Scheme 1 Synthesis of tetra-azide-porphyrin 3 and capping group 4.
7092 | Dalton Trans., 2012, 41, 7092–7097
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3-(Bromomethyl)benzaldehyde was prepared by reduction of
commercially available 3-(bromomethyl)benzonitrile using
DiBAL-H in toluene.10 Reaction with pyrrole in the presence of
catalytic boron trifluoride etherate afforded 5,10,15,20-tetrakis
(α-bromo-m-tolyl)porphyrin, 1, in 30% yield via a modification
of the Lindsey protocol.11 Stirring porphyrin 1 with sodium
azide in DMSO gave tetra-azide porphyrin 2 which upon metal-
lation using Zn(OAc)2·2H2O in CH2Cl2 : CH3OH (v/v 9 : 1)
gave the zinc-porphyrin derivative 3 in 80% yield over two
steps. The required tetra-alkyne aryl capping group 4 was pre-
pared by condensation of ten equivalents of propargyl alcohol
with benzene-1,2,4,5-tetracarbonyl chloride formed from
benzene-1,2,4,5-tetracarboxylic acid and thionyl chloride
(Scheme 1).8
Zinc-porphyrin cage 5 was prepared via a copper(I)-catalysed
alkyne-azide cycloaddition (CuAAC) reaction between 5,10,15,
20-tetrakis(α-azido-m-tolyl)zinc porphyrin 3 and capping group
4 in the presence of copper-tetrakisacetonitrile hexafluorophos-
phate and triethylamine in DMF. After purification using pre-
parative thin layer chromatography, the zinc-porphyrin-cage
compound 5 was isolated in 17% yield (Scheme 2).
Both porphyrin-cage receptors 5 and 6·(PF6)4 were character-
ised by NMR spectroscopy, mass spectrometry and UV/Visible
spectroscopy (see Experimental section and ESI†).
X-ray crystallography
Crystals of zinc metalloporphyrin cage 5·5(C3H6O) suitable for
single crystal X-ray diffraction structural analysis were grown by
the slow evaporation of an acetone solution of the cage receptor.
The structure (Fig. 1) reveals the open nature of the three-dimen-
sional cavity where an anion can potentially be bound. The four
triazole groups are aligned perpendicular to the cage in the solid
state but the flexibility of the receptor should allow for strong
induced-fit anion binding. It can be seen that the four meso-
phenyl protons pointing into the cavity, together with the triazole
protons provide a suitable binding pocket for anion coordination
to the porphyrin-bound zinc(II) centre. The presence of five-co-
ordinate zinc(II), with an acetone solvent molecule as the axial-
coordinating ligand, is also apparent.
The novel tetra-triazolium cage receptor 6·(PF6)4 was pre-
pared in 32% yield via reaction of 5 with five equivalents of
Me3O·BF4 in anhydrous CH2Cl2 followed by anion exchange
(Scheme 2).
Anion binding studies
A preliminary 1H NMR anion binding investigation of 5 and
TBA·Cl was undertaken in acetone-d6 solution (Fig. 2). Upon
Scheme 2 Synthesis of zinc-porphyrin cage 5 and tetracationic-porphyrin cage 6·(PF6)4.
Fig. 1 Capped stick model (left) and space filling representation (right) of the X-ray crystal structure of 5·5(C3H6O). Colour scheme: grey = C;
blue = N; red = O; purple = Zn.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 7092–7097 | 7093

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Fig. 4 Colour of receptor 5 before (left) and after addition of 10
equivalents of anions in acetone.
the axial ligation of the halide anion to the Lewis acidic zinc
centre.13 An isobestic point is observed with increasing anion
concentration which corresponds to a 1 : 1 receptor : anion
binding stoichiometry. It is noteworthy that acetone solutions of
zinc receptor 5 are pink in colour and addition of anions resulted
in the solutions changing colour (Fig. 4).‡
Job plot analyses14 confirmed a 1 : 1 host : guest binding stoi-
chiometry for both cage receptors. The anion binding properties
of zinc tetraphenylporphyrin15 (ZnTPP) were also investigated as
a control, in order to elucidate the contribution of the triazole-
capping framework of receptor 5 to anion binding strength and
selectivity. Association constants for 1 : 1 stoichiometric com-
plexes were determined using the Specfit® computer program16
and are reported in Tables 1 and 2.
1
Fig. 2 Partial H NMR spectra of a 2 mM solution of porphyrin 5 in
the presence of (a) 0, (b) 1 and (c) 10 equivalents of TBA·Cl in acetone-
d6 at 293 K. Left inset: porphyrin 5. Right inset: changes in chemical
shift of proton e on addition of TBA·Cl. (Square data points represent
experimental data; continuous line represents theoretical binding
isotherm).
Neutral cage host 5 was found to bind anions strongly in
acetone, with large association constant values for F− and SO4
2−
in particular. Indeed, the receptor is shown to be selective for F−
over other halide anions, despite its small size. This is likely to
be a result of fluoride’s greater basicity and possibly it is bound
as the trihydrate complex. Receptor 5 exhibits low binding
affinity for larger, more diffuse Br− and I− anions. Sulfate is
bound very strongly by porphyrin 5 with an association constant
an order of magnitude higher than for the other basic oxoanions,
which is presumably a consequence of the sulfate anion’s higher
charge. Amongst the singly-charged anions, the anion selectivity
trend displayed by 5 in general correlates with anion basicity
AcO− ∼ H2PO4− ≫ Cl− > Br− > I−.
The data in Table 1 also highlight a significant increase in
anion binding strength for cage receptor 5 compared with acyclic
ZnTPP, particularly for F− and Cl−, where additional hydrogen-
bond-donating triazole units provide a complementary binding
cleft for harder, spherical anions (Fig. 2).
The anion recognition properties of the positively-charged,
tetra-triazolium zinc porphyrin cage 6·(PF6)4 were also probed
using UV/visible spectroscopy and the association constants for
complex formation in 5% water : acetone are reported in Table 2.
As anticipated, even in the presence of water, the tetracationic
cage 6·(PF6)4 is a superior anion complexant to host 5. In this
aqueous medium the binding affinity of positively-charged caged
receptor 6·(PF6)4 for F− and Cl− is of similar magnitude and is
significantly larger than with Br− or I−. All oxoanions are bound
strongly in 5% water : acetone and receptor 6·(PF6)4 demon-
strates a clear preference (∼5-fold) for the sulfate dianion.
Fig. 3 Changes in the Soret band component of the UV/visible absorp-
tion spectrum of a 2 μM solution of porphyrin 5 upon addition of
TBA·Cl in acetone at 293 K.
addition of chloride significant downfield shifts in the receptor’s
triazole, g, and ortho-phenyl, e, cavity protons were observed.
This suggests the chloride anion is binding within the cage, co-
ordinating to both the triazole and phenyl C–H groups.
WinEQNMR212 analysis of the titration data gave an association
constant, K > 104 M−1 following the ortho-phenyl proton, e.
The anion recognition and sensing properties of cage porphyr-
ins 5 and 6·(PF6)4 were investigated by UV/visible spectroscopic
titrations. Both receptors exhibit characteristic metalloporphyrin
absorption spectra with strong Soret band absorbances in the
400–450 nm region as well as weaker Q band absorbances in the
500–650 nm region.
Anion titration experiments in acetone and acetone–water
solvent mixtures revealed significant perturbations of the respect-
ive porphyrin receptor’s Soret band as a function of concen-
tration of TBA anion salts. In a typical titration experiment
(Fig. 3), upon addition of chloride, a bathochromic shift in the
maxima of the absorbance bands is observed. This arises from
‡For positively-charged receptor 6·(PF6)4 in acetone–water mixtures,
however, the concentrations required for naked-eye anion sensing
resulted in precipitation of the complex from solution.
7094 | Dalton Trans., 2012, 41, 7092–7097
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Table 1 Association constants, K (M−1), for 1 : 1 complexes of
porphyrin host 5 and ZnTPP with various anionsa
molecular sieves. Pyrrole was distilled over CaH2, under reduced
pressure and stored at −25 °C under N2. TBA2·SO4 was azio-
troped with toluene and stored in a dessicator containing P2O5.
TBA salts of Cl−, Br−, I−, AcO−, H2PO4− were stored in a dessi-
cator and TBAF·3H2O was used immediately after purchase
from Sigma-Aldrich. Water was deionised and micro-filtered
using a Mill-Q® Millipore machine. Where anhydrous solvents
were used, they were degassed with N2, and dried by passing
through an MBraun MSPS-800 column.
Anion
5
ZnTPP
F−
79 707 (8989)
12 191 (159)
255 (13)
20 850 (988)
8092 (318)
149 (5)
Cl−
Br−
I−
<50
<50
AcO−
H2PO4
22 202 (893)
21 657 (989)
100 785 (4858)
18 971 (786)
23 691 (801)
91 537 (2556)
−
2−
SO4
1H, 13C, 19F, 31P NMR spectra were recorded on a Varian
Mercury-VX 300, a Varian Unity Plus 500 or a Bruker AVII500
with cryoprobe at 293 K. Mass spectra were obtained using a
micromass LCT (ESMS) instrument. Electronic absorption
spectra were recorded on a PG instruments T60U spectrometer.
Melting points were recorded on a Gallenkamp capillary melting
point apparatus and are uncorrected.
a K values calculated by analysis of the anion induced changes in the
Soret band using Specfit® software. All anions added as their TBA
salts. Solvent: acetone. Temperature: 293 K.
Table 2 Association constants, K (M−1), for 1 : 1 complexes of
porphyrin host 6·(PF6)4 with various anionsa
b
c
Anion
6·(PF6)4
6·(PF6)4
5,10,15,20-Tetrakis(α-bromo-m-tolyl)porphyrin, 117
d
d
F−
8666 (312)
7449 (112)
<50
Cl−
3-(Bromomethyl)benzaldehyde (4.50 g, 22.6 mmol) and pyrrole
(1.57 mL, 22.6 mmol) were dissolved in anhydrous, degassed
CH2Cl2 (2.5 L) in a 3-necked, 3 L round bottomed flask. EtOH
(17.0 mL) was added and the solution was purged with N2 for
10 min and wrapped in foil. BF3·OEt2 (0.93 mL, 7.54 mmol)
was added via syringe and the reaction mixture stirred in the
dark at r.t. for 70 min whilst continuously degassing with N2.
Et3N (1.26 mL, 9.04 mmol) was added, followed by p-chloroanil
(4.17 g, 17.0 mmol) and the reaction mixture was refluxed for
1 h. After cooling to r.t., all volatiles were removed in vacuo.
The residue was redissolved in CH2Cl2 and passed through a plug
of silica, eluting with CH2Cl2 to give compound 1 as a purple
solid (0.66 g, 0.67 mmol, 30%). λmax(acetone)/nm: 415 (ε/dm3
mol−1 cm−1 631 500) 512 (23 920), 546 (11 380), 589 (8360),
644 (6060); δH (300 MHz, CDCl3) 8.87 (8H, s, pyrrole-ArH),
Br−
—
—
I−
<50
d
AcO−
H2PO4
134 214 (1060)
123 452 (12 221)
517 726 (73 517)
−
d
2−
SO4
252 988 (1426)
a K values calculated by analysis of the anion induced changes in the
Soret band using Specfit® software. All anions added as their TBA
salts. Temperature: 293 K. b Solvent: 5% water : acetone. c Solvent: 15%
water : acetone. d Soret band perturbations too small to determine an
association constant.
The optical anion sensing properties of 6·(PF6)4 were also
−
assessed in 15% water : acetone for F−, Cl−, AcO−, H2PO4 and
SO42− (Table 2). Porphyrin 6·(PF6)4 exhibits strong and selective
sulfate binding whereas with the singly-charged anions minimal
perturbations of the Soret band were observed which suggests
these anions are not bound in this more competitive aqueous
solvent mixture.
3
8.27 (4H, s, phenyl-H2), 8.17 (4H, d, J = 7.5 Hz, phenyl-H6),
3
3
7.84 (4H, d, J = 7.5 Hz, phenyl-H4), 7.75 (4H, t, J = 7.5 Hz,
phenyl-H5), 4.79 (8H, s, –CH2–), −2.80 (2H, s, pyrrole-NH). m/z
(ES): 987.0 ([M + H]+. C48H35Br4N4 requires 987.0).
Conclusions
5,10,15,20-Tetrakis(α-azido-m-tolyl)porphyrin, 2
The anion binding properties of a neutral tetra-triazole zinc(II)
metalloporphyrin cage receptor and a novel positively-charged
triazolium cage host system have been investigated by
UV/visible spectroscopy. With strongly bound anions a distinc-
tive naked-eye colorimetric response is observed. UV/visible
anion titration experiments reveal that both host systems exhibit
strong anion binding affinities forming 1 : 1 stoichiometric com-
plexes with a range of halides and oxoanions in acetone and
acetone–water mixtures. Specifically, the positively-charged tria-
zolium porphyrin cage displays a marked preference for sulfate
in 15% water–acetone.
Compound 1 (500 mg, 0.507 mmol) was dissolved in DMSO
(100 mL). NaN3 (329 mg, 5.05 mmol) was added and the reac-
tion stirred at r.t. under N2 for 16 h. After cooling to 0 °C, H2O
(100 mL) was added and the mixture extracted with CH2Cl2 (3 ×
100 mL). The combined organic phases were washed with H2O
(100 mL), dried over anhydrous MgSO4, filtered and the solvent
removed in vacuo. The crude residue was purified by column
chromatography (SiO2, CH2Cl2 : 60–80 petroleum ether (v/v
3 : 2)) to give 2 as a purple solid (382 mg, 0.485 mmol, 90%).
Mp: 192–194 °C; λmax(acetone)/nm: 415 (ε/dm3 mol−1 cm−1
271 000) 512 (19 940), 545 (8280), 589 (5660), 645 (3880); δH
3
(300 MHz, CDCl3) 8.86 (8H, s, pyrrole-ArH), 8.22 (4H, d, J =
6.5 Hz, phenyl-H6), 8.19 (4H, s, phenyl-H2), 7.83–7.76 (8H, m,
phenyl-H4,-H5), 4.66 (8H, s, –CH2–), −2.79 (2H, s, pyrrole-
NH); δC (75.5 MHz, CDCl3) 142.6, 134.4, 134.3, 133.8, 131.2,
127.8, 127.3, 119.6, 54.8; m/z (ES): 835.3223 ([M + H]+.
C48H35N16 requires 835.3225).
Experimental
Unless otherwise stated, commercially available solvents (HPLC
grade) and reagents were used without further purification.
Triethylamine was distilled from KOH and stored over 3 Å
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 7092–7097 | 7095

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3
7.79 (4H, d, J = 7.8 Hz phenyl-H4), 7.67 (4H, s, triazole-H),
[5,10,15,20-Tetrakis(α-azido-m-tolyl)porphyrin]zinc(II) complex, 3
7.36 (2H, s, ArH), 7.10 (4H, s, phenyl-H2), 5.95 (4H, d, J =
16.4 Hz, –OCH2–), 5.80 (4H, d, J = 16.4 Hz, –OCH2–), 5.15
2
Compound 2 (382 mg, 0.485 mmol) was dissolved in CH2Cl2 :
CH3OH (v/v 9 : 1, 20 mL) and Zn(OAc)2·2H2O (502 mg,
2.29 mmol) was added. The reaction was stirred under N2 at r.t.
for 16 h. The solvent was removed in vacuo, the residue redis-
solved in CH2Cl2 (100 mL) and washed with water (5 ×
100 mL). The organic layer was dried over anhydrous MgSO4,
filtered and the solvent removed in vacuo. The crude residue was
purified using column chromatography (SiO2, CH2Cl2) to give 3
as a purple solid (360 mg, 0.401 mmol, 88%). Mp: decomposed
> 200 °C; λmax(acetone)/nm: 428 (ε/dm3 mol−1 cm−1 485 000)
560 (20 120), 599 (9120); δH (300 MHz, CDCl3) 8.93 (8H, s,
pyrrole-ArH), 8.21 (4H, d, 3J = 7.5 Hz, phenyl-H6), 8.14 (4H, s,
2
(4H, d, 2J = 12.8 Hz, –NCH2–), 5.06 (4H, d, 2J = 12.8 Hz,
–NCH2–). δC (125.8 MHz, 9 : 1 CDCl3:CD3OD) 164.9, 149.6,
149.4, 144.1, 141.0, 133.1, 133.0, 132.4, 132.4 (sic), 129.0,
126.8, 125.9, 125.5, 119.5, 58.2, 53.4. m/z (ES): 1325.2888
([M + Na]+. C70H46NaN16O8Zn requires 1325.2868).
Porphyrin cage 6·(PF6)4
Porphyrin cage 5 (22.0 mg, 0.0169 mmol) was dissolved in
anhydrous CH2Cl2 (10 mL), Me3O·BF4 (12.6 mg, 0.0852 mmol)
was added and the reaction mixture stirred under N2 at r.t. for
3 days. CH3OH : Et3N (v/v 1 : 1) was added and the volatiles
were removed in vacuo. Following purification using preparative
thin layer chromatography (SiO2, CH3CN : H2O : sat. KNO3(aq)
(v/v 14 : 2 : 1)) the crude reside was dissolved in acetone : H2O :
sat. NH4PF6(aq) (v/v 100 : 2 : 1). The acetone was removed
in vacuo and the resulting purple precipitate was isolated by fil-
tration as 6·(PF6)4 (10.7 mg, 5.5 μmol, 32%). Mp: decomposed
> 281 °C; λmax(acetone)/nm: 425 (ε/dm3 mol−1 cm−1 409 000),
554 (14 900), 593 (4440); δH (500 MHz, CD3CN) 8.76 (4H, s,
pyrrole-ArH), 8.72 (4H, s, pyrrole-ArH), 8.55–8.53 (8H, m, tria-
3
phenyl-H2), 7.78 (4H, t, J = 7.5 Hz, phenyl-H5), 7.72 (4H, d,
3J = 7.5 Hz, phenyl-H4), 4.55 (8H, s, –CH2–); δC (300 MHz,
DMSO-d6) 149.3, 143.0, 134.3, 133.9, 131.6, 129.5, 127.8,
127.1, 120.0, 53.6; m/z (ES): 931.1984 ([M
+
Cl]−.
C48H32ClN16Zn requires 931.1981).
Tetra(prop-2-yn-1-yl) benzene-1,2,4,5-tetracarboxylate, 4
1,2,4,5-Benzenetetracarboxylic acid (1.00 g, 3.93 mmol) was
suspended in SOCl2 (20 mL) and DMF (5 drops, cat.) was
added. The reaction mixture was heated to reflux and stirred
under N2 for 16 h until the solution became homogenous. The
SOCl2 was removed by distillation and the residue dissolved in
anhydrous CH2Cl2 (20 mL). This was added dropwise to a solu-
tion of propargyl alcohol (2.30 mL, 39.3 mmol) and Et3N
(6 mL, 43 mmol) in anhydrous CH2Cl2 (100 mL). The reaction
mixture was stirred under N2 at r.t. for 16 h after which it was
washed with water (3 × 100 mL), dried over anhydrous MgSO4,
filtered and the solvent removed in vacuo. The crude residue
was purified by column chromatography (SiO2, CH2Cl2 :
CH3OH (v/v 95 : 5)) to give 4 as a white solid (1.37 g,
3.67 mmol, 86%). Mp: 113–115 °C; δH (300 MHz, CDCl3) 8.17
(2H, s, ArH), 4.96 (8H, d, 4J = 2.5 Hz, –CH2–), 2.58 (4H, t, 4J =
2.5 Hz, alkyne-CH); δC (75.5 MHz, CDCl3) 164.7, 133.8, 130.0,
76.6, 76.0, 53.8; m/z (ES): 429.0582 ([M + Na]+. C22H14NaO8
requires 429.0581).
zolium-H & phenyl-H6), 7.97 (4H, t, J = 7.7 Hz, phenyl-H5),
3
3
7.93 (4H, d, J = 7.7 Hz, phenyl-H4), 7.37 (2H, s, ArH), 7.24
(4H, s, phenyl-H2), 6.153 (8H, s, –OCH2–), 5.34 (4H, d, J =
14.4 Hz, –NCH2–), 5.14 (4H, d, J = 14.4 Hz, –NCH2–), 4.11
(12H, s, –NCH3); δC (125.8 MHz, CD3CN) 163.6, 149.8, 144.0,
137.4, 133.6, 132.7, 132.3, 132.0, 131.9, 131.9 (sic), 131.2,
129.6, 127.4, 126.8, 119.6, 56.9, 54.1, 38.61; δF (282.4 MHz,
CD3CN) −72.9 (d, 1J = Hz, 709 Hz, PF6); δP (121.6 MHz,
1
CDCl3) −139.3 (sept, J = 709 Hz, PF6). m/z (ES): 1797.2874
([M − PF6]+. C74H58F18N16O8 P3Zn requires 1797.2835).
X-ray crystallography
Single crystals of 5·5(C3H6O) were grown by slow evaporation
of an acetone solution of 5. X-ray diffraction data were collected
using graphite monochromated Cu Kα radiation (λ = 1.54184 Å)
on a Oxford Diffraction SuperNova diffractometer. The diffracto-
18
meter was equipped with a Cryostream N2 open-flow cooling
Porphyrin cage 5
device, and the data were collected at 150(2) K. Series of
ω-scans were performed in such a way as to collect all unique
reflections to a maximum of 0.80 Å. Cell parameters and inten-
sity data (including inter-frame scaling) were processed using
CrysAlis Pro.19 The structure was solved by charge-flipping
methods using SUPERFLIP20 and refined using full-matrix
least-squares on F2 within the CRYSTALS suite.21 All non-
hydrogen atoms were refined with anisotropic displacement par-
ameters. Hydrogen atoms were generally visible in the difference
map and their positions and displacement parameters were
refined using restraints prior to inclusion into the model using
riding constraints.22
Porphyrin
3 (90.0 mg, 0.100 mmol), [Cu(NCCH3)4]PF6
(8.00 mg, 21.5 μmol), and Et3N (60.0 μL, 0.4 mmol) were dis-
solved in anhydrous DMF (200 mL). Capping group 4 (40.0 mg,
0.100 mmol) was added and the reaction mixture was stirred
under N2 at 75 °C for 3 days. The reaction mixture was then
cooled, the solvent reduced to 3 mL in vacuo. The reside was
redissolved in CH2Cl2 (100 mL) and EtOAc (100 mL) and
washed with water (2 × 100 mL), filtered, washed with water
(2 × 100 mL), dried over anhydrous MgSO4 and the solvent
removed in vacuo. The crude residue was purified by preparative
thin layer chromatography (SiO2, 95 : 5 CH2Cl2 : CH3OH) to
give 5 as a purple solid (22.6 mg, 0.0173 mmol, 17%). Mp:
decomposed >245 °C; λmax(acetone)/nm: 422 (ε/dm3 mol−1
cm−1 439 500), 553 (5140), 592 (1600); δH (500 MHz, CDCl3)
8.75 (4H, s, pyrrole-ArH), 8.71 (4H, s, pyrrole-ArH), 8.43 (4H,
d, 3J = 7.8 Hz, phenyl-H6), 7.86 (4H, t, 3J = 7.8 Hz, phenyl-H5),
Acknowledgements
We thank the EPSRC (L.C.G.), Trinity College and the Claren-
don Fund (N.G.W.) for funding, Prof. S. Faulkner for use of UV/
7096 | Dalton Trans., 2012, 41, 7092–7097
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