Pyrrole-based metallo-macrocycles and cryptands

Article abstract of DOI:10.1039/b210099a

The synthesis of dithiocarbamate ligands based on a pyrrole framework is reported. These ligands self-assemble with zinc(II), nickel(II) and copper(II) to afford neutral, dinuclear metallomacrocycles and trinuclear metallocryptands. The assembled metallo compounds have been characterised by a range of techniques, including ¹H NMR. UV-vis spectroscopy, elemental analysis, mass spectrometry and X-ray crystallography. Some preliminary anion binding studies have also been conducted, using electronic spectroscopy and electrochemistry. The nickel macrocycles showed some affinity for acetate, whereas the copper cryptand showed affinity for benzoate anions. The copper cryptand also exhibited a significant electrochemical response to a range of anions.

Full text of DOI:10.1039/b210099a

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Pyrrole-based metallo-macrocycles and cryptands
Paul D. Beer,*a Andrew G. Cheetham,a Michael G. B. Drew,b O. Danny Fox,a
Elizabeth J. Hayesa and Toby D. Rollsa
a Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford,
South Parks Road, Oxford, UK OX1 3QR. E-mail: paul.beer@chem.ox.ac.uk
b Department of Chemistry, University of Reading, Whiteknights, Reading, UK RG6 6AD
Received 15th October 2002, Accepted 9th December 2002
First published as an Advance Article on the web 21st January 2003
The synthesis of dithiocarbamate ligands based on a pyrrole framework is reported. These ligands self-assemble with
zinc(), nickel() and copper() to afford neutral, dinuclear metallomacrocycles and trinuclear metallocryptands.
The assembled metallo compounds have been characterised by a range of techniques, including 1H NMR, UV-vis
spectroscopy, elemental analysis, mass spectrometry and X-ray crystallography. Some preliminary anion binding
studies have also been conducted, using electronic spectroscopy and electrochemistry. The nickel macrocycles showed
some affinity for acetate, whereas the copper cryptand showed affinity for benzoate anions. The copper cryptand also
exhibited a significant electrochemical response to a range of anions.
Introduction
The synthesis of two- and three-dimensional macrocyclic and
cage-like host molecules using metal-directed self-assembly is a
current area of intense research activity.1–8 Through prudent
choice of multidentate ligand and stereochemical requirement
of the mediating metal ion, the resulting self-assembled poly-
metallic structures may be designed to exhibit unique redox,
magnetic and photochemical properties, and have the potential
to bind, sense and react together with guest substrates.9–12
Because assembly of such receptors with labile metal ions
is often a thermodynamically driven process, yields of self-
assembled products can often far exceed those created by
formation of covalent bonds.
Presently the field is dominated by square planar platinum()
and palladium() metals in combination with various oligo-
pyridine ligands,2,13,14 copper(), nickel(), silver(), and iron()
helical structures of oligobipyridyls12,15 and pseudo-octahedral
titanium(), aluminium(), iron() and gallium() com-
plexes of oligocatecholate ligands leading to triple helicates and
tetrahedral clusters.15,16
To date the use of pyrrole-based ligands in metal-directed
self-assembly has born great similarity to that of pyridyl-based
Scheme 1 Preparation of acyclic transition metal complexes of
pyrrole-based ligands.
ligands in the field, with the pyrrole N atom coordinating
directly to a metal ion.17–20 Sessler and coworkers have used
calixpyrroles for anion recognition,21,22 and the tripodal pyrrole
solvent mixture. Recrystallisation from dichloromethane–
ethanol mixtures afforded analytically pure complexes in yields
of 42% for (2-Ni) and 50% for (2-Zn).
The pyrrole-based metallo-macrocycles were synthesised
synthon has already been used to synthesise cryptands which
have been shown to bind small neutral molecules.23 We report
here the metal-directed self-assembly of novel pyrrole-based
metallo-macrocycles and cryptands which are designed to
according to the procedure illustrated in Scheme 2. Vilsmeier–
coordinate anions via their pyrrole NH groups, precluding
Haack formylation of dimethyldipyrromethane 3 gave 4 which
direct metal ion coordination to the deprotonated pyrrole N
was condensed with two equivalents of benzylamine to give the
atoms. This has necessitated the incorporation of another
Schiff base compound 5 in 89% yield. Sodium borohydride
reduction in methanol afforded the diamine 6 as a white solid in
56% yield. The metallo-macrocycles (7-M, M = Ni, Zn-pyr, Pd)
were prepared in very good yields by the same one-pot pro-
cedure with carbon disulfide, base and either nickel() acetate,
K2PdCl4 or zinc acetate in 4 : 1 THF–H2O solutions. The bi-
ligand into the target structures, namely the dithiocarbamate
(dtc) group, which we have recently used as a self-assembling
construction motif in the synthesis of nanosized resorcarene-
based transition metal polymetallic assemblies,24,25 copper()–
dtc macrocycles26–28 and catenanes.29
nuclear zinc() metallo-macrocycle was isolated as the pyridine
adduct.
Results and discussion
Synthesis of acyclic and macrocyclic pyrrole metal dtc complexes
Characterisation
Acyclic “model” pyrrole–metal–dtc complexes were initially
prepared via the synthetic procedure shown in Scheme 1. The
nickel() and zinc() dtc complexes of 2 were prepared in a one-
pot synthesis from amine 1 by reaction with carbon disulfide,
KOH and either nickel() or zinc() acetate in a 4 : 1 THF–H2O
All these new acyclic and macrocyclic metal–dtc complexes
were characterised by a variety of techniques including 1H
NMR spectroscopy, UV-vis spectroscopy, mass spectrometry,
elemental analysis (see Experimental section) and in some cases
by X-ray crystal structure determination.
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 6 0 3 – 6 1 1
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Scheme 2 Synthetic route to pyrrole-based metallo-macrocycles.
Table 1 Selected mean structural parameters for the three crystal
structures
X-Ray structural investigations of (2-Ni), (7-Ni), (7-Pd) and
(7-Zn-pyr)
The crystal structure determinations of (2-Ni), (7-Ni), (7-Pd)
and (7-Zn-pyr) have been carried out.
M–M/Å
M–S/Å
pyrrole N–pyrrole N/Å
The structure of (2-Ni) is shown in Fig. 1, and it can be seen
that the molecule contains a crystallographic centre of sym-
metry. The nickel() ion (d8) has a distorted square-planar
coordination geometry, with the two independent Ni–S dis-
tances equivalent at 2.202(3) and 2.207(4) Å. The benzyl groups
are positioned mutually trans to each other, minimising steric
repulsion.
(7-Ni)
6.63
6.66
8.54
2.19
2.33
2.39a
3.63, 10.95
3.65, 11.32
2.96, 11.32
(7-Pd)
(7-Zn-pyr)
a Average coordination sphere distance including the Zn–pyr coordin-
ate bond.
Fig. 1 Crystal structure of (2-Ni) with ellipsoids at 30% probability.
Fig. 2 Crystal structure of (7-Ni) with ellipsoids at 20% probability.
The structure of (7-Pd) is isostructural.
Fig. 2 shows the crystal structure of (7-Ni), which is
isomorphous with (7-Pd). Both have their low-spin d8 metal
ions coordinated in a square-planar environment, maximizing
LFSE. Illustrative structural parameters for all three metallo-
macrocycles are given in Table 1. The pyrrole N–pyrrole N
distances tabulated are the lengths of the short and long sides
of a parallelogram with a pyrrole N atom at each corner.
The difference in M–S bond length leads to significant
changes in the angles subtended at the metal which are 79.0(1)–
80.0(1)Њ for Ni and 75.2(1)–75.6(1)Њ for Pd although the overall
planarity of the coordination spheres remains unchanged.
Least squares planes calculations on the four sulfur atoms in
the equatorial planes show that the metal atoms are distorted
slightly from the plane (0.07, 0.06 Å for Ni; 0.07, 0.07 Å for Pd)
and that in each dimer the two equatorial planes intersect at
angles of 32.8 and 33.2Њ, respectively. The twisted macrocyclic
loop adopts a quasi figure-of-eight topology. Binuclear metal
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Synthesis of trinuclear cryptands
Analogous Schiff base condensation reactions of 5,5Ј,5Љ-
triformyl-1-ethyltripyrromethane 932,33 with the appropriate
amines followed by NaBH4 reduction produced the respective
amines 12 and 13 (Scheme 3).
Initial attempts to prepare the target metallo-cryptands using
an analogous one-pot metallo–dtc procedure produced in-
soluble products regardless of the identity of the metal salt
or the secondary amine reactants suggesting that polymeris-
ation had occurred. However, using less concentrated solutions
of reactants, high dilution conditions, the trinuclear metallo-
cryptands were isolated in yields ranging from 13 to 87%.
Characterisation
Fig. 3 The structure of (7-Zn-pyr) with thermal ellipsoids at 20%
probability.
These complexes were characterised by a range of techniques
including H NMR, UV-vis spectroscopy, mass spectrometry
1
and elemental analysis (see Experimental section). The neutral
metallo-cages are not particularly suitable for ESMS, but they
do tend to form adducts with Group 1 metal ions such as Naϩ
and Kϩ. The addition of a metal salt such as KPF6 can signifi-
cantly improve the ESMS spectrum. The ESMS data obtained
is tabulated in Table 2 and the spectrum of (15-Ni) is shown in
Fig. 4.
complexes of cyclooctapyrroles have been shown to adopt a
chiral figure-of-eight topology.30,31
The structure of the (7-Zn-pyr) complex is shown in Fig. 3,
and once again the dimer contains a crystallographic centre
of symmetry. Each zinc atom is five-coordinate, so that the
coordination sphere of Zn (d10) has a distorted square-based
pyramidal geometry with the Zn atom positioned above the
basal plane. It is noticeable that the Zn–S bonds to these axial
atoms are at 2.555(4), 2.656(4) Å significantly longer than the
Zn–S bonds to equatorial atoms S(12) and S(30) which are
2.366(3) and 2.353(3) Å, respectively. Though the structure of
(7-Zn-pyr) is complicated by the effects of pyridine coordin-
ation to Zn, we see that the macrocyclic loop in this complex
remains twisted. In the solid state, the twist in (7-M) has the
effect of reducing the size of the cavity within the macrocyclic
loop. If this twist is manifested in solution, it may reduce the
potency of (7-M) as hosts for anions.
Anion binding studies
The use of the pyrrole group in anion recognition has received
considerable recent attention. Of particular note are the
calixpyrroles, which bind anions via the pyrrole NH groups.21,22
The anion binding properties of the metallo-macrocycles and
-cryptands synthesized here are therefore of interest.
Investigation of the anion binding properties of (7-Ni) and (2-Ni)
1
The H NMR spectra of the metallo-macrocycles are complex
and are not simplified at higher temperature. For this reason,
Scheme 3 Synthetic route to pyrrole-based metallo-cryptands.
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Fig. 4 Observed ESMS spectrum and calculated isotopic clusters for (15-Ni).
The electronic absorption transition bands were assigned by
reference to the literature.35,36 Excellent agreement between
experiment and binding curves derived theoretically by Spec-
fit34 for 1 : 1 complexation was observed for (7-Ni) and Ni-
(dedtc)2, allowing the calculation of the corresponding stability
constants; the 1 : 1 stoichiometry was confirmed by Job’s
method.37 Specfit could not fit the data for (2-Ni), probably due
to 2 : 1 acetate: (10-Ni) binding becoming significant at higher
acetate concentrations. Interestingly, Ni(dedtc)2, with no
hydrogen bond donor groups, binds acetate with K ≈ 5 × 104
M
Ϫ1 in the solvent mix used. Although the stability constant for
the macrocycle (7-Ni) is significantly larger (K ≈ 1 × 107 MϪ1),
this increased affinity for acetate may be due to the extra Ni
atom per molecule, rather than coordination to the pyrrole
NHs. This rationalization is in accord with the twisted solid-
state structure of the macrocycle: twisting in solution might
effectively close the cavity to potential guest species.
Fig. 5 Changes in the UV-Vis absorption spectrum of (7-Ni) in 70 : 30
DCM–MeCN on the addition of TBA acetate; experimental (circles)
and theoretical (line) binding curves for 1 : 1 association (inset).
Investigation of the anion binding properties of (14-Ni), (15-Ni)
and (14-Cu)
Table 2 ESMS data for the metallo-cages
1
Unfortunately, the H NMR spectra of the metallo-cryptands
[M ϩ H]ϩ
[M ϩ Na]ϩ
[M ϩ K]ϩ
[M ϩ Cu]ϩ a
(14-Ni) and (15-Ni) are complex and very broad, and were
therefore deemed unsuitable for the study of anion binding.
Investigations were however carried out with (14-Cu) by moni-
toring changes in the UV-vis spectra of CHCl3 solutions upon
addition of aliquots of TBA chloride, benzoate and dihydrogen
phosphate. Significant shifts were observed upon addition of
TBA benzoate (Fig. 6). The experimental binding curves
showed a large change in gradient at a guest concentration
of 2.5 × 10Ϫ5 M, indicating the formation of a complex of
1 : 1 stoichiometry. Specfit34 was used to calculate a stability
constant (Table 4). Surprisingly, the addition of the other
TBA salts produced very small shifts, preventing the reliable
determination of stability constants with Specfit. This would
seem to suggest that (14-Cu) binds benzoate in preference to
chloride and dihydrogen phosphate.
Metallo-cage
(14-Ni)
(15-Ni)
(14-Cu)
—
1773.88
—
1843.40
—
—
1859.39
1810.85
1874.46
—
1835.8
—
a Cuϩ may be present as an impurity in the ESMS spectrometer or
acetonitrile solvent.
studies to investigate whether (7-Ni) binds anionic guests were
carried out by monitoring changes in the UV-vis spectrum
of (7-Ni) in 7 : 3 DCM–MeCN on the addition of aliquots of
tetrabutylammonium (TBA) acetate, chloride, bromide and
iodide. Substantial shifts (principally in absorbance) in the
(7-Ni) spectrum were observed when TBA acetate was added
(Fig. 5), allowing the calculation of a stability constant using
the Specfit computer program,34 but not for the addition of
the other TBA salts. The changes in the UV-Vis spectra of
the model compound (2-Ni) and of nickel diethyldithiocarb-
amate (Ni(dedtc)2) on the addition of TBA acetate were
then recorded under the same conditions to allow comparison
(Table 3).
Electrochemical study of (14-Cu)
The incorporation of copper() centres into the cages intro-
duces a redox active moiety. The potentials at which reduction
(CuII/I) and oxidation (CuII/III) occur are dependent upon the
environment around the redox centre. Beer’s redox active
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Table 3 Principal UV-Vis absorptions (200–500 nm), isobestic points and 1 : 1 stability constants with TBA acetate, where applicable, for (7-Ni),
(2-Ni) and Ni(dedtc)2
LC
MLCT
MLCT
Complex
λ/nm
ε/MϪ1 cmϪ1
λ/nm
ε/MϪ1 cmϪ1
λ/nm
ε/MϪ1 cmϪ1
Isobestic point(s)/nm
log10 K/MϪ1 (1:1 complex)
(7-Ni)
231
77,600
327
328
325
62,500
43,800
25,300
395
395
388
13,200
8,000
3,800
317
297, 254
293, 253
7.06 0.41
Not fitted
4.71 0.04
(2-Ni)
227, 238a
240
41,200, 40,800a
30,300
Ni(dedtc)2
a Band shoulder.
Table 4 Isobestic point and calculated stability constant for the 1 : 1
(14-Cu)–benzoate complex
Complex
Isobestic point/nm
263
log10 K (for 1 : 1 complex)
(14-Cu)
5.73 0.18
Fig. 6 Changes in the UV-Vis absorption spectrum of (14-Cu) in
CHCl3 upon addition of TBA benzoate; experimental (circles) and
theoretical (line) binding curves for 1 : 1 association (inset).
Fig. 7 (a) Changes in the square-wave voltammogram of the CuII/III
couple of (14-Cu) upon the addition of 5 equivalents of TBA chloride.
(b) Changes in the square-wave voltammogram of the CuII/I couple of
(14-Cu) upon the addition of 5 equivalents of TBA chloride.
dtc–copper() macrocycles demonstrated that the presence
of an anionic substrate can affect the redox potential of
the CuII/III dtc redox couple. The resulting cathodic shifts indi-
cate that the presence of the anion stabilises the copper()
centre.26
effectively stabilize the copper() oxidation state, as seen
previously.26
Similar effects were observed in the CuII/I couple, in that two
reduction waves appear on addition of an anionic guest species
(Fig. 7(b)). The addition of an anion would once again be
expected to produce a cathodic shift in the reduction couple.
One wave does indeed appear at a more cathodic potential,
while the second wave is only moderately perturbed. This
splitting was again observed for all three anions, though the
sizes of the two peaks relative to one another altered on chang-
ing the anion. For dihydrogen phosphate the peak at the more
negative potential dominated, whereas for chloride it was the
reverse situation.
The electrochemical studies of (14-Cu) were carried out in
DCM using an Agϩ/Ag reference electrode with TBA tetra-
fluoroborate as supporting electrolyte. The cyclic voltam-
mograms of (14-Cu) showed both redox couples to be irrevers-
ible, with an Epa value of 0.36 V and an Epc of Ϫ0.83 V (scan
rate 100 mV sϪ1). The single, broad oxidation and reduction
waves, also seen in the square wave voltammograms, suggest
three overlapping one-electron waves, implying similar coordin-
ation environments for the three copper centers.
Anion binding studies were carried out with 2.5 × 10Ϫ6 mol
of (14-Cu) in DCM, using an Agϩ/Ag reference electrode with
TBA tetrafluoroborate as supporting electrolyte. The initial
The exact cause of this peak splitting is still under
investigation. A possible explanation may be that complexation
of the anion inside the cryptand results in the copper centers
becoming inequivalent. Asymmetric binding of the anion, to
only one or two arms of the cryptand, would result in
the respective copper centers being in different stereochemical
and electronic environments. It is apparent however that the
presence of an anion elicits a significant electrochemical
response.
square-wave voltammograms (using a scan rate of 100 mV sϪ1
)
of both redox couples were recorded, five equivalents of the
TBA salt of chloride, benzoate and dihydrogen phosphate were
added, and the voltammograms re-recorded.
The square-wave voltammogram for the CuII/III couple upon
the addition of TBA chloride is shown in Fig. 7(a). Upon addi-
tion of chloride, the original wave appears to split into two,
suggesting that in some way the presence of the halide anion
alters both the electronic and stereochemical environments of
the copper() centres. The splitting into two oxidation peaks
was also observed on the addition of benzoate and dihydrogen
phosphate, although the effects were not as pronounced. The
presence of one cathodically shifted peak is concomitant with
anion binding, since the presence of a complexed anion would
Conclusion
The preparation and characterisation of new pyrrole-based
dithiocarbamate metallo-macrocycles and cryptands has been
described. The bis- and tris-pyrrole compounds have proven
to be useful synthons in the metal-directed synthesis of
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Table 5 Crystallographic data
(2-Ni)
(7-Ni)
(7-Pd)
(7-Zn-pyr)
Empirical formula
Formula weight
C28H26N2NiS4
577.46
C58H68N8Ni2O4S8
1315.10
C60H73N8O4.5Pd2S8
1447.54
C78H80N12S8Zn2
1572.76
Crystal system
Space group
Triclinic
P1
Triclinic
P1
Triclinic
P1
Triclinic
P1
¯
¯
¯
¯
a/Å
b/Å
c/Å
α/Њ
6.294(10)
10.323(14)
10.909(17)
100.75(1)
93.28(1)
106.73(1)
662.2(17)
1, 1.448
1.068
12.996(17)
16.75(2)
17.05(2)
68.67(1)
83.41(1)
80.28(1)
3404(7)
2, 1.283
0.846
13.160(17)
16.82(2)
17.26(2)
68.39(1)
81.78(1)
79.00(1)
3475(8)
2, 1.383
1.383
10.696(15)
11.949(15)
16.07(2)
85.96(1)
73.81(1)
79.75(1)
1941(5)
1, 1.346
0.884
β/Њ
γ/
V/Å3
Z, Dc/Mg cmϪ3
µ/mmϪ1
Unique reflections
Data/restraints/parameters
Final R indices [I > 2σ(I )], R1
wR2
2120
2120/0/160
0.0832
11522
11522/0/691
0.0991
11783
11783/0/733
0.0762
6942
6942/0/441
0.0764
0.2298
0.2479
0.2244
0.1185
R indices (all data), R1
wR2
0.1552
0.2688
0.490, Ϫ0.701
0.1638
0.2628
0.626, Ϫ0.878
0.1433
0.2632
1.111, Ϫ1.320
0.1931
0.1402
0.415, Ϫ0.257
Largest diff. peak, hole/e ÅϪ3
these molecules. X-Ray analysis of the metallo-macrocycles
reveals a twisted loop, which effectively reduces the size of
the macrocyclic cavity. If present in solution this twisted
conformation may account for the apparent lack of anion
binding capabilities observed in the UV-vis titration studies.
However the nickel macrocycle (7-Ni) was shown to bind
acetate. UV-vis anion-binding studies have shown the copper
metallo-cryptand (14-Cu) to preferentially bind benzoate.
Chloride and dihydrogenphosphate anions produced only small
perturbations in the electronic spectrum of the cryptand.
Electrochemical studies of the copper cryptand reveal peak
splitting of both the oxidation and reduction waves upon addi-
tion of anions, although the exact cause of this is still under
consideration. It is apparent however that a significant electro-
chemical response to the presence of anions is observed, and
therefore these cryptands warrant further investigation as
potential self-assembled anion receptors.
CCDC reference numbers 195408–195411
See http://www.rsc.org/suppdata/dt/b2/b210099a/ for crystal-
lographic data in CIF or other electronic format.
General procedure for preparation of the dtc complexes (2-M)
1H-pyrrol-2-ylmethylbenzylamine 1 (1 equivalent, prepared
as previously reported)42 was dissolved in THF and CS2
(1.1 equivalents) added. KOH (1 equivalent) and the M()
salt (1 equivalent, see below) were dissolved in water and added
to the solution, the base was added before the M() salt. The
THF : H2O ratio (by volume) after addition of both the base
and the M() salt was 4 : 1. The mixture was allowed to stir at
room temperature for 10 h and at this point, more water was
added until a solid precipitate was obtained. This was filtered
off and recrystallised from DCM–EtOH: for (2-Ni), the solid
recovered included crystals suitable for analysis by single crystal
X-ray diffraction.
Experimental
(2-Ni). Colour: dark green; M() salt = Ni(OAc)2ؒ4H2O;
yield = 50%; H NMR (CDCl3): δ 4.92 (s, 4H, CH2Ph), 5.06
1
General
(s, 4H, CH2–pyrrole), 6.15 (s, 4H, pyrrole H3 ϩ H3Ј over-
lapping pyrrole H4 ϩ H4Ј), 6.84 (s, 2H, pyrrole H5 ϩ H5Ј), 7.40
(br m, 10H, Ph), 9.14 (br s, 2H, pyrrole NH). Analysis: Calc. for
C26H26N4S4Ni: C, 53.7, H, 4.5, N, 9.6. Found: C, 53.7, H, 4.5,
N, 9.5%; ESMS [C26H26N4S4Ni ϩ Cl]Ϫ: m/z observed 615.08,
calc. 615.01.
Elemental analyses were carried out by the Inorganic
Chemistry Laboratory Microanalysis Service. NMR spectra
were recorded on a Varian Mercury 300 spectrometer, using
the deuterated solvent signal as an internal reference. Electro-
spray mass spectrometry was carried out on a Micromass
LCT spectrometer. UV-Vis spectra were recorded on a Perkin-
Elmer Lambda 6 spectrophotometer. Electrochemical studies
were carried out on an EG&G Princeton Applied Research
Potentiostat/Galvanostat model 273.
(2-Zn). Colour: white; M() salt = Zn(OAc)2ؒ4H2O; yield =
1
42%; H NMR (CDCl3): δ 4.60 (s, 4H, CH2Ph), 4.71 (s, 4H,
CH2–pyrrole), 6.14 (s, 4H, pyrrole H3 ϩ H3Ј overlapping
pyrrole H4 ϩ H4Ј), 6.83 (s, 2H, pyrrole H5 ϩ H5Ј), 7.35 (br m,
10H, Ph), 8.79 (br s, 2H, pyrrole NH). Analysis: Calc. for
C26H26N4S4Znؒ3H2O: C, 48.6, H, 5.0, N, 8.7. Found: C, 48.5,
H, 4.1, N, 8.4%; ESMS [C26H26N4S4Zn Ϫ H]Ϫ: m/z observed
585.37, calc. 585.02.
Crystal structure determinations
Crystal data for (2-Ni), (7-Ni), (7-Pd) and (7-Zn-pyr) are given
in Table 5 together with refinement details. Crystal data was
collected with Mo-Kα radiation using the MARresearch Image
Plate System. The crystals were positioned at 70 mm from the
Image Plate. 100 frames were measured at 2Њ intervals with a
counting time of 2 min. Data analyses were carried out with the
XDS program.38 The four structures were solved using direct
methods with the Shelx86 program.39 Apart from the solvent
molecules, all non-hydrogen atoms were refined with aniso-
tropic thermal parameters. The hydrogen atoms bonded to
carbon were included in geometric positions and given thermal
parameters equivalent to 1.2 times those of the atom to which
they were attached. Empirical absorption corrections were
carried out using DIFABS.40 The structures were refined on F 2
using Shelxl41 to convergence.
5, 5Ј-Diformyl-1,1-dimethyldipyrromethane 4
1,1-Dimethyldipyrromethane 3 (5.69 g, 32.7 mmol, prepared
as previously reported)5 was dissolved in DMF (50 ml) and
benzoyl chloride (21 ml) added slowly at 0 ЊC. The solution
was stirred at this temperature for 2 h and then at room
temperature for a further 2 h, at which point the imine
salt began to precipitate. To ensure complete precipitation,
toluene (50 ml) was added and the mixture stirred for a
further hour. The imine salt was filtered off and dissolved
immediately in 70% aqueous ethanol (100 ml) containing
Na2CO3 (5.0 g). This mixture was refluxed for 15 min, diluted
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608

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with water (125 ml) and the resulting precipitate collected
and recrystallised from EtOH to give 5.09 g (22.1 mmol,
68%) of 4 as a pale yellow solid: H NMR (CDCl3): δ 1.76
(3, 6H, CH3), 6.24 (m, 2H, pyrrole H3 ϩ H3Ј), 6.85 (m, 2H,
pyrrole H4 ϩ H4Ј), 9.27 (s, 2H, CHO), 10.89 (br s, 2H, pyrrole
NH).
overlapping pyrrole H4 ϩ H4Ј), 7.10–7.43 (br m, 20H, Ph),
8.01–8.37 (br m, 4H, pyrrole NH). Analysis: Calc. C, 49.4, H,
4.9, N, 7.9 for C58H60N8S8Pd2ؒ4H2O. Found: C, 49.0, H, 4.8, N,
7.3%; ESMS [C58H60N8S8Pd2 ϩ K]ϩ: m/z observed 1377.08,
calc. 1377.04.
1
(7-Zn-pyr). Colour: white; M() salt = Zn(OAc)2ؒ2H2O;
dissolved in pyridine and precipitated by addition of water;
recrystallised from pyridine–di-n-butyl ether giving X-ray
quality crystals; yield = 87%; 1H NMR (CDCl3): δ 1.57 (s,
12H, CH3), 4.86 (s, 8H, CH2Ph), 5.20 (s, 8H, pyrrole–CH2), 5.90
(s, 4H, pyrrole H3 ϩ H3Ј), 6.08 (s, 4H, pyrrole H4 ϩ H4Ј),
7.14–7.24 (m, 26H, Ph overlapping pyridine H3 ϩ H4 ϩ H5),
7.86 (m, 4H, pyrrole NH), 8.84 (m, 4H, pyridine H2 ϩ H6).
Analysis: Calc. for C68H70N10S8Zn2: C, 57.7, H, 5.0, N, 9.9.
Found: C, 57.4, H, 4.9, N, 9.9%.
Imine 5
Imine 5 was prepared by a modification of a previously
reported method.9 5.09 g (22.1 mmol) of 5, 5Ј-diformyl-1,1-di-
methyldipyrromethane 4 was dissolved in THF (70 ml) and
cooled to 0 ЊC. Benzylamine (5.2 ml) was added dropwise. After
15 min, the solution was allowed to warm to room temperature
and stirred for 10 h. The solvent was removed under reduced
pressure and the resulting solid recrystallised from the mini-
mum volume of hot Et2O to give 8.08 g (19.8 mmol, 89%) of
imine 5 as a pale yellow solid: 1H NMR (CDCl3): δ 1.66 (s, 6H,
CH3), 4.66 (s, 4H, CH2Ph), 6.07 (d, 2H, J 3.5 Hz, pyrrole H3 ϩ
H3Ј), 6.42 (d, 2H, J 3.5 Hz, pyrrole H4 ϩ H4Ј), 7.30 (m, 10H,
1-Ethyltripyrromethane 8
1-Ethyltripyrromethane 8 was prepared by the method of Lind-
sey and coworkers32 as modified by Wang and Bruce.33 Triethyl
orthopropionate (8.2 ml) was dissolved in an excess of freshly
distilled pyrrole (50 ml). TFA (0.5 ml) was added and the
mixture stirred under nitrogen; the solution turned dark red in
colour. After 5 min, the reaction was quenched with 0.2 M
NaOH (50 ml) giving a bright yellow emulsion. Ethyl acetate
(50 ml) was added and the organic phase separated and dried
over anhydrous MgSO4. Ethyl acetate and unreacted pyrrole
were removed under reduced pressure to yield the crude prod-
uct, which was stirred in cold ethanol. The product was filtered
off, washed with cold ethanol and dried under vacuum to give
Ph), 8.04 (s, 2H, CH᎐N–); ESMS [C H N ϩ H]ϩ: m/z
observed 409.24, calc. 409.30.
᎐
27 28
4
Amine 6
Amine 6 was prepared by a modification of a previously
reported method.9 Imine 5 (1.0 g, 2.45 mmol) was dissolved in
deoxygenated methanol (100 ml) and NaBH4 (0.5 g) added
slowly at 0 ЊC. The solution was allowed to warm to room
temperature and then refluxed for 10 h. The solvent was par-
tially evaporated and 50 ml of water added to destroy the
excess NaBH4. The water layer was extracted three times with
30 ml of Et2O, and the Et2O fractions combined and dried
over MgSO4. Filtration and evaporation of the solvent gave
1
5.59 g (23.4 mmol, 57%) of 8 as a white powder; H NMR
(CDCl3): δ 0.92 (t, 3H, J 7.3 Hz, CH3), 2.32 (q, 2H, J 7.3 Hz,
CH3CH2), 6.18 (m, 6H, pyrrole H3 ϩ H3Ј ϩ H3Љ overlapping
pyrrole H4 ϩ H4Ј ϩ H4Љ), 6.65 (q, 3H, H5 ϩ 5Ј ϩ 5Љ), d 7.89 (br
s, 3H, NH).
1
0.57 g (1.38 mmol, 56%) of amine 6 as a white fluffy solid: H
NMR (CDCl3): δ 1.62 (s, 6H, CH3), 3.63 (s, 4H, CH2Ph), 3.65
(s, 4H, CH2–pyrrole) 5.92 (m, 4H, pyrrole H3 ϩ H3Ј over-
lapping pyrrole H4 ϩ H4Ј), 7.25 (m, 10H, Ph), 8.47 (br s, 2H,
CH2NHCH2). Analysis: Calc. for C27H32N4: C, 78.6, H, 7.8, N,
13.6. Found: C, 78.3, H, 8.0, N, 13.4%; ESMS [C27H32N4 ϩ H]ϩ:
m/z observed 413.22, calc. 413.27.
5,5Ј,5Љ-Triformyl-1-ethyltripyrromethane 9
5,5Ј,5Љ-Triformyl-1-ethyltripyrromethane 9 was prepared using
a modification of previously reported methods.43 1-Ethyl-
tripyrromethane 8 (3.0 g, 12.6 mmol) was dissolved in dry
DMF (115 ml) and cooled to 0 ЊC. POCl3 (7.0 ml) was added
dropwise. The mixture was heated to 60 ЊC for 2 h and then
hydrolysed (80 ЊC) in water (1.3 l) containing NaOH (19.2 g).
The product precipitated out as a brown solid after 1 h and was
filtered off, dried under vacuum and purified by column chrom-
atography on silica (DCM–MeOH, 50:1 v/v) to give 2.768 g of 9
General procedure for preparation of the dtc macrocycles (7-M)
Amine 6 (1 equivalent) was dissolved in THF and CS2 (2.2
equivalents) added. KOH (2 equivalents) and the M() salt
(1 equivalent, see below) were dissolved in water and added to
the solution; the base was added before the M() salt. The
THF: H2O ratio (by volume) after addition of both the base
and the M() salt was 4 : 1. The mixture was allowed to stir at
room temperature for 10 h; at this point, more water was added
until a solid precipitate was obtained. This was filtered off and
purified as described below.
1
(8.57 mmol, 68%) as a fluffy white solid; H NMR (CDCl3): d
1.00 (t, 3H, J 6.8 Hz, CH3), d 2.60 (q, 2H, J 6.8 Hz, CH3CH2),
6.22 (s, 3H, pyrrole H3 ϩ H3Ј ϩ H3Љ), 6.88 (s, 3H, pyrrole H4 ϩ
H4Ј ϩ H4Љ), 9.08 (s, 3H, CHO), 11.53 (s, 3H, pyrrole NH).
Imine 10
(7-Ni). Colour: dark green; M() salt = Ni(OAc)2ؒ4H2O;
chromatographed on silica (CHCl3) with the forerunning band
collected and recrystallised from 1,2-dichloroethane–diiso-
propyl ether giving X-ray quality crystals; yield = 86%; 1H
NMR (CDCl3): δ 1.65 (s, 6H, CH3), 4.45–5.00 (br m, 16H,
CH2Ph overlapping CH2-pyrrole), 5.80–6.36 (br m, 8H, pyrrole
H3 ϩ H3Ј overlapping pyrrole H4 ϩ H4Ј), 7.00–7.50 (br m,
20H, Ph), 8.08–8.50 (br m, 4H, pyrrole NH). Analysis: Calc. C,
52.3, H, 5.3, N, 8.4 for C58H60N8S8Ni2ؒ5H2O. Found: C, 52.0, H,
5.3, N, 7.8%.
Imine 10 was prepared by a modification of a previously
reported method.42 5,5Ј,5Љ-Triformyl-1-ethyltripyrromethane 9
(750 mg, 2.32 mmol) was dissolved in THF (85ml) and cooled
to 0 ЊC. Benzylamine (3.3 equivalents) was added dropwise.
After 15 min, the solution was stirred at 60 ЊC for 15 h. The
solvent was removed under reduced pressure and the resultant
solid recrystallised from DCM–hexane to give 1.15 g (1.95
mmol, 84%) of imine 10 as dark red crystals: 1H NMR
(CDCl3): δ 0.89 (t, 3H, J 7.2 Hz, CH3), 2.41 (q, 2H, J 7.2 Hz,
CH3CH2), 4.64 (s, 6H, CH2Ph), 6.12 (d, 3H, J 3.5 Hz, pyrrole
H3 ϩ H3Ј ϩ H3Љ), 6.42 (d, 3H, J 3.5 Hz, pyrrole H4 ϩ H4Ј ϩ
(7-Pd). Colour: yellow; M() salt = K2PdCl4; chromato-
graphed on silica (CHCl3) with the forerunning band collected
and recrystallised from 1,2-dichloroethane–diisopropyl ether
H4Љ), 7.30 (br m, 15H, Ph), 8.04 (s, 3H, CH᎐N–).
᎐
Imine 11
1
giving X-ray quality crystals; yield = 68%; H NMR (CDCl3):
δ 1.60 (s, 6H, CH3), 4.65–4.93 (br m, 16H, CH2Ph overlap-
ping CH2-pyrrole), 5.87–6.28 (br m, 8H, pyrrole H3 ϩ H3Ј
Imine 11 was prepared similarly to imine 10. 5,5Ј,5Љ-Triformyl-
1-ethyltripyrromethane 9 (1.02 g, 3.16 mmol) was dissolved in
D a l t o n T r a n s . , 2 0 0 3 , 6 0 3 – 6 1 1
609

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THF (40 ml) and cooled to 0 ЊC. Cyclohexylamine (3.3 equiv-
alents) was added dropwise. After 15 min the mixture was
stirred at 60 ЊC for 15 h. The solvent was removed under
reduced pressure and the resultant oil was placed under vacuum
to remove any unreacted amine and residual solvent, giving
1.55 g (2.98 mmol, 94%) of imine 11 as a light pink fluffy solid;
1H NMR (CDCl3): δ 0.95 (t, 3H, CH3), 1.00–1.90 (m, 30H,
cyclohexyl-CH2), 2.55 (q, 2H, CH3CH2), 3.10 (m, 3H, cyclo-
hexyl-CH), 6.10 (s, 3H, H3 ϩ 3Ј ϩ 3Љ), 6.42 (s, 3H, H4 ϩ 4Ј ϩ
Calc. for C99H97N15S12Zn3: C, 57.2, H, 4.7, N, 10.1. Found: C,
56.7, H, 4.7, N, 9.8%
(14-Cu). The dark brown solid was recrystallised from
DCM–EtOH to give the pure product; yield = 67%; ESMS
[C84H82N12S12Cu3 ϩ K]ϩ, m/z observed 1874.46, calc. 1874.09.
Analysis: Calc. for C84H82N12S12Cu3ؒ5H2O: C, 52.4, H, 4.8, N,
8.7. Found: C, 52.2, H, 4.5, N, 8.8%
4Љ), 7.90 (s, 3H, CH᎐N–).
(15-Ni). The green solid was chromatographed on silica
(DCM–MeOH, 100 : 1) with the forerunning band collected
and recrystallised from DCM–EtOH; yield = 51%; H NMR
᎐
1
Amine 12
(CDCl3): δ 0.80–2.10 (br m, 66H, CH3 overlapped with cyclo-
hexyl-CH2), 2.30–2.50 (br s, 10H, CH3CH2 overlapped with
cyclohexyl-CH), 4.20–4.40 (br s, 12H, CH2–pyrrole), 5.90–6.40
(br m, 12H, pyrrole H3 ϩ H3Ј ϩ H3Љ overlapped with pyrrole
H4 ϩ H4Ј ϩ H4Љ), 8.20–9.20 (br m, 6H, pyrrole NH); ESMS
[C78H100N12S12Ni3 ϩ H]ϩ, m/z observed 1773.88, calc. 1773.33.
Analysis: Calc. for C78H106N12S12Ni3: C, 52.9, H, 6.0, N, 9.5.
Found: C, 52.7, H, 5.7, N, 9.4%
Amine 12 was prepared by a modification of a previously
reported method.42 Imine 10 (1.15 g, 1.95 mmol) was dissolved
in deoxygenated methanol (150 ml) and excess NaBH4 (4.50 g)
added slowly at 0 ЊC. The solution was allowed to warm to
room temperature and then refluxed under nitrogen for 2 h.
Solvent was partially evaporated and 100 ml water added to
destroy the excess NaBH4. The water layer was extracted
3 times with 60 ml of Et2O, and the Et2O fractions combined
and dried over MgSO4. Filtration and removal of the solvent
under reduced pressure gave 706 mg (1.18 mmol, 61%) of amine
12 as a yellow oil, which was used without further purification;
1H NMR (CDCl3): δ 0.91 (t, 3H, J 7.3 Hz, CH3), 2.30 (q, 2H,
J 7.3 Hz, CH3CH2), 3.67 (s, 6H, CH2Ph), 3.68 (s, 6H, CH2–
pyrrole), 5.96 (m, 3H, pyrrole H3 ϩ H3Ј ϩ H3Љ), 6.01 (m, 3H,
pyrrole H4 ϩ H4Ј ϩ H4Љ), 7.25 (m, 15H, Ph), 8.27 (br s, 3H,
CH2NHCH2).
Acknowledgements
We thank the EPSRC for a postdoctoral fellowship (O. D. F.,
E. J. H.) and the EPSRC and the University of Reading for
funds for the Image Plate system (M. G. B. D.).
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Amine 13
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atography on silica (100 : 1 CHCl3–MeOH) with the fore-
running band collected and recrystallised from DCM–EtOH;
1
yield = 87%; H NMR (CDCl3): δ 0.89–1.10 (br s, 6H, CH3),
2.10–2.40 (br s, 4H, CH3CH2), 4.40–4.90 (br m, 24 H, CH2–
pyrrole overlapped with CH2Ph), 5.90–6.40 (br m, 12H, pyrrole
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D a l t o n T r a n s . , 2 0 0 3 , 6 0 3 – 6 1 1
610

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