Hemicryptophane-assisted electron transfer: A structural and electronic study

Article abstract of DOI:10.1039/c2dt31530k

Three copper(ii)@hemicryptophane complexes with various cavity sizes and shapes, Cu(ii)@1, Cu(ii)@2 and Cu(ii)@3, were synthesized and characterized by near-IR/vis and EPR spectroscopies. The spectroscopic data are consistent with the presence of a trigonal-bipyramidal geometry of the N₄Cu· H₂O core, in accord with the energy-minimized structures obtained from DFT calculations. Cyclic voltammetry studies in CH₂Cl ₂ showed irreversible redox processes, whereas electrolysis coulometry indicated that Cu(ii)/Cu(i) complexes could be interconverted. Electrochemistry data of the complexes stress the crucial role of the cage structure of the hemicryptophane in the thermodynamics of the electron transfer. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c2dt31530k

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Hemicryptophane-assisted electron transfer:
a structural and electronic study†
Cite this: Dalton Trans., 2013, 42, 1530
a
b
c
a
Olivier Perraud, Jean-Bernard Tommasino, Vincent Robert, Belén Albela,
a
a
a
Lhoussain Khrouz, Laurent Bonneviot, Jean-Pierre Dutasta* and
Alexandre Martinez*
a
Three copper(II)@hemicryptophane complexes with various cavity sizes and shapes, Cu(II)@1, Cu(II)@2
and Cu(II)@3, were synthesized and characterized by near-IR/vis and EPR spectroscopies. The spectro-
scopic data are consistent with the presence of a trigonal-bipyramidal geometry of the N
accord with the energy-minimized structures obtained from DFT calculations. Cyclic voltammetry studies
in CH Cl showed irreversible redox processes, whereas electrolysis coulometry indicated that Cu(II)/Cu(I)
4 2
Cu·H O core, in
Received 11th July 2012,
Accepted 22nd October 2012
2
2
DOI: 10.1039/c2dt31530k
complexes could be interconverted. Electrochemistry data of the complexes stress the crucial role of the
cage structure of the hemicryptophane in the thermodynamics of the electron transfer.
www.rsc.org/dalton
molecular hosts. Indeed, inspired from the cryptophane struc-
Introduction
9
ture, which is constructed from two cyclotriveratrylene (CTV)
1
0
The elaboration of molecular containers that mimic the active units, the hemicryptophanes, introducing dissymmetry at
site of metalloproteins is very attractive, as they can act as the molecular cavity level, are ditopic host molecules, which
1
1
supramolecular catalysts or receptors, and lead to better were found to be efficient molecular receptors, supramolecu-
1
12
understanding of the protein function. For instance, enzymes lar catalysts, and led to the design of novel molecular mech-
1
3
14
copper monooxygenases involving Cu(II)/Cu(I) redox processes anical components as propellers
or gyroscopes.
For
(dopamine β-monooxygenase (DβM) and peptidylglycine instance, oxidovanadium–hemicryptophane complexes were
α-hydroxylating monooxygenase (PHM)) play an important role synthesized and were found to be efficient supramolecular
in biology by performing highly selective and efficient trans- catalysts for sulfoxidation, thus mimicking haloperoxidase
1
2b
formations. They are still a challenging source of inspiration enzymes.
This class of molecular receptors combine all the
2
for chemists seeking to model the enzymes machinery. Supra- important elements required to design a biomimetic system of
molecular systems combining a biomimetic copper(II) coordi- the mononuclear copper enzymes: (i) its cavity allows the
nation core and a lipophilic cavity have been developed inclusion of organic guests, (ii) it prevents the formation of
bringing new insights into the chemical and redox properties binuclear species and (iii) it includes a ligand that can
resulting from the specific environment of mono-copper complex a metal ion and thus mimic the active center of the
3
,4
sites. Among the supramolecular building blocks, such as enzymes. Herein we report on the first synthesis and structural
5
6
7
8
calixarenes, resorcinarenes, curcubiturils, or cyclodextrins,
characterization of copper(II) complexes based on hemicrypto-
able to give rise to biomimetic systems of such enzymes, hemi- phane ligands 1–3 (Fig. 1). Insights into their redox behaviors
cryptophanes appear as a particularly interesting class of are provided by electrochemical studies and suggest that the
hemicryptophane pocket is likely to assist the electron
transfer.
a
Laboratoire de Chimie, CNRS, Université Claude Bernard Lyon 1, École Normale
Supérieure de Lyon, 46 Allée d’Italie, F-69364 Lyon, France.
E-mail: alexandre.martinez@ens-lyon.fr, jean-pierre.dutasta@ens-lyon.fr;
Fax: +33 4 7272 8860; Tel: +33 4 7272 8382
Results and discussion
Synthesis of the Cu@hemicryptophane complexes
b
Laboratoire des Multimatériaux et Interfaces, CNRS, Université Claude Bernard
Lyon 1, 2 Avenue Grignard, F-69622 Villeurbanne, France.
E-mail: jbtomasi@univ-lyon1.fr; Tel: +33 4 7244 8220
Hemicryptophanes 1 and 3 were synthesized according to our
previously reported procedure. This modular approach was
c
Laboratoire de Chimie Quantique, Institut de Chimie, UMR CNRS 7177, Université
15
de Strasbourg, 4 rue Blaise Pascal, F-67070 Strasbourg, France.
E-mail: vrobert@unistra.fr; Tel: +33 3 6885 1302
also applied to prepare the new host 2 (Scheme 1). The cyclo-
triveratrylene derivative 4 was synthesized in two steps accord-
1
13
†
Electronic supplementary information (ESI) available: H and C NMR spectra,
1
6
voltammogram. See DOI: 10.1039/c2dt31530k
ing to a known procedure and was then reacted with
1
530 | Dalton Trans., 2013, 42, 1530–1535
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Fig. 1 Hemicryptophane hosts 1–3.
Fig. 2 Copper(II)@hemicryptophane complexes.
Fig. 3 Near-IR/vis spectra of Cu(II)@hemicryptophane-1 ( ), -2 ( ) and -3
) complexes (CH Cl , T = 298 K).
(
2
2
Scheme 1 Synthesis of hemicryptophane host 2.
6
-hydroxy-2-naphthaldehyde in DMF in the presence of
Cs CO to give the precursor 5. The condensation of 5 with tris
2
3
3 3
(2-aminoethyl)-amine (tren) diluted in a CHCl –CH OH
mixture followed by a reduction step with sodium borohydride
afforded the hemicryptophane 2 in 42% yield.
Hemicryptophane copper(II) complexes were synthesized by Fig. 4 Experimental (solid lines) and simulated (dashed lines) EPR spectra (X
band) of Cu(II)@1 (a), Cu(II)@2 (b) and Cu(II)@3 (c) hemicryptophane complexes
the reaction of the ligands 1–3 with stoichiometric amounts of
2 2
in frozen CH Cl (115 K). Experimental conditions: ν = 9.4 GHz; power = 20 mW;
copper(II) perchlorate in a dichloromethane–methanol mixture
to produce the pale green cupric Cu(II)@1, Cu(II)@2 and
Cu(II)@3 complexes in 82%, 92% and 91% yields, respectively
amplitude modulation = 2.0 G.
(Fig. 2).
absorption at 870 nm, 834 nm and 860 nm respectively as well
Following this strategy, we were able to successfully encage as a shoulder in the region of 700 nm (Fig. 3). These obser-
the copper(II) ion into the cavity of the hemicryptophane hosts. vations are characteristic of d–d transitions of copper(II) com-
Moreover, the formation of these copper complexes is very ver- plexes in a trigonal-bipyramidal geometry.18
satile, as we can easily modulate the size and shape of the mo-
EPR measurements
lecular cavity of the hemicryptophane ligands. It was thus
important to investigate and compare the structures and redox Electron paramagnetic spectroscopy (EPR) was used in order
properties of these different complexes.
to have a better insight into the geometry around the metal
ion. The EPR spectra of the Cu(II) complexes were recorded in
Electronic spectroscopy
frozen CH
2
Cl
2
solution at 115 K (Fig. 4). All the samples are
= 2.00–2.02, g
hemicryptophane complexes in CH Cl show a maximum 2.13–2.14 and g3 = 2.20–2.22) with a resolved hyperfine
The near-IR/vis spectra of the Cu(II)@1, Cu(II)@2 and Cu(II)@3 characterized by a pseudo-axial EPR signal (g
1
2
=
2
2
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Table 1 Electrochemical, near-IR/vis and EPR data for Cu@1, Cu@2 and Cu@3
hemicryptophane complexes in CH
saturated calomel electrode
2 2
Cl . Potentials are defined with respect to a
λ
max/nm
EPR parameters
−4 −1
pa(2)/V (ε/M cm−1
−
1
)
(A/10 cm )
Complex
E
pc(1)/V
E
Cu(II)@1 −0.91
Cu(II)@2 −0.70
Cu(II)@3 −0.68
+0.45
870 (181)
834 (316)
860 (280)
g
g
g
g
g
g
g
g
1
2
3
1
2
3
1
2
= 2.010 (66.7)
= 2.136 (40.0)
= 2.220 (116.7)
= 2.023 (66.7)
= 2.131 (40.0)
= 2.225 (126.7)
= 2.000 (56.7)
= 2.138 (51.7)
= 2.197 (108.3)
+0.79
+0.10
Fig. 6 Cyclic voltammograms of Cu@1 (a), Cu@2 (b) and Cu@3 (c) hemicryp-
−
1
tophane complexes in CH
respectively.
2
Cl
2
at 300, 500 and 100 mV
s
scan rates,
G
3
171°, 175° and 171° for Cu@1, Cu@2 and Cu@3, respectively.
Furthermore, the three hosts maintain an almost C -symmetri-
3
cal molecular cavity, as reported for such ligands in the solid
2
2
state. However, the DFT optimized structures emphasize the
great difference in size of the three cage compounds. The local
environment of the Cu(II) ion governs the association with the
hemicryptophane and there is no need for a specific cavity
shape. Nevertheless, such observation suggests that these pro-
totypes can be used to modulate other properties such as elec-
tron transfer in bio-inspired complexes.
Electrochemical studies
Electrochemistry of the Cu(II)@1, Cu(II)@2 and Cu(II)@3 hemi-
Fig. 5 DFT-optimized structures of Cu(II)@hemicryptophane complexes.
Copper atoms are shown in green.
cryptophane complexes was performed under anaerobic and
2 2
anhydrous conditions in CH Cl . The Cu(II)/Cu(I) processes,
studied by cyclic voltammetry, are clearly irreversible (Fig. 6).
structure (A = 57–68 × 10 , A2 = 40–52 × 10−4 and A3
1
−
4
=
1
They are characterized by a reduction peak at Epc-1(1) =
08–127 × 10− cm ) (Table 1). The g-values are typical for a
X coordination sphere with a slightly distorted TBP geome-
try around the copper(II) ion. The R value, (g − g )/(g −
g2), was equal to 1.50, 1.15 and 2.34 for Cu@1, Cu@2 and
Cu@3, respectively, which suggests a higher trigonal distortion
for the two former complexes, with R values closer to 1.
Indeed, all the complexes present a g < 2.04 and R > 1, which
4
−1
1/2
p
−0.91 V, Epc-2(1) = −0.70 V and Epc-3(1) = −0.68 V and the i /v
N
4
(
i : peak current; v: scan rate) remains nearly constant with
p
1
9
20
2
1
3
−1
−1
v ranging from 100 mV s to 500 mV s . A sluggish re-
oxidation peak at Epa-1(2) = 0.45 V, Epa-2(2) = 0.79 V and Epa-3(2)
=
0.10 V is observed for Cu@1, Cu@2 and Cu@3 hemi-
1
9
cryptophane complexes, respectively.
1
Therefore, it appears that their oxidation and reduction
potentials are strongly dependent on the structure of the cavity
since Cu@1, Cu@2 and Cu@3 hemicryptophane complexes
only differ by their aromatic linkers. This emphasizes the
crucial role played by the host structure in the thermodynamic
properties of a system presenting a hydrophobic cavity. Electro-
lysis coulometry performed at reduction potential of each
Cu(II) complex is consistent with the exchange of 1 electron
per mole. Moreover, it can be noticed that no deposit of metal
copper(0) on the working electrode is observed during the cou-
lometric reduction.
is consistent with the unpaired electron of the Cu(II) ion occu-
2
pying predominantly a dZ orbital (considering the z axis paral-
1
9
lel to the pseudo-C3 symmetry axis). Molecular complexes
1
8a
with tren ([Cu(tren)(NH
3
)](ClO
4
)
2
)
and methyl-tren ligands
1
8b,21
(
[Cu(Me tren)](ClO ) or [CuX(Me tren)X])
present axial
3
4 2
6
EPR signals (g|| ∼ 2.0 < g⊥ ∼ 2.2) typical of undistorted TBP
geometries, thus indicating that the confinement imposed by
the hemicryptophane entity may promote an angular distor-
tion around the metal ion (vide infra).
Molecular modelling
At the same time scale of the coulometry, the reduction of
Further insight into the geometry of the copper complexes can Cu@1 leads to new oxidation and reduction peaks on the
be obtained from Density Functional Theory (DFT) calcu- cyclic voltammogram (Fig. S5 in ESI†). These new processes
lations. In the optimized geometries of the complexes, studied by cyclic voltammetry are reversible and different from
copper(II) adopts a slightly distorted trigonal-bipyramidal geo- that of the free ligand. This experimental observation strongly
metry, in agreement with the previous near-IR/vis and EPR suggests the formation of a stable copper(I) complex lacking
data (Fig. 5). The copper–nitrogen distances are similar in the coordination of a water molecule, during the electrochemical
three complexes: 2.1 Å and 2.2 Å for the tertiary and secondary process. The low concentration of water in solution, inducing
nitrogen atoms respectively, and the O–Cu–Napical angles are a slow coordination rate at the cyclic voltammetry time scale,
1
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Experimental
General
All reactions were carried out under argon by means of an
inert gas/vacuum double manifold and standard Schlenk tech-
niques. Dichloromethane was dried and degassed on a solvent
station by passage through an activated alumina column fol-
lowed by an argon flush. Other solvents were dried prior to use
1
13
over molecular sieves. H and C NMR spectra were recorded
at 500.1 MHz and 125.7 MHz respectively; chemical shifts are
1
reported relative to the residual protonated solvent signal ( H,
1
3
C). Mass spectra were recorded by the Centre de Spectromé-
trie de Masse, Institut de Chimie, Lyon. EPR spectra were
recorded on a Bruker Elexys 500 spectrometer (X-band). Fitting
of the EPR spectra was performed by using the EasySpin soft-
ware. The UV-Vis/NIR spectra were recorded with a Jasco V-570
spectrophotometer. The electrochemical studies of the copper
Scheme 2 Square scheme redox pathway for the Cu@hemicryptophane complexes were performed with a three-electrode cell (WE:
complexes.
glassy carbon, RE: calomel, CE: Pt). All potentials are defined
relative to a saturated calomel electrode. The experiments were
controlled by an AMEL 7050 – all in one potentiostat moni-
tored by a computer. Solvents (CH Cl , CH OH, CHCl , DMF)
2 2 3 3
can indeed account for the reversibility of this process. The
Cu(I) species, after a counter electrolysis, can be regenerated
into the initial Cu(II) complexes qualitatively characterized by
cyclic voltammetry. Both forms, Cu(II) and Cu(I) complexes,
can be interconverted by electrolysis indicating a full chemical
reversibility. This redox behavior, associated with a coordi-
were dried and kept under N . All experiments were performed
2
−3
with ∼10 M solutions of electroactive species with 0.2 M
+
−
15 15
16
Bu
4
N PF
6
supporting salt. Compounds 1,
3
and 4 were
prepared according to the published procedures.
nation/decoordination process of the ligand, has been already Synthesis of the ligands
observed by Reinaud et al. with copper@tren-calixarene
HEMICRYPTOPHANE 2. To a solution of the precursor 5 (200 mg,
.20 mmol) in a mixture of chloroform and methanol (80 mL,
4
a
complexes.
0
Thus, the redox pathway can be summarized as displayed
in Scheme 2. (i) After reduction (Epc(1)), the Cu(I)@hemicrypto-
phane water complex obtained is unstable since reduction is
irreversible. (ii) Due to the poor affinity of Cu(I) centres toward
O donor ligands, a fast de-coordination of the water molecule
occurred, leading to the formation of a water free four coordi-
nated Cu(I) complex. (iii) It can be oxidized at a more anodic
potential. (iv) This oxidation gives a very unstable Cu(II)
species, which binds a water molecule to give the initial
complex.
v/v 1/1) was added dropwise a solution of tris(2-aminoethyl)
amine (33 μL, 0.22 mmol) in a mixture of chloroform and
methanol (40 mL, v/v 1/1) for 2 h and the mixture was stirred
for 7 h. Sodium borohydride (200 mg, 5.3 mmol) was added to
the reaction mixture cooled to 0 °C, and was then allowed to
warm up to room temperature and stirred overnight. The sol-
vents were removed under vacuum. The residue was dissolved
in chloroform (40 mL) and 10% aqueous NaOH (25 mL). The
aqueous phase was extracted with chloroform (2 × 20 mL) and
the organic layers were washed with 10% aqueous NaOH (2 ×
3
0 mL), dried over Na SO , filtered and evaporated under
2 4
vacuum. The crude product was purified by column chromato-
graphy on silica gel using a 90 : 10 : 2 mixture of dichloro-
Conclusion
methane, methanol and triethylamine as an eluent to give the
1
In conclusion, the syntheses of the first copper complexes of hemicryptophane host 2 (92 mg, 42% yield). H NMR
3
hemicryptophane hosts have been described. Physical–chemi- (500.1 MHz, 298 K, CDCl ) δ 7.30 (d, 3H, J = 8.4 Hz, ArH);
cal studies indicated that the Cu(II) ion is encaged inside the 7.03–7.09 (m, 9H, ArH); 7.05 (s, 3H, ArH); 6.85 (s, 6H, ArH);
cavity of the host molecule and adopts a slightly distorted tri- 6.60 (dd, 3H, J = 8.9 and 2.2 Hz, ArH); 4.79 (d, 3H, J = 13.7 Hz,
2 2 2
gonal-bipyramidal geometry. The supramolecular structure ArCH Ar); 4.50–4.55 (m, 3H, OCH ); 4.34–4.40 (m, 3H, OCH );
appears on the one hand to stabilize the Cu(II) complexes 4.22 (t, 6H, J = 4.90 Hz, OCH ); 3.64 (s, 9H, OCH ); 3.63 (d, 3H,
2
3
since it prevents any dimerization or decomposition of J = 13.3 Hz, ArCH
2
N); 3.57 (d, 3H, J = 13.7 Hz, ArCH
N); 2.54–2.69 (m, 12H, NCH
C NMR (125.7 MHz, 298 K, CDCl ) δ 156.8 (C O); 148.7
2
Ar); 3.52
the complex, and on the other hand to affect the redox (d, 3H, J = 13.3 Hz, ArCH
2
2
CH N).
2
1
3
properties of the metal center. These systems are to be con-
3
Ar
sidered as synthetic platforms to vary the Cu(II) active site by (CArO); 146.5 (CArO); 133.6 (CAr); 133.2 (CAr); 131.9 (CAr); 129.3
maintaining the local environment and varying the (CArH); 128.9 (CAr); 127.2 (CArH); 126.9 (CArH); 126.5 (CArH);
pocket size.
119.4 (C H); 116.7 (C H); 113.7 (C H); 107.3 (C H); 67.6
Ar Ar Ar Ar
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(
(
OCH
2
); 67.5 (OCH
2
); 56.0 (OCH
3
); 52.9 (NCH
2
Ar); 47.7
Cu(II)@2: near-IR/vis (CH
2
Cl
2
, 298 K): λmax = 834 nm, ε =
NCH CH N); 36.7 (ArCH Ar). ESI-MS m/z: found 1101.5362 316 cm−
1
M
−1
(shoulder at 698 nm, ε = 311 cm
−1
M ). EPR
−1
2
2
+
2
−4
−1
[M + H] ; calcd for C69
H
73
N
4
O
9
: 1101.5372. IR (KBr) ¯ν = (frozen CH
2.131 (A = 40.0 × 10 cm ); g
COMPOUND 5. A solution of 4 (500 mg, 0.69 mmol), aldehyde cm ). Anal. calcd for [C H Cl CuN O ·H O]·2CH Cl
2 2 1 1 2
Cl , 115 K): g = 2.023 (A = 66.7 × 10 cm ); g =
−
1
−4
−1
−4
2
931, 1606, 1508, 1263 cm . M.p. > 310 °C (decomp.).
2
3 3
= 2.225 (A = 126.7 × 10
−
1
6
9
72
2
4
17
2
2
2
(
(
389 mg, 2.26 mmol) and Cs
2 3
CO (985 mg, 3.02 mmol) in DMF (1551.68): C, 54.96; H, 5.07; N, 3.61. Found: C, 55.15; H, 5.12;
2
+
10 mL) was stirred overnight at 80 °C. The mixture was cooled N, 3.62. ESI-MS m/z: found 581.7313 [M − H
2
O] (calcd for
to room temperature, the solvent was evaporated off and 10% C H CuN O : 581.7292). IR (KBr) ¯ν = 3257, 2929, 2869, 1606,
6
9
72
4 9
−
−1
aqueous NaOH (40 mL) was added. The aqueous mixture was 1508, 1265, 1089, 622 (ClO
extracted with CH Cl (80 mL) and the organic phase was Cu(II)@3: near-IR/vis (CH
washed with 10% aqueous NaOH (2 × 40 mL) and with dis- 280 cm−
tilled water (40 mL), then dried over Na SO , filtered and evap- 115 K): g
orated under vacuum. The crude product was taken in a × 10 cm−1); g = 108.3 × 10 cm−1). Anal. calcd
= 2.197 (A
3
4
) cm
.
2
2
2
Cl , 298 K): λmax = 860 nm, ε =
2
1
−1
M
(shoulder at 700 nm). EPR (frozen CH Cl ,
2 2
= 56.7 × 10− cm ); g
4
−1
2
4
1
= 2.000 (A
1
2 2
= 2.138 (A = 51.7
−
4
−4
3
CH Cl –Et O mixture, filtered and evaporated to give the pre- for [C H Cl CuN O ·H O]·3CH Cl (1486.43): C, 48.48; H,
2
2
2
57 66
2
4
17
2
2
2
1
cursor of cyclization 5 (573 mg, 83% yield). H NMR 5.02; N, 3.77. Found: C, 48.58; H, 5.22; N, 3.73. ESI-MS m/z:
500.1 MHz, 298 K, CDCl
−
+
(
3
) δ 10.06 (s, 3H, CHO); 8.22 (s, 3H, 1058.4115 [M − H
2 4 11
O + HCOO ] (calcd for C58H67CuN O :
ArH); 7.88 (d, 3H, J = 8.4 Hz, ArH); 7.84 (d, 3H, J = 9.0 Hz, 1058.4097). IR (KBr) ¯ν = 3284, 2933, 2873, 1602, 1511, 1263,
−
−1
4
ArH); 7.73 (d, 3H, J = 8.4 Hz, ArH); 7.19 (s, 3H, J = 9.0 Hz, ArH); 1087, 757, 624 (ClO ) cm .
7
3
9
.15 (b, 3H, ArH); 6.95 (s, 3H, ArH); 6.82 (s, 3H, ArH); 4.75 (d,
Molecular modelling
Ab initio geometry optimizations were performed using the
H, J = 13.8 Hz, ArCH Ar); 4.33–4.43 (m, 12H, OCH ); 3.70 (s,
2
2
13
H, OCH
3
2
); 3.55 (d, 3H, J = 13.8 Hz, ArCH Ar). C NMR
1
7
(125.7 MHz, 298 K, CDCl
3
) δ 192.0 (CHO); 159.2 (CArO); 148.8
Gaussian 03 package within an unrestricted DFT framework.
A combination of unrestricted BP86 functional and double-
zeta 6-31G all electron basis sets for light elements and a
double-zeta with diffuse 6-31+G was used to carry out the pre-
liminary geometry optimizations. Then, a triple-zeta (6-311G)
quality basis set was introduced on the Cu and nearest-neigh-
bour N atoms to confirm that the core part geometry is not
modified. We checked using the hybrid B3LYP functional that
our results do not suffer from the change of the exchange–
correlation functional.
(C O); 146.7 (C O); 138.1 (C ); 134.2 (C H); 133.4 (C );
Ar
Ar
Ar
Ar
Ar
1
1
32.5 (CAr); 132.0 (CAr); 131.2 (CArH); 128.1 (CAr); 127.8 (CArH);
23.7 (CArH); 120.1 (CArH); 117.2 (CArH); 114.1 (CArH); 107.2
(C H); 68.2 (OCH ); 66.8 (OCH ); 56.2 (OCH ); 36.5 (ArCH Ar).
Ar 2 2 3 2
+
56 12
ESI-MS m/z: found 1003.3657 [M + H] , calcd for C63H O :
1
1
003.3688. IR (KBr) ¯ν = 2935, 1689, 1625, 1510, 1475,
265 cm− . M.p. = 131 °C.
1
Synthesis of the Cu(II) complexes
Safety note: Caution! Perchlorate salts of metal complexes with
organic ligands are potentially explosive and should be
handled only in small quantities with appropriate precautions.
Hemicryptophane 1, 2 or 3 (41 mg, 44 μmol; 53 mg,
Notes and references
4
(
1
8
μmol and 35 mg, 37 μmol, respectively) and Cu-
ClO (H O) (19.4 mg, 52 μmol; 21.6 mg, 58 μmol and
6.0 mg, 43 μmol, respectively) were dissolved under argon in
a mixture of dry CH Cl (3 mL), MeOH (200 μL) and triethyl-
1 (a) A. J. Kirby, Angew. Chem., Int. Ed. Engl., 1996, 35, 707–
724; (b) J. K. M. Sanders, Chem.–Eur. J., 1998, 4, 1378;
(c) J.-M. Lehn, Rep. Prog. Phys., 2004, 67, 245;
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4
)
2
2
6
2
2
amine (7 μL, 50 μmol). The solution was stirred at room temp-
erature for 90 min and solvents were removed under reduced
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35, 43; (b) J. P. Klinman, Chem. Rev., 1996, 96, 2541;
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pressure. The residue was dissolved in CH
washed with water (3 × 5 mL), dried over Na SO
2
Cl
2
(20 mL),
2
4
, filtered and
concentrated under reduced pressure. Precipitation from
pentane afforded pale green powders (44 mg, 82%; 61 mg,
9
2% and 41 mg, 91% for Cu(II)@1, Cu(II)@2 and Cu(II)@3,
respectively).
Cu(II)@1: near-IR/vis (CH
2
Cl
2
, 298 K): λmax = 870 nm, ε =
2
Cl ,
1
−1
1
1
×
81 cm−
M
(shoulder at 700 nm). EPR (frozen CH
2
−
4
−1
15 K): g = 2.010 (A = 66.7 × 10 cm ); g = 2.136 (A = 40.0
1
1
2
2
−
4
−1
−4
−1
10 cm ); g
3
= 2.220 (A
3
= 116.7 × 10 cm ). Anal. calcd
O]·2CH Cl ·C 12 (1471.63): C,
2.23; H, 5.62; N, 3.81. Found: C, 52.31; H, 6.08; N, 3.67.
for [C57
H
66Cl
2
CuN
4
O
17·H
2
2
2
5
H
5
2
+
2 4 9
ESI-MS m/z: 506.7081 [M − H O] (calcd for C57H66CuN O :
5
1
06.7057). IR (KBr) ¯ν = 3259, 2931, 2869, 1610, 1511, 1261,
4 For the calix[6]tren-based copper complexes, see:
(a) G. Izzet, B. Douziech, T. Prang, A. Tomas, I. Jabin, Y. Le
087, 622 (ClO4−) cm
−1
.
1
534 | Dalton Trans., 2013, 42, 1530–1535
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