A zinc porphyrin bearing two lateral dpp-containing rings and its [3]pseudorotaxane (dpp: 2,9-diphenyl-1,10-phenanthroline)

Article abstract of DOI:10.1002/ejoc.200900136

A zinc porphyrin attached to two dpp-containing rings was prepared from a 31-membered ring with an attached pendent aldehyde function and. 5-mesityldipyrromethane by using the synthetic method introduced long ago by Lindsey and his group. The obtained por

Full text of DOI:10.1002/ejoc.200900136

FULL PAPER
DOI: 10.1002/ejoc.200900136
A Zinc Porphyrin Bearing Two Lateral dpp-Containing Rings and Its
[3]Pseudorotaxane (dpp: 2,9-diphenyl-1,10-phenanthroline)
Cécile Roche,[a] Angélique Sour,*[a] Frédéric Niess,[a] Valérie Heitz,[a] and
Jean-Pierre Sauvage*[a]
Keywords: Rotaxanes / Copper / Porphyrins / Macrocycles / Template synthesis
A zinc porphyrin attached to two dpp-containing rings was
prepared from a 31-membered ring with an attached pen-
dent aldehyde function and 5-mesityldipyrromethane by
using the synthetic method introduced long ago by Lindsey
and his group. The obtained porphyrin is of the ABAB type,
with two mesityl groups on the 5- and 15-positions and two
macrocycles on the 10- and 20-positions. From this com-
pound, a [3]pseudorotaxane was obtained in good yield from
the reaction of the porphyrin with two equivalents of a cop-
per(I) salt followed by the addition of two equivalents of 2,9-
dianisyl-1,10-phenanthroline.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2009)
formation of the desired interlocking structures. Along this
line, the recently published work on a [3]rotaxane acting
as an adaptable receptor is particularly illustrative.[27] The
present report is concerned with the synthesis of a porphyr-
inic compound consisting of a central porphyrin bearing
two laterally disposed dpp-containing macrocycles and its
reaction with copper(I) atoms in the presence of additional
chelates to afford a new [3]pseudorotaxane.
Introduction
The synthesis of porphyrin-containing catenanes and rot-
axanes has experienced a rapid development since the first
templated strategies reported more than 15 years ago.[1,2]
These compounds are highly promising species in relation
to models of the photosynthetic reaction centre and natural
antenna, which are the key components of photosynthetic
organisms. They are also potentially important in the field
of molecular machines.[3,4] Besides the originally developed
covalent approach, noncovalent strategies turned out to be
very efficient, as they can lead to highly complex structures
in a few steps from prefabricated porphyrinic compounds.
Both the coordination chemistry approach and the organic
one, based on π–π interactions between aromatic fragments
and/or hydrogen bonds, have led to spectacular interlocking
porphyrinic assemblies.[5–14] Interesting work on multicom-
ponent but noninterlocking systems assembled through
noncovalent interactions has also been reported by several
research teams.[15–23]
Results and Discussion
Design of the System
The copper(I)-templated synthesis of multirotaxanes may
necessitate the preparation of components containing sev-
eral coordinating rings. An alternative strategy is that of
the “daisy chain” approach,[28] based on ring-and-thread
conjugates, which has also been successfully exploited in
combination with copper(I)[29] to afford [3]- and [4]rotax-
anes. Recently, we reported the high-yield formation of
[4]rotaxanes consisting of two bismacrocycles and two rods
able to thread the rings.[27] In the previous examples,[27,29]
the connecting unit between the ring and the thread or be-
tween the two rings was located at the back of the 1,10-
phenanthroline chelate (i.e., it involved the 5- and 6-posi-
tions) and it was extremely rigid. We wanted to make and
study less-constrained systems consisting of coordinating
rings attached to the central aromatic connector (porphyr-
ins in the present case) by a single C–C linker located on
the same side as the coordinating site of the 1,10-phenan-
throline. In addition, it appeared particularly important to
perform the reaction in a straightforward fashion with only
a few steps within the overall synthetic process. The general
By exploiting a copper(I)-based template approach, our
group has described numerous porphyrin-containing cate-
nanes and rotaxanes and their energy and electron-transfer
properties.[3,4] Usually, the key components are porphyrin-
coordinating ring conjugates.[24–26] The ring contains a dpp
fragment that is ideally adapted to the formation of tetrahe-
+
dral copper(I) complexes of the Cu(dpp)2 family. Such
complexes constitute the entanglements necessary for the
[a] Laboratoire de Chimie Organo-Minérale, Institut de Chimie,
CNRS UMR 7177, Université de Strasbourg,
4, rue Blaise Pascal, 67070 Strasbourg Cedex, France
E-mail: a.sour@chimie.u-strasbg.fr
sauvage@chimie.u-strasbg.fr
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structure of the target compounds is represented in
The porphyrinic compound schematically represented in
Scheme 1, as well as the corresponding threaded species Scheme 1 could lead to a [4]rotaxane by threading two two-
([3]pseudorotaxane).
chelate molecular rods through the cyclic components of
the molecule or, if the peripheral rings turn out to be flexi-
ble enough, to a [2]pseudorotaxane consisting of a single
rod passing through the rings of the same porphyrinic com-
pound.
Synthesis of the Porphyrin-Based Molecule Bearing Two
Peripheral Coordinating Rings
Scheme 1. General structure of the compounds consisting of two
peripheral rings attached to the central porphyrin on two meso car-
bon atoms trans to each other. The chelating unit is indicated as
an arc of a circle and the porphyrin is represented by a lozenge. The
copper(I)-driven threading of an open chain coordinating fragment
should lead to a doubly threaded species consisting of three inde-
pendent organic components ([3]pseudorotaxane).
The chemical structure of the target molecule is depicted
in Figure 1 as is the sequence of chemical reactions leading
to its preparation. The synthetic route chosen for the prepa-
ration of zinc porphyrin 1, bearing two lateral rings, was to
prepare 31-membered macrocycle 3 containing a benzalde-
Figure 1. Preparation of compound 1, consisting of a central Zn-complexed porphyrin nucleus attached to two coordinating 31-membered
rings through single carbon–carbon bonds.
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A Zinc Porphyrin Bearing Two Lateral dpp-Containing Rings
hyde function and then to form the porphyrin by a conden- ture. The reaction turned out to be very slow. After 20 h we
sation reaction with a dipyrryl methane derivative.
obtained the desired porphyrin in poor yield (Ͻ2%). We
Macrocycle 3 was prepared by the cyclisation reaction performed other condensation reactions with different con-
of ditosylate 2 (obtained in two steps following a literature centrations of TFA and observed that 5 equivalents of TFA
procedure)[24] with 3,5-dihydroxybenzaldehyde in the pres- were necessary to allow efficient condensation. After chro-
ence of Cs2CO3 at 90 °C. After purification, the compound matographic purification, the porphyrinic site was metall-
was obtained as a white powder in a very satisfactory 57% ated with zinc acetate. Further treatment with an EDTA
yield. The porphyrin was then formed by condensation of solution to remove zinc(II) from the 1,10-phenanthroline
macrocycle 3 with 5-mesityldipyrromethane (4). The latter chelate afforded compound 1 in 19% yield. It was fully
compound was chosen as it increases the solubility of the characterised by 1H NMR spectroscopy and mass spec-
1
corresponding porphyrin, it reduces scrambling of the vari- trometry. The H NMR spectrum of 1 in CD2Cl2 shows
ous groups during the condensation reaction and it prevents two doublets for the pyrrolic protons, which is in accord-
π-stacking of the porphyrins. We chose the [2+2] McDon- ance with a 5,15-meso-substituted porphyrin.
ald-type condensation, a reaction introduced by Lindsey et
Compound 1 was designed to be a good candidate for
al.,[30] to minimise the formation of the cis-A2B2-type por- threading. 2,9-Dianisyl-1,10-phenanthroline is known to
phyrin. We followed the condensation conditions described thread rapidly and to form stable four-coordinate CuI com-
by Lindsey et al.[31] 5-Mesityldipyrromethane and the plexes. This chelate was thus selected as the threading
macrocyclic aldehyde [10 m in CH2Cl2 containing 18 m element (Figure 2). Compound 1 and Cu(CH3CN)4PF6
trifluoroacetic acid (TFA)] were stirred at room tempera- (2 equiv.) were first mixed in dichloromethane under an
Figure 2. The threading reaction affording pseudorotaxane 62+·2PF6. (a) Schematic representation of the double threading reaction and
(b) the same reaction with the real molecules.
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C. Roche, A. Sour, F. Niess, V. Heitz, J.-P. Sauvage
FULL PAPER
atmosphere of argon and compound 5 (2 equiv.) was sub-
6
2+ turned out to be much shorter (τ2 = 0.15Ϯ0.05 ns) than
sequently added, which led to desired pseudorotaxane that of copper-free compound 1. This observation is not
62+·2PF6 in quantitative yield after workup. This compound especially surprising and is in line with previous work on
was characterised by 1H NMR, 2D COSY and ROESY related compounds containing zinc porphyrins and copper
+
spectroscopy and mass spectrometry.
complexes of the Cu(dpp)2 family.[25] The singlet excited
The 1H NMR spectrum of 62+·2PF6 (Figure 3) shows state of the zinc porphyrin is rapidly quenched by the cop-
that the threading reaction leading to this compound modi- per(I) complex owing to the presence of a low-lying triplet
fies the chemical shifts of most of the hydrogen atoms. In MLCT state.
particular, the 3-, 8-, o- and m-protons undergo a strong
upfield shift, which is characteristic of “threaded” com-
plexes.[32] In addition, the CH2O protons of the ring in com-
Conclusions
pound 1 come out as only two distinct signals. The cop-
A porphyrin attached to two coordinating macrocycles
per(I) threading enhances the dissymmetry of the CH2O
on the 5- and 15-positions of the tetrapyrrolic ring was syn-
protons of the ring and four CH2O signals are observed.
thesised by a condensation reaction. In a first step, a new
dpp-containing ring was prepared in good yield by a classi-
cal macrocycle-forming reaction. The macrocycle is a 31-
membered ring that contains a benzaldehyde group. In the
presence of 5-mesityldipyrromethane and under Lindsey’s
conditions, this compound leads to the desired porphyrin
in an acceptable yield of 19% after metallation by zinc ace-
tate. In order to demonstrate that porphyrin 1 can be used
in the construction of molecular machines based on rela-
tively complex interlocking systems, a double prototypical
threading reaction was carried out successfully with a sim-
ple chelate (2,9-dianisyl-1,10-phenanthroline) in the pres-
ence of copper(I).
Experimental Section
General: Nuclear magnetic resonance (NMR) spectra were ac-
quired with a Bruker AM300 spectrometer. The spectra were refer-
enced internally to residual proton solvent reference. Mass spectra
(ES-MS) were recorded with a VG BOIQ triple quadrupole spec-
trometer by the Service de Spectrométrie de Masse (ISIS, Stras-
bourg). Dry solvents were distilled from suitable drying agents
Figure 3. 1H NMR spectra (aromatic region) of compounds 1 (up-
per) and 62+ (bottom) in CD2Cl2.
(CaH2 for CH2Cl2 and CH3CN). Commercial chemicals were at the
best-available grade and used without further purification. Column
The absorption and emission spectra of compounds 1
chromatography was carried out by using silica gel (Merck Kiesel-
and 62+ were measured in degassed dichloromethane at
gel, silica gel 60, 0.063–0.200 mm). Compound 2,[24] [Cu(MeCN)4]-
room temperature. The Soret band is typically observed at
(PF6),[34] 5-mesityldipyrromethane (4),[35] and 2,9-dianisyl-1,10-
phenanthroline[36] were synthesised according to literature pro-
cedures. UV/Vis absorption spectra were recorded with a Kontron
UVIKON 860 spectrophotometer. Emission spectra were recorded
with a Fluorolog FL3–22 de HORIBA Jobin Yvon spectrophotom-
eter. Lifetime measurements were detected by a TCSPC (time-
correlated single-photon counting) technique with a NanoLED-
370 electroluminescent diode as the excitation source.
421 nm, whereas the Q-bands are observed at 548 and
1
585 nm for both compounds. The MLCT (metal-to-ligand
charge transfer) band of tetrahedral copper(I) complexes
containing two ligands of the dpp family, and thus similar
to the present complexes, have weak extinction coefficients
(a few thousands) relative to those of zinc porphyrins (ten
to one hundred times more intense).[33] They are thus diffi-
cult to detect in the presence of a porphyrin as a result of Macrocycle 3: A suspension of Cs2CO3 (2.1 g, 5.9 mmol) in DMF
(150 mL) was degassed under an atmosphere of argon and heated
to 50 °C. In a separate flask, a mixture of ditosylate phenanthroline
derivative 2 (1.00 g, 1.20 mmol) and 3,5-dihydroxybenzaldehyde
(0.160 g, 1.20 mmol) in DMF (100 mL) was degassed, transferred
to an addition funnel and added drop by drop to the suspension
over a period of 4 h. The mixture was then heated to 90 °C and
stirred under an atmosphere of argon for 16 h. The warm mixture
was filtered, and the solid residue was washed with DMF (100 mL).
After evaporation, the remaining solid was dissolved in dichloro-
methane, washed with water (3ϫ100 mL) and dried with Na2SO4.
spectral overlapping between the Soret and/or Q-bands of
the porphyrin and the 1MLCT band. The emission maxima
are also observed at a typical wavelength (646 nm after exci-
tation at 548 nm) for both compounds. The emission life-
times of compounds 1 and 62+ were measured at 650 nm
after excitation at 370 nm (which was the only excitation
wavelength available for emission-lifetime measurements).
The emission lifetime of zinc complex 1 was consistent
with simple zinc-complexed porphyrin monomers (τ1
=
1.85Ϯ0.20 ns).[25] The emission lifetime of pseudorotaxane After evaporation, the crude product was purified by silica gel
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A Zinc Porphyrin Bearing Two Lateral dpp-Containing Rings
chromatography (dichloromethane/methanol, 100:1) to yield
macrocycle 3 as a pale-yellow solid (0.440 g, 57%). 1H NMR
(300 MHz, CDCl3): δ = 9.84 (s, 1 H, aldehyde H), 8.41 (d, 3J =
9.0 Hz, 4 H, Ho), 8.26 (d, 3J = 8.4 Hz, 2 H, H3,8), 8.07 (d, 3J =
Acknowledgments
We are grateful to the CNRS for financial support. We also thank
the Ecole Normale Supérieure (Paris) for a fellowship to C. Roche.
We are also grateful to Dr. J.-P. Collin for his kind support.
3
8.4 Hz, 2 H, H4,7), 7.75 (s, 2 H, H5,6), 7.14 (d, J = 9.0 Hz, 4 H,
Hm), 7.03 (d, 4J = 2.4 Hz, 2 H, HoЈЈ), 6.91 (t, 4J = 2.3 Hz, 1 H,
HpЈЈ), 4.32–4.36 (m, 4 H, CH2), 4.20–4.23 (m, 4 H, CH2), 3.93–3.97
(m,
8 H, CH2) ppm. ES-MS: m/z = 643.25 [M +
H]+.
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ZnII–Porphyrin 1: To a solution of macrocyclic aldehyde 3 (350 mg,
0.546 mmol) in dry dichloromethane (55 mL) was added trifluoro-
acetic acid (218 µL, 2.93 mmol) and 5-mesityldipyrromethane (4;
147 mg, 0.546 mmol). The flask was protected from light, and the
solution was stirred for 2 h under an atmosphere of argon. DDQ
(2,3-dichloro-5,6-dicyanobenzoquinone; 210 mg, 0.869 mmol) was
added, and the solution was stirred under an atmosphere of argon
for an additional 1 h. A solution of Na2CO3 (1.4 g) in water
(40 mL) was added, and the solution was stirred vigorously for
30 min. The two phases were separated, and the aqueous layer was
washed with dichloromethane (2ϫ15 mL). The organic solvents
were evaporated, and the compound was purified by silica gel
chromatography (dichloromethane/methanol, 100:0.5). After a sec-
ond purification by flash chromatography (silica; dichloromethane/
methanol, 100:0.2), the free-base porphyrin (97 mg, 0.053 mmol)
was obtained and directly metallated. It was dissolved in dichloro-
methane (80 mL) and a solution of Zn(OAc)2·2H2O (95 mg,
0.430 mmol) in methanol (20 mL) was then added. The mixture
was heated at reflux for 8 h. Then, an aqueous solution of [EDTA]-
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separated and washed with water (3ϫ30 mL). After evaporation,
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(300 MHz, CD2Cl2): δ = 8.92 (d, J = 4.7 Hz, 4 H, HpyA), 8.67 (d,
3
3
3J = 4.6 Hz, 4 H, HpyB), 8.45 (d, J = 8.8 Hz, 8 H, Ho), 8.28 (d, J
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12 H, CH3o) ppm. UV/Vis (CH2Cl2): λ (log ε) = 421 (5.76), 549
(4.37), 585 (3.63) nm. ES-MS: m/z = 1833.51 [M + H]+.
Pseudorotaxane 62+: A degassed solution of [Cu(MeCN)4](PF6)
(5.15 mg, 13.8ϫ10–6 mol) in CH3CN (3 mL) was added by cannula
to a degassed solution of 1 (12.2 mg, 6.65ϫ10–6 mol) in CH2Cl2
(10 mL), and the mixture was stirred under an atmosphere of argon
for 30 min. A degassed solution of 2,9-dianisyl-1,10-phenan-
throline (5; 5.42 mg, 13.8ϫ10–6 mol) in CH2Cl2 (5 mL) was then
added by cannula. After stirring for 3 h at room temperature, the
solvent was evaporated. The solid was dissolved in acetonitrile and
filtered. The solvent was then evaporated to give pseudorotaxane
62+·2PF6 in quantitative yield (18.0 mg). 1H NMR (300 MHz,
CD2Cl2): δ = 8.90 (d, 3J = 4.8 Hz, 4 H, HpyA), 8.64 (d, 3J = 8.4 Hz,
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(s, 12 H, OMe), 2.35 (s, 6 H, CH3p), 1.68 (s, 12 H, CH3o) ppm.
UV/Vis (CH2Cl2): λ (log ε) = 421 (5.84), 548 (4.51), 585 (3.79) nm.
ES-MS: m/z = found 1371.37 [M / 2]+.
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Received: February 10, 2009
Published Online: April 22, 2009
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