Open and closed states of a porphyrin based molecular turnstile

Article abstract of DOI:10.1039/c1dt00004g

The molecular turnstile 1 composed of a stator based on an Sn(iv)-porphyrin bearing two sets of monodentate coordinating sites (pyridyl and benzonitrile) and a handle bearing a 2,6-pyridinediamide moiety as a tridentate unit was synthesised. In the absence of metal behaving as a blocking agent, the handle freely rotates around the stator (open state). In the presence of Pd(ii), the closed state of the turnstile 1-Pd resulting from the simultaneous binding of the metal centre by both the dianionic tridentate site and one of the two pyridyl units is generated. The reaction of 1-Pd with the organometallic 2,6-diphenylpyridine Pt(ii) complex 11 leads to the heterotrinuclear (Pt, Sn, Pd) species 13, resulting from the binding of the platinum complex by 1-Pd. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt00004g

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PAPER
Open and closed states of a porphyrin based molecular turnstile†
Thomas Lang, Ernest Graf,* Nathalie Kyritsakas and Mir Wais Hosseini*
Received 3rd January 2011, Accepted 31st January 2011
DOI: 10.1039/c1dt00004g
The molecular turnstile 1 composed of a stator based on an Sn(IV)–porphyrin bearing two sets of
monodentate coordinating sites (pyridyl and benzonitrile) and a handle bearing a 2,6-pyridinediamide
moiety as a tridentate unit was synthesised. In the absence of metal behaving as a blocking agent, the
handle freely rotates around the stator (open state). In the presence of Pd(II), the closed state of the
turnstile 1–Pd resulting from the simultaneous binding of the metal centre by both the dianionic
tridentate site and one of the two pyridyl units is generated. The reaction of 1–Pd with the
organometallic 2,6-diphenylpyridine Pt(II) complex 11 leads to the heterotrinuclear (Pt, Sn, Pd) species
13, resulting from the binding of the platinum complex by 1–Pd.
Introduction
The control of motion in molecular systems is a matter of
current interest. Inducing the relative movements in discrete
molecular assemblies composed of several components by external
stimuli has been a topic of intense research for almost two
decades.1–12 Several abiotic molecular motors and machines have
been designed.2 In particular, translational and rotary systems
have been reported.3–7 Examples of molecular rotors,13 cars,14
wheelbarrows15 and turnstiles16–19 have been also published. On
the biotic side, several biological molecular motors have been
discovered.20
In the continuation of our investigations on the control of
molecular motions,17–19 here we report on the design, synthesis
and characterization of a new molecular turnstile composed of a
porphyrin based stator and a coordinating handle.
Results and discussion
Design of the system
Scheme 1 Structures of turnstiles 1 and 1–Pd and labelling of hydrogen
atoms.
As stated above, the turnstile 1 (Scheme 1) is composed of
two parts, a stator and a handle connected together through
a Sn(IV) centre. The stator is based on a tetraarylporphyrin of
the trans-A2B2 type bearing at the meso positions two pyridyl
and two benzonitrile units. In order to impose the divergent
orientation of monodentate sites, they are connected to the
porphyrin backbone at the position 4 of the aromatic moiety. The
handle is a bis-monodentate ligand composed of two terminal
coordinating sites (two mono functionalised resorcinol moieties)
allowing connection of the handle to the stator through Sn–O
bonds, a tridentate (2,6-pyridinediamide moiety) coordinating site
symmetrically located at the centre of the handle and two spacers
(triethyleneglycol chains) connecting the two resorcinol moieties
to the tridentate unit. 2,6-Pyridinediamide was chosen as the
tridentate site because of its propensity to form a neutral complex
with metal centres such as Pd(II).
Synthesis of the turnstile 1 and 1–Pd
The synthesis of the turnstile 1 requires the preparation of the
porphyrin derivative 2 and its metallated derivative 4 and of the
handle 9 and its Pd(II) complex 9–Pd, (Scheme 2). The synthesis
of both 9 and 9–Pd has been previously reported.19
The synthesis of the porphyrin 2, achieved in 11% yield,
was based on the condensation, in presence of TFA, of the
Laboratoire de Chimie de Coordination Organique (UMR-UDS-CNRS
7140), Universite´ de Strasbourg, Institut Le Bel, 4 rue Blaise Pascal,
CS 90032, 67081, STRASBOURG CEDEX, France. E-mail: hosseini@
unistra.fr
† CCDC reference number 810526. For crystallographic data in CIF or
other electronic format see DOI: 10.1039/c1dt00004g
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˚
porphyrin core with Sn–N distances in the 2.090(4)–2.094(4) A
˚
range and two chloride anions (dSn–Cl = 2.425(3) A).
The octahedron around the metallic centre is almost perfect with
N–Sn–Cl, Cl–SnCl and N–Sn–N angles of 89.30(14)–90.70(14)◦,
179.999(1)◦ and 180.0(2)◦ (89.60(15)–90.40(15)◦ for N–Sn–Ncis
angle) respectively. The meso substituents are tilted with respect
to the porphyrin plane with CCCC dihedral angles of -87.3◦
and 84.1◦ for the pyridine moieties and -77.4◦ and 78.7◦ for the
benzonitrile moieties.
The open state of the turnstile 1 was prepared upon conden-
sation at room temperature of the dihydroxo derivative of the
Sn–porphyrin 4 with the handle 9 in CH2Cl2 for three days. The
desired compound 1 was obtained in 68% yield upon precipitation
from a toluene–pentane mixture.
For the preparation of the closed state of the turnstile 1–Pd,
two different strategies were explored. The first consisted of the
condensation at room temperature of the Sn–porphyrin derivative
4 with the palladium complex of the handle 9–Pd in CH2Cl2.
The second strategy was based on the condensation of 1 with
Pd(CH3CN)4(PF6)2 in a CH2Cl2–CH3CN mixture. However, the
reaction was not quantitative and ca. 20% of unreacted product
1 as well as ca. 15% of a compound with decoordination of
the handle (appearance of signals corresponding to resorcinol
moieties between 6 and 7 ppm, see Table 1) were also observed.
The synthesis of the model compound 5 was achieved in
quantitative yield in an NMR tube upon condensation at room
temperature of the porphyrin derivative 4 with 2 equivalents of
3-methoxyphenol in CDCl3 for one week.
Scheme 2 Structures of compounds 2–9 and 9–Pd and labelling of
hydrogen atoms.
dipyrromethane derivative 6 with 4-pyridinecarboxaldehyde 7 in
a CH2Cl2–EtOH mixture followed by the oxidation of the formed
porphyrinogen using DDQ.21 Following a reported procedure,22
compound 6 was prepared in 63% yield upon reaction of an excess
of pyrrole with p-cyanobenzaldehyde in the presence of TFA.
The reaction of the porphyrin 2 with SnCl2·2H2O in refluxing
pyridine gave the dichloro Sn–porphyrin 3 in 90% yield.23 The
latter was converted in 83% yield into its dihydroxo derivative 4
upon treatment with K2CO3 in a CH2Cl2–MeOH mixture.24
The structure of the precursor porphyrin 3 was investigated
in the solid state by X-ray diffraction on single crystal obtained
upon slow diffusion of pentane into a CH2ClCH2Cl solution
of compound 3 (Fig. 1). The crystal (orthorhombic, Pnna) was
composed of compound 3 and solvent molecules which could not
be identified and the structure was solved using the PLATON-
SQUEEZE command (Fig. 1). No distortion from planarity of the
porphyrin core is observed. The Sn(IV) atom lying on an inversion
centre and thus located in the centre of the porphyrin cavity, is
hexacoordinated and surrounded by four nitrogen atoms of the
Solution characterisation of the turnstile 1
The model compound 5 was studied in solution by 1H-NMR
(Table 1). As expected,25 due to the magnetic anisotropy of the
porphyrin backbone, protons of the 3-methoxyphenol moiety
exhibit a strong upfield shift indicating the coordination to the
Sn(IV) centre located within the tetraaza core of the porphyrin.
The open state of the turnstile 1 resulting from the coordination
of the handle 9 to the stator and the closed state 1–Pd obtained
upon simultaneous binding of Pd(II) by the tridentate site of the
handle and the monodentate unit of the stator were also studied
by 1- and 2D-NMR experiments (COSY and ROESY) (Table 1,
Fig. 2, Fig. 3 and Fig. 4). In agreement with the above mentioned
observations for the model compound 5, protons of resorcinol
units in 1 and 1–Pd were found to be significantly upfield shifted
(Table 1).
For the open state of the turnstile 1 (Fig. 2a (at 300 MHz) and
Fig. 3, top (at 500 MHz)), the observation, at room temperature,
Table 1 1H-NMR chemical shift (d, ppm) of turnstiles 1, and 1–Pd, 5, 8
and handles 9 and 9–Pd
Hh
Hi
Hj
Hk
1a
1.22
1.22
1.37
6.43
6.42
6.36
1.51
1.58
1.47
6.45
6.36
6.36
5.54
5.57
5.53
7.14
7.05
7.06
5.34
5.37
5.38
6.51
6.46
6.36
1–Pda
5b
8b
9b
9–Pdc
a 500 MHz, CD2Cl2. b 300 MHz, CDCl3. c 300 MHz, CD3CN.
Fig. 1 Crystal structures of compound 3. H atoms and solvent molecules
are omitted for the sake of clarity. For bond distances and angles, see text.
3518 | Dalton Trans., 2011, 40, 3517–3523
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Fig. 2 Portion of the 1H-NMR spectra (300 MHz, CD2Cl2) and
assignment of signals between 10–7.5 ppm of the open 1 (a) and the closed
1–Pd (b and c) states of the turnstile. The closed state was generated by
condensation between the porphyrin 4 and the metallated handle 9–Pd (a)
and upon addition of Pd(CH3CN)4(PF6)2 to 1 respectively. *Corresponds
to unreacted 1.
Fig. 4 Portions of the 2-D ROESY investigations (500 MHz, CD2Cl2)
showing through space correlations for the open 1 (top) and the closed
1–Pd (bottom) states of the turnstile.
equivalent H atoms. This implies an east–west type differentiation
of the porphyrin core. For the closed state of the turnstile 1–Pd,
resulting from the binding of Pd(II) by only one of the two pyridyl
units, one would expect the differentiation of the two pyridines.
This was indeed the case and four doublets (Ha, Ha¢, Hb and Hb¢)
were observed. Furthermore, the observation of two signals for the
two benzonitrile groups (He and Hf) indicated that, as expected,
they remained undifferentiated.
It is worth noting that the turnstile 1 displays two sets of two
coordinating sites (two pyridyl and two benzonitrile moieties)
with different coordination propensities. The NMR investigation
clearly shows that only the pyridyl unit is involved in the binding
of Pd(II). The structural discussion above was further confirmed
by a 2-D ROESY investigation (Fig. 4, bottom) which revealed
the presence of through space correlations between a¢ proton of
the coordinated pyridyl unit and protons l and m of the handle as
well as between proton b¢ and protons n, o, p and q.
Fig. 3 Portion of the 1H-NMR spectra (500 MHz, CD2Cl2) and
assignment of signals between 10–7.2 ppm of the open 1 (top) and the
closed 1–Pd (bottom) turnstiles.
of two doublets for the b-pyrrolic hydrogen atoms Hc and Hd
implies a C2v symmetry which is compatible either with the free
rotation of the handle around the O–Sn–O axis or a fast oscillating
process on the NMR time scale of the handle between the two
opposite pyridine units of the stator interacting with the 2,6-
pyridinediamide moiety of the handle through an H-bond. This
is further substantiated by non differentiation of the two pyridyl
groups, i.e. only two doublets are observed for protons Ha and Hb.
As one could expect, the same holds for the two benzonitrile units
(only two doublets for protons He and Hf). The free rotation of
the handle proposed above was also demonstrated by 2D-NMR
ROESY experiments (Fig. 4, top).
Switching between two closed states
The ROESY experiment at room temperature revealed the
absence of through space specific correlations between the handle
and pyridyl meso substituents. Indeed, both pyridyl and benzoni-
trile groups indifferently exhibit through space correlations with
the handle implying thus the absence of specific positioning of the
latter (Fig. 4, top).
By design, the turnstile 1 in its open state possesses, on the stator,
two different coordinating sites (pyridyl and benzonitrile) and a
tridentate moiety on the handle (Fig. 5a).
As mentioned above, the closed state of the turnstile 1–Pd is
generated upon binding of Pd(II) by both the pyridyl moiety of the
stator and the 2,6-pyridinediamide unit belonging to the handle
leaving thus uncoordinated the two benzonitrile groups. For the
switching between the two possible closed states (Fig. 5b and 5c),
the first attempt consisted of the use of the organometallic Pt(II)
complex 11, prepared by the reaction of the compound 10 with
For the closed state of the turnstile 1–Pd resulting from the
simultaneous binding of Pd(II) by the tridentate site of the handle
and one of the two pyridyl units of the stator, the lowering of
1
the symmetry of the molecule is clearly visible on the 1-D H-
26
NMR spectrum (Fig. 2c (at 300 MHz) and Fig. 3, bottom (at 500
MHz)). Indeed, the observation of four doublets for the b-pyrrolic
signals (Hc, Hc¢, Hd and Hd¢) indicates a doubling of the number of
K2PtCl4 (Scheme 3), for the blockage of the two pyridyl sites.
The latter event should lead to the decomplexation of the pyridyl
and its binding to the complex 11 and therefore its replacement by
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Fig. 6 Portion of the 1H-NMR spectra (CD2Cl2, 300 MHz) and
assignment of signals between 10–7 ppm of complexes 11 (a), 12 (b), 13a (c)
13b (d) and 1–Pd (e). *Corresponds to complex 11. aFrom the condensation
of 9–Pd with 1 equivalents of 12, bfrom addition 2.2 equivalents of 11 to
the compound 1–Pd.
Fig. 5 Schematic representation of the open (a), three closed states (b),
(c) and (d) of the molecular turnstile composed of a stator equipped with
a hinge (light blue) bearing two different (blue and red) interaction sites (e
and f) and two handles based on a tridentate coordination pole (purple)
and of its metal complex. The green sphere represents a metal with square
planar coordination geometry. The circle with a red sphere represents a
competitive protected metal complex.
remaining pyridyl unit. Unfortunately, increasing the amount of
the competing metal complex 11 from 2.2 to 5.9 eq. had no effect
on the process. In order to generate the closed state of the turnstile
for which the two pyridyl units are engaged in the binding of Pt(II)
and one of the two benzonitrile groups involved in the binding
of Pd(II) (Fig. 5c), the binuclear porphyrin complex 12 was first
prepared in 66% yield upon condensation of the complex 11 with
the porphyrin 4. Again, in an NMR tube, at room temperature, the
reaction of the precursor porphyrin derivative 12 with the handle
1
9–Pd in CD2Cl2 was monitored by H-NMR which revealed the
completion of the process after ca. 5 days (Fig. 6).
Once again, instead of the desired complex described above
(Fig. 5c), the heterotrinuclear species 13 was exclusively obtained.
A possible explanation for the exclusive formation of the
complex 13 may be related on one hand to the substantial
difference in the binding ability between benzonitrile and pyridyl
groups, the latter being considerably stronger, and on the other
hand to the rather low difference in the affinity of the pyridyl site
for Pd(II) and the organometallic Pt(II) complex 11. Furthermore,
the intramolecular binding process occurring between the pyridyl
of the stator and the Pd(II) centre complexed by the handle
leading to the complex 13 seems favourable with respect to the
intermolecular complexation, affording the desired closed state of
the turnstile.
Conclusions
Scheme 3
A molecular turnstile 1 composed of an Sn(IV)–porphyrin based
stator bearing two sets of trans pyridyl and benzonitrile monoden-
tate ligands located at the meso positions and a handle bearing a
2,6-pyridinediamide moiety as a tridentate coordinating site was
designed and prepared. As expected, in the absence of an effector,
the free rotation of the handle around the stator corresponding to
the open state of the turnstile was demonstrated. In the presence of
Pd(II) as a blocking effector, the closed state of the turnstile (1–Pd)
resulting from the simultaneous binding of the metal centre by one
of the two pyridyl units located on the stator and the dianionic 2,6-
pyridinediamide tridentate moiety belonging to the handle was
obtained. The switching of the closed state mentioned above to
a benzonitrile group completing the coordination sphere around
Pd(II) centre.
The reaction of 1–Pd with 2.2, 3.4 and 5.9 equivalents of the
complex 11 in CD2Cl2 was carried out in an NMR tube and
1
the process was monitored by H-NMR (Fig. 6). Surprisingly,
the reaction in the presence of 2.2 eq. of 11, afforded only the
complex 13 (Scheme 3). The latter is a trinuclear species bearing an
Sn(IV) atom in the centre of the porphyrin, a Pd(II) simultaneously
coordinated to the handle and one of the two pyridyl groups of
the stator and a Pt(II) centre surrounded by the ligand 10 and the
3520 | Dalton Trans., 2011, 40, 3517–3523
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the one based on the replacement of the pyridyl unit by one of
the two benzonitrile groups was attempted by the addition of the
organometallic Pt(II) complex 11. The latter experiment, instead of
producing the desired closed state, generated the heterotrinuclear
(Pt, Sn, Pd) species 13 corresponding to the binding of the
platinum complex 11 by the closed state 1–Pd. The substitution
of the benzonitrile units by other ligands displaying stronger
coordination propensity is currently under investigation.
3J = 5.0 Hz), 9.21 (dd, 4H, Pya, 3J = 4.0 Hz, 4J = 1.5 Hz), 9.40 (t,
3
2H, NHt, J = 6.0 Hz). 13C-NMR (CD2Cl2, 125 MHz) d (ppm):
40.3, 66.9, 70.1, 70.4, 71.1, 103.0, 104.1, 110.7, 113.2, 119.4, 120.1,
120.9, 125.0, 127.0, 130.1, 131.5, 133.2, 133.2, 135.7, 139.2, 145.5,
147.0, 147.4, 149.0, 149.5, 149.7, 156.0, 157.7, 164.5. MS for 5
(C75H61N11O10Sn: 1395.06 g mol-1): m/z 698.69 (M + 2H+).
Compound 1–Pd. Under argon, in a dry 50 mL two-necked
round bottom flask, to a solution of compound 4 (13 mg, 20 mmol,
1 eq.) in CH2Cl2 (8 mL), a solution of handle 9–Pd (10 mg,
10 mmol, 0.8 eq.) in CH2Cl2 (30 mL) was added. The reaction
mixture was stirred at room temperature for 11 days. The solvent
was evaporated to dryness and the residue was recrystallised from
a toluene–pentane mixture (1 : 3, 105 mL) to yield the desired
complex 1–Pd (21 mg, 90%) as a purple solid.
Experimental
General procedure
CH3CN and CHCl3 were dried over molecular sieves; THF
and CH2Cl2 were dried and distilled over sodium and CaH2,
respectively. Triethylamine was dried and distilled over KOH.
Analytical ethanol, methanol and pyridine were used without
further purification. 1H- and 13C-NMR spectra were acquired
at 25 ◦C unless otherwise stated on either a Bruker AV 300,
Bruker AV 400 or a Bruker AV 500 spectrometers, with the
deuterated solvent as the lock and residual solvent as the internal
reference. Absorption spectra were recorded using an Uvikon XL
spectrophotometer. Infrared spectra were recorded either on a
Perkin Elmer FTIR-1600 (KBr), or on a FTIR-8400S (ATR, Pike
miracle germanium). Mass spectrometry analyses were performed
by the Service de Spectrometrie de Masse, UdS, Strasbourg. X-Ray
crystallography: data were collected on a Bruker SMART CCD
diffractometer with Mo-Ka radiation. The structures were solved
using SHELXS-97 and refined using SHELXL-97. The crystal
contained solvent molecules which could not be identified and the
structure was solved using the PLATON-SQUEEZE command.
Compound 1–Pd was also synthesised upon addition of a
CH3CN (5 mL) solution of Pd(CH3CN)4(PF6)2 (6.5 mg, 11.6 mmol,
1.3 eq.) to a CH2Cl2 (5 mL) solution containing both turnstile 1
(12.3 mg, 8.8 mmol, 1 eq.) and an excess of Et3N (22 mL, 220 mmol,
25 eq.).
IR (KBr, cm-1): 2227 (CN). UV (CH2Cl2, lmax (log e)): 425 (5.6),
561 (4.3), 600 (3.9). 1H-NMR (CD2Cl2, 500 MHz) d (ppm): 1.22
4
3
4
(t, 2H, Arh, J = 2.5 Hz), 1.58 (ddd, 2H, Ari, J = 8.0 Hz, J =
4
2.0 Hz, J = 1.0 Hz), 3.25–3.42 (m, 4H, OCH2l), 3.48–3.73 (m,
8H, NCH2q, OCH2m), 3.73–3.90 (m, 8H, OCH2n,o), 4.03 (br, 4H,
OCH2p), 5.37 (ddd, 2H, Ark, 3J = 8.0 Hz, 4J = 2.5 Hz, 4J = 1.0 Hz),
5.57 (t, 2H, Arj, 3J = 8.0 Hz), 7.79 (d, 2H, Pyr, 3J = 7.5 Hz), 8.13 (t,
1H, Pys, 3J = 7.5 Hz), 8.21 (dd, 4H, Arf, 3J = 7.0 Hz, 4J = 1.5 Hz),
3
4
8.35 (m, 4H, Are), 8.43 (dd, 2H, Pyb, J = 4.0 Hz, J = 1.5 Hz),
8.55 (dd, 2H, Pyb¢, 3J = 5.0 Hz, 4J = 1.5 Hz), 9.03 (d, 2H, b-pyr.c¢,
3
3J = 5.0 Hz, JSn–H = 17.0 Hz), 9.07 (d, 2H, b-pyr.d¢, J = 5.0 Hz,
JSn–H = 16.5 Hz), 9.19 (dd, 2H, Pya, 3J = 4.0 Hz, 4J = 1.5 Hz), 9.25
(d, 2H, b-pyr.d, 3J = 5.0 Hz, JSn–H = 17.5 Hz), 9.40 (d, 2H, b-pyr.c,
3J = 5.0 Hz, JSn–H = 17.0 Hz), 9.78 (dd, 2H, Pya¢, 3J = 5.0 Hz, 4J =
1.5 Hz). 13C-NMR (CD2Cl2, 125 MHz) d (ppm): 48.0, 67.2, 70.2,
71.3, 71.7, 71.7, 102.6, 104.4, 110.9, 113.5, 119.1, 121.0, 124.4,
127.0, 130.2, 131.4, 131.5, 132.4, 133.4, 133.5, 133.7, 135.6, 141.1,
145.3, 146.8, 146.9, 147.2, 147.7, 149.3, 152.8, 153.3, 156.1, 157.6,
171.6. MS for 6 (C75H59N11O10PdSn: 1499.47 g mol-1): m/z 753.64
(M + H+ + Li+).
Crystallographic data for 3. C44H24Cl2N8Sn, M = 854.30,
˚
˚
orthorhombic, Pnna,◦a = 28.3515(17) A, b = 14.9001(9) A, c =
◦
◦
3
˚
˚
12.9781(8) A, a = 90 , b = 90 , g = 90 , U = 5482.5(6) A , Z =
4, m = 0.594 mm-1, refls measured: 60675, independent refls: 6384
[R(int) = 0.0514], final R indices [I > 2s(I)]: R1 = 0.0775, wR2 =
0.1938, R indices (all data): R1 = 0.1372, wR2 = 0.2069, GOF on
F2: 1.033.
Synthesis. Compounds 6,22 9,19 9–Pd19 and 1126 have been
prepared following reported procedures.
Compound 2. Under argon, in a 250 mL two-necked round-
bottom flask, compound 6 (2.1 g, 8.5 mmol, 1 eq.) was dis-
solved in 150 mL of a CH2Cl2–EtOH (95 : 5) mixture before 4-
pyridinecarboxaldehyde 7 (0.8 mL, 8.5 mmol, 1 eq.) was added
and the solution degassed for 15 min. In the dark, TFA (1.9 mL,
25.6 mmol, 3 eq.) was added to the mixture and the solution stirred
at room temperature over night. The supernatant was transferred
into a 500 mL round-bottom flask. The residue was dissolved in 80
mL of THF and triethylamine (3.8 mL) was added to neutralise
the TFA. To the combined organic phases, a solution of DDQ
(2.9 g, 12.8 mmol, 1.6 eq) in THF (80 mL) was added and the
mixture stirred at room temperature for 2 days. The crude product
was purified by chromatography (SiO2, CH2Cl2–CH2Cl2–MeOH
(98 : 2)) to yield the porphyrin derivative 2 (315 mg, 11%) as a
purple solid.
Compound 1. Under argon, in a dry 100 mL round-bottom
flask, a mixture of compound 4 (50 mg, 60 mmol, 1 eq.) and
compound 9 (38 mg, 60 mmol, 1 eq.) was dissolved in 50 mL of
CH2Cl2. The reaction mixture was stirred at room temperature
for 3 days. The solvent was evaporated to dryness and the residue
recrystallised in a toluene–pentane mixture (1/2, 100 mL) to yield
the desired complex 1 (57 mg, 68%) as a brick red solid. IR
(KBr, cm-1): 3361 (NH amide), 2226 (CN), 1673 (CO amide).
UV (CH2Cl2, lmax (log e)): 425 (5.6), 560 (4.4), 599 (3.9). 1H-NMR
(CD2Cl2, 500 MHz) d (ppm): 1.22 (t, 2H, Arh, 4J = 2.5 Hz), 1.51
3
4
4
(ddd, 2H, Ari, J = 8.0 Hz, J = 2.0 Hz, J = 1.0 Hz), 3.22–3.27
(m, 4H, OCH2l), 3.49–3.53 (m, 4H, OCH2m), 3.65–3.75 (m, 12H,
OCH2n,o, NCH2q), 3.79 (t, 4H, OCH2p, 3J = 5.5 Hz), 5.34 (ddd, 2H,
Ark, 3J = 8.0 Hz, 4J = 2.5 Hz, 4J = 1.0 Hz), 5.54 (t, 2H, Arj, 3J =
8.0 Hz), 8.09 (dd, 1H, Pys, 3J = 8.0 Hz, 3J = 7.5 Hz), 8.20 (d, 4H,
IR (KBr, cm-1): 3313 (NH), 2226 (CN). UV (CH2Cl2, lmax (log
3
3
4
1
Arf, J = 8.5 Hz), 8.31 (dd, 4H, Pyb, J = 4.0 Hz, J = 1.5 Hz),
8.34 (d, 4H, Are, 3J = 8.5 Hz), 8.39 (d, 2H, Pyr, 3J = 8.0 Hz), 9.10
(d, 4H, b-pyrd, 3J = 5.0 Hz, JSn–H = 17.0 Hz), 9.20 (d, 4H, b-pyr.c,
e)): 418 (5.5), 512 (3.7), 549 (3.1), 588 (3.1), 643 (2.5). H-NMR
(CDCl3, 300 MHz) d (ppm): -2.90 (br, 2H, NH), 8.10 (d, 4H, Ar,
3J = 8.5 Hz), 8.16 (dd, 4H, Py, 3J = 4.5 Hz, 4J = 1.5 Hz), 8.34 (d,
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4H, Ar, 3J = 8.5 Hz), 8.81 (d, 4H, b-pyr., 3J = 5.0 Hz), 8.86 (d, 4H,
b-pyr., J = 5.0 Hz), 9.07 (dd, 4H, Py, J = 4.5 Hz, J = 1.5 Hz).
13C-NMR (CDCl3, 100 MHz) d (ppm): 112.4, 117.7, 118.4, 128.6,
130.4, 131.2, 134.8, 146.5, 148.1, 150.3.
JSn–H = 14.5 Hz), 9.58 (dd, 4H, Py, 3J = 5.0 Hz, 4J = 1.5 Hz, JPt-H
44.0 Hz).
=
3
3
4
Compound 13. This compound has been obtained using two
different strategies (Strategy A: starting from turnstile 1–Pd;
Strategy B: starting from compound 12).
Compound 3. In a 250 mL round-bottom flask, to a solution
of compound 2 (263 mg, 0.4 mmol, 1 eq.) in pyridine (65 mL),
SnCl2·2H2O (267 mg, 1.2 mmol, 3 eq.) was added and the solution
refluxed over night. The solvent was removed under vacuum and
the residue was filtered over celite and the latter was washed with
CH2Cl2. After removal of the solvent, compound 3 (305 mg, 90%)
was obtained as a purple solid.
Strategy A: In a 10 mL round-bottom flask, turnstile 1–Pd (9.0
mg, 6 mmol, 1 eq.) and complex 11 (6.8 mg, 13 mmol, 2.2 eq) were
dissolved in 2 mL of CH2Cl2. The reaction mixture was stirred
1
at room temperature for 7 days. H-NMR analysis showed that
compound 13 was formed. Upon further addition of 1.2 eq and
2.5 eq of the complex 11, the mixture was exclusively composed of
the complex 13 and free 11.
IR (KBr, cm-1): 2227 (CN). UV (CH2Cl2, lmax (log e)): 426 (5.5),
1
560 (4.0), 598 (3.6). H-NMR (CDCl3, 300 MHz) d (ppm): 8.18
Strategy B: In a 5 mL round-bottom flask, compound 12 (2
mg, 1 mmol, 1 eq.) and handle 9–Pd (1 mg, 1 mmol, 1 eq.) were
dissolved in 0.5 mL of CD2Cl2. The reaction was monitored by
1H-NMR and after 5 days compound 13 was formed.
(d, 4H, Ar, 3J = 8.5 Hz), 8.27 (dd, 4H, Py, 3J = 4.5 Hz, 4J = 1.5 Hz),
8.46 (d, 4H, Ar, 3J = 8.5 Hz), 9.16 (dd, 4H, Py, 3J = 4.5 Hz, 4J =
3
1.5 Hz), 9.19 (d, 4H, b-pyr., J = 5.0 Hz, JSn–H = 11.0 Hz), 9.24
3
4
(d, 4H, b-pyr., J = 5.0 Hz, JSn–H = 10.5 Hz). 13C-NMR (CDCl3,
1H-NMR (CD2Cl2, 300 MHz) d (ppm): 1.22 (d, 2H, Arh, J =
75 MHz) d (ppm): 113.2, 118.5, 119.7, 129.6, 131.1, 132.9, 133.1,
135.2, 145.5, 145.9, 148.3.
2.5 Hz), Ari protons are not visible owing to overlap with the H2O
signal, 3.34 (m, 4H, OCH2l), OCH2q,m are not visible owing to
overlap with the CH3 signal of the free 11, 3.76 (m, 8H, OCH2n,o),
4.00 (m, 4H, OCH2p), 5.37 (dd, 2H, Ark, 3J = 8.0 Hz, 4J = 2.5 Hz),
5.57 (t, 2H, Arj, 3J = 8.0 Hz), signals corresponding to Pyr, Py and
Ph of complexed 11 are not distinguishable from those of Py and
Ph of the free 11, 8.10 (t, 1H, Pys, 3J = 8.0 Hz), 8.20 (d, 4H, Arf,
3J = 8.0 Hz), 8.36 (m, 4H, Are), 8.55 (m, 4H, Pyb,b¢), 9.03 (d, 2H,
b-pyrr.c–, 3J = 5.0 Hz), 9.07 (d, 2H, b-pyrr.d¢, 3J = 5.0 Hz), 9.33 (d,
Compound 4. In a 250 mL round-bottom flask, to a solution
of compound 3 (285 mg, 0.3 mmol, 1 eq.) in a CH2Cl2–MeOH
4 : 1 mixture (50 mL), K2CO3 (2.0 g, 14.5 mmol, 43 eq.) was added
and the solution refluxed for 4 h. The organic layer was washed
with distillated water (2 ¥ 50 mL) and dried over MgSO4. After
removal of the solvent under vacuum, the residue was filtered on
an alumina column (CHCl3–CHCl3–MeOH (99 : 1)) to yield the
compound 4 (225 mg, 83%) as a purple solid.
3
2H, b-pyrr.d, J = 5.0 Hz, JSn–H = 17.5 Hz), 9.52 (d, 2H, b-pyrr.c,
3J = 5.0 Hz, JSn–H = 17.5 Hz), 9.62 (dd, 2H, Pya, 3J = 5.0 Hz, 4J =
1.5 Hz, JPt-H = 44.5 Hz), 9.77 (dd, 2H, Pya¢, 3J = 5.0 Hz, 4J = 1.5 Hz).
IR (KBr, cm-1): 3635 (OH), 2227 (CN). UV (CH2Cl2, lmax (log
e)): 425 (5.9), 559 (4.4), 598 (4.0). 1H-NMR (CDCl3, 300 MHz) d
(ppm): -7.46 (br, 2H, OH), 8.17 (d, 4H, Ar, 3J = 8.5 Hz), 8.28 (dd,
3
4
3
Acknowledgements
4H, Py, J = 4.5 Hz, J = 1.5 Hz), 8.47 (d, 4H, Ar, J = 8.5 Hz),
3
3
9.11 (d, 4H, b-pyr., J = 5.0 Hz), 9.14 (dd, 4H, Py, J = 4.0 Hz,
4J = 1.5 Hz), 9.17 (d, 4H, b-pyr., 3J = 5.0 Hz). 13C-NMR (CDCl3,
75 MHz) d(ppm): 113.1, 118.6, 119.0, 119.8, 129.7, 131.0, 133.0,
135.4, 145.4, 146.1, 146.4, 148.8.
We thank the Universite´ de Strasbourg, the International Centre
for Frontier Research in Chemistry (FRC), Strasbourg, the Institut
Universitaire de France, the Ministry of Education and Research
and the CNRS for financial support.
Compound 5. In an NMR tube, porphyrin 4 (4.0 mg, 5 mmol,
1 eq.) and 3-methoxyphenol (1.4 mg, 11 mmol, 2.2 eq.) were
dissolved in 0.5 mL of CDCl3. After 7 days, the condensation
reaction was found to be terminated.
Notes and references
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1H-NMR (CDCl3, 300 MHz) d (ppm): 1.33 (t, 2H, Ara, J =
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