A platinum turnstile with a palladium lock

Article abstract of DOI:10.1039/c3dt50809a

An organometallic molecular turnstile composed of a stator based on an α,ω-diphosphine bearing, in a symmetric fashion, the 2,6-pyridyl diamide moiety as a central tridentate chelating unit and a rotor composed of Pt(ii) equipped with two pyridyl groups in trans configuration was designed. The switching between its open and closed states using Pd(ii) was investigated both in solution and in the solid state. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3dt50809a

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A platinum turnstile with a palladium lock†
Cite this: Dalton Trans., 2013, 42, 9740
Nicolas Zigon, Aurélie Guenet, Ernest Graf,* Nathalie Kyritsakas and
Mir Wais Hosseini*
Received 26th March 2013,
Accepted 1st May 2013
An organometallic molecular turnstile composed of a stator based on an α,ω-diphosphine bearing, in a
symmetric fashion, the 2,6-pyridyl diamide moiety as a central tridentate chelating unit and a rotor com-
posed of Pt(II) equipped with two pyridyl groups in trans configuration was designed. The switching
between its open and closed states using Pd(II) was investigated both in solution and in the solid state.
DOI: 10.1039/c3dt50809a
www.rsc.org/dalton
Introduction
Dynamic molecular systems for which the intramolecular
motion can be tuned is of interest for the design of molecular
motors and machines.1–10 Many design principles dealing
with translational or rotational dynamic molecular assemblies
controlled by a variety of external stimuli such as pH, photo-
chemical or redox processes, metal binding have been
reported.11–18 As prototypes of rotary dynamic systems, mole-
cular turnstiles have been reported by others19–21 and by us.22–29
This type of systems is based on two interconnected parts, a
stator and a rotor. In the absence of external stimulus, the
system is in its open state and the rotor freely rotates around
the stator. In the presence of an external effector, the rotational
movement is blocked and the system is in its closed state.
In a preliminary investigation, we have reported an organo-
metallic Pt(II) based turnstile for which the switching between
the open and closed states was achieved by complexation of an
Ag+ cation and its removal by a Br− anion.30
Fig. 1 Schematic representation of a bismonodentate podand bearing at its
extremities two coordinating sites (a), its obturation by a metal centre bearing
two monodentate coordinating sites in trans configuration leading to a turnstile
in its open state (b) and the locking of the rotational movement by a second
metal centre leading to the closed state of the turnstile (c).
Mass spectrometry was performed by the Service de Spec-
trometrie de Masse, University of Strasbourg.
Single-crystal analysis
Data were collected at 173(2) K on a Bruker APEX8 CCD diffr-
actometer equipped with an Oxford Cryosystem liquid N2
device, using graphite-monochromated Mo-Kα (λ = 0.71073 Å)
radiation. For both structures, diffraction data were corrected
for absorption. Structures were solved using SHELXS-97 and
refined by full matrix least-squares on F2 using SHELXL-97.
The hydrogen atoms were introduced at calculated positions
and not refined (riding model).31
Here we report on the design, synthesis and structural ana-
lysis, both in the solid state and in solution, of a new Pt(II)
based molecular turnstile in its open (Fig. 1b) and closed
states generated upon binding of Pd(II) (Fig. 1c).
Experimental part
Crystallographic data for 1. C126H140N10O17P4 Pt2, C4H10O,
ˉ
Characterization techniques
M = 2580.54, triclinic, space group P1, a = 15.7504(7) Å, b =
1H-, 31P- and 13C-NMR spectra were recorded at 25 °C on either
Bruker AV 300, Bruker AV 400 or Bruker AV 500 spectrometers
in deuterated solvents and the residual solvent peak was used
as the internal reference.
19.2503(8) Å, c = 23.5828(10) Å, α = 98.761(2)°, β = 92.067(2)°,
γ = 107.459(2)°, V = 6715.9(5) Å3, T = 173(2) K, Z = 2, Dc = 1.276
Mg m−3, μ = 2.190 mm−1, 125 016 collected reflections, 35 268
independent [Rint = 0.1063], GooF = 1.060, R1 = 0.0922, wR2 =
0.2144 for I > 2σ(I) and R1 = 0.1587, wR2 = 0.2329 for all data.
Crystallographic data for 1-Pd. C61H63N5O8P2PdPt, C6H14O,
Molecular Tectonic Laboratory, UMR UDS-CNRS 7140, Université de Strasbourg,
ˉ
CHCl3, M = 1579.13, triclinic, space group P1, a = 7.9136(2) Å,
Institut Le Bel, 4, rue Blaise Pascal, F-67000 Strasbourg, France
†Electronic supplementary information (ESI) available. CCDC 929708 and
929709. For ESI and crystallographic data in CIF or other electronic format see
DOI: 10.1039/c3dt50809a
b = 18.6050(4) Å, c = 23.8040(5) Å, α = 96.7200(10)°, β =
90.6200(10)°, γ = 96.4710(10)°, V = 3457.45(14) Å3, T = 173(2) K,
Z = 2, Dc = 1.517 Mg m−3, μ = 2.501 mm−1, 85 720 collected
9740 | Dalton Trans., 2013, 42, 9740–9745
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reflections, 18 604 independent [Rint = 0.0682], GooF = 1.024, added simultaneously. The mixture was further stirred at 20 °C
R1 = 0.0404, wR2 = 0.0812 I > 2σ(I) and R1 = 0.0654, wR2
0.0901 for all data.
=
overnight. After the removal of the solvent under reduced
pressure, the mixture was purified by column chromatography
(SiO2, CH2Cl2–MeOH 99/1 to 95/5) affording the desired com-
pound 7 in 49% yield (160 mg) as a white solid. 1H-NMR
(CDCl3, 300 MHz): δ (ppm) = 2.51 (dt, 4H, PCH2, J = 10.9 Hz,
J = 6.9 Hz), 3.62–3.83 (m, 24H, OCH2), 4.04 (dt, 4H, PCH2-CH2,
J = 10.9 Hz, J = 6.9 Hz), 7.15–7.49 (m, 20H, PPh2), 7.96 (t, 1H,
Synthesis
THF, CH2Cl2 and triethylamine were distilled over sodium,
CaH2 and KOH, respectively. Analytical grade CH3CN was used
without further purification.
3
3
pyr, J = 7.7 Hz), 8.29 (d, 2H, pyr, J = 7.7 Hz), 8.73 (br t, 2H,
Compounds 2,25 3,32,33 4,28 28 and 834 (Scheme 1) were syn-
5
3
NH, J = 5.9 Hz); 13C-NMR (CDCl3, 125 MHz): δ = 28.8 (PCH2,
thesized following described procedures.
virtual t,35 JP–C = 46.6 Hz), 39.6 (NCH2), 67.6 (PCH2CH2), 70.2,
70.4, 70.7, 70.8, 71.0 (OCH2), 124.8 (pyr), 128.5 (Ph, virtual t,35
JP–C = 5.3 Hz), 130.8 (Ph, virtual t,35 JP–C = 54.8 Hz), 131.1 (Ph),
133.5 (Ph, virtual t,35 JP–C = 4.9 Hz), 138.7 (pyr), 149.1 (pyr),
164.1 (CO); 31P-NMR (CDCl3, 121.5 MHz): δ (ppm) = 3.92 (JP–Pt
= 3632 Hz). MS (ESI): m/z calcd for C47H57Cl2N3O8P2PtNa+:
Compound 6. Compound 5 (1.03 g, 1.52 mmol) was dis-
solved in 30 mL of THF at 0 °C, and KPPh2 (0.5 M in THF,
6.4 mL, 2.1 eq.) was added dropwise during 30 min. After the
addition was completed, the mixture was allowed to reach
slowly 25 °C. After 4 h, the solution was filtrated on Celite and
evaporated to dryness. Column chromatography (Al2O3,
CH2Cl2–MeOH 100/0 to 90/10) afforded compound 6 as a
slightly yellowish oil (0.25 g, 19% yield). 1H-NMR (CDCl3,
400 MHz): δ (ppm) = 2.31 (br t, 4H, PCH2, J = 7.5 Hz),
3.45–3.67 (m, 28H, OCH2), 7.25–7.40 (m, 20H, Ph), 7.93 (t, 1H,
3J = 7.8 Hz, pyr), 8.28 (d, 2H, 3J = 7.8 Hz, pyr), 8.40 (br, 2H,
1142.25 g mol−1; found: 1142.24 g mol−1
.
Compound 1. Compound 7 (40 mg, 0.036 mmol) and ethy-
nylpyridine 8 (11 mg, 0.107 mmol, 3 eq.) were dissolved in a
degassed THF–NEt3 1 : 1 mixture (10 mL) and degassed by
freeze–thaw cycles. After one cycle, CuI (1 mg, 0.005 mmol,
0.14 eq.) was added to the cold mixture. After 5 more cycles,
the reaction mixture was heated to 55 °C and stirred overnight.
After filtration on Celite and evaporation of the filtrate, the
mixture was purified by column chromatography (SiO2,
CHCl3–MeOH 99/1 to 90/10) affording the desired product 1 in
71% yield as a yellow solid (32 mg). 1H-NMR (CD2Cl2,
NH); 13C-NMR (CDCl3, 100 MHz): δ (ppm) = 28.8 (PCH2, JP–C
=
13.1 Hz), 39.7 (NCH2), 68.7 (PCH2CH2), 70.1, 70.2, 70.4, 70.6,
70.8 (OCH2), 125.0 (pyr), 128.6 (Ph, JP–C = 6.8 Hz), 128.8 (Ph),
132.8 (Ph, JP–C = 18.9 Hz), 138.4 (Ph, JP–C = 13.1 Hz), 138.8
(pyr), 149.1 (pyr), 163.9 (CO); 31P-NMR (CDCl3, 162 MHz): δ
(ppm) = −22.4
3
500 MHz): δ (ppm) = 3.21 (m, 4H, Hl), 3.38 (q, 4H, NCH2, J =
Compound 7. Under argon and at 25 °C, 300 mL of anhy-
drous and degassed CH2Cl2 was introduced into a dry 1 L
three-necked round-bottomed flask and the solution was
stirred. Using a syringe pump (1 mL h−1), an anhydrous and
degassed CH2Cl2 (15 mL) solution of compound 6 (250 mg,
0.29 mmol, 1 eq.) and an anhydrous and degassed CH2Cl2
(15 mL) solution of CODPtCl2 (110 mg, 0.29 mmol, 1 eq.) were
5.9 Hz), 3.45–3.58 (m, 20H, OCH2), 3.89 (m, 4H, Hk), 6.70 (d,
4H, Ht, 3J = 4.6 Hz), 7.41–7.51 (m, 12H, Ho–p), 7.82 (m, 8H, Hn),
3
3
8.00 (t, 1H, Ha, J = 7.8 Hz), 8.28 (d, 2H, Hb, J = 7.8 Hz), 8.31
(d, 4H, Hu, 3J = 4.6 Hz), 9.16 (br t, 2H, Hv, 3J = 6.6 Hz);
13C-NMR (CD2Cl2, 125 MHz) (assignments according to HSQC
1
and HMBC 2D H-13C NMR experiments): δ (ppm) = 28.9 (Cl,
virtual t,35 JP–C = 18.8 Hz), 40.0 (Ce), 67.4 (Ck, virtual t,35 JP–C
4.1 Hz), 70.1, 70.7, 70.8, 70.9, 70.9 (Cf–j), 109.5 (Cq, JPt–C
=
=
259.4 Hz), 115.6 (Cr, JPt–C = 29.6 Hz), 124.8 (Cb), 126.0 (Ct),
128.7 (Co, virtual t,35 JP–C = 5.5 Hz), 131.1 (Cp), 131.6 (Cm,
virtual t,35 JP–C = 28.6 Hz), 134.0 (Cn, virtual t,35 JP–C = 6.2 Hz),
136.5 (Cs), 139.0 (Ca), 149.6 (Cu), 149.7 (Cc), 164.3 (Cd); 31P-NMR
(CD2Cl2, 161.98 MHz): δ (ppm) = 5.79 (JP–Pt = 2511 Hz).
MS (ESI): m/z calcd for C61H65N5O8P2PtH+: 1253.40 g mol−1
found: 1253.40 g mol−1
;
.
Compound 1-Pd. To a solution of compound 1 (6 mg,
4.8 μmol) in a CH2Cl2–CH3CN 1/1 mixture (4 mL) a CH2Cl2
solution (0.5 mL) of Pd(OAc)2 (1.2 mg, 5.3 μmol, 1.1 eq.) was
added. After 5 days at 25 °C, the mixture was evaporated to
dryness under reduced pressure. The residue thus obtained
was purified by preparative layer chromatography (PLC, SiO2,
CH2Cl2–MeOH 93/7) to yield the desired complex 1-Pd in 54%
1
yield as a yellow solid (3.5 mg). H-NMR (CDCl3, 500 MHz): δ
(ppm) = 3.03 (br t, 4H, He, 3J = 4.8 Hz), 3.25 (m, 4H, Hl),
3.48–3.60 (m, 16H, OCH2), 3.65 (m, 4H, OCH2), 3.79 (m, 4H,
3
Hk), 6.22 (br d, 2H, Ht, J = 4.7 Hz), 7.45 (m, 8H, Ho), 7.49 (m,
3
3
4H, Hp), 7.60 (d, 2H, Ht′, J = 5.2 Hz), 7.65 (d, 2H, Hb, J = 7.8
Hz), 7.81 (m, 8H, Hn), 8.00 (t, 1H, Ha, 3J = 7.8 Hz), 8.11 (br, 2H,
Scheme 1 Formula of compounds 1–8 and of 1-Pd and assignment of
H atoms.
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3
Hu), 8.90 (d, 2H, Hu′, J = 5.3 Hz); 13C-NMR (CDCl3, 125 MHz) permit the free rotation of the rotor around the stator, was
1
(assignments according to HSQC and HMBC 2D H-13C NMR based on CPK models. As the rotor, Pt(II), used as the hinge,
experiments): δ (ppm) = 28.8 (Cl, virtual t,35 JP–C = 18.5 Hz), was equipped with two 4-ethynylpyridyl units in trans configur-
47.3 (Ce), 67.1 (Ck, virtual t,35 JP–C = 4.1 Hz), 70.9, 71.1, 71.1, ation. The choice of the CuC bond between the metal centre
71.2 (Cf–j), 106.9 (Cr′), 111.7 (Cr), 124.1 (Cb), 125.3 (Ct), 128.5 and the pyridyl group was made for synthetic reasons. The
(Ct′), 128.8 (Co, virtual t,35 JP–C = 5.1 Hz), 131.1 (Cm, virtual t,35 junction between the pyridyl groups and the metal centre was
JP–C = 28.6 Hz), 131.3 (Cp), 134.0 (Cn, JP–C = 6.0 Hz), 139.3 (Cs′), organometallic in nature and based on Pt–C bonds. Finally, as
140.7 (Ca), 149.1 (Cu), 152.6 (Cu′), 153.2 (Cc), 171.4 (Cd); an effector, Pd(II) was used. It is worth noting that owing to the
31P-NMR (CDCl3, 121.5 MHz): δ (ppm) = 3.67 (JP–Pt = 2496 Hz). dianionic nature of the 2,6-pyridyl diamide moiety under alka-
MS (ESI): m/z calcd for C61H63N5O8P2PdPtH+: 1357.28 g mol−1
;
line conditions, the closed state of the turnstile 1-Pd is a
neutral species.
found: 1357.29 g mol−1
.
The synthesis of 1 required 9 synthetic steps (Scheme 1, see
the Experimental section). Intermediates 2,25 3,32,33 4,28 528
and 834 were synthesized following described literature
procedures.
Results
The design of the turnstile 1 (Scheme 1) is based on our pre-
The condensation of the diacylchloride pyridine derivative
vious studies on porphyrin22–29 or platinum30 based turnstiles 2 with the oligoethyleneglycol bearing an amino group 3 in
and inspired by the reported investigations by Gladysz et al. on CH2Cl2 in the presence of Et3N afforded the diol 4 which was
molecular gyroscopes.21 The herein reported design is based activated into its dimesylate derivative 5 upon treatment with
on a stator, an α,ω-bismonodentate ligand bearing in a sym- mesylchloride (MsCl) in THF in the presence of Et3N as a base
metrical fashion a tridentate chelating unit (Fig. 1a) and a and para-dimethylaminopyridine (DMAP) as a catalyst.
rotor composed of a metal centre as a hinge to which two iden-
Dropwise addition of a solution of KPPh2 in dry THF into a
tical monodentate coordinating sites in trans disposition are solution of 5 in dry THF at 0 °C afforded compound 6 in 19%
attached (Fig. 1b). In the absence of external stimulus, the yield. Attempts to improve the yield by performing the reaction
rotor freely rotates around the stator defining thus the open at −78 °C or by increasing the number of equivalents of KPPh2
state of the turnstile. In the presence of a metal centre as an from 2.1 to 4.2 were unsuccessful. The obtained low yield may
effector offering four free coordination sites occupying the be attributed to the presence of acidic H atoms of the amide
apices of a square, its simultaneous binding by the tridentate groups. Upon condensation of the podand 6 with CODPtCl2
chelating units of the stator and by one of the two pyridyl (1,5-cyclooctadiene = COD) under high dilution conditions in
groups of the rotor blocks the rotational movement (Fig. 1c) CH2Cl2, the metallamacrocycle 7 was obtained in 49% yield.
leading thus to the closed state of the turnstile. Although the Finally, the substitution of the two chloride anions by two
design principle proposed in this contribution might appear ethynylpyridines 8, prepared following
a published pro-
to be rather similar to the one previously reported by us,30 it cedure,29 was achieved in a NEt3–THF 1 : 1 mixture, affording
nevertheless differs substantially. Indeed, the previous system the turnstile 1 in its open state in 71% yield.
was based on monodentate pyridyl groups both on the stator
The metallation of the turnstile 1, leading to its closed state
and on the rotor and the locking of the turnstile was achieved 1-Pd, was achieved in 54% yield by treatment of 1 with 1.1 eq.
by a silver cation. This system was shown to oscillate between of Pd(OAc)2 in a CH2Cl2–CH3CN 1/1 mixture at 25 °C.
two closed states. In order to overcome this feature, the mono-
The structure of both the turnstiles in its open state 1 and
dentate coordinating site was replaced by a tridentate chelating in its closed state 1-Pd was established in the solid state by
unit on the stator in 1 (Scheme 1). Consequently, owing to the X-ray diffraction on single crystals. In both cases, crystals were
high affinity of the chelating moiety for metal cations adopting obtained at 25 °C upon slow diffusion of Et2O or iPr2O
a square planar type geometry, i.e. Pd(II) or Pt(II), no oscillatory vapours into a CHCl3 solution of 1 or 1-Pd respectively (see the
movement between two closed positions should be observed.
It may be of interest to notice that the system presented
Experimental section).
For the turnstile 1, the crystal (triclinic, P1) is composed of
ˉ
above could be described as a sequential process leading from 1 and Et2O solvent molecule (Fig. 2). Since the latter was found
a podand to a binuclear metallamacrobicyclic architecture. to be disordered, the structure was solved using the squeeze
Indeed, the binding of the first metal centre by the podand command.36 The Pt(II) centre adopts a slightly distorted
(Fig. 1a) leads by an obturation process to a metallamacrocycle square-planar geometry with P–Pt–C angle in the 86.2–92.0°
(Fig. 1b). The complexation of the second metal centre gener- range and P–Pt–P and C–Pt–C angles of 177.11(9) and
ates the metallamacrobicycle (Fig. 1c).
176.6(4)° respectively. The Pt(II) centre is surrounded by two C
The translation of the above mentioned design principle and two P atoms in trans dispositions with Pt–P and Pt–C dis-
into molecules is given in Scheme 1. As the stator, the α,ω-di- tances of 2.298(2), 2.295(2) Å and 1.999(7), 2.010(10) Å respecti-
phosphine 6 based on the 2,6-pyridyl diamide moiety was vely. For the ethynylpyridyl moieties, the Pt–C–C and C–C–C
chosen. The spacers used to connect the diphenylphosphine angles are in the 175.9–177.6° and 179.2–176.3° range respecti-
groups to the pyridyl derivative were –(CH2)2–O(CH2)2–O vely. The two amide groups are in trans configuration with
(CH2)2–O(CH2)2– fragments. The length of the latter, chosen to OCNH dihedral angles of ca. 179.1 and 178 9° and CvO and
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Fig. 4 A portion (aromatic region) of the 1H-NMR spectra (500 MHz, CD2Cl2,
298 K) between 6 and 9.2 ppm of 1 (bottom) and of 1-Pd (top). For hydrogen
atoms assignments see Scheme 1.
Fig. 2 Crystal structure of 1 showing the establishment of H bonds between
the two amide NH groups and the pyridyl moiety connected to the Pt(II) centre
(green) by an ethynyl spacer. H atoms except the two involved in H-bonding
patterns and solvent molecules are not represented for clarity. For bond
distances and angles see the text.
two longer Namide–Pd distances of ca. 2.05 Å. The last NPtPy–Pd
distance is ca. 2.03 Å. Finally, the Pt–Pd distance within the
heterobinuclear species is 9.46 Å.
N–C bond distances in the ca. 1.24–1.25 Å and ca. 1.31–1.32 Å
range respectively. Interestingly, two H bonds between the H
atom of the two amide groups and one of the two ethynylpyri-
dyl moieties pointing towards the handle are observed in the
solid state with NH–N distances of ca. 2.33 and 2.37 Å.
Both compounds 1 and 1-Pd were fully characterised
in solution in CD2Cl2 and their dynamic behaviour studied by
1- and 2-D NMR. For both compounds all hydrogen atoms
1
have been assigned (Scheme 1). The H-NMR spectrum of the
turnstile 1 at 25 °C was found to be well resolved and displayed
only two doublets for Hu and Ht atoms (Fig. 4, bottom). This
observation implies either a fast free rotation of the rotor
around the stator or a rapid oscillatory movement, with respect
to the NMR time scale. The oscillation should take place
between two closed states of the same energy for symmetry
reasons by the formation of H-bonds between the two amide
NH donor sites and the pyridyl moiety of the rotor. This, as
mentioned above, is substantiated by the solid state structure
of 1 (Fig. 2). In order to investigate the nature of the move-
ment, i.e. free rotation or oscillation, compound 1 was studied
by 2D ROESY NMR (Fig. 5, top). The latter experiment revealed
in addition to the expected correlations between chemically
connected H atoms, such as Hv and He, Hn and Hj–l–k, through
space correlations between Hu and Ht hydrogen atoms of the
pyridyl moiety of the rotor and H atoms of the stator. This
indicates that, at 25 °C, the rotor oscillates between two posi-
tions. This type of behaviour has been previously observed for
porphyrin based molecular turnstiles.27 The decrease in temp-
erature from 25 °C to −85 °C, although leading to broadening
of signals, did not cause the splitting of Hu and Ht doublets
into two sets of signals corresponding to Hu, Hu′ and Ht, Ht′
implying that the oscillatory process was not blocked at
−85 °C.
ˉ
For 1-Pd, the crystal (triclinic, P1) in addition to the turn-
stile contained iPr2O and CHCl3 solvent molecules (Fig. 3). As
in the case of 1, the Pt(II) centre adopts nearly the same geo-
metry with some slightly different metrics (P–Pt–C angle in the
88.44–91.99° range and P–Pt–P and C–Pt–C angles of 172.22(4)
and 177.92(16)° respectively). The metal centre is connected to
two C and two P atoms in trans dispositions with Pt–P and Pt–
C distances of ca. 2.31 and 1.99 Å respectively. For the ethynyl-
pyridyl moieties, the Pt–C–C and C–C–C angles are ca. 177.4,
178.6° and 179.2, 180.0° respectively. The two amide groups
are again in trans configuration with OCNPd dihedral angles
of ca. −171.2 and −177.5° and CvO and N–C bond distances
of ca. 1.24 Å and ca. 1.34 Å respectively. The Pd(II) centre
adopts a distorted square planar geometry with ⊖NPy–Pd–NPy
= 180.0°, ⊖Namide–Pd–Namide = 160.8°, ⊖Namide–Pd–NPy in the
80.4–80.5° range and ⊖Namide–Pd–NPyethynyl in the 99.0–100.2°
range. The distortion is brought by the tridentate chelating
unit which imposes one short NPy–Pd distance of 1.93 Å and
The closed state of the turnstile 1 was generated upon
binding of Pd(II) playing the role of an effector. The complexa-
tion event led to a less symmetric species 1-Pd as shown by the
1H-NMR spectrum (Fig. 4, top). In particular, the two doublets
corresponding to Ht (6.70 ppm) and Hu (8.31 ppm) in 1 are, as
expected, split into four doublets Ht (6.22 ppm) and Hu
(8.11 ppm) and Ht′ (7.60 ppm) and Hu′ (8.90 ppm) corres-
ponding to H atoms of the unbound and bound pyridyl units
of the rotor respectively.
Fig. 3 Crystal structure of the Pt (green)–Pd (orange) heterobinuclear metalla-
macrobicycle 1-Pd showing the locking of the turnstile upon binding of Pd(II).
Owing to coordination of the Pd atom, Ht′ and Hu′ are
downfield shifted. The upfield shift observed for the Ht and
H
atoms and solvent molecules are not represented for clarity. For bond
distances and angles see the text.
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Conclusions
In conclusion, the Pt(II) based molecular turnstile 1 was
designed, synthesised and characterised and its dynamic be-
haviour in solution was established by 1- and 2-D NMR experi-
ments. Owing to the presence of H-bond donor sites on the
stator (two NH amide groups) and acceptor site (pyridyl
moiety) on the rotor, both in the solid state and in solution an
intramolecular H-bond is formed. Since the turnstile 1 is
equipped with two identical coordinating sites (pyridyl units)
on the rotor, the turnstile oscillates between two positions at
25 °C. The locking of the turnstile was achieved using Pd(II) as
an effector. The structure of 1-Pd was established both in the
solid state by X-ray diffraction and in solution by NMR investi-
gations. Based on the design principles reported here, other
organometallic turnstiles using different metal centres and
effectors are currently under investigation.
Acknowledgements
Financial support from the University of Strasbourg, the Inter-
national Centre for Frontier Research in Chemistry (FRC),
Strasbourg (post-doctoral fellowship to A.G.), the Institut Uni-
versitaire de France, the CNRS and the Ministry of Education
and Research (PhD fellowship to N.Z.) is acknowledged.
Fig. 5 Portions of the 2D-NMR correlation maps (1H–1H ROESY, CD2Cl2, 298 K,
500 MHz) showing, in addition to the expected cross peaks, through space
correlations between the rotor and the stator parts of the turnstile in its open
(1, top) and closed states (1-Pd, bottom).
Notes and references
Hu atoms might be due to the shielding effect brought by
the close proximity of phenyl groups located on the P atom.
Furthermore, Hb and He signals are significantly upfield
shifted with Δδ = −0.63 and −0.35 ppm. Finally, the signal
at 9.16 ppm corresponding to Hv (NH of the amide groups)
in 1 disappears implying also the binding of the Pd(II)
cation.
1 J.-P. Sauvage, in Molecular machines and motors, structure
and bonding, ed. J.-P. Sauvage, Springer, Berlin, Heidelberg,
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Observations on 1-Pd in the solid state by X-ray diffraction
1
and in solution by H-NMR were further substantiated by 2D
ROESY experiments in CD2Cl2 at 25 °C (Fig. 5, bottom).
Indeed, the bidimensional NMR study revealed, in addition to
the expected correlation peaks, through space interactions
between the Ht′ and Hu′ atoms of the pyridine of the rotor co-
ordinated to the Pd(II) centre and H atoms belonging to the
stator (Ht′ with Hl, Hk and Hj–f and Hu′ with He and Hj–f). Fur-
thermore, as expected, no correlation peaks between Ht and
Hu atoms of the unbound pyridine of the rotor and H atoms of
the stator were observed. These features clearly demonstrate
that, upon the binding of Pd cation, the turnstile is locked
without oscillation between two sites as observed for the turn-
stile 1 discussed above.
Owing to the design of the turnstile, in particular the pres-
ence of Pt–P junctions, the CN− anion as a competing ligand
with the pyridyl unit of the rotor could not be used since it
would lead to the destruction of the complex. The opening of
the system was attempted using acidic conditions in order to
protonate the pyridyl moiety of the rotor. Unfortunately, the
presence of H+ led to the decomposition of the complex.
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