Copper(I)-induced threading of two bis-macrocycles on two rods: A cyclic [4]rotaxane

Article abstract of DOI:10.1039/b601703g

A cyclic pseudo-rotaxane tetramer has been synthesised quantitatively at room temperature by threading two two-coordination site rods through two bis-macrocycles in the presence of copper(i) as a template. the Royal Society of Chemistry and the Centre Nat

Full text of DOI:10.1039/b601703g

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LETTER
www.rsc.org/njc | New Journal of Chemistry
Copper(I)-induced threading of two bis-macrocycles on two rods: a cyclic
4]rotaxane
[
´
Jean-Paul Collin, Julien Frey, Valerie Heitz, Efstathia Sakellariou, Jean-Pierre
Sauvage* and Christian Tock
Received (in Montpellier, France) 6th February 2006, Accepted 13th April 2006
First published as an Advance Article on the web 17th May 2006
DOI: 10.1039/b601703g
A cyclic pseudo-rotaxane tetramer has been synthesised quanti-
tatively at room temperature by threading two two-coordination
site rods through two bis-macrocycles in the presence of
copper(I) as a template.
2D interlocking network, as shown in Scheme 1. Purely
organic systems displaying the same topological properties
8
have recently been reported by Arico et al. One of the key
´
factors to the success of the present threading reaction, leading
to the [4]pseudo-rotaxane, is the rigidity of the organic frag-
ments used. In fact, these ligands cannot easily lead to other
discrete complexes than the desired 4-metal system. Two
phenanthrolines attached back to back and included in a
Introduction
Within the last two decades, the field of catenanes and
1
6
rotaxanes has experienced
a
spectacular development.
bis-macrocycle were previously published by our group,
Whereas the synthesis of such relatively simple compounds is
well documented, the elaboration of multirotaxanes incorpor-
ating several rings and several thread-like fragments is still
challenging, especially if precisely defined species are to be
whereas the bis-bidentate thread built around a 4,7-phenan-
throline nucleus is a new compound, synthesised as described
in Scheme 2.
2
obtained. The copper(I) templated strategy proposed long
ago has been extended to more and more complex molecules,
3
incorporating several metal centres. As far as Cu(I)-com-
plexed rotaxanes are concerned, two compounds are worth
noting which contain 4 metal centres: a [5]rotaxane with
4
porphyrinic stoppers and a cyclic rotaxane tetramer whose
organic components consist of a coordinating ‘‘filament’’
5
appended to a ring.
Recently, our group has reported an unusual topology
consisting of a large ring threading the two halves of a bis-
6
macrocycle (‘‘handcuff’’). Such a topology had already been
0
0
Scheme 2 Synthesis of the 3,8-bis(4 -(4-methoxyphenyl)-2 -pyridyl)-
4,7-phenanthroline fragment. Reagents and conditions: (i) 5-bromo-2-
7
reported by Becher et al., containing totally different compo-
9
trimethylstannyl pyridine, Pd(PPh
methoxyphenylboronic acid, K CO
3
)
4
, toluene, 140 1C, 18 h; (ii) 4-
nents. The bis-macrocycle used for this synthesis can be
utilised for constructing more complex systems such as, in
particular, a rotaxane tetramer or its non-stoppered analogue,
as depicted in Scheme 1.
2
3
, Pd(PPh , DMF, 120 1C, 18 h.
3 4
)
The backbone of the central 4,7-phenanthroline unit forces
the two bipyridine chelates in the same direction and provides
the system with the required rigidity.
1
was obtained in 80% overall yield from commercially
available 4,7-phenanthroline, following the procedure described
1
in the literature. The bis-bidentate ligand 2 was prepared by
0
9
Stille coupling of 1 with 2-trimethylstannyl-5-bromopyridine in
87% yield. The crude product was filtered over celite, washed
Scheme 1 Transition metal-directed formation of a cyclic pseudo-
rotaxane tetramer; the black dot represents a metal centre and the
U-shaped symbol corresponds to a bidentate chelate.
with MeOH and Et O and, subsequently, extracted from the
2
celite with hot chloroform in which it is slightly soluble. The
ligand was then elongated by a Suzuki coupling with 4-meth-
oxyphenylboronic acid. After following the same work-up
procedure as for compound 2, the final ligand was obtained
By taking advantage of the template effect of Cu(I) we could
assemble two bis-macrocycles and two linear threads to form a
1
in 64% yield. All compounds were characterised by H-NMR
and ES-mass spectroscopy (ES-MS).
The final threading reaction of two bis-bidentate linear axles
with two bis-macrocycles 4, using the template effect of Cu(I) is
described in Scheme 3.
Laboratoire de Chimie Organo-Mine´rale, LC3 UMR 7177 du CNRS,
Institut Le Bel, Universite´ Louis Pasteur, 4 rue Blaise Pascal, 67070
Strasbourg Cedex, France. E-mail: sauvage@chimie.u-strasbg.fr
1
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4
1
.
Scheme 3 Transition metal directed threading step leading to the 4-copper(I) centre threaded network species 5
A degassed solution of [Cu(CH
3
CN)
4
](PF
6
) in acetonitrile
hedral environment and hence the Cu(I) is strongly stabilised.
The electronic properties of the compound are in perfect
agreement with its structure. Three different absorption bands
was added to a suspension of the bis-macrocycle 4 in freshly
distilled dichloromethane. After 15 h, the bis-bipyridine thread
6
3
was added as a solid to the orange solution. Both the bis-
are observed in the UV region (lmax B 240 nm, e B 1.03 ꢂ 10
ꢁ
1
ꢁ1
5
ꢁ1
ꢁ1
macrocyle 4 as well as the thread are barely soluble in the
solvents used. Interestingly, coordination of the various li-
gands to the Cu(I) centres makes them perfectly soluble, just as
L mol cm , lmax B 263 nm, e B 9.36 ꢂ 10 L mol cm
6 ꢁ1 ꢁ1
and lmax B 355 nm, e B 1.35 ꢂ 10 L mol cm ), which
correspond to ligand-localised transitions. A much less intense
band, which is very likely to correspond to a Metal-to-Ligand
Charge Transfer (MLCT) transition, is observed in the visible
41
well as the target molecule 5 . After one week at room
temperature and in the absence of light, the solvents were
evaporated and the final compound was extracted from water
with dichloromethane and then precipitated in a saturated
ꢁ1
ꢁ1
region (lmax B 585 nm, e B 5900 L mol cm ). The MLCT
band appears at unusually low energy for bis-diimine copper(I)
1
1
KPF
6
solution. The thermodynamically most stable four-Cu(I)
complexes, which is in agreement with the strong p-accepting
nature of the organic ligands used, in agreement with previous
observations made on copper(I) complexes with related
41
containing threaded species 5 was obtained in 95% yield as
1
a greenish brown solid and was characterised by H-NMR
12
II
I
(
500 MHz) as well as COSY and ROESY NMR and ES-MS.
ligands. Cyclic voltammetry shows that the Cu /Cu couple
1
41
The H-NMR spectrum of the final copper(I) complex 5 is
has a redox potential around 0.6 V vs. SCE in acetonitrile, in
1
accordance with previously reported values for similar systems.
3
shown in Fig. 1; the chemical shifts of the complex and the
building blocks 3 and 4 are listed in Table 1. Important
changes, ranging from ꢁ0.9 to ꢁ1.3 ppm, can be seen for
In conclusion, the gathering and threading effect of
copper(I) turned out to be, once again, particularly efficient.
It allowed assembly of a pseudo-rotaxane tetramer quantita-
tively from 4 organic fragments. In the future, such complex
structures will be incorporated in new and more sophisticated
molecular machines involving the motion of two-dimensional
molecular networks.
5 ,6
H of the thread and Ho,m of the bis-macrocycles compared
0 0
to the free ligands (see Scheme 3 for numbering). Clear
evidence for the threading of the linear bis-bipyridine ligands
through the 30-membered rings is provided by 2D-ROESY
NMR. Dipolar coupling between the hydrogen atoms of the
pentaethyleneglycol chains with H
2 3
and H of the thread is
0 0
observed. The ES-MS spectrum shows one peak at m/z
Experimental
41
9
15.2614 corresponding to [5] (calcd. 915.2621).
4
Compound 5 contains four identical Cu(I) centres, each
1
Instrumentation
0
1
one being coordinated to 1,10-phenanthroline and 2,2 -bipyr-
idine type ligands. Each metal centre is roughly in a tetra-
H-NMR spectra were acquired on a Bruker AM 300 (300 MHz)
spectrometer, operating at 300.17 MHz, using the deuterated
1 41
Fig. 1 H-NMR (500 MHz) spectrum of compound 5 (aromatic region), (also see Table 1).
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1
Table 1 H-NMR (500 MHz) chemical shifts for 3, 4 and [5 ](4PF ).
41
6ꢁ a,b
H
4,7
H
1
0
H
2
0
H
3
0
H
4
0
H
5
0
H
3,8
H
o
0
H
6
0
H
o
H
m
0
H
m
4
1
5
3
4
10.02
9.54
9.44
8.76
8.56
8.61
8.56
8.33
8.56
8.27
9.13
8.24
7.57
7.71
7.43
8.75
7.34
7.06
7.15
6.10
10.19
ꢁ0.17
8.72
8.28
ꢁ0.94
7.36
ꢁ1.26
c
Dd ꢁ0.48
The very poor solubility of 3 and 4 in normal organic solvents did not allow NMR studies without protonating these ligands so as to dissolve
0.10
0.20
0.05
ꢁ0.13
ꢁ0.86
ꢁ0.14
ꢁ1.32
ꢁ0.06
a
b
them. Solvent: CD
41
c
41
2
Cl
2
þ 3% TFA for 3 and 4, CD
2
Cl
2
for 5
.
Dd = d(5 ) ꢁ d(3 or 4).
3
3
solvent as the lock and residual solvent as the internal reference.
Mass spectra were obtained by using a VG-BIOQ triple
quadrupole, positive mode (ES-MS). UV/Vis spectrometry
was done on a BIO-TEC UVIKON XL spectrometer.
H
4
0
0
), 8.73 (d, J = 8.2 Hz, 2H; H
2
0
), 8.58 (d, J = 8.8 Hz, 2H;
), 7.72 (d, J = 8.9 Hz, 4H; H ), 7.6 (d,
0
), 3.99 (s, 6H; HOMe). ES-MS: m/z (%) =
3
H
3
), 8.50 (s, 2H; H
6
0
0
o
3
J = 8.8 Hz, 4H; Hm
1
547.225 (100) [M þ H ].
4
1
Syntheses
4-Copper(I) centre threaded species network (5 ). To the bis-
ꢁ5
macrocycle (4) (50 mg, 4.32 ꢂ 10 mol) in argon atmosphere,
0
3
,8-Bis(4-bromo-2 -pyridyl)-4,7-phenanthroline (2). 5-Bro-
4
a
0 mL of freshly distilled dichloromethane and then 20 mL of
freshly degassed solution of MeCN containing [Cu
mo-2-trimethylstannyl pyridine (1.96 g, 6.05 mmol) and 3,8-
dibromo-4,7-phenanthroline (1) (1.00 g, 2.96 mmol) were
dissolved in dry toluene (130 mL) and the mixture was
ꢁ5
(
MeCN) ](PF ) (33.3 mg, 8.94 ꢂ 10 mol) were added. After
4
6
ꢁ
5
1
5 h of stirring, the thread (3) (23.6 mg, 4.32 ꢂ 10 mol) was
3 4
degassed. To this solution, Pd(PPh ) (230 mg, 0.2 mmol)
added as a solid and the solution was left at room temperature
for 7 days in the absence of light. The solvents were then
evaporated and the product extracted from water with di-
was added and the resulting reaction mixture further degassed
for 5 min. It was then refluxed (140 1C) under argon for 18 h.
Another 160 mg of catalyst were added and the reaction
stirred for a further 44 h under reflux. Evaporation of toluene
afforded the crude product as a grey solid that was washed
chloromethane. After precipitation from a saturated KPF
solution 78 mg of the green-brownish product was obtained
6
41 1
2 2
with 95% yield. 5 : H-NMR (500 MHz, CD Cl ): d = 10.02
with MeOH (2 ꢂ 150 mL) and Et
2
O (2 ꢂ 150 mL). Compound
3
d, J = 8.2 Hz, 8H; H4,7), 9.54 (d, J = 8.9 Hz, 4H; H
3
(
(
(
1
0
), 8.76
(
2) was extracted from the remaining solid by washing it 5
3
d, J = 9.0 Hz, 4H; H
3
), 8.61 (d, J = 8.6 Hz, 4H; H
0
0
), 8.33
2
3
times with 150 mL of chloroform. After evaporating the
chloroform and washing the grey solid again with MeOH
3
dd, J = 8.6 Hz and J = 2.2 Hz, 4H; H
4
4
), 8.27 (d, J = 1.8
0
4
3
3
Hz, 4H; H5 ), 8.24 (d, J = 8.2 Hz, 8H; H ), 7.57 (d, J = 9.1
0
3,8
and Et
2
O, 1.26 g of a greyish yellow solid were obtained (87%
3
3
), 7.34 (d, J = 8.4 Hz, 8H; H ),
Hz, 8H; H
0
), 7.43 (s, 4H; H6
0
1
yield). 2: H-NMR (300 MHz, CDCl
o
o
3
): d = 9.05 (d, J = 8.7
3
7.06 (d, J = 9.1 Hz, 8H; H
3
0
), 6.10 (d, J = 8.5 Hz, 8H; H ),
m
4
), 8.80 (d, J = 2.4 Hz, 2H; H
3
), 8.64 (d, J = 8.6 Hz, 2H; H
3
), 8.74 (d, J = 8.7
m
Hz, 2H; H1
0
0
0
5
3.95–3.78 (m, 92H; H–O–CH –CH –O– þ HOMe). ES-MS: m/z
Hz, 2H; H2
3
3
0
), 8.31 (s, 2H; H6
0
),
2
2
41
(%) = 915.261 (100) [M ].
4
.03 (dd, J = 8.4 Hz and J = 2.4 Hz, 2H; H
8
0
). FAB-MS:
4
1
m/z (%) = 493 (100) [M þ H ].
Acknowledgements
0
0
3
,8-Bis(4 -(4-methoxyphenyl)-2 -pyridyl)-4,7-phenanthroline
0
We would like to thank the CNRS for financial support. We
are also grateful to the French Ministry of Education for
fellowships (J.F. and C.T.) and the Luxembourg Ministry of
Research for financial support (C.T.).
(
3). A suspension of 3,8-bis(4-bromo-2 -pyridyl)-4,7-phenan-
throline (2) (200 mg, 0.4 mmol), 4-methoxyphenylboronic acid
134 mg, 0.88 mmol, 2.2 eq.) and potassium carbonate (425
mg, 2 mmol, 2.5 eq.) in 25 mL DMF was degassed (3 times
vacuum/argon) and Pd(PPh (46 mg, 0.04 mmol, 10% mol)
(
3 4
)
was added. The solution was then heated up to reflux (120 1C)
under argon and stirred for 3 h, then 15 mg of catalyst were
added. After another 18 h of heating, the reaction mixture was
cooled down to room temperature and poured into 250 mL of
water. The product thus precipitated with impurities and was
then filtered over celite and washed with EtOH. The celite–
product mixture was then washed with dichloromethane
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388 | New J. Chem., 2006, 30, 1386–1389
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