A highly rigid ditopic conjugate with orthogonal coordination axes and its zinc(II) and copper(II) complexes

Article abstract of DOI:10.1039/b713367g

A highly rigid ditopic ligand has been prepared which consists of a terpy fragment connected in the back to a phen nucleus via a 1,4-phenylene linker. The chemical structure of the presently reported ligand is such that the coordination axes of the two ch

Full text of DOI:10.1039/b713367g

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PAPER
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A highly rigid ditopic conjugate with orthogonal coordination axes and
its zinc(II) and copper(II) complexesw
ˆ
´
Benoıt Champin, Valerie Sartor and Jean-Pierre Sauvage*
Received (in Montpellier, France) 31st August 2007, Accepted 15th January 2008
First published as an Advance Article on the web 5th February 2008
DOI: 10.1039/b713367g
A highly rigid ditopic ligand has been prepared which consists of a terpy fragment connected in
the back to a phen nucleus via a 1,4-phenylene linker. The chemical structure of the presently
reported ligand is such that the coordination axes of the two chelates are orthogonal to one
another. The reaction of this phen–terpy conjugate with zinc(II) surprisingly affords in good yield
a dinuclear complex in spite of the tension of the generated structure, whereas coordination of
copper(II) centres to the two-chelate ligand enables the formation of the trinuclear complex also.
Introduction
The coordination properties of multi-chelate ligands, and in
particular the nature of the multi-metallic assemblies obtained
after complexation to various metal centres, are strongly depen-
dent on the mutual arrangement of the coordinating subunits
within the multifunctional ligand. As far as we know, two-chelate
ligands in which the coordination axes of the constitutive chelates
are orthogonal to one another are far from being common in the
literature. Generally speaking, multi-chelate ligands containing
two or several aromatic polyimines have been extensively used, in
conjunction with ruthenium(II) and related second and third row
d6 transition metals (Os(II), Re(I), Rh(III) and Ir(III)), especially in
relation to electron and energy transfer processes.1–8 They have
also been frequently utilised to construct elegant multinuclear
architectures such as grids,9 helical complexes,10,11 racks,12,13 etc.,
or new topologies such as knots14,15 or rotaxane oligomers.16–18
In most cases, the axes of the individual chelates belonging to the
multisite ligand are antiparallel or parallel to one another,
although different situations can also be found.
Fig. 1 Formation of M(A)(B) complexes should lead to oriented
cyclic structures. Depending on the coordination sphere geometry of
the transition metal used, various rings and nuclearities could be
obtained. (A = bidentate; B = terdentate).z
appropriate positions (40 position of terpy and 3 position of
phen) so as for the coordination axes to be perpendicular to
one another. The geometry of terpy is indeed very appropriate
to an axial functionalization in the back (via the 40 position).
The terpy nucleus is functionalized at the 5 and 500 positions
with methyl groups. The phen unit bears an anisyl group,
By contrast, two-chelate ligands with orthogonal coordina-
tion axes for the chelates (Fig. 1) should favour the formation
of novel multinuclear complexes and lead to well-defined
transition metal-incorporating assemblies.19–21
1
which will act as a H NMR probe during the synthesis.
The aim of this full paper is to give extensive details on the
synthetic procedure used to obtain the phen–terpy conjugate,
whose coordination to zinc(II) metal centres was briefly revealed
in a preliminary report.24 The influence of the metal centres on
the nuclearities of the structures obtained will be discussed
through the study of coordination chemistry with copper(II).
If the complexed metal M has a strong preference for
5-coordinate situations, M(A)(B) complexes should be strongly
favoured versus symmetrical complexes of the M(A)2 or M(B)2
type. In the present paper, we would like to report the synthesis
and the coordination properties of such a 2-chelate ligand,
containing a terpy (terpy = 2,20:60,200-terpyridine) unit at-
tached to a phen (phen = 1,10-phenanthroline) nucleus.y
The rigid linker used (1,4-phenylene) has been chosen to be
as short and rigid as possible, and connects the two chelates via
Results and discussion
Synthesis of the acyclic phen–terpy conjugate
The strategy to obtain the desired molecule is straightforward:
each chelate is introduced in a fragment, and both of them are
´
Laboratoire de Chimie Organo-Minerale, LC 3, UMR 7177 du
CNRS, Universite´ Louis Pasteur, Faculte´ de Chimie, 4 rue Blaise
Pascal, 67070 Strasbourg Cedex, France. E-mail: sauvage@chimie.u-
strasbg.fr; Fax: +33 (0)3 90 24 13 68; Tel: +33 (0)3 90 24 13 61
w Electronic supplementary information (ESI) available: Structures
and atom numbering for all molecules; expanded isotopic distribution
patterns for [T + BF4]5+ and [D + BF4]3+. See DOI: 10.1039/
b713367g
z Recently, the synthesis of various metallamacrocycles using terpy-
based ligands has been reported by Constable et al.22
y It should be noted that recently, the synthesis of a ligand incorpor-
ating directly bonded phen and terpy nuclei has been reported by
Gavina and Tatay.23 In that case, the phen unit is connected to the 5
position of the terpy.
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diketone intermediate, which was not isolated. After playing
the role of a base in the first step, ammonium acetate enabled
the central ring of the terpyridine to close and thus afforded
the final compound 5 in 60% yield after column chromato-
graphy. This new compound has been fully characterized by
1H and 13C NMR spectroscopy, HMQC and HMBC 2D
1H–13C experiments, EI-MS and elementary analysis.
It should be noted that compound 5 could also be prepared
via an alternative route, replacing acetic acid by methanol. In
that case, terpy 5 spontaneously precipitated out of the solu-
tion mixture, and no further purification was needed. The
overall yield was the same as in the first route. This optimized
synthetic pathway afforded multigram quantities of terpyri-
dine 5.
In order to make a Suzuki coupling between the two
chelating fragments, one of them should bear a boronic acid
(or ester) function. In spite of the ‘‘synthetic price’’ of the terpy
moiety 5, we decided to modify the functionality at the back of
the terpy by changing the bromine atom for a boronic ester
function in presence of bis(neopentyl glycolato)diboron
(B2neo2) according to the well described procedure30 (Scheme
1). Remarkably, compound 6 was thus obtained in quantita-
tive yield from 5, and was fully characterized.
Scheme 1 Synthesis of the 2-site ligand 1. Reagents and conditions: (i)
4-bromobenzaldehyde, MeOH–NaOH(aq), 30 min; (ii) I2, pyridine,
reflux 1 h, rt 14 h; (iii) NH4OAc, AcOH, reflux 7 h, rt 14 h; (iv)
Pd(dppf)Cl2, KOAc, B2neo2, dioxane, 80 1C, 18 h; (v) Pd(PPh3)4,
Na2CO3, p-anisylboronic acid, toluene–H2O, reflux, 14 h; (vi)
Pd(PPh3)4, Na2CO3, reflux, 30 h.
coupled under Suzuki classical conditions (Scheme 1). The
spacer between both chelates was decided to be incorporated
in the terpy fragment using the Krohnke synthesis. As far as
¨
Synthesis of the phen building block. In order to incorporate
the phen nucleus in a thread with axial symmetry, a phen
substituted in the 3 and 8 positions was necessary. Synthesis of
the dissymmetrical phen unit could be achieved in one step
from 3,8-dibromo-1,10-phenanthroline.31,32 In order to incor-
porate only one anisyl group, a statistical Suzuki coupling
reaction32,33 was performed under classical conditions, using
0.9 equivalents of p-anisylboronic acid, Na2CO3 as a base, and
Pd(PPh3)4 as a catalyst (Scheme 1). The mono-coupled
product 7 was isolated in 46% yield.
the phen fragment is concerned, dissymmetry had to be
introduced so as to have an anisyl unit on one side, and a
precursor to the Suzuki coupling on the other side.
Synthesis of the terpy moiety. The Krohnke synthetic path-
¨
way relies on the coupling of an azachalcone with a pyridinium
iodide, and in our case, both of these building blocks are
obtained from the same compound: 2-acetyl-5-methylpyridine
2 (Scheme 1). As the terpy moiety is a central building block,
each step of the synthesis was optimized in order to obtain the
highest possible yields and the largest amount of compound 5.
Compound 2 had previously been made by reacting a
Grignard reagent with the nitrile derivative.25 We developed
a new efficient route inspired by the procedure described by
Holm et al.,26 which afforded 2 in 52% yield.
Connection of phen and terpy nuclei. A final Suzuki coupling
reaction between 6 and 7 under classical conditions yielded the
phen–terpy conjugate 1 (24%), containing 7 conjugated
6-membered aromatic rings.
Compound 1 has been fully characterized by 1H and 13C
Compound 3 was obtained thanks to a classical Clai-
sen–Schmidt condensation between an aldehyde with no a-
hydrogens (4-bromobenzaldehyde) and ketone 2 (Scheme 1).
The crossed-coupling reaction was carried out in methanol in
the presence of a strong base (NaOH, 1 M). The b-hydroxy
ketone was thus formed, but the conditions used were suffi-
cient to cause dehydration. The a,b-unsaturated ketone 3,
referred to here as azachalcone because of the presence of
the pyridyl nucleus, was thus produced in good yield (86%
after recrystallization),27,28 and has been fully characterized by
1H and 13C NMR spectroscopy, and EI-MS.
1
NMR spectroscopy, HMQC and HMBC 2D H–13C experi-
ments, HR ES-MS and DOSY (diffusion-ordered spectro-
scopy).
Coordination studies on the phen–terpy conjugate
Zinc(II) assemblies. Zn2+ forms stable 5-coordinate com-
plexes and most of the time it is sufficiently labile to allow
formation of coordination compounds under thermodynamic
control.34 This metal was thus selected for complexation
studies with ligand 1.24
For entropic reasons, the reaction between Zn2+ and 1 is
expected to lead to the smallest possible complex.z Never-
theless the size of the species obtained has to be compatible
with the coordination constraints imposed by the metal and
the ligand. If distortion of the Zn2+ coordination sphere and/
or of the ligand backbone costs less than the entropic price
Compound 4 was obtained by reaction between 2 and 1.1
equivalents of iodine under argon in freshly distilled pyridine,
which played here both the role of solvent and reagent.29 The
final product 4 precipitated out of the solution mixture and
was obtained in a good yield (74%) after recrystallization
(Scheme 1).
Terpyridine 5 was obtained following the Krohnke proce-
¨
dure, between azachalcone 3 and pyridinium iodide 4 in acetic
z Translational entropy would favour formation of the highest num-
ber of small particles, while conformational entropy would favour the
formation of polymers.
acid (Scheme 1). A Michael addition afforded in a first step a
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needed to build the large ideal 4-metal species, lower nuclea-
rities will be formed. This is the case in the present system. To
our surprise, the dimer was the sole complex formed (78%
yield), without formation of tetramer nor even trimer com-
plexes. The chemical structure of [Zn2ꢁ(1)2]4+ (D = dimer)
was proven by electrospray ionization mass spectroscopy (ES-
MS) and 1H NMR spectroscopies. HR ES-MS analysis of the
yellow solid (Fig. 2) revealed three major peaks at mass-to-
charge (m/z) ratios of 343.6, 507.8, and 836.1, corresponding
to [D]4+, [D + OTf]3+, and [D + 2OTf]2+, respectively
(Fig. 2), a situation that is consistent with the proposed dimer
compound [Zn2ꢁ(1)2]ꢁ4OTf.
A DOSY experiment carried out on a solution of the yellow
solid in MeOD (Fig. 3) revealed unambiguously the presence
of a single species, characterized by its diffusion coefficient
(D = 470 mm2 sꢂ1; ligand 1 in CD2Cl2: D = 1000 mm2 sꢂ1
and its hydrodynamic radius (rH = 8.5 A; monomer 1: rH
)
=
5.3 A). Computational simulation of the hydrodynamic radius
of an ellipsoid object which matches the experimental value of
the radius enabled us to predict the size of the product in
solution: a = 14 A and b = c = 6 A. The object is thus a
prolate ellipsoid, which is consistent with the proposed dimer
compound [Zn2ꢁ(1)2]ꢁ4OTf. Considering both the results of
ES-MS and DOSY experiments, we can tell that the sole
product formed during the complexation process is the dimer
species [Zn2ꢁꢁꢁ(1)2]ꢁꢁꢁ4OTf.
Moreover, 1H NMR spectroscopy (Fig. 3) clearly shows
what was expected for a dimer species: the geometry around
the zinc centre is so distorted that the p2 proton of the phen
moiety of one terpy–phen conjugate points right in the shield-
ing cone of the central ring of the terpy fragment of the other
two-site ligand, and consequently the p2 proton signal is
strongly shifted upfield (Dd = ꢂ2.82 ppm).
Fig. 3 (Top) 1H NMR spectra (aromatic region) of 1 and its zinc
dimer complex [Zn2ꢁ(1)2]ꢁ4OTf. (Bottom) DOSY experiment on the
dimer complex in MeOD. Apart from the MeOH broad signals, a
single product is present.
The present example tends to indicate that entropy is the
prevailing factor in the complexation process: the reaction
leads to the smallest possible complex in spite of probable
distortion in the Zn2+ coordination sphere and constraints
within the organic ligand 1. Obviously, the use of transition
metal centres other than Zn2+ with more demanding stereo-
electronic requirements, making distortion more difficult,
should favour formation of trimers or tetramers.
Copper(II) complexes. The achievement of such complicated
structures around metal centres is in our case carried out under
thermodynamic control, thanks to labile coordination bonds
between the ligands and the metal centre. Indeed the system
has to have the possibility to create and break bonds at will, so
that it can self-repair its own mistakes, and eventually con-
verge to the most stable product, this one being hopefully the
desired one. The most commonly encountered copper(II)
complexes have a coordination number (CN) of 5 (square
pyramidal or trigonal bipyramidal geometries) or 6 (octa-
hedral arrangement, with Jahn–Teller distortion). In spite of
its paramagnetic character, which prevents us from using
NMR spectroscopy to identify species formed, copper(II)
was thus an attractive candidate, especially considering its
more demanding stereoelectronic requirements.
The choice of the counterion was again crucial: it should be
as little coordinating as possible in order to avoid its coordi-
nation to the copper centre, which should remain 5-coordi-
nate. Among the various copper(II) salts available,
tetrafluoroborate copper(II) was selected. The coordination
experiment was carried out by mixing equimolar amounts of
ligand 1 in CH2Cl2 and Cu(BF4)2 in CH3CN, respectively
(Scheme 2). The solution turned instantaneously olive green,
which is characteristic of Cu(II) complexes bearing phen and
terpy units in their coordination sphere.35–37 The solution was
Fig. 2 HR ES-MS of the zinc(II) dimer complex and expanded
isotopic distribution patterns for [D]4+, which correlate well with
the calculated distributions of the dimer [Zn2ꢁ(1)2].
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Fig. 4 HR ES-MS of the mixture of copper(II) dimer and trimer
complexes [Cu2(1)2]4+ and [Cu3(1)3]6+ (D and T, respectively). Inset:
the m/z ratio experimental region (1st line) at 342.6 is a superposition
of the calculated isotopic patterns of the dimer (2nd line) and the
trimer complexes (3rd line).
Moreover, cyclic voltammetry of a DCM–MeCN (80 : 20)
solution of the olive-green solid showed two reversible reduc-
tion waves at, respectively, +0.15 V and ꢂ0.05 V (vs. SCE).
These values are reminiscent of the ones obtained for
5-coordinate copper species.35–37 Nevertheless, it should be
noted that the sole results of respectively the EPR and CV
study can not be fully conclusive. But considering the ES-MS
analysis of the solution that proved unambiguously the for-
mation of both the dimer and the trimer species, the EPR and
CV results corroborate these conclusions.
Scheme 2 Formation of the dimer and trimer complexes, and mole-
cular model of the trimer species (Chem 3D software), whose energy
was minimized using MM2 software.
Hence, changing the nature of the metal centre cause a
noteworthy modification of the assembly process and yields
once again the dinuclear, but also, for the first time with this
ligand, the trinuclear complex. As expected, the copper(II)
centre managed to impose a more controlled geometry in its
inner coordination sphere than the d10 metal centre zinc(II),
thus disfavouring the formation of the highly distorted dimer
and enabling the trimer to exist.
allowed to stir for 19 h at room temperature, and by addition
of diethyl ether a green solid precipitated out. It was recovered
in a good yield (89%).
The composition of the mixture was first investigated using
ES-MS (Fig. 4 and ESIw). It clearly showed the presence of
two species corresponding to the dimer (D) and the trimer (T).
The respective amount of each compound could not be
evaluated since intensity of peaks in the ES-spectrum is
connected to the amount of product by a response factor,
which is specific to each species.
Conclusions
In this paper, we present the synthesis of a new highly rigid
ditopic ligand whose chelate coordination axes are perpendi-
cular to one another. The synthesis has been optimized and a
sequence of several Suzuki C–C coupling reactions afforded
the desired product, which was fully characterized. Coordina-
tion chemistry of such a ditopic ligand with zinc(II) afforded in
good yield a dimeric structure as the sole product. Contrary to
what was expected from the ideal geometries of the ligand and
of the zinc(II) coordination sphere, neither the trimer nor the
tetramer species could be observed. Formation of the dimer
The major peaks at mass-to-charge (m/z) ratios of 342.6,
428.5, 557.2 and 772.2 correspond to the trimer species [Cu3ꢁ
(1)3]6+ (T), with, respectively, no BF4 as counterion [T]6+
,
,
ꢂ
one counterion [T + BF4]5+, two counterions [T + 2BF4]4+
and three counterions [T + 3BF4]3+. The other peaks at
342.6, 485.8 and 772.2 correspond to the dimer species [Cu2ꢁ
ꢂ
(1)2]4+ (D), with, respectively, no BF4 as counterion [D]4+
,
one counterion [D
+ , and two counterions
BF4]3+
[D + 2BF4]2+. The m/z ratio regions at 342.6 and 772.2 are
thus superpositions of the isotopic patterns of both the dimer
and the trimer species, as shown in Fig. 4.
has been proven by ES-MS, H NMR and diffusion-ordered
1
spectroscopies. By changing the nature of the metal ion to
copper(II), we obtained in a good yield a mixture of trimer and
dimer structures, as shown by ES-MS, EPR and CV.
The EPR spectrum of the frozen solution obtained at 100 K
was also consistent with a mixture of two species, although
further work will be needed to fully understand the EPR data.
It thus appears that translational entropy is a very impor-
tant factor in such complexation processes, leading to the
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smallest possible structure, in spite of the enthalpic cost of the
probable distortion in the zinc(II) coordination sphere and
constraints within the ligand. Such behaviour could be mod-
erated by introducing a metal with more stereoelectronic
requirements, making distortion more difficult. These results
should enable preparation of multi-rotaxanes by adapting the
presently reported methodology to a cyclic derivative of
ligand 1.
using the double titration method described by Gilman and
Cartledge38
Synthesis of compounds
2-Acetyl-5-methylpyridine: 2. 2-Bromo-5-methylpyridine
(10 g; 58 mmol) in anhydrous diethyl ether (150 mL) was cooled
to ꢂ78 1C under argon. n-butyllithium (38 mL; 64 mmol) was
added dropwise to the solution mixture. After addition was
complete, the reaction mixture was allowed to warm to ꢂ40 1C
for 30 min; a dark-red solution resulted. N,N-Dimethylaceta-
mide (6 mL; 64 mmol) was added dropwise and cautiously at
ꢂ78 1C. The mixture was then allowed to warm to ꢂ40 1C for
2.5 h, and hydrolysed with saturated aqueous NH4Cl solution.
The aqueous layer was separated, washed with diethyl ether, and
the united ether extracts were washed with water, dried over
anhydrous MgSO4, and evaporated to give a brown oil (4.5 g).
Chromatography (silica, CH2Cl2–MeOH 100% to 98%) gave
4.12 g (30 mmol; 52%) of 2 as a yellow oil. dH (300 MHz,
CDCl3): 2.40 (s, 3H, CH3); 2.69 (s, 3H, CH3CO); 7.61 (dd, 1H,
H4, J = 8.0 Hz, J0 = 0.6 Hz); 7.93 (d, 1H, H3, J = 8.0 Hz); 8.47
(dd, 1H, H6, J = 0.6 Hz).
Experimental
General points
Instrumentation. Nuclear Magnetic Resonance (NMR)
spectra for 1H and 13C were acquired on either a Bruker
AVANCE 300 (300 MHz), a Bruker AVANCE 400 (400
MHz) or a Bruker AVANCE 500 (500 MHz) spectrometer.
1
Carbons were assigned using HMQC and HMBC 2D H–13C
HETCORR experiments. Mass spectra were obtained using a
VG ZAB-HF (FAB) spectrometer, a VG-BIOQ triple quadru-
pole, positive mode or a Bruker MicroTOF spectrometer (ES-
MS). Cyclic voltammetry experiments were performed using
an EG&G Princeton Applied Research 273A potentiostat, a Pt
working electrode, a Pt counter electrode, a KCl-saturated
calomel electrode (SCE) or a silver wire as reference, and
0.1 M Bu4NPF6 as the supporting electrolyte. The EPR
spectra were recorded on an X-band Bruker spectrometer
(ESP-300-E) equipped with a rectangular TE 102 cavity. The
static field was measured with an NMR Gaussmeter (Bruker
ER035) while the microwave frequency was simultaneously
recorded with a frequency counter (HP-5350 B). Solutions
were degassed by bubbling argon directly into the EPR tube
prior to measurements. Temperature was measured with a
thermocouple (AuFe/Chromel) introduced inside the tube 1.5
cm from the bottom. An ESR900 cryostat (Oxford Instru-
ments) was used for the low-temperature measurements.
Computer simulations of the EPR spectra were performed
with the help of Simfonia (BRUKER) and WINEPR soft-
wares. UV-visible absorption spectra were performed using a
Kontron UVIKON 860 spectrophotometer.
4-Bromo-20-azachalcone: 3. 4-Bromobenzaldehyde (6.25 g;
33.8 mmol) was dissolved in 80 mL methanol and 25 mL
NaOH (1 M). 2-Acetyl-5-methylpyridine 2 (4.56 g; 33.8 mmol)
dissolved in methanol was added and a precipitate appeared
after 5 min. The reaction mixture was stirred for 30 more
minutes. The resulting precipitate was filtered off, dissolved in
CH2Cl2 and washed once with water. The organic phase was
dried over Na2SO4, filtered, and evaporated to dryness. The
residue was recrystallized from methanol to give 3 as a light-
yellow solid. Yield 8.76 g (29 mmol; 86%). dH (300 MHz,
CDCl3): 2.44 (s, 3H, CH3); 7.56 (m, 4H, Harom); 7.66–7.69
(dm, 1H, H4, J = 8.2 Hz); 7.81–7.86 (d, 1H, Ha, J = 16.1 Hz);
8.08–8.11 (dm, 1H, H3, J = 8.2 Hz); 8.26–8.31 (d, 1H, Hb, J =
16.1 Hz); 8.55 (m, 1H, H6); dC (75 MHz, CDCl3): 121.6; 122.7;
129.9; 130.1; 132.0; 134.5; 137.4; 142.8; 149.3; 153.7;
155.6; 158.0; 196.1; m/z (EI-MS): 301.0 (3, calc. for
C15H12BrNO: 301.0).
1-(5-Methyl-2-pyridylacetyl)pyridinium iodide: 4. To a solu-
tion of iodine (10.50 g; 41.4 mmol) in freshly distilled pyridine
(50 mL) was added 2-acetyl-5-methylpyridine 2 (5.08 g; 37.6
mmol). The mixture was refluxed under argon for 1 h, and
then stirred at room temperature overnight. The resulting
green precipitate was filtered off, washed with pyridine and
recrystallized from absolute ethanol. Yield 9.479 g (27.9 mmol;
74%). dH (300 MHz, DMSO-d6): 2.47 (s, 3H, CH3); 6.48
Chromatographic supports. Thin-layer chromatography was
performed using glass or plastic sheets coated with silica or
neutral alumina. They were examined after dipping in an
aqueous iron(II) solution (terpyridines), after oxidation with
iodine (other organic compounds) or under a UV lamp.
Column chromatography was carried out on silica gel (Kie-
selgel 60 (0.063–0.200 mm), Merck) or alumina (Aluminoxid
90 standardized (0.060–0.200 mm), Merck).
0
(s, 2H, CH2); 7.97 (m, 2H, H3-H4); 8.24–8.29 (dd, 2H, H2 ,
J = 7.8 Hz, J0 = 6.7 Hz); 8.71 (m, 1H, H6); 8.70–8.75 (tt, 1H,
0
0
0
H3 , J = 7.8 Hz, J = 1.4 Hz); 8.99–9.02 (dd, 2H, H1 , J =
5.5 Hz, J0 = 1.2 Hz).
Solvents and chemicals. Some solvents were dried in the
laboratory by distillation under argon, over the appropriate
drying agent: diethyl ether and dioxane over sodium–benzo-
phenone, dichloromethane over CaH2, and pyridine over
KOH. All other anhydrous solvents used are commercially
available (‘‘analytical grade’’): dimethylformamide (dried with
molecular sieves) and methanol. All commercial chemicals
were of the best commercially available grade, and were used
without further purification, except n-BuLi which was titrated
40-(4-Bromophenyl)-5,500-dimethyl-2,20:60,200-terpyridine: 5.
4-Bromo-20-azachalcone 3 (6.04 g; 20 mmol), 1-(5-methyl-2-
pyridylacetyl)pyridinium iodide 4 (6.80 g; 20 mmol) and
ammonium acetate (39.3 g; 35 mmol) were dissolved in
50 mL of glacial acetic acid and refluxed for 7 h. The reaction
mixture was kept at room temperature for 14 h and was then
made alkaline with NaOH (10 M). The reaction mixture was
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extracted with CH2Cl2. The combined organic phases were
dried with anhydrous MgSO4 and evaporated on aluminium
oxide. Chromatography (400 g aluminium oxide, pentane–
CH2Cl2–EtOAc (8 : 2 : 1)) gave 4.98 g (12 mmol; 60%) of 5 as
a light-yellow solid. dH (300 MHz, CDCl3): 2.43 (s, 6H, CH3);
9.18–9.19 (d, 1H, Hp2, J = 2.4 Hz); 9.40–9.41 (d, 1H, Hp9
J = 2.4 Hz).
,
Acyclic phen–terpy conjugate: 1. To a degassed solution of 3-
bromo-8-(4-methoxyphenyl)-1,10-phenanthroline (7, 49 mg;
0.134 mmol) and Pd(PPh3)4 (7.8 mg; 0.007 mmol) in 10 mL
of toluene were added, under argon, 1 mL of a degassed
solution of 2 M aqueous Na2CO3 and a solution of 40-(4-
(neopentyl glycolatoboron)phenyl)-5,500-dimethyl-2,20:60,200-
terpyridine (6, 62 mg; 0.138 mmol) in 5 mL of toluene. It is
very important to respect the following sequence in the addi-
tions: (a) bromophenanthroline in toluene, (b) 3 vacuum–
argon cycles, (c) addition of the catalyst, (d) 3 vacuum–argon
cycles, (e) addition of the degassed solution of Na2CO3, (f) 3
vacuum–argon cycles, (g) addition of the degassed solution of
the boronic ester. The reaction was monitored by TLC, and
after 30 h of reflux, the reaction mixture was allowed to cool to
room temperature. The solvent was removed by rotary eva-
poration and the crude mixture was taken in CH2Cl2 and
washed with water. The combined organic layers were dried
over Na2SO4 and the solvent evaporated. Chromatography
(aluminium oxide, CH2Cl2 to CH2Cl2–MeOH (99 : 1)) gave
20 mg (0.032 mmol; 24%) of pure product 1 as a white solid.
00
7.61–7.64 (dm, 2H, Hm2); 7.67–7.69 (dm, 2H, H4-H4 , J = 8.0
00
Hz); 7.76–7.79 (dm, 2H, Ho2); 8.53–8.56 (d, 2H, H3-H3 , J =
00
0
0
7.9 Hz); 8.54 (m, 2H, H6-H6 ); 8.63 (s, 2H, H3 -H5 ); dC (125
MHz, CDCl3): 18.43 (CH3); 117.96 (30); 120.92 (3); 123.34 (x);
128.93 (o2); 132.02 (m2); 133.61 (5); 137.43 (4); 137.63 (y);
148.93 (40); 149.56 (6); 153.65 (2); 156.17 (20); m/z (EI-MS):
414.9 (5, calc. for [M]: 415.1); anal. calc. for C23H18BrN3: C,
66.36; H, 4.36; N, 10.09. Found: C, 66.38; H, 4.52; N, 10.01%.
40-(4-(Neopentyl glycolatoboron)phenyl)-5,500-dimethyl-2,20:-
60,200-terpyridine: 6. A round-bottom flask was charged with
Pd(dppf)Cl2 (6 mg; 0.007 mmol), KOAc (70.7 mg; 0.721
mmol), bis(neopentyl glycolato)diboron (B2neo2, 57 mg;
0.252
mmol)
and
40-(4-bromophenyl)-5,500-dimethyl-
2,20:60,200-terpyridine (5, 100 mg; 0.240 mmol) and flushed
with nitrogen. Freshly distilled dioxane (10 mL) was then
added and the mixture was heated at 80 1C for 18 h. It was
then diluted with toluene and the resulting solution washed
with water. The toluene layer was dried over Na2SO4 and the
solvent removed by rotary evaporation. The residue was dried
overnight on a vacuum pump giving 6 as a brownish white
solid (quantitative yield). It was used directly for the next step
without further purification. dH (300 MHz, CDCl3): 1.05 (s,
6H, CH3neo); 2.43 (s, 6H, CH3); 3.81 (s, 4H, CH2neo); 7.65–7.69
dH (300 MHz, CDCl3): 2.44 (s, 6H, CH3); 3.90 (s, 3H, OCH3);
7.08–7.11 (dm, 2H,0Ho1, J = 8.8 0H0 z); 7.67–7.71 (dm, 2H, H4-
00
H4 , J = 8.1 Hz, J = 2.0 Hz, J = 0.5 Hz); 7.72–7.75 (dm,
2H, Hm1, J = 8.8 Hz); 7.88 (d, 2H, Hp5,p6, J = 1.5 Hz);
7.91–8.11 (dd, 4H, Hm2-Ho2, J = 8.3 Hz); 8.34 (d, 1H, Hp7
,
J = 2.3 Hz); 8.46 (d, 1H, Hp4, J = 2.3 Hz); 8.57 (m, 2H, H6-
0
00
00
(ddd, 2H, H4-H4 , J = 8.2 Hz, J = 2.2 Hz, J = 0.7 Hz);
00 00 0
H6 ); 8.56–8.58 (d, 2H, H3-H3 , J = 7.4 Hz); 8.75 (s, 2H, H3 -
00
7.88–7.94 (dm, 4H, Hm2-Ho2); 8.54–8.56 (d, 2H, H3-H3 , J =
0
H5 ); 9.42 (d, 1H, Hp9, J = 2.25 Hz); 9.50 (d, 1H, Hp2, J =
0
00
7.5 Hz); 8.54–8.56 (dt, 2H, H6-H6 , J = 2.2 Hz, J = 0.7 Hz);
2.25 Hz); dC (75 MHz, CDCl3): 18.48 (CH3); 55.47 (OCH3);
114.78 (o1); 118.16 (30); 120.96 (3); 127.06 (p5); 127.24 (p6);
127.97 (m2); 128.21 (o2); 128.37 (p13); 128.67 (p14); 128.69
(m1); 130.00 (p); 132.59 (p7); 133.41 (p4); 133.57 (5); 134.92
(x); 135.46 (p8); 137.44 (4); 138.68 (y); 144.72 (p11); 145.40
(p3); 146.02 (p12); 149.30 (p2); 149.36 (p9); 149.43 (40); 149.62
(6); 153.80 (2); 156.19 (20); 160.07 (i); m/z (HR ES-MS):
622.254 (1, calc. for [M + H]: 622.260); DOSY NMR
(500 MHz, CD2Cl2): D = 1000 mm2 sꢂ1; rh = 5.3 A.
0
0
8.69 (s, 2H, H3 -H5 ); dC (75 MHz, CDCl3): 18.44 (CH3); 21.95
(CH3neo); 31.92 (Cneo); 72.35 (CH2neo); 118.29 (30); 120.90 (3);
126.46 (o2); 132.77 (x); 133.41 (5); 134.38 (m2); 137.36 (4);
140.55 (y); 149.55 (6); 150.13 (40); 153.88 (2); 155.97 (20); m/z
(ES-MS): 450.24 (6, calc. for [M]: 450.23).
3-Bromo-8-(4-methoxyphenyl)-1,10-phenanthroline: 7. To a
degassed solution of 3,8-dibromo-1,10-phenanthroline
(100 mg; 0.296 mmol) and Pd(PPh3)4 (18 mg; 0.015 mmol)
in 5 mL of toluene were added, under argon, 1.5 mL of a
degassed solution of 2 M aqueous Na2CO3 and a solution of
p-anisylboronic acid (45 mg; 0.296 mmol) in 2 mL of toluene
with a few drops of methanol. It is very important to respect
the following sequence in the additions: (a) dibromophenan-
throline in toluene, (b) 3 vacuum–argon cycles, (c) addition of
the catalyst, (d) 3 vacuum–argon cycles, (e) addition of the
degassed solution of Na2CO3, (f) 3 vacuum–argon cycles, (g)
addition of the degassed solution of the boronic acid. The
reaction was monitored by TLC, and after 14 h of reflux, the
reaction mixture was allowed to cool to room temperature.
The solvent was removed by rotary evaporation and chroma-
tography (aluminium oxide, pentane–CHCl3 (1 : 1)) gave 50
mg (0.137 mmol; 46%) of pure product as a slightly yellow
solid. dH (300 MHz, CDCl3): 3.90 (s, 3H, OCH3); 7.06–7.11
(dm, 2H, Ho1, J = 8.8 Hz); 7.70–7.75 (dm, 2H, Hm1, J = 8.9
Hz); 7.72–7.89 (dd, 2H, Hp5,p6, J = 9.0 Hz); 8.33–8.34 (d, 1H,
Dimer complex with zinc(II): [Zn2ꢁ(1)2]ꢁ4OTf. Phen–terpy
conjugate 1 (10 mg; 0.016 mmol) was dissolved in 0.25 mL
of CD2Cl2. A solution of Zn(OTf)2 in CD3OD (23.8 mg in
1 mL) was prepared, and 0.25 mL (0.016 mmol) was added to
the ligand solution, which became clear and orange. The
solution was transferred to an NMR tube and the reaction
1
was monitored by H NMR spectroscopy. After 6 h at room
temperature and 22 h at 30 1C, the NMR spectrum remained
the same as after 1 h of reaction. The solvent was then
evaporated and the crude mixture taken in methanol, filtered,
and the filtrate evaporated to dryness yielding [Zn2ꢁ(1)2]ꢁ4OTf
as a yellow solid (10.5 mg; 78%). dH (500 MHz, CD3OD): 2.37
(s, 6H, CH3); 4.02 (s, 3H, OCH3); 6.68 (s, 1H, Hp2); 7.35–7.37
(d, 2H, Ho1, J = 8.85 Hz); 7.64–7.66 (dm, 2H, Hm2, J =
8.0 Hz); 8.12 (m, 2H, H4); 8.14–8.16 (dm, 2H, Ho2, J =
00
8.0 Hz); 8.20 (m, 4H, Hp5-Hp6-Hm1); 8.25 (m, 2H, H6-H6 );
00
8.44–8.46 (d, 1H, Hp9); 8.76–8.78 (d, 2H, H3-H3 , J = 8.1 Hz);
0 0
8.94 (m, 1H, Hp4); 9.04 (s, 2H, H3 -H5 ); 9.39 (s, 1H, Hp7); m/z
H
p7, J = 2.4 Hz); 8.40–8.41 (d, 1H, Hp4, J = 2.3 Hz);
ꢀc
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(HR ES-MS): 342.592 (calc. for [Zn2(1)2]4+: 342.590); 506.439
(calc. for [Zn2(1)2, OTf]3+: 506.438); 834.681 (calc. for
8 E. C. Glazer, D. Magde and Y. Tor, J. Am. Chem. Soc., 2005,
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16, 277.
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and A. De Cian, Angew. Chem., Int. Ed., 2000, 39, 1295.
17 M. C. Jimenez-Molero, C. Dietrich-Buchecker and J. P. Sauvage,
Chem.–Eur. J., 2002, 8(6), 1456.
18 T. Kraus, M. Budesinksy, J. Cvacka and J.-P. Sauvage, Angew.
Chem., Int. Ed., 2006, 45(2), 258.
19 M. Fujita, M. Tominaga, A. Hori and B. Therrien, Acc. Chem.
Res., 2005, 38(4), 371.
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853.
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Rev., 2004, 33(3), 133.
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Neuburger, S. Schaffner, E. R. Schofield and C. B. Smith,
Chem.–Eur. J., 2006, 12(17), 4600.
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[Zn2(1)2, 2OTf]2+
: 834.637); DOSY NMR (500 MHz,
CD3OD): D = 470 mm2 sꢂ1; rh = 8.5 A; ellipsoid parameters:
a = 14 A; b = c = 6 A.
Dimer and trimer complexes with copper(II): [Cu2(1)2]ꢁ4BF4
and [Cu3(1)3]ꢁ6BF4. Phen–terpy conjugate 1 (12.5 mg; 0.020
mmol) was dissolved in 2 mL of CH2Cl2. A solution of
Cu(BF4)2 in CH3CN (47.7 mg in 10 mL) was prepared, and
1 mL was added to the ligand solution, which turned instan-
taneously clear and olive green. The solution was left to stir for
19 h at room temperature, and by addition of diethyl ether, a
green solid precipitated out, which was then filtered, washed,
dissolved again in an acetone–acetonitrile–methylene chloride
mixture, and recovered as a solid by addition of diethyl ether
in a good yield (13.8 mg; 89%). m/z (HR ES-MS): 342.6107
(calc. for [Cu2(1)2]4+
: :
342.5909; calc. for [Cu3(1)3]6+
342.5912); 428.5336 (calc. for [Cu3(1)3, BF4]5+: 428.5102);
485.8158 (calc. for [Cu2(1)2, BF4]3+: 485.7893); 557.1697 (calc.
for [Cu3(1)3, 2BF4]4+: 557.1386); 772.2273 (calc. for [Cu2(1)2,
2BF4]2+: 772.1861; calc. for [Cu3(1)3, 3BF4]3+: 772.1864);
UV-Vis (CH2Cl2
(1.2 ꢃ 105); 359 (9.2 ꢃ 104); 573 (560).
+ n-Bu4NPF6 0.1 M) lmax (e): 292
Acknowledgements
Funding by the Region Alsace and the CNRS (fellowship to
´
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B. C.) is gratefully acknowledged. We warmly thank Dr Lionel
Allouche for the DOSY NMR experiments and explaining the
ins and outs of this technique, and Patrick Wehrung for his
professionalism and efficiency in the ES-MS measurements.
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1054 | New J. Chem., 2008, 32, 1048–1054