Metallacyclophanes formed by a tetrapyrazolyl ligand and copper(II) cation

Article abstract of DOI:10.1039/b006665f

Using a tetrakis(pyrazolyl)benzene ligand and CuCl₂ or Cu(CF₃SO₃)₂ salts, binuclear metallamacrocycles of cyclophane type have been exclusively obtained; structural characterisation by X-ray on single-crystal re

Full text of DOI:10.1039/b006665f

Metallacyclophanes formed by a tetrapyrazolyl ligand and copper(II) cation
Abdelaziz Jouaiti, Marielle Lo¨ı, Mir Wais Hosseini* and Andre´ De Cian
Laboratoire de Chimie de Coordinaiton Organique, Universite´ Louis Pasteur, F-67000 Strasbourg, France, UMR
CNRS 7513. E-mail: hasseini@chimie.u-strasbg.fr
Received (in Cambridge, UK) 15th August 2000, Accepted 18th September 2000
First published as an Advance Article on the web 19th October 2000
Using a tetrakis(pyrazolyl)benzene ligand and CuCl2 or
Cu(CF3SO3)2 salts, binuclear metallamacrocycles of cyclo-
phane type have been exclusively obtained; structural
characterisation by X-ray on single-crystal reveals that in
both cases, chloride or triflate anions are coordinated to Cu
metal centres adopting a square pyramial coordination
geometry.
Metallamarocycles, macrocyclic frameworks based on inter-
connection of organic ligands by metal cations, have been
attracting much attention over the past decade. Although the
first examples were reported by Saalfrank et al.1 and Fujita,2
many other groups are now active in the design and synthesis of
metallamacrocyles.3 However, as connecting metallic centres
the majority of examples reported so far are based on the use of
diamagnetic transition metals such as Pd(II) and Pt(II) requiring
square coordination geometry. Thus, using these metals, a
variety of metallamacrocycles has been reported using ligands
such as 4,4A-bipyridine, pyrimidine, bipyrazine, 4,7-phenan-
throline or bis-pyridines interconnected by rigid or flexible
spacers.4 Using pyrazolyl based ligands, we have previously
reported the formation of metallamacrocycles and metal-
latubulanes.5
Here, we report the design of new ligands based on pyrazolyl
units as coordination sites and its self-assembly into binuclear
metallamacrocycles using pentacoordinated paramagnetic
Cu(II) cation.
Ligands 1 and 2 (Scheme 1), both based on aromatic cores
(benzene or biphenyl) and bearing four pyrazolyl units, are
designed to act as tetradentate ligands. For ligand 1, two
different arrangements of the coordination sites may be
envisaged leading to either a seven (1A) or an eight membered
ring cyclic system (1B) upon chelating to metal cations
(Scheme 1). In both cases, owing to the disposition of the
coordination sites ligand 1 may form metallamacrocyles in the
presence of metals requiring square, octahedral or square
pyramidal coordination geometry. For the latter case, the two
possibilities (4A and 4B) are shown (Scheme 1). Ligand 2 was
designed as an extended analogue of ligand 1 thus allowing an
increase in the size of the metallamacrocycle.
Scheme 1
solution of CuCl2 or Cu(OTf)2 (5 mg) into a CHCl3 solution of
ligand 1 (2 mg). For both complexes, their structure was
investigated in the cystalline state by X-ray crystallography.
The reaction of 1 and CuCl2 in CHCl3–MeOH afforded a
green crystalline material which was structurally characterised
by X-ray diffraction (Fig. 2).† The solid contains the complex
unit [12Cu2(Cl2(CuCl4)2)] and two MeOH and CHCl3 solvent
molecules with no specific interactions with the complex. The
cationic part of the complex is indeed a metallamacrocycle
composed of two ligands 1, two Cu(II) cations and two Cl2
Ligand 1 was first prepared in 8% yield by reacting
1,2,4,5-tetrachlorobenzene with sodium pyrazolate in DMF at
95 ° C for 3 d. The yield could be increased to 68% by using
1,2,4,5-tetrabromobenzene and under reflux for 72 h. Pure
compound 1 was obtained as a colourless solid after chromatog-
raphy (SiO2, CH2Cl2–MeOH) and was characterised by X-ray
crystallography† (Fig. 1) which revealed the following relevant
bond distances and angles (dNN = 1.37 Å, dC(Ph)N = 1.42 Å;
NNCC dihedral angles of 225.8 and 277.2°). Ligand 2 was
6
prepared by a nickel coupling reaction using NiBr2(PPh3)2 in
the presence of Zn and NEt4I in THF using compound 3 as the
starting material. The latter was obtained upon treatment of
1,3,5-benzene by sodium pyrazolate in DMF at 95 °C for 4 d in
22% yield after chromatography [Al2O3, CH2Cl2–hexane
(8/2)].
Cu(II) was selected as the metal ion because of its
paramagnetic nature and the fact that it forms pentacoordinated
complexes. Both the chloride and triflate Cu(II) complexes have
been obtained as single-crystals upon slow diffusion of a MeOH
Fig. 1 The X-ray structure of free ligand 1. H atoms are omitted for clarity,
for bond length and distances see text.
DOI: 10.1039/b006665f
Chem. Commun., 2000, 2085–2086
This journal is © The Royal Society of Chemistry 2000
2085

Fig. 4 The X-ray structure of the metallamacrocycle [12Cu2(CF3SO3)2]2+
obtained between 1 and Cu(CF3SO3)2. Then triflate anions are disordered.
H atoms, anions and solvent molecules are omitted for clarity.
Fig. 2 The X-ray structure of the metalloamacrocycle [12Cu2Cl2]2+ obtained
between 1 and CuCl2. H atoms, anions and solvent molecules are omitted
for clarity.
coordination networks with tubular topology.5,7,8 In relation to
this, it may be of interest that, since the two anions occupying
the summit of the square pyramid on each Cu centre are oriented
in a divergent fashion, by interconnecting the metalloacyclo-
phanes new types of coordination polymers may be obtained
using bridging bidentate anionic ligands such as azido or
isocyanato anions.
In conclusion, the synthesis of paramagnetic binuclear copper
metallacyclophanes has been achieved and their solid state
structural elucidation revealed that the Cu(II) cation adopts a
slightly distorted square pyramidal geometry with the axial
position occupied either by chloride or triflate anion. The
formation of extended metallacyclophanes using ligand 2 is
being currently pursued. Furthermore, the interconnection of
the obtained metallamacrocyles leading to paramagnetic coor-
dination networks through the substitution of monodentate
coordinated anions by bidentate anions is currently under
investigation.
anions. Owing to the parallel orientation of the two phenyl
rings, the binuclear metallamacrocycle is of the cyclophane type
with an internal cavity of 4.29 3 7.42 Å (Scheme 1). The
coordination sphere around the pentacoordinated Cu(II) cations
is composed of four nitrogen atoms belonging to two ligands 1
and one chloride anion with a slightly distorted square
pyramidal geometry. The two poles of the ligand 1, composed
each of two pyrazolyl moieties (dNN = 1.37 Å, dC(Ph)N = 1.42
Å; NNCC dihedral angle of 57.8°) and occupying the square
base in the coordination sphere around the metal, act as
bidentate units and form two seven membered metallarings of
type 4A (Scheme 1) with Cu–N distances of ca. 2.01 Å and
NCuN angles of 86.9–91.4° (Scheme 1). The axial position is
occupied by a Cl anion with Cu–Cl distance of 2.44 Å. The two
positive charges on the [12Cu2Cl2]2+ complex are neutralised by
a [CuCl4]22 anion with dCuCl = 2.283 Å and ClCuCl angle of
90° (Fig. 3).
The [12Cu2(CF3SO3)2(CF3SO3)2] complex was obtained as a
blue-violet crystalline solid upon reaction of
1 and
Notes and references
Cu(CF3SO3)2 in CHCl3–MeOH. The latter complex was also
structurally characterised by X-ray diffraction (Fig. 4).† The
solid contains the complex unit [12Cu2(CF3SO3)2(CF3SO3)2]
and two CH2Cl2 solvent molecules with no specific interactions
with the complex. The triflate anions are disordered. The
cationic part of the complex of type 4A (Scheme 1) shows
almost identical structural features as the above chloride
complex (Scheme 1). Again a metallamacrocycle (internal
cavity of 4.16 Å 3 7.29 Å) composed of two ligands 1, two
Cu(II) cations and two triflate anions is observed. The
coordination sphere around the pentacoordinated Cu(II) cations
is, as in the chloride case, comprised of four nitrogen atoms
belonging to two ligands 1 and one triflate anion (dNN = 1.38
Å dC(Ph)N = 1.42 Å; NNCC dihedral angles of 259.6 and 58.9°,
Cu–N distances of ca. 1.99 Å and NCuN angles of 87.4–92.6°.
Interestingly, the axial position is occupied by a triflate anion
with Cu–O distance of 2.20 Å. The two positive charges on the
[12Cu2(CF3SO3)2]2+ complex are neutralised by two external
triflate anions (Fig. 4).
† Crystal data: (colourless, 294 K), C18H14N8, M = 342.37, triclinic, a =
6.384(1), b = 7.007(1), c = 9.941(1) Å, a = b = 76.00, g = 80.00, U =
416.5(2) Å3, Z = 1, space group P1, Dc = 1.36 g cm23, m = 0.089 mm21
,
¯
1508 data with I > 3s(I), R = 0.040, Rw = 0.0649. [(12Cu2Cl2(CuCl4))],
(green, 294 K), 2(CuClC18H14N8)·CuCl4·2CHCl3·2MeOH, M = 1390.91,
orthorhombic, a = 10.0302(5), b = 11.3568(6), c = 23.5388(7) Å, U =
2681.3(4) Å3, Z = 2, Immm, Dc = 1.72 g cm23, m = 1.830 mm21, 1486
data with I > 3s(I), R = 0.042, Rw = 0.052. [12Cu2(CF3SO3)2(CF3SO3)2],
(blue-violet, 173 K), C38H28Cu2F6N16O6S2·2CF3SO3·2CH2Cl2
M =
1577.95, orthorhombic, a = 19.7081(7), b = 17.9293(6), c = 17.1966(6)
Å, U = 6076.5(6) Å3, Z = 4, space group Cmca Dc = 1.72 g cm23, m =
1.121 mm21, 2127 data with I > 3s(I), R = 0.077, Rw = 0.096. Data for
all 3 structures have been obtained on a Nonius Kappa CCD (Mo-Ka)
diffractometer Structural determinations were performed using the Nonius
OpenMolenN package.9 CCDC 182/1781. See http://www.rsc.org/supp-
data/cc/b0/b006665f/ for crystallographic data in .cif format.
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We have previously reported examples of metallatubulanes
based on interconnection of metallamacrocyles into infinite 1-D
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Fig. 3 The packing of the dicationic metallamacrocycle [12Cu2Cl2] and
CuCl4 anions. H atoms and solvent molecules are not presented for
clarity.
22
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Chem. Commun., 2000, 2085–2086