Synthesis of copper halide coordination polymers with ligands formed by in situ cyclization of 2-aminopyrimidine and ethanol

Article abstract of DOI:10.1002/ejic.200701126

The design and synthesis of coordination polymers from transition metals and organic ligands have been extensively studied for their crystallographic diversity and potential applications. Recently, the synthesis of coordination polymers by hydro(solvo)thermal in situ metal/ligand reactions has drawn great interest because of its potential to generate novel coordination architectures and new organic reactions. As described in our manuscript, the nitrogen heterocyclic 2,3-dihydroimidazo[1,2-a]pyrimidine (C₆H ₇N₃) ligand was synthesized by an in situ reaction starting from 2-aminopyrimidine and ethanol. At the same time, two luminescent copper halide coordination polymers, (CuCl)₃C₆H ₇N₃ and (CuI)₂C₆H₇N ₃, were assembled under solvothermal conditions. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200701126

SHORT COMMUNICATION
DOI: 10.1002/ejic.200701126
Synthesis of Copper Halide Coordination Polymers with Ligands Formed by In
Situ Cyclization of 2-Aminopyrimidine and Ethanol
Minghui Bi,[a] Guanghua Li,[a] Jia Hua,[a] Yingjie Lin,[a] Junjun Cao,[a] Zhan Shi,*[a] and
Shouhua Feng[a]
Keywords: Coordination polymers / Copper / Halides / In situ cyclization
The design and synthesis of coordination polymers from tran-
sition metals and organic ligands have been extensively
studied for their crystallographic diversity and potential ap-
plications. Recently, the synthesis of coordination polymers
by hydro(solvo)thermal in situ metal/ligand reactions has
drawn great interest because of its potential to generate
novel coordination architectures and new organic reactions.
As described in our manuscript, the nitrogen heterocyclic
2,3-dihydroimidazo[1,2-a]pyrimidine (C6H7N3) ligand was
synthesized by an in situ reaction starting from 2-amino-
pyrimidine and ethanol. At the same time, two luminescent
copper halide coordination polymers, (CuCl)3C6H7N3 and
(CuI)2C6H7N3, were assembled under solvothermal condi-
tions.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
their self-assembly under solvothermal conditions to afford
luminescent a copper(I) layer and a chain polymer, (CuCl)3-
C6H7N3 (1) and (CuI)2C6H7N3 (2) (C6H7N3 = 2,3-dihy-
droimidazo[1,2-a]pyrimidine), respectively. We found an in
situ cycloaddition of 2-aminopyrimidine and EtOH.
Introduction
Hydro(solvo)thermal in situ metal/ligand reactions, as a
new bridge between coordination chemistry and organic
synthetic chemistry,[1] are of great interest for the discovery
of novel coordination architectures Ϫ especially those that
are inaccessible by direct preparation Ϫ and organic reac-
tions.[2] Although in situ metal/ligand reactions have been
extensively investigated for many decades, only a few kinds
of organic ligand in situ reactions have been found under
hydro(solvo)thermal conditions, such as the transformation
of inorganic and organic sulfur,[3c] dehydrogenative carbon–
carbon coupling,[3b] hydroxylation of aromatic rings,[3a] and
cycloaddition of organic nitriles with azide and ammo-
nia.[3d] The exploration of new in situ metal/ligand reactions
has remained a challenge for researchers in both coordina-
tion and organic chemistry.
Results and Discussion
Single-crystal X-ray structure analysis of the two com-
pounds showed that compound 1 is a two-dimensional in-
organic–organic CuCl coordination polymer and that com-
pound 2 is a one-dimensional hybrid CuI chain. The struc-
ture of compound 1 can be decomposed into two parts of
crystallographically independent metal atom centers (Fig-
ure 1). The Cu center, a Cl atom, and the ligand make up
a metal–ligand chain, and the Cu center adopts a distorted
tetrahedral geometry coordinated to two Cl atoms and two
N atoms from the ligand. The other part of the structure is
a (CuCl)6 chain, which is constructed by combination of
two chair-shaped trinuclear Cu3Cl3 units that are joined
through six Cl anions. The unit structure feature of the
chain is similar to the double six-membered (D6R, hexago-
nal prism) rings found in zeolites, and this structure is an
important and attractive unit in zeolites.[6] As shown in Fig-
ure 1, each metal–ligand chain connects two double six-
membered rings through the Cl atoms to form the 2D grid
of compound 1. The structure of compound 2 is a zigzag
ladder chain; each copper cation serves as a tetrahedral co-
ordination site where each iodine anion is coordinated to
three copper cations (Figure 2). This structure can be
attributed to the ligand, and it is different from other ladder
A few kinds of ligand in situ reaction have been found
in copper halides system,[4] but the use of the reduction of
Cu2+ to Cu+ is rare relative to the efforts directed towards
1–
CuX (X = halide).[5] Because the oxidation ability of XO4
is much stronger than that of Cu2+, we used not only the
1–
reduction of Cu2+ to Cu+, but also the reduction of XO4
to X– in order to discover novel structures. In this com-
munication, we report two examples of the simultaneous
1–
redox of Cu2+ to Cu+ and XO4 to X– (X = Cl, I) and
[a] State Key Laboratory of Inorganic Synthesis & Preparative
Chemistry, College of Chemistry, Jilin University,
Changchun 130012, P. R. China
Fax: +86-431-85168624
E-mail: zshi@mail.jlu.edu.cn
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2008, 1035–1038
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M. Bi, G. Li, J. Hua, Y. Lin, J. Cao, Z. Shi, S. Feng
SHORT COMMUNICATION
chains reported so far. The distance of the two coordination
One of the interesting features in the synthesis of the two
nodes of the ligand is 2.4 Å, which is shorter than twice the compounds is that during the hydrothermal reaction, the
bond length of CuI making the ladder zigzag.
nitrogen heterocyclic 2,3-dihydroimidazo[1,2-a]pyrimidine
ligand was formed in situ, as illustrated in Scheme 1.
Among the solvothermal in situ reactions reported, cyclo-
addition reactions are rare. The synthesis of 3,5-dimethyl-
1,2,4-triazole under solvothermal conditions is the only
cycloaddition reaction that has been reported,[8] and the
formation of a ligand by ethanol reactions has never been
reported. So, this is the first example of a nitrogen hetero-
cycle synthesized by an ethanol in situ reaction. The synthe-
sis of 2,3-dihydroimidazo[1,2-a]pyrimidine was reported by
Kochergin and coworkers in a routine organic reaction by
using 1,2-dibromoethane and 2-aminopyrimidine,[9] but the
generation of 1,2-diiodoethane was impossible under our
reaction conditions. According to the mechanism proposed
by Kochergin, we speculate that the mechanism for the for-
mation of 2,3-dihydroimidazo[1,2-a]pyrimidine in our sys-
tem involves four steps. The first step is the conversion of
some ethanol into iodoethane, which is an easy reaction
because there are some I– anions in our system (we checked
the liquid after the reaction and found the I– anions). The
second step is the alkylation of 2-aminopyrimidine, in
which iodoethane attacks the N atom of the 2-aminopyrim-
idine ring to destroy aromaticity (this step is similar to the
Kochergin routine[9]). The third step, which is the most im-
portant one, is HIO4 oxidation of –CH3 to –CHO. The
fourth step is the formation of the five-membered ring.
Each –CHO and each –NH2 dehydrate to generate 2,3-dihy-
droimidazo[1,2-a]pyrimidine. To test our mechanism, we
used trapping agents such as hydrazine and 1,2,4-triazole
to capture the aldehyde intermediates. Unfortunately, our
reaction system involves oxidative and high-temperature
conditions, in which the trapping agent is not stable. So, we
Figure 1. Two-dimension net of compound 1 (a) and connection
between the six-membered rings (b).
Figure 2. Single zigzag ladder chain of compound 2.
Like most crystals synthesized by solvothermal reactions, had to choose an indirect method to prove our hypothesis.
the two compounds are stable in air and water but soluble By using 2-aminopyrimidine and 2-bromoacetaldehyde as
in aqueous HCl. Copper halides are easily dissolved in starting chemicals, we obtained 2,3-dihydroimidazo[1,2-a]-
CH3CN but the ligand is indiscerptible, which facilitates the pyrimidine, which is a good attestation to our hypothesis
isolation of the pure ligand. After characterizing its struc- (see Figure S2, Supporting Information).
ture by X-ray single-crystal structure analysis, we also car-
ried out 1H NMR spectroscopic measurements of the li-
1
gand to ensure its structure. The H NMR spectrum of the
ligand [(500 MHz, [D6]DMSO, 25 °C): δ = 3.9 (t, J = 10 Hz,
2 H), 4.6 (t, J = 10 Hz, 2 H), 6.9 (t, J = 5 Hz, 1 H), 8.4 (d,
J = 5 Hz, 1 H), 8.6 (d, J = 2.5, 1 H) ppm] is consistent with
the assigned structure, which indicates that our determi-
nation of the crystal structure is correct (see Figure S1, Sup-
porting Information). Nitrogen heterocyclic complexes, as
key units in medicinal chemistry and versatile intermediates
in organic synthesis, have been extensively studied in or-
ganic synthetic chemistry for the past years.[7] Continuous
Scheme 1. The in situ reaction of 2-aminopyrimidine and EtOH.
efforts have been focused on the search for simpler but more
efficient synthetic procedures for heterocycles. Relative to
Similar to other in situ reactions, pressure also proved to
conventional routes, metal/ligand in situ reactions are sim- be effective for the dehydrogenation of methyl when a suit-
ple and convenient synthetic procedures for nitrogen-con- able transition-metal salt was present. We speculate that the
taining heterocycles; thus they represent attractive and oxidation of Cu2+ to Cu+ is very important, because when
interesting methods in synthetic organic and medicinal we changed Cu to other metals such as Zn, Mn, or Co this
chemistry.
reaction did not proceed.
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 1035–1038

Synthesis of Copper Halide Coordination Polymers
109.91(2)°, β = 100.64(3)°, γ = 109.24(2)°, V = 515.8(6) Å3, Z = 2,
ρcalcd. = 3.232 gcm–3, R1 = 0.0400 [2336 IϾ2σ(I)] and wR2 =
0.0924 (all 5095 unique data) for 116 variables, GOF = 1.077.
CCDC-655716 and -655717 (for 1 and 2, respectively) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Similar to other copper halide complexes, the two com-
pounds exhibit photoluminescent properties (see Figures S3
and S4, Supporting Information). Intense emission oc-
curred at 585 nm for compound 1 and at 582 nm for com-
pound 2 (λex = 390 nm) in the solid state at room tempera-
ture. According to the photoluminescent properties of other
copper halide clusters, the origin of the emission of the two
compounds is likely to involve the cluster-centered triplet
excited state mixed with some halide-to-metal charge trans-
fer (3LMCT) character. The existence of a “metal-cluster-
centered” excited state is supported by a Cu···Cu nonbond-
ing interaction.[10]
Supporting Information (see footnote on the first page of this arti-
cle): Crystal data and structural refinement data, selected bond
lengths and angles, selected synthetic procedures, X-ray diffraction
patterns, and solid-state emission spectra of compounds 1 and 2.
Acknowledgments
Conclusions
This work was supported by the National Natural Science Founda-
tion of China (No. 20121103, 20671040, and 20601010), the
National High-Tech R&D Program (863 program) of China, and
the Fuk Ying Tung Education Foundation.
In summary, we prepared two copper halide compounds
by a solvothermal redox reaction and in situ ligand synthe-
sis, which provides a new strategy for the preparation of
coordination polymers and nitrogen heterocycles. As we
know, nitrogen-containing heterocycles are structural con-
stituents of many bioactive natural products, medicinally
important compounds, and organic materials. The nitrogen
heterocyclic compound 2,3-dihydroimidazo[1,2-a]pyrimid-
ine, which contains two activated nitrogen atoms, can act
as a template for solid frameworks or as a starting material
for the conversion of other ring systems, as it contains un-
saturated C–N bonds. We will continue to work in this area,
and we expect that more progress will be made on the pres-
ent reaction, for example, by using other alcohols, such as
propanol and butanol.
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Experimental Section
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¯
group P1, a = 7.781(5) Å, b = 8.648(6) Å, c = 9.163(7) Å, α =
Eur. J. Inorg. Chem. 2008, 1035–1038
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M. Bi, G. Li, J. Hua, Y. Lin, J. Cao, Z. Shi, S. Feng
SHORT COMMUNICATION
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Received: October 17, 2007
Published Online: January 25, 2008
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Eur. J. Inorg. Chem. 2008, 1035–1038