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Chemistry Letters Vol.37, No.9 (2008)
Facile Preparation of Polytopic Azoles: Synthesis, Characterization,
and X-ray Powder Diffraction Studies of 1,4-Bis(pyrazol-4-yl)-
and 1,4-Bis(tetrazol-5-yl)benzene
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Angelo Maspero, Simona Galli, Norberto Masciocchi, and Giovanni Palmisano
Dipartimento di Scienze Chimiche e Ambientali, Universit a` dell’Insubria, via Valleggio 11, 22100 Como, Italy
(Received May 22, 2008; CL-080516; E-mail: simona.galli@uninsubria.it, angelo.maspero@uninsubria.it)
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Two polytopic azoles, 1,4-bis(pyrazol-4-yl)benzene and
,4-bis(tetrazol-5-yl)benzene, were prepared in sizable amounts
bis(malondialdehyde) (5) (or its synthetic equivalents) with
hydrazine. Within this context, vinamidinium salts [readily
accessible through a Vilsmeier–Haack–Arnold (VHA) formyla-
1
by high yield syntheses employing, in mild conditions, cheap re-
actants and, whenever possible, aqueous solutions. The two spe-
1
0
tion ] have also been successfully utilized to construct substitut-
11
1
13
cies were characterized by H and C NMR spectroscopy and
by thermal analyses, the latter evidencing their high chemical
and thermal stability. X-ray powder diffraction methods dis-
closed their non isomorphous crystal structures, in which indi-
vidual molecules interact via hydrogen bonds to form two-di-
mensional sheets.
ed pyrazoles. It is of interest to note that very few 4-aryl-sub-
stituted pyrazoles have been prepared by such procedure. Such
considerations lead to the generation of the bis(vinamidinium)
8
salt 4 as one possible intermediate (Scheme 2). Thus, 1 was best
prepared from commercially available p-phenylenediacetic acid
(3) by a sequence of reactions commencing with the VHA
ꢁ
reaction (POCl3, DMF, 90 C, 11 h; overnight at rt) followed
by quenching (H2O, rt) and metathesis with NaClO4 in water.
Tackling the necessity of isolating the rather unstable tetralde-
hyde 5, the resulting bis(perchlorate) 4 was directly reacted
with hydrazine monohydrate (refluxing EtOH, 1 h) to provide
the required 1 (76% over two steps). Its D2h symmetry was
Polyazoles have recently witnessed a blooming interest, due
to their application in the pharmaceutical industry (as antifungal,
antiprotozoal, and antihypertensive agents), as well as flame
retardants1 or corrosion inhibitors in a number of industrial
processes, along with chemical mechanical planarization of
1
clearly evident in its greatly simplified H NMR spectrum and
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2
3
semiconductors and antifreeze formulations. Moreover, their
deprotonated forms have been extensively used in the formation
of porous coordination polymers (PCP’s) capable of selective
8
four-line C NMR spectrum.
Commercially available terephthalonitrile could be convert-
ed to the bistetrazole 2, either by cycloaddition with sodium
azide in the presence of triethylammonium chloride (refluxing
4
gas adsorption and sensing, or of spin crossover for high-tech
applications.5 Therefore, the quest for novel and accessible
routes to polyazoles, employing cheap reactants in mild and en-
vironmentally friendly conditions, has been widely pursued,
making these species readily, and widely, available.
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toluene) or, more preferably, by reacting it with stoichiometric
13
NaN3 in the presence of ZnBr2 in refluxing water. Utilization
of the Demko Sharpless protocol allowed for the conversion of
terephthalonitrile to the ligand 2 in 75% yield (and 36 h) without
need of organic solvents and large excess of sodium azide.
Interestingly, also the use of stoichiometric amounts of
ZnCl2 allows the recovery of 2, although in slightly lower yield
In the realm of PCP’s, there appear very promising those
polyazoles whose length can be modulated by a ‘‘linear’’ spacer
separating the heterocycles: indeed, they can tune the distance
between the polyazole-bridged transition-metal ions, thus allow-
ing the optimization of the PCP’s (electrical, magnetic, catalytic,
sorptive) functional properties, as it has already been properly
shown in two seminal papers by Long and co-workers.6
With the goal of preparing 1,4-bis(azolyl)benzenes to be po-
tentially exploited as long spacers in polynuclear coordination
(ca. 60%). During the syntheses in aqueous environment, the
already known hydrated form of 1,4-bis(tetrazol-5-yl)benzene,
.
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.
2
H2O, is formed (XRPD and IR evidences). 2 H2O is quanti-
ꢁ
tatively transformed into 2 by heating it at 90 C overnight in
an oven (XRPD and IR evidences). Differently, when toluene
is employed as a solvent, the anhydrous form 2 is directly
recovered.
6
complexes and, possibly, nanostructured PCP’s, we tailored
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the syntheses of 1,4-bis(pyrazol-4-yl)benzene (H2bpb, 1) and
8
1,4-bis(tetrazol-5-yl)benzene (H2btb, 2; see Scheme 1). The
pure, crystalline phases, isolated in sizeable amounts, were
1
13
fully characterized by H and C NMR spectroscopy, thermal
TG and DSC) analyses and, above all, ab initio X-ray powder
diffraction (XRPD) methods.
could be derived by heterocyclization of p-phenylene-
(
1
H
H
N
N
N
N
N
N
N
N
N
N
N
N
H
H
1
2
ꢁ
Scheme 1. Schematic drawing of the 1,4-bis(pyrazol-4-yl)-
benzene (1, left) and 1,4-bis(tetrazol-5-yl)benzene (2, right)
molecules.
Scheme 2. a) POCl3, DMF, 90 C, 11 h then H2O; b) NaClO4,
H2O c) N2H4, H2O, EtOH reflux 1 h; d) NaN3, ZnBr2, reflux
36 h.
Copyright Ó 2008 The Chemical Society of Japan
Maspero, Angelo
