Finally, it is interesting to note that 3,4-dicyanopyridine un-
dergoes regioselective reaction with the azide ion in the presence
of MnII at room temperature. Only the 4-cyano-group reacts
with the azide, producing 5-(3-cyano-4-pyridyl)-1H-tetrazole
(2a). Furthermore, 2a is formed, even in the presence of a large
(10-fold) excess of NaN3. Such regioselectivity opens up the
potential for preparing pyridyl-substituted tetrazoles.
talline 5-(2-pyridyl)-1H-tetrazole 0.27 g (yield 46% based on 2-
cyanopyridine) was produced. Anal. Calc. for C6H5N5 (1a): C,
48.98; H, 3.43; N, 47.60. Found: C, 48.93; H, 3.48; N, 47.58%.
IR/cm−1: 3090w, 3064w, 1747w, 1639w, 1603m, 1559s, 1485s,
1450s, 1401m, 1384m, 1285m, 1261m, 1159m, 1069m, 1025s,
1
949m, 795s, 743s, 704m, 631m. H NMR (DMSO-d6 solvent):
8.86 (m, 1H), 8.28 (m, 1H), 8.14 (m, 1H), 7.70 (m, 1H).
5-(3-cyano-4-pyridyl)-1H-tetrazole (2a).
Experimental
Method A. This was prepared as for 1a, and 4 mmol
pyridine-3,4-dicarbonitrile and 4 mmol NaN3 were used. Yield:
0.38g, 56% based on pyridine-3,4-dicarbonitrile. Anal. Calc. for
C7H4N6 (2a): C, 48.84; H, 2.34; N, 48.82. Found: C, 48.79; H,
2.37; N, 48.78%. IR/cm−1: 3058w, 3024w, 2239m, 1738w, 1577s,
1548m, 1480s, 1403s, 1262m, 1215m, 1189m, 1043s, 865s, 817s,
All reagents were used as received from commercial sources.
The C, H, N microanalyses were carried out on a Carlo Erba
1108 Elemental Analyser by the University of Newcastle upon
Tyne microanalytical service. Infrared spectra (KBr pellets) were
recorded on a Perkin-Elmer 598 spectrometer. 1H NMR spectra
were recorded on a Bruker Avance 300 spectrometer.
1
743m, 587m. H NMR (DMSO-d6 solvent): 9.42 (s, 1H), 9.18
(d, 1H, J = 5.1 Hz), 8.27 (d, 1H, J = 5.1 Hz).
Method B:. Similar to Method A, but 4 mmol pyridine-3,4-
dicarbonitrile and 10 mmol NaN3 were used (yield 0.40 g, 58%
based on pyridine-3,4-dicarbonitrile). Microanalyses, infrared
and 1H NMR spectra confirm the identity of the product.
Syntheses
[Mn{5-(2-pyridyl)-tetrazolato}2(H2O)2] (1). Mn(NO3)2·4H2O
(2 mmol), NaN3 (4 mmol) and 2-cyanopyridine (4 mmol) were
added to 30 mL mixed solvent (methanol : water, 1 : 2), then
stirred at room temperature in air for 2 h. A small amount of
white precipitate was generated which was removed by filtration.
The filtrate (pH ca. 8) was slowly evaporated in air for 5 days
and colourless plate-like crystals of 1 were obtained (0.41 g;
54% yield based on Mn). Crystals of 1 are slightly soluble in
methanol or water and insoluble in ethyl acetate. Anal. Calc.
for C12H12MnN10O2 (1): C, 37.61; H, 3.16; N, 36.55. Found:
C, 37.63; H, 3.18; N, 36.56%. IR/cm−1: 3051w, 1608s, 1569m,
1465m, 1441s, 1291m, 1168m, 1058m, 1033m, 804s, 756s, 731s,
718m, 683m, 639m.
5-(4-pyridyl)-1H-tetrazole (3a).
Method A. This was prepared as for 1a,. Yield: 0.28 g, 48%
based on 4-cyanopyridine. Anal. Calc. for C6H5N5 (3a): C, 48.98;
H, 3.43; N, 47.60. Found: C, 48.92; H, 3.47; N, 47.56%. IR (KBr
pellet)/cm−1: 3084w, 3028w, 2968w, 1720w, 1594s, 1544s, 1498s,
1414s, 1384m, 1262m, 1206m, 991m, 937w, 779s, 747m, 664m.
1H NMR (DMSO-d6 solvent): 8.87 (d, 2H, J = 6.0 Hz), 7.88 (d,
2H, J = 6.0 Hz).
Method B. Similar to Method A, but the reaction solution
was heated at 60 ◦C for 3 h (yield: 0.44 g, 74% based on 4-
1
cyanopyridine). Microanalyses, infrared and H NMR spectra
[Mn{5-(3-cyano-4-pyridyl)tetrazolato}2(H2O)3(MeOH)] (2).
The procedure is identical to that of 1 except that 4 mmol of
pyridine-3,4-dicarbonitrile was used in place of 2-cyanopyridine.
In this case, 8 mmol NaN3 was used and the stirring time
increased to 4 h. The filtrate (pH 8–9) was slowly evaporated
in air for 9 days and colourless crystals of 2 were obtained
(0.50 g, 52% yield based on Mn). 2 is soluble in methanol, slightly
soluble in water and insoluble in ethyl acetate. Anal. Calc. for
C15H16MnN12O4 (2): C, 37.28; H, 3.34; N, 34.78. Found: C, 37.31;
H, 3.35; N, 34.80%. IR/cm−1: 3062w, 2239m, 1701m, 1608s,
1558m, 1447s, 1399m, 1372m, 1217m, 1195m, 1067s, 854m, 812s,
726s, 691s, 591m.
confirm the identity of the product.
Investigation of Catalysis by MnII. Mn(NO3)2·4H2O (0.1 g,
0.4 mmol), NaN3 (0.26 g, 4 mmol) and 4-cyanopyridine (0.416 g,
4 mmol) were added to 30 mL of mixed solvent (methanol :
water, 1 : 2), and stirred at room temperature for 24 h. The
methanol in the solution was removed in vacuo and then the
pH of the solution was adjusted to ca. 4.0 using 3 M HCl.
Upon acidification, ethyl acetate (30 mL) was added to the
mixture and stirred vigorously. The organic layer was separated
and the aqueous layer extracted again with another 30 mL
ethyl acetate. The ethyl acetate from the combined extracts was
removed in vacuo, and 0.32 g of white powder produced. The
powder product was characterised by H NMR spectroscopy;
this indicated it is a mixture containing ca. 15% of 5-(4-pyridyl)-
1H-tetrazole and 85% of 4-cyanopyridine.
It should be noted that 5-(4-pyridyl)-1H-tetrazole is more sol-
uble in water than 4-cyanopyridine. Consequently, the amount
of 5-(4-pyridyl)-1H-tetrazole in the reaction mixture prior to
workup could be somewhat higher than 15 : 85.
1
[Mn{5-(4-pyridyl)-tetrazolato}2(H2O)4]·2H2O (3). This was
prepared as for 1, with 4-cyanopyridine used in place of 2-
cyanopyridine. The filtrate (pH ca. 9) was slowly evaporated
in air for one week and colourless needle-like crystals of 3
were obtained (0.44 g, 48% yield based on Mn). 3 is soluble
in methanol, slightly soluble in water and insoluble in ethyl
acetate. Anal. Calc. for C12H20MnN10O6 (3): C, 31.64; H, 4.43;
N, 30.77. Found: C, 31.62; H, 4.45; N, 30.74%. IR/cm−1: 3078w,
1685w, 1624s, 1562m, 1447m, 1432s, 1378m, 1221m, 1157m,
1014s, 878m, 837m, 752m, 730m, 712s, 665m, 650m, 631m.
X-Ray crystallography
X-Ray diffraction studies of crystals 1 (size 0.30 × 0.30 ×
0.10 mm3) and 3 (size 0.22 × 0.20 × 0.14 mm3) were performed
on a Bruker SMART CCD area diffractometer, using Mo-Ka
5-(2-pyridyl)-1H-tetrazole (1a). The procedure is similar to
that of 1 but the generated precipitate was not removed after the
mixture solution was stirred for 3 h. The solvent was removed in
vacuo and the resulting solid powder washed with 10 mL ethyl
acetate to remove any unreacted 2-cyanopyridine. The crude
solid product {containing Mn–(2-PTZ) complex and inorganic
salts} was added to 10 mL water with stirring, and then the pH
of the aqueous solution (containing a white precipitate) adjusted
to ca. 4.0 using 3 M HCl. Upon acidification, the original
precipitate dissolved and another precipitate was produced.
Ethyl acetate (30 mL) was added to the mixture and stirred
vigorously until no solid was present. The organic layer was
separated and the aqueous layer extracted again with a further
30 mL of ethyl acetate. The ethyl acetate from the combined
extracts was removed in vacuo, and the colourless microcrys-
˚
radiation (k = 0.71073 A). Due to size limitations, data for 2 (size
0.04 × 0.04 × 0.04 mm3) were collected at station 9.8 of the SRS,
˚
Daresbury (k = 0.6948 A). Crystal data and other experimental
information are given in Table 7, with further details in the ESI†.
Semi-empirical absorption corrections, based on repeated and
symmetry-equivalent reflections.15 The structures were solved
by direct methods and refined by full-matrix least-squares on all
unique F2 values.16 Anisotropic displacement parameters were
assigned to all the non-hydrogen atoms. In all three cases the
hydrogen atoms on oxygen were refined with the O–H bond
˚
lengths restrained to 0.84(3) A; the hydrogen atoms on carbon
were placed in idealized positions and allowed to ride on their
respective parent atoms.
D a l t o n T r a n s . , 2 0 0 5 , 2 3 8 8 – 2 3 9 4
2 3 9 3