The structure of tris(3′,5′-dimethyl-pyrazol-1-yl)-s-triazine and its use as a ligand in coordination chemistry

Article abstract of DOI:10.1023/B:COHC.0000010658.00722.90

The crystal and molecular structure of the title compound (Me ₂-TPzT) has been determined by X-ray analysis. The observed molecular conformation presents the nitrogen atoms of three pyrazole rings in the same relative positions. The molecules are joined through intermolecular contacts forming chains that are arranged in a distorted hexagonal symmetry. Two complexes containing this ligand have been prepared: [{Pd(en)} ₃(Me₂-TPzT)](PF₆)₆ and [{Ag(PPh ₃)}₃(Me_2-TPzT)](ClO₄)₃, which, due to their insolubility, have been characterized only by microanalysis, IR, ¹H NMR and, in the latter case, by mass spectrometry.

Full text of DOI:10.1023/B:COHC.0000010658.00722.90

Chemistry of Heterocyclic Compounds, Vol. 39, No. 10, 2003
THE STRUCTURE OF TRIS(3',5'-DIMETHYL-
s
PYRAZOL-1-YL)- -TRIAZINE AND ITS USE
AS A LIGAND IN COORDINATION CHEMISTRY
A. Guerrero1, F. A. Jalon1, B. R. Manzano1, R. M. Claramunt2, P. Cabildo2, L. Infantes3,
F. H. Cano3, and J. Elguero4
The crystal and molecular structure of the title compound (Me2-TPzT) has been determined by X-ray
analysis. The observed molecular conformation presents the nitrogen atoms of three pyrazole rings in the
same relative positions. The molecules are joined through intermolecular contacts forming chains that are
arranged in a distorted hexagonal symmetry. Two complexes containing this ligand have been prepared:
[{Pd(en)}3(Me2-TPzT)](PF6)6 and [{Ag(PPh3)}3(Me2-TPzT)](ClO4)3, which, due to their insolubility, have
been characterized only by microanalysis, IR, 1H NMR and, in the latter case, by mass spectrometry.
Keywords: X-ray crystallography, pyrazole, s-triazine, palladium and silver complexes.
INTRODUCTION
Following the standard classification of heteroaromatic compounds, ligands used in coordination
chemistry can be divided into azoles and azines [1-3]. Trofimenko's scorpionates [4, 5] belong to the first class
and pyridine and phenanthroline derivatives to the second one [6-8]. Many groups have successfully used
ligands containing both azoles and azines. We have devoted some efforts to explore the structure, properties,
and coordinative abilities of 2,4,6-tris(pyrazol-1-yl)-1,3,5-triazines of general formula 1.
3
4
R
R
3'
4'
N
5
2'
3
1'
N
R
5'
2
1
5
N
4
N
R
N
6
N
N
5
N
3
4
R
R
N
5
R
3
4
R
R
1-5
2 R3 = R4 = R5 = H, TPzT; 3 R3 = R5 = H, R4 = Me, Me-TPzT; 4 R3 = R5 = H, R4 = Br, Br-TPzT; 5 R3 = R5 = Me, R4 = H, Me2-TPzT
__________________________________________________________________________________________
1
Departamento de Quimica Inorganica, Organica y Bioquimica, Facultad de Quimicas, Universidad de
2
Castilla la Mancha, Avda. C. J. Cela, 10, E-13071 Ciudad Real, Spain. Departamento de Quimica Organica y
Biologia, Facultad de Ciencias, UNED, Senda del Rey, 9, E-28040 Madrid, Spain. Departamento de
3
Cristalografia, Instituto de Quimica-Fisica "Rocasolano", CSIC, Serrano, 119, CSIC, E-28006 Madrid, Spain.
4 Instituto de Quimica Medica, Centro de Quimica Organica "Manuel Lora Tamayo", CSIC, E-28006 Madrid,
Spain; e-mail: igmbel7@iqm.csic.es. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1584-
1591, October, 2003. Original article submitted October 28, 2002.
1396
0009-3122/03/3910-1396$25.00©2003 Plenum Publishing Corporation

We have described the structure of tris(pyrazol-1-yl)-s-triazine (TPzT 2), both in the solid state (X-ray)
and in the gas phase (electron diffraction) [9], its basicity in water, and the X-ray structure of its picrate [10].
More recently, we reported other azol-1-yl-s-triazines [11] as well as tris-pyrazolyl-s-triazines with the pyrazolyl
substituents linked by the carbon [12]. Concerning their properties, we have described the behavior of the
palladium(II) complexes of tris(4-methylpyrazol-1-yl)-s-triazine (Me-TPzT, 3) and tris(4-bromopyrazol-1-yl)-s-
triazine (Br-TPzT 4) [13] and published a review on this topic [14]. Tris(3,5-dimethylpyrazol-1-yl)-s-triazine
(Me2-TPzT 5, the pyrazole part is usually named dmpz) was used by Orrell to prepare Re fluxional complexes
[15, 16] and by Chinese authors to obtain Eu(III) complexes and to demonstrate that their luminescence is
sensitive to π–π stacking and H-bonding interactions [17].
In the present paper we will discuss the structure of the ligand Me2-TPzT 5 and its Pd(II)/en
(en = ethylenediamine) 6 and Ag(I)/PPh3 7 complexes.
H C
3
–
H C
3
–
(PF
)
6
(ClO
)
3
6
4
NH
2
N
N
N
H N
2
CH
CH
3
PPh
3
3
Ph P
N
N
3
N
Ag
Pd
Ag
NH
N
H
2
Pd
N
N
N
2
H C
N
3
H C
3
N
N
N
N
N
N
CH
3
CH
3
N
N
Pd
H C
3
Ag
H C
3
H C
3
H C
3
NH
2
H N
PPh
2
3
7
6
RESULTS AND DISCUSSION
X-Ray Crystallographic Study
Since the structure has been deposited at the Cambridge Structural Database (CCDC number 188 400),
the geometrical parameters corresponding to Me2-TPzT 5 are not reported. A perspective drawing of the
molecule with the atom-labeling scheme is shown in Fig. 1. The bond lengths and angles are similar to those
observed in the TPzT molecule 2 [9]. The only difference concerns the effect of the methyl groups at positions 3
and 5 of the pyrazole ring. Comparison of the internal angles of the five-membered rings in the title compound
with those of the not disordered in the TPzT molecule (one out of three) [9] reveals the influence of the methyl
substituents [18,19] contracting the ipso angle and expanding the adjacent ones.
The nitrogen atoms, N(i2), of the pyrazole rings present the same relative position with respect to the
central triazine ring. The whole molecule does not have not planar conformation, because of the twist of one of
the dimethyl-3,5-pyrazole rings, 10° between the planes of the pyrazole and triazine rings (the two others are
nearly planar). In solution, we have estimated, from its NMR data, that Me2-TPzT 5 should have a dihedral
angle of 4.5° [11], which compares well with the average value of the three torsion angles, 4.0°.
In the crystal structure of the title compound the molecules, related by a glide symmetry plane, form
chains along the a axis through π···π and C–H···N interactions (Table 1, Figs. 2a and 2b). These chains pack in a
distorted hexagonal topology [20], as we can see in Fig. 2a, that is, leaving out distances and angles, each
molecular chain along the a-axis is surrounded by another six closer to the first. These chains are joined through
methylpyrazole ring contacts to form sheets perpendicular to the direction (001). The crystal is formed by the
1397

Fig. 1. Molecular structure of the title compound showing the atom numbering.
Thermal ellipsoids are drawn at 30% probability level and H atoms are represented by spheres of 0.1 Å.
union of these sheets through van der Waals interactions, one sheet slipped with regard to another so as to form
the mentioned mode of packing. This mode is very frequent in organic crystal structures, associating molecules
as to form the initial chain. It gives rise, when the actual size of the molecules (and so that of the chains) comes
into play, to the most frequent space groups appearing in organic structures. There are no voids in the structure,
within a 1.4 Å radius ball, and the total packing coefficient is 0.66 [21].
TABLE 1. Geometry Intermolecular Contacts (Distances, Å, and Angles,
deg.) for Compound 5.
c0103 and ci1i5 represent the centroids of the rings (N(1), C(1)···C(3)) and
(N(i1), N(i2)···C(i5)) respectively (i = 1-3)
D–H
H···A
D···A
D–H···A
c0103···c1115 (x–1/2, 1/2–y,z)
c0103···c3135 (1/2+x, 1/2–y,z)
C37–H373···N2 (1/2+x, 1/2–y,z)
C37–H372···N3 (x–1/2, 1/2–y,z)
C16–H162···N22 (1/2+x, 1/2–y,z)
C17–H171···N12 (1/2+x, 1/2–y,z)
C26–H263···c2125 (1/2+x,–y–1/2,z)
3.607(3)
3.517(3)
3.617(8)
3.764(7)
3.812(8)
3.395(7)
3.797(9)
1.11(7)
0.95(7)
0.93(6)
1.00(7)
1.01(5)
2.63(7)
2.89(7)
2.94(6)
2.80(7)
2.99(5)
149(5)
153(5)
157(5)
118(5)
138(3)
1398

a
b
Fig. 2. Crystal structure of the title compound along the a (a) and b (b) axis showing hexagonal topology in the
packing of the chains and the herringbone like mode respectively
Formation of Complexes from Compound 5
Complexes [{Pd(en)}3(Me2-TPzT)](PF6)6 (6) and [{Ag(PPh3)}3(Me2-TPzT)](ClO4)3 (7) were prepared
as described in the experimental part. Both have three metallic centers, which has never been previously
observed with TPzT-type ligands (the described complexes have one or two metals [13, 15, 16, 17, 22]). They
are moderately air-stable in the solid state. Unfortunately, they are very insoluble in organic solvents to the point
13
that, in general, neither C NMR spectra nor crystals for X-ray crystallography could be obtained. However, a
1H NMR spectrum has been recorded (saturated solutions, see Table 2). They have been characterized by
microanalysis, IR, as well as by FAB+/MS (FAB+ = fast atom bombardment in the positive mode) in the case
-
of 7. For compound 6, the IR characteristic bands of the PF6 anion (840 cm-1, broad, and 655 cm-1, narrow) and
the ν(N–H) stretching of the ethylenediamine (en) ligand (3334 and 3341 cm-1) [23] were observed. In
FAB+/MS this compound is too insoluble in the matrix and no interesting peaks were found. In IR, compound 7
1399

1
TABLE 2. H NMR Chemical Shifts of the Free Ligand 5 and Its Two
Complexes 6 and 7 at 300 K
1
δ
H NMR spectrum, , ppm (J, Hz)
Com-
pound
Solvent
Me2-TPzT
4'-H
Other ligands
3'-Me
5'-Me
CDCl3*
CDCl3
CD3CN
Acetone-d6
CD3CN
2.09
2.32
2.28
2.26
2.30
5.87
6.09
6.20
6.22
6.32
2.59 (J4'5' = 0.75)
2.80 (J4'5' = 0.8)
2.76 (J4'5' = 0.85)
2.84 (J4'5' = 0.9)
2.58
—
—
—
5
—
~2.6 and 3.92 (br, NH2);
2.67 (s, CH2CH2)
7.50-7.63 (phenyl)
6
Acetone-d6
2.15
6.39
2.76
7
_______
* From reference [16] at 303 K (it seems that there was a TMS error of
0.22 ppm in these data).
-
showed the characteristic bands of the ClO4 anion at 1089 cm-1 (broad and intense) and 622 cm-1 (narrow) [24].
In FAB+/MS, a low-intensity peak at 1772 Da (M+) was observed together with peaks corresponding to the loss
-
+
of ClO4 and AgPPh3 fragments (see Experimental).
The 1H NMR data reported in Table 2 help to establish that the complexes have the proposed structures.
For instance, in complex 6, the ratio of en to dmpz is approximately 1:1 and there is only one group of signals
corresponding to a C3 symmetry. The effect of complexation on the chemical shifts (solvent CD3CN) is small
and only noticeable on 5'-Me. The same happens in complex 7 where there are three phenyl groups (15 protons)
for each dmpz methyl group (3 protons). Here, the effects are small on all signals (solvent acetone-d6). These
conclusions were supported by the study of the NC vibrations in the aromatic rings: free ligand 5 1587 and
1541 cm-1, complex 6 1592 and 1556 cm-1, and complex 7 1589 and 1534 cm-1. It appears that the complexes are
not contaminated with the ligand.
Although we have been unable to grow crystals of 6 and 7, the collection of spectroscopic data we
obtained make us confident that the structures proposed for these three metallic derivatives are correct.
EXPERIMENTAL
The synthesis of complexes 6 and 7 was carried out under an atmosphere of dry oxygen-free nitrogen
using standard Schlenk techniques. Solvents were distilled from the appropriate drying agents and degassed
before use. PdCl2(en) [25] and AgClO4(PPh3) [26] were prepared as described in the literature. Safety note:
Perchlorate salts of metal complexes with organic ligands are potentially explosive.
Elemental analyses were performed with a Perkin–Elmer 2400 microanalyzer. IR spectra were recorded
as KBr pellets with a Perkin–Elmer PE 883 IR spectrometer. Mass spectra were recorded in a VG Autospec
instrument using FAB ionization and a nitrobenzyl alcohol matrix. Melting points were determined on a hot-
stage microscope and are uncorrected. The NMR spectra of the ligand were recorded on a Bruker DRX 400
1
15
1
spectrometer working at 400 (for H), 100 (for 13C), and 40 MHz (for N). The H NMR spectrum of 6 and 7
were recorded on a Varian Unity 300 instrument (1H at 300 MHz). Tetramethylsilane was used as external
standard for H and 13C NMR and external nitromethane for 15N NMR. The usual NMR sequences have been
1
used [27].
1400

s
Tris(3,5-dimethylpyrazol-1-yl)- -triazine 5
( ). In a three-necked round bottomed flask provided with a
reflux condenser, argon atmosphere, and magnetic stirring, NaH (2.0 g, 60%, 50 mmol) washed with anhydrous
pentane to remove the mineral oil in anhydrous THF (150 ml) was placed. 3,5-Dimethylpyrazole (4.33 g,
45 mmol) was added to this mixture in small portions and the reaction mixture stirred at room temperature for
2 h. Then 2,4,6-trichloro-1,3,5-triazine (2.65 g, 14.5 mmol) in dry THF (50 ml) was added dropwise, and the
orange-reddish reaction mixture stirred overnight. After evaporation of the solvent, the crude residue was
washed with water and the insoluble orange solid obtained by filtration dried. Column chromatography over
Merck silica gel 60 afforded pure compound 5, mp 241-244°C (although this compound 5 has been described
three times [15-17] no melting point was reported). Rf 0.71 (chloroform–methanol, 10:1) on TLC aluminium
sheets of silica gel Merck 60 F254 (layer thickness 0.2 mm). Yield 30%. Mass spectra (m/e, relative intensity
higher than 10%): 363 ([M]+, 52), 348 (28), 268 (25), 242 (15), 227 (12), 201 (13), 149 (15), 122 (13), 120 (15),
13
107 (17), 106 (17), 97 (16), 96 (26), 95 (100). C NMR spectrum (CDCl3), δ, ppm (J, Hz): 164.3 (C(2), C(4),
2
C(6), of triazine ring; 14.0 (1J = 127.9, 3'-Me); 153.3 (2J = J = 5.9, C(3')); 111.9 (1J = 174.2, C(4')); 15.5
(1J =130.3, 5'-Me); 144.4 (2J = 2J =7.4, C(5')). 15N NMR spectrum (CDCl3), δ, ppm: -167.1 (N(1), N(3), N(5), of
triazine ring); -166.5 (N(1), pyrazole); -81.6 (N(2'), pyrazole (inverse gate)); 15N NMR spectrum (DMSO-d6):
N-triazine, not observed, pyrazole: 165.4 (N(1'), 77.5 (N(2'), (gs-HMBC). Assignments made on the basis of
gs-HMQC (1J) and gs-HMBC (nJ) correlations and analogy with other reported pyrazole and triazine derivatives
[11-13]. Found, %: C 59.55; H 5.92; N 34.29. C18H21N9. Calculated, %: C 59.49; H 5.82; N 34.69.
s
Tris(ethylenediaminepalladium)tris(3,5-dimethylpyrazol-1-yl)- -triazine Hexafluorophosphate
[{Pd(en)}3(Me2-TPzT)](PF6)6 (6). The compound was prepared in two steps. First, to a solution of PdCl2(en)
(75 mg, 0.32 mmol) in THF (20 ml) was added AgPF6 (199 mg, 0.79 mmol). The mixture was stirred 12 h at
room temperature protected from light. Then, the white precipitate of AgCl was filtered off over cellite and
washed with THF till the solution remained perfectly transparent. The solution was evaporated under vacuum to
isolate the [Pd(en)(THF)2](PF6)2 adduct in the form of a beige solid that was washed with diethyl ether,
yield 97%. In the second step, to a solution of the adduct (180 mg, 0.30 mmol) in THF (20 ml) was added
Me2-TPzT 5 ligand (36.3 mg, 0.10 mmol) and immediately a white precipitate appeared, which was filtered off,
washed with diethyl ether, and dried. Beige solid, yield 82% (143 mg). Found, %: C 17.09; H 3.15; N 12.67.
C24H45F36N15P6Pd3. Calculated, %: C 16.64; H 2.62; N 12.13. Maybe the compound contains some ethylene-
diamine of crystallization.
s
Tris(triphenylphosphinesilver)tris(3,5-dimethylpyrazol-1-yl)- -triazine Perchlorate [{Ag(PPh3)}3(Me2-
TPzT)](ClO4)3 (7). To a solution of Me2-TPzT 5 (49 mg, 0.13 mmol) in freshly distilled acetone (20 ml) was
added AgClO4(PPh3) (194 mg, 0.41 mmol), taking care to protect the reaction from light. After 2 h under
stirring, a beige precipitate appeared, the stirring was continued for 3 h, then the solution was filtered and the
solid washed with diethyl ether and dried. Yield 90% (207 mg). FAB+/MS (m/e, relative intensity): 1772 (M+,
11), 1672 ([M - ClO4]+, 47), 1202 ([M - Ag(PPh3) - 2 ClO4]+, 22), 1103 ([M - Ag(PPh3) - 3ClO4]+, 61), 732
([M - 2Ag(PPh3) - 3 ClO4]+, 100), 740 ([M - 2 Ag - 3 PPh3 - 3 ClO4]+, 81). Found, %: C 49.13; H 3.65; N 7.58.
C72H66Ag3Cl3N9O12P3. Calculated, %: C 48.80; H 3.75; N 7.11.
X-Ray Analysis
Data collection was carried out at room temperature on a four-circle diffractometer (Seifert
XRD3000-S), using graphite monochromated CuKα radiation. A summary of data collection and refinement
details is given in Table 3. The structure was solved by direct methods, SIR92 [28], and refined with full matrix
least squares procedures on Fobs. Owing to the low value of the ratio of freedom (3.6), we refined alternatively
non-hydrogen and hydrogen atoms so as to use ratios of freedom of above 4.8. The atomic scattering factors
were taken from the International Tables for X-Ray Crystallography [29] and most of the calculations were
carried out with the XTAL [30], PESOS [31], and PARST [32] programs running on an AXP 600 computer.
1401

TABLE 3. Crystal Data and Structure Determination Details at Room
Temperature for 5
Chemical formula
Formula weight
Crystal habit
C18H21N9
363.4
Colorless needle
0.78 0.13 0.13
× ×
R, %
wR, %
Crystal system
Space group
4.1
5.0
Orthorhombic
Pna21
4-35
Crystal size, mm
Dc (g·cm-3), F(000)
1.281, 768
range for lattice
θ
parameters (°)
Wavelength, Å
1.5418
No. of reflections for
57
lattice parameters
Absorption coefficient, cm-1
θmax
No. Reflex. Independent
No. Reflex. Observed
6.77
66.6
1623
1172
a, Å
7.9413(8)
12.5552(15)
18.9006(19)
1884.5(4)
4
0.001
±0.25
b, Å
c, Å
V, Å3
[2 (I) criterion]
Z
σ
Secondary extinction (104)
Maximal thermal value, Å2
0.187(7)
U11(C26) = 0.131(6)
Final shift/error
F peaks, eÅ-3
∆
ACKNOWLEDGMENT
This work has been financed by DGES/MCyT (Project Nos. BQU-2000-0252 and BQU-2002-00286).
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