2,3,5,6-Tetra(pyrazin-2-yl)pyrazine: a novel bis-bidentate, bis-tridentate chelator

Article abstract of DOI:10.1016/j.tetlet.2009.04.098

Novel 10-nitrogen ligand, 2,3,5,6-tetra(pyrazin-2-yl)pyrazine, has been synthesized in four steps. This compound shows different conformations and the crystal structure of one of them has been established. This structure is sustained by non-classical H-bonds and π···π interactions among heteroaromatic rings.

Full text of DOI:10.1016/j.tetlet.2009.04.098

Tetrahedron Letters 50 (2009) 4030–4032
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
2,3,5,6-Tetra(pyrazin-2-yl)pyrazine: a novel bis-bidentate,
bis-tridentate chelator
a
b
a
b
Carolina B. P. Ligiero , Lorenzo C. Visentin , Rosana Giacomini , Carlos A. L. Filgueiras ,
a,
*
Paulo C. M. L. Miranda
Instituto de Química, Universidade Estadual de Campinas, UNICAMP, Campinas, SP, PO Box 6154, 13083-970, Brazil
a
b
Instituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 28013-602, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel 10-nitrogen ligand, 2,3,5,6-tetra(pyrazin-2-yl)pyrazine, has been synthesized in four steps. This
compound shows different conformations and the crystal structure of one of them has been established.
Received 26 February 2009
Revised 14 April 2009
Accepted 15 April 2009
Available online 3 May 2009
This structure is sustained by non-classical H-bonds and
p
ꢀꢀꢀ
p
interactions among heteroaromatic rings.
Ó 2009 Published by Elsevier Ltd.
Recent interest in polybasic ligands bearing pyridine or pyra-
resulted in very low yields of the desired ligand. Also, this reaction
gave poorer yields at higher temperatures, with sonication, or with
microwave heating.
1
zine moieties such as 2,3,5,6-tetra(pyrid-2-yl)pyrazine (1, tppz)
and tetrapyrido[3,2-a:2 ,3 -c: 3 ,2 -h:2 ,3 -j]phenazine (2, tpphz)
0
0
00 00
000 000
2
is devoted to their ability to form a plethora of coordination modes
with metallic centers (Fig. 1). Many other syntheses of bridging li-
gands with multidentate binding sites are also described.3
All compounds were fully characterized by 1H NMR, 13C NMR,
IR, elemental analyses, and HRMS. As anticipated, the pyrazine
1
moieties gave very similar and characteristic patterns in
H
4
These molecules can coordinate to form transition metal arrays
NMR: three groups of signals ranging from d 8.40 to d 8.73, d
5
1
and dendrimers with implications for the development of
8.50 to d 8.77, and d 9.12 to d 9.30. We noted by H NMR and HMQC
numerous applications, such as photoelectrochemical cells, photo-
conversion and light-harvesting devices, and organic/inorganic
light-emitting diodes. One could imagine an analogous structure
to 1 with the replacement of the pyridine units by pyrazines. In this
case the final structure should be 2,3,4,5-tetra(pyrazin-2-yl)-pyra-
zine (3, tpzpz). This compound will have 10 nitrogen atoms: six in a
potential bis-tridentate binding system and four in a bis-bidentate
binding system, significantly increasing the amount of coordina-
tion modes, compared to the seven modes shown by 1.6
experiments, at least three coexisting atropisomeric conformations
1
1
6 7 2
for 3 in DMSO-d , DMF-d , or D O/TFA-d solution. High-temper-
1
ature H NMR at 120 °C showed significant reduction of the num-
ber and complexity of lines, but unfortunately this temperature
was insufficient for the complete coalescence of each group of sig-
nals. HRMS showed a mass/charge ratio of 393.1341 for the [M+1]+
13
ion (m/z = 393.1327 calculated for C20H N10).
To put this idea into practice 1,2-di(pyrazin-2-yl)ethene-1,2-
diol (7) was prepared in 73% yield by benzoin coupling of pyra-
zine-2-carbaldehyde (6) in water with 10 mol % potassium cya-
7
nide (Scheme 1). An increase in the catalyst loading in this
reaction led to invariably lower yields. Intermediates 5 and 6 are
well-known compounds and were prepared by classical methodol-
8
9
ogies in 93% and 68% yields from the commercially available pyr-
azine-2-carboxylic acid (4). Tpzpz (3) was obtained in 37% yield
following a modification of the procedure successfully imple-
mented by Goodwin and Lions10 in their syntheses of compound
1. Thus, we submitted compound 7 to condensation with ammo-
nium acetate in pyridine at 80 °C.
Attempts to perform this reaction in molten ammonium acetate
or in other solvents such as DMSO, 2,6-lutidine, and DMF failed or
Figure 1. Structures of 2,3,5,6-tetra(pyrid-2-yl)pyrazine (1, tppz), tetrapyrido[3,2-
0
0
00 00
000 000
*
Corresponding author. Tel: +55 19 3521 3083; fax: +55 19 3521 3023.
E-mail address: miranda@iqm.unicamp.br (P.C.M.L. Miranda).
a:2 ,3 -c:3 ,2 -h:2 ,3 -j]phenazine (2, tpphz), and 2,3,4,5-tetra(pyrazin-2-yl)pyra-
zine (3, tpzpz).
0
040-4039/$ - see front matter Ó 2009 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2009.04.098

C. B. P. Ligiero et al. / Tetrahedron Letters 50 (2009) 4030–4032
4031
The numbering scheme and molecular structure of tpzpz (3) are
shown in Figure 2. It belongs to the P2 /c space group, and its con-
formation is quite similar to that of tppz (1), although it is less dis-
1
1
1
torted. C1–C2–C3–N2 and C2–C1–C7–N4 dihedral angles are,
respectively, 34.8(1) and 42.8(1)° for tpzpz (3) and 50 and 53° for
1
1
tppz (3). These lower dihedral angles lead to a closer distance be-
tween nitrogens N2 and N4. Therefore, the N2–N4 distance for
1
1
tpzpz (3) is 2.96 Å, and for tppz (1) it is 3.24 Å.
X-ray diffraction data also show intermolecular interactions in
the solid. The crystalline structure of tpzpz (3) is stabilized by
1
2
two C–HꢀꢀꢀN non-classical H-bonds. These weak hydrogen bonds
have lengths within the 2.50–2.61 Å range, as shown in Figure 3.
Angles for C10–H10ꢀꢀꢀN3 and C5–H5ꢀꢀꢀN4 are 146 and 141 degrees,
respectively. These values are in accordance with the literature for
1
2a,12b
similar cases.
presented among pyrazine rings was 3,88 Å. This
shows solid body azimuthal angle (h) of 32.3° and Euler angle
yaw ( ) of 19.7°. These values suggest crystal structure stabiliza-
tion occurring also by interactions among heteroaromatic
The smallest centroid–centroid distance (Rcen
)
p
ꢀꢀꢀ interaction
p
c
pꢀꢀꢀp
1
3
rings. The lattice grows in the [1 0 0] direction and [1 0 1] diago-
nal plane. This leads to 2D self-arrangement. Tpzpz (3) molecules
also stack in the [0 1 0] direction.
Scheme 1. Reagents and conditions: (a) dry MeOH, H
dry THF, ꢁ82 °C, 1.5 h, 68%; (c) KCN, water, rt, 1 h, 73%; and (d) NH
0 °C, 1 h, 37%.
2
SO
4
, rt, 72 h, 93%; (b) LiAlH
4
,
In summary, a novel bis-bidentate/bis-tridentate chelator con-
taining 10 nitrogen atoms was synthesized. Tpzpz (3) is not planar,
but it is less distorted than its analogue, tppz (1), suggesting a
4
OAc, pyridine,
8
H9
N5
C5
N3
H5
H6
C9
C8
C4
H4
H8
H10
C10
N1
C6
N4
C7
C3
N2
C1
C2
N2 i
N4 i
i
N1
i
N3
i
N5
Figure 2. ORTEP drawing of tpzpz (3) with thermal parameters at a level of 50% probability.
Figure 3. 2D lattice of tpzpz (3) via C–HꢀꢀꢀN non-classical H-bonds. Symmetry code (i) = ꢁ1 + x, ½ ꢁ y, ꢁ½ + z and (ii) = 1 + x, ½ ꢁ y, ½ + z.

4
032
C. B. P. Ligiero et al. / Tetrahedron Letters 50 (2009) 4030–4032
greater ability to form transition metal arrays. Tpzpz (3) shows four
non-classical H-bonds per molecule stabilizing the crystal struc-
ture. In addition, tpzpz (3) molecules mount in the [0 1 0] direction
2. (a) Pourtois, G.; Beljonne, D.; Moucheron, C.; Schumm, S.; Mesmaeker, A. K.;
Lazzaroni, R.; Brédas, J. L. J. Am. Chem. Soc. 2004, 126, 683–692; (b)
Boisdenghien, A.; Moucheron, C.; Mesmaeker, A. K. Inorg. Chem. 2005, 44,
7678–7685.
showing
p
ꢀꢀꢀ
p
stacking in the crystal.
3. (a) Constable, E. C. Coord. Chem. Rev. 2008, 252, 842–855; (b) Swiegers, G. F.;
Malefetse, T. J. Chem. Rev. 2000, 100, 3483–3538; (c) Preston, A. J.; Gallucci, J. C.;
Parquette, J. R. Org. Lett. 2006, 8, 5885–5888; (d) Lainé, P.; Bedioui, F.;
Ochsenbein, P.; Marvaud, V.; Bonin, M.; Amouyal, E. J. Am. Chem. Soc. 2002, 124,
1364–1377; (e) Mato, A. F.; Blanco, G.; Quintela, J. M.; Peinador, C. Tetrahedron
Further studies on this ligand are ongoing and will include a
careful evaluation of photophysical and electrochemical properties
of the self-assembly of ligand-transition metals bridged supramo-
lecular structures.
2008, 64, 3446–3456; (f) Zong, R.; Wang, D.; Hammitt, R.; Thummel, R. P. J. Org.
Chem. 2006, 71, 167–175; (g) Angaridis, P.; Berry, J. F.; Albert Cotton, F.;
Murillo, C. A.; Wang, X. J. Am. Chem. Soc. 2003, 125, 10327–10334; (h) Brown,
D.; Muranjan, S.; Jang, Y.; Thummel, R. Org. Lett. 2002, 4, 1253–1256.
Acknowledgments
4.
(a) Kelch, S.; Rehahn, M. Macromolecules 1997, 30, 6185–6193; (b) Torres, S. F.;
Hutcthison, G. R.; Soltzberg, L. J.; Abruña, H. D. J. Am. Chem. Soc. 2006, 128,
We are grateful to Fapesp and Cnpq for financial support of this
work. We also thank Professor R. Guimarães (LDRX, IF-UFF), for
permitting the use of diffractometer, and Professor Carol H. Collins
1
513–1522; (c) Yuasa, J.; Fukuzumi, S. J. Am. Chem. Soc. 2008, 130, 566–575.
5. Leveque, J.; Elias, B.; Moucheron, C.; Mesmaeker, A. K. Inorg. Chem. 2005, 44,
93–400.
Bitzer, R.; Gil, R. A. S. S.; Filgueiras, C. A. L. J. Braz. Chem. Soc. 2006, 17, 1600–
604.
7. Buelher, C. A.; Addleburg, J. W.; Glenn, D. M. J. Org. Chem. 1955, 20, 1350–1355.
3
6.
(
IQ-UNICAMP) for helpful suggestions on English grammar and
1
style.
8
.
Ellingson, R. C.; Henry, R. L.; McDonald, F. G. J. Am. Chem. Soc. 1945, 67, 1711–
733.
Rutner, H.; Spoerri, P. E. J. Org. Chem. 1963, 28, 1898–1899.
1
Supplementary data
9.
1
1
0. Goodwin, H. A.; Lions, F. J. Am. Chem. Soc. 1959, 81, 6415–6422.
1. (a) Bock, H.; Vaupel, T.; Näther, C.; Ruppert, K.; Havlas, Z. Angew. Chem., Int. Ed.
Engl. 1992, 31, 299–301; (b) Padgett, C. W.; Pennington, W. T.; Hanks, T. W.
Cryst. Growth Des. 2005, 5, 737–744.
Details of the syntheses of compounds 3, 5, 6, and 7, crystallo-
graphic information, supplementary figures, XRD, NMR spectra,
and MS for compound 3 and NMR spectra and MS for compound
12. (a) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48–76; (b) Ohkita, M.; Kawano,
M.; Suzuki, T.; Tsuji, T. Chem. Commun. 2002, 3054–3055; (c) Jeffrey, G. A.;
Maluszynska, H.; Mitra, J. Int. J. Biol. Macromol. 1985, 7, 336–348; (d) Raymo, F.
M.; Bartberger, M. D.; Houk, K. N.; Fraser Stoddart, J. J. Am. Chem. Soc. 2001, 123,
9264–9267.
7
are available in this supplementary material. The crystal struc-
ture for 3 has been deposited at the CCDC and allocated the depo-
sition number 690110. Supplementary data associated with this
Letter can be found, in the online version, at doi:10.1016/
j.tetlet.2009.04.098.
13. (a) Hunter, C. A.; Lawson, K. R.; Perkins, J.; Urch, C. J. J. Chem. Soc., Perkin Trans. 2
2001, 651–669; (b) Jaffe, R. L.; Smith, G. D. J. Chem. Phys. 1996, 105, 2780–2788;
(
c) Hobza, P.; Selzle, H. L.; Schlag, E. W. J. Am. Chem. Soc. 1994, 116, 3500–3506.
References and notes
1
.
(a) Bera, J. K.; Campos-Fernández, C. S.; Rodolphe, C.; Dunbar, K. R. Chem.
Commun. 2002, 2536–2537; (b) Bitzer, R. S.; Teles, W. M.; Abras, A.; Ardissom, J.
D.; Filgueiras, C. A. L. J. Braz. Chem. Soc. 2005, 16, 963–968.