PtII-promoted [2 + 3] cycloaddition of azide to cyanopyridines: Convenient tool toward heterometallic structures

Article abstract of DOI:10.1021/ic8014223

The [2 + 3] cycloaddition reactions (which are greatly accelerated by microwave irradiation) of the di(azido)platinum(II) compounds cis-[Pt(N ₃)₂(PPh₃)₂] (1) with cyanopyridines NCR (2) (R = 4-, 3-, and 2-NC

Full text of DOI:10.1021/ic8014223

Inorg. Chem. 2008, 47, 11334-11341
PtII-Promoted [2 + 3] Cycloaddition of Azide to Cyanopyridines:
Convenient Tool toward Heterometallic Structures
Suman Mukhopadhyay,† Bhaswati Ghosh Mukhopadhyay,† M. Fa´tima C. Guedes da Silva,†,‡
Jamal Lasri,† M. Ad´ılia Janua´rio Charmier,†,‡,* and Armando J. L. Pombeiro†,*
Centro de Qu´ımica Estrutural, Complexo I, Instituto Superior Te´cnico, TU Lisbon, AV. RoVisco
Pais, 1049-001, Lisbon, Portugal, and UniVersidade Luso´fona de Humanidades e Tecnologias,
ULHT Lisbon, AV. Campo Grande n° 376, 1749-024, Lisbon, Portugal
Received July 29, 2008
The [2 + 3] cycloaddition reactions (which are greatly accelerated by microwave irradiation) of the di(azido)platinum(II)
compounds cis-[Pt(N3)2(PPh3)2] (1) with cyanopyridines NCR (2) (R ) 4-, 3-, and 2-NC5H4) give the corresponding
bis(pyridyltetrazolato) complexes trans-[Pt(N4CR)2(PPh3)2] (3) [R ) 4-NC5H4 (3a), 3-NC5H4 (3b), and 2-NC5H4 (3c)].
Compound 3c has been characterized as the N1N2-bonded isomer in the solid state by X-ray crystallography and
represents the first bis(tetrazolato) complex of this kind. Complexes 3a and 3b have been used as metallaligands
to generate heteronuclear coordination polymers in the presence of copper nitrate. A one-dimensional supramolecular
architecture was obtained as the exclusive product, {trans-[Pt2(N4CR)4(PPh3)4Cu]n(NO3)2n · nH2O (4·nH2O) (R )
4-NC5H4), when 3a was employed, whereas with 3b the heteronuclear square complex trans-
[Pt(N4CR)2(PPh3)2Cu(NO3)2(H2O)]2 (5) (R ) 3-NC5H4), composed of Pt/Cu ions, was obtained. All the isolated
complexes were characterized by IR, elemental, and (for 3b, 3c, 4, and 5) X-ray structural analyses. Complexes
1
3 were additionally characterized by H, 13C, and 31P {1H} NMR spectroscopies.
Introduction
of the cases, self-assembly of organic ligands with inorganic
metal ions are a key step and is a widely used approach
where the success depends on the availability of programmed
metal-based building blocks. Among several synthetic schemes,
the in situ generation of tetrazole-based ligands to produce
coordination polymers by a hydrothermal process where the
cycloaddition reaction between an azide and a nitrile takes
place has recently been studied,5 but this procedure is hitherto
confined to the generation of homometallic supramolecular
aggregates. Tetrazolato ligands with a pyridyl sidearm have
been successfully used to generate a porous body-centered
cubic type framework with copper ions.6 Moreover, among
the numerous coordination polymeric structures reported so
Syntheses of homo- and heterometallic coordination
polymers using organic and inorganic linkers to develop new
materials with interest in several areas (such as electronic
devices and materials as single-molecule transistors1 and
single-molecule magnets,2 catalysis,3 sensors, storage, and
separation devices4) have attracted much attention. Of
particular synthetic relevance to generate such structures is
the attempt to get control over the whole process. In most
* To whom correspondence should be addressed. E-mail: pombeiro@
ist.utl.pt.
†
Instituto Superior Te´cnico.
Universidade Luso´fona de Humanidades e Tecnologias.
‡
(1) (a) Launay, J.-P. Chem. Soc. ReV. 2001, 30, 386. (b) Liang, W.; Shores,
M. P.; Bockrath, M.; Long, J. R.; Park, H. Nature 2002, 417, 725.
(2) (a) Gatteschi, D.; Caneschi, A.; Pardi, L.; Sessoli, R. Science 1994,
265, 1054. (b) Zaleski, C. M.; Depperman, E. C.; Kampf, J. W.; Kirk,
M. L.; Pecoraro, V. L. Angew. Chem., Int. Ed. 2004, 43, 3912. (c)
Osa, S.; Kido, T.; Matsumoto, N.; Re, N.; Pochaba, A.; Mrozinski, J.
J. Am. Chem. Soc. 2004, 126, 420.
(3) (a) Abrantes, M.; Valente, A.; Pillinger, M.; Gonc¸alves, I. S.; Rocha,
J.; Roma˜o, C. C. J. Catal. 2002, 209, 237. (b) Kirillov, A. M.;
Kopylovich, M. N.; Kirillova, M. V.; Haukka, M.; Guedes da Silva,
M. F. C.; Pombeiro, A. J. L. Angew. Chem., Int. Ed. 2005, 44, 4345.
(c) Kirillov, A. M.; Kopylovich, M. N.; Kirillova, M. V.; Karabach,
E. Yu.; Haukka, M.; Guedes da Silva, M. F. C.; Pombeiro, A. J. L.
AdV. Synth. Catal. 2006, 348, 159.
(4) (a) Pan, L.; Adams, K. M.; Hernandez, H. E.; Wang, X.; Zheng, C.;
Hattori, Y.; Kaneko, K. J. Am. Chem. Soc. 2003, 125, 3062. (b)
Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43,
2334. (c) Kitagawa, S.; Uemura, K. Chem. Soc. ReV 2005, 34, 109,
and references therein.
(5) (a) Zhang, X.-M.; Zhao, Y. F.; Wu, H.-S.; Batten, S. R.; Ng, S. W.
Dalton Trans. 2006, 3170. (b) Wang, X.-S.; Tang, Y.-Z.; Huang, X.-
F; Qu, Z.-R.; Che, C.-M.; Chan, P. W. H.; Xiong, R.-G Inorg. Chem.
2005, 44, 5278. (c) Xiong, R.-G.; Xue, X.; Zhao, H.; You, X.-Z.;
Abrahams, B. F.; Xue, Z. Angew. Chem., Int. Ed. 2002, 41, 3800.
(6) Luo, T.-T.; Hsai, H.-L.; Yang, S.-L.; Liu, Y. H.; Yadav, R. D.; Su,
C.-C.; Ueng, C.-H; Lin, L. G.; Lu, K. L. Angew. Chem., Int. Ed 2005,
44, 6063.
11334 Inorganic Chemistry, Vol. 47, No. 23, 2008
10.1021/ic8014223 CCC: $40.75  2008 American Chemical Society
Published on Web 10/22/2008

[2 + 3] Cycloaddition of Azide to Cyanopyridines
Preparations. Complexes 3a-c. These complexes can be
prepared by two different methods. The first method is by refluxing
a solution of the starting complex 1 along with an excess of the
corresponding cyanopyridine in DMF, and the second one is by
using focused microwave irradiation.
i. Refluxing. A solution of 1 (0.080 g, 0.10 mmol) and
4-cyanopyridine (2a) (0.104 g, 1.00 mmol) in DMF (8 mL) was
refluxed for 12 h, whereupon the solvent was removed in vacuo.
The oily residue was treated with diethyl ether to obtain, upon
stirring, a white semicrystalline solid. The solid was washed
repeatedly with 5 mL portions of diethyl ether, and the resultant
compound was recrystallized from a dichloromethane/diethyl ether
mixture to produce the off-white crystalline compounds trans-[Pt{5-
(4-pyridyl)-tetrazolato}2(PPh3)2] (3a).
far, heterometallic coordination networks are not very
common but can be synthesized by using, for example,
cyanide, oxalate, or nitrite as bridging units.7 The use of
metal complexes as building blocks (metallaligands), apart
from those with such bridging ligands,7 to get a better control
over the tuning of the desired heterometallic coordination
polymer structure is still sparse in comparison with the
application of pure organic ligands.8 Examples of formation
of discrete heterometallic clusters, namely of the molecular
square type, by using metallaligands are even rarer in
literature.9
In our previous studies we have shown that the diazido-
platinum(II) complexes cis-[Pt(N3)2(PPh3)2] react with a
variety of nitriles to undergo [2 + 3] cycloaddition reactions
producing trans-5-substituted tetrazolato complexes
[Pt(N4CR)2(PPh3)2].10 In continuation of that study we have
used different cyanopyridines to form cycloadded platinum
complexes, trans-[Pt(N4CR)2(PPh3)2] (3), which themselves
can be used as metallaligands, providing a convenient
methodology toward the synthesis of heteronuclear com-
plexes of platinum with interesting molecular architectures.
Hence, herein we also report the syntheses of a molecular
square structure and a one-dimensional (1D)-supramolecular
architecture with a rhombus-like grid, composed by PtII and
CuII ions bridged by pyridyltetrazolato ligands.
Complexes 3b and 3c were prepared analogously, but by using
3-cyanopyridine and 2-cyanopyridine, respectively.
ii. Focused Microwave Irradiation. In this method, identical
amounts of the reagents described above were added to a cylindrical
Pyrex tube that was then placed in the focused microwave reactor.
The system was left under irradiation for 1 h at 125 °C. The solvent
was then removed in vacuo, and the resulting oily residue was treated
in a manner similar to that described above to obtain the white
crystalline solid of 3a. Complexes 3b and 3c were synthesized in an
identical way.
Trans-[Pt{5-(4-pyridyl)-tetrazolato}2(PPh3)2] (3a). 60% (method
1
i) and 62% (method ii) yields. IR (cm-1): 1634 (CdN). H NMR
Experimental Section
(CDCl3), δ 7.22-8.54 (m, 38H, aromatic). 13C{1H} NMR (CDCl3),
δ 120.22-149.86 (Caromatic) and 162.12 (CdN). 31P{1H} NMR
(CDCl3), δ 16.58 (JPt-P ) 2673 Hz). Anal. calcd for PtC48H38N10P2:
C, 56.91; H, 3.75; N, 13.83; found: C, 56.12; H, 3.67; N, 13.97.
Trans-[Pt{5-(3-pyridyl)-tetrazolato}2(PPh3)2] (3b). 65% (method
General, Materials, and Measurements. Solvents were pur-
chased from Aldrich and were dried by usual procedures. Cis-
[Pt(N3)2(PPh3)2] (1)11 was prepared according to a published
procedure. C, H, and N elemental analyses were carried out by the
Microanalytical Service of the Instituto Superior Te´cnico. 1H, 13C,
and 31P{1H} NMR spectra (in CDCl3 and in d6-DMSO) were
measured on a Varian Unity 300 spectrometer at ambient temper-
1
i) and 60% (method ii) yields. IR (cm-1): 1656 (CdN). H NMR
(CDCl3), δ 7.19-8.70 (m, 38H, aromatic). 31P{1H} NMR (CDCl3), δ
16.71 (JPt-P ) 2693 Hz). Anal. calcd for PtC48H38N10P2: C, 56.91; H,
3.75; N, 13.83; found: C, 55.45; H, 3.90; N, 13.75. Due to poor
solubility, reliable results were not obtained for 13C NMR spectroscopy.
Trans-[Pt{5-(2-pyridyl)-tetrazolato}2(PPh3)2], N1N2-bonded
isomer (3c). 55% (method i) and 60% (method ii) yields. IR (cm-1):
1617 (CdN), 1H NMR (CDCl3), δ 7.44-8.66 (m, 38H, aromatic).
13C{1H} NMR (CDCl3), δ 121.57-151.09 (Caromatic). 31P{1H} NMR
(CDCl3), δ 4.79 (JPt-P ) 2430 Hz). Due to the poor solubility, the
obtained signals were very weak and could not be properly
analyzed. Anal. calcd for PtC48H38N10P2: C, 56.91; H, 3.75; N,
13.83; found: C, 55.45; H, 3.90; N, 13.75.
1
ature. H, 13C, and 31P chemical shifts (δ) are expressed in ppm
relative to Si(Me)4 (1H and 13C) or 85% H3PO4 (31P). J values are
in Hertz. Infrared spectra (4000-400 cm-1) were recorded on a
Bio-Rad FTS 3000MX and a Jasco FT/IR-430 instruments in KBr
pellets, and the wavenumbers are in cm-1. The microwave
irradiation experiments were undertaken in a focused microwave
CEM Discover reactor (10 mL, 13 mm diameter, 300 W) that is
fitted with a rotational system and an IR detector for temperature.
(7) (a) Miasaka, H.; Matsumoto, N.; Re, N.; Gallo, E.; Floriani, C. Inorg.
ˆ
Chem. 1997, 36, 670. (b) Ohba, M.; Fukita, N.; Okawa, H. J. Chem.
Soc., Dalton Trans. 1997, 1733. (c) Kahn, O.; Bakalbassis, E.;
Mathoniere, C.; Hagiwara, M.; Katsumata, K.; Ouahab, L. Inorg.
Chem. 1997, 36, 1530.
Complex 4.
A solution of 0.012 g (0.050 mmol) of
Cu(NO3)2 ·3H2O in 10 mL of methanol was added dropwise to a
solution of 0.101 g (0.100 mmol) of complex 3a in 20 mL of
dichloromethane with constant stirring until a clear blue solution was
obtained. It was stirred for 1 h and then filtered. The resultant solution
was left in the air for slow evaporation. After ca. 4-5 days, a blue
crystalline compound was obtained along with X-ray diffraction quality
(8) (a) Hess, J. L.; Conder, H. L.; Green, K. N.; Darensbourg, M. Y. Inorg.
Chem. 2008, 47, 2056. (b) Pattacini, R.; Giansante, C.; Ceroni, P.;
Maestri, M.; Braunstein, P. Chem. Eur. J. 2007, 13, 10117. (c) Stork,
J. R.; Thoi, V. S.; Cohen, S. M. Inorg. Chem. 2007, 46, 11213. (d)
Zhang, H.; Dechert, S.; Linseis, M; Winter, R. F.; Meyer, F. Eur.
J. Inorg. Chem. 2007, 46, 4679. (e) Zhang, S.-S.; Zhan, S.-Z.; Li, M.;
Peng, R.; Li, D. Inorg. Chem. 2007, 46, 4365. (f) Halper, S. R.; Do,
L.; Stork, J. R.; Cohen, S. M. J. Am. Chem. Soc. 2006, 128, 15255.
(g) Wang, X.; Sheng, T.-L.; Fu, R.-B.; Hu, S.-M.; Xiang, S.-C.; Wang,
L.-S.; Wu, X.-T. Inorg. Chem. 2006, 45, 5236. (h) Murphy, D. L.;
Malachowski, M. R.; Campana, C. F.; Cohen, S. M. Chem. Commun.
2005, 5506. (i) Noro, S.-i.; Miyasaka, H.; Kitagawa, S.; Wada, T.;
Okubo, T.; Yamashita, M.; Mitani, T Inorg. Chem. 2005, 44, 133. (j)
Braunstein, P.; Clerc, G.; Morise, X.; Welter, R.; Mantovani, G. Dalton
Trans. 2003, 1601. (k) Clerac, R.; Miyasaka, H.; Yamashita, M.;
Coulon, C. J. Am. Chem. Soc. 2002, 124, 12837.
(10) (a) Mukhopadhyay, S; Lasri, J.; Janua´rio Charmier, M. A.; Guedes
da Silva, M. F. C.; Pombeiro, A. J. L Dalton Trans. 2007, 5297. (b)
Mukhopadhyay, S; Lasri, J.; Janua´rio Charmier, M. A.; Guedes da
Silva, M. F. C.; Pombeiro, A. J. L. Acta Crystallogr. 2007, E63,
m2656.
(9) Teo, P.; Foo, D. M. J.; Koh, L. L; Andy Hor, T. S Dalton Trans.
2004, 3389.
(11) Erbe, J.; Beck, W. Chem. Ber. 1983, 116, 3867.
Inorganic Chemistry, Vol. 47, No. 23, 2008 11335

Mukhopadhyay et al.
Table 1. Relevant Crystal Data for 3b, 3c, 4, and 5
3b
3c
4
5
empirical formula
formula weight
cryst system
space group
a (Å)
C48H38N10P2Pt
1011.90
C48H38N10P2Pt
1011.90
C96H76CuN20P4Pt2
2087.36
Orthorhombic
Pbcn
27.0000(15)
17.135(1)
21.9480(13)
90
C96H80Cu2N24O14P4Pt2
2434.99
Triclinic
Triclinic
Triclinic
j
j
j
P1
P1
P1
8.3626(3)
11.6149(4)
11.6592(3)
69.129(1)
83.727(1)
81.956(1)
1045.59(6)
1
12.153(8)
12.336(8)
16.907(11)
88.584(15)
74.856(13)
72.836(14)
2334(3)
13.4734(3)
14.0405(2)
15.9240(3)
83.711(1)
71.975(1)
75.227(1)
2768.32(9)
1
b (Å)
c (Å)
R (deg)
ꢀ (deg)
90
90
γ (deg)
V (Å)3
10154.1(10)
4
1.365
Z
F
2
calcd(g cm-3
)
1.607
504
1.440
1008
1.4561
1210
F(000)
4148
N° reflections coll.
No. reflections unique
R1, wR2 (obs refls)
R1, wR2 (all data)
GOF
8493
3596
0.0259, 0.0576
0.0264, 0.0579
1.041
15642
8331
0.0577, 0.1216
0.1022, 0.1349
0.899
39880
9235
0.0315, 0.0732
0.0483, 0.0777
1.016
27350
10109
0.0370, 0.0889
0.0476, 0.0926
1.081
Largest diff. peak (hole) (e Å-3
)
0.951 (-0.483)
2.516 (-1.446)
0.728 (-1.217)
1.337 (-1.214)
crystals. It was separated by filtration, washed with diethyl ether, and
dried in vacuo.
[Pt2{5-(4-pyridyl)-tetrazolato}4(PPh3)4Cu]n(NO3)2n ·nH2O (4·n-
H2O). 60% yield. IR (cm-1): 1617 (CdN), 1384 (NO3) Anal. calcd
for Pt2CuC96H78N22O7P4: C, 51.71; H, 3.50; N, 13.82; found: C,
51.36; H, 3.59; N, 13.36.
Least square refinement with anisotropic thermal motion parameters
for all the non-hydrogen atoms and isotropic for the remaining
atoms were employed.
For 3c, 4, and 5 there are disordered solvent in the structures.
Attempts were made to model them, but were unsuccessful.
PLATON/SQUEEZE15 was used to correct the data. Potential
solvent volumes of 332.6 (3c), 2246.1 (4), and 518.0 (5) Å3 were
found. A total of 146.2 (3c), 296.5 (4), and 28.9 (5) electrons per
Complex 5.
A solution of 0.024 g (0.10 mmol) of
Cu(NO3)2 ·3H2O in 10 mL of methanol was added dropwise to a
suspension of 0.101 g (0.10 mmol) of complex 3b in 20 mL of
dichloromethane with constant stirring, giving a clear blue solution
after five minutes. This was further stirred for 1 h and then filtered.
The resultant solution was left in air for slow evaporation. A blue
crystalline compound was obtained along with X-ray diffraction
quality crystals after standing for ca. one week. The solid was
separated by filtration, washed with diethyl ether, and dried in
vacuo.
[Pt{5-(3-pyridyl)-tetrazolato}2(PPh3)2Cu(NO3)2(H2O)]2 ·CH3OH·
H2O (5·CH3OH·H2O). 60% yield. IR (cm-1): 1656 (CdN), 1384
(NO3) Anal. calcd for Pt2Cu2C97H86N24O16P4: C, 45.71; H, 3.38;
N, 13.20; found: C, 46.68; H, 3.31; N, 13.06.
unit cell of scattering were located in the voids. The stoichiometries
-
were tentatively calculated as 1CHCl3 + 1MeOH (3c), 2NO3
+
1H2O (4), and 1MeOH + 1H2O (5) molecules, which result in 152
(3c), 296 (4), and 28 (5) electrons per unit cell. The modified data
set improved the R1 values by ca. 10% (3c), 64% (4), and 46%
(5). The maximum and minimum peaks in the final difference
electron density map are generally located close to the platinum
atoms. Additionally, a disorder model was included for two of the
phenyl rings of the phosphines in 5, which are disordered between
two positions.
Crystallographic parameters and residuals are given in Table 1.
Complex 6. Treatment of complex 3c with copper nitrate by a
similar method to that described above for 4 and 5 furnished an
insoluble sky-blue powder that could not be properly characterized
due to its poor solubility and noncrystalline nature.
Results and Discussions
Treatment of the diazidoplatinum(II) complex 1 with a
cyanopyridine 2 [R ) 4-NC5H4 (2a), 3-NC5H4 (2b), and
2-NC5H4 (2c)] in refluxing DMF for 12 h furnishes the
corresponding bis(pyridyltetrazolato) complexes 3, isolated
as white crystalline solids in moderate yields (ca. 60-55%)
(Scheme 1). These reactions could be greatly accelerated
under microwave irradiation (100 °C, 300 W), leading only
in 1 h to yields that are comparable to those obtained after
12 h under conventional heating, as we have observed10 in
other cases. The tetrazolato complexes were obtained via [2
+ 3] cycloaddition of the organonitriles with the ligated
azides. Cis-to-trans isomerization also occurred upon heating,
indicating that the trans isomer of the bis(tetrazolato) product
is thermodynamically more favorable than the cis one.
Crystal Structure Determination of 3b, 3c, 4, and 5. Single
crystals of 3b and 3c were obtained by diffusing diethyl ether in
chloroform solutions of the respective complexes. Crystals of 4
and 5 that weresuitable X-ray diffraction were obtained from the
reaction mixture. Intensity data were collected using a Bruker AXS-
KAPPA APEX II diffractometer using graphite monochromated
Mo KR radiation. Data were collected 150 K using ω scans of 0.5°
per frame, and a full sphere of data was obtained. Cell parameters
were retrieved using Bruker SMART software and were refined
using Bruker SAINT on all the observed reflections. Absorption
corrections were applied using SADABS. Structures were solved
by direct methods by using the SHELXS-97 package12 and were
refined with SHELXL-9713 with the WinGX graphical user
interface.14 All hydrogens were inserted in calculated positions.
(12) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(13) Sheldrick, G. M. SHELXL-97; University of Gottingen: Germany,
1997.
(14) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(15) Spek, A. L. Acta Crystallogr., Sect. C 1990, 46, C34.
11336 Inorganic Chemistry, Vol. 47, No. 23, 2008

[2 + 3] Cycloaddition of Azide to Cyanopyridines
Scheme 1
Scheme 2
Scheme 3
Related thermal isomerizations of cis-[PtCl2(RCN)2] into
trans-[PtCl2(RCN)2] have been reported previously.16
The use of a metal complex with a free potential
coordinating center is a known strategy to generate mixed-
metal coordination polymers with different topologies.17
For this purpose we have used the bis(pyridyltetrazolato)
complexes 3, which bear two uncoordinated pyridyl
(17) (a) Wheatley, N.; Kalck, P. Chem. ReV. 1999, 99, 3379. (b) Sharma,
S.; Singh, S. K.; Pandey, D. S. Inorg. Chem. 2008, 47, 1179. (c)
Biswas, C.; Mukherjee, P.; Drew, M. G. B.; Gomez-Garcia, C. J.;
Clemente-Juan, J. M.; Ghosh, A. Inorg. Chem. 2007, 46, 10771. (d)
Zhang, H.; Dechert, S.; Linseis, M.; Winter, R. F.; Meyer, M. Eur.
J. Inorg. Chem. 2007, 4679.
(16) (a) Svensson, P; Lovqvist, K.; Kukushkin, V. Y.; OskarssonÅ, Acta
Chem. Scand. 1995, 49, 72. (b) Uchiyama, T.; Toshiyasu, Y.;
Nakamura, Y.; Miwa, T.; Kawaguchi, S Bull. Chem. Soc. Jpn., 1981,
54, 181.
Inorganic Chemistry, Vol. 47, No. 23, 2008 11337

Mukhopadhyay et al.
Scheme 4
Table 2. Selected Bond Distances and Angles for 3b, 3c, 4·nH2O and
5·CH3OHa
3b
3c
4
5
Bond Lengths (Å)
Pt1-P1
2.3234(9)
2.3234(9)
1.995(3)
2.350(3)
2.343(3)
1.971(8)
1.989(8)
2.3273(11) 2.3140(13)
2.3235(11) 2.3298(13)
Pt1-P1a
Pt1-N11
Pt1-N21
2.001(3)
2.008(3)
2.037(3)
2.033(3)
2.005(4)
2.002(4)
2.002(4)
2.009(4)
2.167(4)
2.007(4)
2.907(6)
2.032(4)
2.593(5)
Cu1-N14
Cu1-N24a
Cu1-O10
Cu1-O11
Cu1-O12
Cu1-O21
Cu1 -O22
Bond Angles (°)
P1-Pt1-P2
174.43(9)
89.3(2)
88.3(2)
93.2(2)
89.5(2)
176.9(3)
168.66(4)
92.83(10)
86.05(10)
92.23(10)
90.30(10)
172.08(13)
173.96(4)
89.58(13)
90.34(13)
89.35(13)
90.92(13)
178.26(18)
P1-Pt1-N11
89.49(10)
P1-Pt1-N21
P2-Pt1-N11
P2-Pt1-N21
Figure 1. Molecular structure of 3b with atomic numbering scheme
(ellipsoids are drawn at 30% probability).
N11-Pt1-N21
P1b-Pt1-N11
90.52(10)
89.49(10)
P1b-Pt1-N11b
N14-Cu1-N24a
N14-Cu1-N24c
N24a-Cu1-N24c
O10-Cu1-O11
O10-Cu1 -O12
O10 -Cu1-O21
O10-Cu1-O22
O10-Cu1-N14
O11-Cu1-O12
O11-Cu1-O21
O11 -Cu1-O22
O11-Cu1-N14
O11-Cu1-N24a
O12 -Cu1-O21
O12 -Cu1-O22
O12 -Cu1-N14
O12 -Cu1-N24a
O21-Cu1-O22
O21-Cu1-N14
O21-Cu1-N24a
O22-Cu1 -N14
O22-Cu1-N24a
92.31(13)
179.45(14)
87.21(13)
165.20(17)
113.16(19)
69-90(18)
85.67(19)
139.97(19)
99.75(17)
73.7(4)
106.0(4)
81.3(3)
123
106
129
103.5(4)
103.5(4)
116.8(5)
119.6(7)
123.6(6)
123.5(3)
124.0(4)
112.3(4)
a Symmetry operation to generate the atom: (a) x, -1 + y, z (4) and -x,
1
-y, 2-z (5); (b) 2 - x, 2 - y, -z; (c) 1 - x, -1 + y, /2 - z.
N-atoms per platinum atom. Such pyridyl moieties are
expected to bind to other metal sites, and copper nitrate
was taken as a metal center source, keeping also in mind
the coordinating ability of nitrate ion to fulfill suitable
copper coordination geometry. A dichloromethane solution
(or suspension) of each of complexes 3 was treated
dropwise with a methanolic solution of Cu(NO3)2 to afford
a clear blue solution from which, in the case of using 3a
and 3b, the crystalline heteronuclear PtII/CuII compounds
4 and 5, respectively, with bridging pyridyltetrazolato
ligands (Schemes 2 and 3), could be isolated upon slow
solvent evaporation in air.
Figure 2. Molecular structure of 3c with atomic numbering scheme
(ellipsoids are drawn at 30% probability).
The obtained complexes 3 were characterized by elemental
1
analyses; IR, H, 13C{1H}, (for 3a and 3c), and 31P{1H}
spectroscopies; and X-ray crystal structure analyses (for 3b
and 3c). Their IR spectra display a band within the
1617-1656 cm-1 range due to the tetrazolato ring,18 quite
distinct from the typical azide band at 2055 cm-1 in 1. The
(18) Lin, P.; Clegg, W.; Harrington, R. W.; Henderson, R. A. Dalton Trans.
2005, 2388.
11338 Inorganic Chemistry, Vol. 47, No. 23, 2008

[2 + 3] Cycloaddition of Azide to Cyanopyridines
Figure 3. ORTEP diagram of the asymmetric unit of 4 with atom labeling scheme. Thermal ellipsoids are drawn at 30% probability. All hydrogens were
omitted for clarity.
Figure 4. Extended 1D structure of 4 viewed down the crystallographic axis c.
31P{1H} NMR spectra of 3a-c exhibit a singlet with
platinum satellites, at δ 16.6, 16.7, and 4.79, with JPt-P of
2673, 2693, and 2430 Hz, respectively. These coupling
values clearly show the trans configuration of the phos-
phines,19 and the singlet resonance indicates the existence
of only one type of N-coordination for each pyridyltetrazole
ligand, contrary to the alkyl tetrazolato complexes obtained
from an alkyl nitrile.10 In 3a and 3b, both bulky pyridyltet-
razolato rings are equivalent and bind the metal only by the
N2-atom (Scheme 4a), as shown by X-ray analysis of 3b
(see below), thus minimizing the steric congestion. However,
complex in common organic solvents) show the nonequiva-
lence of the two pyridyl groups, which was confirmed by
X-ray crystallography (see below) and which revealed the
asymmetric nature of the complex with the N1N2-coordina-
tion mode (Scheme 4b) of the tetrazolato ligands. The
elemental analyses of 3-5 confirm their analytical purity
and are consistent with the formulations authenticated by
the X-ray diffraction studies as indicated below.
A strong band at 1384 cm-1 for both complexes 4 and 5
is assigned20 to the CuII-bound monodentate NO3 ligand.
-
1
for complex 3c, the H and 13C NMR spectra (although the
The triphenyl phosphine ligands are detected by their
characteristics bands at ca. 1436 and 695 cm-1. No band
that could be due to N-H stretching or bending was
observed, indicating the retention of the anionic nature of
latter was not well-resolved due to poor solubility of the
(19) (a) Guedes da Silva, M. F. C.; Branco, E. M. P. R. P.; Wang, Y.;
Frau´sto da Silva, J. J. R.; Pombeiro, A. J. L.; Bertani, R.; Michelin,
R. A.; Mozzon, M.; Benetollo, F.; Bombieri, G. J. Organomet. Chem.
1995, 490, 89. (b) Michelin, R. A.; Bertani, R.; Mozzon, M.; Bombieri,
G.; Benetollo, F.; Guedes da Silva, M. F. C.; Pombeiro, A. J. L.
Organometallics 1993, 12, 2372.
(20) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coor-
dination Compounds, 3rd ed.; Wiley-Interscience: New York, 1978.
Inorganic Chemistry, Vol. 47, No. 23, 2008 11339

Mukhopadhyay et al.
Interestingly, the structure of 3c reveals (Figure 2) that,
although one of the tetrazolato rings is coordinated by the
N2-nitrogen atom, the other is coordinated via the N1-nitrogen
atom of the ring. The less sterically favorable N1-coordination
for one of the pyridyltetrazolato ligands conceivably results
from the coordinative interaction (2.966(9) Å) between the
metal and the nitrogen atom (N14) of the pyridine ring, which
thus almost takes the apical position of a distorted, pseu-
dosquare-pyramidal coordination geometry. A similar type
of coordinative interaction has been reported earlier for a
MnII complex.18 The measured angles of N14, the metal,
and the coordinating atoms of the basal plane lie in the
112.13-65.86° range. Both tetrazolato rings are almost
planar, but they are mutually twisted by 23.58° to each other,
unlike in the related known compounds.10 To the best of
our knowledge, compound 3c provides the first example of
an N1N2 isomer isolated in the solid state, among the bis-
tetrazolato transition metal complexes reported so far.
Compound 4 is a 1D-type coordination polymer in which
the metallaligand 3a acts as a building block, thus leading
to an asymmetric unit containing one Pt center (3a) and one
Cu bound to the N-atom of a pyridyl ring (Figure 3). In the
polymeric network that is thus constructed, the coordination
environment of the PtII atom is square-planar, and it consists
of two triphenylphosphine ligands in trans position along
with two 5-substituted tetrazolato ligands that coordinate in
the N2N2-mode. The Cu(II) center in 4 also adopts a square-
planar geometry, with the metal bound to the N-atoms of
four pyridyl rings from the metallaligands 3a. All the bond
distances and angles are within the ranges reported earlier
for comparable compounds.10 Structure 4 qualifies as a
heterometallic supramolecular square: the nearest distance
between two adjacent copper atoms in a chain is 17.135 Å,
the same as the unit cell parameter b, whereas the nearest
Pt · · · Pt separation is 10.323 Å. Additionally, the shortest
interchain Pt · · ·Cu, Cu · · ·Cu, and Pt · · ·Pt distances are 8.524,
15.989, and 9.221 Å, respectively. These distances consider-
ably exceed the sum of the van der Waals radii of two Pt or
two Cu atoms, hence the chains are effectively separated,
as shown in Figure 4 (additional views are shown in the
Supporting Information). A van der Waals-based space filling
model of the structure indicates that, although there might
be room for small molecules to enter the center of the square,
the pendant phenyl rings of the phosphines may block the
access, not only to the central core but also to the interchain
channels, thus eliminating any 3D channels that would
otherwise exist. The framework contains disordered nitrate
anions and water molecules, for which a reasonable refine-
ment was not possible.
Figure 5. ORTEP diagram of the asymmetric unit of 5 with atom labeling
scheme. Thermal ellipsoids are drawn at 30% probability. All hydrogens
were omitted for clarity.
Figure 6. The heterobimetallic square of 5. Phenyl rings of PPh3 as well
as hydrogen atoms were omitted for clarity.
the tetrazolato ligand. The IR spectra of 4 and 5 show typical
broad bands in the 3260-3225 cm-1 range due to the
stretching frequency of the water molecule.21
The single-crystal X-ray diffraction structural analyses of
complexes 3b, 3c, 4, and 5 confirm their formulations. Selected
bond lengths and angles are reported in Table 2. In compound
3b the platinum atom is in an inversion center and lies in a
slightly distorted square-planar environment consisting of the
two nitrogen atoms of the tetrazolate ligands and the two
phosphorus atoms of the phosphines, in mutual trans positions
(Figure 1). Both tetrazolates are coordinated to the metal center
by the N2-nitrogen atom of the ring, as previously described
for the related complex trans-[Pt(N4CPh)2(PPh3)2],10 thus
providing the most sterically favorable N2N2-coordination mode.
Moreover, the overall bond distances and angles for this
analogue10 and 3b (Table 2) are identical.
In complex 5 the metallaligand 3b provides the required
angle for bridging between platinum and copper atoms to
form a molecular square-type structure (Figures 5 and 6).
Unlike other molecular squares where the metal atoms are
usually positioned at the vertices, here they take the positions
at the midpoint of the arms (Figure 6). The platinum atoms
are square planar, and the observed bond distances and angles
are comparable to those for the noncoordinated metallaligand
3b. The Pt-N bonds are slightly elongated with respect to
(21) Kirillov, A. M.; Karabach, Y. Y.; Haukka, M.; Guedes da Silva,
M. F. C.; Sanchiz, J.; Kopylovich, M. N.; Pombeiro, A. J. L. Inorg.
Chem. 2008, 47, 162.
11340 Inorganic Chemistry, Vol. 47, No. 23, 2008

[2 + 3] Cycloaddition of Azide to Cyanopyridines
3b, possibly due to the stretching arising from the coordina-
tion of the N-atom of the pyridyl ring to copper. The
coordination environment of the Cu(II) atom is best described
as a distorted octahedron with two mutually trans-pyridyl
ligands defining the axial positions and one water and two
nitrate ligands, one of which is coordinated in the η2- and
the other is in the η1-mode, defining the equatorial positions.
The Pt · · · Pt distance in the ring is of 11.520 Å, whereas the
Cu· · ·Cu distance is 11.921 Å. Extensive intra and intermo-
lecular contact interactions were detected. In particular, the
hydrogen bonds involving the coordinated water molecule
and the nitrate oxygen of a vicinal tetramer (H10B · · · O12,
2.2300 Å´) contribute to stabilize the structure.
Although the presence of different linkage isomers of
bis(tetrazolato) complexes had been reported in solution, on
account of the ambidentate nature of the tetrazolato ligand,
only the N2N2 isomer had been found in the solid state. This
work also shows for the first time, to our knowledge, that
the N1N2 isomer can be sufficiently stable to be isolated and
fully characterized by X-ray diffraction, provided the steri-
cally unfavorable N1 coordination component is promoted
by interaction of the metal with a suitable tetrazolato
substituent such as a pyridyl group, as in the case of complex
3c.
Acknowledgment. This work has been partially supported
by the Fundac¸a˜o para a Cieˆncia e a Tecnologia (FCT) and
its POCI 2010 program (FEDER funded) (Portugal). S.M.
expresses his gratitude to the FCT for his postdoc fellowship
(grant SFRH/BPD/14690/2003). B.G.M. and J.L. thank FCT
and IST for their research grant and contract within Cieˆncia
2007 program, respectively.
Conclusions
In this work we have used the cycloaddition reaction
between a PtII-bound azide and different cyanopyridines as
a strategic and convenient tool to generate metalla-pyridyltet-
razolate ligands of the type 3. Hence, compounds 3a and 3b
can be used successfully as metallaligands upon reaction with
copper(II) nitrate, providing heteronuclear PtII/CuII complexes
with unusual structures, namely, a molecular square type
structure and an 1D-supramolecular architecture. The nitrate
ion appears to play a relevant role for the products syntheses,
since we have failed to obtain analogous compounds using
other anions whose effects are currently under investigation.
Supporting Information Available: An extended view of the
2-D structure 4 and a CIF file containing the above mentioned
compounds are provided. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC8014223
Inorganic Chemistry, Vol. 47, No. 23, 2008 11341