Activation of C-CN bond of propionitrile: An alternative route to the syntheses of 5-substituted-1H-tetrazoles and dicyano-platinum(II) species

Article abstract of DOI:10.1016/j.poly.2008.06.031

Reaction of trans-[Pt(N₄CR)₂(PPh₃)₂] 1 (R = Me 1a, Et 1b, Ph 1c, CH₂CH₂Ph 1d) with propionitrile under reflux gives trans-[Pt(CN)₂(PPh₃)₂] 2 along with 5-substitued-1H-tetrazoles N₄CR 3 (R = Me 3a, Et 3b, Ph 3c, CH₂CH₂Ph 3d) in moderated to good yield, respectively. Treatment of cis-[Pt(N₃)₂(PPh₃)₂] 5 with alkynes HC{triple bond, long}CR′ 6 (R′ = Ph 6a, p-MeC₆H₄ 6b) under focused microwave irradiation leads, upon azide replacement, to the formation of the dialkynyl complexes trans-[Pt(C{triple bond, long}CR′)₂(PPh₃)₂] 7 (R′ = Ph 7a, p-MeC₆H₄ 7b) which also furnish the dicyano-platinum complex 2 in refluxing propionitrile. In both cases, the reactions leading to the formation of 2 proceed via an unusual oxidative addition, involving NC-C bond cleavage of two propionitrile molecules, and a reductive elimination process.

Full text of DOI:10.1016/j.poly.2008.06.031

Polyhedron 27 (2008) 2883–2888
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Activation of C–CN bond of propionitrile: An alternative route to the syntheses
of 5-substituted-1H-tetrazoles and dicyano-platinum(II) species
Suman Mukhopadhyay a, Jamal Lasri a, M. Fátima C. Guedes da Silva a,b, M. Adília Januário Charmier a,b,
,
*
Armando J.L. Pombeiro a,
*
a Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
b Universidade Lusófona de Humanidades e Tecnologias, Av. Campo Grande n° 376, 1749-024 Lisbon, Portugal
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of trans-[Pt(N4CR)2(PPh3)2] 1 (R = Me 1a, Et 1b, Ph 1c, CH2CH2Ph 1d) with propionitrile under
reflux gives trans-[Pt(CN)2(PPh3)2] 2 along with 5-substitued-1H-tetrazoles N4CR 3 (R = Me 3a, Et 3b,
Ph 3c, CH2CH2Ph 3d) in moderated to good yield, respectively. Treatment of cis-[Pt(N3)2(PPh3)2] 5 with
alkynes HC„CR0 6 (R0 = Ph 6a, p-MeC6H4 6b) under focused microwave irradiation leads, upon azide
replacement, to the formation of the dialkynyl complexes trans-[Pt(C„CR0)2(PPh3)2] 7 (R0 = Ph 7a,
p-MeC6H4 7b) which also furnish the dicyano-platinum complex 2 in refluxing propionitrile. In both
cases, the reactions leading to the formation of 2 proceed via an unusual oxidative addition, involving
NC–C bond cleavage of two propionitrile molecules, and a reductive elimination process.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 17 March 2008
Accepted 19 June 2008
Available online 11 August 2008
Keywords:
Platinum complexes
Propionitrile
Bond activation
5-Substitued-1H-tetrazoles
1. Introduction
now studied the reaction of propionitrile with a series of tetrazo-
lato trans-[Pt(N4CR)2(PPh3)2] complexes and herein we report this
Tetrazoles constitute an important class of compounds with
applications in areas of medicinal chemistry [1] and material sci-
ence [2], and are precursors for nitrogen-containing heterocycles
[3]. In 1958, Finnegan et al. [4] published the synthesis of 5-
substituted tetrazoles by heating nitriles and sodium azide in
DMF. Later on several synthetic methods based on [2+3] cycload-
dition of organonitriles and azides have been reported, by using
tin or silicon azides [5], a strong Lewis acid [6] or a strong acidic
media [4,7]. Sharpless and Demko [8] improved the method by
using a zinc salt as the Lewis acid and performing the reactions
in aqueous media. Pizzo and coworkers [9] efficiently synthesized
tetrazoles by the addition of trimethylsilyl azide to organic ni-
triles using tetrabutylammonium fluoride as catalyst. The use of
nanomaterials as catalysts [10] and microwave irradiation [11]
to shorten the reaction time has been also reported by different
authors. Moreover, we have recently reported [12] the formation
of 5-ethyl-1H-tetrazole by refluxing cis-[Pt(N3)2(PPh3)2] or the
tetrazolato complex trans-[Pt(N4CEt)2(PPh3)2] in propionitrile. To
explore the scope and generality of this method to the synthesis
of 5-R-1H tetrazoles, where R is an alkyl or aryl group, we have
generalized and easy pathway for obtaining such substituted tet-
razoles in good yields. They were isolated upon liberation of the
corresponding tetrazolato ligands from the precursor platinum
complexes on treatment with propionitrile.
On the other hand it has been found that cyanide is among the
few ligands with the capability to stabilize both low- and high-va-
lent transition metal complexes, and its high electronic and coordi-
native versatility has allowed the formation of a variety of cyano
complexes [13]. Unfortunately, the synthesis of cyano-transition
metal complexes usually involves hazardous chemicals such as
an alkali metal cyanide. A limited number of other sources of cya-
no-ligands are known but usually they concern only specific cases.
Among them, formaldoxime [14], diaminomaleonitrile [15] and
diiminosuccinonitrile [16] were used to synthesize some copper
and cobalt cyano-complexes, while trimethylsilyl cyanide (NCSiM-
e3) was applied to the preparation of cyano- and isocyano-com-
plexes of rhenium [17] and iron [17a,18]. The cyano ligand can
also be obtained by deprotonation of ligated isocyanide CNH and
aminocarbyne CNH2 [17a,17b,17c,17e,18]. Oxidative addition of
an organonitrile or ethylcyanoformate at a zero-valent group 10
transition metal has been also reported to produce a cyano-com-
plex of the corresponding metal ion [19]. In the current work we
have achieved the synthesis of trans-[Pt(CN)2(PPh3)2] starting from
bis(tetrazolato) or bis(alkynyl) platinum(II) complexes where the
solvent propionitrile acts as the precursor of the cyano-ligands.
* Corresponding authors. Address: Centro de Química Estrutural, Complexo I,
Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal.
E-mail addresses: adilia.charmier@ist.utl.pt (M.A. Januário Charmier), pombeiro@
ist.utl.pt (A.J.L. Pombeiro).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.06.031

2884
S. Mukhopadhyay et al. / Polyhedron 27 (2008) 2883–2888
(CDCl3), d 6.27–6.92 (m, 10H, C6H5), 7.33–7.86 (m, 30H, P(C6H5)).
2. Experimental
31P{1H} NMR (CDCl3), d 18.60 (JPt–P = 2650 Hz). Anal. Calc. for
PtC52H40P2: C, 67.75; H, 4.37. Found: C, 67.32; H, 4.46%. Due to
poor solubility no reliable results were obtained for 13C NMR
spectroscopy.
2.1. General and physical measurements
Solvents were purchased from Aldrich and dried by usual proce-
dures. Trans-[Pt(N4CR)2(PPh3)2] 1 [R = Me 1a, Et 1b, Ph 1c], trans-
[Pt(CN)(N4CEt)(PPh3)2] 4 and cis-[Pt(N3)2(PPh3)2] 5 were prepared
according to published procedures [12,20]. C, H and N elemental
analyses were carried out by the Microanalytical Service of the
Instituto Superior Técnico. 1H, 13C and 31P{1H} NMR spectra (in
CDCl3) were measured on a Varian Unity 300 spectrometer at
ambient temperature. The chemical shifts (d) are expressed in
2.2.3. trans-[Pt(p-MeC6H4C„C)2(PPh3)2] (7b)
This compound was prepared by a similar method to that used
for 7a, but by using 1-ethynyl-4-methylbenzene as the solvent.
Yield: 62%. IR (cmꢀ1): 2105 (C„C). 1H NMR (CDCl3), d 2.16 (s,
6H, CH3), 6.16–6.73 (m, 8H, C6H4), 7.34–7.82 (m, 30H, P(C6H5)).
31P{1H} NMR (CDCl3), d 18.55 (JPt–P = 2655 Hz). Anal. Calc. for
PtC54H44P2: C, 68.27; H, 4.67. Found: C, 67.98; H, 4.82%. Due to
poor solubility no reliable results were obtained for 13C NMR
spectroscopy.
ppm relative to Si(Me)4 (1H and 13C) or 85% H3PO4 31P). J values
(
are in Hertz. Infrared spectra (4000–400 cmꢀ1) were recorded on
a Bio-Rad FTS 3000MX and a Jasco FT/IR-430 instruments in KBr
pellets and the wavenumbers are in cmꢀ1
.
2.2.4. trans-dicyano bis(triphenylphosphine)platinum(II) complex 2
and 5-substituted-1H-tetrazoles
This compound was prepared in identical ways starting from
1a, 1c, 1d, 7a or 7b by refluxing any of these complexes in propio-
nitrile for 24 h. The following synthesis is described as a represen-
tative case.
Electrospray mass spectra of 5-substituted-1H-tetrazoles were
carried out with an ion-trap instrument (Varian 500-MS LC Ion
Trap Mass Spectrometer) equipped with an electrospray (ESI) ion
source. The solutions (in CH2Cl2) were continuously introduced
into the mass spectrometer source with a syringe pump at a flow
rate of 10 lL/min. The drying gas temperature was maintained at
A
solution of trans-[Pt(N4CCH3)2 (PPh3)2] 1a (0.088 g,
350 °C and dinitrogen was used as nebulizer gas at a pressure of
35 psi. Scanning was performed from m/z = 50–1500. The com-
pounds were observed in the negative mode (capillary volt-
age = ꢀ4000 V). The microwave irradiation experiments were
0.10 mmol) in NCEt (8 mL) was refluxed for 24 h whereupon the
solvent was removed to half of its volume in vacuo. The reaction
mixture was left to cool to room temperature and was treated with
diethyl ether (5 mL). The white solid 2 was isolated by filtration
and washed with diethyl ether for several times and chromato-
graphic purification of the complex on SiO2 was carried out using
dichloromethane/diethyl ether (10:1). The mother liquor was
evaporated to dryness and the resulting compound was identified
as 5-methyl-1H-tetrazole.
undertaken in
a focused microwave CEM Discover reactor
(10 mL, 13 mm diameter, 300 W) which is fitted with a rotational
system and an IR detector of temperature.
2.2. Compounds preparation
A slight modification was followed when starting from trans-
[Pt(5-ethyltetrazolato)2(PPh3)2] 1b. When refluxing its solution in
propionitrile, the intermediate complex trans-[Pt(CN)(5-ethyltet-
razolato)(PPh3)2] 4 started to precipitate after 6 h, whereupon
5 mL of DMF (dimethylformamide) was added to solubilize the
complex, thus allowing the reaction to proceed further.
2.2.1. trans-[Pt(5-phenethyltetrazolato)2(PPh3)2] (1d)
(i) By refluxing: A solution of cis-[Pt(N3)2(PPh3)2] 5 (0.080 g,
0.10 mmol) in NCCH2CH2Ph (8 mL) was refluxed for 12 h where-
upon the solvent was removed in vacuo. The oily residue was
treated with diethyl ether to obtain, upon stirring, a white semi-
crystalline solid. This was washed repeatedly with 5 mL portions
of water, and then with ethanol and lastly with diethyl ether.
Recrystallization from a chloroform/diethyl ether mixture gave
off-white crystals of trans-[Pt(5-phenethyltetrazolato)2(PPh3)2] 1d.
(ii) By focused microwave irradiation: In this method, identical
amounts of the reagents described above were added to a cylindri-
cal Pyrex tube which was then placed in the focused microwave
reactor. The system was left under irradiation for 1 h at 100 °C.
The solvent was then removed in vacuo and the resulting oily res-
idue was treated in a manner similar to that described above to ob-
tain a white crystalline solid of 1d. Yield: 52% (method i) and 50%
(method ii). IR (cmꢀ1): 1629 (C@N). 1H NMR (CDCl3), d 2.51 (m, 8H,
CH2), 7.11–7.51 (m, 40H, aromatic). 13C{1H} NMR (CDCl3), d 27.19
(CH2), 34.47 (CH2), 125.84–141.79 (Caromatic), 164.46 (C@N).
31P{1H} NMR (CDCl3), d 16.51 (JPt–P = 2726 Hz). Anal. Calc. for
PtC54H48N8P2: C, 60.79; H, 4.50; N, 10.50. Found: C, 60.49; H,
4.30; N, 10.39%.
2.2.5. trans-[Pt(CN)2(PPh3)2] (2)
Yield: 60%. IR (cmꢀ1): 2129 (C„N). 1H NMR (CDCl3), d 7.43–7.72
(m, 30H, aromatic). 13C{1H} NMR (CDCl3), d 125.70 (C„N), 128.49–
141.08 (Caromatic). 31P{1H} NMR (CDCl3), d 14.42 (JPt–P = 2377 Hz).
Anal. Calc. for PtC38H30N2P2: C, 59.14; H, 3.92; N, 3.63. Found: C,
59.13; H, 3.90; N, 3.25%.
2.2.6. 5-Methyl-1H-tetrazole (3a)
Yield: 70%. IR (cmꢀ1): 1629 (C@N). 1H NMR (CDCl3), d 2.60 (s,
3H, CH3). 13C{1H} NMR (CDCl3), d 9.18 (CH3), 153.21 (C@N). ESI-
MS, m/z 83 [MꢀH]ꢀ.
2.2.7. 5-Ethyl-1H-tetrazole (3b)
Yield: 75%. All the spectroscopic and ESI-MS data are in agree-
ment with those reported earlier [18].
2.2.8. 5-Phenyl-1H-tetrazole (3c)
2.2.2. trans-[Pt(C„CPh)2(PPh3)2] (7a)
Yield: 80%. IR (cmꢀ1): 1636 (C@N). 1H NMR (CDCl3), d 7.43–
8.16 (m, 5H, aromatic). 13C{1H} NMR (CDCl3), d 126.34–133.93
(Caromatic), 158.49 (C@N). ESI-MS, m/z 145 [MꢀH]ꢀ.
A solution of cis-[Pt(N3)2(PPh3)2] 5 (0.080 g, 0.10 mmol) in eth-
ynylbenzene (3 mL) was taken in a cylindrical Pyrex tube which
was then placed in the focused microwave reactor. The system
was irradiated for 1 h at 100 °C. Then the mixture was cooled
and excess of diethyl ether was added to precipitate a yellow com-
pound which was isolated by filtration and washed with diethyl
ether and dried at room temperature. The resultant compound
7a was recrystallized from a dichloromethane and diethyl ether
solvent mixture. Yield: 65%. IR (cmꢀ1): 2109 (C„C). 1H NMR
2.2.9. 5-Phenethyl-1H-tetrazole (3d)
Yield: 77%. IR (cmꢀ1): 1634 (C@N). 1H NMR (CDCl3), d 3.09 (t,
JHH = 9 Hz, 2H, CH2), 3.24 (t, JHH = 9 Hz, 2H, CH2), 7.12–7.54 (m,
5H, aromatic). 13C{1H} NMR (CDCl3), d 25.40 (CH2), 33.64 (CH2),
126.58–139.61 (Caromatic), 155.94 (C@N). ESI-MS, m/z 173 [MꢀH]ꢀ.

S. Mukhopadhyay et al. / Polyhedron 27 (2008) 2883–2888
2885
Table 1
R
Summary of crystal data, data collection and structure refinement for the X-ray
diffraction study of complexes 2 and 7a
N
N
N
2
7a
N
N
Ph3P
Ph3P
C
C
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
38H30N2P2Pt
C52H40P2Pt
921.86
orthorhombic
Pbca
18.051(2)
9.5650(11)
22.929(2)
90
90
90
3958.9(8)
4
1.547
N
N
N
EtCN
771.66
triclinic
P1
Pt
Pt
2HN
+
reflux, 24 h
N
N
N
PPh3
PPh3
ꢀ
N
9.1519(20)
9.6660(26)
10.3888(22)
109.959(13)
90.901(14)
108.283(16)
812.4(4)
1
N
2
R
b (Å)
c (Å)
3a: R = Me
3b: R = Et
3c: R = Ph
a
(°)
R
b (°)
3d: R = CH2CH2Ph
1a: R = Me
1b: R = Et
1c: R = Ph
c
(°)
V (Å3)
Z
q
l
1d: R = CH2CH2Ph
(g cmꢀ3
(Mo K
)
1.577
4.445
a
)
3.662
Scheme 1.
Number of reflections measured
Number of reflections unique
Number of reflections observed
Rint
R1, wR2 (all data)
R1, wR2 (obs. refl.)
7409
2805
2802
0.0339
0.0243, 0.0572
0.0242, 0.0572
1.034
28382
8069
4091
0.0410
0.0797, 0.0611
0.0262, 0.0476
0.913
Et
Goodness-of-fit
N
N
N
N
N
Ph3P
C
C
Ph3P
C
N
N
EtCN
Pt
Pt
HN
+
DMF, reflux, 24 h
N
2.3. Single-crystal X-ray crystallography
PPh3
PPh3
N
N
Single crystals of 2 were obtained by diffusing diethyl ether in
dichloromethane solutions of the complex. X-ray diffraction suit-
able crystals of 7a were obtained by slow evaporation of the reac-
tion mixture.
Et
2
4
3b
Scheme 2.
X-ray intensity data were measured at 150 K on a Bruker AXS-
In all the above cases the dicyano-complex 2 precipitates on
KAPPA APEX II CCD-based diffractometer (Mo
Ka radiation,
addition of diethyl ether and is further purified chromatographi-
cally using dichloromethane/diethyl ether as eluent. Evaporation
of the mother liquor provides the respective 5-substitued-1H-tet-
razole 3 (Scheme 1) as an off-white solid.
k = 0.71073 Å) using omega scans of 0.5° per frame, and a full
sphere of data was obtained. Raw data frame integration and cor-
rections were performed with Bruker SAINT. An empirical absorption
correction was applied with SADABS. Direct methods structure solu-
tion were performed with SHELXS-97 package [21] and refined with
SHELXL-97 [22] with the WinGX graphical user interface [23]. All
hydrogens were inserted in calculated positions. Least square
refinement with anisotropic thermal motion parameters for all
the non–hydrogen atoms and isotropic for the remaining atoms
were employed. Crystallographic parameters and residuals are
given in Table 1.
The dialkynyl complexes trans-[Pt(C„CR0)2(PPh3)2] 7 (R0 = Ph
7a, p-MeC6H4 7b), analogous to the dicyano compound 2, were ob-
tained by reaction of cis-[Pt(N3)2(PPh3)2] 5 with ethynylbenzene 6a
or 1-ethynyl-4-methylbenzene 6b, respectively (reaction a,
Scheme 3), under focused microwave irradiation (1 h, 100 °C,
300 W). This unexpected overall replacement of the azide ligands
by alkynyl groups occurs instead of the anticipated formation of
triazolato complexes upon metal-promoted [2+3] cycloaddition
3. Results and discussion
R´
C
The phenethyltetrazolato complex trans-[Pt(N4CR)2(PPh3)2] 1d
(R = CH2CH2Ph) was prepared by using either the traditional
refluxing method or by microwave irradiation (M.W.) as reported
in a previous paper for the synthesis of the analogous complexes
1a (R = Me), 1b (R = Et) and 1c (R = Ph) [12]. Treatment of any of
these complexes with an excess of propionitrile in refluxing condi-
tions leads ultimately to the dicyano-PtII compound trans-
[Pt(CN)2(PPh3)2] 2, isolated as a white crystalline solid in moderate
yield (ca. 60%), with concomitant formation of the corresponding
5-substituted-1H-tetrazoles 3 in good yields (ca. 80%) (Scheme 1).
The dicyano-complex 2 was synthesized and reported for the
first time by Bailar et al. [24], using [PtCl2(PPh3)2] and KCN as
the source of the cyano-ligand. When starting from trans-
[Pt(N4CEt)2(PPh3)2] 1b, the addition of a small amount of DMF is
required to prevent the precipitation of the intermediate mono-cy-
ano complex trans-[Pt(CN)(N4CEt)(PPh3)2] 4. This intermediate has
been isolated by a method described elsewhere [12] and converts
to trans-[Pt(CN)2(PPh3)2] 2 by dissolving in DMF and then refluxing
a propionitrile solution for 24 h (Scheme 2).
Ph3P
Ph3P
N3
Ph3P
C
C
M.W., 100 ºC, 1 h
(a)
Pt
+2 HC
N3
C
R´
Pt
PPh3
6a: R´ = Ph
6b: R´ = p-MePh
C
5
R´
7a: R´ = Ph
7b: R´ = p-MePh
N
EtCN
Ph3P
C
reflux, 24 h
-
2 HC
C
R´
Pt
(b)
C
PPh3
N
2
Scheme 3.

2886
S. Mukhopadhyay et al. / Polyhedron 27 (2008) 2883–2888
Table 2
between the ligated azides and the alkynes. Complex 7a was pre-
viously synthesized [25] starting from cis-[PtCl2(PPh3)2]. Both 7a
and 7b have been characterized by means of IR, 1H, and 31P{1H}
NMR spectroscopies, elemental analyses and X-ray crystallograph-
ically (for complex 7a). The observed spectroscopic data are in
accordance with those of related alkynyl complexes reported else-
where [26]. The dialkynyl complexes 7a and 7b also furnish the
dicyano-platinum complex 2 upon refluxing in propionitrile for
24 h (reaction b, Scheme 3).
The formation of the dicyano-platinum(II) complex 2 is believed
to proceed, in all the cases, via activation of the C–CN bond in pro-
pionitrile. In fact, all the attempts to transform the bis(tetrazolato)
complexes 1 or the dialkynyl complexes 7 into 2 in the absence of
propionitrile have failed (the starting materials were then recov-
ered quantitatively), namely when a CH2Cl2 solution of 1 or 7
was refluxed for 36 h or heated under focused M.W. irradiation
(2 h, 100 °C), also in solid phase (SiO2) without solvent. These re-
sults indicate that propionitrile is the precursor of the cyanide li-
gand in complex 2.
A possible pathway for the conversion of the bis(tetrazolato)
complexes 1 or the dialkynyl compounds 7 into 2 is proposed in
Scheme 4. It involves an oxidative addition of propionitrile (which
thus undergoes NC–C bond cleavage) to PtII to give a cyano-ethyl-
PtIV intermediate (reaction a, Scheme 4), followed by b-elimination
from the ethyl ligand to form ethylene, and reductive elimination
of the corresponding 5-substituted-1H-tetrazole 3 or alkyne 6 to
yield the mixed cyano-tetrazolato or cyano-alkynyl platinum(II)
complex, respectively (reaction b, Scheme 4). In most of the cases
the high solubility of these mono-cyano complexes in propionitrile
allows the reaction to proceed further towards a second oxidative
addition of EtCN and reductive elimination step (reaction c,
Scheme 4), ultimately giving the dicyano-complex 2. The evolution
of ethylene gas assists in driving these reactions. Efforts to isolate
the intermediate mixed cyano-tetrazolato or cyano-alkynyl com-
plexes failed except in the case of trans-[Pt(N4CEt)2(PPh3)2] 1b
where trans-[Pt(CN)(N4CEt)(PPh3)2] 4 precipitates from the reac-
tion mixture due to its poor solubility in propionitrile. Quantitative
recovery of complex 1a or 1c upon prolonged refluxing in benzoni-
trile or in acetonitrile, respectively, i.e. N„CR solvents with R
groups which can not undergo b-elimination, reinforces the pro-
posed mechanistic pathway.
Selected bond distances (Å) and angles (°) for complexes 2 and 7a
2
7a
Bond lengths
Pt1–P1
Pt1–C1
N1–C1
C1–C2
2.3210(12)
1.987(5)
1.154(7)
2.3118(7)
2.004(3)
1.204(4)
Bond angles
P1–Pt1–C1
P1–Pt1–C1a
Pt1–C1–C2
Pt1–C1–N1
88.25(13)
91.75(13)
86.68(8)
93.34(8)
173.0(2)
176.8(4)
a
Symmetry operation to generate equivalent atom: ꢀx, ꢀy, ꢀz.
The 5-substituted-1H-tetrazoles 3 were isolated in good yields
(ca. 80%) and characterized by IR, 1H and 13C NMR spectral data
and electrospray mass spectrometry (ESI-MS). The 13C NMR reso-
nances of the tetrazole ring carbon atoms C=N (153.2–
159.9 ppm) are observed at a higher field than those of the corre-
sponding complex precursors 1 (ca. 164 ppm).
The obtained complex 2 was characterized by elemental analy-
sis, IR and 1H, 13C{1H} and 31P{1H} spectroscopies. The IR band at
2129 cmꢀ1 and the 13C resonance at 125.7 ppm confirm the pres-
ence of the cyano ligand in the complex [27]. In the 31P{1H} NMR
spectrum, the J(31P-195Pt) value of 2726 Hz is typical for the trans
configuration in solution [28].
The single-crystal X-ray diffraction structural analyses of 2 and
7a confirm the formulations of the respective complexes. Selected
bond lengths and angles and crystallographic data are given in
Tables 1 and 2. The crystal structure of trans-[Pt(CN)2(PPh3)2] with
one methanol molecule as solvent of crystallization was reported
previously [29].
In both compounds 2 and 7a, the metal center is essentially
square-planar, the Pt atoms lie on inversion centers and the bulky
PPh3 ligands are mutually trans (Figs. 1 and 2). The bond lengths
CH3
CH2
Ph3P
C
L
Ph3P
L
L
Ph3P
L
L
EtCN
(a)
, -LH
-
CH2 CH2
(b)
Pt
Pt
Pt
C
PPh3
PPh3
N
PPh3
N
R
N
1 : L =
7 : L =
N
EtCN
(c)
N
N
-
CH2 CH2
C
CR´
N
C
Ph3P
LH
N
Pt
+
C
PPh3
N
N
N
3 : L =
6 : L =
2
N
R
C
CR´
Fig. 1. Molecular structure of trans-[Pt(CN)2(PPh3)2] 2 with atomic numbering
Scheme 4.
scheme (ellipsoids are drawn at 50% probability).

S. Mukhopadhyay et al. / Polyhedron 27 (2008) 2883–2888
2887
The extension of these methods to the preparation of (i) other cy-
ano-complexes, namely of the types [Pt(CN)2L2] and [Pt(CN)2X2L2]
(X = single-electron donating ligand, L = two-electron donor li-
gand), without the need to use toxic chemicals (such as an alkali
metal cyanide) and (ii) other 5-substituted tetrazoles (simply by
changing the R group of the organonitrile NCR precursors), are
worth to be pursued.
Acknowledgements
This work has been partially supported by the Fundação para a
Ciência e a Tecnologia (FCT) and its POCI 2010 program (FEDER
funded) (Portugal). S.M. and J.L. express gratitude to the FCT for
their post-doc. fellowships (grants SFRH/BPD/14690/2003 and
SFRH/BPD/20927/2004).
Appendix A. Supplementary data
Fig. 2. Molecular structure of trans-[Pt(C„CPh)2(PPh3)2] 7a with atomic numbering
scheme (ellipsoids are drawn at 50% probability).
CCDC 680289 and 680290 contain the supplementary crystallo-
graphic data for 7a and 2. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2008.06.031.
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