Microwave synthesis of bis(tetrazolato)-PdII complexes with PPh3 and water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA). the first example of C-CN bond cleavage of propionitrile by a PdII Centre

Article abstract of DOI:10.1016/j.jorganchem.2011.07.047

[2 + 3 Cycloaddition reactions of the di(azido)-Pd^II complex trans-[Pd(N₃)₂(PPh₃)₂ (1) with an organonitrile RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N₄CR)₂(PPh₃)₂ (3) [R = Me (3a), Ph (3b), 4-ClC₆H₄ (3c), 4-FC ₆H₄ (3d), 2-NC₅H₄ (3e), 3-NC ₅H₄ (3f), 4-NC₅H₄ (3g). The reaction of trans-[Pd(N₃)₂(PPh₃)₂ (1) with propionitrile (2h) also affords, apart from trans-[Pd(N₄CEt) ₂(PPh₃)₂ (3h), the unexpected mixed cyano-tetrazolato complex trans-[Pd(CN)(N₄CEt)(PPh₃) ₂ (3h′) which is derived from the reaction of the bis(tetrazolato) 3h with propionitrile, with concomitant formation of 5-ethyl-1H-tetrazole, via a suggested unusual oxidative addition of the nitrile to Pd^II. The [2 + 3 cycloadditions of [Pd(N₃) ₂(PTA)₂ (4) (PTA = 1,3,5-triaza-7-phosphaadamantane) with RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N₄CR)₂(PTA)₂ (5) [R = Ph (5a), 2-NC₅H₄ (5b), 3-NC₅H₄ (5c), 4-NC₅H₄ (5d). All these reactions are greatly accelerated by microwave irradiation (1 h, 125 °C, 300 W). Taking advantage of the hydro-solubility of PTA, a simple liberation of 5-phenyl-1H-tetrazole from the coordination sphere of trans-[Pd(N₄CPh)₂(PTA)₂ (5a) was achieved. The complexes were characterized by IR, ¹H, ¹³C{¹H} and ³¹P{¹H} NMR spectroscopies, ESI⁺-MS, elemental analyses and, for 3b, also by X-ray structure analysis. Weak agostic interactions between the CH groups of the triphenylphosphines and the palladium(II) centre were found.

Full text of DOI:10.1016/j.jorganchem.2011.07.047

Journal of Organometallic Chemistry 696 (2011) 3513e3520
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Microwave synthesis of bis(tetrazolato)-PdII complexes with PPh3 and
water-soluble 1,3,5-triaza-7-phosphaadamantane (PTA). The first example
of CeCN bond cleavage of propionitrile by a PdII Centre
,
a
,
,
b
,
a,d
Jamal Lasri a , María José Fernández Rodríguez c, M. Fátima C. Guedes da Silva a , Piotr Smolenski
,
*
*
ꢀ
Maximilian N. Kopylovich a, João J.R. Fraústo da Silva a, Armando J.L. Pombeiro a
,
*
a Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal
b Universidade Lusófona de Humanidades e Tecnologias, Av. Campo Grande nꢀ 376, ULHT Lisbon, 1749-024 Lisbon, Portugal
c Grupo de Química Organometálica, Departamento de Química Inorgánica, Facultad de Química, Universidad de Murcia, Apdo. 4021, Murcia 30071, Spain
d Faculty of Chemistry, University of Wrocław, ul. F. Joliot-Curie 14, 50-383 Wrocław, Poland
a r t i c l e i n f o
a b s t r a c t
[2 þ 3] Cycloaddition reactions of the di(azido)-PdII complex trans-[Pd(N3)2(PPh3)2] (1) with an orga-
nonitrile RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-[Pd(N4CR)2(PPh3)2]
(3) [R ¼ Me (3a), Ph (3b), 4-ClC6H4 (3c), 4-FC6H4 (3d), 2-NC5H4 (3e), 3-NC5H4 (3f), 4-NC5H4 (3g)]. The
reaction of trans-[Pd(N3)2(PPh3)2] (1) with propionitrile (2h) also affords, apart from trans-
Article history:
Received 7 May 2011
Received in revised form
21 July 2011
Accepted 29 July 2011
[Pd(N4CEt)2(PPh3)2]
(3h),
the
unexpected
mixed
cyano-tetrazolato
complex
trans-
[Pd(CN)(N4CEt)(PPh3)2] (3h0) which is derived from the reaction of the bis(tetrazolato) 3h with pro-
pionitrile, with concomitant formation of 5-ethyl-1H-tetrazole, via a suggested unusual oxidative addi-
tion of the nitrile to PdII. The [2 þ 3] cycloadditions of [Pd(N3)2(PTA)2] (4) (PTA ¼ 1,3,5-triaza-7-
phosphaadamantane) with RCN (2), under heating for 12 h, give the bis(tetrazolato) complexes trans-
[Pd(N4CR)2(PTA)2] (5) [R ¼ Ph (5a), 2-NC5H4 (5b), 3-NC5H4 (5c), 4-NC5H4 (5d)]. All these reactions are
greatly accelerated by microwave irradiation (1 h, 125 ꢀC, 300 W). Taking advantage of the hydro-
solubility of PTA, a simple liberation of 5-phenyl-1H-tetrazole from the coordination sphere of trans-
[Pd(N4CPh)2(PTA)2] (5a) was achieved. The complexes were characterized by IR, 1H, 13C{1H} and 31P{1H}
NMR spectroscopies, ESIþ-MS, elemental analyses and, for 3b, also by X-ray structure analysis. Weak
agostic interactions between the CH groups of the triphenylphosphines and the palladium(II) centre
were found.
Keywords:
1,3,5-Triaza-7-phosphaadamantane (PTA)
Azides
Nitriles
[2 þ 3] Cycloadditions
Tetrazoles
Microwaves
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
polycyclic fused tetrazoles can be synthesized via intramolecular
[2 þ 3] cycloaddition [6]. The cycloaddition can also be promoted by
Tetrazoles constitute an important class of compounds with
applicationsinareasofcoordinationchemistry, materialsscienceand
medicinal chemistry [1e4]. They can be synthesized by [2 þ 3]
cycloaddition of an organonitrile with an azide, but only a few acti-
vatednitriles are knownto undergothis reactionin anintermolecular
fashion [5]. When the azide and the nitrile moieties are in the same
molecule, the rate of cycloaddition can be greatly enhanced and
usingfluorous tinortrimethylsilyl azide[7], astrongLewisacid[8], or
a strong acidic media [9]. Sharpless et al. [10] improved the synthetic
method by using a zinc salt as the Lewis acid and performing the
reaction in aqueous medium. Amantini et al. [11] efficiently synthe-
sized tetrazoles by reaction of trimethylsilyl azide with a nitrile using
tetrabutylammonium fluoride as catalyst. The use of nanocrystalline
ZnO asanheterogeneous catalyst[12]andmicrowaveirradiation[13]
to shorten the reaction time have also been reported. Phthalonitrile
and terephthalonitrile react with azides in the presence of a metal
chloride to give mono-tetrazoles [14].
* Corresponding authors. Centro de Química Estrutural, Complexo I, Instituto
Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon,
Portugal. Tel.: þ351 21 841 92 37.
Moreover, the formation of substituted tetrazoles can be achieved
by using an azide coordinated to a transition metal and free organo-
nitriles [15], isocyanides [16a] or isothiocynates [16b]. For example,
we have shown [17] that the di(azido) complexes of the type cis-
E-mail addresses: jamal.lasri@ist.utl.pt (J. Lasri), fatima.guedes@ist.utl.pt
(M. F. C. Guedes da Silva), pombeiro@ist.utl.pt (A.J.L. Pombeiro).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.07.047

3514
J. Lasri et al. / Journal of Organometallic Chemistry 696 (2011) 3513e3520
R
[Pt(N3)2(PPh3)2] can react with nitriles NCR to give the bis(te-
trazolato) compounds trans-[Pt(N4CR)2(PPh3)2] from which the tet-
razoles can be liberated. Very recently, we have reported that [2 þ 3]
cycloaddition of cis-[Pt(N3)2(PPh3)2] with 4-cyanobenzaldehyde
furnishes a (formylphenyl)tetrazolate complex that reacts with
2-dimethylaminoethylamine to give the corresponding Schiff base
derivative, the latter undergoing hydrolysis in the presence of a metal
salt, while the reactions of di(azido) complexes with dicyano-
benzenes give (cyanophenyl)tetrazolate complexes [18]. In addition,
the reactions of bis(tetrazolato)-PtII compounds with propionitrile
furnish mono- or dicyano-complexes, via an unusual oxidative
addition involving NCeC bond cleavage of one or two propionitrile
molecules, respectively [17aec]. Onthe otherhand, in organometallic
chemistry, activation of carbonecarbon bonds has been a popular
topic and a few examples of NCeC bond cleavage in organonitriles by
group 10 transition metal complexes are known [19] when the metals
are in zero oxidation state. Moreover, the first example of CeC
cleavage by oxidative addition of the CeCN bond to a Rh(I) centre has
been recently reported [20].
1
N
2
2
1
R
R
N
N
N
N
1
1
2
1
N
2
N
N
N
2
N
N
N
N
N [Pd] N
[Pd] N
N [Pd] N
1
N
N
N
N
N
N
2
R
R
(a) N 1
R
(c) N 1 2-coordination
N
N
1-coordination
(b) N 2
N
2-coordination
Scheme 2.
Thus, the aims of the current work are: i) to extend the number of
trans tetrazolato-PdII complexes synthesized by [2 þ 3] cycloaddition
of a nitrile with an azide coordinated to a palladium(II) metal centre
usingPPh3 andhydrosolublePTAligands;ii)tocheck ifthementioned
reaction of azido-PdII species with propionitrile as a starting material
involves carbonecarbon bond cleavage similarly to that observed for
the tetrazolato-PtII complexes; iii) to investigate the effect of focused
microwave irradiation (M.W.), since M.W. is an alternative way to the
traditional refluxing method with the possible advantages [24] of
increasing the selectivity and reducing the reaction time.
Concerning the PdII-assisted [2 þ 3] cycloadditions of azides to
organonitriles, Beck and co-workers [21] have investigated the
reaction of benzonitrile with [Pd(N3)2(PPh3)2], by the traditional
heating method, leading to cis-[Pd(N4CPh)2(PPh3)2] and the struc-
ture of the cycloadduct was confirmed by X-ray diffraction analysis.
In this case, both 5-phenyltetrazolato ligands are coordinated to Pd
by the N2 atom. On the other hand, the crystal structure of the
related complex cis-[Pd(N4CMe)2(PMe2Ph)2] demonstrates that
both tetrazolato rings are N1-bonded [22].
2. Results and discussion
2.1. Complexes with PPh3
Treatment of the di(azido)-PdII complex trans-[Pd(N3)2(PPh3)2]
(1) with an organonitrile RCN (2), under heating for 12 h, gives the
corresponding
bis(tetrazolato)
compounds
trans-
The coordination chemistry of the aqua-soluble phosphine
1,3,5-triaza-7-phosphaadamantane (PTA) and derived species has
received an increased interest in recent years, in view of the good
solubility of their complexes in water, thus making possible their
efficient application in aqueous phase catalysis, as water-soluble
antitumour agents and photoluminescent materials [23]. Four-
and five-coordinated diazido-platinum(II) complexes cis-
[Pt(N3)2(PTA)2] and [Pt(N3)2(PTA)3] were obtained by us [17a], in
reaction of cis-[Pt(N3)2(PPh3)2] with stoichiometric amounts of PTA.
[2 þ 3] Cycloadditions with organonitriles NCR give the bis(te-
trazolato) trans-[Pt(N4CR)2(PTA)2] species [17a], from which the
tetrazoles can be liberated and also conveniently isolated in a pure
form on account, on one hand, of the high water solubility of the
concomitantly formed PTA-platinum complex and, on the other
hand, of the water insolubility of the tetrazole which spontaneously
precipitates out from the solution. In this way, the 5-substituted
tetrazoles were obtained and isolated as solids by an easy single-
pot process upon simple treatment of the respective tetrazolato
complexes with aqueous diluted HCl. However, the generality of
this rather convenient preparative method was not established.
[Pd(N4CR)2(PPh3)2] (3) [R ¼ Me (3a), Ph (3b), 4-ClC6H4 (3c), 4-FC6H4
(3d), 2-NC5H4 (3e), 3-NC5H4 (3f), 4-NC5H4 (3g)], isolated as white
or yellow crystalline solids in moderate yields (ca. 65e54%)
(Scheme 1). When using a liquid organonitrile (2ae2b), this
behaves also as the solvent whereas, in the case of solid nitriles
(2ce2g), dimethylformamide (DMF) is the solvent used. The reac-
tions are undertaken either in solvent refluxing conditions (for
12 h) by conventional heating or under focused microwave (M.W.)
irradiation (1 h, 125 ꢀC, 300 W). The latter method greatly accel-
erates the reactions, leading only in 1 h to yields that are compa-
rable to those obtained after 12 h under conventional heating. The
R
N
N
N
N3
Ph3P
Ph3P
N
Reflux, 12 h
Pd
N
R
Pd
+
or M.W., 125 oC, 1 h
N
PPh3
PPh3
N
N
N3
2a: R = Me
2b: R = Ph
N
1
2c: R = 4-ClC6H4
2d: R = 4-FC6H4
2e: R = 2-NC5H4
2f: R = 3-NC5H4
2g: R = 4-NC5H4
R
3a: R = Me
3b: R = Ph
Fig. 1. Thermal ellipsoid plot, drawn at the 50% probability level, of the trans 5-
phenyltetrazolato palladium(II) complex 3b with atomic numbering scheme.
Selected bond lengths (Å) and angles (ꢀ): Pd1ꢁP1 2.3469(4), Pd1ꢁN2 1.9953(15),
3c: R = 4-ClC6H4
3d: R = 4-FC6H4
3e: R = 2-NC5H4
3f: R = 3-NC5H4
3g: R = 4-NC5H4
P1ꢁPd1ꢁN2 91.49(4), N2ꢁPd1ꢁP1a 88.50(4).
p/p and agostic interactions (shown as
dashed lines): centroid/centroid 3.6536(12) Å; d(H12/Pd1) 3.40 Å,
:(C12eH12/Pd1) 107.09ꢀ; d(H36/Pd1) 2.93 Å, :(C36eH36/Pd1) 119.51ꢀ.
Hydrogen atoms not involved in fundamental interactions are omitted for clarity.
Symmetry code to generate equivalent atoms: a) ꢁx,1ꢁy,1ꢁz.
Scheme 1.

J. Lasri et al. / Journal of Organometallic Chemistry 696 (2011) 3513e3520
3515
Et
Et
N
N
N
N
N
Ph3P
N3
N3
Ph3P
N
Ph3P
Reflux, 12 h
N
N
N
+
Et
Pd
Pd
+
Pd
N
or M.W., 125 ºC, 1 h
PPh3
N
N
PPh3
C
N
PPh3
2h
N
1
3h
3h´
Et
Scheme 3.
tetrazolato-PdII complexes are formed via [2 þ 3] cycloaddition of
the organonitriles with the ligated azides.
Nevertheless, the 31P{1H} NMR spectrum of 3a synthesized by
conventional heating methods (reflux, 12 h) shows only three
The obtained complexes 3 were characterized by elemental
analyses, IR and 1H, 13C{1H} and 31P{1H} spectroscopies, and ESIþ-
MS. Their IR spectra do not show the typical azide band at ca.
signals at d 17.65, 23.02 and 29.19, probably due to the conversion of
the cis isomer (31P{1H} NMR
more stable trans form.
d 18.08) into the thermodynamically
2036 cmꢁ1 and display
a
new strong band within the
Inourprevious work [17c], wefoundthatthe5-phenyltetrazolato-
1615e1638 cmꢁ1 range due to the tetrazole ring, in agreement with
the literature [17]. No band assigned to NeH stretching or bending
was observed, in contrast to typical bands of triphenylphosphine
ligands at ca. 1436 cmꢁ1 and 693 cmꢁ1, which are also displayed by
the starting complex 1. The 13C{1H} NMR spectra of complexes 3
show the characteristic signal in the 151e164 ppm range due to the
carbon of the tetrazolato ring.
PtII complex trans-[Pt(N4CPh)2(PPh3)2] exhibits one signal at
d 17.11
(JPteP ¼ 2720 Hz) in the 31P{1H} NMR spectrum, due to the presence of
only one isomer in solution. Moreover, the single trans isomer was
prepared by both conventional heating methods and under M.W.
irradiation. However, the 31P{1H} NMR spectrumof the analogous PdII
complex [Pd(N4CPh)2(PPh3)2] (3b) prepared under M.W. irradiation
(1 h, 125 ꢀC, 300 W) shows three resonances at
29.25. When 3b is prepared under solvent refluxing conditions (12 h),
only one signal at
18.40 is observed in its 31P{1H} NMR spectrum.
d 18.40, 22.82 and
Moreover, the NMR spectra of 3 often display more than one
peak for each particular type of atoms, what can be accounted for
by linkage isomerism due to the possible ambidentate behaviour of
the tetrazolate ligand which, in principle, can bind to the metal
through either the N1 or the N2 atom leading to the possibility of
existence of several isomers (N1N1, N2N2 and N1N2 combinations),
in addition to cis- and trans-isomers [17c] (Scheme 2). However,
N2N2-coordinated is sterically favourable and is that established in
the solid state by X-ray diffraction (see below).
d
This is indicative that in this case the possible cis/trans-isomers (with
different coordination modes) can also convert into the thermody-
namically more stable trans one, and in order to avoid steric
congestion, both the bulky phenyltetrazolato rings are conceivably
coordinated to the metal centre only by the N2 atom [17c].
The single crystal X-ray diffraction analysis of 3b confirms the
proposed structure. The ORTEP drawing in Fig.1 clearly displays the
N2N2-coordination mode of the tetrazolato ligands. The metal lies
on a crystallographic inversion point in a slightly distorted square-
For instance, the 1H NMR spectrum of cis/trans-
[Pd(N4CMe)2(PPh3)2] (3a) shows four signals for the methyl
protons at
spectrum four resonances for the methyl carbon are detected at
9.93, 9.95, 10.60 and 10.69, suggesting the presence of four
isomers in solution. In the 31P{1H} NMR spectrum, also four signals
d
1.88, 2.01, 2.21 and 2.24, whereas in the 13C{1H} NMR
N
d
N
+2 PTA
P
Ph3P
N3
N3
P
N3
N
-2 PPh3
were observed at d 17.65, 18.08, 23.02 and 29.19. Those four isomers
Pd
Pd
concern 3a obtained under M.W. irradiation (1 h, 125 ꢀC, 300 W).
N
CH2Cl2, r.t., 1 h
N3
PPh3
N
Et
1
Et
N
4
CH3
N
N
N
N
N
C
CH2CH3
CH
Pd
C
Ph3P
2N
Ph3P
N
Reflux, 12 h
N
N
N
R
2h
Pd
N
2
N
or M.W., 125 ºC, 1 h
N
N
PPh3
N
N
PPh3
N
N
R
N
Et
3h
N
Et
N
N
N
-
H2C CH2
N
N
P
N
Pd
N
N
P
Et
N
N
N
N
N
N
N
N
N
+
HN
N
N
Ph3P
N
R
Pd
5a: R = Ph
Et
C
PPh3
5b: R = 2-NC5H4
5c: R = 3-NC5H4
5d: R = 4-NC5H4
N
3h´
Scheme 4.
Scheme 5.

3516
J. Lasri et al. / Journal of Organometallic Chemistry 696 (2011) 3513e3520
H
N
Ph
+
N
N
N
Ph
N
N
N
Cl
Cl
P
P
N
N
N
0.5 M HCl
Reflux, 1 h
HN
N
2
Pd
Pd
H
+
N
Cl2
N
N
P
N
P
N
N
N
N
N
N
N
N
+
Ph
5a
6
Scheme 6.
planar geometry with the two tetrazolato rings in mutually trans
position. The tetrazole rings are essentially planar and their phenyl
moieties are twisted out of the N4C plane with a dihedral angle of
16.43ꢀ. Moreover, the phenyl substituents attached to the tetrazo-
lato rings are oriented in the opposite direction (anti orientation),
while the phosphine groups take a staggered conformation. The
PdꢁN bond distance (1.9953(15) Å) is comparable with those found
(ca. 2.08 Å) in other bis-tetrazolato Pd(II) complexes [21,22], and is
somewhat shorter than the sum of the metal and nitrogen covalent
Complex 3h0 cannot be isolated in a pure form, by thermal
heating or under M.W. irradiation, and a mixture of 3h and 3h0 was
obtained. The mixture has been characterized by IR and 1H, 13C{1H}
and 31P{1H} NMR spectroscopies, and ESIþ-MS. The IR spectrum of
the mixture shows a strong band at 1630 cmꢁ1 due to the tetrazole
rings and a band at 2139 cmꢁ1 is assigned to
n(CN) of the cyano
ligand (complex 3h0). The 13C{1H} NMR resonances at 126.9 and
166.5 ppm confirm the presence of cyano and tetrazolato ligands,
respectively [17]. The 31P{1H} NMR spectrum of the reaction
radii (1.39 þ 0.68 Å) suggesting a partial
p
-character in this bond.
mixture shows two resonances at
intensities).
d 23.0 and 30.2 (3:1 relative
The PdeP bond distance (2.3469(4) Å) is also shorter than the metal
and phosphorus covalent radii (1.39 þ 1.05 Å), what is commonly
found in mutually trans-phosphines.
2.2. Complexes with PTA
The complex molecule conformation is stabilized by intra-
molecular
p/p interaction involving the tetrazole ring and the
As mentioned above, PTA can be an alternative and useful
phosphine for further applications in aqua-systems. Hence, we
decided to synthesize analogous complexes with PTA instead of
PPh3, and to carry out the liberation of ligated tetrazole in aqueous
medium. The reaction of stoichiometric quantities of PTA and trans-
[Pd(N3)2(PPh3)2] (1) (Pd:PTA ¼ 1:2) in CH2Cl2 at room temperature
leads to the precipitation of [Pd(N3)2(PTA)2] (4) as an yellow
microcrystalline solid in 60% yield (Scheme 5). Complex 4 is stable
in the solid state and in solution. The bis(tetrazolato) complexes
trans-[Pd(N4CR)2(PTA)2] (5) [R ¼ Ph (5a), 2-NC5H4 (5b), 3-NC5H4
(5c) or 4-NC5H4 (5d)] were synthesized by reaction of
[Pt(N3)2(PTA)2] (4) with the appropriate organonitrile NCR (2), and
the reaction is accelerated by M.W. (125 ꢀC, 1 h, 300 W). They were
isolated in moderate yields (ca. 50e55%) as yellow powders
(Scheme 5). The tetrazolato-PdII complexes 5ae5d are formed via
[2 þ 3] cycloaddition of the organonitriles with the ligated azides
and they are stable in the solid state. Complex 5a is soluble in
middle polar solvents, such as CHCl3 and CH2Cl2, sparingly soluble
in polar ones such as H2O, MeOH, MeCN and Me2SO, while
compounds 5be5d are insoluble in common organic solvents and
water.
phosphine C11 > C16 phenyls (centroid/centroid distance of
3.6536(12) Å). Moreover, reasonably strong intramolecular agostic
interactions were also found, involving the metal and aromatic
phosphine hydrogens (H12/Pd1 3.40 Å, C12eH12/Pd1 107.09ꢀ;
H36/Pd1 2.93 Å, C36eH36/Pd1 119.51ꢀ). Therefore, the above
considered square-planar geometry around the Pd(II) centre in 3b
can be envisaged as a distorted octahedron if the longer agostic
Pd1/H interactions are taken into consideration.
Similarly to the case of platinum(II) complexes [17c], the reac-
tion of propionitrile (2h) with trans-[Pd(N3)2(PPh3)2] (1), by
refluxing for 12 h or under M.W. irradiation (1 h, 125 ꢀC, 300 W),
gives not only the expected trans-[Pd(N4CEt)2(PPh3)2] (3h), but also
the cyano-complex trans-[Pd(CN)(N4CEt)(PPh3)2] (3h0) (Scheme 3).
The formation of 3h0 is believed to proceed via the bis(te-
trazolato) compound 3h, propionitrile being the precursor of the
cyanide ligand. The initial formation of complex 3h via the [2 þ 3]
cycloaddition of the propionitrile (as observed with the other
nitriles) with a ligated azide is kinetically driven and such
a complex, upon prolonged reaction time, converts into the ther-
modynamically more stable cyano-complex 3h0.
A possible pathway for the unexpected conversion of 3h into the
corresponding cyano-complex 3h0 is proposed in Scheme 4. It
involves an oxidative addition of propionitrile (which thus
undergoes NCeC bond cleavage [17c,19,20]) to PdII to give a cyano-
Compounds 4 and 5 have been characterized by elemental
analyses, IR and NMR spectroscopies. The IR spectrum of 4 exhibits
the typical azide band (2037 cmꢁ1). The 13C{1H} NMR spectrum of
5a shows the characteristic signal at 165 ppm due to the tetrazolato
ring carbon. The 1H NMR spectra of 4 and 5a at room temperature
show two types of methylene protons. One of them, PeCH2eN,
ethyl-PdIV intermediate, followed by
b-elimination from the ethyl
ligand to form ethylene,1 and reductive elimination of 5-ethyl-1H-
tetrazole, which could be isolated and characterized by IR, 1H and
13C{1H} NMR spectroscopies and ESIþ-MS.
occurs as a broad singlet at
d 4.35 and 4.20, respectively. The second
type, NeCH2eN, displays for 4 and 5a an AB spin system centred at
d
4.47 and 4.44 (JAB ¼ 13 and 15 Hz), respectively, assigned to the
NeCHaxeN and the NeCHeqeN protons [23]. The 31P{1H} NMR
spectra of 4 and 5a display singlets at ꢁ30.2 and ꢁ47.3 ppm,
respectively.
1
Ethylene cannot be detected in solution by NMR on account of its too low
amount relatively to that of the propionitrile solvent bearing the interfering strong
propyl NMR resonances. However, the formation of ethylene is corroborated by the
stoichiometry of the reaction (Scheme 4).
Liberation of the ligated tetrazole from the coordination sphere
of the bis(tetrazolato)-PdII complex trans-[Pd(N4CPh)2(PTA)2] (5a)

J. Lasri et al. / Journal of Organometallic Chemistry 696 (2011) 3513e3520
3517
Table 1
multifunctionality of the tetrazolato and of the cyano-tetrazolato
complexes provides a potential convenient entry to polynuclear
assemblies which deserves to be explored.
Taking advantage of the hydro-solubility of PTA, a simple
liberation of the ligated tetrazolate from the coordination sphere of
trans-[Pd(N4CPh)2(PTA)2] was achieved, similarly to related Pt(II)
Crystal data and structure refinement details for trans-
[Pd(N4CPh)2(PPh3)2] (3b).
Compound
3b
empirical formula
fw
C50H40N8P2Pd
921.24
l
(Å)
complexes, what constitutes
a
convenient metal-mediated
cryst syst
space group
a (Å)
b (Å)
c (Å)
Triclinic
P-1
synthetic method for substituted tetrazoles.
Finally, microwave irradiation promotes the [2 þ 3] cycloaddi-
tion of organonitriles with azide, resulting in a pronounced short-
ening of the reaction time relatively to the conventional heating.
8.7688 (3)
11.7142 (4)
11.7416 (4)
68.890 (2)
76.809 (3)
72.483 (2)
1063.20 (7)
1
a
b
g
(deg)
(deg)
(deg)
V (Å3)
4. Experimental
Z
rcalcd (g/cm3)
1.439
0.558
4.1. General procedures, materials and measurements
m
(Mo-K
a
) (mmꢁ1
)
no. of collected reflns
no. of unique reflns
Rint
25117
6886
0.0403
0.0373, 0.0821
1.049
Solvents were purchased from Aldrich and dried by usual
procedures. Trans-[Pd(N3)2(PPh3)2] (1) [26] and PTA [27] were
prepared according to published procedures. C, H and N elemental
analyses were carried out by the Microanalytical Service of the
Instituto Superior Técnico. 1H, 13C{1H} and 31P{1H} NMR spectra (in
CDCl3 or DMSO-d6) were measured on a Bruker Avance II 300 and
400 MHz (UltraShieldÔ Magnet) spectrometer at ambient
Final R1,a wR2b (I ꢂ 2
s
)
GOF on F2
a
R1 ¼ SjjFoj ꢁ jFcjj/SjFoj.
b
wR2 ¼ [S[w(F2o ꢁ F2c)2]/S[w(F2o)2]]1/2
.
temperature. 1H, 13C{1H} and 31P{1H} chemical shifts (
expressed in ppm relative to Si(Me)4 (1H and 13C{1H}) or 85% H3PO4
31P). Infrared spectra (4000e400 cmꢁ1) were recorded on a Bio-
d) are
was achieved by treatment with aqueous HCl, similarly to the
previously described [17a] reaction of the platinum compounds
trans-[Pt(N4CR)2(PTA)2] (R ¼ Ph, 4-ClC6H4 or 3-NC5H4) with diluted
HCl (Scheme 6). The method is simple and convenient in terms of
providing an easy separation of the tetrazole products. It involves
refluxing a suspension of 5a in aqueous 0.5 M HCl for 1 h. The
precipitate formed during the reaction was separated by filtration
and a white solid was then extracted with chloroform, and shown
(by IR and NMR spectroscopies) to be the corresponding 5-phenyl-
1H-tetrazole (yield ca. 50%) [17a]. The remaining white-yellow
precipitate is completely insoluble in chloroform, and, by IR (KBr)
and elemental analysis, was shown to be [PdCl2(PTA-H)2]Cl2 (6)
(PTA-H ¼ N-protonated PTA cation). Its insolubility in common
solvents precluded NMR analysis, but it is deprotonated by base
(NaOH) to give the expected known [PdCl2(PTA)2] [28], as proved
by 31P{1H} NMR in a D2O solution with NaOH.
(
Rad FTS 3000MX instrument in KBr pellets and the wavenumbers
are in cmꢁ1. Electrospray mass spectra were carried out with an
ion-trap instrument (Varian 500-MS LC Ion Trap Mass Spectrom-
eter) equipped with an electrospray (ESI) ion source. The solutions
in methanol were continuously introduced into the mass spec-
trometer source with a syringe pump at a flow rate of 10 mL/min.
The drying gas temperature was maintained at 350 ꢀC and dini-
trogen was used as nebulizer gas at a pressure of 35 psi. Scanning
was performed from m/z ¼ 50 to 1500. The microwave irradiation
experiments were 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.
3. Conclusions
4.2. Preparations
In this work we have shown that the di(azido) compounds
trans-[Pd(N3)2(PPh3)2] and [Pd(N3)2(PTA)2] (which are hydro-
soluble) are good starting materials for a variety of trans bis(5-
substituted tetrazolato)-PdII complexes derived upon [2 þ 3]
cycloadditions with nitriles. We also found that propionitrile, on
reaction with trans-[Pd(N4CEt)2(PPh3)2] (3h), undergoes an
unusual NCeC bond cleavage behaving as a source of a cyano ligand
to give trans-[Pd(CN)(N4CEt)(PPh3)2] (3h0) and 5-ethyl-1H-tetra-
zole, via a suggested unusual oxidative addition of this nitrile to PdII
4.2.1. Complexes 3ae3b
These complexes can be prepared by two different methods. The
first one by refluxing the solution of the starting complex trans-
[Pd(N3)2(PPh3)2] (1) in the respective nitrile, and the second one by
using focused microwave irradiation.
(i) By refluxing: A solution of trans-[Pd(N3)2(PPh3)2] (1) (20.0 mg,
0.028 mmol) in acetonitrile (2a) or benzonitrile (2b) (4 mL) was
refluxed or heated at 100 ꢀC (in the case of benzonitrile) for 12 h
whereupon the solvent was removed in vacuo. The residue was
washed with diethyl ether to obtain a white or yellow semi-
crystalline solid. Recrystallization from a chloroform/diethyl
ether mixture gave complexes 3a or 3b, respectively. Single
crystals of complex 3b suitable for X-ray structural analysis
were obtained by slow evaporation of a chloroform solution.
(ii) By focused microwave irradiation: In this method, identical
amounts of the reagents described above were added to
a cylindrical Pyrex tube which 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 solid residue was treated in a manner similar to that
described above to obtain a white crystalline solid of 3a or 3b.
followed by
b-H-elimination from the derived ethyl ligand and
reductive elimination of the tetrazole. This provides, to our
knowledge, the first example of synthesis of a mixed cyano-
tetrazolato palladium(II) complex, which is obtained by CeC bond
cleavage of an organonitrile.
The trans arrangement of the two tetrazolato ligands appears to
be the most favourable one, in contrast to the previous reports
[21,22,25], as clearly established by X-ray diffraction analysis.
Different linkage isomers, on account of the ambidentate character
of the tetrazolato ligand that can coordinate by either the N1 or the
N2 mode, have been spectroscopically detected in solution, but the
resolved crystal structure of complex 3b shows that, in the solid
state, the mode of tetrazolato binding is through the N2atom. The

3518
J. Lasri et al. / Journal of Organometallic Chemistry 696 (2011) 3513e3520
4.2.2. Complexes 3ce3g
solvents (CDCl3, MeOD-d4 or DMSO-d6). 31P{1H} NMR (CDCl3),
d
23.50. Anal. Calcd for PdC48H38N10P2: C, 62.44; H, 4.15; N, 15.17.
(i) By refluxing: To a 4 mL solution of trans-[Pd(N3)2(PPh3)2] (1)
(20.0 mg, 0.028 mmol) in DMF was added 4-chlorobenzonitrile
(2c), 4-fluorobenzonitrile (2d), 2-cyanopyridine (2e), 3-
cyanopyridine (2f) or 4-cyanopyridine (2g) (0.280 mmol).
The resulting mixture was refluxed for 12 h. The solution
became turbid as the product started to precipitate. The
mixture was cooled and the solid was filtered off, washed
several times with 5 mL portions of diethyl ether, and dried in
vacuo to give the final complex 3c, 3d, 3e, 3f or 3g, respectively.
(ii) By focused microwave irradiation: Complexes 3ce3g were
also prepared by dissolving the above mentioned amounts of
the reagents in 4 mL of DMF and irradiating the solution with
focused microwave for 1 h at 125 ꢀC. They precipitated as
white or yellow solids which were washed several times with
diethyl ether and dried in vacuo.
Found: C, 62.33; H, 4.44; N, 15.45. ESIþ-MS, m/z 924 [M þ 1]þ.
4.2.8. Trans-[Pd(N4C(3-NC5H4))2(PPh3)2] (3f)
61% (method i) and 60% (method ii) yield. IR (cmꢁ1): 693 and
1436 (PPh3), 1630 (C]N). 1H NMR (CDCl3),
d
7.44e7.72 (m, 38H,
128.40e134.02 (Caromatic). The
signal of the imine moiety (C]N) could not be observed even after
more scans. 31P{1H} NMR (CDCl3),
29.25. Anal. Calcd for
aromatic). 13C{1H} NMR (CDCl3),
d
d
PdC48H38N10P2: C, 62.44; H, 4.15; N, 15.17. Found: C, 62.38; H, 4.55;
N, 15.37. ESIþ-MS, m/z 924 [M þ 1]þ.
4.2.9. Trans-[Pd(N4C(4-NC5H4))2(PPh3)2] (3g)
63% (method i) and 65% (method ii) yield. IR (cmꢁ1): 694 and
1436 (PPh3), 1619 (C]N). 1H NMR (CDCl3),
d
7.19e7.67 (m, 38H,
120.80e150.15 (Caromatic), 161.67,
161.87, 162.09 and 162.50 (C]N). 31P{1H} NMR (CDCl3),
18.96,
aromatic). 13C{1H} NMR (CDCl3),
d
d
24.22, 26.34 and 29.41 (only the signal in italic was observed when
the complex was obtained under refluxing conditions). Anal. Calcd
for PdC48H38N10P2: C, 62.44; H, 4.15; N, 15.17. Found: C, 62.41; H,
4.20; N, 15.27. ESIþ-MS, m/z 924 [M þ 1]þ.
4.2.3. Trans-[Pd(N4CMe)2(PPh3)2] (3a)
60% (method i) and 58% (method ii) yield. IR (cmꢁ1): 693 and
1436 (PPh3),1630 (C]N). 1H NMR (CDCl3),
d
1.88, 2.01, 2.21 and 2.24
(6H, CH3), 7.30e7.72 (m, 30H, aromatic). 13C{1H} NMR (CDCl3),
9.93, 9.95,10.60 and 10.69 (CH3),125.44e135.64 (Caromatic),151.44,
156.74, 157.01 and 161.27 (C]N). 31P{1H} NMR (CDCl3),
17.65,
d
4.2.10. Preparation of trans-[Pd(N4CEt)2(PPh3)2] (3h), trans-
[Pd(CN)(N4CEt)(PPh3)2] (3h0) and 5-ethyl-1H-tetrazole
d
18.08, 23.02 and 29.19 (the signal in italic was not observed when
the complex was prepared under refluxing conditions). Anal. Calcd
for PdC40H36N8P2: C, 60.27; H, 4.55, N, 14.06. Found: C, 60.51; H,
4.31; N, 14.30. ESIþ-MS, m/z 798 [M þ 1]þ.
A solution of trans-[Pd(N3)2(PPh3)2] (1) (20.0 mg, 0.028 mmol)
in propionitrile (2h) (4 mL) was refluxed for 12 h or irradiated
under M.W. (1 h, 125 ꢀC, 300 W) whereupon the solvent was
removed in vacuo. The white solid (3h and 3h0) was filtered off and
washed with diethyl ether for several times. The mother liquor was
evaporated to dryness and the resulting compound was identified
as 5-ethyl-1H-tetrazole.
4.2.4. Trans-[Pd(N4CPh)2(PPh3)2] (3b)
58% (method i) and 62% (method ii) yield. IR (cmꢁ1): 693 and
1437 (PPh3), 1638 (C]N). 1H NMR (CDCl3),
d
7.21e7.59 (m, 40H,
126.24e135.52 (Caromatic), 164.54
18.40, 22.82 and 29.25 (only the
aromatic). 13C{1H} NMR (CDCl3),
(C]N). 31P{1H} NMR (CDCl3),
d
4.2.11. Trans-[Pd(N4CEt)2(PPh3)2] (3h) and trans-
[Pd(CN)(N4CEt)(PPh3)2] (3h0)
d
signal in italic was observed when the complex was obtained under
refluxing conditions). Anal. Calcd for PdC50H40N8P2: C, 65.19; H,
4.38; N, 12.16. Found: C, 65.56; H, 4.19; N, 11.93. ESIþ-MS, m/z 922
[M þ 1]þ.
IR (cmꢁ1): 2139 (C^N), 1630 (C]N). 1H NMR (CDCl3),
d
0.84e1.33 (m, 9H, CH3), 2.18e2.37 (m, 6H, CH2), 7.35e7.69 (m,
60H, aromatic). 13C{1H} NMR (CDCl3),
10.87, 12.41 and 12.55 (CH3),
18.64 and 18.78 (CH2), 126.97 (C^N), 127.59e134.39 (Caromatic),
d
166.53 (C]N). 31P{1H} NMR (CDCl3),
d
23.0 and 30.2. ESIþ-MS, m/z
4.2.5. Trans-[Pd(N4C(4-ClC6H4))2(PPh3)2] (3c)
825 [M þ 1]þ (3h) and 755 [M þ 1]þ (3h0).
55% (method i) and 58% (method ii) yield. IR (cmꢁ1): 691 and
1438 (PPh3), 1630 (C]N). 1H NMR (CDCl3),
d
7.19e7.79 (m, 38H,
4.2.12. 5-ethyl-1H-tetrazole
aromatic). 13C{1H} NMR (CDCl3),
d
127.39e135.63 (Caromatic). The
IR (cmꢁ1): 1638 (C]N). 1H NMR (CDCl3),
d
1.30 (t, JHH ¼ 7.6 Hz,
signal of the imine moiety (C]N) could not be observed even after
3H, CH3), 2.87 (q, JHH ¼ 7.6 Hz, 2H, CH2).13C{1H} NMR (CDCl3),
more scans and/or by using DMSO-d6 as solvent. 31P{1H} NMR
d
14.16 (CH3), 19.33 (CH2), 159.86 (C]N). ESIþ-MS, m/z 99 [M þ 1]þ.
(CDCl3),
NMR in DMSO-d6 at
d
18.53, 20.05, 22.91 and 29.23 (only one signal of 31P{1H}
d
25.65 was observed when the complex was
4.2.13. [Pd(N3)2(PTA)2]$CH2Cl2, (4)$CH2Cl2
To solution of trans-[Pd(N3)2(PPh3)2] (1) (200.0 mg,
obtained under refluxing conditions). Anal. Calcd for
PdC50H38N8P2Cl2: C, 60.65; H, 3.87; N, 11.32. Found: C, 60.41; H,
3.71; N, 11.50. ESIþ-MS, m/z 991 [M þ 1]þ.
a
0.28 mmol) in dichloromethane (25 mL), PTA (88.0 mg,
0.56 mmol) was added. The mixture was stirred for ca. 1 h under
dinitrogen at room temperature. The yellow precipitate was
separated from the brown solution by filtration, washed with
chloroform (3 ꢃ 10 mL) and dried in vacuo to afford complex 4 as
a yellow microcrystalline solid. Yield of 4$CH2Cl2 60% (85 mg).
Complex 4 is soluble in H2O and DMSO, slightly soluble in MeOH
and CH2Cl2, and insoluble in C6H6. [Pd(N3)2(PTA)2]$CH2Cl2,
C13H26Cl2N12P2Pd (589.7): calcd. C 26.48, N 28.50, H 4.44; found C
4.2.6. Trans-[Pd(N4C(4-FC6H4))2(PPh3)2] (3d)
54% (method i) and 56% (method ii) yield. IR (cmꢁ1): 694 and
1451 (PPh3), 1615 (C]N). 1H NMR (DMSO-d6),
d
7.26e7.71 (m, 38H,
129.17e133.71 (Caromatic),
161.11, 161.83 and 162.41 (C]N). 31P{1H} NMR (DMSO-d6),
25.50.
aromatic). 13C{1H} NMR (DMSO-d6),
d
d
Anal. Calcd for PdC50H38N8P2F2: C, 62.74; H, 4.00; N, 11.71. Found: C,
62.41; H, 4.21; N, 11.49. ESIþ-MS, m/z 958 [M þ 1]þ.
26.00, N 29.11, H 4.45. IR (KBr): 2930 (s br) n(CH), 2037 (s br)
n
(N3), 1278 (m), 1242 (s), 1099 (m), 1014 (s), 972 (s), 943 (s), 904
4.2.7. Trans-[Pd(N4C(2-NC5H4))2(PPh3)2] (3e)
(m), 805 (m), 741 (m), 582 (m) (PTA) cmꢁ1. 1H NMR (DMSO-d6):
60% (method i) and 62% (method ii) yield. IR (cmꢁ1): 719 and
d
5.75 (s, CH2Cl2, 2H), 4.53 HA and 4.41 HB (JAB ¼ 13.0 Hz,
1450 (PPh3), 1619 (C]N). 1H NMR (CDCl3),
d
7.34e7.75 (m, 38H,
NCHAHBN, 12H), 4.35 (s, PCH2N, 12H). 13C{1H} NMR (DMSO-d6):
aromatic). The 13C{1H} NMR spectrum was not possible to obtain
d
72.6 (s, NeCH2eN, PTA), 55.8 (s, CH2Cl2), 52.3 (br. s, PeCH2eN,
due to the very poor solubility of the complex 3e in common
PTA). 31P{1H} NMR (DMSO-d6):
d
ꢁ30.2 (s).

J. Lasri et al. / Journal of Organometallic Chemistry 696 (2011) 3513e3520
3519
4.2.14. Trans-[Pd(N4CPh)2(PTA)2]$PhCN, (5a)$PhCN
Additionally, the ESIþ-MS spectrum showed the expected isotopic
pattern centred at m/z 491 ([M þ 1]þ), thus confirming the
formation of [PdCl2(PTA)2] upon neutralization of 6.
A mixture of [Pd(N3)2(PTA)2]$CH2Cl2 (4$CH2Cl2) (59.0 mg,
0.10 mmol) and PhCN (5 mL, 48.5 mmol) was added to a cylindrical
Pyrex tube which was then placed in the focused microwave
reactor. The system was left under irradiation for 1 h at 125 ꢀC (the
same product was obtained when the mixture of reagents was
refluxed for 12 h). After reaction, the excess of PhCN was removed
in vacuo and the resulting residue was washed repeatedly with
10 mL portions of diethyl ether. Recrystallization from a dichloro-
methane/diethyl ether mixture gave yellow microcrystals of trans-
[Pd(N4CPh)2(PTA)2]$PhCN (5a$PhCN). Yield 55% (45 mg). Complex
5a is soluble in DMSO, CHCl3 and CH2Cl2, sparingly soluble in H2O,
and insoluble in diethyl ether and C6H6. Trans-[Pd(N4CPh)2(PTA)2]$
PhCN, C33H39N15P2Pd (814.1): calcd. C 48.68, N 25.81, H 4.83; found
C 48.38, N 24.76, H 4.50. IR (KBr): 2931 (m br), 2230 (w), 1629 (m),
1443 (m), 1384 (m), 1369 (w),1285 (m), 1245 (m), 1101 (m), 1013 (s),
975 (s), 945 (s), 800 (m), 741 (m), 580 (m) cmꢁ1. 1H NMR (CDCl3):
4.2.17. 5-phenyl-1H-tetrazole
Yield: 80%. IR (cmꢁ1): IR (cmꢁ1): 1636 (C]N). 1H NMR (CDCl3),
d
7.43e8.16 (m, 5H, aromatic).13C{1H} NMR (CDCl3),
d 126.34e133.93
(Caromatic), 158.49 (C]N). ESIꢁ-MS, m/z 145 [M ꢁ H]ꢁ.
4.3. Crystal structure determination
Single crystals of 3b suitable for X-ray analysis were obtained by
slow evaporation of a chloroform solution at room temperature.
Intensity data were collected using a Bruker AXS-KAPPA APEX II
diffractometer using graphite monochromated Mo-K
a radiation.
Data were collected at 150 K, using omega scans of 0.5ꢀ per frame
and a full sphere of data was obtained. Cell parameters were
retrieved using Bruker SMART software and refined using Bruker
SAINT on all the observed reflections. Absorption corrections were
applied using SADABS [29]. Structures were solved by direct
methods by using the SHELXSe97 package [30] and refined with
SHELXLe97 [30]. Calculations were performed with the WinGX
System-Version 1.80.03 [31]. All hydrogens were inserted in
calculated positions. Least square refinement with anisotropic
thermal motion parameters for all the nonehydrogen atoms and
isotropic for the remaining were employed. Crystal data and details
of data collection for 3b are given in Table 1.
d
8.18e7.45 (m, 2Ph
þ
PhCN, 15H), 4.48 HA and 4.40 HB
(JAB ¼ 15.0 Hz, NCHAHBN, 12H), 4.20 (s, PCH2N, 12H). 13C{1H} NMR
(CDCl3,): d 165.0 (s, N4C), 126.4e135.0 (Caromatic), 73.1 (s, NeCH2eN,
PTA), 50.9 (br s, PeCH2eN, PTA). 31P{1H} NMR (CDCl3):
d
ꢁ47.3 (s).
4.2.15. Trans-[Pd(N4C(n-NC5H4))2(PTA)2], (5b) (n ¼ 2), (5c) (n ¼ 3)
and (5d) (n ¼ 4)
A mixture of [Pd(N3)2(PTA)2]$CH2Cl2 (4$CH2Cl2) (59.0 mg,
0.10 mmol) and n-cyanopyridine (104 mg, 1.0 mmol) in DMF (5 mL)
was added to a cylindrical Pyrex tube which was then placed in the
focused microwave reactor. The system was left under irradiation
for 1 h at 125 ꢀC (the same products were obtained when the
mixture of reagents in DMF was refluxed for 12 h). After reaction,
the solvent was removed in vacuo and the resulting residue was
washed repeatedly with 10 mL portions of ethanol and diethyl
Acknowledgement
This work has been partially supported by the Fundação para
a Ciência e a Tecnologia (FCT), Portugal, and its Strategy Programme
PEst-OE/QUI/UI0100/2011 (FEDER funded) as well as by the KBN
program (Grant No. N204 280438), Poland. J. L. and M. N. K. express
gratitude to the FCT and the Instituto Superior Técnico (IST) for
their research contracts (Ciência 2007 program). M. J. F. R. is
grateful to the Ministerio de Educación y Ciencia (Spain) for a pre-
doctoral fellowship. The authors gratefully acknowledge Dr. Maria
Cândida Vaz (IST) and Dr. Conceição Oliveira for the direction of the
elemental analysis and ESI-MS services, respectively, and the
Portuguese NMR Network (IST-UTL Centre) for providing access to
the NMR facility.
ether giving yellow microcrystals of
NC5H4))2(PTA)2]. Yield: (5b) 55% (39 mg), (5c) 50% (36 mg) and (5d)
52% (37 mg). Complexes 5be5d are insoluble in common organic
trans-[Pd(N4C(n-
solvents
and
water.
Trans-[Pd(N4C(n-NC5H4))2(PTA)2],
C24H32N16P2Pd (713.0): calcd. C 40.43, N 31.43, H 4.52; found: (5b),
C 40.50, N 30.11, H 4.50; (5c), C 40.98, N 32.00, H 4.48; (5d), C 40.40,
N 31.00, H 4.50.
IR (KBr) (5b): 2933 (m br), 1671 (m), 1619 (m), 1449 (m), 1421
(m), 1284 (m), 1168 (m), 1010 (s), 974 (s), 945 (s), 808 (m), 580 (m)
cmꢁ1; (5c): 2933 (m br), 1634 (m), 1423 (m), 1284 (m), 1241 (m),
1097 (m), 1011 (s), 974 (s), 945 (s), 807 (m), 580 (m) cmꢁ1; (5d):
2936 (m br), 1671 (w), 1622 (m), 1446 (m), 1420 (m), 1283 (m), 1242
(m), 1097 (m), 1036 (m), 1011 (s), 973 (s), 944 (s), 803 (m), 700 (m),
580 (m) cmꢁ1.
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A yellow suspension of trans-[Pd(N4CPh)2(PTA)2]$PhCN, (5a)$
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