Hemilabile and luminescent palladium(II) azo-2-phenylindole complexes

Article abstract of DOI:10.1016/j.jorganchem.2012.11.036

The synthesis of three azoderivatives {R¹-N=N-R² with R¹ = 2-phenylindole and R² = 4-Me-C₆H ₄- (2a), 4-Cl-C₆H₄- (2b) or 2-phenylindole (2c)} and the study of their reactivity in front of Pd(II) salts are described. Treatment of 2a or 2b with PdCl₂ in a CH₂Cl ₂:CH₃OH mixture at 298 K followed by the action of PPh₃ produced the cyclopalladated complexes: [Pd(κ²- C,N)Cl(PPh₃)] (3a and 3b) with a σ{Pd-C(indole)} bond. For 2c, metallation takes place on the same position but required stronger reaction conditions {Pd(OAc)₂ in acetic acid at 398 K}. A comparative study of the spectroscopic and photo-optical properties of ligands 2a-2c and their palladium(II) derivatives (3a-3c) is also reported. Addition of PPh₃ to CH₂Cl₂ solutions of compounds 3a-3c produced the opening of the six-membered metallacycle and the formation of the trans-[Pd(κ¹-N)Cl(PPh₃)₂] derivatives (4a-4c). The crystal structures of 3c·CH₂Cl₂, 4a, 4b and 4c·3/2CH₂Cl₂·1/2H₂O confirm the mode of binding and the anti-(E) configuration of 2a-2c in the complexes as well as the relative disposition of the remaining ligands bound to the Pd(II) atom. Solution studies reveal that in CDCl₃, the Pd-N bond of 4a-4c is hemilabile. Computational studies (at DFT or PM6 level) have also been performed in order to rationalize the high degree of regioselectivity of the cyclopalladation process and the solution behaviour of 4a-4c.

Full text of DOI:10.1016/j.jorganchem.2012.11.036

Journal of Organometallic Chemistry 726 (2013) 21e31
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Hemilabile and luminescent palladium(II) azo-2-phenylindole
complexes
,
b
b
,
b
b
Asensio González a , Jaume Granell , Concepción López , Ramon Bosque , Laura Rodríguez ,
*
*
Mercè Font-Bardia c, Teresa Calvet d, Xavier Solans d
a Laboratori de Química Orgànica, Facultat de Farmàcia, Institut de Biomedicina (IBUB), Universitat de Barcelona, Av. Joan XIII. s/n, 08028 Barcelona, Spain
b Departament de Química Inorgànica, Facultat de Química, Universitat de Barcelona, C/Martí i Franquès 1-11, E-08028 Barcelona, Spain
c Unitat de Difracció de Raigs-X, Centre Científic i Tecnològic de la, Universitat de Barcelona, Solé i Sabarís 1-3, 08028 Barcelona, Spain
d Departament de Cristal$lografia, Mineralogia i Dipòsits Minerals, Facultat de Geologia, Universitat de Barcelona, Martí i Franquès s/n, E-08028 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
The synthesis of three azoderivatives {R1eN]NeR2 with R1 ¼ 2-phenylindole and R2 ¼ 4-MeeC6H4e
(2a), 4-CleC6H4e (2b) or 2-phenylindole (2c)} and the study of their reactivity in front of Pd(II) salts are
described. Treatment of 2a or 2b with PdCl2 in a CH2Cl2:CH3OH mixture at 298 K followed by the action
Article history:
Received 19 September 2012
Received in revised form
31 October 2012
of PPh3 produced the cyclopalladated complexes: [Pd(k s{Pd
2-C,N)Cl(PPh3)] (3a and 3b) with a
Accepted 16 November 2012
eC(indole)} bond. For 2c, metallation takes place on the same position but required stronger reaction
conditions {Pd(OAc)2 in acetic acid at 398 K}. A comparative study of the spectroscopic and photo-optical
properties of ligands 2ae2c and their palladium(II) derivatives (3ae3c) is also reported. Addition of PPh3
to CH2Cl2 solutions of compounds 3ae3c produced the opening of the six-membered metallacycle and
Keywords:
Luminescence
Hemilability
Azocompounds
Cyclopalladation
Indole
the formation of the trans-[Pd(k
1-N)Cl(PPh3)2] derivatives (4ae4c). The crystal structures of 3c$CH2Cl2,
4a, 4b and 4c$3/2CH2Cl2$1/2H2O confirm the mode of binding and the anti-(E) configuration of 2ae2c in
the complexes as well as the relative disposition of the remaining ligands bound to the Pd(II) atom.
Solution studies reveal that in CDCl3, the PdeN bond of 4ae4c is hemilabile. Computational studies (at
DFT or PM6 level) have also been performed in order to rationalize the high degree of regioselectivity of
the cyclopalladation process and the solution behaviour of 4ae4c.
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
of N-donor ligands are particularly relevant in homogeneous
catalysis, luminescence, liquid crystals, optical resolution and bio-
The chemistry of azobenzene derivatives has stimulated
research efforts directed towards their use as materials for digital
storage, as building blocks in supramolecular systems, switches in
nanomolecular devices and polymer materials [1e3]. However,
very few studies have been addressed specifically to the prepara-
tion of azoindole derivatives [4].
On the other hand, palladium coordination chemistry has
undergone a fast development in recent years [5]. Special attention
has been paid to complexes with nitrogen donors such as amines,
imines, azo and heterocyclic compounds [6]. Examples of their
utility in homogeneous catalysis or in macromolecular chemistry
[6c,6d] have been reported. In addition, cyclopalladated complexes
logical active materials [7e11].
A few 2-phenylindoles and their palladium(II) and platinum(II)
complexes have been recently published [12]. Azoindoles are not
common, only a few examples of palladium(II) complexes [13],
have been reported, but products arising from cyclopalladation of
azo-2-phenylindole derivatives are still unknown.
In this paper we present three azo derivatives R1eN]NeR2
{R1 ¼ 2-phenylindole and R2 ¼ 4-MeeC6H4e (2a), 4-CleC6H4e
(2b) or 2-phenylindole (2c), shown in Scheme 1} and the study of
their reactivity in front of palladium(II) salts. In addition, the
presence of one (in 2a, 2b) or two (in 2c) bulky 2-phenylindole
units may also introduce significant steric effects that may affect
the properties and reactivity of the ligands and their cyclo-
palladated derivatives. For instance, the hemilability [14] of the
ligands, that is relevant in view of their utility in homogeneous
catalysis [15,16].
* Corresponding authors.
E-mail address: conchi.lopez@qi.ub.es (C. López).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.11.036

22
A. González et al. / Journal of Organometallic Chemistry 726 (2013) 21e31
Scheme 1. Synthesis of the azocompounds and the palladium (II) complexes. Key reagents and conditions: i) (R3eC6H4N2)Cl, 0e20 ꢀC, 30 min then NaOAc to 298 K ii) 3-diazo-2-
phenylindole, HOAc, 80 ꢀC 2 h, iii) MeI, 40% NaOH, CH2Cl2, 2 h. iv) PdCl2, MeOH: CH2Cl2 (1:1), 24h, followed by treatment with PPh3 in CH2Cl2; v) Pd(OAc)2 in acetic acid 100 ꢀC, 3h
followed by treatment with LiCl first and PPh3 later on and vi) PPh3 in CH2Cl2.
2. Results and discusion
It is well-known that cyclopalladation of N-donor ligands
proceeds in two steps: the binding of the ligand through the N atom
to the palladium, followed by the activation of the CeH bond. The
use of molecular models reveals that: a) in 2c the environment of
the donor atoms is more crowded than in 2a and 2b, and conse-
quently, this reduces the accessibility of the Pd(II) atom. Moreover,
for the intermediate formed in the first step, the CeH bond of the
indole ring (A) has a better orientation towards Pd(II) than the CeH
bonds on the ortho sites of the phenyl rings C or D and it is closer to
the Pd(II) centre. These findings could explain why in all cases
metallation occurs on ring A.
2.1. Synthesis
Compounds 2ae2b were prepared from commercially available
2-phenylindole using
a straightforward two-steps procedure
[Scheme 1,i) and ii)], based on the electrophilic coupling on position
3 of the indole ring, using diazotized para-substituted anilines [17]
to give the precursors 1a and 1b, and the subsequent treatment
with methyl iodide in CH2Cl2 and NaOH (40%) under phase-transfer
catalysis [18].
The azoindoles 1c and 2c have been described in the reaction of
1-methyl-2-phenylindole and 2-phenylindole respectively with
nitrous acid [19]. The classical preparative method for azobi-
s(indole) 1c requires the coupling of 3-diazo-2-phenylindole
(available through a three-steps protocol: nitrosation, reduction
to amine and diazotization) with 2-phenylindole in acidic media
[20]. Due to the easier availability of 3-diazo-2-phenylindole in one
step [21] in this work we have used a slightly modified procedure
based on the synthesis of the precursor 1c [Scheme 1, iii)] followed
by the subsequent methylation of the nitrogen using the same
method as for 2a and 2b [Scheme 1, ii)].
Treatment of 2a or 2b with PdCl2 in a CH2Cl2emethanol (1:1)
mixture at 298 K for 48 h produced a solid that reacted with PPh3
(in a 1/1 M ratio) giving the palladacycles 3a and 3b, respectively
[Scheme 1, iv)]. In contrast with these results when the reaction
was carried out using 2c instead of 2a or 2b, no evidences of the
formation of any cyclopalladated complex was observed. However,
the treatment of 2c with Pd(OAc)2, that is a more potent metallating
agent than PdCl2, in acetic acid at 100 ꢀC produced after treatment
with PPh3 complex 3c [Scheme 1, v)]. It should be noted that the
cyclometallation of 2ae2c takes place with completely regiose-
lectivity at the peri-position of the indole.
2.2. Structures
It is well-known that for azo-derivatives R1eN]NeR2 the
relative disposition of the substituents (E- or Z-) affects their
spectroscopic and photochemical properties as well as their reac-
tivity [22]. NMR spectra of 1ae1c and 2ae2c in CDCl3 at 298 K
indicated the presence of only one isomer in solution [23]. Since all
azo-2-phenylindole derivatives described so far adopt the E- form
in solution as well as in the solid state [24e26], we assumed that
1ae1c and 2ae2c were the E- isomers. Computational studies at
the DFT level [27] for 2a confirmed this hypothesis, the existence of
CeH/N contacts in the two conformers of 2a (Fig. 1, forms I and II)
and also that form II was (ca. 5.74 kcal/mol) more stable than form
I. Due to the similarity between 2a and 2b, we assumed that for 2b,
form II would also be the most stable one.
The crystal structure of 3c$CH2Cl2 (Fig. 2), reveals that the Pd(II)
atom is bound to the azo nitrogen N(3) and the carbon atom C(1) on
the ortho site of the phenylindole moiety, forming a six-membered
palladacycle with a twisted boat conformation [28]. The PdeC(1)
and PdeN(3) bond distances fall in the ranges reported for
[Pd(k2-C,N)Cl(PPh3)] and the C(1)ePdeN(3) bond angle [89.94(9)ꢀ]

A. González et al. / Journal of Organometallic Chemistry 726 (2013) 21e31
23
Fig. 1. Optimized geometries of the two forms (I and II) of ligand 2a. Showing the most relevant CeH/N distances. In form I the shortest CeH/N contact takes place between the
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
N(3) atom and the H(5) atom (2.478 A), and the distance N(2)/H(1)(indole) is 2.940 A. For form II: Distances N(3)/H(1) ¼ 2.467 A, N(2)/H(8) ¼ 2.556 A and N(2)/H(5) ¼ 2.580 A}.
is bigger than those found in the Cambridge Crystallographic Data
Base, for analogous palladacycles [in the range 81.7ꢀe86.3ꢀ] [24].
The remaining two coordination sites of the Pd(II) atom are occu-
pied by the phosphorus atom of the PPh3 ligand, in a cis-arrange-
ment to the metallated carbon [bond angle C(1)ePde
P(1) ¼ 90.4(7)ꢀ], and the Clꢁ ligand.
in fluorescence imaging microscopy and for the labelling of
biomolecules such as DNA [31]. In addition, palladacycles derived
from azobenzene with interesting photo-optical properties have
also been described [7aec,32,33]. In view of this and in order to
examine the effects induced by: a) the nature of the substituent R3
of the 4-R3eC6H4e rings in 2ae2b and 3ae3b and b) the
replacement of the phenyl rings of 2a, 2b, 3a or 3b by a 2-
phenylindole unit on the potential luminescence of the ligands
and their palladacycles, we also studied their absorption and
emissive properties.
The UVevis. spectra of ligands 2ae2c in CH2Cl2 at 298 K
(Table 1) showed the typical pattern of 2-phenylindole derivatives
[30,33,34]. For the palladacycles 3ae3c three bands were detected
in the spectra, of which those at higher energies appears in the
same range as those of the free ligands and are due to a metal
perturbed intraligand transition (MPILT). The third and new band is
affected by the polarity of the solvent [35] and is assigned to the
ꢀ
The N(2)eN(3) bond length [1.286(3) A] is similar to the values
found for most 2-phenylindole containing azoderivatives [24e26],
and the ligand adopts the E- form [torsion angle C(7)eN(2)eN(3)e
C(16) ¼ 175.3(4)ꢀ]. The two indoles are nearly planar, form an angle
of 30.1ꢀ and the phenyl rings are twisted in relation to the
coordination plane of the palladium(II) [29]. For this arrangement
ꢀ
of substituents, the distances N(2)/H(15) [2.78 A] and N(2)/H(18)
ꢀ
[2.72 A], suggest weak intramolecular CeH/N contacts.
2.3. Photo-optical properties
metal to ligand charge transfer transition (MLCT): 4d(Pd) /
orbitals of the cyclometallated ligand [7aec,32,33,36].
p*
One of the main interests of phenylindole derivatives arises
from their potential luminescence [30,31] that makes them useful
ꢀ
Fig. 2. ORTEP plot of 3c. Hydrogen atoms have been omitted for clarity. Selected bond lengths (in A) and bond angles (in deg.): PdeCl(1), 2.4180(9); PdeN(3) 2.148(2); PdeP(1),
2.2739(12); PdeC(1), 2.032(2); C(1)ePdeN(3), 89.94(9); P(1)ePdeC(1), 90.40(7), P(1)ePdeCl(1), 92.09(3) and N(3)ePdeCl(1) 89.93(3).

24
A. González et al. / Journal of Organometallic Chemistry 726 (2013) 21e31
Table 1
Absorption and emission properties of the free ligands 2ae2c and the cyclopalladated complexes 3ae3c in CH2Cl2 solution at 298 K {wavelengths, li (i ¼ 1,2 or 3) excitation
wavelength lexc. And lmax in nm and extinction coefficients εi (in Mꢁ1 cmꢁ1) and quantum yields,
F
a}.
Emission data, lmax
Absorption spectroscopic data
l1 (ε1)
l2 (ε2)
l3 (ε3)
lexc.
Solid state
In solution
F
Free ligands
2a
2b
2c
381 (27.0 ꢃ 103)
386 (11.8 ꢃ 103)
301 (6.9 ꢃ 103)
275 (45.6 ꢃ 103)
273 (101. ꢃ 103)
232 (10.8 ꢃ 103)
e
e
e
280
280
300
e
e
e
430
396
415, 379,
363 and 349
0.0015
0.0012
0.17
Cyclopalladated complexes:
3a
b
468 (20.6 ꢃ 103)
326 (22.3 ꢃ 104)
326 (62.7 ꢃ 103)
326 (92.4 ꢃ 104)
269 (18.4 ꢃ 104)
255 (49.1 ꢃ 103)
234 (66.3 ꢃ 103)
480
275
480
275
520
594
e
e
408
0.0018
e
b
3b
472 (16.6 ꢃ 103)
518 (20.0 ꢃ 103)
590
e
395
610
0.0016
0.0053
3c
630
a
Quantum yields referred to quinine sulphate in H2SO4 1 N (for 2ae2c and 3ae3b) and to [Ru(bipy)3]2þ in H2O (for 3c).
No emission was observed.
b
We also explored the potential emissive properties of 2ae2c and
observed (lexc ¼ 520 nm) [37]. This reflects once more the relevancy of
the presence of two phenylindole groups on the photo-optical proper-
ties of the azo-compounds (2ae2c) and their palladium(II) complexes
(3ae3c). It should be noted that for (3ae3c), the emission wavelength
was similar to those reported for related mononuclear cyclopalladated
azobenzenes {500 nm ꢂ lmax ꢂ 650 nm} [7a,b,31,32].
complexes 3ae3c in the solid state and in CH2Cl2 solution at 298 K.
The free ligands were not emissive in the solid state, but in solution
they became luminescent upon excitation at lexc ¼ 280 nm (for 2a
and 2b) or 300 nm (for 2c). It should be noted that the quantum
yield of 2c (Table 1) is significantly higher than those of 2a and 2b,
in which the R3 unit is a 4-methyl or 4-chlorophenyl group.
The emission spectra of solid samples of the palladacycles 3a and 3b
(at lexc ¼ 480 nm) at 298 K showed a broad emission band in the range
590e595 nm; while for 3c a stronger emission (at lem ¼ 630 nm) was
The crystal structure of 3c (described above) revealed that the
metallated and non-metallated indole units are not coplanar and
this can modify the aromaticity of the ligand. It is well known that
photophysical properties of palladium(II) complexes are dependent
ꢀ
Fig. 3. ORTEP plot of 4a. Hydrogen atoms have been omitted for clarity. Selected bond lengths (in A) and bond angles (in deg.): PdeCl(1), 2.4187(17); PdeP(1), 2.3389(13); PdeP(2),
2.3422(12); PdeC(1), 1.994(4); P(1)ePdeP(2), 169.13(4); P(1)ePdeC(1), 85.25(11); Pd(2)ePdeC(1) 86.61(11) and P(2)ePdeCl(l), 91.43(5).

A. González et al. / Journal of Organometallic Chemistry 726 (2013) 21e31
25
Fig. 4. ORTEP plot of 4b. Hydrogen atoms have been omitted for clarity. PdeCl(1), 2.4188(19); PdeP(1), 2.3329(10); PdeP(2), 2.3389(11); PdeC(1), 1.995(3); P(1)ePdeP(2),
188.71(3); P(1)ePdeC(1), 84.89(9); P(2)ePdeC(1), 86.56(9) and P(2)ePdeCl(l), 91.18(4).
on a wide variety of factors including the nature of the ligands
bound to the Pd(II) as well as the existence of Pd/Pd and/or
550 cmꢁ1) showed the typical pattern reported for complexes of
the type trans-[Pd(
1-C)X(PPh3)2] [40].
p/p
k
interactions between vicinal molecules. In the crystal structure of
3c: a) the shortest Pd/Pd distance is 8.306 A and allows us to
discard the existence of any interaction between them and b) the
The crystal structures of 4a, 4b and 4c$3/2CH2Cl2$1/2H2O
(Figs. 3e5) revealed that existence of molecules of 4ae4c in which
the palladium(II) atom is bound to the C(1) atom of the 2-
phenylindol, thus confirming that metallation occurred at the A
ring. The three remaining coordination sites are occupied by
a chloride and the phosphorous atoms of two different PPh3
molecules in a trans- arrangement. In 4a and 4b the two PdeP bond
ꢀ
molecules are assembled mainly by CeH/p and CeH/Cl inter-
molecular interactions.
.The excitation of CH2Cl2 solutions of 3a and 3b (at lexc ¼ 480 nm)
produced no significant emission (Table 1). According to the bibli-
ography this is commonly due to the presence of low-lying metal
centredexcitedstatesthatdeactivatethe potentiallyemitting metal-
lengths are similar and fall in the range of other trans-[Pd(k
1-C)
Cl(PPh3)2] derivatives [24,40,41]. However, in 4c, these two PdeP
distances are different and bigger than in 4a and 4b or in its
precursor 3c. This can be related to the stronger steric hindrance
induced by the presence of two bulky 2-phenylindole units bound
to each one of the nitrogen atoms of the azo group.
In the three cases the azo ligands are in the E configuration and
they adopt form II shown in Fig. 1. As a consequence of the nearly
coplanar arrangement of the 4-substituted phenyl ring and the azo
functionality, the H atoms on the ortho sites of the 4-R4eC6H4e
unit are close to the nitrogen atoms of the eN]Ne group [42]. In
4c, there are also CeH/N contacts but the distances N/H are
bigger [43] than in 4a and 4b. Comparison of the structures of 3c
and 4c also reveals that the transformation of 3c into 4c requires
a change of the relative orientation of the azo moiety in relation to
the PdeC bond [from form I (in 3c) to form II (in 4c)].
to-ligand charge transfer [4d(Pd) /
p (ligand)] and the ligand
centred levels [38].
In contrast with the results obtained for 3a and 3b, complex 3c
was strongly luminescent under the same conditions and the
emission spectra obtained when excited at 520 nm showed a band
at low energies (lmax ¼ 610 nm). The red-shift emission of 3c with
respect with that of 2c (and corresponding larger Stokes’ shift)
suggests a phosphorescence origin of this emission band.
2.4. Study of the reactivity and stability of 3ae3c
We also evaluated the stability of the PdeN bond in 3ae3c using
the typical procedure based on their reaction with nucleophiles
[39,40]. Treatment of 3a, 3b or 3c with an excess of PPh3 produced
4ae4c [Scheme 1, vi)]. IR spectra of 4ae4c in the range (500e
Finally, it should be noted that in the three complexes the
separations between the palladium(II) atom and the nitrogen N(3)

26
A. González et al. / Journal of Organometallic Chemistry 726 (2013) 21e31
Fig. 5. ORTEP plot of 4c. In both cases hydrogen atoms have been omitted for clarify. PdeCl(1), 2.438(2); PdeP(1), 2.3549(17); PdeP(2), 2.3710(17); PdeC(1), 2.118(2); P(1)ePdeP(2),
166.24(5); P(1)ePdeC(1), 86.48(10); P(2)ePdeC(1) 88.41(10) and P(2)ePdeCl(l), 94.27(5).
(in 3a and 3b) or the N(2) atom for 3c, are small (2.961, 2.998 and
ꢀ
3.328 A, for 4a, 4b and 4c, respectively), they hardly exceed the sum
ꢀ
of the van der Waals radii of the Pd and N atoms (1.63 and 1.55 A,
respectively) [44]. In addition, for compounds 4a and 4b the angles
N(3)-Pd-ligands are close to 90ꢀ [45], thus suggesting that the N(3)
atom lies on the axial direction. In 4c the N(2) atom has a similar
orientation.
Compounds 4ae4c are stable in the solid state, but they exhibit
an interesting behaviour in solution. First, their ESI mass spectra
were essentially the same as those of their corresponding parent
complex 3ae3c. The 31P{1H} NMR spectra of 4a and 4b showed
broad and poorly defined signals at 298 K; but at 240 K a narrow
singlet [at
exclusively and its position was similar to those of related trans-
[Pd(
1-C)X(PPh3)2] [39,40].
The 31P{1H} NMR spectrum of 4c (in CDCl3 at 298 K) showed
three singlets of which that at
¼ 20.3 ppm is assigned to 4c; while
the other two singlets (at
¼ 39.7 and ꢁ6.0 ppm) correspond to 3c
and the free PPh3. When this solution was cooled to 240 K, the
intensity of the signal at w20 ppm increased while the other two
d
¼ 17.26 (for 4a) and 17.30 ppm (for 4b)] was observed
k
d
d
d
nearly vanished (Fig. 6). These findings suggest that in CDCl3
solution, a dynamic process involving the cleavage of one of the two
PdeP bonds of 4c, the release of this ligand and the formation of 3c
takes place. These results are specially outstanding because they
allow a fine tuning of the environment of the Pd(II) atom by
a simple change of the temperature.
Fig. 6. 31P{1H} NMR spectra of a solution of 4c in CDCl3 at 298 K and at 240 K, showing
(as insets) expansions of the two additional and low intense signals due to the minor
components (3c and the free PPh3).
Secondly, when PPh3 was added to diluted solutions of 4c in
CDCl3 the signal due to the 31P nuclei of 3c decreased thus

A. González et al. / Journal of Organometallic Chemistry 726 (2013) 21e31
27
Table 2
solution, but in these cases the emission band is shifted to lower
energies when compared with those of the free ligands.
Values of the variation of the free energy (DGT in kcal/mol), for the reaction
4c / 3c þ PPh3 determined with the PM6 computational method [in vaccum or in
The study of the reactivity of 3ae3c with PPh3 produced the
CHCl3 at different temperatures (T)].
cleavage of the PdeN bond and the formation of trans-[Pd(k
1-C)
D
GT (in kcal/mol)
Cl(PPh3)2] (4ae4c). These compounds are stable in the solid state
but in solution they undergo a “base-off/base-on” process that
involves the dissociation of one of the two PPh3 ligands and the
formation of the corresponding palladacycle (3ae3c) in which the
azo ligand behaves as a bidentate {N,C(indole)}ꢁ group.
T (in K)
In vacuum
In CHCl3
300
240
100
ꢁ18.71
ꢁ14.95
ꢁ6.04
ꢁ16.91
ꢁ13.53
ꢁ5.51
The transformations 4 / 3 þ PPh3 are reversible (by cooling or
by an addition of PPh3 at 298 K) and these changes produced
significant variations in the 1H and 31P{1H} NMR spectra, thus
allowing to tune the properties and/or reactivity of these products
in view of their utility in synthesis, catalysis or the design of
sensors, etc. It should be noted that palladated complexes showing
a behaviour similar to those of 4ae4c are extremely scarce.
Among the complexes presented here, compound 3c is the best
candidate to explore these fields due to its higher emissive effi-
ciency both in solution and in the solid state. Further studies on
these areas are currently under way.
indicating that the reaction 4c / 3c þ PPh3 is reversible. It should
be noted that organometallic compounds showing this type of
behaviour, that involves the decoordination/coordination of
a ligand (“base off/base on” processes), are specially attractive in
view of the potential utility in homogeneous catalysis where
complexes with hemilabile ligands play a key role [14e16].
In a first attempt to rationalize the solution behaviour of
compound 4c, we decided to undertake DFT calculations [27] for
the three products involved in the equilibrium: 4c $ 3c þ PPh3. In
the first stage, the optimization of the geometries of the three
molecules involved in the reaction was carried out; later on their
total energies (ET) were determined. The results obtained revealed
4. Experimental section
4.1. Materials and methods
that the difference of
D
ET {defined as
D
ET ¼ {[ET (for 3c) þ (ET (for
PPh3)] ꢁ ET(for 4c)} in vacuum was 7.15 kcal/mol, but this value
4-Chloro and 4-methyl anilines, 2-phenylindole, PdCl2,
Pd(AcO)2, LiCl and PPh3 were obtained from commercial sources
and used as received and 3-diazo-2-phenylindole was prepared as
reported [21]. Solvents were distilled and dried before use [47].
Elemental analyses were carried out at the Serveis de Científico-
Tècnics (Universitat Barcelona). Mass spectra (MALDI-TOF for 2c or
ESIþ in the remaining cases) were performed at the Servei d’Es-
pectrometria de Masses (Universitat de Barcelona). Infrared spectra
were obtained with a Nicolet 400FTIR instrument using KBr pellets
and only the most relevant absorptions of the new products are
presented in the following sections.
decreased by ca. 6.8 kcal/mol) when the effect induced by the CHCl3
solvent was considered (
As described above, the behaviour of 4c in CDCl3 is temperature
dependent. This prompted us to undertake a theoretical estimation
D
ET ¼ 0.34 kcal/mol).
of the variation of the free energy
DGT of the reaction
4c / 3c þ PPh3 at different temperatures. It should be noted that
the bulky PPh3 ligands are involved in this process and conse-
quently simplified models (commonly based in the replacement of
the PPh3 by PH3 or PMe3) could not be used. In addition, molecules
of 4c (C66H53ClN4P2Pd) are complex and huge and this made the
calculations at a DFT level extremely complex, difficult and slow.
High resolution 1H NMR spectra and the two-dimensional {1He
1H}-NOESY and COSY experiments were registered with a Varian
VRX-500 or a Bruker Avance DMX-500MHz instruments. Except
where quoted the solvent used for NMR experiments was CDCl3
(99.9%) and the references were SiMe4 [for 1H NMR] and P(OMe)3
Thus, we decided to determine the
DGT for the reaction
4c / 3c þ PPh3 in vacuum and in CHCl3 at three different
temperatures (T ¼ 300, 240 and 100 K) at a PM6 computational
level [46]. As shown in Table 2 for a given constant temperature the
DGT (in solution) <
DGT (in vacuum) and higher temperatures
[
d
(
31P) ¼ 140.17 ppm] for 31P NMR and b) these NMR studies were
produced a decrease of the calculated
D
GT in both cases (vacuum
performed at 298 K. The chemical shifts (d) are given in ppm and
and solution), thus from a thermodynamic point of view the
proclivity of 4c to undergo the cleavage of the PdeN bond and the
formation of 3c and free PPh3 is favoured at higher temperatures. In
fact the calculation of the enthalpy of the process (
formation enthalpies of 3a, 4a and PPh3 obtained from program,
indicated that it was endothermic (
the coupling constants (J) in Hz. In the characterization section of
each product the assignment of signals detected in the 1H NMR
spectra refers to the labelling patterns presented in Scheme 1. UVe
vis. spectra of CH2Cl2 solutions of the free ligands 2ae2c and the
palladacycles 3ae3c and 4ae4c were recorded at 298 K with a Cary
100 scan 388 Varian UV spectrometer and their emission and
excitation spectra of 2ae2c and 3ae3c were obtained on a Horiba
JobineYvon SPEX Nanolog-TM spectrofluorimeter at 298 K. Total
luminescence quantum yields were measured at 298 K relatively to
DH), using the
D
H ¼ 4.3 kcal/mol) This is
consistent with the results obtained from the variable temperature
31P{1H} NMR studies of compound 4c.
3. Conclusions
quinine sulphate in 1 N H2SO4 (
f
¼ 0.54) (for 2ae2c, 3a and 3b) or
to [Ru(bipy)3]Cl2 in water (
f
¼ 0.042) (for 3c) as standard
The results presented here reveal that despite the azo deriva-
tives 2ae2c exhibit different CeH bonds susceptible to be activated
in all cases the cyclopalladation occurs at the peri position of the
indole ring yielding six-membered palladacycles (3ae3c).
The study of the photo-optical properties of 2ae2c and 3ae3c,
not only reveals that they are luminescent in CH2Cl2 solutions at
298 K, but also provides conclusive evidence of the influence of the
nature of substituent R2 of the R1eN]NeR2 ligands. The
symmetrically substituted ligand 2c is a more powerful emitter
than 2a and 2b where R2 is the 4-methyl (or 4-chloro) phenyl.
Palladacycles 3ae3c are luminescent in the solid state and in
references.
4.2. Preparation of the precursors (1ae1c)
4.2.1. 2-Phenylindole-3-azo-(40-methylbenzene), 1a
To a suspension of p-toluidine (2.30 g, 21.5 ꢃ 10ꢁ3 mol) in 6 M
hydrochloric acid (90 mL) was added dropwise NaNO2 (1.52 g,
22.0 ꢃ 10ꢁ3 mol) in water (8 mL) at 0 ꢀC. The reaction mixture was
stirred for 15 min and then a solution of sodium acetate (8 g) in
water (50 mL) was added over 10 min at 0 ꢀC. A solution of 2-
phenylindole (3.5 g, 18.0 ꢃ 10ꢁ3 mol) in ethanol (50 mL)/DMF

28
A. González et al. / Journal of Organometallic Chemistry 726 (2013) 21e31
(10 mL) was then added over 15 min under cooling and then
allowed to warm slowly to room temperature and stirred over-
night. Water (50 mL) was added; the brown-red solid formed was
collected by filtration, washed with water (25 mL) and finally dried
under vacuum (4.42 g,14.2 ꢃ 10ꢁ3 mol, 79%). It was used in the next
step without further purification. Anal. (%) Calc. for C21H17N3: C
81.00, H 5.50 and N 13.49; found: C 80.86, H 5.71 and N 13.27; MS
(%) Calc. for C21H16ClN3: C 72.93, H 4.66, N 12.15; found C 72.6, H
4.5, N 12.3. MS (ESIþ): 346.11 {[M] þ H}þ. IR data:
n
¼ 1468 and
1249 cmꢁ1 na (eN]Ne) and ns (eN]Ne), respectively. 1H NMR
(400 MHz, CDCl3):
d
¼ 3.82 (s, 3H, NMe); 7.36 (d, 2H, JHH ¼ 8.6, H9);
7.30e7.60 (m, 8H, aromatic); 7.70 (d, 2H, JHH ¼ 8.6, H8); 8.64 (d, 1H,
JHH ¼ 8.0, H1).
(ESIþ): 312.15 {[M] þ H}þ. IR data:
n
¼ 3418,
n
(NeH); 1454 and
4.3.3. 1,10-Dimethyl-2-phenylindole-3-azo-(2-phenylindole), 2c
To a solution of 2-phenylindole-3-azo-(2-phenylindole), 1c
(1.18 g, 2.86 ꢃ 10ꢁ3 mol), Aliquat 336 (0.8 g, 1.9 ꢃ 10ꢁ3 mol) and 40%
NaOH (12 mL) in CH2Cl2 (50 mL) was added, methyl iodide (2.27 g,
1 mL, 16 ꢃ 10ꢁ3 mol) and stirred for 24 h at room temperature. A
yellow precipitate appeared which was filtered, washed with water
(3 ꢃ 20 mL) and dried under vacuum to give 2c (0.97 g,
2.2 ꢃ 10ꢁ3 mol, 77%). Anal. (%) Calc. for C30H24N4: C 81.79, H 5.49, N
12.72; found: C 81.5, H 5.62, N 12.5. MS (Maldi-TOFþ) m/z ¼ 440.2
1233 cmꢁ1 na (eN]Ne) and ns (eN]Ne), respectively. 1H NMR
data:
d
¼ 9.68 (br. s, 1H, >NH), 2.22 (s, 3H, eMe), 8.60 (d, 1H,
3JH,H ¼ 7.8, H1), 6.92 (t, 1H, 3JH,H ¼ 7.8, H2), 7.12 (t, 1H, 3JH,H ¼ 7.8, H3)
and 7.30e7.50 (m, 10H, H4eH9).
4.2.2. 2-Phenylindole-3-azo-(40-chlorobenzene), 1b
This product was obtained following the procedure described
above for 1a, but using 2.74 g of p-chloroaniline (21.5 ꢃ 10ꢁ3 mol),
as starting material instead of the p-toluidine (yield 4.89 g,
14.7 ꢃ 10ꢁ3 mol, 82%). Anal. (%) Calc. for C20H14ClN3: C 72.40, H 4.25
and N 12.66; found C 72.55, H 4.40 and N 12.50. MS (ESIþ): 332.09
[M]þ. IR data:
n
¼ 3060, 3044, 2929 and 2856,
n (CeH); 1467 and
1254 in cmꢁ1 na (eN]Ne) and ns (eN]Ne), respectively. 1H NMR
data (in dmso-d6, 400 MHz):
d
¼ 3.78(s, 6H, 2-NMe); 7.05(td,
3
{[M] þ H}þ. IR data:
n
¼ 3418,
n
(NeH); 1455 and 1232 cmꢁ1
,
na (e
3JH,H ¼ 8.0, JH,H ¼ 1.0, H3a and H3b); 7.25 (td, JH,H ¼ 8.1 and
4JH,H ¼ 1.1, 2H, H2 and H2b); 7.54 (d, 3JH,H ¼ 8.0, 2H, H4 and H4b); 7.64
(m, 6H, 2H6, H7, 2H6b and H7b); 7.79 (dt, 3JH,H ¼ 8.2 and 4JH,H ¼ 1.8,
4H, 2H5 and 2H5b) and 8.10 (d, 2H, H1 and H1b).
3
N]Ne) and ns (eN]Ne), respectively. 1H NMR data:
d
¼ 9.52 (br. s,
1H, >NH), 8.61 (d, 1H, 3JH,H ¼ 7.7, H1), 7.01 (t, 1H, 3JH,H ¼ 7.7, H2), 7.18
(t, 1H, 3JH,H ¼ 7.7, H3) and 7.280e7.52 (m, 10H, H4eH9).
4.2.3. 2-Phenylindole-3-azo-(2-phenylindole), 1c
4.4. Preparation of the palladium(II) complexes
A solution of 2-phenylindole (0.65 g, 3.37 ꢃ 10ꢁ3 mol) and 3-
diazo-2-phenylindole (0.74 g, 3.37 ꢃ 10ꢁ3 mol) in CH3COOH
(25 mL) was heated under stirring at 80 ꢀC for 2 h. The reaction
mixture was cooled to 298 K, evaporated to dryness under reduced
pressure and the crude solid washed with ether (2 ꢃ 4 mL). The
brown solid was collected and dried to give the azo-bis-indole 1c
(1.18 g, 2.8 ꢃ 10ꢁ3 mol, 85%) that was used in the next step without
further purification. Characterization data: Anal.(%) Calc. for
C28H20N4: C, 81.53, H, 4.89 and N, 13.58; found C 81.31, H 5.02 and N
4.4.1. Compound 3a
A mixture of azoindole 2a (429 mg, 1.4 ꢃ 10ꢁ3 mol) and PdCl2
(280 mg,1.4 ꢃ10ꢁ3 mol) in 50 mL of methanol-dichloromethane (in
a 1:1 ratio) was stirred at 298 K for 48 h. The precipitate formed was
filtered off, washed with methanol. Then, it was treated with PPh3
(310 mg, 1.2 ꢃ 10ꢁ3 mol) in 50 mL of a MeOH: CH2Cl2 (a 1:1)
mixture and stirred at 298 K for 24 h, After this period it was filtered
and the filtrate was concentrated in vacuo. The red solid obtained,
after addition of diethylether, was recrystallized from CH2Cl2eether
and dried in vacuo to obtain 3a as a red solid (yield: 520 mg,
0.84 ꢃ 10ꢁ3 mol, 60%). Anal. (%) Calc. for C40H33ClN3PPd: C 65.94, H
4.57 and N 5.77; found: C 65.9, H, 4.3 and N 5.8. MS-positive ESI:
13.43. MS (ESIþ): 413,18 {[M] þ H}þ. IR data:
n
¼ 3291,
n (NeH);
1447 and 1235 cmꢁ1): na (eN]Ne) and ns (eN]Ne), respec-
tively. 1H NMR data:
d
¼ 9.79 (br. s, 2H, >NH), 6.90 (t, 2H, 3JH,H ¼ 7.7,
H2 and H2b), 7.00 (t, 2H, JH,H ¼ 7.7, H3 and H3b) and 7.15e7.50 (m,
3
14 H, H4a,beH9a,b).
692.13 {[M] ꢁ Cl}þ. IR data:
n
¼ 3050, 2914 and 2844,
n (CeH); 1460
and 1295 na (eN]Ne) and ns (eN]Ne), respectively; 529, 507 and
4.3. Preparation of the ligands (2ae2c)
506 cmꢁ1 (PPh3). 31P{1H} NMR:
d
¼ 40.16, s. 1H NMR (250 MHz,
CDCl3):
d
¼ 2.28 (s, 3H, Me); 3.86 (s, 3H, NMe); 6.50 (t, 1H,
3
4.3.1. 1-Methyl-2-phenylindole-3-azo-(40-methylbenzene), 2a
3JHH ¼ 8.0, H3); 6.59 (t, 1H, JH,H
¼
3JH,P ¼ 8.1, H2); 6.89 (d, 1H,
3
To a solution of 2-phenylindole-3-azo-(40-methylbenzene) 1a
(1.24 g, 4.0 ꢃ 10ꢁ3 mol), Aliquat 336 (0.8 g, 1.9 ꢃ 10ꢁ3 mol) and 40%
NaOH (12 mL) in CH2Cl2 (125 mL) was added methyl iodide (2.27 g,
1 mL, 16.0 ꢃ 10ꢁ3 mol) and stirred for 24 h at 298 K. After this
period, water (75 mL) was added and the mixture was transferred
to a separating funnel. The layers were separated and the aqueous
phase was extracted with CH2Cl2 (20 mL). The combined organic
extracts were dried over Na2SO4, filtered and concentrated. Further
purification by flash chromatography (Silica gel, ether/CH2Cl2 5:5)
gave 2a (1.0 g, 3.1 ꢃ10ꢁ3 mol, 77%) as an orange solid. Anal. (%) Calc.
for C22H19N3: C 81.20, H 5.89, N 12.91; found for C22H19N3: C 81.0, H
3JH,H ¼ 8.0, H4); 7.09 (d, 2H JHH ¼ 8.2, H5); 7.29e7.78 (m, 22H,
aromatic).
4.4.2. Compound 3b
This complex was obtained using the same procedure as that
described above for 3a, but using 277 mg (0.8 ꢃ 10ꢁ3 mol) of 2b,
142 mg (0.8 ꢃ 10ꢁ3 mol) of PdCl2 and 183 mg (0.7 ꢃ 10ꢁ3 mol) of
PPh3 (yield: 262 mg, 4.0 ꢃ 10ꢁ4 mol, 50%). Anal. (%) Calc. for
C39H30Cl2N3PPd: C 62.54, H 4.04, N 5.61; found: C 62.5, H 3.9, N 5.5.
MS(ESIþ): 714.09 {[M] ꢁ Cl}þ. IR data:
n
¼ 3046, 2923 and 2848,
n
(CeH); 1461 and 1288 na (eN]Ne) and ns (eN]Ne), respectively;
6.0, N 12.7. MS (ESIþ): 326.16 {[M] þ H}þ. IR data:
n
¼ 1459 and
529, 511 and 498 cmꢁ1 (PPh3). 31P{1H} NMR:
d
¼ 41.44, s. 1H NMR
1252 cmꢁ1 na (eN]Ne) and ns (eN]Ne), respectively. 1H NMR
(250 MHz, CDCl3):
d
¼ 3.87 (s, 3H, NMe); 6.52 (t, 1H, 3JH,H ¼ 7.8, H3);
(250 MHz, CDCl3):
d
¼ 2.34 (s, 3H, Me); 3.82 (s, 3H, NMe); 7.20 (d,
6.61 (t, 1H, 3JH,H ¼ 4JP,H ¼ 7.8, H2); 6.90 (d, 1H, 3JH,H ¼ 7.9, H4); 7.29e
2H, JHH ¼ 8.5, H9); 7.30e7.60 (m, 7H, aromatic); 7.70e7.80 (m, 3H,
H8, H4); 8.70 (d, 1H, JHH ¼ 8.2, H1).
7.80 (m, 24H, aromatic).
4.4.3. Compound 3c
4.3.2. 1-Methyl-2-phenylindole-3-azo-(40-chlorobenzene), 2b
This product was obtained following the procedure described
above for 2a, but using the 2-phenylindole-3-azo-(40-chloroben-
zene), 1b (1.33 g, 4.0 ꢃ 10ꢁ3 mol), instead of 1a. This product was
isolated as an orange solid (yield: 1.2 g, 3.5 ꢃ 10ꢁ3 mol, 87%). Anal.
Ligand 2c (0.44 g, 1.0 ꢃ 10ꢁ3 mol), Pd(OAc)2 (0.246 g,
1.1 ꢃ10ꢁ3 mol) and 50 mL of acetic acid were introduced in 100 mL
flask and the mixture was stirred at 100 ꢀC for 3 h. Then cooled to
room temperature and evaporated under reduced pressure. The
residue was treated with CH2Cl2 (250 mL), filtered through celite

A. González et al. / Journal of Organometallic Chemistry 726 (2013) 21e31
29
and the solution was concentrated in vacuum. The deep-red solid
formed was treated with 50 mL of acetone and 170 mg of LiCl
(4.0 ꢃ 10ꢁ3 mol) and the reaction mixture was stirred for 24 h at
298 K. The solid formed was filtered through a short pad (ca. 1 cm)
of silica using CH2Cl2 as solvent to yield 0.434 g of a red solid that
was collected by filtration and air-dried. Afterwards it was sus-
pended in 50 mL of CH2Cl2, treated with triphenylphosphine
(524 mg, 2.0 ꢃ 10ꢁ3 mol) and the mixture was stirred for 24 h. The
resulting solution was evaporated to dryness and purified by silica
gel column chromatography with ether as eluant. The deep garnet
band eluted was collected and concentrated to dryness. The solid
formed was dissolved in the minimum amount of CH2Cl2 and slow
evaporation of this solution at 278 K produced 3c as a crystalline
sample (yield: 0.75 g, 0.8 ꢃ 10ꢁ3 mol, 62%) of 3c as a deep-red solid.
Anal. (%) Calc. for C48H38ClN4PPd$CH2Cl2: C 63.38, H 4.34, N 6.03;
found: C 63.15, H 4.30, N 5.98. MS (ESIþ): 807.2 {[M] ꢁ CleCH2Cl2}þ
C
65.3,
H
4.6,
ꢁ
N
4.5. MS (ESIþ): 807.2 {[M]
ꢁ
(solvation
(solvation
molecules)
Cl}þ
and
545.1
{[M]
ꢁ
molecules) ꢁ Cl ꢁ (PPh3)}þ. IR data:
n
¼ 3050, 2919 and 2859,
n (Ce
H); 1430 and 1254 na (eN]Ne) and ns (eN]Ne), respectively; 525,
512 and 507 cmꢁ1 (PPh3). 1H NMR (250 MHz, at 240 K and
c ¼ 4 ꢃ 10ꢁ2 M):
d
¼ 3.07 (s, 3 H, Me), 3.72 (s, 3 H, Me), 5.12 (s, 3H,
CH2Cl2), 6.30 (br, 1H, H2), 6.60 (d, 1H, JH,H ¼ 7.4, H3), 6.80 (d, 1H,
3JH,H ¼ 7.6, H4), 7.80 (d, 1H, 3JH,H ¼ 7.4, H5b), 7.93 (d, 2H, 3JH,H ¼ 7.4,
1.0, H6b), 6.90e7.70 (m, 37H, H5, H1beH4b, H6a,beH7a,b and protons
of the PPh3 ligands) 31P{1H} NMR (at 240 K and c ¼ 4 ꢃ 10ꢁ2 M):
3
d
¼ 20.3, s (see text and Fig. 6).
4.5. Crystallography
A prismatic crystal of 3c$CH2Cl2, 4a, 4b or 4c$3/2CH2Cl2$1/2H2O
(sizes in Table 3) was selected and mounted on a MAR345 diffrac-
tometer an image plate detector. Unit-cell parameters were deter-
mined from 3997 (for 3c$CH2Cl2), 304 (for 4a), 25 (for 4b) and 205
and 545.1 {[M] ꢁ Cl ꢁ (PPh3) ꢁ CH2Cl2}þ. IR data:
n
¼ 3043, 2906
and 2843,
n (CeH); 1456 and 1274, na (eN]Ne) and ns (eN]Ne),
respectively; 530, 512 and 502 cmꢁ1:(PPh3). 1H NMR data:
d
¼ 3.57
(for 4c$3/2CH2Cl2$1/2H2O) reflections {in the ranges, 12ꢀ <
q
< 21ꢀ,
< q
< 31ꢀ, respectively) and
(s, 3 H, Meb), 3.81(s, 3 H, Me), 6.38 (t, 1H, 3JH,H ¼ 7.8, H3), 6.42 (dd,
3ꢀ < 31ꢀ, 12ꢀ < 21ꢀ, and 3ꢀ
<
q
<
q
1H, 3JH,H ¼ 7.8 and 4JP,H ¼ 7.2, H2) 6.80 (d, 1H, 3JH,H ¼ 7.8, H4) 7.05 (t,
refined by least-squares method. Intensities were collected with
graphite monochromatized Mo Ka radiation. The number of
reflections collected were 43,288 (for 3c), 23,851 (for 4a), 14,018
(for 4b) and 27,382 (for 4c$3/2CH2Cl2$1/2H2O), in the ranges
3
3
1H, JH,H ¼ 7.5, H2b), 7.20 (t, 1H, JH,H ¼ 7.5, H3b), 8.40 (d, 1H,
3JH,H ¼ 7.5, H1b), 7.69 (d, 1H, 3JH,H ¼ 7.3, H5), 7.80 (d, 2H, 3JH,H ¼ 7.3,
H
5b) and 7.30e7.55 (m, 22H, H4b, H6, H6b, H7 and protons of the
PPh3). 31P{1H} NMR:
d
¼ 39.7, s.
2.61ꢀ
1.38ꢀ
ꢂ
q
ꢂ 32.45ꢀ, 2.57ꢀ
< q < q
< 30.00ꢀ, 2.02ꢀ < 29.97ꢀ and
ꢂ
q
ꢂ 32.03ꢀ, for 3c, 4a, 4b and 4c, respectively}, of which
4.4.4. Compound 4a
12,745 (for 3a), 12,264 (for 4a) were non-equivalent by symmetry.
The number of reflections assumed as observed applying the
condition I > 2s(I). were 9598, 9003, 12,149 and 10,198 (for
3a$CH2Cl2, 4a, 4b and 4c$3/2CH2Cl2$1/2H2O, respectively). Lorentz-
polarization and absorption corrections were made.
A mixture of 3a (85 mg, 9 ꢃ 10ꢁ5 mol) and PPh3 (144 mg,
3.6 ꢃ 10ꢁ4 mol) in 50 mL of CH2Cl2 was stirred for 2 h at 298 K and
then filtered. The filtrate was concentrated in vacuum. Addition of
diethylether gave a red solid obtained, that was later on recrystal-
lized from CH2Cl2eether and dried in vacuum to obtain 4a as a red
solid (yield: 85 mg, 8.5 ꢃ 10ꢁ5 mol, 95%). Anal. (%) Calc. for
C58H48ClN3P2Pd: C 70.31, H 4.88, N 4.24; found: C 70.1, H 4.7, N 4.2
These structures were solved by Direct methods, using SHELXS
computer program [48] and refined by full-matrix least-squares
method with SHELX97 computer program [49] using 43,288,
14,018, 23,851, and 27,382 reflections for 3c$CH2Cl2, 4a, 4b and
4c$3/2CH2Cl2$1/2H2O, respectively, (very negative intensities were
not assumed). The function minimized was SwjjFoj2 ꢁ jFcj2j2,
MS(ESIþ): 692.13 {[M] ꢁ ClePPh3)}þ. IR data:
n
¼ 3040, 2910 and
2844,
n (CeH); 1434 and 1189 na (eN]Ne) and ns (eN]Ne),
respectively; 521, 510 and 496 (in cmꢁ1) (PPh3). 31P{1H} NMR
(240 K):
d
¼ 17.26, s. 1H NMR (250 MHz, CDCl3):
¼ 2.35 (s, 3H, Me);
d
where w ¼ [
s
2(I) þ 0.0597P)2 þ 0.0901P]ꢁ1 (for 3c CH2Cl2),
3.50 (br s, 3H, NMe); 6.20e6.50 (br m, 2H, H3 and H2); 6.70 (d, 1H,
w
w
¼
[
s
2(I)
þ
(0.0401P)2
þ
þ
3.9847P]ꢁ1 (for 4a) and
JHH
¼
7.7, H4); 7.29e7.78 (m, 22H, aromatic); 7.85 (d, 2H,
¼
[
s
2(I)þ(0.0493P)2
0.4243P]ꢁ1
(for
4b),
JHH ¼ 7.2H5).
w ¼ [
s
2(I) þ (0.1136P)2 þ 0.6964P]ꢁ1 (for 4c$3/2CH2Cl2$1/2H2O),
and P ¼ (jFoj2 þ 2jFcj2)/3; f , f ’, and f ” were taken from the bibli-
ography [50]. All H atoms were computed and refined, using
a riding model with an isotropic temperature factor equal to 1.2
times the equivalent temperature factor of the atom which are
linked. The final R (on F) factor was 0.0470, 0.060, 0.05 and 0.084 for
3c$CH2Cl2, 4a, 4b and 4c$3/2CH2Cl2$1/2H2O, respectively and the
wR(on (jFj2) values equal to 0.0710 (for 3c$CH2Cl2), 0.0148 (for 4a),
0.098 (for 4b) and 0.248 (for 4c$3/2CH2Cl2$1/2H2O). Further details
concerning the resolution and refinement of these crystal struc-
tures are given in Table 3.
4.4.5. Compound 4b
This product was obtained using the same procedure as that
described above for 4a, but using 82 mg (1.1 ꢃ 10ꢁ4 mol) of 3b and
115 mg (4.4 ꢃ 10ꢁ4 mol) of triphenylphosphine (yield: 105 mg,
1.0 ꢃ 10ꢁ4 mol, 95%). Anal. (%) Calc. for C57H45Cl2N3P2Pd: C 67.70, H
4.49,
N
4.2; found:
C
67.5;
¼ 3045, 2929 and 2847,
H 4.6, N
4.2. MS(ESIþ) 714.09
{[M] ꢁ Cl ꢁ PPh3)þ. IR data
n
n (CeH); 1437
and 1192 na (eN]Ne) and ns (eN]Ne), respectively; 521, 511 and
508 cmꢁ1 (PPh3). 31P{1H} NMR (240 K):
d
¼ 17.30, s. 1H NMR
(250 MHz, CDCl3):
d
¼ 3.50 (br s, 3H, NMe); 6.20e6.50 (br m, 2H, H3,
H2); 6.77 (d, 1H, 3JHH ¼ 7.2, H4); 7.29e7.78 (m, 22H, aromatic); 7.93
(d, 2H, 3JHH ¼ 8.5 Hz, H5).
4.6. Computational details
4.4.6. Compound 4c$3/2CH2Cl2$1/2H2O
DFTcalculations of 3c, 4c and the free PPh3 have been performed
at the B3LYP level [51] using the Gaussian 03 software [27]. The
basis set has been chosen as follows: LANL2DZ [52] for Pd and Cl,
including polarization functions for Cl [53], 6-31G [54], for
hydrogen [55], and 6-31G(d) including polarization functions [56]
for the remaining atoms. Solvent effects have been calculated
using the C-PCM model.13Semiempirical calculations have been
performed with the PM6 method, using the MOPAC2009 software
[46b]. Solvent effects have been taken into account using the
COSMO model [46].
Compound 3c$CH2Cl2 (30 mg, 3.2 ꢃ 10ꢁ5 mol) was dissolved in
15 mL of CH2Cl2, then PPh3 (17 mg, 6.5 ꢃ 10ꢁ5 mol) was added and
the reaction mixture was stirred at 298 K for 1 h. After this period
the solution was concentrated in a rotary evaporator to ca. 1 mL,
and transferred to a small vessel. The addition of diethylether
(1.0 mL) and the slow diffusion of this solvent at 298 K produced
monocrystals of 4c$3/2CH2Cl2$1/2H2O that were collected and air
dried (yield: 34 mg, 2.7 ꢃ 10ꢁ5 mol, 85%). Anal. (%) Calc. for
C66H53ClN4P2Pd$3/2CH2Cl2$1/2H2O: C 65.26, H 4.62, N 4.51; found:

30
A. González et al. / Journal of Organometallic Chemistry 726 (2013) 21e31
Table 3
Crystal data and details of the refinement of the crystal structures of compounds 3a CH2Cl2, 4a, 4b and 4c 3/2CH2Cl2$1/2H2O.
3a CH2Cl2
49H40Cl3N4PPd
4a
4b
4c 3/2CH2Cl2$1/2H2O
Chemical formula
C
C56H48ClN3P2Pd
C56H48Cl2N3P2Pd
(C66H53ClN4P2Pd)2
3CH2Cl2$H2O
2484.62
0.2 ꢃ 0.1 ꢃ 0.1
Formula weight
Crystal size/mm ꢃ
mm ꢃ mm
928.57
0.2 ꢃ 0.1 ꢃ 0.1
990.78
0.2 ꢃ 0.1 ꢃ 0.1
1011.20
0.2 ꢃ 0.1 ꢃ 0.1
Crystal system
Space group
Monoclinic
P21/c
14.216(6)
18.909(5)
16.536(6)
90.0
102.64(2)
90.0
293(2)
4337(3)
4
Triclinic
P-1
Triclinic
P-1
Triclinic
P-1
ꢀ
a/A
11.402(6)
12.106(4)
18.110(7)
99.12(2)
97.44(2)
92.78(3)
293(2)
2441.3(18)
2
1.348
11.344(8)
12.015(3)
18.111(11)
99.65(3)
96.98(6)
92.13(3)
293(2)
2411(2)
2
13.657(7)
15.905(7)
16.135(7)
90.98(3)
90.98(3)
111.81(2)
293(2)
3252(3)
1
ꢀ
b/A
ꢀ
c/A
a
/deg.
/deg.
b
g
/deg.
T/K
V/A
3
ꢀ
Z
Dcalc/Mg ꢃ mꢁ3
1.422
0.689
1.393
0.604
1.269
0.541
m
/mmꢁ1
0.542
F(000)
range for data
collection/deg.
N. of collected
reflections
1896
1020
1036
1276
Q
From 2.61
to 32.45
43,288
From 2.57
to 32.44
23,831
From 2.02
to 29.97
14,019
From 1.38
to 32.03
27,382
N. of unique
12,745 {0.0416}
12,955 {0.0595}
14,019 {0.0119}
16,144 {0.0798}
reflections {R(int)}
N. of parameters
Goodness of fit on F2
542
1.124
587
1.240
587
1.014
610
1.116
R indices {I > 2
s
(I)}
R1 ¼ 0.0470,
wR2 ¼ 0.1165
R1 ¼ 0.0710,
wR2 ¼ 0.1261
R1 ¼ 0.0639,
wR2 ¼ 0.1644
R1 ¼ 0.0642,
wR2 ¼ 0.1645
R1 ¼ 0.0496,
wR2 ¼ 0.0986
R1 ¼ 0.1174,
wR2 ¼ 0.1171
R1 ¼ 0.0837,
wR2 ¼ 0.2252
R1 ¼ 0.1216,
wR2 ¼ 0.248
R indices (all data)
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Acknowledgements
This work was supported by the Ministerio de Ciencia e Innova-
ción of Spain {grants: CTQ2009-11501 (subprogram BQU)}, FEDER
Funds and by the Generalitat de Catalunya (grant number 2009-
SGR-1111).
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Appendix B. Supplementary information
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2012.11.036.
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