Synthesis and characterization of new heterocyclic Schiff base palladacycles: Ring activation through N-oxide formation

Article abstract of DOI:10.1016/j.poly.2009.07.058

Reaction of the Schiff base ligand derived from 4-pyridinecarboxaldehyde NC₅H₄C(H){double bond, long}N[2′,4′,6′-(CH₃)C₆H₂], (1), with palladium(II) acetate in toluene at 60 °C for 24 h gave [Pd{NC₅H₄C(H){double bond, long}N[2′,4′,6′-(CH₃)C₆H₂]}₂(OCOCH₃)₂], (2), with two ligands coordinated through the pyridine nitrogen. Treatment of the Schiff base ligand derived from 4-pyridinecarboxaldehyde N-oxide, 4-(O)NC₅H₄C(H){double bond, long}N[2′,4′,6′-(CH₃)C₆H₂], (4), with palladium(II) acetate in toluene at 75 °C gave the dinuclear acetato-bridged complex [Pd{4-(O)NC₅H₃C(H){double bond, long}N[2′,4′,6′-(CH₃)C₆H₂]}(OCOCH₃)]₂, (5) with metallation of an aromatic phenyl carbon. Reaction of complex 5 with sodium chloride or lithium bromide gave the dinuclear halogen-bridged complexes [Pd{4-(O)NC₅H₃C(H){double bond, long}N[2′,4′,6′-(CH₃)C₆H₂]}(Cl)]₂, (6) and [Pd{4-(O)NC₅H₃C(H){double bond, long}N[2′,4′,6′-(CH₃)C₆H₂]}(Br)]₂, (7), after the metathesis reaction. Reaction of 6 and 7 with triphenylphosphine gave the mononuclear species [Pd{4-(O)NC₅H₃C(H){double bond, long}N[2′,4′,6′-(CH₃)C₆H₂]}(Cl)(PPh₃)], (8) and [Pd{4-(O)NC₅H₃C(H){double bond, long}N[2′,4′,6′-(CH₃)C₆H₂]}-(Br)(PPh₃)], (9), as air stable solids. Treatment of 6 and 7 with Ph₂P(CH₂)₂PPh₂ (dppe) in a complex/diphosphine 1:2 molar ratio gave the mononuclear complexes [Pd{4-(O)NC₅H₃C(H){double bond, long}N[2′,4′,6′-(CH₃)C₆H₂]}(PPh₂(CH₂)₂PPh₂)][Cl], (10), and [Pd{4-(O)NC₅H₃C(H){double bond, long}N[2′,4′,6′-(CH₃)C₆H₂]}(PPh₂(CH₂)₂PPh₂)][PF₆], (11), with a chelating diphosphine. The molecular structure of complex 9 was determined by X-ray single crystal diffraction analysis.

Full text of DOI:10.1016/j.poly.2009.07.058

Polyhedron 28 (2009) 3607–3613
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and characterization of new heterocyclic Schiff base
palladacycles: Ring activation through N-oxide formation
a
a
Nina Gómez-Blanco a, Jesús J. Fernández a, , Alberto Fernández , Digna Vázquez-García ,
*
Margarita López-Torres a, Antonio Rodríguez a, José M. Vila b,
a Departamento de Química Fundamental, Universidad de La Coruña, E-15071 La Coruña, Spain
*
b Departamento de Química Inorgánica, Universidad de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
a r t i c l e i n f o
a b s t r a c t
Reaction of the Schiff base ligand derived from 4-pyridinecarboxaldehyde NC5H4C(H)@N[20,40,60-
(CH3)C6H2], (1), with palladium(II) acetate in toluene at 60 °C for 24 h gave [Pd{NC5H4C(H)@N[20,40,60-
(CH3)C6H2]}2(OCOCH3)2], (2), with two ligands coordinated through the pyridine nitrogen. Treatment
of the Schiff base ligand derived from 4-pyridinecarboxaldehyde N-oxide, 4-(O)NC5H4C(H)@N[20,40,60-
(CH3)C6H2], (4), with palladium(II) acetate in toluene at 75 °C gave the dinuclear acetato-bridged complex
[Pd{4-(O)NC5H3C(H)@N[20,40,60-(CH3)C6H2]}(OCOCH3)]2, (5) with metallation of an aromatic phenyl car-
bon. Reaction of complex 5 with sodium chloride or lithium bromide gave the dinuclear halogen-bridged
complexes [Pd{4-(O)NC5H3C(H)@N[20,40,60-(CH3)C6H2]}(Cl)]2, (6) and [Pd{4-(O)NC5H3C(H)@N[20,40,60-
(CH3)C6H2]}(Br)]2, (7), after the metathesis reaction. Reaction of 6 and 7 with triphenylphosphine gave
the mononuclear species [Pd{4-(O)NC5H3C(H)@N[20,40,60-(CH3)C6H2]}(Cl)(PPh3)], (8) and [Pd{4-
(O)NC5H3C(H)@N[20,40,60-(CH3)C6H2]}-(Br)(PPh3)], (9), as air stable solids. Treatment of 6 and 7 with
Ph2P(CH2)2PPh2 (dppe) in a complex/diphosphine 1:2 molar ratio gave the mononuclear complexes
[Pd{4-(O)NC5H3C(H)@N[20,40,60-(CH3)C6H2]}(PPh2(CH2)2PPh2)][Cl], (10), and [Pd{4-(O)NC5H3C(H)@
N[20,40,60-(CH3)C6H2]}(PPh2(CH2)2PPh2)][PF6], (11), with a chelating diphosphine. The molecular structure
of complex 9 was determined by X-ray single crystal diffraction analysis.
Article history:
Received 17 May 2009
Accepted 17 July 2009
Available online 6 August 2009
Keywords:
Cyclometallation
Heterocycle
Palladium
Crystal structure
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
the palladium atom [21], in which case the use of indirect methods
may be necessary to metallate the ligand [19]. In our quest for new
The chemistry of cyclometallated transition metal complexes
has been of interest to the organometallic chemist [1,2] not only
due to their synthetic and structural characteristics but also to
their growing applications such as the use in catalytic and syn-
thetic processes [3], as chiral auxiliaries [4] or as building blocks
for complex molecular architectures [5]. They also show interest-
ing mesogenic [6], luminescent, electronic properties [7] and po-
tential applications in medicine and biology [8].
This has prompted our interest in the synthesis of new cyclo-
metallated metalloligands bearing uncoordinated pyridine rings.
Ligands with pyridine rings have been extensively studied as build-
ing blocks in the construction of supramolecular assemblies
[9–17]; yet, few examples in which the heterocyclic ring is part
of a cyclometallated ligand have been reported [18–20]. This is
probably due to the ease with which the pyridine nitrogen coordi-
nates to the metal center, precluding the access of the C–H bond to
types of metalloligands bearing cyclometallated units we studied
the reaction between the Schiff base 1, bearing a pyridine ring,
and palladium(II) acetate that only gave a complex with the ligand
coordinated to the palladium atom through the pyridine nitrogen,
and no palladium–carbon bond formation. We reasoned that by
protecting the pyridine nitrogen we could preclude N-coordination
and favour C-metallation; consequently, reaction of 1 with MeI
gave the N-methylated Schiff base 3 that, however, did not in turn
produce the expected cyclometallated complex; nevertheless, the
analogous N-oxide Schiff base was readily metallated, bringing
forth
a
new family of potentially oxygen coordinating
metalloligands.
2. Results and discussion
For the convenience of the reader the compounds and reactions
are shown in Schemes 1 and 2. The compounds described in this
paper were characterized by elemental analysis (C, H, N), and IR
and 1H, 13C{1H} and 31P{1H} spectroscopy (see Section 3) and, in
part, by mass spectrometry and X-ray single crystal diffraction
* Corresponding authors. Fax: +34 981 167065 (J.J. Fernández), +34 981 595012
(J.M. Vila).
E-mail addresses: qiluaafl@udc.es (J.J. Fernández), josemanuel.vila@usc.es
(J.M. Vila).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.07.058

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N. Gómez-Blanco et al. / Polyhedron 28 (2009) 3607–3613
(Pd(OAc)2, CH2Cl2, r.t.; K2PdCl4, H2O, r.t.; Li2PdCl4, MeOH, r.t.) failed
to produce the expected complexes.
However, treatment of the N-oxide of the Schiff base, 4, with
Pd(OAC)2 in toluene at 75 °C for 48 h gave the dimer 5, metallated
at the aromatic C6 carbon atom. The IR spectrum of 5 showed the
N
m(C@N) stretching band (see Section 3) shifted to lower frequency
(compared to the free imine) in agreement with nitrogen coordi-
nation to metal center [22]. This was supported by the character-
istic upfield shift (0.43 ppm) of the NMR signal for the imine
proton, observed in the cyclometallated complexes as a conse-
quence of N-coordination [23,26–28]. The IR spectrum showed
N
N
i
AcO Pd OAc
N
mas(COO) and m ,
s(COO) at 1577 and 1420 cmꢀ1
N
to strong bands
respectively, in accordance with bridging acetate groups
[24,26,28]. The trans geometry of the cyclometallated moieties
was determined by the presence at 2.44 ppm of a singlet signal
in the 1H NMR spectrum, assigned to the two equivalent methyl
acetate protons [29]. Complex
5 was also characterized by
N
13C{1H} NMR spectroscopy, being the most noticeable feature
the shift to higher frequency of the C6, C@N, and C1 resonances
(as compared to the uncoordinated ligand or the non cyclometal-
lated complex 2), confirming the formation of the cyclometallated
ring [25,30,31]. The FAB-mass spectrum showed at 809 amu the
cluster of peaks assigned to [{(L-H)(OAc)Pd}2]+ (L-H = cyclometal-
lated ligand), thereby confirming the dinuclear nature of the com-
plex [32].
1
ii
2
Me
N+
I-
i
Complex 5 readily experimented metathesis reactions with so-
dium chloride or lithium bromide in acetone/water or methanol/
water, respectively, to give the corresponding complexes with
bridging halide ligands 6 and 7. The mass spectra showed peaks as-
signed to [{(L-H)XPd}2H]+ (X = Cl, 763 amu; X = Br, 853 amu), con-
sequent with the dinuclear formulation of the complexes. The IR
and 1H NMR spectra were similar to those for complex 5, being
the most noticeable differences the absence of the characteristic
acetate bridging ligand signals.
N
3
Scheme 1. (i) Pd(OAc)2, toluene, 60 °C; (ii) MeI, toluene, 90 °C.
Reaction of the halide-bridged complexes 6 and 7 with triphen-
ylphosphine in chloroform gave the mononuclear complexes 8 and
9, respectively, which were fully characterized (see Section 3). The
IR spectra of these complexes showed the typical low-frequency
analysis. Reaction of the Schiff base ligand 1 with palladium(II)
acetate in toluene at 60 °C for 24 h gave the non-cyclometallated
complex 2 with two ligands coordinated to the palladium atom
through the pyridine nitrogen. The doublet signals assignable to
the H2/H6 protons, in the 1H NMR spectrum, was in agreement
with absence of PdꢀC bond formation in 1. The values shown by
shift of the
HC@N and H5 protons were coupled to the 31P nucleus [d ca.
8.08 ppm (J(PH) = 7.8 Hz) and ca. 7.0 ppm (J(PH) = 3.9 Hz),
m
(C@N) band (vide supra). In the 1H NMR spectra the
d
respectively], and the 31P{1H} NMR spectra showed singlet reso-
nances at ca. 39.5 ppm. In the 13C{1H} spectra the low-field shift
observed for the C6, C@N, and C1 resonances was similar to those
found in the spectrum of 5 (vide supra) and the C5, resonance
showed the coupling to the 31P nucleus [J(C5P) ca. 11]. The mass
spectra of 8 and 9 showed peaks centred at 607 amu corresponding
to the loss of the halide ligand and, for complex 8 at 643 amu as-
signed to the molecular ion.
the m
(C@N) stretch, 1610 cmꢀ1, in the IR spectrum and by the the
HC@N resonance in the 1H NMR spectrum, 8.22 ppm, were similar
to those for the free ligand, in accordance with the absence of
bonding between the palladium and the non-aromatic iminic
nitrogen [22,23]. Two strong bands at 1300 and 1555 cmꢀ1 were
assigned to the symmetric and asymmetric
m(COO) vibrations,
respectively, in agreement with those expected for mono-coordi-
nate acetato ligands [24,25]. The 1H NMR spectrum showed a sin-
glet signal for the acetate CH3COOꢀ protons at 2.29 ppm and the
13C{1H} NMR two signals assigned to the CH3COO and the CH3COO
acetate carbons at 178.36 and 23.23 ppm, respectively. Regardless
of the reaction conditions used (dichloromethane, room tempera-
ture; acetic acid, reflux) the reaction between ligand 1 and palla-
dium(II) acetate gave in all cases the coordination complex 2 and
not the expected cyclometallated compound.
The pyridine nitrogen of ligand 1 could be N-methylated with
MeI in toluene at 90 °C in order to hinder its coordination through
the pyridine nitrogen and, consequently, favour the cyclometalla-
tion reaction. However, reaction of the methylated Schiff base 3
with palladium(II) acetate under analogous reaction conditions as
used in the synthesis of 2 (toluene, 60 °C) did not yield the desired
product; instead of this a large amount of black palladium ap-
peared in the reaction tube and an untreatable reaction mixture
was isolated from the solution. Other reaction conditions
2.1. Molecular structure of complex 9
Suitable crystals were grown by slowly evaporating a chloro-
form solution of 9. The molecular structure is illustrated in Fig. 1.
The asymmetric unit comprises two solvent molecules of chlo-
roform and a molecule of complex 9; molecules of 9 are aligned
along the a-axis and packed in layers parallel to a and c, between
which the chloroform solvent molecules are located. The palladium
atom is bonded in a slightly distorted square-planar geometry to
the C(1) carbon atom of the pyridine ring, the imine N(1) atom,
the Br(1) atom and to the P(1) phosphorus atom of the triphenyl-
phosphine ligand. The angles between adjacent atoms in the coor-
dination sphere of palladium are close to the expected value of 90°
with the most noticeable distortions corresponding to the bite an-
gle C(1)–Pd(1)–N(1) of 81.06(9)°. The sum of the angles about pal-
ladium is approximately 360°.

N. Gómez-Blanco et al. / Polyhedron 28 (2009) 3607–3613
3609
O-
N+
PPh3
X
Pd
N
8: X = Cl
9: X = Br
iii
O-
O-
O-
N+
N+
N+
5
6
3
2
AC
O
2
X
2
1
Pd
ii
Pd
i
N
Hi
15
N
N
7
13
12
11
8
9
10
14
4
6: X = Cl
5
7: X = Br
iv
O-
+
N+
Ph2
Pa
Pd
X-
Pb
N
Ph2
10: X = Cl
11: X = PF6
Scheme 2. (i) Pd(OAc)2, toluene, 75 °C; (ii) complex 6: NaClaq, acetone; complex 7: LiBraq, methanol; (iii) PPh3, chloroform; (iv) complex 10: dppe, chloroform; complex 11:
dppe, NH4PF6, acetone.
The geometry around palladium is planar [mean deviation from
the least square plane Pd(1), C(1), N(1), P(1), Cl(1), (plane 1), of
0.097 Å] and approximately co-planar with the metallated ring
[Pd(1), C(1), C(5), C(6), N(1); mean deviation 0.0035 Å (plane 2)]
and with the pyridine ring [plane 3, mean deviation of 0.0050 Å]
(angles between planes are: plane 1:2, 0.7°; plane 1:3, 0.9°; 2:3,
1.0°). The Pd–N(1), 2.099(2) Å, Pd–C(1), 2.016(2), Pd(1)–P(1),
2.246(1) and Pd(1)–Br(1), 2.459(1), bond distances are within the
range found earlier [33–36].
the mononuclear complexes, 10 and 11, respectively, as air-stable
solids which were fully characterized (see Section 3). The mainꢀdif-
ference between them was the counter ion [Clꢀ in 10 and PF6 in
11] in spite of which, the NMR spectra showed significant differ-
ences indicating that the interaction between the anion and the
cation remains in solution. In the 1H NMR spectrum of 10 the
HC@N resonance at d 8.44 ppm was a singlet; however, in the spec-
trum of 11 it appeared as a doublet at 8.10 ppm, by coupling to the
31P nucleus trans to nitrogen (J(HP) = 7.5 Hz); less significant shifts
were observed for the signals assigned to the H3 and H9/H11 pro-
tons. The 31P{1H} NMR spectra showed two doublets for the two
non-equivalent phosphorus nuclei, but in the spectrum of 10 the
Reaction of complexes
6 and 7 with the diphosphine
Ph2P(CH2)2PPh2, (dppe), in a 1:2 molar ratio (followed by treat-
ment with ammonium hexafluorophosphate in the case of 7) gave

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N. Gómez-Blanco et al. / Polyhedron 28 (2009) 3607–3613
H3PO4 (
31P{1H}) and were recorded on a Bruker AV-300F spec-
trometer. All chemical shifts were reported downfield from stan-
dards. The FAB mass spectra were recorded using a FISONS
Quatro mass spectrometer with a Cs ion gun; 3-nitrobenzyl alcohol
was used as the matrix. The ESI mass spectra were recorded using a
QSTAR Elite mass spectrometer, using dichloromethane/acetoni-
trile or dichloromethane/ethanol as solvents.
3.2. Syntheses
3.2.1. Preparation of NC5H4 C(H)@N[20,40,60-(CH3)C6H2] (1)
4-(COH)NC5H4 (0.173 g, 1.61 mmol) and 2,4,6-Me3C6H2NH2
(0.211 g, 1.56 mmol) were added to 50 cm3 of dry chloroform.
The mixture was heated under reflux in a Dean-Stark apparatus
for 48 h. After cooling to room temperature, the solvent was evap-
orated to give a yellow oil. Yield: 93%. Anal. Calc. for: C15H16N2: C,
80.2; H, 7.2; N, 12.5. Found. C, 80.0; H, 6.9; N, 12.7%. IR:
m
(C@N) = 1605m cmꢀ1. NMR 1H (300.13 MHz, CDCl3, d ppm, J
Hz): d = 8.79 [m, 2H, H3/H5]; 8.23 (s, 1H, Hi); 7.78 [m, 2H,
H2/H6]; 6.91 (s, 2H, H9/H11); 2.30 (s, 3H, –CH3); 2.12 (s, 6H, 2CH3).
3.2.2. Preparation of [Pd{NC5H4C(H)=N[20,40,60-
(CH3)C6H2]}2(OCOCH3)2] (2)
A pressure tube containing Schiff base 1 (0.150 g, 0.666 mmol),
palladium(II) acetate (0.150 g, 0.668 mmol) and 20 cm3 of dry tol-
uene was sealed under argon. The resulting yellow solution was
stirred for 24 h at 60 °C. The green solid obtained was filtered off
and dried in vacuo. Yield: 46%. Anal. Calc. for C34H38N4O4Pd re-
quires: C, 60.7; H, 5.7; N, 8.3. Found: C, 60.5; H, 5.4; N, 8.6%. IR:
Fig. 1. Molecular structure of Pd{4-(O)NC5H3C(H)=N[20,40,60-(CH3)C6H2]}(Br)
(PPh3)], 9. Ellipsoids drawn at the 40%. Selected bond distances (Å) and angles (°):
Pd(1)–N(1) 2.099(2), Pd(1)–C(1) 2.016(2), Pd(1)–Br(1) 2.459(1), Pd(1)–P(1)
2.246(1), C(1)–C(5) 1.418(3), C(5)–C(6) 1.443(3), N(1)–C(6) 1.284(3), N(2)–O(1)
1.304(3); N(1)–Pd(1)–C(1) 81.06(9), N(1)–Pd(1)–Br(1) 90.85(6), C(1)–Pd(1)–Br(1)
171.87(7), N(1)–Pd(1)–P(1) 175.56(6), C(1)–Pd(1)–P(1) 94.54(7), Br(1)–Pd(1)–P(1)
93.57(2).
m
(C@N) = 1610s; [
mas(COO) = 1558s,
m
s(COO) = 1300s]cmꢀ1. NMR
1H (300.13 M, CDCl3,
d
ppm, Hz): d = 8.84 [d, 2H, H3,H5
J
3J(H2H3) = 6.6]; 8.22 (s, 1H, Hi); 7.82 [d, 2H, H2, H6,
3J(H6H5) = 6.6]; 6.95 (s, 2H, H9/H11); 2.29 (s, 3H, –OAc); 1.89 (s,
3H, –CH3); 2.10 (s, 6H, 2CH3). NMR 13C{1H} (75.47 MHz, CDCl3, d
ppm, J Hz): d = 178.36 (s, –CO2CH3); 158.76 (s, Ci); 122.13 (s, C3/
C5); 147.33, 144.83, 134.25, 126.75 (s, C1, C7, C10); 129.01 (s,
C2/C6); 128.22 (s, C8/C12); 123.03 (s, C9/C11); 23.23 (s, –CO2CH3);
20.76 (s, C13/C15); 18.22 (s, C14).
signals appeared high-field shifted (d 55.18, 39.98 ppm;
J(PP) = 22.7 Hz, for 10 vs. d 61.12, 46.47 ppm; J(PP) = 24.5 Hz for
11). The resonance at lower frequency was assigned to the phos-
phorus nucleus trans to the phenyl carbon atom, in accordance
with the higher trans influence of the latter with respect to the
C@N nitrogen atom [37]. The 13C{1H} spectra showed the HC@N
resonance coupled to the trans-nitrogen phosphorus nuclei and
considerably high-field shifted in the case of 10 [d 164.66 ppm,
J(CP) = 2.0 Hz; 180.11 ppm, J(CP) = 3.1 Hz for 10 and 11, respec-
tively]. The C5 and C6 resonances also showed coupling to the
phosphorus nucleus.
3.2.3. Preparation of [4-(Me)NC5H4C(H)=N{20,40,60-(CH3)C6H2}][I] (3)
A pressure tube containing Schiff base 1 (0.180 g, 0.803 mmol),
IMe (0.114 g, 0.803 mmol) and 20 cm3 of dry toluene was sealed
under argon. The resulting yellow solution was stirred for 24 h at
90 °C. The orange solid obtained was filtered off and dried in vacuo.
Yield: 22%. Anal. Calc. C16H19N2I requires: C, 52.5; H, 5.2; N, 7.6.
Accordingly, the most significant differing shifts in the 1H and
13C MNR spectra of complexes 10 and 11 corresponded to the
HC@N group. This is indicative that in solution the interaction be-
tween the cation and its counteraction takes place through the
imine proton. This feature may be used to determine the anions
present in the solution and, therefore, complexes 10 and 11 may
be used as anion sensors.
In the mass spectra of 10 and 11 the cluster of peaks centred at
743 amu were assigned to the [{(L-H)Pd(dppe)}]+ fragment due to
the loss of the counterion. Conductivity measurements were in
accordance with a 1:1 electrolyte formulation.
Found: C, 52.6; H, 5.4; N, 7.6%. IR:
(300.13 MHz, CDCl3, ppm,
m
(C@N) = 1610s cmꢀ1. NMR 1H
J Hz): d = 8.31 [d, 2H, H3/H5,
d
3J(H2H3) = 6.6]; 8.47 (s, 1H, Hi); 8.52 [d, 2H, H2/H6,
3J(H2H3) = 6.6]; 6.93 (s, 2H, H9/H11); 4.77 (s, 3H, N–CH3); 2.36
(s, 3H, –CH3); 2.16 (s, 6H, 2CH3). Specific molar conductivity
Km = 97.5 cm2 molꢀ1(in dry acetonitrile).
Compound 4 was obtained as yellow solid, following a similar
procedure to that used in the preparation of 1.
3.2.4. Preparation of 4-(O)NC5H4C(H)=N[20,40,60-(CH3)C6H2] (4)
Yield: 93%. Anal. Calc. C15H16N2O requires: C, 75.0.2; H, 6.7; N,
3. Experimental
11.7. Found: C, 75.5; H, 6.6; N, 12.0%. IR: m .
(C@N) = 1603m cmꢀ1
3.1. General remarks
NMR 1H (300.13 MHz, CDCl3, d ppm, J Hz): d = 8.27 [d, 2H, H3/
H5, 3J(H2H3) = 7.2]; 8.15 (s, 1H, Hi); 7.78 [d, 2H, H2/H6,
3J(H2H3) = 7.2]; 6.90 (s, 2H, H9/H11); 2.29 (s, 3H, –CH3); 2.11 (s,
Solvents were purified by standard methods [38]. Chemicals
were reagent grade. Microanalyses were carried out using a Carlo
Erba Elemental Analyser, Model 1108. IR spectra were recorded
as KBr discs on a Satellite FTIR. NMR spectra were obtained as
CDCl3 solutions and referenced to SiMe4 (1H, 13C{1H}) or 85%
6H, 2CH3). NMR 13C{1H} (75.47 MHz, CDCl3,
d ppm, J Hz):
d = 157.76 (s, Ci); 147.57 (s, C7); 139.60 (s, C3/C5); 133.92,
132.91 (s, C1, C10); 128.89 (s, C9/C11); 126.79 (s, C8/C12);
124.70 (s, C2/C6); 20.70 (s, C14); 18.19 (s, C13/C15).

N. Gómez-Blanco et al. / Polyhedron 28 (2009) 3607–3613
3611
3.2.5. Preparation of [Pd{4-(O)NC5H3C(H)=N[20,40,60-
(CH3)C6H2]}(OCOCH3)]2 (5)
C1, C6); 136.25 (s, C10); 135.20 [d, C-orto, 2J(C-orto,P) = 11.8];
135.12 (s, C3); 131.34 [d, C-para, 4J(C-para,P) = 2.6]; 129.91 (s,
C8/C12); 129.66 (s, C-ipso, 1J(C-ipso,P) = 43.8]; 128.47 [d, C-meta,
3J(C-meta,P) = 11.2]; 128.38 (s, C9/C11); 123.39 (s, C2); 21.0 (s,
C14); 19.10 (s, C13/C15). NMR 31P{1H}(121.50 MHz, CDCl3, d
ppm): 39.66 (s). FAB-mass: [{(L-H)Pd(PPh3)}]+ = 607.1; [{(L-
H)Pd(PPh3)(Cl)}]+ = 643.1 amu.
A pressure tube containing Schiff base 4 (0.196 g, 0.816 mmol),
palladium(II) acetate (0.186 g, 0.816 mmol) and 20 cm3 of dry tol-
uene was sealed under argon. The resulting yellow solution was
stirred for 48 h at 75 °C, filtered trough celite to remove the black
palladium formed and the solvent removed under vacuum. The
brown oil obtained was tritured with ether to give a brown solid
which was filtered off and dried in vacuo. Yield: 93%. Anal. Calc.
C34H36N4O6Pd2 requires: C, 50.4; H, 4.5; N, 6.9. Found: C, 48.9; H,
Compound 9 was obtained as a yellow solid following a similar
procedure.
4.3;
m
N,
6.6%.
IR:
m
(C@N) = 1576s;
[
m
as(COO) = 1577s,
3.2.9. Preparation of [Pd{4-(O)NC5H3C(H)=N[20,40,60-
(CH3)C6H2]}(Br)(PPh3)] (9)
s(COO) = 1420s]cmꢀ1. NMR 1H (300.13 MHz, CDCl3, d ppm, J Hz):
d = 8.10 [dd, 1H, H3, 3J(H2H3) = 6.6, 4J(H3H5) = 1.8]; 7.72 (s, 1H,
Hi); 7.48 [d, 1H, H5, 4J(H3H5) = 1.8]; 7.14 [d, 1H, H2,
3J(H2H3) = 6.6]; 6.91 (s, 2H, H9/H11); 2.44 (s, 3H, –OAc); 2.34 (s,
3H, –CH3); 1.63 (s, 6H, 2CH3). NMR 13C{1H} (75.47 MHz, CDCl3, d
ppm, J Hz): d = 180.96 (s, –CO2CH3); 172.89 (s, Ci); 148.34 (s, C7);
142.61, 141.89 (s, C1, C6); 140.38, 135.76 (s, C3, C5); 137.69 (s,
C8/C12); 131.83 (s, C10); 128.84 (s, C9/C11); 121.97 (s, C2);
22.76 (s,–-CO2CH3); 20.80 (s, C13/C15); 18.26 (s, C14). FAB-mass:
Yield: 66%. Anal. Calc. C33H30BrN2OPdP.CHCl3 requires: C, 50.6;
H, 3.9; N, 3.5. Found: C, 51.0; H, 4.3; N, 3.7%. IR:
m
(C@N) = 1580m cmꢀ1. NMR 1H (300.13 MHz, CDCl3, d ppm, J
Hz): d = 8.09 [d, 1H, Hi, 4J(PHi) = 7.8]; 7.82 [dd, 1H, H3,
3J(H2H3) = 6.3, 4J(H3H5) = 1.5]; 7.19 [d, 1H, H2, 3J(H2H3) = 6.3];
7.00 [dd, 1H, H5, 4J(PH5) = 3.9 , 4J(H3H5) = 1.5]; 6.88 (s, 2H, H9/
H11); 2.32 (s, 6H, –2CH3); 2.28 (s, 3H, –CH3). NMR 13C{1H}
(125.76 MHz, CDCl3, d ppm, J Hz): d = 174.73 (s, Ci); 154.54 (s,
C7); 145.88, 144.42 (s, C1, C6); 144.98 [d, C5, 3J(C5P) = 11.4];
136.15 (s, C10); 135.16 (s, C3); 135.07 [d, C-orto, 2J(C-or-
to,P) = 11.7];131.27 [d, C-para, 4J(C-para,P) = 2.5]; 130.62 (s, C8/
C12); 129.98 (s, C-ipso, 1J(C-ipso,P) = 54.9]; 128.38 [d, C-meta,
3J(C-meta,P) = 11.2]; 128.23 (s, C9/C11); 123.20 (s, C2); 20.97 (s,
C14); 19.18 (s, C13/C15). NMR 31P{1H} (121.50 MHz, CDCl3, d
ppm): 39.39 (s). ESI-mass: [{(L-H)Pd(PPh3)}]+ = 607.12 amu.
[{(L-H)Pd}2H]+ = 691.1;
[{(L-H)2(OAc)Pd2}H]+ = 751.1;
[{(L-
H)(OAc)Pd}2H]+ = 809.1 amu.
3.2.6. Preparation of [Pd{4-(O)NC5H3C(H)=N[20,40,60-(CH3)C6H2]}(Cl)]2
(6)
A solution of 5 (0.103 g, 0.128 mmol) in 20 cm3 of acetone was
treated with a saturated solution of NaCl in water until complete
solution. After stirring for 24 h the yellow precipitate formed was
filtered off, washed with water and dried under vacuum. Yield:
82%. Anal. Calc. C30H30N4O2Cl2Pd2 requires: C, 47.3; H, 4.0; N, 7.3.
3.2.10. Preparation of [Pd{4-(O)NC5H3C(H)=N[20,40,60-
(CH3)C6H2]}(PPh2(CH2)2PPh2)]-[Cl] (10)
Found: C, 47.4; H, 3.8; N, 7.0%. IR:
m
(C@N) = 1583m cmꢀ1. NMR
Ph2P(CH2)2PPh2 (0.022 g, 0.055 mmol) was added to a suspen-
sion of 6 (0.020 g, 0.026 mmol) in chloroform (10 cm3). The mix-
ture was stirred for 24 h, the solvent removed under vacuum and
the residue formed recrystallized form chloroform/hexane to give
a yellow solid which was filtered off and dried in vacuo. Yield:
49%. Anal. Calc. C41H39ClN2OP2Pd requires: C, 63.2; H, 5.0; N, 3.6.
1H (300.13 MHz, DMSO-d6, d ppm, J Hz): d = 8.28 (s, 1H, H5);
8.26 (s, 1H, Hi); 8.00 [d, 1H, H3, 3J(H2H3) = 5.7]; 7.41 [d, 1H, H2,
3J(H2H3) = 5.7 ]; 6.92 (s, 2H, H9/H11); 2.23 (s, 3H, –CH3); 2.19 (s,
6H, 2–CH3). ESI-mass: [{(L-H)ClPd}2H]+ = 762.98 amu.
3.2.7. Preparation of [Pd{4-(O)NC5H3C(H)=N[20,40,60-(CH3)C6H2]}(Br)]2
(7)
Found: C, 63.1; H, 4.7; N, 3.5%. IR: m
(C@N) = 1576m cmꢀ1. NMR
1H (300.13 MHz, CDCl3, d ppm, J Hz): d = 8.44 (s, 1H, Hi); 8.04 [d,
1H, H3, 3J(H2H3) = 6.0]; 6.78 (s, 2H, H9/H11); 2.30 (s, 3H, –CH3);
1.92 (s, 6H, 2CH3); (H5, occluded). NMR 13C{1H} (125.76 MHz,
CDCl3, d ppm, J Hz): d = 164.66 [d, Ci, 3J(CiPa) = 2.0]; 161.85 [dd,
C6, 2J(C6Pb) = 134.4 , 2J(C6Pa) = 3.5]; 148.59 (s, C7); 142.67 (m,
C5); 140.14 (s, C1); 134.87 (s, C3); 133.13 [d, C-orto, 2J
(C-orto,Pb) = 11.4]; 133.02 (s, C10); 132.94 [d, C-orto, 2J(C-orto,-
Pa) = 11.2]; 132.29 [d, C-para, 4J(C-para,Pb) = 2.3]; 131.43 [d, C-para,
4J(C-para,Pa) = 2.1]; 129.48 [d, C-meta, 3J(C-meta,Pb) = 11.2]; 129.19
[d, C-ipso, 1J(C-ipso,Pa) = 38.7]; 129.16 [d, C-meta, 3J(C-meta,-
Pa) = 10.2]; 128.60 (s, C9/C11); 127.87 [d, C-ipso, 1J(C-ip-
so,Pb) = 53.1]; 127.48 (s, C8/C12); 123.66 [d, C2, 4J(C2,P) = 8.4];
20.82 (s, C14); 18.62 (s, C13/C15). NMR 31P{1H} (121.50 MHz,
CDCl3, d ppm, J Hz): 55.18 [d, Pa, nJ(Pa,Pb) = 22.7]; 39.98 [d, Pb,
nJ(Pa,Pb) = 22.7] ppm. ESI-mass: [{(L-H)Pd(dppe)}]+ = 743.15 amu.
Specific molar conductivity: Km = 81.2 cm2 molꢀ1(in dry
acetonitrile).
A brown solution of 5 (0.127 g, 0.157 mmol) in 15 cm3 of meth-
anol was treated with a saturated solution of LiBr in water (ca.
15 cm3). After stirring for 24 h the yellow–green precipitate
formed was filtered off, washed with water and dried under vac-
uum. Yield: 85%. Anal. Calc. C30H30N4O2Br2Pd2 requires: C, 42.3;
H, 3.5; N, 6.6. Found: C, 42.5; H, 3.4; N, 6.6%. IR: m(C@N) = 1600m
sh cmꢀ1. NMR 1H (300.13 MHz, DMSO-d6, d ppm, J Hz): d = 8.38
(br, 1H, H5); 8.29 (s, 1H, Hi); 7.98 [dd, 1H, H3, 3J(H2H3) = 6.6,
4J(H3H5) = 1.8]; 7.40 [d, 1H, H2, 3J(H2H3) = 6.6 ]; 6.94 (s, 2H, H9/
H11); 2.24 (s, 3H, –CH3); 2.20 (s, 6H, 2CH3). FAB-mass: [{(L-
H)BrPd}2H]+ = 853.4 amu.
3.2.8. Preparation of [Pd{4-(O)NC5H3C(H)=N[20,40,600-
(CH3)C6H2]}(Cl)(PPh3)] (8)
PPh3 (0.033 g, 0.124 mmol) was added to a suspension of 6
(0.047 g, 0.062 mmol) in chloroform (15 cm3). The resulting orange
solution was stirred for 24 h and the solvent removed under vac-
uum to give an orange oil which was recrystallized form chloro-
form/hexane and the resulting yellow solid filtered off and dried
in vacuo. Yield: 63%. Anal. Calc. C33H30ClN2OPdP.CHCl3 requires:
C, 53.5; H, 4.1; N, 3.7. Found: C, 53.0; H, 4.0; N, 4.0%. IR:
3.2.11. Preparation of [Pd{4-(O)NC5H3C(H)=N[20,40,60-
(CH3)C6H2]}(PPh2(CH2)2PPh2)]-[PF6] (11)
Ph2P(CH2)2PPh2 (0.030 g, 0.075 mmol) was added to a suspen-
sion of 7 (0.032 g, 0.038 mmol) in acetone (10 cm3). The mixture
was stirred for 45 min after which an excess of ammonium hexa-
fluorophosphate (ca. 1:6 molar ratio) was added. The mixture
was stirred for a further 1 h, the complex precipitated out by addi-
tion of water, stirred for a further 24 h filtered off and dried in va-
cuo, to give the final compound as a pale yellow solid. Yield: 21%.
Anal. Calc. C41H39F6N2OP3Pd requires: C, 55.4; H, 4.4; N, 3.1. Found:
m
(C@N) = 1581m cmꢀ1. NMR 1H (300.13 MHz, CDCl3, d ppm, J
Hz): d = 8.07 [d, 1H, Hi, 4J(PHi) = 7.8]; 7.80 [dd, 1H, H3,
3J(H2H3) = 6.3 , 4J(H3H5) = 1.8]; 7.19 [d, 1H, H2, 3J(H2H3) = 6.3];
7.05 [dd, 1H, H5, 4J(PH5) = 3.9 , 4J(H3H5) = 1.8]; 6.86 (s, 2H, H9/
H11); 2.31 (s, 6H, –2CH3); 2.25 (s, 3H, –CH3). NMR 13C{1H}
(125.76 MHz, CDCl3, d ppm, J Hz): d = 174.34 (s, Ci); 153.61 [d,
C7, 3J(C7P) = 2.5]; 145.30 [d, C5, 3J(C5P) = 11.2]; 144.98, 144.47 (s,
C, 55.0; H, 4.3; N, 3.2%. IR:
m
(C@N) = 1575m cmꢀ1. NMR 1H

3612
N. Gómez-Blanco et al. / Polyhedron 28 (2009) 3607–3613
(300.13 MHz, CDCl3, d ppm, J Hz): d = 8.10 [d, 1H, Hi, 4J(PHi) = 7.5];
7.88 [d, 1H, H3, 3J(H2H3) = 6.3]; 6.29 (s, 2H, H9/H11); 2.17 (s, 3H, –
CH3); 1.97 (s, 6H, 2CH3); (H5, occluded). NMR 13C{1H}
(125.76 MHz, CDCl3, d ppm, J Hz): d = 180.11 [d, Ci, 3J(CiPa) = 3.1
]; 159.48 [d, C6, 2J(C6Pb) = 117.2]; 145.88 (s, C7); 144.94 [dd, C5,
3J(C5Pb) = 11.1, 3J(C5,Pa) = 6.3]; 133.93 (s, C3); 133.88, 133.66 (s,
C, C10); 133.68 [d, C-orto, 2J(C-orto,Pb) = 11.9]; 133.48 [d, C-para,
4J(C-para,Pb) = 2.6]; 133.10 [d, C-orto, 2J(C-orto,Pa) = 11.9];132.10
[d, C-para, 4J(C-para,Pa) = 2.4]; 130.26 [d, C-meta, 3J(C-me-
ta,Pb) = 11.4]; 129.36 [d, C-meta, 3J(C-meta,Pa) = 10.4]; 129.00 (s,
C9/C11); 127.90 (s, C8/C12); 126.42 [d, C-ipso, 1J(C-ipso,Pa) = 41.7
]; 125.42 [d, C2, 4J(C2,Pb) = 5.7]; 124.73 [d, C-ipso, 1J(C-ip-
so,Pb) = 52.8]; 20.76 (s, C14); 18.62 (s, C13/C15). NMR 31P-{1H}
(121.50 MHz, CDCl3, d ppm, J Hz): 61.12 [d, Pa, 2J(Pa,Pb) = 24.5];
46.47 [d, Pb, 2J(Pa,Pb) = 24.5] ppm. ESI-mass: [{(L-H)Pd(dppe)}]+ =
743.16 amu. Specific molar conductivity Km = 82.1 cm2 molꢀ1
(in dry acetonitrile).
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C33H30BrN2OPPdꢁ2CHCl3; M = 926.61. Orthorhombic, a =
13.192(3), b = 19.889(5), c = 29.047(3) Å, U = 7621(4) Å3, Z = 8,
Dc = 1.615 g cmꢀ3, Space Group Pbca,
l(Mo Ka ,
) = 2.029 mmꢀ1
T = 100 K. Three-dimensional, room temperature X-ray data were
collected on a Bruker X8 Apex diffractometer using graphite-
monochromated Mo
measured, all of which were corrected for Lorentz and polarisation
effects and for absorption using a semi-empirical correction based
on symmetry-equivalent and repeated reflections (max, min trans-
missions 0.83, 0.45), 7263 independent reflections exceeded the
Ka radiation. Of the 43653 reflections
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atoms were included in calculated positions and refined in riding
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for all 9490 unique data), with allowance for the thermal anisot-
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CCDC 730623 contains the supplementary crystallographic data
for compound 8. 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:
deposit@ccdc.cam.ac.uk.
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Acknowledgments
[12] M. Ferrer, A. Gutiérrez, M. Mounir, O. Rossell, E. Ruiz, A. Rang, M. Engeser,
Inorg. Chem. 46 (2007) 3395.
We thank the Ministerio de Educación y Ciencia (Projects
CTQ2006-15621-C02-01/BQU and CTQ2006-15621-C02-02/BQU),
the Xunta de Galicia (Projects INCITE07PXI103083ES and INCI-
TE08ENA209044ES), and the Universidad de la Coruña for financial
support.
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