New palladium(II) cyclometallated compounds derived from trans-cinnamalylideneimines via C-H activation of an sp2-aliphatic carbon atom

Article abstract of DOI:10.1016/S0020-1693(02)01156-8

Treatment of the Schiff-base ligands C₆H₅C(H)=C(R)C(H)=NCy (R=H, a; R=Me, b) with Pd(OAc)₂ gave the acetato-bridged dinuclear compounds [Pd{C₆H₅C=C(R)C(H)=NCy}(O₂CMe)]₂ (R=H, 1a; R=Me, 1b) after C-H activation of the aliphatic carbon atom. Reaction of 1a and 1b with aqueous sodium chloride gave the dinuclear chloro-bridged compounds [Pd{C₆H₅C=C(R)C(H)=NCy}(X)]₂ (R=H, 2a; R=Me, 2b), which could also be prepared by treatment of the ligands with Li₂[PdCl₄] in methanol. Reaction of 1a with aqueous sodium bromide or iodide gave the halide-bridged species [Pd{C₆H₅C=C(H)C(H)=NCy}(X)]₂ (X=Br, 3a; X=I, 4a). Treatment of 1a and 1b with Tl(acac), Tl(C₅H₅) or PPh₃, as appropriate, gave the mononuclear complexes [Pd{C₆H₅C=C(R)C(H)=NCy}(acac)], (R=H, 5a; R=Me, 3b) [Pd{C₆H₅C=C(H)C(Me)=NCy}(C₅H₅)] (4b) and [Pd{C₆H₅C=C(H)C(Me)=NCy}(PPh₃)] (5b).

Full text of DOI:10.1016/S0020-1693(02)01156-8

Inorganica Chimica Acta 342 (2003) 145Á150
/
www.elsevier.com/locate/ica
New palladium(II) cyclometallated compounds derived from trans-
H activation of an sp2-aliphatic carbon
atom
cinnamalylideneimines via CÃ
/
Silvia Tenreiro a, Gemma Alberdi a, Javier Mart´ınez a, Margarita Lo´pez-Torres b,
Juan M. Ortigueira a, Ma Teresa Pereira a, Jose´ M. Vila a,ꢀ
´ ´
Departamento de Quımica Inorganica, Universidad de Santiago de Compostela, E-15782 Santiago de Compostela, Spain
a
b
´
Departamento de Quımica Fundamental, Facultad de Ciencias, Universidad de La Corun˜a, E-15071 La Corun˜a, Spain
Received 15 February 2002; accepted 31 May 2002
Dedicated to Professor Joachim Strahle on the occasion of his 65th birthday.
¨
Abstract
Treatment of the Schiff-base ligands C6H5C(H)Ä
dinuclear compounds [Pd{C6H5CÄC(R)C(H)ÄNCy}(O2CMe)]2 (Rꢁ
carbon atom. Reaction of 1a and 1b with aqueous sodium chloride gave the dinuclear chloro-bridged compounds [Pd{C6H5CÄ
C(R)C(H)ÄNCy}(X)]2 (RꢁH, 2a; RꢁMe, 2b), which could also be prepared by treatment of the ligands with Li2[PdCl4] in
methanol. Reaction of 1a with aqueous sodium bromide or iodide gave the halide-bridged species [Pd{C6H5CÄC(H)C(H)Ä
NCy}(X)]2 (XꢁBr, 3a; XꢁI, 4a). Treatment of 1a and 1b with Tl(acac), Tl(C5H5) or PPh3, as appropriate, gave the mononuclear
complexes [Pd{C6H5CÄC(R)C(H)ÄNCy}(acac)], (RꢁH, 5a; RꢁMe, 3b) [Pd{C6H5CÄC(H)C(Me)ÄNCy}(C5H5)] (4b) and
[Pd{C6H5CÄC(H)C(Me)ÄNCy}(PPh3)] (5b).
# 2002 Elsevier Science B.V. All rights reserved.
/
C(R)C(H)Ä
/
NCy (Rꢁ
/
H, a; Rꢁ
/
Me, b) with Pd(OAc)2 gave the acetato-bridged
/
/
/
H, 1a; Rꢁ
/
Me, 1b) after CÃ
/H activation of the aliphatic
/
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/
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/
/
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Keywords: Palladium; Schiff-base; Cyclometallation; CÃH Activation; Tertiary phosphine
/
1. Introduction
compounds prepared by direct metallation of an organic
moiety by palladium as the metal atom, i.e. the
palladacycles, are among the most abundant, especially
when the metallated carbon atom, bearing sp2-hybridi-
zation, is part of an aromatic ring. In addition to the
abundant examples in the literature, we have dealt with
In the past years, increasing attention has been
dedicated to cyclometallated compounds [1Á6] in view
/
of their ever growing chemistry and of the many
applications they present, such as their use in organic
and organometallic synthesis [7], in optical resolution
[8], in the synthesis of new metal mesogenic compounds
[9], in biologically active compounds [10,11], in catalytic
materials [12], and to promote unusual coordination
environments [13], to name but a few. Numerous factors
are involved in the synthesis and stability of cyclome-
tallated compounds, among which the nature of the
ligand, the number and type of donor atoms, the metal,
and ring size should be emphasized [2]. In particular,
complexes derived from potentially [C, N, X], (XꢁO, S,
/
N) terdentate ligands, such as semicarbazones [14,15],
thiosemicarbazones [16,17] or Schiff-bases [18,19], as
well as imidazoles [20] and ferrocenylimines [21]. Never-
theless, Schiff-base palladacycles where metallation is
directly produced at an aliphatic sp2-carbon atom are
scarce, and to the best of our knowledge the examples
that are known are derived from insertion reactions of a
previously metallated aromatic carbon atom [22]. More
recently, activation of the CÄ
achieved by platinum(II) [23], and addition of an AuÃ
bond across a styryl double bond [24] has been reported,
/
N bond in imines has been
ꢀ Corresponding author. Tel.: ꢂ
981-595 012
E-mail address: qideport@usc.es (J.M. Vila).
/
34-981-563 100x14255; fax: ꢂ34-
/
/X
0020-1693/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 0 - 1 6 9 3 ( 0 2 ) 0 1 1 5 6 - 8

146
S. Tenreiro et al. / Inorganica Chimica Acta 342 (2003) 145Á
/150
although in both cases the CÃ
/
H bond remains after
metal linkage to the carbon atom.
Our aim was to prepare palladacycles by activation of
a non-aromatic CÃ
/
H bond, with displacement of the
hydrogen atom, for which purpose, we chose Schiff-base
ligands derived from trans-cinnamaldehyde and a-
methyl-trans-cinnamaldehyde; accordingly, the four
ligand atoms which conform the metallacycle when an
aryl carbon is metallated, Fig. 1(a), would now be part
of an aliphatic chain as in Fig. 1(b).
Consequently, herein, we report the synthesis of
cyclopalladated complexes derived from C6H5C(H)Ä
/
C(H)C(H)Ä
/
NCy and C6H5C(H)Ä
/
C(Me)C(H)Ä
/
NCy
with palladium(II) salts and the reactivity of the
resulting compounds.
2. Results and discussion
For the convenience of the reader the compounds and
reactions are shown in Schemes 1 and 2. The com-
pounds described in this paper were characterized by
elemental analysis (C, H, N) and by IR spectroscopy
Scheme 1. (i) Li2[PdCl4], MeOH; (ii) Pd(OAc)2, AcOH; (iii) NaCl,
acetone/water; (iv) NaX, acetone/water.
1
(data in the Section 3) and by H and 31P{1H} NMR
spectroscopy (see Table 1). The ligands were prepared
by reaction of trans-cinnamaldehyde or a-methyl-trans-
cinnamaldehye and cyclohexylamine as appropriate;
they showed the characteristic n(CÄ
IR spectra. The 1H NMR spectrum for ligand a showed
an ABX pattern for the H7ÃH9 protons (H7, H8, AB
/N) stretch in the
/
part, d 6.91; H9, X part, d 8.04), whilst for ligand b, two
singlets were assigned to the H7, d 6.78, and H9, d 8.02,
protons (see Table 1). In both spectra the H9 proton was
shifted to higher frequency due to the deshielding effect
of the CÄ/N double bond. From the ligands new
cyclometallated compounds were obtained which are
shown in Schemes 1 and 2. Preparative details, char-
acterizing microanalytical data, IR and NMR data are
in the Section 3 and in Table 1.
Scheme 2. (i) TlCp, chloroform; (ii) Tl(acac), chloroform; (iii) PPh3,
acetone/water; (iv) PPhEt2, acetone/water.
Reaction of the Schiff-base ligands C6H5C(H)Ä
C(H)C(H)ÄNCy (a) and C6H5C(H)ÄC(Me)C(H)ÄNCy
(b) with palladium(II) acetate in glacial acetic acid, gave
the dinuclear cyclometallated complexes [Pd{C6H5CÄ
/
/
/
/
Fig. 1. Metallacycle ligand atoms with C(sp2)aromatic (a) and
C(sp2)aliphatic (b) carbons.
/

S. Tenreiro et al. / Inorganica Chimica Acta 342 (2003) 145Á
/150
147
Table 1
a
b
c,d
31P and 1H NMR data
Compound 31P
Aliphatic
Aromatic
7.27 [m, 5H, H2ÃH6]
a
1a
8.04[t,1H, H9]; 6.91[m, 2H, H7, H8]
7.93[d, 2H, J(HH)ꢁ13.6, H9]; 6.77[d, 2H, J(HH)ꢁ13.6, H8]; 2.4[s, 3H, 7.94[dd, 2H, 3J(HH)ꢁ8.1,]; 4J(HH)ꢁ1.5, H2,
O2CMe]
8.03[d, 2H, 3J(HH)ꢁ13.7, H9]; 6.78[d, 2H, 3J(HH)ꢁ13.7, H8]
7.48Á
/
3
3
H6]; 7.57Á
/
7.30 [m, 3H, H3ÃH5]
3
2a
3a
4a
5a
7.94[d, 2H, J(HH)ꢁ6.7, H2, H6]; 7.59Á
/
7.35 [m,
7.40 [m,
7.38 [m,
3H, H3ÃH5]
8.02[d, 2H, 3J(HH)ꢁ13.6, H9]; 6.78[d, 2H, 3J(HH)ꢁ13.6, H8]
8.05[d, 2H, 3J(HH)ꢁ13.4, H9]; 6.60[d, 2H, 3J(HH)ꢁ13.4, H8]
7.94[d, 2H, J(HH)ꢁ7.0, H2, H6]; 7.47Á
/
3
3H, H3ÃH5]
7.95[d, 2H, J(HH)ꢁ7.5, H2, H6]; 7.52Á
/
3
3H, H3ÃH5]
8.02[d, 2H, 3J(HH)ꢁ13.6, H9]; 6.78[d, 2H, 3J(HH)ꢁ13.6, H8]; 5.30[s, 1H, 7.94[dd, 2H, 3J(HH)ꢁ8.2, 3J(HH)ꢁ1.5,H2,
CH(acac)]; 2.17[s, 3H, Me(acac)]; 2.09[s, 3H, Me(acac)]
8.02[s,1H, H9]; 6.78[s,1H, H7]; 2.15[s, 3H, Me(C8)]
7.95[s, 1H, H9]; 2.17[s, 3H, Me(C8)]; 1.94[s, 3H, O2CMe]
7.69[s, 2H, H9]; 3.00[s, 3H, Me(C8)]
7.69[s, 1H, H9]; 5.45[s, 1H, CH(acac)]; 3.00[s, 3H, Me(C8)]; 2.20[s, 3H,
Me(acac)]; 2.13[s, 3H, Me(acac)]
7.68[s, 1H, H9]; 5.30[s, 5H, C5H5]; 3.00[s, 3H, Me(C8)]
H6]; 7.53Á7.35 [m, 3H, H3ÃH5]
/
b
7.42Á
7.90Á
7.56Á
7.54Á
/
7.28[m, 5H, H2ÃH6]
7.20[m, 5H, H2ÃH6]
7.09[m, 5H, H2ÃH6]
6.91[m, 5H, H2ÃH6]
1b
2b
3b
/
/
/
4b
5b
7.61Á
/
6.91[m, 5H, H2ÃH6]
6.80[m, 5H, H2ÃH6]
21.44s 7.65[s, 1H, H9]; 3.00[s, 3H, Me(C8)]
7.59Á
/
a
b
c
In CDCl3. Measured at 100.6 MHz (approximately 20 8C); chemical shifts (d) in ppm (90.1) to high frequency of 85% H3PO4.
In CDCl3, unless otherwise stated. Measured at 250 MHz (aproximately 20 8C); chemical shifts (d) in ppm (90.01) to high frequency of SiMe4.
Coupling constants in Hz.
d
s, singlet; d, doublet; dd, doublet of doublets; t, triplet; m, multiplet.
C(H)C(H)Ä
C(Me)C(H)Ä
were fully characterized. The IR spectra of 1a and 1b
showed the n(CÄ
N) stretch at 1610 and 1608 cmꢃ1
/
NCy}(O2CMe)]2 (1a) and [Pd{C6H5CÄ
/
C(H)C(H)Ä
/
NCy}(X)]2, (Xꢁ
/
Br, 3a; XꢁI, 4a), which
/
/
NCy}(O2CMe)]2 (1b), respectively, which
were fully characterized (see Table 1, Section 3). The IR
spectra showed the absence of the acetate bands, and for
/
,
2a and 2b, the appearance of two n(PdÃ
/Cl) bands,
respectively, shifted to lower wavenumbers (as com-
pared with the free ligand) due to N-coordination of the
imine [25,26]. The IR spectra also showed strong bands
assigned to the symmetric and asymmetric n(COO)
vibrations, in agreement with those expected for brid-
ging acetate ligands [27] (see Section 3). Only one singlet
resonance was assigned to the 2 equiv. methyl acetate
groups, in each spectrum, in accordance with the
presence of the anti isomer for both 1a and 1b.
Metallation of the ligand through the aliphatic carbon
atom C7 is clear for 1a, from the absence of the ABX
system of the aliphatic chain, which was substituted by
an AB pattern with 3J(HH) approximately 13 Hz;
whereas for 1b, the H7 singlet was absent and only
one singlet resonance appeared which was assigned to
H9 (see Table 1). The resonance corresponding to the
consistent with an asymmetric Pd2Cl2 bridging unit [29].
Alternatively, compounds 2a and 2b could be made by
treatment of a and b with Li2[PdCl4] in methanol in
good yield (see Section 3).
Reaction of 2b with PPh3 in a 1:2 molar ratio gave the
mononuclear cyclometallated complex [Pd{C6H5CÄ
C(H)C(Me)ÄNCy}(Cl)(PPh3)] (5b), in a typical bridge-
splitting reaction. In the H NMR spectrum the C(H)Ä
/
/
1
/
N resonance was a singlet, hence not showing coupling
to the phosphorus nucleus; and in the 31P{1H} spectrum
the resonance of the coordinated phosphine was a
singlet at d 21.44. Although triphenylphosphine tends
to adopt a trans to nitrogen disposition, these findings
are in agreement with a phosphorus trans to carbon
geometry. For a phosphorus trans to nitrogen arrange-
ment greater d-values would be expected for the
phosphorus resonance [30,31], in accordance with the
higher trans influence of the carbon atom with respect
C(H)Ä
/
N proton in the 1H NMR spectra was only
slightly shifted by approximately 0.1 ppm to lower
frequency consequent upon coordination of the imine
group to the palladium atom via the lone pair of the
nitrogen atom [28].
to the CÄ
the C(H)Ä
stems from the n(PdÃ
/
N nitrogen atom [32], as well as coupling of
N resonance to the 31P nucleus. Further proof
Cl) band in the IR spectrum. The
/
/
The reaction of 1a and 1b with aqueous sodium
value of 350 cmꢃ1 is in accordance with the chlorine
atom trans to nitrogen, as a trans to carbon geometry
would give a band at lower wavenumbers [29]. In the
present case, we suggest that steric hindrance of the C7-
phenyl ring with the phosphine ligand prevents the latter
to occupy the trans to nitrogen coordination site.
chloride
[Pd{C6H5CÄ
[Pd{C6H5CÄ
and reaction of 1a with aqueous sodium bromide or
iodide gave the halide-bridged complexes [Pd{C6H5CÄ
gave
C(H)C(H)Ä
C(Me)C(H)Ä
the
chloro-bridged
complexes
/
/
NCy}(Cl)]2
(2a) and
/
/
NCy}(Cl)]2 (2b), respectively,
/

148
S. Tenreiro et al. / Inorganica Chimica Acta 342 (2003) 145Á150
/
Reaction of 2b with larger quantities of PPh3, 1:4 molar
ratio or greater, did not produce opening of the
metallated ring, nor did compound 2b react with more
basic phosphines such as PPhEt2 (see Scheme 2).
Treatment of 2a or 2b with thallium cyclopentadienyl
or with thallium acetylacetonate gave the monuclear
Santiago using a Carlo-Erba Elemental Analyzer,
Model 1108. IR spectra were recorded as KBr pellets
on a PerkinÁElmer 1330 and on a Mattson (Servicio de
/
Espectroscop´ıa of the University of Santiago) spectro-
photometers. NMR spectra were obtained as CDCl3 or
(CD3)2CO solutions and referenced to SiMe4 (1H, 13C)
or 85% H3PO4 (31P{1H}) and were recorded on Bruker
WM-250, AMX-300 and AC-200 spectrometers. All
chemical shifts were reported downfield from the
standards.
compounds
(3b) and [Pd{C6H5CÄ
complex [Pd{C6H5CÄ
[Pd{C6H5CÄ
C(H)C(H)Ä
C(H)C(Me)Ä
/
C(H)Ã
NCy}(acac)] (5a) and
NCy}(C5H5)] (4b),
/
C(Me)Ä
/
NCy}(acac)]
/
/
/
/
as air-stable solids which were fully characterized (see
Section 3). The 1H NMR spectra showed singlet
resonances at d 5.30 (5a), d 5.45 (3b); d 2.17 (5a), d
2.20 (3b) and d 2.09 (5a), d 2.13 (3b), assigned to the
The synthesis of C6H5C(H)Ä
/
C(R)C(H)Ä
/
NCy (RꢁH,
/
Me) was performed by heating a chloroform solution of
the appropriate quantities of trans-cinnamaldehyde or
of a-methyl-trans-cinnamaldehyde and cyclohexylamine
CH and to the 2 inequiv. CÃ
/
Me groups, respectively. In
the 1H NMR spectra of 4b a singlet resonance was
assigned to the 5 equiv. protons of the C5H5 ring.
Also noticeable in the 1H NMR spectra of com-
in a DeanÁStark apparatus under reflux.
/
pounds 1aÁ
phenyl ring protons, which appeared separated from the
multiplet ascribed to the H3ÃH5 proton signals and
shifted towards lower field, at approximately d 7.94, due
to the deshielding effect of the CÄN double bond (see
Table 1). For compounds 1bÁ5b a multiplet was
observed for the H2ÃH6 phenyl ring protons; however,
the signal for 1b expanded as far as d 7.90, whereas for
2bÁ5b the lowest value for the multiplet was d 7.61 (in
4b). This seems to indicate that the CÄN group does not
affect protons H2 and H6 in 2bÁ5b, which could be due
/
5a were the resonances of the H2 and H6
3.1.1. C6H5C(H)Ä
C15H19N (213.3): Calc. C, 84.4; H, 9.0; N, 6.6. Found:
C, 84.0; H, 8.9; N, 6.5%. IR (KBr, n cmꢃ1): 1622m (CÄ
N).
/
C(H)C(H)Ä
/
NCy (a)
/
/
/
/
/
3.1.2. C6H5C(H)Ä
/
C(Me)C(H)Ä
/
NCy (b)
C16H21N (227.4): Calc. C, 84.5; H, 9.3; N, 6.2. Found:
C, 84.3; H, 9.1; N, 6.0%. IR (KBr n cmꢃ1): 1620m (CÄ
N).
/
/
/
/
to rotation of the phenyl ring away from the co-
planarity of the metallated ring. Further evidence for
this assumption was the Me(C8) resonance, for which
3.2. Preparation of the complexes
3.2.1. Synthesis of [Pd{C6H5CÄ
NCy}(O2CMe)]2 (1a)
A mixture of C6H5CÄ
/
C(H)C(H)Ä
/
values of d 2.17 (1b) and d 3.00 (2bÁ5b) were found; the
/
former datum close to the one observed in the 1H NMR
spectrum of the free ligand b, d 2.15. We also tentatively
suggest that the aforementioned rotation of the aro-
matic ring brings the Me(C8) group closer to the
deshielding region of the phenyl ring and the corre-
sponding resonance is thus shifted to lower field.
Presently, we are in the process of studying related
compounds which will enable us to gather further data
in order shed new light regarding the precise disposition
of the phenyl ring as well as other interesting properties
of these complexes.
/
C(H)C(H)Ä
/NCy (310 mg, 1.45
mmol) and palladium(II) acetate (300 mg, 1.34 mmol) in
glacial acetic acid (40 cm3) was refluxed under dry
dinitrogen for 3 h. After cooling the mixture to room
temperature (r.t.) the acetic acid was removed under
vacuum. The residue was treated with water and
extracted with dichloromethane. The combined extracts
were dried over anhydrous sodium sulfate, filtered and
concentrated in vacuo to give an orange oil. This was
chromatographed on a column packed with silica-gel.
Elution with dichloromethane removed unchanged
starting material. Elution with dichloromethaneÁ
/
ethanol(0.5%) afforded the final product as a yellow
powder after concentration. Yield: 389 mg, 77%.
C34H42N2O4Pd2 (775.5): Calc. C, 54.0; H, 5.6; N, 3.7.
Found: C, 53.9; H, 5.5; N, 3.6%. IR (KBr, n cmꢃ1):
3. Experimental
All reactions were carried out in an atmosphere of dry
nitrogen. Solvents were purified by standard methods
[33]. Chemicals were reagent grade. Palladium(II) ace-
tate was purchased from Alfa Products, thallium
acetylacetonate, thallium cyclopentadienyl, trans-cinna-
maldehyde and a-methyl-trans-cinnamaldehyde, and
the phosphines PPh3 and PEt2Ph were purchased form
Aldrich-Chemie. Microanalyses were carried out at the
Servicio de Ana´lisis Elemental at the University of
1600m (CÄ
/
N), 1585s (nasCOO), 1410s (nsCOO).
Compound 1b was prepared similarly.
3.2.2. Synthesis of [Pd{C6H5CÄ
/
C(Me)C(H)Ä
/
NCy}(O2CMe)]2 (1b)
Yield: 393 mg, 75%. C36H46N2O4Pd2 (783.6): Calc. C,
55.2; H, 5.9, N, 3.6. Found: C, 55.0; H, 5.8; N, 3.4%. IR

S. Tenreiro et al. / Inorganica Chimica Acta 342 (2003) 145Á
/150
149
(KBr n cmꢃ1): 1605m (CÄ
(nsCOO).
/
N), 1575s (nasCOO), 1410s
3.2.8. [Pd{C6H5CÄ
/
C(Me)C(H)Ä
/
NCy}(acac-O,O)]
(3b)
Yield: 48 mg, 82%. C21H27NO2Pd (431.9): Calc. C,
58.4; H, 6.3; N, 3.2. Found: C, 58.1; H, 6.1; N, 3.1%. IR
3.2.3. Synthesis of [Pd{C6H5CÄ
NCy}(Cl)]2 (2a)
/
C(H)C(H)Ä
/
(KBr, n cmꢃ1): 1603m (CÄ
Compound 4b was prepared in a similar fashion to 5a
but using Tl(C5H5).
/
N), 1582m, 1514m (CÃ
/
O).
3.2.3.1. Method 1. An aqueous solution of NaCl
(approximately 10ꢃ2 M) was added dropwise to a
solution of 1a (58 mg, 0.07 mmol) in acetone. The
product immediately precipitated out as a yellow solid.
After stirring for 10 h the solid was filtered off and dried
in vacuo. Yield: 47 mg, 87%. C30H36Cl2N2Pd2 (708.37):
Calc. C, 50.9; H, 5.1; N, 4.0. Found: C, 50.7; H, 5.0; N,
3.2.9. [Pd{C6H5CÄ
/
C(Me)C(H)Ä
/
NCy}(C5H5)] (4b)
Yield: 44 mg, 81%. C21H25NPd (397.9): Calc. C, 63.4;
H, 6.3; N, 3.5. Found: C, 63.3; H, 6.2; N, 3.3%. IR
(KBr, n cmꢃ1): 1607m (CÄ
/
N).
3.9%. IR (KBr, n cmꢃ1): 1600m (CÄ
(PdÃCl).
/N), 286m, 230m
3.2.10. Synthesis of [Pd{C6H5CÄ
NCy}(Cl)(PPh3)] (5b)
/
C(Me)C(H)Ä
/
/
To a suspension of the cyclometallated halide-bridged
complex (2b) (100 mg, 0.13 mmol) in 15 cm3 of
dichloromethane, PPh3 (68 mg, 0.26 mmol) was added.
The mixture was stirred for 8 h, after which the white
solid formed was filtered off and recrystallized from
3.2.3.2. Method 2. To a stirred solution of lithium
tetrachloropalladate in methanol (30 cm3), prepared in
situ from 210 mg (1.18 mmol) of palladium(II) chloride
and 100 mg (2.33 mmol) of lithium chloride, 240 mg
(1.13 mmol) of the Schiff-base C6H5C(H)Ä
/
C(H)C(H)Ä
/
dichloromethaneÁhexane. Yield: 125 mg, 73%.
/
NCy (a) were added. The mixture was stirred for 48 h at
r.t. The precipitate was filtered off and washed with
methanol. Yield: 239 mg, 80%.
C34H35ClNPPd (630.5): Calc. C, 64.8; H, 5.6; N, 2.2.
Found: C, 64.7; H, 5.3; N, 2.1%. IR (KBr, n cmꢃ1):
1617m (CÄ
/
N), 350m (PdÃ/Cl).
Compounds 3a, 4a, (Section 3.2.3.1) and 2b, were
prepared similarly.
3.2.4. [Pd{C6H5CÄ
/
C(H)C(H)Ä
/
NCy}(Br)]2 (3a)
References
Yield: 43 mg, 82%. C30H36Br2N2Pd2 (797.3): Calc. C,
45.2; H, 4.6; N, 3.5. Found: C, 45.0; H, 4.4; N, 3.4%. IR
[1] S. Trofimenko, Inorg. Chem. 12 (1973) 1215.
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(KBr, n cmꢃ1): 1603m (CÄ
/N).
[4] I. Omae, Organometallic Intramolecular-Coordination Com-
pounds, Elsevier, Amsterdam, 1986.
3.2.5. [Pd{C6H5CÄ
/
C(H)C(H)Ä
/
NCy}(I)]2 (4a)
Yield: 45 mg, 79%. C30H36I2N2Pd2 (891.3): Calc. C,
40.4; H, 4.1; N, 3.1. Found: C, 40.1; H, 4.0; N, 2.9%. IR
[5] V.V. Dunina, O.A. Zalevskaya, V.M. Potapov, Russ. Chem. Rev.
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(KBr, n cmꢃ1): 1605m (CÄ
/N).
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Tetrahedron 48 (1992) 2427.
3.2.6. [Pd{C6H5CÄ
/
C(Me)C(H)Ä
/
NCy}(Cl)]2 (2b)
[8] B.S. Wild, Coord. Chem. Rev. 166 (1997) 296.
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Yield: 45 mg, 75% (Section 3.2.3.1); 243 mg, 78%
(Section 3.2.3.2). C32H40Cl2N2Pd2 (736.4): Calc. C, 52.2;
H, 5.5; N, 3.8. Found: C, 52.0; H, 5.3; N, 3.7%. IR
[10] C. Navarro-Ranninger, I. Lo´pez solera, J. Rodr´ıguez, J.L.
Garc´ıa-Ruano, P.R. Raithby, J.R. Masaguer, C. Alonso, J.
Med. Chem. 36 (1993) 3795.
(KBr, n cmꢃ1): 1611m (CÄ
/
N), 287m, 238m (PdÃ
/Cl).
[11] C. Navarro-Ranninger, I. Lo´pez-Solera, V.M. Gonza´lez, J.M.
Pe´rez, A. Alvarez-Valde´s, A. Mart´ın, P.R. Raithby, J.R. Masa-
guer, C. Alonso, Inorg. Chem. 35 (1996) 5181.
3.2.7. Synthesis of [Pd{C6H5CÄ
/
C(H)C(H)Ä
/
NCy}(acac-O,O)] (5a)
To a suspension of 2a (50 mg, 0.07 mmol) in chloro-
form (25 cm3), thallium-2,4-pentanedionate (4 mg, 0.014
mmol) was added and the mixture stirred at r.t. for 4 h.
The resulting mixture was filtered over celite, concen-
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Ferna´ndez, M. Lo´pez-Torres, H. Adams, Organometallics 18
(1999) 5484.
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Castineiras, D. Lata, J.J. Ferna´ndez, A. Ferna´ndez, J. Organo-
˜
trated
dichloromethaneÁ
in
vacuo,
and
recrystallised
hexane to give the required complex
from
/
met. Chem. 556 (1998) 21.
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Pereira, J.J. Ferna´ndez, J.M. Vila, H. Adams, J. Organomet.
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as a yellow solid. Yield: 50 mg, 85%. C20H25NO2Pd
(417.8): Calc. C, 57.5; H, 6.0; N, 3.4. Found: C, 57.2; H,
5.9; N, 3.2%. IR (KBr, n cmꢃ1): 1604m (CÄ
/N), 1580m,
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˜
1515m (CÃ
/O).
Compound 3b was prepared similarly.
Chem. Soc., Dalton Trans. (1999) 4193.

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/